w^m COLUMBIA LIBRARIES OFFSITE HEALTH SCIENCES STANDARD HX64088537 Q P34 . K63 1 893 Hand-book of physiol Ololumbta llntupratly l\(o > in tl|p ditg of Npw fork 3Frnm tijp iCtbrarg nf (Eljurrljill (Earmalt. M. B. \ . > > -^ /-i^C^ ^::.■A^^ Cdt<:oc<:^t^. ^^ L^ J7 S/ Digitized by the Internet Archive in 2010 with funding from Open Knowledge Commons (for the Medical Heritage Library project) http://www.archive.org/details/handbookofphysio1893kirk HAND-BOOK OF PHYSIOLOGY. BLDDD-5PECTRA COMPARED WITH SPECTRUM DP ARGAND- LAMP 1 Spectrum oT Ardand-lamp with FrauntiDfErs lines in position. 2 Spectrum oP Dxyhsmoplohln m diluted blood. .'3 Spectrum nP Reduced nEmoQlnbin. 4 Spectrum oP Carbanic oxide MffirnoQlobin. 5 Spectrum oP AcidHsmatin m etherial solution. 6 Spectrum oP Alkaline HEmatm. 7 Spectrum Dp ChlDroForm extract oF aciriulated Dx-Bile. 8 Spectrum oP MEthsmo^labin. 9 Bpectrom oP PiffimachrnrnD^En. 10 Spectrum oP HEmatoporphyrin. Mosfofthp ubov'p Spec fret httiT bpen ifnnm Frnnt observations hy MTWlepmik ECS. KIEKES' HAND-BOOK OF PHYSIOLOGY HAND-BOOK OF PHYSIOLOGY BY W. MOKRANT BAKER, F.KC.S. LATE SURGEON TO AND LECTURER ON PHYSIOLOGY AT ST. BARTHOLOMEW'S HOSPITAL, ETC. AXD VINCENT DORMER HARRIS, M.D. Lond., F.R.C.R EXAMINER IN PHYSIOLOGY AT THE CONJOINT BOARD OF THE ROYAL COLLEGES OP PHYSICIANS AND SURGEONS, AND IN THE UNIVERSITY OF DURHAM; DEMONSTRATOR OF PHYSIOLOGY AT ST. BAKTHOLOMEW"s HOSPITAL; PHYSICIAN TO THE VICTORIA PARK HOSPITAL FOR DISEASES OF THE CHEST THIRTEENTH EDITION WITH UPWARDS OF FIVE HUNDRED ILLUSTRATIONS INCLUDING MANY IN COLORS NEW Y^ORK WILLIAM WOOD & COMPANY 1893 PEEFACE TO THE THIRTEENTH EDITIOISr. In the preparation of a new edition of this Handbook the Authors have endeavored to furnish the student with an account of Physiology brought up as far as possible to the present time. The account does not profess to be exhaustive, but it is one upon which, they venture to think, a knowledge of Physiology may be safely based. The whole book has undergone a very thorough revision, and the scope of the work has been to some extent enlarged. The Authors have, however, kept constantly in view the fact that the medical student, for whom the book is specially intended, studies Physiology only as an introduction to Medicine, and does not require such minute detail as would be necessary for one whose sole object of study is Physiology. It would be out of place to mention the names of all the important works dealing with the subject of Physiology in its various branches, of which free use has been made in preparing the present edition, but the Authors would specially desire to record their obligation to those (text-books and monographs) of Professors M. Foster, Schiifer, Halli- burton, Stohr, Cadiat, McKendrick, Sherrington, Mott, and Waller. They would also tender their thanks to their colleagues Dr. Gow and Mr. Paterson, for revising respectively the chapters on Generation and on the Teeth; to Dr. Cautley, for kindly reading through the chief portion of the proof sheets, and to Professor Lowne for several sugges- tions and corrections. Mr. Danielsson has undertaken and carried out with much skill the whole of the new illustrations. W. MORRANT BAKER. VINCENT D. HARRIS. WiMPOLE Street, W., Augtist, 1892. V 374600 CONTENTS. CHAPTER I. PAGE The Phenomena of Life, 1 Properties of Protoplasm, 3 Structure of Protoplasmic Cells, 9 The Cell Nucleus, 11 Cell Division, 13 Plants compared with Animals, 15 CHAPTER II. The Functions op Organized Cells, 20 CHAPTER III. The Structure of the Elementary Tissues, 24 Epithelial Tissues, 26 Connective Tissue, 38 The Teeth, 67 Development of Teeth, 74 Muscular Tissue, . 79 Nervous Tissue, 89 CHAPTER IV. The Chemical Composition op the Body, 102 Organic Substances, 103 Inorganic Substances, 114 CHAPTER V. The Blood, 117 Coagulation, 119 The Corpuscles, 129 Chemical Composition, 137 Development of Corpuscles, 154 CHAPTER VI. The Circulation of the Blood, 158 The Heart 159 The Arteries, 167 The Capillaries, 170 vii Vlll CONTENTS. PAGE The Circulation of the Blood {Continued). The Veins, 173 The Action of the Heart, 176 Blood Pressure, 191 The Arterial Flow, 199 The Venous Flow, 212 Local Peculiarities, 216 The Regulation of the Flow, 219 Proofs of the Circulation of the Blood, 237 CHAPTER VII. Respiration, 239 The Respiratory Apparatus, 240 The Respiratory Mechanism, 249 Respiratory Changes, 259 Special Respiratory Acts, 266 Nervous Mechanism, 269 Effect on the Circulation, 275 Asphyxia, 280 CHAPTER VIII. Food and Digestion, 285 Organic Nitrogenous Foods, 285 Organic Non-Nitrogenous Foods, 288 Mineral Foods, 288 Liquid Food, . . .289 The Mouth and Mastication, 290 The Salivary Glands, 292 The Tongue, . 803 Deglutition, 309 The Stomach, 310 The Intestines, 326 The Pancreas, 334 The Liver, 340 Digestion in Small Intestine, 353 Digestion in Large Intestine, 355 Micro-Organisms in Intestines, 356 Movements of the Intestines, 357 Action of Nervous System, 358 Fseces, 359 CHAPTER IX. Absorption, 363 Methods, 363 The Lymphatic System 367 The Lymph and Chyle, 376 Channels of Absorption, 377 Where Absorption may take place, 379 CONTEXTS. IX CHAPTER X. PAGE Excretion, 381 The Kidneys, 381 The Urine, 390 Method of Excretion of Urine, 403 Passage of Urine into Bladder, 409 The Skin, 410 Functions of the Skin, 417 CHAPTER XL The Metabolism of the Tissues, 421 Muscular Metabolism, 421 Muscle at Rest, 423 Muscle in Activity, 426 Muscle in Rigor Mortis, 440 Action of the Voluntary Muscles, 441 Action of the Involuntary Muscles, 446 Electrical Currents in Nerves, 446 CHAPTER XII. The Metabolism of the Tissues, 453 Glandular Metabolism, - 453 Secreting Glands 458 The Mammary Glands, 462 Milk 465 Metabolism in the Liver, 467 Formation of Bile, 467 Glycogenesis, 468 Formation of Urea, 471 Metabolism in Vascular Glands, 476 CHAPTER XIII. AiS'iMAL Heat, 488 Production of Heat, 490 Regulation of the Temperature, 493 CHAPTER XIV. Nutrition and Diet, 499 Requisites of a Normal Diet, 506 Variations in Diet Tables, 509 Income and Output of Energj', 509 CHAPTER XV. The Production of the Voice, 514 Laryngoscope, 519 Movements of the Vocal Cords, 522 The Voice in Singing and Speaking, 523 CONTENTS. CHAPTER XVI. PAGE The Nervous System, 530 Functions of Nerve-Fibres, 530 The Spinal Cord and its Nerves, 537 Functions of Spinal Nerve-roots, 546 Functions of the Spinal Cord, 547 The Relations of the Different Parts of the Brain, .... 556 The Bulb, 563 Functions of the Bulb, 568 The Cranial Nerves, 571 The Pons Varolii, 587 The Crura Cerebri 588. Corpora Striata, 590 Optic Thalanii, 591 Corpora Quadrigemina, 591 Corpora Geniculata, 591 Corpora Dentata, 591 The Cerebrum, 591 Motor Areas of the Cerebral Cortex, 599 Functions of the Cerebrum 606 Sensory Centres, 612 The Cerebellum, .... 615 The Sympathetic System, 621 CHAPTER XVII. The Senses 638 Sense of Touch, 631 Sense of Taste, 638 Sense of Smell, 641 Sense of Hearing, 646 Sense of Sight, 663 CHAPTER XVIII. The Reproductive Organs, . . . 712 Of the Female, 712 Of the Male, 718 CHAPTER XIX. Development, 734 The Changes in the Ovum, 734 Development of Organs, 756 APPENDIX 793 INDEX, 805 FAHEENHEIT and CENTIGRADE SCALES. F. 500° 401 39e 38:3 374 350 :M7 338 3-29 320 311 303 2*y 275 286 248 239 230 212 203 194 176 167 140 122 113 105 104 100 C. 260° 205 200 195 190 ISO 175 170 165 160 155 150 140 135 130 120 115 110 100 95 75 60 50 45 40.54 40 37.8 98.5 95 - 4 - 13 36.0 35 30 25 20 10 5 0 - 5 - 10 - 15 -20 -25 - 30 - 40 - 60 1 deg. F. 1.8 '• 3.6 " 4.5 " 5.4 .54°C. 1°C. 2°U. 2 .5°C. 3°C. To convert de- grees F. into de- grees C, subtract 32. and multiply To convert de- grees C. into de- grees F., multiply b}' I. and add 32°. MEASUREMENTS. FRENCH INTO ENGLISH. LENGTH. 1 m^tre "i 10 decimetres I = 39..37 English 100 centimetres f inches. 1,000 millimetres j (or 1 yd. and 3}^ in.) 1 decimetre ) 10 centimetres >• = 3.037 inches 100 millimetres j (or nearly 4 inches.) 1 centimetre ( — .3937 or about 10 millimetres (" (nearly g inch.) 1 millimetre = nearly ^^ inch. Or, One Metre = 39.37079 inches. (It is the ten-millionth part of a quarter of the meridian of the earth.) 1 Decimetre = 4 in. 1 Centimetre = f^ in. 1 Millimetre =V5in. Decametre = b2.80 feet. Hectometre ;= 109..36 yds. Kilometftj = 0.62 miles. One inch = 2.539 Centimetres. One foot — 3.047 Decimetres. One yard = 0.91 of a Metre. One mile = 1.60 Kilometre. The cubic centimetre (1.5.432 grains — 1 gramme) is a standard at 4° C, the grain at 16°.66 C. WEIGHT. (One gramme is the weight of a cubic centimetre of water at 4° C. at Paris). 1 gramme 1 10 decigrammes i = 15.4.32349 grs. 100 centigrammes f (or nearly 1.5}.^). 1,000 milligrammes J 1 decigramme j 10 centigrammes ^ = rather more 100 milligrammes ) than IJ^ grain. 1 centigramme 10 decigrammes = rather more than 5^5 grain. 1 milhgramme = rather more than 2^ grain. Or 1 Decigramme =; 2 dr. 34 gr. 1 Hectogrm. = 3!^ oz. (Avoir.) 1 Kilogrm. =. 21b. 3oz. 2 dr. (Avoir.) A grain equals about 1.16 gram., a Troj' oz. about 31 gram., a lb. Avoirdupois about ^ Kilogrm.. and 1 cwt. about 50 Kilogrms. CAPACITY. 1.000 cubic decimetres '. = 1 cubic 1.000.000 cubic centmietres ) metre. 1 cubic decimetre or 1,000 cubic centimetres Or ^=1 litre. One Litre = 1 pt. 15 oz. 1 dr. 40. (For simplicity. Litre is used to signify 1 cubic decimetre, a little less than 1 Englisli quart.) Decilitre (100 c.c.) Centilitre (10 c.c.) Millilitre(l c.c.) lieealitre Hectolitre = S]4 oz. = 24 dr. = 17 m. = 2J gal. = 22 gals. Kilolitre (cubic mStre) = 271^^ bushels. A cubic inch = 16.38 c.c. : a cubic foot = 2S.315 cubic dec, and a gallon — 4.54 litres. CONVERSION SCALE. To convert Grammes to Ounces avoir- dupois, multiply by 20 and divide by 567. To convert Kilogrammes to Pounds. multiply by 1,000 and divide by 454. To convert Litres to Gallons, mul- tiply by 22 and divide by 100. To convert Litres to Pints, multiply by 88 and divide by 50. To convert Millimetres to Inches. multiply by 10 and divide by 254. To convert Metres to Yards, multi- ply by 70 and divide by 64. SURFACE MEASURE. 1 square metre — about 1.550 sq. inches. Or 10.000 sq. centimetres, or 10.75 .sq. ft. 1 sq. inch = about 6 4 sq. centimetres. 1 sq. foot = •• 930 ■' ENERGY MEASURE. 1 kilogrammetre=about7.24 ft. pounds. 1 foot pound = •• .1381 kgm. 1 foot ton = •• 310 kgm. HEAT EQUIVALENT. 1 kilocalorie = 424 kiiogrammetres. ENGLISH MEASURES. Apothecaries Weight. ' Avoirdupois VTeight. 7000 grains = 1 lb. Or 437.5 grains = 1 oz. 16 drams = 1 oz. 16 oz. = 1 lb. 28 lbs. =; 1 quarter. 4 quarters = 1 ewt. 20 cwt. = 1 ton. Measure of 1 d^cini^tre, or 10 centimetres, or 100 millimetres. III!! I I ! I I I I 1 I III Cranium - 7 Cervical Vertebrae Clavicle. Scapula. 12 Dorsal Vertebrae. Humerus. 5 Lumbar Vertebrae. — Ilium. Ulna. Radius. Pelvis. Bones of the Carpus. Bones of the Meta^ carpus. Phalanges of Fingers. Femur. ~ Patella. Tibia. Fibula. Bones of the Tarsus. Bones of the Meta- tarsus. Phalanges of Toes. THE SKELETON (after Holden). Highest , point of Crest of the nium. Symphysis Puhis. DIAGRAM OF THORACIC AND ABDOMINAl, REGIONS. A. Aortic Valve. M. Mitrai Valve. P. Pulmonary Valve. r. Tricuspid Valve. Handbook of Physiology. CHAPTER I. THE PHEIS^OMENA OF LIFE. HuMAX Physiology is the science which treats of the various pro- cesses or changes which take place during life in the organs and tissues of the body of man. These processes, however, must not be considered as by any means peculiar to the hiiman organism since, putting aside the properties which serve to distinguish man from other animals, us well as those which mark out one animal from another, the changes which go on in the tissues of man go on much in the same way in the tissues of all other animals as long as the}" live. Furthermore it is found that similar changes proceed in all living vegetable tissues; they indeed constitute what are called vital j^fienomena, a,Tid are those proper- ties which mark out living from non-living material. The lowest types of life, whether animal or vegetable, are found to consist of minute masses of a jelly-like substance, which is now gener- ally known under the name of 2)rotoj)Ia>ose of replacing waste of its tissue consequent ujion mani- festation of energy. The respiratory process of absorbing oxygen goes on at the same time. The processes which take place in cells, both animal and vegetable, are summed up under the term metabolism (from iJ-zTafiuk-fj, change). The changes which go on are of two kinds, viz., assimilation, or building up, and disassimilation, or breaking down ; they may be also called composition or decom- position, or, using the nomenclature of Gas- kell, anabolism or constructive metabolism, and kataholisni or destructive metabolism. In the direction of anabolism two processes occur, viz., the building up of materials which it takes in, and secondly, the building up of its own substance by those or other mate- rials. As we shall see in a subsequent para- graph, the process of anabolism differs to some extent in vegetable and animal cells. The katabolism of the cell consists in chem- ical changes which occur in the cell-substance itself, or in substances in contact with it. The destructive metabolism of a cell is increased by its activity, but goes on also during quiescence. It is jorobably of the nature of oxida- tion, and results in the evolution of carbonic anhydride and water on the one hand, and in the formation of various substances on the other, some of which may be stored up in the cell for future use, and are called secretions, and others, like the carbonic anhydride and certain bodies containing nitrogen, are eliminated as excretioois. 4. The Poicer of Growth.— In protoplasm then, it is seen that the two processes of waste and repair go on side by side, and as long as they are equal the size of the animal remains stationary. If, however, the building up exceed the waste, then the animal grows ; if the waste ex- Fig. 6.— Cells from the staminal hairs of Tradescantia. A, Fresh in water; B, tlie same cell after sliglit electrical stimulation; o, b, region stimulation ; c, ri, clumps and knobs of contracted protoplasm. (Kiihne.) S HANDBOOK OF PHYSIOLOCJY. ceed the repair, the animal decays; and if decay go on beyond a certain point, life becomes impossible, and the animal dies. Growth, or the inherent power of increasing in size, although essen- tial to our idea of life, is not, it must be recollected, confined to living beings. A crystal of common salt, for example, if placed under appro- priate conditions for obtaining fresh material, will grow in a fashion as definitely characteristic and as easily to be foretold as that of a living creature; but the growth of a crystal 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. In a living structure, where growth occurs, it is by addition of new matter, not to the surface only, but throughout every part of the mass. Again, all living structures are subject to constant decay. Thus, a man's body is not composed of exactly the same particles day after day, although to all intents he remains the same individual. Almost every part is changed by degrees; but the change is so gradual, and the re- newal 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 condi- tion of its existence. That which is true of structures which never had to do with life is true also with respect to those which, although they are formed by living parts, are not themselves alive. Thus, an oyster- shell is formed by the living animal which it incloses, but it is as lifeless as any other mass of inorganic matter; and in accordance with this circumstance its growth takes place layer by layer, and it is not subject to constant decay and reconstruction. The hair and nails are examjiles of the same fact. In connection, too, with the growth of lifeless ma-sses there is uo alteration in the chemical composition 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 vegetable, as the materials which serve ultimately to build them up are much altered before they are finally assimilated by the structures they are destined to nourish. The growth of all living things has a definite limit, and the law which governs this limitation of increase in size is so invariable that we should be as much astonished to find an individual plant or animal without limit as to growth as w'ithout limit to life. 5. The Poioer of Reprodxidion. — The amoeba, to return to our former illustration, when the growth of its protoplasm has reached a certain point, manifests the power of reproduction, by splitting up into (or in THE PHENOMENA OF LIFE. 9 some other way produoing) two or more parts, each of which is capable of independent existence. The new amoebae manifest the same projaer- ties as their parent, perform the same functions, grow and reproduce in their turn. This cycle of life is being continually passed through. In more complicated structures than the amoeba, the life of indi- vidual protoplasmic cells is probably very short in comparison wkh 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. It is now very generally believed that every cell is descended from some pre-existing (mother-) cell. This derivation of cells from cells Fig. r.— Diagram of an ovum (a) undergoing segmentation— In (h) it has divided into two, in (c) into four; and in (d) tbie process has ended in the production of tlie so called "mulberrj' mass." (Frey.) takes place by (1) gemmation, which essentially consists in the budding off and separation of a portion of the parent cell; or (3) fission or divi- sion. The exact manner of the division of cells is a matter of some diffi- culty, and will not be described until the subject of the structure of protoplasmic cells has been considered. Structure of Protoplasmic Cells. It was formerly the custom to consider protoplasm to be homogene- ous; it was so described by Engelmann; it api3ears, however, that this idea requires modification, and that in the majority of cells, if not in every cell, two parts can be made out in the protoplasm, viz., a fine network or spongework of fibrils of a firmer consistence than the more fluid part which is contained within its interstices. The amount of the two j^arts in each cell varies; in young cells the more fluid part is more developed, and as time goes on the fibrillary meshwork increases. The intra-cellular meshwork has been called by different names, protoplasma, reticulum, or siJongiojjlasm, while the more fluid substance has received the names jJaraplasma, enchyUma, or liiialoplasm. The reticulum is more refractile than its contents, is elastic and extensile, has an affinity for staining reagents. The hyaloplasm has no such affinity. The arrangement of the reticulum varies considerably in different cells, and even in different parts of the same cell. Sometimes, for ex- ample (fig. 8), the meshwork has an elongated radial arrangement from 10 HANDBOOK OF PHYSIOLOGY. the nucleus; iit others, the meshwork is more evenly disposed, as in fig. 9. At tlie junctions of the fibrils there are usually slight enlarge- ments or nodes. In some cells, particularly in plants, but also in some fixed animal cells, such as compose epithelial membranes, there is a tendency toward , Membrane of nucleus. ,>l'\^j^l Achromatic substance of pXv^TJ^iSji" nucleus. :;--V-rr_i?:l Chromatic substance of nucleus. Fig. 8.— Cell with its reticulum disposed radially ; from the intestinal epithelium of a worm. (Carney.) a formation of a firmer external envelope, constituting in vegetable cells a membrane distinct from the more central and more fiuid part of the protoplasm. In such cases the reticulum at the periphery of the cell is made up of very fine meshes. The membrane when formed is usually pierced with pores by which fluid may pass in, or through which pro- trusion of the protoplasmic filaments forming the cell's connection with other cells surrounding it may take jDlace. It is an exceedingly interesting question whether in cells the one Fig. 9. — (a.) The colorless blood-corpuscle showing the intra-cellular network, and two nuclei with intra-nuclear network, (b.; Colored blood-corpuscle of newt shuwing the intra-cellular net- work of fibrils. Also oval nucleus composed of limiting membrane and fine intra-nuclear network of fibrils. X 800. (Klein and Noble Smith.) part of the protoplasm can exist without the other. Schiifer summar- izes the matter thus:— "There are cells, and unicellular organisms both animal and vegetable, in which no reticular structure can be made out, and these mat/ be formed of hyaloplasm alone. In that case, this must be looked upon as the essential part of protoplasm. So far as amoeboid phenomena are concerned it is certainly so; but whether the chemical THE PHEXOMEXA OF LIFE. 11 changes which occur in many cells are effected by this or by spongio- plasm is another matter." Another question about which there is some difference of opinion is, which part of the protoplasm is chiefly contractile. It is usually con- cluded that this property rests in the meshwork, but there seems a considerable amount of evidence in favor of the view that part if not all of the contractility resides in the hyaloplasm; for example, in ama3- boid cells the pseudopodial protoplasm are certainly made of this and not of spongioplasm, and when the corpuscle is stimulated the hyalo- plasm flows back into the reticular network. If the view that the hyalo- plasm is chiefly contractile be a correct one, the sijecial condition of an amoeboid cell must be considered to be condition of contraction, and the flowing out of the process to be relaxation. The Cell Nucleus. Nearly all cells at some period of their existence possess nuclei. As has been incidentally suggested the origin of a nucleus in a cell is the first trace of the differentiation of protoplasm. The existence of nuclei was first pointed out in the year 1833 by Robert Brown, who observed them in vegetable cells. They are either small transparent vesicular bodies containing one or more smaller particles (nucleoli), or they are semi-solid masses of protojjlasm 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 protoj^lasm itself, and thus Beale is fully justified in comprising both under the term "ger- minal matter." They exhibit their vitality by initiating, in the major- ity of cases, the process of division of the cell into two or more cells (fission) by first themselves dividing. Distinct observations have been made showing that spontaneous changes of form may occur in nuclei as also in nucleoli. Histologists have long recognized nuclei by two important char- acters : — (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 chemi- cal difference between the protoplasm of the cells and nuclei, as the former is destroyed by these reagents. (2.) Their quality of staining in solutions of carmine, hematoxylin, etc. Nuclei are most commonly oval or round, and do not generally conform to the diverse shapes of the cells; they are altogether less vari- able 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 13 HANDBOOK OF PHYSIOLOGY. whole of the cell, as is the case in the lymjjh corpuscles of lymphatic glands, and in some small nerve cells. Their position in the cell is very variable. In many cells, especially where active growth is jDrogressing, two or more nuclei are present. Structure of Nuclei. The nucleus when in a condition of rest is bounded by a distinct membrane, possibly derived from the spongioplasm of the cell. Besides Node of meshwork Node of meshwork .^»-Nuclear membrane. Nucleolus. Nuclear matrix. Nuclear meshwork. Fig. 10.— The resting nucleus— diagrammatic. (Waldeyer.) the membrane the nucleus consists of two parts, viz., (1) of a reticular network, consisting of anastomosing fibrils made up according to Eabl (fig. 10) of primary and thicker fibres and thinner connecting branches. This network has a marked affinity for staining of reagents and hence is called clii'omoplasm. The fibres are not without structure, since in certain cases they have been shown to consist of minute highly-refract- ing particles which stain deeply imbedded in a regular series in a struc- ..--'*' p.cj Fig. 11. — Diagram of nucleus showing the arrangement of chief chromatic filaments, a. Viewed from the side, tlie polar end being uppermost, p.c.f.. Primary chromatic filaments; «,., nucleolus; n.o.vi., node of meshwork. «. Viewed at the polar end. l.c.f., Looped chromatic filament; «./., ir- regular filament. (Rabl.) tureless matrix forming the filament, the former being called chromatin and the latter «c/iro?>/f/if« from their respective reaction to stains. Ac- cording to some histologists, nucleoli are the mere thickenings of the reticulum at the nodes or junctions of the fibrils, but others consider them to be distinct rounded bodies free from the meshwork. (2) The second part of the nuclear contents is of a homogeneous material rich in proteids but not necessarily fluid, which fills up the THE PHENOMENA OF LIFE. 13 mesh work. This material has but slight affinity for stains, and hence is called achromatic substance or nuclear matrix. Cell Division. The division of a cell is preceded by division of its nucleus. Nuclear division may be either (1) simple or direct, which consists in the simple exact division of the nucleus into two equal parts by constriction in the centre, which may have been preceded by division of the nucleoli; or (2) indirect, which consists in a series of changes which goes on in the arrangement of the nuclear reticulum, resulting in the exact division of the chromatic fibres into two parts which form the chromoplasm of the daughter nuclei. Indirect division is called karyokinesis (xdpuov, a kernel), or mitotic {jiiro^, a thread), and direct division is called amitotic or akinetic {xi.'riffi'} Fig:. 12 Karyokinesis. a, Ordinary nucleus of a columnar epithelial cell; b, c, the same nucleus in the stage of convolution; d, the wreath or rosette form; e, the aster, or single star; f, a nuclear spindle from the Deseemet's endothehum of the frog's cornea; G, h, i, diaster; k, two daughter nuclei. (Klein.) movement). It is now believed that the mitotic nuclear division is all but, if not quite, universal. Somewhat different accounts of the stnges of the nuclear division have been given by different authorities, according to the kind of cell in which the nuclear changes have been studied. The following will summarize the stages of karyokinesis as observed by Klein : The nucleus in a resting condition, i.e., before any changes preceding division occur, consists of a very close meshwork of fibrils, which stain deeply in carmine, embedded in protoplasm, which does not possess this property, the whole nucleus being contained in an envelope. The first change consists of a slight enlargement, the disappearance of the envel- ope and the increased definition and thickness of the nuclear fibrils, which are also more separated than they were and stain better. This is the stage of convolution (fig. 11, B, c). The next step in the process is. 14 HANDBOOK OF PHYSIOLOGY. the arrangement of the fibrils into some definite figure by an alternate looping in and out around a central space, by which means the rosette or ivreath stage (fig. 12, d) is reached. The loops of the rosette next be- come divided at the periphery and their central points become more angular, so that the fibrils divided into portions of about equal length are, as it were, doubled at an acute angle, and radiate V-shaped from the centre, forming a star (aster) or wheel (fig. 12, e), or perhaps from two centres, in which case a double star (diaster) results (fig. 12, g, h. Achromatic spiral Figr. 13.— Early stages of Ivaryokinesis. a. The thicker primary fibres remain and the achro- matic spindle appears, b. The thick fibres split into two and the achromatic spindle becomes longi- tudinal. (Waldeyer.) and I). After remaining almost unchanged for some time, the V-shaped fibres being first re-arranged in the centre, side by side (angle outward), tend to separate into two bundles which gradually assume position at either pole. From these groups of fibrils the two nuclei of the new cells are formed (daughter nuclei) (fig. 12, k), and the changes they pass through before reaching the resting condition are exactly those through which the original nucleus (mother nucleus) has gone, but in a reverse ^^^^^r>K, --. Pole of spindle. Outer granular zone. VA j^\^A SpUt fibres. liL Inner clear zone. 'J ' 'iJijn, Polar corpuscle. Fig. 14. — Monaster stage of karyokinesls. (Waldeyer.) order, viz., the star, the rosette, and the convolution. During or shortly after the formation of the daughter nuclei the cell itself becomes con- stricted and then divides in a line about midway between them. According to Waldeyer the stages are somewhat different, the first (ihange {spirem stage) which occurs is that the fine fibrils of the reticu- lum of the resting nucleus disappear, leaving the thicker more or less V-shaped skeins remaining (fig. 13, a). These thick loops then split longitudinally into two finer threads, and at the same time the achromatic THE PHENOMEXA OF LIFE. 15 spindle appears. The spindle then assumes a more central direction at right angles to the skeins (fig. 13, b), which it did not occupy before, so that the nucleus has two poles, the terminations of the spindle, at each of which is developed a corpuscle {polar corpuscle) — the inclosing membrane is lost, and the matrix of the nucleus becomes continuous with that of the cell; the hyaloplasm separates into two zones, a granu- \ _F'"^ uniting ■"" fllaments. Fig. 15.— Metakinesis— chromatic figure, spindle, a. Early stage, b. Later stage, c. Latest stage —formation of diaster. (Waldeyer.) lar zone at the periphery and a clear zone in the centre; this is the monaster stage. The chromatic fibres, at first with their angles toward the centre, then arrange themselves {metakinesis) with their looj^s toward the poles, and move along the spindle further and further from each other, being connected by the fine fibres of the spindle only. In this way. around each pole, loops of fibres are grouped, which soon take the arrangement and appearance of the primary chromatic fibres {diaster). Next the new nuclear membrane begins to form, and the jDolar corpuscle Remains of spindle. Line of separation of the two cells. Antipole of daugh- ter nucleus. Lighter substance of the nucleus. Cell protoplasm. HUus. Fig. 16.— Final stages of karyokinesis. In the lower figure the changes are still more advanced than in the upper. (Waldeyer.) disappears. Thus are two daughter nuclei formed {dispirem stage). The cell itself divides, and the nuclear fibres of the daughter nuclei as- sume the arrangement of the resting nucleus. Differences between Animals and Plants. Having considered at some length the vital proj)erties of protoplasm, as shown in cells of vegetable as well as of animal organisms, we are now in a position to discuss the question of the differences betwee^i jJlants and 16 HANDBOOK OF PHYSIOLOGY. animals. It might at the outset of our inquiry have seemed an unnec- essary thing to recount the distinctions which exist between an animal and a vegetable as they are in many cases so obvious, but, however great the differences may be between the higher animals '-ind plants, in the lowest of them the distinctions are much less plain. In the first place, it is important to lay stress upon the differences between vegetable and animal cells, first as regards their structure and next as regards their functions. (].) It has been already mentioned that in animal cells an envelope or cell-wall is by no means always present. In adult vegetable cells, on the other hand, a well-defined cellulose wall is highly characteristic; this, it should be remembered, is non-nitrogenous, and thus differs' chemically as well as structurally from the contained protoplasmic mass. Moreover, in vegetable cells (fig. 17, b), the protoplasmic contents of the cell fall into two subdivisions: (1) a continuous film which lines the interior of the cellulose wall; and (2) a reticulate mass containing Fig. 17. — (a.) Young vegetable cells, showing cell-cavity entirely filled with granular protoplasm inclosing a large oval nucleus, with one or more nucleoli, (b.) Older cells from same plant, show- ing distinct cellulose-wall and vacuolation of protoplasm. the nucleus and occupying the cell cavity; its interstices are filled with fluid. In young vegetable cells such a distinction does not exist; a finely granular protoplasm occupies the whole cell-cavity (fig. 17, a). Another striking difference is the frequent presence of a large quan- tity of intercellular substance in animal tissues, while in vegetables it is comparatively rare, the requisite consistency being given to their tissues by the tough cellulose walls, often thickened by deposits of lignin. As an example of the manner in which this end is attained in animal tissues, may be mentioned the deposition of lime salts in a matrix of intercellular substance which occurs in the formation of bone. As regards the respective functions of animal and vegetable cells, one of the most important differences consists in the power which vege- table cells possess of being able to build up new complicated nitrogenous and non -nitrogenous bodies out of very simple chemical substances ob- tained from the air and from the soil. They obtain from the air, oxy- gen, carbonic anhydride, and water, as well as traces of ammonia gas; and from the soil they obtain water, ammonium salts, nitrates, sulphates, THE PHENOMENA OF LIFE, 17 and phosphates, and sucli bases as potassium, calcium, magnesium, so- dium, iron, and others. The majority of plants are able to work up these elementary compounds into other and more complicated bodies. This they are able to do in consequence of their containing a certain coloring matter called clilorophyll, the presence of which is the cause of the green hue of plants. In all plants which contain chlorophyll two processes are constantly going on when they are exposed to light : one, which is called trtie respiration and is a process common to animal and vegetable cells alike, consists in the taking of the oxygen from the at- mosphere and the giving out of carbon dioxide; the other, which is peculiar apparently to bodies containing chlorophyll, consists in ihe taking in of carbon dioxide and the giving out of oxygen. It seems that the chlorophyll is capable of decomposing the carbon dioxide gas and of fixing the carbon in the structures in the form of some new com- pound, one of the most rapidly formed of which is darcli. The first step in the formation of starch is the union of carbon dioxide and water to form formic aldehyde, C02+Il20 = CH204-02, oxygen being evolved; then by polymerization the formation of sugar thus, 6 CIl20 = C6Hi206; and by dehydration, C6H12O6 — Ii20 = C6Hio05, the production of starch. In this way is starch synthesized or built up. Vegetable protoplasm by the aid of its chlorophyll is able to build up a large number of bodies besides starch, the most interesting and important being proteid or albumin. It appears to be a fact that the power which bodies possess of being able to synthesize is to a large extent dependent upon the chlo- rophyll they contain. Thus the power is only present to any marked extent in the plants in v/hicli chlorophyll is found and is absent in those Avhich do not possess it; while on the other hand it is present in the extremely few animals which contain it and is absent except in certain rare instances as one of the properties of animal protoplasm. It must be recollected, however, that chlorophyll without the aid of the light of tlie sun can do nothing in the way of building up substances, and a plant containing chlorophyll when placed in the dark, as long as it liyes, and that is not as a rule long, acts as though it did not contain any of that substance. It is an interesting fact that certain of the bac- teria have the chlorophyll replaced by a similar pigment which is able to decompose carbon dioxide gas. Animal cells, except in the very rare cases above alluded to, do not possess the power of building up from simple materials ; their activity is chiefly exercised in the opj)Osite direction, viz,, they have brought to them as food the complicated compounds produced by the vegetable kingdom, and with them they are able to perform their functions, set- ting free energy in the direction of heat, motion, and electricity, and at the same time eliminating such bodies as carbon dioxide and water, and producing other bodies, many of which contain nitrogen, but which are 2 18 HANDBOOK OF PHYSIOLOGY. derived from decomposition, and only in very rare cases from building up. It must be distinctly understood, however, that there are instances of animal cells performinci^ synthetic functions and of combining two simpler compounds to produce one more comjilex, and it is quite possi- ble that many of the processes performed by the cells of certain organs are instances of synthesis, and not as they have been described of break- ing down ; and the reverse is undoubtedly the case with vegetable cells, so that it is impossible to generalize to a greater extent than to say that the tendency of the activity of the vegetable cell is chiefly toward syn- thesis, and of the animal cell toward analysis. With reference to the substance chlorophyll it is necessary to say a few words. It has been noted that the synthetical operations of vege- table cells are peculiarly associated with the possession of chlorophyll and that these operations are deiDendent upon the light of the sun. It has been further shown that a solution of chlorophyll has a definite absorption spectrum when examined with the spectroscope, and that it is particularly those parts of the solar spectrum corresponding to these absorption bands which are chiefly active in the decomposition of car- bonic anhydride, and that, moreover, the position of the maximum absorp- tion corresponds with the maximum of energy of light. In the synthet- ical processes of the plant then, by aid of its chlorophyll, the radiant energy of the sun's rays becomes stored up or rendered potential in the products formed. The potential energy is set free, or is again made kinetic, when these products simply by combustion produce heat, or when they are taken into the animal organism and used as food and to produce heat and motion. The influence of light is not an absolute essential to animal life; in- deed, it is said not to increase the metabolism of animal tissue to any extent, and the animal cell does not receive its energy directly from the sun's light, nor yet to any extent from the sun's heat, but from the products formed by vegetable metabolism supplied as food, either di- rectly, as in the case of herbivora, or indirectly in the case of carnivora. The potential energy of these food stuffs is set free in the destructive metabolism of the animal cell already alluded to. But it must be always recollected that anabolism is not peculiar to vegetable, or katabolism to animal cells; both processes go on in each, but the cJiief function, as far as we know at present of the former, is to transform kinetic into po- tential energy, and of the latter to render potential energy kinetic, as in heat, motion, and electricity. With reference to the food of plants, it should not be forgotten that some of the lowest forms of vegetable life, e.g., the bacteria, will live only in a highly albuminous medium, and in fact seem to require for their growth elements of food stuffs which we shall see later on are es- THE PHEXOME>rA OF LIFE. 19 seutial to animal life. In their metabolism, too, they very closely ap- proximate to animal cells, not only requiring an atmosphere of oxygen, but giving out carbonic anhydride freely, and secreting and excreting many very complicated nitrogenous bodies, as well as forming proteid, carbohydrates, and fat, requiring heat but not light for the due perform- ance of their functions. (2.) There is, commonly, a difference in general chemical composition between vegetables and animals, even in their lowest forms ; for associated with the protoplasm of the former is a considerable amount of cellulose, a substance closely allied to starch and containing carbon, hydrogen, and oxygen only. The presence of cellulose in animals is much more rare than in vegetables, but there are many animals in which traces of it may be discovered, and some, the Ascidians, in which it is found in consider- able quantity. The presence of starch in vegetable cells is very charac- teristic, though, as we have seen above, it is not distinctive, and a sub- stance, glycogen, similar in composition to starch, is very common in the organs and tissues of animals. (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 mo- tion is now known, howe.ver, 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 ex- hibit ciliary or amoeboid movements of a like kind to those seen in amoebge; and even among the higher orders of plants, many, e.^., i)w/ifea Muscijmla (Venus's fly-trajD), and Mimosa sensitiva (Sensitive plant), ex- hibit such m.otion, 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 joower 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 ani- mals 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 di- gestive canal. This distinction then is not a cardinal one. CHAPTER II. THE FUNCTIONS OF ORGANIZED CELLS. As we proceed upward in the scale of life from unicellular organisms, we find that another phenomenon is exhibited in the life history of the higher forms, namely, that of Development. An amceba comes into be- ing derived from a previous amoeba; it manifests the properties and performs the functions of its life which have been already enumerated; it grows, it reproduces itself, whereby several amoebas result in place of one, and it dies. It cannot be said to develop, however, unless the for- mation of a nucleus can be considered as an indication of such a process. In the higher organisms it is different; they, indeed, begin as a single cell, but this cell on division and subdivision does not form so many *aSi*''*-^SiI3=» < Fig. 18.— Transverse section througrh embryo chick (26 hours). «, Epiblast; ft, mesoblast: c, hypoblast; d, central portion of mesoblast, which is liere fused with epiblast; e, primitive groove; /, dorsal ridge. (Klein.) independent organisms, but produces the material from which, by devel- opment, the complete and perfect whole is to be derived. Thus, from the spherical ovum, or germ, which forms the starting-point of animal life and which consists of a protoplasmic cell with a nucleus and nucle- olus, in a comparatively short time, by the process of segmentation which has been already mentioned, a complete membrane of cells, polyhedral in shape from mutual pressure, called the Blastoderm, is formed, and this speedily divides into two and then into three layers, chiefly from the rapid proliferation of the cells of the first single layer. These layers are called the Epiblast, the Mesoblast, and the Hypoblast (fig. 18). It is found in the further development of the animal that from each of these layers is produced a very definite part of its completed body. For example, from the cells of the epiblast are derived, among other 20 THE FUXCTIONS OF ORGAXIZED CELLS. 21 ■structures, the skin and the central nervous system ; from the mesobkst is derived the flesh or muscles of the body, and from the hypoblast the epithelium of the alimentary canal and some of the chief glands, and so on. It is obvious that the tissues and organs so derived exhibit in a vary- ing degree the primary properties of jDrotoplasm. The muscles, for example, derived from certain cells of the mesoblast are particularly con- tractile and respond to stimuli readily, while the cells of the liver, although possibly contractile to a certain extent, have to do chiefly with the processes of nutrition. Thus, in development, we see that as the cells of the embryo in- crease in number it speedily becomes necessary for the organism to depute to different groups of cells, or to their equivalents {i.e., to the tissues or organs to which they give rise), special functions, so that the Tarious functions which the original cell may be supposed to discharge, and the various properties it maybe supposed to possess, become divided up among various groups of resulting cells. The work of each group is specialized. As a result of this division of labor, as it may be called, these functions and properties are, as might be expected, develoj^ed and made more perfect, while the tissues and organs arising from each group of cells are developed also, with a view to the more convenient and effective exercise of their functions and employment of their pro^v erties. In studying the functions of the human body it is necessary first of all to know of what it is composed, of what tissues and organs it is made up; this can of course only be ascertained by the dissection of the dead body, and thus it comes that Anatomy (avar/.avw, to cut up) the science which treats of the structure of organized bodies, is closely associated with physiology; so closely, indeed, that Histology (iVr.)?, a web), which is especially concerned with the minute or microscopic structure of the tissues and organs of the body, and which is strictly s2Deaking a depart- ment of anatomy, is usually included in works on physiology. There is much to be said in favor of such an arrangement, since it is impossible to consider the changes which take jflace in any tissue during life, apart from the knowledge of the structure of the tissues themselves. To understand the structure of the human body in an intelligent wa}', much help is obtained from the study of the structure of other animals, from the lowest to the highest, which is the province of Comparative Anatomy ; while Embryology, which is concerned Avith the mode of origin of the various tissues in the embryo of each animal, and which is usually studied at the end of physiology, should from some i^oints of view be considered as an introduction to the subject. A second important essential to the right comprehension of the changes which take place in the living organism is a knowledge of the chemical composition of the body. Here, however, we can only deal 22 HANDl'.OOK OF PHYSIOLOGY. with the chemieal composition of tlie dead, body, and it is as well at once to admit that there may be many chemical differences between living and not living tissues; but as it is imjicjssible to ascertain the exact chemical composition of the living tissues, the next best thing which can be done is to find out as much as 2)ossible about the com- position of the same tissues after they are dead. This is the assistance which the science of Chemistry can afford to the physiologist, and the same science is concerned with the composition of the ingesta and egesta, as well as with that of the fluids of the body. Having mastered the structure and composition of the body, we are brought face to face with physiology proj^er, and have to investigate the vital changes which go on in the tissues, the various actions taking jihice as long as the organism is at work. The subject includes not only the observation of the manifest processes which are continually taking place in the healthy body, but the conditions under which these are brought about, the laws which govern them and their effects. We know from our study of biology that the cells of which the tis- sues are composed cannot live without food, both solid and liquid. In a complicated organism like the body of man, the tissues cannot sujijDly themselves with food directly like the amoeba, and so it comes that the various tissues are furnished with what they require by means of a fluid, the blood, which is carried to them in tubes or canals, the blood- vessels, which are distributed to every region of the body. In order that the blood shall reach all parts, the system of vessels in which it is con- tained is supplied with a central pumping organ, the heart. Then we find that as the oxygen, which is one of the requisites of the life of the tissues, and which is carried to the tissues by the blood, is used up, a special means is provided by respiration, or breathing, by means of which the blood is exposed to a new supply of oxygen of the air, which is taken into special organs, the lungs, for the purpose, and which at the same time allows of the elimination of the carbonic anhydride the blood conveys from the tissues. Then again, as the solid food for the tissues cannot be conveyed in the blood in the exact form in which it is introduced into the body, a special and complicated apparatus is pro- vided, that of digestion, by means of which the necessary changes are brought about in the food. The digested food is then absorbed and carried to the blood, either directly with little further change by means of another system of vessels in connection with the blood-vessels, the lymplialic vessels, or after jDassing through a special organ or gland, the liver, by means of which some further changes take place. In the digestive apparatus we have the organs, the stomach and intestines, into which the food is received for the ^iurpose of being acted upon by cer- tain chemical agents, of which ferments, bodies which are capable of setting up profound changes in other bodies without themselves under- THE FUNCTIONS OF ORGANIZED CELLS. ^ 23 going change, are the most important; there is added the apparatus by means of which the altered food stuffs are absorbed or reach the two systems of blood-vessels already mentioned, and a muscular apparatus contained in the walls of the intestinal tube by means of which that part of the food which is not fit for absorption is removed from the body. In addition to this excretory apparatus we have another, the kidneys, which are concerned with the removal of certain substances from the blood which have served their purpose in the economy. Then we have the muscular system, which by its special power of contraction is capable of bringing about all the movements of the body — those of the frame, the head, arms, legs, etc., as well as those of the heart, the vessels, the alimentary canal, and the like. The nervous sys- tem, by the aid of which the processes of the living body may be regu- lated and controlled. Lastly, we have a special system — that of the generative system, by means of which the reproduction of the species may take place. To these subjects, the merest outline of which has been here sketched, our attention has to be given in the succeeding chapters, but it may be well to mention as a preliminary that the information about them which we have at our disposal has been derived from many sources, the chief of which are as follows : — (1.) From actual observation of the various phenomena occurring in the human body from day to day, and from hour to hour, as, for exam- ple, the estimation of the amount and composition of the ingesta and egesta, the respiration, the beat of the lieart, and the like; (3.) From observations upon other animals, the bodies of which we are taught by comparative anatomy approximate to the human body in structure; (3.) From observations of the changes produced by experiment upon the various processes in such animals; (4.) From observations of the changes in the working of the human body produced by disease; (5.) From observations upon the gradual changes which take place in the functions of organs when watched in the embryo from their earliest beginnings to their completed development. In accordance with the plan sketched out' above, the next chapter will be devoted to a consideration of the minute structure of the ele- mentary tissues, and the one after that to a jDreliminary account of the chemical composition of the body. These two chapters will serve as an introduction to the study of the problems of physiology proper, which will be commenced in Chapter V. CHAPTER III. THE STRUCTURE OF THE ELEMENTARY TISSUES. The careful examination of the minute anatomy of the body has shown that there are certain elementary structures, of which, alone or when combined in varying proportions, the whole of the organs and tissues of the body are made up. These Elementary Tissues are four in number, called: (1.) The Epitlielial ; (2.) The Cofinective ; (3.) The Mnsctdar, and (4.) 7'he Nervous. To these four, some would add a fifth, looking upon the Blood and Lympli, containing, as they do, formed elements in a fluid menstruum, as a distinct tissue. All of these elementary tissues consist of cells and of their altered equivalents. It will be as well therefore to indicate some of the differ- ences between the cells of the body. They are named in various ways, according to their shape, situation, contents, origin, awd functions. (a.) From their shape, cells are called spherical or spheroidal, which is the typical shape of the free cell; this maybe altered to polyhedral when the pressure on the cells in all directions is nearly the same; of this the primitive segmentation cells afford an example. The discoid form is seen in blood-corpuscles, and the scale-like form in superficial epithelial cells. Some cells have a jagged outline and are then called prickle cells. Cells of cylindrical, conical, or prismcitic form occur in various places in the body. Such cells may taper off at one or both ends into fine processes, in the former case being caudate, in the latter fusiform. They may be greatly elongated so as to become fibres. Cells "with hair-like processes, or cilia, projecting from their free surfaces, are a special variety. The cilia vary greatly in size, and may even exceed in length the cell itself. Finally, cells may be hranched or stellate with long outstanding processes. (J.) From their situation cells may be called /re(?, as in the blood, or comhined, when connected together or with other elements to form organs and tissues. (c.) From their contents cells are called, when containing fat for example, /a«f cells ; when containing Y^gra^wi, pigment cells, etc. (fZ.) From their function cells are called secreting, protective, sensi- tive, contractile, and the like. (e.) From their origin cells are called epiblastic and mesoblastic and Tiypoblastic. 24 THE STRUCTURE OF THE ELEMENTARY TISSUES. '^5 Modes of Connection. — Cells are conuected together to form tissues in various ways. (1.) By mean of a cementing intercellular substance. This is prob- ably always present as a transparent, colorless, viscid, albuminous sub- stance, even between the closely apposed cells of epithelium, while in the case of cartilage it forms the main bulk of the tissue, and the cells only appear as imbedded in, not as cemented together by, the intercel- lular substance. This intercellular substance may be either homogene- ous or fibrillated. In many cases {e.g., the cornea) it can be shown to •contain a number of irregular branched cavities, which communicate witli each other, and in which branched cells lie: through these branch- ing spaces nutritive fluids can find their way into the very remotest parts of a non-vascular tissue. As a special variety of intercellular substance must be mentioned the basement membrane {memhrana projyria) which is found at the base of the epithelial cells in most mucous membranes, and especially as an Investing tunic of gland follicles which determines their shape, and which may persist as :). hyaline saccule after the gland cells have all been discharged. (2.) By anastomosis of their processes. This is the usual way in which stellate cells, e.g. of the cornea, are united : the individuality of ■each cell is thus to a great extent lost by its connection with its neigh- bors to form a reticulum: as an example of a network so produced we may cite the stroma of lymphatic glands. Sometimes the branched processes breaking up into a maze of minute fibrils, adjoining cells are connected by an intermediate reticu- lum : this is tlie case in the nerve cells of the spinal cord. Derived Tissue-elements.— Besides the Cell, which may be termed the primary tissue-element, there are materials which may be termed secondary or derived tissue-elements. Such are Intercellular substance. Fibres, and Tubules. a. Intercellular substance is probably in all cases directly derived from the cells themselves. In some cases {e.g. cartilage), by the use of re:igents the cementing intercellular substance is, as it were, analyzed into various masses, each arranged in concentric layers around a cell or group of cells, from which it was probably derived. /?. Filrres. In the case of the crystalline lens, and of muscle both striated and non-striated, each fibre is simply a metamorphosed cell: in the case of a striped fibre, the elongation being accompanied by a mul- tiplication of the nuclei. The various fibres and fibrillaj of connective tissue result from a gradual transformation of an originally homogene- ous intercellular substance. Fibres thus formed may undergo great <.'hemical as well as physical transformation : this is notably the case with yellow elastic tissue, in which the sharply defined elastic fibres, 26 HAXDBOOK OF PHYSIOLOGY. possessing great jDower of resistance to reagents, contrast strikingly witli the honiogeueous matter from which they are derived. y. Tubules, such as the capillary blood-vessels, which were originally supposed to consist of a structureless membrane, have now been proved to be composed of flat, thin cells, cohering along their edges. Decay and Death of Cells.— There are two chief ways in which the comparatively brief existence of cells is brought to an end. (1) Mechan- ical abrasion, (2) Chemical transformation. 1. The various epithelia furnish abundant examples of mechanical abrasion. As it approaches the free surface, the cell becomes more and more flattened and scaly in form and more horny in consistency, till at length it is simply rubbed off as in the epidermis. Hence we find epi- thelial cells in the mucus of the mouth, intestine, and genito-urinary tract. 2. In the case of chemical transformation the cell-contents undergo- a degeneration Avliich, though it may be pathological, is very often a normal process. Thus we have (a) fatt// metamorphosis producing oil-globules in the secretion of milk, fatty degeneration of the muscular fibres of the uterus- after the birth of the fo3tus, and of the cells of the Graafian follicle giving rise to the "corpus luteum." (b) Pirjmetdary degeneration from, deposit of pigment, e.g. in the epithelium of the air vesicles of the lungs, (c) Calcareous degeneration, which is common in the cells of many cartilages. I. The Epithelial Tissues. The term epithelium is applied to the cells covering the skin, the mucous and serous membranes, and to those forming a lining to other parts of the body as well as entering into the formation of glands. For example: — Epithelium clothes (1) the whole exterior surface of the body, form- ing the epidermis with its appendages — nails and hairs; becoming con- tinuous at the chief orifices of the body — nose, mouth, anus, and urethra — with the (2) ej)ithelium which lines the whole length of the (3) respi- ratory, alimentary, and genito-urinary tracts, together with the ducts of their various glands. Epithelium also lines the cavities of (4) the brain and the central canal of the spinal cord, (5) the serous and synovial membranes, and (6) the interior of all blood-vessels and lymphatics. Epithelial cells possess an intracellular and an intranuclear network (p. 9 and 10). When combi^ied together to form a tissue, they are held together by a clear, albuminous, cement-substance, scanty in amount. The viscid semi-fluid consistency both of cells and intercellular sub- stance permits such changes of shape and arrangement in the individual THE STRUCTURE OF THE ELEMEXTARY TISSUES. 27 cells as are necessary if the epithelium is to maintain its integrity in organs the area of whose free snrface is so constantly changing, as the stomach, lungs, etc. Thus, if there be but a single layer of cells, as in the epithelium lining the air vesicles of the lungs, the stretching of this membrane causes such a thinning out of the cells that they change their shape from spheroidal or short columnar, to squamous, and vice versa, when the membrane shrinks. Epithelial tissues are non-vascular, that is to say, do not contain blood-vessels, but in some varieties minute channels exist between the cells of certain layers through w^hich they may be supplied with nour- ishment from the subjacent blood-vessels. Xerve fibres are suj^jjlied to the cells of many epithelia. Epithelial tissue is classified according as tiie cells composing it are arranged in a single layer when it is ni/njjle, or in several layers when it is called stratified or laminated, or in two or three layers occupying a position between the other two forms, when it is termed transitional. Of each form, when there are several varieties, they are named accord- ing to the shaj)e of the cells composing it. Classification of Epithelium. (a) Simple. — (1.) Squamous, scaly, pavement, or tessellated; (3.) Spheroidal or glandular; (3.) Columnar, cylindrical, conical or goblet- shaped; (4.) Ciliated. (b) Transitional. (c) Stratified. (a) Simple Epithelium. Squamous Epitlielium. — This form of epithelium is found arranged as a single layer of flattened cells, as («) the pigmentary layer of the retina, and forms the lining of {h) the interior of the serous and syno- vial sacs, (c) the alveoli of the lungs, and {d) of the heart, blood- and lymph-vessels. It consists of cells, which are flattened and scaly, with a more or less irregular outline. In the pigment cells of the retina there is a deposit of pigment in the cell-substance. This pigment consists of minute molecules of a colored substance, melanin, imbedded in the cell-substance and almost concealing the nucleus, which is itself transparent. In white rabbits and other albino animals, in which the pigment of the eye is absent, this layer is found to consist of colorless pavement epithelial cells. The squamous epithelium which is found as a single layer lining the serous membranes, and the interior of blood- and lymphatic-vessels, is generally called by a distinct name — Endothelium. •28 HANDBOOK OF PHYSIOLOGY. The presence of endothelium in any locality may be demonstrated by staining the part lined by it with silver nitrate, which brings into view ±he intercelluar cement substance. It is found that when a small portion of a perfectly fresh serous Fig. 19.— Piginent-cells from the retina. A, Cells still culieiiug, seen on their surface; o, nucleus "indistinctly seen. In the other cells the nucleus is concealed by the pigment granules, b. Two cells rseen in profile; a, the outer or posierior part containing scarcely any pigment. X 310. (Heule.) membrane for example (fig. 20), is immersed for a few minutes in a solution of silver nitrate, and exposed to the action of light, the silver is precipitated in some form in the intercellular cement substance, and the endothelial cells are thus mapped out by fine, dark, and generally sinuous lines of extreme delicacy. The cells vary in size and shape, and .areas a rule irregular in outline; those lining the interior of blood - Fig. 20.— A piece of the omentum of a cat, stained in silver nitrate. X 100. The tissue forms a ''fenestrated niernbrnne,''' that is to say, one which is studded with lioles or windows. In the figure these are of various shapes and sizes, leaving trabeeula?, the basis of which is fibrous tissue. The trabecute are of various sizes and are covered witli endothelial cells, the nuclei of which have been made evident by staining with hfeiiiatoxylin after the silver nitrate has outlined the cells by staining the intercellular substance. ( Y. D. Harris. ) vessels and lymphatics being spindle-shaped Avith a very wavy outline. They inclose a clear, oval nucleus, which, when the cell is viewed in profile, is seen to project from its surface. The nuclei are not however evident unless the tissue which has been already stained in silver nitrate. THE STRUCTURE OF THE ELEMENTARY TISSUES. 29- is placed in another dye, sucii as h^ematoxylin, which has the property of selecting and staining its nuclei. Endothelial cells in certain situations may be ciliated, e.g., those of the mesentery of the frog, especially during the breeding season. Fig. 81. — Abdominal surface of central tendon of the diaphragm of rabbit, showing the general- polygonal shape of the endothelial cells: each cell is nucleated. (Klein.) x 300. Besides the ordinary endothelial cells above described, there are found on the omentum and parts of the pleura of many animals, little- bud-like processes or nodules, consisting of small polyhedral granular- cells, rounded on their free surface, which have multiplied very rapidly by division (figs. 22 and 23). These constitute what is known as ge7'- minating endothelium. The process of germination doubtless goes on in health, and the small cells which are thrown off in succession are- Fig. 22.— Peritoneal surface of a portion of the septum of the great lymph-sacs of frog. The- stomata, some of which are open, some collapsed, are surrounded by endothelial cells. (Klein.) X 160. carried into the lymphatics and contribute to the number of the lymph corpuscles. The buds may be enormously increased both in number and size in certain diseased conditions. On those portions of the peritoneum and other serous membranes in whicli lymphatics abound apertures (fig. 22) are found surrounded by small, more or less cubical, cells. These apertures are called siomafa. They are particularly well seen in the anterior wall of the great lymph 30 HAXDIiOOK OF PHYSIOLOGy. sac of the frog (fig. 22), and in the omentum of the rabbit. These are really the open mouths of lymphatic vessels or spaces, and through Fig '^3.— A portion of the great omentum of dog, which shows, among the flat endothelium of the surface, small and large groups of germinating endothelium between which are many stomata. (Klem.j X 300. them lymph-corpuscles and the serous fluid from the serous cavity pass into the lymphatic system. They should be distinguished from smaller and more numerous apertures between the cells which are not lined by Fig. 24. Fig. 25. Fig. 24.— A small piece of the liver of the horse. (Cadiat.) Fig. 25.— Glandular epitlielium. Small lobule of a mucous gland of the tongue, showing nu- cleated glandular cells. X 200. (V. D. Harris.) small cells, although the surrounding cells seem to radiate from them, filled up by intercellular substance or by processes of the cells under- neath. These are called pseudo-stomata (fig. 23). THE STRUCTURE OF THE ELEMENTARY TISSUES. 31 In the neighborhood of the stomata the cells often manifest indica- tions of germinating. They mu}^ be either large with two or more nuclei, or about half the size of the generality of cells. Germinating cells of this kind or of the kind above described, are generally very granular. Spheroidal or glandular epifhelium forms the active secreting agent in the glands, the cells are however not always of the same shape but may be besides the typical spheroidal, polyhedral from mutual pressure, or even columnar. Examples of glandular epithelium are to be found in the liver (fig. 24), in the secreting tubes of the kidney, and in the salivary (fig. 25) and gastric glands. Columnar epithelium (fig. 28, a and b) as a single layer lines (a.) the mucous membrane of the stomach and intestines, from the cardiac Fig. 26. Fig. 27. Fig. 26.— Columuar epithelial cells from the intestinal mucous membrane of a cat. a and 6, Small cells of the lowest layer: c, superficial layer; d, goblet cells (Cadiat.) Fig. 27.— Goblet cells. (Klein.) orifice of the stomach to the anus, and (b.) wholly or in jjart the ducts of the glands opening on its free surface; also (c.) many gland-ducts in other regions of the body, e.g., mammar}^ salivary, etc. Columnar epithelium consists of cells which are cylindrical or pris- matic in form containing a large oval nucleus. They vary in size and also to a certain extent in shape; the outline is often jagged and irreg- ular from pressure of neighboring cells, but one end of the cell is always narrower than the other, and by this narrower end the cell is as a rule attached to the membrane beneath. The intracellular and intranuclear networks are well developed, and in some cases the spongioplasm is arranged in rods or longitudinal striae at one part of the cell,- generally the attached border, as in some of the cells of the ducts of salivary glands. This may also be the case with the columnar epithelial cells of the alimentary canal which possess an apparently structureless layer on their free surface : such a layer, appearing striated when viewed in sec- tion, is termed the "striated basilar border" (fig. 28, a). The protoplasm of columnar cells may be vacuolated and may also 32 HANDBOOK OF PHYSIOLOGY. contain fat or other substances, of which the most h"kely is mucin or its antecedent mucigen, to be seen in the form of granules. It is to the presence of mucin that a curious transformation which columnar cells may undergo is due, and from which the alteration in their shape whereby "goblet-cells" are produced (fig. 27) arises. These altered cells, are hardly ever evident in a perfectly fresh specimen; but if such a specimen be watched for some time, little knobs are seen gradually to appear on the free surface of the epithelium and are finally detached; these consist of the cell-contents which are discharged by the open mouth of the goblet, leaving the nucleus surrounded by the remains of the protoplasm in its narrow stem. This transformation is a normal process which is continually going- on during life, the discharged cell-contents contributing to form mticus. ,! ig;. 38. — Vertical section of an intestinal villus of a eat. o. The striated basilar border of the epithelium; b, columnar epitheliimi; c, goblet cells; d. central lymph-vessel; e, unstriped muscular fibres; /, adenoid stroma of the villus in which are contained lymph corpuscles. cKlein.) the cells themselves being supposed in many cases after discharge to recover their original shape. Ciliated ejjitheliuni consists of cells which are generally cylindrical in form (figs. 29, 30), but may be spheroidal or even almost squamous. This form of epithelium lines — (a.) the mucous membrane of the respiratory tract beginning just beyond the nasal aperture and com- pletely covering the nasal passages, except the uj^per part to which the olfactory nerve is distributed, and also the sinuses and ducts in connec- tion with-it and the lachrymal sac; the upper surface of the soft palate and the naso-pharynx, the Eustachian tube and tympanum, the larynx, except over the vocal cords, to the finest subdivisions of the bronchi. In part of this tract, however, the epithelium is in several layers, of which only the most superficial is ciliated, so that it should more accu- rately be termed transitional (p. 35) or stratified, (b.) Some portions of the generative apparatus in the male, viz., lining the " vasa eflerentia '* of the testicle, and their prolongations as far as the lower end of the THE STRUCTUKE OF THE ELEMENTARY TISSUES. 33 epididymis; in the female (c.) commencing about the middle of the neck of the uterus, and extending throughout the uterus and Fallopian tubes to their fimbriated extremities, and even for a short distance on the peritoneal surface of the latter, (d.) The ventricles of the brain and the central canal of the spinal cord are clothed with 'ciliated epithe- lium in the child, but in the adult this epithelium is limited to the central canal of the cord. In the embrj^o the jjharynx, oesophagus, and part of the stomach may also be lined with ciliated cells, (e.) The ex- cretory ducts of certain small glands in different localities, (f.) In certain animals, especially the lower vertebrates, ciliated cells line the beginning of the tubes of tlie kidneys. The Cilia are fine hair-like processes Avhich give the name to this variety of epithelium j they vary a good deal in size in different classes Fig. 39. Fig. .30. Fig. 29.— Spheroidal ciliated cells from the mouth of th« frog, x 300 diameters. (Sharpey.) Fig. 30. — Ciliated epithelium fi-oin the human trachea. Large, fully formed cell. 6, Shorter cell; c, developing cells with more than one nucleus. (Cadiat.) of animals, being very much smaller in the higher than among the lower orders, in which they sometimes exceed in length the cell itself. The number of cilia on any one cell ranges from ten to thirty, and those attached to the same cell are often of different lengths, in the huinan trachea measuring j q-Ju to -o^Vo of ^^^ inch, but nearly ten times the length in the cells of the epididymis. The cilia themselves are fine rounded or flattened processes, appar- ently homogeneous, pointed toward their free extremities. According to some observers these processes are connected through intervening knob-like Junctions with longitudinal fibres which pass to the other end of the cell, but which are not connected with the nucleus. When living ciliated epithelium, e.g., from the gill of a mussel, or oyster, or from the mouth of the frog, or from a scniping from a polypus from the human nose, is examined under the microscope in a drop of O.G per cent solution of common salt {normal saline solutioii), the cilia are seen to be in constant rapid motion, each cilium being fixed at one end, and swinging or lashing to and fro. The general impression given 3 34 HANDBOOK OF I'll Y.SIOLOG Y. to the eye of the observer is very similar to tliat produced by waves in a field of corn, or swiftly running and ri^ipling water, and the result of their movement is to produce a continuous current in a definite direc- tion, and this direction is invariably the same on the same surface, being always, in the case of a cavity, toward its external orifice. Ciliary Motion. — Ciliary, which is closely allied to amoeboid and muscular motion, is alike independent of the will, of the direct influence of the nervous system, and of muscular contraction. It may continue for several hours after death or removal from the body, pro- vided the portion of tissue under examination be kept moist. Its inde- pendence of the nervous system is shown also in its occurrence in the lowest invertebrate animals apparently unprovided with anything analogous to a nervous system, in its persistence in animals killed by prnssic acid, by narcotic or other poisons, and after the direct ajiplica- tion of narcotics, such as morphia, ojoium, and belladonna, to the ciliary surface, or of electricity through it. The vapor of chloroform arrests the motion; but it is renewed on the discontinuance of the application. The movement ceases when the cilia are deprived of oxygen, although it may continue for a time in the absence of free oxygen, but is revived on the admission of this gas. Carbonic acid stops the movement. The contact of various substances, e.g., bile, strong acids, and alkalies, will stop the motion altogether; but this seems to depend chiefly on destruction of the delicate substance of which the cilia are composed. Temj^eratures above 45° C. and below 0° C. stop the movement, whereas moderate heat and dilute alkalies are favorable to the action and revive the movement after temporary cessation. The exact explanation of ciliary movement is not known; whatever may be the exact cause, however, at any rate the movement must depend ujoon some changes going on in the cell to which the cilia are attached, as when the latter are cut otf from the cell the movement ceases, and when severed so that a portion of the cilia are left attached to the cell, the attached and not the severed j)ortions continue the movement. The most probable cause of the movement is that it is part of the inherent power which protoplasm possesses and that the cilia are but prolonga- tions of the spongioplasm of the cell. It has been suggested by Engel- mann that if this be the case, the contractile part of the protoplasm is only on the concave side of a curved cilium, and that when this con- tracts that the cilium is brought downward; where relaxation occurs, the cilium rebounds as if by the elastic recoil of the remainder or convex border. As a special subdivision of ciliary action may be mentioned the motion of spermatozoa, which may be regarded as cells with a single cilium. THE STRUCTURE OF THE ELEMENTARY TISSUES. 55 (b) Transitional Epithelium. This term has been applied to cells, which are neither arranged in a single layer, as is the case with simple epithelium, nor yet in many superimposed strata as in laminated; in other words, it is emjDloyed when epithelial cells are found in two, three, or" four superimposed layers. The upper layer may be either single columnar, columnar ciliated, or squamous. When the uj^per layer is columnar or ciliated the second layer consists of smaller cells fitted into the inequalities of the cells above them, as in the trachea (fig. 30). The epithelium which is met with lining the urinary bladder and ureters is, however, the transitional j^wr excellence. In this variety there Fig. 31. Fig.: Fig. 31.— Epithelium of the bladder, a. One of the cells of the first row; b, a cell of the second row; c, cells in situ, of first, second, and deepest layers. (Obersteiner.) Fig. 32. — Transitional epithelial cells from a scraping of the mucous membrane of the bladder of the rabbit. CV. D. Harris.) are two or three layers of cells, the upper being more or less flattened according to the full or collapsed condition of the organ, their under surface being marked with one or more depressions, into which the heads of the next layer of club-shaped cells fit. Between the lower and narrower parts of the second row of cells are fixed the irregular cells which constitute the third row, and in like manner sometimes a fourth row (fig. 31). It can be easily understood, therefoi-e, that if a scraping of the mucous membrane of the bladder be teased, and examined under the microscope, cells of a great variety of forms may be made out (fig. 32). Each cell contains a large nucleus and the larger and superficial cells often possess two. (c) Stratified Epithelium. The term stratified epithelium is employed when the cells forming the epithelium are arranged in a considerable number of superimposed layers. The shape and size of the cells of the different layers, as well as the number of the layers, vary in different situations. Thus the 36 HANDBOOK OF PHYSIOLOGY. superficial cells are as a rule of the squamous, or scaly variety, and the deepest of the columnar form. The cells of the intermediate layers are of different shapes, but those of the middle layers are more or less rounded. The superficial cells are broad and overlap by their edges (figs. 33 and 34). Their chemical corn- Fig. 33.--Sqiiamous epithelium scales from the inside of the mouth. X 260. (Henle.) position is different from that of the underlying cells, as they contain keratin, and are therefore horny in character. The nucleus is often not apparent. The really cellular nature of even the dry and shrivelled scales cast off from the surface of the ej)i- derniis can be proved by the application of caustic potash, which causes them, rapidly to swell and assume their original form. The squamous cells exist in the greatest number of layers in the epi- dermis or superficial part of the skin; the most superficial of these are being continually removed by friction, and new cells from below supply the place of those cast off. The intermediate cells approach more to the flat variety the nearer they are to the surface, and to the columnar as they approach the lowest Fig. 34.— Vertical section of the stratified epithelium of the rabbit's cornea, a. Anterior epithe- lium, showing the different shapes of tlie cells at various deptlis from the free surface; b, a portion of the substance of cornea. (Klein.) layer. There may be considerable intercellular intervals; and in many of the deeper layers of epithelium in the mouth and skin, the outline of the cells is very irregular, in consequence of processes passing from cell to cell across these intervals. Such cells (fig. 35) are termed " ridge and furrow/' " cogged " or " prickle " cells. These " prickles " are prolongations of the intracellular network which run across from cell to cell, thus joining them together, THE STRUCTURE OF THE ELEMENTARY TISSUES. 37 the interstices being filled by the transparent intercellular cement-sub- stance. When this increases in quantity in inflammation the cells are pushed further apart, and the connecting fibrils or " prickles " elongated and therefore more clearly visible. The columnar cells of the deepest layer are distinctly nucleated; they multiply rapidly by division; and as new cells are formed beneath, they press the older cells forward to be in turn pressed forward themselves toward the surface, gradually altering in shape and chemical composition until they are cast off from the surface. Stratified epithelium is found in the following situations: (1.) Form- ing the epidermis, covering the whole of the external surface of the body; (2.) Covering the mucous membrane of the nose, tongue, mouth, pharynx, and oesophagus; (3.) As the conjunctival epithelium, covering the cor- nea; (4.) Lining the vagina and the vaginal j^art of the cervix uteri. Fig. 35.— Jagged cells from the middle layers of pavement epithelium, from a vertical section of the gum of a new-born infant. (Klein.) Functions of Epithelium. — According to function, epithelial cells may be classified as: (1.) Protective, e.g., in the skin, mouth, blood- vessels, etc. (2.) Protective and moving — ciliated epithelium. (3.) Secreting — glandular epithelium; or. Secreting formed elements — epi- thelium of testicle secreting spermatozoa. (4.) Protective and secreti)tg, e.g., epithelium of intestine. (5) Sensoi'ial, e.g., olfactory cells, rods and cones of retina, organ of Corti. Epithelium forms a continuous smooth investment over the whole body, being thickened into a hard, horny tissue at the points most ex- posed to pressure, and developing various appendages, such as hairs and nails, whose structure and functions will be considered in a future chapter. Epithelium lines also ihe sensorial surfaces of the eye, ear, nose, and mouth, and thus serves as the medium through which all impressions from the external world — touch, smell, taste, sight, hearing — reach the delicate nerve endings, whence they are conveyed to the brain. The ciliated epithelium which lines the air-passages serves not only as a jjrotective investment, but also by the movements of its cilia pro- motes currents of the air in the bronchi and bronchia, and is enabled to propel fluids and minute particles of solid matter so as to aid their ex- 38 HANDBOOK OF PHYSIOLOGY. pulsion from the body. In the case of the Fallopian tube, this agency assists tl)e progress of the ovum toward the cavity of the uterus. Of the purposes served by cilia in the ventricles of the brain nothing is known. The epithelium of the various glands, and of the whole intestinal tract, has the power of secretion, i.e., of chemically transforming certain materials of the blood ; in the case of mucus and saliva this has been proved to involve the transformation of the epithelial cells themselves; the cell-substance of the epithelial cells of the intestine being discharged by the rupture of their enveloj^es, as mucus. Epithelium is likewise concerned in the processes of transudation, diffusion, and absorption. It is constantly being shed at the free surface and reproduced in the deeper layers. The various stages of its growth and development can be well seen in a section of any laminated epithelium such as the epidermis. II. The Connective Tissues. This group of tissues forms the Skeleton with its various connections — bones, cartilages, and ligaments - and also affords a supporting frame- work and investment to the various organs composed of nervous, mus- cular, and glandular tissue. Its chief function is the mechanical one of support, and for this purpose it is so intimately interwoven with nearly all the textures of the body that if all other tissues could be removed, and the connective tissues left, we should have a wonderfully exact model of almost every organ and tissue in the body, correct even to the small- est minutiffi of structure. Structure of Connective Tissues in General. Connective tissue is made up of two chief elements, namely, cells and intercellular suhstance. (A.) Cells. — The cells are of two kinds: («.) Fixed Cells. — These are of a flattened shape, with branched pro- cesses, which are often united together to form a network: they can be most readily observed in the cornea, in which they are arranged, layer above layer, parallel to the free surface. They lie in spaces in the inter- cellular or ground substance, which are of the same shape as the cells they contain, but rather larger, and which form by anastomosis a s)'stem of branching canals freely communicating (fig. 36). To this class of cells belong the flattened tendon corpuscles which are arranged in long lines or rows parallel to the fibres (fig. 42). These branched cells, in certain situations, contain a number of pig- ment granules, giving them a dark appearance; they form one variety of pigment cell. Branched pigment cells of this kind are found in the outer layers of the choroid (fig. 37). In many of the lower animals. THE STRUCTUKE OF THE ELEMENTARY TISSUES, 39 such a,s the frog, they are found widely distributed, not only in the skin, but also in internal parts, e.g., the mesentery and sheaths of blood- vessels. In the web of the frog's foot such cells may be seen with pig- ment granules evenly distributed throughout the body of the cell and its processes; but under the action of light, electricity, and other stim- uli, the pigment granules become massed in the body of the cell, leaving the processes quite hyaline; if the stimulus be removed, they will grad- ually be distributed again throughout the processes. Thus the skin in the frog is sometimes uniformly dusky, and sometimes quite light-colored, with isolated dark spots. In the choroid and retina the pigment cells absorb light. (/>.) Amwhoid Cells, of an approximately spherical shape; they have a great general resemblance to colorless blood-corpuscles, with which Fig. 30.— Hoi-izontal preparation of the cornea of frog:, stained in gold chloride; showing the network of branched cornea corpuscles. The ground substance is completely colorless. X 400. (Klein.) some of them are probably identical. They consist of finely granular nucleated protoplasm, and have the property, not only of changing their form but also of moving about, hence they are termed mir/ratori/. They are readily distinguished from the branched connective-tissue corpuscles by their free condition, and the absence of processes. Some are much' larger than others, and are found especially in the sublingual gland of the dog and guinea-pig, and in the mucous membrane of the intestine. A second variety of these cells called plasma cells are larger than the amoeboid cells, apparently granular, less active in their movements. They are chiefly to be found in the inter-muscular septa, in the mucous and snb-mucous coats of the intestine, in lymphatic glands, and in the omen- tum. (B.) Intercellular Substance. — This may be fihrillar, as in the fibrous tissues, and in certain varieties of cartilage; or homogeneous, as in hyaline cartilage. 40 HANDBOOK OF PHYSIOLOGY. The fibres composing the former are of two kinds — (a.) White fibres. (b.) Yellow elastic fibres. (a.) White Fibres. — These are arranged parallel to each other in wavy bundles of various sizes; such bundles may either have a ijarallel ar- ^-^ Fig. 3:. Fig. 38. Fig. 39. X 350. a, CeU Fig. 37.— Ramified pigment cells from the tissue of the choroid coat of the eye. with pigment; 6, colorless fusiform cells. •'Kolliker.') Fig. 38.— Flat, pigmented, branched connective-tissue cells from the sheath of a large blood- vessel of the frog's mesentery: the pigment is not distributed uniformly throughout the substance of the larger cell, consequently some parts of it look blacker than others (uncontracted state). In the two smaller cells most of the pigment is withdrawn into the cell-body, so that they appear smaller, blacker, and less branched, x 3.50. (Klein and Noble Smith.) Fig. 39. — Fibrous tissue of cornea, showing bundles of fibres with a few scattered fusiform cells (a) lying in the inter-fascicular spaces. X 400. (Klein and Noble Smith.) rangement (fig. 39), or may produce quite a felted texture by their inter- lacement. The individual fibres composing these fasciculi are exceedingly fine, varying from -^J^nr to ¥?innT inch, i.e., g-oVo to -nrVo- mm-./ or 0.5 to IP; homogeneous, unbranched, and of the same diameter throughout. They can readily be isolated by macerating a portion of white fibrous tissue {e.g., a small piece of tendon) for a short time in lime, or baryta-water, or in a solution of common salt, or of potassium permanganate: these reagents possess the power of dissolving the cementing inter- fibrillar substance and of thus separating the fibres from each other. By prolonged boil- ing the fibres yield gelatin. (b.) Yellow Mastic Fibres (fig. 40) are of all sizes, from excessively fine fibrils, sihro inch, up to fibres of considerable thickness, •j-jJy-fj- inch (i.e., from about Ip. to 6//) : they are distinguished from white fibres by the following characters: (1.) Their great power of resistance even to the prolonged action of chemical reagents, e.g., caustic soda, acetic acid, etc. (2.) Their well-defined outlines. (3.) * ToVo millimetre = 1 micron, which is represented by the Greek fi. Fig. 40. — Elastic fibres from the ligamenta subflava. x 200. (Sharpey.) THE STRUCTURE OF THE ELEMENTARY TISSUES. 41 Their great tendency to branch aud to form networks by anastomosis. (4.) Their twisted corkscrew-like appearance, and that their free ends usually curl up. (5.) Their yellowish tint and considerable elasticity. (6.) 'Their resistance to hematoxylin and similar reagents, and their affinity for magenta and other aniline staining colors. These fibres yield on boiling not gelatin, but a gelatinous substance called elastin. The chief varieties of connective tissues may be thus classified : I. The Fibro2(s Connective Tissues. A. — Chief Forms, a. White fibrous. h. Elastic. c. Areolar. B. — S'pecial Varieties. a. Gelatinous. b. Adenoid or Eetiform. c. Adipose. II. Cartilage. IIL Bone. I. Fibrous Con'nective Tissues. A. — Chief Forms. — (a.) White Fibrous Tissue. Distribution. — It is found typically in tendon; also in ligaments, in the periosteum and perichondrium, the dura mater, the pericardium, the sclerotic coat of the eye, the fibrous sheath of the testicle; in the fascife and aponeuroses of muscles, aud in the sheaths of lymphatic glands. Structure. — To the naked eye tendons and many of the fibrous membranes, when in a fresh state, present an appearance as of watered silk. This is due to the arrangement of the fibres in wavy parallel bun- dles. Under the microscope the tissue appears to consist of long, often parallel, bundles of fibres (if different sizes. The fibres of the same bun- dle now and then intersect each other. The cells in tendons (fig. 42) are arranged in long chains in the ground substance separating the bun- dles of fibres, and are more or less regularly quadrilateral with large round nuclei containing nucleoli, which are generally placed so as to be contiguous in two cells. Each of these cells consist of a thick body, from which processes pass in various directions into, and partially fill up the spaces between, the bundles of fibres. The rows of cells are separated from one another by lines of cement substance. The cell spaces can be brought into view by silver nitrate. The cells are gener- 42 HANDBOOK OF PHYSIOLOGY. ally marked by one or more lines or stripes when viewed longitudinally. This appearance is really iiroduced by the wing-like processes of the cell which project away from the chief part of the cell in different di- rections. These processes not being in the same plane as the body of the cell are out of focus and give rise to these bright stripes are looked at from above and are in focus. The branched character of the cells is seen in transverse section in fig. 43. (b) Yellow Elastic Tissue. Distribution. — In the ligamentum nuch^e of the ox, horse, and many other animals; in the ligamenta subflava of man; in the arteries, con- stituting the fenestrated coat of Henle; in veins; in the lungs and tra- .,,«\\\ '\\ \l\^] \\\\\ Fig. 42. Fig. 41.— Mature white fibrous tissue of tendon, consisting mainly of fibres with a few scattered fusiform cells. (Strieker.) Fig. 4-3.— Caudal tendon of young rat, showing the arrangement, f onn, and structure of the tendon cells. X 300. (Klein.) chea; in the stylo-hyoid, thyro-hyoid, and crico-thyroid ligaments; in the true vocal chords; and in areolar tissue. Structure. — Elastic tissue occurs in various forms, from a structure- less, elastic membrane to a tissue whose chief constituents are bundles of fibres crossing each other at different angles; when seen in bundles elastic fibres are yellowish in color, but individual fibres are not so dis- tinctly colored. The varieties of the tissue may be classified as follows: («.) Fine elastic fibrils, which branch and anastomose to form a net- work: this variety of elastic tissue occurs chiefly in the skin and mucous membranes, in subcutaneous and submucous tissue, in the lungs and true vocal cords. (b.) Thick fibres, sometimes cylindrical, sometimes flattened like tape, which branch, anastomose and form a network: these are seen most typically in the ligamenta subflava and also in the ligamentum THE STRUCTURE OF THE ELEMENTARY TISSUES. 43 nucha? of such animals as the ox and horse, in which that ligament is largely developed (fig. 40). (c.) Elastic membranes with perforations, e.g., Henle's fenestrated membrane: this variety is found chiefly in the arteries and veins. {(l.) Continuous, homogenous elastic membranes, e.g., Bowman's an- terior elastic lamina and Descemet's posterior elastic lamina, both in the cornea. A certain number of flattened connective-tissue cells are found in the ground substance between the elastic fibres which make up this A'ariety of connective tissue. (c.) Areolar Tissue. Distribution. — This variety of fibrous tissue has a very wide distribu- Fig. 43. Fig. 44. Fig. 4-3.— Transverse section of tendon from a cross section of the tail of a rabbit, showing sheath, fibrous septa, and branched connective-tissue corpuscles. The .spaces left white in the dra,wing represent the tendinous fibres iu transverse section. X ^50. (Klein.) Fig. 44.— Transverse section of a portion of lig. nuchae. showing the outline of the fibres. (After Stohr.) tion and constitutes the subcutaneous, subserous, and submucous tissue. It is found in the mucous membranes, in the true skin, and in the outer sheaths of the blood-vessels. It forms sheaths for muscles, nerves, glands, and the internal organs, and penetrating into their interior, supports and connects the finest parts. Structure. — To the naked eye it apx^ears, when stretched out, as a fleecy, white, and soft meshwork of fine fibrils, with here and there wider films Joining in it, the whole tissue being evidently elastic. The open- ness of the meshwork varies with the locality from Avhich the specimen is taken. Under the microscope it is found to be made up of fine white fibres, which interlace in a most irregular manner, together with a vari- able number of elastic fibres. On the addition of acetic acid, the Avliite fibres swell w^, and become gelatinous in appearance; but as the elastic fibres resist the action of the acid, they may still be seen arranged in 44 HAlS'^DBOOK OF PHYSIOLOGY. various directions, sometimes tijipearing to pass in a more or less circu- lar or spiral manner round a small gelatinous mass of changed white fihres. The cells of the tissue are not arranged in a very regular man- ner, as they are contained in the spaces (areola?) between the fibres. They communicate, liovvever, with one another by branched processes, and also with the cells forming the walls of the capillary blood-vessels in their neighborhood. The fibres are connected together with a certain amount of albuminous cement substance. B. — Special Forms {a.) Gelatinous Tissue. Bistribuiion. — Gelatinous connective tissue forms the chief part of the bodies of jelly-fish; it is found in many parts of the human embryo, Fig. 45. Fig. 46. Fig. 4.5.— Tissue of the jelly of Wharton from umbilical cord, o. Connective-tissue corpuscles; 6, fasciculi of connective tissue; c, spherical formative cells. (Frey.) Fig. 46.— Part of a section of a lymphatic gland, from which the corpuscles have been for the most part removed, showing the adenoid reticulum. ^Klein and Noble Smith.) but remains in the adult only in tlie vitreous humor of the eye. It may be best seen in the last-named situation, in the '' Whartonian jelly" of the umbilical cord, and in the enamel organ of developing teeth. Structure'. — It consists of cells, which in the vitreous humor are rounded, and in the jelly of the enamel organ are stellate, imbedded in a soft jelly-like inter-cellular substance which forms the bulk of the tissue, and which contains a considerable quantity of mucin. In the umbilical cord, that part of the jelly immediately surrounding the stel- late cells shows marks of obscure fibrillation (fig. 45). (i.) Adenoid, this is also called retiform, lym.plioid or Jiimphatic tissue. Distributio)!.- — -This variety of tissue makes up the stroma of the spleen and lymphatic glands, and is found also in the thymus, in the tonsils, in the follicular glands of the tongue, in Peyer's patches, and in the sol- itary glands of the intestines, and in the mucous membranes generally. THE STKUCTURE OF THE ELEMEXTARY TISSUES. 45 Strtictnre. — Adenoid or retiform tissue consists of a very delicate network of minute fibrils, formed originally by the union of processes of branched connective-tissue corpuscles, the nuclei of which, however, are visible only during the early periods of develojjment of the tissue (fig. 46). The nuclei found on the fibrillar meshwork do not form an essential part of it. The fibrils are neither white fibres nor elastic tissue, as they are insoluble in boiling water, although readily soluble in hot alkaline solutions. The lymphoid corpuscles found in the interstices of the tis- sue are small round cells, the protoplasm of which is practically occupied by their spherical nuclei. Development of Fibrous Tissues. — In the embryo the place of the fibrous tissues is at first occujaied by a mass of roundish cells, de- rived from the " mesoblast." Fig. 47. — Portion of subinucous tissue of gravid uterus of sow. a, Branciied cells, more or less spindle-sliaped; 6, bundles of connective tissue. (Klein.) These develop either into a network of branched cells or into groups of fusiform cells (fig. 47). The cells are imbedded in a semi-fluid albuminous substance derived either from the cells themselves or from the neighboring blood-vessels; this afterward forms the cement substance. In it fibres are developed, either by some of the cells becoming fibrils, the others remaining as con- nective-tissue corpuscles, or by the fibrils being developed from the out- side layers of the protoplasm of the cells, which grow up again to their original size and remain imbedded among the fibres. The process gives rise to fibres arranged in the one case in interlacing networks (areolar tissue), in the other in parallel bundles (white fibrous tissue). In the mature forms of purely fibrous tissue not only the remnants of the cell- substance, but even the nuclei, may disappear. The embryonic tissue, from which elastic fibres are developed, is composed of fusiform cells, and a structureless intercellular substance by the gradual fibrillation of which elastic fibres are formed. The fusiform cells dwindle in size and eventually disappear so completely that in mature elastic tissue hardly a trace of them is to be found : meanwhile the elastic fibres steadily in- crease in size. 40 HANDBOOK OF PHYSIOLOGY. Another theory of the development of the connective-tissue fibrils supposes that the_y arise from deposits in the intercellular substance and not from the cells themselves; these deposits, in the case of elastic fibres, appearing first of all in the form of rows of granules, which, joining to- gether, form long fibrils. It seems probable that even if this view be correct, the cells themselves have a considerable infiuence in the pro- duction of the deposits outside them. Functions of Areolar and Fibrous Tissue.— The main function of connective tissue is mechanical rather than vital: it fulfils the subsid- iary but important use of supporting and connecting the various tissues and organs of the body. In glands the trabeculae of connective tissue form an interstitial framework in which the parenchyma or secreting gland-tissue is lodged : in muscles and nerves the septa of connective tissue support the bundles jof fibres which form the essential part of the structure. Elastic tissue, by virtue of its elasticity, has other important uses: Fig. 48.— Ordinarj' fat cells of a fat tract in the omentum of a rat. (Klein.) these, again, are mechanical rather than vital. Thus the ligamentum nuchas of the horse or ox acts very much as an India-rubber band in the same position would; being stretched when the head is lowered for feeding or other purposes and aiding the muscles materially afterward by its contraction, in raising the head to its normal position and keejaing it there. (c.) Adipose Tissue. Didribiition. — In almost all regions of the human body a larger or smaller quantity of adipose or fatty tissue is present; the chief excej)- tions being the subcutaneous tissue of the eyelids, penis, and scrotum, the nymphse, and the cavity of the cranium. Adipose tissue is also absent from the substance of many organs, as the lungs, liver, and others. Fatty matter, but not in the form of a distinct tissue, is also widely present in the body, e.g., in the liver and brain, and in the blood and chyle. Adipose tissue is almost always found seated in areolar tissue, and forms in its meshes little masses of unequal size and irregular shape, to which the terra lohules is commonly applied. THE STEUCTURE OF THE ELEMEXTARY TISSUES. 47 Structure. — Under the microscope adipose tissue is found to consist essentially of little vesicles or cells which present dark, sharply-defined edges when viewed with transmitted light : they are about -^^ or -^ J-^- of an inch in diameter, each consisting of a structureless and colorless membrane or bag formed of the remains of the original protoplasm of the cell, filled with fatty matter, which is liquid during life, but in part solidified after death (fig. 48). A nucleus is always present in some part or other of the cell-protoplasm, but in the ordinary condition of the cell it is not easily or always visible (fig. 49). This membrane and the niicleus can generally be brought into view by staining the tissue: it can be still more satisfactorily demonstrated by extracting the contents of the fat-cells with ether, when the shrunken, shrivelled membranes remain behind. By mutual pressure, fat-cells C "■' 0 Fig. 49. — Group of fat cells (f c) with capillarj' vessels (c). ('Noble Smith.) come to assume a polyhedral figure (fig. 49). When stained witli osmic acid fat-cells appear black. The ultimate cells are held together by capillary blood-vessels (fig. 50); while the little clusters thus formed are grouped into small masses, and held so, in most cases, by areolar tissue. The oily matter contained in the cells is composed chiefly of the compounds of fatty acids with glycerin, which are named olein, siearin, and jml'Dii tin. Development of Adipose Tissue. — Fat cells are developed from connective-tissue corpuscles: in the infra-orbital connective-tissue cells may be found exhibiting every intermediate gradation between an ordi- nary branched connective-tissue corpuscle and mature fat-cell. The process of development is as follows: a few small drops of oil make their appearance in the protoplasm and by their confluence a larger drop is produced (fig. .51) : this gradually increases in size at the expense of the original protoplasm of the cell, which becomes correspondingly dimin- ished in quantity till in the mature cell it only forms a thin crescentic 48 HANDBOOK OF PHYSIOLOGY. film, closely pressed against the cell-wall, and with a nucleus imbetfded in its substance (figs. 48 and 4'J). Fig. 50. — Blood-vessels of adipose tissue. A. Minute flattened fat>lobule, in which the vessels only are represented, a. The terminal artery; v, the primitive vein; b, the fat- vesicles of one border of the lobule separately represented, x 100. b. Plan of the arrangement of the capillaries (c) on the exterior of the vesicles; more highly magnified. (Todd and Bowman.; Under certain circumstances this process may be reversed and fat- cells may be changed back into connective-tissue corpuscles. /If "aX^^?' ''® fj^ ®\9 c--^ ' -. to Fig. 51. \l Fig. 52. Fig. 51.— A lobule of developing adipose tissue from an eight months' foetus, a, Spherical or, from pressure, polyhedral cells with lai-ge central nucleus, surrounded by a finely reticulated sub- stance staining uniformly with hsemato.xyliu. 6, Similar cells with spaces from which the fat has been removed by oil of cloves, c. Similar cells showing how the nucleus with inclosing jirotoplasm is being pressed toward periphery, d, Nucleus of endothehum of investing capillaries. (McCarthy.) Drawn by Treves. Fig. 52.— Branched connective- tissue corpuscles, developing into fai.-cells. (Klein.) Vessels and Nerves. — A large number of blood-vessels are found in adipose tissue, which subdivide until each lobule of fat contains a fine mesh work of capillaries ensheathing each individual fat-globule (fig. THE STKUCTURE OF THE ELEMENTARY TISSUES. 49 oOj. Although nerve fibres pass through the tissue, no nerves have been demonstrated to terminate in it. The Uses of Adipose Tissue. — Among the uses of adipose tissue these are the chief : — a. It serves as a store of combustible matter which maybe reabsorbed into the blood when occasion requires, and, being used up in the meta- bolism of the tissues, may help to preserve the heat of the body. b. That part of the fat which is situate beneath the skin must, by its want of conducting power, assist in preventing undue waste of the heat of the body by escape from the surface. c. As a packing material, fat serves very admirably to fill up spaces, to form a soft and yielding yet elastic material wherewith to wrap ten- der and delicate structures, or form a bed with like qualities on which such structures may lie, not endangered by pressure. As examples of situations in which fat serves such purposes may be mentioned the palms of the hands and soles of the feet and the orbits. d. In the long bones fatty tissue, in the form known as yellow mar- row, fills the medullary canal, and supports the small blood-vessels which are distributed from it to the inner part of the substance of the bone. . II. Cartilage. General Structure of Curtilage. — All kinds of cartilage are composed of cells imbedded in a substance called the matrix: the apparent differ- ences of structure met with in the various kinds of cartilage are more due to differences in the character of the matrix than of the cells. Among the latter, however, there is also considerable diversity of form and size. With the exception of the articular variety, cartilage is invested by a thin but tough firm fibrous membrane called the pericliondrium. On the surface of the articular cartilage of the foetus, the perichondrium is represented by a film of epithelium; but this is gradually worn away up to the margin of the articular surfaces when by use the parts begin to suffer friction. Nerves are probably not supplied to any variety of cartilage. Cartilage exists in three different forms in the human body, viz., 1, Hyaline cartilage, 3, Yelloio elastic-cartilage, and 3, White fibro-cartilage. 1. Hyaline Cartilage. Distribution. — This variety of cartilage is met with largely in the human body — investing the articular ends of bones, and forming the costal cartilages, the nasal cartilages, and those of the larynx with the exception of the epiglottis and cornicula laryngis, as well as those of the trachea and bronchi. Structure. — Like other cartilages it is composed of cells imbedded in 4 50 HANDBOOK OF PHYSIOLOGY. a matrix. The cells, which contain a nucleus with nucleoli, are irregular in shape, and generally grouj)ed together in imtches (fig. 53). The patches are of various shapes and sizes and placed at unequal distances apart. They generally appear flattened near the free surface of the mass of cartilage in which they are placed and more or less perpendicular to the surface in the more-deei3ly seated portions. The matrix of hyaline cartilage has a dimly granular appearance like that of ground glass, and in man and the higher animals has no appar- ent structure. In some cartilages of the frog, however, even when ex- amined in the fresh state, it is seen to be mapped out into polygonal blocks or cell-territories, each containing a cell in the centre, and repre- Fig. 53. Fig. 54. Fig. 5.3.— Ordinary hyaline cartUage from trachea of a child. The cartilage cells are inclosed singly or in pairs in a capsule of hyaline substance. X 150 diams. (Klein and Noble Smith.) Fig. 54. — Fresh cartilage from the Triton. (A. Rollett.) senting what is generally called the capsule of the cartilage cells (tig. 54). Hyaline cartilage in man has really the same structure, which can be demonstrated by the use of certain reagents. If a piece of human hyaline cartilage be macerated for a long time in diluted acid or in hot water 35°-45° C. (95°-113° F.), the matrix, which previously appeared quite homogeneous, is found to be resolved into a number of concentric lamellae, like the coats of an onion, arranged round each cell or group of cells. It is thus shown to consist of nothing but a number of large systems of capsules which have become fused with one another. The cavities in the matrix in which the cells lie are connected to- gether by a series of branching canals, very much resembling those in the cornea: through these canals fluids may make their way into the depths of the tissue. In the hyaline cartilage of the ribs the cells are mostly larger than in the articular variety and there is a tendency to the development of fibres in the matrix (fig. 55). The costal cartilages also frequently be- THE STRUCTURE OF THE ELEMENTARY TISSUES. 51 come calcified in old age, as also do some of those of the larynx. Fat- globules may also be seen in many cartilages (fig. 55). In articular cartilage the cells are smaller and arranged vertically in narrow lines like strings of beads. In the foetus cartilage is the material of which the bones are first constructed; the "model" of each bone being laid down, so to speak, in this substance. In such cases the cartilage is termed temporary. It closely resembles the ordinary hyaline kind; the cells, however, are not grouped together after the fashion just described, but are more uniformly distributed throughout the matrix. A variety of temporary hyaline cartilage which has scarcely any ma- Fig. 55. Fig. 56. Fig. 55.— Costal cartilage from an adult dog, showing the fat globules in the cartilage cells. (Cadiat.) Fig. 50.— Yellow elastic cartilage, (Cadiat.) trix is found in the human subject and in the higher animals generally, in early foetal life, when it constitutes the cliorda dorsalis. Nutrition. — Hyaline cartilage is reckoned among the so-called non- vascular structures, no blood-vessels being supplied directly to its own substance; it is nourished by those of the bone beneath. When hyaline cartilage is in thicker masses, as in the case of the cartilages of the ribs, a few blood-vessels traverse its substance. The distinction, however, between all so-called vascular and non-vascular parts is at the best a very artificial one. 3. Yellow Elastic Cartilage. Distribution. — Tn the external ear, in the epiglottis and cornicula laryngis, and in the Eustachian tube. Structure. — The cells in this variety of cartilage are rounded or oval, with well-marked nuclei and nucleoli (fig. 56). The matrix in which they are seated is composed almost entirely of fine elastic fibres, which 52 HANDBOOK OF PHYSIOLOGY. form an intricate interlacement about the cells, and in their general characters are allied to the yellow variety of fibrous tissue: a small and variable quantity of hyaline intercellular substance is also usually present. A variety of elastic cartilage, sometimes called cellular', is found to form the framework of the external ears of rats, mice, or other small mammals. It is composed, as its name implies, almost entirely of cells which are packed very closely with little or no matrix. When present the matrix consists of very fine fibres which twine about the cells in various directions and inclose them in a kind of network. Elastic car- tilage seldom or never ossifies. 3. White Fibro-Cartilage. Distribution. — White fibro-cartilage is found to occur: — 1. As inter-articular fibro-cartilage, e.g., the semilunar cartilages of the knee-joint. 2. As circumferential or marginal cartilage, as on the edges of the acetabulum and glenoid cavity. 3. As connecting cartilage, e.g., the inter-vertebral fibro-cartilages. 4. In the sheaths of tendons and some- times in their substance. In the latter situ- ation the nodule of fibro-cartilage is called a sesamoid fibro-cartilage, of which a specimen Fig. 57. Fig. 58. Fig. 57.— White flbro-cartilage. (Cadiat.) Fig. 58. — White flbro-cartilage from an iater-vertebral ligament. (Klein and Noble Smith.) may be found in the tendon of the tibialis posticus in the sole of the foot, and usually in the neighboring tendon of the peroneus longus. Structure. — White fibro-cartilage (fig. 58), which is much more widely distributed throughout the body than the foregoing kind, is composed, like it, of cells and a matrix; the latter, however, being made uj) almost entirely of fibres closely resembling those of white fibrous tissue. In this kind of fibro-cartilage it is not unusual to find a great part of its mass composed almost exclusively of fibres, and deriving the name THE STRUCTURE OF THE ELEMEXTARY TISSUES. d3 of cartilage only from the fact that in another portion, continuous with it, cartilage cells may be pretty freely distributed. By prolonged boiling, cartilage yields a substance called cJiondriti — which gelatinizes on cooling. The cells of white fibro-cartilage are as a rule rounded or somewhat flattened but in some places are distinctly branched. Functions of Cartilage. — Cartilage not only represents in the fcetus the bones which are to be formed {temporary cartilage) but also offers a firm, yet more or less yielding, framework for certain parts in the developed body, possessing at the same time strength and elasticity. It maintains the shape of tubes as in the larynx and trachea. It affords attachment to muscles and ligaments; it binds bones together, yet allows a certain degree of movement, as between the vertebra?; it forms a firm framework and protection, yet without undae stiffness or weight, as in the pinna, larynx, and chest walls; it deepens joint cavities, as in the acetabulum, without unduly restricting the movements of the bones. Development of Cartilage. — Cartilage is developed out of an em- bryonal tissue, consisting of cells with a very small quantity of intercel- lular substance: the cells multij^ly by fission within the cell- capsules, while the capsule of the parent cell becomes gradually fused with the surrounding intercellularsubstance. A repetition of this process in the young cells causes a rapid growth of the cartilage by the multiplication of its cellular elements and corresponding increase in its matrix. Thus we see that the matrix of cartilage is chiefly derived from the cartilage cells. III. Bone. Chemical Composifioji. — Bone is composed of earthy and animal mat- ter in the proportion of about 67 per cent of the former to 33 per cent of the latter. The earthy matter is composed chiefly of calcium phos- phate, but besides there is a small quantity (about 11 of the 67 per cent) of calcium carbonate and calcium fluoride, and magnesium phosphate. The animal matter called collagen is resolved into gelatin by boiling. The earthy and animal constituents of bone are so intimately blended and incorporated the one with the other that it is only by chemical action, as for instance by heat in one case and by the action of acids in another, that they can be separated. Their close union too is further shown by the fact that when by acids the earthy matter is dissolved out, or on the other hand when the animal part is burnt out, the shape of the bone is alike preserved. The proportion between these two constituents of bone varies in different bones in the same individual and in the same bone at different ages. Structure. — To the naked eye there appear two kinds of structure 54 HANDBOOK OF PHYSIOLOGY, in different bones, and in different parts of the same bone, namely, the dense or compact, and the spong// or cancellous tissue. Thus, in making a longitudinal section of a long bone, as the humerus or femur, the articular extremities are found capped on their surface by a thin shell of compact bone, while their interior is made up of the spongy or cancellous tissue. The shaft, on the other hand, is formed almost entirely of a thick layer of the compact hone, and this surrounds a central canal, the medullary cavity — so called from its con- taining the medulla or marrow. In the flat bones, as the parietal bone or the scapula, one layer of the cancellous structure lies between two layers of the compact tissue, and in the short and irregular bones, as those of the carpus and tarsus, the cancellous tissue alone fills the interior, while a thin shell of compact bone forms the outside. Marrow. — There are two distinct varieties of marrow — the red and yellotv. Fig. 59. — Cells of the red marrow of the guinea-pig, hiKhly tnagnifiecl. a. A large cell, the nu- cleus of which appears to be partly divided into three by constrictio.is; 6, a cell, the nucleus of which shows an appearance of being constricted into a number of smaller nuclei ; c, a .so-called giant cell, or niyeloplaxe, with many nuclei; d, a smaller myelo-plaxe, with three nuclei; e-i, proper cells of the marrow. (E. A. Schafer.) Red marrow is that variety which occupies the spaces in the cancel- lous tissue; it is highly vascular, and thus maintains the nutrition of the spongy bone, the interstices of which it fills. It contains a few fat-cells and a large number of marrow-cells, many of which are undis- tinguishable from lymphoid corpuscles, and has for a basis a small amount of fibrous tissue. Among the cells are some nucleated cells of very much the same tint as colored blood-corpuscles. There are also a few large cells with many nuclei, termed giant-cells or myeloplaxes, which are derived from over-growth of the ordinary marrow-cells (fig. 59). Yellow marrow fills the medullary cavity of long bones, and consists chiefly of fat-cells with numerous blood-vessels; many of its cells also are in every respect similar to lymphoid corpuscles. THE STEUCTURE OF THE ELEMENTARY TISSUES, 55 From these marrow-cells, especially those of the red marrow, are de- rived, as we shall presently show, large quantities of red blood-corpuscles. Periosteum and Nutrient Blood-vessels. — The surfaces of bones, except the part covered with articular cartilage, are clothed by a tough, fibrous membrane, the jjeriosfeuin; and it is from the blood-vessels which are distributed in this membrane, that the bones, especially their more compact tissue, are in great part supplied with nourishment, — minute branches from the periosteal vessels entering the little foramina on the surface of the bone, and finding their way to the Haversian canals to be immediately described. The long bones are supplied also by a proper nutrient artery which, entering at some part of the shaft so Fig. 60.— Transverse section of compact bony tissue (of humerus). Three of the Haversian canals are seen, witli their concentric rings: also the lacunar, with the canaliculi extending from them across the direction of the lamellae. The Haversian apertures were filled with debris in grind- ing down the section, and therefore appear black in the figure, which represents the object.as viewed with transmitted light. The Haversian systems are so closely packed in this section, that scarcely any interstitial lamellaB are visible. X 150. CSharpey.) as to reach the medullary canal, breaks up into branches for the supply of the marrow, from which again small vessels are distributed to the interior of the bone. Other small blood-vessels pierce the articular extremities for the supply of the cancellous tissue. Microscopic Struct icre of Bone. — "Notwithstanding the differences of arrangement just mentioned, the structure of all bone is found under the microscope to be es3entially the same. Examined with a rather high power its substance is found to contain a multitude of small irregular spaces, approximately fusiform in shape, called lacunae, with very minute canals or canaliculi, as they are termed, leading from them, and anastomosing with similar little prolongations from other lacunae (fig. 60). In very thin layers of bone, no other canals than these may be visible; but on making a transverse section of 56 HANDBOOK OF PHYSIOLOGY. the compact tissue as of a long bone, e.g., the humerus or ulna, the arrangement shown in fig. 60 can be seen. The bone seems mapped out into small circular districts, at or about the centre of each of which is a hole, around which is an appearance as of concentric layers — the lacunm and canalicuU follojving the same con- centric plan of distribution around the small hole in the centre, with which indeed they communicate. On making a longitudinal section, the central holes are found to be simply the cut extremities of small canals which run lengthwise through the bone, anastomosing with each other by lateral branches (fig. 61), Fig. 61.— Longitudinal section from the human ulna, showing Haversian canal, lacunse, and canaliculi. (Kollett.) and are called Haversian canals, after the name of the physician, Clopton Havers, who first accurately described them. The Haversian canals, the average diameter of which is -^^ of an inch, contain blood-vessels, and by means of them blood is conveyed to all, even the densest parts of the bone; the minute canaliculi and lacunae absorbing nutrient matter from the Haversian blood-vessels and con- veying it still more intimately to the very substance of the bone which they traverse. The blood-vessels enter the Haversian canals both from without, by traversing the small holes which exist on the surface of all bones be- neath the periosteum, and from within by means of small channels which extend from the medullary cavity, or from the cancellous tissue. The arteries and veins usually occupy separate canals, and the veins, which are the larger, often present, at irregular intervals, small pouch- like dilatations. THE STRUCTURE OF THE ELEMENTARY TISSUES. 57 The lacunae are occupied by branched cells, Avhich are called hojie- cells, or hone-corjnisdes (fig. 62), which very closely resemble the ordi- nary branched connective-tissue corpuscles; each of these little masses of protoplasm ministering to the nutrition of the bone immediately sur- rounding it, and one lacunar corpuscle communicating with another, and with its surrounding district, and with the blood-vessels of the Haversian canals, by means of the minute streams of fluent nutrient matter which occupy the canaliculi. It will be seen from the above description that bone is essentially connective-tissue impregnated with lime salts: it bears a very close re- semblance to what may be termed typical connective-tissue such as the substance of the cornea. The ^vT""* bone-corpuscles with their pro- Fig. 62. Fig. 63. Fig. 62. — Bone-corpuscles with their processes as seen in a thin section of human bone. (RoUett.) Fig. 63. — Thin layer peeled off from a softened bone. This figure, which is intended to represent the reticular structure of a lamella, gives a better idea of the object when held rather farther off than usual from the eye. X 400. (Sharpey.) cesses occupying the lacunas and canaliculi correspond exactly to the cornea-corpuscles lying in branched spaces. Lamellae of Compact Bone. — In the shaft of a long bone three distinct sets of lamellae can be clearly recognized. (1.) General or fundamental lamellse ; which are most easily tracea- ble just beneath the periosteum, and around the medullary cavity, form- ing around the latter a series of concentric rings. At a little distance from the medullary and periosteal surfaces (in the deeper portions of the bone) they are more or less interrupted by (3.) Special or Haversian lamellae, which are concentrically arranged around the Haversian canals to the number of six to eighteen around each. (3.) Interstitial lamellae, which connect the system of Haversian lamellse, filling the spaces between them, and consequently attaining 58 HANDBOOK OF PHYSIOLOGY. their greatest development where the Haversian systems are few, and vice versa. The ultimate structure of the lamellae appears to be reticular. If a thin film be peeled off the surface of a bone, from which the earthy matter has been removed by acid, and examined with a high power of the microscope, it will be found composed of a finely reticular struc- ture, formed apparently of very slender fibres decussating obliquel}^, but coalescing at the points of intersection, as if here the fibres were fused rather than woven together (fig. 63). In many places these reticular lamellae are perforated by tapering fibres called the Claviculi of Gagliardi, or the perforating fibres of, Sharpey, resembling in character the ordinary white or rarely the elastic Fig. 64. — Lamellae torn off from a decalcified human parietal bone at some depth from the sur- face, a, a, Lamellas, showing reticular fibres; b, b, darker part, where several lamellae are super- posed; c, perforating fibres. Apertures through which perforating fibres had passed, are seen es- pecially in the lower part, a, a, of the figure. (Allen Thomson.) fibrous tissue, which bolt the neighboring lamellae together, and may be drawn out when the latter are torn asunder (fig. 64). These perforating fibres originate from ingrowing processes of the periosteum, and in the adult still retain their connection with it. Development of Bone. — From the point of view of their develop- ment, all bones may be subdivided into two classes. (a.) Those which are ossified directly or from the first in membrane or fibrous tissue, e.g., the bones forming the vault of the skull, parietal, frontal, and a certain portion of the occipital bones. {h.) Those whose form, previous to ossification, is laid down in hya- line cartilage, e.g., humerus, femur. The process of development, pure and simple, may be best studied in bones which are not preceded by cartilage, i.e., membrane- formed {e.g., THE STRUCTURE OF THE ELEMENTARY TISSUES. 59 parietal) ; and without a knowledge of this process (ossification in mem- brane), it is impossible to understand the much more complex series of changes through which such a structure as the cartilaginous femur of the foetus pusses in its transformation into the bony femur of the adult (ossification in cartilage). Ossification in Membrane. — The membrane, afterward forming the periosteum, from which such a bone as the parietal is developed, consists of two layers — an QxlemoX fihroiis, and an internal cellular or osteo-genetic. The external layer is made up of ordinary connective-tissue, being composed of layers of fibrous tissue with branched connective-tissue corpuscles here and there between the bundles of fibres. The internal layer consists of a network of fine fibrils with a large number of nucle- ated cells with a certain addition of albuminous ground or cement sub- stance between the fibrous bundles, some of which are oval, others drawn out into long branched processes: it is more richly supplied with capillaries than the outer layer. The relatively large number of its cellular elements, which vary in size and shape, together with the abundance of its blood-vessels, clearly mark it out as the portion of the periosteum which is immediately concerned in the formation of bone. In such a bone as the parietal, which is represented then when ossi- fication commences by the species of fibrous connective tissue with many cells above indicated, the deposition of bony matter, which is preceded by increased vascularity, takes place in radiating spicule, starting from a centre of ossification, and shooting out in all directions toward the periphery. These primary bony spicule consist of the fibres of the tis- sue which are termed osteogenetic fibres, comjiosed of a soft transparent substance called osteogen, in which calcareous granules are deposited. The fibres are said to exhibit in their precalcified state indications of a fibrillar structure, and are likened to bundles of white fibrous tissue, to which they are similar in chemical composition, but from Avhicli they differ in being stiffer and less wavy. The deposited granules after a time become so numerous as to fill up the substance of the fibres and bon^ Dpiculse result. Calcareous granules are deposited also in the in- terfibrillar matrix. By the junction of the osteogenetic fibres and their resulting bony spiculee a meshwork of bone is formed. The osteo- genetic fibres, which become indistinct as calcification proceeds, are believed to persist in the lamellae of adult bone. The osteoblasts, being in part retained within the bone trabecule thus produced, form bone corpuscles. On the bony trabeculse first formed, layers of osteoblastic cells from the osteo-genetic layer of the periosteum are developed side by side, lining the irregular spaces like an epithelium (fig. 65, b). Lime- salts are deposited in the circumferential part of each osteoblast, and thus a ring of osteoblasts gives rise to a ring of bone with the remaining 60 HANDBOOK OF PHYSIOLOGY. uncalcified portions of the osteoblasts imbedded in it as bone corpuscles, us in the first formation; then the central portion of the bony plate becomes harder and less cancellous. At the same time, the plate in- creases at the periphery not only by the extension of the bony spiculie, but also by deposits taking place from the osteogenetic layer of the periosteum. The primitive spongy bone is formed, and its irregular branching spaces are occupied by processes from the osteogenetic layer of the peri- osteum consisting of numerous blood-vessels and osteoblasts. Portions of this primitive spongy bone are re-absorbed. The osteoblasts are arranged in concentric successive layers and give rise to concentric- Haversian lamellae of bone, while the irregular space in the centre is reduced to a well-formed Haversian canal, containing the usual blood- vessels, the portions of the primitive spongy bone between the Haversian Fig. 65.— Osteoblasts from the parietal bone of a human embiyo, thirteen weeks old. a, Bony septa with the cells of the lacunae; b, layers of osteoblasts; c, the "latter in transition to bone cor- puscles. Highly maguifled. (Gegenbaur.) systems remaining as interstitial or ground-lamellsB (p. 57). The bulk of the primitive spongy bone is thus gradually converted into compact bony-tissue of Haversian systems. Those portions of the ingrowths from the deej)er layer of the periosteum which are not converted into bone remain in the spaces of the cancellous tissue as the red marrow. Ossification in Cartilage, — Under this heading, taking the femur as a typical example, we may consider the process by which the solid cartilaginous rod which represents the bone in the foetus is converted into the hollow cylinder of compact bone with expanded ends formed of cancellous tissue of which the adult femur is made up. We must bear in mind the fact that this foetal cartilaginous femur is many times smaller than the medullary cavity even of the shaft of the mature bone, and, therefore, that not a trace of the original cartilage can be present in the femur of the adult. Its purpose is indeed purely temporary; and, after its calcification, it is gradually and entirely absorbed as will be presently explained. THE STRUCTUKE OF THE ELEMENTARY TISSUES, 61 The cartilaginous rod which forms the foetal femur is sheathed in a membrane termed the pericJiondrium, which so far resembles the peri- osteum described above, as to consist of two layers, in the deeper one of which spheroidal cells i^redominate and blood-vessels abound, while the outer layer consists mainly of fusiform cells which are in the mature tissue gradually transformed into fibres. Thus, the differences between the foetal perichondrium and the periosteum of the adult are such as r'-: : , -;^ usually exist between the embry- U' r .-- onic and mature forms of connec- ; ?:-• ;"\ ^/ ■ .- tive tissue. '^* ,~ ;' Between the hyaline cartilage '{^ 0 ^ of which the foetal femur consists 'r and the bony tissue forming the adult femur, there are two chief intermediate stages — viz. (1) of Fig. 66. Fig. 67. Fig. 66. — Ossifying cartilage showing loops of blood-vessels. Fig. 67.— Longitudinal section of ossifying cartilage from the humerus of a foetal sheep. Cal- cified trabeculae are seen extending between the columns of cartilage cells, c, Cartilage cells. X 140. (Sharpey.) calcified cartilage, and (2) of embryonic spongy bone. These ma- terials, which successively occupy the place of the foetal cartilage, are in succession entirely absorbed, and their place is taken by true bone. The process by which the cartilaginous is transformed into the 62 HANDBOOK OF PHYSIOLOGY. bony femur may however be divided for the sake of clearness into the following six stages : — Stage 1. — Vascularization of the Cartilage. — Processes from the osteogenetic or cellular layer of the perichondrium containing blood- vessels grow into the substance of the cartilage much as ivy insinuates itself into the cracks and crevices of a wall. This begins at the "cen- tres of ossification," from which the blood-vessels spread chiefly up and down the shaft, etc. Thus the substance of the cartilage, which previ- I Fig. 68.— Transverse section of a portion of a metacarpal bone of a fcetus, showing — 1, fibrous layer of periosteum : 2, osteogenetic layer of ditto ; 3, periosteal bone ; 4, cartilage, with matrix gradually becoming calcified, as at 5, with cells in primary areolae ; beyond 5 the calcified matrix is being entirely replaced by spongy bc>ne. X 200. (V. D. Harris.) ously contained no vessels, is traversed by a number of branched anas- tomosing channels formed by the enlargement and coalescence of the spaces in which the cartilage-cells lie, and containing loops of blood- vessels (fig. 66) and spheroidal cells which will become osteoblasts. Stage 2. — Calcification of Cartilaginous Matrix. — Lime salts are next deposited in the form of fine granules in the hyaline matrix of the cartilage, not yet vascularized, and this gradually becomes transformed into a number of calcified trabecule (fig. 68,5), inclosing alveolar spaces, which are the primary areolm, and which contain cartilage cells. By THE STRUCTURE OF THE ELEMENTARY TISSUES. 63 the absorption of some of the trabeculte larger spaces are developed, which contain cartilage-cells for a very short time only, their places being taken by the so-called osteogenetic layer of the perichondrium (before referred to in Stage 1) which constitutes the primary marrow. The cartilage-cells, gradually enlarging, become more transparent and finally undergo disintegration. Stage 3.— Substitution of Embryonic Spongy Bone for Carti- lage.— The cells of the primary marrow arrange themselves as a contin- uous layer like epithelium on the calcified trabecula3 and deposit a layer of bone, and ensheath them : the calcified trabeculae, encased in the sheaths of young bone, become gradually absorbed, so that finally we have trabeculae composed entirely of spongy bone, all trace of the orig- Fig. 69.— A small isolated mass of bone next the periosteum of the lower jaw of human foetus, o, Osteogenetic layer of periosteum, g, multinuclear giant cells, the one on the left acting here probably like an osteoclast. Above c, the osteoblasts are seen to become surrounded by an osseous matrix. (Klein and Noble Smith.) inal calcified cartilage having disappeared. It is probable that the large multinucleated giant-cells termed osieoclasts by Kolliker, which are de- rived from the osteoblasts by the multiplication of their nuclei, are the agents by which the absorption of calcified cartilage, and subsequently of embryonic spongy bone, is carried on (fig. 69, g). At any rate, they are almost always found wherever absorption is in progress. Stages 2 and 3 are precisely similar to what goes on in the growing shaft of a bone which is increasing in length by the advance of the process of ossification into the intermediary cartilage between the dia- physis and epiphysis. In this case the cartilage-cells become fiattened and, multiplying by division, are grouped into regular columns at right angles to the plane of calcification, while the process of calcification extends into the hyaline matrix between them (figs. 67 and 68). 64 HANDBOOK OF PHYSIOLOGY. Stage 4. — Substitution of Periosteal Bone for the Primary Embryonic Spongy Bone. — The embryouic spongy bone, formed as above described, is simply a temporary tissue occupying the place of the fcetal rod of cartilage, once representing the femur; and the stages 1, 2, and 3 show the successive changes which occur at the centre of the shaft. Periosteal bone is at the same time deposited in successive layers -c. Fig. 70. — Transverse section through the tibia of a fcetal kitten, semi-diagrammatic. X 60. P, Periosteum. O, Osteogenetic layer of the periosteum showing tlie osteoblasts arranged side by side, repi'esented as pear-shaped black dots on the surface of the newly-formed bone. 15, The peri- osteal bone deposited in successive layers beneath the periosteum and ensheathiug E, the spongy endochondral bone: represented as more deeply shaded. Within the trabeculse of endochondral spongy bone are seen the remains of the calcified cartilage trabeculae represented as dark wavy lines. C, The medulla, with V, V, veins. In the lower half of the figure tlie endocliondral spongy bone has been completely absorbed. (Klein and Noble Smith.) beneath the periosteum, i.e., at the circumference of the shaft, exactly as described in the section on ossification in membrane, and thus a casing of periosteal bone is formed around the embryonic endochondral spongy bone: this casing is thickest at the centre, where it is first formed, and thins out toward each end of the shaft. The embryonic spongy bone is THE STRUCTURE OF THE ELEMENTARY TISSUES. 65 absorbed, its trabecala? becoming gradually thinned and its meshes en- larging, and finally coalescing into one great cavity — the medullary cavity of the shaft. Stage 5. — Absorption of the Inner Layers of the Periosteal Bone. — The absorption of the endochondral spongy bone is now com- plete, and the medullary cavity is bounded by periosteal bone: the inner layers of this periosteal bone are next absorbed, and the medullary cavity is thereby enlarged, while the deposition of bone beneath the periosteum Fig. 71. — Tranvprse section of femur of a human embryo about eleven weeks old. o, Rudimen- tary Haversian canal in cross-section; b, in longitudinal section; c, osteoblasts; d, newly formed osseous substance of a lighter color; t, that of greater age; /, lacunae with their cells; g, a cell stil? united to an osteoblast. (Frey.) continues as before. The first-formed periosteal bone is spongy in character. Stage 6. — Formation of Compact Bone. — The transformation of spongy periosteal bone into compact bone is effected in a manner exactly similar to that which has been described in connection with ossification in membrane (p. 60). The irregularities in the walls of the areolse in the spongy bone are absorbed, while the osteoblasts which line them are developed in concentric layers, each layer in turn becoming ossified till the comparatively large space in the centre is reduced to a well-formed Haversian canal (fig. 71). When once formed, bony tissue grows to some extent interstitially, as is evidenced by the fact that the lacunse are rather further apart in full-formed than in young bone. 5 66 HANDBOOK OF PHYSIOLOGY. From the foregoing description of the development of bone, it will be seen that the common terms ossification in cartilage and ossificatioti in membrane are aj3t to mislead, since they seem to imply two processes radically distinct. The process of ossification, however, is in all cases one and the same, all true bony tissue being formed from membrane (perichondrium or periosteum); but in the development of such a bone as the femur, which may be taken as the type of so-called ossification in cartilage, lime-salts are first of all deposited in the cartilage; this calci- fied cartilage, however, is gradually and entirely re-absorbed, being ulti- mately replaced by bone formed from the periosteum, till in the adult structure nothing but true bone is left. Thus, in the process of " ossi- fication in cartilage," calcification of the cartilaginous matrix precedes the real formation of bone. We must, therefore, clearly distinguish between calcification and ossification. The former is simply the infil- tration of an animal tissue with lime-salts, and is, therefore, a change of chemical comjiosition rather than of structure; while ossification is the formation of true bone — a tissue more complex and more highly organ- ized than that from which it is derived. Centres of Ossification. — In all bones ossification commences at one or more points, termed centres of ossification. The long bones, e.g., femur, humerus, etc., have at least three such points — one for the ossifi- cation of the sltdft or diapliysis, and one for each articular extremity or epiphysis. Besides these three primary centres which are always present in long bones, various secondary centres may be superadded for the ossification of different processes. Growth of Bone. — Bones increase in lengtJi by the advance of the process of ossification into the cartilage intermediate between the dia- physis and epiphysis. The increase in length indeed is due entirely to growth at the two ends of the shaft. This is proved by inserting two pins into the shaft of a growing bone: after some time their distance apart will be found to be unaltered though the bone has gradually in- creased in length, the growth having taken place beyond and not be- tween them. If now one pin be placed in the shaft, and the other in the epiphysis of a growing bone, their distance apart will increase as the bone grows in length. Thus it is that if the epiphyses with the intermediate cartilage be removed from a young bone, growth in length is no longer possible; while the natural termination of growth of a bone in length takes place when the epiphyses become united in bony continuity with the shaft. Increase in tliichness in the shaft of a long bone occurs by the depo- sition of successive layers beneath the periosteum. If a thin metal plate be inserted beneath the periosteum of a grow- ing bone it will soon be covered by osseous deposit, but if it be put be- THE STRUCTUKE OF THE ELEMENTARY TISSUES. 67 tweenthe fibrous and osteogenetic layers it will never become enveloped in bone, for all the boiae is formed beneath the latter. Other varieties of connective tissue may become ossified, e.g., the tendons in some birds. Functions of Bones. — Bones form the framework of the body; for this they are fitted by their hardness and solidity together with their comparative lightness; they serve both to jDrotect internal organs in the trunk and skull, and as levers worked by muscles in the limbs; not- withstanding their hardness they possess a considerable degree of elas- ticity, which often saves them from fracture. The material of which the chief portion of the teeth is made up, called Dentine, is frequently classed with bone and as one of the con- nective tissues. The other constituents of the teeth also resemble bone in structure to a considerable degree; it will be as well therefore to give in this place some account of the teeth. The Teeth. During the course of his life, man, in common with most other mammals, is provided with two sets of teeth; the first set, called the Pig. 72.-> Normal well-formed jaws, from which the alveolar plate has been in great part removed, so as to expose the developing permanent teeth in their crypts in the jaws. (Tomes.) temporarii or milh teeth, makes its appearance in infancy, and is in the course of a few years shed and replaced by the second or ■permanent set. The temporary or milk teeth have only a very limited term of existence. They are ten in number in each jaw, namely, on either side from the middle line two incisors, one canine, and two deciduous molars, and are replaced by ten permanent teeth. The number of permanent teeth in 68 HANDBOOK OF PHYSIOLOOY. each jaw is, however, increased to sixteen by the development of three molars on each side of the jaw, which are called the permanent or true molars. The following formula shows, at a glance, the comparative arrange- ment and number of the temporary and permanent teeth : — MOLARS. 9 CANINE. 1 Temporary Teeth. Middle Line of Jaw. incisors. incisors. 2 canine. 1 molars. 2=10 2=10 BICUSPIDS TRUE OR PRE- MOLARS. MOLARS. 3 3 CANINE. 1 Permanent Teeth. Middle Line of Jaw. INCISORS. 2 INCISORS. 2 CANINE. 1 BICUSPIDS OR PRE- TRUE MOLARS. MOLARS. From this formula it will be seen that the two bicuspid or pre-molar teeth in the adult are the successors of the two deciduous molars in the child. They differ from them, however, in some respects, the temporary molars having a stronger likeness to the jjermanent than to their imme- diate descendants the so-called bicuspids, besides occupying more space in the jaws. The temporary incisors and canines differ from their successors but little except in their smaller size and the abrupt manner in which their enamel terminates at the necks of the teeth, forming a ridge or thick edge. Their color is more of a bluish-white than of a yellowish shade. The following tables show the average times of eruption of the Temporary and Permanent teeth. In both cases the eruption of any given tooth of the lower precedes, as a rule, that of the corresponding tooth of the upper jaw. Temporary or Milk Teeth. The figures indicate in months the age at which each tooth appears. INCISORS. DECIDUOUS PrRST MOLARS. CANINES. DECIDUOUS SKCOND MOLARS. 6 12 18 24 . THE STKUCTUKE OF THE ELEMENTARY TISSUES. 69 Permanent Teeth. The age at which each tooth is cut is indicated in this table in years. FIRST MOLARS. INCISORS. CENTRALS. LATERALS. BICUSPIDS OR PRE- MOLARS. FIRST. SECOND. 10 11 SECOND MOLAKS. THIRD MOLARS OR WISDOMS. 17 to 25 The times of eruption given in the above tables are only approxi- mate: the limits of variation being tolerably wide. Some children may cut their first teeth before the age of six months, and others not till nearly the twelfth month. In nearly all cases the two central incisors of the lower jaw are cut first, these being succeeded after a short inter- val by the four incisors of the upper jaw; next follow the lateral in- cisors of the lower jaw, and so on as indicated in the table till the com- pletion of the milk dentition at about the age of two years. Certain diseases affecting the bony skeleton, e.g., Rickets, retard the eruptive period considerably. The milk-teeth usually come through in batches, each period of eruption being succeeded by one of quiescence lasting sometimes several months. The milk-teeth shonld be in use from the age of two up to within a few months of the time for tlieir successors to appear. Their retention serves the purpose of preserving the necessary sjiace sufficient for the succeeding permanent teeth to occupy. It is important to notice that it is a molar which is the first tooth to be cut in the permanent dentition, not an incisor as in the case of the temporary set, and also that it appears behind the last deciduous molar on each side. The third molars, often called Wisdoms, are sometimes unerupted through life from want of sufBcient jaw si^ace and the presence of the other teeth: and in highly civilized races there are evidences to show that they are in process of suppression from the dental series; cases of "whole families in which their absence is a characteristic feature beiug occasionally met with. When the teeth are fully erupted it will be observed that the upper incisors and canines project obliquely over the lower front teeth and the external cusps of the upper bicuspids and molars lie outside those of the corresponding teeth in the lower jaw. This arrangement allows to some extent of a scissor-like action in dividing and biting food in the case of incisors; and a grinding motion in that of the bicuspids and molars when the side to side movements of the lower jaw bring the ex- ternal cusps of the lower teeth into direct articulation with those of the 70 HANDBOOK OF PHYSIOLOGY. upper, and then cause them to glide down the inclined surfaces of the external and up the internal cusps of these same upper teeth during the act of mastication. The work of the canine teeth in man is similar to that of his incisors. Besides being a firmly implanted tooth and one of stronger substance than the others, the canine tooth is important in preserving the shape of the angle of the mouth, and by its shape, whether pointed or blunt, long or short, becomes a character tooth of the dentition as a whole in both males and females. Another feature in the fully developed and properly articulated set of teeth is that no two teeth oppose each other only, but that each tooth antagonizes with two, except the upper AVisdom, usually a small tooth. This is the result of the greater width of the upper incisors, which so arranges the " bite " of the other teeth that the lower canine closes in front of the upper one. Should a tooth be lost, therefor?, it does not follow that its former opponent remaining in the mouth is rendered useless and thereby liable to be removed from the jaw by a gradual process of extrusion commonly seen in teeth that have no work to perform by reason of absence of an- tagonists. It is worthy of note that from the age of four years to the shedding of the first milk-tooth the child has no fewer than forty-eight teetn, twenty milk-teeth and twenty-eight calcified germs of permanent teeth (all in fact except the four wisdom teeth, which show no signs of devel- opment until the third year). Structure of a Tooth. A tooth is generally described as possessing a crown, neck, and root or root^. The crown is the portion which projects beyond the level of the gum. The nech is that constricted portion just below the crown which is embraced by the free edges of the gum, and the root includes all be- low this. ** On making longitudinal and transverse sections through its centre (fig. 73, A, b), a tooth is found to be principally composed of a hard material, dentine or ivory, which is hollowed out into a central cavity which resembles in general shape the outline of the tooth, and is called the jnclp cavity from its containing the very vascular and sensitive pulp. The tooth pulp is composed of fibrous connective tissue, blood-vessels, nerves, and large numbers of cells of varying shapes, e.g., fusiform, stel- late, and on the surface in close connection with the dentine a specialized layer of cells called odontoblast,^, which are elongated columnar-looking cells with a large nucleus at the tapering ends or those farthest from THE STKUCTURE OF THE ELEMENTARY TISSUES. 71 the dentine (the layer is sometimes mentioned as the memhrana eboris, from the tenacity with which it clings to the dentine), all are imbedded in a mucoid gelatinous matrix. The blood-vessels and nerves enter the pulp through a small opening at the apical extremity of each root. The exact terminations of the nerves are not definitely known. They have never been observed to enter the dentinal tubes, but they are probably connected with the fibrils in those tubes through the intervention of the odontoblasts and deeper layer of cells. No lymphatics have been traced to the pulp. A layer of very hard calcareous matter, the enamel, caps that part of the dentine which projects beyond the level of the gum; while sheath- Fig. 73. — A. Longitudinal section of a human molar tooth; c, cement; d. dentine; e, enamel; v, pulp cavity (Owen), b. Transverse section. The letters indicate the same as in a. ing the j^ortion of dentine which is beneath the level of the gum, is a layer of true bone, called the cement or crasta petrosa. At the neck of the tooth, where the enamel and cement come into contact, each is reduced to an exceedingly thin layer. The cement overlapping the enamel and being prolonged over it on the surface of the crown of the tooth is a thin membrane called Nasmyth's membrane, or the ruticte of the tooth. The covering of enamel becomes thicker toward the crown, and the cement toward the lower end or apex of the root. I. — Dentine or Ivory. Chemical Compositioti. — Dentine closely resembles bone in chemical composition. It contains, however, rather less animal matter; the pro- portion in a hundred parts being about twenty-eight animal to seventy- two of earthy. The former, like the animal matter of bone, may be resolved into gelatin by boiling. It also contains a trace of fat. The earthy matter is made up chiefly of calcium jyhosphate, with a small por- 72 HANDBOOK OF PHYSIOLOGY. tion of the carbonate, and traces of calcium Jluo?nde and magnesivm ^phosphate. Structure. — Under the microscope dentine is seen to be finely chan- nelled by a multitude of delicate tubes, which, by their inner ends com- Enamel — Dentine. ~. Cement. Fig. 74. — Premolar tooth of cat in situ. municate with the pulp-cavity, and by their outer extremities come into contact with the under part of the enamel and cement, and sometimes BO a. Fig 75.— Section of a portion of the dentine and cement from the middle of the root of an incisor tooth, a, Dental tubuli ramifying and terminating, some of them in the interglobular spaces h and c, which somewhat resemble bone lacunae ; d, inner layer of the cement witli nui^ierous closely set canaUcuh; e, outer layer of cement; /, lacunae; gr, canahculi. X 350. (Kolliker.J even penetrate them for a greater or less distance (figs. 75, 77). The matrix in which these tubes lie is composed of "a reticulum of fine fibres of connective tissue modified by calcification, and where that pro- THE STKUCTURE OF THE ELEMENTARY TISSUES. 7S cess is complete, entirely hidden by the densely deposited lime salts " (Mummery). In their course from the pulp-cavity to the surface the minute tubes form gentle and nearl}^ parallel curves and divide and subdivide dicho- tomously, but without much lessening of their calibre until they are approaching their peripheral termination. From their sides proceed other exceedingly minute secondary canals, Avhich extend into the dentine between the tubules and anastomose with each other. The tubules of the dentine, the average diameter of which at their inner and larger extremity is ^^Vu o^ ^^ inch, contain fine pro- longations from the tooth-pulp, which give the dentine a certain faint sensitiveness under ordinary circumstances and, without doubt, have to do also with its nutrition. These prolongations from the tooth-pulp are probably processes of the dentine-cells or odontoblasts which are branched cells lining the pulp-cavity; the relation of these processes to the tubules in which they lie being precisely similar to that of the pro- cesses of the bone-corpuscles to the canaliculi of bone. The outer portion of the dentine, underlying the cement, and the enamel to a much lesser degree, forms a more or less distinct layer termed the granular or in- tergiohidar layer. It is characterized by the presence of a number of irregular minute cell-like cavities, much more closely packed than the lacunae in the cement, and "communicating with one another and with the ends of the dentine-tubes (fig. 75, b, c), and containing cells like bone- corpuscles. II. — Enamel. Chemical Composition. — The enamel, which is by far the hardest por- tion of a tooth, is composed, chemically, of the same elements that enter into the composition of dentine and bone. Its animal matter, how- ever, amounts only to about 2 or 3 per cent. It contains a larger pro- portion of inorganic matter and is harder than any other tissue in the body. Structure. — Examined under the microscope, enamel is found com- posed of fine hexagonal fibres (figs. 76, 77) -s-^ot o^ ^^ i^^h in diameter, which are set on end on the surface of the dentine, and fit into corre- sponding depressions in the same. They radiate in such a manner from the dentine that at the top of the tooth they are more or less vertical, while toward the sides they tend to the horizontal direction. Like the dentine tubules, they are not straight, but disposed in wavy and parallel curves. The fibres are marked by transverse lines, and are mostly solid, but some of them may contain a very minute canal. The enamel-prisms are connected together by a very minute quantity of hyaline cement-substance. In the deeper part of badly formed en- 74 HAXDBOOK OF PHYSIOLOGY. amels, between the prisms, are small hiaince, or "interglobular spaces" which have the processes or fibrils of the dentine tubes in connection with them (fig. 77, c). A Fig. 76.— Enamel fibres. A, Fragments and single fibres of the transversely-striated enamel, isolated by the action of hydrochloric acid. B, Surface of a small fragment of enamel, showing the hexagonal ends of the fibres with darker centres, or not so highly calcified, x 350. (Kolliker.) III. — Crust a Petrosa. The crusta petrom, or cement (fig. 75, e, d), is composed of true bone, and in it are lacunae (/) and canaliculi {g), which sometimes communi- cate with the outer finely branched ends of the dentine tubules, and generally with the interglobular spaces. Its lamingeareasit were bolted together by perforating fibres like those of ordinary bone (Sharpey's fibres). Cement differs from ordinary bone in possessing no Haversian canals, or, if at all, only in the thickest part. Such canals are more often met with in teeth with the cement hypertrophied than in the normal tooth. Development of the Teeth. Development of the Teeth. — The first step in the development of the teeth consists in a downward growth (fig. 78, a, 1) from the Kete Mal- pighi or the deeper layer of stratified epithelium of the mucous mem- brane of the mouth, which first becomes thickened in the neighborhood of the maxillge or jaws now in the course of formation. This process passes downward into a recess of the imperfectly developed tissue of the embryonic jaw. The downward epithelial growth forms the inimary enamel organ or enamel germ, and its position is indicated by a slight groove in the mucous membrane of the jaw. The next step in the pro- cess consists in the elongation downward of the enamel groove and of THE STRUCTUKE OF THE ELEMENTARY TISSUES. 75 the enamel germ and the inclination outward of the deeper part (fig. 78, B, /■'), which is now inclined at an angle with the upper portion or neck (/), and has become bulbous. After this there is an increased de- velopment at certain points corresponding to the situations of the future milk-teeth. The enamel germ, or common enamel germ, as it may be called, becomes divided at its deeper portion, or extended by further Fig.' Fig. 78 Fig. 77. — Thin section of the enamel and a part of the dentine, a, Cuticular pellicle of the enamel (Nasmyth's membrane); b. enamel fibres, or colmnns with fissures between them and cross striee: c, larger cavities in the enamel, communicating with the extremities of same of the dentinal tubuli (.rf)- X :3oO. (Kolliker.) Fig. 78. — Section of the_upper jaw of a foetal sheep. A. — 1 , Common enamel germ dipping down into the mucous membrane: 2, palatine process of Jaw; S, rete Malpighi. B.— Section similar to A, but passing through one of the special enamel germs here becoming Hask-shaped; c, c', epithelium of mouth; /. neck; /', body of special enamel germ. C. — A later stage; r, outline of epithelium of gum: /, neck of enamel germ: /', enamel organ; p, papilla; s, dental sac forming; f p. the enamel ferm of jiermaneut tooth ; 7n, bone of jaw ; v, vessels cut across. (Waldeyer and Kolliker.) Copied rom Quain's Anatomy. growth, into a number of special enamel germs corresponding to each of the above-mentioned milk-teeth, and connected to the common germ by a narrow neck. Each tooth is thus placed in its own special recess in the embryonic jaw (lig. 78, B, //'). 76 HANDBOOK OF PHYSIOLOGY. As these changes proceed, there grows up from tlie underlying tissue into each enamel germ (fig. 78, c, j)), a distinct vascular ^>a/7i7Zrt (dental papilla), and upon it the enamel germ becomes moulded, and presents the appearance of a cap of two layers of epithelium separated by an in- terval (fig. 78, c,/'). While part of the sub-epithelial tissue is elevated to form the dental papillae, the part which bounds the embryonic teeth forms the dental sacs (fig. 78, c, s) ; and the rudiment of the jaw, at first a bony gutter in v/hich the teeth germs lie, sends up processes forming partitions between the teeth. In this way small chambers are produced in which the dental sacs are contained, and thus the sockets of the teeth are formed. The papilla, which is really part of the dental sac (if one thinks of this as the whole of the sub-epithelial tissue surrounding the enamel organ and interposed between the enamel germ and the develop- ing bony jaw), is composed of nucleated cells arranged in a meshwork. Fig 79. — Part of section of developing tooth of a young rat, showing the mode of deposition of the dentine. Highly magnified, o, Outer layer of fully formed dentine; 6. uncalcified matrix with one or two nodules of calcareous matter near the calcified parts; c, odontoblasts sending processes into the dentine; d, pulp; e, fusiform or wedge-shape cells found between odontoblasts; /. .stellate cells of pulp in fibrous connective tissue. The section is stained in carmine, which colors the un- calcifled matrix but not the calcified part. (E. A. Schafer.) the outer or peripheral part being covered with a layer of columnar nu- cleated cells called odontoblasts. The odontoblasts possibly form the dentine, while the remainder of the papilla forms the tooth-pulp. The method of the formation of the dentine from the odontoblasts is said to be as follows : The cells elongate at their outer part, and these processes are directly converted into the tubules of dentine (fig. 79, c), and, ac- cording to some, into the contained fibrils as well. The continued for- mation of dentine proceeds by the elongation of the odontoblasts, and their subsequent conversion by a process of calcification into dentine tu- bules. The most recently formed tubules are not immediately calcified. The dentine fibrils contained in the tubules are said, by others, to be formed from processes of the deeper layer of odontoblasts, which are wedged in between the cells of the superficial layer (fig. 79, e) which form the tubules only. There are several theories upon these points. The matrix, according to more recent views, is formed by a calcification of the fibrous connective tissue develojied in the papilla. Since the papillse are to form the main portion of each tooth, i.e., the THE STRUCTURE OF THE ELEMENTARY TISSUES. 77 dentine, each of them early takes the shape of the crown of the tooth to which it corresponds. As the dentine increases in thickness the papilla? diminish, and at last when the tooth is cut only a small amount of the papilla remains as the dental pulp, and is supplied by vessels and nerves which enter at the end of the root. The shape of the crown of the tooth is taken by the corresponding papilla, and that of the single or double root by the subsequent constriction below the crown, or by division of the lower part of the papilla. The number of roots being foreshadowed by the number of arteries going to the papilla. The roots Fig. 80.— Vertical transverse section of the dental sac, pulp, etc., of a kitten. «, Dental papilla or pulp; b, the cap of dentine formed upon the summit; c, its covering of enamel; d, inner layer of epitheUum of the enamel organ; e. gelatinous tissue; /, outer epithelial layer of the enamel organ; 3, inner layer, and h. outer layer of dental sac. X 14. (Thiersch.) are not completely formed at the time of the eruption of the teeth, but subsequently. ■• The enamel cap is found later on to consist (fig. 80, d, e,f) of three parts (1) an inner membrane, composed of a layer of columnar epithe- lium in contact with the dentine, called enamel cells, and outside of these one or more layers of small polyhedral nucleated cells {stratum inter- medium of Hannover) ; (2) an outer membrane of several layers of epi- thelium; (3) a middle membrane formed of a matrix of non-vascular, gelatinous tissue, containing stellate cells. The enamel is formed by the enamel cells of the inner membrane, by the elongation of their distal extremities, and the direct conversion of their ends nearest the dentine papilla into enamel. The calcification of an enamel cell or prism 78 HANDBOOK OF PHYSIOLOGY. takes place first at its periphery, the centre remaining for a time trans- jjarent. The cells of the stratum intermedium are used for the regenera- tion of the enamel cells, but these and the middle membrane after a time disappear. The cells of the outer membrane atrophy early and dis- appear. The cement or crusta petrosa is formed from the internal tissue of the tooth sac, the structure and function of which are identical with those of the osteogenetic layer of the periosteum, or, in other words, os- sification in membrane occurs in it. The outer layer or portion of the membrane of the tooth sac forms the fibrous dental per iodeum. This periosteum, when the tooth is fully formed, is not only a means of attachment of the tooth to its socket, but also in conjunction with the indp a source of nourishment to it. Additional laminae of cement are added to the root from time to time during the life of the tooth, as especially well seen in the abnormal condition called exostosis, by the process of calcification taking place in the periosteum. On the other hand absorption of the root may equally occur through tlie same mem- brane. In this manner the first set of teeth, or the milk-teeth, are formed; and each tooth, by degrees developing, presses at length on the wall of the sac inclosing it, and, causing its absorption, is cut, to use a familiar phrase. The temimrary or milk-teeth are speedily replaced by the growth of the permanent teeth, which push their way up from beneath them, ab- sorbing in their progress the whole of the root of each milk-tooth, and leaving at length only the crown as a mere shell, which is shed to make way for the eruption of the permanent teeth. Each temporary tooth is replaced by a tooth of the permanent set which is developed from a small sac set by, so to speak, from the sac of the temporary tooth which precedes it, and called the cavity of reserve (fig. 78, c, fp). Thus the temporary incisors and canines are succeeded by the corresponding permanent ones, the temporary first molar by the first bicuspid, the temporary second molar develops two offshoots, one for the second bicuspid, the other for the permanent first molar. The permanent second molar is budded off from the first jiermanent molar and the wisdom from the permanent second molar. The development of the temporary teeth is said to commence about the sixth week of intra-uterine life, after the laying down of the bony structure of the jaws. Their permanent successors begin to form about the sixteenth week of intra-uterine life. The second permanent molars are believed to originate about the third month after birth, and the wisdom teeth about the third year. THE STRUCTURE OF THE ELEMENTARY TISSUES. 79 III. Muscular Tissue. There are two chief kinds of muscular tissue, differing both in mi- nute structure as well as in mode of action, viz., (1.) the jAain or non- striated, and (2.) the striated. Unstriped or Plain Muscle. Distribution. — Unstriped muscle forms the proper muscular coats (1.) of the digestive canal from the middle of the oesophagus to the in- ternal sphincter ani; (2.) of the ureters and urinary bladder; (3.) of the trachea and bronchi; (4.) of the ducts of glands; (5.) of the gall-blad- der; (6.) of the vesiculffi seminales; (T.) of the pregnant uterus; (8.) of blood-vessels and lymphatics; (9.) of the iris, and some other parts of Fig. 81.— A, Unstriped muscle cells from the mesentery of a newt. The sheath exhibits trans- verse markings, x 180. B. From a similar preparation, showing that each muscle cell consists of a central bundle of fibrils, F (contractile part), connected with the intra-nuclear network, N, and a sheath with annular thickenings, St. The cells show varicosities due to local contraction, and on these the annular thickenings a,re most marked. X 450. (Klein and Noble Smith.) the eye. This form of tissue also enters largely into the composition (10.) of the tunica dartos^lhe contraction of which is the principal cause of the wrinkling and contraction of the scrotum on exposure to cold. Unstriped muscular tissue occurs largely also in the true skin generally, being especially abundant in the interspaces between the bases of the papillae. Hence when it contracts under the influence of cold, fear, electricity, or any other stimulus, the papillae are made unusually prom- inent, and give rise to the peculiar roughness of the skin termed cutis anserina, or goose skin. It occurs also in the superficial portion of the cutis, in all parts where hairs occur, in the form of flattened roundish bundles, which lie alongside the hair-follicles and sebaceous glands. They pass obliquely from without inward, embrace the sebaceous glands, and are attached to the hair-follicles near their base. Structure. — Uustriated muscles are made up of elongated, spindle- shaped, nucleated cells (fig. 81), which in their perfect form are flat, from about j-^Vo to -gVorr of ^^i inch broad (7 to 8/^), and -^ to 3-^ of an inch (jJ^ to -^mm) in length — very clear, granular, and brittle, so that 80 HANDBOOK OF PHYSIOLOGY. when they break they often have abruptly rounded or square extremities. Each cell of these consists of a fine sheath, probably elastic; of a central bundle of fibrils representing the contractile substance; and of an ob- long nucleus, which includes within a membrane a fine network anasto- mosing at the poles of the nucleus with the contractile fibrils. The ends of fibres are usually single, sometimes divided. Between the fibres is an albuminous cementing material or endomysiwn in which are found Fig. 82.— Plexus of bundles of unstriped muscle cells from the pulmonary pleura of the Guiuea-pig. X IHO. (Klein and Noble Smith.) A, Branching fibres; B, their long central nuclei. connective-tissue corpuscles, and a few fibres. The i)ervmy8ium is con- tinuous with the endomysium in the fibrous connective tissue surround- ing and separating the bundles of muscle cells. Striated Muscle. Distribution. — Striated or striped muscle is found in the following situations. It constitutes the whole of the muscular apparatus of the skeleton, of the walls of the abdomen, etc., the whole of those muscles which are under the control of the will and hence termed voluntary, as well as certain other muscles, e.g., of the internal ear and pharynx not directly under the control of the will, and the heart. Structure. — For the sake of description, striated muscular tissue may be divided into two classes, (a.) skeletal, which comprises the whole of the striated muscles of the body except (b.) the heart : — (a.) Skeletal Muscle. — In the majority of cases a skeletal muscle is inclosed in a sheath of areolar tissue called the epimysium, which in some cases is a very thick and distinct investment, while in other cases it is much thinner. The sheath sends in partitions which serve to sup- port the fasciculi or bundles of fibres, of which the muscle is made up, forming more or less distinct sheaths for them, called perimysium. The THE STRUCTURE OF THE ELEMENTARY TISSUES. 81 fibres themselves are supported in their fasciculus b}- a scanty amount of areolar tissue containing plasma cells and termed endomysiimu Within the areolar tissue supporting the fasciculi and between the fibres are contained the blood-vessels and nerves of the tissue. The muscular fibres of each fasciculus are parallel to one another, and generally speaking so are the fasciculi themselves, except that toward their terminations they may converge to their insertion into the tendon of the muscle. The fasciculi extend throughout the whole length of the muscle, but they vary in size and in the number of their con- Fig. 83. Fig. 84. Fig. 83.— Transverse section through muscular fibres of human tongue. The muscle-corpuscles are indicated by their deeply-stained nuclei situated at the inside of the sarcolemma. Each muscle- fibre shows "Cohnheim's flelds," that is, the sarcous elements in transverse section separated by clear (apparently linear) interstitial substance. X 450. (Klein and Noble Smith.) Fig. 84.— Muscular fibre torn across; the sarcolemma still connecting the two parts of the fibre. (Todd and Bowman.) tained fibres, both in different muscles and also in the same muscle, some muscles having coarse, others fine fasciculi. In some cases it would seem that the perimysium is altogether independent of the external sheath of the muscle. As to the fibres of which the bundles are made up, they have a distinct elastic sheath, the sarcolemma; their size varies consid- erably, their cross-section being from lOO.a to 10/./, and as regards their Fig. 85.— Part of a striped muscle-fibre of a water beetle prepared with absolute alcohol. A, barcolemma: B, Krause s memorane. The sarcolemma shows regular bulgings. Above and below Krause s membrane are seen the transparent "lateral discs." The chief mass of a muscular com- partment is occupied by the contractile disc composed of sarcous elements. The substance of the individual sarcous elements has collected more at the extremity than in the centre ■ hence this latter is more trau.spareut The optical effect of this is that the contractile disc appears to possess a median disc (Disc of Hensen). Several nuclei of mu^^cle corpuscles. C and D, are shown, and in them a minute network, x 300. (Klein and Noble Smitli.; shape, it is cylindrical or is triangular, quadrilateral, or pentangular with rounded angles. In length the fibres seldom exceed an inch and a half 6 82 IIANDLOOi: OF PHYSIOLOGY. (3.75 cm). It is thus evident that tlie same fibre does not extend from one end of a muscle to the other, and indeed it is known that in a fas- ciculus fibrils are joined together by rounded or angular extremities in- vested with their proper sheath the sarcolemma. Each muscular fibre then is thus constructed : — Externally is a fine, transparent, structureless membrane, the sarcolemma, which in the form of a tubular investing sheath forms the outer wall of the fibre and which contains the contractile material of which the fibre is chiefly made up. Sometimes, from its comparative toughness, the sarcolemma will remain untorn, when by extension the contained part can be broken (fig. 84), and its presence is in this way best demonstrated. The fibres are of a pale yellow color, and apparently marked by fine striae which pass trans- versely round them, in slightly curved or wholly parallel lines. The A Fig. 86.— A. Portion of a medium -sized human muscular fibre. X 800. B. Separated bundles of fibrils equally magnified; a, a, larger, and 6, b, smaller collections; c, .still smaller; d, d, the smallest whicli could be detached, possibly representing a single series of sarcous element. cShaipey.) sarcolemma is a transparent structureless elastic sheath of great resist- ance which surrounds each fibre (fig. 84). There is still some doubt re- ffarding the nature of the fibrils. A striated muscle fibre, when examined with a sufficiently high power of the microscope, presents the following appearances, longitu- dinally :— (a.) Alternate darh and light parallel transverse stripes, to which this variety of muscle owes its name, the depth of the stripes not always being the same. (b.) With still higher powers of the microscope, the bright stripes THE STRUCTURE OF THE ELEMENTARY TISSUES. 83 may be seen to be divided in the middle line by other very fine trans- verse dark lines, sometimes called Dohie's line. (c.) Each dark stripe may also sometimes be seen to be divided by a clear line, called Henson's disc. (d.) Each fibre presents an appearance of longitudinal striation and after hardening in alcohol may be divided by teasing with needles into longitudinal fibrils, more or less cylindrical or angular, which are named muscle columns or sarcostyles, and extend throughout each fibre. Each of these appears to consist of short columns connected together by bright intervals, the former are the sarcous elements of Bowman. They may possibly be further longitudinally striated^ and so made up of finer fibrillar still. After treatment with reagents the fibre may be split up into trans- verse discs. (e.) On Transverse Section. — The fibre presents most externally, the outline of the sarcolemma. (f.) The muscular substance proper appears to be mapped out into Fig. 87.— Three muscular fibres running longitudinally, and two bundles of fibres in transverse sec- tion, M, from the tongue. The capillaries, C, are injected, x 150. (Klein and Noble Smith.) small polygonal areas by clear lines (fig. 83) called CoJinlieim's fields, the lines giving the appearance of a mesh work. The lines represent the transverse section of the cementing material between the sarcostyles, which is called sarcoj)lasm. (g.) Immediately within the sarcolemma in ordinary muscle or in the centre of the fibre as in the muscle of some insects, are seen clear oval nuclei called muscle nuclei or muscle corpuscle, surrounding which is a certain amount of granular protoplasm (fig. 85). The appearances of the muscle fibre when seen under the micro- scope, cannot be said to be yet thoroughly understood, and have given rise to various theories as to the structure of striped muscle, to several of which it will be as well to allude. Muscle Caskets (Krause) Theory. — According to this view a muscle fibre is made up of transverse compartments, bounded laterally by the sarcolemma, and above and below by a fine membrane, called 84 HAIfDBOOK OF PHYSIOLOGY. Krause's membrane, whicli passes from side to side from the sarcolemma across the light stripe. This membrane corresponds to Dobie's line. The transverse compartments are divided longitudinally into smaller ones by lines which correspond with the boundaries of Cohnheim's areas, and each such compartment is termed a muscle casket. Within the middle part of the casket is a muscle prism made up of darker rods of contractile material called muscle rods, and above and below the muscle prism is a more fluid substance. When the muscle contracts, the fluid substance is pressed more between the muscle rods, causing them to be further away from one another. Muscle Reticulum Theory, — According to the views of certain observers (Ketzius, Melland, Marshall, van Gehuchten, and Carnoy), the Fig. 88 Fisr. 88a. Fig. 88.