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C'k (EXQ.) nwMMsoK OF nmiouwT m mo «ll vNivimnT and thb TinmNART columb ■OHTMBAL WITH OVKR FIVB HUNDRED ILLUSTRATIONS YORK D. APPLETON AND COMPANY tAMDOir: OAXTOR BOUSR, rATnUTOnRK S^UARI 1869 Vl j»g» ' ,- r :• ' ; ' ♦ ,: \ 1 O?^^ ^^^'^ ^'^ Comuavt, IHP, Bt d. appletov and company. 9,0 the memors of ROBERT PALMER HOWARD, M. D., LL. D., I^n BBAK AMD FMOnMM* OT aBDIOIIIB III MCaiU. VMlrMMTT, WHOSE TBACBIMO AMD PSACTIOK BVKB TBITDBD TOWARDS THE SEOOGXltlOM Or THE IMFOkTAKCB OF PBTSIOLOOT TO XEDICINB, AND WHOSE UFE ILLV8THATED WHAT 18 bOrrV AND NOBLE IN HUMAN EXI8TBMCB, TBn WOBX IS DBDIOATID XM BBVBRBNCE AND ORATITVDB. ,t < !)^^$fmmm mmmmmtmiiiMWKm0'i^ Ikia IHiHHHHHHI mam PREFACE. The comparative method, the introduction of the teach* ings of embryology and of the welding principles of evolution as {Mtrt of the essential structure of zoology, may be said to have completely revolutionized that science; and there is scarcely a text-book treating of the subject, however element- ary, which has not been molded in accordance with these guiding lines of thought. So far as I am aware, this can not be said of a single book on the subject of physiology. Feeling, therefore, that the time had come for the appearance of a work which should attempt to do, in some degree at least, for physiology what has been so well done for morphol- ogy, the present task was undertaken. But there were other changes which it seemed desirable to make. I think any one who will examine the methods and reasoning of the physi- ology of the day will not fail, on close scrutiny, to recognize a tendency to speak of certain conclusions, for various organs (and functions), as though they applied to these organs in whatever group of animals found, or, at all events, for man, no matter what the species of the animal that had been ex- perimented upon. For some years I have, in publications of my own original researches, strongly protested gainst such methods as illogical. I am wholly at a loss to understand how a work, built upon the most fragmentary and hetero- geneous evidence, derived from experiments on a few groups of animals, or a certain amount of human clinical or patho- logical evidence, can be fittingly termed a treatise on " human physiology." It will scarcely be denied that conclusions such -i ^&mMki^:^:-' ■■ h.i&l, "'.^4i - K.m " WMI ' r VI ANIMAL PHYSIOLOGY. as this method implies would not be tolerated in the subject of morphology. While in the present work what is strictly applicable to other animals and to man has not always been kept apart, an effort has been made throughout to be cautious in all the conclusions drawn — a state of mind warranted by the past history and the present tendencies of physiology. Until our laboratory methods become more perfected, the comjwrative method more extensively applied, and conclusions drawn from "experiments" modified by comparison with the results of. clinical, pathological, and all other available sources of infor- mation, I feel convinced that we are called upon to teach cautiously and modestly. Treating, as we do in our books, each subject in a separate chapter, there is, as I know by observation, the greatest danger that the student may get the idea that each function of the body is discharged very much independently; accordingly, there has been throughout a most persistent effort made to impress the necessity for ever remembering the absolute de- pendence of all parts. Unless this be thoroughly infused into a student, it is impossible that he can ever understand the wide world of natural objects, or the narrower one of un- natural (in a sense) organisms, as seen in the hospital ward. Recognizing how important it is to teach the young stu- dent to become an observer and an investigator in spirit and in some degree in fact, only such treatment of elaborate methods has been introduced as will enable him to form a general acquaintance with the modes iu which laboratory work is earned on, while simple ways of verifying the essen- tial truths of physiology have been constantly brought before him. As to how far these are actually carried out will de- pend not a little on the teacher. The student who learns thus to observe and to verify will not fail to apply the method in his future career, whatever that may be — ^whether medical or othdr-— nor is he so likely to throw his physiology overboard , as a useless cargo as soon as his primary examination has been passed. PREFACE. ▼ii By frequently calling attention, as has been done through- out, to actually discovered or possible differences in function for different groups of animals, it is believed that the student will become possessed of a spirit of caution in drawing con- clusions that will fit him the better for the hospital ward in another respect, viz., that he will be prepared for those indi- vidual differences actually existing, and which t:eem to have been largely ignored in so many works on physiology, with the natural consequence that the student, not finding his physiology squaring with the facts of the clinique, and not being prepared for the situation, the result is disappointment and disgust, instead of the actual continuation of the study, especially as human physiology. With a view of widening the student's field of vision, sec- tions, under the heading " Special Considerations," have been introduced, which it is hoped will not fail to interest and stimulate. Most teachers of experience will welcome the summary with which each chapter concludes. In connection with no subject perhaps can the art of generalizing be better taught than with physiology, and to this end these brief synoptical sections will, it is thought, prove helpful. Systematic instruction in either macroscopic or microscopic anatomy has not been undertaken — ^in fact, can not be at- tempted, it is believed, except at the expense of physiology proper— in a work of moderate compass. At the same time attention has been called to those points which have a special bearing on each function, and a number of illustrations have been inserted with this object in view. The introduction of the subject of defelopment at so early a stage is a departure that calls for a word of explanation. An attempt has been made to use embryological facts to throw light upon the different functions of the body, and especially their relations and interdependence. It therefore became necessary to treat the subject early. It is expected, however, that the student will return to it after reading the remaining chapters of the work. I I l ll ii Ujjg vili ANIMAL PHYSIOLOGY. As BO large a proportion of those who enter upon the study of medicine begin their career without any adequate preparation in general biology, the subjept, as presented in this work, will, let me hope, meet an actual need, and prove helpful in attaining a broad and sound view of the special doctrines of biology. It is scarcely necessary to iiimark that clinical and path- ological facts have not been introduced with the view of teaching either clinical medicine or pathology, but to indi- cate to the student how his physiology bears on his profes- sion, and how the above-mentioned subjects throw light upon physiology proper and lend interest to that subject. My aim has be ti to make the book, from first to last, educative; and, retaining a vivid recollection of the severe strain put upon the memory of the medical student by our present method of crowding bo much into at most four years of study, an attempt has been made to avoid overloading the book with mer« facts or technical details, as well as to pre- sent the whole subject in as succinct a form as is compatible with clearness. Recognizing, too, the very shifting character of physiological theories, the latter have generally been pretty well kept apart from the actual facts. It is hoped that the abundance of the illustrations will prove more acceptable than would lengthy treatment of sub- jects in the text, for, if the matter of a book is to be digested and assimilated, either by the student of general biology or by the hard-worked medical student, it must not be bulky. The illustrations have been chosen from the best available sources, and the authorship of each one duly acknowledged in the body of the work. Several original diagrams, such as I find exceedingly useful in my own lectures, have been in- troduced. This book is really an embodiment of my own course of lectures, as given during the past two years more especially, and with the highest satisfaction, I think it may be said, to both students and teacher. I have unbounded confidence in the plan of the wprk, and iWiSJ PREFACE. IX I trust that its newness may excuse, to some degree, any shortcomings in the execution. Such a book has become a necessity to myself, and it is hoped will be welcomed by others. I trust the work may prove suitable, not only for the student of human medicine, but for the increasing num- ber of students of comparative or veterinary medicine, who may desire a broad basis for the study of disease in the various animals they are called upon to treat. I have en- deavored to make the work specially acceptable to the stu- dent of general biology. It only remains for me to crave the indulgence of all readers, and to thank my publishers, Messrs. D. Appleton & Co., for their uniform courtesy and the great pains they have taken to present the work in worthy form. Wkslky Mills. PBYBioiioeicAL Laboratory, McGill University, MoNTRKAi., September, 1889. m^'i'Si'iTlK' I irmlMi'iUfl I CONTENTS. I OlMlkAL BlOtOGT Introduction . Tabular statement of the Bubdivisions of Biology ThrCbll . Aninul and vegetable cells Structure of cells . Cell-contents . The nucleus . Tissues . Summary Uniceixulab OBOAinsilS Tl. (VniKTABLB) Teast. Morphological Chemical Physiological . Conclusions S. ProtocooouB Morphological Physiological . Conclusions . UnCRLLUIiAB Akimaui The proteoa animalcule Morphological Physiological . Conclusions . pABAsmc Okoamibms Fungi Muoor mucedo The Bacteria . UxicBU.ui.AB Animals wrra Dipfbbbiitiatiom or The ball-animalcule Structure Fanottons MuLTIOBLLVLAU OBOANMMS The fewh-WBter polyps . T«B Cbll bboomudbbbd Tn Akimal Body-hui epitomiied account of the functions of a mammal Stbuotvbb PA«B 1 1 4 S S 5 7 7 8 8 9 9 9 10 10 10 11 11 11 IS 18 IS IS IS 14 15 15 15 18 90 SO SO SI S8 S8 98 97 I zu ANIMAL PHYSIOLOGY. Nature — Explanfttions and illu»- LiTiNO AMD LivELESs Mattee— General explanation and comparison of their properties Classification or the Animal Kinodom Tabular statement Man's place in the animal kingdom The Law of Periodicity or Rhythm in trations The Law of HABrr. . . Its foundation . . . Instincts The Orioin op the Forms of Life Arguments from : Morphology .... Embryology .... Mimicry . . . Rudimentary organs Geographical distribution Paleontology .... Fossil and existing species . Progression . ' . Domesticated animals Summary Beprodvctiom General TheoTum , The origin and development of the Changes in the ovum itself . The male cell .... The origin of the spermatozoon Fertilisation of the oTum Segmentation and subsequent changes The gastrula . The hen's egg .... The origin of the fowl's egg . Embryonic membranes of birds . The foetal (embryonic) membranes of The placenta .... The disooidal placenta . The metadisooidal placenta . The lonary placenta The diffuse placenta The polycotyledonary placenta ' Mioroaoopic structure of the placenta Illustrations .... Evolution .... Summary .... Tbi Dbtelopmimt or thi Embryo Itsbut Oerm-layen . . < Origin of the vaaouhur system The growth of the emlwyo . oTum mammals PAOB 31 33 85 85 40 40 41 41 48 48 48 48 45 45 45 46 46 47 50 50 M 57 50 60 61 68 68 66 67 68 7S 76 80 81 81 80 86 86 87* 87 80 80 90 M •7 101 &im t PAOI 31 88 85 85 40 40 41 41 48 48 48 48 48 45 45 40 48 47 50 50 M 57 50 00 01 08 88 08 07 OB n 70 80 81 81 80 80 80 87' 87 80 80 00 OS 07 101 CONTENTS. xiii DErELOPMENT OF THE VaBCUI^R SySTEM IN VeRTEBBATES . . . . 108 The later stages of the foetal circulation 108 Detelopxent or the UROOEinTAi. System 108 A as Physioumiicai. Aspects of Dktelopiiemt 112 Menstruation and ovulation 113 The nutrition of the ovum 115 The foetal circulation ... . HO Parturition 120 Changes in the circulation at birth . . . ... . . . 120 Sexual coitus 121 Oroanic Evolution reconsidered 127 Different theories criticised — new views 127 The Chemical Constitution or the Animal Body 185 Proximate principles 187 General characters of proteids . 138 Certain non-crystalline bodies 138 The fats. . 180 Peculiar fats 140 Carbohydrates . . . . . . . . . . • • *** Nitrogenous metabolites 140 Non-nitrogenous metabolites 141 PhtsiolooicaIi Brsrabch and Physiolooical Rbasoninq . . '. 141 The Blood 147 Comparative . . . • • • .148 Corpuscles 140 History of the blood-cells 151 Chemical composition of the blood . • • ' • • « •' 154 Composition of serum 155 Composition of the corpuscles 155 The quantity and dbtribution of the blood 150 The coagulation of the blood . • .137 Clinical and pathol«gi(»l ^03 Summary 106 The Contractili Tissuia 100 General . 100 Comparative 107 Ciliary movements 108 The irritability of muscle and nerve 100 Applications of the Orapbio Mbthod so thr Study or Mubcu Physiology. .- . . . 171 Chronographs and various kinds of i^pantus .... 171-174 A single muscular oontraotion . . . '. 178 Tetanic oontTRictfon 108 The musole-tone 184 The strength of the stimulus 185 The changes in A muscle during oontraotion 188 The elasticity of muscle 187 The electrical phenomena of miuola ....... 186 Chemical changes In muscle . . .108 ThMmwl change* in the contracting BMWole 105 .«- '•**-<«MiM|.!»#NMP9*'M j xiv ANIMAL PHYSIOLOGY. The The The physiology of nerre ElectrotonuB . Pathological and clinical Law of contraction . Electrical organs . Muscular work Circumstances influencing the character of muscular The influence of blood-supply uid fatigue . Separation of muscle from the central nervous system The influence of temperature The intimate nature of muscular and nervous action Unstriped muscle . General .... Comparative . Special considerations . Functional variations . Summary of the physiology of muscle and nerve Nervous System— Gehebal Considebatioms Experimental . Automatism . Conclusions . Nervous inhibition . Circulation or thi Bux>d General .... The mammalian heart . Circulation in the mammal . The action of the liiammalian heart The velocity of the blood and blood-pressure Gtoneral Comparative . The circulation under the microscope . The characten of the blood-flow . Blood-pressure • • • The Heart The cardiac movements The impulse of the heMrt Investigation of the heart-beat from within The cardiac sounds .... Causes of the sounds Bndo-oardiao pressuns The work of tiie heart . Variations in the cardiac pnlntion The pulse Features of an arterial poise-tracing Venous pulse . . . • • Pathologiotl • • • Comparative The beat of {he heart and its modifications The nervous system in relation to the heart Influence of the vagus nerve on the iMart , i.mtmmmmmmtmiii''i'^-'' CONTBNT& XV vity 227 Conolurions Tbe accelerator nerves of the heart Human phyfiology .... The heart in reUtion to Mood-pressare The inflaenoe of the c uantity of blood Condnaions The capillaries Special considerations .... Pathological ..... Personal obsenrations ComparatiTe Evolution Summary of the physiology of the cirouUtion DiewTioir op Food .... Foodstnih, milk, etc Bmtoyologioal Comparative . The digestive juices Saliva and its action Secretion of the different glands Comparative . Pathologioai . Ghutrie juice . Bile General . Pigments Digestive action Comparative . Pancreatic secretion Snocus enteriens . Comparative . Secntion aa a physiological process Secretion of the salivary glands Secretion by the stomadi The secretioa of Ule and panoteatic jnioe The nature of the act at secretion . Self-digestion of the digestive wgans Comparative . The movements of the digestive organs Deglutition Comparative . . The movements of the 9tomaoh Comparative Pkthologioal The intevtinal movements « Defecation Vomiting Comparative Plkthologioal The nmoval of digestive prodoots from the alimentuy 260 270 278 274 275 277 281 286 290 290 29S 296 806 806 807 808 806 808 811 811 812 818 814 814 817 810 819 819 898 828 886 829 880 888 886 881 887 887 889 841 •«*«s^' i iiH l ll,MWH ' IIWHl ' WW'* ! ll" 'lil XVI ANIMAL PHYSIOLOGY. in the alimentary canal Lymph and chyle The movements o£ the lymph— comparative Pathological . Faeces .... Pathological . The changes produced in the food General .... Comparative . Pathological . Special considerations . Various .... Human physiology Evolution Summary Trb Respiratory Ststkm General . . . • Anatomical . The entrance and exit of air . The muscles of respiration Types of respiration Personal observation Comparative .... The quantity of air respired . The respiratory rhythm General . . . • Pathological . Respiratory sounds. Comparison of the inspired and the expired air Respiration in the blood Hemoglobin and its derivatives General .... Blood-spectra . Comparative . The nitrogen and the carbon dioxide of the Foreign gases and respiration Respiration in the tissues .... The nervous system in relation to respiration Nerves and centers concerned The influence of the condition of the blood The Cheyne-Stokes respiration The effects of variations on tl)e atmospheric pressure The influence of respiration on the circulation General Comparative The respiration and circulation in asphyxia Pathological Peculiar respiratory movements . Coughing, Uughing, etc. Comparative Special considerations blood on respiration 881 892 aBit^9Bf0m»i?!.*ti 858 893 CiJNTENTS. Pathological and chemical . Personal observation Evolution .... Summary of the physiology of respiration PRtyrECTITE AND ExCRETOkT FUNCTIOMS OF THE SKIN General Comparative .... The excretory function of the skin Normal sweat .... Pathological .... Comparative — Respiration by the skin Death from suppression of the functions of the skin The excretion of perspiration Experimental .... Human physiology . Absorption by the skin . Comparative . . . Summary .... EsCftETION BT THE KiDNET Anatomical . . . . Comparative .... Urine considered physically and chemically Specific gravity .... Color . . . . • ■ Reaction Quantity Composition : Nitrogenous crystalline bodies Non-nitrogenous organic bodies . Inorganic salts .... Abnormal urine .... Comparative The secretion of urine .... Methods of investigation Theories of secretion . ... Nervous influence .... Pathological The expulsion of urine .... Gleneral ...... Facts of experiment and of experience Pathological Comparative Summary of urine and the functions of the kidneys The Metabolibh op the Body General remarks The metabolism of the liver . The glycogenic function The uses of glycogen Pathological .... Metabolism of the spleen Histological . XVll PAOB 406 , 406 , 409 , 410 , 412 , 413 , 418 , 416 , 415 , 415 , 415 . 416 . 416 . 416 . 417 . 418 . 418 . 418 . 410 . 419 . 419 ; 423 . 422 . 423 . 428 . 428 . 428 . 424 . 424 . 425 . 426 . 426 . 426 . 427 . 428 . 4S» . 429 . 429 480 480 481 481 482 483 484 486 486 486 »IMi«M»« i W^ ' >WW-l«°-W. Ml.- jj^ili ANIMAL PHYSIOLOGY. Ghemicftl ^^ Spleen carrm ^** • The nerroos system in lelation to the q>leen 489 The oonstraotion of fat **® General and experimental ^ Histological *** Changes in the cells of the mammary gland . . . 4tt Milk and colostrum • **^ Nature of fat-formation • • *** Pathological . • • ^^ Comparative *** The metabolic processes concerned in the formation of urea, uric acid, hippuric acid, and allied bodies 446 General discussion 448 Pathological 448 Evolution • • 448 The study of the metabolic processes by other methods .... 449 Various tabuhur statements 400 Starvation and its lessons 400 Comparative . 408 Dieto • *» Feeding experiments 404 General 464 Proteid metabolism 455 Nitrogenous equilibrium • 466 Comparative 466 The effects of gelatine in the diet 457 Fat and carbohydrates 467 Comparative 468 The effects of salts, water, etc., on the diet ...... 458 Pathological 409 The energy of the animal body 409 Tabular statements 460 The sources of muscular energy 461 Animal heat 461 General .461 Comparative 461 The regulation of temperature • • 464 Cold-blooded and warm-blooded animals compared . 465 Theories of heat formation and heat regulation 466 Puthological 467 Special considerations 467 Bvolution . 468 Hibernation 470 Daily variations in temperature in man and other m a mm al s . 470 The influence of the nervous system on metabolism (natritton) . . 471 Bxperiioental facts 471 Discussion of their signiflcanoe • • 4n General considerations, chemical and pathdogioal .... 476 - Bomnuury of metabdism 470 CONTENTS. xix icid. PAOB Tm Spinal Gobd— Obiiirai< 480 General 480 Anatomical 482 The reflex functions of the spinal cord 484 General and experimental 484 Erolation and heredity 48S Inhibition of reflexes . 485 Reflex time 486 The spinal cotd as a conductor of imjmlaes 487 Anatomical 488 Deousaation 480 Pcthologioal 480 Paths of impulses tfl The automatic functions of the spinal cord 488 General 408 Spinal phenomena 408 Special considerations 485 Comparative 405 Evolution 480 Synoptical . 487 The Bbaw .486 GenenJ and anatomical 486 Aninuds diprived of their cerebrum SOO Behavior of various animals and its signiflcance 500 Have the ;iemioirDnlar canals a co-ordinary function t . . . . 502 Experimental, etc 502 Discussion of the phenomena 502 Fcnoed movements 608 Functions of the cerebral convolutions 504 Comparative 505 Individual dilterences in brains 518 The connection of one part of the brain with another .... 518 The cerebral cortex 521 Theories of dilterent ofaserven ........ 582 The droulation in the brain «... 825 8lam>— hibernation— dreaming 526 Hypnotism— catalepsy— somnambulism 628 Firthologioal 580 Cenbal looalixation reconsidered 580 Illustrations of looalixation . ... . " . . . 685 Different methods criticised , . 886 Cerebral time 686 Fonotiont of other portions of the brain 886 The corpus striatum and the optic thalamus 686 Corpora quadrigemina 680 The cerebellum 641 PMhological 641 Crura cerebri and and pons Varolii 641 Pathological . '. . . . 642 Medulla oblongata 642 XX ANIMAL PHYSIOLOGY. Special considetBtions . Embryological Evolution Synoptical Gknekal Remarks cm tbb Sinses Anatomical General principles . The Skin as ak Organ ok Sense Gtoneral . Pathological . Pressure senrntions Thermal sensations Tactile sensibility . The muscular sense General . Pathological . Comparative . Synoptical Vision .... Physical . Anatomical . Embryological Dioptrics of vision Accommodation of the eye Alterations' in the si» of the pupil ° Phenomena and their explanations Pathological . Optical imperfections of the eye Spherical aberration Astigmatism . Chromatic aberration Entoptic phenomena Anomalies of refraction Visual sensations . General . Affections of the retina The nature of the processes which originate visual The laws of retinal stimulation The visual angle Color sensations Theories of color-vision . Color-blindness Ptychologioal aspects of vision The visual field Imperfections of visual perceptions as •* Irradiation," Influence of the pigment of the macula lutea After-images, etc. Misconceptions as to the oompanitive size of objects Subjective phenomena . Co-ordination of the two eyes In vision impulses etc. ^.^iwM>f(^'Mi<>^;;4i^4t44 ^ fcat^ mm- vision CONTENTS. The visual axes Ocular movements . The horopter .... Estimation of the size and distance of objects Solidity Protective mechanisms of the eye Special considerotious . . . Copiparative . Evolution . . . Pathological .... Brief synopsis of the physiology of Ukarino General Anatomical .... The membrana tympani The auditory ossicles . Muscles of the middle ear The Eustachian tube Pathological .... Auditory impulses . Auditory sensations, perceptions, judgments Oeneral Auditory judgment Range of auditory discrimination Special considerations . Comparative .... Evolution .... Synopsis of the physiology of hearing The Sense of Shell Anatomical . . . < General . . . • < Comparative ... The Seitse of Taste Anatomical . . • General .... Experimental . Pathological . Comparative . The Cerbbbo-Spinal System of Nerves 1. Spinal nerves .... General Exception .... Additional experiments . Pathological .... 2. The cranial nerves . General The motor-oculi, or third nerve The trochlear, or fourth nerve The abducens, or sixth neree . The facial, or seventh nerve . xxi 501 C04 5r> 605 596 598 597 600 602 603 604 604 605 600 607 , 606 , 600 , 609 . 610 . 615 . 615 . 615 . 616 . 616 . 616 . 618 . 620 . 620 626 627 627 627 ] ■-, i.,.-t BWteajwwMw w^ xxu ANIMAL PHYSIOLOGY. The trigeminus, or fifth nerve The glosso-pharyngeal, or ninth nerve The pneumogastric, or tenth nerve The spinal accessory, or eleventh nerve The hypoglossal, or twelfth nerve . Relations of the cerebro-spinal and sympathetic systems Recent views on this subject , The Voice and Speech . Physical .... Anatomical ... Laryngoscopic observations . Voice-formation The registers and the falsetto-voice Pathological Comparative Speech . General . Formation of vowels and consonants Whispering . Classification of consonants Pathological . Special considerations . Evolution Summary Locomotion .... Anatomical . •'■. Mechanical Standing. Walking. Running. Jumping .... Hopping .... Comparative : the gait of quadrupeds Evolution Man considbrbd physiolooicau.y Existence Sixe and growth Digestive system Circulatory and respiratory systems Dentition Nervous system Puberty . The sexes Old age . Comparative Death Appendix: Animal Cbxmutrt Index . . . , . ^ AT THE DirrxBENT Pbkiodb or bib 680 640 648 648 644 646 647 640 640 660 660 661 661 662 666 666 666 666 667 660 660 060 650 664 664 666 666 666 667 667 666 668 671 601 ■*SflWtTfr!fl1 •^ smf'!^^^l»i''ISti^JV»^ '^mum 680 688 iMyiiiMiiiiMMiMmyMimiiw&iMiMii AKEMAL PHYSIOLOGY. 659 650 GENERAL BIOLOGY. Introduction. BiOLOOY ifitoi, life; Aoyot, a dissertation) is the science which treats of the nature of living things; and, since the properties of plants and animals can not be explained without some knowledge of their form, this science includes morphol- ogy (fuv^f form ; Xoyot, a dissertation) as well as physiology (^wrw, nature ; Aoyw). ' Morphology describes the various forms of living things and their parts ; physiology, their action or function. (General biology treats neither of animals nor plants exclu- sively. Its province is neither aodlogy nor botany ; but it at- tempts to define what is common to all living things. Its aim is to determine the properties of organic beings as such, rather than to classify or to give an exhaustive account of either ani- mals or planto. Manifestly, before this can be done, living things, both animal and vegetable, must be carefully compared, otherwise it would be impossible to recognize differences and resemblances ; in other words, to ascertain what they have in common. When only the highest animals and plants are contem- plated, the differences between them seem so vast that they i^pear to have, at first sight, nothing in common but that they are living: between a tree and a dog an infant can discrimi- nate; but there are microscopic forms of life that thus far defy the most learned to say whether they belong to the ani- mal or the vegetable world. As we descend in the organic series, the lines of distinction grow fainter, till they seem finally to all but disappear. But let us first inquire : What are the determining charao- 1 ii/i'iv'ji'' *■■ :-'''"-'~<~^' imW rt tohHTT i * ■ » ^ f frm n^ n' ra w i w ?^ iB i Ty iWW i lW W i i i i W tttmrnnmsss. ANIMAL PHYSIOLOOT. teristics of living things as such ? By what barriers are the animate and inanimate worlds separated? To decide this, falls within the province of general biology. Living things grow by interstitial additions of particles of matter derived from without and transformed into their own substance, while inanimate bodies increase in size by superfi- cial additions of matter over which they have no power of decomposition and recomposition so as to make them like themselves. Amonj^ lifeless objects, crystals approach near- est to living forms ; but the crystal builds itself up only from material in solution of the same chemical. composition as itself. The chemical constitution of living objects is peculiar. Car- bon, hydrogen, oxygen, and nitrogen are combined into a very complex whole or molecule, as protein; and, when in com- bination with a large proportion of water, constitute the basis of all life, animal and vegetable, known as protoplasm. Only living things can manufacture this substance, or even protein. Again, in the very nature of the case, protoplasm is con- tinually wasting by a process of oxidation, and being built up from simpler chemical forms. Carbon dioxide is an invariable product of this waste and oxidation, while the rest of the car- bon, the hydrogen, oxygen, and nitrogen are given back to the inorganic kingdom in simpler forms of combination than those in which they exist in living beings. It will thus be evident that, while the flame of life continues to bum, there is constant chemical and physical change. Matter is being continuously taken from the world of things that are without life, trans- formed into living things, and then after a brief existence in that form returned to the source from which they were origi- nally derived. It is true, all animals require their food in or- ganized form— that is, they either feed on animal or plant forms ; but the latter derive their nourishment from the soil and the atmosphere, so that the above statement is a scientific truth. Another highly characteristic property of all living things is to be sought in their periodic changes and very limits dura- tion. Every animal and plant, no matter what its rank in the scale of existence, begins in a simple form, passes through a series of changes of varying degrees of complexity, and finally declines and dies ; which simply means that it rejoins the in- animate kingdom: it passes into another world to which it formerly belonged. Living things alone give rise to living things; protoplasm are the de this, iiicles of leir own superfi- )ower of lem like ch near- ttly from as itself, ar. Car- K>a very in com- the basis a. Only protein. 1 is con- built np ivariable the car- ck to the lan those a evident constant binuously f e, trans- istence in ere origi- >od in or- or plant 1 the soil scientific ng things it6ddur»> ok in the hrough a nd finally IS the in- whioh it rotoplasm GENERAL BIOLOOT. $ alone can beget protoplasm; cell begets cell. Omne animal {anima, life) ex ovo applies with a wide interpretation to all living forms. From what has been said it will appear that life is a condi- tion of ceaseless change. Many of the movements of the pro- toplasm composing the cell-units of which living beings are made are visible under the microscope ; their united effects are open to common observation — as, for example, in the move- ments of animals giving rise to locomotion we have the joint result of the movements of the protoplasm composing millions of muscle-cells. But, beyond the powers of any microscope that has been or probably ever will be invented, there are molecular movements, ceaseless as the flow of time itself. All the processes which make up the life-history of organisms involve this mo- lecular motion. The ebb and flow of the tide may symbolize the influx and efflux of the things that belong to the inanimate world, into and out of the things that live. It follows from this essential instability in living forms that life must involve a constant struggle against forces that tend to destroy it ; at best this contest is maintained successfully for but a few years in all the highest grades of being. So long as a certain equilibrium can be maintained, so long may life con- tinue and no longer. The truths stated above will be illustrated in the simpler forms of plants and animals in the ensuing pages, and will be- come clearer as each chapter of this work is perused. They form the fundamental laws of general biology, and may be formulated as follows : 1. Living matter or protoplasm is characterized by its chem- ical composition; being made up of carbon, hydrogen, oatygen, and niirogen, arranged into a very complex molecule. 2. Its universal and constant waste and its repair by inter- stitial formation of new matter similar to the old. 8. Its power to give rise to new forms similar to the parent ones by a process of division. 4. Its manifestation of periodic changes constituting devel- opment, decay, and death. Though there is little in relation to living beings which may not be appropriately set down under zodlogy or botany, it tends to breadth to have a science of general biology which deals with the properties of things simply as living, irrespective very much as to whether they belong to the realm of animals or plants. The relation of the sciences which may be regarded aasfttw»*iy wii'iW 'wi(ii iw«o(i ii " stance {protoplasm), a cell wall, and a more or less circular body (nudeua) situated generally centrally within ; in which, again, is found a similar structure {nucleoliia). This description applies to both the vegetable and the ani- mal cell ; but the student will find that the greater proportion of animal cells have no cell wall, and that very few vegetable cells are without it. But there is this great difference between the animal and vegetable cell : the former never has a ceUuloae wall, while the latter rarely lacks such a covering. In every case the cell wall, whether in animal or vegetable cells, is of greater consistence than the rest of the cell. This is especially true of the vegetable ceU. It is doubtful whether there are any cells without a nucleus, while not a few, especially when young and most active, pos- sess several. The circular form may be regarded as the typical form of both cells and nuclei, and their infinite variety in size and form may be considered as in great part the result of the action of mechanical forces, such as mutual pressure ; this is, of course, more especially true of shape. Reduced to its great- est, simplicity, then, the cell may be simply a mass of protoplasm with a nucleus. * The Uliutnitions of the sections following will enable tlie student to form • genemliied mental piotura of the cell in all its parts. 6 ANIMAL PHTSIOLOOT. It seems probable that the numerous researches of recent years and others now in progress will open up a new world of cell biology which will greatly advance our knowledge, espe- cially in the direction of increased depth and accuracy. Though many points arer still in dispute, it may be safely said that the nucleus plays, in most cells, a rdfe of the highest importance ; in fact, it seems as though we might regard the nucleus as the directive brain, so to speak, of the individual cell. It frequently happens that the behavior of the body of the cell is foreshadowed by that of the nucleus. Thma fre- dlnairaute. B. preparinc for dlvMon ; tiw contour ia lew defined, siid tte ttbmtliMter nuiid the equntoro^ the MhronwUn spindle, p, monMt«Mti«e 5 the ^on»to nbw ^VM" •• wntripetia equntorial Ve. eS^of which *g»4*be»pwsept5d » double. KiTmigration of the hJifol eMh chromatin loop towwda oppoaite doIm ot tin 19^^ tI dla«5r4«age ; the chromatin forma a atar^ round .each pole pi a attodle. aadi a^be; faw connectoS by etranda of achromatln. O, daughter-wnadi {to|B j titet^br formed •ii»i«< mre, MMlns throuofa their retrosreaalTe devekMiment, whlcb.to completed, in the polar star at the end of the fqiindle to compoaed M protopiaam-ctranuiea « "" ""iJSS' S^uat not be mtotaken fortito ^artwr (Fl. THe <»f« ««» "KJSH* «5^JEf^ the line Unea the achromadn, and the dotted Unea oeU««natoa. (OhMhr modllled from nemmW.) X-Z. diraotradear dlviaton In the odto of the embryonic integument of the Buiopean aoorpion. After Bloohmann (Haddon). quently, if not always, division of the body of the nucleus pre- cedes that of the cell itself, and is of a most complicated cliar- acter {karyokineaia or mitoais). The cell wall is of subordinate importance in the processes of life, though of great value as a mechanical support to the protoplasm of the cell andthe aggre- THE CELL. gations of cells known as tissues. The greater part of a tree may be said to be made up of the thickened walls of the cells, and these are destitute of true vitality, unless of the lowest order ; while the really active, growing part of an old and large tree constitutes but a small and limited zone, as may be learned from the plates of a work on modem botany representing sec- tions of the wood. Animals, too, have their rigid parts, in the adult state espe- cially, resulting from the thickening of a part or the whole of the cell by a deposition usually of salts of lime, as in the case of the bones of animals. But in some cases, as in cartilage, the cell wall or capsule undergoes thickening and consolidation, and several may fuse together, constituting a matrix, which is also made up in part, possibly, of a secretion from the cell pro- toplasm. In the outer parts of the body of animals we have a great abundance of examples of thickening and hardening of cells. Very well known instances are the indurated patches of ffkin {epUTielivm) on the palms of the hands and elsewhere. It will be scarcely necessary to remark that in cells thus altered the mechanical has largely taken the place of the vital in function. This at once harmonizes with and explains what is a matter of common observation, that old men are less active —have less of life within them, in a word, than the young. Chemically, the cellulose wall of plant-cells consists of carbon, hydrogen, and oxygen, in the same relative proportion as exists in starch, though its properties are very difEerent from those of that substance. Turning to cell contents, we find them everywhere made up of a clear, viscid substance, containing almost always granules of varying but very minute size, and differing in consistence, not only in different groups of cells, but often in the same cell, so that we can distinguish an outer portion {edopkum) and an inner more fluid and more granular reg^ion {endoplaam). The nucleus is a body with very clearly defined outline (in some cases limited by a membrane), throughwhich an irregu- lar network of fibers extends that stains more deeply than any other part of the whole cell. Owing to the fact that it is so readily changed by the action of reagents, it is impossible to ascertain the exact chemical com- position of living protoplasm; in consequence, we can only infer its chemical structure, etc., from the examination of the dead substance. In general, it may be said that protoplasm belongs to the ' ; i 8 ANIMAL PHTSI0L06T. class of bodies known as proteids — that is, it consists chemically of carbon, hydrogen, a little sulphur, oxygen, and nitrogen, ar- ranged into a very complex and unstable molecule. This very instability seems to explain at once its adaptability for the manifestation of its nature as living matter, and at the same time the readiness with which it is modified by many circum- stances , so that it is possible to understand that life demands an incessant adaptation of internal to external conditions. It seems highly probable that protoplasm is not a single pro- teid substance, but a mixture of such ; or let us rather say, fur- nishes these when chemically examined and therefore dead. Very frequently, indeed generally, protoplasm contains other substances, as salts, fat, starch, chlorophyl, etc. From the fact that the nucleus stains differently from the cell contents, we may infer a difference between them, physical and especially chemical. It (nucleus) furnishes on analysis nu- cZem, which contains the same elements as protoplasm (with the exception of sulphur) together with phosphorus. Nuclei have great resisting power to ordinary solvents and even the digest- ive juices. Inasmuch as all vital phenomena are associated with proto- plasm, it has been termed the " physical basis of life " (Hux- ley). TiMiiM. — A collection of cells performing a similar physio- logical action constitutes a tissue. (Generally the cells are held together either by others with that sole function, or by cement material secreted by them- selves. An orgcm may consist of one or several tissues. Thus the stomach consists of muscular, serous, connective, and gland- ular tissues besides those constituting its blood-vessels, lym- phatics, and nerves. But all of the cells of each tissue have, speaking generally, the same function. The student is referred to works on general anatomy and histology for classifications and descriptions of the tissues. The statements of this chapter will find illustration in the pages immediately following, after which we shall return to the subject of the cell afresh. lauuurj. — ^The typical cell consists of a wall, protoplasmic contents, and a nucleus. The vegetable cell 1^ a limiting membrane of cellulose. Oells undergo differentiation and may be united into groups forming tissues which serve one or more definite purposes. The chemical constitution of protoplasm is highly complex nNICBLLULAB PLANTa 9 and unstable. The nucleus plays a prominent part in the life- history of the cell, and seems to be essential to its perfect devel- opment and greatest physiological efficiency. F».r UNICELLULAR PLANTS. Ybast {Torukt, Saccharomycea Cerevisue). The essential part of the common substance, yeast, may be studied to advantage, as it affords a simple type of a vast group of organisms of profound interest to the student of physiology and medicine. To state, first, the main facts as ascertained by observation and experi- ment : XorphologiaaL — The particles of which yeast is composed are cells of a circular or oval form, of an average diameter of about x^ of an inch. Each individual tortda cell consists of a trans- parent homogeneous cov- ering {ceHuloae) and gran- ular semifluid contents {protoplaam). Within the latter there may be a space (vacuole) filled with more fluid contents. The various cells pro- duced by buddinjr may t*. L-rhe endogonldte (Meoapore) phiM of ., .... , , ' dnetton— I. e., endoniMHia diTiaion. remain united like strings of beads. Collections of masses composed of four or more subdivisions {aa- eoaporea), which finally separate by rupture of the original cell wall, having thus become themselves inde- pendent cells, may be seen more rarely (endogenous division). VarfoH ■tagM In tiM derekminent of brewerd solution consisting of a dilute solution of cer- tain salts, togf:.ther with sugar. GonduibMi— What are the conclusions which may be legiti- mately drawn from the above facts P That the essential part of yeast consists of cells of about the size of mammalian blood-corpuscles, but with a limiting wall of a substance different from the inclosed contents, which latter is composed chiefly of that substance common to all living things— protoplasm ; that like other cells they reproduce their J. ind, and in this instance by two methods : gemmation giving rise to the bead-like aggregations alluded to above; and in- ternal division of the protoplasm {endogetunu diviaion). From the circumstances under which growth and reproduc- tion take place, it will be seen that the original protoplasm of the cells may increase its bulk or grow when supplied with suitable food, which is not, as will be learned later, the same in all respects as that on which green plants thrive ; and that this may occur in darkness. But it is to be especially noted that the protoplasm resulting from the action of the living cells is wholly different from any of the substances used as food. This power to construct protoplasm from inanimate and. unorgan- ized materials, reproduction, and fermentation are all proper- ties characteristic of living organisms alone. It will be further observed that these changes all take place within narrow limits of temperature; or, to put the matter -vimmam CNICEM LAR PLANTS. 11 3 analyzed, tn, calcium, H, O, N, S, I by drying o a solution carbon di- >me frothy; {fermentor ) process de- j saccharine All of these ; sunlight, tundantly in ation of cer- ay be legiti- of about the imiting wall which latter » all living trodnce their ation giving 3ve; and in- sion). nd reproduc- rotoplasm of applied with ', the same in and that this oted that the ving cells is \atood. This Old unorgan- re all proper- all take place t the matter more generally bat the li -history of thishu-Hble >rpaiism can only be unfolded und«?i ♦^rtH n '-defined ondiuoim. PbotococcuS (Protoco tis pluvi( ,$). The study of this one-celled f nt will wford instructive comparison between the ordinary green iilant jyid the colorless plants or fungi. . ' Like Ibrufa it is selected because of its simple nature, its abundance, and the ease with which it may be obtained, for it abounds in water-barrels, standing pools, drinking-troughs, etc. KoipliologiHiL— Protococcus consists of a structureless wall and viscid granular contents, i e., of cellulose and protoplasm. The protoplasm may contain starch and a red or green color- ing matter (cWoropfcyl). It probably contains a nucleus. The cell is mostly globular in form. »Hk& nc e.*r. thelMrkoCatne. obMrred in the HMtMonr ^,3i*;?t!^j^^^8^'*^i^i^2^.^^.«'*«E^i^'*i^^ ill wall; or lotile form, lulose coat, ;ate again. nrly animal in common irtue of be- aterial into le by analo- ^ > the green L its cfaloro* removal of , while for ler kind of limals; and illy injured mentation. er form we r as readily ^me circum* transparent >rless blood- r, more con- ■ proper cell clear space intervals in enly. This m pulsating >lus may be L parts of its drawn, od as proves ires, besides UNIOBLLAB ANIMALS. 18 inorganic and unorgani^ food, also organized matter in the form of a complex organic compound known as protetn, which ne Wn.9. ■teM. ve-, Fw.ll. na.ll. fte.U. ■ne. -re fte. ire Fie. 14. fto.ia. FM.lfc Fhm. ptotrading to form • pwndopodiam, into drawn wider zA», D. 8.) ^ ^ . .. Fw. 8.-1110 kKsomotor phMB ; tboectoplHm ia Fu..t?fA^i:ir'^sruSss:iph-a a tog«t-rtoor««ta^ am. ««««««-« ItoflS^I«*tto« of U.0 of«rtuw «i«.«rtod ta Fig. 9 .ftor oo«i*eto li«^ of tbBtagMted orgMdu M» luuioMBted nudorgoliig ojeeuon ( i(«nsretloii)*t/)>,iB ^%S;:!^ssz:^sss:^^t^^s^ In tha above dinm; M, ,.„of tiMianw indlTld- .»»r .i-u.™>»«.~™,.-i. Wthat^bonnctooadlTldaaftMt. dS5iiS^SS5«*tatv;«»oto;a«.tliomiclaQa: pt. paoudopo- food-partlrle. contains nitrogen in addition to carbon, hydrogen, and oxygen. In fact. Amoeba can prey upon both plants and animals, and thus use up as food protoplasm itself. The pseudopodia serve the double purpose of organs of locomotion and prehension. This creature absorbs oxygen and evolves carbon dioxide. u ANIMAL PHTSIOLOOT. Inasmnch as any part of the body may serre for the admission, and possibly the digestion, of food and the ejection of the use- less remains, we are not able to define the functions of special parts. Amoeba exercises, however, some degree of choice as to what it accepts or rejects. The movements of the pseudopodia cease when the tempera- ture of the surrounding medium is raised or lowered beyond a certain point. It can, however, survive in a quiescent form greater depression than elevation of the temperature. Thus, at 35° 0., heat-rigor is induced ; at 40° to 45° 0., death results ; but though all movement is arrested at the freezing-point of water, recovery ensues if the temperature be gradually raised. Its form is modified by electric shocks and chemical agents, as well as by variations in the temperature. At the present time it is not possible to define accurately the functions of the vacuoles found in any of the organisms thus far considered. It is worthy of note that Amoeba may spontaneously assume a spherical form, secrete a structureless covering, and remain in this condition for a variable period, reminding us of the similar oehavior of Torula. Amoeba reproduces by fission, in which the nucleus takes a prominent if not a directive part, as seems likely it does in re- gard to all the functions of unicellular organisms. OonoluUnuL— It is evident that Amoeba is, in much of its be- havior, closely related to both colored and colorless one-celled plants. All of the three classes of organisms are composed of protoplasm ; each can construct protoplasm out of that which is very different from it ; each builds up the inanimate inorganic world into itself by virtue of that force which we call vital, but which in its essence we do not understand ; each multiplies by division of itself, and all can only live, move, and have their being under certain definite limitations. But even among forms of life so lowly as those we have been considering, the differences between the animal and vegetable worlds appear. Thus, Amoeba never has a cellulose wall, and can not subsiH on inorganic food alone. The cellulose wall is not, however, invariably present in plants, though this is generally the case ; »ud there are animals (Ascidians) with a cellulose investment. Such are very exceptional oases. But the law that animals must have organized material {protein) as food is without ex- ception, and forms a broad line of distinction between the ani- mal and vegetable kingdoms. Amoeba will receive further consideration later; in the PASAEOnO OBOANISM& 16 admission, the use* of special loice as to tempera- beyond a cent form Thus, at «ults; but t of water, aised. Its its, as well t time it is le vacuoles red. It is assume a remain in the similar us takes a does in re- h of its be* } one-celled omposedof at which is e inorganic 11 vital, but iltiplies by have their ren among dering, the ids appear, not subsi.'^t b, however, iy the case ; nvestment. at animals irithout ex* len the ani* er; in the mean time, we turn to the study of forms of life in many respects intermediate between plants and animals, and full of practical interest for mankind, on account of their relations to disease, as revealed by recent investigations. PABASmO OBGANISMB. The Fungi. Molds (Feniomium Olatusum and Mucor Mucedo). Closely related to IbruJa physiologically, but of more com* plex structure, are the molds, of which we select for convenient study the common green mold (PeniciUium), found growing in dark and moist places on bread and similar substances, and the white mold (Mucor), which grows readily on manure. The fungi originate in spores, which are essentially like Torula in structure, by a process of budding and longitudinal extension, resulting in the formation of transparent branches or tubules, filled with protoplasm and invested by cellulose walls, across which transverse partitions are found at regular intervals, and in which vacuoles are also visible. The spores, when growing thus in a liquid, give rise to up- ward branches (aMrud hyphce), and downward branches or root* lets {submerged hypluz). These multitudinous branches inter- lace in every direction, forming an intricate f elt*work, which supports the green powder (spores) which may be so easily shaken oft from a growing mold. In certain cases the aSrial hyphflB terminate in tufts of branches, which, by transverse division, become split up into spores {Conidia), each of which is similar in structure to a yeast-celL The green coloring matter of the fungi is not chlorophyl. The Oonidia germinate under the same conditions as Torula. Mmot Mnoado.— The growth and development of this mold may be studied by simply inverting a glass tumbler over some horse-dung on a saucer, into which a very little water has been poured, and keeping the preparation in a warm place. Very soon whitish filaments, gradually getting stronger, ap* pear, and are finally topped by rounded heads or spore-cases {Sporangia). These filaments are the hyphat, similar in struct- ure to those of Penioillium. The spore-case is filled with a multitude of oval bodies {spores), resulting from the subdivis- ion of the protoplasm, which are finally released by the spore* { VNkflT< *At**»«iS*iMaw«i»swwsp®i PABASITIC ORGANISMS, 17 FHs. 17 to ttb— III the ftdlowiiiK flfiuca. fto. denotN aMal byptm : «p, i goapore; «v, exoaporium ; mjrjnjroeliiiin ; mc, maeHage ; el,coluiiiell Flo. n.—Spa»hemrlDS hTPlxB of ■ooor. Krowinc from hc mw duiur. no. 18.-TKe MUM, tCMed out wllh needlM (A, 4). Fioa. I>, W, •!.— SueoMrive alagM In the devektpawBt of ttw qionuiffiam. Flo. n.— iMlated ■MTM of IbMar. Fw. at.— GcmiliMttiic ipaTCa ol tba Mine mold. Fm. M.-aaeaMrive MfM In the germination of • rinRle epore. Fiaa. K, M, t7.— fliioewl¥» r*- •- ""^ ' Flo. M.— OueeemlTe itagea oL. eilUum In an ohJaoHElnM < » phaam In the oonJngatlTe nroMM of Muoor. ovaarved daring ten boon In the growth of a oonMlophare of ftni- «oaltara(D,^ ./ rm.m. case becoming thinned to the point of rupture. The devel- opment of these spores takes place in substantially the same manner as those of Penicillium. Sporangia developing spores in this fashion by division of the protoplasm are termed asci, tOid the spores cueosporea. So long as nourishment is abundant and the medium of growth fluid, this asexual method of reproduction is the only one ; but, under other circumstances, a mode of increase, known as cor^jiigation, arises. Two adjacent hyph» enlarge at the ex- tremities into somewhat globular heads, bend over toward each other, and, meeting, their opposed faces become thinned, and the contents intermingle. Tbe result of this union {zygospore) undergoes now certain further changes, the cellulose coat being separated into two— an outer, darker in color {exoeporiutn), and an inner colorless one {endo^oorivm). Under favoring circumstances these coats burst, and a branch sprouts forth from which a vertical tube arises that termiimtes in a sporangium, in which spores arise, as before de- scribed. It will be apparent that we have in Mucor the exem- plification of what is known in biology as "dUemcUion of gen- erations " — ^that is, there is an intermediate generation be- tween the original form and that in which tiie original is again reached. Physiologically the molds closely resemble yeast, some of them, as Muoor, being capable of exciting a fermentation. The ftmgi are of special interest to the medical student, be- cause many forms of cutaneous disease are directly associated with their growth in the epithelium of the skin, as, for exam- ple, common ringworm ; and their great vitality, and the facil- ity with which their spores are widely dispersed, explain the highly contagious nature of such diseases. The media on which they flourish (feed) indicates their great physiological differ- ences in this particular from the green plants proper. They are closely related in not a few respects to an important class of vegetable organisms, known as bacteria, to be considered forth- with. I ■■wii I 18 animal physiology. The Bacteria. The bacteria include numberless varieties of organisms of extreme minuteness, many of them visible only by the help of the most powerful lenses. Their size has been estimated at from tvhnf to ttW of an inch in diameter. They grow mostly in the longitudinal direction, and repro- duce by transverse division, forming spores from which new generations arise. Some of them have vibratile cilia, while the cause of the movements of others is quite unknown. As in many»other lowly forms of life, there is a quiescent as well as an active stage. In this stage {zoogUm fonn) they ,-» « Fio.». f* '^\ no.ao. no. SI. tra.ai Ito. «>.-lUoraoocous, v«7 Uka a ifwra, but uMAlljr much nwllw. •to' U -BS^wT'Tlie omtml flUment praMiitMl thi« wniMitad WMnaee m tto twuU of no. Mr-eMriUimi ; TMrlow tomw. Tta flnt two repnatnt vtbrio, whfcfli Is poHiiiiy omr • na.%!f£$!A MrfM. Mwrn, ihowtiW » qrfrilhun •«gri|irt« in tte are surrounded by a gelatinous matter, probably secreted by themselves. MP rganisms of the help of stimated at , and repro- which new ause of the a quiescent form) they 10. Ml nee M tto TWuU of km. Is poHililj onlr • Mtlncitate. ' seoreted by PARASITIC ORGANISMS. 19 Bacteria grow and reproduce in Pasteur's solution, render- ing it opaque, as well as in almost all fluids that abound in proteid matter. That such fluids readily putrefy is owing to the presence of bacteria, the vital action of which suffices to break asunder complex chemical compounds and produce new ones. Some of the bacteria reqture oxygen, as BaciUus cm- tkracis, while others do not, as the organism of putrefaction. Bacterium termo. Bacteria are not so sensitive to slight variations in tempera- ture as most other organisms. They can, many of them, with- stand freezing and high temperatures. All bacteria and all germs of bacteria are killed by boiling water, though the spores are much more resistant than the mature organisms themselves. Some spores can resist a dry heat of 140" C. The spores, like Torula and Protococcus, bear drying, with- out loss of vitality, for considerable periods. That different groups of bacteria have a somewhat different life-history is evident from the fact that the presence of one checks the other in the same fluid, and that successive swarms of different kinds may flourish where others have ceased to live. That these organisms are enemies of the constituent cells of the tissues of the highest mammals has now been abundantly demonstrated. That they interfere with the normal working of the organism in a great variety of ways is also clear; and certain it is that the harm they do leads to aberration in cell- life, however that may be manifested. They rob the tissues of their nutriment and oxygen, and poison them by the products of the decompositions they produce. But apart from this, their very presence as foreign agents must hamper and derange the delicate mechanism of cell-life. These organisms seem to people the air, land, and waters with invisible hosts far more numerous than the forms of life we behold. Fortunately, they are not all dangerous to the higher forms of mammalian life ; but that a large proportion of the diseases which afflict both man and the domestic animals are directly caused, in the sense of being invariably associated with, the presence of such forms of life, is now beyond doubt. The facts stated above explain why that should be so ; why certain maladies should be infectious ; how the germs of dis- ease may be transported to a friend wrapped up in the folds of a letter. Disease thus caused, it must not be forgotten, is an illustra- wm 30 ANIMAL PHTSIOLOOT. tion of the struggle for existence and the sarvival of the fittest, (if the cells of an organism are mightier than the bacteria, the latter are overwhelmed; but if the bacteria are too great in numbers or more vigorous, the cells must yield ; the battle may waver — now dangerous disease, now improvement — ^but in the end the strongest in this, as in other instances, prevail UNICELLULAB AJUDtAlS WITH DIFFERENTIATION OF STRUCTDBE. The Bell- Animalcule iVorticeUa). Amoeba is an example of a one-celled animal with little per- ceptible differentiation of structure or corresponding division of physiological labor. This is not, however, the case with all unicellular animals, and we proceed to study one of these with considerable development of both. The Bell -animalcule is found in both fresh and salt water, either single or in groups. It is anchored to some object by a rope-like stalk of clear pro- toplasm, that has a spiral appearance when contracted; and which, with a certain degree of regularity, shortens and length- ens alternately, suggesting that more definite movement (con- traction) of the form of protoplasm known as muscle, to be studiv >i later. The body of the creaturais bell-shaped, hence its name ; the bell being provided with a thick everted lip (peristome), covered with bristle-like extensions of the protoplasm (ct2ta), which are in almost constant rhythmical motion. Covering the mouth of the bell is a lid, attached by a hinge r f protoplasm to the body, which may be raised or lowered. A wide, funnel-like depres- sion (cesophagus) leads into the softer substance within which it ends blindly. The outer part of the animal {euUcula) is denser and more transparent than any other part of the whole creature ; next to this is a portion more granular and of inter- mediate transparency between the external and innermost portions (cortical layer). Below the disk is a space (contractile vesicle) filled with a thin, clear fluid, which may bo seen to enlarge slowly and then to collapse suddenly. When the Vorti- cella is feeding, these vesicles may contain food-particles, and in the former, apparently, digestion goes on. Such food vacu- oles (vesicles) may circulate up one side of the body of the ani- mal and down the other. Their exact significance is not known, but it would appear as if digestion went on within them ; and •i*r/*W«v^v■j«^lWS4-~^'S^5I3Ea5»*Sii55«^^ F the fittest octeria, the 00 great in 1 battle may -but in the aiL ltion op bh little per- ing division 3ase with all ►f these with umalcule is )r in groups, of clear pro- tracted; and \ and length- vement (con- misde, to be ts name ; the yme), covered a), which are the mouth of I to the body, 1-like depres- within which {(BtUieula) is of the whole and of inter- id innermost ce (cow^racftk ly bo seen to den the Vorti- particles, and Lch food vacu- idy of the ani- ls not known, lin them ; and U5ICELLULAB ANIMALS. SI possibly the clear fluid with which they are filled may be a spe- cial secretion with solvent action on food. trs fta.«r. na.8B. no. as. noa »4to40.-ln the t««owtog .flgurw Atewtesdhe, ?iJ8^rw^\eSnmlej«/, oontwrtUe ifter ; c. at ; iM, nuolMia ; ^^olUmii of TMtiaellte 'diowliig the crMtnre in FioX^SteSSnTto thewttMided Md to the retrmcted •late. (SurfMe Tiewe.). . .. _ . . ._„.^ Fia. w!-8how« food-vMuolea ; one to the act of tagefr Fio-^w"- A Tortloelto, to whidi the prooees of mulUpUca- K«.1S^''lh?!SSl& W-on ; the production of two to- r,«l5lffiJ.'SS?S?f5^«ctlonhyco«]«girtlan. Fio. 40.— An enoyirted TorfierlU. no.aa. Situated somewhat centrally is a horseshoe-shaped body, with well-defined edges, which stains more readily than the rest of the cell, indicating a different chemicaLcomposition ; and, from the prominent part it takes in the reproductive and other functions of the creature, it may be considered the nucleus Multiplication of the species is either by gemiwaton or by fission. In the first case the nucleus divides and the fragments are transformed into locomotive germs ; in the latter the entire animal, including the nucleus, divides longitudinally, each half becoming a similar complete, independent organism. Still an- jtt ANIMAL PHT8IOL0OY. other method of reproduction is known. A more or less globu- lar body encircled with a ring of cilia and of relatively small size may sometimes be seen attached to the usual form of Vorti- cella, with which it finally becomes blended into one mass. This seems to foreshadow the '' sexual conjugation ** of higher forms, and is of great biological significance. Vorticella may pass into an encysted and quiescent stage for an indefinite period and again become active. The history of the Bell-animalcule is substantially that of a vast variety of one-celled organisms known as Infusoria, to which Amoeba itself belongs. It will be observed that the resemblance of this organism to Amceba is very great ; it is, however, introduced here to illustrate an advance in differentiation of structure ; and to show how, with the latter, there is usually a physiological advance also, since there is additional functional progress or division of labor; but still the whole of the work is done with- in one cell. Amoeba and Vorticella are both factories in which all of the work is done in one room, but in the latter case the machinery is more complex than in the former ; there are cor- respondingly more processes, and each is performed with greater perfection. Thus, food in the case of the Boll-animalcule is swept into the gullet by the currents set up by the multitudes of vibrating arms around this opening and its immediate neigh- borhood ; the contractile vesicles play a more prominent part ; and the waste of undigested food is ejected at a more definite portion of the body, the floor of the oesophagus ; while all the movements of the animal are rhythmical to a degree not exem- plified in such simple forms as Amoeba; not to mention its various resources for multiplication and, therefore, for its perpetuation and permanence as a species. It, too, like all the unicellular organisms we have been considering, is susceptible of very wide distribution, being capable of retaining vitality in the dried state, so that these infusoria may be carried in vari- ous directions by winds in the form of microscopip dust. MULTIOELLULAB OBOANISMB. Thb Fbbsh-Watbr P0LTP8 {Hydra viridia ; Hydra fuaoa). The comparison of an animal so simple in structure, though made up of many cells, as the Polyp, with the more complex organizations with which we shall have especially to deal, may "mm MULTICELLULAR ORGANISMS. 98 globn- vely small 1 of Vorti- lass. This her forms, t stage for history of variety of Amoeba mce of this ' introduced icture ; and ysiological »rogres8 or done with- « in which er case the re are cor- rith greater imalcule is multitudes iate neigh- linent part ; ore definite hile all the e not exem- mention its >re, for its like all the susceptible ; vitality in led in vari- lust. dra fuaca). ure, though >re complex » deal, may be fitly undertaken at this stage. The Polyps are easily obtain- able from ponds in which they are found attached to various kinds of weeds. To the naked eye, they resemble translucent masses of jelly with a greenish or reddish tinge. They range in size from one quarter to one half an inch ; are of an elongated cylindrical form ; provided at the oral extremity with thread- like tentacles of considerable length, which are slowly moved about in all directions ; but they and the entire body may short- en rapidly into a globular mass. They are usually attached at the opposite (aboral) pole to some object, but may float free, or slowly crawl from place to place. It may be observed, under the microscope, that the tentacles now and then embrace some living object, convey it toward an opening (mouth) near their base, from which, from time to time, refuse material is cast out. It may be noticed, too, that a living object within the touch of these tentacles soon loses the power to struggle, which is owing to the peculiar cells (netUe-ceUs, \vrticaHng capsules, nemato- cysts) with which they are abundantly provided, and which se- crete a poisonous fluid that paralyzes prey. The mouth leads into a simple cavity (ccelom) in which digestion proceeds. The green color in Hydra viridis, and the red color of Hydra f usca, is owing to the presence of cidorophyl, the function of which is not known. Hydra is structurally a sac, made up of two layers of cells, an outer (ectoderm) and an inner {endoderm) ; the tentacles being repetitions of the structure of the main body of the animal, and so hollow and composed of two cell layers. Speaking generally, the outer layer is devoted to obtaining information of the surroundings ; the inner to the work of preparing nutriment, and probably, also, discharging waste matters, in which latter assistance is also received from the outer layer. As digestion takes place largely within the cells themselves, or is intracellular, we are reminded of Yorticella and still more of Amoeba. There is in Hydra a genfral advance in development, but not very much in- dividual cell specialization. That of the ucticating capsules is one of the best examples of such specialization in this creature. (X Polyp is like a colony of Amoebee in which some division of utbor (function) has taken place ; a sort of biological state in which every individual is nearly equal to his neighbor, but somewhat more advanced than those neighbors not members of the organization. But in one respect the Polyps show an enormous advance. Ordinarily when nourishment is abundant hydra multiplies by MULTlOBfJiULAB OROANISMa S6 'O ito.A Fif isloii Fio. 44.— Small portion of a transverse section aeroas tlie bodjr of a green hydra (D, S). Flo. 46.— A large brown hydra bearing at the same time bods produced aaezually and sexual Fia.4E^Liwger crik of the ectodHrm Isolated. Note the prociwsss of the cells or Klelnen- beiK's fibers. (F, 8.) An of the cuts on pages, •, 11, IS, IS, 18, 81 and 81, have been seieoted fhim Howes' "AUaa of Biology." budding, and when out into portions each may become a com- plete individual. However, under other circumstances, near the bases of the tentacles the body wall may protrude into little masses if^esiea), in which cells of peculiar formation {Bperma- tozoa) arise, and are eventually set free and unite with a cell {ovum) formed in a similar protrusion of larger size {ovary). iHere, then, is the first instance in which distinctly sexual re- production has been met in our studies of the lower forms of life. This is substantially the same process in Hydra as in mammals. But, as both male and female cells are produced by the same individual, the. sexes are united {hermapJiroditiam) ; each is at once male and female. f Any one watching the movements of a Polyp, and compar- inglt with those of a Bell-animalcule, will observe that the former are much less machine-like ; have greater range ; seem to be the result of a more deliberate choice ; are better adapted to the environment, and calculated to achieve higher ends. In the absence of a nervous system it is.not easy to explain how one part moves in harmony with another, except by that process which seems to be of such wide application in nature, adapta- tion from habitual simultaneous effects on a protoplasm capable of responding to stimuli When one process of an Amoeba is touched, it is likely to withdraw all. This we take to to be due to influences radiating through molecular movement to other parts; the same principle of action may be. extended to Hydra. vThe oftener any molecular movement is repeated, the more it (tends to become organised into regularity, to become fixed in ^its mode of action ; and if we are not mistaken this is a funda- mental law throughout the entire world of living things, if not W all things animate and inanimate alike. To this law we ^shall return. \|ti!it Hydra is a -creature of but very limited specializations; there are neither organs of circulation, respiration, nor excretion. 96 ANIMAL PHYSIOLOGY. if we exclude the doubtful case of the thread-cells {urticafing capsvlea). The animal breathes by the entire surface of the body ; nourishment passes from cell to cell, and waste is dis- charged into the water surrounding the creature from all cells, though probably not quite equally. All parts are not digestive, respiratory etc., to the same degree, and herein does it differ greatly from Amoeba or even Vorticella, though fuller knowl- edge will likely modify our views of the latter two and similar organisms in this regfurd. THB CELL REiCONSIDERED. Having now studied certain one-celled plants and animals, and some very simple combinations of cells (molds, etc.), it will be profitable to endeavor to generalize the lessons these humble organisms convey ; for, as will be constantly seen in the study of the higher forms of life of which this work proposes to treat principally, the same laws operate as in the lowliest living creatures. The most complex organism is made up of tissues, which are but cells and their products, as houses are made of bricks, mortar, wood, and a few other materials, however large or elaborate. The student of physiology who proceeds scientifically must endeavor, in investigating the functions of each organ, to learn the exact behavior of each cell as determined by its own inher- ent tendencies, and modified by the action of neighboring cells. The reason why the function of one organ differs from that of another is that its cells have departed in a special direction from those properties common to all cells, or have become func- tionally differentiated. But such a statement has no meaning unless it be well understood that cells have certain properties in common. This is one of the lessons imparted by the preceding studies which we now review. Briefly stated in language now extensively used in works on biology, the common properties of cells (protoplasm), whether animal or vegetable, whether con- stituting in themselves entire animals or plants, or forming the elements of tissues, are these : The collective chemical processes associated with the vital activities of cells are termed its meta- bolism. Metabolism is constructive when more complex com- pounds are formed from simpler ones, as when the Protococcus- cell builds up its protoplasm out of the simple materials, found in rain-water, which make up its food. Metabolism is destruct- THE ANIMAL BODT. S7 urticating use of the ste is dis- all cells, digestive, it differ er knowl> nd similar d animals, tc.), it will »e humble the study ies to treat iest living of tissues, '6 made of ever large cally must ^n, to learn [)wn inher- ing cells. >m that of I direction some f unc- [> meaning operties in preceding l^iage now operties of ether con- rming the . processes 1 its meta- iplex com- otococcus- als, found s destruct- ive when the reverse process takes place. The results of this process are eliminated as escareta, or useless and harmful prod- ucts. Since all the vital activities of cells can only be mani- fested when supplied with food, it follows that living organisms convert potential or possible energy into kinetic or actual en- ergy. When lifeless, immobile matter is taken in as food and, as a result, is converted by a process of aasimUation into the protoplasm of the cell using it, we have an example of poten- tial being converted into actual energy, for one of the proper* ties of all protoplasm is its contractUUy. Assimilation implies, of course, the absorption of what is to be used, with rejection of waste matters. The movements of protoplasm of whatever kind, when due to a stimulus, are said to indicate irritabUity ; while, if inde- pendent of any external source of excitation, they are denomi- nated automatic. Among agents that modify the action of all kinds of proto- plasm are heat, moisture, electricity, light, and others in great variety, both chemical and mechanical. It can not be too wJl remembered that living things are what they are, neither by virtue of their own organization alone nor through the action of their environment alone (else would they be in no sense dif- ferent from inanimate things), but because of the relation of the organization to the surroundings. Protoplasm, then, is contractile, irritable, automatic., absorp- tive, secretory (and excretory), metabolic, and reprodudive. But when it is affirmed that these are the fundamental prop- erties of all protoplasm, the idea is not to be conveyed that cells exhibiting these properties are identical biologice^ly. No two masses of protoplasm can be quite alike, else would there be no distinction in physiological demeanor— no individuality. Every cell, could we but behold its inner molecular mechanism, differs from its neighbor. When this difference reaches a certain de- gree in one direction, we have a manifest differentiation leading to physiological division of labor, which may now with advan- tage be treated in the following section. THE ANIMAL BODY. An animal, as we have learned, may be made up of a single cell in which each part performs much the same work ; or, if there be differences in function, they are ill-defined as compared mi i lffv iii iiifti i iii i iMiiiiiia'iiaiiiii ii 28 ANIMAL PHYSIOLOGY. with those of higher animals. The condition of things in such an animal as Amoeba may be compared to a civilized commu- nity in a very crude social condition. When each individual tries to perform every office for himself, he is at once carpenter, blacksmith, shoemaker, and much more, with the natural re- sult that he is not efficient in any one direction. A commtmity may be judged in regard to its degree of advancement by the amount of division of labor existing within it. Thus is it with the animal body. We find in such a creature as the fresh-water Hydra, consisting of two layers of cells forming a simple sac, a slight amount of advancement on Amoeba. Its external surface no longer serves for inclosure of food, but it has the simplest form of mouth and tentacles. Each of the cells of the internal layer seems to act as a somewhat improved or specialized Amoe- ba, while in those of the outer layer we mark a beginning of those functions which i;aken collectively give the higher ani- mals information of the surrounding world. niiooking to the existing state of things in the universe, it is plam that an animal to attain to high ends must have powers of rapid locomotion, capacity to perceive what makes for its in- terest, and ability to utilize means to attain this when perceived. These considerations demand that an animal high in the scale of being should be provided with limbs sufficiently rigid to sup- port its weight, moved by strong muscles, which must act in harmony. But this implies abundance of nutriment duly pre- pared and regularly conveyed to the bones and muscles. All this would be useless unless there was a controlling and ener- gizing system capable both of being impressed and originating impressions. Such is found in the nerves and nerve-centers. Again, in order that this mechanism be kept in good running order, the waste of its own metabolism, which chokes and poi- sons, must be got rid of — Whence the need of excretory apparatus. In order that the nervous system may get sufficient informa- tion of the world around, the surface of the body must be pro> vided with special message-receiving offices in the form ot modified nerve-endings. In short, it is seen that an animal as high in the scale as a mammal must have muscular, osseous (and connective), digestive, circulatory, excretory, and nervous tissues ; and to these may be added certain forms of protective tissues, as hair, nails, etc. Assuming that the student has at least some general knowl- edge of the structure of these various tissues, we propose to tell in a simple way the whole physiological story in brief. THE ANIMAL BODY. » in such commu- dividual arpenter, tural re- oiiniuiity it by the is it with jsh-water )le sac, a d surface simplest B internal :ed AmoB- inning of gher ani- rerse, it is ire powers for its in- perceived. L the scale l^d to sup- ust act in duly pre- scles. All and ener- riginating \re-centers. d running >s and poi- apparatus. b informa- st be pro- B form of animal as ir, osseous d nervous protective ral knowl- aose to tell 9f. 1 l*he blood is the source of all the nourishment of the organ- ism, including its oxygen supply, and is carried to every part of the body through elastic tubes which, continually branching and becoming gradually smaller, terminate in vessels of hair- like fineness in which the current is very slow — a condition per- mitting that interchange between the cells surrounding them and the blood which may be compared to a process of barter, the cells taking nutriment and oxygen, and giving (excreting) in return carbonic anhydride. BVom these minute vessels the blood is conveyed back toward the source whence it came by similar elastic tubes which gradually increase in size and be- come fewer. The force which directly propels the blood in its onward course is a muscular pump, with both a forcing and suction action, though chiefly the former. The flow of blood is maintained constant owing to the resistance in the smaller tubes on the one hand and the elastic recoil of the larger tubes on the other ; while in the returning vessels the column of blood is supported by elastic double gates which so close as to prevent reflux. The oxygen of the blood is carried in disks of microscopic size which give it up in proportion to the needs of the tissues past which they are carried. (But in reality the tissues of the body are not nourished directly by the blood, but by a fluid derived from it and resem- bling it greatly in most particulars. This fluid bathes the tissue-cells on all sides. It also is taken up by tubes that convey it into the blood after it has passed through little fac- tories (lymphatic glands), in which it undergoes a regeneration. Since the tissues are impoverishing the blood by withdrawal of its constituents, and adding to it what is no longer useful, and is in reality poisonous, it becomes necessary that new material be added to it and the injurious components withdrawn. The former is accomplished by the absorption of the products of food digestion, and the addition of a fresh supply of oxygen derived from without, while the poisonous ingredients that have found their way into the blood are got rid of through processes thut may be, in general, compaped to those of a sew- age system of a very elaborate character. To explain this re- generation of the blood in somewhat more detail, we must first consider the fate of food from the time it enters the mouth till it leaves the tract of the body in which its preparation is carried on. The food is in the mouth submitted to the action of a series of catting and grinding organs worked by powerful muscles ; f'l 80 ANIMAL PHTSIOLOOY. mixed with a fluid which changes the starchy part of it into sugar, and prepares the whole to pass further on its course : when this has been accomplished, the food is grasped and squeezed and pushed along the tube, owing to the action of its own muscular cells, into a sac (stomach), in which it is rolled about and mixed with certain fluids of peculiar chemical com- position derived from cells on its inner surface, which trans- form the proteid part of the food into a form susceptible of ready use (absorption). When this saccular organ has done its share of the work, the food is moved on by the action of the muscles of its walls into a very long portion of the tract in which, in addition to processes carried on in the mouth and stomach, there are others which transform the food into a condition in which it can pass into the blood. Thus, all of the food that is susceptible of changes of the kind described is acted upon somewhere in the long tract devoted to this task. But there is usually a remnant of indigestible material which is finally evacuated. How is the prepared material conveyed into the blood ? In part, directly through the walls of the minutest blood-vessels distributed throughout the length of this tube ; and in part through special vessels with appropriate cells covering them which act as minute porters (viUi). *(^he impure blood is carried periodicrl? * ^o %n extensive sur- face, usually much folded, and there e;;*» •( in the hair-like tubes referred to before, and thus parts « e excess of car- bon dioxide and takes up fresh oxygen. J..« Ml the functions described do not go on in a fixed and invariable inanner, but are modified somewhat according to circimistances. The for- cing-pump of the circulatory system does not always beat equally fast; the smaller blood-vessels are not always of the same size, but admit more or less blood to an organ according to its needs. \This is all accomplished in obedience to the commao'l.. car- ried from the brain and spinal cord along the nerves. All movements of the limbs and other parts are executed in obe- dience to its behests ; and in order that these may be in accord- ance with the best interests of each particular orgam and the whole animal, the nervous centers, which may be compared to the chief officers of, say, a telegraph or railway system, are in constant receipt of information by messages carried onward along the nerves. The command issuing is always related to the information arriving. 1 All those parts commonly known as sense-organs— the eye« LIVINO AND LIFELESS HATTER. 81 of it into 8 course : iped and ion of its is rolled ical Corn- ell trans- eptible of has done action of le tract in louth and od into a us, all of Mscribedis this task, rial which conveyed Us of the length of ppropriate 0. jnsive sur- ) hair-like uss of car- functions anner, but The for- ways beat »ys of the according nan 'I., car- rves. All led inobe- in accord- Bcn and the tmpared to tern, are in 3d onward related to B— the eye. ear, nose, tongue, and the entire surface of the body — are faith- ful reporters of facts. They put the inner and outer worlds iu communication, and without them all higher life at least must cease, for the organism, like a train directed by a conductor that disreganU the danger-signals, must work its own destruction. Without going into further details, suffice it to say that the pro- cesses of the various cells are subordinated to the general good through the nervous system, and that susceptibility of proto- plasm to stimuli of a delicate kind which enables each cell to adapt to its surroundings, including the influence of remote as well as neighboring cells. Without this there could be no marked advance in organisms, no differentiation of a pro- nounced character, and so none of that physiological division of labor which will be inferred from our brief description of the functions of a mammal. The whole of physiology but illiistrates this division of labor. It is hoped that the above account of the working of the animal body, brief as it is, may serve to uhow the connection of one part functionally with another, for it is much more impor- tant that this should be kept in mind throughout, than that all the details of any one function should be known. LIVINO AND UFELE8S MATTER. In order to enable the student the better to realize the na- ture of living matter or protoplasm, and to render clearer the distinction betw^t n the forms that belong to the organic and inorganic worlds respectively, we shall make some com- parisons in detail which it is hoped may accomplish this ob- ject. (A modem watch that keeps correct time must be regarded as a wonderful object, a marvelous triumph of human skill. That it has aroused the awe of savages, and been mistaken for a living being, is not surprising. But, admirable as is the result attained by the mechanism of a watch, it is, after all, composed of but a few metals, etc., chiefly in fact of two, brass and steel; these ai-e, however, made up into a great number of different parts, so adapted to one another as to work in unison and accomplish the desired object of indicating the time of 4ay. (Now, however well constructed the watch may be, there are waste, wear and tear, which will manifest themselves more and 89 ANIMAL PHYSIOLOGY. more, until finally the machine becomes worthless for the pur- pose of its construction. If this mechanism possessed the power of adapting from without foreign matter so as to con- struct it into steel and brass and arrange this just when re- quired, it would imitate a living organism; but this it can not do, nor is its waste chemically different from its component metals ; it does not break up brass and steel into something wholly different. In one particular it does closely resemble living things, in that it griBidually deteriorates ; but the degra- dation of a living cell is the consequence of an actual change in its component parts, commonly a fatty degeneration. The one is a real transformation, the other mere wear. Had the watch the power to give rise to a new one like itself by any process, especially a process of division of itself into two parts, we should have a parallel with living forms; but the watch can not even renew its own jiarts, much less give rise to a second mechanism like itself. Here, then, is a manifest dis- tinction between living and inanimate things. Suppose further that the watch was so constructed that, after the lapse of a certain time, it underwent a change in its inner machinery and perhaps its outer form, so as to be scarcely recognizable as the same ; and that as a result, instead of indi- cating the hours and minutes of a time-reckoning adapted to the inhabitants of our globe, it indicated time in a wholly dif- ferent way ; that after a series of such transformations it fell to pieces— took the original form of the metals from which it was constructed— we should then have in this succession of events a parallel with the development, decline, and death of living organisms. (la another particular our illustration of a watch may serve a useful purpose. Suppose a watch to exist, the works of which are so concealed as to be quite inaccessible to our vision, so that all we know of it is that it has a mechanism which when in action we can hear, and the result of which we perceive in the movements of the hands on the face; we should then be in the exact position in reference to the watch that we now are as re- gards the molecular movements of protoplasm. On the latter the entire behavior of living matter depends; yet it is abso- lute hidden from us. ^e know, too, that variations must be produced in the mechanism of time-pieces by temperature, moisture, and other influences of the environment, resulting in altered action. The same, as will be shown in later chapters, occurs in protoplasm. CLASSIFICATION OF THE ANIMAL KINGDOM. 88 or the pur- ssessed the as to con- it when re- 8 it can not component something y resemble ; the degra- )ual change ation. The le like itself elf into two us; but the give rise to lanifest dis- ructed that, hange in its ) be scarcely t«ad of indi- 1^ adapted to wholly dif- ons it fell to m which it iccession of ad death of 1 may serve rks of which sion, so that lich when in rceive in the ten be in the iw are as re- >n the latter it it is abso- iiced in the :e, and other action. The protoplasm. This, too, is primarily a molecular effect. If the works of watches were beyond observation, we should not be able to state exactly how the variations observed in different kinds, or even different individuals of the same kind occurred, though these differences might be of the most marked character, such as any one could recognize. Here once more we refer the differences to the mechanism. So is it with living beings: the ultimate molecular mechanism is unknown to us. (Gould we but render these molecular movements visible to our eyes, we should have a revelation of far greater scientific importance than that unfolded by the recent researches into those living forms of extreme minuteness that swarm every- where as dust in a sunbeam, and, as will be learned later, are often the source of deadly disease. Like the movements of the watch, the activities of protoplasm are ceaseless. A watch that will not run is, as such, worthless — it is mere metal — ^has under- gone an immense degradation in the scale of values; so proto- plasm is no longer protoplasm when its peculiar molecular movements cease ; it is at once degraded to the rank of dead matter. The student may observe that each of the four propositions, embodying the fundamental properties of living matter, stated in the preceding chapter, have been illustrated by the simile of a watch. Such an illustration is necessarily crude, but it helps one to realize the meaning of truths which gather force with each living form studied if regarded aright ; and it is upon the (rvtdizaiiQiLPt traji^ that mental growth as well as practical efficiency depends. 0LA88IFI0ATI0N OF THE ANDCAL KINODOM. ( There are human beings so low in the scale as not to possess such general terms as tree, while they do employ names for dif- ferent kinds of trees. The use of such a word as ''tree" im- plies generalization, or the abstraction of a set of qualities from the things in which they reside, and making them the basis for the grouping of a multitude of objects by which we are sur- rounded. Manifestly without such a process knowledge must be very limited, and the world without significance ; while in proportion as generalization may be safely widened, is our progress in the un^eation of knowledge toward which science is tending. But it also follows that without complete knowl- s 84 ANIMAL PHTSIOLOOT. edge there can be no perfect classification of objects; hence, any classification must be regarded but as the temporary creed of science, to be modified with the extension of knowledge. As a matter of fact, this has been the history of all zodlogical and other systems of arrangement. The only purpoee of grouping is to simplify and extend knowledge ; this being the case, it fol- lows that a method of grouping that accomplishes this has value, though the system may be artificial that is based on resemblances which, though real and constant, are associated with differences so numerous and radical that the total amount of likeness between objects thus grouped is often less than the difference. Such a system was that of Linneeus, who classified plants according to the number of stamens, etc., they bore. Seeing that animals which resemble each other are of com- mon descent from some earlier form, to establish the line of de- scent is to determine in great part the classification. Much as- sistance in this direction is derived from embryology, or the history of the development of the individual {ontogeny); so that it may be said that the ontogeny indicates, though it does not actually determine, the line of descent {phytogeny) ; and it is owing to the importance of this truth that naturalists have in recent years given so much attention to comparative embry- ology. It will be inferred that a nattrnd system of classification must be based both on function and structure, though chiefly on the latter, since organs of very different origin may have a similar function ; or, to express this otherwise, homologous structures may not be analogous; and homology gives the better basis for classification. To illustrate, the wing of a bat and a bird are both homologous and analogous; the wing of a butterfly is analogous but not homologous with these ; manifestly, to clas- sify bats and birds together would be better than to put birds and insects in the same group, thus leaving other points of re- lationship out of consideration. The broadest possible division of the animal kingdom is into groups, including respectively one-celled and many-celled forms — i. e., into Protozoa and Metatsoa. As the wider the grouping the less are differences considered, it follows that the more subdivided the groups the more complete is the informa- tion conveynl • thus, to say that a dog is a metazoan is to con- vey a certa. amount of information ; that it is a vertebrate, more ; that it is a mammal, a good deal more, because each of the latter terms includes the former. CLASSIFICATION OF THE ANIMAL KINGDOM.- 85 ts; hence, rary creed edge. As )gical and grouping sase, it fol- ia this has based on associated tal amount than the o classified r bore, ire of com- ) line of de- Much as- ogy, or the logeny); so >ugh it does ny) ; and it ralists have tive embry- cation must iiiefly on the bve a similar 18 structures ;ter basis for d a bird are butterfly is Nstly, to clas- to put birds points of re- gdom is info many-celled e wider the lows that the the informa- Eui is to con- a vertebrate, ause each of Animal King- dom. Inverte- brata. Vertebrata. Protozoa (amoeba, vorticella, etc.). Coelenterata (sponges, jelly-fish, polyps, etc.). Eckinodermata (star-flsh, sea-urchins, etc.). Vermes (worms). Arthropods (crabs, insects, spiders, etc.). Mollusca (oysters, snails, etc.). MoUusooidea (moss-like animals). . Tunicata (ascidians). Pisces (fishes). Amphibia (frogs, menobranchus, etc.). Beptilia (snakes, turtles, etc.). Aves (biids). Mammalia (domestic quadrupeds, etc.). The above classification (of Glaus) is, like all such arrange- ments, but the expression of one out of many methods of view- ing the animal kingdom. I « . the details of classification and for the grounds of that Wb \ave presented, we refer the student to works on zoology; but we advise those who are not familiar with this subject, when a technical term is used, to think of that animal belong- ing to the group in question with the structure of which they are best acquainted. Man's Place in the Animal Kingdom. QEt is no longer the cuistom with zoologists to place man in an entirely separate group by himself ; but he is classed with the primates, among which are also gn^ouped the anthropoid apes (gorilla, chimpanzee, orang, and the gibbon), the monkeys of the Old and of the New World, and the lemurs. So great is the structural resemblance of man and the other primates that competent authorities declare that there is more difference be- tween the structure of the most widely separated members of the group than between certain of the anthropoid apes and man. The points of greatest resemblance between man and the anthropoid apes are the following : The same number of verte- bree ; the same general shape of the pelvis ; a brain distinguish- ing them from other mammals ; and posture, being bipeds. The distinctive characters are size, rather than form of the brain, that of man being more than twice as large ; a relatively larger cranial base, by which, together with the greater size of the jaws, the face becomes prominent ; the earlier closure of the sutures of the cranium, arresting the growth of the brain ; more developed canine teeth and difference in the order of eruption of the permanent teeth ; the more posterior position of the foramen magnum ; the relative length of the limbs to AT 89 ANIMAL PHYSIOLOOT. each other and the rest of the body ; minor differences in the hands and feet, especially the greater freedom and power of apposition of the great-toe. But the greatest distinction between man and even his closest allies among the apes is to be found in the development to an incomparably higher degree of his intellectual and moral nature, corresponding to the differences in weight and structure of the human brain, and associated with the use of spoken and written language ; so that the experience of previous genera- tions is not only registered in the organism (heredity), but in a form more quickly available (books, etc.). The greatest structural difference between the races of men are referable to the cranium; but, since they all interbreed freely, they are to be considered varieties of one species. THE LAW OF PERIODICITY OR RHYTHM IN NATURE. The term rhythm to most minds suggests music, poetry, or dancing, in all of which it forms an essential part so simple, pronounced, and uncomplicated as to be recognized by all with The regular division of music into bars, the recurrence of chords of the same notes at certain intervals, of forte and piano, seem to be demanded by the very nature of the human mind. The same applies to poetry. Even a child that can not under- stand the language used, or an adult listening to recitations in an unknown tongue, enjoys the flow and recurrences of the sounda Dancing has in all ages met a want in human organi- zations, which is partly supplied in quieter inoods by the regu- larity of the steps in walking and similar simple movements. r^ut as rhythm runs through all the movements of animals, so is it also found in all literature and all art. Infinite variety wearies the mind, hence the fatigue felt by the sight-seer. Re- currence permits of repose, and gratifies an established taste or appetite. The mind delights in what it has once enjoyed, in repetition within limita Repetition with variety is manifestly a condition of the growth and development of the mind. This seems to apply equally to the body, for every single function of each organism, however simple or complex it may be, exem- plifies this law of periodicity. The heart's action is rhythmical {beats) ; the blood flows in intermitting gushes from the central pump; the to-and-fro movements of respiration are so regular THE LAW OF PBRIODICITT OB RHTTHH IN NATURE. 87 7es in tlie power of even his relopment and moral structure x>ken and 08 genera- ), but in a ;e8 of men interbreed ;ies. 'TATUBB. !, poetry, or so simple, by all with purrence of ; and piano, iman mind. L not under- citations in noes of the nan organi- >y the regu- ^vements. of animals. Elite variety it-aeer. Re- hed taste or enjoyed, in I manifestly mind. This lie function iy be, exem- rhythmical 1 the central e so regular that their cessation would arouse the attention of the least instructed; food is demanded at regular intervals; the juices of the digestive tract are poured out, not constantly but period- ically; the movements by which the food is urged along its path are markedly rhythmic; the chemical processes of the body wax and wane like the fires in a furnace, giving rise to regular augmentations of the temperature of the body at fixed hours of the day, with corresponding periods of greatest bodily activity and the reverse. (^his principle finds perfect illustration in the nervous sys- tem. The respiratory act of the higher animals is effected through muscular movements dependent on regular waves of excitation reaching them along the nerves from the central cells which regularly discharge their forces along these channels. Were not the movements of the body periodic or rhythmical, instead of that harmony which now prevails, every muscular act would be a convulsion, though even in the movements of the latter there is a highly compounded rhythm, as a noise is made up of a variety of musical notes. The senses are subject to the same law. The eye ceases to see and the ear to hear and the hand to feel if continuously stimulated ; and doubtless in all art this law is unconsciously recognized. That ceases to be art which fails to provide for the alternate repose and excita- tion of the senses. The eye will not tolerate continuously one color, the ear a single sound. Why is a breeze on a warm day so refreshing ? The answer is obvious. (XfOoking to the world of animate nature as a whole, it is n, becomes years of ng irregu- tolerated to saying ity seems oiinded of ly studied, bserved in iselves, the d decrease I and moon s must be- ond recog- i are daily sep, dreams hat is, one a like man- itly in their , but have the life of nd that the he result of md deposi- onomic and n. Periods commercial 1 occur and ct^anges in )11 as other student, are THE LAW OP PERIODICITY OB RHYTHM IN NATURE. 89 the laws of rhythm in disease. Certain fevers have their regu- lar periods of attack, as intermittent fever ; while all diseases have their periods of exacerbation, however invariable the sjrmptoms may seem to be to the ordinary observer or even to the patient himself. Doubtless the fact that certain hereditary diseases do not appear in tLe offspring at once, but only at the age at which they were manifested in the parents, is owing to the same cause. Let us now examine more thoroughly into the real nature of this rhythm which pervades the entire universe. ^ a bow be drawn across a violin-string on which some small pieces of paper have been placed, these will be seen to fly off ; and if the largest string be experimented upon, it can be ob- served to be in rapid to-and-f ro motion, known as vibration, which motion is perfectly regular, a definite number of move- ments occurring within a measured period of time; in other words the motion is rhythmical In strings of the finest size the motion is not visible, but we judge of its existence because of the result, which is in each instance a sound. Sound is to us, however, an affection of the nerve, of hearing and the brain, owing to the ribrations of the ear caused by similar vibra- tions of the violin-strings. The movements of the nerves and nerve-cells are invisible and molecular, and we seem to be justified in regarding molectdar movements as constant and associated with aU the properties of matter whether living or dead. ^We see, then, that all things living and lifeless are in con- staml motion, visible or invisible ; there is no such thing in the universe as stable equilibrium. Change, ceaseless change, is written on all things; and, so far as we can judge, these changes, on the whole, tend to higher development. Neither rhythm, however, nor anything else, is perfect. Even the mo- tions of planets are subject to perturbations or irregularities in their periodicity. This subject is plainly boundless in its scope. We have introduced it at this stage to prepare for its study in detail in dealing with each function of the animal body. If we are correct as to the universality of the law of rhythm, its importance in biology deserves fuller recognition than it has yet received in works on physiology; it will, ac- cordingly, be frequently referred to in the future chapters of this book. " •-I BurnM 40 ANIMAL PHTSIOLOGT. THE LAW OF HABIT. Every one mast have observed in himself and others the tendency to fall into set ways of doing certain things, in which will and clear purpose do not come prominently into view. Further observation shows that the lower animals exhibit this tendency, so that, for example, the habits of the horse or the dog may be an amusing reflection of those of the master. Trees are seen to bend permanently in the direction toward which the prevailing winds blow. The violin that has experienced the vibrations aroused by some master's hand acquires a potential musical capability not possessed by an instrument equally good originally, but the molecular movements of which never received such an educa- tion. It appears, then, that underlying what we call habit, there is some broad law not confined to living things ; indeed, the law of habit appears to be closely related to the law of rhythm we have already noticed. Certain it is that it is inseparable from all biological phenomena, though most manifest in those organ- isms provided with a nervous system, and in that system itself. What we usually call habit, however expressed, has its physical correlation in the nervous system. We may refer to it in this connection later : but the subject has relations so numerous and fundamental that it seems eminently proper to introduce it at this early stage, forming as it does one of those comer-stones of the biological building on which the superstructure must rest. When we seek to come to a final explanation of habit in this case, as in most others, in which the fundamental is involved, we are soon brought against a wall over which we are unable to climb, and through which no light comes to our intellects. We must simply believe, as the result of observation, that it is a law of matter, in all the forms manifested to us, to assume accustomed modes of behavior, perhaps we may say molecular movement, in obedience to inherent tendencies. But, to recog- nize this, throws a flood of light on what would be inexplicable, even in a minor degree. We can not explain gravitation in it- self ; but, assuming its universality, replaces chaos by order in our speculations on matter. Turning to living matter, we look for the origin of habit in the apparently universal principle that primary molecular movement in one direction renders that movement easier after- THB ORIGIN OP THR P0RM8 OF LIFR. 41 others the I, in which into view, ixhibit this I or the dog Trees are which the aroused by ability not ly, but the 1 an educa- bit, there is , the law of rhythm we urable from ihose organ- rstem itself, its physical to it in this imerous and ;ioduce it at ler-stones of e must rest, iiabit in this is involved, are unable intellects, ition, that it s, to assume y molecular ut, to recog- nezplicable, itation in it- by order in 1 of habit in T molecular easier after- ward, and in proportion to the frequency uf repetition ; which is equivalent to saying that functional activity facilitates func- tional activity. Once accepting this as of universal application in biology, we have an explanation of the origin, the compara- tive rigidity, and the necessity of habit. There must be a phys- ical basis or correlative of all mental and moral habits, as well as those that may be manifested during sleep, and so purely in- dependent of the will and consciousness. We are brought, in fact, to the habits of cells in considering those organs, and that combination of structures which makes up the complex individ- ual mammal. It is further apparent that if the cell can trans- mit its nature as altered by its experiences at all, then habits must be hereditary, which is known to be the case. Instincts seem to be but crystallized habits, the inherited results of ages of functional activity in certain well-defined directions. To a being with a hi,9:hly developed moral nature like man, the lam of habit is one of great, even fearful significance. We make t i-day our to-mori ow, and in the present we are deciding the future of others^ as our present has been made for us in part by our ancest^TS. We shall not pursue the subject, which is of boundlef!!; extent Jrurther now, but these somewhat general statements will t^ amplifif^^d and fi.pplied in future chapters. THF iGIN OF Tm /ORMS OF LIFE. /It is a matter of common observation that animals originate from like kinds, and plants from forms ruo .r:bling themselves ; while most carefully conducted experiments have failed to show that living matter can under any circumstances known to us arise from other than living matter. That in a former condition of the universe such may have been the case has not been disproved, and seems to be the logical outcome of the doctrine of evolution as applied to the imiverse generally. ^By evolution is meant the derivation of more complex and di^erentiated forms of matter from simpler and more homogMie- ^vc« r aes. When this theory is applied to organized or liriiig forms, it is termed organic evolution. There are two views of the origin of life: the one, that each distinct group of plants and animals was independently created ; while by " creation " is simply meant that they came into being in a manner we know - wM<".MW^WJ-i;.. ' ^u.' — 42 ANIMAL PHTSIOLOGT. not how, in obedience to the will of a First Catise. The other view is denominated the theory of descent with modification, the theory of transmutation, organic evolution etc., which teaches that all the various forms of life have been derived from one or a few primordial forms in harmony with the recog- nized principles of heredity and variability. The most widely known and most favorably received exposition of this theory is that of Charles Darwin, so that his views will be first presented in the form of a hypothetical case. Assume that one of a group of living forms varies from its fellows in some particular, and mating with another that has similarly varied, leaves progeny inheritinj^ this characteristic of the parents, that tends to be still further increased and rendered permanent by successive pairing with forms possessing this variation in form, color, or whatever it may be. We may suppose that the variations may be numerous, but are always small at the beginning. Since all animals and plants tend to multiply faster than the means of support, a competition for the means of subsistence arises, in which struggle the fittest, as judged by the circumstances, always is the most successful ; and if one must perish outright, it is the less fit. If any variation arises that is unfavorable in this contest, it will render the possessor a weaker competitor: hence it follows that only useful variations are preserved. The struggle for existence is, however, not alone for food, but for anything which may be an advantage to its possessor. One form of the contest is that which results from the rivalry of members of the same sex for the possession of the females ; and as the female chooses the strongest, most beautiful, most active, or the supreme in some respect, it follows that the best leave the greatest number of progeny. This has been termed seeBtud selection. In determining what forms shall survive, the presence of other plants or animals is quite as importuit as the abun- dance of food and the physical conditions, often more so. To illustrate this by an example : Certain kinds of clover are fer- tilized by the visits of the bumble-bee alone ; the numbers of bees existing at any one place depends on the abundance of the field-mice which destroy the nests of these insects ; the numbers of mice will depend on the abundance of creatures that prey on the mice, as hawks and owls ; these, again, on the creatures that specially destroy them, as fuxes, etc. ; and so on, the chain of connections becoming more and more lengthy. If a certain proportion of forms varying similarly were sep- THE ORIGIN OF THE FOBMS OF LIFK 48 The other dification, c, which n derived the recog- Mt widely theory is presented 3f a group cular, and progeny )ndB to be successive 1, color, or itions may Since all means of ) arises, in imstances, 1 outright, vorable in ompetitor: rved. The od,but for ssor. One I rivalry of nalee; and lost active, best leave ned sexual resence of the abun- )re so. To er are fer- umbers of ince of the le numbers At pre;* on fttures that e chain of ' were sep- arated by any great natural barrier, as a chaia of lofty mount- ains or an intervening body of water of considerable extent, and so prevented from breeding with forms that did not vary, it is clear that there would be greater likelihood of their differ- ences being preserved and augpnented up to the point of their greatest usefulness. We may now inquire whether such has actually been the course of events in nature. The evidence may be arranged under the following heads : 1. Mar^koiagf. — Briefly, there is much that is common to entire large groups of animals ; so great, indeed, are the resem- blances throughout the whole animal kingdom, that herein is fotMid the strongest argument of all for the doctrine of descent. To illustrate by a single instance— fishes, reptiles, birds, and mammals possess in common a vertebral colunm bearing the same relationship to other parts of the animal It is because of resemblances of this kind, as well as by their differences, that naturalists are enabled to classify animals. 2. Imlnryvlofy. — In the stages through which animals pass in their development from the ovum to the adult, it is to be ob- served that the closer the resemblance of the mature organism in different groups, the more the embryos resemble one another. Up to a certain stage of development the similarity between groups of animals, widely separated in their post-embryonic life, is marked: thus the embryo of a reptile, a bird, and a mam- mal have much in common in their earlier stages. The embryo of the mammal passes through stages which represent condi- tions which are permanent in lower groups of animals, as for example that of the branchial arches, which are represented by the gills in fishes. It may be said that the developmental his- tory of the individual (ontogeny) is a brief recapitulation of the development of the specieis (phylogeny). Apart from the theory of descent, it does not seem possible to gather the true significance of such facts, which will become plainer after the study of the chapters on reproduction. 3. Miaiary may be cited as an instance of useful adapta- tion. Thus, certain beetles resemble bees and wasps, which lat- ter are protected by stings. It is believed that such groups of beetles as these arose by a species of selection ; those escaping enemies which chanced to resemble dreaded insects most, so that birds which were accustomed to prey on beetles, yet feared bees, would likewise avoid the mimicking forms. 4. Bndiairatary Orgau.— Organs which were once functional 44 ANIMAL PHTSIOLOOT. Fio. 47.— Show* th* embryoi of four uwmn^li In Um thrae oklf (OX nbUt (B), awl a niM (M). T1iir« opmrat, which the thrw eroHHrowi (I, •■Mtly u powiblo. Tho lint, or oMNr omMHomi of th* tlwM WHnSi itaiMorli^ n, ni) rtprwHt. w« wl(«t«d to o onrn v au A ■• row, I. roprawat* • vmt Murif atajio, with (middM) oroi»row, n, wows a i more dofidbntd of the •nbryonln body (the ' ataie, with the flrat rudlmaali of Umba, whiia the Rlll-aMniivi are jrot retalaed. -me tbiriI(loweat)oroae-row,ItI,ihowaaetiU teter atane, wtth uie Umfae • -i -i aitd the itlll-opeBiiuM loat The gOi-opeiilnga, and wtthout Hmfaa, tKe •eeond (middle) oroaa>row, n, Aiowa a aooewhat btor ata«e, with the flrat rudlmaala of Umba, w' " riI(loweat)oroaa-row,ni,ahowaaatiU late I Itlll-opeBiiuM kat The membnuaa and appendagee ^ „ amnion, jrptk-nae, allantola) are omitted, tlie whole Vwrive (iRuraa are alvitly mainlfled. the upper one* more than the lower. To fhoUltat* the oomparlaon. ther ar» all raduoiNl to nearly the same riae in the oute. All the embryoa are aaan ftom the Mt aide : tlw head •strmitr la above, the taaestrami^ below: the arehad bank turned to the rlffat The letter* Indicate the aame narta In all the twelve flguraa, nameljr : v, fore-brain ; «, twixt- brain ; m, mId-braIn t K nhMMiraltt ; n, atlar-brain ; r. apinal marrow : «. noae : a, ejw : o, ear ; k, Rill-arebea ; 9, heart ; w, vertabnl oolumn; /, fore-Umba ; 6, blnd-Umha ; a, tall. (After Haeokel.) oarrttpoiid m THE OBIOIN OF THE FORMS OF LIFE. 4» in a more ancient form, but serve no use in the creatures in which they are now found, have reached, it is thought, their rudiments^ condition through long periods of comparative disuse, in many generations. Such are the rudimentary mus- cles of the eais of man, or the undeveloped incisor teeth found in the upper jaw of ruminants. 6. Oeographiflal DiitribntioB. — It can not be said that animals and plants are always found in the localities where they are best fitted to flourish. This has been well illustrated within the lifetime of the present generation, for the animals intro- duced into Australia have many of them so multiplied as to displace the forms native to that country. But, if we assume that migrations of animals and transmutations of species have taken place, this difilculty is in great part removed. 6. PalMBtology. — The rooks bear record to the former exist- ence of a succession of related forms ; and, though all the in- termediate links that probably existed have not been found, the apparent discrepancy can be explained by the nature of the circumstances under which fossil forms are preserved; and the " imperfection of the geological record." It is only in the sedimentary rocks arising from mad that fossils can be preserved,. and those animals alone with hard parts are likely to leave a trace behind them ; while if these sedimentary rocks with their inclosed fossils should, owing to enormous pressure or heat be greatly changed (metamorphosed), all trace of fossils must disappear — so that the earliest forms of life, those that would most naturally, if preserved at all, be found in the most ancient rocks, are wanting, in consequence of the metamorphism which such formations have tmdergone. Moreover, our knowledge of the animal remains in the earth's crust is as yet very incomplete, though, the more it is explored, the more the evidence gathers force in favor of organic evolu- tion. But it must be remembered that those groups constitut- ing species are in geological time intermediate links. 7. 1 «i|il and Iriatlag BpmiM. — If the animals and plants now peopling the earth were entirely different from those that flour- ished in the past, the objections to the doctrine of descent would be greatly strengthened ; but when it is found that there is in some cases a scarcely broken succession of forms, great force is added to the arguments by which we are led to infer the con- nection of aU forms with one another. To illustrate by a single instance : the existing group of horses, with a single toe to each foot, was preceded in geological I a I 4 46 ANIMAL PHTSIOLOOT. time in America by forms with a greater number of toes, the latter increasing according to the antiquity of the group. Flo. 48.— BoDM of the feet of the dUtorent genera of h^ipu$ (Eooene) : b, foot ot Att/Aitherium (Lower oene) ; ; e, Coot of H^fparUm CPikh These forms occur in succeeding geological formations. It is impossible to resist the conclusion that they are related gene- alogically (phylogenetically). 8. PxoiprMiion.— Inasmuch as any form of specialization that would give an animal or plant an advantage in the struggle for existence would be preserved, and as in most cases when the competing forms are numerous such would be the case, it is possible to understand how the organisms that have appeared have tended, on the whole, toward a most pronounced pro- gression in the scale of existence. This is well illustrated in the history of civilization. Barbarous tribes give way be- fore civilized man with the numberless subdivisions of labor he institutes in the social organism. It enables greater num- bers to flourish as the competition is not so keen as if activities could be exercised in a few directions only. 9. D o nmtioa t ed Animak.— Darwin studied our domestic ani- mals long and carefully, and drew many important conclusions from his researches. He was convinced that they }xad all been derived from a few wild representatives, in accordance with the principles of natural selection. Breeders have, both consciously and unconsciously, formed races of animals from stocks which the new groups have now supplanted ; while primitive man had tamed various species which he kept for food and to assist in the chase, or as beasts of burden. It is impossible to believe that all the different races of dogs have originated from dis- tinct wild stocks, for many of them have been formed within recent periods ; in fact, it is likely that to the jackal, wolf, and THE ORIGIN OP THE FORMS OF LIFE. 47 >f toes, the the group. fox, must we look for the wild progenitors of our dogs. Dar- win concluded that, as man had only utilized the materials Na- ture provided in forming his races of domestic animals, he had availed himself of the variations that arose spontaneously, and increased and fixed them by breeding those possessing the same variation together, so the like had occurred without his aid in nature among wild forms. Evolutionists are divided as to the origin of man himself ; some, like Wallace, who are in accord wi*\ Darwin as to the .„o, foot of Oro- ons. It is lated gene- zation that truggle for s when the ) case, it is e appeared nnced pro- illustrated ve way be- is of labor eater num- f activities nestic ani- onclusions emI all been !e with the onsciously tbks which e man had so assist in to believe from dis- led within I wolf, and « J> no. 4>.— Skeleton of hand or ftm-foot of rix mMnmeh, I, vama ; U, dog ; m, pig ; IV, ox ; V, tapir : VI, horee. r, radtM; u, ulna; a, eMpboid; 6, ■emi-luiwr; e, triquetnim (ounei- fonn) ; d, trapedum ; e, tr»peioid : /, cemtatum (unciform prooeiw) ; g, hamatum (unci- form bone) ; p. pieifbrm ; 1, thumb ; I. digit ; 8, middle finger ; 4. rlng-ilnger ; 6, little finger. (After (Mgenbaur.) origin of living forms in general, believe that the theory of natural selection does not suffice to account for the intellectual and moral nature of man. ^V'allace believes that man's body has been derived from lower forms, but that his higher nature is the result of some unknown law of accelerated development ; while Darwin, and those of his way of thinking, consider that man in his entire nature is but a grand development of powers existing in minor degree in the animals below him in *}-ii scale. Bumauurj.-f Every group of animals and plants tends to in- crease in nuntbers in a geometrical progression, and must, if unchecked, overrun the earth. Every variety of animals and plants imparts to its offspring a general resemblance to itself, but with minute variations from the original. The variations of off spring, may be in any direction, and by accumulation -mmmim 48 ANIMAL PHYSIOLOGY. -"-^!SM^"---.--: THE ORIGIN OP THE FORMS OP LIFE. 49 ' * fiO ANFMAL PHYSIOLOGY. Fio. M.-HMU1 of • nose-ape (Sent- nopitheeut iwMioiu) from Bor- neo. (After*Brdim.) rio. 87.— Head of JulU Pw inuuL (From • pnoto- grsph bjr Hintw.) constitute fixed differences by which a new group is marked off. In the determination of the variations that persist, the law of survival of the fittest operates. REPRObxjC?nON. As has been already noticed, protoplasm, in whatever form, after passing through certain stages in development, undergoes a decline, and finally dies and joins the world of unorganized matter ; so that the permanence of living things demands the constant formation of new individuals. Groups of animals and plants from time to time become extinct; but the lifetime of the species is always long compared with that of the individ- ual Reproduction by division seems to arise from an exigency of a nutritive kind, best exemplified in the simpler organisms. When the total mass becomes too great to be supported by absorption of pabulum from without by the surface of the body, division of the organism must take place, or death ensues. It appears to be a matter of indifference how this is accom- plished, whether by fission, endogenous division, or gemmation, so long as separate portions of protoplasm result, capable of leading an independent existence. The very undifferentiated character of these simple forms prepares us to understand how each fragment may go through the same cycle of changes as the parent form. In such cases, speaking generally, a million individuals tell the same biological story as one; yet these must exist as individuals, if at all, and not in one great united mass. But in the case of conjugation, which takes place some- times in the same groups as also multiply by division > its various forms, there is plainly an entirely new aspect of the ifBtf i w^w wii tTtwr i i: w REPRODUCTION. 51 JuUkPa*- I a, photo- > is marked ist, the law ttever form, b, undergoes morganized emands the of animals the lifetime the wdivid- an exigency ' organisms, ipported by face of the eath ensues. is is accom- gemmation, , capable of ifferentiated trstand how changes as y, a million ; yet these ipreat united place some- 'ision ' ). its ipect of the case presented. We have already shown that no two cells, how- ever much alike they may seem as regards form and the cir- cumstances under which they exist, can have, in the nature of the case, precisely the same history, or be the subjects of ex- actly the same experiences. We have also pointed out that all these phenomena of cell-life are known to us only as adaptations of internal to external conditions ; for, though we may not be always able to trace this connection, the inference is justi- fiable, because there are no facts known to us that contradict such an assumption, while those that are within our knowledge bear out the generalization. We have already learned that liv- ing things are in a state of constant chan|^, as indeed are all things ; we have observed a constant relation between certain changes in the environment, or sum total of the surrounding conditions, as, for example, temperature and the behavipr of the protoplasm of plants and animals ; so that we must believe that any one form of protoplasm, however like another it may seem to our comparatively imperfect observation, is different in some respects from every other — as different, relatively, as two human beings living in the same community during the whole of their lives ; and in many cases as unlike as individuals of veiy different nationality and history. We are aware that when two such persons meet, provided the unlikeness is not so great as to prevent social intercourse, intercommunication may prove very instructive. Indeed, the latter grows out of the former ; our illustration is itself explained by the law we are endeavoring to make plain. It would appear, then, that con- tinuous division of protoplasm without external aid is not pos- sible ; but that the vigor necessary for this must in some way be imparted by a particle (cell) of similar, yet not wholly like, protoplasm. This seems to furnish an explanation of the neces- sity for the conjugation of Mving forms, and the differentiation of sex. Very frequently conjugation in the lowest animals and plants is followed by long periods when division is the prevail- ing method of reproduction. It is worthy of note, too, that when living forms conjugate, they both become quiescent for a longer or shorter time. It is as though a period of preparation preceded one of extraordinary activity. ^We can at present trace only a few of the steps in this rejuvenation of life-stuff. Some of these have been already indicated, which, with others, will now be further studied in this division of our subject, both because reproduction throws so much light on cell-life, and be- cause it is so important for the understanding of the physio- i<>wM i niJro i u I f 62 ANIMAL PHT8I0L00T. logical behavior of tissues and organs. It may be said to be quite as important tliat the ancestral history of the cells of an organism be known as the history of the units composing a community. A, B, and C can be much better understood if we know something alike of the history of their race, their an- cestors, and their own past ; so is it with the study of any indi- vidual, animal, or group of animals or plants. Accordingly, embryology, or the history of the origin and development of tissues and organs, will occupy a prominent place in the va- rious chapters of this work. The student will, therefore, at the outset be furnished with a general account of the subject, while many details* and applications of principles will be left for the chapters that treat of the functions of the various organs of animals. The more knowledge the student possesses of zo- ology the better, while this science will appear in a new light under the study of embryology. Animals are divisible, according to general structure, into Protozoa, or unicellular animals, and Metazoa, or multicellular forms — that is, animals composed of cell aggregates, tissues, or organs. Among the latter one form of reproduction appears for the first time in the animal kingdom, and becomes all but universal, though it is not the exclusive method ; for, as seen in Hydra, both this form of generation and the more primitive gemmation occur. It is known as sexual multiplication, which usually, though not invariably, involves conjugation of two un- like cells which may arise in the same or different individuals. That these cells, known as the male and female elements, the ovum and the spermatozodn, are not necessarily radically differ- ent, is clear f re m the fact that they may arise in the one individ- ual from the iame tissue and be mingled together. These cells, however, li>e all others, tell a story of continual progressive differentiation corp^sponding to the advancing evolution of higher from lower forms. Thus hermaphroditism, or the coex- istence of organs for the production of male and of female cells in the same individual, is confined to invertebrates, among which it is rather the exception than the rule. Moreover, in such hermaphrodite forms the union of cells with greater differ- ence in experiences is provided for by the union of different in- dividuals, so that commonly the male cell of one individual unites with (fertilizes) the female cell of a different individual. It sometimes happens that among the invertebrates the cells produced in the female organs of generation possess the power of division, and continued development wholly independently of ■>rwH i i'W Ht.U-<»ftather functions, but highly specialized in the one direction of exceedingly great capacity for growth and complex division, if we take into ac- count the whole chain of results ; though in considering this it must be borne in mind that after a certain stage of division each individual cell repeats its ancestral history again ; that is to say, it divides and gives rise to cells which progress in turn as well as multiply. From another point of view the ovum is a marvelous storehouse of energy, latent or potential, of course, but under proper conditions liberated in varied and unexpected forms of force. It is a sort of storehouse of biological energy in the most concentrated form, the liberation of which in sim- pler forms gives rise to that complicated chain of events which \ i mmm i iu« i mii 64 ANIMAL PHTSIOLOOT. is termed by tho biologfist development, but which may be ex- pressed hy 1 '■:< > phyBiologist as the transformation of potential into k)u:i; euorgy, or the energfy of motion. Viewed chemic- ally, it it :'■,.