LIBRARY OF THK UNIVERSITY OF CALIFORNIA Received.... Accessions mi r>fiY LIBRARY Shelf No. SAMUEL CARSON & CO, Booksellers and Stationers A MANUAL OF PHYSIOLOGY YEO. A NEW SERIES OF MANUALS FOR MEDICAL STUDENTS. Price of each Book, Cloth, $3.00 ; Leather, $3.50. No. i. WALSHAM. PRACTICAL SURGERY. A Manual for Stu- dents and Physicians. By WM. J. WALSHAM, M.D., Assistant Surgeon to, and Demonstrator of Surgery in, St. Bartholomew's Hospital ; Surgeon to Metropolitan Free Hospital, London, etc. Thoroughly Illustrated. No. 2. WINCKEL'S DISEASES OF WOMEN. By Parvin. A new Enlarged Edition. By Dr. F. WINCKEL, Professor of Gynaecology, etc., Royal University of Munich. The Translation Edited byTHEOPHi- LUS PARVIN, M.D., Professor of Obstetrics and Diseases of Women and Children, Jefferson Medical College, Philadelphia. 132 Engravings. No. 3. GALABIN'S MIDWIFERY. By ALFRED LEWIS GALABIN, M.A., M.D., Obstetric Physician to, and Lecturer on Midwifery and the Diseases of Women at, Guy's Hospital, London, etc. 227 fine Engrav- ings. No. 4. YEO'S PHYSIOLOGY. Fourth Edition. By GERALD F. YEO, M.D., F.R.S.C., Professor of Physiology in King's College, London. Re- vised. 321 carefully printed Illustrations. No. 5. RICHTER'S ORGANIC CHEMISTRY. By Prof. VICTOR VON RICHTER, University of Breslau. Translated from Fourth German Edition by EDGAR F. SMITH, M.A., PH.D., Professor of Chemistry, Uni- versity of Pennsylvania, etc. Illustrated. No. 6. GOODHART AND STARR ON CHILDREN. By J. F. GOODHART, M.D., Physician to the Evelina Hospital for Children ; Assist- ant Physician, Guy's Hospital, London. American Edition. Revised and Edited by Louis STARR, M.D., Clinical Professor of Diseases ot Children in the Hospital of the' University of Pennsylvania ; Physician to the Children's Hospital, Philadelphia. 50 Formulae, and directions for preparing Artificial Human Milk, for the Artificial Digestion of Milk, etc. No. 7. WARING. PRACTICAL THERAPEUTICS. Fourth Edi- tion. With an Index of Diseases. By ED. JOHN WARING, M.D., F.R.C.P. Rewritten and Revised. Edited by DUDLEY W. BUXTON, Assistant to the Professor of Medicine, University College Hospital, London. No. 8. REESE. MEDICAL JURISPRUDENCE AND TOXI- COLOGY. Second Edition. Revised. By JOHN J. REESE, M.D., Professor of Medical Jurisprudence and Toxicology, University of Penn- sylvania, etc. *** Other volumes in Preparation. Complete Catalogues sent free, upon application. Price of each Book, Cloth, $3.00 ; Leather, $3.50. P. BLAKISTON, SON & CO., Medical Publishers & Booksellers, loia Walnut Street, Philadelphia. A MANUAL OF PHYSIOLOGY GERALD F. YEO, M.D.DuBL., F.R.C.S., PROFESSOR OF PHYSIOLOGY IN KING'S COLLEGE, LONDON, ETC. FOURTH AMERICAN FROM THE SECOND ENGLISH EDITION. WITH THREE HUNDRED AND TWENTY-ONE ILLUSTRA- TIONS AND A GLOSSARY. 0^ PHILADELPHIA : P. BLAKISTON, SON & CO., 1012 WALNUT STREET. 1889. BIOLOGY LIBRARY G PRESS OF WM. F. FELL * CO., 1220-24 SANSOM STREET, PHILADELPHIA. PREFACE TO THE SECOND EDITION. IN preparing this edition, I have done my utmost to correct inaccuracies and remove obscurities. The changes rendered necessary by recent research have also been made. Some parts have been rewritten ; notably the chapters on the Central Nervous System, to which additional illustrations have been added. The general arrangement remains the same as that of the First Edition. I am again deeply indebted to my friend, Mr. E. F. Herroun, for much valuable assistance. * KING'S COLLEGE, LONDON. PREFACE TO THE FIRST EDITION. THE present volume has been written at the desire on the part of the Publishers that a new elementary treatise on Physiology should be added to the series of admirable students' manuals which they had previously issued. In carrying this desire into execution, I have endeavored to avoid theories which have not borne the test of time, and such details of methods as are unnecessary for junior students. I do not give any history of how our knowledge has grown to its present standpoint ; nor do I mention the names of the authori- ties upon whose writings my statements depend. I have also omitted the mention of exceptional points, because I find that exceptions are more easily remembered than the main facts from which they differ ; and, since we must often be content with the retention of the one or the other, I have tried to insure that it shall be the more important. While endeavoring to save the student from doubtful and erroneous doctrines, I have taken great care not to omit any important facts that are necessary to his acquirement of as clear an idea as possible of the principles of Physiology. I have not hesitated to lay unwonted stress upon those points which many years' practical experience as a teacher and an ex- aminer has shown me are difficult to grasp and are commonly misunderstood ; and I have treated such subjects as are useful in the practice of medicine and surgery more fully than those which are essential only to abstract physiological knowledge. vii Vlll PREFACE TO THE FIRST EDITION. As medical students are generally obliged to commence the study of Physiology without any anatomical knowledge, I believe it to be absolutely necessary that their first physiological book should contain some account of the structure and relationships of the organs the functions of which they are about to study. I have, therefore, added a short account of the construction of the various parts discussed in each chapter ; it has, however, been found necessary to curtail this anatomical portion to a mere introductory sketch. Numerous illustrations, with full descrip- tions attached to each, are introduced to supplement the explana- tion given in the text. So far as is consistent with an accurate treatment of the sub- ject, I have avoided technical terms and scientific modes of expression. I know that in attempting to explain physiological truths in every-day language and in a plain, common-sense way, I run the risk of appearing to lack the precision that such a subject demands ; but after mature consideration I have come to the conclusion that great scientific nicety and a scholastic style of expression have a deterrent effect upon the beginner's industry ; and I think it is better that he should acquire the first principles of the science in homely language, than pick up tech- nical odds and ends in learned terms the meaning of which he does not comprehend. As many words strange to the first year's student have to be used, and must be learned, it has been thought advisable to add a short glossary, containing an explanation of the most ordinary physiological expressions. Great difficulty is always found in fixing upon a starting point at which to begin the study of Physiology. To begin with the circulation of the blood, which is so essential for the life of every tissue, one should have some knowledge of nerve and PREFACE TO THE FIRST EDITION. ix muscle. To begin with nerves and muscles, the mechanisms and the uses of the blood current should be understood ; and so on, throughout the various systems, which are so inter-dependent that, for the thorough comprehension of any one, a knowledge of all is required. I have, therefore, adopted the time-honored plan of commenc- ing with the vegetative systems and following the course of the aliments to their destination and final application, as I believe this arrangement is open to as few objections as any other known to me. I wish here to express my most cordial thanks to many friends who have aided me with kind assistance and advice. I am deep- ly indebted to Mr. Tyrrell Brooks for the great help he afforded me by compiling the chapters on Development ; and I feel I cannot sufficiently thank Mr. E. F. Herroun for his untiring and valuable assistance in the revision of the proof sheets. To Mr. G. Hanlon I am indebted for the careful and skillful manner in which he has executed the new wood-cuts, most of which he had to copy from rough drawings. KING'S COLLEGE, LONDON. CONTENTS. CHAPTER I. THE OBJECTS OF PHYSIOLOGY. PAGE Introductory Definitions, 25 Structural and Physical Properties of Organisms, 29 Chemical Composition, 29 Vital Phenomena, 3 2 CHAPTER II. GENERAL VIEW OF THE STRUCTURE OF ANIMAL ORGANISMS. Cells, 33 Protoplasm, Nucleus, 35 Cell Wall, 3 6 Cell Contents, 3 6 Varieties of Cells, 3 8 Modifications of Original Cell Tissues, 3^ I. Epithelial Tissues, 43 II. Nerve Tissues, 46 III. Muscle or Contractile Tissues, 5 IV. Connective Tissues, 5 2 CHAPTER III. CHEMICAL BASIS OF THE BODY. Elements in the Body, 62 Classification of Ingredients found in the Tissues, 64 Plasmata, 64 Albuminous Bodies, 66 Classification of Albumins, 68 Albuminoids, 7 1 Products of Tissue Change, 73 Carbohydrates, 77 Fats, 78 Inorganic Bodies, . 79 xi XI 1 CONTENTS. CHAPTER IV. THE VITAL CHARACTERS OF ORGANISMS. PAGE Protoplasmic Movements, 82 Reproduction, 85 Bacteria, 88 Amoeba, 9 1 Paramoecium, . . . .* 93 CHAPTER V. NUTRITION AND FOOD STUFFS. Classification of Foods, 98 Composition of Special Forms of Food, 102 Milk, 102 Cheese, Meat, Eggs, etc., 105 Vegetables, 107 CHAPTER VI. THE MECHANISM OF DIGESTION. Mastication, 112 Deglutition, 113 Nervous Mechanism of Deglutition, 118 Vomiting, 121 Movements of the Intestines, 123 Defecation, 125 Nervous Mechanism of the Intestinal Motion, 128 CHAPTER VII. MOUTH DIGESTION. Salivary and Mucous Glands, 131 Characters of Mixed Saliva, 134 Nervous Mechanism of Secretion of Saliva, 136 Changes in the Gland Cells, 144 Functions of the Saliva, - 146 CHAPTER VIII. THE STOMACH DIGESTION. The Gastric Glands, 148 The Characters of Gastric Juice, 150 Mode of Secretion of Gastric Juice, 152 Action of the Gastric Juice, 154 CONTENTS. XI 11 CHAPTER IX. PANCREATIC JUICE. PAGE Structure of the Pancreas, 1 60 Characters and Mode of Secretion of Pancreatic Juice, 161 Changes in the Gland Cells, 162 Action of Pancreatic Juice on Proteids, 165 Action on Fats, 166 Action on Starch, 167 CHAPTER X. BILE. Functions of the Liver, 168 Structure of the Liver, 169 Method of Obtaining Bile, 174 Composition of Bile, 175 Method of Secretion of Bile, 178 Functions of the Bile, . 180 CHAPTER XI. FUNCTIONS OF THE INTESTINAL Mucous MEMBRANE. Structure of the Small Intestine, ' 182 Method of Obtaining Intestinal Secretion, 184 Character and Functions of the Intestinal Juice, 185 Functions of the Large Intestine, < 187 Putrefactive Fermentations in the Intestine, 188 CHAPTER XII. ABSORPTION. Interstitial Absorption, 190 The Lymphatic System ' ' . . . 191 Structure of Lymphatic Glands, 194 Intestinal Absorption, 199 Mechanism of Absorption, 203 Materials Absorbed, 205 Lymph and Chyle, 208 Movement of the Lymph, 211 CHAPTER XIII. THE CONSTITUTION OF THE BLOOD AND THE BLOOD PLASMA. General Characteristics of the Blood, 214 Amount of Blood in the Body, 215 xiv CONTENTS. PAGE Physical Construction of the Blood, 217 Plasma, 218 Preparation and Properties of Fibrin, 219 Chemical Composition of Plasma, 220 Serum, 223 CHAPTER XIV. BLOOD CORPUSCLES. Proportion of Red to White, 224 White Blood Cells, 225 Origin of the Colorless Blood Cells, 227 The Red Corpuscles, Sizes and Shapes, . . ' ' ' 228 Action of Reagents on Red Corpuscles, 230 Method of Counting Corpuscles 233 Chemistry of the Coloring Matter of the Blood, 235 Spectra of the Haemoglobin, 237 Haematin, Hsemin, etc., . . 240 Development of the Red Discs, 241 The Gases of the Blood, 243 CHAPTER XV. COAGULATION OF THE BLOOD. Formation of the Blood Clot, 245 Circumstances Influencing Coagulation, 247 The Cause of Coagulation, 248 Coagulation in the Vessels, 249 Formation of Fibrin, 252 CHAPTER XVI. THE HEART. Pulmonary and Systemic Circulations, 255 Method of the Circulation of the Blood, 256 The Heart, 258 Arrangement of Muscle Fibre, 259 Minute Structure of the Heart, 261 Action of the Valves, 263 Cycle of the Heart Beat, 265 Movements of the Heart, 268 The Heart's Impulse, 270 Heart Sounds, 272 CONTENTS. XV PAGE Innervation of the Heart, 275 Local Centres, 275 Inhibitory Nerves, 280 Accelerator Nerves, 281 Afferent Cardiac Nerves, 282 CHAPTER XVII. THE BLOOD VESSELS. Structure of the Vessels, 283 The Capillaries, 285 Relative Capacity of the Vessels, 288 Physical Forces of the Circulation, 289 The Blood Pressure, 291 Measurement of Blood Pressure, 297 Variations in the Blood Pressure, 300 Influence of Respiration on the Blood Pressure, 301 The Arterial Pulse, 307 Methods of Obtaining Pulse Tracings, 309 Variations in the Pulse, 312 Velocity of the Blood Current, 313 Controlling Mechanisms of the Blood Vessels, 317 CHAPTER XVIII. THE MECHANISM OF RESPIRATION. Gas Interchange, 323 Structure of the Lungs and Air Passages, 326 The Thorax, 329 Thoracic Movements, 330 Inspiratory Muscles, 333 Expiration, 337 Function of the Pleura, 338 Pressure Differences in the Air, 340 The Volume of Air, 341 Nervous Mechanism of Respiration, 343 Modified Respiratory Movements, 349 CHAPTER XIX. THE CHEMISTRY OF RESPIRATION. Composition of the Atmosphere, 351 Expired Air, 35 2 Changes the Blood undergoes in the Lungs, 354 2 XVI CONTENTS. PAGE Gases in the Blood, 355 Intestinal Respiration, 359 Respiration of Poisonous Gases, 360 Ventilation, 361 Asphyxia, 362 CHAPTER XX. BLOOU-ELABORATING GLANDS. Ductless Glands, 366 Supra-renal Capsule and Thyroid Body, 367 Thymus, 368 Spleen, 369 Functions of the Spleen, 372 Glycogenic Function of the Liver, 373 Glycogen, 375 CHAPTER XXI. SECRETIONS. Lachrymal Glands, 378 Mucous Glands, 379 Sebaceous Glands, 381 Mammary Glands, 382 Composition of Milk, 384 Sudoriferous Glands, 387 Cutaneous Desquamation, 389 CHAPTER XXII. URINARY EXCRETION. Structure of the Kidneys, 391 Blood Vessels of the Kidneys, 393 Urine, 395 Method of Secretion of the Urine, 397 Chemical Composition of Urine, 400 Urea, 400 Uric Acid, 403 Kreatinin, Xanthin, Hippuric Acid, Oxalic Acid, etc., 403 Coloring Matters, 404 Inorganic Salts, 405 Abnormal Constituents, 406 Urinary Calculi, 407 Source of Urea, etc., . 408 CONTENTS. PAGE Nervous Mechanism of the Urinary Secretion, 410 Outflow of Urine, 413 Nervous Mechanism of Micturition, 414 CHAPTER XXIII. NUTRITION. Tissue Changes during Starvation, 417 Food Requirements, , 420 Ultimate Uses of Food Stuffs, 424 CHAPTER XXIV. ANIMAL HEAT. Warm and Cold-blooded Animals, 428 Variations in the Body Temperature, 429 Mode of Production of Animal Heat, 431 Income and Expenditure of Heat, 432 Maintenance of Uniform Temperature, 435 CHAPTER XXV. CONTRACTILE TISSUES. Histology of Muscle, 442 Properties of Muscle in the Passive State, 445 Electric Phenomena of Muscle, 448 Active State of Muscle, 45 l Muscle Stimuli, 45 2 Changes occurring in Muscle on its entering the Active State, 454 Muscle Contraction, 45 Graphic Method of Recording Contraction, 460 Tetanus, Fatigue, etc., 468 Rigor Mortis, 473 Unstriated Muscle, . 475 CHAPTER XXVI. THE APPLICATION OF SKELETAL MUSCLES. General Arrangements, 477 Joints, 47 8 Standing, 4% l Walking and Running, 4^4 XV111 CONTENTS. CHAPTER XXVII. VOICE AND SPEECH. PAGE Anatomical Sketch, 486 Mechanism of Vocalization, 488 Properties of the Human Voice, 491 Nervous Mechanism of Voice, 493 Speech, 494 CHAPTER XXVIII. GENERAL PHYSIOLOGY OF THE NERVOUS SYSTEM. Anatomical Sketch, 496 Functional Classification 498 Chemistry and Electric Properties of Nerves, 500 The Active State of Nerve Fibres, 501 Nerve Stimuli, 5 O1 Velocity of Nerve Impulse, 54 The Electric Changes in Nerves, 506 Electrotonus, 507 Irritability of Nerve Fibres, 508 Law of Contraction, 5 11 Nerve Corpuscles or Terminals, 513 Functions of the Nerve Cells, 515 CHAPTER XXIX. SPECIAL PHYSIOLOGY OF NERVES. Spinal Nerves, 519 The Cranial Nerves, 522 The Trochlear Nerve, Portio Dura, etc., 523 Efferent and Afferent Fibres, 526 Ganglia of the Fifth Nerve, 528 The Gloss o-pharyngeal Nerve, 529 The Vagus Nerve, 530 The Hypoglossal Nerve, 532 CHAPTER XXX. SPECIAL SENSES. Skin Sensations, 537 Nerve Endings, 538 Sense of Locality, 541 Sense of Pressure, 543 Temperature Sense, 545 General Sensations, 547 CONTENTS. XIX CHAPTER XXXI. TASTE AND SMELL. PAGE Sense of Taste, .v . . . 55 Sense of Smell, 553 CHAPTER XXXII. VISION. The Construction of the Eyeball, 557 Dioptric Media of the Eyeball, 560 Structure of the Lens, 5 2 The Dioptrics of the Eye, 564 Accommodation, 57 Defects of Accommodation, 57 2 Defects of Dioptric Apparatus, 574 The Iris, 575 The Ophthalmoscope, 578 Vissual Impressions, 5^ 2 The Function of the Retina, 5^3 Color Perceptions, 59 l Mental Operations in Vision, 594 Movements of the Eyeballs, 595 Binocular Vision, 59^ CHAPTER XXXIII. HEARING. Sound, 598 Conduction of Sound Vibrations through the Outer Ear, 602 Conduction through the Tympanum, 603 Conduction through the Labyrinth, 607 Stimulation of the Auditory Nerve, 610 CHAPTER XXXIV. CENTRAL NERVOUS ORGANS. Nerve Cells, , . . . . 614 The Spinal Cord as a Conductor, 616 The Spinal Cord as a Collection of Nerve Centres, 625 Special Reflex Centres, 632 Automatism, 634 XX CONTENTS. CHAPTER XXXV. THE MEDULLA OBLONGATA. PAGE The Medulla Oblongata as a Conductor, 639 The Respiratory Centre, 640 The Vasomotor Centre, 641 The Cardiac Centre, 643 CHAPTER XXXVI. THE BRAIN. The Mesencephalon and Cerebellum, 648 Crura Cerebri, ". 652 Basal Ganglia, 653 Cerebral Hemispheres, 656 Localization of the Cerebral Functions, 660 CHAPTER XXXVII. REPRODUCTION. Origin of Male and Female Generative Elements, . 666 Menstruation and Ovulation, 669 Changes in the Ovum Subsequent to Impregnation, 671 Formation of the Membranes, .... 675 The Placenta, ' . . 68 1 CHAPTER XXXVIII. DEVELOPMENT. Development of the Vertebral Axis, 686 Development of the Central Nervous System, 691 The Alimentary Canal and its Appendages, 697 The Genito-urinary Apparatus, 702 The Blood-vascular System 708 Development of the Eye, , 721 Development of the Ear, 726 Development of the Skull and Face, ' 729 GLOSSARY, 733 INDEX, , . } 4 3 COMPARISON OF MEASURES. XXI o c a" 1 Pslle'sl o' " 2 "* 8 n f? J^ O ^ * *"* 2 ^ O O !i cr-< -i 1 ^ J 1 * * " " "" 3 *"* A ^ o o* w ^ JO n Q-2> o-2 a-o OJ H 2 - rt 0. S. o S "' ^0 b\ l^lfo^S .'.'..'.'.'.. * 3 2:"" f j* S 1' g '.'.'.'.'.'.'.'. ON o* ** - r* n> n~. o 5 ' 3 ' ' ' 3' 3 ? 1 2 is ' -' ' ' ss H^ h-j p : 3; : : 35: p > a 1 ^j o' i i n 3 M O rt . !2j 3* ON 1 -4 M O ON O O g.O o' V OJ ^O OJ *^| OJ ^O OJ S'pwtSooj p p vb-^ b>jojvboj b O O^O^J O^JOJVO S w r| H ffi W VO "5 On ^ on "^ ^ g 1 O ^ OO*M ^j ^ g n w > o W e W ibic Foot = s Ln U) U> c-n U) O. M U)t_nOJ O Q O ^Oc5 S Ox^ u^ w 8 |i| a; d o 3 cimeters. | OJ (0 OJ OO^OJ ^ po p oo 10 oj p p p !? 10 (g^ > s PRICAL > I. WARRE1S ""3 *v4 O OOt/l Q\ M OJ ij\ c' n O ' O S O ^ vD o'vB O 3 ^ **3 ."j on o'S > " 000010^00^0 w ft ^ W K H E > 3. b> 1 OJ H Kj p I MH n^ H sB w Decimeter; ^\ o ON^-I H o o o *vj **j b ON^J H o b oj ^j *>j o ON^J "- o -p. OJ va ^j o ON^J M "o^!"fc!^oj^j 00^ "o? 5 ' S-'S ^ ?ol 1 1 f O\OJ SO O ^ O O u) uj ou) vo O M O ^H OJ OJ ^OJ \O O O f OJ OJ ONOJ *O O O O "- 1 OJ OJ ONOJ OOOOt-iOJOJON o!| COMMO 5 % ._ - 3 g to to KJ W W M O M M O O M W p p p H--^ II 3* "ON^I ^ II <. > O jg po O*4>. on O O O p M bo ON-^ Ui O O O ONM 00 0^-^ Cn 5 O w d o" 3 tllllll 1 tn -^ 5' o" i 1 O O 1 ! On O\ M OO O\-P k O OOnOn O\M OOO O O Oo^ono^to oo *| ?o w w On o' 1 1 *. II ^ _ t S^aioooooo H.I" 5* E p\0 H W lO^MLn^o S8 S *^ td o* io "o\ b b b b b b *o%QfP ff 35 IH11III Fi|| 1 1 flllllli f- ^^^OCT^O^OoS B c? " ? &~ S" at XX11 COMPARISON OF MEASURES. MEASURES OF WEIGHT. Tons = 20 Cwt. = 15,620,000 Grains. WOOO"1-P]WVOO\ O O O O Osoo TJ- w o o o o o ooo <* 60600066 CORRESPONDING DEGREES IN THE FAHRENHEIT AND CENTIGRADE SCALES. Fahr. Cent. 500 . . . 260.0 450 . . . 232.2 400 . . . 204.4 350 ... 176.7 300 . . . 148.9 212 . . . ICO.O 210 . . . 98.9 205 . . . 96-1 200 . . . 93.3 I 95 . . . 9 0.5 I 9 . . . 87.8 I8 5 . . . 85.0 180 . . . 82.2 175 ... 79.4 170 . . . 76.7 165 . . . 73.9 160 . . . 71.1 155 68.3 150 . . . 65.5 145 . . . 62.8 140 . . . 60.0 135 . . . 57.2 130. . 54.4 125... 517 120 . . . 48.9 II 5 . . . 4 6.1 110 ... 43.3 105 . . . 40.5 100 . . . 37.8 95 ... 35-0 90 ... 32.2 5... 29.4 80 ... 26.7 75 ... 23-9 70 ... 21.1 6 5 ... I8. 3 60 ... 15.5 55 ... 12.8 50 ... 10.0 45 ... 7.2 40 ... 4-4 35 ... i.7 32 ... 0.0 30 ... 1.1 25 ... - 3-9 20 ... 6 7 15 -.. ~ 9-4 10 ... 12.2 5 ... -15.0 O o . . . 17.8 - 5 ... -20.5 10. . . 23.3 15 . . . -26.1 20 . . . 28.9 -25... -31.7 30 . . . 34-4 35 ... -37 2 40 . . . 40.0 45 -42- & -50 . . . -45.6 Cent. Fahr. 100 . . . 212.0 98 ... 208.4 96 ... 204.8 94 ... 201.2 92 ... 197.6 00 ... 194.0 88 ... 190.4 86 ... 1 86.8 8 4 ... 183.2 82 ... 179 6 80 ... 176 o 78 ... 172.4 76 ... 168.8 74 ... 165.2 72. .. 161.6 70 ... 158.0 68 ... I54 . 4 66 ... 150.8 64 ... 147.2 62 ... 143.6 60 . . . 140.0 58 ... 136.4 56 ... 132.8 54 ... 129.2 52 ... 125.6 50 ... 122.0 48 ... 118.4 46 ... 114.3 44 ... 111.2 42 ... io 7 .f c 40 . . . 104.0 38 ... 100.4 36 ... 96 8 34 ... 93-2 32 ... 89.6 30 ... 86.0 28 ... 82 4 26 ... 78.8 24 ... 75-2 22 ... 71.6 20 ... 68 o 1 8 . . . 64.4 16 . . . 60 8 14 ... 57-2 12 ... 53.6 10 ... 50 o 8 ... 46 4 6 ... 42.8 4 ... 39.2 2 ... 35.6 o ... 32.0 2 . . , 28 4 - 4 ... 24.8 6 ... 21.2 8 ... 17.6 10 . . . 14.0 12 . . . 10.4 14 . . . 6.8 1 6 ... 3.2 18 . . . 0.4 20 . . . 4.0 | .00 Hi N IS O t^OO >* M N OO 8 5 HJ" S- O O Q H ONVO OO OOgQOQ^ON 66666666 In Avoirdupois ft>s. = 7000 Grains. N O \T)\O N M fOVO O N N O ^-^O N H O O N W O ^^ N O O Q (N d O ^"O ooooowwo 6 o" o o" o o w N In Troy Ounces = 480 Grains. N OJ IT) M t** CO t*" t-* O ro N ~ in o *"* * ' ' H ' " 5 3 $ S M i? in iiaitf 5 g'9 2 8 : > SuftOQK^S MANUAL OF PHYSIOLOGY CHAPTER I. THE OBJECTS OF PHYSIOLOGY. Biology, the science which deals with living beings, may be divided into two branches, viz. : 1. MORPHOLOGY, which treats of the form and structure of living creatures ; and, 2. PHYSIOLOGY, which attempts to explain the modes of activity exhibited by them during their lifetime, and may therefore be defined as the science which investigates the phenomena presented by the textures and organs of healthy living beings ; or, in short, the study of the actions of organisms in contradistinction to that of their shape and structure. The organic or living world is naturally divided into the Animal and Vegetable kingdoms. We have, therefore, both animal and vegetable morphology and physiology. In studying the vegetable kingdom, the form and structure as well as the activity of plants are associated together to form the subject known as Botany. The physiology of plants need not, therefore, be considered here ; though, indeed, a knowledge of it proves useful in considering many of the processes belonging to animal life. On the other hand, the morphology and the physiology of animals are com- monly taught separately, and in the medical curriculum are made distinct subjects. Morphology includes the external form, the general construc- tion or anatomy of organisms, and the minute structure of their textures as revealed by the microscope. The latter branch of 3 25 26 MANUAL OF PHYSIOLOGY. study, under the name Histology, has now developed into a very extensive subject, which is inseparable from either physiology or anatomy. In this country histology is commonly taught in the medical schools with physiology, because the time of the teachers of morphology is occupied in expounding the nomenclature of descriptive anatomy, while the microscope is in every-day use in the physiological laboratory. Moreover, an adequate knowledge of microscopic methods, and of the various form elements of the different textures of the body, is one of the first essentials for physiological study. As the different actions of the body are performed by different tissues, which in the higher animals are grouped together as dis- tinct organs, a general idea of the position and construction of these different parts of the body must be acquired before the study of physiology can be commenced. Anatomy and general morphology are the frameworks upon which physiological knowl- edge is built up. Some knowledge of these subjects must there- fore precede the study of physiology, in order that the student may be in a position to grasp even the simplest facts connected with any physiological question. * We shall soon find that the assistance of other sciences is also indispensable to physiology. Thus every action of a living texture or tissue is accompanied by some chemical change, the chemical process, in fact, being the common essential part of the phenomena of life. The student of physiology must, then, know something of the science of chemistry ; indeed, the mode of action of chemical elements forms quite as important a groundwork for the study of the activity of the living tissues as their general form or minute structure. Further, the laws which govern the motions of inanimate bodies also control the actions of living tissues, for we cannot claim to understand or recognize the existence of any laws affect- ing living organisms other than those known to be applicable to dead matter. There are a great number of activities shown by living textures which we cannot explain by the recognized laws of chemistry or physics. We therefore use, for convenience' sake, the term "vital phenomena," to indicate processes which are THE OBJECTS OF PHYSIOLOGY. 2J beyond our present chemical and physical knowledge. In using this term we must not think it implies a separate set of natural laws belonging to life. We cannot discover or formulate any special laws affecting living beings only, and therefore we must not assume that any such exist. We must rather endeavor to ex- plain all the so-called ''vital phenomena" by means of the laws known to chemists and physicists. By this means we shall cer- tainly get a closer insight into the processes of life, and if there be laws governing the living beings we may learn to know them. This method of working has already given good results, for within comparatively recent times many of the processes which were regarded as specially vital in character have been shown to be within the power of the experimenter and to depend on purely physico-chemical processes. It is therefore necessary for the physiologist, before he attempts to explain the activities of any organism, to be familiar not only with the structure of its body, but also with the various laws which chemists and physicists teach us control the operations of inanimate matter. The sciences of chemistry and physics may, in fact, be re- garded as the physiology of inorganic matter, just as, when chemistry and physics are applied to the elucidations of the functions of living creatures by the biologist, the study is called physiology. When we consider how far from thoroughly grasp- ing and interpreting all the phenomena presented by the various kinds and conditions of matter the chemist and the physicist still are, we cannot be surprised that those who attempt to explain the- actions of living beings find many processes that they are unable to comprehend. So that when physiologists make use of the convenient term "vital phenomena," it must be remembered that they do not thereby imply the existence of a special living force or any kind of energy peculiar to living creatures. The ultimate object of physiology is not yet within the reach of our modern methods of research. To explain the mode of activity of living beings, and grasp the exact relation borne by their living phenomena to the laws which govern them, is a task of enormous difficulty. Indeed, the manifestations of certain ener 28 MANUAL OF PHYSIOLOGY. gies in living organisms are so complicated that it is often, if not generally, impossible to say exactly how they are brought about, and we are therefore obliged, for the present at least, to be satisfied with the mere recognition and description of the phenomena. Since the human organism is the special study of students of medicine, the contents of this volume should properly be restricted to the physiology of man. But human physiology cannot be studied alone ; because in man we cannot watch sufficiently closely, or question fully, by experiment, the phenomena of life. Further, no sharp line of separation can be drawn between the actions of the various organs of man and those of the lower ani- mals. The consideration of the physiology of those animals which are akin to man must therefore go hand in hand with the study of the physiology of man himself. Much light has been thrown on the actions of the complex textures of the highest animals, by the observation of the activities of the lowest organ- isms, where the manifestations of life may be carefully watched with the microscope in the living animal under its normal conditions. GENERAL CHARACTERS OF ORGANISMS. The term organism, which is commonly used as having the same meaning as living being, owes its derivation to the com- plexity of structure common among the higher forms of life, which are made up of several distinct organs. This organic construction does not hold good as a distinguishing mark between living beings and inanimate matter, because we are acquainted with a vast number of living organisms, both plants and anima4s, which are not made up of organs, but are composed of a minute piece of a soft, jelly-like material, which is simply granular throughout, and devoid of structural differentiation during the life of the creature. We may classify the general characters of living beings as follows : 1. Structural and physical properties. 2. Chemical composition. 3. Activities during life (vital phenomena). CHARACTERS OF ORGANISMS. 29 1. Structural Characters of Organisms. The minute structure of living beings as shown by the microscope no doubt helps to distinguish the textures of organisms from inorganic structures. Although organic textures are found to differ very widely in their characters, they are all related in one respect, namely, that at the earliest period of their existence they consist of a minute mass of a substance called Protoplasm, known as a cell. In plants a cellular structure remains obvious in all parts of the adult, no matter how much the texture may be modified by adaptation to the requirements of any given duty or function. If we examine with the microscope the leaves, bark, wood, or pith of a plant, in all of them a cellular structure can be recognized. In the less developed members of the animal kingdom, and during the initial stages in the existence of the highest animals, the textures are composed exclusively of aggregations of living cell elements. We shall shortly see that in the more fully de- veloped condition of the higher animals, the cells become vari- ously modified in form and function, and the protoplasm manu- factures various structures adapted to the performance of the diverse functions of the different parts. In all organic textures which can be said to be living, cells are dispersed in greater or less number, and regulate their nutrition and repair. 2. Chemical Composition. There are no characters in the chemical composition of the textures of organic beings which can be said to be absolutely distinctive or to separate them from in- organic matter. No doubt their chemical construction frequently exhibits certain peculiarities, not seen in dead matter, which may be taken as characteristic, but living textures only differ in the general plan of arrangement and composition from that most commonly met with in the construction of inorganic materials. In the first place, the great majority of the chemical elements which we know of, take no share in the formation of living creatures, and are never found to enter into their composition. Practically, only fifteen of some seventy elements known to chem- ists take part in making up the tissues of animals. The majority of these are only present in very small quantity and with no 30 MANUAL OF PHYSIOLOGY. great constancy. On the other hand, there are four elements, namely, carbon, oxygen, hydrogen and nitrogen, which are found with such great regularity, and in so great quantity, that they may be said to make up the great bulk (97 per cent.) of the animal frame. The great constancy with which the first three of these elements occur must be regarded as a most important character of organic tissues. Secondly, in organic substances the chemical elements are asso- ciated in much more complex and irregular proportions. Gen- erally, a large number of atoms, of each element, are grouped together to form the molecule, and often the compound is so com- plex that its chemical formula remains a matter of doubt. As an example of the complexity of bodies found in organic analysis, a remarkable substance, called lecithin, which appears in the analysis of protoplasm and many tissues, may be mentioned. Its formula may be expressed thus : /"** TT 3 It is peculiar in containing nitrogen and phosphorus, and in con- struction is said to be like a fat. In inorganic substances, on the other hand, the elements are found to be combined, as a general rule, in simple and regular proportions. The molecules are made up of but few elements arranged in a definite manner and firmly bound together, so that they are not prone to undergo decomposition. As an example, we may take water, which has the well-known formula, H 2 0. Though these bodies may be taken as types of organic and inorganic substances respectively, it must not be imagined that all organic bodies are as complex, irregular and unstable as lecithin, or that 'inorganic compounds, as a rule, are invariably simple and stable like water. It is further remarkable that Carbon an element which is exceptional in forming but few associations in the mineral world, where it chiefly combines with oxygen to form CO 2 is almost CHARACTERS OF ORGANISMS. 3! invariably present in living textures, in which it is combined with hydrogen and nitrogen as well as oxygen in various propor- tions. The constancy of carbon as an ingredient of organic bodies is so great that what formerly was called organic chemis- try is now often called the chemistry of the carbon compounds. These complex associations of many atoms of carbon with many atoms of other elements, are readily dissociated when ex- posed to the air under even slightly disturbing influences. When heated to a certain degree they burn, /. I- T- 3- Shows further diminution of proto- aS the type Of all. The mam Char- plasm and increase in cavity (s) in , c ,1 i i a proportion to the growth of the cell actenstics of these may be briefly wa ii(w). 34 MANUAL OF PHYSIOLOGY. summed up. First, a membranous sac called the cell wall, gen- erally very well denned, and, secondly, within the cell wall vari- ous cell contents. Among the more conspicuous of the latter may be mentioned (i) a soft, clear, jelly-like substance called pro- toplasm, in which lies a nucleus, and (2) certain cavities called vacuoles, which are filled with a clear fluid or cell sap. Further investigation of the life history of cells, particularly in the early stages of their development, showed that the cell wall, which played so important a part in the original conception of a cell, was not always present, but w r as formed by the protoplasm in a later stage of growth. The cell sap and other matters were found to occur less commonly, and appeared still later than the cell wall in the lifetime of the vegetable cell ; hence it was con- FlG. 2. FIG. 3. Diagram of animal cell (ovum). {Gegenbauer?) a. Granular protoplasm. b. Nucleus. c. Nucleolus. Liver cell of man, containing fat globules (b) and biliary matters. {Cadiat.) eluded that they were the outcome of changes due to the activity of the protoplasm, and that this latter was the only essential and formative part of the cell. Subsequently, from the facts that some vegetable cells in the youngest and most active stage of their growth have no limiting wall, and that most animal cells have none during any part of their life, it was proposed to define a cell as a mass of protoplasm containing a nucleus. But further research showed that the nucleus was not always present. In many cryptogamic plants no nucleus can be found, and in some animal cells, which must be regarded as independent individuals (Protamoeba), there is no nucleus at any part of their lifetime. This would lead us to suppose that a mass of protoplasm capable of manifesting all the STRUCTURAL CHARACTERS OF ANIMALS. 35 phenomena of life would be a sufficient definition. Though this is probably correct in a few cases, the vast majority of cells do contain nuclei. As it is difficult to divest our minds of the con- nection between the two, it has been proposed to give the name cytode to the non-nucleated forms, which certainly are very exceptional, reserving the term cell for the common nucleated unit. Each part of the cell may now be considered in the order of its importance, viz., protoplasm, nucleus, cell wall, and cell contents. 1. Protoplasm is commonly seen to be a colorless, pale, milky, semi-translucent substance, more or less altered in appearance by various foreign matters lying in it. These latter also give it a granular appearance, and when dead it commonly exhibits a linear marking or fine network. During life its con- sistence is nearly fluid, varying with the circumstances in which it is placed, from that of a gum solution to a soft jelly. When living unmolested in its normal medium it seems to flow into various shapes, but this is a living action which does not prove it to be diffluent, for any attempt to investigate it by experiment causes a change in its consistence approaching to rigidity. As the full comprehension of the function of this substance lies at the root of the greater part of Physiology, the reader is referred for a detailed account of its properties to Chapter in, on Vital Phenomena, where it will be discussed at greater length. 2. The Nucleus. The majority of independent masses of protoplasm, and all highly organized cells, contain one or more nuclei in their substance. The nucleus is sharply marked off from the protoplasm, and is supposed to be surrounded by a spe- cial limiting membrane. Its presence can generally be made much more conspicuous by treating the cell with certain chemical reagents, notably dilute acids and various dyes. The nucleus is able to resist the action of dilute acetic acid better than the remainder of the cell, so that it stands out clearly, when the rest becomes transparent. Many staining agents, such as magenta (one of the aniline dyes), color the nucleus more quickly and deeply than the protoplasm. Although it is accredited with spe- cial independent movements that occur under certain circum- 36 MANUAL OF PHYSIOLOGY. stances, compared with the protoplasm it is not very contractile. It appears to be intimately associated with the vital phenomena of the cell, and may be said to control or initiate its most important activity, namely, its division. In the nuclear matrix, which is clear and homogeneous, may often be seen an irregular network, one point of which stands out more clearly, and is called the nucleolus. Remarkable changes in the arrangement of this network are seen in some cells to precede the division of the protaplasm. This is called karyokinesis. 3. The Cell Wall. It has already been stated that the most active cells, such as are found in the earliest stages in the life of an organism (embryonic cells), have no inclosing membrane or cell wall. But in the more advanced stages of cell life we find this second form of protoplasmic differentiation to be common enough. In animal cells the limiting membrane has never the same importance as the cell wall in vegetable tissues, where some of the principal textures may be traced to a direct modification of the cell wall, still recognizable as such. Whenever such a limiting membrane exists, it is formed by the outer layers of protoplasm undergoing changes so as to become of greater con- sistence. In the animal tissues the cells form various structures, which are not limiting membranes or cell walls, but rather give the idea of lying between the cells. Hence, in one large group of tissues, they have been called intercellular substance, while in others they appear as materials specially modified for the furtherance of the functions of the special tissues. 4. Cell Contents. Regarding protoplasm as the essential living part of the cell, under this heading will come only those extraneous matters which are the outcome of protoplasmic activity. The cell contents which are present with such constancy and in such variety in vegetable cells, form in them an all-important part ; but in most animal cells the contents do not occupy such a striking position. No doubt animal protoplasm is quite as capable as that of vegetables of making out of its own substance, or the nutriment STRUCTURAL CHARACTERS OF ANIMALS. 37 supplied to it, a great variety of materials, but these are seldom stored in such large quantities in animal cells as in those of plants. In the cells of some kinds of animal textures, particularly that called Connective Tissue, we com- monly find large quantities of fat formed and accumulated to such a degree in the cell that the proto- plasm can be no longer recognized as such. Its remnant is devoted to forming a limiting membrane for the fatty Contents, SO that the Cell Cell from connective tissue containing , . ., . , , large fat globule (a), and showing IS Converted mtO an Oil Vesicle, and protoplasm (/), and nucleus () (m), , , membrane. (Ranvier.) here what may be termed the con- tents become the most important part of the cell. In various glandular cells, as will be seen hereafter, different substances are made and stored up temporarily in the protoplasm. These may be seen as bright refracting granules, which are subsequently discharged in the secretion of the gland. In other cells (liver) nutrient material allied to starch may be deposited in considerable quantity, just as starch is stored in certain cells of plants, but owing to the greater and more con- stant activity of animals, the amount laid by never attains any- thing like that found in the store textures of vegetables, where the result of an entire summer's active work is put by as a pro- vision for the next winter and the fresh burst of energy which follows it in the spring. But while the above are all more or less temporary contents of cells, we have an example of a permanent deposit in them, viz., pigment; this substance is formed by the protoplasm in various parts, and has a special physiological use. Thus in the tissue behind the retina or nerve layer of the eyeball the cells are filled with granules of a pigmented substance, which absorbs the light falling upon it, and thus prevents the reflec- tions which would interfere with the clearness of sight. It also occurs in the skin of the negro and other races, and in 38 MANUAL OF PHYSIOLOGY. that of the frog and other animals, but in these its function is not fully known. Varieties of Cells. Great varieties of cells are found in the various mature tissues of the higher animals, all of which have passed through the stage of being a simple nucleated mass of protoplasm in the earlier periods of their development. All cells may then be divided into two chief types, the indifferent and the differentiated. Under the category of indifferent cells may be placed all such as retain the characters of the first embryonic cells, and have not acquired any special structure or property by which they can be distinguished from the simplest form. Such cells are the only ones in the early stages of the embryo. In the adult tissues they also occur, having various duties to perform. They FIG. 5. Transverse section of Blastoderm, showing the elements in the earlier stage of the develop- ment. A, epiblast ; B, mesoblast; C, hypoblast. are found in the blood and lymph, and scattered throughout the tissues. They are without a cell wall, and have no special con- tents to mark their function. Among the differentiated cells we find many special characters, adapting them to certain special duties, for all these cells are modified from the original type and applied to the performance of some special function. Space prevents even a short enumeration of the varieties of cells met with in the tissues of plants, where they not only carry on the active functions of the organism, but also form the sup- porting structures. The differentiation of a cell is accomplished by its protoplasm, which forms new structural parts, and itself sometimes seems to TISSUE DIFFERENTIATION. 39 diminish in quantity until an element is produced in which there may be no protoplasm recognizable. We find, then, matured and Differentiated cells which vary 1. In shape, being spherical, flattened, fusiform, stellate, etc. 2. In size. 3. In their mode of connection. Cells may also be classified according to their function, e. g., Glandular, Nervous, etc., and the greater portion of the follow- ing pages will be devoted to the functions of these various forms of cells. So long as a cell remains in its indifferent stage it possesses the properties of ordinary protoplasm only; but by its further development it acquires special properties not common to all protoplasm. These properties may or may not be accompanied by structural change. Thus the protoplasm of a gland cell differs in little from that of any other cell except in the capabilities of its nutritive changes and its chemical products ; while on the other hand, those epithelial cells which form the outer layer of the skin lose their protoplasmic characters and are completely modified in structure. TISSUE DIFFERENTIATION. The first stage in the existence of any organism, from the simplest form of plant to man, consists of a single cell (in ani- mals called the ovum or egg), which differs in no essential points of struc- ture from an ordinary cell. There is moreover a class of organisms in which the individuals never go beyond this stage, but pass their entire lifetime in the state Of a Simple Unicellular Organism. Unicellular organism. Small amoeba. . . (Cadiat.) The individuals composing this group (Protista), though insignificant in point of size, may vie with the higher plants and animals in number, species, and vari- ety of form, so that they might well be placed in a kingdom by themselves (as has been proposed), apart from the vegetable and animal kingdoms. MANUAL OF PHYSIOLOGY. The group of these organisms which most resembles animals, is called Protozoa, and is divided from other animal forms by the FIG. 7. Stages in the division of the egg cell (ovum), showing the production of a multiple mass by division. {Gegenbauer.) manner of development of the ovum of the latter, which divides into cells that subsequently become differentiated into tissue. This group is called the Metazoa. In the Protozoa the ovum never divides, the animal always remaining a single cell. On the contrary, the ovum of the Metazoa changes its characters during its development. At first possessing a stage common to both divisions, viz., a single cell, it soon passes through rapid stages of cell proliferation, and is converted into a multiple mass, the mulberry stage or Morula. The cells forming this Morula stage approach the periphery of the mass, where they arrange themselves in two layers, and form a cavity in the centre. This is known as the Gastrula stage. Following, then, this cell multiplication, we find a qualitative differentiation of the cells, by which certain groups of cells assume special peculiarities, fitting them for some specific duty. Thus we arrive at the production of special textures and TISSUE DIFFERENTIATION. 41 organs such as are met with in the higher animals, and which are necessary for the efficient discharge of the various functions carried on during their lives. The division of the original mass of indifferent cells into two layers of special cells is the first step toward tissue differentiation, and in some animals is the only one arrived at in their life history, throughout which they re- main a simple sac made up of an external layer, Ectoderm, and an internal layer, Endoderm. The groups of cells forming the outer and inner layers of this stage of develop- ment, not only form the primitive tissues, but also represent the first appearance of organs or parts with a specific function. The external or ectodermic layer is the Diagral n showing the first dif- supporting, protecting, motor and respi- ratory organ, while the inner or endo- dermic layer is devoted to a primitive * ndoderm - form of digestion, preparing the food for assimilation, and gen- erally presiding over the nutrition of the body. Although this sac-like (Gastrula) stage is supposed to have formed a step in the life history of nearly all animals, yet it forms a less striking part in the development of the individuals as we ascend the scale, and in the higher animals no such stage has been recognized. In the Vertebrates, the germ cells derived from the ovum are from an early period divided into three distinct layers, as those which correspond to the Ectoderm and Endoderm' of the lower organisms form between them a third layer or Mesoblast. From these germinal layers all the organs and tissues of the body are subsequently evolved. In embryological language the three primitive layers are called Epi-, Meso-, and Hypo-blast. Thus it can be seen that, as we can compare the primitive uni- cellular state of the lowest animals with the first egg-cell stage of existence of the highest animals, so we can compare all the steps of tissue and organ differentiation as we trace them in the embryo 4 42 MANUAL OF PHYSIOLOGY. of a mammal, with the steps of elaboration in organic and tex- tural parts that we find in ascending the scale of animal life. The history, then, of the development of any mammal from a single cell or egg to the complex adult individual, is analogous with the more protracted history of the evolution of the animal kingdom from the Protista upward. It is impossible to separate the differentiation of tissues and organs, or to say which is of older date in the history of animal evolution. Even in unicellular animals, where we have no trace of tissue difference (Paramaecium, Vorticella), there being only one cell, we have a distinct foreshadowing of organ and func- FIG 9. Transverse section of blastoderm of chick. A. Epiblast. B. Mesoblast. C. Hypoblast. pr. Primitive groove. tional differentiation (vide Chapter in). And in creatures made of many parts, the same cells have several duties to perform. But when an aggregation of specialized cell units exists, it may be said to be a tissue. If these cells have no very special char- acteristic, then the tissue may be called primitive or embryonic. But, as has just been stated, the aggregation of embryonic cells in the higher forms of life have special characters from the very first, which mark them off from one another as destined for different functions. The middle germ layer (mesoblast) is derived from the upper (epiblast) and lower (hypoblast), the relative amount contributed by each being doubtful. From the earliest period the middle TISSUE DIFFERENTIATION. 43 layer has distinctive characteristics, and ultimately gives rise to a set of tissues which can always be distinguished from those which originate from the upper and lower layers. From the inner and outer germ layers are formed several con- nective tissues, which, in a more or less perfect degree, retain the activity of the original protoplasm, and hence may be called active tissues. From the middle germinal layer is developed a set of textures, in the majority of which the protoplasmic ele- ments are reduced to a minimum, and are therefore grouped together as supporting tissues. The tissues formed in the adult may be classified into four groups : 1. Epithelial Tissues. The primitive surface tissue of the epiblast and the hypoblast, which are variously modi- fied for several distinct functions. 2. Nerve Tissues. Springing from the former, are modified for receiving, conducting, controlling and distributing impressions. 3. Muscle, or Contractile Tissues. In close relation to both the previous and the next groups. 4. Connective Tissues formed only from the middle germ layer. They are much modified in different parts, so as to give shape to the body, and to support and hold the various organs and parts firmly together. They are, in fact, the materials used in the general body architecture. Epithelial Tissue, although the oldest kind of tissue both in the animal series and in the germinal layers, retains the em- bryonic character of being entirely composed of cells placed in close relationship on the interal and external surfaces of the body. The individual cells retain the embryonic character in form and function,, being soft, rounded masses of protoplasm, only altered in shape by the pressure of their neighbors. The cells which lie next the nutrient vessels of the mesoblast are endowed with energetic powers of growth and reproduction. As the young cells are produced they take the place of the parent 44 MANUAL OF PHYSIOLOGY. cell, whose future life history determines the special characters of the different kinds of tissues. Sometimes the cells are retained, as in the skin, and are arranged in several layers, one over the other. As the cells are conveyed from the deeper layer, where they take their origin, toward the surface, the efforts of the waning nutritive power of the protoplasm are devoted to the manufacture of a tough, insol- FIG. 10. Section of the epiderm of the prepuce showing the superimposed layers of cells of a strati- fied epithelium. (Cadtat.) a. Young proliferating cells, b d. Cells advancing toward surface, e. Flattened cell of horny layer, f. Basement membrane, g. Connective tissue. uble substance. The cells thus gradually lose their vital activi- ties, and are converted into horny scales, which form the external protecting skin, and its many modifications that give rise to the different dermal appendages, such as hair, feathers, etc. Instead of a horny substance, the protoplasm may manufacture fat in the bodies of the cells, as seen in the mammary and the EPITHELIAL TISSUE. 45 sebaceous glands of the skin. In other cases the reproductive activity of the cell is in abeyance, and its nutritive energy is devoted to the manufacture of a material which is poured out of FIG. ii. FIG. 12. Two cells of scaly epithelium from the inside of the cheek. (Ranvier.) Section of milk gland of cat, show- ins: secreting cells containing fat globules, and some secretion in alveoli. the cell at certain periods. Thus' we have another function per- formed by the epithelial tissues, namely, that of manufacturing FIG. 13. FIG. 14. Ciliated epithelial cells from the gills of mussel. ( Cadiat.) Stratified ciliated epithelial cells from the trachea of man. ( Ca-diat.) a. Large surface cells, with cilia on surface. b. Lower cells in earlier stage of development. e. Cell charged with mucus. certain materials which, being collected by suitable channels, appear as secretions. 46 MANUAL OF PHYSIOLOGY. The active elements of glandular tissue are epithelial cells whose nutrition leads to the formation of specific chemical pro- ducts within their protoplasm. These products pass out com- monly as fluids, and form various substances of great importance in the economy. A gland is simply a special arrangement of epithelial cells lining the sacs or tubes into which the secretion is poured. Some tracts are covered with fine, moving, hair-like processes, called cilia, which give rise to a slight motion of the fluids in contact with them. The epithelium in various places is thus seen to be modified in different ways, so as to make it suitable for the special function of the part in which it is placed. Other differences will be given in detail with the description of the uses of the many mucous surfaces. The most interesting modifications are those in the special sense organs, where the cells are in immediate connection with nerves, and aid in form- ing the special nerve terminals.* Nerve Tissue. The great nervous centres are formed from the cells of the epiblast, which, in the earliest days of the embryo, form a longitudinal furrow, which sinks into the cells of the mesoblast. By the rapid growth of the latter the depressed part is cut off from the rest of the epiblast, and forms the rudi- ment of the spinal cord and brain. In looking for special con- ducting tissue in animals possessing the most simple structure, we find cells which would seem to possess certainly a twofold, and possibly a threefold function, one of which is conduction. In the so-called ' ' neuro-muscular ' ' cells of the hydra, processes are described as passing off from them, and uniting beneath the ectoderm with other fibre-like processes, which are evidently contractile. Here we find for the first time a portion of proto- plasm specially devoted to acting as a conductor of impulses, and attached by the one end to a contractile fibre, and by the other to a surface (sensory) cell. The intimate relation between the development of nerve and muscle fibres is thus established, and * A further account of the Histology of these tissues will be found in the chapters specially devoted to these subjects. NERVE TISSUE. 47 we have the first indication of a nerve mechanism, viz., a cell capable of receiving stimulations, and a fibre capable of trans- mitting the resulting impulses. As further differentiation pro- FIG. 16. Epithelial cells, some of which are filled with mucus (rf), forming goblet- like cells. (Cadiat.) Neuro-muscular cells of hydra, m. Contractile fibres. (Kleinenberg.) ceeds, each of these parts becomes more distinct from the other, and ultimately the adult nerve tissue is found to be made up of nerve fibres, and special cells, forming nerve endings. FIG. 17. FIG. 18. S. Sensory receiving organ- with attached afferent nerve fibre. G. Central organs ganglion cells. M. Peripheral organ and effe- rent nerve. Three medullated nerve fibres, the medullary sheath of which is stained dark with osmic acid N, Nodes of Ranvier. Two non-medullated nerve fibres, with nuclei in the primitive sheath. The fibres act as lines of communication between ganglion cells ; they connect together the numerous cells in the various 48 MANUAL OF PHYSIOLOGY. parts of the brain and spinal cord, or pass between those of the central nervous organs and ganglia distributed throughout the body, which might be called the peripheral nerve organs. The simplest idea, then, of a special nerve apparatus is a fibre connecting two cells. The peripheral cell may be a receiving organ (Fig. 17, s), from which, when stimulated, impulses are transmitted along the fibre to the central nerve cell, where they give rise to certain impressions, and so we have a sensory nerve apparatus. Or the central nerve cell may be the receiving agent, getting stimuli from its central neighbors, and transmitting FIG. Multipolar cells from the anterior gray column of the spinal cord ot the dog fish (a) lying in a texture of fibrils; (b) prolongation from cells; (c) nerve fibres cut across. (Cadiat.) impulses to a peripheral nerve terminal, by which they are handed over to a muscle (M) or gland, and thus we have a simple motor or secretory apparatus. Where the effect of a stimulus can be definitely traced from one nerve cell to another, and from thence by a second fibre to a third cell, the impulse is said to be reflected by the second cell to the third. And there we have what is called a reflex act. The essential part of a nerve fibre is a kind of protoplasmic band, in which the finest fibrilla or thread-like marking can be NERVE TISSUE. 49 made out with the aid of reagents and a powerful microscope. This is called the axis cylinder. In some nerve fibres (mostly in the brain and spinal cord) the axis cylinder is naked, and even a single fibril may so pass from one cell to another in the brain matter. In other parts the axis cylinder is generally covered by a thin membrane, called the primitive sheath, or with a soft, oil- like substance, called the medullary sheath, or, as is commonly the case in most peripheral nerves, by both. The primitive sheath encloses the medullary sheath, which surrounds the axis cylinder. These fibres are made of peculiarly modified cells, which are, FIG. 20. FIG. 21. Ganglion cells of frog, showing straight and spiral fibres. (After Beale and Arnold.) Cells from the sympathetic ganglion of a cat. The protoplasm is retracted here and there from the cell wall. however, so elongated as not to be very easily recognized as such in adult tissue. The nerve or ganglion cells vary extremely in general form and size. The commonest in the nerve centres are large bodies with a clear, well-defined, vesicular, single nucleus, and distinct nucle- olus ; they have two or more processes, which are connected by nerve fibres to other cells, and to the axis cylinder of nerves. The peripheral nerve cells are generally much modified, and often small compared with those in the centres. Besides the cells in the sporadic ganglia, which are large rounded corpuscles with 5 50 MANUAL OF PHYSIOLOGY. but few processes, there are many other bodies connected with the peripheral nerves which cannot be called ganglion corpuscles. They are nevertheless nerve cells. Muscles or Contractile Tissues. When changes take place in protoplasm adapting it specially for contraction, it is termed muscle tissue. The large masses of this tissue attached to the skeleton so as to move its various parts, form the flesh of the higher animals. Muscle tissue is, almost invariably, con- nected with nerve tissue, and acts in response to stimuli commu- nicated from the nerves. In some of the lower animals, the two tissues are so intimately related that it is not easy to distinguish them, and the development of both progresses equally as we ascend the scale of animal life. They are nearly related in their origin, or even spring from the same primitive tissue. In fact, as has already been mentioned (vide p. 46), they form but one structure in some of the more simple and less differentiated animals. The neuro-muscular tissue, which is formed from the outer layer of the embryo, is the forerunner of the muscles as well as of the nerves of the embryo of the higher animals. In the higher animals and man muscle tissue consists of two distinct kinds of textures, known as (a) Smooth, or non-striated muscle. (<) Striated muscle. In the smooth muscle the individual elements present the characters of an elongated and flattened cell, and contain a single long nucleus. They contract very slowly, and require a com- paratively long time for the nerve influence to affect them, so that an obvious interval exists between the moment of their stimulation and their contraction. They are found in the inter- nal organs and in situations where gradual and lasting contrac- tions are required. They receive their nervous supply generally from the sympathetic system, and perform their duty without our being conscious of their activity or being able to control it by our will. Striated muscle tissue is made up of cylindrical fibres of such length that both extremities cannot be brought into the field of MUSCLE TISSUE. 5 1 the microscope at the same time. Their exact relation to cells is not so easily made out as in smooth muscle, and doubtless varies in different muscles. Sometimes the fibres are made up of single cells, and in other cases they are formed by the permanent fusion FIG. 22. FIG. 23. Cells of smooth muscle tissue from the intestinal tract of fabbit. (Ranvier.) A and B. Muscle cells in which differentiation of the protoplasm can be well seen. (Schafer.) Two fibres of striated muscle, in which the contractile substance (m) has been ruptured and sep- arated from the sarcolemma (a) and (s) ; (/) space under sarco- lemma. (Ranvier.') 52 MANUAL OF PHYSIOLOGY. of several cell elements which never differentiate into separate elements, owing to the imperfect division of the cells, but make up one mass, the multiple nuclei of which alone make its mode of origin apparent. The contractile substance is made up of two kinds of material, one of which refracts light singly, while the other is doubly refracting. These are ranged alternately across the fibre, making the transverse markings or striae from which it gets its name. This striated material is quite soft and is encased in a thin homogeneous elastic sheath called sarcolemma, which fits closely around the soft contractile substance. This form of muscle is the widest departure from the primitive protoplasmic type, being specially modified so as to perform strong and quick contractions. It moves with wonderful rapidity, contracting almost the instant its nerve is stimulated. It forms the great mass of the quick-acting skeletal muscles, being attached to the bones by bands composed of a form of fibrous tissue, which form the tendons and fasciae. Muscles made of striated tissue are commonly under the control of the will, and hence are frequently spoken of as voluntary muscles, but this term is misleading, for many striated muscles are not governed by voluntary control. The Connective Tissue group, coming exclusively from the mesoblast, exhibits very great varieties of form. Its cells differ much from the epithelial cells both in their character and their relations, and particularly in the adult tissues. Under the heading Connective Tissues are generally classed all those which support the frame and hold together the various other tissues and organs. They are 1 . Mucous and retiform connective tissues. 2. White and yellow fibrous tissue. 3. Cartilage. 4. Bone. 5. Endothelium. The cells of all these tissues have the property of manufactur- ing some material which does not generally enclose them as a cell wall, but remains between the cells and forms the intercellular CONNECTIVE TISSUES. FIG. 24. 53 Transverse section of the chorda dorsalis and neighboring substance, a, cartilage cells ; b, cell of the middle layer of embryo; c, mucous tissue; d, boundary of chorda. (Cadiat.) FIG. 25. Cells of mucous tissue with branching processes (B) and a couple of elastic fibres (F). (Ranvier.) 54 MANUAL OF PHYSIOLOGY. substance. The younger the tissue the greater is the proportion of its cellular constituents, and the olde* the tissue the greater will be found the preponderance of the intercellular substance. Mucous Tissue. In certain parts of the embryo and in some of the lower animals a kind of connective tissue is found in which there is but little intercellular substance, the mass of the tissue being thus made up of cells. The cellular connective tissue never forms an important texture in the adult, but is inter- esting as the probable tissue from which the connective tissues are formed in the embryo, and as occurring in abnormal growths or tumors. The first step in its differentiation is the secretion of a large FIG. 26. Portion of tendon from the tail of a young rat, stained with gold chloride, showing arrange- ment of flattened cells on bundles of fibrils. (After Klfin.} quantity of sofl, homogeneous, semi-gelatinous or fluid material like the mucus secreted by epithelium. In this the cells lie, either free or united by long protoplasmic processes. The pro- cesses uniting the cells may not be present, and the cells may be reduced to a minimum, as occurs in the vitreous humor of the eye. But more commonly the soft gelatinous substance is reduced in amount, and the processes connecting the cells are converted into a dense network of delicate threads to form the retiform tissue of lymphoid structures. White Fibrous Tissue. The cells of the last described va- riety may become differentiated by a process of fibrillation. The CONNECTIVE TISSUES. 55 growth of the cells leads to the formation of a fibri Hated sub- stance which ultimately forms the great bulk of the tissue, while the cells become gradually and proportionately fewer in number. In this case only sufficient of the mucous substance generally remains to cement the fibrils together into bundles. A few of the cells, however, remain between the bundles, of fibrils to FIG. 27. FIG. 28. Coarse () and fine (b) yellow elastic fibres after treatment with strong acetic acid (Cadiat.) Elastic membrane from inner coat of aorta, and, below, meshwork of elas- tic fibres from a yellow ligament. (Cadiat.