— Transverse section of one of the truuk muscles of the Hippocampus, stained in chloiide of gold. (Rollett.) Fig. 88a. — Portion of muscle-fibre of Dytiscus, showing network very plainly. One of the trans- verse networks is split off, and some of the longitudinal bars are shown broken off. (After Melland.) part of fresh muscle which is stained in chloride of gold, is a meshwork of fibrils which corresponds to the intracellular meshwork of ordinary protoplasmic cells, i.e., the spongioplasm, and is the part which is the contractile element in muscle. The meshwork on one level is connected with the meshwork on another level by means of longitudinal fibres, at the junction of which the meshes appear more or less knotted (tigs. 88 and 88a). The longitudinal fibres of the network are, according to this theory, the chief agents in the active contraction. The transverse mesh- work is more passively elastic, and may be the cause of the speedy relax- ation of muscle after contraction has ceased. The material filling up the meshwork is a more fluid and non-contractile material. Eollett has minutely criticised the idea of the gold-staining sub- stance of the fibre being the contractile portion. His views are the THE STRUCTURE OF THE ELEMENTARY TISSUES. 85 follon'ing: — That the muscle-fibre consists of longitudinal fibrillse grouped together into muscle columns, which are seen in the transverse section as Cohnheim's fields, and that the intercolumnar material is semi-fluid sorcoplasm. A muscle column consists of segments alter- nately thin and thick, while in the centre of the thin portion is a dark enlargement forming a dot, these dots in Cohnheim's arrangement cor- respond to Krause's membrane. In fresh muscle, at low focus, according to this view, the muscle- columns appear dark and the sarcoplasma appears light, the former are in a line with the granules. At high focus, the reverse is the case, but the dark sarcoplasma is now seen in line with two rows of granules (fig. 89). _ Also, that in gold-stained preparations, the dark row of granules are thicknesses of the sarcoplasma between the thin segments of the muscle ftfttttfftfft' n I I > 4 ' <' ' I < Mfff<'' "'"' ' ' " il I ' M ■ .11'.- I M ill (iM I I . I I M . I . I ._,■..: tTTTTfHYT' Fig. 89. — Diagram of the appearances in fresh muscle-fibre. A. At low focus (b) the muscle colunius appear dark and in a line with the granules, sarcoplasm light. At high focus (a) the sarco- plasm is dark, muscle columns light, and two rows of granules appear in a line with the sarcoplasm and alternating with the muscle columns. (Marshall, after Rollett.) columns, whereas the two rows of granules do not correspond with these, but alternate with them, belonging as they do to the muscle columns, and not to the sarcoplasm. Schiifer has thrown considerable light ujion the controversy by hav- ing actually observed that when a small portion of the living wing- muscle of insects is teased up with needles in a small drop of white of egg, the sarcostyles may easily be separated from their surrounding sarcoplasm, and may be actualUj seen to contract, whereas the sarcoplasm shows no such property. According to this observer such a sarcostyle may be examined thus isolated, both living and after treatment with various reagents, and it shows alternate bright and light stripes, the latter being bisected by a line which corresponds wtili Krause's mem- brane. Krause's membrane divides the sarcostyle into sarcomeres, which contain in the middle the strongly refractive disc-like sarcous element, and above and below it hyaline material, which is bounded by Krause's membrane. The sarcous substance is penetrated by canals, which ex- tend upward and downward from the hyaline substance to the middle. 86 HAISTDBOOK OF PHYSIOLOGY. The sarcous substance stains with hgematoxylin. A light interval may bisect the sarcous substance if the fibre is stretched, which corresponds with Hensen's disc. Appearances under Polarized Light. — The appearances which muscle presents when viewed under polarized light vary according as the fibres are looked at, as fresh in their own plasma, or as hardened fibres i^repared and mounted in Canada balsam. The whole of the living fibre may be doubly refracting, the isotro- pous part appearing as rows of dots separating transversely the princi- pal material of the fibre. Shortly, according to Schafer, it may be said that the sarcoplasm is singly refracting, and that the sarcostyle is in great part doubly refracting. In a fibre which is extended, after it has been hardened in alcohol and mounted in Canada balsam, there are n ,,.„.iiiil hiiiiiiii) iiiiiiiiii IIIIIH llllllllllj WllUi) K H - S.E. 8.E. Fig. 90. Fig. 91. Fig. 90.— Sarcostyles from the wing-muscles of a wasp, a, a'. Sarcostyles stiowing degrees of retraction (? contraction), b. A sarcostyle extended with the sarcous elements separated into two parts, c. Sarcostyles moderately extended (semidiagrammatic). cE. A. Schafer.) Fig. 91. — Diagram of a sarcomere in a moderately extended condition, a, and in a contracted condition, B. k, k, Krause's membranes; h, plane of Henson; s.e., poriferous sarcous elea:er;t. (E. A. Schafer.) alternate dark and light bands, the former corresponding to the light intervals as seen in ordinary light, and the latter to the various elements. When the fibre is more contracted the dark line becomes narrower, and the anisotropous intervals broader, but there is no interval of the bands on contraction. It appears further that the chromatic portion only of the sarcostyles is anisotroiDous, and the sarcoplasm and the remainder of the fibre is isotropous. {b.) Heart Muscle. — The muscular fibres of the heart, unlike those of most of the involuntary muscles, are striated; but although, in this respect, they resemble the skeletal muscles, they have distinguishing characteristics of their own. The fibres which lie side by side are united at frequent intervals by short branches (fig. 92). The fibres are smaller than those of the ordinary striated muscles, and their striation is Ici-s marked. No sarcolemma can be discerned. The muscle-corpuscles r,re situate in the middle of the substance of the fibre; and in correspond- THE STRUCTUEE OF THE ELEMENTARY TISSUES. 87 ence with these the fibres appear under certain conditions subdivided into oblong portions or "cells/' the offsets from which are the means by which the fibres branch and anastomose one with another. It should be noted, however, that the heart muscular fibres are not the only ones which branch, since the fibres of the tongue of the frog, especially where they are attached to the mucous membrane, present this peculiarity; branching muscular fibres have also been noted in the tongue, and in the facial muscles of other animals. And again, in the animals in which two kinds of skeletal muscles occur, red and pale, in the red muscles the fibres are much less distinctly striated transversely, whereas their longitudinal striation is more marked than in the pale variety. They are also finer than other skeletal muscles. It should also m- m^?^- ^Tr. Fig. 92. Fig. 93. • Fig. 92.— Muscular fibre cells from the heart. (E. A. Sehafer.) Fig. 93.— From a preparation of the uerve-teriiiination in the muscular fibres of a snake, a, End plate seen only broad surfaced, b. End plate seen as narrow surface. (Lingard and Klein.) be added that in these red muscles the sarcoplasm is much developed, and the muscle nuclei are very numerous, and may be situated in the middle of the fibre, as is the case with heart muscle fibres. Blood and Nerve Supply. — Tlie voluntary muscles are freely sup- plied with blood-vessels; the capillaries form a network with oblong meshes around the fibres on the outside of the sarcolemma. No vessels penetrate the sarcolemma to enter the interior of the fibre. Xerves also are supplied freely to muscles; the voluntary muscles receiving them from the cerebro-spinal system, and the unstriped muscles from the sympathetic or ganglionic system. The nerves terminate in the muscular fibre in the following ways: — (1.) In unstriped muscle, the nerves first of all form a plexus, called the ground plexus (Arnold), corresponding to each group of muscle bundles; the plexus is m.ade by the anastomosis of the i^rimitive fibrils of the axis-cylinders. From the ground plexus, branches pass oU, and 88 HAXDBOOK OF PHYSIOLOGY. again anastomosing, form plexuses which correspond to each muscle bundle — intennediari/ jjlexuscfs. From these plexuses branches consist- ing of primitive fibrils pass in between the individual fibres and anas- tomose. These fibrils either send off finer branches, or terminate them- selves in the nuclei of the muscle cells. (2.) In striped muscle the nerves end in motorial end-plates, having first formed, as in the case of unstriped fibres, ground and intermediary- Fig. 94.— Two striped muscle-fibres of the hyoglossus of frog, a, Nerve-end plate; 5, nerve- fibres leaving the end-plate; c, nerve-fibres, terminating after dividing into branches d, a nucleus in which two nerve-fibres anastomose. X 600. (Arndt.) plexuses. The fibres are, however, medullated, and when a branch of the intermediary plexus passes to enter a muscle-fibre, its primitive sheath becomes continuous with the sarcolemma, and 'the axis-cylinder forms a network of its fibrils on the surface of the fibre. This network lies embedded in a flattened granular mass containing nuclei of several kinds; this is the motorial end-plate (figs. 93 and 94). In batrachia, be- sides end-plates, there is another way in which the nerves end in the muscle fibres, viz., by rounded extremities, to which oblong nuclei are attached. THE STRUCTURE OF THE ELEMENT ^RY TISSUES. 89 Development. — (1.) Unstriped. — The cells of unstriped muscle are derived directly from embryonic cells, by an elongation of the cell, and its nucleus; the latter changing from a vesicular to a rod shape. (3.) Striped.— Formerly it was supposed that striated fibres were formed by the coalescence of several cells, but recently it has been proved, that each fibre is formed from a single cell, the process involv- ing an enormous increase in size, a multiplication of the nucleus by fis- sion, and a differentiation of the cell-contents. This view differs but little from another, that the muscular fibre is produced, not by multi- plication of cells, but by arrangement of nuclei in a growing mass of protoplasm (answering to the cell in the theory just referred to), which becomes gradually differentiated so as to assume tlie characters of a fully developed muscular fibre. Growth of Muscle. — The growth of muscles both striated and non-striated, is the result of an increase both in the iiumber and size of the individual elements. In the pregnant uterus the fibre-cells may become enlarged to ten times their original length. In involution of the uterus after parturition the reverse changes occur, accompanied gener- ally by some fatty infiltration of the tissue and degeneration of the fibres. IV. Nervous Tissue. Nervous tissue is found under the microscope to consist essentially of two main elements, namely, of nerve fibres and nerve cells. Nerve-Fibres. Varieties. — Nerve fibres are of two chief kinds, medullated or white fibres, and non-mednUated or gray fibres. Medullated Fibres. — Each medullated nerve-fibre is made up of the following parts: — (1.) An external sheath called the primitive nerve sheath, or nucleated sheath of Schwann; (2.) An intermediate or pack- ing substance known as the mednllari/ or 7m/eline sheath, or white sub- stance of Schwann; and (3) internally the axis-cylinder, primitive band, axis band, or axial fibre. Although these parts can be made out in nerves examined some time after death, in a recent specimen the contents of the nerve-sheath appear to be homogeneous. But by degrees they undergo changes which show them to be composed of two different materials. The internal or central part, occupying the axis of the tube, viz., the axis-cylinder, be- comes grayish, while the outer, or cortical portion or white substance of Schwann, becomes opaque and dimly granular or grumous, as if from a kind of coagulation. At the same time fhe fine outline of the previ- ously transparent cylindrical tube is exchanged for a dark double con- 90 HANDBOOK OF PHYSIOLOGY. tour (fig. 95, b), the outer line being formed by the sheath of the fibre, the inner by the murgin of curdled or coagulated medullary substance. The granular material shortly collects into little masses, which distend portions of the tubular membrane; while the intermediate spaces col- laj)se, giving the fibres a varicose, or beaded iippearance (fig. 95, c and d), instead of the previous cylindrical form. The whole contents of the nerve-tubules are extremely soft, for when subjected to pressure they readily pass from one j^'H't of the tubular sheath to another, and often cause a bulging at the side of the mem.brane. They also readily escape, on pressure, from the extremities of the tubule, in the form of a grumous or granular material. The external nucleated sheath of Schwann, also called the neu- rilenwia, is a pellucid membrane forming the outer investment of the Fig. 95. Fig. 96. Fig. 95.— Primitive nerve.-flbres. a. A perfecUy fresh tubule with a single dark outline, b. A tubule or fibre with a double contour from commencing post-mortem change, c. The changes further advanced, producing a varicose or beaded appearance, d. A tubule or fibre, the central part of which, in consequence of still further changes, has accumulated in separate portions within the sheath (Wagner). Fig. 96. — Two nerve-fibres of sciatic nerve, a. Node of Ranvier. b. Axis-cylinder, c. Sheath of Schwann, with nuclei. X 300. (Klein and Noble Smith.) nerve-fibre. Within this delicate structureless membrane nuclei are seen at intervals, surrounded by a variable amount of protoplasm. The sheath is structureless, like the sarcolemma, and the nuclei appear to be within it : together with the protoplasm which surrounds them they are the relics of embryonic cells, and from their resemblance to the muscle corpuscles of striated muscle may be termed nerve-corptiscles. They are easily stained with logwood and other dyes. The medullary or myelin sheath or white substance of Schwann is the part to which the peculiar opaque white aspect of medullated nerves is due. The thickness of this layer in nerve-fibres varies consid- THE STRUCTURE OF THE ELEMENTARY TISSUES. 91 erably, at oue time being very well developed, at another forming but a very thin investment of the axis cylinder. It is a semi-fluid, fatty sub- stance, and in the fibre possesses a double contour. It is said to be made up of a fine reticulum (Stilling, Klein), in the meshes of which is embedded the bright fatty material. It stains well with osmic acid. According to McCarthy this sheath is composed of small rods radiat- ing from the axis-cylinder to the external sheath of SchAvann. Some- times the whole space is occupied by them, while at other times the rods appear shortened and compressed laterally into bundles embedded in some homogeneous substance. According to other ob- servers the sheath is made up of segments which are either cylindrical or funnel-shaped {sections of Lanter- mann). It is not definitely decided that these divisions exist naturallv in the nerve-fibre. In nerves hardened in Fig. yr. Fig. 98. Fig. 97. — A node of Ranvier in a meduUated nerve-fibre, viewed from above. The medullary sheath is interrupted, and the primitive sheath thickened. Copied from Axel Key and Retzius. X 750. (.Klein and Noble Smith.) Fig. 98. — Gray, pale, or gelatinous nerve-fibres. A. From a branch of the olfactory nerve of the sheep: two dark-bordered or white fibres from the fifth pair are associated with the pale olfactory fibres. B. From the sympathetic nerve, x 450. (Max Schultze.) alcohol, it is possible to demonstrate a very chromatic recticulum in the medullary sheath, which is supposed to be of a horny nature, since it offers much resistance both to chemical reagents and to digestive fluids {horuy reiicuJum or neuro-kerafin neticork). The axis-cylinder consists of a large number of ])vimitive fibi-illcp. This is well shown in the cornea, where the axis-cylinders of nerves break up into minute fibrils which form terminal networks, and also in the spinal cord, where these fibrillar form a large part of the gray matter. From various considerations, such as its invariable presence and un- broken continuity in all nerves, though the primitive sheath or the medullary sheath may be absent, there can be little doubt that the axis- cylinder is the essential part of the fibre, the other parts having the subsidiary function of support and possibly of insulation. 92 HANDBOOK OF PHYSIOLOGY. Nodes of Ranvier. — At regular intervals in most medullated nerves the nucleated sheath of Schwann possesses annular constrictions; these are called nodes of Ranvier. At these jjoints (figs. 99, 101), the contin- uity of the medullary white substance is interrupted, and the primitive sheath comes into immediate contact with the axis-cylinder. The seg- ment of the fibre between two nodes is termed an internode, and the length of the interned es varies in different nerves; their average is said to be 1 mm. There is only one nerve nucleus to each internode. At each node the internodes are united within the external sheath by a band, constricting hand of Eanvier (fig. 101), and this stains black with silver nitrate; the axis-cylinders at the nodes also are capable of being m.m.f. .—- — -: .s.m.p. Fig. 99.— Transverse section of the ramus visceralis of the va^s of skate, v.g., visceralis ganglion ; m.m.f., median medullated fibres; s.m.f., small medullated fibres. (T. W. Shore.) stained with the same reagent, and so a node of Eanvier when stained with silver nitrate is marked by a black cross. Size. — The size of the nerve-fibres varies (fig. 99); it is said that the same fibres may not preserve the same diameter through their whole length. The largest fibres are found within the trunks and branches of the spinal nerves, in which the majority measure from 14.4/^ to 19// in diameter. In the so-called visceral nerves of the brain and spinal cord medullated nerves are found, the diameter of which varies from 1.8/^. to 3.6,'j.. In the hypoglossal nerve they are intermediate in size, and gene- rally measure 7.2/j- to 10.8,'j.. Non-medullated Fibres. — The fibres of the second kind (fig. 98) which are also called fibres of Rernak, constitute the principal part of the trunk and branches of the sympatlietic nerves, the whole of the THE STKUCTUEE OF THE ELEMENTARY TISSUES. 93 olfactory nerve, and are mingled in various proportions in the cerebro- spinal nerves. They differ from the preceding chiefly in their fineness, being only about ^ to ^ as large in their course within the trunks and Fig. 100.— Transverse section of the sciatic nerve of a cat about x 100.— It consists of bundles (FuniculO of nerve-fibres ensheathed in a fibrous supporting- capsule, ephieuriuvi. A; eacii bundle has a special sheath (not sufficiently marked out from the epineurium in tiie figure) or perhieurium B; the nerve-flbres N / are separated from one another by endoneurium ; L, lympn spaces; Ar, artery; V, vein; F, fat. Somewhat diagrammatic. (V. D. Harris.) branches of the nerves; in the absence of the double contour; in their contents being apparently uniform ; and in their having, when in bun- dles, a yellowish-gray hue instead of the whiteness of the cerebro-spinal Fig. 101.— Several fibres of a bundle of medullated nerve-fibres acted upon by silver nitrate to show pecuUar Ijeliavior of nodes of Ranvier, N, toward this reagent. The silver has penetrated at the nodes, and has stained the axis-cylinder, M, for a short distance. S, the white substance. CKlein and Xoble Smith.) nerves. These peculiarities depend on their not possessing the outer layer of medullary substance; their contents being composed exclusively of the axis-cylinder. Yet, since many nerve-fibres may be found which appear intermediate in character between these two kinds, and since the 94 HANDBOOK OF PHYSIOLOGY. large fibres, as they approach both their central and their peripheral end, lose their medullary sheath and assume many of the other charac- ters of the fine fibres of the sympathetic system, it is not necessary to suppose that there is any material difference in the two kinds of fibres. The non-medullated fibres frequently branch. It is worthy of note that in the foetus, at an early period of develop- ment, all nerve-fibres are non-medullated. Nerve-trunks. — Each nerve-trunk is composed of a variable num- ber of difi'erent-sized bundles {fnnicidi) of nerve-fibres which have a special sheath {perineurium). The funiculi are inclosed in a firm fibrous sheath (epineuriuni); this sheath also sends in processes of connective Fig. 102.— Small branch of a muscular nerve of the frog, near its termination, showing divisions of the fibres, a, into two ; 6, into three. X 350. (Kolliker.) tissue which connect the bundles together. In the funiculi between the fibres is a delicate supporting tissue (the endoneurium). There are numerous lymph-spaces both beneath the connective tissue investing individual nerve-fibres and also beneath that which surrounds the funiculi. Every nerve-fibre in its course proceeds uninterruptedly from its origin in a nerve-centre to near its destination, whether this be the periphery of the body, another nervous centre, or the same centre whence it issued. Bundles of fibres run together in the nerve-trunk, but merely lie in apposition to each other; they do not unite: even when they anas- tomose, there is no union of fibres, but only an interchange of fibres between the anastomosing funiculi. Although each nerve-fibre is thus THE STRUCTURE OF THE ELEMENTARY TISSUES. 95 single and undivided through nearly its whole course, yet as it ap- proaches the region in which it terminates, individual fibres break up into several subdivisions before their final ending. Plexuses. — At certain parts of their course, nerves form plexuses, in which they anastomose with each other, as in the case of the brachial and lumbar plexuses. The objects of such interchange of fibres are: — («), to give to each nerve passing off from the plexus, a wider connection with the spinal cord than it would have if it proceeded to its destina- tion without such communication with other nerves. Thus, each nerve Fig. 103. Fis. 104. Fig. 103.— Ganglion nerve-corpuscles of different shapes. (Klein and Noble Smith.) Fig. 104. — Different forms of ganglion cells. A. a. round ball-shaped unipolar cell from the human Gasserian ganglion. A X "240. a X 80. Two cells only show the process/,- b. spindle-shaped; r, multipolar ganghou cell from the spinal cord of the ox. x 80. d. D, Purkinjee ganglion cells from human cerebellum ; ax, axis-cyliuder process ; p, protoplasmic process ; h, h, two cells sur- roimded with a nucleated sheath. (Stohr.) by the wideness of its connections is less dependent on the integrity of any single portion, whether of nerve-centre or of nerve-trunk, from which it may spring, {b) Each part supplied from a plexus has wider relations with the nerve-centres, and more extensive sympathies; and, by means of the same arrangement, groups of muscles may be co-ordi- nated, every member of the group receiving motor filaments from the same parts of the nerve-centre, (c) Any given part, say a limb, is less dependent upon the integrity of any one nerve. Nerve Terminations. — As medullated nerve-fibres approach their terminations they lose their medullary sheath and consist then merely of axis-cylinder and j^rimitive sheath. They then lose also the latter and 96 HANDBOOK OF PHYSIOLOGY. only the axis-cylinder is left with here and there a nerve-corpuscle partly rolled round it. Finally, even this investment ceases and the axis- cylinder breaks up into its elementary fibrillae. Nerve-cells. Nerve-cells, also known as nerve-corpuscles, comprise the second principal element of nervous tissue. They are not generally present in nerve-trunks, but are found in collections of nervous tissue called gavglia. They vary considerably in shape, size, and structure in different situations. Fig. 105.— An isolated sympathetic ganglion cell of man, showing sheath with nucleated-ceU lining, B. A. Ganglion cell, with nucleus and nucleolus. C. Branched process. D. Unbranched process. (Key and Retzius.) x 750. Nerve-cells are, as a rule, provided with very large round nuclei in which one or more nucleoli are very marked. The protoplasm of the cells is granular, but may be striated or reticular. They often contain deposits of yellowish-brown pigment. a. Some nerve-cells are small, generally spherical or ovoid, and have a regular uninterrupted outline. These single nerve-cells are most nu- merous in the sympathetic ganglia; each is inclosed in a nucleated sheath, h. Others, which are called caudate or stellate nerve-cells (fig. 103), are larger, and have one, two, or more long processes issuing from them, the cells being called respectively unipolar, bipolar, ov multipolar: which processes often divide and subdivide, and appear tubular and THE STRUCTURE OF THE ELEMEXTARY TISSUES. 97 filled with the same kind of granular material that is contained within the cell. Of these processes some appear to taper to a point and ter- minate at a greater or less distance from the cell ; some appear to anas- tomose with similar offsets from other cells; while generally only one process from each cell is continuous with a nerve-fibre, the prolongation from the cell by degrees assuming the characters of the nerve-fibre with which it is continuous. This is known as the axis-cylinder process. In bipolar-cells, however, one pole may be continuous with a medullated fibre, and the other with a non-medullated one, or both poles may pass into fibres of the one or the other kind. Ganglion-cells are generally inclosed in a transparent membranous capsule similar in appearance to the external nucleated sheath of nerve- fibres : within this capsule is a layer of small fiattened cells. The process of a nerve-cell which becomes continuous Avith a nerve- fibre is always unbranched as it leaves the cell. It at first has all the characters of an axis-cylinder, but soon acquires a medullary sheath, and then may be termed a nerve-fibre. This continuity of nerve-cells and fibres may be readily traced out in the anterior cornua of the gray matter of the spinal cord. In many large branched nerve-cells a distinctly fibrillated appearance is observable; the fibrillar are probably continuous with those of the axis-cylinder of a nerve. Other points in the structure of nerve-cells will be mentioned under the account of the central nervous system. Nerve Terminations. Nerve-fibres terminate perij^herally in many parts of the body in cer- tain special end-organs of which the following are the chief: Pacinian Corpuscle. — The Pacinian bodies or corpuscles (figs. 106 and 107), named after their discoverer Pacini, also called corpuscles of Vater, are little elongated oval bodies, situated on some of the cerebro- spinal and sympathetic nerves, especially the cutaneous nerves of the hands and feet; and on branches of the large sympathetic plexus nbout the abdominal aorta. They often occur also on the nerves of the mes- entery, and are especiall}^ well seen even by the naked eye in the mesen- tery of the cat. They have been observed also in the pancreas, lymphatic glands and thyroid glands, as well as in the penis of the cat. Each cor- puscle is attached by a narrow pedicle to the nerve on which it is situ- ated, and is formed of several concentric layers of fine membrane, con- sisting of a hyaline ground-membrane with connective tissue fibres, each layer being lined by endothelii-im (fig. 107); through its pedicle passes a single nerve-fibre, which, after traversing the several concentric layers and their immediate spaces, enters a central cavity and, gradually losing its dark border and becoming smaller, terminates at or near the distal 7 98 HANDBOOK OF PHYSIOLOGY. end of the cavity, in a knob-like enlargement or in a bifurcation. The enlargement commonly found at the end of the fibre is said by Pacini to resemble a ganglion corpuscle; but this observation has not been con- firmed. In some cases two nerves have been seen entering one Pacinian body, and in others a nerve after jJfissing unaltered through one has been observed to terminate in a second Pacinian corpuscle. The physi- ological import of these bodies is still obscure. The corpuscles of Herbst (fig. 109) are closely allied to Pacinian cor- puscles, except that they are smaller and longer with a row of nuclei around the central termination of the nerve Fig. 106. Fig. 107 Fig. 106. — Extremities of a nerve of the finger with Pacinian corpuscles attached, about the natural size ("adapted from Henle and Kolliker). Fig. 107. — Pacinian corpuscle of the cat's mesentery. The stalk consists of a nerve-fibre (N) vfith its thick outer slieath. The peripheral capsules of the Pacinian coi-puscle are continuous with tiie outer sheath of the stalk. The intermediary part becomes much narrower near the entrance of the axis-cylinder into the clear central mass. A nook-shaped termination witli the end-bulb (T) is seen in the upper part. A blood-vessel (V) enters the Pacinian corpuscle, and apjiroaches the end- bulb ; it pos.sesses a sheath which is the continuation of the peripheral capsules of the Pacinian corpuscle. X 100. (Klein and Noble Smith.) in the core. They have been found chiefly in the tongues of ducks. The capsules are nearer together, and toward the centre the endo- thelial sheath appears to be absent. End-bulbs are found in the conjunctiva, in the glans penis and clitoris, in the skin, in the lips, and in tendon ; each is about g^ inch in diameter, oval or spheroidal, and is composed of a medullated nerve- fibre, which terminates in corpuscles of various shapes, with a capsule THE STRUCTURE OF THE ELEMENTARY TISSUES. 99 containing a transparent or striated mass in the centre of which ter- minates the axis-cjliuder of the nerve-fibre, the ending of which is some- what chihbed (fig. 110). Touch-corpuscles (fig. Ill), are found in the papilla of the skin Fig. 108.— Summit of a Pacinian corpuscle of the human finger, shoeing the endothelial membranes hning the capsules, x 220. (Klein and Noble Smith.) of the fingers and toes, or among its epithelium; they may be simple or compound; when simple, they are large and slightly flattened transpar- ent nucleated ganglion cells, inclosed in a capsule; when compound the Fig. 110. Fig. 109. —A corpuscle of Herbst, from the tongue of a duck, a, Medullated nerve cut away. S'o6?mm, and Po^«ss^ww^.* Few of the elements, however, appear free or uncombined in the an- imal body. They are generally united together in variable proportions to form compounds. The only elements which have been found free in the body are oxygen, nitrogen, and hydrogen, the first two in the blood, and hydrogen as well as oxygen and nitrogen in the intestinal canal. It was formerly thought that the more complex compounds built up by the animal or vegetable or^rn?/.y?;z were peculiar and could not be made artificially by chemists, and under this idea they were formed into a dis- tinct class, termed organic. This idea has long been given up, but the name is still in use with a different signification. The term is now applied simply to the compounds of the element carbon, irrespective of their origin. A large number of the animal organic compounds, particularly those of the albuminous group, are characterized by their complexity. Many elements enter into their composition, thereby distinguishing them from simple inorganic compounds. Many atoms of the same element occur in each molecule. This latter fact no doubt explains the reason of their instability. Another great canse of the instability is the frequent pres- ence of nitrogen, which may be called negative or undecided in its affin- ities and may be easily separated from combination with other elements. * The following table represents the relative proportion of the various ele- ments. — (Marshall. ) Oxygen . Carhon Hydrogen Nitrogen Calcium Phosphorus Sulphur . Sodium Chlorine 102 . 72.0 Fluorine .... .08 . . 13.5 Potassium . . ... .026 . 9.1 Iron ..... .01 . . 2.5 Magnesium . . . . .0012 . 1.3 Silicon .0002 . . 1.15 (Traces of copper, lead, and . 1476 . . .1 .085 aluminium) 100. THE CHEMICAL COMPOSITIOX OF THE BODY. 103 Animal tissues, containing as they do these orgauic nitrog ous com- pounds, are extremely prone to undergo decomposition. They also con- tain much water, a circumstance very favorable to the breaking up of such substances. It is due to this tendency to decomiDosition that we meet with so large a number of decomposition products among the chem- ical substances forming the basis of the animal body. The various substances found in the animal organism may be conven- iently considered according to the following classification: 1. Orgauio — a. Nitrogenous and b. Xon-Nitrogenous. 2. Inorganic. Organic Substances. Nitrogenous organic bodies take the chief part in forming the solid tissues of the body, and are found also to a considerable extent in the circulating fluids (blood, lymph, chyle), the secretions and excretions. They often contain in addition to carbon, hydrogen, nitrogen, and oxy- gen, the elements sulphur and phosphorus; but although the composition of most of them is approximately known, no general rational formula can at present be given. It will be convenient to give an account of the Proteids and Gelatins in this Chapter, as these constitute the most imi3ortant classes of nitro- genous organic substances. The other members are Decomposition prod- ucts, the chief of which is Urea, found for the most part in the urine; Ferments; Pigments; and other bodies and will be more appropriately treated of later on. Proteids are also called Albuminous substances. They are the chief of the nitrogenous org mic compounds and exist in both plants and ani- mals, one or more of them entering as an essential part into the forma- tion of all living tissue. In the lympli, chyle, and blood, they exist abundantly. Very little is known with any certainty about their chem- ical composition. Not a single member of the class has yet been syn- thesized. Their formula is unknown, the chemists who have attemjjtcd to construct it differing very greatly among themselves. In fact the very term proteid is an extremely arbitrary one. It simply means a body which, according to Hoppe-Seyler, contains in its molecule the elements carbon, hydrogen, nitrogen, oxygen, and sulphur, in certain arbitrary but varying amounts, thus — Carbon, from 51.5 to 5-4.5; Hy- drogen, from 6.9 to 7.3; Nitrogen, from 15.2 to 17.; Oxygen, from 20.9 to 23.5; Sulphur, from .3 to 2. Properties of Proteids. — Proteids are for the most part amorphous and non-crystallizable. Certain of the vegetable proteids have, it is said, been crystallized, and according to Hofmeister, Qg^ albumin is also capable of crystallization. They possess as a rule no power (or scarcely any) of passing through animal membranes. They are soluble, but un- 104 HANDBOOK OF PHYSIOLOGY. dergo alteration in composition in strong acids and alkalies; some are soluble in water, others in neutral saline solutions, some in dilute acids and alkalies, few in alcohol or ether. Their solutions exercise a left- handed action on polarized light. The hojie that it may be possible in the immediate future to synthe- size proteids is rendered all the weaker because of the extraordinary variety of compounds obtained by the decomposition of proteids by va- rious chemical methods, the compounds differing according to the method employed. In the body it seems clear that living proteid is built up by the food supplied to it, which necessarily contains proteid derived either from a vegetable or an animal source; how this process takes place we are yet unable to say. In the course of later chapters in this book we shall endeavor to trace the steps of the breaking up of pro- teid in the body, but we may anticipate by mentioning that it is now generally believed that the ultimate products of this decomposition are urea, a body the formula of which is CO (NH2)2, carbon dioxide and water, Avhile the intermediate substances or by products are glycin (C-^HslSiOa), leucine (CbHis NOo), uric acid, and possibly carbohydrate bodies. When proteid material is decomposed by putrefaction, by the action of chemical reagents, e.^^r., acids, alkalies, or by heat, various bodies are produced, of which amido-acids (acids in which one or more of the hydrogen atoms of the radicle of the acid are replaced by amidogen, N Ha) and bodies belonging to the aromatic or benzene series predom- inate. Hence it comes that various theories of the way in which pro- teids are built up have arisen. The one which has appeared to have received the greatest support is that of Latham. This observer has suggested that proteid may he considered as made up of a series of cyan-aJcoliols, (bodies obtained by the union of any aldehyde with hy- drocyanic acid) with a benzene nucleus. Taking ordinary ethyl alcohol, CH3,CH2,OH, as the type, the aldehyde of which is CHs.CHO, the cor- responding cyanalcohol would be CH3,CH,CiSr,0H. Proteids give certain general chemical reactions. They are a little varied in the case of each particular substance. The chief of these are as follows: i. Xantho-Proteic Reaction.— A solution of any proteid boiled with strong nitric acid becomes yellow, and the cooled solu- tion is darkened on the addition of ammonia. In some cases there is first of all a white coagulum thrown down with the acid; this speedily becomes yellow on boiling. ii. Biuret (Piotrowski's) Reaction.— With a trace of copper sulphate and an excess of potassium or sodium hydrate they give a piirple (or rose red); with ammonia instead of the fixed alkalies, a blue coloration. THE CHEMICAL COMPOSITIOIS' OF THE BODY. 105 iii. Millon's Reaction. — With Millon's reagent (a solution of metallic mercury in strong nitric acid), they give a white or pinkish clotted precipitate, becoming more pink or red on boiling. This test is said to be due to the presence of tyro- sine, an aromatic compound in the proteid molecule. iv. Ammonium Sulphate Reaction. — They are, with the ex- ception of j^eptone, entirely j^i'ecipitated from their solu- tions by saturation w'ith ammonium sulphate. Many of the jiroteids give, in addition, the following tests: V. AVith excess of acetic acid, and potassium ferrocyanide, a white precipitate. tI. With excess of acetic acid and a saturated solution of sodium sulphate, on boiling, a white precipitate. This test is often used to get rid of all traces of proteids, except peptones, from solutions, yii. Boiled with strong hydrochloric acid, they give a violet red coloration, viii. With cane sugar and strong sulphuric acid, on heating, they give ?k purplish coloration. ix. They are precipitated on addition of — citric or acetic acid, and picric acid; or citric or acetic acid, and sodium tung- state; or citric or acetic acid, and potassio-mercuric iodide; and with many other metallic salts in solution and by alcohol. Varieties. — Proteids are divided into classes, chiefly on the basis of their solubilities in various reagents. Eacli class, however, if it contains more tlian one substance, ma}' often be distinguished by other proper- ties common to its members. Not every one of the proteids enumerated is contained in the animal tissues, some are used as food. (1.) Xative-AIbumins. — These substances are soluble in water and in saline solutions, and are coagulated, i.e., turned into coagulated j^i'oteid, ■on heating. (2.) Derived- Albumins. — These are soluble in acids or alkalies, in- soluble in saline solutions and in water, and not coagulated on heating. (3.) Globidins. — These are soluble in strong or in weak saline solu- tions, in dilute acids and alkalies, and insoluble in water. They are •coagulated on heating. (4.) Proteoses. — These are soluble in water and dilute saline solutions, precipitated by saturation with magnesium sulphate or else with ammo- nium sulphate; precipitated but not coagulated by alcohol; precipitated by nitric acid, the precipitate being dissolved on heating, and reappears on cooling, not precipitated by heat. (5.) Peptones. — These are soluble in water, saline solutions, acids, or 100 HANDBOOK OF PHYSIOLOGY. alkalies; not iirecipitated on saturation with any neutral salt; tiiey are not coagulated on heating. (6.) Fibrin. — It is insoluble in water, in dilute saline solutions, or in dilute acids or alkalies; soluble in strong saline solutions (partly) and in strong acids; soluble to a certain extent in strong saline solutions and in gastric or pancreatic fluids. (7.) Coagulated Proteids. — These are of two classes, either coagulated by (a) action ol ferments, or (b) heat. These are soluble only in gastric or pancreatic fluids, forming peptones. (8.) Lardacein, or Amijloid substance. — This body is generally in- soluble, even in gastric or pancreatic fluids at ordinary temperatures. It gives a brown coloration with iodine. Native- Albumins. — Of native-albumins there are three varieties: (a) egg albumin; (b) serum-albumin; and (c) cell-albumin. Egg Albumin is contained in the white of the egg. When in solution in water it is a transparent, frothy, yellowish fluid, neutral or slightly alkaline in reaction. It gives all of the general pro- teid reactions. At a temperature not exceeding 40° C. it is dried up into a yellowish, transparent, glassy mass, soluble in water. At a temperature of 70° C. it is coagvlated, i.e., changed into a new substance, coagulated proteid, which is quite insoluble in water. It is coagulated also by the prolonged action of alcohol; by strong mineral acids, especially by nitric acid, also by tannic acid, or carbolic acid; by ethers the coagulum is soluble in caustic sod;i. It is precipitated without coagulation, i.e., forms an insoluble com- pound with the reagent, soluble on removal of the salt by dialysis, with either mercuric chloride, lead acetate, copper sulphate or silver nitrate, the precipitate in each case being soluble in slight excess of the reagent. With strong nitric acid the albumin is precipitated at the point of contact with the acid in the form of a fine white or yellow ring. Serum- Albumin is contained in blood-serum, lymph, serous and syn- ovial fluids, and in the tissues generalh'; it may be prepared from serum after removal of paraglobulin by saturation with magnesium sulphate, by a further saturation with sodium sulphate. It appears in the urine in the condition known as albuminuria. It gives similar reactions to egg-albumin, but differs from it in not being coagulated by ether. It also differs from egg-albumin in not be- ing easily precipitated by hydrochloric acid, and in the precipitate being easily soluble in excess of that acid. Serum-albumin, either in the co- agulated or precipitated form, is more soluble in excess of strong acid than egg-albumin. Derived'Albumins.— There are three substances belonging to this class, a, Acid-Albumin; b. Alkali- Albumin; and c, Caseinogen. THE CHEMICAL COMPOSITIO^T OF THE BODY. 107 Acid-Albumin. — Acid-albumin is made by adding small quantities of dilute acid (of which the best is hydrochloric, .4 per cent to 1 per cent), to either egg- or serum-albumin diluted with five to ten times its bulk of water, and keeping the solution at a temperature not higher than 50° C. for not less than half an hour. It may also be made by dissolving coagulated native-albumin in strong acid, or by dissolving any of the globulins in acids. It is not coagulated on heating, but on exactly neutralizing the solu- tion a fiocculent precipitate is produced. This maybe shown by adding to the acid-albumin solution a little aqueous solution of litmus, and then adding, drop by drop, a weak solution of caustic potash from a burette, until the red color disappears. The precipitate is the derived-albumin. It is soluble in dilute acid, dilute alkalies and dilute solutions of alka- line carbonates. The solution of acid-albumin gives the proteid tests. The substance itself is coagulated by strong acids, e.g., nitric acid, and by strong alcohol; it is insoluble in distilled water, and in neutral sa- line solutions; it is precipitated from its solutions by saturation with sodium chloride. On boiling in lime-water it is partially coagulated, and a further precipitation takes i)laceon addition to the boiled solution of calcium chloride, magnesium sulphate, or sodium chloride. Alkali-Albumin.—li solutions of native-albumin, or coagulated or other proteid, be treated with dilute or strong fixed alkali, alkali-albu- min is produced. Solid alkali-albumin may also be prepared by adding caustic soda or potash, drop by drop, to undiluted egg-albumin, until the whole forms a jelly. This jelly is soluble in dilute alkalies on boil- ing. A solution of alkali-albumin gives the tests corresponding to those of acid-albumin. It is not coagulated on heating. It is thrown down on neutralizing its solution, except in the presence of alkaline phos- phates, in which case the solution must be distinctly acid before a pre- cipitate falls. To dilferentiate between Acid- and Alkali-Albumin, the following method may be adopted. Alkali-albumin is not precipitated on exact neutralization, if sodium phosphate has been previously added. Acid- albumin is precipitated on exact neutralization, whether or not sodium phosphate has been pieviously added. Caseinogen. — Caseinogen is the chief proteid of milk, from which it may be prepared by the following process: The milk should be diluted with three to four times its volume in water, sufficient dilute acetic acid should then be added to render the solution distinctly acid, and the caseinogen which is thrown down may be separated by filtration. It may then be washed with alcohol and afterward with ether, to free it from fat. Caseinogen may also be prepared by adding to milk an excess of crystallized magnesium sulphate or sodium chloride, either of which salt causes it to separate out. 108 HANDBOOK OF PHYSIOLOGY. Caseinogcn gives much the same tests as alkali-albumin. It is solu- ble in dilute acid or alkalies; it is reprecipitated on neutralization, but if potassium phosphate be present the solution must be distinctly acid before the caseinogen is deposited. Globulins. — The globulins give the general proteid tests; are insol- uble in water; are soluble in dilute saline solutions; are soluble in acids and alkalies forming the corresponding derived-albumin. Most of them are precipitated from their solutions by saturation with solid sodium chloride, magnesium sulphate, or other neutral salt. They are coagulated, but at different temperatures, on heating. Globulin or Crystallin. — It is obtained from the crystalline lens by. rubbing it up with powdered glass, extracting with water or with dilute saline solution, and by passing through the extract a stream of carbon dioxide. It differs from other globulins, except vitellin, in not being precipitated by saturation with sodium chloride. Myosin. — The relation of myosin to living muscle will be considered under the head of the physiology of muscle. It may however be pre- jjared from dead muscle by removing all fat, tendon, etc., and washing repeatedly in water, until the washing contains no trace of proteids, mincing it and then treating with 10 per cent solution of sodium chlo- ride, or similar solution of ammonium chloride or magnesium sulphate, which will dissolve a large portion into a viscid fluid, which filters Avith •difficulty. If the viscid filtrate be dropped little by little into a large •quantity of distilled water, a white flocculcnt precipitate of myosin Avill •occur. It is soluble in 10 per cent saline solution; it is coagulated at 60° C. into coagulated proteid; it is soluble without change in very dilute acids; it is precipitated by picric acid, the precipitate being redissolved on boil- ing; it may give a blue color with ozonic ether and tincture of guaiaciim. Paraglobulin.—VQ.Yiig\6h\\\m is contained in plasma and in serum, in serous and synovial fluids, and may be precipitated by saturating plasma after removal of fibrinogen or serum with solid sodium chloride •or magnesium sulphate, as a bulky flocculent substance which can be removed by filtration. It may also be prepared by diluting blood serum with ten volumes of water, and passing carbonic acid gas rapidly through it. The fine precip- itate may be collected on filter, and washed with water containing car- bonic acid gas. It is very soluble in dilute saline solutions (5 to 8 per cent), from which it is precipitated by carbonic acid gas or by dilute acids; its so- lution is coagulated at 70° C; even dilute acids and alkalies convert it into acid- or alkali-albumin. Fibrinogen. — Fibrinogen is contained in blood-plasma, from which it may be prepared by addition of sodium chloride to the extent of 13 per THE CHEMICAL COMPOSITION OF THE BODY. i09^ cent. It may also be prepared from hydrocele fluid or from other serous transudation by a similar method. Its general reactions are similar to those of paraglobulin; its solution is coagulated at 53°-55° C. Its characteristic j^roperty is that, under certain conditions, it forms fibrin. Vitellin. — Vitellin is prepared from yolk of egg by washing with ether until all the yellow matter has been removed. The residue is- dissolved in 10 per cent saline solution, filtered, and poured into a large quantity of distilled water. The 23reci23itate which falls is impure vitel- lin. It gives the same tests as myosin, but is not precipitated on satu- ration with sodium chloride; it coagulates between 70° and 83° C. Globin. — Is the proteid residue of haamoglobiu. Proteoses are intermediate substances of the digestion of other proteids, tlie ultimate product of which is peptone. Peptones. — Pejatone is formed by the action of the digestive iev- menti, jjejjsi)!, or trypsin, on other proteids, and on gelatin. They wil be considered in connection Avith the physiology of digestion, as will also the intermediate compounds. Fibrin. — Fibrin can be obtained as a soft, Avhite, fibrous, and very elastic substance by whijDping blood with a bundle of twigs, and washing the adhering mass in a stream of water until all the blood-coloring mat- ter is removed. Coagulated proteids are formed by the action of heat or of fer- ments upon other proteids; the temperature necessary to produce coag- ulation varying in the manner previously indicated. They may also be- produced by the jDrolonged action of alcohol upon proteids. They are soluble in strong acids or alkalies; slightly so in dilute; are soluble in digestive fluids (gastric and pancreatic). Are insoluble in saline solu- tions. Lardacein is found in organs which are the seat of amyloid degen- eration. It is insoluble in dilute acids and very slightly in gastric juice at the temperature of the body. It is colored brown by iodine and blu- ish-pink by methyl violet. Lardacein is now often classed under the head of gelatins. Tlte Gelatins or Nitrogenous Bodies otltcr than Proteids. — These are nitrogenous organic bodies, the composition of which does not include them in the proteid class of substances. Gelatin. — Gelatin is contained in the form of co/Zf/i^p??, its anhydride, in bone (ossein), teeth, fibrous connective tissues, tendons, ligaments, etc. It may be obtained by prolonged action of boiling water in a Papin's digester or of dilute acetic acid at a low temperature (15° C). Properties. — The percentage composition is 0, 23.21, H. 7.15, N,. 18.32, C, 50.76, S, 0.56. It contains more nitrogen and less carbon than 110 HAXDBOOK OF PHYSIOLOGY. proteids. By some it is said to contiiin no sulphur. It is amorphous, and transparent when dried. It does not dialyse; it is insoluble in cold water, but swells up to about six times its volume: it dissolves readily on the addition of very dilute acids or alkalies. It is soluble in hot water, and forms a jelly on cooling, even when only 1 per cent of gelatin is present. Prolonged boiling in dilute acids, or in water alone, destroys this power of forming a jelly on cooling. A fairly strong solution of gelatin — 2 per cent to 4 per cent — gives the following reactions: (a) With proteid tests: (i.) Xanthoproteic test. — A yellow color but no previous precipitate with nitric acid, becoming darker on the addition of ammonia, (ii.) Biuret test. — A blue color, (iii.) Millon's test. — A pink precipitate, (iv.) Potassium ferrocy- anide and acetic acid. — No reaction, (v.) Boiling with sodium sulphate and acetic acid. No reaction. (b) Special reactions: (i.) No precipitate with acetic acid, (ii.) No precipitate with hydrochloric acid, (iii.) A white precipitate with tannic acid, not soluble in excess or in dilute acetic acid, (iv.) A white precipitate with mercuric chloride, unaltered by excess of the reagent, (v.) A white precipitate with alcohol, (vi.) A yellowish-white precipitate with picric acid, dissolved on heating and reappearing on cooling. Mucin.— Mucin is supposed to be a compound of a proteid, proba- bly a globulin, with animal gum, and is the characteristic component of mucus; it is contained also in foetal connective tissue, in tendons, and salivary glands. It can be obtained from mucus by diluting it with water, filtering, treating the insoluble portion with weak caustic jilkali, and reprecipitating with acetic acid. 'J'he mucins derived from differ- ent sources probably have different compositions. Projjerties. — Mucin has a ropy consistency. It is precipitated by alcohol and by mineral acids, but dissolved by excess of the latter. It is dissolved by alkalies and in lime water. It gives the proteid reaction with Millon's reagent and with nitric acid. Neither mercuric chloride nor tannic acid gives a precipitate with it (?). It does not dialyse. Elastin is found in elastic tissue, in the ligamenta subflava, liga- mentum nucha?, etc. It is insoluble, but swells up both in cold and hot water. Is soluble in strong caustic soda. It is precipitated by tannic acid; does not gelatinize. Gives the proteid reactions with strong nitric acid and ammonia, and imperfectly with Millon's reagent. Yields leucin on boiling with strong sulphuric acid. Chondrin is found in the condition of chondrigen in cartilage. It is a mixture of gelatin with a mucin-like substance, and is obtained from chondrigen by boiling. Properties. — It is soluble in hot water, and in solutions of neutral THE CHEMICAL COMPOSITIOX OF THE BODY. Ill salt, e.g., sulphate of sodium, in dilute mineral acids, caustic potash, aud soda. Insoluble in cold water, alcohol, and ether. It is precipitated from its solutions by dilute mineral acids (excess redissolves it), by- alum, by lead acetate, by silver nitrate, and by chlorine water. On boil- ing with strong hydrochloric acid, it yields grape-sugar and certain ni- trogenous substances. Prolonged boiling in dilute acids, or in water, destroys its power of forming a jelly on cooling. Keratin is obtained from hair, nails, aud dried skin. It contains sulphur evidently only loosely combined. Nuclein. — Found in the nuclei of cells, also in milk, and yolk of egg. It resembles mucin in its tests, but diliers from it in composition as it contains phosphorus in its molecule. Some of the bodies which have been called mucin, are really compounds of nuclein and a j)roteid, generally a globulin. Such is the mucinoid substance in bile. Xon-nitrogenous organic bodies consist of (a) Oils and Fats, which are for the most part mixtures of paJmi- tin, CsiHgoOe, stearin CstHuoOs, and oJein C57H104O6, in different pro- portions. They are formed by the union of fatty acid radicals with the triatomic alcohol. Glycerin C3H3(OH)3, and are etherial salts of that alcohol. The radicals are C18H35O, CiellaiO, and CisHssO, respectively. Human fat consists of a mixture of palmitin, stearin, o-wH olein, of which the two former contribute three-quarters of the whole. Olein is the only liquid constituent. Fats are insoluble in water and in cold alcohol; soluble in hot alco- hol, ether, and chloroform. Colorless and tasteless; easily decomposed or saponified by alkalies or super-heated steam into glycerin and the fatty acids. And (b) Carbohydrates, which are bodies composed of sis or twelve atoms of carbon with hydrogen and oxygen, the two latter elements be- ing in the proportion to form water. There are three main classes of carbohydrates. Atnyloses, CeliioOs, comprising Starch, Dextrin, Glycogen, etc. Sac- cliaroses, C12H22O11, Saccharose, or Cane sugar, Lactose, ]\Ialtose, etc. Glucoses, C6H12O6, Dextrose or Grape sugar, Lsevulose or Fruit-sugar, Inosite, etc. Of these the most important are. Starch (CeHioOa), which is contained in nearly all plants, and in many seeds, roofs, steins, and some fruits. It is a soft white powder composed of granules having an organized structure, consisting of gran- iilose (soluble in water) contained in a coat of ceUuJose (insoluble in water) ; the shape and size of the granules varying according to the source whence the starch has been obtained. It is insoluble in cold water, in alcohol, and in ether; it is soluble after boiling for some time, and may be filtered, in consequence of the swelling up of the granulose. 112 HANDBOOK OF PHYSIOLOGY. wliicli bursts the cellulose coat, and becoming free, is entirely dissolved in water. This solution is a solution of soluble starch or amydin. It gives a blue coloration with iodine, which disappears on heating and returns on cooling. It is converted into dextrine and grape-sugar by diastase or by boiling with dilute acids. Glycogen, which is contained in the liver, is also present to a con- siderable extent in the muscles of very young animals, in the placenta, in colorless corpuscles, and in embryonic tissues. It is freely soluble in Wivtor, and its solution looks opalescent; it gives a port-wine coloration with iodine, which disappears on heating and returns on cooling. It is precipitated by basic lead acetate and insoluble in absolute alcohol and in ether. It exists in the liver during life, but very soon after death is changed into sugar. It is converted into sugar by diastase ferments, or by boiling with dilute acids. Dextrin. — This substance is made in commerce by heating dry po- tato-starch to a temperature of 400°. It is also produced in the process of the conversion of starch into sugar by diastase, and by the salivary and pancreatic ferments. A yellowish amorphous powder, soluble in water, but insoluble in absolute alcohol and in ether. It corresponds almost exactly in tests with glycogen; but one variety (achroo-dextrine) does not give the port-wine coloration with iodine. Cane Sugar or Saccharose, is contained in the juices of many plants and fruits, and is as a rule extracted from the sugar cane, from beetroot, or from the majjle. It is crystalline and is precipitated from concentrated solutions by absolute alcohol. It has no power of reduc- ing copper salts on boiling. It is dextro-rotatory (see Ajipendix). lb is not subject to alcoholic fermentation, until by inversion it is converted into glucose, it chars on addition of sulj)huric acid, and on heating with potassium or sodium hydrate. Lactose is contained in milk. It is less soluble in water than glu- cose; not sweet, and is gritty to the taste; but it is insoluble in absolute alcohol. Undergoes alcoholic fermentation with extreme difficulty; gives the tests similar to glucose, but less readily. It is dextro-rotatory -j-59°. Maltose is formed in the conversion of starch into glucose by the saliva and pancreatic fluids. It is also formed by the action of malt upon starch by the ferment diastase, and in the formation of glucose from starch. It is converted into dextrine by dilute sulphuric acid. It is dextro-rotatory; ferments with yeast; reduces copper salts, and crystallizes in fine needles. Glucose occurs widely diffused in the vegetable kingdom, in diabetic urine, in the blood, etc.; it is usually obtained from grape-juice, honey, beet-root or carrots. It really is a mixture of two isomeric bodies, Dex- trose or grape-sugar, which turns a ray of polarized light to the right (_j_5G°), and Lcevulose or fruit-sugar, which turns the ray to the left. THE CHEMICAL COMPOSITION OF THE BODY. 113 It is easily soluble in water and in alcohol; not so sweet as cane- sugar; the relation of its sweetness to that of cane-sugar is as 3 to 5. It is not so easily charred by strong sulphuric acid as cane-sugar. It is not entirely soluble in alcohol. It undergoes alcoholic fermentation with yeast. Dextrose has the power of reducing the salts of silver, bismuth, mercury, and copper, either to the form of the metal as in the first three cases, or to the form of the sub-oxide in the case with cujjrous salts. Upon this property the chief tests for the sugar, e.g., Trommer's and Bottcher's, depend (see Appendix). When boiled with potash, glucic and melanic acids are formed, and a yellowish fluid results (Moore's test). It is oxidized by the action of nitric acid to saccharic acid. It forms compounds with acids and with potash and lime. It undergoes alcoholic fermentation with yeast, and lactic acid fermentation with bacterina lactis. It forms caramel when strongly heated, and is also charred with strong acids. For the method of quantitative estimation, etc., see Appendix. Laevulose is one of the products of the decomposition of cane-sugar by means of dilute mineral acids, or by means of the ferment suverten in the alimentary canal. It reacts to the same test as glucose, but is non-crystallizable, and is la^vo-rotatory — 1060. It is soluble in water and in alcohol. Its com- pound with lime is solid, whereas that with dextrose is not. Galactose is formed from lactose by the action of dilute mineral acids, or inverting ferments. It undergoes alcoholic fermentation, and reduces copper salts to the suboxide. Inosite. — Inosite is a non-fermentable variety of glucose occurring in the heart and voluntary muscles, as well as in beans and other plants. It crystallizes in the form of large colorless monoclinic tables, which are soluble in water, but insoluble in alcohol or ether, Inosite may be de- tected by evaporating the solution containing it nearly to dryness, and by then adding a small drop of solution of mercuric nitrate, and after- ward evaporating carefully to dryness, a yellowish-white residue is ob- tained ; on further cautiously heating, the yellow changes to a deep rose- color, which disappears on cooling, but reappears on heating. If the inosite be almost pure, its solution may be evaporated nearly to dryness. After the addition of nitric acid, the residue mixed with a little ammonia and calcium chloride, and again evaporated, yields a rose-red coloration. Certain of the monatomic Fatty Acids are found in the body, viz., Formic CHaOa, acetic C2H4O2, and propionic CsHeOa, present ii^ sweat, but normally in no other human secretion. They have been found else- where in diseased conditions. Biitjiric acid, QiW^Oi/i^ found in sweat. Various others of these acids have been obtained from blood,, muscular juice, fasces and urine. 8 114 HANDBOOK OF PHYSIOLOGY. Of the diatomic fatty acids, one acid, Lactic acid, CsHeOs exists in a free state in muscle ])lasma, and is increased in quantity by muscular contraction, is never contained in healthy blood, and when present in abnormal amount seems to produce rheumatism. Of the aromatic series, Benzoic acid, C3 HeOa, is always found in the urine of herbivora, and can be obtained from stale human urine. It does not exist free elsewhere. PlumoL — Phenyl alcohol or carbolic acid exists in minute quantity in human urine. It is an alcohol of the aromatic series. Inorganic Principles. The inorganic ])roximate principles of the human body are numer- ous. They are derived, for the most part, directly from food and drink, and pass through the system unaltered. Some are, however, decom- posed on their way, as chloride of sodium, of which only four-fifths of the quantity ingested are excreted in the same form; and some are newly formed within the body, — as, for example, a part of the sulphates and carbonates, and some of the water. Much of the inorganic saline matter found in the body is a neces- sary constituent of its structure, — as necessary in its way as albumin or any other organic principle; another part is important in regulat- ing or modifying various jihysical processes, as absorption, solution, and the like; while a part must be reckoned only as matter, which is, so to speak, accidentally present, whether derived from the food or the tis- sues, and which will, at the first opportunity, be excreted from the body. Gases. — -The gaseous matters found in the body are Oxygen, Hydro- fjen, Nitrogen^ Carlmretted and ^^ulplinretted hydrogen, and Carbonic acid. The first three have been referred to. Carburetted and sulphu- retted hydrogen are found in the intestinal canal. Carbonic acid is pres- ent in the blood and other fluids, and is excreted in large quantities by the lungs, and in very minute amount by the skin. It will be specially considered in the chapter on Respiration. Water, the most abundant of the proximate principles, forms a large proportion, — more than two-thirds of the weight of the whole body. Its relative amount in some of the principal solids and fluids of the body is shown in the following table (from Robin and VerdeiPs) : — Quantity of Water in 1000 Parts. Teeth . Bones Cartilage Muscles Ligament^ Brain Blood . Synovia 100 Bile 130 Milk . 550 Pancreatic juice 750 Urine 768 Ljniph 789 Gastric juice . 795 Perspiration 805 Saliva 880 887 900 936 960 975 986 995 THE CHEMICAL COMPOSITIOX OF THE BODY. 115 The importance of water as a constituent of the animal body may be assumed from the preceding table, and is shown in a still more striking manner by its withdrawal. If any tissue, as muscle, cartilage, or ten- don, be subjected to heat sufficient to drive off the greater jiart of its water, all its characteristic physical 2)roperties are destroyed ; and what was previously soft, elastic, and flexible, becomes hard and brittle, and horn}^ so as to be scarcely recognizable. In all the fluids of the body — blood, lymph, etc., — water acts the part of a general solvent, and by its means alone circulation of nutrient mat- ter is possible. It is the medium also in which all fluid and solid ali- ments are dissolved before absorjotion, as well as the means by which all, except gaseous, excretory products are removed. All the various j)ro- cesses of secretion, transudation, and nutrition, depend of necessity on its presence for their performance. The greater part, by far, of the water present in the body is taken into it as such from without, in the food and drink. A small amount, however, is the result of the chemical union of hydrogen with oxygen in the blood and tissue. The total amount taken into the body every day is about 4^ lbs.; while an uncertain quantity (perhaps ^ to f lb.) is formed by chemical action within it. — (Dalton). The loss of water from the body is intimately connected with excre- tion from the lungs, skin, and kidneys, and, to a less extent, from the alimentary canal. The loss from these various orgaus may be thus ap- portioned (quoted by Dalton from various observers). From the Alimentary canal (faeces) 4 per cent. " Lungs 30 " " Skin (perspiration) 30 " Kidneys (urine) 46 " 100 Sodium and Potassium Chlorides are present in nearly all parts of the body. The former seems to be especially necessary, judging from the instinctive craving for it on the part of animals in whose food it is deficient, and from the diseased condition which is consequent on its withdrawal. In the blood, the quantity of sodium chloride is greater than that of all its other saline ingredients taken together. In the muscles, on the other hand, the quantity of sodium chloride is less than that of the chloride of potassium. Calcium Fluoride, in minute amount, is present in the bones and teeth, and traces have been found in the blood and some other fluids. Calcium, Potassiwn, Sodium, and Magnesium Phosphates are found in nearly every tissue and fluid. In some tissues— the bones and teeth — the phosphate of calcium exists in very large amount and is the jirin- cipal source of that hardness of texture on which the proper perform- ance of their functions so much depends. The phosphate of calcium is 116 HANDBOOK OF PHYSIOLOGY. intimately incorporated with the organic basis or matrix, but it can be removed by acids without destroying the general shape of the bone; and, after the removal of its inorganic salts, a bone is left soft, tough, and flexible. Potassium and sodium phosphates with the carbonates, maintain the alkalinity of the blood. Calcium Carbonate occurs in bones and teeth, but in much smaller quantity than the phosphate. It is found also in some other parts. The small concretions of the internal ear (otoliths) are composed of crystalline calcium carbonate, and form the only example of inorganic crystalline matter existing as such in the body. Potassium and Sodium Carbonates are found in the blood, and some other fluids and tissues. Potassium, Sodium, and Calcium Sulphates are met with in small amount in most of the solids and fluids. Silicon. — A very minute quantity of silica exists in the urine, and in the blood. Traces of it have been found also in bones, hair, and some other parts. Iron. — The especial place of iron is in haemoglobin, the coloring- matter of the blood, of which a full account has been given with the chemistry of the blood. Peroxide of iron is found, in very small quan- tities, in the ashes of bones, muscles, and many tissues, and in lymph and chyle, albumin of serum., fibrin, bile, milk and other fluids; and a salt of iron, probably a phosphate, exists in the hair, black pigment, and other deeply colored ejiithelial or horny substances, Alumifiium, Manganese, Copper, and Lead. — It seems most likely that in the human body, C02:)per, manganesium, aluminium, and lead are merely accidental elements, which, being taken in minute quantities with the food, and not excreted at once with the fseces, are absorbed and deposited in some tissue or organ, of which, however, they form no nec- essary part. In the same manner, arsenic, being absorbed, may be de- posited in the liver and other parts. CHAPTER Y. THE BLOOD The blood is the fluid medium by means of which all the tissues of the body are directly or indirectly nourished; by means of it also such of the materials which result from the metabolism of the tissues as are of no further use in the economy^, are carried to the excretory organs to be removed from the body. It is a somewhat viscid fluid, and in man and in all other vertebrate animals with the exception of two,* is red in color. The exact shade of red is variable; that taken from the arteries, from the left side of the heart and from the pulmonary veins is of a bright scarlet hue, that obtained from the systemic veins, from the right side of the heart, and from the pulmonary artery, is of a much darker color, and varies from bluish-red to reddish-black. At first sight, the red color appears to belong to the whole mass of blood, but on further examination this is found not to be the case. In reality blood consists of an almost colorless fluid, called plasma or liquor sanguinis, in which are suspended numerous minute rounded masses of proto- plasm, called blood corpuscles, which are, for the most part, colored, and it is to their presence in the fluid that the red color of the blood is due. Even when examined in very thin layers, blood is opaque, on account of the different refractive powers possessed by its two constituents, viz., the plasma and the corpuscles. On treatment with chloroform and other reagents, however, it becomes transparent and assumes a lake color, in consequence of the coloring matter of the corpuscles having been discharged into the plasma. The average specijic gravity of blood at 15^ C. (60'' F.) varies from 1055 to 1062. A rapid and useful method of estimating the specific gravity of blood has been employed by Lloyd Jones. Drops of blood are taken and allowed to fall into fluids of known specific gravity. When the drop neither rises nor sinks in the fluid, it is taken to be of the same specific gravity as that of the stand- ard fiuid. The reaction of blood is faintly alkaline and the taste saltish. Its temperature varies slightly, the average being 37.8° C. (100° F.). The blood stream is warmed by passing through the muscles, nerve cen- tres, and glands, but is somewhat cooled on traversing the capillaries of * The amphioxus and the leptocephalus. 117 118 HANDBOOK OF PHYSIOLOGY. the skin. Recently drawn blood has a distinct odor, which in many cases is characteristic of the animal from which it has been taken. It may be further developed also by adding to blood a mixture of equal parts of sulphuric acid and water. Quantity of the Blood. — The quantity of blood in any animal under normal conditions bears a fairly constant relation to the body- weight. The methods employed for estimating it are not so simple as might at first sight have been thought For example, it vvould not be possible to get any accurate information on the point from the amount obtained by rapidly bleeding an animal to death, for then an indefinite quantity would remain in the vessels, as well as in the tissues; nor, on the other hand, would it be possible to obtain a correct estimate by less rapid bleeding, as, since life would be more prolonged, time would be allowed for the passage into the blood of lymph from the lymphatic vessels and from the tissues. In the former case, therefore, we should nnder-estimate, and in the latter over-estimate the total amount of the blood. Of the several methods which have been employed, the most accurate appears to be the following. A small quantity of blood is taken from an animal by venesection; it is defibrinated and measured, and used to make standard solutions of blood. The animal is then rapidl}^ bled to death, and the blood which escapes is collected. The blood-vessels are next washed out with saline solution until the washings are no longer colored, and these are added to the previously withdrawn blood; lastly the whole animal is finely minced with saline solution. The fluid ob- tained from the mincings is carefully filtered, and added to the diluted blood previously obtained, and the whole is measured. The next step in the process is the comparison of the color of the diluted blood with that of standard solutions of blood and water of a known strength, until it is discovered to what standard solution the diluted blood corresponds. As the amount of blood in the corresponding standard solution is known, as well as the total quantity of diluted blood obtained from the animal, it is easy to calculate the absolute amount of blood which the latter con- tained, and to this is added the small amount which was withdrawn to make the standard solutions. This gives the total amount of blood Avhich the animal contained. It is contrasted with the weight of the animal, previously known. The result of many experiments shows that the quantity of blood in various animals averages jV to -^^ of the total body-weight. An estimate of the quantity in man which corresponded nearly with this proportion, has been more than once made from the following data. A criminal was weighed before and after decapitation; the difference in the weight representing the quantity of blood which escaped. The blood-vessels of the head and trunk were then washed out by the injec- 'HE BLOOD. 119 tion of water, until the fluid which escaped had only a pale red or straw color. This fluid was then also weighed; and the amount of blood which it represented was calculated by comparing the proportion of solid matter contained in it with that of the first blood which escaped on decapitation. Two experiments of this kind gave precisely similar results. (Weber and Lehmann.) It should be remembered, in connection with these estimations, that the quantity of the blood must vary very considerably, even in the same animal, with the amount of both the ingesta and egesta of the period immediately preceding the experiment; it has been found, for example, that the quantity of blood obtainable from the body of a fasting animal rarely exceeds a half of that which is present soon after a full meal. Coagulation of the Blood. One of the most characteristic properties which the blood possesses is that of dotting or coagulating. This phenomenon may be observed under the most favorable conditions in blood which has been drawn into an open vessel. In about two or three minutes, at the ordinary Fig. 117.— Reticulum of fibrin, from a drop of liuman blood, after treatment with rosanilin. (Ranvier.) temperature of the air, the surface of the fluid is seen to become semi- solid or jelly-like, and this change takes place, in a minute or two after- ward iit the sides of the vessel in which it is contained, and then extends throughout the entire mass. The time which is occupied in these changes is about eight or nine minutes. The solid mass is of exactly the same volume as the previously liquid blood, and adheres so closely to the sides of the containing vessel that if the latter be inverted none of its contents escape. The solid mass is the crassamentum or clot. If the clot be watched for a few minutes, drops of a light, straw-colored fluid, the serum, may be seen to make their appearance on the surface, 120 HANDBOOK OF PHYSIOLOGY, and, as they become more and more numerous, to run together, form- ing a complete superficial stratum above the solid clot. At the same time the fluid begins to transude at the sides and at the under-surface of the clot, which in the course of an hour or two floats in the liquid. The first drops of serum appear on the surface about eleven or twelve minutes after the blood has been drawn; and the fluid continues to transude for from thirty-six to forty-eight hours. The clotting of blood is due to the development in it of a substance called fibrin, which appears as a meshwork (fig. 117) of fine fibrils. This meshwork entangles and incloses within itself the blood corpuscles. The first clot formed, therefore, includes the whole of the constituents of the blood in an apparently solid mass, but soon the fibrinous mesh- work begins to contract and the serum which does not belong to the clot is squeezed out. When the whole of the serum has transuded the clot is found to be smaller, but firmer and harder, as it is now made up of fibrin and blood corpuscles only. Thus coagulation rearranges the constituents of the blood ; liquid blood being made up of plasma and blood corpuscles, and clotted blood of serum and clot. Liquid Blood. Plasma. Corpuscles. Serum. Clot. Clotteil Blood. Under ordinary circumstances coagulation occurs before the red cor- puscles have had time to subside; and thus from their being entangled in the meshes of the fibrin, the clot is of a deep red color throughout, probably slightly darker at the most dependent part, from greater accu- mulation of red corpuscles there than elsewhere. When, however, coag- ulation is from any cause delayed, as when blood is kept at a tempera- ture slightly above 0° C. (32° F,), or when clotting is naturally slow, as is the case with horse's blood, or, lastly, in certain diseased conditions, particularly in inflammatory states, time is allowed for the colored cor- puscles to sink to the bottom of the fluid. When clotting after a time occurs, the upper layers of the blood are free of colored corpuscles and consist chiefly of fibrin. This forms a superficial stratum differing in appearance from the rest of the clot, and is of a grayish yellow color. This is known as the bufi/ coat or crusta phlogistica. The buffy coat produced in the manner just described, commonly contracts more than the rest of the clot, on account of the absence of colored corpuscles THE BLOOD. 121 from its moshes, and because contraction is less interfered with by ad- hesion to the interior of the containing vessel in the vertical than the horizontal direction. A cup-like appearance of the buify coat results, and the clot is not only buUed but cupped on the surface. Formation of Fibrin. — That the clotting of blood is due to the grad- ual appearance in it of fibrin may be easily demonstrated. For example, if recently drawn blood be whipped with a bundle of twigs, the fibrin may be withdrawn from the blood before it can entangle the blood cor- puscles within its meshes, as it adheres to the twigs in stringy threads almost free from corpuscles ; the blood from which the fibrin has been withdrawn no longer exhibits the power of spontaneous coagulability. Although these facts have long been known, the closely associated problem as to the exact manner in which fibrin is formed is by no means so simple. It will be most convenient to treat of the question step by step. In the first place it appears that under the ordinary conditions of ex^QTiniQwi, the fibrin is chiefii/, if not entirely derived from the plasma ; for although the colorless corpuscles may be intimately connected with the process, as will be shown later on, yet the colored corpuscles take no active part in it. This statement does not deny the possibility that fibrin may sometimes be derived from the colored corpuscles. Indeed, this is more than probable, as experiments have shown that if a little defibrinated blood be added to serum, the haemoglobin leaves the stroma of the colored corpuscles of the blood, and a substance arises from it called stroma-fibrin, indistinguishable from ordinary fibrin, and the serum is clotted. But normally fibrin is derived from the plasma. Pure plasma may be procured by delaying coagulation in blood by keeping it at a temperature slightly above freezing point, until the colored corpuscles have subsided to the bottom of the containing vessel: the blood of the horse being specially suited for the purposes of this experiment. A portion of the colorless supernatant plasma, if decanted into another vessel and exposed to the ordinary temperature of the air, will coagulate just as though it were the entire blood, producing a clot similar in all respects to blood clot, except that it is almost colorless from the absence of red corpuscles. If some of the plasma be diluted with twice or three times its bulk of normal saline solution,* coagula- tion is delayed, and the stages of the gradual formation of fibrin in it may be conveniently watched. The viscidity which precedes the com- plete coagulation may be actually seen to be due to the formation of fibrin fibrils — first of all at the edge of the fluid containing vessel, and then gradually extending throughout the mass. * Normal saline solution commonly consists of a .6 per cent solution of com- mon salt (sodium chloride) in water. 122 HANDBOOK OF PHYSIOLOGY. If a further portion of plasma_, diluted or not, be whipped with a bundle of twigs, the fibrin may be obtained as a solid, stringy mass, just in the same way as from the entire blood, and the resulting fluid no longer retuins its power of spontaneous coagulability. It is not indeed necessary that the plasma shall have been obtained by the jirocess of cooling above described, as if it had been separated from the corpuscles in any other way, e.g., by allowing blood to flow direct from the vessels of an animal into a vessel containing a third or a fourth of its bulk of a saturated solution of a neutral salt (preferably of magnesium or sodium sulphate) and mixing carefully, will answer the purpose and, just as in the other case the colored corpuscles will subside leaving the clear superstratum of (salted) plasma. In order ' that salted plasma may coagulate, however, it is necessary to get rid of the salts by dialysis, or to dilute it with several times its bulk of water. The second question which must be considered is, from what mate- rials of the plasma is fibrin formedf If plasma be saturated with solid magnesium sulphate or sodium chloride, a white, sticky precipitate called by Denis, by whom it was first obtained, plasmine, is thrown down, after the removal of which, by filtration, the plasma will not spontane- ously coagulate. Plasmine is soluble in dilute neutral saline solutions, and the solution of it speedily coagulates, producing a clot composed of fibrin. Blood plasma therefore contains a substance without which it cannot coagulate, and a solution of which is spontaneously coagulable. This substance is very soluble in dilute saline solutions, and is not, therefore, fibrin, which is insoluble in these fluids. But there is distinct evidence that plasmine is a compound body made up of two or more substances, not all of which are requisite to form a clot, and that it is not mere soluble fibrin. There exists in all the serous cavities of the body in health, e.g., the pericardium, the peri- toneum, and the pleura, a certain small amount of transparent fluid, generally of a pale straw color, which in diseased conditions may be greatly increased. It somewhat resembles serum in appearance, but in reality differs from it, and is probably closely allied to plasma. This serous fluid is not, as a rule, spontaneously coagulable, but may be made to clot on the addition of serum, which is also a fluid which has no tendency of itself to coagulate. The clot produced consists of fibrin, and the clotting is identical with the clotting of plasma. From the serous fluid (that from the inflamed timica vaginalis testis or hydrocele fluid is mostly used) we may obtain, by half-saturating it with .^olid sodium chloride, a white viscid substance as a precipitate which is called fibrinogen. If fibrinogen be separated by filtration, it can be dis- solved in water, as a certain amount of the neutral salt used in precipi- tating it is entangled with the precipitate, and is sufficient to produce a dilute (6 to 8 per cent) saline solution in which fibrinogen, being a body THE BLOOD. 123 of the globulin class, is soluble. The solution of fibrinogen has no tendency to clot of itself, but if blood-serum be added to a solution of fibrinogen, the mixture clots. On the other hand from blood-serum may be obtained, by saturation with one of the neutral salts above-mentioned, a globulin very similar in properties to fibrinogen, which is called senimglobuUn or paragJohu- lin, and it m;iy be separated by filtration and dissolved in a dilute saline solution in a manner similar to fibrinogen. If the solutions of fibrinogen and paraglobulin be mixed, the mix- ture cannot be distinguished from a solution of plasmine, and in a great majority of cases firmly clots like that solution, whereas a mixture of the hydrocele fluid and serum, from which these bodies have been re- spectively taken, no longer manifests the like jjroperty. In addition to this evidence of the compound nature of plasmine, it may be further shown that, if sufficient care be taken, both fibrinogen and paraglobulin may be separately obtained from plasma: the one, fibrinogen, as a flaky precipitate by adding carefully 13 per cent of crystalline sodium chloride to it; and the other, paraglobulin, may be precipitated, after the removal of fibrinogen by filtration, on the further addition (above 20 per cent and to saturation) of the same salt or of magnesium sulphate to the filtrate. It is evident, therefore, that both these substances must be thrown down together when plasma is at once saturated with sodium chloride or magnesium sulphate, and that the mixture of the two corresponds with plasmine. So far it has been shown that plasmine, the antecedent of fibrin, to the possession of which blood owes its power of coagulating, is not a simple body, but is composed of at least two factors — viz., fibrinogen and paraglobulin; there is reason for believing that yet another body is precipitated with them in plasmine. It was at one time thought that the reason why hydrocele fluid coagulated, when serum was added to it, was that the latter fluid sup- plied the paraglobulin which the former lacked; this, however, is not the case, as hydrocele fluid does not lack this body, and moreover, if paraglobulin, obtained from diluted serum by passing a stream of car- bonic acid gas through it, be added, no clotting will take place. But if paraglobulin, obtained by the saturation method, be added to hydrocele fluid, clotting soon follows, as it will also in a mixed solution of fibrin- ogen and paraglobulin, both obtained by the saturation method. From this it is evident that in plasmine there is something more than the two bodies above mentioned, and that this something is precipitated with the paraglobulin by the saturation method, and is not precipitated by the carbonic acid method. The following experiments show that this substance is of the nature of a ferment. If defibrinated blood or serum be kept in a stoppered 124 HANDBOOK OF PHYSIOLOGY. bottle with its own bulk of alcohol for some weeks, all the proteids are precipitated in a coagulated form ; if the precipitate be then removed by filtration, dried over sulphuric acid, finely powdered, and then sus- pended in water, a watery extract may be obtained by further filtration, containing but little proteid. Yet a little of this watery extract will produce coagulation in fluids, e.g., hydrocele fluid or diluted plasma, which are not sjiontaneously coagulable, or which coagulate slowly and with difficulty. It will also cause a mixture of fibrinogen and paraglob- ulin both obtained by the carbonic acid method to clot. The watery extract aj)pears to contain the body which is precipitated with tbe paraglobulin by the saturation method. Its active properties are en- tirely destroyed by boiling. The amount of the extract added does not influence the amount of the clot formed, but only the rapidity of clot- ting, and moreover the active substance contained in the extract evi- dently does not form part of the clot, as it may be obtained from the serum after blood has clotted. So that the substance contained in the aqueous extract of blood appears to belong to that class of bodies which promote the union of, or cause changes in, other bodies, without them- selves entering into union or undergoing change; these are known as jerments. It has, therefore, received the name fibrin ferment. This ferment is developed in blood soon after it has been shed, and its amount continues to increase for some little time (p. 135). So far we have seen that plasmine is a body composed of three sub- stances, viz., fibrinogen, paraglobulin, and fibrin ferment. But we shall see that only two of them are necessary to coagulation. Alex. Schmidt, to whom we are indebted for much of our knowledge of this subject, believed that the three substances are necessary to the production of a clot. He thought that the reason why coagulation does not occur in serum which contains paraglobulin and the fibrin ferment is that serum lacks fibrinogen, and that when it does not occur in fluids which contain fibrinogen, joaraglobulin or the ferment or both are want- ing. Schmidt's view is, however, quite untenable in the face of the fact that a solution of pure fibrinogen will clot firmly on the addition of a solution of fibrin ferment, and that the complemental proposition is equally true, viz., that a mixture of paraglobulin and fibrin ferment (such as exists in serum) will not clot. It is to Hammersten that the credit of clearing up this matter is due; he proved that paraglobulin is not an essential in coagulation, since fibrin is formed from fibrinogen alone by the action of fibrin ferment; so that the ferment which is pre- cipitated with paraglobulin is essential and not that body itself. He showed, however, that paraglobulin possesses the property, in common with many other bodies, of combining with — or decomposing, and so rendering inert — certain substances which have the power of preventing the formation or precipitation of fibrin, such a power belonging for THE BLOOD. 125 example to the free alkalies, to the alkaline carbonates, and to certain salts. He considered that fibrinogen is probably decomposed into fibrin with the production of some other substances; or that it may possibly be bodily converted into it under the action of the ferment. It is now generally believed, however, that the presence of a certain but small amount of salts, especially of sodium chloride, and according to the researches of Green, of calcitwi siilphate, is necessary for coagu- lation, and that without it clotting cannot take place. Certain other changes besides solidification take place in blood when it clots, viz.: — its temperature rises slightly, it becomes less alkaline, the oxygen is diminished, the tension of carbonic anhydride rises, and a trace of ammonia gas is given off. The clotted part is said to become electrically negative to the unclotted part. Sources of the Fibrin Ferment. — Fibrin ferment cannot be obtained in any appreciable amount from blood which is allowed to flow direct from the living vessel into absolute alcohol. It is almost certainly a result of the more or less complete disintegration of the colorless cor- puscles after blood is shed, or of the intermediate corpuscles which will be described later on under the name of hlood platelets. The proofs of this may be briefly summarized as follows: — (1) That all strongly coag- ulable fluids contain these corpuscles almost in direct proportion to their coagulability; (2) That clots formed on foreign bodies, such as needles projecting into the interior or lumen of living blood-vessels, are preceded by an aggregation of colorless corjsuscles; (3) That plasma in which these corpuscles happen to be scanty, clots feebly; (4) That if horse's blood be kept in the cold, so that the corpuscles subside, it will be found that the lowest stratum, containing chiefly colored corpuscles, will, if removed, clot feebly, as it contains little of the fibrin factors; whereas the colorless plasma, especially the lower layers of it in which the colorless corpuscles are most numerous, will clot well, but if filtered in the cold will not clot so well, indicating that when filtered nearly free from colorless corpuscles even the plasma does not contain sufficient of all the fibrin factors to produce thorough coagulation; (5) In a drop of coagulating blood observed under the microscojoe the fibrin fibrils are seen to start from the colorless corpuscles. Nature of the Fibrin Ferment. — Halliburton has brought forward weighty reasons for believing fibrin ferment to be a globulin. Thus, a solution of ferment made according to Schmidt's method, if clear, neu- tral, or faintly alkaline in reaction, does not coagulate on boiling, and gives the proteid tests faintly. If the solution be concentrated, these reactions become more developed, and the proteid present reacts to the test for globulins. The ferment too can be extracted from shreds of fibrin obtained from whipped blood by the method usually employed for dissolving globulins, viz., by an 8 per cent solution of sodium chlor- 126 HANDBOOK OF PHYSIOLOGY. ide, .ind when the globulin is removed from the solution thus obtaiTied, the ferment uction disappears also. A globulin (cell-globulin) with similar characters, which has very powerful ferment properties, can be obtained from the cells of lymphatic glands, which are the precursors of the colorless corpuscles of the blood. Further, the ferment action is destroyed at) a temperature of from 73°-75° C. (165° F.), or if in saline solution at a lower temperature still, 60°-65° C. (145° F ) corre- sponding closely with the coagulating points of proteids and globulins respectively. The explanation of the clotting of blood which has been given in the pre- ceding pages, and which depends chiefly upon the researches of Alex. Schmidt and Hammersten, supposes that it is one of the fermentative actions, so many of which are believed to go on in the living body. Wooldridge contested this view of the process. His researches led him to the belief that coagulation of the blood is a vital process, or rather that it is the last act of vitality displayed by blood plasma, which he considered to be living protoplasm. Some of the results of his experiments may with advantage be here mentioned. Firstly, he showed that plasma itself contains everything that is necessary for coagula- tion. For his experiments he used plasma obtained by injecting a solution of commercial peptone into the veins of an animal and removing blood from it immediately afterward. The blood so obtained does not readily clot, and so allows the separation of the blood -coi'puscles from the plasma, the plasma so obtained being called ijeptone plasma. The whole of the corpuscular elements were removed by repeated treatment with a centrifugal machine. Peptone plasma was shown to clot by the use of some simple mechanical means, e.g., filtering through a clay cell, or through filter paper, or on neutralization with acetic acid, or carbonic acid, or by dilution with water or saline solution. Thus it would appear that if the colorless blood coriJuscles aid coagulation, their influence is only secondary. Secondly, he showed that the imjjortant precui-sor of clotting in this pep- tone-plasma may be separated from it, as a precipitate, if the plasma be kept in ice for some time, and that after its removal the plasma contains only a little fibrinogen capable of clotting by the action of fibrin ferment. If the plasma be diluted with water or slightly acidulated, however, the fibrin fer- ment is able to produce a complete clotting. In peptone plasma, Wooldridge stated that three coagulable bodies exist, which he calls A, B, and C fibrinogen, and which are closely allied to one another. C-fibrinogen is identical with the body which has been hitherto de- scribed as fibrinogen, is present in very small amount, and clots on addition of fibrin ferment. The coagulable matter present in greatest amount is B-fibrin- ogen, which clots on addition of lecithin, or of lymph corpuscles, but not on the addition of fibrin ferment. A-fibrinogen is separated from plasma by cooling, in minute regular rounded granules, from which, if watched under tlie microscope, rounded distinctly biconcave discs are seen to arise, quite in- distinguishable from blood plates; it is not coagulated by fibrin ferment. Finally, he considered that when blood plasma dies, an action takes place between A- and B-fibrinogen, which are both compounds of profceid and leci- thin. The essential of this action is a loss of lecithin on the part of the former and a gain of lecithin on the part of the latter, with the result of the produc- THE BLOOD. 127 tion of fibrin, a third proteid-lecithin compound, while other substances con- tained in tlie serum, including fibrin ferment, are at the same time set free. Thus, fibrin ferment, a body which can convert C-fibrinogen into fibrin, is not present in living plasma, but is a result of its disorganization or death. As the fibrinogen which can be clotted by the ferment is only j^resent in minimal amounts in living plasma, injection of a solution of fibrin ferment or of shed blood does not produce intra- vascular clotting, whereas injection of lymph corpuscles from lymphatic glands or of lecithin, either of which will produce clotting of the other fibrinogens which form the bulk of the coagulable matter in living blood, leads to extensive intra- vascular clotting. Conditions affecting Coagulation. —The coagulation of the blood is hastened by the following means: — 1. Moderate warmth,— from about 37.8-49° C. (100° to 120° F.). 2. Rest is favorable to the coagulation of blood. Blood, of which the whole mass is kept in uniform motion, as when a closed vessel com- pletely filled with it is constantly moved, coagulates very slowly and imperfectly. 3. Contact ivitli foreign matter, QXi.(i especially multiplication of the points of contact. Thus, as before mentioned, fibrin may be quickly obtained from liquid blood by stirring it with a bundle of small twigs; and even in the living body the blood will coagulate upon rough bodies projecting into the vessels. 4. The free access of air. — Coagulation is quicker in shallow than in tall and narrow vessels. 5. The addition of less than twice the bulk of water. The blood last drawn is said, from being more watery, to coagulate more quickly than the first. The coagulation of the blood is retarded, suspended, or pre- vented by the following means: — 1. Coid retards coagulation; and so long as blood is kept at a tem- perature 0"^ C. (32° F.), it will not coagulate at all. Freezing the blood, of course, prevents its coagulation; yet it will coagulate, though not firmly, if thawed after being frozen; and it will do so even after it has been frozen for several months. A higher temperature than -id" C. (120° F.) retards coagulation by coagulating the albumen of the serum, and' a still higher one above 56° C. (133° F.) prevents it altogether. 2. The addition of water in greater 2>ro/)ortio?is than twice the bulk of the blood, also the addition of syrup, glycerine, and other viscid sub- stances. 3. Contact with living tissues, and especially with the interior of a living blood-vessel. Blood may be kept fluid in a tortoise's heart after removal from the body for several days, and if the jugular vein of a horse be ligatured in two places so as to include within it blood, and then be removed from the body and placed in a cool place, the contained blood will remain unclotted for hours or even days. 128 HANDBOOK OF PHYSIOLOGY. 4. Tlte addition of neutral salts in the proportion of 2 or 3 per cent and upwurd. When added in hirge jiroportion most of these saline sub- stances 2^1'tJvent coagulation altogether. Coagulation, however, ensues on dilution with water. The time during which blood can be thus preserved in a liquid taste and coagulated by the addition of water, is quite indefinite. 5. Imperfect aeration, — as in the blood of those who die by asphyxia. G. In inflamniatory states of the system the blood coagulates more slowly aimough more firmly. 7. Coagulation is retarded by exclusion of the blood from the air, as by pouring oil on the surface, etc. In vacuo, the blood coagulates, quickly. Receiving blood into a vessel, well smeared inside with oil, fat, or vaseline, is said also to retard or prevent coagulation, 8. The coagulation of the blood is prevented altogether by the addi- tion of strong acids and caustic alkalies. 9. The injection of co^nmercial peptone containing albumoses, or of various digestive ferments, e.g., trypsin or pepsin, into the vessels of an animal appears to prevent or stay coagulation of its blood if it be killed soon after. The secretion of the mouth of the leech, and possibly the blood squeezed out of its body when full, also prevents the clotting if added to blood. It is stated that the reason why blood does not coagulate in the living I'cssels is, that the factors which are necessary for the formation of fibrin are not in the exact state required for its production, and that at any rate the fibrin ferment is not formed or is not free in the living blood, but that it is produced (or set free) at the moment of coagulation by the disintegration of the colorless (and possibly of the colored) corpuscles. This supposition is certainly plausible, and, if it be a true one, it must be assumed either that the living blood-vessels exert a restraining influ- ence upon the disintegration of the corpuscles in sufficient numbers to form a clot, or that they render inert any small amount of fibrin fer- ment, which may have been set free by the disintegration of a few cor- puscles; as it is certain firstly that corpuscles of all kinds must from time to time disintegrate in the blood without causing it to clot; and, secondly, that shed and defibrinated blood which contains blood corpus- cles, broken down and disintegrated, will not, when injected into the vessels of an animal, under ordinary conditions, produce clotting. There must be a distinct difference, therefore, if only in amount, between the normal disintegration of a few colorless corpuscles in the living unin- jured blood-vessels and the abnormal disintegration of a large number which occurs whenever the blood is shed without suitable precaution, or when coagulation is unrestrained by the neighborhood of the living uninjured blood-vessels. THE BLOOD. 139 The Blood Corpuscles. There are two principal forms of corpuscles, the 7'ed and the white, or, as they are now frequently named, the colored and the colorless. In the moist state, the red corpuscles form about 45 per cent by weight, of the whole mass of the blood. The proportion of colorless corpuscles is only as 1 to 500 or 600 of the colored. Red or Colored Corpuscles. — Human red blood-corpuscles are circular, biconcave discs with rounded edges, from ^-j^^ to :oVo i'l^h in diameter 6// to 8/«, and y2oou i^"'ch or about 2,'j. in thickness, becoming flat or convex on addition of water. When viewed singly they appear of a pale yellowish tinge; the deep red color which they give to the blood being observable in them only when they are seen en masse. They are composed of a colorless, structureless, and transparent filmy framework or stroma, infiltrated in all parts by a red coloring matter termed hwmoglobin. The stroma is tough and elastic, so that, as the corpuscles circulate, they admit of elongation and other changes of form, in adaptation to the vessels, yet recover their natural shape as soon as they escape from compression. The term cell, in the sense of a bag or sac, although sometimes applied, is scarcely applicable to the red blood corpuscle; it must be considered, if not solid throughout, yet as having no such marked difference of consistence in different parts as to justify the notion of its being a membranous sac with fluid contents. The stroma exists in all parts of its substance, and the coloring-matter uni- forml}' pervades this; but at the same time it is probable that the con- sistence of the peripheral part of the protoplasm is more solid than that of the more central mass. The red corpuscles have no nuclei, although, in their usual state, the unequal refraction of transmitted light gives the apisearance of a cen- tral spot, brighter or darker than the border, according as it is viewed in or out of focus. Their specific gravity is about 1088. The corpuscles of all mammals with the exception of the camelidae are circular and biconcave. In the camelidae they are oval and bicon- vex. In all mammals the corpuscles are non-nucleated, and in all other vertebrates (birds, reptiles, amphibia, and fish), the corpuscles are oval biconvex and nucleated (fig. 121). Varieties. — The red corpuscles are not all alike, some being rather larger, paler, and less regular than others, and sometimes flat or slightly convex, with a shining jiarticle apparent like a nucleolus. In almost every specimen of blood may be also observed a certain number of cor- puscles smaller than the rest. They are termed microcytes, or hcema- tiihlasts, and are probably immature corpuscles. It is necessary to take notice that much importance is attached to 9 130 HANDBOOK OF PHYSIOLOGY. one form of these smaller corpuscles named hlood plates by Bizzozero (Blutpliittcben). They are small, more or less rounded or slightly oval granules, slightly if at all colored, and about one third the size of ordi- nary colored corpuscles. From them it is supposed the fibrin ferment is specially derived. They rapidly undergo change in blood, after it has been drawn. They may form masses by coalescing. A peculiar property of the red corpuscles, which is exaggerated iu inflammatory blood, may be here again noticed, i.e., their great tendency to iidhere together in rolls or columns (rouleaux), 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. cor- responding Avith the knots of the net (fig. 118). Hence the clot formed in such a thin layer of blood looks mottled with blotches of pink upon Fig. 118. Fig. 119. Fig. 118.— Red corpuscles in rouleaux. The rounded corpuscles are white or uncolored. Fig. 119.— Corpuscles of tlie frog. The central mass consists of nucleated colored corpuscles. The other corpuscles are two varieties of the colorless form. a white ground, and in a larger quantity of blood such masses help, by the consequent rapid subsidence of the corpuscles, in the formation of the buify coat already referred to. Action of Re-agents. — Considerable light has been thrown on the physical and chemical constitution of red blood-cells by studying the eflfects produced by mechanical means and by various reagents : the following is a brief sum- mary of these re-actions : — 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 supei-ficial pellicle partly differentiated from the softer mass within ; again, if a needle be rapidly drawn across a drop of blood, several corpuscles will be found cut in two, but this is not accompanied by any escape 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, i. Water. — When water is added gradually to frog's blood, the oval THE BLOOD. 131 disc-shaped corpuscles become spherical, and gradually discharge their haemo- globin, a pale, trausjjareiit stroma being left behind ; human red blood-cells change from a discoidal to a spheroidal form, and discharge their cell- contents, becoming quite transparent and all but in- visible. ii. Saline solution produces no appreciable effect on the red blood cells of the frog. In the red blood-cells of man the dis- coid shape is exchanged for a spherical one, with spinous pro- jections, like a horse-chestnut (fig. 120). Their original forms can be at once restored by the use of carbonic acid. iii. 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 nucleus becomes strongly granulated, and all the coloring matter seems to be concentrated in it, Fig. 120. Effect of saline solution. Fig. 131.— The above illustration is somewhat altered from a drawing by Gulliver, in the Proceed. Zool. Society, and exhibits the typical charactei-s 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 remains comparatively uniform, and thus they are, in some animals, much greater, in others much less than the red corpuscle existing side by side with them. the surrounding cell-substance and outline of the cell becoming almost invisi- ble ; after a time the cells lose their color altogether. The cells in the figure (fig. 122) 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. iv. Alkalies cause the red blood-cells to swell and finally to disappear. V. Chloroform added to the red blood- cells of the frog causes them to part J 32 HANDBOOK OF PHYSIOLOGY. with their haemoglobin ; the stroma of the cells becomes gradually broken up. A similar effect is produced on the human red blood-cell. vi. Tannin. — When a 2 per cent fresh solution of tannic acid is applied to frog's blood it causes the appearance of a sharply-defined little knob, project- ing from the free surface {Roberts' macula) : the coloring matter becomes at the same time concentrated in the nucleus, which grows more distinct (fig. 123) . A somewhat similar effect is produced on the human red blood corpuscle. vii. 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. The first effect of the magenta is to cause the discharge of the hemoglobin, 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 es- cape. A similar macula is produced in the human red blood-cells. viii. Boric acid. — A 2 \)er 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. 124). The result of this experiment led Briicke to distinguish the 0 oo Fig. 122. F'ig. 123. Fig. 124. Fig. 135. Effect of acetic acid. Effect of tannin. Effect of boric acid. Effect of gases. colored contents of the cell (zooid) from its colorless stroma (cecoid) . When applied to the non-nucleated mammalian corpuscle its effect merely resembles that of other dilute acids. ix. Ammonia. — Its effects seem to vary according to the degree of concen- tration. 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. Gases. Carbonic acid. — If the red blood- cells of a frog be first exposed to the action of water-vapor (which renders their outer pellicle more readily per- meable 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. 125 show the effect of carbonic acid ; the middle one the effect of the re-admis- sion 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 granula- tion of the nucleus becomes permanent ; it appears to depend on a coagulation of the paraglobulin. Heat.— The effect of heat up to 50^—60° C. (120—140° F.) is to cause the formation of a number of bud-like processes (fig. 126) . Electricity causes the red blood-corpuscles to become crenated, and at leugth mulberry -like. Finally they recover their round form and become quite pale. The Colorless Corpuscles. — In human blood the white or color- jess corpuscles or leucocytes are nearly spherical masses of granular pro- THE BLOOD. 133 toplasm without cell wall. The granular appearance more marked in some than in others {vide infra), is due to the presence of particles probably of a fatty nature. In all cases one or more nuclei exist in each corpuscle. The size of the corpuscle average gsVo of an inch (10/^) in diameter. In health, the proportion of white to red corpuscles, which, taking an average, is about 1 to 500 or 600, varies considerably even in the course of the same day. The variations appear to depend chiefly on the amount and probably also on the kind of food taken; the number of leucocytes being very considerably increased by a meal, and diminished again on fasting. Also in young persons, during pregnancy, and after great loss of blood, there is a larger proportion of colorless blood cor- puscles, which probably shows that they are more rapidly formed under these circumstances. In old age, on the other hand, their proportion is diminished. Varieties. — The colorless corpuscles present greater diversities of form than the red ones. Two chief varieties are to be seen in human Fi~. lir.— A. Three cnloi-eil blood-corpuscles. B. Three colorless blood-coi-puscles acted on by acetic acid ; the nuclei are very clearly visible, x 900. 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 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 form of the others, and are derived from the cells of the lymph. Besides the above-mentioned varieties, Schmidt decribes another form which he looks upon as intermediate between the colored and the color- less forms, viz., corpuscles which contain red granules of hfemoglobin in their protoplasm. The different varieties of colorless corpuscles are especially well seen in the blood of frogs, newts, and other cold-blooded animals. Amoeboid movement. — The remarkable property of the colorless corpuscles of spontaneously changing their shape was first demonstrated by Wharton Jones in the blood of the skate. If a drop of blood be ex- amined with a high power of the microscope on a warm stage, or, in other words, under conditions by which loss of moisture is prevented, 0 134 HANDBOOK OF PHYSIOLOGY. and at the same time the temperature is maintained at about that of the body 37° C. (98.5° F.), the colorless corpuscles will be observed slowly to alter their shapes, and to send out processes at various parts of their circumference. The amoeboid movement which can be demon- strated in human colorless blood-corpuscles, can be most conveniently studied in the newt's blood. The processes which are sent out from the coriiuscle are either lengthened or withdrawn. If lengthened, the pro- toijlasm of the whole corpuscle flows as it were into its process, and the corpuscle changes its position; if withdrawn, protrusion of another proc- ess 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 com- paratively rapid. The activity both in the jDrocesses of change of shape and also of change in position, is much more marked in some corpus- cles, viz., iu the granular variety, than in others. Klein states that in Fig. 138. — Human colorless blood-corpuscles, showing its successive changes of outline within ten minutes when kept moist on a warm stage. CSchofleld.) the newt's blood the changes are especialy noticeable in a variety of tbe colorless corpuscle, which consists of a mass of finely granular proto- plasm with jagged outline, and contains three or four nuclei, or in large irregular masses of protoplasm containing from five to twenty nuclei. Another phenomenon may be observed to occur in the colorless corpus- cles, viz., tlie division of the corjniscles. A cleft takes place in the pro- toplasm at one point, becomes deeper and deeper, 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 remarkably active in their movements. Thus we see that the rounded form which the colorless corpuscles pre- sent 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 reagents upon the colorless corpuscles. — Feeding the corpus- cles.— If some fine pigment granules, e.g., powdered vermilion, be added to a fluid containing colorless blood-corijuscles, 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 em- bedded in their substance. They have also been seen, in diseased states, to contain micro-organisms, e.g., bacilli, and according to some pathologists ai-e capable of destroying them (phagocytosis) . They may too take up other for- eign matter or even other colorless corpuscles. This property of the colorless corpuscles is especially interesting as helping still further to connect them with THE BLOOD. 135 the lowest forms of animal life, and to connect both with the organized 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 blood-corpuscles. — Several methods are employed for counting the blo(xl -corpuscles, most of them depending upon the same princi- ple, i.e., the dilution of a minute volume of blood with a given volume of a colorless solution similar in specific gravity to blood plasma, so that the size and shape of the corpuscles is altered as little as possible. A minute quantity of the well-mixed solution is then taken, examined under the microscope, Healthy bacillus Healthv bacillus — Healthy bacillus Partially digested bacillus Partially digested leucocyte . Nuclei vacuolated Nucleus /it^^^>. Bacillus in leucocyte fSj^'^ Partially digested leucocyte Foreign matter Foreign matter Leucocytes ■ Particles of foreign matter Particles of foreign matter Particles of foreign matter Fig. 129.— Macrophages containing bacilli and other structures supposed to be imdergoing digestion. (Buffer.) either in a flattened capillary tube (Malassez) or in a cell (Hayem & Nachet, Govvers) of known capacity, and the number of corpuscles in a measured lengtli 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 ascertained the number of corpuscles in the diluted blood, it is easy to find out the number in a given volume of normal blood, Gowers' modification of Hayem & Nachet's instru- ment, called by him Hccmacytomcter , consists of a small pipette (a) , which, when filled up to a mark on its stem, holds 995 cubic millimetres. It is fur- nished witli 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 mouth-piece ; 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 screw ; a brass stage plate (c) carrying a glass slide, on which is a cell one- 136 HANDBOOK OF I'HYSIOLOGY. fifth of a millimetre deep, and the bottom of which is divided into one-tenth millimetre squares. On the top of tlie cell rests the cover-glass, which is kept in its place bj' tlie pressure of two springs proceeding from the stage plate A standard saline solution of sodium sulpliate, 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 thoroughl3^ mixed by the 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 layer of diluted blood be- tween the slide and cover-glass is i inch thick. The preparation is then examined under a microscope with a power of about 400 diameters, and focussed until the lines dividing the cell into squares are visible. Fig. 130.— Haemacytometer, 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 the number of white corpuscles noted. By adding together the numbers counted in ten (one-tenth millimetre) squares, and, as the blood has been diluted, mul- tiplying by ten thousand, the number of corpuscles in one cubic millimetre of blood is obtained. The average number of corpuscles per each cubic millimetre of healthy blood, according to Vierordt and Welcker, is 5,000,000 in adult men, and 4,500,000 in women. A hgemacytometer of another form, and one that is much used at the present time, is known as the Thoma-Zeiss hasmacytometer. It consists of a carefully graduated pipette' in which the dilution of the blood is done ; this is so formed that the capillary stem has a capacity equalling one-hundredth of the ball above it. If the blood is drawn up in tlie capillary tube to the line marked 1 (fig. 132) the saline solution may afterward be drawn up the stem to the line 101 ; in this way we have 101 parts of which the blood forms 1. As the con- tents of the stem can be displaced unmixed we shall have in the mixture the THE BLOOD. 137 proper dilution. The blood and the saline solution are well mixed by shaking the pipette, in the ball of which is contained a small glass bead for the pur- pose of aiding the mixing. The other part of the instrument consists of a glass slide (fig. 131) upon which is mounted a covered disc, vi, accurately ruled so as to present one square millimetre divided into 400 squares of one-twentieth M^Mi lv\\\v\\\v»^^\s\\\Wl" ym^mMm//^ Fig. 131.— Thoma-Zeiss Haemacytometer. of a riillimetre each. The micrometer thus made is surrounded by another annul'^r cell, c, which has such a height as to make the cell project exactly one-tenth millimetre beyond ?/i. If a drop of the diluted blood be placed upon tn, and c be covered with a perfectly flat cover-glass, the volume of the diluted blood above each of the squares of the micrometei", i.e., above each -^-q, will be ^^'oo <5f ^ cubic millimetre. An average of ten or more squares are then taken, and this number multiplied by 4000 X 100 gives the number of corpuscles in a cubic millimetre of un- diluted blood. Chemical Composition of the Blood. Before considering the cliemical composition of the blood as a whole, it will be convenient to take in order the composition of the various chief factors which have been set out in the table on p. 120, into which the blood may be separated, viz. : — (1.) The Plasma ; (2.) The Serum ; (3.) The Corpuscles ; (4.) The Fibrin. (1.) The Plasma. — The Plasma, or liquid part of the blood, in which the corpuscles float, may be ob- tained free from colored corpuscles in either of the ways mentioned below. In it are the fibrin factors, inasmuch as when ex- posed to the ordinary temperature of the air it under- goes coagulation 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 5° C. (41° F.) or by the centrifugal machine. The chief methods of obtaining plasma free from corpuscles may be here epitomized : (1) by cold, the temperature should be about 0° C. and may be two or three degrees higher, but not lower. (2) The addition of neutral salts, in certain proportions, either solid or in solution, e.g. of sodium sulphate, if solid 1 part to 13 parts of blood ; if a saturated solution 1 part to 6 parts of blood ; of magnesium sulphate, of a 23;?, or if saturated solution 1 part to 4 of Fig. 132.— Thoma- Zeiss Haemacy IO- meter. 138 HANDBOOK OF PHYSIOLOGY. blood. (3) A third way is to mix frog's blood with an equal part of a 5> of cane sugar, and to get rid of the corpuscles by filtration ; or (4) by the injec- tion of commercial peptone into the veins of certain mammals, previous to bleeding them to death, allowing the corpuscles to subside, and afterward subjecting the supernatant plasma to the action of a centrifugal machine ; by Fig. 133. — Plan and section of centrifugal machine, a, An iron socket secured to top of table b; c, a steel spindle carrjing the turntable d, and turning freely in a : e, a fla.S, so as to illuminate both compartments. By moving K by means of the milled head, T, a position of A' may be found corresponding to the exact intensity of the light passing through the two compartments; this is read off at J/ on the scale P, the division of which corresponds to standard strengths of solutions of hgemoglobin. Distribution of Hemoglobin. — Hemoglobin occurs not only in the red blood-cells of all vertebrata (except amphioxus and leptocephalus whose blood-cells are all colorless,) but also in similar cells in many Worms; moreover, it is found diffused in the vascular fluid of some other worms and certain Crustacea; it also occurs in all the striated mus- cles of Mammals and Birds. It is generally absent from unstriated muscle except that of the rectum. It has also been found in Mollusca in certain muscles which are specially active, viz., those which work the rasp-like tongue. Derivatives of Haemoglobin. Hasmatin. — By the action of heat, or of acids or alkalies in the presence of oxygen, hemoglobin can be split up into a substance called Hcematin, which contains all the iron of the hemoglobin from which it was derived, and a proteid residue. Of the latter it is impossible to say more than that it probably consists of one or more bodies of the globu- lin class. If there be no oxygen present, instead of hematin a body called haemochromogen is produced, which, however, will speedily undergo oxidation into hematin. Hematin 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 Cgg, H70, Ng, Feg, Oio (Hoppe-Seyler). It is insoluble in water, alcohol, and ether; solu- ble in the caustic alkalies; soluble with difficulty in hot alcohol to which is added sulphuric acid. The iron my be removed from haematin by heating it with fuming hydrochloric acid to 160° C. (320° F.), and a new body, hasmatoporphyrin, the so-called iron-free hematin, is pro- duced. Hematoporphyrin (Ces, II-4, Ns, O12, Hoppe-Seyler) may also be obtained by adding blood to strong sulphuric acid, and if necessary filtering the fluid through asbestos. It forms a fine crimson solution, which has a distinct spectrum, viz., a dark band just beyond d, and a second all but midway d and e. It may be precipitated from its acid solution by adding water or by neutralization, and when redissolved in alkalies presents four bands, a pale baud between c and d, a second between d and e, nearer d, another nearer e, and a fourth occupying the chief part of the space between b and f. 150 HANDBOOK OF PHYSIOLOGY. Hcematin in acid solution. — If an excess of acetic acid is added to blood, and the solution is boiled, the color alters to brown from decom- position of haemoglobin and the setting free of hsematin; by shaking this solution with ether, asolution of htematin in acid solution is obtained. The spectrum of the ethereal solution (colored plate) 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 b and f. The first band is by far the most distinct, and the acid aqueous solution of hasmatin shows it plainly. Hmnatin in alkaline solution. — If a caustic alkali is added to blood and the solution is boiled, alkaline lia3matin is produced, and the solu- tion becomes olive green in color. The absorption band of the new compound is in the red, near to d, and the blue end of the spectrum is 1^ n. Fig. 139.— Hasmatoklin crj'stals. (Frey.) Fig. 140.— HEemin crystals. (Frey.) absorbed to a considerable extent. If a reducing agent be added, two bands resembling those of oxy-hsemoglobin, but nearer to the blue, ap- pear; this is the spectrum of reduced hcematin, or haemochromogen. On violently shaking the reduced hsematin with air or oxygen the two bands are replaced by the single band of alkaline haematin. Haematoidin. — This substance is found in the form of yellowish crystals (fig. 139) in old blood extravasations and is derived from the haemoglobin. Their crystalline form and the reaction they give with fuming nitric acid seem to show them to be closely allied to Bilirubin, the chief coloring matter of the bile, and in composition they are prob- ably either identical or isomeric with it. Haemin. — One of the most important derivatives of haematin is haemin. It is usually called Hifdrochlorate of Hcematin (or hydrochlor- ide), but its exact chemical composition is uncertain. Its formula is said to be Cos, H70, Ns, Feo, Oio, 3 Hcl, and it contains 5.18 per cent of chlorine, but by some it is looked upon as simply crystallized haematin. Although difficult to obtain in bulk, a specimen may be easily made for the microscope 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 THE BLOOD. 151 spread out; a cover glass is then placed upon it, and glacial acetic acid added by means of a capillary pipette. The blood at once turns of a brownish color. The slide is then heated, and the acid mixture evapo- rated to dryness at a high temperature. The excess of salt is washed away with water from the dried residue, and the specimen may then be dried and mounted. A large number of small, dark, reddish black crys- tals of a rhombic shape, sometimes arranged in bundles, will be seen if the slide be subjected to microscopic examination (fig. 140). The formation of these haemin crystals is of great interest and im- portance from a medico-legal point of view, as it constitutes the most certain and delicate test we have for the presence of blood (not of ne- cessity the blood of man) in a stain on clothes, etc. It exceeds in deli- cacy even the spectroscopic test. Compounds similar in composition to hsemin, but containing hydrobromic or hydriodic acid, instead of hydro- chloric, may be also readily obtained. B. The Carbon Dioxide Gas in the Blood.— Of this gas in the blood part exists in a state of simple solution in the plasma, and is given up in vacuo (35.2 per cent), and the rest in a state of weak chemical combination. It is believed that the latter is combined with the sodium carbonate in a condition of bicarbonate, and is not given up until an acid is added to the plasma or serum. Some observers consider that part of the gas is associated with the corpuscles. (See also under Resjnrafion.) C. The Nitrogen in the Blood. — The whole of the small quantity of the nitrogen contained in the blood is simply dissolved in the fluid plasma. Chemical Composition of the Blood in Bulk. — Analyses of the blood as a whole differ slightly, but the following table may be taken to represent the average composition : Water 784 Solids- Corpuscles ....... 130 Proteids (of serum) ..... 70 Fibrin (of clot) . . . . . . 2. 2 Fatty matters (of serum) .... 1.4 Inorganic salts (of serum) .... 6 Gases, kreatin, urea and other extractive ) « . matter, glucose and accidental substances ) 216 1000 Variations in the Composition of healthy Blood. 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 153 HANDBOOK OF PHYSIOLOGY. being of somewhat higher specific gravity, from its containiDg a relatively larger quantity of red corpuscles. 2. Pregnancy. — The blood of pregnant women is rather lower than the average specific gravity, from deficiency of colored corpuscles. The quantity of the colorless corj^uscles, on the other hand, and of fibrin, is increased. 3. Age. — The blood of the foetus is very rich in solid matter, and especially in colored corpuscles; and this condition, gradually diminish- ing, continues for some weeks after birth. The quantity of solid matter then falls during childhood below the average, rises during adult life, and in old age falls again. 4. Temperament. — There appears to be a relatively larger quantity of solid matter, and particularly of colored cor]3uscles, 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 gen- erous or poor diet respectively, need be here only referred to. 6. 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 which is so common after either loss of blood, or the abstraction from it of watery fluid, as in cholera, dia- betes, and the like. For some little time after bleeding the want of colored corpuscles is well marked, but with this exception, no considerable alteration seems to be produced in the composition of the blood for more than a very short time; the loss of the other constituents, including the colorless corpuscles, being very quickly repaired. Variations in different parts 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 com- position and general characters are uniform throughout the whole course of the systemic arteries, they are not so throughout the venous system — the blood contained in some veins differing remarkably from that in others. Differences between Arterial and Vetious Blood. — The differences be- tween arterial and venous blood are these : — (a.) Arterial blood is bright red, from the fact that almost all its haemoglobin is combined with oyxgen (Oxy-hsemoglobin, or scarlet hae- moglobin), while the purple tint of venous blood is due to the deoxida- THE BLOOD. 153 tion of a certain quantity of its oxy-hfemoglobin, and its consequent reduction to tlie purple variety (Deoxidized, or purple hgemoglobin). (b.) Arterial blood coagulates somewhat more quickly. (c.) Arterial blood contains more oxygen than venous, and less car- bonic acid. Some of the veins contain blood which differs from the ordinary standard 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, from the gastric and mes- enteric veins, which contain the soluble elements of food absorbed from the stomach and intestines during digestion, and from 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 ac- cording 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, and other soluble matters which may have been absorbed from the alimentary canal, this blood appears to be deficient in solid matters, especially in colored corpuscles, owing to di- lution by the quantity of water absorbed, to contain an excess of proteid matter, and to yield a less tenacious kind of fibrin than that of blood generally. The blood from the splenic vein is generally deficient in colored cor- puscles, and contains an unusually large proportion of proteids. The fibrin obtainable from the blood seems to vary in relative amount, but to be almost always above the average. The proportion of colorless cor- puscles is also unusually large. The whole quantity of solid matter is decreased, the diminution aj)pearing to be of colored corpuscles. The plasma is said to be colored in consequence of its containing dissolved hsematin. 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 colored 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, proteids, and salts than the blood of the portal veins ; but that it yields a much larger amount of extractive matter, in which is one constant element, namely, grape-sugar, which is found, whether saccharine or farinaceous matter has been present in the food or not. 154 HANDBOOK OF PHYSIOLOGY. Development of the Blood-Corpuscles. The first formed blood-corpuscles of the human embryo differ much in their general characters from those which belong to the later periods of intra-uterine, and to all periods of extra-uterine life. Their manner of origin is at first very simple. Surrounding the early embryo is a circular area, called the vascular area, in which the first rudiments of the blood-vessels and blood-corpus- cles are developed. Here the nucleated embryonal cells of the meso- blast, from which the blood-vessels and corpuscles are to be formed, send out processes in various directions, and these joining together, form an irregular meshwork. The nuclei increase in number, and col- lect chiefly in the larger masses of protoplasm, but partly also in the ^J.'^:^5^^..^yfe^ W Fig. 141.— Part of the network of developing blood-vessels in the vascular area of a guinea-pig. bl, blood-corpnscle.s becoming free in an enlarged and hoUowed-out part of the network ; o, process of protoplasm. (E. A. Schafer.) processes. These nuclei gather around them a certain amount of the protoplasm, and becoming colored, form the red blood-corpuscles. The protoplasm of the cells and their branched net-work in which these corpuscles lie then become hollowed out into a system of canals inclos- ing fluid, in which the red nucleated corpuscles float. The corpuscles at first are from about 3 5V0 to y-yo^ of an inch (lO/Jt to 16//) in diameter, mostly spherical, and with granualr contents, and a well-marked nucleus. Their nuclei, which are about xoVo of iin inch (5,^) in diameter, are cen- tral, circular, very little prominent on the surfaces of the corpuscles, and apparently slightly granular or tuberculated. The corpuscles then strongly resemble the colorless corpuscles of the fully developed blood, but are colored. They are capable of amoeboid movement and multiply by division. AVhen, in the progress of embryonic development, the liver begins to be formed, the multiplication of blood-cells in the whole mass of blood ceases, and new blood-cells are produced by this organ, and also by the THE BLOOD. 155 lymphatic glands, thymus, and spleen. These are at first colorless and nucleated, but afterward acquire the ordinary blood-tinge, and resemble very much those of the first set. They also multiply by division. In whichever way produced, however, whether from the original formative Fig. 142.— Development of red corpuscles in connective tissue cells. From the subcutaneous tissue of a new-born rat. h, a cell containing haemoglobin in a diffused form in the protoplasm; h\ one containing colored globules of varying size and vacuoles: h", a cell filled with colored globules of nearly uniform size ; /, /'. developing fat cells. CE. A. Schafer.) cells of the embryo, or by the liver and the other organs mentioned above, these colored nucleated cells begin very early in foetal life to be mingled with colored ;^ow-nucleated corpuscles resembling those of the adult, and at about the fourth or fifth month of embryonic existence are completely replaced by them. Fig. 143.— Further development of blood-corpuscles in connective tissue cells and transforma- tion of the latter into capillary blood-vessels, a. an elongated cell with a cavity in the protoplasm occupied by fluid and by blood-corpuscles which are still globular; b, a hollow cell, the nucleus of which has multiplied. The new nuclei are arranged around the wall of the cavity, the corpuscles in which have now become discoid: c, shows the mode of imion of a "heemapoietic '' cell, which, in this instance, contains only one corpuscle, with the prolongation (bl) of a previously existing vessel; a and c, from the new-born rat; b, from the foetal sheep. (E. A. Schafer.) Origin of the Mature Colored Corpuscles. — The non-nucleated red corpuscles may possibly be derived from the nucleated, but in all probability are an entirely new formation. Their chief origin is: — From the medulla of bone. — It has been shown that colored corpuscles are to a very large extent derived during adult life from the large pale 156 HANDBOOK OF PHYSIOLOGY. cells in the red marrow of bones, especially of the ribs (fig. 144). These cells become colored from the formation of hsemoglobin chiefly in one part of their protoplasm. This colored part becomes separated from the rest of the cell and forms a red corpuscle, being at first cup- shaped, but soon taking on the normal appearance of the mature corpuscle. It is supposed that the protoplasm ma grow up again and form a number of red corpuscles in a similar way. From the tissue of the spleen. — It is probable that colored as well as colorless corpuscles may be produced in the spleen. From Microcytes. — Hayem describes the small particles (Microcytes), previously mentioned as contained in the blood, and which he calls hrematoblasts, as the precursors of the red corpuscles. They acquire color, and enlarge to the normal size of red corpuscles. From the uihite corpuscles. — The belief that the red corpuscles are derived from the white is still very general, although no new evidence has been recently advanced in favor of this view. It is, however, un- certain whether the nucleus of t-he white coj-puscle becomes the red cor- Fig. 144. —Colored nucleated coi-puscles, from the red marrow of the guinea-pig. CE. A. Schafer.) puscle, or whether the whole white corpuscle is bodily converted into the red by the gradual clearing up of its contents with a disappearance of the nucleus. Probably the latter view is the correct one. During foetal life and possibly in some animals, e.g., the rat, which are born in an immature condition, for some little time after birth, the blood discs have been stated by Schafer to arise in the connective tissue cells in the following way. Small globules, of varying size, of coloring matter arise in the protoplasm of the cells, and the cells themselves become branched, their branches joining the branches of similar cells. The cells next become vacuolated, and the red globules are free "in a cavity filled with fluid (fig. 143) ; by the extension of the cavity of the cells into their processes anastomosing vessels are produced, which ulti- mately join with the previously existing vessels, and the globules, now having the size and appearance of the ordinary red corpuscles, are passed into the general circulation. This method of formation is called ijitracellular. Without doubt, the red corpuscles have, like all other parts of the organism, a tolerably definite term of existence, and in a like manner die and waste away when the portion of work allotted to them has been performed. Neither the length of their life, however, nor the fashion of their decay has been yet clearly made out. It is generally believed that a certain number of the colored corpuscles undergo disintegration THE BLOOD. 157 in the spleen ; and indeed corpuscles in various degrees of degeneration have been observed in that organ. Origin of the Colorless Corpuscles. — The colorless corpuscles of the blood are derived from the lymph corpuscles, being, indeed, indis- tinguishable from them; and these come chiefly from the lymphatic glands. Their number is increased by division. Colorless corpuscles are also in all probability derived from the spleen and thymus, and also from the germinating endothelium of serous membranes, and from connective tissue. The corpuscles are car- ried into the blood either with the lymph and chyle, or pass directly from the lymphatic tissue in which they have been formed into the neighboring blood-vessels. Uses of the Blood. 1. To be a medium for the reception and storing of matter, e.g., oxygen and digested food material, from the outer world, and for its conveyance to all parts of the body. 2. To be a source whence the various tissues of the body may take the materials necessary for their nutrition and maintenance; and whence the secreting organs may take the constituents of their various secre- tions. 3. To be a medium for the absorption of refuse matters from all the tissues, and for their conveyance to those organs whose function it is to separate them and cast them out of the body. 4. To warm and moisten all parts of the body. CHAPTER YL THE CIRCULATION OF THE BLOOD. The blood is made to circulate within the system of closed tubes in which it is contained by means of the alternate contraction and relaxa- tion of the heart. The heart is a hollow muscular organ consisting of four chambers, two auricles and two ventricles, arranged in pairs. On Pulmonary artery - Superior cava or vein from head and neck Right auricle Inferior vena cava Right ventricle Portal circulation Second renal circulation Pulmonary capillaries Pulmonary veins Aorta Arteries to head and neck Left auricle ._^ Left ventricle Gastric and intestinal vessels .First renal circulation Systemic capillaries Fig. 145. — Diagram of the circulation. the right and left sides is an auricle joined to and communicating with a ventricle, but the chambers on the right side do not directly commu- nicate with those on the left side. The blood is conveyed away from the left side of the heart (as in the diagram, fig. 145) by the arteries, and returned to the right side of the heart by the veins, the arteries and veins being continuous with each other at one end by means of the heart, and at the other by a fine network of vessels called the capillaries. From the right side of the heart the blood passes to the lungs 158 THE CIRCULATION^ OF THE BLOOD. 159 through the pulmonary artery, then through the pulmonary capillaries, and through the pulmonary veins to the left side of the heart (Fig. 145). Thus there are two circulations through which the blood must pass; the one, a shorter circuit from the right side of the heart to the lungs and back again to the left side of the heart ; the other and larger circuit, from the left side of the heart to all parts of the body and back again to the right side; strictly speaking, however, there is but one complete circulation, which may be diagrammatically represented by a double loop, as in fig. 145, in which there is one continuous stream, the whole of which must, at one part of its course, pass through the lungs. Sub- ordinate to the circulations through the lungs and through the system generally, respectively named the Pulmonary and Systemic, it will be noticed also in the same figure that a portion of the stream of blood having been diverted once into the capillaries of the intestinal canal, and some other organs, and gathered up again into a single stream, is a second time divided in its passage through the liver, before it finally reaches the heart and completes a revolution. This subordinate stream through the liver is called the Portal circulation. A somewhat similar accessory circulation is that through the kidneys, called the Renal cir- culation. Such then is the outline of the course of the circulation. The problems in connection with its maintenance cannot be well under- stood without a more detailed knowledge of the structure and mode of action of the heart, and of the structure and properties of the blood- vessels. These subjects will now be considered seriatim. The Heart. The heart is contained in the chest or thorax, and lies between the right and left lungs (fig. 146), inclosed in a membranous sac — the Peri- cardium, which is made up of two distinct parts, an external fibrous membrane, composed of closely interlacing fibres, which has its base attached to the diaphragm or midriff, the great muscle which forms the floor of the chest tind divides it from the abdomen — both to the central tendon and to the adjoining muscular fibres, while the smaller and upper end is lost on the large blood-vessels by mingling its fibres with that of their external coats; and an internal serous layer, which not only lines the fibrous sac, but also is reflected on to the heart, which it com- pletely invests. The part which lines the fibrous membrane is called the parietal layer, and that inclosing the heart, the visceral layer, and these being continuous for a short distance along the great vessels of the base of the heart, form a closed sac, the cavity of which in health contains just enough fluid to lubricate the two surfaces, and thus to enable them to glide smoothly over each other during the movements of the heart. The vessels passing in and out of the heart receive in- Testments from this sac to a greater or less degree. 160 HANDBOOK OF PHYSIOLOGY. The heart is situated in the chest behind the sternum and costal cartilages, being phiced obliquely from right to left, quite two-thirds of it being to the left of the mid-sternal line. It is of pyramidal shape, with the apex pointing downward, outward, and toward the left, and the base backward, inward, and toward the right. It rests upon the dia- phragm, and its pointed apex, formed exclusively of the left side of the heart, is in contact with the chest wall, and during life beats against it at a point called the apex beat, situated in the fifth left intercostal space, and about three inches from the mid-sternal line. The heart is, as it were, suspended in the chest by the large vessels which proceed from its base, but, excepting at this part, the orgcin itself lies free within the sac of the pericardium. The part which rests upon the diaphragm Right luDg Pulmonary artery Left lung Diaphragm Fig. 146.— View of heart and lungs in. situ. The front portion of the chest-wall, and the outer orparietaHayers of the pleurae and pericardium have been removed. The lungs are partly col- lapsed. is flattened, and is known as the posterior surface, while the free upper part is called the anterior surface. The margin toward the left is thick and obtuse, while the lower margin toward the right is thin and acute. On examination of the external surface the division of the heart into parts which correspond to the chambers inside of it may be traced, for a deep transverse groove called the auricido-ventricular groove divides the auricles which form the base of the heart from the ventricles which form the remainder, including the apex, the ventricular portion being by far the greater; and, again, the inter-ventricular groove runs between the ventricles both front and back, and separates the one from the other. The anterior groove is nearer the left margin and the posterior nearer the right, as the front surface of the heart is made up chiefly of the right ventricle and the posterior surface of the left ventricle. In the THE CIRCULATION OF THE BLOOD. 161 furrows or grooves run the coronary vessels, which supply the tissue of the heart with blood, as well as nerves and lymphatics imbedded in more or less fatty material. The Chambers of the Heart. — The interior of the heart is divided by a longitudinal partition in such a manner as to form two chief cham- bers or cavities — right and left. Each of these chambers is again sub- Fig. 147. — The right auricle and ventricle opened, and a part of their right and anterior walls removed, so as to show their interior, i^. — 1, Superior vena cava ; 2, inferior vena cava ; 2', hepatic veins cut short ; 3, right auricle ; 3', placed in the fossa ovalis, below which is the Eustachian valve ; 3", Is placed close to the aperture of the coronary vein ; +, +. placed in the auriculo-ventricular froove, where a narrow portion of the adjacent walls of the auricle and ventricle has been preserved ; , 4, cavity of the right ventricle, the upper figure is immediately below the semihmar valves ; 4', large columna carnea or museuhis papillaris ; .5, 5', .5", tricuspid valve ; 6, placed in the interior of the pulmonary artery, a part of the anterior wall of that vessel having been removed, and a narrow portion of it preserved at its couimencetnent, where the semilunar valves are attached ; 7, concavity of the aortic arch close to the cord of the ductus arteriosus ; 8, ascending part or sinus of the arch covered at it.s commencement by the auricular appendix and pulmonary artery ; 9, placed between the innominate and left carotid arteries ; 10, appendix of the left auricle ; 11, 11, outside of the left ventricle, the lower figm-e near the apex. (AUen Thomson.) divided transversely into an upper and a lower portion, called respect- ively, as already incidentally mentioned, auricle and ventricle, which freely communicate one with the other ; the aperture of communication, however, is guarded by valves, so disposed as to allow blood to pass freely from the auricle into the ventricle, but not in the opposite direc- 162 HANDBOOK OF PHYSIOLOGY. tion. There are thus four cavities in the heart — the auricle and ventri- cle of one side being quite separate from those of the other (fig. 147). Right Auricle. — The right auricle is situated at the right part of the base of the heart as viewed from the front. It is a thin-walled cavity of more or less quadrilateral shape, prolonged at one corner into a Fig. 148.— The left auricle and ventricle opened and a part of their anterior and left walls re- moved. J4 — The puhnonary artery has been divided at its commencement ; the opening into the left ventricle is carried a short distance into the aorta between two of the segments of the semilunar valves ; and the left part of the auricle with its appendix has been removed. The riglit auricle is out of view. 1, The two right pulmonary veins cut short : their openings are seen within the aia-icle; 1', placed within the cavity of the auricle on the left side of the septum and on the part which forms the remains of the valve of the foramen ovale, of which the erescentic fold is seen toward the left hand of 1' ; 2, a narrow portion of the wall of the auricle and ventricle preserved round the auriculo- ventricular orifice ; 3, 3', the cut surface of the walls of the ventricle, seen to become very much tliinner towards 3", at the apex : 4, a small part of the anterior wall of tin- left ventricle which has been preseiwed with the principal anterior columna carnea or musciihis i)aiiillaris attached to it ; 5, 5, musculi papUlares ; 5', the left side of the septum, between the two ventricles, within the cavity of the left ventricle ; 6, 6', the mitral valve ; 7, placed in the interior of the aorta near its conuneuce- ment and above the three segments of its semilunar valve which are hanging loosely together ; 7', the exterior of the great aortic sinus ; 8, the root of the pulmonary artery and its semilunar valves ; 8', the separated portion of the pulmonary artery remaining attached to the aorta by 9, the cord of the ductus arteriosus ; 10, the arteries rising from the summit of the aortic arch. (Allen Thomson.) tongue-shaped portion, the right auricular appendix, which slightly over- laps the exit of the great artery, the aorta, from the heart. The interior is smooth, being lined with the general lining of the THE CIRCULATION OF THE BLOOD. 163 heart, the endocardium, and into it open the superior and inferior venae cavse, or great veins, which convey the blood from all parts of the body- to the heart. The former is directed downward and forward, the latter upward and inward; between the entrances of these vessels is a slight tubercle called tubercle of Lower. The opening of the inferior cava is protected and partly covered by a membrane called the Eustachian valve. In the posterior wall of the auricle is a slight depression called the fossa ovalis, which corresponds to an opening between the right and left auricles which exists in foetal life. The right auricular appendix is of oval form, and admits three fingers. Various veins, including the coronary sinus, or the dilated portion of the right coronary vein, open into this chamber. In the appendix are closely set elevations of the muscular tissue covered with endocardium, and on the anterior wall of Fig. 149.— Transverse section of bullock's heart in a state of cadaveric rigidity. (Dalton.) 6, Cavity of right ventricle, a, Cavity of left ventricle. the auricle are similar elevations arranged parallel to one another, called miisculi liectinati. Right Ventricle. — The right ventricle occuijies the chief part of the anterior surface of the heart, as well as a small part of the posterior surface : it .forms the right margin of the heart. It takes no part in the formation of the apex. On section its cavity, in consequence of the encroachment upon it of the septum ventriculorum, is semilunar or crescentic (fig. 149); into it are two openings, the auriculo-ventricular at the base and the opening of the pulmonary artery also at the base, but more to the left; the part of the ventricle leading to it is called the conus arteriosus or infundibuluni ; both orifices are guarded by valves, the former called tricuspid and the latter semilunar or sigmoid. In this ventricle are also the projections of the muscular tissue called co- lumncB carnece (described at length p. 178). Left Auricle. — The left auricle is situated at the left and posterior part of the base of the heart, and is best seen from behind. It is quad- rilateral, and receives on either side two pulmonary veins. The auricu- lar appendix is the only part of the auricle seen from the front, and corresponds with that on the right side, but is thicker, and the interior is more smooth. The left auricle is only slightly thicker than the riglit. The left auriculo-ventricular orifice is oval, and a little smaller than 164 HANDBOOK OF PHYSIOLOGY. that on the right side of the heart. There is a slight vestige of the foramen between the auricles, which exists in foetal life, on the septum between them. Left Venli'icle. — Though taking part to a comparatively slight ex- tent in the anterior surface, the left ventricle occupies the chief part of the posterior surface. In it are two openings very close together, viz. the auriculo-ventricular and the aortic, guarded by the valves corre- sponding to those of the right side of the heart, viz. the bicuspid or mitral and the semilunar or si(/7noid. The first opening is at the left and back part of the base of the ventricle, and the aortic in front and toward the right. In this ventricle, as in the right, are the columnae carneae, which are smaller but more closely reticulated. They are chiefly found near the apex and along the ^josterior wall. They will be again referred to in the description of the valves. The walls of the left ven- Fig. 150.— Network of muscular fibres from the heart of a pig. The nuclei of the muscle-corpus- cles are well shown. X 450. (Klein and Noble Smith.) tricle, which are nearly half an inch in thickness, are, with the excep- tion of the apex, twice or three times as thick as those of the right. Capacity of the Chambers. — During life each ventricle is capable of containing about four to six ounces (about 180 grms.) of blood. The capacity of the auricles after death is rather less than that of the ven- tricles: the thickness of their walls is considerably less. The latter condition is adapted to the small amount of force which the auricles require in order to empty themselves into their adjoining ventricles; the former to the circumstance of the ventricles being partly filled with blood before the auricles contract. Size and Weight of the Heart. — The heart is about 5 inches long (about 12.6 cm.), 34 inches (8 cm.) greatest width, and 2^ inches (6.3 cm. ) in its extreme thickness. The average weight of the heart in the adult is from 9 to 10 ounces (about 300 grms.); its weight gradually increasing throughout life till middle age: it diminishes in old age. Structure. — The walls of the heart are constructed almost entirely of layers of muscular fibres; but a ring of connective tissue, to which some of the muscular fibres are attached, is inserted between each auri- cle and ventricle, and forms the boundary of the auriculo-ventricular THE CIKCULATION OF THE BLOOD. 165 opening. Fibrous tissue also exists at the origins of the pulmonary artery and aorta. The muscular fibres of each auricle are in part continuous with those of the other, and partly separate; and the same remark holds true for the ventricles. The fibres of the auricles are, however, quite separate from those of the ventricles, the bond of connection between them being only the fibrous tissue of the auriculo-ventricular openings. The minute structure of the striated muscular fibres of the heart has been already described (p. 86). Endocardium. — As the heart is clothed on the outside by a thin transparent layer of pericardium, so its cavities are lined by a smooth Fig. 151.— Diagram of the circulation thi-ough the heart CDalton). and shining membrane, or endocardium, which is directly continuous with the internal lining of the arteries and veins. The endocardium is composed of connective tissue with a large admixture of elastic fibres; and on its inner surface is laid down a single tesselated layer of flat- tened endothelial cells. Here and there unstriped muscular fibres are sometimes found in the tissue of the endocardium. Valves. — The arrangement of the heart's valves is such that the blood can pass only in one direction (fig. 151). The tricusjjid valve (5, fig. 147) presents three principal cusps or sub- divisions, and the mitral or bicuspid valve has f7V0 such portions (6, fig. 148). But in both valves there is between each two principal portions a smaller one; so that more properly, the tricuspid may be described as consisting of six, and the mitral of four, portions. Each portion is of triangular form. Its base is continuous with the bases of the neighbor- 166 HANDBOOK OF PHYSIOLOGY. ing portions, so as to form an annular membrane around the auriculo- ventricular opening, and is fixed to a tendinous ring which encircles the orifice between the auricle and ventricle and receives the insertions of the muscular fibres of both. In each principal cusp may be distin- guished a central part, extending from base to apex, and including about half its width. It is thicker and much tougher than the border pieces or edges. While the bases of the cusps of the valves are fixed to the tendinous rings, their ventricular surface and borders are fastened by slender ten- dinous fibres, the chordcB tendinew, to the internal surface of tlie walls of the ventricles, the muscular fibres of which project into the ventricular cavity in the form of bundles or columns — the cohimnce carnece. These columns are not all alike, for while some are attached along their whole length on one side, and by their extremities, others are attached only by their extremities; and a third set, to which the name musculi papil- lares has been given, are attached to the wall of the ventricle by one extremity only, the other projecting, papilla-like, into the cavity of the ventricle (4, fig. 148), and having attached to it chords tendinege. Of the tendinous cords, besides those which j^ass from the walls of the ventricle and the musculi j)apillares to the margins of the valves, there are some of especial strength, which pass from the same parts to the edges of the middle and thicker portions of the cusps before referred to. The ends of these cords are spread out in the substance of the valve, giving its middle piece its peculiar strength and toughness; and from the sides numerous other more slender and branching cords are given off, which are attached all over the ventricular surface of the adjacent border-pieces of the principal portions of the valves, as well as to those smaller portions which have been mentioned as lying between each two principal ones. Moreover, the musculi papillares are so placed that, from the summit of each, tendinous cords proceed to the adjacent halves of two of the principal divisions, and to one intermediate or smaller division, of the valve. The preceding description applies equally to the mitral and tricus- pid valve; but it should be added that the mitral is considerably thicker and stronger than the tricuspid, in accordance with the greater force which it is called upon to resist. The semilunar valves guard the orifices of the pulmonary artery and of the aorta. They are nearly alike on both sides of the heart; but the aortic valves are altogether thicker and more strongly constructed than the pulmonary valves, in accordance with the greater j^ressure which they have to withstand. Each valve consists of three parts which are of semilunar shape, the convex margin of each being attached to a fibrous ring at the place of junction of the artery to the ventricle, and the concave or nearly straight border being free, so as to form a little pouch THE CIKCULATION OF THE BLOOD. 167 like a watch-pocket (7, fig. 148). In the centre of the free edge of the pouch, which contains a fine cord of fibrous tissue, is a small fibrous nodule, the corpus Arantii, and from this and from the attached border fine fibres extend into every part of the mid substance of the valve, except a small lunated space just within the free edge, on each side of the corpus Arantii. Here the valve is thinnest, and composed of little more than the endocardium. Thus constructed and attached, the three semilunar pouches are placed side by side around the arterial orifice of each ventricle, which can be separated by the blood passing out of the ventricle, but which immediately afterward are pressed together, so as to prevent any return (6, fig. 147, and 7, fig. 148). This will be again referred to. Opposite each of the semilunar cusps, both in the aorta and pulmonary artery, there is a bulging outward of the wall of the vessel: these bulgings are called the sinuses of Valsalva. Structure. — The valves of the heart are formed essentially of thick layers of closely woven connective and elastic tissue, over which, on every part, is reflected the endocardium. The Arteries. Distribution. — The arterial system begins at the left ventricle in a single large trunk, the aorta, wJiich almost immediately after its origin gives off 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 extremities. The arterial branches wherever given off divide and subdivide, until the calibre of each subdivision becomes very minute, and these minute ves- sels pass into capillaries. Arteries are, as a rule, placed in situations protected from pressure and other dangers, and are, with few exceptions, straight in their course, and frequently communicate (anastomose or inosculate) with other arteries. The branches are usually given off at an acute angle, and the area of the branches of an artery generally ex- ceeds 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 [apr-qpia, the wind- pipe) 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, the pulmonary artery is distributed much as the arteries belong- ing to the general systemic circulation. Structure. — The walls of the arteries are composed of three principal coats, termed («) the external or tunica adventitia, (6) the middle or tunica media, and (c) the internal or tunica intima. 168 HANDBOOK OF PHYSIOLOGY. (a) The external coat or tunica advetititia (figs. 152 and 153, a), tlie strongest and toughest part of the wall of the artery, is formed of areolar 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. 153, e). (b) The middle coat (fig. 153, m) is composed of both muscular and elastic fibres, with a certain proportion of areolar tissue. In the larger arteries (fig. 153) its thickness is comparatively as well as absolutely much greater than in the small, constituting, as it does, the greater part / /I, Fig. 152. Fig. 153. Fig. 154. Fig. 152. — Minute artery viewed in longitudinal section, e, Nucleated endothelial membrane, with faint nuclei in lumen, looked at from above ; i. thin elastic tunica intima ; wi, muscular coat or tunica media ; a, tunica adventitia. (Klein and Noble Smith.) > 2.50. Fig. 153.— Transverse section through a large branch of the inferior mesenteric artery of a pig. e. Endothelial membrane ; i, tunica elastica interna, no subendothehal layer is seen ; in, muscular tunica media, containing only a few wavy elastic fibres ; e, c. tunica elastica externa, dividing the media from the connective tissue adventitia, a. (Klein and Noble Smith.) X 350. Fig. 154.— Muscular fibre-cells from human arteries, magnified 350 diameters. (Kdlliker.) a, Nucleus. 6, aflbre-ceU treated with acetic acid. of the arterial wall. The muscular fibres are unstriped (fig. 154), and are arranged for the most part transversely to the long axis of the artery (fig. 155, 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 various size there is a difference in ihe proportion of the muscular and elastic element, elastic tissue preponderating in the largest arteries, and unstriped muscle in those of medium and small size. (c) 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 mem- brane, the striated or fenestrated coat of Henle, is peculiar in its ten- THE CIRCULATION OF THE BLOOD. 169 dency to curl up, when peeled olf from the artery, and in the perforated and streaked appearance which it presents under the microscope. Its inner surface is lined with a delicate layer of elongated endothelial cells (fig. 153, e), 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, suh-endothelial layer, with branched corpuscles. Fig. 155.— Transverse section of aorta through internal and about half the middle coat. 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 exception of the endothelial lining and the layers of the internal coat immediately 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 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. Nerves. — Most of the arteries are surrounded by a plexus of sympa- thetic nerves, which twine around the vessel very much like ivy round a tree: and ganglia are found at frequent intervals. The smallest arter- ies and capillaries are also surrounded by a very delicate network of 170 HAl^TDBOOK OF PHYSIOLOGY. similar nerve-fibres, many of which appear to end in the nuclei of the transverse muscular fibres (fig. 156). The Capillaries. Distrihidion. — In all vascular textures except some parts of the cor- pora 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 capillaries. They may be seen in all minutely injected preparations. The point at which the arteries terminate and the minute veins com- mence, cannot be exactly defined, for the transition is gradual; bat the Fig. 156 —Ramification of nerves and termination in the muscular coat of a small artery of the frog. (Arnold.) capillary network has, nevertheless, 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 network 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 composed of a single layer of elongated or radi- ate, flattened and nucleated cells, so joined and dovetailed together as to form a continuous transparent membrane (fig. 157). 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 nucleated, and may then be regarded as a miniature representative of the tunica adventitia of arteries. THE CIRCULATIOX OF THE BLOOD, 171 Here and there at the junction of two or more of the delicate endothe- lial cells which compose the capillary wall, pseudo-stomata may be seen. The endothelial cells are often continuous at various points with pro- cesses of adjacent connective-tissue corpuscles. Capillaries are sur- rounded 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 -j^^th of an inch, 12/^1. 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 rela- Fig. 157.— CapiUary blood-vessels from the omentum of rabbit, showing the nucleated endothelial membrane of which they are composed. (Klein and Noble Smith.) tion to the size of their blood corpuscles : thus, in the Proteus, the capil- lary 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 modifications of two chief kinds of mesh, the rounded and the elon- gated. That kind in which the meshes or interspaces have a roundish form is the most common, and j^revails in those parts in which the capillary iietAvork is most dense, such as the lungs (fig. 158), most glands, and mucous membranes, and the cutis. The meshes of this kind of network are not quite circular but more or less angular, some- times presenting a nearly regular quadrangular or polygonal form, but being more frequently irregular. The capillary network with elongated meshes is observed in jiarts in which the vessels are arranged among bundles of fine tubes or fibres, as in muscles and nerves. In such parts, the meshes form parallelograms, the short sides of which may be from three to eight or ten times less than the long ones; the long sides being 172 HANDBOOK OF PHYSIOLOGY. more or less parallel to the long axis of the fibre. The rounded and elongated meshes vary according as the vessels composing them are straight or tortuous. The nunihei' of the capillaries and the size of the meshes in different parts determine in general the degree of vascularity of those parts. The capillary network is closest in the lungs and in the choroid coat of the eye. Tn 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 capillaries, compared with that of the interspaces, is in the proportion of one to Fig. 158. Fig. 158. — Networlv of capillary vessels of the air-cells of the horse's lung magnified, a, a, Capillaries proceeding from 6, 6, terminal brandies of the pulmonary artery. (Frey.) Fig. 159. — Injected capillary vessels of muscle seen with a low magnifying power. (Sharpey.) four, or of one to three. The brain receives a very large quantity of blood; but its capillaries are very minute, and are less numerous than in some other parts. 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. It may be held as a general rule, that the more active the functions of an organ are, the more vascular it is. Her.ce the narrowness of the interspaces in all glandular organs, in mucous membranes, and in grow- ing 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, proba- bly, very little vital change occurs after they are once formed. THE CIRCULATION OF THE BLOOD. 173 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 termi- nate (as regards the systemic circulation) in the two venae cavse and the coronary veins, which enter the right auricle, and (as regards the pul- monary circulation) in four pulmonary veins, which enter the left auricle. The total capacity of the veins diminishes as they approach < .A' 'ii ^. Fig. 160. — Transverse section through a small artery aud vein of the mucous membrane of a child's epiglottis : the artery is thick walled and the vein thin-walled, a. Artery, the 'etter is placed in the hi men of the vessel, e. Endothelial cells with nuclei clearly visible ; these cells appear very thick from the contracted state of the vessel. Outside it a double wavy line jiarks the elastic tunica iutiina. m. Tunica media consisting of unstriped muscular fibres circularl> arranged; their nuclei are well seen. u. Part of the tunica adventitia showing bundles of connective-tissue fibre 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 tlie same as in the artery. The muscular coat of the vein (m) is seen to be much thinner than that of the artery, x 350. (Klein aud Noble Smith.) the heart; but, as a rule, their capacity exceeds by 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 pul- monary arteries. The veins are found after death more or less collapsed, and often contain blood. They are usually distributed in a superficial and a deep set which communicate frequently in their course. Structure. — In structure the coats of veins bear a general resemblance to those of arteries (fig. 160). Thus, they possess outer, middle, and internal coats. The outer coat is constructed of areolar tissue like that of the 174 HANDBOOK OF PHYSIOLOGY. arteries, but is thicker. In some veins it contains muscular fibre-cells, which are arranged longitudinally. The middle coat is considerably thinner than that of the arteries; it contains circular unstriped muscular fibres, mingled with a large pro- rig. 161.— Diagram showingvalves of veins, a, part of a vein laid open and spread out, with two pairs of valves, b, longitudinal section of a vein, showing the apposition of the edges of the valves in their closed state, c, portion of a distended vein, exhibiting a swelling in the situation of a pair of valves. portion of yellow elastic and white fibrous tissue. In the large veins, near the heart, namely the ?'ewfl? caves and pulmonary veins, the middle coat is replaced, for some distance from the heart, by circularly arranged striped muscular fibres, continuous with those of the auricles. Fig. 162. — A, vein with valves open, b, vein with valves closed: stream of blood passing of? by lateral channel. (Dalton.) 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 circula- tion, is effected with the help of the valves, contained in all veins; sub- ject to local pressure from the muscles between or near which they run. THE CIRCULATIOX OF THE BLOOD. 175 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 prevent any movement of blood backward. They are commonly placed in pairs, at various distances in different veins, but almost uniformly in each (fig. 161). 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 junc- tion with the jugular veins. The valves are semilunar; the unattached edge be- ing in some examples concave, in others straight. They are composed of inexten- sile fibrous tissue, and are covered with endothelium like that lining the veins. During the period of their inaction, when the venous blood is flowing in its proper direction, they lie by the sides of the veins ; but when in action, they come together like the valves of the arteries (figs. 161 and 162). Their situation in the superficial veins of the forearm is readily discovered by pressing along its surface, in a direc- tion opposite to the venous current, i.e., from the elbow toward the wrist; when little swellings (fig. 161, o) appear in the position of each pair of valves. These swellings at once disappear when the pres- sure is removed. Valves are not equally numerous in all veins, and in many they are absent al- together. They are most numerous in the veins of the extremities, 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 there are few or none in those which are not subject to muscular pres- sure. 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 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. L>/mphatics of Arteries and Veins. — Lymphatic spaces are present 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 Fig. 103.— Surface view of an artery from tlie mesentery of a frog, en- sheathed iu a peri-vascular lymphatic vessel, a. Theartery, with its circular muscular coat (media) indicated by broad, transverse markings, with an imlication of the adventitia outside. I. LjTiiphatic vessel, its wall is a sim- ple endothelial membrane. (Klein and Xoble Smith. 176 HANDBOOK OF PHYSIOLOGY. tubular vessels. In smaller vessels they appear as sinous spaces lined by endothelium. Sometimes, as in the arteries of the omentum, mesen- tery, and membranes of the brain, in the pulmonary, hepatic, and splenic arteries, the spaces are continuous with vessels which distinctly ensheath them — perivascular lympliatic sheaths (fig. 163). Lymph channels are said to be present also in the tunica media. The Action of the Heart. The heart's action in propelling the blood consists in the successive alternate contraction (systole) and relaxation (diastole) of the mus- cular walls of its two auricles and two ventricles. Action of the Auricles. — The description of the action of the heart may be commenced at that period in each cycle which imme- diately precedes the beat of the heart against the chest wall. The whole heart is then in a passive state; the auricles are gradually filling with blood flowing into them from the veins; and a portion of this blood is passing at once through them into the ventricles, the opening between the cavity of each auricle and that of its corresponding ventricle being, during all ilie pause, free and patent. The auricles, however, receiving more blood than at once passes through them to the ventricles, become, near the end of the pause, fully distended ; and at the end of the pause, they contract and expel their contents into the ventricles. The contraction of the auricles is sudden and very quick; it com- mences at the entrance of the great veins into them, and is thence prop- agated toward the auriculo-ventricular opening; but the last part which contracts is the auricular appendix. The reflux of blood into the great veins during the auricular systole is resisted not only by the mass of blood within them, but also by the simultaneous contraction of the muscular coats with which the large veins are provided near their en- trance into the auricles. Any slight regurgitation from the right auri- cle is limited by the valves at the Junction of the subclavian and internal jugular veins, beyond which the blood cannot move backward; and the coronary vein is preserved from it by a valve at its mouth. The force of the blood propelled into the ventricle at each auricular systole is transmitted in all directions, but being insutficient to open the semilunar valves, it is expended in distending the ventricle. Action of the Ventricles. — The dilatation of the ventricles which proceeds during the chief part of the dilatation of the auricles is com- pleted by the forcible injection of the contents of the latter. Thus distended, the ventricles immediately contract: so immediately, indeed, that their systole looks as if it were continuous with that of the auri- cles. The ventricles contract much more slowly than the auricles, and in their contraction probably always thoroughly empty themselves. THE CIRCULATIOX OF THE BLOOD. 