■! r i; ■•■ ep.'ated story of the production of forms, of greater s\,>-::,Aity and simplicity, from more unstable and com- plex ones, involving throughout the process of oxidation ; for it must ever be kept in mind that life and oxidation are concomi- tant and inseparable. The further study of reproduction in the concrete will render the meaning and force of many of the above statements clearer. The Ovum. The typical female cell, or ovum, consists of a mass of proto- plasm, usually globular in form, containing a nucleus and nu- cleolus. The ovum may or may not be invested by a membrane ; the protoplasm of the body of the cell is usually highly granular, and may have stored up within it a varying amount of proteid material (food-yelk), which has led to division of ova into classes, according to the manner of distribution of this nutri- tive reserve. It is either concentrated at one pole {tdoleeUh- al) ; toward the center {centrolecithal) ; or evenly distributed throughout {alecUhal). Dur- ing development this material is converted by the agency of the cells of the young organ- ism {embryo) into active pro- toplasm; in a word, they feed upon and assimilate or build up this food-stuff into their own substance, as Amceba does with any proteid material it appropriates. The nucleus {germinal resi- de) is large and well-defined, and contains within itself a highly refractive nucleolus {germinal spot). These closely resemble in general the rest of the cell, but stain more deeply and are chemically different in that they contain nudeine {nticleoplcsm, chromatin). It will be observed that the ovun) differs in no essential par- hia; gv, germinal vesiole; gt, Rermliutt ■pot. :''^v.i^'<,!.,t^'^^,-.^~„Miiim-ciiiSiSt.axi^r,taiia.!>im:^^ lay "be ex- potential chemic- forms, of and com- on ; for it concomi- Ition in the Lny of the 38 of proto- ns and nu- brane; the Y granular, i of proteid F ova into this nutri- {telolecith- distributed iaZ). Dur- lis material B agency of ung organ- active pro- I, they feed te or build into their .moeba does material it Tninal vesi- 'ell-defined, in itself a nucleolus lese closely the rest of different in sential par- BEPRODUCTION. 55 Fio. SO.— A huniAii egg (much enUrged) from the oTarjr of a female. The whole egir !■ • simple mhericsl cell. The creMer part of this cell to formed by the egg-yttk, by the gran- ular cell-aubatance (pmtoplaam), oonatoting of Innumerable yelk-granule« with a little inter-eranuUr subetance. In the upper part of the yelk Ilea the briffht, elobular, germ- veeiole. comapondiog with the cell-kernel (nueteiu). Thto containa a darker geniMpot. anaweHng to the nucleolus. The Klobular yelk-nuMs to mnroundrd by a thick, light- colored eKK-membrane (tona pettueuia, or chorion). Thto to traversed by Tery numeroua hair-like lines, radiating toward the central point of the maas : these are the porous canals, through which, in the course of fertHiiatlon, the thread-shaped, active sperm-ceUs penetrate hito the egg-yelk. (HaeckeL) ticular of structure from other cells. Its differences are hidden ones of molecular structure and functional behavior. In ac- cordance with the diverse circumstances under which ova mature and develop, certain variations in structure, mostly of the nature of additions, present themselves. Thus, ova may be naked, or provided with one or more coverings. In vertebrates there are usually two membranes around the protoplasm of the ovum : a delicate covering ( Vi- telline membrane), beneath which there is another, which is sieve-like from numerous perforations {eona radiata, or z. peUiicida). The egg membrane may be impregnated with lime salts (sheU). Between the membranes and the yelk there is a fluid albuminous substance secreted by the glands of the ovi- duct, or by other special glands, which provide proteid nutri- ment in different physical condition from that of the yolk. The general naked-eye appearances of the ovum may be learned from the examination of a hen's egg, which is one of ^mm\ utawi iM i , ntjtjj l UM n ' . »i 56 ANIMAL PHYSIOLOGY. •1")! m III m the most complicated known, inasmuch as it in adapted for development outside of the body of the mother, and must, con- sequently, be capable of preserving its form and essential vital properties in a medium in which it is liable to undergo loss of water, protected as it now is with shell, etc., but which, at the eA.i Fta. 60.— DtagramniAttc aection of an unimpreKnated fowl's egg (Foster and tialfonr, after Allen Thomson). M, blastoderm or cioatricula ; to. y, white yolk ; y. y, yellow yelk ; eh. I, chalaia'; i. m. m, inner layer of shdl membrane ; «. m. outer layer of diell membrane ; t, shell ; a, c. k, air-space ; to, the white of the emr ; v- (i vitelline membrane ; x, the denser albuminous layer tying next the vitelUue membrane, same time, permits the entrance of oxygen and moisture, and conducts heat, all being essential for the development of the germ within this large food-mass. The shell serves, evidently, chiefly for protection, since the eggs of serpents (snakes, turtles, etc.) are provided only with a very tough membranous cover- ing, this answering every purpose in eggs buried in sand or otherwise protected as theirs usually are. As the hen's egg h that most readily studied and most familiar, it may be well to describe it in somewhat further detail, as illustrated in the above figure, from the examination of which it will be ap- parent that the yelk itself is made up of a white and yellow portion distributed in alternating zones, and composed of cells of different microscopical appearances. The clear albumen is stjructureless. The relative distribution, and the nature of the accessory or non-essential parts of the hen's egg, will be understood when it is remembered that, after leaving its seat of origin, which will be presently described, the ovum passes along a tube (oviduct) REPRODUCTION. 67 apted for must, con- intial vital rgo loss of ich, at the id Balfour, after illow yelk ; eh. I, U membrane ; «, « ; X, the deoaer nature, and lent of the , evidently, Ices, turtles, lous cover- in sand or ten's egg iA be well to >ted in the (eill be ap> and yellow sed of cells ilbumen is ccessory or •od when it which will e (oviduct) by a movement imparted to it by the muscular walls of the latter, similar to that of the gullet during the swallowing gf food ; that this tube is provided with glands which secrete in turn the albumen, the membrane (outer), the lime salts of the shell, etc. The twisted appearance of the rope-like structures (chalazce) at each end is owing to the spiral rotatory movement the egg has undergone in its descent. The air-chamber at the larger end is not present from the first, but results from evaporation of the fluids of the albumen and the entrance of atmospheric air after the egg is laid some time. The ORiam and Development of the Ovum. Between that protrusion of cells which gives rise to the bud which develops directly into the new individual, and that which forms the ovary with- in which the ovum as a mod- ified cell arises, there is not in Hyrlra much difference at first to be observed. In the mammal, however, the ovary is a more complex structure, though, relatively to many organs, still simple. It consists, in the main, of connective tissue supplied with vessels and nerves in- closing modifications of that tissue {Oraafian foUides) within which the ovum is matured. The ovum and the follicles arise from an inver- sion of epithelial cells, on a portion of the body cavity {germinal ridge), which give rise to the ovum itself, and the other cells surrounding it in the Graafian follicle. At first these inversions form tubules {egg-tubes) which lat- er become broken up into iso- lated nests of cells, the fore-runners of the Graafian follicles. The Graafian follicle consists externally of a fibrous capsule Fts. 61.— Section through portion of the ovary . D,discuaproligen«;£i, ripe ovum; O, foUioular oelUi of {terminal epithelium ; g, blooil-veaieiR ; X'. germinal vuncle (nuole- ui)and germinal spot (nucleolus) : KB, ger- minal epitbeUum ; If, liquor folUculi ; Mg, membrana or tuqlca granulona, or follicular epttbeltum ; ifb, lona peltuoida ; M, In- growtliM from toe germinal epltlielium, ova- rian tubes, by P!e«aa of which aome of the neata retain tb<$lr oonneotkm with the epithe- lium : S, cavity which appeara within the Oraaflan follicle ; So, itroma of ovary ; I/, theoa foUiPuli or capsule ; V, primitive ova; When an ovum with ita aurrounding cell* ha* become neparated from the nest, it is kn> ;rn as a Graaflan follicle. r mmtni'M i* . 58 ANIMAL PHTSIOLOOT. {tunica fibrosa), in close relation to which is a layer of capillary hlood- vessels {tunica va^culosa), the two together forming the Fio. 88.— Sagittal sectir a of the ovary of on adult bltoh (after Wolder^r}. o. r, ovarian epi- thelium ; n. t, ovarian tubei ; u.f. younger follicln ; o./, older folUcle ; d. p. diocua pro- ItHeruM, with the ovum ; r, epitneliura of a leoond ovum in the tame follicle ; /. c, flbroue coat of the follicit; ; p. e, proper oooi. of the follicle ; «./• epithelium of the foQIcle (mem- braiia granuloRa) : n./. collapaed atioi>hled foUlole ; b. v, blood-veMela ; c. (, cell-tube* of the parovarium, divided longitudlnalhr and tronsvenwljr ; t. rf, tubular depreMrion of the ovanon epithelium, in the tmue of the ovary ; b. e, beginnlnff of the ovarian epithelium, close to the lower border of the ovary. general covering {iunica propria) for the more delicate and im- portant cells within. Lining the tunic is a layer of small, some- what cubical cells {membrana granulosa), which at one part invest the ovum several layers deep {discus proligerus), while tho remainder of the space is filled by a fluid {liquor foUiculi) prohablv either secretes! by the cells themselves, or resulting from the disintegration of some of them, or both. [»f capillary >rming the h.e. o. e, ovuion epl- : d. p. dtacus pro- lltck) ; /. c, flbroiM the foUlcle (mem- ; e. (, cell-tubes of depraaBkm of the r«mii epithelium, i&to and im- small, Home- at one part tenia), while tor foUieuU) OT resulting REPRODUCTION. 59 In viewing a section of the ovary taken from a mammal at the breeding-season, ova and Graafian follicles may be seen in all stages of development — ^those, as a rule, nearest the surface being the least matured. The Graafian follicle appears to pass inward, to undergo growth and development and again retire toward the exterior, where it bursts, freeing the ovum, which is conducted to the site of its future development by appropriate mechanism to be described hereafter. Cltangei in the Ovnm itMl£ — The series of transformations that take place, in the ovum before and immediately after the access of the male element is, in the opinion of many biolo- gists, of the highest significance, as indicating the course evolu- tion has followed in the animal kingdom, as well as instructive in illustrating the behavior of nuclei generally. The germinal vesicle may acquire powers of slow movement (amojboid), and the germinal spot disappear : the former passes to one surface {pole) of the ovum ; both these structures may undergo that peculiar form of rearrangement (karyokinesis) which may occur in the nuclei and nucleoli of other cells prior to division ; in other words, the ovum has features common to it and many other cells in that early stage which precedes the complicated transformations which constitute the future his- tory of the ovum. A portion of the changed nucleus {aster) with some of the protoplasm of the cell accumulates at one surface ( nole), which Fio. SB.— Formation of polar cells In a star-flsh (A»teria» glacialii) (from Gcddea, A— K after Fol, L after O. Hertwis). A, ripe orum with eccentric germinal veaicle and Bpot ; B— D, gradual metamorphosM of Kermlnal vesicle and spot, as seen in the livinK egg, into two asters ; F, formation of flrrt polar cells aad withdrawal of remaining part of nuclear spindle within the ovum ; O, surface view of llvinK ovum in the flrit polar cell ; H, com- pletion of second polar cell ; I. a later stage, sho\/uig the remaining Internal half of the spindle In the form of two clear vesicles ; K, ovum with two poUr cells and radial strln round female pronucleus, as seen in the living egg (E, F, H, and I from picric acid prepa- rations) ; L, expulsion of the first polar cell. (Itaddou.) is termed the upper pole because it is at this region that the epi- thelial cellfe will be ultimately developed, and is separated ; this process is repeated. These bodies {polar cells, polar globules. ; ; 60 ANIMAL PUTSIOLOOT. etc.), then, are simply expelled ; they take no part in the devel- opment of the ovum ; and their extrusion is to be regarded as a preparation for the progress of the cell, whether this event fol- lows or precedes the entrance of the male cell into the ovum. It is worthy of note that the ovum may become amoeboid in the region from which the polar globules are expelled. The remainder of the nucleus {female proimcleus) now passes inward to undergo further changes of undoubted im- portance, possibly those by virtue of which all the subsequent evolution of the ovum is determined. This brings us to the consideration of another cell destined to play a brief but im- portant r6le on the biological stage. The Male Cell {Spermatozoon). This cell, almost without exception, consists of a nucleus (head) and vibratile cilium. However, as indicating that the Fm. M.-Spermstmsoa iiD -Haddoa). Not. dr»wn to aciUe. l.spongn ; S,h]rdrokl ; 8, nema- tode ; 4, oray-fl«li ; ... . .tU ; 6, eleolric ray ; 7, saUuniuider ; A, hone ; U, man. Id ninny ■permatoioa, as in No«. 7 and 9. an extremely delicate vibratile band ia preaent. REPRODUCTION. 61 the devel- :arded as a event fol- the ovum. x)id in the olens) now oubted im- subsequent us to the ef but im- ' a nucleus ag that the latter is not essential, spermatozoa without such an appendage do occur. The obvious purpose of the cilium is to convey the male cell to the ovum through a fluid medium — either the water in which the ova are discharged in the case of most inverte- brates, or through the fluids that overspread the surfaces of the female generative organs. The Origin of the SpemttOMSn.— The structures devoted to the production of male cells (testes), when reduced to their es- hydroM ; 3. nema- U, man. Id mnny present. Fio. 3&.~4iwniiatoi(eiie*to. A-H. Isolated sperm-orlls of the rat, showing the development of thi) npermatoaufln and Urn gradual tnuMformatloD of the nucleus into the ■pennatocoan riMd. In O lbs seminal granule is being oast off (after H. H. Brown). I— H, speita-celli of an ElaHmobranoh. The nucleus of «Mh cell divides Into a large number of daughter- nuclei, each one of which is converted ialo the rod-like bead of a spermatosoOn. NTtrans- verse ssotion of a ripe cell, showii^ the bundle of spermstoaoa and the passive nucleus a— N, after Semper). O-S, spermatogenesis In the earth-worm : O, young sperm-cell ; I . the same divided Into four ; g, spsrmatosphere with the central spertrlilastophore ; K, .) later Bt«ge : 8, nearly mature apeniM^osoa. (After BlomHeld. ) sentials, consist of tubules, of great length in mammals, lined with nucleated epithelial cells, from which, by a series of 62 ANIMAL PHYSIOLOGY. li m changes figured above, a general idea of their development may be obtained. It will be observed that throughout the series the nucleus of the cell is in every case preserved, and finally becomes the head of the male cell. Once more we are led to see the importance of this structure in the life of the cell. Fertilisation of the Oram. — ^The spermatozoon, lashing its way along, when it meets the ovum, enters it either through a special minute gateway {micropyle), or if this be not present — as it is not in the ova of all animals — it actually penetrates the mem- branes and substance of the female cell, and continues active till the female pronucleus is reached, when the head enters and the tail is absorbed or blends with the female cell. The nucleus of the male cell prior to union with the nucleus of the ovum undergoes changes similar to those that the nucleus of the ovum underwent, and thus becomes fitted for its special func- tions as a fertilizer; or perhaps it would be more correct to say that these altered masses of nuclear substance mutually fertil- ize each other, or initiate changes the one in the other which conjointly result in the subsequent stages of the development of the ovum. The altered male nucleus {male pronucleus), on reaching the female pronucleus, finds it somewhat amseboid, a condition which may be shared in some degree by the entire T.PN: V.PN: 11.PN. Flo. M.— FertUiMtion of ovum of a moUuik (Etaiia viritiii). A. Ovum Dending up a protu- berance to meet the apermatoaoOn. B. Aniraaoh oii' nmle pronucleus to meet the female pronucleus. F. PS, female pronucleua ; m.PIf, male pronucleus ; 8, BpermatozoOo. ovum. The resulting union gives rise to the new nucleus {seg- mentation nucleus), which is to control the future destinies of the cell ; while the cell itself, the fertilized ovum {oosperm), enters upon new and marvelous changes. In reality this process was foreshadowed in the dim past of the history of living things by the conjugation of infusoria and kindred animal and vegetable forms. When lower forms (unicellular) conjugate they become somewhat amoeboid sooner REPRODUCTION. 63 )ment may nucleus of es the head Lmportance ing its way ^h a special at — as it is the mem- nues active enters and rhe nucleus f the ovum leus of the pecial func- >rrect to say ually f ertil- 3ther which levelopment niideus), on it amseboid, y the entire -M.PN. mding up a protu- to meet the female permatozotio. nucleus {seg- I destinies of [Q {p6spemi), dim past of of infusoria lower forms oeboid sooner or later, and division of cell contents results. In some cases (septic monads) the resulting cell may burst and give rise to a shower of animal dust visible only by the highest powers of the microscope, each particle of which proves to be the nucleus from which u future ".ndividual arises. The study of reproduction thus establishes the conception of a unity of method throughout the animal and, it may be added, the vegetable kingdom, for reproduction in plants is la all main points parallel to that process in animals. But why that costly loss of protoplasm by polar globules ? For the present we shall only say that it appears necessary to prevent parthenogenesis ; or at least to balance the share which the male and female elements take in the work of producing a new creature. It is to be remembered that both the male and female lose much in the process — blood, nervous energy, etc., in the case of the female, while the male furnishes a thousand-fold more cells than are used. But the period when organisms are best fitted for reproduction is that during which they are also most vigorous, and can best afford the superfluous drain on their energies. Segmentation and Subsequent Changes. After the changes described in the last chapter a new epoch in the biological history of the ovum — now the odsperm (or fer- tilized egg) — begins. A very distinct nucleus {segmentation nucleus) again appears, and the cell assumes a circular outline. The segmentation or division of the ovum into usually fairly equal parts now commences. This process can be best watched in the microscopic transparent ova of aquatic animals which undergo perfect development up to a certain advanced stage in the ordinary water of the ocean, river, lake, etc., in which the adult lives. Segmentation among invertebrates will be first studied, and for this purpose an ovum in which the changes are of a direct and uncomplicated nature will be chosen. The following figures and descriptions apply to a mollur,k ( Elysia viridis) . We distinguish in ova resting stages and stages of activity. It is not, however, to be supposed that absolute rest ever characterizes any living form, or that nothing is tran- H^uring because all seems quiet in these little biological worlds ; for we have already seen reason for believing that life and in- cessant molecular activity nre inseparable. It may be that, in 64 ANIMAL PHTSIOLOOT. the case of resting ova, changes of a more active character than usual are going on in their molecular constitution ; but, on the other hand, there may be really a diminution of these activities in correspondence with the law of rhythm. This seems the more probable. The meaning, however, of a " resting stage " is m Fio. ST.— PrimltiTe egn of Tarioua •nlnwh. p wrfof m lng MMBboid movMnenU (verr much All pniDitlve eras kre naked oella, oapwle of dwnge of form. Within the ■ ■ ■ ■ ■"" " ■ . . - iMmel (the Rwin- piw>piMm (ec^jrelk) Um • Im^ TMicttlar . r k • nuckoliM (germ-uiot); in the nuoleohM • germ-poliit (nucleo- enUrned). lUrli. flndy muiulated , vesicle), and in the latter I .. _ . linua) H otten Tldble. Fig. A t—A 4, Tbm primitiTe egg ol a ohalk qxHiKe (LeMeulmii fMnut), In four oonwoutire conditions of motkm. Fig. B l—B 8. The primitive en of a hermitHsrab (Chimdmeanthu* eomutu»). In eight oonseoutiTe conditfcms of moUoa (after B. Van Beneden). Fig. C 1— C S. PrimMve ent of a cat, in tour dilferent oooditlons of moUon (after PAOger). Fig. i>. PrtanitlTe egg of a trout. Fig. X. PrimitlTe egg of a hen. Fig. F. PrtanUlTe human egg. (Haeckel.) the obvious one of apparent quiescence— cessation of all kinds of movement. Then ensues rapidly and in succession the fol- lowing series of transformations : The nucleolus divides, later EEPRODUCTION. 66 racter than but, on the e activities seems the g stage " is the nucleus, into two parts. These new nuclei then wander away from each other in opposite directions, and, losing their menta (Tery mncb fonn. WlUiiii the kernel (the Renn- [erm-poiiit (nudeo- ■ponKe {btuimlmli primttlTe egc of • M of motioa (after went oondittona of >tU*e em of • hen. of all kinds Bsion the f ol- divides, later Fio. 68.— Karir etagee of Msmentation of a moUtiak, SlyHa vMdia (drawn from the IlTlng esg). A, oosperm in ataie of reat after the eztraoion of the pcdar cells ; B, the nuoleolua atone baa divided ; O, the nucleus is diyiding ; D, the nucleus, as such, nas disappeared, first segmentation furrow appears ; E, later stase ; F, ofiqierm divided into two distinct seKmentation spheres, the clear nuclear space m the center of the aster of granules is growbiflr larow ; O, resting stan of appressed two spheres ; H, I, similar stages in the produraon of four spheres ; K, larmatfDn of eight-celled stage. (Haddon.) character as nuclei and nucleoli, are replaced by asters (polar stars), which seem to arise in the protoplasm of the body of the cell, and which are in close juxtaposition at first, but later separate, the oosperm becoming amoeboid in one region at least. A groove, which gradually deepens, appears on the sur- face, and finally divides the cell into two halves, which at once become flattened against each other. The nucleus may again be recognized in the center of each polar star, while a new nu- cleolus also reappears within the nucleus, when again a brief period of rest ensues. In the division and oioiination of the nucleus, when most complicated (karyokinesis), the changes may be generalized as consisting of division,and segregation, followed by aggregation. The subdivision (aegmentaiion) of the cell, after the quies- cence referred to, again commences, but in a plane at right angles to the first, from which four spheres result, again to be followed by the resting stage. The process continues in the . same way, so that there is a progressive increase in the num- ber of segments, at least up to the point when a large number s h I ee ANIMAL PHT8I0L00Y. has been formed. This is rather to be considered as a type of one form of segmentation than as applicable to all, for even at this early stage differences are to be noted in the mode of segmentation which characterize effectually certain groups of animals ; but in all there is segmentation, and that segmenta- tion is rhythmical. Fie. ao.— The dMTMja of • trog't cfi flrat cleKTjyaeorifi ; C, 4 celM ; D, (10 ttaiM eiilM||«d). A, the pM«nt«eU ; B, the two oelk(4aidiiuaMid4Te(ietatiTe); £; It oella (8 animal and 4 TeKeiaUre) : jr. M oelli (8 animal and 8 Tegetative) ; O, M oella (10 animal and 8 vegetaUve): H. «> onlla; /,48 oelto; K, 64 oella; 2., W alean«eHiella ; Ji; — ' odbdlB animal and MvegetaUve). (HaeckeL) Segmentation results in the formation of a multicellular aggregation which, sooner or later, incloses a central cavity {segmentcUion cavity, blastocele). Usually this cell aggrega- tion {blaatvia, blastosphere) is reduced to a single layer of in- vesting cells. The GMtruIa. — Ensuing on the changes just described are others, which result in the formation of the gastrula, a form of cell aggregation of great interest from its resemblance to the Hydra and similar forms, which constitute in themselves inde- pendent animals that never pass beyond that stage. The blas- tula becomes flattened at one pole, then r* ^pressed, the cells at . as a type of all, for even the mode of ain groups of lat segmenta- u«ntH>eU ; B, the two ); £,Uoelki (8 animal celto (IS MiUnal Mid 8 ft multicellular central cavity I cell aggrega- ffle layer of in- b described are trula, a form of mblance to the lemselves inde- »ge. The bias- sed, the cells at I g) I. I " m iiii •3.5 1 1 |8'fe 85 ' - .-a «» s ^ fs:: s- ■a S *"-il a- |. I fill: J** I I X li Si < O H >J D K !» < P ^^■^5i.il III * 5 :§ -B I & ftl?|6ft 1^ 111 ag ^•s.-5-si rle|^l|| I o J3 11 B " O * $11 a p a is i • ? i « g .^ « 1? •* .15 * . « s 5" • «' a -! « o* J *• *4 a >• a '^p ^ .."s •- fc y a jp E •8 ,* = 9 ^1 g|| tamimmmmmm nrifei * ^.§!^ II .*S1 § & li-ss; ec g -C ^ & :5 5i- 7) fi c MM i» wi) li yn i n w M <' . i i-"if i * 'w ■ M W H -. H - * ■ . ■>■'■ '^. % IMAGE EVALUATION TEST TARGET (MT-3) 1.0 I.I 2.5 1^ 12.2 ■-IM |50 ""'^ ti 20 1.8 1-25 11.4 11.6 L Photographic Sciences Corporation 23 WIST MAIN STRICT WIBSTCR.N.Y. 14S80 (716) S72-4S03 ssM^i^'sm^^^^'^^i^'^^^^^^^'^^^^^^^^^^^'-*^^^*^*'^^^ *' CIHM/ICMH Microfiche Series. CIHM/ICMH Collection de microfiches. Canadian Institute for Historical Microreproductions / Instltut Canadian de microreproductions historiques :V ^S^fPSf^Sf REPKODUCTION. 67 this region becoming more columnar (histological differentia- tion). This depression {invagination) deepens until a cavity is Fio. TO.-Blaatulft and gastrula of amphioxus (Claus, after Hatschek). A, bl^tula with flat- tened lower poJe of brger cells ; B, commenclne invaKinatipn ; C, gaBtnUatlon completedi; the blastopore is stlU widely open, and one of flie two hinder-pole mesoderm cells Is seen at its ventral Up. The cilia of the epiblast cells are not represented. formed (as when a hollow rubber ball is thrust in at one part till it meets the opposite wall), in consequence of which a two- layered embryo results, in which we recognize the primitive ifaouth {blastopore) and digestive cavity {archenteron), the outer layer {ectoderm) being usually separated from the inner {endoderm) by the almost obliterated segmentation cavity. Such a form may be provided with cilia, be very actively loco- motive, and bear, consequently, the greatest resemblance to the permaiient forms of some aquatic animals. The changes by which the segmented oosperm becomes a gastrula are not always so direct and simple as in the above- described case, but the behavior of the cells of the blastosphere may be hampered by a burden of relatively foreign matter, in the form of food-yelk, in certain instances ; so much so is this the case that distinct modes of gastrula formation may be rec- ognized as dependent on the quantity and arrangement of food- yelk. These we shall pass by as being somewhat too compli- cated for our purpose, and we return to the egg of the bird. The Hen'i Egg.— By far the larger part of the hen's egg is made up of yelk ; but just beneath the vitelline membrane a small, circular, whitish body, about four millimetres in diame- ter, which always floats uppermost in every portion of the egg, may be seen. This disk {blastoderm, cicatricula) in the fertilized egg presents an outer white rim {area ojpaca), within which is a transparent zone {area peUmida), and most centrally a some- what elongated structure, which marks off the future being itself {embryo). All of these parts together constitute that por- tion {blastoderm) of the fowl's egg which is alone directly con- cerned in reproduction, all the rest serving for nutrition and 68 ANIMAL PHYSIOLOay. protection. The appearance of relative opacity in some of the parts marked off as above is to be explained by thickening in the cell-layers of which they are composed. The Origin of the Fowl'i Egg.— The ovary of a young but mature hen consists of a mass of connect- ive tissue {stroma), abundantly supplied with blood-vessels, from which hang the capsules which contain the ova in all stages of development, so that the whole suggests, but for the color, a bunch of grapes in an early stage. The ovum at first, in this case as in all others, a single cell, becomes com- plex by addition of other cells {dis- cus proligerus, etc.), which go to make up the yelk. All the other parts of the hen's egg are additions made to it, as explained before, in its passage d(>wn the oviduct. The original ovum remains as the blas- toderm, the segmentation of which may now be described briefly, its character being obvious from an examination of Fig. 72, which rep- resents a surface view of the seg- menting fertilized ovum {oosperm). A segmentation cavity appears early, and is bounded above by a single layer of epiblast cells and below by a single layer of primi- tive hypoblast cells, which latter is soon composed of several layers, Fia. n.-FernliT^newUve organs of while the Segmentation cavity dis- toeJowKalter D«ltoii)^^;^ovarjrj appears. B, OrawiUui follicle, from which the «m haa juBt been diMsharged ; C. yeBt, enterinKupper extremity of oviduct ; D, £, second portion of oviduct, in which the chalaalferous membrane, chatazn, and albumen are formed ; F, third portion, In which the fibrous shell membranes are produced ; G, fourth portion laid open, showing the egg completely cells, arranged irregularly and ly^ formed with lis calcareous shell ; rt, ' , . ,, -n >'j. i. canal through which the egg is ex- mg loOSely in the yelk, COUStltUt The blastoderm of an unincu- bated" but fertilized egg consists of a layer of epiblastic cells, and beneath this a mass of rounded REPRODUCTION. 69 y in some of the t)y thickening in which they are he Fowl's £gg.— »ung but mature mass of connect- na), abundantly )od-vessels, from capsules which in all stages of that the whole he color, a bunch jarly stage. The this case as in all )11, becomes com- f other cells (dis- tc), which go to c. All the other egg are additions plained before, in the oviduct. The nains as the blas- sntation of which :;ribed briefly, its obvious from an 'ig. 72, which rep- view of the seg- 1 ovum {oosperm), m cavity appears nded above by a spiblast cells and e layer of primi- ells, which latter of several layers, itation cavity dis- rm of an unincu- ized egg consists iblastio cells, and mass of rounded rregularly and ly- le yelk, constitut- Fio. 7«.-VariouB -tages In the aeRmentation of a fowl's egg tKOUlker). inir the primitive hypoblast. After incubation for a couple of hours these cell, become differentiated into a lower layer of mZ^ZulnypoUa^t), with -soblastic c^ls sc^^^^^^^^ be tween the epiblast and hypoblast. It is noteworthy that, m the S segmentation will proceed up to a certain stage mdepen- Sy of the advent of the male cell, apparently indicating a tendency to parthenogenesis. Fm 78 -Portion of aeoUon through an unlncubjOed fowl> o^JP™ (»J^' iS?w la^r^wU^Sf 70 ANIMAL PHYSIOLOGY. The fowl's ovum then belongs to the class, a portion of which alone segments and develops into the embryo {meroblastic), in contradistinction to what happens in the mammalian ovum, the whole of which undergoes division {holoblastic) ; a distinction which is, however, superficial rather than fundamental, for in reality in the fowl's egg the whole of the original ovum does eet. ''^■\ *p. FiQ. 74.-SectloM of ovum of a rabbit. HluBtratlnft fprmatton o' tj* P^J*Slt.7^'L^^ ^^, E VmBeneden). A, B, 0, D. are ova to Mcoessive sUges of dewtopment. «p, »oiia peUu- clda ; eet, ectomeres, or outer celta ; ent, entomeres, or toner oeUa. segment. This holoblastic character of the mammalian ovum and its resemblance to the segmentation of those invertebrate forms previously described may become apparent from an ex- amination of the accompanying figures. We shall return to the development of the mammalian ovum later ; in the mean time we present the main features of devel- opment in the bird. Remembering that the development of the embryo proper takes place within the pellucid area only, we point out that the area opaca gradually extends over the entire ovum, inclosing immalian ovum jse invertebrate 3nt from an ex- , ammalian ovum jatures of devel- ( embryo proper lint out that the ovum, inclosing REPRODUCTION. 71 the yelk, so that the original disk which lay like a watch-glass on the rest of the ovum, has grown into a sphere. That portion ijf this area nearest the pellucid zone {area vasctdosa) develops H- Fio. 75.— Dlagraminatic transverse sections through a hjrpothetical nuunmal oosperm (Had- don). A. The yelk of the prlmitiTe mammalian oOsperm is now lost. B. Later stage ; the non-embrronic epiblast nas grown over the emiwyonic area to form the covering cells. ep, epiblast of embryo ; ep', epiblast of yelk-sac ; Ay, primitive hypoblast ; y. «, yelk-sac, or blastodermic vesicle. blood-vessels that derive the food-supplies, which replenish the blood as it is exhausted, from the hypoblast of the area opaca. The first indications of future structural outlines in the embryo is the formation of the primitive streak, an opaque band in the long diameter of the pellu- cid area, opaque in consequence of cell accummulation in that re- gion. Very soon a groove {primi- tive groove) extends throughout this band, which gradually occu- pies a more central position. The relative thickness of the several parts and the arrangement of cells may be gathered from Fig. 76. These structures are only tempo- rary, and those that replace them will be described subsequently. We have thus far spoken of cells as being arranged into epi- blast, hypoblast, and mesoblast. The origin of the first two has been sufficiently indicated. The mesoblast forms the intermediate germinal layer, and is derived from the primitive hypoblast, which diflferentiates into a stratum of flattened cells, situated below the others, and constituting the later hypoblast, and in- Fio. 78.— Surface view of pellucid area of blastoderm of eighteen hours ( Foster and Balfour). H, medullary folds; tnc, med- ullary groove ; pr, primitive groove. 72 ANIMAL PHYSIOLOGY. termediate less closely arranged cells, termed, from their posi- tion, mesoblast. It will be noticed that all future growth of the embryo be- gins axially, at least in the early stages of its development. Ae the subsequent growth and advance of the embryo de- pend on an abundant and suitable nutritive supply, we must now turn to those arrangements which are temporary and of subordinate importance, but still for the time essential to devel- opment. Embryonic Membranes of Birds. It will be borne in mind throughout that the chief food-sup- ply for the embryo bird is derived from the yelk ; and, as would 1"*.. -^ FioB '.7-n.—A aeriea of diMtnuna Intended to facilitate the comprehenaion of the relation* of the membrane* to other parts (after Foster and Balfom-). A, B, C, D, E, F are vertical gections in the lone axis of the embryo at different periods, showing the stages of devel(n>- ment of the amnion and of the yellc-gac. I, U, lU, IV are transverse sections at about the same stages of development. 1, ii, ill, posterior part of longitudinal section, to Ulustrate three stages in formation of the allantois. e, embryo ; », yelk ; pp, pleuroperitoneal cav- ity ; vfT^telline membrane of anmiotic fold ; ol, allantois ; a, amnion ; a', aUmentaiy i be expected, the older the embryo the smaller the yelk, or, as it is now called when limited by the embryonic membranes, the yelksac {umbilical vesicle of the mammalian embryo). The manner in which this takes place will appear upon an inspec- tion of the accompanying figures. Very early in the history of the embryo two eminences, the head and the tail folds, arise, and, curving over toward each fe^'j ifWiiiflfifltill^ from their posi- : the embryo be- evelopment. f the embryo de- supply, we must emporary and of ssential to devel- le chief f ood-sup- k; and, as would ension of the relatioiw of B, C, D, E, F are vertical iog the stages of develop- erae sections at about the linal section, to illustrate pp, pleuroperitoneal cav- amnion ; a', aUmentaiy the yelk, or, as it B membranes, the n embryo). The ■ upon an inspec- vo eminences, the )ver toward each 78 74 ANIMAL PHYSIOLOGY. other, meet after being joined *by corresponding lateral folds. Fusion and absorption result at this meeting-point, in the inclosure of one cavity and the blending of two othere. These >r.e. v. Fio. 80. —Diagrammatic longitudinal section through the axis of an embryo chick (after Foster and Balfour). iV. C, Neural canal ; Ch, notocbord ; Fg, foregut ; T. So, somatc^leure ; F. Sp, splancbnopleure ; S!p, splancbnopleure, forming lower wall of foregut ; Bt, heart ; pp, pleuroperitoneal cavity ; Am, amniotic fold ; £, epiblaat ; M, mesobh.st ; H, hypoblast. folds constitute the amniotic membranes, the inner of which forms the true amnion, the oater the false amnion {serotis mem- brane, suhzonal membrane). Within the amnion proper is the amniotic cavity filled with fluid {liquor amnii), while the space between the true and false amniotic folds, which gradually in- creases in size as the yelk-sac diminishes, forms the pleuro- peritoneal cavity, body cavity, or ccelom. The amniotic cavity also extends, so that the embryo is surrounded by it or lies centrally within it. The enlargement of the ccelom and exten- sion of the false amniotic folds lead finally to a similar meeting and fusion like that which occurred in the formation of the true amniotic cavity. The yelk-sac, gradually lessening, is at last withdrawn into the body of the embryo. Fig. 80 shows how the amniotic head fold arises, from a budding out of the epiblast and mesoblast at a point where the original cell layers of the embryo have separated into two folds, the somatopleure or body fold and the splanchnopleure or vis- ceral fold, owing to a division or cleavage of the mesoblast toward the long axis of the body. Remembering this, it is always easy to determine by a diagram the composition of any one of the membranes or folds of the embryo, for the compo- nents must be epiblast, mesoblast, or hypoblast ; thus, the splanchnopleure is made up of hypoblast internally and meso- blast externally — a principle of great significance, since, as will be learned later, all the tissues of the body may be classified simply, and at the same time scientifically, according to their embryological origin. yfffMWffiiiiiiiipiiiiffi ^I^W^SSlW^^ w^ms^H^m wmm ■- REPRODUCTION. w xg lateral folds. g-point, in the othei's. These Inyo chick (after Foster ; F. So, gonwtt^leure ; of foregut ; Ht, heart ; isobh at ; H, bypoUaat. inner of which yn (serotts mern- on proper is the while the space h gradually in- •ms the pleuro- amniotic cavity id by it or lies elom and exten- similar meeting ation of the true aning, is at last I arises, from a point where the d into two folds, .nopleure or vis- the mesoblast Bring this, it is iposition of any for the compo- >last; thus, the daily and meso- ce, since, as will lay be classified wording to their The allantois is a structure of much physiological impor- tance. It arises at the same time as the amniotic folds are forming, by a budding or protrusion of the hind-gut into the m, position of the mouth ; me, mesentery. pleuro-peritoneal cavity, and hence consists of an outgrowth of mesoblast lined by hypoblast. . , ^, , The outer membrane of the allantois fuses with the subzo- ncd (serous) membrane, and, with the latter extendmg beyond the yelk-sac, incloses the albumen of the egg in a space termed E- -^=SM,v. m. brane. .;-1 76 ANIMAL PHYSIOLOGY. the jUacenial sac by Duval, who has recently described this pro- cess. Villi, or tubular vascular outgrowths, spring from the lining of this sac and serve to convey the absorbed and prob- ably altered albumen to the embryo, in which process of vas- cular transport of nourishment the yelk-sac, that also abounds in blood-vessels as well as the allantois, takes part. The physiological import of the various structures above described will be considered more fully later. At this point a compari- son of the formation of the corresponding parts in mammals will be undertaken. The Fcetal (Embryonic) Membranes of Mammals. The differences between the development of the egg mem- branes of mammals and birds are chiefly such as result from v p.am. rS r0.m.t). r -0.9. -•.t. -am,' ''\ -4a,. -^y U Vs Via. 88. Flu. 84. Fio. 89.— Diagrammatio looKitudlnal aeotion of oOaperm of rabbit at an advanced Rtase of pregnancy (KOUiker, after Bischoff). a, amnion ; al, allantolH with its blood-veaseli ; e, embryo ; da, yeUc^sac : ed, ed', ed", nypoblaatic epithelium of the yelk-sac and its stalk (umbilical vcMicle and cord) : /d, vascular mesoblastic membrane of the umbilical cord and vesicle ; p, placental villi formed by the allantois and subasonal membrane ; r, space filled with fluid between the amnion, the allantois, and the yelk-sac ; tt, sinus terminolis (marginal vltelUoe blood-vessel) ; u, urachus, or stalk of the allantois. Fio. 81.— Diagrammatic dorsal view of an embryo rabbit with its membranes at the stage of nine sonutee (Haddon, after Van Beneden and Julin). ai, allantois, showing from behind the tail fold of the embryo ; am. anterior border of true amnion : a. t', area vasculosa, the outer border of which indicates the farthest extension of the mesoblast ; M, blastoderm, here consisting only of epiblast and hypoblast ; o. m. v. omphalo-mesenterio or vitelline veins ; p. am, proamnion ; pi, non-vascular epiblastic villi of the future placenta ; «. t, si- nus terminalis. the absence in the former of an egg-shell and its membranes, and of yelk and albumen. The mammalian ovum is inclosed by a zona radiata {zona peUiuyida) surrounding another very delicate covering (Fig. 58). The growth of the blastodermic vesicle (yelk-sac) is rapid. REPRODUCTION. 77 )scribed this pro- spring from the iorbed and prob- 1 process of vas- hat also abounds ikes part. The above described )oint a compari- rts in mammals Mammals. f the egg mem- i as result from and, being filled with fluid, the zona is thinned and soon disap- pears. The germinal area alone is made up of three layers of cells (Fig. 10-i), the rest of the upper part of the oosperm being lined with epiblast and hypoblast, while the lower zone of the yelk- sac consists of epiblast only. Simple, non-vascular villi, serving to attach the embryo to the uterine walls, usually project from the epiblast of the subzonal membrane. In the rabbit they do not occur every- where, but only in that region of the epiblast beneath which the mesoblast does not extend, with the exception of a patch which soon appears and demarkates the site of the future placenta. The extension of the mesoblast takes place in every direction from the embryo except directly around the head ; but the two an advanced itase of th JU blood-veflwfi ; e, yelk-sac and ite stalk of the umbilical cord i membrane ; r, space c ; 9t, sinus termlnalis Is. ibranes at the staKe of I showing from behind t'j area vosculoaa, the 'Mast ; M. blastoderm, nesenterio or vitelline ture placenta ; 1. 1, si- ts membranes, im is inclosed another very -sac) is rapid. Fio. 85.— Diagrammatic median vertical longitudinal sections through embryo rabbit (Had- don, after Van Beneden and Julin). A. Bection through embryo of Fig. M. B. Section through embryo of eleven days, at, ollontois ; am, amnion ; a. nw, anterior median plate of mesoblast, formed by the junction of the anterior horns of the area opoca ; a. pi, area placentalis ; a. v, area vaaculoaa ; eft, chorion ; cce, coelom of embryo ; cae', extra-embry- onic portion of the body-cavity ; ep, epiblast ; hy, hypoblast ; m. unsplit mesoblast ; o. a, orifice of amnion ; p{, placenta ; pro. a, proamnion ; «. (, sinus termlnalis ; v, epiblostic vllU of blastodermic veacle. expansions of the mesoblast which mark out this area extend for some distance in front of the head, and ultimately unite ; so that immediately in front of the head there is a circular region in which the blastoderm consists of epiblast and hypo- r 78 ANIMAL PHYSIOLOGY. blast only, forming a cavity into which the anterior part of the embryo early projects {pro-amn 'on). The true amnion arises only from the posterior end of the embryo, and, extending over in a forward direction, meets the raised projection of the pro-amnion with which it fuses. The amniotic cavity becomes one with that space (extra-em- bryonic pleuro-peritoneal cavity) arising from the cleavage of Fio. 86.— Foetal envelopes of a rabbit embryo (Mlnot, after Van Beneden and Julin). Later stage than Fig. 85 B. The amnion has become fused with the blastoderm in front of the embryo, and Its cavity is therefore continnous with the extra-embryonic portion of the liody-cavity in front of the embryo. Al, allantois ; am, amnion ; am', portion of the amnion united with the wbUs of the allantois ; A.pl, area placentalis ; Av, area vasculoea ; Ch, chorion ; Cce, coelom or body-cavity ; Ca", extra-embryo>:ic portion of the body- cavity ; Cael, anterior portion of the same, produced by the fusion of the cavity of the amnion with that of the anterior portion of the area opaca ; Be, epiblast ; £ii, alimentary canal of the embryo ; Bnt, hypoblast ; PI, placenta ; pro. A, proamnion ; T, sinus ter- minalls : V, villi of blastodermic vesicle ; Y, cavity of blastodermic vesicle. the mesoblast, which now advances beyond the head of the em- bryo and the pro-amnion. The pro-amnion by gradual atrophy gives place to the true amnion. At about the same period as these events are transpiring the vascular yelk-sac has become smaller, and the allantois with its abundant supply of blood-vessels is becoming more prominent, and extending between the amnion and subzonal membrane. The formation of the chorion marks an important step in the development of mammals in which it plays an important functional part. It is the result of the fusion of the allantois, which is highly vascular, with the subzonal membrane, the villi of which now become themselves vascular and more complex in other respects. An interesting resemblance to birds has been observed (by Osborn) in the opossum. When the allantois is small the 11^ REPRODUCTION. 19 iterior part of the sterior end of the •ection, meets the ;h it fuses. t space (extra-em- a. the cleavage of '\T. ineden and Julin). Later blastoderm in front of the embryonic portion of the ion ; am', portion of the talis ; Av, area vasculosa ; i>:ic portion of the body- ision of the cavity of the eptblast ; £>i, alimentary proamnion ; T, sinus ter- nic vesicle. e head of the em- r gradual atrophy re transpiring the allantois with its ; more prominent, nal membrane, important step in lays an important n of the allantois, lembrane, the villi tid more complex 3een observed (by tois is small the Fio. 87.-Embryo of dog, twenty-ilve days old, opened on *'^^'^J'*^.J^i.^^,^7^' tral walls have been removed, a, nose-pits; 6. eyes; c, un^CT-Jaw (first BUl-JJon) .. ». wcond giU-arch ; e./, o, h, heart (e, rtehr, /, left auricle; ff.,riKht, *;>«", Ye«Si"l^.;^. i^ (orSin of); fclfc liver (in the miffdie between the two •»«^,w ">« ™* y?*;J5,*£> I, stonlacff ; m. intestine ; n, velk-mc ; o, primUive kidnejs ; P. o"«ntote A**^"^^ i, hind-Umbs. The crooked embryo has been stretched straight. vHaccKel, alter Biachoir.) A.r^ Fio. 8B.— Diaxram of an embryo showing the relations of the vascular allantois to the vlUi of the chorion (Oadlat). e, embryo lying In the cavity of the amnion ; y», yelk-sac j al, al- lantoto ; A. K, allantolo vessels dipping into the vUU of the chorion ; cA, chorion. 80 ANIMAL PHYSIOLOGY. blastodermic vesicle (yelk-sac) has vascular villi, which in all probability not only serve the purpose of attaching the embryo to the uterine wall but derive nourishment, not as in birds, from the albumen of the ovum, but directly in some way from the uterine wall of the mother. It will be remembered that the opossum ranks low in the mammalian scale, so that this resemblance is the more signifi- cant from an evolutionary point of view. The term chorion is now re- stricted to those regions of the Bubzonal membrane to which either the yelk-sac or the allan- tois is attached. The former zone has been distinguished as the false chorion and the latter Fia.SB.-DiasrramofthefOBtalmembraiiMof aS the true chorion. In the the Virginian oposHum (Haddon, after Os- born). Two villi ar " are shown greatly en- larged . The ptoeeaaes of the cells, which have been exaggerated, doubtless corre- spond to the pieudopodia described by Caldwell, al, allantoi i ; am, ainn'on ; s. t, sinus terminalls ; a. z, subzonal mem- brane ; V, villi on the subzonal membrane in the region of the yelk-sac : y«, yelk The vascular splanchnopleure (hy- 6AC pol the nople , , iblast and mesoblast) is indicated by he black line. rabbit the false chorion is very large (Fig. 83), and the (placen- tal) chorion very small in com- parison, but the reverse is the case in most mammals. It will be noted that in both birds and mammals the allantois is a nu- tritive organ. Usually the more prominent and persistent the yelk-sac, the less so the allantois, and vice versa; they are plainly supplementary organs. The Placenta. — This structure, which varies greatly in com- plexity, may be regarded as the result of the union of structures existing for a longer or shorter period, free and largely inde- pendent of each other. With evolution there is differentiation and complication, so that the placenta usually marks the site where structures have met and fused, differentiating a new organ; while corresponding atrophy, obliteration, and fusion take place in other regions. All placentas are highly vascular, all are villous, all dis- charge similar functions in providing the embryo with nourish- ment and eliminating the waste of its cell-life (metabolism). In structural details they are so different that classifications of mammals have been founded upon their resemblances and dif- ferences. These will now be briefly described. In marsupials the yelk-sac is both large and vascular ; the REPRODUCTION. 81 which in all ig the embryo I in birds, from way from the jered that the low in the , so that this le more signifi- lutionary point 'on is now re- regions of the rane to which ac or the allan- The former stinguished as and the latter )rion. In the shorion is very nd the (placen- '■ small in com- reverse is the nmals. It will both birds and lantois is a nu- persistent the raa; they are reatly in com- n of structures I largely inde- diflFerentiation narks the site tiating a new n, and fusion lloiis, all dis- with nourish- (metabolism). issifications of ances and dif- vascular; the allantois small but vascular ; the former is said (Owen) to be attached to the subzonal membrane, the latter not ; but no villi, and consequently no true chorion, is developed. All mammals other than the monotremes and marsupials have a true allan- toic placenta. The Diieoidal Flftoenta.— This form of placenta is that existing in the rodentia, insectivora, and cheiroptera. The condition found in the rabbit is that which has been most studied. The relation of parts is shown in Fig. 83. The uterus of the rodent is two-homed ; so we find in gen- eral several embryos in each horn in the pregnant rabbit. They are functionally independent, each having its own set of mem- branes. It will be observed from the figure that the true vil- lous chorion is confined to a comparatively small region ; there is, however, in addition a false chorion without villi, but highly vascular. This blending of forms of placentation which exist separately in different groups of animals is significant. In the rabbit, at a later stage, there is considerable intermingling of foetal and maternal parts. The Metadiieoidal Pkoenta. — This type, which, in general naked-eye appearances, greatly resembles the former, is found in man and the apes. The condition of things in man is by no means as well understood as in the lower mammals, especially in the early stages ; so that, while the following account is that usually given in works on embryology, the student may as well understand that our knowledge of human embryology in the very earliest stages is incomplete and partly conjectural. The reason of this is obvious : specimens for examination depending on accidents giving rise to abortion or sudden death, often not reaching the laboratory in a condition permitting of trust- worthy inferences. It is definitely known that the ovum, which is usually fer- tilized in the oviduct (Fallopian tube), on entering the uterus becomes adherent to its wall and encapsuled. The mucous membrane of the uterus is known to undergo changes, its com- ponent parts increasing by cell multiplication, becoming in- tensely vascular and functionally more active. The general mucous surface shares in this, and is termed the decidua vera j but the locality where the ovum lodges is the seat of the great- est manifestation of exalted activity, and is termed the decidua serotina; while the part believed to have invested the ovum by fused growths from the junction of the decidua vera and sero- tina is the decidua reflexa. 6 82 ANIMAL PHYSIOLOGY. The decidua serotina and reflexa thus become the outermost of all the coveriijgs of the ovum. These and some other devel- opments are figured below. It is to be remembered, however, that they are highly diagrammatic, and represent a mixture Fio. M. -Series of dlagrama ivpreaenttaig the relattona of the deckliut to the oturi. at different r9riods, in the human aubject. The decidua are darlc, tlie ovum aliaded tranaveraely. In and 5 the chorionic Toacuiar proceaaes are figured (after Dalton). 1. Ovum reatins on the decidua aerotina ; S. Decidua reilexa growing round the ovum ; 8. Completion of the decidua around the ovum ; 4. Villi, growing out all around the chorion ; S. The villi, spe- cially developed at the site of the future placenta, having atrophied elsewhere. of inferences based, some of them, on actual observation and others on analogy, etc. The figures will convey some information, though appear- ances in all such cases must be interpreted cautiously for the reasons already mentioned. During the first fourteen days villi appear over the whole surface of the ovum ; about this fact there is no doubt. At the end of the first month of foetal life, a complete chorion has been formed, owing, it would seem, to the growth of the allantois (its mesoblast only) beneath the whole surface of the subzonal membrane. From the chorionic surface vascular pro- cesses clothed with epithelium project like the plush of velvet. REPRODUCTION. 83 le the outermost )me other devel- ibered, however, ssent a mixture The allantois is compressed and devoid of a cavity, but abun- dantly supplied with blood-vessels by the allantoic arteries and ./ . ,t)r\ to the oTum. at different Rbadecl tranaveraely. In o). 1. Ovum reatine on n ; 8. Completion of the horion ; 8. Tlie vilU, spe- id eiMwliere. observation and AH Fio. 91.-Va8cular system of tlie human (cetus, reprMented diagnmmatically (Huxley). H, heart ; TA. aortic trunk ; c, common carotid artery : c'. external carotid artery ; c", internal carotid artery ; «, subclavian i^tery ; v, vertebral arterv ; 1. 8. 3. 4, 5, aortic arches ; A', dorsal aorta ; o, omphalo-mesenteric artery ; d». vitelline duct ; o\ omphalo- mesenteric vein ; V', unibiUcal vesicle ; tip, portal vein ; L, liver ; u, u, umbiUcal arteries ; u", u", their endings in the placenta ; u', umbiUcal vein ; Dii, ductus venosus ; vA, hepaUc vein ; ev, inferior vena cava ; tii{, iliac veins ; ntal villi being equivalent to so villi fit into cor- jcially thickened condition, under }ment, and atro- adages in mam- an of structure, irt over another uctures are sim- I of the presence n the oile hand, in the mammal lip, on the other ; 'iations, they are 76 common ends. 88 ANIMAL PHYSIOLOGY. tissue, in which capillaries abound, are covered with a flat epi- thelium; the maternal crypts correspond, being composed of a similar matrix, lined with epithelium and permeated by capillary vessels, which constitute a plexus or mesh-work. It thus results that two layers of epithelium intervene between the maternal and f cetal capillaries. The arrangement is substantially the same in the diffuse and the cotyledonary placenta. In the deciduate placenta, naturally, there is greater compli- cation. In certain forms, as in the fox and cat, the maternal tis- sue shows a system of trabeculee assuming a mesied form, in which run dilated capillaries. These, which are 'overed with a somewhat columnar epithelium, are every wh re in contact with the foetal villi, which are themselves covered with a flat epithelium. tF^ Fio. 100. Fio. 101. Fto 100.— Placenta of a sloth. Flat maternal epithelial cells ibown In poaitlon on right side ; on left they are removed and dilated ; maternal veaael with its blood-corpuacteB ezpoaed. Fh>. 101.— Structure of human plaoenta ; da, decidua aerotina : (, trabecubB of aerotina paMiiw to foetal villi ; ca, ourling artenr ; vp, utero-plaoental vein ; x, prolongation of matenuu ' tiarae on eztnior of villua, outside cellular layer e', which may represent either endothe- lium of maternal blood-vessels or delicate connective tissue of the serotina or both ; e' ma- ternal cells of the serotina. In the case of the sloth, with a more discoidal placenta, the dilatation of capillaries and the modification of epithelium are greater. In the placenta of the apes and of the human subject the most marked departure from simplicity is found. The maternal 1 1 with a flat epi- ng composed of I permeated by mesh- work. It tervene between a the diffuse and greater compli- le maternal tis- tt mesied form, ch are 'overed every wh re in es covered with poaiti i-con itlonoD right iMe; l:C0nMi8clea expowd. lUeof aerotiiia paaiiiMr longmUon of matonuil iretwnt either endothe- ^roUna or both ; t' m*- il placenta, the of epithelium an subject the The maternal REPRODUCTION. 89 vessels are said to constitute large intercommunicating sinuses ; the villi may hang freely suspended in these sinuses, or be anchored to their walls by strands of tissue. There is believed to be only one layer of epithelial cells between the vessels of mother and foetus in the later stages of pregnancy. This, while closely investing the fcBtal vessels (capillaries), really belongs to the maternal structures. The significance of thi.s general arrangement will be explained in the chapter on the physiological aspects of the subject. It remains to inquire into the relation of these forms to one another from a phylogenetic (derivative) point of view, or to trace the evolution of the placenta. Srolntion. — Passing by the lowest mammals, in which the placental relations are as yet imjwrf ectly understood, it seems clear that the simplest condition is found in the rodentia. Thus, in the rabbit, as has been described, both yelk-sac and . allantois take a nutritive part ; but the latter remains small. In forms above the rodents, the allantois assumes more and more importance, becomes larger, and sooner or later predomi- nates over the yelk-sac. The discoidal, zonary, cotyledonary, etc., are plainly evolu- tions from the diffuse, for both differentiation of structure and integration of parts are evident. The human placenta seems to have arisen from t*"J diffuse form ; and it will be remem- bered that it is at one period represented by the chorion with its villi distributed universally. The resemblance in the embryonic membranes at any early stage in man and other mammals to those of birds certainly suggests an evolution of some kind, though exactly along what lines that has taken place it is diflScult to determine with exact- ness ; however, as before remarked, nearly all the complications of the higher forms arise by concentration and fusion, on the one hand, and atrophy and disappearance of parts once functionally active, on the other. Smnmary. — The ovum is a typical cell ; unspecialized in most directions, but so specialized as to evolve from itself compli- cated structures of higher character. The segmentation of the ovum is usually preceded by fertilization, or the union of the nuclei of male and female cells, which is again preceded by the extrusion of polar globules. In the early changes of the ovum, including segmentation, periods of rest and activity alternate. The method of segmentation has relation to the quantity and arrangement of the food-yelk. Ova are divisible generally 90 ANIMAL PHYSIOLOGY. into completely segmenting (holoblastic), and those that under- go segmentation of only a part of their substance (meroblastic) ; but the processes are fundamentally the same. Provision is made for the nutrition, etc., of the ovum, when fertilized (oosperm) by the formation of yelk-sac and allan- tois; as development proceeds, one becomes more promiiient than the other. The allantois may fuse with adjacent mem- branes and form at one part a condensed and hypertrophied chorion (placenta), with corresponding atrophy elsewhere. The arrangement of the placenta varies in different groups of ani- mals so constantly as to furnish a basis for classification. What- ever the variations in the structure of the placenta, it is always highly vascular ; its parts consist of villi fitting into crypts in the maternal uterine membrane—both the villi and the crypts being provided with capillaries supported by a connective-tissue matrix covered externally by epithelium. The placenta in its different forms would appear to have been evolved from the diffuse type. The peculiarities of the embryonic membranes in birds are owing to the presence of a large food-yelk, egg-shell, and egg- membranes ; but throughout, vertebrates follow in a common line of development, the differences which separate them into smaller and smaller groups appearing later and later. The same may be said of the animal kingdom as a whole. This seems to point clearly to a common origin with gradual diver- gence of type. THE DEVELOPMENT OF THE EMBRYO ITSELF. We now turn to the development of the body of the animal for which the structures we have been describing exist. It is important, however, to remember that the development of parts, though treated separately for the sake of convenience, really goes on together to a certain extent; that new structures do not appear suddenly but gradually ; and that the same law applies to the disappearance of organs which are being superseded by others. To represent this completely would require lengthy de- scriptions and an unlimited number of cuts ; but with the above caution it is hoped the student may be able to avoid erroneous conceptions, and form in his own mind that series of pictures which can not be well furnished in at least the space we have to devote to the subject. But, better than any abstract state- lIl i jIllyilpjiMLM, hose that under- go (meroblastic) ; the ovum, when k-sac and allan- more promiiient adjacent mein- d hypertrophied elsewhere. The t groups of ani- ification. What- mta, it is always ig into crypts in i and the crypts ionnective-tissue e placenta in its rolved from the mes in birds are ^-shell, and egg- >w in a common [)arate them into and later. The a whole. This 1 gradual diver- 3 ITSELF. ly of the animal ting exist. It is opment of parts, avenience, really structures do not »me law applies ^ superseded by |uire lengthy de- t with the above avoid erroneous jries of pictures e space we have y abstract state- THE DEVELOPMENT OP THE EMBRYO ITSELF. 91 ments or pictorial representations, would be the examination of a setting of eggs day by day during their development under a ® a ® 8 f 11 ^ " Via. l(N.-Varioua lUgM In the derelopmeiit of the frog from Uwent (after Howm). 1. TIm Betrmentlng oTum, ahowiiifr flnt dearage farrow. S. Section of the above Mrignt angles to the furrow. 8. Same, on amwaranoe of aecond furrow, Tiewed •liRhthr from aboye. 4. The latter aeen from beneatL 6. The lame, on aimearance of flnt homontaifurrow. 8. The same, wen from above. 7. Longitudinal wcnon of «. 8 and 0. Two lAaaes In segmentation, on appearance of fourth and ilfth furrows. 10. Longitudinal Tertical section at a slightly later stage than the above. U. Later stage. Unpm- idgnMnted pc^ dividing morarapWr than lower IS. Later phase of 11. isTXonglfiidlnal vertical sectitni of 18. 14. SecmentinK ovum at blastopore stage. 16. Longitud&ial vertical section of same. IS wl 15 K la (all others » B). 16. Longitudinal vertical section of embijo at a stage teter than 14 (1 x 10). ne, nucleus ; c. c, cleavage cavity ; epi ^Whta*.! fj< yeUt-hejS'* lower-layer cells ; M, blastopore ; at, archenteron (mid-gut) : hb, hypoblast ; dm, undiffer- entiated mesoblast ; Ot, notochord ; n. a, neural (cerebro-qmial) axis. hen. This is a very simple matter, and, while the making and mounting of sections from hardened specimens is valuable, it may require more time than the student can spare ; but it is neither so valuable nor so easily accomplished as what we have indicated ; for, while the lack of sections made by the student liawiBMiWtt mam fsismm 02 ANIMAL PHYSIOLOGY. may be made up in ■pari by the exhibition to him of a set of specimens permanently mounted or even by plates, nothing can, in our opinion, take the place of the examination of eggs as we have sUf nrested. It prepares for the study of the development of the mammal, and exhibits the membranes in a simplicity, freshness, and beauty which impart a knowledge that only such direct contact with nature can supply. To proceed with great simplicity and very little apparatus, one requires but a forceps, a glass dish or two, a couple of watch-glasses, or a broad section-lifter (even a case-knife will answer), some water, containing just enough salt to be tasted, rendered lukewarm (blood-heat). Holding the egg longitudinally, crack it across the center transversely, gently and carefully pick away the shell and its membranes, when the blastoderm may be seen floating upward, as it always does. It should be well examined in position, using a hand lens, though this is not essential to getting a fair knowledge ; in fact, if the examination goes no further than the naked-eye appearances of a dozen eggs, selecting one every twenty-four hours during incubation, when opened and the shell and membranes well cleared away, such a knowledge will be supplied as can be obtained from no books or lectures how- ever good. It will be, of course, understood that the student approaches these examinations with some ideas gained from plates and previous reading. The latter will furnish a sort of biological pabulum on which he may feed till he can furnish for himself a more natural and therefore more healthful one. While these remarks apply with a certain degree of force to all the departments of physiology, they are of special importance to aid the constructive faculty in building up correct notions of the successive rapid transformations that occur in the de- velopment of a bird or mammal. Fig. 103 shows the embryo of the bird at a very early period, when already, however, some of the main outlines of structure are marked out. Development in the fowl is so rapid that a few days suffice to outline all the principal organs of the body. In the mammal the process is slower, but in the main takes place in the same fashion. As the result of long and patient observation, it is now set- tled that all the parts of the most complicated organism arise from the three-layered blastoderm previously figured ; every part may be traced back as arising in one or other of these lay- ers of cells — the epiblast, mesoblast, or hypoblast. It frequently him of a set of ates, nothing can, ion of eggs as we the development in a simplicity, rledge that only To proceed with le requires but a itch-glasses, or a wer), some water, idered lukewarm across the center the shell and its floating upward, ined in position, I to getting a fair no further than lecting one every opened and the a knowledge will J or lectures how- that the student leas gained from furnish a sort of II he can furnish ore healthful one. ree of force to all lecial importance p correct notions occur in the de- at a very early main outlines of 6 fowl is so rapid incipal organs of lower, but in the on, it is now set- 1 organism arise y figured ; every ther of these lay- kst. It frequently THE DEVELOPMENT OP THE EMBRYO ITSELF. 93 AS'jfZ happens that an organ is made up of cells derived from more than one layer. Structures may, accordingly, be classified as epiblastic, mesoblastic, or hypoblas- tic; for, when two strata of cells unite in the formation of any part, one is always of subordinate impor- tance to the other : thus the digestive organs are made up of mesoblast as well as hypoblast, but the latter constitutes the essential secreting cell mechanism. As already indi- cated, the embryonic membranes are also derived from the same source. The epihlast gives rise to the skin and its appendages (hair, nails, feath- ers, etc.), the whole of the nervous system, and the chief parts of the or- gans of special sense. The meaoblaat originates the skel- eton, all forms of connective tissue, including the framework of glands, the muscles, an a oen- tral trunk-sone, and a pah* of lateral or parietal sones. iMi HM g Mttu ' !- ; .-- 94 ANIMAL PHYSIOLOGY. of the first twenty-four hours such an appeamnce as that repre- sented in Fig. 104 is presented. Htf" B \ ^"^ i?*!."*?"^*??"® Mctlon through the mediillanr groove and half the blaatodmn of a chick of eighteen hours (Foster and Balfour). E,e~"-'—^- " •-* — ■ "- — -• - m/, medullary fold ; mg. medullary grooye ; ck, i ibiart ; M, meaoblaM ; H, hypoblaM : The mounds of cells forming the medullary folds are seen coming in contact to form the medvXlary {neural) canal. '^"k?*:"^!*?^*']?? ■«*'»'» o' fwjMfyo chick at end of flrrt day (after KOlliker). Jf, meao- SSniL^' ^f^^ Lr''i°^V?'*^P'^ ' * eplblai* : mg, medullary groove ; mf, me- dullary fold ; ch, chorda dorwiis ; P, protovertebral plate ; dm, division of meaobUwi. The notochord, marking out the future bony axis of the body, may also be seen during the first day as a well-marked linear extension, just beneath the medullary groove. The clear- Fio. 108.-TransvM«e iMtlpn of chick at end of second day (KOlliker). E, eptblaat : H. hypo- blast ; «. m, external plate of mewiblast dividing (cleavage of mesoblaat)Ttii./, medullMT Md ; m. g, medullary groove ; ao, aorU ; p, pteuroperttoneal cavity ; P, prutovertebnU age of the mesoblast, resulting in the commencement of the formation of aoinalojdeure (body-fold) and the aplanchnopleure (visceral fold), is also an early and important event. These give rise between them to the pleuro-perUoneal cavity. The portions of mesoblast nearest the neural canal form masses {vertebral platea) distinct from the thinner outer ones {ItUetal platea). THE DEVELOPMENT OP THE EMBRYO ITSELF. 95 ce as that repre- mg tif the blMtodmn of a noblMt ; U, IqrpoblMt : y folds are seen al) canal. terKOlliker). Jf, meao- itlUuy groove ; m/, me- iTiaion of meaoblaat. >ny axis of the 8 a well-marked Qve. The cleav- e.m. K, epibUMt ; H. taw- bbMt) \m.f, medullary vitjr ; P, pnkovertebnU ncement of the ipianchnopleure ent. These give '. The portions lasses {vertebral {lateral pkUes). — f-a.p. The vertebral plates, when distinctly marked off, as repre- sented in the figure, are termed the protovertebrcB {mesoblastic somites), and represent the future vertebra and the voluntary muscles of the trunk ; the former arising from the inner sub- divisions, and the latter from the outer {musde-plates). It will be understood that the pro- tovertebrffi are the results of transverse division of the col- umns of mesoblast that formed the vertebral plates. Before the permanent verte- brsB are formed, a reunion of the original protovertebrse takes place as one cartilaginous pillar, followed by a new segmentation midway between the original divisions. It thus appears that a large number of structures either ap- pear or are clearly outlined dur- ing the first day of incubation : the primitive streak, primitive groove, medullary plates and groove, the neural canal, the head-fold, the cleavage of the mesoblast, the protovertebree, with traces of the amnion and Fio. lOr.— Bmbnro of ohiok, between thirty •nd thlrty-a» houn, viewed from above •8 an opaque object (Faster and Balfour). /. b. foiebrain ;' m. b, midbrain ; h. b, niiul-brain pit; optic veaicle ; au. p, vitelline vein; />. v, t f u auditory pi meaoblMtio loi tton of mediillary fold ; p.r, remains of primitive groove ; a. p, area pellucida. lie : lit. /, line of ■ folds above medullary oftnai ; t. r, alnus rhomboidalis ; (, tail- area opaca. During the second day near- ly all the remaining important structures of the chick are marked out, while those that arose during the first day have progressed. Thus, the medullary folds close ; there is an increase in the number of protoverte- bree ; the formation of a tubular heart and the great blood-ves- sels ; the appearance of the Wolffian duct ; the progress of the head region ; the appearance of the three cerebral vesicles at the anterior extremity of the neural canal ; the subdivision of the first cerebral vesicle into the optic vesicles and the begin- nings of the cerebrum ; the auditory pit arising in the third cerebral vesicle (hind-brain) ; cranial flexure commences; both head and tail folds become more distinct ; the heart is not only •• .UJ,WWW(lMI(.i>.. 96 ANIMAL PHYSIOLOGY. formed, but its curvature becomes more marked and rudiments of auricles arise ; while outside the embryo itself the circula- tion of the yelk-sac is established, the allantois originates, and the amnion makes rapid progress. It may be noticed that the cerebral vesicles, the optic vesi- cles, and the auditory pit are all derived from the epiblastic accumulations which occur in the anterior extremity of the embryo ; and their early appearance is prophetic of their physi- ological importance. The heart, too, so essential for the nutrition of the embryo, by distributing a constant blood-stream, is early formed, and Fta. 108.— Dlumn reprMentiiig under Mrfaoe of an embryo rabUt of nine dajTH wid three t deTelopmmit of the bewt (after Allen Thomwn). A, view of the entire embryo ; B, an enlarged outline of the heart of A ; 0, later itage of thedoTelopment houn old, Uluatrating derel entire embryo ; B, an enlarg of B ; A ft, ununited heart ; o a, aorta ; tw, ▼tteillne Teina. becomes functionally active. It arises beneath the hind-end of the fore-gut, at the point of divergence of the folds of the splanchnopleure, and so lies within the pleuro-peritoneal cav- ity, and is derived from the mesoblast. At the beginning the heart consists of two solid columns ununited in front at first ; later, these fuse, in part, so that they have been compared with an inverted Y, in which the heart itself would correspond to the lower stem of the letter (a) and the great veins (vitelline) to its main limbs. The solid cords of mesoblast become hollow prior to their coalescence, when the two tubes become one. ^ >MUM«i#i(biN4«M«i^iirftK^' ■* iiw»,«iw ) »W M»i », k fi i m im THE DEVELOPMENT OF THE EMBRYO ITSELF. 97 )d and rudiments tself the circula- Ls originates, and a, the optic vesi- m the epiblastic jxtremity of the ic of their physi- in of the embryo, irly formed, and i -* it at nine dajrw wid three lionieaii). Al view ot the ■tage of the development h the hind-end of the folds of the o-peritoneal cav- ;he beginning the L in front at first ; tn compared with correspond to the B (vitelline) to its ome hollow prior le one. The entire blood-vascular system originates in themesoblast of the area opaca especially ; at first appearing in isolated spots which come together as actual vessels are formed. The student who will pursue the plan of examining a series of incubating eggs will be struck with the early rise and raoid progress of the Fia. 10B.-€!blck on third day, nen fMm beneath aa a transparent object, the head betag turned to one aide (Foater and Balfour), o', falM Monion ; Ov*'?^52Ji£. Vi^ShS hemiqdiere; FB, MB, HB, anterior, middle, and pMterJor <»w>»^ '^^^^.S^.^Pg? veBloleTot, auditory veaiole ; o/v, omphalo-meaenteric velna ; fl»^oart ; Ao, buIlniB artej rionis : «*. notodiord ; Ofit, omphalo-meaenterlo arteriea ; Pv, notovwtobrB ; x, point of divergence of the aplanobnopleural folds ; v, termination of the foregut, v. vascular system of the embryo, which takes, when complete, such a form as is represented diagramatically in Fig. 113. The blood and the blood-vessels arise simultaneously from the cells of the mesoblast by outgrowths of nuclear prolifera- tion, and in the case of vessels (Fig. 147) extension of processes, fusion, and excavation. The fore-giU is formed by the union of the folds of the splanchnopleure from before backward, and the hind-gut in a similar manner by fusion from behind forward. 7 g ^ i I fjfmivimj-Lm nstglKKKHi am ■a \'rxLtu »AHM,i»mUll 98 ANIMAL PHYSIOLOGY. The excretory system is also foreshadowed at an early pe- riod by the Wolffian duct (Fig. 114), a mass of mesoblast cells near which the cleavage of the mesoblast takes place. During the latter part of the second day the vascular system, including the heart, makes great progress. The latter, in con- Fio. lll.-DI»gwm»nM«o ontUnM of the ew^arterUtl ayrt^ of *>» ««^J!? JS«f5?«hi!S bryo Wter AUen Thomaon). A. At a period cprreroondtag to the UUrty-jteth or UMrg^ SfttOoup oflnoubirtton: B. I*ter iSge, with two wOrt of •w^"?*"}- *i ^"2? M^rionu of he»rt ; v, TltelUne arterietiTT-5, the aortJo archea. The dotted Unee Indicate the potition of the future arohea. sequence of excessive growth and the alteration of the relative position of other parts, becomes bent up on itself, so that it *t .. uiM llll lHU ill H I iMiwMj WW W i MfcrftaiW THE DEVELOPMENT OP THE EMBRYO ITSELF. 99 L at an early pe- l mesoblast cells I place. Qualn). A repreMnts an ■ ; it, auricle; 8, Tentride; rtertes ; A, united aortae. > vascular system, The latter, in con- « mammal vertebrate em- the thlrt7-Blxth or thirty- aordo archee. h, bulbua , The dotted llnee indicate ion of the relative L itself, so that it presents a curve to the right which represents the venous part and one to the left, answering to the arterial. The rudiments of the auricles also are to be seen. The arterial system is represented at this stage by the ex- panded portion of the heart known as the hvlbus arteriosus, and two extensions from it, the aortee, which uniting above the alimentary canal, form a single ix)sterior or dorsal aorta. From these great arterial ves- sels the lesser ones arise, and by sub- division constitute that great mesh- work represented diagrammatically in Figs. 112, 113, from which the course of the circulation may be gathered. The beating of the heart commences be- fore the corpuscles have become nu- merous, and while the tubular system, through which the blood is to be driven, is still very incomplete. The events of the third day are of the nature of the extension of parts already marked out rather than the formation of entirely new ones. The following are the principal changes: The bending of the head-end down- ward (cranial flexure) ; the turning of the embryo so that it lies on its left side ; the completion of the vitelline circulation ; the increase in the curva- ture of ihe heart and its complexity of structure by divisions ; the appear- ance of additional aortic arches and of the cardinal veins ; the formation of four visceral clefts and five vis- ceral arches; a series of progressive changes in the organs of the special senses, such as the formation of the lens of the eye and a secondary optic vesicle; the closing in of the optic vesicle ; and the formation of the na- sal pits. In the region of the future brain, the vesicles of the cerebral hemispheres become distinct ; the hind-brain separates into cerebellum and medulla oblongata ; the nerves, both cra- ne, lis.— Dtaftram of tiie embiy- onlc Taarular aystem nvieder- ■heim). a, atrium ; A. A, dor- Mi aorta ; Ab, branchial ves- mem ; Acd, caudal artery ; AU, ollantoio (bypoKaatrio) arter- ies: Am^yitemao arteries; B, bulDus arteriosus ; c, c,' exter- nal and internal carotids ; D, ductus CuTleri (precaval veins) ; £, external iliac arterifs; 0. C, posterior cardinal v^n ; /e, common iliao arteries ; K. L, giUolefts; R. ^, right and left roots of the aorta ; 8. S'i branchial coHecting trunks or Teins ; fib, subclavian artery ; 8V, subclavian vein ; S<, sinus venosus; r, ventricle; FC, an- terior cardinal vein ; Vm, vitel- line veins. hM 100 ANIMAL PHYSIOLOGY. nial and spinal, bud out from the nervous centers. The ali- mentary canal enlarges, a fore-gut and hind-gut being formed, the former being divided into oesophagus, stomach, and duode- AA.l S.Ti BjnfJL no. 118.— DiMcrsm of draulation of yelk-wc at end of third day (Forter and BiOtborV Blaatoderai seen from below. Arteries made black. H, heart; AA, ncond, third, a^ fourth aortic arche^ AO, dor^l aorto: L. W. 4, Irft Titelline Mtery; «. W A,tMaX TiteUine artery ; 8. r, ainna terminalla ; L. Of, left vitelline vein ; B. Of. right vitijlllne vein ; S. V, Binus venoms ; D. C, ductus Cuvteri ; S. Ca. V, superior canUnal or Jugular vein ; V. Ca, interior cardinal vein. num; the latter into the large intestine and the cloaca. The lungs arise from the alimentary canal in front of the stomach ; from similar diverticula from the duodenum, the liver and pancreas originate. Changes in the protovertebrae and muscle- plates continue, while the Wolffian bodies are formed and the Wolffian duct modified. Up to the third day the embryo lies mouth downward, but now it comes to lie on its left side. See Fig. 109 with the ac- companying description, it being borne in mind that the view is from below, so that the right in the cut is the left in the em- »nters. The ali- it being formed, och, and duode- .ca.r. Lxf. r (Foster and Balfbar) AA, aecond, third, and artery ; B. Of. A, rteiit n ; B. Of. Tight yftMoe rtor caMlnaror Jugular the cloaca. The b of the stomach ; 1, the liver and )br8B and muscle- formed and the h downward, but . 109 with the ac- d that the view is lie left in the em- THB DEVELOPMENT OP THE EMBRYO ITSELF. 101 Fio. 114. fy. Fio. no. Fio. 116. Fio. I14.-Traiiaverw Mctkm through lumbar region of M«ntaTO at end of fourth djv(Fofr ter and Balfour), ne. neural canal ; or, poiterior root of qxlnal nerve with ganguon , a.r^.SrSSSt: r^.aiiteriorgWS^iSSmnof 'tf^'><«:ii,^-^)f^^^J^^. column In course of formatton ; m. p, muacle-pUte ; (*. nptochwd ; W.B, Wolfflaai ridge , ™o; donal^wta ; v. c. a, portirior'caKUnal Tein : W. d, WoMlan duct ,W. «>, W^SS? bod^. condrtinc of tubules wodMalplghian oorpuaoles; g. e. germinal epitheliuAi ; d, oU- ^tary^mS^ il#rSmSenclng meSentery : ^sonuftopleure ; SP, splanchnopleure ; The V, blood-Tessels ; pp, pleurt^perlSoneal cavjfy. . lis.— Diagram of portion of dlgesUTo tract oi cnicK on luurui u»jr ,«». y""''S" ,*~ bU^Unerepreson&hypoblast; the shaded portion, mesoblast; Iff, lung diverticulum, expanding at bases into primary lung vesicle ; «t, stomach : I, liver ; p, panadas, expanding at bases wto pnmary lung veaicie ; «, ■wnuwu ; i, ii»ci , », u>uc»c«>. no. Iftk-Sead of chick of teird day, viewed sidewise as a transMjent obfect {Huxley). la, cerabrS hemispheres; lb, vesicle of third ventricle; n. mid-brain ; 111, hiDd-brain ; a. oDtlct^cle ; o; nasal pit ; 6. otic vesicle ; d, infundlbulum ; e, pinea body ; h, uotochord; \^lMUr^!^e; VuTseveith nerve; VIU, united glossopharyngeal and pneumogastric nenrca. 1, 8, 8, 4, 6, the five visceral folds. >mmf- 102 ANIMAL PHYSIOLOGY. bryo itself. Fig. 114 gives appearances furnished by a vertical transverse section. The relations of the parts of the digestive tract and the mode of origin of the lungs may be learned from Fig. 116. r,B. Fio. IIV.— Head of chick of fourth day, riewed from below as an opaaua object (Foater and Balfour). The neck is cut acroM between third and fourth vtacwaTfoIda. C. H. cerebral hemtopherea ; F. B, veeiote of third yentricle : Op, erebaU : t^^, ""•■p-'«"\*i'.?'!?"*""iJ!'' cavity of mouth : S. m, superior nuudUary procev (^ F. 1, the flrM ▼iaeeral fold (mandibu- Ur arch) ; F. S, F. •, seocmd and third Tiioeral arches ; ;v, nasal pit An examination of the figures and subjoini'd descriptions must suffice to convey a general notion of the subsequent prog- Fio. 118.— BmbTTO at end of fourth day, seen as a transparent obJecUForter and BaUonr). CH, cewsbMl hemisphere ; F. 0. fore-brata, mr rericle of tUrd vn^cle (th^ju^noe^ ton). wHh pineal gland (PH) proWtag ; M. B, mid-brain ; C6. cerebeUum ; /r. V, fourth ^utricle ;Tlei«; «M cholSajiMt; Cm. '^..•"jUtoiy vejteWjjm. ™P«% m«">«7 prooess ; \F,»F, etc., first, second, etc., visceral folds ; F, fifth nwre; KiJ, seventh nerve: &. PK, rlossopharynfteal nerve Tfto, pneumoMftric. The distrVbuUpn of Uiese nerves Is lUso i^dtoMedrreh: mtodiocd ; Ht.lieart ; MP, mnsdl<>-plates : W, whig : H. L-htodUmb. The amnion has been removed. jli,allantois protruding from out end of aomanosttlkSS. led by a vertical lof the digestive Ibe learned from DEVELOPMENT OP THE VASCULAR SYSTEM. lOS ress of the embryo. Special points will be considered, ei- ,er in a separate chapter now, or deferred for treatment in tb< )ody of the work from time to time, as they seem to throw light upon the subjects under discussion. I DEVELOPMENT OF MO-froBtal vlaoenl lue object (Fo«tM- and foMa. p. H, cerebral al pnc em ; m, fold (mandlbu- ned descriptions inbsequent prog- acA -L. B. cMFoater and Balfour), ■tricle (thalamenoepha- ebellum ; IV. V, tovar& nn, superior maxillary re; FT/, eeventh nerve; itkm of tlieae ner*e« la wing : H. L, Und-Umb. od of Minatieat Jk 5S. THE VASCULAB SYSTEM IN VERTE- BRATES. This subject has been incidentally considered, but it is of such importance morphological, physiological, and pathological, as to deserve special treatment. In the earliest stages of the circulation of a vertebrate the arterial system is made up of a pair of arteries derived from the single btUbus arteriostts of the heart, which, after passing for- ward, bends round to the dorsal side of the pharynx, each giving off at right angles to the yelk-sac a vUeUine artery ; the aortee unite dorsally, then again separate and become lost in the pos- terior end of the embryo. The so-called arches of the aorta are large branches in the anterior end of the embryo derived from the aorta itself. The venous system corresponding to 'the above is composed of anterior and posterior pairs of longitudinal (cardinal) veins, the former (jugular, cardinal) uniting with the posterior to form a common trunk {dtu:tiis Cuvieri) by which the venous blood is returned to the heart. The blood from the posterior part of the yelk-sac is collected by the vUeUiiie veins, which terminate in the median sinus venosiis. The Lattr BtagM of tlw Fatal OinalatioA.— Gorrec^nding to the number of visceral arches five pairs of aortic arches i&rise ; but they do not exist together, the first two having undergone more or less complete atrophy before the others appear. Figs. 119, 120 convey an idea of how the permanent forms (indicated by darker shading) stand related to the entire system of vessels in different groups of animals. Thus, in birds the right (fourth) aortic arch only remains in connection with the aorta, the left forming the subclavian artery, while the reverse occurs in mam- mals. The fifth arch (pulmonary) always supplies the lungs. The arrangement of the principal vessels in the bird, mam- mal, etc., is represented on page 104. In mammals the two primitive anterior abdominal {allantoic) veins develop early and unite in front with the vitelline ; but the right allantoic vein and the right vitelline veins soon disappear, while the long 104 ANIMAL PHTSIOLOGT. common trunk of the allantoic and vitelline veins {ductus veno- sus) passes through the liver, where it is said the ductus veno- 1. Flo. 110.— Dfaurama of the aortic archea of mamnuU (Londoia aiid Stirling, after Batlike). I. Arterial trunk with one pair of arehea, and an indication where the aeoond and third paira will develop. 8. Ideal ataoe of Atc oomiriete archea ; t^ fourth clefta are abown on the left aide. & The two anterior paira of archea have dlaappeared. 4. Transition to the flnal tttLge. A, aortic arch ; ad, doraal aorta ; ax, aubclavlan or axillair artery ; Ce. ex- ternal carotid ; Ci, internal carotkl ; dB, ductua arterioaua Botalll ; P, pulmonary artery ; 8, aulMilaTian artery ; to, truncua arterioaum ; «, vertebral artery. BUS gives oflf and receives branches. The ductus venosus Aran- tii ])ersists throughout life. (Compare the various figures illus- trating the circulation.) Fia. 190.— Diagram HhtimWinr tnnaf ormatlona of aortlo archea in a liaard. A ; a anake, B ; a bbd, ; a mammaL D. Seen from below. (Haddon, after Bathke.)- a, internal caro- tid ; b, external carotid ; c, common carotid. A. d, ductua Botalll between the third and fourth archea ; e, right aortlo arch ; /, aubdavlan ; a, doraal aorta ; k, left aortic arch : i. pulmonary artery : Ic, rudiment of the ductua Botalu between the jMilmonary artery and the aortic archea. B. d, right aortic arch ; e, vertebral artery ; /, left aortic ardii ; h, nulmonary artery ; i, ductua Botalll of the latter. C. d, origin of aorta ; e, fourth arch of the right aide (root of doraal aortat: /, right aubclavian ; g, doraal aorta : h, left aubclavlan (fourth arch of the left aide) : <, pulmonary artery ; k and i, right and lefi ductua Botalll ot the pulmonary arteriea. D. a, origin of aorta ; e, fourth arch of the left aide (root of doraal aorta) : /, doraal aorta ; g, left vertebral artery ; K, left aubclavian ; i, right aub- clavlan (fourth arch of the right aide) ; ie, right vertebral artery ; (, continuation of the right aubclavian ; m, pulmomuy ar^iy ; n, duotua Botalli of the latter (uaually tenned dttettM ot-terionM). t Uaard. A ; s make, B ; thke.)- a, internal oaro- between the third and ta ; ft, left aortic arch : le pulmonary artery and /, left aortic ardii ; h. aorta ; «, fourth arch of M>rta : A, left Bubolavlan > and left ductus Botalli of the left side (root of ubclavian ; i, right nib- ; (, continuation of the ) latter (umalljr termed DEVELOPMENT OP THE VASCULAR SYSTEM. 105 With the development of the placenta the allantoic circula- tion renders the vitelline subordinate, the vitelline and the larger mesenteric vein forming the portal. The jiortal vein at a later period joins one of the vena advehentea of the allantoic vein. At first the vena cava inferior and the ductus venosus enter the heart as a common trunk. The ductus venosus Arantii becomes a small branch of the vena cava. The allantoic vein is finally represented in its degenerated form as a solid cord {round ligament), the entire venous suj)- ply of the liver being derived from the portal vein. The development of the heart has already been traced in the fowl up to a certain point. In the mammal its origin and early progress are similar, and its further histoiy may be gathered from the following series of representations. In the fowl the heart shows the commencement of a division into a right and left half on the third day, and about the fourth week in man, from which fact alone some idea may be gained as to the relative rate of development. The division Fia. 128. Flo. in. Fio. 181.— Development of the heart in the human embryo, from the fourth to the sixth wedt. A. Emtnyo of four weeks (KOUiker, after Ooste). B, anterior, C, portertor views of the heart of an embryo of six weeks (KOUiker, after Eckwr). o. upper Ijinit of buccal cavity ; c. buccal cavity ; 6, lies between the ventral ends of second and third branchial arches ; d, buds of upper limbs ; I, Uver ; /, intestine rl. juperior vena cava ; 1', left superior vena cava ; 1", openioK of inferior vena cava ; 8, 8', right and left auricles ; 3, 8', right and left ventricles ; 4, aortic bulb. . „ _t > ,• > <• .. i . Fig. 188.— Human embryo of about three weeks (Allen Thomson), uv, yelk-sac; ai, allantois; am, amnion ; ae, anterior extremity ; pe, posterior extremity. is effected by the outgrowth of a septum from the ventral wall, which rapidly reaches the dorsal side, when the double ven- tricle thus formed communicates by a right and left auriculo- ventricular opening with the large and as yet imdivided auricle. tUM I lJ'.- i J I '"-■»'i™'A'' »WWIBB« !i«Mm.t.6. duct and also from an intermediate cell-mass, from which lat- ter the Malpighian bodies take rise. The tubes, at first not con- •WMP 108 ANIMAL PHYSIOLOGY. nected with the duct, finally join it. This brgan is continuous with the pronephros ; in fact, all three (pronephros, mesone- phros, and metanephros) may be regarded as largely continua- tions one of another. The metanephros, or kidney proper, arises from mesoblast at the posterior part of the WolflBan body. The ureter origi- Fta. 198.— Section of the Intermediate oell-nuMi of fourth day (Foster and Balfonr, after Wal- deyer). 1 » 1(10. m, mesentery ; L, aomatopleure ; a', portion of the oerminal epitheUum from the dnot of MtUler to formed by involution ; a, thickened portion of the serminal epithelium, in which tbo primitive ova C and o are lying ; E, modified meaoblaat which will form the stroma of the orary ; WK, WoUHan N>dy ; y, WoUBan duct nates first from the hinder portion of the Wolffian duct. In the fowl the kidney tubules bud out from the ureter as rounded elevations. The ureter loses its connection with the Wolffian duct and opens independently into the cloaca. The following account will apply especially to the higher vertebrates : The segmental (archinephric) duct is divided horizontally into a dorsal or Wolffian (mesonephric) duct and a ventral or Miillerian duct. The Wolffian duct, as we have seen, develops into both ureter and kidney proper. To carry the subject somewhat further back, the epithelium lining the coelom at one region becomes differentiated into col- umns or cells {germinal epitheUum) which by involution into the underlying mesoblast forms a tubule extending from before backward and in close relation with the Wolffian duct, thus is continuous >hros, mesone- fely continua- om mesoblast I ureter origi- Balfonr, after Wal- terminal epithelium Ion of the germiiutl ed meaoblaat which uct. San duct. In 9r as rounded the Wolffian lo the higher horizontally a ventral or een, develops le epithelium ited into col- irolution into f from before in duct, thus THE DEVELOPMENT OF THE UROGENITAL SYSTEM. 109 forming the Miillerian dv. t by the process of cleavage and separation referred to on preceding page. Fia. 187.— DiMtrammatlo repreMntaUon of titejenltal orgww ot a human embryo prevlmis to •ezual diSnction (Allen Thomaon). -W, woUXan body : 0e, genital cmd ; m, MOUeriMi ■inus ; cp, tiAorit or penia ; i.[ intestine j ct. duct; W, Wolffian duct: no, urogemuu auius. •!», ouwrui ur yeitm, .. luijmuw , t., cloaca ; if, part from which Oe ncrotum or labia majora are developed ; ot, origin of the ovary or teaUole reqwcUveW; x, part of the WoUBan body dereloped liter bito theconi vaaouloai ; 8, ureter ; 4, bladder ; S, uracfaua. The future of the Miillerian and Wolffian ducts varies ac- cording to the sex of the embryo. Fm, . las.— Diaxram of the mammalian type of male aenial organs (after Qualn). Compare with FlgiTlW. 1». C, Oowper's glaiul ot one aide ; ep, corpora OAvemoaa pento, cut^rt ; e, capuTepididymU to, gunemamdum ; i, rectum ; m, hydatid of Morngnl, the perstatent anlSlor end of the Mmierian duct, the conjoint posterior ends of whfiih form the uterua maacullnua : pr, prostate gland ; «, scrotum ; the increase ange in form, and yet affect ided ; the pel- THE DEVELOPMENT OP THE UROGEmTAL SYSTEM. 118 vis in females alters in shape ; not only do the generative organs themselves rapidly undergo increased development, but certain related glands (mammee) participate; hair appears in certain regions of the body \ the larynx, especially in the male, under- goes enlargement and change in the relative size of parts, re- sulting in an alteration of voice (bi'eaking of the voice), etc. — all in conformity with that excess of nutritive energy which marks this biological epoch. (Correlated with these physical changes are others belonging to the intellectual and moral (psychic) nature equally impor- tant, and, accordingly, the future being depends largely on the full and unwarped developments of these few year£(^ Sexual maturity, or the capacity to furnish ripe sexual ele- ments (cells), is from the biological standpoint the most impor- tant result of the onset of that period termed, as regards the human species, puberty. The age at which this epoch is reached varies with race, sex, climate, and the moral influences which envelop the indi- vidual. In temperate regions and with European races pu- berty is reached at from about the thirteenth to thia eighteenth year in the female, and rather later in the male, in whom de- velopment generally is somewhat slower. Menstruatiok Ain> Ovulation. (In all vertebrates, at periods recurring with great regu- larity, the generative organs of the female manifest unusual activity. This is characterized by increased vascularity of the ovary and adjacent parts; with other changes dependent on this, and that heightened nerve influence which, in the verte- brate, seems to be inseparable from all important functional changes. Ovulation is the maturation and discharge of ova from the Graafian follicles. The latter, reaching the exterior zone of the ovary, becoming distended and thinned, burst ex- ternally and thus free the ovum. The follicles being very vas- cular at this period, blood escapes, owing to this rupture, into the emptied capsule and clots ; and as a result of organization and subsequent degeneration undergoes a certain series of changes dependent on the condition of the ovary and adjacent parts, which varies according as the ovum has been fertilized or liot. When fertilization occurs the Graafian follicle under- goes changes of a more marked and lasting character, becom- ing a true corpus luieum of pregnancy, 8 " i;i l »iM!il »W a» >i » i Ji i »i»»« » «i«i>i»i i . i hare been deprived « (J. WlUUnnsr >m the uterus bhe superficial The Nutrition of the Ovum (oospbrm). This will be best understood if it be remembered that the ovum is a cell, undifferentiated in most directions, and thus a sort of amoeboid organism. In the fowl it is known that the cells of the primitive germ devour, amoeba-like, the yelk-cells, while in the mammalian oviduct the ovum is surrounded by abundance of proteid, which is doubtless utilized in a somewhat similar fashion, as also in the uterus itself, until the embryonic membranes have formed. To speak of the ovum being nour- ished by diffusion, and especially by osmosis, is an unnecessary assumption, and, as we believe, at variance with fundament^ principles; for we doubt much whether any vital process is one of pure osmosis. As soon as the yelk-sac and allantois have been formed, nutriment is derived in great part through 116 ANIMAL PHTSIOLOOT. the vessel-walls, which, it will be remembered, are differentia- ted from the cells of the mesoblast, and, it may well be as- sumed, have not at this early stage entirely lost their amoeboid character. The blood-vessels certainly have a respiratory func- tion, and suffice, till the more complicated villi are formed. The latter structures are in the main similar in build to the villi of the alimentary tract, and are adapted to being sur- rounded by similar structures of maternal origin. Both the maternal crypts and the foetal villi are, though complementary in shape, all biit identical in minute structure in most in- stances. In each case the blood-vessels are covered superfi- cially by cells which we can not help thinking are essential in nutrition. The villi are both nutritive and respiratory. It is no more difficult to understand their function than that of the cells of the endoderm of a polyp, or the epithelial coverings of limgs or gills. Experiment proves that there is a respiratory interchange of gases between the maternal and foetal blood which nowhere mingle physically. The same law holds in the respiration of the ftjetus as in the mammals. Oxygen passes to the region where there is least of it, and likewise carbonic anhydride. If the mother be asphyxiated so is the foetus, and indeed more rapidly than if its own umbilical vessels be tied, for the mater- nal blood in the first instance abstracts the oxygen from that of the foetus when the tension of this gas becomes lower in the maternal than in the foetal blc>od ; the usual course of affairs is reversed, and the mother satisfies the oxygen hunger of her own blood and tissues by withdrawing that which she recently supplied to the foetus. It will be seen, then, that the embryo is from the first a parasite. This explains that exhaustion which pregnancy, and especially a series of gestations, entail& True, nature usually for the time meets the demand by an excess of nutritive energy : hence many persons are never so vigorous in appearance as when in this condition ; often, however, to be fol- lowed by corresponding emaciation and senescence. The full and frequent respirations, the bounding pulse, are succeeded by reverse conditions ; action and reaction are alike present in the animate and inanimate worlds. Moreover, it falls to the parent to eliminate not only the waste of its own organism but that of the foetus ; and not infrequently in the human subject the over- wrought excretory organs, especially the kidneys, fail, entailing disastrous consequences. The digestive functions of the embryo are naturally inact- HWwMBInn] re differentia- y well be as- heir amoeboid piratory func- i are formed. 0. build to the to being sar- in. Both the jmplementary e in most in- vered superfi- ,re essential in iratory. It is m that of the I coverings of ry interchange rhich nowhere respiration of to the region anhydride. If 1 indeed more for the mater- gen from that as lower in the urse of affaire hunger of her jh she recently the embryo is laustion which entails. True, y an excess of so vigorous in rever, to be f ol- >nce. The full e succeeded by ) present in the Is to the parent ism but that of ibject the over- ly fail, entailing aturally inact- THE DEVELOPMENT OP THE UROGENITAL SYSTEM. II7 ive, the blood being supplied with all its needful constituents through the placenta by a much shorter process ; indeed, the placental nutritive functions, so far as the foetus is concerned, may be compared with the removal of already digested material from the alimentary canal, though of course only in a general way. During foetal life the digestive glands are developing, and at the time of birth all the digestive juices are secreted in an efficient condition, though only relatively so, necessitating a special liquid food (milk) in a form in which all the constituents of a normal diet are provided, easy of digestion. Fw. 187.— Hunwa wrnit or embtTM fiwm tiM MeoBd to Um flfteenth week (natural iriM), Men ftom the left Site, the arctoS bade tamed toward the ri^t. (PrlndpaUy after Boker.). n, human emhnro ot 14 dare ; m, of 8 weeks ; JV, of 4 weeln; V. or B weeke ; VI, ot A weeks; vn,o(7weeki; ViuI,oC8weeka: XO, ot It weeks ; ZV, of 16 weeks. Bile, inspissated and mized with the dead and cast-off epi- thelium of the alimentary tract, is abundant in the intestine at birth in the human subject ; but bile is to be regarded perhaps rather in the light of an excretion than as a digestive fluid. The skin and kidneys, though not functionless, are rendered unnecessary in great part by the fact that waste can be and is withdrawn by the placenta, which proves to be a nutritive, re- MMi 118 ANIMAL PHYSIOLOGY. spiratory, and excretory organ ; it is in itself a sort of abstract Ctnd brief chronicle of the whole physiological story in fcetal life. All of the fcetal organs, especially the muscles, abound in an animal starch (glycogen), which in some way, not well under- stood, forms a reserve fund of nutritive energy which is pretty well used up in the earlier months of pregnancy. We may suppose that the amoeboid cells— all the undifferentiated cells of the body — feed on it in primitive fashion ; and it will not be forgotten that the older the cells become, the more do they depart from the simpler habits of their earlier, cruder existence ; , hence the disappearance of this substance in the later months of foetal life. In one respect the foetus closely resembles the adult: it draws the pabulum for all its various tissues from blood which itself may be regarded as the first completed tissue. We are, accordingly, led to inquire how this river of life is distributed ; in a word, into the nature of the foetal circulation. Festal Oixeoktion. — The blood leaves the placenta by the um- bilical vein, reaches the inferior vena cava, either directly (by the dtuivs venoatu), or, after first passing to the liver (by the veruB adveJientes, and rotuming by the vetue revehentes), and proceeds, mingled with the blood returning from the lower ex- tremities, to the right auricle. This blood, though far from being as arterial in character as the blood after birth, is the best that reaches the heart or any part of Uie organism. After arriving at the right auricle, being dammed back by the Eus- tachian valve, it avoids the right ventricle, and shoots on into the left auricle, passing thence into the left ventricle, from which it is sent into the aorta, and is then earned by the great trunks of this arch to the head and upper extremities. The blood returning from these parts passes into the right auricle, then to the corresponding ventricle and thence into the pul- monary artery; but, finding the branches of this vessel un- opened, it takes the line of least resistance through the ductus arteriosus into the aortic arch beyond the point where its great branches emerge. It will be seen that the blood going to the head and upper parts of the body is greatly more valuable as nutritive pabulum than the rest, especially in the quantity of oxygen it contains ; that the blood of the foetus, at best, is rela- tively ill-supplied with this vital essential ; and as a result we find the upper (anterior in quadrupeds) parts of the foetus best developed, and a decided resemblance between the mammalian foetus ftmctionally and the adult forms of reptiles and kindred rt of abstract r in foetal life, abound in an »t well under- bicli is pretty ;y. We may entiated cells id it will not more do they der existence ; later months the adult: it 1 blood which sue. We are, s distributed ; ta by the um- r directly (by 3 liver (by the vehenlea), and . the lower ex- ugh far from r birth, is the anism. After ik by the Eus- shoots on into entricle, from d by the great remities. The > right auricle, I into the pul- his vessel un- igh the d%idns ffhere its great >d going to the re valuable as he quantity of at best, is rela- as a result we the foetus best iie mammalian es and kindred THE DEVELOPMENT OP THE UROGENITAL SYSTEM. 119 groups of the lower vertebrates. But this condition is well enough adapted to the general ends to be attained at this pe- Pdmemary Art. ForammOtalt. EmIaMmVahe. BiglU Amrie.-V«iU. Opming. . IVmoMry Art. Ltfl Auride. ...Left Aurie.-VaU. Opmuig. BepaHeVtin. BramehM of th* / •• .^i UmbUietd Vrin, - < ^=- to thi IAmt. DudmVaumu. iDttnui nUu Arterim. no. laS. -Dii«TMii of the f obUI clrcu]«tk» (Flint). 120 ANIMAL PHYSIOLOGY. rlod — ^the nourishment of structures on the way to a higher path of progress. As embryonic maturity is being reached, preparation is made for a new form of existence ; so it is found that the Eustachian valve is less prominent and the foramen ovale smaller. Partubition. 1*^11 the efforts that have hitherto been made to determine the exact cause of the result of that series of events which make up parturition have failed. This has probably been owing to an attempt at too simple a solution. The fcetus lies surrounded (protected) by fluid contained in the amniotic sac. For its expul- sion there is required, on the one hand, a dilatation of the uter- ine opening (os uieri), and, on the other, a vis a tergo. The lat- ter is furnished by the contractions of the uterus itself, aided by the simultaneous action of the abdominal muscles. Through- out the greater part of gestation the uterus experiences some- what rhythmical contractions, feeble as compared with the final ones which lead to expulsion of the foetus, but to be regard- ed as of the same character. With the growth and functional development of other organs, the placenta becomes of less con- sequence, and a fatty degeneration sets in, most marked at the periphery, usually where it is thinnest and of least uso. It does not seem rational to believe that the onset of labor is referable to any one cause, as has been so often taught; but rather that it is the final ipsue to a series of processes long existing and grad- ually, though at last rapidly, reaching that climax which seems like a vital storm. The law of rhythm affects the nervous sys- tem as others, and upon this depends the direction and co-ordi- nation of those many activities which make up parturition. We have seen that throughout the whole of foetal life changes in one part are accompanied by corresponding changes in oth- ers ; and in the final chapter of this history it is not to be ex- pected that this connection should be severed, though it is not at present possible to give the evolution of this proioess with any more than a general approach to probable correctness. Changes in thb Circulation after Birth. V^hen the new-born mammal takes the first breath, effected by the harmonious action of the respiratory muscles, excited to action by stimuli reaching them from the nerve-center (or ^to a higher ration is made le Eustachian laller. to determine ;s which make t)een owing to es surrounded For its expul- >n of the uter- rgo. The lat- tself , aided by es. Through- )riences some- ired with the t to be regard- nd functional es of less con- marked at the t uso. It does or is referable < rather that it ting and grad- X which seems e nervous sys- >n and co-ordi- p parturition, al life changes iianges in oth- 9 not to be ez- lough it is not I process with irrectness. Birth. >reath, effected uscles, excited erve-center (or THE DEVELOPMENT OP THE UROGENITAL SYSTEM. 121 centers) which preside over respiration, owing to its being roused into action by the lack of its accustomed supply of oxygen, the hitherto solid lungs are expanded ; the pulmonary vessels are rendered permeable, hence the blood now takes the path of least resistance along them, as it formerly did through the ductus arteriosus. The latter, from lack of uso, atrophies in most instances. The blood, returning to the left auricle of the heart from the lungs in increased volume, so raises the pressure in this chamber that the stream that formerly flowed through the foramen ovale from the right auricle is opposed by a force equal to its own, if not greater, and hence passes by an easier route into the right ventricle. The fold that tends to close the foramen ovale grows gradually over the latter, so that it usually ceases to exist in a few days after birth. At birth, ligature of the umbilical cord cuts off the placental circulation ; hence the ductus venosus atrophies and becomes a mere li{;ament. The placenta, being now a foreign body in the uterus, is ex- pelled, and this organ, by the contractions of its walls, closes the ruptured and gaping vessels, thus providing against heemor- rhage. Coitus between the Sexes. In all the higher vertebrates congress of the sexes is essential to bring the male sexual product into contact with the ovum. Fio. UB.— SeoUon of erectUe tiMue (Oftdtat). a, tnOwoute of aonnQoUve ttame, with elastic flban, wMl bandlM of ptain miuaular tiMue (o) ; b, TWiovajipacM (Sohlfw). I 122 ANIMAL PHYSIOLOGY. Ereciion of the penis results from the conveyance of an excess of blood to the organ, owing to dilation of its arteries, and the retention of this blood within its caverns. The structure of the penis is peculiar, and, for the details of the anatomy of both the male and female generative organs, the student is referred to works on this subject ; suffice it to say that it consists of erectile tissue, the chief cha racteristic of which is the opening of the capillaries into cavernous venous spaces {sinuses) from which the veinlets arise ; with such an arrangment the circulation must be very slow— the inflow being greatly in excess df the outflow— apart altogether from the compressive action of certain muscles connected with the organ. As previously explained, the spermatozoa originate in the seminal tubes, from which they find their way to the no M0.-8ection of pMla of three leiiiliilfaroae tulHike of the nt (Bdiafer). a, wMi Oie ■iSroSoSStoMt aSTwoed in de*«lopromt ; 6, mow adranoed : c, M«S!»5Jtf^J«: TSopedqpennittawMt. Between the tubulea are aeen strand* of Intentitiat cells, with Uood-veasele and lymphnqiaoee. seminal vesicles or receptacles for semen till required to be discharged. The spermatozoa as they mature are forced on by fresh additions from behind and by the action of the ciliated cells of the epididymis, together with the wave-like (peristaltic) action of the vas deferens. Discharge of semen during coitus is effected by more vigorous peristaltic action of the vas defer- ens and the seminal vesicles, followed by a similar rhythmical action of the bulbo-cavernosus and ischio-cavernosus muscles, by which the fluid is forcibly ejaculated. Semen itself, though composed essentially of spermatozoa, atitti ■mmiwiraiUlMitwifn mn yance of an f its arteries, bhe details of itive organs, ; suffice it to racteristic of pnous venous nth such an — ^the inflow ogether from ;ted with the i originate in way to the hlter). a, with the oMitalnlng fully de- teratitiiacells, with squired to be ) forced on by yt the ciliated le (peristaltic) during coitus the vas defer- ar rhythmical Losus muscles, spermatozoa, THE DEVELOPMENT OP THE UROGENITAL SYSTEM. 123 is mixed with the secretions of the vas deferens, of the seminal vesicles, of Cowper's glands, and of the prostate. Chemically it is neutral or alkaline in reaction, highly albuminous, and contains nuclein, lecithen, cholesterin, fats, and salts. The movements of the male cell, owing to the action of the tail (ciliiim), suffice of themselves to convey them to the ovi- . n.-Lett broad Ugmment, TiUlojitan tube, ovary, and pMwariuin to tte ^fo^'^^ ■ enle). u, utonUTT teUuiiwi ofiviJlopUm tube ; a, ampuU* ; /, flmbrtoted end of th^ uoe, with the parovarium to Ita right ; o, ovary ; o. I, ovarian Ui^unent. ducts ; but there is little doubt that during or after sexual con- gress there is in the female, even in the human subject, at least Fio. 14B.— Oterut and ovariea of the low, wmi-dlaffiaminatio (after Dalton). o, ovary ; H, Fkllopian tube ; h, horn of the utwua ; b, body 6f the ulenis ; ti, vactoa. in many cases, a retrograde peristalsis of the uterus and ovi- ducts which would tend to overcome the results of the activity f»(f)esmmmi>!!''iit 124 ANIMAL PHYSIOLOGY. of the ciliated cells lining the oviduct. It is known that the male cell can survive in the female prgans of generation for several days, a fact not difficult to understand, from the method of nutrition of the female cell (ovum) ; for we may suppose that both elements are not a little alike, as they are both slightly modified amoeboid organisms. Herroiu Xeehaaiim. — Incidental reference has been made to the directing influence of the nervous system over the events of reproduction ; especially their subordination one to another to bring about the general result. These may now be consid- ered in greater detail. Most of the processes in which the nervous system takes part are of the nature of reflexes, or tiie result of the automa- ticity (independent action) of the nerve-centers, increased by some afferent (ingoing) impressions along a nerve-path. It is not always possible to estimate the exact share each factor takes, which must be highly variable. Certain experiments have assisted in making the matter clear. It has been found that, if in a female dog, the spinal cord be divided when the animal is still a puppy, menstruation and impregnation may occur. If the same experiment be performed on a male dog, erection of the penis and ejaculation of semen may be caused by stimulation of the penis. As the section of the cord has left the hinder part of the animal's body severed from the brain, the creature is, of course, unconscious of anything happening In all the parts below the section, of whatever nature. If the nervi erigentes (from the lower part of the spinal cord) be stimulated, the penis is erected i and if they be cut, this act be- comes impossible, either reflexly by experiment or otherwise. Seminal emissions, it is well known, may occur during sleep, and may be associated, either as result or cause, with voluptu- ous dreams. OPutting all these facts together, it seems reason- able to conclude that the lower part of the spinal cord contains the nervous machinery requisite to initiate those influences (im- pulses) which, passing along the nerves to the generative or- gans, excite and regulate the j^rocesses which take place in them. In these, vascular changes, as we have seen, always play a prominent part. Usually we can recognize some afferent influence, either from the brain (psychical), from the surface — at all events from without that part of the nervous system (center) which functions directly in the various sexual processes. It is com- mon to speak of a number of sexual centers — as the erection THE DEVELOPMENT OP THE UROGENITAL SYSTEM. 125 3wn that the eneration for n the method may suppose ley are both been made to er the events le to another ow be consid- system takes ' the automa- increased by e-path. It is 3 each factor . experiments us been found ied when the ignation may 1 a male dog. Lay be caused ) cord has left )m the brain, ig happening iture. If the inal cord) be it, this act be- or otherwise. during sleep, with voluptu- seems reason- cord contains njBuences (im- y^nerative or- take place in seen, always luence, either -at all events center) which )s. It is com- is the erection center, the ejaculatory center, etc. — ^but we much doubt whether there is such sharp division of physiological labor as these terms imply, and they are liable to lead to misconception ; ac- cordingly, in the present state of our knowledge, we prefer to speak of the sexual center, using even that term in a somewhat broad sense. ^he effects of stimulation of the sexual organs are not con- fined to the parts themselves, but the ingoing impulses set up radiating outgoing ones, which* affect widely remote areas of the body, as is evident, especially in the vascular changes ; the central current of nerve influence breaks up into many streams as a result of the rapid and extensive rise of the outflowing current, which breaks over ordinary barriers, and takes paths which are not properly its own. (Bearing this fact in mind, the chemical composition of semen, so rich in proteid and other material valuable from a nutritive point of view, and consid- ering how the sexual appetites may engross the mind, it is not ^difficult to understand that nothing so quickly disorganizes the^ Whole man, physical, mental, and moral, as sexual excesses, Whether by the use of the organs in a natural way, or from /masturbation. Qfature has protected the lower animals by the strong bar- rier of instinct, so that habitual sexual excess is with them an impossibility, since the females do not permit of the approaches of the male except during the rutting period, which occurs only at stated, comparatively distant periods in most of the higher mammals, (^hen man keeps his sexual functions in subjection to his higher nature, they likewise tend to advance his whole development. Sammury. — Certain changes, commencing with the ripening of ova, followed by their discharge and conveyance into the uterus, accompanied by simultaneous and subsequent modifica- tions of the uterine mucous membrane, constitute, when preg- nancy occurs, an unbroken chain of biological events, though usually described separately for the sake of convenience. When impregnation does not result, there is a retrogression in the uterus (menstruation) and a return to general quiescence in all the reproductive organs. [Parturition is to be regarded as the climax of a variety of rhythmic occurrences which have been gradually gathering head for a long period. The changes which take place in the placenta of a degenerative character fit it for being cast off, and may render this structure to some extent a foreign body before ' ^^-I^■rig;.■-:iJh■■^-l-■>M**^^L--■^fe4«^■i^ta!il^^^-S^^?gn^ji4^-■ 126 ANIMAL PHYSIOLOGY. it and the foetus are finally expelled, so that these changes may constitute one of a number of exciting causes of the increased uterine action of parturition. But it is important to regard the whole of the occurrences of pregnancy as a connected series of processes co-ordinated by the central nervous system so as to accomplish one great end, the development of a new individual. The nutrition T)f the ovum in its earliest stages is effected by means in harmony with its nature as an amoeboid organism ; nutrition by the cells of blood-vessels is similar, while that by villi may be compared to what takes place through the agency ^ of similar structures in the alimentary canal of the adult mam- mal. The circulation of the foetus puts it on a par physiologically with the lower vertebrates. Before birth there is a gradual though somewhat rapid preparation, resulting in changes which speedily culminate after birth on the establishment of the permanent condition of the circulation of extra-uterine life. The blood of the foetus (as in the adult) is the great store- house of nutriment and the common receptacle of all waste products ; these lat ier are in the main transferred to the moth- er's blood indirectly in the placenta ; in a similar way nutri- ment is imported from the mother's blood to that of the foetus. The placenta takes the place of digestive, respiratory, and ex- cretory organs. {Coitus is essential to bring the male and female elements together in the higher vertebrates. The erection of the penis is owing to vascular changes taking place in an organ composed of erectile tissue ; ejaculation of semen is the result of the peri- staltic action of the various parts of the sexual; tract, aided by rhythmical action of certain striped muscles. The spermatozoa, which are unicellular, flagellated (ciliated) cells, make up the es- sential part of semen ; though the latter is complicated by tho addition of the secretions of several glands in connection with the seminal tract. Though competent by their own movements of reaching the ovum in the oviduct, it is probable that the uterus and oviduct experience peristaltic actions in a direction toward the ovary, at least in a number of mammals. ^he lower part of the spinal cord is the seat in the higher mammals of a sexual center or collection of cells that receives afferent impulses and sends out efferent impulses to *1"» sexual organs. Itliis, like all the lower centers, is under the itrol of the higheir centers in the brain, so that its action may be either initiated or inhibited by the cerebrum. changes may the increased to regard the cted series of stem so as to iw individual, is effected by id organism; while that by h the agency le adult mam- lysiologically is a gradual : in changes ablishment of a-uterine life. 9 great store- ) of all waste I to the moth- ar way nutri- of the foetus, fttory, and ex- male elements of the penis is gan composed lit of the peri- ract, aided by ) spermatozoa, ake up the es- licated by the nnection with m movements >able that the in a direction Ells. in the higher that receives I to *1"» sexual the itrol of may be either ORGANIC EVOLUTION RECONSIDERED. 127 OROANIC EVOLUTION RECJONSIDERED. The study of reproduction has prepared the student for the comprehension of certain views of the origin of the forms of life which could not be as profitably considered before. While the great majority of biologists are convinced that there has been a gradual evolution of more complex organisms from simpler ones, and while most believe that Darwin's the- ory furnishes some of the elements of a solution of the problem as to how this has occurred, many still feel that the whole ex- planation was not furnished by that great naturalist. Accordingly, we shall notice very briefly a few of the more important contributions to this subject .rr^ce Darwin's views were published. In America, under the influence of the writings of Cope and Hyatt, a school of evolutionists has been formed, holding doc- trines that constitute a modification of those announced in cruder form by Lamarck, hence termed neo-Lamarckianism. These authors have imported consciousness into the list of factors of organic evolution and given it a prominent place. They regard consciousness as a fundamental property of proto- plasm ; it determines effort and the direction that activity shall take : thus hunger leads to migration, and brings the creature under a new set of conditions which influence its nature. A certain proportion of the changes an animal undergoes are at- tributed to the direct influence of surrounding conditions (en- vironment), but the larger number are owing to efforts involv- ing the greater use of some parts than others, which tends to become habitual. This is the explanation neo-Liamarckianism offers for the origin of variations. It is assumed that the re- sults of use or disuse of parts is inherited, so that the gain or loss is not transient with the individual, but remains with the group. This theory also refers the loss or preservation of certain s*;ructures to " acceleration " or " retardation " of growth ; thus, ii the growth of gills were greatly and progressively retarded during embryonic life, they might become only rudimentary, and this would furnish an explanation of the origin of rudiment- ary organs, though it is clear that use and effort could not di- rectly explain such acceleration or retardation. It is further a fact, which this theory does not explain, that all variations of structure produced by use are not inherited. 'TJ'^.R RVa^-.^ -•Eja^^^ett jj^^-j^Mg^li^iW^i^te^^ : 128 ANIMAL PHYSIOLOGY. \Weismann, in fact, denies that peculiarities acquired dur- ing the lifetime of the adult are passed on to offspring. This writer believes that we must seek in Amceba, as the ancestral representative of the ovum, for the clew to the laws of heredity. The Amoeba must divide or cease to exist as a group form — hence the segmentation of the ovum ; this is but the inherited tendency to divide. What the individual becomes is determined entirely by the ovum, the whole of which does not develop into the new being, but a part is laid aside in reserve as the future ovum. Any variations that show themselves in future indi- viduals are such as arise from the variations of the ovum itself. According to this writer, it is as natural for the offspring to resemble the parent (heredity) in the higher groups of animals as that one Amoeba shouii resemble another, and. for the same reason. Weismann has also attempted to explain the necessity and the significance of the extrusion of polar globules. The first polar globule is expelled from all ova, even those that -can de- velop independent of a male cell (parthenogenetic). This rep- resents that part of the original ovum which determines its peculiarities of form, etc. (ovogenetic idioplasm); while the second polar globule is one half of the nucleus of the mature ovum ready to enter upon development, if fertilized. When the latter takes place, it is joined by the corresponding nuclear substance of the male cell to form the segmentation nucleus. It is this substance (germ-plasma) which determines exactly what line of development, to the minutest details, the ovum shall follow. In the course of time the nucleus would thus come to represent many generations of united plasmas. There must be a limit to this, from the physical necessities of the case ; hence the expulsion of a second polar globule, which also is a provision against parthenogenesis, for in some cases the plasma of the nucleus has the power, without the accession of any male plasma, to segment and develop the mature animal. But in any case there is a great advantage in the union of the two plasmas with their diverse experiences; hence sexual repro- duction, though the most costly apparently, is in reality the most economical for Nature in the end, for higher results are reached, and it seems, in fact, that this lies at the very foun- dation of organic progress. The theory of Brooks may be regarded as eclectic, being a combination of that of WeiSmann and Darwin more particu- larly, with entirely new additions by himself. titm m f> rv n i itif:- icquired dur- spring. This the ancestral 8 of heredity, ^roup form — the inherited is determined ; develop into as the future . future indi- e ovum itself. 6 offspring to ps of animals . for the same necessity and es. The first that can de- c). This rep- letermines its [); while the )f the mature lized. When nding nuclear ttion nucleas. mines exactly ils, the ovum IS would thus bsmas. There es of the case ; hich also is a >es the plasma sssion of any animal. But on of the two sexual repro- in reality the ler results are he very f oun- lectic, being a more particu- OROANIC EVOLQTIUN BECONSIDERED. 129 (hs^Twin believed that every part of the body gave off " gem- mules," or very minute bodies, which were collected into the ovum, and thus the ovum came to be a sort of abstract of the whole body — hence the resemblance of offspring to parents, since the development of the ovum was but that of the gem- mules. Some of the gemmules might remain latent for genera- tions, and then develop ; hence that resemblance often seen to ancestors more remote than the parents (reversion). This is a very brief account of Darwin's hypothesis of pangenesis. This writer, however, never accounted for variations. He spoke of variations as " spontaneous," meaning, not that they were supernatural, but that it was not possible to assign them to a definite cause. To account for variation has naturally been the aim of later writers. How neo-Lamarckianism does this has been already considered. We now give the views of Brooks on this and other points in connection with organic evolution. (This thinker, like Weismann, looks to the fertilized ovum for an explanation of the main facts ; but Brooks refers the origin of variations to the influence of the male cell. This is, of course, a pure hypothesis, but it is in harmony with many facts which were in need of explanation. It had been noticed by Darwin that variations of all kinds were most apt to arise upon alteration in the conditions under which an animal lived. Brooks also believes in gemmules, but does not think they are given off from all parts equally or at all times, but that they are derived from those parts most affected by the change of surroundings ; and since this would influence parts much when for the worse, variation would coincide with suf- fering or need ; hence those very parts would vary, and so pre- pare for adaptation, just when this was most called for by the nature of the case. But the male sexual tion based on- } change ; and that the main •the"8wamp- htly, or one of jur. Romanes !, but not with •ly well. Cer- with one'an- OROANIC EVOLUTION RECONSIDERED. 