} preside over the nutrition of the tissue. Thus is formed the non-elastic or white fibrous tissue of tendon. These fibrils of white fibrous tissue are easily affected by chemical reagents. Weak acids cause them to swell up and become indistinct. Baryta water affects the cement and renders them easily separable. They swell and dissolve in boiling water, yielding gelatine, which forms a jelly on cooling. MANUAL OF PHYSIOLOGY. Yellow Elastic Tissue. In some parts of the body a kind of intercellular substance formed, which dif- FIG. 29 IS fers in many respects from the foregoing. It is highly elastic, does not give gelatine on boiling, and is not af- fected by weak acids or alkalies. In bulk it has a pale yellow color, and is spoken of as yel- low elastic tissue. It is A teased preparation of connective tissue showing fine Sometimes found alone, and coarse elastic fibres mingled with bundles of fibril- fnrmiricr an plasrir hanrl lar tissue and connective tissue corpuscles. m & an or ligament, but more commonly mingled with fibrillar tissue to form the connecting medium which lies under the skin and between the various other textures. FIG. 30. FIG 31. Section of hyaline cartilage from the end of a growing bone, showing a decrease in the intercellular sub- stance compared with the number of cell elements which are ar- ranged in rows. Elastic fibro-cartilage, showing cells in capsules and elastic fibres in matrix. (Cadiat.) CARTILAGE. 57 Cartilage. In this tissue the intercellular substance secreted by the cells is hard, and forms in the earlier stages of its devel- opment cases or cell walls for the cells. These cases subsequently FIG. 32. White fibro-cartilage, showing cells (a) in capsules and fibrillar matrix (6). (Cadiat.) FIG. 33. Transverse section of a system of Havers, showing Haversian canal in centre, with bone cells arranged around it in lacuna, which are connected by the deli- cate canaliculi. ( Cadiat.) increase in thickness, and become fused together into a homo- geneous intercellular substance, where ultimately the areas be- 58 MANUAL OF PHYSIOLOGY. longing to the different cells can no longer be distinguished from one another, so that in the adult tissue there is a tough matrix of intercellular substance, in which the cells are scattered, apparently occupying small cavities. These cells preside over the nutrition of the tissue. The intercellular substance, which is quite homogeneous in common hyaline cartilage, is sometimes modified so as to resemble fibrous tissue, sometimes the fibrillar, and sometimes the elastic form being produced. (Figs. 31 and 3*.) Bone. This is the most marked differentiation of the connec- tive tissue group. The intercellular substance is characterized by containing a great quantity of earthy or inorganic matter (65 %), which gives the bone its enormous strength. The cells of the tissue are enclosed in little cavities called lacunce, which are related by minute canaliculi to each other. The intercel- lular substance is everywhere traversed by the processes of the cells lying in the little canals which connect the lacunae, and thus the adequate nutrition of the tissue is secured. Chemically, bone tissue consists of about Parts. Calcium phosphate, 53 Calcium carbonate, II Magnesium phosphate, calcium fluoride and soda salts, . i Gelatin yielding animal matter, 33 In the formation of bone from fibrous or cartilaginous tissue the original intercellular substance disappears, and a set of cells with new formative powers come upon the field (Fig. 34). These new cells (osteoblasts) cover the growing surface of the bone and secrete and lay down in layers a new kind of intercellular substance, which is the bone matrix. Here and there, at won- derfully regular intervals, an osteoblast ceases to secrete the calcareous intercellular substance, while its neighbors continue formative activity. Consequently, this osteoblast, or as it may now be called young bone cell, becomes surrounded by calcare- ous intercellular substance, and is permanently lodged in the bone tissue. Endothelium. Wherever a surface occurs in the connective tissues it is generally covered by a single layer of thin cells with STRUCTURAL CHARACTERS OF ANIMAL ORGANISMS. FIG. 34. 59 Section through ossifying cartilage and young bone. (Cadiat.) a. Cartilage cells. e. Blood corpuscles. d. Degenerating cartilage cells. f. Osteoblasts. c. Cell space, empty. g. Ditto, of periosteum. d, Spiculae of calcareous deposit. h. Bone cells. 60 MANUAL OF PHYSIOLOGY. a characteristic outline, which can only be made visible by stain- ing the intervening cement substance with silver nitrate. This tissue, which forms the immediate lining of all vessels and spaces developed in the tissues arising from the mesoblast, is called endofhelmm, in contradistinction to the epithelium developed from the epi- and hypo-blast. The Vascular System is developed in the mesoblast with the earliest stages of the connective tissue. The blood vessels, which are chiefly made up of connective tissues, soon traverse all parts of the body, and distribute the nutrient fluid or blood. The blood may be considered as an outcome of the connective tissues, since the corpuscles of the blood are at first formed from the cells of the mesoblast, and later from the connective tissue corpuscles. An arrangement of special cells, such as epithelial or muscle cells, with a special function, constitutes an organ. However, in the higher animals and man an organ is almost invariably a complex structure, having various tissues entering into its con- struction. Thus a skeletal muscle is made up of a quantity of muscle fibres held together by sheets of connective tissue, and attached to bones by connecting bands. It is further traversed by many blood vessels, and the fibres are in immediate relation to certain nerves which terminate in them. The various secret- ing organs are made up of epithelial cells, held together by con- nective tissue in close relation to blood vessels and nerves, and are so arranged that they pour their secretion into a duct. The bones, which are the organs which give the body support, con- tain, in addition to the bone tissue of which they are composed, a great quantity of indifferent cells, fat cells, nerves and blood vessels. They are covered on the outside with a tough vascular coat, which gives them strength, assists their nutritive repair and reproduction, and acts as a point of attachment for the muscles and ligaments. Where the bones are in contact at the joints, they are tipped with hyaline cartilage. If, then, we analyze anatomically the architecture of the STRUCTURAL CHARACTERS OF ANIMAL ORGANISMS. 6 1 human body, we find that it is made up of a number of complex parts, each adapted to some special function, and composed of an association of simple tissues such as the requirements of the special part demand. The general arrangements of these organs and their modes of action will be discussed in future chapters. 62 MANUAL OF PHYSIOLOGY. CHAPTER III. CHEMICAL BASIS OF THE BODY. It seems natural to commence the description of the molecular changes that take place in the various tissues and organs of the body with a brief account of the chemical composition of the most characteristic substances found in animal textures, because none of the processes of cell life, or tissue activity, can be satis- factorily studied without familiarity with the more common terms occurring in physiological chemistry. The chapter on this subject here introduced, is intended rather to give the medical student a general view of the chemical com- position and characters of the substances most frequently met with in the chemical changes specially connected with animal life, than to supply a complete or systematic account of the rela- tionships of the chemical bases of the body, for which reference must be made to more advanced text-books, or treatises on the special subject of physiological chemistry. This review must, for the sake of brevity, be inadequate in the case of many sub- stances, but these will be again referred to when speaking of the function with which they are associated. It has already been stated that of the seventy elements known to chemists, a comparatively small number form the great bulk of the animal body, although traces of many are constantly present. Thus, we shall see that four elements, namely, (i) oxygen, (2) carbon, (3) hydrogen, (4) nitrogen, are present in large proportions in every tissue, and together make up about 97 per cent, of the body; and sulphur, phosphorus, chlorine, fluorine, silicon, potassium, sodium, magnesium, calcium, iron, and in certain animals copper, are indispensable to the economy, and are widely distributed, but are found in comparatively minute quantities. Occasionally traces of zinc, lead, lithium, and other minerals may be detected, but these must be regarded rather as accidental than indispensable ingredients. CHEMICAL BASIS OF THE BODY. 63 The attempt to investigate the composition of a living tissue by chemical analysis, must cause its death, and thus alter the arrangements of its constituents, so that its true molecular con- stitution during life cannot be determined. We know that the composition of all living textures is extremely complicated, having a great number of components, most of which contain many chemical elements associated together in very complex proportions. But as has already been pointed out, the complexity of their chemical constitution is not so wonderful as the fact, which indeed sounds paradoxical, that in order to preserve their elabo- rate composition, they must constantly undergo a change or renewal, which is necessary for, and forms the one essential char- acteristic of, their life. In fact, their complexity and instability is such, that they require constant reconstruction to make up for the changes inseparable from their functional activity. Their chemical constituents are easily permanently dissociated, and the various components are themselves readily decomposed, generally uniting with oxygen to form more stable compounds. The investigation of the chemical changes known as assimila- tion forms a great part of physiological study, and therefore will occupy many chapters of this book. Here we can only call attention to the chief characteristic substances to be found in the animal body, as the result of the primary dissociation or death of the textures, and briefly enumerate the products of their fur- ther decomposition as obtained by the analysis of the different substances. The tissues of the higher animals present a great variety of substances, materially differing in chemical composition ; they have all been made from protoplasm, and contain a proportion of some substance forming a leading chemical constituent of protoplasm. Every living tissue contains either protoplasm or a derivative of it, and the special characters of each tissue depend upon the greater development of some one of these sub- stances. It is of little use 'to classify the numerous chemical constitu- ents found in the animal body in such a systematic manner as to 64 MANUAL OF PHYSIOLOGY. satisfy the rules of modern chemistry, because their classification, from a strictly chemical point of view, does not set forth their physiological importance or express adequately the relation they bear to the vital phenomena of organisms. The following enumeration of the chief chemical ingredients found in the tissues has regard to their physiological dignity as well as to their chemical construction, and will thus, it is hoped, assist the student to distinguish the different groups, and give him a better idea of their vital relationships, than a more strictly systematic classification. (A) NITROGENOUS. I. Complex bodies forming the active portion of many tissues Plasmata, e, g,, protoplasm, blood plasma. II. Bodies entering into the formation of and easily obtained by analysis from Group I, Albumins, e. g., serum albumin. III. Bodies the outcome of differentiation, manufactured in the tissues by Group I, Albuminoids, e. g., gelatin, etc. IV. Bodies containing nitrogen, being intermediate, bye, or effete products of tissue manufacture, e. g., lecithin, urea, etc. (B) NON-NITROGENOUS. V. Carbohydrates in which the hydrogen and oxygen exist in the proportion found in water, e. g-, starch and sugar. VI. Substances containing oxygen in less proportions than the above, e. g., fats. . VII. Salts. VIII. Water. CLASS A. NITROGENOUS. GROUP I. PLASMATA. Under this group may be placed a variety of substances which must be acknowledged to exist in the living tissues as complex chemical compounds, of whose constitution we are ignorant, since it is altered by the death of the tissue. PLASMATA. 65 There are some exceedingly unstable associations of albumin- ous bodies with other substances, and they at once break up into their more stable constituents, albumins, fats, salts, etc., when they are deprived of the opportunities of chemical interchange and assimilation which are necessary for their life. Although we can only theorize as to the real chemical consti- tution of such substances, we must believe that they really exist in the living tissues as chemical compounds, and as chemical compounds endowed with special properties which impart the specific activity of their textures, whose molecular motions, in fact, are the essence of the life of the tissues. Protoplasm. By far the most widely spread and important of these is the soft, jelly-like substance, Protoplasm. This is the really active part of growing textures of all organisms, whether animal or vegetable, and forms the entire mass of those inter- mediate forms of life, the protista, now generally regarded as the original fountain head of life on the globe. This material commonly exists in small independent masses (cells), in which we can watch all the manifestations of life, assimilation, growth, motion, etc., taking place. We must assume that this substance is a definite chemical compound ; and, further, since the living phenomena are exhibited only so long as it preserves its chemical integrity, we may conclude that its manifestations of life depend upon the sustentation of a special chemical equilibrium. Not only is this equilibrium destroyed by any attempt to ascertain the chemical composition of proto- plasm by analysis, but even for its preservation the proto- plasm must be surrounded by those circumstances which are known to be necessary for. life, viz., moisture, warmth, and suit- able nutritive material, or its destruction must be warded off by a degree of cold that checks its chemical activity. If the chemical integrity of protoplasm be destroyed and its death produced, many new substances appear, among which are representatives of each of the great chemical groups found in the animal tissues. Thus, besides water and inorganic salts, we find in protoplasm carbohydrates represented by glycogen, lecithin and other fats, and several albuminous bodies, which will 6 66 MANUAL OF PHYSIOLOGY. be described in the groups to which they belong. In addition to these, protoplasm often contains some foreign bodies which have come from without, and special ingredients of its own manufacture, such as oil, pigment, starch and chlorophyll. Blood Plasma. There is in living blood also a body which must be included in this group, as it undoubtedly has a much more complex constitution than any of the individual albumin- ous bodies, presently to be described, which can be obtained from it. This is proved by the following facts : first, its death is ac- companied by a series of chemical changes, viz., disappearance of free oxygen, diminution of alkalinity, and a rise in tempera- ture, and secondly, certain albuminous bodies appear which were not present in the living plasma. The spontaneous decomposition of separated blood plasma may be delayed by cold : at freezing point the chemical processes are held in check. During life the exalted constitution of the plasma is sustained by certain chemical interchanges which go on between it and its surroundings. This question will be more fully discussed when the coagulation of the blood is described. Muscle Plasma. Likewise, as will be found in the chapter on Muscles, there exists in the soft, contractile part of striated muscle a plasmas which at its death spontaneously breaks up into other distinct albuminous bodies and forms a coagulum. These changes are accompanied by acidity of reaction, the disappear- ance of oxygen and an elevation of temperature, showing that distinct chemical change is taking place. Oxy hemoglobin, the coloring matter of the blood, should be included here among the important chemical bodies more com- plex than the albumins. This singular, body can be broken up into a globulin and a coloring matter, hcematin, containing iron. It differs from all other bodies of a similarly complex nature from the fact that it readily crystallizes, and also in the very remarkable manner in which it combines with oxygen, and again yields it up. GROUP II. ALBUMINOUS BODIES. It is difficult to say how far these bodies exist as such in the living organism, but they can be obtained from nearly all parts, ALBUMINOUS BODIES. 67 particularly those which contain active protoplasm, and after its death they can be detected in abundance. As may be seen, by testing for their presence in living protoplasm, the addition of any chemical reagent or treatment causes its death, so that, although albumins appear in the test tube, this cannot be accepted as proof that they would have answered to the tests before the protoplasm was changed by its death. They do not occur normally in any secretion except those sub- stances which tend to nourish the adult body, and to form and nourish the offspring, viz., the ovum, semen and milk. No satisfactory formula has been suggested to express their chemical composition, but the average percentage of the elements they contain is remarkably alike in all members of the group. This may be said to be in round numbers as follows : Oxygen, 22 per cent. Hydrogen, 7 " Nitrogen, 16 " Carbon, 53 " Sulphur, 2 " They are amorphous, of varying solubility, and, with one exception, indiffusible in distilled water. As far as we know at present, albumins cannot be constructed de novo in the animal body, but must be supplied in one form or another as part of the food. Albumins are therefore always the outcome of the activity of vegetable life. They can be recognized by the following tests : 1 . Strong nitric acid gives a pale yellow color to solutions or solid albumin, especially on heating, which turns to deep orange when ammonia is added (Xanthoproteic test}. 2. Millon's Reagent (acid solution of proto-nitrate of mer- cury) gives a white precipitate which soon turns yellow, changing to rosy-red on boiling, or standing for some days. 3. Solution of caustic soda and a drop of copper sulphate solution give a violet color to the liquid. 4. Acetic acid and boiling give a white precipitate, except with derived albumins and peptones. 68 MANUAL OF PHYSIOLOGY. 5. Acetic acid and potassium ferrocyanide give a flocculent white precipitate, except wtfb. peptones. 6. Acetic acid and equal volumes of sodium sulphate solu- tion give a precipitate on boiling. 7. With sugar and sulphuric acid they become violet. 8. Crystals of picric acid added to solutions dissolve and cause bead-like local coagulations, except with peptones. CLASSIFICATION OF ALBUMINS. Under the head of the albuminous bodies we find several classes which differ from each other in slight but very important points. The first class may be called (A) ALBUMINS PROPER, OR NATIVE ALBUMINS. They consist of 1. Egg Albumin, which does not occur in the ordinary tissues of the animal, can be procured by filtration from the white of an egg. It makes a clear or slightly opalescent solution in water, from which it is precipitated by mercuric chloride, silver nitrate, lead acetate, and alcohol. It is coagulated by heat, strong nitric and hydrochloric acids, or prolonged exposure to alcohol or ether. 2. Serum Albumin, on the other hand, is one of the chief forms of albumin found in the nutrient fluids. It differs from egg albumin in (a) Not coagulating with ether. (/) The precipitate obtained by strong hydrochloric acid being readily redissolved by excess of the acid. (c) Coagulum being more readily soluble in nitric acid. (d) Its specific rotary power being 5 6,. while that of egg albumin is 35.5. (e) If introduced into the circulation, it is not eliminated with urine, as is egg albumin. (B) GLOBULINS. Associated with the last during the life of the tissues we find another class of albumins, namely, the globulins, which do not GLOBULINS AND ALBUMINATES. , 69 dissolve in pure water, but are more or less soluble in a solution of common salt. These may be divided as follows : i.. Globulin (cry stalling occurs in many tissues, but is usually obtained from an extract of the crystalline lens made by tritu- rating it with fine sand in a weak solution of common salt, and then passing a current of carbon dioxide through the solution. The globulin falls, being easily precipitable from its saline solu- tion by very weak acid. This form of globulin does not cause coagulation when added to serous fluids, and in this respect differs from the next members of this division. 2. Paraglobulin (serum globulin] can be obtained by passing through diluted serum a brisk stream of carbon dioxide. It is also precipitated by adding sodic chloride to saturation. When a fluid containing paraglobulin is added to a serous transudation, it causes coagulation of the fluid, giving rise to fibrin. 3. Fibrinogen, a viscous precipitate got from serous fluids or blood plasma in the same way as the last, but with greater dilu- tion and more prolonged use of carbon dioxide. It is similar in its characters to the last, but coagulates at a lower temperature (55 C.) (paraglobulin coagulating at 6o-7o C.). On its addi- tion to defibrinated blood, or a fluid containing paraglobulin, it forms a coagulum. 4. Myosin is obtained from dead muscle, being the soft, jelly- like clot formed during rigor mortis from the dying muscle plasma. It is not so soluble as globulin, for it requires a stronger solution of salt (10 %) to dissolve it, and is precipitated from its saline solution by solid salt or by dilution. It is coagulated at 60 C. 5. Vitellin, a white granular proteid obtained from the yelk of egg. It is very soluble in 10 per cent, saline solution, from which it can be precipitated by extreme dilution, but not by saturation with salt. It coagulates between 70 and 80 C. (C) DERIVED ALBUMINS (ALBUMIN ATES). i. Acid Albumin (syntonin) can be made from any of the pre- ceding by the slow action of a weak acid ; or by adding strong acetic or hydrochloric acids to native albumin, such as exists in 70 , MANUAL OF PHYSIOLOGY. white of egg, and dissolving the jelly thus formed in water. It is only soluble in weak acids exact neutralization precipitating it. With the least excess of alkali the precipitate redissolves, chang- ing into alkali albumin. If it be dissolved in weak acid it will not coagulate on boiling, but it coagulates and becomes incapable of re-solution if heated while precipitated by neutralization. 2. Alkali Albumin. Similar to the last, but produced by the action of either weak alkalies on dilute solutions, or strong solu- tion of potash on white of egg. Its general behavior is the same as the above, but if prepared by strong solution of potash and allowed to stand some time it differs in composition, being de- prived of its sulphur. It can then be distinguished by the absence of the brown coloration which appears on heating acid albumin with caustic potash and lead acetate. 3. Casein is the proteid existing in milk, and resembles alkali albumin in its reactions. It can be precipitated from milk by rennet, or acetic acid in excess, but not by exact neutralization, owing to the presence of neutral potassium phosphate, which must be converted into the acid salt before precipitation begins. (D) FIBRIN. A solid filamentous body, the result of chemical changes accom- panying the death of the blood plasma, during which the so- called fibrin generators are set free. It swells in weak hydro- chloric acid, but does not dissolve while cold. If heated to 60 C. in acid, it changes to acid albumin and dissolves. By 10 per cent, neutral saline solutions, a substance like a globulin may be extracted from it. If heated, it assumes the characters of a coagulated proteid. (E) COAGULATED ALBUMIN. If any of the above be heated over 70 C. (except acid and alkali albumin, which must first be precipitated by neutraliza- tion), they coagulate, and become extremely insoluble and lose their former characters. They are but very slightly acted on by weak acids, even when warmed. Strong acids dissolve them, GLOBULINS AND ALBUMINATES. 71 but this solution is associated with a destructive change. They are, however, converted by the digestive ferments and juices into peptones, and thus dissolved. (F) PEPTONE. This substance is formed by the action of the digestive fer- ments from any of the above albumins, in the stomach by pepsin in the presence of dilute acid, and in the small intestines by tryp- sin in the presence of dilute alkali. This change renders them more soluble and diffusible, and thus enables them to pass out of the alimentary canal into the system, and makes them more suited to take part in the nourishment of the body. The leading characteristics of peptones may be thus enu- merated : 1. Very ready solubility in hot or cold water, acids or alkalies. 2. Not coagulable by heat. 3. They are precipitated by alcohol but not changed to the coagulated form. 4. They diffuse more readily through animal membrane than any other albumins. 5. They are not precipitated by copper sulphate, ferric chlo- ride, or potassium ferrocyanide and acetic acid. 6. They are precipitated by iodine, chlorine, tannin, mer- curic chloride, and the nitrates of silver and mercury. 7. Caustic potash and a trace of copper sulphate added to their solutions give a red color which deepens to violet if too much of the copper salt be used. The formation of peptones is a gradual process having many intermediate steps, in the earlier stages of which precipitates are formed by potassium ferrocyanide and acetic acid. (Vide Chaps, vni and ix, on Chemistry of Digestion.) GROUP III. ALBUMINOIDS. These are the outcome of nutritive modification of protoplasm, and may be said to be directly manufactured by that substance, and to be specially adapted to meet the requirements of certain textures differing widely in function. ' 72 MANUAL OF PHYSIOLOGY. They are allied to one another and to the last group by (a) their percentage composition ; * (<) containing nitrogen ; (V) being amorphous colloids. They differ from albuminous bodies in (a) their solubility ; (/) their behavior to heat, acids, alkalies and the digestive fluids ; and (V) their value as food stuffs. 1. Mucin is the characteristic ingredient of the mucus manu- factured by epithelial cells, and is also found in connective tissue (abundantly in that of the foetus) and in some pathological growths. It gives a peculiar thick ropy consistence to the fluid containing it, enabling it to be drawn into threads. It is precipi- tated by mineral acids, alum and alcohol, and the precipitate swells in water and is redissolved in excess of the acid. With acetic acid a precipitate is formed which does not redissolve in excess of the acid. When boiled with sulphuric acid it yields leucin and tyrosin. 2. Chondrin is obtained by the prolonged boiling in water of slices of cartilage cleared of the perichondrium. On cooling, this solution forms a jelly. The jelly dissolves easily in hot water or alkalies, and can be precipitated by acetic or weak mineral acids, alum or acetate of lead. It gives only leucin on boiling with sulphuric acid. 3. Gelatin is produced by boiling fibrous connective tissues, such as ligaments, tendons, the true skin and bones in water. On cooling, the fluid forms a jelly, which can be dried to a colorless brittle body which swells in cold water and dissolves on being heated. It is not precipitated by acetic acid, but yields precipi- tates with mercuric chloride or with tannin, as seen in making * The following Table gives the composition of the principal albuminoids and albumin : Gelatin. Elastin. 1 Chondrin. Mucin. Keratin. Albumin. c So % 55$ 47 1 5o? 5'* S*-54$ H 7 6 7 6 6-7 N 18 X 7 !4 10 17 J 5-i7 O 23 20 3i 33 21 20-23 s 0.5 0.6 3 2-2.3 PRODUCTS OF TISSUE CHANGE. 73 leather. On boiling with sulphuric acid it yields glycin and leucin but no tyrosin. 4. Elastin is obtained from yellow elastic tissue by boiling with caustic alkalies. It is little affected by boiling water, strong acetic acid, or weak alkalies, but dissolves in concentrated sul- phuric acid. It is precipitated by tannin, and yields leucin when boiled with sulphuric acid. 5. Keratin exists in the epidermic appendages (hair, horn, nails, etc.). It resembles the albuminous bodies in containing a considerable quantity of sulphur, but differs from them and the other albuminoids in general properties. It is soluble in alkalies, swells in strong acetic acid, gives the xanthoproteic reaction, and is insoluble in the digestive juices. GROUP IV. PRODUCTS OF TISSUE CHANGE. INTERMEDIATE OR BYE PRODUCTS. These are protoplasmic manufactures destined for some useful purpose, but they do not long exist in their original form ; being often broken up into other compounds, they are reabsorbed, or pass away with the faeces. These bodies are found in the various secretions. Most of them can be better described with the func- tion of the gland which forms the secretion in which they occur. Attention must here be drawn to certain complex bodies exist- ing in the bile. Some complex nitrogenous substances and the monatomic alcohol, cholesterin, will now also be mentioned. But the reader must remember that chemically they are not con- nected with the other bodies, the description of which immedi- ately follows theirs, namely, the effete products. Bile Salts. Two acids exist in the bile united with soda to form soluble soap-like salts. They may be recognized by the purple-violet color produced by cane sugar and sulphuric acid at a temperature of about 70 C. (Pettenkofer's reaction). Taurocholic Acid, C 26 H 45 NSO 7 , is most plentiful in the bile of carnivora, where it occurs combined with soda. It is decomposed by prolonged boiling with water into taurin and cholic acid, thus : Taurocholic Acid. Taurin. Cholic Acid. C 26 H 45 NS0 7 + H 2 = C 2 H 7 NS0 3 + C 24 H 40 O 5 . 7 74 MANUAL OF PHYSIOLOGY. Glycocholic Add, C 26 H 45 NO 6 , found in the bile of herbivora and man. It crystallizes in fine white, glistening needles. It exists as the glycocholate of soda in the bile. By boiling with weak acid, it yields glycin and cholic acid. Glycocholic Acid. Glycin. Cholic Acid. C 26 H 45 N0 6 + H 2 == C 2 H 5 N0 2 + C 24 H 40 O 5 . In the bile certain matters also exist to which the color is due, the principal being bilirubin in man and carnivora, and biliver- din in herbivora. They are probably derived from the coloring matter of the blood. They can be recognized by treating the solution with nitric acid which is colored with red fumes, when a play of colors is seen passing through stages of green, blue, violet, red and yellow. Lecithin, C^H^NFC),,, is a complex nitrogenous fat found in most tissues and fluids of the body, particularly in the nerve tissues and yelk of egg. It is an interesting product of decom- position of the constituents of the brain, and is related in con- stitution to the neutral fats ; it may be regarded as an acid glycerine ether. It is easily decomposed when heated with baryta water, splitting into glycerin-phosphoric acid, neurin, and barium stearate. Another body called Cerebrin, not containing any phosphorus and of doubtful composition, can be obtained from brain sub- stance, and is also found in nerve fibres and pus corpuscles. It is a light colorless powder which swells in water. Prof agon, C 160 H 308 N 5 PO 35 , is by some supposed to be the chief constituent of brain substance, and by others a mixture of the last two bodies. Neurin (Choltn), C 5 H 15 NO 2 , is an oily liquid only found in the body as a product of the decomposition of lecithin, but it has been obtained synthetically. Cholesterin, C 26 H 44 O -j- H 2 O, exists throughout the body where active tissue change is going on, particularly the nervous centres. It is a monatomic alcohol, and is the only one existing free in the body. It may be obtained from gall stones, some of which consist entirely of cholesterin. It may occasionally be found in a crystallized form in many of the fluids of the body but never WASTE PRODUCTS. 75 in the tears or urine, and only seems to be an effete product, nearly all that produced in the body being discharged with the effete portions of the bile. It may be recognized by the shape of the crystals formed from a solution in alcohol, which are rhombic plates, in which one corner is generally deficient. EFFETE PRODUCTS. These, as has been stated before, are generally the outcome of the active chemical changes necessary for the growth and vitality of the living protoplasm, and are for the most part soon elimi- nated by the excretory glands, so that but small quantities of them can be found in the active tissues where they are produced. Urea, CO(NH 2 ) 2 , is the most important constituent of the urine of mammalia, but not of that of birds or reptiles. Traces of it may be found in the fluids and tissues of the body. It is readily soluble in water and alcohol, and forms crystals when its solution is concentrated. It decomposes when treated with some strong acids or alkalies, taking up water and yielding CO 2 and NH 3 ; and with nitrous acid gives CO 2 -f- N 2 -j- 2(H 2 O). It was the first of the so-called " organic " compounds to be made artificially, being obtained by Wohler in 1828 by mixing watery solutions of potassium cyanate and ammonium sulphate, evapo- rating to dryness and extracting with alcohol, or, in short, by heating ammonium cyanate, with which it is isomeric. Ammonium Cyanate. Urea. NH 4 .CNO = CO.NH 2 .NH 2 . It can now be produced artificially in other ways. It has also been considered a monamide of carbamic acid (CO.OH.NH 2 ), a molecule of hydroxyl being replaced by one of amidogen, NH 2 , thus CO.NH 2 .NH 2 . In the presence of septic agencies, in a watery solution, urea takes up two molecules of water and is converted into ammonium carbonate CO(NH 2 ) 2 -f 2H 2 O = CO(ONH 4 ) 2 . The so-called alkaline fermentation of urine depends upon this change. The reader is referred to the Chapter on Excretions (xxn), where more complete information is given. Kreatin, QH 9 N 3 O 2 , occurs in muscle and many other textures. 76 MANUAL OF PHYSIOLOGY. It may be converted into kreatinin by the action of acids by simple dehydration. It can also be split tip into sarcosin and urea. Kreatinin, C 4 H 7 N 3 O, is a dehydrated form of kreatin, which is a normal constituent of urine. In watery solutions it is slowly converted into kreatin. Allantoin, C 4 H 6 N 4 O 3 , found in the allantoic fluid and the urine of the foetus and pregnant women. It is crystallizable, and is converted into urea and allantoic acid by oxidation. Glycin(Glycocollm Glycocine), C 2 H 2 (NH,)O.OH, is regarded as amido-acetic acid. It does not occur free in the body, but enters into the composition of the bile acids and hippuric acid. It is soluble in water, and insoluble in cold alcohol and in ether. Leuan, C 6 H 10 (NH 2 )O.OH, or amido-caproic acid, is found in the secretion of the pancreas and some other glands. It is one of the principal products of the decomposition of albuminous bodies, from which it can be obtained by boiling with sulphuric acid, in the form of peculiar rounded crystals. Tyrosin, C 9 H U NO 3 , though belonging to a distinct chemical series (aromatic), is only found in company with leucin in the decomposition of albuminous bodies, and normally in the pan- creatic secretion. Its constitution is said to give warranty for the name oxy-phenyl-amido-propionic acid. Taurtn, C 2 H 7 NSO 3 , is a constituent of one of the bile acids, and is also found in muscle juice. It may be regarded as amido- ethyl-sulphonic acid. Uric Acid, C 5 H 4 N 4 O 3 (dibasic), is found in large quantities in the excrement of birds and reptiles, but in a small and variable quantity in the urine of man. Traces have been found in many tissues, in some of which quantities accumulate as the result of pathological processes (gout). It forms salts which are much less soluble in cold than in hot water, and make the common sediment in urine. The acid salts are less soluble than the neutral. The common test for uric acid consists of slowly evaporating the substance to dryness with a little nitric acid, and to the residue adding ammonia, when a bright purple color is produced (murexide test). Uric acid is supposed to be a step NON-NITROGENOUS. 77 in the production of urea, which is one of the results of its oxida- tion in the presence of acids, thus : Uric Acid. Alloxan. Urea. C 5 H 4 N 4 O 3 + H 2 O -f O = C 4 H 2 N 2 O 4 + CO(NH 2 ) 2 . Hippuric Add, C 9 H 9 NO 3 , occurs in considerable quantities in the urine of the horse and herbivora generally. It is found but very sparingly in man's urine, but it appears in large quantities after benzoic acid and some other medicaments have been taken. In constitution it is an amido-acetic acid in which one atom of the hydrogen is replaced by the radical benzoyl (C 7 H 5 O). In the body it is combined with bases, and is formed out of benzoic acid and glycin (amido-acetic acid), thus: Glycin. Benzoic Acid. Hippuric Acid. Water. C 2 H 2 (NH 2 )O.OH + C 7 H 6 O 2 = C 2 H(C 7 H 5 O)(NH 2 )O.OH +H 2 O. By heating or putrefaction it is resolved into these constituents. Indol, C 8 H 7 N, is produced in the intestinal canal by the putre- factive changes brought about by septic agencies during pan- creatic digestion. It gives an odor to the faeces and a red color with nitrous acid. Indican, a peculiar substance sometimes found in the urine and sweat. With oxidizing agents it yields indigo blue. By this fact it is easily recognized. An equal volume of hydrochloric acid and a very small quantity of calcium hypochlorite (bleach- ing lime) is added, and the indigo which is formed can then be dissolved and separated by agitation with chloroform. CLASS B. NON-NITROGENOUS. GROUP V. CARBOHYDRATES. Carbohydrates (general formula, C m H 2n O n ) are bodies in which the hydrogen and oxygen exist in the same proportion as in water, the carbon being variable. The following examples of this group are met with in the textures of the body : Grape Sugar (Dextrose'}, C 6 H 12 O 6 , occurs in minute quantities in the blood, chyle and, lymph. It forms crystals which readily dissolve in their own weight of water. The watery solution has a dextro-rotatory power on the ray of polarized light. When mixed with yeast, the fungus (Sac char omyces cerevisice) of the 78 MANUAL OF PHYSIOLOGY. yeast causes alcoholic fermentation of the sugar, whereby alcohol and carbon dioxide are formed. Dextrose. Alcohol. Moderate heat (25 C.) aids the process, and cold below 5 C. checks it ; an excess of either sugar or alcohol stops it. The presence of casein or other proteid material, when decom- posing, gives rise to lactic fermentation, producing first lactic acid, then butyric acid, carbon dioxide and hydrogen. Dextrose. Lactic Acid. Butyric Acid. C 6 H 12 6 = 2C,H 6 0, = C 4 H 8 2 + 2C0 2 + H 4 . Milk Sugar {Lactose}, C 12 H 22 O n -j- H 2 O, metameric with cane sugar (sucrose). It is the characteristic sugar found in milk. It is not so soluble as dextrose, and does not undergo direct alcoholic fermentation, but under the influence of certain organisms it readily gives rise to lactic acid by lactic fermentation in the same way as dextrose. (See page 102.) Inosit, C 6 H 12 O 6 -f- 2H 2 O, is an isomer of grape sugar, which is incapable of undergoing alcoholic fermentation. It is crystal- lizable, and easily soluble in water. It has no effect on the polarized ray. It is found in the muscles, and also in the lungs, spleen, liver and brain. Glycogen, C 6 H 10 O 5 , a body like dextrin, first found in the liver. It gives an opalescent solution in water, and is readily converted into dextrose by an amylolytic ferment, or weak acids. It has a strong dextro-rotatory power. It can be found in most rapidly growing tissues. (See Glycogenic Function of the Liver.) GROUP VI. FATS. These bodies have the same elements in their composition, but the hydrogen and oxygen have variable proportions not that of water. Fats are found in large masses in some tissues, and also as fine particles suspended in many of the fluids. The fat of adipose tissue in man is a mixture of olein, palmitin and stearin, which are spoken of as the neutral fats. The first is liquid, and the last two solid at normal tempera- tures, and the varying consistence of the fat of different animals INORGANIC BODIES. 79 depends upon the relative proportions of the solid or liquid fats. Fats are soluble in ether and chloroform, but quite insoluble in water. When agitated in water containing an albuminous body, and an alkaline carbonate in solution, fluid fat is broken up into small particles, which remain suspended in the liquid, forming an opaque milky emulsion. Chemically, they are regarded as ethers derived from the triatomic alcohol glycerine, C 3 H 5 (OH) 3 , by replacing the OH group with the radicals of the fatty acids, thus : Glycerine. Palmitic Acid. Tripalmitin. Water. C 8 H 5 (OH) 8 + 3(C 16 H 32 2 ) =C 3 H 5 (C 16 H 31 2 ) 3 + 3 H 2 O. Under the influence of certain ferments they separate into glycerine and the fatty acid, uniting with the necessary elements of water. When the neutral fats are boiled with alkaline solutions they are similarly decomposed, and uniting with the elements of water, form glycerine and fatty acids. The glycerine is thus set free, but the fatty acid combines with the alkaline metal to form a soluble soap. An insoluble soap may be obtained by substituting lead or lime, etc., for the alkali. This splitting up of the neutral fats, stearin, palmitin and olein into sodium stearate, palmitate, or oleate goes on during digestion, and is said to be useful in aiding the absorption of fatty matters. INORGANIC BODIES. Water (H 2 O) is present in nearly all tissues in larger propor- tion than any other compound, making up about 70 per cent, of the entire body weight. The amount in each texture varies, the different tissues having widely different consistence. Water is introduced into the body not only as drink, but a large quantity is also taken with our solid food. It is highly probable that in the chemical changes which take place in the tissues, some water is formed by the oxidation of the hydrogen of the more complex substances. In the economy it acts as the universal solvent in the fluids of 80 MANUAL OF PHYSIOLOGY. the body, and as the agent by means of which the chemical changes of the various organs can be accomplished. Water leaves the body by the lungs as vapor, and by the skin, kidney, and many other glands, as the fluid in which the solids of their secretions are dissolved. Inorganic acids occur in the body either combined, forming salts, in which condition we find several (sulphuric, phosphoric, silicic), or uncombined. In the latter state we have only two, viz. : Hydrochloric Acid, HC1, which is formed in the stomach, and plays an important part in gastric digestion. Carbonic Acid Gas, CO 2 , exists in most of the fluids of the body, having been absorbed by them from the tissues. The venous blood contains a considerable quantity, some of which is got rid of during the passage of the blood through the lungs. It is a waste product, which must be constantly eliminated from the body (see Respiration). Salts. A large number of salts occur in the tissues, generally in small quantity, in solution. In the teeth and in bone tissue salts exist in the solid form, and in much greater proportion than in any of the soft parts. Most of the salts are introduced into the economy with the food, but some, doubtless, are formed in the body itself. Our knowledge of the exact position occupied by the salts in the textures is very incomplete, as their amount is usually estimated from the ash of the tissue which remains after ignition, by which process some become altered, so that it is impossible to say what are the exact salts that are present in the body. They form chemical combinations with the complex organic compounds, which we do not understand, and probably have important functions to perform, such as. rendering certain materials (globulins) soluble, or otherwise facilitating tissue change. The salts pass out of the body in many secretions, largely in the urine, where they influence the elimination of urea, and therefore form an important constituent of that secretion. Common Salt (Sodium Chloride}, NaCl, is the most widely dis- tributed, and is present in greater quantity than any other salt INORGANIC BODIES. 8 1 in all animal fluids and most tissues, except bones, teeth, red blood corpuscles and red muscle. Potassium Chloride commonly accompanies sodium chloride in small quantity. In the red blood corpuscles and in muscle it occurs in greater amount than the sodium salt, while in the blood plasma but little is found in comparison with the sodium salts, and any excess seems to act as a poison to the heart. Carbonates and phosphates of calcium, sodium, potassium and magnesium occur in small quantities in most tissues. The earthy part of bone is chiefly composed of calcium and magnesium phos- phate and calcium carbonate, together with some calcium fluoride. Sulphates of sodium and potassium, probably formed in the body from the oxidation of the sulphur in the complex proteid materials, occur in most tissues, and are removed from the body by the kidneys. Finally, we find two of the elements free in the textures. Of these Oxygen plays by far the most important part. It is widely distributed among the fluids of the body, from which it can be removed by reducing the pressure of oxygen of the atmosphere by means of an air pump. Oxygen is introduced into the body by the lungs, where the blood takes it from the air. In the blood only a small quantity of that which can be removed by the air pump is really free ; the remainder is chemically com- bined with the coloring matter of the blood. It is absolutely necessary for life, as it alone can enable the chemical changes of the tissues, which are mostly oxidations, to go on. It is, in fact, the element necessary for the slow combustion which takes place in the nutrient material after its assimilation. Nitrogen also occurs in the blood, but in insignificant quantity. It is absorbed from the atmosphere as the blood passes through the lungs. So far as we know, it has no physiological importance in the body. 82 MANUAL OF PHYSIOLOGY. CHAPTER IV. THE VITAL CHARACTERS OF ORGANISMS. The manifestation of so-called vital phenomena in man forms the subject-matter of the following chapters, and some explana- tory definition of the vital characters of the simpler organisms will be useful in preparing the beginner's mind for the more intricate questions in human physiology. This, with the fore- going short account of the chemical and structural peculiarities of animals, will complete a rough outline of the general charac- ter of organisms. Protoplasm has already been referred to as the material capable of showing vital phenomena, the most obvious and striking of which are its movements. Besides the common molecular or Brownian movement of the granules in protoplasm which may be seen in most cases where fine granules are suspended in a less dense medium protoplasm can perform motions of different kinds which must be regarded as distinctly vital in character. This movement may be said to be of three different kinds, according to the results produced, viz. : (i) The production of internal currents. (2) Changes in form. (3) Locomotion. In reality, the two latter are dependent on the first. The existence of currents moving from one part of the proto- plasm to another can be well seen in vegetable cells, when the cell wall restricts the more obvious change in form or place. Thus in the cells forming the hair on the stamens of Tradescantia Virginica the various currents can be seen in the layers of proto- plasm which line the cell wall. The granular particles course along in varying but definite directions, passing one another like foot passengers in a crowded street. The first and most obvious result of this is, that the different parts of the substance are frequently brought into con- tact with one another, and thus the products of any chemical PROTOPLASMIC MOVEMENTS. 83 changes taking place at a given part of the cell body are rapidly distributed over the entire mass of the protoplasm. The change inform occurs if there be no definite cell wall as in naked vegetable spores and amoeboid forms of animal life to restrict or direct the current of protoplasm : it flows unto various directions in bud-like processes, which appear at various parts of the protoplasmic mass, so as to cause a constant change in the form of the cell. These outstretched processes sometimes flow together and become fused, often enclosing some of the medium in which the creature is suspended, or catching some foreign particle floating near them. The flowing out of these pseudopodia usually takes place for some time persistently from one side of the cell ; and the body of the cell has to follow, as it were, the protrusion of the processes in such a manner that in a short time definite change in position or movement in a certain direction occurs : thus the protoplasmic unit may be said to perform definite progression or locomotion. All these movements may be seen in the white blood corpuscle of a till jj i An amoeba figured at two different mo- COld-bloOded animal, SUCh as a ments during movement, showing a frog, and still more easily in the cemrarportior 1 " ^f Nudetrs 8 ^) "in- unicellular amoeba. Various influences may be seen to affect the rate of movements and probably influence at the same time the other activities of the protoplasm. Foremost among these must be named: (i) Temperature. If a protoplasmic unit, which is observed to be motile, be gently warmed, the movements become more and more active as the temperature is raised, up to a certain point, about 35-42 C., when a spasm occurs, resulting in the with- drawal of the pseudopodia; soon after this the cell assumes a spherical shape. If the heat be carefully abstracted before it has attained too great a height, the protoplasm may recover and again commence its movements. If, on the other hand, cold be 84 MANUAL OF PHYSIOLOGY. applied to moving protoplasm, the motions become less and less active, and commonly cease at a temperature about or a little above o C. (2) Mechanical irritation also produces a marked effect on the movements of protoplasm. This may be well seen in the behavior of a living white cell of frog's blood under the microscope. It is spherical when first mounted, owing to the rough treatment it goes through while being placed on the glass slide and covered ; shortly its movements become obvious by its change in form, which may again be checked by a sudden motion of the cover glass. (3) Electric shocks given by means of a rapidly-broken induced current cause spasm of the protoplasm, the cell becoming spherical. (4) Chemical stimuli also have a marked effect; carbonic acid causing the movements to cease, and a supply of oxygen making it active. The movements and other activities of protoplasm are, during life, frequently modified and controlled by nerve influence, as will appear in the following pages. This may readily be seen in the stellate pigment cells of the frog's skin, which can be made to contract into spheres by the stimulation of the nerves leading to the part. The motions of protoplasm are thus seen to be affected by external influences, but the most careful observer cannot find physical explanations of the various movements which have been described. It is necessary, therefore, to ascribe this power of motion to some property inherent in the protoplasm, and hence the movements are called automatic. We are unable to follow the chemical processes upon which the activities of the proto- plasm depend, and we therefore call them vital actions ; but we must assume that these so-called vital properties depend on cer- tain decompositions in the chemical constitution of the proto- plasm. We know that some chemical changes take place, as we can find and estimate products which indicate a kind of com- bustion ; but we know little or nothing of the details of the chemical process. From the foregoing description of the manner in which proto- plasm responds to external stimuli, it may be gathered that it is capable of appreciating impressions from without ; indeed, it can be said to feel. We can only judge of the sensitiveness of any CELL DEVELOPMENT. 85 creature by the manner in which it responds to stimuli, and we may therefore conclude that the smallest particle of living proto- plasm is endowed with definite sensitiveness ; this must be noted as one of the most striking properties of protoplasm. Every particle of living protoplasm has the power of assimila- tion. Taking into its structure any nutrient matters it meets with, by flowing around them in the way mentioned, it brings them into direct contact with different parts of its protoplasmic substance. This nutrition of the cells gives rise to their growth, and finally leads to their reproduction. These facts will be more closely examined when speaking of their relation to cell life. FIG. 36. FIG. 37. JL Cells of the yeast plant in process of budding, between which are some bacteria. Cartilage from young animal showing the division of the cells (a, b, c, d). When a certain size has been attained, the cell does not further increase, but prepares to bring forth a cell unit similar to itself. This is spoken of as the reproduction of cells. Different kinds of cell reproduction have been observed, which are all, however, modifications of the same general plan. The first is that by the formation of a bud from the side of the parent cell ; this bud increases in size, and finally detaches itself from the parent and becomes a separate individual. This process, which is called gemmation, can readily be seen in all its stages in growing yeast, where the torula cells have various-sized buds 86 MANUAL OF PHYSIOLOGY. growing from them. If the newly-formed portion be large, nearly equal in size to the cell itself, the process receives the name of fission, or division. In well-marked typical fission the parent cell divides into FlG> 38> two parts of equal size, each of which becomes a perfect individual. Various gradations may be traced between the two processes, so that Cells of a fungus (Glceccapsa) showing different stages . . (1-4) of endogenous division. (After Sachs.') it IS difficult to draw any very distinct line between budding and fission. The budding and fission may be multiple; many buds and several units, products of division, may remain together, and form what is called a colony. When this multiple budding or division takes place, so that the new units are included within the body of the parent cell, then the process is called endogenous reproduction or spore formation. Just as there are gradations between^ budding and fission, so it is difficult to draw a hard and fast line between what may be called multiple fission and spore formation. In tracin'g the stages of development of the highly differentiated cells of some tissues, we have to pass through a series of changes which form a cycle that may well be called the lifetime of the cell. The duration of this cycle varies greatly in different indi- vidual cells. Some cells are very short-lived, being destroyed by their act of secretion ; others probably endure for the lifetime of the animal. The life history of all cells begins with the stage when they are composed entirely of indifferent protoplasm, in which various modifications are subsequently produced. Let us take, as an example, a cell of the outer skin or cuticle, and examine its life history. The cuticle is made up of numerous layers of epithelial cells laid one on the other, and the surface cells are constantly being rubbed or worn off. These cells have their origin from the cells of the deepest layer, which is next to the supply of nutriment. This layer is made up of soft proto- REPRODUCTION. plasmic units, which have, no doubt, certain specific inherited characteristics, but apparently the same as the motile, sentient, growing protoplasm of an indifferent cell. By a process of fission or budding, constantly going on in this deepest layer of cells, new protoplasmic units are produced. These become distinct individuals, and occupy the position of the parent cell, which, having produced offspring, is moved one place nearer the surface, away from the supply of food. The new cell in time gives rise to offspring, and having attained reproductive maturity, in turn is moved onward to the surface. The result of this- is FIG. 39. Division of Egg cell. (Gegenbauer.) that its supply of nutrition diminishes, the evidences of repro- ductive activity disappear, and at a certain point all signs of protoplasmic life are lost. But on its way from the seat of its origin to the surface, it makes use of its limited supply of nutri- tion for the purpose of manufacturing a special kind of material which, if present at all, only occurs in the minutest traces in ordinary protoplasm. As the cell moves toward the surface, it loses its protoplasmic characters, becomes tougher and drier, and finally nothing but the special horny material remains. Thus, from the birth of the cell, its energies are devoted, first, to its 88 MANUAL OF PHYSIOLOGY. own growth, then to the reproduction of its like, and finally to the formation of a material fitted to act as a mechanical protection to the surface of the skin. Having manufactured a certain amount of this material, the protoplasm dwindles, and finally disappears, so that the cell may be said to die. Its horny, in- soluble and impermeable skeleton has, however, yet to do service in the outer layer of the skin while it is passing toward the sur- face, to be in its turn rubbed off. It has already been stated that the material protoplasm, which forms all active cells, is capable of carrying on the many func- tions required for the independent existence of simple creatures. It will be found in the subsequent pages that not only can pro- toplasm perform all the activities necessary for the life history of unicellular organisms, but that it can also work out all the functions of the most complex animals. Indeed, the cells which accomplish the most elaborate functions in man, are but pro- toplasm more or less modified for the special purpose to be attained. The different living operations of many independent unicellular organisms can be more completely watched than the changes which take place in the cells of the higher animals, both on account of their greater size, their freedom, and the more obvi- ous character of the changes taking place in them. The student is therefore advised to spend some time in contemplating the operations which go on in those simple organisms whose life is not complicated by structural or functional elaboration, before attempting to solve the difficult question of the mechanism of the human body. The lowest forms of living creatures that we are acquainted with (micrococcus and bacterium}, are placed among the fungi in the vegetable kingdom. On account of their extremely minute size being hardly visible as spherical or elongated specks with a powerful microscope we can say but little about their struc- ture. They appear to be translucent and homogeneous. Since we use the term protoplasm to denote the material of which the active part of the simplest forms of living beings are composed, we must assume that bacteria are small particles BACTERIA. 89 of that material, but the characters attributed to protoplasm can- not be detected in the minute glistening mass which makes up their body. They are so certain to appear in a couple of days in organic infusions, or in any fluid prone to putrefaction, and multiply with such astounding rapidity, that they have been supposed by some to develop spontaneously. But this is now known not to be a fact. Bacteria can no more than any other form of living thing appear without progenitors. They float inanimate and dry in multitudes through our atmosphere, and adhere to all substances to which the air has free access. The moment they alight upon a suitable habitat,- they burst into prodigious activity, at first forming masses or colonies, which may be seen as a jelly-like scum on the fluid. Such a habitat is supplied by any organic substance capable of ready decomposition, for which process, as is well known, the great requirements for life, moisture and warmth are to a certain degree necessary. Vast varieties of these organisms are now known. They differ slightly in shape, in their habitat, and in their properties. Some are obviously composed of two distinct layers, some are provided with a fine hair-like process, by the lash-like motions of which they move rapidly in a definite direction. They are known to be inseparable from putrefactive changes in organic materials ; without them no putrefaction can go on, since this process is but the product of their living activity. Great heat kills them, too great cold or dryness checks their activity and stops putrefaction. When an organic substance is absolutely protected from their presence by exclusion of the air, etc., no putrefaction occurs, even though it be prone to spon- taneous decomposition, and be placed under favorable circum- stances as to warmth and moisture. Bacteria would not deserve so much notice here were it not for the pathogenic influence some of them have on the higher forms of life. We do not know that they are necessary for any of the more important processes that normally go on in the human body, though they are constantly present in the intestinal tract, and are inseparable from at least one change taking place 90 MANUAL OF PHYSIOLOGY. there that may be regarded as physiological. It is their relation to the diseased state that makes a knowledge of these creatures imperative to medical men. So long as the tissue of a higher animal is healthy and well nourished, the commoner forms of septic bacteria cannot thrive in immediate contact with it. They can only exist in the intestine, etc., because there they find accumulations of lifeless fluids which offer them a suitable nidus. Active living tissues may be said to have antiseptic power, /. e., are able to destroy septic bacteria ; and it is only owing to this bactericide power of our textures, that we can with immunity breathe into our lungs the atmospheric air often crowded with these organisms, and swallow ( multitudes of them with our food. But for it every wound would become putrid, every breath might admit deadly germs to our blood. When the vitality of the body generally is lowered, the vital activity of the tissue may fall below that necessary to insure the death of the bacteria, whose victory is signaled by unwonted and often fatal changes. Morbid fluids allowed to accumulate in the textures facilitate the growth of bacteria, and give rise to various grades of "wound infection." But if all accumulations be avoided, the bacteria brought into relation with the living tissue only irritate it, and cause general fever and local suffering to the patient. They cannot propagate in live tissue as in lifeless fluids. As a rule, the injurious effect of bacteria is in inverse proportion to the vital power of the textures which they invade. This is seen in many cases familiar to the physician and the surgeon. There are, however, many forms of pathogenic bacteria which, if introduced into the system by inoculation, are able to overcome the vital activity of the tissues of certain animals even in the most robust health. We next come to forms of fungus, which set up a process very like putrefaction, such as the yeast plant, Torula cerevisia, which causes alcoholic fermentation in sugar solutions. In the torula an external case containing protoplasm may readily be seen, and multiplication of the cells goes on rapidly by a process of budding. Torulae, however, like bacteria, though called vege- AMCEBA. tables, have not the power of assimilating as ordinary green plants do, but require nutriment to be supplied to them which already contains organic or complex compounds. Structurally but little different from torula is a one-celled plant, the green protococcus, which, like a higher plant, can build up its texture from the simplest food stuffs, and carry on its functions. It consists of a case made of cellulose, within which lies a mass of protoplasm with a nucleus. Their protoplasm is colored green by a peculiar substance called chlorophyll. We shall see presently that it is to protoplasm containing chlorophyll that plants owe all their most characteristic and wonderful properties ; viz., the property of assimilating so as to construct complex carbon com- pounds out of simple inorganic materials. FIG. 40. Two different forms of Amoebae in different phases of movement. Those on the left (after Cadiat.) A and B show an outer clear zone. (Gegenbauer.) The smallest and simplest organisms classed as animals are generally larger than the vegetable cells just alluded to. They consist of protoplasm without any nucleus, and only sometimes with a structural difference between any part of their substance. As an example we may take Protamoeba. This is a small mass of protoplasm without any nucleus, but its outer layer is clearer and less granular than the central part. It can move by sending out protoplasmic processes, in which currents can be observed resembling those in the vegetable cells. Excepting as regards the nucleus, it is much the same as the Amoeba, which can be readily found and watched, and will be more accurately described. The amoeba is a single cell or mass of uncovered protoplasm, 92 MANUAL OF PHYSIOLOGY. containing a well-defined nucleus, within which is a nucleolus. There is also generally a vacuole. The central part of the pro- toplasm is densely packed with coarse granules, but the outer, more active part is structureless and translucent looking, some- what like a fine border of muffed glass, encasing the coarsely granular middle portion. Such an animal has no parts differen- tiated for special purposes, the requirements of its functions being so limited that the protoplasm itself can accomplish them. Thus the processes of protoplasm, which flow out with con- siderable rapidity from the body, frequently encircle particles of nutrient material, and then closing in around them, press them into the midst of the granular central mass. Here they sojourn some time, and during this period no doubt any nutritive pro- perties they possess are extracted from them, and they are then ejected from the plastic substance. This form of assimilation demands no previous preparation of the food such as we shall see takes place in the alimentary tract of man, and in the special organs of the higher animals ; yet it is a form of digestion adequate at least to the requirements of this simple organism. The repeated alteration of relationship between the different parts of the protoplasm, and the surrounding medium during the flow- ing hither and thither of the currents, produces not only a change in the shape and position of the animal, but also acts as a means of distributing the nutriment to the different parts of the body, and of collecting and carrying to the surface the various products of tissue decomposition ; thus the streaming protoplasm does the work of a circulating fluid such as we see in the more elaborate organisms for the distribution of nutriment and elimina- tion of w r aste materials. The surface of the amoeba is sufficient to allow of the gas interchange necessary for -life, and by means of the ever-changing material exposed, sufficent oxygen is taken for its tissue combustions, and so a function of respiration is established . The growth that results from the perfect perform- ance of these vegetative functions proceeds until the maximum size is attained, and further nutritive activity is then devoted to reproduction. When growth ceases, commonly the cell divides and forms two distinct individuals. The movements which form PARAMCECIUM. 