177 differing in this respect from the auricles, in which, even after their complete contraction, a small quantity of blood remains. The shape of both ventricles during systole undergoes an alteration, the left probably not altering in length but to a certain degree in breadth, the diameter in the plane of the base being diminished. The right ventricle does actually shorten to a small extent. The systole has the effect of dimin- ishing the diameter of the base, especially in the plane of the auriculo- ventricular valves; but the length of the heart as a whole is not altered (Ludwig). During the systole of the ventricles, too, the aorta and pul- monary artery, being filled with blood by the force of the ventricular action against considerable resistance, elongate as well as expand, and the whole heart moves slightly toward the right and forward, twisting on its long axis, and exposing more of the left ventricle anteriorly than is usually in front. When the systole ends the heart resumes its former position, rotating to the left again as the aorta and pulmonary artery contract. After the whole of the blood has been expelled from the ventricles, the walls are believed to remain contracted for a short period before the rapid re-dilatation of the chambers begin. Action of the Valves. — (1) The Auriciilo-Ventricular. — The dis- tention of the ventricles with blood continues throughout tlie whole period of their diastole. The auriculo-ventricular valves are gradually brought into place by some of the blood getting behind the cusps and floating them up; and by the time that the diastole is complete, the valves are no doubt in apposition, the completion of this being brought about by the reflux current caused by the systole of the auricles. This elevation of the auriculo-ventricular valves is materially aided by the action of the elastic tissue which has been shown to exist so largely in their structure, especially on the ventricular surface. At any rate at the commencement of the ventricular systole they are completely closed. It should be recollected that the diminution in the breadth of the base of the heart in its transverse diameters during ventricular systole is especially marked in the neighborhood of the auriculo-ventricular rings, and this aids in rendering the auriculo-ventricular valves competent to close the openings, by greatly diminishing their diameter. The mar- gins of the cusps of the valves are still more secured in apposition with another, by the simultaneous contraction of the musculi papillares, whose chords tendineae have a special mode of attachment for this object. The cusps of the auriculo-ventricular valves meet not by their edges only, but by the opposed surfaces of their thin outer borders. The form and position of the fleshy columns on the internal walls of the ventricle no doubt help to produce the obliteration of the ventricu- lar cavity during contraction; and the completeness of the closure may often be observed on making a transverse section of a heart shortly after death, in any case in which rigor mortis is very marked (fig. 149). 178 HANDBOOK OF PHYSIOLOGY. In such a case only a central fissure may be discernible to the eye in the place of the cavity of each ventricle. If there were only circular fibres forming the ventricular wall, it is evident that on systole the ventricle would elongate; if there were only longitudinal fibres, the ventricle would shorten on systole; but there are both. The tendency to alter in length is thus counterbalanced, and the whole force of the contraction is expended in diminishing the cavity of the ventricle; or, in other words, in expelling its contents. On the conclusion of the systole the ventricular walls tend to expand by virtue of their elasticity, and a negative pressure is set up, which tends to suck in the blood. This negative or suctional pressure on the left side of the heart is of the highest importance in helping the pul- monary circulation. It has been found to be equal to 23 mm. of mer- cury, and is quite independent of the aspiration or suction power of the thorax itself, which will be described in a later chapter. The musculi ]3apillares prevent the anriculo-ventricular valves from being everted into the auricle. For the chords tendineae might allow the valves to be pressed back into the auricle, were it not that Avhen the wall of the ventricle is brought by its contraction nearer the auriculo- ventricular orifice, the musculi papillares more than compensate for this by their own contraction — holding the chords tiglit, and, by pulliug down the valves, adding slightly to the force with which the blood is expelled. These statements apply equally to the auriculo-ventricular valves on both sides of the heart; the closure of both is generally complete every time the ventricles contract. But in some circumstances the tricuspid yalve does not completely close, and a certain quantity of olood is forced back into the auricle. This has been called the safety-valve action. The circumstances in which it usually haj^pens are those in which the vessels of the lung are already completely full when the right ventricle contracts, as, e.g., in certain pulmonary diseases, in very active exertions, and in great efforts. In these cases, the tricuspid valve does not com- pletely close, and the regurgitation of the blood may be indicated by a pulsation in the jugular veins synchronous with that in the carotid arteries. It has been shown that the commencement of the ventricular systole precedes the opening of the semilunar valves by a fraction of a second. This would seem to show that the intraventricular j^ressure does not exceed the arterial pressure until the systole has actually begun, for the opening of the valves takes place at once when there is a distinct differ- ence in favor of the intraventricular over the arterial pressure, and con- tinues open only as long as this difference continues. When the arterial begins to exceed the intraventricular pressure, there is, as it were, a reflux of blood toward the heart, and the valves close. The dilatation THE CIKCULATIOJT OF THE BLOOD. 179 of the arteries is, in a peculiar manner, adtiiited to bring this about. The lower borders of the semilunar valves are attached to the inner surface of the tendinous ring, which is, as it were, inlaid at the orifice of the artery, between the muscular fibres of the ventricle and the elastic fibres of the walls of the artery. The tissue of this ring is tough, and does not admit of extension under such pressure as it is commonly exposed to; the valves are equally inextensile, being, as already men- tioned, formed mainly of tough, close-textured, fibrous tissue, with strong interwoven cords. Hence, when the ventricle propels blood through the orifice and into the canal of the artery, the lateral pressure which it exercises is sufficient to dilate the walls of the artery, but not enough to stretch in an equal degree, if at all, the unyielding valves and the ring to which their lower borders are attached. The effect, there- fore, of each such propulsion of blood from the ventricle is, that the wall of the first portion of the artery is dilated into three pouches behind Fig. 164.— Sections of aorta, to show the action of the semilunar valves, a is intended to show the valves, represented by the dotted lines, lying near the arterial walls, represented by the contin- uous outer Hue. b Rafter Hunter) shows the arterial wall cUstended into three pouches uo, and drawn away from the valves, which are straightened into the form of an equilateral triangle as represented by the dotted lines. the valves, while the free margins of the valves are drawn inward toward its centre (fig. 16-i, b). Their positions may be explained by the dia- grams, in which the continuous lines represent a transverse section of the arterial wails, the dotted ones the edges of the valves, firstly, when the valves are nearest to the walls (a), as in the dead heart, and, sec- ondly, when, the walls being dilated, the valves are drawn away from them (b). This position of the valves and arterial walls is retained so long as the ventricle continues in contraction: but as soon as it relaxes, and the dilated arterial walls can recoil by their elasticity, the blood is forced backward toward the ventricles and onward in the course of the circu- lation. Part of the blood thus forced back lies in the pouches (sinuses of Valsalva) (a, fig. 164. b) between the valves and the arterial walls; and the valves are by it pressed together till their thin luuated margins meet in three lines radiating from the centre to the circumference of the artery (7 and 8, fig. 148). The contact of the valves in this position and the complete closure ISO HAiNTDBOOK OF PHYSIOLOGY. of the arterial orifice are secured by the peculiar construction of their borders before mentioned. Among the cords which are interwoven in the substance of the valve are two of greater strength and prominence than the rest; of which one extends along the free border of each valve, and the other forms a double curve or festoon just below the free border. Each of these cords is attached by its outer extremities to the outer end of the free margin of its valve, and in the middle to the corpus Arantii; they thus enclose a lunated sjiace from a line to a line and a half in width, in which space the substance of the valve is much thinner and more pliant than elsewhere. When the valves are pressed down, all these parts or spaces of their surfaces come into contact, and the closure of the arterial orifice is thus secured by the apposition not of the mere edges of the valves, but of all those thin lunated parts of each which lie between the free edges and the cords next below them. These parts are firmly pressed together, and the greater the pressure that falls on them the closer and more secure is their apposition. The corpora Arantii meet at the centre of the arterial orifice when the valves are down, and they probably assist in the closure; but they are not essential to it, for, not unfrequently, they are wanting in the valves of the pulmonary artery, which are then extended in larger, thin, flapping margins. In valves of this form, also, the inlaid cords are less distinct than in those with corpora Arantii; yet the closure by contact of their surfaces is not less secure. Cardiac Cycle. — Taking 72 as the average number of cardiac evolu- tions per minute, each revolution may be considered to occupy f of a second, or about .8, which may be approximately distributed in the following way: — Auricular systole, about . 1 -|- Auricular diastole . . . . 7 = . 8 Ventricular systole " . 3 -(- Ventricular diastole . . .5 — .8 Period of joint auricular and ventricular diastole .4 -|- Period of systole of auricles or ventricles . . .4 = .8 If the speed of the heart be quickened, the time occupied by each cardiac revolution is of course diminished, but the diminution affects only the diastole and i^ause. The systole of the ventricles occujjies very much the same time, whatever the pulse-rate. The exact period in which the several valves of the heart are in action is a matter of some uncertainty; the auriculo-ventricular valves are probably closed during the wliole time of the ventricular contrac- tion, while, during the dilatation and distention of the ventricles, they are open. The semilunar valves are only certainly open during the middle period of the ventricular contraction. THE CIRCULATION OF THE BLOOD. 181 The Sounds of the Heart. When the ear is placed over the region of the heart, two sounds may be heard at every beat of the heart, which follow in quick succession, and are succeeded by a jjoiise or period of silence. The first sound is dull and prolonged; its commencement coincides with the impulse of the heart against the chest wall, and just precedes the pulse at the wrist. The second is shorter and sharper, with a somewhat flapping character, and follows close after the arterial pulse. The periods of time occupied respectively by the two sounds taken together and by the pause, are nearly equal. Thus, according to Walshe, if the cardiac cycle be divided into tenths, the first sound occupies y*^^; the second sound f-^; the first pause (almost imperceptible) ^^; and the second pause -j^^-. The relative length of time occupied by each sound, as compared with the other, is a little uncertain. The diiference may be best appreciated by consider- ing the different forces concerned in the production of the two sounds. In one case there is a strong, comparatively slow, contraction of a large mass of muscular fibres, urging forward a certain quantity of fluid against considerable resistance; while in the other it is a strong but shorter and sharper recoil of the elastic coat of the large arteries — shorter because there is no resistance to the flapping back of the semilunar valves, as there was to their opening. The sounds may be expressed by the words luhh — du}). The events which correspond, in point of time, with i\\ki first sound, are (1) the contraction of the ventricles, (2) the first part of the dilata- tion of the auricles, (3) the tension of the auriculo-ventricular valves, (4) the opening of the semilunar valves, and (5) the propulsion of blood into the arteries. The sound is succeeded, in about one-thirtieth of a second, by the pulsation of the facial arteries, and in about one-sixth of a second, by the pulsation of the arteries at the wrist. The second sound, in point of time, immediately follows the cessation of the ventricular contraction, and corresponds with (a) the tension of the semilunar valves, {b) the continued dilatation of the auricles, (r) the commencing dilatation of the ventricles, and {d) the opening of the auriculo-ventric- ular valves. The iMuse immediately follows the second sound, and corresponds in its first part with the completed distention of the auri- cles, and in its second with their contraction, and the completed disten- tion of the ventricles ; the auriculo-ventricular valves being all the time of the pause open, and the arterial valves closed. Causes. — The exact cause of the first sound of the heart is not known. Two factors probably enter into it, viz., firstly tlie vibration of the auriculo-ventricular valves and of the chordae tendineae. This vibration is produced by the increased intraventricular pressure set up when the ventricular systole commences, which puts the valves on the 182 HANDBOOK OF PHYSIOLOGY. stretch. The question whether this stretched condition of the valve continues throughout tlie whole of the ventricular systole cannot be definitely settled, but if it does not, the valvular element may possibly take part in the j)roduction of the first part of the first sound only. It is not unlikely too that the vibration of the ventricular walls themselves, and of the aorta and pulmonary artery, all of which parts are suddenly put into a state of tension at the moment of ventricular contraction, may have some part in producing the first sound. Secondly, tlie mus- cular sound produced by contraction of the mass of muscular fibres which form the ventricle. Looking ujion the contraction of the heart as a single contraction and not as a series of contractions or tetanus, it is at first sight difficult to see why there should be any muscular sound at all when the heart contracts, as contraction of a single muscle does- Fig. 165. — Scheme of cardiac cycle. The inner circle shows the events which occur within the heart; the outer the relation of" the sounds and pauses to these events. (Sharpey and Gairdner.j not produce sound. It has been suggested, however, that it arises from, the repeated unequal tension produced when the wave of muscular con- tractions passes along the very intricately arranged fibres of the ventric- ular walls. The valvular element is probably the more important of the two factors. The cause of the second sound is more simple than that of the first. It is entirely due to the vibration consequent on the sudden closure of the semilunar valves when they are pressed down across the orifices of the aorta and pulmonary artery. The influence of these valves in pro- ducing the sound was first demonstrated by Hope who experimented with the hearts of calves. In these experiments two delicate curved needles were inserted, one into the aorta, and another into the pulmo- nary artery, below the line of attachment of the semilunar valves, and,, after being carried upward about half an inch, were brought out again, through the coats of the respective vessels, so that in each vessel one THE CIRCULATIOX OF THE BLOOD. 183 valve was included between the arterial walls and the wire. Upon ap- plying the stetlioscope to the vessels, after such an operation, the second sound had ceased to be audible. Disease of these valves, when sufficient to interfere with their efficient action, also demonstrates the same fact by modifying the valvular cause of the second sound or destroying its distinctness. One reason that the second sound is clearer and sharper than the first may be, that the semilunar valves are not covered in by the thick layer of fibres composing the walls of the heart to such an extent as are the auriculo-veutricular. It might be expected therefore that their vibra- tion would be more easily heard by means of a stethoscope applied to the walls of the chest. The contraction of the auricles which takes place in the end of the pause is inaudible outside the chest, but may be heard, when the heart is exposed and the stethoscope placed on it, as a slight sound preceding and continued into the louder sound of the ventricular contraction. The Impulse of the Heart. With each contraction the heart may be felt to beat with a slight shock or impulse against the walls of the chest. The force of the im- pulse and the extent to which it may be perceived beyond this point vary considerably in different individuals, and in the same individual under different circumstances. It is felt more distinctly, and over a larger extent of surface, in emaciated than in fat and robust persons, and more during a forced expiration than in a deep inspiration; for, in the one case, the intervention of a thick layer of fat or muscle between the heart and the surface of the chest, and in the other the inflation of the portion of lung Avhich overlaps the heart, prevents the impulse from being full}^ transmitted to the surface. An excited action of the heart, and especially a hypertrophied condition of the ventricles, will increase the impulse; while a depressed condition, or an atrophied state of the ventricular walls, will diminish it. Cause of the Impulse. — During the j^eriod which precedes the ven- tricular systole the apex of the heart is situated upon the diaphragm and against the chest-wall in the fifth intercostal space. When the ventri- cles contract, their walls become hard and tense, since to expel their contents into the arteries is a distinctly laborious action, as it is resisted by the elasticity of the vessels. It is to this sadden hardening that the impulse of the heart against the chest-wall is due, and the shock of the sudden tension may be felt not only externally, but also internally, if the abdomen of an animal be opened and the finger be placed upon the under surface of the diaphragm, at a point corresponding to the under surface of the ventricle. The shock is felt, and possibly seen more dis- 184 HANDBOOK OF PHYSIOLOGY. tiuctly because of the partial rotation of the heart, already spoken of, along its long axis toward the right. The movement produced by the ventricular contraction against the chest-wall may be registered by means of an instrument called the cardiograj^li , and it will be found to corre- Tube to communicate with tambour. Ivory Tape to attach the instrument knob. to the chest. Tympanum. Fig. 166. — Cardiograph. (Sanderson's.) spond almost exactly with a tracing obtained by the same instrument applied over the contracting ventricle itself. The Cardiograph (fig. 166) consists of a cup-shaped metal box over the open front of which is stretched an elastic India-rubber membrane, upon which is fixed a small knob of hard wood or ivory. This knob, however, may be at- tached, as in the figure, to the side of the box by means of a spring, and may be made to act upon a metal disc attached to the elastic membrane. Screw to regulate elevation of lever. Writing lever. Tambour. Tube to cardiograph. Fig. 167. — Marey's Tambour, to which the movement of the column of air in the first tympanum is conducted by a tube, and from which it is communicated by the lever to a revolving cylinder, so that the tracing of the movement of the impulse beat is obtained. The knob (a) is for application to the chest-wall over the place of the great- est impulse of the heart. The box or tympanum communicates by means of an air-tight tube with the interior of a second tympanum, 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 THE CIRCULATIOX OF THE BLOOD. 185 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 apparatus. This generally consists of a cylinder or drum covered with smoked paper, revolving by clock-work with a definite velocity. The point of the lever writes upon the paper, and a tracing of the heart's impulse or cardiogram is thus obtained. By placing three small India-rubber air bags or cardiac sounds in the interior respectively of the right auricle and 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 one over the other in connection with a registering apparatus (fig. 168), Chau- veau and Marey have been able to rec(n-d and measure with much accuracy the variations of the endocardial pressure and the comparative duration of the contractions of the amides and ventricles. By means of the same apparatus, Fig. 168. -Apparatus of MM. Chauveau and Marey for estimating the variations of endocardial pressure, and production of impulse of the heart. 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 com- posed, have been demonstrated. In the tracing (fig. 169), the intervals between the vertical lines rep- resent periods of a tenth of a second. The parts on which any given vertical line falls represent simultaneous events. It will be seen that the contraction of the auricle, indicated by the marked curve at a in first tracing, causes a slight increase of pressure in the ventricle, which is shown at a' in the second tracing, and produces also a slight impulse, which is indicated by a ' in the third tracing. The closure of the semi- lunar valves causes a momentarily increased pressure in the ventricle at d', affects the pressure in the auricle d, and is also shown in the trac- ing of the impulse d". The large curve of the ventricular and the impulse tracings, between a' and d', and a" and d", are caused by the ventricular contraction, while the smaller undulations, between b and c, b' and c', b" and c", are 186 HANDBOOK OF PHYSIOLOGY. caused by the vibrations consequent on the tightening and closure of the auriculo-ventricular valves. It seems by no means certain that Marey's curves properly represent the variations in intraventricular pressure. Much objection has been taken to his method of investigation. Firstly, because his tambour ar- rangement does not admit of both positive and negative pressure being simultaneously recorded. Secondly, because the method is only applicable to large animals, such as the horse. And thirdly, because the intraven- tricular changes of pressure are communicated to the recording tambour by a long elastic column of air; and fourthly, because the tambour ar- rangement has a tendency to record inertia vibrations. II. D. Eolleston, who has pointed out the above imperfections of Marey's method, has re- investigated the subject with a more suitable apparatus. The method Fig. 169.— Tracings of (1), Intra-auricular. and (2), Intra- ventricular pressures, and (3), of the im- pulse of the heart, to be read from left, to right, obtained by Chauveau and Marey's apparatus. adopted by Rolleston is as follows: a window is made in the chest of an anesthetized and curarized animal, and an appropriately curved glass canula introduced through an opening in the auricular appendix. The canula is then passed through the auriculo-ventricular orifice with- out causing any appreciable regurgitation, into the auricle, or it may be introduced into the cavity of the right or left ventricle by an opening made in the apex of the heart. In some experiments the trocar is pushed through the chest wall into the ventricular cavity. The appa- ratus is filled with a solution of leech extract in .75 per cent saline so- lution, or with a solution of sodium bicarbonate of specific gravity 1083. The animals employed were chiefly dogs. The movement of the column of blood is communicated to the writing lever by means of a vulcanite piston which moves with little friction in a brass tube connected with the glass canula by means of a short connecting tube. When the lower part of the tube (a) is placed in communication with one of the cavities of the heart, the movements of the piston are re- THE CIRCULATION OF THE BLOOD. 187 corded by means of the lever (c). Attached to the lever is a section of a pulley (h), the axis of which coincides with that of the steel ribbon (e); while, firmly fixed to the piston, is the curved steel piston rod (1), from the top of which a strong silk thread (j) passes downward into the groove on the pulley. This thread (j), after being twisted several times round a small pin at the side of the lever, enters the groove in the pulley from above down- ward, and then passes to be fixed to the lower part of the curve on the piston-rod as shown in the smaller figure. The rise and fall of the lever (c) is controlled by the resistance to Fig. 170.— Apparatus for recording the endocardial pressure. (Rolleston.) torsion of the steel ribbon (e), to the middle of which one end of the lever is securely fixed by a light screw clamp (f). At some distance from this clamp — the distance varying with the degree of resistance which it is desired to give to the movements of the lever — are two hold- ers (g.g') which securely clamp the steel ribbon. As the torsion of a steel wire or strip follows Hooke's law, the tor- sion being proportional to the twisting force — the movements of the lever point are proportional to the force employed to twist the steel strip or ribbon — in other words to the pressures which act on the piston (b). To make it possible to record satisfactorily the very varying ventric- ular and auricular pressures, the resistance to torsion of a steel ribbon adapts itself very conveniently. 188 HANDBOOK OF PHYSIOLOGY. This resistance can be varied in two ways, 1st, by using one or more pieces of steel ribbon or by using strips of different thicknesses; or 2d, by varying the distance between the holders (g.g) and the central part of the steel ribbon to which the lever is attached. Eolleston's conclusions are as follows : — 1. That there is no distinct and separate auricular contraction Fig. 171. — Endocardial pressure-curve from the left ventricle. The thorax was opened and a canula introduced through the apex of the ventricle: abscissa is line of atmospheric pressure, g to D represents ventricular contraction; from d to the next rise at g represents tlie ventricular diastole. The notch at the top of wliich is f is a post-ventricular rise in pressure from below that of the atmosphere and not a pre-systolic or auricular rise in pressure. marked in the curves obtained from either right or left ventricles, the auricular and ventricular rises of jiressure being merged into one con- tinuous rise. 2. That the auriculo-ventricular valves are closed before any great rise of pressure within the ventricle above that which results from the auricular systole {a, fig. 172). The closure of the valve occurs probably "Fig. 172.— Curve with dicrotic summit from left ventricle; abscissa shows atmospheric pressure. in the lower third of the rise a b (fig. 172), and does not produce any Tiotch or wave. 3. That the semilunar valves open at the poi7it in the ventricular systole, situated (at g) about or a little above the junction of the mid- dle or upper third of the ascending line (a b), and the closure about or a little before the shoulder (d). 4. That the minimum pressure in the ventricle may fall below that of the atmosphere, but that the amount varies considerably. THE CIRCULATIO^; OF THE BLOOD. 189' Frequency and Force of the Heart's Action. The heart of a healthy adult man contracts about 72 times in a minute; but many circumstances cause this rate, which of course cor- responds with that of the arterial pulse, to vary even in health. The chief are age, temiDcrament, sex, food and drink, exercise, time of day,, posture, atmospheric pressure, temperature; as follows: — (1.) 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 pulsations per minute is 150 Just after birth . from 140 to 130 During the first year 130 to 115 During the second year . . . 115 to 100 Durina: the third vear 100 to 90 About the seventh year About the fourteenth year In adult age In old age In decrepitude . from 90 to 85. 85 to 80 to 70 to 75 to 80 70' 60 65. (2.) Temperament and Sex. — In j^ersons of sanguine temperament,, the heart acts somewhat more frequently than in those of the phleg- matic; and in the female sex more frequently than in the male. (3 and 4.) Food and Drink. Exercise. — After a meal the heart's action is accelerated, and still more so during bodily exertion or mental excitement; it is slower during sleep. (5.) Diurnal Variation. — In health the pulse is most frequent in the morning, and becomes gradually slower as the day advances : and this diminution of frequency is both more regular and more rapid in the evening than in the morning. (6.) Postvre. — The pulse, as a general rule, especially in the adult male, is more frequent in the standing than in the sitting posture, and in the latter than in the recumbent position; the ditference being greatest between the standing and the sitting postures. 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 positions, without the aid of mus- cular effort of the individual, it has been j^roved 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 jjulse being almost entirely prevented when the usually attendant muscular exertion was rendered unnecessary. (7.) Atmospheric Pressure. — The frequency of the pulse increases in a corresponding ratio with the elevation above the sea. (8.) Temperature. — The rapidity and force of the heart's contrac- tions are largely influenced by variations of temperature. The frog's heart, when excised, ceases to beat if the temperature be reduced to- 190 HANDBOOK OF PHYSIOLOGY. 0° C. (32° F.). "When heat is graduully ajjplied to it, both the speed and force of the contractions increase till they reach a maximum. If the temperature 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 tem- perature of the air was maintained at 40".5 C. (105° F.). At 45° C. (113° — 114° F.), the rabbit's heart ceases to beat. In health there is observed a nearly uniform relation between the frequency of the beats of the heart and of the respirations; the propor- tion being, on an average, 1 respiration to 3 or 4 beats. The same rela- tion is generally maintained in the cases in which the action of the heart is naturally accelerated, as after food or exercise; but in disease this relation may cease. In many affections accompanied with increased frequency of the heart's contraction, the respiration is, indeed, also iiccelerated, yet the degree of its acceleration may bear no definite pro- portion to the increased number of the heart's actions: and in many other cases, the heart's contraction becomes more frequent without any accompanying increase in the number of respirations; or, the respiration alone may be accelerated, the number of pulsations remaining station- ary, or even falling below the ordinary standard. The Force of the Cardiac Action. (a.) Ventricular. — The force of the left ventricular systole is more than double that exerted by the contraction of the right ventricle: this difference 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, comj)ared 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 intraventricular pressures during systole in the dog has been found to be 2.4 inches (60 mm.) of mercury in the right ventricle, and C 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 ven- tricle 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 in- fluence of respiration; but without this the negcitive pressure of the left ventricle caused by its active dilatation is about equal to |- of an inch (20 mm. )of mercury. The right ventricle is undoubtedly aided by this suction power of the left, so that the whole of the work of sonductmg the pulmonary THE CIRCULATION OF THE BLOOD. 191 circLilutiou does not fall upon the right side of the heart, but is assisted by the left side. (b.) Auricular. — The maximum pressure within the right auricle is equal to about i of an inch (^U mm.) of mercury, and is probably some- what less in the left. It has been found that during diastole the j^res- sure within both auricles sinks considerably below that of the atmos- phere; 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 respi- ration in the right auricle, this negative pressure is equal to about — 10 mm. In estimating the work done by any machine it is usual to express it in terms of the unit of work. In England, the unit of work is the foot-jjound, and is defined to be the energy expended in raising a unit of weight (1 lb.) through a unit of height (1 ft.) : in France, the kilo- firnm-metre. The work done by the heart at each contraction can be readily found by multiplying the weight of blood expelled by the ven- tricles by the height to which the blood rises in a tube tied into an artery. This height is probably about 9 ft. 3.21 metres in man. Tak- ing the weight of blood expelled from the left ventricle at eacli systole at 6 oz., i.e., | lb., we have 9 X f = 3.375 foot-pounds, or 3.21 X 180 grms. or 578 gram-metres, as the Avork done by the left ventricle at each sys- tole; and adding to this the work done by the right ventricle (about one-fourth that of the left) we have 3.375 + -822 = 4.19 foot-pounds, or 722 gram-metres as the work done by the heart at each contraction. Blood Pressure. The subject of blood-pressure has been already incidentally men- tioned more than once in the preceding pages, the time has now arrived for it to receive more detailed consideration. That the blood exercises pressure upon the walls of the vessels con- taining it, is due to the following facts: — Firstly, that the heart at each contraction forcibly injects a consid- erable amount of blood, viz., 4 to G oz. (120 to 130 grms.) suddenly and quickly into the arteries. Secondly, that the arteries are already full of blood at the com- mencement of the ventricular systole, since there is not sufficient time between the heart beats for the blood to pass into the veins. Thirdly, that the arteries are highly distensible and stretch to ac- commodate the extra amount of blood forced into them ; and Fourthly, ihac there is a distinct resistance interposed to the pas- sage of the blood from the arteries into the veins, from the enormous number of minute vessels, small arteries (arterioles) and capillaries into 192 HANDBOOK OF PHYSIOLOGY. which the main artery has been ultimately broken np. The sectional area of tlie capillaries is several hundred times that of the aorta, and the friction generated by the passage of the blood through these minute channels opposes a considerable hindrance or resistance in its course. The resistance thus set up is called peripheral resistance. The fric- tion is greater in the arterioles where the current is comparatively rapid than in the cajDillaries where it is slow. That the blood exerts considerable pressure upon the arterial walls in keeping them in a stretched or distended condition, may be readily shown by puncturing any artery; the blood is instantly projected with great force tlirough the opening, and the jet rises to a considerable height, the exact level of which varies with the size of the artery .expe- rimented with. If a large artery be punctured, the blood may be pro- jected upward for many feet, whereas if a small artery be similarly dealt with the jet does not rise to such a height. Another marked feature of the jet of blood from a cut artery, particularly well marked if the vessel be a large one, and near the heart, is the jerky character of the outflow. If the artery be cut across, the jet issues with force, chiefly from the central end, unless there is considerable anastomosis of vessels in the neighborhood, when the jet from the joeripheral end may be as forcible and as intermittent as that from the other end. The intermittent flow in the arteries which is due to the intermittent action of the heart, and which represents the systolic and diastolic alterations of blood pressure, may be felt if the finger be placed upon a sufficiently superficial artery. The finger is apparently raised and lowered by the intermittent systolic distention of the vessel, occurring at each heart beat. This intermittent distention of the artery is what is known as the Pulse, to the further consideration of which we shall persently return, but we may say here, that in a normal condition the pulse is a characteristic of the arterial, and is absent from the venous fiow. At the same time it must be recol- lected that in the veins the blood exercises a pressure on its containing vessel, but as we shall see presently this is small when compared with the arterial blood-pressure. As might be expected, therefore, the blood is not expelled with so much force if a vein be punctured or cut, and further, the flow from the cut vein is continuous and not intermittent, and the greater amount of blood comes from the peripheral and not from the central end as is the case when an artery is severed. The result produced by the experiment of cutting or puncturing a blood vessel may be modified by introducing into the vessel a glass tube of a calibje corresponding to that of the vessel, and allowing the blood to rise in it. If the vessel be an artery, the blood will rise several feet, according to the distance of the vessel from the heart, and when it has reached its highest point will be seen to oscillate with the heart's beats. This experiment shows that the pressure which the THE CIRCULATIOX OF THE BLOOD. 193 blood exerts upon the walls of the contained artery, equals the pres- sure of a column of blood of a certain height; in the case of the rab- bit's carotid it is equal to 3 feet of blood, or rather more than 3 feet of water. In the case of the vein, if a similar experiment be performed, blood will rise in the tube for an inch or two only. The usual method of estimating the amount of blood pressure differs somewhat from the foregoing simple experiment. Instead of a simple straight tube of glass inserted into the vessel, a U-shaped tube contain- Fig. Ii3.— Diaprram of mercurial kymograph, a, revolving cylinder, worked by a clOCk-work arrangement contained in the box (b), the speed being regulated by a fan above the box; cylinder supported by an upright (6), and capable of being raised or lowered by a screw (a), by a handle attached to it: d, c, e, represent mercurial manometer, a somewhat different form of which is s.iown in next figure. ing mercury, or a mercurial manometer is employed, and the artery is made to communicate with it by means of a small canula which is inserted into the vessel, and a connecting tube, an arrangement being made whereby the canula, tubes, etc., are filled with a saturated saline solution to prevent the clotting of blood when it is allowed to pass from the artery into the apparatus. The passage of blood is prevented during the arrangement of the details of the experiment by a pair of clamp or bull-dog forceps! The free end of the U-tube of mercury contains a very fine glass piston, the bulbous end of whicli floats upon the surface of the mercury, rising with its rise and oscillating with its oscillations. 13 194 HANDBOOK OF PHYSIOLOGY. As soon iis there is free communication between the artery and the tube of mercury, the blood rushes out and puslies before it the column of mercury. The mercury will therefore rise in the free limb of the tube, and will continue to do so until a point is reached which corresponds to the mean pressure of the blood-vessel used. The blood-pressure is thus communicated to the upper part of the mercurial column; and the depth to which the latter sinks, added to the height to which it rises in the other, will give the height of the mercurial column which the blood- pressure balances; the weight of the saline solution being subtracted. For the estimation of the amount of blood pressure at any given mo- ment, no further apparatus than this, which is called Poiseuilles's h(B- Fig. 174. — Ludwig's Kymograph. The manometer is shown iu lig. 173, D. C. E. The mercury which partially fills tlie tube su]jports a float in form of a piston, nearly filling the tube; a vvu'e is fixeil to the float, and tlie writing style or pen is guided by passing through the bra.ss cap of the tube fixed to the wire; the ijressure is communicated to the mercury by means of a flexible metal tube filled with fluid. mad i/namometer, is necessary; but for noting the variation.'^ of pressure iu the arterial system, as well as its absolute amount, the instrument is usually combined with a recording apparatus, in this form called a kymograph (fig. 173). The recording apparatus "consists of a revolving cylinder (fig. 173, A), which is moved by clockwork, and the speed of which is capable of regulation. The cylinder is covered with glazed paper blackened in the fiame of a lump, and the mercurial mauometer is so fixed (fig, 173, D) that its float provided with a style writes on the cylinder as it revolves. There are many ways in which the mercurial manometer may be varied; in fig. 174 is seen a form, which is known as Ludwig's Kymograph, In order to obviate the necessity of a large quantity of blood entering the tube of the apparatus, it is usual to have some arrangement by means THE CIRCULATION OF THE BLOOD. 195 of which the mercury may be made to rise in the tube of the manometer to the level corresponding to the mean pressure of the artery experi- mented with, so that the writing style simply records the variations of the blood pressure above and below the mean pressure. This is done by causing the saline solution, generally a saturated solution of sodium carbonate or sulphate, to fill the apparatus from a bottle suspended at a height, and capable of being raised or lowered as required for the pur- pose, or by injecting the saline solution into the tube by means of a syringe. The canula inserted and tied into the artery may be of two kinds. In one case a fine glass tube is used with the end drawn out and cut so that its end is oblique, and provided with a shoulder to prevent its coming out easily, the peripheral end of the cut artery being tied to obviate the escape of blood. By this means, the j^ressure communicated to the column of mercury is the forward and not the lateral pressure of blood, or a T-canula may be employed and may be tied into the two ends of a divided artery, and the free arm of the T piece being made Fig. irs. — Normal tracing: of arterial pressure in the rabbit obtained with the mercurial kyrno- graph. The smaller undulations correspond with the heart beats; the larger curves with the respi- ratory movements. cBurdon-Sanderson.) to communicate with the manometer. This communicates the lateral blood 2)ressure. As soon as the experiment is completed, the writing float is seen to oscillate in a regular manner, and a curve of blood pressure is traced upon the smoked paper by the style (or, if a continuous roll of unsmoked paper be used instead, by an inked pen), when a figure similar to fig. 175 will be obtained. This indicates two main variations of the blood pressure; the smaller excursions of the lever corresponds with the systole and diastole of the heart, and the large curves correspond with the respirations, being called the respiratory undulations of blood pressure, to which attention will be directed in the next chapter. Of course, the undulations spoken of are only seen in records of arterial blood pressure; they are more clearly marked in the arteries nearer the heart than in those more remote, in the smaller arteries the amount of the pressure as well as the indication of the systolic rise of pressure, being, comparatively speaking, small. In order to record the undulations of arterial pressure, for some pur- poses it is better to use Fick's Spring Kymograph than the mercurial manometer. Two forms of this instrument are shown in figs. 176 and 196 HANDBOOK OF PHYSIOLOGY. 177. It consists of a hollow C-spring, filled with fluid, the interior of which is made to communicate with the artery by means of a flexible metal tube and canula. In response to the pressure, transmitted to its interior, the spring tends to straighten itself, and the movement thus produced is communicated by means of a lever to a writing style and so to a recording apparatus. This instrument obviates the errors which might be caused by the inertia of the mercury in the mercurial manometer; it also shows in more detail the»variations of the blood pressure in the vessel during and after each individual beat of the heart. Fig. 1?6. — A form of Pick's Spring Kymograph, a, Tube to be counected with artery; c, hollow spring, the movement of which moves b, the writing lever; e, .screw to regulate height of b; d, out- side protective spring; g, screw to fix on the u right of the support. In fig. 178 is seen a tracing taken with Fick's Kymograph from an artery of a dog. As regards the actual amount of blood pressure, 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 capa- ble of supporting a column of 2 to 3.5 inches (50 to 90 mm.) of mercury, in the dog 4 to 7 inches (100 to 175 mm.), in the horse 5 to 8 inches (152 to 200 mm.), and in man the pressure is estimated to be 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 sup- THE CIKCULATIOX OF THE BLOOD. 197 ported 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 equal to 4 lbs. 4 oz. avoirdupois; that in the aorta of the horse being 11 lb. 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 lb. 2 oz. avoirdupois. The amounts above stated represent the arterial tension to the time of the ventricular contraction. Fig. 1((.—Fick's Kymograpli, improved by Hering (after McKendrick). a, Hollow spring filled with alcohol, bearing lever ai-raiisenient b, d, c. to which is attached the marker e; the rod c passes downward into the tube/, containing castor oil, which offers resistance to the oscillations of c; g, syringe for filling the leaden tube b with saturated sulphate of sodium solution, and to apply suffi- cient pressure as to prevent the blood from passing into the tube h at i, the canula inserted into the vessel; I, abscissa-marker, which can be applied U> the moving surface by turning the screw in; fc, screw for adjusting the whi>le apparatus to the moving surface: o, screw for elevating or de- pressing by a rack and pinion movement the Kymograph; u, screw for adjusting the position of the tube /. 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 cit the period of the ventricular systole. The blood-pressure gradually lessens then as we proceed from the arteries near the heart to those more remote, and again from these to the capillaries, and thence along the veins to the right auricle. The blood-pressure in the veins is nowhere very great, but is greatest in the small veins, while in the large veins toward the heart the pressure becomes 7iegative, or, in other words, when a vein is put in connection with a mercurial man- 198 HANDBOOK OF PHYSIOLOGY. ometer the mercury will falliu the arm furthest away from the vein aiid will rise in the arm nearest the vein, the action being that of suction rather than pressure forward. In the large veins of the neck the ten- dency to suck in air is especially marked, and is the cause of death in some surgical operations in that region. The amount of pressure in the brachial vein is said to suj^port 9 mm. of mercury, whereas the pressure in the veins of the neck is about equal to a negative pressure of rather more than -^ inch or — about i to ^ inch or — 3 to — 8 mm. The variations of venous pressure during systole and diastole of the heart are very slight, and a distinct pulse is never seen in veins except under extraordinary circumstances. 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 condi- tions, it appears that the blood-pressure is subject to variations in the capillaries, apparently following the variations of that of the Fig. 178. — Normal arterial tracing obtained with Tick's kymograph in the dog. (Burdon-Sanderson . ) arteries; and that up to a certain jjoint, as the extra vascular pressure is increased, so does the pulse in the arterioles, capillaries, and venules be- come more and more evident. The pressure in the first case (web of the frog's foot) has been found to be equal to about i to f inch or 14 to 20 mm. of mercury; in other experiments to be equal to about | to ^ of the ordinary arterial pressure. The arterial blood-pressure may be made to vary by variations of either of the two chief factors upon which the pressure in the vessels depends, viz., the cardiac contractions and the peripheral resistance. Thus, increase of blood-pressure may be brought about by either (a) a more frequent or more forcible action of the heart, or (b) by increase of the peripheral resistance; and on the other hand, diminution of the blood-pressure may be produced, either by (a) a diminished force or fre- quency of the contractions of the heart, or by (b) a diminished periphe- ral resistance. These different factors, however, although varying con- stantly, are so combined that the general arterial pressure remains fairly constant; for example, the heart may, by increased force or frequency of its contractions, distinctly increase the blood-pressure, but this in- creased action is almost certainly followed by diminished peripheral THE CIRCULATION OF THE BLOOD. 199 resistance, and thus the two altered conditions may balance, with the result of brinoing back the blood-pressure to what it was before the heart began to beat more rapidly or more forcibly. It will be clearly seen that the circulation of the blood within the blood-vessels must depend upon the dimijiution of the pressure from the heart to the capillaries, and from the capillaries to the veins, the blood flowing in the direction of least resistance; we shall presently see further that the general or local flow also depends upon the relations between the heart's action and the peripheral resistance, general or local. The Arterial Flow. The character of the flow of blood through the arterial system de- pends to a very considerable extent upon the structure of the arterial walls, and particularly upon the elastic tissue which is so highly devel- oped in them. The elastic tissue first of all guards the arteries from the suddenly exerted pressure to which they are subjected at each contraction of the ventricles. In every such contraction as is above seen the contents of the ventricles are forced into the iuteries more quickly than they can be discharged through the capillaries. The blood, therefore, being, for an instant, resisted in its onward course, a part of the force with which it was impelled is directed against the sides of the arteries; under this force their elastic walls dil.ite, stretching enough to receive the blood, and, as they stretch, becomiiig 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 arteries are able, by the same elasticity, to resume their former cali- bre; the elastic tissue also equalizes the current of blood by maintaining pressure on it in the arteries during the period at which the ventricles are at rest or are dilating. If the arteries were rigid tubes, the blood, instead of flowing, as it does, in a constant stream, would be propelled through the arterial system in a series of jerks corresponding to the ventricular contractions, with intervals of almost complete rest during the inaction of the ventricles. But in the actual condition of the ves- sels, the force of the successive contractions of the ventricles is expended partly in the direct propulsion of the blood, and partly in the dilatation of the elastic arteries; and in the intervals between the contractions of the ventricles, the force of the i*ecoil is employed in continuing the on- ward flow. Of course the pressure exercised is equally difl'used in every direction, and the blood tends to move backward as well as onward; all movement backward, however, is prevented by the closure of the semi- lunar valves, which takes place at tlie very commencement of the recoil of the arterial walls. 200 HANDBOOK OF PHYSIOLOGY. Thus by the exercise of the ehisticity of the arteries, all the force of the ventricles is expended upon the circulation; for that part of the force which is used up or rendered potential in dilating the arteries is restored or made active or kinetic, in full when they recoil. There is no loss of force; neither is there any gain, for the elastic walls of the artery cannot originate any force for the propulsion of the blood — they only restore that which they received from 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 blood which we see in the capillaries and veins. In the production of a con- tinuous stream of blood in the smaller arteries and capillaries, the re- sistance which is offered to the blood-stream in these vessels is a neces- sary 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 elasticity of walls of the arteries. By means of the elastic and muscular tissue in their walls again the arteries are enabled to dilate and contract readily in correspondence with any temporary increase or diminution of the total quantity of blood in the body; and within a certain range of diminution of the quantity, still to exercise due pressure on their contents. The elastic tissue further assists in restoring the normal channel after diminution of its calibre, whether this has been caused by a contraction of the mus- cular coat, or by the temporary application of a compressing foi'ce from without. This action is well shown in arteries which, having contracted by means of their muscular element, after death regain their average potency on the cessation of post-mortem rigidity. The office of the muscular coat also is employed to adjust the flow of the blood locally, to regulate the quantity of blood to be received by each part or organ, and to adjust it to the requirements of each, accord- ing to various circumstances, but, chiefly, according to the activity with which the functions of each are at different times performed. The amount of work done by each organ of the body varies at different times, and the variations often quickly succeed each other, so that, as in the brain, for example, (luring sleep and waking, within the same hour a part may be now very active and then inactive. In all its active exer- cise of function, such a part requires a larger supply of blood than is sufficient for it during the times when it is comparatively inactive. It is evident that the heart cannot regulate the supply to each part at dif- ferent periods; neither could this be regulated by any general and uni- form contraction of the arteries; but it may be regulated by the power which the arteries of each part have, in their muscular tissue, of con- THE CIKCULATION OF THE BLOOD. 201 tracting so as to diminish, and of passively dilating or yielding so as to permit an increase of, the supply of blood, according to the requirements of the part to which they are distributed. And thus, while the ventri- cles of the heart determine the total quantity of blood, to be sent onward at each contraction, and the force of its propulsion, and while the large and merely elastic arteries distribute it and equalize its stream, the smaller arteries, in addition, regulate and determine, by means of their muscular tissue, the proportion of the whole quantity of blood which shall be distributed to each part. This regiilating function of the arteries is governed and directed by the nervous system in the way to be presently described. The muscular element of the middle coat also co-operates with the •elastic in adapting the calibre of the vessels to the quantity of blood which they contain. For the amount of fluid in the blood-vessels varies very considerably even from hour to hour, and can never be quite con- .stant; and Avere the elastic tissue only present the pressure exercised by the walls of the containing vessels on the contained blood would be sometimes very small, and sometimes inordinately great. The presence of a muscular element, however, provides for a certain uniformity in the amount of pressure exercised; and it is by this adaptive, iiniform, gen- tle, muscular contraction, that the normal tone of the blood-vessels is maintained. Deficiency of this tone is the cause of the soft and yield- ing pulse, and its unnatural excess of the hard and tense one. The elastic and muscular contraction of an artery may also be re- garded as fulfilling a natural jiurpose when, the artery being cut, it first limits and then, in conjunction with the coagulated fibrin, arrests the escape of blood. It is only in consequence of such contraction and co- agulation that we are free from danger through even very slight wounds; for it is only when the artery is closed that the processes for the more permanent and secure prevention of bleeding are established. But there :appears no reason for supposing that the muscular coat assists, to more •than a very small degree, in propelling the onward current of blood. The Pulse. The most characteristic feature, then, of the arterial flow, is its in- termittency, and this intermittent flow is seen or felt as the Pulse. The pulse is generally described as an expansion of the artery pro- duced by the wave of blood set in motion by the injection of blood at each ventricular systole into the already full aorta. As the force of the left ventricle, however, is not expended in dilating the aorta only, the wave of blood jsasses on, expanding the arteries as it goes, running as it were on the surface of the more slowly travelling blood already con- tained in them, and producing the pulse as it proceeds. 202 HANDBOOK OF PHYSIOLOGY. The distention of each artery increases both' its length and its diam- eter. In their elongation, the arteries change their form, the straight ones becoming slightly curved, and those already curved becoming more so; but they recover their previous form as well as their diameter when the ventricular contraction ceases, and their elastic walls recoil. The increase of their (iurves which accomijanies the distention of arteries, and the succeeding recoil, may be well seen in the prominent temporal artery of an old person. In feeling the pulse, the finger cannot distin- guish the sensation produced by the dilatation from that produced by the elongation and curving; that which it perceives most plainly, how- ever, is the dilatation, or return, more or less, to the cylindrical form, of the artery which has been partially flattened by the finger. Fig. 179.— Marey's Sphygmograph, modifled by Mahomed. The pulse— due to any given beat of the heart — is not perceptible- at the same moment in all the arteries of the body. Thus, it can be felt in the carotid a very short time before it is perceptible in the radial artery, and in this vessel again before it occurs in the dorsal artery of the foot. The delay in the beat is in proportion to the distance of the artery from the heart, but the difference in time between the beat of any two arteries probably never exceeds I to -^ of a second. A distinction must be carefully made between the passage of the wave along the arteries and the arterial fiow itself. Both wave and current are present; but the rates at which they travel are very different, that of the wave 1G,5 to ,33 feet per second (5 to 10 metres), being twenty or thirty times as great as that of the current. The Sphygmograph,— Much light has been thrown on what may be called the form of the pulse wave by the sphygmograph (figs. 179 and 182). The principle on which it acts will be seen on reference to- figs. The small button replaces the finger in the act of taking the pulse,. THE CIRCULATION OF THE BLOOD. 203 and is made to rest lightly on the artery, the pulsations of which it is desired to investigate. The up-and-down movement of the button is communicated to the lever, to the hinder end of which is attached a slight spring, which allows the lever to move up, at the same time that Fig. 180.— Diagram of the lever of the Sphjgmograph. it is just strong enough to resist its making any sudden jerk, and in the interval of the beats also to assist in bringing it back to its original position. For ordinary purposes the instrument is bound on the wrist (fig. 181). It is evident that tlie beating of the pulse with the reaction of the spring will cause an up-and-down movement of the lever, the pen of which will write the effect on a smoked card, which is made to move by clockwork in the direction of the arrow\ Thus a tracing of the pulse is obtained, and in this way much more delicate effects can be seen than can be felt on the application of the finger. Fig. 181.— The Sphygmograph applied to the arm. Two forms of sphygmograph are shown in figs. 179, 182, viz. , a modifica- tion of the original instrument of Marey and Dudgeon's. Marey's instrument, and indeed all modifications of it, .suffer from the defect that tliere is no ade- quate method of measuring tlie pressure exercised by the button of the instru- ment upon the artery, and that it is difiicult to be certain of tlie exact position it occupies over the artery. Dudgeon's sphygmograph, although very conven- ient to use, is, according to Roy and Adami, even less satisfactory, and the tracings obtained by it are so disfigured by inertia vibrations as to render them more or less worthless. "The mechanical construction of the instrument is such as to render great inertia vibrations unavoidable. " These authors have 204 HANDBOOK OF PHYSIOLOGY. invented an instrument called a sphygmometer, in which these defects of th: sphygmograph are corrected. Fis- 182.— Dudgeon's Sphj'gmograph. Tlie principle of the sphygmometer of Roy and Adami is shown in the dia- gram (fig. 183). The apparatus consists of a box (a) which is moulded to fit over the end of the radius so as to bridge over the radial artery. Within this is a flexible bag (6) filled with water, and connected by a T tube with a rubber bag (h) and Fig. 183.— Diagrammatic sectional representation of the sphygmometer (Roy and Adami) . a, Box in which the portion of the artery is inclosed; b, thin-walled india-rubber bag filled with water, and communicating through tap, c, with manometer and thick-walled rubber bag, h; d. piston con- nected by rod, e, with recording lever,/: jr. spiral spring attached to axis of lever, and by which the pressure in b, against the piston, d, is counterbalanced; k, skin and subcutaneous tissue; w, end of radius seen in section; ii, radial artery seen in section. THE CIRCULATIOIn^ OF THE BLOOD. 205 mercurial manometer. The fluid in the box may be raised to any desired pressure, and may then be shut off by tap (c) . At the upper part of the box is a circular opening, and resting upon (b) is a flat button (d) , which by means of a short light rod(e) communicates the movement of (6) to the lever (/). To the axis of rotation of this lever is a spiral watch-spring (g) which can be tight- ened at will, so that the lever can be made to take a vertical position at any desired hydrostatic pressure within the box. The movements of the lever are recorded upon a piece of blackened glazed paper made to move in a vertical direction past it. When in use, the box is fixed upon the end of the radius by an appropriate holder, and the pressure is raised to any desired height to which the lever is adapted by tightening or slackening the spring. The tap (c) is then closed. The pressure within the box acts in all directions, and is correctly indicated by the manometer. The tracing of the pulse (sphygmogram), obtained by the use of the sphygniograph, differs somewhat according to the artery upon which it is applied, but its general characters are much the same in all cases. It consists of:— A sudden upstroke (fig. 1984, a), which is somewhat Fig. 184.— Diagram of pulse tracing, a, Upstroke; b, down-stroke: c, pre-dicrotic wave; d, di- crotic ; E, post-dicrotic wave. higher and more abrupt in the pulse of the carotid and of other arteries near the heart than in the radial and other arteries more remote; and a gradual decline (b), less abrupt, and therefore taking a longer time than (a). It is seldom, however, that the decline is an uninterrupted fall; it is usually marked about half-way by a distinct notch (c), called the dicrotic notch, which is caused by a second more or less marked ascent of the lever at that point by a second wave called the dicrotic wave (d) ; not unfrequeutly (in which case the tracing is said to have a double apex) there is also soon after the commencement of the descent a slight ascent previous to the dicrotic notch: this is called the p7-e- dicrotic wave (c), and in addition there may be one or more slight ascents after the dicrotic, called post-dicrotic (e). The explanation of these tracings presents some difficulties, not, however, as regards the two primary factors, viz., the upstroke and downstroke, because they ;ire universally taken to mean the sudden in- jection of blood into the already full arteries, and the gradual fall of the lever signifying the recovery of the arteries by their recoil. These 206 HANDBOOK OF PHYSIOLOGY. points may be demonstnited on a system of elastic tubes, with a syringe to pump in water at regular intervals, just as well as on the radial artery, or on the more complicated system of tubes in which the heart, the arteries, the capillaries and veins are represented, which is known as an arterial schema. If we place two or more sphygmographs upon Tig. 185.— Diagram of the formation of the pulse-tracing, a, Percussion wave; b, tidal wave; c, dicrotic wave. (Mahomed.) such a system of tubes at increasing distances from the pump, we may demonstrate first, that the rise of the lever commences earliest in that nearest the pump, and secondly, that it is higher and more sudden, while at a longer distance from the pump the wave is less marked, and a little later. So in the arteries of the body the wave of blood gradu- ally gets less and less as we approach the periphery of the arterial sys- tem, and is lost in the capillaries, according to Mahomed. By the Fig. 186.— Anacrotic pulse from a case of aortic aneurism, a, Anacrotic wave (or percussion wave); B, tidal or pre-dicrotic wave, continued rise in tension (or higher tidal wave). sudden injection of blood two distinct waves are produced, which are called the tidal and percussion waves. The tidal wave occurs whenever fluid is injected into an elastic tube (fig. 185, b), and is due to the ex- pansion of the tube and its more gradual collapse. The percussion wave occurs (fig. 185, a) when the impulse imparted to the fluid is more sud- THE CIRCULATION OF THE BLOOD. 207 ■den; this causes an abrupt upstroke of the lever, which then falls until it is again caught up perhaps by the tidal wave which begins at the same time but is not so quick. In this way, generally speaking, the apex of the upstroke is double, the second upstroke, the so-called pre-dicrotic elevation of the lever, representing the tidal wave. The double apex is most marked in trac- ings from large arteries, especially when their tone is deficient. In tracings from arteries of medium size, e.g., the radial, on the other hand, the upstroke is usually single. In this case the percussion-impulse is not sufficiently strong to jerk up the lever and produce an effect distinct from that of the tidal wave which immediately follows it, and which continues and completes the distention. In cases of feeble arterial ten- sion, however, the percussion-impulse may be traced by the sphygmo- _graph, not only in the carotid pulse, but also to a less extent in the radial. The interruptions in the downstroke are called the catacrotic waves, to distinguish them from an interruption in the upstroke, called the anacrotic wave, occasionally met with in cases in which the pre-dicrotic or tidal wave is higher than the percussion wave. There is considerable difference of opinion both as to whether the dicrotic wave is present in health, and also as to its cause. The balance of opinion, however, appears to be in favor of the belief that the dicrotic wave to a greater or lesser degree is present in health; in certain condi- tions not necessarily diseased, it becomes so marked as to be quite plain to the unaided finger. Such a pulse is called dicrotic. Sometimes the •dicrotic rise exceeds the initial upstroke, and the pulse is then called hyper-dicrotic. As to the cause of dicrotism, one opinion (1) is that it is due to a recovery of pressure during the elastic recoil, in consequence of a rebound from the periphery. It may indeed be produced on a schema by ob- structing the tube at a little distance beyond the spot where the sphyg- mograph is placed. Against this view, however, is the fact that the notch appears at about the same point in the downstroke in tracings from the carotid as from the radial, and not first in the radial tracing, as it should do, if this theory was correct, since that artery is nearer the periphery than the carotid, and as it does in the corresponding experi- ment with the arterial schema when the tube is obstructed. (2) The generally accepted notion among clinical observers, is that the dicrotic wave is due to the rebound from the aortic valves which causes a second wave; but the question cannot be considered settled, and the presence of marked dicrotism in cases of hemorrhage, of ansemia and of other weakening conditions, as well as in cases of diminished pressure within the arteries, would imply that it may, at any rate sometimes, be due to the altered specific gravity of the blood within the vessels, either directly 208 HANDBOOK OF PHYSIOLOGY. or througli the indirect effect of these conditions on the tone of thj arterial walls. Waves may be produced in any elastic tube when a fluid is being driven through it with an intermittent force, such waves being called waves of oscillation (M, Foster). Their origin has received various ex- planations. In an arterial schema they vary with the specific gravity of the fluid used, and with the kind of tub- ing, and maybe therefore supposed to vary in the body with the condition of the blood and of the arteries. Some consider the secondary waves in the downstroke of a normal tracing to be oscillation waves; but, as just mentioned, even if this be the case, as is most likely with post-dicrotic waves, the dicrotic wave itself is almost cer- tainly due to the rebound from the aortic valves. The anacrotic notch is usually as- sociated with disease of the arteries, e.g., in atheroma and aneurism. The dicrotic notch is called diastolic or aortic, and in point of time indicates the closure of the aortic valves. Of the three main parts then of a pulse-tracing, viz., the percussion wave, the tidal, and the dicrotic, the percus- sion wave is produced by sudden and forcible contraction of the heart, per- haps exaggerated by an excited action, and may be transmitted much more rapidly than the tidal wave, and so the two may be distinct; frequently, how- ever, they are inseparable. The di- crotic wave may be as great or greater than the other two. According to Mahomed, the distinctness of the three waves depends upon the following conditions: — HhQ percussion wave is increased by: — 1. Forcible contraction of the Heart; 2. Sudden contraction of the Heart; 3. Large volume of blood; 4. Fulness of vessel; and diminished by the reversed conditions. The fidal wave is increased by: — I. Slow and prolonged contraction of the Heart; 2. Large volume of blood; 3. Comparative emptiness of Fig. 187. — Diagrams of pulse curves witli exaggeration of one or other of the three waves. A , percussion ; B, tidal; C, dicrotic. 1. Percussion wave very marked; 2, tidal wave sudden; 3. dicrotic pulse curve; 4 and .5, the tidal wave very exaggerated, from high tension, (Mahomed.) THE CIRCULATION OF THE BLOOD. 209 vessels; 4. Diminished outflow or slow capillary circulation; and dimin- ished by the reverse conditions. The dicrotic wave is increased by : — 1. Sudden contraction of the Heart; 2. Low blood pressure; 3. Increased outflow or rapid capillary circulation; 4. Elasticity of the aorta; 5. Relaxation of muscular coat; and diminished by the reversed conditions. In the use of the sphygmograph care must be taken as to the careful regulation of the pressure. If the pressure be too great, the characters of the pulse may be almost entirely obscured, or the artery may be entirely obstructed, and no tracing is obtained ; and on the other hand. B Fig. 188. — A, Kormal pulse-tracing from radial of healthy adult, obtained by the sphygmometer. B, From same artery, with the same extra-ai-terial pressure, taken durmg acute nasal catarrh. if the pressure be too slight, a very small part of the characters may be reuresented on the tracing. It is necessary to mention that Roy and Adami, by comparison of tracings of intra-ventricular pressure with pulse-tracings obtained by the sphygmometer, have come to the following conclusions, difiering from Mahomed (whose de- scription has been chiefly followed in the text) in several particulars. The pulse tracing obtained from the radial of a healthy man is represented in the diagram (fig. 188) . in which the different parts of the tracings are marked out. These may be thus described : — (1) Upstroke, which may vary both in rapidity and in height; the height varies with the volume of blood expelled at each systole, with the amount of peripheral resistance, and with the degree of rigidity of the arterial walls ; the ra- pidity depends upon the rapidity of the outflow from heart. (2) The second part, usually called the percussion wave, is believed by these authors to be due to 14 310 HANDBOOK OF PHYSIOLOGY. the contraction of the papillary muscles, and is hence called by them papillary wave, and corresponds with the distance between the top of the upstrcjke and pre-dicrotic notch (3 in fig. 188). (3) The outflow-remainder wave., or tidal or jire-dicrotic wave (2 to 3) . During this wave tlie outflow from the ventricle ends. (4) The dicrotic notch, due to the inertia of the blood. (5) The post- dicrotic wave, also due to inertia. (6) The rounded shoulder, which lies be- tween the post-dicrotic wave and the lowest point of the tracing. (7) In trac- ings taken near the heart, a small notch and short jjositive wave, corresponding in time with the commencement of the ventricular systole. The Capillary Flow. It is in the capillaries that the chief resistance is offered to the prog- ress of the blood; for in them the friction of the blood is greatly in- Fig. 189.— Capillaries (C.) in the web of the frog's foot connecting a small artery (A) with a small vein V (after Allen Thomson). creased by the enormous multiplication of the surface with which it is brought in contact. When the capillary circulation is examined in any transparent part of a full-grown living animal by means of the microsco^^e (tig. 189), the blood is seen to flow with a constant equable motion ; 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. At the circumference of the stream in the larger capillaries, but sepecially well marked in the small arteries and veins, in contact with the walls of the vessel, and adhering to them, there is a layer of liquor sanguinis 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 movements of the blood-corpuscles. The red corpuscles occupy the middle of the stream and move with comparative rapidity; the colorless corpuscles 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 be at rest; for if any of the corpuscles hap- THE CIRCULATION^" OF THE BLOOD. 211 pen 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 colorless corpuscles and their occasional stoppage may be due to their having a natural tendency to adhere to the walls of the vessels. Sometimes^, indeed, when the motion of the blood is not strong, many of the white corpuscles collect in a capillary vessel, and for a time entirely prevent the passage of the red cor2)uscles. When the peripheral resistance is greatly diminished by the dilata- tion 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 ventricular systole is not converted into a continuous stream by the elasticity of the arteries before the capillaries are reached; and so in- termittency of the flow occurs both in capillaries and veins and a pulse is produced. The same phe- nomenon 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 sys- tole has time to pass on to the capillaries before the next stroke occurs; the amount of blood sent at each stroke being insufficient to pro^Derly distend the elastic arteries. It was formerly supposed that the occurrence of any transudation from the interior of the capil- laries into the midst of the surrounding 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 was ruptured. It is true that an English 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 phenome- non of escape of the blood-corpuscles from the capillaries and minute veins, apart from mechanical injury, were re-discovered by CohnheiiU in 1867. Cohnheim's experiment demonstrating the passage of the corpuscles through the wall of the blood-vessel is performed in the following man- ner. A frog is urarized, that is to say, paralysis is produced by ejecting Fig. 190.— A large ca- pillary from the frog's mesentery eight hours after irritation had been set up, sho-sving emigration of leuco- cytes, o. Cells in the act of traversing the capillary wall; b, some already'escaped. (Frey.) 212 HAXDBOOK OF PHYSIOLOGY. under the skin a minute quantity of the poison called urari; and the abdomen having been ojoened, a portion of small intestine is drawn out, and its transparent mesentery spread out under a microscope. After a variable time, occupied by dilatation, folloviang 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. The process of diapedesis of the red corpuscles, which occurs under circumstances of impeded venous circulation, and consequently increased blood-pressure, resembles closely the migration of the leucocytes, 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 suggested. Some believe that pseudo-stomata between contiguous endo- thelial cells provide the means of escape for the blood-corpuscles. But the chief share in the process is probably to be found in the vital en- dowments with respect to mobility and contraction of the parts con- cerned— both of the corpuscles and of the capillary wall itself. The circulation through the capillaries must, of necessity, be largely influenced by that which occurs in the vessels on either side of them — in the arteries or the veins; their intermediate position causing them to feel at once, so to speak, any alteration in the size or rate of the arterial or venous blood-stream. Thus, the aj^parent contraction of the cnpilla- ries, on the application of certain irritating substances, and during fear, and their dilatation in blushing may be referred primarily to the action of the small arteriss. But however greatly the capillaries may be in- fluenced by the arterial and venous flow, and by the condition of the parts which surround and support them, they, too, must be looked upon not as mere passive channels for the passage of blood, but as possessing endowments of their own 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 some influence in connection with the blood- current. The Venous Flow. The blood-current in the veins is maintained (a) primarily by the vis a tergo of the contraction of the left ventricle; but very effectual assist- ance to the flow is afforded (b) by th ■ action of the muscles capable of pressing on the veins with valves, as well as (c) by the suction action of the heart. The effect of muscular pressure upon the circulation may be thus explained. When pressure is applied to any part of a vein, and the current of blood in it is obstructed, the portion behind the seat of pres- sure becomes swollen and distended as far back as the next pair of THE CIRCULATIOX OF THE BLOOD. 213 valves, which are in consequence closed. Thus, whatever force is exer- cised 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. The circulation might lose as much as it gains by such an action, if it were not for the numerous communications, 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 circula- tion, since the blood, of which the onward course is arrested by the closed valves, can at once pass through some anastomosing cliannel, and proceed on its way by another vein. Thus, therefore, the effect of mus- cular 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 backward is prevented from being a hindrance by the closure of the valves and the anastomoses of the 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 accel- erated. The contraction occurs, on an average, about ten times in a minute; the existence of valves preventing regurgitation, the entire effect of the contractions was auxiliary to the onward current of blood. Analogous phenomena have been observed in other animals. The Velocity of the Flow. The velocity of the blood-current at any given point in the various divisions of the circulatory system is inversely proportional to their sec- tional 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 if a similar corre- spondence 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 represented 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 the aorta. Thus the velocity of blood in the capillaries is not more than jJ-^- of that in the aorta. 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 ventricu- 214 HANDBOOK OF PHYSIOLOGY. lar systole. The rate of movement diminishes during the diastole of the ventricles, and in the parts of the arterial system most distant from the heart. Chauveau has estimated the r.apidity 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 (530-150 mm.). Estimation of the Velocity. — Various instruments have been devised for mesuring the velocity of the blood-stream in the arteries. Ludwig's Stromuhr (fig. 191) consists of a U-shaped glass tube dilated at a and a', the ends of which, h 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 b' the glass part is firmly fixed into metal cylinders, attached to a circu- lar horizontal table, c c', capable of horizontal move- ment on a similar table d d' about the vertical axis mai'ked in figure by a dotted line. The opening in c e , when the instrument is in position, as in fig., cor- responds exactly with those in d d' ; but if c c' be Fig. 191. Fig. 192. Fig. 191. — Ludwig's Stromuhr. Fig. 192. — Diagram of Chauveau's Instrument, o. 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. turned at right angles to its present position, there is no communication be- tween h 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 communication between h and i. The experiment is jier- formed in the following way : — The artery to be experimented upon is divided and connected with two canulae and tubes which fit it accurately with h and i — h the central end, and i the peripheral ; the bulb a is filled with olive oil up to a point rather lower than Tc, and a' and the remainder of a is filled with defibrinated 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 /;, and it pushes before it tJie oil, and that the defibrinated blood into the artery through i. and replaces it in o ; 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 dis- THE CIRCULATION OF THE BLOOD. 215 places 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 canulae 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. Chauveau's instrument, fig. 192, consists of a thin brass tube, a in one side of which is a small perforation closed by thin vulcanized india-rubber. Pass- ing 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 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 HcemafocJi077ieter of Vierordt, and the instrument of Lortet, resemble in principle that of Chauveau. In the Capinaries.— The observation of Hales, E. H. Weber, and Val- entin agree very closely as to the rate of the blood-current in the capil- laries of the frog; and the mean of their estimates gives the velocity of the systewic capillary circulation at abont one inch (25 mm.) per min- ute. The velocity in the capillaries of warm-blooded animals is greater. In the dog gV to yfo- 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 g^th to -gi^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. 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 ui:)on the relative capacities of the arterial and venous systems. If an accurate estimate of the proportionate areas of arteries and the veins correspond- ing 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 ca- pacity 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, about twice or three times as great in the arteries as in the veins, 8 inches (200 mm.) a second. The rate at which the blood moves in the veins gradually increases the nearer it approaches the heart, for the sectional area of the venous trunks, compared with that of the branches opening into them, becomes gradually less as the trunks advance toward the heart. Of the Circulation as a Wlwle. — It would appear that a portion of blood ca7i 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 216 HANDBOOK OF PHYSIOLOGY. 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 an- other. 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 sec- onds; from the jugular vein to the masseteric 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 metatar- sal 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 o£ 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 contained 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 total quantity of blood, and the capacity of the cavities of the heart, have as yet been only approximately ascertained. 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. Local Peculiarities of the Circulation. The most remarkable peculiarities attending the circulation of blood through different oi'gans are observed in the cases of the brain, the erec- tile organs, the hings, the liver, and the kidneys. In the Brain. — For the due performance of its functions the brain requires a large supply of blood. This object is effected through the THE CIRCULATIOX OF THE BLOOD. 217 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 variation from external circumstances than it is in other parts, and so the large arteries are very tortuous and anastomose freely in the circle of Willis, which thus insures that the supply of blood to the brain is uniform, 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 distention; and uniformity of sup- ply 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 communication Avith 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 some 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 distention 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 condition as a mass of nearly incompressible substance placed in a cav- ity with unyielding walls. These conditions of the brain and skull for- merly appeared, indeed, enough to justify the opinion that the quantity of blood in the brain must be at all times the same. But 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, there was congestion of the cerebral vessels; while in death by prussic acid, the quantity of blood in the cavity of the cranium was determined by the position in which the ani- mal was placed after death, the cerebral vessels being congested when the animal was suspended with its head downward, and comparatively empty when the animal was kept suspended by the ears. Thus, 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 simul- taneous diminution or increase 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 218 HANDBOOK OF PHYSIOLOGY. as readily effused, would serve as a kind of suj^plemental fluid to the other contents of the cranium, to keep it uniformly filled in case of variations in their quantity. And there can be no doubt that, although the arrangements of the blood-vessels, to which reference has been made, insure 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 cav- ity 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. 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, carbonates, alkaline and earthy phosphates, minute ti'aces of urea, sugar, sodium lactate, fatty matter, cholesterin, and albumen (Flint). 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 quan- tity of blood, become distended and swollen by it, and pass into the state which has been termed erection. Such structures are the corpora caver- nosa and corpus spongiosiim 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 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 variations of size, col- lapsing in the passive state of the organ, but, for erection, capable of an amount of dilatation 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 distention of the vessels, and, during the state of erection, give to the penis its condition 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 THE CIRCULATION OF THE BLOOD. 219 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 corjsora 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 condi- tion 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 accelerator urinse. Erection results from the distention of the venous plexuses with blood. The j)rincipal 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 ram- ify 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 eiSux 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 assist 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 ad- mit, upon occasion, augmented quantities of blood. The circulation in the Lungs, Liver, and Kidneys will be described under their respective heads. The Regulation of the Blood-Flow. The flow of blood is not always the same, but varies: — (a.) With alterations in the force and frequency of the contractions of the heart ; and (b.) "With variations of the peripheral resistance. It is obvious that the flow of blood may be increased under the following circumstances: — (a.) If the force and frequency of the heart's beats be increased, and the peripheral resistance be (1) unchanged, or be (2) diminished. (b.) If the force and frequency of the heart be unchanged, and the peripheral resistance be diminished. 220 HANDBOOK OF PHYSIOLOGY. And niiiy on the other hand be diminished: — (c.) If the force and frequency of the heart's beats be diminished, and if the peripheral resistance be (1) unchanged, or be (2) in- creased. (d.) If the force and frequency of the heart's beats be unchanged, and the peripheral resistance be increased. When the force and frequency of the heart's contractions are in- creased and at the same time the peripheral resistance is increased, the flow may be increased, diminislied, or unchanged, according as either of the two factors, one of which tends to increase the flow, and the other to diminish it, is more markedly increased, or if they are balanced. The complemental proposition is also true, that the flow may be increased, diminished, or unchanged, when the force and frequency of the heart's contractions are diminished, and the peripheral resistance is diminished. The conditions of increased flow and of increase of blood pressure are not the same. Indeed, the greatest blood-flow may occur when the blood pressure is low, i.e., when the peripheral resistance is diminished and the heart's beat is increased or is unchanged. In fact there is only one condition in which increased blood-flow is accompanied by increased blood-pressure, viz., when the heart's beat is increased and the periphe- ral resistance is unchanged. It will be necessary now to consider (a) the ivays in wliicli the force and frequency of the heart's heats are regulated ; and also (b) the ways in which the peri2)heral resistance is increased or diminished. We shall afterward be in a better position to discuss the variations of blood- pressure produced by different combinations of cardiac and arterial alterations. («.) The force and frequency of the contractions of the heart may be considered to de^Dend upon : 1. The properties and condition of the heart-muscle itself; 2. The influence of the central nervous system ; 3. The amount of the blood passing into the heart's cavities ; 4. The amount of jjressure to be overcome. Each of these factors must be considered seriatim. 1. The properties of the heart-imiscle. — It has already been pointed out that in structure the mugcular fibres of the heart differ from skele- tal muscle on the one hand, and from unstriped muscle on the other, occupying, as it were, an intermediate position between the two vari- eties. The heart-muscle, however, possesses a property which is not possessed by either skeletal or unstriped muscle, namely, the property of rhythmical contractility. The property of rhythmic contraction is shown by the action of the heart within the body; its systole is fol- lowed by its diastole in regular sequence throughout the life of the THE CIRCULATION OF THE BLOOD. 221 individual. The force aud frequency of the systole may vary from time to time as occasion requires, but there is no interruption to the action of the normal heart, or any interference with its rhythmical contrac- tions. Further, we find that in an animal rapidly bled to death, the heart continues to beat for a time, varying in duration with the kind of ani- mal experimentally dealt with, and in the entire absence of blood within the heart-chambers; and still further, if the heart of an animal be re- moved from the body, it still, for a varying time, continues its alternate systolic and diastolic movements. Thus we see that the power of rhythmic contraction depends neither upon connection with the central •c.s.d/. Fig. 193. Fig. 193 B. Fig. 193.— The heart of a frog (Rana esculenta) from the front. V, Ventricle; Ad, right auricle; As, left auricle; B. bulbus arterio-us, dividiug into right and left aortae. (Ecker.) Fig. 193 B.— The heart of a frog (Rana esculenta) from the back. s. v.. Sinus venosus opened ; c. s. .s-., left vena cava superior; c. s. d., right vena cava superior; c. i.. vena cava inferior ; r. p.. vena pulmonales; A.d., right auricle; A.s., left auricle; A.p., opening of communication between tlie right auricle and the sinus venosus, X 2^-3- (Ecker.) nervous system, nor yet upon the stimulation produced by the presence of blood within its chambers — it is automatic. The cause of this rhythmic power has been the subject of much discussion and experi- mental observation. Up to a comparatively short time ago, the remark- able property of the heart to continue its rhythmical contractions after removal from the body was believed to be connected in some way or other with the presence of collections of nerve cells, or ganglia in sev- eral parts of its tissue. Although this idea, as we shall presently see, has now been almost universally given up, it may be as well to describe shortly these ganglia in this place; they have been studied more partic- ularly in the heart of the frog, of the tortoise, and of other cold-blooded animals. 222 HANDBOOK OF PHYSIOLOGY. In the frog's heart (fig. 193) these ganglia consist of three chief groups. The first group is situated in the wall of the sinus venosus at the junction of the Sinus with the auricles (Remak's); the second group is placed near the junction between the auricles and rentricle (Bidder's); and the third in the septum between the auricles (v. BezokVs). The nerve cells of which these ganglia are composed are generally unipolar, and seldom bipolar: sometimes two cells are said to exist in the same envelope, constituting the ticin cells of Dogiel. The cells are large, and have very large round nuclei and nucleoli (fig. 195). Ganglion cells have not been found in the ventricle of the frog's heart below the auriculo-ventricular groove. As regards the automatic movements of the heart removed from the body our chief knowledge has been derived from the stud^ of the hearts of the frog and tortoise IT Fig. 19*. Fig. 194. — Course of the nerves in the auricular partition waU of the heart of a frog. d. Dorsal branch; v. ventral branch, (lacker.) Fig. 195.— Isolated nerve-cells from the frogs heart. I. Usual form. n. Twin cell. C, Capsule; K, nucleus; K', nucleolus; P, process. (Trom Ecker.^ 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 differ- ence from the beat of the heart before removal; it will take place, as we have mentioned, without the presence of blood or other fluid within its chambers. Xot only is this the case, but the auricles and ventricle may be cut off from the sinus, and both parts continue to pulsate, and fur- ther the auricles may be divided from the ventricle with the same result. 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 rhythmical contraction. It will be thus seen that the rhythmical movements appear to be more marked in the parts supplied by the ganglia, as the apical portion of the ventricle, in which ganglia have not been found, does not, under ordinary circumstances, possess the power of automatic movement. It has, however, been shown by C-askell that the extreme apex of the THE CIRCULATION OF THE BLOOD. 233 ventricle of the heart of the tortoise, wliich contains no ganglia, may under appropriate stimuli be made to contract rhythmically. This proves that the muscular tissue of the heart itself is capable of rhyth- mical contraction indeiDcndent of the ganglia. Thus it seems probable that the rhythmic contractility of the heart is a power inherent in the muscular tissue, which is quite independent as far as its commencement, at any rate, is concerned of nerve influence. The heart-muscle exhibits another property which distinguishes it from ordinary skeletal muscle, viz., the way in which it reacts to stimuli. The latter as will be described at greater length in its appropriate place, reacts slightly to a slight stimulus above the minimal, and with an in- crease of the strength of the stimuli will give increasingly ample con- tractions until the maximum contraction is reached; in the case of the heart- beats this is not so, since the ininimum stimulus tvhich has any effect is followed hy tlte maximum contraction; in other words the weak- est effectual stimulus brings out as great a beat as the strongest. There is another great difference between the contraction of the heart and of skeletal muscle, viz., the inability of the former to enter into a state of tetanus under the influence of stimuli repeated very rapidly. If the heart be stimulated by a series of rapid interrupted induction shocks, there is no summation of the contractions, as there would be supposing an ordinary skeletal muscle were stimulated in the same way. This phenomenon is said to be due to the following fact, viz., that in order to produce an extra contraction of the excised frog's heart, the stimulus must be applied during diastole or period of rest or relaxation, and in that case the next contraction happens at an earlier period than if the stimulus were not ajjplied. If applied during the systole, the stimulus has scarcely any effect; the period during which the muscle is refractory to stimuli is much longer in the case of the heart than in the case of other muscles. In order to produce a tetanus in skeletal muscle, the second stimulus must be sent into the muscle before it has had time to recover from the effect of the first stimulus and relax, and so on with the third, fourth, and other stimuli. If, as we may suppose, the same conditions for the production of tetanus are necessary in heart-muscle, the reasons of the impossibility of producing tetanus, i.e. that a stim- ulus applie during contraction is ineffectual, are sufficiently obvious. It appears, however, that if the stimuli are sufficiently strong and rap- idly repeated, the refractory period during which the muscle is prac- tically insensible to stimuli diminishes, and a very rapid repetition of the beats occurs, which may even develop the appearance of an incom- plete, but never of complete tetanus. In connection with the rhythmic contraction of muscle, it is neces- sary to allude briefly to what is known as Stannius' experiment. This experiment consisted originally of applying a tight ligature to the 224 HANDBOOK OF PHYSIOLOGY. heart between the sinus and the auricles, the effect of which is to stop the beat of the heart below the ligature, while the sinus and the veins leading into it continue to beat. If a second ligature be a^jplied at the junction of the auricles and ventricle, the ventricle may begin to beat slowly, while the auricles continue quiescent. In both cases the quies- cent parts of the heart may be made to give single contractions in response to mechanical stimulation. A considerable amount of discussion has arisen as to the explanation of these phenomena. It was suggested that the action of the ligature is to stimulate some inhibitory nervous mechanism in the sinus, whereby the auricles and ventricle can no longer continue to contract, but this suggestion must certainly be given up if the present theory as to the functions of the nerve ganglia be cor- rect. It may be that the effect of Stannius' ligature is simply an exam- ple of what has been called by Gaskell UocTcing. The explanation of this term is as follows : — it appears that under normal conditions the wave of contraction in the heart starts at the sinus and travels down- Avard over the auricles to the ventricle, the irritability of the muscle and the power of rhythmic contractility being greatest in the sinus, less in the auricles and still less in the ventricle, while under ordinary con- ditions the apical portion of the ventricle exhibits very slight irritability and still less power of spontaneous contraction. Thus it may be sup- posed that the wave of contraction beginning at the sinus is more or less blocked by a ring of muscle of lower irritability at its junction with the auricles, and again the wave in the auricles is similarly delayed in its passage over to the ventricle by a ring of lesser irritability, and thus the wave of contraction starting at the sinus is broken as it were both at the auricles and at the ventricle. By an arrangement of ligatures, or better, of a system of clamps, one part of the heart may be isolated from the other portion, and the contraction when stimulated by an induction shock may be made to stop in the portion of the heart-muscle in which it begins. It is not unlikely that the contraction of one portion of the heart acts as a stimulus to the next portion, and that the sinus contrac- tion generally begins first, since the sinus is the most irritable to stimuli, and possesses the power of rhythmic contractility to the most highly developed degree. It must not be thought, however, that the wave of contraction is incapable of passing over the heart in any other direction than from the sinus downward; it has been shown that by application of approprinte stimuli at appropriate instants, the natural sequence of beats may be reversed, and the contraction starting at the arterial part of the ventricle may pass upward to the auricles and then to the sinus in order. An exceedingly interesting fact with regard to the passage of the wave in any direction has been made out by partial division of the mus- cular fibres at any point, whereby one part of the wall of the heart is THE CIRCULATION OF THE BLOOD. 225 left connected with the other parts by a small portion of undivided muscular tissue, and the wave of contraction then being only able to pass to the next portion of the wall every second or third beat. Thus division of the muscle has much the same effect as partial clamping it in the same position, or of a ligature similarly applied, but not tied tightly. It may, therefore, be suggested that Stannius' ligature acts as a partial or complete block, and prevents the stimulus of the sinus-beat from passing further down the heart, but that the parts below the liga- ture may be made to contract by stimuli applied to them directly. Nearly all the information to be obtained as to the phenomena of the contraction of heart-muscle apart from the rhythmic action of the organ itself, may be obtained from a heart to which a Stannius' ligature has been applied; indeed, the eifect of minimal stimuli, the effect of rapidly repeated shocks, and the refractory period of heart-muscle may all be studied from a heart in this condition. The velocity of the wave of contraction in frog's heart-muscle has been shown to be f to | inch, or 10-15 cm. a second. In pointing out the differences between the phenomena of contrac- tion in skeletal and heart-muscle, the similarities between the two are not to be overlooked; thus it has been shown that the effect of cold, heat, fatigue, and other influences have very much the same effect in both cases. 2. The inftuence of the central nervous system. The heart is capable of automatic rhythmic movement, as has been clearly shown by its behavior when removed from the body, and it has been shown further that there is reason for believing that the power resides in the inherent property of its muscle fibres themselves. While in the body, however, the heart's beats are under control of the central nervous system. To this nervous control, we must next direct our at- tention. The influence which is exerted by the central nervous system appears to be of two kinds, firstly, i^i the direction of slowing or inhibit- ing the heats, and secondly, in the direction of accelerating or augment- ing the l>eats. The influence of the first kind is brought to bear upon the heart through the fibres of the vagi nerves, and that of the second kind through the sympathetic fibres. Influence of the Vagi. — It has long been known, indeed ever since the experiments of the Bros. Weber in 1845, that stimulation of one or both vagi produces slowing of the beats of the heart. It has since been shown in all of the vertebrate animals experimented with, that this is the normal action of vagus stimulation. Moreover, section of one nerve, or at any rate of both vagi, produces acceleration of the pulse, and stim- ulation of the distal or peripheral end of the divided nerve produces normally slowing or stopping of the heart's beats. It appears that any kind of stimulus produces the same effect, either 15 226 HANDBOOK OF I'll VSIOLOfi Y. cliemical, mechanical, electrical, or thermal, but that of these the most potent is a rapidly interrupted induction current. A certain amount of confusion has arisen as to the effect of vagus stimulation in conse- quence of the fact that within the trunk of the nerve is contained, in some animals, fibres of the sympathetic, and it depends to some extent upon the exact position of the application of the stimulus, us to the exact effect produced. Speaking generally, however, excitation of any part of the trunk of the vagus produces inhibition, the stimulus being particularly potent if applied to the termination of the vagi in the heart itself, where they enter the substance of the organ at the situation of the sinus ganglia. The stimulus may be applied to either vagus with effect, although it is frequently more potent if applied to the nerve on the right side. The effect of the stimulus is not immediately seen; one or more beats may occur before stoppage of the heart takes place, and slight stimulation may produce only slowing and not complete stoppage "^^lifiiififi Fig. 196. — Tracing showing the actions of the vagus on the heart. Aur., Auricular; vent., ven- tricular tracing. The part between perpendicular lines indicates period of vagus stimulation. C.S indicates that the secondary coil was H cm. from the primary. The part of tracing to the left shows the i-egular contractions of moderate height before stimulation. During stinuilation, and for some time after, the beats of auricle and ventricle are arrested. After they commence again they are single at first, but soon acquire a much greater amplitude than before the application of the stimulus. (From Bruntou, after Gaskell.) of the heart. The stoppage may be due either to prolongation of the diastole, as is usually the case, or to diminution of the systole. Vagus stimulation inhibits the spontaneous beats of the heart only, it does not do away with the irritability of the heart-muscle, since mechanical stim- ulation may bring out a beat during the still-stand caused by vagus stimulation. The inhibition of the beats varies in duration, but if the stimulation be a prolonged one, the beats may reappear before the cur- rent is shut off. When the beats reappear, the first few are usually feeble, and may be auricular only; after a time the contractions become more and more strong, and very soon exceed both in amplitude and. frequency those which occurred before the application of the stimulus (fig. 196). Influence of the Sympathetic. — The influence of the sympathetic may be considered, to a certain extent, as the reverse of that of the vagus. Stimulation of the sympvithetic, even of one side, produces ac- THE CIRCULATION OF THE BLOOD. 227 celerutiou of the heart-beats, and according to certain observers, section of the same nerve produces slowing. The acceleration produced by stim- ulation of the sympathetic fibres is accompanied by increased force, and so the action of the nerve is more properly termed augmentor. The action of the sympathetic differs from that of the vagus in several par- ticulars besides the augmentation which is produced : firstly, the stimulus required to produce any effect must be more powerful than is the case with the vagus stimulation; secondly, a longer time lapses before the effect is manifest; and thirdly, the augmentation is followed by exhaus- tion, the beats being after a time feeble and less frequent. Origin of the cardiac nerve-fibres. — The fibres of the sympa- thetic system, which influence the heart-beat in the frog, leave the spinal cord by the anterior root of the third spinal nerve, and pass thence by the ramus communicans to the third spinal ganglion, thence to the second spinal ganglion, and thence by the annulus of Vieussens Fig. 197. — Tracing showing diminished amplitude and slowing of the pulsations of the auricle and ventricle without complete stoppage during irritation of the vagus. (From Brunton, after Gaskell.) (round the subclavian artery) to the first spinal ganglion, and thence in the main trunk of the sympathetic, to near the exit of the vagus from the cranium, where it joins that nerve and runs down to the heart within its sheath, forming the joint vago-sympathetic trunk. In the dog, the augmentor fibres leave the corfl by the second and third dorsal nerves, and possibly by anterior roots of two or more lower nerves, passing by the rami communicantes to the ganglion stellatum, or first thoracic ganglion, thence by the annulus of Vieussens to the inferior cervical g.nglion of the sympathetic fibres from the annulus, or from the inferior cervical ganglion proceed to the heart. From the fact that the augmentor fibres are joined to the vagus trunk, it may be understood that the effect of the stimulation of the vagus in the frog is not in all cases purely inhibitory, but may be aug- mentor, according to the position where the stimulus is applied, the intensity of the stimulus, and the condition of the heart; if it is beating strongly a slight vagus stimulation will produce immediate inhibition. The fibres of the vagus which pass to the heart arise in the medull.i 228 HANDBOOK OF PHYSIOLOGY. oblongata, in the floor of the fourth ventricle, and in a nucleus of gray matter, the exact position of which will be indicated in a future chapter. It has been found that stimulation of this nucleus, which is called the cardio-inhibitory centre, produces inhibition of the heart-beat. Thus there is no doubt 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 the centre in the medulla oblongata which is always in operation. The restraining influence of the centre in the medulla may be reflexly increased by stimulation of almost any afferent nerve, particularly of the abdominal sympathetic, so as to pro- duce slowing or stoppage of the heart, through impulses from it passing down the vagi. As an example of this reflex stimulation, the well- known effect on the heart of a violent blow on the ei^igastrium may be referred to. The stojjpage of the heart's action in this case is due to the conveyance of the stimulus by flbres of the sympathetic (afferent) to the medulla oblongata, and its subsequent rcjiectioii through the vagi (efferent) to the muscular substance of the heart. It is possible that the power of the medullary inhibitory centre may in a similar manner be reflexly lessened so as to produce accelerated action of the heart. In the mammal the fibres in the vagus, by means of which inhibitory influences are conveyed to the heart, are derived from the spinal acces- sory nerve, since when that nerve is divided certain fibres of the vagus trunk degenerate, and afterwards stimulation of the vagus trunk no longer produces inhibition. The spinal accessory fibres are fine medul- lated fibres, 2,'j- to 3,a in diameter, and may be traced to the heart, and lose their medulla in the ganglia of that organ. The fibres of the vagus traceable into the heart muscle, have been found to be both niedullated and non-medullated when they enter; they pass out of Remak's ganglion more generally as niedullated nerves, forming the nerve-fibres of the septum, but after these septal fibres issue from Bidder's ganglia, they enter the ventricle ag non-medullated nerves, in the frog at any rate, but in mammals a few fibres are niedullated. The sympathetic fibres, on the other hand, reach the heart as non-medullated fibres, having lost their medulla in the sympathetic ganglia. The course of the augmentor fibres in the spinal cord is not known, but it is thought that in all probability they are connected with an aug- mentor centre in the medulla. The circulation of venous blood appears to stimulate the inhibitory centre, and of highly oxygenated the aug- mentor centre. In addition to direct and reflex stimulation it is almost certain that impulses passing down from the cerebrum may have a similar effect. Other Influences Affecting the Heart-Beat. — Alteration of tempera- ture.—The effect of cold is to slow the heart-beats, and if the heart be cooled down to 3° C. (38° F.) it will stop beating. The heart may be THE CIRCULATION OF THE BLOOD. 229 frozen, and when thawed will continue its spontaneous beats. The elfect of heat is to quicken and shorten the heart-beats, but at a moder- ate temperature, 20° C. (68°F.), the contractions are increased in force. At or below 40° C. (104° F.) the contractions are so rapid as to pass into heart-rigor; this may be stopi^ed by cooling. Poisons and other chemical substances.— A large number of chemical substances have a distinct effect upon the cardiac contractions. Of these the most imj^ortant are atroinn and inuscarin. Atropin produces considerable augmentation of the heart-beats, and when acting upon the heart prevents the results of vagus stimulation. Muscarin (obtained from various species of poisonous fungi) pro- duces marked slowing of the heart-beats, and, in larger doses, stoppage of the heart. It produces a similar effect to that of prolonged vagus stimulation, and as in that case the effect can be removed by the action of atropin. Digitalin (the active principle of digitalis purpurea), slows the heart and appears to act by stimulating the vagi. Later on the muscle is also more excitable. Veratrin and aconifin have a similar effect. Nicotine prevents the effect of vagus stimulation. Methods of investigating the Heart-beat. (1) The simplest foi-m of an apjmratus to be used for recording the contrac- tions of the frog's heart consists of a small closed cylindrical box fixed to a stand. At the bottom of the box are two tubes by means of which water at various temperatures may be made to circulate through it, one tube being the inlet and the other the outlet, and they are connected with india-rubber, suit- able for the purpose of conducting water to and from the apparatus. The lever is made of a piece of glass rod which is softened and drawn out in the flame of the blow-pipe a very fine thread, leaving a small piece unaltered to act as a counterpoise. The lever is then passed through a piece of cork and through this cork a fine needle is inserted at right angles to the lever. The needle is made to rest on a support attached above one side of the box in such a way that the lever has free movement up and down. Another small piece of cork is passed along the lever arm and is adjusted and cut so that its point directed downward can rest upon the frog's heart, which is removed from the body and placed upon the top of the box in serum or defibrinated blood. In this way the contractions of the auricles and ventricle are communicated to the lever, and this may be made to write upon a recording cylinder. (2) The variations of endocardial pressure, M-hich correspond, of course, with the various phases of the cardiac cycle, may be recorded by a modifica- tion of the ordinary mercurial manometer. The apparatus is best used with a large frog (Rana esculenta), and the heart is exposed in the usual manner, the pericardium opened. A cut is made into the bulb, and by this means a double or perfusion canula (fig. 198) is passed into the ventricle, a ligature is passed round the heart, and the canula is tied in tightly. The vessels are then di- vided beyond the ligature, and the canula, with the heart attached, is removed. To one stem of the canula a tube is attached, communicating with a reservoir 230 HANDBOOK OF PHYSIOLOGY. of a solution of dried blood iu .0 saline solution, and filtered, which is capa- ble of being raised or lowered in temperature by being surrounded by a metal box which contains hot, cold, or iced water. Attached to the other end is a similar tube, which communicates by a T piece with a small mercurial man- ometer, provided with a writing style, and also with a vessel into which the serum is received. The apparatus being arranged so that the movements of the mercury can be recorded by the float and the writing style on a slowly revolving drum, and after some serum has been allowed to pass freely through the ventricle, both tubes are clipped, the second one beyond the T piece, and the alterations in the pressure are recorded. The effects of fluids at various temperatures and of poisons may be recorded in the manner indicated above. (3) By Roy's Tonometer (fig. 199) the alterations in volume which a frog's heart undergoes during contrac- tion are recorded by the follow- ing means : A small bell -jar, open above, but provided with a firmly fitting cork, in which is fixed a double canula, is ad- justable by a smoothly ground base upon a circular brass plate, Fig. 198. Fig. 199. Fig. 198.— Kronecker's Perfusion Canula, for supplying Fluids to the interior of the Frog's Heart. It consists of a double tube, one outside the other; the end view is shown in the engraving. The inner tube branches out to the left: thus, when the ventricle is tied to the outer tulie of the can- ula, a current of liquid can be made to pass into the heart by one tube and out through the other. Fig. 199.— Roy's Tonometer. about 2 to 3 inches in diameter. The junction is made complete by greas- ing the base with lard. In the plate, which is fixed to a stand adjustable on an upright, are two holes, one in the centre, a large one about one-third of an inch in diameter, to which is fixed below a brass grooved collar, about half an inch deep ; the other hole is the opening into a pipe provided with a tap (stopcock) . The opening provided with the collar is closed at the lower part with a membi-ane of animal tissue, which is loosely tied by means of a ligature around the groove at the lower edge of the collar. To this mem- brane a piece of cork is fastened by sealing-wax, from which passes a wire, which can be attached to a lever, fixed on a stage below the apparatus. When using the apparatus, the bell-jar is fixed by means of lard, and the jar is filled with olive oil. In the way above described, the heart of a large frog is prepared and the canula fixed in the cork is firmly tied into the heart ; the tubes of the canula communicating with the reservoir of serum on the THE CIRCULATIOX OF THE BLOOD. 231 one hand, and with a vessel to contain the serum after it has run through on the other. The canula with heart attaclied is passed into the oil, and the cork firmly secured. By these means the lever will be found to be adjusted to a convenient elevation. The lever is allowed to write on a moving drum, and serum is passed through at various temperatures. After a short time the heart may stop beating ; but two wires are arranged, the one in the canula, the other projecting from the plate in such a way that the heart can be moved against them by shifting the position of the bell-jar a little. The wires act as electrodes, and can be made to communicate with an induction apparatus, so that single induction shocks can be sent into the heart to produce contractions, and if need be, by means of the trigger key, at one definite point in the revo- lution of the recording cylinder. Electrical Phenomena of the Heart-beat. — The phenomena of the natural beat of the heai't are generally considered to indicate that the systolic coutraction is a single and not a tetanic one. The electrical changes support this view. During the contraction a distinct electrical change occurs which is similar to that which happens in skeletal muscle with each contraction. It has been demonstrated that a stanniused frog heart undergoes two changes or phases as regards its electrical con- dition, the first immediately before the contraction, in which the excited part becomes negative to the other parts, contraction following the wave of excitation, and the second during relaxation, in which the cur- rent flows in an opposite way. The Metabolism of the Heart. — Whatever view may be taken of the nature of the rhythmic cardiac contractions, it will be genemlly acknowledged that the contractions cannot long be maintained without a due supply of blood or of a similar nutritive fluid. Some very re- markable facts have been made out about this, in the case of the frog's heart. For instance, it has been shown that normal saline solution is insufficient to maintain the contractions, and that in experiments in which it is necessary to maintain the beats for any length of time failing serum or saline solution of dried blood, the solution should contain some serum-albumin, and that there should also be present some potas- sium chloride, and Dr. Kinger has com];)osed a nutritive fluid which contains chlorides of sodium, potassium, and calcium in small amounts, which is able to maintain the normal beats of the heart. It is therefore very reasonable to suppose that the amount and quality of the blood supplied to the human heart has the greatest influence in maintaining the force and frequency of the rhythmic activity. The view that is taken at present of the action of the heart is one propounded by Gaskell, viz., that in heart muscle as in protoplasm generally, the metabolic pro- cesses are those of anabolism or building up, which takes place during the diastole of the heart, that vagus stimulation helps on this process, iind of catabolism or discharge, which is manifested in the contraction of the heart, and which is accelerated by stimulation of the sympathetic 232 HANDBOOK OF PHYSIOLOGY. fibres. That vagus stimulation is therefore ultimately beneficial to the contractions. The electrical currents set up on the stimulation of the vagus and of the sympathetic are in opposite directions, and so if Gas- kell's contention is correct that the negative variation of the muscle current occurring on sympathetic stimulation is a sign of catabolism, the result of vagus stimulation, viz., a positive variation of the muscle cur- rent, may be supposed to indicate the complementary condition of ana- bolism. 3. The Amount of Blood Passing into the Heart's Cavities. — It is found that in the body at any rate the amount of blood which passes into the cavities of the heart distinctly affects the strength of its beat. Thus if from any cause the blood is diminished the contractions become much Fig. 200.— Plethysmograph. By means of this apparatus, the alteration in volume of the arm, E, which is inclosed 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, fluidpasses 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. Appa- ratus founded upon the same principle have been used for recording alterations in the volume of the spleen and kidney. more feeble, although they may possibly be increased in rapidity. Simi- larly with 4. Ihe Amount of Pressure to he Overcome. — If the aortic pressure is too low the muscle contractions of the heart is not so powerful or effec- tive as if the pressure is normal, whereas too great arterial pressure may be sufficient to delay if not to stop altogether the heart's beats, dilata- tion of its cavities taking place and a condition of asi/stolism (Beau) resulting. Another condition sometimes forgotten should be added as influenc- ing the potency of the cardiac contraction, viz., the heart must have sufficient room to contract, it must not be unduly pressed upon. (b.) The Peripheral Resistance. — The regulation of the amount of resistance to the passage of blood at the perijjhery is principally done THE CIRCULATION" OF THE BLOOD. 233 by the alteration of the calibre of the arterioles. This regulating power is chiefly invested in the nervous system. Its influence is exerted upon the muscular coat of the arteries and not upon the elastic element, which possesses, as must be obvious, rather j^hysical than vital properties. The muscular tissue in the walls of the vessels increases in amount rel- atively to the other coats as the arteries grow smaller, so that in the arterioles it is developed out of all proportion 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 appear- ance of muscular fibres. Thus the nervous system is more powerful in regulating the calibre of the smaller than of the larger arteries. It was long ago shown by Claude Bernard that if the cervical sym- pathetic nerve is divided in a rabbit, the blood-vessels of the correspond- ing side of the head and neck become dilated. This effect is best seen in the ear, which if held up to the light is seen to become redder, and the arteries are seen to become larger. The whole ear is distinctly warmer than the opposite one. This effect is produced by removing the arteries from the influence of the central nervous system, which in- fluence normally 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 is very strong or very long continued, the point of normal con- striction is passed, and the vessels become much more contracted than nor- mal. The natural condition, which is about midway between extreme con- traction and extreme dilatation, is called the natural tone of an artery; if this is not maintained, the vessel is said to have lost tone, or if it is exaggerated, the tone is said to be too great. 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 body there exists a nerve the division of which produces the same effects, viz., dilatation of the vessels; such may be cited as the case with the sciatic, the splanchnic nerves, and the nerves of the brachial plexus: when these are divided, dilatation of the blood-vessels in the parts supplied by them takes place. It appears, therefore, that nerves exist which have a distinct control over the vas- cular supply of every part of the body. These nerves are called vaso- motor; they run now in cerebro-spinal, now in the sympathetic nerve- trunks. Vaso-motor centres. — Experiments by Ludwig and others show that the vaso-motor fibres come primarily from a nucleus of gray matter, vaso-motor centre, in the bulb or medulla oblongata, being situated in the floor of the fourth ventricle, between the calamus scriptorius and 234 HANDBOOK OF PHYSIOLOGY. the corfora quadrigmnina. Thence the vaso-motor fibres pass down in the spinal cord, and issuing with the anterior roots of the spinal nerves, traverse the various ganglia on the prae-vertebral cord of the sympathetic, and, accompanied by branches from those ganglia, pass to their des- tination. Secondary or subordinate vaso-motor centres exist in the spinal cord, and the influence exerted by the chief vaso-motor centre is not only in constant moderate action, but may be altered in several ways, but chiefly by afferent (sensory) stimuli. These stimuli may act in two ways, either increasing or diminishing the usual action of the centre, which maintains a medium tone of the arteries. This afferent influence upon the centre (augmenting or inhibiting) is well shown by the action of a nerve called Fie:. 201 .—Tracing showing the effect on blood-pressure of stimulating the central end of the Deprtssor nerve in the rabbit. To be read from right to left. T. indicates the rate at which the recording surface was travelling, the intervals corresjioiul to seconds: C, the moment of entrance of current; O, moment at which it was shut off. Tlie 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. (Foster.) the depressor, the existence of which was demonstrated by Cyon and Ludwig. It is a small afferent nerve and passes up from the heart in which it takes its origin, and in the rabbit goes upward in the sheath of the su- perior laryngeal briinch of the vagus or with that branch and the vagus itself, communicating by filaments with the inferior cervical ganglion as it proceeds from the heart. If during a blood-pressure observation in a rabbit this nerve be di- vided, and the central end {i.e., that nearest the brain) be stimulated, a remarkable fall of blood-pressure takes place (fig. 201). The cause of the fall of blood-pressure is found to proceed from the dilatation of the vascular district within the abdomen suiDplied by the splanchnic nerves, in consequence of which the vessels hold a much larger quantity of blood than usual. The engorgement of the splanch- nic area very greatly diminishes the amount of blood in the vessels else- THE CIRCULATIOX OF THE BLOOD. 235 where, and so materially diminishes the blood-pressure. The function of the depressor nerve is presumed to be that 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, that the heart cannot, with sufficient ease, propel blood into the already too full or too tense arteries (p. 233). The action of the depressor nerve in causing an inhibition of the vaso-motor centre illustrates the more unusual effect of afferent impulses. As a rule, the stimulation of the central end of an afferent nerve pro- duces a reverse or pressor effect, and increases the tonic influence of the centre, and by causing constriction of the arterioles, either locally or generally, raises the blood-pressure. Thus the effect of stimulating an afferent nerve may be, by its influence on the vaso-motor centre, either to dilate or to constrict the arteries. Stimulation of an afferent nerve too 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 which must evidently have an immense influence in increasing the flow of blood through the part. The vaso-motor centre may not only be reflexly affected, but it may also be affected by impulses proceeding to it from the cerebrum, as in the case of hlusliing from" mind disturbance, or of pallor from sudden fear. It will be shown, too, in the chapter on Respiration that the cir- culation of venous blood may directly stimulate the centre itself. Although the tone of the arteries is influenced by the centres in the cerebro-spinal axis, experiments have proved that this is not the only way in which it may be influenced. 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 local stimulation, e.g., the application of heat or cold, will cause dilatation or constriction. This is probably the effect of the direct stimulation of the muscle of the walls of the vessels. The observations upon the functions of the vaso- motor nerves themselves 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 ends produce constriction; (2) those on division of which momentary dilatation followed by constriction oc- curs, with dilatation on stimulation; (3) those on division of which di- latation 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 236 HANDBOOK OF PHYSIOLOGY. a,nd 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 symiwthetic vaso-constrictors. The vaso-dilator nerves are believed to act upon the bloud-vessels just in the same way as the vagus does upon the heart, they are vuso-inliibitory, or anabolic nerves. In the same way the vaso-constrictor are vaso-augmentor, like the sympa- thetic heart fibres, or in other words, catabolic nerves to the blood-vessels. The following table may serve as summary of the effect of the altera-- Hon of the 'peripheral resistance upon the blood-pressure : — A. An increase of the blood-pressure may be produced: — (1.) By stimulation of the vaso-motor centre in the medulla, either a. Directly, as by carbonated or deoxygenated blood. /?. Indirectly, by impressions descending from the cerebrum, e.g., in sudden pallor. ■y. Reflexly, by stimulation of afferent or pressor nerves any- where, which increases the action of the centre. (2.) By stimulation of the centres in spinal cord. Possibly directly or indirectly, certainly reflexly. (3.) By stimulation of each vascular area 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 the medulla, either (a) Directly, as by oxygenated or aerated blood. (/3) Indirectly, by impressions descending from the cere- brum— e.g., in blushing. (7) Reflexly, by stimulation of the depressor nerve, and con- sequent dilatation of vessels of splanchnic area, and pro- ducing inhibition of the centre by stimulation of other sensory nerves. (3.) By stimulation of the centres in spinal cord. Possibly directly, indirectly, or reflexly. (3.) By stimulation of each vascular area directly, e.g., by means of altered blood, or by heat. Besides the regulation of the heart beat and of the peripheral resist- ance, it must be recollected that other circumstances may affect the blood pressure, of which changes in the blood are the chief. First of all — a. As regards quantity. At first sight it would appear probable that one of the easiest ways to diminish the blood-pressure would be to re- move blood from the vessels by bleeding. It has been found by experi- ment, however, although the blood-pressure sinks while large abstractions of blood are taking place, that 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. THE CIRCULATIOX OF THE BLOOD. 237 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 do- ing maintain pressure on the blood and favor its accumulation in the arterial system. This is due to the stimulation of the vaso-motor cen- tre 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 resist- ance. In the same way it might be thought that injection of blood into the already 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 abstracted, the vaso-motor apparatus must counter- act the great increase of pressure, but now by dilating the small ves- sels, 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 re- membered that the veins are capable of holding the whole of the blood of the body. Further, as we have seen, the amount of blood supplied to the heart, both to its substance and to its chambers, has a marked effect upon the blood-pressure. b. 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 oxygenated 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, and so directly alter- ing the calibre of the vessels. Proofs of the Circulation of the Blood. It seems hardly necessary at the present time to bring forward the proofs that during life the blood circulates within the body; they are so well Jcnown. It is interesting, however, to recount the main argu- ments by which Harvey in the first instance established the fact of the circulation; they were as follows: — 1. That the heart in half an hour propels more blood than the whole mass of blood in the body; 238 HANDBOOK OF PHYSIOLOGY. 3. That the blood spurts with great force and in a jerky manner from an opened artery, such as the carotid, with every beat of the heart ; 3. That if true, the normal course of the circulation would explain why after death the arteries are commonly found empty and the veins full; 4. That if the large veins near the heart be tied in a fish or snake, the heart becomes pale, flaccid, and bloodless; and that on moving the ligature, the blood again flows into the heart. If the artery is tied, the heart becomes distended, the distention lasting until the ligature is removed ; 5. That if a ligature round a limb be drawn very tight, no blood can enter the limb, and it becomes pale and cold. If the ligature be some- what relaxed, blood can enter but cannot leave the limb; hence it be- comes swollen and congested. If the ligature be removed, the limb soon regains its natural appearance; 6. That the valves in the veins only permit the blood to flow toward the heart; 7. That there is general constitutional disturbance resulting from the introduction of a poison at a single point, e.g., snake poison; To these may now be added many further proofs which have accu- mulated since the time of Harvey, e.g. : — 8. That in wounds of arteries and veins; in the former case hemor- rhage may be almost stopped by pressure between the heart and the wound, in the latter by pressure beyond the seat of injury; 9. That 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., may actu- ally be observed under the microscope. 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 circulation. The only part of the circulation which Harvey could not follow was that through the capillaries, for the simple reason that he had no lenses sufficiently powerful to enable him to see it. Malpighi (1661) and Leeuwenhoek (16C8) demonstrated this in the tail of the tad- pole and lung of the frog. CHAPTER YII. RESPIRATION. The maintenance of animal life necessitates the continual absorption of oxygen and excretion of carbonic acid; the blood being, in all ani- mals 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 bv 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, qxq specially constructed for bringing the blood into proximity with the aerating medium (atmospheric air, or water con- taining 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 practically 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 sep- aration 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 difference 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 difference in the respiratory capacity of different animals. The num- ber and size of the red blood-corpuscles, the mechanism of the breathing apparatus, the presence or absence of a pulmonary heart, physiologically distinct from the systemic, are, all of them, conditions scarcely second in importance. It may be as 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-pro- 289 240 HAXDBOOK OF PHYSIOLOGY. cesses of which the production of carbonic acid is the final result. These processes occur in all parts of the body in the substance of the tissues. Of the Respiratory Apparatus. The object of respiration being the interchange of gases in the lungs, it is necessary that the atmospheric air shall pass into them and that the changed air should be expelled from them. The lungs are contained in the chest or thorax, which is a closed cavity having no communica- Fig. 202. Fig. 203. Fig. 203.— Outline showing the general form of the larj-nx, trachea, and bronchi, as seen from before, h, Tlie great cornu of the hyoid bone; e, epiglottis; t, superior, and t', inferior coruu of tl.e thyroid cartilage; c. middle of the cricoid cartilage ; tr, the trachea, sliowing sixteen cartilaginous rings; b, the right, and b', the left bronchus. (Allen Thomson.) x i4- Fig. 203. — Outline showing the general form of the larynx, trachea, and bronchi, as seen from behind, h, Gi-eat cornu of the hyoid bone; f, superior, and t'. the inferior cornu of the thyroid cartilage; e, epiglottis; a, points to the back of both the arytenoid cartilages, which are sur- mounted by the cornicula ; c, the middle ridge on the back of the cricoid cartilage; tr, the pos- terior membranous part of the trachea; 6, 6', right and left bronchi. (Allen Thomson.^ x i^. RESPIRATION. 241 tion with the outside, except by means of the respiratory passages. The air enters these passages through the nostrils or through the mouth, thence it passes through tlie hirynx 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 leads exclusively to the lung; it is formed by the thyroid, cricoid, and arytenoid cartilages (fig. 202), and contains the vocal cords, by the vibration of which the voice is chiefly produced. These vocal cords are ligamentous bands attached to certain cartilages capable of movement by muscles. By their approximation the cords can entirely close the entrance into the larynx; but under ordinary conditions, the entrance of the larynx is formed by a more or less triangular chink between them, called the rima glottidis. 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 ejnglottis (fig. 203, e). The whole of the larynx is lined by mucous membrane, which, however, is extremely thin over the vocal cords. At its lower extremity the larynx joins the trachea.* With the exception of the epiglottis and the so- called cornicnla laryngis, the cartilages of the larynx are of the hyalin variety. The Epiglottis. — The supporting cartilage of the ejjiglottis is com- posed of yellow elastic cartilage, inclosed in a fibrous sheath (perichon- drium), and covered on both sides with mucous membrane. The ante- rior surface, which looks toward the back of the tongue, is covered with mucous membrane, the basis of which is fibrous tissue, elevated toward both surfaces in the form of rudimentary papillfe, and covered with several layers of squamous epithelium. In it ramify capillary blood- vessels, 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, is a number of tubular glands. The posterior or laryn- geal surface of the epiglottis is covered by a mucous membrane, similar in structure to that on the other surface, but its epithelial coat is thin- ner, the number of strata of cells is less, and the papillae few and less distinct. The fibrous tissue which constitutes the mucous membrane is in great j^art of the adenoid variety, and is here and there collected into distinct masses or follicles. The glands of the posterior surface are smaller but more numerous than those of 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 carti- * A detailed account of the structure and function of the Larynx will be found ill a later chapter. i6 242 HANDBOOK OF PHYSIOLOGY. lage pass tnrough and open upon the mucous surface of the other side. Taste goblets have been found in the epithelium of the posterior surface of the epiglottis, and in several other situations in the laryngeal mucous membrane. The Trachea and Bronchi. — The trachea extends from the cricoid cartilage, which is on a level with the fifth cervical vertebra, to a point opposite the third dorsal vertebra, where it divides into the two bronchi. ^-^7 3^'< Fig 204.— Section of the trachea, o, Columnar ciliated epithelium; h and c, proper structure of the mucous membrane, containing elastic fibres cut across transversely; d, submucuous tissue containing mucous glands, e, separated from the hyaline cartilage, g, by a fine fibrous tissue, /; /i, external investment of fine fibrous tissue. (S. K. Alcock . ) one for each lung (fig. 203). 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, and 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 circumfer- ence), and are deficient behind; the interval between their posterior extremities being bridged over by a continuation of the fibrous mem- KESPIRATION". 243 brane in which they are closed (fig. 204). The cartilages of the trachea and bronchial tubes are of the hyaline variety. Immediately within this tube, at the back, is a layer of unstriped muscular fibres, which extends, transversely, between the ends of the cartilaginous rings to which they are attached, and opposite the inter- vals between them, also; their evident function being to diminish, when required, the calibre of the trachea by approximating the ends of the cartilages. Outside there are a few longitudinal bundles of muscular tissue, which, like the preceding, are attached both to the fibrous and cartilaginous framework. The mucous membrane consists to a great extent 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 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 mem- brane. Beneath these are one or more layers of more irregularly-shaped cells. Many of the superficial cells are of the goblet variety. In the deeper part of the mucosa are many elastic fibres between which lie connective-tissue corpuscles and capillary blood-vessels. Numerous mucous glands are situated on the exterior and in the substance of the fibrous framework of the trachea; their ducts perforat- ing the various structures which form the wall of the trachea, and open- ing 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. 202), resem- ble the trachea exactly in structure, with the difference that in them there is a distinct layer of unstriped muscle arranged circularly beneath the mucous membrane, forming the mnscularis mucosm. On entering the substance of the lungs the cartilaginous 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 distributed 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 sub- divisions of the lungs, called lobvles. All the lai-ger branches have walls formed of tough membrane, con- taining portions of cartilaginous rings, by which they are held open, and unstriped muscular fibres, as well as longitudinal bundles of elastic tis- sue. They are lined by mucous membrane, the surface of which, like 244 HANDBOOK OF PHYSIOLOGY. that of the larynx and trachea, is covered with ciliated epithelium, but the several layers become less and less distinct until the lining consists of a single layer of more or less cubical cells covered with cilia (fig. 205). The mucous membrane is abundantly provided with mucous glands. As the bronchi become smaller and smaller, and their walls tliinner, the cartilaginous rings become scarcer and more irregular, until, in the smaller bronchial tubes, they are represented only by minute and scat- tered cartilaginous flakes. And when the bronchi, by successive branches are reduced to about j^ of an inch (.6 mm.) 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, however, by a thin mucous membrane, with ciliated epithe- lium, the length of the cells bearing the cilia having become so far diminished that the cells are now almost cubical. In the smaller bron- <5^o ^i Fig. 205.— Transverse section of a bronchus, about i^ inch in diameter, e. Epithelium (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 ; g, mucous gland. (F. E. Schulze.) chi the circular muscular fibres are relatively more abundant than in the larger bronchi, and form a distinct circular coat. The Lungs and PlenrcB. — 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 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. Each lung is enveloped by a serous membrane — the pleura, one layer of which adheres closely to its surface, 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 membranes, will be best understood by reference to fig. 206. The appearance of a space, however, between RESPIEATION". 245 the pleura which covers the king {visceral layer), and that which lines the inner surface of the chest ( parietal layer), is inserted in the draw- ing only for the sake of distinctness. These layers are, in health, every- wJiere in contact, one with the other; and between them is only just so much fluid as will insure gliding easily, in their expansion and contrac- tion, 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 it and the chest-wall. In other words, the natural elasticity of the lungs would cause them at all times to contract Fig. 206.— Transverse section of the chest. away from the ribs were it not that the contraction is resisted by atmos- pheric pressure which bears only on the inner surface of the air-tubes and air-cells. On the admission of air into the pleural sac, atmospheric pressure bears alike on the inner and outer surfaces of the lung, and their elastic recoil is thus no longer prevented. 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 transparent when the lung is ex- panded, but become smaller, thicker, and granular when the lung col- lapses. In the pleura is a lymph-canalicular system; and connective tissue corpuscles are found in the fibrous tissue which forms its ground- work. The inner, looser, or sub-pleural tissue contains lamellae of fibrous connective tissue and connective-tissue corpuscles between them. Nu- merous lymphatics are to be met with, which form a dense plexus of vessels, many of which contain valves. They are simple endothelial 246 HANDBOOK OF PHYSIOLOGY. 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 the an- terior and internal surfaces of the lungs, the parts which move most Fig. 207.— Ciliary epithelium of the human trachea, a. Layer of longitudinally arranged elastic fibres ; b, basement membrane ; c, deepest cells, circular in form ; d, intermediate elongated cells ; e, outermost layer of cells fully developed and bearing cilia. X 350. (Kolliker.) 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 lob- Fig. 208. i- ig. 209. Fig. 208.— Terminal orauch of a bronchial tube, with its infundibula and air-cells, from the mar- gin of the lung of a monkey, in jected with quicksilver, a. Terminal bronchial twig; bb, infundibula and air-cells. X 10. (F. E. Schulze.) Fig. 209.— Two small infundibula or groups of air-cells, a o, with air-cells, b b. and the ultimate bronchial tubes, c c, with which the air-cells communicate. From a new-born child. (Kolliker.) ules. Each pulmonary lobule may be considered to be a lung in minia- ture, consisting, 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. RESPIRATIOTvT. 247 On entering a lobule, the small bronchial tube, the structure of which has been just described {a, fig. 208), 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 widening out funnel-wise, and its walls being pouched out irregularly into small saccular dilatations, called air-cells (fig. 208, b). Such a funnel-shaped terminal branch of the bronchial tube, with its Fig. 210. — From a section of the lung of a cat stained with sih c i mti ite A. D Alveolar duct or intercellular passage. S. Alveolar septa. N. Alveoli oi air-celk lined w ith laige flat nucleated cells, with some smaller polyhedral nucleated cells. M. Unstriped musculai fibres. L ii cidar muscular fibres are seen surrounding the interior of the alveolar duct, and at one part is seen a group of small polyhedral cells continued from the bronchus. (Klein and Noble Smith.) group of pouches or air-cells, has been called an infundihulum (figs. 208, 209), and the irregular oblong space in its centre, with which the air- cells communicate, 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 even in rows, like minute sacculated tubes; so that a short series of ves- icles, 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 they vary from -^ to ^^y of an inch (.5 to .3 mm.) in diam- eter. Their walls are formed of fine membrane, similar to that of the 248 HANDBOOK OF PIIYSTOLOOY. intercellular passages, and continuous with it, which membrane is folded on itself so as to form a sharp-edged border at each circular orifice of communication between contiguous air-vesicles, or between the vesicles and the bronchial passages. ISiumerous fibres of elastic tissue are spread out between contiguous air-cells, and many of these are attached to the outer surface of the fine membrane of which each cell is composed, im- parting to it additional strength, and the power of recoil after disten- tion. The cells are lined by a layer of epithelium (fig. 210), not pro- vided with cilia. Outside the cells, a network of pulmonary capillaries is spread out so densely (fig. 311) that the interspaces or meshes are even narrower than the vessels, which are, on an average, -joVo ^^ ^^ inch (8//) in diameter. Between the atmospheric air in the cells and the blood in these vessela, nothing intervenes but the thin walls of the Fig. 211.— Capillary network of the pulmonary blood-vessels in the human lung. X 60, (Kolliker.) 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 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 pas- sage, 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-siqJijJy. — The lungs receive blood from two sources, {a) the pulmonary artery, [h] the bronchial arteries. The former conveys venous blood to the lungs for its arterialization, and this blood takes no share RESPIRATION". 249 in the nutrition of the pulmonary tissues througli which it passes, (b) The branches of the bronchial arteries ramify for nutrition's sake in the walls of the bronchi, of the larger pulmonary vessels, in tlie interlobular connective 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 lacuna 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 lym- phatic 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. The Respiratory Mechanism. Eespiration 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 increase 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 pressure 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 ex- terior 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 ex- pansion of the lung. We have now to consider the means by which the respiratory move- ments are effected. Inspiration. — The enlargement of the cnest 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) 250 HANDBOOK OF PHYSIOLOGY. in the lateral and antero-posterior diameters. The muscles engaged in ordinary inspiration are the diaphragm; the external intercostals; parts of the internal intercostals; the levatores costarum; and serratus pos- ticus 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. (i.) The increase in the lateral and antero-posterior diameters of the= Fig. 212 —Diagram of axes of movement of ribs. chest is effected by the raising of the ribs, the greater number of which are attached very obliquely to the spine and sternum. The elevation of the ribs takes place both in front and at the sides — the hinder ends being prevented from performing any upward move- ment by their attachment to the spine. The movement of the front extremities of the ribs is of necessity accompanied by an upward and forward movement of the sternum to which they are attached, the move- ment being greater at the lower end than at the upper end of the latter bone. 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. 212) ; and the other with a line drawn from one of these (head of rib) to the sternum (A B, fig. 212); the motion of the rib around the latter axis being somewhat after the fashion of raising the handle of a bucket. RESPIRATION. 251 The elevation of the ribs is accompauied by a slight opening out of the angle which the bony part forms with its cartilage (fig. 213, 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 inspira- tion, are external intercostals, and that portion of the internal intercostals which is situate between the costal cartilages; and these are assisted by the levator es costarum, and the serratus postic7ts superior. The ac- tion of the levatores and the serratus is very simple. Their fibres, aris- ing from the spine as a fixed point, pass obliquely downward and for- ward 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 Fig. 213. — Diagram of movement of a rib in inspiration. fixed point toward which they can pull the bones to which they are attached. 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. 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 impossible to separate by a hard and fast line the so- called muscles of ordinary from those of extraorditiary ms^imtiow, 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 sternomastoid, the serratus magnus, the pector ales, and the trapezius. 252 HAISTDBOOK OF PHYSIOLOGY. 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 movement of the abdominal walls being here more manifest than that of any other part, it is usual to call this the ahdormnal type of respiration. In men, to- gether with the descent of the diaphragm, and the jmshing forward of the front wall of the abdomen, the chest and the sternum are subject to a wide movement in inspiration {i)iferior costal type). In women, the movement appears less extensive in the lower, and more so in the upper, part of the chest {superioi' costal type). Expiration. — From the enlargement produced in inspiration, the chest and lungs return in ordinary tranquil exj^iration, by their elastic- ity; the force employed by the inspiratory muscles in distending the 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 chest and lungs is sufficient, in ordinary quiet breathing, to expel air from the lungs in the intervals of inspiration, and no muscular power is required. In all voluntary expiratory efforts, however, as in speaking, singing, blowing, and the like, and in many in- voluntary 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 ab- dominal muscles, which, by pressing on the viscera of the abdomen, jDush up the floor of the chest formed by the diaphragm, and by thus making pressure on the lungs, exi^el air from them through the trachea and larynx. All muscles, however, which depress the ribs, must act also as muscles of expiration, and therefore we must conclude that the abdom- inal muscles are assisted in their action by the greater part of the inter- nal intercostals, the triangularis sterni, the serratus posticus inferior and quadratus lumhorum. When by the efforts of the expiratory mus- cles, 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 construction of the chest-walls, there- fore, 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 cohesion as well as 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 EESPIRATIOX. 253 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. Methods of recording Respiratory Movements. The movements of respiration may be recorded graphically in several ways. The ordinary method is to introduce a tube into the trachea of an animal, and to connect this tube by some gutta-iiercha tubing with a T piece introduced into the cork of a large- sized bottle, the other end of the T having attached to it a second piece of tubing, which can remain open or can be partially or completely closed by means of a screw' clamp. Into the cork is inserted a sec- ond piece of glass tubing connected with a Marey's tambour by suitable tubing. This second tube communicates any alteration of the pressure in the bottle of Fig. 214.— Stethograph or Pneumograph, h, tambour fixed at right angles to plate of steel/; c and d. arms by which Instrument is attached to chest by belt e. When the chest expands, the arms are pulled asunder, which bends the steel plate, and the tambour is affected by the pressure of b which is attacheii to it on the one hand, and to the upright in connection with horizontal screw g. (^Modilied from Jlarey"s instrument.) the tambour, and this may be made to write on a recording surface (fig. 173). If the tube attached to the T piece be closed the movements of inspira- tion and expiration are larger than if it were closed. The alteration of the pressure within the lungs on inspiration and expiration is shown by the move- ment of the column of air in the trachea. By these means a record of the respiratory movements may be obtained. Various instruments for recording the movements of the chest by applica- tion of apparatus to the exterior. Such is the stethometer of Burton Sander- son. This consists of a frame formed of two parallel steel bars joined by a third at one end. At the free end of the bars is attached a leather strap, by means of which the apparatus may be suspended from the neck. Attached to the inner end of one bar is a tambour and ivory button, to the end of the other an ivory button. When in use, the apparatus is suspended with the transverse bar posteriori}^, the button of the tambour is placed on the part of the chest the movement of which it is desired to record, and the other button 254 HANDBOOK OF PHYSIOLOGY. is made to press upon the corresponding side of the chest, so that the chest is, as it were, held between a pair of calipers. The tambour is connected by tubing and a T piece with a recording tambour of Marey's, and with a ball, by means of which air can be squeezed into the cavity of the tympanum. When in work the tube connected with the air ball is shut off by means of a screw clamp. The movement of the chest is thus communicated to the recording tambour. A simpler form of this apparatus, called a pneumograph or stethograph, consisting of a thick India-rubber bag of elliptical shape about three inches long, to one end of whicli a rigid gutta-percha tube is attached. This bag may be fixed at any required place on the chest by means of a strap and buckle. By means of the gutta-percha tube the variations of the presssure of air in the Tamboiir. Ivory button. Tube to commu- nicate with re- cording tam- bour. Ball to fill appa- _ ratufl -with air. Fig. 215.— Stethometer. (Burdon Sanderson.) bag produced by the movements of the chest are communicated to a recording tambour. This apparatus is a simplified form of Marey's pneumograph (fig. 214). The variations of intrapleural pressure may be recorded by the introducton of a canula into the pleural or pericardial cavity, which is connected with a mercurial manometer. Finally, it has been found possible in various ways to record the dia- phragmatic movements by the insertion of an elastic bar connected with a tambour into the abdomen below it (phrenograph) , by the insertion of needles into different parts of its structure, or by recording the contraction of isolated strips of the diaphragm. The acts of expansion and contraction of the chest take up under ordinary circumstances a nearly equal time. The act of inspiring air. RESPIRATION. 355 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 res- piratory rhythm may be thus expressed : — Inspiration Expiration 6 7 or 8 A very slight pause. If the ear be placed in contact with the wall of the chest, or be sep- arated from it only by a good conductor of sound or stethoscope, a faint respiratory rnurmtcr is heard during inspiration. This sound varies Fig. 216.— Tracing of the normal diaphragm respirations of rabbit, a, with quick movement of drum. b. with slow movement, j, inspiration, e, expu-ation. To be read from left to right. (Marckwald.) somewhat in different parts — being loudest or coarsest in the neighbor- hood of the trachea and large bronchi (tracheal and bronchial breathing), and fading oft' 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 vesicular 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 distention (Laennec, Skoda), others that it is due to an oscillation of the current of air as it enters the alveoli (Chauveau), while others believe that the sound is produced in the glottis, but that it is modified in its passage to the pulmonary alveoli (Beau, Gee). Respiratory movements of the JVostrils atid of the Glottis. — During 256 HANDBOOK OF PHYSIOLOGY. 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 opening at the upper part of the larynx, however, or rima glottidis, 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 fur- ther likeness between the two acts in that, under ordinary circumstan- ces, the dilatation of the rima glottidis is a muscular act and its contrac- tion chiefly an elastic recoil; although, under various conditions to be hereafter mentioned, there may be in the latter considerable muscular power exercised. Terms used to express Quantity of Air breathed. — a. Breath- ing or tidal air, is the quantity of air which is habitually and almost uniformly changed in each act of breathing. In a healthy adult man it is about 30 cubic inches, or about 500 ccm., or half a litre. b. Comphmental air, is the quantity over and above this which can be drawn into the lungs in the deepest inspiration; its amount varies,, but may be reckonded as 100 cubic inches, or about 1,600 ccm. c. Reserve air. — After ordinary expiration, such as that which expels the breathing or tidal air, a certain quantity of air, about 100 cubic inches (1,600 ccm.) remains in the lungs, which may be expelled by a forcible and deeper expiration. This is termed reserve or supplemental air. d. Residual air is the quantity which still remains in the lungs after the most violent expiratory effort. Its amount depends in great meas- ure on the absolute size of the chest, but may be estimated at about 100 cubic inches, or about 1,600 ccm. to 2,000 ccm. 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 quan- tity, however, is largely increased by exertion; the average amount for a hard-working laborer in the same time being 1,568,390 cubic inches. e. Respirator y Capacity. — The greatest respiratory capacity of the chest is indicated by the quantity of air which a person can exijel from his lungs by a forcible expiration after the deepest inspiration possible; it expresses the power which a person has of breathing in the emergen- cies of active exercise, violence, and disease. The average capacity of an adult, at 15.4° C. (60° F.), is about 225 to 250 cubic inches, or 3,500 to 4,000 ccm. The respiratory capacity, or as John Hutchinson called it, vital capacity, is usually measured by a modified gasometer or spirometer, into which the experimenter breathes, — making the most prolonged expiration possible after the deepest possible inspiration. The quantity of air which is thus expelled • RESPIRATION^. 257 from the lungs is indicated by tlie lieight to which the air chamber of the spirometer rises ; and by means of a scale placed in connection with this, the number of cubic inclies 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 this subject is derived, that at a temperature of 15.4° C. (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 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 ha« not yet been determined. As a general state- ment, however, it may be said that the capacity of respiration is not affected by weights under 161 pounds, or IH 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 abovit the fifteenth to the thirty-fifth year, at tlie 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 of forty years old, of the same height and weight. (John Hutchinson.) The number of respirations in a healthy adult person usually ranges from 14 to 18 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, that the number of resjnrafor>/ 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. The Force of Inspiratory and Expiratory Muscles. — The force witb which the inspiratory muscles are capable of acting is greatest in iiuli- viduals 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 aver- age of men of six feet can elevate only about two and a half inches of t7 25S HANDBOOK OF PHYSIOLOGY. 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 great measure due to the power exerted by the ehistic 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 expiratory 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 " . . . . Ordinary . . . 2.0 " 2.5 " . . . . Strong . . . . 3.5 " 3. 5 " . . . . Very strong . . . 4. 5 " 4.5 " . . . . Remarkable . . . 7.0 " 5. 5 " . . . . Very remarkable . . 5.8 " 6. 0 " . . . . Extraordinary . . . 8. 5 " 7.0 " . . . . 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 lungs. The amount of this elastic resistance was estimated by observing the ele\a- tion of a column of mercury raised by the return of air forced, after deaih, into the lungs, in quantity equal to the known capacity of respiration 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 lbs. The elastic force overcome in ordinary inspiration is, according to the same authority, equal to about 170 lbs. Douglas Powell has shown that within the limits of ordinary tran- quil respiration the elastic resilience of the walls of the chest favors in- spiration; 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 expansion. Under all circumstances, of course, the elastic tissue of the lungs opposes inspiration and favors expiration. 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 regu- late and adapt, in some measure, the quantity of air admitted to 1 he RESPIKATION. "2,59 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 which cannot be ejected by forced expiratory efforts, owing to collapse or other mor- bid conditions of the portion of lung connected with the obstructed tubes (Gairdner). (4) Apart from any of the before-mentioned func- tions, the presence of muscular fibre in the walls of a hollow viscus, such as a lung, is only what might be expected from analogy with other 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. Respiratory Changes in the Air Breathed. Composition of the Atmosphere. — The atmosphere we breathe has, in every situation in which it has been examined in its natural state, a nearly uniform composition. It is a mixture of oxygen, nitrogen, car- bon dioxide, 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 re- maining 21 of oxygen. By weight the proportion is N. 77, 0. 23. The proportion of carbon dioxide is extremely small; 10,000 volumes of atmospheric air contain only about 4 or 5 of that gas. 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 at- mosphere is 1.40 per cent. Compiosition of Air wliicli 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 quantity of oxygen; 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 bet«^een 36°— 37.5° C. (97° and 99.5° F.), 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 in- haled, it acquires nearly that of the blood before it is expelled from the chest. 2. The Carbonic dioxide is increased; but the quantity exhaled in a given time is subject to change from various circumstances. From every volume of air inspired, about 4.8 per cent of oxygen is abstracted; 260 HAXDBOOK OF PHYSIOLOCi V while a rather smaller quantity, 4.3 of carbon dioxide is added in \\<, place: the expired air will contain, therefore, 434 vols, of carbon dioxide in 10,000. The quantity of carbon dioxide exhaled into the air breathed by a healthy adult man, calculating that 22 com. of the 500 ccra. of the air breathed out at each expiration consists of carbon dioxide, and that the rate of respiration is on an average 16, the total amount would be about 506 litres in the 24 hours. From actual experiment this amount seems to be too high, since from the average of many investigations the total amount of carbon dioxide excreted per diem has been found to be about 400 litres, weighing 800 grms., consisting of 218 grms. of C, and 582 grms. of 0. From this has to be deducted about 10 grms. excreted in any other way than by the lungs, it leaves about 215 grms. as the amount of C. excreted by the average healthy man by respiration each day and night, that is about 7 oz., about half a pound. These quantities must be considered approximate only, inasmuch as various circumstances, even in health, influence the amount of carbon dioxide excreted, and, correla- tively, the amount of oxygen absorbed. Circumstances influencing the amount of carbon dioxide excreted. — a. Age and Sex. — The quantity of carbon dioxide exhaled into the air breatlied by- males, regularly inci-eases from 8 to 30 years of age ; from 30 to 50 the quantity, after remaining stationary for a while, gradually diminishes, and from 50 to extreme age it goes on diminishing, till it scarcely exceeds the quantity ex- haled 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 8th year to the age of puberty, when the quantity abruptlj^ ceases to increase, and remains stationary so long as they continue to menstruate. When menstruation has ceased, it soon deci-eases at the same rate as it does in old men. b. Respiratory Movements. — The quicker the respirations, the smaller is the proportionate quantity of carbon dioxide contained in each volume of the expired air. Although the proportionate quantity of carbon dioxide is thus diminished, the absolute amount exhaled within a given time is increased thereby, owing to the larger quantity of air which is breathed in the time. The last half of a vol- ume 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 various temperatures between 3.4° — 23.8° C. (38° F. and 75° F.) show, for warm-blooded animals, that within this range, every rise equal to 5.5° C. (10° F. ) causes a diminution of about 33 ccm. (2 cubic inches) in the quantity of carbonic acid exhaled per minute. d. Season of the Year. — The season of the year, independently of tempera- ture, materially influences the respiratory phenomena ; spring being the season of the greatest, and autumn of the least activity of the respiratory and other functions. e. Purity of the Respired Air. — The average quantity of carbon dioxide KESPIKATIOX. 261 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 carbon dioxide (as is the case when the same air is frequently respired) , then the quantity of carbon dioxide exhaled becomes relatively much less. /. Hygrometric State of Atmosphere. — The amount of carbon dioxide exhaled is considerably influenced by the degree of moisture of the atmosphere, much more being given off when the air is moist than when it is dry. g. Period of the Day. — During the day-time more carbon dioxide is exhaled than corresponds to the oxygen absorbed ; while, on the other hand, at night very much more oxygen is absorbed than is exhaled in carbon dioxide. There is, thus, a reserve fund of oxygen absorbed by night to meet the requirements of the day. If the total quantity of carbon dioxide exhaled in 24 hours be repre- sented by 100, 52 parts are exhaled during the day, and 48 at night. While similarly. 33 j^arts of the oxygen are absorbed during the day, and the remain- ing 67 by night. h. Food and Drink. — By the use of food the quantity is increased, while by fasting it is diminished ; it is greater when animals are fed on farinaceous food than when fed on meat. The effects produced by spirituous drinks de- pend much on the kind of drink taken. Pure alcohol tends rather to increase than to lessen respiratory changes, and the amount therefore of carbon dioxide expired ; rum, ale, and porter, also sherry, have very similar effects. On the other hand, brandy, whiskey, and gin, particularly the latter, almost always lessened the respiratory changes, and consequently the amount of the gas exhaled. i. Exercise. — Bodily exercise, in moderation, increases the quantity to about i- more than it is during rest : and for about an hour after exercise the volume of the air expired in the minute is increased nearly 2,000 ccm., or 118 cubic inches : and the quantity of carbon dioxide about 125 ccm., or 7.8 cubic inches per minute. Violent exercise, such as full labor on the tread-wheel, still fur- ther increases the amount of the acid exhaled. 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 carbon dioxide. For every volume of car- bon dioxide exhaled into the air, 1.17421 volumes of oxygen are absorbed from it, from the result of the experiments to estimate the carbon diox- ide exhaled and the oxygen absorbed, it was found that while about 575 grms. of oxygen appeared in the CO2 exhaled, 700 grms. disappeared froTu the inspired air. 4. Tlie volume of air is diviinished (allowance being made for the ex- pansion in being heated), the loss being due to a portion of oxygen ab- sorbed 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 G.2 volumes per cent of that gas. The quantity of oxygen that does not combine Avith 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 combining 20:^ HANDBOOK OF PHYSIOLOGY. with sulphur and phospliorus to form part of the acids of the sulpliates and phosphates excreted in the urine, and probably also, with the nitro- gen of the decomposing nitrogenous tissues. 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 ex- haled 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 exists in the inspired air. During prolonged fasting, on the contrary, a small quantity appears to be absorbed. 5. Tlie watery vapor is increased. — The quantity emitted is, as a general rule, sufficient to saturate the expired air, or very nearly so. Its absolute amount is, therefore, influenced by the following circum- stances, (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 quan- tity of watery vapor contained in the air j)revious to its being inspired ; because the greater this is, the less will be the amount to comjilete the saturation 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 re- quired to saturate the air; (4), by the length of time which each volume of inspired air is allowed to remain in the lungs; for although, during ordinary respiration, the expired air is always saturated with watery vapor, yet when resi^iration 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. 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 com- bination of oxygen with hydrogen in the system; but the far larger proportion 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 membranes, particularly at the high temiperature of warm-blooded animals. 