131 other while varieties are so invariably ; and it is this that, in the opinion of Romanes and many others, has never been ade- quately explained. Admitting that the tlieories of Romanes, Brooks, and Weis- mann have advanced us on the way to more complete views of the mode of origin of the forms of the organic world, it must still be felt that all theories yet propounded fall short of being entirely satisfactory. It seems to us unfortunate that the sub- ject has not received more attention from physiologists, as without doubt the final solution must come through that sci- ence which deals with the properties rather than the forms of protoplasm ; or, in other words, the fundamental principles underlying organic evolution are physiological. But, in the unraveling of a subject of such extreme complexity, all sci- ences must probably contribute their quota to make up the truth, as many rays of different colors compounded form white light. As with other theories of the inductive sciences, none can be more than temporary ; there must be constant modifi- cation to meet increasing knowledge. Conscious that any views we ourselves advance must sooner or later be modified as all others, even if acceptable now, we venture to lay before the reader the opinions we have formed upon this subject as the result of considerable thought. All vital- phenomena may be regarded as the resultant of the action of external conditions and internal tendencies. Amid the constant change which life involves we recognize two things : the tendency to retain old modes of behavior, and the tendency to modification or variation. Since those impulses originally bestowed on matter when it became living, must, in order to prevail against the forces from without, which tend to destroy it, have considerable potency, the tendency to modi- fication is naturally and necessarily less than to permanence of form and function. From these principles it follows that wben an Amoeba or kindred organism divides after a longer or shorter period, it is not in reality the same in all respects as when its existence began, though we may be quite unable to detect the changes ; and when two inf usorians conjugate, the one brings to the other protoplasm different in molecular behavior, of necessity, from having had different experiences. We attach great importance to these principles, as they seem to us to lie at the root of the whole matter. What has been said of these lower but inde- fas*.®-.*** : '<■ % 132 ANIMAL PHYSIOLOGY. pendent forms of life applies to the higher. All organisms are made up of cells or aggregations of cells and their products. For the present we may disregard the latter. When a muscle- cell by division gives rise to a new cell, the latter is not identi- cally the same iu every particular as the parent cell was origi- nally. It is what its parent has become by virtue of those experiences it has had as a muscle-cell per se, and as a member of a populous biological community, of the complexities of which we can scarcely conceive. Now, as a body at rest may remain so, or may move in a certain direction according as the forces acting upon it exactly counterbalance one another, or produce a resultant effect in the direction in which the body moves, so in the case of he- redity, whether a certain quality in the parent appears in the offspring, depends on whether this quality is neutralized, aug- mented, or otherwise modified by any corresponding quality in the other parent, or by some opposite quality, taken in connec- tion with the direct influence of the environment during devel- opment. This assumption explains among other things why acquired peculiarities (the results of accident, habit, et<;.) may or may not be inherited. These are not usually inherited because, as is to be expect- ed, those forces of the organism which have been gathering head for ages are naturally not easily turned aside. Again, we urge, heredity must be more pronounced than variation. /The ovum and sperm-cell, like all other cells of the body, are tnicrocosms representing the whole to a certain extent in themselves — that is to say, cell A is what it is by reason of what all the other millions of its fellows in the biological republic are ; so that it is possible to understand why sexual cells repre- sent, embody, and repeat the whole biological story, though it is not yet possible to indicate exactly how they more than others have this power. This falls under the laws of speciali- zation and the physiological division of labor ; but along what paths they have reached this we can not determine. Strong evidence is furnished for the above views by the his- tory of disease. Scar-tissue, for example, continues to repro- duce itself as such ; like produces like, though in this instance the like is in the first instance a departure from the normal. Gout is well known to be a hereditary disease ; not only so, but it arises in the offspring at about the same age as in the parent, which is equivalent to saying that in the rhythmical life of rir.Ty".u~~-yj.xi'Am''Uk'hmi:?s,i-'-*sAK^^^^^ ORGANIC EVOLUTION RECONSIDERED. 183 gamsms are ir products, en a muscle- 8 not identi- )11 was origi- tue of those as a member nplexities of move in a on it exactly ant effect in e case of he- pears in the iralized, aug- [ig quality in an in connec- luring devel- frhy acquired may or may to be expect- len gathering B. Again, we ■iation. of the body, ain extent in eason of what fical republic al cells repre- iry, though it ly more than vs of speciali- it along what le. wa by the his- lues to repro- this instance n the normal. >t only so, but in the parent, [imical life of certain cells a period is reached when they display the behav- ior, physiologically, of their parents. iTet gout is a disease that can be traced to peculiar habits of living and may be eventually escaped by radical changes in this respect — that is to say, the behavi«)r of the cells leading to gout can be induced and can be altered ; gout is hereditary, yet eradicable. ^ Just as gout may be set up by formation of certain modes of action of the cells of the body, so may a mode of behavior, in the nervous system, for example, become organized or fixed, be- come a habit, and so be transmitted to offspring. It will pass to the descendants or not according to the principles already noticed. If so fixed in the individual in which it arises as to predominate over more ancient methods of cell behavior, and not neutralized by the strength of the normal physiological ac- tion of the corresponding parts in the other parent, it will reap- pear. We can never determine whether this is so or not before- hand ; hence the fact that it is impossible, es: eciall.y in the ca.i8 of man, whose vital processes are so modified by his p-ychic life, to predict whether acquired variations shall become heredi- tary ; hence also the irregularity which characterizes h'.redity in such cases ; they may reappear in offspring or they :aay not. In viewing heredity and modification it is impossible to get b true insight into the matter without taking into the accovni both original natural tendencies of living matter an(^ thp influ- ence of environment. We only know of vital ma- aiV;u nations in some environment ; and, so far as our experience ^oes, ^ife is impossible apart from the influence of surroundings. With these general principles to guide us, we shall attempt a brief examination of the leading theories of organic evolution. ^irst of all, Spencer seems to be correct in regarding evolu- tion as universal, and organic evolution but one j:Art of a whole. No one who looks at the facts presented in every field of nature can doubt that struggle (opposition, action and reac- tion) is universal, and that in the organic world the fittest to a given environment survives. But Darwin has probably fixed his attention too closely on this principle and attempted to ex- plain too much by it, as well as faik : *:r> see that there are other deeper facts underlying it. VaTia' . on, which this author scarcely attempted to explain, seems to us to be the natural re- sult of the very conditions under which living things have an existence. Stable equilibrium is au idea incompatible with our fundamental conceptions of ]if . Altered function implies al- tered molecular action, which sometimes leads to appreciable 184 ANIMAL PHYSIOLOGY. structural change. From our conceptions of the nature of liv- ing matter, it naturally follows that variation should be great- est, as has been observed, under the greatest alteration in the surroundings. We are but very imperfectly acquainted as yet with the conditions under which life existed in the earlier epochs of the earth's history. Of late, deep-sea soundings and arctic explo- rations have brought surprising facts to light, showing that living matter can exist under a greater variety of conditions than was previously supposed. Thus it turns out that light is not an essential for life everywhere. We think these recent revelations of unexpected facts should make us cautious in as- suming that life always manifested itself under conditions closely similar to those we know. Variation may at one period have been more sudden and marked than Darwin supposes; and there does seem to be room for such a conception as the " extraordinary births " of Mi vart implies ; though we would not have it understood that we think Darwin's view of slow modi- fication inadequate to produce a new species ; we simply vent- ure to think that he was not justified in insisting so strongly that this was the only method of Nature ; or, to put it more justly for the great author of the " Origin of Species," with the facts that have accumulated since his time he would scarcely be warranted in maintaining so rigidily his conviction that new forms arose almost exclusively by the slow process he has so ably described. As there must be all degrees in consciousness, we do not deny that it may be logical to assume some dim spark of this quality in all protoplasm, as Cope insists ; and that it plays a part in determining action and growth there seems to be no doubt. But is it not more philosophical to regard conscious- ness and all allied qualities as correlatives, and uiiderlaid by a molecular constitution with which it is associated as other qual- itiM ? Tt is unduly exalted in the neo-Lamarckian philosophy. ^Te jaust allow a great deal to use and effort, doubtless, and they explain the origin of variations up to a certain point, but the solution is only partial. "Variations must arise a^s we have attempted to explain, and use and disuse are only two of the factors amid many. Correlated growth, or the changes in one part induced by changes in another, is a principle which, though recognized by Darwin, Cope, and others, has not, we think, re- ceived the attention it deserves. To the mind of the physiolo- gist, aU changes must be correlated with others. THE CHEMICAL CONSTITUTION OF THE ANIMAL BODY. 185 nature of liv- 3uld be great- eratiou in the yet with, the epochs of the [ arctic explo- showing that of conditions b that light is k these recent autious in as- ler conditions ^ at one period sfivL supposes; ;eption as the I we would not of slow niodi- B simply vent- ,g so strongly put it more cies," with the «rould scarcely onviction that process he has ess, we do not 1 spark of this hat it plays a leems to be no ard conscious- aiiderlaid by a . as other qual- &n philosophy, doubtless, and tain point, but rise ais we have tnly two of the ihanges in one which, though [;, we think, re- f the physiolo- This principle has played a great part in the development of man, as we shall show later. f Weismann's theories have called attention to the ovum in a new and valuable way, though he seems to have given too ex- clusive attention to the nucleus {germ-plaama) in itself and out of relation to the influence of the countless cells that make up the body and must be constantly determining modi- fications of the generative organs and the sexual cells them- selves ; so that Brooks's explanation, by adding a new factor, or, at least, presenting a new aspect of the case, was called for and seems to be warranted on the general principle that advance in protoplasmic life is dependent on new experiences, and that the male cell represents a little world of the concen- trated experidnces gathered during the lifetime of the or- ganism that produced it. But we must consider the whole doctrine of gemmules as a crude and entirely unnecessary hypothesis. In what sense has the line that evolution has taken been predetermined ? In the sense that all things in the universe are unstable, are undergoing change, leading to new forms and qualities of such a character that they result in a gradual prog- ress toward what our minds can not but consider higher mani- festations of being. The secondary methods according to which this takes place constitute the laws of nature, and as we learn from the progress of science are very numerous. The unity of nature is a real- ity toward which our conceptions are constantly leading us. Evolution is a necessity of living matter (indeed, all matter) as we view it. THE CHEMICAL CONSTTTUTION OP THE ANIMAL BODY. (^ne visiting the ruins of a vast and elaborate building, which had been thoroughly pulled to pieces, would get an amount of information relative to the original structure and uses of the various parts of the edifice largely in proportion to his familiarity with architecture and the various trades which make *hat art a practical success. The study of the chemistry of the animal body is illustrated by such a case. Any attempt to determine the exact chemical composition of living matter must result in its destruction ; and the amount of information conveyed by the examination of the chemical ruins, so to speak. 186 ANIMAL PHYSIOLOGY. will depend a great deal on the knowledge already possessed of chemical and vital processes. (it is in all probability true that the nature of any vital pro- cess is at all events closely bound up with the chemical changes involved ; but we must not go too far in this direction. We are not yet prepared to say that life is only the manifestation of certain chemical and physical processes, meaning thereby such chemistry and physics as are known to us ; nor are we prepared to go the length of those who regard life as but the equivalent of some other force or forces ; as electricity may be considered as the transformed representative of so much heat and vice versa. It may be so, but we do not consider that this view is warranted in the present state of our knowledge. On the other hand, vital phenomena, when our investiga- tioiis are pushed fa,r enough, always seem to be closely asso- ciated with chemical action ; hence the importance to the stu- dent of physiology of a sound knowledge of chemical princi- ples. We think the most satisfactory method of studying the functions of an organ will be found to be that which takes into consideration the totality of the operations of which it is the seat, together with its structure and chemical composition; hence we shall treat chemical details in the chapters devoted to special physiology, and here give only such an outline as will bring before the view the chemical composition of the body in its main outlines ; and even many of these will gather a signifi- cance, as the study of physiology progresses, that they can not possibly have at the present. (f^Bwer than one third of the chemical elements enter into the composition of the mammalian body ; in fact, the great bulk of the organism is composed of carbon, hydrogen, nitro- gen, and oxygen; sodium, potassium, magnesium, calcium, sulphur, phosphorus, chlorine, iron, fluorine, silicon, though occurring in very small quantity, seem to be indispensable to the living body ; while certain others are evidently only pres- ent as foreign bodies or impurities to be thrown out sooner or later. It need scarcely be said that the elements do not occur as such in the living body, but in combination form- ing salts, which latter are usually united with albuminous compounds. As previously mentioned, the various parts which make up the entire body of an animal are composed of living matter i . i very different degrees ; heupe we find in such parts as the bones abundance of salts, relative to the proportion of proteid matter ; a condition demanded by that rigidity without J possessed of iny vital pro- nical changes tion. We are .nifestation of thereby such e we prepared he equivalent be considered [leat and vice it this view is >ur investiga- I closely asso- se to the stu- )mical princi- studying the ich takes into hich it is the composition ; ers devoted to )utline as will f the body in kther a signifi- they can not Dts enter into vit, the great drogen, nitro- ium, calcium, ilicon, though dispensable to itly only pres- im out sooner ments do not dnaiion form- h albuminous IS parts which osed of living in such parts proportion of gidity without THE CHEMICAL CONSTITUTION OP THE ANIMAL BODY. 137 which an internal skeleton would be useless, a defect well illus- trated by that disease of the bones known as rickets, in which the lime-salts are insuflPcient. It is manifest that there may be a very great variety of classifications of the compounds found in the animal 1> -^v according as we regard it from a chemical, physical, or pfcv.s^ological point of view, or combine many aspects in one whole. The latter is, of course, the most correct and profitable method, and as such is impossible at this stage of the student's progress ; we shall simply present him with the following outline, which will be found both simple and com- prehensive.* The subject of Animal Chemistry will be found treated in detail in the Appendix. CHEMICAL CONSTITUTION OF THE BODY. Such food as supplies energy directly must contain carbon compounds. Living matter or protoplasm always contains nitrogenous carbon compounds. In consequence, C, H, O, N, are the elements found in great- est abundance in the body. The elements S and P are associated with the nitrogenous carbon compounds ; they also form metallic sulphates and phos- phates. CI and F form salts with the alkaline metals Na, K, and the earthy metals Ca and Mg. Fe is found in hamoglobin and its derivatives. (^VProtoplasnOjL^wlien submitted to chemical examination, is killed. It Is then found to consist of proteids, fats, carbohy- drate, salines, and extractives. It is probable that when living it has a very complex mole, oule consisting of C, H, O, N, 8, and P chiefly. 1. Organic. (a) Nitrogenous. PROXIMATE PRINCIPLES. ( Proteids. ( Certain crystalline bodies. ^ (b) Non-nitrogenous, j -^^ ^ ^ ^ , ( Mineral salts. 8. Inorganic. ] ^^^^ Salts.— In general, the salts of sodium are more characteris- tic of animal tissues and those of potassium of vegetable tissues. • Taken from the author's " Ootiinesof Lectures on Physiology," W. Drysdalt & Co., Montreal. %^_P!^,:&tiUUiSSim.^^^^ 188 ANIMAL PHYSIOLOGY. Na CI is more abundant in the fluids of animals ; K and phosphates more abundant in the tiaaues. Earthy salts are most abundant in the harder tissues. The salts are probably not much, if at all, changed in their passage through the body. In some cases there is a change from acid to neutral or alkaline. The salts are essential to preserve the balance of the nutri- tive processes. Their absence leads to disease, e. g., scurvy. GENERAL CHARACTERISTICS OF PROTBID8. They are the chief constituents of most living tissues, in- cluding blood and lymph. The molecule consists of a great number of atoms (complex constitution), and is formed of the elements C, H, N, O, S, and P. All proteids are amorphous. All are non-diflfusible, the peptones excepted. They are soluble in strong adds and alkalies, with change of properties or constitution. In general, they are coagulated by alcohol, ether, and heating. Coagulated proteids are soluble only in strong acids and alkalies. Classification and Distinguishing Characters of Proteids. 1. Native albumins : Serum albumin ; egg albumin ; soluble in water. 2. Derived albumins (albuminates) : Acid and alkali albu- min ; casein ; soluble in dilute acids and alkalies, insoluble in water. Not precipitated by boiling. 3. Olobvlina: Globulin (globin) ; paraglobulin ; myosin; fibrinogen. Soluble in dilute saline solutions, and precipitated by stronger saline solutions. 4. Peptones: Soluble in water; diffusible through animal membranes ; not precipitated by acids, alkalies, or heat. De- rived from the digestion (peptic, pancreatic) of all proteids. 6. Fibrin: Insoluble in water and dilute saline solutions. Soluble, but not readily, in strong saline solutions and in dilute acids and alkalies. CERTAIN NON-CRTSTALLINE BODIES. The following bodies are allied to proteids, but are not the equivalents of the latter in the food. imals; E and tissues, uged in their to neutral or ( of the nutri- g., scurvy. IDS. ng tissues, in- boms (complex N, 0,8, and P. }, with change ir, and heating. 3ng acids and of Proteids. mmin; soluble td alkali albu- js, insoluble in ulin; myosin; id precipitated irough animal , or heat. De- lU proteids. ' irline solutions. IS and in dilute B. but are not the THE CHEMICAL CONSTITUTION OP THE ANIMAL BODY. 189 They are all composed of C, H, N, O. Chondrin, gelatin, ceratin have, in addition, S. Chondrin: The organic basis of cartilage. Its solutions set into a firm jelly on cooling. OeMin : The organic basis of bone, teeth, tendon, etc. Its solutions set (glue) on cooling. Elastin : The basis of elastic tissue. Its solutions do not set jelly-like (gelatinize). Mticin : From the secretion of mucous membranes ; precipi- tated by acetic acid, and insoluble in excess. Keratin : Derived from hair, nails, epidermis, horn, feathers. Highly insoluble. Nuclein: Derived from the nuclei of cells. Not digested by pepsin ; contains P but no S. THE PATS. The fats are hydrocarbons ; are less oxidized than the carbo- hydrates; are inflammable; possess latent energy in a high degree. Chemically, the neutral fats are glycerides or ethers of the fatty acids, i. e., the acid radicles of the fatty acids of the oleic and acetic series replace the exchangeable atoms of H in the triatomic alcohol glycerine, e. g. : Olycerine. Pftlmltio add. Gljroeriiie tripcOmltAte or palmitin. ) OH HO.OC.CHm ( O.CO.CH,, C.H. [ OH + HO.OC.CH,, = C,H, ] O.CO.C,.H„ + 3H,0 )0H HO.OC.C..H,, (O.CO.C«H„ A soap is formed by the action of caustic alkalies on fats, e. g. : Tripalmitin, C,H, FoUnlum p«lmitate. (cS..,h..3,KOH, = sj(C"H.O)oJ,Ca.Jo, The soap may be decomposed by a strong acid into a fatty acid and glycerine, e. g. : C,.H„.CO,K + HCl = 0,.H„.CO,H -f- KCl. PotaMium palmltate. Palmitio aoid. The /ate are insoluble in water, but soluble in hot alcohol, ether, chloroform, etc. The alkaline soaps are soluble in water. i*i.'*»«>*WvS 140 ANIMAL PHYSIOLOGY. Most animal fats are mixtures of several kinds in varying proportion ; hence the melting-point for the fat of each species of animal is different. PECULIAR FATS. Lecithin, Protagon, Cerebrin : They consist of C, H, N, O, and the first two of P in addi- tion. They occur in the nervous tissues. i CARBOHTDRATBS. General formula, C» (H,0).. 1. The Sugars: Dextrose, or grape-sugar, C«HhO« + H,0 readily undergoes alcoholic fermentation; less readily lactic fermentation. Lactose, milk-sugar, C„H O,, + H,0 ; susceptible of the lactic acid fermentation. InosU, or muscle-sugar, C.H„0. -•- 2H,0; capable of the lac- tic fermentation. MaUose, C„H„0„ + H.0, capable of the alcoholic fermenta- tion. The chief sugar of the digestive process. All the above are much less sweet and soluble than ordinary cane-sugar. 2. The Starches: Glycogen, C,HwO„ convertible into dex- trose. Occurs abundantly in many foetal tissues and in the liver, especially of the adult animal. Dextrin, C.H,»0„ convertible into dextrose. Soluble in water; intermediate between starch and dextrose; a product of digestion. . j- i < Pathologicdl : Grape-sugar occurs in the urine m duibetes mellitViS. Certain substances formed within the body may be regarded as chiefly waste-products, t ae result of metabolism or tissue- changes. They are divisible into nitrogenous metabolites and non- nitrogenous metabolites. Nitrogenoiia Metc^dites. 1. Urea, uric acid and compounds, kreatinin, xanthin, hypo- xanthin (sarkin), hippuric acid, all occurring in urine. 2. Leucin, tyrosin, taurocholio, and glycocholic acids, which occur in the digestive tract. ids in vaiTdng }f each species of P in addi- C.H„0, + H.0 readily lactic ble of the lactic able of the lac- lolic fermenta- j than ordinary rtible into dex- iies and in the e. Soluble in ose; a product ine in dic^etea [lay be regarded >lism or tissue- olites and non- , xanthin, hypo- L urine. )lic acids, which PHYSIOLOGICAL RESEARCH, PHYSIOLOGICAL REASONING. 141 3. Kreatin, constantly found in muscle, and a few others of less constant occurrence. The above consists of C, H, N, O. Taurocholic acid contains also S. The molecule in most instances is complex. Non-Nitrogenous Metabolites. These occur in small quantity, and some of them are secreted in an altered form. They include lactic and sarcolactic acid, oxalic acid, succinic acid, etc. PHYSIOLOGICAL RESEARCH AND PHYSIOLOGICAL REASONING. We propose in this chapter to examine into the methods employed in physiological investigation and teaching, and the character of conclusions arrived at by physiologists as depend- ent on a certain method of reasoning. [The first step toward a legitimate conclusion in any one of Hie inductive sciences to which physiology belongs is the col- lection of facts which are to constitute the foundation on which the inference is to be based. If there be any error in these, a correct conclusion can not be drawn by any reliable logical process. On the other hand, facts may abound in thou- sands and yet the correct conclusion never be reached, because the method of interpretation is faulty, which is equivalent to saying that the process of inference is either incomplete or in- coirect. The conclusions of the ancients in regard to nature) were usually faulty from errors in both these directions; theys neither had the requisite facts, nor did they correctly interpret those with which they were conversant. (Let us first examine into the methods employed by modem physiologists, and determine in how far they jure reliable. First, there is the method of direct observation, in which no appara- tus whatever or only the simplest kind is employed ; thus, the student may count his own respirations, feel his own heart- beats, count his pulse, and do a very great deal more that will be pointed out hereafter ; or he may examine in like manner an- other fellow-being or one of the lower animals. This method is simple, easy of application, and is that usually employed by the physician even at the present day, especially in private 149 ANIMAL PHYSIOLOOr. practice. The value of the results ohviously depends on the reliability of the observer in two respects : First, as to the ac- curacy, extent, and delicacy of his i)erceptions ; and, secondly, on the inferences based on these sense-observations. Much must depend on practice — ^that is to say, the education of the senses. The hand may become a most delicate instrument of observation ; the eye may learn to see what it once could not ; the ear to detect and discriminate what is quite beyond the uncultured hearing of the many. But it is one of the most convincing evidences of man's superiority that in every field of observation he has risen above the lower animals,, some of which by their unaided senses naturally excel him. So in this science, instruments have opened up mines of facts that must have otherwise remained hidden; they have, as it were, provided man with additional senses, so much have the natural powers of those he already possessed been sharp- ened. HBut the chief value of the results reached by instruments consists in the fact that the movements of the living body can be registered ; i. e., the great characteristic of modem physiol- ogy is the extensive employment of the graphic method, which has been most largely developed by the distinguished French experimenter Marey. Usually the movements of the point of lever are impre^ed on a smoked surface, either of glazed paper or glass, and rendered permanent by a coating of some material applied in solution and drying quickly, as shellac in alcohol. The surface on which the tracing is written may be stationary, though this is rarely the case, as the object is to get a succession of records for comparison ; hence the most used form of writing surface is a cylinder which may be raised or lowered, and which is moved around regularly by some sort of clock-work. It follows that the lever-point, which is moved by the physiological effect, describes cur»^es of varying complexity. That tracings of this or any other character should be of any value for the purposes of physiology, they must be susceptible of relative measurement both for time and space. This can be accomplished only when there is a known base-line or abscissa from which the lever begins its rise, and a time record which is usually in seconds or portions of a second. The first is easily obtained by simply allowing the lever to write a straight line before the physiological effect proper is recorded. Time inter- vals are usually indicated by the interruptions of an electric current, or by the vibrations of a tuning-fork, a pen or writer pends on the as to the ac- tnd, secondly, ;ions. Much Lcation of the nstrument of ice could not ; B heyond the i of the most lat in every wer animals,, ly excel him. lines of facts hey have, as o much have d heen sharp- y instruments iring body can idem physiol- aethod, which lished French f the point of ler of glazed Eiting of some , as shellac in rittenmay be ibject is to get the most used y be raised or f some sort of sh is moved by ig complexity. >tild be of any be susceptible This can be ne or abscissa ecord which is first is easily a straight line [. Time inter- of an electric i pen or writer PHYSIOLOGICAL RESEARCH, PHYSIOLOGICAL REASONING. 143 of some kind being in each instance attached to the apparatus so as to record its movements. As levers, in proportion to their length, exaggerate all the movements imparted to them, a constant process of correction must be carried on in the mind in reading the records of the graphic method, as in interpreting the field of view presented by the microscope. The student is especially warned to carry on this process, otherwise highly distorted views of the reality will become fixed in his own mind ; and certainly a condition of ignorance is to be preferred to such false knowledge as this may become. But it is likewise apparent that movements that would without such mechanism be quite unrecognized may be rendered visible and utilized for inference. There is another source of possible misconception in the use of the graphic method. The lever is sometimes used to record the movements of a column of fluid (manometer. Pig. 207), as water or mercury, the inertia of which is considerable, so that the record is not that of the lever as aflfected by the physiological (tissue) movement, but that move- ment conveyed through a fluid of the kind indicated. Again, all points, however delicate, write with some friction, and the question always arises. In how far is that friction sufficient to be a source of inaccuracy in the record ? When organs are di- rectly connected with levers or apparatus in mechanical rela- tion with them, one must be sure that the natural action of the organ under investigation is in no way modified by this con- nection. From these remarks it will be obvious that in the graphic method physiologists possess a means of investigation at once valuable and liable to mislead. Already/electricity has been extensively used in the researches of physiologists, and it is to this and the employment of photography that we look in the near future for methods that are less open to the objections we have noticed. (Jowever important the methods of physiology, the results are vastly more so. We next notice, then, the progress from methods and observations to inferences, which we shall en- deavor to make clear by certain cases of a hypothetical charac- ter. Proceeding from the brain and entering the substance of the heart, there is in vertebrates a nerve known as the vagus. Suppose that, on stii^ulating this nerve by electricity in a rab- bit, the heart ceases to beat, what is the legitimate inference ? Apparently that, the effect has been due to the action of the 144 ANIMAL PHTSIOLOOT. nerve on the heart, an action excited by the use of electricity. This doefl not, however, according to the principles of a rigid logic, follow. The heart may have ceased beating from some cause wholly unconnected with this experiment, or from the electric current escaping along the nerve and affecting some nervous mechanism within the heart, which is not a part of the vagus nerve ; or it may have been due to the action of the cur- rent on the muscular tissue of the heart directly, or in some other way. But suppose that invariably, whenever this experiment is repeated, the one result (arrest of the beat) follows, then it is clear that the vagus nerve is in some way a factor in the causa- tion. Now, if it could be ascertained that certain branches of the nerve were distributed to the heart-muscle directly, and that stimulation of these gave rise to arrest of the cardiac pulsation, then would it be highly probable, though not certain, that there was in the first instance no intermediate mechanism; while this inference would become still more probable if in hearts totally without any such nervous apparatus whatever, such a result followed on stimulation of the vagus. Suppose, further, that the application of some drug or poison to the heart pro- vided with special nervous elements besides the vagus termi- nals prevented the effect before noticed on stimulating the vagus, while a like result followed under similar circumstances in those forms of heart unprovided with such nervous struct- ures, there would be additional evidence in favor of the view that the result we are considering was due solely to some action of the vagus nerve ; while, if arrest of the heart followed in the first case but not in the second, and this result were invariable, there would be roused the suspicion that the action of the vagus was not direct, but through the nervous structures with- in the heart other than vagus endings. And if, again, there were a portion of the rabbit's heart to which there were distributed this intrinsic nervous supply, which on stimulation directly was arrested in its pulsation, it would be still more probable that the effect in the first instance we have considered was due to these structures, and only indirectly to the vagus. But be it observed, in all these cases there is only probability. The con- clusions of physiology never rise above probability, though this may be so strong as to be practically equal in value to absolute certainty. Would it be correct, from any or all the experi- ments we have supposed to have been made, to assert that the vagus was the arresting (inhibitory) nerve of the heart ? All hearts thus far examined have much in common in structure PHYSIOLOGICAL RESEARCH, PHYSIOLOGICAL REASONING. I45 ctricity. a rigid >m some rom the ig some rt of the the cur- ne other leriment hen it is e causa- aches of and that alsation, lat there a; while n hearts r, such a , further, Bart pro- is termi- ,ting the mstances as struct- the view ne action ^ed in the ivariable, tn of the ires with- here were stributed L directly probable I was due But be it The con- ough this > absolute le experi- t that the art? All structure and function, and in so far is the above generalization probable. Such a statement would, however, be far from that degree of probability which is possible, and should therefore not be ac- cepted till more evidence has been gathered. The mere resem- blance in form and general function does not suffice to meet the demands of a critical logic. Such a statement as the above would not necessarily apply to the hearts of all vertebrates or even all rabbits, if the experiments had been conducted on one animal alone, for the result might be owing to a mere idiosyncrasy of the rabbit under observation. The further we depart from the group of animals to which the creature under experiment be- longs, the less is the probability that our generalizations for the one class will apply to another. It will, therefore, be seen that wide generalizations can not be made with that amount of certainty which is attainable until experiments shall have be- come very numerous and widely extended. A really broad and sound physiology can only be constructed when this science has become much more comparative — that is, extended to many more groups and sub-groups of animals than at present. (To attempt to generalize for the heart, the kidney, the liver, etc., when only the dog, cat, rabbit, and frog, have been made as a rule the subjects of experiment, except for the groups of animals to which the above belong, is not only hazardous but positively illogical ; while to denominate conclusions based on such experiments, even when supplemented by the teachings of disease, " human physiology " is, in the writer's opinion, a wholly unwarrantable proceeding. (jt is this conviction which has had much to do with this book being written; to the introduction of the comparative element ; and the separation so frequently in form as well as in reality of facts and inferences. A genuine human physi- ology, with the exact nature and value of the inferences clearly stated, is yet to be written ; and it seems not only judicious, but demanded as a matter of candor and honesty, to state at the outset to the student what we feel able to teach confidently, and what must be presented as feebly probable or barely pos- sible. ' Human physiology proper must of necessity be accumulated slowly. Much may be, indeed must be, inferred from the ex- periments disease is making ; still, certain forms of accident or surgical operation provide the opportunity to investigate the human body in health or in a moderately near approach to that condition. Close self-observation under a variety of condi- 10 ■Mmm ■ giwam i — Kawniat 1P^ 146 ANIMAL PHYSIOLOGY. tions, SO precisely defined as to meet the demanus ,r' science, may be made by the intelligent student. Much ol '!'.'' .ratjht be verified in the case of other healthy persons. Si>riifc of it is in certain respects of more value than any experiments thct can be made upon the lower animals, for the latter can not communicate to us their sensations; in their case all our in- formation must be derived from the use of our own senses, mostly unaided by any reports of theirs. ^t is not possible during any experiment, especially any one in which vivisection is employed, to observe the animal under conditions that are strictly normal, for, by the very nature of the case, we have rendered it abnormal. We must in all such instances draw conclusions with corresponding caution. It will be understood that the expression "conclusive experi- ment," as applied to such a case, is only approximately correct. (At the present time it is very common to experiment upon organs disconnected, either anatomically or physiologically (functionally), from the rest of the body to a greater or less extent. This is termed the isolated method. It has the advan- tage of being more simple, and permits of the study of certain points apart from others — one factor being considered inde- pendently of the rest in the physiological totaL But, in draw- ing conclusions, it is very important in such a case not to forget the premises. There is manifest danger of making the gener- alization wider than the facts warrant. It is only when such experiments are supplemented by a great many others, and when judged in connection with the action of the organ under consideration, as it is influenced by other organs, that such re- sults can be of great value in building up a normal physiology. To know, for example, that the isolated heart behaves in a cer- tain manner is not useless information, but its value depends entirely on the conclusions drawn from it, especially as to what it is conceived as teaching of the functions of the heart as it beats within the body of an animal while it walks, or flies, or swims, in carrying out the purpose of its being. (We have incidentally alluded to the teaching of 'disease, "disease " is but a name for disordered function. One viewing a piece of machinery for the first time in improper action might draw conclusions with comparative safety, provided he had a knowledge of the correct action of aimilar machines. Our ex- perience gives us a certain knowledge of the f uncticns of our own bodies. By ordinary observation and by experiisent on other animals we get additional data, which, taken with the THE BLOOD. 14T ■ science, <.'' rij^'ht lb of it is lents thnl r can not 11 our in- rn senses, y any one mal under nature of n all such ution. It re experi- ly correct, nent upon iologically ber or less the advan- of certain ered inde- t, in draw- it to forget the gener- when such »thers, and *gan under it such re- )hy8iology. es in a cer- ue depends as to what heart as it or flies, or of disease, ne viewing jtion might i he had a s. Our ex- icns of our eriment on n with the disordered action resulting from gross or molecular injury (disease), gives a basis for certain conclusions as to the normal functions of the human body or those of lower animals. This information is especially valuable in the case of man, since he can report with a fair degree of reliability, in most diseased conditions, his own sensations. It is hoped that this brief treatment of the methods and logic of physiology will suffice for the present. Throughout the work they will be illustrated in every chapter, though not always with distinct references to the nature of the intellectual process followed. Sommury.— ^There are two methods of physiological observa- tion, the direct and the indirect. The first is the simplest, and is valuable in proportion to the accuracy and delicacy and range of the observer ; the latter implies the use of apparatus, and is more complex, more extended, more delicate, and precise. It is usually employed with the graphic method, which has the advantage of recording and thus preserving movements which correspond with more or less exactness to the movements of tissues or organs. It is valuable, but liable to errors in record- ing and in interpretation. ( The logic of physiology is that of the inductive sciences. It proceeds from the special to the general. The conclusions of physiology never pass beyond extreme probability, which, in some cases, is practically equal to certainty. It is especially important not to make generalizations that are too wide. THE BLOOD. It is a matter of common observation that the loss of the whole, or a very large part, of the blood of the body entails death ; while an abundant hsemorrhage, or blood-disease in any of its forms, caases great general weakness. The student of embryology is led to inquire as to the neces- sity for the very early appearance and the rapid development of the blood- vascular system so prominent in all vertebrates. An examination of the means of transit of the blood, as already intimated, reveals a complicated system of tubes dis- tributed to every organ and tissue of the body. These facts would lead one to suppose that the blood must have a tran- scendent importance in the economy, and such, upon the most minute investigation, proves to be the case. The blood has 148 ANIMAL PHYSIOLOGY. been aptly compared to an internal world for the tissues, an- swering to the external world for the organism as a whole. This fluid is the great storehouse containing all that the most exacting cell can demand ; and, further, is the temporary receptacle of all the waste that the most busy cell requires to discharge. Should such a life-stream cease to flow, the whole vital machinery must stop — death must ensue. Comparative. — It will prove more scientific and generally sat- isfactory to regard the blood as a tissue having a fluid and flowing matrix, in which float cellular elements or corpuscles — a view of the subject thvit is less startling when it is remem- bered that the greater part of the protoplasm which makes up the other tissues of the body is of a semifluid consistence. In all animals possessing blood, the matrix is a clear, usually more or Ippg colored fluid. Among invertebrates the color may be pronounced : thus, in cephalopods and some crustaceans it is blue, but in most groups of animals and all vertebrates the matrix is either colorless or more commonly of some slight tinge of yellow. Invertebrates with few exceptions possess only colorless corpuscles, but all vertebrates have colored cells which invariably outnumber the other variety, and display forms and sizes which are sufiiciently constant to be characteristic. In all groups below mam- mals the colored corpus- cles are oval, mostly bi- convex, and nucleated during all periods of the animal's existence ; in mammals they are cir- cular biconcave disks (except in the camel tribe, the corpuscles of which are oval), and in post-embryonic life with- out a nucleus ; nor do they possess a cell-wall The red cells vary in size in different groups and sub-groups of animals, being smaller the higher the place the animal occupies, as a general rule: thus, they are very large iu vertebrates below mammals, in some cases being almost Fio. 143.— loiicocytes of human blood, showing amoB* bold movementM (Landois). Theae movements are not normally in the Mood-Teasels so marked as pic- tured here, so that tbu figure represents an ex- treme case. H THE BLOOD. 149 3 tissues, an- as a whole, bat the most 3 temporary 1 requires to w, the whole generally sat- : a fluid and corpuscles — it is remem- ch makes up sistence. In usually more !olor may be taceans it is rtebrates the some slight ions possess colored cells and display sizes which tly constant 3teristic. In below mam- ored corpus- 1, mostly bi- d nucleated Briods of the :istence ; in hey are cir- icave disks the camel orpuscles of >yal), and in nic life with- lus ; nor do I a cell-wall } vary in size groups and the place the •e very large teing almost Fio. -Photograph of colored frog. 1 X 370. (After FUut. luscies of visible to the unaided eye, while in the whole class of mam- mals they are very minute ; their numbers also in this group are vastly greater than in others lower in the scale. The average size in man is TiW inch ("OOT? mm.) and the number in a cubic mil- limetre of the blood about 5,000,000 for the male and 500,000 less for the female, which would furnish about 250,000,000,000 in a pound of blood. It will be under- stood that averages only are spoken of, as all kinds of variations occur, some of which will be referred to later, and their significance explained. Under the microscope the blood of vertebrates is seen to owe its color to the cells chiefly, and, so far as the red goes, almost wholly. Corpuscles when seen singly are never of the deep red, however, of the blood as a whole, but rather a yellowish red, the tinge varying some- what with the class of ani- mals from which the spec- imen has been taken. Certain other viorpho- logical elements found in mammalian blood deserve bri%f mention, though their significance is as yet a mat- ter of much dispute : 1. The blood - plates {plaques, TuBviatoblasfs, third element), very small, colorless, biconcave disks, which are dejwsited in great num- bers on any thread or similar foreign body introduced into the circulation, and rapidly break np when blood is shed. 2. On a slide of blood that has been prepared for some little orpuwlM from hum«n mibject (Funkey. A few coiorlew corpuackM are aeen among the colored disks, which are many of them arranged In roul«ause. 1 160 ANIMAL PHYSIOLOGY. time, aggregations of very minute granules (elementary gran- ules) may be seen. These are supposed to represent the disin- tegrating protoplasm of the corpuscles. © »^^ i) B I Fio. 14«.— Blood-plaques and their derivatiTea (Landoia, after BinoEPro and Laker}. 1, red blood-eorpuscleB on the flat ; 3, from the side ; 8, unchanged blood-plaques ; 4, lymph- corpuscle surrounded with biood-plaques ; 6, btoud-plaques varioushr altered ; 6, lymph- corpuscle with two masses of fiised blood-plaques and threads of flbrin ; 7, group of blood-plaques fused or run together ; 8, similar small mass of partially dissolved blood- plaques with fibrils of flbrin. The pale or colorleiss corpuscles are very few in number in mammals compared with the red, there being on the average only about 1 in 400 to 600, though they become much more numerous after a meal. They are granular in appearance, and possess one or more nuclei, which are not, however, readily seen in all cases without the use of reagents. They are character- ized by greater size, a globular form, the lack of pigment, and the tendency to amoeboid movements, which latter may be ex- aggerated in disordered conditions of the blood, or when the blood is withdrawn and observed under artificial conditions. It will be understood that these cells (lenrocytes) are not con- fined to the blood, bijt abound in lymph and other fluids. They are the representatives of the primitive cells of the em- bryo, as is shown by their tendency (like ova) t« throw out processes, develop into higher forms, etc. In behavior they strongly suggest Aviaeha and kindred forms. We may, then, say that in all invertebrates the blow!, when it exists, consists of a plasma {liquor sanguinis), in which float the cellular elements which are colorless; and that in verte- brates in addition there are colored cells which are always nu- cleated at some period of their existence. The colorless cells liary gran- ; the disin- THE BLOOD. 151 [ L«ker). 1, rod ques ; 4, lymph- tered ; 6, lymph- in ; 7, group of diaaolvMl blood- number in ihe average nuch more arance, and •eadily seen I character- gment, and may be ex- r when the conditions, re not con- ther fluids, of the em- throw out lavior they )lood, when which float tt in verte- always nu- lorless cells are globular masses of protoplasm, containing one or more nuclei, and with the general character of amceboid organisms. The HisTORir of the Blood-Cells. We have already seen that the blood and the vessels in which it flows have a common origin in the mesoblastic cells of the embryo chick; the same applies to mammals and lower groups. The main facts may be grouped under two head- ings: 1. Development of the blood-corpuscles during embry- onic life. 2. Development of the corpuscles in post-embryonic life. . In the bird and the mammal, cells of the mesoblast in the area opaca give off processes which unite ; later they become hollowed out {vaciwlated)^ and thus foi.a capillaries. At the same time the nuclei of these cells multiply {pro- liferate), gather small por- tions of the protoplasm of the main cells about them, become colored, and thus form the nucleated corpus- cles of the embryo. This, or a similar process, is known to occur in some animals (rat) after birth ; but in the human foetus there is a grad- ual decline in the number of nucleated cells found free in fVia Klnn/l ar\i\ ftf. hirfli fhftv Flo. 147.— Surface view from below of a Biiuai poT- tne DlOOa, ana at Oirin tney tlonof posterior end of pelluoW area of a cfiok arft v«rv rn.r« which is nrob- o' thlrty-slx hours, 1 x 100 (Foster and Bal- are very rare, WUlOll is pi uu j^^^.^ g blood-corpuBcles ; a, Duolel, which aWv f.Vift PARA with most subiequently become nuclei of cells formlnK aoiy me case witu uiubt waUs of bfood-vessels ; p. or. protoplasmic mammals processes, containing nuclei with large nu- While the origin of the red cells, as above described, may be regarded as the earliest and most general, it is not their exclusive source. When the liver has b sen formed this organ seems to carry on a development begun in the spleen, for the nucleated but as yet colorless cells formed in the spleen seem to become pig- mented in the liver. There is also evidence that colored corpuscles may arise by endogenous formation in the lymphatic glands. 152 ANIMAL PHYSIOLOGY. There is no doubt that the greater number of the non-nucle- ated corpuscles are derived from the nucleated forms. Tlie post-embryonic development of colored corpuscles is - aturally less understood from the greater diflBculties attend- c # © O ig Fio. 148. D'la. ISO. Fio. 149. Fio. 151. Fio. 158. oeU or free nucleus. (1 igs. 148- 158, after Osier. ) ing its investigatiin. The following may be regarded as a summary of the chiof facts or rather opinions on this subject: 1. From the colorless cells ; though, whether tho nucleus disappears, or remains to form the chief part of the cell and become pigmented, is undetermined. 2. From peculiar cells of the rod marrow of the bones (ha , trunk, etc.), though there is also some doubt as to whether the itt^iVmi''^\iMS£iiirAiifiiii':t^ THE BLOOD. 153 tton-nucle- puscles is es attend- 2. ), smaller, more ly be even sur- les of the bone to the ordinary rellB of red mar- >>() red corpuscle uucleuB, from the cell, a jBcles. In 4 the prow cells. 6, 1, e ; 8, two micro- lucent, lymphoid arded as a 18 subject : ho nucleus he cell and (Ones (h ;8 ^ whether the nuclei of these cells remain or not ; but as all grades of transi- tion forms have been found in the bone-marrow ; sinn o aneemia occurs in disease of bones; since the bone-marrow has been found in an unusually active condition after hasraorrhage and under other circumstances demanding a rapid replacement of lost cells — there seems to be little room for doubt that in the adult the red marrow of the bones is the chief site of the devel- opment of red corpuscles. It is not, however, the only one, for under peculiar stress of need even the lymphatic glands pro- duce red cells, and the latter have been seen to be budded off from the spleen in a young animal (kid). The colorless cells of the blood first arise as migrated undif- ferentiated remnants of the early embryonic cell colonies. That they remain such is seen by their physiological behavior, to be considered a little later. Afterward they are chiefly produced from a peculiar form of connective tissue known as leucocy- tenic, and which is gathered into organs, the chief function of which (lymphatic glands) is to produce these cells, though this tissue is rather widely distributed in the mammalian body in other forms than these. Summary.— i-The student may, with considerable certainty, consider the colorless corpuscle of the blood as the most primi- tive ; the red, derived either from the white or some form of more specialized cell ; the nucleated, as the earlier and more youthful form of the colored corpuscle, which may in some groups of vertebrates be replaced by a more specialized (or de- graded ?) non-nucleated form mostly derived directly from the former ; that in the first instance the blood-vessels and blood arise simultaneously in the mesoblastic embryonic tissue; that such an origin maj' exist after birth, either normally in some mammals or under unusual functi )nal need ; that the red marrow is the chi«)f birthplace of colored cells in adult life ; that the spleen, liver, lymphatic, glands, and other tissues of similar structure contribute in a less degi oe to the develop- ment ( i ihe rod corpuscles; and thiit tbo last mentioned organs are the chief producers of the colorless amoeboid blood-cells. (^Finally, it is well to remember that Nature's resoxirces in this, as in many other cases, are numerous, and that her mode c>f procedure is not invariable ; and that, if oue road to an end is blocked, another is taken. The Decline and Death of the Blood-Cella.— The bLjod-corpuscles, like other cells, have a limited, duration, with the u.>elieve the iplexity of ( pabulum ived from jtly speak- the blood ly attempt THE BLOOD. 157 to estimate the total quantity of blood in the body of an animal by bleeding is highly fallacious for various reasons. It is im- possible to withdraw all the blood from the vessels by merely opening even the largest of them, and, if it were, the original quantity would be augmented by fluid absorbed into them dur- ing the very act. No method has as yet been devised that is free from objection, hence the conclusions arrived at as to the total quantity of blood are not in accord ; and in the nature of the case no accurate estimate can be made, but about one thir- teenth to one fourteenth may be taken as a fair average ; so that in a man of one hundred and forty pounds weight there should be about ten pounds of blood ; but, of course, this will vary with every hour of the day and will be greatest after a meal. As an example of the methods referred to, we give Welck- er*s, which is briefly as follows : The animal is bled to death from the carotid; a sample of the defibrinated blood (1 cc.) is saturated with carbon monoxide (CO), which gives a perma- nent red color; this diluted with 500 cc. of water furnishes a standard sample. The blood-vessels of the animal are washed out with a '6 per cent solution of common salt, but the Out- flowing stream is colorless ; to this is added the fluid obtained by chopping up the tissues of the animal, steeping, washing out, and pressing. The whole is diluted to give the color of the standard solution, from which the amount of blood in this mixt- ure may be calculated, since every 500 cc. answers to 1 cc. of blood ; the blood obtained by bleeding can, of course, be accu- rately measured. It would be slightly more accurate to make the diluted blood of the animal operated upon the standard without treat- ment with carbon monoxide. Such a method, though the best yet devised, is open to ob- jection also, as will occur to most readers. The relative quantities of blood in different parts of the body have been estimated to be as follows : Liver one fourth. Skeletal muscles ; " " Heart, lungs, large arteries, and veins. " " . Other structures " " The significance of this distribution will appear later. The Coagulation of the Blood. — When blood is removed from its accustomed channels, it undergoes a marked chemical and physical change, termed clotting or coagulation. In the case of most vertebrates, almost as soon as the blood leaves the ves- 158 ANIMAL PHYSIOLOGY. sels it begins to thicken, and gradually acquires a consistence that may be compareti to that of jelly, so that it can no longer be poured from the containing vessel. Though some have rec- ognized different stages as distinct, and named them, we think that an unprejudiced observer might fail to see that there were any well-marked appearances occurring invnriably at the same moment, or with resting stages in the process, as with the development of ova. After coagulation has reduced the blood to a condition in which it is no longer diffluent, minute drops of a thin fluid gradually show themselves, exuding from the main mass, faintly colored, but never red, if the vessel in which the clot has formed has been kept quiet so that the red corpuscles have not been disturbed ; and later it may be noticed that the main mass is beginning to sink in the center (cupping) ; and in the blood of certain animals, as the horse, which clots slowly, the upper part of the coagulum (crassamentum) appears of a lighter color, owing, as microscopic examination shows, to the relative fewness of red corpuscles. This is the buffy-coat, or, as it occurs in inflammatory conditions of the blood, was termed by older writers, the crusta phlogistica. It is to be distinguished from the lighter red of certain parts of a clot, often the result of greater exposure to the air and more complete oxidation in consequence. The white blood-cells, being lighter than the red,' are also more abundant in the. upper part of the clot (buffy- coat). If the coagulation of a drop of blood withdrawn from one's own finger be watched under the microscope, the red cor- puscles may be seen to run into heaps, like rows of coins lying ngainst each other (rouleaux, Fig. 145), and threads of the greatest fineness are observed to radiate throughout the mass, gradually increasing in number, and, at last, including the whole in a mesh^York which slowly contracts. It is the forma- tion of this fibrin which is the essential factor in clotting ; the inclusion of the blood-cells and the extrusion of the serum naturally resulting from its formation and contraction. The great mass of every clot consists, however, of corpus- cles ; the quantity of fibrin, though variable, not amounting to more usually than about •?. per cent in mammals. The forma- tion of the clot does not occupy more than a few minutes (two to seven) in most mammals, including man, but its contraction lasts a very considerable time, so that serum may continue to exude from the clot for hours. It is thus seen that, instead of the plasma and corpuscles of the blood as it exists within the •■•""^'"^^^ ^Ijfj^jK^a^in^ -^*^3^^ insistence no longer have rec- , we think hat there bly at the s, as with ndition in thin fluid ain mass, h the clot scles have the main tnd in the ilowly, the ears of a ws, to the coat, or, as 'as termed Anguished the result idation in an the red, lot {buffy- •awn from le red cor- oins lying bds of the the mass, uding the the forma- »tting; the the serum m. of corpus- ounting to rhe forma- nutes (two jontraction ontinue to . instead of within the THE BLOOD. 159 living body, coagulation has resulted in the formation of two new products— serum and fibrin— differing both physically and chemically. These facts may be put in tabular form thus : Blood as it flows j Liquor sanguinis (plasma), in the vessels. ( Corpuscles. !„ , ( Fibrin. Coagulum ^ corpuscles. Serum. As fibrin may be seen to arise in the form of threads, under the microscope, in coagulating blood, and since no trace of it in any form has been detected in the plasma, and the process can be accounted for otherwise, it seems unjustifiable to assume that fibrin exists preformed in the blood, or arises in any way prior to actual coagulation. Fibrin belongs to the class of bodies known as proteids, and can be distinguished from the other subrP' isions of this group of substances by certain chemical as v s physical charac- teristics. It is insoluble in water and m solutions of sodium chloride; insoluble in hydrochloric acid, though it swells in this menstruum. It maybe whipped out .from the freshly shed blood by a bundle of twigs, wires, or other similar arrangement present- ing a considerable extent of surface; and when washed free ■from red blood-cells presents itself as a whitei, stringy, tough substance, admirably adapted to retain anything entangled in its meshes. If fibrin does not exist in the plasma, or does not arise directly as such in the clot, it must have some antecedents already existing as its immediate factors in the plasma, either before or after it is shed. We shall here present certain facts, and examine the conclu- sions drawn from them afterward : 1. Blood may be prevented from coagulating by receiving it in a solution of a neutral salt (magnesium sulphate, etc.), and upon certain chemical treatment precipitate a body which may be obtained by additional manipulation as a white, flaky sub- stance, that may be shown not to be fibrin, but which will clot and so give rise to this body. Such is the plasmine of Denis. 2. By treatment of plasma with solid sodium chloride, two bodies with different coagulating points, but belonging to the same jr-oup of proteids {globulins, soluble in saline solutions), may be obtained, denominated paraglobulin and fibrinogen re- spectively. 160 ANIMAL PHYSIOLOGY. 3. Paraglobulin may be obtained from serum also, and fibrin- ogen from certain fluids occurring normally {pericardial, pleu- ral, etc.) or abnormally (hydrocele fluid). 4. Serum added to these fluids sometimes induces coagula- tion. 5. Coagulation may occur spontaneously in the above-men- tioned fluids when removed from the natural seat of their for- mation. 6. A preparation, made by extracting serum or the whipped (defibrinated) blood added to specimen^ of certain fluids when they do not coagulate spontaneously, as hydrocele fluid, often induces speedy clotting. 7. This extract (fibrin-ferment) loses its properties on boil- ing, and a very small quantity suffices in most cases to induce the result. For these and other reasons this agent has been classed among bodies known as unorganized fermenta, which are distinguished by the following properties : They exert their influence only under well-defined circum- stances, among which is a certain narrow range of tempera- ture, about blood-heat, being most faA'orable for their action. They do not seem to enter themselves into the resulting prod- uct, but act from without as it were (catalytic action), hence a very small quantity suffices to effect the result. In all cases they are destroyed by boiling, though they bear exposure for* a limited prriod to n, ireezhig temperature. The conclusioi^t ■] awT ^" )m the above statements are these: 1. Coagulation res i . frciu the action of a fibrin-ferment on fibrinogen and r-;- ■..-globulin. 2. Coagulation results from the action of a fibri . i\ ^i'ment on fibrinogen alone. 3. Denis plasmine is made up of fibrinogen and paraglobulin. From observations, microscopic and other, it has been con- cluded that the corpuscles play an important part in coagula- tion by furnishing the fibrin-ferment ; but the greatest diver- sity of opinion prevails as to which one of the morphological elements of the blood furnishes the ferment, for each one of them has been advocated as the exclusive source of this fer- ment by different observers. The above conclusions do not seem to us to follow neces- sarily from the premises. It might be true that a solution of fibrinogen, on having fibrin-ferment added to it, would clot, and yet it would not follow that such was the process of coagula- tion in the blood itself. All specimens of hydrocele fluid, and similar ones not spontaneously coagulable, do not clot when , and fibrin- rdial, pleu- es coagula- ftbove-men- f their for- he whipped fluids when fluid, often ies on boil- 58 to induce it has been enia, which led circum- )f tempera- heir action, ilting prod- on), hence a In all cases xposure fof bs are these : •ferment on ts from the ais plasmine IS been con- in coagula- jatest diver- arphological each one of of this fer- ollow neces- Sk solution of uld clot, and of coagula- )le fluid, and (t clot when •^i^msamtmr-r r ^ ^ ^ •w^. IMAGE EVALUATION TEST TARGET (MT-3) <. 1.0 |^UtK£ Itt liii 12.2 Ml m 1.1 ■" 140 |20 | l;25 |U |L6 V^^^BhB^^^S HOl^^^fll^^^^E IVIH^^^^^^^^B *' .^ •Ifliilr:)! GorpGraticHi n WMT MAIN tTMIT «M||TM,N.V. I4SI0 (7U)tn-4SM «BigWBf.ni» I H ill Series. CIHM/ICMH CIHM/ICMH Collection de microfiches. Canadian Inatituta for Hiatorical Microraproductiona / Inatitut Canadian da microraproductiona hiatoriquaa r- THE BLOOD, 161 i fibrin-ferment is added. Moreover, fibrin-ferment has not been isolated as an absolutely distinct chemical individual, free from all impurities. OBecause fibrinogen and paraglobulin give rise, under certain circumstances (it is asserted), to fibrin, and since plasmine acts likewise, it does not follow that plasmine contains these bodies. Further, it is stated that in the blood. of crustaceans the clot arises from the corpuscles chiefly, which run together and blend into a homogeneous mass. The fibrin so called in such a case differs not a little chemically, it could probably be shown, if our tests were delicate enough to discover it, from that which is denominated fibrin in other cases. " Fibrin-ferment " seems to have been used to cover much ignorance and unnecessary invention, as we shall endeavor to show later on; and we can not but regard the reasoning in regard to the coagulation of the blood as evidence of an erroneous interpretation of certain facts on the one hand, and a large oversight of additional facts on the other hand. (Jn the mean time we turn to certain well-known phenomena which bear a clear interpretation : 1. The blood remains fluid in the vessels for some time after the death of an animal ; clots first in the larger vessels, and keeps fluid longest in the smaller veins. 2. The blood in the heart of a cold-blooded animal, as that of the frog or turtle, which will beat for days after the animal itself is dead, maintains its fluidity, but clots at once on removal. 3. The blood inclosed in a large vein removed be- tween ligatures does not coagulate for many hours (twenty- four to forty-eight). (J'here are also facts of an opposite nature, thus : 1. When blood passes from a blood-vessel into one of the cavities of the body, it clots as if shed externally. 2. If a ligature be passed tightly around an artery so as to rupture the elastic coat, co- agulation ensues at the site of the ligature. 3. A similar clotting results when the inner coat of a blood-vessel is dis- eased, as in the case of roughening of the valves of the heart from inflammation, or the changes that give rise to aneurism of an artery. 4. A wire, thread, or other like foreign bodyi intpsduced into a vein, is speedily covered with fibrin. ^These facts, and others of like character, have been inter- preted as indicating that the living tissues of the blood-vessel or heart in some way prevent coagulation, but as to details there is difference of opinion. Some believe that the fibrin-ferment (essential to coagulation, according to their view) is formed by 11 i les ANIMAL PHYSIOLOGY. K the corpuscles constantly, but in the above cases and during life is not effective because at once removed by the vessel walls ; while others are of opinion that the living cells comjiosing these walls prevent the formation of the ferment. Even when injected into the blood-vessels, fibrin-ferment does not induce coagulation, nor does the constant death of the blood-cells, supposed thus to give rise to this substance, cause clotting. But the truth is, there is no necessity for all these somewhat artificial views, which seem to us to smack more of the labora- tory than of nature. : We would explain the whole matter somewhat thus : "What the blood is in chemical composition and other properties from moment to moment is the result of the complicated interaction of all the various cells and tissues of the body. Any one of these, departing from its normal behavior, at once affects the blood ; but health implies a constant effort toward a certain equilibrium, never actually reached but always being striven after by the whole organism. The blood can no more maintain its vital equilibrium, or exist as a living tissue out of its usual environment, than any other tissue. But the exact circum- stances under which it may become disorganized, or die, are legion ; hence, it is not likely that the blood always clots in the same way in all groups of animals, or even in the same group. The normal disorganization or death of the tissue re- sults in clotting ; but there may be death without clotting, as when the blood is frozen, in various diseases, etc. To say that fibrin is formed during coagulation expresses in a crude way a certain fact, or rather the resultant of many facts. To explain: When gunpowder and certain other ex- plosives are decomposed, the result is the production of cer- tain gases. If we knew these gases and their mode of com- position but in the vaguest way, we should be in much the same position as we are in regard to the coagulation of the blood. ^here is no difficulty in understanding why the blood does not clot in the vessels after death so long as they live, nor why it does coagulate upon foreign bodies introduced into the blood- stream. So long as it exists under the very conditions under which it began its being, there is no reason why the blood should become disorganized (clot). It would be marvelous if it did clot, for then we could not understand how it could ever have been developed as a tissue at all. It is just as reasonable d during life vessel walls ; iposing these )rin-ferment death of the stance, cause )ae somewhat >f the labora- ; thus : What operties from )d interaction Any one of ae affects the 3.rd a certain being striven lore maintain it of its usual jxact circum- d, or die, are (vays clots in L in the same the tissue re- nt clotting, as n expresses in tant of many ain other ex- iiction of cer- node of com- in much the ilation of the he blood does live, nor why nto the blood- ditions under hy the blood I marvelous if it could ever as reasonable THE BLOOD. 168 to ask why does not a muscle-cell become rigid (clot) in the body during life. (Probably in no field in physiology has so much work been done with so little profit as in the one we are now discussing; and, as we venture to think, owing to a misconception of the real nature of the problem. We can understand the practical im- portance of determining what circumstances favor coagulation or retard it, both within the vessels and without them ; but from a theoretical point of view the subject has been exalted out of all proportion to its importance; and we should not have dwelt so long upon it, or burdened the student with some of the theories we have stated, except . in deference to the views held by so many physiologists. (It is not surprising that, looking at the subject with a dis- torted mental perspective, one theory should have replaced an- other with such rapidity. It is, however, of practical impor- tance to the medical student to remember some of the factors that hasten or retard, as the case may be, the coagulation of the blood. Coagulation is favored by gentle movement, contact with foreign bodies, a temperature of about 38° to 40° C, addi- tion of a small quantity- of water, free access of oxygen, etc. The process is retarded by a low temperature, addition of abundance of neutral salts, extract of the mouth of the leech, peptone, much water, alkalies, and many other substances. The excess of carbonic anhydride and diminution of oxygen, seem to be the cause of the slower coagulation of venous blood, hence the blood long remains fluid in animals asphyxiated. A little reflection suffices to explain the action of most of the fac- tors enumerated. Any cause which hastens the disintegration of the blood-cells must accelerate coagulation ; chemical changes underlie the changes in this as in all other cases of vital action. Slowing of the blood-stream to any appreciable extent likewise favors clotting, hence the explanation of the success of the treatment of aneurisms by pressure. It is plain that in all such cases the normal relations between the blood and the tis- sues are disturbed, and, when this reaches a certain point, death (coagulation) ensues, as with any other tissue. OUiiioal tnd PatholiviML— The changes in the blood that characterize certain abnormal states are highly instructive. If blood from an animal be injected into the veins of one of an- other species, the death of the latter often results, owing to non- adaptation to the blood already in the vessels, and to the tissues of the creature generally. The corpuscles break up — the change MMill^ 164 ANIMAL PHYSIOLOGY. of conditions has been too great. Deficiency in the quantity of the blood as a whole {oUgcemia) causes serious change in the functions of the body ; but that a hsemorrhage of considerable extent can be so quickly recovered from by many persons, speaks much for the recuperative power of the blood-forming tissues. Various kinds of disturbances in these blood-forming organs result in either deficiency or excess of the blood-cells, and in some cases the appearance of unusual forms of corpuscles. (Anamia may arise from a deficiency either in the numbers or the quality of the red cells ; they may be too few, deficient ®»**° SS) ^ Via. IM. Fio. 153. Fio. 167. Fio. 168.— OutUnea of red corpuwles in • OMe of profound Anaamla. 1, 1, normal corpuacles ; S, Uu^ red oorpuaole-meRiOooTte ; S, S, Terr irregular f orma-voilUlooTtea ; 4, very ■mall, deep-red oorpuaoles— mlcroQjiiea. . .. ^ j. ... „ ^ Fio. 164.— Origin of micro(7tea from red corpoaelesbjrpraatMi of budding aodflaiion. Speci- men from red marrow. .... .. ^ . Fio. 166.— Nucleated red blood-corpuscle* from blood in cane of leukamta. Fio. ise.— Oorpuaele^ containing red blood-corpuaole*. 1, from blood of child at term ; 8, from blood of a leuktfmio patient. . . ... Fio. 167.— o, 1, 8, 8;apleen-cella containing red blood-corpuaclee. b, from marrow ; 1, cell con- taining nine rednorpuacle* ; S, cell irtth rrddish granular pigment ; 8, fuaiform cell con- taining a lingie red corpuscle. «, oonnectiTe-tisnie corpuHole from subcutaneous tissue of young rat, Mowing the inthujelliilar deretopment of red blood-oorpuscles. (Figs. IS>-16i , after Osier.) in size, or lacking in the normal quantity of heemoglobin. In one form {pemidoua otuemta), which often proves fatal, a variety of forms of the red blood-cells may appear in the blood- stream ; some may be very small, some larger than usual, others le quantity of hange in the considerable lany persons, lood-forming lood-forming e blood-cells, of corpuscles. the numbers few, deficient ) ^ , nomuU oorpuicles ; lioUillooTtea ; 4, very iKkodflMioii. Sped- faUd at term ; 9, from marrow ; 1, cell con- 8, fiMlform cell con- iboutaneoiu tiMue of ■oka. (Flga. 1SS-1S7, moglobin. In roves fatal, a \,T in the blood- n usual, others THE BLOOD. 166 nucleated, etc. Again, the white cells may be so multiplied that the blood may bear in extreme cases a resemblance to milk. In these cases there has been found associated an unusual condition of the bon,e-marrow, the lymphatic glands, the spleen, and, some have thought, of other parts. The excessive action of these organs results in the production and discharge into the blood-current of cells that are immature and embryonic in character. This seems to us an example of a rever.iion to an earlier condition. It is instructive also in that the facts point to a possible seat of origin of the cells in the adult, and, taken in connection with other facts, we may say, to their normal source. These blood-producing organs, having too much to do in disease, do their work badly — ^it is incom- plete. Although the evidence, from experiment, to show that the nervous system in mammals, and especially in man, has an in- fluence over the formation and fate of the blood generally, is scanty, there can be little doubt that such is the case, when we take into account instances that frequently fall under the notice of physicians. Certain forms of aneemia have followed so di^ rectly upon emotional shocks, excessive mental work and worry ,\ as to leave no uncertainty of a connection between these and thei changes in the blood ; and the former must, of course, have acted) chiefly if not solely through the nervous system. It will thus be apparent that the facts of disease are in har- mony with the views we have been enforcing in regard to the blood, which we may now briefly recapitulate. Suniiuury.^^Blood may be regarded as a tissue, with a fluid matrix, in which float cell-contents. Like other tissues, it has its phases of development, including origin, maturity, and death. The colorless cells of the blood may be considered as original undifferentiated embryo cells, which retain their primi- tive character ; the non-nucleated red cells of the adult are the mature form of nucleated cells that in the first instance are colorless, and arise from a variety of tissues, and which in certain diseases do not mature, but remain, as they originally were at first, nucleated. When the red cells are no longer fitted to discharge their functions, they are in some instances taken up by amoeboid organisms (cells) of the spleen, liver, etc. rfhe chief function of the red corpuscles is to convey oxy- gen ; of the white, to develop as required into some more differ- entiated form of tissue, act as porters of food-material, and '^W ammtm 166 ANIMAL PHYSIOLOGY. probably to take up the work of many other kinds of cells when the needs of the economy demand it. The fluid matrix or plasma furnishes the lymph by which the tissues are direct- ly nourished, and serves as a means of transport for the cells of the blood. The chemical composition of the blood is highly complex, in accordance with the function it discharges as the reservoir whence the varied needs of the tissues are supplied ; and the immediate receptacle (together with the lymph) of the entire waste of the body ; but the greater number of substances exist in very minute quantities. The blood must be maintained of a certain composition, varying only within narrow limits, in order that neither the other tissues nor itself may suffer. The normal disorganization of the blood results in coagula- tion, by which a substance, proteid in nature, known as fibrin, is formed, the antecedents of which are probably very variable throughout the animal kingdom, and are likely so even in the same group of animals, under different circumstances ; and a substance abounding in proteids (as does also plasma), known as serum, squeezed from the clot by the contracting fibrin. It represents the altered plasma. Certain well-known inorganic salts enter into the composi- tion of the blood — ^both plasma and corpuscles — ^but the princi- pal constituent of the red corpuscles is a pigmented, ferrugi- nous proteid capable of crystallization, termed heemoglobin. It is respiratory in function. w. \ THE CONTRACTILE TISSUES^^^ That contractility, which is a fundamental property in some degree of all protoplasm, becoming pronounced and definite, giving rise to movements the character of which can be pre- dicted with certainty once the foi-m of the tissue is known, finds its highest manifestation in muscular tissue. Very briefly, this tissue is made up of cells which may be either elongated, fusiform, nucleated, fnely striated lengthwise, but non-striped transversely, united by a homogeneous cement substance, the whole constituting non-striped or involuntary muscle ; or, long nucleated fibers transversely striped, covered with an elastic sheath of extreme thinness, bound together into small bundles by a delicate connective tissue, these again into larger ones, till what is commonly known as a "muscle" L. THE CONTRACTILE TISSUES. 167 inds of cells fluid matrix les are direct- for the cells y complex, in the reservoir ied; and the of the entire bstances exist maintained of row limits, in r suffer. ts in coagula- lown as fibrin, very variable BO even in the tances; and a asma), known ing fibrin. It the composi- )ut the princi- ented, ferrugi- emoglobin. It aperty in some I and definite, 3h can be pre- Is known, finds which may be ed lengthwise, eneous cement »r involuntary iriped, covered 3und together le, these again is a "muscle" is formed. This, in the higher vertebrates, ends in tdugh, inelastic extremities suitable for attachment to the levers it may be required to move {bones). Vm, 1G& Fio. 180. (8«ppey.) i libers Fio. 188.— HuMmlar flbera from the urinary bladder of the hnman wiUect. 1 k 800. 1, 1, 1, nuclei ; H, S, S, borders of some of the fibers ; S, 8, iHolated fibers ; 4, 4, two 1 Joined together at S. Fio. lW.-Huscular fibers from tiie aorta of the calf. 1 x 800. (Sappey.) 1, 1, fibers Joined with each other ; S, 8, 8, isolated fibers. OompaTatiTe. — The lowest animal forms possess the power of movement, which, as we have seen in Amoeba, is a result rather of a groping after food ; and takes place in a direction it is im- possible to predict, though no doubt regulated by laws definite enough,nf] our knowledge were equal to the task of defining them. ^^ Those ciliary movements among the infusorians, connected with locomotion and the capture of food, are examples of a pro- toplasmic rhythm of wonderful beauty and simplicity. Muscular tissue proper fire appears in the Ccelenterata, bui> not as a wholly independent tissue in all cases. In many coelenterates cells exist, the low- er part of which alone forms a delicate muscular fiber, while the superficial portion {myoblast), composing the body of the cell, may be ciliated and is not contractile in any special Flo. l«).-Hyob1a8ts of a Jelly-flsh, the Me- d%ua Aurtlia (Ciaua). iwfiitfi^ 168 ANIMAL PHYSIOLOGY. sense. The non-striped muscle-cells are most abundant among the invertebrates, though found in the viscera and a few other parts of vertebrates. This form is plainly the simpler and more primitive. The voluntary muscles are of the striped variety in articulates and some other invertebrate groups and in all vertebrates ; and there seems to be some relation between the size of the muscle-fiber and the functional power of the tissue — the finer they are and the better supplied with blood, two constant relations, the greater the contractility. Whether a single smooth muscle-cell, a striped fiber {ceU), or a collection of the latter (muscle) be observed, the invariable result of contraction is a change of shape which is perfectly definite, the long diameter of the cell or muscle becoming shorter, and the short diameter longer. Ciliury Morenentti — This subject has been already considered briefly in connection with some of the lower forms of life pre- sented for study. It is to be noted that there is a gradual replacement of this form of action by that of muscle as we ascend the auimal scale ; it is, however, retained even in the highest animals in the discharge of functions analogous to those it fulfills in the invertebrates. Thus, in Vorticella, we saw that the ciliary movements of the peristome caused currents that carried in all sorts of parti- cles, including food. In a creature so high in the scale as the frog we find the alimentary tract ciliated ; and in man himself a portion of the respiratory tract is provided with ciliated cells concerned with assisting gaseous interchange, a matter of the highest importance to the well-being of the mammal. As be- fore indicated, ciliated ceils are found in the female generative organs, where they play a part already explained. It is a matter of no little significance from an evolutionary point of view, that ciliated cells are more widely distributed in the fcBtus than in the adult human subject. As would be expected, the movements of cilia are affected by a variety of circumstances and reagents : thus, they are quick- ened by bile, acids, alkalies, alcohol, elevation of temperature up to about 40° C, etc. ; retarded by cold, carbonic anhydride, ether, chloroform, etc. In some cases their action may be arrested and re-estab- lished by treatment with reagents, or it may recommence with- out such assistance. All this seems to point to ciliary action as falling under the laws governing the movements of protoplasm THE CONTRACTILE TISSUES. 169 indant among id a few other e simpler and >f the striped te groups and ation between power of the »d with blood, ity. 1 fiber (cell), or ;he invariable •h is perfectly sole becoming ady considered ms of life pre- icement of this nd the animal test animals in ■> fulfills in the movements of sorts of parti- be scale as the in man himself th ciliated cells I matter of the . mmal. As be- aale generative i. jx evolutionary r distributed in lia are affected they are quick- >f temperature •nic anhydride, [ and re-estab- >mmence with- iliary action as i of protoplasm in gen al. It is important to bear in mind that ciliary action may go on in the cells of a tissue completely isolated from the animal to \7hich it belongs, and though influenced, as just ex- plained, by the surroQndings, that the movement is essentially automatic, that is, inu .^pendent of any special stimulus, in which respect it differs a good deal from voluntary muscle, which usually, if not always, contracts only when stimulated. The lines along which the evolution of the contractile tissues has proceeded from the indefinite outflowings and withdraw- als of the substance of Amoeba up to the highly specialized movements of a striped muscle-cell are not all clearly marked out ; but even the few facts mentioned above suffice to show gradation, intermediate forms. A similar law is involved in the muscular contractility manifested by cells with other func- tions. The automatic (self-originated, independent largely of a stimtdus) rhythm suggestive of ciliary movement, more manifest in the earlier developed smooth muscle than in the voluntary striped muscle of higher vertebrates, indicating further by the regularity with which certain organs act in which this smooth muscular tissue is predominant, a relation- ship to ciliary movement something in common as to origin — in a word, an evo- lution. And if this be borne, in mind, we believe many facts will appear in a new light, and be invested , with a breadth of meaning they would not otherwise possess. The IrritabiUtj of Kmwle •ad Herve. — An animal, as a frog, deprived of its brain, will remain motion- less till its tissues have died, unless the animal be in some way stimulated. If a muscle be isolated from the body with the nerve to which it belongs, it will also remain passive; but, if an electric current be passed into it, if it be pricked, pinched, touched with a hot body or with certain chemical reagents. Fia. ISl.— Nodes of lUnvier and lines of Fronuum (BkiiTler). A. IntercoaUI nerve of tbe mouw, treated with silver nitrate. B. Kerve-flber from the lotaticnerTe of a full-grown ralibit. jl.nodp of Banvler ; M, meduUarjr mbstanoe rendered tranana>«nt by the action of glycerine; CV,aziii- cylinoer preeenting the linea m Fromann, which are Tery dietinct near the node. The lines are less marked at a distance from the node. ; jSxSSHHiJiai IMMMMMii iMMMM mmsm ?;■ ITO ANIMAL PHYSIOLOGY. contraction ensues ; the same happening if the nerve be thus treated instead of the muscle. The changes in the muscle and the nerve will be seen later to have much in common ; the mus- cle alone^ however, con/racto, undergoes a visible change of form. Now, the agent causing this is a stimvlus, and, as we have seen, may be mechanical, chemical, thermal, electrical, or nerv- ous. As both nerve and muscle are capable of being functionally af- fected by a stimulus, < they are said to be irrita- ble; and, since muscle does not contract with- out a stimulus, it is said to be non-atUomatic. Now, since muscle is supplied with nerves as well- as blood-vessels, which end in a peculiar way beneath the muscle- covering {aarcolemma) in the very substance of the protoplasm {end- 4—5 Via. 162.— Mode of termliuUioii of the motor nenrea (Flint, After Itoa«cet). A. Primitiye faacieulus of the thyro-hyoid muacle of the human subject, and it* nerve-tube: 1, 1, primitive muacular fttadcului: )i, nenre-tube; 8, medullsiy lubstMioe of the tube, which issaen extendingto the terminal plate, where •■ • IbenetOhthe it diwippears ; 4, terminal plate situated aarcolemma— that la to aay, between it and the ele- mentary flhrilUe ; 6, B, aarcolemma. B. PrimltlTe faacicufua of the intercoatal moade of the lisard, in lailaiea) it miffht be that which a nerve-tube terminatea: 1. 1. sheath of the V**''*^)* '•' "mS"" "« «-"»* nerve-tube; 8, nucleua of the AMth : 8, S, aaroo- when mUScle Seemed to lemma becoming oontlnuoua with the aheath ; 4, medullary aubatance of the nerve-tube, oeadng Ije stimulated, aS above abruptly at the aite of the terminal plate ; 6, 5, ter^ . ', . , -■ . , mliuU plate ; «, 6, nuclei of the plate ; 7, 7, granular indicated, the reSPOUSlVe aubatance which forms the principal element of the ^ ,. ^ ,, terminal plate and which Is continuous with the contraction WaS really axis-cylinder ; 8, 8, undulations of the sarcolemma , , ,, ., i reproducing those of the flbrillte ; 9, B, nuclei of the due to the eXClted Uerve **"*" *°"°*' terminals ; and thus has arisen the question, Is muscle of itself really irritable ? What has been said as to the origin of muscular tissue Fio. Its.— Intrafibrlllar tcrminatlona of the motor nerve in atriated muacle, atained with gold chloride (Landoia). points very strongly to an affirmative answer, though it does not follow that a property once possessed in the lower forms of [ APPLICATIONS OP THE GRAPHIC METHOD. 171 erve be thus muscle and on; themus- unge of form. , as we have ical, or nerv- )h nerve and capable of stionally af- a stimulus, to be irrita- since muscle ontract with- ilus, it is said tUomatic. ace muscle is ith nerves as )lood - vessels, in a peculiar ;h the muscle- {sarcaiemma) r substance of Ulasm {end- might be that icle seemed to ited, as above the responsive a was really excited nerve and thus has »ble? nscular tissue :le, lUliied with gold bough it does ower forms of a tissue may not be lost in the higher ; hence the resort to ex- periments which have long been thought to settle the :natter : 1. The curare experiment may be thus performed : Lift up the sciatic nerve of a frog, and ligature the whole limb (ex- clusive of the nerve) so that no blood may reach the muscles ; then inject curare, which paralyzes nerves but not muscles, into the general circulation through the posterior lymph-sac. On stimulating the sciatic nerve the muscles of the leg beneath the ligature contract, while no contraction of the muscles of the opposite leg follows from stimulation of its sciatic nerve. In the latter case the curare has reached the nerve terminals through the blood ; in the former, these were left uninfluenced by the poison. If, now, the muscle itself be directly stimulated in the latter case, contraction follows, from which it is con- cluded that curare has dastroyed the functional capacity of the nerve {ierminals), but not of the muscle. 2. Stimulation of those parts of muscles in which no nervous terminations have been found, as the lower part of the sartorius muscle in the frog, is followed by contraction. 3. Certain substances (as ammonia), when applied directly to the muscle, cause contraction, but are not capable of pro- ducing this effect when applied to the nerve. From these and various other facts it may be concluded that muscle possesses independent irritability. APPLICATIONS OF THE GRAPHIC METHOD TO THE STUDY OP MUSCLE PHYSIOLOGY. It is impossible to study the physiology of muscle to the best advantage without the employment of the graphic method ; and, on the other hand, no tissue is so Well adapted for investi- gation by the isolated method — ^i. e., apart from the animal to which it actually belongs — as muscle ; hence the convenience of introducing at an early period our study of the physiology of contractile tissue and illustrations of the graphic method, the general principles of which have already been considered. The descriptions in the text will be brief, and the student is recommended to examine the figures and accompanying ex- planations with some care. Chronograph^ Bavolviag Oylinden^ «te.— Fig. 164 represents one of the earliest forms of apparatus for the measurement of brief intervals of time, consisting of a simple mechanism for pro- SHHMMttl (■Bft U^ 172 ANIMAL PHYSIOLOGY. ducing the movement of a cylinder, which may be covered with smoked paper, or otherwise prepared to receive impressions made upon it by a point and capa- ble of being raised or lowered, and its movements regulated. The cylinder is ruled vertically into a certain number of spaces, so that, if its rate of revolution is known and is constant (very im- portant), the length of time of any evfmt recorded on the sen- sitive surface may be accurately known. This whole apparatus may be considered a chrono- graph in a rough form. ^ut a tuning-fork is the most relit; We form of chronograph, I a provided it can be kept in con- stant action so long as required ; and is provided with a recording apparatus that does not cause enough friction to interfere with its vibrations. Fig. 166 illustrates one ar- rangement that answers these b', weiritt acting m motive power ; c, d, nnnditinnR f airl v well BmainSiata for regulating %e velocity l^^nuiuoiiH ittiriy weii. of the cylinder ; e, marker recording a The marker, Or chronOgraph, line on cyli '.der, ' _ . in the more limited sense, is kept in automatic action by the fork interrupting the current from a battery at a certain definite rate answering to its own proper note. Fio. 164.— Original chronometer, devlaedby Thomaa Young, for measuring minute portions of time (after MoKendrick), a, cylinder revolving on vertical axis ; Fio. 105.— Myographic tracing, such as la obtained when the cylinder on which it is written does not revolve during the contraction of the muscle (after McKendrick). * Marey's chronograph, which is represented at h above, and in more detail below, in Fig. 167, consists of two electro-magnets armed with keepers, between which is the writer, which has a > covered with 9 impressions oint and capa- r lowered, and pilated. The rertically into of spaces, so revolution is tant (very im- kh of time of d on the sen- be accurately ole apparatus ed a chrono- orm. >rk is the most chronogi'aph, B kept in con- g as required ; th a recording oes not cause interfere with ;rates one ar- 9,nswers these j-ell. ' chronograph, ited sense, is ig the current ing to its own m which tt is written cKendricIc). * t h above, and lectro-magneta iT, which has a APPLICATIONS OP THE GRAPHIC METHOD. little mass of steel attached to it, the whole working in unison with the tuning-fork, so that an interruption of the current 0(9. implies a like change of position of the writing-style, which is always kept in contact with the recording surface. to?SSoh,5K^;K Vf&S totSJX tuning-fork ; - to the battery. Fig. 177 shows the arrangements for recording a dngle muscle contraction, and Fig. 178 the character of the tracing obtained. . ^ * xt A mutele-nerve preparation, which usually consists of the gastrocnemius of the frog with the sciatic nerve attached, lU ANIMAL PHYSIOLOGY. 41 clamped by a portion of the femur cut off with the muscle, is made, on stimulation, to raise a weighted lever which is at- tached to a point writing on a cylinder moved by some sort of clock-work. In this case the cylinder is kept stationary dur- ing the contraction of the mus- cle; hence the records appear as straight vertical lines. For recording movements of S^^"temSrt?fe^«iS»Sm^ great rapidity, so that the in- C:. Ttoe (.«« Ro«ntha). ^^^^^ between them may be apparent, such an apparatus as is figured below (Pig. 169) an- swers well, the vibrations of a tuning-fork being written on a Fia. IflS.— Muacte-nerve preparatton, ahowing gairtrocnemiua muacle, sciatic nerve, and Fw. las.'-apriiw mro((f»ph of Du Boia-BMrmond (after RoaeBthaD^TTiit amngMMnta for iti^Smi^wlSM details an aimilar to tboae for {wndulum myoipraph (Fig. 177). blackened glass plate, shot before a chronograph by releasing a spring. Several records may be made successively by more compli- cated arrangements, as will be explained by another figure later. The Apparatus used for the Stimulation of Muscle. It is not only important that there should be accurate and delicate methods of recording muscular contractions, but that the muscle, is which is at- , writing on a Y some sort of this case the kationary dur- •n of the miis- 3Cords appear sal lines, movements of ) that the in- them may be (Fig. 169) an- g written on a Im) WTMigeineiitii for - mph (FJg. 177). >h by releasing f more compli- another figure X OF MUBCLK. )e accurate and itions, but that APPLICATIONS OP THE GRAPHIC METHOD. 176 there be equally exact methods of applying, regulating, and measuring the stimulus that induces the contraction. Fijr 170 gives a representation of the inductonum of Du Boi8.Reymond, by which either a single brief stimulation or a from ^'•l*«r'i*'T''^SSJ^^^^S!^V^l^e^^e^ litweeii prtai^jr coll and coU. thiM indM^ ««^''i *S»?hS^^ A lume^^DM'r to •ttrmotod from icrew /, wires around Bott Iron of Mfpn .SSfSEriiSSriik iron ceaaes to be a magnet necea- wd current ttaiia brrt^ : Vmt when .^ W^^JJ" '^e^Suto^eated. Thta may iwilr, and, hammw i^^tai^S J?^;J^ ^ S^im»y becSarer i?om diagram, Fte. ^Brisa'g'iSss£?w'.2sfssi^ series of such repeated with great regularity and frequency may be effected. The apparatus consists essentially of a pn- no. 171.-Dlagi»mmaUo repwaenUtton of the working of Big. 170 (after Ro«nthai> I 17« ANIMAL PHYSIOLOGY. mary coil, secondary coil, magnetic interrupter, and a scale to determine the relative strength of the current employed. The instrument is put into action by one or more of the various well-known galvanic cells, of which Daniell's are suitable for most experiments. Fro. ITS. ^»rru»".r2SSiS?&.S^"?^.s^^ S'usO. The lever e lever writes the iBhrid taegalpotae ^^^"WheB' deKi«e of extension effected (Mter mrSt Du Bois-Rermowl (after Bosm welghts'sre ptaoedTin scftle-panF, r RoaentlMl). ^ ^ . . .. The access to, or exclusion of the current from, the induc- torium is effected by some of the forms of keys, a. specimen of which is illustrated in Fig. 173. The moist chamber, or some other means of preventmg the drying of the preparation, which would soon result in impaired action, followed by death, is essential. A moist chamber con- sists essentially of an inclosed cavity, in which is placed some wet blotting-paper, etc., and is usually made with glass sides. The air in such a chamber must remain saturated with mowt- ure. „ti ^ , wkm iivtitkL* APPLICATIONS OF THE OBAPHIC METHOD. 177 ^d a scale to iployed. The the various e suitable for A good knowledge of the subject of electricity is especially valuable to the student of physiology. But there are a few ele- mentary facts it is absolutely necessary to bear in mind : 1. Au induced current exists only at the moment of making or break- ing a primary (battt^i'y) current. 2. At the moment of making, the induced current is in the opposite direction to that of the primary current, and the reverse at breaking. 3. The strength of the induced current varies with the strength of the primary current. 4. The more removed the secondary coil from the primary the weaker the current (induced) becomes. The clock-work mechanism and its associated parts, as seen in Fig. 174, on the right, is usually termed a myograph. ». ITS. in the moistHduunber, I tlw pUteof smoked pUoedf In Male-pan F, • may be attached at b I not pas throuRh the t are of metal, and, on gr than the wtraa. a tt lebment to a table, etc N>m, the induc- I, a specimen of preventing the ult in impaired t chamber con- is placed some ith glass sides, tted with moist- Fio. 174.— Arrangement ot apparatui for tranamimion of mutcular movement bjr tambour* (after McKendriok). a, italvanic element ; 6, prtmanr ooU ; e, aeoondaty otdl ot inducto- rinm ; d, metronome tor interrupting primary draift when induction ourrent ia eent to electrode* k ; h, foroep* for femur : fine muacie, whtdi i* not here repceaeated, 1* attached to tlie receivinir tambour a, by which movement ii traamitted to recording tambour e, whidi write* on cylinder f. Instead of muscular or other movements being communi- cated directly to levers, the contact may be through columns Fia. ITS.— Tambour ot Marey (after McKendrick). a, metaUie caae ; b, thin Indla-nibber i brane; o, thin disk of ahiminiumMppattinglqvaril, a amaU portion of which ciUy la repre- ■entwd ; e, acrew for plaoinii ■uppcrt of lever Terttcally orer e i /, metalUc tuba oommuni- oatinc with cavity of utmbour for aWchmiit to an India-nibber tube. It I ,■ 178 ANIMAL PHTBIOLOOT. of air, which, it will be apparent, must be capable of communi- cating very slight changes if the apparatus responds readily to the alterations in volume of the inclosed air. Fig. 175 represents a Marey's tambour, which consists essen- tially of a rigid metallic case provided with an elastic top, to which a lever is Attached, the whole being brought into com- munication with a column of air in an elastic tube. The work- ing of such a mechanism will be evident from Figs. 174 and 176. Flo. 178.— TMqboun of Mkrejr arfwind (or tnnwrnlMton of mormnMit (•ftar McKendrick). a, neiMag tambour ; b, ImlU-ruDber tube ; e. regiitwring tambour ; d, nplnl at wire, owlBg to elMtlcity at which, when toniion is removed from a, the leTer Mcenda. The greatest danger in the use of such apparatus is not fric- tion but oscillation, so that it is possible that the original move- ment may not be expressed alone or simply exaggerated, but also complicated by additions, for which the apparatus itself is responsible. Apparatus of this kind is not usually employed much for experiments with muscle; such an arrangement is, however, shown in Fig. 174, in which all will be seen — ^a metronome, the pendulum of which, by dipping into cups containing mercury, makes the circuit. Such or a simple clock may be utilized for indicating the longer intervals of time, as seconds. A Single Simple Muscular Contraction. Xqtriamtal Tkoto. — The phases in a single twitch or muscu- lar contraction may be studied by means of the pendulum lonsists essen- Blastic top, to yht into com- e. Thework- B. 174 and 176. It (after McKendritA). or ; d, tpiral o( wire, rer uoenda. ituB is not frio> original move- caggerated, but paratus itself is oyed much for nt is, however, metronome, the ining mercury, be utilized for ds. iCTION. mtch or muscu- the pendulum ii 180 ANIMAL PHTSIOLOOY. the ■craw, d, to in eieotrlooontiiiui^ with the wire,*, of the Mine primuT coil. Thesr: 'it, (I, uA the rod. c, are provided wltnplatinum poinu. and both we inanlMed br tuMtt oi the ebonite block, e. The circuit of the priBUwy oul to which « and y bekMV ■ cloaed ■• lonR M <* and d are in contact When in fta awiiic the tooth, a', knocks e away from u|At to bear on the glass plate, and when at rest describes an aro of a circle of large radlua. ilie tuning-fork, /lends only seen), serres to mark the time (after Foster). myograph (Fig. 177). It consists of a heavy pendulum, which swings from a position on the right to a corresponding one on the left, where it is secured by a catch. During the swing of the pendulum, which carries a smoked glass plate (by means of arrangements more minutely described below the figure), a tuning-fork writes its vibrations on the plate, on which is inscribed the marking indicating the exact moment of the breaking of an electric current, which gives rise to a muscle contraction that is also recorded on the plate. The tracing on analysis presents : 1. The record of a tuning- fork making one hundred and eighty vibrations in a second. 2. The parallel marking of the lever attached to the muscle before it began to rise. 3. A curve, at first rising slowly, and then rapidly to a maximum. 4. A curve of descent similar in character, but somewhat more lengthened. We may interpret this record somewhat thus: 1. A rise of the lever answering to the shortening of the muscle to which it a h ¥m. 178.— Muscle-curre obtained by the pendulum niyagraph (niatar). Bead fMm left to right The latent period to indicated fy the apace between a and b, the length! qf which to meaaur^d by the waves of a tuntn, in a second; and in like manner I be estimated. r one hundred and entity double TibraUoas I the other iduMca of the contraction may is attached following upon the momentary induction shock, as the entrance of the current into the nerve, the stimulation of which causes the contraction, may be called. 3. A period before the contraction begins, which, as shown by the time marking, occupies in this case r^, or about ij^ of a second. In the tracing the upward curve indicates that the contraction is at first rela- rooil. Tbemijif, I br mrmrn ci llwloaKbclaMd •• le Away from d, the I the electrodea oon- The lever, (, the i pUte, and wh«i at ' I only seen), serre* .ulum, which Inding one on the swing of ,te (by means the figure), a on which is >ment of the ) to a muscle i of a tuning- B in a second. o the muscle ig slowly, and ant similar in 1. A rise of cle to which it APPLICATIONS OF THE GRAPHIC METHOD. 181 tively slow, then more rapid, and again slower, till a brief sta- tionary period is reached, when the muscle gradually but rap- idly returns to its previous condition, passing through the same phases as during contraction proper. In other words, there is a period of rising and of falling energy, or of contraction, and relaxation. 4. A period during which invisible changes, as will be explained later, are going on, answering to those in the nerve that cause the molecular commotion in muscle which precedes the visible contraction — the latent period, or the period of latent stimulation. The facts may be briefly stated as follows : The stimulation of a muscle either directly or through its nerve causes contrac- tion, followed by relaxation, both of which are preceded by a latent period, during which no visible but highly important molecular changes are taking place. The whole chain of ev^its is of the briefest duration, and is termed a muscle contraction. The tracing shows that the latent period occupied rather more than ^ second, the period of contraction proper about t^, and of relaxation ^^ second, so that the whole is usuitUy begun and ended within Vr second; yet, as will be learned later, many chemical and electrical phenomena, the concomitants of vital change, are to be observed. In the case just considered it was assumed that the muscle was stimulated through its nerve. Precisely the same results would have followed had the muscle been caused to contract by the momentary application of a chemical, thermal, or me- chanical stimulus. If the length of nerve between the point of stimulation and the muscle was considerable, some difference would be observed . Bead ttom left to ttefengr^orwhiohis fbty double ilfaratiaiiB the oontraotion majr ction shock, as stimulation of L period before time marking. In the tracing is at first rela- Fio. ITS.— Dtagrammatio r e p wcn tatl o a ot the meawrement of yekwitr of Derroua impulse (Feeler). Tracing taken b/ pendulum mjrocraph (Fig. 177). The nerre of lame muacle- nerve preparation iaatlmuiatad in one caae aa nur aa poaiible from maecle, in the other aa neartoitaa pomible. Latent period ia a6, oft*, reapective^. Diflttenoe between oA and oylwttMttML of ooorae. Iragth of time oecnpled bgr nervooa impulae in travrilng along in the latent period if in a second case the nerve were stimu- lated, say, close to the muscle. This is repreflented in Fig. 179, tiiUISgiimmsti-- IT 189 ANIMAL PHTSIOLOGT. in which it is seen that the latent period in the latter case is shortened by the distance from b' to b, which must be owing to the time required for those molecular changes which, occur- ring in a nerve, give rise to a contraction in the muscle to which it belongs ; in fact, we have in this method a means of estimat- ing the rate at which these changes pass along the nerve — ^in other words, we have a means of measuring the speed of the propagation of a nervous impulse. The estimated rate is for the frog twenty-eight metres per second, and for man about thirty- three metres. As the latter has been estimated for the nerve, with its muscle in position in the living body, it must be re- garded rather as a close approximation than as exact as the other measurements referred to in this chapter. It will be borne in mind that the numbers given as repre- senting the relative duration of the events vary with the ani- mal, the kind of muscle, and a variety of conditions affecting the same animal. Tetanic Contbaction. It is well known that a weight may be held by the out- stretched arm with apparently perfect steadiness for a few seconds, but that presently the arm begins to tremble or vi- brate, and soon the weight must be dropped. The arm was maintained in its position by the joint contraction of several muscles, the action of which might be described (traced) by a writer attached to the hand and recording on a moving sur- face. Such a record would indicate roughly what had hap- pened ; but the exact nature of a muscular contraction in such a case can best be learned by laying bare a single muscle, say in the thigh of a frog, and arranging the experiment so that a graphic record shall be made. Using the apparatus previously described (Fig. 177), a second induction shock may be sent into the muscle before the effect Flo. 180.— TtMiiiK of » double mowoUur oontraetioii OVMtar). Ataooiid ioduotioa diook WM ■MitiiitomiiicieiriienitlMdwteroompletod ita oootraoUan m to ImUeaited hr twgiiuiliiK of MooDd riM. DoMad line indicstM what the carra would have tem but tor uitoT > i ii «i r i i M i< i iii Mi i i>i < i i ii ii ii i i ii« ndieated 1v bei^niiiiig m but tor this. Flo. iM.-<3iir»e of complete teUuilccoiitr«jtton(Foitor). It is possible to see in these tracings a genetic relation, the second figure being evidently derivable from the first, and the third from the second, by the fusion of all the curves into one straight line. , , ■. i. v. j j If a muscle, isolated as we have described, be ^f^hed dur- ing the period that it is writing the second and the third r 184 ANIMAL PHTSIOLOOT. tracing, it may be observed that, during that corresponding to the former, though it is shortened, it does not remain equally so throughout, while during the writing of the third tracing there is no variation in its condition appreciable by the eye. What has happened is this : The muscle during the condition figured in the second tracing has periods of alternating contraction and partial relaxation, but during the third case the latter phase has been apparently omitted — the muscle remains in continuous contraction. In reality this is not the case unless we are mis- taken as to the meaning of the muscle-sound. The MwwU Tom. — There are a number of experimental facts from which important conclusions have been drawn, to which attention is now directed : 1. It has been found that a sound may be heard in a still room when one brings the muscles of mastication into action by biting hard; or listens over a contracting bicei)s with a stethoscope, etc. 2. When the wires of a telephone (communicator) are con- nected with a muscle, a sound is heard during the contraction of the muscle. From these facts it was concluded that a muscle when con- tracting gives rise to a sound ; that ietanua, as the form of con- traction we are describing is called, is essentially vibratory in character, which seems to answer to the graphic representations from a muscle when in tetanic contraction, and is in harmony with the case to which we called attention at the commence- ment of this subdivision of the subject. The note heard cor- responded, in the case of an isolated muscle, to the number of stimulations per second ; while for muscles made to contract by the will the note was always the same, answering to about forty vibrations per second; but as forty stimuli are not re- quired within this period of time to induce tetanus, it was thought that this note was probably the harmonic of a lower one answering to twenty vibrations in a second. ■ It has been recently shown that a very much smaller num- ber of vibrations of the muscle can give rise to an audible soimd, so that the explanation it would seem must now be modified; and it is likely that some peculiarities of the ear itself must be taken into the account in the explanation. In making the observations referred to above (in 1), the student will find it very Important to be on his guard against sources of error, especially with the use of a stethoscope. We may safely conclude that, at all events, most of the mus- APPLICATIONS OF THE GRAPHIC METHOD. 185 Bsponding to tin equally so [ tracing there eye. What lition figured ^ntraction and latter phase n continuous we are mis- mental facts ivrn, to which lard in a still >n into action biceps with a ator) are con- le contraction icle when con- le form of con- y vibratory in 'epresentations is in harmony he commence- ote heard cor- ;he number of to contract by tring to about ili are not re- etanus, it was uic of a lower L sinaller num- to an audible must now be ies of the ear planation. In I), the student gainst sources cular contractions occurring within the living body are tetanic — i. e., the muscle is in a condition of shortening, with only very brief -i nd slight phases of relaxation ; and that a comparatively small number of individual contractions suffice for tetanus when caused by the action of the central nervous system; though, as proved by experiments on muscle removed from the body, they may be enormously increased. While a few stimu- latiot s per second suffice to cause tetanus, it will also persist thougli thousands be employed. The Strength of the Btlmiiliu.— We have assumed that in the cases of contraction thus far considered the stimulus was ade- quate to produce the full amount of contraction, or as much as could be obtained. Such a contraction and such a stimulus are spoken of as maximal; but the stimulus might fall a little short of this, and is then termed stib-maa;imal ; or it may be re- garded from the point of view of being the least that will cause a contraction, and is then the minimal stimulus. It is important to note that any sudden change in an electric current will act as an excitant to muscular contraction, but that very considerable changes in the strength of the current if made gradually do not roadt on the muscle. It sometimes hap- pens that a sudden onward push of the secondary coil of an induction-machine will produce either a tetanus (though the terminal wires or electrodes were arranged for a single induc- tion shock) or what is known as a supermaximal contraction — i. e., one in excess of what could be obtained by more gradual advances, which have no effect usually after a certain maxi- mum of contraction is reached. This, we think, a loatter of conBiderable practical importance, and shall refer to its signifi- cance in a later chapter. Since the opening or closing of a key which makes or breaks the current really implies a very great change in the strength of the current affected suddenly — ^that is in fact from to some + quantity or the reverse — we find that usually the most marked contractions occur only at these times, and -this holds, whether the current be slowly or rapidly made and broken (inter- rupted). The nerve being the natural means of conveying a stimu- lus, it is easy to understand how the contraction happens to follow most perfectly and with less strength of stimulus when this structure is excited. A] >8t of the mus- niK;^«Mli>MAting a similar bers lie in con* of contraction rom about the tninates in the racting muscle a beetle's thigh contraction — a le of a billowy, B waves of co^n* if ore remain so APPLICATIONS OP THE GRAPHIC METHOD. 187 during contraction, and that all parts of the muscle-substance seem to share in the changes of form involved. The Elasticity op Muscle. In proportion as bodies tend to resume their original form when altered by mechanical force are they elastic, and the ex- tent to which they do this marks the limit of their elasticity. If a muscle (best one with bundles of fibers of about equal length and parallel arrange- ment) be stretched by a weight attached to one end, it will, on removal of the extending force, return to its original length; and if a series of weights which differ by a common increment be applied in succession and the degrees of extensions compared, a^ may be done by the graphic method, it will be appar- ent that the increase in the extension does not exactly correspond with the increment m the weight, but is proportionally less. With an inorganic body, as a watch-spring, this is not the case. , .^ *i. Further, the recoil of the muscle after the removal of the weight is not perfect fbr all weights ; but within certain narrow limits this is the case, i. e., the elasticity of muscle, though slight (for it is easily over-extended), is perfect. When once a muscle is over-ex- tended, so weighted that it can not reach its original length almost at once, it is very slow to recover, which explains the well-known duration of the effects of sprains, no doubt ^ , owing to some profound molecular change r«.^iMj-D«^Boijjg^ associated with the stretching. - Sufflin^^ The tracings below show at a glance the «^r ito«|U«ajj difference between the elasticity of muscle |*t«i.«uo«««J»,5 and of ordinary bodies. •!«» It is a curious fact that a muscle during the act of contraction is more extensible than when pajs^ve ; a dSLdvantage from a purely physical point of view, but p^ba- bin real advantage as tending to obviate spram by prevent- ing too sudden an application of the extendmg force. ■; ■ I mi ii » iiil m i tt» : im i H t 188 AMIUAL PHTSIOLOOT. It will be borne in mind that the Lmbs are held together as by elastic bands slightly on the stretch, owing to the elasticity I Fio. 16B.— niustratioiia of the dlfferenoe In elMtldty ot loMiiinate mud Mrtag matter (kflar Yco). 1. ShowB gntphlMlly bduiT]ar of a eteel Kpriac nnder equal inerNiients of «>«glit. 8. A similar traciiiff obtained from an India-rubber oand. S. The lame from a frmr'a muscle. Note that Uie ertenrtondflwreMM with egual IncfMnents of weitfit, and that the muscle fldls to return to the original position (absoHMa) after removal of the wei^t. of the muscles. Now, as seen in many tracings of muscular contraction, there is a tendency to imperfect relaxation after contraction — the contraction remainder or elastic after-effect, which can be overcome by gentle traction. In the living body, the weight of the limbs and the action of the stretched muscles on the side of the limb opposite to that on which the muscles in actual contraction aje situated, combine to make the action of the muscle more perfect by overcoming this tendency to im- perfect relaxation, which is probably less marked, independent of these considerations, in the living body. This elasticity of living muscles, which is completely lost on death, is a fair measure of their state of health or organic perfection. Hence that hard (elastic recoil) feeling of the muscles in young and vigorous persons, especially athletes, in whom muscle is brought to^e highest degree of perfection. (This property is then essentially the outcome of vitality, which is in a word the foundation of the differences noted be- tween the elasticity of inorganic and organic bodies. A mus- cle, the nutrition of which is suffering from whatever cause, whether deficient blood-supply, fatigue, or actual difiease, is deficient in elasticity. We wish to emphasize these relations, for we consider it very impoi'tant to avoid regarding vital phe- nomena in the light of physics merely, which the employment of the graphic method (and indeed all methods by which we re> move living things out of their normal relations) fosters. lUelrieal niMiMBtiia of Musi*.— Certain pieces of apparatus imntKK'fmimMi' together as lie elasticity UviiiK matter (after Mrementa of v^ght. ■ame from a frag'a weight, and tint the of tSe weight. s of muscular ilaxation after tic afler-effed, le living body, stched muscles ah the muscles ake the action Bndency to im- d, independent is elasticity of sath, is a fair jction. Hence in young and scle is brought oe of vitality, aces noted be- dims. A mus- hatever cause, aal difiease, is bese relations, ling vital phe- e employment f which we re- fosters, of apparatus APPLICATIONS OF THB GRAPHIC HBTHOD. 189 not as yet referred to are required to demonstrate the electrical condition of muscle. The gcdvcmometer suitable for physio- logical experiments is one having very many coils of extreme- ly fine wire, and so adapted to indicate the presence of currents of slight intensity. In order that it may be ascertained definitely that the cur- rents that deflect the galvanometer needle do not originate out- side of the muscle itself, non-polari»dble electrodes very care- fully made must be used, for the contact of ordinary metallic electrodes with living tissues suffices of itself to generate an electric current, as may be simply illustrated to one's self by placing two coins, one silver and the other copper, in contact with the upper and under surfac-es of the tongue respectively, and meeting in front; a peculiar taste results fronl the current excited. The construction of the non-polarizable electrodes common- ly employed, and as arranged for use, is diagrammatically rep- resented below (Fig. 186). Assuming the apparatus for the detection of electrical cur- rent in muscle to be in working order, a muscle from one of Fio. 186.-Noii-polariiaUa n hc t rodw of Du Boto-Rqrmond (after Rawothal). At c, cli moliteaed wiSiiaMae mHatkm, la laid on atmOi Gla« ajrUiiiiler a la lUled with i aolution of atne NlpiMte, a good ooodnetor, bx which cnrraot la cooveyed to r ~ ~ ' ~ ~ •iiio plala b, and tMuoe to fUvanometar. Up. the cold-blooded animals, prepared as rapidly and carefully as possible, avoiding all contact with foreign Wlies, is cut across the ends transversely, and placed on pads of bibulous paper moistened with physiological ('60-70 per cent) saline solution. The uon-polarisable electrodes connected with the galvanome- ter are brought in contact with the muscle. What results depends on the parts of the muscle that touch the electrodes, and is represented diagramatically in Fig. 187. It will be observed that the diagram indicates that between no current and the strongest obtainable there are all shades of ^ 190 ANIMAL PHTSIOLOGT. strength, according to the parts of the muscle connected by the electrodes. The strongest is that resulting when the superfi- ' Fio. IflT nt a muscle is carbonic an- >rmal tetanus IS of a natural ism {plasma), bstacle to the 7 been urged rect, viz., that e-life; it is, in in most cases. This state can ses by catting readmitting it that the prod- by the blood- ;oIlect and act 1 in permanent their relative le(VonBibra): . 744*6 L56'4 19'3 20-7 37-1 23-0 m 6—265*5 1,000 rtant is creatin body. Certain , kamin, taurin all the tissues, small quantity dscle a peculiar ctent the bodies igh that glyoo- admits of little There is a coloring matter in muscle, more abundant in the red muscles of certain animals than the pale, allied to heemo- globin, if not identical with that body. (It may be stated as a fact, the exact significance of which is unknown, that during contraction tb*^ extractives soluble in water decrease, while those soluble in a. iol increase. ^t will, however, be very plain, from what has been stated in this section, that life processes and chemical changes are closely associated, and to realize this is worth much to the student of Nature. Thermal Changes in the Contracting Muscle. Since very marked chemical changes accompany muscular contraction, it might be expected that there would be some modification in temperature, and probably in the direction of elevation. Experiment proves this to be the case. If a ther- mometer finely graduated be kept among the muscles of the limb of a mammal during the contractions that follow the stimulation of the main nerve, a decided rise of temperature may be noted during the prolonged tetanus that may be thus originated. True, during the contraction of a set of muscles under such circumstances, there is a possible fallacy, from the excess of blood going to the parts owing to dilatation of the blood-vessels, which it would be necessary to exclude — ^i. e., we must either ascertain that such does not take place, or take it into account as a factor in the causation of the rise of tempera- ture. However, by using a delicate thermopyle, a muscle to which no blood passes may be shown to grow warmer daring contraction. But why should a muscle when at rest, as may be shown, maintain a certain temperature, unless chemical changes are constantly taking place P As already stated, such is the case, and the rise on passing into tetanus is simply an expression of increased chemical actionrv — What is the nature of the combustion originating this heat ? Are certain crude materials withdrawn from the blood and burned up directly in the musole-substanoe ; or is the musclev itself continuously building up and tearing down its own sub-( stance, all of which implies oxidation P-nt- /v AH attempts to explain the facts apart from the latter view nave been unsuccessful, and we are forced to conclude that such is the sjmoptical statement of the life-history of muscle. MMMI H I[ H WWI 196 ANIMAL PHTSIOLOOT. No machine known to us resembles muscle except super- ficially. The steam-engine changes fuel into heat and mechani- cal motion, but there the resemblance ends. Muscle changes > its food, or fuel, not directly into either heat or motion, but into) itself; yet as a machine it is more effective than thesteam-*, engine, for more work and less heat are the outcome of its^ activity than is the case with the steam-engine. The Phtsioloot of Nbbvb. Muscle and nerve are constantly associated functionally, and have so much in common that it becomes desirable to study them together. Much that has been established for muscle holds equally well for nerve ; and the latter, though apparently wholly different in structure at first sight, is really not so. Nerve has its protoplasmic part (axis-cylinder), which is the essential structure, its protective sheaths, and its nuclei (nerve- corpuscles) As already indicated, a nerve possesses irritability, and, since a muscle does not respcy^d to an electric current sent through & nerve except when there is a sudden change in the strength of the current, it becomes interesting to learn why this should be the case. liVeriBMrtaL— In Fig. 190 are shown diagrammatically two muscle-nerve prep- arations, and the apparatus necessary for applying a constant current and a ^(momentary) induced current by single shocks to the nerva A strength of current sufficient to cause a (sub-maximal) contraction by an induction shock is determined, and the induotorium left at this graduation. A constant current of moderate strmgih is allowed to pass into the nerves of the preparation. It is found that, in the one case, the muscle contraction is increased, ^^,«^ pSutaTMtw^ ""^^ "* **** other diminished or absent, «q^^^ attend. ""^ ** when the same strength of induction shook is sent into the nerve at the points below the entrance of the constant currentr— that is to say, the irritability of the nerve has been increased or diminished. Flo. IW.— IMagnuBMWtio i«p- naentattoD of the ntetiiod o( tcatliig tbe adtablitty of the nerve in •HdrotamM (LwMloie). rtwtthre polee marked ■«•, negative, -; theoontee of current indi' irmi—>»i»MI mmm APPUCATIONS OP THE OH ('HIC ^KTHOD. 