93 the most striking operations of the amoeba are the same as those which take place in protoplasm, except that they are more rapid and obvious. The clear, outer layer first flows out as a bud-like process, and, as it is gradually enlarging, some of the central granular part of the cell suddenly tumbles into its midst, where it remains, while other pseudopodia are being thrown out in the neighborhood, and the same changes repeated in them. It is difficult to watch the motions of an amoeba without being impressed with the idea that it is not only endowed with sensi- bility, but that it can also discriminate between different objects, for we see it greedily flowing around some food material, while it carefully avoids other substances with which it comes in contact. If a glass vessel containing several amoebae be placed in a window, they will be found to cluster on the side of the glass most exposed to the light. From this it would appear that, in some obscure way, protoplasm can appreciate light, and respond to its influence by moving toward it. This single-celled animal, or nucleated mass of protoplasm, can perform all the functions of a higher animal. It can move from place to place and assimilate nutriment, apparently discriminat- ing between different materials. It distributes nutrient stuffs and oxygen throughout its body by a kind of tissue circulation, and it can appre- ciate and respond to the most delicate form of f stimulus, namely, light, which subtle motion has no effect on the sensory nerve fibres of the higher animals. T 11 i -1 c ii_ Diagram of Para- In some unicellular animals certain parts of the m^dum showing cell are specially modified for the performance of special functions, a division of labor thus taking popia into place which insures the more perfect accomplish- ^k e ' n ! h (/)M d uth! ment of the different kinds of activity. In one ^Ltracrfte'veilP. of the commonest of the Infusoria (Paramcecia cle - ( A f ter Lach - v wtunn.) bursaria}, which swarm in dirty water, this is well exemplified. The outer layer of the flattened body is denser, and forms a kind of fibrillated corticular case (ectosarc), 94 MANUAL OF PHYSIOLOGY. which is covered over with hair-like processes (vibratile cilia), constantly moving in a certain direction, so as to propel the creature rapidly through the water. The internal part of the cell is very soft, almost fluid, and coarsely granular in appearance, containing many bodies which have obviously been introduced from without. This soft internal protoplasm (endosarc) moves slowly round in a definite direction, completing its circuit in one or two minutes, and thus carries on a circulation which mixes the various matters contained in it. At one point of the ectosarc, or cortical layer, an orifice or mouth leading to an cesophageal depression is found. This orifice is lined by moving cilia, which by their vibrations drive the food into the oesophagus, whence it is periodically jerked into the soft internal protoplasm or endo- sarc, together with some water, and thus forms a food vacuole, which is carried round in the circulation of the ectosarc. Besides a well-marked nucleus and nucleolus in the central part of the cell, these paramoecia have one or more clear spaces placed near the surface at the extremities of the animal. These vacuoles suddenly contract, and disappear every now and then. When this contraction occurs, fine canals radiating from the contractile vacuole are distended with the clear fluid which has probably entered the vacuole from without. Thus a permanent set of water vessels carry fluid from the contractile vacuole throughout the endosarc. In such an animal there is a distinct advance of function com- pared with the amoeba ; a more elaborate and specialized method of feeding; a more systematic and regular circulation of nutri- ent matters ; a respiratory distribution of water by the contrac- tile vesicle and its water canals ; more rapid motion ; and more obvious sensation. In the bell animalcule, or Vorticella, the same kind of division of labor exists, but in one of its commonest conditions it is attached by a thin stalk to the stalk of some weed or other object. Besides the ciliary movement we here find that the gen- eral mass of the protoplasm can suddenly and forcibly contract, so as to completely alter its shape, and change the bell into a rounded mass, This spasm of the body is commonly associated PARAMCECIUM. 95 with a wonderfully rapid contraction of the stalk. This stalk consists of a delicate transparent sheath, in the centre of which is a thin thread of pale protoplasm. The rapid contraction of the protoplasm of the stalk and the spasm of the bell occur on the application of the least mechanical excitation, such as a touch to the cover glass. Here in a single cell we have certain portions set apart for special purposes, most of which are the same as in paramcecia. But the animal being attached requires a special way of escaping from its enemies, and hence we find it endowed with three special forms of motion. Besides the ciliary and streaming protoplasmic motion, its body can spasmodically change its shape, and the stalk contracts with a velocity compar- able with that of the most specifically modified contractile tissue (muscle) of the higher animals, by means of which their rapid and varied movements are carried out. 96 MANUAL OF PHYSIOLOGY. CHAPTER V. FOOD. The continuation of life depends on certain chemical changes which are accompanied by a loss of substance on the part of the active tissues. This loss must be made good by the assimilation of material from without, and the manner in which assimilation takes place constitutes one great point of difference between Plants and Animals. In the majority of the former (certain fungi form the main exceptions) the cells in those portions of the plant which are exposed to the light and air contain a peculiar green substance called chlorophyll, and through the agency of this substance they are able to obtain from the inorganic king- dom nearly all the food they require. Water, with such salts as may happen to be in solution, is taken up by the roots, and car- ried through the stem to the leaves ; here the active chlorophyll- bearing cells, under the influence of the sun's rays, cause its elements to unite with the carbon dioxide present in the air, and form various substances, of which we may take starch or cellu- lose as an example. The reaction may be represented chemic- ally, thus : 6C0 2 + 5H 2 = C 6 H 10 5 + I2 . Starch or Cellulose. A large proportion of oxygen is thus set free and discharged into the atmosphere. The most striking property of plant protoplasm is the power of using the energy of the sun's rays to separate the elements of the very stable compounds, carbon dioxide and water, and from the elements thus obtained to make a series of more complex and unstable compounds, which readily unite with more oxygen, and change back to carbonic anhydride and water. The carbon compounds made in and by the protoplasm of the green plants are some of the so-called "organic compounds," FOOD STUFFS. 97 which enter into the composition of both plants and animals, and form an essential part of the food of the latter. They may be divided into three groups . 1 . Carbohydrates bodies so called from the presence of hydro- gen and oxygen in proportion to form water; e.g. : Starch, C 6 H 10 5 = C 6 (H. 2 O) 5 . Grape sugar (dextrose), C 6 H 12 O 6 = C 6 (H 2 O) 6 . Cane sugar (sucrose), C 12 H 22 O n = (C 12 H 2 O) U . 2. Fats compounds of carbon and hydrogen with a less pro- portion of oxygen than the starches, e. g. : Olein (principal constituent of olive oil), C 57 H 104 O 6 . 3. Albuminous bodies which contain nitrogen in addition to carbon, hydrogen and oxygen. These are of complex composition, and, as a rule, cannot be represented by chemical formulae. Animals cannot thrive on the simple forms of food obtainable from the inorganic kingdom, which suffice for the nutrition of a plant. They require for assimilation materials nearly allied in chemical composition to their own tissues ; substances to be used as fuel in producing the activities of their bodies. In short, they require as food the very organic substances which plants spend their lives in making : viz., starches, fats and albuminous bodies. These substances must be supplied to animals ready made, so that directly or indirectly, through the medium of other animals, all these complex substances are the result of work done by vegetable life. The chief acts of animal protoplasm are oxidations, a slow burning away of its substance, which results in the production of inorganic materials like those used by plants as food. Plants use simple food stuffs, and from them manufacture com- plex combustible materials, and thus store up the energy of the sun's rays in their textures. Animals, on the other hand, use complex food stuffs to renew their tissues, which are constantly being oxidized, and by this means the energy for the performance of their active functions is set free. Although the various kinds of food stuffs used by animals are 9 98 MANUAL OF PHYSIOLOGY. highly organized and like the animal tissues in composition, yet they cannot be admitted at once into the economy without hav- ing undergone a special preparation, which takes place in the digestive tract, where the various food stuffs are so changed as to allow them to pass into the fluids of the body. We shall first consider the food stuffs, next their preparation for absorption (digestion), and then the means by which they are distributed to the tissues (circulation). The final step in tracing the assimilation of the food is to follow the intimate processes which go on between the blood, which carries the nutriment, and the different tissues. CLASSIFICATION OF FOOD STUFFS. There are two portals, namely, the lungs and the alimentary canal, by which new materials normally enter the animal body. Within the lungs the blood comes into close relation with the air, and takes from it oxygen. The oxygen is then carried to the various tissues, where it aids in the combustion accompany- ing the life and functions of these tissues. Oxygen is the most abundant element in the body, taking part in almost every chemical change, and its continuous supply is more immediately necessary for life than that of any other substance, yet it is not counted as food, because tissue oxidation is distinguished from tissue nutrition. The details of the union of oxygen with the blood will be found in the Chapter (xix) on Respiration. It is then only to the liquid and solid portions of the material income of an animal that, in short, which it must busy itself to obtain that the term " food " is applied. These are introduced into the alimentary canal, where the nutrient materials are sepa- rated and prepared for absorption, while the portions which are not useful for nutrition are carried away as excrement. We are, therefore, quite prepared to hear that the really nutritious food stuffs are composed of materials which are chemically like the tissues, although, as we shall see, we have no grounds for believ- ing that the different chemical groups of nutritive stuffs are exclusively destined to replace corresponding substances in the CLASSIFICATION OF FOOD STUFFS. 99 body. On the contrary, we have good reason to think that within the body the conversion of one group into another is common. In Chapter in the tissues of the animal body were shown to consist of chemical compounds, which have been classified into certain groups. It has also been stated that the tissues are con- stantly undergoing chemical changes inseparable from their life, and that for these changes a supply of nutritive material is necessary. The nutriment required for an animal is made up of substances which may be divided into the same chemical groups as the tissues of the body, viz., proteids, fats, carbohydrates, salts and water. So that each of the various substances which we make use of as food, contains in varying proportions several of the dif- ferent kinds of nutrient material, either naturally or artificially mixed so as to form a complex mass, the important item water being the only one which is commonly used by itself. These substances may be considered to be the chemical bases of the food, as they are also the chemical bases of the animal body. The following classification shows the relationships between the chief constituents of food, from a chemical point of view, and their distribution in the various substances we eat : I. ORGANIC. 1. Nitrogenous (A) Albuminous abundant in eggs, milk, meat, peas, wheaten flour, etc. (B) Albuminoid in soups, jellies, etc. 2. Non-nitrogenous (A) Carbohydrates (sugar, starch) abundant in all kinds of vegetable food, and in milk, and present in small quantity in meat, fish, etc. (B) Fats in milk, butter, cheese, fat tissues of meat, some vegetables, oils, etc. II. INORGANIC. 1. Salts mixed with all kinds of food. 2. Water mixed with the foregoing or alone. IOO MANUAL OF PHYSIOLOGY. The nutritive value Q{ any kind of food depends upon a variety of circumstances, which may be thus summed up : I. Chemical composition, of which the main points are 1. The proportion "of soluble and digestible matters (true food stuffs) to those which are insoluble and indi- gestible, such as cellulose, keratin, elastic tissue, etc. 2. The number of different kinds of nutrient stuffs pre- sent in it. II. Mechanical Construction. The degree of subdivision in which the substance is introduced into the stomach materially influences its nutritive value, since the smaller the particles the greater the amount of surface exposed to the action of the di- gestive juices. The relation of the nutrient to the non-nutrient parts is also of importance, as is seen where the nutritious starch of various vegetables is enclosed in insoluble cases of cellulose, which, if not burst by boiling, prevent the digestive fluids from reaching the starch. III. Digestibility. This depends partly upon how the sub- stances affect the motions of the intestines, and partly upon their construction. Thus, some substances, such as cheese, though chemically showing evidence of great nutritive properties, by their impermeability resist the digestive juices, and are not very valuable as food. IV. Idiosyncrasy. In different animals and in different indi- viduals, and even in the same individuals under different circum- stances, food may have a different nutritive value. FOOD REQUIREMENTS. Chemically, foods are composed of a limited number of ele- ments similar to those found in the animal tissues, viz., carbon, oxygen, nitrogen and hydrogen, together with some salts. If nothing more were needed by the economy than a supply of these elements and salts in a proportion like that in which they exist in the tissues, such could be easily obtained from inorganic sources ; but, as has already been stated, it is necessary that an FOOD REQUIREMENTS. 101 animal obtain these elements associated in the form of organic materials of complex construction (namely, proteids, etc.). Allowing the necessity of organic food, it might be supposed that since the elements exist in proper proportion in the proteids, an abundant supply of proteids would suffice for all nutritive purposes, and alone form an adequate diet. Theoretically, pro- teid alone ought to be sufficient for nutrition. It, however, has been frequently tested by experiment, and practically decided, Water. Bread Diagram showing the proportion of the principal food stuffs in a few typical comestibles. Ine numbers indicate percentages. Salts and indigestible materials omitted. that an animal will not thrive upon a free supply of pure proteid food alone ; and in the human subject such exclusive diet would induce dangerous abnormal conditions in a short time. Since nitrogen is an important element in nearly all parts of the body, we could hardly expect that a diet composed of non-nitrogenous food stuffs alone could support the animal economy. In short, the results of numerous experiments show that no one group of the food stuffs enumerated can alone sustain the body, but rather 102 MANUAL OF PHYSIOLOGY. prove that a certain proportion of each is absolutely necessary for life. SPECIAL FORMS OF FOOD. The articles of diet we make use of are animal or vegetable, according to the source from which they are derived. It will be seen that a varying quantity of all chemical classes of food stuffs is present in most kinds of food, whether animal or vegetable. The diagram on the preceding page shows the proportion of the more important food stuffs in some examples of the materials commonly used as food. Among animal foods are included milk, the flesh of various animals, and the eggs of birds. These may be more fully described as typical examples. Milk. For a certain period of their lifetime the secretion of the mammary gland forms the only food of all mammals, and it is the one natural product which when taken alone affords ade- quate nutriment. It consists of a slightly alkaline watery fluid, containing 1. Proteids, casein and albumin in solution. 2. Fats, finely divided to form perfect emulsion. 3. Carbohydrate, sugar in solution. 4. Salts, in solution. 5. Water. Owing to the action of certain organisms which readily propa- gate in milk, if exposed to the air at a warm temperature for some time, it loses its alkaline reaction, and becomes sour from the formation of lactic acid from the milk sugar, by a kind of fermentation, the probable equation for which may be written thus: C 6 H r2 6 =2C 3 H 6 3 . Milk Sugar. Lactic Acid. If fresh good milk be allowed to stand, the fatty particles tend to float to the surface, thus forming a layer of cream. The milk of different animals is similar in all essential points, but differs slightly in the relative proportion of the ingredients, as may be seen in the following table : MILK. I0 3 Human. Cow. Goat. Ass. Water, . . . 889.08 857.05 863.58 910.24 Casein, ... "I Albumin, / 39-24 48.28 5.76 33-60 I2. 99 J20.I8 Butter,. . . . 26.66 43-05 4357 12.56 Milk sugar, . . Salts, .... 43-64 I. 3 8 40.37 5-49 40.04 6.22 } 57-02 Solids,. . . . 110.92 142.95 136.42 89.76 IOOO. IOOO. IOOO. IOOO. Milk varies both in the amount of solids in solution and fat, according to the age and general condition of the animal, period of lactation, time of day, etc. Since human milk is much poorer in proteid, fat and salts (see Table), and richer in sugar, than that of the cow and other domestic animals, it is necessary to dilute the latter with water, and add sugar, when it is substituted for human milk in feeding infants. The great value of milk as nutriment depends upon the fact that it contains every class of food stuff, viz., proteids, fat, carbo- hydrates, salts and water, in the proportion demanded by the economy ; the salts in milk being those required for building up the bones of the infant, viz., phosphates and carbonates of lime, etc. The normal variations in these proportions are not very great, but as adulteration with water is common, a knowledge of the method of testing the purity of milk is necessary. Milk Tests. The specific gravity of milk gives an easy measure of the solids in solution, but unfortunately it gives no accurate estimate of the amount of fat suspended in the emulsion. There- fore, to test milk adequately two methods must be employed : one to estimate the degree of density of solution, and the other the degree of opacity of the emulsion. I. To test the density, a specially graduated form of hydro- meter is generally used. This is graduated so as to indicate specific gravities from 1014 to 1042. The latter being the MANUAL OF PHYSIOLOGY. FIG. 43. O "V W ..AJ> fcv?-*' " o o OO< . * -s?^: 54..2 /x Ventricular systole, 0.4" Passive interval, o.6 x/ Or if we assume the human heart to beat some seventy times a minute, each cycle would occupy about ^ of a second, made up as follows : Auricular systole, = ^ of a second. Ventricular systole, = TG " Pause, == T % " The duration of the auricular and ventricular systole varies little except under abnormal circumstances, but the pause is con- stantly undergoing slight changes. In fact, the duration of the general diastole depends upon the rate of the heart beat, being less in proportion as the heart beats more quickly. CARDIAC MOVEMENTS. If the thorax of a recently killed frog be opened, the heart can be observed beating in situ, and the different acts in the cycle studied without difficulty. CARDIAC MOVEMENTS. 269 In mammalians, in order to see the heart in operation, it is necessary to keep up artificial respiration, during which the heart continues to beat regularly, though the thorax be opened. A careful inspection of the beating heart shows that during its cycle of action certain changes take place in the shape and rela- tive position of its cavities. This is owing partly to the change in the amount of their blood contents and partly to the form assumed by the muscular wall when contracting. During the passive interval the auricles are seen to swell grad- ually on account of the blood flowing into them from the veins : when the auricular cavities are nearly full, a contraction, com- mencing in the great venous trunks near the heart, passes with increasing force over the auricles and gives rise to their rapid systolic spasm. The auricles suddenly diminish in size, and ap- pear to become pale. When the blood is being propelled through the auriculo-ventricular openings, the flaccid walls of the ven- tricles appear to be drawn -over the liquid mass by the contrac- tion of the muscular walls of the auricles (just as a stocking is drawn over the foot by the hands), and the base of the ventricles is thus drawn upward. The moment the ventricles have received their full charge of blood from the auricles they contract, becom- ing shorter by the movement of the base toward the apex, and thicker by their elongated cone becoming rounder. The great arteries are at the same time distended with the blood from the ventricle and elongated, their elastic walls being drawn down over the liquid wedge. The soft elastic tissues are thus 'in turn made to slide, as it were, over the incompressible fluid that forms the fulcrum, which the muscular walls use as a purchase. During the systole, when the thorax is open, the ventricles rotate slightly on their long axis, so that the left comes a little forward, and the apex also forward and toward the right. When the systole of the ventricles ceases, they become flaccid and flattened, and the gradual refilling of the cavities begins, as there is nothing to prevent the blood flowing from the veins through the auricles into the ventricles, where the pressure, as in all parts of the thorax, is negative. The semilunar valves being closed, the large arteries grasp firmly the blood, and by their 270 MANUAL OF PHYSIOLOGY. steady resilient pressure force it on toward the distal vessels. During this pause the arteries seem to become shorter and to draw the base of the heart up again by lengthening the flaccid ventricles. The part of the heart which changes its position most is the line between the auricles and ventricles, while the apex remains fixed in one position, only making a very slight lateral and for- ward motion, which probably does not take place within the thorax. If a thin needle with a straw attached be made to enter the apex through the wall of the chest, the straw does not move in any definite direction during the systole, but simply shakes. FIG. 120. Cardiac Tambour, which can be strapped on to chest wall, so that the central button lies over the heart beat, and the pressure may be regulated by the screws at the side. To the tu K ~ bent at right angles is attached the rubber tube which connects the air cavity with that the writing tambour shown in Fig. 119. .tof If, on the other hand, the needle be placed in the base of the ventricles, the straw moves up and down with each systole and diastole. HEART'S IMPULSE. The heart communicates its motion to the chest wall, and the movement can be felt and seen over a limited area, which varies with the thinness of the individual. This cardiac impulse, as the stroke is called, can best be felt in the fifth intercostal space, a little to the median side of the left nipple. It is found to be synchronous with the ventricular systole. During this period HEART S IMPULSE. 27! ventricular systole the base of the ventricles moves downward and becomes thicker. The flaccid cone which is formed by ven- tricles during diastole is somewhat flattened against the chest wall, but during systole it becomes rounded and bulges forward, pushing the chest wall before it. This change in shape is the chief cause of the cardiac impulse. If the ventricles be gently held between the "fingers during their systole, a most striking sensation is given by the change of shape and the sudden hardening of the muscle. The mass in the ventricles, from being quite soft and compressible during diastole, suddenly acquires a wooden hardness, owing to the tightness with which the muscle grasps the fluid, and the greater firmness of the contracting tissue. This hardening gives the sensation of a sudden enlargement. No matter on what surface the finger be placed, the heart seems to give a slight knock in that direction. Thus, when grasped between the forefinger placed below the diaphragm and the thumb on the antero-superior aspect, the impulse is equally felt by each digit. The important items in causing the impulse are, then, the change in shape of the ventricles from a flattened to a rounded cone, and their simultaneous hardening, which no doubt helps to make the movement more distinctly felt through the wall of the chest. The point at which the impulse is best felt corresponds to the anterior surface of the ventricles at a considerable distance above the apex; it is therefore erroneous to call the impulse the "apex beat." The cardiac impulse is a valuable measure of the strength of the systole, and hence is of great importance to the clinical physician. It may be registered by means of an instrument called the Car- diograph. Many such instruments have been devised, most of which work on the same principle, and make a record on a moving surface with a lever attached to a tambour, to which the movements of the chest wall are transmitted from a somewhat similar drum by means of air tubes. In using this plan, so gener- ally employed by Marey, one air tambour (Fig. 1 20) is applied 272 MANUAL OF PHYSIOLOGY. over the heart, the motions of which cause a variation in the tension of the air it contains; these variations are trans- mitted by a tube, / (Fig. 121), to the other tambour (<$), where they give rise to a motion in its flexible surface, to which a delicate lever is attached at (a). HEART SOUNDS. The heart's action is accompanied by two distinct sounds, which can be heard by bringing the ear into firm, direct con- tact with the praecordial region, or indi- rectly by the use of the stethoscope.* One sound follows the other quickly, and then comes a short pause ; conse- quently, they are spoken of as the first and second sounds. The first sound is heard at the begin- ning of the ventricular systole. It is a low, soft, prolonged tone, and is most distinctly heard, over the fifth intercostal space. The second sound is heard at the mo- ment when the two sets of semi lunar valves are closed and made tense, that is when the blood ceases to escape from the ventricles. It is a sharp, short sound, and is best heard at the second costal cartilage on the right side. The cause of the first sound is not so evident. -Possibly several factors aid in its production. The principal events * A flexible stethoscope to listen to one's own heart sounds can easily be made by fitting the mouthpiece to one end of a piece of rubber tubing about 18 inches long, and to the other end the bowl of a wooden pipe. The bowl is applied over the different regions of the heart, and the mouthpiece firmly fitted in the ear. HEART SOUNDS. 273 occurring at the same time as the first sound may be enumerated thus : 1. The heart's impulse. 2. The rush of blood into the arteries. 3. The contraction of the heart muscle. 4. The sudden tension of the ventricular chambers and the auriculo-ventricular valves. It has already been seen that the heart's impulse is caused by a sudden change in shape and density of the muscle, and not by a knock against the chest. The first sound is heard more clearly when the chest wall is removed, so that the apex beating against the thorax cannot help to cause the sound. The character of the sound is quite unlike that which could be produced by the passage of the blood through the arterial orifices. The sound is not unlike the muscular tone which accompanies the continuous (tetanic) contraction of the skeletal muscles. It corresponds in time with the contraction of the cardiac muscle. In disease where the heart muscle is weak, the sound becomes faint or inaudible, although the valves are made tense by an intra-ventricular force sufficient to overcome the pressure in the arteries. Otherwise the circulation would cease. An abnormal presystolic sound, like in character to the systolic sound, is now supposed by some physicians to be produced by the auricular systole ; but this cannot depend on the vibrations of valves. All this evidence tends to show that the sound is produced by the contraction of the muscle tissue of the heart, or, in short, that it depends upon some sudden physical change occurring during the cardiac muscle contraction. Against the view that the muscular tone is the cause of the first sound is urged the supposition that only tetanus causes a muscle sound, and a single contraction is not accompanied by any tone. Though in many ways it differs from the single con- traction of other muscles, yet the heart beat is no doubt a single contraction. But the tone which may be heard during the normal contraction of skeletal muscle has not been proved to depend on regularly recurrent contractions such as occur in the 274 MANUAL OF PHYSIOLOGY. tetanus produced by an interrupted current ; and a kind of thud, very like the first sound of the heart, may be elicited by the single stimulation of a skeletal muscle. On the other hand, the auriculo-ventricular valves are made tense at the beginning of the sound, and injury or disease of these valves is said to be associated with a weak or altered first sound : this is often observed in disease of the mitral valve. The blood is said by some to be necessary for the production of the sound, because the gentle closure and immediate subsequent tension of these valves have a share in causing it. As before remarked, the valvular tension would not account for the presystolic sound occasionally heard, and there is no doubt that the first sound can be heard in an empty heart, removed from the animal, in which the valves cannot become tense, or even in the ventricles after they are separated from the valves. The sound has been analyzed with suitable resonators, and two distinct tones made out one high and short, corresponding to the tension of the valves ; the other long and low, corresponding in duration with the muscle contraction. The reasons given for thinking that the heart muscle cannot produce a tone suggest that the sudden state of tension of the ventricular wall when tightened over the blood may give rise to vibrations, and be an important item in causing the first sound. This would explain the faintness of the sound, both when the valves were injured and the muscle weak, and when the blood was prevented from entering. It would also explain the presys- tolic sound, which requires a certain auricular tension for its production. From the foregoing statements it would appear probable that both the tension of the valves and the muscle are concerned in the production of the first sound. The production of the second sound is more easily explained. Occurring just after the ventricle is emptied, it is synchronous with the closure and sudden tension of the semi lunar valves at the aorta and pulmonary orifices. The blood in the aorta forci- bly closes the valves as soon as the ventricular pressure begins INNERVATION OF THE HEART. 275 to wane. This sudden motion causes a vibration of the valves, which is rapidly checked by the continuous pressure of the col- umn of blood. INNERVATION OF THE HEART. A most interesting phenomenon in the heart's action, and one difficult to explain, is the wonderful regularity of its rhythmical contractions under normal circumstances, and the extreme deli- cacy of the nervous mechanism by which it is regulated. The vast majority of the active contractile tissues of the higher animals is under the immediate direction of the central nervous system. Thus the skeletal muscles are connected with the cerebro-spinal axis by means of nerves, along which impulses pass stimulating the contractile tissue to action. Some muscular organs, as has been seen in the pharynx, oesophagus, etc., though not under the control of the will, are governed altogether by the cerebro-spinal axis ; while others, of which the most striking example is the heart, have, in immediate relation to the tissue, nerve elements capable of exciting them to contraction. It will materially help us in comprehending the nervous mechanisms of the heart if we bear in mind the fact that the muscle tissue of the heart of some animals has quite independ- ently of any nervous influences an inherent tendency to rhyth- mical contraction. This is shown by the following facts. The heart muscle cannot, under any circumstances, remain contracted like a skeletal muscle in tetanus, or like an unstriated muscle in tonus, except when its tissue is spoiled by deficient nutrition, etc. The heart of many of the invertebrate animals contracts rhyth- mically without any nerve elements being found in it by the most careful microscopic examination. A strip cut from the ventricle of the tortoise can, by rapid gentle excitations, be made to beat with an automatic rhythm without the help of any known nerve mechanism. The lower part of the frog's ventricle A^hich is commonly admitted not to contain any nerves beats quite rhythmically if stimulated with a gentle stream of serum and weak salt solution. There is no reason to assume that we cannot 276 MANUAL OF PHYSIOLOGY. concede to muscle tissue, as we do to nerve cells, the property of acting with an automatic rhythm. Although the heart muscle may itself have this tendency to rhythmical contraction, there is no doubt that in all vertebrate animals the rhythm is controlled and regulated by nerves. These may be divided into an intrinsic and extrinsic set. INTRINSIC NERVE MECHANISMS. In cold-blooded animals, such as a frog or tortoise, the heart will beat for days after its removal from the animal, if it be pro- tected from injury and prevented from drying. In warm- blooded animals the tissues lose their vitality very soon after they are deprived of their blood supply ; however, spontaneous rhythmical movements can be seen in the mammalian heart if removed at once after death. The hearts of oxen, rapidly slaughtered, give a few beats after their removal from the thorax. If a blood current be caused to flow through the .vessels of the heart tissue this spontaneous contraction will go on for some time, or will even recommence after having ceased. The hearts of two criminals who were hanged were found to continue to beat for four and seven minutes respectively after the spinal cord and the medulla had been separated. These facts prove conclusively that the stimulus which causes the heart to beat rhythmically arises in the muscle tissue of the organ or in close relation to it. Upon physiological grounds alone we might conclude that in the heart tissue of the vertebrata there exist nerve elements capable of sustaining the rhythmical action, even if we had not anatomical proof of the existence of the ganglionic cells with which we are familiar. Such collections of nerve elements are called automatic centres, and are made up, like all other origins of nerve force, of gan- glionic cells. Since the heart of mammalian animals soon ceases to beat, it forms an unsatisfactory subject for experimental inquiry. The heart's innervation is, therefore, best studied in a cold-blooded animal, where also the mechanisms are probably more simple. The frog, being readily obtainable, is commonly chosen. INTRINSIC NERVE MECHANISMS. 277 After the cycle of the heart's beat has been carefully watched in situ, and when removed from the animal, if the apex of the ventricle be separated from the auricles and sinus venosus and Diagrammatic Plan ot the Cardiac Nerve mechanism. The direction of the impulses is indicated by the arrows. The right and left sides of the figure are used to show one-halt of the fibres. not stimulated in any way, it remains motionless, while the auricles, continue to beat. But it responds by an ordinary single contraction to short direct stimulus, and if the stimulus be kept 278 MANUAL OF PHYSIOLOGY. up it beats rhythmically. If the auricles be removed from the ventricle so as to leave the line of union attached to it, both con- tinue to beat. But each part beats with a different rhythm, and under like conditions the auricles continue to beat longer than the ventricles. If the heart be made into three zigzag strips by a couple of partial transverse incisions, the rhythm of the sinus is carried by the muscle tissue to the very apex (Engelmann). The auricles beat even when subdivided; and the dilated termination of the great vein, called the sinus venosus, opening into the right auricle, when quite separated from the rest of the heart, continues to beat longer and more regularly than any other part. When the entire heart is intact this sinus seems to be the starting point of the heart beat. This experimental evidence of the presence of nerve centres in certain parts of the heart muscle of the frog is supported by the results of anatomical investigations, for the microscope shows that there are many ganglionic cells distributed throughout the heart tissue, and that they are located just where we should expect from the above facts. That is to say, there are none in the substance of the ventricles, while there are several groups of cells scattered around its base in the auriculo-ventricular groove (Bidder). There are others in the walls of the auricles, particu- larly in the septum, and the greatest number are found in the walls of the sinus venosus (Remak). The ganglia in the sinus venosus are most easily stimulated, and are probably the only ones which habitually act as auto- matic centres. They certainly take the initiative in the ordinary heart beat, and regulate the rhythm of the contraction of the auricles and ventricles. This seems more than probable from the following facts : i. The ordinary contraction wave starts from the sinus venosus. 2. This part beats longer and more steadily than the others when separated from the animal. 3. When cut off from the sinus the beat of the heart becomes weak, uncertain, and changes its rhythm. 4. When the sinus venosus is physiologically separated by a ligature from the auricles and ventricle, both the latter cease to beat, while the motions of the sinus continue. If a EXTRINSIC CARDIAC NERVES. 279 slight stimulus, such as the touch of a needle, be then applied to the auriculo-ventricular margin, it gives rise to a series of rhyth- mical contractions. Or if the ventricle be separated from the auricles by incision through the auriculo-ventricular groove, the former commences to beat rhythmically, while the auricles com- monly remain motionless. These latter observations (experiments of Stannius) have been explained in various ways, supposing the ligature either (i) to excite some inhibitory nerve mechanism or (2) cut off the excit- ing influence of the sinus. The most probable explanation seems to be the following. When cut off by ligature from the sinus venosus, the heart fails to contract spontaneously because the initiatory stimulus, which habitually arrived from the sinus by means of the conducting power of the muscle tissue, can no longer pass the block in that tissue. When the ventricle is cut away from the auricles, the incision is sufficient stimulus to the cells in the groove to make them excite its rhythmical contrac- tions. Although we cannot adequately explain the relationships borne by the different sets of ganglia in the frog's heart to one another, there seems no doubt that the following conclusions may be accepted as proven, and are, in all probability, applicable to the hearts of mammals. That nerve centres exist in the muscle tissue of the heart, some of which are capable of originat- ing stimuli for the rhythmically contracting muscle. That there exist other ganglionic groups which help to regulate and dis- tribute the stimuli in sequence throughout the several cavities. EXTRINSIC CARDIAC NERVES. The intrinsic nerve mechanism of the heart just described is under the immediate control of the great nervous centres through the medium of fibres passing from the medulla oblongata by the vagus and sympathetic nerves. Some of these fibres check the action of the intrinsic ganglia, and cause the heart to beat more slowly ; hence they are called inhibitory. Others quicken the beat, and are called acceleratory. 280 MANUAL OF PHYSIOLOGY. INHIBITORY NERVES OF THE HEART. It was observed by Weber (i) that electric stimulation of the vagus nerve caused a slowing of the heart's rhythm, and if in- creased gave rise to a standstill of the heart in diastole ; (2) that the heart beat gradually recommenced soon after the stimulus had been removed. On the other hand (3) the section of both vagi produced an increase in the rapidity of the heart beat, varying according to the kind of animal experimented upon. Section of only one vagus, however, has not this effect. From these experiments it would appear i. That some fibres FIG. 123. Tracing, showing the effect ol weak Stimulation ot Vagus Nerve. Stimulus applied be- tween vertical lines. (Recording surface moved from left to right.) of the vagus bear impulses of a checking or inhibitory nature to the intrinsic nerves of the heart. 2. That these influences are constantly in operation, or, in other words, the vagi exert a tonic inhibitory influence on the rapidity of the heart beat. 3. The tonic action of one vagus bears inhibitory influence sufficient to regulate the heart's action. This tonicity of the vagus inhibition is more marked in dogs and man than in rabbits > and is reduced to a minimum in frogs, where section of the vagi produces very little effect on the rate of the beat. Vagus inhibition is increased by the following circumstances (a) certain psychical phenomena, such as terror, which may pro- THE ACCELERATOR NERVES. 28 1 duce a temporary standstill ; (^) deficiency of arterial blood in the medulla oblongata ; (^ increase of the blood pressure within the cranium ; and (d") reflexly by the stimulation of many afferent nerves, particularly those bearing impulses from the abdominal viscera to the medulla, and the afferent fibres of the opposite vagus. The following drugs affect the cardiac nerve mechanisms : Muscarin produces diastolic standstill of the heart by exciting the local inhibitory ganglia or vagus terminals. Atropin causes quickening of the heart's action by paralyzing the endings of the vagus, and also those intrinsic mechanisms which are supposed to have an inhibitory effect. Nicotin produces at first a slowing of the heart by stimulating the inhibitory tone of the vagus. This is soon followed by exhaustion of the terminals and a con- sequent quickening of the heart beat. Large doses of curare paralyze the inhibitory fibres. Digitalis excites the vagus centre in the medulla, and thereby reduces the rapidity of the heart's beat. THE ACCELERATOR NERVES. It has been found that stimulation of the cervical portion of the spinal cord causes quickening of the heart beat. This occurs even after the possibility of increase of blood pressure has been removed by section of the splanchnic nerves, and the tonic inhibition of the vagi has been cut off by their section. In the cervical portion of the spinal cord nerve channels must exist which are capable of stimulating the muscle fibres of the heart, so as to cause it to beat more quickly. These accelerator fibres pass from the cord through the communicating branches to the last cervical or first dorsal sympathetic ganglion, and thence to the heart. Stimulation of the ganglia, or of the branches passing thence to the heart, quickens its beat. The effect of stimulus applied to these nerves does not begin to show itself until a comparatively long time after it has been applied, and the acceleratory effort continues for a considerable time after the stimulus is removed. Stimulation of the accelerator fibres has less effect than the inhibition of the vagus, which follows stimulation whether the accelerators are stimulated or not, while 24 282 MANUAL OF PHYSIOLOGY. the action of the accelerators is suspended so long as the vagus is being stimulated. An analogy exists between the nervous mechanism of the heart and that of the blood vessels (to be described in a future chapter) which may help in their better comprehension. Both the heart and vascular muscles can work automatically ; though no ganglionic cells can be found in the latter. Both are regulated by central influences. The heart receives constant inhibitory dilator impulses by the vagus, and occasional motor (accelerator) impulses by the sympathetic. The vessels receive constant motor (constrictor) impulses by the sympathetic and occasional inhibitory (dilator) impulses from other nerves. The motor influences are supposed to act by increasing the chemical activity of the tissue (anabolic action), while the inhibitory impulses lessens the tissue change (katabolic action). AFFERENT CARDIAC NERVES. Besides the nerve channels bearing impulses to the heart, others pass from the heart to the medulla, probably having their origin in the inne? lining of the heart, which is the part most sensitive to stimulus. These fibres appear to be of two kinds, one of which (in vagi) affects the cardio-inhibitory centre and diminishes the pulse rate ; the other (depressor) affects the vaso-inhibitory centre and lowers the blood pressure. Increase of the intra-ventricular pressure stimulates both these sets of fibres, and thus we see that over-filling of the heart from increase of blood pressure, etc., causes retardation of its beat, and an equilibrium is established between the general blood pressure and the force of the heart beat. ARTERIES. 283 CHAPTER XVII. THE BLOOD VESSELS. The channels which carry the blood through the body form a closed system of elastic tubes, which may be divided into three varieties : 1. Arteries. 2. Capillaries. 3. Veins. The arteries and veins serve merely to conduct the blood to and from the capillaries, where the essential function of the blood, viz., its chemical interchange with the tissues, is carried on. ARTERIES. The arteries are those vessels which carry the blood from the heart to the capillaries. The great trunk of the aorta, which springs from the left ventricle, gives off a series of branches, which in turn subdivide more and more freely in proportion to their distance from the heart. Arterial twigs of considerable size here and there form connections with those of a neighboring trunk (anastomoses} ; but these unions are simple junctions ot single branches, never so complex as to be worthy of the name of a network or plexus, such as those seen in the capillaries or in the veins. The walls of the arteries are made up of three coats : 1. An external tough layer of white fibrous tissue, which gives strength to the vessels, restricts their elasticity like the webbing in the wall of rubber water hose, and also acts as a bond of union between them and the neighboring tissues. This coat (tunica adventitid] carries the minute vessels, necessary for the nutrition of the vessel wall, and nerves. 2. The middle coat (tunica media) forms the more character- istic part of the arterial structure, being a mixture of elastic tissue 284 MANUAL OF PHYSIOLOGY. and unstriated muscle. It is much thicker in the arteries than in the veins, where its special functions are not required. It FIG. 124. FIG. 125. Transverse Section of part of the Wall of the Posterior Tibial Artery (man). (Schfi/er.) (a) Endothelium lining the vessel, appearing thicker than natural from the contraction of the outer coats. (b) The elastic layer of the intima. (c) Middle coat composed of muscle fibres and elastic tissue. (d) Outer coat consisting chiefly of white fibrous tissue. differs somewhat in character in arteries of different calibre, being much thicker in the large vessels; This change occurs gradually on passing along the diminishing branches. In the large arteries and the arterioles the middle coat differs essen- tially both in structure and in function, and in each class of vessel it forms the most import- ant part for the due perform- ance of their respective func- tions. In the large vessels it is made up of fibres and sheets of elastic tissue woven into a dense feltwork, interspersed with a Portion ot Small Artery from Submucous few muscle Cells. In the Smallest Tissue of Mouse's Stomach, stained with . . 1 . gold chloride, showing the nuclei of the arteries Or arterioles, On the muscle cells (M) passing transversely ,111 r i around the vessel to form the middle Other hand, the great lliaSS OI the coat, outside which is the fibrous tissue -in j r of the o\iter coat (F). Around the vessel middle COat IS made Up OI several fine nerve fibrils form a net- , n - i , , work (N). muscle cells, the elastic tissue being but sparsely represented. Between the large arteries and the capillaries every grade of CAPILLARIES. 285 transition may be found ; the elastic tissue gradually becoming less abundant and the muscle elements relatively more numerous in proportion as the capillaries are approached. 3. The internal lining (tunica intima) of the arteries is com- posed of a delicate, elastic, homogeneous membrane lined with a single layer of endothelial cells. The intima may be said to be continuous throughout all the vessels and the heart cavities. It is thus seen that the large arteries have extremely elastic FIG. 126. Capillary Network ot a Lobule ot the Liver. and firm walls, capable of sustaining considerable pressure. The smaller the calibre of the arteries becomes the more the general property of elasticity and resiliency is reinforced by that of vital contractility due to the greater relative number of muscle cells contained in the middle coat. CAPILLARIES. The frequently branching arterioles finally terminate in the capillaries, in which distinct branches can no longer be recog 286 MANUAL OF PHYSIOLOGY. nized, but the thin canals are interwoven into a network of blood channels, the meshes of which are made up of vessels, all of which have about the same calibre. They communicate indefi- nitely with the capillary meshworks of the neighboring arte- rioles, so that any given capillary area appears to be one continuous network of tubules, connected here and there with the similar networks from distinct arterioles, and thus any given capillary area may be fed with blood from several different sources. The walls of the capillaries are composed of a single layer of elongated endothelial cells (possibly lining an invisible membrane) cemented edge to edge to form a tube. They are FIG. 127. Capillary Network of Fat Tissue. (Klein.} soft and elastic, and permeable not only to the fluid portion of the blood, but also, under certain circumstances, to the cor- puscles. It is, in fact, in these networks that the essential function of the circulation is carried on, viz., the establishment of a free interchange between the tissues and the blood. The characters of the capillary network vary in the different tissues and organs ; the closeness and wideness of the meshes may be said to be in proportion to the functional activity or inactivity of the organ or tissue in question, a greater amount of blood being required in the parts where energetic duties are performed. SECTIONAL AREA OF VESSELS. 287 VEINS. The veins arise from the capillary network, commencing as radicles which unite in a way corresponding to the division of the arterioles, but they form wider and more numerous channels. They rapidly congregate together to make comparatively large vessels, which frequently intercommunicate and form coarse and irregular plexuses. The general arrangement of the structures in the walls of the veins is like that of the arteries ; they also have three coats, the external, middle and internal ' ; the tissues of each differing but little from those of the arteries. The external coat is like that of the arteries, but is not quite so strong. The middle coat, however, in the large veins, is easily distinguished from that of the large arteries by being much thinner, owing to the paucity of yellow elastic tissue. It is also characterized by its relative richness in muscle fibre. The structure of the middle coat of the small veins can be distinguished from that of the arterioles by the comparative sparseness of the muscle cells run- ning around the tubes. The inner coat of the veins is practically the same as that of the arteries. The veins are capable of considerable distention, but, though possessed of a certain degree of elasticity, they are much inferior to the arteries in resiliency. In a large proportion of veins, valve- like folds of their lining coat exist, which prevent the backward flow of blood to the capillaries and insure its passage toward the heart. These valves resemble in their general plan the pocket valves that protect the great arterial orifices of the heart. They vary much in arrangement, there being commonly two or sometimes only one flap or pocket entering into the formation of the valve. They are closely set in the long veins of the extremities, in which the blood current has to move against the force of gravity. AGGREGATE SECTIONAL AREA OF THE VESSELS. The general aggregate diameter of the different parts of the vascular system varies greatly. The combined calibre of the branches of an artery exceeds that of the parent trunk, so that the aggregate sectional area of the arterial tree increases as one 288 MANUAL OF PHYSIOLOGY. proceeds from the aorta toward the capillaries. After the muscular arterioles are passed the general diameter of the vascular system suddenly increases immensely, and in the capil- laries it reaches its maximum, the aggregate sectional area of which is said to be several (5 to 8) hundred times as great as that of the aorta. The aggregate sectional area of the veins diminishes as the tribu- taries unite to form main trunks, and reaches its minimum at the entrance of the vena cava into the right auricle. FIG. 128. Diagram intended to give an idea cf the aggregate sectional area of the different parts of the vascular system. (A) Aorta. (C) Capillaries. (V) Veins. The transverse measurement of the shaded part may be taken as the width ot the various kinds of vessels, supposing them fused together. The capacity of the veins is, however, everywhere much greater than that of the corresponding arteries, the least difference being near the heart, where the calibre of the venae cavoe is more than twice that of the aorta. After this brief anatomical sketch, the most important proper- PHYSICAL FORCES OF THE CIRCULATION. 289 ties of each part of the vascular system may be summarized thus: 1 . The structure of the walls of the large arteries shows them to be capable of sustaining considerable pressure, and of exerting powerful and continuous elastic recoil on the blood. 2. In the small arteries, as well as this elasticity, frequent variation in their calibre occurs, dependent on the con- traction of their muscular coat which regulates the blood flow. 3. In the capillaries we find extreme thinness, elasticity, and permeability of their wall, which presents an immense surface, so as to allow free interchange between the blood and the surrounding textures. 4. The veins have yielding and distensible walls, capacity to accommodate a large quantity of blood, and valves to prevent its backward flow upon the capillaries. 5. The aggregate sectional area of the systemic capillaries is about three hundred times that of the great veins, and seven hundred times that of the aorta, so that the current of the blood must be proportionately slower in the capillary network. PHYSICAL FORCES OF THE CIRCULATION. A liquid flows through a tube as the result of a difference of pressure in the different parts of the tube. The liquid moves from the part where the pressure is higher toward that where it is lower, except where sudden and great variations of calibre occur. ^ The energy of the flow corresponds with the amount of differ- ence in the pressure, and varies in proportion to it, being con- * Although in the whole course of any system of tubes the flow of liquid must take place from the part of higher to that of lower pressure, yet if a narrow tube open abruptly into one the diameter c-f which for a short length is much greater, the diminution of velocity in the wide tube may cause the local pressure in it to exceed that in the narrower tube im- mediately preceding ; so that the liquid would be actually flowing, for a short distance, from a point of lower to a point of higher pressure. 2 5 2pO MANUAL OF PHYSIOLOGY. tinuous so long as the pressure is unequal in different parts, and ceasing when it is equalized throughout the tube. If liquid be forcibly pumped into one extremity of a long tube, such as a garden hose, a pressure difference is established, the FIG I2 pressure becoming greater at the end into which the liquid is pumped, a current consequently takes place toward the open end. R - H - So lon g ^ the free or distal end of the tube is quite open and on the same level as the rest, no very great pressure can be brought to bear on the walls ot Diagram ot Circulation, showing right the tube, HO matter llOW forcibly (R H) and left (L H) hearts, and the pul- monary (P) and systemic (S) sets of the pumping may go on, as the capillaries. . liquid easily escapes, and there- fore flows the more quickly as the pumping becomes more ener- getic. If, however, the outflow be impeded by raising the distal end of the tube to any considerable height, or by partially clos- ing the orifice with a nozzle or rose, then the pressure within the tube can be greatly increased by energetic pumping, and the tube being elastic will be distended. It can be further observed in this common operation that the smaller the orifice of the nozzle the greater the pressure in the tube with a given rate of working the pump ; and, the orifice remain- ing the same, the pressure will increase in proportion as the pump is more energetically worked. Or in other words, the pressure within the tube will depend on (#) the energy used at the pump, and (<) the degree of impediment offered to the outflow. If the tube be resilient, and the nozzle have a small orifice so that a high pressure can be established within the tube, it will be found that the liquid will flow from the nozzle in a continuous stream, and will not follow the jerks communicated by the pump. That is to say, the interrupted energy of the pump is stored up by the elastic tube and converted into a continuous pressure exerted on the fluid. But if the tube be quite rigid, or the ori- fice too wide to allow the pressure within the tube to be raised BLOOD PRESSURE. 29 T sufficiently high, then the fluid will flow out of the end of the tube in jets which correspond with the strokes of the pump ; z. ), which is turned by the handle (U). (Hermann.') Contractile Arterioles. Injuries of the nervous centres are often associated with paralysis of the muscular arterioles and fall of blood pressure ; but the effect upon the blood pressure of dilata- tion of the small arteries can be best seen by experimenting on the nerves that control their contraction. If paralysis or inhibi- tion of the vasomotor mechanisms be experimentally produced, MEASUREMENT OF BLOOD PRESSURE. 297 the result on the arterial pressure is the same, a sudden fall, which may reach that of the atmosphere. The chief opposition to the outflow of blood from the arteries being removed, they cease to be tense, even though the ventricle continue to beat and pump the blood into them. MEASUREMENT OF THE BLOOD PRESSURE. The first attempt at direct measurement of blood pressure was made by the Rev. Stephen Hales about the middle of the last century, who, wishing to compare the motion of fluids in animals with that in plants, connected a tube with an artery of a living animal, and found that the blood was ejected with considerable force, and that when the artery of ahorse was brought into union with a long upright tube, the blood reached a height of about three yards. The column of blood is not now used as a measure, because so much blood leaving the vessels tends to empty them and to reduce the pressure in the arteries ; besides, the coagulation of the blood soon stops the experiment. We now employ the mer- curial manometer, which consists of a column of mercury in a U-shaped tube. To prevent coagulation, the tube between the mercury and blood is filled with a solution of sodium carbonate, the pressure being regulated to equalize as nearly as possible that of the blood. A rod is made to float upon the mercury, in the open side of the tube, and to the upper extremity of this a writing apparatus can be attached, so that by the movements of the mer- cury, a graphic record of the blood pressure and its variation can be traced on a regularly moving surface. This instrument, known as Ludwig's Kymograph, is that used in all ordinary measurements and experiments on blood pressure. In order to overcome the inertia of the mercurial column, another manometer has been devised, which will be mentioned in speaking of the character of the curve (p. 302). When an experiment of long duration has to be made, a recorder with a rolled strip of paper can be employed (Fig. 133). The modern accurate methods of research have taught us the differences in pressure that exist in the various parts of the 298 MANUAL OF PHYSIOLOGY. vascular system. However, direct measurement can only be accomplished in vessels of such a size as to admit a cannula, hence the pressure in the capillaries in the very minute arteries and veins can only indirectly be estimated. The pressure in all parts of the vascular system is subject to frequent variations to be presently mentioned, but this table may be useful in giving a FIG. 133. Ludwig's Kymograph with continuous paper. The instrument consists of an iron table, above which the recording surface is slowly drawn past the writing points from an endless roll of paper on the left by the motion ol the cylinder (C), and rolled up on a spindle next the driving-wheel on the right. The mercurial manometers are so fixed on (D) that the open ends come in front of the firm roller upon which the paper rests. The writing style can be seen rising from these tubes while the other limbs of the manometers lead through the stop-cocks to the tubes which are in communication with the blood vessels. The time is recorded by means of a pen attached to the electro-magnet (M), which_ by a "breaking" clock is demagnetized every second. The moment at which a stimulus is applied is marked on the zero line by a key to which another pen is attached near the time marker. general idea of the average permanent differences that exist in the different vessels of large animals and man. Large arteries (Carotid, Horse) -f 160 mm. mercury. Medium " (Brachial, Man) -f- 120 mm. Capillaries of Finger -j- 38 mm. Small Veins of Arm -j- 9 mm - Large Vein of Neck I to 3 mm. RECORD OF BLOOD PRESSURE. 2 99 If the different parts of the circulation be represented on the base line H. A. c. v., these letters corresponding to heart, arteries, capillaries, and veins respectively, and if the height of the blood pressure be represented on the vertical line in mm. Hg., the curve /z, a, c, v, would give about the relative pressure in the various parts of the circulation. This shows that in the receiv- ing chamber of the heart the pressure is negative, while the FIG. 134. Diagram showing the relative height ot the blood pressure in the different regions of the vessels. H. Heart, a. Arterioles. v. Small Veins. A. Arteries, c. Capillaries. V. Large Veins. H. V. being the zero line (==-- atmospheric pressure), the pressure is indicated by the height of the curve. The numbers on the left give the pressure (approximately) in mm. of mercury. ventricular pump drives it to the height of the arterial pressure 1 60 mm. Hg. In the arteries the pressure is everywhere high, while just before the blood reaches the capillaries a sudden fall occurs. The variation after this is merely a gentle descent until the large venous trunks are reached, where the blood pressure is below zero, /. e., below the pressure of the atmosphere. From a purely physical point of view the ventricle may be 300 MANUAL OF PHYSIOLOGY. regarded as pumping the blood up to an elevated high-pressure reservoir of small capacity (the arteries), from which it rapidly falls by numerous outlets into an expansive, low-lying irrigation basin (the wide capillaries), while it slowly trickles back to the well (the auricle), which lies below the surface pressure. From this diagram the following points can be gathered : 1. The great difference between the pressure on the arterial and venous sides of the circulation. 2. The comparatively slight difference in pressure in the different parts of the arterial or of the venous systems respectively. 3. The suddenness of the fall in the pressure between the small arteries and the capillaries, where the great resistance to the outflow is met with. 4. In the large veins the pressure of the blood is habitually below that of the atmosphere, only becoming positive during forced expirations. VARIATIONS IN THE BLOOD PRESSURE. If the blood pressure be recorded with Lud wig's Kymograph, a tracing will be obtained which shows that the pressure under- goes periodic elevations and depressions of two different kinds. The smaller oscillations are found to correspond with the heart beat, the larger waves have the same rhythm as the respiratory movements, and the average elevation of the mercurial column is spoken of as the mean pressure. In the large arteries of the warm-blooded animals this mean pressure varies with the size of the animal from 90 mm., mercury, to more than 200 mm. In cold-blooded animals it is comparatively low, from 22 mm. in the frog (Volkmann) to 84 mm. in a large fish. v The general mean pressure in the arteries is increased by (i), increased action of the heart ; (2), increased contraction of the muscular coat of the arteries ; (3), sudden increase in the quantity of blood. When the change is gradual, the vessels adapt them- selves to the increase. The opposite of these conditions may be said to have a contrary effect. INFLUENCE OF RESPIRATION ON BLOOD PRESSURE. 3 OI The character of the change in pressure which accompanies the heart's systole is not shown exactly in the tracing obtained by the mercurial manometer, owing to the sluggishness of the move- ment of the mercurial column, which, as it were, 'rubs off the apices of the curves. But with the spring manometer of Fick, the details of these oscillations are marked. They are of course synchronous with the arterial pulse, and follow the variations of FIG. 135. Blood-pressure Curve, drawn by mercurial manometer. O .r = zero line,_y _y' = curve with large respiratory waves and small waves of heart impulse. A scale is introduced to show height of pressure. tension, as will be described when treating of that subject. Figs. 136 and 137.) (See INFLUENCE OF RESPIRATION ON BLOOD PRESSURE. The explanation of the respiratory undulations in the tracing of the blood pressure is difficult. Though many causes have been assigned, no single one appears to explain adequately all the 3 02 MANUAL OF PHYSIOLOGY. changes that may occur in this phenomenon. At first sight the respiratory movements and consequent pressure changes within - FIG. 136. FIG. 137. Fick's Spring Manometer. A hollow C-shaped spring (A), made of extremely thin metal, is fixed at (bb), where its cavity communicates with the tube (K). The top of the C is connected at (a) with the writing lever. Any increase of pressure in the tube (K) causes the spring to expand and move the writing point (G) up and down. the thorax would seem to give a simple mechanical explanation 01 the variation in pressure. But if the change occurring in the intra-thoracic pressure be examined carefully, it will be found not to correspond exactly with the so-called respiratory wave of the pressure curve in the arterial system. The amount ot pressure exercised on the pericardial contents by the lungs varies with the respiratory movements. It is slightly Tracing of blood pressure taken with Fick's manometer. INFLUENCE OF RESPIRATION ON BLOOD PRESSURE. 