6. A small quantity of ammonia is added to the ordinary constitu- ents 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. EESPIKATIO]Sr. 363 T. The quantity of organic matter in the breath is increased. It is due to the presence of this organic matter that air containing the prod- ucts of respiration is more injurious than it might be expected to be from the amount of CO2 it contains. The condensed aqueous vapor is found soon to decompose and to contain substances which are of a poisonous nature. Method of Experiment. — The following represents the kind of experiment by which the foregoing 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 car- bonic acid. The air which has been breathed by the animal is luade to bubble thi-ougli lime-water, which at once becomes turbid and soon quite milky from the precipitation of calcium carbonate ; and it finally passes through strong sulphuric acid, which, b}' tiuning brown, indicates the presence of organic matter. The watery rapor in the expired air will condense inside the bottle if the surface be kept cool. By means of an apparatus sufficiently large and well- constructed, experiments of the kind have been made extensively on man. How the Changes in the Air are effected. — The method by which fresh air is inhaled and expelled from the lungs has been explained. It remains to consider how it is that the blood absorbs oxygen from, and gives u]^ 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 (about .500 ccm.) at each inspiration, and that this is of course insufficient to fill the lungs, but it mixes with the stationary air by diffusion, 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 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 oxygen in the proportion of 8 to 12 vols, per cent of blood, as the difference between the amount of oxygen in arterial and venous blood is no less. It seems therefore somewhat difficult to under- stand hov/ this can be accomplished at the low partial pressure of oxygen in the pulmonary air. But as Avas pointed out in a previous Chapter (IV.), the oxygen is not simply dissolved in the blood, but is to a great extent chemically combrned with the haemoglobin of the red corpuscles; and when a fluid contains a body which enters into loose chemical com- bination in this way with a gas, the tension of the gas in the fluid is not directly proportional to the total quantity of the gas 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 heemoglobin, viz., 1.59 cm. for 1 grm. haemoglobin). On the 264 HANDBOOK OF PHYSIOLO(iY. other hand, if the substance be not saturated, i.e., if it be not combined with as niucli of the gas as it is capable of taking up, further combina- tion 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 oxygen 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 temjDcrature 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 ha?mo- globin is very nearly saturated with the gas. As regards the elimination of carbon dioxide from the blood, there is evidence to show that it is given up by a process of simple diffusion, the only condition necessary for tlie process being that the tension of the carbonic acid of the air in the pulmonary alveoli should be less than the tension 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. Respiratory Changes in the Blood. Circnlation of Blood in the Besjnratory Organs. — To be exposed 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 through the pulmonary capillaries in steady streams, and slowly enough to per- mit 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 simi^lest 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 passtiges; and the veins de- rived 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 junction, and incapable of closing the orifice of either of the veins between which they are placed. The pulmonary circulation also is un- affected by changes of atmospheric pressure, and is not exposed to the RESPIRATION. 265 influence of the j)ressure of muscles: the force by which it is accom- plished, and the course of the blood are alike simple. Changes in the Blood. — 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. The cause of this has been already shown to be that the arterial blood contains a greater quantity of scarlet or oxyhaemoglobin; 2d, and in connection with the preceding change it gains oxygen ; 3f7, it loses carbon dioxide. It w^as incidentally mentioned in the Chapter on the Blood that the carbon dioxide which is carried by the blood to be eliminated by the lungs is not simply dissolved in the plasma. It is combined with some substance in the blood, and when it is carried to the lungs this substance must undergo decomposi- tion. What is the nature of the compound it forms is not known, but it appears most likely that the gas is combined in the plasma with the sodium carbonate which it contains. It has also been suggested that as the carbon dioxide of the entire blood is more easily given up to the vacuum of a mercurial air-pump than is the gas of the serum correspond- ing to the blood taken, that the corpuscles of the blood exercise some power in promoting the decomposition of the substance with which the gas is combined in the plasma. The plasma or serum will not give up the whole of its carbon dioxide until the addition of an acid, when the last portion, 2 to 5 per cent, comes off, the entire blood gives up the whole of its carbon dioxide to the action of the mercurial pump, and does not require the action of an acid. It may be mentioned that, ae- ■ cording to some, the carbon dioxide is combined with proteid, either in the plasma or in the red blood-corpuscles; 4/*/?, it becomes slightly cooler; oth, it coagulates sooner and more firmly, apparently containing more fibrin. The oxygen absorbed into the blood from the atmospheric air in the lungs is combined cliemically 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 con- tact with the tissues. In these tissues, a certain portion of the oxygen, which the arterial blood contains, disappears, and a proportionate quan- tity of carbon dioxide and water is formed. The venous blood, contain- ing the new-formed carbon dioxide, returns to the lungs, where a portion of the carbon dioxide is exhaled, and a fresh supply of oxygen is taken in. In what way these changes are brought about will be next discussed. Respiratory Changes in the Tissues. The changes which occur in the composition of the blood during its ■ circulation are believed to take place in the tissues, and particularly in the muscles. The changes are, as we have just mentioned, chiefly the 266 HANDBOOK OF PHYSIOLOGY. removal of oxygen from and the addition of carbon dioxide to tlie blood. These changes are sometimes spoken of as internal res2Diration. The- oxygen carried by the corpuscles of the blood in the form of oxyhgemo- globin is given ujd to the tissues, as the tension of the gas within them is very small. The gas thus set free is apparently seized upon by the protoplasm of the tissues and built up into its molecule, and thus assists in the process of anabolism, possibly uniting with some compound somewhat in the same manner but more firmly than it does with hemo- globin. The low oxygen pressure of the tissues thus allows a constant abstraction of the gas from the blood. The process of katabolism, or breaking down, is always associated with the evolution of carbon diox- ide, so that as the blood passes through the tissues containing little of this gas, the high tension of the gas in the tissues permits of its passage into the blood. It has been proved that the process of the evolution of carbon dioxide from living muscle will go on for a time in the absence of a supply of free oxygen, and so it is clear that the former gas is not derived directly from the combustion of the carbon in the presence of the latter gas. It was at one time believed that the carbon dioxide of venous blood resulted from the oxidation of substances in the blood itself. It has, however, been shown that the blood itself has very slight oxidizing powers, and that in the frog the whole of the blood may be replaced by saline solution without producing any marked effect upon the metabolism of the body. It is obviously nnlikely that any but very slight oxidation could go on in such a medium. It has moreover been demonstrated that the tension of carbon dioxide in the tissues is con- siderably greater in the tissues than it is in the venous blood. Special Respiratory Acts. It will be well here, perhaps, to explain certain special respiratory acts, which appear at first sight somewhat complicated, but cease to be so when the mechanism by which they are performed is clearly under- stood. The diagram (fig. 219) shows that the cavity of the chest is sep- arated from that of the abdomen by the diaphragm, which, when acting, will lessen its curve, and thus descending, will push dowmvard and forward the abdominal viscera; while the abdominal muscles have the opposite effect, and in acting will jiush the viscera upward and back- ward, and with them the diaphragm, supposing its ascent to be not from any cause interfered with. It will also be seen that the lungs communicate with the exterior of the body through the trachea and larynx, and further 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 ex- terior of the body through the oesophagus, pharynx, and mouth; while RESPIRATIOX. 267 below the rectum opens at the anus, and the bladder through the ure- thra. All these openings, through which the hollow viscera communi- cate with the exterior of the body, are guarded by muscles, called sphincters, which can act independently of each other. Sighiny. — In sighing there is a somewhat prolonged inspiration; the air almost noiselessly joassiug in through the glottis, and by the elastic recoil of the lungs and chest- walls, and probably also of the abdominal walls, being suddenly expelled. In the first, or inspirafonj part of this act, the descent of the dia- phragm presses the abdominal viscera downward, and of course this pressure tends to evacuate the contents of such of them as communicate with the exterior of the body. Inasmuch, however, as their various openings are guarded by sphincters, in a state of constant tonic contrac- tion, there is no escape of their contents, and the air simjily enters the lungs. In the second, or expiratory part of the act, pressure is also made on the abdominal viscera in the opposite direction, by the recoil of the abdominal Avails; 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 of the stomach, rectum, and bladder, act in the same manner as before. Hiccovgh resembles sighing in that it is an inspiratory act: but tlie inspiration is sudden instead of gradual, the diaphragm acting suddenly and spasmodically; and the air, suddenly rushing through the unpre- pared rima glottidis, causes vibration of the vocal cords and the jDecu'iar sound. Coughinfi. — In the act of coughing there is most often first of all a deep inspiration, followed by an expiration; but the latter, instead of being easy and uninterrupted, as in normal breathing, is obstructed, the glottis being momentarily closed by the approximation of the vocal cords. The abdominal muscles, then 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 noisily open the vocal cords which oppose its outward passage. In this way considerable force is exercised, and mucus or any other matter that may need expulsion from the air- passages is quickly and sharply expelled by the outstreaming current of air. It will be evident on reference to fig. 217, that pressure exercised by the abdominal muscles in the act of coughing, acts lis forcibly 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 there is of necessity 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 effec- tive at one part only, at the rima glottidis. 268 HANDBOOK OF PHYSIOLOGT, 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 contrac- tion 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 bv means of the expiratory muscles. The vocal cords, by the Fig. 217. muscles of the larynx, are put in a jDroper position and state of tension for vibrating as the air jDasses over them, and sound is produced. The sound is moulded into articulate speech by the tongue, teeth, lips, etc. — the vocal cords producing the sound only, and having nothing to do with articulation. Singing. — Singing resembles speaking in the manner of its produc- tion; the laryngeal muscles, by variously altering the position and de- gree 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. — Snifhng is produced by a rapidly repeated but incomplete RESPIRATIOX. 269 action of the diaphragm and other inspiratory muscles. The mouth is closed, and the whole stream of air is made to enter the air-passages through the nostrils. The alse nasi are commonly at the same time instinctively dilated. Sobbing. — Sobbing consists of a series of convulsive inspirations, at the moment of which the glottis is usually more or less closed. Laughing. — Laughing is made up of a series of short and rapid expi- rations. Yaivning. — Yawning is an act of inspiration but is unlike most of the preceding actions as it is 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 charac- ter of yawning probably depends on the fact that the muscles concerned are themselves at all times more or less used involuntarily, 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 atmosjihere 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 e(iuilibrium, therefore, can be restored only by the entrance of some- thing 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. The Nervous Apparatus of Respiration. Like all other functions of the body, the discharge of which is nec- essary to life, respiration is essentially an involuntary act. Unless these were the case, life would be in constant danger, and Avould cease on the loss of consciousness for a few moments, as in sleep. It is, however, also necessary that respiration should be to some extent under the con- trol of tho will. For were it not so, it would be impossible to j^erform those respiratory acts which have been just discussed, such as speaking,, singing, and the like. 270 HANDBOOK OF PHYSIOLOGY. It has been known for centuries that there exists a district of the. central nervous system on the destruction of which both respiration and life cease. All attempts to localize this district, however, before those of Flourens were unsuccessful. Flourens, after many series of experiments as to the exact position of what he called the "knot of life" (noeud vital), placed it in the fourth ventricle, at the point of the V in the gray matter at the lower end of the calamus scriptorius; a dis- trict of considerable size, viz., 5 mm., on both sides of the middle line. Observers subsequent to Flourens have attempted to show that the chief respiratory centre on the one hand is situated higher up in the nervous system, e.g., in the floor of the third ventricle (Christian!), or in the corpora quadrigemina (Martin and Booker, Christiani, and Stanier), or on the other hand, lower down in the spinal cord, and that the medullary centres, if they exist, are either accessory or subservient to such centres. The balance of experimental evidence, however, is to prove that the sole centres for respiration is a limited district in the medulla oblongata in close connection with the vagus nucleus on each side, with which they are probably identical. The destruction of this district stops respira- tion forever; whereas, if it be left in connection with the muscles of respiration by their nerves, although the remainder of the central nervous system be separated from it, respiration continues. It may be considered ;ilmost certain that the medullary centre is the only true respiratory centre, and that the observations of Langendorif, that in newly-born animals in which the medulla has been cut immediately or a few milli- metres below the point of the calamus scriptorius respiration continues for some time as in normal animals cannot be received. We are indebted to Marckwald for much information on this subject, and he has come to the conclusion that normal respiration does not occur after division of the bulb from the cord, and that the so-called respiratory movements noticed by Langendorff are merely tetanic contractions of the respira- tory muscles with which often enough other muscles take part. The action of the medullary centre is to send out impulses during inspiration, which cause respiratory movements of the muscles — («) of the nostrils, and jaws through the facial and inferior division of the fifth nerves; {h) of the glottis, chiefly through the inferior laryngeal branches of the vagi; {c) of the intercostal and other muscles which produce raising of the ribs, chiefly through the intercostal nerves, and {(1) of the diaphragm through the phrenic nerves. If any one of these sets of .nerves be divided, respiratory movements of the corresponding part cease. Similarly it may be supposed that the centre sends out impulses dur- ing expiration to certain other muscles. It has been suggested, however, that the centre consists of two parts, or is double, and that it is made up of an inspiratory centre, which is constantly in action, and of an ex- RESPIKATION". 27 H piratory centre, which acts less generally, inasmuch as ordinary tranquil expiration is seldom more than an elastic recoil, and not a muscular act to any marked degree. Assuming this view of the double centres to be correct, of their ex- act mode of action there is some difference of opinion; it is now generally thought that they act automatically, but are influenced by afferent im- pulses from the j)eriphery, as well as by impulses passing down from the cerebrum. The centre is, in other words, both automatic and re- flex. It will be simplest to discuss its reflex function first of all. Action of Afferent Stimuli. — {a) Action of the vagi. — If both vagi be divided in the neck, the respirations become much slower and deeper; this may be the case, but to a less marked degree, if one of the nerves is divided instead of both. If the central end of the divided nerve be stimulated with a weak interrupted current, the most constant effect is that the respirations are quickened, and if the stimuli are properly reg- ulated, the normal rhythm of respiration may be resumed. If the stimuli be repeated with sufficient quickness, after a while the breathing is brought to a stand-still at the height of inspiration by tetanus of the diaphragm. Sometimes, however, stimulation of the central end of the divided vagi produces still greater slowing than that which follows the division, so that if it be continued, the respirations cease, with the diaphragm in a condition of complete relaxation. Marckwald considers that the differences in the effects of vagus stimulation are due to the stimulus being applied to the nerve at different periods in the respira- tory cycle, and that the action of the vagus may be to call forth either inspiration or expiration — the impulses passing up the vagi being neces- sary to the production of the normal respiratory rhythm. The fibres of the vagus are used under the following circumstances, those fibres which tend to inhibit expiration and to stimulate inspiration are stim- ulated at their distribution in the lung when the lung is empty and in a condition of expiration, and the fibres which tend to inhibit inspira- tion and to promote expiration are stimulated when the lung is fully ex- panded. The afferent impulses are the results of mere mechanical stimulation, and do not depend upon the chemical nature of the gases within the pulmonary alveoli. The vagus always acts upon the centres as a stimulator of discharge, or exciter of catabolism. {b) Action of the superior laryngeal nerves.— If the superior laryngeal branch of the vagus be divided, which usually produces no apparent effect, and the central end be stimulated, the effect is very constant, respirations are slowed, but there is a tendency toward expi- ration, as is shown by the contraction of the abdominal muscles. Thus if the vagus fibres contain fibres which stimulate inspiration and inhibit expiration, as well as other fibres which have the reverse effect, the su- perior laryngeal fibres inhibit inspiration and stimulate expiration. 272 HANDBOOK OF PHYSIOLOGY. The superior laryngeal nerves are true expiratory nerves, and may be set in action when the mucous membrane of the larynx is irritated. They are not constantly in action like the vagi. (c) Action of the glosso-pharyngeal nerves. — It has been as- certained, chiefly by the researches of Marckwald, that while division of the glosso-pharyngeal nerves produces no effect upon respiration, stim- ulation of them causes inhibition of inspiration for a short period. This action accounts for the very necessary cessation of breathing during swallowing. The effect of the stimulation is only temporary, and is followed by normal breathing movements. {d) Action of other sensory nerves. — The respiratory centres are as a rule stimulated to produce respiration by impressions conveyed by sensory nerves, e.g., the nerves of the skin; cold water applied to the sui-face is almost invariably followed by a deep inspiration. Stimu- lation of the splanchnics and of the abdominal branches of the vagi produce expiration. The fifth nerves, as well as the glosso-pharyngeal and the superior laryngeal, inhibit inspiration, but they tend to produce a gradual slowing and not an absolute inhibition, as do the glosso- pharyngeal. It must be remembered that although many sensory nerves may on stimulation be made to produce an effect upon the respiratory centres, there is no evidence to show that any one of them, except the vagi, is constantly in action. The vagi indeed are, as far as we know, the only normal regulators of respiration. Automatic Action of the Respiratory Centres. — Although it has been very definitely proved that the respiratory centres may be affected by afferent stimuli, and particularly by those reaching them through the vagi, there is reason for believing that the centres are capable of sending out efferent impulses to the respiratory muscles without the action of any afferent stimuli. Thus, if the brain be removed above the bulb, respiration continues. If the spinal cord be divided below the bulb, the facial and laryngeal respiratory movements continue, although no affer- ent impulses can reach the centres except through the cranial sensory nerves, and tliese, as we have seen, are not always in action, and indeed may be divided without producing any effect, when the bulb and cord are intact. As has been shown, too, respiration continues when the vagi are divided. All of these experiments render it highly probable that afferent impulses are not required in order that the respiratory centres should send out efferent impulses of some kind to the respiratory mus- cles; these centres, then, are automatic. How they act in the absence of afferent stimuli has been demonstrated by Marckwald. He has shown — (rt) firstly, that if the bulb be separated from the brain, and the vagi be then cut, there is first of all inspiratory spasm followed by irregular spasm of muscles both of inspiration and expiration, and death; {h) RESPIRATIOX. 273 secondly, that if the vagi are divided, the respirations, although altered in character, are regular, but that if then the brain is separated from the medulla, the same respiratory spasms occur. From these experiments it is concluded that the automatic action of the centres consists in the liberation of respiratory spasms only, and not of regular rhythmic move- ments; but that impressions reaching the centres either from the cere- brum or through the vagi, prevent the gathering tension in the centres from becoming too great, and convert the spasms which would other- wise arise into regular movements. The chief ditference between the action of the vagi and of the cerebral tracts, is that the former are always in action, whilst the latter are not. When the vagi are in action and the higher centres are not, periodic respiration takes place, that is to say, respirations occurring in groups, each such group being followed by a pause; a type of respiration known as Cheyne- Stokes breathing, to which. we shall return presently. It will be thus seen that even the ordinary action of the respiratory centres is to a large extent reflex, and depend- ent upon vagus or cerebral stimulation. Method of Stiniulation of the Respiratory Centres. — Apart then from afferent impulses, the respiratory centres are capable of working auto- matically, and this fact has been explained by the supposition that they are stimulated to action by the condition of the blood circulating through them, since when the blood becomes more and more venous the action of the centres becomes more and more energetic, and if the air is pre- vented from entering the chest, the respiration in a short time becomes very labored. Any obstruction to the entrance of air indeed, whether partial or complete, is followed by an abnormal rapidity of the inspira- tory acts. The condition caused by any incerference with the free ex- change of gases in the lungs, or by any circumstance in consequence of which the oxygen of the blood is used up in an abnormally quick man- ner, is known as dyspncea. If the aeration of the blood is much inter- fered with, not only are the ordinary respiratory muscles employed, but also those muscles of extraordinary inspiration and expiration which have been previously enumerated. Thus as the blood becomes more and more venous, the action of the medullary centres becomes more and more active. The question has been much debated as to what quality of the venous blood it is which causes this increased activity; whether it is its deficiency of oxygen or its excess of carbonic acid. It has been answered to some extent 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 that it cannot therefore be due to the accumulation of carbonic acid; and on the other, that if plenty of oxygen is supplied, true dyspnoea does not occur, although the carbonic acid of the blood is in excess. It is highly probable, therefore, that the respiratory centres may be stimu- 274 HANDBOOK OF PHYSIOLOGY. lated to action by the absence of sufficient oxygen in the blood circulat- ing in it, and not by the presence of an excess of carbonic acid. But this is not all, since it has been j^i'oved by Marckwald that the medullary centres are capable of acting for some time in the absence of any circulation, and after excessive bleeding. The view taken by this author with regard to the action of the centres is as follows : the respiratory centres are set to act by the condition of their metabolism, much in the same way as the heart is set to beat rliythmically. When anabolism is completed, catabolism or discharge occurs, and this alter- nate but crude and spasmodic action will occur Avithout a definite blood- supply, as long as the centres are proj^erly nourished and stimulated by their own intercellular fluid. The afferent impulses brought by the vagi, in consequence of the stimulation of their terminal fibres in the lungs, have a tendency to bring about catabolism, and to convert crude respi- ratory spasms into regular and rhythmic discharges. In the absence of the vagus stimulation, the impulses from the cerebrum may be effectual for the same purpose. It is unreasonable to think, however, that the respiratory centres are independent of the character of the blood-supply either as regards quan- tity or quality. This must have a great influence ujoon their irritability; it is certain, for example, that venous blood greatly increases the respi- ratory movements, first of all both of inspiration and of expiration, and then of the latter to a greater degree. It may be that the diminution of oxygen in the blood acts as a stimulator of catabolism, in both in- spiratory and expiratory centres, but j^'ii'ticularly in the latter, in a manner similar to but not identical with, that of the vagus. It has also been shown that the presence of the products of great muscular metabo- lism in the blood will greatly increase the irritability of the respiratory centres, even if the blood itself be not particularly venous in character. It appears that the inspiratory and expiratory respiratory centres are bilateral, and that each pair may act independently, since the bulb may be divided longitudinally, and then if one vagus be divided, the respi- ratory rhythm on the two sides of the body becomes unequal, the move- ments of the side upon which the vagus is divided being slower than on the other side, while stimulation of the divided nerve acts only upon the movements of its own side. Apncea. — When we take several deep inspirations in rapid succes- sion by voluntary effort, we find that we can do without breathing for a much longer time than usual; in other words, several rapid respirations seem to inhibit for a time normal respiratory movements. It was thought that the reason for this partial cessation of respiration, which was called apnma, is that by taking several deep breaths we overcharge our blood with oxygen, and that as the respiratory centre can only be stimulated by blood in which the standard of oxygen is below a certain RESPIRATION. 275 level, no respiratory impulses can occur until the oxygen tension of the blood reach that level. This idea must now be modified, if not given up, in face of the experiments, e.g., those of Hering, on cats' blood during apnoea, which have shown that animals in a condition of apnoea may have less and not more oxygen in their blood than in a normal state, although the carbonic anhydride is less. One view now taken of the cause of apnoea is that by rapid inflations of the lungs impulses pass up by the vagi, by means of which inspiration is after a while inhibited; ns flatter, the pressure then began to fallrapidly (5), and continued to fall un,.il some time after artificial respiration was resumed. CM. Foster.) blood-pressure is two-fold. In the first place the cardio-inliihitory centre is stimulated during the fall of blood-pressure, and produces a slower rate of heart-beat, which will be noticed in the tracing (fig. 220). The undulations during the decline of blood-pressure are therefore 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 sends out rhythmical impulses, by which undula- tions of blood-pressure are produced, quite independent of the so-called 280 HANDBOOK OF PHYSIOLOGY. respiratory unduliitions. The action of this centre in producing such unduhitions is thus demonstrated. In an animal under the influence of urari, a record of whose blood-pressure is being taken, and where artificial respiration has been stopped, and both vagi cut, the blood- pressure curve rises at first almost in a straight line, but after a time rhythmical undulations occur (called Traube's or Traube-Herinxfs curves); there may be upward of ten of the respiratory undulations in one Traube-Hering curve. They continue as long as the blood-pressure continues to rise, and only cease when the vaso-motor centie and the heart are exhausted, when the pressure falls. The undulations cannot depend upon anything but the vaso-motor centre, as the mechanical effects of respiration have been eliminated by the urari and by the cessation of artificial respiration, and the effect of the cardio-inhibitory centre has been removed, by the division of the vagi. The rhythmic rise of blood-pressure is most likely due to a rhythmic constriction of the arterioles followed by a rhythmic fall of pressure and relaxation, both being due to the action of the vaso-motor centre. The vaso-motor centre, therefore, as well as the cardio-inhibitory, is capable of produc- ing rhythmical undulations of blood-pressure. Cheyne-Stokes' hreathing is a rhythmical irregularity in respirations which has been observed in various diseases, and is especially connected with fatty degeneration of the heart. Eespirations 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, after which the inspirations become less and less deep, until they cease after a slight pause altogether. This phenomenon appears to be due to the want of action of some of the usual cerebral influences which pass down to and regulate the discharges of the respiratory centres. Whatever is the exact quality of the venous blood which excites the respiratory centre to produce normal respirations, there can be no doubt that as the blood becomes more and more venous from obstruction to the entrance of air into the lung, or from the blood not taking up from the air its usual supply of oxygen, the respiratory centre becomes more active and excitable, and a condition ensues, which passes rapidly from Hyijerjiuoea (excessive breathing) to the state of Dyspnrea (difficult breathing), and afterward to ^isphi/xia ; and the latter, unless relieved, quickly ends in death. The ways by which this condition of asphyxia may be produced are very numerous: — As, for example, by the j^revention 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, by interference with the due in- terchange of gases between the air and the blood. The symptoms of asphyxia may be divided into three groups, which EESPIRATION". 281 correspond with the stages of the condition which are usually recog- nized, these are (1), the stage of exaggerated breathing; (2), the stage of convulsions; (3), the stage of exhaustion. In the first stage the breathing becomes more rapid and at the same time more deep than usual, the inspirations at first being especially ex- aggerated and prolonged. The muscles of extraordinary inspiration are called into action, and the effort to respire is labored and painful. This is soon followed by a similar increase in the expiratory efforts, which become excessively prolonged, being aided by all the muscles of extra- ordinary expiration. During this stage, which lasts a varying time, from a minute upward, according as the deprivation of oxygen is sudden ov gradual, the lips become blue, the eyes are prominent, and the ex- pression intensely anxious. The prolonged respirations are accompanied by a distinctly audible sound; the muscles attached to the chest stand out as distinct cords. This stage includes the two conditions hyperpnoea and dyspnoea already spoken of. It is due to the increasingly powerful stimulation of the respiratory centres by the increasingly venous blood. In the second stage, which is not marked out by any distinct line of demarcation from the first, the violent expiratory efforts become con- Tulsive, and then give way, in men and other warm-blooded animals at any rate, to general convulsions, which arise from the further stimula- tion of the centres. The spasms of the muscles of the body in general occur, and not of the respiratory muscles only. The convulsive stage is a short one, and lasts far less than a minute. The t/iird stage or stage of e.rltanstion. In it, the respirations all but •cease, the spasms give way to flaccidity of the muscles, there is insensi- bility^ the conjunctivae are insensitive and the pupils are widely dilated. JEvery now and then a prolonged sighing inspiration takes place, at longer and longer intervals until they cease altogether, and death en- sues. During this stage the pulse is scarcely to be felt, but the lieart may beat for some seconds after respirations have quite ceased. The condition is due to the gradual paralysis of the respiratory centre by the prolonged action of the increasingly venous blood. As with the first stage, the duration of the second and third stages ■depends whether the manner of the deprivation of oxygen is sudden or gradual. The convulsive stage is short, lasting, it may be, only one minute. The third stage may last three minutes and U2:)ward. The conditions of the vascular system in asphyxia 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; (o) Circulation of impure (non-aerated) blood in all parts of the body. After death from asphyxia it is found in the great majority of cases that the right side of the heart, the pulmonary arteries, and the systemic 282 HANDBOOK OF PHYSIOLOGY. veins are gorged with dark, almost black blood, and the left side of the lieart, the pulmonary veins, and the arteries are empty. The explana- tion of these appearances maybe thus summarized: when respiration is stopped, venous blood at first passes freely through the lungs to the left heart, and so to the great arteries. When it reaches the arterioles either by its direct action upon their muscular tissue, or more probably through the medium of the vaso-motor centres, the arterioles contract, particularly those of the splanchnic area, the blood-pressure rises and the left side of the heart becomes distended. This latter effect may be from the extra action of the right heart, but is more probably due to the increased peripheral resistance, and its slower beat. Although the arterioles are contracted, a little blood is allowed to j^ass through them, and this highly venous bluod, favored by the labored respiratory move- ments, arrives at the right side of the heart. When it reaches the pul- monary arterioles it gives rise to the same contraction in them as it did in the systemic vessels. This obstruction to the circulation through the lungs causes a distended condition of the right heart and the pul- monary artery, and on the other hand, produces a greatly diminished blood-flow through the pulmonary veins and to the left side of the heart, resulting after a time in practical emptiness. So that in the third stage of asphyxia it is stated by some observers that the left heart gets into the condition in which it is found after death. Others think that the empty condition of the left heart is a post-mortem phenomenon. In the first and second stages of tiie condition the blood-pressure continu- ously rises until it reaches a point far above the normal. The veins are greatly engorged, so that when pricked they act as arteries, inasmuch as they eject the blood for some distance. Both sides of the heart and the pulmonary vessels are engorged with blood, at any rate during the greater portion of these stages, and at the third stage blood-j^ressure falls rapidly. Cause of death. — 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 occurs chiefly in the later stages of asphyxia, the obstruction being chiefly in the arterioles, which contract under the influence of the vaso-motor centre, or possibly of a special part of it, which governs the action of the pulmonary blood-vessels. (2) Accumulation of blood, with consequent distention of the right side of the heart and of the 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 stimulated by blood deficient in oxygen, cause contraction of all the small arteries with increase of arterial tension, and as an immediato RESPIKATIOlSr. 283 consequence the filling of the systemic veins, (b) The increased arterial tension is followed by inhibition of the action of the heart, and the heart, contracting less frequently, and also gradually enfeebled by defi- cient supply of oxygen, becomes over-distended with blood which it cannot expel. At this stage the left as well as the right cavities are over-distended. The ill effects of these conditions are to be looked for partly in the heart, the muscular fibi-es 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 ob- longata. (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 coronary arteries, on the muscular substance of the heart. The excita- bility of both nervous and muscular tissue is dependent on a constant and large supply of oxygen, and, Avheu this is interfered with, excita- bility is rapidly lost. Effects of hreatiting gases other fJuoi the atmosphere. — The diminu- tion of oxygen has a more direct influence in the production of the usual symptoms of asphyxia than the increased amount of carbon dioxide. Indeed, the fatal effect of a gradual accumulation of carbon dioxide in the blood, when a due supply of os3'gen is maintained, resembles- rather the action of a narcotic poison than it does asphyxia. Then again we must carefully distinguish the asphyxiating effect of an insufficient supply of oxygen from the directly poisonous action of such gases as carbonic oxide, which is contained 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 entering into combination with the hsemoglobin of the blood-corpuscles and thus expelling the oxygen. The partial pressure of oxygen in the atmosphere may be considerably increased without much effect. Hydrogen may take the place of nitrogen if the oxygen is in the usual proportion with no marked ill effect. Sulphuretted hydrogen interferes with the oxygenation of blood. Nitrous oxide acts directly on the nervous system as a narcotic. Certain gases, such as carbon dioxide in more than a certain proportion; sulphurous and other acid gases, ammonia, and chlorine produce spasmodic closure of the glottis, and are irrespirable. As conditions causing asphyxia in addition to the obstruction to the trachea or elsewhere, and the prevention of the meeting of the blood 284 HANDBOOK OP PHYSIOLOGY. and the air in the lung tissue by the blocking of one or more branches of the pulmonary artery, may be mentioned the following: Alteration in the atmospheric jjressure. — The normal condition of breathing is that the oxygen of the air breathed should be at the pres- sure of \ of the atmosphere, viz., | of 760 mm. of mercury, or 152 mm., but it is found that life may be carried on by gradual diminution of the oyxgen pressure to considerably less than one half of this, viz., to 76 mm,, or -^^ partial pressure, which is reached at an altitude above 15,000 feet.* Any pressure less than this may begin to produce altera- tions in the relations of the gases in the blood, and if an animal is sub- jected suddenly to a marked decrease of barometric pressure, and so of oxygen pressure (below ? per cent), it is thrown into convulsions, and it is found that the gases are set free in the blood-vessels, no doubt carbon dioxide and oyxgen as well as nitrogen, although the latter is the only one of the three gases the jjresence of which in the vessels in death from this condition of affairs has been proved; the others are said to be reabsorbed. Other derangements may precede this, e.g., bleeding from the nose, dyspncea, and vascular derangement. On the other hand, the oygxen may be gradually increased to a considerable extent without marked effect, even to the extent of 8 or 10 atmospheres, but when the oxygen pressure is increased up to 20 atmospheres the animals experi- mented upon by Paul Bert died with severe tetanic convulsions. The alteration of pressure above or below a certain average affects primarily the gaseous interchange in the lungs, jyul then that in the tissues gene- rally, but signs of dyspnoea may be produced as well either by cutting off the sup2)ly of blood to the medullary centres, or by warming the hlood of the carotid arteries which supply them. The cause in the former case being the deprivation of oxygen and the accumulation of the car- bon dioxide, and of the latter, the increased metabolism of the centre set up by the warmed blood. * For an interesting account of the symptoms produced by diminished atmos- pheric pressure in those mounting to very high altitudes, Whymper's "Travels amongst the Andes of the Equator" may be consulted. CHAPTEE YIII. FOOD AND DIGESTION. The object of digestion is to bring the materials of the food into such a condition that they may be taken up by the blood and lymphatic vessels, and so rendered available for the wants of the system. Very few of these materials are fit for this purpose when taken into the body, and the majority would therefore be to all intents and purposes quite useless unless digested. It is unnecessary to mention all the various substances which may have been used as food at some time or another, and we shall confine our attention, therefore, to the chief and most familiar articles of diet. We find, then, that foods may be divided into classes corresponding closely to those employed to describe the chief substances of which the animal body consists. This classification may be recapitulated as fol- lows : — ORGANIC. I. Foods primarily containing Nitrogenous substances, consisting of Pro- teids, e. (/., albumen, casein, myosin, gluten, legumin and their allies; and Gelatins, e.g., gelatin, elastin, and chondrin. II. Food primarily containing Non-Nitrogenous substances, comprising : (1.) Amyloid or saccharine bodies, chemically known as carbo-hydrates; e. g. , starches and sugars. (2.) Oils and fats. — These substances contain carbon, hydrogen, and oxy- gen, but the oxygen is less in amount than in the amyloids and saccharine bodies. INORGANIC. I. Foods which supply Mineral and saline matter. II. Liquid food containing chiefly Water. Man requires that the chief part of his food should be cooked, Yerj few organic substances can be properly digested without previous ex- posure to heat and to other manipulations which constitute the process of cooking. Organic nitrogenous foods. a. — The Flesh of Animals, e.g., 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 1G.5, and 285 286 HANDBOOK OF PHYSIOLOGY. pork, 10; beef is also firmer, more satisfying, and is supjjosed 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; chiefly myosin, and one or more glohulins; serwn-albumin, gelatin (from the interstitial fibrous connective tissue); elastin (from the elastic tissue), as well as lumio- globin. (3) Fatty matters, including lecithin and cholesterin. (3) Ex- tractive matters, some of which are agreeable to the palate, e.g. osmazome, and others, which are weakly stimulating, e.g., creatin. 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 some animals, in the form of inosite, dextrin, grape sugar, and (in young animals) ghjcogen. Beef. — Lean . Fat . Mutton. — Lean Fat . . . Veal .... Pork.— Fat 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 j)art in the supply of nitrogenous substances, and n\^o fish — salmon, eels, etc., and shell-fish, e.g., lobster, crab, mussels, oysters, shrimps, scollops, cockles, etc. Table of Percentage Composition of Poultry and Fish. — (Letheby.) W^ater. Albumen. Fats. Salts. Poultry 74 21 3.8 1.2 ' (Singularly devoid of fat, and is therefore generally eaten with bacon or pork.) Beef, iBY ) Mutton, Pork, AND Veal. >a 1 . } ater. Albumen. Fats. Salts. 72 19.3 3.6 5.1 51 14.8 29.8 44 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 Water. Albumen. Fats. Salts. 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 (7.39 consist of non-nitrogenous matter and loss.) (Payen.) Even now the list of fleshy foods is not complete, as the flesh of nearly all animals has been occasionally eaten, and we may presume FOOD AND DIGESTION. 28? that except for difference of flavor, etc., the average composition is nearly the same in every case. b. Milk* — -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 caseinogen, and serum or lact-albiimin. (2) Fats in the cream. (3) Carbo-hydrates in the form of lactose or milk sugar. (4) '^•aXi^, chie^j calcium i^hosphate ; and (5) Water. From it we obtain {a) clieese, which is the clotted caseinogen or casein precipitated Avith more or less of 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 precipi- tated casein is allowed to ripen, by which process some of the al- bumin is further split up, with formation of fat. (,5) Cream, consists of the fatty globules encased in caseinogen and serum-albumin, and which being of low specific gravity float to the surface, {y) Butter, or the fatty matter deprived of its proteid envelope by the process of churning. {(i) Buttermilk, or the fluid obtained from cream after butter has been formed; very rich therefore in nitrogen. (;) HV/py, or the fluid which remains after the precipitation of casein; it contains sugar, salt, and a small quantity of albumen. Table of Composition of Milk, Butter- milk, Cream, and Cheese. — (Letheby AND Pa yen. ) Nitrogenous mattei-s. Fats. Lactose. Salts. Water. Milk {Cow) .... 4. 1 3. 9 5. 3 . 8 86 Buttermilk .... 4.1 .7 6.4 .8 88 Cream . . . . . 2.7 26.7 2.8 1.8 66 Cheese.— Skim. ... 44.8 6.3 — 4.9 44 Cheese.— Cheddar . . . 28.4 81.1 — 4.5 36 Non-nitrogenous matter and loss. Cheese.— Neufchatel (Fresh). 8. 40.71 36.58 .51 36.58 c. Eggs. — The yolk and albumen of eggs are in the same relation as food for the embryos of oviparous animals that milk is to the young of mammalia, and afford another example of the natural admixture of the various alimentary principles. The proteids of eggs are egg-albumin and globulins, of which the vitelUn of the yolk is most important; nuclein in combination with iron is also found. In addition to the three common fats there is a yellow fat, lutein (lipoehome), a small quantity of grape sugar; lecitliin, and cliolesterin and inorganic salts, chiefly potassium chloride and phosphates. Table op the Percentage Composition of Fowls' Eggs. White Yolk itrogenous substances. Fats. Salts. Water. 20.4 1.6 78 16. 30.7 1.3 53 *The details of the comijosition of milk will be discussed in the Chapter on Secretion. 288 UANDBOOK OF PHYSIOLOGY. d. Legumi)ious friiifs are used by vegetarians, as the chief source of the nitrogen of the food. Those chiefly used are j'jea*, 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. Organic non-nitrogenous foods. 1. Carbo-Tiych'ates. — 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 carbo-hydrate is supplied in an ordinary diet. It contains starch, dextrin, and a little sugar. It also, besides these, contains gluten, composed of several vegetable proteids, and a small amount of fat. Table of Percentage Composition of Bread and Flour. Nitrogenous matters. Carbo- hydrates. Fats. Salts. Water. 8.1 51. 1.6 2.^ 37 10.8 70.85 o 1.7 15 Bread Flour .... Various articles of course besides bread are made from flour, e.g., sago, macaroni, biscuits, etc. There is dextrine and a small amount of dextrose in bread, particularly in the crust. h. Vegetables, especially potatoes. They contain starch and sugar. In cabbage, turnips, etc., the salts of potassium are abundant. c. Fruits contain sugar, and organic acids, tartaric, malic, citric, and others. d. Sugar, chiefly saccharose, used pure or in various sweetmeats. //. Oils and fats. — The substances supplying the oils and fats of the food are chiefly butter, bacon and lard (pig's fat), suet (beef and mutton fat), and vegetable oils. These contain olein, stearin, and palmitin. Butter contains others in addition, while vegetable oils, as a rule, con- tain no stearin. Mineral or Inorganic Foods. The salts of the food. — Nearly all the foregoing substances in the preceding classes, contain a greater or less amount of the salts required in food, but green vegetables and fruit supply certain salts, chiefly potassium, without which the normal health of the body cannot be maintained. Sodium chloride is an essential food; it is contained in nearly all solids, but so much is required that it has also to be taken as a condi- ment. Potassium salts are supplied in muscle, nerve, in meats generally, and in potatoes. Calcium salts are supplied in eggs, blood of meat, wheat and vegetables. Iron is contained in haemoglobin, in milk, eggs, and FOOD AND DIGESTION. 289 vegetables. It is derived in all cases, so it is supposed, by organic compounds, into which it is built up during plant life, or during the life of other animals (haBmatogens). 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 astringent of the nature of tannin, and an alkaloid, theine. The composi- tion of coffee is very nearly similar to that of tea. Cocoa, in addition to similar substances contained in tea and coffee, contains fat, albumin- ous 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 its 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. The effect of cooking. — In general terms this may be said to make the food more easily digestible; this usually implies two alterations, — food is made more agreeable to the palate and also more pleasing 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 indirect heat of the fire, as iii broiling, baking, or frying, or to hot water, as in boiling or stewing. The effect of heat upon {a) flesh is to coagulate the albumen and coloring matter, to solidify fibrin, and to gelatinize ten- dons 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 sur- face certain erapyreumatic bodies, which are agreeable both to the taste and smell. By placing meat in hot water, the external coating of albu- men 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 sim- mering at a much lower temperature, and the "troth" will then contain the gelatin and extractive matters of the meat, as well as a certain amount of albumen. The addition of salt will help to extract myosin. The effect of boiling {b) an Qg^ is to coagulate the albumen, which helps to render it more easily digestible. Upon (c) milk, the effect of 19 290 HANDBOOK OF PHYSIOLOGY, heat is to produce a scum composed of albumen and ii little caseinogeu (the greater part of the caseinogen being uucoagulated) with some fat. Upon (tl) vegetables, the cooking j)roduces the necessary effect of ren- dering them softer, so that they can be more readily broken up in the mouth; it also causes the starch grains to swell up and burst, and so aids the digestive fluids in penetrating into their substance. The albu- minous matters are coagulated, and the gummy, saccharine and saline matters are removed. The conversion of flour into dough is effected by mixing it with water, and adding a little salt and a certain amount of yeast. Yeast consists of the cells of an organized ferment {Torula cerevism), and it is by the growth of this plant, changing by ferment action the sugar produced from the starch of the flour, that a quantity of carbonic acid gas and alcohol is formed. By means of the former the dough rises. Another method of making dough consists in mixing the flour with water containing a large quantity of carbonic acid gas in solution. By the action of heat during baking [d) the dough continues to ex- pand, and the gluten being coagulated, the bread sets as a permanently vesiculated mass. The food is first of all received into the mmith, and is subjected to the action of the teeth and tongue, being at the same time mixed with the first of the digestive juices — the saliva. It is then swallowed, and, passing through the phanjnx and cesophagus into the stomach, is sub- jected to the action of the gastric juice — the second digestive juice. Thence it passes into the intestines, where it meets with the hile, the pancreatic juice, and the intestinal juices, all of which exercise an in- fluence u23on the portion of the food not already absorbed from the stomach. By this time most of the food is digested, and the residue of undigested matter leaves the body in the form of forces by the external opening of the bowel. The Mouth is the cavity contained between the jaws and inclosed by the cheeks laterally, the lips anteriorly; behind, it opens into the pharynx by the fauces, and is separated from the nasal cavity above, by the hard palate in front, and the soft palate behind, which forms its roof. The tongue forms the lower part or floor. In the jaws are con- tained the teeth, and when the mouth is closed these form its anterior boundaries. The whole of the cavity of the mouth is lined with strati- fied epithelium, of which the superficial layers are squamous. This epithelium is continuous at the lips with that of the skin anteriorly, and posteriorly with that of the pharynx. The mucous membrane itself, varying in thickness in various parts, and consisting of a fine areolar connective, in which is found ade^ioid tissue in considerable amount, is provided with numerous small t^ibular glands lined with FOOD AND DIGESTION. 291 columuar epithelium, and resembling in structure the mucous salivary glands, to be presently described. Into the buccal cavity open the ducts of the salivary glands, which are three in number on either side. In the mouth, then, the food is subjected to the action of the teeth, or is masticated, and is mixed with saliva. These processes of mastica- tion and in salivation must be considered more in detail. Mastication. — The act of chewing, or mastication, is performed by the biting and grinding movement of the lower range of teeth against the upper. The simultaneous movements of the tongue and cheeks assist partly by crushing the softer portions of the food against the hard palate and gums, and thus supplementing the action of the teeth, and partly by returning the morsels of food to the action of the teeth, again and again, as they are squeezd out from between them, until the have been sufficiently chewed Muscles. — The simple up and down, or biting movements of the lower jaw, are performed by the temporal, masseter, and internal ptery- goid 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 mus- cles, the muscle of one side acting alternately with the other. When both external pterygoids act together, the lower jaw is pulled directly forward, so that the lower incisor teeth are brought in front of the level of the upper. Temporo-maxillary Fibro- Cartilage. — The function of the inter- articulo-fibro-cartilage of the temjioro -maxillary joint in mastication is to serve : — (1) As an elastic pad to distribute the pressure caused by the exceedingly powerful action of the masticatory muscles. (2) As a joint surface or socket for the condyle of the lower jaw when the latter has been partially drawn forward out of the glenoid cavity of the tem- poral bone by the external pterygoid 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. Nervous Mechanism. — The act of mastication is partly voluntary and partly reflex and involuntary. The consideration of such nervous actions will come hereafter. It will suffice here to state that the affer ent nerves chiefly concerned are the sensory branches of the fifth and the tenth or glosso-pharyngeal, and the efferent are the motor branches of the fifth and the twelfth (hypoglossal) cerebral nerves. The nerve- centre through which the reflex action occurs, and by which the move- ments of the various muscles are harmonized, is situated in the medulla oblongata. In so far as mastication is voluntary or mentally perceived, it is under the influence of the cerebral hemispheres. Insalivation. — The act of mastication is much assisted by the saliva 292 HANDBOOK OF PHYSIOLOGY. 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 iiisalivation. The Salivary Glands. The glands which secrete the saliva in the human subject are the salivary glands proper, viz., the parotid, the sub-maxillary, and the sub-lingual, and numerous smaller bodies of similar structure, and with separate ducts, which are scattered thickly beneath the mucous mem- brane of the lips, cheeks, soft palate, and root of the tongue. Structure. — The salivary glands are compound tubular or tubulo- racemose glands. They are made up of lobules. Eacli lobule consists of the branchings of a subdivision of the main duct of the gland, which Fig. 221.— Section of sub-maxillary gland of dog. Showing gland cells, h. and a duct, a, in section. (Kolliker.) is generally more or less convoluted toward its extremities, and some- times, according to some observers, sacculated or pouched. The con- vluted 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 homogenous ground- substance. Within, upon this membrane, which forms the tube, the nucleated salivary secreting cells, of cubical or columnar form, are ar- ranged parallel to one another enclosing a central canal. The granular appearance frequently seen in the salivary cells is due to the very dense network of fibrils which they contain. When isolated, the cells not in- frequently 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 epithe- FOOD AND DIGESTION. 293 lium with elongated nuclei. The intercalary ducts pass into the intra- lobular ducts by a narrowed neck, lined with cubical cells with small nuclei. The intralobular duct is larger in size, and is lined with large columnar nucleated cells, the parts of which, toward the lumen of the tube, present 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 out- side 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, the cells of which contain an intracellular net- work 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 Fig. 223.— From a section through a true salivary gland, a, The gland alveoli, lined with albuminous •' salivary cells ; " b. intralobular duct cut transversely. (Klein and Noble Smith.) mixed with mucus, or pure mucus, and therefore the glands have been -classified as: — (1) True salivary (jlamU (called most unfortunately by some, serous glands), e.g., the parotid of man and other animals, and the submaxil- lary of the rabbit and guinea-pig (fig. 222). In this kind the alveolar lumen is small, and the cells lining the tubule are short granular colum- nar 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 the sympathetic, the cells become smaller and their contents more opaque; the granules first of all disappearing from the outer j)art 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 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 294 HANDBOOK OF PHYSIOLOGY. columnar cells with irregular or flattened nuclei near the basement mem- brane. 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. 223). When the gland is secreting, as well as on stimulation of the nerve, mucigen is con- verted into mucin, and the cells swell up, appear more transparent, and stain deeply in logwood (fig. 224). After stimulation, the cells become smaller, more granular, and more easily stained, from having discharged their contents. The nuclei appear more distinct, {h) Crescent.^ of Gla- nuzzi, sometimes called the Semihmes of Ihidenliain (fig. 223), which are crescentic masses of granular parietal cells found here and there be- tween the basement membrane and the central cells. The cells com- posing the mass are small, and have a very dense reticulum, the nuclei Fig. 233. Fig. 234. Fig. 22.3. — From a section through a mucous gland in a quiescent state. The alveoli are lined with transparent mucous cells, and outside these are the semilunes. The cells should have been represented as more or less granular. (Heidenhain.) Fig. 224. — A part of a section through a mucous gland after prolonged electrical stimulation. The alveoli are lined with small granular cells. (Lavdovs^ i.) are spherical, and increase in size during secretion. In the mucous gland there are some large tubes, lined with large transparent central cells, and having besides a few granular parietal cells; other small tubes are lined with small granular parietal 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, while 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 principally contained in the connective tissue of the alveoli, 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, pene- trate the basement membrane of the alveoli and enter the salivary cells. The blood-vessels form a dense capillary network around the ducts FOOD AXD DIGESTION. 295 of tiie iilveoli, being carried iu by the fibrous trabeciilas between the alveoli, in which also begin the lymphatics by lacunar spaces. The so-called mucous glands of the mouth and tongue present in some cases the structures of mucous, in others of serous glands. Saliva. Saliva, as it commonly flows from the mouth, is the mixed secretion of the salivary glands proper and of the glands of the buccal mucous membrane and tongue; it is often mixed with air, which, being retained by its viscidity, makes 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 minute 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 mem- brane of the mouth and tongue, and the so-called salivary corjjuscles, 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, leaviijg the super- natant salivary fluid transparent and colorless, or with a pale bluish- gray tint. It also contains various kinds of micro-organisms (bacteria). In reaction, the saliva, when first secreted, appears to be always alka- ine.. During fasting, the saliva, although secreted alkaline, shortly becomes neutral; especially when it is secreted slowly and is allowed to mix with the acid mucus of the mouth, by which its alkaline reaction is reutralized. Chemical Composition of Mixed Saliva (Frerichs). Water 994.10 Solids : — Ptyalin . 1.41 ' Fat 0.07 ' Epithelium and Proteids (including Serum- Albumin, Globulin, Mucin, etc.) , 2.13 Salts :— Potassium Sulpho-Cyanate Sodium Phosphate ..... Calcium Phosphate .... Magnesium Phosphate ... Sodium Chloride .... PotassiuUi Chloride ..... 2.29 5.9 1000 The mucin is the largest representative of the organic nitrogenous class of bodies in the saliva; it may be thrown down by addition of acetic acid, if sodium chloride be absent. It gives the three chief pro- 29G HANDBOOK OF PHYSIOLOGY. teid reactions, and may easily be sjDlit up by the action of a dilute min- eral acid into a proteid, and a substance which will reduce copper sul- phate solutions, but which is not exactly a sugar. The presence of potassium sulphoci/at/die (or tJiiocyanate] (CNKS) in saliva, may be shown by the blood-red coloration which the fluid gives with a solution of ferric chloride (FeaCle), and which is bleached on the addition of a solution of mercuric chloride (HgCla), but not by hydrochloric acid. Rate of Secretio7i 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 j^robably from 1 to 3 joints (^ to 1^ litres). Uses of Saliva. — The purposes served by saliva are {a) mechanical and {b) chemical. a. Mechanical. — (1) It keeps the mouth in a due condition of moist- ure, 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 tlie 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 swallov/ed. To this purpose the saliva is adapted both by quantity and quality. For, speaking generally, the quantity secreted during feeding is in direct j)roportion 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 secretion 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 oesojihagus. (b) Chemical. — The chemical action which the saliva exerts upon the food in the mouth is to convert the starchy materials which it contains into sugar. This power the saliva owes to one of its constituents ^^^//rt- lin, which is a nitrogenous body of uncertain composition. It is classed among the unorganized ferments, which are substances capable of pro- ducing changes in the composition of other bodies with which they come into contact, without themselves undergoing change or suffering dimin- ution. The conversion of the starch under the influence of the ferment into sugar takes place in several stages, and in order to understand it. FOOD AND DIGESTION. 297 a knowledge of the structure and composition of starch granules is nec- essary. A starch granule consists of two parts : an envelope of cellulose, which does not give a blue color with iodine except on addition of sul- phuric acid, and of gramdose, which is contained within, and which gives a blue with iodine alone. Briicke states that a third body is con- tained in the granule, which gives a red with iodine, viz., erythro- granulose. On boiling, the granulose swells up, bursts the envelope, and the whole granule is more or less completely converted into a paste or gruel, which is called gelatinous starch. When ptyalin or other amylolytic ferment is added to boiled starch, sugar almost at once makes its appearance in small quantities, but in addition there is another body, intermediate between starch and sugar, called ei-ytliro-dextrin, which gives a reddish-brown coloration with iodine. As the sugar increases in amount, the erythro-dextrin disap- pears, but its place is taken in part by another dextrin, achroo-dextrin, which gives no color with iodine, but may be thrown down with alcohol. However long the reaction goes on, it is unlikely that all the dextrin becomes sugar. Next with regard to the kind of sugar formed, it is not glucose but maltose, the formula for which is C12H02O11. Maltose is allied to sac- charose or cane-sugar more nearly than to glucose; it is crystalline; its solution has the property of polarizing light to the right to a greater degree than solutions of glucose (3 to 1) ; it is not so sweet, and reduces copper sulphate less easily. It can be converted into glucose by boiling with dilute acids. According to Brown and Heron the reactions may be represented thus : — One molecule of gelatinous starcli is converted by the action of an amylolytic ferment into n molecules of soluble starch. One molecule of soluble starch = 10 (Cr2H2oO,o) + 8 (H2O), which is further con- verted by the ferment into 1. Ervthro-dextrin (giving red with iodine) -|- Maltose. 9 (Ci.H^oOu,) (C:2H.,20„) then into 2. Ervthro-dextrin (giving yellow with iodine) -|- Maltose. ' 8 (C,.,H.,oO,„) 2 (C,2Ho.,0x,) next into 3. Achi-oo-dextrin -{- Maltose. 7 (CioH^oOio) 3 (C,2H.,20n) And so on ; the resultant being : — 10 (Ci^H^oOio) + 8 (H2O) = 8 (C^H^^On) + 2 (Ci^H^oO.o) Soluble starch Water Maltose Achroo-dextrin. Test for Sugar. — 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. The action of saliva o?i starch is facilitated by : {a) Moderate heat, about 37.8° C. (100° F.). (b) A slightly alkaline medium, (c) Removal 298 HANDBOOK OF PHYSIOLOGY. of the changed material from time to time. Its action is retarded hi/ : (a) Cold; a temperature of 0° C. (32° ¥.) sto]3s it for a time, but does not destroy it, whereas a high temperature above 760°C. (140° F.) de- stroys 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 or diastasic ferment. Starch appears to be the only principle of food upon which saliva acts chemically : the secretion has no apparent influence on any of the other ternary principles, such as sugar, gum, cellulose, or on fat, and seems to be equally destitute of power over albuminous and gelatinous substances. Saliva from the parotid is less viscid; less alkaline, the first few drops discharged in secretion being even acid in reaction; clearer, al- though it may become cloudy on standing from the precipitation of calcium carbonate from escape of carbon dioxide; and more watery than that from the submaxillary. It has moreover a less powerful action on starch. Sublingual saliva is the most viscid, and contains more solids than either of the other two, but has little diastasic 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. The salivas of the dog, cat, bear, and pig are almost inactive, whereas that of monkeys, rabbits, mice, squirrels, and guinea-pigs, are strongly diastasic. The Nervous Mechanism of the Secretion of Saliva. The secretion of saliva is under the control of the nervous system. It is a reflex action. Under ordinary conditions it is excited by the stimulation of the peripheral branches of two nerves, viz., the gustatory or lingual branch of the inferior maxillary division of the fifth nerve, and the glosso-pltaryngeal part of the eighth pair of nerves, which are distributed to the mucous membrane of the tongue and pharynx con- jointly. The stimulation occurs on the introduction of sapid substances into the mouth, and the secretion is brought about in the follwing w;iy. From the terminations of the above-mentioned sensory nerves distrib- uted in the mucous membrane an impression is conveyed upward (afferent) to the special nerve centre situated in the medulla-oblongata which controls the process, and by it is reflected to certain nerves sup- plied to the salivary glands, which will be presently indicated. In other words, the centre, stimulated to action by the sensory impressions car- ried to it, sends out impulses along efferent or secretory nerves siipplied to the salivary glands, which cause the saliva to be secreted by and dis- charged from the gland cells. Other stimuli, however, besides that of FOOD AND DIGESTION". 299 the food, and other sensory nerves besides those mentioned, may j^ro- duce reflexly the same effects. For example, saliva may be caused to flow by irritation of the mucous membrane of the mouth with mechani- cal, 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 ojytic nerves by the sight of it, and of the auditory nerves by the sounds which are known by experience to accompany the preparation of a meal, may also, in the hungry, stimulate the nerve centre to action. In addi- tion to these, as a secretion of saliva follows the movement of the mus- cles of mastication, it may be assumed that this movement stimulates the secreting nerve fibres of the gland, direct or reflexly. From the fact that the flow of saliva may be increased or diminished by mental emo- tions, it is evident that impressions from the cerebrum also are capable of stimulating the centre to action or of inhibiting its action. Salivary secretion may also be excited by direct stimulation of the centre in the medulla. On the Submaxillary Gland. — The subm^axillary gland has been the gland chiefly employed for the purpose of exj)erimentally demonstrating the influence of the nervous system upon the secretion of saliva, because 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 /acta/ [ov portio dura of the seventh pair of nerves), in the canal through which it passes in the temporal bone, in its passiige 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. 225, eh. /.), after quitting the temporal bone, passes downward and forward, under cover of the external ptery- goid muscle, and joins at an acute angle the lingual or gustatory nerve, proceeds with it for a short distance, and then passes along the submax- illary gland duct (fig. 225, sm. d.), to which it is distributed, giving branches to the submaxillary ganglion (fig. 225, sm. r//.),and sending others to terminate in the superficial muscles of the tongue. It consists of fine medullated fibres which lose their medulla in the gland. 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 stimulation 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 stimu- lated, an abundant secretion of saliva ensues, and the blood supply is enormously increased, the arteries being dilated. The veins even pul- sate, and the blood contained within them is more arteriarthan venous in character. 300 HANDBOOK OF PHYSIOLOGY. 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 divided, the gland, released from nervous control, may secrete con- tinuously and abundantly ( imralytic secretion). The abundant secretion of saliva, which follows stimulation of the chorda tympani, is not merely the result of a filtration of fluid from Fig. 225.— Diagrammatic representation of the sub-maxillary gland of the dog with its nerves and blood-vessels. (This is not intended to illustrate the exact anatomical relations of the several struc- tures.) sm. gld., the submaxillary gland into the duct (sm. d.~) of which a canula has been tied. The subungual g-land and duct are not shown, n. I., 71. I'., the lingual or gustatory nerve ; ch. t., ch. t'., the chorda tympani proceeding from the facial nerve, becoming conjoined with the lingual at ii. ?'., and afterward diverging nnd passing to the gland along the duet ; S7n. gl., sub-maxillary ganglion with its roots; n, ?., the lingualnerve proceeding to the tongue ; a. car., the carotid artery, two branches of which, ct. sm. a. and r. sin. p., pas'; to the anterior and posterior parts of the gland ; V. sm., the anterior and posterior veins from the gland ending in v.j.. the jugular vein ; v. sym., the conjoined vagus and sympathetic trunks ; gl. cer.s.. the superior-cervical ganglion, two branches of which forming a plexus, a.f., 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 theyascend to the brain by the lingual and descend by the chorda tympani. ( M. Foster.) 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-pres- sure in the arteries, and also that when into the veins of the animal experimented upon some atrojnn has been previously injected, stimula- tion of the peripheral end of the divided chorda produces all the vascu- lar 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 stimulated with an interrupted current, a secretion of saliva ensues for a short time, although the blood supply is necessarily absent. These FOOD AND DIGESTION. 301 experiments serve to prove that the chorda contains two sets of nerve fibres, one set {vaso-dilator) M^hich, when stimuhited, 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 atropiu, 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 experiments 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 ganglion is ever the nerve centre which controls the secretion of the submaxillary gland. On the Parotid Gland. — The nerves which influence secretion in the parotid gland are branches of the facial (lesser superflcial petrosal) and of the sympathetic. The former nerve, after passing througli the optic ganglion, joins the auriculo-temporal branch of the fifth cerebral nerve, and, with it, is distributed to the gland. The nerves by which the stimulus ordinarily exciting secretion is conveyed to the medulla ob- longata, are, as in the case of the submaxillary gland, the fifth, and the glosso-pharyngeal. The pneumogastric nerves convey a further stimu- lus to the secretion of saliva, when food has entered the stomach; the nerve centre is the same as in the case of the submaxillary gland. Changes in tlie 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, viz., whether to (1) the true salivary, or (2) to the mucous type. In the former case, it has been noticed, as has been already described, that during the rest which follows an active secretion the lumeii of the alveo- lus becomes smaller, the gland cells larger and very granular. During secretion the alveoli and their cells become smaller, and the granular appearance 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. 226).' 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 ele- 302 HANDBOOK OF PHYSIOLOGY. ments 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 these granules, with or without previous change. The granules are taken to represent the chief substance of the salivary secre- tion, 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 tlie 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 dis- charge 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 mucus-secreting gland, the changes in the cells dkring secre- tion have been already spoken of. They consist in the gradual secre- rig, 226.— Alveoli of true salivary gland. A, at rest; B, in the first stage of secretion ; C, after pro- longed secretion. (Langley.) tion by the protoplasm of the cell of a substance called imicigen, 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. The materials which they have incorporated with them- selves are almost at once given up again, in the form of a fluid (secre- tion), which escapes from the ducts of the gland; and the cells, them- selves, undergo disintegration— again to be renewed, in the intervals of the active exercise of the functions. The source whence the cells obtain the materials of their secretion is the blood, or, to speak more accu- rately, the plasma, which is filtered off from the circulating blood into the interstices of the glands as of all living textures. FOOD AXD DIGESTION". 303 The Tongue. Structure. — The tongue is a muscular organ covered by mucous membrane. The muscles, which form the greater part of the substance of the tongue {intrinsic muscles) are termed Unguales; and by these. Fig. 227. — Papillar surface of the tongue, with the fauces and tonsils. 1, 1, circumvallate pa- pillae, in front of 2, the foramen csecum; 3, fungiform papilla? ; 4. filiform and conical papillae ; 5, transverse and oblique rugae ; 6, mucous glands at the base of the tongue and in the fauces; 7. tonsils; 8, part of the epiglottis ; 9, median glosso-epiglottidean fold (fraenimi epiglottidis). (From Sappey.) which are attached to the mucous membrane chiefly, its smaller and more delicate movements are chiefly performed. By other muscles {extrinsic muscles), as the genio-hyoglossus, the styloglossus, etc., the tongue is fixed to surrounding parts, and by this group of muscles its larger movements are performed. The mucous membrane of the tongue resembles other mucous mem- 304 HANDBOOK OF PHYSIOLOGY. branes in essential points of structure, but contains yainllui, more or less peculiar to itself; peculiar, however, in details of structure and ar- rangement, not in their nature. The tongue is beset with numerous mucous follicles and glands. The larger i)ai)ill(B of the tongue are thickly set over the anterior two-thirds of its upper surface, or dorsum (fig. 227), and give to it its characteristic roughness. In carnivorous animals, especially those of the cat tribe, the papillae attain a large size, and are developed into sharp recurved horny spines. Such papillae cannot be regarded as sensitive, but they en- able the tongue to play the part of a most efficient rasp, as in scraping bones, or of a comb in cleaning fur. Their greater prom- inence than those of the skin is due to their interspaces not being filled up with epithe- lium, as the interspaces of the papilla of the skin are. The papilla3 of the tongue present several diversities of form; but Fig. 228. Fig. 229. Fig. 228.— Section of a mucous gland from the tongue. A, opening of the duct on the free sur- face; C, Ijasement 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 90. (Klein and Noble Smith.) Fig. 229. — Vertical section of a circumvallate iiapilla of the calf 1 and 3, epithehal layers covering it ; 2, taste goblets ; 4 and 4', duet of serous gland opening out into the pit in which papilla is situated; 5 and 6, nerves ramifying within the papilla. CEngeluiann.) three principal varieties, differing both in seat and general characters, may usually be distinguished, namely, the (1) circumvallate, the (2) fungiform, and the (3) filiform papillae. Essentially these have all of them the same structure, that is to say, they are all formed by a projec- tion of the mucous membrane, and contain special branches of blood- vessels and nerves. In details of structure, however, they differ consid- erably one from another. The surface of each kind is studded by minute conical processes of mucous membrane, which thus form secondary papillae. (1.) Circumvallate. — These papillae (fig. 229), eight or ten in num- FOOD AND DIGESTION. 305 Iser, are situate in two V-shaped lines at the base of the tongue (1, 1, fig. 227). They are circular elevations from oVth to ya^h of an inch wide, (1 to 2 mm.), each with a central depression, and surrounded by a circular fissure, at the outside of which again is a slightly elevated ring, both the central elevation and the ring being formed of close-set simple papilla. (2.) Fungiform. — The fungiform papillse (3, fig. 227) are scattered chiefly over the sides and tip, and sparingly over the middle of the dor- sum, of the tongue; their name is derived from their being usually nar- rower at their base than at their summit. They also consist of groups of simple papillse (A. fig. 200), each of which contains in its interior a loop of capillary blood-vessels (B.), and a nerve-fibre. (3.) Conical or Filiform. — These, which are the most abundant pa- pillae, are scattered over the whole surface of the tongue, but especially Fig. 230.— Surface a.nd section of the fungiform papillae. A, the surface of a fungiform papilla, partially denuded of Its epithelium; jJ, secondary papillae: e, epithelium. B, section of a fungiform papilla with the blood-vessels injected : a, artery : i\ vein; c. capillary loops of similar papillae in the neighboring structure of the tongue; d, capillary loops of the secondary papillae; e, epithelium. (From Kiilliker, after Todd and Bowman.) over the middle of the dorsum. They vary in shape somewhat, but for the most part are conical or filiform, and covered by a thick layer of epidermis, which is arranged over them, either in an imbricated manner, or is prolonged from their surface in the form of fine stiff projections, hair-like in appearance, and in some instances in structure also (fig. 231). From their peculiar structure, it seems likely that these papillae have a mechanical function, or one allied to that of touch rather than of taste ; the latter sense being probably seated especially in the other two varieties of papillte, the circumvallate and the fungiform. The epitlielium of the tongue is stratified with the upper layers of the squamous kind. It covers every part of the surface; but over the fungiform papillte forms a thinner layer than elsewhere. The epithelium covering the filiform papillae is extremely dense and thick, and, as befoi-e mentioned, projects from their sides and summits in the form of long, stilf, hair-like processes (fig. 231). Many of these processes bear a close resemblance to hairs. Blood-vessels and nerves are supplied freely to 20 306 HANDBOOK OF PHYSIOLOGY. the papillae. The nerves in the fungiform and circumvallate papillae form a kind of plexus, spreading out brushwise (fig. 231), but the exact mode of termination of the nerve-filaments is not certainly known. In the circumvallate papillse of the tongue of man peculiar struc- tures known as gustatory buds or taste goblets, have been discovered. They are of an oval shape, and consist of a number of closely packed, very narrow and fusiform, cells {gustatory cells). This central core of gustatory cells is in- closed in a single layer of broader fusiform cells {incas- ing cells). The gustatory cells terminate in fine spikes not unlike cilia, which project on the free surface (fig. 232 a). These bodies also occur side bv side in considerable num- Fig. 231. Fig. 332. Fig. 231 .—Two filiform papillas, one with epithelium, the other without, ^.—d, the substance of the papillae dividing at their upper extremities into secondary papilte : a. artery, and v. vein. dividing into capillary loops ; e. epithelial covering, laminated between the papillae, but extended into hair-like processes. /. from the extremities of the secondary papillae. (From KoUiker, after Todd and Bowman.) , , , , . , . ., Fig. 232.— Taste-goblet from dog's epiglottis Gaiyngeal surface near the base), precisely similar in structure to those foimd in the tongue, a. depression in epithelium over goblet; below the letter are seen the fine hair-like processes in which the cells terminate : c. two nuclei of the axial (gusta- torv; cells. The more superficial nuclei belong to the superficial (incasing) cells ; the converging lines indicate the fusiform shape of the incasing cells. X 400. (Schofield.) hers in the epithelium of the papilla foliata, which is situated near the root of the tongue in the rabbit, and also in man. Similar taste-goblets have been observed on the posterior (laryngeal) surface of the epiglottis. The Pharyxx. The portion of the alimentary canal which intervenes between the mouth and the oesophagus is termed the Pharynx. It will suffice here to mention that it is constructed of a series of three muscles with stri- FOOD AND DIGESTION". 307 ated fibres {constnctors), which are covered by a thin fascia externally, and are lined internally by a strong fascia (pharyngeal 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 swallowing, is identical with it in general structure. The epithelium of this part of the pharynx, like that of the mouth, is strati- fied and squamous. The pharynx is well supplied with mucous glands (fig. 228). Between the anterior and posterior arches of the soft palate are sit- uated the Tonsils, one on each side. A tonsil consists of an elevation of the mucous membrane representing 32 to 15 orifices, which lead into Fig. 233, Fig. 234. Fig. 2.33.— Lingual follicle or crypt, a, involution of mucous membrane with its papillae; 6, lymphoid tissues, with several lymphoid sacs. CFrey.^ Fie. 234.— Vertical section through a crypt of the human tonsil. 1, entrance to the crypt ; 2 and 3, the framework or adenoid tissue; 4, the inclosing fibrous tissue ; a and b, lymphatic follicles; 5 and 6, blood-vessels. (Stohr.) crypts or recesses, in the walls of which are placed nodules of adenoid or lymphoid tissue (fig. 234). 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 papillae formed of adenoid tissue. The tonsil is bounded by a fibrous capsule (fig. 234, 4). Into the crypts open the ducts of numerous mucous glands. The viscid secretion which exudes from the tonsils serves to lubri- cate the bolus of food as it passes them in the second part of the act of deglutition. 308 HANDBOOK OF PHYSIOLOGY. The CEsophagus or Gullet. The Esophagus or Gullet, 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. Structure. — The oesophagus is made up of three coats — viz., the outer, muscular; the middle, suJmiucous ; and the inner, mucous. The muscular coat is covered externally by a varying amount of loose fibrous ~^~ -x-^r X-''' .^ Fig 235.— Section of the mucous membrane of the oesophagus. tissue. It is composed of two layers of fibres, the outer being arranged longitudinally, and the inner circularly. At the upper part of the (esoph- agus 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 m.oreand more numerous, and toward the end of the tube form the entire coat. The muscular coat is con- nected with the mucous coat by a more or less developed layer of areolar tissue, which forms the submucous coat (fig. 335, /), in which is con- tained in the lower half or third of the tube many mucous glands, the ducts of which, passing through the mucous membrane, open on its sur- face. Separating this coat from the mucous membrane proper is a well- FOOD AKD DIGESTION. 309 developed layer of longitudinal, unstriated muscle, called the muscularis mucosie. The mucous membrane is composed of a closely felted mesh- work of fine connective tissue, which, toward the surface, is elevated into rudimentary papilla?. It is covered with a stratified epithelium, of which the most superficial layers are squamous. The epithelium is ar- ranged 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 (fig. 241). Deglutition. 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 ante- rior arch of the fauces; in the second, the morsel is carried through the pharynx; and in the third, it reaches the stomach through the oesopha- gus. These three acts follow each other rapidly. (1.) The first act may be voluntary, although it is usually performed unconsciously; the mor- sel 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 posterior orifice of the nose and the upper oj^ening of the larynx with- out touching 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 con- tracting on it and then behind it. The root of the tongue being re- tracted, and the larynx being raised with the pharynx and carried for- ward under the base of the tongue, the epiglottis is pressed over the upper opening of the larynx, and the morsel glides past it; the closure of the glottis being additionally secured by the simultaneous contraction of its own muscles: 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 posterior 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. 310 HANDBOOK OF PHYSIOLOGY. raised up to receive it, in its turn contracts, and forces it onward into the oesophagus. The passage of the bolus of food through the constric- tors of the pharynx is counted by some as a distinct stage. (3.) In the third act, in whicli the food passes through the oesophagus, every part of that tube, as it receives the morsel and is dilated by it, is stim- ulated to contract: hence an undulatory contraction of the oesophagus, which is easily observable in horses while drinking, joroceeds rapidly along the tube. It is only when the morsels swallowed are large, or taken too quickly in succession, that the progressive contraction of the oesophagus is slow, and attended with pain. Division of both pneumo- gastric nerves paralyzes the contractile power of the oesophagus and food accordingly accumulates in the tube. The second and third parts of the act of deglutition are involuntary. Nervous Meclianism. — The nerves engaged in the reflex act of deglu- tition are : — sensory, branches of the fifth cerebral sujiplying the soft pal- ate; glosso-pharyngeal, supplying the tongue and pharynx; the superior laryngeal branch of the vagus, supplying the epiglottis and the glottis; while the motor fibres concerned are : — branches of the fifth, sujoplying part of the digastric and mylo-hyoid muscles, and the muscles of masti- cation; the facial, supplying the levator palati; the glosso-pharyngeal, supplying the muscles of the pharynx; the vagus, supplying the muscles of the larynx through the inferior laryngeal branch, and the hypoglos- sal, 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 pneumo-gastrics, 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 gravity. Thus, horses and many other animals habitually drink up- hill, and the same feat can be performed by jugglers. The Stomach. In man and those Mammalia which are provided with a single stom- ach, it consists of a dilatation of the alimentary canal placed between and continuous with the oesophagus, which enters its larger or cardiac end on the one hand, and the small intestine, which commences at its narrowed end or pylorus, on the other. It varies in shape and size ac- cording to its state of distention. Structure. — The stomach is composed of four coats, called respectively —(1) an external or peritoneal, (2) muscular, (3) submucous, and (4) mucous coat; with blood-vessels, lymphatics', and nerves distributed in and between them. (1) The peritoneal coat has the structure of serous membranes in FOOD AXD DIGESTION. 311 general, to be presently described. (2) The mtiscular coat consists of three separate layers or sets of fibre, which, according to their several directions, are named the longitudinal, circular, and oblique. The lon- gitudinal set are the most superficial: they are continuous with tlie longitudinal fibres of the oesophagus and spread out in a diverging man- ner over the cardiac end and sides of the stomach. They extend as far as the pylorus, being especially distinct at the lesser or upper curva- ture of the stomach, along which they pass in several strong bands. The next set are the circiila?' or transverse fibres, which more or less completely encircle all parts of the stomach ; they are most abundant at the middle and in the p3^1oric por- tion of the organ, and form the chief part of the thick projecting ring of the pylorus. These fibres are not simple circles, but form double or figure-of-8 loops, the fibres intersect- ing very obliquely. The next, and consequently deepest set of fibres, are the oblique, continuous with the circular muscular fibres of the oesophagus, and having the same double-looped arrangement that prevails in the preceding layer : they are comparatively few in number, and are placed only at the cardiac orifice and portion of the stomach, over both surfaces of which they are spread, some passing obliquely from left to right, others from right to left, around the cardiac orifice, to which, by their interlacing, they form a kind of sphincter, continuous with that around the lower end of the oesophagus. The muscular fibres of the stomach and of the in- testinal canal are unstriated, being composed of elongated, spindle- shaped fibre-cells. (3) and (4) The mucous membrane of the stomach, which rests upon a layer of loose cellular membrane, or submucous tissue, is smooth, Fig. 236.— From a vertical section through the mucous membrane of the cardiac end of stomach. Two peptic glands are shown with a duct common to both, one gland only in part. a, duct with columnar epithelium becoming shorter as the cells are traced downward; ii, neck of gland tubes, with central and parietal or so-called peptic cells; 6, fundus with curved csecal extremity— the parietal cells are not so numerous here. X 400. (Klein and Noble Smith.) 312 HANDBOOK OF PHYSIOLOGY. level, soft, and velvety; of a pale pink color during life, and in the con- tracted state thrown into numerous, chiefly longitudinal, folds or rugge, which disappear when the organ is distended. The basis of the mucous membrane is a fine connective tissue, which approaches closely in structure to adenoid tissue; this tissue supports the tubular glands of which the superficial and chief joart of the mucous membrane is composed, and passing up between them assists in binding them together. Here and there are to be found in this coat, immedi- ately underneath the glands, masses of adenoid tissue sufficiently marked to be termed by some lymphoid follicles. The glands are sepa- rated from the rest of the mucous membrane by a very fine homogene- ous basement membrane. At the deepest part of the mucous membrane are two layers (circu- lar and longitudinal) of unstriped muscular fibres, called the miiscularis 7nucosce, which separate the mucous membrane from the Gcanty sub- mucous tissue. Fig. 237.— Transverse section through lower part of peptic glands of a cat. a, peptic cells; b, small spheroidal or cubical cells; c, transverse section of capillaries. (Frey.) When examined with a lens, the internal or free surface of the stom- ach presents a peculiar honeycomb appearance, produced by shallow polygonal depressions, the diameter of which varies generally from -oTToth to ^^th of an inch (about 125/^) ; but near the pylorus is as much as yio^th of an inch (250/ji). They are separated by slightly elevated ridges, which sometimes, especially in certain morbid states of the stom- ach, bear minute, narrow vascular processes, which look like villi, and have given rise to the erroneous supposition that the stomach has absorbing villi, like those of the small intestines. In the bottom of these little pits, and to some extent between them, minute openings are visible, which are the orifices of the ducts of perpendicularly arranged tubular glands (fig. 236), imbedded side by side in sets or bundles, on the surface of the mucous membrane, and composing nearly the whole structure. The glands of the mucous membrane are of two varieties, (a) Peptic, (b) Pyloric or Mucous. {a) Peptic glands are found throughout the whole of the stomach except at the pylorus. They are arranged in groups of four or five. FOOD A?s"D DIGESTION". 313 which are separated by a fine connective tissue. Two or three tubes often open into one duct, which forms about a third of the wliole length of the tube and opens on the surface. The ducts are lined with co- lumnar epithelium. Of the gland tube proper, i.e., the part of the gland below the duct, the upper third is the nec/c and the rest the bodi/. The neck is narrower than the body, and is lined with granular cubical cells which are continuous with the columnar cells of the duct. Between these cells and the membraua propria of the tubes, are large oval or spherical cells, opaque or granular in appearance, with clear oval nuclei, bulging out the membrana propria; these cells are called peptic or jJa- rietal cells. They do not form a continuous layer. The body, which is broader than the neck and terminates in a blind ex- tremity ov fundus near the muscularis mu- Fig. 238, Fig. 239. Fig. 2.38.— Section showing the pyloric glands, s, free surface; d, ducts of pyloric glands; n, neck of same; m, the gland alveoli; mm, muscularis mucosae. (Klein and Noble Smith.) Fig. 2:W.— Plan of the blood-vessels of the stomach, as they would be seen in a vertical section. a, arteries, passing up from the vessels of submucous coat; 6, capillaries branching between and around the tubes; c, superficial plexus of capillaries occupyingtheridgesof the mucousmembrane; d, vein formed liy t!ie imion of veins v.'hicli, having collected the blood of the superficial capillary plexus, are seen passing down between the tubes. (Brinton.) cos£e, is lined by cells continuous with the cubical or central cells of the neck, but longer, more columnar and more transparent. In this part are a few parietal cells of the same kind as in the neck (fig. 236). As the pylorus is approached the gland ducts become longer and the tube proper becomes shorter, and occasionally branched at the fundus. {h) Pyloric Glands. — These glands (fig. 238) have much longer ducts than the peptic glands. Into each duct two or three tubes open by very short and narrow necks, and the body of each tube is branched. 314 HANDBOOK OF PHYSIOLOGY. wavy, and convoluted. The lumen is very large The duots are lined with columnar epithelium, and the neck and body with shorter and more granular cubical cells, which corres^jond with the central cells oi' the peptic glands. During secretion the cells become, as in the case of the peptic glands, larger and the granules restricted to the inner zone of the cell. As they approach the duodenum the pyloric glands become larger, more convoluted and more deeply situated. They are directly continuous with Brunner's glands in the duodenum, (Watney.) Changes in the gland cells during secretion. — The chief or cubical cells of the peptic glands, and the corresponding cells of the pyloric glands during the early stage of digestion, if hardened in alcohol, appear swollen and granular, and stain readily. At a later stage the cells be- come smaller, but more granular and stain even more readily. The parietal cells swell up, but are otherwise not altered during digestion. The granules, however, in the alcohol-hardened specimen, are believed not to exist in the living cells, but to have been 2irecipitated by the hardening reagent; for if examined during life they appear to be con- fined to the inner zone of the cells, and the outer zone is free from granules, whereas during rest the cell is granular throughout. These granules are thought to be pepsin, or the substance from which jDcpsin in formed, pepsinogen, which is during rest stored chiefly in the inner zone of the cells and discharged into the lumen of the tube during secretion. (Langley.) Lymphatics. — Lymphatic vessels surround the gland tubes to a greater or less extent. Toward the fundus of the peptic glands are found masses of lymphoid tissue which may appear as distinct follicles, somewhat like the solitary glands of the small intestine. Blood-vessels. — The blood-vessels of the stomach, which first break up in the sub-mucous tissue, send branches upward between the closely packed glandular tubes, anastomosing around them by means of a fine capillary network, with oblong meshes. Continuous with this deeper plexus, or prolonged upward from it, so to speak, is a more superficial network of larger capillaries, which branch densely around the orifices of the tubes, and form the framework on which are moulded the small elevated ridges of mucous membrane bounding the minute, polygonal pits before referred to. From this superficial network the veins chiefly take their origin. Thence passing down between the tubes, with no very free connection with the deeper infer-tubular capillary plexus, they open finally into the venous network in the submucous tissue. Nerves. — The nerves of the stomach are derived from the pneumo- gastric and sympathetic, and form a plexus in the sub-mucous and mus- cular coats containing many ganglia (Remak, Meissner). FOOD AND DIGESTION. 315 Gastric Juice. The functions of the stomach are (a) to secrete a digestive fluid, the gastric juice, to the action of which the food is subjected after it lias entered the cavity of the stomacli from the oesopliagus; (b) to thor- oughly incorporate the fluid with the food by means of its muscular movements; and (c) to absorb such substances as are ready for absorp- tion. While the stomach contains no food, and is inactive, no gastric fluid is secreted; and mucus, which is either neutral or slightly alkaline, covers its surface. But immediately on the introduction of food or other substance, the mucous membrane, previously quite pale, becomes slightly turgid and reddened with the influx of a larger quantity of blood; the gastric glands commence secreting actively, and an acid fluid is poured out in minute drops, which gradually run together and flow down the walls of the stomach, or soak into the substances within it. Chemical Composition. — The first accurate analysis of gastric juice was made by Prout : but it does not appear to have been collected in any large quantity, or pure and separate from food, until the time when Beaumont was enabled, by a fortunate circumstance, to obtain it from the stomach of a man named St. Martin, in whom there existed, as the result of a gunshot wound, an opening leading directly into the stomach, near the upper extremity of the great curvature, and three inches from the cardiac orifice. The introduction of any mechanical irritant, such as the bulb of a thermometer, into the stomach, through this artificial opening, excited at once the secretion of gastric fluid. This was drawn off, and was often obtained to the extent of nearly an ounce. The in- troduction of alimentary substances caused a much more rapid and abundant secretion than did other mechanical irritants. Xo increase of temperature could be detected during the most active secretion; the thermometer introduced into the stomach always stood at 37.8° C. (100° F.) except during muscular exertion, when the temperature of the stom- ach, like that of other parts of the body, rose one or two degrees higher. The chemical composition of human gastric juice has been also in- vestigated by Schmidt. The fluid in this case was obtained by means of an accidental gastric fistula, which existed for several years below the left mammary region of a patient between the cartilages of the ninth and tenth ribs. The mucous membrane was excited to action by the introduction of some hard matter, such as dry peas, and the secretion was removed by means of an elastic tube. The fluid thus obtained was found to be acid, limpid, odorless, with a mawkish taste — with a specific gravity of 1002 to 1010. It contained a few cells, seen with the micro- scope, and some fine granular matter. The analysis of the fiuid obtained in this way is given below. The gastric juice of dogs and other animals 31G HANDBOOK OF PHYSIOLOGY. obtained by the introduction into the stomach of a clean sponge tlirough an artificially made gastric fistula, shows a decided difference in comjao- sition, but possibly this is due, at least in part, to admixture with food. CHEMICAL COMPOSITION OP GASTRIC JUICE. Dogs. Human. Water 971.17 994.4 Solids 28.82 5.39 Solids- Ferment — Pepsin 17.5 3.19 Hydrochloric acid (free) 2.7 .2 Salts- Calcium, sodium, and potassium, chlorides ; and calcium, magnesium, and iron, phosphates 8.57 2.18 The quayitity of gastric juice secreted daily has been variously esti- mated; but the average for a healthy adult may be assumed to range from ten to twenty pints in the twenty-four hours. The acidity of the fluid is due to frefe hydrochloi'ic acid, although other acids, e.g, lactic, acetic, butyric, are not infrequently to be found therein as products of gastric digestion or abnormal fermentation. The amount of hydro- chloric acid varies from 2 to .2 per 1000 parts. In healthy gastric juice the amount of free acid may be as much as .3 per cent. There is but little doubt that hydrochloric acid is the proper acid of healthy gastric juice, and various tests have been used to prove this; most of these depend upon changes produced in aniline colors by the action of hydrochloric acid, even in minute traces, whereas lactic and other organic acids have no such action. Of these tests the following may be mentioned. An aqueous alkaline solution of 00 tropceolin, a bright yellow dye, is turned red on the addition of a minute trace of hydrochloric acid; and aqueous solutions of methyl violet and gentian violet are turned blue under the same circumstances. The lactic acid sometimes present in the contents of the stomach is derived partly from the sarcolactic acid of muscle, and partly from lactic acid fermentation of carbohydrates. Lactic acid (CsHeOa), if jiresent, gives the following test. A solution of 10 cc. of a 4 per cent aqueous solution of carbolic acid, 20 cc. of water, and one drop of liquor ferri perchloride is made, forming a blue-colored mixture; a mere trace of free lactic acid added to such a solution causes it to become yellow, whereas hydrochloric acid even in large amount only bleaches it. As regards the formation of pepsin and acid, the former is produced by the central or chief cells of the peptic glands, and also most likely by t?ie similar cells in the pyloric glands: the acid is chiefly found at the surface of the mucous membrane, but is in all probability formed by the FOOD AND DIGESTION. 317 parietal cells of the peptic glands, hence called oxyntic, as no acid is formed by the pyloric glands in which this variety of cell is absent. The ferment Pepsin can be procured by digesting jjortions of the mucous membrane of the stomach in cold water, after they have been macerated for some time in water at a temperature 37° — 37.8° C. (80° — 100° F.). The warm water dissolves various substances as well as some of the pepsin, but the cold water takes up little else than pepsin, which is contained in a grajash-brown viscid fluid, on evaporating the cold solution. The addition of alcohol throws down the i5ei:)sin in grayish-white flocculi. Glycerine also has the property of dissolving out the ferment ; and if the mucous membrane be finely minced. and the moisture removed by absolute alcohol, a powerful extract may be obtained by throwing into glycerine. Functions. — {a) The chief digestive power of the gastric juice de- pends on the j)epsin and acid contained in it, both of which are, under ordinary circumstances, necessary for the process. The general effect of digestion in the stomach is the conversion of the food into chyme, a substance of varying composition according to the nature of the food, yet always presenting a characteristic thick, pultaceous, grumous consistence, with the undigested portions of the food mixed in a more fluid substance, and a strong, disagreeable acid odor and taste. The chief function of the gastric juice is to convert proteids. into jicptones. This action may be shown by adding a little gastric juice (natural or artificial) to some diluted egg-albumin, and keeping the mix- ture at a temperature of about 37.8° C. (100° F.) ; it is soon found that the albumin cannot be precipitated on boiling, but that if the solution be neutralized with an alkali, a precipitate of acid-albumin is thrown down. After a while the acid-albumin disappears, so that no precipitate results on neutralization, and finally it is found that all the albumin has been changed into another proteid substance which is not precipitated on boiling or on neutralization. This is 0,2^^^ peptone, but in the conver- sion of the albumin into peptone there are various intermediate prod- ucts called proteoses. Of these there are two chief forms, viz., /;ro/o- albumose and deutero-albumose. Characteristics of Peptones. — Peptones have a certain characteristic which distinguishes them, from other proteids. They are diffusible, i.e., they possess the property of passing through animal membranes. In their diflusibility peptones differ remarkably from egg-albumin, and on this ditfusibiliiy depends one of their chief uses. Egg-albumin as such, even in a state of solution, would be of little service as food, inasmuch as its indiffusibility would effectually prevent its passing by absorption into the blood-vessels of the stomach and intestinal canal. AVhen completely changed by the action of the gastric juice into pep- tones, albuminous matters diffuse readily, and are thus quickly absorbed. 318 HANDBOOK OF PHYSIOLOGY, After entering the blood the peptones are very soon again modified, so as to reassunie the chemical characters of albumin, a change as nec- essary for preventing their diffusing out of the blood-vessels, as the previous change was for enabling them to pass in. This is effected, probably, in great part by their passage through the vascular walls. Products of Gastric Digestion. — The chief product of gastric diges- tion is undoubtedly peptone. It should be stated, however, that the conversion of native albumin into acid-albumin may be effected by the hydrochloric acid alone, the further action is undoubtedly due to the ferment and the acid acting together, as although under high pressure any acid solution may, it is said, if strong enough, produce the entire conversion into peptone, under the condition of digestion in the stomach this would be quite impossible; and, on the other hand, pepsin will not act without the j^resence of acid. The production of the two forms of peptone above mentioned is usually recognized. Their differences in chemical properties have not yet been made out, but they are distin- guished by this remarkable fact, that the pancreatic juice, while pos- sessing no action over the anti-peptone, is able to convert the hemi- peptone into two nitrogenous crystallizable bodies, leucin and tyrosin. Pepsin acts the part of a hydrolytic ferment (proteolytic), and appears to cause hydration of albumen, peptone being a highly hydrated form of albumin. According to recent observatio7is a molecule of albumen may be considered to be made up of two parts, a hemi-albumin moiety and an anti-albumin moiety, and the conversion of these parts by the action of gastric juice has been drawn up into the following table by Halliburton from the researches of Neumeister. Albumin. Hemi-Albumin. Anti-Albumin. I 1 Proto-Albumose. Hetero-Albumose. Anti-Albuminate. I I I Hemi-deutero Ampho-deutero Anti-Albumid. Albumose. Albumose. | I I Anti-deutero Albumose. Hemi-Peptone. Ampho-Peptone. Anti-Peptone. Proto-albumose, the first product, is soluble in either hot or cold water, as well as in hot or cold saline solution, but is precipitated by saturation with solid sodium chloride or magnesium sulphate, as well as with solid ammonium sulphate. On the addition of copper sulphate it is precipitated, and the precipitate is redissolved on addition of caustic potash forming a rose red solution (biuret test). Hetero-alhumose differs from proto-albumose in being insoluble in hot or cold water; it is soluble in hot or cold saline solutions, but is precip- FOOD AND DIGESTION. 319 itated, not coagulated, at a temperature of 65° 0. In all other respects it resembles proto-albumose. Deutero-albumose is soluble in hot or cold water, as well as in hot or cold saline solution. It is not precipitated by saturation with solid sodium chloride or magnesium sulphate, but m all other respects re- sembles the other albumoses. Peptone reacts to the same test as deutero-albumose, but is not pre- cipitated on saturation with ammonium sulphate. In the above table then the ultimate result is seen to be peptone; hemi-albumin yielding proto-albumose and hetero-albumose in the first instance; then hemi-deutero-albumose, then hemi-peptone; anti-albumin yielding first hetero-albumose and anti-albuminate (or acid-albumin), then anti-deutero-albumose; anti-albumid, an insoluble product, slowly yielding anti-deutero-albumose, and finally anti-peptone. The term ampho-deutero-albumose, and ampho-pejDtone indicating a mixture of the hemi and anti products respectively. Circumstances favoring Gastric Digestion. — 1. A temperature of about 37.8° C. (100° F.) ; at 0° C. (32° F.) it is delayed, and by boiling is altogether stopped. 2. An acid medium is necessary. Hydrochloric is the best acid for the purpose. Excess of acid or neutralization stops the process. 3. The removal of the products of digestion. Excess of peptone delays the action. a. Fibrin is first dissolved, forming a solution of globulins. The intermediate products of the digestion of globulins are called globuloses; of vitellin, vitelloses; of casein, caseinoses; of myosin, myosinoses. These are practically the same as albumoses, and are included under the term proteoses. b. Proteids. — All proteids are converted by the gastric juice into peptones, and, therefore, whether they be taken into the body in meat, eggs, milk, bread, or other foods, peptone is still the resultant. c. Milk is curdled, the casein being precipitated, and theu dissolved. The curdling is due to a special ferment of the gastric juice, and is not due to the action of the free acid only. The effect of rennet, which is a decoction of the fourth stomach of a calf in brine (rennet), has long been known, as it is used extensively to cause precipitation of casein in cheese manufacture. The ferment which produces this curdling action is distinct from pepsin, and is called rennin. d. Gelatin is dissolved and changed into peptone, as are also chondrin and elastin; but mncin, and the horny tissues, which contain keratin generally are unaffected. e. On the amylaceous articles of food, and upon pure oUnginous prin- ciples the gastric juice has no action. In the case of adipose tissue, its effect is to dissolve the areolar tissue, albuminous cell-walls, etc., which 320 HANDBOOK OF PHYSIOLOGY. enter into its composition, by which means the fat is able to mingle more uniformly with the other constituents of the chyme. The gastric fluid acts as a general solvent for some of the saline constituents of the food, as, for example, particles of common salt, which may happen to have escaped solution in the saliva; while its acid may enable it to dissolve some other salts which are insoluble in the latter or in water. /. It also dissolves cane sugar, and by the aid of its mucus (which may contain an inverting ferment) causes its conversion in part into grape sugar. g. The action of the gastric juice in preventing and checking putre- faction has been often directly demonstrated. Indeed, that the secre- tions which the food meets with in the alimentary canal are antiseptic in their action, is what might be anticipated, not only from the proneness to decomposition of organic matters, such as those used as food, especially under the influence of warmth and moisture, but also from the well-known fact that decomposing flesh {e.g., high game) may be eaten with impunity, while it would certainly cause disease were it allowed to enter the blood by any other route than that formed by the organs of digestion. Time occupied in Gastric Digestion. — Under ordinary conditions, from three to four hours may be taken as the average time occupied by the digestion of a meal in the stomach. But many circumstances will modify the rate of gastric digestion. The chief are: the nature of the food taken and its quantity (the stomach should be fairly filled — not distended) ; the time that has elapsed since the last meal, which should be at least enough for the stomach to be quite clear of food; the amount of exercise previous and subsequent to a meal (gentle exercise being fa- vorable, over-exertion injurious to digestion) ; the state of mind (tran- quillity of temper being essential, in most cases, to a quick and due di- gestion), and the bodily health. Movements of the Stomach. — The gastric fluid is assisted in accom- plishing its share in digestion by the movements of the stomach. In granivorous birds, for example, the contraction of the strong muscular gizzard affords a necessary aid to digestion, by grinding and triturating the hard seeds which constitute part of the food. But in the stomachs of man and other Mammalia the movements of the muscular coat are too feeble to exercise any such mechanical force on the food; neither are they needed, for mastication has already done the mechanical work of a gizzard; and experiments have demonstrated that substances are digested even inclosed in perforated tubes, and consequently protected from mechanical influence. The normal actions of the muscular fibres of the human stomach appear to have a three-fold purpose: (1) to adapt the stomach to the FOOD AND DIGESTIOlSr. 321 quantity of food in it, so that its walls may be in contact with the food on all sides, and, at the same time, may exercise a certain amount of compression upon it ; (2) to keep the orifices of the stomach closed until the food is digested; and (3) to perform certain peristaltic movements, whereby the food, as it becomes chymified, is gradually propelled toward, and ultimately through, the pylorus. In accomplishing this latter end, the movements without doubt materially contribute toward effecting a thorough intermingling of the food and the gastric fluid. "When digestion is not going on, the stomach is uniformly contracted, its orifices not more firmly than the rest of its walls; but, if examined shortly after the introduction of food, it is found closely encircling its contents, and its orifices are firmly closed like sphincters. The cardiac orifice, every time food is swallowed, opens to admit its passage to the stomach, and immediately again closes. The pyloric orifice, during the first part of gastric digestion, is usually so completely closed, that even when the stomach is separated from the intestines, none of its contents escape. But toward the termination of the digestive process, the pylorus seems to offer less resistance to the passage of substances from the stom- ach; first it yields to allow the successively digested portions go through it; and then it allows the transit of even undigested substances. It ap- pears that food, so soon as it enters the stomach, is subjected to a kind of peristaltic action of the muscular coat, whereby the digested portions are gradually moved toward the pylorus. The movements were observed to increase in rapidity as the process of chymification advanced, and were continued until it was completed. The contraction of the fibres situated toward the pyloric end of the stomach seems to be more energetic and more decidedly peristaltic than those of the cardiac portion. Thus, it was found in the case of St. Mar- tin, that when the bulb of the thermometer was placed about three inches from the pylorus, through the gastric fistula, it was tightly embraced from time to time, and drawn toward the pyloric orifice for a distance of three or four inches. The object of this movement appears to be, as just said, to carry the food toward the pylorus as fast as it is formed into chyme, and to propel the chyme into the duodenum; the undigested portions of food being kept back until they are also reduced into chyme, or until all that is digestible has passed out. The action of these fibres is often seen in the contracted state of the pyloric portion of the stom- ach after death, when it alone is contracted and firm, while the cardiac portion forms a dilated sac. Sometimes, by a predominant action of strong circular fibres placed between the cardia and pylorus, the two por- tions, or ends as they are called, of the stomach, are partially separated from each other by a kind of hour-glass contraction. By means of the peristaltic action of the muscular coats of the stomach, not merely is chymified food gradually propelled through the pylorus, but a kind of 322 HANDBOOK OF PHY.SIOLOGT. double current is continually kept up among the contents of the stomach, the circumferential parts of the mass being gradually moved onward toward the pylorus by the contraction of the muscular fibres, while the central portions are propelled in the opposite direction, namely toward the cardiac orifice; in this way is kept up a constant circulation of the contents of the viscus, highly conducive to their free mixture with the gastric fluid and to their ready digestion. Influence of the Nervous System. — The normal movements of the stomach during gastric digestion do not appear to be so closelv con- Fig. 240.— Very diagrammatic representation of the nerves of the alimentary canal. Oe to Ret, the various parts of the alimentary canal from oesophagus to rectum; L. V, left vagus, ending on front of stomach; rl, recurrent laryngeal nerve, supplying upper part of oesophagus; R.V, right vagus, joining left vagus in oesophageal plexus; ce.pl, supplying the posterior part of stomach, and continues as R'V to join the solar plexus, here represented by a single ganglion, and connected with the inferior mesenteric ganglion m.gl.; a, branches from the solar plexus to stomach and small intestine, and from the mesenteric ganglia to the large intestine; Spl.inaj., large splanchnic nerve, arising from the thoracic ganglia and rami communicantes; r.c, belonging to dorsal nerves from the tith to the 9th (or 10th); Spl.min., small splanchnic nerve similarly from the 10th and 11th dorsal nerves. These both join the solar plexus, and thence make their way to the alimentary canal; c.r., nerves from the ganglia, etc.. belonging to 11th and 12th dorsal and 1st and 3d lumbar nerves, proceeding to the inferior mesenteric ganglia (or plexus), m.gl., and thence by the hypogastric nerve, n.hyp., and the hypogastric nerve, n.hyp., and the hypogastric plexus, pi. hyp., to the circular muscles of the rectum ; l.r., ner%-es from the 2d and 3d sacral nerves, S.2, S.3 (nervi erigentes) proceeding by the hypogastric plexus to the longitudinal muscles of the rectmn. (M. Foster.) nected with the plexuses of nerves and ganglia contained in its walls as was formerly supposed. The action, however, appears to be set up by the presence of food within it. The stomach is, moreover, directly con- nected with the higher nerve-centres by means of branches of the vagi and of the splanchnic nerves through the solar plexus. The exact function of the vagi in connection with the movements is not certainly known. Irritation of the vagi produces contraction of the stomach, if digestion is proceeding; and on the other hand, peristaltic action is retarded, although it is not stopped, when these nerves are di- FOOD AND DIGESTION. 323 vided. On the other hand, there are other nerve-fibres, which reach tlie stomach and intestines through the solar plexus. These fibres pass from the spinal cord in the anterior roots of the nerves from the sixth to the twelfth dorsal process in the splanchnic nerves to the solar plexus, and thence to the stomach. Stimulation of the splanchnics causes stoppage of the muscular movements as well as constriction of the blood-vessels. Thus it seems 2)robable that automatic peristaltic contraction is inher- ent in the muscular coat of the stomach, and that the central nervous system is only employed to regulate it by impulses passing down by tlie vagi or splanchnic nerves. Bernard, watching the act of gastric digestion in dogs which had fistulous openings into their stomachs, saw that immediately on the di- vision of their vagi nerves, the process of digestion was stopped, and the mucous membrane of the stomach, previously turgid with blood, became pale, and ceased to secrete; but although division of both vagi always temporarily suspends the secretion of gastric fluid, and so arrests the process of digestion, being occasionally followed by death from inani- tion; yet the digestive powers of the stomach may be completely restored after the operation, and the formation of chyme and the nutrition of the animal may be carried on almost as perfectly as in health. Bernard further found that stimulation of the vagi excited an active secretion of the fluid and that stimulation of the splanchnics caused a diminution and even a complete arrest of the secretion. Stimulation of the vagi at any rate produces an effect, besides peris- talsis of the stomach, it causes dilatation of the blood-vessels of the or- gan, in other words acts as a vaso-dilator nerve. The influence of the higher nerve-centres on gastric digestion, as in the case of mental emotion, is too well known to need more than a ref- erence. Digestion of the Stomach after Death. — If an animal die during the pro- cess of gastric digestion, and when, therefore, a quantity of gastric juice is present in the interior of the stomach, the walls of this organ itself are frequently themselves acted on by their own secretion, and to such an extent, that a perforation of considerable size may be produced, and the contents of the stomach may in part escape into the cavity of the abdo- men. This phenomenon is not infrequently observed in post-mortem ex- aminations of the human body. If a rabbit be killed during a period of digestion, and afterward exposed to artificial warmth to prevent its temperature from falling, not only the stomach, but many of the sur- rounding parts will be found to have been dissolved (Pavy). From these facts, it becomes an interesting question why, during life, the stomach is free from liability to injury from a secretion, which, after death, is capable of such destructive effects. It is only necessary to refer to the idea of Bernard, that the living 324 HANDBOOK OF PHYSIOLOGY. stomach finds protection from its secretion in the presence of epithelium and mucus, which are constantly renewed in the same degree that they are constantly dissolved, in order to remark that although the gastric mucus is probably protective, this theory, so far as the epithelium is concerned, has been disproved by experiments of Pavy's, in which the mucous membrane of the stomachs of dogs was dissected off for a small space, and, on killing the animals some days afterward, no sign of diges- tion of the stomach was visible. " Upon one occasion, after removing the mucous membrane, and exposing the muscular fibres over a space of about an inch and a half in diameter, the animal was allowed to live Fig 341.— Auerbach's nerve-plexus in small intestine. The plexus consists of flbrillated sub- stance, and is made up of trabeculae of various thiclOGY. (2.) Follicles of adenoid or lymplioid 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. lleo-cmcal Valve. — The ileo-C£ecal valve is situate at the place of junction of the small with the large intestine, and guards against any reflux 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 some of the circular muscular fibres of the intestine, which are contained between the outer 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 csecum are contained be- tween the outer opposed surfaces of the folds of mucous membrane which form the valve, the longitudinal muscular fibres and the peri- toneum 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 manner, therefore, the folding inward of these two last-named structures is preserved, while on the other hand, by dividing the longitudinal muscular 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 continuous 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 gastric juice, such of it 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, as well as to the secretion (succus entericus) which is poured out into the intestines from the glands lining them. The Pancreas, and its Secretion. The Pancreas is situated within the curve formed by the duo- denum; 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 FOOD AND DIGESTION". 335 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 intra-lobular ducts, and these again by their division and branching form the gland tissue proper. The intralobar ducts correspond to a lobule, while between them and the secreting tubes or alveoli are longer or shorter intermediary ducts. The larger ducts possess a very distinct lumen and a membrana propria lined with columnar epithelium, 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, f^ - i Si2^s^ Fig 251.— Section of the pancrea-s of a dog during digestion, a, alveoli lined with cells, the outer zone of which is well stained with hasmatoxylin ; d, intermediary duct lined with squamous epithebnm. x 350. (Klein and Noble Smith.) with a membrana propria lined with a single layer of flattened elongated cells. The alveoli are branched and convoluted tubes, with a membrana propria lined with a single layer of columnar cells. They have no distinct lumen, the centre portion of the tube being occupied by fusi- form or branched cells. Heidenhain has observed that the alveolar 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, 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 and stored up in the protoplasm of the cells, from 336 HANDBOOK OF PHYSIOLOGY. the material supplied to it by the blood. The granules are thought to consist of material from which, under certain conditions, the ferments of the gland are developed, and which is therefore called Zymogen. In addition to the ordinary alveoli of the pancreas there are found distri- buted irregularly in the gland other collections of cells of a different character. They are considerably smaller, their protoplasm is more granular, and is less easily stained with haematoxylin, and their nuclei are small and deeply staining, being situated also more toward the centre of the cells. The collections of cells vary in size and shape, and sometimes seem to be mere masses of protoplasm witli nuclei undifferen- tiated into cells. These nests of cells are sometimes seen to consist of distinct columns of cells. No distinct basement membrane, however, can be made out as bounding these columns. The special form of nerve terminations, called Paciiiian corpuscles, are often found in the pancreas. Fig. 252.— Section of the pancreas of armadillo, showing the two kinds of gland-structure. (V. b. Harris.) The Pancreatic Juice. — The secretion of the pancreas has been obtained 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. 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, cut up into small pieces, by keeping it for some days in absolute alcohol, and then, after the entire removal of the alcohol, by pounding up these pieces into a pulpy mass and 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 the removal from the body often appears to contain none of the ferments. This FOOD AND DIGESTIGlSr. 337 seems to indicate that the conversion of zymogen in the gland into the ferment only takes place dnring the act of secretion, and that although the gland always contains in its cells the materials (trypsinogen) oiit 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. Many other vehicles may be employed instead of glycerin, e.g., brine, chloroform, water, dilute methylated spirit acidulated with acetic acid. Properties. — Pancreatic juice is colorless, transparent, and slightly viscid, alkaline in reaction. It varies in specific gravity from 1010 to 1015, according as it is obtained from a permanent fistula — then more watery — or from a newly-opened duct. The solids vary in a temporary fistula from 80 to 100 parts per thousand, and in a permanent one from 16 to 50 per thousand. Chemical Composition of the Pancreatic Juice. From a permanent fistula. (Bernstein.) Water 975 Solids — Ferm'^nts (including trypsin, amylopsin, rennet, and steapsin) : Proteids, including Serum Albumin and \ Casein . [■ 17 Leucin and Tyrosin ; Fats and Soaps . ) Inorganic residue, especially Sodium \_ 8 Carbonate S 25 1000 Functions. — (1.) By the aid of its proteolytic ferment, tri/psin, it converts p7-ofeids i7ito pepto)ies, the intermediate products being almost the same as in the case of gastric digestion, Avith the exception that the initial change does not produce syntonin or acid-albumin as in gastric digestion, but alkali-albumin. Of the final products, hemi- and anti- peptone, the hemipeptone is capable of being converted by (?) the action of the pancreatic ferment into leucin or amido-caproic acid (CeHisNOo) and tyrosin* or amido-oxyphenyl-propionic acid (CgHnlSrOs), but is not so charged by pepsin : the antipeptone cannot be further split up by the pancreatic juice. The products of pancreatic digestion are sometimes further complicated by the appearance in a pancreatic diges- tive fluid, of certain faecal substances of which indol (C3H2N), skatol (C9H9N), j9/ie?io? (CeHeN) and napthilamine a.re the most important. * Propionic acid, C3H6O2 ; in which one H is replaced by the radicle oxyphenyl, C6H4OH, and a second H, by amidogen NH2. Thus C3H4 (NHj) CeH^OH. 0^ = 03, HnNO,. 22 338 HANDBOOK OF PHYSIOLOGY. These further products are produced by the presence of numerous micro-organisms of the intestines. All the albuminous or proteid substances which have not been con- verted into pejDtone and absorbed in the stomach, and the partially changed substances, i.e., the proteoses may be converted into peptone by the pancreatic juice, and then in part into leucin and tyrosin. The action of the pancreatic juice upon the gelatins, or nitrogenous bodies other than proteids, is not so distinct. Mucin can, however, be dissolved, but not keratin in horny tissues. Gelatin itself is formed into l^eptone [gelatin-peptone'). The ferment trypsin acts best in an alka- line medium, and is by far the most active of the pancreatic ferments. It is more powerful than pepsin in its action both on jiroteids and gelatins. (2.) Starch is converted into maltose and then into glucose in an exactly similar manner to that which happens with the saliva; erythro- and achroo-dextrine being intermediate jjroducts. If the sugar which is at first formed is maltose, the ferment of the pancreatic juice after a time completes the whole change of starch into glucose. This distinct amylolytic ferment in the pancreatic juice which cannot be distinguished from ptyaline, is called Amylopsin. (3.) Pancreatic juice possesses the property of curdling milk, con- taining a special (rennet) ferment for that purpose. The ferment is distinct from trypsin, and will act in the presence of an acid (W. Eoberts). It is best extracted by brine. The milk-curdling ferment of the pancreas is, in some pancreatic extracts, extremely powerful, inso- much that 1 cc. of a brine extract will coagulate 50 cc. of milk in a minute or two. (4.) Oils and fats are emtilsiHed and sap)07iified by pancreatic secre- tion. The terms emnlsification and saponifcation may need a little ex- planation. The former is used to signify an important mechanical change in oils or fats, whereby they are made into an emulsion, or in other words are minutely subdivided into small particles. If a small drop of an emulsion be looked at under the microscope it will be seen to be made up of an immense number of minute rounded particles of oil or fat, of varying sizes. The more complete the emulsion the smaller are these particles. An emulsion is formed at once if oil or fat, which nearly always is slightly acid from the presence of free fatty acid, is mixed with an alkaline solution. Saponification signifies a distinct chemical change in the composition of oils and fats. An oil or a fat be- ing made up chemically of glgcerin, a triatomic alcohol, and one or more fatty acid radicles, when an alkali is added to it, and heat is applied, two changes take place : firstly, the oil or fat is split up into glycerin, and its corresponding fatty acid; secondly, the fatty acid combines with the alkali, to form a soap which is chemically known as stearate, oleate. FOOD AND DIGESTION". 339 or palmitate of potassium or sodium. Thus saponitication means a chemical splitting up of oils or fats into new compounds, and emulsifi- cation means merely a mechanical splitting of them up into minute par- ticles. The pancreatic juice has been for many years credited with the possession of a special ferment, which was called by Claude Bernard steapsin, and which was supposed to aid in one or both of these pro- cesses. It appears very doubtful, however, if the mechanical splitting up of fats by the alkaline pancreatic juice is a ferment action at alL and as regards the chemical action it has been recently shown that only the pancreatic juices of certain animals have any power in this direction of a ferment character, and that even in these cases the ferment is only present in the fresh juice or gland, and that the presence of alcohol or other hardening agent for the latter entirely destroys its action. Several cases have been recorded in which the pancreatic duct beiug ob- structed, so that its secretion could not be discharged, fatty or oily matter was abundantly discharged fi'om the intestines. In nearly all these cases, indeed, the liver was coincidentally diseased, and the change or absence of the bile might appear to contribute to the result ; yet the frequency of extensive dis- ease of the liver, unaccompanied by fatty discharges 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. Conditions favorable to the Action. — These are almost precisely sim- ilar to those which have been mentioned as favorable to the action of the saliva, and the reverse. The secretion of the pancreatic juice aj)- pears to be, at any rate in some animals, e.g., the rabbit and dog, almost continuous; the flow, however, is not uniform, the amount increases immediately after taking food, and the maximum amount occurs two or four hours after, but again between the fifth and sixth hour increases somewhat. The nervous mechanism of pancreatic secretion is not at present understood, and the endings of its nerve-fibres from the splanch- nics and right vagus nerves in all probability, through the solar plexus, have not been demonstrated in the gland cells. Increased flow of secre- tion will occur on stimulation of the spinal cord or bulb, or of the gland itself, even after division of the vagus. Stimulation of the central end of the divided vagus will inhibit the secretion, and a similar effect is produced on stimulation of other afferent nerves. It seems highly prob- able, therefore, that there is a central mechanism for the regulation of tlie secretion of the pancreas similar to that which exists for the sali- vary glands, but the nerves which pass to and from the centre and the position of the centre itself, have not yet been demonstrated. The gland will continue to secrete after the section of all of its nerves, and in this respect is said to differ from the salivary glands. The secretion appears to be called forth on the introduction of food into the stomach, 340 HANDBOOK OF PHYSIOLOGY. when the blood-vessels of the gland become much dilated, and the se- cretion continues, as we have seen, for many hours after a meal; indeed, may be continuous. The pressure of the secretion is not so great as in the case of the salivary glands; the maximum pressure in the duct is said not to exceed IT mm. of mercury. The amount of secretion per diem is approximately estimated to be 200 grms. The Liver. The Liver, the largest gland in the body, situated in the abdomen on the right side chiefly, is an extremely vascular organ, and receives its supply of blood from two distinct sources, viz., from the portal vein and from the hepatic artery, while the blood is returned from it into the Fig. 253.— The under surface of the liver, g. b., ^all-bladder: h. d., common bile-duct; h. a., hep- atic artery; v. p., portal vein; l. q.. lobulus quadratus; l. s., lobulus spigelii; l. c, lobulus cauda- tus; D. v., ductus venosus; u. v., umbilical vein. (Noble Smith.) vena cava inferior by the hepatic vein^. Its secretion, the hile, is con- veyed 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 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 in- vesting the lobules. At the transverse fissure it is merged in the areolar investment called Glisson's capsule, which, surrounding the portal vein^ hepatic artery, and hepatic duct, as they enter at this part, accompanies them in their branches throufrh the substance of the liver. FOOD AXD DIGESTION". 341 Structure. — The liver is made up of small roundish or oval portions called lobules, each of which is about gV of an inch (about 1 mm.) in diameter, and composed of the minute branches of the portal vein, he- patic artery, hepatic duct, and hepatic vein; while the interstices of these Fig. 254.— A. Liver-cells. B. Ditto, containing various-sized particles of fat. vessels are filled by the liver cells. The hepatic cells (fig. 254), which form the glandular or secreting part of the liver, are of a spheroidal form, somewhat polygonal from mutual pressure about g^ to ydVo ii^ch (about -gig to ^V mm.) in diameter, possessing one, sometimes two nuclei. The cell-substance contains numerous fatty molecules, and some yellow- ish granules of bile-pigment, as well as a variable amount of glycogen. Fig. ~55. -Longitudinal section of a portal canal, containing a portal vein, hepatic artery and hepatic duct, from the pig. p, branch of vena nort», situate in a portal canal formed among the lobules ot the liver, /, i, 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; o, hepatic artery; d, hepatic duct, x 5. (Kiernan.) > > f j - The cells sometimes exhibit slow amoeboid movements. They are held together by a very delicate sustentacular tissue, continuous with the in terlobular 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 342 HANDBOOK OF PHYSIOLOGY. 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. 255. Running together through the substance of the liver, they are contained in small channels called portal canals, their immediate in- vestment being a sheath of areolar tissue continuous with Glisson's cap- sule. To take the distribution of the portal vein first : — In its course through the liver this vessel gives olf small branches which divide and subdivide between the lobules surrounding them and limiting them, and from this circumstances called inter-lohwVAv veins. From these small vessels a dense capillary network is prolonged into the substance of the lobule. Fig. 256.— Capillary network of the lobules of the rabbit's liver. The figure is taken from a very successful injectiou of the hepatic veins, made by Harting: it shows nearly the whole of two lo- bules, and parts of three others : p, portal branches running in the interlobular spaces; h, hepatic veins penetrating and radiating from the centre of the lobules. X 45. (Kolliker.) 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 t;?/r«-lobular. This arrangement is well seen in fig. 256, which represents a transverse section of a lobule. The small intra-lohxAskV veins discharge their contents into veins called sub-\6h\x\QX {li li It, fig, 257); while these again, by their union, form 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 infe- rior vena cava, just before its passage through the diaphragm. The 5M5-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 Avhich the lobules are connected with the snhlohular veins by means of the small intralobular vein?, has been likened to a twig FOOD AND DIGESTION. 343 having leaves without footstalks — the lobules representing the leaves, and the sublobular vein the small branch from which it springs. Fig. 257. Fig. 258. Fig. 257.— Section of a portion of liver passing longitudinally through a considerable hepatic vein, from the pig. h, hepatic venous trunk, against w-iiieh the sides of the lobules (7) are applied; h, h, h, sublobular hepatic veins, on which the bases of tlie lobules rest, and through the coats of which they are seen as polygonal figures; i, mouth of the intralobular veins, opening into the sub- lobular veins; i', intralobular veins shown passing up the centre of some divided lobules; 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.) Fig. 258.— Portion of a lobule of liver, a, bile capillaries between Uver-cells, the network in which is well seen; b, blood capillaries. X 350. (Klein and Noble Smith.) The hepatic artery, the chief function of which is to distribute blood for nutrition to Glisson's capsule, the walls of the ducts and blood-ves- sels, and other parts of the liver, is distributed in a very similar manner P/'. Fig. 259.— Hepatic cells and bile capillaries, from the liver of a child three months' old. Both figures represent fragments of a section carried through the periphery of a lobule. The red cor- puscles of the blood are recognized by their circular contour; yp, corresponds to an interlobular vem m immediate 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. CE. Hering.) to the portal vein, its blood being returned by small branches either 344 HANDBOOK OF PHYSIOLOGY. into tlie ramifications of the portal vein, or into the capillary plexus of the lobules which connects the inter- and m^ra-lobular veins. 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. 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. 258 and 259). The Gall-bladdee. The Gall-bladder (g. b. fig. 253) 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 ftmckis, 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) iha fibrous or areolar coat, constructed of tough fibrous and elastic tissue, with which is mingled a considerable number of plain muscular 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 honey- combed appearance from a number of tiny polygonal depressions with intervening ridges, by which its surface is mapped out. In the cystic 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 interval of digestion. The gall-bladder and all the main biliary ducts are provided with mucous glands, which open on the internal surface. Functions of the Liver. The function of the liver in connection with digestion is to secrete the bile, and may be now considered. The other functions in connec- tion with the general metabolism of the body, and particularly its gly- cogenic function, will be considered later on. First of all it will be as well to take the composition and functions of the bile, and afterward to discuss its mode of secretion. FOOD AND DIGESTION. 345 The Bile. Properfies. — The bile is a somewhat viscid fluid, of a yellow or reddish- yellow or green color, a strongly bitter taste, and, when fresh, with a scarcely perceptible odor : it has a neutral or slightly alkaline reaction, and its specific gravity is about 1020. Its color and degree of consist- ence vary much, quite indeiDendent 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, darker, and more bitter, mainly from its greater degree of concentration, on account of partial absorption of its water, but also from being mixed with mucus. Chemical Composition of Human Bile. (Frerichs.) Water 859.3 Solids— Bile salts 91.5 Fat 9.3 Cholesterin 3.6 Mucus and coloring matters . . 39. 8 Salts 7.7 140.8 1000.0 (a) Bile salts, sometimes termed Bilin, can be obtained as colorless, 'exceedingly deliquescent crystals, soluble in Avater, 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 formula of the former salt being C26H43"N'aN06, and of the latter C26H44NaN07S. The bile acids are easily decomposed by the action of dilute acids or alkalies thus : C.BH43NOe + H^O = C.HsNO, + C.4H4„05 Glycocholic Acid. Glycin. Cholic Acid. and C.5H46NO,S + H.O == C.2H7NO3S + C04H40O5 Taurocholic Acid. Taurin. Cholic Acid. Glycin, or glycocin, is amido-aGetic acid, i.e., acetic acid C2H4O2, with one of the atoms of H replaced by the radical amidogen NH.2,C2H3(NH2)0.2, C2H6N2O. Taurin likewise is amido-isethionic acid. Isethionic acid is sul- phurous acid H2SO3, in which an atom of H is replaced by the monotoniic radicle oxy-ethylene, C2H4OH, viz., H(C2H40H)S03, and in amido-isethionic acid, the OH hydroxyl in this radicle is replaced by amidogen NH2, thus H(C2H4NH2)S03 = C2H,NS03. The proportion of these two salts in the bile of different animals varies, e.g.. in ox bile the glycocholate is in great excess, whereas the bile of the dog, cat, bear, and other carnivora contains taurocho- late alone; in human bile the glycocholate is in excess (4.8 to 1.5). Preparation of Bile Salts. — Bile salts may be prepared in tlie following manner : mix bile which has been evaporated to a quarter of its bulk with 346 HANDBOOK OF PHYSIOLOGY. animal charcoal, and evaporate to perfect dryness in a water bath. Next ex- tract the mass while still wai-m with absolute alcohol. Separate the alcoholic extract by filtration, and to it add perfectly anhydrous ether as long as a pre- cipitate 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 glycocholate may be separated from the tauro- cholate 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 taurocholate 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 sulphide, filtering and allowing the acids to separate out by the ad- dition of Avater. The Test for bile salts is known as Pettenkofer's. If to an aqueous solution of the salts strong suljjhuric 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 deep cherry red to purjole color is developed. The reaction 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 substance which gives the reaction is furfur- aldehyde, formed by the action of sulphuric on sugar. Furfur -aldehyde with cholalic acid gives the red color. The spectrum of Pettenkofer's reaction, when the fluid is moder- ately diluted, shows four bands — the most marked and broadest 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. {h) The yellow coloring matter of the bile of man and the Carnivora is termed Bilirubin or Bilifulvin (C16H18N2O3) crystallizable and in- soluble in water, soluble in chloroform or carbon disulphide; a green coloring matter, Biliverdin (C16H20N2O5) which always exists in large amount in the bile of Herbivora, being formed from bilirubin on expo- sure to the air, or by subjecting the bile to any other oxidizing agency, as by adding nitric acid. Biliverdin iB soluble in alcohol but insolu- ble in water, in chloroform and almost in ether. It is not crystalline. When the bile has been long in the gall-bladder, a third pigment, Bili- prasin, 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 character- istic 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. FOOD AXD DIGESTIOX. 347 hand iit F. The bile of the sheep and ox give three bands in a thick layer, and four or five bauds 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 coloring matters of the blood and of the bile, and it may be added, between these and that of the urine {uvohiUti), and of the faeces {stercobiU n) 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 identi- cal with ffz/drohilirubin, a substance which in alkaline solution gives a green fluorescence with zinc chloride, which is obtained from bilirubin by the action of sodium amalgam, or by the action of sodium amalgam on alkaline hajraatin; both urobilin and hydrobilirubin giving a charac- teristic absorption band between b and F. They are also identical with stercobiliu, which is formed in the alimentary canal from bile pigments. Fig. 260.— Crystalline scales of cholesterin. The 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 final yellow substance has been called clioletelin. The spectrum of Gmelin's test gives a black band extending from near b to beyond F. {r) Fatty si(bst(mces are found in variable proportions in the bile. Besides these saponifiable fats, there is a small quantity of Cholesterin,. which is an alcohol, and, with the free fats, is probably held in solution by the bile salts. It is a body belonging to the class of monatomic alco- hols (C26II44O), and crystallizes in rhombic plates (fig. 260). It is in- soluble in water and cold alcohol, but dissolves easily in boiling alcohol or in 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 chloro- form. Lecithin (C44H90NPO9), a phosphorus-containing body and Neu- rin (C5H15NO2), are also found in bile, the latter probably as a decom- position product of the former. 348 HANDBOOK OF PHYSIOLOGY, (d) Tlie 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 decom- position of the bile; for, according to Berzelius, if the mucus be sej)a- rated, it will remain unchanged for many days. (e) The Saline or inorganic constituents of the bile are similar to those found in most other secreted fluids. It is possible that the car- bonate 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. — Small amounts of carbonic acid, oxygen, and nitrogen gases, may be extracted from bile. Functions of the Bile. — Respecting the functions discharged by the bile in digestion, there is little doubt that it {a) assists in emulsifying the fats of the food, and thus rendering them capable of passing into the lacteals by absorption. 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 unaffected, 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. It is, however, the combined action of the bile with the pancreatic juice to which the emulsifi cation is due rather than to that of the bile alone. The bile itself has a very feeble emulsifying power. (5) 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 certain but not very con- siderable antiseptic power, and may serve to prevent the decomposition of food during the time of its sojourn in the intestines. Experiments show that the contents 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 jaun- dice, from the diarrhoea which accompanies excessive secretion of bile, .and from the purgative properties of ox-gall. (e) The bile appears to have the power of xrreciintating the gastric FOOD AXD DIGESTION. 349' proteoses and peptones, together with the pepsin, which is mixed up with them, as soon as the contents of the stomach meet it in the duodenum. The purpose of this operation is probably both to delay any change in the proteoses until the jiancreatic juice can act upon them, and also to prevent the j)epsin from exercising its solvent action on the ferments of tlie pancreatic juice. (/) As an excrementitious substance, the bile may serve especially as a medium for the sejjaration of certain highly carbonaceous substances from the blood; and its adaptation to this purjiose is well-illustrated by the peculiarities attending its secretion and disposal in the foetus. Dur- ing intra-uterine life, the lungs and the intestinal canal are almost in- active; there is no respiration of open air or digestion of food; these are unnecessary, on account of the supply of well-elaborated nutriment received by the vessels of the fcetus 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 concentrated bile, mixed with intestinal secretion, and this constitutes the meconium, or fgeces of the foetus. In the foetus, therefore, the main purpose of the secretion of bile must be directly excretive. Probably all the bile secreted in foetal life is incorjjorated 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, j)revious to its distribution to the several organs of the body; and the abstraction of certain sub- stances will purify it, as in extra-uterine life it is purified by the sejDara- tion of carbon dioxide and water at the lungs. Mode of Secretion and Discharge. — The secretion of bile is contin- ually going on, but is 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 surface. 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 minutes after the introduction of food into the stomach, the bile began to flow abun- dantly, and continued to do so during the whole period of digestion. The bile is formed in the hepatic cells; thence, being discharged into the minute hepatic ducts, it passes into the larger trunks, and from the main hepatic duct may be carried at once into the duodenum. This probably happens only while digestion is going on, i.e., for 5 to 7 hours after the introduction of food into the stomach; 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 diges- 350 HANDBOOK OF PHYSIOLOGY. tion, it is discharged into the intestine. The gall-bladder tlius fulfils its office, that of a reservoir; for its presence enables bile to be con- stantly 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 simjjle. The orifice through which the common bile-duct communi- cates with the duodenum is narrower than the duct, and appears to be closed, except when there is sufficient j^ressure 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 orifice 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 unstri^jed 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. Bile is not pre-formed in the blood. As just observed, it is secreted by the hepatic cells, although some of its constituents may be brought to them almost in the condition for immediate secretion. The blood from which the liver cells secrete the bile is that applied to them by the portal vein. This is shown by the alterations which occur in the pro- cess on the alteration of the pressure in the portal system. If the portal vein be obstructed, the amount of bile secreted diminishes, and is ulti- mately suppressed, death resulting. It has, however, been shown that under extraordinary circumstances bile may be secreted by the aid of the blood from the hepatic artery, since if a branch of the portal vein be tied, the part of the liver su^jplied by it continues to secrete bile, though in diminished quantity. When the discharge of the bile into the intestine is prevented by an obstruction of some kind, as by a gall- stone blocking the hepatic duct, it is reabsorbed in great excess into the blood, and, circulating with it, gives rise to the well-known phenom- ena of jaundice. This is explained by tbe fact that the pressure of secretion in the ducts although normally very low, not exceeding 15 mm. in the dog, is still higher than that of the portal veins, and if it exceeds 16 mm. the secretion although formed ceases to be poured out, and if the opposing force be increased, the bile passes into the blood- vessels through the lymphatics, and the yellow color appears in the skin and in the secretions, and constitutes the condition of jaundice. In jaundice the fseces are light colored and highly offensive, there is con- FOOD AXD DIGESTION. 351 stipation, the heart beats slowly, and from the presence of bile salts as well as bile pigment in the blood, the red blood corpuscles may be in part dissolved. The latter action results in the presence of hasmoglobin and of an additional amount of bile pigment in the urine. Disposal of the Bile. — The simple excretion of the foetal bile makes it probable that the bile in extra-uterine life is also, at least in part, des- tined to be discharged as excrementitious. The analysis of the faces shows, however, that (except when rapidly discharged in purgation) they contain very little of the bile secreted, probably not more than one-six- teenth part of its weight, and that this portion includes chiefly its col- oring matter in the form of stercobilin, and some of its fatty matters and mucin, but its salts to only a very slight degree, almost all of Avhich have been reabsorbed from the intestines into the blood. The bilirubin is in part converted into urobilin and is reabsorbed and excreted by the kidneys in the urine. The elementary composition of bile-salts shows such a preponderance of carbon and hydrogen that probabl}^ after absorption, they combine with oxygen, and are excreted in the form of carbonic acid and water. The change after birth, from the direct to the indirect mode of excre- tion 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 largely maintained by that of the parent, but, in extra-uterine life, there is (as one may say) a waste of material for heat when any excre- tion is discharged unoxidized; the carbon and hydrogen of bilin, there- fore, instead of being ejected in the fisces, to a very large extent (viz., I), are reabsorbed, in order that they may be combined with oxygen, and that in the combination heat may be generated. It appears that tauro- cholic acid may easily be split up in the intestine into taurin and chola- lic acid, and the same is probable of glycocholic acid. Taurin, giycin, and cholalic acid have all been detected in small amounts in the fseces. So that the bile is in part excreted, but in part is reabsorbed from the intestine (chiefly the large), and returned to the liver. What may be the ultimate destination of these altered or unaltered constituents is un- known. Giycin is supposed to go partly to form urea, and taurin is ex- creted to a slight extent in the urine as tauro-carbamic acid, but it is probable that although part of this may unite to re-form glycocholic or taurocholic acid, the remainder is united with oxygen, and is burnt off in the form of carbonic acid and water. A substance, contained in the fseces, and named stercorin, is closely allied to cholesterin. Ten grains and a half of stercorin 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 ex- cretory, not only for such hydro-carbonaceous matters as may need ex- 352 HANDBOOK OF PHYSIOLOGY. pulsion from the blood, but that it serves for the direct purification of the stream which, arriving by the portal vein, has just gathered up vari- ous substances in its course through the digestive organs — substances which may need to be expelled, almost immediately after their absorp- tion. 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 gen- eral 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 me- tallic 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 j^robable truth of this supposition. The secretion of the bile by the hepatic cells is undoubtedly influenced by the amount of blood supj)lied to them. This is well seen after a meal, when the amount of blood j^assing through the portal circulation incon- sequence of the congestion of the secreting organs of the abdomen is greatly increased, and with it the bile secretion. It is, however, probable that the secretion of the cells is in some more direct way under the con- trol of the nervous system, but how this influence is exercised is un- known. The antecedents of the various substances of the bile from which the cells manufacture its chief constituents are not exactly known. It is surmised that the bilirubin is formed from ha3moglobin brought- from the spleen either actually dissolved in the jjlasma of the blood or in such a condition in the corpuscles as to be easily acted upon by the liver cells, by which the iron is separated. The bile salts are, at any rate in part, formed simply by the conjunction of glycin and taurin with cholalic acid, all of which may be brought to the liver in the portal blood, but failing this it is probable that the hepatic cells can produce these substances anew. 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 Lieberkiilin's) from other secretions poured into the canal (gastric juice, bile, and pancreatic se- cretion), but little is known regarding the comjjosition of the intestinal juice, or succus entericus. 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 is said to be able to convert proteids into peptones, and to convert starch into sugar, but the evidence in favor of these actions is insufficient. The chief function of the juice is to act FOOD AXD DIGESTION. 353 upou sugars. It possesses the power of converting cane into grape sugar, and maltose into glucose. It also contains a milk-curdling fer- ment. The reaction which represents the conversion of cane sugar into grape sugar may be represented thus: 2 C,oHo,0„ + 2 HnO = CioH.^Oi, + C1.H24O1, Saccharose. Water. Dextrose. Lagvulose. The conversion is probably effected by means of a hydrolytic ferment, iiivertin (Bernard). 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 an uniform mass all the varieties of food that reach it through the oesophagus, but especially to dissolve the nitrogenous portion by means of its secretion. The fatty matters, during their sojourn in the stomach, become more thoroughly mingled with the other constituents of the food taken, but are not yec in a state fit for absorption. The conversion of starch into sugar, which began in the mouth, has been interfered with, if not altogether stopped. The soluble matters — both those which were so from the first, as sugar and saline matter, and the gastric pejo- tones — have begun to disappear by absorption into tlie blood-vessels, and the same thing has befallen such fluids as may have been swallowed. 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 con- version into sugar, and as it becomes sugar, also dissolving in the fluids with which 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 digestible, and will be finally expelled as part of the fasces. 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 tliat 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 contin- ues so as far as the ileo-caecal valve. 23 354 HANDBOOK OF PHYSIOLOGY. 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, al- lotted respectively to the bile and to the pancreatic secretion, is still un- certain. 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. (6.) It is emulsionized, i.e., its par- ticles are minutely subdivided and diffused, so that the mixture assumes the condition of a milky fluid, or emulsion. As will be seen in the next Chapter, most of the fat is absorbed by the lacteals of 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 chiefly to the action of the pancreatic juice. The pepsin is rendered inert by being precipitated together with the gastric peptones and proteoses, as soon as the chyme meets with bile. By these means the pancreatic ferment trypsin is enabled to proceed with the further conversion of the proteo- ses into peptones, and part of the peptones (hemipeptone) into leucin and tyrosin. Albuminous substances, which are chemically altered in the process of digestion (peptones) and gelatinous matters similarly changed, are absorbed by the blood-vessels and lymphatics of the intes- tinal mucous membrane. Albuminous matters, in state of solution, Avhich 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 in the form of glucose or of maltose or of both as it is formed, is dissolved in the intestinal fluids, and is absorbed chiefly by the blood-vessels. (4.) Saline and saccliarine matters, such as common salt, and 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 intes- tine; the blood-vessels, as in the last case, being chiefly concerned in the absorption. 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, FOOD AND DIGESTION. 355 are absorbed probably very soou after their entrance into the intestine; the fluidity of the contents of the latter being preserved more by the •constant secretion of fluid by the intestinal glands, pancreas, and liver, than by any given portion of fluid whether swallowed or secreted, re- maining long unabsorbed. From this fact, therefore, it may be gathered that there is a kind of circulation constantly proceeding from the intes- tines 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 w'ould be too much drained, were it not that the same fluid after secretion is again reabsorbed into the current of blood— going into the blood charged with nutrient products ■of digestion — coming out again by secretion through the glands in a comparatively uncharged condition. At the lower end of the small intestine, the chyme, still thin and pultaceous, is of a light yellow color, and has a distinctly faecal odor. This odor depends upon the formation of indol and other substances to he again alluded to. In this state it passes through the ileo-ca3cal open- ing into the large intestine. Summary of the Dig-estive 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 of the food's passage through the upper part of the intestinal ■canal. From the absence of villi, however, we may conclude that ab- sorption, especially of fatty matter, is in great part comj^leted in the small intestine; while, from the still half-liquid, pultaceous consistence of the chyme when it first enters the cgecum, 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 matters or in the digestive fluids, or both. The acid reaction, which had disappeared in the small bowel, again becomes very manifest in the caecum — probably from acid fermentation processes in ■some of the materials of the food. There seems no reason to conclude that any special secondary diges- tive process occurs in the caecum or in any other part of the large in- testine. 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 enemata, so frequently given when from any cause ihere is difficulty in introducing food into the stomach. In ordinary 356 HANDBOOK OF PHYSIOLOGY. healthy digestion, however, the changes which ensue in tlie chyme after its passage into the large intestine, are mainly the absorption of the more liquid parts; the chief function of the large intestine being to act as a reservoir for the residues of digestion before their expulsion from the body. Action of Micro-organisms in the Intestines. Certain changes take place in the intestinal contents independent of, or at any rate supplemental to the action of the digestive ferments. These changes are brought about by the action of micro-organisms or bacteria. We have indicated elsewhere that the digestive ferments are examples of i(7iorg((nized ferments^ so bacteria are examples of organized ferments. Organized ferments, of which the yeast plant, torula 'ooo' ,00° l,'\ $ ■^^^ 7 ^ Fig. 261. — Types of micro-organisms, a, micrococci arranged singly; in twos, diplococci— if all the micrococci at a were grouped together, they would be called staphylococci— and in fours, sar- cinae: 6, micrococci, in chains streptococci ; c and d, bacilli of various kinds, one is represented with flagellum; e, various forms of spirilla; /, spores, either free or in bacilli. {saccharomyces) cerevisue, may be taken as a typical example, consist of unicellular vegetable organisms, which when introduced into a suitable culture medium grow with remarkable rapidity, and by their growth produce new substances from those sujDplied to them as food. Thus for example, when the yeast cell is introduced into a solution of grape sugar, it grows, and on the one hand alcohol, and on the other hand carbon dioxide are produced. These substances are not the direct result of the life of the cell, but probably arise from the formation of some chemical substances allied to the unorganized ferments which greatly increase in amount with the multiplication of the original cell. In all such fer- mentative processes, organisms analogous to the yeast cell are present, and it is not strange that if the ferment cell is introduced into a suit- able medium, it may by its rapid reproduction have power to convert an unlimited amount of one substance into anol^ier. Speaking generally a special variety of cell is concerned with each ferment action, thus one variety has to do with alcoholic, another with lactic and another with acetous fermentation. A considerable number of species of bacteria FOOD AND DIGESTION. 357 exist in the body during life, chiefly in connection with the mucous membranes, particulurly of the digestive tract. These bacteria are unicellular organisms, devoid of chlorophyll, sometimes called Jii 1.559 1.565 1.08 Cholesterin . . ' . . ) Fatty matter and Soaps a trace 8.601 .93 Salts .585 .711 .44 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 to 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 an- ■ other series of experiments, the quantity of lymph traversing the tho- racic duct of a dog in twenty-four hours was found to be about equal to two-thirds of the blood in the body. Chaxnels of Ai^sorption. The Lacteals. — During the passage of the chyme along the intestinal canal, its completely digested parts are absorbed into the blood and distributed in the mucous membrane. The absorption into both sets oi vessels is carried on most actively hut not exclusively , in the villi of tha- small intestine; for in them 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 I digestion, from the contents of the intestines, is effected chiefly through 378 HANDBOOK OF PHYSIOLOGY. the epithelial cells which line the intestinal tract, and especially those which clothe the surface of the villi. Thence, the fatty particles are passed on into the interior of the lacteal vessels, but how they pass, and what laws govern their passage, are not at present exactly known. The lymph-corpuscles of the villi are however, in some animals, e.g., the rat and frog, important agents in effecting the passage of -fat-joarticles into the lacteals. These cells take up the fat whicli has passed through the columnar cells and then, by reason of their amseboid movement, carry Fig, 272.— Section of the villus of a rat killed during; fat absorption, ep, epithelium ; str, striated border; c, lymph-cells ; c', lymph-cells in the epithelium; 1, central lacteal containing disintegrating lymph-corpuscles. (E. A. Schafer.) it in to the lacteal. When arrived there they break up and set free both fat and proteid matter thereby. The process of absorption is assisted by the pressure exercised on the contents of the intestines by their contractile walls; and the absorp- tion of fatty particles is also facilitated by the presence of the bile, and the pancreatic and intestinal secretions, which moisten the absorbing surface. TJie Lymphatics. — The lymph is diluted liquor sangi(inis, which is always exuding from the blood-capillaries into the interstices of the tis- sues 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 • ABSORPTIOX. 379 in the vessels of the part from which the lymph is exuded. Thus it ap- pears that the coagulability of the lymph, although always less than, is directly proportionate to that of the blood; and that when fluids are in- jected into the blood-vessels in sufficient quantity 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, md, 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 maj be absorbed by the lym- Fig. 273. — Mucous membrane of frog's intestine during fat absorption, ep, epithelium; str, striated border; C, lymph corpuscles ; i, lacteal. (E. A. Schafer.) phatics, and elaborated with the other contents of the lymph in passing through the glands. The Blood- Vessels. — In the absorption by the lymphatic or lacteal vessels just described tbere appears something like the exercise of choice in the materials admitted into them. This is not the case with the blood-vessels; it apjjears 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. Where absorption may take place. In the alimentary canal. — The greatest activity of absorption occurs in the alimentary canal. In it the materials of the duly digested food find their way by means of this process on the one hand into the blood- vessels of the portal circulation, and on the other into the lacteal vessels which are, as we shall see presently, the commencements of the lym- phatic vessels of the intestines. Through the shin. — It has been shown that 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 spe- 380 HANDBOOK OF PHYSIOLOGY. cific influence upon syphilis, and excites salivation; potassio-tartrate of antimony may excite vomiting, or an eruption extending over the whole body; and arsenic may produce poisonous 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 ski?i. 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 well-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 rapidly, 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, are found to recover both their weight and plumpness very rapidly when immersed in water. When merely the tail, posterior extremities, and posterior j^art of the body of the lizard are immersed, the water absorbed is 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 assu:ige 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. Through the Lung a. — It is a remarkable fact that not only is the epithelium of the pulmonary epithelium able to allow the passage through it of gases and volatile substances, but that also under certain conditions fluids such as water may also be absorbed, and besides this, the presence of carbon particles in the bronchial glands and elsewhere in connection with the lungs must point to the pulmonary epithelium as the only possible channel of their absorption. CHAPTER X. EXCRETION. We have now considered the methods by which the food is digested and prepared for absorption as well as the methods by which the changed materials reach the general blood-stream, either by means of the lymphatics of the intestinal walls or by the capillaries of the portal circnlation. The most difficult problems of jDhysiology yet remain to be discussed, and these are those concerned with the exact changes which take place in the tissues and organs of the body, when they are supplied with the food necessary for their life. In order to be in a condition to discuss these questions from the best possible standpoint, it will be as well first of all to consider the forms in Avhich the waste materials re- sulting from the metabolism of the tissues leave the body, and the methods of their elimination. This has to a certain extent been already considered, we have seen how carbon dioxide and other matters are elim- inated by the lungs, and further, we have devoted some time to the con- sideration of the amount and composition of the fgeces. The highly important functions of the kidneys, in excreting the urine, and of the skin remain, and it is to these that we must now direct our attention. The Structure and Functions of the Kidneys. 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 vertebra?; the right being slightly below the left in consequence of the position of the liver on the right side of the abdo- men. They are about 4 inches long, 2^ inches broad, and l-j inch thick. The weight of each kidney is about 4| oz. Structure. — The kidney is covered by a tough fibrous capsule, which is slightly attached by its 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 j)ortion of the organ. At the hiliis or notch of the kidney, it becomes continuous with the external coat of the upper and dilated part of the ureter (fig. 274). On dividing the kidney into two equal parts by a section carried 381 38y HANDBOOK OF PHYSIOLOGY. through its long convex border (fig. 274), the main part of its substance is seen to be composed of two chief portions called respectively cortical and medullary, the latter being also sometimes called pyramidal, from the fact of its being composed of about a dozen conical bundles of urine tubes, each bundle forming what is called a pyramid. The upper part of the ureter or duct of the organ, is dilated into the pelvis ; and this, again, after separating into two or three principal divisions, is finally subdivided 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 / ^< 'tmiP^^' Fig. 274. Fig:. 275. Fig. 374.— Plan of a longitudinal section through the pelvis and substance of the right kidney, J^ ; a, the cortical substance ; 6, b. broad part of the pyramids of Malpighi ; c, c, the divisions of the pelvis named calyces, laid open ; c', one of those unopened ; d, summit of the pyramids of papillae projecting into calyces ; e, e, section of the narrow part of two pyramids near the calyces; p, pel- vis or enlarged divisions of the ureter within the kidney; m, the ureter; s, the sinus; h, the hilus. Fig. 275.