197 except saper- and mechttni- uscle changes ^ otion, but into) lan the steam-, mtcome of its) nctionally, and Table to study led for muscle iigh apparently really not so. ), which is the B nuclei (nerve- ■ritability, and, ic current sent ^hen there is a trength of the resting to learn use. , 190 are shown iscle-nerveprep- ratus necessaky current and a irrent by single int RuflBcient to mtraction by an rmined, and the graduation. A erate strength is ) nerves of the that, in the one ion is increased, ished or absent, ih of induction rve at the points —that is to say, d or diminished. It is found that when the constant (p' iu-izuig) ( rent is pass- ing from above downward — that is, t\en the < liode (n< na- tive pole) is on the side toward the muscle — the ii rita ili f the nerve is increased, and the reverse when the opposit i ditions prevail. ^his altered condition is known as eledr place to some extent of that constant nerve influence which\ we believe is being exerted in the higher animals toward( the maintenance of the regularity of their cell-life (metabol^ ism). P a t hoiogiwl and GUniML-Ot is believed that in the nerves of man, within his living body, the electrotonic condition can be induced as in an isolated piece of nerve. Hence, the value of the constant current in diminishing nerve irritability in neu- ralgia and allied conditions. Apparatus of great nicety of con- struction and capable of generating, accurately measuring, and conveniently applying electrical currents of different kinds, now adds to the resources of the physician. But we are prob - ably as yet only on the threshold of electro-therapeutics. Law of OoatnetiMi (IHiBlatiwi).— A giveiTpiece of nerve is stimulated only by the appearance of catelectrotonus, and the disappearance of anelectrotonus ; but the disappearance of cat- electrotonus and the appearance of anelectrotonus are without effect (Pflflger). This so-ctilled law is supposed to explain the following facts, which may be thus expressed in tabular form (after Landois) : wm ienced (indif- en change in An equally been caused, n of a muscu- od purpose if ence that one 'ails to notice uddenly or as I attention is ion or the re- ition of such biology; but wn experience Qg stimulated Br a change in luestion. (^e res so rea^ a lut. It seems, of taking the nflnence which dimals toward( [•life (metabol^ Q the nerves of nditioncan be ;e, the value of lability in neu- ; nicety of con- neasuring, and ifferent kinds, it we are prob - kpeutics. jce of nerve is •tonus, and the earance of cat- us are without to explain the I tabular form APPLICATIONS OP THB GRAPHIC MEl'HOD. 199 8TRBNOTH OF CURRBNT. AacnDiiia. PBaCINDINS. OnckMiDff. OnopvnlBg. On elMing. On opening. Weak C C R R C C C C C R Mecliam c Strong R R =r rest ; C = contFution. BmMmI OrgttM. — Electrical properties can be manifested by a large number of fishes; and the subject is of special theoretical interest. It is now established that the development of electrical organs points to their being specially modified muscles — tissues, in fact, in wliich the contractile substance has disap- peared and the nervous elements become predominant and peculiar. No work is done, but the whole of the chemical energy is represented by electricity. Functionally an electric organ (which usually is some form of cell, on the walls of which nerves are distributed, in- closing a gelatinous substance, the whole being very suggestive of a galvanic battery) closely re- sembles a muscle-nerve prepara- tion or its equivalent in the nor- mal body. The electric organs ex- perience fatigue ; have a latent period; their discharge is tetanic (interrupted) ; is excited by me- chanical, thermal, or electrical Htimuli; and the effectiveness of the organs is heightened by elevation of temperature, and the reverse by cooling, etc. - ' ' Muscular Work. If during a given period one of two persons raises a weight through the same height but twice as frequently as the other, it is plain that he does twice the work ; from such a case we may deduce the rule for calculating work, viz., to multiply the weight and height together. 1M.-Tbe eleetrie-fUh torpedo, dia- ■ected to show electric uqwrBtw (Huxley), b, branchiee ; c, brain ; e, dectric organ; g. cranium; me, qiinal cord ; h, nerves to pectoral flns ; nl, nerri laterales; »p, branches of pneu- mogaatrlo nerves to electric organs ; o, eye. 200 ANIMAL PHTSIOLOOT. The effectiveness of a given muscle must, of course, depend on the degree to which it shortens, which is from one hidf to three fifths of its length ; and the number of fibers it contains — i. e., upon its length and the area of its cross-section, taking into account in connection with the first factor the arrange- ment of the fibers; those muscles in which the fibers run longitudinally being capable of the greatest total shortening. There is, as shown by actual experimental trial, a relation between the work done and the load to be lifted. With double the weight the contraction may be as great as at first, or even greater ; but a limit is soon reached beyond which contraction is impossible. This principle may be stated thus : The contrac- tion is a ftmction of the stimtdua, and is illustrated by the diagram below (Fig. 193). .< -r--i-rrT"nTTT-T-r-n-.- lanwMtfBouooMTOTSwniiio Fio. 181— OiagTMn of muKukur contracUona whh wme itimului and increMiiic wetghu. The DUmbera reimwnt gnmmM (McKJendrick). It has been shown experimentally that the chemical inter- changes in a muscle, acting against a considerable resistance, are incrtosed — i. e., the metabolism and the working tension are related. These experimental facts harmonize with our experience of a sense of satisfaction and effectiveness in the use of the muscles when weights are held in the hands; and it must be a matter of practical importance that each person should, in taking, systematic^ exercise, keep to that kind j^ich^dpes not ei|ber overweight or underweight the musclM! Circumstances influbnciko the Charactbb of Muscular AND Nervous Activity. Th« InflvMM* of Blood4hipplj. IMfW.— Fig. 194 shows at a glance differences in the curves made by a contracting muscle suffering from increasing fatigue. Suppose that in such a case the blood had been withheld from the muscle, and that it is now admitted, an almost im- mediate effect is se^-n in the nature of the contractions ; but even if only saline solution had been sent through the vessels of the muscle, a similar change would have been noticeable. We may fairly conclude that the blood and saline removed something which had been exercising a depressing effect on the MHTM iirse, depend one half to it contains ition, taking the arrange- fibers run hortening. il, a relation With double irst, or even contraction The contrac- rated by the T-T-1- www Hing weight*. The Lemical inter- ile resistance, g tension are tr experience le use of the it must be a tn should, in lich does not >r Muscular 14 shows at a lOting muscle teen withheld 0. almost im- raotions; but ;h the vessels n noticeable, line removed : effect on the APPUCATIONS OF THE GRAPHIC METHOD. 901 vitality of the muscle. In a working muscle, like all living tissues, there are products of vital action (metabolism) that are UODT. no. iai-nally, the axis- ipward, only to ' of the nerve is iter toward the ing. Its irrita- r than usual to at current; but ition and disap> the history. It oal importance, of th6 constant ady endeavored 1 frog be placed it be gradually ; the spinal cord I 43° to 60° 0. is cnownas"heat- APPLICATIONS OP THE GRAPHIC METHOD. ao8 ^Thert are some advantages in investigating changes in tem- perature by the graphic method. Curves from a muscle-nerve preparation show that elevation of temperature shortens the latent period and the curve of contraction. Lowering the tem- perature has an effect exactly opposite, as might be supposed, and these changes take place in the muscles of both cold-blooded and warm-blooded animals, though more marked in the latter. The modifications evident to the eye are accompanied by others, chemical in nature, and a comparison of these shows that the rapidity and force of the muscular contraction run parallel with the rapidity and extent of the chemical changes. (^Certain drugs also modify the form of the muscle-curve very greatly, so that it appears t]^at the molecular action which un- derlies all the phenomena of muscle and nerve (for what has been said of muscle applies also to nerve, if we substitute nervous impulse for contraction) can go on only within those narrow bounds which, one realizes more and more in the study of physiology, are set to the activities of living things. What is the IntiMsts Vatnrt «f Musalar and Mmrwou Actioat— The answers to these questions, to which some allusion has been already made, are by no means certain. Some believe that, since the nitrpgeneous waste of the body, if judged by the urea of the urine, is not augmented, some carbohydrate breaks up, which would be in accord with the fact that the gaseous inter- change of the body generally is increased during exercise, espe- cially the excretion of carbonic anhydride. Upon the whole, however, such a view does not harmonise well with the behavior of protoplasm generally, and it is. possi- ble to conceive of other processes which would give rise to car- bonic anhydride and additional waste products. ( It seems to be likely that the muscle protoplasm builds up and breaks down as a whole ; that this is constantly going on ; ' and that the oxygen which is stored away (intra-molecular) \ suffices for immediate use; but that when % contraction takes I place all the chemical pro co w oo are heightened, so that we ^ may conceive most naturally of the various aspects of muscular life as phases of a whole, the parte of which are closely linked I together. A Another unsettled point is the explanation of the fact that 'a nerve, when stimulated nearer the nerve-center, gives rise to a more marked contraction, with the same stimulus than when excited nearer the muscle. ^me suppose that the change that in a nerve constitutes an ii twaWiili'liijili WUiltliti-ttKl-jiUt 204 ANIMAL PHYSI0L007. impulse gathers force as it proceeds — ^the avalanche theory of Pflfiger ; but it would seem more natural to refer this effect to the jn^eater irritability of the nerve nearer the centers. (The chemistry of dead nerves throws extremely littld light on the nature of nervous processes. The latter seem, in fact, to be accompaioed by chemical changes which almost ei^tirely elude our methods of detection and estimation. Relatively to the chemical the dggtrical phenomena are predominant; ^ut nerve-fo rceis not ele ctadcal lorce, nor are we p repar ed yet to teach that iTlsthe equivalent df that or nay otiimtatwl^^a to us. '■ \j^e fact that a nerve maintained in a condition approxi> mately normal may be stimulated for hours without exhaus- tion, has led some to adopt the tempting conclusion that there are no invariable chemical accompaniments of nervous excita- tion. But in this and all other instances we think that general principles must not be readily set aside by special cases, and we should ourselves hesitate to adopt any opinion so contrary to aU that is known of organic processes as this theory implies, except on the amplest and clearest evidence ; and we lay the more stress on this, because we think it is a sample of the sort of reasoning that is apt to become over-potent with those that derive their conclusions wholly or chiefly from laboratory ex- periments, to the neglect of wider observations, which put the more limited, and possibly more accurate, ones derived from the former source, in a truer light, and enable us to establish juster relations. Unbtsipbd Musclb. vThi» form of muscular tissue is JDharaoterised by its long latent period, its slow wave of contraction,Jt s not pasisintrm to tetanus, and the progress of the contraotionTCSbg in ei^er a traSsverse or longitudinal direction, a wave of contraction in one cell being capable of setting itp a correspmiding wave in adjoining cells even when no uerve-fibers are distributed to them. It is excited, though less readily, by all the kinds of stimuli that act upon striped muscle. In the higher groups of A animals this tissue is chiefly confined to the viscera of the / chest and abdomen, constituting in the case of some of them ) thej^reater part of the whole organ. ^-^ ^pie slow but powerful and rhythmical contraction of this form of muscle adapts it well to the part such organs play in '^^'^^mmfsw^si^mimammmsssmm iche theory of this effect to aters. aly Uttle light seem, in fact, hnost eiTtirely Belatiyely to ominant; ^ut repared yet to r fomTj^D^o. ition approxi- thout exhaos- sion that there lervons excit«- ik that general icial oases, and on so contrary theory implies, nd we lay the iple of the sort irith those that laboratory ex* , which put the I derived from us to establish Bed by its long lot pasising into dug in eiweFa contraction in Midingwave in distributed to 11 the kinds of igher groups of >l viscera of the / f some of them J traction of this L organs play in APPLICATIONS OF THE GRAPHIC METTHOD. 906 the economy. There are variations, however, in the rapidity, force, regularity, and other qualities of the contraction in dif- ferent parts: thus, it is comparatively rapid in the iris, and ex- tremely powerful and regular in the uterus, serving to produce that prolonged yet intermittent pressure essential under the circumstances (expulsion of the foetus). Oompanttfiii — Muscular contraction is relatively sluggish and prolonged among the invertebrates, to which, however, the movement of the wings of insects is a marked exception, some of them having been shown by the graphic method to vibrate some hundreds of times in a second; ' The slow movements of the snail are proverbial. As a rule, the strength of the muscles of the invertebrates is incomparably greater than that of vertebrates, as witness the powerful grasp of a crab's claw or a beetle's jawsr~' These facts are in harmony with the generally slow metab- olism of most invertebrates and the lower vertebrates. The muscles of the tortoise contract tardily but with great power, resist fatigue well, retain their vitality under unfavor- able conditions, and after death for a very long period (days). Without resorting to elaborate experiments, the student may convince himself of the truth of most of the above state- ments by observing the movements of a water-snail attached to a glass vessel ; the note made by the bussing of an insect, and comparing it with one approaching it in pitch sounded by some instrument of music; the force necessary to witiidraw the foot or tail of a tortoise ; the peristaltic movements of the intestine and other organs in a freshly killed animal ; or the action of a bee, wasp, or wood-boring beetle on the cork of a bottle in which one of them may be inclosed. SPKOXAL Ck>N8II>KBATION8. In the case of weakly (phthisical) persons a sharp tap on the chest will often produce a contraction -of the muscles thus stimulated ; but, in addition, a local contraction lasting some little time, known as a wheai or idio-muscular contraction, fol- lows. This phenomenon seems to be the result of a special irritability in such muscles. ^fomp may arise under a great variety of circumstances,^ but it seems to be in all raset either a complete prolonged tet»-/ nu8j.in which there is unusual muscular shortemng in severe) I, aileast* or the perristence of a contraction remainder. / piiM-aiiMaialidiiifaU OTtiiriiilfilf 206 ANIMAL PHTSIOLOOY. ^The great differences known to exist between individuals 6f the same species in strength, endurance, fleetness, and other particulars in which the muscles are concerned, raise numer- orxs interesting inquiries. The build of the greyhound or race- horse suggests in itself part of the explanation on mechanical principles, lung capacity, etc. But when it is found that one dog, horse, deer, or man excels another of the same race in swiftness or endurance, and there is nothing in the form to furnish a solution, we are prompted to ask whether the muscles may not contract more energetically, experience a shortening of the latenc period, or other phase of contraction; or whether they produce less of waste-products or get rid of them more rapidly. The whole subject is extremely complicated, and we may say here that there is some evidence to show that in races of dogs and other animalp which surpass their fellows, the nerve regulating the heart and lungs (vagus) has greater power ; but, leaving this and much more out of the account, it is likely there are individual differences in the functional nature of the muscle. Of equal or more importance is the energizing influ- ence of the nervous system, which probably under great excite- ment (public boat-races, etc.) acts to produce in man those supermaximal contractions which seem to leave the muscle long the worse of its unusual action. The nerve-centers, it is likely, suffer still more from excessive discharge of nerve-force (as we may speak of it lur the present) necessary to originate the muscular work. Hence the importance of training to minimize the noKi-effective expenditure, ascertain the capacity possessed, learn the direction in which weaknesses lie ; and equally important the muoh-negleoted period of rest before actual contests— if such are to be undertaken at all— lo that all the activities of the body may gather head, and thus be prepared to meet the unusual demand upon them. iTJie law of rhythm in organic nature is beautifully illus- trated by the behavior of nerve and especially muscle ; at least it is more obvious in the case of muscle, at this stage of oUr progress. (The regularity with which one phase succeeds another in a single contraction ; the essentially rhythmic (vibratory) char- acter of tetanus, fatigue and recovery ; the recurrence of in- crease and decrease in the muscle and nerve currents — ^in fact, the whole history of muscle is ^a admirable commentary on the truth of the law of rhythm, into which in further detai? space will not permit us to enter. "•^MM •f APPLICATIONS OF THE GRAPHIC METHOD. 207 individuals 6f 38S, and other raise numer- lound or race- on mechanical ound that one same race in the form to er the muscles a shortening »n ; or whether of them more icated, and we w that in races ir fellows, the greater power ; unt, it is likely I nature of the ergizing influ- er great excite- in man those ive the muscle ve-centers, it is ) of nerve-force iiry to originate of training to in the capacity lesses lie; and of rest before at all— io that d, and thus be n. lautifuUy illus- nnscle ; at least is stage of otir ids another in a ibratory) char- surrenoe of in- rrents — ^in fact, lommentary on further detail U[t is a remarkable fact that the endurance of man, especially civilized man, seems to be greater than that of any other mam- mal. It may be hazardous to express a dogmatic opinion as to the reason of this, but the influence of thelmindjover the body w unquestionably greater in man than in any other animal ; and, if we are correct in assigning so much importance to the influence of the tiervous system in maintaining the proper molecular balance which is at the foimdation of the highest good of an organism, we certainly think that it is in this direc- tion we must look for the explanation of the above-mentioned fact, and much more that would otherwise be obscure in man's functional life. ToaetioBal Variatirai, — We have endeavored, in treating this subject of muscle, to point out how the phenomena vary with the animal, the kind of muscle, and the circumstances under which they are manifested. It may be shown that every one of the qualities which a muscle possesses, varies with the tem- perature, the blood-supply, the duration of its action, the char- acter of the stimulus, and other modifying agents. Not only are there great variations for different groups of animals, but lesser ones for individuals ; though the latter are made more evident indirectly than when tested by the usual laboratory methods ; but tliey must be taken account of if we would iu- derstand animals as they are. Some of these will be referred to later. If a muscle-cell be regarded in the aspect that we are now emphasizing, its study will tend to impr^ those fundamental biological laws, the comprehension of which is of more impor- tance than the acquisition of any number of facts, which, how- evtsr interesting, can, when isolated, profit little. ( Jfccp eriment has not done much directly, and it seems can not at present, for the phjrsiology of man, though more may be accomplished as regards muscle and nerve than some other tissues. It is, of course, possible to measure the rapidity of the passage of a nervous impulse and to study electrical phe- nomena generally to some extent. Putting all that is known together, it would appear that, without referring to minor dif- ferences which unquestionably exist, the muscle and nerve physiology of man corresponds pretty closely with that of one of the highest mammals, and, as compared with the lower ver- tebrates, his muscles and nerves possess an irritability of a very exalted type, with, however, a corresponding loss or dif- ference in other directions. mmmmmmm 208 ANIMAL PHYSIOLOGY. Baamuy of fh« Fhyiiology of Mvid* and V«rf«.— The move- ments of a muscle are distinguished from those of other forms of protoplasm by their marked definiteness and limitation. The contraction of a muscle-fiber (cell) results in an increase in its short transverse diameter, and a diminution of its long diameter, without appreciable change in its total bulk. Muscle and nerve are not automatic, but are irritable. Though muscle normally receives its stimulus through a nerve, it possesses independent irritability. Stimuli may be mechanical, chemical, thermal, electrical, and in the case of muscle, nervous ; and to be effective they must be applied suddenly and last for a brief but appreciable time. Electrical stimulation, especially, is only effective when there is a sudden change in the force or direction of the cur- rents. This applies to both muscle and nerve. A muscular contraction consists of three phases: the latent period, the period of rising, and the period of falling energy, or of contraction and relaxation. When the phase of relaxation is minimal and that of con- traction approaches continuity, a tetanxis results. The contrac- tions of the muscles in situ are tetanic, and are accompanied by a low sound, evidence in itself of their vibratory character. The prolonged contraction of a muscle leads to fatigue; owing in part, at least, to the accumulation of waste-products within the muscle which depress its energies. This is a necessary consequence of the fact that all proto- plasmic activity is accompanied by chemical change, and that some of these processes result in the formation of products which are hurtful and are usually rapidly expelled. Muscular contraction is accompanied by chemical changes, in which the formation of carbon dioxide, and some substance that causes an acid reaction to take the place of an alkaline or neutral one. Since free oxygen is not required for the act of contraction, but is still used up by a contracting muscle, it may be assumed that the oxygen that plays a part in actual con- traction is intra-molecular. Chemical changes are inseparable from the vital processes of all protoplasm, and the phenomena of muscle show that they are constantly in operation, but exalted during ordinary contraction and that tetanic condition which precedes and may end in coagulation of muscle plasma and the formation of myosin. The latter is a r^ult of the disorganioation of muscle, and has points of resemblance to the coagulation of the blood. mfan APPLICATIONS OF THE GRAPHIC METHOD. 909 The move- of other forms imitation. in an increase ion of its long 1 hnlk. are irritable. m>ugh a nerve, , electrical, and stive they must reciable time, effective when ition of the cur- ases: the latent falling energy, knd that of con- The contrac- re accompanied Ltory character, iads to fatigue; waste'prodncts t that all proto- hange, and that ion of products )lled. lemical changes, some substance >f an alkaline or )d for the act of ig muscle, it may "t in actual oon- « vital processes nscle show that during ordinary sh precedes and the formation of Eation of muscle, ion of the blood. mm>: (The contraction of a muscle, i^d the passage of a nervous impulse, ore accompanied by electrical changes. Whether cur- rents exist in uninjured muscle and nerve is a matter of con- troversy. All physiologists agree that they exist in muscle (and nerve) during functional activity. This electrical condi- tion Is termed the " negative variation " by those believing in currents of rest, and the " current of action ** by those holding opposite opinions. The current is of momentary duration, and is manifested during the latent period of muscle, in which also the chemical changes take place ; so that a muscular contrac- tion must be regarded as the outcome of the events of the latent period, which is, therefore, though the shortest, the most important of the phases of a muscular contraction. (j>uring the passage of a constant (polarizing) cunent from a battery through a nerve, it undergoes a change in its irrita- bility and shows a variation in the electro-motive force of the ordinary nerve-current (eleotrotonus). This fact is of thera- peutic importance. The electrical phenomena of nerve are alto- gether more prominent than the chemical, iif» reverse of which is true of muscle. The activity of a muscle (and nerve proba- bly) is accompanied by the generation of heat, an exaltation of which takiss place during muscular contraction. Rigor mortis causes an increase in temperature and the chemical interchanges which accompany the other phenomena. A muscle may also become rigid by passing into rigor cdloria. Living muscle is translucent, alk^ine or neutral in reaction, and elastic ; dead muscle, opaque, acid in reaction, and devoid of elasticity, but firmer than living muscle, owing to coagula- tion of the muscle-plasma. Dead nerve undergoes similar changes. The elasticity of muscle is restricted but perfect within its own limits. It differs from that of inorganic bodies in that the increments of extension are not directly proportional to the in- crements of the weight. When overstretched, muscle does notr return to its original length (loss of elasticity>, hence the serious) nature of sprains. It is important to regard muscular elasticity as an expres- sion of vital propertie& llie work done by a muscle is ascertained by multiplying the load lifted by the height; and the capacity of an individual muscle will vary with its length, the arrangement of its fibers, and the area of its cross-section (i. e., on the number of fibers). The work done may be regarded as a function of the resist- 14 j| ■--1 210 ANIMAL PHTSIOLOOT. ance (load), as the contraction is also a function of the stimulus. The separation of a muscle from its nerve by section of the lat- ter leads to certain changes, most rapid in the nerve, which show that the two are so related that prolonged independent vitality of the muscle is impossible, and make it highly proba- ble that muscle is constanUy receiving some beneficial stimulus from nerve, which is exalted and manifest when contraction takes place. The study of the development of the electrical cells of cer- tain fishes shows that they are greatly modified muscles in which contractility, etc., has been exchanged for a very decided exaltation of electrical properties. It is likely, though not) demonstrated, that all forms of protoplasm undergo electricals changes — ^that these, in fact, like chemical phenomena, are vital^ constants. ^ The phases of the contraction of smooth muscular tissue are all of longer duration ; the contraction-wave passes in different directions, and may spread into celln devoid of nerves, which we think not unlikely also to be the case, though less so, for all forms of muscle. The smooth muscle-cell must be regarded as a more primi- tive, less 8peciali2sed, form of tissue. Variations in all the phe- nomena of muscle with the animal and the circumstances are clear and impressive. Finally, muscle illustrates an evolution of structure and function, and the law of rhythm;^" THE NEBY0U8 STBTESL-OENERAL CONSIDERATIONS. Since in the higher vertebrates the nervous system is domi- nant, regulating apparently every process in the organism, it will be well before proceeding further to treat of some of its functions in a general way to a greater extent than we have yet done. Manifestly it must be highly important that an animal shall be able to place itself so in relation to its surroundings that it may adapt itself to them. Prominent among these adaptations are certain movements by which food is secured and dangers avoided. The movements having a central origin, a peripheral mechanism of some kind must exist so as to place the centers in connection with the outer world. Passing by the evolution of the nervous system for the present, it is found that in verte- brates generally there is externally a modification of the epi- ^IftlBllfMyjpJCtiiii n[iw«iiiisrnftiBiiiiiiii>iMitii THE NKRVOUS STSTEM— GENERAL CONSIDERATIONS. 211 the stimulus, ion of the lat- nerve, which independent highly proba- ficial stimulus m contraction al cells of cer- ed muscles in a very decided 7, though not> ergo electrical< mena,areyiti^ Bular tissue are ises in different nerves, which 1 less so, for all } a more primi- I in all the phe- tmmstances are es an evolution m/" IDERATIONS. system is domi- the organism, it it of some of its han we have yet i on animal shall 'oundings that it hese adaptations ired and dangers gin, a peripheral place the centers by the evolution md that in verte- lation of the epi- •iiMT'Tiiilinifflfllllltf"'' thelial covering of the body {end-organ) in which a nerve ter- minates, which latter may be traced to a cell or cells removed from the surface {center), and from which in most cases other nerves proceed. (The nervous system, we may remind the student, consists in vertebrates of icentem'in which nerve-cells abound, imited by nerve-fibers andlby the most delicate form of connective tissue known, in connection with which there are incased strands of protoplasm or nerves as outgrowths. The main centers are, of course^ tggr^fated ia the brain and spinal cord^ It is possible to conceive of the work of a nervous system carried on by a single cell and an afferent and efferent nerve ; but inasmuch as such an arrangement would imply that the central cell should act the part of both receiving and origi- nating impulses (except it were a mere conductor, in which case there would be no advantage whatever in the existence of a cell at all), according to the principle of the physiological division of labor, we might expect that there would be at least tjgp cen- tral cells— one toreceive and the other to transmit impulses — oratleast that there should be some qiecialiaation among the central cells; and we shall have good reason later to believe that this has reached a surprising degree in the highest ani- mals. [Moreover^ it would be a great advantage if the termination of the ingoing (afferent) nerve should not lie exposed on the surface, but be protected by some form of cell that had also the power to transmit to it the impressions received from without, in a form suitable to the nature of the nerve and the needs of the^organism. [So that a complete mechanism in its simplest form would f urmsh : 1. A peripheral cell or nerve end-organ. 3. An affer- ent or sensory nerve. 3. Two or more central cells. 4. An efferent nerve, usually connected with — 5. A muscle or other form of cell, the action of which may be modified by the out- going nerve, or, as we should prefer to say, by the central nerv- ous cells through the efferent nerve. The advantages of the principal cells ^ing within and protected are obvious. When, then, an impression made on the peripheral cell is carried inward, there modified, and results in an outgoing nerv- ous imptdse answering to the afferent one, giving rise to a mus- cular contraction or other effect not confined to the recipient cells, the process is termed rejlesc acHon.-^ (^The great size, the multiplicity of forms, the distinct out- ■'■* 3f 9ia ANIMAL PHTSIOLOOT. r\ line and large nuclei of nerve-cells, suggest the probability that they play a very important part, and such is found to be the case. Indeed, in some sense the rest of the nervous system may be said to exist for them. Probably nerve-cells do sometimes act as mere conductors of nervous impulses originating elsewhere, but such is their lowest function. Accordingly, it is found that the nature of any reflex action depends most of all on the behavior of the central cells. Clt can not be too well borne in mind that nerves are con- ductors and such only, '^ey never originate impulBes. The properties considered in the last chapter are common to all kinds of nerves known ; and though we must conceive that there are some differences in the form of impulses, these are to be traced, not to the nerve primarily, but to the organ in which it ends peripherally or to the central cells. To return to reflex action, it is found that the muscular re- sponse to a peripheral irritation varies with the point stimu- lated, the intensity of the stimulus, etc., but is, above all, de- termined by the central cells. Nerve influence may be considered as following lines of least resistance, and there is much evidence to show that an impulse having once taken a certain path, it ij easier for it to pass in this direction a second time, so that we have the founda- tion of the laws of habit and a host of interesting phenomena in this simple principle. It is found that, in a frog deprived of its brain and sus- pended by the under jaw, there is no movement unless some stimulus be applied ; but if this be done under suitable condi- tions, instructive results follow, which we now proceed to indi- cate briefly. The experiments are of a simple character, which any student may carry out for himself. S^niamtaL— Preparing a frog by cutting off the whole of the upper jaw and brain-case after momentary ancesthesia, suspend the animal by the lower jaw and wait till it is perfect- ly quiet. Add to water in a beaker sulphuric acid till it tastes distinctly but not strongly sour, to be used as a stimulus. 1. Apply a small piece of bibulous paper, moistenoi with the acid, to the iKier part of the thigh of the animal. The leg will be drawn up and the paper probably removed. Remove the paper and cleanse the spot. 2. Apply a similai^ piece of paper to the middle of the abdomen ; one or both legs will probably be drawn up, and wipe off the offending body. 3. Let the foot of he probability is found to be lervous system ere conductors t such is their the nature of >ehavior of the leryes are w)n- opnljses. are common to it conceive that ses, these are to organ in which te muscular re- le point stimu- I, above all, de- iowing Imes of show that an easier for it to lave the f ouiida- ing phenomena brain and sus- 9nt unless some suitable condi- proceed to indi- iharacter, which U off the whole tary anesthesia, till it is perfect- icid till it tastes 1 a stimulus. 1. (3i with the acid. The leg will be lemove the paper ) of paper to the ill probably be . Let the foot of THE NERVOUS 8YSTBM-0ENERAL CONSIDERATIONS. 218 thefroff hang in the liquid; after a few moments it will be will be drawn up. 5. Apply stronger acid to the i°"d« f *^« right thigh; the whole frog may be convulsed, or the left leg m!y be put in action after the right. Even if ^^^ ^t^^^J "\K ^^r be applied near the anus, it will be removed by thft hind- W 6^ Beneath the skin of the back (posterior lymph-sac) inject a few drops of liquor strychnia of the P^"?7^J^ after a few minutes apply the same sort of stimulus to the thigh as before. The effects follow more quickly and are IhmmammmouuaI WNMIIV dNTM" 'INHHrrailYOINTM AUTOatATNi /•IMOIIV CIU. «M0 AmntNT nhwi r MOTOM ecu. ANO trnMNTMRM rMOTM ecu wrm imMNTMCIWC much more marked-the animal, it may be, passing intoa gen- ^'IC.t^ents may be varied, but ^ce to es^li^ the following conclusions: 1. The stimulus is not immediate- ly effective, but requires to act for a certain variable period, depending chiefly on the condition of the central nervous sys- tern 2. The movements of the muscles harmonize (are oo-ordi- nat^d),and tend to accomplish some end-are purposive, if 214 ANIMAL PHYSIOLOGY. the nerve alone and not the skin be stimulated, there may be a spasm only and not adaptive movement. 3. Nervous impulses, when very abundant, may pass along unaccustomed or less ac- customed paths (experiment 4 and 6). This is sometimes spoken of as the radiation of nervous impulses. The sixth experiment is very important, for it shows that the result varies far more with the condition of the nervous centers (cells) than the stimulus, the part excited, or any other factor. Antomatiiin. — But, seeing that these central cells have such independence and controlling power, the question arises. Are these, or are there any such cells, capable of originating im- pulses in nerves wholly independent of any stimulus from without ? In other words, have the nerve-centers any true automatism ? Apparently this quality is manifested by imi- cellular organisms of the rank of Amoeba. Has it been lost, or has it become a special characteristic developed to a high degree in nerve-cells ? We shall present the facts and the opinions based on them as held by the majority of physiologists, reserving our own criticisms for another occasion : 1. The medulla oblongata is supposed to be the seat of numerous small groups of cells, to a large extent independent of each other, that are constantly sending out nervous impulses which, pixxseeding to certain sets of muscles, maintain them in rhythmical action. One of the best known of these centers is the respiratory. 3. The poste- rior lymph hearts of the frog are supplied by nerves (tenth pair), which are connected, of course, with the spinal cord. When these nerves are cut, the hearts for a time cease to beat, but later resume their action. 3. The heart beats after all its nerves are cut, and it is removed from the body, for many hours, in cold-blooded animals. 4. The contractions of the intestine take place in the absence of food, and in an isolated piece of the gut. The intestine, it will be remembered, is abundantly supplied with nerve-elements. 5. In a portion of the ureters, from which it is believed nerve-cells are absent; rhytlimical action takes place. Oond m i oim — -1. Whether the action of the respiratory aa similar centers could contimie in the absence of all stimuli can not be considered as determined. 2. That there are regular rhythmical discharges from the spinal nerve-cells along the nerves to the lymph heartis seems also doubtful. 3. Later in- vestigations render the automaticity of the heart more unoer- ? THE NERVOUS SYSTEM— GENERAL CONSIDERATIONS. 216 re may be a rous impulses, (med or less ac- letimes spoken it shows that of the nervous i, or any other 'cells have such on arises. Are )riginating im> stimulus from nters any true ifested by uni- %a it been lost, oped to a high based on them trying our own ia oblongata is ips of cells, to a are constantly ar to certain sets )n. One of the 3. The poste- f nerves (tenth be spinal cord. le cease to beat, ats after all its for many hours, >f the intestine olated piece of is abundantly of the ureters, nt,- rhythmical espiratory an all stimuli can re are regular sells along the 1. 3. Later in- 't more unoer- J) tain than ever, so that the result stated above (3) must not be interpreted too rigidly. Similar doubts hang about the other cases of apparent au- tomatism. As regards the various comparatively isolated collections of cells known as ganglia, the evidence, so far as it goes, is against their possessing either automatic or reflex action; and new views of their nature will be presented in due course. Herroui InhiUtton. — If the pneumogastric nerve passing from the medulla to the heart of vertebrates be divided and the lower (peripheral) end stimulated, a decided change in the action of the heart follows, which may be in the direction of weakening or slowing, or positive arrest of its action. Assuming, for the present, that the cells (center) of the me- dulla have the power to bring about the same result, it is seen that such nervous influence is preyentijire or inhibitory of the normal cardiac beat, so that the vagus is tenned an inhibitory nerve. Such inhibition plays a very important part in the economy of the higher animals, as will become more and more evident as we proceed. The nature of the influences that pro- duce such remarkable results will be discussed when we treat of the heart An illustration will probably serve in the mean time to make the meaning of what has been presented in this chapter more clear and readily grasped. In the management of railroads a very great variety of complicated results are brought about, owing to system and orderly arrangement, by which the wishes of the chief mana- ger are carried out. Telegraphing is of necessity extensively employed. Sup- pose a message to be conveyed from one office to another, this may (1) simply pass through an intermediate office, without special cognizance from the operator in charge ; (2) the operator may receive and transmit it unaltered ; (3) he may be required to send a message that shall vary from the one he receives in a greater or less degree ; or (4) he may arrest the command alto- gether, owing to the facts which he alone knows and upon which he is empowered always to act according to his best dis- cretion. (in the first instance, we have an analogy with the passage of a nervous impulse through central fibers, or, at all events, unaffected by cells ; in the second, the resemblance U to cells acting as conductors merely ; in the third, to the usual behavior »«fe»iiA*aik£(Mit>^.aKlW«i*!v,ii*^^ 216 ANIMAL PHYSIOLOGY. of the cells in reflex action ; and, in tlie fourth, we have an in- stance of inhibition. The latter may also be rendered clear by the case of a horse and its rider. The horse is controlled by the rider, who may be compared to the center, through the reins answering to the nerves, though it is not possible for either rider or reins to originate the movements of the animal, except as they may be stitnuli, which latter are only effective when there are suitable conditions— when, in fact, the subject is irritable in the physiological sense. ' THE CIRCULATION OF THE BLOODT^ Every tissue, every cell, requiring constant nourishment, some means must necessarily have been provided for the con- veyance of the blood* to a^l parts of the organism. We now enter upon the consideration of the mechanisms by which this is accomplished and the method of their regulation. Let us consider possible mechanisms, and then inquire into their defects and the extent to which they are found embodied in nature. Th«it there must be a central pump of some kind is evident. Assume that it is one-chambered, and with an outflo-r p^-ie which is continued to form an inflow-pipe. This might 'L'?> , vided with valves at the openings, by which energy woul saved by the prevention of regurgitation. In such a syi . - things must go from bad to worse, as the tissues, by constantly using up the prepared material of the blood, and adding to it their waste products, would effect their own gradual starvation and poisoning. It might be conceived, however, that waste at all events was got rid of Vy the blood being conducted through some elimi- nating organs ; and assume that one such at least is set aside for respiratory work. If the blood in its course anjrwhere passed through such organs, the end would be attained in some degree ; but if the division of labor were coosiderabld, we should suppose that, gaseous interchange being so very important as we have been led to see from the study of the chapters on gen- eral biology, and on muscle, organs to accomplish this work might receive the blood in due course and return it to the cen- tral pump in a condition eminently fit from a respiratory point of view. Such, however, would neceBsarily be associated with a more THE CIBODLATION OF THE BLOOD. 217 re have an in- dered clear by itroUed by the ugh the reins 'or either rider mal, except as ve when there ict is irritable : nourishment, ed for the con- ism. We now by which this ion. m inquire into rand embodied dnd is evident, n outflow 7^P© I might be < - lergywoul such a syi ;. .. , by constantly nd adding to it dual starvation b all events was gh some elimi> tast is set aside iirse anjrwhere ;tained in some >tbld, we should y important as lapters on gen- lish this work a it to the oen- spiratory point ad with a more complicated pump ; and, if this were so constructed as to pre- vent the mixture of blood of different degrees of functional value, higher ends would be attained. Turning to the channels themselves in which the blood flows, a IHtle consideration will convince one that rigid tubes are wholly unfit for the purpose. Somewhere in the courbe of the circulation the blood must flow sufficiently slowly, and through vessels thin enough to permit of that interchange be- tween the blood and the tissues, through the medium of the lymph, which is essential from every point of view. The main vessels must have a strength sufficient to resist the force with which the blood is driven into them. Now, it is possible to conceive of this being accomplished with an intermittent flow ; but manifestly it would be a great advantage, from a nutritive aspect, that the flow and therefore the supply of tissue pabulum be constant. With a pump regu- larly intermittent in action, provided with valves, elastic tubes having a resistance in them somewhere sufficient to keep them constantly over-distended, and a collection of small vesselt; with walls of extreme thinness, in which the blood-current is great- ly slackened, a steady blood-flow would be nudntained, as the student may readily convince himself, by a few experiments of a very simple kind : 1. To show the difference between rigid tubes and elastic ones, let a piece of glass rod, drawn out at one end to a small diameter, have attached to the other end a Higginson's (two- bulb) syringe, communicating with a vessel containing water. Every time the bulb is squeezed, water f< )W8 from the end of the glass rod, but the outflow is perfectly intermittent. 2. On the other hand, with a long elastic tube of India-rub- ber, ending in a piece of glass rod drawn out to a point as be- fore, if the action of the pump (bulb) be rapid the outflow will be continuous. An apparatus that every practitioner of medi- cine requires to use answers perha|N9 still better to illustrate these and other principles of the circulation, such as the pulse, the influence of the force and frequency of the heart-beat on the blood-pressure, etc. We refer to a two-bulb atomiser, the bulb nearer the outflow serving to maintain a constant air-pressure. We may now examine the most perfect form of heart known, that of the mammal, in order to ascertain how far it and its adjunct tubes answer to a priori expectations. Tha IfaiiiiatiaB BMuri— In order that the student may gain a correct and thorough knowledge of the anatomy of the heart 218 ANIMAL PHT8IOL0OT. and the working of its various parts, we recommend him to pursue some such course as the following : 1. To consult a number of plates, such as are usually fur- nished in works on anatomy, in order to ascertain in a general way the relations of the heart to other organs, and to the chest wall, as well as to become familiar with its own structure. 2. To supplement this with reading the anatomical descrip- tions, without too great attention to details at first, but with the object of getting his ideas clear so far as they go. 3. Then, with plates and descriptions before him, to examine several dead specimens of the heart of the sheep, ox, pig, or other mammal, first somewhat generally, then systematicidly, with the purpose of getting a more exact knowledge of the various structures and their anatomical as well as physiological relations. We would not have the student confine his attention to any single form of heart, for each shows some one structure better than the others; and the additional advan- tages of comparison are very great. The heart of the ox, from its sise, is excellent for the study of valvular action, and the framework with which the muscles, valves, and vessels are connected; while the heart of the ^ig (and dog) resemble the human organ more close- ly than most others that can be obtained^ It will be found very helpful to perform some of the dissections under water, and by the use of this or some other fluid the action of the valves may be learned as it can no. 196.— The left auricle wad Tentriole o|Miied and f Uielr welle removed to ibow their oantiee ThomaoB). 1, rlRbt jmlmoiiMT vein cut " caWtjr or Mt euricle; |, thick imll of ■Mrt'of (Zleii ■hort : 1' caWtjr oT (rft euricle ; f, thick mUI of left ventricle: 4, portion o( the Mwae with papiUarr muacle attached ; S, 6', the other papiUaiT mua- clee ; 8, one eegment of the mitral valre ; 7, in aorta la placed over the wmihuar valvaa. THE CIBCULATION OF THE BLOOD. Sltf nmend him to ■e usaally fur- in in a general nd to the chest structure, omical descrip- first, but with >ygo. lim, to examine leep, ox, pig, or systematically, owledge of the structures and tomical as well ogical relations, ould not have nt confine his to any single heart, for each ne one structure Lan the others; dditional ad van- comparison are A. The heart of From its sice, is for the study of action, and the rk with which sles, valves, and are connected; I heart of the ipig j) resemble the rgan more clocfe- nost others that »taihed» [1 be found very A) perform some iissections under id by the use of lome other fluid m of the valves earned as it can in no other way. By a little manipulation the heart may be so held that water may be poured into the orifices, prepared by a removal of a portion of the blood-vessels or the auricles, when the valves may be seen closing together, and thus revealing their action in a way which no verbal or pictorial representa- tions can do at all adequately. -<" >aut< su:r i.f.i HtLl MMT V.r# Vm. 107.— View of Om oriileM of tto hawt (Rm briow, the whole of Om vnitrielM hairtng been cut ewagr (after Huxiqr). KAV, richt •uricufe-Tentrleular orlllce, eumuiHled by the thnw flan, t.t).l, t.v.t, f. «. a, of theVtoMpid valve, which «w ■tretehed br weMita attached to tliftc*ordiBletul-Teiitrieularorillae,ete. i>i4,orUlce of the pulinonanr aiterr. the lemlhiiiar valvM wip we Ht ed aa havinc mat and ekMed together. .<10, orifloe of the aorta. A heart thoroughly boiled and allowed to get cold shows, on being pulled somewhat apart, the course, attachment, and other features of the fibers very well, as also the skeleton of the organ, which may be readily sepan»ted. When this has all been done, the half is not yet accom- plished. A visit to an abattoir will now repay amply for the time spent. Animals are there killed and eviscerated so rapidly that an observer may not only gain a good' practical acquaint- ance with the relations of the heart to other parts, but may often see the organ still living and exemplifying that action peculiar to it as it gradually approaches quiescence and death —a matter of the utmost importance. If the student will ther compare what he has learned of the mammalian heart in this way with the behavior of the heart of a frog, snake, fish, turtle, or other animal that may be killed after brief ether narcosis, w^.thout cessation of the heart's ao- 220 ANIMAL PHYSIOLOGY. tion he will have a broader basis for his cardiac physiology than is usual ; and we think we may promise the medical stu- dent, who will in tnis XA ^.^ss^BSBs-^ and other ways that may occur to him supplement the usual work on the human cadaver, a pleasure and profit in the study of h«irt- dis- ease which come in no other way. With the view of assisting the obser- vation of the student as regards the heart of the mammal, we would call special at- tention to the follow- ing points among others: Its method of on the left pMt or i.^ K «M. ««».«- » — u-r-"»ui Suspension, chiefly by ^i&SS?«.'^2Sfw'»SS its Veat vessels; the •en**- strong fibrous frame- work for the attachment of valves, vessels, ^f*! ™^f?f- ^^^] the great complexity of the arrangement of the latter ; the various lengths, mode of attachment, and the strength of the inelastic chordae tendineie ; the papillary muscles which doubt- less act at the moment the valves flap l>ack, thus preventang the latter l^eing carried too far toward the auricles, the pocket- ing action of the semilunar valves, with their strong margin i^d meeting nodules {corpora aurarUii) ; the relative thickness of auricles and ventricles, and the much «^ter^cknes« of the walls of the left than of the right ventricle-difiEerences which are related to the work these parts perform. The latter may be well seen by making transverse sections of the heart of an animal, especially one that has been blea to death, which specimen also shows how the contraction of the heart obliterates the ventricular cavity. tt ^11 also be well worth -' ile to follow up the course of the coronary arteries, noting e, ecially their point of origm. •Se examination of the valves of the smaller hearts of cold- bloodrLimals is a matter of greater difficulty and is f aoih- Huxley). PA, pulmonMjr artery, wjjtt «» Jjv^^!^ 8 THE CIRCULATION OP THE BLOOD. 821 iac physiology le medical stu- vho will in this bher ways that occur to him )ment the usual on the human er, a pleasure profit in the of h«irt-dis- which come in ter way. 1th the view of ling the obser- n of the student igards the heart 10 mammal, we d call special at- on to the f oUow- points among rs: Its method of ension, chiefly by ;reat vessels; the ig fibrous f rame- od muscle-fibers; I the latter; the i strength of the Bles which doubt- , thus preventing ricles, the pooket- (ir strong margin relative thickness >ater thickness of fcricle— -dififerences fonp. ransverse sections t has been blea to contraction of the JT up the course of point of origin. Her hearts of cold- culty and is facili- tated by dissection under water with the help of a lens or dis- secting microscope; but even without these instruments much may be learned, and certainly that the valves are relatively to those of the mammaUan heart imperfectly developed, will be- come very clear. ClBCULATION OF THE BLOOD IN THE MAMMAL. It is highly important and quite possible in studying the circulation to form a series of mental pictures of what is trans- piring It will be borne in mind that there is a set of elastic tubes of relatively thick walls, standing open when cut across, dividing into smaller and smaller branches, and finally ending in vessels of more thar- ')web fineness, and opening out into others, that become u < m^O THB CIBOULATION OF THB BLOOD. 388 McMoiMd are* of the ■ ■ ijV.i nels or cones with the smaller end toward the heart and the widest portions representing the capillaries. Thb Action or ths Mammalian Hbast. Verjr briefly what takes place may be thus stated: The right auricle contracting squeeses the blood through the au- riculo-ventricular opening into the right ventricle, never quite emptying itself probably ; immediately after the right ventricle contracts, by which its valves are brou^t into sudden tension and apposition, thus preventing reflux into the auricle ; while the blood within it takes the path of least resistance, and the only one open to it ' ito the pulmonary artery, and by its branches is conveyed to the capillaries of the lungs, from which it is returned freed from much of its carbonic anhy- dride and replenished with oxygen, to the-left auricle, whence it proceeds in a similar manner into the great arterial main, the aorta, for general distribution throughout the smaller arteries and the capillaries to the most remote as w6ll as the nearest parts, from which it is gathered up by the veins and returned laden with many impurities, and robbed of a large proportion of its useful matters, to the right side of the heart. It will be remembered that corresponding subdivisions of each side of the heart act simultaneously, and that any decided i^sms^^ims^si 'm^^^iummmmmKsmmmm 9H ANIMAL PHYSIOLOGY. departure from this harmony of rhythm would lead to serious disturbance. Superior VenftOav*. InferiqrVenfcCaTfc CapUUriMof UTer. Portal Vein. CanUIariMOftlie H)!ad,etc. FulmaMrr Capn- luiM. Main Arterial Trunk. CapiUariesof Splanchnic Area. CapOlariea of Trunk and Lower Ez- tremitiee. , Sr BdSl«2S^1S«^t parta the capillaries, in which it would be much the s owest and, getting by degrees faster, would reach a speed m the largest veins approaching that of the corresponding arteries. THE CIRCULATION OP THE BLOOD. 225 lead to serious lof the .etc. 'Cmta- KiUnAitertalTniiik. C* urilUuiMof Splanchnic . Area. CapUlariM . uii. ji i>:iii; pressure is not known, but is probably high, we may suppose not less thim 150 to 200 mm. After the fikct that there is a certain considerable blood- pressure, the other most important one to notice is that this blood-pressure is constantly varying during the experiment, and, as we shall give reason to believe, in the normal animal ; and to these variations and their causes we shall presently turn our attention. THE HEART. The heart, being one of the great centers of life, to speak figuratively, it demands an unusually close study. •s The Cardiac Movkments. There is no special difficulty in ascertaining the outlines of the heart by means of percussion on either the dead or the living subject, Quite otherwise is it with the changes in form which accompany cardiac action. Attempts have been made to ascertain the alterations in position of the heart with respect to other parjts, and especially its own alterations in shape dur- ing a systole, the chest being unopened, by the use of needles thrust into its substance through the thoracic walls ^ but the results have proved fallacious. Again, casts have been made of the heart after death, in a condition of moderate extension, prior to rigor mortis; and also when contracted by a hardening fluid. 7^ese methods, like all others as yet employed, are open to serious objections. Following the rapidly beating heart of the mammal with the eye produces uncertainty and confusion of mind. We look to instantaneous photography to furnish a possible way out of the difficuttyT r it may be very confidently said that the mode of contrac- tion of the hearts of different groups of vertebrates is i ^ariab le^ though it seems highly probable that the divergences for mam- mals are slight. The most that can be certainly afllrmed of the mammalian heart is, that during contraction of the ventri- cles they become more conical ; that the long diameter is not appreciably altered ; that the antero - posterior diameter is iniliil iKiii miiifaliliil'iri'i THE CIRCULATION OP THE BLOOD. 288 [erent animals, to the result, lorse the arte- gr 100 to 176, |iot known, but to 200 mm. lerable blood- Ice is that this le experiment, formal animal ; presently turn f life, to speak the outlines of le dead or the hanges in form e been made to irt with respect s in shape dur- ) use of needles walls ^, but the ftve been made srate extension, by a hardening >loyed, are open 9 mammal with aind. We look ible way out of ode of contrao- »tes is i ^ariab le^ ences for mam- nly aflHrmed of a of the ventri> diameter is not or diameter is lengthened ; and that the left ventricle at least turns on its own axis from left to right. This latter may be distinctly made out by the eye in watching the heart in the opened chest. The Impulse of the Heart. When one places his hand over the region of the heart in man and other mammals, he experiences a sense of pressure varying with-the part touched, and from moment to momep^ Instruments constructed to convey this movement to recording levers also teach that certain movements of the chest wall cor- respond with the propagation of the pulse, and therefore to the systole of the heart. It can be recognized, whether the hand or an instrument be used, that all parts of the chest wall over the heart are not equally raised at the one instant. If the beat- ing heart be held in the hand, it will be noticed that during systole there is a sudden hardening. The relation of the apexi to the chest wall is variable for different mammals, and with \ different positions of the body in man. ^As a result of the investigation which this subject ha^ re- ceived, i|i may be inferred that the sudden tension of the heart, owing to the ventricle contracting over its fluid contents, causes in those cases in which during diastole the ventricle lies against the chest wall, a sense of pressure beneath the hand, which is usually accompanied by a visible movement upward in some part of the thoracic wall, and downward in adjacent parts. The exact characters of the cardiac impulse are very variable with different human subjects. The term " apex-beat " is fre- quently employed instead of cardiac impulse, on the assump- tion that the apex of the heart is brought into sudden contact with the thoracic walls from which it is supposed to recede during diastole. But, in some positions of the body at all events in a certain proportion of cases, the apex of the heart lies against the chest wall during diastole, so that in these instances certainly such a view would not be wholly correct. But we would not deny that in some subjects there may be a genuine knock of the apex against the walls of the chest during the ventricular systole. lit will not be forgotten that the heart lies in a pericardial (sac, moistened with a small quantity of albuminous fluid ; and that by this sac the organ is tethered to the walls of the chest by its mediastinal fastenings; so that in receding from the chest wall the latter may be drawn after it ; though this might SinM««i.>^ii,iilj* eimulmi 234 ANIMAL PHTSIOLOOT. also follow from the intercostal muscles being simply unsup- ported when the heart recedes. Invbstioation of thb Hkart-Beat fbom within. By the use of apparatus introduced within the heart of the mammal and reporting those changes susceptible of graphic record, certain tracings have been obtained about the details of Fio. int.— Marey't oardiao MMUid wiiieh mar ba UMid to asplan the diainben at Urn haait (aftei Foater). a, ia made of rubber aireldied over a wire framework, with metallic ■npporta above and below ; b, la a long tube. which here are uncertainty and disagreement, though they seem to establish the nature of the main features of the cardiac beat clearly enough. An interpretation of such tracings in the Bight aurtole. Bight Tentarlcto. Cardiac impiilae. Fta. WO.— Slmultaneotia tradnga from the interior of the right auricle, from the Interior of the right tentrlde, and of the oardiao impute, in the hone (after Obauveau and Marejr). Tracinga to be read from left to right, and the ref erenoea abora are in the order from wn to bottom. A completo cardiac cycle la included between the thick TerUeal Unea I and u. The thin vertical Itnea indicate tenoia of a aeoond. The gradual riae of nreaMire within the Tentrlcle (middle tnudng) during diaat«de, the auddeo riae with the mtoie, ita nalntenanoe with oacillationa for an apiMveiable time, it* aoddan Call, eto., are all well ahown. Tberaia diiagraement aa to the exact meaning of the minor ourraa In the larger onea. light of our general and special knowledge warrants the fol- lowing statement. w^'«'<> iW ^»W'>'^' , w i. »i ai i i < tf i Aiiiia Bii< CT i( rt w M iiii i '(>i iMMP THE GIBCULATION OF THE BLOOD. 985 I simply unsup- WITHIN. le heart of the lible of graphic it the details of dumben oC the hewt. mework, with metallic 1. Both auricular and ventricular systole are sudden, but the latter is of very much greater duration. 2. While the chest wall feels the ventricular systole, the au- riculo-ventricular valves shield the auricle from its shock. 3. During diastole in both chambers the pressure rises gradually from the inflow of blood ; and the auricular contrac- tion produces a brief, decided, though but slight rise of press- ure in the ventricles. 4. The onset of the ventricular systole is rapid, its maximum pressure suddenly reached, and its duration considerable. The relations of these various events, their duration, and the corresponding movements of the chest wall, may be learned by a study of the above tracing which the student will find worthy of his close attention. it, though they as of the cardiac I tracings in the V BVtwiriole. Bight rentricle. OirdlM impulM. , from the interior of the ChauTceu Mid Meresr). i« in the order from top dr Tertieal Itnce I and n. M of srcMure within the mtifle, lie mninteiwnae III well ilMwii. There ie rarrants the f ol- Thb Cabdiac Sounds. Two sounds, differing in pitch, duration, and intensity, may be heard over the heart, ^Len the chest is opened and the heart listened to by means oi' a stethoscope. These sounds may also be heard, and present the same characters when the heart is auscultated through the chest wall ; hence the cardiac im- pulse can take no essential part in their production. The sounds are thought to be fairly well represenic ^, so far as the human heart is concerned, by the syllables lub, dv/p; the first soimd being longer, louder, lower-pitched, and " boom- ing" in quality; the second short, sharp, and high-pitched. In the exposed heart, the first sound is heard most distinct- ly over the base of the organ or a little below it; while the sec- ond is communicated most distinctly over the roots of the great vessels — that is to say, both spunds are heard best over the auriculo- ventricular and semiliuiar valves respectively. When the oh«3t wall intarvenes between the heart and the ear, it is foimd that the second sound is usually heard most distinctly over the second costal cartilage on the right ; and the first in the fifth costal interspace where the heart's impulse is also often most distinct. In these situations the arch of the aorta in the one case, and the ventricular walls in the other, are close to the situations referred to during the cardiac systole; hence it is inferred that, though the sounds do not originate directly beneath these spots, they are best propagated to the chest widl at these points. There are, however, individual differences, owing to a va- iii»rtniiiiiiiiii«,-a.,-,.»--i'»i 286 ANIMAL PHTSIOLOOT. riety of causes, which it is not always possible to explain fully in each case, but owing doubtless in great part to variations in the anatomical relations. The Oaiism of the Bowids of fhe Heart— There is general agree- ment in the view that the second sound is owing to the closure of the semilunar valyes of the aortic and pulmonary vessels ; the former, owing to their greater tension inconsequence of the higher blood-pressure in the aorta, taking much the larger share in the production of the sound, as may be ascertained by listen- ing over these vessels in the exposed heart. When these valves are hooked back, the second sound disappears, so that there can be no doubt that they bear some important relation to the cau- sation of the sound. In regard to the first sound of the heart the greatest diver- sity of opinion has prevailed and still continues to exist. The following among other views have been advocated by physi- ologists : 1. The first sound is caused by the tension and vibration of the auriculo-ventricular valves. 2. The first sound is owing to the contractions of the large mass of muscle composing the ventricles. 3. The sound is directly traceable to eddies in the blood. In favor of the first view it was argued that by agreement the second sound was valvular, and why not the first ?— And again that malformations of the valves gave rise to " murmurs " (" bruits"), whicu either obscured or replaced the true sound. The second opinion was supported by the fact that the larger the heart the more powerful the sound ; that when the blood was cut off from the heart by ligature of the vessels success- ively, the sound coidd still be heard ; that with fatty degenera- tion of the muscle-fibers of the heart, it had been found that the sound was weak — and similar arguments. Recently it has been contended very strongly that the first sound may be heard by a double stethoscope placed 6ver an ex- cised, bloodless, mammalian heart, or even ventricle, while it still beats. The third opinion was less vigorously upheld, but certain experiments and physical phenomena were pointed to in sup- port of it. Against the arguments adduced above it may be stated that the first sound may be conceived as overpowered by a hruU without being replaced by it in the proper sense of the word. It is well known that the cardiac muscle is peculiar, occupying «^W ) n ?^' W WBiw tana ewqww J^'-fti'JWf-. »g fl i tm^M-m THE CIRCULATION OP THE BLOOD. 987 ► explain fully } variations in general agree- : to the closure Lonary vessels ; sequence of the he larger share iined by listen- en these valves > that there can bion to the cau- greatest diver- I to exist. The ated by physi- nd vibration of }ns of the large n the blood, t by agreement the first ?— And 3 to "murmurs" lie true sound, t that the larger when the blood vessels success- fatty degenera- oeen found that jly that the first aced 6ver an ex- mtricle, while it lield,but certain >inted to in sup- ay be stated that du^ by muscular contraction alone P To this it haj been wphed that the sudden tension of the ventricuh^r wall when tightened over the blood may give rise to vibrations that account for the sound; and recentinvestigationshave shown thatthevibi^ions that rive rise to the sound emitted by a contracting skelet^ muscle may be fewer than was once supposed. The statement that a sound may be heard from the excised ^'e'^*""}^^^^®' *^^ circumstances above mentioned has not beeu demed; but ite sourcehas been traced to the action of *^« j\f 'V!*^^*^*^' stethoscope!, e., some beUeve the sound to ^'JT*^" ^ of extrinsic origin. Most physicians would be very l^th to abandon the view that the valves are always to be taken into seripus account as a factor in the eausation of the ^""JT' .--Sut. looking at the whole question broadly, is it not unrea. (sonable to explain the sound resulting from such a complexact Mthe contraction of the heart and what it implies m the light W any single factor ? That such narrow and exclusive vie^ should have been propagated, even by eminent physiologiste. should admonish the student to receive with great caution ex- 288 ANIMAL PHT8I0L0OT. planationa of the working of complex organs, based on a single experiment, observation, or argument of any kind. The view we recommend the student to adopt in the light of our present knowledge is, that the first sound is the result of several causative factors, prominent among which are the sud- den tension of the auriculo- ventricular valves, and the contrac- tion of the cardiac muscle, not leaving out of the account the possible and probable influence of the blood itself through eddies or otherwise; nor would we ridicule the idea that in some cases, at all events, the sound may be modified in qiiality and intensity by the shock given to the chest wall during sys- tole. Bndo-Cardiac Prkssubks. Bearing in mind the relative extmt of the pulmonary and systemic portions of the circulation, we should suppose that the resistance to be overcome in opening the aortic valves and lifting the column of blood that keeps them pressed together, would be much g^reater in the left ventricle than in the right ; or, in other words, that the intra-ventricular pressure of the left side of the heart would greatly exceed that of the right, and this is confirmed by actual experiment. By means of an instrument known as the maximum and minimum manometer, the highest and lowest pressure within any chamber of the heart may be learned approximately. As a specimen measurement it may be stated that it has been found that in a dog the greatest pressure was 140 mm. of mer- cury for the left ventricle, for the right only 60, and for the right auricle 20. But it is also found— a matter not quite so obvious — ^that Sk minimum pressure proportionate to the maxi- mum may exist in all the chambers of the heart; and the press- ure may fall below that of the atmosphere, or be negative. By the same method it was found that in a dog the negative pressure varied between —62 and —20 mm. of mercury for the left ven- tricle and — 17 to — 16 mm. for the right, with — 12 to —7 mm. for the right auricle. As will be shown later, part of this diminished preiteure is due to the effect of the respix-atory movements ; and, indeed, more recent experiments seem to show that ordinarily, with the heart beating with its usual rate and force, the nega- tive pressure or suck from its own action is comparatively slight. The discussion of the cause of this negative pressure, like the related subject of the cause of the heart's diastole, has given rise to much difference of opinion. I'l ' i Di wmmMJWiJri w jaoww i w i M i U LBi iimft ii K i r m THE CIBCULATION OF THE BLOOD. 289 111 led on a single d. in the light of 8 the result of are the snd- d the contrac- he account the itself through e idea that in ified in quality all during sys- mlmonary and d suppose that >rtic valves and ressed together, ui in the right ; pressure of the at of the right, ) maximum and pressure within roximately. As bat it has been 140 mm. of mer- 60, and for the ter not quite so ate to the maxi- t; and the press- be negative. By negative pressure for the left ven- 12 to —7 mm. for f this diminished aovements; and, ' that ordinarily, 1 force, the neg^ is comparatively )gative pressure, irt's diastole, has Some find it difficult to understand how the heart after sys- tole may regain its original form apart from the assistance of diastolic muscles, which are assumed to act so as to antagonize those causing systole. Others think the elasticity of the heart's muscle sufficient of itself to account for the organ's return to its original form. But there is surely a misconception involved in both of these views. If small portions of the heart of the frog, tortoise, or other cold-blooded animal, just removed from the body, be observed under a microscope it will be seen that they alternately con- tract and relax. Now, it is only necessary to suppose that the relaxation of the heart is complete after each systole, to under- stand how even an empty heart regains its diastolic form. That there should be a negative pressure in, say, the left ventricle, follows naturally enough from the fact that not only are the contents of the ventricle expelled with great sudden- ness, but that its walls remain (see Figa 210 and 214) pressed together for a considerable portion of the time occupied by the whole systole; so that in relaxation it follows that there must no. SlS.-1>ia«ram riMmlK *>» NiatlTO Mglit o( tto blood-imMira In dMOraat pM^ TMoolar nralani toflarrm). A, taMrt ; a, artattotai : «, mall vrins ; il, wtartea ; e, cm>- Mood gilwwiiTilirifafdby the ht^teot Ui*« "^ .-~~-i— . «^ pww e, apiirazimatoljr, in mm. of merourjr. vo« 1. v.) sftmosphorfc ThenmdMnoB the* Ml gtni the be an empty cavity to fill, or that there must be an aspiratory effect toward the ventricle ; hence also one factor in the closure of the semilunar valves. mJWil.WWUMlUJi.l'U i .-Mlu * 240 ANIMAL PHrSIOLOOY. It thus appears that the heart is not only a force>pump but also to some extent a e. c't' ;^ >nmp; and, if so, the aspirating effect must express itself > ■ vhe threat veius, lacking valves as they do, at their entrance i 'A^-i heart ; hence, with each dias- tole the blood would be sucked on into the auricles, a result that is intensified by the respiratory movements of the thorax. BelatiT* Time ooovpisd byth* ▼•rioni FhMM«f th* Cardiae 0yd*. — The old and valuable diagram reproduced below is meant to convey through the eye the relations of the main events in a complete beat of the heart or cardiac cycle. The relative length of the sounds; the long period occupied by the pause ; the duration of the ventricular systole, which it is to be observed is in excess of that of the first sound, are among the chief facts to be noted. The tracings of Chau- veau and Marey, obtained from the heart of the horse> which has a very slow rhythm, show that of the whole period, the auricular systole occupies | or ^ of a second ; the ventricular systole, f or ^ of a sec- ond ; and the diastole, f or ^ of a second. With the more rapid beat in man (70 to 80 per minute), the duraticm of the cardiac cycle may be estimated at about ^ of a second, and the probable proportions for each event are about these: The auricular systole, ^ of a second; the ventricular systole, ^ of a second ; and the pause, ^ of a second. ^ It will be noted that the pause of the heart is M^ual in dura- / tion to the other events put together; and even assuming that there is some expenditure of energy in the return (relaxation) of the heart to its passive form, there still remains a consider- able interval for rest, so that this organ, the very type of cease- less activity, has its periods of complete repose. Fio. 814. — Dia^raiii nptmeaOat the moweauita •ndMMadaoC IIm aautdumgrncariimocrck (aflarSharpejr). THE CIRCULATION OP THE BLOOD. 241 'orce-pump but the aspirating king valves as with each dias- iricles, a result ements of the OazdlMCTol*. ow is meant to lain events in a The relative ihe sounds; the occupied by the duration of the systole, which observed is in )hat of the first among the chief noted. usings of Chau- Marey, obtained eart of the horse> us a very slow how that of the iod,the auricular supies I or A of the ventricular or ^ of a Bee- per minute), the id at about -^ of li event are about ; the ventricular i second. is equal in dura- >n assuming that turn (relaxation) mains a consider- ery type of cease- The Work of the Heart. Since the pressure against which the heart works must, as we shall see, vary from moment to moment, and sometimes very considerably, the work of the heart must also vary within wide limits, even making allowance for large adaptability to the bur- den to be lifted ; for it will be borne in mind that the degree to which the heart empties its chambers is also variable. ' If one knew the quantity of blood ejected by the left ven- tricle, and the rate of the beat, the calculation of the work done would be an easy matter, since the former multiplied by the latter would represent, as in the case of a skeletal muscle, the work of the muscles of the left ventricle ; from which the work of the other chambers might be approximately calculated. The work of the auricles must be slight, considering that the filling of the ventricles is not dependent solely upon their con- traction, that they empty themselves very imperfectly, and that the tracing on Marey's curves (Fig. 210), representing the effect of their contraction on the intraventricular pressure is but smalL Notwithstanding, as they largely determine by their contraction and the quantity they throw into the ventri- cles how full the latter shall be in a given instance, they really have a very large share in determining the total work of the ventricles and the whole heart. /^> The right ventricle, it is estimated does from one fourth to ^one third the work of thold ox 40 Thb Pulse. Natiu'ally the intermittent action of the heart gives rise to corresponding phenomena in the elastic tubes into which it may be said to be continued, for it is very desirable to keep in mind the complete continuity of the vascular system. The following phenomena are easy of observation : When a finger-tip is laid on any artery, an interrupted pressure is felt ; if the vessel be laid bare (or observed in an old man), it may be seen to be moved in its bed forward and upward ; the press- ure i8 loss the farther the artery from the heart ; if the vessel be opened, blood flows from it continuously, but in spurts ; if one finger be laid on the carotid and another on a distant ves- sel, as one of th^ arteries of the foot, it may be observed (though it is not easy, from difficulty in attending to two events hap- pening so very close together) that the beat in the nearer ves- sel precedes by a slight interval that in the more distant. Investigating the latter phenomenon with instruments, it is found that an appreciable interval, depending on the distance apart of the points observed, intervenes. Whau is the explanation of these facts ? The student may get at this by a few additional observa- tions that can bo Easily made. 1. r2 Old age. 82-88 rs 56-60 70 40- 46 ffi 66-60 10 66-60 20 60-70 40 100-120 9 OX, are as fol> r. 02-182 100-120 68 1 64 old 66-68 46 d ox 40 art gives rise to IS into which it rable to keep in jrstem. vation : When a pressure is felt ; Id man), it may nrard ; the press- rt ; if the vessel mt in spurts; if on a distant ves* observed (though two events hap- 1 the nearer ves- re distant, nstruments, it is on the distance litional observa- THE CIRCULATION OP THE BLOOD. 245 If water be sent through a long elaittic tube (so coiled that points near and remote may be felt at the same time) by a bulb syringe, imitating the heart, and against a resistance made by drawing out a glass tube to a fine XK>int and inserting it into tne terminal end of the rubber tube, an intermittent pressure like that occurring in the artery may be observed ; and further Fio. 916.— Mwey'a meotntxm for showtnK Um mode in whidi ths duIm la propagated in tlie arteriea. B, a niSber pump, with TaiTea to pravent regurgitation. The wonting of tlie apparatus will be apparent mm Um inepeotion of the iigure. that it does not occur at precisely the same moment at the two points tested. Information more exact, though possibly open to error, may be obtained by the use of more elaborate apparatus, and the graphic method. Fig. 216 gives an idea of the main features of th9 pulse-trac- ings of an arterial scheme or arrangement of tubes in supposed imitation of the conditions existing in ^e vascular system of the mammalian body. Attention is especially directed to the abrupt ascent, the more gradual descent, uid the secondary waves, which are either waves of oscillation or reflex waves. It may also be noticed that the rise is later as the part of the tube at which it occurs is more distant from the pump ; also that it gets gradually less in height and at the same time that all the secondary waves are diminished or iotally disap- pear ; and with the exception of the latter these results hold good of the pulse in the arteries of a living animal. By measurement it has been ascertained that in man the pulse- wave travels at the rate of from five to ten metres per sec- ond, being of course very variable in velocity. It would seem that the more rigid the arteries the more rapid the rate, for in Mi * tm WW wwm i if Mt ii n i H i i w M i min Hww*^ 246 ANIMAL PHYSIOLOGY. children with their more elastic arteries the speed is slower; and the same principle is supposed to explain the higher veloci- wvXaKaAaaaKaa/vvvvv alaat an elMtlc tube Into which fluid la foroed By the sudden rtroke of a pump. The imU indicate the onwaiil and the reflected wafja the gradual flattenUiK and \otal or partial extinction of the wuvee are noteworthy (after Harey). ty noticed in the arteries of the lower extremities. But with such a speed as even five metres a second it is evident that witU a systole of moderate duration (say "3 second) the most distant arteriole will have been reached by the pulse-wave before that «ysfcole is completed. It is known that the blood-current at its swiftest has no Huch speed as this, never perhai s exceeding in man half a metre per second, so that the pulse and t^^e ' lood-current must be two total) J distinct things. iwiniiwar' I 'I'litunii mmm THE CIRCULATION OP THE BLOOD. 247 The student may very simply iUustrate this matter for him- self. By tapping sharply against a pipe through which a stream is flowing slowly and quietly, a wave may be seen to arise and pass with considerable velocity along the moving water, and with a speed far in excess of the rapidity of the main current. When the left ventricle throws its six ounces of blood into vessels already full to distention, there must be consider- able concussion in consequence of the rapid and forcible nature of the cardiac systole, and this gi\ es rise to a wave in the blood which, as it passes along its isurface, causes each part of every artery in succession to respond by an elevation above the gen- eral level, and it is this which the finger feels when laid upon an artery. That there is considerable distention of the arterial system with each pulse may be realized in various ways, as by watch- ing and feeling an artery laid bare in its course, or in very thin or very old people, and by noticing the jerking of one leg crossed over the other, by which method in fact the pulse-rate may be ascertained. And that not only the whole body but^ the entire room in which a person sits is thrown into vibration '. by the heart's beat, may be learned by the use of a telescope to \ observe objects in the room, which may thus be seen to be in) motion. FeatoTM of an Artorial PulM-Tnuifaf . — In order to judge of the nature of arterial tracings, it is important that the circum- stances under which they are obtained shoiild be known. The movements of the vessel wall in most mammals stiit- n plwwd a> om. uMi roke of » pump. The iteUening Mid total or ties. But wit>j idiant that wiiii he most distant ave before that jwiftest has no an half a metre < mt must be two Fio. mr.—Mbrer'i ImprovMt n;>hyKiiK«Ta|ih MTMyrad for UkloR • tnwlnc. A, Heel spring ; B. ttttt lever ; C, wriUiw-terer ; C\ Urn free wrftiag end ; D, acrew forl>riiiRinK B in con- tact with C ; a, lUde wlHi Mnoked paper : B, olook-work ; L, wsrew for increaaiBK the preesure : .W. dial Indlcattnff the amount of iMc«nire ; K, K, a trape fo rjtein g the InMru- * **- - ^ -' ' - *' —■ ' or M|iport (By rum Bnmwsll). mnnt to the arm, and the latter to the dPUble-lncUiied iMIIWWWmK'WWgW 248 ANIMAL PHTSIOLOOY. able for experiment and in man is so slight that it becomes ne- cessary to exaggerate them in the tracing, hence long levers are used to accomplish this. The sphygmograph is the usual form of instrument em- ployed for the purpose. It consists, essentially, of a clock-work for moving a smoked surface (mica plate commonly) on which the movements of a lever-tip, answering to those of a button placed on the artery, are re- corded. Considering the nature of the pulse and the apparatus em- ithe eMenaupMtot the inatnim^ ployed to Write its characters, it B",ottbe1dtorfieverisinco^Mir«1Si will be seen that the possible the writityt-lerer, C. 'Smn iiK>?«meiit __„____ _* ->«_-»_ ___ ».,,,„«_^„„ or the Htoei qpriiig at A", comninnicA. sources Of error are numerous. IS^iaffi^-K^S'^^^Sl.'SfflSl?'" Different observers have, as a matter of fact, even with the same sort of instrnaient obtained tracings differing not a little in character. Aa tht> subjoined figures show, the pressure ex- erted upon a vessel may so alter the result that entire features of the tracing may actually disappear. The sphygmograph, even in the most skillful hands, has proved somewhat disap- pointing OS a physiological and especially as a clinical instru- ni tnt, though it is not without a certain value. We shall do well to inquire whether there are any features in common in tracings obtained in various ways, and which have therefore in all probability a real foundation in nature. An inspection of a ISST^'Sr, AAAAMAAMAAAyU diverse cdnditions, seems to show that in all of them there oc- curs, more or less marked, the follow- ing : 1. \n upward curve. 2. A downward curve, rendered irreg- ular by the occurrence of peaks or crests and notclies. The first of these are termed the predicrotic notch and crest., Hi^d the succeeding ones the dicrotic notch and crest. The latter woem to be the more constant. Fw. 119.— Pnlae-tnMdiiK from carotid artaiT oT healthy mM (after MoemiJ; 8e of a button artery, are re- he nature of the apparatus em- ts characters, it at the possible ire numerous, ervers have, as , even with the »ring not a little he pressure ex- t entire features sphygmograph, omewhat disap- i clinical instru- ire any features vays, and which ion in nature. roUd artary of hMlthy enoemeM ot expaMton riw; C, diorotio waaMl- wdMy «»▼• ; p. Match moobOpit wave. Carro lag-fork with ten double icrotic notch and notch and crest. That these are genuine, answer of real and corresponding elevations of the arterial wall and of the blood-current itself, seems probable from the study of a hcemau- togram. The latter may be obtained by allowing the blood from a cut artery to spurt against a piece of paper drawn in front of the blood- stream. It is also as- serted that by a tele- phonic connection with an artery both the pri- mary pulse-wave and the dicrotic wave may be heard. More rarely there are interruptions in the first upward curve, termed antwrotio curves, as distinguished from those in the downward curve known as kcUaerotic. It has been generally admitted that the first marked upward curve is due to the systolic shock. The following are, in an.-AoM)rotioiNii»tnM3incfn>mcaroUdof brief, some of the views ''^^^ that have been entertained in regard to the minor features of the tracings : (a.) That the predicrotic wave-crest is owing to the sudden arrest of the flow from the ventricle. (6.) That the dicrotic wave is a wave of oscillation. Fig. tn.' -PulM-ciirve from radial of man. Tkken with aa eztnHraaoular praawire of 70 nun. of taeroarj. The cwTfed Intermpted Mnee ibow the dt a t a n oefrom oneaMithertaitinieot the «hlef phawa ot the potae- wvn. x,thecoiiimenoement,aiMl^,theclaaeaf ex- paiMJkiii of atterr ; p, predicrotic notidi : d, dicrotic notdi; Cdicroao orea* ' " the pok^dicrotlc notdi. mcroHc noion : a, aioroiic />, poat-dicrotle creat ; /, ^fYWW Fm, Fto. SSiS.— Two grades of marked dicrotiam in radial pulae of man (typhoid f^verv (c.) That it is a wave of reflection from the periphery. (d.) That it is caused by the sudden closiire of the aortic valves. It appears to be now pretty well agreed that the theory of reflection is untenable on physical principles; that a high blood-f>re88ure tends to render the kataomtic markings less i-«aa'iinwli.mMi< :~ r rr'..'" . \"m-mm!m wfmm 950 ANIMAL PHYSIOLOGY. distinct, and the reverse when the pressure is low, as after hiemorrhages. These features are especially marked m the no. ns.— Normal putae^sarre in the aorU from the dog. dicrotic pulse of fever, ete., when the blood-pressure is low and may be recognized even by the hand. The anacrotic crests and notches are abnormal, and probably » due to excessive rigidity of the arteries. Certain it is that, without any change in the heart-beat, changes in the tracings may arise, owing to modifications in the periphery of the vascular system. We do not propose to discuss the above-men- ito. «»*-^^'»«S[^"^£ tioned views of the causation of the minor the^^^wcMTUina features of the tracings in detail, about '**°' which the greatest diflferences of opinion still prevail. Even if all the characteristics of an arterial tracing could be ob- tained from an arti- ficial schema, it would not follow that the conditions in each case were the same ; in fact, as we view the mat- ter, it would be all but impossible that such should be the case. Bubbev tubes are not comparable to arteries; and espe- cially not to arteri- oles and capillaries. Bearing in mind the peculiar nature of the blood-corpuscles; their relation to the walls of the vessels in which they flow; the relation of the Fio. aB.^bifliMBoe of the exterior o(,the !«■ in the pNMure Mipiied to (eztr»-vMculMr) on the form of ^SMTwUh an extHWUftwHa Brewire of, ino, TO mm.. In a', to 80 mm., rati in a", to mm. merciuy. 8MMI« THB CIRCITLATION OF THB BLOOD. 251 low, as after larked in the ire is low and uacTotic crests and probably the arteries, at any change m the tracings Lcations in the ^stem. We do le above-men* >n of the minor 1 detail, about ices of opinion of an arterial le prMMm applied to ■acuter) on the ronn of » mMi of twenM'-MTMi Hure of, in o, TV mm., im.m««ui7. relation to the relation of the no. ns.— IXorotlc pulM-curre due to luemoRliagie. Ftam carotid o( rabbit, with extra-Taacular pr c w w i r e of, in a, BO mm., 6, of 40 mm., c, of W mm., and d, of 10 mm. vaeKurr. (Thia and the precc«ling lix tracinfi from Foater.I blood to the nutrition of the tissues; the fact that all the tubes that compose the vascular system are made up of living cells ; that some of these ,^ ^ cells (in arterioles and capillaries) are in a semi-fluid condition — in a word, that the conditions of the cir- culation as a whole are aui generis, be- cause of their vitality — it seems to us amaz- ing that purely physical explanations, such as would answer for a pump and set of rubber tubes, should ever have been deemed satisfactory. The whole subject seems to be involved in a gross misconception, and should be regarded, we must think, from an entirely new standpoint. Temnis Pnlas. — Apajrt from the variations in the caliber of the great veins near the heart, constituting a sort of pulse, though due to variations in intra-cardiac pressure, a venous pulse proper is rare as a normal feature. One of the best- known examples of such occurs in the salivary gland. When, during secretion, the arterioles are greatly dilated, a pulse may be witnessed in the veins into which the capillaries open out, owing to diminution in the resistance which usually is suffi- ciently great to obliterate the pulse-wave. PsyudogioaL — In severe cases of heart-disease, owing to cardiac dilatation or other conditions, giving rise to incompe- tency of the tricuspid valves, there may be with each ventricu- lar systole a back-flow, visible in the veins of the neck. A>^ A venous pulse is a phenomenon, it will be evident, that always demands special investigation. It means that the usual bounds of nature are for some good reason.being over^stepped. Oom p ara t lti. — Before entering on the consideration of j^ue- nomenathat all are agreed are purely vital^we call attention to the circulation in forms lower than the mammal, in order to give breadth to the student's views and prepare him for the special investigations, which must be referred to in subsequent chapters ; and which, owing to the praviou^ narrow limits (re- searches upon the frog and a few well-known mammals) having at last been overleaped, have opened up entirely new aspects of cardiac phy8iology-H>ne might almost say revolutionized the subject. X-lV^ . . ■sn^'^T*^:;!^ '.v,'; 252 ANIMAL PHYSIOLOGY. h Owing to the limitations of our space, the references to lower forms must be brief. We recommend the student, however, to push the subject further, and especially to carry out some of the experiments to which attention will be directed very shortly. In the lowest organisms (Infuaorians) represented by Amoe- ba, Vorticella, etc., there are, of course, no circulatory organs, unless the pulsating vaf:'aoief: of some forms mark the crude beginnings of a heart. It w ill be bomo in mind,^ however, that there is a constant streaming of the protoplasm itself within the organism. Among Goelenterates (Figs. 254, 255) the digestive system, as yet but imperfectly developed, seems to embody in itself a sort of combination of the functions of the preparation and distribu- tion of elaborated food ; and it is worth while to note that even in the highest animals the digestive tract remains in close con- nection with the circulatory system. The heart is first represented, as in worms, by a pulsatile tube, which may, as in the earth-worm, extend throughout the greater part of the length of the animal, and has usually dorsal and ventral and transverse connections. The dilatations of the transverse portions in one division {metamere) of the animal seem to foreshadow the appearance of auricles. The pulsation of the dorsal vessel in a large earth-worm is easy of observation. In the mollusks the heart consists of a ventricle and one or more auricles, and these chambers give off and receive large vessels (Fig. 227). These hearts may be observed ptdsating with the naked eye or a lens in the clam, oyster, or snail, and are to be looked for in the first two on the side of the animal toward the hinge of the shell. It is worthy of note that in cephalopod mollusks (Cuttle- fish, Poulpe) there are branchial hearts, which may be re- garded in the light of pulsatile venous expansions, a remnant, perhaps, of conditions found in lower forms, in which we have seen that the rhythmically contracting tube plays a prominent In amphioxus, which is often instanced as the lowest verte- brate, the blood-vessels, including the portal vein, are pulsatile, while there is no distinct and separate heart ; but, in connection with the above observations in cephalopods, it is to be r** THE CIRCULATION OP THE BLOOD. 868 mces to lower h the subject xperiments to ited by AmoB- latory organs, »rk the crude however, that itself within iive system, as In itself a sort 1 and distribu- note that even 8 in close con- by a pulsatile hroughout the usually dorsal n one division 9 appearance of earth-worm is cle and one or i receive large 1 the naked eye > be looked for •d the hinge of jUusks (Cuttle- ch may be re- ons, a remnant, which we have lys a prominent he lowest verte- in, are pulsatile, at, in connection it is to be r*- marked that in this creature there are contractile dilatations at the bases of the branchial arteries. "^Ai y (Siipfa oAeJuoUf), trfewed from ). B^t^lm ; C, wntride : ^o Hid Jo', Mtwior and poate- V&, M^Mlor Teuk «ink : re", iwrtntor ym^ '^Zt^i "^ KJr, advriieiit brMwhtel TC«da (htm nchm •rterjM) ; Kh, of tlM Mme ; At, AV, MiriclM reoeirlng the revebent Fia. Mf7.— Circulatory and the donal aide (aftei rior aorta ; V. lateral appendasea of the veius; branchial heart; Ap, a| " branchial y v m »\» (branc In some Ascidians the heart is of a somewhat crescentic form, and has the remarkable property of beating for a time in one direction, then stopping and reversing its rhythm. In a transparent specimen, under the microscope, this can be seen admirably. In the crab the heart lies within a pericardium, loosely at- tached, the main vessels being connected with the pericardium and not directly with the heart. The heart sucks its blood from the pericardial cavity through four valvtdar openings. In such a creature as the scorpion there is a chambered heart, with a division for each principal segment of the animal's body (Fig. 308). While in moUusks, crustaceans, and other groups, the vas- cular system does not form a connected whole, the scorpion is exceptionally advanced in this respect, being provided with capillaries, or tubes closely representing them. Among most of the invertebrates the blood, after leaving the arteries, passes into rather wide, irregular spaces among the various tissues, from which it is taken up by the veins without the intervention of an intermediate set of vessels. The circulatory system of an insect or crustacean may be i k ' jM> W iwwi « w ' ^i^ ''W '*M»* *i«i i i uii.iiM i i'W W 4iiiJU WW* iwa»w 1^^— - — 354 ANIM/L PHYSIOLOOT. viewed microscopically i a aquatic forms, which are often quite transparent, especially i a the larval condition. Although the respiratory system will be treated from the comparative point of view, the student will do well to note now t'mmiimmmmm r ^, IMAGE EVALUATION TEST TARGET (MT-3) 1.0 V^ 1^ FhotograiJlic Sdenoes Carporatioii as WIST MAM STRHT WnSTII,N.Y. 14SI0 (7l«)l7a>4S03 - i^wfiBI r x CIHM/ICMH Collection de ■-\fmtasfm 266 ANIMAL PHYSIOLOGY. k -^ Passing on to the vertebrates, in the lowest group, the fishes, the heart consists of two chambers, an auricle and a ventricle, the latter being supplemented by an extension {bulbu8 arterio- stu) pulsatile in certain species; and an examination of the course of the circulation will show that the heart is through- out venous, the blood being oxidized in the gills after leaving the former. Among the amphibians, represented by the frog, there are two auricles separated by an almost complete septum, and one A^f f^ rw. FM Fto. . ni-TlMfNK^heMt, wen from llMfKmL the MTtieandMoCtteMt rite Iwvt.«,TeMc*nkbU(8riar;j».ei(, pofaiMMMUiMaiH tniiik^r,tnuiciNaitMfc)MM;«.vMrtride(Ho«rca). ^ _. . .j _ v .•„ no. ■S.-neiMn^MwlMmMiiiid,tlwitauNT«MMMlw«lv bMBopca^ rimhMiricalw vahM. (In I.) p.«,imlinoMur]r v^b; t.«, rimavcwMiM; «a'',ria»«u- rieotorTidTe. oSiar MMfaMt •■ in ■%• Mi (Howw). ventricle characterised by a spongy arrangement of the mus- cle-fibers of its walla. In the reptiles the division between the auricles is complete, and there is dne ventricle which shows imperfect subdivisions. In the crocodile, however, the heart consists of four per- fectly divided chambers. Of the two aortic arches, one arises together with the pulmonary artery from the right ventricle, and, as it ciosses over, the left communicates with it* by a small opening, so that, although the arterial and the venous blood are completely separated in the heart, they intermingle outside of this organ. In birds the circulatory system is substantially the same as in mammals ; but in all vertebrate forms below birds the blood distributed to the tissues is imperfectly ozidiiied or is partially venous. ^ \ roup, the fishes, ind a ventricle, bfdbus arterio- tination of the at is through- 8 after leaving frog, there are Bptum, and one » hft itde Iwvf ng beea heU, IMfalMMMUlMaiH opHMd up to ihow the nmemm ; va", rimi-Mi- at of the mus* sles is complete, ct subdivisions, ts of four per- ■ches, one arises right ventricle, th it' by a small 6 venous blood rmingle outside illy the same as birds the blood d or is partially THE Cl&CULATION OF THE BLOOD. 367 As an example of the influence of valves and of blood-press- ure on the distribution of the blood we may take the case of the turtle, in which the subject has been most carefully studied. ..«« iio. m' v7,. nkt {Ul •»r.*V 7*/ Fu>. tM.-TlM hMrt, dtane tricoIirTahrw havtac tha r^ ^ — «ai«»; A. «, ~ ; MctleHali] olriiiiktlnii (iftw J Fw. MB, ftoM tiw front, the Tentral wall and one of the Miricnlo-Ten- ' (1 M &) The rod, peMring (ram the ventricle Into «.J».«^.' W Ivthe blood flowinc wo the oerotid nnd aortic t»MVBtrjat iwlmowary Vein ; va", linitwirtaalar wtfi — rhiile witflenlir val**; «a. «, eeaifchmar ' vaHe (aeiitiiin) a( {qrlanftani ; p. CM', point of SfklSL' »"? ^^^'^'^^ As a result of the entire arrangement, the least oximaea blo^^ to the lungs, and the most aSrated to the head and anterior narte of the animal. _. i.i„ „«,«. fe the frog and otheroreatures, with three fanperfectlysepa. rated heart cavities, a similar result is attained. "^^^!L^ in »* r" t. the '»^. .7^^" iMmmato, iiiclodtog man, wiU b* «w>M«it, Md xt la en«o»liy •aaf THE GIBCULATIOM OF THE BLOOD. S69 lelf with some of lich the arrange- ]L.X idlp,MR|iid- BOSarOagMi- C. V, oSmm vnomim. C. p. fj. B.AO,. ithat,a8thesyetole ) cavum pulmonum : the heart wall, and om the purer blood. ,the least oxidiaed bted to the head and ee imperfectly aepa^ ined. fo^al conditions in , and it is especially to be observed that in the case of the foetus and these lower groups of vertebrates the brain and anterior parts — that is, the most important portions of the animal functionally, the parts on which the rest depend for their well-being (since the brain is the seat of all the main directive centers)— are fed with the best blood the organism possesses, a fact which probably explains in part the relatively large size of these portions of the body early in foetal life and throughout its duration. We now urge upon the student the importance of making some observations for himself upon the heart of the frog, tur^ tie, snake, fish, or other of the cold-blooded animals. At- tention should be given chiefly to the functions of the heart, though to do this intelligently it must be preceded by some study of the anatomy of the organ. It will be understood that any directions we may give for the manipulative part of the work will be of the simplest kind, and rather suggestive of the general method of procedure than intended to illustrate the best methods. In reality, it is better for exact investigation of the heart that no auffisthetic be given, and an animal may be rendered insensible by a sudden blow upon the head, which, as we shall show later, may be painless. However, it will be, upon the whole, perhaps, best that the animal be given a few whiffs of dther beneath some (glass) vessel, and as soon as it becomes insensible, to withdraw the aneesthetic, remove or crush the head (brain), so that throughout the investigation there may be neither interference with the heart from this organ nor any doubt about the animal's insensibility. It is well to open the abdomen a little below the heart, so that the latter may be exposed, with its pericardium intact, when the relations of the l-aati to the surrounding parts may be noticed. What strikes every observer is the sluggish action of the hearts of these animals— a great advantage in attenvpting to estimate roughly the relative time occupied by the systole and diastole, of the different chambers; the peculiar vermiform nature of the contraction; the changes of color dependent on the degree to which any chamber is filled with blood; and many of those minor details important in nwking up a total general impression, but not readily expressed in words. After the animal has been bled, the heart's action may still be profitably studied; and, finally, it may be learned that the i Sli f iiHf 900 ANIMAL PHTSIOLOOT. V heart will pulsate when removed, either entire or after being divided into sections. In another specimen it would be desirable to allow the heart, to be kept bathed in serum or physiological saline solu< tion, to beat as long as it will, and to note the various phases of irregularity, weakening, and cessation of action in its dif- ferent parts. It is also highly instructive to observe the effect of ligating off certain of the chambers from the rest of the organ. * Any one who makes a few such observations will be pre- pared to comprehend readily any of the experiments on ,the hearts of the cold-blooded animals, and will be able, especially if he has followed out earlier recommendations as to the study of the heart of the xdammal, to form a mental picture of what is transpiring within his own breast, which is one of the most dosirable accomplishments — ^in fact, the best test of real knowl- edge. Whatever ground for differences of opinion there may be as to the extent to which the phenomena we have as yet been describing are mechanical in their natiure, all are agreed that such explanations are insufficient when applied to the facts witb which we have yet to deal They, at all events, can be regarded only as the result of vitality. C^lien one reflects upon the vicissitudes through which an animal must pass daily and hourly, necessitating either that they be met by modified action of the organs of the body or that the destruction of the organism ensue, it becomes clear that the varying nutritive needs of each pait must be met by changes in the circulatory system. These changes may affect any part of the entire arrangement, and it rarely happens, as will appear, that one part is modified without a correspond- ing one, very frequently of a different kind, taking place in some other. What these various correlated modifications are, and how they are brought about, we shall now atten^pt to describe, and it will greatly assist in the comprehension of the whole if the student will endeavor to keep a clear mental pict- ure of the parts before his mind throughout, using the figures and verbal descriptions only to assist in the construction of such a mental image. We shall begin with the vital pump— the heart. ■mrr ■ L., , .m..!tiU.,..,UU.a.tL. .- ■JL-' THE CIBCULATION OF THE BLOOD. 261 3 or after being lie to allow the rical saline solu- a various phases iction in its dif- effect of ligating le organ. * ions will be pre- leriments on ,the M able, especially IS as to the study il picture of what B one of the most «st of real knowl- ion there may be ) have as yet been 11 are agreed that plied to the facts all events, can be through which an itating either that ms of the body or e,it becomes clear li must be met by changes may affect rarely happens, as hout a correspond- id, taking place in 1 modifications are, ill now attempt to >mprehension of the a clear mental pict- it, using the figures the construction of th the vital pump— Thk Beat of the Heart and its Modifications. As has been already noted, the cardiac muscle has features peculiar to itself, and occupies histologically an intermediate place between the plain and the striped muscle-cells, and that the contraction of the heart is also intermediate in character, and is best seen in those forms of the organ which are some- what tubular and beat slowly. But the contraction, though peristaltic, is more rapid tf this region were beart ceased to beat > action of the inner r explanations have s been thrown upon , consequoice of in- arious cold-blooded 9 hearts of the Che- wcial attention, and suits, to the general g from recent com- )fer. the main facts : ir in which the sub- lien kept under the B, auricles, sinus. Aed by section, Hgar ture, or otherwise, either together or singly, continue to beat, whether amply provided with or surrounded by blood. 8. The ventricle thus separated displays less tendency to beat independent of some stimulus (as feeding under pressure), though a very weak one usually suffices — i. e., its tendency to spontaneous rhythm is less marked than is the case with the other parts of the heart. These remarks apply to the hearts of Chtioniana — ^fishes, snakes, and some other cold-blooded animals. 4. In certain fishes (skate, ray, shark) the beat may be. re* versed by stimulation, as a prick of the ventricle. This is accomplished with more difficulty in other cold-blooded animals, and still more so in the mammaL 6. In certain invertebrates, notably the F&ulpe (Octopus), a careful search has revealed no nerve^sells, yet their hearts con- tinue to beat when their nerves are severed, on section of parts of the organ, etc. 6. A strip of the muscle from the ventricle of the tortoise, when placed in a moist chamber and a current of electricity passed through it for some hours, will commence to pulsate ai^ continue to do so after the current has been withdrawn; and this holds when the strip is wholly free from nerve-cella From the above facts certain inferences have been drawn : 1. It has been concluded that the sinus is the originator and director of the movements of the rest of the heart. 2. That this is owing to the ganglia in its walls. While all recognize the importance of the sinus, some physiologists hold to the gangli- onic influence as essential to the heart-beart, still ; while others, influenced by the facts mentioned above, are disposed to regard them as of very doubtful importance — at all events, as origina- tors of the movements of the heart The tendency now seems to be to attach undue importance to the spontaneous contractility of the heart-muscle; for it by no means follows logically that, because a muscle treated by electricity, when out off from the usual nerve influence that we believe is being constantly exerted on the heart like other or- gans, will contract and continue to do so in the absence of the stimulus, it does so normally; or, because some hearts beat in the absence of nerve-cells, that therefore nerve-cells are of no account in any case. Such views, when pressed to the extreme, lead to as narrow conceptions as those they are intended to re- place. Taking into account the facts mentioned and others we have M4 ANIMAL PHTtUOLOOT. not space to enumerate, we submit the following as a safe view to entertain of the beat of the heart in the light of our present knowledge : Recent investigations show clearly that there are great dif- ferences in the hearts of animals of diverse groups, so that it is not possible to speak of "the heart" as though our remarks applied equally to this organ in all groups of animals. (It must be admitted that our understanding of the hearts of the cold-blood animals is greater than of the mammalian heart ; while, so far as exact or experimental knowledge is concerned, the human heart is the least understood of all, though there is evidence of a pathological and clinical kind and subjective experience on which to base conclusions possessing a certain value ; but it is clear to those who have devoted attention to (Comparative physiology that the more this subject is extended .the better prepared we shall be for taking a broad and sound view of the physiology of the human heart and man's other organs. Whatever may be said of the invertebrates, among which greater simplicity of mechanism doubtless prevails, there can be.no doubt that the execution of a cardiac cycle of the htert in all vertebrates, and especially in the higher, is a very com- plex .process from the number of the factors involved, their in- teraction, and their normal variation with circumstances; and we must therefore be suspicious of any theory of excessive sim- plicity in this as well as other parts of physiology. We submit, then, the following as a safe provisional view of the causation of the heart-beat : 1. The factors entering into the causation of the heart-beat of all vertebrates as yet examined are : (a) A tendency to spon- taneous contraction of the muscle-cells composing the organ ; (b) intra-cardiac blood-pressure; (c) condition of nutrition as determined directly by the nervous supply of the organ and in- directly by the blood. 3. The tendency to spontaneous contraction of muscle-cells is most marked in the oldest parts of the heart (a g., sinus), ancestrally (phylogenetically) considered. 3. Intra-oardiac pressure exercises an influence in determin- ing the origin of pulsation in probably all hearts, though like other factors its influence varies with the animal group. In the moUusk (and allied forms) and in the fish it seems to be the controlling factor. 4. We must recognize the power one cell has to excite when THE CIRCULATION OP THE BLOOD. 866 I as a safe view of our present re are great dif- ■oups, so that it gh our remarks limals. of the hearts of immaliau heart ; {e is concerned, though there is and subjective eesing a certain >ted attention to iject is extended >road and sound and man's other )s, among "which ■evails, there can iycle of the hbart Br, is a very com- Involved, their in- rcumstances; and r of excessive sim- logy. rovisional view of of the heart-beat tendency to spon- [KMBittg the organ ; >n of nutrition as the organ and in- Dn of muscle-cells leart (a g., sinus), lence in determin- earts, though like ikuimal group. In ti it seems to be the has to excite when in action neighboring heart-cells to contraction. The abilityN that one protoplasmic cell-mass has to initiate in others, under^ certain circumstances, like conditions with its own, is worthy j of more serious consideration in health and disease than it has) yet received. 5. The influence of the cardiac nerves becomes more pro- nounced as we ascend the animal scale. Their share in the heart's beat will be considered later. 6. Apparently in all hearts there is a functional connection leading to a regular sequence of beat in the different parts, in which the sinus or its representatives (the terminations of great veins in the heart) always takes the initiative. One part hav- ing contracted, the others must necessarily follow ; hence the rapid onset of the ventricular after the auricular contraction in the mammal, and the long wave of contraction that seems to pass evenly over the whole organ in cold-blooded animals. The basis of all these factors is to be sought finally in the Cn^iua:cdsorUiv^^^lja£.£xo^^ A heart in its most devel- oped form still retains, so to speak, the inherited but modifietl Amoeba in its every cell. Whether the intrinsic nerve -cells of the heart take any share directty in the cardiac beat must be considered as yet undetermined. Possibly they do modify motor impulses from nerves, while again it may be that they have an influence over nutritive processes only. The subject requires further study, both anatomical and physiological. Intlukncb of the YAQvar Nerve upon the Heart. The principal facts in this connection may be stated as fol- lows, and apply to all the animals thus far examined : 1. In all cases the action. of the heart is modified by stimu- lation of the medulla oblongata or the vagus nerve. 2. The modification may consist in prompt arrest of the heart, in slowing, in enf eeblement of the beat, or a combination of the two latter effects^ 3. After the application of the stimulation there is a latent period before the effect is manifest, and the latter may outlast the stimulation by a considerable period. 4. In most animals the sinus venosus and auricles are af- fected before the ventricles, and the vagus may influence these parts when it is powerless over the ventricle. 5. After vagus inhibition, the action of the heart is (almost AMIMAL PHYSIOLOGY. jlMMilMM^^ JiUlJUUiMI naUngoa it. foTAOoMider- we may «y i^ *, wki.,g <»P«*»y of th« h»rt U t™- porarily increased. .fficieDor ol the heart is in pro- attotilflttonViiOW. ^.n i. feeble "'■|;^-'^^^TJi^^pSJ^ttw1.^t in proportion to its needs. ^Th»" * ^"^^ '^ de^rves to receive » 8«^«r^^'!^^te in histological altem- 7. Section of both vag^ '^''^^JS^Z^i^eZion, which tlonsintheheart'Bstmctu^,c^e^«»t^^^ ^^ ^^ strains of life. .,~> aia'>i"" "*"' li THE CIHCULATION OF THE BLOOD. 967 : variable, but in force. (AJliliUl/Ul/ TbbeNiid(romri«M nnieleTM' r u K In g on It. ■ToOMmd iMteMMTMl k It iMtad for » ooiMUer- le heart is tem- j heart is in pro- 1 cases when the \ rgmngv^ililo 001 re darhred light be said to be nportant law that liistological altera- )generation, which ity and eicpoee it tquently recurring 8. In the cold-blooded animals the heart may be kept at a standstill by vagus stimulation till it dies, a period of hours (one case of six hours reported for the sea-turtle). 9. Certain drugs (as atropine), applied directly to the heart, or injected into the blood, prevent the usual action of the vagus. 10. During vagus arrest the heart substance undergoes a change; reisulting in an unusual dilatation of the organ. This may be witnessed whether the heart contains blood or not. 11. The heart may be arrested by direct stimulation, espe- cially of the sinus, and at the points at which the electrodes are applied there is apparently a temporary paralysis. The same alteration in the beat may be noticed, as when the main trmik of the vagus is stimulated. 12. The heart may be inhibited through stimulation of vari- ous parts of the body, both of the surface and internal organs (reflex inhibition). 13. One vagus being divided, stimulation of its upper end may cause arrest of the heart. 14. Stimulation of a small part of the medulla oblongata will produce the same result, provided one or both vagi be intact. 15. Section of both vagi in some animals (the dog notably) increases the rate of the cardiac beat. The result of section of one pneumogastrio nerve is variable. The heart's rhythm is usufJly to some extent quickened. 16. During vagus inhibition from any cause in mammals and many other animals, the heart responds to a single stimu- lus, as the prick of a needle, by at least one beat. An observer studying for himself the behavior of the heart in several groups of animals with an open nund, for the purpose of observing all he can rarther than proving or disjnroving some one point, becomes strongly impressed with the variety in unity that runs through cwrdiao physiology, including the influence of nerve- cells (centers) through nerves; for it will not be forgotten that normally nerves originate nothing, being conductors only, so that when the vagus is stimulated by us we are at the most but imitating in a rough way the wcKrk of central nerve-cells. We can only mentioiL a few points to illustrate this. In the frog a succession of light taps, or a single sharp one ("Klopfversuch*' of Qolta), wiU usually arrest the heart re- flmdy; though somettmes it is very difficult to accomplish. But in the fish the ease with which the heart may be reflexly sefwjf! MRRKa f l i l WJ BWWMl i iiitwwjatutiwiwwi ii iwiii yBWiiilBi^^ S168 ANIMAL PHYSIOLOGY. inhibited bv Kentle stimtilation of almost any portion of the ::S;^woXrfuL Again,in some animals the vagus arreBt. ItVacw. B«w(. Bmteabofvliadull*. ^^-s^^sstssLSsss: ^flgnBkNW'ra> y& AMwMita «h. lieMt for oriy . brirf period, wh« it Vr»k. .way toto !♦. ragna inhibition— i. »., It *o«» not re»pono w • u. •^^ ta ™»jiy .c««.to ««i« to *«* *';i!sin;; «athological ' and clinical as well as physiological, ^e student may believe^ that the vagus nerve, like the other nerves of the body, accord- ing to our own theory, exercises a constant beneficial, guiding^ —let us say determining— influence over the metabolism of the ^ organ it supplies; and we here suggest that, if this view were< applied to the origin and course of cardiac disease^ it would^ result in a gain to the science and art of mediciivi. The Accblbratos (AuoMBirroR) Nntyn of •osm Hbabt. It has been known for many years that in the dog, cat, rab- bit, and- some other mammals, there were -nerves proceeding from certain of the ganglia of the sympathetic chain high up, stimulatioa of which led to an aooelffiratioa of the heart-beat. Very recently these nerves have been traced in a number of eold-blooded animals, and the whde subject placed on a broader and soundw basis. THE CntCULATION OF THB BLOOD. 971 disorders of/ angaish or^ application i >i&t to infla- life-processeBJ cold-blooded rates, cofwisto proper and system. ' utritive pro- ire. This has « oonstntctive catabolic) me- n of the body >wiiig anabolic any more ry of the body of vhat in all 9 implied that kenupwMrd in y certain down- s too rigid and ce, pathological int may believe^ le body, accord- teficial, guiding^ tabolism of the « this view were< isease, it woold^ ne. There are variations in the distribution of these nerves for different groups of animals, but it will suflBoe if we indicate their course in a ig^neral way, without special reference to the variations for each animal group : 1. These nerves emerge from the spinal cord (upper dorsal region), and proceed upward before being distributed to the heart 2. They may leave for their cardiac destination either at (a) the first theraoic (or basal cardiac ganglion, as it might be named in this case), (6) the in- ferior cervical ganglion, (e) the annulus of VieussensyOr (d) the middle cervical ganglion. lO — lOonL AOMlMMtar Oniter tai Itodnll*. Supgrior Oar«iMd GwnHoB. WddtoOw*lMd« InCarior OBrriad a«i«liaa. Bagtoaornntl UUwatanitor X« BMrt. r TKB Hbabt. le dog, cat, rab- rves proceeding chain high up, the heart-beat, n a number of )ed (ma broader 'JTll Their course haa been traoed by physiological methods ; thus it has been found that, in all animals Munined, stimulation of the signal cord or tiie various parts mentioned above, or nofve bmnches from them, gave rise elttor to acceleration of 97S ANIMAL PHT8I0L0OT. §'■■ the cardiac beat or augmentation of its force, or to both, as is commonly the case. In every instance the work of the heart is increased, so that they may be called more appropriately augmerUor nerves; and their effect may be more evident on one part of the heart, as regards increase of the force of the beat, than on another. They require for their fullest effect a rather strong and con- tinuous stimulation (interrupted current), and the augmenta^ tion outlasts the stimulus a considerable period. The samiB law applies to them as to the vagus nerve, viz., that the result is inversely proportional to the rhythm of the heart at the period of stimulation; a slow-beating heart will be more augmented proportionally than a rapidly-pulsating organ. It is noticeable that after one or more experiments the heart often falls into an irregular or weakened action quite the re- verse of what ensues when the vagus is stimulated. But it has als3 been observed that certain of the vagus fibers on stimula- tion give rise to a like result. Further, it is found that the electrical condition of the heart is different, according as the inhibitory or other fibers of the heart are stimulated. The latter fact seemed to poiat strongly to a fundamental difference in their effect on cardiac metabo- lism ; hence it is proposed to speak of the vagus as a vago- sympathetic nerve, containing inhibitory fibers proper and sympathetic or motor fibers to be classed with the nerves that were formerly known as "accelerators," and to be compared in their action to the ordinary motor nerves of voluntary muscles. Indeed, these conceptions will probably give rise to a broader view of the whole nervous system, especially as regards the relations of the nerves themselves. Certainly the augmentor nerves to which we are now refer- ring exhaust the heart, lead it to expend its nutritive capital, and leave it worse than before. One can understand the ad- vantage in the heart having a double supply of nerve-fibers with opposite action; and it is worthy of special note in this connection that, when the vagus (vagOHsympathetic) is stimu- lated at the same time as the augmentors, the inhibitory effect, preservative of nutritive resources, prevails. It will be seen that the heart may be made to do increased work in three ways i Firstly, the relaxation of a normal inhibi- tory control through the vagus nerve by the cardio-inhibitory center; secondly, through Uie sympathetic (motor) fibers in i jll l KHW ' j. i ■! THB GIBGULATION OF TH£ BLOOD. 278 both, as is I the heart propriately evident on orce of the ' ig and oon- augmenta- Le samiB law le result is ; the period augmented ts the heart uite the re- But it has on stimula- of the heart ibers of the int strongly iac metabo- as a vago- proper and nerves that e compared t voluntary to a broader regards the e now ref er- tive capital, and the ad- nerye-fibers note in this ic) is stimu- t)itory effect, lo increased irmal inhibi- io-inhibitory }r) fibers in the vagus itself ; and, finally, through fibers with similar action in the sympathetic system, usually so called. The share taken by these factors is certainly variable in dif- ferent species of animals, and it is likely that this is true of the same animals on different occasions. It is also conceivable, and indeed probable, that they act together at times, the inhibi- tory action being diminished and the augmentor influence in- creased. Huuui Phyiiokfy. — Of the three cardiac nerves — superior, middle, and inferior— the strongest, which is the middle one, passes from the inferior cervical ganglion to the middle, from which it proceeds to the heart, and the inferior, may be re- garded as the chief augmentor cardiac nerves. That man's pneumogastric contains inhibitory fibers is evi- dent from the experiment of Czermak, who, by pressing a bony tumor in his neck against his vagus nerve, could arrest his heart Another individual could arrest his heart-beat at will, and if not through the vagus, how ? We are probably all aware of alterations in the rhythm of , the heart from emotiona During a period of intense, brief, sympathetic anxiety, as in w;atching two competitors during a' severe struggle for supremacy, a change in the rhythm of the heart, amounting, it may be, to momentary arrest, may be observed. Enough has been said, we trust, to show that the nerves of the heart can no longer be regarded merely as the reins for^ bridling the cardiac steed; but that all the phenomena of accel- eration, slowing, or other changes of rhythm, are only the out-' ward evidences of profound vital changes accompanied by cor responding chemical and electrical effects. If these views bCj correct, nervous influence must play no small part in the causa-^ tion and modification of disordered conditions; and we would extend such a view to all the organs of the body, and especially in the case of man. The heart's rhythm can, however, be^ modified in other ways than we have as yet described. Though an isolated heart, fed by seruin or some artificial nutritive fluid, may beat well for a time,, it is liable to peri- odic interruptions, which are probably owing to its imperfect nutrition. [llany drugs greatly modify the heart-beat ; but, in attempt- ing to explain how the result is accomplished, the difficulty is in unraveling the part each anatomical element plays in the total result. Does the drug act on the muscular tissue, the 18 j ii. « i!i i4immal according to the blood-pressure, when the vagi nerves are cut, and considering the dominance of the central nervous system, it does not seem likely that it should resign the con- trol of so important a matter. Experiment bears this out. There is some evidence for believing that not only may the vagus itself act as an afferent sensory nerve, but that the de- pressor nerve, to be shortly referred to more particularly, is also such a sensory nerve. However, such a view does not exclude previously men- tioned factors, and there can be little doubt that in forms below mammals the muscular tissue is to some degree self -regulative; and it is not likely that this quality is wholly lost even in the highest mammals. THE GIROULATIOK OP THE BLOOD. 275 it the heart a. such cases, BUBB. [lOut the cir- in either the iblood-presa- len the heart eliasticity of ^ a matter of Dccur is pre- seen ; but, so e weaker the d the blood- to the condi- the vascular Ive that there ) beat of the blatter again «lf— the arte- id that, apart ^lls regulate 18 made upon »rf ectly in the le yag^ nerves intral nervous esigh the con- 9ars this out. only may the t that the de- articularly, is sviously men- n forms below elf -regulative; st even in the ^•-^ The effedt of vagu8 stimulation on the blood-pressure is always very marked, as would be supposed. To examine an extreme case, suppose the heart arrested for a few seconds, the elastic recoil of the arteries continues to maintain for a time the blood-pressure, though there is, of course, an immediate and pronounced fall. And it may be remarked, by-the-way, that in cases of fainting, when the heart ceases to beat, or beats in the feeblest man- ner, the importance of this arterial elas- ticity as a force, maintaining the circulation for sev- eral seconds at least, is of great importance. As seen in the tracing, the beats, when the heart 1 commences its ac '^aKl^gSS'rb&SSS^SSr^ tion again, tell on SL'^'^iTSi&rS'tff^SSlI^^ the comparatively ttgpyll>rcliM«etwrotth>cnw^qgriiliigbloo* |ii« M M T8 slack walls of the arteries, distending them greatly, and this may be made evident by the sphygmograph as well as the manometer ; indeed, may be evident to Ihe fii^;er, the jmlse resembling in some features that following excessive loss of blood. If the heart has been merely slowed, or its pulsation weak- ened, the effects will of course be less marked. Tks (towBttty of llotd.-- The blood-pressure may also be augmented, the cardiac frequency remaining tlM same, by the quanti^ of blood ejected from the ventricles, which again depends on the quantity entering them, a factor determined by the o(mdition of the vessels, and to this we shall presently turn. ' In consequence of changes in different parts of the system by way of compensation, results follow in an animal which might not have been anticipated. Thus, bleeding, unlesa to a dangerous extreme, does not lower the blood-pressure except temporarily. It is estimated that the body can adapt itself to a loss of as much as 3 per cent of the body-weigfai The adaptation is probably not through absorption chiefly. iWh;***-*'.'