303 decreased during inspiration and increased during expiration. The differences thus produced, however, are during ordinary respiration very slight (probably i mm., mercury). So slight a variation as i mm., mercury, cannot, by direct action on the aortic arch, cause the change of several millimetres which we see in the respiratory undulation in the arterial pressure. We must, therefore, seek the explanation in the changes it causes in the great veins. Owing to the lungs being very elastic and constantly tending to shrink away from the costal pleura, the pressure in the pleural cavity is less than that of the atmosphere which distends the FIG. 138. Blood pressure and Respiratory Tracings recorded synchronously recording surface moving from right to left showing that the variations in pressure in the arteries (con- tinuous line) and in the thoracic cavity (dotted line) do not exactly correspond, the latter continuing to fall after the blood pressure has commenced to rise. lungs, /. e., the pleural pressure is negative. All the viscera in the thoracic cavity are habitually under the influence of the negative pressure. Thus the elastic lungs exert a kind of trac- tion on the pericardium, and tend to cause a negative pressure within the heart and great systemic vessels, both arteries and veins. The influence is more felt by the thin-walled venae cavae in which the blood pressure is low than in the thick-walled arte- ries where it is high. The flow of blood into the left auricle from the pulmonary vessels is not influenced by the negative pressure, as pressure of the atmosphere cannot reach them. 304 MANUAL OF PHYSIOLOGY. It has been suggested that by facilitating the flow into the thorax from the great veins, the amount of blood entering the right auricle during inspiration may be increased, and thus the left ventricles may be better filled and made to beat more actively, so as to cause an elevation in the arterial pressure. The sequence of events may be read as follows. During inspi- ration the negative pressure on the right heart is increased ; the atmospheric pressure acting on the tributaries of the superior vena cava is unchanged, while the pressure in the abdominal cavity is increased, and the inferior vena cava compressed by the muscular action. The blood thus flows more readily into the right heart, and consequently the lungs receive a larger supply of blood during this period. In expiration, on the other hand, the intra-thoracic pressure becomes less negative, the compression of the abdominal viscera is relieved, and the flow into the auricle loses somewhat in force. But this view appears to leave the pulmonary circulation out of the question in a way hardly justifiable, since the lungs must be traversed by the blood before the increased inspiratory inflow to the right auricle can affect the left ventricle or the systemic arteries. It must be carefully borne in mind that the left side of the heart works under different conditions, for the variations of pres- sure affect both the pulmonary veins and the left auricle simi- larly, since they are both included in the thoracic cavity, and are both subjected to a slightly varying negative pressure. The aid given to the flow into the right heart by the low intra-thoratic pressure is quite absent on the left side, as the inflow is not assisted by atmospheric pressure ; so that the thoracic movements do not exert any influence on the flow of blood from the pul- monary veins to the systemic arteries. While inspiration is taking place, the lungs receive a larger supply of blood. From the relatively small amount of blood in these organs it is pro- bable that this slight excess has little or no influence on the amount entering the left side of the heart. The left ventricle may receive an amount of blood during expiration slightly in excess of that which it receives during inspiration. This can INFLUENCE OF RESPIRATION ON BLOOD PRESSURE. 305 have but little direct effect on the pressure in the great arterial trunks. It is more than probable that excess of blood in the heart cavities does not mechanically influence the beat or the blood pressure, but rather acts as a nervous stimulus, and excites the inhibitory centre of the heart and the depressor centres which control the arterioles. The rejection of this indirect mechanical explanation appears necessary from the following facts : 1. The rise in pressure is not exactly synchronous with expiration or inspiration. 2. The heart beats more slowly during expiration than inspiration. 3. This difference at once disappears if the vagi be cut and the respiratory wave becomes greatly modified. 4. Variations in the pressure like the respiratory wave occur after the respiratory movements have quite ceased. 5. The respiratory wave is observed when artificial respira- tion is employed, in which the forcing of air into the lungs is the cause, and not the result of the thoracic movements, so that the pressure effects are reversed. We may conclude that a sympathy in action can be recognized in the working of the respiratory, vascular and cardiac nerve mechanisms. The undulations known as Traube's Curves occurring in cura- rized animals when no respiratory movements are performed, have been explained by referring them to a stimulation by impure blood of the vasomotor centre, which by rhythmical impulses increases the contraction of the arterioles and causes a rhythmical variation in the blood pressure. This explanation when applied to the respiratory waves seems to be rendered unsatisfactory by the fact that these undulations go on even when the arterioles are cut off from their chief nerve centres by sections of the spinal cord. So that if these undulations are to be referred to nerve mechanism we are ignorant of the course 26 306 MANUAL OF PHYSIOLOGY. taken by the nerve impulses, for any rhythmical sympathy existing between the respiratory and vasomotor nerve centres in the medulla cannot well influence the vessels when the cord is cut. Thus we seem forced to fall back upon the muscular coats of the arteries for an explanation of the respiratory variation in the blood pressure, and to accord to this tissue automatic rhyth- mical contractility. The blood pressure in the capillaries cannot be directly measured by the means above described ; it is difficult to estimate, and very variable. The slightest change of pressure in the corre- sponding veins or arteries causes the pressure in the capillaries to rise or fall. Thus, variations in pressure are constantly occurring in the capillaries, which cause an alteration in the rate of flow, or even a retrograde stream in some parts of the network. The regulation of the blood supply, and, therefore, of the pres- sure in the capillaries, is under the control of the small arterioles which supply them ; a slight relaxation of the muscle of the arterioles causes great increase in the amount of blood flowing through the capillaries, as can readily be seen with the micro- scope. The blood pressure in the veins must be less than that in the capillaries, and, as has been said, must diminish as the heart is approached, where in the great veins (superior cava) the pres- sure is said to be rather below that of the atmosphere ( 3 to 5 mm., mercury). During inspiration the minus pressure may become further lowered, while, on the other hand, it is only by very forced expiration that it ever becomes equal to or at all above that of the atmosphere. . This is a most important fact, as the suction considerably helps the flow of blood from the veins, and also the current of fluid from the thoracic duct that bears the chyle from the intestines and the fluid collected from the tissue drainage back to the blood. The pressure of the blood in the veins may be said to be gen- erally nil, since the veins are nowhere overfilled with blood. THE ARTERIAL PULSE. 307 The pressure, on the other hand, that can be registered and measured depends upon forces communicated from without, namely : (i) gravity ; (2) the elastic pressure of the surrounding tissue; and (3) the pressure exerted by the muscle during con- traction. This pressure is increased by any circumstance which impedes the flow of blood through the right side of the heart, through any large vein, or through the pulmonary circulation ; but when no abnormal obstacle exists in the venous blood cur- rent the pressure in those vessels can never attain any great height, for, as we have seen, the large trunks are constantly being emptied by the heart's action. Most circumstances which tend to lower arterial pressure also tend to raise the pressure in the veins, so that when the heart's action is weak or its mechanism faulty the venous pressure rises. In the veins of the extremities the pressure greatly depends on the position of the limb, as it varies almost directly with the effect of gravity. In the pulmonary circulation the direct measurement of the intra-vascular pressure is rendered extremely difficult, and pos- sibly erroneous, by the fact that to ascertain it the thorax has to be opened. It has been found in the pulmonary artery to be in a dog 29.6 mm., in a cat 17.6 mm., and in a rabbit 12 mm. of mercury. THE ARTERIAL PULSE. Each systole of the ventricle sends a quantity of blood into the aorta, and thus communicates a stroke to the blood in that vessel. The incompressible fluid causes the tense arterial wall to distend still further, and the shock to the column of blood is not transmitted onward directly by the fluid, but causes the elas- tic walls of the arteries to yield locally, and thus it is converted into a wave which passes rapidly along those vessels. This motion in the walls of the vessel can be felt wherever the artery can be reached .by the finger, but best, as is the case in the radial and temporal arteries, where the vessel is superficial and lies on some unyielding structure, such as bone. 308 MANUAL OF PHYSIOLOGY. This motion of the vessel wall is called the arterial pulse. It consists of a simultaneous widening and lengthening of the artery. The arteries near the heart are more affected by the pulse wave than those more remote, the wave becoming fainter and fainter as it travels along the branching arteries. In the smallest arteries it is hardly recognizable, and under ordinary circumstances is quite absent in the capillaries and veins. The diminution in the pulse wave in the smaller arteries chiefly depends upon the fact that the force of the wave is used up in distending the successive parts of the arteries. In the small arteries the extent of surface to which the pulse wave is communicated is great, and thereby the wave is much decreased. It is probable that reflected waves pass from the peripheral end of the arterial tree the contracted arterioles and meeting the pulse wave in the small arteries help to obliterate it. So long as the arterioles are contracted to the normal degree no pulsation is communicated to the capillaries, because the wave, reaching the arterioles, is reflected by them. The pulse wave can easily be shown to take some time to pass along the vessels. Near the orifice of the aorta the arterial distention occurs practically at the same time as the ventricular systole, but even with comparatively rough methods the radial pulse can be observed to be a little later than the heart beat. The difference of time between the pulse in the facial and the dorsal artery of the foot has been estimated to be one-sixth of a second, and the difference in the distance of these vessels from the heart is about 1500 mm., so that the rate at which the pulse wave travels is nearly 10 metres per second. The velocity of the wave is said to depend upon the degree of elasticity of the walls of the vessels, and it would appear to be quicker in the lower than in the upper extremities. The time that the wave takes to pass any given point must be equal to the time taken to produce it, that is to say, the time the ventricle occupies in sending a new charge of blood into the aorta, which is about one-third of a second. Knowing the rate at which the wave travels (10 m. per sec.) and the time it takes to pass any given point (^ sec.), its length may be calculated to PULSE TRACINGS. 39 be about three metres, or about twice as long as the longest artery. Thus the pulse wave reaches the most distant artery in one-sixth of a second, or about the middle of the ventricular FIG. 139. Marey's Sphygmograph. The frame (B, B, B) is fastened to the wrist by the straps at B, B, and the rest of the instru- ment lies on the forearm. The end of the screw (V) rests on the spring (R), the button ot which lies on the radial artery. Any motion of the button at R is communicated to V, which moves the lever (L) up and down. When in position, the blackened slip of glass (P) is made to move evenly by the clockwork (H) so that the writing point draws a record 01 the movements of the lever. systole, and when the wave has passed from the arch of the aorta, its summit has just reached the arterioles. Numerous instruments have been invented for the demonstration and graphic representation of the pulse in the human being. Of these the one in general use is Marey's Sphygmograph (Fig. 139), FIG. 140. Tracing drawn by Marey's Sphygmograph. The surface moved from right to left. The vertical upstrokes show the period when the shock is given by the systole of the ventricle. The upper wave on the downstroke shows when the blood has ceased to enter the aorta. Then comes the dicrotic depression, which is a negative wave produced by the momentary backflow in aorta, and the dicrotic elevation caused by the closure of the valves. by means of which a graphic record of the pulse is made, in the form of a tracing of a series of elevations and depressions (Fig. 140). The elevations correspond to the onset of a wave, and the 310 MANUAL OF PHYSIOLOGY. depressions to its departure, or to the temporary rise and fall of the arterial pressure. In the falling part of the curve an irregu- larity caused by a slight second wave is nearly always seen. This is called the dicrotic wave. Sometimes there are more than one of these secondary waves, the most constant of which is a small wave preceding the dicrotic, called predicrotic ; but the dicrotic is always more marked than any other. Several waves of oscillation can be seen as a gradually decreasing series in tracings taken from elastic tubes, but we cannot say positively that they occur in the arteries. When several secondary waves exist in the pulse curve, the smaller ones probably depend on oscillations caused by the lever of the instrument. The dicrotic wave does not depend on the instrument, because in most cases the skilled finger laid on the radial artery at the wrist can easily detect it, and it can be directly seen in the vessel when the pulsation in the arteries is visible, or when a jet of blood escapes from an artery. When a new charge of blood is shot into the aorta the elastic wall of the vessel is suddenly stretched. At the same time a shock is given to the column of blood, and the fluid next the valves is moved forward with great velocity. Owing to its inertia the fluid tends to pass onward from the valves, and thus allows a momentary fall in pressure which is at once followed by a slight reflux of the blood and the forcible closure of the valves. The first crest or apex of the pulse curve corresponds to the shock given by the systole, and is greatly exaggerated by the inertia of the lever. The crest of the predicrotic wave marks the moment when the blood ceases to flow from the ventricle, and, therefore, it is the real head of the pulse. wave. The dicrotic wave has been explained as (i) a wave of oscil- lation, (2) a wave reflected from the periphery, or (3) a wave from the aortic valves. i. If the first, it should be less marked than the predicrotic, which by this theory is said to be the first wave of oscillation, for each succeeding oscillation is less than its forerunner. But, as already mentioned, the dicrotic is invariably the larger. PULSE TRACINGS. 711 o 2. There are many reasons why it cannot be a wave of reflec- tion from the periphery of the arterial tree; viz., (i) Its curve is not found to be nearer the primary wave when the peripheral vessels are approached. (2) The arterioles which form the peripheral resistance are at too irregular distances to give one definite wave of reflection. (3) It is seen in the spurting of an artery cut off from the periphery. (4) It increases with greater elasticity and low tension, which cause the reflected waves to diminish. 3. The dicrotic notch then most probably depends upon a negative centrifugal wave, caused by the sudden stoppage of the inflow and the momentary reflux of blood during the closure of the valves ; and the dicrotic crest is, no doubt, produced by the completion of their closure, at which moment the sudden check given to the reflux of the blood column causes a positive centrifugal wave to follow the primary wave of the pulse. The view that the reflux of blood and the closure of the valves produce the dicrotic wave is supported by the fact that the con- ditions which increase the dicrotism viz. (i) sharp, strong sys- tole, (2) low tension, and (3) perfect resiliency promote the recoil and closure; and, on the other hand, the conditions which interfere with the closure of the valves also diminish the dicrotic wave in the most marked degree, viz. (i) inefficiency of the aortic valve, and (2) a rigid calcareous condition of the arteries. It can be shown in an elastic tube, fitted with a suitable pump and sphygmographs, that when its outlet is closed a positive wave is reflected from the distal end back to the pump, and when the outlet is opened a negative centripetal wave is reflected. This fact assists in explaining the variations in the character of the pulse curve of the radial artery where the equidistance of the derived arterioles enables the reflected waves to have consider- able effect. When the arterioles are constricted (a condition corresponding to the closure of tube) a positive centripetal wave is reflected, and is added to the pulse wave so as to diminish the dicrotic notch, and give the curve known as characteristic of the " high-tension " pulse seen in Bright's disease. (Fig. 141, n.) On the other hand, when the arterioles are widely dilated (cor- 312 MANUAL OF PHYSIOLOGY. responding to the open condition of the tube) a negative wave is reflected, and is subtracted from the force of the pulse wave so as to exaggerate the dicrotic notch, and give the tracing character- istic of the "low-tension" pulse seen in fever, etc. (Fig. 141, mo The mean rate of the pulse varies in different individuals, seventy-two per minute being a fair average for a middle-aged adult. It varies also with many circumstances, which, though purely physiological, must be borne in mind in taking the pulse as a clinical guide. i. Age. At birth it is about 140 per minute, and is, generally FIG. 141. I. Scheme of Normal Pulse Curve : a, Entrance of ventricular stream into the aorta, the lever is jerked too high, reaching*; ab shows real summit of waves; b, point at which stream from ventricle ceases ; c, negative wave caused by (i) sudden cessation of inflow and slight reflux of blood ; d, point of closure of aortic valves ; e, positive wave from valves (dicrotic wave). The time may be measured on abscissa at a' b' d'. II. Scheme of High Tension Pulse Curve (constricted arterioles). A. Curve of radial pulse, which is the resultant of positive reflected wave C added to the primary curve B. III. Scheme of Low Tension Pulse Curve (dilated arterioles). A. Radial pulse curve, which is the resultant of the negative reflected wave C subtracted from the primary wave B. (After Grashey.} speaking, quicker in young than in old people, commonly falling to 60 in aged persons. 2. Sex. It is more rapid in females than in males. 3. Posture. It is quicker standing than lying, particularly if a patient who has been lying down, stand or sit up, the pulse becomes more rapid. 4. The time of day. At its minimum at midnight, it gains in rapidity till 9 o'clock in the morning; falls in the daytime, and rises in the evening till 6 o'clock. 5. Muscular exercise quickens it. VELOCITY OF BLOOD CURRENT. 313 6. It is quicker during inspiration than expiration. 7. It increases with increase of temperature. 8. It is variously affected by emotions. VELOCITY OF THE BLOOD CURRENT. The velocity of the blood must not be confounded with the velocity of the pulse wave, which bears to it the same relation as the surface waves on a river do to the rate of the stream of water. It has already been mentioned that the general bed of the blood increases from the aorta to the capillaries, and decreases from the capillaries to the vena cava. The branches or tribu- taries of an artery or vein have collectively a larger sectional area than the vessel from which they spring or to which they lead respectively ; or, in other words, if we imagined the whole vascular system fused together into one tube it would form two somewhat irregular cones, one corresponding to the arteries and the other to the veins, with their bases placed at the capillaries and their apices at the heart. Between the two cones a still wider portion would represent the aggregate sectional area of the capillaries. (Fig. 128, p. 288.) Since the same quantity of blood must pass through each sec- tion of these cones in a given time, the rate at which it flows must vary greatly in the different parts, being faster in propor- tion as the diameter of the part is narrower, in accordance with the well-known physical law that with the same quantity of liquid flowing, its velocity changes inversely with the square of the diameter of the tube ( V ^- g j . Thus, the mean velocity of the flow in the arteries becomes slower as the capillaries are ap- proached, and in the wide bed of the latter the rate of the cur- rent is reduced to a minimum. In the small veins the rate is slower than in the larger trunks, but on the venous side its rapid- ity never reaches that of the aorta, where it may be said to move at least twice as quickly as in the vena cava. The following table may be useful in giving a general idea of the average velocity in different parts of the circulation : 27 314 MANUAL OF PHYSIOLOGY. Near valves of aorta while the ventricles are contracting it reaches 1 200 mm. per sec. Descending aorta, 300-600 Carotid, 205-357 Radial, 100 mm. per sec. Metatarsal, 57 Arteiioles, 50 Capillaries, 0.5 Venous radicles, 25 Small veins on dorsum of hand, ... 50 Venae cavse, 200 In the aorta near the valves the blood current varies in rapidity, because the flow through the aortic orifice is inter- mittent, and this variation must be more or less communicated to the neighboring arteries in the form of an increase of rapidity coincident with the beat of the arterial pulse. The variation in^ the rate of the blood flow which is caused by the heart beat diminishes with the force of the pulse as the smaller arteries are approached, and finally ceases completely in the capillaries, where under ordinary circumstances the flow is perfectly con- tinuous. In the first part of the aorta the velocity of the blood flow is reduced to nil after each ventricular beat, while in the capillaries no change is perceived. Between these two extremes all gradations may be found, which follow the same rules as the pulse. The general mean velocity varies directly with the blood pressure, which bears a generally inverse relation to the calibre of the arteries. The velocity in any one artery and its branches will vary with the calibre of those vessels, which are constantly undergoing local changes in size. Generally speaking, quick heart beats cause increase in velo- city of the stream, but no definite or invariable relation exists between the rate of the heart beat and the current of the blood. The vasomotor influences have, no doubt, much more effect than the heart beat on the rate of the stream in the smaller vessels the calibre of which they control. In looking at the blood passing through the small vessels of a transparent tissue, such as the frog's tongue or web, it appears that different parts of the column of fluid move with different velocities. Down the centre of the stream the red corpuscles are VELOCITY OF BLOOD CURRENT. 315 seen coursing rapidly, while between the central part and the vessel wall on each side a pale line of plasma can be recognized, FIG. 142. Small portion of Frog's Web, very highly magnified. (Huxley.) A. Wall of capillary vessels. B. Tissue lying between the capillaries. C. Epithelial cell of skin, only shown in part of specimen where the surface is in focus. D. Nuclei of epithelial cells. E. Pigment cells contracted. F. Red corpuscles (oval in the frog). G. H. Red corpuscles squeezing their way through a narrow capillary, showing their elasticity. I. White blood cells. 31 6 MANUAL OF PHYSIOLOGY. which seems to flow more slowly and to carry with it only a few white corpuscles. In the veins the velocity varies greatly with a variety of cir- cumstances which have little or no effect on the arterial flow. Thus, the position of the body or limb, the activity of the neigh- boring muscles and the respiratory movements alter it, but as a general rule the flow in the veins is pretty steady, there being no pulsation or corresponding variation of velocity. In the large vessels the onward flow is affected by the contraction of the auricles. During the auricular systole the veins cannot empty themselves, and therefore there is a slight check to the onward flow, and the velocity of the current is correspondingly reduced. In cases where the auricles are dilated and distended with blood this may cause a definite pulsation, which becomes visible in the great veins of the neck. WORK DONE BY THE HEART. The amount of work done by any form of engine may be expressed as so many kilogrammetres per hour. That is to say, the numbers of kilogrammes it could raise to the height of one metre in that time. The left ventricle moves with each systole about 0.188 (Volk- m'ann) kilogrammes of fluid against an arterial pressure corre- sponding to 3.21 (Bonders) metres height of blood, /. e., 0.188 X 3.21 = 0.604 kilogrammetres for each systole. This at 75 per minute for 23 hours would be 0.604 X 75 X 6 X 24 = 65,230 kilogrammetres. The right ventricle does about one-third as much work as the left, making a total of 86,970 kilogrammetres for the ventricles. Or, in other words, the heart of a man weighing twelve stone does as much work in twenty-four hours as would be required to lift his body 1248 yards into the air, /. e., nearly ten times as high as the steeple of St. Paul's Cathedral. VASOMOTOR NERVES. 317 CONTROLLING MECHANISMS OF THE BLOOD VESSELS. VASOMOTOR NERVES. That the arteries possessed elastic resiliency and vital contrac- tility which regulated the amount of blood flowing to any given part was observed by John Hunter in studying inflammation. The muscle cells have long since been clearly demonstrated in the middle coats of the arteries, but nothing was known of the nervous channels which bore the stimulus to the vessels, or the nerve centres which regulated their contraction, until compara- tively recent times. The first definite knowledge concerning special nerves for the control of the muscular wall of the vessels is due to Claude Ber- nard. He showed that cutting the sympathetic nerve in the neck was followed by an increase in temperature of that side of the head, and a great dilatation of the arteries. It was further observed that stimulation of the superior gan- glion of the sympathetic brought about an opposite result, namely, a fall in temperature and contraction of the vessels on the side at which the stimulus was applied. If the stimulus was increased, the vessels contracted more than the normal, but on cessation of the stimulus they became dilated above the normal and the temperature again rose ; the effects of the stimulus gradually passed off. ' From this it was concluded that the sym- pathetic in the neck contained constrictor fibres which conveyed impulses causing habitual tonic contraction of the vessel wall, corresponding to what was already recognized as arterial tone. On section of the nerve the tonic contraction disappeared, but on gentle stimulation it reappeared, and if more strongly stimulated an excessive contraction set in causing occlusion of many of the vessels. Subsequent experiments have shown that all the vessels are supplied with similar vasomotor (constrictor) nerves, section of which causes dilatation, while stimulation causes contraction of the vessels in the territory presided over by the stimulated nerves. It has also been shown that the vaso-constrictor nerves for all parts of the body come from the cerebro-spinal axis, passing out 31 8 MANUAL OF PHYSIOLOGY. from the spinal cord as extremely fine medullated fibres (white rami communicantes) by the anterior roots of all the spinal nerves between the 2d thoracic and 2d lumbar. They join the sympathetic, which may be regarded as a chain of vasomotor ganglia, and are distributed to the vessels either as special nerves, branches of the sympathetic, as the splanchnics, or with the gen- eral peripheral nerve trunks. Although stimulation of almost any nerve causes vascular contraction, it has been shown that in some parts stimulation gives rise to an opposite result, viz., vascular dilatation. Thus, stimulation of the chorda tympani or nervi erigentes is followed by dilatation of the arterioles of the submaxillary gland and penis respectively. This dilatation is caused by the nerve impulses checking the normal contraction by inhibiting the activity of the vascular muscles. It is believed that all arterioles may be influenced by such fibres, but the greater power of the constric- tor fibres in most nerves prevents their demonstration. These vaso-dilator fibres also come from the central nervous system, but leave it by routes quite different from those traversed by the vaso-constrictor fibres, and are not connected with the sympathetic ganglia. They pass out above by the vagus and glosso-pharyngeal nerves and below with the lower sacral nerves. No vaso-inhibitory fibres have been found to pass by the other spinal roots. VASOMOTOR CENTRES. The nerve cells which govern the majority of the vasomotor channels, lie in the upper part of the medulla oblongata in the floor of the fourth ventricle. This is proved by two facts: ist, most of the brain may be removed without diminishing the arterial tone ; and 2d, if the spinal cord be cut below the medulla (artificial respiration of course being kept up), the mean blood pressure is found to fall immediately, almost to the level of the atmospheric pressure, owing to the relaxation of the smaller arteries consequent on the paralysis of their muscular coat. The changes in the capillary circulation caused by vascular paralysis can be seen in the web of a frog in which the medulla VASOMOTOR CENTRES. 319 has been destroyed (pithed) while the circulation is being studied. The small arteries dilate and the pulse becomes appa- rent in the capillaries, and even in the veins. It seems probable that in the medulla oblongata a vasomotor centre exists, which can regulate the contraction of all the vessels, and keep them constantly more or less contracted. This slight general vascular constriction is spoken of as the arterial tone. The existence of such a centre in the medulla, and of nerve channels in the cord leading from it, is made certain by the fact FIG. 143. vv .UUUUU(JUULAJUUU( JLJ _JLJUULJUL AJUULJUUL, Kymographic tracing showing the effect on the blood-pressure curve of stimulating the central end of the depressor nerve in the rabbit. The recording surface moving from left to right. (C) Commencement and (O) cessation of stimulation. There is considerable delay (latency) in both the production and cessation of the effect. (T) Marks the rate at which the recording surface moves, and the line below is the base line. (Foster.) that if a gentle stimulus be applied to a certain part of the medulla, or just below it, simultaneous general vascular constric- tion sets in, as indicated by a great and sudden rise in the blood pressure. Pressor Influences. The action of the vasomotor centre can be increased, the tone of the vessels elevated, and the pressure raised, either by (i) direct or (2) reflex excitation. Directly, if the blood flowing through the medulla contains too little oxygen or too much waste products it stimulates the centre and the 320 MANUAL OF PHYSIOLOGY. blood pressure rises. This may be seen by temporarily suspend- ing artificial respiration during an experiment on blood pressure, when the pressure rises considerably. Reflexly, the activity of the vasomotor centre can be increased by (i) the stimulation of any large sensory nerve or (2) by sudden emotion (fear). Depressor Influences. The tone of the arteries may be dimin- ished by inhibiting the activity of the vasomotor centre by the stimulation of a certain afferent nerve, the anatomy of which has been made out in the rabbit and some other animals, and proba- bly has its analogue in man. It passes from the inner surface of the heart to the vasomotor centre in the medulla. The effect of stimulation of this nerve in lowering the blood pressure is so great that it is called the depressor nerve. Some emotions (shame) may also reduce the activity of the centre, as seen in blushing, which is simply dilatation of the facial vessels. Subsidiary Centres. Besides this chief vasomotor centre it is probable that in the higher animals, as certainly is the case in the frog, other centres are distributed throughout the spinal cord which are able to take the place of the great primary centre. After the spinal cord has been cut high up, the hinder extremities more or less recover their vasomotor power in a few days, and destruction of the lower part of the spinal cord causes renewed vasomotor paralysis. In frogs this recovery takes place rapidly, the centres being less confined to the medulla than is the case in the more highly organized animals, but in the rabbit and dog it has been observed to occur more slowly. Besides keeping up the normal tone, the arterial nervous mechanisms have the function of regulating the amount of blood supplied to various organs or parts at different times. Both vaso- motor and dilator or inhibitory impulses are probably employed for this purpose. REGULATION OF THE DISTRIBUTION OF THE BLOOD. The various experimental results recently obtained on this subject (too numerous to be mentioned here), show that the vascular nerve mechanisms are very complex. The supposition of some such arrangements as the following may help the student. REGULATION OF THE DISTRIBUTION OF THE BLOOD. 321 1. The blood vessels have muscular elements which, though commonly controlled by nerves, are capable of automatic activity. A supply of arterial blood is sufficient stimulus for their moderate action, and mechanical or other local stimulus is capable of exciting increased constriction. We know that such automatic contractile elements exist in some of the lower animals (snail's heart, hydra, etc.), and we have no reason to doubt their existence in mammals. Moreover, such a view obviates the necessity of supposing that local nerve elements exist which cannot be recognized morphologically. 2. In the medulla oblongata there exist nerve cells which exert a constant influence over the activity of the vascular muscles. These groups of nerve cells which compose the vascular nerve centres may be divided into motor and inhibitory. From these centres impulses of two distinct kinds emanate, the one increasing the action of the contractile elements, and the other diminish- ing it. They are intimately connected with the centres which preside over the functional activity of the various viscera, and are also closely related to the nerves coming from all parts of the circulatory apparatus. 3. Direct communication between these vasomotor and vaso- inhibitory centres and the blood vessels is kept up by means of efferent nerve channels, some bearing stimulating (vaso-constric- tor) others inhibitory (vaso-dilator) impulses. 4. The activity of the contractile elements of any given vas- cular area may be altered by influences from different sources. () Local influences are brought but little into play, but, if the part be cut off from the nervous centres, they are capable of controlling the local blood supply by changing the degree of local arterial constriction. (/5) Central influences from the medulla are habitually in action, affecting all the vessels and keeping up the vascular tone. These impulses are variously modified by changes occurring in distant parts of the, circulatory apparatus, and can be regarded as a general regulating mechanism. They pass through the sympathetic chain. (^) Special influences, which are associated with the functions of the different parts and organs, are only called into operation during the performance of 322 MANUAL OF PHYSIOLOGY. the function, whatever it may be. These impulses are probably conveyed by the same nerves as excite the various forms of func- tional activity. These three modes of regulation have different powers in dif- ferent parts, and thus we find that section or stimulation of cer- tain nerves gives vasomotor effects which appear contradictory. Section of a sensory nerve causes temporary vasomotor para- lysis, owing to the tonic constrictor influence being cut off. Stimulation of the peripheral stump causes vaso-constriction from excitation of the fibres bearing these impulses. The stimulation of a motor nerve causes an increase in the flow of blood through the muscle, /. H, CH 4 , and poison- \ ous organic matter. About one-seventh of the O which is used does not take part in the production of the CO.,, but this proportion may vary greatly. Thus, the estimation of the CO 2 can give no sure guide to the amount of O taken up ; and each gas has to be estimated sepa- rately if an accurate measurement be required. The average amount per diem may be said to be : Carbon dioxide given off about Oxygen consumed " Water given off ' . . . . 800 grammes. . . 700 . 500 The amounts of O taken up and of CO 2 given off differ in 30 354 MANUAL OF PHYSIOLOGY. different individuals and in the same individuals under varying circumstances, among which the following may be enumerated : 1. Increase in the rapidity or the depth of respiratory move- ments, accompanied by an increase in the tidal stream, produces an increase of the total amount of CO 2 given off, while the per- centage in the volume of expired air is diminished. 2. It varies with age. The amount increases with age up to 30 years, and then remains constant. 3. Sex ; is less in women than in men, but it increases in preg- nancy. 4. With muscular activity it is notably increased. 5. Change of temperature of the air has a marked influence on the CO 2 output of cold-blooded animals, which is increased in direct proportion to the elevation of temperature. The effect on warm-blooded animals is the opposite, so long as they can regulate their temperature. The sustentation of the body temperature in cold weather is accompanied by a distinct increase in the output of carbon dioxide. 6. The time of day : a maximum is arrived at about midday and a minimum about midnight. 7. An increase in the amount of carbon dioxide in the atmos- phere diminishes the amount given off from the lungs. CHANGES THE BLOOD UNDERGOES IN THE LUNGS. In order to understand how the oxygen and the carbonic acid pass to and from the blood in the pulmonary capillaries we must know the relationship of these gases to the blood in the arterial and venous sides of the circulation. In the chapter on the blood (pp. 243, 244) it is stated that both the oxygen and the carbon dioxide can be removed from the blood by the mercurial air pump, and that the greater part of these gases are chemically united with some of the constituents of the blood, and that a different quantity of each gas is found in arterial and venous blood. Now that we know the change from the venous to the arterial condition to take place during the passage of the blood through the pulmonary capillaries, where it is exposed to the air, we may assume that the acquisition of CHANGES OF BLOOD IN LUNGS. 355 oxygen and the loss of CO 2 form the essential difference between venous and arterial blood. From either kind of blood about 60 volumes of gas may be extracted from every 100 volumes of blood with the mercurial gas pump. The composition of this gas varies considerably in venous, but not very much in arterial blood. An average is given in the following table : O vols. f. CO vols. $. N vols. $. Arterial, ........ 20 39 1-2 Venous (about), .... 8-10 46-50 1-2 The more rapidly, after bleeding, the gases are removed, the greater is the proportion of O that can be obtained, as delay allows some of it to combine with easily oxidized substances in the blood itself. The amount of oxygen varies in different parts of the venous system. In the blood of an animal dying of slow asphyxia only traces of oxygen can be found, and these soon dis- appear after death. The proofs that O is, for the most part, in chemical combination with the haemoglobin of the red blood corpuscles, and not merely absorbed, as one might be led to suppose from its coming away when the pressure is reduced, are numerous and satisfactory. 1. When arterial blood is submitted to gradual diminution of pressure in the mercurial air pump the oxygen does not come away in accordance with the established law of the absorption of gases (Henry-Dalton) by coming off in proportion to the dimi- nution of the pressure. At first only traces appear (probably the small amount really dissolved), and when the pressure has been re- duced to a certain point, about one-fifth of that of the atmosphere, the oxygen comes off suddenly ; after which little more can be obtained by further reduction of pressure. Haemoglobin com- bines with O in the same way, very rapidly at first, even when the pressure is low. 2. If the oxygen were only in a state of absorption, the blood, while passing through the pulmonary capillaries, could only take up about 0.4 volume per cent., which would be inadequate for life. We know that the quantity of O going to the blood from the air in the alveoli cannot well be explained on physical 356 MANUAL OF PHYSIOLOGY. grounds alone ; and when an animal dies of asphyxia from want of ventilation in a limited space, all the O of the air in the space is absorbed. Since the partial pressure of the O in the chamber falls to zero while some still exists in the haemoglobin, it cannot be the pressure which makes the O pass into the blood. 3. Another conclusive proof that the union of the O with the haemoglobin is really a chemical one, is given by the spectroscopic examination of a haemoglobin solution. When deprived of its O, and after the admixture of the air, quite dissimilar spectra are seen, as already pointed out in Chapter xiv. (Fig. 155, p. 357-) 4. The amount of O taken up by the blood is not always in proportion to the pressure of that gas, but rather to the amount of haemoglobin in the blood ; and we therefore find the adequacy of the respiratory function of the blood going hand in hand with its richness in haemoglobin, and thus the " shortness of breath " of anaemic and chlorotic individuals is explained. 5. The oxygen can be displaced by the chemical union of other gases with the haemoglobin. Our knowledge concerning the relation of the CO 2 to the con- stituents of the blood is less definite. It does not all exist as a mere physical solution, for it comes off irregularly under the air pump, and does not exactly obey the Henry-Dalton law of the absorption of gases. Part comes off easily and part with difficulty. It is not associated with the corpuscles, for more of this gas can be obtained from serum than from a like quantity of blood. It is more easily removed from the blood than from the serum, a certain proportion (about 7 per cent, of the whole) remaining, in the serum in vacuo, until dis- sociated by the addition of an acid or a piece of clot containing corpuscles. If bicarbonate of soda be added to blood from which all the gas has been removed, still more CO 2 can be pumped out, from which it would appear that something exists in the blood capable of dissociating CO 2 from sodium bicarbonate. It has been suggested that the CO 2 is in some way associated (possibly as sodium bicarbonate) with the plasma of the blood, and that the corpuscles have the power of acting like a weak CHANGES OF BLOOD IN LUNGS. Crt 19 357 ^AIHL-11^ L- 155. Spectra of Oxyhaemoglobin, reduced haemoglobin, and CO-haemoglobin, (Gant- e.) i, 2, 3, and 4. Oxyhaemoglobin increasing in strength or thickness of solution. 5. Reduced haemoglobin. 6. CO-haemoglobin. 35 8 MANUAL OF PHYSIOLOGY. acid, and of dissociating it from the soda, and thus raising its tension in the blood. The great importance of the chemical nature of the union between the O and haemoglobin for external respiration becomes most striking when the actual manner in which the entrance of the O is effected is taken into account. It must be remembered that the further we trace the air down the passages, the less will be the percentage of O found in it, and, therefore, a less pressure exerted by that gas. This is shown by the fact that the air given out by the latter half of a single ex- piration has less O and more CO 2 than that of the first half. The most impure air lies in the alveoli of the lungs, for, since the tidal air scarcely fills the larger tubes, the air in the alveoli is only changed by diffusion with the impure air of the small bronchi. Any impediment to the ordinary ventilation of the alveoli so reduces the percentage, and, therefore, the tension of the O, that it would probably sink below that in the blood, and in that case, were it not a chemical union, the O would escape more readily from the blood in proportion as its tension in the blood exceeded that of the air of the alveoli. We know, how- ever, that the blood retains a considerable quantity of oxygen even in the intense dyspnoea of suffocation. In the same way the difference of tension of the CO. 2 in the alveolar air and in the blood hardly explains the steady manner in which the CO 2 escapes, and it has, therefore, been suggested that this escape also depends in some way upon a chemical pro- cess, possibly connected with the union of the O and haemoglobin ; because the admission of O to the blood seems to facilitate the exit of the CO 2 . The following table gives the approximate tension of the two gases in the different steps of the interchange in the case of dogs with a bronchial region occluded so that the air it contained could be examined. It shows that the tensions are such as to enable physical absorption to take some share in the entrance of the O as well as in the escape of the CO 2 . A separate column gives the volumes per cent, of each gas, corresponding to these tensions as compared with the atmospheric standard. The phys- INTERNAL RESPIRATION. 359 ical process must occur before the oxygen and the haemoglobin meet, since the latter is bathed in the plasma, and further sepa- rated from the alveolar O by the vessel wall and epithelium. C0 2 Tension in mm. Hg. Correspond- ing Volume per cent. Tension in mm. Hg. Correspond- ing Volume per cent. In arterial blood, . . In venous blood, . . . In air of alveoli, . . . In expired air In atmosphere, . . . 21. 41. 27. 21. 038 2.8 5-4 if 0.04 29.6 22. 27.44 126.2 158. 3-9 2 -9 3-6 16.6 20.8 INTERNAL RESPIRATION. The arterial blood, while flowing through the capillaries of the systemic circulation and supplying the tissues with nutriment, undergoes changes which are called internal or tissue respiration, and which may be shortly defined to be the converse of pul- monary or external respiration. In the external respiration the blood is changed from venous to arterial ; whereas in internal respiration the blood is again rendered venous. There can now be no doubt that these chemical changes take place in the tissues themselves, and not in the blood as it flows through the vessels. The amount of oxidation that takes place in the blood itself is indeed very small. The tissues, however, along with the substances for their nutrition, extract a certain part of the O from the blood. In the chemical changes which take place in the tissues, they use up the oxygen, which rapidly disappears, the tension of that gas becoming very low ; at the same time other chemical changes are indicated by the appear- ance of CO 2 . The disappearance of the O and the manufacture of CO 2 do not exactly correspond in amount, and they, doubtless, often vary in different parts and under different circumstances. Of the intermediate steps in the tissue chemistry we are ignorant. We do not know the way in which the oxygen is induced by the tissues to leave the haemoglobin ; we can only say that the tissues 360 MANUAL OF PHYSIOLOGY. have a greater affinity for O than the haemoglobin has, and they at once convert the O into more stable compounds than oxy- haemoglobin, and ultimately manufacture CO 2 , which exists in the tissues and fluids of the body at a higher tension than even in the venous blood. RESPIRATION OF ABNORMAL AIR, ETC. The oxygen income and carbonic acid output are the essential changes brought about by respiration, therefore the presence of oxygen in a certain proportion is absolutely necessary for life. The 21 per cent, of O of the atmosphere suffices to saturate the haemoglobin of the blood, and 14 per cent, of O has been found to be capable of sustaining life without producing any marked change in respiration. Dyspnoea is produced by an atmosphere containing only 7.5 per cent, of O. This dyspnoea rapidly increases as the percent- age of O is further decreased, and when it gets as low as 3 per cent, suffocation speedily ensues. The output of CO 2 can be accomplished if the lungs be venti- lated by any harmless or indifferent gas, and since the manufac- ture of the CO 2 does not take place in the lungs, its elimination can go on independently of the quantity of O in them. The 79 per cent, of N contained in the atmosphere has a passive duty to perform in diluting the O and facilitating the escape of the CO 2 from the lungs. Indifferent gases are those which produce no unpleasant effect of themselves, but which, in the absence of O, are incapable of sustaining life, such as nitrogen, hydrogen, and CH 4 . Irrespirable gases are such as, owing to the irritating effect on the air passages, cannot be respired in quantity, as they cause instant closure of the glottis. In small quantities they irritate and produce cough, and if persisted in, inflammation of the air passages; among these are chlorine, ammonia, ozone, nitrous, sulphurous, hydrochloric, and hydrofluoric acids. Poisonous gases are those which can be breathed without much inconvenience, but when brought into union with the blood cause death. Of these there are many varieties, (i) Those which VENTILATION. 361 permanently usurp the place of oxygen with the haemoglobin, viz. : carbon monoxide (CO), hydrocyanic acid (HCN). (2) Narcotic: () Carbonic dioxide (CO 2 ), of which 10 per cent, is rapidly fatal, i.o per cent, is poisonous, and over o.i per cent, injurious. (/9) Nitrogen monoxide (N 2 O).' Both of these gases lead to a peculiar asphyxia without convulsions, (j) Chloroform, ether, etc. (3) Sulphuretted hydrogen (H 2 S), which reduces the oxyhaemoglobin and produces sulphur and water. (4) Phos- phuretted hydrogen (PH 2 ), arseniuretted hydrogen (AsH 2 ), and cyanogen gas (C 2 N 2 ) also have specially poisonous effects. VENTILATION. In the open air the effects of respiration on the atmosphere cannot be appreciated, but in enclosed spaces, such as houses, rooms, etc., which are occupied by many persons, the air soon becomes appreciably changed by their breathing. The most important changes are (i) removal of oxygen, (2) increase in carbonic acid, and (3) the appearance of some poison- ous materials which, though highly injurious, cannot be deter- mined. The deficiency in oxygen never causes any inconvenience, as it is never reduced below what is sufficient for the saturation of the haemoglobin. The excess of CO 2 seldom gives any incon- venience, since the air becomes disagreeably fusty or stuffy long before the amount of CO 2 from breathing has reached o. i per cent., which amount of pure CO 2 can be inspired without any unpleasantness. It is, then, the exhalations coming from the lungs, and probably skin, some of which must have a poisonous character, that render the proper supply of fresh air imperative. The difficulty of determining the presence of the poisonous organic materials makes it convenient to use the amount of CO 2 present in the air as the means of measuring its general purity. For this we must suppose that the relation between the poisonous organic ingredients and the CO 2 is constant. Air which is rendered impure by breathing becomes disagree- able to the sense of smell when the CO 2 has reached the low standard of .06 or .08 per cent., that is to say, scarcely twice as much CO 2 as is contained in the pure atmosphere. Supposing 362 MANUAL OF PHYSIOLOGY. that air is unwholesome when its impurities are appreciable by the senses, then, if the animal body be the source of the CO 2 , .06 per cent, of this gas makes the air unfit for use. An adult man disengages more than half a cubic foot of CO.; in one hour (.6, Parkes), and consequently in that time he renders quite unfit for use more than 1000 cubic feet of air, by raising the percentage of CO.; to . i (0.4 being initial, and .06 respiratory). It is obvious that the smaller the space and the more confined, the more rapidly will the air become vitiated by respiration. It becomes necessary for health, therefore, to have not only a certain cubic space and a certain change of air for each individual, but the cubic space and the change of air should bear to each other a certain proportion, in order that the air may remain sufficiently pure. The space allowed in public institutions varies from 500 to 1500 cubic feet per head, in such apartments as are occupied by the individuals day and night. As a fair average 1000 cubic feet may be fixed as the necessary space in a perfect hygienic arrangement. In order to keep this perfectly wholesome and free from a stuffy smell, and the CO 2 below .06 per cent., it is necessary to supply some 2000 cubic feet of air per head per hour. To give the necessary supply of fresh air without introducing draughts or greatly reducing the temperature of the room is no easy matter, and forms the special study of the hygienic engineer. ASPHYXIA. If an adequate supply of oxygen be withheld and its percent- age in the blood is reduced to a certain point, the death of the animal follows in three to five minutes, accompanied by a series of phenomena commonly included under the term asphyxia. This may be divided into four stages, i. Dyspnoea. 2. Convulsion. 3. Exhaustion. 4. Inspiratory spasm. As asphyxia is a mode of death the symptoms of which the physician can be called upon to treat, he should be able to recognize its different phases. If the air passages be closed completely the respirations become deep, labored and rapid. The respiratory efforts are more and more energetic, and the various supplementary muscles are called ASPHYXIA. 363 into play one after the other, until gradually the second stage is reached in about one minute. As the struggles for air become more severe, the inspiratory muscles lose their power, and the expiratory efforts become more and more marked, until finally the entire body is thrown into a general convulsion, in which the traces of a rhythm are hardly apparent. This stage of convulsion is short, the expiratory muscles becoming suddenly relaxed by exhaustion. Then the longest stage arrives, in which the animal lies almost motionless, making some quiet inspiratory attempts. These be- come gradually deeper and slower, until they are nothing more than deep gasps separated by long irregular intervals. The pupils of the eyes become widely dilated, the pulse can hardly be felt, and the animal lies apparently dead, when often, after a surprisingly long interval, one or more respiratory gasps follow, and with a gentle tremor the animal stretches itself in a kind of tonic inspiratory spasm, after which it is no longer capa- ble of resuscitation. This last pulseless stage, to which the term asphyxia is more properly confined, is the most irregular in dura- tion, but always the longest. The blood of an animal which has died of asphyxia is nearly destitute of oxygen, the haemoglobin being in a much more reduced condition than is found in venous blood. The first and most obvious effect produced by the circulation of blood so defi- cient in oxygen is excessive stimulation of the respiratory centre, which causes the extreme and varied actions just described. In the first stage of asphyxia, the venous blood, reaching the systemic arterioles, affects their muscular walls, exciting the vaso-con- strictor mechanism, so as to cause a rapid and considerable rise in blood pressure and consequent distention of the left ventricle. The general constriction of the small arteries may be brought about by the venous blood acting as a stimulus to the cells of the medullary and spinal vasomotor centres, or more probably it acts as a direct stimulant to the muscle cells of the arterioles themselves. The centres in the medulla which govern the inhib- itory fibres of the pneumogastric are also stimulated, and con- sequently the heart beats more slowly. The increase in arterial 364 MANUAL OF PHYSIOLOGY. tension and the slow beat give rise to distention of the ventricle, which, when a certain point is reached, impedes the working of the heart, and its muscle begins to beat more and more feebly, so that in the third stage the pulse can hardly be felt. The mus- cular arterioles then become exhausted and relax, the blood pressure falls rapidly, and with the death of the animal it reaches the level of atmospheric pressure. Both sides of the heart and great veins are engorged with blood in the last stage of asphyxia ; the cardiac muscle being exhausted, from want of oxygen, is unable to pump the blood out of the veins or empty its cavities. Owing to the force of the rigor mortis vt the left ventricle, and the greater capacity of the systemic veins, the left side is found comparatively empty some time after death, and at post-mortem examination the right side alone is found over-filled. BLOOD-ELABORATING GLANDS. 365 CHAPTER XX. BLOOD-ELABORATING GLANDS. In the preceding chapters we have seen that the blood under- goes important changes as it courses through the different parts of its circuit. Where it comes in contact with the tissues it yields to them nutrient material for assimilation, and oxygen for their metabolism, and carries away from them some waste products. In the lungs it receives oxygen and gives off carbonic acid. While it flows through the minute vessels of the alimentary tract, some of the materials elaborated by the digestion of food are absorbed, and directly added to the blood ; at the confluence of the great veins in the neck the stream, composed of lymph and chyle, is poured into the blood before it enters the heart, so as to be thoroughly mingled with it on its return from the general circulation. Moreover, in various glands, different substances are used in the manufacture of their secretions. Thus there is a kind of material circulation, a constant income and output going on in the blood itself as it passes through the different parts of the body. The investigation of the exact changes which take place in the blood in each organ or part is surrounded with difficulty, and in many cases it is quite impos- sible to ascertain what changes occur. In some parts it may be made out by noting the results produced, or the substances given off or taken up by the blood, as seen in the changes found in the air after its exposure to the blood in the lungs, where we can definitely state that the blood has lost or gained certain materials, and is so far altered. In other parts, such as the muscles or the ductless glands, where, no doubt, profound changes in the blood occur, we have no separate outcome which we can analyze, and we must therefore trust altogether for the elucidation of the change going on in them to the differences which may be found to exist in the blood flowing to, and that flowing from, such an organ. For this purpose one can either examine samples of the 3 66 MANUAL OF PHYSIOLOGY. FIG. 156. blood from the artery and vein of the organ, while the ordinary circulation is going on, or, immediately after the removal of the organ, by causing the artificial stream of blood to flow through it ; then the changes brought about in the blood in its pas- sage through the organ will give the required information. It can be seen, from the fore- going enumeration of processes, that some organs have a double function as regards the blood. Thus, in the lung there is both renovation by taking in oxy- gen, and purification by getting rid of carbon dioxide. The textures in their internal respi- ration take the nutriment and oxygen, and give the blood CO.; and various other waste products of tissue change. DUCTLESS GLANDS. There is a certain set of organs which have but slight traits of resemblance to one Vertical section of the Supra-renal Capsule, another, and in consequence of er. fa Q want o f , more accurate i. Cortex. 2. Medulla, a. Fibrous capsule. . 6. External cell masses. c. Columnal knowledge aS tO their CXact layer, d. Internal cell masses, e. Medul- . ' . , . lary substance, in which lies a large vein, function, and the fact that they partly seen in section/". .. , . , do not pour their products into ducts, but probably into the blood current, are commonly grouped together as ductless or blood glands. It has been shown that a great part of the absorbed nutrient material passes through a special set of vessels called the lacteals or lymphatics, and in so doing has to traverse peculiar organs THYROID BODY. 367 called lymphatic glands, where it is no doubt modified, and has added to it a number of cells (lymph corpuscles) which sub- sequently are poured into the large veins with the lymph and become important constituents of the blood. Some of these blood glands are doubtless nearly akin to the lymphatic glands already described (Fig. 151), their duty being the further elaboration and perfection of the blood. In this group are commonly placed the supra-renal capsules, the thy- roid, the thymus, and the spleen. FIG. 157. Section of the Thyroid Gland of a child, showing two complete sacs and portions of others. The homogeneous colloid substance is represented as occupying the central part of the cavity of the vesicles, which are lined by even cubical epithelium. (Schafer.) SUPRA-RENAL CAPSULE. With regard to the function of the supra-renal capsule we may say that nothing definite is known. The cortical part is said to resemble the lymph follicles in structure, while the central part, on account of its numerous peculiar, large cells and great richness in nerves, has been explained as belonging to the nervous system. THYROID BODY. The thyroid is made up of groups of minute closed sacs embedded in a stroma of connective tissue, lined with a single 3 68 MANUAL OF PHYSIOLOGY. row of epithelium cells, and filled with a clear fluid containing mucin. In the adult the sacs are commonly much distended with a colloid substance and peculiar crystals, and the epithelium has disappeared from their walls. Although said to be rich in lymphatics and to contain follicular tissue, positive proof of the FIG. 158. Portion of Thymus re- moved from its envel- ope and unraveled so as to show the lobules (f>, b) attached to a central band of connective tissue (a). FIG. 159. Magnified section of a portion of injected Thymus, showing one complete lobule, with soft central part (cavity) (&), and parts of other lobules. ( Cadiat.) (a) Lymphoid tissue, (c) Blood vessels, (d) Fibrous tissue. FIG. 160. Elements of Thymus (high power). corpuscles. (Cadiat.} (a) Lymph (l>) Epithelioid nests of Hassall. relation of the thyroid body to the lymphatic system is still wanting. THYMUS GLAND. The functional activity of the thymus is restricted to that period of life when growth takes place most rapidly. It is well SPLEEN. 369 developed in the foetus, and increases in size for a couple of years after birth ; but it gradually diminishes in bulk and loses its original structure during the later periods of childhood, so as to become completely degenerated and fatty in the adult. It is composed of numerous little follicles of lymphoid tissue collected into groups or lo.bules connected to a kind of central stalk. The lymphoid follicles of the young thymus have some likeness to those of the intestinal tract, but they differ from these agminate glands not only in arrangement but also in having peculiar small nests of large cells (corpuscles of Hassall) in the midst of the adenoid tissue of which they are made up. On account of the structure of the lobules being so nearly identical with that of a lymphatic gland, and from its great richness in lymphatic vessels, the thymus is said to be related to the lymphatic system, and is supposed to play an importent part in the elaboration of the blood during the earlier stages of animal life. SPLEEN. Structure. The spleen also resembles a lymphatic organ in structure, but differs from it in the relation borne by the blood FIG. 161. (a) Trabeculae of the Spleen. (K) Artery cut obliquely. (Cadiat.) to the elements of the follicular tissue. It is encased in a strong capsule made of fibrous tissue and unstriated muscle cells. From this many branching prolongations pass into the substance of the 370 MANUAL OF PHYSIOLOGY. FIG. 162. Reticulum of the Spleen Pulp injected with colorless gelatine. (Cadiat.) (a) Meshes made of endoihelium. (b) Lacunar spaces, through which the blood flows. (c) Nuclei of endothelium. organ, so as to traverse the soft, red, spleen pulp. In these tra- beculae or prolongations from the capsule are found the branches of the splenic artery, dividing into smaller twigs without anas- tomosis. On leaving the tra- beculae the arteries break up sud- denly into a brush-like series of small branches, ending in capil- laries, which are lost in the pulp where the small veins may be seen to commence. Between the trabeculae are found two distinct kinds of tis- sue : (i ) Rounded masses of lym- phoid tissue, called Malpighian bodies, scattered here and there through the organ ; and (2) the peculiar soft splenic pulp making up its bulk. The small rounded masses of lymph follicular tissue are situated on the course of the fine arterial twigs. The delicate adenoid reticulum which holds the lymph cells together is inti- mately connected with the vessel wall. The pale appearance of these follicles, which distinguishes them from the surround- ing splenic pulp, depends on the number of the white cells which are packed in the meshes of this perivascular adenoid tissue. The splenic pulp consists of a system of communicating lacunar spaces lined with endothelium. Into these spaces the blood is poured from the arteries, and thus mingles with vast numbers of white cells. Besides the ordinary blood discs and the white cor- puscles or lymph cells, many peculiar cells are found in the spleen pulp. Some of these look like lymph cells containing little masses of haemoglobin, and appear to be transitions from the colorless to the red corpuscles, while some small, misshapen, red corpuscles are regarded as steps in a retrograde change in the discs. But few, if any, lymph channels lead from the spleen pulp, and only a relatively small number pass out from the hilus, SPLEEN. 