— A. Portion of a secreting tubule from the cortical substance of the kidney, b. The epi- thelial or gland-cells. X 700 times. 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 tubes, the tuhuli urini- feri, which, by one extremity, in the cortical portion, end commonly in little saccules containing blood-vessels, called Malpigkian bodies, and, by the other, opened through the papillae into the pelvis of the kidney, and thus discharge the urine which flows through them. 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. Tuhuli Uriniferi. — The tubuli uriniferi (fig. 275) are composed of EXCRETION. 383 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^Jo of an inch {^^ mm.) in diameter, and are found Fig. 276— A diagram of the sections of uriniferous tubes. A, Cortex limited externaUy by the capsule: u, subcapsular layer not containing: Malpighian corpuscles; a', inner stratum of cortex, also without Malpighian capsules : B, boundary layer; C, papillary part next the boundary layer; 1, Bowman s capsule of Malpighian corpuscle; 2, neck of capsule; 3, proximal convoluted tubule; 4. spiral tubule; 5. descending limb ot Henle's loop; (5, the loop proper; 7, thick part of the ascending hmb ; 8, spiral part of ascending limb; 9. narrow ascending limb in the medullarv ray; 10, the ir- regular tubule; 11, the intercalated section, or the distal convoluted tubule; 13, the curved collect- ing tubule; 13, the straight collecting tubule of the medullary ray ; 14, the collecting tube of the boundary layer; 15, the large collecting tube of the papillary part which, joining with similar tubes, forms the duct. (Klein.) to be made up of several distinct sections which differ from one another very markedly, both in situation and structure. According to Klein, the following segments may be made out: (1) The Malpighian corpus- 384 HANDBOOK OF PHYSIOLOGY. cle (figs. 276, 281), composed of a hyiiline membrana propria, thickened by a varying amount of fibrous tissue, and lined by flattened nucleated epithelial plates. This capsule is the dilated extremity of the urinif- erous tubule, and contains within it a glomerulus of convoluted capil- lary blood-vessels supported by connective tissue, and covered by flat- tened epithelial plates. The glomerulus is connected with an efferent and an afferent vessel. (2) The constricted 7ieck of the capsule (fig. 276, 2), lined in a similar manner, connect it with (3) The Proximal convoluted tubule, which forms several distinct curves and is lined with Fig. 277. — 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 ar- ranged 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.) 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 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 downward 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 Ilenle, which is a very narrow tube lined with flattened nucleated cells. Passing vertically upward just as the tube reaches the boundary layer (7), it suddenly enlarges and be- comes lined with polyhedral cells. (8) About midway in the boundary EXCRETION. 385 layer the tube again narrows, forming the ascending sjnral of Henh's hop, but is still lined with polyhedral cells. At the point where the tube enters the cortex (9) the ascending limb narrows, but the diameter 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 tuhule," 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 distal convoluted tube or intercalated sectioti of Schweig ger-Seidel, which is identical in all respects with the j)roximal convoluted tube (12 and 13). The curved and straight collecting tubes, the former entering the latter Fig. 278. — Transverse section of arenal papilla; o, large tubes or papillary ducts; 6, c, and d, smaller tubes of Henle; e, /, blood capillaries, distinguished by their flatter epithelium. (Cadiat.) 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 papillary layer, and, joining with other collecting tubes, forms larger tubes, which finally open at the apex of the papilla. These col- lecting tubes are lined with transparent nucleated columnar or cubical cells (U, 15). 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 intra- nuclear as well as of the intra-cellular network of fibres, of which the vertical rods are most conspicuous. 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 25 386 HANDBOOK OF PHYSIOLOGY. that the pigment passes through the cells, rods, and nucleus themselves. Klein, however, believes that the pigment passes through the intercel- lular 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 {centrotuhular mem- brane). Blood-supplij. — In connection with the general distribution of blood-ves- sels to the kidney, the Malpigliian Corpuscles may be further considered. They (fig. 280) 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 ^^-^ of an inch {\ mm.). Each of them is composed, as we have seen above, of the diluted extremity of an uriniferous tube, or Malpigliian capsule, which incloses a tuft of blood-vessels. The renal artery divides into sev- eral branches, which, passing in iit the hilus of the kidney, and covered by a fine sheath of areolar tissue de- rived from the capsule, enter the substance of the organ chiefly in the intervals between the papillae, and at the junction between the cortex and the boundary layer. The main branches then pass almost horizon- llXna^rfatemlSlFeftl^^ tally, forming more or less complete up- ward 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 and shorter branches, which ultimately supply the Malpigliian bodies. The small afferent artery (figs. 380 and 281) which enters the Mal- pigliian corpuscle, breaks up in the interior as before mentioned into a Fig. 279. — Vascular supply of kidney, a, part of arterial arch ; 6. iaterlobular artery; c, cortex;/, capillaries of medulla; g, venous „„„],„„ .,„.] „ivino- nflF l-.vinr.lioo arch; 7i, straight veins of medulla; J, vena stel- aiCUCS, ana glVlUg On DianCUCS lula; i, interlobular vein. (Cadiat.) EXCRETIOX. 387 dense convoluted and looped capillary plexus, which is ultimately gath- ered up again into several small efferent vessels, comparable to minute veins, which leave the capsule at one or more places near the point at Fig 280.— 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, p, surrounding the tube, and finally terminate in the branch of the renal vein e (after Bowman). 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 Fig. 281.— Malpighian capsule and tuft of capillaries, injected through the renal artery with colored gelatin, a, glomerular vessels : h. capsule ; c, anterior capsule; d, glomerular artery ; e, efferent veins; /, epithelium of tubes. (Cadiat.) the tubule, from whose dilated end it liad 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. These small veins piss into others which form venous arclies correspond- 388 HANDBOOK OF I'HYSIOLOGY. ing to the arterial arches, but which are more distinct, situated between the medulla and cortex. Thus in the kidney, the blood entering by the renal artery traverses two sets of capillaries before 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 tlirust into the dilated extremity of the urinary tubule, which finally com})letely invests it. Thus the Malpighian capsule is lined by a parietal layer of squa- mous cells and a visceral or reflected layer immediately covering the vas- cular tuft (fig, 282), and sometimes dipping down into its interstices. This reflected layer of epithelium is readily seen in young subjects, but \ V*^ cannot always be demonstrated in (-^hj^^-^ I ^ J the adult. (See figs. 282 and 283.) / j[ \> '^^^ ] \ ' J r^. 1 Fig. 282. Fig. 2a3. Fig. 282.— Transverse section of a developing Malpighian capsule and tuft (human). X 300. From a fcetus at about the fourth month: o, flattened cells growing to form the capsule; b, 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 b'ood-ves.sels. (W. Pye. ) Fig. 283. — Epithelial elements of a Malpighian capsule and tuft, with the commencement of a urinary tubule showing the afferent and efferent vessel ; a, layer of flat epithelium forming the capsule; b, similar, but rather larger epithelial ceUs, placed in the walls of the tube; c, cells, covering the vessels of the capillary tuft; cl, commencement of the tubule, somewhat narrower that the rest of it. (W. Pye.) The vessels which 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 ending 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 the nutrition of the different parts of the organ; and in the pyramids,, between the tubes, there are numerous straight vessels, the vasa recta, some of which are branches of vasa eff'erentia from Malpighian bodies, and therefore comparable to the venous plexus around the tubules in EXCRETION. 389 the cortical portion, while others arise directly as small branches of the renal arteries. Between the tubes, vessels, etc., which make uj) 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 of each side. This consists of both medullated and uon-medullated nerve-fibres, the former of varying size, and of nerve-cells. The renal plexus is derived from the solar plexus, particularly from the semilunar ganglion. The renal plexus is thus indirectly connected with the vagi and with the splanchnic nerves. It is also directly connected with them by fibres which pass to them without first joining the solar plexus. Fibres from the anterior roots of the eleventh, twelfth, and thirteenth dorsal nerves in the dog also pass to the same plexus, either directly through the sympathetic chain or by first passing into the solar plexus. Fig. 2&i.— Epithelium of the bladder: a, one of the cells of the first row; b, a cell of the second row; c. cells i)i situ, of first, second, and deepest layers. (Obersteiner.) The Ureters. — The duct of each kidney, or nreter, is a tube about the size of a goose-quill, and from twelve 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 its inter- nal surface. Structure. — It is constructed of three principal coats {a) an outer, tow g\\, fibrous and elastic coat; {h) a middle muscular coat, of which the fibres are unstriped, and arranged in three layers — the fibres of the cen- tral layer being circular, and those of the other two longitudinal in direction; and (r) 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. 284) is alike stratified and of a some- what peculiar form ; the cells on the free surface of the mucous mem- brane being usuuUy 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 va- 390 HANDBOOK OF PHYSIOLOGY. rions lengths, among wliich, again, the deepest cells of the epithelium are found spheroidal, irregularly oval, spindle-shai^ed or conical. The Urinary Bladder. — The urinary bladder, which forms a re- ceptacle 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 continuous with the urethra, being called its cervix or neck. Sti uctiire. — It is constructed of four principal coats — serous, mus- cular, areolar or submucous, and mucous, {a.) The serous coat, which covers only the posterior and upper part of the bladder, has the same structure as that of the peritoneum, 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 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 muscular 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 connec- tive tissue with a large proportion of elastic fibres. {(I) The mucous membrane, which is rugose in the contracted state of the organ, does not differ in essential structure from mucous membranes in general. Its epithelium is stratified and closely resembles that of the pelvis of the kidney and the ureter (fig. 284). 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 lympli-vessels, and with nerves. The latter are both medullated and non-medullated fibres, both branches from the sacral plexus (spinal) and hypogiistric plexus (sympathetic). Ganglion-cells are found, here and there, in the course of the nerve-fibres. The Urine. Physical Properties. — Healthy urine is a perfectly transparent, am- ber-colored liquid, with a peculiar, but not disagreeable odor, a bitterish taste, and slight acid reaction. Its specific gravity varies from 1015 to 1025. On standing for a short time, a little mucus appears in it as a flocculent cloud. Chemical Composition. — The urine consists of water, holding in solu- tion certain organic and saline matters, as its ordinary constituents, and occasionally various other matters; some of the latter are indications of diseased states of the system, and others are derived from unusual articles of food or drugs taken into the stomach. EXCRETION. 391 Chemical Composition of the Urixe. Water 967 Solids- Urea 14.230 Other nitrogenous crystalline bodies — Uric acid, principally in the form of alka- line Urates, a trace only free. Creatinin, Xanthin, Hypoxathin. Hippuric acid. Mucus, Pigments, and Ferments. Salts : — Inorganic— Principally Sulphates, Phosphates, and Chlorides of Sodium and Potassium, with Phosphates of Magnesium and Calcium, traces of Silicates and Chlorides. 10.635 } 8.135 Organic — Lactates, Hippurates, Oxalates, Acetates and Formates, which only appear occasion- ally, j — 33 Sugar a trace sometimes. Gases (nitrogen and carbonic acid principally) . 1000 Reaction. — The normal reaction of the urine is slightly acid. This acidity is due to acid phosphate of sodium, and is less marked soon after meals. The urine contains no appreciable amount of free acid, as it gives no precipitate of sulphur with sodium hyposulphite. After stand- ing for sometime the acidity increases from a Jiind of acid fermentation, due in all probability to the presence of mucus and fungi, 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, due to the presence of one or more specific micro-organisms {micrococcus urece). The urea takes up two molecules of water — a strong ammoniacal and foetid odor appears, and deposits of triple phosphates and alkaline urates take place. This does not occur unless the urine is freely exj)osed to the air, or, at least, until air has had access to it. Reaction of Urine in Different Classes of Animals. — In most herbivorous ani- mals the urine is alkaline and turbid. The difference depends not on any peculiarity in the mode of secretion, but on the difference in the food on which the two classes subsist; for when carnivorous animals, such as dogs, are re- stricted 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 reac- tion 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 car- 392 HANDBOOK OF PHYSIOLOGY. bonic or vegetable acids ; for these latter are changed into alkaline carbonates previous to elimination by the kidneys. Average daily quantity of the chief urinary constituents (modified from Parkes). Water . ' . Solids — Urea Creatinin . Uric Acid Hippuric Acid . Pigment and Extract- tives Sulphuric Acid . Phosphoric Acid . Chlorine Ammonia Potassium . Sodiuni Calcium Magnesium . 1500 cc. or 52i oz. Per Kilo of body weight. 23. grms. 33.180 grms .910 " " 512.4 grains. 14.0 .5 .0140 " .555 " " 8.569 " .0084 " .400 " " 6.16 " .0060 " 10. .. « 154. " .1510 " 2.013 " " 30.98 " . 0480 " 3.164 " " 48.80 " .0305 " 7. 000 " *' 107.8 " .1260 " .770 " " 11.8 " 2. 500 " " 38.5 •' 11.090 " " 170.78 " .260 " " 4. " .207 " " 3. " 72. Variations in the Quantity of the Constituents. — From the propor- tions given in the above table, most of the constituents are, even in health, liable to variations. The variations of the water in different seasons, and according to the quantity of drink and exercise, have al- ready been mentioned. The water of the urine is also liable to be influ- enced by the condition of the nervous system, being sometimes greatly increased, e.g., in hysteria and in 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 augmented 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.(j., the various forms of albuminuria, the quantity may be considerably 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 channel 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 gavity by 2.33. Thus, in urine of sp. gr. 1025, 2.33 X 25 = 58.25 grains of solids, are contained in 1000 grains of the urine. In using this method it must be remembered that the limits of errors are much wider in diseased than in healthy urine. Variations in the Specific Gravity.— The average specific gravity of the human urine is about 1020. 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 EXCRETION. 393 secreted; by the length of time which has elapsed since the last meal; and by several other accidental circumstances. The existence of these causes of difference in the composition of the urine has led to the secre- tion being describe^l 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 terms lirifia jjotus indicates the urine secreted shortly after the intro- duction of any considerable quantity of fluid into the body: and the iurina cibi, the portions secreted during the period immediately succeed- ing a meal of solid food. The last kind contains 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. The specific gravity of the urine may thus, consistently with health, range widely on both sides of the usual average. It may vary from 1015 in the winter to 1025 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; sometimes descending, in albu- minuria, to 1004, and frequently ascending in diabetes, when the urine is loaded with sugar, to 1050, or even to 1060. Quant it II. — The total quantity of urine passed in twenty-four hours is affected by numerous circumstances. On taking the mean of many observations by several experiments, 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 Ir-l^ fluid ounces (1^ to 2 litres). Abnormal Constituents. — In disease, or after the ingestion of special foods, various abnormal substances occur in urine, of which the follow- ing may be mentioned — Serum-albumin, Globulins, Ferments (appa- rently present in health also), Proteoses, Peptone, Blood, Sugar, Bile acids and pigments, Casts, Fats, various Salts taken as medicine, Micro- organisms of various kinds, and other matters. The Solids of the Urine. Urea (CH4X2O). — Urea is the principal solid constituent of the urine, forming nearly one-half of the total quantity. It is also the most important ingredient, since it is the chief substance by which the ■nitrogen which is derived from the metabolic changes iii the tissues as well as that which is derived from any superfluous food is excreted 394 HANDBOOK OF PHYSIOLOGY. from the body. For its removal, the secretion of urine seems especially- provided ; and by its retention in the blood the most pernicious effects are produced. Properties. — Urea, like the other solid constituents of the urine, exists in a state of solution. When in the solid state, it appears in the Fig. 2S5. — Crystals of Urea. form of delicate silvery acicular crystals, which, under the microscope, appear as four-sided prisms (fig. 285). It may be obtained in this state by evaporating urine carefully to the consistence of honey, acting on the inspissated mass with four parts of alcohol, then evaporating the alcoholic solution to dryness, and purifying the residue by repeated solution in water or in alcohol, 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 (figs. 286 and 287). Urea is colorless when pure; when impure it may be yellow or Fig. 286.— Crystals of Urea nitrat^e. Fig. 387.— Crystals of Urea oxalate. brown: it is without smell, and of a cooling nitre-like taste; it has neither an acid nor an alkaline reaction, and deliquesces in a moist and warm atmosphere. At 15° C. (59° ¥.) it requires for its solution less than its own weight of water; it is dissolved in all proportions by boil- ing water; but it requires five times its weight of cold alcohol for its solution. It is insoluble in ether. At 120° C. (248° F.) it melts with- EXCRETION. 395 out undergoing decomposition; at a still higher temperature ebullition takes place, and carbonate of ammonium sublimes. When heated with water in a sealed tube to 100° C, urea splits up into carbonic acid and ammonia; when heated to a high temperature urea loses ammonia and lirst yields biuret, C2H5N3O2, which gives a rose color with caustic potash and a trace of copper sulphate, and afterward cyanuric acid, C3H3O3N3, which gives a violet color with caustic potash and a trace of copper sul- phate. It is decomposed by sodium hypochlorite or hypobromite or by- nitrous acid, with evolution of N. It forms compounds with acids, of which the chief are urea hydrochloride, CH4jSr20.HCL; urea nitrate, CH4lSroOHN03; and urea phosphate, CH4N2O.H3PO4. It forms com- pounds with metals such as HgO.CH4N20; with silver CH2N20Ag2; and with salts such as HgClo and IIgN03. Chemical Nature. — Urea is isomeric with ammonium cyanate NH4,CN0. It was first of all artificially prepared from that substance. It may also he produced artificially by treating carbonyl chloride (CO CI2) v^\i\\ ammonia; or hy heating ethyl carbonate with ammonia CO qq'jj'* + 2 NH3 = TyJTT CONoHi 2C2H6O ; by heating ammonium carbonate CO Q]sf|j = CON2H4 -|- H2O ; by adding water to cyanamide CN.NH2, or by evaporating ammonium cyanate in aqueous solution.- It is usually considered to be a diamide of carbonic acid, in other words, carbonic acid, CO (OH) '2, with two of hydroxyl, (OH) '2, replaced by two of amidogen (NH2)'2. It may also be written as if it were a monamide of carbamic acid (COOHNHo), thus CONH2.NH2; one of amidogen, NH2, in the latter replacing one of hydroxyl in the former. Decomposition of the urea with development of ammonium carbonate takes place from the action of the bacteria (micrococcus urese), when urine is kept for some days after being voided, and explains the ammo- niacal odor then evolved. The urea is sometimes decomposed before it leaves the bladder, when the mucous membrane is diseased, and the mucus secreted by it is both more abundant, and, probably, more prone to act as a ferment; but decompositLon does not often occur unless atmospheric germs have had access to the urine. Variations in the Quantitfi excreted. — The quantity of urea excreted is, like that of the urine itself, subject to considerable variation. For a healthy adult about 512.4 grains (about 33.18 grms.) per diem may be taken as rather a high average. Its percentage in healthy urine is from 1.5 to 2.5. Its amount is materially influenced by diet, being greater when animal food is exclusively used, less when the diet is mixed, and least of all with a vegetable diet. As a rule, men excrete a larger quan- tity than women, and persons in the middle periods of life a larger quantity than infants or old people. The quantity of urea excreted by 396 HANDBOOK OF PHYSIOLOGY. •children, relatively to their body-weight, is much greater than by adults; Thus the quantity of urea excreted per kilogram of weight was found to be, in a child, 0.8 grm.; in an adult only 0.4 grm. Regarded in this way, too, the excretion of carbonic acid gives similar results, the pro- portions in the child and adult being as 82 : 34. The quantity of urea does not necessarily increase and decrease with that of the urine, tliough 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 diseases the quantity is reduced considerably below the healthy stan- dard, while in other affections it is above it. Quantitative Estimation. — There are two chief methods of estimating the amount of urea in the urine. (1.) By decomposing it by means of an alkaline solution of sodium hypobromite, or hypochlorite, and calculating the amount in a measured quantity, by collecting and measuring the amount of nitrogen evolved under such circumstances. Urea contains nearly half its weight of nitrogen, hence the amount of the gas collected may be taken as a measure of the urea decomposed, remembering that 1 litre of nitrogen at the standard temperature and pressure weighs 14 X -08936, or 1.251 grms. The percentage of urea can thus 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. The reaction is CONn H4 -\- 3NaBrO + 2NaH0 = 3NaBr + 3HoO + NaoCOs + N^. (2. ) By precipitating the urea by adding to a given amount of urine, freed from sulphates and phos- phates, a standard solution of mercuric nitrate from a burette, vmtil the whole of it has been thrown down in an insoluble form ; then reading oflF the exact amount of the mercuric nitrate solution, which it was necessary to use. As the amount of urea which each cubic centimetre of the standard solution will precipitate is previously known, it is easy to calculate the amount in the sam- ple of urine taken. The precipitate which is formed was generally said to be composed of mercuric oxide and urea. Some, liowever, now consider that it is a mixture of mercuric nitrate itself and urea. Uric Acid (C5H4N4O3), — Uric or lithic acid is rarely absent from the urine of man or animals, though in the feline tribe it seems to be sometimes entirely replaced by urea. Properties. — Uric acid when pure is colorless, but when deposited from the urine is yellowish-brown. It crystallizes in various forms, of which the most common are smooth transparent, rhomboid plates, diamond-shaped plates, hexagonal tables, etc. (fig. 288). It is odorless and tasteless. It is very slightly soluble in cold water, and a little more so in hot water, quite insoluble in alcohol and ether. It dissolves freely in solution of the alkaline carbonates and other salts. EXCRETION. ■ 397 The proportionate quantity of uric acid varies considerably in different animals. In man, and Mammalia generally, especially the Herbivora, it is comparatively 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 Qaanfitij. — The quantity of uric acid, like that of nrea, 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 unnaturally large quaiitities; 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 about one-third of a gramme. Condition in the Urine. — The condition in which uric acid exists in solu ion in the urine has formed the subject of some discussion. The uric acid exists as urate of soda, produced by the uric acid as soon as it is formed combining with part of the base of the alkaline sodium phos- phate of the blood. Ilippuric acid, which exists in human urine also,. acts upon the alkaline phosphate in the same way, and increases still more the quantity of acixl 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 bases- sodium and ammonium takes place in the blood, or in the act of secre- tion in the kidney: the latter is more likely; 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, e.g., hydrochloric or nitric. When excreted in excess, however, it is deposited in a crystalline form (fig. 288), mixed with large quanti- ties of ammonium or sodium urate. In such cases it may be produced for microscopic examination by gently warm^ing 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 gran- ules of ammonium or sodium urate. When deposited in crystals, it is most frequently in rhombic or diamond-shaped lamina?, but other forms- are not uncommon (fig. 288). When deposited from urine, the crystals- are generally more or less deeply colored, from being combined with the Coloring principles of the i^rine. Tests. — There are two chief tests for uric acid besides the micro- 398 HANDBOOK OF PHYSIOLOGY. scopic evidence of its crystalline structure: (1) The Miid.e, Indiccm; or more probably a salt of indoxyl-sulphuric acid. It yields indigo blue when treated with strong hydrochloric acid and left to stand for some hours exposed to the air; the indigo may be separated by treatment with boiling chloroform, which takes it up, forming a blue solution. There is a similar compound of skatol and sulphuric acid which is sometimes recognized in the urine, by the production of a red color when nitric acid is added to it. Many medicinal substances color the urine, for instance Rhubarb, Santonin, Senna, Fuchsine, Carbolic Acid. Bromides and Iodides yield Bromine or Iodine, when nitric acid is added to the urine of patients taking these drugs. In the case of iodides 400 HANDBOOK OF PHYSIOLOGY. the liberated iodine communicates a strong mahogany color to the urine thus treated. Mucus. — Mucus in the urine consists principally of the epithelial debris from the mucous surface of the urinary passages. Particles of epithelium, in greater or less abundance, may be detected in most sam- ples of urine, especially if it has remained at rest for some time, and the lower strata are then examined (fig. 290). As urine cools, the mucus is. sometimes 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 undergoes decomjjosition. The presence of the decomposing mucus- excites chemical changes in the urea, whereby carbonate of ammoniumi is formed, which, combining with the excess of acid in the superphos- phates in the urine, produces insoluble neutral or alkaline phosiDhates of calcium and magnesium, and phosphate of ammonium and magne- sium. 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, forming a thick tena- cious sediment. Extractives. — In addition to those already considered, urine cow- tains a considerable number of nitrogenous compounds. These are usually described under the generic name of Extractives. Of these, the chief are: (1) Kreatinin (C4H7N3O), a substance derived, probably, from the metamorj^hosis of muscular 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 (C5N4H4O2), when isolated, is an amorjDhous powder soluble in hot water; (3) SarTcin, or hypo-xantliin (C5N4H4O); (4) Oxalnric acid (C3H4N2O4), in combi- nation with ammonium in the urine of the new-born child; (5) Allantoin (C4H6N4O3). 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 ujjon as normal constitueiits of urine. Saline Matter. — (a) 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 enumer- ated 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 burning. 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. EXCRETIO]Sr. 401 must be formed in the blood, or in the act of secretion of urine ; the sulj^hur of which the acid is formed being probably derived from the decomposing nitrogenous tissues, the other elements of which are re- solved into urea and uric acid. It may be in part derived also from the sulphur-holding taurin and n/.sii)i, 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 generated during combination with the sulphur is one of the subordinate means by which the animal tempera- ture 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 removed from urine, sulphuric acid may be formed by drying and burn- Fig. 290. Fig. 291. Fig. 290. — Mucus deposited from urine. Fig. 291. — Urinarj' sediment of triple phosphates (large 'prismatic crystals) and urate of ammo- nium, from urine which had undergone alkaline fermentation. ing it with nitre. From three to five grains of sulphur are thus daily excreted. The combination in which it exists is uncertain : possibly it is in some compound analogous to cystin or cystic oxide. Sulphuric acid also exists normally in the urine in combination with phenol (C'eHeO) as phenol-sulphuric acid or its corresponding salts, with sodium, etc. (1) The pliospTioric acid in the urine is combined jjartly with the alkalies, partly with the alkaline earths — about four or five times as much with the former as with the latter. In blood, saliva, and other alkaline fluids of the body, phosi^hates 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 discharged at the kidneys, namely, the uric, hip- puric, and sulphuric acids, all of which are neutralized with soda, 26 402 HANDBOOK OF PHYSIOLOGY. 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 osseous tissue the urine derives a large quantity of this salt. The de- composition of other tissues also, but especially of the brain and nerve- substance, furnishes large supplies of phosjihorus to the urine, which pliosphorus is supposed, like the sulphur, to be united with oxygen, and tlien 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 jjhosphates are more abundant after meals, whether of animal or vegetable food, and are diminished after long fasting. The alkaline phosphates are in- Fig. 292.— Crystals of Cjstiii. Fig:. 293.— Crj'stals of Calcium Oxalate. creased after animal food, diminished after vegetable food. Exercise increases the alkaline, but not the earthy phosphates. Phosphorus uncombined with oxygen appears, like sulphur, to be excreted in the urine. When the urine undergoes alkaline fermentation phosphates are deposited in the form of a urinary sediment, consisting chiefly of ammonio-mangesium phosphates (triple phosphate) (fig. 291). This compound does not, as such, exist in healthy urine. The ammonia is chiefly or wholly derived from the decomposition of urea. (r.) The Chlorine' ol the urine occurs chiefly in combination with sodium (next to urea, sodium chloride is the most abundant solid con- stituent of the urine), but slightly also with ammonium, and, perhaps, potassium. As the chlorides exist largely in food, and in most of the animal fluids, their occurrence in the urine is easily understood. Occasional Constituents.— (7?/.?^m (C3H7N SO2) (fig. 292) is an occasional constituent of urine. Tt resembles taurin in containing a large quantity of sulphur— more than 25 per cent. It does not exist in hetdthy urine. Another common morbid constituent of the urine is Oxalic acid, EXCKETION. 403 which is frequently deposited in combination with calcium (fig. 293) as a urinary sediment. Like cystin, but much more commonly^ it is the chief constituent of certain calculi. Of the other abnormal constituents of the urine which were men- tioned on p. 393, 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 Excretion of Urine. 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 im- portant part of the uriruiry 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. 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 de- pends almost entirely upon the blood-jDressure in the glomeruli. The greater the blood-pressure in the arterial system generally, and consequently in the renal arteries, the greater, cceteris j^aribiis, will be the blood-pressure in the glomeruli, and the greater the quantity of urine separated; but even without increase of the general blood-pres- sure, if the renal arteries be locally dilated, the pressure in the glomeruli will be increased and with it the secretion of urine. All the causes, therefore, which increase the general blood-pressure will secondarily increase the secretion of urine. Of these — (1) The heart's action is amongst the most important. When the cardiac contractions are increased in force or frequency, increased diuresis is the result. (2) Since the connection between the general blood-pressure and the nervous system is so close it will be evident that the amount of urine secreted depends greatly upon the influence of the latter. This may be demonstrated experimentally. 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 404 HANDBOOK OF PHYSIOLOGY. passed, but in a, different way, viz., by constricting the arteries generally, and, among others, the renal arteries; the diminution of blood-pressure resulting from tlie 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 which produces local dilatation without greatly diminishing the general blood-pressure will cause an increase in the quantity of fluid passed. (3) The fact that in summer or in hot weather the urine is dimin- ished 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, Fig. 294.— Diagram of Roy's Oncometer, o, represents tlie kidney inclosed in a metal box, which opens by hinge/; b, the renal vessels and duct. Surrounding the kidney are two chambers formed by membranes, the edges of which are tirmly fixed by being clamped between the outside metal capsule, and one mot representeil in the figiwe) inside, the two being firmly screwed together by screws at /i, and below. The membranous chamber below is filled witli a varying amount of warm oil, accorchng to the size of tl.e kiilney experimented with, through ihe opening then closed with the plug i. After the kidney has been inclosed in the capsule, the membrano'is chamber above is filled with warm oil through the tube e, which is then closed by a tap (not represented in the diagram); the tube d communicates with a recording apparatus, and any alteration in the volume of tne kidney is communicated by the oil in the tube to the chamber d of the Oncograph, fig. 295. 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 jji-oportional to each other. The intimate conuection which exists between the volume of the kidney and the variations of blood -pressure is exceedingly w^ell shown with the Oncometer, introduced by Roy, which is a modification of the plethysmo- graph, fig. 394. By means of this apparatus any alteration in the volume of the kidney is communicated to an apparatus [oncograph], capable of recording graphically, with a writing lever, siich variations. EXCRETION. 405 It has 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 accomjaanied by a corresponding increase of volume. Increase of volume is followed uy 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 further observed that certain substances, when injected into the blood, will also produce an increase in volume of the kidney, a;id consequent increased flow of urine, without affecting the general blood-pressure — Fig:. 295. — Roy's Oncograph, or apparatus for recording alterations in the volume of the kidney, etc., as shown by the oncometer — (,', upright, supporting recording lever I, which is raised or lowered by needle b, which works through/, and which is attached to the piston e, worlving in the chamber d. witli which the tube from the oncometer comnumicates. The oil is preventi'd fi( mi lii-ing squeezed out as tlie piston descends by a meaibraue, which is clamped between the ring-shaped surfaces of cylinder by the screw i worliing upward; the tube h is for filling the instrument. such bodies as sodium acetate and other diuretics. These observations appear to prove that local dilatation of the renal vessels may be produced by alterations in the blood acting upon a local nervous mechanism, as this happens when all of the renal nerves have been divided. The altera- tions are not only produced by the addition of drugs, but also by the in- troduction of comparatively small quantities of water or saline solution. To this alteration 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 effects of meals, etc., observed by Roberts. The renal excretion is increased after meals and diminished during fasting and sleep. The increase begins within the first hour after breakfast, and continues during the succeed- ing two or three hours; then a diminution sets in, and continues until an hour or two after dinner. The effect of dinner does not appear until 406 HANDBOOK OF PHYSIOLOGY. two or three hours after the meal; and it reaches its maximum about the fourth hour. From this period the excretion steadily decreases until bed-time. During sleep it sinks still lower, and reaches its mini- mum— being not more than one-third of the quantity excreted during the hours of digestion. The increased amount of urine passed after drinking large quantities of fluid probably depends upon the diluted condition of the blood thereby induced. The following table * will help to explain the dependence of the filtration function upon the blood-pressure and the nervous system: — Table of the jielation 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 the force or frequency of heart-beat, 2. Constriction of the small arteries of areas other than that of the kidney. h. By increasing the local blood-pressure, by relaxation of tlie renal artery, -without compensating relaxation el'seivhere ; by 1. Division of the renal nerves (causing polj'uria). 2. Division of the renal nerves and stimulation of the cord, below tlie medulla (causing greater polyuria) . 3. Division of the splanchnic nerves ; but the polyuria produced is less than in 1 or 2, as these nerves are distributed to a wider area, and tlie dilatation of the renal arterj^ is accompanied by dilatation of other vessels, and therefore with a somewhat di- minished general blood supply. 4. Puncture of the floor of fourth ventricle or mechanical irritation of the superior cervical ganglion of the sympathetic, possibly from the production of dilation of the renal arteries. B. Secretion of urine may be diminished a. By diminishing the general blood-pressiire; by 1. Diminution of tlie force or frequency of the heart-beats. 2. Dilatation of capillary areas other than that of the kidney. 3. Division of spinal cord below the inedulla, which causes dilata- tion of general abdominal area, and urine generally ceases being secreted. 6. By increasing the blood-presstire, by stimulation of the spinal cord below^ the medulla, the constriction of the renal arterj^, which follows, 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 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 * Modified from Foster. EXCRETION". 407 order by ligature 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 certain constituent parts of the blood to be filtered oft', and not others. Secretion. — That there is a second part in the process of the excre- tion of urine, which is true secretion, is suggested by the structure of the tubnli uriniferi, tind the idea is supported by various experiments. It will be remembered that the convoluted portions of the tubules are lined with an epithelium, which bears a close resemblance to the secre- tory epithelium of other glands, whereas the Malpighian capsules and portions of the loops of Henle are lined simply by flattened epithelium. The two functions of the different parts of an uriniferous tube are, then, suggested by the ditTerences of epithelium, and also by the fact that the blood supply to the different parts is different, since, as we have seen, Fig. 296. — Curve taken by renal oncometer compressed — with that of ordinary blood-pressure, o, Kidney curve; 6, blood-pressure curve. (Roy.) the convoluted tubes are surrounded by capillary vessels derived from the breaking up of the efferent vessels of the Malpighian tufts. As to the functions of the different parts of the uriniferous tubes in the secretion of urine, two chief theories have been brought forward. The first, suggested by Bowman (1843), and still generally accepted, 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 inorganic salts. The second, suggested by Ludwig (1844), is that in the glomeruli are 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 o£ 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 j)romoted 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. The first theory is, however, more strongly supported by direct experiment. By using the kidney of the newt, which has two distinct vascular 408 HANDBOOK OF PHYSIOLOGY. supplies, one from the renal artery to the glomeruli, and the other from the renal-portal vein to the convoluted tubes, Nussbaum has shown that certain substances, e.g., peptones and 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, that is to say, if it is certain that ligature of the renal artery assists the circulation through the glomeruli, which, however, is denied by Adami. Heidenhain also has shown by experiment that if a substance (sodium sulph-indigotate), 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 circumstances, swept away from them by the flushing of them which ordinarily takes place with the watery part of urine derived from the glomeruli. It therefore is jirobable that the cells, if they excrete the pigment, excrete urea and other substances also. But urea acts somewhat differently 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 condi- tions. 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 for believing that part of the increase of the secretion is due to the direct stimulation of the cells by the urea continued in the blood. To sum up, then, the relation of the two functions: (1.) The process of filtration, by which the chief part, if not the whole, of the fluid is eliminated, 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, dependent upon blood-pressure, is accomplished by the cells of the convoluted tubes, and is sometimes (as in the case of the elimination of urea and similar substances) accompanied by the elimination of copious EXCKETION. 409 fluid, produced by the chemical stimulation of the epithelium of the same tubules. The Passage of Urine into the Bladder. As each portion of urine is secreted it propels that which is already in the uriniferous tubes onward into the pelvis of the kidney. Theuce 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 tissures in the anterior or lower j^art of the walls of the abdo- men, and of the front 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 regular rate, nor is there a synchronism in its move- ment through the two ureters. During fasting, two or three drojDS 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 aided by the peristaltic contractions of the ureters, and is increased in deep inspiration, or by straining, and in active exercise, and in fifteen or twenty minutes after a meal. The urine collecting is jarevented from regurgitation into the ureters by the mode in which these pass through the walls of the blad- der, 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 oj^en 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. In so far, however, as it is a voluntary act, it is performed by means of the abdominal and other expiratory muscles, which in their contraction, as before explained, press on the abdominal viscera, the diaphragm being fixed, and cause the expulsion of the contents of those whose siDhincter muscles are at the same time relaxed. The muscular coat of the blad- der co-operates, in micturition, by reflex involuntary action, with the abdominal muscles; and the act is completed hy the accelerator urinm, which, as its name implies, quickens the stream, and expels the last drop 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, 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 intestinal worms, or other such irritation. Generally the 410 HANDBOOK OF PHYSIOLOGY. afferent impulse which calls into action the desire to micturate is excited by over-distentiou of the bladder, or even by a few drojDS of urine^ passing into the urethra. This passes up to the lumbar centre (or cen- tres) and produces on the one hand inhibition of the sphincter and on the other hand contraction of the necessary muscles for the expulsion of the contents of the bladder. The Structure and Functions of the Skin. The skin serves — (1), as an external integument for the protection of the deeper tissues, and (3), as a sensitive organ in the exercise of touch, a subject to be considered in the Chapter on the Special Senses; it is also (3), an important secretory and excretory, and (4), an absorb- ing organ, already noticed, p. 412; wliile it plays an important part in 5) the regulation of the temperature of the body. (See the Chapter on Animal Heat.) Structure. — The skin consists principally of a vascular tissue named the corium, derma, or cutis vera, and of an external covering of epithe- lium termed the epidermis or cuticle. Within and beneath tiie corium are imbedded several organs with special functions, namely, .S'?yc?or(/(?ro%s glands, seiaceous glands, and hair follicles ; and on its surface are sensi- tive papillcB. 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 sizes; it closely resembles in its structure the epithe- lium of the mucous membrane that lines the mouth. The following four layers may be distinguished in a more or less developed form. 1. Stratum corneum (fig. 297, a), consisting of 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 jialms 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 distinguished 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 mucosmn consists of many strata. The deepest cells, placed immediately above the cutis 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 EXCRETION. 411 of the more superficial layers are considerably flattened. The deeper surface of the rete mucosum is accurately adapted to the i^apillse of the true skin, being, as it were, moulded on them. It is very constant in thickness in ail parts of the skin. The cells of the middle layers of the stratum Malpighii are almost all connected by processes, and thus form prickle cells (fig. 35). The pigment of the skin, the varying quan- tity of which causes the various tints observed in difl'erent individuals and different races, is contained in the deeper cells of rete mucosum; the pigmented cells as they approach tlie free surface gradually losing their color. Epidermis maintains its thickness in spite of the constant ... .7 0/ ■I r\ \ Fig. 297.— Vertical section of the epidermis of the prepuce, a, stratum corneum, of very few layers, the stratum luciduni anil sti-atum granulosum not being distinctly represented; b. c, d and e, the layers of the stratum .Alalpifj:!!!!. a certain number of the cells in layers (/ and e showing signs of segmentation; layer c consists ohietly of prickle or ridge and furrow cells; /, basement membrane; g, cells in cutis vera. (Cadiat.) wear and tear to which it is subjected. The columnar cells of the deep- est layer of the rete mucosum elongate, and their nuclei divide into two (fig. 297, e). Lastly the upper part of the cell divides from the lower; thus from a long columnar cell are produced a polyhedral cell 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 pressure: they also become gradually horny by evaporation and transformation of their protoplasm into ceratin, till at last by rubbing in ordinary wear and tear they are detached as dry horny scales at the free surface. There is thus a constant production of fresh cells in the 412 HANDBOOK OF PHYSIOLOGY. deeper layers, and a constant throwing off of old ones from the free sur- face. When these two processes are accurately balanced, the epidermis maintains its thickness. When, by intermittent pressure a more active cell-growth is stimulated, the production 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 the 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 sensi- tive and vascular cutis from injury from without, as to limit the evap- oration of fluid from the blood-vessels. The adaptation of the epider- mis to the latter purposes may be well shown by exposing to the air two dead hands or feet, of 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 corium or cutis vera, which rests upon a layer of adipose and cellular tissue of varying thickness, is a dense and tough, but yielding and highly elastic structure, composed of fasciculi of areolar tissue, interwoven in all directions, and forming, by their interlace- ments, 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. 398) : but, in the superficial parts, they are small or entirely oblit- erated. Unstriped muscular fibres are also abundantly present. Papillae. — The cutis vera presents numerous conical papillae, with a single or divided free extremity, which are more prominent and more densely set at some parts than at others. This is especially the case on the palmar surface on the hands and fingers, and on 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 easily seen 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 yto of an inch (^ mm.), and at their base they measure about -^ of an inch in diameter. Each papilla is abundantly supplied with blood, re- ceiving from the vascular plexus in the cutis one or more minute arte- rial twigs, which divide into capillary loops in its substance, and then reunite into a minute vein, which passes out at its base. This abun- dant supply of blood explains the turgescence or kind of erection which they undergo when the circulation through the skin is active. The majority, but not all, of the papillae contain also one or more terminal EXCRETIOJiT. 413 nerve-fibres, from the ultimate ramifications of the cutaneous plexus, on which their exquisite sensibility depends. The 7ierve-terminations in the skin have been described under the Sensory Xerve Terminations (p. 104 et seq.). 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, sur- c — 7'rV^H^ w Fig. 298. — 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.) rounded by blood-vessels and embedded in the subcutaneous adipose tissue (fig. 298, C). From this mass, the duct ascends, for a short dis- tance in a spiral manner through the deeper part of the cutis, then passing straight, and then sometimes again becoming spiral, it passes through the epidermis and opens by an oblique valve-like aperture. In the parts where the epidermis is thin, the ducts themselves are thinner and more nearly straight in their course (fig. 298). The duct, which maintains nearly the same diameter throughout, is lined M'ith a 414 HANDBOOK OF PHYSIOLOGY. layer of columnar epithelium (fig. 299) continuous with the epidermis; while the part which passes through the epidermis is a mere passage through the epidermal cells not being bounded by any special lining; but the cells which immediately form the boundary of the canal in this part are somewhat ditlerently arranged from those of the adjacent cuti- cle. The coils or terminal portions of the gland are lined with at least two layers of short columnar cells with very distinct nuclei (fig. 299), and possess a large lumen distinctly bounded by a special lining of cuticle. The sudoriferous glands are abundantly distributed over the whole surface 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 by which the peculiar odorous matter of the axillae is secreted Fig. 299. — Terminal tubules of sudoriferous glands, cut in various directions from the skin'^of the pig's ear. (V. D. Harris.) form a nearly complete layer under the cutis, and are like the ordinary sudoriferous glands, except in being larger and having very short ducts. The peculiar bitter yellow substance secreted by the skin of the ex- ternal auditory jDassage is named cerumen, and the glands themselves cernuiinous glands; but they do not much differ in structure from the ordinary sudoriferous glands. {b) Sebaceous Glands. — The sebaceous glands (figs. 298, 303), like sudoriferous glands, are abundant in most parts of the surface of the l)ody, particularly in parts largely supplied with hair, as the scalp and face. They 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 racemose glands composed of an aggregate of small tubes or sacculi lined with columnar epithelium and filled with an opaque white substance, like soft ointment, which consists of broken-up epithelial cells which have undergone fatty degeneration. Minute capillary vessels overspread them; and their ducts open on excretions". 415 •either 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 gener- ally two or more glands to each hair (fig. 298). 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 edges turned upward (fig. 301, 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- monly, in the human subject, occupies the whole inside of the hair; but Fig. 300. — Transverse section of a hair and hair-follicle made below the opening of the sebace. gland, o, medulla or pith of the hair: b. fibrous layer or cortex; c, cuticle; d, Huxley's layer .,'. Henle's layer of mternal root-sheath; /and g. layers of external roo^sheath, outside of ^ is a li.;Ot layer, or "glassy membrane," which is equivalent to the basement membrane; h, fibrous coat of hair sac ; 2, vessels. (Cadiat.) in some cases there is left a small central space filled by a subsw'.nce called the mef/?f//rt or ^j?77^, composed of small collections of irregularly shaped cells, containing sometimes pigment granules or fat, bnt inostly air. The follicle, in which the root of each hair is contained (fig 302), forms a tubular dej)ression from the surface of the skin, — descending into the subcutaneous fat, generally to a greater depth than the sudor- iferous glands, and at its deepest part enlarging in a bulbous form, and often curving from its previous rectilinear course. It is lined through- out by cells of epithelium, continuous with those of the epidermis, and its v.alls are formed of pellucid membrane, which commonly in the follicles of the larc-est hairs has the structure of vascular fibrous tissue. 416 HANDBOOK OF PHYSIOLOGY. At the bottom of the follicle is a small papilla, or projection of true skin, and it is by the jjroduction and outgrowth of epidermal 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 Fig. 301.— Surface of a white hair, magnified 160 diameters. The wave lines mark the upper or free edges of the cortical scales. B, separated scales, magnified 350 diameters. (Kolliker.) 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. 302). This epidermal lining of the hair-follicle, or roof-sheath of the hair, is composed of two layers, the inner one of which is so moulded on the imbricated scaly cuticle of the hair, that its inner surface becomes im- bricated also, but of course in the opposite direction. When a hair is Fig. .302.— Longitudinal section of a hair follicle, o, Stratum of Blalpighi, deep layer forming the external root-sheath, and continued to the surface of the papilla to form the medullary sheath of the hair; 6, second external sheath; c. internal root-sheath; d, fibroid sheath of the hair: e, medullary sheath or medulla; /, hair papilla; g, blood-vessels of the hair-papilla; h, fibro-vascular sheath. (Cadiat.) pulled out, the inner layer of the root-sheath and part of the 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 flat- tened, and of more horny consistence. That specially modified portion EXCRETION". 417 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, while the front part is free and projects beyond the extremity of the digit. The intermediate por- tion of the nail rests by its broad under surface on the front part of the matrix, which is here called the hed of the nail. This part of the matrix is not uniformly smooth on the surface, but is raised in the form of longitudinal and and nearly parallel ridges or lamina?, on which are moulded the epidermal cells of which the nail is made up. The growth of the nail, like that of the hair, or of the epidermis gen- erally, 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 surface of the matrix, it can receive no fresh addition from beneath, and is simply moved forward hj the growth at its root, to be at last worn away or cut off. Functions of the Skin. The function of the skin to be considered in this chapter is that of the excretion of the sweat. The fluid secreted by the sweat-glands is usually formed so gradually that the watery portion of it escapes by evaporation as fast as it reaches the surface. But during strong exer- cise, exposure to great external warmth, in some diseases, and when evaporation is prevented, the secretion becomes more sensible, and col- lects on the skin in the form of drops of fluid. The perspiration, as the term is sometimes employed in physiology, includes all that portion of the secretions and exudations from the skin which passes off by evaporation ; the siveat 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 distinction, the former is called insensible perspiration; the latter sensible perspira- tion. 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 secretions. The secretion of the sebaceous glands and hair-follicles consists of cast-off epithelium cells, with nuclei and granules, together with an oily 27 418 HANDBOOK OF PHYSIOLOGY. 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 unctu- ous coating, or vernix 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 evaporation from the surface, and guarding the skin from the effects of the long- Fig. 303.— Sebaceous gland from human skin. (Klein and Noble Smith.) continued action of moisture. But while it thus serves local purposes, its removal from the body entitles it to be reckoned among the excre- tions of the skin. Chemical Composition of Sweat. Water .995 Solids :— Organic Acids (formic, acetic, butyric, pro- ) q picnic, caproic, caprylic) . . ) ' Salts, chiefly sodium chloride . . . .1.8 Neutral fats and cholesterin . . . .7 Extractives (including urea), with epithelium 1.6 5 1000 The sweat is a colorless, slightly turbid fluid, alkaline, neutral or acid in reaction, of a saltish taste, and peculiar characteristic odor. Of the several substances it contains, however, only the carbonic acid and water need particular consideration. Watery Vapor. — The quantity of watery vapor excreted from the EXCRETIOX. 419 skin is on an average between 1^ and 2 lb daily (about 1 kilo). This subject has been very carefully investigated 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 remained quiet for several hours, after which time he was again weighed. The difference in the two weights indicated the amount of loss by pulmonary exhalation. Having taken off the air- tight dress, he was immediately weighed again, and a fourth time after a certain interval. The difference between the two weights last ascer- tained gave the amount of the cutaneous and pulmonary exhalation to- gether; 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 loss 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 state, and the stillness of the atmosphere. But, of the variations to which it is subject under the influence of these conditions, no calcula- tion has been exactly made. Carbonic Acid. — The quantity of carbonic acid exhaled by the skin on an average is about yl-g- to ^^ 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 between 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 remembered 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. 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 M-adding, and to have died when the wadding was removed. Influence of the Xervous System. Experiments seem to show that the mode of the secretion of sweat is more or less like that of the secretion of saliva. The chief difference between the two processes appears to be this, that increased blood sup- 420 HANDBOOK OF PHYSIOLOGY. ply, of itself, is able to produce a secretion of sweat, whereas this is not the case with the salivary secretion In the case of the sweat-glands, it is practically certain that they are also under the control of efferent im- pulses passing to them from the sjiecial sweat centres in the brain and spinal cord through special sweat nerves. Thus, if the sciatic nerve be divided in a cat and the peripheral end be stimulated, beads of sweat are seen to appear upon the pad of the corresponding foot, although at the same time the blood-vessels are constricted or whilst the aorta is pressed upon, whereas if atropin have been injected previously to the stimulation, no sweat appears, although dilatation of the vessels be present. Secretion of sweat, too, may be reflexly brought about. The exact way in which various conditions producing an extra secre- tion of sweat act, is somewhat uncertain. The circulation of venous blood in the central nervous system, however, appears to be the cause of the sweating of phthisis and of dyspnoea generally. If the cat whose sciatic nerve be divided be rendered dyspnoeic, abundant sweat occurs upon the foot of the uninjured, arid none on the injured side. The effect of heat in producing sweating may be both local and general, and again, the various drugs which produce an increased secretion of sweat do not all act in the same way; thus, there is reason for thinking that pilocarjnn acts upon the local apparatus, that stryclmia and picrotoxin act upon the sweat centres, and that nicotin acts both upon the central and upon the local apparatus. The special sweat-nerves appear to issue from the spinal cord, in the case of the hind limb of the cat by the last two or three dorsal and first two or four lumbar nerves, pass to the abdominal sympathetic and from thence to the sciatic nerve. In the case of the fore limb, the nerves leave the cord by the 5th and 6th cervical nerves into the thoracic sym- pathetic, and then join the brachial plexus, reaching the arm through the median and ulnar nerves. It will be as well to repeat here the other functions which the skin subserves. In addition to its excretory oflSce, we have seen that it acts as a channel for absorption. It is also concerned with a special sense, viz., that of touch, to the consideration of which as well as to its func- tion of regulating the temperature of the body we shall presently return. It should be recollected, however, that apart from these special func- tions, 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, while readily yield- ing and adapting itself to their various movements and changes of position. CHAPTER XI THE METABOLISM OF THE TISSUES. We have now to consider the various changes occurring in the tissues and organs of the body which maybe considered as intermediate between those already described, viz., the digestion and absorption of food on the one hand, and the excretion of waste products on the other. These processes take place principally in the muscles and glands of the body, and it will be as well to direct our attention to the metabolism first of all in muscle, and secondly in the glands not directly concerned in the digestive processes. Muscular Metabolism. The muscles make up about one-half of the total body weight. The principal substance which can be extracted from muscle, when examined after death, is the proteid body, JIi/osi», some of the reactions of which have been already discussed, p. 108. I'his body appears to bear some- what the same relation to the living muscle, as fibrin does to the living blood, since the coagulation of muscle after death is due to the formation of myosin. Thus, if coagulation be delayed in muscles removed imme- diately from recently killed animals, by subjecting them to a temperature below 0°C„, it is possible to obtain from them by expression a viscid fluid of slightly alkaline reaction, called musde-jilasma (Klihne, Halli- burton). And muscle plasma, if exposed to the ordinary temperature of the air (and more quickly at 37°-40° C), undergoes coagulation much in the same way as, under similar circumstauces, does blood i)lasma, separated from the blood corpuscles by the action of a low temperature. The appearances presented by the fluid during the process are also very similar to the phenomena of blood-clotting, viz., that first of all an in- creased viscidity appears on the surface of the fluid, and at the sides of the containing vessel, which gradually extends throughout the entire mass, until a fine transparent clot is obtained. In the course of some hours the clot begins to contract, and to squeeze out of its meshes a fluid corresponding to blood-serum. In the course of coagulation, therefore, muscle plasma separates into muscU-dot and miisde-serum. The muscle clot is the substance myosin. It differs from fibrin in being easily soluble in a 2 per cent solution of hydrochloric acid, and in a 10 per cent solu- 422 HANDBOOK OF PHYSIOLOGY. tion of sodium chloride. It is insoluble in distilled water, and its solu- tions coagulate on aj)plication of heat. It is in short a. globulin. During the process the reaction of the fluid becomes distinctly acid. The coagulation of muscle plasma cannot only be prevented by cold, but also, as Halliburton has shown, by the presence of neutral salts in certain proportions; for example, of sodium chloride, of magnesium sulphate, or of sodium sulphate. It will be remembered that this is also the case with blood plasma. Dilution of the salted muscle plasma will produce its slow coagulation, which is prevented by the presence of the neutral salts in strong solution. It is highly probable that the formation of muscle-clot is due to the presence of a ferment (myosin-ferment). The antecedent myosin in liv- ing muscle has received the name of myosinogen, in the same way as the fibrin-forming element in the blood is called fibrinogen. Myosinogen is, however, made up of two globulins, which coagulate at the tempera- tures 47° C. and 56° C. respectively. Myosin may also, as we have before mentioned, p. 421, be obtained from dead muscle by subjecting it, after all the blood, fat, and fibrous tissue, and substances soluble in water have been removed, to a 10 per cent solution of sodium chloride, or 5 per cent solution of magnesium sulphate, or 10 to 15 per cent solution of ammonium chloride, filtering and allowing the filtrate to drop into a large quantity of water; the myosin separates out as a white flocculent precipitate. A very remarkable fact with regard to the properties of myosin has been demonstrated by Halliburton, namely, that a solution of dead muscle in strong neutral saline solution, possesses very much the same properties as muscle plasma, and that if diluted with twice or three times its bulk of water, myosin will separate out as a clot, which clot can be again dissolved in a strong neutral saline solution, and the solution can be again made to clot on dilution. This process can often be re- peated ; but in the fluid which exudes from the clot there is no proteid present. Myosin when dissolved in neutral saline fluids is converted in- to myosinogen, but reappears on dilution of the fluid. Muscle clot is almost pure myosin; but it appears to be combined with a certain amount of salts, for if it be freed of salts, especially of those of calcium, by prolonged dialysis, it loses its solubility. If a small amount of cal- cium salts be added, however, it regains that pro^Derty. Muscle serum is acid in reaction, and almost colorless. It contains three proteid bodies, viz. — («) kglohuUn (myoglobulm), which can be pre- cipitated by saturation with sodium chloride, or magnesium sulphate, and which can be coagulated at 63° C. (145° F.). (b) Serum-albumin {myo- albnmin), which coagulates at 73° C. (163° F.), but is not precipitated by saturation with either of those salts. And (c) Myo-albumose, which. THE METABOLISM OF THE TISSUES. 423 is neither precipitated by heat, nor by saturation with sodium chloride or magnesium sulphate, but may be precipitated by saturation with am- monium sulphate. It is closely connected with, even if it is not itself, myosin ferment. Neither casein nor peptone has been found by Halli- burton in muscle extracts. In extracts of muscles, especially of red muscles, there 'is a certain amount of Hmmoglobin^ and also of a pigment special to muscle, called by McMunn Mijo-lmmatin, which has a spectrum quite distinct from haemoglobin, viz., a narrow band just before D, two very narrow between D and E, and two other faint bands, nearly violet, E b, and between E and F close to F. In addition to muscle ferments, already mentioned, muscle extracts contain certain small amounts ot pepsin and Jibrin ferment, and also an amylolytic ferment. Certain acids are also present, particularly sarco-lactic, as well as acetic and formic. Of carbohydrates, glycogen and glucose (or maltose), also inosite. Nitrogenous crystalline bodies, such as lcreatin,hreatinin,xanthin, "hypo-xantliin, or carnin, taurin, urea, in very small amount, uric acid and inosmic acid. Salts, the chief of whicli is potassium phosphate. Muscle at Rest. Physical Condition. — During rest or inactivity a muscle has a slight but very perfect Elasticity; it admits of being considerably stretched, but returns readily and completely to its normal condition. In the liv- ing body the muscles are always stretched somewhat beyond their natural length, they are always in a condition of slight tension; an arrangement which enables the whole force of the contraction to be utilized in ap- proximating the points of attachment. It is obvious that if the muscles were lax, the first part of the contraction until the muscle became tight would be wasted. There is no d6ubt that even in a condition of rest Oxygen is abstracted from the Mood, and carbonic acid is given out by a muscle; for the blood becomes venous in the transit, and since the muscles form by far the largest element in the composition of the body, chemical changes must be constantly going on in them as in other tissues and organs, although not necessarily accompanied by contraction. When cut out of the body such muscles retain their contractility longer in an atmosphere of oxygen than in an atmosphere of hydrogen or carbonic acid, and during life, an amount of oxygen is no doubt necessary to the manifestation of energy as well as for the metabolism going on in the resting condition. The reaction of living muscle in a resting or inactive condition is neutral or faintly cdkaline. 424 HANDBOOK OF PHYSIOLOGY, In muscles whicli have been removed from the body, it lias been found that for some little time electrical currents can be dcnionsirated jmssing from point to point on their surface; but as soon as the muscles die or enter into rigor mortis, these currents disapjjear. The demonstration of muscle currents is usually done as follows : — The frog'& muscles are the most convenient for experiment ; and a muscle of regular shape, in which the fibres are parallel, is selected. The ends are cut off by- Fig. 304.— Reflecting galvanometer. (Thomson.) A. The galvanometer, which consists of two systems of small astatic needles suspended by a fine hair from a support, so that each set of needles is within a coil of fine insulated copper wire, that forming the lower coil is wound in an opposite direction to the upper. Attached to the upper set of needles is a small mirror about 54 inch in diameter; the light from the lamp at B is thrown upon this Uttle mirror, and is re- flected upon the scale on tlie other side of B, not shown in figure. The coils / I are arranged upon brass uprights, and their ends are carried to the binding screws. The whole apparatus is placed upon a vulcanite plate capable of being levelled by the screw supports, and is covered by a brass-bound glass shade, L. the cover of which is also of brass, and supports a brass rod, 6, on which moves a weak curved magnet, m. C is the shunt by means of which the amount of the current sent into the galvanometer may be regulated. When in use the scale is placed about three feet from the galvanometer, which is arranged east and west, the lamp is lighted, the mirror is made to swing, and the light from the lamp is adjusted to fall upon it, and it is then regulated until the reflected spot of light from it falls upon the zero of the scale. The wires from the non-polarizable electrodes touching the muscU^ are attached to the outer binding screws of the galvanometer, a key intervening for short-circuiting, or if a portion only of the current is to pass into the galvanometer, the shunt should interv<>iie as well with the appropriate plug in. When a current passes into the galvanometer the needles and, with them, the mirror, are turned to the right or left according to the direction of the current. The amount of the de- flection of the needle is marked on the scale by the spot of light travelling along it. clean vertical cuts, and the resulting piece of muscle is called a regular muscle prism. The muscle prism is insulated, and a pair of non-polarizable electrodes connected with a very delicate galvanometer (fig. 304) is applied to various points of the prism, and by a deflection of the needle to a greater or less extent THE METABOLISM OF THE TISSUES. 425 in one direction or anothex', the strength and direction of the currents in the piece of muscle can be estimated. It is necessary to use non-polarizable and not metallic electrodes in this experiment, as otherwise there is no certainty that the whole of the current observed is communicated from the muscle itself, and is not derived from the metallic electrodes arising in consequence of the action of the saline juices of the tissues upon them. The form of the non- polarizable electrodes is a modification of Du Bois Eeymond's apparatus (fig. 305), which consists of a somewhat flattened glass cylinder, a, drawn abruptly Fig. 305.— Diagram of Du Bois Reymond's non-polarizable electrodes, a. Glass tube filled with a saturated solution of zinc sulphate, in the end, c, of which is china clay drawn out to a point; in the solution a well amalgamated zinc rod is immersed and connected, by means of the wire which passes through a, with the galvanometer. The remainder of the apparatus is simply for convenience of application. The muscle and the end of the second electrode are to the right of the figure. to a point, and fitted to a socket capable of movement, and attached to a stand, A, so that it can be raised or lowered as required. The lower portion of the cylinder is filled with china clay moistened with saline solution, part of which projects through its drawn-out point ; the rest of the cylinder is fitted with a saturated solution of zinc sulphate into which dips a well amalgamated piece of zinc connected by means of a wire with the galvanometer. In this way the zinc sulphate forms a homogeneous and non-polarizable conductor between the zinc and the china clay. A second electrode of the same kind is, of course, necessary. In a regular muscle prism the currents are found to be as follows: — If from a point in the surface a line — the equator — be drawn across the muscle prism equally dividing it, currents pass from this point to points away from it, which are weak if the points are near, and increased in strength as the points are further and further away from the equator ; the strongest passing from the equator to a point representing the middle of the cut ends (fig. 306, 2) ; currents also pass from j^oints nearer the equator to those more remote (fig. 300, 1, 3, 4,), but not from points equally distant or iso-electric points (fig. 306, 6, 7, 8). The cut ends are always negative to the equator. These currents are constant for some time after removal of the muscle from the body, and in fact remain as 426 HANDBOOK OF PHYSIOLOGY long as the muscle retains its life. They are in all ])robaLility due to chemical changes going on in the muscles. The currents are diminished by fatigue and are increased by an increase of temperature within natural limits. If the uninjured tendon be used as the end of the muscle, and the muscle be examined without re- moval from the body, the currents are very feeble, but they are at once much increased by injuring the muscle, as by cutting off its tendon. The last observation appears to show that they are right who believe that the currents do not exist in uninjured muscles in situ, but that in- jury, either mechanical, chemical or thermal, will render the injured part electrically negative to other points on the muscle. In a frog's heart it has been shown, too, that no currents exist during its inactivity, but that as soon as it is injured in any way they are developed; the in- jured part being negative to the rest of the muscle. The currents which Fig. 306. — Diagram of the currents in a muscle prism. (Du Bois Reymond.) have been above described are called either natural muscle currents or currents of rest, according as they are looked upon as always existing in muscle or as developed when a part of the muscle is subjected to injury; in either case, up to a certain point, it is agreed that the strength of the currents is in direct proportion to the injury. Muscle in Activity. The property of muscular tissue, by which its peculiar functions are exercised, is its Contractility, which is excited by all kinds of stimuli ap- plied either directly to the muscles, or indirectly to them through the medium of their motor nerves. This property, although commonly brought into action through the nervous system, is inherent in the muscular tissue. For — (1.) it may be manifested in a muscle which is isolated from the influence of the nervous system by division of the nerves supplying it, so long as the natural tissue of the muscle is duly nourished; and (2.) it is manifest in a portion of muscular fibre, in which, under the microscope, no nerve-fibre can be traced. (3.) Substances such as THE METABOLISM OF THE TISSUES. 427 urari., which paralyze the nerve-endings in muscles, do not at all dimin- ish the irritability of the muscle itself. (4.) When a muscle is fatigued, a local stimulation is followed by a contraction of a small part of the fibre in the immediate vicinity without any regard to the distribution of nerve-fibres. If the removal of nervous influence be long continued, as by division of the nerves supplying a muscle, or in cases of paralysis of long-standing, the irritability, I.e., the power of responding to a stimulus, maybe lost; but probably this is chiefly due to the impaired nutrition of the muscular tissue, which ensues through its inaction. The irritability of muscles is also soon lost, unless a suj^ply of arterial blood to them is kept up. Thus, after ligature of the main arterial trunk of a limb, the power of moving the muscles is partially or wholly lost, until the collateral cir- culation is established; and when, in animals, the abdominal aorta is tied, the hind legs are rendered almost powerless. The same fact may be readily shown by compressing the abdominal aorta in a rabbit for about 10 minutes; if the pressure be released and the animal be placed on the ground, it will work itself along with its front legs, while the hind legs spra,wl helplessly behind. Gradually the muscles recover their power and become quite as efficient as before. So, also, it is to the imperfect supply of arterial blood to the muscular tissue of the heart, that the cessation of the action of this organ in as- phyxia is in some measure due. The Phenomena of Muscular Contraction. The power which muscles possess of contraction may then be called forth by stimuli of various kinds, and these stimuli may also be applied di- rectly to the muscle or indirectly to the nerve supplying it. There are distinct advantages, however, in applying the stimulus to the nerve, as it is more convenient, as well as more potent. The stimuli are of four kinds, viz. : — (1.) Mechanical stimuli^ as by a blow, pinch, prick of the muscle or its nerve, will produce a contraction, repeated on the repetition of the stimulus; but if applied to the same point for a limited number of times only, as such stimuli will soon destroy the irritability of the preparation. (2.) Thermal Stimuli. — If a needle be heated and applied to a muscle or its nerve, the muscle will contract. A temperature of over 37.8° C. (100° F.) will cause the muscles of a frog to pass into a condition known as heat rigor. (3.) Chemical Stimuli. — A great variety of chemical substances will excite the contraction of muscles, some substances being more potent in irritating the muscle itself, and other substances having more effect upon the nerve. Of the former mav be mentioned, dilute acids, salts of cer- 428 HANDBOOK OF PHYSIOLOGY, tain metals, e.g.^ zinc, copper and iron; to the latter belong strong glycerin, strong acids, ammonia and bile salts in strong solution. (4.) Electrical Stimuli. — For the purpose of experiment electrical stimuli are most frequently used, as the strength of the stimulus may be more conveniently regulated. Any form of electrical current may be employed for this purpose, but galvanism or the induced current is usu- ally chosen. Galvanic currents are usually obtained by the employment of a continuous current battery such as that of Daniell, by which an electrical current which varies but little in intensity is obtained The battery (fig. 307) consists of a positive plate of well -amalgamated zinc immersed in a porous cell, containing dilute sulphuric acid ; and this cell is again contained within a large copper vessel (forming the negative plate) , containing besides a saturated solution of copper sulphate. The electrical current is made continuous by the use of the two fluids in the following manner. The action of the dilute sulphuric acid upon the zinc plate partly dissolves it, and liberates hydrogen, and this gas passes through the porous vessel, and decomposes the copper sulphate into copper ChSO-^ Fig. 307.— Diagram of a Dauiell's battery. and sulphuric acid. The former is deposited upon the copper plate, and the latter passes through the porous vessel to renew the sulphuric acid which is being used up. The copper sulphate solution is renewed by spare crystals of the salt, which are kept on a little shelf attached to the copper plate, and slightly below the level of the solution in the vessel. The current of electricity supplied by this battery will continue without variation for a considerable time. Other continuous current batteries, such as Grove's, may be used in place of Daniell 's. The way in which the apparatus is arranged is to attach wires to the copper and zinc plates, and to bring them to a key, which is a little appa- ratus for connecting the wires of a battery. One often employed is Du Bois Reymond's (fig. 308) ; it consists of two pieces of brass about an inch long, in each of which are two holes for wires and binding screw, to hold them tightly; these pieces of brass are fixed upon a vulcanite plate, to the under surface of which is a screw clamp by which it can be secured to the table. The interval between the pieces of brass can be bridged over by means of a third thinner piece of similar metal fixed by a screw to one of the brass pieces, and capable of movement by a handle at right angles, so as to touch the other piece of brass. If the wires from the battery are brought to the inner binding screws, THE METABOLISM OF THE TISSUES, 429 and the bridge connects them, the current passes across it and back to the battery. Wires are connected with the outer binding screws, and the other ends are joined together for about two inches, but, being covered except at their points, are insulated ; the uncovered points are about an eighth of an Fig. 308.— A. Du Bois Reymond's Key. B. Mercury Key. inch apart. These wires are ihe electrodes, and the electrical stimulus is applied to the muscle through them, if they are placed behind its nerve. When the connection between the two brass plates of the key is broken by depressing the handle of the bridge, the key is then said to be opened. An induced current is developed by means of an apparatus, called an induc- Fig. 309. — Du Bois Reymond's induction coil. tion coil, and the one employed for physiological purposes is mostly Du Bois Reymond's, the one seen in fig. 309. Wires from a battery are brought to the two binding screws d' and d, a key intervening. These binding screws are the ends of a coil of coarse covered wire 430 HANDBOOK OF PHYSIOLOGY. c, called the primary coil. The ends of a coil of finer covered wire g, are attached to two binding screws to the left of the figure, one only of which is visible. This is the secondary coil, and is capable of being moved nearer to c along a gi-oove and graduated scale. To the binding screws to the left of g, the wires of electrodes used to stimulate the muscle are attached. If the key in the cir- cuit of wires from the battery to the primary coil (primary circuit) be closed, the current from the battery passes through the primary coil, and across the key to the battery, and continues to pass as long as the key continues closed. At the moment of closure of the key, at the exact instant of the completion of the primary circuit, an instantaneous current of electricity is induced in the secondary coil, g, if it be sufficiently near and in line with the primary coil ; and the nearer it is to e, the stronger is the cvirrent induced. The current is only momentary in duration and does not continue during the w^hole of the period while the primary circuit is complete. When, however, the primary current is broken by opening the key, a second, also momentary, current is induced in g. The former induced current is called the making and the latter the breaking shock ; the former is in the opposite direction to, and the latter in the same as, the primary current. The induction coil may be used to produce a rapid series of shocks by means of another and accessory part of the apparatus at the right of the fig. , called the magnetic intemipter. If the wires from a battery are connected with the two pillars by the binding screws, one below c, and the other, a, the course of Fig. 310. —Diagram of the course of the current in the magnetic interrupter of Du Bois Rey- mond's induction coil. (Helmholz's modification.) the cun-ent is indicated in fig. 310, the direction being indicated by the arrows. The current passes up the pillar from e, and along the springs if the end of d is close to the spring, the current passes to the primary coil c, and to wires covering two upright pillars of soft iron, from them to the pillar a, and out by the wires to the battery ; in passing along the wire, h, the soft iron is con- verted into a magnet, and so attracts the hammer, /, of the spring, breaks the connection of the spring with d\ and so cuts off the current from the primary coil, and also from the electro-magnet. As the pillars, h, are no longer mag- netized the spring is released, and the current passes in the first direction, and is in like manner interrupted. At each make and break of the primary current, currents corresponding are induced in the secondary coil. These cur- rents are opposite in direction, but are not equal in intensity, the break shock being greater. In order that the shocks should be nearly equal at the make and break, a wire (fig. 310, e') connects e and d' , and the screw d' is raised out of reach of the spring, and d is raised (as in fig. 310) , so that part of the cur- THE METABOLISM OF THE TISSUES, 431 rent always passes through the primary coil and electromagnet. When the spring touches d, the current in b is diminished, but never entirely withdrawn, and the primary current is altered in intensity at each contact of the spring with d, but never entirely broken. Record of Muscular Contraction under Stimuli. — The muscles of the frog are most convenient for the purpose of recording contractions. The frog is pithed, that is to say, its central nervous system is entirely destroyed by the insertion of a stout needle into tlie spinal cord, and the parts above it. One of its lower extremities is used in the following manner. The large trunk of the sciatic nerve is dissected out at the back of the thigh, and a pair of electrodes is Fig. 311. — An'anffement of the apparatus necessary for recording; muscle contractions ■with a revolving cylinder carrying' smoked y)aper. A, Revolving cylinder; B, the frog arranged upon a cork-covered board which is capable of being raised or lowered on the upright, which also can be moved along a solid triangular bar of metal attached to the base of the recording apparatus— the tendon of the gastrocnemius is attached to the writing lever, properly weiglited, by a ligature. The electrodes from the secondary coil pass to the apparatus— being, for the ■sake of convenience, first of all brought to a key, D ( Du Bois Reymond's) ; C, the induction ■coil; F, the battery (in this fig. a bichromate one); E, the key (Morse's) in the primary circuit. inserted behind it. The tendo-achillis is divided from its attachment to the OS calcis, and a ligature is tightly tied round it. This tendon is part of the broad muscle of the thigh (gastrocnemius), which arises from above the con- dyles of the femur. The femur is now fixed to a board covered with cork, and the ligature attached to the tendon is tied to the upright of a piece of metal bent at right angles (fig. 311, b), which is capable of moverment about a pivot at its knee, the horizontal portion caiTving a writing lever (myograph) . When the muscle contracts, the lever is raised. It is necessary to attach a small weight to the lever. In this arrangement the muscle is in situ, and the nerve disturbed from its relations as little as possible. The muscle may, however, be detached from the body with the lower end of 432 HANDBOOK OF PHYSIOLOCiV Fig. 312.— Moist Chamber. the femur from which it arises, and the nerve going to it may be taken away with it. The femur is divided at about the lower third. The bone is held in a firm clamp, the nerve is placed upon two electrodes connected with an induc- tion apparatus, and the lower end of the muscle is connected by means of a ligature attached to its tendon with a lever which can write on a recording apparatus. To prevent evaporation this so-called nerve-muscle preparation is placed under Fig. 313.— Simple form of pendulum myograph and accessory parts. A, Pivot upon which pendulum swings : 2?, catch on lower end of myograph opening the key, C, in its swing ; D, a spring-catch which retains myograph, as indicated by dotted lines, and on pressing down the handle of which the pendulum swings along the arc to D on the left of figure, and is caught by its spring. THE METABOLISM OF THE TISSUES. 433 a glass shade {moist cltamber, fig. 312), the air in which is kept moist by means of blotting paper saturated with saline solution. Effects of a Single Induction Shock. — With a nerve-muscle preparation arranged in either of the above ways, on closing or opening the key in the pri- mary circuit, we obtain and can record a contraction, and if we use the clock- work apparatus revolving rapidly, a curve is traced such as is shown in fig. 314. Another way of recording the contraction is by the use of the pendulum myograph (fig. 313) . Here the movement of the pendulum along a certain arc is substituted for the clockwork movement of the other apparatus. The pen- dulum carries a smoked glass plate uj^on which the writing lever of a myo- graph is made to mark. The opening or breaking shock is sent into the nerve-muscle preparation by the pendulum in its swing opening a key (fig. 313, C.) in the primary circuit. Single Muscle Contractions. — The tracing {muscle curve) ob- tained of a single muscle contraction or twitch is seen in fig. 314, and may be thus explained. The upper line (m) represents the curve traced by the end of the lever in connection with a muscle after stimulation of the muscle by a single Fi^. 314. — Muscle-curve obtained by means of the pendulum myograph, .s, indicates the exact instant of the induction sliock; c, commencement; and m x, the maximum elevation of lever; t, the line of a vibrating tuning-fork. (M. Foster.) induction-shock: the middle-line (/) is that described by the marking- lever, and indicates by a sudden drop the exact instant at which the induction-shock was given. The lower wavy line (t) is traced by a vibrating tuning-fork, and serves to measure precisely the time occupied in each part of the contraction. It will be observed that after the stimulus has been applied, as indi- cated by the vertical line s, there is an interval before the contraction commences, as indicated by the line r. This interval, termed (a) the latent period, when measured by the number of vibrations of the tun- ing-fork between the lines .s and r, is found to be about y^ sec. The latent period is longer in some muscles than in others, and differs also according to the condition of the muscie, being longer in fatigued mus- 28 434 HANDBOOK OF PHYSIOLOGY. cles, and the kind of stimulus employed. During the latent period there is no apjJcweiit change in the muscle. The second part is the {h) stage of contraction proper. The lever is raised by the sudden contraction of the muscle. The contraction is at first very rapid, but then progresses more slowly to its maximum, indi- cated by the line m x, drawn through its highest point. It occupies in the figure y|o sec. {<;) The next stage, stage of elongation. After reaching its highest point, the lever begins to descend, in consequence of the elongation of the muscle. At first the fall is rapid, but then be- <;omes more gradual until the lever reaches the abscissa or baseline, and the muscle attains its pre-con traction length, indicated in the figure by the line c'. The stage occujjies jf ^ second. Very often after the main xjoutraction the lever rises once or twice to a slight degree, producing Fig. 315.— Tracing of a double muscle-curve. To be read from left to right. While the muscle was engaged in the first contraction (whose complete course, had nothing intervened, is indicated by the dotted line), a second induction-shock was thrown in, at such a time that the second contraction began just as the fir.st was beginning to decline. The second curve is seen to start from the first, as does the first from the base line. (M. Foster.) curves, one of which is seen in fig. 315. These contractions, due to the elasticity of the muscle, are called most "in-operly {d) Stage of elastic after-vibration, or contraction remainder. The muscle curve obtained from the heart differs from that of other striped muscles in the longer duration of the effect of stimulation; the descending curve also is more prolonged. The greater part of the latent period is taken up by changes in the muscle itself, and the remainder occupied in the propagation of the shock along the nerve. Tetanus. — If we stimulate the nerve-muscle preparation with two induction shocks, one immediately after the other, when the point of stimulation of the second one corresponds to the maximum of the first, a second curve (fig. 315) will occur, which will commence at the highest point of the first and will rise nearly as high, so that the sum of the height of the two curves almost exactly equals twice the height of the first. If a third and a fourth shock be passed, a similar effect will en- THE METABOLISM OF THE TISSUES. •435 sue, and curves one above the other will be traced, the third being slightly lower than the second, and the fourth than the third. If a more numerous series of shocks occur, however, the lever after a time ceases to rise any further, and the contraction, which has reached its maxi- mum, is maintained. The condition which ensues is called Tetanus. Fig. 316.— Curve of tetanus, ootained from the gastrocnemius of a frog, where the shocks were sent in from an induction coil, about sixteen times a second, by the interruption of tlie primary current by means of a vibrating spring, which dipped into a cup of mercury, and broke the primary current at each vibration. A tetanus is really a summation of contractions, but unless the stimuli become very rapid indeed, the muscle will still be in a condition of vi- bratory contraction and not of unvarying contraction. If the shocks, however, be repeated at very short intervals, being 15 per second for the frog's muscle, but varying in each animal, the muscle contracts to its utmost suddenly and continues at its maximum contrac- tion for some time and the lever rises almost perpendicularly, and then describes a straight line (fig. 317). If the stimuli are not quite so rapid Fig. 317.— Curve of tetanus, from a series of very rapid shocks from a magnetic interrupter. the line of maximum contraction becomes somewhat wavy, indicating a slight tendency of the muscle to relax during the intervals between the stimuli (fig. 316). Muscular Work. — We have seen that icorh is estimated by multi- plying the weight raised, by the height through which it has been lifted. It has been found that in order to obtain the maximum of work a mus- cle must be moderately loaded: if the weight is increased beyond a cer- tain point, however, the muscle becomes strained and raises it through 436 HANDBOOK OF PHYSIOLOGY. SO small a distance tliat less work is accomplished. If the load is still further increased, the muscle is completely overtaxed and cannot raise the weight. No work is then done at all. Practical illustrations of these facts must be familiar to every one. The power of a muscle is usually measured by the maximum weight which it will support without stretching. In man this is readily determined by weight- ing the body to such an extent that it can no longer be raised on tiptoe : thus the power of the calf-muscles is determined. The power of a muscle thus esti- mated depends of course upon its cross-section. The power of a human muscle is from two to three times as great as a frog's muscle of the same sectional area. • Fatigue of Muscle, — A muscle becomes rapidly exhausted from re- peated stimulation, and the more rapidly, the more quickly the induc- tion-shocks succeed each other. This is indicated by the diminished height of the muscular contractions. A fatigued muscle has a much longer latent period than a fresh one. The slowness with which muscles respond to the will when fatigued must be familiar to every one. In a muscle which is exhausted, stimulation only causes a contraction producing a local bulging near the point irritated, A similar effect may be produced in a fresh muscle by a sharp blow, as in striking the biceps smartly with the edge of the hand, when a hard muscular swelling is instantly formed. Accompaniments of Muscular Contraction. (1.) Heat is developed in the contraction of muscles. Becquerel and Breschet found, with the thermo-multiplier about ,5° C. of heat produced by each forcible conti-aption of a man's biceps; and when the actions were long continued, the temperature of the muscle increased 1°. This estimate is probably high, as in the frog's muscle a considerable contraction has been found to produce an elevation of temperature equal on an average to less than ^° C. It is not known whether this develop- ment of heat is due to chemical changes ensuing in the muscle, or to the friction of its fibres vigorously acting : in either case, we may refer to it a part of the heat developed in active exercise. (2.) Sound is produced as mentioned above, when muscles contract forcibly. Wollaston showed that this sound might be easily heard by placing the tip of the little finger in the ear, and then making some muscles contract, as those oi the ball of the thumb, whose sound may be conducted to the ear through the substance of the hand and finger. A low shaking or rumbling sound is heard, the height and loudness of the note being in direct proportion to the force and quickness of the mus- cular action, and to the number of fibres that act together, or, as it were, in time. THE METABOLISM OF THE TISSUES. 437 (3.) Changes in Shape. — There is a considerable difference of opinion as to the mode in which the transversely striated muscular fibres con- tract. The most probable account is, that the contraction is effected by an approximation of the constituent parts of the fibrils, which, at the instant of contraction, without any alteration in their general direc- tion, become closer, flatter, and wider; a condition which is rendered evident by the approximation of the transverse strias seen on the surface of the fasciculus, and by its increased breadth and thickness. The appearance of the zigzag lines into which it was supposed the fibres are thrown in contraction, is due to the relaxation of a fibre which has been recently contracted, and is not at once stretched again by some antago- nist fibre, or whose extremities are kept close together by the contractions of other fibres. The contraction is therefore a simple and, according to Ed. "Weber, a uniform, simultaneous, and steady shortening of each fibre and its contents. What each fibril or fibre loses in length, it gains in thickness : the contraction is a change of form not of size ; it is, there- fore, not attended with any diminution in bulk, from condensation of the tissue. This has been proved for entire muscles, by making a mass of muscles, or many fibres together, contract in a vessel full of water, with which a fine, perpendicular, graduated tube communicates. Any diminution of the bulk of the contracting muscle would be attended by a fall of fluid in the tube; but when the experiment is carefully per- formed, the level of the water in the tube remains the same, whether the muscle be contracted or not. In thus shortening, muscles appear to swell vp, becoming rounder, more prominent, harder, and apparently tougher. But this hardness of muscle ■I EL Fig. 318. — The microscopic appearances during a muscular contraction in the individual fibrillar, after Engehnaun. 1. A passive muscle-fibre; c to d = doubly refractive discs, with median disc a b in it: h and g are lateral discs: f and e are secondary discs, only slightly doubly refractive; fig. on right same fibre in polarized light: bright part is doubly refracted, black ends not so. 2. Transition stage; and ;^. Stage of entire contraction: in each case the right-hand figure represents the effect of polarized light. cLandois after Engelmaun.) in the state of contraction is not due to increased firmness or condensa- tion of the muscular tissue, but to the increased tension to which the fibres, as well as their tendons and other tissues, are subjected from the resistance ordinarily opposed to their contraction. When no resistance is offered, as when a muscle is cut off from its tendon, not only is no hardness perceived during contraction, but the muscular tissue is even 438 HANDBOOK OF PHYSIOLOGY. softer, more extensile, and less elastic than in its ordinary uncontracted state. During contraction in each fibre it is said that the anisotropous or doubly refractive elements become less refractive and the singly re- fractive more so (fig. 318). (4.) Chemical Changes. — (a) The reaction of the muscle which is normally alkaline or neutral becomes decidedly acid, from the develop- ment of sarcolactic acid, {h) The muscle gives out carbonic acid gas and takes up oxygen, the amount of the CO^ given out not appearing to be entirely dependent upon the 0 taken in, and so doubtless in part arising from some other source. (c) Certain imperfectly understood chemical changes occur, in all probability connected with {a) and {b). Glycogen is diminished, and glucose, or muscle sugar (inosite) appears; the extractives are increased. (5.) Electrical Changes. — AVhen a muscle contracts the natural muscle current or currents of rest undergo a distinct diminution, which is due to the appearance in the actively contracting muscle of currents in an opposite direction to those existing in the muscle at rest. This causes a temporary deflection of the needle of a galvanometer in a direction opposite to the original current, and is called by some the negative vari- ation of the muscle current, and by others a current of action. Conditions of Contraction. — {a) The irritability of muscle, as indicated by length of latent period, velocity and extent of contraction, is greatest at a certain mean tern i:)eratu re; {b) after a number of con- tractions a muscle gradually becomes exhausted; (r) the activity of muscles after a time disappears altogether when they are removed from the body or the arteries are tied ; [d) oxygen is used up in muscular contraction, but a muscle Aviil act for a time in vacuo or in a gas which contains no oxygen; in this case it is of course using up the oxygen already in store; {e) the contraction is greater if the stimulus is applied to the nerve, than if it be applied to the muscle directly. Response to Stimuli. — The two kinds of fibres, the striped and the unstriped, have characteristic differences in the mode in which they act on the application of the same stimulus; differences which may be ascribed in great part to their respective differences of structure., but in some degree, possibly, to their respective modes of connection with the nervous system. When irritation is applied directly to a muscle with striated fibres, or to the motor nerve supplying it, contraction of the part irritated, and of that only, ensues; and this contraction is instan- taneous, and ceases on the instant of withdrawing the irritation. But when any part with unstriped muscular fibres, e.g., the intestines or bladder, is irritated, the subsequent contraction ensues more slowly, extends beyond the part irritated, and, witli alternating relaxation, con- tinues for some time after the withdrawal of the irritation. The differ- THE METABOLISM OF THE TISSUES. 439 ence in the modes of coutractiou of the two kinds of muscular fibres may be particularly illustrated by the effects of the repeated stimuli with the magnetic interrupter. The rapidly succeeding shocks given by this means to the nerves of muscles excite in all the transversely stri- ated muscles, except in the case of the heart, a fixed state of tetanic contraction as previously described, which lasts as long as the stimulus Fig:. 319. — Muscle-curves from the gastrocnemius of a frog, illustrating effects of alterations in temperature. is continued, and on its withdrawal instantly ceases; but in the muscles with unstriped fibres they excite a slow vermicular movement, which is comparatively slight and alternates with rest. It continues for a time after the stimulus is withdrawn. In their mode of responding to these stimuli, all the skeletal mviscles, or those with transverse stria?,- are alike ; but among those with unstriped fibres there are many differences — a fact which tends to confirm the opinion that their pecviliarity depends as well on their connection with nerves and ganglia as on their own properties. The ureters and gall-bladder are the parts least excited by stimuli ; they do not act at all till the stimulus has been long applied, and then contract feebly, and to a small extent. The contractions of the caecum and stomach are quicker and wider spread : still quicker those of the iris, and of the urinary bladder if it be not too full. The actions of the small and large intestines, of the vas deferens, and pregnant uterus, are j^et more vivid, more regular, and more sustained ; and they require no more .stimulus than thijt of the air to excite them. The heart, on account, doubtless, of its striated muscle, is the quickest and most vigorous of all the muscles of organic life in contracting upon irritation, and appears in this, as in nearly all other respects, to be the con- necting member of the two classes of muscles. All the muscles retain their property of contracting under the influence of stimuli applied to thena or to their nerves for some time after death, the period being longer in cold-blooded than in warm-blooded Vertebrata, and shorter in Bii'ds than in Mammalia. It would seem as if the more active the respiratory process in the living animal, the shorter is the time of dviration of the irrita- bility in the muscles aft^-r death ; and this is confirmed by the comparison of different species in the same order of Vertebrata. But the i:)eriod during which this irritability lasts is not the same in all persons, nor in all the muscles of the same person. In a man it ceases, according to Nysten, in the following order: — first in the left ventricle, then in the intestines and stomach, the urinary bladder, right ventricle, oesophagus, iris ; then in the voluntary mus- cles of the trunk, lower and upper extremities ; lastly, in the right and left auricle of the heart. 440 HANDBOOK OF PHYSIOLOGY. Muscle in Rigor Mortis. After the muscles of the dead body have lost their irritability or capa- bility of being excited to contraction by the application of a stimulus, they spontaneously pass into a state of contraction, apparently identical with that which ensues during life. It affects all the muscles of the body; and, when external circumstances do not prevent it, commonly fixes the limbs in that which is their natural posture of equilibrium or rest. Hence, and from the simultaneous contraction of all the muscles of the trunk, is produced a general stiffening of the body, constituting the rigor mortis or post- mortem rigidity. When this condition has set in, the muscle [a) 'becomes acid in reaction (due to development of sarcolactic acid), (Z*) gives off carhonic acid in great excess, (c) diminishes in volume slightly, (d) becomes shortened and opaque, its substance setting firm. Eigor comes on much more rapidly after muscular activity, and is hastened by Avarmth. It may be brought on, in muscles exposed for experiment, by the action of distilled water and many acids, also by freezing and thawing. Cause. — The immediate cause of rigor seems to be a chemical one, namely, the coagulation of the muscle plasma. We may distinguish three main stages — (1.) Gradual coagulation. (2.) Contraction of coag- ulated muscle-clot (myosin), and squeezing out of muscle-serum. (3.) Putrefaction. After the first stage, restoration is possible through the circulation of arterial blood through the muscles, and even when the second stage has set in, vitality may be restored by dissolving the coag- ulum of the muscle in salt solution, and j^assing arterial blood through the vessels. In the third stage recovery is impossible. It has been noticed that the relaxation in muscles after rigor some- times occurs too quickly to be caused by putrefaction, and the suggestion that in such cases at any rate such relaxation is due to a ferment-action is very plausible. It is known that pepsin is present in muscles, and that this ferment will act in an acid medium. The conditions for the solution of the coagulated myosin are therefore present as the reaction of rigored muscle is acid. Order of Occurrence. — The muscles are not affected simu*ltaneously oy rigor mortis.. It affects the neck and lower jaw first; next, the upper extremities, extending from above downward; and lastly, reaches the lower limbs; in some rare instances only, it affects the lower extremities before, or simultaneously Mdth, the upper extremities. It usually ceases in the order in which it begins: first at the head, then in the upper extremities, and lastly in the lower extremities. It never commences earlier than ten minutes, and never later than seven hours after death; and its duration is greater in proportion to the lateness of its accession. THE METABOLISM OF THE TISSUES, 441 Heat is developed during the passage of a muscular fibre into the condi- tion of rigor mortis. Since rigidity does not ensue until muscles have lost the capacity of being excited by external stimuli, it follows that all circumstances which cause a speedy exhaustion of muscular irritability, induce an early oc- currence of the rigidity, while conditions by which the disappearance of the irritability is delayed, are succeeded by a tardy onset of this rigidity. Hence its speedy occurrence, and equally speedy departure in the bodies of persons exhausted by chronic diseases; and its tardy onset and long continuance after sudden death from acute diseases. In some cases of sudden death from lightning, violent injuries, or paroxysms of passion, rigor mortis has been said not to occur at all; but this is not always the case. It may, indeed, be doubted whether there is really a comj^lete absence of the post-mortem rigidity in any such cases; for the experi- ments of Brown-Sequard make it probable that the rigidity may supervene immediately after death, and then pass away with such rapidity as to be scarcely observable. The occurrence of rigor mortis is not prevented by the previous exist- ence of paralysis in a part, provided the j^aralysis has not been attended with very imperfect nutrition of the muscular tissue. The rigidity affects the involuntary as well as the voluntary muscles, whether they be constructed of striped or unstriped fibres. The rigidity of involuntary muscles with striped fibres is shown in the contraction of the heart after death. The contraction of the muscles with unstriped ^res is shown by an experiment of Valentin, who found that if a grad- uated tube connected with a portion of intestine taken from a recently- killed animal, be filled with water, and tied at the opposite end, the water will in a few hours rise to a considerable height in the tube, owing to the contraction of the intestinal walls. It is still better shown in the arteries, of which all that have muscular coats contract after death, and thus present the roundness and cord-like feel of the arteries of a limb lately removed, or those of a body recently dead. Subsequently they relax, as do all the other muscles, and feel lax and flabby, and lie as if flattened, and with their walls nearly in contact. Action of the Voluntary Muscles. The greater part of the voluntary muscles of the body act as sources of power for moving levers, — the latter consisting of the various bones to which the muscles are attached. Examples of the three orders of levers in the Human Body. — All levers have been divided into three kinds, according to the relative position of the power, the tceight to be removed, and the axis of motion or fulcrum. In a lever of the first kind the potver vi at oneexti-emity of the lever, the iceight at the other. 442 HANDBOOK OF PHYSIOLOGY, and the fulcrum between the two. If the initial letters only of the power, weight, and fulcrum be used, the arrangement will stand thus :— P. F. W. A poker as ordinarily used, or the bar in fig. 320, may be cited as an example of this variety of lever ; while, as an instance in which the bones of the human 9 -au Fig. 320. skeleton are used as a lever of the same kind, may be mentioned the act of raising the body from the stooping posture by means of the hamstring muscles attached to the tuberosity of the ischium (fig. 320) . In a lever of the second kind, the arrangement is thus : — P. W. F. ; and this leverage is employed in the act of raising the handles of a wheelbarrow, or in stretching an elastic band, as in fig. 321. In the human body the act of open- ing the mouth by depressing the lower jaw is an example of the same kind — ClasticHBano Fig. 321. the tension of the muscles which close the jaw representing the weight (fig. 321). In a lever of the third kind the arrangement is — F. P. "W. , and the act of raising a pole, as in fig. 322, is an example. In the human body there are numerous examples of the employment of this kind of leverage. The act of bending the fore-arm may be mentioned as an instance (fig. 322). The act of biting is another example. At the ankle we have examples of all three kinds of lever. 1st kind — Ex- tending the foot. 3d kind — Flexing the foot. In both these cases the foot represents the weight : the ankle joint the fulcrum, the power being the calf muscles in the first case and the tibialis anticus in the second case. 2d kind — THE METABOLISM OF THE TISSUES. 443 When the body is raised on tiptoe. Here the ground is the fulcrum, the weight of the body acting at the ankle joint the weight, and the calf muscles the power. In the human body, levers are most frequently used at a disadvantage as regards power, the latter being sacrificed for the sake of a greater range of motion. Thus in the diagrams of the first and third kinds it is evident that the power is so close to the fulcrum, that great force must be exercised in order to produce motion. It is also evident, however, from the same diagrams, that Fig. .322. by the closeness of the power to tlie fulcrum a great range of movement can be obtained by means of a comparatively slight shortening of the muscular fibres. The greater number of the more important muscular actions of the human body — those, namely, which are arranged harmoniously so as to subserve some definite purpose or other in the animal economy — are de- scribed in various parts of this work, in the sections which treat of the physiology of the processes by which these muscular actions are resisted or carried out. There are, however, one or two very important and somewhat complicated muscular acts which may be best described in this place. Walking. — In the act of walking, almost every voluntary muscle in the body is brought into play, either directly for purposes of progression, or indirectly for the proper balancing of the head and trunk. The muscles of the arms are least concerned ; but even these are for the most part instinctively in action to some extent. Among the chief muscles engaged directly in the act of walking are those of the calf, which, by pulling up the heel, pull up also the astragalus, and with it, of course, the whole body, the weight of which is transmitted through the tibia to this bone (fig. 328) . When starting to walk, say with the left leg, this raising of the body is not left entirely to the muscles of the left calf, but the trunk is thrown forward in such a way, that it would fall prostrate were it not that the right foot is brought forward and planted on the ground to sup- port it. Thus the muscles of the left calf are assisted in their action by those muscles on the front of the trunk and legs which, by their contraction, pull the body forward ; and, of course, if the trunk form a slanting line, with the in- clination forward, it is plain that when the heel is raised by the calf-muscles. 444 HAXDBOOK OF PHYSIOLOGY, the whole body will be raised, and pushed obliquely forward and upward. The successive acts in taking the first step in walking are represented in fig. 323, 1, 2, 3. Now it is evident that by the time the body has assumed the position No. 3, it is time that the right leg should be brought forward to support it and pre- vent it from falling prostrate. This advance of the other leg (in this case the right) is effected partly by its mechanically swinging forward, pendulum- wise, and partly by muscular action ; the muscles used being — 1st, those on the front of the thigh, which bend the thigh forward on the pelvis, especially the rectus femoris, with the psoas and the iliacus ; 2dly, the hamstring muscles, which slightly bend the leg on the thigh ; and, Sdly, the muscles on the front of the leg, which raise the front of the foot and toes, and so prevent the latter in swinging forward from hitching in the ground. The second part of the act of walking, which has been just described, is shown in the diagram (4, fig. 323) . When the right foot has reached the ground the action of the left leg has not ceased. The calf-muscles of the latter continue to act, and by pulling up the heel, throw the body still more forward over the right leg, now bearing nearly the whole weight, until it is time that in its turn the left leg should swing forward, and the left foot be planted on the ground to prevent the body from falling prostrate. As at first, while the calf-muscles of one leg and foot are preparing, so to tpeak, to pws/i the body forward and upward from behind by raising the heel, the muscles on the front of the trunk and the same leg (and of the other leg, except when it is swinging forward) are helping the Fig. 323. act by pulling the legs and trunk, so as to make them incline forward, the rotation in the inclining forward being effected mainly at the ankle joint. Two main kinds of leverage are, therefore, employed in the act of walking, and if this idea be firmly grasped, the details muII be understood with com- parative ease. One kind of leverage employed in walking is essentially the same with that employed in pulling forward the pole, as in fig. 322. And the other, less exactly, is that employed in raising the handles of a wheelbarrow. Now, supposing the lower end of the pole to be placed in the barrow, we should have a very rough and inelegant, but not altogether bad representation of the two main levers employed in the act of walking. The body is pttZ/ed forward by the muscles in front, much in the same way that the pole might be by the force applied at P., while the raising of the heel and 2iushing forward of the trunk by the calf- muscles is roughly represented on raising the handles of the barrow. The manner in which these actions are performed alternately by each leg, so that one after the other is swung forward to support the trunk, which is at the same time pushed and p>uUed forward by the muscles of the other, may be gathered from the the previous description. THE METABOLISM OF THE TISSUES, ■445 There is one more tiling to be especially noticed in the act of walking. In- asmuch as the body is being constantly supported and balanced on each leg alternately, and therefore on onl}- one at the same moment, it is evident that there must be some provision made for throwing the centre of gravity over the line of support formed by the bones of each leg, as, in its turn, it supports the weight of the body. This may be done in various wajs, and the manner in which it is effected is one element in the differences which exist in the walk- ing of different people. Thus it may be done by an instinctive slight rotation of the pelvis on the head of each femur in turn, in such a manner that the centre of gi'avity of the body shall fall over the foot of this side. Thus when the body is pushed onward and upward by the raising, say, of the right heel, as in fig. 323, 3, the pelvis is instinctively by various muscles made to rotate on the head of the left femur at the acetabulum, to the left side, so that .the weight may fall over the line of support formed by the left leg at the time that the Fig. 3*4. iHght leg is swinging forward, and leaving all the work of support to fall on its fellow. Such a " rocking" movement of the trunk and pelvis, however, is accompanied by a movement of the whole trunk and leg over the foot which is being planted on the ground (fig. 324) : the action being accompanied with a compensatory outward movement at the hip, more easily appreciated by looking at the figure (in which this movement is shown exaggerated) than described. Thus the body in walking is continually rising and swaying alternately from one side to the other, as its centre of gravity has to be brought alternately over one or other leg ; and the curvatures of tlie spine are altered in corre- spondence with the varying position of the weight which it has to support. The extent to which the body is raised or swayed differs much in different people. In walking, one foot or the other is always on the ground. Tlie act of leaping or jumping, consists in so sudden a raising of the heels by the sharp and strong contraction of the calf-muscles, that the body is jerked off the groimd. At the same time the effect is much increased by first bending the thighs on the pel- 446 HANDBOOK OF PHYSIOLOGY. vis, and the legs on the thighs, and then suddenly straightening out the angles thus formed. The share which this action has in producing the effect may be easily known by attempting to leap in the upright posture, with the legs quite straight. Running is performed by a series of rapid low jumps with each leg alter- nately ; so that, during each complete muscular act concerned, there is a moment when both feet are off the ground. In all these cases, however, the description of the manner in which any given effect is produced, can give but a very imperfect idea of the infinite number of combined and harmoniously arranged muscular contractions which are necessary for even the simplest acts of locomotion. Action of the Involuntary Muscles. — The involuntary muscles are for the most part not attached to bones arranged to act as levers, but enter into the formation of such hollow parts as require a diminution of their calibre by muscular action, under particular circumstances. Ex- amples of this action are to be found in the intestines, urinary bladder, heart and blood-vessels, gall-bladder, gland-ducts, etc. The difference in the manner of contraction of the striated and non- striated fibres has been already referred to (p. 438) ; and the peculiar vermicular or peristaltic action of the latter fibres has also been described. Electkical Cureents IX Nerves. The electrical condition of nerves is so closely connected with the phenomena of muscular contraction, that it will be convenient to con- sider it in the present chapter. If a piece of nerve be removed from the body and subjected to exami- nation in a way similar to that adopted in the case of muscle, which has been described, electrical currents are found to exist which correspond exactly to the natural muscle currents, and which are called natural nei've currents or currents of rest, according as one or other theory of their existence be adopted, as in the case with muscle. One point (equator) on the surface being positive to all other points nearer to the cut ends, and the greatest deflection of the needle of the galvanometer taking place when one electrode is aj)plied to the equator and the other to the centre of either cut end. As in the case of muscle, these nerve currents undergo a negative variation when the nerve is stimulated, the variation being momentary and in the opposite direction to the natural currents; and are similarly known as the currents of action. The cur- rents of action are propagated in both directions from the point of the application of the stimulus, and are of momentary duration. Rheoscopic Frog. — This negative variation may be demonstrated by means of the following experiment.— The new current produced by stimulating the nerve of one nerve-muscle preparation may be used to stimulate the neiwe of a second nerve-muscle preparation. The foreleg of a frog with the nerve going to the THE METABOLISM OF THE TISSUES. 447 gastrocnemius cut long is placed upon a glass plate, and arranged in such way that its nerve touches in two places the sciatic nerve, exposed but preserved in situ in the opposite thigh of the frog. The electrodes from an induction coil are placed behind the sciatic nerve of the second preparation, high up. On stimulating it with a single induction shock, the muscles not only of the same leg are found to undergo a twitch, but also those of the first preparation, although this is not near the electrodes, and so the stimulation cannot be due to an escape of the current into the first nerve. This experiment is known under the name of the rheoscopic frog. Nerve-stimuli. — Xerve-fibres require to be stimulated befor ethey can manifest any of their properties, since they have no power of themselves of generating force or of originating impulses. The stimuli which are capable of exciting nerves to action are, as in the case of muscle, very diverse. They are very similar in each case. The mechanical, chem- ical, thermal, and electric stimuli which may be used in the one case are also, with certain differences in the methods employed, efficacious in the other. The chemical stimuli are chiefly these: withdrawal of water, as by drying, strong solutions of neutral salts of potassium, sodium, etc., free inorganic acids, except phosphoric; some organic acids; ether, chloroform, and bile salts. The electrical stimuli employed are the induction and continuous currents concerning which the observations in reference to muscular contraction should be consulted, \yeaker efec- trical stimuli will excite nerve than will excite muscle; the nerve stimuli appears to gain strength as it descends, and a weaker stimulus applied far from the muscle will have the same effect as a stronger one applied to the nerve near the muscle. It will be ouly necessary here to add some account of the effect of a constant- curvent^ such as that obtained from a Daniell's battery, upon a nerve. This effect may be studied with the apparatus described before. A pair of electrodes is placed behind the nerve of the nerve-muscle prep- aration, with a Du Bois Reymond's key arranged for short circuiting the battery current, in such a way that when the key is opened the cur- rent is sent into the nerve, and when closed the current is cut off. It will be found that with a current of moderate strength there will be a contraction of the muscle both at the opening and at the closing of the key (called respectively making and breaking contractions), but that during the interval between these two events the muscle remains flaccid, provided the battery current continues of constant intensity. If the current be a very weak or a very strong one the effect is not quite the same; one or other of the contractions may be absent. Which of these contractions is absent depends upon another circumstance, viz., the direction of the current. The direction of the current may be ascending or descending: if ascending, the anode or positive pole is nearer the muscle than the cathode or negative pole, and the current to return to 448 HANDBOOK OF PHYSIOLOGY. the battery has to pass up the nerve; if descending, the position of tht electrodes is reversed. It will be necessary before considering this ques- tion further to return to the apparent want of effect of the constant current during the interval between the make and break contraction : to all appearances no change is produced, but in reality a very important alteration of the irritability is brought about in the nerve by the passage of this constant (polarizing) current. This may be shown in two ways, first of all by the galvanometer. If a piece of nerve be taken, and if at either end an arrangement be made to test the electrical condition of the nerve by means of a pair of non-polarizable electrodes connected with a galvanometer, while to the central portion a pair of electrodes con- nected with a Dauiell's battery be applied, it will be found that the natural nerve-currents are profoundly altered on the passage of the con- stant current in the neighborhood. If the polarizing current be in the same direction as the latter the natural current is increased, but if in the direction opposite to it, the natural cuiTcnt is diminished. This change, produced by the continual passage of the battery-current through a portion of the nerve, is to be distinguished from the negative varia- tion of the natural current to which allusion has been already made, and which is a momentary change occurring on the sudden application of the stimulus. The condition produced by the passage of a constant current is known by the name of Electrotonus. A second way of showing the effect of the polarizing current is by taking a nerve-muscle preparation and applying to the nerve a pair of electrodes from an induction coil, while at a point further removed from the muscle, electrodes from a Daniell's battery are arranged with a key for short circuiting and an apparatus (reverser) by which the battery current may be reversed in direction. If the exact point be ascertained to which the secondary coil should be moved from the primary coil in order that a minimum contraction be obtained by the induction shock, and the secondary coil be removed slightly further from the primary, the induction current cannot now produce a contraction; but if the polarizing current be sent in a descending direction, that is to say, with the cathode nearest the other electrodes, the induction current, which was before insufficient, will prove sufficient to cause a contraction; whereby indicating that with a descending current the irritability of the nerve is increased. By means of a somewhat similar experiment it may be shown that an ascending current will diminish the irritability of a nerve. Similarly, if instead of applying the induction electrodes below the other electrodes they are applied between them, like effects are demonstrated, indicating that in the neighborhood of the cathode the irritability of the nerve is increased by the passage of a constant current, and in the neighborhood of the anode diminished. This in- THE METABOLISM OF THE TISSUES, 449 crease in irritability is called catelectrotonus, and similarly the decrease is called anelectrotonus. As there is between the electrodes both an increase and a decrease of irritability on the passage of a po- larizing current, it must be evident that the increase must shade off into the decrease, and that there must be a neutral point where there is neither increase nor decrease of irritability. The position of this neutral point is found to yary with the intensity of the polarizing cur- rent— when the current is weak the point is nearer the anode, when -<-sr« J: Fig. 325. — Diagram iUustrating the effects of various intensities of the polarizing currents. n, n', nerve; a, auode: A-, cathode; the curves above indicate increase, and those below decrease of irritability, and when the current is small the increase and decrease are both small, with the neutral point near a, and so on as the current is increased in strength. strong nearer the cathode (fig. 325) ; when a constant current passes into a nerve, therefore, if a contraction result, it may be assumed that it is due to the increased irritability produced in the neighborhood of the cathode, but the breaking, contraction must be produced by a rise in irritability from a lowered state to the normal in the neighborhood of the anode. The contractions produced in the muscle of a nerve- muscle preparation by a constant current have been arranged in a table which is known as Pfliiger's Law of Contractions. It is really only a statement as to when a contraction may be expected : — Strength of Current used. Descending Current. Ascending Current. Make. Break. Make. Break. Very Weak Weak Moderate Yes. Yes. Yes. Yes. No. No. Yes. No. No. Yes. Yes. No. No. No. Yes Strong Yes The difficulty in this table is chiefly in the effect of a weak ascending current, but the following statement may remove it. The increase of irritability at tlie cathode when the current is made is more potent to produce a contraction than the rise of irritability at the anode when the current is broken ; and so with weak currents the only effect is a con- traction at the make of both currents. The descending current is more 450 HANDBOOK OF PHYSIOLOGY. potent than the ascending (and with still weaker currents is the only one which produces any effect), since the cathode is near the muscle. In the case of the ascending current the stimulus has to pass through a district of diminished irritability, which with a very strong current acts as a block, being of considerable amount and extent, but with a weak current being less considerable both in intensity and extent, only slightly affects the contraction. As the current is stronger however, recovery from anelectrotonus, is able to produce a contraction as well as catelectrotonus ; a contraction occurs both at the make and the break of the current. The absence of contraction with a very strong ■current at the break of the ascending current maybe explained by sup- posing that the region of fall in irritability at the cathode blocks the istimulus of the rise in irritability at the anode. Thus we have seen that two circumstances influence the effect of the ■constant current upon a nerve, viz., the strength and direction of the current. It is also necessary that the stimulus should be applied swf7- denly and not gradually, and that the irritability of the nerve sliould he normal; not increased or diminished. Sometimes (when the prepara- tion is sj^ecially irritable?) instead of a. simple contraction a tetanus occurs at the make or break of the constant current. This is especially liable to occur at the break of a strong ascending current which has been passing for some time into the preparation; this is called Ritter'r tetanus, and may be increased by passing a current in an opposite di- rection or stopped by passing a current, in the same direction. Muscular and Nervous Metabolism. The question of the metabolism of muscle both in a resting and in an active condition has for many years occupied the attention of physiolo- gists. It cannot be said even now to be thoroughly understood. Most ■of the facts with reference to the subject have been already mentioned. We may shortly recapitulate them here: — First, muscle during rest ab- sorbs oxygen and gives out carbon dioxide. This has been shown by an analysis of the gases of the blood going to and leaving muscles. During activity, e. g., during tetanus, the same interchange of gases takes place. but the quantities of the oxygen absorbed and of the carbon dioxide given up are increased, and the 23roj)ortion between them is altered thus : — Venous Blood. O, less than Arterial Blood. CO2, more than Arterial Blood. Of resting muscle 9 per cent. 6.71 per cent. Of active muscle 12.26 per cent. 10.79 per cent. THE METABOLISM OF THE TISSUES. 451 There is then a greater proportion of carbon dioxide produced in muscle during activity than during rest. During rigor mortis there is also an increased production of carbon dioxide. Second, muscle during rest produces nitrogenous crystallizable sub- stances, such as kreatin, from the metabolism which is constantly going on in it during life ; in addition there is in all probability sarcolactic acid formed and other non-nitrogenous matters. During activity the nitrogenous substances, such as kreatin, undergo very slight, if any, increase — about the amount produced during rest — • but the sarcolactic acid is distinctly increased; sugar (whether glucose or maltose is uncertain) is also increased, whereas the glycogen is dimin- ished. During rigor mortis the sarcolactic acid is also increased, and in ad- dition myosin is formed. From these data it is assumed that the processes which take place in resting and active muscle are somewhat different, at any rate in degree. From actively contracting muscle, also, there are obtained an increased amount of heat and mechanical work, more potential is converted into kinetic energy. Many theories have been proposed to explain the facts of muscular energy. It has been suggested by Herman that muscular activity de- pends upon the splitting up and subsequent re-formation of a complex nitrogenous body, called by him Inogen. When this body so splits up there result from its decomposition, carbon dioxide, sarcolactic acid, and a gelatin o-albuminous body. Of these the carbon dioxide is carried away by the blood stream ; the albuminous substance and possibly the acid, at any rate in part, go to re-form the inogen. The other materials of which the inogen is formed are supplied by the blood ; of these mate- rials we know that some carbohydrate substance and oxygen form a part. The decomposition, although taking place in resting muscle, reaches a climax in active muscle, but in that condition the destruction of inogen largely exceeds restoration, and so there must be a limit to muscular activity. But this is not the only change going on in muscle, there are others which afiect the nitrogenous elements of the tissue, and from them result the nitrogenous bodies of which kreatin is the chief; these changes may be unusually large during severe exercise. It has been further suggested that, as myosin is undoubtedly formed in rigor mortis, when the muscle becomes acid and gives off carbon dioxide, that myosin is also formed when muscle contracts, and that, in other words, contraction is a condition akin to partial death. The electrical reaction appears to justify this; both contracted and dead muscle are negative to living muscle, when at rest. What happens to 452 HANDBOOK OF PIIYSIOLOGy, the myosin which is formed when muscle contracts, if this view be the correct one, is unknown. Halliburton suggests that the myosin which can be made to clot and unclot easily enough outside the body, is able to do the same thing in the body. It is possible that the clotting of myosinogen which is supposed to occur during contraction, is not of the same intensity or extent as that which occurs post mortem. The rela- tion of the hypothetical inogen to the rest of the muscle-fibre is unde- termined. It may be that tlie inogen is formed by the activity of the muscle-protoplasm, and stored up within itself, and that duriug rest of muscle it is gradually used up, whereas in activity it is suddenly and explosively decomposed. In the rest of the fibre the nitrogenous meta- bolism continues much the same during rest as during activity. Again, histologically, the question as to which is the contractile and which is the non-contractile part of muscle, has been, as we have seen (p. 84 et seq.), a matter of much controversy. As regards nervous metabolism, we have little knowledge of anything except the electrical phenomena which have been already considered. For the maintenance of nervous irritability, oxygen is required ; to form this, it has been suggested that the nervous impulse is the result of processes of an oxidative character, etc. The chief seat of the metabo- lism is no doubt the axis-cylinder. The question whether a nervous impulse is possibly an electrical change, as has been asserted by some, cannot be at present settled, but if it be so, at any rate it differs essenti- ally from an ordinary current, if in no other respect, at any rate in the rate of transmission, CHAPTEE XII. METABOLISM OF THE TISSUES. Glandular Metabolism, It is the function of gland cells to produce by the metabolism of their protoplasm certain substances called secretions. These materials are of two kinds; viz., those which are employed for the purpose of serving some ulterior office in the economy, and those which are discharged from the body as useless or injurious. In the former case, the separated materials are termed true secretions; in the latter they are termed excre- tions. The secretions as a rule consist of substances which do not pre-exist in the same form in the blood, but require special cells and a process of elaboration for their formation, e.g., the liver cells for the forma- tion of bile, the mammary glaud-cells for the formation of milk. The excretions, on the other hand, conmiouly 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 excre- tory organ, the separation of an excretion is prevented, and an accumu- lation 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 Avith those that are most elabo- rated ; for after the removal of the sj^ecial organ by which each of them is manufactured, the secretion 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-absorbed into the blood, and afterward discharged from it by exudation in other ways; but these are not instances of true vicarious secretions, and must not be so regarded. The circumstances of their formation, and their final destination, are, however, the only particulars in which secretions and excretions can be distinguished; for, in general, the structure of the jmrts engaged in eliminating excretions is as complex as that of the parts concerned in the formation of secretions. And since the diiierences of the two processes of separation, corresponding with those in the several purposes and des- tinations of the fluids, are not 3'et ascertained, it will be sufficient to speak in general terms of the process. 454 HANDBOOK OF PHYSIOLOGY. Every secreting apparatus possesses, a sessential parts of its structure, a simple and almost textureless membrane, named the primary or iase- ment-membrane; certain cells; and hlood-vessels. These three structural elements are arranged together in various ways; but all the varieties may be classed under one or other of two principal divisions, namely, mem- branes and glands. Organs and Tissues of Secretion. The principal secreting organs are the following: — (1) the serous and synovial membranes; (2) the mucous membranes with their special glands, e.g., the buccal, gastric, and intestinal glands; (3) the salivary glands and pancreas; (4) the mammary glands; (5) the liver; (6) the lachrymal gland; (7) the kidney and skin; and (8) the testes. The structure and functions of the glands secreting materials used in digestion we have already considered, and they need not detain us here. The functions of the kidney and skin have also been dealt with. The lachrymal gland will be considered with the rest of the optic apparatus and the testes in the Chapter on Generation. There remain, then, the serous and mucous membranes and the mammary gland to be here described, and also that part of the secreting function of the liver which is concerned with the formation of glycogen and of urea. (1.) Serous and Synovial Membranes. — Serous membranes are of two principal kinds: 1st. Those which line visceral cavities, — the arach- noid, pericardium, pleurcB, peritoneum, and timicce vaginales. 2d. The synovial memhranes lining the joints, and the sheaths of tendons and ligaments, with which, also, are usually included the synovial bursce, or burscB mucosa', whether these be subcutaneous, or situated beneath tendons and 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 viscsra invested by a serous membrane are, as it were, j^ressed 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 Fal- lopian tubes into the abdominal cavity, — an arrangement which exists in man and all Vertebrata, with the exception of a few fishes. The serous membranes are especially distinguished by the characters of the endothelium covering their free surface: it always consists of a single layer of polygonal cells. The ground substance of most serous membranes consists of connective-tissue corpuscles of various forms lying in the branching spaces which constitute the lymph canalicular system, and interwoven with bundles of white fibrous tissue, and nu- METABOLISM OF THE TISSUES. 455 meroiis delicate elastic fibrill*, together with blood-vessels, nerves, and lymphatics. In relation to the process of secretion, the layer of connec- tive tissue serves as a groundwork for the ramification of blood-vessels, nerves, and lymphatics. But in its usual form it is absent in some in- stances, as in the arachnoid covering the dura mater, and in the interior of the ventricles of the brain. The primary membrane and epithelium Fig. 326.— Section of synovial membrane, a. Endothelial covering of the elevations of the membrane; 6, subserous tissue containing fat and blood-vessels; c, ligament covered by the sy- novial membrane. (Cadiat.) are alwa\s present, and are concerned in the formation of the fluid by which the free surface of the membrane is moistened. Fimctions. — 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 al- most constant motion upon one another and the walls of the abdomen. Fluid. — The fluid secreted from the free surface of the serous mem- branes is, in health, rarely more than sufficient to ensure the mainte- nance 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 serous sac consti- tutes dropsy of the sac. 456 HANDBOOK OF PHYSIOLOGY, The fluid naturally secreted by the serous membranes appears to be identical, in general and chemical characters, with very dilute liquor sanguinis. It is of a pale yellow or straw-color, slightly viscid, alkaline, and on account of the presence of albumen, 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 moistened, 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 diifer from the fluids 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 bile when present in the blood, and are not colored by madder, or other similar substances introduced abundantly into the blood. It is also probable that the formation of synovial fluid \& a process of more genuine and elaborate secretion, by means of the epithelial cells on the surface of the membrane, and especially of those which are accumu- lated on the edge and processes of the synovial fringes; for, in its pecu- liar density, viscidity, and abundance of albumen, synovia differs alike from the serum of blood and from the fluid of any of the serous cavities. (2.) Mucous Membranes. — The mucous memhranes line all those passages by v/hich internal parts communicate with the exterior, and by which either matters are eliminated from the body or foreign sub- stances taken into it. They are soft and velvety, and extremely vascu- lar. 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 perios- teum ; 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 &nd 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 ffall-bladder. METABOLISM OF THE TISSUES. 457 2. The Eespiratory 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 Eustachian tubes and lines the tym- panum and the inner surface of the membrana 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 {},- mm.) in diameter, and continuous with it is a layer of delicate epithelial membrane which extends into the pulmonary cells. 3. The Genito-urinary tract, which lines the whole of the urinary pas- sages, 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 glands connected with them : and in the female becomes continuous Avith the serous membrane of the abdomen at the fimbria of the Fallopian tubes. Structure. — These mucous tracts, and different portions of each of them, jiresent certain structural peculiarities, adapted to the functions which each part has to discharge; yet in some essential characters the mucous membrane is the same, from whatever part it is obtained. In all the principal and larger parts of the several tracts, it j^resents, as just remarked, an external layer of epithelium, situated upon a basement membrane, and beneath this,, a stra-tum of vascular tissue of variable thickness, containing lymphatic vessels and nerves. The vascular stratum, together with the basement membrane and epithelium, in differ- ent cases, is elevated into minute papilhi? and villi, or depressed into involutions in the form of glands. But in the prolongations of the tracts, where they pass into gland-ducts, these constituents are reduced in the finest branches of the ducts to the epithelium, the primary or base- ment-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, sim- ple, 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 between the epithelium-cells of mucous membranes and 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 458 HANDBOOK OF PHYSIOLOGY. more or less viscid, grayish, or semi-transparent fluid, of alkaline reac- tion 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 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 secreting glands present, amid manifold diversities of form and composition, a general plan of structure; all contain, and appear con- structed with particular regard to the arrangement of the cells, which, as already expressed, both line their tubes or cavities as an epithelium, and elaborate, as secreting cells, the substances to be discharged from them. Ty2)es of Secreting Glands. — Secreting glands may be classified accord- ing to certain types, which are the following: — 1. The simjile tubular gland (a, fig. 327), examples of which are furnished by the follicles of Lieberkiihn, and the tubular glands of the stomach. They are simple tubular depressions of the mucous membrane, the wall of which is formed of primary membrane and is lined with secreting cells arranged as an epithelium. To the same class may be referred the elongated and tor- tuous sudoriferous glands. 2. The co7npou7id tubular glands (d, fig. 327) form another division. These consist of main gland-tubes, which divide and subdivide. Each gland may be made up of the subdivisions of one or more main tubes. The ultimate subdivisions of the tubes are generally highly convoluted. They are formed of a basement-membrane, lined by epithelium of various forms. The larger tubes may have an outside coating of fibrous, areolar, or muscular tissue. The kidtiey, testes, salivary glands, pan- creas, Brunner''s glands, with the lachrymal and mammary glands, and some mucous glands are examples of this type but present more or less marked variations among themselves. 3. The aggregate OY racemose glands, in which a number of vesicles or acini are arranged in groups or globules (c, fig. 327). The meibomicm follicles are examples of this kind of gland. There seem to be glands of mixed character, combining some of the characters of the tubular with others of the racemose type ; these are called tubulo-racemose or tubulo- acitious glands. These glands differ from each other only in secondary points of structure : such as, chiefly, the arrangement of their excretory ducts, the grouping of the acini and lobules, their connection by areolar tissue, and supply of blood-vessels. The acini commonly appear to be formed by a kind of fusion of the walls of several vesicles, which thus METABOLISM OF THE TISSUES. 459 combine to form one cavity lined or filled with secreting cells which also occupy recesses from the main cavity. The smallest branches of the gland-dncts sometimes open into the centres of these cavities; some- times the acini are clustered round the extremities, or by the sides of the ducts: but, whatever secondary arrangement there may be, all have the same essential character of rounded groups of vesicles containing Fig. 327.— Plans of extension of secreting membrane by inversion or recession in form of cav- ities. A, Simple glands, viz., T. med Cart: cricoidea.- Xag: crico-tracheae. Cart: traclieale, (?«. Stemo-liyoideua i''~ - mj. Steraorhyoidcasi m. Stemo-hfoideud, m. Crico-thyroideuSi Fie 341 —The Larynx, as seen from the front, showing the cartilages and ligaments. ' cles, with the exception of one crico-thyroid, are cut off short. (Stoerk.) The mus- the respiratory apparatus. In many animals, the sound admits of being variously modified and altered during and after its production; and, in man, one such modification occurring in obedience to dictates of the cerebrum, is speech. It has been proved by observations on living subjects, by means of the laryngoscope (p. 519), as well as by experiments on the larynx taken from the dead body, that the sound of the human voice is the result of the vibration of the inferior laryngeal ligaments, or the true vocal 514 THE PRODUCTIOX OF THE VOICE. 515 cords which bound the glottis, caused by currents of expired air impelled over their edges. If a free opening exists in the trachea, the sound of the voice ceases, but it returns if the opening is closed. An opening into the air-passages above the glottis, on the contrary, does not prevent the voice being produced. By forcing a current of air through the larynx in the dead subject, clear vocal sounds are elicited, through the epiglottis, the upper ligaments of the larynx or false vocal cords, the ventricles between them and the inferior ligaments or true vocal cords, and the upper part of the arytenoid cartilages, be all removed; provided the true vocal cords remain entire, with their points of attachment, and be kept tense and so approximated that the fissure of the glottis may be narrow. The vocal ligaments or cords, therefore, are regarded as the proper organs for the production of vocal sounds: the modifications of these sounds being effected, as will be presently explained, by other parts, viz., by the tongue, teeth, lips, etc. The structure of the vocal cords is adapted to enable them to vibrate like tense membranes, for they are essentially composed of elastic tissue; and they are so attached to the cartilaginous parts of the larynx that their position and tension can be variously altered by the contraction of the muscles which act on these parts. Thus it will be seen that the larynx is the organ of voice. It may be said to consist essentially of the two vocal cords and the various car- tilaginous, muscular, and other apparatus by means of which not only can the ajDcrture of the larynx (rima glottidis), of which they are the lateral boundaries, be closed against the entrance and exit of air to or from the lungs, but also by means of which the cords themselves can be stretched or relaxed, brought together and separated in accordance with the conditions that may be necessary for the air in passing over them, to set them vibrating to produce the various sounds. Their action in respiration has been already referred to. Anatomy of the Larynx. — The principal parts entering into the formation of the larynx (figs. 342 and 343) are — the thyi'oid cartilage ; the cricoid cartilage ; the two arytenoid cartilages ; and the two true vocal cords. The epiglottis (fig. 343) , has but little to do with the voice, and is chiefly useful in protect- ing the vipper part of the larynx from the entrance of food and drink in deglutition. It also probably guides mucus or other fluids in small amount from the mouth around the sides of the upper opening of the glottis into the pharynx and oesophagus : thus preventing them from entering the larynx. The false vocal cords and the ventricle of the larynx, which is a space between the false and the true cord of either side, need be here only referred to. Cartilages. — (a) The thyroid cartilage (fig. 342, 1 to 4) does not form a com- plete ring around the laiynx, but only covers the front portion. (&) The cricoid cartilage (fig. 342, 5, 6) , on the other hand, is a complete ring ; the 516 HANDBOOK OF PHYSIOLOGY. back part of the ring being much broader than the front. On the top of this broad portion of the cricoid are (c) the arytenoid cartilages (fig. 342, 7) , the connection between the cricoid below and arytenoid cartilages above being a joint with synovial membrane and ligaments, the latter permitting tolerably free Fig. 342. —Cartilages of the larynx seen from the front. 1 to 4, thyroid cartilage; 1, verti- cal ridge or pomuni Adami ; 2, right ala: .3, superior, and 4, inferior cornu of the right side; 5, 6, cricoid cartilage; 5, inside of the posterior part; 6, antei-ior narrow part of the ring; 7, arytenoid cartilages. X M- motion between them. But although the arytenoid cartilages can move on the cricoid, they of course accompany the latter in all its movements, just as the head may nod or turn on the top of the spinal column, but must accompany it in all its movements as a whole. Joints and Ligaments. — The thyroid cartilage is also connected with the cricoid, not only by ligaments, but also by joints with synovial membranes ; the lower corniia of the thyroid clasyjing, or nipping, as it were, the cricoid between them, but not so tightly but that the thyroid can revolve, within a Ijf^, Ary.-ep%Iott. Caiti Wrisberg'ii Cart, Santorinl Cart, an'ten. True. lauscnl. TUg. erico-aiyten. Efg, cfiffltof-crico. post, "sup.. Cornuinfer. Hgj, carafcsaicoyjost.jnt. Cart, traciiero -- Tars mcmbraa. t«^^^ Fig. 343.— The larynx as seen from behind after removal of the muscles. The cartilages and lig- aments only renaain. (Stoerk.) certain range, around an axis passing transversely through the two joints at which the cricoid is clasped. The vocal cords are attached (behind) to the front portion of the base of the arytenoid cartilages, and (in front) to the re-entering angle at the back part of the thyroid ; it is evident, therefore, that all THE PRODUCTION OF THE VOICE. ol7 movements of either of these cartilages must produce an effect on them of some kind or other. Inasmuch, too, as the arytenoid cartilages rest on the top of the back portion of the cricoid cartilage, and are connected with it by capsular and other ligaments, all movements of the cricoid cartilage must move the arytenoid cartilages, and also produce an effect on the vocal cords. Intrinsic 31uscles. — The intrinsic muscles of the laiynx are so connected with the laryngeal cartilages that by their contraction alterations in the con- dition of the vocal cords and glottis are produced. They are usually divided into four classes according to their action, viz., into abductors, adductors, sphinctevs, and tensors. The Abductors, the crico-arytenoidei, widen the glottis, by separating the cords ; the Adductors, consisting of the thyro-ary-epiglottici, the arytenoideus posticus sen transversus, the thyro-arytenoidei externi, t\ie crico- arytenoidei laterales, and the thyro-arytenoidei interni, approximate the vocal cords, diminish the rima glottidis, and act generally as Sphincters and sup- porters of the glottis. Finally, the Tensors of the cords put the cords on the stretch, with or without elongating them ; the tensors are the crico-thyroidei and the thyro-arytenoidei interni. The attachments and the action of the muscles will be readily understood from the following table. All the muscles are in pairs excej^t the arytenoideus posticus. Table of the several Groups op the Intrinsic Muscles of the Larynx and their attachments. Group. Muscle. Attachments. Action. I. Abductors. Crico-aryte- noidei pos- tici. This pair of muscles arises, on either side, from the posterior surface of the corresponding half of the cricoid cartilage. From this depression their fibres con- verge on either side upward and outward to be inserted into the outer angle of the base of the arytenoid cartilages behind the crico-arytenoid laterales. Draw inward and backward the outer angle o f arytenoid carti- lages, and so ro- tate out w a r d the processus vo- calis and widen the glottis. II. and III. Adductors and Sphincters. In three lay- ers : (a) Outer layer, Thy- r o - ar y - e p i g 1 ot- tici. A pair of muscles. Flat and nar- row, which arise on either side from the processus muscularis of the arytenoid cartilage, then pass- ing vipward and inward cross one another in the middle line to be inserted into the upper half of the lateral border of the opposite arytenoid cartilage and the poste- rior border of the cartilage of Santorini. The lower fibres run forward and downward to lie inserted into the thj-roid carti- lage near the commissure. The fibres attached to the cartilage of Santorini are continvied forward and upward into the ary-epiglot- tic fold. Help to narrow or close the rima glottidis. 518 HANDBOOK OF PHYSIOLOGY. Group. II. and III. Adductors and Sphincters. — continued. Muscle. (b) 3fiddle layer. i. Aryte- noid e us posticus. ii. Thyro- aryteno i - d e i e X - terni. ATTACHMENT.S. A single muscle. Half-q u a d r i- lateral, attached to tlie borders of the arytenoid cartilages, its fibres running horizontally be- tween the two. Draws together the arytenoid carti- lages and also de- presses them. When the mus- cle is paralj'zed, the inter- carti- laginous pa-rt of the cords cannot come together. A pair of muscles. Each of which consists of three chief portions — lower, middle, and upper The lower and principal fibres may be further divided into two layers, internal and external. These fibres arise side by side from the lower half of the inter- nal surface of the thyroid carti- lage, close to the angle, and from the fibrous expansion of the crico- thyroid ligament, and are insert- ed into the lateral border of the arytenoid cartilage. The inner fibres run horizontally, to be at- tached to the lower half of this border, and the outer fibres pass obliquely ovitwai'd to be inserted into the upper half, while some pass to the cartilage of Wrisbvirg and the ary -epiglottic fold. 111. Crico- A pair of muscles. They arise on aryteno i -' either side from the middle third of the upper border of the cricoid cartilage and are inserted into the whole anterior margin of the base of the arytenoid cartilage. Some of their fibres join the thyroid- ary-epiglottici. dei later- ales. (c) Inner- most lay er, Thyro- ar ytenoi- dei i n - terni. Approximate the vocal cords by drawing the processus mus- cularis of the arytenoid carti- lages forward and downward and so rotate the processus vocalis inward. A pair of muscles. They arise on Render the vocal either side, internally from the cords tense and angle of the thyroid cartilage, i rotate the aryte- internal to the last described; noid cai'tilages muscle ( (b), iii.), and running and approximate parallel to and in the substance of the processus the vocal cords are attached pos- vocalis. teriorly to the processus vocalis along their whole length and to the adjacent part of the outer surface of the arytenoid carti- lages. THE PRODUCTION OF THE VOICE. 519 Group. IV. Tensors. MUSCL~. Crico - 1 h y- roidei. Attachments. A pair of fan-shaped muscles at- tached on either side to the cricoid cartilage below ; from the mesial line in front for nearly one-half of its lateral circumference back- ward the fibi-es pass upward and outward to be attached to the low- er border of the thyroid cartilage and to the front border of its lower cornea, Action. Thyro - ary- teno i d e i interni. The most posterior part is almost a distinct muscle and its fibres are all but horizontal : some- times this muscle is described as consisting of two layers, super- ficial with cortical fibres, deep with oblique fibres, described under Group III. The thyroid carti- lage being fixed by its extrinsic muscles, the front of the cri- coid cartilage is drawn upward, and its back, with the aryte- noids attached, is drawn down. Hence the vocal cords are elon- gated a n t e r o - posteriorly and put upon the stretch. Paral- ysis of these muscles causes an inability to produce high notes. Described above. Nerve Supply. —In the performance of the functions of the larynx the sensory filaments of the superior laryngeal branch of the vagus supply that acute sen- sibility by which the glottis is guarded against the ingress of foreign bodies, or of irrespirable gases. The contact of these stimulates the nerve filaments ; and the impression conveyed to the medulla oblongata, whether it produce sensation or not, is reflected to the filaments of the recurrent or inferior laryngeal branch, and excites contraction of the muscles that close the glottis. Both these branches of the vagi co-operate also in the production and regulation of the voice ; the inferior laryngeal determining the contraction of the muscles that vary the tension of the vocal cords, and the superior laryngeal conveying to the mind the sensation of the state of tliese muscles necessary for their contin- uous guidance. And both the branches co-operate in the actions of the larynx in the ordinary slight dilatation and contraction of the glottis in the acts of expiration and inspiration, and more evidently in those of coughing and other forcible respiratory movements. The laryngoscope is an instrument emploj^ed in investigating during life the condition of the pharynx, larynx, and trachea. It consists of a large concave mirror with perforated centre and of a smaller mirror fixed in a long handle. It is thus used : the patient is placed in a chair, a good light (argand burner, or lamp) is arranged on one side of, and a little above his head. The operator fixes the large mirror round his head in such a manner, that he looks through 520 HANDBOOK OF PHYSIOLOGY. the central aperture with one eye. He then seats himself opposite tlie patient, and so alters the position of the mirror, which is for this purpose provided with a ball and socket joint, that a beam of light is reflected on the lips of the patient. The patient is now directed to throw his head slightly backward, and to open his mouth ; the reflection from the mirror lights up the cavity of the mouth, and by a little alteration of the distance between the operator and the patient the point at which the greatest amount of light is reflected by the mirror — in other words its focal length — is readily discovered. The small mirror fixed in the handle is then warmed, either by holding it over the lamp, or by putting it into a vessel of warm water ; this is necessary to prevent the condensation of breath upon its surface. The degree of heat is regulated by ligiBxy epigloto - Cal•t^'^Vrisbel•gii4- Cart. SanloTini ffli CxicD-aryteflOid. Tfost, * C'omu inferior Xig. cerato-cric. ■Ears- post. Inf. membi-ant f lEars. cartUag. ' „ ^ WSuB Fig. 344.— Tiie larynx as seen from behind. To show the intrinsic muscles posteriorly. (Stoerk.) applying the back of the mirror to the hand or cheek, when it should feel warm without being painful. After these preliminaries the patient is directed to put out his tongue, which is held by the left hand gently but firmly against the lower teeth by means of a handkerchief. The warm mirror is passed to the back of the mouth, until it rests upon and slightly raises the base of the uvula, and at the same time the light is directed upon it : an inverted image of the larynx and trachea will be seen in the mirror. If the dorsum of the tongue be alone seen, the handle of the mirror must be slightly lowered vmtil the larynx comes into view ; care should be taken, however, not to move the mirror upon the uvula, as it excites retching. The observation should not be prolonged, but should rather be repeated at short intervals. The structures seen will vary somewhat according to the condition of the parts as to inspiration, expiration, phonation, etc. ; they are (figs. 347) first, and apparently at the posterior part, the base of the tongue, immediately below which is the accurate outline of the epiglottis, with its cushion or tubercle. Then are seen in the central line the true vocal cords, white and shining in their normal condition. The cords approximate (in the inverted image) posteriorly ; THE PRODUCTION OF THE VOICE. 521 between them is left a chink, narrow while a high note is being sung, wide during a deep inspiration. On each side of the true vocal cords, and on a higher level, are the pink false vocal cords. Still more externally than the Fig. 345. parts of the Laryngoscope. false vocal cords is the aryteno-epigJottidean fold, in which are situated upon ■each side three small elevations : of these the most external is the cartilage of Wrisherg, the intermediate is the cartilage of Santori)ii, while the summit of the arytenoid cartilage is in front, and somewhat below the preceding, being Fig. 346. —To show the position of the operator and patient when using the Laryngoscope. only seen during deep inspiration. The rings of the trachea, and even the bifurcation of the trachea itself, if the patient be directed to draw a deep breath, may be seen in the interval between the true vocal cords. 522 HAXDBOOK OF rHYSIOLOGY. Movements of the Vocal Cords. In Bespiration. — The position of the vocal cords in ordinary tran- quil breathing is so adapted by the muscles, that the opening of the glottis is wide and triangular (fig. 347, b) becoming a little wider at Fig. 347. — Three laryngoscopic views of the superior aperture of the larynx and surrounding parts. A, the glottis during the emission of a high note in singing; B, in easy and quiet inha- lation of air; C, in the state of the widest possible dilatation, as in inhaling a very deep breath. The diagrams A', B', and C, show in horizontal sections of the glottis the position of the vocal ligaments and arytenoid cartilages in the three several states represented in the other figures. In all the figm-es, so far as marked, the letters indicate the parts as follows, viz. : /, the base of the tongue; e, the upper free part of the epiglottis; e'. the tubercle or cushion of the epiglottis; ph, part of the anterior wall of the pharynx behind the larynx ; in the margin of the aryteno- epiglottidean fold iv. the swelling of the membrane caused by the cartilages of Wrisberg; s, that of the cartilages of Santorini ; a. the tip or summit of the "arytenoid cartilages; c r, the true vocal cords or lips of the rima glottidis; c v s, the superior or "false vocal cords; between them the ventricle of the larynx ; in C, tr is placed on the anterior wall of the receding trachea, and b indicates the commencement of the two bronchi bevond the bifurcation which may be brought into view in this state of extreme dilatation. (Quain after Czermak.) each inspiration, and a little narrower at each expiration. On making a rapid and deep inspiration the opening of the glottis is widely dilated (fig. 347, c), and somewhat lozenge-shaped. In Vocalization. — At the moment of the emission of a note, it is nar- rowed, the margins of the arytenoid cartilages being brought into contact and the edges of the vocal cords approximated and made parallel, at the same time that their tension is much increased. The higher the note produced, the tenser do the cords become (fig. 347, a); and the range of THE PRODUCTION OF THE VOICE. 523 a voice dei:)encls, of course, in the main, on the extent to whicli the degree of tension of the vocal cords can be thus altered. In the produc- tion of a high note the vocal cords are brought well within sight, so as to be plainly visible with the help of the laryngoscope. In the utter- ance of grave tones, on the other hand, the epiglottis is depressed and brought over them, and the arytenoid cartilages look as if they were trying to hide themselves under it (fig. 34:8). The epiglottis, by being Fig. 348. —View of the upper part of the larvnx as seen by means of the laryngoscope during the utterance of a grave note, c, Epiglottis: s", tubercles of the cartilages of Santorini ; a, aryt- enoid cartilages; 2, base of the tongue; ph.the posterior wall of the pharynx. (Czermak.) somewhat pressed down so as to cover the superior cavity of the larynx, serves to render the notes deeper in tone and at the same time somewhat duller, just as covering the end of a short tube placed in front of caoutchouc tongues lowers the tone. In no other respect does the epiglottis appear to have_any effect in modifying the vocal sounds. The degree of approximation of the vocal cords also usually corre- sponds with the height of the note produced ; but probably not always, for the width of the aperture has no essential influence on the height of the note, as long as the vocal cords have the same tension : only with a wide aperture the tone is more difficult to produce and is less perfect, ^the rushing of the air through the aperture being heard at the same time. No true vocal sound is produced at the posterior part of the aperture of the glottis, that, viz., which is formed by the space between the arytenoid cartilages. For if the arytenoid cartilages be approximated in such a manner that their anterior processes touch each other, but yet leave an opening behind them as well as in front, no second vocal tone is produced by the passage of the air through the posterior opening, but merely a rustling or bubbling sound ; and the height or pitch of the note produced is the same whether the posterior part of the glottis be open or not. The Voice in Singing and Speaking. Varieties of Vocal Sounds. — The laryngeal notes may observe three different kinds x)f sequence. The first is the monotonous, in which the- notes have nearly all the same pitch as in ordinary speaking; the variety of the sounds of speech being due to articulation in the mouth. 524 HANDBOOK OF PHYSIOLOGY. In speaking, however, occasional syllables generally receive a higher intonation for the siike of accent. The second mode of sequence is the successive transition from high to low notes, and vice versa, without intervals; such as is heard in the sounds, which, as expressions of pas- sion, accompany crying in men, and in the howling and whining of dogs. The third mode of sequence of the vocal sounds is the musical, in which each sound has a determinate number of vibrations, and the numbers of the vibrations in the successive sounds have the same relative proportions that characterize the notes of the musical scale. In different individuals this comprehends one, two, or three octaves. In singers — 'that is, in persons apt for singing — it extends to two or three octaves. But the male and female voices commence and end at •different points of the musical scale. The lowest note of the female voice is about an octave higher than the lowest of the male voice; the highest note of the female voice about an octave higher than the highest •of the male. The compass of the male and female voices taken together, or the entire scale of the human voice, includes about four octaves. The principal difference between the male and female voice is, therefore, in their 2^ itch; but they are also distinguished by their tone, — the male voice is not so soft. The voice presents other varieties besides that of male and female; there are two kinds of male voice, technically called the bafis and tenor, and two kinds of female voice, the contralto and soprano, all differing from each other in tone. The bass voice usually reaches lower than the tenor, and its strength lies in the low notes; while the tenor voice extends higher than the bass. The contralto voice has generally lower notes than the soprano, and is strongest in the lower notes of the female voice; while the soprano voice reaches higlier in the scale. But the difference of compass, and of power in different parts of the scale, is not the essential distinction between the different voices; for bass singers can sometimes go very high, and the contralto frequently sings the high notes like soprano singers. The essential difference between the base and tenor voices, and between the contralto and soprano, consists in their tone or timhre, which distinguishes them even when they are singing the same note. The qualities of the bary- tone and mezzo-soprano voices are less marked; the Jr/rt/^owe being in- termediate between the bass and tenor, the mezzo-soprano between the contralto and soprano. They have also a middle position as to pitch in the scale of the male and female voices. The differences in the pitch of the male and the female voices depends on the different length of the vocal cords in the two sexes; their relative length in men and women being as three to two. The difference of the two voices in tone or timbre, is owing to the different nature a7id form of the resounding walls, which in the male larynx are THE PKODUCTIOX OF THE VOICE. 