*'^) IIIW i l il l. lW IltiMM 276 ANIMAL PHTSIOIiOOT. k ft- I but through constriction of the vessels by the vaso-motor nerves. Again, an injection of fluid into the blood does not cause an appreciable rise of blood-pressure, so long as the nervous sys- tem is intact ; but, if by section of the spinal cord the vaso- motor influences are cut off, then a rise may take place to the extent of 2 to 8 per cent of the body- weight, the extra quan- tity of fluid seeming to be accommodated in the capillaries and smaller veins. These facts are highly significant in illustrat- ing the adaptive power of the circulatory system (protective in its nature), and are of practical importance in the treatment of disease. ^We think the benefit that sometimes follows bleeding has not as yet received an adequate explanation, but we shall not attempt to tackle the problem now. Changes in the circulation depend on variations in the size of the blood-vessels. It is important in considering this subject to have clear no- tions of the structure of the blood-vessels. It will be borne in mind that, while muscular elements are perhaps not wholly lacking in any of the arteries, they are most abundant in the smallest, the arterioles, which by their variations in size are best fitted to determine the quantity of blood reaching any organ. It is well known that nerves derived chiefly from the sympathetic system pass to blood-vessels, though their exact mode of termination is obscure. We may now examine into the nature of certain facts, which may be stated briefly thus : 1. In certain vascular areas of some vertebrates, as in the vessels of the ear of the rabbit and this animal's saphena artery, rhythmical variations in the size of the small arteries may be observed ; also in the veins of the bat's wing and of the fins of certai];|i fishes (e. g., caudal vein of the eel), as well as in certain arteries of some groups of the cold-blooded animals. 2. Under the microscope the arterioles of various parts of the frog, including those of the muscles, may be seen to vary apparently spontaneously, and may through stimulation be made to depart widely from their usual size. 3. Section of a large number of nerves is followed by red- dening of the parts to which they are distributed. This is well seen when the cervical sympathetic of the rabbit is divided ; tiie ear becomes redder, owing to obvious dilatation of its blood- vessels; and warmer, owing to the increased quantity of blood in it, etc. It has also been noticed in cas e s of paralysis, and THE OIBCULATION OF THE BLOOD. 277 vaBo-motor not cause an aervous sys- ■d the vaso- place to the extra quan- pillaries and in illustrat- protective in treatment of bleeding has we shall not Le circulation lis. ive clear no- i be borne in i not wholly ndant in the s in size are reaching any jfly from the li their exact n facts, which tes, as in the [lal's saphena small arteries ng and of the , as well as in d animals, rious parts of seen to vary bimulation be lowed by red- . This is well B divided; the L of its blood- mtity of blood paralysis, and especially in gunshot and other wounds involving nerves, that vaso-motor effects have followed. 4. Section of certain nerves, as the nervi erigentea of the penis, is not followed by dilatation ; but these nerves and the chorda tympcmi supplying the salivary gland are examples of so-called vaao-dikUors, inasmuch as their stimulation gives rise to enlargement of the caliber of the arterioles in their area of distribution. 5. On the other hand, such a nerve as the cervical sympa- thetic, as may be readily shown in the rabbit, when its periph- eral end is stimulated, gives rise to constriction, and hence is termed a vaao-constrictor. 6. When, however, the divided sciatic nerve is stimulated peripherally, the result may be either constriction or dilata- tion. 7. When the spinal cord of an animal is divided across, there is vascular dilatation of all the parts below the section (loss of arterial tone) ; but in time the vessels return to their usual size (restoration of arterial tone). 8. On destmction of a certain minute portion of the medulla oblongata, there is a general loss of arterial tone. This area (center) extends in the rabbit from a short distance below the corpora quadrigemina (1 to 2 mm.) to within 4 to 6 of the calamus scriptorius, as ascertained by the effects on the vessels of cutting away the medulla in thin transverse sections. At the spot indicated there is a collection of large multipolar nerve-cells (antero-lateral nucleus of Clarke). OoadwAaM. — 1. There are vaao-m/oior nerves of two kind»— vcMO-etmsMdort and vaao-dUaHora — ^which may exist in nerve- trunks either alone or mingled. Examples of the former are found in the cervical sympa- thetic, splanchnic, etc., of the latter in the chorda tympani, nerves of the muscles and nervi erigentea (from the first, second, and third sacral nerves), while the sciatic seems to contain both. 3. Impulses are- constantly passing frtfm the medullary vaso-motor center along the nerves to the blood-vessels, hence their dilatation after section of the nwves: The nerves are traceable to the spinal cord, and in some part of their course run, as a rule, in the sympathetic system. 3. Impulses pass at intervals to the areas of distribution of vaso-dilators along those nerves, the effect of which is to dilate the vessels through their influence, as in other cases, on the muscular coat. ' jmmmmmitm.mM ' mmlmMmimL»JimiM i , i mm i iiiii. ' i,y i itimmK lism has been r anatomically e lately shown I the effect on laracter of the ^ als tested, bat ids during the(^ ew our expres-/ laws of physi-N i has prevailecL/ THE CIBCULATION OF THB BLOOD. 879 r. to so large an extent np to the present time ; but that our widen- ing experience shows (what ought to have been expected) that the greatest allowance mast be made for group if not individ- ual variations ever> where. There is also evidence to show that th(* mode of st imulation in experimental cases causes the result to Vary. From such facts as are stated in paragraph seven, it is inferred that there are voso-motor centers in the spinal cord which are usuaUy subordinated k) the main center in the me- dulla, but which in the absence of the control of the chief cen- ter in the medulla assume an independent regulating influence. A local vaso-motor mechanism does not seem to us neces- sary to explain the changes which the blood-vessels undergo, and should not be adopted as an article of physiological faith till demonstrated to exist. If we assume that the independent contractility oi muscle-cells is retained in the blood-vessels, and that, when freed from the influence of the central nervous system, which becomes more and more dominant as we ascend the animal scale, there is a reversion to an ancestral condition, a new light is thrown upon the facts. Qtjs a case of J3ld habits joining sway when the check-rein of nervous iiofluence is re- move?; and, as we shall ahow from time to time, this law applies to everyoigan of ^ebody. Moreover, not to go beyond the varoJarsyiteSi- , this ind ependent rhythmic activity is seen in the isolated sections of the pulsatile veins of the bat's wing, devoid, so far as we know, of nervous cells. Such facts lend some color to the view that, after distention of the vessels by the cardiac systole, the return to their previous sise is aided by rhythmical contractions of the muscle-cells. Let us now consider certain other well-known experimental facts : 1. There is a nerve with variable origin, course, etc., in dif- ferent mammals, but in the rabbit given off from eitiier the vagus, the superior laryngeal, or by a branch from each, which, running near the sympathetic nerve and the carotid artery, reaches the heart, to which it is distributed. This is known as the depressor nerve. a. The vagi nerves having been divided, stimulation of the centand eaxd of the cut depressor nerve is followed by a fall in blood-pressure, which may not be accompanied by any altera- tion in the cardiac rhythm. 3. This effect may in great part be prevented if the splanoh- nio nerves be divided previous to stimulation of the depressor. 4. If the splanchnic area (region of the main abdominal '•n\ *^w>iMtfW«n«w<«»')lni*i gS;at&-'W:aa WA ' JBa8i»Wl a wmu.j < w!ty T U , ^j»!ilBU ' ii*Ji%uiHrji^i, i iiii u M jgQ ANIMAL PHYSIOIXXJY. Viscera) be inspected during the fall in blood-pressure, it may be n> ticed that there is vascular fuUnees under these ciroum- stanctib* 1 1. IK 4. * These results are interpreted as being due to afferent im- pulses ascending the depressor, acting on the vaso-motor center, ■tfamW (Fatter). and interfering with (inhibiting) the outflow of efferent, con- strictive, or tonic impulses, which start from the vaso-motOT c^ter, descend the c6rd, and find their way to the organs of the region in question, in consequence of which the mus- cuhir «)ats of the arterioles rehix, more blood flows to th^8 area which is very large, and the general bloci-pressure is A«ain. if the centna end of one of the main neriree-e. g., sciatS-be stimulated, a marked change in the b^>od.pres8ure results^but whether in the direction of nse or fall seems to depend upon the condition of the central nervous system, for, wiS the Mimal under the influence of chloral, there is a faU ; if under urari, a rise. . ^ * tx.^^ It is not to be supposed that the change in «fy « *Jf«« oases is confined to any one vascular ^^^jT'Tf^^l^^lrTi it is this or that, according to the nerve stimulated, the condi- tion of the centers, and a number of other o"?^*^^^ Moreover, it is important to bear in mind that ^*^ »f^ «f blood-pressure in one region there may be a <^™rt'»8 "^ in another. With these considerations m mind, it wUl be ajh parent that the changes in the yascuhur system during the ■it ^ a wi iiifc Mw*i' iii» ^ *iw««i THE CIBCULATION OF THE BLOOD. 281 iBure, it may lese ciroum- a£Eerent im- aotor center, LAJUUU Btral end of Uwd»- which the nooitfnc raa throwa into IM ^, and ontlMtii th* efferent, can- tie va80>motor the organs <^ icli the mns- flowB to this od-preissore is I nerves— e.g., blood-pressure fall seems to 09 system, for, there is a fall; d aAy of these iably, but that bted, the oondi- ciroamstances. b with a fall of responding rise 1, it will be ap- nn daring the coarse of a single hoar are of the most complex and variable character. Though special attention has been drawn to such rhyth- mical variations as may be witnessed in the rabbit's ear, bat's wing, etc., there can be little doubt that changes as markedj though posisibly less distinctly rhjrthmical, are constantly tak^ ing place in the vertebrate body, and especially in that of man,<, with his complex emotional nature and the many vicissitudes; /of modeni ci^^^uedHBIe. The frequent changes in color in the faces <7^Dertam people are in this connection suggestive, though we hope we have made it clear that these vascular modifica- tions are dependent chiefly on centripetal influences from every quarter, though actually brought about, by centrifugal im- pulses. Whether there is a rhythm obscured by minor rh3rthms, owmg to an independent or automatic action of the vaso-motor center, though not improbable, must be regarded as undeter- mined as yet. The question of the distribution of vaso-motor nerves to veins is also one to which a definite answer can not be given. Thk CapillabixsJ 7 The cells of which the capillaries are composed have a con- tractility of their own, and hence the caliber of the capillaries is not determined merely by the arterial pressure or any similar mechanical effect. Certain abnormal conditions, induced in these vessels by the application of irritants, cause changes in the blood-flow, which can not be explained apart from the vitality of the ves- sels themselves. Watched through the microscope under such circumstances, the blood-corpuscles no longer pursue their usual course in the mid-stream, but seem to be generally distributed and to hug the walls, one resalt of which is a slowing of the stream, wholly independent of events taking place in other Jressels. It is thus seen that in this condition {ataait) the capillaries have an in- dependent influence essentially vital We say independent, for it is stiU an open question whether nerves are distributed to capillaries or not. That inflammation, in which also the walls undergo such serious changes that white and even red blood- cells may pass through them (diapedesia), is not uninfluenced by the nervous system, possibly induced through it in certain cases, if not all, seems more than probable. --^ tm.'i^c:t^.i'»m'm»f » *TmtMm»MM I m»nmmmimm0im ■MttMaWMtHUMi 288 ANIMAL PHTSIOLOOT. But when we consider the lymphatic system new light will, it is hoped, be thrown upon the subject of the nature and the influences which modify the capillaries. One thing will be clear from what has been said, that even normally the capil- laries must exert an influence of the nature of a resistance, owing to their {Mculiar vital properties; and, as we have already intimated, such considerations should not be excluded from any conclusions we may draw in regard to tubes that are made up of living cells, whether arteries, veins, or capillaries, though manifestly the applicability to capillaries with their less modified or more primitive structure is stronger. It has now become clear that the circulation may be modi- fied either centrally or peripherally ; that a change is never purely local, but is correlated with other changes; that the whole is, in the higher animals, directly under the dominion of the central nervous system; and that it is through this part chiefly that harmony in the vascular as in other sys- tems and with other systems is established. To have ade- quately grasped this conception is worth more than a knowl- edge of all the details. Special Coksiokkationb. BXlwlo g toaL— Changes may take place either in the sab- stancd of the cardiac muscles, in the vidves, or in the blood-ves- sels, of a nature unfavorable to the welfare of the body. Some of these have been incidentally referred to already. Hypertrophy, or an increase in the tissue of tiie heart, is generally dependent on increased resistance, either within or without the heart, in the region of the arterioles or capillaries. Imperf eotipns of the aortic valves may permit of regurgitation of blood, entaUing an extra effort if it is to be expelled in addi- tion to the usual quantity, which again leads to hjrpertrophy ; but this is often succeeded by dilatation of the chambers of tiie heart one after the other, and a host of evils growing out of this, largely dependent on imperfect venous circulation, and increased venous pressure. And it may be here noticed that^ «rterial and venous pressures »r% as a general rule, in inverse) proportion to each other. If the quantity of blood in the ventricle, in consequence of regurgitation, idiould prove to be greater than it can lift (eject), the heart ceases to bdat in diastole; hence some of the] sudden deaths from disease of the aortic valves. lltMMMUMi'MMMkillWMUMM f light will, ore and the ing will be y the capil- resistaace, 18 we have be excluded bes that are capillaries, with their BT. lay be modi- ige is never es; that the le dominion ihroogh this I other sys- o have ade- lan a knowl- in the 8ab> he blood-ves- body. Some ^ the heart, is ler within or >r capillaries, regurgitation elled in addi- ijjrpertrophy ; unbers of l^e owing oat of mlation, and noticed that^ lie, in invwse; consequence n it can lift e some of th^ THE CIBCULATION OF THE BLOOD. 888 As a result of fatty, or other forms of degeneration, the heart may suddenly rupture under strains. Actual experiment on the arteries of animals recently dead, including men, shows that the elasticity of the arteries of even adult mammals is as perfect aa tliat of the vessels of the child, so that man ranks lower thaa other animals in this respeci After middle life the loss of arterial elasticity is consider- able and progressive. The artariea may undergo a degenera- tion from fatty changes or deposit of lime ; such vessels are, of oomrse^ liable to mpfcure ; hence one of the frequent modes of death amoig old persons is from paralysis traceable to rupture of vessels in the IvailC^ These and oth«r changes also cause the heart more work, and may lead to hypertrophy. Bven in young persons the stn^ of a prokniged athletic career may entail hypertn^hy or some other form of haart'diseasflC^ We mention sneh facts as these to show the more clearly how important is balance kbA the power of ready adaptatiIIMi»BlliiMi erses, in all probability serves the same purpose. Ivotaittoa. — The com- parative sketch we have given of the vascular sjrs- tem will doubtless sug- gest a gradual evolution. We observe throughout a. dependence and resem- blance which we think can not be otherwise ex- plained. The similarity of the foetal circulation in the mammal to the permanent circu- lation of lower groups has much meaning. Even in the high- est form of heart the original pulsatile tube is not lost The great veins stiU contract in the mammal ; the sinus venosus is probably the result of Mending and expansion. The later differentiations of the parts of Che heart are^learly related to the adaptation to alteied surroundings. Such is seen in the f CBtal heart and oiroulation, and has probably been the deter^ mining cause of the forms which the circulatory orgahs have assumed. It is a fact that the part of the heart that survives the long- est o&der adverse conditions is that which bears the stamp of gntatest ancestral antiquity. It (the sinus vmosus) may not be less under nervous control, but it certainly is least depend- ent on the nervous qrttem, and has the greatest automaticity. It is surely fortunate for man that this i>art of the reptilian heart is represented in his own. In oases of fainting, partial drowning, or other instances of impending death, this part, with riM. SO'.-VdHaf UwftMto(ttalMn»(«flw 386 ANIMAL PHYSIOLOGY. the auricles it may be, continues to beat when the ventricles have ceased ; and we have learned that so long as these parts are functionally active there is a greater probability that the quiescent regions may recommence. Activity begets activity, in cardiac muscle-cells at least. How are these facts to be explained apart from evolution P The law of rfc|j^fcm in organic nature finds some of its most evident exemplifications in the circulation. Most of the rhythms are compound, one being blended with or superim- posed on another. Even the apparent irregularities of the nor- mal heart are rhythmical, such as the very marked slowing and other changes accompanying expiration, especially in some animals. We trust we have made it evident that the greatest allow- ance must be made for the animal group, and some even for the individual, in estimating any one of the factors of the cir- culation. We know a good deal at present of cardiac physiol- ogy, but we do not know a physiology of "the heart" in the sense in which we understand that term to have been used till recently— i. e., we are not in a position to state the laws that-/ , apply to all forms of heart. taantry of th* Vkyridogj of th* OixmOfftimi.— In the mammal the circulatory apparatus forms a closed system consisting of a central pump or heart, arteries, capillaries, and veins. All the parts of the vascular system are elastic, but this property is most developed in the arteries. Since the tissue-lymph is prepared from the blood in the capillaries, it may be said that the whole circulatory system exists for these vessels. As a result of the action of an intermittent pump on elastic vessels against peripheral reristance, in consequence of which the artmes fire always kept more than full (distended), the flow through the capillaries and veins is constant-ra very great advantage, enabling the capillaries to accomplish their work thetic, accelerator, or motor fibers. The inhibitory fibers can arrest, slow, or weaken the cardiac b^at; the sympathetic accelerate it or augment its force. When botii are stimulated together, the inhibitory prevail. These nerves, as also the accelerators, exercise a profound influencci upon the nutrition of the heart, and effect its electri- cal condition when stimulated, and we may believe when influ- enced by their own centers. The inhibitory fibers tend to preserve and restore cardiac energy; the sympathetic, whether in the vagus or as the aug- mentors, the reverse. The vagus nerve (and probably the de- pressor) acts as an afferent, cardiac sensory nerve reporting on the intra -cardiac pressure, etc., and so enabling the vaso- motor and cardio-inhibitory centers, which are, it would seem, capable of related and harmonious action to act for the general good. The arterioles must be conceived as undergoing very fre- quent changes of caliber. They are governed by the vaso- -.-»-/■, ■■., «.Jii''-.'e''^»'»^''K^iMaw«.-V«*-*"": ■it;^irt»ji9iri.7'«.«»''^ THE CIRCULATION OF THB BLOOD. 989 Bver, the ten- rhe work of it ejects and an elevation aat, in conse- dood-Btreom. in every di- as compared in force, fre- and numer- 3d by the cen- 1 the medulla kking up the ing degrees of md the needs xlif y the beat Bvagi nerves, bh a center in the medulla, eration of the beat, or both In ttie verte- » vagoHBjrmpa- r, and sympa* :en the cardiac ent its force. ry prevail. Be a profound (ect its eleotri- ve when influ- •eetore cardiac or as the aug- obablythe de- e reporting on ling the vaso- It would seem, for the general ©ing very fre- . by the vaso- motor center, situated in the medulla, and possibly certain sub- ordinate centers in the spinal cord, througli voso-motor nerves. These are (a) vaso-constrictors, which 'untain a constant but variable degree of contraction of the mu-ole-cells of the vessels; (b) vaso-dilators, which are not in constant functional activity ; and (c) mixed nerves, with both kinds. An inherited tendency; to rhythmical contraction throughout the entire vascular sys- tem, including the vessels, must be taken into account. The depressor nerve acts by lessening the tonic contraction of (dilating) the vessels of the splanchnic area especially. It is important to remember that all the changes of the vascular system, so long as the nervous system is intact — i. e., so long as an animal is normal — are correlated ; and that the action of such nerves as the depressor is to be taken rather as an example of how some of these changes are brought about, mere chapters in an incomplete but voluminous history, if we could but write it all. The changes in blood-pressure, by the addition or rismoval of a considerable quantity of blood, are slight, owing to the sort of adaptation referred to above, effected through the nervous system. Finally, the capillary circiilation, when studied microscopically, and especially in disordered cour ditions, shows clearly that the vital properties of these vessels have an important share in determining the character of the circulation in themselves directly and elsewhere indirectly. The study of the circulation in other groujM shows that below birds the arteriid and'venous blood undergoes mixture somewhere, usually in the heart, but that in all the Vertebrates the best blood is invariably that which passes to the head and upper regions of the body. The deficiencies in the heart, owing to the imperfections of valves, septa, etc., are in part counter- acted in some groups ,by pressure relations, the blood alwiays flowing in the direction of least resistance, so that the above- mentioned result is achieved. Capillaries are wanting in most of the invertebrates, the blood flowing from the arteries into spaces (sinuses) in the tis- sues. It is to be noted that a modified blood (lymph) is also found in the interspaces of the cells of organs. Indeed, the circulatory system of lower forms is in many respects analogous to the lymphatic system of higher one& w I Mil l * 990 ANIMAL PHTSIOLOGT. DIQBBnON OF FOOD. tA The processes of digestion may be considered as having for their end the preparation of food for entrance into the blood. This is in part attained when the insohible parts have been rendered soluble. At this stage it becomes necessary to inquire as to what constitutes /ood or a food. Inasmuch as animals, unlike plants, derive none of their food from the atmosphere, it is manifest that what they take in by the mouth must contain every chemical element, in some form, that enters into the composition of the body. But actual experience demonstrates that the food of animals must, if we except certain salts, be in organized form — i. e., it must approximate to the condition o^ the tissues of the body in a large degree. Plants, in fact, are necessary to animals in working up the elements of the earth and air into form suit- able for them. Foodstuffs are divisible into : I. Organic. 1. Nitrogenous. (a.) Albumina (5.) Albuminoids (as gelatine). 8. Non-nitrogenous. (a.) CarV^hydrates (sugars, starches). , ib.) Fatfa. II. Inorganic, 1. Water. 8. Salt& Animals may derive the whole of their food from the bodies of other animals (oomtvoro); from vegetable matter exclusively {herbivora) ; or from a mixture of the animal and vegetable, as in the case of the pig^ bear, and man himself {omnivora). (U has been found by feeding experiments, carried out mostly on oogs, that animals die when they lack any ore of the con- stituents of food, though they live longer on the nitrogenous than any other kind. In some instances, as when fed on gela- tine and water, or sugar and water, the animals died almost as soon as if they had been wholly deprived of food. But it has also been observed that some animals will all but starve rather than eat certain kinds of food, though chemically sufficient. Mrwa IMHMiiiHiniMf DIQBSnON UP OOD. Ml 'od as having anoe into the rts have been sary to inquire none of their at they take in ment, in some ood of animals I f orm— i, e., it i of the body in to animals in into form suit- food from the Bgetable matter the animal and id man himself brried out mostly or a of the oon- the nitrog^enous hen fed on gela- s died almost as ood. But it has mt starve rather ioally sufficient. We must thus reoognize something more in an anin Itan merely the mechanical and chemical processes which o ice to aooomplish digestion in the laboratory. A food must e not only sufficient from the chemical and physical point vipiw, but be capable of being acted on by the digestive juices, and of such a nature as to suit the particular animal that eats it To illustrate, bones may be masticated and readily digested by a hyena, but not by an ox or by man, though they meet the conditions of a food in containing all the requisite constituents. Further, the food that one man digests readily is scarcely digesti>'> ble at all by another ; and it is within the experience of every) one that a frequent change of diet is absolutely necessary. ^-^ Since all mammals, for a considerable period of their exist- ence, feed ujwn milk exclusively, this must represent a perfect or typical food. It will be worth while to examine the compo- sition of milk. The various substances composing it, and their relative proportions for different animals, may be seen from the following table, which is based on a total of 1,000 parts : Hum. Oow. OoO. Water 888^ 887-OB 868-88 GHain Albamin. Butter. 88-84 80*60 48-64 1-88 i 48-98 } 5-78 48-06 40-87 S-48 88-60 . 18-89 48-57 40D4 6-88 Milk-cucar bmTT:.:. .:::. Total Kdids.. llQrn 148-86 186-48 010-84 90-18 18-66 67-08 88-78 The fact that human milk is poorer in proteids and fats especially is of practical importance, for, when cow's milk is sub- stituted in the feeding of infants, it should be diluted, and sugar and cream added if the normal proportions of mother's milk are to be retained. 1. The proteids of milk are f (a.) An albumin very like semm-«lbumki. (fi.) Casein, normally in suspension, in the form of extremely minute particles, which contributes to the opacity of milk. It can be removed by filtration through porcelain ; and pre- cipitated or coagulated by acids and by rennet, an extract of the mucous membrane of the calf's stomach. After this coagu- lation, whev, a fluid more or less clear, separates, which con- tains the salts and sugar of milk and most of the water. Much of the fat is entangled with the casein. ] I »niei«us>a,t«»Ki«i)Hi 292 ANIltAL PHYSIOLOGY. Casein, with Bome fht, makes up the greater {^ i,rt of dh^efleV 2. F(Us. — Milk is an emulsion — i. e., contains fat euspdnded in a fine state of division. The globules^ ^hioh vary greaitly in size, are surrounded by an envelope of proteid matter. This covering ib broken up by churning, allowing the fatty globules to run together and form butter. Butter consists chiefly of olein, palmitin, and stearin, but contains in smaller quantity a variety of other fats^ The ran- cidity of butter is due to the presence of free fatty acids, espe- cially butyric. The fat of milk uBually rises to the surface as cream when milk is allowed to stand. 3. Milk-sugar, which is converted into lactic acid, probably by the agency of some form of micro^>rganism, thus furnish- ing acid sufficient to cause the precipitation or coagiilation 6f the casein. Mnk-mgw. iMtioMid. C.H..O.= «C.H.O. V Milk, when fresh, should be neutral or faintly alkaline. 4. SoMs (and other extractive^), consistiiig of phosphateis of calcium, potassium, and magnei^ium, potassium chloride, with traces df iron and other substances. j ^ can bf9 readily understood yfby childrein fed on milk rarely suffer froni that deficiency of ci^ium salts in the bones leading to rickets, to common' in ill-fed (^Idren. It thus appears that milk contains all the constituents requisite for the building up of the healthy mammalian body; and experiments prove that these exist in proper proportions and in a readjly digestible form. The author has found that a large number bf uiqiials, into the usual food of which, in the adult form, milk does npt enter, like most of our wild. mammals, as well ^JEf mo^ l^rids, will not only take milk but soon learn to like ii, and thrive Well upon it. Since the embryo chick lives upon the egg, it utiis^t have been supposed that eggs would form excenent 'fdod for adult animals, and bommon experience proves this t6 m |he okse ; while chemical analysis shows that they, like, mil'ki. bb9- tain all the necessary food constituents. Meat (muscld, with fat chiefly) is also, of course^ a valuable food, abbuiiditig'.ii^ proteids. Cereals contain starch in large proportion, but ailsd^^ mixture of proteids. Chreen vegettMes contain litile actual 'nS;t-, tritive material, but are useful in furnishing salts 'Imd s^ial ', substances, Iem certain compounds of siilphur which, in SOjOQ^ litt- ' understood way, act beneficially on the metabolism of' the fxMly'. irt of dhfee^i fat suspended ary greaitly in matter. This fatty globules Ld stearin, but ata Tberaia- ;ty acids, espe- is cream when acid, probably , thus f uraish- coagiilation of J alkaline, phosphateis of chloride, with . on milk rartily 9 bones leading 18 apx>ear8 that: the building up jnts prore that ftdily digestible iber tof iuii?iials, , MSk does npt ^ mbikt biijds, , and thrive Well B ?gg» it.vriii^t celient fbCKi for I this t6 be the likes" milWc^^- it (muscle, with 1, abbuiidiAgii^ »rtion,biitaa86>' Utile actual rW- altsand E^iia;! lich, i^ 9ojtt6 xll- iismoY'thetiody'. DIQBSTION OF FOOD. They also seem to stimulate the flow of healthy dig^rtive ^uids. Cfmdimenta act chiefly, perhaps, in the latter way. (Te»> coffee, etc., contain alkaloids, which it is likely have a conservative effect on tissue waste, but we really know very little as to how it is that they prove so beneficial. Though they are recognized to have a powerful effect on the nervous system as stimulants, nevertheless it would be erroneous to suppose that their action was confined to this alone. ^aagmfig^^i^^t^i 994 ANMAL PHTBIOLOGY. It is plain that if , in the digestive tract foods are changed in aolubmty and actual chemical constitution, this must have been brought ^bout by chemical agencies. That food is broken ^^t X very commencement of the alimentary trwt is a Ztt o? Sirobservation; and that there Aould be a ^^ movement of the food from one part of the canal to & fto.»l. huip; a. ! «,« iX •*.« Dvasmovi another, where a different fluid is seoreted, would be expected. As a matter of fact, mechanioal and chemical forces play a large part in the actual preparation of the food for absorption. Behind these lie, of course, the vital properties of the glands, which prepare the active fluids from the blood, so that a study of digestion naturally divides itself into the consideration of — Ito. ■&— ilmtNoOM a. .mSS!StAS!^&£SSA^' 1. The digestive juices; 8. The secretory processes; and, S. The muscular and nervous mechanism by which the food is carried from one part of the digestive tract to another, and the waste matter finally expelled. rra. M.-Uw|ttadliial wtfMl Motta of bo«]r «( iMOh, JEMrMtfo wyi«t«i«aW»»<'gJ!?'^Mg- lateyoisilsaL— The alimentary tract, as we have seen, is formed by an infolding of the splanohnopleure, and, according as the growth Is moreor loss marked, does thaoanal become itmu 9K HmUAh PHYSIOLOGY. iio^aoas ot remain «>mewhat straight. The aUtnefltary 1*act Df a mammal passes through stages of development which cor- respond with the permanent form of other groups of verte- brates, according to a general law of ev^ution. Ihasmuch as the embryonic gut is formed of mesoblast and hypoblast, it is easy to «flder«ti¥nd why the developed tract should so mvana- bly coi^sist of glandular structures and muscular tissue dis- posed in a certain regular arrangement. The fact that all the %| SB ■■>■■ I . #- l^ainMtlMbrMntMita MO 0» uBODiVEW* poiatoT organs that pour digestive juioe. into the ^^i«»«'^i»'y .*^*" oX~wths t^m it serves to explain why the«» should remain r^siologioal connection with an anatomical isolation. The general r^mblance of the epithelium t^^S^^^^*' «^^^„^ narts widely separated, also becomes clear, as well as many 5?^r ^nS ^r^n nit now wf er to in det«lV to <«e who realizeTthe significance of the laws of d«went (evolution). ■■' . 0«ipli«*«»»^ssmf ifflMSKiSWHWliWIW^WiwRW rnQsaraoH A)V food. SOI fnentary 1*act mt whicli cor- >up8 of verte- Inasmuch as ypoblast, it is lid BO invaria- lar tissue dis- ct that all the I ota«l(afler BooMMii). aSuHL taammAm Si ainoe OMtr «>*»*■ ariyiMph, Mia rfgte ii#^NIeH ^ themselves, in a form snitlMe for assimi- lation. This is a beginning' of that cHifercnittatioti of function ..di HMMifiMMHk MMMMaaMM S98 ANIMAL PHTBIOIiOOY. which is carried so far among the higher yertebratoa. Bnl^ as recent investigations have shown, such intra-oellalar digestion exists to some extent in the alimentary canal of the highest members of the vertebrate group (see page 345). The means for grasping and triturating food amoi^s: in- vertebrates are very complicated and varied, as are also thow adapted for sucking the juices of prey. Examples to hand are to be found in the crab, crayfish, spider, grasshopper, beetti^ ■to. ase, •.■tonwcli; r.natnm; a,tmmt r.«,rMaliac: k,lMM(; l,hm(OaodiM BalJiiiloliMn- bw); m to •xtataal laStun; •mjuiii* adm ormMlli nSSa wMi Mciotbodf ; /, foot; iijiD iiiiiiliul. iiiiial. mil imlilii ■iihiiiiiiilii tiiiilh ■igiimliil iiiiiiiil tiiWil etc., on the one hand, and the butterfly, house-fly, leech, eta, on the other. The digestive system of the earth-worm has been studied with some care. It illustrates a sort of extra-corporeal diges- tion, in that it secretes a fluid from the mouth which seems to act both chemically and mechanically on the starch-graiiis of the leaves on which it feeds. It is provided with an organ in which, as with birds, small stones are found,'80 that the imperfections of its mouth are compensated for by this gissard which triturates the food. Its caldferous glands supply the alkaline fluids necessary to neutralise the humus acids of de- caying leaves, for intestinal digestion only proceeds in an alka- line medium. The gastric mill of a crab (Fig. Siia) is a provision of ob- vious valuQ in so voracious a oreatursw «^sai!?t-:>«A>i[«i«g!m!ami^v!»issm^miK^ DIOBBTION OF FOOIK S89 Uea. Bu%M liar digestion I the highest d amons ™~ ire alaothoM » to hand are io^ipear, beetle^ orop; _. ohun- bodr;/, MdiwudgnJM. >-fly, leech, etc., 18 been studied Borporeal diges- which seems to te starch-graips I with *n organ md,'BO that the r by this giszard Bkuds supply the bus Boids of de- seeds in an alka- proTision of ob- (iefore passing on to higher groups, it will b* well to bear in mind that the digestiw organs are to be lagMidAdas the out- come both of he- redity and adap- .jtSTK tation to circum- stancea We find parts of the in- toatine, e. g., re- tained in some animals in whose economy thej seem to serve little if any good purpose, as the vermiform ap- pendix of max Adaptation has been illustrated in the lifetime of a single indi- vidual in a re- markable ner ; thus, a gull,by being fed on grain, has had its stomach, nat- urally thin and soft-waUed, con- verted into a muscular gia- sard. (^oe diges- tion is a process in which the mechanical and chemical are both involved, and the food of mimals difl«ps t^v .«> so widely, great variety in the aUmentair tract, b^ jw^ tomical and physiological, must be expected. y«»*«»JJ* '^J myvA usually be eaftmi in much larger bulkto ««^*^* needed elemMits; hMioe ttie great tength of intestina habitually ^0itij^jauiSi3BSiSSSSm fpttp4, ilk )i9FWvqT«up animals, a^sodate^ often with, a capaciou» a|a4 oUml>9i^ ftQma. ,A m geBtion is almost confined to the last division, which may be compared to the simple stomach of the Camivora or of man; and, before the food reaches this region, it has been thoroughly masticated and mixed with saliva. . «».-Stoni«oh, pmoreM, lam Bvw; a.giOI-MaMM': S>Mfct* •MtiaB of I, antwrior aarface of : 4, pwArior mrf aoe of atomaMi ; S, yarSrin! '^j^Jfl^'^ n'''niMirw?nf ^liiaiTiiUiffn'Trir-'^ • IS, dModeniiin; IS, upper tx- SSonTn. aS*^ flaxiMot talon ;l| reotum ; ll, urlnanr Madder. •te: (after Swer). »,=r • ...-.— «i» . -,-, Jmsmi 4, pQaterfor_ lobiM lS«em of Uv«r : 6, ooeUao^; MMramig7 < ' The reticulum is especially adapted for holding water, which may serve a good purpose in moistening and thinning the con- tents of the stomach. In the camels and llamas a portion of the stomach is made up of pouches, which can be closed with sphincter muscles, and thus shut off the water-supply in sep- arate tanks, as it were. The stomach of the horse is small, though the intestine, especially the large gut, is capacious. The stomach is divisible into a cardiac region, of a light cQlor iiiternally, aud lined with epithelium, like tiuit of the /j \r " iiiTi \'ii' I iiw'ii ill ' 1" ' '' " "'''^'•'^'^^ OlOBSTIOM OF POOD. ao8 oawphagoB, and a redder pyloric area, in which the greater p«rt of the digestive procesa goes on. Fie. Ma-BtooMdi of dof «Mv CSiMmMi) i^iqrlonii. The mouth parts, even in some of the higher vertebrates, as the Camivoroi serve a prehensile rather than a digestive pur- pose. This is well seen in the dog, that bolts his food; but in this and allied groups of mammals gastric digestion is very activ& Bta. «l-4taBaral«iidtatma«lriro(«dg*B(iaatt(tflerOhurr«M». ^ 804 ANIMAL PHTSlOIiOOVl The teeth a- triturating orgMUi find their h^wt^ej-^^ ment in ruminants, the combined side-toHnde and f orwwd*alid- Ckward motion of the jaws rendering them very effective. r \%^^^'^ im:: tStti ; T MoMpM teeth ; «, motai* In Camiwm the teeth serve for grasping and tearing, while in the InseeHvom the tongue, as also in certain birds (wood- peckers), is an important organ for securing food. It is to be noted, too, that, while the horse crops grass by biting it off, the ox uses the tongue, as well as the teeth and lips, to secure the mouthful; . ' i ■!ft??w»w«R«n?7?^ DI0K8TI0N OF FOOD. 805 -»» «M_nMwmi vhw oT dicMiiw ■ppwrtfl* c( fowl (aftM* dukuneMi;. 1, (wgae; fi 80 806 ANIMAL PHT8IOL0OT. ot daoimml flHcnre : 10, Meoad bnuieh of mom ; 11. oiMb of fliMitiiiir vorttai of imwll It. niUl brtMrtlM ; ir, tmniwa poitlaa of thS lBt(MM,JlM^ la, la, fTM eztrHnltlM tajba its, Nctaan { !•, It, lifl Mm of Uw ; n, rkritt lobo ; II, nU-blMMer daeia; the two paacrMUe dueU ai* !&• moat Mitt rior, the oiMMte or bawitie to la tho Blddla. and tha oyalio duct to iMMlarior : SL I M, di^ihragnMtto aaiAtoC fauw ; 16, ovaiy (la a rtata of aliophrrra^ o*tdiaet. Man's teeth are somewhat intermediate in form between the carnivorous and the herbivorous type. Birds lack teeth, but the strong muscular gizzard suffices to grind the food against the small pebbles that are habitually swallowed. The crop, well developed in granivorous birds, is a dilata- tion of the OBSophagns, serving to store and soften the food. In the pigeon a glandular epithelium in the crop secretes a milky-looking substance, that is regurgitated into the. mouth of the young one, which is inserted within that of the parent bird. The proventrioulus — an enlargement just above the gizzard —is relatively to the latter very thin-walled, but provides the true gastric juicea Certain plants digest proteid matter, like animals ; thus the sun-dew (Droaera), by the closure of its leaves, captures insects, which are digested and the products absorbed. The digestive fluid consists of a pepsin-containing secretion, together with formic acid. Thb Dioxsnvs Juicbs. l«]ifa.-rThe saliva as fotmd in the month is a mixture of the secretion of three pairs of glands, alkaline in reaction, of a specific gravity of 1009 to 1006, with a small percentage of solids ('S per cent), consisting of salts and organic bodies (mucin, proteids). Saliva serves mechanical functions in articulation, in moist- ening the food, and dissolving out some of its salts. But its principal use in digestion is in reducing starchy matters to a soluble form, as sugar. So far as known, the other constituents of the food are not changed chemically in the mouth. Ths Amflfliytl* AoUm of lidifa.— Starch exists in grains, sur- rounded by a ceUvhae covering, which saliva does not digest ; hence its action on raw starch is slow. It is found that if a specimen of boiled stuch not too thick be exposed to a small quantity of saliva at the temperature of the body or thereabout (37* to 40" 0.), it will speedily undergo certain changes : 1. After a very short time sugar may be detected by Feh- -lAsm m a DIGESTION Oir FOOD. 807 Ihk portiaa o( famll iMfcedoacMhride bis, free •xtrMBMc* • : 15, nctnm : l*. |M:n,MU-blMMer; laaNtMinoatMit^ nops m* p .oviduct. u between the ack teeth, but e food against 08, IS a dilata-, n the food, crop secretes a nto the. mouth ; of the parent }ye the gizzard it provides the mals ; thus the aptures insects. The digestive together with is a mixture of in reaction, of a 1 percentage of organic bodies lation, in moist- } salts. But its hy matters to a her constituents aouth. !8 in grains, sur- does not digest ; ch not too thick 9 temperature of peedily undergo letected by Fob- ling's solution (copper sulphate in an excess of sodium hydrate, the sugar reducing the cupric hydrate to cuprous oxide on boiling). At this early stage starch may still be detected by the blue color it gives with iodine ; but later, instead of a blue, a purple or red may appear, indicating the presence of dextrin, which may be regarded as a product intermediate between starch and sugar. 3. The longer the process continues, the more sugar and the less starch or dextrin to be detected; but, inasmuch as the quantity of sugar at the end of the process does not exactly correspond with tiie original quantity of starch, even when no starch or dextrin is to be found, it is believed that other bodies are formed. One of these is achroodextrin, which does not give a color reaction with iodine. The sugars formed* are: (a) Dextrose, (b) Maltose, which has less reducing power over solutions of copper salts, a more pronounced rotatory action on light, etc. It is found that the digestive action of saliva, as in the above-described experiment, will be retarded or arrested if the sugar is allowed to accumulate in large quantity. That diges- tion in the month is substantially the same as that just de- scribed can be easily shown by holding a solution of starch in the mouth for a few seconds, and then testing it for sugar, when it will be invariably found. While salivary digestion is not impossible in a neutral medium, it is arrested in an acid one even of no great strength (less than one per cent), and goes on best in a feebly alkaline medium, which is the condlUon normally in the mouth. Though a temperature about equal to that of the^body is best adapted for salivary digestion, it will proceed, we have ourselves found, at a higher temperature than digestion by any other of the juices, so far as man is concerned — ^a fact to be connected, in all probability, with his habit for ages of taking very warm fluids into the mouth. The active principle of saliva is ptyalin, a nitrogenous body which is assumed to exist, for it has never been perfectly iso- lated. It belongs to the class of unorganized ferments, the properties of which have been already referred to before (page 160). OharaoUrirtlos of th« BMirttioii of fh* SiflEwont CHandi.— Parotid saliva is in man not a viscid fluid, but clear and limpid, con<- taining very little mucin. Submaxillary saliva in most animals ANIMAL PHTSIOLOOT. and in man is viscid, while the secretion of the sublingual gland is still more viscid. CoimpuKtit*.— Saliva differs greatly in activity in different animals; thus saliva in the dog is almost inert, that of the pai'otid gland quite so ; in the cat it is but little more effective ; and in the horse, ox, and sheep, it is known to be of very feeble digestive power. In man, the Guinea-pig, the rat, the hog, both parotid and submaxillary saliva are active; while in the rabbit the sub- maxillary saliva, the re /erse of the preceding, is almost in- active, and the parotid secretion very powerful. An aqueous or glycerine extract of the salivary glands has digestive properties. The secretion of the different glands may be collected by passing tubes or cannulas into thoir ducts. PathologiflaL — Potassium sulphocyanate (which gives a red color with salts of iron) is sometimes present normally, but is said to be in excess in certain diseases, as rheumatism. The saliva, normally neutral or only faintly acid, may be- come very much so in the intervals of digestion The rapid decay of the teeth occurring during and after pregnancy seems in certain cases to be referable in part to an abnormal condition of t)ie saliva, and in part to the drain on the lime salts in the construction of the bones of the fostus. The tartar which collects on the teeth consists largely of earthy phosphates. QMtrie JoiM. — Qastric juice may be obtained from a fistu- lous opening into the stomach. Such may be made artificially by an incision over the organ in the midcUe line, catching it up and stitching it to the edges of the wound, incising and insert- ing a special form of cannula, which may be closed or opened at will.. Digestion in a few cases of accidental gastric fistulsB has been made the subject of careful study. The most instructive case is that of Alexis St. Martin, a French Oanadian, into^ whose stomach a considerable opening was made by a gunshot- / wound. Gastric juice in his case and in the lower animals with arti- ficial openings in the stomach, has been obtained by irritating the mucous lining mechanically with a foreign body, as a feather. The great difficulty in all such cases arises from the imjpoB- sibility of being certain that such fluid is normal ; for the con- ditions which call forth secretion are certainly such as the stomach never experiences in the ordinary course of events, iMi npi ?^^^5?|^^S| DIGESTION OP POOD. 309 bie sublingual y in different t, that of the aore effective ; of very feeble h parotid and ftbbit the sub- , is almost in-' try glands has fferent glands ito their ducts, ch gives a red Drmally, but is Latism. J acid, may be- ion The rapid fter pregnancy x> an abnormal kin on the lime iUB. sists largely of id from a fistu- aade artificially ), catching it up ising and insert- dosed or opened itric fistidffi has most instructive Canadian, into*^ ie by a gunshot- 1 limals with arti- led by irritating lody, as a feather, from the impos- lal ; for the con- nly such as the lourse of events, and we have seen how saliva varies, according as the animal is fasting or feeding, etc. Bearing in mind, then, that our knowledge is possibly only approximately correct, we may state what is known of the se- cretions of the stomach. The gastric secretion is clear, colorless, of low specific grav- ity (1001 to 1010), the solids being in great part made up of pep- F» aw -GMtric Biitula in caM of St. lUrtin (aftw Bewmioiit). A, A, A.B, borders of open- IM i^i^M^rc, toft idpple ; fiTciieirt ; « oteaWce. from wound nutde for i»mo»»l o7n^^£)eofoiirtUi«e ; F, iff S\ dcrtrlce* of orisUwl wound. sin with a small quantity of mucus, which may become excess- ive in disordered conditions. There has been a good deal of dispute as to the acid found in the stomach during digestion. It is now generally agreed that during the greater part of the digestive process there in free hydrochloric acid to the extent of about '2 per cent. It is maintained that lactic acid exists normally in the early B,\Age» of digestion, and it is conceded that lactie, butyric, acetic, and other acid* may be present in certain forms of disordered digestionr^ It is also generally acknowledged that in mammals the work of the stomach is limited, so far as actual chemical changes go, to tjie conversion of the proteid constituents of food into peptone. Fats may be released from their proteid coverings (cells), but neither they nor starches are in the least altered chemically. Some have thought that in the dog there " a slight digestion of fats in the stomach. The solvent IS w^m^^mmm- -^^ 810 ANIMAL PHTSIOLOOT. power of the gastric juice is greater than can be accounted for by the presence of the acid it contains merely, and it has a marked antiseptic action. Digestive processes may be conducted out of the body in a very simple manner, which the student may carry out for himself. To illustrate by the case of gastric digestion: The mucous membrane is to be removed from a pig's stomach after its surface has been washed clean, but not too thoroughly, chopped up fine, and divided into two parts. On one half pour water that shall contain "2 per cent hydrochloric acid (made by adding 4 to 6 cc. commercial acid to 1,000 cc. water). This will extract the pepsin, and may be used as the menstruum in which the substance to be digested is placed. The best is fresh fibrin whipped from blood recently shed. Since the fluid thus prepared wiU contain traces of peptone from the digestion of the mucous membrane, it is in some respects better to use a glycerine extract of the same. This is made by adding some of the best glycerine to the chopped-up mucous membrane of the stomach of a pig, etc., well dried with bibulous paper, letting the whole stand for eight to ten days, filtering through cotton, and then through coarse filter-paper. It will be nearly colorless, clear, and powerful, a few drops suf- ficing for the Work of digesting a little fibrin when ad iei >» some two per cent hydrochloric acid. Digestion goes on best at about 40° C, but will procei ' the cold if the tube in which the materials have been placed is frequently shaken. It is best to place the test-tube containing them in a beaker of water kept at about blood-heat. Soon the fibrin begins to swell and also to melt away. After fifteen to twenty minutes, if a little of the fluid in the tube be removed and filtered, and to the filtrate added carefully to neutralization dilute alkali, a precipitate, insoluble in water but soluble in excess of alkali (or acid), is throwi\ dowou This is in most respects like acid-albumen, but has been called para- peptone. The longer digestion proceeds, the lees is there of this and the more of another substance, peptone, so that the former is to be regarded as an intermediate product Peptone is distinguished from albuminous bodies or proteids by — 1. Not being coagulable from its aqueous solutions on boiling. 8. Diffusing more readily through animal membranes. 8. Not being precipitated by a number of reagents that usually act on proteids. In artificial digestion it is noticeable that much more fibrin L be accounted rely, and it has the body in a carry out for digestion: The pig's stomach ;oo thoroughly, 1 one half pour ric acid (made i. water). This menstruum in he best is fresh ices of peptone it is in some same. This is he chopped-up well dried with lit to ten days, rse filter-paper, k few drops suf- when ad Je'i o (rill procet ' been placed is ube containing leat. Soon the the fluid in the added carefully oluble in water m down. This sen called para- less is there of ne, so that the duct. Peptone proteids by — 1. ons on boiling, branes. 8. Not hat usually act loh more fibrin DIOBSTION OP FOOD. 811 or other proteid matter will be dissolved if it be finely divided and frequently shaken up, so that a greater surface is exposed to the digestive fluid. The exact nature of the process by which proteid is changed to peptone is not certainly known. Since starch on the addition of water becomes sugar (C«Hh Oi+H|0 = C«HiiO«), and since peptones have been formed through the action of dilute acid at a high temperature or by superheated water alone, it is possible that the digestion of both starch and proteids may be a hydration; but we do not know that it is such. As already explained, milk is curdled by an extract of the stomach (rennet) ; ai^l this can take place in the absence of all acids or anything else that might be suspected except the real cause ; there seems to be no doubt that there ia a distinct fer- ment which produces the coagulation of milk which results from the precipitation of its casein. The activity of the gastric juice, and all extracts of the mu?i cous membrane of the stomach, on proteids, is due to pepsin, &j nitrogenous body, but not a proteid. like other ferments, the conditions under which it is effect- ive are well defined. It will not act in an alkaline medium at all, and if kept long in such it is destroyed. In a neutral me- dium its power is suspended but not destroyed. Digestion will go on, though less perfectly, in the presence of certain other acids than hydrochloric. As with all digestive ferments, the activity of pepsin is wholly destroyed by boiling. When a large quantity of cane-sugar is taken into the stomach, an excess of mucus is poured out which converts it, presumably by moamfi of a special ferment, into dextrose. nil, — ^The composition of human bile is stated in the fol- lowing table: Water 8»-90 per cent. Bile^alts 6*11 " ^ Fats and soaps. -• 2 Cholesterin 0*4 " " Lecithin.... :... 1« " " Mucin 1-8 " " Ash M- 0-61 " " ^le color of the bile of man is a rich golden yellow. When it oi^tains much mucus, as is tiie case when it remains long in the gall-bladder, it is ropy, though usually dear. Bile may cont^n small quantities of iron, manganese, and copper, the ^mm» m^mmmmmimmamam ^vr 312 ANIMAL PHY8I0L00T. latter two especially being absent from all other fluids of the body. Sodium chloride is the most abundant salt. Bile must be regarded as an excretion as well as a secretion ; the pig- ments, copper, manganese, and perhaps the iron and the cho- lesterin being of little or no use in the digestive processes, so far as known. The bUe-aaiis are the essential constituents of bile as a digestive fluid. In man and many other animals, they con- sist of taurocholate and glycocholate of sodium, and may be obtained in bundles of needle-shaped crystals radiating from a common center. These salts are soluble in water and alco- holj with an alkaline reaction, but insoluble in ether. .Glycocholic acid may be resolved into oholalic (cholic) acid and glycin (glycocoU) ; and taurocholio add into cholalic acid and taurin. Thus : Olyoodtolieacid. ClHdalle acid. Olycte. C»H«NO. + H,0 = CkH«0, + C,H,NO*. IteiroehoUcacid. CholaUe add. Ttortn. CwHmNSOt + H» = CmHmO, -f CHfNSO,. GlycocoU (glycin) is amido-acetic acid — CH <^^' Taurin, amido-isethionic acid. and SO H CtH4<^m^^» and may be made artificially from isethionic acid. It is to be noted that the bile acids both contain nitrogen, but that chololic acid does not. The decomposition of the bile acids takes place in the alimentary canal,.and the glycin and taurin are restored to the blood, and are possibly used afresh in the construction of the bile acids, though this is not defi- nitely known. BUie*PigiiiMits. — ^The yellowish-red color of the bile is owing to BUirvbin (OuHnXiOt), which may be separated either as an amorphous yellow powder or in tablets and prisms. It is soluble in chloroform, insoluble in water, and but partially soluble in alcohol and ether. It makes up a large part of gall-stones, which contain, besides oholesterin, earthy salts in abundance. It may be oxidized to BiUverdin (CitHiiN/)4), the natural green pigment of the bile of the herbivora. When a drop of. nitric add, containing nitrous add, is added to bile, it under- ^.. T-r- DIGESTION OF FOOD. 818 ir fluids of the It. Bile must Btion ; the pig- and the cho- re processes, so of bile as a (nals, they con- m, and may be radiating from irater and alco- »ther. lie (oholic) acid ito cholalic acid rein, win. nade artificially intain nitrogen, ition of the bile the glycin and ibly used afresh this is not defi> le bile is owing irated either as i ptisms. It is d but partially a large part of earthy salts in O4), the natural Wihen a drop of. bile, it under- goes a series of color changes in a certain tolerably constant order, becoming green, greenish-blue, blue, violet, a brick red, and finally yellow; though the green is the most characteristic and permanent. Bach one of these represents a distinct stage of the oxidation of bilirubin, the green answering to biliverdin. Such is Omelin's test for bile-pigments, by which they Inay be detected in urine or other fluids. CJhej^bsence of proteids in Wle^iSJtoJ)enotedj/ " Tha IMgwttfa At/Om of BUa.— ^li^So far ais known, its action on proteids is niL When bile is added to the products of an artificial gastric digestion, bile-salts, peptone, pepsin, and para- peptone are precipitated and redissolved by excess. 2. It is slightly solvent of fats, though an emulsion made with bile, is very feeble. But it is likely helpful to pancreatic juice, or more efficient itself when the latter is present. With free f Jttty acids it forms soaps, which themselves help in emulsifying fat. 3. Membranes wet with bile allow fats to pass more readily ; hence it is inferred that bile assists in absorption. 4. When^ bile is not poured out into the alimentary canal whe faeces i become clay-colored and ill-smelling, foul gases being secretedj in abundance, so that it would seem that bile exercises an anti- septic influence. It may limit the quantity of indal formed. It is to be understood that these various properties of bile are to be traced almost entirely to its salts ; though its alkaline reaction is favorable to digestion in the intestines, apart from its helpfulness in soap-forming, etc. 6. (R is thought by some that the bile acts as a stimulant to the intestinal tract, giving rise to 'peristaltic movements, and also, mechanically, as a lubri- cant of the f CBces. ^ the opinion of many, an excess of bile naturally poured out causes diarrhoea, and it is well known that bile given by the mouth acts as a pturgative. However, we must distinguish between the action of an excess and that of the quantity secreted by a healthy individual. The acid of the stonukch has probably no effect allied to that probuced by giving acids medicinally, which warns ns that too much must not be made out of the argument from bilious diarrhoea. 6./^ before intimated, a great part of the bile must be regardecTas excrementitious. It looks as though much of the effete heemo- globin of the blood apd of the cholesterin, which represents possibly some of the waste of nervous metabolism, were expelled from the body by the bile. The cholalic acid of the faeces is derived from the deoompcsition of the bile acids. Part of their mucus must also be referred to the bile, the quantity originally 8U ANIMAL PHTSIOLUGY. present in this fluid depending much on the length of its stay in the gall-bladder, which secretes this substance. 7. There is throughout the entire alimentary tract a secretion of mucus which must altogether amount to a large quantity, and it has been suggested that this has other than lubricating or such like functions. It appears that mucus may be resolved into a pro- teid and an aniitial gum, which latter, it is maintained, like vegetable gums, assists emulsification of fats. If this be true, and the bile is, as has been asserted, possessed of the power to break up this mucus (mucin), its emulsifying effect in the in- testine may indirectly be considerable. Bile certainly seems to intensify the emulsifying power of the pancreatic juice. There does not seem to be any ferment in bile, unless the power to change starch into sugar, peculiar to this secretion in some animals, is owing to such. Compmtif*.— The bile of the cwnivora and omnivora is yellowish-red in color ; that of herbivora green. The former contains taurocholate salts almost exclusively ; in herbivorous animals and man there is a mixture of the salts of both acids, though the glycocholate predominates. Fm. a88.-aftn-btadder, ductua diotodoahai moAmm'MB (•»« Le^toiv "6, iMVMttia diMt ; e. bpenlnt of Moood duot ot duataiidbil»4uot; «,«,ffikNlMiQ r,f. «H (aftflr Le Bon), a, MiMitaddar ; MM ; d, n of mucus f, and it has f or such like d into a pro- ntained, like this be true, the power to ct in the in- tainly seems tic juice. ie, unless the a secretion in omnivora is The former herbivorous >f both acids. I), a, MlMitaddar; of miun pMwrMtie r a good deal a temporary ih emphasiies the necessity for caution in drawing conclusions about the digestive juices as obtained by our present methods. The freshest juice obtainable through a recent fistulous opening in the pancreatic duct is clear, colorless, viscid, alka- line in reaction, and with a very variable quantity of solids (two to ten per cent), less than one per cent being inorganic matter. Among the organic constituents the principal are albumin, alkali-albumin, peptone, leucin, tyrosin, fats, and soaps in small amount. The alkalinity of the juice is owing chiefly to sodium #.' * :■¥ Vto. M.-0lf3riUlii Of leudn (Ftanke). Fre. a70.-Or]ratala of tyitMiii (rmike). carbonates, which seem to be associated with some proteid body. There is little doubt that leucin, tyrosin, and peptone arise from digestion of the proteids of the juice by its own action. liptriaMBtiL— If the pancreatic glands be mostly freed from adhering fat, cut up, and washed so as to get rid of blood; then minced as fine as possible, and allowed to stand in one-per- cent sodium-carbonate solution at a temperature of 40° C, the following results may be noted: 1. After a variable time the reaction may change to acid, owing to free fatty acid from the decomposition (digestion) of neutral fats. 2. Alkali-albu- min, or a body closely resembling it, may be detected and sep- arated by neutralization. 8. Peptone may be detected by the use of a trace of copper sulphate added to a few drops of caustic alkali, which becomes red if this body be present. 4. Alter a few hours the smell becomes feecal, owing in part to indd, which gives a violet color with chlorine-water; while under the microscope the digesting mass may be seen to be swarming 'imimis^& ■ mmummi&nMmmi'Mmm&'mm r 816 ANIMAL PHYSIOLOGY. with bacteria. 5. When digestion has proceeded for some time, leucin and tyroain may be shown to be present, though their satisfactory separation in crystalline form involves somewhat elaborate details. These changes are owing to self-digestion of the gland. All the properties of this secretion may be demonstrated more satisfactorily by making an aqueous or, better, glycerine extract of the pancreas of an ox, pig, etc., and carrying on arti- ficial digestion, as in the case o* a peptic digestion, with fibrin. In the CMC of the digestion of iat, the emulsifying power of a < watery extract of the gland may be shown by shaking up a little melted hog's lard, olive-oil (each quite fresh, so as to show no acid reaction), or soap. Kept under proper conditions, free acid, the result of decomposition of the neutral fats or soap into free acid, etc., may be easily shown. The emulsion, though allowed to stend long, persists, a fact which is availed of to produce more palatable and easily assimilated preparations of cod-liver oil, etc., for medicinal use. Starch is also converted into sugar with great ease. ^ short, the digestive juice of the pancreas is the most complex and complete in its action of the whole series. It is amyloljrtic, proteolytic, and steaptic, and these powers have been attributed to three distinct termentar—amylopain, trypsin, and steapain. Proteid digestion is carried further tlum by the gastric juice, and the quantity of crystalline nitrogenous products formed is in inverse proportion to the amount of peptone, from which it seems just to infer that part of the' original peptone has been converted into these bodies, which are fouud to be abundant or not in an artificial digestion, according to the length of time it has lasted — ^the longer it has been under way the more leucin ' and tyrosin present. Leucin is another compound into which the amido(NH«) group enters to make amido-caproic acid— one of the fatty series — ^while tyrosin is a very complei^ member of the aromAtic series of oompound& CfkxM complicated are the chemical effects of the digestive jmces; and it seems highly probable that these are only some of the compounds into which the proteid is broken up. These crystalline bodies may be made artificially by the long-continued action under heat of aoi^s and alkalies, in pro- teid or gelatinous matter, though it can not be said that these / facts have as yet thrown much light upon their formation inr^ the^digestive organs, /^ough putrefactive changes with formation of indd, etc.. ei¥i DIQBSTION OF FOOD. 817 or some time, though their res somewhat self -digestion lemonstrated ter, glycerine ying on arti- i, with fibrin, g power of a haking up a so as to show nditions, free fats or soap ilsion, though availed of to eparations of eat ease. (Si Qost complex is amylolytic, len attributed d steapsin. gastric juice, icts formed is rom which it one has been I abundant or >ngth of time B more leucin ' d into which oic acid— one 91^ member of B&ted are the seems highly aponnds into oially by the kalies, in pro- id that these / formation inr-*" of indol, etc.. occur in pancreatic digestion, both within and without the body, they are to be regarded as accidental, for by proper pre- cautions digestion may be carried on in the laboratory without their occurrence, and they vary in degree with the animal, tha individual, the food, and other conditions. It is not, however. M v/* *oftl / ■® FM. sn.-lIicr«M>rKMitania of bus* taitefiiM (^»«.I*»«2^):_.ilJ**l2*™-?*? cimmmiie ; a, bMterinm tacUa •BroseoM; «. 4. bwge.lMettU of Mewrtock, wltih iMrtial endoMnous , not«-tomuktiaa ; 5, tuIoih «UfM »l'**«w*" ■ mkmmmum mmm w WM|NMP*'liDl food ; tranalM Mlioimt In eoMe o«m- NHCMiitiioiiri after taking 1 ■ m tan mlwiten. Vood waa takan at B and O. i&aMsraUModitla. 1kiidiaiiramT«7 (It seems impossible to explain these facts, especially the first rapid discharge of fluid apart from the direct influence of the nervous system. (Upon the whole, the evidence seems to show that tiie press* ure in the bilenluctB is greater than in the veins that unite to make up the portal system ; but there are difficulties in the investigation of such and kindred subjects as regards the liver, owing to its peculiar vascular supply. It wiU be borne in mind that the liver in mammals oonsUrtM of a mass of blood-vessels, between the meshes of which are packed innumerable cells, and that around the latter meander the bile oapillaviee; that the portal vem breaks up into the interlobular, from which capil- laries arise, that terminate in the central intralobular veins, which make up the hepatic veiuletoor termiiiate in these vessels But the structure is complicated l^ Uie branches of the hepatic artery, which, an arterioles and capillaries, enters to some extent into the formation of the lobtilar vessels. It is remarkable that^ the cells of the liver are so similar, considering the complicate^ functions they appear to discharge. •«<«•*<■*■ DIOBSnON OF FOOD. 886 I by a sudden bsequent fall. «l7lBl»H0 ■IM (after N. ■BOimt In cat 7. TlilidiM'Mn^'VT especially the K3t inflnecce of that i&e press* is that unite to ftculties in the l^rds the liver, borne in mind f blood-vessels, »rable cells, and KtieB', that the •m which capil- alobular veins, in these vessels B of the hepatic I to some extent emarkable that^ the complicate^ (X question of interest, though difficult to answer, is the extent to which the various constituents of bile are manufact- ured in the liver. Taurin, for example, is present in some of I MMm: I, «, 1. 1. taMoMv ' AIM with ft daik injMlioii. Si itadBCtadwHh ;A»,».».»,1 thd tissues, but whether tiliis is used in the manufacture of taurocholic acid or whether the latter is made entirely anew, and possibly by a method in which taurin never ap- pears as such, is an open question. It is highly prob- able that a portion of the bile poured into the intes- tine is absorbed either as such or after partial decom- position, the products to be used in some way in the economy and presumably in the construction of bile by the liver. There are many facts, including some patho- logical phenomena, that point clearly to the forma- tion of the pigments of bile from hemoglobin in some of its stages of degeneration^ flttotogiaat^When the liver fails to act either from de- rm. m.-FartioB oC tHHwrene MeUMtvr ItepiUlo lomde or rMMti mainUIeil 400 diMuaten t, 0, g, wpmM/ Vi&^Mto!? I, Mood- {.UTMMselta.' iimmm iMmm B B Jt a i ii^wiWw i w g fift fi4.- 8S9 ANIMAL PHYSIOLOOT. rangement of its cells primarily or owing to obstruction to the outflow of bile leading to reabsorption by the liver, bile acids land bile pigments appear in the urine or may stain the tissues, (indicating their presence in excess in the blood. "yThis action of one gland (kidneys) foriiiother is highly suggestive, and specially important io bear in mind in medical practice, both in treatment and prognosis. The chances of re- covery when only one excreting gland is diseased are much greater evidently than when several are involved. Such facts as we have cited show, moreover, that there are certain common fundamental principles underlying secretion everywhere — a statement which will be soon more fully illioatrated. The Natubb or thb Act of Sbobbtion. We are now about ^to consider some investigations, more particularly their results, which are of extraordinary interest. The secreting cells of the salivary, the pancreatic glands, and the stomach have been studied by a combination of histo- logical and, more strictly, physiological methods, to which we shall now refer. Specimens of iihese glands, both before and after prolonged secretion, under stimulation of these nerves, were hardened, stained, and sections prepared. As was to be expected, the results were not entirely satisfactory under these methods; however, the pancreas of a living rabbit has been viewed with the microscope in its natural condition; and by this plan, especially when supplemented by the more involved and artificial i^ethod first referred to, results have been reached rm. W7.— Portion of p a wcr wi t ot rabbit (aft* KMme Md L»). A rapicMnta (laiid at rMrt ; B,d«ria«i "— which may be ranked among the greatest triumphs of modem physiology. -m DIGESTION OF FOOD. 887 "uction to the rer, bile acids n the tissues, ler is highly nd in medical shances of re- ed are much Such facts rtain common erywhere — a id. ION. g;ations, more lary interest, reatic glands, ktion of histo- i, to which we th before and these nerves. As was to be ry under these bbit has been ition; and by more involved e been reached naMta^uidatrwt; phs of modem (^me of these we now proceed to state briefly. To begin with the pancreas, it has been shown that, when the gland is not secreting — i. e., not discharging its prepared fluid — or dur- ing the so-called resting stage, the appearances are strikingly different from what they are during activity. The cell pre- sents during rest an inner granular zone and an outer clearer zone, which stains more readily, and is relatively small in size. The lumen of the alveolus is almost obliterated, and the in- dividual cells very indistinct. After a period of secreting activity, the lumen is easily perceived, the granules have dis- appeared in great part, the cells as a whole are smaller, and have a clear appearance throughout. Coincident with the changes in the gland's cells it is to be noticed that more blood passes through it, owing to dilatation of the arterioles. Fio. 878.— SMtton of muoous gUnd («(t«r Lftvdowiky). In A, gtand at nat ; In B, after McntliiK Bk WNiie noM. Again, the course of the changes in the salivary glands, whether of the mucous or serous variety, is very similar. In the mucous gland in the resting stage the cells are large, and hold much clear matter in the interspaces of the cell network ; and, as this does not stain readily, it can not be ordinary protoplasm. This, when the gland is stimulated through its nerves, disappears, leaving the containing cells smaller. It , has become mucin, and may itself be called mucinogen. It is to be noted that, as the cells become more protoplasmic, less burdened with the products of their activity, the nucleus becomes more prominent, suggestive of its having a probable directive influence over these manufacturing processes. Substantially the same chain of events has been established for the serous salivary glands and the stomach, so that we may safely generalize upon these well-established facts. . ,: I mfOKitm msHat. -tsmmeemm (ii>iiiiiiii>iw« i waMM i aaM BaB!!a 898 ANIIIAL PHTS10L06T. It seems clear that a series of changes constructive and, from one point of view, destructive, following the former are con- ria.an>.-Cluuigeatii B, atteriiiodera£i9, C after stantly going on in the glands of the digestive organ& Proto- plasm under nerve influence constructs a certain substance, which is r^n antecedent of the final product, which we term a ferment, ic is now customary to speak of these changes as constructive (anabolic) and destructive (katabolic), though we have already pointed out (page 270) that this view is, at best, only one way of looking at the matter, and we doubt if it may not be cramping and misleading. . ^We must also urge caution in regard to the conception to be associated with the use of the terms '* resting " and " active '* stage. It is not to be forgotten that strictly in living cells there is no absolute rest— such means death ; but, if these terms be understood as denoting but degrees of activity, they need not mislead. It is also more than probable that in certain of the glands, or in some animals, the processes go on simultane- ously : the protoplasm being renewed, the zymogen, or mother- ferment, being formed, and the latter converted into actual fer- ment, all at the same time. It has been pointed out that chorda saliva is usually more watery than t|iat secreted under stimulation of the sympathetic. When atrcpine is injected there is no discharge whatever, not- withstanding that the usual vascular dilatation follows, from which it is clear that the water is actually secreted. ®ie nature of secretion is now tolerably dear ag a whole;, though it is to be remembered that this account is but general, and that there are many minor difFerenoes for each gland and variations that can scarcely be doaominated minor for different animals. Evidently no theory of filtration, no process depend- ing solely on blood-pressure, will apply here. And if in this, the best-studied case, mechanical theories of vital processes utterly fail, why attempt to fasten them upon other glands, as tmmmffMi^iim^- ve and, from ner are con- f). A. dnrinK 'Mtj ■gmmnwrtn l^ns. Proto- n substance^ :li we term a 3 changes as i), though we w is, at best, ibt if it may K)nception to Emd "active" I living cells if these terms ity, they need in certain of m simultane- n, or mother* ito actual fer- uBually more I sympathetic, rlwtever, not- f ollows, frcmi 1 raK a whole;. B but general, ioh gland and r for different ocess depend- nd if in this, ital processes tier glands, as DIGESTION OF FOOD. 829 the kidneys and the lungs, or, indeed, apply such crude concep- tions to the subtle processes of living protoplasm anywhere or in any form P It is somewhat remarkable that an extract of a perfectly fresh pancreas is not proteolytic ; yet the gland yields such an extract when it has stood some hours or been treated with a weak acid. These facts, together with the microscopic appear- ances, suggested that there is formed a forerunner^ to the actual ferment — a zymogen, or mother-ferment, which at the mbment of discharge of the completed secretion is converted into the actual ferment. We might, therefore, speak of a pepsinogen, typsinogen, etc., and, though there may be a cessation in the series of processes, and no doubt there is in some animals, this may not be the case in all or in all glands. BMNtiaa I17 fhs BtoouMh.— The glands of the stomach differ in most animals in the cardiac and pyloric regions. In those of the former sone, both cent. jJ, columnar, aiid parietal (ovoid) cells are to be recognized. It was thought that possibly the latter were concerned in the secretion of the acid of the stomach, but this is by no means certain. Possibly these, like the demilune cells of the pancreas, may be the progenitors of the central (chief) cells. The latter certainly secrete ;:;'ep8in, and probably also rennet. Mucus is secreted by the cells lining the neck of glands and covering the mucous membrane inter- vening between their moutha The production of hydrochloric acid by any act of secretion is not beUeved in by all writers, some holding that it is derived from decomposition of sodium chloride, possibly by lactic acid. So simple an origin is not probable, not being in keeping with what we know of chemical processes within the animal body. MfrlMgMfein of ths IMgtittv* Oifaai.— -It has been found, both in man and other mammals, that when death follows in a healthy subject while gastric digestion is in active progress and the body is kept warm, a part of the stomach itself and often adjacent organs are digested, and the question is con- stantly being TaJsedj QlVhy dow noi the stCTmachjigest itself during, life? To this it has teen answored^hat the gastric jmoe iiToonstantly being neutralised by the alkaline blood ; and, again, that the very vitality of a tissue gives it the neces- sary resisting powers, a view contradicted by an experiment which is conclusive. If the legs of a living frog be allowed to hang against the inner walls of the stomach of a mammal when gastric digestion is going on, they will be digested. ^4ii^^^^'-!2-''ri''ri0-ih.iitK^y}h:'r^f'JI»^^ ,ijusii,yw!i»jwi*»,»' 380 ANIMAL PHYSIOLOGY. The first view (the alkalinity of the blood) would not suffice to explain why the pancreas, the secretion of which acts beet in an alkaline medium, should not be digested. ^t seems to us there is a good deal of misconception about the facts of the case. Observation on St. Martin shows that the secretion of gastric juice runs parallel with the need of it, as dependent on the introduction of food, its quantity, quality, etc.* Now, there can be little doubt that, if the stomach were abundantly bathed when empty with a large quantity of its own acid secretion, it would suffer to some extent at least. But this is never the case ; the juice is carried off and mixed with the food. This food is in constant motion and doubtless the inner portions of the cells, which may be regarded as the discharging region, while the outer (next the blood capillaries, the chief manufacturing region of the digestive ferment) are frequently renewed. Such considerations, though they seem to have been some- what left out of the case, do not go to the bottom of the matter. Amoeba and kindred organisms do not digest them- selves. Some believe that the little pulsatile vacuoles of the Inf usorians are a sort of temporary digestive cavities. I^But, to one who sees in the light of evolution, it must be clear that a structure could not have been evolved that would bejelf -destructive. The difficulty here is that which lies at the very basis of all life. We might ask. Why do living things live, since they are constantly threatened with destruction from within as from without ? Whyjdo not tibLeJlYer^ kidney, a;nd oth er gla nds^that secrete noxious substancee^ poison themsels^ We can not in~defail explain these things ; but we wish to make it clear that the difficulty as regards the stomach is not peculiar to that gland, and that even from the ordinary point of view it has been exaggerated. , OompantiTe. — More careful examination of the stomachs of some mammals has revealed the fact that in several animals, in which the stomach appears to be simple, it is in reality compound. There are different grades, however, which may be regarded as transition forms between the true simple stomach and that highly compound form of the organ met with in the ruminants. It has been shown recently that the stomach of the hog has an oesophageal dilatation; aud that the entire organ may be divided into several sones with different kinds of glandular idviriniiiiaui 881 Id not suffloe ch acts beet jption about shows that 16 need of it, bity, quality, bomach were uitity of its ent at least. E and mixed nd doubtless arded as the d capillaries, ferment) are e been some- tttom of Hbe digest them- cuoles of the dies. 1, it must be d that would y basis of all ince they are bhin as from tr glands that "We'can not nake it clear )t peculiar to int of view it e stomachs of eral animals, is in reality r, which may true simple le organ met if the hog has irgan may be of glandular Fm. no:-Iirterlar of bone'sitainiidi (after CbMnrem). , A, toft ■•o ; B, right mm; C, dnodHua dllatatloiL DIGESTION OF FOOD. epithelium, etc. These portions differ in digestive power, in the characteristics of the fluid secreted, and other details be- yond those which a superficial examination of this organ would lead one to suspect. The stomach of the horse represents a more advanced form of compound stomach than that of the hog, which is not evi- dent, however, until its glandular structure is examined closely. The entire left portion of the stomach represents an oesophageal dilata- tion lined with an epithelium that closely resembles that of the oesoph- agus, and with little if any digest- ive function. It thus appears that the stomach of the horse is in reali- ty smaller, as a true digestive gland, than it seems, so that a great part of the work of digestion must be done in the intestine; though in this animal, if the food be retained long as it is in the hog, which is not, however, the general opinion as regards the stomach of the horse, salivary digestion may continue for a considerable period after the food has left the mouth. The secretion of mucus by the stomach in herbivora is abundant. The Movements of the Digestive Organs.*^ As with other parts of the body, so in the alimentary tract, the slower kind of movement is carried out by plain muscu- lar fibers ; and the movements, as a whole, belong to the class known as peristaltic ; in fact, it is only at the beginning of the digestive tract that voluntary (striped) muscle is to be found and to a limited extent in the part next to this— i. e., in the oesophagus. Teeth in the highly organized mammal are remarkable in being to the least degree living struotares of any in the entire Mumal, thus being in marked contrast to other organs. The enamel covering their exposed surfaces is the hardest of all the tissues and is necessarily of low vitality. We have already alluded to the difference in the teeth of different animals, and their relation to customary food and digestive functions. In fact, it is dear that the teeth and all the parts of the digestive .W«t»miM )I IWW*l»ii'IMBi.(red, it is rapidly propelled on- ward by the tongfue, the oesophagus and ^sharynx being largely passive at the time, though contracting slowly afterward ; at the same time the larynx as a whole is raised, the epiglottis pressed down,' chiefly by the meeting of the tongue and itself, while its cushion lies oVer the rima gltMidis, which is closed or all but closed by the action of the sphincter muscles of the larynx, so that the food passes over and by this avenue of life, not only closed but covered by the glottic lid. The latter is not so essential as might be supposed, for persons in whom it was absent have been known to swallow fairly well. The ascent of the larynx any one may feel for himself ; and the be- havior of the pharynx and larynx, especially the latter, may he viewed by the laryngoscope. The grip of the pharyngeal muscles and the oesophagus may be made clear by attaching a piece of food (meat) to a string and allowing it to be partially swallowed. The upward movement of food under the action of the con- strictors of the pharynx is anticipated by the closure of the passage by the palato-glossi of the anterior pillars of the fauces. The circular muscular fibers of the gullet are probably the most important in squeezing on the food by a peristaltic move- ment, passing progressively over the whole tube, though the longitudinal also take part in swallowing, perhaps, by steady- ing the organ. Swallowing will take place in an animal so long as the medulla oblongata remains intact ; and the center seems to lie higher than that for respiration, as the latter act is possible when, from slicing away the medulla, the former is not. An- encephalous monsters lacking the cerebrum can swallow, suck, and breathe. Food placed in the pharynx of animals when unconscious is swallowed, proving that volition is not essential to the act; but our own consciousness dedlares that the first stage, or the removal of the food from the mouth to the pharynx,i8 volun- tary. When we seem to swallow voluntarily there is in reality a stimulus applied to the fauces, in the absence t>f food and drink, either by the back of the tongue or by a little .^iva. It thus appears that deglutition is an act in the main reflex, though initiated by volition. The afferent nerves concerned are usually the glosso-pharyngeal, some branches of the fifth. UMiltrifB-rr-T'^"-^^"''''^ DIOESTION OF FOOD. 885 en the mor- "opelled on- aing largely terward; at le epiglottis Band itself, is closed or Bcles of the 9nue of life, he latter is in whom it well. The and the be- latter, may pharyngeal attaching a be partially L of the con- >sure of the f the fauces. >robably the italtic move- , though the B, by steady- long as the seems to lie b is possible is not. An- rallow, suck, unconscious [to the act; stage, or the ax,'is volun- in reality a d and drink, a. main reflex, IS concerned of the fifth. and of the vagus. The efferent nerves are those uf the numer- ous muscles concerned. When food has reached the gullet, it is, of course, no longer under the control of the will. Section of the vagus or stimulation of this nerve modifies the action of the oesophagus, though it is known that contrac- tions may be excited in the excised organ ; but no doubt nor- mally the movements of the gullet arise in response to natural nerve stimulation. OompantiT*. — That swallowing is independent of gravity is evident from the fact that long-necked animals (horse, giraffe) can and do usually swallow with the head and neck down, so that the fluid is rolled up an inclined plane. The peristaltic nature of the contractions of the gullet can also be well seen in such animals. In the frog the gullet, as well as the mouth, is lined with ciliated epithelium, so that in a recently killed animal one may watch a slice of moistened cork disappear from the mouth, to be fgund shortly afterward in the stomach. The rate of the descent is surprising — in fact, the movement is plainly visible to the unaided eye. TIm MofOBMito of the ItoimMh.— The stomach of mammals, including man, is provided with three layers of muscular fibers : 1. External longitudinal, a continuation of those of the oesopha- gus. 2. Middle circular. #3. Internal oblique. The latter are i Fia. ML— HnmMi itonwcii (after Sappey). 1. osMphagiM : », cinNilar flben at oeaqpbaseal openlnc; 8, 8, drcnlar flben at leiaer cnrratiire ; 4, 4, circular flben at the pylorus ;&, 6. «, 7, 8, oblique flben ; 9, 10, flben of thi* layer oorerinc the gratter pouch ; n.porttDnot ■tomach from which theae flben have been remoTed to ihow the aubJiMwnt circular flbers, 836 ANIMAL PHTSIOLOOT. i the least perfect, viewed as an investing coat. The pyloric end of the stomach is best supplied with muscles ; where also there is a thick muscular ring or sphincter, as compared with which the cardiac sphincter is weak and ill-developed. The movements of the stomach begin shortly after a meal has been taken, and, as shown by observations on St. Martin, continue for houm, not constantly, but periodically. The effect of the conjoint action of the different sets of muscular fibers is to move the food from the cardiac toward the pyloric end of the stomach, along the greater curvature and back by the lesser curvature, while there is also, probably, a series of in-and-out currents to and from the center of the food-mass. The quantity of food is constantly being lessened by the removal of digested portions, either by the blood-vessels of the organ or by its passing through the pyloric sphincter. The empty stomach is quiescent and contracted, its mucous membruie being thrown into folds. The movements of the stomach may be regarded as reflex, the presence of food being an exciting cause, though probably not the only one ; and so largely automatic is the central mech- anism concerned, that but a feeble stimulus suffices to arouse them, espeokiliy at the accustomed time. Of the paths of the impulses, either afferent or efferent, little is known. Certain effects follow section or stimulation of the vagi or splanchnics, but these can not be predicted with certainty, or the exact relation of events indicated. CB is said that the movements of the stomach cease, even when it is full, during sleep, from which it is argued that gas- tric movements do normally depend on the influence of the nervous system. However, the subject is too obRcure at pres- ent for further discussion. Comiuititii^— Recent investig^tiooB on the stomach of the pig indicate that in this animal the omitents of the two aids of the stomach may long remain but little mingled; imd eaob is certainly the casein this organ among ruminants. P»thokgiaal.-^8tention of the stomach, eitiier jfrom excess of food or gas arising from fermentative chuiges, or by secre- tion from the blood, may cauw, by upward presmire on the diaphragm, etc., uneasiness from hunpwed respiration, and ir- regularity of the heart, possibly, also, in part traceable to the physical interference with its movements. After great and prolonged distention there niay be weakened digestion for a considerable interval. It seems not improbable that this is to tumtm mmmmm iiiuci'.'iSMSVcviM&it'V-' 3 pyloric *nd re also there i with which after a meal 1 St. Martin, r. The effect ular fibers is rloric end of by the lesser >f in-and-out rhe quantity il of digested an or by its ;y stomach is mng thrown ded as reflex, igh probably ientral mech- }es to arouse t or efferent, timulation of ■edicted with h cease, even aed that gas- iuence of the cure at pr«9- )mach of the e two Olds of ; imd audi is r from excess I, or by secre- NNKire on the ation, and ir- iceable to the er great and gestion for » bat this is to DIOBOTION OF FOOD. be explained, not alone by the impaired elasticity (Tiitality) of the muscular tissue, but also by defective secreting power. It is not necessary to impress the lesson such facts oohvey. The latMtiiial ]bfaMBta.^The circular fibers pli^ a much more important part than the longitudinal, being, in fact^ much more developed. It is also to be remembered that herves in the form of plexuses (of Auerbach and Meissner) abound in its walls. Normally the movement, slowly progressive, with occasional baitings, is from above downward, stopping at the ileo-ceecal valve ; the movements of the large gut being apparently mostly independent. Movements may be excited by external or internal stimula- tion, and may be regarded as reflex ; in which, however, the tendency for the central cells to discharge themselves is tio great (automatic) that only a feeble stimulus is required, the normal one being the presence of food. It is noticeable in a recently killed animal, or in one in the last stages of asphyxia, tr^t the intestines contract vigorously. Whether this is due to the action of blood overcharged with carbonic anhydride and deficient in oxygen on the centers pre- siding over the movements, on the nerves in the intestinal walls, or on the muscle-cells directly, is not wholly clear, but it is probable that all of these may enter into the restllt. The vagus nerve, when stimulated, gives rise to movements of the intestines, while the splanchnic seems to have the reverse effect ; but the cerebrum itself has an influence over the movements of the gut, as is plain from the diarrhoea traceable to unusual fear or anxiety. There is little to add in regard to the move- ments of the large intestine. They are, no doubt, of consider- able importance in animals in which it is extensive. Normally they begin at the ileo-ceecal valve. B«feaalim.-*-The removal of the waste matter from the ali- Tnentary tract is a complicated process, in which both smooth andstriped muscle, the spinal cord, and the brain take part. /ptefecation may take place during the unconsciousness of sleep or of disease, and so be wholly indlependent of the will ; but, as we well know, this is not usually the case. Against ac- cidental discharge of fsBces there is a provision in the sphinc- ter ani, the tone of which is lost when the lower part of the spinal cord is destroyed. We are conscious of being able, by an effort of will, to prevent the relaxation of the sphincter or to increase its holding power, though the latter is probably almost ■iiati!.>#ii i»,' I 'lwitiWHi i Mi i mmMmi i i*«nu i i>mwu i B " 888 ANIMAL PHTSIOLOOT. wholly due to the action of extrinsic muscles ; at all events any one may convince himself that the latter may he made to take a great part in preventing f eooal discharge, though whether the tone of the sphincter can be increased or not by volition it is difficult to say. What happens during an ordinary act of defecation is about as follows : After a long inspiration the glottis is closed ; the diaphragm, which has descendea, remains low, affording, with the obstructed laryngeal outlet, a firm basis of support for the action of the abdominal muscles, which, bearing on tha intes- tine, forces on their contents, which, bef pre the act has been called for, have been lodged mostly in the large intestine ; at the same time the sphincter ani is relaxed and peristaltic move- ments accompany and in some instances precede the action of the abdominal muscles. The latter may contract vigorously on a full gut without success in the absence of the intestinal peri- stalsis, as too many cases of obstinate constipation bear witness. like deglutition, and unlike vomiting, there is usually both a voluntary and involuntary part to the act. Though the will, through the cerebrum, can inhibit defeca- tion, it is likely that it does so through the influence of the cerebrum on some center in the cord ; for in a dog, the lumbar cord of which has been divided from the dorsal, the act is, like micturition, erection of the penis, and others which are under the control of the will, still possible, though, of course, performed entirely unconsciously. Vowiriiy. — If we consult our own consciousness and observe to the best of our ability, supplementing information thus gained by observations arent that vomiting implies a series of co-ordi- nated movements, into which volition does not enter either necessarily or habitually. There is usually a preceding nausea, with a temporary flow of saliva to excess. The act is initiated by a deep inspiration, followed by closure of the glottis. Whether the glottis is closed during or prior to the entrance of air is a matter of disagreement. At all events, the dia- phragm descends and remains fixed, the lower ribs being I'e- traoted. The abdominal muscles then acting against this sup- port, force out the contents of the stomach, in which they are assisted by ilie essential relaxation of the cardiac sphincter, the s'Lortimmg of the oesophagus by its long^itudinal fibers, and the extension aud straightening of the neck, together with the open- ing of the mouth. illiilMi i]l«»liii>i>— llii til events any onade to take 1 whether the volition it is ation is about is closed; the fording, with ipport for the on the intes- act has been I intestine; at istaltic move- the action of vigorously on ntestinal peri- 1 bear witness. i usually both nhibit def eoa- fluence of the ig, the lumbar the act is, like I are under the rse, performed 88 and observe ormation thus ver animals, it ries of co-ordi- >t enter either ceding nausea, act is initiated )f the glottis. 10 the entrance rents, the dia- ribs being ve- (Mnst this sup- !^hich they are a sphincter, the fibers, and the r with the open- DIOBSTION OP POOD, 839 As the expulsive effort takes place, it is accompanied by an expiratory act which tends to keep the egesta out of the larynx «nd carry them onward, though it may also contrihute to over- come the resistance of the elevated soft palate, which serves to protect the nasal passages. The stomach and oesophagus are not wholly passive, though their part is not so important in the adult as might be inferred from observing vomiting in infants, the peristalsis of these organs apparency sufficing in them to empty the stomach. Retching may be very violent and yet ineffectual when the cardiac sphincter is not fully relaxed. The pyloric outlet is usually closed, though in severe and long-continued vomiting bile is often ejected, which must have reached the stomach through the pylorus. Gompantivs.— The ease with which some animals vomit in comparison with others is extraordinary, as in camivora like our dogs and cats ; a matter of importance t6 an animal ac- customed in the wild state to eat entire carcasses of animals — hair, bones, etc., included. The readiness with which an animal vomits depends in great part on the conformation and relations of the parts of its digest- ive tract. The horse vomits with difficulty— its stomach and its car- diac opening being small and peculiar in shape (Figs. 261 and 280), while its cBSophagus is long. The stomach of the htunan being during infantile life is less pouched than in the adult, which in part explains the ease with which infants vomit. But the matter is complex; much depends on the proper co-ordinations being made, and, this being well or ill accom- plished, accounts for the variations in the ease with which dif- ferent persons vomit. Patliatotiflal.— Vomiting may arise from the presence of renal or biliury calculi (reflex action) ; from disease of the cerebrum or the medulla ; from obstruction in the pyloric region or in the intestines ; from emotions ; from revived unpleasant men- tal dissociations; from nauseous tastes, etc. It may be qnes- tiohable whether some of these are properly termed " patho- logical." Pyrosis is due to the anti-peristaltic action of the stomach and oesophagus alone, so that it is a sort of partial vomiting mad allied to the regurgitation of special secretions, as from the crops of pigeons, or of food from the stomachs of ruminants. We have known oases in which anti-peristalsis was conflndd to '840 ANIMAL PHYSIOLOGY. the pharynx alone. Some persona seem to have acquired the power of regurgitating food and masticating it afresh. The excessive vomiting following ohstruction of the howels is comparahle to the unusual action of the heart, ureter, blad- der, etc., when there is hindrance to the outflow. As we have already explained for the heart, we regard this as the resump- tion of a power of independent action seen in ancestral forms and marked when the nervous system is no longer exercising its usual control and direction. Not that this or similar be- havior may not result from excessive stimulation, loading to unusual central nervous discharge, but it certainly does happen independraitly of the nervous system, and may be witnessed in the hearts of cold-blooded animals when all their nerves are divided. Similarly, the habit of regurgitating the food is intelligible in the light of evolution. The fact that mammals are descended from lower forms in which unstriped muscle-cells go to form organs that have a rhythmically contractile function, renders it clear why this function may become, as in ruminants, spe- cialized in certain parts of the digestive tract ; why carnivora should vomit readily, and why human subjects should learn to regurgitate food. Th«re is, so to speak, a latent inherited ca- pacity which may be developed into actual function. Apart fi-om this it is difficult to understand such cases at all. The vomiting center is usually located in the medulla, and is represented as working in concert with the respiratory center. But when we consider that there is usually an increased flow of saliva and other phenomena involving additional central nervous influence, we see reason to believe in co-ordinated action implying the use of parts of the central nervous System not so closely connected anatomically as the respiratory and vomiting centers are assumed to be. Indeed, as we before indicated, it does not seem probable that the doctrin.. of centers in its present form, especially with such precise limitations, both anatomically and physiologically, will continue to be maintained. We seem to hav« been over- looking the connection of parts while occupied with defining their limits. It is not, however, yec possible to substitute other explanations that shall be wholly satisfactory ; and we make these remarks to keep the student expectant of progress, for, as a distinguished exponent of » ence has said, " When VScienct adopts a [rigid] creed^she commits suicidey We do no+ know thi$ part ta^n, if anyTl^TEe splanchnic acquired the resh. [)f the howelfl ureter, blad- As we have I the resump- cestral forms ;er exercising r similar be- >n, loading to J does happen ) witnessed in ir nerves are is intelligible are descended Us go to form Lction, renders iminants, spe- vhy carnivora hould learn to I inherited ca- iction. Apart it all. ) medulla, and dratory center, increased flow itional central II co-ordinated lervous System sspiratory and seem probable especially with )hysiologically, lave been over- [ vdth defining » to substitute ictory; and we mt of progress, 8 said, "\nien ide^J The splanchnic ' -irnip i wii l M i llBl* ' DIGESTION OF FOOD. Ml or other nervee of the sympathetic system ; but, f roin the fact that discharge of the gastric contents is impossible when the vagi are cut, it is likely that the efferent impulses, determining the relaxation of the cardiac sphincter, descend by these nerves, while the chorda tympani is concerned, of course, in the secre- tion of saliva. But it will be clear, from the facts of the case, that many nerves, both afferent and efferent, are concerned ; and it is more than likely that our explanations of the (^ntire process are quite inadequate to unravel its real complexity. ThnapeutiM. — The evidence from the use of drugs seems tu emphasize the last statement. At all events, emetics act in a variety of ways, and differently in different animals. The Removal of Diqbsted Products from the Aliment- ary Canal. The glands of the stomach are simply secretive, and all ab- sorption from this organ is either by blood-vessels directly or by lymphatics; at least, such is the ordinary view of the sub- ject— whether it is not too narrow a one remains to be seen. It is important to reinember that the intestinal mucous membrane is supplied not only with secreting glands but lym- phatic tissue, in the form of the solitary and agminated glands (Peyer's patches) and thickly studded with villi, giving the I'mall gut that velvety appearance appreciable even by the naked eye. It wUl not be forgotten that the capillaries of the digestive organs terminate in the veins of the portal system, and that the blood from these parts is conducted through the liver before it reaches the general circulation. The lymphatics of these organs form a part of the general lymphatic eystem f)f the body ; but the peculiar way in which absorption is effected "hj villi, and the fc ot that the Ijrmphatics of the intestbie, etc., at one time (fasting^ contain ordinary lymph and at another (after meals) the products of digestion, imparts to them a physiological character of their own. Absorption will be the better understood if we treat now of lymph and chyle and \,he lymph vascular system, which were purposely postponed till the present; though its connection with the vascular system is as close and important as with the digestive organs. The lymphatic system, as a whole, more closely resembles the venous than the arterial vessels. We may speak of lym- 342 ANIMAL PHYSIOLOGY. phatio capillaries, which are, in essential points of structure, like the arterial capillaries ; while the larger vessels may be compared to veins, though thinner, being provided with valves and having very numerous anastomoses. These lymphatic capillaries begin in spaces between the tissue-cells, from which they take up the effete lymph. It is interesting to note that there are also perivascular lymphatics, the ex- istence of which again shows how close is the relation between the blood vascular and lym- phatic systems, and as we would suppose, and as is actually found to be the case, between the contents of each. Lynph ud Chyle. — If one compares the mes- entery in a kitten, when fasting, with the same part in an animal that was killed some hours after a full meal of milk, it may be seen that the formerly dear lines indicating the course of ne m-vai»«i ot tie lymphatics and ending in glands have in ijnqphatic»(SMve7). the latter case become whitish (hence their name, Iticteala), owing to the absorption of the emulsified fat of the milk. rta. M.-0riste «( I nMMiwmMI — L : A, ortgte ( OUMrCMMH. J (attM- LMdoto). I. From eNrMJ c) : s, Ijrmpb-OMiata oammtwiaiitecbr ' I IV uSm of Ijnnpli-OMuai; ff, K, w Xwtth of dlaoliraim of lum. u. NriTM- ..,_j«gtMiMifHa mmmm<' ential points laries; while red to veins, ^h valves and OSes. These aces between take up the to note that latics, the ex- w close is the lar and lym- suppose, and , between the tares the mes- ^th the same d some hours f be seen that ' the course of ands have in (hence their lulsified fat of Im of dlwliraim of wMiIfmiSaiVMal dMllum. u. Nrivas- DIOBSTION OF FOOD. 348 Microscopic examination shows the chyle to contain (when coagulated) fibrin, many leucocytes, a few developing red cor- puscles, an abundance of fat in the for Ji both of very minute oil-globules and particles smaller still. Fro. )».— MttaUnmCnMidaodMninorrab- Vw. M.— VBH fliled with tet, firom amdl Mt, two bom anarluTtacbcM fed with iatoMiie oC «« «nanled orimiMU, one nMltodlwtt«r(nink*). bowaflardMlhd'Uiiln). There are also present fatty acids, soaps small in quantity as compared with the neutral fats, also a little cholesterin and lecithin. But chyle varies very ^ widely even in the same ammal at different times. To the above must be added proteids (fibrin, serum-albumin, and globulin); extractives (sugar, urea, lea- cli ) ; and salts in which sodium chloride is abundant. The composition of lymph is so similar to that of chyle, and both to blood, that lymph might, with a fair degree of ac- curacy, be regarded as blood wi^out its red corpuscles, and chyle as lymph with much neu- tral fat in a vwy fine state of division. some bimfam uid amphibians, there are lymph hearts. In tl* ftfog timre are two ouBtBa/ry and two aaoral lymph hearte. Tlie latter are, «[^pecially, easily seen, and there is no doubt, that they are ttodw the control of the nervous system. Fw. m.-^Ck^ Men Jram «he. ^fe»^ erimtaial Dke). BbowB SnegniBalM iftfittTS.— In some fishes, M4 ANIMAL PHT8L0L00T. In the mAmmalB no such special helps for the propulsion of lymph exist. .. . Ther^ is little doubt that the blood -pressure is always higher than the lymph-pressure^ and when the blood-vessels t^^am^uT ^^w««Snflt«Hbiet Jut More it mptlw 86lo'tii»«iic««yifeBi tdhgrU are dilated the fluid within the perivwoular lymph-channels is likely ccMnpreased ; mviKmlar exercise must act on the lymph- channels as on veins, both being provided with valves, though themselves readily compressible ; the inspiratory efforts, e^ cially when forcible, assist in two ways: by the compressing effect of the respiratory muscles, and by the aspirating effect of the negative pressure within the thorax, producing a similar aspirating effect within the great veins, into which the large lymphatic trunks empty. The latter are provided at this point with valves, so that there is no back-flow; and, with the posi- tive pressure within the large lyai^tic trunks (thoracic duct, etc.), the idiypieitl conditions are favorable to the outflow of lymph or ok^le. DIGESTION OF FOOD. 845 I is always lood-vessels Our knowled^ of the nature of the passage of the chyle from the intestines into the blood is now dearer than it was till recently, though still incomplete. The exact structure of a villus is to be carefully considered. If we assume that the muscular cells in its structure have a rhythmically contractile function, the blind terminal portion of the lacteal inclosed within the villus must, after being emptied, act as a suction-piunp to some extent; at all events, the conditions as to pressure would be favorable to inflow of any material, especially fluid without the lacteal. The great diiBculty hitherto was to understand how the fat found its to duot; S, T«oep- i-chahnelsis the lymph- lures, though efforts, espe- comiff^Ming rating effect ing a similar ch the large at this point ith the pofii- horacic duct, le outflow of Fro. M. way through the vilius into the blood> for, thftt most of it passes in this direction there is little doubt. It is now known thttt leucocytes (amoeboids, phagocytes) migrate from wiihiii the villus oatwftrd, and^nay even reach its surface; that they take up (eat) f^t^pwrticles from the 846 ANIMAL PHYSIOIAXJY. ;^?<^' ^1^^ ^^>^-ss^ ^^\ '/:■ -ii: ^- ..■ -.HIT' r ~ -" ^ ' 1 1^ ; E^ m l^fWi^iMHr:.. rm. iiao. atwnx*, iMjvlitly r«dHiMd firam • r, Ji^ Hi a« Jl« epithelium of the yiUns, ond^ independently tiiemaelves, carry them inward, reach the central lacteal and breakup, thus releas- ing the fat. How the fat gets into the covering epithelium is MaBiiiwWfiiiwtn 'm -'W' ^y^''* ^'*^j taMIB)(«ltar ob ; f, dnadaamn : nmlyes, cany p^thnsreleas- epithelitun is DIGESTION OF FOOD. 347 not yet so fully known — possibly by a simi- lar inceptive process ; nor is it ascertained what constructive or other chemical pro- cesses they may perform ; though it is not at all likely that the work of the amoeboid cells is confined to the transport of fat alone, but that other matters are also thus removed inward to the lacteal. liptrimMteL— If two frogs under the influence of urari, to remove the effect of muscular movements, be placed under ob- servation, the one having its brain and spinal cord destroyed, the other intact, in both the aorta divided across, and normal saline solution injr d into the posterior lymph-sac (benea xe skin of the back), it will be found, on suspending the two by the lower jaw, that, in the frog, with the nerve - centers uninjured, abundance of saline fluid is taken up from the dor- sal sac and expelled through the aorta, but in the other case none, the heart remaining all but empty. n». ANIMAL PHYSIOLOGY. Different interpretations have been put upon this experi- ment. Some point to it as clear proof of the influence of the B lep Fio. IM.-A. SmUob of rmmtinlimtA i 0T, ■trialed koidtr: c IjrnvkMdli ^e*,^ 4lMoria partial explanatibn of the iailu*© of absorp- tion; but, when a multitude of other facte are ^ken into account, tihere seems little reason to doubt that so important a process ae absorption can not f ail ip be mgulated by tiie nerv- ous center?. The danger of foimding any impbiftalat conclu- sion on a single experiment is very great. Again, if the leg of a hog, exolu^ve of the nerves, be liga- tured, the limb will be foia^. to swell nqiidly if placed in water, which is not true of a dead limb. This is addiaoed as evidence for the iiidependenee of the abtewptive process and the circula- tion; and; since section of tlie sciatie nerve is said to arrest absorption, such an experiment, taken together with the two his experi- mce of the tH:: ' ■^ ep, eiittlielliim ; itnl lactaid ooo- MliMdiDllIK tat le f ailiire of tion of the il tone, the dng, in fact, ed that the riment; the > of abnorp- ^ken into important a Yjf ttie nerv- babt condu- -ves, be liga- »d in water, as evidence the circula- id to arrest ith the two lAil t MijiiiiJWitiiiA'jg ig i ^ r ^. .^;^. v^, ^.v^. k I IMAGE EVALUATION TEST TARGET (MT-3) 1.0 I.I 11.25 |4S ■£0 Hi m |28 |25 |Z2 2.0 4.0 U 11.6 - 6" PhotDgraphic Sciences Corporation 23 WIST MAIN STRUT WnSTIR.N.Y. 14SM (716)t72-4S03 Wit". :_.;,..^.;i*i:|',-.v_i3i-«**t.-- .rption is con- xsdss of the re- almost wholly ley are opposed ad are not sup- certain foreign flood or the ail- ing to physical testine can act ; anoes physical DIGESTION OF FOOD. 861 principles actually do explain the whole, which we do not grant, it would by no means follow that such was the natural behav- ior of this organ in the discharge of its ordinary functions. When we consider that the blood tends to maintain an equi- librium, it must be evident that the removal of substances from the alimentary canal, unless there is to be excessive activity of the excretory organs and waste of energy both by them and the digestive tract, must in some degree depend on the demand for the products of digestion by the tissues. That there is to some extent a corrective action of the excretory organs always going on is no doubt true, and that it may in cases.of emergency be great is also true ; but that this is minimized in ways too complex for us to follow in every detail is equally true. Diges- tion waits on appetite, and the latter is an expression of the needs of the tissues. We believe it is literally true that in a healthy organism the rate and character of digestion and of the removal of prepared products are largely dependent on the con^ion of the tissues of the body. (why is digestion more perfect in overfed individuals After a sOort fast ? The whole mtftter is very complex, but we think it is infinitely better to admit ignorance than attempt to ex- plain by principles that doviolence to our fundamental con- ceptions of life processea To introduce " ferments " to explain so many obscure ppints in physiology, as the conversion of peptone in the blood, for example, is taking refuge in a way that does no credit to science. Without denying that endosmosis, etc., may play a part in the vital processes we are considering, we believe a truer view of the whole matter will be ultimately reached. In the mean time we think it best to express our belief tl^t we are igiiOTant of the realjig^t ure of absorption iujgreat p^tThut weffiink tEK73T^"^iSiraSary "tfifcr w^ as doing for the digested food (chyle, etc.) some such work as certain other glands do for the blood, we would be on the way to a truer con- ception of the real nature of the processes. ' It would then be possible to understand that proteids either in the form of soluble or insoluble substances, including pep- tone, might be taken in hand and converted by a true vital process into the constituents of the blood. r If we were to regard the kidney as manufacturing useful iusCead of harmful products, the resemblance in behavior would in many points be parallel. We have seen that mechanical explanations of the functions of the kidney have failed, and n'aill!i»aB5 M>IW.tiW. ' 'W( '' aWllW^^ ' lUlWIW ' JWIJIII>'l» i J » ..UJfeJ » Jll!lil,!IWM»M i i.lUIII)lMu.i<'IWU, i| l!l mmn'mmmmmmli^ S5i ANIMAL PllYSIOLOOY. Chat it must be regarded even in those parts that eliminate most water as a genuine secreting mechanism. We wish to present a somewhat truer conception of the lymph that is separated from the capillaries and bathes the tissues. We would regard its separation as a true secretion, and not a mere diffusion depend«9nt wholly on blood-pressure. The mere ligature of a vein does not sufBce to cause an excess of diffusion, but the vaso^motor nerves have been shown to be concerned. The effusions that result from pathological pro- cesses do not correspond with the Ijntnph — ^that is, the nutrient material — ^provided by the capillaries for the tissues. These vessels are more than mere carriers ; they are secretors — ^in a sense they are glands. We have seen that in the fcetus they function both as respiratory and nutrient organs in the allan- tois and yelk-sac, and, in our opinion, they never wholly lose this function. The kind of lymph that bathes a tissue, we believe, depends on its nature and its condition at the time, so that, as we view tissue-lymph, it is not a mere effusion with which the tissues, for which it is provided, have nothing to do. The differences may be beyond our chemistry to determine, but to assume that all lymph poured out is alike is too crude a conception to meet the facts of the case. Qlands, too, it will be remembered, derive their materials, like all other tissues, not directly from the blood, but from the lymph. We believe that the cells of the") Capillaries, like all others, are influenced by the nervous system, [ notwithstanding that nerves have not been traced terminating] in them. It is to be borne in mind that the lymph, like the blood, receives tissue waste-products — in fact, it is very important to realize that the lymph is, in the first instance, a sort of better blood — an improved, selected material, so far as any tissue is concerned, which becomes gradually deteriorated (toe Fig. 8S9). We have not the space to give all the reasons on which the opinions expressed above are founded ; but, if the student has become imbued with the principles that pervade this work thus far, he will be prepared for the attitude we have taken, and sympathize with our departures from the mechanical (physical) phmblogy. We think it would be a gt«at gain for physiology if the use of the term " absorption," as applied to the alimentary tract, were given up altogether, as it is sure to lead to the substitu- niOBSTIOX OF FOOD. 368 at eliminate ption of the i bathes the tion, and not )BSUTe. The an excess of shown to be ological pro- the nutrient isnes. These cretora — in a e fcBtus they in the allan- r wholly lose ieve, depends it, as we view ti the tissues, he differences assume that ption to meet nbered, derive stly from the le cells of the"^ »rvous system, [ d terminatingj ke the blood, important to sort of better any tissue is (toe Fig. 829). on which the le student has ;his work thus tve taken, and leal (physical) ogy if the use mentary tract, o the substitu- tion of the gross conceptions of physical processes instead of the subtle though at present rather indefinite ideas of vital processes. We prefer ignorance to narrow, artificial, and erro- neous views. PAthologioaL — Under certain circumstances, of which one- is obstiruction to the venous circulation qr the lymphatics, fluid may be poured out or effused into the neighboring tissues or the serous cavities. This is of very variable composition, but always contains enough salts and proteids to remind one of the blood. Such fluids are often spoken of as "lymph/' though the resemblance to normal tissue-lymph is but of the crudest kind; and the condition of the vessels when it is secreted, if such a term is here appropriate, is not to be compared to the natural separation of the normal lymph — in fact, were this not so, it would be like the latter, which it is not. When such effusions take place th^y are in themselves evidence of altered (and not merely increased) function. Thit iMMb — The feeces may be regarded in at least a three- fold aspect. They contain undigested and indi^tible rem- nants, the ferments and certain decomposition products of the digestive fluids, and true excretory matters. In carnivorous and omnivorous animals, including man, the undigested materials are those that have escaped the action of the secretions— such as starch and fats— together with those substances that the digestive juices are powerless to attack, as homy matter, hairs, elastic tissue, etc. In vegetable feeders a larger proportion of chlorophyl, cel- Moee, and starch will, of course, be' found. These, naturally, are variable with the individual, the spe- cies, and the vigor of the digestive oi^ns at the time. Besides the above, certain products are to be detected in the fsBces plainly traceable to the digestive fluids, and showing that they have undergone chemical decomposition in the ali- mentary tract, such as cholalic acid, altered, coloring-matters like urobilin, derivable probably from bilirubin ; also oholes- terine, fatty acids, insoluble soaps (caldum, magnesium), to- gether wtth ferments, having the pn^perties of pepsin and am ylo psin. Mucus is also abundant in tiie feeces. nV'e know little of the excretory products proper, as they prolSably normally exist in small quantity, and it is not impos- sible that some of the products of the decomposition of the digestive juices may be reabsorbed and worked over or excreted by the kidneys, etc. »:>:<^\)^»^•^^~ja l l ^ JaMlWg ta>^rt^?l> Wll4 ll U,^l».^Jll■^uftll^l l ^lJ l ■ >■ ;^ SM AinMAL PHYSIOLOGY. \- There is, however, a recognized non-nitrogenous crystalline body known as excretin, which contains sulphur, salts, and pigments, and that may rank perhaps as a true excretion of th6 intestine. It is well known that bacteria abound in the alimentary tract, though their number is depisndent on a variety of circum- stances, including the kind of food and the condition in which it is eaten. These minute organisms feed, of course, and to get their food produce chemical decompositions. SkaUjH and indoi are possibly thus produced, and give the f eecal odor to the con- tents of the intestine. But as yet our ignorance of these mat^ ters is greater than our knowledge— a remark which applies to the excretory functions of the alimentary tract generally. PatludogiML — The facts revealed by clinical and pathological study leave no doubt in the mind that the intestine at all events may, when other glands,^like the kidney, are at fault, undertake an unusual share of excretory work, probably even to the length of discharging urea. Obscure as the subject is, and long as it may be before we know exactly what and how matter is thus excreted, we think that it will greatly advance us toward a true conception of the vital processes of the mammalian body if we regard the ali- mentary tract as a collection of organs with both a secreting and excreting function ; that what we have been terming ab- sorption is in the main, at least, essentially secretion or an allied process; and that the parts of this long train of organs are mutually dependent and work in concert, so that, when one is lacking in vigor or resting to a greater or less degree, the others make up for its diminished activity ; and that the whole must work in harmony with the various excretory organs, as an excretor itself , and in unison with the general state of the econ- omy. We are convinced that even as an excretory mechanism one part may act (vicariously) for another. (Pf course, in disease the condition of the fnces is an indica- tion of the state of the digestive organs ; thus color, consistence, the presence of food in lumps, the odor, and many other points tell a plain story of work left undone, ill-done, or disordered by influences operating from within or fnnn without the tract. The intelligent physician acts the part of a qualified inspector, surveying the output of a great factory, and drawing conclu- sions in regard to the kind of work which the operatives have performed. f DIGESTION OF FOOD. 855 [g crystalline r, salts, and excretion of 9 alimentary ty of circum- ion in whicli se, and to get liol and indai >r to the con- »f these mat^ Lch applies to) nerally. [ pathological B at all events lit, undertake . I to the length be before we jted, we think :;eption of the )gard the ali- bh a secreting a terming ab- on or an allied of organs are fc, when one is ;ree, the others lie whole must organs, as an ,te of the econ- iry mechanism 38 is an indica- or^ consistence, ly other points , or disordered ihout the tracti ified inspector, rawing conclu* >peratives have The Changes produced in the Food in the Alimentary Canal. "We have now considered the method of secretion, the secre- tions themselves, and the movements of the various parts of the digestive tract, so that a brief statement of the results of all this mechanism, as represented by changes in the food, will be appropriate. We shall assume for the pi^sent that the effects of the digestive juices are substantially the same in the body as in artificial digestion. Among mammals food is, in the mouth, comminuted (except in the case of the camivora, that bolt it almost whole, and the ruminants, that simply swallow it to be regurgitated for fresh and complete mastication), insalivated, and, in most species, chemically changed, but only in so far as starch is concerned. Deglutition is the result of the co-ordinated action of many muscular mechanisms, and is reflex in nature. The oesophagus secretes mucus, which lubricates its walls, and aids mechan- ically in the transport of the food from the mouth to the stom- ach. In the stomach, by .the action of the gastric juice, food is further broken up, the proteid covering of fat-cells is digested, and the structure of muscle, etc., disappears. Proteid matters rm. MH.—1imtn tokcotnu tood (•ftir BNnanl). a, < [•ftar BNoanl). a, darflban tatn^biah i; g,mart, in form but little changed, is probably dealt with by the absorbents. Proteid digestion is continued, and, besides peptones, ni- trogenous crystalline bodies are fofmed (lencin and tyrosin), but under what conditions or to what extent is not known ; though the quantity is likely very variable, both with the spe- cies of animitl and the circumstances, such as quantity and quality of food ; and it is likely also dependent not a little on the rate of absorption. It seems altogether probable that in those that use an excess of nitrogenous food mor? of these bodies are formed, and thus give an additional work to the ex- creting organs, including the Uver. But the absence of albu- min from healthy faeces points to the complete digestion of proteids in the alimentary canaL Plainly the chief work of intestinal digestion is begun and carried on in the upper part of the tract, where the ducts of the main glands are to be found. The contents of the intestine tmKna. with bacteria, though I " DiaBSTION UP FOOD. 867 ip into free in the atom- Dt go on to starch con- od-mass be- . one to two ftpidity even I certain ex- acous mem- ^ ;ar resulting to some ex- 9 blood from 1 on into the ile, the para- >rtain of the n of the pep- red, and pep- to speak, for 1 one part of but we must nnulsified by on ; a portion on, while an robably dealt peptones, ni- and tyrosin), ) not known; with the spe- quantity and not a little on »bable that in Enor9 of these rork to the ex- tsence of albu- B digestion of chief work of the upper part ids are to be toteria, though these are probably kept under control to some extent by the bile, the functions of which as an antiseptic we have already considered. The removal of fats by the villi will be shortly considered. The other products of digestion probably find their way into the general circulation by the portal blood, passing through the liver, which organ modifies some of them in ways to be examined later. The valmdM conniventes greatly increase the surface of the intestine, and retard the movements of the partially digested mass, both of which are favorable. The peristaltic movements of the small gut serve the obvious purpose of moving on the digesting mass, thus making way for fresh additions of chyme from the stomach, and carrying on the more elaborated con- tents to points where they can receive fresh attention, both digestive and absorptive. Goapanti?*. — ^In man, the camivora, and some other groups, it is likely that digestion in the large intestine is slight, the work being mostly completed— at all events, so far as the action of the secretions is conoenied— before this division of the tract is reached, though doubtless absorption goes on there also. The muscular strength of this gut is important in the act of defecation. But the great size of the large intestine in ruminants— in the horse, etc.— together with the bulky character of the food of such animals, points to the existence of possibly extensive processes of which we are ignorant. It is generally believed that food remains but a short time in the stomach of the horse, and that the ceecum is a sort of reservoir in which digestive processes are in progress, and also for water. FermerUaiions go on in the intestine, and probably among ruminants they are numerous and essential, though our actual knowledge of the subject is very limited. The gases found in the human stomach are atmospheric air (s¥n»llowed) and carbon dioxide, derived from the blood. Those of the intestine are nitrogen, hydrogen, carbonic anhydride, Bulphureted hydrogen, and marsh-gas, the quantity varying considerably with the diet fttiukfiflaL — In subjects of a highly neurotic temperament and imstable nervous system it sometimes happens that im- mense quantities of gas are belched from an empty stomach or distend the intestines. It is known that the oxygen swallowed is absorbed into the -x-^rdinary sense: ;es8 depending, us system, le of great im- portance. It is as yet more of an art than a science ; the cook has outstripped the physiologist, if not the chemist also, in this direction. We can not explain fully why food prepared by certain meiliods and served in courses of a certain established order is so suited to refined man. A part is known, but a great deal remains to be discovered. We may, however, notice a few points of importance in regard to the preparation of food. It is now well established by experience that animals kept in confinement must have, in order to escape disease and attain the best results on the whole, a diet which not only imitates that of the corresponding wild forms generally, but even in details, with, it may be, altered proportions or added constitu- ents, in consequence of the difference in the environment. To illustrate : poultry can not be kept healthy confined in a shed without sand, gravel, old mortar, or some similar preparation ; and for the best results they must have green food also, as lettuce, cabbage, chopped green clover, grass, etc. They must not be provided with as much food as if they had the exercise afforded by running hither and thither over a large field. We have chosen this case bebause it is not commonly recognized that our domesticated birds have been so modified that special study must be made of the environment in all cases if they are not to degenerate. The facts in regard to homed cattle, horses, and dogs are perhaps better known. But all these instances are simple as compared with man. The lower mammals can live and flourish witii comparatively little change of diet ; not so man. He demands diet not only dissimilar in its actual grosser nattire, but.differently prepared. In a word, for the efferent oarvous impulses, on which the digestive processes depend to be properly supplied, it has be- come necessary that a variety of afferent impulses (through eye, ear, nose, palate) reach the nervous centers, attuning them to harmony, so that they shall act, yet not, interfere With one another. ^Oooking greatly alters the chemical composition, the me- chanical condition, and, in consequence, the flavor, the digesti- bility, and the nutritive value of foods. To illustrate: meat in its raw condition would present mechanical difficulties, the di- gestive fluids permeating it less completely ; an obstacle, how- ever, of far greater magnitude in the case of most vegetable foods. By cooking, certain chemical compounds are replaced by others, while some may be wholly removed. As a rule. .U.VJjJ.