371 so that the splenic artery and vein must be regarded as taking the places of the afferent and efferent lymph channels. Chemical Composition of the Spleen Pulp. Chemical examina- tion shows the splenic pulp to have remarkable peculiarities. Al- though so full of blood, which is generally alkaline, the spleen is acid in reaction, and contains a great quantity of the oxidation products (so-called extractives] commonly found as the result of active tissue change. The chief of these are uric acid, leucin, xanthin, hypoxanthin, inosit, lactic, formic, succinic, acetic and butyric acids. It also contains numerous pigments, rich in carbon, but little known, which are probably the outcome of destroyed haemoglobin. A peculiarly suggestive constituent is an albumi- nous body containing iron. The ash is found to contain a con- siderable quantity of oxide of iron, to be rich in phosphates and soda, with but small quantities of chlorides and potassium. Changes in the Blood in the Spleen. If the blood flowing in the artery to the spleen be compared with that in the vein, the dif- ference gives us the changes the blood has undergone in the organ, and hence is of great importance. In the blood of the vein is found an enormous increase in the number of white cor- puscles (i white to 70 red in the vein, as against i to 2000 in the splenic artery). The red corpuscles from the vein are smaller, brighter, less flattened than those of ordinary blood ; they do not form rouleaux, and are more capable of resisting the injurious influence of water. The blood of the splenic vein is also said to have a greater proportion of water, and to contain an unusual quantity of uric acid and other products of tissue waste. The amount of blood in the spleen varies greatly at different times. Shortly after meals the organ becomes turgid, and remains enlarged during the later periods of digestion. Pathological Changes. The size of the spleen, which may be taken as a measure of its blood contents, is also altered by many abnormal conditions of the blood. Thus, in all kinds of fever, particularly ague and typhoid, and in syphilis, the spleen becomes turgid, and in some of these diseases it remains swollen for some time. In a remarkable disease, leucocythaemia, in which the white blood cells are greatly increased in number, and the red 37 2 MANUAL OF PHYSIOLOGY. ones are comparatively diminished, the spleen, in company with the lymphatic glands, is often found to be profoundly altered and diseased, and commonly immensely enlarged ; but, on the other hand, advanced amyloid degeneration of the spleen may occur without any notable alteration taking place in the number or properties of the blood corpuscles. Extirpation of the Spleen. The spleen may be removed from the body without any marked changes taking place in the blood or the economy generally. It is said that if an animal whose spleen is extirpated be allowed to live for a certain time, the lym- phatic glands increase in size, or become swollen. In attempting to assign a definite function to the spleen all the foregoing facts must be carefully reviewed, and the peculiarity of its (i) structure, (2) chemical composition, (3) the changes the blood undergoes while flowing through it, (4) the variations in blood supply which follow normal and pathological changes in the economy, and (5) the absence of effect following its extirpation, must all be borne in mind. Its structure teaches us that it is intimately related to lymphatic glands. The Malpighian bodies are simply lymph follicles, and the pulp may be regarded as a sinus like that of a lymph gland, with this difference, that it is traversed by blood instead of lymph. The cell elements found in it indicate that not only white cells are rapidly generated, but also that these cells have some peculiar relationship to haemoglobin, fes they are often found to contain some. The varieties in size, form, and general appearance of the red corpuscles can be accounted for by either their destruction or their formation occurring in this organ. Its chemical composition also shows that certain special changes go on in the pulp, and that probably stages of the construction or destruction of haemoglobin are here accomplished may be inferred from the peculiar association of iron with albuminous bodies. From the characters of the blood flowing from the spleen it has been argued that, besides an enormous production of white corpuscles, the destruction of the red discs goes on, while some new discs are formed, probably by means of the white cells GLYCOGENIC FUNCTION OF THE LIVER. 373 making haemoglobin in their protoplasm, which, gradually dis- appearing, leaves only the red mass of haemoglobin. The increased activity of the spleen after meals, and in certain abnormal states of the blood, as shown by its containing more blood, distinctly points out that some form of blood elaboration goes on in it, which is nearly related to, or associated with, nutri- tion. FIG. 163. Section of Spleen through a lymph follicle (Malpighian body) (a) injected to show the vessel (c) entering the follicle, the lyrnphoid tissue of which is pale in comparison with the pulp (6), the meshes of which are filled with injection. (Cadiat.) The swelling of the lymphatic glands after extirpation of the spleen confirms its relation to these organs, and the fact is un- disputed that it is a source of the white corpuscles of the blood ; but the paucity of evidence after this operation as to changes in the number or character of the red discs proves that if the spleen be either the place of origin or destruction of the red corpuscles it cannot be the only organ in which they are produced or destroyed. GLYCOGENIC FUNCTION OF THE LIVER. Of all the organs that modify the composition of the blood flowing through them, the liver plays the most important part in elaborating the circulating fluid. The elimination of the various 374 MANUAL OF PHYSIOLOGY. constituents of the bile, which has already been mentioned as necessary for the purification of the blood, and useful in aiding absorption, is probably but a secondary function of this great gland. The production of a special material animal starch essential to the nutrition FIG. i6 4 . and growth of the textures is probably the most im- portant duty of the liver cells, and possibly the con- stituents of the bile are but the by-products, which must be got rid of, result- ing from unknown this and other chemical pro- cesses. In the digestive chapter on the secretions the structure of the liver was mentioned, and attention was directed to the peculi- arities of its double blood supply. A relatively small arterial twig carries blood to it from the aorta, while the great portal veins dis- tribute to it all that large r -11 i i v Of blood which flows through the intestinal tract and the spleen. The blood in the vena porta during digestion can hardly be called venous blood, for much more passes through the intestinal capillaries when digestion is going on than is necessary for the nutrition of the tissue of the intestinal wall. The portal blood is also to be distinguished from ordinary venous blood from the fact that it has just been enriched with a quantity of the soluble materials taken from the intestinal canal, namely, pro- Diagram of the Portal Vein (/ v) arising in the ali- i mentary tract and spleen (s), and [carry ing the blood Supply GLYCOGEN. 375 teids, sugar, salts, and possibly some fats ; and it has been further modified by the changes taking place in the spleen. It is from this blood that the liver cells manufacture the starch- like substance above mentioned. Animal starch was discovered by Claude Bernard, and called by him Glycogen, on account of the great facility with which it is converted into sugar in the presence of certain ferments which exist in the liver itself and in most tissues after death. Shortly after the death of an animal the tissue of the liver, and also the blood contained in the hepatic veins, are extremely rich in sugar, which has been formed by the fermentation of the hepatic glycogen. The quan- tity of sugar increases with the length of time that has elapsed since the death of the animal, and is minimal, if not nil, if the liver or hepatic blood be taken for examination while the tissue elements are still alive. The peculiar blood of the great portal vein coming from the stomach, intestines, and the spleen has then to pass through a second set of capillaries in the liver, and undergoes such important changes that this organ must be regarded as occupy- ing a foremost position among the blood glands. Differences of the utmost importance have long been thought to exist between the blood going to and that coming from the liver, and to it has even been attributed paramount utility as a blood elaborator ; but the scientific knowledge of its power in this respect must date from the discovery of its glycogenic function. GLYCOGEN. Glycogen is a substance nearly allied to starch in its chemical composition, and is converted with great readiness into grape sugar by the action of certain ferments and acids. Many of the animal textures contain these ferments, among others the liver itself, at least when its tissue is dying ; and consequently the liver with the blood coming from it (if examined in an animal some time dead) does not contain glycogen, but sugar which has been formed from it. If a piece of liver taken from an animal immediately after it is killed be plunged into boiling water, so as to check the action of the ferment, no trace of sugar is found 376 MANUAL OF PHYSIOLOGY. in it, but only glycogen. After the lapse of a little time another piece of the same liver, which has lain at the ordinary room temperature, will give abundance of sugar. The mode of preparation of glycogen depends upon the fore- going facts. The perfectly fresh liver taken from an animal killed during digestion is rapidly subdivided in boiling water. When the ferment has been destroyed by heat the pieces of liver are rubbed up to a pulp in a mortar, and then reboiled in the same fluid. The liquor is then filtered, and from the filtrate the albuminous substances are precipitated with potassio-mercuric iodide and hydrochloric acid, and removed on a filter. From this filtrate the glycogen may be precipitated by alcohol, caught on a filter, washed with ether to remove fat, and dried. Glycogen thus prepared has the following properties. It is a white powder, forming an opalescent solution in water, which becomes clear on the addition of caustic alkalies. It is insoluble in alcohol and ether. With a solution of iodine it gives a wine- red color, and not blue, like starch, which it otherwise much resembles in chemical relationship. Glycogen is widely distributed among many other parts besides the liver, namely, in all the tissues of the embryo, and in the muscles, testicles, inflamed organs, and pus of adults ; in short, where any very active tissue change or growth is going on, some traces of glycogen can be found. Some light is thrown upon its origin by the fact that the amount of glycogen in the liver depends in a great measure on the kind and quantity of food used. It rapidly increases with a full, and decreases with a spare diet, though it never disappears even in prolonged starvation. The formation of glycogen is much more dependent on the carbohydrate food than on the proteid, for it rapidly rises with increase in the quantity of sugar taken, and falls, as in starvation, when pure proteid (fibrin) without any carbohydrate is used either with or without fat. Although the large supply of glycogen normally manufactured in the liver is probably derived from the sugar of the food, we must not conclude from this that the liver cells cannot make glycogen from other materials. Possibly anything that suffices GLYCOGEN. 377 for the nutrition of their own protoplasm enables the cells to produce glycogen. The slowness with which glycogen disappears in starvation would seem to point to this. The ultimate destiny and physiological application of glycogen* have been for some time vexed questions. Whether it is con- verted into sugar, and as such carried off by the blood of the tissues, or whether it is simply distributed as glycogen, is dis- puted by different observers, while others say glycogen is a step in the formation of fat out of carbohydrate. The want of clear evidence on the subject, together with the obvious chemical difficulties, force us to abandon the theory that fat can be an immediate outcome of liver glycogen, though we must admit that carbohydrates, or any form of nutriment, may indirectly aid in the ultimate formation of fat by protoplasm. The difficulty of determining the exact amount of sugar or glycogen in the blood makes this a very unsatisfactory means of determining .the physiological application of liver glycogen. It seems probable that glycogen forms the general carbohydrate nutriment of the textures the diffusible sugar being transformed in the liver, into indiffusible glycogen, in order that it may be distributed throughout the various tissues without being lost in the excretions. 37$ MANUAL OF PHYSIOLOGY. CHAPTER XXI. . SECRETIONS. The secretions which are poured into the alimentary tract have been already described in the chapter on digestion. There are other glands which can now be conveniently considered, since they more or less alter the blood flowing through them, and thus may be said to aid slightly in the perfect elaboration of that fluid. They are, however, subservient to very different func- tions, some having merely local offices to perform, and others having duties allotted to them of the greatest general importance to the economy. This becomes obvious from a glance at the following enumeration of the remaining glandular organs. Secreting glands (other than those forming special digestive juices) : Lachrymal. Mammary. Mucous. Sebaceous. Excreting glands : Sudorific. Urinary. SURFACE GLANDS. LACHRYMAL GLANDS. Most vertebrate animals that live in air have a gland in con- nection with the surface of their eyes, which secretes a thin fluid, to moisten the conjunctiva. This fluid commonly passes from the eye into the nasal cavity, and supplies the inspired air with moisture. The lachrymal fluid is clear and colorless, with a distinctly salty taste and alkaline reaction. It contains only about i per cent, of solids, in which can be detected some albumin, mucus, and fat (i per cent.), epithelium (i per cent.), as well as sodium chloride and other salts (.8 per cent.). The secretion is produced continuously in small amount, but is subject to such considerable and sudden increase, that at times MUCOUS GLANDS. 379 it cannot all escape by the nasal duct, but is accumulated in the eyes until it overflows to the cheek as tears. This excessive secretion may be induced by the application of stimuli to the conjunctiva, the lining membrane of the nose, or the skin of the face, or by strong stimulation of the retina, as when one looks at the sun. A similar increase of secretion follows certain emotional states consequent on grief or joy. These facts show that the secretion of the gland is under nervous control, the impulses stimulating secretion commonly starting either from the periph- ery, and passing along the sensory branches of the fifth or along the optic nerve, or from the emotional centres in the brain, and arriving at the gland in a reflex manner. The amount of secretion can also be augmented by direct stimulation of the lachrymal nerves, so that in all probability these are the efferent channels for the impulse. MUCOUS GLANDS. In connection with mouth and stomach secretions, mention has been made of glands which are elongated saccules lined with clear cells with highly refracting contents (Fig. 165). They are distributed over all mucous membranes, and are the chief source of the thick, tenacious, clear, alkaline, and tasteless secretion called mucus. This material contains about five per cent, of solid matters, of which the chief is mucin, the characteristic material of mucus, which swells up in water and gives the peculiar tenacity to the fluid. It is precipitated by weak mineral and acetic acids ; and, as the precipitate with the latter does not redissolve in an excess, this acid becomes a good test to distinguish it from its chemical allies. Mucin is not precipitated by boiling. Mucus also con- tains traces of fat and albumin, and inorganic salts, viz., sodium chloride, phosphates and sulphates, and traces of iron. The fluid is secreted either by the special mucous glands, or it may be produced by the epithelium of the mucous surfaces. The cells produce in their protoplasm a quantity of the secretion, which may often be seen to swell them out to a considerable extent. This clear fluid is then expelled, and the altered cells 3 8 MANUAL OF PHYSIOLOGY. are repaired or replaced. Many form elements, like the remains of epithelial cells, are found in the secretion ; and also round nucleated masses of protoplasm similar to white blood corpuscles after the imbibition of water. In the abnormal secretion of a mucous surface during inflammation these mucous corpuscles are, as well as the general amount of secretion, greatly increased, so that the secretion may become opaque, and may appear to be purulent. The chief object of the secretion seems to be to protect the mucous surfaces, which are rich in delicate nerves and vessels, FIG. 165. Section of the Mucous Membrane of the upper part of nasal cavity showing 'numerous Mucous Glands cut in various directions, a, Surface epithelium; b, gland saccule lined with secreting cells ; c, connective tissue. (Caetiat.) and are subjected to many injurious influences of a chemical or mechanical nature. It is analogous to the keratin of the epi- dermis, and may be regarded as an excretion, since it is not absorbed, but is cast out from the mucous passages, and passes from the intestinal tract with the faeces, and from the air passages as sputum, etc. SEBACEOUS GLANDS. 381 SEBACEOUS GLANDS. These belong to the outer skin, and commonly open into the follicles of the hairs, but also appear on the free surface of the lips and prepuce, etc., where no hairs exist. The secretion cannot be collected in great quantity in a normal condition, but, as far as can be made out, it is composed of neutral fat, soap, and an albuminous body allied to casein, and organic salts and water, about 60 per cent. The secretion contains the remains of numerous epithelial FIG. 166. Section of Skin showing the roots of three hairs and two large sebaceous glands (d). (Cadiat.) cells which are thrown off from the inner surface of the glands, while they are undergoing a peculiar kind of fatty change. These cells gradually get quite broken down during their so- journ in the gland alveoli, and the secretion is finally pressed out by the band of smooth muscle which usually embraces the gland and squeezes it against the hair fallicle. This secretion, the use of which is to lubricate the surface with a fatty material, is cast off with the desquamated epithelium and the hairs. The Meibomian glands of the eyelids are analo- 3 82 MANUAL OF PHYSIOLOGY. gous structures, and are specially elaborated for the lubrication of the ciliary margin. The glands about the prepuce and clito- ris are also analogous to the sebaceous glands ; in some animals (Castor) they secrete a peculiarly odoriferous material. MAMMARY GLANDS. The secretion of milk only takes place under certain circum- stances and continues for a limited period. As the name of the glands implies, they are present in all mammalian animals. The activity of the gland commences in the later stages of pregnancy, FIG. 167. Section of Mammary Gland during active lactation (human), (a) Saccules lined with regular epithelium. (f>) Connective tissue between the alveoli. (Cadiat) and then continues, if the secretion be regularly withdrawn from the gland, for some 9 to 1 2 months. During pregnancy the breasts undergo certain preparatory changes prior to the appearance of the milk. They increase in bulk, owing to the greater blood supply, and to certain changes in the cell elements of the glands, which are compound saccular glands. Each breast contains a series of some ten to twelve glands, with distinct ducts ; upon these there are dilatations that act as reservoirs, in which, during active lactation, the secretion is stored until needed. MILK. 383 The alveoli are chiefly saccular in form, and are lined with a single layer of glandular epithelium, and, during active lacta- tion, contain but little fat, though in the later stages of preg- nancy, before the secretion is established, the cells contain quan- tities of large fat globules. MILK. Milk is a yellowish-white, perfectly opaque, sweetish fluid, with an alkaline reaction and a specific gravity of about 1030. When exposed to the air, particularly in warm weather, the milk soon loses its alkalinity, first becoming neutral, and subsequently acid ; the milk is then said to have " turned sour," but its ap- pearance is not greatly changed. When it has stood a very long time it may crack or curdle, and separate into two parts one a thick, white curd and the other a thin, yellowish fluid. This turning sour and ultimate curdling depends upon a change brought about in one of its most important constituents, namely, milk sugar, by means of a process of fermentation. The milk sugar, in the presence of certain forms of bacteria, ferments and gives rise to lactic acid. When the quantity of lactic acid is sufficient, it not only makes the milk sour, but also precipitates another of its important constituents, namely, casein. This albu- minous body in its coagulation entangles the fat of the milk, and we have thus formed the curd of cracked milk, while the whey consists of the acid, salts, and remaining milk sugar. Although the curdling of milk depends on the coagulation of an albuminous body, it is never produced by boiling fresh milk, because the chief proteid is casein, a form of derived albumin (alkali-albumin), which does not coagulate by heat. When milk is preserved from impurities and kept in a cool place, a thick yellow film soon collects on the top of the fluid ; the thickness of this layer the cream may be taken as a rough gauge of the richness of the milk. Milk consists of a fine emul- sion of fat, the suspended particles of which are kept from run- ning together by a superficial coating of dissolved casein. When left at rest, the light fatty particles float on the top and form cream. 384 MANUAL OF PHYSIOLOGY. When the mammary glands commence to secrete, the milk contains numerous peculiar structural elements, which subse- quently disappear from the secretion, but which are of consider- able interest in relation to the physiological process of the secre- tion. These are the colostrum corpuscles, which consist of large spherical masses of fine fat globules held together by the remains of a gland cell, which encloses the fat globules as a kind of sac or case, and in which at times a nucleus can be made out. CHEMICAL COMPOSITION. The most remarkable point about the chemical composition of milk is the large proportion of proteid and fat it contains ; this renders it unique among the secretions. There are two distinct albuminous bodies present, viz. : casein, which appears identical with alkali-albumin, and another form of albumin allied to serum- albumin. The jfo/r are present in the shape of globules of various sizes, being in the condition of a perfect emulsion, as above stated. They consist of glycerides of palmitic, stearic and oleic acids. The milk sugar is very like glucose or grape sugar, but not so soluble. It has the peculiarity of undergoing lactic fermenta- tion. Of the inorganic constituents of milk the most important are phosphates and carbonates of the alkalies, /. and thlis the P ower of retention is overcome. The moment the balance of power is thus x turned in favor of the expelling agencies, a , inal muscles are made drop of urine reaches the beginning of the by 2 to force some urine into the neck of the urethra and excites reflexly the spinal bladder, whence im- pulses pass by 3 to in- centres, and thus brings about the complete hibit the sphincter cen- _ , tre and excite the de- evacuation of the bladder without further trusor through 4. voluntary effort. The nervous mechanism that controls the act of micturition con- sists essentially of ganglionic centres which are situated in the R. ^c spi i n m puises' atTe! "bdder is dis- we/i7/,the tonus of the spinal centre stimulat- ing the sphincter is checked, and the abdom- EVACUATION OF THE BLADDER. 415 lumbar enlargement of the spinal cord, and of two sets of nerve channels passing to and from these centres. The centres may be said to be composed of functionally distinct parts a retaining and evacuating part. The retaining centre causes the sphincter muscle to contract. The evacuating centre can excite the detru- sor to action. One set of nerve channels (3, 4, R, T) communi- cates between these centres and the urinary organs (B), and the other (i, 2) between the cord centres and the cerebral hemi- spheres (c). That which connects the special lumbar centres with the bladder, contains efferent fibres of two kinds, going to the antagonistic muscles, the sphincter vesicae (T), and the detrusor urinae (4) respectively, and afferent fibres of different kinds ; those (R) going from the bladder to the nerve cells in the cord which stimulate them and cause the sphincter to remain tonically contracted ; those passing from the mucous membrane of the urinary passages to the ganglionic cells in the cord have two functions ; one (4) excites the contractions of the detrusor urinae and the other (3) inhibits the tonic action of the retaining centre. The action of the ganglionic cells that stimulate the sphincter muscle can to a certain extent be either aided or checked by means of voluntary or other cerebral influences, so that two kinds of fibres a stimulating and inhibitory one' must pass from the hemispheres to the micturating centre in the cord. Those cells which govern the motions of the detrusor seem to be least under voluntary control, and are probably only stimu- lated to action by the impulses arising from the urinary passages, and hence are simply reflex, centres. The effect of certain emotions on the act of micturition seems to show that those ganglion cells in the cord which cause the bladder to contract are connected with the higher centres. Thus, extreme terror (in a dog at least) often causes a forcible expul- sion of urine, and great anxiety or impatience seems in man often to have a checking influence, causing great delay in initiating micturition. 41 6 MANUAL OF PHYSIOLOGY. CHAPTER XXIII. NUTRITION. We can compare the incomings and outgoings of the economy, and should now be in a position to see what light can be thrown by this comparison upon the actual changes which take place in the textures of the body. We have seen that the income is made up of substances be- longing to the same groups of materials as are found in the body, viz., albumins, fats, carbohydrates, salts, and water, introduced by the alimentary canal, and oxygen, which is acquired by the respiratory apparatus ; while the outgoings consist of urea from the kidneys, carbonic acid from the lungs, certain excrement from the intestine and other mucous passages, sweat, sebaceous secretion, epidermal scales, from the skin ; together with a quan- tity of water from all these ways of exit. The milk, ova, and semen may be here omitted, being regarded as exceptional losses devoted to special objects. In order that the body may be kept in its normal condition, it is necessary that the income should at least be equal to the outgoings of all kinds, and, except where growth is going Jon rapidly, an income equal to the expenditure ought not only to suffice, but ought to be the most satisfactory for the economy. We know that animals can live for some considerable time without food, in which case a certain expenditure of material derived from the body itself is necessary to. sustain life, and therefore the outgoings continue. We ought thus to be able to arrive in a very simple manner at the minimal expenditure ne- cessary for the sustentation of the body. We shall find, however, that (i) an income equal to this minimal expenditure (that of starvation) does not at all suffice to keep up the body weight, and that (2) a considerable margin over and above this mini- mum is necessary in order to establish the nutritive equilibrium ; (3) further, that the proportion of material eliminated and stored TISSUE CHANGES IN STARVATION. 417 up in the body respectively varies as the income is increased ; (4) and finally, that the quality of the food /. e., the proportion of each group of food stuff present in the diet has an important influence on the quantity required to establish the equilibrium, and that best suited to cause increase of weight or to fatten. It will be convenient to consider the following different cases in succession. 1. No income, except oxygen, /. e., starvation. 2. An income only equal to the expenditure found during starvation. 3. Establishment of perfect nutritive equilibrium. 4. Excessive consumption. TISSUE CHANGES IN STARVATION. As is well known, deprivation of oxygen by cessation of the respiratory function almost immediately puts an end to the tissue changes necessary for life, so that the oxygen income can- not be interfered with, or the experiment comes to an end. It has also been found that a small supply of water to drink makes the investigation of the various tissue changes more reliable, by facilitating them and prolonging life. We therefore speak of a total abstinence from solids as starvation. When deprived of food, those tissues upon the activity of which life immediately depends must feed upon materials stored up in some tissues of less vital importance to the animal. The first questions to discuss are how much the body loses daily in weight during the time that it is thus feeding on itself, and how far the different individual tissues contribute to this loss. The general loss of weight is directly estimated by weighing the animal, and the loss of the individual tissues is calculated by a careful analysis of the various excreta, by which the exact amount of nitrogen, carbonic acid, etc., is ascertained : the nitro- gen corresponds to the loss of muscle ; and the carbon (after excluding that portion which is the outcome of muscle change, which may be calculated from the nitrogen) corresponds to the fats oxidized. Loss of Weight. It has been found that a starving animal 41 8 MANUAL OF PHYSIOLOGY. loses weight rapidly at first, and subsequently more slowly. The cause of this difference is that the food last eaten continues to have influence during the first three or four days, and the mate- rials eliminated are proportionately large in quantity. When the influence of the food taken prior to starvation has ceased, the daily amount of materials eliminated is much reduced, and remains nearly constant, decreasing slightly in proportion as the body weight diminishes slowly until the animal's death. Adult animals generally live until they have lost about half of their normal body weight. Young animals die when they have lost about 20 per cent, of their weight. Relative Loss in Various Tissues. Roughly speaking, we may take the body of a man to be made up of the following propor- tions of the more important textures : Muscles, 50 per cent. Skin and fat, 25 " Viscera, 12 " Skeleton, 13 " Seeing that the muscle tissue contributes such a large propor- tion to the body weight, we cannot be surprised that in starva- tion the greatest absolute loss occurs in this tissue, except in the case of excessively fat animals. Next comes adipose tissue, which almost entirely disappears, so that the relative loss is here greatest, but the absolute loss varies in proportion to the fatness of the animal at the beginning of the investigation. The spleen and liver lose more than half their weight, and the amount of blood is greatly reduced. The smallness of the loss that occurs in the great nervous centres is very striking. They seem to feed on the other tissues. The following table gives the approximate percentage of loss which takes place in each individual tissue during starvation : Fat, 97.0 per cent. Muscle, 30.2 " Liver, 56.6 " Spleen, 63.1 " Blood, 17.6 Nerve centres, . . . o " With regard to the portals by which the various materials make their escape, it has been found that practically all the nitrogen INCOME EQUAL TO OUTPUT OF STARVATION. 4*9 passes off with the urine, and about nine-tenths of the carbon escapes by the lungs as CO 2 , the remaining one-tenth passing off by the intestine and kidneys. Three-fourths of the water is found in the urine, and one-fourth goes off from the skin and lungs. The following table shows the items of the general loss, and the amount per cent, which passes out by the chief channels of exit : Total Elimination. Via Kidneys. Lungs and Skin. Excrement. Water, . . . Carbon, . . . Nitrogen, . . Salts, .... 995-34 gnn. 205.96 " 30.81 10.03 " 70.2 per cent. 6.4 " IOO.O " 97.0 " 26.1 percent. 92.6 " 3.7 percent. 1.9 24 " As the loss of weight of an animal's body during starvation is at first rapid and then more gradual, so also the amount of mate- rial eliminated is found to diminish much more slowly after the first few days. This is well seen from the nitrogenous elimina- tion. For the first four days the fall in the amount of urea excreted is very rapid, it then decreases slowly and almost con- stantly until the death of the animal. The subsequent fall is in proportion to the slow decrease in weight of the animal. This has led to the conclusion that the nitrogenous material eliminated during a full diet comes partly from used-up nitrogenous tissues, and partly from nitrogenous materials which have never really entered into the composition of the tissue, but are the surplus of nitrogenous food. Hence, two kinds of proteid are supposed to exist in the body, viz., (i) that forming part of the tissues, and (2) that circulating as a ready supply for the nutritive demands of the tissues. AN INCOME EQUAL TO THE OUTPUT OF STARVATION. In the second case mentioned, namely, where an amount of food is supplied which is just equal to the expenditure which was found to take place during starvation, one might suppose that the diet, though minimal, would yet suffice to preserve the nor- 420 MANUAL OF PHYSIOLOGY. mal body weight. Practice, however, shows this to be far from being the case. An animal fed on diet equal in quantity to the outgoings dur- ing starvation continues to lose weight, and the quantity of nitro- genous substance eliminated (urea) is in excess of the low standard found during complete abstinence from food. From this it would appear that even when supplied with an amount of nitrogenous material equal to that used by the tissues during starvation, an animal takes a further supply from its own tex- tures, and eliminates some of the nitrogenous nutriment without using it. The body subsists on the scanty allowance of nutriment it borrows from the tissues during starvation only so long as there is absolutely no food income. When food is supplied, an increased expenditure is set up, the income is exceeded, and a deficit occurs in the nitrogen balance. Or, probably, some of the nitrogenous nutriment is rendered useless by the processes it undergoes in the intestine, even when the quantity is not sufficient to support the equilibrium (compare pp. 165, 166, 409, 410). It follows, then, that feeding an animal on an amount of food stuffs exactly corresponding to the quantity of nutriment ab- stracted from its own textures during total abstinence is only a slower form of starvation. With regard to nitrogenous substances, it has been proved that nearly three times as much as the amount eliminated during starvation is required to establish an equilibrium between the income and expenditure of those special substances, and that less than this leads to a distinct nitrogenous deficit. NUTRITIVE EQUILIBRIUM. The third case mentioned, viz., that in which the nutritive equilibrium is exactly maintained, so that the body weight remains unaltered, is the most important one for us to determine, since its final settlement would enable us to fix the most bene- ficial standard of diet. Unfortunately, this case is also the most difficult upon which to come to a satisfactory conclusion, for the following reasons : i. The elaborate nature of the conditions imposed during the NUTRITIVE EQUILIBRIUM. 421 experiment makes it difficult to carry on the investigation with scientific accuracy. 2. Even when the amounts of gain and loss exactly correspond we cannot say that we have the best dietary ; because some of the income may be quite useless, and pass through the economy without performing any function, and yet appear in the output so as to give an accurate balance. 3. We have just seen that the relative amounts of outgoings and of material laid by as store are altered and regulated by the quantity of income. And we find that the quality of the income, /. e., the relative proportions of the various food stuffs, has a material influence on the quantities of material laid by and eliminated respectively. We must, therefore, consider the efficacy of each of the groups of the food stuffs when employed alone and mixed in different proportions. 4. Different animals seem to have different powers of assimi- lation ; and under various circumstances the requirements and assimilative power of the same animal may vary. Nitrogenous Diet. An animal fed upon a purely meat diet requires a great amount of it to sustain its body weight. It has been found that from -^ to ^5 of the body weight in lean meat daily is necessary to keep an animal alive without either losing or gaining weight. If more than this amount be supplied the animal increases in weight, and as its weight increases a greater amount of meat is required to keep it up to the new standard. So that, to produce a progressive increase of weight with a purely meat diet, it is necessary to keep on increasing the quantity of meat given. The reason of this is found in the fact that albu- minous diet causes an increase in the changes occurring in the nitrogenous tissues. If an animal which is in extremely poor condition be given an ad libitum supply of lean meat, only a limited portion of the albuminous substance is retained in the tissues. By far the larger proportion of the nitrogenous food is given off and is represented in the urine by urea, and a comparatively small proportion is stored up. If this large supply of meat diet be continued for some time, less and less of the albuminous material is stored, 422 MANUAL OF PHYSIOLOGY. more and more being eliminated as urea, until finally the urea excreted just corresponds to the albuminous materials in the ingesta. When only meat is given, it must be supplied in large quantities to maintain the balance of nitrogenous income and expenditure, which is spoken of as nitrogenous equilibrium. Upon the occurrence of a change in the amount of nitrogenous ingesta this nitrogenous equilibrium varies, and it takes some time to become reestablished, because a decrease in the meat diet is accompanied by a decrease in the weight of the animal, and an increase causes it to put on flesh. For each new body weight there is a new nitrogenous equilibrium, w r hich is only attained after the disturbed relation between the nitrogenous ingesta and excreta has been readjusted. The increase of weight which follows a liberal meat diet depends in a great measure on fat being stored up in the body. Much more of this material is made than could come from the fat taken with the meat ; hence, we must conclude that it is made from the albuminous parts of the meat. Non-nitrogenous Diet. The effect of a diet without any albu- minous food is that the animal dies of starvation nearly as soon as if deprived of all forms of food, with the exception that the weight of the body is much less reduced at the time of death. Mixed Diet. The addition of fat or sugar to meat diet allows of a considerable reduction in the supply of meat, both the body weight and nitrogenous tissue change preserving their equilibrium on a smaller amount of food. It has been estimated that the nitrogenous tissue change is reduced seven per cent, by the addi- tion of fat, and ten per cent, by the addition of carbohydrate food to the meat diet ; therefore less meat is wanted to make up nitrogenous tissues. Further, fats and sugars, which obviously cannot of themselves form an adequate diet, since they contain no nitrogen, seem to have the power of accomplishing some end in the economy which, in their absence, requires a considerable expenditure of nitrogenous materials to bring about. Fats and sugars, then, supply to the body readily oxidizable materials, and thus shield the albuminous tissues from oxidation, as well as reduce absolutely the nitrogenous metabolism. NUTRITIVE EQUILIBRIUM. 423 It would further appear from the experience gained from the stall feeding of animals that a good supply of carbohydrates, together with a limited quantity of nitrogenous food, is admirably adapted to produce fat. Since much more fat has been found to be produced in pigs than could be accounted for by the albu- minous and fatty constituents of their diet, we must suppose that from their carbohydrate food fat can be manufactured in their body. Much of the difficulty found in reconciling the opinions of different authors concerning the sources of fat in the body can be removed, and some knowledge of the manufacture of fats from the food stuffs can be gained by bearing in mind the properties of the protoplasm. There can be no doubt that protoplasm, if properly nourished, can manufacture fat. As examples, we may take the cells of the mammary gland and connective tissue. This fat production may be regarded as a secretion of fat, though only in one of the examples given does it appear externally as a definite secretion milk. We cannot scrutinize the chemical methods by which this change is brought about in protoplasm, any more than those which give rise to the special constituents of other secretions. We know that protoplasm uses as pabulum, albumin, fat, and carbohydrate, and we have no reason to doubt that the proportion of these materials found to form the most nutritious diet for the body generally, is also the proportion in which protoplasm can best make use of them. Probably cells which secrete a material containing nitrogen, such as mucin- yielding gland cells, require a greater proportion of albumin. Those cells which produce a large quantity of non-nitrogenous material may not require more nitrogen than is necessary for their perfect re-integration as nitrogenous bodies. In the manu- facture of their secretion, they only require a pabulum which contains the same chemical elements as are to be found in the output. In the case of fat formation a supply of fat or carbo- hydrate ought to suffice if accompanied by a small amount of albuminous substance. If these non-nitrogenous substances be withheld, the protoplasm could no doubt obtain the quantity of carbon, hydrogen, and oxygen requisite to manufacture fat from 424 MANUAL OF PHYSIOLOGY. albumin, but this would not be economical, for a large amount of nitrogen would be wasted. Fat cannot be produced by the tissue cells without nitrogen in the diet, because the fat-manufacturing protoplasm cannot live without nitrogen, which is absolutely necessary for its own assimilative re-integration. A good supply of nitrogenous food aids in fattening, since it gives vigor to all the protoplasmic metabolism, and among them fat formation. The albuminoid substance gelatine, which is an important item in the food we ordinarily make use of, is able to effect a saving in the albuminous food stuffs. Although it contains a sufficiently large proportion of nitrogen, it cannot satisfactorily replace albumin in the food. Indeed, in spite of the great similarity in its chemical composition to albuminous bodies, it can no better replace the proteids in a dietary than fat or carbohydrate ; and, although an animal uses up less of its tissue nitrogen on a diet containing gelatine and fat than when it is fed on fat alone, it dies of starvation almost as soon as if its diet contained no nitrogenous substance. EXCESSIVE CONSUMPTION. The last case we have to consider is that in which the supply of food material is in excess of the requirements of the economy. This is certainly the commonest case in man. Much of the surplus food never really enters the system, but is conveyed away with the faeces. In speaking of pancreatic digestion, reference has been made to the possible destiny of excess of nitrogenous food. In the intestine, some of it is decomposed into leucin and tyrosin, which are absorbed into the intestinal blood vessels. In the body these substances undergo further changes, which probably take place in the liver. As a result of the absorption of leucin, a larger quantity of urea appears in the urine, and hence the leucin formed in the intestine by prolonged pancreatic digestion is an important source of urea. This view is supported by the almost immediate increase in the quantity of urea eliminated when albuminous food is taken in large quantity. EXCESSIVE CONSUMPTION. 425 From the fact that a considerable amount of fat may be stored up by an animal supplied with a liberal diet of lean meat, we must conclude that part at least of the surplus albumin goes to form fat. It has been suggested that, after sufficient albumin has been absorbed for the nutritive requirements of the nitrogenous tissues, the rest is split up into two parts, one of which is imme- diately prepared for elimination as urea by the liver, and the other undergoes changes, probably in the same organ, which result in its being converted into fat. It would further seem probable, from the manner in which the urea excretion changes during starvation, that, as before men- tioned, the absorbed albumin exists in the economy in two forms : one in which it has been actually assimilated by the nitrogenous tissues and forms part of them, and hence is called organ albumin ; the other, which is merely in solution in the fluids of the body, being in stock, but not yet ultimately assimilated, and hence called circulating albumin. The latter passes away during the first few days of starvation, being probably broken up to form urea, and a material which serves the turn of non- nitrogenous food. The organ albumin appears to supply the urea after the circulating albumin has completely disappeared. From the foregoing it will be gathered that we cannot say what are the exact destinies of the various food stuffs in the body. Proteids are not exclusively utilized in the re-integration of proteid tissues, as an excess gives rise to a deposit of fat. Carbohydrates are not employed simply to replace the carbohy- drates constituting part of the tissues, but, as will be shown when speaking of muscle metabolism, they are intimately related to the chemical changes which take place during the activity of that tissue. If fats are chiefly devoted to the restitution of the fat of the body, they certainly are not the only kind of food from which fat can be made. We may say, then, that all food stuffs are destined to feed the living protoplasm, whether it be in the form of gland cells, the cells of the connective tissues, or muscle plasma, so that all the food stuffs that are really assimilated contribute to the main- tenance of protoplasm "and subserve its various functions. 36 426 MANUAL OF PHYSIOLOGY. Besides nourishing itself and keeping itself up to a certain standard composition, protoplasm, or rather the various proto- plasmata, can make the different chemical materials we find in the body. Some produce fat, some animal starch (glycogen), and others manufacture the various substances we find in the secretions; while yet another group is devoted to setting free and utilizing the energy of the various chemical associations. But all the food we eat is not assimilated ; indeed, the destiny of the numerous ingredients of our complex dietaries is not easily traced. Of food stuffs proper, the following classification may be made, showing that even the same stuff may meet with a different fate under different circumstances : 1. Stuffs which never enter the economy (faeces). 2. Materials absorbed and arriving at the blood are at once carried to certain portals of excretion (excess of salts). 3. Substances which are broken up in the intestine to facilitate their elimination (excess of proteid). 4. Substances absorbed and carried along by the fluids, but not really united to the tissues (circulating albumin). 5. Materials which after their absorption are really assimilated by the protoplasm of the tissues (a certain amount of all food stuffs). 6. Substances which, after their assimilation by the proto- plasm, reappear in their original form and are stored up (fats). . The question of the exact amounts and materials required to form the most economic and wholesome dietary is one of too great practical importance to receive adequate attention in this manual. As a rule, men, like other animals, partake of food largely in excess of their physiological requirements when they can get it. This may be seen by contrasting one's own daily food with the amount which has been found to be adequate in the case of indi- viduals who have not the opportunity of regulating their own supplies of comestibles. An adult man should be well nourished if he be supplied with the following daily diet : ULTIMATE USES OF FOOD STUFFS. 427 Albuminous foods, . 100 grms. or 3.5 ozs. Fats, 90 " 3.1 " Starch, , 300 " " 10.7 " Salts, 30 " " i.o " Water, 2000 " " 3 pints. As a matter of fact, many persons do thrive on a much less quantity of proteid than that given in this table, but in their cases the fats and starches should be proportionately increased. Such a dietary could be obtained from many comestibles alone, and hence the taste of the individual may be exercised in selecting his food without much departing from such a standard. Individual taste commonly selects foods with too much proteid /. e.j an excess of nitrogen while the cheapness of vegetable products dictates their use in greater abundance as food. Compare Chap, v, p. 101, where the quantity of the different food stuffs in some of our common articles of diet is given. 428 MANUAL OF PHYSIOLOGY. CHAPTER XXIV. ANIMAL HEAT. The bodies of most animals are considerably warmer than their surroundings. Part of the energy set free by the chemical changes in the animal tissues appears as heat which is devoted to this purpose. Warm-blooded animals are those which habitually preserve an even temperature, independent of the changes which take place in that of the medium in which they live ; and, as the term warm blooded implies, their temperature is, as a rule, higher than the surrounding air or water. Cold-blooded animals, on the other hand, are those whose temperature is considerably affected by, or more or less closely follows, that of the medium surround- ing them. The blood of all mammalia has pretty much the same tempera- ture as that of man, about 37.5 C., and probably varies under similar circumstances. But birds, the other class of warm-blooded animals, have a temperature about 4 or 6 C. higher than that of mammals. The blood of those animals whose temperature follows the changes that occur around them is generally from i to 5 C. higher than the medium in which they live. They produce some heat, though it be small in quantity, and since they have no spe- cial plan for its regulation, it does not remain at a fixed standard. In every part where active oxidation takes place, heat is pro- duced ; so even in invertebrate animals an elevation of tempera- ture occurs ; this can be ascertained where they exist in masses, as in bee hives, an active hive sometimes reaching a temperature of 35 C. Instead of the term "warm-blooded," it is more accurate to apply to animals whose temperature remains uniformly even, and independent of their surroundings, the term ' '' Homceother- mic" (of constant temperature), and to animals with temperatures varying with their surroundings " Poikilothermic" (of changing temperature), instead of the words warm and cold blooded. NORMAL TEMPERATURE. 429 MEASUREMENT OF TEMPERATURE. On account of the slight amount of variation that occurs in the temperature of man, all the changes can be measured with a thermometer having a short scale of some twenty degrees, each degree of which occupies considerable length on the instrument, so that very slight variations may be easily appreciated. Such thermometers, with an arrangement for self-registering the maxi- mum height attained by the column of mercury, are in daily use for clinical observation, for the temperature of the body is now a most important aid to diagnosis and prognosis in a large class of diseases. As heat is constantly being lost at the surface of the body, the skin is colder than the deeper parts, and in order to avoid varia- tions caused by this surface loss which depends in a measure on the temperature of the air special arrangements are neces- sary to prevent the thermometer being too much influenced by it. The instrument may be brought into close proximity to the deeper parts by being introduced into one of the mucous passages, where it is closely surrounded by vascular tissue. In animals, the rectum is the most convenient part for the application of the thermometer, but in clinical practice it is usually placed under the tongue, or in the armpit, the bulb being held so that on all sides it is in contact with the skin and protected from the cool air. The variations at different parts of the body are but slight, and the average normal surface temperature in man is found to be about 37 C. NORMAL VARIATIONS IN TEMPERATURE. I. The temperature of the whole body normally undergoes cer- tain variations, some of which are: i. Regular and periodical, depending upon the time of day, the ingestion of food, and the age of the individual. 2. Accidental, such as those caused by mental or bodily exertion. (a] The temperature is highest between 4 and 5 P.M. and lowest between 2 and 4A.M., the transition being gradual. This diurnal variation, which normally does not much exceed i C., is much exaggerated in certain fevers. 43 MANUAL OF PHYSIOLOGY. (^) The temperature rises after a hearty meal and falls during fasting. During starvation the temperature sinks gradually until the death of the individual. (c) The temperature is highest at birth, and falls about i C. between that and the age of 50 years; in extreme old age it is said that it again rises. (*/) Muscular exertion, which gives the individual the sensa- tion of great warmth, only changes the temperature of the blood about .5 C. The very high temperature which accompanies the disease tetanus, where all the muscles are thrown into a state of spasm, probably depends more on pathological changes than on muscular action. ( I 57 units of heat. In warming tidal air, ...... 140,064 " " By the evaporation of 656 grm of water from the air passages, . . 397>53^ " By surface loss 2,092,243 " " From this it appears that more than three-quarters of our heat is lost by the skin (77.5 per cent.) ; by pulmonary evapora- tion, 14.7 per cent. ; in heating the air breathed, 5.2 per cent. ; in heating ingesta, 2.6 per cent. MAINTENANCE OF UNIFORM TEMPERATURE. In order that the vital processes of man and the other homceo- thermic animals should go on in a normal manner, it is neces- sary that their mean temperature remain nearly the same, and we have seen that under ordinary circumstances it varies only about one degree below or above the standard 37 C., notwith- standing the changes taking place in the temperature around us. Thus we can live in any climate, however cold or warm, and if our body temperature remains unaltered, we suffer no imme- diate injury. There is a limit, however, to this power of maintaining a uni- form standard temperature. If a mammal be kept for some time in a moist medium, where evaporation cannot take place, at a temperature but little higher than its body, say over 45 C., its temperature soon begins to rise, and it dies with the signs of dyspnoea and convulsions (probably from the nervous centres being affected) when its temperature arrives at 43-45. If placed in water at freezing point an animal loses its heat quickly, and when its body temperature has fallen to about 20 C. it dies in a condition resembling somnolence, the circulation and respiration gradually failing. Since a variation of more than one or two degrees in the tem- perature of our bodies interferes with the vital activities of the controlling tissue in the nervous centres, it is, of course, of the utmost importance that adequate means for the regulation of the mean temperature of our bodies should exist. The temperature of an animal's body must depend on the relations existing between the amount of heat generated in the 436 MANUAL OF PHYSIOLOGY. tissues and organs and the amount allowed to escape at the sur- face, and these must closely correspond in order that the heat of the body may remain uniform. Both these factors are found to be very variable. Every increase in the activity of the muscles, liver, etc., causes a greater production of heat, while a fall in external temperature or increase in the moisture of cool air causes a greater escape of heat from the surface. The maintenance of uniform temperature may be accom- plished by (i) variations in the heat income, so arranged as to make up for the irregularities of expenditure, or (2) varia- tions in the loss to compensate for the differences of heat generated. Since the temperature and moisture of our surroundings are constantly varying between tolerably wide limits, the amount of heat given off by our bodies must also vary. In cold, damp weather a great quantity of heat is lost in comparison with that which escapes from the body when the air is dry or warm. If the heat generated had to make up for the changes in the heat lost, we should expect to find a correspondingly great differ- ence in the amount of heat generated at different times of the year. No doubt we have some evidence in the keener appetite or use of more fuel, and the natural tendency to active muscular exertion during cold weather, to show that a greater amount of combustion takes place in winter than in summer. Further, if the preservation of a uniform body temperature depend solely upon the variations in the amount of income keeping pace with the variation in the expenditure, we should find it inconvenient to set our muscular or glandular tissues in action except when the external temperature was such as would enable us easily to get rid of the increased heat following their activity. It no doubt appears that the general tissue combustion, as measured by the amount of CO 2 given off, increases when we are placed in colder surroundings such as a cold bath; still, it is probable that the variations in heat income have but secondary regulating influence on the body temperature. If the rate of income have any regulating influence, we are ignorant of the manner in which such influence is exerted, for it must act more slowly and cannot HEAT REGULATION. 437 follow so closely, as the variations in expenditure do, extrinsic changes of temperature. On the other hand, we know that the amount of heat expendi- ture may be varied by mechanisms which are almost self regu- lating. It has already been stated that the great majority of the heat is lost by the parts in contact with the air, namely, the skin and air passages. In these places the warm blood is exposed to the cool air, and loses much of its heat by radiation, conduc- tion and evaporation. It is obvious that the greater the quantity of blood thus exposed for cooling, the greater will be the amount of heat lost in a given time by the body as a whole. If we review the circumstances which interfere with the uni- formity of the temperature of the body, we shall see that each one is accompanied by certain physiological actions which tend to compensate for the disturbing influences. The chief common events tending to make our temperature exceed or fall short of its normal standard may be enumerated as follows, and the explanation of their modes of compensation will at the same time be given : COMPENSATION FOR INTERNAL VARIATIONS. A casual increase in the heat income may be induced by any increased chemical activity in the tissues, notably the action of the muscles and large glands. When this increased heat is com- municated to it, the warm blood, by the help of certain nerve centres, brings about the following results : (a) An acceleration of respiratory movement, increasing the amount of cold air to be warmed and saturated with moisture by the air passages, and facilitating the escape of the surplus caloric. (^) Relaxation of the cutaneous arterioles, exposing a greater quantity of blood to the cooling influence of the air. (c) Greater rapidity of the heart beat, supplying a greater quantity of blood to the air passages and to the surface vessels, (V) An increase in the amount of sweat secreted, affording opportunity for greater sur- face evaporation. As examples of these points may be mentioned active muscular exercise, which daily experience shows us is always accompanied 438 MANUAL OF PHYSIOLOGY. by quick breathing, rapid heart's action, and a moist skin. The increased production of heat in fever gives rise to the same results, with the exception of the secretion of the sweat, which want (probably owing to the toxic inhibition of the special nerve mech- anisms of the glands) is an important deficiency in the heat-regu- lating arrangements, and has much to do with the abnormally high temperature of the disease. When a lesser quantity of heat is produced, owing to inactivity of the heat-producing tissues, the reverse takes place, namely, the respiration and heart's action are slow, the skin is pale and dry, so that little heat can escape. COMPENSATION FOR EXTERNAL VARIATIONS OF TEMPERATURE. When the temperature of the air rises much above the aver- age, the escape of heat is correspondingly hindered ; and when the general body temperature begins to rise by this retention of caloric, we have the sequence of events detailed in the last para- graph. But before the blood can become warmer by the influ- ence of the increased external temperature, the warm air, by stimulating the skin, brings about certain changes, independent of the body temperature, which satisfactorily check the tendency to an abnormal rise. This can be shown by the local application of external heat, by means of which (a) a rush of blood to the skin, and (/) copious sweat secretion may be induced in a part. This is brought about by impulses sent directly from the skin to the centres regulating the vasomotor and secretory mechanisms, and thus causing vascular dilatation and secretive activity. If a part only be warmed, a local effort is made to cool that part, and this has but little influence on the general body temperature. When, however, the atmosphere becomes very warm, all the cutaneous vessels dilate simultaneously, and the escape of heat is greatly increased ; while, at the same time, so much blood being occupied in circulating through the skin, the deeper heat pro- ducing tissues are supplied with less blood, and therefore gener- ate a less quantity of heat. Thus a marked rise in the external temperature, which at first sight would seem to impede the escape HEAT REGULATION. 439 of heat from the body, really facilitates it, by causing, through the vascular and glandular nerve mechanisms of the skin, a greater exposure of the blood to the cooler air, and a greater quantity of moisture to be evaporated from the warm skin. When the temperature of the air reaches that of the body, the only way of disposing of the heat generated in the body is by evaporation, for radiation and conduction become impossible. In animals like man, whose cutaneous moisture is great, external heat seldom causes marked change in the rate of breathing, but in animals whose cutaneous secretion is limited, external heat distinctly affects their respiratory movements, as may be seen by the panting of a dog on a very warm day, even when the animal is at rest. Almost more important than facilitating the escape of heat in very warm weather, are the arrangements for preventing its loss when the surroundings are unusually cold. In this case, the cold, acting as a stimulus to the vaso-constrictor nerve agencies of the skin, causes the blood to retire from surface and fill the deeper organs, where more heat is produced. This bloodless skin and the underlying fat then act as a non-conducting layer or boundary protecting the warm blood from the cooling exposure. At the same time the secretion of the sweat is controlled by a special nerve mechanism, which lessens evaporation and soon checks the secretion, thereby enabling the body to remain, at the normal standard temperature. It would then appear that the chief factors regulating the body temperature belong to the expenditure department, and may be said to be (a) variation in the quantity of blood exposed to be cooled, and () variation in the quantity of moisture produced for evaporation. These regulators have to compensate not only for differences of external temperature, but also for great fluctuations in the amount of heat produced in the tissues. The regulating power of the skin, etc., appears to be adequate for the perfect maintenance of uniform temperature only within certain limits. When these limits are passed by the rise or fall in the surrounding medium, the preservation of a uniform tern- 440 MANUAL OF PHYSIOLOGY. perature soon becomes impossible. These limits vary much in different animals, many of which have special coverings protect- ing them from external influences, and retain their warmth in a temperature seldom above o C. In man the limits vary accord- ing to many circumstances, e.g., both extremes of age are more sensitive to changes of temperature. It would appear that for about 10 C. above and below the body temperature our skin- regulating mechanisms are adequate, but beyond these limits external changes affect our general temperature, and if continued become injurious. Of course, by imitating with clothing tKe natural protection with which some animals are endowed, we can aid the normal regulating factors, and bear much greater extremes of temperature with safety or even comfort. It is somewhat surprising that our bodies are always at the same temperature, no matter how hot or cold we feel. This is quite true, and our sensations of being hot or cold are explained as follows : When we feel hot our cutaneous vessels are full of warm blood, and this communicates to the cutaneous nerve ter- minals the sensory nerves the sensation of general warmth. On the other hand, when the cutaneous vessels are empty, the sensory nerves are directly affected by the cold of the external air. Since the full or empty state of the vessels of the skin depends generally on the heat or cold of the air, we use the expressions "it is hot or cold " and "we are hot or cold," as synonymous, because both ideas arise from the state of the skin. But we can make ourselves feel warm by violent exercise even on a frosty day, because we generate so much heat by muscular action that the cutaneous vessels have to be dilated in order to get rid of the surplus, and our skin vessels being full we feel warm. Our feelings, when we say we are warm or cold, simply depend upon our cutaneous vessels being full or empty of warm blood. The local appreciation of differences of temperature will be discussed in the chapter dealing with the sense of Touch. CONTRACTILE TISSUES. 