525 much more extensive, aud form a more acute angle anteriorly. The different qualities of the tenor and bass, and of the alto and soprano voices, probably dej)end on some peculiarities of the ligaments, and the membranous and cartilaginous parietes of the laryngeal cavity,, which are not at jn'esent understood, but of which we may form some idea,, by recollecting that musical instruments made of different materials, e.g., metallic and gut-strings, may be tuned to the same note, but that each w.'ll give it with a peculiar tone or tinihre. The boy's larynx resembles the female larynx; their vocal cords before puberty are not two-thirds the length of the adult cords; and the angle of their thyroid cartilage is as little prominent as in the female larynx. Boys' voices are alto aud soprano, resembling in pitch those of women, but louder, aud differing somewhat from them in tone. But, after the larynx has undergone the change produced during the period of development at puberty, the boy's voice becomes bass or tenor. AVhile the change of form is taking place, the voice is said to crack; it- becomes imperfect, frequently hoarse and crowing, and is unfitted for singing until the new tones are brought under command by practice. In eunuchs, who have been deprived of the testes before puberty, the voice does not undergo this change. The voice of most old people is deficient in tone, unsteady, and .more restricted in extent: the first defect is- owing to the ossification of the cartilages of the larynx and the altered condition of the vocal cords ; the want of steadiness arises from the loss of nervous power and command over the muscles ; the result of which is here, as in other parts, a tremulous movement. These two causes com- bined render the voices of old people void of tone, unsteady, bleating, and weak. In any class of persons arranged, as in an orchestra, acording to the character of voices, each would possess, with the general characteristics of a bass, or tenor, or any other kind of voice, some peculiar character by which his voice would be recognized from all the rest. The condi- tions that determine these distinctions are, however, quite unknown. They are probably inherent in the tissues of the larynx, and are as indiscernible as the minute differences that characterize men's features; one often observes, in like manner, hereditary and family peculiarities of voice, as well marked as those of the limbs or face. Most persons, particularly men, have the power, if at all capable of singing, of modulating their voices through a double series of notes of different character: namely, the notes of the natural voice, or chest- notes, and the falsetto notes. The natural voice, which alone has been hitherto considered, is fuller, and excites a distinct sensation of much stronger vibration and resonance than the falsetto voice, which has more a flute-like character. The deeper notes of the male voice can 526 UANDBOOK OF I'lIYSIOLOGY. be produced ouly with the natural voice, the highest witli the falsetto only; the notes of middle pitch can be jiroduced either with the natural or falsetto voice; the two registers of the voice are therefore not limited in such a manner as that one ends when the other begins, but they run in part side by side. The natural or chest-notes are, as we have seen, produced by the or- dinary vibrations of the vocal cords. The mode of j)roduction of the falsetto notes is still obscure. By Miiller they were thought to be due to vibrations of only the inner borders of the vocal cords. In the opinion of Petrequin and Diday, they do not result from vibrations of the vocal cords at all, but from vibra- tions of the air j^assing through the aperture of the glottis, which they believe assumes, at such times, the contour of the emhouchure of a flute. Others, considering some degree of similarity which exists between the falsetto notes and the peculiar tones called harmonic, which are pro- duced when, by touching or stopping a harp-string at a particular point, only a portion of its length is allowed to vibrate, have supposed that, in the falsetto notes, j)ortions of the cords are thus isolated, and made to vibrate while the rest are held still. The question cannot yet be settled; but any one in the habit of singing may assure himself, both by the difficulty of passing smoothly from one set of notes to the other, and by the necessity of exercising himself in both registers, lest he should become very deficient in one, that there must be some great difference in the modes in which their respective notes are produced. The intcli of the note., which depends upon the rajoidity of the vibra- tions, is altered by alterations of the vocal cords, and so the strength of the voice is in proportion {a) to the degree to which the vocal cords can be made to vibrate; and partly {b) to the fitness for resonance of the membranes and cartilages of the larynx, of the parietes of the thorax, lungs, and cavities of the mouth, nostrils, and communicating sinuses. It is diminished by anything which interferes with such capability of vibration. The intensity or loudness of a given note with maintenance of the same pitch, cannot be rendered greater by merely increasing the force of the current of air through the glottis; for increase of the force of the current of air, coeter is paribus^ raises the pitch both of the natural and the falsetto notes. Yet, since a singer possesses the power of increasing the loudness of a note from the faintest ])iano to fortissimo without its pitch being altered, there must be some means of compensating the tendency of the vocal cords to emit a higher note when the force of the current of air is increased. This means evidently consists in modify- ing the tension of the vocal cords. When a note is rendered louder and more intense, the vocai cords must be relaxed by remission of the THE PRODUCTIOX OF THE VOICE. 527 muscular action, in propoi'tion as the force of the current of the breath through the glottis is increased. When a note is rendered fainter, the reverse of this must occur. The arches of the palate and the uvula become contracted during the formation of the higher notes; but their contraction is the same for a note of given height, whether it be falsetto or not; and in either case the arches of the palate may be touched with the finger, without the note being altered. Their action, therefore, in the production of the higher notes seems to be merely the result of involuntary associate ner- vous action, excited by the voluntarily increased exertion of the muscles of the larynx. If the palatine arches contribute at all to the production of the higher notes of the natural voice and the falsetto, it can only be by their increased tension strengthening the resonance. The office of the ventricles of the larynx is evidently to afford a free space for the vibrations of the lips of the glottis; they may be com- pared with the cavity at the commencement of the mouthpiece of trum- pets, which allows the free vibration of the lips. Speech. — Besides the musical tones formed in the larynx, a great number of other sounds can be produced in the vocal tubes, between the glottis and the external apertures of the air-passages, the combination of which sounds by the agency of the cerebrum into different groups to designate objects, properties, actions, etc., constitutes language. The languages do not employ all the sounds which can be produced in this manner, the combination of some with others being often difficult. Those sounds which are easy of combination enter, for the most part, into the formation of the greater number of languages. Each language contains a certain number of such sounds, but in no one are all brought together. On the contrary, different languages are characterized by the prevalence in them of certain classes of these sounds, while others are less frequent or altogether absent. Articulate Sounds, — The sounds produced in speech, or the articu- late sounds, are commonly divided into vowels and consonants: the dis- tinction between which is, that the sounds for the former are generated by the larynx, while those for the latter are produced by interruption of the Current of air in some part of the air-passages above the larynx. The term consonant has been given to these because several of them are not properly sounded, except consonantly with a vowel. Thus, if it be attempted to pronounce aloud the consonants b, d, and g, or their modi- fications, p, t, k, the intonation only follows them in their combination with a vowel. To recognize the essential properties of the articulate sounds, it is necessary first to examine them as they are produced in whispering, and then investigate which of them can also be uttered in a modified character conjoined with vocal tone. By this procedure we 528 HANDBOOK OF PHYSIOLOGY. lind two series of sounds: in one the sounds are mute, and cannot be uttered with a vocal tone; the sounds of the other series can be formed independent!}' of voice, but are also capable of being uttered in con- junction with it. All the vowels can be expressed in a whisper without vocal tone, that is, mutely. These mute vowel-sounds differ, however, in some meas- ure, as to their mode of production, from the consonants. All the mute consonants are formed in the vocal tube above the glottis, or in the cavity of the mouth or nose, by the mere rushing of the air between the surfaces differently modified in disposition. But the sound of the vowels, even when mute, has its source in the glottis, though its vocal cords are not thrown into the vibrations necessary for the production of voice ; and the sound seems to be jiroduced by the passage of the current of air between the relaxed vocal cords. The same vowel-sound can be pro- duced in the larynx when the mouth is closed, the nostrils being open^ and the utterance of all vocal tone avoided. The sound, when the mouth is open, is so modified by varied forms of the oral cavity, as to assume the characters of the vowels a, e, i, O, u, in all their modifications. " The cavity of the mouth assumes the same form for the articulation of each of the mute vowels as for the corresponding vowel when vocal- ized; the only difference in the two cases lies in the kind of sound emitted by the larynx. It has been pointed out that the conditions necessary for changing one and the same sound into the different vowels, are differences in the size of two parts — the oral canal and the oral open- ing; and the same is tlie case with regard to the mute vowels. By oral canal, is meant here the space between the tongue and palate : for the pronunciation of certain vowels both the opening of the mouth and the space just mentioned are widened; for the pronunciation of other vowels both are contracted ; and for others one is wide, the other contracted. Admitting five degrees of size, both of the opening of the mouth and of the sjDace between the tongue and palate, Kempelen thus states the dimensions of these parts for the following vowel-sounds: — Size of oral opening. Size of oral canal. 5 ... 3 4 ... 2 3 ... 1 2 ... 4 1 ... 5 Another important distinction in articulate sounds is, that the utter- ance of some is only of momentary duration, taking place during a sud- den change in the conformation of the mouth, and being incapable of prolongation by a continued expiration. To this class belong b, p, d, and the hard g. In the utterance of other consonants the sounds may- be continuous; they may be prolonged, ad libitum, as long as a particu- lar disposition of the mouth and a constant expiration are maintained. Vowel. Sound. a as in " far" a " " name" e " " theme" o " " go" oo " " cool" THE PRODUCTION OF THE VOICE, 529 Among these consonants are h, m, n, f, s, r, 1. Corresponding differences in respect to the time tliat may be occupied in their utterance exist in the vowel sounds, and princi})ally constitute the differences of long and short syllables. Thus the a as in far and fate, the o as in go and fort, may be indefinitely prolonged; but the same vowels (or more properly different vowels expressed by the same letters), as in can and fact, in dog and rotten, cannot be prolonged. All sounds of the first or explosive kind are insusceptible of com- bination with vocal tone (intonation), and are absolutely mute; nearly all the consonants of the second or continuous kind may be attended with intonation. Ventriloquism. — The peculiarity of speaking, to which the term ventriloquism is applied, appears to consist merely in the varied modi- fication of the sounds produced in the larynx, in imitation of the modi- fications which voice ordinarily suffers from distance, etc. From the observations of Miiller and Colombat, it seems that the essential mechanical parts of the process of ventriloquism consist in taking a full inspiration, then keeping the muscles of the chest and neck fixed, and speaking with the mouth almost closed, and the lips and lower jaw as motionless as possible, while air is very slowly expired through a very narrow glottis ; care being taken also, that none of the expired air passes through the nose. But, as observed by Miiller, much of the ventrilo- quist's skill in imitating the voices coming from particular directions, consists in deceiving other senses than hearing. We never distinguish very readily the direction in which sounds reach our ear; and, when our attention is directed to a particular point, our imagination is very apt to refer to that point whatever sounds we may hear. Action of the Tongue in Speech. — The tongue, which is usually credited with the power of speech — language and speech being often employed as synonymous terms — -plays only a subordinate, although very important part. This is well shown by cases In which nearly the whole organ has been removed on account of disease. Patients who recover from this operation talk imperfectly, and their voice is considerably modified ; but the loss of speech is confined to those letters in the pro- nunciation of which the tongue is concerned. Stammering depends on a want of harmony between the action of the muscles (chiefly abdominal) which expel air through the larynx, and that of the muscles which guard the orifice (rima glottidis) by Avhich it escapes, and of those (of tongue, palate, etc.) which modulate the sound to the form of speech. Over either of the groups of muscles, by itself, a stammerer may have as much power as other people. But he cannot harmoniously .irrange their conjoint actions. 34 CHAPTER XVI THE NERVOUS SYSTEM. The nervous system consists of the following parts: firstly, of large masses of nervous matter situated within the bony cranium and spinal column, and constituting the brain and spinal cord; secondly, of smaller masses of nervous matter, situated for the most part in the abdominal and thoracic cavities, but also in the neck and head, and constituting what are known as sympathetic ganglia; thirdly, of cords of nerve-fibres which connect the central nervous system with the periphery and with the so-called sympathetic ganglia, which are not in reality a system independent of the brain and cord as was formerly taught, but are really part and parcel of the same system ; and fourthly, of peripheral organs in connection with the beginnings or endings of the nerves at the periphery of the body. It will be necessary to consider these several parts of the nervous system seriatim; it will be most useful for the understanding of the subject, however, to proceed first of all with the consideration of the properties of nerve-fibres, as this forms the most elementary portion of the subject. Nerve-fibres. — The structure of the ditferent kinds of nerve-fibres has been already dealt with (p. 89, et seg.) ; their function remains to be considered here. Function of Nerve -fibres. The office of nerve-fibres is to conduct impressions. From the account of nervous action previously given (p. 447 et seq.) it will be readily understood, that nerve-fibres may be stimulated to act by any- thing which, with sufficient suddenness, increases their irritability; but tljey are incapable of originating of themselves the condition necessary for the manifestation of their own energy. The stimulus produces its effect upon the termination of the nerve stimulated, being conducted to it by the nerve-fibre. The efl'ect of the stimulus upon a nerve therefore depends upon the nature of its end-organ. A length of a nerve trunk when freshly removed from the body, if stimulated midway between its extremities, will, as shown by the deflection of the needle of a galvanometer' at either end, conduct the electrical impressions in either direction, and it may be considered therefore only an accidental circumstance as i1 were, whether when in situ it has conducted impressions to the central THE NERVOUS SYSTEM. 531 nervous system from the periphery, or from the central nervous system to the muscles or other tissues. The same fibre cannot be used for the one purj)ose at one time, and for the other at another, simply because of the nature of its terminal organs. Thus, when a cerebro-spinal nerve- fibre is irritated in the living body as by pinching, or by heat, or by electrifying it, there is, under ordinary circumstances, one of two effects, — either there is pain, or there is twitching of one or more muscles to which the nerve distributes its fibres. From various considerations it is certain that pain is always the result of a change in the nerve- cells of the brain. Therefore, in such an experiment as that referred to, the irritation of the nerve-fibre is conducted in one of two direc- tions, i.e., either to the brain, which is the central termination of the fibre, when there is pain, or to a muscle, which is the peripheral ter- mination, when there is movement. The effect of this simple experiment is a type of what always occurs when nerve-fibres are engaged iir the performance of their functions. The result of stimulating them, which roughly imitates what happens naturally in the body, is found to occur at one or other of their ex- tremities, central or peripheral, never at both; and in accordance with this fact, and because, for any given nerve-fibre, the result is always the same, nerve-fibres have been commonly classed as sensory or motor. This is not altogether accurate, and the terms centrifugal or afferent and centripetal or efferent are more properly used, since the result of stimulating a nerve of the former kind is not always the production of pain or other form of sensation, nor is motion the invariable result of stimulating the latter. The term intercentral is applied to those nerve-fibres which connect more or less distinct nerve-centres, and may, therefore, be said to have Tio peripheral distribution, in the ordinary sense of the term. Impressions made upon the terminations or upon the trunk of a centripetal nerve may cause (a) pain, or some other kind of sensation ; {b) special sensation; or (c) reflex action of some kind; or {d) inhibition, restraint of action. Similarly imiDressions made upon a centrif- ugal nerve may cause {a) contraction of muscle (motor nerve) ; {b) it may influence nutrition (trophic nerve) ; or (c) may influence secretion (secretory nerve) ; or [d) inhibit, augment, or stop any other efferent action. It is a law of action in all nerve-fibres, and corresponds with the con- tinuity and simplicity of their course, that an impression made on any fibre, is simply and uninterruptedly transmitted along it, without itself being imparted or diffused to any of the fibres lying near it. It is possible that the mere passage of a nerve impulse along a nerve-fibre, Iiowever, may produce some effect upon the neighboring nerve-fibres. 532 HANDBOOK OF PHYSIOLOGY. Their adaptation to the purpose of simple conduction is, perhaps, due to the contents of each fibre being completely isolated from those of ad- jacent fibres by the myelin sheath in which each is inclosed, and which acts, it may be supposed, just as silk, or other non-conductors of elec- tricity do, which, when covering-a wire, prevent the electric condition of the wire from being conducted into the surrounding medium. Velocity of a Nervoiis Iminihe. — The change which a stimulus sets up in a nerve, of the exact nature of which we are unacquainted, appears to travel along a nerve-fibre in both directions with considerable velocity in the form of a wave. Helmholtz and Baxt have estimated the average rate of conduction in human motor nerves at 111 feet (nearly 29 metres) per second ; this result agreeing very closely with that previously obtained. It is probably rather under than over the average velocity. Eutherford's observations agree with those of Von Wittich, that the rate of transmis- sion in sensory nerves is about 140 feet (42 metres) per second. The velocity of the nerve impulse in motor nerves has been calculated by notic- ing the duration of the interval between two contractions of the same muscle when stimulated by means of two pairs of electrodes, one placed behind the nerve close to the muscle, and the second placed at a known distance further away from the muscle. The contraction ensues when the stimulus is applied further from the muscle later than the other case, and the interval between the two contractions is occupied by the passage of the impulse down the nerve. With these data it is concluded that the velocity of the passage of the nerve impulse in a frog's motor nerve is 28 to 30 metres per second. In the human motor nerve, cal- culated by applying the stimulus through the skin instead of directly to the nerve, the velocity is greater, viz., about 33 to 50 metres per second. In sensory nerves the velocity is said to be about 30 to 33 metres per second. Various conditions modify the rate of transmission, of which temperature is one of the most important, a very low or a very high temperature diminishing it ; fatigue of the nerve acting in the same direction, but increase of the stimulus up to a certain point increas' ing it, as does also the catelectrotonic condition of the nerve. Tlie Gerehro-Sjjinal Nervous System, — The parts of which this sys- tem is composed are the following: {a) the spinal cord and its nerves; (J) the brain made up of cerebrum, crura cerebri and the ganglia in con- nection with them, pons varolii, cerebellum, and the medulla oblongata or bulb which connects the upper parts of the system with the spinal cord, or medulla spinalis. All of these parts of the nervous system are nerve-centres, in con- tradistinction to nerve- trunks, and differ from the nerves in being made up of nerve-cells and their branchings as well as of nerve-fibres. There are THE NERVOUS SYSTEM. 533 other ganglia besides these, distributed elsewhere and not within the cranium and spinal column, but these are, for the sake of convenience, considered apart, under the head of the sympathetic system, as they present some differences to the more central ganglia. The cerebro-spinal centres then are distinguished from mere nerve- trunks by the possession of nerve-cells; these are, as we have seen in a former chapter (p. 96 et seq.), of different kinds; they very possibly differ in function. It is, however, to the possession of ganglion-cells that the increase of the functions of nerve-centres over that of nerve- trunks is credited. Before turning to the discussion of the functions of the spinal cord it will be as well to devote a little time therefore to the question of the functions of the nerve-centres in general. The ganglia of the sympathetic system also contain nerve-cells, but to these it is supposed a different use is to be assigned, and what is said as to the functions of nerve-ganglia in this place is only to be applied to those of the cerebro-spinal centres. Functions of Nerve-centres. Reflex action, — One of the chief functions o? nerve-cells appears to be the power of sending out impulses to the periphery along efferent nerves in response to impulses reaching them through afferent nerves. This power is sometimes called the conversion of an afferent into an efferent impulse. If may be supposed that an impulse j^assing to a nerve-cell may ]3roduce such a change in its metabolism that a discharge of energy ensues. This discharge is in some way passed down an efferent nerve as stimulus, and effects some change — motor, secretory, or nutri- tive, at the peripheral extremity of the latter — the difference in effect depending on the kind of peripheral-nerve termination. The reflex action may be limited in its effect, or it may be extensive. Reflex movements, oc- curring quite independently of sensation, are generally called excito-motor; those which are guided or acompanied by sensation, but not to the extent of a distinct perception, or intellectual process, are termed sensori-motor. {a) For the manifestation of every reflex action, these things are necessary: (1), one or more perfect afferent fibres, to convey an impres- sion; (2), a nervous centre for its reception, and by which it may be re- flected ; (3), one or more efferent nerve-fibres, along which the impres- sion may be conducted to (4) the muscular or other tissue by which the effect is manifested. In the absence of any one of these conditions, a proper reflex action cannot take jilace. {b) All reflex actions are essentially involuntai'i/, though most of them admit of being modified, controlled, or prevented by a voluntary effort. 534 HANDBOOK OF PHYSIOLOGY, (c) Eeflex actions performed in health have, for the most part, a dis- tinct purpose, and are adapted to secure some end desirable for the well- being of the body; but, in disease, many of them are irregular and purposeless. (d) Muscular contractions produced by reflex action are often more sustained than those produced by the direct stimulus of motor nerves, themselves. The irritation of a muscular organ, or its motor nerve, produces contraction lasting only so long as the irritation continues;, but irritation applied to a nervous centre through one of its centripetal nerves, may excite reflex and harmonious contractions, which last some time after the withdrawal of the stimulus. Relations hehveen the Stimulus and the Effect produced. — Certain rules showing the relation between the resulting reflex action and the stimulus- have been drawn up by Pflilger, as follows : — 1. Laiv of unilateral reflection. — A slight irritation of the surface supplied by certain sensory nerves is reflected along the motor nerves of the same region. Thus, if the skin of a frog's foot be tickled on the right side, the right leg is drawn up. 2. Law of symvi^trical reflection. — A stronger irritation is reflected, not only on one side, but also along the corresponding motor nerves of the opposite side. 3. Law of intensity. — In the above case, the contractions will be- more violent on the side irritated, but it must not be assumed that the effect is always in proportion to the strength of the stimulus. 4. Laiu of radiation. — If the irritation (afferent impulse) increases, it is reflected along other motor nerves till at length all the muscles of the body are thrown into action. In the simplest form of reflex action a single nerve-cell with an afferent and an efferent fibre may be supposed to be concerned, but in the majority of actual actions many cells are probably engaged, the stimu- lus being distributed, which act in concert or co-ordination. The reflex effect produced by a stimulus applied to a sensory surface depends, however, not only upon the strength of the stimulus, but also upon other circumstances, the most important of which is the condi- tion of the nerve-centre itself. Looking upon the effect produced as- the result of the discharge as it were of energy from the centre, it may be supposed that sometimes the centre is in a more explosive condition than at another ; this is shown for example in the case of a frog poisoned by strychnine, when the slightest stimulus applied to the skin will pro- duce the most violent and general tetanic spasms, while under ordinary circumstances the contraction of a few muscles only would result. We must also suppose that the centres are particularly sensitive to particu- lar kinds of stimuli, sometimes producing very extensive and violent THE NERVOUS SYSTEM. 535 muscular actions in response to a slight stimulus of a special kind. Such a condition is illustrated in the violent and general muscular spasms occurring when a small particle of food passes into the larynx, violent expiratory spasms accompanied by contractions of other muscles taking place. A nerve-centre must be considered as capable by its connections with efferent nerves of producing most extensive muscular movements, and when from any reason, either by the intensity of the afferent stimuli reaching it, or by the special nature, extent, or point of appli- cation of the afferent stimuli, or by special changes in its own metabol- ism brought about by poison or by some other mean's, a maximum dis- charge takes place, the resulting movements are most extensive. Under ordinary conditions, however, a slight stimulus produces, as above men- tioned, only a moderate discharge from the centre, the movement being to a certain extent co-extensive with the strength of the stimulus. The time taken in a reflex action has been found to be .066 to .058 second, but this is only a rough and arbitrary estimation. Automatism. — A second function which appears to be possessed by certain nerve-centres and not by others is that of automatic action or autom.atism. By this is meant that it is not dependent for its discharge upon any afferent stimuli, but that it is capable of sending out of itself efferent impulses of various kinds. The centre may be supjDosed to do this by the nature of its own metabolism, anabolism or building up of the explosive substance being followed by katabolism or its discharge. So that the centre sends out its impulses to muscles rhythmically. Such a power of nutomatism we have seen is attributed to the respiratory cen- tres in the bulb. Inhibition and Augmentation. — Not only may movements of muscles, discharge of secretion from gland-cells and the like be produced by afferent impulses reaching nerve-centres, but also inhibition of action which is already taking place. This is well seen in the matter of the inhibitory action of the vagus upon the cardiac contractions. The vagi convey to the heart impulses from the cardio-inhibitory centres which have a restraining action upon the contractions of the heart, as is seen by the increase in the frequency of the heart-beats when the vagi are divided; but we have seen that appropriate afferent stimuli, as, for example, when applied to the abdominal sympathetic, may increase the action of the centre to such an extent that the heart may be altogether stopped in diastole. In such a case the result of the afferent stimuli upon the centre has been to produce complete inhibition and not mus- cular contraction. This is not the only example of inhibition which might be instanced ; the action of almost any centre may be inhibited by impulses reaching it; indeed the effect of afferent impulses upon a 536 HANDBOOK OF PHYSIOLOGY. centre may be not only not to set it into activity, but to prevent or 8top an action already going on. On the other hand, the action of afferent impulses upon a nerve-centre may be to augment, render more of S/iitud Cora 1st DoAFai Vertebra. ^fSfunulCorA \ fC%< \ cranium and trunk of the body has been rpmov^H h^'^.^'^T"'. '^"l?"- ^he right half of the brain and .spinal eord have also beLremovT«,^i ^L^ vertical section: the membranes of the cranial, ancf of all spinal nerves rfffherTX^i'/^*'''' roots and first part of the fifth and ninth the wall of the skulfand on the several v?rt-hr^' ^^""^ dissected out and laid separately on the cranio-spinal cavity. (Af tir Bourglry ) ^PP^^'^e to the place of their natural exit from powerful or extensive, and increase in a certain direction an action already m course. Such may be well illustrated by the action of the THE NERVOUS SYSTEM. 537 vagi upon the respiratory centres to which attention has been drawn in the chapter ujion respiration. Membranes of the Brain and Spinal Cord. — The Brain and Spinal Cord are enveloped in three membranes — (1) the Dura Mater, (3) the Arachnoid, (3) the Pia Mater. (1) The Dura Mater, or external covering, is a tough membrane composed of bundles of connective-tissue wiiich cross at various angles, and in whose inter- stices branched connective-tissue corpuscles lie : it is lined by a thin elastic mem- brane, and on the inner surface and where it is not adherent to the bone, on the outer surface also is a layer of endothelial cells very similar to those found in serous membranes. (3.) The Arachnoid is a much more delicate mem- brane, very similar in structure to the dura mater, and lined on its outer or free surface by an endothelial membrane. (3. ) The Pia Mater consists of tw^o chief layers, between which numerous blood- vessels ramify. Between the arachnoid and pia mater is a netwoi-k of fibrous- tissue trabeculae sheathed with endothelial cells : these sub-arachnoid ti-abeculae divide up the sub arachnoid space into a number of irregular sinuses. There are some similar trabeculae, but much fewer in number, traversing the sub-dural space, i.e., the space between the dura mater and arachnoid. Pacchionian bodies are growths from the sub-arachnoid network of connec- tive-tissue trabeculje which project through small holes in the inner layers of the dura mater into the venous sinuses of that membrane. The venous sinuses of the dura mater liave been injected from the sub-arachnoidal space through the intermediation of these villous outgrowths. The Spinal Cord and its Nerves. Tlie Spinal cord is a cyliudriform column of nerve-substance con- nected above with the brain through the medium of the bulb, and ter- minating below, about the lower border of the first lumbar vertebra, in a slender filament of gray substance, the Jihini terminale, which lies in the midst of the roots of many nerves forming the cauda equina. Structure. — The cord is composed of white and gray nervous sub- stance, of which the former is situated externally, and constitutes its chief portion, while the latter occupies its central or axial portion, and is so arranged, that on the surface of a transverse section of the cord it appears like two somewhat crescentic masses connected together by a narrower portion or isthmus (fig. 350). Passing through the centre of this isthmus in a longitudinal direction is a minute canal (central canal), Avhich is continued through the whole length of the cord, and opens above into the space at the back of medulla oblongata and pons Varolii, called the fourth ventricle. It is lined by a layer of columnar ciliated epithelium. The spinal cord consists of two exactly symmetrical halves, separated anteriorly and posteriorly by vertical ^'6\s?, their decussation; c, e, olivary bodies; d, d, restiform bodies; e, arciform fibres; /, fibres passing from the auterior column of the cord to the cerebellum ; gr, anterior col- umn of the spinal cord; h, lateral column; p, pons Varolii; i, its upper fibres; 5, 5, roots of the fifth pair of nerves. Fig. 359. — Dorsal or posterior surface of the pons Varolii, corpora quadrigemina, and me- dulla oblongata. The peduncles of the cerebellum are cut short at the side, a, o, the upper pair of corpora quadrigemina ; 6, 6, the lower ; /, /, superior peduncles of the cerebellum ; c, eminence connected with the nucleus of the hypoglossal nerve; e, that of the glosso-pharyngeal nerve; i, that of the vagus nerve; d, d, restiform bodies; p, p, posterior pyramids; i\ v, groove in the middle of the fourth ventricle, ending below in the calamus scriptorius ; 7, 7, roots of the auditory nerves. postero-median and postero-external columns are also represented at the posterior or dorsal aspect of the cord as the fasciculus gracilis and the fasciculus cuneatus. The posterior pyramids of the medulla which in- clude these two columns of white matter soon become much increased in width by the addition of a new column of white matter outside the other two which is known as the fasciculus of Rolando. The lateral col- umns of the cord undergo considerable change and are scarcely repre- sented as such in the bulb. It may be said then that the bulb at its commencement differs only slightly in size from the cord with which it is continuous. It soon 564 HANDBOOK OF THYSIOLOGY. becomes larger both laterally and antero-posteriorly, and after a tinie opens out on the dorsal surface into a space which is known as the fourth ventricle, and from being a cylinder with a central canal, it is flattened out on one surface by the gradual approach of the central canal to that Jin Fig 360 —Dorsal or posterior view of the medulla, fourth ventricle, and mesencephalon (natural size), v-i^--, line of the posterior roots of the spinal nerves; p.m./., posterior median fissure- /.o., funiculus gracilis; cl., its clava; /.c, funiculus cuneatus; f.R., funiculus of Rolando- r b , restiform body; c.s., calamus scriptorius: Z, section of ligula or tajnia; part of choroid plexus is seen beneath it; /.r. , lateral recess of the ventricle; str., striae acusticae; t./. , inferior fossa- s f , posterior fossa; between it and the median sulcus is the fasciculus teres; cbl cut surface of the cerebellar hemisphere; nd., central or gray matter; s.m.v., superior medullary velum ; Ing., ligula; s.c.p., superior cerebellar peduncle cut longitudinally; «-., combined section of the three cerebellar peduncles ; f.o.s. , c.q.L, corpora quadrigemina (su- perior and inferior) ; fr. , f rsenulum ; /. , fibres of the fillet seen on the surface of the tegmen- tum- c, crusti; l.g.. lateral groove; c.g.i., corpus geniculum internus; th., posterior part of thalamus; p., pineal body. The Roman numbers indicate the corresponding cranial nerves. (E. A. Schafer.) surface. The central canal of the cord, therefore, is directly continuous with the fourth ventricle. If the bulb be examined on its anterior or ventral surface it is found that the anterior fissure, which is a continuation of the same fissure in the cord, is occupied at the most posterior part by fibres which are crossing from one side to the other; the central canal being pushed now toward the posterior surface. This is what is known as the anterior decussation of the medulla oblongata. It is formed of the fibres which in the cord occupy the postero-lateral region and are called the crossed pyramidal fibres. The lateral pyramidal fibres of either side after cross- ing in the middle line in this way become part of the anterior pyramid THE ISTEKVOUS SYSTEM. 565 of the opposite side; the rest of the pyramid being made up of the fibres from the anterior column of the cord known as the direct or uncrossed pyramidal fibres. These two pyramidal strands of fibres are those which degenerate on lesions of certain parts of the cerebrum which are known as the motor areas of the cortex. They can therefore be traced downward on such lesions as tracts of degeneration. They are the fibres of commu- nication between the cerebral cortex and the different segments of the spinal cord. The anterior pyramids of the bulb are marked out by the exit from that part of the nervous axis to the outside of them, of a nerve, the 12th or hypoglossal. More laterally than this nerve, there soon becomes very prominent on either side a rounded elevation or col- umn which is known as the olivary body. It is not seen at the begin- ning of the bulb at its junction with the cord, bat begins at a lower level than the opening of the fourth ventricle. On the further side of the olivary body is seen the line of origin of fibres of the 11th, 10th, and 9th nerves, and from this to the posterior fissure is the posterior pyramid. The whole of that part of the medulla which is situated laterally between the olivary body and the posterior fissure is known as the resti- form body; it is continued forward on either side as the inferior peduncle of the cerebellum. The changes which are noticed by the study of series of sections of the bulb from below upward may be summarized thus: In the dorsal or posterior region, the posterior cornua are pushed more to each side, and the substance of Rolando is increased and becomes rounded, reaching almost to the surface of the bulb on each side, a small tract of longitu- dinal fibres of the ascending root of the 5th nerve only intervening. There is a great increase of the reticular formation around the central canal, and the lateral approaches the anterior cornu. Then at the ven- tral or anterior aspect the decussation of the lateral fibres begins. By this crossing over of the fibres, the tip of the gray anterior cornu is cut off from the rest of the gray matter. The central canal is pushed further toward the posterior surface, first of all by the decussation of the anterior pyramids just mentioned, and later on, i.e., above, by another decussa- tion of fibres more dorsal. These fibres of the second decussation as they cross form a median raphe and also help to break up the remaining gray matter into what is called a reticular formation. There has been some little doubt as to the origin of these descussating fibres, but the best authorities now consider them to be, at any rate in part, the fibres from the nuclei of the fasciculus gracilis and fasciculus cuneatus of either side, and look upon tliem as a sensory decussation. At the pos- terior part soon there appear in the columns of white matter of the fasciculus gracilis and fasciculus cuneatus new masses of gray matter. The lateral horn approaches the anterior ; but soon the latter is pushed 566 HANDBOOK OF PHYSIOLOGY. further and further toward the centre, while the lateral horn remains near the lateral surface. The anterior gray m.atter becomes broken up and merged into the reticular formation. There is also a similar reticu- lar 'formation both toward the centre and also laterally in the dorsal region. At the level where the central canal opens into the 4th ventri- cle, the posterior pyramids diverging to form the lower and outside boundaries, and inclosing a space, the calamus scriptorius, between them, there are to be made out various masses of gray matter in addi- tion to the reticular formation, viz., the nuclei of the fasciculus gracilis '/• ¥ '"i9 U Fig. 361.— Anterior or dorsal section of the medulla oblongata in the region of the superior pyramidal decussation. «.»»./., anterior median fissure; /.a., superficial arciform fibres emerging from the fissure; py. , V)yramid; n.ar., nuclei of arciform fibres; /.a., deep arciform becoming superficial; o, lower end of olivary nucleus; n.l., nucleus lateralis; /. r., formatio reticularis; f.a."^, arciform fibres proceeding from the formatio reticularis; t/. , substantia ge- latinosa of Rolando; a. T^ , ascending root of fifth nerve; 71. c, nucleus cuneatus; n. c. ', external cuneate nucleus ; n.g., nucleus gracilis; /.fir., funiculus gracilis; p.m.f., posterior median fis- sure; c.c. , central canal surrounded by gray matter, in which are n.XL, nucleus of the spinal accessory, and n.XIL, nucleus of the hypoglossal; s.d., superior pyramidal decussation. (Modified from Schwalbe. ) and fasciculus cuneatus (361, n.g. and n.c), which are at this level, however, already diminishing and are lost at a level of the pons Varolii. The olivary bodies extend forward almost to the level of the pons. They consist of gray and white matter. The gray matter consists of a plicated thinnish strand containing small nerve-cells, folded upon itself in the form of a loop, with the ends turned inward and slightly dorsal (Fig. 362, o) . The gray loop is filled with and covered by white matter, part of the fibres passing through the gray. Internal to the olivary body on either side are two small masses of gray matter, one more ventral to the other, called accessory olives, ex- ternal and internal, and on the surface of the anterior pyramid on either THE NERVOUS SYSTEM. 56^ side a small mass of gra}' matter, external arcuate nucleus; laterally another mass of the same material, the representative of the lateral nu- cleus of the cord, is seen, viz., the antero-lateral nucleus, which gives origin to the spinal accessory nerve. It will be necessary to follow as shortly as possible the fibres of the spinal cord upward into the bulb and beyond: — The crossed and direct pyramidal tracts have already been described. Nothing definite is known of the antero-lateral descending tracts. The cerebellar tracts pass laterally into the restiform bodies and go to the nX- Fig. 362.— Section of the meduHa oblongata at about the middle of the olivary body, f.l.a., anterior median fissure; n.ar., nucleus arciformis; p., pyramid; XII., bundle of hypoglossal nerve emerging from the surface; at 6, it is seen coursing between the pyramid and the olivary nucleus, o. ; /.a. e. , external arciform fibres; n.l., nucleus lateralis; a., arciform fibres passing toward restiform body, partly through the substantia gelatinosa, g., partly superficial to the ascending root of the fifth nerve, a, V. ; X, bundle of vagus root emerging; /.?-., formatio retic- ularis; c.r., corpus restiform, beginning to be formed, chiefly by arciform fibres, superficial and deep; n.c, nucleus cuneatus; n.g., nucleus gracilis ; (, attachment of the ligula; /.s., funi- culus solitarius ; n. X. , n. X. ', two parts of the vagus nucleus ; n. XII. , hypoglossal nucleus ; n. t. , nucleus of the funiculus teres; n.am., nucleus ambiguus; ?-. , raphe; A., continuation of the anterior column of cord; o', o", accessory olivary nucleus; p.o., pedunculus olivae. (Modified from Schwalbe.) cerebellum. The antero-lateral ascending tracts appear to have the same destination and pass directly or indirectly into the cerebellum. The fibres of the postero-median and postero-external columns end in the nuclei of the fasciculus gracilis and cuneatus respectively, either in or about the cells contained in those nuclei ; at any rate, ascending de- generation of these columns cannot be traced above these nuclei. The rest of the fibres of the cord appear to end in the reticular for- mation of the bulb. The bundle of fibres constituting the ascending root of the 5th nerve appears to correspond with the tract of Lissauer. Connectio7is of the bulb with the cerebrum and cerebellum. — In addition 568 HANDBOOK OF PHYSIOLOGY. to the pyramidal tracts connecting the bulb with the cerebrum and" the direct cerebellar and the antero-lateral ascending tract connecting it with the cerebellum, there are other connections of the bulb with the cerebrum, and with the cerebellum, not actually direct. (1.) Fibres from the nucleus gracilis and nucleus cuneatus, which, as we have said, are the bulbar endings of the fibres of the postero- median and postero-external columns of the cord, pass in sets as it were in the following m.anner : — (a.) Internal arcuate fibres. — Some pass down and inward to the other side in the reticular formation, forming in part the superior or sensory decussation, and in the inter-olivary region become longitudinal in a band of fibres called the fillet, which passes upward. These fibres are probably augmented by the addition of fibres from the anterior columns of the cord. (b.) External arcuate fibres also decussate in the same way, pass down along the anterior fissure, and then running outward superficially over the anterior pyramid and olivary body, reach the restiform body and pass to the side of the cerebellum opposite to their nuclei of origin. These fibres appear to have some relation with the external arcuate nu- clei. They connect one side of the spinal cord with the opposite side of the cerebellum through the gracile and cuneate nuclei. (6'.) Direct lateral fibres pass to the restiform body and so to the same side of the cerebellum. (2.) Fibres from the olivary body pass to the opposite side of the cerebellum probably through the reticular formation. (3.) Arciform fibres. — Fibres from the nucleus of the 8th or auditory nerve in the floor of the 4tli ventricle, pass to the same side of the cere- bellum. Functions of the Medulla Oblongata ok Bulb, The functions of the bulb are those of, {a.) conduction; (i.) reflex action; and (c.) automatism. («.) Conduction. — x\s a conductor of impressions, the medulla oblon- gata has a wider extent of function than any other part of the nervous system, since it is obvious that all impressions passing to and fro be- tween the brain and the spinal cord must be transmitted through it. {b.) Reflex Action. — As a nerve centre by which impressions are reflected, the medulla oblongata also resembles the spinal cord ; the only difference between them consisting of the fact that many of the reflex actions performed by the former are much more complicated than any performed by the spinal cord. It has been proved by repeated experiments on the lower animals that the entire brain may be gradually cut away in successive portions, THE ]S"ERVOUS SYSTEM. 569 and yet life may continue for a considerable time, and the respiratory movements be uninterrupted. Life may also continue when the spinal cord is cut away in successive portions from below upward as high as the point of origin of the phrenic nerve. In amphibia, the brain has been all removed from above, and the cord, as far as the medulla oblon- gata, from below; and so long as the medulla oblongata was intact, respiration and life were maintained. But if, in any animal, the me- dulla oblongata is wounded, particularly if it is wounded in its central part, opposite the origin of the vasi, the respiratory movements cease, and the animal dies asphyxiated. And this effect ensues even when all parts of the nervous system, except the medulla oblongata, are left intact. Injury and disease in men prove the same as these experiments on animals. Numerous instances are recorded in Avhich injury to the me- dulla oblongata has produced instantaneous death; and, indeed, it is through injury of it, or of the part of the cord connecting it with the origin of the phrenic nerve, that death is commonly produced in frac- tures attended by sudden displacement of the upper cervical vertebrae. Special Centres. In the medulla are contained a considerable number of centres which preside over many important and complicated co-ordinated movements of muscles. Tl\« majority of these centres are («.) reflex centres simply, which are stimulated by afferent or by voluntary impressions. Some of them are {b.) automatic centres^ being capable of sending out efferent impulses, generally rhythmical, without previous stimulation by afferent or by voluntary imprevssions. The automatic centres are, however, gen- erally influenced by reflex or by voluntary impulses. Some again of the centres, whether reflex or automatic, are (c.) control centres, by which subsidiary spinal centres are governed. Finally the action of some of the centres is {(I.) tonic, i.e., they exercise their influence either directly or through another apparatus, continuously and uninterruptedly in main- taining a regular action. Simple Reflex centres. (1.) Bilateral centres for the co-ordinated movements of Mastication^ the afferent and efferent nerves of which have been already enumerated (p. 291.) (2.) Bilateral centres for the movements of Deglutition. The medulla oblongata appears to contain the centre whence are derived the motor impulses enabling the muscles of the palate, pharynx, and oesophagus to produce the successive co-ordinate and adapted movements necessary to the act of deglutition (p. 310), This is proved by the persistence of swallowing in some of the lower animals after destruction of the cerebral 570 HANDBOOK OF PHYSIOLOGY. hemispheres and cerebelhim; its existence in anencephalous monsters; the power of swallowing possessed by the marsupial embryo before the brain is developed; and by the complete arrest of the power of swallow- ing when the medulla oblongata is injured in experiments. (3.) Bilateral centres for the combined muscular movements of Sucking, the motor nerves concerned being the facial for the lips and mouth, the hypoglossal for the tongue, and the inferior maxillary divi- sion of the 5tli for the muscles of the jaw. (4:.) Bilateral centres for the Secretion of Saliva, which have been already mentioned (p. 298.) (5.) Bilateral centres for Vomiting (p. 326). (6.) Bilateral centres for Coughijig, which are said to be independent of the respiratory centre, being situated above the inspiratory part of that centre. (7.) Bilateral centres for Sneezing, connected no doubt with the resi^iratory centre. (8.) Bilateral centres for the Dilatation of the pupil, the fibres from which pass out partly in the third nerve and partly through the spinal cord (through the last two cervical and two upper dorsal nerves) into the cervical sympathetic. (b.) Automatic centres. (1.) Resjnratory centres. — The action of the respiratory centre has been already discussed. It is only necessary to i-epeat here that although it can be influenced by afferent impulses, it is also automatic in its action, being capable of direct stimulation, as by the condition of the blood circulating within it. It is also bilateral. It probably consists of an inspiratory part and of an expiratory part. The centre is capable of being influenced both reflexly and to a certain extent also by voluntary impulses. The vagus influence is j)robably constant in the direction of stimulating the inspiratory portion of the centre, whereas the influence of the superior laryngeal is not always in action, and is inhibitory. (2.) Cardio-Inliibitory centres. The action of these centre in main- taining the proper rhythm of the heart through the vagus fibres, which terminate in a local intrinsic mechanism, has been already discussed. The centre can be directly stimulated, as by the condition of the blood circulating within it, and also indirectly by afferent stimuli, especially by stimulating the abdominal sympathetic nerves, but also by stimulat- ing any sensory nerve, including the vagus itself. (3.) ^cceZem^or centres for the heart. The centres from which arise the accelerator fibres of the heart, in the medulla. They are automatic but not tonic in action. (4.) Vaso-motor centres, which control the unstriped muscle of the arteries, are also situated in the medulla. Like the respiratory centre, THE NERVOUS SYSTEM. 571 they are bilateral. As has already been pointed out, these centres may be directly or reflexly stimulated, as well as by impressions conveyed downward from the cerebrum to the medulla. The condition of the blood circulating in them is the direct stimulus. Its influence is no doubt a tonic or else a rhythmic one. It is also supposed that there is in the medulla a special vaso-dilator centre not acting tonically, stimu- lation of which produces vascular dilatation. The diabetic centre is probably a part of the vaso-motor centre, at any rate stimulation of it causes dilatation of the vessels of the liver. (5.) Bilateral chief centres for the secretion of Sweat exist in the medulla. The centres on either side control the subsidiary spinal sweat centres. They may be excited unequally so as to produce unilateral sweating. They are probably automatic and reflex. (6.) Bilateral Spasm centres are said to be present in the medulla, on the stimulation of which, as by suddenly produced excessive venosity of the blood, general spasms of the muscles of the body are produced. {c.) Control centres. These are centres whose influence may be directed to controlling the action of subsidiary centres. They are — (1.) The Respiratory centres, which probably control the action of other subordinate centres in the spinal cord. (2.) The Cardio-Inhibitory centres, which act upon a local ganglionic mechanism in the heart. (3.) The Accelerator centres, if they exist, probably act through a local mechanism in the heart. (4.) The Vaso-motor centres control spinal as well as local tonic centres. (5.) The medullary Sweat centres control the spinal sweat centres. {d.) Tonic centres. Of the centres whose action is tonic or con- tinuous up to a certain degree, may be cited the vaso-motor and the car- dio-inhibitory . It should not be forgotten that in the medulla are the centres for the special senses. Hearing and Taste, and that other special centres are supposed to be localized there, of which may be mentioned one, the hypothetical Inhibitory heat centre, which controls the production of heat by the tissues, independently of the vaso-motor centre. The Cranial Nerves. The cranial nerves consist of twelve pairs; they appear to arise (su- perficial origin) from the base of the brain in a double series, which extends from the under surface of the anterior jiart of the cerebrum to the lower end of the medulla oblongata. Traced into the substance of the brain and medulla, the roots of the nerves are found to take origin from various masses of gray matter. 572 HANDBOOK OF PHYSIOLOGY. The roots of the first or olfactory and of the second or optic nerves will be mentioned elsewhere. The third and fourth nerves arise from gray matter beneath the corpora quadrigemina; and the roots of origin of the remainder of the cranial nerves can be traced to gray matter in the floor of the fourth ventricle, and in the more central jiart of the medulla, around its central canal, as low down as the decussation of the pyramids. According to their several functions the cranial nerves may be thus arranged : — • a. Nerves of special sense b. Nerves of common sensation c. Nerves of motion d. Mixed nerves Olfactory, Optic, Auditory, part of the Glosso- pharyngeal, and part of the Fifth. The greater portion of the Fifth. Third, Fourth, lesser division of the Fifth, Sixth, Facial, and Hypoglossal. Glosso- pharyngeal. Vagus, and Spinal accessory. The physiology of the First, Second, and Eighth will be considered with the organs of Special sense. The Ilird Nerve {Motor Oculi). Origin. — The third nerve arises in three distinct bands of fibres from the gray matter surrounding the aqueduct of Sylvius near the middle line ventral to the canal. The nucleus of origin consists of large multi- Fig. 363.— Section through anterior corpus quadrigeminum and part of optic thalamus, s., Aqueduct of Sylvius ; gr. , gray matter of the aqueduct ; c. q. s. , quadrigeminal eminence ; I. , stratum lemnisci; o. , stratum opticum ; c. , stratum cinereum; Th., pulvinate of optic thala- mus; c.g.e., c.g.i., lateral and median corpora geniculata; br.s., br.i., superior and inferior brachia;/., fillet; p. i., posterior longitudinal bundle: r., raphe; III., third nerve, and ?i. 7/7., its nucleus; I. p. p., posterior perforated space; s.n., substantia nigra, above this is the tegmen- tum with the circular area of the red nucleus; cr., crusta; 77., optic tract; M. , medullary centre of hemisphere ; n.c, nucleus caudatus; st., stria terminalis. (After Quain, from Meynert.) polar ganglion-cells, and extends to the back part of the third ventricle as far as the level of the anterior corpus quadrigeminum. The fibres pass from their origin partly through the red nucleus to their superficial THE NERVOUS SYSTEM, 573 origin iu front of the pons, at the median side of each crus. They de- cussate with their fellows in the middle raphe. The nerve is connected with the optic nerve. Function. — It supplies the levator palpebrae superioris muscle, and all of the muscles of the eyeball, excejDt the superior' oblique to which Fig. 364. —Diagram of a longitudinal section through the pons, showing the relation of the nuclei for the ocular muscles. CQ, corpora quadrigemina; 3, third nerve; iii, its nucleus; 4, fourth nerve; iv, its nucleus, the posterior part of the third; 6, sixth nerve. The probable position of the centre and nerve fibres for accommodation is shown at a and o', for the reflex action of iris, at 6, and 6' ; for the external rectus muscles, at c, c'. The lines beneath the floor of the fourth ventricle indicate fibres, which connect the nuclei. (Gowers.) the fourth nerve is appropriated, and the rectus externus which receives the sixth nerve. Through the medium of the ophthalmic or lenticular ganglion, of which it forms what is called the short root, it also supj^lies motor filaments to the iris and ciliary muscle. The fibres which sub- serve the three functions, accommodation, contraction of the pupil, and nerve-supply to the external ocular muscles, arise from three distinct groups of cells. When the third nerve is irritated within the skull, all those muscles to which it is distributed are convulsed. When it is paralijzed or divided the following effects ensue: — (1) the up23er eyelid can be no longer raised by the levator palpebral, but droops (ptosis) and remains gently clos^l over the eye, under the unbalanced influence of the orbicularis palpebrarum, which is supplied by the facial nerve : (2) the eye is turned outward and downward (external strahismus) by the unbalanced action of the rectus externus and superior oblique to which the sixth nerve is appropriated; and hence, from the irregularity of the axes of the eyes, double sight, diplopia, is often experienced when a single object is within view of both the eyes: (3) the eye cannot be moved either upward, down- ivard, or inward: (4) the pupil I)ecomes dilated (mydriasis): (5) the eye cannot accommodate for short distances. The IVth Nerve (Trochlearis) . Or if/ in. — The IVth nerve arises from a nucleus consisting of large multipolar ganglion cells situated below, i.e., ventral to the aqueductus of Sylvius, which extends from the back part of the nucleus of the third nerve to the hind level of the posterior corpus quadrigeminum. The fibres from either side sweep round the central gray matter, and 574 HANDBOOK OF PHYSIOLOGY. reach the valve of Vieusseus, where they decussate in the middle line and appear at the front of the pons at the lateral edge of the crus. The Fig. 365. —Fourth ventricle with the medulla oblongata and the corpora quadrigemina. The reman numbers indicate superficial origins of the cranial nerves, while the otlier numbers in- dicate their deep origins, or the position of their central nuclei. 8, 8', 8", 8'", auditory nuclei nerves; t, funiculus teres; A., B, corpora quadrigemina ; eg, corpus geniculatum; p, c, pedun- culus cerebri ; m, c, p, middle cerebellar peduncle ; s, c, p, superior cerebellar peduncle ; i, c, p, inferior cerebellar peduncle; /, c, locus caeruleus; e, t, eminentia teres; o, c, ala cinerea; a, n, accessory nucleus; o, obex; c, clava; /, c, funiculus cuneatus; /, g, funiculus gracilis. nucleus of the fourth nerve on either side is connected with those of the third and sixth nerves. Functions. — The IV th nerve is exclusivel}^ motor, and supj)lies only the trochlearis or obliquus superior muscle of the eyeball. The Vth Nerve (Trigeminus). Origin. — The Vth or Trigeminal nerve resembles, as already stated, the spinal nerves, in that its branches are derived through two roots; namely, the larger or sensory, in connection with which is the Gasserian ganglion, and the smaller or motor root which has no ganglion, and which passes under the ganglion of the sensory root to join the third branch or division which ensues from it. The fibres of origin of the fifth nerve come from the floor of the fourth ventricle. The motor root to the inside of the sensory, about the middle of each lateral half. The sensory fibres, however, can be traced down in the medulla oblongata as far as the upper part of the cord. From the motor nucleus there stretches forward as far as the anterior corpus quadrigeminum a bundle of long fibres termed the descending root, which has attached to it sparse spheroidal nerve-cells. It is also connected with the locus caeruleus. The sensory nucleus outside the motor has connected with it a tract of THE NERVOUS SYSTEM. 575 fibres from the cord as low as the second cervical nerve, and this forms a tract at the tip of the posterior cornu, between it and the restiform body. No nerve cells are connected with it. The roots can be traced obliquely through the pons Varolii, beneath the floor of the front part of the fourth ventricle. The motor root is in a position median to sensory. The nerve appears at the ventral surface of .the pons near its front edge, at some distance from the middle line. Function. — The first and second divisions of the nerve, which arise wholly from the larger root, are purely sensory. The third division being joined, as before said, by the motor root of the nerve, is of course •both motor and sensory. (a.) Motor. — Through branches of the lesser or non-ganglionic j)or- tion of the fifth, the muscles of mastication, namely, the temporal, mas- seter, two pterygoid, anterior part of the digastric, and mylohyoid, derive their motor nerves. Filaments are also supplied to the tensor tynipani and tensor palati. The motor function of these branches is proved by the violent contraction of all the muscles of mastication in experimental irritation of the third or inferior maxillary division of the nerve; by paralysis of the same muscle, when it is divided or disorgan- nvm Fig:. 366. —Section across the pons, about tlie middle of the fourth ventricle, pxj. , pyramidal bundles; po., transverse fibres passing jjOj, behind, andpoj, in front ot py. ; r., raphe; o.s., su- perior olive; a. I'., bundles of ascending root of V. nerve inclosed in a prolongation of the sub- stance of Rolando; F/. , the sixth nerve, nVL, its nucleus; VII., facial nerve; VII. a., in- termediate portion, n.VII, itsnuclevis; VIII., auditory nerve, nVIIL, lateral nucleus of the auditory. (After Quain.) ized, or from any reason deprived of power; and by the retention of the power of these muscles, when all those supplied by the facial nerve lose their power through paralysis of that nerve. The last instance proves best, that though the buccinator muscle gives passage to, and receives )76 HANDBOOK OF PIIYSIOLOGT. some filaments from, a buccal branch of the inferior division of the fifth nerve, yet it derives its motor power from the facial, for it is paralyzed together with the other muscles that are supplied by the facial, but retains its power when the other muscles of mastication are paralyzed. Whether, however, the branch of the fifth nerve which is supplied to the buccinator muscle is entirely sensory, or in j)art motor also, must remain for the present doubtful. From the fact that this muscle, be- sides its other functions, acts in concert or harmony with the muscles of Fig. 367. — Greneral plan of the branches of the fifth pair. J^.— 1, lesser root of the fifth pair; 2, greater root passing forward into the Gasserian ganglion; 3, placed on the bone above the ophthalmic nerve, which is seen dividing into the supra-orbital, lachrymal, and nasal branches, the latter connected with the ophthalmic ganglion ; 4, placed on the bone close to the foramen rotundum, marks tlic sujifiidr maxillary division, which is connected below with the spheno-palatine ganglion, and passes forward to the infra-orbital foramen; 5, placed on the bone over the foramen ovale, marks tlie inferior maxillary nerve, giving off the anterior auricular and muscular branches, and continued by the inferior dental to tlie lower jaw, and by the gus- tatory to the tongue; a, the submaxillary gland, the sulimaxillary ganglion placed above it in connection with the gustatory nerve; 6, the chorda tympaui ; 7, the facial nerve issuing from the stylomastoid foramen. (Charles Bell.) mastication, in keeping the food between the teeth, it might be sup- posed from analogy, that it would have a motor branch from the same nerve that supplies them. There can be no doubt, however, that the so-called buccal branch of the fifth is, in the main, sensory ; although it is not quite certain that it does not give a few motor filaments to the buccinator muscle. (b.) Sensory. — Through the branches of the greater or ganglionic portion of the fifth nerve, all the anterior and antero-lateral parts of the THE NERVOUS SYSTEM. 577 face and head, with the exception of the skin of the parotid region (which derives branches from the cervical spinal nerves) , acquire com- mon sensibility; and among these parts may be included the organs of special sense, from which common sensations are conveyed through the fifth nerve, and their special sensations through their several nerves of special sense. The muscles, also, of the face and lower jaw acquire muscular sensibility, through the filaments of the ganglionic portion of the fifth nerve distributed to them with their proper motor nerves. The sensory function of the branches of the greater division of the fifth nerve^ is proved, by all the usual evidences, such as their distribution in parts that are sensitive and not capable of muscular contraction, the exceeding sensibility of some of these parts, their loss of sensation when the nerve is paralyzed or divided, the pain without convulsions produced by mor- bid or experimental irritation of the trunk or branches of the nerve, and the analogy of this portion of the fifth to the posterior root of the spinal nerve. Other Functions. — In relation to muscular movements, the branches of the greater or ganglionic portion of the fifth nerve exercise a mani- fold influence on the movements of the muscles of the head and face and other parts in which they are distributed. They do so, in the first place (a), by providing the muscles themselves with that sensibility without which the mind, being unconscious of their position and state, cannot voluntarily exercise them. It is, probably, for conferring this sensibility on the muscles, that the branches of the fifth nerve commu- nicate so frequently with those of the facial and hypoglossal, and the nerves of the muscles of the eye; and it is because of the loss of this sensibility that when the fifth nerve is divided, animals are always slow and awkward in the movement of the muscles of the face and head, or hold them still, or guide their movements by the sight of the objects toward which they wish to move. (b.) Again, the fifth nerve has an indirect influence on the muscular movements, by conveying sensations of the state and position of the skin and other parts: which the mind perceiving, is enabled to determine appropriate acts. Thus, when the fifth nerve or the infra-orbital branch is divided, the movement of the lips in feeding may cease, or be imper- fect. (c.) An intimate connection with muscular movements through the many reflex acts of muscles of which it is the necessary excitant. Hence, when it is divided and can no longer convey impressions to the nervous centres to be thence reflected, the irritation of the conjunctiva produces no closure of the eye, the mechanical irritation of the nose excites no sneezing. (d.) Through its ciliary branches and the branch which forms the 37 578 HANDBOOK OF PHYSIOLOGY. long root of the ciliary or ophthalmic ganglion, it exercises also some influence on the movements of the iris. When the trunk of the oph- thalmic portion is divided, the pupil becomes, according to Valentin, contracted in men and rabbits, and dilated in cats and dogs; but in all cases, becomes immovable even under all the varieties of the stimulus of light. How the fifth nerve thus affects the iris is unexplained ; it has been ingeniously suggested the influence of the fifth nerve on the move- ments of the iris may be ascribed to the affection of vision in consequence of the disturbed circulation or nutrition in the retina, when the normal influence of the fifth nerve is disturbed. In such disturbance, increased •circulation making the retina more irritable might induce extreme con- traction of the iris. Trophic influence. — The morbid effects which division of the fifth nerve produces in the organs of special sense, make it probable that, in the normal state, the fifth nerve exercises some special or troi)liic influ- ence on the nutrition of all these organs; although, in part, the effect of the section of the nerve is only indirectly destructive by abolishing sensation, and therefore the natural safeguard which leads to the pro- tection of parts from external injury. Thus, after such division, within a period varying from twenty-four hours to a week, the cornea begins to be opaque; then it grows completely white; a low destructive inflamma- tory process ensues in the conjunctiva, sclerotica, and interior parts of the eye; and within one or a few weeks, the whole eye may be quite disorganized, and the cornea may slough or be penetrated by a large ulcer. The sense of smell (and not merely that of mechanical irritation of the nose), may be at the same time lost or gravely impaired ; so may the hearing, and commonly, whenever the fifth nerve is paralyzed, the tongue loses the sense of taste in its anterior and lateral parts, and ac- cording to Gowers in the posterior part as well. In relation to Taste. — The loss of tactile sensibility as well as the sense of taste, is no doubt due {a) to the lingual branch of the fifth nerve being a nerve of tactile sense, and also because with it runs the chorda tympani, which is one of the nerves of taste; partly, also, it is due {h), to the fact that this branch supplies, in the anterior and lateral parts of the tongue, a necessary condition for the proper nutrition of that part; while {c), it forms also one chief link in the nervous circle for reflex action, in the secretion of saliva. But, deferring this question until the glosso-pharyngeal nerve is to be considered, it may be observed that in some brief time after complete paralysis or division of the fifth nerve, the power of all the organs of the special senses may be lost ; they may lose not merely their sensibility to common impressions, for which they all depend directly on the fifth nerve, but also their sensibility to their several peculiar impressions for the reception and conduction of which THE NERVOUS SYSTEM. 579 they are purposely constructed and supplied with special nerves besides the fifth. The facts observed in these cases can, perhaps, be only ex- plained by the influence which the fifth nerve exercises on the nutritive processes in the organs of the special senses. It is not unreasonable to believe, that, in paralysis of the fifth nerve, their tissues may be the seats of such changes as are seen in the laxity, the vascular congestion, oedema, and other affections of the skin of the face and other tegumen- tary parts which also accompany the paralysis; and that these changes, which may appear unimportant when they affect external parts, are suflBcient to destroy that refinement of structure by which the organs of the special senses are adapted to their functions. The VI th Nerve {AMucens). Origin. — The Vlth nerve arises from a compact oval nucleus, situ- ated somewhat deeply at the back part of the pons near the middle of the floor of the fourth ventricle. The eminentia teres marks its posi- tion. It contains moderately large nerve-cells with distinct axis cylin- der processes. It is connected (fig. 3G4) with the nuclei of the third, fourth, and seventh nerves. It is nearer the middle line than the nuclei of the fifth and seventh. The root is thin, and passes ventrally and laterally through the reticular formation, to the surface, which it reaches at the hind end of the pons opposite the front end of anterior pyramid. Functions. — The sixth nerve is exclusively motor, and supplies only the rectus externus muscle of the eye. The rectus externus is convulsed, and the eye is turned outward, when the sixth nerve is irritated; and the muscle is paralyzed when the nerve is divided. In all such cases of paralysis, the eye squints inward, and cannot be moved outward. In its course through the cavernous sinus, the sixth nerve forms larger communications with the sympathetic nerve than any other nerve within the cavity of the skull does. But the imjDort of these communi- cations with the sympathetic, and the subsequent distribution of its filaments after joining the sixth nerve, are quite unknown. The Vllth Nerve {Facial). Origin. — The faciat, or portio dura of the seventh pair of nerves, arises from the floor of the central part of the fourth ventricle behind and in line with the motor nucleus of the fifth, to the outside of and deeper down than the nucleus of the sixth. The nucleus is narrower in front than behind, and consists of large cells with well marked axis cylinder-processes, which are gathered up at the dorsal surface of the nucleus to form a root. The root describes a loop round the nucleus of 580 HANDBOOK OF PHYSIOLOGY. the sixth nerve, running forward for some little distance dorsal to the nucleus, then descending vertically, passing to outside of its own nucleus between it and the ascending root of fifth nerve. It emerges at the hinder margin of the pons lateral to the sixth nerve, opposite the front edge of the groove between the olivary and restiform bodies. It may be connected with the hypoglossal nucleus. There are two roots; the lower and smaller is called the portio intermedia. Functions. — The seventh nerve is the motor nerve of all the muscles of the face, including the platysma, bat not including any of the mus- cles of mastication already enumerated; it supjilies, also, the parotid gland, and through the connection of its trunk with the Vidian nerve, by the petrosal nerves, some of the muscles of the soft palate, probably the levator palati and azygos uvulae. By its tympanic branches it sup- plies the stapedius and laxator tympani ; and through the optic ganglion, the tensor tympani ; through the chorda tympani it sends branches to the submaxillary gland and to the lingualis and some other muscular fibres of the tongue, and to the mucous membrane of its anterior two- thirds; and by branches given off before it comes upon the face, it sup- plies the muscles of the external ear, the posterior part of the digas- tricus, and the stylo-hyoideus. Beside its motor influence, the facial is also, by means of the fibres which are supplied to the submaxillary and parotid glands, a secretory nerve. For, through the last-named branches, impressions may be con- veyed which excite increased secretion of saliva. Paralysis of Facial Nerve. — When the facial nerve is divided, or in any other way paralyzed, the loss of power in the muscles which it sup- plies, while proving the nature and extent of its functions, displays also the necessity of its perfection for the perfect exercise of all the organs of the special senses. Thus, in paralysis of the facial nerve, the orbicu- laris palpebrarum being powerless, the eye remains open through the unbalanced action of the levator palpebrae; and the conjunctiva, thus continually exposed to the air and the contact of dust, is liable to re- peated inflammation, which may end in thickening and opacity of the cornea. These changes, however, ensue much more slowly than those which follow paralysis of the fifth nerve, and never bear the same de- structive character. The sense of hearing, also, is impaired in many cases of paralysis of the facial nerve; not only in such as are instances of simultaneous dis- ease in the auditory nerves, but in such as may be explained by the loss of power in the muscles of the internal ear. The sense of smell is com- monly at the same time impaired through the inability to draw air briskly toward the upper part of the nasal cavities in which part alone the olfactory nerve is distributed; because, to draw the air perfectly in THE NERVOUS SYSTEM, 581 this direction, the action of the dilators and compressors of the nos- trils should be perfect. Lastly, the sense of taste is impaired, or may be wholly lost in paral- ysis of the facial nerve, provided the source of the paralysis be in some part of the nerve between its origin and the giving off of the chorda tym- pani. This result, which has been observed in many instances of disease of the facial nerve in man, appears explicable on the supposition that the chorda tympani is the nerve of taste to the anterior two-thirds of the tongue, its fibres being distributed with the so-called gustatory or lingual branch of the fifth. Some look upon the chorda as partly or entirely made up of fibres from the fifth nerve, and not strictly speaking as a branch of the facial; others consider that it receives its taste fibres from communications with the glosso-2:)haryngeal. Together with these effects of paralysis of the facial nerve, the mus- cles of the face being all powerless, the countenance acquires on the paralyzed side a characteristic, vacant look, from the absence of all ex- pression : the angle of the mouth is lower, and the paralyzed half of the mouth looks longer than that on the other side; the eye has an unmean- ing stare. All these peculiarities increase, the longer the paralysis lasts; and their appearance is exaggerated when at any time the muscles of the opposite side of the face are made active in any expression, or in any of their ordinary functions. In an attempt to blow or whistle, one side of the mouth and cheeks acts properly, but the other side is mo- tionless, or flaps loosely at the impulse of the expired air ; so in trying to suck, one side only of the mouth acts; in feeding, the lips and cheeks Are f)Owerless, and on account of paralysis of the buccinator muscle food lodges between the cheek and gums. The Vlllth Nerve (Auditory). Origin. — The Vlllth iierve arises from two nuclei, median and lat- eral^ in the floor of the fourth ventricle, in the anterior part of the bulb in front and to the side of the twelfth nerve; it extends from the middle line to the outside margin of the ventricle. There is also an accessory nucleus situated on the ventral surface of the restiform body. The nerve leaves the surface of the brain from the ventral surface of the fore-part of the restiform body at the hind margin of the pons in two roots. One winds round the restiform body dorsal to it and the other passes median to it. The former is called the dorsal root. The latter is called the ventral root. Most of the fibres of the dorsal root {cochlear) •end in cells of the accessory nucleus, but fibres emerging from this nu- cleus pass inward to the bulb, superficially, forming the stria} acusticm in the floor of the fourth ventricle and end in the median nucleus. Most 582 HANDBOOK OF PHYSIOLOGY. of the fibres of the veutral root {vestihular) end in cells of the lateral nucleus. The cells of the median nucleus are small, those of the lateral nucleus large. Functions. — The cochlear branch is the auditory nerve proper, and the vestibular is distributed to the semicircular canals, the utricule and saccule, parts of the internal ear not directly concerned with hearing. The IXth Nerve {Glosso-Pharyiigeal). Origin. — The glosso-j^haryngeal nerves (ix. , fig. 364), in the enume- ration of the cerebral nerves by numbers according to the position in which they leave the cranium, ai'e considered as divisions of the eighth- pair of nerves^ the vagus and spinal accessory nerves being included with them. The union of the nuclei is indeed so intimate that it will be a». well to take the origins of the ninth, tenth, and eleventh nerves together. These three nerves emerge from the bulb and spinal cord in their numerical order from above downward, the huTbar portion from the lat- eral aspect of the bulb in a line between the olivary and restiform bodies;, and the spinal portion from a line intermediate between the anterior and posterior nerve roots as far down as the sixth or seventh cervical. The combined glosso-pharyngeal-accessory- vagus nucleus appears tO' consist of two parts, viz., one median or common origin, having con- spicuous nerve-cells of moderate size, and three lateral origins, having but few cells of small size. These are— i. the nucleus ambiguus, which lies on the lateral side of the reticular formation and is the origin of the' vagus; ii. the fasciculus solitarius, situated in the bulb, ventral and a. little lateral to the combined nucleus, is also called the ascending root, of the glosso-pharyngeal nerve or the respiratory bundle ; and iii. the- spinal jjortion which takes origin from a group of cells lying in the ex- treme lateral margin of the anterior cornu. This is the origin of the spinal accessory ; it corresponds to the antero-lateral nucleus of the bulb, and the lateral part of tlie gray matter of the spinal cord. The fibres of the spinal origin of the nerve pass from these cells, through the lateral column to the surface of the cord. The fibres from the combined nucleus, chiefly from the median piart,. pass in a ventral and lateral direction through the reticular formation, then ventral to or through the gelatinous substance and strand of fibres- connected with the fifth nerve, to the surface of bulb. The fibres from the nucleus amMguiis join the combined nerve, but especially the vagus. The bundles of fibres of the fasciculus solitarius start in the lateral gray matter of the cervical cord and higher in the reticular formation* of the bulb, run longitudinally forward to pass into the roots of the ninth nerve. THE NERVOUS SYSTEM. 583 IXth Xerve. — Distrihution. — Tlie glosso-pharyngeal nerve gives fila- ments through its tympanic branch (Jacobson's nerve), to the fenestra ovalis and fenestra rotunda, and the Eustachian tube, parts of the mid- dle ear; also, to the carotid plexus, and through the petrosal nerve, to the spheno-palatine ganglion. After communicating, either within or without the cranium, with the vagus, and soon after it leaves the cra- nium, with the sympathetic, digastric branch of the facial, and the accessory nerve, the glosso-pharyngeal nerve parts into the two principal divisions indicated by its name, and supplies the mucous membrane of the posterior and lateral walls of the upper part of the pharynx, the Eustachian tube, the arches of the palate, the tonsils and their mucous membrane, and the tongue as far forward as the foramen csecum in the middle line, and to near the tip at the sides and inferior part. Functions. — The glosso-pharyngeal nerve contains some motor fibres, together with those of common sensation and the sense of taste. 1. Motor fibres are distributed to the j)alato-pharyngeus, the stylo- pharyngeus, palato-giossus, and constrictors of the pharynx. 2. Sensory fibres in the parts which it supplies, and a centripetal nerve through which impressions are conveyed to be reflected to the ad- jacent muscles. 3. Fibres for the nerve of taste (from its fibres derived from the fifth, Gowers), in all the parts of the tongue and palate to which it is distributed. After many discussions, the question. Which is the nerve of taste? — the chorda tympani, the gustatory, or the glosso-pharyngeal? — may be most probably answered by stating that they are not them- selves, strictly speaking, nerves of this special function, but through their connection with the fifth nerve. For very numerous experiments and cases have shown that when the trunk of the fifth nerve is paralyzed or divided, the sense of taste is completely lost in the superior surface of the anterior and lateral parts of the tongue, at the back of the tongue, and on the soft palate and palatine arches. The loss is instantaneous after division of the nerve, and, therefore, cannot be ascribed wholly to the defective nutrition of the part, though to this, perhaps, may be ascribed the more complete and general loss of the sense of taste when the whole of the fifth nerve has been paralyzed. The Xth Nerve ( Vagus or Pneumogastric) . The origin of the Vagus nerve is, as we have Just seen, situated in the lower half of the calamus scriptorius in the ala cinerea (fig. 365). Its nucleus is said to represent the cells of Clarke's (posterior vesicular) column of the spinal cord. In origin it is closely connected with the ninth, eleventh, and the twelfth. The combined glosso-pharyngeal- 584 HANDBOOK OF PHYSIOLOGY, vago-accessory nuclei lie outside of, close to, and parallel with the nucleus of the twelfth. Distributioti. — It supplies sensory branches, which accompany the sympathetic on the middle meningeal artery, and others which supply the back part of the meatus and the adjoining part of the external ear. It is connected with the petrous ganglion of the glosso-pharyngeal, by means of fibres to its jugular ganglion; with the sjiinal accessory which supplies it with its motor fibres for the larger and upper portion of the cBsophagus, and with its inhibitory fibres for the heart; also with the twelfth; with the superior cervical ganglion of the sympathetic; and with the cervical plexus. It has, of all the nerves, the most varied dis- tribution and functions, either through its own filaments, or through those which, derived from other nerves, are mingled in its branches. The parts supplied by the branches of the vagus are as follows: — (1.) By its pharyngeal branches, which enter the pharyngeal plexus, a large portion of the mucous membrane, and, jjrobably, all the muscles of the pharynx. (2.) By the sujyerior laryngeal nerve, the mucous membrane of the under service of the epiglottis, the glottis, and the greater part of the larynx, and the crico-thyroid muscle. (3.) By the inferior laryngeal nerve, the mucous membrane and mus- cular fibres of the trachea, the lower part of the pharynx and larynx, and all the muscles of the larynx except the crico-thyroid. (4.) By its (esophageal branches, the mucous membrane and muscular coats of the oesophagus. (5.) Through the cardiac tierves, moreover, the branches of the vagus form a large portion of the supply of nerves to the heart and the great arteries. (G.) Through the anterior and the posterior pulmonary plexuses to the lungs. (7.) Through its gastric branches to the stomach; and to the intes- tines, and kidneys, by its terminal branches. (8.) Through its he2)atic and splenic branches, the liver and the spleen are partly supplied with nerves. Fimctions. — Throughout its whole course, the vagus contains both sensory and motor fibres. To summarize the many functions of this nerve, which have been for the most part considered in the preceding chapters, it may be said that it supplies (1) motor influence to the pharynx and oesophagus, stomach and intestines, to the larynx, trachea, bronchi, and lung; (2) sensory and, in part, (3) vaso-motor influence, to the same regions; (4) inhibitory influence to the heart; (5) inhibi- THE NERVOUS SYSTEM. 585 tory afferent impulses to the vaso-motor centre ; (6) excito-secretory to the salivary glands; (7) excito-motor in coughing, vomiting, etc. Effects of Section. — Division of both vagi, or of both their recurrent Fig. 368.— View of the nerves IX, X, and XI, their distribution and connections on the left side. 2-5. — 1, Pneumogastric nerve in the neck: 2, ganglion of its tninli : 8, its union with the spinal accessory ; 4, its union with the hypoglossal ; 5, pharyngeal branch ; (i, superior laryn- geal nerve; 7, external laryngeal ; 8, laryngeal plexus; 9, inferior or recurrent laryngeal ; 10, superior cardiac branch; 11, middle cardiac; 12, plexiform part of the nerve in the thorax; 13, posterior pulmonary plexus; 14, lingual or gustatory nerve of the inferior maxillary; 15, hypo- glossal, pa.ssing into the muscles of the tongue, giving its thyro-hyoid branch, and uniting with twigs of the lingual; 16, glosso-pharyngeal nerve; 17, spinal accessory nerve, uniting by its inner branch with the pneumograstric. and by its outer, passing into the sterno-mastoid muscle; 18, second cervical nerve; 19, third; 20. fourth; 21. origin of the phrenic nerve, 22, 23, fifth, sixth, seventh, and eighth cervical nerves, forming with the first dorsal the brachial plexus; 24, su- perior cervical ganglion of the sympathetic; 25, middle cervical ganglion; 26, inferior cervical ganglion united with the first dorsal ganglion; 27, 28, 29, 30, second, third, fourth, and fifth dorsal ganglia. (From Sappey after Hirschfeld and Leveill6.) branches, is often very quickly fatal in young animals; but in old ani- mals the division of the recurrent nerve is not generally, and that of both the vagi is not always, fatal, and, when it is so, death ensues slowly. 586 HANDBOOK OF PHYSIOLOGY. This difierence is, that the yiekliug of the cartilages of the larynx in young animals permits the glottis to be closed by the atmospheric pres- sure in inspiration, and so they are quickly suffocated unless tracheotomy be performed. In old animals, the rigidity and prominence of the aryt- enoid cartilages prevent the glottis from being completely closed by the atmospheric pressure; even when all the muscles are paralyzed, a por- tion at its posterior part remains open, and through this the animal continues to breathe. In the case of slower death, after division of both the vagi, the lungs are commonly found gorged with blood, oedematous, or nearly solid, from a kind of low pneumonia, and the bronchial tubes full of frothy bloody fluid and mucus, to which, in general, the death may be ascribed. These changes are due, in part, to the passage of food and of the various secretions of the mouth and fauces through the glottis, which, being deprived of its sensibility, is no longer stimulated or closed in conse- quence of their contact. The Xlth Nerve {Spinal Accessory). Origiti and Connections. — The nerve arises by two distinct origins — one from a centre in the floor of the fourth ventricle, partly but chiefly in the medulla, and connected with the glosso-jiharyngeal- vagus-nucleus; the other, from the outer side of the anterior cornu of the spinal cord as low down as the fifth or sixth cervical nerve. The fibres from the two origins come together at the jugular foramen, but separate again into two branches, the inner of which, arising from the medulla, joins the vagus, to which it supplies its motor fibres, consisting of small me- dullated or visceral nerve-fibres, while the outer consisting of large medullated fibres, supplies the trapezius and sterno-mastoid muscles. The small-fibred branch is said to arise from a nucleus corresponding to the posterior vesicular column of Clarke. The principal branch of the accessory nerve, its external branch, then suj^plies the sterno-mastoid and trapezius muscles; and, though pain is produced by irritating it, is composed almost exclusively of motor fibres. The internal branch of the accessory nerve supplies chiefly viscero-motor filaments to the vagus. The muscles of the larynx, all of which, as already stated, are supplied, apparently, by branches of the vagus, are said to derive their motor nerves from the accessory; and (which is a very significant fact) Vrolik states that in the chimpanzee the internal branch of the accessory does not join the vagus at all, but goes direct to the larynx. Among the roots of the accessory nerve, the lower or external, aris- ing from the spinal cord, appears to be composed exclusively of motor THE XERVOUS SYSTEM. 587 fibres, and to be destined entirely to the trapezius and extending from the back of the fourth ventricle to the level of the olivary bodies close to the middle line, inside the combined nucleus of the ninth, tenth, and eleventh nerves. The Xllth Nerve {Hypoglossal). Origin and Connections. — The nerve arises from a large-celled and very long nucleus in the bulb, extending from the back of the fourth ventricle to the level of the olivary bodies close to the middle line, inside the combined nucleus of the ninth, tenth, and eleventh nerves. Fibres ■from this nucleus run from the ventral surface through the reticular formation in a series of bundles passing between the olivary nucleus lat- erally and the anterior pyramid and accessory olive medially, to gain the surface. The nerve emerges from a groove between the anterior pyramid and olivary body. The fibres of origin are continuous with the anterior roots of the spinal nerves. It is connected with the vagus, the superior cervical ganglion of the sympathetic and with the upper cervical nerves. Distrihution. — This nerve is the motor nerve to the muscles con- nected with the hyoid bone, including those of the tongue. It supplies through its descending branch [descendens noni), the sterno-hyoid, sterno-thyroid, and omo-hyoid; through a special branch, the thyro- hyoid, and through its lingual branches, the genio-hyoid, stylo-glossus, hyo-glossus, and genio-hyo-glossus and linguales. Functions. — The function of the hypoglossal is exclusively motor. As a motor nerve, its influence on all the muscles enumerated above is shown by their convulsions when it is irritated, and by their loss of power when it is paralyzed. The effects of the paralysis of one hypo- glossal nerve are, however, not very striking. Often, in cases of hemi- plegia involving the functions of the hypoglossal nerve, it is not possible to observe any deviation in the direction of the protruded tongue; prob- ably because the tongue is so compact and firm that the muscles on either side, their insertion being nearly parallel to the median line, can push it straight forward or turn it for some distance toward either side. The Pons Varolii. The pons Varolii is generally spoken of as a great commissure of fibres; of fibres which connect the two halves of the cerebellum and of fibres which connect the bulb and spinal cord with the upper part of the brain. Although this is true it must not be forgotten that the pons contains several masses of gray matter, and also in addition smaller col- lections of nerve-cells. It is found that on section the following parts 588 HANDBOOK OF PHYSIOLOGY. may l)o made out in its structure, begiuning from the anterior or ven- tral surface. (a.) Transverse or commissural fibres connecting the one side of the cerebellum with the other, forming the middle peduncle. These fibres emerge from the lateral parts of the white substance of the hemispheres, having come from the superficial gray matter of the whole surface, from the median vermis, and from the lateral hemispheres. Some of these fibres are truly commissural and j^robably connect the same points on the surfaces of the two halves; some end in the gray matter of the same side of the pons on the ventral surface, and others cross to the oj)posite side of the pons and then become longitudinal, passing on to the teg- mentum, a system of fibres and gray matter to be immediately described. (b.) Fibres longitudinal in direction which are arranged in larger or smaller bundles separated by gray matter; some of these fibres are what are called the pyramidal fibres, which pass down to the anterior pyra- mids of the bulb. (c.) The dorsal portion of the pons is made up to a considerable ex- tent of the reticular formation of the tegmental region together with one or two distinct bundles of longitudinal fibres: i., the chief, situated toward the junction of the ventral two thirds with the dorsal third, is the Jillet, which consists of two portions, outer and median; and ii., the second, a bundle of similar fibres, jmsterior longittidinal himdles, is situ- ated between the two divisions of the fillet below the lateral and to the outer side of the median. {d.) In the fore part of the pons, a mass of gray matter containing pigment, the locus cmruleus, possibly forming the origin of the fifth nerve, and in the back part a second mass of gray matter, the siq)erior olive. The Crura Cerebri. The crura cerebri (iii, fig. 354) diverge from the anterior edge of the pons Varolii and pass upward on either side toward the cerebral hemispheres. At their anterior termination each of them appears to have upon its dorsal surface, to the inner and outer sides respectively, two large masses of gray matter which have been already spoken of, viz., the optic thalamus and the corpus striatum. These bodies are not only as it were placed upon the surface of each crus, but are also deeply em- bedded in its substance. The crus is found to be made up of two principal parts : — [a.) The one, the tegmentum, situated for the most j)art on the dorsal aspect, is composed chiefly of gray matter and some longitudinal fibres. And ib.) the other, the crusta, situated toward the other surface, is composed almost entirely of longitudinal fibres. It is known also as the THE NERVOUS SYSTEM. 589 pes. Separating these two parts, is a mass of gray matter of the shape of a lens, called the locus or nucleus niger or suhstantia nigra. The tegmentum situated dorsally ends for the most part in the neighborhood of the optic thalamus and the j)arts beneath. In conse- quence of this the fibres of the pes are allowed to come dorsally and to proceed between the optic thalamus and the more posterior part (the lenticular nucleus) of the corpus striatum, on their course to the cere- bral cortex. "When in this situation they form a compact mass of fibres. As they pass more dorsally the fibres spread out in the form of a fan, and this arrangement is called the corona radiata. The fibres of the pes ^ A' which are medullated. The general arrangement of the layers in the cortex is as follows: — It is described as consisting of five layers (Mey- nert) (fig. 373). 1. Superficial layer with abundance of neuroglia and a few small multipolar ganglion-cells. 2. A thin layer of a large number of closely packed small ganglion-cells of pyramidal shape. 3. The most important layer, and the thickest of all : it contains many large pyramidal ganglion cells, each with a pro- cess running off from the apex vertically toward the free surface, and lateral processes at the base which are always branched. Also a median process from the base of each cell which is unbranched and becomes continu- ous with the axis-cylinder of a nerve-fibre. The bundles of fibres spread ont in this layer. 4. Numerous ganglion-cells, some large and others small, forming the granular formation of Meynert. 5. Spindle-shaped and branched ganglion-cells of moderate size arranged chiefly parallel to the free surface {vide fig. 373). This layer is remarkable in heing broken up by fibres arranged in groups passing to the outer layers. It is a noticeable fact that the different layers do not bear the same relation to one another in thickness in different regions. In the area about the fissnre of Rolando, which we shall presently see is called the motor area, the large pyramidal cells are con- spicuous in size and number, and numerous large cells are found in the fourth layer. These latter attain their greatest develop- ment in the pre-ceutral and post-central convolutions. The granular layer is very marked in the occipital region, forming a distinct and broad division of the fourth layer, and being present elsewhere. The large cells are scarce. In the frontal region, the pyramidal and fourth layers are well marked, but the cells are less numerous; the nuclear layer is very distinct. The pyra- midal cells are those from which motor or efferent fibres originate. Chemical Composition. — The chemistry of nerves and nerve-cells has been chiefly studied in the brain and spinal cord. Nerve matter con- Fig. 373.— The layers of the cortical s''a.v matter of the cere- brum. (Meynert. ) 596 HANDBOOK OF PHYSIOLOGY. tains several albuminous and fatty bodies (cerebrin, lecithin, and some others), also fat matter which can be extracted by ether (including cho- lesterin) and various salts, especially Potassium and Magnesium phos- phates, which exist in larger quantity than those of Sodium and Calcium. Arrangement of f/ie parts of the cerebrum. — The great relative and absolute size of the Cerebral hemispheres in the adult man, masks to a f^'i'll. Process of cell of .- Purkinj6 passing into molecular ' layer. A chief process of cell of Pur- kinj6. Body of the same 'hlTv cell. W^ A X i s - c y Under Vg^^ process. "'"""! ... Fig. 374. Fig. 37.5. Fig. 374.— Diagrammatic horizontal section of a vertebrate brain. The figures serve both for this and the next diagram. Mb, mid-brain: what lies in front of this is the fore-, and what lies behind, the hind-brain; Li, lamina terminalis; Olf, olfactory lobes; Hmp, hemispheres; Th. E. thalamencephalon ; Pw, pineal gland; Pi/, pituitary body ; F.M, foramen of Munro ; cs, corpus striatum; Th, optic thalamus; CC, crura cerebri : the mass lying above the canal rep- resents the corpora quadrigemina ; Cb, cerebellum; I^IX, the nine pairs of cranial nerves; 1, olfactory ventricle ; 2, lateral ventricle ; 3, third ventricle ; 4, fourth ventricle ; -f, iter a tertio ad quartum ventriculum. (Huxley.) Fig. 375.— Section through the gray matter of the human cerebellum, treated according to Golgi's method (Stohr). great extent the real arrangement of the several parts of the brain, which is illustrated in the two accompanying diagrams. From these it is apparent that the parts of the brain' are disposed in a linear series, as follows (from before backward) : olfactory lobes, cere- bral hemispheres, optic thalami, and third ventricle, corpora quadri- gemina, or optic lobes, cerebellum medulla oblongata. This linear arrangement of parts actually occurs in the human foetus; THE NERVOUS SYSTEM. 597 and it is permanent in some of tlie lower Vertebrata, e.g., Fishes, in which the cerebral hemispheres are represented by a pair of ganglia intervening between the olfactory and the optic lobes, and considerably smaller than the latter. In Amphibia the cerebral lobes are further developed, and are larger than any of the other ganglia. In reptiles and birds the cerebral ganglia attain a still further devel- opment, and in mammalia the cerebral hemispheres exceed in weight all the rest of the brain. As we ascend the scale, the relative size of the cerebrum increases, till in the higher apes and man the hemispheres, which commenced as two little lateral buds from the anterior cerebral vesicle, have grown upward and backward, completely covering in and hiding from view all the rest of the brain. At the same time the smooth Fig. 376. — Longitudinal and vertical diagrammatic section of a vertebrate brain. Letters as before. Lamina terminalis is represented by the strong black line joining Pn and Py. (Huxley. ) surface of the brain, in many lower mammalia, such as the rabbit, is replaced by the labyrinth of convolutions of the human brain. Weight of the Brain. — The braiu of an adult man weighs from 48 to 50 oz. — or about 3 lbs. (about 1550 grms.) . It exceeds in absolute weight that of all the lower animals except the elephant and whale. Its weight, relatively to that of the body, is only exceeded by that of a few small birds, and some of the smaller monkeys. In the adult man it ranges from -^^ — gL of the body weight. Variations. Age. — In a new-born child the brain (weighing 10 to 14 oz. ) is •j\j of the body weight. At the age of 7 years the weight of the brain already averages 40 oz., and about 14 j'ears the brain not infrequently reaches the weight of 48 oz. Beyond the age of forty years the weight slowh' but steadily declines at the rate of about 1 oz. in 10 years. Sex. — The average weight of the female brain is less than the male : and this difference persists from birth throughout life. In the adult it amounts to about 5 oz. Thus the average weight of an adult woman's brain is about 44 oz. Intelligence. — The brains of idiots are generally much below the average, some weighing less than 16 oz. Still the facts at present collected do not war- rant more than a very general statement, to which there are numerous excep- tions, that the brain weight corresponds to some extent with the degree of intelligence. There can be little doubt that the complexity and depth of the convolutions, which indicate the area of the gray matter of the cortex, corre- spond with the degree of intelligence. 598 HANDBOOK OF PHYSIOLOGY. Weight of the Sj^inal Cord. — The spinal cord of man weighs from 1 — 1^ oz. ; its weight relatively to the brain is about 1 : 36. As we descend the scale, this ratio constantly increases till in the mouse it is 1 : 4. In cold-blooded animals the relation is reversed, the spinal cord is the heavier and the more important organ. In the newt, 2:1; and in the lamprey, 75 : 1. Distinctive Characters of the Human Brain. — The following characters dis- tinguish tlte brain of man and apes from those of all other animals, (a.) The rudimentary condition of the olfactory lobes, {h. ) A perfectly defined fissure of Sylvius, (c. ) A posterior lobe completely covering the cerebellum, (d.) The presence of posterior cornua in the lateral ventricles. The most distinctive points in the human hrain, as contrasted with that of apes, are: — (1.) The much greater size and weight of the whole brain. The brain of a full-grown gorilla weighs only about 15 oz. (450 grms.), which is less than \ the weight of the human adult male brain, and barely exceeds that of the human infant at birth. (2. ) The much greater complexity of the con- volutions, especially the existence in the human brain of tertiary convolutions Fig. 377.— Brain of the Orang, % natural size, showing the arrangement of the convolutions. Sy, fissure of Sylvius; R, fissure of Rolando; E P, external perpendicular fissure; Olf, olfactory lobe; Cb, cerebellum; PV. pons Varolii; MO, medulla oblongata. As contrasted with the human brain, the frontal lobe is short and small relatively, the fissure of Sylvius is oblique, the temporo-sphenoidal lobe very prominent, and the external perpendicular fissure very well marked. (Gratiolet. ) in the sides of the fissures. (3.) The greater relative size and complexity, and the blunted quadrangular contour of the frontal lobes in man, which are relativelj' both broader, longer, and higher, than in apes. In apes the frontal lobes j)roject keel -like (rostrum) between the olfactory bulbs. (4.) The much greater prominence of the temporo-sphenoidal lobes in apes. (5.) The fissure of Sylvius is nearly horizontal in man, while in apes it slants considerably up- ward. (6.) The distinctness of the external perpendicular fissure, which in apes is a well-defined almost vertical "slash," while in man it is almost obscured by the annectent gyri. Most of the above points are shown in the accompanying figure of the brain of the Orang. THE NERVOUS SYSTEM. 599 The Motor areas of the Cerebral Cortex. The experiments upon the brains of various animals by means of electrical stimulation have demonstrated that there are definite re- Fig. 379. Fies 378 and 379.— Brain of dog, viewed from above and in profile. F, frontal fissure some- times termed crucial sulcus, corresponding to the fissure of Rolando in man. S, Assure of Sylvius, around which the four longitudinal convolutions are concentrically arranged ; 1, tlexion of head on the neck, in the median line; 2, flexion of head on the neck with rotation toward the side of the stimulus; 3, 4, flexion and extension of anterior limb; 5, 6, flexion and extension of posterior limb; 7, 8. 9, contraction of orbicularis oculi. and the facial muscles in general. The unshaded part is that exposed by opening the skull. (Dal ton.) gions of the cerebral cortex the stimulation of which produces definite movements of co-ordinated groups of muscle of the opposite side of the body. Fritsch and Hitzig were the first to show that the cere- GOO HANDBOOK OF PHYSIOLOGY. bral cortex responded to electric irritation. They employed a weak con- stant current in their experiments, applying a pair of fine electrodes not more than -^^ in. apart to different parts of the cerebral cortex. The results thus obtained have been confirmed and extended by Ferrier and many others, chiefly with induction currents. The fundamental phenomena observed in all these cases may be thus epitomized : — (1). Excitation of the same spot is always followed by the same movement in the same animal. (2). The area of excitability for any given movement is extremely small, and admits of very accurate defini- tion. (3). In different animals excitations of anatomically corresponding spots produce similar or corresponding results. The various definite movements resulting from the electric stimulation of circumscribed areas of the cerebral cortex, are enumerated in the de- scription of the accompanying figures of the dog and monkey's brain. In the case of the dog, the results obtained are summed up as fol- lows, by Hitzig: — {a.) One portion (anterior) of the convexity of the cerebrum is motor; another portion (posterior) is non-motor, {h.) Electric stimu- lation of the motor portion produces co-ordinated muscular contraction on the opposite side of the body. (c. ) With very weak currents, the contractions produced are distinctly limited to particular groups of muscles; with stronger currents the stimulus is communicated to other muscles of the same or neighboring parts, {d.) The portions of the brain intervening between these motor centres are inexcitable by similar means. Motor ial area of the Monkey'' s Brain. — According to the observations of Ferrier, confirmed and extended by later experimenters, stimulation of various parts of the monkey's brain, as indicated by the numbers in figs. 380, 381, produces movements of definite muscles, thus: — Stimulation of the district marked 1, causes movement of hind foot: of 2, chiefly adduction of the foot; of 3, movements of hind foot and tail; of 4, of latissimus dorsi ; of 5, extension forward of arm; a, i, c, d, movements of hand and wrist; of 6, supination and flexion of forearm; of 7, elevation of the upper lip; of 8, conjoint action of eleva- tion of upper lip and depression of lower; of 9, opening of mouth and protrusion of tongue; of 10, retraction of tongue; of 11, action of platysma; of 12, elevation of eyebrows and eyelids, dilatation of pupils, and turning head to opposite side; of 13, eyes directed to opposite side and upward, with usually contraction of the pupils; of 13', similar action, but eyes usually directed downward; of 14, retraction of oppo- site ear, head turns to the opposite side, the eyes widely opened, and pupils dilated; of 15, stimulation of this region, which corresponds to THE NEKVOUS SYSTEM, 601 the tip of the uncinate couvoh^tiou, causes torsion of the lip and nostril of the same side. It is thus seen that the motor areas chiefly correspond with the ascending frontal and ascending parietal convolutions, and that the movements of the leg are represented at the upper part of these con- volutions, then follow from above downward the centres for the arms, the face, the lips, and the tongue. According to the further researches of Schiifer and Horsley, electrical stimulation of the marginal convolution internally at the parts cori-e- sponding with the ascending frontal and parietal convolutions, from Fig. 380. Fig. 381. Figs. 380 and 381.— Diagrams of monkey's brain to show the effects of electric stimulation of cer- tain spots. (According to Ferrier.) before backward, produces movements of the arm, of the trunk, and of the leg. A good deal of doubt was thrown upon the experiments of Ferrier by Goltz and other observers, from the results of excising the so-called motor areas of the dog's brain. It was found that the part might be sliced away or washed away with a stream of water, but that no perma- nent parah'sis ensued. More extensive observations however, have confirmed Ferrier's original statement, at any rate with regard to the monkey's brain. Destruction of the motor areas for the arm produces at any rate some permanent paralysis of the arm of the opposite side, and similarly of that for the leg, paralysis of the opposite leg. If both areas are destroyed permanent hemiplegia ensues. Paralysis of so extensive and permanent character G02 HANDBOOK OF PHYSIOLOGY. does not, however, appear tlie rule when the bram of a dog is used instead of that of the monkey. It is suggested that in the animal lower in the scale, the functions which in the monkey are discharged by the cortical centres may be subserved by the basal ganglia. Motorial Areas of the Human Brain. — It is naturally of great impor- tance to discover how far the result of experiments upon the dog and monkey hold good with regard to the human brain. Evidence furnished by diseased conditions is not wanting to supjiort the general idea of the existence of cortical motorial centres in the human brain (fig. 382). Parietal lobe (line indicates fissure of Rolando). Occipital lobe. Fissure of Sylvius. Temporal lobe. Fig. 382. — Diagram to indicate position of centres on the external surface of the brain, exact position of the centres may be seen on comparison with fig. 370. The So far, however, it has been possible to localize motor functions in the frontal and ascending parietal convolutions only, to the convolutions which bound the fissure of Eolando, and to those on the inner side of the hemispheres which correspond thereto, and j^ossibly to the frontal lobe in front of the ascending convolution. The position of the centres is probably much the same as in the mon- key's brain — those for the leg above, those for the arm, face, lips, and tongue from above downward. Destruction of these parts causes pa- ralysis, corresponding to the district affected, and irritation causes con- vulsions of the muscles of the same part. Again, a number of cases are on record in which aphasia, or the loss of power of expressing ideas in words, has been associated with disease of the posterior part of the lower or third frontal convolution on the left side. This condition is usually associated with paralysis of the right side (right hemiplegia). This district of the brain is now generally known as the motor area; and there seems no doubt whatever that from this area pass the nerve- THE NERVOUS SYSTEM. 6oa fibres which proceed to the spinal cord, and are there represented as the pyramidal tracts. This is the reason, no doubt, that movements are produced on stimu- lation of the white matter after the superficial gray matter of the animal's brain has been sliced off. Moto}' tracts in the hrain. — These motor fibres are connected with the pyramidal cells of the cortex, and are indeed their continuations. It will be necessary, therefore, to trace them from the cortex down- ward. From the motor area of the cortex they converge to the inter- Tig. 383. —Diagram to show the connecting of the Frontal Occipital Lobes with the Cere- bellum, etc. The dotted lines passing in the crusta (too), outside the motor fibres, indicate the connection between the temporo-occipital lobe and the cerebellum, f.c. , the fronto-cerebellar fibres, which pass internally to the motor tract in the crusta; i.f. , fibres from the caudate nucleus to the pons, fr., frontal lobe; Oc, occipital lobe; af. , ascending frontal; ap. , ascend- ing parietal convolutions; pcf. , precentral fissure in front of the ascending frontal convolution; PR., fissure of Rolando; ipp. , interparietal fissure, a section of crus is lettered on the left side. SN. , substantia nigra; py. , pyramidal motor fibre, which on the right is shown as continuous lines converging to pass through the posterior limb of ic. internal capsule (the knee or elbow of which is shown thus *) upward into the hemisphere and downward through the pons to cross at the medulla in the anterior pyramids. (Gowers.) nal capsules, and pass down to the crusta of the crus in the way already indicated. In the internal capsule the fibres which pass onward and downward to the pyramidal tracts of the spinal cord do not occupy more than a small section, namely, that part known as the knee, and the anterior two-thirds of the posterior segment (fig. 384). In this district the fibres for the face, arm, and leg, are in this relation : those for the face and tongue are just at the knee, and below or behind them come first the fibres for the arm and then those for the leg. The more accurate arrangement of these fibres in the monkey's brain from above down are those for the eye, head, tongue, mouth, shoulder. 604 HANDBOOK OF PHYSIOLOGY. elbow, digits, abdomen, lip, knee, digits. These fibres come for the most part from the part of the cortex on either side of the fissure of Kolando, hence called the Rolandic area on either side. But the areas Fig. 384.— Diagram to show the relative positions of the several motor tracts in their course from the cortex to the crus. The section through the convolution is vertical; that through the internal capsule, I, C, horizontal; that thi-ough the crus again vertical. C, N, caudate nucleus; O, TH, optic thalamus; L3 and L3, middle and outer part of lenticular nucleus; /, a, I, face, arm, and legfiljres. The words in italic indicate corresponding cortical centres. (Gowers.) for the liead and eyes lie more anterior in the frontal lobe, to the front of the precentral sulcus, that for the head above that for the e3^es, and an area for the trunk (not indicated in the fig. 383), is situated more toward the middle line of the hemisphere, internal to that for the leg. But there are other fibres which are arranged in front of the pyramidal fibres in the front limb of the capsule, as well as others behind them in the hind limb of the capsule. Those in front are from the anterior part of the frontal lobe, and these in passing into the crus are found on the median side of the pyramidal fibres (fig. 383). They appear to end in the gray matter of the pons, and there to be connected with fibres from the middle peduncle of the opposite side of the cere- bellum. Those behind the pyramidal fibres in the hind limb of the cap- sule are from the temfporal-occipital lobe. These fibres pass into the crus to the outer side of the pyramidal fibres (fig. 383), they probably also end in the gray matter in the same way. There are other fibres from the corpus striatum, from both nuclei, but particularly from the caudate nucleus, which pass to the crus, and are situated between the pyramidal tract and the locus niger (fig. 383), some of which terminate in that nucleus, while others terminate in the pons. Besides the above fibres, all of which are believed to be efferent fibres, and are at any rate fibres of descending degeneration, there are fibres which pass from the cortex to the optic thalamus and tegmentum, fibres of ascending degeneration THE NERVOUS SYSTEM. 605 found in the internal capsule, viz., those from the frontal lobes are situated at the extreme tip of the front limb, in front of the motor fibres from the same district, and others from the temporal-occipital district converge to the posterior part of the hind limb. Those passing between the occipital lobe and the optic thalamus are believed to be concerned with vision, and are called fibres of the ojJtic radiation. It may be as well to mention here that some other fibres from the temporo-occipital lobe pass into the optic thalamus, without forming a part of the internal capsule. The optic thalamus then receives fibres from nearly all parts of the ■cerebral cortex, some of which are not found in the internal capsule. The tegmentum, the afferent or sensory tract of the crus to a great ex- tent ends in the optic thalamus, and is, therefore, connected through it with nearly all parts of the cortex, indirectly. It is also more directly connected with cortex {a) by fibres of the optic radiation which do not go to the optic thalamus, {h) by fibres from the frontal and parietal lobes, which pass through the lenticular nucleus, and {c) by fibres from both the lenticular and caudate nuclei of the corpus striatum. In the tegmentum the longitudinal fibres may be thus enumerated : — («.) The fillet, which consists of fibres from the sensory decussation of Fig. 385.— Vertical section througii the cerebrum and basic ganglia to show the relations of the latter, co, cerebral convolutions ; c.c, cori)us callosum; v. I., lateral ventricle; f, fornix; vlIL, third ventricle; n.c, caudate nucleus; tl(. ojitic thalamus; n.L, lenticular nucleus; c.i., internal capsule; c.L, claustrum; c.e., external capsule; m, corpus mammillare; t.o., optic tract; s.t.t., stria terminalis; 7f.«., nucleus amygdalae ; cm, soft commissure. (Schwalbe.) the bulb, which becomes longitudinal in the inter-olivary region, and in its course upward, from masses of gray matter, such as the superior olive; it divides into two bundles, (i.) Lateral, ends in gray matter of posterior corpus quadrigeminum and in white matter beneath the anterior, and (ii.) median, ends in anterior corpus quadrigeminum and 606 HANDBOOK OF PHYSIOLOGY. in the corpus subthalamicum, thence to the optic thalamus and the cere- bral cortex, {b.) Posterior longitudinal bundles. — A bundle of fibres which appear to begin the bulb as certain fibres of the anterior column of the cord, which are the short longitudinal commissures between segments of the cord. It is traceable upward as far as the nucleus of the third nerve. It is supposed to connect the nuclei of the fourth and sixth nerves with the third, and with the anterior corpus quadrigeminum. (c.) Superior peduncle of the cerebellum. This arises on either side from the superficial gray matter, but chiefly from the corpus dentatum, and passes forward outward beneath the posterior corpus quadrigeminum, and beneath it and the anterior corpus quadrigeminum decussates with its fellow; the fibres then pass forward in the anterior district of the tegmentum and end in the red nucleus. (fZ.) Fibres from the corpora quadrigemina. From each corpus quad- rigeminum passes forward and downward a tract called the brachium. The anterior brachium goes to the lateral corpus geniculatum, and then to the optic tract, other fibres pass into the tegmentum, and thence directly to the occipital cortex. The posterior brachium goes to the median corpus geniculatum, thence to the tegmentum, and through it possibly to the temporal region of the cerebral cortex. Commissural fibres. — In addition to the fibres of the corpus callosum, which connect all parts of the hemispheres, and fornix, there are three other commissures, the anterior white commissure, and the posterior white commissure in the third ventricle connect by white fibres the two sides of the brain. The fibres in the anterior come from the temporo- sphenoidal convolution chiefly, but a few are part of the olfactory tract. The posterior connects the optic thalami and tegmenta. The middle is chiefly composed of gray matter, but also contains some transverse fibres. Functions of the Cerebrum. Speaking in the most general way, and for the present omitting the accumulating evidence in favor of the direct representation of the various co-ordinated movements of the muscles of the body in ganglia situated in different parts of the cerebral cortex, it may be said that: — (1.) The cerebral hemispheres are the organs by which are perceived those clear and more impressive sensations which can be retained, and regarding which we can judge. (2.) The cerebrum is the organ of the will, in so far at least as each act of the will requires a deliberate, how- ever quick determination. (,3.) It is the means of retaining impressions of sensible things, and reproducing them in subjective sensations and ideas. (4.) It is the medium of all the higher emotions and feelings, and THE NERVOUS SYSTEM. 607 of the faculties of judgment, understandiug, memory, reflection, induc- tion, imagination and the like. Evidence regarding the jahysiology of the cerebral hemispheres, has been obtained, as in the case of other parts of the nervous system, from the study of Comparative Anatomy, from Pathology, and from Experi- ments on the lower animals. The chief evidences regarding the func- tions of the cerebral hemispheres derived from these various sources, are briefly these: — 1. Any severe injury of them, such as a general concus- sion, or sudden pressure by apoplexy, may instantly deprive a man of all power of manifesting externally any mental faculty. 2. In the same ■general proportion as the higher mental faculties are developed in the Vertebrate animals, and in man at different ages and in different indi- viduals, the more is the size of the cerebral hemispheres developed in comparison Avith the rest of the cerebro-spinal system. 3. No other part of the nervous system bears a corresponding proportion to the develop- ment of the mental faculties. 4. Congenital and other morbid defects of the cerebral hemisphere are, in general, accompanied by correspond- ing deficiency in the range or power of the intellectual faculties and the higher instincts. 5. Eemoval of the cerebral hemispheres in one of the lower animals produces effects corresponding with what might be antici- pated from the foregoing facts. Effects of the Bemoval of the Cerebrum. — The removal of the cere- brum in the lower animals apjaears to reduce them to the condition of a mechanism v/ithout spontaneity. In the case of the frog, when the cerebral lobes have been removed, the animal appears similarly deprived of all power of spontaneous move- ment. But it sits up in a natural attitude, breathing quietly; when pricked it jumps away; wlien thrown into the water it swims; when placed upon the palm of the hand it remains motionless, although, if the hand be gradually tilted over till the frog is on the point of losing his balance, he will crawl up till he regains his equilibrium, and comes to be perched quite on the edge of the hand. This condition contrasts with that resulting from the removal of the entire brain, leaving only the spinal cord ; in this case only the simpler reflex actions can take place. The frog does not breathe, he lies flat on the table instead of sitting up; when thrown into a vessel of water he sinks to the bottom; when his legs are pinched he kicks out, but does not leap away. A pigeo)i from which the cerebrum has been removed will remain motionless and apparently unconscious unless disturbed. When dis- turbed in any way it soon recovers its former position; when thrown into the air it flies. In mammals it is difficult to remove the cerebral hemispheres, but in those animals in which the operation has been carried ou.t, as for example COS HANDBOOK OF PHYSIOLOGY. in the rabbit and rat, a result very similar to those observed in the case of the frog and pigeon has been obtained. The animal is able to maintain its equilibrium, to run or jump, and in fact carry out all the most compli- cated co-ordinated movements, but it is unable to originate them without stimulation. In the case of the dog, however, it has been found impos- sible to remove the whole brain, but when it has been removed piece- meal the animal may be kept alive for some time, and can carry out co- ordinated movements well, and even manifest intelligence. It is quite evident, therefore, that the apparatus for carrying out co- ordinated movements is in these animals not localized either in the cere- brum or in the spinal cord, and must therefore be connected in some way with the parts of the brain below the cerebrum and above the cord. There is no reason why such an arrangement may not be supposed to exist in the human brain. We must look upon the cerebrum, however, for the originator of vol- untary movements. As regards the theory, of the localization of different movements in different parts of the cerebral cortex which as we have seen has received so much support from observation on animals such as the dog and the monkey, at any rate, we may say that certain parts of the cerebral cortex appear to be highly sensitive to electrical stimuli, particularly the Rolandic area and the frontal lobe in front of it. Stimulation of cer- tain other regions, viz., of the occipital region, of the parietal and tem- poral region, and of the gyrus fornicatus and the frontal region in front of the motor area, does not give rise to such movements. Such observa- tions as it has been jiossible to make on man show that the localization of movement on the human cerebral cortex is, if anything, superior to that observed in monkeys. We have, of course, but few data upon Avhich to base our conclusion, except such as have been, obtained from the observation of the symptoms of disease, but with the hel]) of these we may assume that in the cerebral cortex the co-ordinated movements of the body in some way are represented. The cases which have given us most of our knowledge upon the subject are those in which haemorrhages have occurred in different parts of the brain, followed by paralysis of the opposite side of the body. These hgemorrhages chiefly occur in the neighborhood of the corpus striatum. The paralysis of the extremities is practically permanent, although, as a rule, the muscles connected with the trunk are not paralyzed. This means that some interruption has taken place between the cerebral cortex and the paralyzed muscles, and if the lesion is a destroying one, the connection is never re-established. In the case of the animals, such as the dog, this is not the case, as the paralysis is temporary. It is supposed that in man not only the more highly skilled movements but all voluntary movements of the muscles are THE XERVOUS SYSTEM. 609 actually represented in the cortical areas, and that the pyramidal tracts are actually essential for voluntary movements. If the pyramidal tracts be partially or wholly destroyed, anywhere in their course, a paralysis corresponding with the amount destroyed invariably follows. In the dog experiments have shown that this is not the case, and the conduction of voluntary impulse to muscles may take place, for example, in other parts of the cord besides the pyramidal tract, after hemisection. The pyramidal tracts in man, however, must be considered also as the only path connecting the cortical centres with the co-ordinated centres lower down in the brain, as, for example, in the bulb. The impulses which pass down from the cortex, whatever they may be, are not however of necessity connected with consciousness, and many volun- tary movements of a complicated nature may take place really better with- out consciousness than with it. This is shown in such co-ordinated movements as writing, walking, marching, and the like, all of which are acquired with time and much labor, but when once perfect in the individual, can best be performed without voluntary effort. Such move- ments must be represented by impulses passing in the pyramidal tracts, for if they are interrupted, the movements are no longer performed. What is the actual meaning of the origination of a voluntary action performed by what is actually an effort of the will, we are unable to say. Hso doubt imj^ulses from the periphery conducted to the cerebral cortex along all kinds of afferent channels must have something to do with it; directly or indirectly, sooner or later. In the human cortex it would seem that the apparatus for j^erforming all manner of possible co-ordi- nated movements which may result in speech or action, are stored. This apparatus is capable of being set in action either in the absence of con- sciousness by afferent stimuli of some kind directly, or by what may be, indirectly or remotely, in some way the result of afferent stimuli, viz., the will. It is also probable that the will of another may take the place of the man's own will, and may call forth movements, actions, and speech, all of which are, as it were, ready to be called forth by a stimu- lus of some kind. It may be supposed that the condition of develop- ment of the brain inherited by the individual has something to do both with the potentialities of the apparatus for co-ordinated acts, which he receives at birth, and with the way in which the apparatus is set in motion. Unilateral Action. — Respecting the mode in which the brain dis- charges its functions, there is no evidence whatever. But it appears that, for all but its highest intellectual acts, one of the cerebral hemi- spheres is sufficient. For numerous cases are recorded in which no mental defect was observed, although one cerebral hemisphere was so disorganized or atrophied that it could not be supposed capable of dis- 39 610 HANDBOOK OF PHYSIOLOGY. charging its functions. The remaining hemisphere was, in these cases, adequate to the functions generally discharged by both; but the mind does not seem in any of these cases to have been tested in very high intellectual exercises; so that it is not certain that one hemisphere will suffice for these. In general, the brain combines, as one sensation, the impressions which it derives from one object through both hemispheres, and the ideas to which the two such impressions give rise are single. In relation to common sensation and the efforts of the will, it must always be remembered that the impressions to and from the hemispheres of the brain are carried across the middle line; so that in destruction or com- pression of either hemisphere, whatever effects are produced in loss of sensation or voluntary motion, are observed on the side of the body ■opposite to that on which the brain is injured. Sleep. — All parts of the body which are the seat of active change require periods of rest. The alternation of work and rest is a necessary condition of their maintenance, and of the healthy performance of their functions. These alternating periods, however, differ much in duration in different cases ; but, for any individual instance, they preserve a general and rather close uniformity. Thus, as before mentioned, the periods of rest and work, in the case of the heart, occupy, each of them, about half a second ; in the case of tlie ordinary respiratory muscles the periods are about four or five times as long. In many cases, again (as of the voluntary muscles during violent exercise) , while the periods during active exertion alternate very frequently, yet the expenditure goes far ahead of the repair, and. to compensate for this, an after repose of some hours becomes necessary ; the rhythm being less perfect as to time, than in the case of the mu.scles concerned in circulation and respiration. Obviously, it would be impossible that, in the case of the brain, there should be short periods of activity and repose, or in other words, of conscious- ness and unconsciousness. The repose must occur at long intervals ; and it must therefore be proportionately long. Hence the necessity for that condition which we call Sleep; a condition which seeming at first sight exceptional, is only an unusually perfect example of what occurs, at varying intervals, in every actively working portion of our bodies. A temporary abrogation of the functions of the cerebrum imitating sleep, may occur, in the ease of injury or disease, as the consequence of two appar- ently widely different conditions. Insensibility is equally produced bj^ a deficient and an excessive quantity of blood within the cranium (coma) ; but it was once svipposed that the latter offered the truest analogy to the normal con- dition of the brain in sleep, and in the absence of any proof to the contrary, the brain was said to be during sleep congested. Direct experimental inquiry has led, however, to the opposite conclusion. By exposing, at a circumscribed spot, the surface of the brain of living animals, and protecting the exposed part by a watch-glass, Durham was able to prove that the brain becomes visibly paler (anaemic) during sleep ; and the anaemia of the optic disc during sleep, observed by Hughlings Jackson, may be taken as a strong confirmation, by analogy, of the same fact. A very little consideration will show that these experimental results corre- spond exactly with what might have been foretold from the analogy of other THE NEKVOUS SYSTEM. 611 physiological conditions. Blood is svipplied to the brain for two partly dis- tinct purposes. (1.) It is supplied for mere nutrition's sake. (2.) It is neces- sary for bringing supplies of potential or active energy {i.e. , combustible matter or heat) which may be transformed by the cerebral corpuscles into the various manifestations of nerve-force. During sleep blood is requisite for only the first of these purposes ; and its supply in greater quantity would be not only useless, but by supplying au excitement to work, when rest is needed, would be positively harmful. In this respect the varying circulation of blood in the brain exactly resembles that which occurs in all other energy -transforming parts of the body ; e.g., glands or muscles. At the same time, it is necessary to remember that the normal angemia of the brain which accompanies sleep is probably a result, and not a cause of the ■quiescence of the cerebral functions. What the immediate cause of this periodical partial abrogation of functions is, however, we do not know. Somnambulism and Dreams. — What we term sleep occvirs often in very differ- ent degrees in different parts of the nervous system ; and in some parts the expression cannot be used in the ordinary sense. The phenomena of di^eams and somnambtdism are examples of differing degrees of sleep in different parts of the cerebro-spinal nervous system. In the former case the cerebrum is still partially active ; but the mind-products of its action are no longer corrected by the reception, on the part of the sleeping sensorium, of impressions of objects belonging to the outer world ; neither can the cerebrum, in this half-awake condition, act on the centres of reflex action of the voluntary muscles, so as to cause the latter to contract — a fact within the painful experience of all -who have suffered from nightmare. In somnambulism the cerebrum is capable of exciting that train of reflex nervous action which is necessary for progression, while the nerve-centre of muscular se7ise (in the cerebellum?) is, presumably, fully awake ; but the .sen - sorium is still asleep, and impressions made on it are not sufiiciently /eZf to rouse the cerebrum to a comparison of the difference between mere ideas or memories and sensations derived from external objects. The centres for muscular co-ordmations. — In asserting that the co- ordination of complicated muscular movements is connected with the middle parts of the brain below the cerebrum and above the bulb, we were stating a fact deduced from experiments upon animals. The exact way in which these parts of the brain are concerned it is difficult to understand. It appears, however, that co-ordinated movements such as standing, walking, and the maintenance of the equilibrium generally, require to be guided and governed by afEerent impulses, which tell of the condition of the body and of its relations to its environment (" its position in space"). The afferent impulses are firstly visual and tactile sensations, secondly sensations by which we appreciate the condition of our muscles (muscular sense), and thirdly^ as appears from experiments on pigeons and other animals, sensations produced by the pressure, in different directions, of the fluid in the semicircular canals of the in- ternal ear. Experiments show that when the horizontal semicircular canal ii G12 HANDBOOK OF PHYSIOLOGY. divided in a pigeon, inco-ordination occurs, with a constant movement of the head from side to side, and similarly, when one of the vertical canals is operated upon, up and down movements of the head are ob- served. The bird is unable to fly in an orderly manner, flutters and falls when thrown into the air, and, moreover, is able to feed with difficulty. Hearing remains unimpaired. So that inco-ordination depends upon deficiency or disorder of normal ampullar influences. It will be recollected that the semicircular canals are supplied with a nerve, the vestibular branch of the auditory, which is connected with the bulb. It is probable that the various afferent impulses upon which co-ordina- tion and the maintenance of the equilibrium depend are gathered up, as it were, in the tegmental system from the bulb ujDward, since this region is so intimately connected with the bulb and cord posteriorly, and with the optic thalamus and corpora quadrigemina anteriorly. In addition to the tegmentum, however, the cerebellum and pons are in some way concerned, because of their intimate connection with the spinal cord and bulb, the cerebellum being further connected with the auditory nerve on the one hand, and with the gray matter in connection with the tegmentum on the other hand. Sensory Centres. There is evidence that fibres from the nerves of special sense are specially connected with definite and distinct parts of the cerebrum. Visual or Optic Centre. — The termination of the optic nerve in each eye, the retina, to the structure of which we shall return when treating of the eye, is so arranged that when we look at an object with both eyes symmetrical parts of each retina are used. For example, if we look at an object to the left, an image of that object is focussed upon the right half of both retinae, viz., upon the temporal side of the right retina, and upon the nasal side of the left retina. The optic nerve- fibres of these symmetrical parts of the retina are gathered together behind where the optic nerves decussate, viz., in the optic chiasma. The fibres which come from the right side of both eyes are contained in the optic tract of the same side, viz. , the right, those from the right eye being outside of the others. In the same w\ay the left optic tract con- tains internally fibres from the left side of the right eye and externally those from the left side of the left eye. On the inner border of the optic chiasma and tract there are also commissural fibres which pass from one side of the brain to the other; these are fibres which connect one median corpus geniculatum with the other. They are called the inferior or arcuate commissure. The optic tract thus formed then passes back- THE XERVOUS SYSTEM. 613 ward and terminates in three distinct nuclei, viz. , the pulvinar of the optic thalamus, the median corpus quadrigemiuum and the lateral corpus geniculatum. These nuclei waste if the ej'es are removed from an adult animal ; and if from a newly born animal they do not develop. The optic chiasma in its course gives off fibres which are connected with the nucleus of the third nerve. It appears that some of the fibres of the optic tract pass directly into the cerebral cortex without joining with the optic thalamus, corpus quad- rigemiuum or corpus geniculatum. It was shown above that the fibres of the cerebral cortex, known as the optic radiation, pass from the occipital region to the three nuclei about which we are speaking, viz., into the pulvinar of the optic thala- mus, the anterior corpus quadrigemiuum and lateral corpus geniculatum. Tig. 386.— Mesial aspect of human cerebral hemisphere to indicate position of centres. The exact position of the centres will be seen by comparing this figure with figure 372. and it is known that when the occipital cortex is removed, these three waste. It has been further sliown that in a newly born auimal the removal of such a region is followed by imperfect development of the parts in question. If one optic nerve be divided blindness of the corresponding eye results, but if one optic tract be divided there is a half blindness, which is called hemianopsia, hemianojna, or hemiopia, right or left, according as the right or left field of vision is cut off. It is highly probable that the occipital lobe (figs. 382, 386), and particularly the cuneus, is concerned as a so-called visual centre, since not only is it connected with the optic nerves, as we have seen, but also because the removal of the right occipital lobe in an animal (monkey), is followed by left hemiopia, removal of the left by right hemiopia, and removal of both occipital lobes by total blindness. Some have connected the angular 614 HANDBOOK OF PHYSIOLOGY. gyrus also with vision as the centre, while others look upon it merely as an accessory centre. Olfactory centre.— The olfactory nerve differs from the other cranial nerves. In reality it is a representative of the olfactory lobes of other animals, which are part of the cerebrum. It originates as an off-shoot from the cerebral vesicle, the front part of which is developed into the bulb of the olfactory nerve, while the back forms its peduncle. The nerve, the cavity of which is filled up in the fully developed condition with neurogliar substance, lies upon the cribriform plate of the ethmoid bone, and is contained in a groove of the frontal lobe on its under sur- face. On examination of the bulb it is found to be thus made up. Beneath the neurogliar layer is a layer of longitudinal fibres and a few nerve-cells, next to this is a layer of small cells (nuclear layer), fibres; from the layer of nerve-fibres passing through it. The nuclear layer is also separated into groujos of cells by an inter- lacing of the fibres. The next layer is thick and is composed of neuroglia, and some fibres, some of which are medullated, as well as of cells more or less pyramidal in shape. Below this layer is the layer of olfactory glomeruli. These glomeruli are small coils of olfactory fibres inclosing small cells and granular matter. Fibres of the olfactory nerve proper are found below this layer and pass to be distributed to the olfactory mucous membrane. They are thought to have origin in the glomeruli. The peduncle of the nerve or the olfactory tract as it is sometimes called, is made up of longitudinal fibres originating in the bulb, with neuroglia and some nerve-cells. The fibres of the olfactory tract have been traced into the nucleus, amygdala? and its junction with the hippocampal gyrus in the temporal lobe (fig. 386). The hippocampus must be in some way connected with smell, since a lesion of it, leaving the olfactory tract uninjured, seriously interferes with that sense. Taste centre. — It is very uncertain where the taste centre is situated, if such exist. It has been placed in the temjjoral lobe, not far from that of smell (fig. 386). Anditory centre. — The position of this centre is uncertain. It has been localized in the superior temporal convolution (fig. 382). Experi- ments have been made which connect auditory impulses on either side with the posterior corpus quadrigeminum and the median corpus genicu- latum, for when the internal ear is destroyed there results atrophy of these bodies as well as of the lateral fillet of the opposite side ; and on the other hand, destruction of the part of the temporal lobe above indicated is similarly followed by atrophy of the nuclei of the same side. If these results be confirmed by additional experiments, it would make it plain that these nuclei bear much the same relation to the sense of hearing THE XERVOUS SYSTEM. 615 as do the anterior corpus qnadrigeminum and the lateral corpus geni- culatum to the sense ot sight. FuxcTiONS OF Corpora striata and Optic Thalami. llie corpora striata. — The idea formerly held that the corpora striata are concerned in the transmission of motor impulses, or that they are the great motor ganglia at the base of the brain, rests upon insufficient evidence. Lesions of the corpora striata produce hemiplegia only because of the pressure-effects tliey exercise upon the internal capsule close by. The caudate nucleus is connected with the opposite side of the cere- bellum by fibres which conduct downward, and the lenticular nucleus is connected Avith the cerebellum by fibres from the tegmentum and superior cerebellar peduncles which conduct upward. It is suggested that the corpora striata are central organs analogous to the cerebral cortex itself. " The analogy to those parts of the cortex that are connected with the cerebellum is rendered still greater by the fact that a lesion, even an extensive lesion, may exist in either the caudate or lenticular nucleus, and so long as it does not interfere with the functions of the motor or sensory parts of the internal capsules it causes no persistent symptoms." (Gowers. ) The optic thalami. — That the optic thalami are the great sensory centres at the base of the brain — Avhich was a view held by many until recently — does not seem to be based upon sufficiently accurate observa- tions. The important relation to the tegmentum of its own side would make it appear as being specially concerned with the sensory fibres pass- ing to the cerebrum, for which it probably forms a relay. Its connection with the optic nerves has been commented upon above. Fibres connect the optic thalamus too with the superior peduncle of the cerebellum of the ojiposite side. Lesions of the optic thalamus do not of themselves produce entire loss of sensation. If such a symptom follows, it is due to pressure upon, or injury to, the posterior limb of the internal capsule. The optic thalamus is connected with visual sensations, and may be a reflex-centre for some of the higher reflex actions. Of the functions of the external capsule and of the clatistrum nothing definite is known. The Cerebellum. The Cerebellum (7, 8, 9, 10, fig. 354) is composed of an elongated central portion or lobe, called the vermiform processes, and two hemi- spheres. Each hemisphere is connected with its fellow, not only by 616 HANDBOOK OF PHYSIOLOGY. means of the vermiform processes, but also by a bundle of fibres called the middle cms or peduncle (the latter forming the greater part of the pons Varolii), while the superior crura with the valve of Vieussens connect it with the cerebrum (5, fig. 387), and the inferior crura (formed by the prolonged restiform bodies) connect it with the medulla oblongata (3, fig. 387). SlrncUire. — The cerebellum is composed of white and gray matter, the latter being external, like that of the cerebrum, and like it, infolded, so that a larger area may be contained in a given space. The convolu- tions of the gray matter, however, are arranged after a different pattern, as shown in fig. 387. Besides the gray substance on the surface, there Fig. 387.— CerebeUum in section and fourth ventricle, with the neighboring parts. 1, Median groove of fourtli ventricle, ending below in the calamus scriptorius, with the longitu- dinal eminences formed by the fasciculi teretes, one on each side; 2, the same groove, at the place where the white streaks of the auditory nerve emerge from it to cross the floor of the ven- tricle; 3, inferior crus or peduncle of the cerebellum, formed by the restiform body; 4, posterior pyramid; above this is the calamus scriptorius; 5, superior crus of cerebellum, or processus e cerebello ad cerebrum Cor ad testes) ; 6, 6, fillet to the side of the crura cerebri ; 7, 7, lateral grooves of the crura cerebri ; 8, corpora quadrigemina. (From Sappey after Hirschfeld and Leveillfi.) is, near the centre of the white substance of each hemisphere, a small capsule of gray matter called the corpus dentahim (fig. 388, cc?), resem- bling very closely the corpus deyitatum of the olivary body of the medulla oblongata (figs. 362, 388, o). If a section be taken through the cortical portion of the cerebellum, the following distinct layers can be seen (fig. 389) by microscopic ex- amination. (1.) Immediately beneath the pia mater [p m) is a layer of consid- erable thickness, which consists of a delicate connective tissue, in which are scattered several spherical corpuscles like those of the granular layer of the retina, and also an immense number of delicate fibres passing up toward the free surface and branching as they go. These fibres are THE NERVOUS SYSTEM. 617 chiefly the processes of the cells of Piirkinje. (2.) The cells of PurMnje (fig. 375 and 389). These are a single layer of very large (40/i X 30,y,) branched nerve-ceils, with large round nuclei, each of which gives off a Fig. 388. — Outline sketch of a section of the cerebeUum, showing: the corpus dentatum. The section has been carried through tixe left lateral part of the pon.s, so as to divide the superior pe- duncle and pass nearly through the middle of the left cerebellar hemisphere. The olivary body has also been divided longitudinally so as to expose in section its corpus dentatum. c r, crus cerebri; /, flUet; q. corpora quadrigemina; s p, superior peduncle of the cerebellum divided; m p, middle peduncle or lateral part of the pons Varolii, with fibres passing from it into the white stem; a v, continuation of the white stem radiating toward the arbor vitae of the folia; c d, corpus dentatum ; o, olivary body with its corpus dentatum ; p, anterior pyramid. (Allen Thomson.) %. single unbranched process downward, and numerous processes upward into the external layer, some becoming continuous with the scattered corpuscles of that layer. (3.) The nuclear or granular layer (g), con- sisting of immense numbei's of corpuscles closely resembling those of the nuclear layers of the retina. Some of these corpuscles belong to the neuroglia, but others are small nerve cells which terminate in processes "which end in minute branchings. One of the processes sends a branch outward to the molecular layer. (4. ) Nerve-fihre layer (/. ) Bundles of nerve-fibres forming the white matter of the cerebellum, which, from its branched appearance, has been named the ai'hor vitce. Some of these fibres pass out to join with the cells of Purkinje, and others pass further outward into the molecular layer, where losing their me- dullas, they divide into fibres which form part of the layer. In the molecular layer, then, there are four sets of fibres, those passing ofi^ from the cell proper to the layer, those from the nuclear layer, those from the cells of Purkinje, and the fibres from the central gray matter. Functions of the Cerebellum. (1.) With the exception of its middle lobe, the cerehellum is itself in- sensible to irritation and may be all cut away without eliciting signs of pain (Longet). Its removal or disorganization by disease is also generally unaccompanied by loss or disorder of sensibility; animals from which it is removed can smell, see, hear, and feel pain, to all ajjpearances, as per- fectly as before (Flourens; Magendie). It cannot, therefore, be regarded as a principal organ of sensation. Yet, if any of its crura be 618 HANDBOOK OF PHYSIOLOGY. touched, pain is indicated; and, if tlie restiform tracts of the medulla oblongata be irritated, the most acute suffering apjoears to be produced. (2.) Co-ordination of Movements. — In reference to motion, the experi- ments of Longet and many others agree that no irritation of the cerebel- . pa Fig. 389.— Vertical section of dog's cerebellum; p w, pia mater; p, corpuscles of Purkinj§ which are branched nerve-cells lying in a single layer and sending single processes downward and more numerous ones upward, which branch continuously and extend through the deep "molecular layer" toward the free surface; g, dense layer of ganglionic corpuscles, closely re- sembling nuclear layers of retina; /, layer of nerve-fibres, with a few scattered ganglionic cor- puscles, This last layer (//) constitutes part of the ichUe matter of the cerebellum, while the layers between it and the free surface are gray matter. (Klein and Noble Smith.) lum produces movement of any kind. Remarkable results, however, are produced by removing parts of its substance, Flourens (whose experi- ments have been confirmed by those of Bouillaud, Longet, and others) extirpated the cerebellum in birds by successive layers. Feebleness and THE ISTERYOUS SYSTEM. 61& want of harmony of muscular movements were the consequence of remov- ing the superficial layers. When he reached the middle layers, the ani- mals became restless without being convulsed; their movements were violent and irregular, but their sight and hearing were perfect. By the time that the last i^ortion of the organ was cut away, the animals had entirely lost the powers of springing, flying, walking, standing, and preserving their equilibrium. When an animal in this state was laid upon its back, it could not recover its former posture, but it fluttered its. wings, and did not lie in a state of stupor ; it saw the blow that threatened it, and endeavored to avoid it. Volition and sensation, therefore, were not lost, but merely the faculty of combining the actions of the muscles;, and the endeavors of the animal to maintain its balance were like those of a drunken man. The experiments afforded the same results when repeated on all classes of animals; and from them and the others before referred to, Flourens inferred that the cerebellum belongs neither to the sensory nor the intel- lectual apparatus; and that it is not the source of voluntary movements, although it belongs to the motor apparatus; but is the organ for the co- ordination of the voluntary movements, or for the excitement of the com- bined action of muscles. Such evidence as can be obtained from cases of disease of this organ, conflrms the view taken by Flourens: and, on the whole, it gains sup- port from comparative anatomy: animals whose natural movements- require most frequent and exact combinations of muscular actions being- those whose cerebella are most developed in proportion to the spinal cord. We must remember, too, that the cerebellum is connected with the posterior columns of the cord as well as with the direct cerebellar tract, both of which probably convey to the middle lobe muscular sensations. It is also connected with the auditory nerves and bulb by the internal and external acute fibres; and with the tegmentum through the red nuclei. Its connection with the efl'erent tracts from the difl'erent cerebral lobes through the pons is also highly important. Movements of the eyes also occur on direct stimulation of the middle lobe. It seems, therefore, to be connected in some way with all of the chief sensory impulses which have to do with the maintenance of the equilibrium, and is generally included in the nervous apparatus which is supposed to govern this func- tion of our bodies. Foville supposed that the cerebellum is the organ of vmscidar sense, i. e. , the organ by which the mind acquires that knowledge of the actual state and position of the muscles which is essential to the exercise of the will upon them ; and it must be admitted that all the facts just referred to are as well explained on this hypothesis as on that of the cerebellum being the organ for combining 630 HANDBOOK OF PHYSIOLOGY. moTements. A harmonious combination of muscular actions must depend as much on the capability of appreciating the condition of the muscles with regard to their tension, and to the force with which they are contracting, as on the power which any special nerve-centre may possess of exciting them to contrac- tion. And it is because the power of such harmonious movement would be equally lost, whether the injury to the cerebellum involved injury to the seat of muscular sense, or to the centre for combining muscular actions, that ex- periments on the subject afford no proof in one direction more than the other. Forced Movements. — The influence of each half of the cerebellum is directed to muscles on the opposite side of the body; and it would appear that for the right ordering of movements, the actions of its two halves must be always mutually balanced and adjusted. For if one of its crura, or if the pons on either side of the middle line, be divided, so as to cut off from the medulla oblongata and spinal cord the influence of one of the hemispheres of the cerebellum, strangely disordered movements ensue (forced movements). The animals fall down on the side opposite to that on which the crus cerebelli has been divided, and then roll over continuously and repeatedly; the rotation being always round the long axis of their bodies, and generally from the side on which the injury has been inflicted. The rotations sometimes take place with much rapidity; as often, according to Magendie, as sixty times in a minute, and may last for several days. Similar movements have been observed in men; as by Serres in a man in whom there was apoplectic effusion in the right crus cerebelli ; and by Belhomme in a woman, in whom an exostosis pressed on the left crus. They may, perhaps, be explained by assuming that the division or injury of the crus cerebelli produces paralysis or imper- fect and disorderly movements of the opposite side of the body; the animal falls, and then, struggling with the disordered side on the ground, and striving to rise with the other, pushes itself over; and so again and again, with the same act, rotates itself. Such movements cease when the other crus cerebelli is divided ; but probably only because the paralysis of the body is thus made almost complete. Other varieties of forced movements have been observed, especially those named " circus movements," when the animal operated upon moves round and round in a circle ; and again those in which the animal turns over and over in a series of somersaults. Nearly all these movements may result on section of one or other of the following parts; viz., crura cerebri, medulla, pons, cerebellum, corpora quadrigemina, corpora striata, optic thalami, and even, it is said, of the cerebral hemispheres. Functions of the Corpora Quadrigemina and Geniculata. The corpora quadrigemina are the homologues of the optic lobes in birds, amphibia, and fishes. The anterior pair may be regarded as the THE KERVOUS SYSTEM. 621 principal nerve-centres for visual sensations, the posterior possibly with auditory sensation. Functions. — (1) The experiments show that removal of the anterior corpora quadrigemina wholly destroys the power of seeing; and diseases in which they are disorganized are usually accompanied by blindness. Atrophy of them is also often a consequence of removal of the eyes. Destruction of one of the anterior corpora quadrigemina (or of one optic lobe in birds) produces hemiopia of opposite field of vision. This loss of sight is the only apparent injury of sensibility sustained by the removal of the corpora quadrigemina. The (2) removal of one of them affects the movements of the body, so that animals rotate, as after division of the crus cerebri, only more slowly: but this may be due to giddiness and partial loss of sight. (3) The more evident and direct influence is that produced on the iris. It contracts when the anterior corpora quadrigemina are irritated: it is always dilated when they are removed : so that they may be regarded, in some measure at least, as the nervous centres governing its move- ments, and adapting them to the impressions derived from the retina through the optic nerves and tracts. (4) The centre for the co-ordination of the movements of the eyes is also contained in them. This centre is closely associated with that for contraction of the pupil, and so it follows that contraction or dilatation follows upon certain definite ocular movements. As we have seen, the lateral corpus geniculatum is associated on either side with the anterior corpus quadrigeminum, and the median corpus geniculatum with the posterior corpus quadrigeminum. TJie iSi/nijjafhetic System. — Having in the preceding chapters com- pleted the description of the Cerebro-spinal nervous system proper, there remains to be considered the structure and functions of the so-called Sympathetic nervous system, and to this it is now necessary to direct attention. It should, however, be distinctly borne in mind that the cerebro- spinal and sympathetic systems are not distinct from one another. The separation of the one from the other may be considered to be purely for the sake of convenience. Distribution. — It consists of: (1) A double chain of ganglia and fibres, which extends from the cranium to the pelvis, along each side of the vertebral column, and from which branches are distributed both to the cerebro-spinal system, and to other parts of the sympathetic system. With these may be included the small ganglia in connection with those branches of the fifth cerebral nerve which are distributed in the neigh- borhood of the organs of special sense : namely, the Oplitlialmic^ Otic, 622 HANDBOOK OF PnYSIOLOGT. Fig. 390.— Diaerammatic view of the Sympathetic cord of the right side, show- ing Its connections with the principal cerebro-spinal nerves and the main prae- aortic plexuses. K- CFrom Quain's Anatomy. J) Cerehro-spinal nerves.— Vl., a portion of the sixth cranial as it passes through the cavernous sinus, receiving two twigs from the carotid plexus of the sympathe- tic nerve; O, ophthalmic ganglion con- nected by a twig with the carotid plexus; M, connection of the sphenopalatine ganglion by the Vidian nerve with the carotid plexus; C, cervical plexus; Br, brachial plexus; D 6. sixth intercostal nerve; D 12, twelfth; L 3, third lumbar nerve; S 1, first sacral nerve; S3, third; S 5, fifth; Cr, anterior crural nerve; CV, great sciatic ; pn, vagus in the lower part of the neck; r, recurrent nerve winding round the subclavian artery. Symjwthetic Cord -c, superior cervi- cal ganglion; c', second, or middle; c", in- ferior: from each of these ganglia cardiac nerves (all deep on this side ) are seen de- scending to the cardiac plexus; d 1, placed immediately below the first dorsal sympathetic ganglion; d 6, is opposite thesi.xth; 1 1, first lumbar ganglion; c g, the terminal or coccygeal ganglion. Prcnaorticand Visceral Plexuses.— pp, pharyngeal, and, lower down, laryngeal plexus; pU post-pulmonary plexus spreading from the vagus on the back of the right bronchus; co, on the aorta, the cardiac plexus, towardswhieh, inaddition to the cardiac nerves from the three cer- vical sympathetic gangha, other branch- are seen descending from the vagus I recurrent nerves; co, right or poste- - and CO', left or ant. coronary plexus; esophageal plexus in long meshes on gullet: sp, great splanchnic nerve Ml med by branches from the fifth, sixth, seventh, eighth.and ninth dorsal ganglia; -f, small splanchnic from the ninth and tenth; -\- -f , smallest or thu'il splanchnic from the eleventh; the first and second of these are shown joining the solar plexus, s o; the third descending to the renal plexus, re; connecting branches between the solar plexus and the vagi are also rep- resented; pn', above the place where the right vagus passes to the lower or pos- terior surface of the stomach; pn", the left distributed on the anterior or upper surface of the cardiac portion of the or- gan: from the solar plexus large branch- es are seen sm-rounding the arteries of the cceliac axis, and descending to m s, the sup. mesenteric plexus; opposite to this is an indication of the suprarenal plexus; below r e (the renal plexus), the spermatic plexus is also indicated ; a o, on the front of the aorta, marks the aortic plexus, formed by nerves descending from the solar and sup. mesenteric plex- uses and from the lumbar gangha; mi, the inf. mesenteric plexus surroimding thecorrespondingartery;/i2/, hypogastric plexus placed between the common iliac vessels, connected above with the aortic plexus, receiving nerves from the lower lumbar ganglia, and dividing below into the right and left pelvic or inf. hypogas- tric plexuses; pi, the right pelvic plexus; from this the nerves descending are join- ed by those from the plexus on the sup. hemorrhoidal vessels, vii', by nerves from the sacral ganglia, and by visceral nerves from the tliird and fourth sacral ^MiMj^i. spinal nerves, and there are thus formed the rectal, vesical, and other plexuses, which ramify upon the viscera, as towards ir, and v, the rectum and bladder. THE NERVOUS SYSTEM. 623 SpJieno-paJatine and Suhnaxillary ganglia. (2) Various ganglia and plexuses of nerve-fibres which give off branches to the thoracic and ab- dominal viscera, the chief of such plexuses being the Cardiac, Solar, and Ui/jjogastricj but inintimate connection with these are many second- ary plexuses, as the Aortic, Spermatic, and Renal. To these plexuses, fibres pass from the praevertebral chain of ganglia, as well as from cerebro- spinal nerves. (3) Various ganglia and plexuses in the substance of many of the viscera, as in the Stomach, Intestines, and Urinary l)ladder. These, which are, for the most part, microscopic, also freely communi- cate with other parts of the sympathetic system, as well as, to some ex- tent, with the cerebro-spinal. (I) By many, the ganglia on the Pos- terior roots of the spinal nerves, on the Glossopharyngeal and Vagus, and on the Sensory root of the Fifth cerebral nerve (Gasserian ganglion) , are also included as sympathetic-nerve structures. Class if cation. — Gaskell's researches have suggested a convenient classification for the sympathetic ganglia into: (1.) The main sympa- thetic chain, extending from above downward, in the form of connected ganglia lying upon the bodies of the vertebrae, which may be called lateral or vertebral ganglia. (2). A more or less distinct chain, prever- tebral in position, consisting of the semi-lunar, inferior mesenteric and similar plexuses, which may be called collateral ganglia. (3.) Ganglia situated in the organs and tissues themselves, called terminal ganglia. (4.) The ganglia of the posterior roots of the spinal nerves. The connection between these parts is as follows : the visceral branch or ramus communicaus of each spinal nerve, which is one of the divi- sions of a typical spinal nerve — the others being the dorsal and ventral — passes first of all into the lateral chain; from this chain branches, rami efferentes, pass into the collateral ganglia, and from these again other branches pass off into the organs to end in the terminal ganglia. In the thoracic region the rami communicantes are composed of two parts, white and gray. The former can be traced backward into both spinal nerve-roots of their corresponding spinal nerve ; and in the other direc- tion partly into the lateral sympathetic chain, and partly into the great splanchnic nerves and so into the collateral ganglia without entering the lateral chain at all. The upper white rami (from the 2nd to the 5th), however, proceed upward and join the superior cervical ganglion instead of passing downward into the sj)lanchnics. Other branches go downward into the lumbar and sacral plexuses. The gray rami of all the spinal nerves are the only apparent representatives of the visceral branches in the regions above the 2nd thoracic nerve-root, and below the 2nd lumbar nerve-root, with the exception of the roots of the 2nd and 3rd sacral nerves, which have also white rami, and consist of non- medullated fibres, and pass from the ganglia to be distributed chiefly to 624 HANDBOOK OF PHYSIOLOGY. the spinal column, to the spinal membranes and to the spinal nerve-roots themselves. We must look upon the white rami then as the visceral branches proper. A peculiarity in the structure of these white medullated visceral nerves is the fineness of their fibres. They are a third or a fourth of the diameter of ordinary medullated fibres, measuring 1.8// to 2.7/^ instead of 14.4/z to 19//. Such fibres are a peculiarity of the spinal nerve-roots, chiefly in the thoracic region, but they are also found in the second and third sacral nerves, and constitute there the nervi erigentes which pass, directly to the hypogastric ^olexus, and not first of all into the lateral chain. From this plexus branches pass upward into the inferior mesenteric ganglia and downward to the bladder, rectum and generative organs. These nerves, called by Graskell^;e/y('c splanchnic nerves, differ from the rami viscerales of the thoracic region only in not communicat- ing with the lateral ganglia; the branches which pass upward from the thoracic region to the neck, he calls cervical splancJmics, and the splanchnics proper abdominal splanchnics. The white rami viscerales of the upper cervical and cervico-cranial regions do not run with their corresponding gray rami, but form, Gaskell thinks, the internal branch of the spinal accessory nerve, which contains small medullated fibres similar to those of the visceral branches in the thoracic region. This branch passes into the ganglion of the trunk of the vagus. Small visceral fibres exist too in the roots of the vagus, and in those of the glosso-pharyn- geal in connection with the ganglion of the trunk and ganglion petrosum, as well as in the chorda tympani, in the small petrosal and in other cranial visceral nerves. Functions. — The researches of Gaskell have, however, done much to clear up the former confusion as to the functions of the sympathetic; and in the following account the description of the functions, as given by that observer, is followed. The efferent iierve fibres of the sympathetic system supply {a) the muscles of the vascular system, to which they send vaso-motor fibres, i.e., vaso-constrictor and cardiac augmentor or accelerator., and vaso-in- hibitory fibres, i.e.., vaso-dilator and cardiac inhibitory; (b) the visceral muscles, to which they send both viscero-motor and viscero-inhibitorg fibres, (c) The secretory gland-cells. (a) i. Vaso-motor or Vaso-constrictor and Cardio-augmentor Fibres. — The vaso-motor nerves for all parts of the body come from the central ner- vous system, and pass out from the spinal cord in the white rami viscerales of the thoracic region from the second thoracic to the second lumbar nerve- roots inclusive, as fine medullated fibres ; they then pass to the lateral or main sympathetic chain, become non-medullated, and are distributed to their muscles either directly or through terminal ganglia. Thus the aug- THE NERVOUS SYSTEM. 625 mentor nerves of the heart arise in the thoracic rami, pass upward through tlie ganglion stellatum (first thoracic ganglion), the anuulus of Yieussens and the inferior cervical ganglion, and are distributed to the heart ; the vaso-motor roots of the brachial plexus, in the anterior roots of the second and lower thoracic nerves, and reach that plexus by the same ganglion ; the vaso-motor nerves of the foot leave the spinal cord high up, and reach the sympathetic lateral ganglia above the origin of the sciatic nerve, into which they pass through the abdominal sympa- thetic. In all cases the nerves lose their medulla in the ganglia. Similiirly the vaso-motor nerve supply for the blood-vessels of the head and neck and of the abdomen is derived from the cervical and abdominal splanchnics respectively, or from the corresponding rami efPerentes of the upper lumbar ganglia. The lateral sympathetic chain Gaskell proposes to call the chain of vaso-motor ganglia. ii. Vaso-inhibitory or Vaso-dilator, and Cardio-inhihitory Fibres. — Of these, which are doubtless as widely distributed as the vaso-motor fibres, we have distinct proof in the existence of fibres separate from vaso-motor, e.g.., in the inhibitory nerve of the heart, the cardio-vagus; in the chorda tympani; in the small petrosal, and inthenervi erigentes. These nerve-fibres, as far as we know at present, leave the central nervous system among the fine medullated nerves of the cervico-crania"! and sacral rami communicantes, do not enter the lateral ganglia, but pass without losing their medulla into the collateral or terminal ganglia. {b.) i. Viscero-motor Fibres. — These fibres, upon which depend the peristaltic movements of the thoracic portion of the oesophagus, and of the stomach and intestines, arise from the central nervous system, as the fine medullated fibres of the upper portion of the cervical region, not in the spinal nerve-roots of that region, but as the bundles of fibres which may be called the rami viscerales of the vagus and accessory nerves. They pass to the ganglion of the trunk of the vagus, where they lose their medulla. ii. Yi.icero-Inliibitory Fibres. — It appears that the nerve supply to the circular muscles of the alimentary canal and its ap^iendages, is con- tained in the abdominal splanchnics, and consists of those fibres which have not passed through the lateral chain, and which therefore retain their medulla until they reach the proximal or collateral chain, (c.) Glandular Nerve-Fibres. — A double nerve supply, in all proba- bility coinciding with the supply to the visceral muscles, has been demonstrated in the cases of the submaxillary, parotid, and lachrymal glands, and in these cases the course of the fibres is very similar to that of the corresponding fibres for the vaso-muscular supply. Thus 40 626 HANDBOOK OF PHYSIOLOGY. the sympathetic suj)ply for these glands passes along with the vjiso- motor fibres from the cervical splanchnic (or sympathetic trunk), and superior cervical ganglion; while the cerebro-spinal supply comes from the rami viscerales of the cranial nerves in conjunction with the vaso- dilator fibres. Central Oriffm of the Rami Viscerales. — There appears to be the strongest presumption that the white rami of the thoracic region arise in the spinal cord in, or are connected with, the cells of the posterior vesicular column of Clarke. This conclusion is based upon the fact that these special cells are found in the three regions already mentioned, and in those only where the white rami of fine medullated fibres exist, viz., in the cervico-cranial regions, in the spinal accessory, in the thoracic region, and in the sacral region. But it is probable that the fibres are also connected with the cells of the lateral horn of the gray matter of the spinal cord, and its representative in the medulla, the antero-lateral nucleus of Clarke. In a paper supplementary to his first account of the sympathetic system, Gaskell traced the nerve fibres of the anterior nerve roots to the various groups of nerve cells in the spinal cord thus: (i.) Efferent nerves to somatic muscles arise from group of cells of anterior cornua ; (ii.) efferent nerves to striated splanchnic muscles from cells of the trac- tus intermedio-lateralis. (iii-) Anabolic or inhibitory nerves to glands, muscles of viscera, and vessels of splanchnic system from cells of Clarke's column; (iv. ) motor nerves to visceral muscles from solitary cells at the base of the posterior cornu ; and (v.) motor or catabolic nerves to glands and vascular muscles from small cells of the lateral cornu. Structure and Functions of the Ganglia.