■^"^ff ttl ^l,J^ ^ ^j^■,;aaWi^!Jt^J -: M ' -S^iJ!H^!■^^ '^ Wg|T-^.. ita^l.-jl8L»»^ 800 ANIMAL I HY8I0L00Y. i^ s. ym^ boiling is not a good form of preparing meat, because it with- draws not only salts of importance, but proteids and the ex- tractives — nitrogenous and other. Beef-tea is valuable chiefly because ot these extractives, though it also contains a little gelatine, albumin, and fats. Salt meat furnishes less nutri- ment, a large part having been removed by the brine; not- withstanding, all persons at times, and some frequently, find such food highly beneficial, the effect being doubtless oot con- fined to the alimentary tract. Meat, according to the heat employed, may be eo cooked as to retain the greater part of its juices within it or the reverse. With a high temperature (66° to 70" C.) the outside in roasting may be so quickly hardened as to retain the juices. In feeding dogs it is both physiological and economical to give the animal the broth as well as the meat ', 'i;clf . The poor man may get excellent food cheaply by using *ot alone the rived from it. of more food> n which tiiat/ bt too high tk) Au's appetite, user than onr h, by calcula- ich man equal ^ith the lower At the same down general r serve to cor- in habits that d body and a Inence of the lussiono as the be suggestive ore of hunger usually in eat- Is thirsty, the Lg tiie mouth, If partially re- fcime the thirst ness has been DIOBSTION OF FOOD. 861 relieved by the natural secretions. If, however, fluid be intro- duced into the blood either directly or through the alimentary canal, the thirst is also relieved speedily. 7he fact that we know when to stop drinking water shows of itself that there must be local sensations that guide us, for it is not possible to believe that the whole of the fluid taken can at once have en- tered the blood. Again, in the case of hunger, the introduction of innutritions matters, as earth or sawdust, will somewhat relieve the urgent sensations in extreme cases ; as will also the use of tobacco by smokers, or much mental occupation, though the latter is rather illustrative of the lessening of l^e consciousness of the ingoing impulses by diverting the attention from them. But hunger, like thirst, may be mitigated by injections into the intestines or the blood. It is, therefore, clear tiiat, while in the case of hunger and thirst there is a local expression of a need, a peculiar sensation, more pronounced in certain parts (the fauces in ihe case of thirst, the stomach in that of hunger), yet these may be appeased from within through the medium of the blood, as well as from without by the contact of food or water, as the case may be.' Up to the present we have assumed that the changes wrought in the 'food in the alimentary tract were identical with those produced by the digestive ferments as obtained by extracts of the organs naturally producing them. But for many reasons it seems probable that artificial digestion can not be regarded as parallel with the natural processes except in a very general way. When we take into account the absence of muscular movements, regulated according to no rigid prin- ciples, but varying with innumerable circumstances in all probability ; the absence of the influence of the nervous sys- tem determining the variations in the quantity and compo- sition of the outflow of the secretions; the changes in the rate of soHsalled absorption, which doubtless influences also the act of the secretion of the juices— by these and a host of other con- siderations we are lead to hesitate before we commit ourselves too i^ireservedly to the belief that the processes of natural digmstion can be exactly imitated in the laboratory. ^piat is it which enables oiie man to digest habitually what may be almost a poison to another P How is it that each one can dispose readily of a food at one time that at another is quite indigestible P To reply that, in the one case, the digestive flidds are poured out and in the other not, is to go little below i miiMi ai H i nni ii .' a«lBiBi «*«iM i nn.,jc gaBM i i t mmww i wmLmv^^iw fflBa 862 ANIMAL PHYSIOLOOT. r K |i the surface, for one asks the reason of this, if it be a fact, as it no doubt is. When we look further into the peculiarities of digestion, etc., we recognize the influence of race as such, and in the race and the individual that obtrusive though ill-under- stood fact— the force of habit, operative here as elsewhere. And there can be little doubt that the habits of a people, as to food eaten and digestive peculiarities established, become or- ganized, fixed, and transmitted to posterity. It is probably in this way that, in the course of the evolu- tion of the various groups of animals, they have coins to vary BO much in their choice of diet and in their digestive proo ocsoo , did we but know them thoroughly as they are; for to assume that even the digestion of mammals can be summed up in the simple way now prevalent seems to us too broad an assump- tion. The field is very wide, and as yet but little explored^ Xuuui nyiLdoKj.— -The study of Alexis St. Martin has fur- nished probably the best example of genuine human physiology to be found, and has yielded a harvest rich in results. We suggest to the student that self-observation, without interfering with the natural processes, may lead to valuable knowledge ; for, though it may lack" some of the precision of laboratory experiments, it will prove in many respects more instructive, suggestive, and impressive, and have a bearing on medical practice that will make it telling. Not that we would be understood now or at any time as depreciating laboratory experiments; but we wish to point out from time to time how much may be learned in ways that are simple, inexpensive, and consume but little time. The lato of rh/yilhim, is illustrated, both in health and disease, in striking ways in the digestive tract. An individual long accustomed to eat at a certain hour of the day will experience at that time not only hunger, but other sensations, proi>ably referable to secretion of a certain quantity of th^ digestive juices and to the movements that usually accompany the pres- ence of food in the alimentary tract. Some persons find their digestion disordered by a change in the hours of meals. It is well known that defecation at periods fixed, even within a few minutes, has become an established habit with hosts of people ; and the same is to a degree true of dogs, ets., kept in confinement, that are taught cleanly habits, and encouraged therein by reg^ular attention to their needa Now and then a case of what is very similar to regurgita- tion of food in ruminants is to be found among human beings. k fact, a8 it iliaritiesof 1 sucli, and I ill-under- elsewhere. eople, as to become or>- theevolu- lae to vary Bproceaaes, rtoaarame d up in the axL asaump- :plored« tin has fur- physiology on, without to valuable precision of spects more , bearing on Eit we would ; laboratory bo time how inexpensive, and disease, ividual long II experience [18, proi)ably h9 d^^tive my the pres- am find their leals. , even within rith hosts of et3., kept in . encouraged lio regurgita- Lunan beings. DIOBSTION OF FUOD. 968 This is traceable to habit, which is bound up with the law of rhythm or periodic increased and diminished activity. Indeed, every one sufficiently observant may notice in him- self instances of the application of this law in the economy of his own digestive organs. This tendency is important in preserving energy for higher ends, for such is the result of the operation of this law every- where. , The law of correlation, or mutual dependence, is well illus- , trated in the series of organs composing the alimentary tract. The condition of the stomach has its counterpart in the rest of the tract : thus, when St. Martin had a disordered stomach, the epithelium of his tongue showed corresponding changes. We have already referred to the fact that one part may do extra work to make up for the deficiencies of another. It is confidently asserted of late that, in the case of persons long unable to take food by the mouth, nutritive substances given by enemata find their way up to the duodenum by anti- peristalsis. Here, then, is an example of an acquired adaptive arrangement under the stress of circumstances. ' (It can not be too much' impressed on the mind that in the complicated body of the mamnud the work of any one organ is constantly varying with the changes elsewhere. It is this mutual dependence and adaptation—an old doctrine, too much left out of sight in modem physiology — ^whioh makes the at- tempt to completely unravel vital processes well-nigh hopeless ; though each accumulating true observation gives a better in- sight into this kaleidoscopic mechanism. ■ We have not attempted to make any statements as to the quantity of the various secretions discharged.. This is large, doubtless, but much is probably reabsorbed, either altered or unaltered, and used over again. In the case of ftatuU» the con- ditions are so unnatural that any conclusions as to the normal quantity from the data they afford must bejbighly unsatisfac- tory. Moreover, the quantity must be very variable, accord- ing to the law we are now. considering. It is well known that dry food provokes a more abundant discharge of saliva, and this is doubtless but one example of many other relations be- tween the character of the food and the quantity of secretion provided. ! ■folvtlBB. — We have from time to time either distinctly pointed out or hinted at the evolutionary ioiplioations of the facts of this department of physiology. The structure of the 1 I mm 864 ANIMAL PHYSIOLOGY. ws ■: digestive organs, plainly indicating a rising scale of complexity with greater and greater differentiation of function, is, beyond question, an evidence of evolution. The law of natural selection and the law of adaptation, giving rise to new forms, have both operated, we may believe, from what can be observed going on around us and in our- selves. The occurrence of transitional forms, as in the epi- thelium of the digestive tract of the frog, is also in harmony with the conception of a progressive evolution of structure and function. But the limits of space will not permit of the enumeration of details. SnuMcy. — A very brief risumi of the subject of digestion will probably Bu^lce. Food is either organic or inorganic and comprises proteids, fats, carbohydrates, salts, and water ; and each of these must enter into the diet of all known animals. They must also be in a form that is digestible. Digestion is the reduction of food to a form such that it may be further dealt with by the aliment- ary tract prior to bmng introduced into the blood (absorption). Tbis is effected in different parts of the tract, the various con- stituents of food being differently modified, according to the secretions there provided, etc. The digestive juices contain essentially ferments which act only under definite conditions of chemical reaction, temperature, etc. @!he dianges wrought in the food are the following : starches are converted into sugars, proteids into peptones, and fats into fatty acids, soaps, and emulsion ; which alterations are effected by ptyaUn and amylopmn, pepsin and trypsin, and bile and pancreatic steapsin, rs^wctively. Outside the mueous membrane mmtaining the glands are muscular ogats, serving to bring about the movements of the food along the digestive tract and to expel the faces, the.circu- lar fibers being the more important These movements and the processes of secretion and so-called absorption are under the control of thenervous system. The preparation of the digestive secretions involves a series of changes in the epithelial cells concerned, which can be dis- tinctly traced, and take place in response to nervous stimula- tion. These we regard as inseparably bound up with the healthy life of the cell. To be natura), it must secrete. The blood-vessels of the stomach and intestine and the villi of the latter receive the digested food for further elaboration III r riiiiyi'tftiV^r--mVil^lrilif^-- ^"''^-^■■ ■^ ht im . ii ii ' ik^ mmigiijjjj^ complexity 1, is, beyond adaptation, aay believe, uad in our- in the epi- in harmony »f stracture jrmit of the of digestion ses proteids, ' these must aust also be jtion of food thealiment- [absorption). various con- rding to the ices contain conditions of ng: starches Bad fats into 1 are effected ind bile and e glands are nneats of the les, thedrcu- oents and the re under the elves a series ;h can be dis- ^ous stimula- h the healthy ) and the villi nr elaboration 80o ANIMAL PHYSIOLOGY. thoracic chamber may be said to be reserved for circulatory and respiratory organs which, we again point out, are so related that they really form parts of one system. The mammal's blood requires so much a§ration (ventilation) that the lungs are very large and the respiratory system has become greatly specialized. We no longer find the skin or ali- mentary canal taking any large share in the process ; and the lungs and the mechanisms by which they are made to move the gases with which the blood and tissues are concerned become very complicated. Ighniwry . tr: Our stupes of muscle phyiidogy should have made clear the fact that tissue-Ufe impUes the comtant consumption of oxygen and discharge of carbtmio anhydride, and that the pro- cesses which give raw to this are going on at a rapid rate ; so that the demands of tiie animal for oxygen constantly may be readily understood if one assumes, what can be shown, though less readily than iri the ca«e of muscle, that all the tissues are constantly craving, as it were, for this essential oxygen— well called "vital-ahf." IM» ** II H '!P'ti» V '»M» ■ ' ^■:*ie9iA t^'4tW'«UtjM aMtj<^w uj i«* i tM \i- »iatifcli i"e**» ^ t^'^lMtt'l*"'^ t-r.-rv^.iffyV-'t.'KM^ I I ) . Ill ■^^■'^■■^•■■••^ii ii nn ii i wi i ii n ii »i i . circtilatory e BO related rentilfttion) gystem has gkin or ali- Msa; and the to move the med become THE BBSPIBATORT SYSTEM. m vv made clear nuumption of 1 that the pro- rapid rate ; 80 itantly may be Ethowh, though the tiseaes are [ oxygen— well Bespiratilm may, then, be regarded from a physical and chemical point of view, though in this as in other instances we VM. m.-' iteU hM : 8, diririM to aiddfe lolw ; a, Sviiiaa to 1^ orliiftimiflr: ll,dlfWi»tolo««rlol»: U,lt,ia;lil,«&iiMtoramlflairtfciMof bnmdilft; U,U, iM^tenta, in oaatoar ; 14, 14, mnintt o( liuiga ; U, U, baaa o( taiaga. muAt be on our guard against rqpsrding physiological processes as ever purely physical or purely ohemicak The respiratory process in the mammalj unlUce the frog^ consists of an active and a (largely) passive phase. The air is not pumped into the lungs, but sucked in. So great is the coniplexity of the lungs in the: mammal) that the frog's lung (which may be readily understood by blowing it up by inserting a small pipe in the glottic opening^of the animal and then ligaturing the distended organ) may be compared to a single infuudibulum of the mam- malian lung. Assuming that the student is somewhat conversant with the 868 ANIMAL PHYSIOLOGY. coarse and fine anatomy of the respiratory organi, we call at- tention to the physiological aspects of some points. The lungs represent a membranous expansion of great extent, lined with flattened cells and supporting innumerable capillary blood-ves- sels. The air is admitted to the complicated foldings of this membrane by tubes which remain, throughout the greater part of their extent, open, being oompoeed of cartilaginous rings, completed by soft tissues, of which plain muscle-oells form an Ftt. aa-MoM «( m important part, serving to maintain a tonic resistance against pulmonary and bronchial pressure, as well as serving to aid in the act of coughing, ete., so important in expellihg foreign bodies or preventing their ingress. The bronchial .iAbM inre lined with a mucous membrane, kept moist by the leeretionB of ito i^Umds, and covered with ciliated epithelium, as are also the nasal passages, irhich by the outward currents they create, favor diffusion of gases, and removal of excess of mucus. The thoracic walls and the lungs themselves are covered with a tough but thin membrane lined with flattened cells, which secrete a small quantity of fluid. Mwmwwf w Bii nw i we call at- The lungs lined with blood-vea- igs of this reaterpart ions ringSy la f oim aa Mr «v ince against rving to aid ling foreign I membrane, iovered with », frhich by [>f gases, and nd the lungs nbrane lined tity of fluid. THB BESPIRATORT SYSTEM. 869 that serves to maintain the surrounding parts in a moist con* dition, thus lessening friction. The importance of this ar- VMw Mi-SMtim of Hm Mtai^iSdnilM). •,~a,~^«i waSi of tiM tkKOh ; '!>, imaa i rangement is well seen when, in consequence of in fl ammation of this pleura, it becomes dry, giving rise during each respira- tory movement to a friction-sound and a painful sensation. It will not be forgotten that this membrane extends over the diaphragm, and that, in consequence of the lungs completely filling all the space (not occupi^ by other organs) during every position of the chest-walls, the costal and pulmonary pleural surfaces are in constant contact By far the greater part of the lung-substance consists of elastic tissue, thus adapting the principal respiratory organs to that amount^of distention and recoil to which they are ceaselessly subjected during the en- tire lifetime of the animal. Thb Entsaitcb and Exit op Air. Since the lungs fill up so completely the thoracic cavity, manifestly any <^ange in the sise of the latter must lead to an increase or diminution in the quantity of j^r they contain. Since the air within the respiratory organs is being constantly M ,j,^i^in«,,#«»iWfcTO*nw«. 870 ANIMAL PHTSIOLOOT. robbed of its oxygen, and rendered impure by the addition of carbonic dioxide, the former must be renewed and the latter expelled ; and, as mere diffu- sion takes place too slowly to accomplish this in the mam- mal, this process is assisted by the nervous system set- ting certain muscles at work to alter the size of the chest cavity. Because of the ribs being placed obliquely, it fol- lows that their elevation will , result in the enlargement of the thoracic cavity in the au- tero-poeterior diameter; and, as the chest, in consequetice, gets widw from above down- ward, also in the transverse diameter; which is more- over asristed by the eversion of the lower borders of the ribs; and, if the convexity of fhe diaphragm were dimin- ished by its contraction and consequent descent, it would follow that the chest would be in- creased in the vertical diameter also. All these events, favor- able to the entrance of air, actuaUy take phice through agencies we must now consider. The student is recommended to look into the insertion, etcir of the muscles concerned, to which we can only briefly refer. « . * xv The act of inspiration commences by the fixation of the uppermost ribs, beginning with the first two, by means of the soofent muscles, this act being followed up by the contraction of the external interoostals, leading to the elevation of the other ribs; at the same time, the arch of the diaphregm de- scends in consequence of the contraction of its various mus- cular bundles. Under these circumstances, the air from with- out must rush in, or a vacuum be formed in the thoracic cavity ; and, since there is free access for the air through tiie glottic opening, the lungs are of necessity expanded. This in- going air has had to overcome the elastic resistance of the lungs, which amounts to about 5 millimetres of mercury in man, as ascertained by tying a manometer in the windpipe of ■ ' V ^ J B iWiB B M W Wffl i m)! < w w» a ' ^*wWJ'^ •i^umm i^y imi ^ki^vm^^i'^^''^^ addition of 1 the latter . mere diffu- loo slowly to in the mam> I is assisted system set- cles at work of the chest ) of the ribs iquely,itfol- levation will argement of ityintheau- uneter; and, consequetice, above down- le transverse oh is more- the evendon >rder8 of the convexity of were dimin- itraction and would be in- ivents, f avor- >ngh agencies inded to look , to which we ntion of the means of the le contraction ration of the iaphragm de- various mus- dr from with- the thoracic T through the ded. This in- stance of the )f mercury in le windpipe of THE BBSPIRATORT STSTBM. Wl a dead subject, and then opening the thorax to equalize the inside and outside pressures, when the lungs at once collapse and the manometer shows a rise of the mercury to the ex- tent indicated abova To this we must add the influence of the tonic contraction of the bronchial muscles before re- ferred to, though this is prob- ably not very great That there are variations of intrapulmonary pressure may be ascertained by con- necting a manometer with one nostril — the other being closed —or with the windpipe. The mercury shows a negative pressure with each inspirato- ry, and a positive with each expiratory act This may amount to from 30 to 70 mil- limetres with strong inspira- tion, and 60 to 100 in forcible expiration. When inspiration ceases, the elastic recoil of the rib carti- lages and the ribs themselves, and of the sternum, the weight Vm- 3m. -pifimmiiutie wpwwirtaUiMi of mMw ttjmwknmm in ianinaiM (Om- 5f^)-_.^?i?^ *SSf<^ thnmgh moomI AoailKUMto. The brokwiMHl dotted *-— theMMutarttodaMntaftto to ofdioMy and la dev iMvIm- ■I 1 -T ■% ^■■^ * ' -wr ' 'V g'™«< '^vv>'' iff'T!SS.^2J!5*ff*» '38*^52.2' Wn^thorMlo Mid eztemia MitulMflMrttrt£«iM£ofaiMltebMM«nM^^ t ii aM awewMl; teri|lit< At OM part (8) an •laMciaii InagB. The OMrcutT (.Jar. laMt-L^ ■ tlwajttMiial^ I a hole in Jar, (attar ahrandi- ofttMjariB itwOlbe ■*r. '-'rr~^~-^''^fr-'if^> ^ .^^-i^* ^^ 'fi ^^ (i miitiii..i <' r"»^^ 873 AKIMAL PUYSIOLOOT. fto. aOB.— Donal vtew oC four wMfM •«•«>«"»«* »'_^«ft*. 52''tt2 torn MMl tatoworti* (SCS *££ ton : % f xtarwUliitMvartal : t, in- of these parts and that of the attached nmwles. etc., awiBts to the return of the chest to its original position, entirely indepen- dently of the action of muscles. Moreover, with the descent of the diaphragm the abdominal viscera have been thrust down and com- pressed together with their mcluded gases; when this muscle relaxes, they naturally exert an upward pressure. Putting these events together, it is not difficult to un- derstand why the air should be squeeaed out of the lungs, the elas- ticity of which latter is, as we have shown, an important factor in itself. Tha MvsdM of BMpintira^The diaphragm may be considered the most important single respiratory muscle, and can of itself maintain respiration. The »odUni are important as fixators of the ribs ; the levalores eostartm, and exUnud irUercosUds, as normal eie- vators. The quadrahu himborum Assists the diaphragm by fixing the last rib. These, with the serraiua portieua superior, may be regarded as the principal muscles called into action in an ordinary inspiration. The muscles used in an ordinary ex- piratory act are the internal iniercoa- tola, the trtaingvlaria demi, and ser- ratits poaiieu8 inferior. In forced inspiration the lower ribs are drawn down and retracted, giving support in their fixed position to the dia- phragm. The scaleni, pectorales, serratus magnus, latissimus dorsi, and others are called into action ; but when dyspnoea becomes extreme, as in one with a fit of asthma, nearly all the muscles of the body may be called into play, even the muscles of the face, which are not normally active at all or but very shghtly m natural breathing. 'oSSr'QiukiiiMd nSSSS InthtoeMetlMitaia •tiaa to aUMidtd with <"*■ THE RBSPIBATORT SYSTBlL 878 ;., assists in ily indepen- )f muscles, cent of the nal viscera 1 and com- eir included icle relaxes, an upward lese events Icult to un- should be igs, the elas- I, as we have ctor in itself. IntiMk— The osidered the respiratory elf maintain I of the ribs; I normal ele* ^(•ftarQnikiiiMd I. iuTBZ taqoM n. DniW^deMiin- Iwaaad ooamwner- idilwvvWble. Soeb tt PHiMMft in iBMV MWlBWllldl ndtdwtth"' Faeial and laryngeal reapiraiion is best seen in such animals as the rabbit, auii it is this condition which is approximated in disordered states in man — in fact, when from any cause in> spiration is very labored (aHthma, diphtheria, etc.). In man and most mammals, unlike the frog, the glottic opening is never entirely closed during any part of the respira- tory act, though it undergoes a rhythmical change of size, widening during inspiration and narrowing during expiration, in accordance with the action of the muscles attached to the arytenoid cartilages, the action of which may be studied in man by means of the laryngoscope. The abdominal muscles have a powerful rhythmical action during forced respiration, though whether they function dur- ing ordinary quiet breathing is undetermined ; if at all, prob- ably but slightly. Though the removal of the external inter- costab in the dog and some other animals revMtls the fact that the internal intercostals contract alternately with the dia- phragm, it must not be regarded as absolutely certain that such is their action when their companion miiscles are present, for Nature has more ways than one of accomplishing the same pur- pose—a fact that seems oftdn to be fprgotten in reasoning from experiments. This result, however, carries some weight with it. Types of Xsspintiioiii.— There are among mammals two princi- pal types of breathing recognizable — ^the costal (thoracic) and abdominal — ^according as the movements of the chest or the abdomen are the more pronounced. In the civilized white woman, even in the female child, the upper thorax takes a larger share in respiration than in the male sex. This has been explained, on the one hand, as being due to artificial influences, modes of dress, and their inherited effects ; and on the other to natural ones, the crowding of the respiratory organs, owing to the contents of the pelvio and abdominal cavities encroaching on the thorax, in consequence of the enlargement of the uterus during pregnancy. It has, however, been maintained recently that an examination of pure-blooded Indian girls does not show the features of respira- tion just noticed as characteristic of the breathing of white females, the inference from which is obvious. But, again, it i8> to be remembered that the Indian and other women retaining^ primitive habits possess a power of adaptation to the demands | of the pregnant condition no longer shown by white women. Thoracic breathing in females is probably the result of several co-operating causey of which xtmge in dress is on& -, ■ iw g w w wMm m i lu i -wi ' i J.>^miww i . i 874 ANIMAL PHYSIOLOOT. PMNMnal ObMTfKkioB.— The student would do well at this stage to test the t itements we have made in regard to the respira- tory movemems on the human subject especially. This he can very well do in his own person when stripped to the waist before a mirror. Many of the abnormalities of the forced res- piration of disease may be imitated— in fact, this is one of the departments of physiology in which the human aspects may be examined into by a species of experiment on one's self that is as simple as it is valuable. tm. m.~Fnt¥la Omteri, m aaitea uuMHdllflM in • teftarHuainr). th* out mmMMi thaw firam tta oalaareoai tiba. a, braaohlal hood-Un 9, OfB. (hinB«teiMU»«)«sMM«i tiba. a, braaohlal (TMplntotT) phUBM, tJhmuiuiUf mmuw ; o, ai vtHiorMdofmjr; e,iM«w; il,itoaMah ;«,«»■; /,liM«{ HMMMHMNMHlMkMWi t this stage he respira- '. This lie X) the waist forced res- one -of the spects may i'B self that THE BBSPIRATOBT SYSTEM. 878 Ito. SOB. no. m. rm. «IS.-Vertioia tnuiwrane mcUoh oT (MribwitMr miMHl (^MdoH) ttooo;^ hevt (^ter HnzlaTi. r, ««ntriale: ii. auriolM: r, nelam; js pwlowdim: <, fmiw, «, o^ lnf«»in*fcm(altSirBiiSC A, bwwdilri Mtwy ; ^. hrMnJ^M BliiwMi fao w iec U oB ; 0«BVMWttft.~It is hoped that the various figures accompa- nied by descriptions^ introduced in this and other chapters, will make the relations of the circulation and respiration in the va- -w-— iMim»iwi' il>»ii>i»i»«H''»'' r>«M 876 ANIMAL PHYSIOLOGY. rious classes of animals, whether terrestrial or aquatic, evident without extended treatment of the subject in the text. What w& rNktM. Fw.aoQ. Fm, we are desirous of impreiasing is that throughout the entire ani- mal kingdom respiration is essentially the same process; that r». ni.- 0. Hoiv finally it resolves itself into tisarue-brcathing : the appropria- tion of oxygen and the excretion of carbon dioxide. Since the manner in which oxygen is introduced into the lungt ^d foul gases expelled from them in some reptiles and amphibiaas, is krgely different from the method of respiration in the mam- mal, we call attention to this process in an animal readily watched— the common frog. This creature, by depressing the floor of the mouth, enlarges l^s air-spaoe in this region and consequently the air freely enters through the nostrils; wher^ upon the latter are dosed by a sort of valve, the glottis opened MMM l iilmMi i w i ii i wW i ic. evident rt. What M.tia tier BlanohArd). er Ducta). pm. ) entire ani- ocess; that I mm: a,an; o, «Mhka«|iMrtara. ■ rli^iMSMdoC I appropna- b Since the tgs imd foul ipbibiaiui, is n the mam- mal readily [iresBing the region and rili; irhere- ottiii opened THE RBSPIRATOBY SYSTEM. 877 and the air forced into the lungs by the elevation of the floor of the mouth. By a series of flank movements the elasticity of the lungs is aided in expelling the air tl^rough the now open nostrils. The respiration of the turtle and some other reptiles is somewhat similar. In the case of aquatic animals^ both in- W». Wi.-qtt e wi" yMi BrlMlBal«teM»(i(tnuikOrfl|rSWMr)- l.l.a f l M w rtw i nl hraCcirTloainM r ?ii iwn Mth vertebrate and vertebrate, excepting mammals, the blood is freely exposed in the gillt to oxygen dissolved in the water as it is to the same gas mixed with nitrogen in terrestrial animals. In the land-snail, land-crab, etc., we Imve a sort of intermedi- ate condition, the gills being kept moist It is not to be for- 878 ANIMAL PHTSIOLOGT. gotten, however, that normally the respiratory tract of mam- mals is never other than slightly moist. Thb Quantitt of Ant bkspibbd. We distinguish hetween the quantity of air that usually is moved by the thorax, and that which may be respired under special effort, which, of course, can never exceed the capacity of the respiratory organs. Accordingly, we recognise: 1. Tidal air, or that which passes in and out of the respiratory passages in ordinary quiet breathing, amounting to about 500 cc., or thirty cubic inches. 2. Complemenial air, which may be voluntarily inhaled by a forced inspiration in addition to the tidal air, amounting to 1,600 cc, or about 100 cubic inches. 3. SupplemerUal {reserve) air, which may be expelled at the end of a normal respiration — ^L e., after the expulsion of the tidal air, and ifhich represents the quantity usually left in the lungs after a normal quiet expiration, amounting to 1,500 cc. 4. Reaiduai atr,, which can not be voluntarily expelled at all, amounting to about 2,000 cc, or 120 cubic inches. The vital capacity is estimated by the quantity of air that may be expired after the most forcible inspiration. This will, of course, vary with the age, which determines largely the elas- ticity of the thorax, together with sex, position, height, and a variety of other circumstiuioes. But, inasmuch as the result may be greatly modified by practice, like the power to expand the chest, the vit^l capacity is not so valuable an indication as might at first be supposed. It is important to bear in mind that the tidal air is scarcely more than snfficient to fill the upper air-passages and larger bronchi, so that it reqtures from five to ten respirations to re- move a quantity of air inspired by tai ordinary Act. Very much muft, therefore, depend on diffusion, the quantity of air remaining in the lungs after each breath being the sum of the residual and reserve air, or about 8,500 oc. (890 cubic inches). Oonsidering the creeping slowness of the capillary dronlation, it would not be supposed that the respiratory process in its essential parts shotdd be the nipid one that a greater move* ment of the air would imply. ma of mam- luaaUy is ired under e capacity bat wbicli nary quiet ibic inches, laled by a jonting to al {reserve) respiration . represents rmal quiet ..which can at 2,000 cc, of air that This will, )ly the elas- >ight, and a I the result r to expand idioation as r is scarcely and larger ktions to re> *ot. Very intityofair I sum of the bio inches), cirenlation, rooess in its eater move* THB BBSPIBATORY ST8TSM. Thb Rkspibatoby Rhtthm. 879 In man, and most of our domestic mammals, a definite rela- tion between the cardiac and respiratory movements obtains, there being about four to five heart-beats to one respiration, which would make the rate of breathing in man about sixteen to eighteen per minute. Usually, of course, the largest animab have the slower pulse and respiration; and this is an invariable rale for the varieties of a species, as observable in the canine race, to mention a well-known instance. The rate uf the respiratory movements is to some extent a measure of the ntpidity of the oxidative processes in the body, as witness the slow and intermittent breathing of cold-bloodeid animals as compared with the more rapid respiration of birds and mammals (Fig. 313). Palhiologiesl. — ^Any condition that lessens the amount of re- spiratory surface, or diminishes the mobility of the chest-walls is usually accompanied by accelerated movements, but beneath this is the demand for oxygen, part of the avenues by which this gas usually enters, having been dosed or obsirnoted by the disease. So that it is not' suxprising that, in consequence of the effusion of fluid into the thoracic cavity, leading to the compression of the lung, the oppodte one should be called into more frequent use, and even enlarge to meet the 'demand. These facts show how urgent is the need for constant ventila- tion of the blood, and at the same time how great is the power of adaptation to meet the emeigency. The difference between the inq»iratory and the expiratory rhythm may be gathered by watching the movements of the bared chest, or more accurately from a graphic record. It is usually considwed that expiration is only tUghtly longer than inspiration, and ttiat any marked deviation from this relation should arouse suspicion of disease. Normally the respiratory pause is very slight, so that inspiration seems to follow di- rectly on expiration ; though the latter act reminds us of the prolongation of the ventricular systole after the blood is ex- pelled. If, in the tracing, the small waves on the upper part of the expiratory curve really represent the effect of the heart-beat, it makes it easier to understand how such might assist in venti- lating the blood when the respirations occur only once in a considerable interval and very feebly then, as in hibernating animals or individuals that have fainted ; though it must be 880 ANIMAL PHYSIOLOGY. remembered that diffusion is a ceaseless process in all Hving vertebrates. It is scarcely necessary to point out that the respiratory - rAA/ -^AAr WlAA/l/WVUia 0mmM0mmnfum\j\S)imm^ ■hiUow, MMl in ml (IMP- movements are increased by exercise, emotions, position, sea- son, hour of the day, taking meals, etc. mammm l,)l tfMM It »MtH i MKHm it all liying aspiratory /XT ^A/1 ifWW groups of KMsition, THB RBSPIBATORT STSTBM. 881 ^fK^^^/^J\^r^f^rJA/^^^\N'^VA^ Wm. S14.—Tnoiiigt of ni|riratlMo(kan»iHiM at iMt and after ezeroin (•Iter ThMriMOtor). /, iMpiration ; Ji; caanntiaii. 8|«eaa bstwaen vertloal HnM indioata tUM Mcioili ot oiw aeoondea*^ 1, aimial atandhn at rwt; 1. alter walk at IWr mlnntaa; 7 and ft attet trottiiis; •, afterabrinf rcat: U, after trotting and nmntaig (oraomeminiitaa; 17,aftw nattngfKnnlaitforadMcttiiM; »1, tradiig at awd ot eKpa nm ant. Bai^ntorj Saniidiy— The entrance and exit of air are accom- panied by certain sounds, which vary with each part of the respiratory tract. To these sonnds names have been given, but as they are sqmewhat inconstant in their application, or at least have several sjrnonyms, we paw them by, recommending the student to actually learn the nature of the respiratory murmurs by listening to the normal chest in both man and the lower ani- mals. With the use of a douUe stethoscope he may practice upon himself, though not so advantageously as in fhe case of the heart. The sounds are caused in part by the friction of the air, though they are probably complex, several factors entering into their causation. Comparison of thb Inbpirbd and Expirbd Ant. The changes that take place in the air respired may be briefly stated as follows : 888 ANIMAL PHYSIOLOGY. y - 1. Whatever the condition of the inspired air, that expired is about saturated with aqueous vapor — ^i. e., it contains all that it is capable of holding at the existing temperature. 2. The temperature of the expired air is about that of the blood itself, so that if the air is very cold when breathed, the body loses a great deal of its heat in warming it. The expired air of the nasal passages is slightly warmer than that of the mouth. 3. Experiment shows that the expired air is really dimin- ished in volume to the extent of from one fortieth to one fiftieth of the whole. Since two volumes of carbonic anhydride require for their composition two volumes of oxygen, if the amount of the former gas expired be not equal to the amount of oxygen inspired, some of the latter must have been tised to form other combinations. -^, amounting to rather less than 1, is called the respiratory coefficient. 4. liie ^fference between inspired and expired air may be gathered from the following : OsTgm. mtroiHi. Ovbonle dknlde. V luvinddf -. aO«10 79-180 (HMO Bxpii^air 1«<»8 79-897 4-880 From which the most important conclusions to be drawn are, that the expired air is poorer in oxygen to the extent of 4 to 5 per cent, and richer in carbonic anhydride to somewhat leas tham this amount. From experiment it has been ascertained that the amount of carbonic dioxide is for the average man 800 grammes (406 litres, equivalent to 218*1 grammes carbon) daily, the oxygen actuijly used for the same period being 700 grammes. But the variations in such cases are veiry great, so that these num- bers must not be interpreted too rigidly. Ibqierience proves that, while chemists often work in laboratories in which the percentage of carbonic anhydride (from chemical decomposi- tions) reaches 6 per cent, an ordinary room in which theafnount of this gas reaches 1 per cent is entirely unfit for occupation. This is not because of the amount of the parbon dioxide pres- ent, but of other impurities which seem to be excreted in pro- portion to the amount of this gas, so that the latter may be taken as a measure of these poisona What these are is as yet almost entirely unknown, buir ti»t they are poisons is beyond doubt. Small effete particles oi iiii)rtiiiiiMfciii«i4t^ w lat expired ins all that ;hat of the eaihed, the Ixe expired that of the ally dimin- one fiftieth ride require I amount of of oxygen form other 1, is called air may be }Mbaiiledii»>d«. (HMO 4-880 y be drawn le extent of somewhat the amount ammes (406 the oxygen mmes. But these num- ence proves 1 which the decomposi- theatnount occupation. lioxide pres- ■eted inpro- tter may be ^ft,bat tiiat particles of THE BESPIRATOBT STSTBM. 888 onoe-living protoplasm are carried out with the breath, but these other substances are got rid of from the blood by a vital process of secretion (excretion), we must believe; which shows that the lungs to some degree play the part of gls ' ', and that their whole action is not to be explained as if they « ^re merely moistened bladders acting in accordance with ordinary physical law& ' An estimation of the amount of atmospheric air required may be calculated from data already given. Thus, assuming that a man gives up at each breath 4 per cent of carbon dioxide to the SOO co. of tidal air he expiree, and breathes, say, seventeen times a minute, we get for the amount of air thus charged in one hour to the extent of 1 i>er cent : SOO X 4 X 17 X 60 s 3,040,000 cc., or 2,040 litres. But if the air is to be contaminated to the extent of only ^ per cent of carbonic anhydride, the amount should equal at least 8,040 X 10 hourly. Rkspibatiok in thb Blood. It may be noticed that arterial blood kept in a confined space grows gradually darkey in color, and that the original bright scarlet hue may be restored by shaking it up with air. When the blood has passed through the capillaries and reached the veins, the color has changed to a sort of purple, character- istic of venous blood. Putting these two facts toge^er, we are led to suspect that the change has been caused in some way by oxygen. Exact experiments with an appropriate form of blood- pump show that from one hundred volumes of blood, whether arterial or venous, about sixty volumes of gas may be obtained ; that this gas consists chiefiy of oxygen and carbonic anhydride, but that the proportions of each present depends upon whether the blood is arterial or venous. The following table will make this clear r ArterUblood. Venoiu UoocL. OUIM. OHlM)iiieulv«tw»wi ^ud A I(tS?Mok i bJiSi?^i*iS^g^« ottt abloodh iOwMiWteto «>» JS™"^ ;i,*»« (AfMrlVMlMr.) thnmi^*. TlMOoadttiflniiBd«r«Uidi tli* 0mm cdH ia th« BlMd.— If a flaid, as water, be exposed to a mixture of gases whicli it cm LO caTb6iuc rcentage of i mad B v?**** of tiw aloiHiock NlJdwOOIUIMtM Mreanr. aad tlie 10 oil* tBffWll^ 6* 'iaiatuninind iMtaMt drivw ool fMunmoCilanl i|trMai«M*«i — If » hich it position is : Carbon 68-85 Hydrogen r... 7*88 Nitrogen. 16*17 Oxygen..... ......: 81*84 Iron '43 Bulphur '39 togethor with 3 to 4 per cent of water of crystallization. The formula assigned is: CwHtMOmNiMFeSt. The molecular constitution is not known, and the above formula is merely an approximation, which will, however, serve to convey an idea ■^ — " .^ -.f f ' -f T- ""''."iM i 386 ANIMAL PHTSIOLOOT. of the great complexity uf this compound. The presence of iron seems to be of great importance. If not the essential respiratory constituent, cer- tainly the administration of this metal in some form proves very valuable when the blood is deficient in heemtglobin. This substance can be recogniaed most certainly by the spectroscope. The ap- pearances vary with the strength of the solution, and, as this test for blood (hnmoglobin) is of much practical importance, it ¥rill be necessary to dwell a little upon the subject ; though, after a student has once rec- ognized clearly the differ- ences of the spectrum ap- pearances, he has a sort of Icnowledge that no verbal description can convey. This is easily acquired. One only needs a small, flat-sided bot- tle and a pocket - spectro- scope. Filling the bottle half-full of water, and getting the spectroscope so focused that the Fraunhofer lines appear distinctly, blood, blood-stained serum, a solution of hamoglobin-crystals, or the essential sub- stance in any form of dilute solution, may be added drop by drop till changes in the spectrum in the form of dark bands appear. By gradually increasing the quantity, appearances like those figured below may be observed, though, of course, much will depend on the thickness of the layer of fluid as to the quantity to be added before a particular band comes into view. When wishing to be precise, we speak of the most highly oxidized form of heemoglobin as oxy-hflemoglobin (0-H), and the reduced form as hamoglpbin simply, or reduced heemo- globin(H). ' By a comparison of the spectra it will be seen that the bands Tut. a6.-0nntiriltod hMBOtfoMii (OMtiH^ a. 6, orntali f iom tcoow wood of dim ; e, B liiood of oat; ii,o( GnliiM-piK; •> o( ;/,o« ■MM presence of le eflsential tituent, cer- listration of Bome form aable when leficient in ice can be sertainlyby . The ap- with the e solution, b for blood B of much ance, it will Iwell a little st; though, las once rec- the differ- lectrum ap- as a sort of , no verbal onvey. This L One only ftt-sided bot- cet - spectro- the bottle focused that >lood-8tained flsential sub- ied drop by I dark bands appearances h. of course, [)f fluid as to i comes into most highly a (0-H),and luced heemo- lat the bands THB BESPIRATOBT SYSTEM. 887 of oxy-hffimoglobin lie between the D and j; lines; that the left band near D is always the moat definite in outline and the most pronounced in every respect except breadth ; that it is in weak solutions the first to appear, and the last to disappear on f.atiV.>\^Vn 888 ANIMAL PHTSIOLOOY. reduction ; that there are two instances in which there may be a single band from heemoglobin — ^in the one case when the solu- tion is very dilute and when it is very concentrated. These need never be mistaken for each other nor for the band of re- duced heemoglobin. The latter is a hasy broad band with com- paratively indistinct outlines, and darkest in the middle. It will be further noticed that in all these instances, apart from the bands, the spectrum is otherwise modified at each end, so that the darker the more centrally placed characteristic bands, the more is the light at the same time out off at each end of the spectrum. If, now, to a specimen showing the two bands of oxy-heemo- globin distinctly a few drops of ammonium sulphide or other reducing agent be added, a change in the color of the solution will result, and the single hasy band characteristic of heemo- globin will appear. It is not to be supposed, however, that venous blood gives this Bpe«jtrum. Even after asphyxia it will be difficult to see this band, for usually some of the oxy-heemoglobin remains reduced ; but it is worthy of note, as showing that the appear- ances are normal, that the blood, viewed through thin tissues when actually circtdating, whether arterial or venous, gives the spectrum of oxy-heBmoglobin. At the same time there can be no doubt that the changes in color which the blood under- goes in passing through the capillaries is due chiefly to loss of oxygen, as evidenced by the experiments before referred to ; and the reason that the two bands are always to be seen in venous blood is simply that enough oxy-heemoglobin remains to give the two-band spectrum which prevails over that of (reduced) heemoglobin. We are thus led by many paths to the important conclusion that the red corpuscles are oxygen-carriers, and, though this may not be and probably is not their only func- tion, it is without doubt their principal one. Of their oxygen they are being constantly relieved by the tissues; hence the necessity of a circulation of the blood from a req)iratory point of vidw. There are other gases that can replace oxygen and form compounds with heemoglobin ; L<)nce we have GO-heemoglobin and NO-heemoglobin, which in turn are replaced by oxygen with no little difficulty— a fact which explains why carbonic oxide is so fatal when respired, and, as it is a constituent of illuminat- ing gas, the cause of the death of those inhaling the latter is often not far to seek. Blood may, in fact, be saturated with iilfiiiliriiiTi THE RESPIRATORY SYSTEM. 889 ere may be m the solu- »d. These band of re- l with com- idle. mces, apart led at each aracteristic off at each oxy-hflBmo- de or other the solution Ic of heemo- blood gives fficult to see bin remains the appear- thin tissues enous, gives me there can blood under- »fly to loss of jrredto; and en in venous lains to give of (reduced) he important »rrier8, and, ir only func- their oxygen «; hence tiie (iratory point ;en and form ^-heemoglobin f oxygen with bonic oxide is of illuminat- g the latter is kturated with carbonic oxide by allowing illuminating gas to pass through it, when a change of color to a cherry red may be observed, and which will remain in spite of prolonged shaking up with air or attempts at reduction with the usual reagenta Heemoglobin may be resolved into a proteid (globin) not well understood, and hanudin. This happens when the blood is boiled (perhaps also in certain cases of lightning-stroke), and when strong acids are added. Hsematin is soluble in dilute acids and alkalies, and has then characteristic spectra. Alkaline hematin may be re- duced ; and, as the iron can be separated, resulting in a change of color to brownish red, after which there are no longer any reducing effects, it would seem that the oxygen-carrying power and iron are associated. This ' iron-free htematin is named hamaioporphyrin or Ttamatoin. Hamin is hydrochlorate of hematin (Teichmann's crystals), and may be formed by adding glacial acetic acid and common salt to blood, dried blood-clot, etc., and heating to boiling. This 'is one of the best tests for blood, valuable in medico-legal and other cases. When oxy-hsemoglobin stands exposed to the air, or when diffused in urine, it changes' color and becomes^ in fact, another i^ubstance — metJuemoglobin, irreducible by other gases (CO, etc.), and not surrendering its oxygen in vacuo, though giving it up to ammonium sulphide, becoming again oxy-heemoglobin, when shaken up with atmospheric air. Its spectrum differs from that of oxy-heemoglobin in that it has a band in the red end of the spectrum between the C and D lines. HameUoidin is some- times found in the body as a remnant of old blood-clots. It is probably closely allied to if not identical with the bUirubin of bile. Ooiq^anittft.— While hemoglobin is the respiratory agent in all the groups of. vertebrates, this is not true of the inverte- brates. Red blood-cells have as yet been found in but a few species, though heemoglobin does exist in the blood plasma of several groups, to one of which the earth-worm and several other annelids belong. It is interesting to note that the respir- atory compound in certain families of crustaceans, as the com- mon crab, horseshoe-crab (limulus), etc., is blue, and that in this substance copper seems to take the place of iron. Tht Vitngw miA tin Ouboi DlMdd* «f tlw Hood.— The little nitrogen which is found in about equal quantity in venous and arterial blood, seems to be simply dissolved. The relations of carbonic anhydride are much more complex and obscure. The 890 ANIMAL PHTSIOLOGT. main facts known are that — 1. The quantity of this gas is as great in serum as in blood, or, at all events, the quantity iu serum is very large. 2. The greater part may be extracted by an exhaustion-pump ; but a small percentage (3 to 6 volumes per cent) does not yield to this method, but is given off when an acid is added to the serum. 3. If the entire blood be sub- jected to a vacuum, tLe whole of the COt is given off. From these facts it has been conclude:^ that the greater part of the COt exists in the plasma, associated probably with sodium salts, as isodium bicarbonate, but that the corpuscles in some way determine its relations of association and disassociation. Some think a good deal of this gas is actually united with the red corpuscles. We may now inquire into the more intimate nature of respi- ration in the blood. From the facts we have stated it is obvi- ous that respiration can not be wholly explained by the Henry- Dalton law of pressures or any other physical law. It is also plain that any explanation which leaves out the principle of pressure must be incomplete. While there is in oxy-heemoglobin a certain quantity of oxy- gen, which is intra-molecular and incapable of removal by re- duction of pressure, there is also a portion which is subject to this law, though in a peculiar way; nor is the question of temperature to be excluded, for experiment shows that less oxygen is taken up by blood at a high than at a low tempera- ture. We have learned that, in ordinary respiration, the propor- tion of carbonic dioxide and oxygen in (Ufferent parts of the respiratory tract must vary greatly ; the air of necessity being much less pure in the alveoli than in the larger bronchi. From experiments on blood, venous and arterial, to deter- mine the conditions of pressure, temperature, etc, under which the injurious gas is got rid of and the necessary one absorbed, it has been found that the partial pressure of oxygen in the lungs is sufficient to bring about that surrender of oxygen to the blood necessary to keep it all but saturated with this gas as it is believed to be ; and that, so far as carbonic anhydride is concerned, the same law holds—i a, the partial pressure in the blood is ordinarily greater than in the alveoli. By means of an apparatus by which one of the smaller bronchi may be occluded for a certain period, and also allow of withdrawal of samples of the air in the occluded portion of lung from time to time, to ascertain its composition, attempts THE BBSPIBATORT 8T8TE1L 891 is gas M as [quantity iu ctracted by I 6 volumes in off when . Qod be sub- ff. greater part iritb sodium les in some lassociation. »d with the are of respi- d it is obvi- ' the Henry- r. It is also principle of itity of oxy- noval by re- LS subject to question of nrs that less owtempera- the propor- parts of the lessity being >nchi. ial, to deter- under which ne absorbed, ygen in the >f oxygen to rith this gas io anhydride pressure in the smaller d also allow Bd portion of on, attempts have been made to determine the pressure relations within an alveolus. It is maintained that while the partial pressure of the carbonic anhydride rises and of the oxygen sinks, still that they remain such as to favor respiration. It is also found that, in the asphyxia following occlusion of the trachea, the tension of oxygen is always greater, and of carbonic anhydride less, ia the alveoli than in the blood. On the other hand it is stated that oxy-IuBmoglobin is found in the blood whoa every trace of oxygen is removed from a chamber in which an asphyxiating animal is breathing, so that it is argued that partial pressures alone can not explain the facts of respiration, and that this function is fundamentally a chemical process; and it is cus- tomary to speak of the oxygen of oxy-hemoglobin as being in a state of " loose chemical combination." The entire truth seems to lie in neither view, though both are partially correct The view expressed by some phjrsiologists, to the effect that diffusion explains the whole matter, so far, at least, as carbonic anhydride is concerned, and that the epithelial eejls of the lung have no share in the rospiratory process, does not seem to be in harmony either with ttie facts of respiration or with the laws of biology in general. Why not say at once that the facts of respiration show that, here as in other parts of the economy, while physical and chemical laws, aa we hnoto tJiem, stand related to the vital processes, yet, by reason of being vital processes, we can not explain tiiem according to the theories of either ph3ir8iai or chemistry ? Surely this very subject show^ that neither chemistry nor physics is at present adequate to/ explain such processes. It is, of course, of value to know the circumstances of tension, temperature, etc., under which respi- ration takes place. We, however, maintain that these are con- ditions only—essential no doubt, "but, though important, that they do not make up the process of respiration. But, because we do not know the real explanation, let us not exalt a few facts or theories of chemistry or phyidos into a solution of a complex problem. Besides, some of tiie experiments on which the oondiosions have been based are questionable, inasmuch as they seem to inducN» artificial conditions in the animals oper- ated upon ; and we have already insisted on the blood being regarded as a living tissue, behaving differently in the body and when isolated from it, so that even in so-ci^ed blood-gas experiments there may- be sources of fallacy inherent in the nature of the case. 892 ANIMAL PHYSIOLOGY. Vordgn 0mm and SMpintion. — ^These are divided into : 1. Indifferent gases, as N, H, CH*, which, though not in themselves injurious, are entirely useleM to the economy. 3. Pbisonotia gases, fatal, no matter how abundant the nor* mal respiratory food may be. They are divisible into: (a) those that kill by displaqing oxy^n, as NO, GO, HON ; (&) narcolie gases, as CO*, NtO, producing asphyxia when present in large quantities; (c) reducing gases, as HiS,(NH«)iS, PH(,As^C»N(, which rob the heemoglobin of its oxygen. There are probably a number of poisonous products, some of them possibly gasee^ produced by the tissues themselves and eliminated normally by the respiratory tract; and these are doubtless greatly augmented, either in number or quantity, or both, when other excreting organs are disordered. Respiration in the Tissues. We first direct attention to certain striking facts : 1. An isolated (frog's) muscle will continue to contract for a considerable period and to exhale carbon dioxide in the total absence of oxygen, as in an atmosphere of hydrogen; though, of course,'there is a limit to this, and a muscle to which either no blood .flows, or only venous blood, soon shows signs of fatigue. 2. In a frog, in which physiological saline solution has been substituted for blood, the metabolism will continue, carbonic anhydride being exhaled as usual. 8. SubetancM, which are readily oxidized* when introduced into the blood of a living animal or into that blood when withdrawn undergo but little oxidative change. 4, An raitire frog will respire oar> bonic dioxide for hours in an atmosphere of nitrogen. Such facts as these seem to teach certain lessons dearly. It is evident, first ^f all, that the oxidative prooessM that give rise to carbon dioxide occur chiefly in the Hssues and not in the blood ; that in the case of muscle the oxygen that is Used is first laid by, banked as it were against a time of need, in tiici form of intra-moleoular oxygen, which is again set free in the form of carbon dioxide, but by what seriM of changM we are quite un- able tu say. "IRiough our knowledge of the rMpiratory prooessM of muscle is greater than for any other tissue, there seems to be no reason to believe that th6y are essentially diflFerent else- where. The ad vantagM of this .banking of oxygen are, of course, obvious ; were it otherwise, the life of every cell mui^ be at the mercy of the ^lightest interruption of the flow of blood, the THB RBSPIRATORT ST8TE1L 898 nto: Lgh not in omy. it the nor- ): (a) those [b) narcotie tit in large AbH.,C.Ni^ iucts, some aselves and 1 these are [uantity, or i: iontract for in the total »n; though, rhich either rs signs of ine solution 11 continue. Substances, the blood of wn undergo respire oar^ m. I clearly. It hat give rise I not in the I tised is first . thet form of L the form of ure quite un- jry processes ere seems to lifferent else- ,re, of course, ust be at the >f blood, the / 1«WB entrance of air, etc. Even as it is, the need of a oonatant supply of oxygen in warm-blooded animals is much greater than in cold-blooded creatures, which can long endure almost entire cessation of both respiration and circulation, owing to the com- paratively slow rate of speed of the vital machinery. If one were to rely on mere appearances he might suppose that in the more active condition of certain organs there was less chemical interchange (respiration) between the blood and the tissues than in the resting stage, or, properly speaking, more tranquil stage, for it must be borne in mind tiiat a living cell is never wholly at rest; its molecular changeejwe cease- less. It happens, e, g., that wE^ToBriwi giJii^ads (saiivMyTi'e Siecreting actively, the blood flowing from them is less venous in appearance than when not functionally active. This is not because less oxygen is used or lees abstracted from the blood, but because of the greatly increased qieed of the blood-flow, so that the total supply to draw from is so much larger that, though more oxygen is actually used, it is not so much missed, nor do the greater additions of carbon dioxide so rapidly pol- lute this rapid stream. It is thus seen that throughout the animal kingdom respira- tion is fnndMnentally the same process. It is in every case finally a consumption of oxygen and production of carbonic anhydride by the individual cell, whether that be an Amceba or an element of man's brain. These are, however, but the\ beginning and end of a very complicated biological history of ( by far the greater part of which nothing is yet known ; and itN must be admitted that diffusion or any physical explanationj carries us but a litUe way on toward the understanding of it. "^ The Nbsvous Stbtuc in Relation to Rmhpibation. We have considered the muscular movements by which the air is made to enter and leave the lungs in consequence of changes in the diameters of the air-inclosing case, the thorax. It remains to examine into the means by which these muscles were set into harmonious action so as to accomplish the pnr^ pose. The nerves supplying the musdee of req>iration are de- rived from the spinal cord, so that they must be under the dominion of central nerve-oells situated either in the cord or the brain. Is the influence that proceeds outward generated within the cells independently of any afferent impulses, or is it dependent on such causes f Let us appeal to facts. 894 ANIMAL PHTSIOLOGT. 1. If the phrenics, an intercostal nerve, etc., be cut, there is a corresponding pan^ysis of the mnscle supplied. 2. If the spinal cord be divided below the mednlla oblongata, there is a cessation of all respiratory movements except those of the larynx and face, which also disappear if the facial and inecur- rent laryngeal nerves be divided. 3. So long as the medulla remains, respiration may continue; but if even a small part of this region, situated below the vaso-motor center between this and the ccdamus acriptorius (respiratory center, ruBud vital), be injured, death ensues rapidly. Plainly, then, there are cen- tral cells which originate the impulses that energize the mus- cles. It remains to inquire still whether they an: independent (automatic) centers, or are influenced by impulsv>8 reaching them from without. Is the government absolute, or subject to the will of the multitudinous cells of the organic common- wealth ? Again let us appeal to facts: 1. If one vagus nerve be cut, a change is observable in the re s p i rat o ry rhjrthm, which is much more pronounced if both nerves be divided. Respiration becomes slower, and the pause between inspiration and expira- tion greatly leiigthened, though th^ gaseous interchange re- mains much as before. S. If one suddenly step into a cold bath, he naturally draws a long breath. Again, the respiration is very greatly idtered in conaequenoe of emotional clumges; indeed, there iis probably no rhythm in the body more subject to frequent obvious altwation than that of respiration. 8. Stimulation of the central end of such a nerve as the sciatic causes marked change in the rhythm of breathing. 4. Stimu- lation of the central end of the vagus usually quickens res- piration, whil^ stimulation of the central end of the superior laryngeal has the opposite effect. If the current be strong, respiration may bo arrested in each instance, though in a differ- ent manner. In the case of vagus stimulation the result id inspiratory spasm, and of the superiw laryngeal eitpiratory spasm. These and a host of additional facts, experimental and other, show that the central impulses are modified by afferent im- pulses reaching the center through appropriate nerves. More- over, drugs seem to act directly on tiie center through the blood. The vagus is without doubt the afferent respiratory nerve, though how it is affected, whether by the mechanical movement THE BBSPIRATORT STBTBM. 896 ;nt, tiliere is . 2. If the I, there is a bose of the I and recur- the medulla imall part of Mtween this noRvd vital), , lere are cen- ize the mtis- independent .808 reaching or subject to nic common- lerve be cut, im, which is Bespiration 1 and ezpira- terohange re- p into a cold be respiration »nal clumges; more subject ispiration. 8. as the sciatic ig. 4. Stimu- quickens res- f the superior tnt be strong, ighinadiffer- L the result id aal expiratory ntal and other, f afferent im- lerves. More- r through the ►iratory nerve, ioal movement of the lungs merely, by the condition of the blood as regards its contained gases, or, as seems most likely, by a combination of circumstances into which these enter and are probably the Bntn oteoe meduffc A»m whtek -imnOm ModMrliig rmplnUim man proceed. Jfi^pli'iiCof y inaumeduna. Vm. m.-I>iacnm latoBdMl la BJptMt tortf.— > OrtatMOMimrw / fum/n taqwtawi ptrotery eetdn tv'* ooorw of ImpolMa. o(f«|ilratloa. Arrawa principal, is not demonstrably clear. When othons function as afferent nerves^ capable of modifying the action of the respira- ffiiMiwiliiwiiiiiiitw 396 ANIMAL PHYSIOLOGT. ¥ tory center, they are probably influenced by the respiratory condition of the blood, though not necessarily exclusively. But when all the principal a£Ferent impulses are cut off by division of the nerves reaching the respiratory center directly or indirectly, respiration will still continue, provided the motor nerves and the medulla remain intact. The center, then, is not, mainly at least, a reflex but an auto- matic one, though its action is modified by afferent impulses reaching it from eVery quarter. Since respiration continues when the medulla is divided in the middle line, yet is modified unilaterally when one vagus is divided, it is inferred that the respiratory center is double, that each half usually works in harmony with the other, but that each can act independently. Though it seems clear enough that the respiratory center is automatic, and that its action is modified according to the con- dition of the organism generally, as communicated to it by the various afferent nerves and the blood itself, yet the exact man- ner of its action — ^why inspiration follows up expiration— has not been clearly explsdned. Some assume that during expira- tion inspiratory impulses are gathering head and finally check expiration by originating inspiration, while these are opposed by another process which at length gives rise to enough resist- ance to check inspiration, and originate expiration ; and this theory becomes more complete if an expiratory as well as in- spiratory center be assumed. We have hitherto spoken only of a single respiratory cen- ter in the medulla, but certain experimental facts throw addi- tional light on the subject. In young mamnuils— e. g., kittens— it is found that, in the absence of the medulla* respiratory movements may be induced by stimulating (pinching) the turiace, especially if the action of the spinal cord be Augmented by the administration of strychnia. From this it hew been inferred that there are respir- ' atory centers in the spinal cord, subordinate to the main cen- ter in the medulla. Oonndering the imperfect nature of the respiratory act as thus induced, and the circumstances of the case, the conclusion has the appearance of being a little strained. But quite recently it has been shown that ba. the adult dog when the cord is severed below the medulla* and artificial res- piration maintained for some time, on ceasing this, breathing begins spontaneously and continues for a considerable period ; and the expiratory phase of req>iration in this case is the most marked. It has been argued from this experiin^:,%ai^ tliere respiratoi^y sively. J cut oflE by ter directly 1 the motor rat on auto- oit impalses n continues \ is modified >ed that the ly works in lependently. ry center is j; to the con- to it by the ) exact man- iration— has iringexpira- &nally check are opposed lOugh resist' on; and this swell as in- piratory cen- I throw addi- 1 that, in the ty be induced if the action nistration of erearerespir-' lie main cen- lature of the itances of the little strained, the adult dog [ artificial res- his, breathing srable period; kse is the most ant t^t there THB RESPIBATORT STSTEBL 897 arc both inspiratory and expiratory centers in the spinal cord. But, as we have pointed out, on more than one occasion, we must always be on our guard in interpreting the behavior of one i>art when another is out of gear. There is so much latent resource, so great a power to resume functions normally laid aside, if not wholly in great part, that we should hesitate be- fore inferring that the spinal cord usually takes a prominent share in originating the impulses which govern respiration. Notwithstanding the suggestiveness of such exi)eriments, we do not think they make the medulla appear in a less important light as the part of the nervous system dominant in respira- tion ; though there may be nervous machinery in the cord usu- ally in feeble action, susceptible of assuming a more exalted functional HUe when occasion urgently demands and when en- couraged, so to speak, to do so, as in the experiments referred to above; indeed such, upon our own theory of physiological reversion, would natturally be the case. We must, however, draw the line between what is and what may be is function. The Tnfliwioe ef fhe Ooodttlm «f the Btooi ia XeipintioB^— If for any reason the tissues are not receiving a due supply of oxygen, they manifest their disapproval, to speak figuratively, by reports to the responsible center in the medulla, and if the medulla is a sharer in the lack, as it naturally would be, it takes action independently. One of the most obvious instances in which there is okygen starvation is when there is hindrance to the entrance of air, owing to obstruction in the respiratory tract. At first the breathing is merely accelerated, with perhaps some increase in the depth of the inspirations {hyperpn creaoing to the normaL Apncea has been interpreted in two ways. Some think that it is due to fatigue of the muscles of respiration or the respira> tory center; others that the blood has under these circum- stances an excess of oxygen, whidi so influences the respiratory center that it is quieted (inhibited) for a time. The latter yiew is that usually sidopted ; but, considering that apfMsa results from the sobbing of children following a pro- longed fit of crying, also in Cheyne-Stokes and other abnonnal forms of breathing, and thai the blood is normally almost satu- rated with oxygen, it will be agreed that there is a good deal to be said for the first view, especially thai part of it which represents the cessation uf breathing as owing to excessive activity and exhaustion of the respiratory centw. We find such a calm in asphyxia after the convulsive storm. Is it, then, the excessive accumulation of carbon dioxide or the deficiency of oxygen that induces dyspnoea f Considering that the former gas acts as a narcotic, and does not induce con- vulsions, even when it, constitutes a large percentage of the atmosphere breathed, and that the need of oxygen for the tis- sues is constant, it certainly seem^ most reasonable to conclude that the phenomena of dyspnoea are owing to the lack of oxy- gen chiefly, at least ; thxHigh the presence of an excess of car- bonic anhydride may take some share in arousing that vigorous effort on the part of the n«irvous system, to restore the func- tional equilibrium, so evident under the circumstances. Ths dh^MMtos B s sp i fati o B ( gto ws n aaX— There is a form of breathing occurring under a variety of abnormal circum- stances, xa which the respirations gradually reach a maximum (dyspnoaa), and then as gradually decline to absolute cessation (apnoea). The pause may last a su^rising length of time (one half to three quarters of a minute), when this form of breathing again repeats itself. It has been compared to the periodic grouping of heart-beats (Luciani groups), occurring when the organ is suffering. There is abundant cause usually for ex- haustion of the center, on account of disordered blood or an insufficient supply to the Inain. This phenomenon and apnoea bring out clearly the rhythmic character of those processes. mmmtm >W)M.M.i W ^ i iw II THE RBSnBATORT 8T8TEM. 899 mars cheat looession of interrupted radoally in- » think that therespira- ese ciromn- respiratory ideringthat wing apro- HrabnOTmal alinoet satu- a good deal of it which to excessive r. We find I. tn dioxide or Ck>nsidering ; induce con- itage of the a for the tis- ) to conclude lack of oxy- xcessof car- ihat vigorous >Te the funo- nces. lere is a form rmal circum- i a maximum lute cessation of time (one L of breathing the periodic ing when the tually for ex- . blood or an }n and apnoea Dse processes. like respiration, which in the nature of the case must be in the higher groups of vertebrates ceaseless, and it is not surpris- ing that, like a lame dog, which prefers progression by three legs to none at all, the ever-active center will keep up its rhythm as long as it can— perfectly, if possible, and, if not perfectly, as well as it can. We mean to imply that its action must be rhythmic, or cease entirely. ThB ElTBCTS OF VaBIATIONS IK THK ATMOSPHBBIO PBB88UBE. These depend in great part upon the suddenness with which the change is made. When an individual ascends a high mountain or rises in a balloon, parts in contact with the air become reddened and swollen, owing to the distention of the small vessels, which may result in heemorrhages. There is dif- ficulty in breathing, the respirations become more rapid, as also the pulse. If the lowering of pressure amounts to from one third to one half, the quantity of oxygen in the blood is dimin- ished, and the carbon dioxide impeif ectly excreted. Owing to the excess of blood in the superficial parts, the internal organs become ansBmic, and there is consequently diminished secretion of urine and a variety of other disturbances, with general weak- nes& The blood-pressure is also altered. Sudden diminution of pressure gives rise to a liberation of gas— chiefly nitrogen— within the blood-vensels, which causes death by blocking the circulation in the small vessels (hence also the danger from section of a large vein in surgical opera- tions about the neck, tilie air being liable to be sucked in, owing to the negative pressure). Increase in the atmospheric pressure when not very great gives rise to symptoms akin to those of narcotic poisoning; but when the increase amounts to twenty atmospherei^ animals die, as if asphyxiated, with convukdims. Neither the assump-i tion of oxygen nor the separation of carbon dioxide takes place] to the usual extent; and it is interesting to note that microV organisms are killed under similar circumstances. With considerable diminution of pressure, though not suf- ficient to lead to a fatal result, symptoms the opposite of those described above occur. Thus, there is paleness of the surface, respiration is easy, the capacity of the lungs i^ increased, owing, it is thought, to the greater descent of the diaphragm, in con- sequence of the compression of tixe gases of the intestines. «wuy i i' i wwW.' 400 ANIMAL PHT8IOL0OT. Urine is secreted in excess, there is more muscular energy, and the metabolism of the body generally is accelerated. Air under altered pressure has been employed as a therapeutic agent, but a little reflection will make it clear that it is a remedy to be used with the greatest care, especially when there is disease of the heart, blood-vessels, etc. Thk Influbncb of RmpnuTiOM ok ths Oibculation. An examination of tracings of the intra-thoracic and blood- pressure, taken simultaneously, shows (1) that during inspira- tion the blood-pressure rises and the intra-thoracic pressure falls ; (2) that during expiration the reverse is true ; and (8) that the heart-beat is slowed, and has a decided effect on the form of the pulse. But it also appears that the period of highest blood-pressure is just after expiration has begun. Vto. Its. totJmtmpmJtmr iMHlnMtai 9m tm,jmA thwatMrljr aUka m We must now attempt to explain how these changes are brought about By intra-thoracic p r e s su re is meant the press- ure the lungs exert on the costal pleura or any organ within the chest, which must differ from intra-pulmonary pressure and the pressure of the atmosphere, because of the resistance of the lungs by virtue of their own elasticity. . It has been noted that even in death the lungs remain par- tially distended ; and ibhat when the thorax is opened the pul- monary collapse which follows demonstrates that their elas- ticity amounts to about five millimetres of mercury, which must, of course, represent but a small portion of that elasticity which may be brought into play when these organs are greatly distended, so that they never press on the costal walls, heart. nergy, and Air under I agent, but medy to be g disease of (JLATION. ! and blood- ing inspira- sio pressure uid (2) that m the form I of highest a. Wood- cnrvoot tato«- I changes are tnt the press- organ within nary pressure the resistance s remain par- tened the pul- lat their elas- arcury, which that elasticity bus are greatly tl walls, heart. THB BBSPIRATOBT STSTEM. 401 etc., with a pressure equal to that of the atmosphere. It follows that the deeper the inspiration the greater the difference be- tween the intra-thoracio and the atmospheric pressure. Even in expiration, except when forced, the intra-thoracic pressure remains less, for the same reason. These conditions must have an influence on the heart and blood-vessels. Bearing in mind that the pressure without is practically constant and always greater than that within the thorax, the conditions are favorable to the flow of blood toward the heart As in inspiration, the pressure on the great veins and the heart is diminished, and, as these organs are not rigid, they tend to expand within the thorax, thus favoring an on- ward flow. But the opposite effect would follow as regards the large arteries. Their expansion must tend to withdraw blood. During expiration the conditions are reversed. The effects on the great veins can be observed by laying them bare in the neck of an animal, when it may be seen that during inspiration they become partially collapsed, and refilled during expiration. In consequence of the marked thickness of the coats of the great arteries, the effect of changes in intra-thoracic pressure must be slight. The ccmi'paratively thin-walled auricles act somewhat as the veins, and it is likely that the increase of pressure during expiration must favor, so far as it goes, the cardiac systole. More blood, then, entering the right side of the heart dur- ing inspiration, more will be thrown into the systemic circula- tion, unless it be retained in the lungs, and, unless the effect be counteracted, the arterial pressure will rise, and, as all the con- ditions are reversed during expiration, we look for and find exactly opposite results. The lungs themselves, however, must be taken into the account. During inspiration room is pro- vided for an increased quantity of blood, the resistance to its flow is lessened, hence more blood reaches the left side of the heart The immediate effect would be, notwithstanding, some diminution in the quantity flowing to the left heart, in conse- quence of the sadden widening of the pulmonary vessels, the reverse of which would follow during expiration; hence the period of highest intra-thoracio pressure is after the onset of the ex|Hratory act During inspiration the descent of the dia- phragm compressing the abdominal organs is thought to forpe on blood from the abdominal veins int6 the thoracic vena cava. That the respiratory movements do exert in some way a pronounced effect on tiie circulatimparative- ic pressure as blood by 3ady witbin Q passes on lition. The The heart's o-inhibitory iir when the extoit. phenomena in some ani- observed in ded that one fct such pro- ( of disease; L this respect » which have iped into the 5 usual press- Y pressure is qteriment, be steady rise of in^ the respir- ratibe-Hering ji nerves are pressure that ings may still These are the ion as to their fBoe to explain >n, but believe ? of the arteri- oles affected through vaso-motor nerves in obedience to the medullary center which operates by their agency; and that ^^^•J?'*-r^5'*'*'^M blood-OTMMDe in niMt to tlioir Tnnb»-HMrii« encna (after Foatw). yw.wM** undulatloM bdioM Trmoiw Battag cunca; tboM aatt in riat, eOecta of nqrintlaa;MidUMHniUlMt,oCtlwpiilw. when this center is disabled its subordinates in the spinal cord take upon them the task. It has also been suggested that there may be a local vaso-motor mechanism acted upon by the ve- nous blood or that the muscle-cells themselves may be influ- enced by the unnatural condition of the blood in asphyxia. These curves, however, also appear during respiration that deviates but little from the normal. It is to be borne in mind that the tracings on which we have based our reasoning do not represoit what takes place in every mode of breathing. The subject is one of great com- plexity. Doubtless mechanical explanations go a long way here, but they are so mixed up with factors that play a part more or less prominent, though difficult to isolate in individual instances, and in no wise to be explained as other than vital effects, that one must exercise the usual caution ; the more so as it is found upon actual experiment that the outcome, as regards bloofl-pressure, is not always quite what would have been expected, reasoning from the principles of physics alone. That there are rhythms within rhythms in the vascular an<] respiratory system, rendering the subject complex beyond thej power of experiments fully to unravel, is a conviction that w^ think will deepen in the minds of physiologists. ia>M»»»!i » ii ri wili wtiW H K W i B i M V 404 ANIMAL PHYSIOLOOr. The Beipixfttioii and Cixeolatimi in Afphyxia.— A most in8truct-> ive experiment may be arranged thus : Let an ansesthetized rabbit, cat, or such-like animal, have the carotid of one side connected with a glass tube as before described (page 229), by which the blood-pressure and its changes may be indicated, and, when the normal respiratory acts have been carefully observed, proceed to notice th» effecto on the blood-pressure, etc., of pumping air into the chest by a bellows, of hindering the ingress of air to a moderate degree, and of struggling. With a small animal it will be difficult to observe the respiratory effects on the blood-pressure by simply watching the oscillations of the fluid in the glass tube, but this is readily enough nuwle out if more elaborate arrangements be made, so that a graphic tracing may be obtained. But the main events of asphyxia may be well (perhaps best) studied in this manner : Let the trachea be occluded (ligatured). At once the blood- pressure will be f^n to rise and remain elevated for some time, then gradually fall to zero. These changes are contemporane- ous with a series of remarkable manifestations of disturbance in the respiratory system as it at first appears, but in reality due to widespread and profound nutritive disturbance. So far as the breathing is concerned, it may be seen to become more rapid, deeper, and labored, in which the expiratory phase be- comes more than proportionably marked (dyspinoea) ; this is fol- lowed by the gradual a limal, have )e as before tre and its respiratory 9 th& effects chest by a rate degree, > difficult to e by simply ibe, but this igements be lerhapsbest) ;e the blood- r some time, atemporane- disturbance ut in reality mce. So far become more ry phase be- ); thisisfol* those usually les into a ter- I of a nerve- but usually stion, during ionless oondi- which inspi- U floaUy, the BMordaxed, »m peristaltic , ehds a strike three stages, one another : 8. Stage of iressure rises, first instance tenter, and in THE BBSPIBATORT SYSTEM. 405 the second to its exhaustion and the weakening of the heart- beat. These violent movements are owing, we repeat, to the action of blood deficient in oxygen on the respiratory center (or cen- ters), leading to inordinate action followed by exhaustion. iiie duration of the stages of asphyxia varies with the ani- mal, but rarely exceeds five minutes. In this connection it may be noted that newly-born animals (kittens, puppies) bear im- mersiorf in water for as much as from thirty to fifty minutes, while an adult dog dies within four or five minutes. This is to be explained by the feeble metabolism of new-bom mam- mals, which so slowly uses up the vital air (oxygen). If the chest of an animal be opened, though the respiratory muscles contract as usual there is, of course, no ventilation of the lungs, which lie collapsed in the' chest; and the animal dies about as quickly as if its trachea were occluded. It passes through all the phases of asphyxia as in the former case ; but additional information may be gained. The heart is seen to beat at first more quickly and forcibly, later vigorously though slower, and finally both feebly and irregularly, till the ventri- cles, then the left auricle, and finally the right auricle cease to beat at all or only at long intervals. The terminations of the great veins (representing the sinus venosus) beat last of alL At death the heart and great veins are much distended with blood, the arteries comparatively empty. Even after rigor mortis has set in, the right heart is still much engorged. These phenomena are the result of the operation oi* several causes. The increasingly venous blood at first stimulates the heart probably directly, in part at least, but later has the con- trary effect. The nutrition of the organ suffers from the de- graded blood, from which it must needs derive its supplies. The caiitO'inhibitory center probably has a large share in the slowing of the heart, if not also in quickening; it Whether the accelerator fibers of the vagus or sympathetic play any part is uncertain. The increase of peripheraT resistance caused by the action of the vaso-mot6r center makes it more difficult for the heart to empty its left side and thus receive the venoua blood as it pours on. At the same time the deep inspirations (when the chest is unopened) favor the onflow of venous blood; and in any case the whole venous system, including the right heart, tends to become engorged from these several causes act- ing together. The heart gives up the struggle, unable to main- tain it, but not so long as it can beat in any part. mmmmmmmi0 406 ANIMAL PHTSIOLOGT. The share which the elasticity of the arteries takes in forcing on the blood when the heart ceases, and the contraction of the muscular coat of these vessels, especially the smaller, must not be left out of the account in explaining the phenom- ena of asphyxia and the post-mortem appearances. FathologiiML — ^The importance of being practically as well as theoretically acquainted with the facts of asphyxia is very great. The appearance of the heart and venous system gives une- quivocal evidence as to the mode of derth in any casb of as- phyxia; and the contrast between the heart of an animal bled to death, or that has died of a lingering disease, and one drowned, hanged, or otherwise asphyxiated, is extreme. We strongly recommend the studeni; to asphyxiate some small mammal placed under the influence of an ansesthetic, and to note the phenomena, preferably with the chesi opened ; and to follow up these observations by others after the onset of rigor mortis. Pecuuar Respiratort Movbmbnts. Though at first sight these seem so different, and are so as regards acts of expression, yet from the respiratory point of view they resemble each other closely; they are all reflex, and, of course, involuntary. Many of them have a common purpose, either the better to ventilate the lungs, to clear them of foreign bodies, or to prevent their ingress. Cotighing, in which such a purpose is evident, is made up of several expiratory efforts preceded by an inspiratory act. The afferent nerve is usually the vagus or laryngeal, but may be one or more of several others. The glottis presents characteristic appearances, being closed and then opened suddenly^ the mouth being kept opisn. Coughing is often induced in attempting to examine the ear with instruments. (Reflex act.) Laughing is very similar to the last, so far as the behavior of the glottis is concerned, though it usually acts more' rapidly, of course. Several expirations follow a deep inspiration. Crying is essentially the same as laughing, but the facial expression is different, and the lachrymal gland functions exces- sively, though with some persons this occurs during laughter also. ScMnng is made up of a series of inspirations, in which the glottis is partially closed, followed by a deep expiration. M>«wMaKMiltellMMflMliiwn>i litMiMWiiUilii 3 takes in sontraction le smaller, le phenom- r as well as very great, gives une- casb of as- . nimal bled e, and one me. xiate some aneesthetic, )si opened; ir the onset d are so as ry point of I all reflex, a common ) clear them made np of •y act. The but may be being closed pen. nine the ear the behavior lore' rapidly, ■alion. it the facial ctions exces- ng laughter n which the THB BBSPIBATOBT STSTBM. 407 Yawning involves a deep-drawn, slow inspiration, followed by a more sudden expiration, with a well-known depression of the lower jaw and usually stretching movements. Sighing is much like the preceding, though the mouth is not opened widely if at all, nor do the stretching movements com- monly occur. Hieeough is produced by a sudden inspiratory effort, though fruitless, inannuch as the glottis is suddenly closed. It is spoken of as spasm of the diaphragm, and when long continued is very exhaustive. Sneezing is the result of a powerful and sudden expiratory act following a deep inspiration, the moutii being usually closed by the anterior pillars of the fauces against the outgoing cur- rent of air, which then makes its exit through the nose, while the. glottis is forcibly opened after sudden closure. It will be noticed that in most of theao acts the glottis is momentarily closed, which is never the case in mammals during quiet res- piration. This temporary occlusion of the respiratory passages, per- mits of a higher intrapulmonary pressure, which -is very effect- ive in clearing the passages of excess of muctis, etc., when the glottis is suddenly opened. Though the acts described are all involuntary, they may most of tiiem be imitated and thus studied deliberately by the studout. It will also appear, con* sidering the many ways in which some if not all of them may be brought about, that if the medullary center is responsible for the initiation of tiiem, it must be accessible by numberless paths. OoapanttTa.— Few of the lower animals cough with the same facility as man, while laughing is all but unknown, crjring and sobbing rare, though the whining of dogs is allied to the cry- ing of human beings. Sneesing seems to be voluntary in some animals, as squir- rels, when engaged in toilet operations, etc. Barking is voluntary, and in mechanism: resembles cough- ing, the voci^ cords being, however, more definitely employed, as also in growling. Bawling, neighing, braying, etc., are made up of long expira- tory acts, preceded by one or more inspirations. The vocal coids are aliso rendered tense. mmiiMt t mM t atMmMm.mi> ti umut«mmi i mmtiim> 408 ANI2IAL PHYSIOLOGY. Special Considerations. Pathologioal ud GUnieaL— The number of diseases that lessen the amount of available pulmonary tissue, or hamper the move- ments of the chest, are many, and only the briefest reference can be made to a few of them. Inflammation of the lungs may render a greater or less por- tion of one or both lungs solid ; inflammation of the jAewra (pleuritis, pleurisy) by the drjmess, pain, etc., may restrict the thoracic movements; phthisis may solidify or excavate the lungs, or by pleuritic inflammation glue the costal and pulmonary pleural surfaces together; bronchitis clog the tubes and other air-passages with altered secretions ; emphysema (distention of air-cells) may destroy elasticity of parts of the lung; pneumct- thorax from rupture of the lung-tissue and consequent accumu- lation of gases in the pleural cavity, or pleurisy with effusion, render one lung all but useless from pressure. In all such cases Nature attempts to make up what is lost in amplitude by increase in rapidity of the respiratory movements. It is inter- esting to note too how the other lung, in diseased conditions, if it remain unaffected, enlarges to compensate for the loss on the opposite side. When the muscles are weak, especially if there be hindrance to the entrance of air while the thoracic move- ments are marked, there may be bulging inward of the inter- costal spaces. Normally, this would also occur, as the intra-thoracic press- tire is less than the atmospheric, were it not for the fact that the intercostal muscles when contracting have a certain resist- ing power. The imperfect respiration of the moribund, permitting the /accumulation of carbonic anhydride with its soporific effects, smooths the descent into the valley of the shadow of death ; so that there may be to the uninitiated the appearance of a suffer- ing which does not e^st, consciousness itself bemg either wholly or partially absent. The dyspnoea of anemic jwrsons, whether from sudden loss of blood or from imperfect )rmiewal of the haemoglobin, shows that this substance has a respiratory function; while informs of cmrdiac disease with regurgitation, etc., the blood may be imperfectly oxidised, pdviag rise to la- bored respiration. Penonal Obiimit|oin.-~As hinted from time to time during the treatment of this subject, there is a large number of facts the student may verify for himself. MitaiiiMiHMMMlWMin <>mm »MMP THE BBSPIRATORT SYSTEM. 409 that lessen the move- ; reference >r less por- the pleura estrict the 9 the lungs, pulmonary i and other stention of ;; pnewna- at accumu- th efiFusion, 11 all such iplitude by It is inter- tnditions, if loss on the lly if there •acic move* { the inter* traoic press- le fact that rtainresist- mitting the »rific effects, )f death ; so ) of a snffer- leiiQg either nio persons, feet )miewal ^respiratory gurgitation, ig rise to la- time during iher of facts A simple way of proving that CO. is exhaled is to bi-eathe (blow) into a vessel containing some clear solution of quick- lime (CaO), the turbidity showing that an insoluble salt of lime (GaCOa) has hem formed by the addition of this gas. The functions of most of the respiratory muscles, the phe- nomena of dyspnoea, apnoea (by a series of long breaths), partial asphyxia by holding the breath, and many other experiments, simple but convincing, will occur to the student who is willing to learn in this way. The observation of respiration in a dreaming animal (dog) wiQ show how mental occurrences affect the respiratory center in the absence of all the usual outward influmices. The respira- tion of the domestic animals, of tl- r og, turtle, snake, and fish are easily watched if these cold-b.c jded animals be placed for observation beneath a glass vessel Their study will teach how manifold are the ways by which the one end is attained. Com- pare the tracings of Fig. 313. IfdutiOB. — ^A study of embryology shows that the respirsr tory and circulatory systems d^lop together; that the vascu- lar system functions largely a/a respiratory system also in cer- tain stages, and remains such, from a. physiological point of view, throughout embryonic life. The changes that take place in the vascular system— the heart, especially— of the mammal when the lungs have become functionally active at birth, show how one set of organs modi- fies the other. When one considers, in addition to tibese facts, that the digestive as well as the vascular and respiratory organs are represented in one group of structures in a jelly-fish, and that the lungs of the mammal are derived from tiie same mesoblast as gives rise to the digestive and circulatory organs, many of the relations of these systems in the highest groups of animals become intelligible; but unless there be descent with modifica- tion, these facts, clear enough from an evolutionary standpoint, are isolated and out of joint, bound together by no common principle that satisfies a philosophical biology. It has been found that in hunting-dogs and wild rabbits the vagus is more efficient than in other races of dogs and in rab- bits kept in confinement ; and pomibly this inay in part account for the greater speed and« especially the endurance of the former. The very conformation of some animals, as the grey- hound, with his deep chest and capacious lungs, indicates an unusual respiratory capacity. ■\)i&m0tae»vimn9mtmUHi ii in i tl i it i i iliili oAivtl^ 410 ANIMAL PHYSIOLOOT. The law cf habU is well illustrated in the case of divers, who can bear deprivation of air longer than those unaccustomed to such submersion in water. Oreater toleration on the part of the respiratory center has probably much to do with the caee, though doubtless many other departures from the normal occur, either independently or correlated to the changes in the respin^ tory center. luuuury of Am VbjtUlogj flf BMpintioB.— The purpose of repiration in all animals is to furnish oxygen for the tissues and remove the carbonic anhydride they produce, which in all vertebrattf is accomplished by t^ie exposure of the blood in capillaries io thn ^^^iscspheriu air, either free or dissolved in water. A membrane lined with cells always intervenes between the capillaries and the air. The air may be pumped in and out, or sucked in and forced out. Xtsplntiini ia the Wawwai— The air enters the lungs, owing to the enlargement of the chest in three directions by the action of certain muscles. It leaves the lungs because of thjeir own elastic recoil and that of the chest-wall chiefly. Inspiration is active, expiration chiefly passive. The diaphragm is the principal muscle of respiration. In some animals there is a well-marked facial and laryngeal as well as thoracic respiration. Respiration is rhythmical, con- sisting of inspiration, succeeded without appreciable pause by expiration, the latter being in health of only slightly longer duration. There is also a definite relation between the number of respirations and of heart-beats. According as respiration is normal, hurried, labored, or interrupted, we describe it as eupnoM, hyperpncea, dyapnim, and apncM. The intra-thoracic pressure is never equal to the atmospheric— -i. e., it is always negative— except in forced expiration ; and the lungs are never collapsed so long as the chest is unopened. The expired air differs from that inspired in being of the temperaiture of the body, saturated with moisture, and containing about 4 to 6 per cent less oxygen and 4 per cent more carbonic anhydride, besides certain indifferently known bodies, the result of tissue metabolism, excreted by the lungs. The quantity of iair actually moved by a respiratory act, as compared with the total capacity of the respiratory organs, is smaU ; hence a great jmrt nmst be played by diffusion. The portion of air that can not be removed from the lungs by any respiratory effort is relatively large. i\timt»M'MMmi ■M«»i««««**»*l(aBMPW»*»ls^W . ' THE BBSPIBATORT SYSTEM. 411 iver8,wlio Lstomed to he part of the cmk9, rmal occur, heTespyr»> ptirpoee of the tissaes hich in all e blood in isBolved in les between and forced ingB, owing 7 the action f their own uspiration is liration. In aryngeal as kimioal, con- >le pause by jhtly longer the number espiration is iscribe it as itra-thoracic it is always Lgs are never I expired air ratnre of the , kbout 4 to 5 ic anhydride, rait of tiflsae ratory act, as nry organs, is ffosion. The lungs by any It is customary to distinguish tidal, complementary, supple- mentary, and residual air. The vital capacity is estimated by the quantity of air the respiratory organs can move, and is very variable. The blood is the respiratory tissue, through the mediation of its red cells, by the heemoglobin they contain. This sub- stance is a ferruginous proteid, capable of crystallisation, and assuming under chemical treatment many modifications. When it coixUuns all the oxygen it can retain, it is said to be saturated, and is called oxy -heemoglobin, in which form it exists (with some reduced heemoglobin) in arterial blood, and to a lesser extent in venous blood, which differs from arterial in the rela- tive proportions of heemoglobin (reduced) it contains, as viewed from the respiratory standpoint. Oxy-heemoglobin does not assume or part with its oxygen, according to the Heury-Dalton law of pressures, nor is this gas in a state of ordinary chemical combination. It is found that the oxygen tension of the blood is lower and that of carbonic anhydride higher than in the air of the alveoli of the lungs, while the same may be said of the tissues and -the blood re- spectively. This has been-, however, recently again denied. Respiration is a vital process, though certain physical con- ditions (temperature and pressure) must be rigidly maintained in order that the gaseous interchanges shall take place. Res- piration is always fundamentally bound up with the metabo- lism of the tissues themselves. All animal cells, whether they exist as unicellular animals (Amoeba) or as the components of complex organs, use up oxygen and produce. carbonic dioxide. Respiratory organs, usually so called, and the respiratory tissue par exetiBence (the blood) are only snppleihentaiy mechanisms to facilitate tissue respiration. C-rbonic anhydride exists in blood probably in combination with sodium salts, though the whole matter is very obscure. Respiration, like all the other functions of the body, is con- trolled by the central nervous system thrdugh nerves. The medulla oblongata is chiefly concerned, and especially one small pari; of it known as the respiratory center. It is possi- ble, even probable, that there are subordinate centers in the ooid, which, under peculiar circumstances, assume importance; but how far they act in concert with the medullary center, oil whether they act at all wheia normal conditions prevail, is aiv open question. The vagus is the principal afferent respiratory nerve. The *is:tiyvBOTECTIVE AND EXCBXTOBT FUNCfTIONS OF THE SKIN. As has been intimated from time to time, thus far, as a result of the metabolism of the tissues, certain products require constant removal- from the blood to prevent poisonous effects. These substances are in all probability much more numerous than physiological chemistry has as yet distinctly recognized or, at all events, isolated. Quantitatively considered, the niost important are oarbonio anhydride, water, urea» and, of less im- portance, perhaps, certain salts. In many invertebrates and in all vertebrates several organs take part in this work of elimination of waste products or puri- fication of the blood, one set of which— the respiratory — ^we have just studied ; and we now continue the consideration of the subject of excretion, this term being reserved for the pro- cess of separating harmful products from the blood and dis- charging them from the body. We strongly reeommend the student to make the study of excretion comparative in the sense of noting how one organ engaged in the process sujyplements auother. A clear under- ^ .- PROTECTIVE AND EXCRBTORY FUNCTIONS OP THE SKIN. 418 re snpply- lls, etc. on is BU8- i taking a id cardio- \ie respira- jxpiration. Bse phases expiration. < i and nerv- , which we ) access of respiratory • changes in «phyxia. oea, one of same time two, and a derations in THE SKIN. IS far, as a acts require ions effects. 9 numerous 'recognized ad, the ihost , of less im- reral organs ticts or puri- liratory — ^we ideration of for the pro- x)d and dis- the study of vr one organ clear under- standing of this relation even to details makes the practice of medicine more scientific and practically effective, and gives physiology greater breadth. The skin has a triple function : it is protective, excretory, sensory, and, we may udd, nutritive (absorptive) and respira- tory, especially in some groups of animals. As a sensory organ, the skin will receive attention later. Proksetiv* Foafltiim of th« lkla.—Gomp«nkiTe.— Among many groups of invertebrates the principal use of the exterior cover- ing of the body ia manifestly protection. Among these forms, an internal skeleton being absent, the exo-skeleton is developed externally, and serves not only for protection, but for the at- tachment of muscles, as seen in crustaceans and insects. But this part of the subject is too large for detailed treatment in such a work as this. Turning to the vertebrates, we see scales, bony plates, feathers, spines, hair, etc., most of them to be regarded as modifications of the epidermis, always useful, and frequently also i^^^^^^^^^^^^H omammtal. '^^^^^^H^^^Hi Primitive man was probably much more hin; ate than his mod- FM. Km. an.-SiMlof4wrmM |l«adB. 1 » «> (After Sqpiwjr.) lJi.„^._^ . V»mL—Maim«rSlaat imim at hMid •book o i wlH i lf m tatk iW (After 84i«^> 1> !• >• ^ ixcreting organs, ?w the lungs and kidneys, and largely upo' the teinperatuve as a physical condition. When the watery vapor is carried off, befc o it c *n condense, the perspiration is said to be inaenaible : when «mall droplets become visible, aenaOtAe. As to whether the ono or the ;i,her is predominant will, of course, depend on the rapidity ; re- newal of the air, its humidity, and its temperature, impart from the temperature, the amount of sweat is i 1 vs need by the quality and quantity of food and, especially of < nnk taken, the amount of exercise, and psychic conditions ; not to speak of the effect of drugs, poisons, or disease. Perspiration in man is a clear fluid, mostly colorless, with a characteristic odor, devoid of morphological elements (except epidermal scales), and alkaline in reaction. It may be acid from the admixture of the secretion of the sebaceous glanda Its solids (less than 2 per cent) consist of sodium salts, mostly chlorides, cholesterin, neutral fats, and traces of urea. The acids of the sweat belong to the fatty series (acetic, buty- ric, formic, propionic, caprylic, caproic, etc.).' FttttoliOglML— The sweat may contain blood, proteids, abun- dance of urea (in cholera), uric aovj, xalates, sugar, lactic acid, bile, indigo and other pigments. Aany medicines are elnii- nated in part through the skiiu ■•qinliMi 1^ tlM SkiL— Ctmpazatif*.— In reptiles and batra- chians, with smooth, moist ukin, the respiratory functions of this organ are of greal< importance; hence these animals can live long under water. 416 ANIMAL PHTSI0L0G7. It is estimated that in the frog the greater part of the car- bonic anhydride of the body- waste is eliminated by the skin. Certainly frogs can live for days immersed in a tank supplied with ninning water ; and it is a significant fact that in this animal the vessel that gives rise to the pulmonary art«ry sup- plies also a cutaneous branch. The respiratory capacity of the skin in man and most mam- mals is comparatively small under ordinary circumstances. The amount of carbonic anhydride thus eliminated in twenty- four hours in man is estimated at not more than 10 grammes. It varies greatly, however, with temperature, exercise, etc. The skin is highly vascular in mammals, and its importance as a heat regulator is thus very great. When an animal is varnished over, its temperature rapidly falls, though heat production is in excess. From the fact that life may be prolonged by diminishing loss of heat through wrapping up the animal in cotton-wool, it is inferred that depression of the temperature is, at all events, one of the causes of death. Though the subjiect is obscure, it is likely that th^ retention of poisonous products so acts as to derange metabo-S lism, as well as poison directly, which might thus lead to the? disorganisation of the machinery of life to the point of disrupt tion or death. It is also possible that the reduction of the tem- perature from dilatation of the cutaneous vessels may be so great that the animal is cooled below that point at wMch the vital functions can continue. Thb Excrbtion of Pbrspibation. In secretion in the wider sense we find usually certain nerv- ous and vascular effects associated. The vessels supplying the r.land are dilated during the most active phase, and at the same i)ime nervous impulses are conveyed to the secreting cells which stimulate them to action. There is a certain proportion of water given off by traneiiiration; but the sweat, as a whole, even the major part of the water, is a genuine seoreticm, the result of the metabolism of the cells. Certain experimental facts deserve consideration in this con- nection : 1. If, in the oat, the sciatic nerve be divided and its distal end stimulated, even when the vessels of the leg are liga- tured, the corresponding foot sweats. %. The vessels being un- touched and atropin injected into the blood, no sweating occurs on stimulation of the nerve, though the vessels of the foot of thecar- y the skin, ik supplied hat in this artery sup- most mam- umstauces. in twenty- ) grammes, se, etc. importance ure rapidly le fact that at through ferred that t the causes jly that th^ ige metabo-S lead to the) it of disrupt of the tem- may be so t -which, the ertain nery- ipplying the at the same ; cells which roportion of as a whole, Ksrei^cm, the I in this oon> rided and its leg are liga- >ls being un- ating occurs of the foot PROTECTIVE AND EXCRETORY FUNCTIONS OP THE SKIN. 417 dilate. 3. If a kitten with divided sciatic, and as a consequence dilated blood-vessels in the corresponding limb, be placed in a warm oven, the other feet will sweat, while the one the nerves going to which have been divided remains dry. 4. Perspira- tion will take place in a cat that has just died under the cir- cumstances mentioned in 1. From these experiments it is clear that nervous influences alone, in the absence of any vas- cular changes, or in the total deprivation of blood, suffice to induce the secretion of perspiration. If the central stump of the divided sciatic be stimulated, sweating of the other Umbs follows, showing that perspiration may bf a reflex act. It is found that stimulation of the periph- eral end of the divided cervical sympathetic leads to sweating on the corresponding side of the face. Kvnui Jhpkiogf. — Certain nerves (e. g., the cervical sym- pathetic) have been stimulated with results similar to those obtained in other animals. We think these experiments and certain pathological phenomena, to be presently mentioned, of importance beyond their immediate application. They seem to show the influence of nerves over vital processes in the clearest way, and render it probable- that this is the essential element in the highest vertebrates, and not the blood-supply, which, though important, is subsidiary. The path of the sweat-nerves is somewhat similar to that of the vaso-mator fibers, running mostly i-a the sympathetic in some part of their course. Whether there is a dominant center in the medulla and subor- dinate ones in the cord is a matter of uncertainty ; though, that the cerebrum can exercise a powerful influence over the sudor- ific glands is evident from the effect of emotions. Certain drugs seem to act on the centers through the blood ; others on either the nerve terminals or the gland-cells them- selves. It is true that some of these will induce sweating after the nerves have been divided, though conclusions as to the nor- tnal action of a part from such experiments must be drawn with the greatest caution. In our opinion they are rather suggest- ive than demonstrative in themselves, and the views we enter- tain of normal function should be formed from h consideration of all the e^'^dence rather than that from a single experiment, however striking in itself. jjfWeating during dyspnoea and from fear, when the cutane- ous surfaces are pale, as well as in the moribund, shows also the independent influence over the sudorific glands of the nerv- ous system. Heat induces sweating by acting both reflexly and II immu mmmmmim 418 ANIMAL PHTSIOLOOT. directly on the sweat-centers we may suppose. Unilateral sweating is known as a pathological as well as experimental phenomenon. Perspiration may be either increased or dimin- ished in paralyzed limbs, according to circumstances. It is possible that there is a paralytic secretion of sweat as of saliva. The subject is very intricate and will be referred to again on aocoimt of the light it throws on metabolic processes generally. Absorption by the skin in man and other mammals is, under natural conditions probably very slight, as would be expected when it is borne in mind that the true skin is covered by sev- eral layers of cells, the outer of which are hardened. Ointments may unquestionably be forced in by rubbing; and perhaps absorption may take place when an animal's tis- sues are starving, and food can not be made available through the usual channels. ItisjCOTtain that ^braded surface s are aj source of danger, from affording^ means of entrance for < CO* f orjgeinaK^ 'stated m works on Oompan^f*. — K is uisually stated m works on physiology that the horse sweats profusely, the ox less so; the pig in the snout ; and the dog, cat, rabbit, rat, and mouse, either not at all or in the feet (between the toes) only. That a closer observa- tion of these animals will convince any one that the latter statements are incorrect, we have no doubt. These animals, it is true, do not perspire aenaMy to any great extent; but to maintain that their akin has no excretory function is an error. Wtmmuj. — ^The skin of the mammal has protective, sensory, respiratory, and excretory functions. The respiratory are in- significant under ordinary circumstances in this group, though well marked in reptiles and especially in batraohians (frog, menobranchus). Sweating is probably dependent on the action of centers situated in the brain and spinal cord, through nerves that run generally in sympathetic tracts during some part of their course. While the functicm of sweating may go on inde- pendently of abundant blood*supply> it ^is usually associated with increased vascularity. Sweat contains a very small quantity of solids, il alkaline in reaction when pure, but liable to be acid f nnn the admixture of sebaceous matter that has undergone decomposition. Sebum onsists chiefly of olein, palmitin, soaps, cholesterin, and ex- tractives of little known composition. The salty taste of the perspiration is due chiefly to sodium chloride, and its smell to volatile fatty acids ; especially is this so of the sweat of certain parts of the body of man and other mammals. ilMIIMilUlMli mimmUiiimik Unilateral perimental L or dimin* aces. It ia 18 of saliTS. to again on s generally, lis is, under be expected red by sev- « »y rubbing; mimal's tis* ble through^ rfaces are &. physiology le pig in the ler not at all Mer observar it the latter le animals, it :tent; but to I is an error, tive, sensory, atory are in- roap, though chians (frog, on the action rough nerves some part of y go on inde> ily associated Is, i« alkaline ihe admixture ition. Sebum erin, and ex- y taste of the id its smell to reat of certain 1 BXCBBTION BT THE KIDNKT. 419 it<:v i i Mfdi n r *mmii>iiN m The functional activity of the skin varies with the tempera- ture, moisture, etc., of the air and certain internal conditions; especially is it important to remember that it is one of a series of excreioi' organs which act in harmony to eliminate the waste OL uhe body, so that when one functions more the other may and usually does function less. The protective function of the skin and its modified epithe- lium (hair, horns, nails, feathers, etc) is in man slight, but very important in many other vertebrates, among which provision against undue loss of temperature is one of the most constant- ly operative, and enables a vast number of groups of animals to adapt successfully to their varying surroundings. EXCRETION BY THE KIDNET. The kidney in man and other mammals may be described as a very complex arrangement of tubes lined witii many different forms of secreting cells, sur- rounded by a great mesh- work of capillaries^ bound together by connective tis- sue, tho quantity varying wifli the animal, and the whole inclosed in a capsula The organ is well supplied with lymphatics and nerves. Though the tubes are so complex, the kidney may be divided into SEOnes which contain mostly but one kind of tubule. Oomparttifs.— Among the lowest forms, the Infuaori- ana and Coeienteraies, ex- cretory organs have not been definitely traced. In the Vermes, organs known as nephridia (segmental or- gans, see Figs. 358, 357) are supposed to act the part of the kidney in some fashion. These ara long, often ooUed 430 ANIMAL PHYSIOLOGY. ttibes lined with cells, and with an internal, cilated, ftumel- shaped extremity opening into the body cavity. In such cnw- nwUc). A. OivlBMiwo(jortteia ij^rtMCfc B. "" . body:«- ; I,J;aw. ooBUBimi- tubw. Sa. BMlioBofaMighttube. »jt««tilftaBi»afeiteitraiiii !'aiii iiii« * ^'w«'--' sd, ftumel- such cms- EXCSBTION BY THE KIDNEY. 4S1 lollMT I manrtMe; S,nw taceans as tho crayfish the green gland is supposed to repre- sent a kidney. It does not open into the body cavity like the preceding and the following form of the organ. It is well sup- plied with capillaries. The organ of Bojanus (Fig. 306) is the tiiMi'i* Fia. an.-Blood^vMMli of MUpiBlalu bodtaa and oomotaiwd *>iili>»S*JiiS!S^i!lSSS!'S£i, main excretory channel in many groups of moUusks. In in- sects the long, coiled Malpighian tubules, which open into the intestine, are believed to secrete both bile and uric acid. Among vertebrates, till the reptiles are reached, the kidney is a persistent Wolffian body, hence its more simple form. ._J iv ANIMAL PHYSIOLOGY. In most fishes the kidney i» a very elongated organ, though in the lowest it consists of little more than tubules, coiling but ►0 slightly, ending by one extrem- ity in a glomerulus and by the other opening into a long com- mon efferent tube or duct. The glomerulus is, however, pecul- iar to the vertebtite kidney. The graded complexity in ar- rangement, etc., of the tubes is *B represented well in the figure below. It is a significant fact that the kidney of the human subject is lobulated in the em- bryo, which condition is persist- ent in some mammals (rumi- nants, etc.). (Ab the lungs are the organs employed especially for the elimination of carbonic anhy- dride, so the kidneys are above all others the exoretors of the nitrogenous waste products of the body chiefly in the form of uric acid or urea. Before treat- ing of secretion by the kidney it will be well to examine into the physical and chemical prop- erties of urine with some detail, especially on account of its great impor^nce in the diagnosis of disease. UbINK CONSIDKBLi) PHYSICALLY AND OHBMICALLY. Urine is naturally a fluid of very variable composition, espe- cially regarded Quantitatively-* fact to be borne m Mnd m considering all statements of the constitution of this fluid. BdmUo flxatitj.— Urine must needs be heavier than water, on account of the large variety of solids it contains. The average specific gravity of the urine for the twenty-f our hours is 1016 to loao. It is lowest in the morning and varies greatly witn the quantity and kind of food eaten, the activity of the lungs and especially of the skin, with emotions, etc. dMribaUon of tubulM at k>dMT(< Hnxlesr). C, corttoal i«Khm ; 0, b« ttj KNie, conUiniiut targe P«* o^rrT. •M the main outsDW tunulaa. IBSiMMl EXCBBTION BY THK KIDNEY. 428 kidney it a, though Is of little filing but ke extrem- ,nd by the long com- iuct. The rer, pecul- » kidney, ity in ar- te tubes is the figure ficant fact he human in the em- L is persist- als (rumi- the organs f for the onic anhy- 1 are above tors of the )roducts of he form of ef ore treat- the kidney mical prop- K>unt of its CALLT. mtion^espe- in inind in Isflmd. an water, on rhe average ours is 1015 ipreatly with )f the lungs dolor.— A light straw color, which is also very variable, being increased in depth either by the presence of an excess of pigment or a diminution of water. There are probably several pigments, among which occur urcbUin, derived probably from bile pigment; urochrome, becoming red on oxidation; and indican, which may be oxidized to indigo. This XMMtlon of human urine is acid, owini; to acid salts, espe- cially acid sodium phosphate (NaH,P04). There is usually but a trifling qvantity, if any, of free acid in the urine when secreted. The acidity diminishes after meals, and the urine may be neutral or alkaline when the food is wholly vegetable, or unduly acid when the diet is entirely fleshy. Qniatlty.— Usually about 1,500 c.c. or from 50 to 52 ounces (two pints) in twenty-four hours. This is, of course, like the specific gravity, highly variable, and frequently they run par- allel with each other. The following tabular statement Will prove useful for refer- ence: QuarUUative Estimation of the CwuiUuenis of the Urine for Tiventy-four flows {after Parkes). Wa,tm Tota^ BolidB. . . Utw Uricaoid Hippario aoid. Creatfnin Pigment, etc. Siuphi man of 66 Una. Ipharie acid . Ph(M|riiorio aoid. ClilonDe Ammonia PotaMium * Sodium Galoium Magnesium FwiklloM body weight. 28-000 11000 •5000 -0064 •0000 •0140 •1510 •0806 •OffiO •IMO Attention is directed more particularly to the preponderance among the solids of urea, and sodium chloride, for the latter is the form in which a large part of the sodium reappears. We may say that in round niunbers about 35 grammes or 600 grains (2 to 3 per vent) of urea are excreted daily. VitnfmoBt OryitaUiM ledlM.— These are the dezivatives of the metabolism of the body, and not in any appreciable degree drawn from the food itself. Besides urea, and of much less MM! 4U ANIMAL PHTSIOLOOT. importance, occarring in small quantities, are bodies that may be regarded as less oxidized forms of nitrogenous metabolism, such as creatinin, xanthin, hypoxauthin (sarkin), hippuric acid, ammonium oxalurate, and urea, C/O^t^g*. The latter was first prepared artificially from ammonium cyanate, ^^ > O, with which it is isomeric. When air has free access to urine for some time in a warm room, the urea becomes ammonium carbonate by hydration, probably owing to the influence of micro-organisms, thus: CO (NH»)i + 2 H,0 s (SUt), COt; hence the strong ammonioal smell of old urine, urinals, etc. Uric acid (CiH4N4(\) occurs sparingly (see table), combined with sodium and ammonium chiefly as acid salt& Since these salts are not so soluble in cold as in warm water, they often fall as a sediment in the vessel in which the urine stands, and present a brick-red or fawn color. Uric acid is itself rather insoluble in cold water or hydro- chloric acid, though soluble in alkalies; hence it may be obtained by adding hydrochloric acid to the urine in the cold. When it is in excess it may separate out on standing, forming characteristic cdorcd (dark-red) crystals, adhering to the sides of the vessel, floating on the top of the urine, or as a sediment at the bottom (like red-pepper grains). V4»<«ttrogiB0U OigaiilD Bo4iM.— Whether traces of sugar are normal in urine is as yet undetermined. Certain acids occur, at least frequently, in small quantities, and combined mostly with bases. Among these are lactic, formic, oxalic, succinic, etc. A series of well-known aromatic bodies occurs in urine, especially in that of the horse, cow, etc. These are phenol, oresol, pyrocatechin, which occur not free, but united with std- phurio acid. \. IiungaaiA lattn — These are mostly in simple solution^ in urine, and not, as in some other fluids of the- body, united with pro- teid bodies. The salts are chlorides, phosphates, sulphates, nitrates, and carbonates, the first three being the most Abun- dant; the bases being sodium, potassium, calcium, magnesium. Since the earthy salts can not remain in solution in an alkaline fluid, they are usually found as a sediment when the urine loses its acid reaction. The phosphates are to be traced to the food, to the phosphorus of proteids, $nd to phosphorized fats (leci- thin). The sulphates are derived from those of the food and from the sulphur of the proteids of the body. So much of the liilwwiiiii tniiiiri I that may etabolism, puric aoid, latter was in a warm hydration, sms, thus: Etmmonical , combined Since these they often itands, and ' or hydro- it may be in the cold, [g, forming bo the sides a sediment f sugar are kcids occur, aed mostly c, succinic, ■s in urine, ure phenol, d with sul* >n^ in urine, d with pro- sulphates, most Abun- nagnesium. an alkaline urine loses to the food, I fats (leci- e food and luch of the EXCRETION BT THE KIDNEY. 498 carbonates as is not derived directly from a corresponding sup- ply in the food may be traced to the oxidation of certain or- ganic salts, as citrates, tartrates, etc. Doubtless mapy bodies appear either regularly or occasion- ally in urine that have so far escaped detection, which are, like the poisonous exhalations of the lungs, not the less important because unknown to science. Abnflimuil Vrint. — ^There is not a substance in the urine that does not vary under disease, while the possible additions act- ually known are legion. These may be derived either from the blood or from the kidneys and other jMtrts of the urinary tract. The kidneys seem to take upon themselves more readily than any other organ the duty of eliminating foreign matters from the body. But this aspect of the subject is too wide for detailed consideration in this work. The student of medicine should be thoroughly familiar with the urine in its normal condition before he enters upon the examination of the variations produced by disease. This is not difficult, and much of it may be carried out with but a meager supply of apparatus. For this purpose,- however, we recommend some work devoted to the chemical and micro- scopic study of the urine. It greatly assists to remember a few points in regard to solubilities. From a physiologici^ point of view, the urine and its variations, as the result of changes in the organism, may be observed with advantage in one's own person— e. g., the influ- ence of food and drink, temperature, emotions, etc. Oompantlt*.— The urine of most vertebrates is of higher spe- cific gravity than that of man. In fishes, reptiles, and birds, uric acid replaces urea, and is very abnndaht. In these animals most of this substance is white. The urine is passed with the f seces. Among mammals the urine of the camivora is strongly acid, perhaps owing in great part to the flesh on which they feed; and abounds in phosphates and, in some instances, sul- phates. The urine is sq concentrated in some cases that we have known urea nitrate to cryktalliae out on the addition of nitric acid without requiring condensation. The urine of the herbivora is alkaline, and abounds in salts of calcium, especially carbonates. It is also of high sjiecific gravity, and grows rapidly dark in color when passed, owing probably tu the presence of the aromatic compounds referred to above, derived from the food. In certain groups of inverte- brates uric acid seems to be a normal excretion. [^Mteiitt^MnMriMtaiM •aoH 4M ANIMAL PHTSIOLOOY. The Skcbbtion of Ubink. Among experimental facts from which important conclu- sions have been drawn are the following (whto blood-pressure within the kidney is referred to, it will be understood that the glomeruli are meant): 1. Section of the spinal cord, which greatly lowers the general blood-pressure, is followed by dimi- nution or total arrest of the secretion of urine. 2. Section of the renal nerves, and to a less extent of the splanchnics de- creases the flow of urine. 3. Stimulation of the spinal cord after section of the above nerves (which raises the blood-press- ure in the kidney by elevating the general blood-pressure) in- creases the flow of urine. 4. Certain diuretics increase the blood-pressure, either generally or in the kidney, while others act on the renal epithelium, apparently independently of blood- pressure. By means of apparatus adapted to register the changes of volume the kidney undergoes, it is found that the kidney not only responds to every general change in blood-pressure, but Tta. kIdMj ; T, tlni»ciirT«, to each heart-beat— that is, its volume varies momentarily. This shows how sensitive it is to variations in blood-pressure. From the above and other experiments it has been concluded that the secretion of urine is largely dependent on blood-press- ure. Until very recently certain experiments (of NusslMium) were considered as favoring the view that the activity of the glomeruli was of a wholly or greatly different character from that of the tubules. In the amphibia (frog, newt, etc.) there is a double renal blood-supply. The glomeruli derive their blood from the renal artery, and the tubules from the renal-portal system. The vein returning the blood from the lower extrem- ity divides (Fig. 331) at the upper part of the thigh into two branches, one of which, entering tiie kidney, breaks up into BXCRBTION BY THE KIDNBT. 4t7 it conolti- l-pressure 1 that the >rd, which I by dimi- Section of chnics de* ;>iiial cord lood-press- essure) in- sreaae the bile others f of blood- changes of kidney not Bssure, but Bnjr). »mentarily. pressure. I concluded ilood-press- IS'ussbaum) vity of the actor from be.) there is their blood ■enal-portal rer extrem- h into two ,ks up into oapillaries around the tubules, which inosculate to some extent with the veseels emerging from the glomeruli It was found that when certain substences were injected into the blood they no longer appeared in the urine after the renal artery had been tied, from which it was concluded that they were secreted only by the glomeruli, and that the blood of the renal-portal vein did not find access to the glomeruli This conclusion was a pretty bold leap, but there was some show of reason for it. More recently, however, these experimente have been demon- strated to be, to a certain extent, unreliable, and that the pas- sage of blood from the venous capillaries backward can really take place, to some extent, after a time. Theories legarding the secretion of urine may be divided into those that are almost wholly mechanical, partly mechani- cal, and purely secretory: 1. To the first class belongs that of Ludwig, which teaches that very diluto urine is separated from the blood in the glomeruli, and by a process of endosmosis and absorption of water by the tubular capillaries is gradually concentrated to the normal. 2. As an example of the second class is that of Bowman, who maintained that the greater part of the water and some of the more soluble and diffusible salte are separated by the glomeruli but the characteristic constituente of the urine by the epithelium of the renal tubules. 