441 CHAPTER XXV. CONTRACTILE TISSUES. In the lower forms of organisms the motions executed by pro- toplasm suffice for all their requirements. Thus the amoeba manages to pass through its lifetime with no other kind of motion at its disposal than the flowing circulation and the budding out of its soft protoplasm. A vast number of minute organisms depend wholly upon the protoplasmic stream and the twitching of cilia for their digestive and progressive movements. Before we leave the class of animals which never pass beyond the uni- cellular stage, we find, however, examples in which a portion of their protoplasm is specially adapted to the performance of sud- den and rapid motions. The protoplasm so modified in function deserves the name of contractile material. Thus, though the protoplasm which lies within the stalk of the bell animalcule is morphologically undifferentiated, it can contract with such rapidity that the eye cannot follow the motion. As we ascend in the scale of animal life, the necessity for motions of various rapidity and duration at the command of the animal becomes more and more urgent, and so we find not only one, but several kinds of tissue specially adapted for carrying out motions of different rate and duration. As a general rule, the more rapid the contraction it performs the more the tissue differs from the original type of protoplasm ; and the slower and more persistent the contraction, the more the tissue elements resemble protoplasmic cells. Thus, in the minute blood vessels, as we have seen, a very prolonged form of contrac- tion, only varied by partial relaxations, is the rule, and gives rise to the tone of the arterioles, and the contractile elements differ but little from ordinary protoplasmic cells. The intestinal move- ments are rapid compared with those of the arterial muscles, and in them we find a thin, elongated form of muscle cell. In the heart a forcible and quick contraction takes place, which, how- 442 MANUAL OF PHYSIOLOGY. FIG. 177. ever, is slow when compared with the sudden jerk of a single spasm of a skeletal muscle, and its texture is different, being a form intermediate between the "slow-contract- ing smooth muscle and the quick-contracting striated skeletal muscle. By borrowing examples from the lower animals, this parallelism of structural differen- tiation and increase of functional energy can be more perfectly demonstrated, and we can make out a gradual scale of increasingly rapid motion corresponding with greater complexity of structure. HISTOLOGY OF MUSCLE. The term muscle includes the textures in which the protoplasm is specially differentiated for purposes of contraction. The muscle tissues of the higher animals may be divided into two classes: (i) non-striated or smooth, and (2) striated, in which again there are some slight variations. The non- striated muscle tissue is that in which the elements are most like contractile proto- plasmic cells, and have so far retained the typi- cal form as to be easily recognizable as cells when separated one from the other. These cells are more or less elongated, flattened, homo- geneous elements with a single, long, rod-shaped nucleus and no cell wall. . They are tightly cemented together by a tough elastic substance, so that their tapering extremities fit closely together and form commonly a dense mass or Muscle ceils, showing sheet. Sometimes they branch more or less different condition oi i -\ -\ i j the protoplasm of the regularly, and then are arranged m net- works. These cells vary greatly in size as well as in the relation of their length to their width, in some places deserving the HISTOLOGY OF MUSCLE. 443 FIG. 178. name fibres, or fibre cells, and in others being only elongated cells. The striated muscle tissue is that of which the skeletal muscles and the heart are composed. It therefore forms the larger pro- portion of the animal, known as flesh. The flesh can, by judi- cious dissection, easily be divided into single parts called muscles, each of which contains many other tissues, and is so attached as to carry on certain movements, and may, therefore, be regarded as an organ. Such a muscle is enclosed in a sheath of connective tissue, for which sheet-like partitions or septa pass into the mass of the muscle and divide it into bundles of fibres, which they enclose. These septa also act as the bed in which the vessels and nerves lie. The tissue of the heart differs from the striated muscle in being made up of truncated, oblong branching cells with a central nucleus and no sarcolemma (see page 262). The bundles of fibres of skeletal muscle vary much in size, giving a coarse or fine grain in different mus- cles ; they are composed of a greater or less number of fibres, which, lying side by side, run parallel one to the other. The single fibres of striated milSCle Vary in , . / i \ i reaching 4-5 C1T1. (2 inches), but being on an average much shorter, they only extend the entire length of a muscle in the case of very short muscles. In long muscles their tapering points are made to correspond with those of other fibres to which they are firmly attached. The soft fibres are pressed by juxtaposition into prismatic forms, so that in a fresh condition they appear polygonal in transverse section. When freed from all pressure or traction they become cylindrical, and the transverse striation . . Short striated cells of the heart length, Sometimes muscles, separated one showing the truncated (a), or divided (c), ends and branches (b). 444 MANUAL OF PHYSIOLOGY. FIG. 179. \\ of the contractile substance appears regular, and is easily recognized. Each fibre consists of a deli- cate case of thin, elastic, homogeneous membrane, forming a sheath called sarcolemma, within which the essential contractile substance is enclosed. The soft contractile substance completely fills and distends the elastic sarcolemma, so that when the latter is broken its con- tents bulge out or escape. After death, particularly if preserved in weak acid (HC1), the striation becomes more marked, and the dead and now rigid contractile substance can easily be broken up into transverse plates or discs. Besides the transverse striation, a longi- tudinal marking can be seen in the muscle fibre, which indicates the sub- division of the contractile substance into thin threads called primitive fibrillae. Each primitive fibril shows a transverse marking, corresponding with the trans- verse striation, which divides the fibrils into short blocks called sarcous, or muscle elements. These markings, and the transverse striations of the muscle fibre in general, depend on different parts of the contractile substance having different powers of refraction, and giving the appearance of dark and light hands. In the muscle fibre are found long in \-viuciJ LUC; v-iiiuacmc _ , ., , 1 substance (m) has been rup- granular masses like protoplasm ; these tured and separated from i r i ^.-i i the sarcolemma (a) and (s) ; are the nuclei of the Contractile Sub- (B) shows a thin strip of rri1 , i r j j torn contractile substance Stance. They lllUSt not be COnfoUllded markings" a^cie^^S) with the nuclei of the sarcolemma, which are much more numerous along the edge Two fibres of striated muscle, in which the contractile PROPERTIES OF MUSCLE. 445 of the fibre, or with the other short nuclei seen in such numbers between the fibres, which indicate the position of the capillary vessels. It is stated that each striated muscle fibre has a nerve fibre passing directly into it, but the exact details of the mode of union in mammalia are not yet satisfactorily made out. PROPERTIES OF MUSCLE IN THE PASSIVE STATE. Consistence. The contractile substance of muscle is so soft as to deserve rather the name fluid than solid ; it will not drop as a liquid, but its separate parts will flow together again like half-melted jelly. In this respect it resembles the protoplasm of some elementary organisms, the buds from which are so soft that they can unite around foreign bodies and yet have sufficient consistence to distinguish them from fluid. Chemical Composition. The chemical constitution of the con- tractile substance of muscle in the living state is not accurately known. The death of the tissue is accompanied by certain changes of a chemical nature which give rise to a kind of coagulation, resulting in the formation of two substances, viz., muscle serum and muscle clot or myosin. This coagulation can be postponed almost indefinitely in the contractile substance of the muscles of cold-blooded animals, by keeping the muscle after its removal at about 5 C. In this way a pale yellow, opales- cent, alkaline juice may be pressed out of the muscle, and separated on a cold filter. This substance turns to a jelly at freezing point, and if brought to the ordinary temperature of the room it passes through the stages of coagulation seen in the contractile substance of dead muscle, and gives the same fluid serum and clot of myosin. Since a frog's muscle can be frozen and thawed without the tissue being killed, it is supposed that the thick juice is really the contractile substance, which has been called muscle plasma. The coagulation of muscle plasma reminds us in many ways of the clotting of the blood plasma, but the muscle clot, or myosin, is gelatinous and not in threads like fibrin. It is a tin, and is soluble in 10 per cent, solution of salt. It is 446 MANUAL OF PHYSIOLOGY. readily changed into syntonin or acid albumin, and forms the preponderant albuminous substance of muscle. The serum of dead muscle has an acid reaction, and contains three distinct albuminous bodies coagulating at different tem- peratures, one of which is serum-albumin, and another a derived albumin, potassium-albumin. The serum of muscle also contains : (i) Kreatin, kreatinin, xanthin, etc. (2) Haemoglobin. (3) Grape sugar, muscle sugar, of inosit, and glycogen. (4) Sar- colactic acid. (5) Carbonic acid. (6) Potassium salts; and (?) 75 P er cent, of water. Traces of pepsin and other fer- ments have also been found. FIG. 180. 1. Shows graphically the amount of extension caused by equal weight increments applied to a steel spring. 2. Shows graphically the amount of extension caused by equal weight increments applied to an india-rubber band. 3. The same applied to a frog's muscle. Showing the decreasing increments of extension ; the gradual continuing stretching, and the failure to return to the abscissa when the weight is removed. Chemical Change. In the state of rest a certain amount of chemical change constantly goes on, by which oxygen is taken from the haemoglobin of the blood in the capillaries, and car- bonic acid is given up to the blood. These changes seem necessary for the nutrition, and therefore the preservation of the life and active powers of the tissue, because if a muscle after removal be placed in an atmosphere free from oxygen, it more quickly loses its chief vital character, viz., its irritability. ELASTICITY OF MUSCLE. 447 Elasticity. Striated muscle is easily stretched, and, if the extension be not carried too far, recovers very completely its original length. That is to say, the elasticity of muscle is small or weak, but very perfect. When a muscle is stretched to a given extent by a weight say of i gramme if another gramme be then added, it will not stretch the muscle so much as the first did ; and so on if repeated gramme weights be added one after the other, each succeeding gramme will cause less extension of the muscle than the previous one ; so that the more a muscle is stretched the more force is required to stretch it to the given extent, or, in other words, the elastic force of muscle increases with its extension. If a tracing be drawn, showing the extending effect of a series of equal weights attached to a fresh muscle, it will be found that a great difference exists between it and a similar record drawn by inorganic bodies or an elastic band of rubber. When a weight is applied to a muscle, it does not immediately stretch to the full extent the weight is capable of effecting, but a certain time, which varies with circumstances, is required for its complete extension. The rate of extension is at first rapid, then slower, until it ceases. As a muscle loses its powers of contrac- tion from fatigue, it becomes more easily extended. Dead muscle has a greater but less perfect elasticity than living, /. e., it requires greater force to stretch it, but does not return so perfectly to its former shape. The importance of the elastic property of muscle in the movements of the body is noteworthy. The muscles are always in some degree on the stretch (as can be seen in a fractured patella, the fragments of which remain far apart and cause the surgeon much anxiety), and brace the bones together like a series of springs, the various skeletal muscles being so arranged as to stretch others by their contraction. When one muscle for example, the biceps contracts, it finds an elastic antagonist already tense, and has to shorten this antagonist as it contracts itself. The triceps in this case acts as a weak spring, opposing the biceps, and it gently returns to its natural length when the contraction of the biceps ceases. The muscles are kept tense and ready for action by their mere 44-8 MANUAL OF PHYSIOLOGY. elasticity, and have to act against a gentle spring-like resistance, so that the motions occur evenly, and there is no jarring or jerk- ing, as might take place if the attachments of the inactive muscles were allowed to become slack. Electric Phenomena, In a living muscle electric currents may be detected, having a definite direction, and certain relations to the vitality of the tissue. As they seem to be invariably present in a passive muscle, they have been called natural muscle currents. They are generally studied in the muscles of cold-blooded animals after removal from the body. The muscle is spoken of as if it were a cylinder, with longitudinal and transverse sur- Non-polarizable Electrodes. The glass tubes (a a) contain sulphate of zinc solution (z. s.), into which well amalgamated zinc rods dip. The lower extremity is plugged with china clay (ch. c.), which protrudes at (<:') the point. The tubes can be moved in the holders (h h), so as to be brought accurately into contact with the muscle. (Foster.) faces corresponding to its natural surface and its cut extremities. In such a block of frog's muscle the measurement of the electric currents requires considerable care, because they are so difficult to detect that a most sensitive galvanometer must be used ; and such an instrument can easily be disturbed by currents due to bringing metal electrodes into contact with the moist saline tissues. Specially constructed electrodes must be used to avoid these currents of polarization taking place in the terminals touching the muscle. These are called non-polarizable electrodes, and may be made on the following plan : Some innocuous ELECTRIC PHENOMENA OF MUSCLE. 449 material moistened in saline solution (.65 per cent.) is brought into direct contact with the muscle, and, by means of saturated solution of zinc sulphate, into electrical connection with amalga- mated zinc terminals from the galvanometer. Thus the muscle is not injured, and the zinc solution prevents the metal termi- nals from producing adventitious currents. Small glass tubes drawn to a point, the opening of which is plugged with china clay moistened with salt solution, make a suitable receptacle for the zinc solution. If a pair of such electrodes be applied to the middle of the longitudinal surface at (e) (Fig. 182), and of the transverse surface at (/), respectively, and then be brought into connection with a delicate galvanome- ter, it is found that a current passes through the galvanome- ter from the longitudinal to the transverse surface. A current in this direction can be detected in any piece of muscle, no matter how much it be divided longitudinally, and probably would be found in a single fibre, had we the means of examining it. The nearer to the centre of the longitudinal and transverse sections the electrodes are placed, the stronger will be the cur- rent received by them. If both the electrodes be placed on the longitudinal section or on the transverse surfaces, a current will pass through the galvanometer from that electrode nearer the middle of the longitudinal section (called the equator of the muscle cylinder) to the electrode nearer the centre of the trans- verse section (pole of muscle cylinder). If the electrodes be placed equidistant from the poles or from the equator no current can be detected. The central part of the longitudinal surface of a piece of muscle is then positive, compared with the central part of the extremities or transverse sections. And between these parts the equator and poles of the muscle cylinder, where the differ- ence is most marked are various gradations, so that any point near the equator is positive when compared with one near the poles. There is, then, a current passing through the substance of the piece of muscle from both the transverse sections or extremities of the muscle block to the middle of the longitudinal surface, 38 450 MANUAL OF PHYSIOLOGY. whether it be a cut surface (longitudinal section) or the natural surface of the muscle. This is called the muscle current, or sometimes natural muscle current. If the cylinder in the accompanying figure be taken to repre- sent a block of muscle, e would correspond to the equator, and p to the poles, and the arrow heads show the direction of the currents passing through the galvanometer, the thickness of the lines indicating their force. The dotted lines o are connected FIG. 182. Diagram to illustrate the currents in muscle. (e) Equator, corresponds to the centre of the muscle cylinder. (p) Polar regions of cylinder representing the extremities of the muscle. The arrow heads show the direction of the surface currents, and the thickness of lines indicates the. strength of the currents. (After Fick.) with points where the electro-motive force is equal, and, there- fore, no current exists. The electro-motive force of the muscle current in a frog's gracilis has been estimated to be about .05-. 08 of a Daniell cell. It gradually diminishes as the muscle loses its vital properties, and is also reduced by fatigue. The electro-motive force rises with the temperature from 5 C. until a maximum is reached at about the body temperature of mammals. These muscle currents are very weak if the uninjured muscle ACTIVE STATE OF MUSCLE. 45 I be examined in situ, the tendon being used as the transverse section ; they soon become more marked after the exposure of the muscle, and if the tendon be injured they appear at once in almost full force. In animals quite inactive from cold the muscles naturally are but slowly altered by exposure, etc., and the muscle currents do not appear for a considerable time, which is shortened on elevating the temperature. It has, therefore, been supposed that in the perfectly normal state of a living animal there are no muscle currents so long as the muscle remains in the passive state. ACTIVE STATE OF MUSCLE. A muscle is capable of changing from the passive elongated condition, the properties of which have just been described, into a state of contraction or activity.. Besides the change in form, obvious in the contracted state of the muscle, its chemical, elastic, electric, and thermic properties are altered. The capability of passing into this active condition is spoken of as the irritability of muscle. This is directly dependent upon its chemical condi- tion, and therefore related to its nutrition and to the amount of activity recently exerted, which, as will hereafter appear, changes its chemical state. Under ordinary circumstances, during life, the muscles change from the passive state into that of contraction in response to cer- tain impulses communicated to them by nerves, which carry impressions from the brain or spinal cord to the skeletal muscles. The influence of the will generally excites most skeletal muscles to action. Nearly all muscular contraction depends on nervous impulses of one kind or another. But there are many other influences which, when applied to a muscle, can bring about the same change. These influences are called stimuli. We utilize the nerve belonging to a muscle in order to throw it into the contracted state, but the great majority of stimuli can bring about the change when applied to the muscle directly. Since the nerves branch in the substance of the muscle, and are distributed to the individual fibres, it might, as has been argued, be the stimulation of the terminal nerve ramifications that 452 MANUAL OF PHYSIOLOGY. brings about the contraction, even when the stimulus is applied to the muscle directly, for the terminal branches of the nerves are affected by the stimulus applied to the muscle. That muscles can be stimulated without the intervention of nerves is satisfactorily proved by the following facts : 1 . Some parts of muscles, such as the lower end of the sarto- rius, and many muscular structures which have no nerve ter- minals in them, respond energetically to all kinds of muscle stimuli. 2. There are some substances which act as stimuli when applied directly to the muscle, but have no such effect upon nerves, viz., ammonia. 3. For some time after the nerve has ceased to react, on account of its dying after removal from the body, the attached muscle will be found quite irritable if directly stimulated. 4. The arrow poison, Curara, has the extraordinary effect of paralyzing the nerve terminals, so that the strongest stimulation of the nerve calls forth no muscle contraction. If the muscles in an animal under the influence of this poison be directly stimu- lated, they respond with a contraction. MUSCLE STIMULI. The circumstances which call forth muscle contraction may be enumerated thus : 1. Mechanical Stimulation. Any sudden blow, pinch, etc., of a living muscle causes a momentary contraction, which rapidly passes off when the irritation is removed. 2. Thermic Stimulation. If a frog's muscle be warmed to over 30 C. it will begin to contract, and before it reaches 40 C. it will pass into a condition known as heat rigor, which will be mentioned presently. If the temperature of a muscle be reduced below o C. it shortens before it becomes frozen. 3. Chemical Stimulation. -A number of chemical compounds act as stimuli when they are applied to the transverse section of a divided muscle. Among these may be named : (i) the mineral acids (HC1, . i per cent.) and many organic acids; (2) salts of iron, zinc, silver, copper and lead ; (3) the neutral salts of the MUSCLE STIMULI. 453 alkalies of a certain strength ; (4) weak glycerine and weak lactic acid ; these substances only excite nerves when concen- trated ; (5) bile is also said to stimulate muscle in much weaker solutions than it will nerve fibres. 4. Electric Stimulation. Electricity is the most convenient form of stimulation, because we can accurately regulate the force of the stimulus. The occurrence of variation in the FIG. 183. Du Bois-Reymond's Inductorium with Magnetic Interrupter. c. Primary coil through which the primary, inducing, current passes, on its way to the electro-magnet (6). i. Secondary coil, which can be moved nearer to or further from the primary coil (c), thereby allowing a stronger or weaker current to be induced in it. This induced current is the stimulus. b. Electro-magnet, which on receiving the current breaks the contact in the circuit of the pr.mary coil by pulling down the iron hammer (A), and separating the spring from the screw of e. When using Helmholtz's modification (g 1 ), e is screwed up, and the current brings the spring in contact with the point of the pillar (a), and so demagnetizes (b) by "short circuiting " the battery. When tetanus is to be produced, the wires from the battery are to be connected with g and a. Wheu a single contraction is required, the magnetic interrupter is cut out by shifting the wire from a to the binding screw to the right off. intensity of an electric current passing through a muscle causes it to contract. The sudden increase or decrease in the strength of a current acts as a stimulus, but a current of exactly even intensity may pass through a muscle without further exciting it, after the initial contraction has ceased. A common method of producing such a variation is that of opening or closing an 454 MANUAL OF PHYSIOLOGY. electric circuit of which the muscle forms a part, so as to make or break the current ; and thus a variation of intensity equal to the entire strength of the current takes place in the muscle, and acts as a stimulus. The direct current from a battery (continuous current) is used to stimulate a muscle in certain cases, but a current induced in a secondary coil by the entrance or cessation of a current in a primary coil of wire (induced current} is more commonly employed on account of the greater efficacy of its action. The instrument used for this purpose in physiological laboratories is Du Bois-Reymond's inductorium, in which the strength of the stimulus can be reduced by removal of the secondary coil from the primary. It is supplied with a magnetic interrupter, by means of which repeated stimuli may be given by rapidly making and breaking the primary current (interrupted current) (Fig. 183). The irritability of muscle substance is not so great as that of the motor nerves ; that is to say, a less stimulus applied to the nerve of a nerve-muscle preparation* will cause contraction than if applied to the muscle directly. In experimenting on the con- traction of muscle, as already stated, the nerve is commonly used to convey the stimulus, because, when an electric current is applied to the nerve, the stimulus is the more safely and com- pletely distributed throughout the muscle fibres than when it is applied directly. CHANGES OCCURRING IN MUSCLE ON ITS ENTERING THE ACTIVE STATE. Changes in Structure. The examination of muscle with the microscope during its contraction is attended with considerable difficulty, and in the higher animals has not led to satisfactory results. In the muscles of insects, where the differentiation of the contractile substance is more marked, certain changes can be observed. The fibres, and even the fibrillae within them, can easily enough be seen to undergo changes in form corresponding to those * By a nerve-muscle preparation is meant a muscle of a frog (commonly the gastroc- nemius and the half of the femur to which it is attached) and its nerve, which have been carefully separated from other parts and removed from the body. CHANGES DURING CONTRACTION. 455 of the entire muscle, namely, increase in thickness and diminution in length. A change in the position and relative size of the singly and doubly refracting portions of the muscle element has been described, and some authors state that the latter increases at the expense of the former after an intermediate period in which the two substances seem fused together. Chemical Changes. During the contracted condition, the chemical changes which go on in passive muscle are intensified, and certain new chemical decompositions arise of which not much is known. Active muscle takes up more oxygen than muscle at rest, as is shown by the facts that, during active muscular exercise, more oxygen enters the body, by respiration, and the blood leaving active muscles is poorer in oxygen than when the same muscles are passive. This absorption of oxygen may be detected in a muscle cut out of the body, but a supply of oxygen is not neces- sary for its contraction, since an excised frog's muscle will con- tract in an atmosphere containing no oxygen. From this it would appear that a certain ready store of oxygen must exist in some chemical constituent of the muscle substance. It is possible that some chemical compound, constantly renewed by the blood, is the normal source of oxygen, and not the oxyhaemo- globin. The amount of CO 2 given off by a muscle increases in its state of activity. This may be seen (a) by the greater elimina- tion from the lungs during active muscular exercise, and (ft) by the fact that the venous blood of a limb, when the muscles are contracted, contains more CO 2 than when they are relaxed. (/) The increase of CO 2 can also be detected in a muscle removed from the body and kept in a state of contraction. (d) This increase in the formation of CO 2 takes place whether there is a supply of oxygen or not, (e) and the quantity of CO 2 given off exceeds the quantity of oxygen that is used up. So that it is not exclusively from the newly-supplied oxygen that the CO 2 is produced. Muscle tissue, when passive, is neutral or faintly alkaline ; during contraction, however, it becomes distinctly acid. The 456 MANUAL OF PHYSIOLOGY. litmus which it changes from blue to red is permanently altered, and the conclusion follows that CO 2 is not the only acid that makes its appearance. The other acid is sarcolactic add, which is constantly present in muscle after prolonged contraction, and varies in amount in proportion to the degree of activity the muscle has undergone. If artificial circulation be kept up in the muscle, the quantity of sarcolactic acid found in the blood is very great. It varies directly with the CO 2 , which would seem to suggest a relationship between the origin of the two acids. The amount of glycogen and grape sugar is said to diminish in muscle during its activity, and it is stated that sarcolactic acid can be produced from these carbohydrates by the action of certain ferments. Active muscle contains more of those substances than can be extracted by alcohol, and less that are soluble in water than passive muscle. The chemical changes which take place during muscle con- traction are probably the result of a decomposition of some car- bohydrates, in which the albuminous substances do not take any part that requires their own destruction. This seems sup- ported by the fact that the increased gas exchange in muscle during active exercise can be recognized in a corresponding alteration in the gas exchange in pulmonary respiration ; and there seems no relation between muscular labor and the amount of nitrogenous waste, as estimated by the urea elimination, which we should expect if muscular activities were the outcome of a decomposition of nitrogenous (albuminous) parts of the muscle substance. The chemical changes, then, said to take place in muscle during its contraction are : 1. The contractile substance, which is normally neutral or faintly alkaline, becomes acid in reaction, owing to the formation of sarcolactic acid. 2. More oxygen is taken up from the blood than when the muscle is at rest. This using up of oxygen occurs also in the isolated muscle, and its amount appears to be independent of the blood supply. CHANGES IN ELECTRICAL STATE. 457 3. The extractives soluble in water decrease ; those soluble in alcohol increase. 4. A greater amount of CO 2 is given off, both in the isolated muscle and in the muscles in the body, and the change in the quantity of CO 2 has no exact relation to that of the oxygen used. 5. A diminution is said to occur in the contained glycogen, and certainly prolonged inactivity causes an increase in the amount of glycogen. 6. A peculiar muscle sugar makes its appearance. I. Change in Elasticity. The elasticity of a muscle during its state of contraction is less than in the passive state. That is to say, a given weight will extend the same muscle more if attached to it while contracted (as in tetanus) than when it is relaxed. The contracted muscle is then more extensible. If a weight which is just over the maximum load the muscle can lift be hung from it and the muscle stimulated, it should become extended, because the change to the active state lessens its elastic power, while it cannot contract, being over-weighted. II. Electrical Changes. If a muscle, in connection with a galvanometer, so as to show the natural current, be stimulated by means of the nerves, a marked change occurs in the current. The galvanometric needle swings toward zero, showing that the current is weakened or destroyed. This is called the negative variation of the muscle current, which initiates the change to the active condition. When the muscle receives but a momentary stimulus sufficient to give a single contraction, this negative variation takes place in the current, but, owing to its extremely short duration, the galvanometric needle is prevented by its inertia from following the change. Only the most sensitive and well-regulated instruments show the electric change of a single contraction, but when the muscle is kept contracted by a series of rapidly repeated stimulations the inertia of the needle is readily overcome. Rheoscopic Frog. The negative variation of a single contrac- tion can be easily shown on the sensitive animal tissues. For this purpose the sciatic nerve of a frog's leg is placed upon the 39 45 8 MANUAL OF PHYSIOLOGY. surface of the gastrocnemius of another leg, so as to pass over the middle and the extremity of the muscle. When the second (stimulating) muscle is made to contract, its negative variation acts as a stimulus to the nerve lying on it, and so the first (stimulated) muscle contracts. Not only does this show the negative variation of a single contraction, but it also demon- strates that the continued (tetanic) contraction, produced by interrupted electric stimulation, is associated with repeated nega- tive variations. We shall see that the continued contraction is brought about by a rapidly repeated series of stimulations, so that the electric condition of the stimulating muscle undergoes FIG. 184. Diagram illustrating the arrangement in the Rheoscopic Frog. A = stimulating limb. >=^ stimulated limb. The current from the electrodes passes into nerve (N) of stimulating limb (A), causing its gastrocnemius to contract. Where- upon the negative variation of the natural current between + and stimulates the nerve (N'), and excites the muscles of 13 to action. a series of variations. The contraction of the stimulated muscle, whose nerve lies on the stimulating muscle, responds to the electric variations of the stimulator, and contracts synchronously with it. If an isolated part of a muscle be stimulated, the contraction passes from that point as a wave to the remainder of the muscle. This contraction wave is preceded by a wave of negative varia- tion which passes along the muscle at the rate of three metres per second (the same rate as the contraction wave), lasting at any one point .003 of a second, so that the negative variation is over MUSCLE CONTRACTION. 459 before the contraction begins, for the muscle requires a certain time, called the latent period, before it commences to contract. The origin of the electric currents of muscle will be discussed with nerve currents, to which the reader is referred. III. Temperature Change. Long since it was observed in the human subject that the temperature of muscles rose during their ac- tivity. In frog's muscle a contraction lasting three minutes caused an elevation of .18 C. A single contraction is said to produce a rise varying from .001 to .005 C., according to circumstances. The production of heat is in proportion to the tension of the muscle. When the muscles are prevented from shortening, a greater amount of heat is said to be produced. The amount of heat has also a definite relation to the work performed. Up to a certain point the greater the load a muscle has to move, the greater the heat produced ; when this maximum is reached any further increase of the weight causes a falling off in the heat production. Repeated single contractions are said to produce more heat than tetanus kept up for a corresponding time. The fatigue which follows prolonged activity is accompanied by a diminution in the production of heat. IV. Change in Form. The most obvious change a muscle undergoes in passing into the active state is its alteration in shape. It becomes shorter and thicker. The actual amount of shorten- ing varies according to circumstances. (a) A muscle on the stretch when stimulated will shorten more in proportion than one whose elasticity is not called into play before contraction, so that a slightly weighted muscle shortens more than an unweighted one with the same stimulus. (<) The fresher and more irritable a muscle is, the shorter it will become in response to a given stimulus ; and, conversely, a muscle which has been some time removed from the body, or is fatigued by prolonged activity, will contract proportionately less, (c) Within a certain limit, the stronger the stimulus applied the shorter a muscle will become. (//) A warm temperature augments the amount of shortening, the amount of contraction of frogs' muscles increasing up to 33 C. A perfectly active frog's muscle shortens to about half 460 MANUAL OF PHYSIOLOGY. its normal length. If much stretched and stimulated with a strong current it may contract nearly to one-fourth of its length when extended. Muscles are seldom made up of perfectly parallel fibres, the direction and arrangement varying much in different muscles. The more parallel to the long axis of the muscle the fibres run, the more will the given muscle be able to shorten in proportion to its length. The thickness of a muscle increases in proportion to its short- ening during contraction, so that there is but little change in bulk. It is said, however, to diminish slightly in volume, becom- ing less than y^ 1 ^ smaller. This can be shown by making a muscle contract in a bottle filled with weak salt solution so as to exclude all air, and to communicate with the atmosphere only by a capillary tube into which the salt solution rises. The slightest decrease in bulk is shown by the fall of the thin column of fluid in 'the tube. Since a muscle loses in elastic force and gains but little in density during contraction, the hardness which is communicated to the touch depends on the difference of tension of the semi- fluid contractile substance within the muscle sheath. THE GRAPHIC METHOD OF RECORDING MUSCLE CON- TRACTION. In order to study the details of the contraction of muscle, the graphic method of recording the motion is applied. The curve may be drawn on an ordinary cylinder moving sufficiently rapidly. Where accurate time measurements are required, it is better to use one of the many special forms of instruments, called myographs, made for the purpose. The principle of all these instruments is the same ; namely, an electric current, which passes through the nerve of a frog's muscle connected with the marking lever, is broken by some mechanism, while the surface is in motion ; the exact moment of breaking the contact can be accurately marked on the recording surface, by the lever which draws the muscle curve, before the instrument is set in motion. The rate of motion is registered by a tracing drawn by a tuning fork of known rate of vibration. PHASES OF A SINGLE CONTRACTION. 461 In order that the muscle-nerve preparation may not be injured by the tissues becoming too dry, it is placed in a small glass box, the air of which is kept moist by a damp sponge. This moist chamber is used when any living tissue is to be protected from drying. The first myograph used was a complicated instrument devised by Helmholtz ; in which a small glass cylinder is made to rotate rapidly by a heavy weight, and when a certain velocity of rotation is attained, a tooth is thrown out by centrifugal force, which breaks the circuit of the current passing through the nerve of the muscle. The tendon is attached to a balanced lever, at one end of which hangs a rigid style pressed by its own weight against the glass cylinder. When the circuit is broken the muscle con- tracts, raises the lever, and makes the style draw on the smoked- glass cylinder. Fick introduced a flat recording surface moving by the swing of a pendulum, by which the abscissa is made a segment of a circle, and not a straight line, and the rate varies, so that the different parts of the curve have varying time values. The curves given in the following woodcuts are drawn with the Pendulum Myograph. Du Bois-Reymond draws muscle curves on the smoked surface of a small glass plate contained in a frame, which is shot by the force of a spiral spring along tense wires, and on its way breaks the contact. The trigger used for releasing the spring sets a tuning fork at the same time vibrating (Spring Myograph}. SINGLE CONTRACTION. In response to an instantaneous stimulus, such as occurs in the secondary coil on breaking the primary current, a muscle gives a momentary twitch or spasm, commonly spoken of as a single contraction, which is of so short duration, that without the graphic method of recording the motion we could not appreciate the phases which are seen in the curve. The curve drawn on the recording surface of a pendulum myograph, by such a single contraction, is represented in Fig. 185. The short vertical stroke on the abscissa, or base line, is drawn by touching the lever when the muscle is in the uncon- 462 MANUAL OF PHYSIOLOGY. tracted state, and indicates the time of stimulation. The upper curved line is drawn by the lever during the contraction of the muscle. In such a curve the following stages are to be distinguished : 1. A short period between the moment of stimulation and that at which the lever begins to rise, during which the muscle does not move. This is known as the latent period. In the skeletal muscles of the frog this period lasts nearly .01 sec. 2. A period during which the lever rises, at first slowly, then more quickly, then again slowly, until it ceases to rise. This stage has been called the period of rising energy. It lasts about .04 sec. 3. When the highest point is attained the lever commences to fall, at first slowly, then more quickly, and at last slowly. FIG. 185. Curve drawn by a frog's gastrocnemius on the Pendulum Myograph ; below is seen the tuning-fork record of the time occupied by the contraction. Parallel to the latter is the abscissa. The little vertical mark at the left shows the moment of stimulation, and the distance from this to the beginning of the rise of the curve gives the latent period, which is followed by the ascent and descent of the lever. There is then no pause at the height of contraction. The stage of relaxing has been called the period of falling energy. It occupies, when quite fresh, about the same time as the second period, viz., about .04 sec. Thus, a stimulus occupying an almost immeasurably short time sets up a change in the molecular condition, which, taking nearly -fa sec. to run its course, and requiring y^- sec. before it exhibits any change of form, then in T ^Q- sec. attains the maxi- mum height of contraction, and, without waiting in the con- tracted condition, spends T -J^ sec. in relaxing. The latent period which appears in a single contraction curve PHASES OF A SINGLE CONTRACTION. 463 drawn by a muscle stimulated in the usual way, through the medium of a nerve, is not entirely occupied by preparatory changes going on in the substance of the muscle, but a certain part of the time recorded as latent period corresponds to the time required for the transmission of the impulse along the nerve. This may be shown by stimulating first the far end of the nerve, and then the muscle itself. In this case two curves will be drawn, having different latent periods, that obtained by direct stimulation of the muscle being shorter, and representing the real latent period, while the longer one includes the time taken by the impulse to travel along the piece of nerve between the electrodes and the muscle. Wave of Contraction. If one extremity of the muscle be stimulated without the aid of the nerve (it is best to employ a muscle from a curarized animal), the contraction passes along the muscle from the point of stimulation in a wave which travels at a definite rate of 3-4 metres per sec. in a frog, and 4-5 metres per sec. in a mammal. Reduction of temperature and fading of vital activity cause the velocity of the wave to be lessened, until finally the tissue ceases to conduct ; then only a local contraction occurs, severe stimulus causing simply an eleva- tion at the point of contact. This seems analogous to the idio- muscular contraction, which marks the seat of severe mechanical stimulation after the general contraction has ended. VARIATIONS IN THE PHASES OF A SINGLE CONTRACTION. The latent period varies much in different kinds of muscle, in the same kind of muscle of different animals, and in the same individual muscle under different conditions. As a rule, the slow-contracting muscles have a longer latent period. Thus the non-striated slow-contracting muscles found in the hollow viscera have a latent period of some seconds. The striated muscles of cold-blooded animals have a longer latency than the same kind of muscle in birds and mammalia. The same gastrocnemius of a frog has a shorter latent period when strongly stimulated, or when its temperature is raised, and vice versa. The latent period is considerably lengthened by fatigue. If 464 MANUAL OF PHYSIOLOGY. the weight be so applied that it does not extend the muscle before contraction, but only bears on it the instant it commences to shorten, the duration of the latent period increases in proportion to the weight the muscle has to lift. The dtiration of the single contraction of striated muscle varies in different cases and under varying circumstances. With submaximal stimulation the length of the curve increases with the strength of the stimulation. When the maximal strength of stimulus (/. e. , that exciting a maximal contraction} is reached, no further lengthening of the curve takes place. The greatest difference is observed in the muscles found in dif- ferent kinds of animals. The contraction of some kinds of mus- cle tissue (non-striated muscle of mollusca, for example) occupies several minutes, and reminds one of the slow movement of protoplasm ; while the rapid action of the muscle of the wing of FIG. 186. Curves drawn by the same muscle in different stages of fatigue A, when fresh; B, C, D, E, each immediately after the muscle had contracted 200 times. Showing that fatigue causes a low, long contraction. a horsefly occurs 330 times a second. Various gradations between these extremes in the rapidity of muscle contraction may be found in the contractile tissues of different animals. The fol- lowing table gives the rate of contraction of some insects' mus- cles, which may help to show the extent of these variations : Horsefly, 330 contractions per second. Bee, 190 " Wasp, no Dragonfly, 28 " Butterfly, 9 " " Among the vertebrata the duration of the contraction of the skeletal muscles varies considerably, according to the habits of the animal. The limb muscles of the tortoise and the toad take VARIATIONS IN THE SINGLE CONTRACTION. 465 a very long time to finish their contraction ; other muscles of the same animals act more quickly, but do not attain the rapidity of contraction of the skeletal muscles of warm-blooded animals. The duration of a single contraction of the same muscle is also FIG. 187. Six curves drawn by the same muscle when stretched by different weights. Showing that as the weight is increased the latency becomes longer and the contraction less in height and duration. capable of considerable variation. It seems to be lengthened by anything that leads to an dccumulation of the chemical pro- ducts which arise from muscle activity. Hence fatigue or over- stimulation causes a slow contraction (Fig. 186). FIG. 188. Curves drawn by the same muscle at different temperatures. Showing that with elevation of temperature the latency and the contraction become shorter. (The muscle had been previously cooled.) Moderate increase of temperature greatly shortens the time occupied by the single contraction of any given muscle. Exces- sive heat causes a state of continued contraction. 466 MANUAL OF PHYSIOLOGY. The reduction of temperature causes a muscle to contract more slowly, and when extreme, the muscle remains contracted long after the stimulus is removed. The altitude of the curve which represents the extent of the FIG. Curves drawn by the same muscle while being cooled. Showing that the latency and the contraction become longer as the temperature is reduced. contraction varies in the same way as the latent period and the duration. MAXIMUM CONTRACTION. The extent to which a muscle will contract depends upon the conditions in which it is placed, and varies with the load, its FIG. 190. Pendulum Myograph tracings showing summation. i. Curve of maximum contraction drawn by first stimulus, the exact time of application o which is shown by the small upstroke of the left hand of the base line. Maximum contraction resulting from second simple stimulation given at the moment indicated by the other small upstroke. al indicated by the 2. Maximum contraction resulting indicated by the other small upstroe. 3. Curve drawn as the result of double stimulation sent in at an interval indicated distance between the upstrokes, showing summation of stimulus and consequent i in contraction over the " maximum contraction" irritability, the temperature, and the force of the stimulus. A fresh muscle at the ordinary temperature, with a medium load, will contract more and more as the intensity of the current MAXIMUM CONTRACTION. 467 employed increases. There is a limit to this increase, and with comparatively weak stimulation an effect is produced which cannot be surpassed by the same muscle with further increment of stimulus. The height of the contraction is the same for all medium stimuli while the muscle is fresh. This is called the maximum contraction, being the greatest shortening which can be produced by a single stimulus. Summation. Each time a muscle receives an induction shock of medium strength, it responds with a "maximal contraction," but this is not the maximum amount the muscle can contract with repeated stimulation. If a second stimulus be given while the muscle is in the contracted state, a new maximum contrac- tion is added to the contraction already arrived at by the muscle at the moment of the second stimulation. If stimulated when the lever is at the apex of the curve, the sum of 'the effect pro- duced will be equal to two maximum contractions. If applied in the middle of the period of the ascent or descent of the lever, a second stimulation gives rise to i^ maximum con- tractions, and so on, in various parts of the curve, a new maxi- mum curve is produced, arising from the point at which the lever is when the second stimulus is applied (Fig. 190). During the latent period a second stimulation produces the same effect, but the summation only begins at the end of the latent period of the second contraction, when the effect of the first stimulus is as yet small. It is difficult to demonstrate the summation when the stimuli are very close, but if the second stimulus comes after an interval of more than -g-i-g- sec., summa- tion can easily be appreciated. This summation of effect also takes place when the stimulus is insufficient to produce a maximum contraction. The first few weak stimuli give rise to the same extent of contraction as if the muscle were at its normal length at the time of each succes- sive stimulation. The following tracings (Figs. 191-193) show the effects of repeated stimulations applied at the various periods indicated by the numbers on the abscissa line. MANUAL OF PHYSIOLOGY. TETANUS. If a series of stimuli be applied in succession, at intervals less than the duration of a single contraction, a summation of con tractions occurs, which results in the accumulation of effect until the muscle has shortened to about one-half of the length it FIG. 191. Curve of tetanus resulting from 30 stimulations per second, drawn by a frog's muscle on a drum, the surface of which moves 1.5 centimetres per second. The stimulation com- mences at " 30," and ceases just before the lever begins to fall. No trace of the indi- vidual contractions of which the tetanus is composed can be recognized. attains during a single contraction, or about one-fourth the normal length of the relaxed muscle ; it then remains contracted to the same extent for some time, and does not shorten further, though the stimulus be increased in rate or strength. As long as the stimuli are continued, the various single contractions FIG. 192. Curve ot tetanus composed of imperfectly fused contractions resulting from 12 stimulations per second. The serrations on the left of the curve indicate the individual contractions. caused by the individual shocks are fused together (Fig. 191) ; but if the intervals between the stimuli be nearly as long as the time occupied by a single contraction, the line drawn by the lever will show notches indicating the apices of the fused single contractions (Figs. 192 and 193). TETANUS. 469 This condition of summation of contractions is called tetanus, and is said, by some, to be the manner in which muscular motion is produced by the action of the nerves in obedience to the will. With from fifteen a second to upwards of many hundreds of induced shocks one can produce tetanus in a frog's muscle. The lowest rate of electric stimulation at which human muscle passes into complete tetanus is about 25 per sec. The number of stim- uli required varies with the *rate of contraction of the muscle employed, the quick-contracting bird's muscle requiring 70 per second, while the exceptionally slow-moving tortoise muscle only requires 3 per second. According to some, there is a limit to the number of stimuli which will cause tetanus 360 per second is named as the maximum for a certain strength of FIG. 193. Tetanus produced by 8 stimulations per second. The more perfect fusion of the single contractions shown toward the end of the curve depends on the altered condition of the muscle. stimulus ; with stronger stimuli, even when more frequent, tetanus occurs. It has been shown that many thousand stimuli per second can cause tetanus even with very weak currents. If tetanus be kept up for some seconds, and the stimulation be then suddenly stopped, the lever falls rapidly for a certain distance, but the muscle does not quite return to its normal length for some few seconds. This residual contraction is easily overcome by any substantial load. If kept in a state of tetanus by weak stimulation, after some time the muscle commences to relax from fatigue, at first rapidly, then more slowly. This falling off of the tetanic contraction may be prevented by increasing the stimulus. 470 MANUAL OF PHYSIOLOGY. MUSCLE TONE. Although the tracing drawn by a lever attached to a muscle in tetanus is straight, and does not show any variation in the tension of the tetanized muscle, some variations in tension must occur, since a low humming sound is produced during contrac- tion. A muscle tone, like the purring of a cat, can be heard by applying the ear firmly over any large muscle (biceps) while in tetanus, by throwing the muscles attached to the orbit and Eustachian tube into powerful action, or by spasm of the muscles in mastication. The number of vibrations which has been estimated to occur in the voluntary contraction of human skeletal muscles does not produce an audible note ; hence it has been supposed that the note we hear has been an overtone. When a muscle is thrown into tetanus by a current interrupted by a tuning fork, a tone is produced which corresponds with that of the fork causing the interruption in the current by definite vibrations, which regulate the number of stimulations the muscle receives. If, on the other hand, a contraction of the muscle be brought about by stimulating the spinal cord, with the same rate of breaking the current, the normal muscle tone is produced, as if the contrac- tion were the result of a nerve impulse coming from the brain. There is no satisfactory proof, however, that the variation in tension of the continuous contraction of voluntary muscle is strictly rhythmical. The sensation of a sound like the muscle tone is produced by any nearly periodic vibrations of less rate than 25 per second. The pitch of the muscle tone varies with the tension of the membrana tympani. Hence, it has been sug- gested that it corresponds with the resonant tone proper to the membrane of the drum ; which may be evoked by any trembling movements of the muscle fibres due to slight variations in the force or distribution of the impulses transmitted by the motor nerves. IRRITABILITY AND FATIGUE. The activity of the muscle tissue of mammalian animals is closely dependent upon a good supply of nutrition, and if its blood current be completely cut off by any means for a length FATIGUE. 471 of time, it loses its power of contracting. While the muscle remains in the body, and is kept warm and moist by the juices in the tissues, it will live a very considerable time without any blood flowing through it, and it at once regains its contractility when the blood stream is again allowed to flow through its ves- sels. This is seen when the circulation of a limb is brought to a standstill by means of a tourniquet or a tightly applied band- age. A mammalian muscle soon ceases to be irritable and dies when removed from the body, but its functional activity may be .renewed by passing an artificial stream of arterial blood through its vessels, and an isolated muscle may thus be made to contract repeatedly for a considerable time. On the other hand, the muscle of a cold-blooded animal will remain alive for a long time many hours if kept cool and moist. When its functional activity is about to fade, it may be revived by means of an artificial stream of blood caused to flow through its vessels, just as in the case of the mammalian muscle. Common experience teaches us that even when well supplied with blood our muscles become fatigued after very prolonged exertion, and are incapable of further action. This occurs all the more rapidly when anything interferes with the flow of blood through them, such as using our arms in an elevated position ; the simple operation of driving in a screw overhead is soon fol- lowed by pain and fatigue in the muscles of the forearm, though the same amount of force could be exerted when the arms are in a lower posture, without the least feeling of fatigue. The difficulties of experimenting with the muscles of mammals make the frog muscle the common material for investigation, and from it we learn the following facts : 1. When removed from the body and deprived of its blood supply, the muscle of a cold-blooded animal slowly dies from want of nutrition. If it be placed under favorable circumstances, and allowed perfect rest, it may live twenty-four hours. If it be frequently excited to action, on the other hand, it rapidly loses its irritability, being worn out by fatigue. 2. From a muscle removed from a recently-killed animal, we 472 MANUAL OF PHYSIOLOGY. learn, that even without a supply of blood the muscle tissue is capable of recovering from very well-marked fatigue, if it be allowed to rest for a little time, so that the muscle has in itself the material requisite for the recuperation. The first question then is, What causes the loss of irritability which we call fatigue ? And the second is, By what means is the muscle enabled to return to a state of functional activity ? We know that the mere life of a tissue must be accompanied by cer- tain chemical changes which require (a) a supply of fresh mate- rial, and (^) the removal of certain substances which are the outcome of the tissue change. In the case of muscle, this chemical interchange is constantly but slowly going on between the contractile substance and the blood. When the muscle contracts, much more active and prob- ably different changes go on in the contractile substance, more new material being required, and more effete matter being pro- duced. It is probable that the accumulation of these effete mat- ters is the more important cause of the loss of irritability in a muscle, for a frog's muscle, when quite fatigued, may be rendered active again by washing out its blood vessels with a stream of salt solution of the same density as the serum (.6 per cent. NaCl), and thus removing the injurious " fatigue stuffs," as they have been called. It is found that a very minute quantity of lactic acid injected into the vessels of a muscle destroys its irritability, and brings it to a state resembling intense fatigue. Of the new materials required for the sustentation of muscle irritability, oxygen is among the most important, though its supply is not absolutely necessary for the recuperation of a partially exhausted, isolated frog's muscle. The slow recovery of a bloodless muscle from fatigue may be explained by supposing time to be necessary for the reconstruc- tion of new contractile material, and probably, also, for a second- ary change to. take place in the effete materials, by which they become less injurious. When working actively the muscles require an adequate sup- ply of good arterial blood in order to ward off exhaustion ; and, as already explained in speaking of the vasomotor influences, a RIGOR MORTIS. 473 muscle receives a greater supply of blood when actively con- tracting than when in the passive state. The irritability of a muscle and the rate at which it becomes exhausted may be said to depend upon : 1 . The adequacy of its blood supply : the better the supply of new material and the more quickly the injurious effete materials are removed, the more work a muscle can do without becoming exhausted. 2. Temperature has a marked effect on the irritability of muscles, as well as upon the form of this contraction. Low tem- peratures approaching 5 C. diminish the irritability of a muscle, but do not seem to tend toward more rapid exhaustion. High temperatures approaching 30 C. increase the irritabil- ity, and at the same time rapidly bring about fatigue. At about 35 C. an isolated frog's muscle begins to pass into heat tetanus, and permanently loses its irritability. 3. Functional activity is accompanied by an increased blood supply, and a more perfect nutrition of the muscles, hence activ- ity is advantageous for their growth and power ; while, on the other hand, continued and prolonged inactivity causes a lower- ing of the nutrition and loss of irritability. Thus, when the nerves supplying the voluntary muscles are injured, there is con- siderable danger of atrophy and tissue degeneration of the muscles ; the contractile substance becomes replaced by fat granules. This degeneration also occurs in the stump when a limb is amputated, the distal attachments of the muscles having been cut they cannot act, and after some time they become com- pletely atrophied, so that muscle tissue can hardly be recognized in them. DEATH RIGOR. The death of muscle tissue is associated with a set of changes which, in some respects, resemble those observed in its active state. The most obvious phenomenon is an unyielding contrac- tion, which causes the stiffening of the body after death. Hence, it is called rigor mortis. The muscles harden ; lose their elastic- ity, and the tissue is torn if forcibly stretched. When isolated, the muscle is seen to be opaque, and its reaction is found to be 40 474 MANUAL OF PHYSIOLOGY. distinctly acid. A considerable quantity of heat is developed during the progress of the rigor. The electric currents alter in direction and finally disappear. The period at which rigor comes on and its duration depend on (a) the state of the muscles, and () the circumstances under which they are placed at the time of death. All influences which tend to cause death of the tissue induce early rigor of short duration, viz., (i) Prolonged activity as may be shown in a muscle artificially tetanized, or seen in an animal whose death was preceded by intense muscular exertion causes rigor to appear almost immediately, and to terminate rapidly. (2) High temperature facilitates the production of rigor in dying muscles ; indeed, a temperature not much exceeding that normal to the tissue induces rigor. This form of contraction, which is called heat rigor, is brought about in mammalian muscles by a temperature of about 50 C., and in frog's muscles below 40 C. If, however, the temperature of a muscle be suddenly raised to the boiling point, it is killed, and the chief phenomena of rigor are prevented from occurring. (3) Freezing postpones the changes in the muscles upon which rigor depends. (4) Stretch- ing, or any mechanical excitation which tends to injure the tissue, causes it to pass more rapidly into rigor. (5) The appli- cation of water and of a number of chemical substances cause muscles quickly to pass into a state of rigor similar to that which ordinarily follows the death of the tissue. (6) Any stoppage in the blood current normally flowing through a muscle, after some time makes it pass into a state of rigidity like rigor mortis, but this may be removed by allowing the blood to flow freely again through the muscle. It is generally admitted that rigor mortis depends on the ten- dency of the muscle plasma to coagulate and give rise to myosin and muscle serum. This is, in most respects, comparable with the coagulation of the blood, and may also depend upon the action of some ferment, of which there is no lack in dead muscle tissue. Compare the paragraph on chemistry, pp. 445, 446. Most of the phenomena of the process of muscle rigor remind us of the changes already described as occurring in muscle, when UNSTRIATED MUSCLE. 475 it passes from the passive to the active state. Thus, the shorten- ing of the fibres, the evolution of heat, and the chemical changes may be said to be identical in contraction and rigor mortis. The electrical changes are, however, very transitory, and the rigor is accompanied by loss of elasticity and irritability. Opacity of the tissue marks its later stages. Thus, while dying, the muscle tissue may be said to go through a series of events analogous to those which would occur in a prolonged contraction without any period of recuperation. The idea has naturally suggested itself to the minds of physiologists, that the active state of muscle depends upon chemical changes which are the initial steps in the coagulation of the contractile substance, when the muscle is dying. The muscle tissue is sup- posed to contain a special proteid of extremely intricate and unstable chemical constitution, which is constantly undergoing slow molecular change, and which, if not reintegrated by con- stant assimilation, would pass into coagulation. Under the influ- ence of stimuli a comparatively sudden and intense molecular disturbance is brought about, which produces shortening of the fibres, and the same chemical changes as precede the coagulation. .Before the stage of coagulation appears a chemical rearrange- ment takes place, the result of which is the reconstruction of the unstable complex proteid. If nutriment be withheld, or if the stimulation be too powerful, the recovery cannot take place, and we find the muscle passing from a state of physiological contraction to one of intense exhaustion, and then to coagulation and death. UNSTRIATED MUSCLE. So far reference has only been made to the skeletal muscles, the fibres of which are marked by transverse striations, and whose single contraction is extremely rapid and short. The contractile tissues which carry on the movements in the various organs of the body are not striated fibres, but, as has been already stated, consist of elongated flattened cells with rod- shaped nuclei. They occur generally in the form of sheets or layers, forming coats for the organs in which they lie. Their single contraction is slow and prolonged, and is generally trans- 476 MANUAL OF PHYSIOLOGY. mitted from one muscle cell to another as a kind of sluggish wave. They are not capable of passing into a tetanic state of contraction, like striated muscles. The slowest contraction seems to be that of the muscle cells in the walls of the blood vessels. These remain in a state of partial contraction, which undergoes a brief and temporary rhythmical relaxation. The most forcible aggregate of unstriated muscle elements is met with in the uterus. This organ, which has very exceptional motor powers to perform, contracts in some- what the same way as the muscles of the blood vessels, but more quickly, and with longer rhythmical intervals of partial relaxa- tion. The muscular wall of the intestine, and the iris, are among the most rapidly contracting smooth muscles. The chemical properties of the smooth muscle are somewhat similar to those of striated skeletal muscles, and they pass into a state of rigor, while dying, which seems to depend on the same causes as the rigor mortis already described. APPLICATION OF SKELETAL MUSCLES. 