— The sympathetic ganglia all contain— (1.) nerve-fibres traversing them; (3.) nerve-fibres originating in them, (3.) nerve or ganglion -cor j)uscles, giving origin to these fibres; and (4.) other corpuscles that appear free. In the sym- pathetic ganglia of the frog, ganglion-cells of a very complicated struc- ture have been described by Beale, and subsequently by Arnold. The cells are inclosed each in a nucleated capsule : they are pyriform in shape, and from the pointed end two fibres are given off, which gradually acquire the characters of nerve-fibres, one of them is straight, and the other (which sometimes arises from the cell by two roots) is spirally coiled around it. According to Gaskell the functions of the main sympathetic ganglia are the following : — (1.) They effect the conversion of medullated into non-medullated fibres; (2.) They possess a nutritive influence over the nerves which pass from them to the periphery; (3.) They increase the number of fibres at the same time as they cause the removal of the medulla. As regards their possession of the usual properties of nerve- THE NERVOUS SYSTEM. 627 centres little or nothing is certainly known. It appears unlikely that they possess the reflex functions of the spinal centres. As a contribution toward the explanation of the nervous mechanism of nutrition comes in Gaskell's theory of cataholic and anabolic nerves. He supposes that every tissue is supplied with two sets of nerves, the former of which corresponds with the motor nerve, the viscero-motor and the cardio^augmentor, by the stimulation of which an increase of the metabolism takes place, and which is followed by exhaustion. It may be accompanied either by contraction of a muscle or by an increase of contraction. Such a nerve is excellently illustrated by the sympa- thetic augmentor or accelerator nerve of the heart, on stimulation of which an increase in the force and frequency of the heart takes place, followed after a time by exhaustion. A catabolic nerve stimulates the destructive metabolism which is always going on in a tissue. The anabolic nerve is the exact opposite of the catabolic nerve in function. It subserves constructive metabolism. Stimulation of the nerve pro- duces diminished activity, repair of tissue and building up. An exam- l^le of this kind of nerve is seen in the cardiac vagus, stimulation of which produces inhibition. Inhibition must generally be looked upon as an anabolic process. It will be seen that the results of stimulation of the nerves to the salivary glands, discussed in a former chapter, appear to support the theory, that the processes of constructive and destructive metabolism are under the control of separate nerve-fibres. In the case of the sub- maxillary gland for example, if the sympathetic fibres be stimulated, a catabolic efEect is produced, and the materials of secretion are formed at the expense of the protoplasm (this action in the case of the gland Heidenhain calls trophic) ; if on the other hand the chorda tympani or the secretory nerve be stimulated, two things happen, one being the discharge of water and the materials of secretion from the gland cells, and the other the building up or reconstruction of the protoplasm of the cells. A part of this action at any rate is anabolic, and similar to the action of inhibitory nerves. CHAPTER XVII. THE SENSES. General Co?isiderafions. — Through the medium of the nervous sys- tem the mind obtains a knowledge of the existence both of the various parts of the body, and of the external world. This knowledge is based upon sensatiofis resulting from the stimulation of certain centres in the brain, by irritations conveyed to them by afferent nerves. Under normal circumstances, the following structures are necessary for sensation: (a) A peripheral organ for the reception of the impression ; (b) a nerve for conducting it; (c) a nerve-centre for feeling or perceiving it. Classiiication of Sensations. — Sensations may be conveniently classed as (1) common and (3) special. (1.) Common Sensations. — Under this head fall all those general sensations which cannot be distinctly localized in any particular part of the body, such as fatigue, discomfort, faintness, satiety, together with Imnger and thirst, in which, in addition to a general discomfort, there is in many persons a distinct sensation referred to the stomach or fauces. In this class must also be placed the various irritations of the mucous membrane of the bronchi, which give rise to coughing, and also the sensations derived from various viscera indicating the necessity of ex- pelling their contents; e.g., the desire to defecate, to urinate, and, in the female, the sensations which precede the expulsion of the foetus. We must also include such sensations as itching, creeping, tickling, tingling, burning, aching, etc., some of which come under the head of 2)ain: they will be again referred to in describing the tactile sense. It is impossible to draw a very clear line of demarcation between many of the common sensations above mentioned, and the sense of touch, which forms the connecting link between the general and special sensations. Touch is, indeed, usually classed with the special senses, and will be considered in the same group with them; yet it differs from them in being common to many nerves. Among common sensations some would rank the muscular sense, which has been already alluded to. It is by means of this sense that we become aware of the condition of the mus- cles, and thus obtain the information necessary for their adjustment to various purposes — standing, walking, grasping, etc. This muscular sensibility (to which we shall again refer) is shown in our power to esti- THE SENSES. 629 mate the difEerences between weights by the different muscular efforts necessary to raise them. It must be carefully distinguished from the sense of contact and of pressure, of which the skin is the organ. When standing erect, we can feel the ground (contact) , and further there is a sense of pressure, due to our feet being pressed against the ground by the weight of the body. Both these are derived from the skin of the sole of the foot. If now we raise the body on the toes, we are conscious (muscular sense) of a muscular effort made by the muscles of the calf, which overcomes a certain resistance. (2.) Special Sensations. — Including the sense of touch, the special senses are five in number — Touch, Taste, Smell, Hearing, Sight. The most important distinction between common and special sensa- tions is that by the former we are made aware of certain conditions of various jiarts of our bodies, while from the latter we gain our knowledge of the external world also. This difference will be clear if we compare the sensations of pain and touch, the former of which is a common, the latter a special sensation. " If we place the edge of a sharp knife on the skin, we feel the edge by means of our sense of touch; we perceive a sensation, and refer it to the object which has caused it. But as soon as we cut the skin with the knife, we feel pain, a feeling which we no longer refer to the cutting knife, but which we feel within ourselves, and which communicates to us the fact of a change of condition in our own body. By the sensation of pain we are neither able to recognize the object which caused it, nor its nature." In studying the phenomena of sensation, it is important clearly to understand that the sevsorium, or seat of sensation, is in the brain, and not in the particular organ through which the sensory impression is re- ceived. In common parlance we are said to see with the eye, hear with the ear, etc., but in reality these organs are only adapted to receive impressions which, being conducted to the sensorium, through their re- spective nerves give rise to sensation. Hence, if the optic nerve is severed, vision is no longer possible: since, although the image falls on the retina as before, the sensory im- pression can no longer be conveyed to the sensorium. When any given sensation is felt, all that we can with certainty affirm is that some part of the brain is excited. The exciting cause may be some object of the external world, j^roducing an objective sensation; or the condition of the sensorium may be due to some excitement Avithin the brain itself, in which case the sensation is termed subjective. The mind habitually re- fers sensations to external causes; and hence, whenever they are subjec- tive we can hardly divest ourselves of the idea of an external cause, and an illusion is the result. Xumberless examples of such illusions might be quoted. As familial 630 HANDBOOK OF PHYSIOLOGY. cases may be mentioned, humming and buzzing in the ears caused by some irritation of the auditory nerve or centre, and even musical sounds and voices (sometimes termed auditory spectra) ; also so-called optical illusions: objects are described as seen, although not present. Such illusions are most strikingly exemplified in cases of delirium tremens or other forms of delirium, and may take the form of cats, rats, creeping loathsome forms, etc. Causes of Illusions. — One uniform internal cause, whicli may act on all the nerves of the senses in the same manner, is capillary congestion. This one cause excites in the retina, while the eyes are closed, the sensa- ions of light and luminous flashes; in the auditory nerve, the sensation of humming and ringing sounds; in the olfactory nerve, the sense of odors; and in the nerves of feeling, the sensation of pain. In the same way, also, a narcotic substance introduced into the blood, excites in the nerves of each sense peculiar symptoms: in the optic nerves, the appear- ance of luminous sparks before the eyes ; in the auditory nerves, tinnitus aurimn; and in the common sensory nerves, the sensations of creeping over the surface. So, also, among external causes, the stimulus of elec- tricity, or the mechanical influence of a blow, concussion, or pressure, excites in the eye the sensation of light and colors; in the ear, a sense of aloud sound or of ringing; in the tongue, a saline or acid taste; and in the other parts of the body, a perception of peculiar jarring or of the mechanical impression, or a shock like it. Experiments seem to have proved, however, that none of the nerves of special sense possess the faculty of common sensibility. Perceptions. — The habit of constantly referring our sensations to ex- ternal causes, leads us to interpret the various modifications which external objects produce in our sensations, ?is, properties of the external bodies themselves. Thus we speak of certain substances as possessing a disagreeable taste and smell; whereas, the fact is, their taste and smell are only disagreeable to us. It is evident, however, that on this habit of referring our sensations to causes outside ourselves (perception), de- pends the reality of the external world to us ; and more especially is this the case with the senses of touch and sight. By the co-operation of these two senses, aided by the others, we are enabled gradually to at- tain a knowledge of external objects which daily experience confirms, until we come to place unbounded confidence in what is termed the evidence of the senses. Judgments. — We must draw a distinction between mere sensations, and the judgments based, often unconsciously, upon them. Thus, in looking at a near object, we unconsciously estimate its distance and say it seems to be ten or twelve feet off: but the estimate of its distance is in reality a judgment based on many things besides the appearance of THE SENSES, 631 the object itself; among which may be mentioned the number of inter- vening objects, the number of steps which from jjast experience we know we must take before we could touch it, and many others. The Special Senses. I. Touch. Seat. — The sense of touch is not confined to particular parts of the body of small extent, like the other senses; on the contrary, all parts capable of perceiving the presence of a stimulus by ordinary sensation are, in a certain degrees, the seat of this sense ; but touch should not be considered as a mere modification or exaltation of common sensation or sensibility. For although the nerves on which the sense of touch de- pends, are the same as those which confer ordinary sensation on the different parts of the body, viz., those derived from the posterior roots of the nerves of the spinal cord, and the sensory cerebral nerves, yet it seems jirobable that the nerve-fibres which subserve the special sense of touch are provided with special end organs. All parts of the body supplied with sensory nerves are thus, in some degree, organs of touch, yet the sense is exercised in perfection only in those parts the sensibility of which is extremely delicate, e.g., the skin, the tongue, and the lips, which are provided with abundant papillae. A peculiar and, of its own kind in each case, a very acute sense of touch is exercised through the medium of the nails and teeth. To a less extent the hair may be reckoned an organ of touch ; as in the case of the eye- lashes. The sense of touch renders us conscious of the presence of a stimulus, from the slightest to tlie most intense degree of its action, by that indescribable something which we call feeling, or common sensa- tion. The modifications of this sense often depend on the extent of the I)arts affected. The sensation of pricking, for example, informs us that the sensitive fibres are intensely affected in a small extent ; the sensation of pressure indicates a slighter affection of the parts in the greater ex- tent, and to a greater dejith. It is by the depth to which the parts are affected that the feeling of pressure is distinguished from that of mere contact. Varieties. — {a) The sense of touch proper, tactile sensibility or pres- sure, {b) temperature. These when carried beyond a certain degree are merged in the sensation of (c) pain. Touch proper. — In almost all parts of the body which have deli- cate tactile sensibility the epidermis, immediately over the papilla, is moderately thin. When its thickness is much increased, as over the heel, the sense of touch is very much dulled. On the other hand, when it is altogether removed, and the cutis laid bare, the sensation of con- 632 HANDBOOK OF PHYSIOLOGY. tact is replaced by one of pain. Further, in all highly sensitive parts, the papilliB are numerous and highly vascular, and the sensory nerves are connected with special end-organs which have been described p. 97 et seq. The special endings of the nerves which have to do with touch may, however, be here again mentioned. They are of two kinds, viz., (a) touch corjmscles, which are found chiefly in the hands and feet, particu- larly on the palmar surface of the hands and fingers, but also on the under surface of the forearm, nipple, eyelids, lips, and genital organs. Touch corpuscles are situated in the cutis vera, (b) end hulbs, which are found in conjunctivee and other mucous membranes, the lijis, genital organs, tongue, rectum, and elsewhere, but not in the skin proper. As regards the Pacinian corpuscles and similar end-organs, which are so widely distributed, and which may be in some way connected with the sensation, when they are found in the skin they are situated very deeply in the cutis vera or in the subcutaneous tissue. They are extremely numerous on the nerves of the palmar surface of the fingers. In all of these endings, and in similar ones found in other animals, the nerve ends, as in axis cylinder, in a special development of the connective tis- sue sheath. In addition to these special nerve-endings, nerve-fibres appear to terminate everywhere in the skin between the cells of the Malpighian stratum of the epidermis in the ends, and in certain animals some of them appear to end in special and rather large cells. It is practically impossible to distinguish between what is called mere contact and touch in which the element of pressure comes in. The acuteness of the sense of touch depends very largely on the cutane- ous circulation, which is of course largely influenced by external temper- ature. Hence the numbness, familiar to every one, produced by the application of cold to the skin. Acuteness of the Se7ise. — The perfection of the sense of touch on different parts of the surface is proportioned to the power which such parts possess of distinguishing and isolating the sensations produced by two points placed close together. This power depends, at least in part, on the number of primitive nerve-fibres distributed to the part; for the fewer the primitive fibres which an organ receives, the more likely is it that several impressions on different contiguous points will act on only one nervous fibre, and hence be confounded, and perhaps produce but one sensation. Experiments have been made to determine the tactile properties of different parts of the skin, as measured by this power of distinguishing distances. These consist in touching the skin, while the eyes are closed, with the points of a pair of compasses sheathed with cork, and in ascertaining how close the points of compasses might be brought to each other, and still be felt as two bodies. THE SENSES. 633 Table of variations in the tactile sensibility of the different parts, — The mea- surement indicates the least distance at which the t ' 2iair of comjxisses could be separately distinguished. Tip of tongue ....... Palmar surface of third phalanx of forefinger Palmar surface of second phalanges of fingers Red surface of under-lip .... Tip of nose ....... Middle of dorsum of tongue .... Palm of hand ....... Centre of hard palate ...... Dorsal sui-face of first phalanges of fingers Back of hand ...... Dorsum of foot near toes ..... ■Gluteal region ...... Sacral region Upper and lower parts of forearm Back of neck near occiput .... Upper dorsal and mid-lumbar regions . Middle part of forearm Middle of thigh Mid-cervical region Mid-dorsal region CO blui ted 2w 'nts of a (E. H Weber. ) 2\ inch 1 mm. 1 b( 2 (( 12 i u 4 i( i u 4 a i " 6 " i " 8 " t\ u 10 " i " 12 " tV " 14 u H " 35 " 1^ u 37 (( li " 37 u, n " 37 " li •' 37 u. 2 " 50 " 2 " 50 " 3+ " 63 " 4 " 63 " 2i " 63 " 2i " 63 a Moreover, in the case of the limbs, it was found that before they were recognized as two, the points of the compasses had to be further separated when the line joining them was in the long axis of the limb, than when in the transverse direction. According to Weber the mind estimates the distance between two points by the number of unexcited nerve-endings which intervene be- tween the two points touched. It would appear that a certain number of intervening unexcited nerve-endings are necessary before two points touched can be recognized as separate, and the greater this number the more clearly are the points of contact distinguished as separate. By practice the delicacy of a sense of touch may be very much increased. A familiar illustration occurs in the case of the blind, who, by constant practice, can acquire the power of reading raised letters the forms of which are almost if not quite undistinguishable by the sense of touch to an ordinary person. Localization. — The power of correctly localizing sensations of touch is gradually derived from experience. Thus infants when in pain sim- ply cry, but make no effort to remove the cause of irritation, as an older child or adult would, doubtless on account of their imperfect knowledge of its exact situation. Illusions. — The different degrees of sensitiveness possessed by differ- ent parts may give rise to errors of judgment in estimating the distance between two points where the skin is touched. Thus, if blunted points of a pair of compasses (maintained at a constant distance apart) be slowly drawn over the skin of the cheek toward the lips, it is almost im- possible to resist the conclusion that the distance betAveen the j)oints is 634 HANDBOOK OF PHYSIOLOGY. gradually increasing. When they reach the lips they seem to be consid- erably further apart than on the cheek. Thus, too, our estimate of the size of a cavity in a tooth is usually exaggerated when based upon sensa- tion derived from the tongue alone. Another curious illusion may here be mentioned. If we close the eyes, and place a small marble or pea between the crossed fore and middle fingers, we seem to be touching two marbles. This illusion is due to an error of judgment. The marble is touched by two surfaces which, under ordinary circumstances, could only be touched by two separate marbles, hence the mind, taking no- cognizance of the fact that the fingers are crossed, forms the conclusion that two sensations are due to two marbles. Temperature. — The whole surface of the body is more or less sen- sitive to difiPerences of temperature. The sensation of heat is distinct from that of touch : and it would seem reasonable to suppose that there are special nerves and nerve-endings for temperature. At any rate the power of discriminating temperature may remain unimpaired when the sense of touch is temporarily in abeyance. Thus if the ulnar nerve be compressed at the elbow till the sense of touch is very much dulled in the fingers which it supplies, the sense of temperature remains quite unaffected. The sensations of heat and cold are often exceedingly fallacious, and in many cases are no guide at all to the absolute temperature as indi- cated by a thermometer. All that we can with safety infer from our sensations of temperature, is that a given object is warmer or cooler than the skin. Thus the temperature of our skin is the standard; and as this varies from hour to hour according to the activity of the cutane- ous circulation, our estimate of the absolute temperature of any body must necessarily vary too. If we put the left hand into water at 5° C. (40° F.) and the right into water at 45° C. (110° F.), and then immerse both in water at 27° C. (80° F.), it will feel warm to the left hand but cool to the right. Again, a piece of metal which has really the same temperature as a given piece of wood will feel much colder, since it con- ducts away the heat much more rapidly. For the same reason air in motion feels very much cooler than air of the same temperature at rest. In some cases we are able to form a fairly accurate estimate of abso- lute temperature. Thus, by plunging the elbow into a bath, a practised bath-attendant can tell the temperature sometimes within half a degree centigrade. The temperatures which can be readily discriminated are between 10°-45° C. (50°-115° F. ); very low and very high temperatures alike produce a burning sensation. A temperature appears higher according to the extent of cutaneous surface exposed to it. Thus, water of a tem- perature which can be readily borne by the hand, is quite intolerable if ' THE SENSES. 635 the whole body be immersed. So, too, water appears much hotter to the hand than to a single finger. The delicacy of the sense of temperature coincides in the main with that of touch, and appears to depend largely on the thickness of the skin; hence, in the elbow, where the skin is thin, the sense of tempera- ture is delicate, though that of touch is not remarkably so. Weber has further ascertained the following facts: two compass points so near to- gether on the skin that they produce but a single impression, at once give rise to two sensations, when one is hotter than the other. More- over, of two bodies of equal weight, that which is the colder feels heavier •than the other. As every sensation is attended with an idea, and leaves behind it an idea in the mind which can be reproduced at w'ill, we are enabled to com- pare the idea of a past sensation with another sensation really present. Thus we can compare the weight of one body with another which we had previously felt, of which the idea is retained in our mind. Weber was indeed able to distinguish in this manner between temperatures, experienced one after the other, better than between temperatures to which the two hands were simultaneousl}^ subjected. This power of comparing present with past sensations diminishes, however, in propor- tion to the time which has elapsed between them. After -sensations left by impressions on nerves-of common sensibility or touch are very vivid and durable. As long as the condition into which the stimulus has thrown the organ endures, the sensation also remains, though the excit- ing cause should have long ceased to act. Both painful and pleasurable sensations afford many examples of this fact. Subjective sensations, or sensations dependent on internal causes, are in no sense more frequent than in the sense of touch. All the sensations of pleasure and pain, of heat and cold, of lightness and weight, of fa- tigue, etc., may be produced by internal causes. Neuralgic pains, the sensation of rigor, formication or the creeping of ants, and the states of the sexual organs occurring during sleep, afford striking examples of subjective sensations. The mind has a remarkable power of exciting sensations in the nerves of common sensibility : just as the thought of the nauseous excites sometimes the sensation of nausea, so the idea of pain gives rise to the actual sensation of pain in a part predisi^osed to it; numerous examples of this influence might be quoted. Pain. — xVs regards painful sensations, three views can be taken : 1, that it is a special sensation provided with a special conducting apparatus in each part of the body; 2, that it is produced by an over-stimulation of the special nerves concerned with touch or temperature, or of the other nerves of special sense; or 3, that it is an over-stimulation of the nerves of common sensation, which tell us of the condition of our own 636 HANDBOOK OF PHYSIOLOGY. bodies, both of the surface and also of the mternal organs. There seems to be much in favor of all of these views. It is, however, certain that even if any variety of pain be a special sensation, some kind of pain may be produced by stimulation of the bare sensory nerves apart from any special form of nerve termination. It is said that the main difference between the common sensation which tells us of the condition of all parts of the body and of which thirst and hunger are but exam- ples, the one informing us of the condition of the palate and the other of the state of our stomach, and the special sense of touch and tempera- ture, is that the latter are provided with special apparatus. By means of this apparatus we are able to localize tlie sensation from which it is possible to form judgments. Such a special apparatus is evidently not absolutely essential for the sensation of pain, but this does not exclude the idea that pain may result from over-stimulation of a nerve of special sense or of its termination. The Muscular Sense. ^The estimate of a weight is usually based on two sensations: 1, of pressure on the skin, and 2, the muscular sense. The estimate of weight derived from a combination of these two sensations (as in lifting a weight) is more accurate than that derived from the former alone (as when a weight is laid on the hand) ; thus Weber found that by the former method he could generally distinguish 19| oz. from 20 oz., but not 19f oz. from 20, while by the latter he could at most only distinguish 14-^ oz. from 15 oz. It is not the absolute, but the relative, amount of the difference of weight which we have thus the faculty of perceiving. It is not, however, certain, that our idea of the amount of muscular force used is derived solely from the muscular sense. We have the power of estimating very accurately beforehand, and of regulating, the amount of nervous influence necessary for the production of a certain degree of movement. When we raise a vessel, with the contents of which we are not acquainted, the force we employ is determined by the idea we have conceived of its weight. If it should happen to contain some very heavy substance, as quicksilver, we shall probably let it fall; the amount of muscular action, or of nervous energy, which we had exerted being insufficient. The same thing occurs sometimes to a person descending stairs in the dark; he makes the movement for the descent of a step which does not exist. It is possible that in the same way the idea of weight and pressure in raising bodies, or in resisting forces, may in part arise from a consciousness of the amount of nervous energy transmitted from the brain rather than from a sensation in the muscles themselves. The mental conviction of the inability longer to support a weight must also be distinguished from the actual sensation of fatigue in the muscles. THE SEXSES. 637 So, with regard to the ideas derived from sensations of touch com- bined with movements, it is doubtful how far the consciousness of the extent of muscular movement is obtained from sensations in tlie muscles themselves. The sensation of movement attending the motions of the hand is very slight ; and persons who do not know that the action of particular muscles is necessary for the production of given movements, do not suspect that the movement of the fingers, for example, depends on an action in the forearm. The mind has, nevertheless, a very definite knowledge of the changes of position produced by movements; and it is on this that the ideas which it conceives of the extension and form of a body are in great measure founded. There is no marked development of common sensibility to be made oat in muscles: they may be cut without the production of pain. On the other hand, there is no doubt that afferent impulses must pass upward from muscles and tendons acquainting the brain with their condition. This, then, must be a special sense. It has been suggested that the minute end-bulbs of Golgi found in tendons, and that the Pacinian corpuscles in the neighborhood of joints, are the terminal organs of this special sense. Judgment of the Form and Size of Bodies. — By the sense of touch the mind is made acquainted with the size, form, and other external char- acters of bodies. And in order that these characters may be easily ascertained, the sense of touch is especially developed in those parts which can be readily moved over the surface of bodies. Touch, in its more limited sense, or the act of examining a body by the touch, consists merely in a voluntary employment of this sense combined with move- ment, and stands in the same relation to the sense of touch, or common sensibility, generally, as the act of seeking, following, or examining odors, does to the sense of smell. The hand is the best adapted for it, by reason of its peculiarities of structure, — namely, its capability of pronation and supination, which enables it, by the movement of rota- tion, to examine the whole circumference of the body; the power it possesses of opposing the thumb to the rest of the hand, and the relative mobility of the fingers; and lastly from the abundance of the sensory terminal organs which it possesses. In forming a conception of the figure and extent of a surface, the mind multiplies the size of the hand or fingers used in the inquiry by the number of times which it is con- tained in the surface traversed; and by repeating this process w4th regard to the different dimensions of a solid body, acquires a notion of its cubical extent, but, of course, only an imperfect notion, as other senses, e.g.., the sight, are required to make it complete. It is impossible in this consideration to say how much of our knowl- edge of the thing touched depends upon pressure and how much upon, the muscular sense. 638 HANDBOOK OF PHYSIOLOGY. II. Taste. Conditions necessary. — The conditions for the perceptions of taste are: — 1, the presence of a nerve and nerve-centre with special endow- ments; 2, the excitation of the nerve by the sapid matters, which for this purpose must be m a state of solution; 3, a temperature of about 37° to 40° C. (98° to 100° F,). The nerves concerned in the production of the sense of taste have been already considered (p. 302 et seq.) The mode of action of the substances which excite taste consists in the production of a change in the condition of the gustatory nerves, and the conduction of the stimulus thus produced to the nerve-centre; and, according to the difference of the susbtances, an infinite variety of changes of condi- tion of the nerves, and consequently of stimulations of the gustatory centre, may be induced. The matters to be tasted must either be in solution or be soluble in the moisture covering the tongue; hence insolu- ble substances are usually tasteless, and produce merely sensations of touch. Moreover, for the perfect action of a sapid, as of an odorous sub- stance, it is necessary that the sentient surface should be moist. Hence, when the tongue and fauces are dry, sapid substances, even in solution, are with difficulty tasted. The nerves of taste, like the nerves of other special senses, may have their peculiar properties excited by various other kinds of irritation, such as elec- tricity and mechanical impressions. Thus, a small current of air directed upon the tongue gives rise to a cool saline taste, like that of saltpetre ; and a distinct sensation of taste similar to that caused by electricity, may be pro- duced by a smart tap applied to the papillae of the tongue. Moreover, the mechanical irritation of the fauces and palate produces the sensation of nausea, whicli is probably only a modification of taste. Seat. — The principal seat (apparent seat, that is, to our senses) of the sense of taste is the tongue. But the result of experiments as well as ordinary experience show that the soft palate and its arches, the uvula, tonsils, and probably the upper part of the pharynx, are also endowed with taste. These parts, together with the base and posterior parts of the tongue, are supplied with branches of the glosso-pharyngeal nerve, and evidence has been already adduced that the sense of taste is conferred upon them by this nerve. In most, though not in all persons, the an- terior parts of the tongue, especially the edges and tip, are endowed with the sense of taste. The middle of the dorsum is only feebly en- dowed with this sense, probably because of the density and thickness of the epithelium covering the filiform papillae of this part of the tongue, which will prevent the sapid substances from penetrating to their sensi- tive parts. Other Functions. — Beside the sense of taste, the tongue, by means THE SENSES. 639 also of its papilla, is endued (2) especially at its side and tip, with a very delicate and accurate sense of touch, which renders it sensible of the impressions of heat and cold, pain and mechanical pressure, and conse- quently of the form of surfaces. The tongue may lose its common sen- sibility, and still retain the sense of taste, and vice versa. This fact renders it probable that, although the senses of taste and of touch may be exercised by the same papilla? supplied by the same nerves, yet the nervous conductors for these two different sensations are distinct, just as the nerves for smell and common sensibility in the nostrils are dis- tinct; and it is quite conceivable that the same nervous trunk may con- tain fibres differing essentially in their specific properties. Facts already detailed seem to prove that the lingual branch of the fifth nerve is the conductor of sensations of taste in the anterior part of the tongue ; and it is also certain, from the marked manifestations of pain to which its division in animals gives rise, that it is likewise a nerve of common sen- sibility. The glosso-pharyngeal also seems to contain fibres both of common sensation and of the special sense of taste. The functions of the tongue in connection with (3) speech, (4) mas- tication, (5) deglutition, (0) suction, have been referred to in other chapters. Taste and Smell: Fei'cepfiofis. — The concurrence of common and two kinds of special sensibility, i.e., touch and taste in the same part, makes it sometimes difficult to determine whether the impression produced by a substance is perceived through the ordinary sensitive fibres, or through those of the sense of taste. In many cases, indeed, it is probable that both sets of nerve-fibres are concerned, as when irritating acrid substances are introduced into the mouth. Much of the perfection of the sense of taste is often due to the sapid substances being also odorous, and exciting the simultaneous action of the sense of smell. This is shown by the imperfection of the taste of such substances when their action on the olfactory nerves is prevented by closing the nostrils. Many fine wines lose much of their apparent excellence if the nostrils are held close while they are drunk. Varieties of Tastes. — Among the most clearly defined tastes are the siveet and bitter (which are more or less opposed to each other), the acid, alkaline, salt, and metallic tastes. Acid and alkaline taste may be ex- cited by electricity. If a piece of zinc be jilaced beneath and a piece of copper above the tongue, and their ends brought into contact, an acid taste (due to the feeble galvanic current) is produced. The delicacy of the sense of taste is sufficient to discern 1 part of sulj)huric acid in 1000 of water; but it is far surpassed in acuteness by the sense of smell. Ex- periments have shown that it is possible to entirely do away with the power of tasting bitters and sweets while the taste for acids and salts 640 HANDBOOK OF PHYSIOLOGY. remains. This is done by chewing the leaves of an Indian plant (Gymnema sylvestre). It has also been shown that the power of tasting sweet substances disappears before that of tasting bitter. Other experi- ments have shown that the apparatus for salt and for acid tastes are distinct. It is also demonstrable that bitters are most appreciated at the back and sweets at the tip of the tongue, that salts are also most potent at the tip, and acids at the sides of the tongue. All these tastes then, are almost certainly provided with a distinct apparatus. It is clear there- fore that the taste buds cannot be the only terminal organs for the sense of taste, if from no other reason, at any rate from their exceedingly limited distribution in the human tongue. Although the taste apparatus is bilateral the sensation or perception is single, and in this resjject taste resembles vision. After-taste. — Very distinct sensations of taste are frequently left after the substances which excited them have ceased to act on the nerve ; and such sensations often endure for a long time, and ^modify the taste of other substances ap])lied to the tongue afterward. Thus, the taste of sweet substances spoils the flavor of wine, the taste of cheese improves it. There appears, therefore, to exist the same relation between tastes as between colors, of which those that are opposed or complementary render each other more vivid, though no general principles governing this rela- tion have been discovered in the case of tastes. In the art of cooking, however, attention has at all times been paid to the consonance or har- mony of flavors in their combination or order of succession, just as in painting and music the fundamental jsrinciples of harmony have been employed empirically while the theoretical laws were unknown. Frequent and continued repetitions of the same taste render the per- ception of it less and less distinct, in the same way that a color becomes more and more dull and indistinct the longer the eye is fixed upon it. Thus, after frequently tasting first one and then the other of two kinds of wine, it becomes impossible to discriminate between them. The simple contact of a sapid substance with the surface of the gustatory organ seldom gives rise to a distinct sensation of taste ; it needs to be diffused over the surface, and brought into intimate contact with the sensitive parts by compression, friction, and motion between the tongue and palate. Subjective Sensatiotis of Taste. — The sense of taste seems capable of being excited only by external causes, such as changes in the conditions of the nerves or nerve-centres, produced by congestion or other causes, which excite subjective sensations in the other organs of sense. But little is known of the subjective sensations of taste; for it is difficult to distinguish the phenomena from the effects of external causes, such as changes in the nature of the secretions of the mouth. THE SENSES. 641 III. Smell. Conditio7is necessary. — (1.) The first conditions essential to the sense of smell are a special nerve and nerve-terminations in the form of special cells, the changes in whose condition stimulate a special nerve-centre, and are perceived in sensations of odor, for no other nervous structure is capable of these sensations, even though acted on by the same causes. The same substance which excites the sensation of smell in the olfac- tory centre may cause another peculiar sensation through the nerves of taste, and may produce an irritating and burning sensation on the nerves of touch ; but the sensation of odor is yet separate and distinct from these, though it maybe simultaneously perceived. (2.) The material causes of odors are, usually, in the case of animals living in the air, Fig. 391.— Nerves of the septum nasi, seen from the right side. -i.—l. the olfactory bulb; 1, the olfactory nerves passing through the foramina of the cribriform plate, and descending to be distributed on the septum ; 3, the internal or septal twig of the nasal branch of the ophthal- mic nerve; 3, naso-palatine nei-ves. (From Sappey, after Ilirschfeld and Leveill^.) either solids suspended in a state of extremely fine division in the atmos- phere ; or gaseous exhalations often of so subtle a nature that they can be detected by no other reagent than the sense of smell itself. The matters of odor must, in all cases, be dissolved in the mucus of the mucous membrane before they can be immediately applied to, or affect, the olfactory nerves; therefore a further condition necessary for the. perception of odors is, that the mucous membrane of the nasal cavity: be moist. When the Sclmeiderian membrane is dry, the sense of smell is impaired or lost; in the first stage of catarrh, when the secretion of mucus within the nostrils is lessened, the faculty of perceiving odor is either lost, or rendered very imperfect. (3.) In animals living in the air, it is also requisite that the odorous matter should be transmitted in a current tlirough the nostrils. This is effected by an insjjiratory move- 41 G42 HANDBOOK OF PHYSIOLOGY. ^„ ment, the mouth being closed; hence we have voluntary influence over the sense of smell; for by interrupting respiration we prevent the per- ception of odors, and by repeated quick inspiration, assisted, as in the act of sniffing, by the action of the nostrils, we render the imj^ression more intense. An odorous substance in a liquid form injected into the nostrils appears incapable of giving rise to the sensation of smell; thus Weber could not smell the slightest odor when his nostrils were completely filled with water containing a large quantity of eau-de-Cologne. jfy - ^.:^^ "^^^^ ^^^^ '^^ ^^^ entirely an organ for the seat " - of smell. In fact the nasal cavities are divided p ^ into three districts called respectively, (a) 7'egio p- vestibularis, which is the entrance to the cavity. It is lined with a mucous membrane very closely __^^ ^ resembling the skin, and contains hair (vibrissce) Fis.393.— Section through witli sabaccous ghiuds ; {b) regio respiratoria, the olfactory mucous uiem- t • t • i i n i i.ji ^ brane of the new-hora child, wliich mcludes the lowcr mcatus 01 the nose, and a, non-nuclear ; and b, nucle- n,, i j- l^ i i / \ • i • ated portions of the epithe- all the rcst 01 the nasal r)assages except (c), it is lium; c, nerves; del, glands, i -n i -, -, i , • marked out by Schuitze as covcred With iiiucous membrane covcrcd by strati- Bowman's. (M. Schuitze.) r. i i -i- j. n -^.i t rr>i bed columnar ciliated epithelium. Ihe mucosa is thick and consists of fibrous connective tissue, it contains a certain num- ber of tubular mucous and serous glands; and (r) regio olfactoria, which includes the anterior two-thirds of the superior meatus, the middle meatus, and the upper half of the septum nasi. It is cf a yellowish color. It con- sists of a thicker mucous membrane than in (/>), made up of loose areolar connective tissue covered by epithelium of a special variety, resting upon a basement membrane. The cells of the epithelium are of several kinds, firstly, columnar cells not ciliated (fig. 394), consisting of a granular body containing pigment, with the broad end at the surface, and below taper- ing into an irregular branched process or processes, the terminations of which are lost in the next layer — each cell has a conspicuous ovoid nucleus, staining well in ha?matoxylin — these cells are the continuations of the columnar ciliated epithelium of {b). The second kind consists of a small cell body with large spherical nucleus, staining imperfectly in hfematoxylin, situated between the ends of the first kind of cell, and sending upward a process to the surface between the cells of the first kind, and from the other pole of the nucleus a process toward the mucosa. The latter process is very delicate and may be varicose. The upper process may be prolonged beyond the surface as a cilium. These cells are numerous, and the nuclei of the cells not being on the same level, a comparatively thick nuclear layer is the result. Below them is a layer of irregular branched nucleated cells placed upon the basement THE SENSES. 643 membrane. It is doubtful if all the nuclei of the nuclear layer send processes in both directions to the surface and to the mucosa. In the mucosa are peculiar glands, small and twisted, made up of large cells arranged parallel inclosing a canal, and called Bowman's glands. They are probably serous or mucous secreting glands. The branches of the olfactory nerves retain much of the same soft and grayish texture which distinguishes those of the olfactory tracts within the cranium. Their filaments, also, are peculiar, more resembling those of the sympathetic nerve than the filaments of the other cerebral nerves do, containing no outer white substance, and being finely granular and nucleated. The fibres are supposed to terminate in the processes of the second variety of cell lining the olfactory mucous membrane, and called rod cells, the columnar cells are looked upon only as supporting cells. Some, however, look upon both kinds of cells as olfactory in function. The sense of smell is derived exclusively through those parts of the nasal cavities in which the olfactory nerves are distributed; the accessory cavi- ties or sinuses communicating with the nostrils seem to have no relation to it. Air impregnated with the vapor of camphor was injected into the front- al sinus through a fistulous opening and odorous substances have been ii.jected into the antrum of Ilighmore; but in neither case was any Fig:. 393. — Nerves of the outer waUs of the nasal fossa?. 3-5. — 1, network of the branches of the olfactory nerve, descending upon the region of the superior and middle turbinated bones: 2, external twig of the ethmoidal branch of the nasal nerves; 3, spheno-palatine ganglion; 4, ramification of the anterior palatine aerves; 5, posterior, and 6, middle divisions of the palatine nerves; 7, branch to the region of the inferior turbinated bone; 8, branch to the region of the superior and middle turbinated bones; 9, naso-palatine branch to the septum cut short. (Froo) Sappey, after Hirschfeld and Leveill6.) odor perceived by the patient. The purposes of these sinuses appear to be, that the bones, necessarily large for the action of the muscles and other parts connected with them, may be as light as possible, and that there may be more room for the resonance of the air in vocalizing. 644 HANDBOOK OF PHYSIOLOGY. The former purpose, which is in other bones obtained by filling their cavities with fat, is here attained, as it is in many bones of birds, by their being filled with air. Other Functions of the Nasal Region. — All parts of the nasal cavities, whether or not they can be the seats of the sense of smell, are endowed with common sensibility by the nasal branches of the first and second divisions of the fifth nerve. Hence the sensations of cold, heat, itch- ing, tickling, and pain; and the sensation of tension or pressure in the nostrils. That these nerves cannot perform the function of the olfac- tory nerves is proved by cases in which the sense of smell is lost, while the mucous membrane of the nose remains susceptible of the various modi- fications of common sensation and of touch. But it is often difficult to distinguish the sensation of smell from that of mere feeling, and to ascertain what belongs to each separately. This is the case particularly Fig. 394. — Cells from the olfactory regions of the rabbit, st. Supporting cells; ?% ?•', varieties of rod-cells; /, ciliated cell; s, cilia-like process; 6, cells from Bowman's gland. (Stohr.J) with the sensations excited in the nose by acrid vapors, as of ammonia, horse-radish, mustard, etc., which resemble much the sensations of the nerves of touch; and the difficulty is the greater, when it is remem- bered that these acrid vapors have nearly the same action upon the mucous membrane of the eyelids. It was because the common sensi- bility of the nose to these irritating substances remained after the destruction of the olfactory nerves, that Magendie was led to the erro- neous belief that the fifth nerve might exercise this special sense. Varieties of Odorous Sensations. — Animals do not all equally perceive the same odors ; the odors most plainly perceived by an herbivorous animal and by a carnivorous animal are different. The Carnivora have the power of detecting most accurately by the smell the special peculiarities of animal matters, and of tracking other animals by the scent; but have apparently very little sensibility to the odors of plants and flowers. Herbivorous animals are peculiarly sensitive to the latter, and have a narrower sensibility to animal odors, especially to such as proceed from other individuals than their own species. Man is far inferior to many THE SENSES, 645 animals of both classes (which appear to have a special epithelial arrangement called Jacobson''s orgcm, for the purpose of ''scent"), in respect of the acuteness of smell ; but his sphere of susceptibility to various odors is more uniform and extended. The cause of this diiference lies probably in the endowments of the cerebral parts of the olfactory appa- ratus. The delicacy of the sense of smell is most remarkable; it can dis- cern the presence of bodies in quantities so minute as to be uudiscover- able even by spectrum analysis; yTo.o^Tro-.-oo-g- of ^ grain of musk can be dis- tinctly smelt (Valentin). Opj)osed to the sensation of an agreeable odor is that of a disagreeable or disgusting odor, which corresponds to the sensa- tions of pain, dazzling and disharmony of colors, and dissonance in the other senses. The cause of this difference in the effect of different odors is unknown; but this much is certain, that odors are pleasant or offensive in a relative sense only, for many animals pass their existence in the midst of odors which to us are highly disagreeable. A great difference ill this respect is, indeed, observed amongst men: many odors, generally thought agreeable, are to some persons intolerable; and different per- sons describe differently the sensations that they severally derive from the same odorous substances. There seems also to be in some persons an iusensibility to certain odors, comparable with that of the eye to cer- tain colors; and among -different persons, as great a difference in the acuteness of the sense of smell as among others in the acuteness of sight. "NVe have no exact jDroof that a relation of harmony and disharmony exists between odors as between colors and sounds; though it is probable that such is the case, since it certainly is so with regard to the sense of taste ; and since such a relation would account in some measure for the differ- ent degrees of perceptive power in different persons; for as some have no ear for music (as it is said), so others have no clear ai^preciation of the relation of odors, and therefore little pleasure in them. Subjective sensations. — Tbe sensations of the olfactory nerves, iude^ pendent of the external application of odorous substances, have hitherto been little studied. The friction of the electric machine jsroduces a smell like that of phosphorus. Ritter, too, has observed, that when a galvanic current is applied to the organ of smell, besides the impulse to sneeze, and the tickling sensation excited in the filaments of the fifth nerve, a smell like that of ammonia was excited by the negative pole, and an acid odor by the positive jjole; whichever of these sensations were jn'o-- duced, it remained constant as long as the circle was closed, and changed to the other at the moment of the circle being opened. Subjective sen sations occur frequently in connection with the sense of smell. Fre- quently a person smells something which is not present, and which othev persons cannot smell; this is very frequent with nervous people, but it oc- casionally happens to every one. In a man who was constantly conscious 646 HANDBOOK OF PHYSIOLOGY. of a bad odor, the arachnoid was found after death to be beset with deposits of bone, and a lesion in the middle of the cerebral hemispheres was also discovered. Dubois was acquainted with a man who, ever after a fall from his horse, which occurred several years before his death, believed that he smelt a bad odor. I\'. Hearing. Anatomy of the Ear. — For descriptive purposes, the Ear, or Organ of Hearing, is divided into three parts, (l)the external, (2) the middle, and (3) the internal ear. The two first are only accessory to the third Fig. 395. — Diagrammatic view from before of the parts composinpc the orpan of hearing of tke left side. The temporal bone of the left side, with the accdiiipanying soft parts, has been detached from the head, and a section has been carried throut,'h it transversely, so as to remove the front of the meatus externus, half the tympanic membrane, the upper ami anterior wall of the tympanum and Eustachian tube. The meatus internus has also been opened, and the bony labyrinth exposed Vjy the removal of tlie surroundinf; parts of the petrous bone. 1, the pinna and lobe; 2. 2', meatus externus; 2', membrana tympani ; 3, cavity of the tympanum; 3', its opening backward into the mastoid cells; between 3 and 3', the chain of small bones; 4, Eusta- chian tube; 5, meatus internus, containing the facial (uppermost) and the auditory nerves; 6, placed on the vestibule of the labyrinth above the fenestra ovalis; a, apex of the petrous bone; S, internal carotid artery; c, styloid process; d, facial nerve issuing from the stylo-mastoid Iforamen; e, mastoid process; /, squamous part of the bone covered by integument, etc. C Arnold.) or internal ear, which contains the essential parts of an organ of hear- ing. The accompanying figure shows very well the relation of these divisions, one to the other (fig. 395). External Ear. — The external ear consists of the jnnna or auricle and the external auditory canal or meattis. The principal parts of the pin?ia (fig. 395) are two prominent rims inclosed one within the other [helix and antihelix), and inclosing a cen- tral hollow named the concha; in front of the concha, a prominence THE SENSES. G47 directed backward, the tragus, and opposite to this one directed for- Avard, the antitragus. From the concha, the auditory canal, with a slight arch directed upward, i)asses inward and a little forward to the membrana tympani, to which it thus serves to convey the vibrating air. Its outer part consists of fibro-cartilage continued from the concha; its iniier part of bone. Botli are lined by skin continuous with that of the pinna, and extending over the outer part of the memhrana tympani. Toward the outer part of the canal are fine hairs and sebaceous glands, while deeper in the canal are small glands, resembling the sweat- glands in structure, which secrete the cerumen. Middle Ear or Tympanum. — The middle ear, or tympanum (3, fig. 395), is separated by the meml)rana tympani from the external auditory canal. It is a cavity in the temporal bone, opening through its anterior and inner w'all into the Eustachian tube, a cvlindriform Fig. Fig. 398. 1, the head; 2, neck; 3, short Fip. 396.— The hammer-bone or malleus, seen from the front, process; 4. long process. (Schwalbe.) Fig. 397.— The incus, or anvil-bone. 1. body; 2, ridged articulation for the malleus: 4, pro- cessus brevis, with 5. rough articular surface for ligamem of incus; 6, processus magnus, with articulating surface for stapes ; V, nutrient foramen. (Schwalbe. ) Fig. 398.— The stapes, or stirrup-bone. 1, base; 2 and 3, arch; 4, head of bone, which articu- lates with orbicular process of tne incus; 5. constricted part of neck; 6, one of the crura. (Schwalbe.) flattened canal, dilated at both ends, composed partly of bone and partly of elastic cartilage, and lined with mucous membrane, which forms a communication between the tympanum and the pharynx. It opens into the cavity of the pharynx just behind the posterior aperture of the nos- trils. The cavity of the tympanum communicates posteriorly with air cavities, the wrt^/otf/ ce/fe in the mastoid process of the temporal bone; but its only opening to the external air is through the Eustachian tube (4, fig. 395). The walls of the tympanum are osseous, except where aper- tures in them are closed wdth membrane, as at the fenestra rotunda and fenestra ovalis, and at the outer part where the bone is rei^laced by the membrana tympani. The cavity of the tympanum is lined with mucous membrane, the epithelium of which is ciliated and continuous with that of the pharynx. It contains a chain of small bones {ossicula auditus) which extends from the membrana tympani to the fenestra ovalis. 648 HANDBOOK OF PHYSIOLOGY. The memhrana tympani is placed in a slanting direction at the bot- tom of the external auditory canal, its plane being at an angle of about 45° with the lower wall of the canal. It is formed chiefly of a tough and tense fibrous membrane, the edges of which are set in a bony groove; Fig. 399.— Interior view of the tympanum, with membrana tympani and bones in natural position. 1, Membrana tympani ; 2, Eustachian tube; 3, tensor tympani muscle; 4, lig. mallei super. ; 6, corda-tympani nerve; a, 6, and c, sinuses about ossicula. (Schwaltoe.) its outer surface is covered with a continuation of the cutaneous lining of the auditory canal, its inner surface with part of the ciliated mucous membrane of the tympanum. The ossicles axe three in number; named malleus, incus, and stapes. The malleus, or hammer-bone, is attached by a long slightly-curved pro- cess, called its handle, to the membrana tympani ; the line of attachment being vertical, including the whole length of the handle, and extending from the upper border to the centre of the membrane. The head of the malleus is irregularly rounded; its neck, or the line of boundary between it and the handle, supports two processes; a short conical one, which receives the insertion of the tensor ti/mpani, and a slender one, 2)rocessus gi'acilis, which extends forward, and to which the Iclt afar tipnpnni muscle is attached. The incus, or anvil-bone, shaped like a bicuspid molar tooth, is articulated by its broader part, corresponding with the surface of the crown of a tooth, to the malleus. Of its two fang-like processes, one, directed backward, has a free end lodged in a depression in the mastoid bone ; the other, curved downward and more pointed, articulates by means of a roundish tubercle, formerly called os orbicnlare, with the stapes, a little bone shaped exactly like a stirrup, of which the base or bar fits into the fenestra ovalis. To the neck of the stapes, a short process, correspond- ing with the loop of the stirrup, is attached the stapedius muscle. The bones of the ear are covered with mucous membrane reflected over them from the wall of the tympanum ; and are movable both altogether and one upon the other. The malleus moves and vibrates with every movement and vibration of the membrana tympani, and its move- ments are communicated through the incus to the stapes, and through THE SEXSES. 649 It to the membrane closing the fenestra ovalis. The malleus, also, is movable in its articulation with the incus; and the membrana tympani moving with it is altered in its degree of tension by the laxator and tensor tympani muscles. The stapes is movable on the process of the incus, when the stapedius muscle acting, draws it backward. The axis round which the malleus and incus rotate is the line joining the pro- cessus gracilis of the malleus and the posterior (short) process of the incus. The Internal Ear. — The proper organ of hearing is formed by the distribution of the auditory nerve within the internal ear, or lahyrintli, a set of cavities within the petrous portion of the temporal bone. The bone which forms the w^alls of these cavities is denser than that around it, and forms the osseous labyrinth; the membrane within the cavities forms the memhranoiis labyrinth. The membranous labyrinth contains a fluid called endolymph; while outside it, between it and the osseous labyrinth, is a fluid called perilymph. This fluid is not pure lymj)h ; as it contains mucin. The osseous labyrinth consists of three principal parts, namely the vestibtile, the cochlea, and the semicircular canals. The vestibule is the middle cavity of the labyrinth, and the central organ of the whole auditory apparatus. It presents, in its inner wall, Fig. 400. Fig. 401. Fig. 400. — Right bony labyrinth, viewed from the outer side. The specimen here represented Is prepared by separating piecemeal the looser substance of the petrous bone from the dense wails which immediately inclose the labjTinth. 1, the vestibule; 2, fenestra ovalis; 3. superior semicircular canal ; 4, horizontal or external canal ; 5, posterior canal ; *. ampullte of the semi- circular canals; C, first turn of the cochlea; 7, second turn; 8, apex; 9, fenestra rotunda. The smaller figure in outline below shows the natural size. ^p. (Sommering.) Fig. 401.— Vie-\ of the interior of the left labjTinth. The bony wall of the labyrinth is re- moved siperiorly and externally. 1. Fovea hemielliptica: 2. fovea heniispherica : 3, common opening of the sunerior and posterior semicircular canals; 4, opening of the aqueduct of the vestibule; 5, the superior. 6, the posterior, and 7, the external semicircular canals; 8. spiral tube of the cochlea (scala tj-mpani) ; 9, opening of the aqueduct of the cochlea ; 10. placed on the lamina spiralis in the scala vestibuli. -^ (Sommering.) several openings for the entrance of the divisions of the auditory nerve; in its outer wall, the fenestra ovalis (2, fig. 400), an open- GoO HANDBOOK OF PHYSIOLOGY. ing filled by the base of the stapes; in its posterior and superior walls, five openings by which the semicircular canals communicate with it: in its anterior wall, an opening leading into the cochlea. The hinder part of the inner wall of the vestibule also presents an opening, the orifice of the aquceductus vestibuli^ a canal leading to the posterior mar- gin of the petrous bone, with uncertain contents and unknown purpose. T\\Q semicircular canals (figs. 400, 401) are three arched cylindriform bony canals, set in the substance of the petrous bone. They all open at both ends into the vestibule (two of them first coalescing). The ends of each are dilated just before opening ifito the vestibule; and one end being more dilated than the other is called an amjmlla. Two of the canals form nearly vertical arches ; of these the superior is also anterior ; the posterior is inferior; the third canal is horizontal, and lower and shorter than the others. The cochlea (6, 7, 8, figs. 400 and 401), a small organ, shaped like a common snail-shell, is situated in front of the vestibule, its base resting on the bottom of the internal meatus, where some apertures transmit to it the cochlear filaments of the auditory nerve. In its axis, the cochlea is traversed by a conical column, the modiolus, round which a spiral canal winds with about two turns and a half from the base to the apex. At the apex of the cochlea the canal is closed ; at the base it presents three openings, of which one, already mentioned, communicates with the vestibule; another called fenestra rotunda, is separated by a membrane from the cavity of the tympanum ; the third is the orifice of the aquceductus coclilece, a canal leading to the jugular fossa of the petrous bone, and corresponding, at least in obscurity of purpose and origin, to the aquseductus vestibuli. The spiral canal is divided into two passages, or scala?, by a partition of bone and membrane, the lamina spiralis. The osseous part or zone of this lamina is connected with the modiolus. The Membranous Labyrinth. — The membranous labyrinth corre- sponds generally with the form of the osseous labyrinth, so far as regards the vestibule and semicircular canals, but is separated from the walls of these parts by perilymph, except where the nerves enter into connection within it. The labyrinth is a closed membrane containing endolymph, which is of much the same composition as perilymph, but contains less solid matter. It is somewhat viscid, as is the iierilymph, and it is secreted by the epithelium lining its cavity; all the sonorous vibrations impressing the auditory nerves in these parts of the internal ear, are conducted through fluid to a membrane suspended in and containing fluid. In the cochlea, the membranous labyrinth completes the septum between the two scal.ce, and incloses a spiral canal, previously mentioned, called canalis membranaceus or canalis cochlem (fig. 403). The fluid in. THE SEXSES. 651 the scalce of the cochlea is continuous with the peril3^mph in the vesti- bule and semicircular canals, and there is no fluid extenud to its lining membrane. The vestibular 2:)ortiou of the membranous labyrinth cam- prises two, probably communicating cavities, of which the larger and upjDcr is named the utricuJus; the lower, the sacculus. They are lodged in depressions in the bony labyrinth, termed respectively /orfYf hemieUiptica and fovea liemispherira. Into the former open the orifices of the membranous semicircular canals; into the latter the canalis cocMece. The membranous labyrinth of all these parts is laminated, transparent, very vascular, and covered on the inner surface with nucleated cells, of which those that line the ampullar are prolonged into stiff hair-like pro- cesses; the same appearance, but to a much less degree, being visible in the utricule and saccule. In the cavities of the utriculus and sacculus j-re small masses of calcareous particles, otoconia or otoliths; and the Fia:. 402.— View of the osseous cochlea divided through the middle. 1, central canal of the \aodiolus; a, lamina spiralis ossea; 3, scala tympani ; 4, scala vestibuli; 5, porous substance of l;he modiolus near one of the sections of the canalis spiralis modioli. X 5. (Arnold.^ same, although in more minute quantities, are to be found in the interior (»f some other parts of the membranous labyrinth. Auditory Nerve. — All the organs now described are provided for the appropriate exposure of the filaments of the auditory nerve to sonorous vibrations. It is characterized as a nerve of special sense by its softness (whence it derived its name ot portio mollis of the seventh pair), and by the fineness of its component fibres. It enters the bony canal (the meatus auditorius interims), with the facial nerve and the nervus intermedins, and, traversing the bone, enters the labyrinth at the ang]^ between the base of the cochlea and the vestibule, in two divisions; one for the ves- tibule and semicircular canals, and the other for the cochlea. There are two branches for the vestibule, one, superior, distributed to the utricule and to the superior and horizontal semicircular canals, r^nd the other, inferior, ending in the saccule and posterior semicircular .'-anal. Where the nerve comes in connection with the utricule and tc-.ccule, the structure of the membrane is modified somewhat and the }»laces are called maculm acusticm. The epithelium in this region is, as 've shall see directly, considerably specialized, and where the nerve is in connection with the ampullae of the semicircular canals, too, the struct- i^re is altered, becoming elevated into a horse-shoe ridge, which projects 652 HANDBOOK OF PHYSIOLOGY. iuto the interior of the cavity, forming the crista acustica. Here, too, the epithelium is of a special kind. The nerve fibres spread out and radiate on the inner surface of the membranous labyrinth: their exact termination is uncertain. The distribution of the other division of the auditory nerve, the cochlear, will be more clearly understood after the description of the cochlea itself. Structure. — The structure of the membranous labyrinth consists of three coats, externally a layer of areolar tissue, next a hyaloid membrane, elevated into minute papillse, and internally a layer of flattened epi- thelium. At the position where the branches of the vestibular branch of the auditory nerve join it, viz., at the saccule, utricule, and ampullae of the semicircular canals, there is a marked difference in the structure, the external and middle layers are thicker and the epithelium becomes columnar. The epithelium in which the fibres of the vestibular nerve are said to terminate are of two kinds, called cylinder or hair cells, and rod cells. The hair cells occupy only one-half of the thickness of the membrane; from their inner end hair-like processes project into the cavity of the labyrinth. Their outer end is rounded and contains n large round nucleus. To these cells the primitive fibrillae of the axis cylinders pass up, some of them being distinctly varicose. The exact relation of the nerve fibrillge to the hair-cells is unknown; by some tlmy are believed actually to enter the cells, by others they are stated to form a kind of nest of fibrillae into which the cells fit. The rod-cells are of somewhat varying form. They are elongated cells extending from the surface to the basement membrane, broad at the upper or surface end, and containing oval nuclei toward their attached end, but not exactly at the same level in all cases. These nuclei, therefore, form a distinct broad nuclear layer on a vertical section of the membrane, as the cellt; are numerous, much more so, indeed, than the other variety of cell. The lower or attached part of the cell may be branched. The membranous part of the cochlea, with a muscular zone, forming its outer majjgin, is attached to the outer wall of the canal. Commen(i- ing at the base of the cochlea, between its vestibular and tympanic open- ings, it forms a partition between these apertures; the two scalae are, therefore, in correspondence with this arrangement, named 'scala vesti- iuli and scala tympatii (fig. 403). At the apex of the cochlea, the lamina spiralis ends in a small hamnlus, the inner and concave part of which, being detached from the summit of the modiolus, leaves a small aperture named helicotrema, by which the two scalae, separated in all the rest of their length, communicate. Besides the scala vestibuli and scala tympani, there is a third space- between them, called scala media or canal memhranaceus (CC, fig. 403). In section it is triangular, its external wall being formed by the wall of THE SENSES. 653 the cochlea, its upper wall (separating it from the scala vestibuli) by the membrane of Reissner, and its lower wall (separating it from the scala tympani) by the basilar membrane, these two meeting at the outer edge of the bony lamina spiralis. Following the turns of the cochlea to its apex, the scala media there terminates blindly ; while toward the base of the cochlea it is also closed with the exception of a very narrow pas- sage (canalis reuniens) uniting it with the sacculus. The scala media (like the rest of the membranous labyrinth) contains endolympli. Organ of Corti. — Upon the basilar membrane are arranged cells of various shapes. About midway between the outer edge of the lamina Fig. 403.— Section through one of the coils of the cochlea C) by changing the position either of the retina or of the lens, so that whether the object be near or distant, the focal points to which the rays are converged by the lens may always fall exactly on the retina. The amount of either of these changes, which would be required in even the widest range of vision, would be extremely small. For, from the refractive powers of the media of the eye, the dif- 682 HANDBOOK OF PHYSIOLOGY. f erence between the focal distances of the images of an object at a distance, and of one at the distance of four inches, is only about 0,143 of an inch (3.5 mm.). On this calculation the change in the distance of the retina from the lens required for vision at all distances, supposing the cornea and lens to remain the same, Avould not be more than about one line. The adaptation of the eye for objects at different distances is pri- marily due to a varying shape of the lens, its front surface becoming more or less convex, according as the distance of the object looked at is near or far. The nearer the object, the more convex, up to a certain limit, the front surface of the lens, and vice versa; the back surface tak- ing little or no share in the production of the effect required. And this surface, which during rest is more convex than the anterior, becomes the less convex of the two during accommodation. The following simple experiment illustrates this point: If a lighted candle be held a little to one side of a person's eye, an observer looking at the eye from the other side sees three distinct images of the flame (fig. 423). The first and brightest is (1) a small erect image formed by the anterior convex surface of the cornea ; the second (2) is also erect, but larger and less distinct than the preceding, and is formed at the anterior convex surface of the lens; the third (3) is smaller, inverted, and indistinct; it is formed at the posterior surface of the lens, which is concave forward, and therefore, like all concave mirrors, gives an inverted image. If now the eye under observation be made to look at a near object, the second image becomes smaller, clearer, and approaches the first. If the eye be now adjusted for a far point, the second image enlarges again, becomes less distinct, and recedes from the first. In both cases alike the first and third images Fig. 423. — Diagram showing three reflections of a candle. 1, From the anterior surface of cornea ; 2, from the anterior surface of lens ; 3, from the posterior surface of lens. For further explanation, see text. The experiment is best performed by employing an instrument invented by Helmholtz, termed a Phakoscope. remain unaltered in size, distinctness, and relative position. This proves that during accommodation for near objects the curvature of the cornea, and of the ^josterior of the lens, remains unaltered, while the anterior surface of the lens becomes more convex and approaches the cornea. THE SEXSES. 683 The experiment (fig. 423 a) is more striking when two candles are used, and the images of the two candles from the front surface of the lens during accommodation not only approach those from the cornea, B Fig. 423 A. Fig. 4-,'4. Fig. 433 A.— Diagram of Sanson's images. A, when the eyes are not, and B, when they are focussed for near objects. The fig. to the right in A and B is the inverted image from the pos- terior surface of the lens. Fig. 424,— Phakoscope of Helmlioltz. At B B' are two prisms, by which the light of a candle is concentrated on the eye of the person experimented with at C. A is the aperture for the eye of the observer. The observer notices three double images, as in fig. 423, reflected from the eye under examination when the eye is fixed upon a distant object: the position of the images having been noticed, the eye is then made to focus a near object, such as a reed pushed up by C; the images from the anterior surface of the lens will be observed to move toward each other, in consequence of the lens becoming more convex. but also apjiroach one another, and become somewhat smaller. [San- son''s images.) Mechanism of accommodation. — The lens having no inlierent power of contraction, its changes of outlines must be jiroduced by some power from without; this j)ower is supplied by the ciliary muscle. It is some- times termed the tejisor clioroidece. Its action is to draw forward the choroid, and by so doing to slacken the tension of the suspensory liga- ment of the lens which ari.ses from it. The anterior surface of the lens is kept flattened by the action of this ligament. The ciliary muscle during accommodation by diminishing its tension, diminishes to a pro- portional degree the flattening of which it is the cause. On diminution or cessation of the action of the ciliary muscle, the lens returns to its former shape, by virtue of the elasticity of the suspensory ligament (fig. 425). From this it will appear that the eye is usually focussed for distant objects. In viewing near objects the pupil contracts, the opposite effect taking place on withdrawal of the attention from near objects, and fixing it on those distant. 684 HANDBOOK OF PHYSIOLOGY. Range of Distinct Vision. JVear-point. — In every eye there is a limit to the power of accommodation. If a book be brought nearer and nearer to the eye, the tyjie at last becomes indistinct, and cannot be brought into focus by any effort of accommodation, however strong. This, which is termed the near-jwint, can be determined by the foUow- Fig. 425. — Diagram representing by dotted lines the alteration in the shape of the lens on ac- commodation for near objects. (E. Landolt.) ing experiment {Sclieiner). Two small holes are pricked in a card with a pin not more than a twelfth of an inch (2 mm.) apart, at any rate their distance from each other must not exceed the diameter of the pu- pil. The card is held close in front of the eye, and a small needle viewed through the pin-holes. At a moderate distance it can be clearly focussed, but when brought nearer, beyond a certain point, the image appears double or at any rate blurred. This point where the needle ceases to ajipear single is the near-point. Its distance from the eye can of course be readily measured. It is usually about 5 or G inches (13 cm.). In the accompanying figure (fig. 426) the lens J represents the Fig. 426. — Diagram of experiment to ascertain the minimmn distance of distinct vision. eye; e/"the two pin-holes in the card, nn the retina; a represents the po- sition of the needle. When the needle is at a moderate distance, the two pencils of light coming from e and/, are focussed at a single point on the retina 7i7i. If the needle be brought nearer than the near-point, the strongest effort of accommodation is not sufficient to focus the two pen- THE SENSES. 685 cils, they meet at a point beliiud the retina. The effect is the same as if the retina were shifted forward to mm. Two images h.g. are formed, one from each hole. It is interesting to note that when two images are produced, the lower one g really appears in the position q, while the upper one appears in the position p. This may be readily verified by covering the holes in succession. During accommodation two other changes take place in the eyes, (1) The eyes converge by the action of the extra-ocular muscles chiefly by the internal and inferior recti, or internal and superior recti. The superior oblique and the inferior oblique may also be used to turn the eye upward or downward. Movements of the Eye. — The eyeball possesses movement around three axes indicated in fig. 427, viz., an antero-posterior, a vertical, and a transverse, passing through a centre of rotation a little behind the centre of the optic axis. The movements are accomplished by pairs of muscles. Direction of Movement. By what muscles accomplished. Inward ..... . Internal rectus. Outward External rectus. yy T \ Superior rectus. '-'P^'^''^ ] Inferior oblique. T~, 1 i Inferior rectus. Downward ] Superior oblique. T , 5 1 ( Internal and superior rectus. Inward and upward . ._ • • -j inferior oblique. ._ , , , , ( Internal and inferior rectus. Inward and downward . . . . -^ Superior oblique. ^ . . , , \ External and superior rectus. Outward and upward . . . ", inferior oblique ^ , , T , 1 S External and inferior rectus. Outward and downward . . . j Superior oblique. (2) The second change which takes place in the eyes is, that the piqnls contract. The contraction of all of the muscles which have to do with accommodation, viz. , of the ciliary muscle, of the recti muscles, and of the sphincter pupilla3 is under the control of the third nerve. But the superior oblique may also be employed, in which case the fourth nerve is also concerned. Contraction of the pupil may also occur under the following circum- stances: (1) On exposure of the eye to a bright light; (2) on the local application of eserine (active principle of Calabar bean) ; (3) on the administration internally of opium, aconite, and in the early stages of chloroform and alcohol poisoning; (4) on division of the cervical sympathetic or stimulation of the third nerve, and dilatation of the pupil occurs (1) in a dim light; (2) when the eye is focussed for distant ob- jects; (3) on the local application of atropine and its allied alkaloids; (4) on the internal administration of atropine and its allies; (5) in the later stages of poisoning by chloroform, opium, and other drugs; (6) on paralysis of the third nerve ; (7) on stimulation of the cervical 686 HANDBOOK OF PHYSIOLOGY. sympathetic, or of its centre in the floor of the front of the aqueduct of Sylvius. The contraction of the pupil appears to be under the control of a centre in the bull) or in the corpora quadrigemina, and this is reflexly stimulated by a bright light, and the dilatation when the reflex centre is not in action is due to the more powerful sympathetic action; but in addition, it appears that both contraction and dilatation may be Fig. 427. —Diagram of the axes of rotation to the eye. The thin lines indicate axes of rotation, the thick the position of muscular attachment. produced by a local mechanism, u23on which certain drugs can act, which is independent of and probably often antagonistic to the action of the central apparatus of the third and sympathetic nerve. The action of the fifth nerve upon the jsupil is not well understood, but its apparent effect in producing dilatation is due to the mixture of sympathetic fibres with its nasal branch. The sympathetic influence upon the radiating fibres is believed to be conveyed not by the long ciliary branches of that nerve, but by the short ciliary branches from the ophthalmic ganglion. The close sympathy subsisting between the two eyes is nowhere better shown than by the condition of the pupil. If one eye be shaded by the hand its pupil will of course dilate; but the pupil of the other eye will also dilate, though it is unshaded. Defects in" the Optical Apparatus. Defects in the Refracting Media. — Under this head we may con- sider the defects known as (1) Myopia, (2) Hypermetropia, (3) Astig- matism, (4) Spherical Aberration, (5) Chromatic Aberration. THE SENSES. G87 The normal (emmetropic) eye is so adjusted that parallel raj-s are brought exactly to a focus on the retina without any effort of accommo- dation (1, fig. 428). Hence all objects except near ones (practically all objects more than twenty feet off) are seen without any effort of accom- modation; in other words, the far-point of the normal eye is at an infinite distance. In viewing near objects we are conscious of the effort (the con- traction of the ciliary muscle) by which the anterior surface of the lens is rendered more convex, and rays which would otherwise be focussed heliind the retina are converged upon the retina (see dotted lines 2, fig. 428). Fig. 428. —Diagram showing— 1, normal Ct^mmetropic^) eye briiitrinK paraUel rays exactly to a focus on the retina: 2, normal eye adaiHed to a near point: without accommodation the rays would be focussed behind the retina, but by increasing the curvature of the anterior surface of the lens (shown by a dotted line) the rays "are focussed on the retina (as indicated by the meet- ing of the two do'tted lines); i. hypermetropic eye. in this case the axis of the eye is shorter, and the lens flatter, than normal; parallel rays are focussed behind the retina; 4, myopic eye; in this case the axis of the eye is abnormally' long, and the lens too convex; parallel rays are focussed in front of the retina. 1. Myopia (short-sight) (4, fig. 428).— This defect is due to an abnor- mal elongation of the eyeball. The eye is usually larger than normal and is always^ longer than normal; the lens is also probably too convex. The retina is too far from the lens and consequently parallel rays are G88 HANDBOOK OF PHYSIOLOGY, focussed in front of the retina, and, crossing, form little circles on the retina; thus the images of distant objects are blurred and indistinct. The eye is, as it were, permaiiently adjusted for a near-point. Rays from a point near the eye are exactly focussed in the retina. But those which issue from any object beyond a certain distance {far-point) cannot be distinctly focussed. This defect is corrected hy concave glasses which cause the rays entering the eye to diverge; hence they do not come to a focus so soon. Such glasses of course are only needed to give a clear vision of distant objects. For near objects, except in extreme cases, they are not required. Hy2)ernietro2na (long-sight) (3, fig. 428). — This is the reverse defect. The eye is too short and the lens too flat. Parallel rays are focussed leliind the retina: an effort of accommodation is required to focus even parallel rays on the retina; and when they are divergent, as in viewing a near object, the accommodation is insufficient to focus them. Thus in well-marked cases distant objects require an effort of accommodation and near ones a very powerful effort. Thus the ciliary muscle is con- stantly acting. This defect is obviated by the use of convex glasses, which renders the pencils of light more convergent. Such glasses are of course especially needed for near objects, as in reading, etc. They rest the eye by relieving the ciliary muscle from excessive work. 3. Astigmatism. — This defect, which was first discovered by Airy, is due to a greater curvature of the eye in one meridian than in others. The eye may be even myopic in one plane and hypermetropic in others. Thus vertical and horizontal lines crossing each other cannot both be focussed at once; one set stands out clearly and the others are blurred and indistinct. This defect, which is present in a slight degree in all eyes, is generally seated in the cornea, but occasionally in the lens as well; it may be corrected by the use of cylindrical glasses (i.e., curved only in one direction). 4. Sjjherical Aberration. — The rays of a cone of light from an object situated at the side of the field of vision do not meet all in the same point, owing to their unequal refraction ; for the refraction of the rays which pass through the circumference of a lens is greater than that of those traversing its central portion. This defect is known as spherical aberration, and in the camera, telescope, microscope, and other optical instruments, it is remedied by the interposition of a screen with a circu- lar aperture in the path of the rays of light, cutting off all the marginal rays and only allowing the passage of those near the centre. Such cor- rection is effected in the eye by the iris, which forms an annular diaphragm to cover the circumference of the lens, and to prevent the rays from passing through any part of the lens but its centre which cor- responds to the pupil. The posterior surface of the iris is coated with THE SENSES. 689 pigment, to prevent the passage of rays of light through its substance. The image of an object will be most defined and distinct when the pupil is narrow, the object at the proper distance for vision, and the light abundant ; so that, while a sufficient number of rays are admitted, the narrowness of the pupil may prevent the production of indistinctness of the image by aplierical aberration. But even the image formed by the rays passing through the circumference of the lens, when the pupil is much dilated, as in the dark, or in a feeble light, may, under certain circumstances, be well defined. Distinctness of vision is further secured by the pigment of the outer surface of the retina, the posterior surface of the iris and the ciliary processes, which absorbs any rays of light that may be reflected within the eye, and prevents their being thrown again upon the retina so as to interfere with the images there formed. The pigment of the retina is especially important in this respect; for with the exception of its outer layer the retina is very transparent, and if the surface behind it were not of a dark color, but capable of reflecting the light, the luminous rays which had already acted on the retina would be reflected again through it, and would fall upon other parts of the same membrane, producing both dazzling from excessive light, and indistinctness of the images. 5. Chromatic Aberration. — In the passage of light through an ordi- nary convex lens, decomposition of each ray into its elementary colored part, commonly ensues, and a colored margin appears around the image, owing to the unequal refraction which the elementary colors undergo. In optical instruments this, which is termed chromatic aherration., is con- nected by the use of two or more lenses, difiiering in shape and density, the second of v/hich continues or increases the refraction of the rays produced by the first, but by recombining the individual parts of each ray into its original white light, corrects any chromatic aberration which may have resulted from the first. It is probable that the unequal refrac- tive power of the transparent media in front of the retina may be the means by which the eye is enabled to guard against the effect of chromatic aberration. The human eye is achromatic, however, only so long as the image is received at its focal distance upon the retina, or so long as the eye adapts itself to the different distances of sight. If either of these conditions be interfered with, a more or less distinct appearance of colors is produced. An ordinary ray of white light in passing through a prism, is refract- ed, i.e.., bent out of its course, but the different colored rays which go to make up white light are refracted in different degrees, and therefore appear as colored bands fadic/g off into each other: thus a colored band known as the " spectrum" is produced, the colors of which are arranged as follows — red, orange, yellow, green, blue, indigo, violet; of these 44 690 HANDBOOK OF PHYSIOLOGY. tlie red ray is the least, and the violet the most refracted. Henee, as Ilelmholtz has shown, a small white object cannot be accurately focussed on the retina, for if we focus for the red rays, the violet are out of focus, and vice versa : such objects, if not exactly focussed, are often seen sur- rounded by a pale yellowish or bluish fringe. For similar reasons a red surface looks nearer than a blue one at an equal distance, because, the red rays being less refrangible, a stronger effort of accommodation is necessary to focus them, and the eye is adjusted as if for a nearer object, and therefore the red surface apj^ears nearer. From the insufficient adjustment of the image of a small white ob- ject, it appears surrounded by a sort of halo or fringe. This phenom- enon is termed Irradiation. It is from this reason that a white square on a black ground appears larger than a black square of the same size on a white ground. As an 02:)tical instrument, the eye is stqjerior to the camera in the following, among many other particulars, which may be enumerated in detail. 1. The correctness of images even in a large field of view. 2. The simplicity and efficiency of the means by which chromatic aberra- tion is avoided. 3. The perfect efficiency of its adaptation to different distances. In the photographic camera, it is well known that only a com- paratively small object can be accurately focussed. In the photograph of a large object near at hand, the upper and lower limits are always inore or less hazy, and vertical lines appear curved. This is due to the fact that the image produced by a convex lens is really slightly curved and can only be received without distortion on a slightly curved concave screen, hence the distortion on a flat surface of ground glass. It is different with the eye, since it jiossesses a concave background, upon which the field of vision is depicted, and Avitli which the curved form of the image coincides exactly. Thus, the defect of the camera obscura is entirely avoided ; for the eye is able to embrace a large field of vision, the margins of which are depicted distinctly and without distortion. If the retina had a plane surface like the ground glass plate in a camera, it must necessarily be much larger than is really the case if we were to see as much; moreover, the central portion of the field of vision alone would give a good clear picture (Bernstein). Defective Accoinmodation — Preshijojna. — This condition is due to the gradual loss of the power of accommodation which is part of the general decay of old age. In consequence the patient would be obliged in read- ing to hold his book further and further away in order to focus the letters, till at last the letters are held too far for distinct vision. The defect is remedied by weak convex glasses, which are very commonly worn by old people. It is due chiefly to the gradual increase in density of the lens, which is unable to swell out and become convex when near THE SENSES. G91 objects are looked at, and also to a weakening of the ciliary muscle, and a general loss of elasticity in the parts concerned in the mechanism. Visual Sexsatioxs. Excitation of the Retina. — Light is the normal agent in the ex- citation of the retina. The only layer of the retina capable of reacting to the stimulus is the rods and cones. The proofs of this statement may be summed up thus: — (1.) The point of entrance of the optic nerve into the retina, where the rods and cones are absent, is insensitive to light and is called the hlind spot. The phenomenon itself is very readily demonstrated. If we direct one eye, the other being closed, ujion a jjoint at such a dis- tance to the side of any object, that the image of the latter must fall upon the retina at the point of entrance of tlie optic nerve, this image is lost either instantaneously, or very soon. If, for example, we close the left eye, and direct the axis of the right eye steadily toward the circular spot here represented, vrhile the page is held at a distance of about six inches from the eye, both dot and cross are visible. On gradually in- creasing the distance between the eye and the object, by removing the book farther and farther from the face, and still keeping the right eye steadily on the dot, it will be found that suddenly the cross disajipears from view, while on removing the book still farther, it suddenly comes in sight again. The cause of this phenomenon is simply that the por- tion of retina which is occupied by the entrance of the optic nerve, is quite blind; and therefore that when it alone occupies the field of vision, objects cease to be visible. (2.) In the fovea centralis and macula lutea which contain rods and cones but no oi3tic nerve-fibres, light pro- duces the greatest effect. In the latter, cones occur in large numbers, and in the former cones without rods are found, whereas in the rest of the retina which is not so sensitive to light, there are fewer cones than rods. We may conclude, therefore, that cones are even more im.jDortant to vision than rods. (3.) If a small lighted candle be moved to and fro at the side of and close to one eye in a dark room while the eyes look steadily forward into the darkness, a remarkable branching figure {Purlcinje's figures) is seen floating before the eye, consisting of dark lines on a reddish ground. As the candle moves, the figure moves in the opposite direction, and from its whole appearance there can be no doubt that it is a reversed picture of the retinal vessels projected before the eye. The two large branching arteries passing up and down from the optic disc are clearly visible together with their minutest branches. 692 HANDBOOK OF PHYSIOLOGY. A little to one side of the disc, in a part free from vessels, is seen the yellow spot in the form of a slight depression. This remarkable apjiear- ance is due to shadows of the retinal vessels cast by the candle. The branches of these vessels are chiefly distributed in the nerve-fibre and ganglionic layers; and since the light of the candle falls on the retinal vessels from in front, the shadow is cast behind them, and hence those elements of the retina which perceive the shadows must also lie behind the vessels. Here, then, we have a clear proof that the light-perceiving elements of the retina are not the fibres of the optic nerve forming the innermost layer of the retina, but the external layers of the retina, rods and cones, which indeed appear to be the special terminations of the optic nerve-fibres. Duration of Visual Sensations. — The duration of the sensation pro- duced by a luminous impression on the retina is always greater than that of the impression which produces it. However brief the luminous impres- sion, the effect on the retina always lasts for about one-eighth of a second. Thus, supposing an object in motion, say a horse, to be revealed on a dark night by a flash of lightning. The object would be seen apparently for an eighth of a second, but it would not appear in motion; because, although the image remained on the retina for this time, it was really revealed for such an extremely short period (a flash of lightning being almost instantaneous) that no appreciable movement on the part of the object could have taken place in the period during which it was revealed to the retina of the observer. And the same fact is proved in a reverse way. The spokes of a rapidly revolving wheel are not seen as distinct objects, because at every point of the field of vision over which the revolving spokes pass, a given impression has not faded before another comes to replace it. Thus every part of the interior of the wheel appears occupied. The duration of the after -sensation, produced by an object, is greater in a direct ratio with the duration of the impression which caused it. Hence the image of a bright object, as of the panes of a window through which the light is shining, may be perceived in the retina for a con- siderable period, if we have previously kept our eyes fixed for some time on it. But the image in this case is negative. H, however, after shutting the eyes for some time, we open them and look at an object for an instant, and again close them, the after-image \& positive. Intensity of Visual Sensations. — It is quite evident that the more luminous a body the more intense is the sensation it produces. But the intensity of the sensation is not directly proportional to the intensity of the luminosity of the object. It is necessary for light to have a cer- tain intensity before it can excite the retina, but it is impossible to fix an arbitrary limit to the power of excitability. As in other sensations, so THE SENSES. 693 also in visual sensations, a stimulus may be too feeble to produce a sen- sation. If it be increased in amount sufficiently it begins to produce an elfect which is increased on the increase of the stimulation ; this in- crease in the effect is not di7'ecily proportional to the increase in the excitation, but, according to Fechner''s Imv, " as the logarithm of the stimulus," i.e., in each sensation, there is a constant ratio between the increase in the stimulus and the increase in the sensation, this constant ratio for each sensation expresses the least perceptible increase in the sensation or minimal increment of excitation. This law, which is true only within certain limits, may be best understood by an example. When the retina has been stimulated by the light of one candle, the light of two candles will produce a difference in sensation which can be distinctly felt. If, however, the first stimulus had been that of an electric light, the addition of the light of a candle would make no difference in the sensation. So, generally, for an addi- tional stimulus to be felt, it may be proportionately small if the original stimulus have been small, and must be greater if the original stimulus have been great. The stimulus increases as the ordinary numbers, while the sensation increases as the logarithm. Part of the light which enters the eye is absorbed and produces some change in the retina, of which we shall treat further on; the rest is reflected. Every one is perfectly familiar with the fact, that it is quite impos- sible to see the fundus or back of another person's eye by simply looking into it. The interior of the eye forms a perfectly black background to the pupil. The same remark applies to an ordinary photographic camera, and may be illustrated by the difficulty we experience in seeing into a room from the street through the window, unless the room be lighted within. In the case of the eye this fact is partly due to the feebleness of the light reflected from the retina, most of it being absorbed by the retinal pigment, as mentioned above; but far more to the fact that every such ray is reflected straight to the source of light (e.g., candle), and cannot, therefore, be seen by the unaided eye without intercepting the incident light from the candle, as well as the reflected rays from the retina. This difficulty is surmounted by the use of the ophthalmoscope. The ophthalmoscope, brought into use by Helmholtz, consists in its simplest form of o, a sliglitly concave mirror of metal or silvered glass perforated in the centre, and fixed into a handle ; and b, a biconvex lens of about 2^— S inches focal length. Two methods of examining the eye with this instrument are in common use — the direct and the indirect: both metliods of investigation should be employed. A normal eye should be examined ; a drop of a solution of atro- pia (two grains to the ounce) or of homatropia hydrobromate, should be in- stilled about twenty minutes before the examination is commenced ; the ciliary muscle is thereby paralyzed, the power of accommodation is abolished, and the 694 HANDBOOK OF PHYSIOLOGY. pupil is dilated. This will materially facilitate the examination ; but i-t is quite possible to observe all the details to be presently described without the use of this drug. The room being now darkened, the observer seats liimself in front of the pei'son whose eye he is about to examine, placing himself upon a some- what higlier level. A brilliant and steady liglit is placed close to the left ear of the patient. The atropia having been put into the right eye only of the pa- tient, this eye is examined. Taking the mirror in his right hand,, and looking through the central hole, the operator directs a beam of light into the eye of Fig'. 429. — Diagram to illustrate the action of the Ophthalmoscope, when a plane concave glass is used. c. observer's eye. The light reflected from any point, d, on retina of a, would naturally be fooussed at e ; if the lens 6 is used it would be focussed at r, in other words, at back of c. The image would be enlarged, as though of Y Gv-. Fig. 434. ^iolei Ihlue (^reeji Fiff. 434. — Diagram of the three primary color sensations. (Young-Helmholtz theorj' ) 1, is the red; 2, green, and 3, violet, primary color sensations. The lettering indicates the colors of the spectrum. The diagram indicates by the height of the curve to what extent the several primary sensations of cmor are excited by vibrations of different wave lengths. Fig. 435. — Diagram of the various simple and compound colors of light, and those which are complemental of each other, i.e.. which, when mixed, produce a neutral gray tint. The three simple colors, I'ed. yellow, and blue, are placed at the angles of an equilateral triangle, which are connected together by means of a circle; the mixed colors, green, orange, and violet, are placed intermediate Vietween the corresponding simple or homogeneous colors; and the com- plemental colors, of which the pigments, when mixed, would constitute a gray, and of which the prismatic spectra would together p)oduce a white light, will be found to be placed in each case opposite to each other, but connected by a line passing through the centre of tlie circle. The fig- ure is also useful in showing the further shades of color which are complementary of each other. If the circle be supposed to contain every transition of color between the six marked down, those which, when united, yield a white or gray color, will always be found directly op- posite to each other ; thus, for example, the intermediate tint between "orange and red is com- plemental of the middle tint between green and blue. substance, the visual sensation is gray; but in the other pairs when this is the case, no sensation occurs. The rays of the spectrum to the left produce changes in the red-green substance only, with a resulting sensa- tion of red, while the (orange) rays further to the right affect both the red-green and the yellow-blue substauces; blue rays cause constructive changes in the yellow-Viue substances but none in the red-green and so on. These changes produced in the visual substances in the retina are perceived by the brain as sensations of color. The spectra left by the images of Avhite or luminous objects are ordinarily white or luminous; those left by dark objects are dark. Some- times, however, the relation of the light aud dark parts in the image 704 HANDBOOK OF PHYSIOLOGY. may, under certain circumstances, be reversed in the spectrum; what was bright may be dark, and wliat was dark may appear light. This occurs whenever the eye, which is the seat of the spectrum of a luminous object, is not closed, but fixed upon another bright or white surface, as a white wall, or a sheet of white paper. Hence the spectrum of the sun, which, while light is excluded from the eye, is luminous, appears black or gray when the eye is directed upon a white surface. The explanation of this is, that the part of the retina which has received the luminous image remains for a certain period afterward in an exhausted or less sensitive state, while that which has received a dark image is in an unexhausted, and therefore much more excitable condition. The ocular spectra which remain after the impression of colored ob- jects upon the retina are always colored; and their color is not that of the object, or of the image produced directly by the object, but the oppo- site, or complemental color. The spectrum of a red object is, therefore, green; that of a green object, red; that of violet, yellow; that of yellow, violet, and so on. The reason of this is obvious. The part of the retina which receives, say, a red image, is wearied by that particular color, but remains sensitive to the other rays which with red make up white light ; and, therefore, these by themselves reflected from a white object produce a green hue. If, on the other hand, the first object looked at be green, the retina being tired of green rays, receives a red image when the eye is turned to a white object. And so with the other colors; the retina while fatigued by yellow rays will suppose an object to be violet, and vice versa; the size and shape of the spectrum correspond- ing with the size and shape of the original object looked at. The colors which thus reciprocally excite each other in the retina are those placed at opposite points of the circle in fig. 435. The peripheral jjarts of the retina do not react to rays of red. The area of the retina which is capable of receiving impressions of color, and therefore the field of vision, is slightly different for each color. Color Blindness or Daltonisin. — Daltonism or color-blindness is a by no means uncommon visual defect. One of the commonest forms is the inability to distinguish between red and green. The simplest explana- tion of such a condition is, that the elements of the retina which receive the impression of red, etc., are absent, or very imperfectly developed, or, according to the other theory, that the red-green substance is absent from the retina. Other varieties of color blindness in which the other color-perceiving elements are absent have been shown to exist occasionally. The Eeciprocal Action of Different Parts of the Retina. Although each elementary part of the retina represents a distinct portion of the field of vision, yet the different elementary parts, or sensi- THE SENSES. 705 tive points of that membrane, have a certain influence on each other ; the particular condition of one influencing the other, so that the image perceived by one part is modified by the image depicted in the other. The phenomena which result from this relation between the different parts of the retina, ma}^ be arranged in two classes: the one including those where the condition existing in the greater extent of the retina is imjjarted to the remainder of that membrane; the other, consisting of those in which the condition of the larger portion of the retina excites, in the less extensive portion, the opposite condition. 1. When two opposite impressions occur in contiguous parts of an image on the retina, the one impression is, under certain circumstances, modified by the other. If the impressions occupy each one-half of the image, this does not take place ; for in that case, their actions are equally balanced. But if one of the impressions occupies only a small part of the retina, and the other the greater part of its surface, the latter may, if long continued, extend its influence over the whole retina, so that the opposite less extensive impression is no longer perceived, and its place becomes occupied by the same sensation as the rest of the field of vision. Thus, if we fix the eye for some time upon a strip of colored paper lying upon a white surface, the image of the colored object, espe- cially when it falls on the lateral parts of the retina will gradually dis- appear, and the white surface be seen in its place. 2. In the second class of phenomena, the affection of one part of the retina influences that of another part, not in such a manner as to ob- literate it, but so as to cause it to become the contrast or oj^posite of itself. Thus a gray spot upon a white ground appears darker than the same tint of gray would do if it alone occupied the whole field of vision, and a shadow is always rendered deeper when the light which gives rise to it becomes more intense, owing to the greater contrast. The former phenomena ensue gradually, and only after the images have been long fixed on the retina ; the latter are instantaneous in their production, and are permanent. In the same way, also, colors may be produced by contrast. Thus, a very small dull gray strip of paper, lying upon an extensive surface of any bright color, does not appear gray, but has a faint tint of the color which is the complement of that of the surrounding surface. A strip of gray paper upon a green field, for example, often appears to have a tint of red, and when lying upon a red surface, a greenish tint; it has an orange-colored tint upon a bright blue surface, and a bluish tint upon an orange-colored surface; a yellowish color upon a bright violet, and a violet tint upon a bright yellow surface. The color excited thus, as a contrast to the exciting color, being wholly independent of any rays of the corresponding color acting from without upon the retina, must arise as 45 7ud HANDBOOK OF PHYSIOLOGY. an oppos.ce or antagonistic condition of tliat membrane; and the opposite conditions of wliicli the retina thns becomes the subject would seem to balance each other by their reciprocal reaction. A necessary condition for the production of the contrasted colors is, that the part of the retina in which the new color is to be excited, shall be in a state of comparative repose; hence the small object itself must be gray. A second condition is, that the color of the surrounding surface shall be very bright, that is, shall contain much white light. Binocular Vision. Although the sense of sight is exercised by the two eyes, yet the im- pression of an object conveyed to the mind is single. V^arious theories have been advanced to account for this phenomenon. By Gall it was supposed that we do not really employ both eyes si- multaneously in vision, but always see with only one at a time. This especial employment of one eye in vision certainly occurs in persons whose eyes are of very unequal focal distance, but in the majority of individuals both eyes are simultaneously in action, in the perception of the same object; this is shown by the double images seen under certain conditions. If two fingers be held up before the eyes, one in front of the other, and vision be directed to the more distant, so that it is seen singly, the nearer will appear double; while, if the nearer one be regarded, the most distant will be seen double; and one of the double images in each case will be found to belong to one eye, the other to the other eye. Diplopia. — Single vision results only when certain parts of the two retinas are affected simultaneously; if different parts of the retina re- ceive the image of the object, it is seen double. This may be readily illustrated as follows: — the eyes are fixed upon some near object, and one of them is pressed by the thumb so as to be turned slightly in or out; two images of the object (Diplopia) are at once perceived, just as is frequently the case in persons who squint. This diplopia is due to the fact that the images of the object do not fall on corresponding points in the two retinse. The parts of the retinas in the two eyes which thus correspond to each other in the property of referring the images which affect them simultaneously to the same spoi in the field of vision, are, in man, just those parts which would correspond to each other, if one retina were placed exactly in front of, and over the other (as in fig. 436). Thus, as we have noticed in speaking of the distribution of the optic nerve- fibres, the temporal portion of one eye corresponds to, or, to use a better term, is identical Avith the nasal portion of the other eye; or a of the THE SENSES. 707 eye a (fig. 43G), with a of the eye b. The upper part of one retina is also identical with the upper part of the other; and the lower parts of the two eyes are identical with each other. The distribution of the optic nerve-fibres correspond with their distribution. The identical points on the upper and lower parts of the retinse may also be shown by the fol- lowing simple experiment. Pressure upon any part of the ball of the eye, so as to affect the retina, produces a luminous circle, seen at the opposite side of the field of vision to that on which the pressure is made. If, now, in a dark room, we press with the finger at the uj)per part of one eye, and at the lower part of the other, two 'luminous circles are seen, one above the other; so, also, two figures are seen when pressure is made simultaneously on the two outer or the two inner sides of both eyes. It is certain, therefore, that neither the upper part of one retina and the lower part of the other are identical, nor the outer lateral parts of the two retina?, nor their inner lateral portions. But if pressure be made with the fingers upon Fig. 4.36. — Diagram to show the corresponding parts of both retina. both eyes simultaneously at their lower part, one luminous ring is seen at the middle of the upper part of the field of vision; if the pressure be applied to the upper part (3f both eyes a single luminous circle is seen in the middle of the field of \dsion below. So, also, if we press upon the outer side a of the eye a, and upon the inner side «' of the eye b, a single spectrum is produced, and is apparent at the extreme right of the field of vision ; if upon the point h of one eye, and the point V of the other, a single spectrum is seen to the extreme left. The spheres of the two retinge may, therefore, be regarded as lying one over the other, as in c, fig. 436 ; so that the left portion of one eye lies over the identical left portion of the other eye, the right portion of one eye over the identical right portion of the other eye ; and with the upper and lower portions of the two eyes, a lies over a', h over h , and c over c' . The points of the one retina intermediate between a and c are again identical with the corresponding points of the other retina between a' and c' ; those between h and c of the one retina, with those between V and c of the other. If the axes of the eyes, A and b- (fig. 437), be so directed that they meet at a, an object at a will be seen singly, for the 708 HANDBOOK OF PHYSIOLOGY. point a of the one retina, and a of the other are identical. So, also, if the object /5 be so situated that its image falls in both eyes at the same distance from the central point of the retina, — namely, at l in the one eye, and at V in the other, — [i will be seen single, for it affects identical parts of the two retinae. The same will apply to the object y. In quadrupeds, the relation between the identical and non-identical parts of the retina cannot be the same as in man; for the axes of their eyes generally diverge, and can never be made to meet in one point of an object. When such an animal regards an object situated directly in front of it, the image of the object must fall, in both eyes, on the outer portion of the retinae. Thus the image of the object a (fig. 438) will fall at a' in one, and at a!' in the other: and these points a' and a" must be identical. So, also, for distinct and single vision of objects, h or c, the Fig. 437. Fig. 438. Fig. 437.— Diagram to show the simultaneous action of the eyes in viewing objects in dif- ferent directions. Fig. 438. —Diagram to show the corresponding parts of the retina in the horse. points V and V or c' c\ in the two retinae, on which the images of these objects fall, must be identical. All points of the retina in each eye which receive rays of light from lateral objects only, can have no corre- sponding identical points in the retina of the other eye; for otherwise two objects, one situated to the right and the other to the left, would appear to lie in the same spot of the field of vision. It is probable, therefore, that there are in the eyes of animals, parts of the retinae which are identical, and parts which are not identical, i.e.^ parts in one which have no corresponding parts in the other eye. And the relation of the two retinae to each other in the field of vision may be represented as in fig. 439. The cause of the impressions on the identical points of the two retinae giving rise to but one sensation, and the perception of a single image, THE SEXSES, 709 must either lie in the structural organization of the deeper or cere- bral portion of the visual apparatus, or be the result of a mental opera- tion; for in no other case is it the property of the corresponding nerves of the two sides of the body to refer their sensations as one to one spot. Many attempts have been made to explain this remarkable relation between the eyes, by referring it to anatomical relation between the optic nerves. The circumstance of the inner j^ortion of the fibres of the two optic nerves decussating at the commissure, and passing to the eye of the opposite side, while the outer portion of the fibres continue their course to the eye of the same side, so that the left side of both retinae is formed from one root of the nerves, and the right side of both retinae from the outer root, naturally led to an attempt to explain the phenomenon by this distribution of the fibres of the nerves And this explanation is favored by cases in which the entire of one side of the retina, as far as the central jDoint in both eyes, sometimes becomes insensible. But Midler has endeavored to show the inadequateness of this theory to ex- plain the phenomenon, unless it be supposed that each fibre in each cere- bral portion of the optic nerves divides in the optic commissure into two Fig. 440.— Diagrams to iUustrate tliree theories to explain the action of symmetrical parts of the retina. branches for the identical points of the two retinae, as is shown in a, fig. 440. But there is no foundation for such supjDOsition. By another theory it is assumed that each optic nerve contains exactly the same number of fibres as the other, and that the corresponding fibres of the two nerves are united in the sensorium (as in fig. 440, b). But in this theory no account is taken of the partial decussation of the fibres of the nerves in the optic commissure. 710 HANDBOOK OF PHYSIOLOGY. According to a third theory, the fibres a and «', fig, 440, c, coming from identical points of the two retinae, are in tlie optic commissure brought into one optic nerve, and in the brain either are united by a loop, or spring from the same point. The same disposition prevails in the case of the identical fibres I and V . According to this theory, the left half of each retina would be represented in the left hemisphere of the brain, and the right half of each retina in the right hemisphere. Another explanation is founded on the fact, that at the anterior part of the commissure of the optic nerve, certain fibres pass across from the distal portion of one nerve to the corresponding portion of the other nerves, as if they were commissural fibres forming a connection between the retinae of the two eyes. It is supposed, indeed, that these fibres may connect the corresponding parts of the two retinas, and may thus explain their unity of action ; in the same way that corresponding parts of the cerebral hemispheres are believed to be connected together by the com- missural fibres of the corpus callosum, and so enabled to exercise unity of function. Judgment of Solidity. — On the whole, it is probable, that the power of forming a single idea of an object from a double impression conveyed F 1 Fig. 441.— Diagrams to iUustrate how a judgment of a figure of three dimensions is obtained. by it to the eyes is the result of a mental act. This view is supported by the same facts as those employed by Wheatstone to show that this power is subservient to the purpose of obtaining a right perception of bodies raised in relief. When an object is placed so near the eyes that to view it the optic axes must converge, a different perspective projec- tion of it is seen by each eye, these perspectives being more dissimilar as the convergence of the optic axes becomes greater. Thus, if any figure of three dimensions, an outline cube, for example, be held at a moderate distance before the eyes, and viewed with each eye successively while the head is kept perfectly steady, a (fig. 441) will be the picture presented to the right eye, and b that seen by the left eye. Wheatstone has shown that on this circumstance depends in a great measure our conviction of the solidity of an object, or of its projection in relief. If different perspective drawings of a solid body, one representing the image seen by the right eye, the other that seen by the left (for example, the drawing THE SENSES. 711 of a cube, a, b, fig. 441) be presented to corresponding parts of the two retina?, as may be readily done by means of the stereoscope, the mind will perceive not merely a single representation of the object, but a body projecting in relief, the exact counterpart of that from which the draw- ings were made. By transposing tAvo stereoscopic pictures a reverse effect is produced ; the elevated parts appear to be depressed, and rice versa. An instru- ment contrived with this purpose is termed apsei(dosc02)e. Viewed with this instrument a bust appears as a liollow mask, and as may readily be imagined the effect is most bewildering. There can be no doubt in order that the image of an object should fall upon corresponding points in the two retinae, it is essential that the move- ments of the eyes should be accurately co-ordinated, and the method of this co-ordination is not so easily understood when examined carefully. Thus, suppose the eyes be directed downward and to the left. On the left side, the inferior rectus, the external rectus, and the superior oblique would contract, and, on the right side the inferior rectus, internal rectus, and superior oblique. In other words, a different set of muscles on either side, and suj^plied to a certain extent by different nerves. There must be some co-ordinating centre for these binocular movements. It is thought that this centre is localized in the anterior corpus quadrigemi- num, since stimulation of it causes conjugal lateral movement of the visual axes to the opposite side, and stimulation at another spot produces move- ments downward and inward. The posterior longitudinal bundle of fibres described as found in the pons and crus, appears to be concerned in some way with the simultaneous movement of the eyes; it appears to unite the nuclei of the three nerves to the ocular muscles, the sixth, fourth, and third. In it are said to be contained fibres from the sixth nerve of the opposite side which go to the nucleus of the third nerve of the same side; and this would serve to connect the nerve supply of the internal rectus of one side, and the external rectus of the other side. It appears, how- ever, that there is no evidence to assume that the fibres of the sixth nerve decussate, but thpse of the fourth nerve do entirely, and those of the third, partially. CHAPTER XVIII. THE REPRODUCTIVE ORGANS. Before describing the method of Keproduction, or the way which the species is propagated, it will be advisable to describe The Genital Orgaxs of the Female. The female organs of generation (fig. 442) consist of two ovaries, the function of which is the formation of ova; of a Fallopian tube, or oviduct, connected with each ovary, for the purpose of conducting the ovum from the ovary to the uterus in the cavity of which, if impreg- Fig. 442. —Diagrammatic view of the uterus and its appendages, as seen from behind. The uterus and upper part of the vagina have been laid open by removing the posterior wall ; the Fallopian tube, round ligament, and ovarian ligament have been cut short, and the broad liga- ment removed on the left side; it, the upper part of the uterus; c, the cervix opposite the os in- ternum; tlie triangular shape of the uterine cavity is shown, and the dilatation of the cervical cavity with the rugae termed arbor vitae; v, upper part of the vagina ; od. Fallopian tube or oviduct; the narrow communication of its cavity with that of the cornu of the uterus on each side is .seen; ?, round ligament; /o, ligament of the ovary; o, ovary; (, wide outer part of the right Fallopian tube; fi, its fimbriated extremity; po, parovarium; h, one of the hydatids fre- quently found connected with the broad ligament. }^. (Allen Thomson.) nated, it is retained until the embryo is fully developed, and fitted to maintain its existence independently of internal connection with the parent; and, lastly, of a canal, or vagina, with its appendages, for the reception of a male organ in the act of copulation, and for the subsequent discharge of the foetus. The Ovaries. — The ovaries are two oval compressed bodies, situated in the cavity of the pelvis, one on each side, and are adherent to the posterior surface of the broad ligament by their anterior border. This THE REPRODUCTIVE ORGANS, 713 "border of the ovary is called the hilum, and it is at this point that the blood-vessels and nerves enter it. Each ovary measures about an inch and a half in length (3.75 cm.), three quarters of an inch in width (1.86 cm.), and nearly half an inch (1.25 cm.) in thickness, and is attached to the uterus by a narrow fibrous cord (the ligament of the ovary), and, more slightly, to the Fallopian tubes, by one of the fimbriae into which the walls of the extremity of the tube expand. Structure. — A layer of condensed connective tissue, called the tunica albnginea, surrounds the ovary, and this is covered on the outside by epi- thelium (germ-epithelium), the cells of which although continuous with, FiR. 443. — View of a section of the ovary of the cat. 1, outer covering and free border of the ovary; 1', attached border; 2, the ovarian stroma, presenting a fibrous and vascular struct- ure; 3, granular substance lying external. to the fibrous stroma; 4, blood-vessels; 5, ovigerms in their earliest stages occupying a part of the granular layer near the surface; 6, ovigerms which have begun to enlarge and to pass more deeply into the ovary; 7, ovigerms round which the Graafian follicle and tunica granulosa are now formed, and which have passed somewhat deeper into the ovary and are surrounded by the fibrous stroma; 8, more advanced Graafian follicle with the ovum imbedded in the layer of cells constituting the proligerous disc; 9, the most ad- vanced follicle containing the ovum, etc. ; 9', a follicle from which the ovimi lias accidentally escaped; 10, corjjus luteum. x 6. (Schron.) and originally derived from, the squamous epithelium of the peritoneum, are short columnar (A, fig, 444). The internal structure of the organ consists of a peculiar soft fibrous tissue — a kind of undeveloped connective tissue, with long nuclei closely resembling unstriped muscle (C, fig. 444) — or stroma, abundantly supplied with blood-vessels, and having embedded in it, in various stages of development, numerous minute follicles or vesicles, the Graafian follicles, or sacculi, containing the ova (fig. 444). If the ovary be examined at any period between early infancy and advanced age, but especially during that period of life in which the power of conception exists, it wnll be found to contain a number of these vesicles. Immediately after the tunica albuginea (fig. 444) they are small and numerous, either arranged as a continuous layer, as in the •cat or rabbit, or in groups, as in the human ovary. These small follicles 714 HANDBOOK OF PHYSIOLOGY. embedded in the soft stroma of fine connective tissue and unstriped muscle form here the cortical layer; they are sometimes called ovisacs. Each of the small follicles of this layer has an external membranous envelope, or membrana propria. This envelope or tunic is lined with a Fig. 444. — Section of the ovary of a cat. A, germinal epithelium; B, immature Graafian follicle; C, stroma of ovary; D, vitelline membrane containing the ovum; E, Graafian follicle showing lining cells; F, follicle from which the ovum has fallen out. (V. D. Harris.) layer of nucleated cells, forming a kind of epithelium or internal tunic, and named the ynemhrana granulosa. The cavity of the follicle is filled up by a nucleated mass of protoplasm inclosed in a very delicate mem- brane, which is the Ovum. The large spherical nucleus contains one or more nucleoli. The nucleus is known as the germinal vesicle, and the nucleolus as the germinal spot. The central portion of the stroma of the ovary extends from the cor- tical layer to the hilum of the organ, at which enter the numerous arteries, fibrous tissue, and unstriped muscle, forming a highly vascular zona vasculosa. Within this central zone are contained the fully-devel- oped Graafian follicles, varying in size however, but considerably larger than those of the cortical layer. In these follicles the cavity is not nearly filled by the ovum, which is attached at one side to the zona granulosa by a collection of small cells, the discus proligerus, the remainder of the cavity being filled with fluid, the liquor folliculi. The envelope of the ovum, or zona pellucida, is much thicker. The zona granulosa is formed of several layers of cells, instead of one only. Its membrana propria is much thicker, so as to form a distinct fibrous in- vestment; the membrana fibrosa and the blood-vessels surrounding it are numerous, and may be said to form a membrana vasculosa about it. Tjie human ovum measures about y^ of an inch (about .2 mm.) in diameter. Its external investment, or the zona pellucida, or vitelline THE REPRODUCTIVE ORGANS. 715 membrane^ is a transparent membrane, about arW ^f an inch (10m) in thickness, which under the microscopic appears as a bright ring (fig. 445), bounded externally and internally by a dark outline. Within this transparent investment or zona pellucida, and usually in close contact with it, lies the yolk or viteUus, which is composed of granules and glob* nles of various sizes, imbedded in a more or less fluid substance. The smaller granules, which are tbe more numerous, resemble in their appear- ance, as well as their constant motion, pigment-granules. The larger granules or globules, which have the aspect of fat-globules, are in greatest number at the periphery of the yolk. The number of the gran- ules is greatest in the ova of carnivorous animals. In the human ovum their quantity is comparatively small. In the substance of the yolk is imbedded the germinal vesicle, or ves- icula germinativa, 5-^ of an inch (.05 mm.) (fig. 445). The vesicle is of greatest relative size in the smallest ova, and is in them surrounded closely by the yolk, nearly in the centre of which it lies. During the development of the ovum, the germinal vesicle increases in size much less rapidly than the yolk, and comes to be placed near to its surface. It consists of a fine, transparent, structureless membrane, containing a clear, watery fluid, in which are sometimes a few granules; and at that part of the periphery of the germinal vesicle which is nearest to the periphery of the yolk is situated the germinal spot, or macula germinativa, of a finely Nucleus or germinal vesicle. Nucleolus or germinal spot. Space left by retraction of yolk. Yolk or vitellus. Vitelline membrane. Fig. 445. — Semidiagrammatie represention of a himsan ovxmi, showing the parts of an animal cell. (Cadiat.) granulated appearance and of a yellowish color, strongly refracting the rays of light. Such are the parts of which the Graafian follicle and its contents, including the ovum, are composed. With regard to the mode and order of development of these parts there is considerable uncertainty. The Graafian follicles are formed in the following manner : — The em- bryonic ovary is covered with short columnar cells, or the so-called germ- inal epithelium. The cells of this layer undergo proliferation, so as to form several strata, and grow into tlie ovarian stroma as longer or shorter 710 HANDBOOK OF PHYSIOLOGY, columns or tubes. By degrees these tubes become cut off from the surface epithelium, and form cell nests, small, if near the surface, larger if in the depth of the stroma. The nests increase in size from multiplication of their cells, and may even give off new nests laterally by constriction of them in various directions. Certain of the cells of the germinal epithelium enlarge, and form ova ; and the formation of ova also takes place in the nests Avithin the stroma. The ova of a nest may multiply by division. The small cells of a nest surround the ova, and form their membrana granulosa, and the stroma growing up separates the surrounded ova into so many Graafian follicles. The other layers, namely, the mem- brana fibrosa and the membrana vasculosa, are derived from the stroma. The smallest follicles are formed at the surface, and make up the cor- tical layer. It is said by some that the superficial follicles as they ripen become more deeply placed in the ovarian stroma; and, again, that as they increase in size, they make their way toward the surface (fig, 443). When mature, they form little prominences on the exterior of the ovary, covered only by a thin layer of condensed fibrous tissue and epithe- lium. Only a few follicles ever reach maturity. From the earliest infancy, and through the whole fruitful period of life, there appears to be a constant formation, development, and matura- Fig. 446.- -Germinal epithelium of the ssrface of the ovary of five days' chick, blasts; 6, larger ovoblasts. (Cadiat.) a, small ovo- tion of Graafian vesicles, with their contained ova. Until the period of puberty, however, the process is comparatively inactive; for, previous to this period, the ovaries are small and pale, the Graafian vesicles in them are very minute, and probably never attain full development, but soon shrivel and disappear, instead of bursting, as matured follicles do; the contained ova are also incapable of being impregnated. But, coin- cident with the other changes which occur in the body at the time of puberty, the ovaries enlarge, and become very vascular, the formation of Graafian vesicles is more abundant, the size and degree of development attained by them are greater, and the ova are capable of being fecun- dated. The Fallopian Tubes (Oviducts). — The Fallopian tubes are about four inches in length (10 cm.), and extend between the ovaries and the THE REPRODUCTIVE ORGANS. 717 upper angles of the uterus. At the point of attachment to the uterus, each tube is very narrow ; but iu its course to the ovary it increases to about an eighth of an inch (3 mm.) in thickness; at its distal extremity, which is free and floating, it bears a number of fimbrim, one of which, longer than the rest, is attached to the ovary. The canal by which each tube is traversed is narrow, especially at its point of entrance into the uterus, at which it will scarcely admit a bristle; its other extremity is wider, and opens into the cavity of the abdomen, surrounded by the zone of fimbriis. Externally, the Fallopian tube is invested with peritoneum; internally, its canal is lined with mucous membrane, which is apt to be thrown into numerous longitudinal folds, covered with ciliated epithe- lium: between the peritoneal and mucous coats the walls are comjiosed, like those of the ut'erus, of fibrous tissue and unstriped muscular fibres, chiefly circular in arrangement. The Uterus. — The uterus {u. c, fig. 442) is a somewhat pyriform shaped organ, and in the unimpregnated state is about three inches (7.5 cm.) in length, two (5 cm.) in breadth at its upper part ov fundus, but at its lower jiointed part, neck or cervix, only about half an inch (1.25 cm.). The part between the fundus and neck is termed the hody of the uterus: it is about an inch (2.5 cm.) in thickness. Structure. — The uterus is constructed of three principal layers, or coats — serous, fibrous and muscular, and mucous, {a) The serous coat, which has the same general structure as the peritoneum, covers the organ before and behind, but is absent from the front surface of the neck. (J)) The middle coat is composed of unstriped muscle, arranged in the human uterus in three layers from without inward, longitudinal, circular, oblique and circular. They become enormously developed dur- ing pregnancy. The arteries and veins are found in large numbers in the outer part of their coat, so as to form almost a special vascular coat. (t) The mucous membrane of the uterus is lined by columnar ciliated epithelium, which extends also to the interior of the tubular glands, of which the mucous membrane is largely made up. In the cervix uteri the mucous membrane is arranged in jiermanent longitudinal folds, 2)ahncB 2)licut(B. The glands of this part are of the tubulo-racemose type, branching repeatedly and extending deeply into the substance of the cervix. They are lined by columnar epithelium, and open on the ridges and furrows of the mucous membrane. They secrete a thick glairy mucus, resembling unboiled white of egg. The mucous membrane of the cavity of the body of the uterus forms a thin membrane about -^ inch (1 mm.) thick, and is covered on its surface by columnar ciliated epithelium. Imbedded in its substance are numerous simple tubular glands set somewhat obliquely and lined with columnar ciliated epithelium. These glands often bifurcate at their 718 HANDBOOK OF PHYSIOLOGY. lower ends. The glands are imbedded in a delicate connective tissue, consisting of round and spindle-shaped cells. The cavity of the uterus corresponds in form to tliat of the organ itself: it is very small in the uuimpregnated state, the sides of its mucous surface being almost in contact. Into its upper part, at each side, opens the canal of the corresponding Fallopian tube: below, it communicates with the vagina by a fissure-like opening in its neck, the as uteris the margins of which are distinguished into two lips, an anterior and pos- terior. The Vagina is a membranous canal, five or six inches (12.5 to 15 cm.) long, extending obliquely downward and forward from the neck of the uterus, which it emt/races, to the external organs of generation. It is lined with mucous membrane, covered with stratified squamous epithelium, which in the ordinary contracted state of the canal is thrown into transverse folds. External to the mucous membrane the walls of the vagina are constructed of unstriped muscle and fibrous tissue, within which in the submucosa, esj)ecially around the lower part of the tube, is a layer of erectile tissue. This exists also in the mucosa. The lower extremity of the vagina is embraced by an orbicular muscle, the spliinder vagince; its external orifice, in the virgin, is partially closed by a fold or ring of mucous membrane, termed the hymen. The external organs of generation consist of the clitoris, a small elongated body, situated above and in the middle line, and constructed of two erectile masses or corpora cavernosa. They are not perforated by the urethra; of two folds of mucous membrane, termed laMa interna, or nymphce; and, in front of these,of two other folds, the labia externa, ov pudenda, formed of the external integument, and lined internally by mucous membrane. Between the nymphse and beneath the clitoris is an angula space, termed the vestibule, at the centre of whose base is the orifice of the meatus urinarius. Numerous mucous follicles are scattered beneath the mucous membrane composing these parts of the external organs of generation; and at the side of the lower part of the vagina are two larger lobulated glands, vulvo-vaginal or Duverney's glands, which are analogous to Cow- per's glands in the male. The ducts of these glands are about ^ inch (12.5 mm.) long and open immediately external to the hymen at the mid-point of the lateral wall of the vaginal orifice. The vulvo-vaginal glands secrete a thick brownish mucus. The Genital Organs of the Male. The male organs of generation comprise the two Testes, in which the semen is formed ; each with a duct, the Vas Deferens, and accessory Vesicula Semmalis; the Penis, an erectile organ, through which the THE REPRODUCTIVE ORGANS. 719 semen as well as the urine is discharged. The Prostate gland^ the exact function of which is not understood, is generally included in the same class. The Testes. — The secreting structure of the testicle and its duct are disposed of in two contiguous, parts (1) the body of the testicle proper, inclosed within a thick and tough white fibrous membrane, the tunica albuginea, on the outer surface of which is the serous covering formed by the tunica vaginalis, and (2) the epididymis and vas deferens. The Vas deferens, or duct of the testicle, which is about two feet (60 cm.) in length, is constructed externally of connective tissue, and internally is lined by a mucous membrane, covered with columnar epithe- lium ; while between these two coats is a middle coat, very firm and tough, made up of unstriped muscle, chiefly arranged longitudinally, but also containing some circular fibres. When followed back to its origin, the vas deferens is found to pass to the lower part of the epididymis, with Fig. 447. Fig. 448. Fig. 447.— Plan of a vertical section of fie testicle, showing the arrangement of the ducts. The true length and diameter of the ducts have been disregarded, a a, tubuli seminiferi coiled up in the separate lobes; 6, tubuli recti or vasa recta; c, rete testis; d, vasa efEerentia ending in the coni vasculosi ; I, e, g, convoluted canal of the epididymis ; h, vas deferens ; /, section of the back part of the tunica albuginea; i, ?, fibrous processes running between the lobes; s, me- diastinum. Fig, 448. — Section of the epididymis of a dog.— The tube is cut in several places, both trans- versely and obliquely; it is seen to be lined by a ciliated epithelium, the nuclei of which are well shown, c, connective tissue. (Schofleld.) which it is directly continuous (fig. 447) , and assumes there a much smaller diameter with an exceedingly tortuous course. The Epididymis, which is lined, except at its lowest part, by co- 720 HANDBOOK OF PHYSIOLOGY. luinnar ciliated epithelium (fig. 447), is commonly described as con- sisting (fig. 447) of a, globus minor {g), the body (e), and the globus 7naj or {I.) When unravelled it is found to be constructed of a single tube, meas- uring about twenty feet in length. At the globus major this duct divides into ten or twelve small branches, the convolutions of which form coniform masses, named Coni vasculosi; and the ducts continued from these, the Vasa efferetitia, after anastomosing, one with another in what is called the Rete testis, lead finally as the Tubuli recti ov Vasa recta to the seminal tubules (tubuli seminiferi), which form the proper substauce of the testicle. The epithelium lining the coni vasculosi and vasa etferentia is columnar and ciliated ; that of the rete testis is squamous. The seminal tubules are arranged in lobules, separated from one another by incomplete fibrous septa or cords, which pass from the front of the tunica albuginea internally to a firm incomplete vertical septum of thick extending fibrous tissue at the posterior border, from the upper to near the lower part, called the corjms Highmori, or tnediastiniim testis. Through this very firm fibrous tissue pass the seminal tubes from the vasa recta. The tunica albuginea is covered by a very fine plexus of blood-vessels internally, derived from the spermatic vessels. The fibrous cords which may contain unstriped muscle are also covered with a similar capillary plexus. Tubuli Semhiiferi. — The seminal tubes, which compose the paren- chyma of the testicle, are loosely arranged in lobules between the connec- tive tissue septa. They are relatively large, very wavy, and much convoluted; and they possess a few lateral branches, by which they become connected Fig. 449.— From a section of the testis of dog, showing portions of seminal tubes. A, semi- nal epithelial cells, and numerous small cells loosely arranged ; B, the small cells or sperm- atoblasts converted into spermatozoa; groups of these in a further stage of development. (Klein.) into a network. They form terminal loops, and in the peripheral por- tion of the testis the tubules are possessed of minute lateral caecal branchlets. Each seminal tubule in the adult testis is limited by a membrana THE REPRODUCTIVE ORGANS. 721 propria, which appears as a hyaline elastic membrane, but which is really made up of several incomplete layers of flattened cells, contain- ing oval flattened nuclei at regular intervals. Inside this membrana propria are several layers of epithelial cells, the seminal cells (fig. 449). These consist of two or more layers, the outermost being situated next the membrana propria. These cells are of two kinds, those that are in Fig 450.— Section of a tubule of the testicle of a rat, to show the formation of the sperm- atozoa; a spermatozoa; 6, seminal cells; c. spermatoblasts, to which the spermatozoa are still adherent ; d, membrana propria ; e, flhro-plastic elements of the connective tissue. (Cadiat. ) a resting state, which generally form a complete layer, and those that are in a state of division, of which there may be two layers. The latter are called mother cells, and the smaller cells resulting from their division are called daughter cells or spermatoblasts. From these the sperma- tozoa are formed, their head corresponding with the nuclei of the daughter cells; and during their development they lie in groups (figs. 449,450), and are supported by irregular masses of so-called nutritive cells; but when fully formed, they become detached, and fill the lumen of the seminiferous tubule (fig. 450). This detachment is effected by the liquefaction of the nutritive cells in which the groups of spermatozoa are imbedded. In the fine connective tissue which supports the tubules of the testis, are to be found flattened and nucleated epithelial cells, probably the remains of the Wolffian body. The lymphatics of the testes are numer- ous, and may be injected by inserting the needle of an injecting syringe into the tunica albuginea, and pressing in the injection with slight effort. The Vesiculae Seminales. — The vesiculae seminales have the appear- ance of outgrowths from the vasa deferentia. Each vas deferens, just 46 722 HANDBOOK OF PHYSIOLOGY. before it enters the prostate gland, through part of which it passes to terminate in tlie urethra, gives oft a side branch, which bends back from it at an acute angle: and this branch dilating, variously branching, and pursuing in both itself and its branches a tortuous course, forms the vesicula seminalis. Structure. — Each vesicula may be unravelled into a single branching tube sacculated, convoluted, and folded up. The structure resembles closely that of the vasa deferentia. The mucous membrane, like that of the gall-bladder, is minutely wrinkled and set with folds and ridges arranged so as to give it a finely reticu- lated appearance. The Penis. — The penis is composed of three long more or less cylindrical masses, inclosed in remarkably firm fibrous sheaths, of Fig. 451.— Dissection of the base of the bladder and prostate gland, showing the vesiculae seminales and vasa deferentia. a, lower surface of the bladder at the place of reflection of the peritoneum ; 6, tlie part above covered hy the peritoneum ; ?', left vas deferens, ending in e, the ejaculatory duct; the vas deferens has been divided near », and all except the vesical por- tion has been taken away; s, left vesicuhv setniiialis joining the same duct; s, s, the right vas deferens and right vesicula seminalis, which has been unravelled; », under side of the prostate gland; m, part of the urethra; w, u. the xu-eters (cut short), the right one turned aside. (Haller.) which two, the corpora cavernosa^ are alike, and are firmly joined together, and receive below and between them the third part, or corpus spongiosum. The urethra j^asses through the corpus spongiosum. The penis is attached to the S3'mphysis pubis by its root. The enlarged ex- tremity or glans penis is continuous with the corpus spongiosum. The integument covering the penis forms a loose fold from the junction of the glans with the body, called the prepuce or foreskin. THE KEPRODUCTIVE ORGANS. 723 Structure. — [a.) The urethra is lined by stratified pavement epithe- lium in the prostatic portion; in front of the bulb the eijithelium becomes columnar, while at the fossa navicularis it is again lined with stratified j)avement epithelium. The mucous membrane consists chiefly of fibrous connective-tissue, intermixed with which are many elastic fibres. It is surrounded by unstriped muscular tissue. In the inter- Fig. 452.— Erectile tissue of the human penis, a, fibrous trabeculae with their ordinary capiUaries; 6, section of the venous sinuses; c, muscular tissue. (Cadiat.) mediate portion many large veins run amongst the bundles of muscular tissue. Many mucous glands, glands of Littre^ are present. {p.) The coriwra cavernosa, a true erectile structure, are surrounded by a dense fibrous and elastic sheath, and from the inner surface of this, and from the septum which sejaarates the two corpora cavernosa, pass numerous bundles of fibrous, elastic, and plain muscular fibres, called trabecnlce, and these by their anastomosis form a series of irregular spaces. These spaces are lined with endothelium, and are filled with venous blood. The inter-trabecular sjaaces or sinuses of one corpus cavernosum anastomose with those of the other, especially in front where the dividing septum is incomplete, (c. ) The corpus spongiosum urethra consists of an inner portion or plexus of longitudinal veins, and of an outer or really cavernous portion identical in structure with that which has just been described. The lymphatics of the penis are very numerous, both superficially and also around the urethra. They join the inguinal glands. The nerves, derived from the pudic nerves and hypogastric plexus, are distributed to the skin and mucous membrane and to the corpora cavernosa and spongiosum respectively. The nerves are provided with end bulbs and Pacinian corpuscles in the glans penis, and form also a dense subepithelial plexus. Gowpefs glands, are two small glands, the ducts of which open into 724 HANDBOOK OF PHYSIOLOGY. the second part of the urethra. They are small round bodies, of the size of a pea, yellow in color, resembling the sublingual gland; in structure they are compound tubular mucous glands. The Prostate Gland. — The prostate is situated (fig. 451) at the neck of the urinary bladder, and incloses the commencement of the urethra. It is somewhat chestnut-shaped. It measures an inch and a half in breadth, and an inch and a quarter long, and half an inch in thickness. Structure. — The prostate is made up of small compound tubular glands imbedded in an abundance of muscular fibres and connective tissue. The glandular substance, which is nearly absent from the front part of the organ, consists of numerous small saccules, opening into elongated ducts, which unite into a smaller number of excretory ducts. The acini Big. 453.— Section of a smaU portion of the prostate, o, gland duct cut across obliquely ; 6, gland structm-e; c, prostatic calculus. (Cadiat.) of the upper part of the prostate are small and hemispherical ; while in the middle and lower parts the tubes are longer and more convoluted. The acini are of two kinds, namely, those («) lined with a single layer of thin and long columnar cells, each with an oval nucleus in outer part of wall; and those {h) acini resembling the foregoing, but with a second layer of small cortical, polyhedral, or fusiform cells between the mem- brana propria and the columnar cells. The ducts, twelve to twenty in number, open into the urethra. They are lined by a layer of columnar cells, beneath which is a layer of small polyhedral cells. The tunica adventitia consists of dense fibrous tissue of two layers, between which is situated a plexus of veins. Large vessels pass into the interior of the organ, to form a broad, meshed, capillary system. Nerves with numerous large ganglion-cells surround the cortex. Pacinian bodies are sometimes found in the substance of the organ. THE EEPEODUCTIVE ORGANS, 725 The muscular tissue of the prostate not only forms the chief part of the stroma of the gland, but also forms a continuous layer inside the fibrous sheath, as well as a layer surrounding the urethra, which is con- tinous with the sphincter vesicae. Physiology of the Sexual Organs. Of the Female. — In the process of development in the ovary of individual Graafian vesicles, it has been already observed, that as each increases in size, it gradually approaches the surface of the ovary, and when fully ripe or mature, forms a little projection on the exterior. Coincident with the increase in size, caused by the augmentation of its liquid contents, the external envelope of the distended vesicle becomes very thin and eventually bursts. By these means, the ovum and fluid contents of the vesicle are liberated, and escape on the exterior of the ovary, whence they pass into the Fallopian tube or oviduct, the fimbri- ated processes of the extremity of which are supposed coincidentally to grasp the ovary, while the aperture of the tube is applied to the part corresponding to the matured and bursting vesicle. In animals whose special capability of being impregnated occurs at regular periods, as in the human subject, and most mammalia, the Graafian vesicles and their contained ova appear to arrive at maturity, and the latter to be discharged at such jDcriods only. But in other animals, e.g., the common fowl, the formation, maturation, and dis- charge of ova appear to take place almost constantly. It has long been known, that in the so-called ovijjarous animals, the separation of ova from the ovary may take place indei)endently of im- pregnation by the male, or even of sexual union. And it is now established that a like maturation and discharge of ova, independently of coition, occurs in mammalia, the periods at which the matured ova are separated from the ovaries and received into the Fallopian tubes being indicated in the lower mammalia by the phenomena of heat or rut: in the human female, altliough not always with exact coincidence, by the phenomena of menstruation. If the union of the sexes take place, the ovum may be fecundated, and if no union occur it perishes. That this maturation and discharge occur periodically, and only during the phenomena of heat in the lower mammalia, is made jsrobable by the facts that, in all instances in which Graafian vesicles have been found presenting the appearance of recent rupture, the animals were at the time, or had recently been, in heat ; that on the other hand, there is no authentic and detailed account of Graafian vesicles being found ruptured in the intervals of the period of heat; and that female animals do not admit the males, and never become impregnated, except at those periods. 726 • HANDBOOK OF PHYSIOLOGY. Belation of Menstruation to the Discharge of Ova. — The human female is subject to the same law as the females of other mammiferous animals; her ova are matured and discharged from the ovary independent of sexual union. This maturation and discharge occur, moreover, periodically at or about the epochs of menstruation. The evidence of the j)eriodical discharge of ova at the menstrual periods is that in most cases in which signs of menstruation have been found in the uterus, follicles in a state of maturity or of rupture have been seen in the ovary ; and although conception is not confined to the periods of menstruation, yet it is more likely to occur about a menstrual epoch than at other times. The exact relation between the discharge of ova and menstruation is not very clear. It was formerly believed that the monthly flux was the result of a congestion of the uterus arising from the enlargement and rupture of a Graafian follicle; but though a Graafian follicle is, as a rule, ruptured at each menstrual epoch, yet several instances are recorded in which menstruation has occurred where no Graafian follicle can have been ruptured, and on the other hand cases are known where ova have been discharged in araenorrhaeic women. It must therefore be admitted that menstruation is not dependent on the maturation and discharge of ova. It was, moreover, formerly understood that ova were discharged toward the close or soon after the cessation of a menstrual flow. Obser- vations made after death, and facts obtained by clinical investigation, however, do not support this view. Eupture of a Graafian follicle does not happen on the same day of the monthly period in all women. It may occur toward the close or soon after the cessation of a flow; but only in a small minority of the subjects examined after death was this the case. On the other hand, in almost all such subjects of which there is record, rupture of the follicle appears to have taken place before the commencement of the catamejiial flow. Moreover, the custom of the Jews — a prolific race, to whom by the Levitical law sexual intercourse during the week following menstruation was forbidden — militates strongly in favor of the view that concej)tion usually occurs before and not soon after a menstrual epoch, and necessarily, therefore, for the view that ova are usually discharged before the catamenial flow. This, to- gether with the' anatomical condition of the uterus just before the catamenia, seems to indicate that the ovum fertilized is that which is discharged in connection with the first absent, and not that with the last present menstruation. Though menstruation does not appear to depend upon the discharge of ova, yet the presence of the ovaries seems necessary for the perform- ance of the function; for women do not menstruate when both ovaries THE REPRODUCTIVE ORGANS. 727 have been removed by operation. Some instances have been recently recorded, indeed, of a sanguineous discharge occurring periodically from the vagina after both ovaries have been previously removed for disease ; and it has been inferred from this that menstruation is a function inde- pendent of the ovary : but this evidence is not conclusive, inasmuch as it is possible that portions of ovarian tissue were left after the operation. Source and Characters of Menstrual Discharge. — The menstrual dis- charge is a thin sanguineous fluid, having a peculiar odor. It is of a dark color, and consists of blood, epithelium, and mucus from the Fig. 454. Fig. 455. Fig. 456. Fig. 454.— Diagram of uterus just before menstruation; the sliaded portion represents the thiclcened mucous membrane. Fig. 45.5.— Diagram of utei-us when menstruation has just ceased, showing the cavity of the ut«rus deprived of mucous membrane. Fig. 456.— Diagram of uterus a week after the menstrual flux has ceased: the shaded portion represents renewed mucous membrane. (J. Williams.) uterus and vagina. The mensirual flow is preceded by a general engorg- ment of all the pelvic organs with blood. The cervix and vagina become darker in color and softer in texture, and the quantity of mucus secreted by the glands of the cervix and body is increased. The uterine mucous membrane is swollen and the glands are elongated and tortuous. The discharge of blood, the source of which is the mucous membrane of the body of the uterus, is probably associated with uterine contractions. There is great difference of opinion as to whether or not any of the uterine mucous membrane is normally shed during the process of men- struation. John Williams believes that the whole of the mucous mem- brane of the body of the uterus is thrown off at each monthly period, 728 HANDBOOK OF PHYSIOLOGY. forming a true decidua mensfruaUs (fig. 454), while Moricke and others believe that the mucous membrane remains intact. Leopold believes that red blood corpuscles escajae from the congested capillaries and un- dermine the superficial epithelium, and that in this way the superficial layer of the mucous membrane is eroded and subsequently regenerated. It is probable that menstruation is not a sign of the capability of being impregnated, as much as of disajipointed impregnation, Me7isirual Life. — The occurrence of a menstrual discharge is one of the most prominent indications of the commencement of puberty in the female sex; though its absence even for several years is not necessarily attended with arrest of the other characters of this period of life, or with inaptness for sexual union, or incapability of impregnation. The average time of its first appearance in females of this country and others of about the same latitude, is from fourteen to fifteen ; but it is much influenced by the kind of life to which girls are subjected, being accel- erated by habits of luxury and indolence, and retarded by contrary conditions. Its appearance may be slightly earlier in persons dwelling in warm climes than in those inhabiting colder latitudes. Much of the influence attributed to climate appears due to the custom prevalent in many hot countries, as in Hindostan, of giving girls in marriage at a very early age, and inducing sexual excitement previous to the proper menstrual time. The menstrual functions continue through the whole fruitful period of a woman's life and usually cease between the forty- fifth and fiftieth years. The several menstrual periods usually occur at intervals of a lunar month, the duration of each being from three to six days. In some women the intervals are so short as three weeks or even less; while in others they are longer than a month. The periodical return is usually attended by pain in the loins, a sense of fatigue in the lower limbs, and other symptoms, which are different in different individuals. Menstru- ation does not usually occur in pregnant women, or in those who are suckling; but instances of its occurrence in both these conditions are by no means rare. Corjnis Luteuin. — Immediately before, as well as subsequent to, the rupture of a Graafian follicle, and the escape of its ovum, certain changes ensue in the interior of the vesicle, which result in the production of a yellowish mass, termed a Corpus luteum. When fully formed the corpus luteum of mammiferous animals is a roundish solid body, of a yellowish or orange color, and composed of a number of lobules, which surround, sometimes a small ca\dty, but more frequently a small stelliform mass of white substance, from which deli- cate processes pass as septa between the several lobules. Very often, in the cow and sheep, there is no white substance in the centre ; and the THE REPRODUCTIVE ORGANS. 729 lobules projecting from the opposite walls of the Graafian follicle appear in a section to be separated by the thinnest j^ossible lamina of semi- transparent tissue. When a follicle is about to burst and expel the ovum, it becomes highh' vascular and ojiaque; and, immediately before the rupture takes place, its walls appear thickened on the interior by a reddish glutinous or fleshy-looking substance. Immediately after the rupture, the inner layer of the wall of the vesicle appears pulpy and llocculent. It is thrown into wrinkles by the contraction of the outer layer, and, soon, red fleshy mammillary processes grow from it, and gradually enlarge till they nearly fill the vesicle, and even protrude from the orifice in the external covering of the ovary. Subsequently this orifice closes, but the fleshy growth within still increases during the earlier period of preg- nancy, the color of the substance gradually changing from red to yellow, and its consistence becoming firmer. The human corpus luteum (fig. 45?) differs from that of the domestic quadruped in being of a firmer texture, and having more frequently a Fig. 45".— Corpora lutea of different periods. B, corpus luteum of about the sixth week after impregnation, showing its plicated form at that period. 1, substance of the ovary; 2, sub- stance of the corpus luteum : 3, a grayish coagulum in its cavity. (Paterson. ) A, corpus lu- teum two days after delivery; D, in the twelfth week after delivery. (Montgomery.) persistent cavity at its centre, and in the stelliform cicatrix, which re- mains in the cases where the cavity is obliterated, being proportionately of much larger bulk. The quantity of yellow substance formed is also much less: and although the deposit increases after the vesicle has burst, yet it does not usually form mammillary growths projecting into the cavity of the vesicle, and never protrudes from the orifice, as is the case in other Mammalia. It maintains the character of a uniform, or nearly uniform, layer, which is thrown into wrinkles, in consequence of the contraction of the external tunic of the vesicle. After the orifice of the vesicle has closed, the growth of the yellow substance continues dur- ing the first half of pregnancy, till the cavity is reduced to a compara- tively small size, or is obliterated ; in the latter case, merely a white stelliform cicatrix remains in the centre of the corpus luteum. An effusion of blood generally takes place into the cavity of the fol- 730 HANDBOOK OF PHYSIOLOGY. licle at the time of its rupture, esjDecially in the human subject, hni it has no share in forming the yellow body; it gradually loses its coloring matter. The serum of the blood sometimes remains included within a cavity in the centre of the coagulum, and then the decolorized fibrin forms a membraniform sac, lining the corpus luteum. At other times the serum is removed, and the fibrin constitutes a solid stelliform mass. The yellow substance of which the corpus luteum consists, both in the human subject and in the domestic animals, is a growth from the inner surface of the ruptured follicle, the result of an increased devel- oj)ment of the membrana granulosa. The first changes of the internal coat of the Graafian vesicle in the process of formation of a corpus luteum seem to occur in every case in which an ovum escapes; as well in the human subject as in the domestic quadrupeds. If the ovum is impregnated, the growth of the yellow sub- stance continues during nearly the whole period of gestation and forms the large corpus luteum commonly described as a characteristic mark of impregnation. If the ovum is not impregnated, the growth of yellow substance on the internal surface of the vesicle proceeds, in the human ovary, no further than the formation of a thin layer, which shortly dis- appears; but in the domestic animals it continues for some time after the ovum has perished, and forms a corpus luteum of considerable size. The fact that a structure, in its essential characters similar to, though smaller than, a corpus luteum observed during pregnancy, is formed in the human subject, independent of impregnation or of sexual union, coupled with the varieties in size of corpora lutea formed during preg- nancy, necessarily renders unsafe all evidence of previous impregnation founded on the existence of a corpus luteum in the ovary. The folllowing table by Dalton, expresses well the differences between the corpus luteum of the pregnant and unimpregnated condition respectively : — Corpus Luteum of Menstru- Corpus Luteum of Pregnancy, ation. Three-quarters of an inch in diameter ; central clot reddish ; con- voluted wall pale. Larger; convoluted wall bright yel- low ; clot still reddish. At the end of three weeks One month . Two months Six months Nine months Smaller ; convoluted wall bright yellow ; clot still reddish. Reduced to the condition of an insignificant cica- trix. Absent. Absent. Seven-eighths of an inch in dia- meter ; convoluted wall bright yellow ; clot jDerfectly decolor- ized. Still as large as at end of second month ; clot fibrinous ; convoluted wall paler. One-half an inch in diameter; cen- tral clot converted into a radi- ating cicatrix ; the external wall tolerably thick and convoluted, but without any bright yellow color. THE KEPEODUCTIYE ORGAXS. 731 Of the Male. — In order that the ovum should be fecundated, it is necessary that it should meet with the seminal fluid of the male. This is accomplished by the junction of the sexes in the act of coition, whereby the seminal fluid is discharged into the neighborhood of, if not within, the cervix uteri. Before considering the changes which are produced in the ovum by impregnation, it will be as well to describe the nature of the seminal fluid. This consists essentially of the semen se- creted by the testes, and to this are added a material secreted by the vesiculse seminales, as well as the secretion of the prostate gland, and of Cowper's glands. Portions of these several fluids are discharged, to- gether with the proper secretion of the testicles. The semen is a viscid, whitish, albuminous fluid of a peculiar odor. It contains epithelium, granules or colorless particles, and large num- bers of sijermatozoa, which are the characteristic and essential elements. Fig. 458. Fig. 459. Fig. 458.— Spermatic filaments from the human vas deferens. 1, magnified 300 diameters; 2, magnified 800 diameters; a, from the side; 6, from above. (From KoUiker.) Fig. 459. — Spermatozoa. 1, Of salamander; 2, hmnan. (H. Gibbes. ) The spermatozoa are minute bodies each consisting of a flattened oval head and attached to it a long slender tapering mobile flagellum or tail. In some forms of spermatozoa there is a small middle piece interposed between the head and the tail. The head is about -g-oVotli i^^ch (about 4/x) long and y-g-J-j^th inch (about 2. 5/x) broad. The tail is about -j-^^jj-oth to ^Q^Qgth inch (5/^-6,a) long. The spermatozoa possess the power of active movement, and it is by this sinuous, cilia-like movement that they are propelled in the female and so helped in their progress to meet the ovum. The lashing cilium-like movement of a spermatozoon may 732 HANDBOOK OF PHYSIOLOGY. go on for hoars or days in the alkaline fluids of the body. It is stopped by any of the agencies which stop ciliary movement, e.g,^ acids, or strong alkalies, alcohol, chloroform, cold to 0° C, and heat above 50° 0. On examining the spermatozoon of Triton cristatus, one of the am- phibia which possess the largest spermatozoa of all vertebrate animals, H. Gibbes found that the organism consisted of {a) a long pointed head, at the base of which is (J), an elliptical structure joining the head to {a), a long filiform body; [d), a fine filament, much longer than the body, is connected with this latter by (e), a homogeneous membrane. The head, as it appears in the fresh specimen, has a different refrac- tive power from that of the rest of the organism, and with a high power appears to be a light green color; there is also a central line running up it, from which it appears to be hollow. The elliptical structure at the base of the head connects it with the long threadlike body, and the filament springs from it. While the spermatozoon is living, this filament is in constant mo- tion; at first this is so quick that it is difficult to see it, but as its vital- ity becomes impaired the motion gets slower, and it is then easily per- ceived to be a continuous waving from side to side. The spermatozoa of all mammalia examined, consisting of man, bull, dog, liorse, cat, ing, mouse, rat, guinea-pig, had instead of the long-pointed head of the amphibian, a blunt thick process of different shapes in the different animals; and from the root or neck of this proceeded the long filament just as in the amphibia, only so delicate as to be invisible except with very high powers. In man the head (fig. 459) is club-shaped, and from its base springs the very delicate filament, which is three or four times as long as the body; and the membrane which attaches it to the body is much broader, and allows it to lie at a greater distance from the body than in the sper- matozoa of any other Mammal examined. From his investigation, Gibbes concluded: — 1st, that the head of the spermatozoon is inclosed in a sheath, which is a continuation of the membrane which surrounds the filament, and connects it to the body, acting in fact the part of a mesentery. 2ndly. That the substance of the head is quite distinct in its composition from the elliptical structure, the filament and the long body, and that it is readily acted on by alkalies; these reagents have no effect, however, on the other part, exempting the membraneous sheath. 3rdly. That this elliptical structure has its analogue in the mammalian spermatozoon; in the one case the head is drawn out as a long pointed process, in the other it is of a globular form, and surrounds the elliptical structure. 4tlily. That the motive power lies, in a great measure, in the filament and the membrane at- taching it to the body. THE REPEODrCTIYE ORGAXS. 733 The spermatozoa are derived from the breaking up of the seminal cells or daughter cells. They must be looked upon as modified cells. The occurrence of spermatozoa in the impregnating fluid of nearly all classes of animals, proves that they are essential to the process of impregnation, and their actual contact with the ovum is necessary for its development. The seminal fluid is, probably, after the period of puberty secreted constantly, though, except under excitement, very slowly, in the tubules of the testicles. From these it passes along the vasa deferentia into the vesiculee seminales, whence, if not expelled in emission, it may be dis- charged, as slowly as it enters them, either with the urine, which may remove minute quantities, mingled with the mucus of the bladder and the secretion of the prostate, or from the urethra in the act of defalca- tion. To the vesiculiB seminales a double function maybe assigned; for they both secrete some fluid to be added to that of the testicles, and serve as reservoirs for the seminal fluid. The former is their most con- stant and probably most important office; for in the horse, bear, guinea- pig, and several other animals, in whom the vesiculae seminales are large and of apparently active functions, they do not communicate with the vasa deferentia, but pour their secretions, separately, though it may be simultaneously, into the urethra. There is a complete want of information respecting the nature and purposes of the secretions of the prostate and Cowper's glands. That they contribute to the right composition of the impregnating fluid, is shown both by the position of the glands and by their enlarging with the testicles at the approach of an animal's breeding time. But that they contribute only a subordinate part is shown by the fact, that, when the testicles are lost, though these other organs be perfect, all procrea- tive power ceases. The fluid part of the semen or liquor seminis has not been satisfac- torily analyzed : but Henle says it contains fibrin, because shortly after being discharged, flocculi form in it by spontaneous coagulation, and leave the rest of it thinner and more liquid, so that the filaments move in it more actively. The chief constituents of the semen are said to be a variety of nnclein, which does not contain sulphur; cevtain p7'oteids, one of which contains four per cent, of sulphur; lecithin; cholesterin; fat, and extractives. CHAPTER XIX. DEVELOPMENT. Changes which occur in the Ovum. Of the changes which take place in the ovum, some occur before and are as it were preparatory to impregnation, and others ensue after impregnation. It will be as well to consider the respective changes separately. Changes inior to Imijr eg nation. — These changes especially concern the germinal vesicle, and have been observed chiefly in the ova of low types. The ovum when ripe and detached from the ovary consists, it will be remembered, of a granular yolk inclosed within the protoplasmic zona pellucida, and containing the germinal vesicle and germinal spot situ- ated eccentrically. The yolk granules are of different sizes, from the minutest molecules uj) to a diameter of tthto^^^ ^o y-^o^th of an inch (about 25,^.). The germinal vesicle consists of reticulated protoplasm inclosed in a distinct membrane, and containing one or more nucleoli or germinal spots. The primary change observed in the ovum consists in alterations in the shape of the vesicle, the disaj^pearance of its pro- toplasmic reticulum, and of its inclosing membrane, with a consequent indentation and indistinctness of its outline. Its protoplasm becomes to a considerable extent confounded with the yolk substance, and its germinal spot disappears. The next step in the process is the appear- ance in the yolk of two stars in a clear space near the j)oles of the vesi- cle elongated to a certain extent, and from this results a nuclear sinndle, corresponding to a nucleus in the process of division, with the stars at either end lying near the surface of the yolk. This spindle next becomes vertical, and the star nearer the surface protrudes from the ovum envel- oped in a protoplasmic mass, which by constriction forms the first jt)o/ar cell. A second polar cell arises in the same way. From the remainder of the spindle within the yolk two or three vesicles arise, and by the junction of these a single nucleus is formed, which is called i\ie female pro-nucleus. This is clearly derived from the original germinal vesicle. It must be remembered that these changes have been so far observed only in a certain number of instances. It is very possible, not to say probable, that such changes are universal in the animal kingdom (Balfour). Balfour's view as to the formation of the polar bodies may be given DEVELOPMENT. 