8. As an ex^ ample of the third is the theory of Heidenhain, who attributed little to blood-pressure in itself, and much, if not the whole, to the secreting activity of the epithelium of the tubules more par- ticularly. This physiologist showed that while ligature of a vein raised the blood-pressure within a glomerulus, it was not followed by any increase in the quantity of the secretion, but by ite actual arrest He also showed that injection of a colored substance (sodium sulphindigodate) into the blood, after the pressure had been greatly lowered by section of the spintd cord, led to ite appearance in the urine ; and microscopic exam- ination showed that it had passed through the epithelial cells of the tubules, not of the glomeruli It is found, however, that after the removal of a ligature applied to the renal artery the urine is albuminous, showing that the cells have been plainly injured by the operation ; hence Heidenhain's experiment described above is not valid against the blood-pressure theory. Moreover, too much must not be inferred from the action of foreign substances under the ab- normal conditions of such an experiment, t While some physi- ologists claim that the glomeruli are filtering mechanisms, they 4S8 ANIMAL PHTSIOLOOr. |\. explain that filtration is not to be und^ir i -ju Iii itS ordinary laboratory acceptation, but that the glonu .;' ''>.c:riminate as to what they allow to pam, yet they in ) ray explain how this is done. They make the whole process depend ou blood- pressnre, and attribute little special action to the flat epithe- lium of the Malpighian capsules. Though we can not admit the full force of Heidenhain's ex- periments as he interprets them, we still believe that his views are most in harmony with the general laws of biology and the special facts of renal secretion. Recently, after a repetition of Nussbaum's experiments, and the institution of others, it has been rendered clear that the mechanical theory of the work of the kidney can not hold, even of the glomeruli, which are shown to be, as we should have expected, true secreting organs. Now, there can be no doubt that blood-pressure is a most im- portant determining condition here as in other secreting pro- cesses, in the mammal at all events ; but whether of itself or because of the influence it has on the rapidity of blood-flow, it is difficult to determine ; or rather whether solely to the latter, for that the constant supply of fresh blood is a regular con- dition of normal secretion there can be no doubt. Further, it seems probable that blood-pressure has more to do with the secretion of water than any other constituent of urine. But we maintain that it shotild be called a genuine secretion, and that nothing is gained by using the term *' filtration "—on the contrary, that it is misleading, and tends to divert attention from the real though often hidden nature of vital processes. The facts of disease and the evidence of therapeutics, we think, all favor such a view of the work of the kidneys. (iTerves having an influence over the secretion of urine simi- lar to those acting on the digestive glands have not yet been determined. The powerful influence of emotion, especially in those of unstable nervous system, over the secretion of urine shows that there must be nervous channels tiirough which the nerve-centers act on the kidneys ; though whether the results are not wholly dependent upon vaso-motor effects may' be con- sidered as an open question by many. We think such a view improbable in the highest degree. The most recent investiga- tions would seem to show that the vaso-motor fibers run in the dorsal nerves, especially the eleventh, twelfth, and thirteenth, and that cc these the vaso-constrictors are the hesL developed. PttihskgioaL — ^When the kidneys are excised, the ureters ligatured, or when the former are so diseased as to be inca- MM EXCRETION BY THE KIDNEY. 499 B ordinary iminate as plain how on blood- lat epithe- ihain's ex- ; his views ly and the petition of lers, it has lie work of which are ng organs. k most im- reting pro- >f itself or [)od-flow, it I the latter, tgnlar con- Further, it [o with the irine. But iretion, and a"— on the t attention [ processes. }, we think, urine simi- )t yet been specially in m of urine L which the the results aay'be con- luch a view k investiga- 1 run in the thirteenth, leveloped. the xireters to be inca- pable of performing their functions, death is the result, being preceded by marked depression of the brain-centers passing into coma. Elxactly which of the retained products brings about these results is not known. They are likely due to sev- eral, and it impresses on the mind the importance of those processes by which the constantly accumulating waste is elimi- nated. Uric acid when not removed from the blood and tissues is supposed to be the exciting cause of gout. An excess in the ) f5rm of urates retained or deposited in certain parts, especially ( the joints, is frequently at all events an accompaniment of this ) disease. Thk Expulsion or Urine. We now present in concise form certain facts on which to base opinions as to the nature of the processes by which the bladder is emptied. It will be borne in mind that the secretion of urine is con- stant, though of course very variable; that the urine is con- veyed in minute quantities by rhythmically contractile tubes (ureters) which open into the bladder obliquely ;• and that the bladder itself is highly muscular, the cells being arranged both circularly and obliquely, with a special accumulation of the circular fibers around the neck of the organ to form the sphinc- ter vesica. 1. It is found that the pressure which the sphincter of the bladder can withstand in the dead is much less (about one third) than in the living subject. 2. We are conscious of being able to empty the bladder, whether it contains much or little fluid. 3. We are equally conscious of an urgency to evacuation of the vesical contents, according to the fullness of the organ, the quality of the urine, and a variety of other conditions. 4. Emotions may either retard or render micturition urgent. 5. In a dog, in which the cord has been divided in the dorsal region some months previously, micturition may be induced reflexly, as by sponging the anus. 6. In the paralyzed there may be retention or dribbling of urine. 7. In cases of urethral obstruction from a calculus, stricture, etc.-, there may be excess- ive activity of the muscular tissue of the bladder-walls. 8. Evacuation of the bladder may occur in the absence of con- sciousness (sleep). The most obvious conclusions from these facts are that-^1. The urine finds its way to the bladder partly through muscular (peristaltic) contractions of the ureters, partly through gravity, 480 ANIMAL PHYSIOLOGY. \ in man at all events, and partly from tlie pressure within the tubules of the kidneys themselves. 2. The evacuation of urine may take place independently of the will (see 8), and is a reflex (5) act. 3. Micturition may be initiated by the will, which is usually the case, when by the action of the abdominal muscles a little urine is squeezed into the urethra, upon which afferent impulses set up contractions of the bladder by acting on the detrusor center of the cord and at the same time inhibit the center presiding over the sphincter (if such there be), permit- ting of its relaxation. 4. Emotions seem to interfere with the ordinary control of the brain-centers over those in the spinal cord. S. It may be assumed that the normal tone of the sphincter of the bladder is maintained reflexly by the spinal cord. The unwonted muscular contraction associated with an obstruction to the outflow of urine may be in part of nervous origin, but is also, in all probability, owing in some degree to the muscle-cells resuming an independent contrac^lity, due to what we recogniafe as the principle of reversion. The same is seen in the heart, ureters, and similar structures. Fafhokgiml. — ^There may be incontinence of urine from pa- ralysis, the cerebral ccr.tbxtt being unable to control those in the spinal cord. Dribbling of urine may be due to retention in the first instance, the tone of the sphincter being finally over- come, owing to increase of pressure within the bladder. Over- distention of the bladder may arise in. consequence of lack of tone in the muscular walls, though this is rare. Strangury is due to excessive aoticm of the walls of the bladder and the sphincter, brought about reflexly, when the organ is unduly irritable, as in inflammation, after the abuse of certain drugs (cantharides), etc. Oaaptntit*. — In man the last drops of urine are expelled by the action of the bulbo-oavemosus muscle and perhaps some others. In the dog and many other animals the regulated and voluntary use of this muscle, marked in a high degree^ produces that interrupted flow so characteristic of the micturition of these animals. IttUMtfy.-— Urine is in man a fluid of speoiflc gravity 1010 to 1020, acid in reaction, pale yellow in color, and containing certain saltu, pigments, and nitrogenous bodies. The chief of the latter is urea, which is excreted daily to the extent of about one ounce (800 grains). The kidneys and skin especially supplement one anothe^ fmd normally great activity of the one implies lessened acfj IM i llUMMi MMMMMIil vithin the a. of urine is a reflex which is muscles h afferent ag on the ihibit the ), permit- e with the the spinal ne of the the spinal d with an >f nervous ) degree to ity, due to be same is i from pa- il those in atention in nally over- ler. Over- of lack of 'rangury is ar and the is unduly tain drugs )xpelled by haps some ulated and e^ produces tnrition of ravity lOlS containiug he chief of at of about le anotheM MBsened ac^ THE METABOLISM OF THE BODT. 481 tivity of the other. This is availed of in the treatment of dis- Both the Malpighian capsules and the renal tubules have a true secretory function, though the larger part of the water of urine is secreted by the former. Blood-pressure is an important condition of E.ecretion, though it is likely that this is so chiefly because it favors a rapid renewal of the blood circulating through the organ. Whether there are nerves that influence^ secretion directly, as in the case of the skin, is not determined/ /Suppression of the renal functions leads to symptoms in wMch the nervous system is recognized as suffering to the extent ofteiL fif coma, ending in dejath. The urine of most other animals is more concentrated than that of man ; this secretion in carnivora being acid, and in herluvora alkaline in reaction when passed a short time. Out* iuformatioi- in regard to the kidneys has been derived experimentally chiefly from the study of the frog and a few of the domesticated mammals, especiallv the dog ; and as regards some points of interest, so far as imne is concerned, from, the bird (guano), and the horse, ox (aromatic compounds), etc. Man's urine has been thoroughly studied ; but the nature of > the act of renel secretion is in his case a matter of inference] from the facts of pathology, clinical medicine, therapeutics, etc. ) THE METABOLIBM OF THE BODT. In the widest sense the term metaboliem may be conven- iently applied to all the numerous changes of a chemical kind, resulting from the activity of the protoplasm of any tissue or organ. In a more restricted meaning it is confined to changes tmdergone by the food from the time it enters till it leaves the body, iu. so far as these are not the result of obvious mechani- cal causes. The sense in which it is employed in the present chapter will be plain from the context, though usually we shall be concerned with those changes effected in the as yet compara- tively unprepared products of digestion, by which they are ele- ' vated to a higher rank and brought some siepa nearer to the final goal toward which they have been tending from the first. As yet our attempts to trace out these steps Lave been little"^ better than the fruitless efforts of a lost traveler u> find a road,) the general direction of which he knows, but the ways by which j it is reached only the subject of plausible conjecture. But/ mmt 482 ANIMAL PHYSIOLOOT. any theories that, like a scaffolding, allow of or help to addi- tional investigation, and in any way lead out into a clearer light, are not without value ; and on this principle we shall treat the subject, spending but little time in barren fields except as they have an interest from the suggestiveness of the results, even though negative. ^ The Metabolism ov the Liybb. This organ has two well-recognized functions : 1. The for- mation of bile. 2. The formation of glycogen. We have already considered the first, and ascertained how little is positively known. Let us now examine the second. Glycogen may be obtained from the liver of mammals, such as the rabbit, by rapidly killing the animal, excising the warm still living organ, cutting into fine pieces, throwing them into boiling water, removing after a few minutes and grinding in a mortar and reimmersing in the boiling water ; on now passing the latter through a coarse filter a turbid, ^t^it ish fluid is ob- tained containing the extracted glycfii^^s proved by giving a red color with solution of iodine. The substance may be ob- tained as a whitish amorphous powder, having the chemical com- position of stArch, and has in fact been termed animal starc h. By appropxiate treatment it may be converted into^ugu^by a process of hydration (CtHwO* + HfO = OtHitOi). If, after the death of an animal, the liver be kept at body temperature for, say, an hour, very little glycogen can be recov- ered from it, but instead abundance^ of sugar. These facts sug- gest that the sugar present represents the original glycogen, and that the converniun has been effected by some ferment, which does not act during life, though why no< is one of the"^ problems ranking with the non-digestion of the stomach by its/ own ferments, etc. We have already expressed our doubts as to the justifia- bility of resorting to so many " ferments " to explaiu the facts of physiology, and in the present case there is another possible view of the ntatter. It is conceivable that the conversion, under these circumstances, of the glycogen into sugar, may be an act of the dying protoplasm of the liver-cells ; and there are experimental results which tend to strengthen such a view. The prir^ciiMtl facts an to the storage of glycogen in the liver may be briefly stated tlius : 1. Glycogen has been found in the liver of a laurge number m^ lammk^ p to addi- a clearer I we shall Ten fields Less of the . The for- aihed how lecond. mals, such ; the warm them into inding in a )w passing luid isob- by giving may be ob- mical com- al starc h. bo(sug^A>y jpt at body ,n be recov- 9 facts sug- 1 glycogen, le ferment, one of the nach by i^ he justifia- Lu the facts ler possible conversion, jfar, may be id there are a view, in the liver pge number THE METABOLISM OF THE BODY. 483 of groups of animals including some invertebrates. 2. Among mammals it is most abundant when the animal feeds largely on carbohydTates. 3. It is found in the liver of the camivora, and in those of omnivora, when feeding exclusively on flesh. 4. When an animal starves (does not feed), the glycogen grad- ually disappears. 5. A fat-diet does not give rise to glycogen. 6. During early foetal life glycogen is found in all the tissues, but later it is restricted more and more to the liver, though even in adults it is to be found in various tissues, especially the muscles, from which it is almost never absent. From the facts the inference is plain that glycogen is formed from carbohydrate materials ; or, to be rather more cautious, that the formation of this substance is dependent on the pres- ence of such material in the food. Inasmuch as glycogen oc- curs in muscle, it does not follow, from the fact of its presence in the liver of carnivorous animals, that it is manufactured from proteid substances, though this is not more difficult to understand chemically than the formation of fat from this source which is well established. ^ -Starch, it is well known, occurs abundantly in- plants, and %ere is no doubt that the sugar often present in abundance has starch as its antecedent, and vice versa. Analogy, then, points .to such a relation between carbohydrate food and glycogen for- mation on the one hand, and reconversion of glycogen into sugar on the other. And recent investigations tend to show that plant metabolism bears a greater resemblance to that of animals than was till recently supposed, thus giving greater force to the argument from analogy, though this ie recognized as fl^^nerally a dangerous one. Assuming this relation between food-stuffs and glycogen to hold, the question arises. How is the substance formed by the liver ? There are three conceivable methods : 1. The liver-cells may, we know not how, simply dehydrate the sugar of diges- tion as carried to them in the portal blood. 2. The cells may manufacture glycogen from their own protoplasm, in which process the portal sugar is in some way used. 3. The liver-cells may always he engaged in the construction of glycogen as the gastric cells of pepeinogen, but the accumulation or removal of the substanbd depends on the oluuraoter of the food especially ; thus, if the latter abounds in carbohydrates, the blood will be well supplied with sugar, so that the glycogen need not undergo its usual conversion into that substance. None of these views, haaJtweo^definitely proved to be the correct one. MUMfea iTijinl Ar ilJ^T'irili, iiiin-rli^Vttrr 484 ANIMAL PHYSIOLOGY. TIm Vim of Olyoogen.— Whether the blood of the hepatic vein contains more sugar than that of the portal vein has long been a subject of controversy. If the affirmative could be established, it would be pretty clear that glycogen stored in the liver-cells was transformed into sugar, possibly by a process of hydration. But, considering the rapidity of the blood-stream, it is easy to understand that a large amount of sugar might be conveyed IfiXnMIMNNlnMft JM0Maicrfeie Vena &paUn Xivmph- dloiKl Lymphatle BUnivemOtttmueab, IvavMpaeef AUmentary Uraet Fio. 88B.— Diagnun intendad to iUiatrate the seneral r«l«tian« of blood and lymph to milab- oUam (nutriUoii) : and the method hy wUcti Uie portal, Ijmphatic, and seneral Tenoaa ■yatema are related to the allmwiHiy traet. into the general circulation, and yet the blood, whether of the hepatic vein or of other parts, contain but a small quantity at any one time. The blood is kept of a certain fairly constant composition, both by the action of the excreting organs and by the withdrawal from it of supplies for the tissues. Moreover, that correlation of functional work on which we have already insisted, is not to be forgotten. One must not conceive of the liver-cells or any others doing their work independently of the condition of their fellow cell-units in the organic common- wealth. We mean to say rhat the amount of glycogen trans- formed to sugar will depend on a great many circumstances outside of the liver itself. Such aspects of the case have been rather overlooked. According to uiother theory, glycogen is an intermediate product between sugar and fat, but of this there is very little evidence indeed ; and, besides, fat formation is otherwise well enough accounted for, thouf'h, of course, too much stress must not be laid upon such an argcvnei ^. jWhat is the fate of the transformed glycogen ? What be- (^mes of the sugar ? We can answer, negatively, that it is not jDBHiriaWiiii m 1 THE METABOLISM OP THE BODY. 485 vpatic vein long been stablished, liver-cells txydration. lis easy to conveyed t, (((MM ecO*, MS lymph to iii<wer line iMUoMiBa ttme maridnca. It is known that this constituent of the urine is increased in intermittent fever (ague), in which disease the spleen is often' greatly enlarged. The vascular engorgement and the height- ened metabolism of the spleen seem to be associated ; and the fact that the uric-acid diathesis is often intensified if not origi- nated by overfeeding, suggests a connection between the spleen and the digestive system at all event& Much as there is that^ remains obscure, we think it can not be doubted, on the evi- ( dence furnished, that the spleen must serve some very impor-( tant purpose in the economy, apart from its relations to the/ blood, noticed in an earlier chapter. CJhe dominion of the nervous system over tiie spleen is evi- dent from various facts. The spleen may be diminished in size either generally by the stimulation of the vagus or splanchnic nerves directly, or reflexly through stimulation of one of the afferent nerves ; and, locally, by direct application of the elec- trodes to the surface of the organ. .Stimulation of the medulla itself also leads to contraction of the organ. It would seem that not only the arteries but the organ as a whole is main- tained in a state of tonic contraction to a certain extent by the agency of the nervous system. Not only so, but, if we may judge from the analogy of other organs, we may believe that its metabolism is directly controlled by the nervous system. ^^ rf.,>k-ytW 440 ANIMAL PHYSIOLOGY. The Construction op Fat. It is a well-known fact that, speaking generally, a diet rich in carbohydrates favors fat formation, both in man and other animals ; though it is not to be forgotten that many persons seem to be unable to digest such food, or, c.t all events, to as- similate it so as to 'form fat to any great extent. Persous given to excessive fat production are as frequently as not sparing users of fat itself. It is possible in man and probable in ruminants that fer- mentations may occur in the intestines giving rise to fatty acids which are possibly converted into fats by the cells of the villi or elsewhere. Certain feeding experiments favor the view that carbohydrates may be converted into fat or in some way give rise to an increase in this substance ; for it is to be borne in mind that fat may arise from a certain diet in various ways other than its direct transformation into this substance itself. There are certain facts that make it clear that fat can be .formed from proteids : 1. A cow will produce more butter than can be accounted for by the fat in her food alone. 2. A bitch which had been fe<1 on meat produced more fat in her milk than could have been derived directly from her food, and this, when the animal was gaining in weight, which is usually to be traced to the addition of fat ; so that the fat of the milk was not, in all probability, derived from that of the dog's body; and, as will be seen presently, can be accounted for without such a supposition. 3. It has been shown by analysis that 472 parts of fat were deposited in the body of a pig for evOTv 100 in its food. rTnese facts of themselves su£Bce to show that fat can be fonned from proteid, or at least that proteid food can of itself give rise to a metabolism, resulting in fat formation ; and the latter is probably the better way to state the case in the present condition of knowledge. An examination of the percentage composition of proteid and urea renders a possible construction of fat from proteid conceivable and in harmony with other better known physi- ological facts. Outon. Hydrosaa Nttrasen. Oiyiieii. Snl^ilMir. Proteid 5SO0 7-80 15*58 88-04 M8 Uiwi aMK) 6-66 48-«7 a«-67 It will be seen that, if we assume that the urea discharged represents the whole of the nitrogen that passes through the a diet rich . and other ny persons ents, to as- •so us given V ot sparingj ;s that fer- fatty acids of the villi le view that le way give )e home in rious ways ^nce itself. fat can he butter than 2. A bitch B her milk >d, and this, 3 usually to ot the milk f the dog's counted for by analysis of a pig for I fat can be can of itself on; and the 1 the present a. of proteid rom proteid aown physi- i8-04 a discharged through the THE METABOLISM OP THE BODY. 441 body, there would remain for disposal otherwise a large amount of carbon, for there is nearly three times as much of this ele- ment in proteid as in urea; so that it is possible, from a chemi- cal point of view, to understand the origin of fat from the pro- teid food ; but too much importance must not be attached to such speculations. (That fat is a real formation, dependent for its composition on the work of living tissues, is clear from the well-known fact that the fat of one animal differs from that of another, and that it preserves its identity, no matter what the food may be, or in what form fat itself may be provided. Certain constituents of the animal's fat may be wholly absent from the fat of its food, yet they appear just the same in the fat produced under such diet. Even bees can construct their wax from proteid, or use unlike substances, as sealing-wax. But histological examination of forming adipose tissue itself throws much light upon t} jject Fat-«ells are those in which the protoplasm has buuu largely replaced by fat. The latter is seen to arise in the former as very smedl glohules vUl \* Ite. 184.— KMiuBMr rUimI of huniMi femftto (ptter li6gMlm\ 1, rinflK, or dilatation of one at lacttftoroDi duota ; S, extnmitiM ct the duels ; 8, lobuka of glaiid ; 4, nipple, retracted to cartar; i,»niM. :^£&,y^^smiaiSi,ismm^ii^^s^mmS!is^mKMmmsi^^^mm>m mm ftmS^fii^rf^W^^^ 441 ANIMAL PHYSIOLT'Cr. which run together more and more till they may wholly re- place the original protoplasm. The history of the mammary gland is, perhaps, still more instructive. In this case, the appearance of the cells during lactation and at other periods is entirely different. Fat may Via. BIB.— Sectloa of mammur glaaA (oMer «a4-i Be of gland; JV, nlpiiM; A, adnt of gta_ folds In wide mllk-duoti; A, wotioa of ^hiMtar milk-duct in nipple. ,j)o<«oir (after TliaiilMaBr). lfii,Mil>> X m.4, nilk-diKte ; C, milk-oifltemi ; /, ; «, exteriMl lUn ; It. m. d, narroir he seen to arise within these cells and be extruded, perhaps in the same way as an Amoeba gets rid of the waste of its food. So far as the animal is conoemed, milk is an excretion in ar limited sense. m perhaps in if its f dod. etion in a l i» iii .. .i Ljj.,j i »j7; ?%»g j<;.j!; i i^ i !^iV! !! »;ji^ii * «^ ' "''"i ' *._f^j m !■■ . ! L 'i . ' . •r' ' '' M ';> .. ..v '^ "'- ' . V " ' w. ' . ' . 'rr*'*— '•*•"';'■'■'■' ',■ yv-' IMAGE EVALUATION TEST TARGET (MT-3) ^ ^ 1.0 1.1 1^121 ■2.5 122 ^^ ■■■ ■tt Itt 12.2 •^ |£0 12.0 |g5 |U, MI.6 -^ Photographic Sdenoes Carporation ^ as WKT MAM STRMT WIISTIt,N.V. 14SM (71«)t7a-4S0S ^^-^^X KMKI iMlili •^^Kanif CIHM/ICMH Microfiche Series. CIHIVI/ICIVIH Collection de microfiches. Canadian Inatituta for Historical IMicroraproductions / Inttitut Canadian da microraproductions historiquas rr L i a»a^aM#3«afl^^rf»s5iy4«igis»^^ THE METABOLISM OP THE BODY. 443 It is, in the nature of the case, impossible to follow with the eye the formation and separation of milk-sugar, casein, etc. Fio. m.— I. Adnw from nuunma of * Mtch irtieii iBBcUve (after Beidenliain). n. DuHng MoreUoa ot milk, a, b, mUk-^obules ; e, d, «, cokNtrum-corpuaclM ; /, pale cella. But the whole process is plainly the work of the cells, and in no mechanical sense a mere deposition of fat, etc., from the blood; and the same view applies to the construction of fat by connective (adipose) tissue. Fw. Mr. r». 888. r». 88i'.-BamMi milk-RlolmlM, from « hMltby I]ria«-genou8. We e species and to which one lation (excre- 3king to pre- tre important purposes are probably served, as will appear from later consid- erations. PathologiML— Corpulence, or excessive fat formation, leading to the hampering of respiration, the action of the muscles, and, to a certain extent, many other functions of the body, does not arise usually till after middle life, when the organism has seen its best day& It seems to indicate, if we judge by the frequency of fatty degeneration after disease, that the proto- plasm stops short of its best metabolism, and becomes de- graded to a lower rank; for certainly adipose tissue does not occupy a high place in the histological scAle. Many persons given to excessive fat formation are fond of saccharine and amylaceous foods; but the fact that, under the strictest diet, the abnormality can be but moderately controlled, shows that the main point is, the existence of. the habit of certain cells naturally to form fat, which, in disease, becomes exaggerated, or is taken up by others that normally have little share in such work. Such pathological facts throw a good deal of light upon the general nature of fat excretion, as it would be better to term it, perhaps, and seem to warrant the view that we have presented of the metabolic-processes. yLlthough the nerves governing the secretion of milk have not been traced, there can be no doubt that the nervous system controls this gland also. The influence of the emotions on both the quantity and quality of the milk in the human subject and in lower animals is well known. There seems to be no doubt that milk of an injurious if not absolutely poisonous character may be formed under the influence of depressing or unusually exciting emotions, as grief, rage, etc. We know less about the influence of the nervous system in fat formation elsewhere, though it is well enough established that personsjpfow thin under worr y as w ell as excessive mentaland physical exertion. XnTiffie lattefoase, itis not improbable that the bverwbrlced muscles may draw, in some way, on the stored fat. At the same time, fat formation may be interfered with, and be an ex- pression of the unnatural conditions generally that have been established. Such cases mre too complex to permit of being completely unraveledT"- — Ow^anliv*.— While breeders recognize certain foods as tending to fat formation and others to milk production, it is interesting to note that their experience shows that race and individuality, even on the male side, tell. The same conditions being in all respects observed, one breed of' cows gives more !ia3srssr:'T!?sT?mCT'tH??M!»ws^^ t.p i IWWI 'mmmmm 446 ANIMAL PHYSIOLOGY. f and better milk than another, and the bull is himself able to { transmit this peculiarity ; for, when crossed with other breeds, ■ he improves the milking qualities of the latter. Individual \ differences are also well known. N The Metabouc Procbssbs concerned in the Formation OP Urea, Uttic Acid, Hippurio Acid, and Allied Bodies. Creatin is represented by the formula C«HtNiOt, and crea- tinin by C«H,N,0— that is, the latter may be regarded as the firmer dehydrated. Creatinin occurs, as we have seen, in urine, and the question arises. Is the creatin of muscle the antecedent of the creatinin of urine? Creatin when injected into the blood reappears as creatinin in the urine ; but the latter sub- stance is not increased by exercise, though the creatin of the muscles is, while, like urea, creatin is augmented by a proteid (flesh) diet. It is not clear, then, that the creatin of muscle has any definite relation to the creatinin of urine. But crea- tin occurs not only in muscle, but in a variety of other tis- sues, including the nervous; in fact, it maybe regarded as one of the products of proteid metabolism. Putting these facts along with the absence of urea itself from muscle and many other tissues, there is some probability in the view that creatin is one of the aptecedents of urea; possibly it is one of the products which the kidneys directly convert into urea. There are several facts which i>oint to the liver as being the seat of urea formation: 1. Leucin, when taken in large quantities, reappears in the urine as urea, or, at all events, is followed by an increase in the excretion of urea by the kid- neys. 2. In certain diseases of the liver (acute atrophy) urea is largely replaced in the urine by leucin and tyrosin. Now, since the consumption of much proteid matter is soon fol- lowed by an excess of urea in the urine, and since in such cases it is likely that a good deal of leucin and it& compan- ion, tyrosin, are formed in the digestive tract, which we may suppose are carried directly by the portal blood to the liver, the conclusion has been drawn from this and the facts just mentioned, as well as others, that the Jiver^isjk fwrner^ (urea. , "^ nself able to other breeds, Individual Formation iND Allied Oi, and crea> arded as the een, in urine, le antecedent ;ted into the le latter sub- reatin of the by a proteid in of muscle e. But crea- of other tis- » regarded as Putting these 1 muscle and in the view possibly it is convert into iver as being iken in large ; all events, is i by the kid- itrophy) urea rrosin. Now, r is soon f ol- since in such i it& oompan- •hich we may to the liver, the facts just ) a former of THE METABOLISM OF THE BODY. Urea may be prepared artificially, as represented by the f ol lowing equations : 1. ^^dy is a stage I, since it re- it this is not in the urine, them is very le very great- ;apacity, uric rine, and not ence by man 1 in quantity, ions of urates / lit of proteid 1 the outcome physiological ^cal evidence *ion between ;tional resem- different in izcessive pro- inderstood in lown that this tx>lic habit of i to offspring, c acid may be 3 acid may be as: •^ + H,0. Id. 1 is swallowed it is said that THE METABOLISM OP THE BODY. 449 when blood containing benzoic acid is mixed with fresh minced kidney it is transformed to hippuric acid. Hay contains a ben- zoic compound, so that it is not diflBcult to find a starting-point for the hippuric acid of the herbivora. In these instances it is assumed that glycin is added in the kidneys ; but, as a matter of fact, this substance has not as yet been found anywhere in the body, though it is possible to conceive that, like peptone, it might be formed and disappear (be used) as fast as gen- erated. (The above is one of the clearest cases favoring the view that the chemical processes of the body do really very much resem- ble those of the laboratory. But, considering the difficulty as to glycin, and that the liver also can form hippuric acid under similar circumstances (those mentioned above), and that there are several laboratory methods for the synthesis of hippuric acid, it behooves us to be cautious even in this case, the chain of facts being by no means complete. Pt the origin of the allied bodies— xanthin, etc.— or their fate and purpose, we know very little. Their resemblance chemically to certain alkaloids in tea, coffee, etc., is suggestive. Are they natural stimulantj ? The Study of the Metabolic Processes by other Methods. (it will be abundantly evident that our attempts to follow the changes which the food undergoes from the time of its introduction into the blood until it is removed in altered form from the body has not been as yet attended with great success. It is possible to establish relations between the ingesta and the egesta, or the income and output w!; ch have a certain value. It is important, however, to remeu; ■ k-v that, when quantitive estimations have to be made, a small exror in the data becomes a large error in the final estimate; one uptrue assumption may vitiate completely all the conclusions. In discussing the subject we shall introduce h number of tables, but it will be remembered that the results obtained by one investigator differ from those obtained by another; and that in all of them there are some deviations from strict ac- curacy, so that the results must be regarded as only approxi- mately correct. It is, however, we think, better to examine such statistical tables of Mialyses, etc., than to rely on the mere verbal statement of certain results, as it leaves mote i9 litlUUJMWIIWIH I r= ;■ 460 ANIMAL PHTSIOLOOr. room for individual judgment and the assimilation of such ideas as they may suggest outside of the subject in hand. The subject of diet is a very large one ; but it will be evi- dent on reflection that, before an average diet can be prescribed on any scientific grounds, the composition of the body and the nature of those processes on which nutrition generally depends must be known. Not a little may be learned by an examination of the behavior of the body in the absence of all diet, when it may be said to feed on itself, one tissue sup- plying another. All starving animals are in the nature of the case carnivorous. Composition of the Mammalian Body. Adult man. New-bom child. Skeleton Muscles. 18-9 41-8 1-7 7-3 18-2 GO ID 17-7 22-9 Thoracic viscera Abdominal viscera. 11-5 Pat I 20-0 16-8 Skin Brain ■^ I- \ For the cat an analysis has yielded the following : Muscle and tendons 45*0 per cent. Bones 147 " Skin 120 ** Mesentery and adipose tissue 8*8 ** Liver 48 ** Blood (escaping at death) 6'0 '* Other organs and tissues 137 *' The large proportional weight of the muscles, the similarly large amount of blood they receive, which is striking in the case of the liver, also ciuggest that the metabolism of these structures is very active, and we should expect that they would lose greatly during a starvation period. It is a matter of common observation that animals do lose weight' and grow thin under such circumstances, which means that they must lose in the muscles and the adipose tissue. Attempts have been made to determine exactly the extent to which the various tissues do suffer during complete abstinence from food, and this may be gathered from l^e table given below. ■tarfalUm. — A cat weighing 3,464 grammes lost before deatii on the eight^nth day 1,197 grammes in weight. Of this about IvlC on of such hand. will be evi- 9 prescribed e body and n generally rned by an )sence of all I tissue sup- lature of the Mevr-born child. 17-7 22« 8-0 11-5 |2(M) 15-8 ) per cent. r " r " the similarly iriking in the liism of these 3ct that they It is a matter ght'and grow lat they must upts have been 5h the various rom food, and r. Bt before death Of this about THE METABOLISM OF THE BODY. 451 204 grammes (17 per cent) was in albuminous matter; 132 grammes (11 per cent) loss of fat ; 863 grammes loss of water, 71 per cent of the total body weight. It will not be forgotten that about three fourths of the body is made up of water, so that the loss of so large an amount of the latter during starvation is not wholly inexpli- cable. In the case of another cat during a starvation period of thir- teen days 734 grammes of solids were lost, of which 248 grammes were fat and 118 muscle — ^i. e., about one half of the total loss was referable to these two tissues alone. The other tissues lost as follows, estimated as dry solids : Adipose tissue 97*0 per cent. Spleen 631 ** Liver 56-6 " Muscles 30-2 Blood 17-6 " Brain and spinal cord 0*0 " It will be observed (a) that the loss of the fatty tissue was greatest, nearly all disappearing ; {b) that the glandular struct- ures were next in order the greatest sufferers; (c) that after them come the skeletal muscles. Now, it has been already seen that these tissues all engage in an active metabolism with the exception of adipose tis- sue. The small loss on the part of the heart, which is still less for the nervous system, is especially noteworthy. Two ex- planations are possible. On the one hand, we may suppose that their metabolism is active, but that they feed in some sense on the other tissues, and thus preserve themselves from loss of substance. But, again, we have seen that the functional activity of the nervous system is not accompanied by any very marked chemical phenomena that we have succeeded in detect- ing, at all events; and litjtle is known of the_metab olism_or tha heart itse^ . Do its pulsations fromlong habit go on with little expenditure of energy, as is the case with the automatic workman engaged in. a narrow round of duty ? Has the nerv- ous system in the course of its evolution acquired the power of accomplishing much, like persons with special aptitudes, with little loss of energy ? It is not possible to decide exactly what share these sevend factors may take ; though that they all and others as yet unrecognized do share in the general result seems probable. The loss of adipose tissue is so striking i ':ss s>¥.»fv> ' ii'«aXumxM'mMM!Sm!mm'mAV^ 453 ANIMAL PHTSIOLOOT. V that we must regard it as an especially valuable storehouse of energy, available as required. When we turn to the urine for information, it is found that in the above case 27 grammes of nitrogen were excreted and almost entirely, of course, in the form of urea ; and since the loss of nitrogen from the muscles amounted to 15 grammes, it will appear that more than one half of the nitrogenous excreta is traceable to the metabolism of muscular tissue. It has been customary to account for the urea in two ways : first, as derived from the metabolism of the tissues as such, and continuously throughout the whole starvation period ; and, secondly, from a stored surplus of proteid which was assumed to be used up rapidly during the early days of the fasting, and was the liutti8 consumption of certain investigators. OompMratiT*. — Experiment has shown that the length of time during which different groups of animals can endure com- plete withdrawal of food is very variable, and this applies to individuals as well as species. That such differences hold for the human subject is well illustrated by the history of the sur- vivors of wrecks. Making great allowances for such devia- tions from any such results as can be established by a limited number of experiments, it may be stated that the human being succumbs in from twenty-one to twenty-four days; dogs in good condition at the outset in from twenty-eight to thirty days; small m.ammals and birds in nine days, and frogs in nine months. ^Very much depends on whether water is allowed or not — ^lif e lasting much longer in the former case. The very young and the very old yield sooner than persons of middle age. It has been estimated that strong adults die when they lose ^ of the body weight. Well-fed animals lose weight more rapidly at first than afterward. Diet.— ^11 experiments and observations tend to show that an animal can not remain in health for any considerable period without having in its food proteids, fats, carbohydrates, and salt« ; indeed, sooner or later deprivation of any one of these will result in death. Estimates based on many observations have been made of the proportion in which these substances should enter into a normal diet. In the nature of the case, for a creature like man especially, whose adaptive power is so great that he can learn to live under a greater variety of conditions than any other animal, any figures on this subject must be interpreted as being but a very general statement of the case. WUhJ- THE METABOLISM OF THE BODY. 453 rehouse of found that jreted and 1 since the rammes, it JUS excreta [t has been as derived •ntinuously dly, from a be used up IB the luxiis > length of endure com- s applies to ceshold for Y of the sur- Buch devia- by a limited luman being ys; dogs in ht to thirty md frogs in «r is allowed e. The very tis of middle ie when they lose weight to show that erable period lydrates, and one of these been made of I enter into a creature like it that he can ons than any }e interpreted We give another series of tables, founded on experiments by different investigators from which a number of conclusions may be drawn : The Requirements of an Adult Man for Twenty-four Hours. FOOD IN GRAXMES. At n>M. (Flayfalr.) Moderate work. (MotoMbott.) Laborloua work. (Playfalr.) (V. Pettenkofer and V. VoU.) Proteids 70-87 28-35 810-20 130 84 404 165-92 70-87 567-50 187 Fats Carbohydrates , . . . 117 852 Ingesta of an Adult working moderately ( Vierordt). H N O 120 grammes albumin, containing 64-18 70-20 146-62 8-60 10-96 2033 18-88 28-84 90 grammes fats, containing 9-54 880 mrammes starch, coataiiuuir 162-85 Total 281-20 80-10 18-88 200-78 It has further been estimated that 744 grammes of oxygen are respired, 2,818 grammes water drunk, and 32 grammes of salts consumed. The total ingesta have been estimated at ^ of the body weight ; and the daily metabolism of the body is calculated as leading to the transformation of 6 per cent of the water, 6 per cent of the fat, 1 per cent of the proteids, and 4 per cent of the salts of the body. T^e Egesta of an Adult working moderately. H,0 H N o By respiration Bv transoiration 880 660 1,700 128 248-8 2-0 0-8 20H) •J • • *8-8' 8-0 t • • • • 16-8 8-0 65115 T2 By urine .11-1 By foces 12-0 Total.. 2,818 281-2 6-8 18-8 681-45 If .we lay down the rule as has been done, that the nitrog- enous should bear the proportion of 1 to 3 t - 4 i of non-ni- trogenous, an inspection of the following analytical table will show how these various food-stuffs conform to such an estimate. mem »ibHm!X!' ! s*^MmmiiiismMmimmi i mam 454 ANIMAL PHYSIOLOGY. For the herbivora from 1 to 8-9 (some claim 1 to 6J) is the estimated ratio of nitrogenous to non-nitrogenous foods : Nitro. Non-nltro. Veal 10 1 Hare's flesh 10 2 Beef 10 17 Lentils 10 21 Beans 10 22 Peas 10 23 Mutton 10 27 Pork 10 80 Cow's mUk 10 80 mtro. Non-nitro. Human milk. 10 37 Wheaten-flour. 10 46 Oatmeal 10 50 Rye-meal. 10 . 57 Barley-meal 10 57 White potatoes 10 86 Blue potatoes 10 115 Ricfr. 10 123 Buckwheat-meal 10 130 One investigator estimates that in order to get the one hun- dred and thirty grammes of proteids required by an adult man engaged at moderate labor, the foUowirt? proportions of differ- ent kinds of foods must be eaten : Qnunmes. Cheese. 888 Lentils 491 Peas 582 Beef. 614 Eggs 968 Orammes. Wheaten bread 1,444 Rice 2,562 Rye-bread 2,875 Potatoes.. 10,000 One conclusion that is most obvious from the above is that, in order to obtain the amount of proteids needed from certain kinds of food, enormous quantities must be eaten and digested ; and as there would be in such cases an excess of carbohydrates, fats, etc., unnecessary work is entailed upon the organism in order to dispose of this. Feeding Experiments {Ingesta and Egesta). If all that enters the body in any form be known, and all that leaves it be equally well known, conclusions may be drawn in regard to the metabolism the food has undergone. The pos- sible sources of fallacy will appear as we proceed. The ingesta, in the widest sense, include the respired air as well as the food ; though from the latter must be subtracted the waste (undigested) matters that appear in the faeces. The ingesta when analyzed include carbon, hydrogen, oxygen, ni- trogen, sulphur, phosphorus, water, and salts, their source being the atmosphere and the food-stuffs. / The egesta the same, and chiefly in the form of carbonic an- hydride, of water from the lungs, skin, alimentary canal, and THE METABOLISM OF THE BODT. 455 o 5i) is the tods: itro. Non-nitro. 10 87 10 10 10. 10 10 10 10 10 46 50 57 57 86 115 123 180 lie one hun- i adult man ns of differ- Orammes. 1,444 2,562 2,875 10,000 bove is that, from certain id digested ; rbohydrates, organism in rfa). own, and all lay be drawn 10. The pos- »spired air as >e subtracted f eeces. The , oxygen, ni- their source carbonic an,- ry canal, and kidneys, of salts and water from the skin and kidneys, and of nitrogen, chiefly as urea almost wholly from the kidneys. Usu- ally in experimental determinations the total quantity of the nitrogen of the urine is estimated. If free nitrogen plays any part in the metabolic processes it is unknown. A large number of feeding experiments have been made by different investigators, chiefly, though not exclusively, on the lower animals. Some such method as the following has usu- ally been pursued : 1. The food used is carefully weighed and a sample of it analyzed, so that more exact data may be obtained. 2. The amount of oxygen used and carbonic anhydride exhaled, as well us the amount of water given off in any form, is esti- mated. 3. The amount of the nitrogenous excreta is calculated, chiefly from an analysis of the urine, though any loss by hair, etc., is also to be taken into account. It has been generally assumed that the nitrogen of the ex- creta represents practically the whole of that element entering the body. This has been denied by some investigators. The respiratory products have been estimated in various ways. One consists in ineasuring the quantity of oxygen sup- plied to the chamber in which the animal under observation is inclosed, and analyzing from time to time samples of the air as it is drawn through the chamber ; and on these results the total estimates are based. It will appear that even errors in calculating the composi- tion of the food— and this is very variable in different samples, e. g., of flesh ; or any errors in the analysis of the urine, or in the more difficult task of estimating the respiratory products, may, when multiplying to get the totals, amount to serious de- partures from accuracy in the end ; so that all conclusions in such a complicated case must be drawn with the greatest cau- tion. But it can not be doubted that such investigations have proved of much practical and some scientific value. The labor they entail is enormous. Proteid Ibtaboliim.— If we conceive of a structural unit or cell as made up of a genuine protoplasni constituting its mesh-' work and holding in the interstices certain substances that are not part of itself, strictly speaking, the question arises, Are these latter used up in the metabolic ptocess as such, or do they become a part of the true protoplasm before they undergo the changes referred to above? Some writers speak of "organ albumin " and " circulating albumin," and they believe that the latter, by which is meant the proteid material found every- Mnm MiMMinigiiilil 456 ANIMAL PHYSIOLOOT. where in the fluids of the body, as opposed to the former as constituting organized tissues, undergoes changes of a retro- grade kind without ever becoming organ albumin, while the term luxus consumption was applied to the metabolism of pro- teids in the blood. The latter is not now believed to occur. But whether a portion of the urea that represents, in the main, the results of proteid metabolism is not derived from the metabolism of the material in the interspaces of the tissues (circulating proteids on which the cells are supposed to act and in which they effect changes without making these pro- teids a part of themselves), is uncertain. Hitrogenovf Equililnriiiiii. — It is possible to so feed an animal, say a dog, that the total nitrogen of the ingesta and egesta shall be equal ; and this may be accomplished without the ani- mal losing or gaining weight appreciably or again while he is gaining. If there be a gain, it can usually be traced to the formation of fat, so that the proteid, we may suppose, has been split up into a part that is constructed into fat and a part which is represented by the urea, the fat being either used up or stored in the body. Moreover, an analysis of a pig that had been fed on a fixed diet, and a comparison made with orte of the same litter killed at the commencement of the experi- mentj showed that of the dry nitrogenous food only about seven per cent in this animal and four per cent in the sheep had been laid away as dry proteid. It is perfectly plain, then, that proteid diet does not involve only proteid construction within the body. Compuratiye.— The amount of flesh which a dog, being a car- nivorous animal, can digest and use for the maintenance of his metabolio processes is enormous ; though it has been learned that ill-nouirished dogs can not even at the outset of a feeding experiment of this kind maintain the equilibrium of their body weight on a purely flesh diet (fat being excluded). They at once commence to lose weight— i. e., they draw upon their own limited store of fat. - * The digestion of herbivora being essentially adapted to a vegetable diet, they can not live at all upon flesh, while a dog can consume for a time without manifest harm i^ to ^ of its body-weight of this food. Man, when fed exclusively on meat soon shows failure, he being unable to digest enough to supply, the needed carbohy- drates, etc. But the large amount of urea in the urine of car- nivorous animals generally, and the excess found in the urine ■MMMMMMMTM THE METABOLISM OF THE BODV. 457 former as if a retro- while the im of pro- to occur, the main, from the ihe tissues sed to act these pro- an animal, Eind egesta at the ani- rhile he is ced to the ppose, has I fat and a either used a pig that iewith oiie the experi- only about I the sheep ilain, then, mstruction >eing a car- lance of his )en learned )f a feeding their body ). They at 1 their own apted to a nrhile a dog to ^ of its failure, he id oarbohy- rine of car- n the urine of man when feeding largely on a flesh diet, show that .the pro- teid metabolism is under such circumstances very active. It is also a well-known observation that carnivorous ani- mals (dogs) are more active and display to a greater extent their latent ferocity, evidence of their descent from wild car- nivorous progenitors, when like them they feed very largely on flesh. The evidence seenis to .point pretty clearly to the con- clusion that a nitrogenous (flesh) diet increases the activity of the vital processes of the body, and e>^cially the proteid me- tabolism. Some have explained this result on the assumption that such diet led to an increase in the red corpuscles of the blood, and hence in the oxygen-supply ; but mere abundance of sup- ply will never of itself explain results in a living organism. It may be and probably is true that such a diet augments the activity of the oxidative processes, but the reason of this lies deeper, we think, than the explanations as yet offered assume. That an excess of proteids may be stored, as it seems, is true of fats and carbohydrates, to be used in the hour of need, seems not improbable, though this has not as yet been shown to be the case. But in all these considerations it must be borne in mind that the metabolic processes go on in the tissues and not in the blood, and probably not in the lymph. Not that these fluids (tissues) are without their own metabolic processes for and by themselves ; but what is meant to be conveyed is that the metabolic processes of the body generally do not take place in the blood. Hm Vffeoti of Oektine in tlis Diet.— Actual experiment shows that this substance can not take the place of proteid, though it also makes it evident that less of the latter suffices when mixed with a certain proportion of gelatine ; and it has been suggested that it is split up into a fatty portion and urea, and that it thus, by aiding in the formation of fat, preserves some of the proteid for other uses than fat construction. This theory, however, is not well substantiated. It will be borne in mind that ordinary flesh contains, as we find it naturally in the carcass, not only some fat, but a good deal of fibrous tissue, which can be con- verted by heating into gelatine. Vkto and OurboliydntM. — It is a matter of common observa- tion and of more exact experiment that even a carnivorous ani- mal thrives better on a diet of fat and lean meat than on lean flesh alone. Thus, it has been found that nitrogenous equi- librium was as readily established by a due mixture of fat and I I MMMMa 458 ANIMAL PHYSIOLOGY. i";. lean as upon twice the quantity of lean flesh alone. It is plain, then, that the metabolism is actually slowed by a fatty diet. When an animal is given but little fat, none whatever is laid up, but all the carbon of the fat can be accounted for in the excreta, chiefly as carbonic anhydride. Again, the fatty por- tion remaining constant, it has been found that increasing the proteid leads not to a storage of the carbon of the proteid ex- cess, but to an increased consumption of this element. It is then possible to understand how excessive consumption of pro- teids may lead, as seems to be the case, to the disappearance of fat and loss of weight, so that a proteid diet increases not only nitrogenous but non-nitrogenous metabolism. That carbohy- drates mixed with a due proportion of the other constituents of a diet do increase fat formation is well established ; though there is* no equally well-grounded explanation of how this is accomplished. Upon the whole, it seems most likely that fat can be directly formed from carbohydrates, or, at all events, that they directly give rise to fat if they are not converted themselves into that substance. Comparative.— It is found that there are relations between the food used and the quantity of carbonic dioxide expelled which are instructive. The formula following show the amount of oxygen necessary to convert a starch and a fat into carbonic anhydride and water : 1. C.H..O, + Q„ = 6(CO,)4-MH.O). 2. C«HmO, -f Om. = 67(00.) + 62(H.O). It will be observed that in the first case the oxygen used to oxidize the starch has all reappeared as CO., while in the sec- ond only 1 14 parts out of 160 so reappear. As a matter of fact, more of the oxygen used does in herbivora reappear as CO,, and less as water, while the reverse holds for the carnivora, the proportion being, it is estimated, as from 90 to 60 per cent. This is to be explained by the character of the fo6d in each instance, for this relation no longer holds during fasting, when the herbivorous animal becomes carnivort)us in the sense that it consumes its own tissues. To most persons the carbohydrates are more digestible than fats, though they have less potential energy, as will shortly be seen. TlM BfliNte of 8a]l% Wat«r, «|o., in tlw Biet— We have already considered how salts in the form of condiments may beneficially influence the digestion ; but, when we come to inquire as to the It is plain, fatty diet, ver is laid for in the fatty por- reasing the proteid ex- tent. It is lion of pro- 3earance of es not only A carbohy- onstituents Bd; though how this is ily that fat all events, ; converted ns between de expelled the amount ito carbonic gen used to e in the sec- ktter of fact, tear as COt, .rnivora, the SO per cent, odd in each usting, when e sense that restible than will shortly lave already ' beneficially lire as to the THE METABOLISM OP THE BODV. 459 part they play when introduced into the blood, we soon find that our knowledge is very limited. Sulphur, and especially phosphorus, seem to have some im- portant use which quite eludes detection. It is important to remember that certain salts are combined with proteids in the body, possibly to a greater extent than we can learn from the mere analysis of dead tissues. Pafhokgiiwl.— The withdrawal of any of the important salts of the body soon leads to disease, clear evidence in itself of their great importance. This is notably the case in scurvy, in which disease the blood seems to be so disordered and the nutrition of the vessel-walls so altered that the former (even some of the blood-cells) passes through the latter. Wstor. — The use of water certainly has a great influence over the metabolic processes of the body. The temporary ad- dition or withdrawal of even a few ounces of water from the regular supply of a dog in the course of a feeding experiment greatly modifies the results obtained for the time. It is well known that increase of water in the diet leads to a corresix)nd- ing increase in the amount of urea excreted. It is likely that even yet we fail to appreciate the great part which water plays in the animal economy. y The Energy of the Animal Body. As already explained, we distinguish between potential or latent and actual energy. All the energy of the body is to be traced to the influence of the tissues upon the food. Energy may be estimated as mechanical work or as heat, and the one may be converted into the other. All the processes of the organism involve chemical changes, and a large propor- tion of these are of the nature of oxidations ; so that, speak- ing broadly, the oxidations of the animal body are the sources of its energy ; and in estimating the quantity of energy, either as heat or work, that a given food-stuff will produce, one must consider whether the oxidative processes are complete or par- tial • thus, in the case of proteid food, if we suppose that the urea exci-eted represents the form in which the oxidative pro- cesses end or are arrested, we must, in estimating the actual energy of the proteid, subtract the amount of energy that would be produced were the urea itself completely oxidized (burned). If the amount of heat that a body will produce in its com- HMMh MIMM ANIMAL PHYSIOLOGY. bustion be known, then by the law of the conversion and equiv- alence of energy the mechanical equivalent can be estimated in that particular case. The heat-producing power of different substances can be directly learned by ascertaining the extent to which, when fully burned (to water and carbonic anhydride), they elevate the temperature of a given volume of water ; and this can at once be translated into its mechanical equivalent of work, so that we may say that one gramme of dry proteid would give rise to a certain number of gramme-degrees of heat or kilogramme- metres of work. A few figures will now show the relative values of certain food-stuffs : ' 1 gramme proteid 1 gramme urea. Available energy of the proteid Gram.-deg. 5,108 785 4368 Kilomet. 3,161 811 1,850 The reason of the subtraction has been explained above. Taking another diet in regard to which the estimates differ somewhat from those given previously, but convenient now as showing how equal weights of substances produce very dif- ferent amounts of energy, we find that — KilMnet. 100 grammes proteid yield 100 grammes fat yield. . . . , 240 grammes starch yield. ToUl 185,000 884,100 307,080 966,780 In other words, nearly a million kilogramme-metres of en- ergy are available from the above diet for one day, provided it be all oxidized in the body. (Food^stuffs, then, with the oxygen of the air, are the body's sources of energy. What are the forms in which its expendi- ture appears ? We may answer at once, heat and mechanical work ; for it is assumed that internal movements, as those of the viscera, and all the friction of the body, all its molecular motion, all secretive processes, are to be regarded as finally augmenting the heat of the body. Heat is lost by the skin, lungs, urine, and feeces. ■«it^ a and equiv- estimated iu nces can be 1, when fully elevate the i can at once rork, so that I give rise to kilogramme- the relative Kilomet. a,iot 811 1,850 }d above, imates differ nient now as ice very dif- '• Kilmnet. 185,000 884,100 807,080 066,780 m metres of en- lay, provided ire the body's I its expendi- d mechanical ts, as those of its molecular led as finally 5 by the skin, THE METABOLISM OF THE BODY. 461 The amount of work which a man or other animal can do on a given diet may be estimated without the same sources of fallacy as attend the calculation of the heat expenditure ; for, when an animal is confined in a calometric chamber, the con- ditions of the normal metabolism are not observed. The Sources of Muscular Energy. EsperimenteL— Two physiologists (Fick and Wislicenus) as- cended a mountain, noting the conditions under which their metabolism was performed, and drew certain conclusions in re- gard to the question now being considered. They lived exclu- sively on a non-nitrogenous diet while the work was being done, and estimated the amount of urea excreted at the same time. Assuming that the urea does represent the proteid metabolism (oxidation) which bore, of course, a definite relation to the energy available, it was found that in the case of each of them this was only about half enough to account for the work done. Even making large allowances for error in the estimates, if this experiment is to be trusted at all, it is plain that the energy of the muscles of the body is not derivable from their proteid metabolism ; and there are other facts which point in the same direction. It is found, when an isolated muscle is studied, that its continued contraction does not produce nitrogenous bodies, but very different ones, such as carbonic anhydride. The quantity of the latter may be augmented many times by work. But it is no longer believed that the severest labor appreciably in- creases the secretion of urea. The division of foods into heat-producers and tissue-builders is unjustifiable, as will appear from what has just been stated, as well as from such facts as the production of fat from proteid food, thus ahowing that the latter is indirectly a producer of carbonic anhydride, assuming that fat is oxidized into that substance. Animal Heat. Though a large part of the heat generated within the body is traceable to oxidations taking place in the tissues, it is better to speak of the heat as being the outcome of all the chemical processes of the organism ; and though heat may be rendered lat«nt in certain organs for a time, in the end it must reappear. While all the tissues are heat-producers (thermogenic), the ex- J I 462 ANIMAL PHTSIOLOQT. V tent to which they are such would depend, we should suppose, upon the degree to which they were the seat of metabolic pro- cesses ; and actual tests establish this fact. Thus, among glands the liver is the greatest heat-producer ; hence the blood from this organ is the warmest of the whole body. The muscles also are especially the thermogenic tissue. The temperature of the blood in the hepatic vein is warmer than that in the portal, a clear evidence that the metabolism of this organ has elevated the temperature of the blood flowing through it. The temperature of the blood (its own metabolism being slight) is a pretty fair indication of the resultant effect of the production and the loss of heat. For obvious reasons, the temperature of different parts of the body of man and other animals varies. The statements of observers in regard to the temperature of various animals and of different parts of the body disagree in a way that \^ould be puzzling, were it not known how difficult it is to procure perfectly accurate thermometers, not to mention individual differences. The axillary temperature is about 37*5** C. ; that of the mouth a little higher, and of the rectum or vagina slightly more elevated. The mean temperature of the blood is placed at 39° C. It is a very striking fact, however, that the different parts of the body ordinarily accessible by a thermometer vary so little — not more perhaps thftn a degree or a degree and a half. The temperature of the hepatic vein has been put down as 39*7°, and it contains the warmest blood of the body. OompanliTe. — ^The tem])erature of various groups of animals has been stated to be as follows: Gull, 37*8°; swallow, 44*03°; dolphin, 35*5°; mouse, 41*1°; snakes, 10° to 12°, but higher in large specimens (python). Cold-blooded animals have a temperature a little higher (less than 1° 0. nvoally) than the surrounding air. During the swarming of be^ the hive temperature may rise from 32° to 40°. All cold-blooded animals have probably a higher temperature in the breeding-season. In our domestic mammals the normal temperature is not widely different from that of man. Variations in the (werage temperature are dependent on numerous causes which may affect either the heat induc- tion or heat loss : 1. Change of climate has a very slight but real influence, the temperature being elevated a fraction ^f a degree when an individual travels from tilie poles toward a m fit rn K tmiiem (i.-VarlatioiM of tbeJMj ttmpentan tn heitlth durimr M boon: L., after Lieber- meiiter ; J., after JOiseiiMii (from Ludois). "«ubi« 340. It will be noticed that the period of greatest bodily warmth is between about four and seven o'clock in the after- noon and the minimum temperature between two and five in the morning. ut will be inferred, from the facts and figures already cited, that different kinds of food have considerably different capacity for heat production. The following estimates will still further tend to illustrate this: Animal diet produces 8,779,634 heat-units Food free from nitrogen 2,069,600 " '* Mixeddiet 2,200,200 " " Absenceof food, the heat amoimts to.. 2,012,816 " " ftt is well known that a m Lj.um. t )iifi i mmmmmmmimmmm 464 ANIMAL PHYSIOLOGY. formation on this subject, the numbers denoting the heat- units produced : BESTING DAY. BMt, le hours. Sleep, 8 houn. 2470-4 820 Total, 2790-4 Beat, 8 hn. 1285-2 WORKING DAT. Work, 8 tar*. 216-90 Sleep, 8 hn. 820 Total, 3724-8' It appears from a multitude of considerations that the body is like a steam-engine, producing heat and doing work ; but it is found that while a very good steam-engine, as a result of the chemical processes going on within it, converts \ of the poten- tial energy of its supplies into mechanical work, the other | appearing as heat, the body produces ^ as work and .f as heat, from its income of food and oxygen. While it is perfectly clear that it is in the metabolic pro- cesses of the body that we must seek for the final cause of the heat produced, it is incumbent on the physiologist to explain the remarkable fact that the mammalian body maintains, under a changing external temperature and other climatic conditions, and with a varying diet, during rest and labor, a • temperature varying within, usually, no more than a fraction of a degree centigrade. This we shall now endeavor to explain in part. (Tlie Eegnlatioii of Ttrnperatore. — It is manifest from the facts adduced that so long as life lasts heat is being of necessity con- stantly produced. If there were no provision for getting rid of a portion of this heat, it is plain that the body would soon be consumed as effectually as if it were placed in a furnace. We observe, however, that heat is being constantly lost by the breath, by perspiration (insensible), by conduction and radia- tion from the surface of the body, and periodically by the urine and fseces. We have seen that, while heat is being pro- duced in all the tissues and organs of the body, some are es- pecially thermogenic, as the glands and muscles. The skin presents an extensive surface, abundantly supplied with blood- vessels, which when dilated may receive a large quantity of blood, and when contracted may necessitate a much larger in- ternal supply, in the splanchnic region especially. It is a mat- ter of common observation that, when an individual exercises, the skin becomes flushed, and so with the increased production of heat, especially in the muscles (see page 195), there is a pro- vision for unusual escape of the surplus; at the same time sweat breaks out visibly, or if not, the insensible perspiration I *Wmw*i ifJmijiiiii-miWiMiiiiN iiWjl> ii»iiiMWiiwniiHni'i|i(iiTi"-nri"i'"^^'f'"' ■9S-9- THE METABOLISM OF THE BOOT. 465 the heat- glerp, 8 hn. k the body irk ; but it suit of the the poten- he other I I as heat, abolic pro- ause of the to explain maintains, jr climatic nd labor, a a fraction r to explain m the facts cessity con- tting rid of aid soon be mace. We lost by the and radia- ally by the i being pro- )me are es- , The skin with blood- qnantity of h larger in- It is a mat- al exercises, production ere is a pro- same time perspiration is generally increased ; and this accounts for an additional in- crement of loss ; while the lungs do extra work and exhale an increased quantity of aqueous vapor, so that in these various ways the body is cooled. Manifestly there is some sort of co- ordination between the processes of heat production and heat expenditure. ^The vaso-motor, secretory, and respiratory func- tions are modified. Even if an individual do no work at all, as when in a Turkish bath, it becomes evident, to one submitting to the experiment (for such it is or may become), that the pulse and respirations are quickened and that there is copious secretion of sweat following on reddening of the skin, owing to vascular dilatation. Exact quantitative estimation of the heat produced, as seen above, and of the oxygen used, the car- bonic anhydride and watery vapor exhaled, shows that the organs of which we are speaking are not only apparently but actually doing more work. . It is usual to quote the case of Drs. Fordyce and Blagdon, who learned to endure without injury a heat of 137° C. (260° F.), to illustrate the great adap- tability of our own organism in this respect We may suppose that the various co-ordinations effected, chiefly at all events through the central nervous system, and not by the direct ac- tion of Hie heat upon local nervous mechanisms, or the tissues themselves directly, are reflexea (i%e production of Tiedt, however, seems to be equally under the influence of the nervous system, though we know less about the details of the matter. A cold-blooded animal differs from a warm-blooded one in that its temperature varies with the surrounding medium more; hence the terms poikilothermer and homoiolhertner for cold- blooded and warm-blooded, would be appropriate. Such an animal, as a frog or turtle, may have its chemical processes slowed or quickened, almost like those going on in a test-tube or crucible, by altering the temperature. Very different is it, as we have seen, in the normal stats Qf the animal with any mammal Hence hibernation or an allied state has become a necessary protection for poDdlothermers, otherwise they would perish outright, and the groups become extinct in north- em latitudes. Now, whmi a mammal is poisoned with curare, it becomes like a poikilothermer. Like the latter, under in- crease of temperature, it too uses more oxygen and produces more carbonic anhydride. When certain parts of the brain are divided or punctured, a fall, similar to that observable when curare is given, is observable, so \- m ■mmmMML : i 466 ANIMAL PHYSIOLOGY. It is plain that vaso-motor changes alone can not explain these effects ; and, though possibly a part of the rise of tem- perature, following exposure of the naked body in a cool air, may be accounted for by the increased metabolism of internal organs, accompanying the influx of blood caused by constric- tion of the cutaneous capillaries, it is probable that in this as in so many other instances the blood and circulation have been credited with too much, and the direct influence of the nervous system on nutrition and heat production overlooked or under- estimated. The thermogenic center has not yet been definitely located, though some recent investigations seem to favor a spot in or near the corpus striatum for certain mammals. Some in- vestigators also recognize a cortical heat-center. It has been suggested that we may to advantage speak of a thermotoxic (regulative of loss) and a thermogenic mechanism (regulative of production), and even a tJiermolytic or discharging mechan- ism. It has been further suggested that different nerve-fibers may be concerned in the actual work of conveying the different impulses of these respective mechanisms to the tissues ; and the whole theory has been framed in accordance with the prevalent conception of metabolism as consisting of anabolism and ca- tabolism, or constructive and destructive processes. But these theories have not yet been confirmed by experiments on ani- mals, though they are, in the opinion of their authors, in har- mony with the facts of fever. Certainly, any theory that will imply that vital processes are more under the control of the nervous system than has hitherto been taught, will, we think, advance physiology, as will shortly appear from our own dis- cussion of the influence of the nervous system on the various metabolic processes generally. The phenomena observable in an animal gradually freezing to death point strongly to the direct influence of the nervous system on the production as well as the regulation of heat. The circulation must of course be largely concerned, but it ap- pears as though the nervous system refused to act when the temperature falls below a certain point. A low temperature favors hibernation, in which we believe the nervous system plays the chief part, though the temperature in itself is not the determining cause, as we have ourselves proved. The fact that the whole metabolism of a hibernating animal is lowered, that ^Sth this there is loss of consciousness much more profound that in ordinary sleep, of itself seems to indicate that the nerv- ous system is at the bottom of the whole matter. 'HWII (1*UW(MU1««M . injm m Mi w mm i lWK ' :-H f H^Tra i T. a THE METABOLISM OF THE BODY. 467 )t explain le of tem- i cool air, I internal f constric- in this as have been le nervous I or under- i definitely tvor a spot Some in- :t has been hermotoxic [regulative Lg mechan- lerve-fibers le different 98 ; and the e prevalent 3m and ca- But these ^nts on ani« ors, in har- ry that will itrol of the 1, we think, ur own dis- the various lly freezing he nervous on of heat. , but it ap- st when the emperature ouB system f is not the he fact that >wered, that re prof oimd bt the nerv- PatkftkfiflaL — It is found that many drugs and poisons lower temperatun*, acting in a variety of ways. In certain dis- eases, as cholera, the temperature may sink to 23° G. in extreme casea In^fore death supervenes. When the temperature of the blood i.s raised 6° C. (as in sunstroke, etc.), death occurs; and it is well known that prolonged high temperature leads to fatty degeneration of the tissues generally. All the evidence goes to show that in fever both the heat production and the heat ex- penditure are interfered with ; or, at least, if not always, that there may be in certain cases such a double disturbance. In fever excessive consumption of oxygen and production of car- bon dioxide occur, the metabolism is quickened, hence its wast- ing (consuming) effects ; the rapid respiration tends to increase the thirst, from the extra amount of aqueous vapor exhaled. The body is actually warmest during the " cold stage " of ague, when the vessels of the skin are constricted and the patient feels cold, because the internal metabolism is heightened ; while the " sweating stage " is marked by a natural fall of tempera- ture. The fact that the skin may be dry and pale in fever shows that the thermotoxic nervous mechanism is at fault ; but the chemical facts cited above (excess of GO*, etc.) indicate that the thermogenic mechanism is also deranged. Special Gonsidbrations. (? If the student wiU now read afresh what has been written under the above heading in relation to the subject of digestion, it will probably appear in a new light. We endeavored to show that, according to that general principle of correlation which holds throughout the entire organism, and in harmony with certain facts, we were bound to believe that digestion and as- similation, or, to speak in other terms, the metabolic processes of the various tissues, in a somewhat restricted sense, were closely related. Beneath the common observation that " diges- tion waits on appetite " lies the deeper truth that food is not prepared in the alimentary canal (digested) without some rela- tion to the needs of the system generally. In other words, the voice of the tissues elsewhere is heard in the councils of the digestive track, and is regarded ; and this is effected chiefly through the nervous system. Qlnttony may lead to vomiting or diarrhoea — plain ways of getting rid of what can not be digested. But how is it that a hungry man who has been with- out food for twenty-four hours can digest with ease a quantity /I II si-' 408 ANiMAL PHYSIOLOGY. of food, ^akeii at one meal, that would otherwise lead to the above-not d attempts at its removal ? It is a mistake to ex- plain the result with reference to the alimentary tract alone. The entire metabolism of the body has a voice in the matter. From this point of view, the benefit of abstinence from spe- cific articles of diet, partial or complete, of taking at times very light meals, and much more that experience warrants, receives an explanation. Too little attention seems to have been given to this aspect of the subject that we are now en- deayoring to present briefly. (Until the nature of metabolism is more completely under- stood, it will be impossible to treat the subject of diet, either in hc^th or disease, with such confidence as to enable us to prescribe upon scientific principles alone. Very much must still be empirical, the outcome of trial and result, which is, however, after all, experiment in a crude form ; and individxial peculiarities that are inscrutable in their nature will always be encountered. Notvrithstanding, if physicians will avail them- selves of the best that is known in the realm of physiologi- cal dietetics, and then contribute the results of their observa- tions in accurate form, substantial progress will be made in due time. lTobitl0iL-^Ve have already alluded to some of those modi- fications in the form of the digestive organs that indicate an unexpected plasticity, and impress the fact of the close rela- tion of form and function. The conversion of a sea-gull into a graminivorous bird, with a corresponding alteration in the na- ture of the form of the stomach (it becoming a gizzard), with doubtless modifications in the digestive processes, when re- garded more closely, implies coadaptations of a very varied kind. These are as yet but imperfectly known or understood, and the subject is a wide and inviting field for the physiolo- gist. Darwin and others have indicated, though but imper- fectly, some of the changes that are to be regarded in animals as correlations ; but in physiology the subject has received but little attention as yet. We have in several parts of this work called attention to it; but the limits of space prevent us dmag little more than attempting to widen the student's field of vision by introducing such considerations. The influence of climate on metabolism, an undoubted fact, has many implica- tions. /Any one who keeps a few wild animals in confinement un- dei> close observation, and endeavors to ascertain how their 'wiaiwgwg!iii L'iij i m i ii iiB t g i. ' ..a!iiui!i THE METABOLISM OF THE BODY. 460 Eld to the kke to ex- act alone, le matter, from spe- ; at times warrants, B to have e now en- ely under- iiet, either able us to inch must , which is, individual I always be vail them- physiologi- ir observa- ye made in ihose modi- indicate an close rela- -guU into a a in the n«- a»rd), with when re- rery varied understood, e physiolo- but imper- in animals 'eceived but if this work tnt us d(HBg it's field of influence of huy implica- Aement un- how their natural, self-chosen diet may be varied when confined, will be astonished at the plasticity of their instincts, usually con- sidered as so rigid in regard to feeding. These facts help one to understand how by the law of habit and heredity each group of animals has come to prefer and flourish best upon a certain diet. But habit itself implies an original deviation some time, in which is involved, again, plasticity of nature and power to adapt as well as to organize. With- out this, evolution of function is incomprehensible ; but with this principle, and the tendency for what has once been done to be easier of repetition ; and, finally, to become organized, a flood of light is thrown upon the subject of diet, diges- tion, and metabolism generally. On these principles it is possible to understand those race differences, even individ- ual differences, which as facts must be patent to all observ- ers. Every individual's ovm history will teach him that he can learn to digest and assimilate what was once all but a poison to his organism; so that it becomes comprehensible how a Chinaman, for example, can, not only remain in health,\ but do a large amount of work daily on a diet on which the ordinary Englishman might well-nigh starve before he could adapt himself to it. (R is also a well-established fact that whole families crave and seem to require certain articles of diet in excess, as com- pared with the majority — e. g., a meat diet. In some in- stances, at all events, this can be traced to pathological excess in the ancestors. It is important to recognize, however, that while such a^Bet upon the whole may be the best that can be appropriated at the time, it is associated with certain aberrations of function which it is desirable to correct; hence the wisdom of withholding from such people, even children, to a certain extent, the meai which they so much crave. The habit of the metabolism mS^Tbi 'modified. The rapid rate of speed of the metabolic processes, which an excess of such a diet is apt to beget, leads to various bad results, such as great irritability of the nervous system, and a general lack 61 stability and equi- po^tt^he vital machtne.^^" le principle of natural selection has clearly played a great in determining the diet of a species; the surviving emi- grants to a new district must be those that can adapt to the local environment best, including the food which the region supplies. The greater capability of resisting hunger and thirst in some iudividuals of a species implies great differences in the meta- 470 ANIMAL PHTSIOLOGT. bolic processes, though these are mostly unknown to us ; and the same remark applies to heat and cold. It seems clear that hibernation is an acquired habit of the whole metabolism, with great changes in the functional condi- tion of the nervous system recurring periodicaUy, and, in fact, dependent on these, by which certain large divisions, as the reptiles, amphibianii, and certain mammals among vertebrates, are enabled to escape individual death and extinction as groups. We may suppose that, for example, among invertebrates, by a process of natural selection, those survived that could thus adapt themselves to the environment; while, among mammals, hibernation may be considered as a process of reversion, per- haps, for the homoiothermer becomes very much a poikilo- thermer during hibernation, the latt«r again reverting to a condition existing in lower forms, and not wholly unlike that of plants in winter. This can be understood on the princi- ple of the origin of higher from lower forms; otherwise it is difficult to understand why similar states of the metabolism should prevail in groups widely separated in form and func- tion. If all higher groups bear a derivative relation to the lower, what is common in their nature, as we usually find them, as well as the peculiar resemblances of the metabolism of higher to lower forms in sleep, hibernation, etc., can be imderstood in the light of physiological reversion. The origin of a homoiothermic (warm-blooded) condition itself is to be sought for in the principle of natural selection. It was open to certain organisms, we may assume, either to adapt to a temperature much below that of their blood, or to hibernate; failing to make either adaptation would result in death ; and gradually, no doubt, involving the death of num- berless individuals or species, the resisting power attained the marvelous degree that we are constantly witnessing in all homoiothermers. The daily variations of the bodily temperature in homoio- thermers is a beautiful example of the law of rhythm evident in the metabolism. Hibernation is another such. While these are cleur cases, it is without doubt true that, did we but know more of the subject, a host of exampleB of the operation of this law might be instanced. We can but touch on these subjects enough to show that they deserve an attention not as yet bestowed on them ; and to the thoughtful it will be evident that their influence on prac- tical life might be made very great were they but rightly ap- lailriWIUllilKitMl us; and ibit of the >nal condi- id, in fact, ns, as tlie ertebrates, as groups, rates, by a ;ould thus mammals, trsion, per- a poikilo- rting to a inlike that ;he princi* herwise it aetabolism and f uuc- ion to the iually find aetabolism tc., can be 1 condition I selection. , either to •lood, or to i result in thof num* stained the ling in all in homoio- im evident Vhile these )but know tion of this I show that em ; and to }e on prao- rightly ap* iiwUft-wwia BW THE HETABOUSM OF THE BODY. 471 prehended. In that preventive medicine of the future to which we fondly look to advance the welfare of mankind, such consid-i orations must largely enter. The Influence of the Nervous System on Metabolism (Nutrition). This subject is of the utmost importance, and has not re- ceived the attention hitherto, in works on physiology, to which we believe it is entitled, so that we must discuss it at some length. ^e may first mention a number of facts on which to base conclusions : 1. Section of the nerves of bones is said to be fol- lowed by a diminution of their constituents, indicating an alteration in their metabolism. 2. Section of the nerves sup- plying a cock's comb interferes with the growth of that ap- pendage. 3. Section of the spermatic nerves is followed by de- generation of the testicle. 4. After injury to a nerve or its center in the brain or spinal cord, certain affections of the skin may appear in regions corresponding to the distribution of that nerve : thus, herpes zoster is an eruption that follows frequently the distribution of the intercostal nerve. 6. When the motor cells of the anterior horn of the spinal cord or cer- tain cells in the pons, medulla, or cms cerebri are disordered, there is a form of muscular atrophy which has been termed "active," inasmuch as the muscle does nbt waste merely, but the dwindling is accompanied by proliferation of the muscle nuclei. 6. In ocufedectt&i^tiA bed-sores form within a few hours or days of the appearance of the cerebral or spinal lesion, and this with every precaution to prevent pressure or the other conditions that favor the formation of such sores. 7. After section of both vagi, death results after a period, varying in time, as do also the symptoms, with the animal. In some ani- mals pneumonia seems to account for death, since it is found that, if this disease be prevented, life may, at all events, be greatly prolonged. The pneumonia has been attributed to paralyses of the muscles of the larynx, together with loss of sensibility of the larynx, trachea, bronchi, and the lungs, so that the glottis is not closed during deglutition, and the food, finding its way into the lungs, has excited the disease by irrita- tion. The possibility of vaso-motor changes is not to be over- looked. In birds, death may be subsequent to pneumonia or to inanition from paralysis of the oesophagus, food not being - ..HMHiWMHW lM ITS ANIMAL PHTSIOLOOT. swallowed. It is noticed that in these creatures there is fatty (and sometimes other) degeneration of the heart, liver, stomach, and muscles. 8. Section of the trigeminus nerve within the skull has led to disease of the corresponding eye. This opera- tion renders the whole eye insensible, so that the presence of offending bodies is not recognized ; and it has been both as- serted" and denied that protection of the eye from these pre- vents the destructive inflammation. With the loss of sensi- bility there is also vaso-motor paralysis, the intra-ocular ten- sion is diminished, and the relations of the nutritive lymph to the ocular tissues are altered. But all disturbances of the eye in which there are vaso-motor alterations are not followed by degenerative changes. 9. Degeneration of the salivary glands follows section of their nerves. 10. After suture of long-di^ vided nerves, indolent ulcers have been known to heal with^ great rapidity. This last fact especially calls for explanation. It will be observed, when one comes to examine nearly all such instances as those referred to above, that they are complex. Undoubtedly, in such a case as the trigeminus or the vagi, many factors contribute to the destructive issue ; but the fact that many symptoms and lesions are concomitants does not, of itself, negative the view that there may be lesions directly dependent on the absence of the functional influence of nerve- fibers. We prefer, however, to discuss the subject on a broader basis, and to found opinions on a wider survey of the facts of ph^ology. rAf ter a little time (a few hours), when the nerves of the sub- maxillary gland have been divided, a flow of saliva begins and is continuous till the secreting cells become altered in a way visible by the microscope. Now, we have learned that proto- plasm can discharge all its functions in the lowest forms of .animals and in plants independently of nerves altogether. What, then, is the explanation of this so-called "paralytic secretion " of saliva ? The evidence that the various functions of the body as a whole are discharged as individual acts or series of acts correlated to other functions has been abundantly shown; and, looking at the matter closely, it must seem un- reasonable to suppose that this would be the case if there was not a close supervision by the nervous system over even the details of the processes. We should ask that the contrary be proved, rather than that the burden of proof shotdd rest on the other side. Let us assume that such is the case ; that the entire behavior of every cell of the body is directly or indirectly con> rtrfniilii m t D HiM i fmo m lattA^dMMMiMMIlM THE METABOLISM OF THE BODY. 478 re is fatty ', 8tomacli, rithin the his opera- resence of I both as- these pre- t of sensi- icular ten- I lymph to at the eye Uowed by Biry glands )f long-di^ heal withj :planation. ly all such ) complex, the vagi, it the fact oes not, of as directly B of nerve- t a broader he facts of of the sub- begins and in a way hat proto- it forms of altogether, "paralytic i functions aal acts or abundantly ; seem un- there was even the ontrary be rest on the ; the entire rectly con- trolled by the nervous system in the higher animals, especially mammals, and ask. What facts, if any, are opposed to such a view ? We must suppose that a secretory cell is one that has been, in the course of evolution, specialized for this end. What- ever may have been the case with protoplasm in its unspecialized form, it has been shown that gland-cells can secrete independ- ently of blood-supply (pages 321, 416) when the nerves going to the gland are stimulated. Now, if these nerves have learned, in the course of evolution, to secrete, then in order that they shall remain natural (not degenerate) they must of necessity secrete ; which means that they must be the subject of a chain of meta- bolic processes, of which the final link only is the expulsion of formed products. Too much attention was at one time directed to the latter. It was forgotten, or rather perhaps unknown,'^ that the so-called secretion was only the last of a long series of/ acts of the cell. True, when the cells are left to themselves, when no influences reach them from the stimulating nervous centers, their metabolism does not at once cease. As we view it, they revert to an original ancestral state when they per- formed their work, lived their peculiar individual life as less specialized forms wholly or partially independent of a nervous system. But such divorced cells fail; they do not produce normal saliva, their molecular condition goes wrong at once, and this is soon followed by departures visible by means of the microscope. But just as secretion is usually accompanied by excess of blood, so most functional conditions, if not all, de- mand an unusual supply of pabulum. This is, however, no more a cause of the functional condition than food is a cause of a man's working. It may hamper, if not digested and assimi- lated. It becomes, then, apparent that the essential for metab=^ olism is a vital connection with the dominant nervous system.'^ It has been objected that the nervous system has a metab- olism of its own independent of other regulative influences; but in this objection it seems to be forgotten that the nervous system is itself made up of parts which are related as higher and lower, or at all events which intercommunicate and ener- gize one another. Wo have learned that one muscle-cell hafT^ power to rouse another to activity when an impulse has reached ' it from a nervous center. Doubtless this phenomenon has many parallels in the body, and explains how remotely a nerv- ous center may exert its power. It enables one to understand to some extent many of those wonderful co-ordinations (obscure in detail) that are constantly taking place in the body. We mmi iUlH mtM iiHMIIli 474 ANIMAL PHYSIOLOOy. thitik the facts as they accumulate will more and more show, as has been already urged, that the influence of blood-pressure on the metabolic (nutritive) processes has been much over- estimated. They are not essential but concomitant in the highest animals. Turning to the case of muscle we find that when a skeletal muscle is tetanized the essential chemical and electrical phenomena are to be regarded as changes differing in degree only from those of the so-called resting state. There is more oxygen used, more carbonic anhydride excreted, etc. The change in form seems to be the least important from a physio- logical point of view. Now, while all this can go on in the absence of blood or even of oxygen, it can not take place with- out nerve influence or something simxilating it. Cut the nerve7 of a muscle, and it undergoes fatty degeneration, and atrophies.) True, this may be deferred, but not indefinitely, by the applica- tion of electricity, acting somewhat like a nerve itself, and in- ducing the approximately normal series of metabolic changes. If, then, the condition when not in contraction (rest) differs from the latter in all the essential metabolic changes in rate or degree only; and if the functional condition or accelerated metabolism is dependent on nerve influence, it seems reason- able to believe that in the resting condition the latter is not withheld. Certain forms of paralysis (e. g., hysterical) are not followed by atrophy. Why ? Because in this form the nerve influence is still exerted. ^^he recent investigations on the heart make such views as we are urging clearer stilL It is known that section of the vagi leads to degeneration of the cardiac structure. We now know that this nerve contains fibers which have a diverse action on the metabolism of the heart, and that, according as the one or the other set is stimulated, so does the electri- cal condition vary ; and everywhere, so far as known, a differ- ence in electrical conditions seems to be associated with a difference in metabolism, which may be one of degree only, perhaps, in many instances — still a difference. The fiicts as brought to light by experimental stimulation harmonize with the facts of degeneration of the cardiac tissue on section of the vagi ; but this is only clear on the view we are now presenting, that the action of the nervous system is not only imiversal, Cbutthst it^is jcqnjrfflwi^^ that function is not an isolated and inclipendent condition of an organ or tissue, but a part of a long series of metabolic changes. Il h crue that one or more KM bhbi Qore show, d-pressure mch over- mt in the e find that 3mical and li£fering in , There is I, etc. The 1 a physio- on in the alace with- t the nerve7 . atrophies.] lie applica- elf , and in- c changes, est) differs 3 in rate or iccelerated ms reason- ,tter is not )t followed a influence sh views as ;ion of the We now a diverse according the electri- n, a differ- ed with a jgree only, le facts as ionize with tion of the presenting, universal, tolated and b part of a ne or more THE METABOLISM OF THE BODY. 476 of such changes may be arrested, just as all of them may go on at a less rate, if this actual outpouring of pancreatic secre- tion is not constant ; but secretion is. not summed up in dis- charge merely ; and, on the other hand, it would seem that in some animals the granules of the digestive glands are being renewed while they are being used up, in secreting cells. The processes may be simultaneous or successive. Nor do we wish to imply that the nervous system merely holds in check or in a very general sense co-ordinates processes that go on unorigi- nated by it. We think the facts warrant the view that they are in the highest mammals either directly (mostly) or indirectly originated by it, that they would uQtu^ke place in the absence of this constant nervous, influence. The facts^? common ob- servation, as well as the facts of disease, point in the strongest way to such a conclusion. Every one has experienced the in- fluence, on not one but many functions of the body, we might say the entire metabolism, of^ depressing or exalting emotions. The failure of appetite and loss of flesh and mental power under thelnfluence ot gnet or worry, tell a plain story. Such broad facts afeoFmfinitely more value in settling such a question as that now discussed than any single experiment. The best test of any theory is the extent to which it will explain the whole round of facts. Take another instance of the influence over me^bolism of the nervous system. (^very athlete knows that he may overtrain — i. e., he may use his muscles so much as to disturb the balance of his powers somewhere— very frequently his digestion; but often there seems to be a general break — ^the whole metabolism of the body seems to be out of gear. JfjivBassume a constiuit nervous influ- ence over the metabolic processes, this is comprehensible. The ^enteii can produce only so mu^ of what we may call nerv- ous force, using the term in the sense of directive power ; and if this be unduly diverted to the muscles, other parts must suffer. (The same holds of^exoesdve mental jBj)pLics>tjon^ (On this view also^e value of rest or change of occupation becos)^fie_clMrr The nervdtn centers are not without some r»-< semblance to a battery ; at most, the latter can generate only a( definite quantity of electricity, and, if a portion of this be di- / verted along one conductor, less must remain to pass by anyi other. rlt is of practical importance to recognize that under great excitement unusual discharges from a nerve-center may lead to unwonted f imctional activity : thus, under the stimulus of tmmsa 476 ANIMAL PHTSIOLOOY. :•« the occasion a man may in a boat-race originate muscular con- tractions that he could not by the strongest efforts of his will call forth under other .circumstances. Such are always dan- gerous. We might speak of a reserve or residual nerve force, the expenditure of which results in serious disability. It als07 applies to mental and emotional effects as well as muscular, s ' and seems to us to' throw light upon many of the failure s und ^ (juctiess^ Xso called) of life. " ~ ""^"^ (^ iseems thai our past views of secretion and nutrition have been partial rather than erroneous in themselves, and it is a question whether it would not be well to substitute some other terms for them, or at least to recognize them more clearly as phases of a universal metabolism. (V^ a^^pear to be^^^ in^making a wider generalization. To regard processes con- cerned in building up a tissue as i4>art from those that are rec- ognized as constituting its function, seems, with the knowledge we at present possess, to be illogical and unwise. Whether, . in the course of evolution, certain nerves, or, as seems more likely, certain nerve-fibers in the body of nerve-trunks, have become the medium of impulses that are restricted to regulat- ing certain phases of metabolism — as, e. g., expulsion of formed products in gland-cells— is not, from a general point of view, improbable, and is a fitting subject for further investigation. But^it will be seen that we should regard all nerves as "tro- phic " in the wider sense. M^hai is nic«t needed, apparently, is a^ mqrejust eistimatibn of the relative parts played by blood and^ Ijlood-prQssure, i^djhe direct influence of the nervous system/ on^e life-work j>f the oeUT^ These views are greatly iatfengQi- ened by the facts, welTlniown to every observer of disease in the human subject. The preponderating development of the (cerebrun|/in man must be taken into account in the working of every organ. ToJiaye a^erithjr jtomewh, Uyer^^lrid^^ j!tc.^is not jBnough ; for ,r«Oi£a]|hjJ^l the parts of that great complex of or^^s we call the brain must not only work,Jbut, V^i in concert. . ^^e must regard the ^rvous centeriMas the source of cease- less pulses that operate upon~air parts, originating and con- trolling the entire metabolism, of which what we term func- tions are but certain phases, parts of a whole, but essential for the health or normal condition of the tissues. Ag^nst^uskjl .view ire^now no fiicts, eith9r-«f the he^ or disordered orj- ganism. IvBuurj of MttaboHi I— -Very briefly, and somewhat incom- (. ■liMI ,1 lull iiiiii <"• scular con- of his will Iways dan- aerve force, ity. It als07 i muscular, s allures and^ britiou have and it is a some other e clearly as B warranted ocesses con- ihat are rec- I knowledge Whether, seems more runks, have L to regidat- n of formed nt of view, vestigation. res as *'tro- >arently,isa^ y blood and^ 70US system/ ly stfengQi- f disease in nent of the ;he working er^Jridneys, f that great y work,Jbut, rceof oease- ag and con- ) term func> essential for ainstjBuslL§ Isordered or^ what incom- "Tl ■.U THB METABOLISM OF THE BODY. 477 pletely, we may sum up the chief results of our present knowl- edge (and ignorance) as follows : (uHycogen is found in the livers of all v ^-tebrate and some invertebrate animals. The quantity varies with the diet, being greatest with an excess of carbohydrates. It seems likely that glycogen is manufactured from the pro- toplasm of the liver-cells, though it is possible that the latter may act on substances contained in the lymph, and convert them into glycogen which they store up. The phenomena of diabetes meUHua seem to indicate that vaso-motor effects in the liver are not essential to the formation of the excess of sugar in that disease, which excess is only one symptom, there being frequently also a largely increased secretion of urea; but inas- '■^^^k^ilhe juervous system is greatly deranged in this malady, {EeTsymptoms, etc., of the disease as a whole may be rather regarded as showing how important is the due influence of thepiervous system. (Glycogen may be regarded as stored material to be convert- ed into (feugay, as required by the organism ; though the fexact useof the sugar and the method of its disposal are(unknown. \^a^ is not stored up in the body as the result of being merely picked out from the blood ready made ; but is a genuine product of the metabolism of the tissues, and may be formed from fatty, carbohydrate, or proteid food. This becomes es- pecially clear when the difference in the fat of animals from that on which they feed is considered, as weU as the direct re- sults of feeding experiments, and the nature of the secretion of milk. (^e liver seems be engaged in a very varied round of meta- bofic processes: the manufacture of bile, of glycogen, of urea, and probably of many other substuices, some known and others unTmown, as chemical individuals. Urea is in great part probably only appropriated by the kidney-cells (Amoeba- like) from the blood in which it is found ready-made; though it may be that a part is formed in these'oells, either from bodies some steps on the way toward urea, or out of their pro- topbasm^m fsA seems to be by the cells of the mammary gland. . (Jhe leucin (and tyrosin ?) of the digestive canal sustains some relation to the manufacture of urea by the liver, and possibly by the spleen and other orgems; for an animal diet increases these products, and also the urea excreted. Creatin, one of the products of proteid metabolism, and possibly allied bodies, may be oonsidered as in a certain sense antecedents of i* ■ •r 478 ANIMAL PHTSIOLOOT. urea : uric acid, however, does not seem to be such, nor is it to be regarded as a body that has some of it escaped complete oxidation, but rather as a result of a distinct departure of the metabolism ; and there are facts which seem to indicate that the uric-acid metabolism is the older, frora an evolutionary point of view, and that in mammals, and especially in man, as the results of certain errors there may be a physiological (or pathological) reversion. Hippuric acid, as replacing uric acid in the herbivora, may be regarded in a similar light. (^ur knowledge of the metabolism of the spleen, beyond its relations to the formation of (blood-cells/ and their disintegra- tion, is in the suggestive rather than the positive stage. It seems highly probable that this organ plays a very important part, the exact nature of which is as yet^nknown^ fWhen an animal starves, it may be considered as feeding on its own tissues, the more. active and important utilising the others. Notwithstanding, organs with i very active metabo- lism, as the muscles and glands, lose weiq^ht to a large extent. The presence of urea to an amount not very greatly below the average in health, shows that there is an active proteid metab- olism then as at all times in progress. ( (General experience and exact experiments prove that, while an animal's diet may be supplied with special regard to fatten- ing, to increase working power, or simply to maintain it in health, as evidenced by breeding capacity, form, etc., in all cases there must be at least a ^urtsin minimum quantity of each of the food-stuffs. No one food can be said to be exclusively fattening, heat-forming, or musple-forming. /A carbohydrate diet tends to production of fat ; flesh, and oth^r proteid food to supply muscular energy, but the latter also produces fat, and a diet of flesh mixed with fat or gelatin will serve the purposes of the econoiny better than one contain- ing a very much larger quantity of proteid alone. Muscular energy, as is to be inferred from the excreta, is not the result of nitrogenous metabolism alone ; and in arranging any diet for man or beast the race and the individual must be consid- «red. Animals can not be treated as machines, like engine!*) using similar quantities of fuel ; though this holds far more of p man than the lower animals — ^i. e., the results may be predicted) from the diet with far less certainty in the case of man than of i other mammala (Food is related to excreta in a definite way, so tkat all that enters as food must sooner or later appear as urea, salts, oar- tatla^v I nor is it to id complete ture of the dicate that rolutionary in man, as ological (or g uric acid t. , heyond its disintegra- 9 stage. It IT important s feeding on tilising the Ive metabo- arge extent, y below the )teid metab- ) that, while rd to f atten- intain it in ., in all cases y of each of exdusivdy t ; flesh, and it the latter at or gelatin one contain* ). Muscular »t the result ing any diet st be consid- like engine^N I far more of ^ be predicted) man than of 1 that aU that », salts, oar- THK METABOLISM OP THh BODY. 4 bonic anhydride, water, etc. These are individually to be garded as the final links in a long chain of metabolic procat- s or rather a series of these. Fats and carbohydrates are rej sented finally as carbonic anhydride and water principally, pro- teids as urea. (Nitrogenous foods may be regarded as accelerating the metabolic processes generally and proteid metabolism in par- ticular, while fats have the reverse effect ; hence fat in the diet renders a less quantity of proteid sufficient. Qelatine seems to act when mixed with proteid food either like an additional quantity of proteid, or possibly like fat, at all events under such circumstances less proteid sufficea These facts have a bearing not only on health but on econ- omy, in the expenditure for food. (Baits hold a very important place in every diet, though their exact influence is in great part unknown. The heat of the body is the resultant of all the metabolic processes of the organism, especially the oxidative ones. Certain food-stuffs have greater potential capacity for heat formation than others ; but, finally, the result depends on whether the organism can best utilize one or the othdr. A certain body temperature, varying only within narrow limits, is maintained, partly by regulation of the supply and p^Iy by the regulation of the loss. nBoth these fure, ia health, under the directicm of the nervous system, and both are co-ordinated by the same. Ijoss is chiefly through, the skin and lungs ; gain chiefly through the organs of most active metabolism, as the muscles and glands. Vaso-motor effects play a great part in the escape of heat. Animals may be divided into poikilothermers and homoio- thermers, or cold-blooded and warm-blooded animals, accord- ing as their body heat varies with or is independent of the ex- ternal changes of temperature. All the facts go to show that in mammals the processes of the body (metabolism) can con- tinue only within a slight range of variations in temperature, though the npwf^rd limit is narrower than the downward. (Jjpon the whole, the evidence justifies the conclusion that thenervo^_8yat§Si^ is concerned in all the metabolic processes of^lfiebody in mammals including man, and that, as we descend the scale, the dominion of the nervous system becomes less till we reach a point when protoplasm goes through the whole cycle of its changes by virtue of its own properties uninfluenced by any modification of itself in the form of a nervous system. f mll^ 480 ANIMAL PHYSIOLOGY. ^ THE SPINAL CORD.—GENERAL. Among the higher vertebrates the spinal cord is found to consist of nerve-cells, nerve-fibres, and a delicate connective tis- sue binding them together; while these different structures are arranged in definite forms, so that a cross-section anywhere pre- sents a characteristic appearance, the more important gangli- onic nerve-cells being internal and forming a large part of ! ; the gray matter of the cord. All the various regions of this organ or series of organs are connected with one another, white wtth white and gray matter, as well as white with gray sub- -im^metsmm THE SPINAL CORD.— GENERAL. 481 gtauce. The cord may be regarded either as an instrument for the reception and generation of impulses independent of the \ found to lective tis- ctures are where pre- nt gangli- j^e part of ifaram;>,oM«bel- pons of this lother, white ih gray sub- F». SM.— TmwvOTw Motion of mfaial onrd of dtild six months old, at middle oC lumbwr r«gion,iliowinKeq)eeiallytlwnMnio(gn»MtMtMice. IxSO. (Aftar Oerlnch.) a,ante- rior oMumna ; b, poaterlor oolnmna ; e, Inwr nl oolamM : d. nnt«rior root* ; e, poaterior root* ; /, anterior white oomiiiliire : g, aa uU ' a l eanal lined by epittiellal eeUa ; k, oon- necUve-UHue nbatanoe aurroundlnK It ; t, tnaa*crM libers of gra/ oommlMure in iront, and k, the same behind oentnri canal ; I, two reins cot across ; m, anterior comua ; n, great l at er al ceU group of anterior oomua ; o. leaser anterior odi gvMm (oohunn) ; p, s m a l l Mt median oril group ; g, posterior coraua ; r, ascending CMwicttll In posterior brain ; or as a conductor of afferent and efferent impulses des- tined for the brain or originating in that organ. As a matter of fact, however, it is better to bear in mind that the cord and brain constitute one organ or chain of organs, which, as we have learned from our studies in development, are differentia- tions of one common track, originating from the epiblast. While the brain and the cord may act independently to a very large extent, as may be shown by experiment, yet it can not be too well borne in mind that in the actual normal life of an animal such purely independent behavior must be exceed- ingly rare. We are constantly in danger, in studying a sub- ject, of making in our minds isolations which do not exist in nature. When one accidentally sits upon a sharp object, he 81 t •im 489 ANIMAL PHYSIOLOGY. rises suddenly without a special efiEort of will power ; he experi- ences pain, and has certain thoughts about the object, etc. ria MK.-anmD«>f Mik In ootUMCtion with anterior r«N)ti of •|rfMlMrTM,a«*9W ■4Sd w^^ anterior rooto. Now, in reality this is v^ry complex, though it can be ana- lyzed into its factors. Thus, afferent nerves are concerned, the spinal cord as a reflex center, efferent nerves to the muscles called into action, the cord as a conductor of impulses which re- sult in sensations, emotions and thoughts referable to the brain ; so that if we would grasp the state of affairs it is of importance 0mm atmam WMWM JJ. he experi- M i^eB in te«na- •nee of Miterlor >d with libera of Ban beana- icemed, the she muscles js which re- o the brain ; importance THE SPINAL CORD.— OENBRAL. 488 to so combine the various processes in our mental conception that it shall in our minds form that whole which corresponds FialM. '^■J**-.:J?; ¥?P- yf- • 'ffy'w nerwmbir Md commanloMloa of Its bnuKdiea witli bteUr with nature, as we have been insisting upon fn the last chapter. With this admonition, and assuming a good knowledge of the W r» >) iiH»H BI w.'lw i|i iw i«M(*wPiw>- 484 ANIMAL PHTSIOLOOT. fi^neral and minute anatomy of the spinal cord, we shall pro- ceed to discuss its functions. The Reflex Functions of the Spinal Cord. The following experimental observations may readily be made by the 8tu^3nt himself : Let a decapitated frog be sus- pended freely (from the lower jaw). It hangs motionless and limp at first, but when it recovers from the shock (abolition of function) to the spinal cord produced by the operation, it may be shown that this organ is functional : 1. When a piece of bibulous paper dipped in dilute acid is placed upon the thigh, the leg is drawn up and wipes away the offending body. 21 If the paper be placed on the anus, both legs may be drawn up, either successively or simultaneously. 3. If the leg of one side be allowed to hang in the dilute acid, it will be withdrawn. 4. If a small piece of blotting-paper dipped in the acid, be placed on the thigh, and the leg of that side gently held, the other may be drawn up and remove the object. It may be noticed that in every case a certain interval of time elapses before the result follows. Upon increasing the strength of the acid very much this interval is shortened, and the number of groups of muscles called into action is increased. Again, th^ result is not the same in all respects when the nerve of the leg is directly stimulated, as when the skin first receives the impression. Section of the nerves of the parts abolishes these effects ; so also does destruction of the spinal cord, or the part of it with which the nerves of the localities stimulated are connected ; and more dxact experiments show that in the absence of the gray matter the section of the pos- terior or anterior roots of the nerves also renders such mani- festations as we have been describing impossible. These experiments and others seem to show that an afferent nerve, an efferent nerve, and one or more central cells are necessary for a reflex action ; that the latter ie only a perfectly co-ordinated one when the skin (end-organs) and not the nerve-trunks are stimulated ; that there is a latent period of stimulation, suggesting a central "summation" of impulses necessary for the effect ; that the reflex is not due to the mere passage of impulses from an afferent to an efferent nerve through the cord, but implies important processes in the cen- tral cells themselves. The latter is made further evident from the fact that (I) strychnia greatly alters reflex action by short- iiMkmm mimmium THE SPINAL C0RD.-6BKERAL. 486 mil pro- D. adily be 5 besus- aless and [)litioii of n, it may , piece of he thigh, iy. ^If irawn up, B^ of one ihdrawn. I acid, be held, the iterval of wing the ened, and increased, when the skin first the parts he spinal localities mis show f the pos- Lch mani- n afferent cells ave perfectly not the period of impulses the mere ant nerve thecen- lent from by short- ening the latent period and extending the range of muscular action, which, it has been shown, is not due to changes in the nerves themselves. A very slight stimulus suflBces in this in- stance to cause the whole body of a decapitated frog to pass into a tetanic spasm. We must suppose that the processes usually confined to certain groups of central cells have in such a case involved others, or that the " resistance " of the centers of the cord has been diminished, so that many more cells are now involved; hence many more muscles called into action. Normally there is resistance to the passage of an impulse to the opposite side of the cord, as is shown by the fact that when a slight stimulus is applied to the leg of one side the reflex is confined to this member. It is evident, then, that the reflex resulting is dependent on (1) the location of the stimulus, (2) its intensity and duration, (3) its character, and (4) the condition of the spinal cord at the time. Occasionally on irritating one fore-limb the opposite hind one answers reflexly. Such is a " crossed reflex," and is the more readily induced in animals the natural gait of which involves the use of one fore-leg and the opposite hind-limb together. Reflexes are often spoken of as purposive, and suggest at first intelligence in the cord ; but such phenomena are explained readily enough without such a strained assumption. EwjiiUion, heredity, and the law of habit, apply here as else- where. The relations of an animal to its environment must necessarily call into play certain nervo-muscular mechanisms, which from the law of habit come to act together when a stimulus is applied. Naturally those that make for the welfare of the animal are such as are most used under the influence of the intelligence of the animal— i. e., of the domination of the higher cerebral centers, so that when the latter are removed it is but natural that the old mechanisms should be still employed. Moreover, the reflex movements are not always beneficial, as when a decapitated snake coils itself around a heated iron under reflex influence, which is readily enough understood if we remember the tuihit of coiling aroimd objects, and what this involves — vis., organised tendencies. T^piiMMaii of BefoM,— It can be shown in the case of a frog that still retains its optic lobes and the parts of the brain pos- terior to them that, wh^n these are stimulated at the same time as the leg, the reflex, if it occurs at all, is greatly delayed. On the othei* hand, in the case of d<^, from which a part iyaii) i^JtHi^imdimm^ MP 486 ANIMAL PHTSIOIiOOT. of the cerebral cortex has been removed, the refletes are much more prominent than before. Experience teaches us that the acts of defecation, micturition, erection of the penis, and many others, are susceptible of arrest or may be prevented entirely when the usual stimuli are still active, by emotions, etc. These and numerous other facts tend to show that the higher centers of the brain can control the lower; and it is not to be doubted that pure reflexes during the waking hours of the higher animals, and especially of man, are, much less numerous than among the lower vertebrates. The cord is the servant of the brain, and a faithful and obedient one, except in oases of disease, to some forms of which we have already referred. Certain recent experiments iihow in the clearest way how the conditions of the central nervous system, and especie^y in the first instance, the brain determines the reflex time to which we shall presently refer : thus, among other influences, music and even different airs greatly alter the reflex-time, and, indeed, the whole character of the act (tendon-reflex). It is not to be supposed, however, that the processes that are clearly cerebral, and which modify normal reflexes so greatly, are all of the nature of inhibitions, or that they are at all fully understood. They are unquestionably very complex in nature, and probably too intricate to be completely un> raveled. Btflnc Time.— One of the most satisfactory methods of ascer- taining the length of time a reflex act occupies is the follow- ing: Let an electric stimulus be applied to one of the eyelids, whereupon both blink. The whole interval, minus the latent period of the orbicularis muscle and the time occupied in the transmission of the necessary nervous impulses over the nerves concerned (the fifth and facial) to and from the centers involved (medulla), giveis the duration of the processes in the brain-cells. The whole period in one instence was '0662 seconds, which, re- duced as indicated, gives '065S as the time required for the changes that take place in the brain-oells. It will, of course, be understood that at best these figures are but an approximation, owing to several possible sources of error ; also that, as has been already stated, the actual period varies with the condition of each subject at the time of ex- periment, not to mention the variations for individuals and groups of animals. In the instance chosen the brain itself was the center involved, but the same laws apply to the reflex mechanisms of the cord. 1 / 'iiiiiiiid laiwiii THE SPINAL COBD.-GBKBRAL. 487 The Spinal Cord as a Conductor of Impulses. Before considering the results arrived at in this connection, some brief account of the methods applied in the investigation of the subject is called for, to enable the student to appreciate their difficulties and possible fallacies, as well as such grounds of certainty as there may be for the conclusions reached. Three or four methods of research have been employed : 1. Sections of the spinal cord of varying extent, both unilateral and bilateral. In estimating the value to be attached to the symptoms following, the difficulties in limiting the section, the interference of haemorrhage, the inevitable results of operative shock, and, as in all experiments on the nervous system of ani- mals, the danger of misinterpreting the symptoms, must be given due weight. 3. Attempts have been made to determine the course and relations of nerve-fibers by ascertaining the order in which the different portions of the spinal nerve-fibers receive their investing myelin, those with the longest course being the latest to be thus completed. This is the method of Fleohsig, who has mapped out the cord into a series of columns, to be referred to again presently. The method is open to the objection of all anatomical ones. It is a remarkable fact that, by strictly physiological methods (i e., ascertaining the function of parts), nervous tracts have been traced, which were quite unsuspected as the result of anatomical investigation alone. Nevertheless, this method, taken with others now under con- sideration, has rendered important service. 8. Following upon experimental sections, as well as in consequence of certain dis- eases in the brain and cord, fibers have been found to degenerate along certain definite paths, owing, it is believed, to being cut off from their trophic centers; so that if, after section of the cord, there is degeneration of fibers downward, it is inferred that the trophic cells lie above the seat of degeneration and the reverse. This may be called the pathological (Wallerian) method, and in conjunction with clinical evidence has, in the case of man especially, been the chief source, perhaps, of our knowledge in regard to the conducting paths in the humAU cord; though other methods, as carried out in the lower ani- mals, have yielded results which have been supplementary and corrective; and in truth a variety of means must be employed, and the greatest caution observed, or the inferences drawn will be partial if not actually erroneous. It is to be carefully borne in mind now, and when studying I tmmSKmm Wfim>^ 488 ANIMAL PHYSIOLOGY. the brain, that a conducting path in the nervous centers is not synonymous with conducting fibers. The cells themselves and the neuroglia probably are also conductors. We shall now en- deavor to map out, as estab- lished by the method of Flech- sig. Waller, and others, the main fiber tracts of tha spinal cord. 1. Antero- median Cdkmma (columns of Tdrck). These probably decussate in the cerv- cial region, where they are most marked, constituting the direct or uncrossed pyramidal trapt, and disappear in the lower dor- sal region. Secondary deg^eration en- sues in these tracts upon cer- tain brain-lesions, in the motor 2^S„±5'^^glSS5SS&S%! regions. «. Crossed Pyramidai Tracts. — ^"ihey pass forward to form part of the anterior pyramids of the medulla after decussation in their lower part. Similarly to the first, degeneration follows in tbese tracts when there are brain-lesions of the motor area. H^ice, both of these constitute descending motor paths. 9. Anterior FasetcvH (fundamental or ground bundle). — They possibly connect the gray matter of the cord with that of the medulla. 4. Anterwr Eadieular Zones, in the anterior part of the lat- eral column. 6. Miseed Lateral CoZuntTM.— These and tiie preceding are functionally similar to & Xeither 8, 4, nor 6 degenerate, on section of the cord, from which it is inferred that they have trophic cells both above imd below. 6. Dweel Cerd>eaar Tracis.—TheBe bundles, passing by the funiculi graciles or posterior pyramids of the medulla, reach the cerebellum by its inferior peduncles. These fasciculi enlarge from their site of origin in the lum- bar cord upward. After section of the cord they show ascend- ing degeneration, so that it seems probable that their trophic on the teachings of locomotor ataxia in the human subject. The symptoms of this disease are found associated with lesions of the posterior columils of the cord. The essential feature is an inability to co-ordinate movements, though muscular power may be unimpaired. But such inco-ordination is not usually the only symptom; and, while the disease seems usually to begin in Burdach's columns, the columns of Gtoll, the posterior nerve-roots, and even the cells of the posteirior comtia, may be involved, so that the subject becomes very complicated. Go-ordination of muscular movements is normally dependent upon certain afferent sensory impulses, themselves very com- plex. It is to be remembered also that there are numberless V^mf. fto. sir.— DtaiTun to ilhiitrale pw*«M» ("ww J Iqr Hbcra c( nervMOOli OB connecting links between the two sides of the cord and be- tween its different columns of an anatomical kind, not to men- tion the possibly numerous physiological (functional) ones. We have stated above that section of one lateral half of the cord is followed by loss of sensation on the opposite side of the body ; but directly the contrary has been maintained by other observers ; while still others maintain that the effects are not ^^ ;li a case, 9ir sensa- ui>on the ject. The lesions of ktare is an lar power >t usually isually to ) posterior ■ntia, may mplicated. dependent very com- umberless OliOB rd and be- lot to men- l)one8. half of the side of the d by other ots'arenot THE SPINAL COBD.-OBXBRAL. 491 confined to one side, though most pronounced on the side of the section. The same remark applies to motion. While there is considerable agreement as to the pyramidal tracts of the lateral column, the functions of the rest of these divisions of the cord are by no means well established. It is possible that vasomotor, respiratory, and probably other kinds of impulses, pass by portions of the lateral tracts other than the crossed pyramidal. When a lateral half of the cord is divided, the loss of function is not permanent in all instances, but has been recovered from without any regeneration of the divided fibers ; and even when a section has been made higher up on the opposite side, partial recovery has again followed : so that it would appear that impulses had pursued a zigzag course in such cases. We do not think that such experiments show that impulses do not usually follow a definite course, but that the resources of nature are great, and that, when one tract is not available, another is taken. It is plain that impulses do not in any case travel by one and the same nerve-fiber throughout the cord, for the size of this organ does not permit of such a view being entertained ; at the same time there is i relation between the size of a cross* section of the cord at any one point and the number of nerves connected with it at that region. T IT m n I SMTtd. T trm n I XwMter. iznTmvnnT IT m B I vmranr it ut Bortot. Ctmfeol. n I Fto. SIB.— IMatnm to tmatrate rriattreaiid itlMohiteuteiit of (l)gf«y mirtt^ mBOi lnwiei)iMlTB»wiiMwi«l«wMottpliialc(>rtLjaid(a)ieettoiial>wMoCaeTwml^^ We may attempt to trace the paths of impulses in the cord somewhat as follows: 1. Volitional impulses decussate chiefly in the medulla oblongata, but also, to some extent, throughout the whole length of the spinal cord. They travel in the lateral columns (crossed pyramidal tracts chiefly, if not exclusively), and eventually reach the anterior roots of the nerves through the anterior gray comua, passing to them, possibly, by the ante- 498 ANIMAL PHTSIOIiOOT. rioT columns. From the cells of the anterior cornna, impulses travel by the anterior nerve-roots to the motor nerves, by which connection is made with the muscles. 