477 CHAPTER XXVI. THE APPLICATION OF SKELETAL MUSCLES. The consideration of the many varieties of muscles, and the various modes in which they are attached to the bones that they are destined to move, belongs to the department of practical anatomy, and needs no mention here. As a general but by no means universal rule, a muscle has one attachment which is fixed, commonly spoken of as its origm, and a second, called its inser- tion, upon which it acts by approximating it to the origin. Mus- cles usually pass in a straight line between their two attachments, but sometimes they act round an angle by sliding over a pulley, or by means of a small bone in the tendon, like the patella. The muscles are so attached that they are always slightly on the stretch, and thus, at the moment they begin to contract, they are in an advantageous position to bring their action to bear on the bones which they move. When the contraction ceases, the bones are drawn back to their former position without any sudden jerk or jar. The muscles act upon the bones as levers, by working upon the short arm of the lever, so that more direct force is required on the part of a muscle than the weight of the body moved ; but from this arrangement considerable advantages are gained, viz., that a small contraction of the muscle causes an extensive excur- sion of the part moved, and much greater rapidity of motion is attained. All the three orders of levers are met with in the movements of the different bones of the skeleton ; often, indeed, all three varieties are found in the same joint, as the elbow, where the simple extension and flexion motions of the biceps and triceps muscles give us good examples (Fig. 194). The first order of lever is used when the triceps is the power and draws upon the olecranon, thus moving the hand and fore- arm around the trochlea, which acts as the fulcrum. This is 478 MANUAL OF PHYSIOLOGY. FIG. 194. shown in the upper diagram, in which the hand is striking a blow with a dagger. The second order comes into play when the hand, resting on a point of support, acts as the fulcrum, and the triceps pulling on the olecranon is the power which raises the humerus, upon which is fixed the body or weight (middle diagram). The third order may be exemplified by the action of the biceps in ordinary flexion of the elbow. Here the muscle, which is the power, is placed between the fulcrum- represented by the lower end of the humerus and the weight which is car- ried by the hand (lower diagram). The various groups of muscles which are so arranged as to assist each other when acting together, are called syner- getic, and those which, when contracting at the same time, oppose each other, are called antagonistic. The same muscles may, in different positions of a joint or in combination with other muscles, have totally different actions, at one time being synergetic and at another antago- nistic. -Thus, the sterno-mastoid mus- cle may, in different positions of the head, either bend the cranium backward or forward, and so cooperate with two sets of muscles which are definitely an- tagonistic to one another. the mode of Diagrams showing action of the three orders of levers (numbered from above downward) illustrated by the action of the elbow joint. JOINTS. The unions between the bones of the skeleton are very varied in function and character. They may be classed as : i. SUTURES, in which the bones are firmly united by rugged surfaces without the interposition of any cartilage. They are practically only the lines of union of different bones, which grow together to form a single bone. JOINTS. 479 2. SYMPHYSES, in which two bony substances are strongly cemented together by ligaments, and a more or less thick adher- ent layer of fibre-cartilage, are joints allowing of some move- ment, which is, however, very limited. 3. ARTHROSES, or true movable joints, such as are commonly met with in the extremities. They are characterized by a syno- vial sac lining the surrounding ligaments, and two smooth sur- faces of cartilage which cover over the bony extremities taking part in the articulation, and form what are called the articular sur- faces. The synovial sac is strengthened by a loose membranous covering the capsular ligament which is attached round the edge of the cartilages next to the periosteum, which here ceases. The articular surfaces are always in exact and close contact, being pressed together rpy the following influences: (i) The elastic tension and tonic contraction of the surrounding muscles, which exert considerable traction on them. . (2) The traction of the surrounding ligaments, which in some cases holds the bones firmly together, no 'matter what their relative positions may be. This can be well seen in the knee joint, in which a comparatively small number of the ligaments suffice to keep the articular surfaces in contact. (3) The atmospheric pressure also tends to hold the bones in close apposition, as may be seen in the hip joint, which is not easily disarticulated, even when all the surrounding structures and the ligaments have been severed. The synovial joints may be classified according to the form of their surfaces, or their mode of motion as follows : 1. Flat articular surfaces held together by a short rigid cap- sule, allowing of but very slight gliding movement ; examples of this form of joint are to be found in the tarsus and the articular processes of the vertebrae. 2. Hinge joints, in which the surfaces are so adapted that only one kind of motion can take place. A groove-like cavity in one bone fits closely and glides around the axis of a roller on the other bone, while the sides of the joint are kept tightly together by means of small lateral ligaments. Examples of this form of joint are to be found between the phalanges of the digits and at the humero-ulnar joint. 480 MANUAL OF PHYSIOLOGY. 3. The rotary hinge, or pivot joint, in which a part moves round the axis of the bone, instead of the axis of rotation being at right angles to both bones, forming the joint as in an ordinary hinge. Such joints are seen at the head of the radius and at the articulation between the atlas and the odontoid process of the axis. 4. A saddle-shaped joint is a kind of double hinge, in which each of the articulating bones forms a partial socket and roller, and hence there are two axes of rotation, placed more or less at right angles one to the other. A good example of this kind of joint occurs between the thumb and one of the wrist bones. 5. Spiral articulations are modifications of the hinge, in which the surface of the roller does not run " true," but becomes eccen- tric, so that the surface of the roller forms, really, part of a spiral, by means of which the bone articulating with it is forced away from the central axis of rotation and becomes jammed, as if stopped by a wedge. The best example of this is the knee. In this joint the axis of rotation (c) % is near the posterior sur- faces of the bones, and passes transversely through the condyles of the femur, the surfaces of which form an arc, the centre cor- responding to the axis of motion. In ordi- nary flexion the head of the tibia (F) moves on the arc around the axes so as to partially relax the lateral ligament and allow of some rotation on the axis of the tibia. When the head of the tibia moves forward, in exten- sion (E), it becomes wedged against the ante- rior part of the articular surface of the femur (w), which presents an eccentric, spiral-like curve, departing more and more from the centre of rotation as the articular surface of the tibia proceeds forward. The effect of this is, that in extension of the leg the ligaments are made tense, and the bones are firmly locked together. Owing to the inequality between the size of the internal and external con- dyles, the axis of rotation is not at right angles to the axis of the FIG. 195. Diagram of the action ot the knee joint. W = articular surface of femur. E = tibia in position of extension. F = tibia in position of flexion. C = centre of rotation. STANDING. 481 femur, but is at such an angle that extreme extension causes a slight amount of outward motion of the leg. 6. In the ball and socket joints the name of which implies their mechanism the most varied movements occur. (Hip and shoulder.) STANDING. In order that an elongated rigid body may stand upright, it is only necessary that a line drawn vertically through its centre of gravity should pass within its basis of support, and, if the latter be sufficiently wide, the object will remain permanently in that position. The human body, in the first place, is not rigid, and in the second place the basis of support is too small to insure a satisfactory degree of steadiness. The act of standing must, therefore, be accomplished by the action of certain mus- cles, which are employed in preventing the different joints from bending, and in so balancing the various parts of the body as to keep the whole frame from toppling over. In order to economize muscular energy while standing, we may lock the more important joints, and thus depend rather on the passive ligaments than upon muscular action for the rigidity of the body. With this object we are taught to place the heels together, turn out the toes, bring the legs parallel by approxi- mating them, and, extending the knees to the utmost, to straighten and to throw back the trunk so as to render tense the anterior hip ligaments, to direct the face straight forward so as to balance the head evenly, and to let the arms fall by the sides. In this position, as a soldier stands at attention, the knee and hip joints remain fixed, without any effort on the part of the muscles, but it is far from being the most comfortable attitude one can assume for prolonged standing, and hence the position known best by the order "stand at ease" is adopted if more complete rest is desired. In this position the weight of the body is usually allowed to rest on one leg, while the other lightly touches the ground to form a kind of stay, and relieve the muscles which surround the supporting ankle from too great an effort of balancing. At the same time the knee is extended, and the pelvis becomes somewhat oblique, so as to bring it more directly 482 MANUAL OF PHYSIOLOGY. over the head of the femur. In ordinary easy standing, the joints are not usually kept locked by the tension of the ligament- ous structures, but their position is constantly being very slightly altered, so as to vary the muscles employed in preserving the balance and thus prevent fatigue. The joints most exercised in the erect posture are the follow- ing: 1. The ankle has to support the weight of the entire body, while the joint is neither flexed nor extended to its utmost, and cannot be fixed in this position by ligamentous arrangements. The foot being placed on. the ground, resting on the heel and the balls of the great and little toes, is supported in an arch-like form by strong though elastic ligaments, which allow but little motion in the numerous joints. The bones of the leg can move in the freest way, backward or forward, over the articular surface of the astragalus, which forms the roller of the hinge, lateral motion being prevented by the malleoli. The line passing through the centre of gravity of the body generally falls slightly in front of the axis of rotation of the ankle joint, so that the entire body tends to fall forward at the ankles. This tendency is checked by the powerful calf muscles, which, attached to the calcaneum by means of the strong tendo-Achillis, keep the parts in such a position that an exact balance is almost constantly kept up. 2. The knee joint, when completely extended, requires no mus- cular action to prevent it from bending, because the line of gravity then passes in front of the axis of rotation, and the weight of the body tends to bend the knee backward. This is impossible, on account of the strong ligaments which exert their traction behind the axis of rotation. As a rule, these ligaments are not put on the stretch in this way, but the joint is held, by muscular power, in such a position that the line of gravity passes just through, or very slightly behind, the axis of rotation of the joint, so that, if anything, there is a slight tendency for the knee to bend. This is completely checked, and the body balanced, by the powerful extensor muscles of the thigh. 3. In the hip joints, which have to support the trunk and head, the line of gravity falls just behind the line uniting the joints STANDING. 483 when the person is perfectly erect, so that here the body has a tendency to fall backward. This is prevented by the strong ilio- femoral ligament. When, however, the knee is not straightened to the full extent, so that the line of gravity passes through or a little behind the axis of rotation of that joint, then the pelvis is very slightly flexed on the femora, so that the axis of the joints lies exactly in or a little behind the line of gravity, and thus the body inclines rather to fall forward. This tendency is prevented by the powerful glutei muscles, which also enable us to regain the erect posture after bending the trunk forward. The motions of which the pelvis and vertebral column are capable are too slight to deserve attention here. The vertebral column, wedged in as it is between the two innominate bones, may be taken, together with the pelvis, as forming a very yield- ing and elastic, but practically jointless pillar, the 'upper part of which can alone be bent to such an extent as to require mention in discussing the mechanism of station. The individual joints between the cervical vertebra permit but a slight amount of movement when taken separately, but by their aggregate motion they enable considerable extension and flexion of the neck to take place. These motions follow so closely, and are so inseparably associated with those of the head on the upper vertebra, that there is no need to consider them separately from the latter. The atlanto-occipital joints admit of some little lateral movement, but that in the antero-posterior direction is much the more import- ant, but even this would be insignificant were it not associated with the movements between the other cervical vertebrae. The cranium has then to be balanced on the top of a flexible column, and rests immediately in a kind of socket, which can move as a double hinge around two axes at right angles one to the other. The vertical line from the centre of gravity of the cranium must vary with every forward, backward, or lateral movement of the head or neck, but in the erect posture it passes a little in front of the axis of rotation of the atlanto-occipital joint, and somewhat behind the curve of the cervical vertebrae, so that the head may be said to be poised on the apex of the verte- 484 MANUAL OF PHYSIOLOGY. bral column, with some tendency to fall forward. There are no ligamentous structures which can lock the joints so as to keep the head in the erect position ; therefore, without the aid of mus- cular force, the head will fall forward or backward, according to the position it may be in when the muscles suddenly relax, as happens in falling asleep in an upright posture. From the foregoing facts it will be seen that there exists a kind of coordinated antagonism at work in ordinary easy stand- ing which keeps the elastic, pliable body upright, without the rigidity adopted when standing " at attention." The muscular action is more exercised when we are not on steady ground, and varied coordination becomes necessary ; for instance, when we go on board ship for the first time. Standing then takes some little time to become easy, and requires new associations of move- ment. The gastrocnemius and soleus relax the ankle in a degree just proportionate to the amount of flexion of the knee permitted by the quadriceps extensor cruris, while, simultaneously, the great gluteal muscle allows the body to incline forward so as to keep its centre of gravity in the proper relation to the basis of sup- port. WALKING AND RUNNING. Walking is accomplished by poising the weight on one foot and then tilting the body forward with the other, which is then swung in front and placed on the ground to prevent falling. These acts are performed alternately by each leg, so that the "swinging limb" becomes the "supporting limb " of the next step. The swinging leg is described as having two phases, (i) active, while pushing off from the ground, and (2) passive, while swinging forward like a pendulum. In starting, one foot is placed behind the other, so that the line of gravity lies between the two, the hindmost limb having the ankle and knee a little bent. By suddenly straightening these joints it gives a " push off" with the toes and propels the body forward, so as to move it around the axis of motion of the fixed, or supporting ankle joint. At the end of the swing, the pendulous leg comes to the ground, and leaves the other limb in the attitude ready for the push off. Thus, on level ground walking is carried on, with but small mus- WALKING AND RUNNING. 485 cular exercise ; but in ascending an incline or going up stairs, the supporting limb has to elevate the body at each step by extending the knee and ankle joints by the thigh extensors and the calf muscles. Running is distinguished from walking by the fact that, while in the latter both feet rest on the ground for the greater part of each pace, in the former the time that either foot rests on the ground is reduced to a minimum, and the body can never be said to be balanced on either leg, so that, in fact, there is no longer a "support limb." The legs are kept in a semiflexed position, ready for the push off or spring, which is so forcibly carried out that the body is propelled through the air without any support between each step, and has a constant tendency to fall forward. Thus, an interval of greater or less duration, according to the pace, exists during which both the feet are off the ground, because, the moment either foot comes to the ground, it at once executes a new spring without waiting for the swing of the other. 486 MANUAL OF PHYSIOLOGY. CHAPTER XXVII. VOICE AND SPEECH. The human voice is produced by an expiratory blast of air being forced through the narrow opening at the top of the wind- pipe, called the glottis. This glottis, which lies in the lower part of the larynx, is bounded on each side by the edges of thin, elas- tic, membranous folds that project into the air passages. These membranous folds, called the vocal cords, are set vibrating by the current of air from below, and in turn communicate their vibrations to the air in the air passages situated above them. ANATOMICAL SKETCH. The vocal apparatus produces sound in the same manner as a musical instrument of the reed-pipe variety. If we compare it with the pipe of an organ, we find all the parts of the latter represented. The lungs within the moving thorax act as the bellows. The bronchi and trachea are the supply pipes and air box. The vocal cords are the vibrating tongues ; while the larynx, pharynx, mouth and nose act as the accessory or resonating pipes. The blast of air is produced and regulated by the respi- ratory muscles ; and special intrinsic muscles of the larynx change the conditions of the vocal cords so as to alter the pitch of the notes produced. Other sets of muscles, by altering the conditions of the resonating pipes, give rise to many modifications in the vocal tones, and thus produce what is called speech. The larynx, which may be regarded as the special organ of voice, is made up of four cartilages, viz., the ericoid, thyroid and two arytenoids, jointed together so as to allow of considerable motion. Of these the inferior, the ericoid, is attached to the trachea, which it joins to the others. It forms a ring, which is thin in front, but deep and thick behind, owing to a peculiar projection upward of its posterior part. The thyroid consists of two side wings so bent as to form the greater part of the anterior ANATOMICAL SKETCH. 487 FlG - and lateral boundaries of the voice box, and can be felt easily in the front of the throat. It is articulated to the sides of the cri- coid by its two inferior and pos- terior extremities, so that the upper part of the cricoid carti- lage can move backward and forward. The arytenoid carti- lages are little three-sided pyra- midal masses placed on the upper surface of the posterior part of the cricoid, to which they are attached by a loose joint. They are so placed that one surface looks inward, the second backward, and the third forward and outward, while the inferior surface rides on the cricoid. One point looks for- ward, and to it is attached the vocal cord on each side, hence it has been called the vocal process. The apex, which Igoks outward and backward, gives attachment tO SOme Of the in- Anterior half of a transverse vertical section trinsic muscles, and hence has been called the muscular pro- cess. The thyroid cartilage is con- nected with the cricoid below, and with the hyoid bone above by ligaments and tough membranes, which hold the parts together, fill in the intervals, and complete the skeleton of the larynx. The vocal cords are composed of small strands of elastic tissue, which are stretched between the anterior processes of the aryte- noid cartilages and the inferior part of the thyroid, where they are attached side by side to the posterior surface of the angle through the larynx near its middle, seen from behind. More is cut away on the upper part of the right side. i. Upper di- vision of the laryngeal cavity; 2. Central portion ; 3. Lower portion continued into 4, trachea ; e, epiglottis ; e' , its cushion ; t, thyroid cartilage seen in section, vl, true vocal cord at the rima glottidis ; j, ventricle of larynx ; s' ', saccule. (A. Thom- son.') 488 MANUAL OF PHYSIOLOGY. formed by the junction of the two lateral parts or alse of the thy- roid. The mucous membrane which lines the larynx is thin, and closely adherent over the vocal cords. The surface of the laryngeal cavity is smooth and even, the lining membrane passing over the cartilages and muscles so as to obliterate all ridges except the vocal cords and two others, less sharply defined, called the false vocal cords, which lie parallel to and above the true vibrat- ing cords. Between these is the cavity known as the ventricle of the larynx. MECHANISM OF VOCALIZATION. Shape of the Opening of the Glottis. Taking the thyroid cartilage as the fixed base, the cri- coid and arytenoid cartilages undergo move- ments which bring about two distinct sets of changes in the glottis and its elastic edges, namely, (i) widening and narrowing the open- ing; (2) stretching and relaxing of the vocal cords. During ordinary respiration the glottis remains about half open, being slightly wid- ened during inspiration (B'). During forced inspiration the glottis is widely dilated by mus- cular action (c'). If an irritating gas be inspired, the glottis is tightly closed by a spas- modic action of certain muscles, so that the true vocal cords act as a kind of valve. During vocalization the glottis is formed into a narrow chink with parallel sides (A'), while the cords are made more or less tense, accord- ing to the pitch of the note to be produced ; both these changes are brought about by muscular action. The opening of the chink of the glottis is accomplished chiefly by a muscle called the posterior crico-arytenoid, which passes from the posterior surface of the cricoid cartilage to the outer Diagrams taken from the laryngoscopic view of the larynx, showing in trans- verse section the po- sition in which the vocal cords and the arytenoid cartilages are supposed to be during different ac- tions of the larynx. A'. Vocal chink, as in singing. B'. In easy, quiet inha- lation of air. C'. In forced inspira- tion. MECHANISM OF VOCALIZATION. 489 and posterior angle of the arytenoids. By pulling the latter point downward and backward it separates the arytenoid carti- lages, particularly at their anterior extremity, where the cords are attached. In this action it is aided by a small muscle con- necting the posterior surfaces of the arytenoid, namely, the pos- terior arytenoid, which tends, when the two arytenoid cartilages are held apart, to rotate them, so that the vocal processes are separated. FIG. 198. Diagram of the side view of the larynx, showing the position of the vocal cords (V). (Huxley.} Ar. Arytenoid cartilage. Hy. Hyoid bone. Tk. Thyroid cartilage. Cr. Cricoid cartilage. Tr. Trachea. C. th. Crico-thyroid muscle. Th. A. Thyro-arytenoid muscle. Ep. Epiglottis. Diagram of the opening of the larynx from above. (Huxley?) Th. Thyroid cartilage. Cr. Cricoid cartilage. Ary. Superior extremities of the arytenoid cartilages. V. Vocal cords. Th. A. Thyro-arytenoid muscles. C. #. /. Lateral crico-arytenoid muscle. C. a. p. Posterior crico-arytenoid muscle. A. r.p. Posterior arytenoid muscle. The narrowing of the glottis is executed by the lateral crico- arytenoids which run upward and backward from the antero- lateral aspect of the cricoid to the muscular processes of the arytenoid cartilages.' They pull the muscular processes forward, and thus rotate the arytenoid cartilages so as to approximate the vocal processes to one another, while any tendency toward pull- ing apart the bodies of the cartilages, owing to the downward direction of the muscle, is overcome by the posterior arytenoid 49 MANUAL OF PHYSIOLOGY. muscle and those muscular bands which pass from the posterior surface of the arytenoid cartilages to the epiglottis and the upper part of the thyroid cartilage, the external thyro-arytenoid, and the thyro-ary-epiglottic muscles (Henle). The other fibres, which pass directly from the arytenoid to the thyroid cartilages internal and external thyro-arytenoid muscles in the same direction as the vocal cords, complete the closure by helping to press together the vocal processes, and by approximating the cords themselves. In spasmodic closure of the glottis, all these latter muscles act violently together, and have been grouped by Henle as the constrictor of the glottis. Relaxation of the vocal cords accompanies voluntary closure of the glottis, as in holding the breath, when the false vocal cords are said to have a valvular action. The muscular fibres which run from the arytenoid cartilages to the thyroid, nearly parallel to the true vocal cords, are those concerned in the act of relaxation when the cords are active. They pull forward the arytenoid cartilages, and at the same time draw the upper part of the cricoid slightly forward. These muscles have the all- important action of adapting the edges of the cords and the neighboring surfaces to the exact shape most advantageous to their vibration. The tightening of the vocal cords is caused by a single muscle, the crico-thyroid, which, on the outer side of the larynx, passes downward and forward from the lower part of the thyroid to the anterior part of the cricoid cartilage. It pulls the anterior part of the cricoid cartilage upward, causing it to rotate round an axis passing through its thyroid joints. The upper part of the cricoid, which carries the arytenoids, moves backward, the attach- ments of the vocal cords are separated, and the membranes are thus put on the stretch. The requirements necessary for the production of voice are the following : 1 . Elasticity of the vocal cords and smoothness of their edges ; freedom from all surface irregularity, such as would be caused by thick mucus adhering to them, or by any abnormality. 2. The cords must be very accurately adjusted, and closely ap- PROPERTIES OF THE HUMAN VOICE. 491 proximated together, so that they almost touch evenly through- out their entire length. 3. The cords must be held in a certain degree of tension, or their vibration cannot produce any vocal tone, but only a raucous noise. 4. The air must be propelled through the glottis by a forced expiration. The normal expiratory current is too gentle to give the necessary vibration. After the operation of tracheotomy, the air escapes through the abnormal opening, and sufficient pressure cannot be brought to bear on the cords, so no vocal sound can be produced, and the person speaks in a whisper, unless the exit of air through the tracheotomy tube is prevented by placing the finger temporarily upon the opening. PROPERTIES OF THE HUMAN VOICE. In the voice we can recognize the properties noted in other kinds of sound. These are quality, pitch and intensity. 1. The quality of vocal sound is almost endless in variety, as is shown by the vocal capabilities of different individuals. The quality of any musical sound depends upon the relative power of the fundamental tone, and of the overtones that accom- pany it. The less the fundamental tone is disturbed by overtones, the clearer and better is the voice. This difference in quality of the human voice depends upon the perfectness of the elasticity, the relation of thickness to length, surface smoothness, and other physical conditions of the cords themselves, and the exactitude with which the muscles can adapt the surfaces. For "singing well, much more is necessary than good quality of tone, which is common enough. The muscles of the larynx, thorax, and mouth must all be educated to an extraordinarily high degree. 2. The pitch of the notes produced in the larynx depends upon first, the absolute length of the vocal cords. This varies with age, particularly in males, whose vocal organs undergo rapid growth at puberty, when vocalization is uncertain from the rapid changes going on in the part ; hence the voice is said to crack. The vocal cords of women have been found by measure- ment to be about one-third shorter than those of men, and people 49 2 MANUAL OF PHYSIOLOGY. with tenor voices have shorter cords than basses or baritones. Secondly, on the tension of the cords : the tighter the vocal cords are drawn by the crico-thyroid muscles, the higher the notes produced ; and the well-known singer Garcia believed he observed with the laryngoscope the vocal processes so tightly pressed together as to impede the vibration of the posterior part of the cords, and by this means they could be voluntarily shortened. 3. Intensity or loudness of the voice depends on the strength of the current of air. The more powerful the air blast the greater the amplitude of the vibrations, and hence the greater the sound produced. The narrower the chink of the glottis, and the tighter the parallel cords are stretched, the less is the amount of air and the weaker is the blast required to set them vibrating ; and vice versa, the looser the cords and the wider apart they are, the greater the volume and the force of the air current necessary for their complete vibration. Hence it is that an intense vibration or loud note can be produced much more easily with notes of a high pitch than with very low notes, and we find singers choosing for their telling crescendo some note high up in the range of their voice. The human voice, including every kind, extends over about three and a half octaves. -Of this wide range a single individual can seldom sing more than two octaves. The soprano, alto, tenor, and bass forming a descending series, the range of each one of which considerably overlaps the next in the scale. Durin'g the ordinary vocal sounds, the air, both in the resonat- ing tubes above the larynx and in the windpipe coming from below, is set vibrating, so that the trachea and bronchi act as resonators as well as the pharynx, mouth, etc. This may be recognized by placing the hand on the thorax, when a distinct vibration is communicated from the chest wall. Such tones are, therefore, spoken of as chest notes. Besides the chest tones of the ordinary voice, we can produce notes of a higher pitch and a different quality, which are called head notes, since their produc- tion is not accompanied by any vibration of the chest wall. The physical contrivance by means of which this falsetto voice is NERVOUS MECHANISM OF THE VOICE. 493 brought about is not very clearly made out. The following are the more probable views : (i) It has been suggested that in falsetto only the thin edges of the cord vibrate, the internal thyro-arytenoid muscles keeping the base of the cord fixed ; while with chest tones a greater surface of the cord is brought into play. (2) The cords are said to be wider apart in falsetto than in chest notes, and hence the trachea, etc., ceases to act as a resonator. (3) Or the cords may be arranged so that only one part of them, the anterior, can vibrate, and thus they act as shortened cords, a " stop " being placed on the point where the vibrations cease, by the internal thyro-arytenoid muscle. The production of a falsetto voice is distinctly voluntary, and is probably dependent upon some muscular action in immediate relation to the cords, for it is always associated with a sensation of muscular exertion in the larynx, as well as with changes that take place in the conformation of the mouth and other resonat- ing tubes. NERVOUS MECHANISM OF VOICE. The nervous mechanism, by means of which vocal sounds are produced, is among the most complexly coordinated actions that regulate muscular movements. Like respiration, vocalization at first seems a simple voluntary act, sounds of various kinds being produced at will by the indi- vidual. No doubt the respiratory muscles, which work the bel- lows of the voice organ, are under the control of the will so long as the respiration is not interfered with. The mouth and throat muscles, which shape the resonating tube, are also voluntary. But the intrinsic muscles of the larynx are only voluntary in a certain sense, while in another they are distinctly involuntary, as may be seen in spasm of the larynx ; for they are, in part at least, controlled by impulses which arise at the organ of hearing and pass to some coordinating centre, which arranges the finer muscular movements necessary to produce a certain note. When we sing a note just struck on a musical instrument, we set the expiratory, the mouth, and the special vocalizing muscles in readiness, by a voluntary act, for the proper application of the air blast ; but the exact tuning of the vocal cords is accomplished, 494 MANUAL OF PHYSIOLOGY. in some measure at least, reflexly by impulses arriving from the ear at a special coordinating nervous centre, the education of which is in advance of that of the voluntary centres, and, there- fore, can only be controlled by the latter in persons specially educated in singing. Some persons who can sing a given note with promptness and exactitude, without any effort, would find much difficulty in overcoming, by volition, the accuracy of this perfect reflex mechanism. In fact, a person with a naturally " good ear " finds it difficult to sing out of tune, even if he try. Though we feel that we have command over the pitch of the sounds produced in the larynx, we ow r e much of our accuracy to the aid given by our sound-appreciating organs and the nerve centres in connection with them. SPEECH. The variations in vocal sounds which give rise to speech are not produced in the larynx, but in the throat, mouth and nose. When unaccompanied by any vocal sound, speech only gives rise to a whisper ; but when a vocal tone is at the same time produced, we have the ordinary loud speaking. Since vocal tones can only be produced by expiration, so we can only speak aloud by means of an expiratory current of air ; but an inspiratory current may be made to give rise to a kind of whisper. Speech is composed of two kinds of sounds, in one of which the sounds must be accompanied by a vocal tone, and are, hence, called "vowels; " in the other no vocal tone is necessary, but changes in shape take place in the resonating chambers, so as to give rise to noises called consonants. As the pronunciation of the consonants is always accompanied by some vowel sound, and as the difference between the vowels is brought about by changes in the shape of the mouth, the distinction between the two sets of sounds is rather artificial than real. The production of the different vowel sounds depends upon such a change being brought about in the shape of the mouth cavity and aperture, that a resonator, with a different individual note, is formed for each particular word. The sounds called consonants are caused by some check or SPEECH. 495 impediment being placed in the course of the blast of air issuing from the air passages. They maybe classified, according to the part at which the obstruction occurs, as follows : 1. Labials, when the narrowing takes place at the lips, as in pronouncing b, p,f, v. 2. Dentals, when the tongue causes the obstruction by being pushed against the hard palate or the teeth, as in /, d, s, I. 3. Gutturals, when the posterior part of the tongue moves toward the soft palate or pharynx, as in saying k, g, gh, ch, r, Consonants may also be divided into different groups, accord- ing to the kind of movements which give rise to them. 1. Explosives are produced by the sudden removal of the obstruction, as with p, d, k. 2. Aspirates are continuous sounds caused by the passage of a current of air through a narrow opening, which may be at the lips, as in/, at the teeth as with s, or at the throat as in ch. 3. Resonants are the sounds requiring some resonance of the vocal cords, and the air current is suddenly checked by closure of the lips, as in ;//, or the dental aperture as in n or ng. 4. Vibratory, of which r is the example, requires a peculiar vibration of the vocal cords, while either the dental or the gut- tural aperture is partially closed. 49^ MANUAL OF PHYSIOLOGY. CHAPTER XXVIII. GENERAL PHYSIOLOGY OF THE NERVOUS SYSTEM. ANATOMICAL SKETCH. The nervous system includes the various mechanisms by which the distant parts of the body are kept in functional relationship with one another. By it the condition of the surroundings and the various parts of the body are communicated to a central department (cerebro-spinal axis) which in turn regulates and controls the activities of the various organs. It is made up of two varieties of tissue, both of which pos- sess special vital properties. The one, nerve fibres, composed of thread-like strands of protoplasm, connects the elements of the other, nerve corpuscles, which form the peripheral or central ter- minals of the fibres. Nerve fibres are simply special conducting agents, having at one extremity a special terminal, or nerve cell, for sending impulses, and at the other end a nerve cell for receiving the impulses. These terminal organs, between which the nerve fibres pass, are the agents which determine the direc- tion in which the impulse is to travel along the nerve. The sending organ may be at the peripheral end of the nerve, and the receiver in the nerve centres, as in the case of an ordi- nary cutaneous nerve, which carries impulses from the skin to the brain ; or the sending organ may be at the centre, and the receiving organ at the periphery, as in the case of the nerves conveying impulses from the brain to the muscles. The former kind of nerves are called afferent, carrying cen- tripetal impulses, and the latter efferent, carrying centrifugal im- pulses. Nerves are capable of carrying impulses in either direc- tion, as has been proved by cutting the afferent lingual and the efferent hypoglossal nerves, and causing the proximal end of the former to unite with the distal end of the latter, which is dis- tributed to the muscles of the tongue. When the union has taken place, a stimulus applied to the upper part which was nor- NERVOUS TISSUES. 497 mally afferent, or sensory, carries motor impulses to the muscles, /. ) Excito-reflex nerves communicate impulses to central nerve elements, and give rise to some action, without exciting mental perception. Such nerves regulate the viscera. According to the result of the excitation arising from their impulse, they are termed excito-motor, excito-secretory, and excito-inhibitory, etc. (c) Mixed 'nerves act as sensory and reflex nerves ; these are the most numerous, the sensory or reflex action depending upon the condition of the nerve centres. II. EFFERENT NERVES, which carry impulses from the centres to the various organs throughout the body. According to the effect produced by their excitation, they are termed : MODE OF INVESTIGATION. 499 (a) Motor, conveying impulses to muscles and exciting them to contract. (jf) Secretory, the stimulation of which calls forth the activity of a gland. (f) Inhibitory, when they check or prevent some activity by the impulses which they carry. (<5) Vasomotor nerves, which regulate the contraction of the muscular coat of the blood vessels. (e) Trophic, thermic, electric nerves are also to be named, the two former being of doubtful existence, and the latter being only found in those animals which are capable of emitting electric discharges, such as electric fishes. III. INTERCENTRAL NERVES act as bonds of union between the several ganglion cells of the nervous centres, which are con- nected, in a most elaborate manner, one with the other. The terminals of these fibres are possibly both receiving and direct- ing agents, and the delicate strands of protoplasm communi- cating between them probably convey impulses in different directions, but of this we can have no definite knowledge, although such a supposition would aid us in forming a mental picture of the manner in which the wonderfully complete inter- central communications are accomplished. MODE OF INVESTIGATION. In order to understand the functions of the different nerves a knowledge of their central connections and their peripheral dis- tribution is necessary. But anatomical research, unaided by ex- perimental inquiry, does not suffice to determine their function. The procedure adopted in testing the function of a nerve is the following : The nerve is exposed and cut, and it is observed whether there be any loss of sensation or muscular paralysis in the part to which it passes. The end connected with the centres is spoken of as the central or proximal end, and that leading to the distribution of the nerve is called the peripheral or distal end. Each of these cut ends is then stimulated, and the results are observed. If the nerve be purely motor, stimulation of the proximal end will yield no result, but when the distal end is 500 MANUAL OF PHYSIOLOGY. irritated, movements follow. If, on the other hand, it be a sen- sory nerve, stimulation of the distal end gives no result, and that of the proximal end produces signs of pain. CHEMISTRY OF NERVE FIBRES. The axis cylinder of nerves is probably composed, as already mentioned, of protoplasm; further than that nothing is known of its chemical properties. The medullary sheath yields certain substances which are related to the fats, and can be extracted with ether and chloroform. Among these is the peculiar com- pound nitrogenous fat, lecithin, containing phosphorus, also cholesterin, cerebin, and kreatin. ELECTRIC PROPERTIES OF NERVES. Like muscle, nerves may be regarded as having a state of rest and a state of activity, but the two states are not obvious in the same striking way as they are in muscle, nor do we know much of the physical properties of nerve. While at rest, however, it shows electric phenomena similar to those which have already been described as belonging to muscle tissue. These electrical currents are contemporaneous with the life of the nerve, and they undergo the same variation as occurs in muscle when the nerve passes into the active state ; that is, when it transmits an impulse. The so-called natural current of nerve is practically the same as that of muscle, passing in the nerve to the central part from the cut extremities of the fibre ; that is to say, the current passes through the galvanometer from the electrode leading from the mid- dle of the nerve, to that applied to the extremity. The electro- motive force of a small nerve is much less than that of a muscle. In a frog's sciatic it has been estimated to be 0.02 of a Daniell cell. The natural current of the frog's nerve is said to increase in intensity in proportion to the increase in temperature up to about 20 C., after which it decreases. Experiments on nerve currents must be carried on with all the precautions mentioned in speaking of muscle currents, and with the non-polarizable electrodes there figured (page 448). NERVE STIMULI. 50! THE ACTIVE STATE OF NERVE FIBRES. Nerves pass into a state of activity in response to a variety of stimuli, but their active condition cannot be readily recognized, because the only change we can detect in the nerve is that which takes place in the electric state. If it be connected with its terminals, we learn when a nerve is carrying an impulse from the results occurring in them on stimulation. In the case of an afferent nerve, we get evidence of a sensation, and when the nerve is efferent, for example, bearing impulses from the centres to the muscles, we judge of the state of activity of the nerve by the muscle contraction. For experimental purposes we use the nerve and the muscle of a frog. This nerve-muscle preparation is made from the leg of a frog : the sciatic nerve is carefully prepared from the thigh and abdominal cavity without being dragged or squeezed, and the gastrocnemius is separated from all its attachments except that to the femur, about two-thirds of which bone is left, so that the preparation may be fixed in the clamp. In fact, the method used for the direct stimulation of muscle is also employed for the study of the excitability of nerve fibres. NERVE STIMULI. Besides the normal physiological impulse which comes from the cells in connection with the nerve fibres, a variety of stimuli may excite their active state. These nerve stimuli differ little from those which are found to affect muscle, when applied directly to that tissue. They may be enumerated as follows : 1. Mechanical Stimulation. Almost any mechanical impulse, applied to any part of a nerve, causes its excitation. The stimulus must have a certain degree of intensity, and definite, though it may be of very short duration. If mechanical stimuli be fre- quently applied to a nerve in the same place, the irritability of the part is soon destroyed ; but if fresh parts of the nerves be stimulated, at each application the nerve passes into a state of tetanus, as shown by the contraction of the muscle to which it is supplied. 2. Chemical Stimulation. Loss of water by the tissue of the nerve, whether this be caused by evaporation, or facilitated with 502 MANUAL OF PHYSIOLOGY. blotting paper, exposure over sulphuric acid, or the addition of solutions of high density, such as syrup, glycerine, or strong salt solution. The application of strong metallic salts or acids ; or alcohol and ether, also a solution of bile irritates nerves ; weak alkalies, except ammonia, which has no effect on nerve, although it acts on muscle when applied directly to that tissue. 3. Thermic stimulation occurs when sudden changes are brought about, approaching either of the extreme temperatures at which the nerve can act ; /. C Diagram of lens viewed from the side at different periods of life, a, At birth ; b, Adult; c, Old age. (Allen Thomson.} with the vitreous humor, may be said to be enclosed in the hya- loid membrane, which, in front, is thickened and attached to the ciliary part of the choroid and the capsule. Thus, any tension exercised by the suspensory ligament tends to tighten the ante- FIG. 219. Showing early stages of the development of the lens, c, Epithelial tissue about to form the lens ; o, Optic cup ; a, Epidermis. (Cadiat.) rior part of the capsule and flatten the anterior surface of the lens. The shape of the lens varies at different times of life, being nearly spherical in the infant and tending to become less convex in old age (Fig. 218). The lens is developed from the outer 562 MANUAL OF PHYSIOLOGY. layer of the embryo by the gradual thickening and growing inward of the epithelium, which meets the optic cup, and after a time is cut off from the parent tissue. The stages of its develop- ment may be followed in the preceding wood-cuts (Fig. 219). The lens is composed of a number of peculiar band-like cells, derived from the epithelium. These are cemented together in FlG. 220. A further stage of the development of the lens. (Cadiat.) a, Elongating epithelial cells forming lens ; b, Capsules ; c, Cutaneous tissue becoming con- junctiva; d, e, Two layers of optic cup forming retina ; f, Cell of mucous tissue of the vitreous humor ; g, Intercellular substance ; h., Developing optic nerve. parallel rows, eccentrically arranged in layers. These bands are hexagonal in transverse section, and in the younger periods of life may be seen to contain nuclei. In the living state the lens is perfectly transparent, but after death it becomes slightly opaque. The nutriment for the adult lens is derived from the vessels of the choroid, which, however, THE DIOPTRIC MEDIA OF THE EYEBALL. 563 do not come into direct communication with its texture. On this account the nutrition of the lens is not so perfect as that of many other tissues, and is but imperfectly repaired after injury, FIG. 221. Fragment of lens teazed out to show the separate fibres. (Cadiat.~) a, b, and c show fibres with different sized nuclei. which always leaves more or less opacity. Even without injury, opacity, giving rise to cataract, sometimes occurs during life. 5 6 4 MANUAL OF PHYSIOLOGY. Chemically, the lens is made up of globulin, and furnishes a ready source for obtaining this form of albumin for examination. DIOPTRICS OF THE EYE. Light travels through any even transparent body, such as the atmosphere, in a straight line. But when it meets any change in density, particularly when it has to pass obliquely into a FlG. 222. Diagram showing the course of parallel rays of light from A in their passage through a biconvex lens L, in which they are so refracted as to bend toward and come to a focus at a point F. denser medium, the ray is bent so as to run in a direction more perpendicular to the surface of the denser body. The degree of bending or refraction of the rays depends on the difference in optical density of the two media and the angle at which the ray strikes the surface of the more dense. On its way to the sensitive retina, the light has to pass FIG. 223. Diagram showing the course of diverging rays, which are bent to a point further from the lens than the parallel rays in last figure. through the various transparent media just named, viz., the cornea, the aqueous humor, the crystalline lens, and the vitreous humor. On entering these media, which have different densities, the rays of light emitted by any luminous body become bent or refracted, so that they are brought to a focus on the retina, just MEDIA AND REFRACTING SURFACES. 565 in the same way as parallel rays of light from the sun may be focused on a near object by means of an ordinary convex lens. Only so much light reaches the fundus of the eye as can pass through the opening in the iris, so that a comparatively narrow and varying beam is admitted to the chamber in which the nerve endings are spread out for its reception. If we hold a biconvex lens at a certain distance from the eye and look out of the window through it, we see an inverted image of the landscape. If we place a piece of transparent paper behind the lens, we can throw a representation of the picture on it, which will be seen to be inverted. This power of convex lenses is employed in the instrument used for taking photographs, called a camera, which consists of a box or chamber into which the light is allowed to pass through a convex lens, so that an inverted image of the objects before it is thrown upon a screen of ground glass within the box. When the sensitive plate re- places the screen, the light coming through the lens makes a photograph. Just in the same way an inverted image of the things we look at is thrown on the retina by the refracting media of the eye. This may be seen in a dark room, if a candle be placed at a^ suitable distance in front of the cornea of an eye taken from a recently killed white rabbit. When cleared of fat and other opaque tissues, the sclerotic is transparent enough to act as a screen upon which the inverted candle flame can be recognized. Though our organ of vision is often compared to a camera obscura, the refractions of light which occur in it are far more complex than those taking place in that simple instrument. In the latter we have only two media the glass lens and the air ; in the eye, on the other hand, we have several, which are known to have a distinct refractive influence on the rays which pass through the pupil. THREE MEDIA AND REFRACTING SURFACES. Since the surfaces of the cornea, however, are practically parallel, we may neglect the difference between it and the aqueous humor, and look upon the two as one medium, having 566 MANUAL OF PHYSIOLOGY. in front the shape of the anterior surface of the cornea, and be- hind, the anterior surface of the lens, so as to form a concavo- convex lens. We thus have only three media to consider, viz., (1) the aqueous humor and cornea; (2) the lens and its capsule ; and (3) the vitreous humor. And only three refracting surfaces need be enumerated, viz., (i) the anterior surface of the cornea; (2) the anterior surface of the lens ; and (3) the posterior surface of the lens. These refracting surfaces may all be looked upon as portions of spheres whose centres lie in the same right line, and hence may be said to have a common axis. The eye may be regarded as an optical system, centred round an axis which passes through FIG. 224. Showing the course of the rays of light rom two luminous points to the retina. The rays etc., are collected :omes the upper. from the point a. on passing through the cornea, lens, etc., are collected on the retina at b. Those from a' meet at b' , and thus the lower point becom< the middle point of the cornea in front, and the central depres- sion (fovea centralis) of the retina behind. This is spoken of as the optic axis of the eye. The rays of light entering the eye are most strongly refracted at the surface of the cornea, because they have to pass from the rare medium, the air, to the denser cornea and aqueous humor. So also more bending of the rays occurs between the aqueous humor and the anterior surface of the lens than between the pos- terior surface of the lens and the vitreous humor. The lens is not of the same density throughout, but denser in the centre, and being made up of layers, the central part refracts more than the outer layers. MEDIA AND REFRACTING SURFACES. 567 The manner in which the inversion of the image is produced by a convex lens is shown in the preceding figure, in which the lines correspond to the rays passing from two points through the lens. If the arrow a a' be taken for the object, from either extremity of it rays pass through, and are more or less bent by the lens. It will be sufficient to follow the course of three rays from the head of the arrow. One of these passes through the centre of the lens, and leaves it in the same direction which it entered, because the two surfaces at the points where it entered and left may be re- garded as parallel, and so cause no refraction. The rays which do not pass through the centre are bent on entering and on leaving the lens, so that they all meet at the same point and there pro- duce an image of the head of the arrow, at b' . In the same way the feather end of the arrow is produced at b ; the position of the image of the object is thus reversed by the light rays passing through the lens. In a biconvex lens, with two surfaces of the same degree of convexity, the central point through which the rays pass without being refracted is easily made out, as it is the geometrical centre of the lens. This central point is spoken of as the optical centre. With systems of lenses of varying convexity, and more than one in number, as we have in the eye, where the rays of light are bent at different surfaces, it is much more difficult to determine the optical centre. However, by means of the measurements made by Listing, two points close together are known, which may be said to correspond practically with the optical centres of the eye; they lie in the lens, between its centre and posterior surface. The path of the various rays may thus be exactly made out.* The rays which come from a distant luminous point and fall upon the eye, are refracted by the cornea and aqueous humor, so as to be made convergent on their way to the lens ; they are then * The impossibility of making clear the important relationships, such as nodal points, and other constants of the eye in a short text-book, and the deterrent effect exerted upon the mind of a junior student by brief incomprehensible statements, have induced the author to omit this part of the subject. He must refer those who are anxious to learn the cardinal points of the eye, to the more advanced text-books. 568 MANUAL OF PHYSIOLOGY. further bent at the surfaces of the lens, so that they are brought exactly to a point on the retina. That is to say, for distant luminous points, the retina lies exactly in the plane of focus of the dioptric media of the normal eye. This convergence of the rays to a point on the retina, is the first essential for seeing clear and distinct images ; for if the rays from each point of a luminous body were not united on the retina as points, the effects of the different rays from the various points of a body would become mixed, and there would be loss of defi- nition of its image. The rays from any bright point which enter the eye through the pupil may be imagined to form a luminous cone, the point of which lies at the retina, and its base at the pupil. After their union at the point of the cone, the rays would diverge again if the retina were not there to receive them. SCHEINER'S EXPERIMENT. It may be seen from the foregoing figure that if the retina, which normally would lie at 2, were placed nearer the dioptric apparatus, say at i, or further from it, at 3, it would not meet the exact point of the luminous cone, but would receive the rays either before they came to a point, or after they had diverged from it. Thus indistinct rings of light would be seen instead of one luminous point, and an image would be blurred and indefinite. From this it follows that the eye, when quite passive, can only get an exact image of bodies which are placed at a certain dis- tance from it, just as, for any given state of a camera, only those bodies in one plane come into focus and give a clear picture on the screen. If the dioptric apparatus of the eye were rigid and unalterable, since the relation of the retina to it is permanently the same, we could only see those objects clearly which are at a given distance from the eye. We know, however, that we see as distinct an image of distant as of near objects, and we can look through the window at a distant tree, or can adjust our eyes so as to see a fly walking on the window pane. We cannot see both distinctly at the same moment. This power of focusing may SCHEINER S EXPERIMENT. 5 6 9 FIG. 225. To illustrate Schemer's experiment ; for ex- planation, see text. be demonstrated by what is known as Scheiner's experiment, which is carried out in the following way. Two pin holes are made in a card at a distance from each other not wider than the diam- eter of the pupil. The card is then brought close to the eye, so that a small object such as the head of a bright pin can be seen through the holes. The dioptric media being fixed, moving the object nearer to or further from the eye would have the same effect as changing the relation of the retina to m n or p q in Fig. 225, by means of which we may explain the following observa- tions : (i) The eye being fixed upon the object (of which only one image is seen), move the pin rapidly away ; two objects now appear, showing that the rays coming through the holes have met before they reach the retina, as at p q. (2) Move the pin near the eye ; again two very blurred objects are seen, for the rays have not met when they strike the retina, as at m n. (3) Keep- ing the object in the same position, alter the gaze, as if to look first at distant and then at near objects ; in both extremes two images are seen. (4) When the object is in exact focus, as at near limit is about 12 cm. or 5 inches, but it varies in different individuals. For objects that are over 10 metres distance, very little change in the eye is required to see each distinctly, and the nearer the object approaches, the more frequently the adjustment of the eye has to be altered to see it clearly. When the eye is focused for any point within the limits of distinct vision, a certain range of objects at different distances from the eye can be recognized without moving the adjustment. The range of this power is measured on the line of vision, and called the focal depth. In the distance we can take in a great depth of landscape, without effort or fatigue ; but when looking at near objects the focal depth is less, and we must constantly accommodate our eyes afresh in order to see clearly objects at slightly different distances because of the shallowness of the focal depth in the nearer parts of visual distance. The method by which the accommodation of the eye is effected differs from anything that can be applied to an artificial optical instrument, and is more perfect. The following alterations are observed to occur in the eye during active accommodation, /. e., when looking at near objects : (i) The iris contracts so that the pupil becomes smaller; (2) the central part of the anterior surface of the crystalline lens moves slightly forward, pushing before it the pupillary margin of the iris, so that the lens becomes more convex ; (3) the posterior MECHANISM OF ACCOMMPDATION. 571 surface of the lens also becomes more convex, owing to the general change of shape of the lens, but the centre of this surface does not change its position ; (4) both eyes converge. These changes can be seen in the accompanying diagram, showing a section of the lens, cornea and ciliary region (Fig. 226), in the left-hand side of which the lens is drawn in the position it assumes when accommodated for near objects. These movements can be seen in life by observing the changes in rela- tive positions, etc., of the reflections of a candle flame thrown from the cornea and the two surfaces of the lens. On the cor- nea is seen a bright upright flame : next comes a large diffused reflection from the anterior surface of the lens, and at the other Diagram showing the changes in the lens during accommodation. The muscle on the right is supposed to be passive as in looking at distant objects, the ligament (L), is, therefore, tight, and compresses the anterior surface of the lens (A) so as to flatten it. On the left the ciliary muscle (M) is contracting so as to relax-the ligament, which allows the lens to be- come more convex. This contraction occurs when looking at near objects. side of this a small, inverted image of the flame reflected from the posterior surface of the lens. When the adjustment is changed by looking from a far to a near object, the image on the front of the lens becomes smaller and moves toward the centre of the pupil. The image on the back of the lens also becomes smaller, but does not change its position. The amount of movement has been accurately measured by a special instru- ment called an ophthalmometfr. The motions can be more exactly studied by means of the phakoscope, a dark box, in which prisms are placed before the observed eye, and each image is made double. The change in relative position of the two is more readily recognized than a mere change of size of the one. 572 MANUAL OF PHYSIOLOGY. Muscular Mechanism of Accommodation. The alteration in the shape of the lens is accomplished by the action of the muscular layer, already named, which radiates from the edge of the cornea to the ciliary region of the choroid coat, where it is attached. When the ciliary muscle contracts, it draws the choroid coat and the connections of the suspensory ligament of the lens slightly forward, the junction of the cornea and sclerotic being its fixed point. Under ordinary circumstances, the eye being at rest, the suspensory ligament is tense and exerts a radial traction on the anterior part of the capsule of the lens, tending to stretch it flat ; this affects the shape of the soft lens and reduces its convexity. When the ciliary muscle shortens, it draws forward the attach- ment of the suspensory ligament, relaxes it, and removes the ten- sion of the capsule, so that the unconstrained elastic lens bulges into its natural form. The posterior surface cannot extend back- ward, because there it is in contact with the vitreous humor, which is held more firmly against it by the increased tension of the hyaloid membrane during the contraction of the ciliary muscle. Some circular muscular fibres help to relax the ligament and relieve it from the increased pressure which the contraction of the radiating fibres must indirectly cause on the vitreous humor. The act of accommodation is a voluntary one, the nerve bear- ing the impulse to the ciliary "and iris muscles, coming from the 3d nerve by the ciliary branches of the lenticular ganglion. The local application of the alkaloid of the belladonna plant (atropin) causes paralysis of the ciliary muscle and wide dilatation of the pupil ; and the alkaloid of the Calabar bean (physostigmin) produces contraction of the muscle of accommodation and extreme contraction of the pupil. DEFECTS OF ACCOMMODATION. Myopia. It has been said thatthe "near limit" of distinct vision differs in many persons from the twelve centimeters of the normal emmetropic eye, and it is found that the power of accom- modation varies very much in different individuals. Thus, in "short-sighted" people, who have myopic eyes, /. vr^:Afj(iitf ^&Mr&V^V^ IK impl? 5 ^i^R%?? ^V^wnfif^v \i ^?*** . Jf*: * . v* I' 1 L ^i r-^i ^ n"!" &1WK ji*^ !j n I Peripheral. 2 Small angular cells. .3 Pyramidal cells. 4 Granular stratum. 5 Ganglionic cells. G Spindle cells. Section through the cor- tex of temporal lobe of monkey, showing the series of layers of nervous cells with dif- ferent characters. 656 MANUAL OF PHYSIOLOGY. both sensory and motor, defects have been observed in the patients. We must remember that the occurrence of motion as the result of stimulation, or the absence of muscular power as the result of destruction of the optic thalami, must not be accepted as good evidence of the motor function of the nerve cells of this part, because these results may depend on the indirect influence of the sensory impulses coming from these cells. CEREBRAL HEMISPHERES. It is now universally regarded as a recognized fact that the hemispheres of the brain are the seat of the mental faculties FIG. 258. Upper surface of the hemispheres of monkey, showing details of motor areas. References as in next figure, (ferrier.) perception, memory, thought and volition. The cerebral cortex is the part of the nervous system in which the subjective percep- tion of the various sensory impulses takes place, and in which CEREBRAL HEMISPHERES. 657 impulses are converted into impressions or mental operations. It is in the cortical nerve cells that the so-called voluntary impulses, causing movement of the skeletal muscles, have their origin. It is thus a sensory and a motor organ. But it has a far wider range of function than is expressed by saying it is both sensory and motor. Thus restricted, its function would be no higher than FIG. 259. Left hemisphere of monkey, showing details of motor areas indicated by the movements following stimulation of, 1. Superior parietal lobule ; exciting advance of the hind limb. 2. Top of ascending frontal and parietal convolutions ; flexion and outward rotation of thigh ; flexion of toes. 3. On ascending frontal convolution near semi-lunar sulcus ; movements of hind limb, tail and extremity of trunk. 4. On adjacent margins of ascending frontal and parietal convolution ; adduction and extension of arm, pronation of hand. 5. Top of ascending frontal near superior frontal convolution; forward extension of arm. a, b, c, d, On ascending parietal ; movements of various muscles of the fore-arm. 6. Ascending frontal convolution; flexion of fore-arm and supination of hand which is brought toward mouth. 7. Retraction and elevation of corner of mouth. 8. Elevation of nose and lip. 9 and 10. Opening mouth and motions of tongue. 11. Retraction of angle of mouth. 12. Middle and superior frontal convolutions ; movements of head and eyelids. 13 and 13'. Anterior and posterior limbs of angular gyms ; movements of eyeballs. 14. Superior temporo-sphenoidal convolution, ear pricked and head moved. 15. Movement of lip and nostril. (Ferrier.) that of the nerve centres in the spinal cord, etc. The cells of the cortex of the brain seem to differ from those of the lower nerve centres, which can only receive, and at once send out corres- ponding impulses, in this : when an impulse arrives at certain cerebral cells, it there excites a change, which, besides producing 658 MANUAL OF PHYSIOLOGY. an immediate effect, leaves a more or less permanent impression. The impression persisting, if the cell be well- supplied with chemical energy in the shape of nutriment, it may be reproduced at a subsequent period. This revival of impressions, the effects of past stimulations, or "recollection," is exclusively the prop- erty of the cerebral cortex, and to it the hemispheres owe their mental faculties. During our lifetime sensory impulses are con- tinually streaming into the cells of the cortex of the brain from the peripheral sensory organs. Thus innumerable impressions are stored up in. the nerve cells. The effect of the continuing FIG. 260. Dark shading indicates the extent of a lesion of the gray matter of the right hemisphere of a monkey followed by complete motor paralysis of the limbs of the opposite side with- out impairment of sensation. (Ferrier.