735 in his own words: — '' My view amounts to the following, viz., that after the formation of the j^olar-cells, the remainder of the germinal vesicle within the ovum (the female pro-nucleus) is incapable of further devel- opment without the addition of the nuclear part of the male element (spermatozoon), and that if polar-cells were not formed, partheftogenesis might normally occur." Changes following Impregnation. — The process of impregnation of the ovum has been observed most accurately in the low'er types. In mammalia, although spermatozoa pass in numbers through the volk envelope, yet their further progress is only inferred from observations on the lower animals. The process in asterias glacialis, according to Bal- four, is as follows: — The head of a single spermatozoon joins with an elevation of the yolk substance, the tail remaining motionless, and then disappearing. The head enveloped in the protoplasm then sinks into the yolk and becomes a nucleus, from which the yolk substance is arranged in radiating lines. This is the male pro-nucleus. At first, at some dis- tance from the female pro-nucleus, it after a wdiile approaches nearer, and the female pro-nucleus, which was before inactive, becomes active. The nuclei at last meet and unite. The result of their union is the/rs^ segmentation sphere, or blasto-spJiere. It is a nucleated protoplasmic cell. The changes which have resulted in the formation of the blasto-sphere or primitive segmentation, germ are followed by the process known as segmentation of the yolk. This process and the earlier stages in development are so fundamen- tally similar in all vertebrate animals, from fishes up to man, that the gaps existing in our knowledge of the process in the higher mammalia, such as man, may be, in part, at any rate, filled up by the more accu- rate knowledge which we possess of the development of the ovum in such animals as the trout, frog, and fowl. One important distinction between the ova of various vertebrata should be remembered. In the iien's egg, besides the shell and the white or albumen, two other structures are to be distinguished — the ge7-7n, often called the cicatricula or "tread," and the yolk, inclosed in its vitelline membrane. The gei'm is (as was mentioned in the description already given) essentially a cell, consisting of protoplasm inclosing a nucleus and nucleolus. It alone participates in the process of segmentation, the great mass of the yolk (food- yolk) remaining quite unaffected by it. Since only the germ, which forms but a small portion of the yolk, undergoes segmentation, the ovum is called mero- blastic. In the mammalia, on the other hand, there is no large unsegmented mass corresponding to the food-yolk of birds ; the entire ovum undergoes segmenta- tion, and is hence termed holoblastic. The eggs of fishes, reptiles, and birds, are meroblastic, while those of am- phibia and mammalia are holoblastic. Of the changes which the mammalian ovum undergoes previous to 73G HANDBOOK OF PHYSIOLOGY. the formation of the embryo, those which occur while it is still in the ovary are independent of impregnation : others take place after it has reached the Fallopian tube. The knowledge we possess of these changes is derived almost exclusively from obser- vations on the ova of the bitch and rabbit : but it may be inferred that analogous changes ensue in the human ovum. As the ovum approaches the middle of the Fallopian tube, it begins to receive a new investment, consisting of a layer of transparent albuminous or glutinous sub- stance, which forms upon the exterior of the zona pellucida. It is at first exceed- ingly fine, and owing to this, and to its transparency, is not easily recognized, but at the lower part of the Fallopian tube it acquires considerable thickness. Secjmentation. — The first visible result of fertilization is a slight amoeboid move- ment in the protoplasm of the ovum: this has been observed in some fish,' in the frog, and in some mammals. Immediately succeeding to this the process of segmen- tation commences, and is completed dur- ing the passage of the ovum through the Fallopian tube. In mammals, in which the process is an example of complete seg- mentation, the yolk becomes constricted in the middle, and is surrounded by a furrow which, gradually deepening, at length cuts it in half, while the same pro- cess begins almost immediately in each half of the yolk, and cuts it also in two. The same process is repeated in each of the quarters, and so on, until at last by continual cleavings, the whole yolk is changed into a mulberry-like mass of small and more or less rounded bodies, sometimes called vitelline spheres, the whole still inclosed by the zona pellucida (fig. 460). Each of these lit- tle spherules contains a transparent vesicle, like an oil-globule, which is seen with difficulty, on account of its being enveloped by the yolk-gran- ules which adhere closely to its surface. Fig. 460. — Diagrams of the vari- ous stages of cleavage of the yolk. (Dalton.) DEVELOPMENT. 737 The cause of this singuhir siibdivisiou of the yolk is quite obscure : though the immediate agent in its production seems to be the central vesicle contained in each division of the yolk. Originally there was prob- ably but one vesicle, situated in the centre of the entire granular mass of the yolk, and probably derived in the manner already described from the germinal vesicle. This divides and subdivides: each successive divi- sion and subdivision of the vesicle being accompanied by a corresponding division of the yolk. About the time at which the mammalian ovum reaches the uterus, the process of division and subdivision of the yolk appears to have ceased, its substance having been resolved into its ultimate and smallest divisions, while its surface presents a uniform finely-granular aspect, instead of its late mulberry-like appearance. The ovum, indeed, ap- pears at first sight to have lost all trace of the cleavage process, and, with the exception of being j^aler and more translucent, almost exactly resembles the ovarian ovum, its yolk consisting apparently of a confused mass of finely granular substance. But on a more careful examination, it is found that these granules are aggregated into numerous minute spheroidal masses, each of which contains a clear vesicle or nucleus in its centre, and is, in fact, an emhryonal cell. The zona pellucida, and the layers of albuminious matter surrounding it, have at this time the same character as when at the lower part of the Fanoj)ian tube. The passage of the ovum, from the ovary to the uterus, occupies probably eight or ten days in the human female. When the peripheral cells, which are formed first, are fully devel- oped, they arrange themselves at the surface of the yolk into a kind of membrane, and at the same time assume a polyhedral shape from mutual pressure, so as to resemble pavement epithelium. The deeper cells of the interior pass gradually to the surface and accumulate there, thus in- creasing the thickness of the membrane already formed by the more superficial layer of cells, while the central part of the yolk remains filled only with a clear fluid. By this means the yolk is shortly converted into a kind of secondary vesicle, the walls of which are composed exter- nally of the original vitelline membrane, and within by the newly formed cellular layer, the blastoderm or germinal membrane, as it is called. Segmentation in the Chick. — The embryo chick affords an illustra- tion of what is known as incomplete or partial segmentation, or mero- blastic segmentation. In the youngest ova the germinal vesicle is situ- ated subcentrally, but as development jiroceeds it passes to the periphery, and the protoplasm surrounding it remaining free from yolk granules, the germinal disc is formed. This germinal disc is not marked out by any sharp line from the remaining protoplasm, but passes insensibly into it. The first change consists in the appearance of a f urroAV run- 47 738 HANDBOOK OF PHYSIOLOGY. ning across the disc dividing it into two; it does not extend across the whole breadth. A second furrow, at right angles, cutting the first a little eccentrically, next apj^iears, and the disc is thus cut into four quadrants. The furrows do not extend through the whole thickness of the disc, and the segments are not separated out on the lower aspect. The quadrants are next bisected by radiating furrows, and the disc is thus divided into eight parts. The central portion of each segment is now cut off from the peripheral furrow, so that a number of smaller central and larger peripheral portions result. As the primary division was eccentric and the succeeding followed the same plan, there results a bilateral symmetry; but the relation of the axis of symmetry and the long axis of the embryo is not known. Eapid division of the segments by furrows in various directions now ensues, and the small central por- tions are more rapidly broken np than the larger, and therefore become more numerous. During this superficial segmentation a similar process goes on throughout the whole mass, and division goes on not only by vertical but also by horizontal furrows. The result of this process of segmentation is that the original germinal disc is cut into a large num- ber of small rounded protoplasmic cells, small in the centre, larger to the periphery, and that the superficial cells are smaller than those be- low: the two original layers of the blastoderm are thus early rei^resented. The process of segmentation proceeds at the jjeriphery of the ger- minal disc, and at the same time further division of the cells at the Fig. 461.— Vertical section of area peHucida and area opaca (left extremity of figure) of blastoderm of a fresh-laid egg funincubated). S, superflcial layer corresponding to epiblast; i), deeper layer, corresponding to hypoblast, and probably in part to mesoblast; M, large "formative cells," filled with yolk granules, and lying on the floor of the segmentation cavity; A, the white yolk immediately underlying the segmentation cavity. (Strieker.) centre proceeds. The nucleus of the original cell divides coincidently with the protoplasm, and so it comes that the protoplasmic masses are nucleated; and besides this, nuclei derived from the original nucleus are found in the ovum below the area of segmentation, and from these by the protoplasm which surrounds them being constricted off with them, supplementary segmentation masses come to be formed. The blastoderm is thus formed as the result of segmentation, and between it and the subjacent white yolk is a cavity containing fluid. The segmen- tation having been completed toward the centre, although it still pro- ceeds at the periphery, the superficial layer of the blastoderm becomes DEVELOPMENT. 739 a layer of columnar nucleated cells, and the lower layer consists of larger masses indistinctly nucleated, still granular and rounded, irregularly disposed. In the segmentation cavity are the supplementary segmenta- tion masses or formative cells. When the egg is incubated, raj^id changes take j)lace in the blasto- derm, resulting in the formation first of all of two, then of the three layers, which have been already mentioned in the first chapter. The superficial, or epiblast, does not at first enter into these changes, but Fig. 462. — Impregnated egg, with oommeuceuieut of formation of embryo; showing the area germinativa oV embryonic spot, the area pellucida, and the primitive groove or trace. (Dalton.) continues to be a layer of nucleated columnar cells. But in the lower layer of larger rounded cells certain of the cells become flattened hori- zontally, their granules disappear, and the nuclei become distinct. A membrane of flattened nucleated cells is then formed, first of all toward the centre of the area, afterward peripherally also : this is the hypoblast. Between the two layers some cells, not belonging to either layer, remain. These cells are almost entirely at the back part of the area. The for- mation of the intermediate layer of mesoblast is more complicated, and will now be described. At this period it is necessary to return to the surface view of the blastoderm. Before incubation it is seen to consist of a more or less circular transparent area, the area pellucida, surrounded by an opaque rim, which is called the area opaca. The area opaca rests upon the white yolk: beneath the area i)ellucida is a cavity containing fiu id. In the centre of the area pellucida is a white shining spot, or nucleus of Pander, shining through. This is the upper dilated extremity of the flask-shaped accumulation of white yolk upon whicli the blastoderm rests. The yellow yolk consists of spheres 25/-t to IOO/ji in diameter, filled with highly refractive granules of an albuminous nature, and the white yelk being distinguished from the yellow not only by its lighter color, but also because its vesicles are smaller than those of the yellow. Each con- 740 HANDBOOK OF PHYSIOLOGY. tains u highly refractive body. Some large spheres contain a number of spherules. Some of these are vacuolated. The white yolk not only en- velopes the yellow yolk in a thin layer, and merges with the central flask-shaped mass, already mentioned, but also is found in the yellow yolk, forming with it alternate layers. Except that the central shining opacity of the pellucid area has dis- appeared, that the size of the area has increased, and that the opaque Fig. 46.3, — Transverse section through embryo chick (26 hours). «, epiblast; b, mesoblast; c, hypoblast; rf, central portion of mesoblast, which is here fused with epiblast; e, primitive groove; /, dorsal ridge. (Klein.) area has also increased, no other change can be remarked up to the for- mation of the two complete layers. There is, however, a slight ill- defined opacity at the posterior part of the area pellucida, known as the embryonic shield. This opacity is probably due to the intermediate cells already mentioned as existing between the epiblast and hypoblast. In the posterior j)art of the area pellucida now appears an opaque streak which extends about a third of the diameter of the area toward the middle line. This is the Primitive streak. It is found on trans- verse section of the blastoderm in this neighborhood to be due to a pro- liferation downward of cells two or more deep from the epiblast. The area pellucida now becomes oval. As the primitive streak becomes more C7^ " Fig, 464.— Diagram of transverse section through an embryo before the closing-in of the medullary groove, ni, cells of epiblast lining the medullary groove which will form the spinal cord; h, epiblast; d, hypoblast; ch, notochord; tt, proto vertebra; sp, mesoblast; w, edge of lamina dorsalis, folding over medullary groove. (Kolliker.) defined the area pellucida changes its oval for a pear shape, but the streak increases in size faster than the area, and so after a time is about two-thirds of its length. In the primitive streak a groove, the primi- tive groove, runs along its axis. From the primitive streak the cells from the under surface of the epiblast now extend as lateral wings to the edge of the pellucid area; they are not joined with the hypoblast. The DEVELOPMENT. 741 intermediate layer of cells in this position producing the primitive streak is a portion of the intermediate layer or mesoblast. It is formed chiefly from the epiblast, but laterally, especially in the front part of the primitive streak, it appears to be derived at any rate in part from the cells of the primitive lower layer. At the most anterior part of the i)rimitive streak, at the point which corresponds to the future posterior end of the embryo, the three layers are all joined together. The next important change which occurs is found in the hypoblast in front of the primitive streak. The irregular layer of primitive cells of which it is composed, split into two layers, the lower consisting of flat- rig. 465.— Portion of the germinal membrane, with rudiments of the embryo; from the ovxim of a bitch. The primitive groove, a, is not yet closed, and at its upper or cephalic end presents three dilatations, b, which correspond to the three divisions or vesicles of the brain. At its lower extremity the groove pre.sents a lancet-shaped dilatation (sinus rhomboidalis) c. The margins of the groove consist of clear pellucid nerve-substance. Along the bottom of the gi-oove is observed a faint streak, which is probably the chorda dorsalis. d. Vertebral plates. (Bischofif.) tened cells which forms the hypoblast proper and an upper consisting of several layers of stellate cells, the mesoblast. In the preceding account of the formation of the blastodermic layers, Bal- four's description has been chiefly followed. It differs somewhat from that which was formerly given. The mesoblast was described as arising from the hypoblast, together with some of the large formative cells, which migrate by amceboid movement round the edge of the hypoblast (fig. 466, M), and no differ- •ence was made in the formation of the mesoblast in the primitive streak and elsewhere. There now appears in the middle line extending forward from the primitive streak an opaque line, which proceeds almost to the anterior 742 HANDBOOK OF PHYSIOLOGY. edge of the area pellucida, stopping short at a transverse crescent-shaped line, the future headfokl. I'his line is the commencing notochord. It is a collection of niesoblastic cells from the hypoblast in the middle line, and remains connected with the latter after the lateral portions of the mesoblast have become quite detached from it. The notochord and the hypoblast from which it arises are continued posteriorly into the primitive streak. Thus the mesoblast of the area on either side of the middle line in which the embryo is formed arises from the hypoblast, as does also the notochord. In the formation of the medullary plate which now appears, the epiblast is concerned. In the middle line above the collection of cells that will become the notochord that layer becomes thickened. The sides of the central thickened portion are elevated somewhat to form the medullary folds inclosing between them the medullary groove. From this medullary plate is formed the central nervous system. Although behind the groove is a shallow one, if it be traced forward it becomes deeper and narrower, and at the headfold the folds curve round and meet in the middle line. Anterior to the headfold is a second fold parallel to it, which is the commencing amnion. '^ itf ' COO „„» j-" ,SCi A Fig. 466. —Vertical section of blastoderm of chick (1st day of incubation). S, epiblast con- sisting of short columnar cells; D, hypoblast, consisting of a single layer of flattened cells; M, "formative cells." They are seen on the right of the figure, passing in between the epiblast and hypoblast to form the mesoblast; A, white yolk granules. Many of the large "formative cells" are seen containing these granules. (Strieker. ) The medullary canal is bounded by its two folds or longitudinal ele- vations, laminae dorsales, which are folds consisting entirely of cells of the epiblast: these grow up and arch over the medullary groove (fig. 464) till after some time they coalesce in the middle line, converting it from an open furrow into a closed tube — the neural canal or the prim- itive cerebro-spinal axis. Over this closed tube, the walls of which con- sist of more or less cylindrical cells, the superficial layer of the epiblast is now continued as a distinct membrane. The union of the medullary folds or laminae dorsalis takes place first about the neck of the future embryo; they soon after unite over the region of the head, while the closing in of the groove progresses much more slowly toward the hinder extremity of the embryo. The medullary groove is- by no means of uniform diameter throughout, but even before the dorsal laminae have united over it, is seen to be dilated at the ante- DEVELOPMEXT. 743 rior extremity and obscurely divided by constrictions into the three primary cerebral vesicles. The part from which the sjDinal cord is formed is of nearly uniform calibre, while toward the posterior extremity is a lozenge-shaped dilatation, sinus rhom- boidalis, which is the last ly^vt to close in (fig. 465). While the changes which have been de- scribed are taking place in the area pellu- cida, which has enlarged to a certain extent, the area opaca has also considerably extended. The hypoblast and mesoblast have also been prolonged laterally, not by mere extension, but also from the germinal wall, which is made up of the thickened edge of the blasto- derm, together with formative cells of the yolk; on each side of the notochord and medullary canal, the mesoblast remains as a longitudinal thickening. It now however splits horizontally into two layers or laminae {parietal and visceral) : of these the former, when traced out from the central axis, is seen to be in close appo- sition with the epiblast, and gives origin to the parietes of the trunk, while the latter adheres more or less closely to the hypoblast, and gives rise to the serous and muscular walls of the alimentary canal and several other parts. The xinited parietal layer of the mesoblast with the epiblast is termed somatopleure, the united visceral layer and hypoblast, splanchnopleure. The space between them is the pleuro-peritoneal cavity, which becomes subdivided by subsequent partitions into pericardium, pleura, and peritoneum. The splitting of the mesoblast extends almost to the medullary canal, but a portion on either side ( P. r*. fig. 468) remains undi- vided, the vertebral plate. The divided portion is known as the late- ral plate. The longitudinal thickening of the vertebral plate is seen after a while to be divided at right angles to the medullary canal by bright transverse lines into a number of square segments. These seg- Fig. 46r.— Embryo chick (36 hours), viewed from beneatli as a transparent object (magnified). pi, outline of peUucid area, FB, fore-brain, or first cerebral vesi- cle: from its sides i)roject op, the optic vesicle; SO, backward limit of somatopleure fold, "tucked in" under head; o, head-fold of true amnion; a', reflected layer of am- nion, sometimes termed "false amnion;" sp, backward limit of splanchnopleure folds, along which run the omphalomesaraic veins uniting to form /(,the heart, which is continued forward into 6a, the bulbus arteriosus; d, the fore-gut, lying behind the heart, and having a wide crescentic opening between the splanchno- pleure folds; HB, hind-brain; MB, mid-brain; pv, jirotoverte- br£e Ij'iug behind the fore-gut; mc, line of junction of medullary folds and of notochord ; vpl, ver- tebral plates; pr, the primitive groove at its caudal end. (Foster and Balfour.) 744 HANDBOOK OF PHYSIOLOGY. ments, which are the surface appearance of cubes of mesoblast, are the mesoblastic somites or protovertebrae. The iirst three or four of the protovertebraj make their appearance in the cervical region, while one or two more are formed in front of this point: and the series is continued backward till the whole medullary canal is flanked by them >sy TT r A Fig. 468. —Transverse section through dorsal region of embryo chick C4.5 hrs.). One half of the section is represented; if completed it would extend as far to the left as to the right of the line of the medullary canal (Mc). A, epiblast; C, hypoblast, consisting of a single layer of flattened cells; J/c, medullary canal ; Pi\ protovertebra ; Wd, Wolffian duct; So\ somatopleure ; .S/), splanchnopleure; ;?p, pleuro-peritoneal cavity; ch, notochord; ao, dorsal aorta, containing mood cells ; v, blood-vessels of the yolk-sac. (Foster and Balfour. ) (fig. 467). That which is first formed corresponds to the second cervi- cal vertebra. From these somites the vertebra? and the trunk muscles are derived. Head and Tail Folds. Body Cavity. — Every vertebrate animal con- sists essentially of a longitudinal axis (vertebral column) with a neural canal above it, and a body-cavity (containing the alimentary canal) beneath. We have seen how the earliest rudiments of the central axis and the neural canal are formed ; we must now consider how the general body- Fig. 469. —Diagrammatic longitudinal section through the axis of an embrj-o. The head-fold has commenced, but the tail-fold has not yet appeared. FSo, fold of the somatopleure; Fsp, fold of the splanchnopleure; the line of reference, Fso. lies outside the embryo in the "moat," which marks off the overhanging head from the amnion ; D, inside the embryo, is that part which is to become the fore-gut; Fso and Fsp, are both parts of the head-fold, and travel to the left of the figure as development proceeds ; pjy, space between somatopleure and splanchnopleure, pleuro-peritoneal cavity; Am, commencing head-fold of amnion; NC. neural canal; Ch, noto- chord; Ht, heart; A, B, C, epiblast, mesoblast, hypoblast. (Foster and Balfour.) cavity is developed. In the earliest stages the embryo lies flat on the surface of the yolk, and is not clearly marked off from the rest of the blastoderm: but gradually the head-fold or crescentic depression (with DEVELOPMENT. 745 its concavity backward) is formed in the blastoderm, limiting the head of the embryo; the blastoderm is, as it were, tucked in under the head, which thus comes to project above the general surface of the membrane : a similar tucking in of blastoderm takes place at the caudal extremity, and thus the head and tail folds are formed. Similar depressions mark off the embryo laterally, until it is com- pletely surrounded by a sort of moat which it overhangs on all sides, and which clearly defines it from the yolk. This moat runs in further and further all round beneath the over- hanging embryo, till the latter comes to resemble a canoe turned upside- Fig. 470.— Diagrammatic section showing the relation in a mammal between the primitive alimentary canal and the membranes of ihe ovum. The stage represented in this diagram cor- responds to that of the fifteenth or seventeenth day in the human embryo, previous to the ex- pansion of the allantois; c. tlie villous chorion; a. the amnion; a', the place of convergence of the amnion and reflection of the false amnion a" a", or outer or corneous layer; e, the head and trunk of the embryo, comprising the primative vertebrte and cerebro-spinal axis; i, i, the simple alimentary canal in its upper and lower portions. Immediately beneath the right hand i is seen the fcetal heart, lying in the anterior part of the pleuro-peritoneal cavity; v, the yolk-sac or umbilical vesicle; r i\ the vitello-intestinal opening; i<, the allantois connected by a pedicle with the anal portion of the alimentary canal. (Quain.) down, the ends and middle being, as it were, decked in by the folding or tucking in of the blastoderm, while on the ventral surface there is still a large communication with the yolk, corresponding to the well or undecked portion of the canoe. This communication between the embryo and the yolk is gradually contracted by the further tucking in of the blastoderm from all sides, till it becomes narrowed down, as by an invisible constricting band, to 74G HA nOOK OP PHYSIOLOGY. a mere pedicle which pusses out of the body of the embryo at the point of the future umbilicus. The downwardly folded portions of blastoderm are termed the vis- ceral plates. Thus we see that the body-cavity is formed by the downward folding of the visceral plates, just as the neural cavity is produced by the up- ward growth of the dorsal lamini^", the difference being that, in the vis- ceral or ventral lamina?, all three layers of the blastoderm are concerned. The folding in of the splanchnopleure, lined by hypoblast, pinches off, as it were, a portion of the yelk-sac, inclosing it in the body-cavity. This forms the rudiment of the alimentary canal, which at this period ends blindly toward the head and tail, while in the centre it communi- cates freely with the cavity of the yolk-sac through the canal termed vitelline or omphalo-mesenteric duct. The yolk-sac thus becomes divided into two portions which communi- cate through the vitelline duct, that portion within the body giving Fig. 471. Fis. 472. Figs. 471, 472 and 473. — Diagrams showing three successive stages of development. Trans- verse vertical sections. The yolk-sac, ?/.«, is seen progressively diminishing in size. In the embryo itself the medullary canal and notochord are seen in section, rf', in middle figure, the alimentary canal, becoming pinched off, as it were, from the yolk-sac; a' in right-hand fig>n-e, alimentary canal completely closed; o, in last two figures, amnion; etc. cavity of amnion filled with amniotic fluid ; pp, space between amnion and chorion continuous with the pleuro-perito- neal cavity inside the body; vt. vitelline membrane; ys, yolk-sac, or umbilical vesicle. (Foster and Balfour.) rise, as above stated, to the digestive canal, and that outside the body remaining for some time as the umhUiccd vesicle (fig. 473, ys.). The hypoblast forming the epithelium of the intestine is of course continuous with the lining membrane of the umbilical vesicle, while the visceral plate of the mesoblast is continuous with the outer layer of the umbilical vesicle. All the above details will be clear on reference to the accompanying diagrams. At the posterior end of the embryo chick, when the amniotic fold is commencing to be formed, and the hind fold of the splanchnopleure has commenced, there remains for a time a communication between the neural canal and the hind gut, which is called the neurenteric canal. DEVELOPMENT. 747 It passes in at the point where the notochord falls into the primitive streak. The anterior part of the primitive streak becomes the tail swelling, the posterior part atrophies, and the corresponding lateral part of the hlastoderm forms part of the body-wall of the embryo. The anterior part of the medullary canal having been completely roofed in, the foremost portion undergoes dilatation, and a bulb, the first or anterior cerebral vesicle, results. From either side of this dilatation a process, the cavity of which is in communication with it, is separated olf, which is called the optic vesicle. Behind the tirst cerebral vesicle two other vesicles now arise, the second or middle, and the third or posterior cerebral vesicle, and at the posterior part of the head two small pits, the auditory vesicles or pits, are to be seen. The folding of the head, it should be recol- lected, is the cause of the iuclosure below the neural canal (fig. -IGO) of a canal ending blindly, which has in front the splanchnopleure, and which is just as long as the involution of that membrane. This canal is the fore-gut. In the interior of the splanchnopleure fold below it (as seen in fig. -109) in the pleuro-peritoneal cavity the heart is formed, \t the point where the splanchnopleure makes its turn forward. It irises as a thickening of the mesoblast on either side as the two splanchno- pleure folds diverge, and of a thickening of the mesoblast at the point of divergence. So that at first the rudiment of the heart is like an inverted V, which by the gradual coming together of the diverging cords is converted into an inverted Y. The cylinders become hollowed out, and are thus converted inta tubes, which then coalesce. Layers are separated off toward the interior, which become the epithelial lining, and the mass of the mesoblast sur- rounding this, afterward form the muscle and serous covering, while at first the rudimentary organ is attached to the gut by a mesoblastic mes- entery, the mesocardimn. FcETAL Membranes. Umbilical Vesicle {Yolk-sac). — The splanchnopleure, lined by hy- po])last, forms the yolk-sac in reptiles, birds, and mammals; but in amphibia and fishes, since there is neither amnion nor allanfois, the wall of the yolk-sac consists of all three layers of the blastoderm, inclosed, of course, by the original vitelline membrane. The body of the embryo becomes in great measure detached from the yolk-sac or umbilical vesicle, which contains, however, the greater part of the substance of the yolk, and furnishes a source whence nutri- ment is derived for the embryo. This nutriment is absorbed by the numerous vessels (omphalo-mesenteric) which ramify in the walls of the yolk-sac, forming what in birds is termed the area vasculosa. In 748 HANDBOOK OF PHYSIOLOGY. birds, the contents of the yolk-sac afford nourishment nntil the end of incubation, and the omphalo-meseuteric vessels are developed to a corre- sponding degree; but in mammalia the office of the umbilical vesicle ceases at a very early period, as the quantity of the yolk is small, and the embryo soon becomes independent of it by the connections it forms with the parent. Moreover, in birds as the sac is emptied, it is gradu- .ally drawn into the abdomen through the umbilical opening, which then Fig. 475. Fig, 474. — Diagram sliowiug vascular area in the chick, a, area pellucida; 6, area vasculosa; 'C, area vitellina. Fig. 475.— Human embryo of flf til week with umbilical vesicle; about natural size. CDalton.) The human umbilical vesicle never exceeds the size of a small pea. closes over it: but in mammalia it always remains on the outside; and as it is emptied it contracts (fig. 473), shrivels up, and together with the part of its duct external to the abdomen, is detached and disapj)ears, either before or at the termination of intra-uterine life, the period of its disappearance varying in different orders of mammalia. When blood-vessels begin to be developed, they ramify largely over the walls of the umbilical vesicle, and are actively concerned in absorb- ing its contents and conveying them away for the nutrition of the •embryo. At an early stage of development of the foetus, and some time before the completion of the changes which have been just described, two im- portant structures, called respectively the amnion and the allantois, begin to be formed. Amnion. — The amnion is produced as follows: — Beyond the head- and tail-folds before described (p. 744), the somatopleure coated by epi- blast, is raised into folds, which grow up, arching over the embryo, not only anteriorly and posteriorly but also laterally, and all converging toward one point over its dorsal surface (fig. 476). The growing up of these folds from all sides and their convergence toward one point very closely resembles the folding inward of the visceral plates already de- scribed, and hence, by some, the point at which the amniotic folds meet over the back has been termed the amniotic vmhilicus. The folds not only come into contact but coalesce. The inner of DEVELOPMEXT. ^ 749* the two layers forms the true amnion, while the outer or retiected layer, sometimes termed the false amnion, coalesces with the inner surface of the original vitelline membrane to form the subzonal membrane or false chorion. This growth of the amniotic folds must of course be clearly distinguished from the very similar process, already described, by which at a much earlier stage the walls of the neural canal are formed. The cavity between the true amnion and the external surface of the embryo becomes a closed space, termed the amniotic cavity {ac, fig. -473). At first, the amnion closely invests the embryo, but it becomes grad- ually distended with fluid {liquor amnii), which, as pregnancy advances, reaches a considerable quantity. This fluid consists of water containing small quantities of albumen and urea. Its chief function during gestation appears to be the me- chariical one of affording equal support to the embryo on all sides, and of protecting it as far as possible from the effects of blows and other injuries to the abdomen of the mother. The embryo up to the end of pregnancy is thus immersed in fluid, which during parturition serves the important purpose of gradually and evenly dilating the neck of the uterus to allow of the passage of the fcetus: when this is accomplished the amniotic sac bursts, and the icaters escape. On referring to figs. 471, 472 and 473, it will be obvious that the cavity outside the amnion^, between it and the false amnion, is continu- ous with the pleuro-peritoneal cavity at the umbilicus. This cavity is not entirely obliterated even at birth, and contains a small quantity ©f fluid, which is discharged during parturition either before, or ab the same time as the amniotic fluid. AUantois. — Into the pleuro-peritoneal space the allantois sprouts out, its formation commencing during the development of the amnion. Growing out from or near the hinder j)ortion of the intestinal canal {c, fig. 47G), with which it communicates, the allantois is at first a solid pear-shaped mass of splanchnopleiire ; but becoming vesicular by the projection into it of a hollow outgrowth of hypoblast, and very soon simply membraneous and vascular, it insinuates itself between the amni- otic folds, just described, and comes into close contact and union with the outer of the two folds, which has itself, as before said, become one with the external investing membrane of the egg. As it grows, the allantois develops muscular tissue in its external wall and becomes ex- ceedingly vascular; in birds (fig. 477) it envelops the whole embryo — taking up vessels, so to speak, to the outer investing membrane of the egg, and lining the inner surface of the shell Avith a vascular membrane, by these means affording an extensive surface in which the blood may be aerated. In the human subject and in other mammalia, the vessels carried out by the allantois are distributed only to a special part of the^ 750 HANDBOOK OF PHYSIOLOGY. outer niembrano or false chorion, where, by interlacement with the vas- cular system of the mother, a structure called the placenta is developed. In mammalia, as the viscei'al lamina? close in the abdominal cavity, the allantois is thereby divided at the umbilicus into two portions; the rnter part, extending from the umbilicus to the cJiorion, soon shrivelling; while the inner part remaining in the abdomen, is in part converted into the urinary bladder; the portion of the inner part not so converted, extending from the bladder to the umbilicus, under the name of the iirachns. After birth the umbilical cord, and with it the external and shrivelled portion of the allantois, are cast ofE at the umbilicus, while the urachus remains as an impervious cord stretched from the top of the urinary bladder to tlie umbilicus, in the middle line of the body, Fig. 470. Fig. 477. Fig. 476. — Diagram of fecundated egg. a, umbilical vesicle; 6, amniotic cavity; c, allantois. (Dalton.) Fig. 477. — Fecundated egg with allantois nearly complete, n, inner layer of amniotic fold; fc, outer layer of ditto; c, point where the amniotic folds come in contact. The allantois is seen penetrating between the outer and inner layers of the amniotic folds. This figure, which represents only the amniotic folds and the parts within them, should be compared with figs. 478, 479, in which will be found the structures external to these folds. CDalton.j immediately beneath the joarietal layer of the peritoneum. It is some- times enumerated among the ligaments of the bladder. It must not be supposed that the phenomena which have been suc- cessively described, occur in any regular order one after another. On the contrary, the development of one part is going on side by side with that of another. The Chorion. — It has been already remarked that the allantois is a structure which extends from the body of the foetus to the outer in- vesting membrane of the ovum, that it insinuates itself between tlie two layers of the amniotic fold, and becomes fused with the outer layer, which has itself become previously joined with the vitelline membrane. By these means the external investing membrane of the ovum, or the true chorion, as it is now called, represents three layers, namely, the original vitelline membrane, the outer layer of the amniotic fold, and the allantois. Very soon after the entrance of the ovum into the uterus, in the human subject, the outer surface of the chorion is found beset with fine DEVELOPMENT. 751 processes, the so-called chorion villi {a, figs. 478, 470), Avhich give it a rough and shaggy appearance. At first only cellular in structure, these little outgrowths subsequently become vascular by the development in Fig. 478. Fis.479. Figs. 478 and 479. — a. chorion with villi. The villi are shown to be best developed in the part of the chorion to which the allantois is extending: this portion ultimately becomes the placenta; h, space between the two layers of the amnion; c, amniotic cavity : d. situation of the intestine, showing its connection with'the umbilical vesicle; e, umbilical vesicle;/, situation of heart and vessels ; 3, allantois. them of loops of capillaries (fig. 480) ; and the latter at lengtli form the minute extremities of the blood-vessels which are, so to speak, conducted from the fa?tus to the chorion by the allantois. The function of the villi of the chorion is evidently the absorption of nutrient matter for the foetus; and this is probably supplied to them at first from the fluid matter, secreted by the follicular glands of the uterus, in which they are soaked. Soon, however, the foetal vessels of the villi come into more intimate relation with the vessels of the uterus. The part iit which this relation between the vessels of the foetus and those of the parent ensues, is not, however, over the whole surface of the chorion; for, although all the villi become vascular, yet they become indistinct or disappear except at one part where they are greatly devel- oped, and by their branching give rise, with the vessels of tlie uterus, to the formation of the placenta. To understand the manner in which the foetal and maternal blood-vessels come into relation with each other in the placenta, it is necessary briefly to notice the changes which the uterus undergoes after impreg- nation. These changes consist especially of alterations in structure of the superficial part of the mucous membrane which lines the interior of the uterus, and which forms, after a kind of development to be imme- Fig. 480. 752 HANDBOOK OF PHYSIOLOGY. diately described, the memhrana decklua, so called on account of its being discharged from the uterus at birth. Formation of the Placenta. The mucous membrane of the human uterus, which consists of a matrix of connective tissue containing numerous corpuscles, and is lined internally by columnar ciliated epithelium, is abundantly beset with tubular glands, arranged perpendicularly to the surface (fig. 481). These Fig. 481. — Section of the lining membrane of a human utenis at the period of commencing pregnancy showing the arrangement and other peculiarities of the glands, d, d, d, with their orifices, a, a, a, on the internal surface of the organ. Twice the natural size. follicles are very small in the unimpregnated uterus; but when examined shortly after impregnation, they are found elongated, enlarged, and much waved and contorted toward their deep and closed extremity, which is planted at some depth in the tissue of the uterus, and may dilate into two or three closed sacculi. The glands are lined by columnar ( (?) ciliated) epithelium and they open on the inner surface of the mucous membrane by small round ori- fices set closely together (a, a, fig. 481). On the internal surface of the mucous membrane may be seen the circular orifices of the glands, many of which are, in the early period of pregnancy, surrounded by a whitish ring, formed of the epithelium which lines the follicles. Coincidently with the occurrence of pregnancy, important changes occur in the structure of the mucous membrane of the uterus. The epithelium and sub-epithelial connective tissue, together with the tubu- lar glands, increase rapidly, and there is a greatly increased vascularity of the whole mucous membrane, the vessels of the mucous membrane becoming larger and more numerous; while a substance composed chiefly of nucleated cells fills up the interfollicular spaces in which the blood- vessels are contained. The effect of these changes is an increased thick- nes, softness, and vascularity of the mucous membrane, the superficial part of which itself forms the membrana decidua. The object of this increased development seems to be the production. DEVELOPMENT. ?03 of nutritive materials for the ovum ; for the cavity of the uterus shortly becomes filled with secreted fluid, consisting almost entirely of nucleated cells in which the chorion villi are imbedded. When the ovum first enters the uterus it becomes imbedded in the structure of the decidua, which is yet quite soft, and in which soon afterward three portions are distinguishable. These have been named the decidua vera, the decidua rejlexa, and the decidua serotina. The first of these, the decidua vera, lines the cavity of the uterus; the second, or decidua reflexa, is a part of the decidua vera which grows up around the ovum, and wrapping it closely, forms its immediate investment. The third, or decidua serotina, is the part of the decidua vera which becomes especially developed in connection with those villi of the cho- rion, which, instead of disappearing, remain to form the foetal part of the ijlacenta. In connection with these villous processes of the chorion, there are developed degressions or crypts in the decidual mucous membrane, which correspond in shape with the villi they are to lodge; and thus the chori- onic villi become more or less imbedded in the maternal structures. Fig. 482.— Diagram of an early stage of the fonnation of the human placenta, a, embryo; 6, amnion ; c, placental vessels ; d, decidua reflexa ; e, allantois ; /, placental villi ; o, mucous membrane. (,Cadiat.) These uterine crypts, it is important to note, are not, as was once sup- posed, merely the open mouths of the uterine follicles. As the ovum increases in size, the decidua vera and the decidua reflexa gradually come into contact, and in the third month of preg- nancy the cavity between them has almost disappeared. Though the two layers come into contact at the third month, they are not closely amalgamated until the end of the sixth month. The Placenta. — During these changes the deeper part of the mu- 48 754 HANDBOOK OF PHYSIOLOGY. cous membrane of the uterus, at and near the region where the placenta is placed, becomes hollowed out by sinuses, or cavernous spaces, which communicate on the one hand with arteries and on the other with veins of the uterus. Into these sinuses the villi of the chorion protrude, pushing the thin wall of the sinus before them, and so come into inti- mate relation with the blood contained in them. There is no direct comniunication between the blood-vessels of the mother and those of the foetus; but the layer or layers of membrane intervening between the Fig. 483. — Diagrammatic view of a vertical transverse section of the uterus at the seventh or eighth week of pregnancy, c, c, c', cavity of uterus, which becomes the cavity of the decidua, opening at c, c, the cornua, into the FaUopian tubes, and at c' into the cavitj' of the cervix, which is closed by a plug of mucus; d \\_ decidua vera; d ?-, decidua reflexa, with the sparser villi imbedded in its substance ; d s, decidua serotina, involving the more developed chorionic viili of the commencing placenta. The foetus is seen lying in the amniotic sac; passing up from the umbilicus is seen the umbilical cord and its vessels, passing to their distribution in the villi of the chorion ; also the pedicle of the yolk-sac, which lies in the cavity between the amnion and chorion. (Allen Thomson.) blood of the one and of the other offer no obstacle to a free interchange of matters between them by diffusion and osmosis. Thus the villi of the chorion containing foetal blood, are bathed or soaked in maternal blood contained in the uterine sinuses. The arrangement may be roughly compared to filling a glove with foetal blood, and dipping its fingers into a vessel containing maternal blood. But in the fcetal villi there is a constant stream of blood into and out of the loop of capillary blood-vessels contained in it, as there is also into and out of the maternal sinuses. DEVELOPMENT. 755 It would seem that, at the villi of the placental tufts, where the foetal and maternal portions of the placenta are bi'ought into close rela- tion with each other, the blood in the vessels of the mother is separated from that in the vessels of the foetus by the intervention of two distinct sets of nucleated cells (fig. 484). One of these [b) belongs to the maternal portion of the placenta, is placed between the membrane of the villus and that of the vascular system of the mother, and is prob- ably designed to separate from the blood of the parent the materials destined for the blood of the foetus; the other (/) belongs to the foetal portion of the placenta, is situated between the membrane of the villus and the loop of vessels contained within, and probably serves for the absorption of the material secreted by the other sets of cells, and for its conveyance into the blood-vessels of the foetus. Between the two sets of cells with their investing membrane there exists a space (d), into which it is possible that the materials secreted by the one set of cells of the villus are j^oured in order that they may be absorbed by the other set, and thus conveyed into a foetal vessel. Not only, however, is there a passage of materials from the blood of the mother into that of the foetus, but there is a mutual interchange of Fig. 484. — Extremity of a placental villus, a, lining membrane of the vascular system of the mother; b. cells immediately lining a; cl, space between the maternal and fcEtal portions of the villus; e, internal membrane of the villus, or external membrane of the chorion; /, internal cells of the villus, or cells of the chorion; g, loop of umbilical vessels. (Goodsir. ) materials between the blood both of foetus and of parent ; the latter sup- plying the former with nutriment, and in turn abstracting from it materials which require to be removed. The placenta, therefore, of the human subject is composed of a foetal part and a maternal part, — the termi placenta properly including all that entanglement of foetal villi and maternal sinuses, by means of whicli the blood of the foetus is enriched and jjurified after the fashion necessary for the proper growth and development of those parts which it is designed to nourish. The whole of this structure is not, as might be imagined, thrown off immediately after birth. The greater part, indeed, comes away at that time, as the ufter-hirtli; and the separation of this portion takes place by a rending or crushing through of that part at which its cohe- sion is least strong, namely, where it is most burrowed and undermined 756 HANDBOOK OF PHYSIOLOGY, by the cavernous spaces before referred to. In this way it is cast off with the fcetal membrane and the decidua vera and reflexa, together with a part of the decidua serotina. The remaining portion withers, and disappears by being gradually either absorbed, or thrown off in the uterine discharges or the lochia, which occur at this period. A new mucous membrane is of course gradually developed, as the old one, by its transformation into the decidua, ceases to perform its original functions. The umbilical cord, which in the latter part of fcetal life is almost solely composed of the two arteries and the single vein which respectively convey fatal blood to and from the placenta, contains the remnants of other structures which in the early stages of the development of the embryo were, as already related, of great comparative importance. Thus, in early foetal life, it is composed of the following parts : — (1. ) Externally, a layer of the amnion, reflected over it from the umbilicus. (2) The um- bilical vesicle with its duct and appertaining omphalo-mesenteric blood vessels. (3.) The remains of the allantois, and continuous with it the urachus. (4.) The umbilical vessels, which, as just remarked, ultimately form the greater part of the cord. The Development of the Okgans. Before considering very briefly* the main points in the development of the chief organs and tissues of the body, it will be useful to have before us the following table, compiled by Schiifer, f showing the differ- ent parts derived from the three blastodermic layers: — From the Upiblasf. — The whole of the nervous system, including not only the central organs (brain and spinal cord), but also the peri- pheral nerves and sympathetic. The epithelial structures of the organs of special sense. The epidermis and its appendages, including the hair and nails. The epithelium of all the glands ojoening upon the surface of the skin, including the mammary glands, the sweat glands and the sebaceous glands. The muscular fibres of the sweat glands. The epithelium of the mouth (except that covering the tongue, and the adjacent posterior part of the floor of the mouth, which is derived from the hypoblast), and that of the glands opening into it. The enamel of the teeth. The epithelium of the nasal passages, of the adjacent upper part of the pharynx and of all the cavities and glands opening into the nasal pas- sages. * For a more detailed account the reader is referred to special text-books of embrj^ology. f Quain's Anatomy, Xth Ed., Vol. I., Part I., p. 25. DEVELOPMEXT. r57 From the Mesohlast. — The urinary and generative organs (except the epithelium of the urinary bhidder and urethra). All the voluntary and involuntary muscles of the body (except the muscular fibres of the sweat glands). The whole of the vascular and lymphatic system, including the :5orous membranes and spleen. The skeleton and all the connective tissues and structures of the body. From the Ili/pohlasf. — The epithelium of the alimentary canal from the back of the mouth to the anus, and that of all the glands which open into this part of the alimentary tube. The epithelium of the Eustachian tube and tympanum. The epithelium of the bronchial tubes and air sacs of the lungs. The epithelium lining the vesicles of the thyroid body. The epithelial nests of the thymus. The epithelium of the urinary bladder and urethra. It remains now to consider in succession the development of the several organs and systems of organs in the further progress of the ,' / r / -^^—Al Fig. 485.— Embryo chick f4th day"), viewed as a transparent object, lying on its left side (magnified). C H, cerebral hemispheres: F B. fore-brain or vesicle of third ventricle, with P»i, pineal gland projecting from its summit; MB, mid-brain; C6, cerebellum; IV. r, fourth ven- tricle; I/, lens; c h .s, choroidal slit; Cen F, auditory vesicle; s m, superior maxillary process; \F, 2F, etc., first, second, third, and fourth visceral folds; V. fifth nerve, sending one branch (ophthalmic) to the eye, and another to the first visceral arch; VII, seventh nerve, passing to the second visceral arch ; G Ph, glosso-pharyngeal nerve, passing to the third visceral arch ; P g, pneumogastric nerve, passing toward the foiirtli vi.sceral arch; i v, investing mass; ch, noto- chord ; its front end cannot be seen in the living embryo, and it does not end as shown in the fig- ure, but takes a sudden bend downward, and then terminates in a point; Hf. heart seen through the walls of the chest: MP, inuscle plates; W. wing, showing commencing differentiation of segments, corresponding to arm. forearm, and hand; H L. hind-limb, as yet a shapeless bud, showing no differentiation. Beneath it is seen the curved tail. (Foster and Balfour.) embryo. The accompanying figure (fig. 485) shows the chief organs of the body in a moderately early stage of development. The Vertebral Column and Cranium. — The primitive part of the vertebral column in all the vertebrata is the chorda dorsalis or note- 758 HANDBOOK OF PHYSIOLOGY. chord, whicli consists entirely of soft cellular cartilage. This cord tapers to a point at the cranial and caudal extremities of the animal. In the progress of its development, it is found to become inclosed in a membranous sheath, which at length acquires a librous structure, com- posed of transverse annular fibres. The chorda dorsalis is to be regarded as the azygos axis of the spinal column, and, in particular, of the future bodies of the vertebrae, although it never itself passes into the state of hyaline cartilage or bone, but remains inclosed as in a case within the persistent parts of the vertebral column which are developed around it. It is permanent, however, only in a few animals: in the majority only traces of it persist in the adult animal. In many fish no true vertebrae are developed, and there is every graduation from the amphioxus, in which the notochord persists through life and there are no vertebrae, through the lampreys in which there are a few scattered cartilaginous vertebrae, and the sharks, in which many of the vertebrge are partly ossified, to the bony fishes, such as the cod and herring, in which the vertebral column consists of a number of distinct ossified vertebra, with remnants of the notochord between them. In amphibia, reptiles, birds, and mammals, there are distinct vertebrae, which are formed as follows: — The mesoblastic somites, which have been already mentioned (p. 799), send processes downward and inward to surround the notochord, and also upward between the medullary canal and the epiblast covering it. In the former situation, the cartilaginous bodies of the vertebrae make their appearance, in the latter their arches, which inclose the neural canal. The vertebrae do not exactly correspond in their position with the protovertebrae : but each permanent vertebra is developed from the con- tiguous halves of two protovertebras. The original segmentation of the protovertebrae disappears and a fresh subdivision occurs in such a way that a permanent invertebral disc is developed opposite the centre of each protovertebra. Meanwhile the protovertebrae split into a dorsal and ventral portion. The former is termed the musculo-cuta neons plate, and from it are developed all the muscles of the back together with the cutis of the dorsal region (the epidermis being derived from the epiblast). The ventral portions of the protovertebrae, as we have already seen, give rise to the vertebras and heads of the ribs. The chorda is now inclosed in a case, formed by the bodies of the vertebrae, but it gradually wastes and disappears. Before the disappear- ance of the chorda, the ossification of the bodies and arches of the verte- bra begins at distinct points. The ossification of the body of a vertebra is first observed at the point where the two primitive elements of the vertebrae have united DEVELOPMENT. 759 inferiorly. Those vertebra which do not bear ribs, such as the cer- vical vertebrse, have generally an additional centre of ossification in the transverse process, which is to be regarded as an abortive rudi- ment of a rib. In the foetal bird, these additional ossified portions exist in all the cervical vertebrae, and gradually become so much developed in the lower part of the cervical region as to form the upper false ribs of this class of animals. The same parts exist in mammalia and man; those of the last cervical vertebrsB are the most developed, and in chil- dren may, for a considerable period, be distinguished as a separate part on each side like the root or head of a rib. The true cranium is a prolongation of the vertebral column, and is developed at a much earlier period than the facial bones. Originally, it is formed of but one mass, a cerebral capsule, the chorda dorsalis being continued into its base, and ending there with a tapering point. At an early period the head is bent downward and forward round the end of the chorda dorsalis in such a way that the middle cerebral vesicle, and not the anterior, comes to occupy the highest position in the head. Pituitary Body. — In connection with this must be mentioned the development of the pituitary body. It is formed by the meeting of two outgrowths, one from the foetal brain, which grows downward, and the other from the epiblast of the buccal cavity, which grows up toward it. The surrounding mesoblast also takes part in its formation. The con- nection of the first process with the brain becomes narrowed, and per- sists as the infundibulum, while that of the other process with the buccal cavity disappears completely at a spot corresponding with the future position of the body of the sphenoid. Cranium. — The first appearance of a solid support at the base of the cranium observed by Muller in fish, consists of two elongated bands of car- tilage (trabeculfe cranii), one on the right and the other on the left side, which are connected with the cartilaginous capsule of the auditory ap- paratus, and which diverge to "inclose the pituitary body uniting in front to form the septum nasi beneath the anterior end of the cerebral capsule. Hence, in the cranium, as in the spinal column, there are at first developed at the sides of the chorda dorsalis two symmetrical ele- ments, which subsequently coalesce, and may wholly inclose the chorda. The brain-case consists of three segments: occipital, parietal, and frontal, corresponding in their relative position to the three primitive cerebral vesicles; it may also be noted that in front of each segment is developed a sense-organ (auditory, ocular, and olfactory, from behind forward). The basis cranii consists at an early period of an unsegmented cartilaginous rod, developed round the notochord, and continued for- ward beyond its termination into the trabeculm cranii^ which bound the pituitary fossa on either side. 760 HANDBOOK OF PHYSIOLOGY, In this cartilaginous rod three centres of ossification appear: basi- oecipital, basi-sphenoid, and pre-sphenoid, one corresponding to each segment. The bones forming the vault of the skull, viz., the frontal, parietal, squamous portion of temporal and the squamo-occipital, are ossified in membrane. The Visceral Clefts And Arches. As the embryo enlarges, the heart, Avhicli at first occupied a position close to the cranial flexure, is carried further and further backward until a considerable part, in which the mesoblast is undivided, intervenes between Fig. 486. — A. MagTiified view from before of the head and neck of a human embryo of about three weeks (from Ecker.)— 1, anterior cerebral vesicle or cerebrum; 2, middle ditto; 3, middle or fronto-nasal process; 4, superior maxillary process; 5, eye; 6, inferior maxillary process, or first visceral arch, and below it the first cleft ; 7, 8, 9, second, third, and fourth arches and clefts. B. Anterior view of the head of a human foetus of about the fifth week (from Ecker, as before, fig. IV.). 1, 2, 3, 5, the same parts as in a; 4, the external nasal or lateral frontal process: 6, the superior maxillary process; 7, the lower jaw; X, the tongue; 8, first branchial cleft becom- ing the meatus auditorius externus. it and the head. This becomes the neck. On section it is seen that in it the whole three layers are represented in order, and that there is no interval between them. In the neck thus formed soon appear the vis- ceral or branchial clefts on either side, in series, across the axis of the gut not quite at right angles. They are four in number, the most anterior being first found. At their edges the hypoblast and their epiblast are continuous. The anterior border of each cleft forms a fold or lip, the branchial or visceral fold. The posterior border of the last cleft is also formed into a fold, so that there are four clefts and five folds, but the three most anterior are far more prominent than the others, and of these the second is the most conspicuous. The first fold nearly meets its fellow in the middle line, the second less nearly, and the others in order still less so. Thus in the neck there is a triangular interval, into which by the splitting of the mesoblast at that part the pleuroperitoneal cavity extends. The branchial clefts and arches are not all permanent. The first arch gives off a branch from its front edge, which passes forward to meet its fellow, but these offshoots do not quite meet, being separated DEVELOPMENT, 761 by a process which grows downward from the head. Between the branches and the main first fold is the cavity of the mouth. The branches represent the superior maxilla, and the main folds the mandible or lower jaw. The central process, which grows down, is the fronto-nasal pro- cess. In this way the so-called visceral arches and clefts are formed, four on each side (fig. 486, a). From or in connection with these arches the following parts are devel- oped : — The first arch (mandibular) contains a cartilaginous rod (Meckel's ■cartilage), around the distal end of which the lower jaw is developed, while the malleus is ossified from the proximal end. When the maxillary processes on the two sides fail partially or com- pletely to unite in the middle line, the well-knoAvn condition termed ■cleft palate results. When the integument of the face presents a similar deficiency, we have the deformity known as hare-lip. Though these two ^^^y xpy^ Fig. 487.— Embryo chick C4th clay), viewed as a transparent object, lying on its left side (magnified). C H, cei-ebral hemispheres; F B, fore-brain or vesicle of third ventricle, with P/i, pineal gland projecting from its summit; MB, mid-brain; C b, cerebellum; IV. V, fourth ven- tricle: L, lens; c h ,s, choroidal slit: Cen. V, auditory vesicle; s ni, superior maxillary process: IF, 2F, etc., first, second, third, and fourth visceral folds; F, fifth nerve, sending one branch (ophthalmic) to the eye, and another to the first visceral arch; TV/, seventh nerve, passing to the second visceral arch; G. Ph, glosso-pharyngeal nerve, passing to the third visceral arch; P (/^ pneumogastric nerve, passing toward the fourth visceral arch; i v, investing mass ; c h, notochord; its front end cannot be seen in the living embryo, and it does not end as shown in the figu^'e, but takes a sudden bend downward, and then terminates in a point; Ht, heart seen through the walls of the chest; MP. muscle-plates; W, wing, showing commencing differentia- tion of segnients, corresponding to arm, forearm, and hand; S &', somatic stalk; Al, allantois; H L, hind-limb, as yet a shapeless bud, showing no differentiation. Beneath it is seen the curved tail. (Foster and Balfour.) deformities frequently co-exist, they are by no means always necessarily associated. The upper part of the face in the middle line is developed from the so-c&Wed frontal- nasal process (a, 3, fig. 486.) From the second arch 762 HANDBOOK OF PHYSIOLOGY. are developed the incus, stapes, and stapedius muscle, the styloid process of the temporal bone, the stylo -hyoid ligament, and the smaller cornu of the hyoid hone. From the ^A/rfZ visceral arch, the greater cornu and body of the hyoid bone. In man and other mammalia the /owr/A visceral arch is indistinct. It occupies the position where the neck is afterward developed. A distinct connection is traceable between these visceral arches and certain cranial nerves : the trigeminal, the facial, the glosso-pharyngeal, and the vagus. The ophthalmic division of the trigeminal supplies the fronto-nasal process; the sujDcrior and inferior maxillary divisions supply the maxillary and mandibular arches respectively. The facial nerve distributes one branch (chorda tympani) to the first visceral arch, and others to the second visceral arch. Thus it divides, inclosing the first visceral cleft. Similarly, the glosso-pharyngeal divides to inclose the second visceral cleft, its lingual branch being distributed to the second, and its pharyngeal branch to the third arch. The vagus, too, sends a branch (pharyngeal) along the third arch, and in fishes it gives off paired branches, which divide to inclose several successive branchial clefts. The Extremities. The extremities are developed in a uniform manner in all verte- brate animals. They appear in the form of leaf-like elevations from the ^.^ Fig. 488.— A human embryo of the fourth week, 31^ lines in length.—], the chorion; 3, part of the amnion; 4, umbilical vesicle with its long pedicle passing into the abdomen; 7, the heart; 8, the liver; 9, the visceral arch destined to form the lower jaw, beneath which are two other visceral arches separated by the branchial clefts; 10, rudiment of the upper extremity; 11, that of the lower extremity; 12, the umbilical cord; 15, the eye; 16, the ear; 17, cerebral hemi- spheres; 18, optic lobes, corpora quadrigemina. (Miiller. )• parieties of the trunk (see fig. 488) , at points where more or less of an arch will be produced for them within. The primitive form of the extremity is nearly the same in all vertebrata, whether it be destined for DEVELOPMENT. ' 763 swimming, crawling, walking, or flying. In the human foetus the fin- gers are at first united, as if webbed for swimming; but this is to be regarded not so much as an approximation to the form of aquatic animals, as the primitive form of the hand, the individual parts of which subsequently become more completely isolated. The fore-limb always appears before the hind-limb, and for some time continues in a more advanced state of development. In both limbs alike, the distal segment (hand or foot) is separated by a slight notch from the proximal part of the limb, and this part is subsequently divided again by a second notch (knee or elbow-joint). The Vascular System. — At an early stage in the development of the embryo-chick, the so-called area vasculosa begins to make its ajDpear- ance. A number of branched cells in the mesoblast send out processes which unite so as to form a network of protoplasm with nuclei at the nodal points. A large number of nuclei acquire red color ; these form the red blood-corpuscles. The protoplasmic processes become hollowed out in the centre so as to form a closed system of branching canals, in the walls of which the rest of the nuclei remain imbedded. In the blood-vessels thus formed, the circulation of the embryonic blood com- mences. According to Klein, the first blood-vessels in the chick are developed from embryonic cells of the mesoblast, which swell up and become vacuo- lated,while their nuclei undergo segmentation. These cells send out proto- plasmic processes, which unite with corresponding ones from other cells, and become liollow^ed,give rise to the cai^illary wall composed of endothelial cells; the blood corpuscles being budded off from the endothelial wall by a process of gemmation. Heart. — About the same early period the heart makes its appearance as a solid mass of cells of the splanchnopleure in the manner before indi- cated. At this period the anterior part of the alimentary tube ends blindly beneath the notochord. It is beneath the posterior end of this fore-gut that the heart begins to be developed. The heart when first formed is made up of two not quite complete tubes which coalesce to form one, and so when the cavity is hollowed out in the mass of cells, the central cells float freely in the fluid, which soon begins to circulate by means of the rhythmic pulsations of the embryonic heart. These pulsations take place even before the appearance of a cavity, and immediately after the first laying down of the cells from which the heart is formed, and long before muscular fibres or ganglia have been formed in the cardiac walls. At first they seldom exceed from fifteen to eighteen in the minute. The fluid within the cavity of the heart shortly assumes the characters of blood. At the same time, the cavity 764 HANDBOOK OF PHYSIOLOGY, itself forms a communication with tlie great vessels in contact with it, and the cells of which its walls are comprised are transformed into fibrous and muscular tissues, and into epithelium. In the developing chick Fig. 489. Fig. 491. Fig. 489. — Capillary blood-vessels of the tail of a young larval frog, a, capillaries perme- able to blood ; 6, fat granules attached to the walls of the vessels, and concealing the nuclei ; c, hollow prolongation of a capillary, ending in a point; d, a branching cell with nucleus and fat- granules; it communicates by three branches with prolongation of capillaries already formed; €, e, blood corpuscles still containing granules of fat. x 350 times. cKoUiker. ) Fig. 490. —Development of capillaries in the regenerating tail of a tadpole, a bed, sprouts and cords of protoplasm. CArnold. ) Fig. 491.— The same region after the lapse of 24 hours. The "sprouts and cords of proto- plasm" have become channelled out into capillaries. (Arnold.) it can be observed with the naked eye as a minute red pulsating little mass before the end of the second day of incubation. Blood-vessels. — ^Blood-vessels appear to be developed in two ways, ac- cording to their size. In the formation of large blood-vessels, masses of embryonic cells similar to those from which the heart and other struct- ures of the embryo are developed, arrange themselves in the position, form, and thickness of the developing vessel. Shortly afterward the cells in the interior of a column of this kind sem to be developed into blood- DEVELOPMENT. 763 corpuscles, while the external layer of cells is converted into the walls of the vessel. In the development of capillaries another plan is pursued. This has been well illustrated by Kolliker, as observed in the tails of tadpoles. The first lateral vessels of the tail have the form of simple arches, pass- ing between the main artery and vein, and are produced by the junction of prolongations, sent from both the artery and vein, with certain elon- gated or star-shaped cells, in the substance of the tail. When these arches are formed and are permeable to blood, new prolongations pass from them, join other radiated cells, and thus form secondary arches. In this manner, thecapillary network extends in proportion as the tail increases in length and breadth, and it, at the same time, becomes more dense by the forma- tion, according to the same plan, of fresh vessels within its meshes. The prolongations by which the vessels communicate with the star-shaped cells, consist at first of narrow pointed projections from the side of the vessels, which gradually elongate until they come in contact with the radiated processes of the cells. The thickness of such a prolongation often does not exceed that of a fibril of fibrous tissue, and at first it is perfectly solid; but, by degrees, especially after its junction with a cell, or with another prolongation, or with a vessel already permeable to blood, it enlarges, and a cavity then forms in its interior (see figs. 491, 492). This tissue is well calculated to illustrate the various steps in the devel- opment of blood-vessels from elongating and branching cells. In many cases a whole network of capillaries is developed from a net- work of branched, embryonic connective-tissue corpuscles by the join- Fig. 492. — Capillaries from the vitreous humor of a foetal calf. Two vessels are seen con- nected by a "cord" of protoplasm, and clothed with an adventitia, containing numerous nuclei, a, insertion of this "cord " into the primary walls of the vessels. (Frey.) ing of their processes, the multiplication of their nuclei, and the vacuo- lation of the cell-substance. The vacuoles gradually coalesce till all the partitions are broken down, and the originally solid protoplasmic cell- substance is, so to speak, tunnelled out into a number of tubes. Capillaries may also be developed from cells which are originally spheroidal, vacuoles form in the interior of the cells gradually becoming 766 HANDBOOK OF PHYSIOLOGY. united by fine protoplasmic processes: by the extension of the vacuoles into them, capillary tubes are gradually formed. Morphology. Heart. — When it first appears, the heart is approxi- mately tubular in form, being at first a doiible fvbe then a single one. It receives at its two posterior angles the two omphalo-mesenteric or vitel- line veins, and gives off anteriorly the primitive aorta (fig. 493). The junction of the two veins which pass into the auricle becomes removed farther and farther away from the heart, and the vessel thus formed is called sinus venosus near to the auricle, and ductus venosus farther away, or if it be called by one name that of meatus venosvs may be used. It soon, however, becomes curved somewhat in the shape of a horse- shoe, with the convexity toward the right, the venous end being at the same time drawn up toward the head, so that it finally lies behind and somewhat to the right, of the arterial. It also becomes partly divided by constrictions into three cavities. Of these three cavities which are developed in all vertebrata, that at the venous end is the simple auricle, with the sinus venosus, that at the arterial end the bulbus arteriosus, and the middle one is the simple ven- tricle. These three parts of the heart contract in succession. The auricle and the bulbus arteriosus at this period lie at the extremities of the Fig. 493. -FcEtal heart in successive stages of development. 1, venous extremity ; 2, arterial ex- tremity; 3, 3, pulmonary branches; 4, ductus arteriosus. (Dalton.) horse-shoe. The bulging out of the middle portion iuferiorly gives the first indication of the future form of the ventricle (fig. 493). The great curvature of the horse-shoe by the same means becomes much more developed than the smaller curvature between the auricle and bulbus; and the two extremities, the auricle and bulb, approach each other superiorly, so as to produce a greater resemblance to the later form of the heart, while the ventricle becomes more and more developed in- DEVELOPMENT. 767 feriorly. The heart of fishes retains these cavities, no further division by internal septa into riglit and left chambers taking place. In amphibia, also, the heart throughout life consists of the three muscular divisions which are so early formed in the embryo and the sinus venosus; but the auricle is divided internally by a septum into a pulmonary and systemic auricle. In reptiles, not merely the auricle is thus divided into two cavities, but a similar septum but incomplete is more or less developed Fig. 494.— Heart of the chick at the 45th, 65th, and 85th hours of incubation. 1, the venous trunks; 2, the auricle; 3, the ventricle; 4, the bulbus arteriosus. (Allen Thomson.) in the ventricle. In birds and mammals, both auricle and ventricle undergo complete division by septa; while in these animals as well as in reptiles, the bulbus aortte is not permanent, but becomes lost in the ven- tricles. The septum dividing the ventricle commences at the apex and extends uj^ward. The subdivision of the auricles is very early fore- shadowed by the outgrowth of the two auricular appendages, which occurs before any septum is formed externally. The septum of the auricles is developed from a semilunar fold, which extends from above downward. In man, the septum between the ventricles, according to Meckel, begins to be formed about the fourth week, and at the end of eight weeks is complete. The septum of the auricles, in man and all animals which possess it, remains imperfect throughout foetal life. When the partition of the auricles is first commencing, the two vence cavae have different relations to the two cavities. The superior cava enters, as in the adult, into the right auricle; but the inferior cava is so placed that it appears to enter the left auricle, and the posterior part of the septum of the auricles is formed by the Eustachian valve, which extends from the point of entrance of the inferior cava. Subsequently, however, the septum, growing from the anterior wall close to the upper end of the ven- tricular septum, becomes directed more and more to the left of the vena cava inferior. During the entire period of foetal life, there remains an opening in the septum, which the valve of the foramen ovale, devel- oped in the third month, imperfectly closes. The bulbus arteriosus^ which is originally a single tube, becomes gradually divided into two by the growth of an internal septum, which springs from the posterior wall, and extends forward toward the front wall and downward toward the ventricles. This partition takes a some- what spinal direction, so that the two tubes (aorta and pulmonary artery) 7G8 HANDBOOK OF PHYSIOLOGY. wliicli result from its completion, do not run side by side, but are twisted round each other. As the septum grows down toward the ventricles, it meets and coa- lesces with the upwardly growing ventricular septum, and thus from the right and left ventricles, which are now completely separate, arise respectively the pulmonary artery and aorta, which are also quite dis- tinct. The auriculo-ventricular and semi-lunar valves are formed by the folds of the endocardium. At its first appearance, as we have seen, the heart is placed just beneath the head of the foetus, and is very large relatively to the whole body ; but with the growth of the neck it becomes further and further removed from the head, and is lodged in the cavity of the thorax. Up to a certain period the auricular is larger than the ventricular divi- sion of the heart; but this relation is gradually reversed as development proceeds. Moreover, all through fcetal life, the walls of the right ven- tricle are of very much the same thickness as those of the left, which may probably be exi^lained by the fact that in the foetus the right ven- tricle has to propel the blood from the pulmonary artery into the aorta, and thence into the placenta, Avhile in the adult it only drives the blood through the lungs. Arteries. — The primitive aorta arises from the bulbus arteriosus and divides into two branches which arch backward, one on each side of the foregut and unite again behind it, and in front of the notochord into a single vessel. This gives off the two omphalo-mesenteric arteries, which distribute branches all over the yolk-sac; this area vasculosa in the chick attaining a large development, and being limited all round by a vessel known as the sinus termiualis. The blood is collected by the venous channels, and returned through the omphalo-mesenteric veins to the heart. Behind this pair of primitive aortic arches, four more pairs make their appearance sucessively, so that there are five pairs in all, each one running along one of the visceral arches. These five are never all to be seen at once in the embryo of higher animals, for the two anterior pairs gradually disappear, while the pos- terior ones are making their appearance, so that at length only three remain. In fishes, however, they all persist throughout life as the branchial arteries supplying the gills, while in amphibia three pairs persist through- out life. In reptiles, birds, and mammals, further transformations occur. In reptiles the fourth pair remains throughout life as the permanent right and left aorta; in birds the right one remains as the permanent DEVELOPMENT. 769 aorta, curving over the right bronchus instead of the left as in mammals. In mammals the left fourth aortic arch develops into the permanent aorta, the right one remaining as the subclavian artery of that side. Thus the subclavian artery on the right side corresponds to the aortic arch on the left, and this homology is further confirmed by the fact that Fig. 495.— Diagram of the aortic arches in a mammal, sliowing transformations which give rise to the permanent arterial vessels. A, primitive arterial stem or aortic bulb, now divided into .4, the ascending part of the aortic arch, and p, the pulmonary ; a a', right and left aortic roots ; A', descending aorta: 1, 2, 3, 4, 5, the five primitive aortic or branchial arches; /, //, ///, /f' the four branchial clefts which, for the sake of clearness, have been omitted on the right side! The permanent sj'stemic vessels are deeply, the pulmonary arteries lightly, shaded ; the parts of the primitive arches which are transitory are simply outlined; f, placed between the per- manent common carotid arteries; ce, external carotid arteries; c /, internal carotid arteries; s, right subclavian, rising from the right aortic root beyond the fifth arch; r, right vertebral froui the same, opposite the fourth arch ; v' s\ left vertebral and subclavian arteries rising together from the left or permanent aortic root, opposite the fourth arch; ;j. pulmonary arteries rising together from the left fifth arch ; d, outer or back part of the left fifth arch, forming ductus arteriosis; j} n, p n\ right and left pneumogastric nerves descending in front of aortic arch, with their recurrent branches represented diagrammptically as passing behind, to illustrate the relations of these nerves respectively to the right subclavian artery (4) and the arch of the aorta and ductus arteriosus id). (Allen Thomson, after Rathke.) the recurrent laryngeal nerve hooks under the subclavian on the right side, and the aortic arch on the left. The third aortic arch remains as the internal carotid artery, while the fifth disappears on the right side, but on the left forms the pulmo- nary artery. The distal end of this arch originally opens into the descend- ing aorta, and this communication (which is permanent throughout life in many reptiles on both sides of the body) remains through- out fcetal life under the name of ductus arteriosus: the branches of the i:)ulmonary artery, to the right and left lung, are very small, and most of the blood which is forced into the j)ulmonary artery passes through the wide ductus arteriosus into the descending aorta. All these j^oints will become clear on reference to the accompanying diagram (fig. 495). 49 770 HANDBOOK OF PHYSIOLOGY. As the umbilical vesicle dwindles in size, the portion of the omphalo- mesenteric arteries outside the body gradually disappears, the part inside the body remaining as the mesenteric arteries. Meanwhile with the growth of the allantois two new arteries {iwibil- ical) appear, and rapidly increase in size till they are the largest branches of the aorta: they are given off from the internal iliac arteries, and for a long time are considerably larger than the external iliacs which supply the comparatively small hind-limbs. Veins. — The chief veins in the early embryo may be divided into two groups, visceral and parietal: the former includes the omphalo- Fig. 496. Fig. 497 Fig. 490. —Diagram of young embryo and its vessels, showing course of circulation in the umbilical vesicle; and also that of the allantois Cnear the caudal extremity), vi'hich is just com- mencing. ( Dalton. ) Fig, 497. —Diagram of embryo and its vessels at a later stage, showing the second circula- tion. The pharynx, cesophagus, and intestinal canal have become further developed, and themes- enteric arteries have enlarged, while the umbilical vesicle and its vascular branches are very much reduced in size. The large umbilical arteries are seen passing out in the placenta. (Dalton.) mesenteric and umbilical, the latter the jugular and cardinal veins. The former may be first considered. The earliest veins to appear in the foetus are the omphalo-mesenteric or vitelline, which return the blood from the yolk-sac to the developing auricle. As soon as the placenta with its umbilical veins is developed, these unite with the omphalo-mesenteric, and thus the blood which reaches the auricle comes partly from the yolk-sac and partly from the placenta. The right omphalo-mesenteric and the right umbilical veins soon disappear, and the united left omphalo-mesenteric and umbilical veins pass through the developing liver on the way to the auricle. Two sets of vessels make their appearance in connection with the liver (vente hepaticre advehentes, and revehentes), both opening into the united omphalo-mesenteric and umbilical veins, in such a way that a portion of the venous blood traversing the latter is diverted into the developing DEYELOPMEXT. 771 liver, and, having passed through its capillaries, returns to the umbili- cal vein through the vena? hepaticse revehentes at a point nearer the heart (see fig. 498) . The portion of vein between the afferent and effe- rent veins of the liver becomes the ductus venosus. The ven^e hepaticae Fig. 498. —Diagrams illustrating the development of veins about the liver. B, d c, ducts of Cuvier, right and left; c a, right and left cardinal veins; o. left omphalo-meseuteric vein; o', right ompiialo-mesenteric vein, almost shrivelled up; n tt', umbilical veins, of which u', the riglit one, has almost disappeared. Between the venas cardinales is seen the outline of the rudiment- ary liver with its venas hepaticae adveheutes, and revehentes. Z>, ductus venosus; I', hepatic veins; c i, vena cava inferior; P, portal vein; P'P', venae advehentes; hi, mesenteric veins. (KoUilier.) advehentes become the right and left branches of the jiortal vein, the venas hepaticse revehentes become the hepatic veins, which open just at the junction of the ductus venosus with another large vein (vena cava inferior), which is now being developed. The mesenteric portion of the omphalo-mesenteric vein returning blood from the developing intes- tines remains as the mesenteric vein, which, by its union with the sijlenic vein, forms the jiortal. Thus the foetal liver is supplied with venous blood from two sources, through the umbilical and portal vein respectively. At birth the circu- lation through the umbilical vein of course completely ceases and the vessel begins at once to dwindle, so that now the only venous supply of the liver is through the portal vein. The earliest appearance of the parietal system of veins is the formation of two short transverse veins (ducts of Cuvier) opening into the auricle on either side, which result from the union of an anterior cardinal, afterward forming a jugular, vein, collecting blood from the head and neck, and a posterior cardinal vein which returns the blood from the Wolffian bodies, the vertebral column, and the parieties of the trunk. This arrangement persists throughout life in fishes, but in mammals the following transformations occur. As the kidneys are developing a new vein appears (vena cava infe- rior), formed by the junction of their efferent veins. It receives branches from the legs (iliac) and increases rapidly in size as they grow; further up it receives the hepatic veins, which by now have lost their original opening into the ductus venosus. The heart gradually descends into 772 HANDBOOK OF PHYSIOLOGY. the thorax, causing the ducts of Cuvier to become oblique instead of transverse. As the fore-limbs develop, the subclavian veins are formed. A transverse communicating trunk now unites the two ducts of Cuvier, and gradually increases, while the left duct of Cuvier becomes almost entirely obliterated (all its blood jjassing by the communicating trunk to the right side) (fig. 499, c.d.). The right duct of Cuvier remains as the right innominate vein, while the communicating branch forms the left innominate. The remnant of the left duct of Cuvier generally remains as a fibrous band, running obliquely down to the coro- nary vein, which is really the proximal p)art of the left duct of Cuvier. In front of the root of the left lung, another relic may be found in the Fig. 499.— Diagrams iUustrating the development of the great veins, d c, ducts of Cuvier ; j", jugular veins; h, hepatic veins; c, cardinal veins; .s, subclavian vein; j i, internal jugular vein; je, external jugular vein; a 2, azygos vein; c i. inferior vena cava; r, renal veins; il, iliac veins; h ij, hypogastric veins. (Gegenbaur.) form of the so-called vestigial fold of Marshall, which is a fold of peri- cardium running in the same direction. In many of tflie lower mammals, such as the rat, the left ductus Cuvieri remains as a left superior cava. Meanwhile, a transverse branch carries across most of the blood of the left posterior cardinal vein into the right; and by this union the great azygos vein is formed. The upper portions of the left posterior cardinal vein remains as the left superior intercostal and vena azygos minor. Circulation of Blood in the Fcetus. The circulation of blood in the foetus differs considerably from that of the adult. It will be well, perhaps, to begin its description by trac- DEVELOPMENT. 773 ing the course of the blood, which, after being carried out to the pla- centa by the two umbilical arteries, has returned, cleansed and replen- ished, to the foetus by the umbilical vein. It is at first conveyed to the under surface of the liver, and there the stream is divided, — a part of the blood passing straight on to the in- L. ^itbclaf _X'_ '--->rV=i sexual distinction, as seen from before, sr, the supra-renal bodies; ?-, the kidneys; ot^ common blastema of ovaries or testicles ; W, Wolffian bodies ; u\ W' olfflan ducts ; m m, Miillerian ducts ; g c, genital cord; ug, sinus urogenitalis ; i, intestine; cl, cloaca. (Allen Thomson.) tal end of the genital cord, and is, of course, therefore, the homologue^ in the male, of the vagina and uterus in the female. The external parts of generation are at first the same in both sexes. The opening of the genito-urinary apparatus is, in both sexes, bounded by two folds of skin, Avhile in front of it there is formed a penis-like- body surmounted by a glans, and cleft or furrowed along its under sur- face. The borders of the furrows diverge posteriorly, running at the sides of the genito-urinary orifice internally to the cutaneous folds just mentioned. In the female, this body becoming retracted, forms the clitoris, and the margins of the furrow on its under surface are converted into the nymphae or labia minora, the labia majora pudenda being con- stituted by the great cutaneous folds. In the male foetus, the margins DEVELOPMENT. 791 of the furrow at the under surface of the penis unite at about the four- teenth week, and form that part of the urethra which is included in the penis. The large cutaneous folds form the scrotum, and later (in the eighth month of development), receive the testicles, which descend into them from the abdominal cavity. Sometimes the urethra is not closed, and the deformity called hypospadias then results. The appearance of hermaphroditism may, in these cases, be increased by the retention of the testes within the abdomen. APPENDIX. CLASSIFICATION OF THE ANIMAL KINGDOM. A.— VERTEBRATA. Mammalia Monodelphia Primates Cheiroptera Insectivora Carnivora Proboscidea Hyracoidea Ungulata Sirenia Cetacea Rodentia . Edentata Didelphia . Ornithodelphia AVES Carinatae Ratitae . Reptilia Crocodilia Ophidia Chelonia Lacertilia Amphibia Anura Urodela Pisces Typical examples. Man, ape. Bat. Hedgehog. Cat, dog, bear. Elephant. Hyrax. Horse, sheep, pig. Dugong. Whale. Rabbit, rat. Armadillo. Kangaroo. Duck-billed platypus Fowl, duck. Ostrich. Crocodile. Snake. Tortoise. Lizard. Frog. Newt. Lamprey, shark, cod. B. — INVERTEBRATA. MOLLUSCA Odontophora Lamellibranchiata Brachiopoda Polyzoa Arthropod A Crustacea Arachnida Insecta Myriapoda echinodermata . Vermes Annelida . Platyhelminthes . Nemathelminthes CCELENTERATA Actinozoa Hydrozoa Protozoa Whelk, snail. Mussel, oyster. Terebratula. Sea mat. Lobster. Scorpion, Bee, fly. Centipede. Sea stars. spider. Earthworm. Tapeworm, fluke. Round -worm, thread -worm. Sea anemone. Hydra. Amoeba, Vorticella. 794 APPENDIX. Organic Chemical Substances. Nearly all of the most important substances found in the animal body have been mentioned and described in the preceding pages. It will be only necessary here to add some brief notes. Certain terms have been used without explanation. Hydrocarbons. — Compounds of carbon and hydrogen. Carbon being a tetrad element, the simplest hydrocarbon is C'''H'4, methane or marsh gas. It is found in the gases of the alimentary canal (intestines) (p. 361). It is the first of the series known as paraffins. The different members of the series increase by CHg, so that the next paraffin is C2H6 Ethane; C3 He propane, and so on. The general formula being CnH2„+2. Alcohols. — From a hydrocarbon, by substituting OH (hydroxyl) for H, we obtain the corresponding alcohol; thus from CH3H we obtain CH3 OH, methyl alcohol; from C2H5H, C2H5 OH, ethyl alcohol; from C3H7H, C3 H7 OH, propyl alcohol and the like. They are hydrates of the hydrocarbons. Ethers. — The ethers are obtained from their corresponding alcohols by dehydration; e.g., 2(C2H5) OH - H2O = (C2H5)20, ethylic ether. Aldehydes. — The aldehydes are obtained by oxidation of alcohols thus:— C2H5 OH + 0 = CH3 COH + H20 ethyl aldehyde. Acids.^ — The acids are obtained by further oxidation, one atom of 0 being substituted for H2, e.g., CH3 CO OH, acetic acid. The series of acids obtained from the first series of paraffins is known as fatty acids ; those which are most familiar as fatty acids being C4H8O21, butyric acid ; C6H12O2, caproic acid; Qm^zi^^ palmitic, 2M^ C18 H36 O2, stearic, derived from C4 Hio {hutane), Ce Hu {hexane), C16H34 {hecdecane), and Cig H38, respectively. Soaps and Fats. — The fatty acids in combination with soda or potash, or similar bases, form soaps, and Avhen combined with glycerine form fats. Other series of liydrocarhons. — The first series of paraffins consists of saturated hydrocarbons; many other series exist, however, in which the C is unsaturated. Their general formulae are as follows : CnH2n; CnH2n-2; CnH2n-4; GJi-2xx-%, 'ind SO OU. From each series of hydrocarbons, the corresponding alcohols, acids, aldehydes, and ethers are obtainable. The alcohols derived from series of ethene, C2H4, are called glycols. But in glycols there are two OH united to the radicle instead of one — these are therefore called diatomic alcohols; and similarly acids, of two kinds, may be obtained, by the sub- stitution of one or of two atoms of 0 for the corresponding H2 or H4. An example or two may be cited: — C2 H4, ethene ; C2 H4 OH, ethene glycol ; C2 H4 O3, glycolic acid / APPENDIX. 795 C'i H2 O4, oxalic acid ; and C3 He, propene ; C3 He OH2, propene glycol ; C5 Hs O3, lactic acid ; Cg H4 O4, malonic acid. The next series of hydrocarbons, On H2n-2, is represented by C2 H2 acetylene ; the next CnH2„_4, terebinthene, Cio Hie; the next C„H2„_6, by benzene, Ce He. From these we obtain triatomic alcohols, e.g. glycerin, C3 Hs OH3, tetratomic alcohols, e.g. erythrite, C4 He OH4, and hexatomic alcohols,. e.g., mannite, Ce Hs OHe ; from the last, the carbohydrates are derived. Of the hydrocarbons, only one is, as we have said, found in the body,, viz., methane; of the alcohols, cholesterine, O26 H43 OH, a monatomic,. and glycerine, C3 H3 OH3, a triatomic alcohol. Phenol, Ce H3 OH, found in combination in the urine and faeces. Of the aldehydes and ketones (analogous products to aldehyde, ob- tained from isomeric alcohols). Acetone, or propyl ketone, is found in blood and in urine, particularly in diabetes. The glucoses are aldehydes of mannite, and the other carbohydrates are derived from that class. Fatty Acids. — Formic, acetic, propionic, butyric, caproic and caprylic, are all more or less represented in the secretions and tissues of the body. Palmitic and stearic in fats. Glycol Acids. — Lactic acid, of which there are three isomeric bodies, and leucic acid and two other acids, oxalic and succinic. Amido-Acids. — These may be looked upon as either ammonia, in which one or more atoms of H are replaced by the acid radicles; or as acids in which one or more of the H atoms of the acid radicle are re- placed by amidogen NH2. Of these the following are important: — Glycin, C2 H3 (NHo) O2, amido-acetic acid. Leucine, Cs Hn NH2 O2, amido-caproic acid. Tyrosine, C9 Hn NO3, amido-oxyphenyl-propionic acid. Sarcosine = methyl glyciji, C3 H: NO2. Creatine = sarcosine -J- cyanamide, CN NHa = C4 Hg N3 O2. Creatinine = creatin — H2O = C4 H7 N3 0. Taurine, C2 H7 NSO3, is amido-isethionic acid. Cystine, C3 H7 X5 O3, amido-lactic acid in which one H is replaced byHS. Of these bodies it is only necessary to mention the following: — Glycin, Glycocol, Glycocin, or ) ^^ ^^ ^^^ f^^^ (n^'nu )• Amido-aretic acid. \ ^ \^V u±i / This substance occurs in the body in combination as in the biliary acids, but is never free. Glycocholic acid, when treated with weak acids,. with alkalies, or with baryta water, splits up into cholic acid and glycin,. or amido-acetic acid. Thus: C2eH43N06 + H2O = C26 H40 O5 + C2 H5 NO2. Glycocholic acid + water = cholic acid + glycin, and under sim- 796 APPENDIX. ilar circumstances Taurocholic acid splits up into cholic acid and taurin : C26 H45 O3 NSO2 + H2O = C26 H40 O5 + C2 H7 NSO3, or araido-isethi- onic. Taurocholic acid + water = cholic acid and taurin. Glycin oc- curs also in hippuric acid. It can be prepared from gelatin by the action of acids or alkalies, and can also be obtained from hippuric acid. Sarcosi7i or Methyl ) ^i xj Air* f nxr /NH CHsN t+ i„ „ ^^^ Glycin, \^'^' ^^' i " ^^' \C0 OH )• ^^ ^' ^ ^^°- •stituent of creatin, and also of caffeine, but has never been found free in the human body. It may be obtained from these bodies by boiling with baryta water. Leucm or Amido- \ CgHigNOa {= CH3.CH2CH2CH2.CH(NH2)CO OH caproic Acid, •occurs normally in many of the organs of the body, and is a product of the pancreatic digestion of proteids. It is present in the urine in certain diseases of the liver in which there is loss of substance, esj)e- cially in acute yellow atrophy. It occurs in circular oily discs or crys- tallizes ia plates, and can be prepared either by boiling horn shavings, or any of the gelatins with sulphuric acid, or out of the products of pancreatic digestion. Creatin, C4 H9 N3 O2, is one of the primary j^roducts of muscular dis- integration. It is always found in the juice of muscle. It is generally •decomposed in the blood into urea and sarcosin, and seldom, unless under abnormal circumstances, apjoears as such in the urine. Treated with either sulphuric or hydrochloric acid, it is converted into creatinin; thus — C4 H9 N3 O2 = C4 Ih N3 0 + H2 0. It has been made synthetically by bringing together cyanimide and «arcosine. Creatinin, C4 H7 N3 0, is present in human urine, derived from oxi- dation of creatin. It does not appear to be present in muscle. Taurin or Amido- )^^ H, NSO3 ( - C2 H4 (%%r ^^) is a constit- tsethionic Acid, ) ^ \iMi2 / uent of the bile acid, taurocholic acid, and is found also in traces in the muscles and lungs. It has been prepared synthetically from isethionic acid. It is a crystalline substance, very stable. Benzoyl Amido-Acids. '''ZZ^^ \ C' H. NO3 = (C. H. CONH OH. 00 OH), a nor- mal constituent of human urine, the quantity excreted being increased "by a vegetable diet, and therefore it is present in greater amount in the urine of herbivora. It may be decomposed by acids into glycin and Ijenzoic acid. It crystallizes in semi-transparent rhombic prisms, almost insoluble in cold water, soluble in boiling water. APPENDIX. 797 Tyrosin, Cg Hn NO3, is fouud generally together with leucin, in cer- tain glands, e.g., pancreas and spleen; and chiefly in the products of pancreatic digestion or of the putrefaction of proteids. It is found in the urine in some diseases of the liver, especially acute yellow atrophy. It crystallizes in fine needles, which collect into feathery masses. It gives the j^roteid test with Millon's reagent, and heated with strong sul- phuric acid, on the addition of ferric chloride gives a violet color. Lecithin, C42 ^m PN O9, is a complex nitrogenous fatty body, con- taining phosphorus, which has been found mixed with cerebrin and oleo- i:)hosphoric acid in the brain. It is also found in blood, bile and serous fluids, and in larger quantities in nerves, pus, yelk of egg, semen, and white blood-corpuscles. On boiling with acids it yields cholin, glycero- phosphoric acid, palmic and oleic acids. Cerehi-in, Cn H33 NO3, is found in nerves, pus corpuscles, and in the brain. Its chemical constitution is not known. It is a light amorphous powder, tasteless and odorless. Swells uja like starch when boiled with water, and is converted by acids into a saccharine substance and other bodies. The so-called Protagon is a mixture of lecithin and cerebrin. Uric Acid, C5 H4 N4 O3, occurs in the urine, sparingly in human urine, abundantly in that of birds and reptiles, where it represents the chief nitrogenous decomposition product. It occurs also in the blood, spleen, liver, and sometimes is the only constituent of urinary calculi. It is probably converted in the blood into urea and carbonic acid. It generally occurs in urine in combination with bases, forming urates, and never free unless under abnormal conditions. A deposit of urates may occur when the urine is concentrated or extremely acid, or when, as during febrile disorders, the conversion of uric acid into urea is incom- pletely performed. Composition. — Very uncertain; has been however recently produced artificially, but it is not easily decomposed; it may be regarded as diu- reide of tartronic acid. The chief product of its decomposition is urea. Xanthin, C5 H4 ^4 O2, has been obtained from the liver, spleen, thymus, muscle, and the blood. It is found in normal urine, and is a constituent of certain rare urinary calculi. Hgpoxantliin, C5 H4 N4 0, or sarcin, is found in juice of flesh, in the spleen, thymus, and thyroid. Guanin, C5 H5 N5 0, has been found in the human liver, sjjleen, and faeces, but does not occur as a constant product. Allantoin, C4 He N4 O3, found in the allantoic fluid of the foetus, and in the urine of animals for a short period after their birth. It is one of the oxidation products of uric acid, which on oxidation gives urea. In addition to the above compounds and probably related to them, are certain coloring and excrementitious matters, which are also most likely distinct decomposition compounds. 798 APPENDIX. Pigments, Etc. Biliruhin, Cg Hg NO2, is the best known of the bile pigments. It is hest made by extracting inspissated bile or gall stones with water (which dissolves the salts, etc.), then with alcohol, which takes out cholesterin, fatty and biliary acids. Hydrochloric acid is then added, which decom- poses the lime salt of bilirubin and removes the lime. After extracting with alcohol and ether, the residue is dried and finally extracted with ■chloroform. It crystallizes of a bluish-red color. It is allied in com- position to hfematin, as has been described. Biliverdin, Cs Hg ISTOa, is made by passing a current of air through an alkaline solution of bilirubin, and by preciptation with hydrochloric acid. It is a green pigment. BiUfusciJi, Cg Hu NO3, is made by treating gall stones with ether, then with dilute acid, and extracting with absolute alcohol. It is a non-crystallizable brown pigment. Billprasin is a pigment of a green color, which can be obtained from gall stones, and from bile which has been allowed to decompose. BiUliumin (Staedeler) is a dark brown earthy-looking substance, of which the formula is unknown. Urochrome and Urobilin occur in bile and in urine; the latter is probably identical with stercohilin, which is found in the fasces. Uro- erytlirin is one of the coloring matters of the urine. It is orange red and contains iron, as is also Chohtelin. Melmmi is a dark brown or black material containing iron, occurring in the lungs, bronchial glands, the skin, hair, and choroid. Hcematin has been fully treated of, p. 149, et seq. Indican is supposed to exist in the sweat and urine. It has not, however, been satisfactorily isolated. Indigo, Cs H5 Ng 0, is formed from indican, and gives rise to the bluish color which is occasionally met with in the sweat and urine. • Indol, Cs Ha N, is found in the -faeces, and is formed either by de- composition of indigo, or of the proteid food materials. It is supposed to give the characteristic disagreeable smell to faeces. Nitrogenous Bodies of Uncertain Nature. Ferments are bodies which possess the property of exciting chemical changes in matter with which they come in contact. They are at pres- ent divided into- two classes, called (1) organized, and (3) unorganized or soluble. (1.) Of the organized, yeast may be taken as an example. Its activ- ity depends upon the vitality of the yeast cell, and disappears as soon as the cell dies, neither can any substance be obtained from the yeast by means of precipitation with alcohol or in any other way which has the APPENDIX. 799 power of exciting the ordinary change i^roduced by the plant itself. The action of micro-organisms in the alimentary canal and elsewhere is •also an example of the same nature. (2.) Unorganized or soluble ferments are those which are found in secretions of glands, or are produced by chemical changes in animal or vegetable cells in general; when isolated they are colorless, tasteless, amorphous solids soluble in water and glycerin, and precipitated from the aqueous solutions by alcohol and acetate of lead. Chemically many of these are said to contain nitrogen. Mode of act ion. — Without going into the theories of how these un- organized ferments act, it will suflBee to mention that: (L) Their activity beyond a certain point does not depend upon the actual amount of the ferment present. (2.) That the activity is de- stroyed by high temperature, and various concentrated chemical re- agents, but increased by moderate heat, about 40° C, and by weak solu- tions of either an acid or alkaline fluid. (3.) The ferments themselves appear to undergo no change in their own composition, and waste very slightly during the process. The chief classes of unorganized ferments are : — (1.) Amylolytic, which possess the j)roperty of converting starch into glucose. They add a molecule of water, and may be called hydro- lytic. The principal amylolytic ferments are Ptyalin, found in the saliva, and a ferment, probably distinct, in the jDancreatic juice, called Ami/IojJsin. These both act in an alkaline medium. Amylolytic fer- ments have been found in the blood and elsewhere. (2.) Proteolytic convert proteids into peptones. The nature of their action is probably hydrolytic. The proteolytic ferments of the body are called Pepsin, acting in an acid medium from the gastric juice. Trypsin, acting in an alkaline medium from the pancreatic juice. The Succus entericus is said to contain a third such ferment. (3.) Inversive, which convert cane sugar or saccharose into grape sugar or ghicose. Such a ferment was found by Claude Bernard in the Succus entericus; and probably exists also in the stomach mucus. (4.) Ferments loliicli act upon fats. — Such a body, called Steapsin, lias been found in pancreatic juice. (5.) Milk-curdling ferment s. — It has been long known that rennet, a decoction of the fourth stomach of a calf, in brine, possessed the power of curdling milk. This power does not depend upon the acidity of the gastric juice, since the curdling will take place in a neutral or alkaline medium; neither does it depend upon the pepsin, as pure pep- sin scarcely curdles milk at all, and the rennet which rapidly curdles milk has a very feeble proteolytic action. From this and other evidence it is believed that a distinct milk-curdling ferment exists in the stom- 800 APPENDIX. ach. W. Roberts has shown that a similar but distinct ferment exists in pancreatic extract, which acts best in an alkaline medium, next best in an acid medium, and worst in a neutral medium. The ferment of rennet acts best in an acid medium, and worst in an alkaline, the reaction ceasing if the alkalinity be more than slight. Also in the Succus entericus. In addition to the above ferments, many others most likely exist in the body, of which the following are the most important: (6.) Fibrin-forming ferment (Schmidt), (see p. 125, et seq.), found in the blood, lymph and chyle. (7.) A ferment ivliicli converts glycogen into glucose in the liver; being therefore an amylolytic ferment. (8.) Myosin ferment. Carbo-hydrates or Amyloids. The divisions of carbo-hydrates, and the chief substances forming each class with their properties, have been already given (p. Ill, et seq). The following additional information may be useful. The glucoses may be considered as the aldehydes of mannite, thus : CHa OH ) CHa OH (CH 0H)4 \ Ce Hu Oe, (CH 0H)4 \ Ce H12 0, CH2 OH J CO H mannite. glucose. The Saccharoses or sncroses are made up of two volumes of glucose minus one molecule of water. Ce H12 Oe + Ce H12 Oe — H2 0 = C12 H22 On. The amyloids are anhydrides of the glucoses, Ce H12 Oe — H2 0 = CeHioOs. Tests for Glucose. — (i.) Trommer's. — This test depends upon the power sugar possesses of reducing copper salts to their sub-oxide. It is done in the following way : — An excess of caustic potash and then a solution of copper sulphate, drop by drop, are added to the solution containing the sugar in a test-tube, as long as the blue precipitate which forms redissolves on shaking the tube. The upper portion of the fluid is then heated, and a yellowish-brown precipitate of copper suboxide ap- pears. The test may also be done by taking only a drop or two of the copper sulphate solution. (ii.) Moore's. — If a solution of sugar in a test-tube is boiled with caustic potash, a brown coloration appears. (iii.) Fermentation. — If a solution of sugar be kept in the warm plate for a time after the addition of yeast, the sugar is converted into alcohol and carbon dioxide. (CeHjoOe = 2C2H5OH + 2CO2.) (iv.) BottcJier's test. — A little bismuth oxide or subnitrate and an excess of caustic potash are added to the solution in a test-tube, and the mixture is heated ; the solution becomes at first gray and then black. APPENDIX. 801 (v.) Picric acid test. — To the solution about a fourth of its bulk of picric acid (saturated solution) and an equal quantity of caustic potash are added, and the solution is boiled; the liquid becomes of a very deep coflfee-brown. (vi.) Indigo-carmine test. — Add a solution of indigo carmine to color sugar solution distinctly blue, and add solution of sodium carbonate, and heat. The blue color changes to purple and then to brown and yellow, but is restored on shaking the solution. (vii.) Phenyl liiidrazine test. — A solution of phenyl hydrazine hy- drochloride and sodium acetate is added. Keep in water- bath at boiling for some minutes, then cool. Yellow crystals result. Quantitative Estimation of Grape Sugar. 1. Feliling's Metliod. — Solution required = copper suljihate and caus- tic soda, with some sodic potassic tartrate of such a strength that 10 c.c. of solution contain the amount of cupric oxide which 0.5 grm. of sugar can reduce to cuprous oxide. (This solution should be freshly pre- pared.) It is made as follows: Take of sulphate of copper, 4:0 grms. ; neutral tartrate of potash, 160 grms.; caustic soda (sp. gr. 1.12), 750 grms.; add distilled water to 1154.5 c.c. Each 10 c.c.^contains .05 grm. of sugar. Method. — Take 10 c.c. of the saccharine solution free from albumen, and add 90 c.c. of distilled water. Place this in a burette. Put into a flask or dish 10 c.c. of the standard solution, and dilute with four times its bulk of water and boil. Eun into it, from burette, some of the diluted urine, say 20 c.c, and boil. Allow precipitate to settle, and if supernatant fluid is still blue, add, say, 5 c.c. from burette, and boil again, and so on, till the fluid ceases to have a blue tinge, taking care, toward the end of the process, to add only a few drops each time. If, after adding 20 c.c. of diluted urine and boiling, the fluid has been decolorized, too much of the solution has been added, and another esti- mation with a second 10 c.c. of standard solution must be made, but less than 20 c.c. of the saccharine solution should be added (say 10 c.c.) in first instance. When the number of c.c. of diluted urine required to decolorize the solution has been determined, that volume contains the amount of sugar necessary to reduce 10 c.c. of standard solution, i.e., .05 grm. But one- tenth only of this is the saccharine solution, .*. one-tenth of number of c.c. used contains .05 grm. of sugar. From this, the percentage can be easily calculated. 2. Pavy's Modification of Fehling's Method. — By Fehling's method it is difficult and tedious to judge of the point of complete reduction of the cupric oxide. Dr. Pavy, accordingly, uses a strongly ammoniacal solution of the above. A certain amount is introduced into a small 51 802 APPENDIX. flask, which is then heated till the vapor of ammonia escapes by a nar- row tube. The sugar solution is then allowed to flow from a burette into the flask until the blueness has disappeared, the solution being kept boiling all the time. The blueness is apt to disappear suddenly, and care should therefore be taken toward the end of the process. Calculate as in Fehling's method. 3. Estimation of sugar hrj fermentation. — In the case of saccharine urine, it is allowable as a single test to use the following method: — Take specific gravity of urine before and after fermentation. Each degree of specific gravity lost by the urine represents one grain of sugar per ounce of urine. 4. Sugar may also be estimated by adding yeast to urine, and col- lecting the carbon dioxide evolved. The carbon dioxide is a measure of the amount of sugar present. 5. The estimation may also be done by the saccharimeter, an instru- ment for the estimation of the degree of joolarization which a ray of light undergoes in passing through a solution of sugar, either to the left or to the right. Urea, 00 (NH2)2. The properties and relations of urea have been treated of at some length in the chapter upon excretion. There re- mains to be described the method of its quantitative estimation in the urine. There are two chief methods, viz. : — (i.) Hypobromite Method. — One of the forms of apparatus employed in this method (Russell and West's) consists of («) a water-bath sup- ported by three iron bands, arranged as a tripod. The bath is provided with a cylindrical depression, and with a hole, into which fits a perfo- rated india-rubber cork; (f) a bulb tube with a constricted neck; {c) a ^lass rod provided with an india-rubber band at one extremity; ((/) a pipette of five cubic centimetres capacity ; (f) a graduated glass collect- ing tube; (/) a spirit lamp; {(j) a wash-bottle with distilled water; (A) hypobromous solution. The hypobromous solution is made in the fol- lowing way: three and a half ounces (100 grm.) of solid caustic soda is dissolved in nine ounces (300 grm.) of distilled water. When the solu- tion is cold, seven drachms (25 c.c.) of pure bromine are to be added carefully and gradually. The mixture is not to be filtered ; it keeps badly, and for this reason it should be made shortly before it is required ; or the solution of caustic soda in water may be made in large quantities as it does not undergo any change, the bromine in the jJi'opei' propor- tion being added at the time it is required for use. Method. — Fill the pipette to the mark on the stem with the urine to be examined; pour the 5 c.c. of urine thus measured oat into the bulb; fill up the bulb tube as far as the constricted neck with distilled water from the wash-bottle; insert the glass rod (c) in such a way that the india-rubber band at the extremity fills up the constricted neck; the APPEN'DIX. 803 diluted urine should exactly occupy the bulb and neck of the tube, no bubble of air being below the elastic band on the one hand, while on the other the fluid should not rise above the band; in the former case a little more water should be added, in the latter a fresh portion of urine must be used, and the experiment repeated. After adjusting the glass rod, fill up the rest of the bulb tube with hypobromous solution; it will not mix with the urine so long as the rod is in place. The water-bath having been previously erected, and the india-rubber cork fixed firmly into the aperture, the bulb tube is to be thi'ust from below through the perforation in the cork. The greater part of the tube is then beneath the watei'-bath, the upper extremity alone being grasped by the cork. Fill the water-bath half full of water, fill also the grad- uated glass tube {(/) with water, and invert it iu the bath; in doing this no air must enter the tube, which when inverted should be com- pletely filled with water. Now slide the graduated tube toward the orifice of the bulb tube, at the same time withdrawing the glass rod which projects into the bath through the cork. At the instant that the rod is withdrawn the hypobromous solution mixes with the diluted urine, and a decomposition takes place represented thus: C01Sr2H4 + SNaBrO + 2NaH0 = 3 NaBr + 3HoO + Na^COs + N2. Urea + sodium hypobromite -f- caustic soda = sodium bromide -j- water + sodium carbon- ate + nitrogen. The nitrogen produced is given off as gas, and dis- places the water in the graduated tube, which is held over it. The gas is at first evolved briskly, but afterward more slowly; to facilitate its evolution, the bulb of the tube may be slightly warmed with a spirit lamp ; as a rule, however, this is unnecessary. After ten minutes, the amount of water displaced by the gas should be read off on the tube, which is divided into tenths. Each number on the tube represents one gram of urea in 100 c.c. of urine. Normal urine should yield roughly 1.5-2.5 parts of nitrogen by this test. If 5 c.c. of urine gives off more nitrogen than fills the tube to iii., dilute the urine with an equal volume of water, and take 5 c.c. ; read off and multiply by two.* Several apparatus may be employed instead of the one described, viz., those of Duj^re, Gerard, and Squibb. The chemical reactions in each case are the same. (ii.) Liebig's Method. — This method is of greater accuracy. The soli/tions required are (a) haryta mixture = 2 vols, of saturated solution of barium nitrate and 1 vol. of saturated solution of barium hydrate; il)) standard solution of mercuric filtrate, such that 1 c.c. will precij)itate .01 grm. of urea, and (r) a solution of carbonate of soda. Method. — Take 40 c.c. of urine, add 20 c.c. of {a), filter off the pre- cipitate of sulphates and phosphates; keep the filtrate. Fill a burette * Several corrections have to be made befoi'e the result can be considered as accurate ; for these the detailed accounts in practical handbooks of Phj^siology should be consulted. 804 APPENDIX. with {b), and take 15 c.c. of the filtrate in a dish. Let {h) fall drop by drop into the 15 c.c. in the dish, stirring constantly. Have ready a glass plate with several separate drops of {c), and from time to time add a drop of the urine mixture by means of a glass rod to one of the drops. When a yellow color first appears in a drop of the NaCOs, the mercuric nitrate is just in excess. Eead the burette. Calculate as follows: 1 c.c. of mercuric solution precipitates .01 grm. of urea .*. the No. of c.c. used X .01 = amount of urea in 15 c.c. of filtrate, i.e., in 10 c.c. of urine. But 10 c.c. of urine usually contains enough NaCl to act on 2 c.c. of mercury solution.* Hence, when reckoning the number of c.c. of standing mercury solution used, a deduction of 2 c.c. must always he made. Quantitative Estimation of Chlorides. LieMg's Method. — The solutions required are a baryta mixture as above; and {b) standard solution of mercuric nitrate, such that 1 c.c. would be capable of decomposing .01 grm. of sodium chloride. Method. — Take 40 c.c. of urine free from albumen, and add 20 c.c. of {a). Filter. Take 15 c.c. of filtrate and place in a flask or dish, adding a drop or two of nitric acid. Fill a burette with {b), and slowly run some of this solution into the filtrate in the dish, stirring constantly. As soon as a distinct cloud appears in the diluted urine, and does not disappear on stirring, then all the sodium chloride in urine has been decomposed. Eead burette. Calculate as follows : 1 c.c, of mercury solution decomposed .01 grm. of NaCl, .*. the number of c.c. used X .01 grm. = number of grms. of NaCl in 15 c.c. of filtrate, i,e., 10 c.c. of urine. Quantitative Estimation of Phosphates. The solutions required are («) solution of sodium acetate, containing 100 grm. of sodium acetate, 100 c.c. of acetic acid, and 900 c.c. of distilled water; {b) a solution of uranium acetate or nitrate, such that 1 c.c. will precipitate .005 grm. of phosphoric acid; and (c) a solution of ferro- cyanide of potassiimi. Method. — Take 50 c.c. of urine. Add some (a) solution, and heat on water-bath to nearly 100° C. Fill burette with {b), and allow this to fall into the urine slowly. Have ready a glass plate with several distinct drops of potassium ferro-cyanide solution. From time to time add a drop of urine mixture to one of the drops; and when there fiest ap- pears a reddish-brown color in a drop of potassium ferro-cyanide, all the phosphates are precipitated. Read burette. Calculate thus: 1 c.c. precipitates .005 grm. of phosphoric acid, .-. the number of c.c. used X .005 grm. = number of grms. of phosphoric acid in 50 c.c. of urine. * This is only a rough estimate. INDEX. Abdominal muscles, action of in res- piration, 352 Aberration, chromatic, 689 spherical, 688 Absorbents. See Lymphatics. Absorption, 363 by blood-vessels, 319 by lacteal vessels, 377 by lymphatics, 378 channels of, 377 conditions for, 364 by the skin, 379 methods, 363 process of osmosis, ib. rapidity of, 365 See Chyle, Lymph, Lymphatics, Lac- teals. Accelerator centre, 570 Accidental elements in human body, 116 Accommodation of eye, 681 defects of, 687 Achroo- dextrin, 297 Acids, 794 in gastric juice, 316 Acid -albumin, 107 Acini of secreting glands, 458 Actinic rays, 696 Adenoid tissue, 44 Adipose tissue, 46. See Fat. development, 47 situations of, 46 structure of, 47. use, 49 Adrenals, 484 After-birth, 755 Air, atmospheric, composition of, 259 breathing, 256 complemental, ib. reserve, ib. residual, ib. tidal, ib. changes by breathing. 259 quantity breathed, 256 transmission of sonorous vibrations through, 655 in tympanum, or hearing, 656 et seq. undulations of, conducted by ex- ternal ear, 654 Air-cells, 247 Air-tubes. See Bronchi. Albumin, 105 acid, 107 action of gastric fluid on, 317 et seq. alkali. 107 characters of, ib. chemical composition of, 103 derived, 106 egg, 106 native, 106 serum, 106 of blood, 139 Albuminoids, 109 Albuminous substances, 103 action of gastric fluid on, 317 of pancreas on, 337 Albumoses, 318 Alkali-albumin, 107 Allantoin, 400 AUantois, 749 Alloxan, 398 Aluminium, 116 Ammonia, cyanate of, isomeric with urea, 395 exhaled froni lungs, 262 urate of, 397 Ammonium sulphate reaction, 105 Amnion, 748 fluid of, 749 Amoeba, 4 Amoeboid movements, 133 cells, 4 colorless corpuscles, 134 cornea- cells, 666 protoplasm, 5 Tradescantia, 5 Amphioxus, 758 Ampulla, 650 Amyloid substance, 109 Amyloids or Starches, 111 action of pancreas and intestinal glands, 338 of saliva on, 297 Amylopsin, 338, 354 Amyloses, 111 Anabolic nerves, 607 Anelectrotonus, 449 Angle, optical, 680 Angulus opticus seu visorius, ib. Animal heat. See Heat and Tempera- ture. 806 INDEX. Animals, distinctive characters, 15 V. plants, 15 Antialbumose, 318 Antihelix, 646 Antipeptone, 319 Antitragus, 674 Aphasia, 602 Apnoea, 274 Appendices epiploicae, 332 Appendix vermiformis, ib. Aquaeductus, cochlear, 650 vestibuli, ib. Aqueous humor, 676 Arachnoid, 537 Arches, visceral, 760 Area germinativa, 739 opaca, ib. pellucida, ib. vasculosa, 747 Areolar tissue, 43 Arsenic, 116 Arterial tension, 192 Arteries, 167 circulation in, 199 velocity of, 213 distribution, 167 muscular contraction of, 233 effect of cold on, 201 effect of division, ib. elasticity, 199 purposes of, ib. muscularit}', 200 governed by nervous system, 233 purposes of, ib. nerves of, 169 nervous system, influence of, 233 office of, ib. pressure of blood in, 191 pulse. See Pulse. rhythmic contraction, 192, 201 et seq. structure, 167 et seq. distinctions in large and small ar- teries, ib. systemic, 159 tone of, 233 velocity of blood in, 213 Articulate sounds, classification of, Vowels and Consonants, 527 Arytenoid cartilages, 516 effect of approximation, 517 movements of, ib. Asphyxia, 280 causes of death in, 282 experiments on, 283 symptoms, 280 Astigmatism, 688 Atmospheric air, 284. See Air. pressure in relation to respii'ation, ib. Auditory canal, 654 et seq. function, ib. Auditory centre, 614 Auditory nerve, 651, 654 distribution, ib. Auerbach's plexus, 327 Auricles of heart. See Heart. Automatic action, 439 cerebrum, 606 et seq. medulla oblongata, 570 et seq. respiratory, 272 Axis-cylinder of nerve-fibre, 91 Bacterium lactis, 467 Barytone voice, 524 Basement- membrane, 454 Bass voice, 524 Battery, Daniell's, 428 Benzoic acid, 114 Bicuspid valve, 177 Bidder's ganglia, 222 Bile, 354 antiseptic power, 384 coloring matter, 346 composition of, 345 digestive propei'ties, 348 excrementitious, 349 fat made capable of absorption by, 348 functions in digestion, 348 mixture with chyme, 349 mucus in, 348 natural purgative, 349 process of secretion, ib. re -absorption, 350 salts, 348 secretion and flow, 349 secretion in foetus, ib. tests for, 346, uses, 348 Bilifulvin, Biliprasin, Bilirubin, Bili- verdin, 346 Bilin, 345 preparation of, ib. re- absorption of, 351 Binocular vision, 706 Bioplasm, 2. See Protoplasm. Biuret test, 104 Bladder, urinary. See Urinary Blad der. Blastema. See Protoplasm. Blastodermic membrane, 20, 737 Blind spot, 691 Blocking, 224 Blood, 117 arterial and venous, 152 buffy coat, 120 chemical composition, 151 coagulation, 119 et seq. color, 117 coloring matter, 144 et seq. coloring matter, relation to that of bile, 150 composition, chemical, 137 variations in, 152 corpuscles or cells of, 129. See Blood - corpu scles. INDEX, 807 Blood — continued. corpuscles, red, 139 white, 132 crystals, 144 cupped clot, 121 development, 154 extractive matters, 140 fattv matters, ih. fibrin, 121 separation of, 122 gases of, 142 haemoglobin, 144 hepatic, 153 odor or halitus of, 118 plasma, 117 portal, characters of, 153 quantity, 118. reaction, 117 saline constituents, 141 serum of, 139 specific gravity, 117 splenic, 153 structural composition, 129 temperature, 117 uses, 157 of various constituents, ih. variations of, in different circum- stances, 151 in different parts of body, 152 Blood-corpuscles, red, 129 action of reagents on, 130 chemical composition, 141 development, 154 disintegration and removal, 479 method of counting, 135 rouleaux, 130 specific gravity, 129 stroma, ih. tendency to adhere, 130 varieties, 129 vertebrate, various, 131 Blood -corpuscles, white, 132 amoeboid movements of, 134 derivation of, 157 formation of, in spleen, 156, 479 locomotion, 133 varieties, ih. Blood-crystals, 144 Blood pressure, 191 et seq. in veins. 197 in capillaries, 198 osmotic character of, 211 et seq. influence of nervous system on, 233 Blood-vessels, absorption by, 397 Bone, 53 canaliculi, 55 cancellous, 54 chemical composition, 53 compact, 54 development, 58 et seq. functions, 67 growth, 66 Haversian canals, 56 Bone — continued. lacunae, 55 lamellse, 57 marrow, 54 medullary canal, ih. periosteum, 55 structure, 53 Branchial clefts, 760 Brain. See Cerebellum, Cerebrum, Pons, etc. adult, 596 amphibia, 597 apes, 598 birds, 597 capillaries of, 216 child, 596 circulation of blood in, 216 convolutions, 591 female, 597 fish, 597 gorilla, 59§, idiots, 597 lobes, 591 male, 597 mammalia, ih. orang, 598 proportion of water in, 114 quantity of blood in, 216 rabbit, 597 reptiles, ih. weight, ih. relative, ih. Breathing. See Respiration. Bronchi, arrangement and structure of, 242 Bronchial arteries and veins, 248 Brunner's glands, 329 Buffy coat, formation of, 221 Bulb. See Medulla oblongata. Bulbus arteriosus, 767 Burdach's column, 542 Butyric acid, 113. Calcification compared with ossifi- cation, 66 Calcium salts, 145 Calorimeter, 491 Calyces of the kidney, 382 Canal, alimentary. See Stomach, In- testine, etc. external auditory, 646 function of. 654 spiral, of cochlea, 651 Canaliculi of bone, 55 Canal of Schlemni, 671 of Petit, 676 Cancellous texture of bone, 54 Cane sugar, 112 Capacity of chest, vital, 256 Capillaries, 170 circulation in, 210 development, 734 et seq. influence of on circulation, 211 lymphatic, 369 808 INDEX. Capillaries — continued. network of, 171 number, 173 passage of corpuscles through walls of, 311 pressure in, 198 resistance to flow of blood in, 310 still layer in, ib. structure of, 170 Capsule of Glisson, 340 Capsules, Malpighian, 387 Carbohydrates, 111, 800 Carbonic acid in atmosphere, 359 in blood, 151 effect of, 375 exhaled from skin, 419 increase of in breathed air, 359 in lungs, 265 in relation to heat of body, 492 Brown ian movement, 3 Carburetted hydrogen, 114 Cardiac orifice of stomach, action of, 335 sphincter of, ih. relaxation in vomiting, ih. Cardiac revolution, 180 Cardiograph, 184 Cardio- inhibitory centre, 337 Carotid gland, 587 Cartilage, 49 articular, 51 cellular, 53 chondrin obtained from, 53 classification, 49 development, 53 elastic, 51 fibrous, 53. See Fibro-cartilage. function, 53 hyaline, 49 matrix, 49 nutrition, 51 ossification, 60 perichondrium of, 49 structure, 49 temporary, 51 uses, 53 varieties, 49 Cartilage of external ear, used in hear- ing, 655 Cartilages of larynx, 515 Casein. See Milk. Caseinogen, 107 Cauda equina, 537 Cavity of reserve, 78 Cause of fluidity of living blood, 138 Cell globulin, 136 Cells, 3 amoeboid, 4 blood. -See Blood-corpuscles. cartilage, 50 chemical transformation, 36 ciliated, 33 classification, 24 connective tissue, 38 Cells — continued. decay and death, 36 definition of, 3 epithelium, 36. See Epithelium, fission, 13 formative, 739 functions, 3 et seq. gemmation, 9 modes of connection, 35 nutrition, 7 olfactoi-y, 641 organized, 20 pigment, 37 reproduction, 9 segmentation, 20 structure, 9 et seq. transformation, 26 varieties, 24 vegetable, 16 distinctions from animal cells, 15 et seq. Cellular cartilage. See Cartilage. Cellulose, 19 Cement of teeth. See Teeth. Centres, nervous, etc. See Nerve- centres, of ossification, 59 Centrifugal machine, 138 Centrifugal nerve-fibres, 531 Centripetal nerve-fibres, ib. Cerebellum, 615 co-ordinating function of, 618 cross-action of, ib. effects of injury of crura, ib. of removal of, ib. functions of, ib. in relation to sensation, 617 to motion, ib. to muscular sense, 619 structure of, 615 Cerebral hemispheres. See Cerebrum. Cerebral nerves, 571 third, 572 effects of irritation and injury of, ib. relation of to iris, 573 fourth, 573 fifth, 574 distribution of, ib. effect of division of, 575 inflvience of, on muscles of mastication, 575 on organs of special sense, 578 relation of, to nutrition, 578 resemblance to spinal nerves, 574_ sensory function of gi'eater division of fifth, 576 sixth, 579 communication of, with sympa- thetic, ib. seventh, 579 eighth, 581 ninth, 583 tenth, 583 INDEX. 809 Cerebral nerves — continued. eleventh, 586 twelfth, 587 Cerebration, unconscious, 610 Cerebrin. 596 Cerebro-cerebellar fibres, 604 Cerebro- spinal fluid, relation to cir- culation, 318 Cerebro- spinal nervous system, 532 et seq. See Brain, Spinal Cord, etc. Cerebrum, its structure, 591 chemical composition, 596 convolutions of, 591 et seq. crura of, 588 development, 776 distinctive character in man, 598 effects of injury, 607 removal, 607 electrical stimulation, 600 functions of, 606 gray matter, 594 in relation to speech, 603 other parts, 556 et seq. localization of functions, 600 structure, 594 et seq. unilateral action of, 609 weight, 597 white matter, 594 Chambers of the eye, 676 Characteristics of organic compounds, 103 Chemical composition of the human body, 103 Chest, 340 Cheyne- Stokes' breathing, 280 Chlorides in urine, estimation of, 803 Chlorine, 115 Chlorophyll, 17 Cholesterin, 347 Choletelin, 347 Chondrin, 53, 110 Chorda dorsalis, 743 Chorda t>-mpani, 299 et seq. Chordae tendinete. See Heart. Chorion, 750 Choroid coat of eye, 667 blood-vessels, 668 Choroidal fissure, 685 Chromatic aberration, 689 Chromophanes, 696 Chyle, 376 et seq. coagulation of, ib. Chvle-corpuscles, 376 Chvme, 371 CiHa, 33 Ciliary epithelium, 32 function of, 34 Ciliary motion, 34 nature of, ib. Ciliary muscles, 668 action of in adaptation to distances, 684 Ciliarj' processes, 668 Circulation of blood, 158 Circulation of blood — continued. action of heart, 159 brain, 316 capillaries, 310 course of, 158 et seq. discovery, 237 erectile structures, 218 forces regulating, 219 influence of respiration on, 275 peculiarities of, in different parts, 215 proofs, 237 pulmonary, 248 systemic, 159 in veins, 212 velocity of, 215 Circumvallate papillae, 304 Claustrum, 590 Clefts, visceral, 760 Clitoris, 718 development of, 790 Cloaca, 789 Clot or coagulum of blood. See Coag- ulation. Coagulation of blood, 119 absent or retarded, 126 conditions affecting, ib. theories of, 125 of chyle, 376 of lymph, ib. Coagulated proteids, 109 Coccygeal gland, 487 Cochlea of the ear, 650 office of, 659 Cohnheim's fields, 83 Cold-blooded animals, 489 Colloids, 367 Colostrum, 465 Color-blindness, 704 Colors, optical phenomena of, 703 et seq. Color sensations, 702 theories of, ib. Columnar epithelium, 31 Complemental air, 256 colors, 704 Conducting paths in cord, 543 Conjunctiva, 664 Connective tissues, 38 classification, 41 corpuscles of, 41 fibrous, ib. gelatinous, 44 general structure of, 38 retiform, 45 varieties, 41 Contraction of pupil, 685 Control centres, 571 Convolutions, cerebral, 591 et seq. Co-ordination of movements, 611 Cooking, effect of, 289 Copper, an accidental element in the body, 116 Corona radiata, 589 810 INDEX. Cord, spinal. See Spinal Cord. Corium, 412 Cornea, 665 coi"puscles, 666 nerves, ib. structure, 665 Corneo-scleral junction, 670 Corpora Arantii, 167 geniculata, 591, 620 quadrigemina, ib. their function, ib. striata, 590 their function, 615 Corpus callosum, 558 dentatuni of cerebellum, 591 of olivary body, 565 luteum. 738 of human female, 729 of mammalian animals, tb. of menstruation and pregnancy compared, 730 Cori3uscles of blood, 129. See Blood-cor- puscles. Corti's rods, 653 et seq. office of, 650 Cowper's glands, 731 Cranial nerves. See Cerebral nerves. Cranium, development of, 757 Crassamentum, 119 Crescents of Gianuzzi, 294. See Semi- lunes of Heidenhain. Crico-arytenoid muscles, 517 Cricoid cartilage, 515 Crossed pyramidal ti-act, 543 Crura cerebelli, 616 effect of dividing, 619 et seq. of irritating, ib. cerebri, 588 their office, 588 Crusta, 588 Crusta petrosa, 74 phlogistica, 120 Crystallin, 108 Crystalline lens, 669 in relation to vision at different dis- tances, 682 Crystalloids, 365 Cupped appearance of blood-clot, 121 Curdling ferments, 466 Currents of action, 438 ascending, 447 continuous, 428 descending, 447 induced, 430 muscle, 426 natural, ib. negative variation, 438 nerve, 448 polarizing, ib. rest, 426 Cuticle. See Epidermis, Epithelium. Cutis vera, 412 Cystic duct, 340 Cystin in urine, 402 Daltonism, 704 Dan i ell's battery, 428 Decidua, menstrualis, 728 reflexa, 753 serotina, ib. vera, ib. Decomposition, tendency of animal compounds to, 103 Decomposition-products, 104 Decussation of fibres in medulla ob- longata, 564 in spinal cord, 549 of optic nerves, 612 Defecation, mechanism of. 554 influence of spinal cord on, 554 Degeneration method, 542 Deglutition. See Swallowing. Dentine, 71 Depressor nerve, 234 Derived albuinins, 106 Derma, 412 Descemet's membrane, 666 Deutero-albumose, 319 Development, 734 of organs, 756 alimentary canal, 781 arteries, 768 blood-vessels, ib. brain, 775 capillaries, 768 cranium, 758 ear, 781 extremities, 762 eye, 778 face and visceral arches, 760 fibrous tissue, 45 heart, 763 liver, 783 lungs, 785 medulla oblongata, 776 muscle, 89 nerves, 774 nervous system, 774 nose, 781 organs of sense, 778 pancreas, 783 pituitarj' body, 759 respii-atory apparatus, 785 salivary glands, 783 spinal cord, 775 teeth, 74 vascular system, 763 veins, 770 vertebral column and cranium, 752 visceral arches and clefts, 760 of Wolffian bodies, urinary appara- tus and sexual organs, 786 Dextrin, 112 Dextrose, ib. Diabetes, 471 Diapedesis of blood -corpuscles, 212 I]S"DEX. 811 Diaphragm. See Inspiration, etc. Diastase of liver, 469 Diet, 506 e^seg. Digestion, 285 in the intestines, 353, 355. See Gas- tric fluid. Food, Stomach. Dilatation of pupil, 685 Diplopia. 706 Direct cerebellar tract, 543 . pyramidal tract, 543 Dorsal laminae, 743 Double hearing, 663 vision, 706 Dreams, 611 Drowning, cause of death in, 280 Ductless glands, 758 Ducts of Cuvier, 772 Ductus arteriosus, 774 venosus, 773 closure of, 774 Duverney's glands, 718 Dj^spnoea, 380 Ear, 646 bones or ossicles of, 647 function of, 657 development of, 781 external, 646 function of, 654 internal, 649 function of, 659 middle, 647 function of, 655 Egg-albumin, 106 Elastic cartilage, 51 fibres, 40 tissue, 42 Elastin, 41, 110 Electricity, in muscle, 425 nerve, 446 retina, 696 Electrotonus, 448 Elementary svibstances in the human body, 103 accidental, 116 Embryo, 734 et seq. See Development. Embryological method, 542 Embryonic shield, 740 Emmetropic eye, 687 Emotions, connection of, with cerebral hemispheres, 608 Emulsification, 338 Enamel of teeth, 73 Enamel organ, 74 , Enchj'lema, 9 End-bulbs, 98 End -plates, motorial, 88 Endocardiac pressure, 186 Endocardium, 165 Endolymph, 653 Endosmometer, 364 Endothelium, 37 distinctive characters, ib. Endothelium — continued. germinating, 39 Energy, daily amount expended in body, 510 Epencephalon, 777 Epiblast, 20, 739 Epidermis, 410 Epididymis, 719 Epiglottis, 341 structure, 341 Epithelial tissues, 26 Epithelium, ib. ciliated, 33 cogged, 36 columnar, 31 cylindrical, ib. glandular, ib. goblet-shaped, 31 simple, 27 spheroidal, 31 squamous or tessellated, 27 stratified, 35 ti'ansitional, ib. Erect position of objects, perception of, 696 Erectile structures, circulation in, 218 Erection, ib. cause of, ib. influence of muscular tissue in, ib. a reflex act, 555 Erythro-granulose, 297 Ery thro- dextrin, ib. Ethers, 794 Eustachian tube, 647 function of, 658 Excretion, 381 Exercise, effects of, on production of carbonic acid, 261 on temperature of body, 489 Expenditure of body, 509 et seq. Expiration, 253 influence of, on circulation, 278 mechanism of, 353 muscles concerned in, ib. relative duration of, 355 Expired air, properties of, 359 et seq. Extremities, development of, 763 Eye, 664 adaptation of vision at difi'erent dis- tances, 681 et seq. blood-vessels, 676 development of, 778 optical apparatus of, 677 refracting media of, 678 resemblance to camera, ib. Eyelids, 663 development of, 780 Eyes, simultaneous action of, in vision, 705 Face, development of, 761 Facial nerve, 579 effects of paralysis of, 580 812 INDEX. Facial nerve — continued. relation of, to expression, 581 Faeces, composition of, 359 quantity of, ib. Fallopian tubes, 716 Fasting, influence on secretion of bile, 503 Fat, See Adipose tissue. action of bile on, 348 of pancreatic secretion, 338 of small intestine on, 354 absorbed by lacteals, 377 formation of, 501 situations, where found, 46 uses of, 49 Fatty acids, 113, 795 Fechner's law, 693 Fehling's method for sugar in urine, 801 Female generative organs, 713 Fenestra ovalis, 649 rotunda, 650 Ferments, 356 Fibres of Muller, 676 Fibrils or filaments, 13 Fibrin, 109, 141 in chyle, 377 ferment, 125 formation of, 123 sources and properties of, 109 Fibrinogen, 122 et seq., 108 Fibrinoplastin, ib. Fibi-o-cartilage, 53 classification, ib. development, 53 white, 52 yellow, 51 Fibrous tissue, 41 white, ib. yellow, 43 development, 45 Fick's kymograph, 195 Field of vision, actual and ideal size of, 698 Fifth nerve. See Cerebral Nerves. Fillet, 605 Filtration, 403 Flesh, of animals, 285 Fluids, passage of, through membranes, 363 Fluoride of calcium, 115 Focal distance, 681 Foetus, circulation in, 772 communication with mother, 754 membranes, 747 et seq. Folds, head and tail, 744 Follicles, Graafian. See Graafian Ves- icles. Food, 385 classification of, ib. digestibility of articles of, 386 value dependent on, ib. improper, 504 Food — continued. of man, 506 too little, 501 too much, 505 vegetable, contains nitrogenous prin- ciples, 288 Foot-pound, 191 Foot- ton, ib. Forced movements, 620 Form of bodies, how estimated, 700 Formation of fat, 503 et seq. urinary solids, 475 Formic acid, 113 Fornix, 558 Fourth cranial nerve. See Cerebral nerves. Fovea centralis, 675 Fundus of eye, 693 Fundus of uterus, 717 Funiculus of Rolando, 563 Furfur aldehyde, 346 Fuscin, 696 Galactophorous ducts, 463 Galactose, 113 Gall-bladder, 344 structure, ib. Galvanometers, 424 Ganglia. See Nerve-centres. Ganglion, Gasserian, 623 Gases, 114 in bile, 348 in blood, 143 extraction from blood, ib. in stomach and intestines, 360 in urine, 391 Gastric glands, 313 Gastric juice, 315 acids in, 316 acid, test for, ib. action of, on nitrogenous food, 319 on non- nitrogenous food, ib. on saccharine and amyloid prin- ciples, ib. characters of, 315 composition of, 316 digestive power of, 317 experiments with, 317 pepsin of, 316 quantity of, 316 secretion of, 333 how excited, ib. influence of, nervous system on, 323 Gelatin, 109 as food, 505 action of gastric juice on, 319 action of pancreatic juice on, 338 Gelatinous substances, 109 Generation and development, 712 Generative organs of the female, 713 of the male, 718 Gerlach's network, 540 Germinal area, 737 epithelium, 713 INDEX. 813 Germinal membrane, spot, 3, 715 vesicle, ib. Giant cells, 54 Gland. See names of different. Gland, prostate, 724 Glisson's capsule, 342 Globulin, 108 distinctions from albumin, ib. Globus, major and minor, 720 development, 786 Glosso-pliaryngeal nerve, 272, 582 communications of, 583 motor filaments, 583 a nerve of common sensation and of taste, ib. Glottis, action of laryngeal muscles on, 517 forms assumed by, 522 narrowing of, proportioned to height of note, 523 respiratory movements of, 523 Glucose, 111, 112, 800 in liver, 468 test for, 113 Gluten in vegetables, 288 Glycerine. Ill, 338 Glycin, 345, 795 Glycocholic acid, 345 Glycogen, 19, 112 characters, 113 destination, 469 preparation, ib. quantity formed, ib. variation with diet, ib. Glycosuria, 470 artificial production of, ib. Gmelin's test, 347 Golgi, 101 Goll's column, 542 Graafian vesicles, 718 formation and development of, 718 et seq. i-elation of ovum to, ib. rupture of, changes following, 728 et seq. Granular layers of retina, 673 Grape-sugar. See Glucose. Gray matter of cerebellum, 562 of cerebrum, ib. of crura cerebri, ib. of medulla oblongata, ib. of pons Varolii, ib of spinal cord, 540 Groove, primitive, 740 Growth, 7 coincident with development, 8 of bone, 66 not peculiar to living beings, 8 Habitual movements, 609 Haematin, 149 hydrochlorate of, 150 Haemadvnamometer, 194 Haematoidin, 150 Hjematoporphyrin, 149 Haemin, 150 Ha?mochromogen, ib. Ha^mocytometer, 136 et seq. Haemoglobin, 144 et seq. action of gases on, 146 derivatives of, 149 distribution, 144 estimation of, 147 spectrum, 146 Hair-follicles, 415 their secretion, 471 Hairs, 415 structure of, ib. Hamulus, 653 Hassall. concentric corpuscles of, 481 Haversian canals. 56 Head -folds, 744 Hearing, anatomy of organ of, 646 double, 662 impaired by lesion of facial nerve, 580 influence of external ear on, 654 of labyrinth, 659 of middle ear, 665 physiology of, 654 See Sound, Vibrations, etc. Heart, 159 et seq. action of, 176 accelerated, 226 force of, 189 frequency of, ib. inhibited, 225 after removal, 221 rhj'thmic, 220 et seq. work of, 191 auricles of, 161, 168 See Auricles, capacity, 164 chambers, 161 chordae tendineae of. 166 columnae carnae of, ib. course of blood in, 159 development, 766 electrical phenomena, 231 endocardium, 165 force, 189 frog's, 331 ganglia of, ib. impulse of, 183 tracing by cardiograph, 184 et seq, influence of pneumogastric nerve 335 of sympathetic nerve, 326 investing sac, 159 metabolism, 331 muscular fibres of, 86, 164 musculi papillaries, 66 nervous connections with other or- gans, 337 rhythm, 330 nervous system, influence on, 32£ revolution of, 180 814 INDEX. Heart — contimied. rhythmical contractility, 320 situation, 159 sounds of, 181 causes, 181 structure of, 164 valves, 165 arterial or semilunar, 166 function of, 179 auriculo-ventricular, 164 function of, 177 ventricles, their action, 163 work of, 191 Heat, animal. See Temperature. influence of nervous system, 495 of various circumstances on, 494 et seq. losses by radiation, etc., 493 sources and modes of production, 490 Heat centres, 497 Heat-producing tissues, 491 Heat or rut, analogous to menstruation, ib. Height, relation to respiratory ca- pacity, 257 Helicotrema, 652 Helix of ear, 646 Hemispheres, Cerebral. See Cerebrum. Herbivorous animals, perception of odors by, 644 Hering's theory, 702 Hetero-albumose, 318 Hiccough, mechanism of, 267 Hippuric acid, 475 Horse's blood, peculiar coagulation of, 120 Hunger, sensation of, 628 Hyaloplasm, 9 Hybernation, state of thymus in, 482 Hydrobilirubin. 347 Hydrocarbons, 794 Hydrocele fluid, 122 Hydrogen, 114 Hydrolytic ferments, 799 Hymen, 718 Hypermetropia, 688 Hyperpnoea, 280 Hyperpyrexia, 489 Hypoblast, 20 Hypoglossal nerve, 587 Hypoxanthin, 400 ^ Ideas, connection of, with cerebrum, 606 Ileo-csecal valve, 334 Illusions, 629 Image, formation of, on retina, 680 Impulse of heart, 183 Income and output of energy, 509 Incus, 648 function of, 656 Indican, 399 Indigo, ib. Indol, 337 Induction coil, 429 current, ib. Infundibulum, 247 Inhibitory influence of pneumogastric nerve, 225 Inhibitory heat-centre, 498 Inogen, 451 Inorganic matter, distinction from or- ganized, 102 principles, 114 Inosite, 113 Insalivation, 291 Inspiration, 249 elastic resistance overcome by, ib. extraordinary^ 251 force employed in, 257 influence of, on circulation, 275 mechanism of, 249 Intercellular substance, 39 passage, 247 Intercostal muscles, action in inspira- tion, 251 et seq. in expiration, 252 Internal capsule, 589 Intestinal juice, 352, 355 Intestines, digestion in, gases, 360 large, digestion in, 355 movements, 357 small, changes of food in, 353 Inversive ferments, ib. Involuntary muscles, actions of, 446 structure of, 79 Iris, 668 action of, ib. et seq. in adaptation to distances, 686 development of, 780 Iron, 116 Irradiation, 690 Jacobson's nerve, 583 Jaw, interarticular cartilage, 291 Judgment, 637 Juice, gastric, 315 pancreatic, 336 Jumping, 446 Kaeyokinesis, 13 Karyomitosis, ib. Katabolic nerves, 627 Katelectrotonus, 448 Keratin, 111 Key, 428 Kidneys, their structure, 381 blood-vessels of, how distributed, 386 capillaries, of, ib development of, 785 function of. See Urine. Malpighian corpuscles of, 383 nerves, 389 tubules of, 382 et seq. Kreatin, 423, 796 INDEX. 815 Kreatinin, 423, 400, 796 Kymograph, 194 tracings, 195 spring-, 196 Labia, externa and interna, 718 Labyrinth of the ear. See Ear. Lachrymal apparatus, 664 gland, ib. Lacteals, 331 Lactic acid, 114 in gastric fluid, 316 Lactose, 112 LaBvulose, ib. Laminae dorsales, 742 ■viscerales or ventrales, 746 Lardacein, 109 Large intestine. See Intestine. Larynogscope, 519 Larynx, construction of, 240, 515 muscles of, 517 nerves of, 519 variations in according to sex and age, 524 vocal cords of, 515 Lateral plate, 743 Lateral ventricles, 558 Laughing, 269 Law of contraction, 449 Lead an accidental element, 116 Leaping, 446 Lecithin, 347 Lens, crj'.stalline, 669 Lenticular ganglion, relation of third nerve to, 573 nucleus, 590 Leucin, 337 Leucocytes. See Blood corpuscles (white) . Lieberkuhn's glands, 328 Lingual branch of fifth nei've, 578 Lips, influence of fifth nerve on move- ments of, 575 Liquor amnii, 749 Liquor sanguinis, or plasma, 117 Liver, 340 action of, on albuminous matters, 472 on saccharine matters, 468 blood-vessels of, 342 capillaries of, ib. cells of, 341 circulation in, 342 development of. 783 functions of, 153, 467 et seq. gh'cogenic function of, 468 secretion of. See Bile. structure of, 341 sugar formed by, 468 et seq. Loop of Henle, 384 Ludwig's air-pump, 142 Lungs, 244 blood -supply, 248 capillaries of, ib. Lungs — continued. cells of, 246 changes of air in, 259 changes of blood in, 264 circulation in, 248 contraction of, 253 coverings of, 245 development of, 785 lobes of, 246 lobules of, ib. lymphatics, 249 muscular tissue of, 245 nerves, 249 nutrition of, 248 position of, 244 structure of, 246 Luxus consumption, 504 Lymph, 376 compared with chyle, 377 with blood, ib. current of, 371 quantity formed, 377 Lymph-corpuscles, ib. Lymph-hearts, structure and action of, 372 relation of to spinal cord, ib. Lymphatic glands, 372 Lymphatic vessels, 367 absorption by, 378 arteries and veins of, 175 communication with serous cavities, 370 communication with blood-vessels, 368 course of fluid in, 371 distribution of, 367 origin of, 369 structure of, 371 et seq. valves of, 371 Lymphoid or retiform tissue, 44. See Adenoid Tissue. Macula germinativa, 715 Male sexual functions, 731 Malleus, 648 function of, 655 Malpighian bodies or corpuscles of kidney, 383. See Kidney, corpuscles of spleen, 478 et seq. Maltose, 112, 297 Mammary glands, 462 evolution, 463 involution, 464 lactation, ib. structure, 462 Mandibular arch, 761 Manganese, 116 Mastication, 291 centre, 291 fifth nerve supplies muscles of, 291 muscles of, ib. Mastoid cells, 647 Meatus of ear, 646 Medulla oblongata, 562 et seq. 816 INDEX. Medulla oblongata— cow^wMed. columns of, ib. conduction of impressions, 568 decussation of fibres, 5(54 effects of injury and disease of, 569 fibres of, how distributed, 563 functions of, 568 et seq. important to life, 569 nerve-centres in, ib. pyramids of, anterior, 563 posterior, ib. structure of, ib. Medullary folds, groove, ib. plate, ib. Meissner's plexus, 337 Melanin, 696 Membrana decidua, 753 granulosa, 714 development of into corpus luteum, 729 limitans externa, 674 interna, 672 Membrana propria or basement mem- brane. See Basement Membrane, tympani, 648 office of, 656 Membrane, blastodermic, 737 of the brain and spinal cord, 537 vitelline, 714 Membranes of brain, 537 Membranes, mucous. See Mucous mem- branes. Membranes, passage of fluids through. See Osmosis. Membranes, serous. See Serous mem- branes. Membranous labyrinth. See Ear. Memory relation to cerebral hemi- spheres, 606 et seq. Menstrual discharge, composition of, 727 Menstruation, 725 coincident with discharge of ova, ib. corpus luteum of, 730 time of appearance and cessation, 728 Mercurial manometer, 193 Mesencephalon, 777 Mesoblast, 20, 739 Mesocephalon, 777 Metencephalon, ib. Methaemoglobin, 147 Micro-organisms in intestines, 356 Micturition, 409 Milk, as food, 287 chemical composition, 466 properties of, ib. secretion, of 464 Milk-curdling ferments, 466, 799 Milk-globules, 465 Milk-teeth, 67 et seq. Millon's reagent and test, 105 Mind, cerebral hemisphere the organs of, 606 Modiolus, 650 Molars. See Teeth. Molecular base of Chyle. See Chyle. Molecular layers, 673, 674 Morphological development,. 20 Motor areas, 599 Motor impulses, transmission of in cord, 549 nerve- fibres, 531 laws of action of, ib. Moutli, changes of food in, 290 et seq. Movements, of eyes, 685 of intestines, 357 protoplasm, 4 Mucigen, 302 Mucin, 110 Mucous membrane, 456 basement membrane of, 457 epithelium-cells of, ib. See Epithe- lium. digestive tract, 456 gastro- pulmonary tract, ib. genitourinary tract, 457 gland -cells of, 457 of intestines, 458 of stomach, ib. of uterus, changes of in pregnancy, 752 respiratory tract, 456 Mucus, 457 Muller's fibres, 672 Murexide, 398 Muscle, 79 activity, 426 casket, 83 chemical constitution, 421 clot, 422 contractility, 426 contraction, mode of, 433 corpuscles, 83 curves, 434 development, 89 disc of Hensen, 83 elasticity, 423 electric currents in, 424 fatigue, 436 curves, ib. growth, 89 heart, 86 heat developed in contraction of, 436 involuntary, 446 actions of, 447 metabolism, 421 natural currents, 424 nerves of, 87 non-striated, 79 physiology of, 421 plain, 79 plasma, 421 reaction, 422 response to stimuli, 427 et seq INDEX. 817 Muscle — continued. rest of, 423 reticulum, 84 rigor, 440 sarcolemnia, 82 serum, 421 shape, changes in, 437 skeletal, 80 sound, developed in contraction of, 436 source of action of, 451 stimuli, 427 striated. 80 structure, ib. et seq. tetanus, 434 twitch, 433 unstriped, 79 voluntary, 80 actions of, 441 work of, 435 Muscular action, 426 conditions of, 438 force, 435 Muscular irritability, 427 duration of, after death, 441 Muscvilar motion, 426 et seq. sense, 636 Muscularis mucosas, 331 Musical sounds, 661 Myo-albumin, 422 Myograph, 431 pendulum, 432 Myo-haematin, 423 Myopia, or short-sight, 687 Myosin, 108, 422 ferment, 422 Myosinogen, 422 Nails, 416 growth of, 417 sti-ucture of, ib. Nasal cavities in relation to smell, 641 et seq. Native albumins, 106 Near point, 684 Nerve-centre, 533. See Cerebellum, Cerebrum, etc. ano- spinal, 554 automatic action, 570 cardio-inhibitory, ib. cilio-spinal, 570 deglutition, 569 diabetic, 571 erection, 555 gen i to -urinary, ib. mastication, 569 micturition, 554 muscular co-ordination, 611 reflection in, 533 laws and conditions of, 534 respiratory, 270 secretion of saliva, 299 sweat, 571 vaso-motor, 233 vesico-spinal, 554 52 Nerve-corpuscles, 96 et seq. caudate or stellate, ib. polar, ib. Nerves, 530 action of stimuli on, 447 currents of, 446 afferent, 531 axis-cylinder of, 91 cells, 96 centrifugal, 531 centripetal, ib. cerebrospinal, 532 classification, 89 conduction by, 530 et seq. rate of, 532 cranial. See Cerebral Nerves. efferent, 531 electrical currents of, 446 functions of, 530 funiculi of, 94 gray, 89, 92 impressions on, referred to pe- riphery 531 inhibitory. See Inhibitory Action. intercentral, 531 laws of conduction, 531 et seq. medullary sheath, 90 medullated, 89 neurilemma, 90 nodes of Ranvier, 92 non- medullated, 92 nuclei, 90 plexuses of, 95 primitive nerve sheath, 90 size of, 92 spinal. See Spinal Nerves. stimuli, 447 structure, 89 sympathetic. See Sympathetic nerve. terminations of, 95 central, ib. in cells, ib. in corpuscles of Golgi, 100 in corpuscles of Grandry, 101 in corpuscles of Herbst, 98 in end- bulbs, ib. in motorial end-plates, 88 in networks or plexuses, ib. in Pacinian corjiuscles, 97 in touch-corpuscles, 99 trophic, 626 varieties of, 89, 531 velocity of nerve force, 532 Nervous force, velocity of, ib. Nervous system, 530 cerebro-spinal, 532 development, 774 sympathetic, 621 Neural canal, 742 Neurenteric canal, 746 Neurilemma, 90 Neurin, 347 Neuroglia, 538 818 INDEX. Nitrogen, 114 in relation to food, 285 et seq. Nitrogenous compounds, 285 non- nitrogenous compounds, 288 Nitrogenous equilibrium, 503 Nitrogenous food, effects of, 502 Nodal point, 678 Nodes of Ranvier, 29 Nose. See Smell. development of, 781 Notochord, 742 Nuclein, HI Nucleoli, 2 Nucleus, 2, 11 et seq. division, 13 position, 11 staining of, ib. structure, 12 Nutrition, 499 Nymphse, 718 Odontoblasts, 76 Odors, 644 causes of, 641 et seq. different kinds of, 644 perception of, ib. varies in different classes, ib. relation to taste, 639 Oleaginous principles, digestion of. 111 Oleic acid. 111 Olfactory cells, 642 centre, 614 nerve, ib. subjective sensations of, 645 Olivary body, 565 fasciculus, ib. Omphalo-mesenteric arteries, 768 duct, 746 veins, 770 Oncograph, 404 Oncometer, ib. Ophthalmoscope, 693 Optic centres, 612 lobes, corpora quadrigemina, homo- logues of, 620 functions of, ib. nerve, decussation of, 612 thalamus, function of, 591, 615 vesicle, primary, 776 secondary, ib. Optical angle, 680 apparatus of eye, 677 Optogram, 695 Ora serrata of retina, 671 Organ of Corti, 653 Organic compounds in body, 103 instability of, ib. Organs of sense, development of, 778 Os uteri, 718 Osseous labyrinth, 649 Ossicles of the ear, 647 Ossification, 59 et seq. Osteoblasts, 59 v Osteoclasts, 63 Otoconia, or Otoliths, 651 Ovaries, 712 Graafian vesicles in, 713 Ovisacs, ib. Ovum, ib. action of seminal fluid on, 735 et seq. changes of, in ovary, 734 previous to formation of embryo, ib. subsequent to cleavage, 736 et seq. in uterus, 734 et seq. leaving of yolk, 736 connection of with uterus, 734 discharge of from ovary, ib. formation of, 715 germinal vesicle and spot of, 714 et seq. impregnation of, 735 structure of, 714 un impregnated, 734 Oviduct, or Fallopian tube, 716 Oxaluric acid, 400 Oxygen, 102 Pacinian bodies or corpuscles, 97, 336 Pain, 635 Pancreas, 334 development of, 783 functions of, 337 et seq. structure, 334 Pancreatic fluid, 336 Papillae, of the kidney, 382 of skin, distribution of, 412 of tongue, 304 Paraglobulin, 108, 123 Par vagum. See Pneumogastric nerve. Paraplasma, 9 Paraglobulin, 108 Partial pressui'e, 143 Parotid gland, saliva from, 298 nerves influencing secretion by, 301 Pars ciliaris retinae, 676 Patellar reflex, 51 Pavy's method, 801 Pelvis of the kidney, 382 Penis, 722 structure, ib. Pepsin, 316 Pepsinogen, 314 Peptic cells, 313 Peptones, 109 Perceptions, 630 Perfusion canula, 229 Pericardium, 159 Perilj'mph, or fluid of labyrinth of ear, 649 Peripheral resistance, 192, 232 Peristaltic movements of intestines, 357 of stomach, 320 Permanent teeth. See Teeth. INDEX. 819 Perspiration, cutaneous, 417 insensible and sensible, ib. ordinary constituents of, ib. Pettenkofer's test, 346 Peyer's glands, 329 patches, ib. structure of, 330 Pflliger's law, 449 Phagocj^tosis, 134 Phakoscope, 683 Pharj;nx, 306 action of in swallowing, ib. influence of glosso-pharyngeal nerve on, ib. of pneumogastric nerve on, ib. Phenol, 114, 337 Phenomena of life, 1 Phosphates, 115 Phosphates, estimation of in urine, 804 Phosphorus in the human body, ib. Phrenograph, 254 Pigment cells of retina, 675 Pineal gland, 486 Piotrowski's reaction, 104 Pituitary body, 486 development, 759 Placenta, 752 foetal and maternal, ib. Plasma of blood, 137 salts of, 139 Plasm ine, 122 composition, ib. nature of, ib. Plethysmograph, 232 Pleura, 245 Pleuro- peritoneal cavity, 743 Plexus, terminal, 101 Pneumogastric nerve, 583 distribution of, ib. influence on action of heart, 225 deglutition, 584 gastric digestion, ib. larynx, ib. lungs, ib. oesophagus, ib. pharynx, 584 respiration, 271 mixed function of, 584 origin from medulla oblongata, 583 Pneumograph. 24 Polar ceil, 734 Pons Varolii, its structure, 587 functions, ib. Portal blood. See Liver. Potassium, 116 sulphocyanate, 296 Pregnancy, absence of menstruation during, 726 et seq. corpus luteum of, 729 Presbyopia, 690 Pressor nerves, 234 Primitive groove, 740 streak, ib. Primitive nerve-sheath, or Schwann's sheath, 90 Pro-nucleus, female, 735 male, ib. Propionic acid, 113 Prosencephalon, 776 Prostate gland, 724 Proteids, 103 chemical properties, 103 et seq. physical properties, ib. tests for, ib. varieties of, ib. Proteoses, 109, 318 Proto-albumose, 318 Protoplasm, 1 chemical characters, 3 movement, 4 physical characters, 3 et seq. physiological characters, ib. repi'oduction, 8 structure of cells, 9 Proloplasma, ib. Proto- vertebrae, 744 Pseudoscope, 711 Pseud o-stomata, 30 Ptyalin, 296 action of, ib. Puberty, changes at period of, 728 indicated by menstruation, ib. Pulmonary artery, valves of heart, 166 Pulse, arterial, 192 et seq. Pui-kinje's figures, 691 Pyramidal tracts, 543 et seq. Pyramids of medulla oblongata, 563 Quantity of air breathed, 256 blood, 118 et seq. saliva, 296 Eami viscerales, 623 efl'erentes, ib. communicantes, ib. Recurrent sensibility, 546 Reflex actions, 533 augmentation, 535 conditions necessary to, 534 cutaneous, 551 inhibition of, 535 irregular in disease, 553 laws of, 534 morbid, 553 muscle, 551 of medulla oblongata, 568 et seq. of spinal cord, 550 purposive in health, 533 Refracting media of eye. 678 Refraction, laws of, ib. Regions of body. See Frontispiece. Relations of different parts of brain, 556 Remak, 2 820 INDEX. Remak's ganglia, 222 Rennin, 319, 338, 799 Requisites of diet, 506 Reserve air, 256 Residual air, ib. Respiration, 239 abdominal type, 253 changes of air, 259 of blood, 264 of the tissues, 265 costal type, 252 foi'ce, 257 frequency, 257 influence of nervous system, 269 mechanism, 249 et seq. movements, 249 methods of recording, 253 nitrogen in relation thei-eto, 262 ■organic matter excreted, 263 quantity of air changed, 256 relation to the pulse, 257 suspension and arrest, 291 et seq. types of, 252 Hespiratory acts, special, 266 apparatus, 239 capacity of chest, 257 cells, 246 movements, 249 axes of rotation, 250 et seq. of glottis, '255 influence on amount of carbonic acid, 260 on arterial tension, 275 et seq. rate, 257 relation to pulse rate, ib. size of animal, ib. relation to will, 269 et seq various mechanism, 266 muscles, 249 et seq. daily work, 258 power of, ib. nerve-centre, 269 rhythm, 255 sounds, ib. Restiform bodies, 565 et seq. Retiform or adenoid, or lymphoid tis- sue, 44 Heticulum, 9 Retina, 671 blind spot. 691 blood-vessels, 676 duration of impression on, 692 of after-sensations, ib. excitation of, 691 focal distance of, 681 fovea centralis, 671 functions of, 691 image on, how formed distinctly, 680 inversion of, how corrected, 696 insensible at entrance of optic nerve, 691 layers, 671 in quadrupeds, 708 Retina — continued. reciprocal action of parts of, 704 in relation to direction of visioi', 691 to motion of bodies, 699 to single vision, 705 to size of field of vision, 697 structure of, 671 visual purple, 695 Rheoscopic frog, 446 Rhinencephalon, 776 Rigor mortis, 440 affects all classes of muscles, 440 phenomena and causes of, ib. Ritter's tetanus, 450 Rods and cones, 674 Rolandic area, 604 Rotatory movements, 620 Running, mechanism of, 446 Rut or heat, 725 Saccharine principles of food, diges- tion of, 288 Saccharoses, 112 Sacculus, 651 Saliva, 295 composition, ib. process of secretion, 301 quantity, 296 rate of secretion, ib. uses, ib. Salivary glands, 292 develoimient of, 783 influence of nervous system, 298 mixed, 294 nerves, ib. secretion, 295 structure, 292 true, 293 varieties, ib. Sanson's images, 683 Saponification, 338 Sarcode, 2. See Protoplasm. Sarcosin, 473, 796 Scheiner's experiment, 684 Schematic eye, 680 Schiff's test, 398 Schneiderian membrane, 641 Sclerotic, 664 Sebaceous glands, 414 their secretion, 417 Secreting glands, 453, 458 aggregated, ib. convoluted tubular, ib. tubular or simple, ib. Secreting membranes. See Mucous and Serous membranes. Secretion, 453 apparatus necessary for, 458 et seq. changes in gland-cells during, 460 circumstances influencing, 461 discharge of, ib. influence of nervous system, 461 of urine, 406 INDEX. 831 Secretion — con tin ned. process of physical and chemical, 460 Segmentation of cells, 736 in chick, 737 ovum, ib. Semen, 731 composition of, 733 filaments or spermatozoa, 731 tubes. 720 Semicircular canals of ear, 650 development of, 781 et seq. use of, 659 Semilunar valves. See Heart valves. Semilunes of Heidenhain, 294. Sensation, 628 color, 702 common, 628 conditions necessaiy to, ib. excited b}' mind, ib. by internal causes, ib. of motion, 636 nerves of, 546 of pain, 635 of pressure, 631 special, 629 nerves of, 571 stimuli of, 531 of special, ib. subjective, 632. See also Special Senses. tactile, 631 temperature, 634 tickling, 628 touch, 631 of weight, 636 Senses, special, 628 organs of, development of, 778 Sensorium, 629 Sensory centres in cerebral cortex, 612 Sensorj' impressions, conduction of, 548 b}' spinal cord, ib. in brain, 606 nerves, 548 Serine, 139 Serous membranes, 454 arrangement of, ib. communication of lymphatics with, 454 fluid secreted by, ib. functions, ib. lining joints, etc. , 454 et seq. visceral cavities, ib. structure of, 454 Serum, of blood, 139 albumin, 106 separation of, 139 Seventh cerebral nerve. See Cerebral nerves. Sexual organs and functions in the female, 712 in the male, 718 Sighing, mechanism of, 267 Sight, 663. See Vision. Silica, parts in which found, 116 Silicon, ib. Sinuses of dura mater, 217 et seq. of Valsalva, 167 Sixth cerebral nerve, 579 Size of field of vision, 698 Skatol, 337 Skeleton. See Frontispiece. Skin, 410 absorption by, 379 of metallic substances, ib. of water, ib. , cutis vera of, 412 epidermis of, 410 evaporation from, 493 excretion by, 417 exhalation of carbonic acid from, 419 of watery vapor from, ib. functions of, 417 papilla? of, 412 perspiration of, 417 rete mucosum of, 410 sebaceous glands of, 414 structure of, ib. sudoriferous glands of, 413 Sleep, 610 Small intestine, 326 Smell, sense of, 641 conditions of, ib. different kinds of odors, 644 impaired by lesion of facial nerve, 581 impaired by lesion of fifth nerve, 578 internal excitants of, 645 limited to olfactory i-egion, 641 structure of organ of. ib. subjective sensations, 644 varies in difl'erent animals, ib. Sneezing, centre, 570 mechanism of, 268 Sniffing, mechanism, of, 268 smell aided by, 642 Soaps, 794 Sobbing, 269 Sodium, 115 Solitary glands. See Pej^er's. Soluble ferments, 355 Somatopleure, 743 Somnambulism, 611 Sonorous vibrations, how communi- cated in ear, 654 et seq. in air and in water, ib. See Sound. Sound, binaural sensations, 662 conduction of by ear, 654 heart, 181 movements and sensations produced by, 663 perception, of direction of, 661 of distance of, 662 822 INDEX. Sound — continued. permanence of sensation of, ib. production of, 661 subjective, 663 Source of water, 114 Spaces of Fontana, 670 Spasms, reflex acts, 534 centre, 571 Speaking, 268 mechanism of, 527 Special senses, 631 Speech, 527 Spermatozoa, development of, 731 form and structure of, ib. function of, 735 motion of, 731 Spherical aberration, 688 correction of, ib. Sphincter ani. See Defsecation. vesicae, 390 Sphygmograph, 202 tracings, 203 et seq. Sphygmometer, 204 Spinal accessory nerve, 586 Sijinal cord, 537 automatism, 535 canal of, 537 centres in, 553 a collection of nervous centres, ib. columns of, 538 commissures of, ib. conduction of impressions by, 546 et seq. course of fibres in, 543 development of, 775 fissures and fui'rows of, 537 functions of; 546 of columns, 543 influence on lymph-hearts, 555 on sphincter ani, 554 on tone, 555 morbid irritability of, 553 nerves of, 544 reflex action of, 550 inhibition of, 552 special centres in, 553 structure of, 537 et seq. tracts, 543 weight, 598 relative, ib. white matter, 537 gray matter, 540 Spinal nerves, 544 origin of, 544 et seq. physiology of, 546 Spindle, 15 Spirem, 14 Spirometer, 256 Splanchnopleure, 743 Spleen, 477 functions, 479 hilus of, 477 influence of nervous system, 480 Malpighian corpuscles of, 478 Spleen — continued. pulp, 477 et seq. stroma of, ib. structure of, ib. trabecular of, 477 et seq. Spongioplasm, 9 Spontaneous movement, 4 Spot, germinal, 715 Stannius' experiments, 233 Stapes, 648 Starch, 17 digestion of, in mouth, 290 Starvation, 501 et seq. Steapsin, 339 Stearic acid. 111 Stearin, ib. Stercorin, 551 allied to cholesterin, ib. Stereoscope, 700 Stethograph, 254 Stethometer, ib. Stimuli, protoplasmic, 6 St. Martin, Alexis, case of, 315 Stomach, 310 blood-vessels, 314 development, 782 et seq. digestion in, 317 circumstances favoring, 319 products of, 318 digestion after death, 323 glands. 312 lymphatics, 314 movements, 320 influence of nervous system, 322 mucous membrane, 311 muscular coat, 311 nerves, 314 secretion of. See Gastric fluid. structure, 310 temperature, 319 Stomata, 29 Stratum intermedium (Hannover), 77 Striated muscle. See Muscle. Stroma-fibrin, 121 Stromuhr, 214 Structure of cells, 9 Submaxillary gland, 294 et seq. Substantia nigra, 389 Succus entericus, 352 functions of, 352 Sucking, mechanism of, 269 centre, 570 Sudoriferous glands. -See Skin. Sugar. See Glucose. estimation of, 801 et seq. Sulphates, 116 in tissues, ib. in urine, 400 Sulphuretted hydrogen, 357 Superior laryngeal nerve, 271 Suprarenal capsules, 484 development of, 787 disease of, relation to discoloration of skin, 486 IXDEX. 823 Suprarenal capsules — continued. structure, 484 Swallowing, 809 centre, 310 nerves engaged, ih. Sweat, 417 Sympathetic nervous system, 621 distribution, ih. divisions of, ib. fibres, differences of from cerebro- spinal fibres, 624 functions, 624 et seq. ganglia of, 623 action of, 624 et seq. structure, 623 in substance of organs, 621 heart, 226 structure of, 626 Synovial fluid, secretion of, 455 membranes, 454 Svstemic circulation. See Circulation. vessels, ib. Systole of heart, 176 Table of diet, 507 Taste, 638 after- tastes, 640 centre, 614 conditions for perception of, 638 connection with smell, 639 impaired by injury of facial nerve, 580 of fifth nerve, 583 nerves of, ib. seat of, 638 subjective sensations, 640 varieties. 639 Taste -goblets, 306 Tauriu. 345 Taurocholic acid, ib. Teeth, 67 development, 74 eruption, times of, 68 structure of, 70 et seq. temporary and permanent, 68 et seq. Tegmentum, 588 Temperature, 488 average of body, ib. changes of, effects of, 488 et seq. circumstances modifying, 492 of cold-blooded and warm-blooded animals, 489 in disease, ib. loss of, 492 maintenance of, 490 of Mammalia, Birds, etc., 489 regulation of, 492 sensation of variation of. 634. See Heat. Temporo-maxillary fibro-cartilage, 291 Tendon-reflex, 551 Tension, arterial, 191 of gases in lungs, 264 Tensor choroideaj, 683 Tensor tympaui muscle, 648 office of, ib. Testicle, 719 development, 788 descent of, ib. structure of, 719 et seq. Tetanus, 434 Thalamencephalon, 776 Thalami optici, function of, 615 Thermogenesis, 491 et seq. Thermogenic nerves and nerve-centres, 496 Thirst, 628 Thoracic duct, 368 Thymus gland, 480 function of, 482 structure, 481 Thvro-arytenoid muscles, 518 Thyroid-gland, 483 function of, 484 structure, 483 Timbre of voice, 524 Tone of blood-vessels, 233 of muscles, 555 of voice, 524 Tongue, 303 action of in deglutition, 309 epithelium of, 305 papilla? of, 304 parts most sensitive to taste, 639 structure of, 303 Tonic centres, 571 Tonometer. 230 Tonsils, 307 Touch, 631 after sensation, 634 conditions for perfection of, 631 connection of with muscular sense, 636 co-operation of mind with, 637 hand an organ of, 632 illusions, 633 modifications of, 631 special organs, 632 subjective sensations, 634 the tongue an organ of, 638 various degrees of in different parts, 632 Touch -corpuscles, 632 Trachea, 242 Tracts in the spinal cord, 543 Traube-Hering's curves, 280 Tricuspid valve, 165 Trigeminal or fifth nerve, 574 Trommer's test, 297 Trophic nerves, 578 Trypsin. 336 Tubes, Fallopian. See Fallopian tubes. Tubuli seminiferi, 720 uniferi, 382 et seq. Tunica albuginea of testicle, 716 Tympanum or middle ear, 647 development of, 781 functions of, 656 824 INDEX. Tympanum or middle ear — continued. membrane of, 647 structure of, ib. use of air in, 655 Types of respiration, 249 Tyrosin, 337 Ulceration of parts attending inju- ries of nerves, 578 Umbilical arteries, 773 cord, ib. vesicle, 746 Unicellular organisms, 1 Unorganized ferments, 317 Unstriped muscular fibre, 79 development, 89 distribution, 79 structure, ib. Urate of ammonium, 397 of sodium, ib. Urea, 393 apparatus for estimating quantity, 802 chemical composition of, 393 identical with cyanate of ammo- nium, lb., 395 properties, 394 quantity, 392 in relation to muscular exertion, 473 sources, 471 Ureter, 389 Uric acid, 396 condition in which it exists in urine, 397 forms in which it is deposited, 396 proportionate quantity of, 397 source of, 397 tests, 397 variations in quantity, 397 Urina sanguinis, potus, et cibi, 393 Urinary bladder, 390 development, 789 nerves, 390 structure, 390 Urinary ferments, 391 Urine, 390 abnormal, 393 analysis of, 391 chemical composition, ib. coloring matter of, 398 cyst in in, 402 decomposition by mucus, 400 effect of blood -pressure on, 408 expulsion, 409 extractives, 400 flow of into bladder, 409 gases. 403 hippuric acid in, 398 mucus in, 400 oxalic acid in, 402 physical characters, 390 pigments, 398 quantity of chief constituents, 392 Urine — con tinned. reaction of, 391 in different animals, ib. made alkaline by diet, 391 saline matter, 400 secretion, 403 rate of, ib. solids, 392 variations of, ib. specific gravity of, 392 variations of, ib. urates, 397 urea, 393 uric acid in, 396 variations of specific gravity, 392 of water, 392 Urobilin, 398 Urochrome, ib. Uroerythrin, 399 Uromelanin, ib. Uterus, 717 change of mucous membrane of, 752 et seq. development of in pregnancy, ib. follicular glands of, 752 structure, 717 Vagina, structure of, 718 Vagus nerve. See Pneumogastric. Valves of heart, 165. See Heart valves. Valvulse conniventes, 327 Vas deferens, 719 Vasa effereutia of testicle, 720, 788 recta of testicle, ib. Vascular area, 763 Vascular glands, 476 in relation to blood, 487 several offices, of, ib. Vascular system, development of, 763 Vaso-constrictor nerves, 236 Vaso-dilator nerves, ib. Vaso-motor nerves, 233 effect of section, 233 ef seq. influence upon blood-pressure, 236 Vasomotor nerve-centres, ib., 283 reflection, 285 Vegetables and animals, distinctions between, 15 Veins, 173 circulation in, 215 et seq. rate of, 215 cardinal, 770 collateral circulation in, 175 development, 770 distribution, 178 influence of gravitation in, 212 parietal system of, 771 et seq. pressure in, 197 rhythmical action in, 218 structure of, 178 umbilical, 772 valves of, 174 velocity of blood in, 215 visceral system of, 771 et seq. IXDEX. 825 Velocih' of blood in arteries, 213 in capillaries, 215 in veins, ib. of circulation, 213 of nervous force, 533 conditions modifying, ib. Venae hepaticae advehentes, 771 i-evehentes, ib. Ventricles of heart. See Heart. Vertebra?, development of, 757 Vertebral plate, 743 Vesicle, germinal, 715 Vesicula germinativa, ib. Vesicular semiuales, 721 structure, ib. A^'ibrations, conveyance of to auditory nerve, 655 et seq. Villi in chorion, 751 in placenta, 755 of intestines, 330 Visceral arches, development of, 760 connection with cranial nerves, 762 laminje or plates, 746 Visceral plates, ib. Viscero- inhibitory nerves, 625 motor, ib. Vision, 663 angle of, 680 at different distances, adaptation of eye to, 681 et seq. centre, 612 corpora quadrigemina, tlie principal nerve-centres of, 620 correction of aberration, 688 et seq. of inversion of image, 696 defects of, 686 et seq. distinctness of, how secured, 681 et seq. duration of sensation in, 692 estimation of the form of objects, 700 of their dii'ection, ib. of their motion, 701 of their size, 699 field of. size of, 698 focal distance of, 681 impaired by lesion of fifth nerve, 578 influence of attention on, 701 purple, 695 single, with two eyes, 705 et seq. Visual directioD, 700 Vitellin, 109 Vitelline duct, 783 Vitelline membrane, 714 spheres, ib. Vitreous humor, 676 Vocal cords, 515 et seq. action of in respiratory actions, 522 approximation of, effect on height of note, 523 vibrations of, cause voice, 515 Voice, 514 et seq. Vomiting, 325 action of stomach in, 325 centre, 326 nerve-actions in, 326, 570 voluntary and acquired, ib. V'owels and consonants, 527 Vulvo- vaginal or Duverney's glands, 718 Walking, 443 Wallerian method, 542 Water, 114 forms large part of human body. 114 Wave of blood causing the pulse, 202 velocity of, ib. Wharton's jelly, 44 White corpuscles. See Blood-corpus- cles, white ; and Lymph-corpuscles. White fibro-cartilage. See Fibro-car- tilage. white, fibrous tissue, 41 Willis, circle of, 217 Wolffian bodies, 786 et seq. Wooldridge, 126 Work of heart, 191 Xanthin, 475 Xantho-proteic reaction, 104 Yawning, 269 Yellow elastic fibre, 40 fibro-cartilage, 51 spot of Sommering, 671 Yolk, or vitellus, 715 changes of, in Fallopian tube, 736 cleaving of, ib. constriction of, by ventral laminas, 746 Yolk-sac, 746 et seq. Young-Helmholtz theory. 702 ZiMMERMANN, corpuscles of, 483 Zona pellncida, 714 Zonule of Zinn. 676 Zymogen, 336 -IK'S'"'' "W .;'!■ .-^ id