} c, Fissure of Rolando ; T:'-X// ^ ^3tX^- ^^>- . Wolffian duct. ug. Urogenital sinus. cp. Clitoris, or penis, z. Intestine, cl. Cloaca. Is. Part from which the scrotum or the labia majora are developed, ot. Origin of the ovary or testicle respectively, .r. Part of Wolffian body subsequently developed into the coni vasculosi. to the splanchnopleure, and partly from the mesoblast surrounding the Wolffian body. The germinal epithelium, the cells of which are not so well developed as in the female, sends processes into the mesoblast, and these are said to form the spermatic cells, the mesoblast becoming differentiated around them to form the walls of the tubuli semi ni fen. yo6 MANUAL OF PHYSIOLOGY. The Wolffian duct, which persists as the vas deferens, aids in forming the testicle, the epididymis being merely a convoluted part of it, and the vas aberrans one of the caecal tubes in con- nection with the duct. The coni vasculosi are thought to be formed from some of the tubules of the Wolffian body ; they are connected to the testicle by means of a tube which is split up into a number of divisions forming the vasa efferentia. FIG. 298. Diagram of the sexual organs of the male embryo. (Allen Thomson. 3. Ureter. 4. Bladder. 5. Urachus. t. Testicle, m. Atrophied duct of Miiller (hydatid of Morgagni). e. Epididymis. g. Gubernaculum testis. as. Vesicula seminalis. i. In- testine. pr. Prostate. IV. Organ of Giraldes. vh. Vas aberrans. vd. Vas deferens. C. Cowper's gland, cp. Penis, sp. Spongy part of the Urethra, t'. Position the testicle . . , ultimately assumes, s. Scrotum. The Wolffian duct forms, beside the vas deferens, the vesicula seminalis (which is merely a blind diverticulum from its ex- tremity), and terminates in the ejaculatory duct. The two Miillerian ducts, in the male, join and form a single tube ; this is not further developed, but atrophies, leaving as its representative the sinus pocularis, which is situated in the floor THE MULLERIAN DUCT. 707 of the prostate. The upper extremities of the Mullerian ducts form the hydatids of Morgagni. The ovary, like the testicle, is formed from the germinal epi- thelium, which multiplies and forms a projection close to the Wolffian body. The cells of the epithelium become involuted and surrounded by the uncleft mesoblast, to form ova and Graafian follicles. The glandular part of the ovary thus arises from the germinal epithelium, and its stroma springs from the mesoblast in the neighborhood of the Wolffian body. FIG. 299. Diagram of the sexual organs of a female embryo. (Allen Thomson.) f. Fimbriated extremity of the left Fallopian tube. W. Remains of the Wolffian tubes, g. Round ligaments, o. Ovary, po. Parovarium. u. Uterus. dG. Remains of the Wolf- fian duct, or duct of Gaertner. m. Right Fallopian tube cut short. ?y. Right obliterated Wolffian duct. va. Vagina. 3. Ureter. 4. Bladder. 5. Urachus. h. Inferior opening of vagina. C. Gland of Bartholin. z/. Vulva, sc. Vascular bulb. cc. Clitoris, n. Nympha. /. Labium. i. Rectum. The ducts of Miiller are the precursors of the female genital passages. They approach one another and unite along a certain distance at their lower extremities. Of this united part, the upper end forms the uterus, and the lower the vagina, while the unimited parts of the Mullerian ducts form the Fallopian tubes, which become connected with the ovaries, while their cavities remain continuous with the pleuroperitoneal space. In the female, -the Wolffian duct and body atrophy, the paro- 708 MANUAL OF PHYSIOLOGY. varium being in the adult the representative of the Wolffian body. The bladder is merely a dilated portion of that part of the allantois which is in immediate connection with the alimentary canal, and the urachus is the narrowed part of the allantois connecting the bladder to the remainder of the allantois which is without the body walls of the foetus. While the alimentary canal is in connection with the allantois, the intestinal and genito-urinary passages open into a common cavity at their termination ; this is the cloaca, and it is in the further development of the embryo that a septum arises, dividing this into an alimentary or anal portion, and an anterior or urinary portion. The septum, dividing the urogenitary from the alimen- tary portion of the cloaca, forms, externally, the perinseum. At the aperture of the cloaca an eminence arises which de- velops into the penis in the male, the clitoris in the female. Around this eminence is a fold of integuments, which forms the labia in the female, the scrotum in the male. In the female this integumentary covering enlarges much more than the clitoris and covers it in, the urethral orifice opening just below the clitoris. In the male, the urethral orifice at first opens at the base of the penis, but eventually a groove is formed on the under surface of this organ, which becomes converted into a canal, and forms the urethra. BLOOD-VASCULAR SYSTEM. In the mammalian embryo this may be appropriately divided into two systems of different dates ; the first, or early circulation, which is confined to the yolk sac ; and the second, or later cir- culation, which passes through the placenta. - The Primitive Heart arises from the splanchnopleural layer of the mesoblast, just at the point where this forms the under wall of the fore part of the alimentary canal. When the formation of the folds of the embryo was described, it was stated that the groove of 'the cephalic fold tended to grow backward toward the tail end of the embryo. This groove is limited behind by the somatopleural layer of the mesoblast, and posteriorly to this is FIG. 300. Transverse section through the region of the heart of a rabbit's embryo of nine days old. (Kolliker.) jj. Jugular veins, ao. Aorta, ph. Fore -gut. bl. Blastoderm, hp. Body wall reflected in ect. ent. Hypoblast. e' . Prolongation of hypoblast between the two halves of the heart. ah. Outer wall of the heart. /. Cavity of the pericardium, ih. Inner lining of the heart. ect. Epiblast. df. Visceral mesoblast. FIG. 301. Diagrammatic views of the under surface of an embryo rabbit of nine days and three hours old, showing the development of the heart. (Allen Thomson.) A, View of entire embryo. B, an enlarged outline of the heart of A. C, a later stage of the development of B. hh. Ununited heart, aa. Aortae. W. Vitelline veins. 7io MANUAL OF PHYSIOLOGY. a cavity formed by the cleavage of the mesoblast, called the pleuroperitoneal cavity. In the early stages of development, the posterior wall of this small cavity is formed by the splanchno- pleural layer of the mesoblast. The heart arises at the point at which the splanchnopleure tends to travel forward to meet the uncleft mesoblast, and thus completes the pleuroperitoneal cavity. The heart consists at first of a single cylinder, which in the FIG. 302. FIG. 303. Human embryo of about three weeks. (Allen Thomson.} uv. Yolk sac. al. Allantois. am. Amnion. ae. Anterior extremity. pe. Posterior extremity. Development of the heart in the human embryo, from the fourth to the sixth week. A. Embryo of four weeks. (Kolliker after Coste.) B. Anterior, and C. posterior views of the heart of an embryo of six weeks. (Kolliker after Kcker.) a. Upper limit of buccal cavity, c. Buccal cavity, b. Lies between the ventral ends of the 2d and 3d branchial arches, d. Buds of upper limbs, e. Liver, f. Intestine, i. Supe- rior vena cava. i'. Left superior vena cava or connection between the left brachio-cepha- lic vein and the coronary vein. i". Opening of inferior vena cava. 2. 2.' Right and left auricles. 3. 3.' Right and left ventricles. 4. Aortic bulb. human embryo is probably formed by the coalescence of two primary tubes. At first it has no distinct cavity, but soon the cells of the mesoblast within the mass forming the heart become transformed into blood corpuscles, and thus it is hollowed out. A layer of endothelial cells line the cavity, and become the endocardium. The primitive heart is connected at its upper end with the DEVELOPMENT OF THE HEART. 711 two aortae, and at its lower end with the omphalo-mesenteric veins. After a time the tube shows signs of division into three parts ; the upper part becomes the aortic bulb, next to which is formed the cavity of the ventricle, continuous with which is the auricu- ffiB Diagram of the circulation of a chick at the end of the third day. (Foster and Balfour.} H. Heart. A A. Aortic arches (zd, 3d and 4th). Ao Dorsal aorta. L. of A., R. of A., Right and left omphalo-mesenteric arteries. S. T. Sinus terminalis. R. of., and L.of. Right and 1 ft omphalo-mesenteric veins. S. V. Sinus venosus. D. C. Duct of Cuvier. S. Ca. and V. Ca. Superior and inferior cardinal veins. lar space. The tube also, which at first lies in a straight line, now becomes twisted on itself, the auricular part becoming posterior and superior, while the ventricle, with the aortic bulb, remains anterior and somewhat below. 712 MANUAL OF PHYSIOLOGY. Each primitive cavity of the heart is divided into two by the gradual growth of partitions, and thus the four permanent heart cavities are developed. Externally a notch shows the division of the ventricle into right and left cavities, while from the inside of the right wall there grows a projection which subdivides the ventricle internally. This septum is, however, not at once complete at its upper part, a communication between the right and left sides of the heart remaining for some time above this partition. With the growth of the inter-ventricular septum, the external notch becomes less prominent, but is permanently recognizable as the inter-ventri- cular groove. In the auricles a fold develops from the anterior wall, which ultimately unites with a process of later development from the posterior wall. This septum is not complete during fcetal life, but is interrupted by an opening leading from one auricle to the other, called the foramen ovale. Simultaneously with the appearance of the posterior process of the septum, another fold arises, which is placed at the mouth of the inferior vena cava, and forms the Eustachian valve. The aortic bulb likewise, by a projection from the inner wall of the cavity, becomes divided into two canals, the anterior of which remains in continuity with the right ventricle, while the posterior is continuous with the left ventricle. The anterior thus becomes the pulmonary artery, and the posterior the permanent aorta. The primitive circiilations of a human embryo may be divided into two, which differ in their time of appearance and in the accessory organs to which they are distributed. Though they may, for the sake of clearness, be described as two independent circulations, they are not strictly so, as they exist for a short time coincidently, and arise in connection with one another from the same heart. (a) The earlier or vitelline circulation is that which is directed to the yolk sac, the embryo obtaining nourishment from the vitellus or yolk ; this is an organ of quite secondary importance in the mammalian embryo, and hence this circulation may be VITELLINE CIRCULATION. ^3 better studied in some such animal as the chick, which depends, throughout its embryonic life, on the vitellus for nourishment. In the human embryo the vitelline circulation is chiefly of im- portance for the few days immediately preceding the develop- ment of the placental circulation. The aortic bulb is continuous with two vessels which run on FIG. 305. Diagram of the vascular system of a human foetus. (Huxley.) //.Heart. T. A. Aortic trunk, c. Common carotid artery, c'. External carotid artery. c. Internal carotid artery, j. Subclavian artery v. Vertebral artery, i 2.3.4.5, Aortic arches. A . Dorsal aorta, i. Omphalo-mesenteric artery, dv. Vitelline duct, o' '. Om- phalo-mesenteric vein. v> '. Umbilical vesicle, vp Portal vein L. Liver, uu Umbilical arteries. u"u". Their endings in the placenta u' '. Umbilical vein. Dv. Ductus venosus 7>A. Hepatic vein. cv. Inferior vena cava. vil. Iliac veins, az. Vena azvgos. vc Pos- terior cardinal vein. DC. Duct of Cuvier. /'.Lungs. either side of the primitive pharynx ; these are the aort^e, and from each of them a large branch is given off. These omphalo- mesenteric arteries pass to the yolk sac, and' there become split up into a number of small vessels, the blood from them being returned partly by corresponding omphalo-mesenteric veins, partly by a large vein running round the periphery of the vas- 60 714 MANUAL OF PHYSIOLOGY. cular area known as the sinus terminalis. The sinus terminalis opens partly into the right and partly into the left omphalo- mesenteric veins, which subsequently unite into a common venous trunk, called the sinus venosus, which is continuous with the primitive auricle. This vitelline circulation in the human embryo persists but a short time. After the fifth or sixth week of foetal life it becomes obliterated, the yolk then being atrophied, and the placental cir- culation well developed. (<) The later or placental circulation is developed in the meso- blastic layer of the allantois, especially in that part which is in relation with the decidua serotina. The allantois, when fully developed, extends to the chorion, over which it spreads, sending in processes to occupy the villi. These chorionic villi are em- bedded in the decidua of the uterus, and are especially developed at the upper part, which is in connection with the decidua sero- tina or maternal placenta. The primitive aortae, which were at first two separate tubes, become united in the dorsal region of the embryo, so that the two aortic arches end in a single vessel, which extends to the middle of the embryo, and there divides into two branches, each of which gives off a vessel called the vitelline or omphalo- mesenteric artery. From the branches of the aortae arise two large vessels, which, running along the allantois, spread out over the chorion, being especially directed to the upper part of this membrane ; these are the umbilical or hypogastric arteries, which carry the blood from the aortse to the foetal placenta. Veins arise from the terminal networks of these arteries, and combine to form the two umbilical veins. ' The umbilical veins take a similar course to the arteries, and convey the blood to the venous trunk formed by the junction of the omphalo-mesenteric veins. After a time the right umbilical and right omphalo-mesenteric veins disappear, while from the trunk formed by the junction of the left umbilical and left omphalo-mesenteric veins, branches are given off to the liver (venc? advehentes}, and at a point THE ARTERIAL SYSTEM. 715 nearer the heart, vessels are received from the liver (pence revehentes}. To the part of the vessel intervening between the origin of the venae advehentes and the entrance of the venae revehentes is given the name of the ductus venosus. Thus it may be seen that in the placental circulation the blood is conveyed from the aorta, by the umbilical arteries, to the fcetal placenta, undergoes changes, owing to its close relation- FIG. 306. Diagram of the heart and principal arteries of the chick. (Allen Thomson.) B. and C. are later than A. i, i. Omphalo-mesenteric veins. 2. Auricle. 3. Ventricle. 4. Aortic bulb. 5, 5. Primi- tive aortae. 6, 6. Omphalo-mesenteric arteries. A. United Aorta. ship to the maternal blood. From the placenta it is returned by the umbilical vein, which sends a part through the liver and a part direct to the heart. The more minute details of fcetal circulation will be described later on. The Arterial System. Around the pharynx are developed five pairs of aortic arches. These commence anteriorly from the two primitive aortae, and, passing along the side of the pharynx, end in the aortae as they descend to become united in the dorsal 7 i6 MANUAL OF PHYSIOLOGY. FIG. 307. ci P 7 region of the embryo. The points of origin of the arches are termed their anterior roots, and the points of termination their posterior roots. Though all these arches do not exist at the same time, still, in describing the vessels which arise from them, they may be conveniently consid- ered together. On the right side the fifth arch disappears completely. On the left side the anterior root and neighboring part of the fifth arch are transformed into the pulmonary artery ; the remaining part of this arch continues as the ductus arteriosus, which connects the pulmonary artery with the permanent aorta. The fourth left arch, in mammalia, becomes the per- manent aorta. At the junc- tion of the fourth and fifth left posterior roots the left sub- clavian artery is given off. In birds the right fourth arch is transformed into the perma- nent aorta; and in examining the development of the aortic arch of the chick, it must be borne in mind that it is on the opposite side to that it occupies in man. On the right side the anterior root of the fourth arch, and the part of the aortic trunk leading to it, persist as the innominate artery, the fourth arch being represented by the right subclavian artery. The part of the primitive aortic trunk joining the fourth and Diagram of the aortic arches ; the permanent vessels arising from them are shaded darkly. (Allen Thomson, after Rathke.} I J 2 .34>5- Primitive aortic arches of right side. I, II, III, IV. Pharyngeal clefts of the left side, showing the relationship of the clefts to the aortic arches. A. Aorta. P. Pulmonary artery, d. Ductus arteriosus. a'. Left aortic root. a. Right aortic root. A'. Descending aorta, pn. pn> '. Right and left vagi. j. s'. Right and left subclavian arteries. i>. v' . Right and left vertebral arteries, c. Common carotid ar- teries, ce. External carotid, ci ci' . Right and left internal carotid. AORTIC ARCHES. 717 third right anterior roots becomes the common caro- tid artery of the same side, while arising from this is the internal carotid, which, taking the position of the third arch, passes to the posterior roots, and occupies the trunk of the primitive aorta from the third to the first arches. The external carotid, arising from the common carotid at the third an- terior root, occupies the position of the vessel join- ing this root to those of the second and first arch. On the left side the common carotid and its branches are developed similarly to those on the right, the only difference being that the common carotid arises from the aorta and not from the innominate. The iliac arteries are developed from the hypo- gastric. At first they ap- pear as branches, but with- the growth of the limbs they become so much larger that after birth they appear to be the main branches from the point of division of the Fi G . 3 o8. A. Plan of principal veins of the foetus of about four weeks old. B. Veins of the liver at an earlier period. C. Veins after the establishment of the placental circulation. D. Veins of the liver at the /. Primitive jugular veins, etc. Ducts of Cuvier. ca. Cardinal veins, ci. Inferior vena cava. /. Duc- tus venosus. u. Umbilical vein. p. Portal vein. o. Vitelline vein. cr. External iliac veins. 44 2 - of heart, 443. passive state of, 445. plasma, 66. properties of, 445. rate of contractions in insects, 464. Muscle, rheoscopic frog, 457. rigor mortis, 473. sarcolemma, 51, 444. single contraction, 461. stimulation of, 452. striated, 50, 443. summation, 467. tetanus, 468. tone, 470. tracings, 462. wave of contraction, 463. Muscles of deglutition, 115. of the eyeballs, 595. of the iris, 577. 75 2 INDEX. Muscles of the larynx, 326, 489. of mastication, 1 13. origin and insertion of, 477. of respiration, 333. the three orders of levers, 478. Muscular fibres of heart, 259. Muscularis mucosse, 183, 201. Myograph, pendulum, 461. spring, 461. Myopia, 572. Myosin, 69. NASAL ganglion, 528. Native albumins, 68. Nausea, 548. Nerve, 496, 519. III, motor oculi nerve, 522. IV, trochlear nerve, 523. V, trigeminus, or trifacial nerve, 525. VI, abductor nerve of the eye, 523- VII, (portio dura) motor nerve of the face, 524. VIII, vagus, 530. VIII, glosso-pharyngeal nerve, 529- VIII, spinal accessory nerve, 529- IX, hypoglossal nerve, 532. active state of, 501. anode, 503. ascending current, 512. axis cylinder, 49, 498. Auerbach's plexus, 127. breaking shock, 502. breaking tetanus (Ritters' te- tanus,) 502. cathode, 503. ciliary ganglion, 528. descending current, 512. electric change in, 506. electrical properties of, 500. electrotonus, 507. ganglion cells, 49, 521. irritability of nerve fibres, 508 law of contraction, 511. making shock, 503. mechanism of heart, 277. medullary sheath, 49, 498. medullated fibres, 47, 497. Nerve cells, 49. functions of, 515. in spinal cord, 616. endings, 47, 513. in the ear, 608. in the eye, 585: in nose, 553. in the skin, 538. in tongue, 552. fibre, chemistry of, 500. fibres in spinal cord, 616. force, velocity of, 504. Meissner's plexus, 129. multipolar cells, 48. -muscle preparation, 501. natural current in, 500. negative variation, 506. non-medullated fibres, 47, 497. nodes of Ranvier, 47, 497. otic ganglion, 528. polarizing current, 507. primary coil, 54- primitive sheath, 49, 498. proximal and distal end, 499. roots in medulla oblongata,639. secondary coil, 504. sensory cells, 46. spinal cord, 615. spinal, 519. stained with osmic acid, 47, 497- stimulation of, 501. submaxillary ganglion, 529. tissue, 46. to spheno-palatine ganglion, 528. Nerves, afferent, 47, 498. efferent, 47, 498. anterior roots of, 519. posterior roots of, 519. cranial, 522. functional classification of, 498. Nervous control of the blood vessels, 321. mechanism of respiration, 347- of salivary se- cretion, 136. of urinary se- cretion, 410. of voice, 493. organs, central, 614. INDEX. 753 Neurin, 74. Neuroglia, 497, 614. Neuro-muscular cells of hydra, 47. Nitrogen in the blood, 244. in the tissues, 81. Nitrogenous diet, 421. ingredients in the tissues, 64. Non-medullated nerve fibres, 47, 497. Non- nitrogenous diet, 422. ingredients of the body, 77. Non- striated muscle, 50, 442. Nose, development of, 730. nerve endings in the, 553. Notochord, 673. Nuclear matrix, 36. Nucleus, method of staining, 35. Nucleolus, 36. Nutrition, 416. Nutritive equilibrium, 420. materials in vegetable food, 1 08. value of food, loo. ODONTOBLASTS, 114. (Esophagus, development of, 701. histology of, 117. Olein, 78. Ophthalmic ganglion, $28. Ophthalmometer, 571. Ophthalmoscope, 578. Optic nerve, 560. thalami, 638, 654. Organic substances, 30. substance, instability of, 31. Organisms, chemical composition of, 30- death of, 32. general characters of, 28. reproduction of, 32. vital characters of, 82. Origin of white blood corpuscles, 227. Osseous spiral lamina, 608. Ossicles of ear, 605. Ossifying cartilage, 59. Osteoblasts, 58. Otic ganglion, 528. Otoliths, 608. Ovary, 668. Ovoid cells of stomach glands, 149. Ovulation, 669. Ovum, 668. changes in the, 671. division of, 40. Oxalic acid in the urine, 404. Oxygen, 353. in the blood, 243. in the tissues, 81. Oxyhasmoglobin, 66, 235, 237, 357. composition of, 235. preparation of, 236. DACINIAN corpuscles, 540. r Pain, 547. Palmitin, 78. Pancreas, 160. changes in the cells during secretion, 162. nervous influence on the, 162. development of, 700. Pancreatic fistula, 161. juice, action on fat, 166. action on proteids, 165. action on starch, 167. artificial, 161. characters of the se- cretion, 161. Papillae of tongue, 131, 551. Paraglobulin (fibrinoplastin), 69, 221. Paramoecium, 42, 93. Parapeptone, 155. Pavy's solution, 146. Pendulum myograph, Pick's, 461. Peduncles of the cerebrum, 638. Pepsin, 151. Peptic cells, 153. Peptone, 71. absorption of, 205. tests for, 71. Perilymph, 607. Peristaltic contraction of intestine, 124. Perspiration, 388. Pettenkofer's test for bile salts, 73,177. Peyer's patches, 202. Phakoscope, 571. Pharynx, muscles of, 115. Phosphates in the tissues, 81. in the urine, 405. Physical forces of the circulation, 289. 754 INDEX. Physiology, objects of, 25. Picric acid test for albumin, 68. Pigment cells, 37. of the eye, 590. Placenta, 68 1. uses of the, 685. Plant cell, 33. Plasma, 218. chemical composition of, 220. of the blood, coagulation of, 219. method of obtaining from blood, 219. Plasm ata, 64. Pleura, 327. functions of the, 338. Pneumogastric nerve, 348. Poikilothermic animals, 428. Poisonous gases, 360. Polarizing current, 507. Pons varolii, 638, 652. Portal system, development of, 714. vein, 169, 374. Portio dura, seventh nerve, 5 2 4- mollis, 598. Porus opticus, 585. Posterior roots of spinal cord, 616. Potassium chloride in the tissues, 81. Potatoes as food, 107. Presbyopia, 573- Primitive groove, 42. Products of tissue change, 71. Protagon, 74. Protamoeba, 91. Protista, 39. Protococcus, 91. Protoplasm, 29. assimilation of, 85. change in form, 83. of cell, 34. in the tissues, 65, structure of, 35. Protoplasmic movements, 83, 84. Protozoa, 40. Pseudopodia of amoeba, 83. of white blood corpus- cles, 226. Ptyalin, 145. Puerile breathing, 343. Pulmonary circulation of the blood, 258. Pulp cavity of the teeth, 112. Pupil of the eye, 558. Pulse, 307. Marey's sphygmograph, 309. tracings, 309. variations in the, 312. Purkinje's cells in the cerebellum, 649. figures, 587. Putrefactive fermentation in the intes- tine, 1 88. Pylorus, 1 20. (~\ UADRATUS lumborum, 334. RANVIER'S nodes, 47, 497. Receptaculum chyli, 194. Recording apparatus, 297. Rectum, in. Red blood corpuscles, 217. Reduced haemoglobin, 237. Reflex action, 48, 516, 627. inhibition of, 629. Reflex centres, special, 632. Reflexion, 516, 634. Refraction, 564. Reproduction, 666. of cells, 85, 87. Respiration, 323. asphyxia, 362. changes in the air, 352. changes in the blood during, 354. chemistry of, 351. complemental air, 342. construction of thorax, 329- diffusion, 342. expiration, 337. expired air, 352. frequency of, 331. functions of the pleura, in lower animals, 324. inspiration, 333. internal or tissue, 359. mechanism of, 323. muscles of, 333. nervous mechanism of, 343- of abnormal air, 360. poisonous gases, 360. INDEX. 755 Respiration, pressure differences in the air, 340. reserve air, 341. residual air, 342. sounds of, 343. tidal air, 341. ventilation, 361. vital capacity, 342. vital point, 344. volume of air, 341. Respiratory centre, 640. movements, 330. sounds, 343. wave, 301. Retention of urine in the bladder, 412. Retina, function of the, 583. pigment cells of, 590. ophthalmic view of the, 581. structure of, 583. Rheoscopic frog, 457. Ribs, 336. Rigor mortis, 473. Rater's tetanus, 502. Rods and cones of the retina, 585. Rods of Corti, 610. O ACCHAROMYCES cereviske, 77, O 85. Sacculated glands, 131. Saccule of semicircular canals, 608. Saliva, action on food, 144. chemistry of, 135. effect of drugs on secretion of, 138. effect of nervous influence, 138. method of secretion, 136. Salivary gland, 133. histology of, 142. Salts as food, 109. Salts in the tissues, 80. Saponification, 166. Sarcolemma of muscle, 51, 444. Scaleni muscles, 335. Scaly epithelium, 45. Schemer's experiment, 569. Sclerotic, 557. Sebaceous glands, 381. Secreting glands, 378. Secretion, 378. Secretion of urine, 395. Segmentation sphere, "672. Semicircular canals, 608. Semilunar valves, 263. Sensations, general, 547. Sensory nerve cells, 46. Sensory nerves, 631. Serum albumin, 68. compositi m of, 223. globulin, 221. separation of, 219. Sexual organs, development of, 708. Sexual reproduction, 666. Shivering, 549. Sighing, 350. Sight, 556. Skatol, 189. Skin, cutaneous desquamation, 389. general sensations, 537, 547. glands of, 381. Krause's end bulbs, 539. nerve endings in, 538. sense of temperature, 545. Skull, development of, 729. Smell, 553. Sneezing, 350. Sobbing, 350. Sodium chloride in the tissues, 80. Solitary glands, 202. Somatopleure, 674. Sound, 598. direction of, 613. tuning forks, 599. vibrations through the tym- panum, 603. Special senses, 534. hearing, 598. smell, 553. taste, 550. touch, 537. vision, 556- Spectra of blood, 357. of haemoglobin, 237. Spectrum, analysis of the, 592. Speech, 486. Spermatozoa, 667. Sphenopalatine ganglia, 528. Spherical aberration, 574- Spheroidal cells of stomach glands, 149. Sphygmograph, 309. Spinal accessory nerve, 529. Spinal cord, 615. 756 INDEX. Spinal cord, automatic centres in the, 635. . automatism, 634. cellular columns in the, 625, 626. cervical region, 619. collection of nerve cells in the, 625. coordination, 634. course of fibres in, 624. development of, 688. dorsal region, 618. experiments on the, 622. lumbar region, 618. motor channels, 631. of embryo, 620. pyramidal tracts of, 619. reflex action, 627. roots of nerves of, 616, 617. sensory channels, 631. white tracts on, 619. Splanchnopleure, 674. Spleen, changes of blood in the, 371. development of, 701. extirpation of the, 372. function of, 372. structure of, 369. Spring myograph, 461. Standing, 481. Stapes, 605. Starch as food, 107. converted into grape sugar, .145- microscopic appearance of, 109. tests for, 146. Starvation, 417. Steapsin, 186. Stearin, 78. Steno's duct, 134. Stomach, digestion, 148. histology of, 148. motion of the, 120. nervous influence on, 121. walls of the, 119. Stomata, 197. Stratified epithelium, 44. Striated muscle, 50, 443. Stroma of the blood, 232. chemistry of the, 241. Submaxillary ganglion, 529. Sudoriferous glands, 387. Sulphates in the tissues, 81. in the urine, 405. Summation, 467. Supporting tissues, 43. Supra-renal capsule, 367. Sweat glands, 387. Symphyses, 479. Syntonin, 69. Systemic circulation of the blood, 258. Systole of heart, 267. TACTILE impressions, 542. sensations, 537. Tambour (Marey's), 271. Taste, 550. Taste buds, 552. Taurin, 76. Taurocholic acid, 73, 176. Tegmentum, 652. Teeth, development of, 1 14. structure of the, 112. Temperature, maintenance of uniform, 435- measurement of, 429. normal variations in, 429. Tendon cells stained with gold, 54. Testicle, 667. Tests for albumin, 67. for peptone, 71. Tetanus of muscle, 468. Thermic stimulation of muscle, 452. nerve, 502. Thermometer, clinical, 429. Thirst and hunger, 548. Thoracic duct, 191, 212. lymph of, 208. Thorax, construction of, 329. Thrombosis, 251. Thymus gland, 368. Thyroid body, 367. cartilage, 487. Timbre of a note, 600. Tissue changes in starvation, 417. change, products of, 71. connective, 52. differentiation, 39. epithelial, 43. lymphoid, 195. mucous, 54. muscle, 50, 442. INDEX. 757 Tissue nerve, 46, 496. white fibrous, 54. yellow elastic, 56. Tissues, classification of, 43. Titillation, 549. Tones, 600. Tongue, 550. taste buds of, 552. Torula cerevisia, 90. Touch, 537. cells, 539. corpuscles (Meissner's), 538. general sensation, 547. sense of locality, 541. sense of pressure, 543. Tradescantia virginica, 82. Tricuspid valve of the heart, 259. Trigeminus nerve, 525. Trochlear nerve, 523. Trommer's test, 146. Trypsin, 164, 1 86. Tubules of kidney, 392. Tubuli seminiferi, 667. Tunica adventitia, 283. intima, 285. granulosa, 669. media, 283. Tuning forks, 599. Tympanum of ear, 603. Tyrosin, 76. in pancreatic digestion, 166. UMBILICAL cord, 685. Unicellular organism, 39. Unstriated muscle, contraction of, 475- Urachus, 68 1. Urea, 75, 400. artificial preparation of, 75. estimation of, 402. source of, 408. Ureters, 411. Uric acid, 76. in the urine, 403. murexide test for, 76. Urinary calculi, 407. Urine, 395. abnormal constituents in the, 406. acid fermentation of the, 407. chemical composition of, 400. coloring matter of, 404. Urine, inorganic salts in the, 405. quantity secreted, 396. retention of, 412. secretion of, 397. source of urea, 408. specific gravity of, 396. Urinary excretion, 391. secretion, nervous mechanism of, 410. Urobilin, 404. Urochrome, 404. Uroerythrin, 405. Uterus, 666. WACUOLES, 34, 94. Vagus nerve, 280, 530. Vagus, stimulation of, 280. Valentine's method, estimating amount of blood, 216. Valsalva's experiment, 606. Valves in lymph vessels, 213. of heart, 262. of veins, 287. of the heart, action of, 263. Valvulae conniventes, 160, 182. Vasa deferentia, 667. motor centre, 641. motor nerves, 317. Vascular system, development of, 60, 708. Vegetable cells, 33. food, 107. Veins, coats of, 287. valves of, 287. Velocity of the blood current, 313. Venae advehentes, 714. Vena cava, 259. porta, 374. Venous system, development of, 718. Ventilation, 361. Ventricles of brain, 638. of heart, 259. Vesiculae seminalis, 667. Vessels, lymphatic, 197. Vibration, 599. Villi, 183. lacteals in, 199. Vision, 556. accommodation, 57- astigmatism, 574. binocular, 596. chromatic aberration, 574. INDEX. Vision, color blindness, 594. color perceptions, 591. complementary colors, 592. conditions affecting, 589. convergent rays, 567. entoptic images, 575. function of the retina, 583. hypermetropia, 573. irradiation, 589. judgment of distance, 597. judgment of size, 597. light impressions, 582. mental operations in, 594. myopia, 572. negative after image, 589. ophthalmoscope, 578. positive after image, 589. presbyopia, 573. Purkinje's figures, 587. refraction, 564. retinal stimulation, 587. Scheiner's experiment, 568. spherical aberration, 574. Vital capacity, 342. characters of organisms, 82. phenomena, 26, 32. point, 344. Vitellin, 69. Vitelline membrane, 670. Vitreous humor, 560. Vocal cords, 487. Voice and speech, 486. nervous mechanism of, 493. . properties of the human, 491. Volition, 634. Vomiting, 121. Vorticella, 42, 94. WALKING and running, 484. Warm-blooded animals, 428. Waste products of animal body, 75. Water H 2 O, 30, 79. Water as food, 108. Weber's method, estimating amount of blood, 215. Welcker's method estimating amount of blood, 216. Wharton's duct, 134. White blood corpuscles, 225. fibro cartilage, 57. fibrous tissue, 54. substance of Schwann, 498. Wolffian bodies, 702. V"ANTHIN in the urine, 403. <. Xanthoproteic test, 67. V AWNING, 350. Yeast plant, 77, 85, 90. Yellow elastic tissue, 56. spot, 587. Yolk of egg, 670. sac, 678. ZONA pellucida, 670. tendinosa, 260. Zymogen, 164. CATALOGUE No. 7. OCTOBER, 1889. A CATALOGUE OF BOOKS FOR STUDENTS, INCLUDING THE ? QUIZ-COMPENDS ? CONTENTS. PAGE PAGE New Series of Manuals, 2,3,4,5 Obstetrics. ... 10 Anatomy, Biology, Chemistry, . 6 ii 6 Pathology, Histology, . Pharmacy, . Physical Diagnosis, ii 13 ii Children's Disease s, 7 Physiology, . IX Dentistry, 8 Practice of Medicine, 12 Dictionaries, 8 Prescription Books, 12 Eye Diseases, Electricity, . 8 9 PQuiz-Compends ? Skin Diseases, '5 16 13 Gynaecology, Hygiene, IO 9 Surgery, Therapeutics, 13 g Materia Medica, . 9 Throat, XI Medical Jurisprudence Miscellaneous, 9 10 Urine and Urinary Organs, 14 Venereal Diseases, . . 14 PUBLISHED BY P. BLAKISTON, SON & CO., Medical Booksellers, Importers and Publishers. LARGE STOCK OF ALL STUDENTS' BOOKS, AT THE LOWEST PRICES. 1012 Walnut Street, Philadelphia. *** For sale by all Booksellers, or any book will be sent by mail, postpaid, upon receipt of price. Catalogues of books on all branches of Medicine, Dentistry, Pharmacy, etc., supplied upon application. "An excellent Series of Manuals." Archives of Gyneecology A NEW SERIES OF STUDENTS' MANUALS On the various Branches of Medicine and Surgery. Can be used by Students of any College. Price of each, Handsome Cloth, $3.00. Full Leather, $3.50. The object of this series is to furnish good manuals for the medical student, that will strike the medium between the compend on one hand and the prolix text- book on the other to contain all that is necessary for the student, without embarrassing him with a flood of theory and involved statements. They have been pre- pared by well-known men, who have had large experience as teachers and writers, and who are, therefore, well informed as to the needs of the student. Their mechanical execution is of the best good type and paper, handsomely illustrated whenever illustrations are of use, and strongly bound in uniform style. Each book is sold separately at a remarkably low price, and the immediate success of several of the volumes shows that the series has met with popular favor. No. 1. SURGERY. 236 Illustrations. A Manual of the Practice of Surgery. By WM. J. WALSHAM, M.D., Asst. Surg. to, and Demonstrator of Surg. in, St. Bartholomew's Hospital, London, etc. 228 Illustrations. Presents the introductory facts in Surgery in clear, precise language, and contains all the latest advances in Pathology, Antiseptics, etc. " It aims to occupy a position midway between the pretentious manual and the cumbersome System of Surgery, and its general character may be summed up in one word practical." The Medi- cal Bulletin. " Walsham, besides being an excellent surgeon, is a teacher in its best sense, and having had very great experience in the preparation of candidates for examination, and their subsequent professional career, may be relied upon to have carried out his work successfully. Without following out in detail his arrange- ment, which is excellent, we can at once say that his book is an embodiment of modern ideas neatly, strung together, with an amount of careful organization well suited to the candidate, and, indeed, to the practitioner." British Medical Journal. Price of each Book, Cloth, $3.00 ; Leather, $3.50. THE NEW SERIES OF MANUALS. No. 2. DISEASES OF WOMEN. 13O Illus. NEW EDITION. The Diseases of Women. By DR. F. WINCKEL, Professor of Gynaecology and Director of the Royal University Clinic for Women, in Munich. Translated from the German by DR. J. H. WILLIAMSON, under the supervision of, and with an introduction by, The- ophilus Parvin, M.D., Professor of Obstetrics and Diseases of Women and Children in Jefferson Med- ical College. 140 Engravings, most of which are new. Second Edition, Enlarged. " The book will be a valuable one to physicians, and a safe and satisfactory one to put into the hands of students. It is issued in a neat and attractive form, and at a very reasonable price." Boston Medical and Surgl. Journal. No. 3. OBSTETRICS. 227 Illustrations. A Manual of Midwifery. By ALFRED LEWIS GALABIN, M.A., M.D., Obstetric Physician and Lecturer on Mid- wifery and the Diseases of Women at Guy's Hospital, London; Examiner in Midwifery to the Conjoint Examining Board of England, etc. With 227 Illus. " This manual is one we can strongly recommend to all who desire to study the science as well as the practice of midwifery. Students at the present time not only are expected to know the principles of diagnosis, and the treatment of the various emergen- cies and complications that occur in the practice of midwifery, but find that the tendency is for examiners to ask more questions relating to the science of the subject than was the custom a few years ago. * * * The general standard of the manual is high ; and wherever the science and practice of midwifery are well taught it will be regarded as one of the most important text-books on the s ubj ect." London Practitioner. No. 4. PHYSIOLOGY. Third Edition. 321 ILLUSTRATIONS AND A GLOSSARY. A Manual of Physiology. By GERALD F. YEO, M.D., F.R.C.S., Professor of Physiology in King's College, London. 321 Illustrations and a Glossary of Terms. Third American from second English Edition, revised and improved. 758 pages. This volume was specially prepared to furnish students with a. new text-book of Physiology, elementary so far as to avoid thories which have not borne the test of time and such details of methods as are unnecessary for students in our medical colleges. "The brief examination I have given it was so favorable that I placed it in the list of text-books recommended in the circular of the -Prof. Lewis A. Stimson, M.D., Price of each Book, Cloth, $3.00; Leather, $3.50. placea it in tne nstoi text-Books n University Medical -College." j 57 East 33d Street, New York. THE NEW SERIES OF MANUALS. No. 5. ORGANIC CHEMISTRY. Or the Chemistry of the Carbon Compounds. By Prof. VICTOR VON RICHTER, University of Breslau. Au- thorized translation, from the Fourth German Edition. By EDGAR F. SMITH, M.A., PH.D. ; Prof, of Chemistry in University of Pennsylvania; Member of the Chem. Socs. of Berlin and Paris. " I must say that this standard treatise is here presented in a remarkably compendious shape." J. W. Holland, M.D., Professor of Chemistry , Jefferson Medical College, Philadelphia. " This work brings the whole matter, in simple, plain language, to the student in a clear, comprehensive manner. The whole method of the work is one that is more readily grasped than that of older and more famed text-books, and we look forward to the time when, to a great extent, this work will supersede others, on the score of its better adaptation to the wants of both teacher and student." Pharmaceutical Record. " Prof, von Richter's work has the merit of being singularly clear, well arranged, and for its bulk, comprehensive. Hence, it will, as we find it intimated in the preface, prove useful not merely as a text-book, but as a manual of reference." The Chemical News, London. No. 6. DISEASES OP CHILDREN. A Manual. By J ; F. GOODHART, M.D., Phys. to the Evelina Hospital for Children ; Asst. Phys. to Guy's Hospital, London. American Edition. Edited by Louis STARR, M.D., Clinical Prof, of Dis. of Children in the Hospital of the Univ. of Pennsylvania, and Physician to . the Children's Hospital, Phila. Containing many new Prescriptions, a list of over 50 Formulae, conforming to the U. S. Pharmacopoeia, and Directions for making Artificial Human Milk, for the Artificial Digestion of Milk, etc. " The author has avoided the not uncommon error of writing a book on general medicine and labeling it ' Diseases of Children,' but has steadily kept in view the diseases which seemed to be incidental to childhood, or such points in disease as appear to be so peculiar to or pronounced in children as to justify insistence upon them. * * * A safe and reliable guide, and in many ways admirably adapted to the wants of the student and practitioner." American Journal of Medical Science. Price of each Book, Cloth, $3.00 ; Leather, $3.50. THE NEW SERIES OF MANUALS. No. 6. Goodhart and Starr : Continued. "Thoroughly individual, original and earnest, the work evi- dently of a close observer and an independent thinker, this book, though small, as a handbook or compendium is by no means made up of bare outlines or standard facts." The Therapeutic Ga- zette, " As it is said of some men, so it might be said of some books, that they are 'born to greatness.' This new volume has, we believe, a mission, particularly in the hands of the younger members of the profession. In these days of prolixity in medical literature, it is refreshing to meet with an author who knows both what to say and when he has said it. The work of Dr. Goodhart (admirably conformed, by Dr. Starr, to meet American require- ments) is the nearest approach to clinical teaching without the actual presence of clinical material that we have yet seen." New York Medical Record. No. 7. PRACTICAL THERAPEUTICS. FOURTH EDITION, WITH AN INDEX OF DISEASES. Practical Therapeutics, considered with reference to Articles of the Materia Medica. Containing) also, an Index of Diseases, with a list of the Medicines applicable as Remedies. By EDWARD JOHN WARING, M.D., F.R.C.P. Fourth Edition. Rewritten and Re- vised. By DUDLEY W. BUXTON, M.D., Asst. to the Prof, of Medicine at University College Hospital. " We wish a copy could be put in the hands of every Student or Practitioner in the country. In our estimation, it is the best book of the kind ever written." N. Y. Medical Journal. No. 8. MEDICAL, JURISPRUDENCE AND TOXICOL.OG-Y. New, Revised and Enlarged Edition. By John J. Reese, M.D., Professor of Medical Jurispru- dence and Toxicology in the University of Pennsyl- vania ; President of the Medical Jurisprudence Society of Phila. ; 2d Edition, Revised and Enlarged. " This admirable text-book." A mer.Jour. of Med. Sciences. " We lay this volume aside, after a careful perusal of its pages, with the profound impression that it should be in the hands of every doctor and lawyer. It fully meets the wants of all students He has succeeded in admirably condensing into a handy volume all the essential points." Cincinnati Lancet and Clinic. Price of each Book, Cloth, $3,00 ; Leather, $3.50. 6 STUDENTS' TEXT-BOOKS AND MANUALS. ANATOMY. Holden's Anatomy. A manual of Dissection of the Human Body. Fifth Edition. Enlarged, with Marginal References and over 200 Illustrations. Octavo. Cloth, 5.00; Leather, 6.00 Bound in Oilcloth, for the Dissecting Room, $4.50. " No student of Anatomy can take up this book without being pleased and instructed. Its Diagrams are original, striking and suggestive, giving more at a glance than pages of text description. * * * The text matches the illustrations in directness of prac- tical application and clearness of detail." New York Medical Record. Holden's Human Osteology. Comprising a Description of the Bones, with Colored Delineations of the Attachments of the Muscles. The General and Microscopical Structure of Bone and its Development. With Lithographic Plates and Numerous Illus- trations. Seventh Edition. 8vo. Cloth, 6.00 Holden's Landmarks, Medical and Surgical. 4th ed. Cloth, 1.25 Heath's Practical Anatomy. Sixth London Edition. 24 Col- ored Plates, and nearly 300 other Illustrations. Cloth, 5.00 Potter's Compend of Anatomy. Fourth Edition. 117 Illus- trations. Cloth, i.oo; Interleaved for Notes, 1.25 CHEMISTRY. Hartley's Medical Chemistry. A text-book prepared specially for Medical, Pharmaceutical and Dental Students. With 40 Illustrations, Plate of Absorption Spectra and Glossary of Chemi- cal Terms. Cloth, 2.50 *#* This book has been written especially for students and phy- sicians. It is practical and concise, dealing only with those parts of chemistry pertaining to medicine ; no time being wasted in long descriptions of substances and theories of interest only to the advanced chemical student. Bloxam's Chemistry, Inorganic and Organic, with Experiments. Seventh Edition. Enlarged and Rewritten. Nearly 300 Illus trations. Cloth, 4.50 ; Leather, 5.50 Richter's Inorganic Chemistry. A text-book for Students. Third American, from Fifth German Edition. Translated by Prof. Edgar F. Smith, PH.D. 89 Wood Engravings and Colored Plate of Spectra. Cloth, 2.00 Richter's Organic Chemistry, or Chemistry of the Carbon Compounds. Translated by Prof. Edgar - F. Smith, PH.D. Illustrated. Cloth, 3.00; Leather, 3.50 JKf" See pages 2 to j for list of Students' Manuals. STUDENTS' TEXT-BOOKS AND MANUALS. 7 Chemistry : Continued. Trimble. Practical and Analytical Chemistry. A Course in Chemical Analysis, by Henry Trimble, Prof, of Analytical Chem- istry in the Phila. College of Pharmacy. Illustrated. Second Edition. 8vo. Cloth, 1.50 Tidy. Modern Chemistry. 2d Ed. Cloth, 5.50 Leffmann's Compend of Chemistry. Inorganic and Organic. Including Urinary Analysis and the Sanitary Examination of Water. New Edition. Cloth, i.oo; Interleaved for Notes, 1.25 Muter. Practical and Analytical Chemistry. Second Edi- tion. Revised and Illustrated. Cloth, 2.00 Holland. The Urine, Common Poisons, and Milk Analysis, Chemical and Microscopical. For Laboratory Use. sd Edition, Enlarged. Illustrated. * Cloth, i.oo Van Niiys. Urine Analysis. Illus. Cloth, 2.00 "Wolff's Applied Medical Chemistry. By Lawrence Wolff, M.D., Demonstrator of Chemistry in Jefferson Medical College, Philadelphia. Cloth, i.oo CHILDREN. Goodhart and Starr. The Diseases of Children. A Manual for Students and Physicians. By J. F. Goodhart, M.D., Physi- cian to the Evelina Hospital for Children ; Assistant Physician to Guy's Hospital, London. American Edition, Revised and Edited by Louis Starr, M.D., Clinical Professor of Diseases of Children in the Hospital of the University of Pennsylvania; Physician to the Children's Hospital, Philadelphia. Containing many new Prescriptions, a List of over 50 Formulae, conforming to the U. S. Pharmacopoeia, and Directions for making Arti- ficial Human Milk, for the Artificial Digestion of Milk, etc. Cloth, 3.00; Leather, 3.50 Day. On Children. A Practical and Systematic Treatise. Second Edition. 8vo. 752 pages. Cloth, 3.00 ; Leather, 4.00 Meigs and Pepper. The Diseases of Children. f Seventh Edition. 8vo. Cloth, 5.00; Leather, 6.00 Starr. Diseases of the Digestive Organs in Infancy and Childhood. With chapters on the Investigation of Disease, and on the General Management of Children. By Louis Starr, M.D., Clinical Professor of Diseases of Children in the Univer- sity of Pennsylvania; with a section on Feeding, including special Diet Lists, etc. Illus. Cloth, 2.50 >8S~ See pages 13 and ib for list of ? Quiz- Compends ? 8 STUDENTS' TEXT-BOOKS AND MANUALS. DENTISTRY. Fillebrown. Operative Dentistry. 330 Illustrations. Just Ready. Cloth, 2.50 Flagg's Plastics and Plastic Filling, sd Ed. Preparing. Gorgas. Dental Medicine. A Manual of Materia Medica and Therapeutics. Third Edition. Cloth, 3.50 Harris. Principles and Practice of Dentistry. Including Anatomy, Physiology, Pathology, Therapeutics, Dental Surgery and Mechanism. Twelfth Edition. Revised and enlarged by Professor Gorgas. 1028 Illustrations. Cloth, 7.00 ; Leather, 8.00 Richardson's Mechanical Dentistry. Fifth Edition. 569 Illustrations. 8vo. Cloth, 4.50; Leather, 5.50 Stocken's Dental Materia Medica. Third Edition. Cloth, 2.50 Taft's Operative Dentistry. Dental Students and Practitioners. Fourth Edition, too Illustrations. Cloth, 4.25 ; Leather, 5.00 Talbot. Irregularities of the Teeth, and their Treatment. Illustrated. 8vo. Cloth, 2.00 Tomes' Dental Anatomy. Third Ed. 191 Illus. Preparing. Tomes' Dental Surgery. 3d Edition. Revised. 292 Illus. 772 Pages. Cloth, 5.00 DICTIONARIES. Cleaveland's Pocket Medical Lexicon. Thirty-first Edition. Giving correct Pronunciation and Definition of Terms used in Medicine and the Collateral Sciences. Very small pocket size. Cloth, red edges .75 ; pocket-book style, i.oo Longley's Pocket Dictionary. The Student's Medical Lexicon, giving Definition and Pronunciation of all Terms used in Medi- cine, with an Appendix giving Poisons and Their Antidotes, Abbreviations used in Prescriptions, Metric Scale of Doses, etc. 24mo. Cloth, i.oo; pocket-book style, 1.25 EYE. Arlt. Diseases of the Eye. Including those of the Conjunc- tiva, Cornea, Sclerotic, Iris and Ciliary Body. By Prof. Von Arlt. Translated by Dr. Lyman Ware. Illus. 8vo. Cloth, 2.50 Hartridge on Refraction. 4th Ed. Cloth, 2.00 Macnamara. Diseases of the Eye. 4th Edition. Revised. Colored Plates and Wood Cuts and Test Types. Cloth, 4.00 Meyer. Diseases of the Eye. A complete Manual for Stu- dents and Physicians. 270 Illustrations and two Colored Plates. 8vo. Cloth, 4.50; Leather, 5.50 Fox and Gould. Compend of Diseases of the Eye and Refraction. 2d Ed. Enlarged. 71 Illus. 39 Formulae. Cloth, i.oo ; Interleaved for Notes, 1.25 -ftS" See pages 2 to 5 for list of Students' Manuals. STUDENTS' TEXT-BOOKS AND MANUALS. 9 ELECTRICITY. Mason's Compend of Medical and Surgical Electricity. With numerous Illustrations. i2mo. Cloth, i.oo HYGIENE. Parkes' Practical Hygiene. Seventh Edition, enlarged. Illus- trated. 8vo. Cloth, 4.50 Wilson's Handbook of Hygiene and Sanitary Science. Sixth Edition. Revised and Illustrated. Cloth, 2.75 MATERIA MEDICA AND THERAPEUTICS. Potter's Compend of Materia Medica, Therapeutics and Prescription Writing. Fifth Edition, revised and improved. Cloth, i.oo; Interleaved for Notes, 1.25 Biddle's Materia Medica. Eleventh Edition. By the late John B. 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Reese, M.D., Professor of Medical Juris- prudence and Toxicology in the Medical Department of the University of Pennsylvania; President of the Medical Juris- prudence Society of Philadelphia ; Physician to St. Joseph's Hospital ; Corresponding Member of The New York Medico- legal Society, ad Edition. Cloth, 3.00 ; Leather, 3.50 Woodman and Tidy's Medical Jurisprudence and Toxi- cology. Chromo-Lithographic Plates and 116 Wood engravings. Cloth, 7.50; Leather, 8.50 J&y See pages 15 and ib for list of ? Quiz- Commends ? 10 STUDENTS' TEXT-BOOKS AND MANUALS. MISCELLANEOUS. Allingham. Diseases of the Rectum. Fourth Edition. Illus- trated. 8vo. Paper covers, .75 ; Cloth, 1.25 Beale. Slight Ailments. Their Nature and Treatment. Illus- trated. 8vo. Cloth, 1.25 Domville on Nursing. 6th Edition. Cloth, .75 Fothergill. Diseases of the Heart, and Their Treatment. Second Edition. Svo. Cloth, 3.50 Gowers. Diseases of the Nervous System. 341 Illus- trations. Cloth, 6.50; Leather, 7.50 Mann's Manual of Psychological Medicine, and Allied Ner- vous Diseases. Their Diagnosis, Pathology and Treatment, and their Medico-Legal Aspects. Illus. Cloth, 5.00 ; Leather, 6.00 Tanner. Memoranda of Poisons. Their Antidotes and Tests. Sixth Edition. Revised by Henry Leffmann, M.D. Cloth, .75 Parvin. Lectures on Obstetric Nursing. 32mo. Cloth, .75 OBSTETRICS AND GYNAECOLOGY. Byford. Diseases of Women. The Practice of Medicine and Surgery, as applied to the Diseases and Accidents Incident to Women. By W. H. Byford, A.M., M.D., Professor of Gynaecology in Rush Medical College and of Obstetrics in the Woman's Med- larged. With 306 Illustrations, over 100 of which are original. Octavo. 832 pages. Cloth, 5.00; Leather, 6.00 Cazeaux and Tarnier's Midwifery. 'With Appendix, by Munde. The Theory and Practice of Obstetrics ; including the Diseases of Pregnancy and Parturition, Obstetrical Operations, etc. By P. Cazeaux. Remodeled and rearranged, with revi- sions and additions, by S. Tarnier, M.D., Professor of Obstetrics and Diseases of Women and Children in the Faculty of Medicine of Paris. Eighth American, from the Eighth French and First Italian Edition. Edited by Robert J. Hess, M.D., Physician to the Northern Dispensary, Philadelphia, with an appendix by Paul F. Munde, M.D., Professor of Gynaecology at the N. Y. Polyclinic. Illustrated by Chromo-Lithographs, Lithographs, and other Full-page Plates, seven of which are beautifully colored, and numerous Wood Engravings. Students' Edition. One Vol., Svo. Cloth, 5.00; Leather, 6.00 Lewers' Diseases of Women. A Practical Text-Book. 139 Illustrations. Cloth, 2.25 Parvin's Winckel's Diseases of Women. Edited by Prof. Theophilus Parvin, Jefferson Medical College, Philadelphia. 117 Illustrations. Second Edition, Revised and Enlarged. See Cloth, 3.00; Leather, 3.50 Morris. Compend of Gynaecology. Illustrated. In Press. &g- See pages 2 to 5 for list of New Manuals. STUDENTS' TEXT-BOOKS AND MANUALS. 11 Obstetrics and Gynaecology : Continued. Winckel's Obstetrics. A Text-book on Midwifery, includ- ing the Diseases of Childbed. By Dr. F. Winckel, Professor of Gynaecology, and Director of the Royal University Clinic for Women, in Munich. Authorized Translation, by J. Clifton Edgar, M.D., Lecturer on Obstetrics, University Medical Col- lege, New York, with nearly 200 handsome illustrations, the majority of which are original with this work. Octavo. In press. Landis' Compend of Obstetrics. Illustrated. 4th edition, enlarged. Cloth, i.oo ; Interleaved for Notes, 1.25 Galabin's Midwifery. A New Manual" for Students. By A. Lewis Galabin, M.D., F.R.C.P., Obstetric Physician to Guy's Hospital, London, and Professor of Obstetrics in the same Insti- tution. 227 Illustrations. Seepages. Cloth, 3.00; Leather, 3.50 Glisan's Modern Midwifery. 2d Edition. Cloth, 3.00 Rigby's Obstetric Memoranda. By Alfred Meadows, M.D. 4th Edition. Cloth, .50 Meadows' Manual of Midwifery. Including the Signs and Symptoms of Pregnancy, Obstetric Operations, Diseases of the Puerperal State, etc. 145 Illustrations. 494 pages. Cloth, 2.00 Swayne's Obstetric Aphorisms. For the use of Students commencing Midwifery Practice. 8th Ed. i2mo. Cloth, 1.25 PATHOLOGY. HISTOLOGY. BIOLOGY. Bowlby. Surgical Pathology and Morbid Anatomy, for Students. 135 Illustrations. i2mo. Cloth, 2.00 Davis' Elementary Biology. Illustrated. Cloth, 4.00 Rindfleisch's General Pathology. By Prof. Edward Rind- fleisch. Translated by Wm. H.Mercur, M.D. Edited by James Tyson, M.D., Professor of Clinical Medicine in the University of Pennsylvania. i2mo. Cloth, 2.00 Gilliam's Essentials of Pathology. A Handbook for Students. 47 Illustrations. lamo. Cloth, 2.00 ***The object of this book is to unfold to the beginner the funda- mentals of pathology in a plain, practical way, and by bringing them within easy comprehension to increase his interest in the study of the subject. Gibbes' Practical Histology and Pathology. Third Edition. Enlarged. i2mo. Cloth, 1.75 Virchow's Post-Mortem Examinations. 2d Ed. Cloth, i.oo PHYSICAL DIAGNOSIS. Bruen's Physical Diagnosis of the Heart and Lungs. By Dr. Edward T. Bruen, Assistant Professor of Clinical Medicine in the University of Pennsylvania. Second Edition, revised. With new Illustrations. i2mo. " Cloth, 1.50 ee pages 15 and ib for list of ? Quiz- Compends f 12 STUDENTS' TEXT-BOOKS AND MANUALS. PHYSIOLOGY. Yeo's de Physiology iges. 321 carefully pr ssary and Index. See Page 3. Cloth, 3.00; Leather, 3.50 Brubaker's Compend of Physiology. Illustrated. Fourth Edition. Cloth, i.oo ; Interleaved for Notes, 1.25 Stirling. Practical Physiology, including Chemical and Ex- perimental Physiology. 142 Illustrations. Cloth, 2.25 Kirke's Physiology. New i2th Ed. Thoroughly Revised and Enlarged. 502 Illustrations. Cloth, 4.00; Leather, 5.00 Landois' Human Physiology. Including Histology and Micro- scopical Anatomy, and with special reference to Practical Medi- cine. Third Edition. Translated and Edited by Prof. Stirling. 692 Illustrations. Cloth, 6.50; Leather, 7.50 " With this Text-book at his command, no student could fail in his examination." Lancet. Sanderson's Physiological Laboratory. Being Practical Ex- ercises for the Student. 350 Illustrations. 8vo. Cloth, 5.00 Tyson's Cell Doctrine. Its History and Present State. Illus- trated. Second Edition. Cloth, 2.00 PRACTICE. Roberts' Practice. New Revised Edition. A Handbook of the Theory and Practice of Medicine. By Frederick T. Roberts, M.D. ; M.R.C.P., Professor of Clinical Medicine and Therapeutics in University College Hospital, London. Seventh Edition. Octavo. Cloth, 5.50 ; Sheep, 6.50 Hughes. Compend of the Practice of Medicine. 3d Ed. Two parts, each, Cloth, i.oo; Interleaved for Notes, 1.25 PART i. Continued, Eruptive and Periodical Fevers, Diseases of the Stomach, Intestines, Peritoneum, Biliary Passages, Liver, Kidneys, etc., and General Diseases, etc. PART n. Diseases of the Respiratory System, Circulatory System and Nervous System ; Diseases of the Blood, etc. Tanner's Index of Diseases, and Their Treatment. Cloth, 3.00 " This work has won for itself a reputation. ... It is, in truth, what its Title indicates." TV. Y. Medical Record. PRESCRIPTION BOOKS. Wythe's Dose and Symptom Book. Containing the Doses and Uses of all the principal Articles of the Materia Medica, etc. Seventeenth Edition. Completely Revised and Rewritten. Just Ready. 32mo. Cloth, i.oo; Pocket-book style, 1.25 Pereira's Physician's Prescription Book. Containing Lists of Terms, Phrases, Contractions and Abbreviations used in Prescriptions, Explanatory Notes, Grammatical Construction of Prescriptions, etc., etc. By Professor Jonathan Pereira, M.D. Sixteenth Edition. 32mo. Cloth, i.oo; Pocket-book style, 1.25 pages 2 to 5 for list of New Manuals. STUDENTS' TEXT-BOOKS AND MANUALS. 13 PHARMACY. Stewart's Compend of Pharmacy. Based upon Remington's Text-Book of Pharmacy. Second Edition, Revised. Cloth, i.oo ; Interleaved for Notes, 1.25 SKIN DISEASES. Anderson, (McCall) Skin Diseases. A complete Text-Book, with Colored Plates and numerous Wood Engravings. 8vo. Just Ready. Cloth, 4.50; Leather, 5.50 " We welcome Dr. Anderson's work not only as a friend, but as a benefactor to the profession, because the author has stricken off mediaeval shackles of insuperable nomenclature and made crooked ways straight in the diagnosis and treatment of this hitherto but little understood class of diseases. The chapter on Eczema is alone worth the price of the book." Nashville Medical News. " Worthy its distinguished author in every respect ; a work whose practical value commends it not only to the practitioner and stu- dent of medicine, but also to the dermatologist." James Nevens Hyde, M.D., Prof, of Skin and Venereal Diseases, Rush Medical College, Chicago. Van Harlingen on Skin Diseases. A Handbook of the Dis- eases of the Skin, their Diagnosis and Treatment (arranged alpha- betically). By Arthur Van Harlingen, M.D., Clinical Lecturer on Dermatology, Jefferson Medical College; Prof, of Diseases of the Skin in the Philadelphia Polyclinic. ad Edition. Enlarged. With colored and other plates and illustrations. 12010. Cloth, 2.50 Bulkley. The Skin in Health and Disease. By L. Duncan Bulkley, Physician to the N. Y. Hospital. Illus. Cloth, .50 SURGERY. Jacobson. Operations in Surgery. A Systematic Handbook for Physicians, Students and Hospital Surgeons. By W. H. A. Jacobson, B.A., Oxon. F.R.C.S. Eng. ; Ass't Surgeon Guy's Hos- pital ; Surgeon at Royal Hospital for Children and Women, etc. With 199 finely printed illustrations. 1006 pages. 8vo. Cloth. $5.00 ; Leather, $6.00 Heath's Minor Surgery, and Bandaging. Ninth Edition. 142 Illustrations. 60 Formulae and Diet Lists. Cloth, 2.00 Horwitz's Compend of Surgery, including Minor Surgery, Amputations, Fractures, Dislocations, Surgical Diseases, and the Latest Antiseptic Rules, etc., with Differential Diagnosis and Treatment. By ORVILLE HOKWITZ, B.S., M.D., Demonstrator of Anatomy, Jefferson Medical College ; Chief, Out- Patient Surgi- cal Department, Jefferson Medical College Hospital. 3d edition. Very much Enlarged and Rearranged. 91 Illustrations and 77 Formulas. i2mo. No. q ? Quiz- Compend? Series. Cloth, i.oo; Interleaved for the addition of Notes, 1.25. Pye's Surgical Handicraft. A Manual of Surgical Manipula- tions, Minor Surgery, Bandaging, Dressing, etc., etc. With special chapters on Aural Surgery, Extraction of Teeth, Anaes- thetics, etc. 208 Illustrations. 8vo. Cloth, 5.00 Swain's Surgical Emergencies. New Edition. Illus. Clo.,i.so Hf- Set pages 13 and ibfor list of ? Quiz-Compends t 14 STUDENTS' TEXT-BOOKS AND MANUALS. Su rge ry : Continued. Walsham. Manual of Practical Surgery. For Students and Physicians. By WM. J. WALSHAM, M.D., F.R.C.S., Asst. Surg. to, and Dem. of Practical Surg. in, St. Bartholomew's Hospital, Surgeon to Metropolitan Free Hospital, London. With 236 Engravings. See Page 2. Cloth, 3.00; Leather, 3.50 THROAT. Mackenzie. Diseases of the CEsophagus, Nose and Naso- Pharynx. By Sir Morell Mackenzie, M.D., Senior Physician to the Hospital for Diseases of the Chest and Throat ; Lecturer on Diseases of the Throat at the London Hospital, etc., with Formulae and 93 Illustrations. Being Vol. u, complete in itself, of Dr. Mackenzie's text-book on the Throat and Nose. Cloth, 3.00; Leather, 4.00 " It is both practical and learned ; abundantly and well illustrated ; its descriptions of disease are graphic and the diagnosis the best we have anywhere seen." Philadelphia Medical Times. Cohen. The Throat and Voice. Illustrated. Cloth, .50 James. Sore Throat. Its Nature, Varieties and Treatment. izmo. Illustrated. Paper cover, .75; Cloth, 1.25 URINE, URINARY ORGANS, ETC. Acton. The Reproductive Organs. In Childhood, Youth, Adult Life and Old Age. Seventh Edition. Cloth, 2.00 Beale. Urinary and Renal Diseases and Calculous Disorders. Hints on Diagnosis and Treatment. 12010. Cloth, 1.75 Holland. The Urine, and Common Poisons and The Milk. Chemical and. Microscopical, for Laboratory Use. Illus- trated. Third Edition. i2mo. Interleaved. .Cloth, i.oo Ralfe. Kidney Diseases and Urinary Derangements. 42 Illus- trations. i2mo. 572 pages. Cloth, 2.75 Legg. On the Urine. A Practical Guide. 6th Ed. Cloth, .75 Marshall and Smith. On the Urine. The Chemical Analysis of the Urine. By John Marshall, M.D., Chemical Laboratory, thriv. of Penna; and Prof. E. F. Smith, PH.D. Col. Plates. Cloth, i.oo Thompson. Diseases of the Urinary Organs. Eighth London Edition. Illustrated. Cloth, 3.30 Tyson. On the Urine. A Practical Guide to the Examination of Urine. With Colored Plates and Wood Engravings. 6th Ed. Enlarged. i2mo. Cloth, 1.50 Bright's Disease and Diabetes. Illus. Cloth, 3.50 Van Nuys, Urine Analysis. Illus. Cloth, 2.00 VENEREAL DISEASES. Hill and Cooper. Student's Manual of Venereal Diseases, with Formulae. Fourth Edition. i2mo. Cloth, i.oo Durkee. On Gonorrhoea and Syphilis. Illus. Cloth, 3.50 &3=- See pages 15 and ib for list of ? Quiz- Commends .* NEW AND REVISED EDITIONS. PQUIZ-COMPENDS? The Best Compends for Students' Use in the Quiz Class, and when Pre- paring for Examinations. Compiled in accordance with the latest teachings of promi- nent lecturers and the most popular Text-books. They form a most complete, practical and exhaustive set of manuals, containing information nowhere else col- lected in such a condensed, practical shape. Thoroughly up to the times in every respect, containing many new prescriptions and formulas, and over two hundred and thirty illustrations, many of which have been drawn and engraved specially for this series. The authors have had large experience as quiz-masters and attaches of colleges, with exceptional opportunities for noting the most recent advances and methods. The arrangement of the subjects, illustrations, types, etc., are all of the most approved form, and the size of the books is such that they may be easily carried in the pocket. They are constantly being revised, so as to include the 'latest and best teachings, and can be used by students of any college of medicine, den- tistry or pharmacy. Cloth, each $1.00. Interleaved for Notes, $1.25. No. i. HUMAN ANATOMY, "Based upon Gray." Fourth Edition, including Visceral Anatomy, formerly published separately. Over 100 Illustrations. By SAMUEL O. L. POTTER, M.A., M.D., late A. A. Surgeon U. S. Army. Professor of Practice, Cooper Medical College, San Francisco. Nos. 2 and 3. PRACTICE OF MEDICINE. Third Edition. By DANIEL E. HUGHES, M.D., Demonstrator of Clinical Medi- cine in Jefferson Medical College, Philadelphia. In two parts. PART I. Continued, Eruptive and Periodical Fevers, Diseases of the Stomach, Intestines, Peritoneum, Biliary Passages, Liver, Kidneys, etc. (including Tests for Urine), General Diseases, etc. PART II. Diseases of the Respiratory System (including Phy- sical Diagnosis), Circulatory System and Nervous System; Dis- eases of the Blood, etc. *#* These little books can be regarded as a full set of notes upon the Practice of Medicine, containing the Synonyms, Definitions, Causes, Symptoms, Prognosis, Diagnosis, Treatment, etc., of each disease, and including a number of prescriptions hitherto unpub- lished. (OVER.) BLAKISTON'S ? QUIZ-COMPENDS ? Continued. Bound in Cloth, $1.00. Interleaved, for Notes, $1.25 No. 4. PHYSIOLOGY, including Embryology. Fourth Edition. By ALBERT P. BRUBAKER, M.D., Prof, of Physiology, Penn'a College of Dental Surgery ; Demonstrator of Physiology in Jefferson Medical College, Philadelphia. Revised, Enlarged and Illustrated. No. 5. OBSTETRICS. Illustrated. Fourth Edition. By HENKY G. LANDIS, M.D., Prof, of Obstetrics and Diseases of Women, in Starling Medical College, Columbus, O. Revised Edition. New Illustrations. No. 6. MATERIA MEDICA, THERAPEUTICS AND PRESCRIPTION WRITING. Fifth Revised Edition. With especial Reference to the Physiological Action of Drugs, and a complete article on Prescription Writing. Based on the Last Revision of the U. S. Pharmacopoeia, and including many unofficinal remedies. By SAMUEL O. L. POTTER, M.A., M.U., late A. A. Surg. U. S. Army; Prof, of Practice, Cooper Medical College, San Francisco. Improved and Enlarged, with Index. No. 7. GYNAECOLOGY. A Compend of Diseases of Women. By HENRY MORRIS, M.D., Demonstrator of Obstetrics, Jefferson Medical College, Philadelphia. No. 8. DISEASES OF THE EYE AND REFRACTION, including Treatment and Surgery. By L. WEBSTER Fox, M.D., Chief Clinical Assistant Ophthalmological Dept., Jefferson Med- ical College, etc., and GEO. M. GOULD, M.D. 71 Illustrations, 39 Formulae. Second Enlarged and Improved Edition. Index. No. 9. SURGERY. Illustrated. Third Edition. Including Fractures, Wounds, Dislocations, Sprains, Amputations and other operations; Inflammation, Suppuration, Ulcers, Syphilis, Tumors, Shock, etc. Diseases of the Spine, Ear, Bladder, Tes- ticles, Anus, and other Surgical Diseases. By ORVILLE HORWITZ, A.M., M.D., Demonstrator of Anatomy, Jefferson Medical Col- lege. Revised and Enlarged. 77 Formulae and 91 Illustrations. No. 10. CHEMISTRY. Inorganic and Organic. For Medical and Dental Students. Including Urinary Analysis and Medical Chemistry. By HENRY LEFFMANN, M.D., Prof, of Chemistry in Penn'a College of Dental Surgery, Phila. A new Edition, Revised and Rewritten, with Index. No. ii. PHARMACY. Based upon " Remington's Text-book of Pharmacy." By F. E. STEWART, M.D., PH. G., Quiz-Master at Philadelphia College of Pharmacy. Second Edition, Revised. Bound in Cloth, $1. Interleaved, for the Addition of Notes, $1.25. Jg^f These books are constantly revised to keep up with the latest teachings and discoveries, so that they contain all the new methods and principles. No series of books are so complete in detail, concise in language, or so well printed and bound. Each one forms a complete set of notes upon the subject tinder consideration. UNIVERSITY OF CALIFORNIA LIBRARY THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW DEC 18 1916 20 1916 M 30m-l,'15 YC169367 caps? Y4 UNIVERSITY OF CALIFORNIA LIBRARY