2. Sensory im- pulses enter the cord from the afferent nerve-fibers by the pos- terior nerve-roots, passing probably by the posterior columns to the posterior comua, thence to the lateral columns, decussation being largely immediate though not completed for some dis- tance up the cord. i Ha^ 6S24J I' LOWER LIMIT OF MKDULU oerebelUr flben ; 4, 4', flben retetad to " mnfC^^ieiiM, ture. Tha motor il(«ateriorliorB). _._ Ithirttliew tpoaterior (Tt would seem that the lateral columns are the great high- ways of impulses; though in all instances it is likely that the gray matter of tl^ cor^ plays an important part in modify- ing them before they reach their destination. Some observers MMiMiia la, impttlBes nerves, by Sensory im- by the pos- > columns to decussation }r some dis- i.r. luUilr a,«^,'). ft upon It. e great high- kely that the •t in modify- >me observers THE SPINAL COKD.-QBNERAL. 498 believe that sensory impulses giving rise to pain travel by the gray matter of the cord nlmost exclusively. It would be easy to lay out the paths of impulses in a more definite and dog- matic manner ; but the evidence does not seem to warrant it, and it is better to avoid making statements that may require serious modification, to say the least, in a few months. The prominent principle to bear in mind seems to be that while there are tracts in the cord of the animals that have been exam- ined and probably of all that have well-formed spinal cords, along which impulses travel more frequently and readily than along others, it is equally true that these paths are not invaria- ble, nor are they precisely the same for all groups of animals. The cord can not be considered independently of the brain ; and there can be no doubt that the paths of impulses in the former are related to the constitution, anatomical and physiological, of the latter. It is still a matter of dispute whether the cord is itself irritable to a stimulus. As a whole it is without doubt ; as also the white matter by itself. The gray matter is certainly conducting, but whether imtable or not is still doubtfuL Why the sensibility of the side of the body on which one lateral half of the cord has been divided should be increased (hypereesthe- sia), is also tmdetermined. Possibly it is due to a temporary disturbance of nutrition, or the removal of certain usiutl inhibi- tory influences from above, either in the cord or brain. Thb Automatic Functions of the Spinal Cobd. Reference has been already made to the fact that when por- tions of a mammal's cerebrum are removed the reflexes of the cord become more pronounced, owing apparently to the removal of influences operating on the cord from higher centers. When the cord itself is completely divided across, it often happens (in the dog, for example) that there are rhythmic movements of the posterior extremities — ^i. e., when the animal has recovered from the shock of the operation — that part of the cord now independent of the rest and of the breftn seems to manifest an unusual automatism. The question, however, may be raised as to whether this is a purely automatic effect, or the result of reflex action. But, whichever view be entertained, these phenomena certainly teach the dependence of one part upon another in the normal animal, and should make one cau- tious in drawing conclusions from any kind of experiment, in regard to the normal functions. As we have often urged in 4M ANIMAL PHTSIOLOOr. the foregoing chapters, what a part may under certain circtun- stances manifest, and what its behavior may be as usually placed in its proper relations in the body, are entirely different, or at least may be. When one leg is laid over the other and a sharp blow struck upon the patella tendon, the leg is jerked up in obedience to muscular contraction. It is not a little difiScult to determine whether this result is due to direct stimulation of the muscle or to reflex action, the first link in the chain of events necessary to call it forth originating in the tendon; hence the term tendon-reflex. But at present it is safer to speak of it as the " knee-jerk," or the " tendon-phenomenon." It disappears, however^ when the spinal cord is destroyed or is diseased, as in locomotor ataxia, or when the nerves of the muscles or the posterior nerve-roots are divided, showing that the integrity of the center, the nerves, and the muscles are all essential. There are normally many such phenomena (reflexes) besides the " knee-jerk." Anol-her question very difficult to decide is that relating to the usual condition of the muscles of the living animal. It is generally admitted that the muscles of the body are all in a somewhat stretched condition, but it is not so clear whether the skeletal muscles are under a constant tonic influence like those of the blood-vessels. It is certain that, when the nerves going to a set of muscles are cut, when even the posterior roots of the nerves related to the part involved are divided or the spinal cord destroyed, there is an unusual flaccidity of the limb involved. But the natural condition may be, it has been suggested, the result of reflex action. The subject is probably more complex than it has hitherto been considered. The facts of such a case — those of the tendon-phenomenon and similar ones— would be better understood if the spinal cord, the nerves, and the muscles associated with them, were regarded as parts of a whole so connected in their functions that severance of any one of them leads to disorder of the rest. That the colls of the cord are constantly exercising an influence through the nerv^royed or is Tes of the owing that jcles are all a (reflexes) relating to imal. It is are all in a ar whether Suence like the nerves terior roots ided or the iity of the it has been is probably henomenon the spinal them, were r functions of the rest, ui influence turn do not r influenced 3 the condi- )d, the case, ly reflex, or )y any com- te unjustifi- ism of parts is both constant and essential to their well-being ; and in such a case as that now considered it may be that a certain degree of tonus is normal to a healthy muscle in its natural surround- ings in the body. There is now considerable evidence in favor of placing cer- tain centers presiding over the lower functions, as micturition, defecation, erection of penis, etc., in the spinal cord of mam- mals, especially its lower part — which centers, if they be not automatic, are not reflex in the usual sense ; but their considera- tion is better attempted in connection with the treatment of the physiology of the parts over which they preside. Special Considerations. OompantlTe. — Among invertebrates thev« is, of course, no spinal cord, but each segment of the animal is enervated by a special ganglion (or ganglia) with associated nerves. Never- theless, these are all so connected that there is a co-ordination, though not so pronounced as in the vertebrate, iu which the actual structural bonds are infinitely more numerous, and the functional ones still more so. From this result possibilities to the vertebrate unknown to lower forms ; at the same time, in- dependent life and action of parts are necessarily much greater among invertebrates, as evidenced especially by the renewal of the whole animal from a single segment in many groups, as in certain divisions of worms, etc. It also follows from the same facts that a vertebrated ani- mal must suffer far more from injury, in consequence of this greater dependence of one part on another ; a thousand things may disturb that balance on which its well-being, indeed, its very life hangs. It is noticeable, moreover, that, as animals occupy a higher place in the organic scale, their nervous sys^ tern becomes more concentrated; ganglia seem to have been fused together, and that extreme massing seen in the spinal cord and brain of vertebrates is foreshadowed. In the chapters on the brain numerous illustrations of the nervous system in lower forms will be found. ^he fact that the brain and cord arise from the same germ layer, and up to a certain point are developed almost precisely alike, is full of significance for physiology as well as morphol- ogy. That original deep-lying coimection is never lost, though functional differentiation keeps pace with later morphological differentiation. But even among vertebrates the spinal cord 496 ANIMAL PHTSIOLOGY. shows a complexity gradually increasing with ascent in the organic series. In the lowest of the fishes or vertebrates {Am- phwxua lanceolatus) the creature possesses a spinal cord only and no brain, so that an opportunity is afforded of witness- ing how an animal deports itself in the absence of those direct- ive functions, dependent on the existence of higher cerebral centers. The Lancelet spends a greai part (>f its life buried in mud or sand on the bottom of the ocean, and its existence is very similar to that of an invertebrate, though, of course, the dependence of parts on each other is somewhat greater. BralntioB. — According to the general law of habit and in- heritance, we should suppose that at birth each group of ani- mals would manifest those reflex and other functions of the cord which were peculiar to its ancestors. Observation and experiment both show that reflexes, etc., are hereditary ; that they tend to become more and more so with each generation ; and at the same time that habit or exorcise is essential for their perfect development. They stand, in fact, in the same relation as instincts, which are closely connected with them. Like the latter, they may be modified by way of increase or diminution and otherwise. To illustrate, it can not be doubted that gallop- ing is the natural gait of horses, as shown by the tendency of even good trotters to "break" or pass into a gallop; but it is equally well known that famous trotters breed trotters. In other words, an acquired gait becomes organized in the nervous system (especially) of the animal, and is transmitted with more and more fixity and certainty with the lapse of time. But all experience goes to show that walking, running, or any of the movements of animals are, when fully formed as habit-reflexes, dependent for their initiation on the will in most but not all instances, and require for their execution certain combinations of sensory and other afferent impulses, and the integrity of a vast complex of nervous connections in the spinal cord. J I is well known that one in a period of absent-mindedn^ walk into a building to which he was accustomed to go years before, though not of late, showing plainly that volition was not momentarily required for the act of walking and all else that is involved in the above behavior. It suggests that certain nervous and muscular connections have been formed, function- ally at least. Plainly, then, we should not expect each indi- vidual man's spinal cord to be the same, but that the series of mechanisms of which every spinal cord is made up should differ with experience ; and if this holds for individuals, how much cent in the brates (Am- kl cord only of witness- ihose direct- ler cerebral life buried existence is ' course, the ater. ibit and In- roup of ani- tions of the rvation and ditary; that generation ; bial for their ame relation a. Like the r diminution i that gallop- tendency of >p; but it is trotters. In I the nervous )d with more me. But all r any of the abit-reflexes, ) but not all sombinations ategrity of a cord. t-mindedn^ itomed to go that volition g and all else 9 that certain led, function- 3t each indi- the series of should differ s, how much THE SPINAL CORD.-OENERAIi. 497 more must it be true of different groups of animals, the habits of which differ so widely ! Experiment has proved this also so far as it has gone ; hence the great danger of laying down laws for the spinal cord from the investigation of one animal or even one group. Recent investigations have shown that, in persons crippled from birth, or for long periods, reflexes which had never been properly established may, as the result of opera- tive procedure, become possible through training. It has also been shown, both by experiment Mid clinical experience of the kind referred to, that when certain reflexes are imperfectly de- veloped others are also defective, again impressing the im- portance of that balance of development which is essential to health or the normal condition of an animal. This subject is very wide, of great practical importance, and deserves consider- ation beyond what our limits of space will allow. All the facts go to show that the cord is made up of nervous mechanisms — if we may so speak — which are naturally associ- ated, both structurally and functionally, with certain nerves and muscles ; these, like the paths which impulses take to and from the brain, though usual, are not absolutely fixed, though more so as reflex than conducting paths, while they are con- stantly liable to be modified in action by the condition of neighboring groups of mechanisms, etc. We have said less about the gray matter of the cord as a conductor than its importance perhaps deserves. It is believe^ \ by many that impulses which give rise to sensations of pain/ always travel by the( gfray mattery and there is not a little evi-' dence to shoW that, when none of the white columns are avail- able owing to operative procedure, disease, or other disabling cause, the gray matter will conduct impulses that usually pro- ceed by other tracts. BjnoptieaL — The spinal cord is composed of large ganglionic nerve-cells, fibers, and connecting neuroglia. Functionally it is a conductor, the seat of certain automatic centers and of reflex mechanisms. Probably in every case the one function is to a certain extent associated with the other — i. e., when the (X>rd acts reflexly it is also a conductor, and the cells concerned are so readily excited to certain discharges of nervous energy that automaticity is suggested, and so in other instances: thus, in the case of automaticity, reflex influence or afferent impulses are with difficulty entirely excluded from consideration. The great majority of conducting fibers seem to cross either in the cord itself or in the medulla oblongata. The conducting n i ■5 1 I WIMDKHllMtlWI iiMiBiMMmiiawnaMMMiiiii^ *#* 498 ANIMAL PHYSIOLOGY. paths that have been shown by pathological and clinical inves- tigation to be best marked out in the spinal cord are those for voluntary motor impulses. So far as the functions of the hu- man organ are concerned, clinical and pathological facts have thrown the greatest amount of direct light on the subject; but the inferences thus drawn have been modified and supple- mented by the results of experiments on certain other mam- It is especially important to bear in mind that, while certain conducting paths are usual, they are not invariable; in like manner, reflex impulses may not be confined to usual groups of cells, but may extend widely, and so bring into action a large number of muscles. The resulting reflex in any case is depend- ent on the character, intensity, and location of the stimulus, and especially on the condition of the central cells involved. In the whole functional life of the cord the influence of higher centers in the organ itself and especially in the brain is to be considered. The cord is rather a g^up of organs than a single one. s. THE BRMN. The methods of investigating the functions of the brain are analogous to those employed for the cord, and may be classed as physiological proper and pathological, though, as a matter of fact, neither one nor the other is now considered as reliable when taken alone. With the pathological is generally in- cluded the clinical method; and the conclusions thus derived, are corrected and supplemented by the results obtained by sec- tion, removal, or other operative procedure affecting parts of the brain. The difiRculties are still great-er than in the case of the cord; ob account of the extreme complexity of the organ, especially in. the higher mammals and man. At the outset we may remark that the whole subject will be studied more profitably if it be borne in mind that— 1. The brain is rather a collection of organs, bound together by the closest anatomical and physiological ties than a single one; in consequence of which it is quite impossible to understand the normal function of one part without constantly bearing in mind this relationship. This aspect of the subject has not re- ceived the attention it deserves. No one regards the aliment- ary tract as a single organ ; but it is likely that the dependence functionally of one part of the digestive oanal upon another _i>4&S3|WKi£& oical invea- re those for ; of the hu- facts have abject; but ind supple- other mam' hile certain ble; in like al groups of stionalarge ie is depend- lie stimulus, [la involved. ce of higher rain is to be han a single he brain are iy be classed , as a matter d as reliable generally in- thus derived, ained by sec- ting parts of in the case of >f the organ, subject will thai— 1. The lather by the dngleone; in iderstand the bearing in lot has not re- the aliment- le dependence upon another THE BRAIN. 499 is not more intimate than that established in that great collec- tion of organs crowded together and making up the brain. 2. Since the relative size, position, and anatomical connections of the parts that make up the brain are different in different groups of animals, not to speak of the fact that the functions of any part of the brain of an animal, like that of its spinal cord, already alluded to, must depend in great part upon its own and its inherited ancestral experiences, it follows that the greatest caution must be exercised in applying conclusions true of one group of animals to another. As we shall point out, the neglect of this precaution has led to needless contro- versy and much misunderstanding. 3. It follows, from what has been referred to in 1 above, that conclusions based upon the behavior of an animal after section or removal of a part of the brain must be, until at least corrected by other facts, received with some hesitation. 4. It also might be inferred from 1 that it is desirable to study the simpler forms of brain found in the lower vertebrates, in order to prepare for the more elaborate development of the encephalon in the higher mammals and in man. 6. The embryological development of the organ also throws much light upon the whole subject. The student will see from these remarks that a sound knowl- edge of the anatomy of the brain and its connections is indis- pensable for a just appreciation of its physiology; nor must such knowledge be confined to the human or any other single form of the organ. There is only one way by which this can be attained : dissection, with the help of plates and descriptions. The latter alone frequently impart ideas that are quite errone- ous, though they serve an especially good purpose in helping to fix the pictures of the natural objects, and iu reviving them when they have become dim. It is neither difficult to obtain nor to dissect the brain of the fish, frog, bird, etc. Valuable material may be saved and the subject approached profitably, if, prior to the dissection of a hu- man brain, a few specimens from some group or groups of the domestic animals be examined. However useful artificial brain preparations may be, they are so far from nature in color, con- sistence, and many other properties, that, taken alone, they cer- tainly may serve greatly to mislead ; and we hope the student will allow us to urge upon him the methods above suggested for getting real lasting knowledge. The figures given below may prove helpful when supplemented as we advise. The great difference in total size, and in the relative propor- wiwiiirittMi:;i'iiMiiti(iiMiiiaw mmm 600 ANIMAL PHYSIOLOGY. tion, situation, etc., of parts, will, however, be obvious, from the figures themselves; and as we have already pointed out more than once, the preponderance of the cerebrum in man must ever be borne in mind in the consideration of his entire organization, whether physical, mental, or moral ; or, to put the matter otherwise, all man's functions are the better under- stood by the. remembrance of this one fact, which will be at once illustrated when we consider the result of removal of the cerebrum in animals. Animals dbpkivbd op the Cerebrum. The cerebrum may be readily removed from a frog, without producing either severe prolonged shock or any considerable hromorrhage. Such an animal remains motionless, unless when stimulated, though in a somewhat different position from that of a frog having only its spinal cord. It can, however, crawl, leap, swim, balance itself on an inclined plane, and when leaping avoid obstacles. One looking at such an animal per- forming these various acts would scarcely suspect that any- thing was the matter with it, so perfectly executed are its movements. We are forced to conclude, from its remaining quiet, except when aroused by a stimulus, that its volition is lost ; but, apart from that, and ttie fact that it evidratly does not see as well as before, it appears to be normal, (it has^p intelligenWireotive power over its movements. It remains, ThereiOTe, to ejq^ainTiow irtrtfiatrttSey are so much more complete, so much better co-ordinated in the entire animal than when only the spinal cord is left. It seems to be legitimate to infer that the other parts of the brain contain the nervous machinery for this work, which is usually stimulated to action by the will, but which an external stimulus may simulate. All the connections, structural and functional, are present, except those on which successful volition depends. The frog with the cord only, sinks at once when thrown into water; when gently placed on its back, it may and probably will remain in that position, without an attempt at recovery. There is, in fact, verv limited power of co-ordination. Removal of the cerebral lobes in the bird is more likely to be attended with diflttculties, and conclusions must be drawn with greater caution. But a pigeon may be kept alive after such an operation for months. It can stand, balancing on one leg ; recover its posi- vions, from pointed out iim in man f his entire ; or, to put Btter under- i will be at loval of the rog, without sonsiderable unless when n from that n, however, le, and when [ animal per- ct that any- ated are its 18 remaining 8 volition is idently does 1. (tt has jip It remains, much more animal than legitimate to the nervous ,ted to action mulate. All eeent, except 'rog with the when gently ooaib in that e is, in fact, ore likely to ist be drawn )peration for aver its posi- THE BRAIN. 601 tion when placed on its side; fly when thrown into the air; it will even preen its feathers, pick up food, and drink water. /Its movements are such as might be those of a stupid, drowsy, lor probably intoxicated bird; but it is plainly endowed with '.vision, though not as good as before. But spontaneous move- ments are absent, and the peeking at food, etc., must be consid- ered as associated reflexes, and as such are very interesting, in that they show how machine-like, after all, many of the appar- ently volitional acts of animals really are. In a mammal so great is the shock, etc., resulting from the operative procedure, that the actual functions of the remaining parts of the brain, when the cerebral convolutions are removed, are greatly ob- scured ; nevertheless, little doubt is left on the mind that homol- ogous parts discharge analogous functions. It can walk, run, leap, right itself when placed inan unnatural position, eat when food is placed in its mouth, and avoid obstacles in its path, though not perfectly. Yet it remains motionless unless stimu- lated ; all objects before its eyes impress it alike if at all. (j^e animal evidently has neither volition nor intelligence; Now, if iny of the parts between the oerebrum and the medulla be removed, the creaturer shows lessened co-ordinating power ; so that the inference, that these various parts are essential consti- tuents of a complex mechanism, all the components of which are necessary to the highest forms of muscular co-ordination and probably other functions, is unavoidable. rrhere are all degrees of consciousness, and it is quite impos- sible to determine the extent to which this is interfered with in animals treated as described. While there can be no doubt that for th» possession of the higher forms of consciousness (as for the perfection of all visual and other sensory processes) the Voere]^um_i8 necessary. It would, however, be very hazardous to state that, apart from this part of the brain, consciousness did not exist. Whe^ the whole enoephalon is removed, the spinal cord alone remaining, it would not be legitimate to in- fer consciousness in the sense in whioE that word is tisuaily implied ; at the same time, in the intact vertebrate, we may believe that consciousness is in some sense, at least re- lated in indefinable ways to all the vital processes, if not their actual resultant ; inasmuch as, either directly or indi- rectly, the nervous system in all its parts is functionally con- nected, and influences and is itself influenced by every cell in the body. Since we are dealing with co-ordinated movements, we may I * , I 602 ANIMAL PHYSIOLOGY. how treat of the functions of a portion of the ear, according to our present classification. Have the Sehicibcular Canals a Go-ordinatino Function ? Physiologists have as yet heen unable to assign to the semi- circular canals a function in hearing, and upon certain results, partly of disease but chiefly of experiment, it has been con- cluded, though somewhat dubiously, that they are concerned with those sensations that conduce to or are essential to main- tenance of the sense of equilibrium ; in a word, that they are the organs of that sense in the samb way that the eye is the organ of vision. Iq^triawAtaL— When in a bird, as a pigeon, one of the mem- branous semicircular canals'On one side is cut through, move- ments of the head, varying with the canal cut, result ; though these are not permanent, when the operation is unilateral. After the bilateral operation a bird flies with difficulty, eats and drinks, but not as usual, and behaves generally in a way to in- dicate loss of co-ordination. It appears to be dizzy. It can hear well, and is not paralyzed, nor is there even weakness of the muscles. The phenomena in other animals, while not quite the same, indicate that the essential failure is in co-ordination of muscular movements. When the peculiar movements of the head or eyes, at first ensuing on operation, are permanent, it is iwssible that there may have been injury, either primary or secondary, to the cerebellum or other parts of the brain. There are Very many ways in which giddiness and consequent inco^ ordination may be induced in man and the lower animals. When this is brought about by rapid rotation, both the disturb- ance in the distribution of the blood within the cranium and actual displacement of brain-substance, or at least molecular disorder, must be at the bottom of the matter. ^ Meniere's disease, vertigo is a prominent symptom in certain cases, but absent in others. Again, it is asserted that vertigo may be induced in animals in which both auditory nerves are divided. For our own part, we lielieve an undue im- portance has been attached to the sen xiular canals in the present connection. Experiments on an mals can not aJone solve such problems as this, for the reason that we can never know, except in the vaguest way, their states of consciousness. Indeed, the latter must always be interpreted by our own, or THE BBAIN. 608 Eiccording to [NATINQ to the semi- "tain results, IS been con- 's concerned tial to main- hat they are le eye is the of the mem- ■ough, move- mlt ; though s unilateral, ilty, eats and a way to in- It can hear kness of the aot quite the ordination of nents of the manent, it is primary or >rain. There lequent inco^ irer animals. 1 the disturb- cranium and st molecular symptom in asserted that oth auditory an undue im- canals in the oi not alone ve can never onsciousness. r our own, or remain inscrutable ; so that it follows that human conscious- ness must be the final court of appeal ; and that we must de- pend more upon clinical and pathological investigation than upon experiment ; but even this is not final, and in the end our own conscious experience will alone enable us to interpret facts of the character now discussed. Assume that a human subject has been operated upon as above indicated, and feels so dizzy that he is unable to walk steadily, and ]>o8sibly unable to re- main standing. If interrogated, what would be the answers given by an accurate reporter, with no bias from any theory whatever bearing on thfi subject ? As we conceive, somewhat as follows: "How d' y u feel ? Why can you not rise and remain standing, or ytuik i" "I feel all confused. I can not stand or walk because I do not seem to be able to make out what I should do. I have no clear ideas of things about me, and so do not know how to proceed." Put in more abstract or generalized form, this amounts to saying : "(£>m so confused by conflicting sensations that all my old judgments about the world are upset, yet memory and reason, in so far as I can exer- cise them, tell me that they are wrong, and I fear to act, and so remain still ; or, when I do try to stand or walk, my confusion leads to a sort of loss of control over my thoughts and feelings, and therefore my will-power, so that any effort to walk is fee- bly directed by will, and little regulated by my usual feelings; hence I accomplish little, and lose confidence in myself^ Such may be considered an attempt, and only fairly successful, no doubt, so great is the complexity of the state of consciousness resulting, to describe the condition of a human being under such circumstances, as derived from a consultation with our experiences under peculiar conditions, as the various forms of giddiness, intense and sudden surprise, and a host of others not readily named but still real. With a bird or quadruped the case must be somewhat similar. It has been suggested that there is experimental evidence to show a power of estimation of the distance and direction through which a human subject is moved, independent of the data fur- nished by other senses, as sight, tactile, and muscular sensation, etc. When an individual, blindfolded, lies upon a flat surface and is gently rotated through a certain angle, it is said that the subject of the experiment can make a fair estimate both of the direction and distance through which he is moved, from which it is argued that there is a sense answering to this result, and located, presumably, in the semicircular canals. But, in the f. I I iiaimmKmiimiiikmalm inwwii.iiWiiwiniiii'iiiiu 604 ANIMAL PHYSIOLOGY. first place, we very much doubt whether, in such »n experi- ment, tactile and muscular sensation is in abeyance, and, in the second place, if it were, there are associated sensations, pos- sibly from the vascular and lymphatic systems, and many other sources within, which can not be ignored. We do not •even yet seem to be suflBciently alive to the delicacy and the immense variety of our sensations, some of which are abso- lutely indefinable ; otherwise we do not think such experiments as that above cited would be adduced in proof of a special sense of equilibrium. Qjntil farther evidence is forthcoming, then, we are not in- clined to give assent to the existence of any mechanism in the senuciccular canals, affording sensory data so enti/ely different from those furnished by other recognized (and unrecognized) sense-organs, that upon them alone, or in a manner entirely their own, arises a consciousness of equilibrium. We are in- clined to regard the latter as depending upon the fusion in con- sciousness of a vast complex of sensations ; and that upon the whole being there represented, or a portion wanting, depends either the preservation of equilibrium, or a partial or entire loss of the same. Nevertheless, it is higUy probable that sensory impulses of a very important character, in addition to such as are essential for hearing, may proceed from the semicircular canals, and indeed other parts of the labyrinth of the ear. V Forced Movsmknts. When certain portions of the brain of the mammal have been injured, movements of a special character result, and, inasmuch as they aii*e not voluntary, in the ordinary sense at least, have been spoken of as forced or compulsory. The move- ments may be classified according as they are aroimd the long vertical or the transverse axis of the body of the animal. Hence there are " circus " movements, when the creature siiiiply turns about in a circle, " rolling " movements, etc. These and others may be toward or from the side of injury. While in some cases there may be a certain amount of muscular weakness in consequence of the injury, which may, in part, account for the direction of the movements, this is not so in all cases; nor does it, in itself, explain the fact of their being plainly not volun- taixin the usual sense. cThe parts of the brain, which, when injured, are most liable to be followed by forced movements are the basal ganglia (cor- nmiiii unriiiWiri ITTrTTT'- »n experi* Lce, and, in ations, pos- and many We do not «y and the ix are abeo- xperiments f a special are not in- lism in the fly different recognized) ler entirely We are in- don in con* %t upon the ag, depends r entire loss liat sensory n to such as emicircular leear. mmal have result, and, iry sense at The move- nd the long nal. Hence imply turns ) and others ile in stnne vreakness in >unt for the »s; nor does f not volun- I most liable fanglia (cor- THB BKAIN. 505 pora striata and optic thalami), the crura cerebri, corpora quad- rigemina, pons Varolii, and medulla oblongata, and especially if the section be unilateral. We have already seen that several of these parts are concerned in muscular co-ordination ; hence the disorderly character of any movements that might now re- sult when any part of this related mechanism is thrown out of gear, so to speak ; but, apart from that, we think that the view presented in the previous sections is applicable in this case also, while the forced movements themselves throw light upon the symptoms following injury to the semicircular canals. When that constant afflux of sensory impulses toward the nervous centers is interfered with, as must be the case in such sections as are now referred to, it is plain that the balance in consciousness must be disturbed ; confusion results, and it is not surprising that, instead of a passive condition, one marked by disorderly movements should result in an animal, since movement so largely enters into its life-habits. It is important to remember, in this connection, that the great highway of im- pulses between the cerebral cortex and other parts of the brain and the spinal cord lies in the very parts of the encephalon we are now considering. ■ Functions or thb Ckrebbal Convolutions. C o apa r a t if. — It will conduce to the comprehension of this subject if some reference be now made to the development of the brain in the different groups of the animal kingdom. (^vertebrates not only have no cerebrum, but no brain in the strict sense of the term as applied to the higher mammals. In most forms of this great subdivisicm of the animal kingdom, the first or head segment is provided with ganglia arranged in the form of a collar around the oesophagus, by means of com- missural nerve connections; so that the nervous supply of the head is not widely different from that of the other segments of the body. But as we ascend in the scale among the in- vertebrates these ganglia become more crowded together, and so resemble the vertebrate brain with its massed ganglia and numerous connections through nerve-fibers, etc. But in this respect we find great difference among vertebrates. We can recognize, on passing upward from the Amphioxua, destitute of a brain proper, to man, all gradations in the form, relative sizgt multiplicity of connecting ties, etc. /Speaking generally, there is great difference in the weight ; :WtK|iMiti>Bi.tliWWlMl iwtiitiiWfltrtiiit utmmmm mmmimmi 606 ANIMAL PHTSIOLOGT. fta. 351. Fw. aw.— NerroiN urt^m ot madlciiMl Iceoh (•fter Ow««). a, double mpr«>oempliMMl ipuiSliaa comiected wttb mdimenUuT ocelli (6, 6) by nervet ; c, double iiifnMMoplMaedl gMiglioaic niMB, wfaidi In conUimous with double ventnl oora, IWTiiiir oompound nnsilft •t NNter Interrala Fia. «U.-}fenroai qratem of the oominon muMel (after Owen). I, labial ganglia ooonected by a ahort conunlMiM above and in fMnt o? moi^ ; b,b, branchial ganBla, eanaectwl in Uke maiuHr, and united by tour aervoue ooMto M. d) wUh labial ganiRla : », Ulobed pedal ganglion aendiiw braaehea to the muscular foot (r), and cloaely unlMwith the "auditorr laoailea" Q) : h, h', drcum-paliial plexua; y, byaras, by which the animal can attach ilaelt to fofaiiEa bodtea (anchor) of the cerebrum, both relative and absolute. In all animals be- low the primates (man and the apes) the cerebellum is either not at all or but imperfectly covered by the cerebrum ; while in man, so great is the relative size of the latter, that the^ cerebellum is scarcely visible from above. If we ex(;ept the elephant, in which the brain may reach the weight of ten pounds, and the whale with its brain of more than five pounds in the largest specimens, the brain of man is even absolutely heavier than that of any other animal, which is in great part due to the preponderating development of the cerebrum. While the cerebral surface is smooth in all the lower verte- brates, and but little convoluted imtil the higher mammals are ^ai^iii ..ji. I J ^1 1 t^ At l l tfl ii il 1ltfai. »i ^ i i »i i^ ^ W il> i'* *rum. lower verte- ammals are rf. .■■'" Tin. '< THE BBAIN. m I Fta.1 rn. 854. na.aB6w Fra. aw.-ir«r*oas vyrtem of * wklte ant, IWihm 'tttet QeKenbMir and Lemte). S** g»--SywM *y*em of a water beHle, ZMUIbum (after Gegenbaur)/^ "* • ■»••— Herwwi mtem of a fljr, JAiaea (after Gteeenbaur and Blandiard). o. eyee ; plM«eal gangUon ; gr, gr*, gr*, tvaSd _„ Mowcw janulla. '"••J5sr";P'2??*wB?*ffi ** A orah. IWiHurtif tmlga, ..i, A/awtng considerable ttuion ot faniga (after Mtfne-Mwarda). a, ftiMd oereliral ganc^ ; b.^W oMnplWKeal corda ; , me- Tanw: t, nppw nwdi of TBgua; shMoCvagw. THE BRAIN. 60» reached, the brain of the primates, and especially of man, has its surface enormously increased, owing tu its numerous fis- sures and convolutions, which, in fact, arise from the growth of the organ being out of proportion to that of the bony case in which it is contained; and since those cells which go to '^^-"^iiiMrt^W^ t 9 '<&'- Fia. 880.— Brain and apinal cord of frog (Bastian). A, otfactory lobe* ; B, cerebral lobeR ; R, pineal body ; C, D, optic lobes ; E, oerebeUum ; U, ■pinal oord. The cerebelluin la notably amall. make up the gray matter and are devoted to the highest func- tions, are disposed over the surface, the importance of the fact in accounting for the su^ierior intelligence of the primates, and especially of man, be jmes apparent. Depth of Assuring is, however, of more importance than aultiplicity of furrows ; and it may be observed that in*: HigCire is not always in pro- portion to the extent to which the cerebral surface is broken 7M.M1. FM. SM). 'POm above (Huxley). A, tbe olfactory nerves or lobM, '•jtt ; B, the cerebral nemi*id>erea : C, the optic loban D, Flo. MO.— Bratai of the pike. *<*>■ and beneath thnn the optic ■ the cerebdium. Fio. 881.— Tbe bitain of edible frotr (Antia ewMieafa). 1x4. (Afen- Huxley.) L. ol. the riilnenaephalan, or olfaotory lobea, with /. the olfactory nerves : He, tbe cerebral henrf Bpheree : Fk. o, the thalamenoeidialon with the pineal riand, Ph ; L. op. optic lobea ; C, oerebeUum ; a.rk,thr i'oiuth ventricle ; 3to, medulla oblongata. np into fisexr ;S iud convolutions. The depth of the gray mat- ter is also very wriable, and seems to betur an important rela- tion to psychic development. Man's brain, then, is character- ized by its great size and oomplezity ; while those parts treated l i Bwa.'4t;-aw- ' .jj.>jjjk..asj.jiiiMiii ii iHMia « a i » tta'.'juuttw» ' m ii Jj,< ! M'.'« i jii«jistwj |i>i jM. > i .;^ ^ ^ SB ftlO ANIMAL PHYSIOLOGY. ^^ Fio. an-Braiim of » Miard (PaammomurM* B^mgalmMi mdofa bM (JMM«:ito mOiifMm) ItilMiaitiMUiid and Tertical Motion. The upMr fl«ii« rMpnMnts tte UwirdHi brain ; the towSfttSTof Th« bird (■««• Hwdey andTSnilB. !«««« ■• to the PNW^ ttawcj orawtTl, lanUtia (erminaUf, or uWlor widl of Oie tiiird Tentrioio ; /. U, fonunenof teriarmmDiiMUN ; <« JndioitfM tha enot noint of exit of the (omrth piUr from Uwt put of Mm brain whiA anairan to the tahw of ViMMMna. ft- ^ j'iv^^ntifntfH^trn^ani t iii vr rt»i»> - -*-«h«e«?w«»*rt«iiift" : ea »bifd(ifcfea- Iwtiey). A, B, ninMU Klsnd; ib^um ; JM>, A mttm; Pu, ir.a \Ori$aaaopatia) jrdHi bnUn ; tbe teovMait flgwp, . jr, f onunea of ntomre : p, pot- (ram Uwt iMTt THE BRAIN. 611 Fw. SM. Fto. aUB. Fia. sat. F10.8M.— Brain of ptaeoD (afler Ferrler). A, cerebral hwnl^iliew ; B, optfas lobe ; C, cere- bellum, the Ikteriulobes of which are Teiy nulL Fio. 886.— Brain and q>inal cord of chick at aizteen dagra old ; optic lobea, 6, are bUU in con- tact (after Owm and Andennn). Flo. aw.— Brain and iMUt of apinal cord of chick twenty daja old, Bhowlmr optic lobes widely ■eparated and cerefaellum, e, largely devekqped. elsewhere, concerned in co-ordination, vision, etc., are well developed, the cerebrum, especially its lobes as distinguished from its basal ganglia, is, out of all proportion, greater than in any other animaL Vnl> 808> Ho. aor.— Outer rarfaoe of brain of bone (after BoDy and Leuret). «. otftatonr lobe : ft, hip- pocampal lobe (procMm pyrtformto) : 1, S. 8, lobes of cerebeUum ; o. ''^*||^ wwdrigemina, In front of which Is the ptosal body. The osrebel- " '' '«»BMav<,rrt»hit,» plg.—d a ohlmpiMW. dmwnof iwriy tiMMunealMOlutoaiaeCHiizlMF). Tlw rabMt% iMta to at the tdpttlWBl(*i,te the middle: the cMmpUMel. loweat Oi;ollMtoi7MMS ikfKWtal lolw) B.ocetoMl^^ '.F itr I.F inperior, midaie, Mul inteior fronUI nri ',A.P, .iurterpiNulital ; P. P. DortWwviigtai Kyri; i;,mloueof8olMM; 1>. i>t. |M)«Mro>|»rletaI lobule ; O. flT. extenufl perpgidleiil y oroodpito-temporalndoae: ^n, aiiRatar gms : B, S, 4, MUMteiit gyri ; .i. T, If. T, P. r, thethiwitemparal,Mid AOe,JilOe^/.oOKethiwoool|ittdKM weighs about three pounds on the average, that of the male being a few ounces (f otir to six) heavier than that of the female. The individual and race differences, though considerable, ar<) ^^'wnkiiipaBiimifwitiM iilii iM iJg^iiMllWMMiMM bebrates is , and as a m of man « bwinior nearly I, In the middle; itlobe: atem- paanra-paratal 11 perpandlonlar I the male bhe female, erable, am THE BRAIN. 518 not comparable in degree to those that distinguish man from even the highest apes, the br^ of the latter weighing not 5??ro ^^^ ^^*' one third as muchaslEat of the KimanTsub-, jsct While it has been showii that indtvidtisllnen and women may reach even distinction in the intellectual world, having '^'•1^'°^^'^^ ombral hwilnlietMaf the nUMt, itg.nA cUmMikMe. drawn m 6^^SSl^ Sn^SS^' ^ W|iI?H»iBjDrfwloS; c;M.aiioliwte; Jf. miuBiSu cTS- loi«l gyH ; /. /► totonial l«rpeiidlcntar ; fl5r«aoMrtoe ; *l^ brains of average or even sub-medium weight ; and while idiots have been known to possess brains abnormally heavy, it is( nevertheless true that bndn-weight and thfe higher powers of man bear a close though not invariable relationship. The apparent discrepancies are susceptible of explanation. HMMMtUimte; 614 ANIMAL PHYSIOLOGY. I > CM. Ami. Tm. K\.-Vnin of diimpMiMe, put of right beniiplMre being cut vnj w m to axpoM Tto^'^fSSS^i^^SiS^^^rb^^.ri.l. b'-5.«»ofttie««ll«teT«r mslor in dMoSStag •ornu; fcrn. WwooMnpujmlnor taportartorcorou j/l^ ^nri Sitamid pMTMdkmter Amuni : Jcropercuium : I, A, mommUiic tronUI ; B, B. Moending parM«l ooBfolatloii. MWMWaJMHMWIJ'I I IWIWM M 'W* *' ''!' 1 ff» ct. -Am, ly WM toaxpoM ( the nMllMt erer wtween theM two : CO. hlppoaunpiw i;B,B. aaoending filfi JJo. sn.— n«ln of onuif , ride view (after Vogt and Gntiolet). " Vm. 8T4.— Bntai of • Hottastot woman. ""'nnr'^*'^ *^^<%!!?* **>" celebrated mathematioian and artronomer (an«r Vogt and fta'tifSSSL JS^£SSf'*JteSi*5" tW« tart. bnUn and the two flHTiiiS^ ?Sl ^ ^iS^^^^^SSL^^SfhS!.! ^'^. J*"^ f~ Intended to Uluftrate racial and IndtTMuat ^erenoea on the one hand, and the greater reaemblanoe to lower forme of the brain of the more degraded raoee of men. !1 iA» iiiiriU i H iili ^'^m .: < ■'^^<**»*'*^^iiilU!miB!»KifmiimtaiaiiviiK^siiiK ?' IS- :; if 518 ANIMAL PHYSIOLOGY. vidual elements, especially of the cortical cells, both as the re- suit of innate, inherited powers, and as altered by education, is, of course, a matter of great importance. By education we m@an all those influences that have been brought to bear upon these cells from without, of whatever kind. Apart, too, from all these considerations, it must be clear that what any set of cells can accomplish, be they brain-cells or other, must depend largely upon their capacity to appropriate nourishment, which will in turn be modified by blood-supply, the behavior of ex- creting organs, etc. In a word, the intellectual achievements are dependent on a great variety of factors. The brain and other parts are so mutually dependent that they can not be un- derstood by any isolated consideration of the one or the other.N It is not to be supposed that an individual with a poor respir- ) atory, circulatory, and digestive system, no matter what the ' possibilities of his cerebrum, can ever rank with an organism ' admirably balanced in these respecta The Oonneetion of m» Part of tho Bndn with aaotlior.— Though it has long been known that the different parts of the brain were connected by bridges of fibers {commissures, etc.), the physiological significance of the fact seems to have been largely ignored, and even at the present day is too little considered. 1. Cerebral fibers pass between the convolutions of this part of the brain and the cerebellum ; between the former and the main basal ganglia ; between the gray matter of the convolutions on the same side, and between the latter and those on the opposite halves ; between the gray matter of the cortex and the internal capsule, the corpora striata, optic thalami, pons Varolii, the medulla oblongata, and so to the spinal cord. The course of the latter tracts of fibers have been, especially by the help of pathology, definitely followed. Some of these connections are given in more detail below : • 1. Cerebro-cerdteUar fibers, (a.) From the cortical cells of the anterior cerebral lobe to the pons Varolii, passing through the internal capsule and thence through the lower and outer part of the eras cerebri {crusta), (6.) Fibers from the occipital and temporo-sphenoidal lobes, passing by the crusta, reach the upper surface of the cerebellum. 2. Fibers bridging the two sides of the cerebrum, (a.) By means of the corpus callosum chiefly, passing from the gray matter in the first instance. (&.) From the temporo-sphenoidal lobe on each side through the corpora striata and anterior com- missure, (c.) Fibers from the upper part of the crus cerebri ■-.; A ft W»Wl > #_iWJ, l . | UM«iagnHUiwtlc repratenution of the ooune of mne of the flbera in the cerebrum (Itfter Le Bon). w i iiyffi wtW )B «i bj. i f iw i:*w ww >a > wiw4'i i tw i Mwu'a i M^ WJuiWMHBk.tftlft*»*l K * *am^m» i iiiaMi ( Lv te 9 tei m i- ^ ^f ;ftt ■''i 590 ANIMAL PnrSlOLOOY. some seem to pass directly downward through the internal cap- sule. It is held by many that the fibers passing through the posterior portion of the ii)temal capsule are derived from the posterior lobe of the cerebrum, and are the paths of sensory im- pulses upward ; while the rest of the internal capsule is made up of fibers from the anterior, and especially the middle portion of the cerebral cortex (motor area), and these fibers are the paths of motor (e£ferent) impulses. Ot now becomes clearer that the brain is constituted a whole by such connections ; and that, apart from the multiplicity of cells with different functions to perform, situated in different areas, the complexity and at the same time the unity of the encephalon becomes increasingly evident, merely upon anatomi- cal grounds ; but we shall find such a view still further strength- ened by study of the functions of the various parts. While the tracts enumerated are anatomical and have been clearly traced, there can be little doubt that many others yet remain to be »W I CTA u CAUOIO-MARSniAL ■CPTUM LUCI FISSURCOmOLANDe ArrcNwi coMMistuM Munivr MrUNDiWU •PTKTHALAMUC KHCRVI ' AOUtDUCTOrsnMUS.' nNEALfiUlK:' CORPORA OlMORIttMINA' TRAMSVIRSC nSSURC VALVC or VICUStENt 4n vnrrmctx no. an.— Median laaghwUiial wction of human brain, ■wnt-dlagraininaHe (attar FUnt). marked out ; and that, apart from such collections of fibers, we must recognize functional paths by the neuroglia, and possibly '^"*«vnfe«iM|MiiH internal cap- through the ed from the f sensory im- Mule is made iddle portion bers are the ;uted a whole ultiplicity of I in different unity of the pon anatomi- ;her strength- i. While the ilearly traced, remain to be SURCOFROlAMDe kCALCARINC 1 FIttUM rriMMSVimc nssuRC ' VALVE or VIEUStENt '4" vnrrmcu natic (•ftcr Flint). L8 of fibers, we k, and possibly THE BRAIN. 591 others still. It is not to be forgotten that in the brain, as in the spinal cord, nerve-cells are themselves conductors, and while there may be certain areas within which the resistance is such that impulses are usually confined to them, it is also true that, as in the cord, there may be a kind of overfiow. Adjacent colls, possibly widely separated cells, may become involved. We shall return to this important subject again, however, as, without recognizing such relationships, it seems to us quite impossible to understand the facts as we find them in the working of the body and the mind. The Gwebral Cortex.— We may now proceed to inquire what are the functions of the c^ of the gray matter covering the surface of the cerebrum, (before the birth of physiology as a science^allj recognized and taught that the encephalon is a col- '^nSl^S^SSSMrBSEST'***^ lection of organs ; that these have separate functions ; that the relative size of each determines the degree of its functional ac- tivity ; and that the cranium developing in proportion to the growth of the brain, the former might give information as to the probable size of what lay beneath it in different regions. n-sMBitmmmK/cr'- • ■-TTt*ff.t^rt»a®«*Wr V , . &2S ANIMAL PHISJ^/ 'V. It will be seen that, a» thus inter, 'A, phrenology is a very different thing from what usually passes under +hat name, and is paraded before wondering audiences by ignorant charlatans. In the main the doctrines of fOall^ are not without a certain! foundation in facts ; and the modem theory of localization of' function bears a strong resemblance to what Qall taughty though with greater limitations. ftam"*** Wn. 981— Diamuninatio rapreMnUtkm of internal mrfaoe of rMit oerrtml hemtophere, aa aeen in vemcal longituduial mndiMi aeotioii (after Flint and Ecker). /Among the more modern observers, ||Touren8/held that re- moval of small portions of the cerebral cortex produced no effect on either will-power or intelligence, but that if carried far enough both volition and intelligence were completely de- stroyed. Later observers, say, of ten years ago, maintained that the whole or the greater part of the cerebral cortex might be mapped out into areas with a definite function. The meth- ods of investigation have been clinico-pathological and physio- logical. It was found that, on stimulating certain areas of the cortex (e. g., the so-called motor area), certain movements followed, but that similar results were obtained when the f)lectrodes were applied directly to the white matter underlying the cortex; hence the results of such experiments were not conclusive. It was held that, if certain regions thus respondent to a stimulus were removed, the movements of corresponding muscles should be abolished ; in other words, there should be localized paraly* > tiil i jiifw » jiy!Sjaw ! t PW i i ^ ^ f: ww» w « w^ nlM gy 18 a very A name, and , charlatans, lit a certain] ;alization of }all taugbty ral hemisphere, as leld that re- produced no At if carried mpletely de- maintained x>rtex might Themeth- and physio- of the cortex its followed, tetrodes were the cortex; nclusive. It K> a stimulus iscles should lized paraly- THE BRAIN. 528 sis. It was then asserted by certain experimenters that such was the case, while others strenuously denied this. By com- na. 88S.— Outer Murfaoe of oerebrum (after Elzner). The shaded portion representii Me motor in man and the monkey— i. e., the area which moat observers MieTe to be associated with certain Toluntair moreinents of the limbs, etc. bining the method of stimulation with that of ablation (or the removal of definite portions of the cortex), a very extensive localization was established by certain observers (Hitzig, Fer- rier, etc.). This was not confined to motor functions, but in- volved sensory ones. rOn the other hand, one physiologist ((<&oltz][Jias from the first maintained, as the result of experiments on the dog, that localization of the character described by the above-mentioned observers does not exist. He finds that no amount of ablation of the cerebrum will lead to paralysis, and that, if lesions in any part bebut extensive enough, the sensory perceptions and the intelligence of the animal aro impaired. It is found that the movements of dogs, after the removal of a considerable por- tion of the cerebral cortex are awkward ; that one or all of the animal's sensory perceptions may be impaired ; that, in fact, the creature may be reduced to a mere eating and drinking machine, as it were ; but that paralysis proper does not exist. (I k 624 ANIMAL PHYSIOLOGY. ' About the same time another experimenter (Munk) had been attempting to map out the region of the cortex concerned in vision. As a result of removal of different portions of the occipital lobe in dogs, he had concluded that a portion of this lobe constituted the cortical visual center, and, further, that the blindness resulting from such operations as are now under consideration was either " absolute " or " psychical " ; by which was meant, in the first instance, an inability to bring the images of the retina into consciousness, and, in the second, inability to interpret visual sensations intelligently, the one or the other result being dependent on the part of the limited visual center that was removed. This may be regarded as perhaps the most extreme form of sensory localization yet taught. (^oltz, as a result of his latest experiments, not only denies that operations ou the occipital lobe are peculiar in producing visual disturbances, but points out that these lead to sensory defects overlooked by Munk. This observer (Goltz), as a result of comparing a dog, with both anterior cerebral lobes removed, with others from which were removed, in the one case, the right, and in the other the left corresponding parts (anterior cerebral lobec^, since he finds the dog with both removed in a worse condition than would be represented by the joint result of the addition of the imperfections of the other two, concludes that one cerebral lobe may, to a certain extent, take up the functions of another. In other words, he admite localization but only of the roughest kind. A view advanced by(ScJiiff deserves probably more consid- eration than it has received, viz., that motor areas are so related to tactile sensations arising in different parts of the body that when the former are stimulated the resulting movements are really reflex — i. e., the stimulation of the cortex replaces the afferent sensory impulses, which usually are associated with the movements in question. In the mean time it has been found that in many cases it was possible to locate the site of a brain-lesion (tumor, etc.) by the symptoms, chiefly motor, of the patient ; and brain-surgery has in consequence entered upon a new era of development. Tumors thus localized have been removed sucoessfully, and the patients restored to health. As a result of the various kinds of observations and discussions on this subject of late years, the localizationists are willing to admit that the areas of the cortex can not be marked off msthematioally^that, in fact, they " overlap." This is in itself an important concession. Again, immattHnm mmm \ mmi THE BRAIN. (Mun 625 nnk) had ex concerned trtions of the >rtion of this farther, that re now tinder I " ; by which ig the images I, inability to or the other visual center laps the most t only denies in producing ad to sensory z), as a result •bes removed, me case, the arts (anterior removed in a e joint result wo, concludes take up the 3 localization more consid- are so related the body that ovements are replaces the sociated with nany cases it imor, etc.) by braiuHSurgery development, fully, and the rious kinds of ate years, the of the cortex in fact, they sion. Again, there is less confidence in the location of the various sensory centers than of the motor centers. Most investigators are be- lievers in a " motor area " par excellence (for the arm, leg, etc.) around the fissure of Rolando. This view is now, so far as man is concerned, widely accepted. There is agreement in placing the sensory centers behind the above-mentioned motor area, and especially in the occipital lobes. The tendency to locate a visual center in this region is growing stronger. There is much disagreement as to the other sensory centers formerly placed in the angular gyrus and tem- poro-sphenoidal lobes. The intellectual faculties have not been^ located in any such sense as Gall and his followers attempted to establish. The first two frontal convolutions are those per- haps to which localization has as yet been least applied. Chiefly on clinical and pathological grounds a center for speech has long been loca^«d in the third (left) frontal convolution (Broca's) and parts immediately behind it. It has been observed that, when dise^^ attacks this area,'sp<)ech is interfered with in some way. (We may say then, generally, that the tendency at the present time, both on the part of physiologists and clinical observers, is to admit localization to some degree and in some sense. This has been the result in part of experiments on the dog and es- pecially on the monkey, combined with the discussion of clini- cal cases >rhich resulted in death (followed by an autopsy), or of others marked by a successful diagnosis and removal of lesions or other treatment. In other words, the truth, if it will be «x)ached at all, must be reached by the method we have ad- vocated throughout this work— the discussion of the results of as many different methods as can be brought to bear on this or any other subject. Neither the experimental nor the pathologi- cal method can settle such complex questions, as we shall en- deavor to show when we return to the subject later. Tkt Oinulakiffii in tlM Bnin. — The brain, being inclosed within an air-tight bony case, its circulation is of necessity peculiar. Since any undue compression of the eucephalon may lead to oven a fatal stupor, it is clear that there must exist some pro- vision to permit of the excess of arterial blood that is required for unusual activity of the brain. It is to be borne in mind that tbe fluid within the ventricles is continuous, through the foramen of Majendie in the roof of thts fourth ventricio, with that surrounding the spinal cord (spinal cavity) ; ro that an increase in the volume of the encephalon in consequence of an aflSux of blood might be in some degree compensated by an J 626 ANIMAL PHYSIOLOGY. (bMux of the cerebro-spinal fluid. The part played by this ar- rangement has, however, been probably overestimated. But the peculiar venous sinuses do, it is likely, serve to regulate the blood-supply ; being very large, they may answer as tem- porary overflow receptacles. An inspection of the fontanelles of an infant reveals a beating corresponding with the pulse ; and, when a large part of the cranium is removed in an animal, a plethysmograph shows a rise in volume corresponding with the pulse and the respiratory movements, as in the case of the fontanelles. But, besides these, periodic waves of contraction are now known to pass over the cerebral arteries. Whether the latter is part of a general wave traversing the whole arterial system is as yet uncertain. Though there is considerable anastomosis of vessels in the encephalon, it is not equal to what takes place in' many other organs. It is well known that a clot or other plug within a cerebral vessel is more serious than in many other regions, which is partly to be explained by the lack of sufficient anastomosis for the vascular needs of the parts. It is also well known that, in organs which constitute parts of a related series, as the different divisions of the alimentary tract, all are not usually at the same time vas- cular to the same extent. While they act functionally in rela- tion to each other, they exemplify also a certain degree of inde- pendence. Such a condition of things is now known to exist in the brain — i. e., certain areas may be abundantly supplied with blood as compared with others ; and it seems highly probable that a condition of equal arterial tension throughout is scarcely a normal condition. Though the quantity of blood contained within the vessels of the whole brain at any one time is not so large as in some other organr (glands), yet the foregoing facts and the rapidity of the flow must be take^^ into account. The capillaries are very close and abundant, in the gray matter es- pecially ; and it is to be borne in mind that it is chiefly these vessels which are concerned in the actual metabolism (nutri- tion) of parts. However, the chemical changes in the nervous system being feeble, it would appear probable that it does its work with less consumption of pabulum than other parts of the body. We wish to lay stress on the local nature of vas- cular dilatation in the brain as, it greatly assists in explaining certain phenomena about to be considered. Sto^lf.-^bservitions upon animals from which portions of the cranium had been removed, so that the brain was visible, show that during sleep the blood-vessels are much less promi- mmm MMMM tmm THE BRAIN. 627 id by this ar- imated. But 9 to regulate swer as tem- e fontanelles >h the pulse; in an animal, ponding with le case of the f contraction raversing the )ugh there is ilon, it is not s. It is well )ral vessel is i partly to be the vascular organs which t divisions of ),m.e time vas- nally in rela- 3gree of inde- irn to exist in (upplied with fhly probable )ut is scarcely od contained ime is not so regoing facts ccount. The ay matter es- I chiefly these >olism (nutri- 1 the nervous at it does its ther parts of ature of vas- n explaining li portions of ft was visible, ih less promi- nent than usual ; and it is well known that means calculated to diminish the circulation in the brain, as cold and pressure, favor sleep. It is also well established by general experience that withdrawal of the usual afferent impulses through the various senses favors sleep. A remarkable case is on record of a youth whose avenues for sensory impressions were limited to one eye and a single ear, and who could be sent to sleep by closing these against the outer world. Yet this subject after a long sleep would awake of his own accord, showing that, while affer- ent impulses have undoubtedly much to do with maintaining the activity of the cerebral centers, yet their automaticity (in- depspdence) must also be recognized. (^It is a matter of common experience that weariness, or the exhaustion following on pain, mental anxiety, etc., is favor- able to sleep. A good deal of light is thrown on this subject by hiberna- tion, particularly in mammals. From special study of the subject we have ourselves learned that, however temperature and certain other conditions may influence this state, it will appear at definite periods in de- fiance, to a large extent, of the conditions prevailing. Hiber- nrvtion, we are convinced, is marked by a general slowing of all of the vital processes in which the nervous system takes a prominent part. (^Sleep and hibernation are closely related. In both there is a diminution of the rate of the vital processes, as shown by the income and output, measured by chemical stand- ards, with of course obvious physical signs, as slowed respira- tion, circulation, etc. While sleep, then, is primarily the re- sult of a rhythmical retardation of the vital processes, especially within the nervous system, it is like hibernation in some de- gree (in the lowest creatures, without a nervous system) the outcome of that rhythm impressed on every cell of the organ* ism and the influence of which is felt in a thousand ways, that no^^ubt we are quite unable to recognize. /Dreaming is a partial activity of the mind, corresponding doubtless to functional wakefulness or relatively increased ac- tion of some limited part or parts of the brain. It is now all but certain that these parts are more vascular— i. e., we must reckon with a localized vascularity and functional activity. If this be recognised, almost all the peculiarities of the dreaming state may be understood. Dreams usually lack some elements that give the conapl(eit9ne88' and consistency of waking thought— a matter readily understood, as well as the unrest of a dreamy J 588 ANIMAL PHYSIOLOGY. night, by the facts above considered. It is, moreover, highly probable that not only different parts of the brain have a dif- ferent psychical function, but iJso that in any one chain of thought or state of consciousness only a certain number of parts are prominently engaged ; and that what is termed confusion of mind is probably a result of the activity of certain other centers to a degree unusual — ^L e.,they are relatively too obtru- sive, hence that balance essential to all normal activity, psy- chical and other, is lost. Specialization, physiological division of labor, holds here as elsewhere. Hypnotim. — Ey the help of the above principles the subject of hypnotism, now of absorbing interest, may be in great part explained. This condition is characterized by loss of volition and judgment. It may be induced in man and certain other animals by prolonged staring at a bright object, assisted by a concentration of the attention on that alone, as far as possible, combined with a condition of mental passivity in other respects. The individual gradually becomes drowsy, and finally falls into a state in mar.y respects strongly resembling sleep. With each recurrence, the hypnotic condition is usually more readily in- duced, and persons have passed into it in the entire absence of the usual procedure, having simply been told that they would be thus affected at a given hour. There is no special influences emanating from peculiarly gifted mediums, and most persons] may be hypnotised to a greater or less degree, though with ) unequal readiness. The manifestations are very variable, but are usually char- acterized by either total abolition of certain sensory percep- tions, by their enfeeblement, or by one or both of these, com- bined possibly with exaltation of others. Thus, aneesthesia may be so great that surgical operations may be performed without consciousness of pain. The muscular sense may be good, so that the sub^oct can write well. He may smell better than usual, so as to be able to detect persons by the odors from a portion of their clothing, like a dog. There may coexist, with vision for form, color-blindness. These are to be regarded mere- ly as examples, from numberless curious combinations. Again, the affection of sense may be bilateral or only unilateral. Hypnotism proper may be combine .1 with catalepsy, a con- dition in which the limbs remain rigid i~^ ^ hatever condition they may be placed. Modifications of the vascular and respira- tory systems occur. Other animals have been hypnotized, as MlilMfaMltMMWii MNaWm< Bover, highly 1 have a dif- one chain of mber of parte ed confusion certain other sly too obtru- activity, pay- holds here as es the subject in great part )ss of volition certain other assisted by a ar as possible, other respects. lally falls into p. With each )re readily in- bire absence of at they would ecial influences most persons^ though with) ) usually char- nsory percep- of these, com- is, aneesthesia be performed sense may be ly smell better he odors from y coexist, with ■egarded mere- ,tions. Again, lilateral. Ualepsy, a con- ever condition ar and respira- hypuotized, as THE BBAIN. 629 the fowl, rabbit, Guinea-pig, crayfish, frog, etc. This condition is readily induced in the common fowl, more especially the wilder individuals, by holding the creature with the bill down on a table and the whole animal perfectly quiet for a short time. Upon the removal of the pressure the bird remains per- fectly passive and apparently asleep for some little time. The subject of hypnotism and allied conditions has of late received close attention from a large number of observers. Among other surprising results as the consequence of " hypnotic suggestion," certain pathological effects have been produced : thus, placing a piece of tissue-paper on the skin, with the sug- gestion that an actual blister is being applied, has resulted in the usual effects of such treatment. ( Somnambvlism is very similar to hypnotism. Individuals have been known to walk, ride, climb, go upon a journey and pay toll, and also to perform their ordinary avocations. A student has been known to write a sermon, read it over, and make corrections, and when a piece of pasteboard was placed before his eyes this still went on, showing that the images were mental. Without being actually hypnotized, by careful observation of one's experiences for a considerable period, one may catch, as it were, the realization, at different times, of the various phenomena that characterize the hypnotic condition, even to details — though not, of course, in that complex combination which would result in such partial or complete loss of conscious- ness as marks the actual condition ; for in that case observa- tion would be very difficult, if not impossible. To illustrate our meaning briefly, one may walk a considerable distance, noticing absolutely nothing consciously, but wholly absorbed in one idea, or possibly without any distinct train of thought. In such a case ther«^> is neither vision, hearing, no^* tactile sensation in the ordinary ^imm. Tho person is, in fact, for the tune practi- cally in the soranambulistic condition or one closely allied to it. There are times wh<»n vision is in abeyance, or only one eye used. Though apparently looking, we do not see. The sensory perceptions from the skin may be so purely unilateral that the other side is practically aneesthetic from close attention to the condition of one side. All are familiar with unilateral vaso- motor effects, such as the redness and " burning " of one cheek or one ear, and so of many other expcriunces that might be re- ferred to did space permit. Such realizations furnish the highest kind of knowledge, we might say the only truo knowledge. 680 ANIMAL PHYSIOLOGY. ft Pathology sheds some light on this subject. In diseases of the membranes of the brain, all the sensory phenomena may be so heightened as to become painful. Slight sounds, a little light, feeble vibrations, a gentle touch, all give rise to effects out of proportion to the usual ones. From the close proximity of these membranes to the cerebral cortex, we may assume that they are affected. This, together with the results of stimula- tion and removal of the surface of the brain, brings us some way on toward an explanation of sleep, dreaming, hibernation, hypnotism, and cerebral localization itself. One physiologist has given, as an explanation of hypnotism, etc., inhibition of the cells of the cerebral cortex, and this, with- in limits, is no doubt true. The facts of hypnotism and allied phenomena seem most of all to emphasize the dependence of the central cells when acting normally on afferent impulses. But we have already dwelt on this important subject suffi- ciently to render our meaning clear. Cbbebral Localization rsconsidbrbd. An examination of the phenomena of the states recently considered can leave no doubt in the mind that certain parts of the brain, even certain portions of the cerebrum, may be active while the remaining ones are in abeyance or but feebly engaged ; and, as has been seen, our every-day experience is an illustration of the same fact. The circulation in the brain points clearly to its being a collection of organs, with a certain degree of inde- pendence. It is therefore unreasonable to assume that all parts of the cerebral cortex discharge equally the same functions. On the other hand, it is just as unwarrantable to assume that, in the face of all the facts of physiology as now known to us, there are very precisely limited areas with as exactly restricted functions discharged independently of all the other parts. As we have frequently insisted, the functions of an organ are alone normal when in proper relation to all the parts with which it is connected — ^that is, in fact, with the entire body. We learned that any conclusions based on artificial fistulee of the digestive orf:iv>s could be only approximately correct at best, and might be very far from the truth in the sense to which we now refer. To assume tiuii there is only one path by which certain classes of impulses mU'Sf travel in the spinal cord has been shown to be unwarranted. Therefore, to argue that because the removal of ft certain portion of the brain either is or is not followed by [n diseases of inomena may mnds, a little rise to effects ose proximity y assume that ts of stimula- rings us some I, hibernation, of hypnotism, md thi8,with- sm and allied dependence of rent impulses, subject suflfi- BED. itates recently ertain parts of may be active iebly engaged; an illustration sints clearly to legree of inde- e that all parts Ame functions. assume that, rr known to us, EMJtly restricted her parts. As 3rgan are alone 3 with which it y. We learned if the digestive test, and might 1 we now refer, certain classes »en shown to be the removal of lot followed by THE BRAIN. 631 no. aM.— Lateral mirfam of bnin of monkqr, dlqtlajliif motor (after Honlqr and Via. MS. -Median surfaoe of hnbt of moDkey (after Horatey and Schlfer). Figs. 384 and ass may be Mid to embody Ike vtews of Horaley and Sohkfer oiore eapeoiaar. m ragaru to motor looaluatioD, certain aKxiitications or-Unw of function, proves that this part is or is tix>t «>oncemed with that particular kind of activity, does not seem to be logical { J 589 ANIMAL PUYSIOLOOr. Bi-J§* i I I 1 I I ! i t luwiiMiM" iiiiiuwiiwriifwiiiiiiMiiMWi ip imnw m' \ i I I '65 ^^•i; j' THE BRAIN. 083 iM 534 ANIMAL PHTSIOLOOT. If it be true, as it unquestionably is, that a certain region of the cortex or other portion of the brain is normal only when in relation with others, it follows that mere removal can not entirely solve such problems as the function of the different parts. Nor does it follow, because a localization, meeting the needs of practical medicine and surgery, has been established, that therefore we are justified in assuming that a scientific lo- calization rests upon the same grounds. Any theory that fails to recognize both the interdependence of parts and the resources of nature in substituting one part for another functionally, overlooks principles of very wide application in biology. We must express our conviction that neither ablation, stimulation^ pathological observation, the results of surgical interference, nor the facts of clinical medicine, can any of them singly settle such questions. The comparative method has been as yet but little used. Conclusions in regard to the monkey have been applied not only to man but other animals; and thatihe Experiments upon dogs should result in changes or the absence of changes, to which there is uo correspondence in the monkey, has hardly been recognized as it should. It is only by the synthetical method, as we have so often urged, that even an approximation to the truth or a part of it can be attained. Results from one method or another, taken alone, may be positively misleading, unless interpreted in the light of many other facts. The in- terpretation is the difficult portion of the task in the study of localization ; but, before we are prepared to formulate a correct and comprehensive theory, we must begin lower in the animal scale, extend observations over a large number of animals, and complete these by pathological and clinical observations on man and other mammals. If the spinal cord becomes func- tionally what it is in any case largely through the life experi- ences of the individual, this must also apply to the brain, hencQ we must look for individual as well as gn^up differences. The loss of speech (aphasia), in consequence of lesions in the left third frontal convolution, was formerly pointed to as un- doubted evidence of localization ; but, the more this subject has been studied, the more clearly it has been perceived that even in this case the theories of a rigid localization break down. The speech-center has had its boundaries extended ; and it turns out that a'vast complex of connections must be consid- ered, many of which are not confined to the third frontal con- volution or its neighborhood. mm^'.-'a**'i»iuf»i'aia»tmmHmmtm ;ertain region lal only when loval can not the different , meeting the m established, i scientific lo- 9ory that fails 1 the resources functionally, biology. We n, stimulation^ I interference, !n singly settle >ut little used, m applied not leriments upon of changes, to ey, has hardly ihe synthetical approximation jsults from one ely misleading, facts. The in- n the study of mlate a correct * in the animal of animals, and jbservations on becomes func- the life experi- ;he brain, hence ifferences. of lesions in the ointed to as tm- this subject has ieived that even )reak down, xtended; and it must be consid- lird frontal con- THE BRAIK. 535 /There is a kind of experimental evidence that throws a good deal of light on the present discussion. It is found that, when certain drugs have been administered, the irritability of the cortex is either increased or diminished, according to the stage of action of the drug (morphia, etc.). It is not impossible that epileptiform convulsions may result from the application of a stimulus of almost any strength, though this result does not follow when the electrodes are applied to the underlying white substance. The disease epilepsy ha^ been known to fol- low injuries to the cranium or the brain membranes, in conse- quence of which the cells themselves of the cortex have been altered in function. Moreover, the epileptiform movements may be in such cases confined to certain muscles, thus pointing to a motor localization. If a muscle contraction, as the result of stimulation of a rr - area (the animal being under the in- fluence of morphia), . ecorded by the graphic method, and the sciatic nerve then divided, in repeating the original experiment, it will be seen that the whole character of the curve is altered, the latent period having been lengthened, and the height of the curve lessened. This points to an inhibitory influence exer- cised over the cortical motor cells,by afferent influences, and we are at once reminded of Schiff's theory ; but most of all do such experiments enforce that close relationship of all parts of the body which finds its reflection in the brain cortex as elsewhere. We have dwelt upon the subject of cerebral localization at length, because of its great practical and scientific importance, not alone for medicine and physiology, but in the allied depart- ment of psychology. In conclusion, we may express the view that there is in the cerebral cortex a localization of function, variable for each group of animals, and to some extent for each individual ; that it is not of a character to be mapped out by mathematical lines ; that in case of disease or injury one part may to a certain extent take up the functions of another ; that the functions of any part, however .limited, are only to be understood when taken in connection with all other parts of the cortex, of the brain, and, in fact, of the entire body. These views we believe to be borne out by the facts of physiological experiment, clinical medicine, operative surgery, pathology, sleep, dreaming, hypnotism, the nature of the cerebral circu- lation, and the general truths of biology. Oanlnal Time. — We have already considered cerebral reflex time, and now proceed to examine into the period occupied by a mental operation involving attention and volition. J fmm mmmm ! ' •■ J 686 ANIMAL PHYSIOLOGY. When a subject makes some signal in response to a stimu- lus, we recognize three parts to the entire chain of events : 1. The time occupied in the passage of the afferent impuliies in- ward along certain lengths of nerve from a peripheral sense- organ. 2. The time taken up by the processes of the central cells before the efferent nervous discharge takes place. 3. The time consumed by the passage of the efferent impulses from the center to the muscl? involved. The whole interval is termed the reaction4ime, whilo the second constitutes the redticed re- aviion-time. As the first and third probably vary but little, it is highly probable that the difference in the reaction-time obsex vable in different individuals, and very much modified by thr> condition at the moment (as fatigue), and especially by practice, is trace- able to the central cells. In popular language, some pennons are, as compared with others, slow thinkers. Thiu factor iu the "personal equation," so called. There are, of Coui-se, many sources of error in .such calculations, but approximate results of value may be reached. It would appear that the reaction period for tactile is shorter than for visual or audit )ry sensa- tions, while that of vision is longer than for hearing. The respe^;tive periods have been set down as about ^ of a second for viftion, \ for audition, and \ for feeling. Ti.e cputral processes may be reckoned to take (for percep- tlo ' nd < ',V,tion) about -^ot a, second. li dis*^ ; iminations have to be made — so as to decide, e. g., T '\. ther it is the right or the left side of the body that has iioon touched — a longer time is, of course, required, and the re- action period in this case also varies greatly. It has been set dovn as occupying from gV to | of a second. Prom these con- siderations, it will be plain that " the lightning-like rapidity of thought " is a rather extravagant figure of speech. Functions of other Portions op the Brain. Certain parts of the encephalon are spoken of as the basal ganglia, prominent among which are the corpus striatum and the optic thalamus. Th* Oorpiii Striatum and the Optie Thaluiu.— The corpus striatum consists of several parts, the main divisions being an intra-ventricular portion or caudate nucleus, and an extra- ventriculnr part or lenticular nucleus. Between these lies the internal capsule, through which ■^ — -r-:ismltm Be to a stimii- of events: 1. impuliies in- pheral sense- >f the central )lace. 3. The [npulses from rval is termed le redvcfid re- le, it is highly o1}seivable in iho. condition ctice, is trace- sonie persons m factor is the <:;oui*se, many ximate results t the reaction ndit dry sensa- hearing. The I ^ of a second ke (for percep- o decide, e. g., body that has •ed, and the re- It has been set rom these con- ?-like rapidity Braik. of as the basal s striatum and I.— The corpus sions being an and an extra- through which >iii.tiV ^ -r-'f t" r IMAGE EVALUATION TEST TARGET (MT-3) 1.0 I.I ■50 "^^ M^H 1^ 1^ 12.2 u ■yuu L25 114 11.6 — 6" R' «^'3' °!» / Photographic Sciences Corporation 23 WEST MAIN STRUT WHSTCR.N.Y. 14580 (716) 872-4503 CIHM/ICMH Microfiche Series. CIHM/ICIVIH Collection de microfiches. Canadian Institute for Historical Mlcroreproductlons / Instltut Canadian de microreproductlons historiques *Wli (f r t, , S3 THE BRAIN. 687 pass fibers that spread out toward the cortex, as the corona radiaia. i Fta KB.— TnMvene McUon of cerebral hemispliereB, at level of cerebral „ IMtoD). 1, great tongitudinal llMure : 9, part of Mune between occipital lobea (afttr anterior part ii^3^;i?'t»lte', 7,'-^^ lA* ;iJf'2!.i^ii:i^^ .■ .'NT''UI;?^^f*^^>--, % o< lenficuUr nuolew ; &Vo( oplto aateaiH ; ^ 4, of oorpom qiMdric«5na : ^ diMot ttwn to cor^ rf^ a, «,«)«• tram oorpon quiidriiiemlii* to tagmwitum a m. f urttwr liiiri ooid ;«. IT, antorte, awl 1^ IT, iKNrtertor raoto ; a, a, aytrtem of MWM^ flben ; c c, oommMMinl flban. and their relations to the movements of the pupil, will he considered later. However, the actual centers for these func- tions seem to lie in the anterior portion of the floor of the aqueduct of Sylvius, and are indirectly affected by stimulation of the corpora quadrigemina. Extirpation of these parts on ij#wfiffii«iiwi«riTiMi^^ MMimfliiiiWfaiWM^ r 540 ANIMAL PHTSIOLOOT. K one. side produces blindness of the opposite eye, and in birds, etc., the same result follows when their homologues — the optic lobes — are similarly treated. There can be no doubt, therefore, that they are a part of the central nervous machinery of vision, and it seems to be probable that the anterior parts of the cor- pora quadrigemina alone have this visual function. But, since it is the opposite eye that is affected, and in some animals (rabbits) that alone, we are led to infer a decussation of the optic fibers, or at least of impulses. In dogs, on the other hand, the crossing seems to be but partial. From the fact that only a part of the visual field is wanting (hemianopsia — ^i. e., that only the half of the usual field of view is visible), and, since there may be hemianopsia of both eyes, with unilateral disease of the brain, it has been inferred that in man the decussation is also incomplete. We may remark incidentally that it has lately been maintained that removal of one occipital lobe in the monkey leads to heminopsia of the opposite eye. These parts, as we have already seen, take some share in the co-ordination of muscular movements, and give rise to forced movements after unilateral injury. It begins to appear that there are several parts of the brain concerned with vision. After removal of almost any part of the cerebral cortex, if of sufficient extent, vision is impaired. We may say, then, that, before an object is " seen " in the high- est sense, processes beginning in the retina undergo further elaboration in the corpora quadrigemina, optic thalami, and, finally, in the cerebral cortex. We may safely assume that the part played by the latter is of very great importance, making the perception assume that highest completeness which is of very varying character, no doubt, with different groups of animals. In a sense, all mammals may see alike, and, in an- other sense, they may see things very differently ; for, if we may judge by the diffeiwnces in this respect between educated and uneducated men, the great dissimilarity lied in the inter- pretation of what is seen ; in a word, the cortex has to do with the perfecting of visual impulses. Nevertheless, a break any- where in the long and complicated chain of processes must lead to some serious impairment of vision. Much of the same sort of reasoning applies to the other senses and also to speech. /~XTo speak, therefore, of a visual center or a speech center in any very restricted sense is unjustifiable ; at the same time, it is becoming clearer that there is in the occipital lobe, rather than in other parts of the cortex, an area which takes a pecul- THE BRAIN. 641 id in birds, 1 — ^the optio b, therefore, ry of vision, of the cor- But, since me animals ktion of the other hand, 3t that only- lb — ^i. e., that ), and, since teral disease decussation that it has kl lobe in the These parts, >rdination of sments after of the brain any part of is impaired, in the high- ergo further halami, and, ume that the iince, making i which is of it groups of e, and, in an- y ; for, if we reen educated in the inter- as to do with a break ony- ises must lead the same sort o speech. )ech center in same time, it d lobe, rather takes a pecul- iar and special share in elaborating visual impulses into visual sensations and perceptions; and there can be little doubt that the other senses are represented similarly in the cerebral cortex. The C0r«Mlii]ii.-<(Both physiological and pathological re- search point to the conclusion that the cerebellum has an im- portant share in the co-ordination of 'muscular movements. Ablation of parts of the organ leads to disordered movements; and, when the whole is removed in the bird, co-ordination is all but impossible, and the same holds for mammals. Section of the middle peduncle of one side is liable to give rise to roll- ing forced movements. In fact, injury to the cerebellum causes symptoms very similar to those following section of the semi- circular canals, so that many have thought that in the latter case the cerebellum had itself been injured. PathfllogiaaL — Tumors and other lesions frequently, though not invariably, give rise to unsteadiness of gait, much like that affecting an intoxicated person. It may safely be said that the cerebellum takes a very prominent share in the work of the muscular co-ordination of the body. As has already been pointed out, several tracts of the spinal cord make connection with the cerebellum, and it is not to be forgotten that this part of the brain has, in general, most ex- tensive connections with other regions. Insufficient study has as yet been given to the cerebellum, and it is likely that the part it takes in the functions of the eucephalon is greater than has yet been rendered clear. -ZChe old notion that thw^q^^ bears any direct relation to the sexual fnnctioM seems to3§^ #iiK6nnonndatiomr"in&a8 now been clearly demonstrated: fl^t the lower re^on of the spinal cord is, in the dog and prob- ably most mammals, the part of the nerve-centers essential forj the sexual processes. Onuft Otnbri and Pons VanliL— As has been already noted, the peduncles (crura) are the paths of impulses from certain parts of the cerebral cortex, the basal ganglia, and the spinal cord. The functions of the gray matter of the crura are un- known. But, since forced movements ensue on unilateral sec- tion, it is plain that they also have ta do with muscular co- ordination. The transverse fibers of the pons Varolii connect the two halves of the cerebellum. Its longitudinal fibers have extensive connectitms— the anterior pyramids and olivary bodies of the medulla, the lateral, and perhaps also a part of the posterior MHMKMMWIMHItHfeHMHiiKHWtilM '>raW£H M IMW i> i l i< i MlM l liawa < *MV. aat-;i^ 542 ANIMAL PHYSIOLOGY. .'.iS* columns of the cord, while upward these fibers connect with the crura cerebri and so with the cortex. PathiolofiML— Paralysis of the face usually occurs on the same side as that of the rest of the body ; hence it must be inferred that there is a decussation somewhere of the fibers of the facial nerve ; but there is much still to be learned about this subject. Madnlla OUongata.— In some animals (frogs) it is certainly known that this region of the brain has a co-ordinating func- tion, and it is probable that it is concerned with such uses in all animals that possess the organ, or rather collection of organs, seeing that this part of the brain must be regarded as especially a mass of centers, the functions of which have been already considered at length. So long as the medulla is intact, life may continue; but, except under special circumstances, which do not invalidate this general statement, its destruction is followed by the death of the animal. We may simply enumerate the centers that are usually | located in the medulla: The respiratory (and convulsive), car- dio-inhibitory, vaso-motor, center for deglutition, center for the movements of the gullet, stomach, etc., and the vomiting center ; center for the secretion of saliva and possibly other of ^ the digestive fluids. Some add a diabetic and other centers. Special Considbbations. liiilirsridiigieal. — The further we progress in the study of the nervous system, the greater the significance of the facts of its early development becomes. It will be remembered that from that uppermost epiblastic layer of cells so early nuirked off in the blastoderm, is formed the entire nervoxis system, including centers, nerves, and end organa The brain may be regarded B^Ck an.— Vertieal longitttdlnalMctloD of brain of hninmemtiqrooC fourth Int. (After ShMiiey and Reicbert.) e, cerebral bemlqidiera : oe, corpus calkMuin begimiiiiK to paw back ; /, foramen of Munro ; o, membrane over tbird Tentrlcle and tbe pineal body ; Ih, thalamus ; S, third Tentrlcle ; /, olfaottirjr bulb ; eg, corpora quadrlgemlna ; er, omm cerebri, and abore tbem, aqueduct of SylVtas, atUI wmIb ; &, cerebellum, and below it tte fourth ventricle; pv, pons VaroUi ; m, medulla Oblongata. %^-. THE BRAIN. 648 }nnect with ;urs on the it must be he fibers of i about this is certaixily ukting f unc- auch uses in >n of organs, 18 especially een already kct, life may I, which do L is followed are usually] ulsive), car- , center for le vomiting bly other of , r centera itndy of the ) facts of its d that from orked off in n, including be regarded as a specially differentiated part of the anterior region of the medullary groove and its subdivisions ; and the close relation of the eye, ear, etc., to the brain in their early origin, is not without special meaning, while the more diffused sensory de- velopments in the skin connect the higher animals closely with the lower — even the lowest, in which sensation is almost wholly referable to the surface of the body. MBtraeki. 1 ■>. Miim beeinninR to ItheplMalb^; gmiliuk; cr, onm 1, MKl balow it the Fw. IBS. Ito. a8B.M)utMr aurlMe of hamaa fostel brain at riz montha, diowiiMr otIrIii ct prinoipsl flMorcs (after Siiarpqr and B. Wagner). F, frontal lobe ; P, parietal ; O. occ^al ; T, tenponl ; tt,a,a, fktnt aiipearanoe of wretnl frontal oonTolutfons ; «, «, sylvian flMore ; »', anterior diTUrioa ot eame ; C. central lobe of iiland of Bell ; r, flmire of Rolando ; p, «ztemal perpendlealarflMare. Ho. 818.— Upper mrlkee ot brain repreaented in Fig. OqO (after Sharpey and R. Wagner). Without some knowledge of the mode of development of the encephalon, it is scarcely possible to appreciate that rising grade of complexity met with as we pass from lower to higher groups of animals, especially noticeable in vertebrates ; nor is it possible to recognize fully the evidence fovmd in the nervous system for the doctrine that higher are derived from lower forms by a process of evolution. XvdvUoB. — ^The same law ap' mIps to the nervous system as to other parts of the organism, vi: ., that the individual devel> opment (ontogeny) is a synoptical representation, in a general way, of the development of the group (phylogeny). A com- parison of the development of even man% brain reveals the fact that, in its earliest stage, it is scarcely, if at all, distinguishable from that of any of the lower vertebrates. There is a period when even this, the most convoluted of all brains, is as smooth and devoid of gyri as the brain of a frog. The extreme com- plexity of the human brain is referable to excessive growth of iiwiW«itei enable us to to be given to ication of the"^/ aysiology, and^ mpport of Bci-) i we are deveW II higher ends^ tical motor re- icular develop- e been wont to ), tactile sensi- is in harmony . to the mutual )r. Both theo- retically and practically it is important to recognize that the value of vision, indeed, the extent to which we " see," is in no small degree related to what we feel. The carpenter judges dis- tances well by his eye, because he is constantly correcting his visual judgments by his tactile sense, his muscular sense, etc. We must point out, however, that the special developments of disease at the present day point to the dangers of an undue use or development of the cerebrum. That balance indispen4 sable for health must be preserved, if the race is to avoid degen-i eration. SyaoptioaL-^Thcre is as yet no systematized clear physiology of " the brain." We are conversant with certain phenomena referable to this organ in a number of animals, chiefly the higher mammals ; but our knowledge is as yet insufficient to generalize, except in the broadest way, regarding the functions of the brain — i. e., to determine what is common to the brains of all vertebrates and what is peculiar to each group. Referring, then, to the higher mammals, especially to the dog, the cat, the monkey, and man, we may make the following statements : The medulla oblongata is functionally the ruler of vegeta- tive life — the lower functions ; and so may be regarded as the seat of a great number of "centers," or collections of cells with functions to a large degree distinct, but like close neighbors, with a mutual dependence. Phylogenetically (ancestrally) the medulla is a very ancient region, hence the explanation apparently of so many of its functions being common to the whole vertebrate group. Parts of the mesencephalon, the pons Varolii, the optic lobes or corpora quadrigemina, the crura cerebri, etc., are not only connecting paths between the cord and cerebrum, but seem to preside over the co-ordination of muscular movements, and to take some share in the elaboration of visual and perhaps other sensory impulse& The cerebellum may have many functions unknown to us. Its connections with other parts of the nerve-centers are numer- ous, though their significance is in great part unknown. Both pathological and physiological investigation point to its hay- ing a large share in muscular co-ordination. Iljs certain tha t the cerebrum is the part of the brain essen- tial foira3r~{E(Oijpier psychic manifestations in the most ad^ vanc(^ mammals and in man. '-' (The preponderating development of man's cerebrum ex- plains at once his domination in the animal world, his power > I 548 ANIMAL PHYSIOLOGY. over the inanimate forces of Nature and his peculiar infirmitiesi tendencies to a certain class of diseases, etc.— in a word, man is man, largely by virtue of the size and peculiarities of this part of his brain. Modern research has made it clear also that there is a " pro- jection" of sensory and motor phenomena in the cerebral cor- tex ; in other words, that there are sensory and motor centers in the sense that in the cortex there are certain cells which have an important share in the initiation of motor impulses, and oth- ers employed in the final elaboration of sensory ones. It is even yet premature to dogmati-^ie in regard to the site of these centers ; especially are we not i.-eady for large generali- zations. In man the convolutions around the fissure of Rolando constitute the motor area best determined. The whole subject of cortical localization requires much ad- ditional study, especially by the comparative method in the widest sense— i. e., by a oomparisou of the results of operative procedure in a variety of groups of auimals, and the results of clinical, pathological, physiological, and psychological investi- gation. Especially must allowance be made for differences to be observed, both for the group and the individual; and also for the influence which one region exerts over another. Be- tween the weight of the cerebrum, the extent of its cortical surface, and psychic power, there is a general relationship. GENERAL REMARKS ON THE SENSES. Our studies in embryology have taught us that all the vari- ous forms of end-organs are developed from the epiblast, and Fio.M8.-P»pOUBof bMii of palm of hMid (after Sm»p?y). A woular network In all •"■ ^^Uid in some nen^ and UMStUeoorpuMdaa, enter Uiepapllln. ^r infirmities^ word, man is } of this part ere is a " pro- cerebral cor- notor centers s which have ilses, and oth- ^rd to the site \Tge generali- re of Rolando ires much ad- lethod in the } of operative the results of igical investi- differences to .ual ; and also another. Be- >f its cortical itionship. GENERAL REMARKS ON THE SENSES. 649 so may be regarded as modified epithelial cells, with which are associated a vascular and nervous supply. These end-organd are at once protective to the deli- cate nerves which terminate in them, and serve to convey to the latt^er peculiar impressions which are widely different in most in- stances from those resulting from the direct contact of the nerve with the foreign body. All are ac- quainted with the fact that, when Fm.aM. FlO.40a IJo. m.-Ooraoaole of Vater (After Bnw). Flo. «W.-Xiid-bunM (oorpuMlM) of Kiwue (after Ludden). A, from conjunctiva of man : B, from conlunctiTact calf. It mar be notloed that in aU Ume caWtbe nerve kMsa Us non n w entl i l part* Iwf ore entering Uie oorpuade. the epithelium is removed, as by a blister, we no longer possess tactile sensibility of the usual kind, and experience pain on contact with objects ; in a word, the series of connections neces- sary to a sense-perception is broken at the commencement. Seeing that all the end-organs on the surface of the body have a common origin morphologically, it would be reasonable to expect that the senses would have much in common, espe- cially when these organs are all alike connected with central nervous cells by nerves. As a matter of fact, such is the case, and in every instance we can distinguish between sensory im- pulses generated in the end-organ, conveyed by a nerve inward, and those in the cells of these central nervous systems, giving timim tutummm 550 ANIMAL PHYSIOLOGY. rise to certain molecular changes which enable the mind or the ego to have a perception proper; which, when taken in con- nection with numerous past experiences of this and other senses, furnishes the material for a sensory judg- ment. The chief events are, after all, internal, and hence it is found that the higher in the scale the animal ranks, the more developed its nervous centers, espe- cially its brain, and the more it is able to capitalize its sensory impulses; also the greater the degree of possible improvement by Fio. m.-v»wm with saaguon odb (O) benerth • experience, a difference well (^tfcJSmtST'^''""'**"''"'''*^ seen in blind men whose ability to succeed in life without vision is largely in proportion to their innate and acquired mental powers. Inasmuch as all cells require rest, one would expect that under constant stimulation fatigue would soon result and perceptions be imperfect. Hence it happens that all the senses fail when exercised, even for but a short pe- riod, without change of stimulus leading to alteration of con- dition in the central cells. The change need not be one of en- tire rest, but merely a new form of exercise. Hence the fresh- ness experienced by a change of view on passing through beau- tiful scenery. Exhaustion may not be confined wholly to the central ner ^e- cells, but there can be little doubt that they are the most af- fected. Since also there must be a certain momentum, so to speak, to molecular activity, it is not surprising that we find that the sensation outlasts the stimulus for a brief period ; and this applies to all the senses, and necessarily determines the rapidity with which the successive stimuli may follow each other without causing a blending of the sensations. Thus, then, in every sense we must recognize (1) an end- organ in which the chain of processes begins ; (2) a conducting nerve through which (3) the central nerve-cells are affected; and we may speak, therefore, of (1) sensory impulses and (2) THE SKIN AS AN OBOAN OF SENSK 551 the mind or taken in con- amerous past if this and 'umishes the sensory judg- events are, lal, and hence it the higher the animal ire developed senters, espe- lin, and the I to capitalize apulses; also be degree of rovement by lifferencewell men whose cceed in life r innate and require rest, fatigue would ce it happens lut a short pe- ration of con- , be one of en- nce the f resh- ;hrough beau- sentralner^e- ) the most af- aentum, so to : that we find if period ; and etermines the y follow each 18. se (1) an end- I a conducting I are affected; julses and (2) sensations, when these give rise to affections of the central nervous cells resulting in (1) perceptions and (2) judgments, when we take into account the psychic processes ; and, from the nature of cell-life generally, we must recognize a certain inten- sity of the stimulus necessary to arouse a sensation and a limit within which alone we have power to discriminate (range of stimulation and perception) ; and also a limit to the rapidity wjith which stimuli may succeed each other to any advantage, so as to give rise to new sensations ; and a limit to the endur- ance of the apparatus in good working condition corresponding: to clear mental perceptions, together with the value of past ex- perience in the interpretation of our sensations. THE SEIN AS AN OBOAN OF SENSE. Bearing in mind that all the sensory organs originate in the ectoderm, we find in the skin even of the highest animals the power to give the central nervous system such sense-im- pressions as bear a relation to the original undifferentiated sensations of lower forms as derived from the general surface of the body, bat with less of specialization than is met with in the sense of hearing and vision ; so that it is possible to under- stand how it is that the skin must be regarded not only as the original source of sensory impulses for the animal kingdom, but why it still remains perhaps the most important source of information in regard to the external world, and the condition of our own bodies ; for it must be remembered that the data afforded for sensory judgments by all the other senses must be interpreted in the light of information supplied by the skin. We really perceive by the eye onlj-^ retinal images. The dis- tance, position, shape, etc., of objects are largely determined by feeling them, and thus associating with a certain visual sensa- tion others derived from the skin and the muscles, which latter are, however, generally also associated with Jactile sensations. It is recorded of those blind from birth that, when restored to sight by surgical operations, they find themselves quite unable to interpret their visual sensationis ; or, in other words, seeing they do not understand, but must learn by the other sens^, especially tactile sensibility, what is the real nature of the objects that form images on their retinae. All objects seen appear to be against the eyes, and any idea of distance is out of the question. KMKIIWattllWllltW ■MM mmmmt^' . .j/IUMj.S^_ i AJ_ !ii .t'ai ' 3 * 552 ANIMAL PHTSIOLOOY. In man special forms of end-organs are found scattered over tUe skin, mucous and serous surfaces of the body, such as Pacinian corpuscles, touch-corpuscles, end-bulbs, etc. • while in lower forms of vertebrates many others are found in parts where sensibility is acute. There seems to be little doubt that these are all concerned with the various sensory impulses that originate in the parts where they are found, but it is not pos- sible at present to assign definitely to each form its specific function. It has been contended that the various specific sensations of taste, as bitter, sweet, etc., are the result of impulses con- veyed to the central nervous system by fibers that have this function, and no other ; and a like view has been maintained for those different sensations that originate from the skin. For such a doctrine there is a certain amount of support from experiment as well as analogy ; but the more closely the subject is investigated the more it appears that the complexity of our sensations is scarcely to be explained in so simple a way as many of these theories would lead us to believe. Whether there are nerve-fibers, with functions so specific, must be re- garded as at least not yet demonstrated. Let us now examine into the facts. What are the different sensations, the origin of which must be in the first instance sought in the skin, as the impulses aroused in some form of end-organ or nerve-termination ? Suppose that one blindfolded lays his left hand and arm on a table, and a piece of iron be placed on the palm of his hand, he may be said to be conscious of the nature of the sur- face, whether rough or smooth, of the form, of the size, of the weight, and of the temperature of the body ; in other words, the subject of the experiment has sensations of pressure, of tactile sensibility, and of temperature at least, if not also to some extent of muscular sensibility. But if the right hand be used to feel the object its form and surface characters can be much better appreciated; while, if the body be poised in the hand, a judgment as to its weight can be formed with much greater accuracy. The reason of the former is to be sought in the fact that the finger-tips are relatively very sensitive in man, and that from experience the mind has the better learned to interpret the sensory impulses originating in this quarter ; which again resolves itself into the particular condition of the central nerve-ceUs associated with the nerve-fibers that convey inward the impulses from those regions of the skin. Mani- THE SKIN AS AN ORGAN OF SENSE. 653 attered over ly, such as c. • while in ud in parts doubt that apulses that is not pos- its specific sensations ipulses con- it have this . maintained n the skin, ppport from f the subject exity of our tie a way as ). Whether must be re- }he different irst instance ome form of ad and arm palm of his 3 of the sur- ) size, of the jther words, pressure, of ' not also to ight hand be cters can be Kxised in the Iwith much i)e sought in sensitive in etter learned this quarter ; dition of the 1 that convey skin. Mani- festly if there be a sense referable to the muscles (muscular sense) at all, when they are contracted at will the impression must be clearer than when they but feebly respond to the mere pressure of some body. It is possible, as every one knows, to attend only to the data afforded by one set of impulses, such as those associated with our sensations of weight, temperature, etc., but such requires special attention ; and as in the case of the eye we consider the object as a whole, its color, form, size, anri other qualities, so does the mind form its complete conception by a synthesis or union of a variety of sensory data. Regarding the skin as a whole, we may speak of the skin-sense as we do of the ocular sense or vision. The separate treatment of tactile, thermal, and other forms of sensibility under sejurate headings is a matter of convenience ; but there is considerable danger that we over- look the great fundamental fact that our knowledge of objects (is^rimarilg^^hetic and no t_analytic. True, in disease, when one or more sets of the data of sense as derived from the skin is wanting, the others can be appreciated, and these alone. Nevertheless, such is an abnormal condition, and in that case the outer world passes to a large extent beyond the degree of control natural to man. ■ Patholffgiftri. — It does happen in certain forms of disease, notably of the spinal cord, that tactile sensibility is retained and thermal lost, or the muscular sense impaired. Such per- sons are plainly reduced at once to the condition, not only of being without certain sensory impressions, but in consequence unable to use others which they do possess to the same extent as before. A man with that affection of the spinal cord known as locomotor ataxy may have tactile and thermal sensibility, yet be unable to use these, in the absence of the muscular sense to enable him to be his own master, except when he calls in the help of his eyes, as, e. g., in walking. It is thus seen how all the various sources of information from the skin and muscles blend psychically to produce a conception which, as a whole, corresponds to "seeing." The defects just referred to are in a measure comparable to color- blindn^s. With this warning we shall now attempt to state some of the main facts in regard to the different functions of the skin as a sensory or^n, especially endeavoring to trace parallel laws for this and the other senses. ■ ;-i(:v«:';'^-,'rt^i'- ■ '■ 654 ANIMAL PHTSIOLOOr. PRESSUBB Sensations. 1. There is a relation between the intensity of the stimulus and the sensation resulting, and this limit is narrow. The greater the stimulus the more pronounced the sensation, though ordinary sensibility soon passes into pain. Weber's law (to be explained later) holds in the case of the skin as for other senses. 2. The duration of the sensation is very brief. It is said that a card in which holes have been punched, so that when in rota- tion it may bear on the skin, may be made to touch one of its holes against the finger as often as fifteen hundred times in a second before the sensations are fused. 3. The law of contrast may be illustrated by passing the finger up and down in a ves- sel containing mercury, when the pressure will be felt most dis- tinctly at the point of contact of the fluid. 4. Pressure is much better estimated by some parts than others ; hence the use of the tips of the fingers in coimting the pulse, palpating tumors, etc. Thermal Sensations. 1. The law of contrast is well illustrated by this sense ; in fact, the temperature of a body exactly the same as that of the part of the skin applied to it can scarcely be estimated at alL The first plunge into a cold bath gives the impression that the water is much colder than it seems in a few seconds after, when the temperature has in reality changed but little ; or, perhaps, the subject may be better illustrated by dipping one hand into warmer and the other into colder water than that to be ad- judged. The sample feels colder than it really is to the hand that has been in the warm water, and warmer than it is to the other. 2. The limit within which we can discriminate is at most small, and the nicest determinations are made within about 27° and 33° C. — i. e.> not far from the normal temperature of the body. 3. Variations for the different parts of the skin are easily ascertained, though they do not always correspond to those most sensitive to changes in pressure. The cheeks, lips, and eyelids are very sensitive to pressure. fBecent investigations have revealed the fact that there are in the skin "pressure-spots," and "cold-spots " and "heat- spots" — i. e., the skin may be mapped out into very minute areas which give when touched a sensation of pressure differ- ent from that produced by the same stimulus in the intermedi- ate regions ; and in like manner are there areas which are sen- e stimulus row. The on, though law (to be bher senses, said that a en in rota- I one of its times in a of contrast m in a ves- It most dis- ire is much e use of the amors, etc. IS sense ; m that of the lated at alL on that the after, when or, perhaps, e hand into ^t to be ad- the hand 1 it is to the e is at most in about 27* iture of the te skin are rrespond to cheeks, lips, that there and **heat- ery minute jsure differ- e intermedi- dch are sen- THE SKIN AS AN ORGAN OF SENSE. 555 sitive to warm and to cold bodies respectively, but not to both ; and these do not correspond with the pressure-spots, nor to those that give rise when touched to the sensation of pain. These spots are not placed symmetrically on both sides of the same individual, nor on corresponding parts of different indi- viduals. So much has been ascertained by experiment. It is believed by some of the investigators that these areas are con- nected with the nerve-centers by nerve -fibers devoted to con- ducting impulses corresponding to the sensations which have the beginning of their formation in the different kinds of spots. The latter, however, has not been demonstrated. C^hile there can be no doubt that these investigations have furnished additional facts of great importance, they can not be considered as making the whole subject of sensation by the skin perfectly clear. For example, how are we to explain why a cold body feels heavier than a warm one, as may easily be demonstrated to one's own satisfaction by placing a large coin cooled down to near the freezing-point on the forehead beside a warmer one ? We think such facts are calculated to enforce the lesson which we have been endeavoring to impress, viz., that our sensations are never single (thermal, tactile, etc.), but are compound, one or the other element preponderating; and that all interpretations of sense must take into accoimt this fact — ^and the very important one— that every sensory impres- sion is interpreted in the light of our past experience, as well as that of the immediate present. It has been shown, also, that the extent of the area of skin stimulated determines to a large degree the quality of the re- sulting sensation. Thus, the temperature of a fluid does not seem the same to a finger and the entire hand. This fact is not irreconcilable with the existence of the various kinds of ther- mal spots, referred to above, but it does re-enforce the view we are urging of the complexity of those sensations which seem to us to form simple wholes — as, indeed, they do — just as a piece of cloth may be made up of an unlimited number of different kinds of threads. Tactile Sensibility. As a matter of fact, one may learn, by using a pair of com- passes, that the different parts of the surface of our bodies are not equally sensitive in the discrimination between the contact of bodies — i. e., the judgment formed as to whether at a given mUsmMmmm 666 ANIMAL PHYSIOLOGY. instant the skin is being touched by one or two points is de- pendent on the part (. ". the body with which the points are brought into contact. The following table will make this clear, the numbers indi- cating the distance at which the two points of a pair of com- passes must be apart in order that they shall not give rise to the judgment of one point of contact, but be recognized as two: XUIiiiMtrMk Tip of tongue VI Palm of last phalanx of finger 2'2 Palm of second phalanx of finger 4*4 Tip of nose 6*6 Whitish part of lips 8*8 Back of second phalanx of finger. 11*1 Skin over malar bone 15*4 Back of hand 29*8 Forearm 39*6 Sternum 44*0 Back 66*0 There seem to be areas of skin which give rise when pricked to the sensation of pain ; but, whether we should distinguish be- tween tactile and pressuire sensation by reference to correspond- ing spots, does not yet seem clear. Certain it is that exercise of these and all the senses greatly improves them, though it is likely that such advance must be referred rather to the central nerve-cells than to the peripheral mechanism. Careful comparison of blind and seeing children has shown that the blind, in forming their judgments, appar- ently from sensations derived through the skin, in reality use much collateral help, which is very variable and certainly widely different, according to the past experience and general intelligence of the individual. We practically distinguish between a great many sensations that we can neither analyze nor describe, though the very variety of names suflGlces to show how much our interpretation of sense depends on past experience. We are always able to define the part of our bodies touched, and with great accuracy, no doubt, owing to the simultaneous use in early months and years of our lives of vision and the senses resident in the skin. There are, however, transient illusions of sense which illus- trate the remark just made. If a small marble be placed be- ^mmmmmmimmmmtmm THE SKIN AS AN OROAN OF SENSE. 657 oints is de- points are nbers indi- air of com- Bfive rise to zed as two: en pricked inguish he- orrespond- ses greatly ce must be peripheral ig children nts, appar- reality use L certainly ad general sensations 1 the very erpretation Bs touched, nultaneous on and the rhich illus- placed be- tween the radial side of one finger and the ulnar side of the other (Aristotle's experiment), the subject of the experiment being blindfolded, it will be judged as two marbles at first, though the tactile impression is soon corrected, especially if the eyes be opened. These surfaces of the fingers have not been accustomed to touch at the same time the one body, hence the illusion. An impression made on the trunk of a nerve is referred to the peripheral distribution of that nerve in the skin ; thus, if the elbow be dipped in a freezing mixture, the skin around the joint will experience the sensation of cold, but a feeling of pain will be referred to the distribution of the ulnar nerve in the hand and arm. The same principle is illustrated by the com- mon experience of the effects of a blow over the ulnar nerve^ the pain being referred to the peripheral distribution ; also by the fact that pain in the stump of an amputated limb is thought to arise in the missing toes, etc. It is said that when skin< transplanted from the forehead to the nose, to repair missing, 7 parts, is touched, the sensation is located in the original site/ of the skin (forehead). In all such facts we see how dependent/ are all our sensory judgments on our past experience, illustrat- ing the very important truth. With its wide ramifications, that, in a physiological sense, as well as in many others, our^past_ makes our own future and that of the race to a very large e^ent^ The Musculab Sense. Every one must be aware how difficult, it is to regulate his movements when the limbs are cold or otherwise deadened in sensibility. We know too that, in judging of the muscular effort necessary to be put forth to accomplish a feat, as throw* ing a ball or lifting a weight, we judge by our past experi- ence. It is ludicrous to witness the failure of an individual to take up a mass of metal which was mistaken for wood. In these facts we recognize that in the successful use of the mus- cles we are dependent, not alone on the sensations derived from the skin, but also from the muscles themselves. True, the mus- cles are not very sensitive to pain when cut; it does not, how- ever, follow that they may not be sensitive to that different effect, their own contraction ; whether the numerous Pacinian bodies around joints, or the end-organs of the nerves of mus- cles are directly concerned, is not determined. Ftthdogioal.— The teaching of disease is plainly indicative of MM J 5fi8 ANIMAL PHTSIOLOOY. the importance of sensations derived both from the skin and the muscles for co-ordination of muscular movements. In locomotor ataxy, in which the power of muscular co- ordination is lost to a large extent, the lesions are in the pos- terior columns of the spinal cord, or the posterior roots of the nerves, or both, and these are the parts involved in the trans- mission of afferent impulses. Whether the muscular sense also implies a central " neural " sense, or consciousness of the changes of central origin, associ- . ated with the execution of a movement as distinct from the impressions derived from the muscles, is a matter of dispute. But the student will be already prepared for our answer to this question. The evidence of experiment seems to point to a dis- tinct source of information in the muscles. We would take along with this the additional data of sense afforded by the skin, the "sense of effort" and other factors, as stored past experi- ence, which must be very variable for the individual, as any one may observe by watching the muscular efforts of others and himself. OompuratiTe. — The more closely the higher vertebrates are observed, the more convinced does one become that those sen- sory judgments, based upon the information derived from the skin and muscles, which they are constantly called upon to form are in extent, variety, and perfection scarcely if at all surpassed by those of man. Of course, a sensory judgment in man, with his excessive cerebral development, may by associations in his experience be worked up into elaborate judgments impossible to the brutes, but we now refer to the judgments of sense in themselves. The lips, the ears, the vibrissee or stiff hairs, especially about the lips, the nose, in some cases the paws, all afford deli- cate and extensive sensory data. It is a remarkable fact that the most intelligent of the groups of animals have these sensory surfaces well developed, as witness the elephant with his wonderful trunk, the hand of the monkey, and the paws and vibrissfe of the cat and dog tribe. On the other hand, the groups with hoofs are notably inferior in the mental scale. When we pass to the lower forms of in- vertebrates the appreciation of vibrations of the air or water in which they live, of its temperature, of its pressure, must be considerable to enable them to adapt themselves to a suitable environment. VISION. 559 ) skin and iscular co- ll the pos- 3ot8 of the the trans- 1" neural" l^n, associ- . b from the of dispute, wer to this nt to a dis- irould take )y the skin, ast experi- iial, as any I of others )brates are those sen- 1 from the ion to form I surpassed man, with bions in his impossible of sense in , especially afford deli- ent of the developed, ;, the hand sat and dog bly inferior onus of in- dr or water re, must be a suitable (We have not spoken of sensations derived from th- internal organs and surfaces. These are ill-defined, and we know them mostly either as a vague sense of comfort or discomfort, or as actual pain. We are quite unable to refer them at present to special forms of end-organs. They are valuable as reports and warnings of the animal's own condition. After-impressions (" after-images ") of all the senses referred to exist, mostly positive in nature — i. e., the sensation renfiains when the stimulus is withdrawn. SynoptiMl. — The information derived from the skin in man and the other higher vertebrates relates to sensations of press- ure, temperature, touch, and pain. The muscles also supply information of their condition. In how far these are referable to certain end-organs in the skin is uncertain. There are der- mal areas that give rise to the sensations of heat, cold, pressure, and pain. Whether these are connected with nerve-fibers that convey no other forms of impulses than those thus arising is undetermined. In all these senses the laws of contrast, duration of the im- pression, limit of discrimination, etc., hold. The sensory judgments based on sensations derived from the skin are syntheses or the result of the blending of many component sensations simultaneous in origin. <^1 our sensory judgments are very largely dependent on our past experience. VISION.^ Light and vision are to some degree correlatives of each other. Light is supposed to have as its physical basis the vibra- tions of an imponderable ether. Such is, however, to a non- seeing animal as good as non-existent, so that we may look at this subject either with the eyes of the physiologist or the phys- icist, according as we regard the cause of the effects or the latter and their relations to one another.. It is, however, im- possible to understand the physiology of vision without a sound knowledge of the anatomy of the eye, and an apprehen- sion of at least some of the laws of the science of optics. The student is, therefore, recommended to learn practically the coarse and microscopic structure of the eye in detail. The eyes of mammals are sufficiently alike to make the dissection of any of them profitable. Bullocks' eyes are readily obtainable, and from their large size may be used to advantage. We recom- > ; tmrnm^im^^mm 560 ANIMAL PHYSIOLOGY. Fio. «».-Eye tMrttally diMctod (atter tepmjr). 1, »Egg««TSi'.*iii' k^^uh^MES^ bMk io M fouBOOTw the choroid oort ; S. oprnefc«HT|^ and fo^^ ooM ; «. cauwl of Bchleinm ; 7, external nirfaoe of cborold, travened by one of the long ciUarr •rteriee and br olllarT nenrea ; 8, central Tcaael, into which the vata vortuoia ^^ ;Tl«roh«old loneTfi, ciliary netve. ; 18. long Hilary aiteiy ; 18, anterior dllary artcdlea ; 14, Iria ; U, Tawniiar dnde of hia ; 16, pupU. mend one to be boiled hard, another to be frozen, and sections in different meridians to be made, especially one vertical longi- -SUPERIOR RECTUS m CHOROID OPTIC NERVr CHOROID -INnRIORMBnW Fia. MIt.— Section of human eye, aomewhat diagra mm a tic (after Flint). VISION. S61 tudinal section. Other specimens may be dissected with and without the use of water. ■clerotio dlHMted Mck with Mdarotie t>y one of the Iook b« oata vortieota IS, anterior cilUur and sections Brtical longi- ITUS -CHOROID IgPTtC NERVr ROlO nw }T Flint). ria. «H.— Certain parts of ere. 1 » 10. (After Sappejr.) 1, 1, orjntaiUiw tona ; t, hjralotd membrane ; 8, ■onule of Zlnn; 4, iria; S, a dUaoy prooeaa; t.radiatlns libera of ciliary muscle ; 7, section of droular portion of ciliarjr muscle ; 8, venous plenis of cUiarr mus- cle; », 10, sclerotic coat; 11, IS, cornea; IS, epithelial lajrer ol come*; 14, Descemefs membrane ; 15, pectinate Uitament of iris ; 16, epitlielium of membrane ot Desoemec ; 17, union of sdMrotlo coat with cornea ; 18, section of canal of B c falwnm , Assuming that some such work has been done, and that the student has become quite familiar with the general structure of the eye, we call attention specially to the strength of the sclerotic coat ; the great vascularity of the choroid coat and its terminal ciliary processes, its pigmented character adapting it for the absorption of light ; the complicated structure and pro- tected position of the retinal expansion. It may be said that the whole eye exists for the retina, and that the entire mechan- ism besides is subordinated to £he formation of images on this nervous expansion. The eye of the mammal may be regarded as an arrangement of refracting media, protected by coverings, with a window for the admission of light, a curtain regulating the quantity admitted ; a sensitive screen on which the images are thrown; surfaces for the absorption of superfluous light; 86 iBiiiiiiWMniiiiinilMn 562 ANIMAL PHYSIOLOGY. apparatus for the protection of the eye as a whole, and for preserving exposed parts moist and clean. Em' ryologieaL — We have already learned that the first indi- cation (. ' the eye is the formation of the optic vesicle, an out- g^o^Hh from the first cerebral vesicle. This optic vesicle be- comes more contracted at the base, and the optic stalk remains as the oDtic nerve. Fio. laL Fia. 405. Fia. 406.— SecUon ttiroiwfa head of chick on third day, ahowing orUrfn of eye (after Teo). a, epiblast undergoing tUckeniiig to form lena ; o, optic n^hUe ; v„ flrrt cerebral veeiole ; v., posterior cerebral Teaide. It will be observed tliat Uie retina is alread;^ disUnotly in- Fio. 406.— Later stagos in development of eye (after Ctediat). a, epibUMt ; c, devd«>ping lens ; o, opUc vesicle. At an early stage of development (second or third day in the chick) the outer portion of the optic vesicle is pushed inward, so that the cavity is almost obliterated ; the anterior portion, becoming thickened, ultimately forms the retina proper, while the posterior is represented by the tesselated pigment layer of the choroid. As this retinal portion breaks away from the superficial epi- thelium, the latter forms an elliptical mass of cells, the future lens, the changes of which in the formation of the cells peculiar to the lens illustrate to how great lengths differentiation in structure is carried in the development of a single organ. It will thus be seen that the most essential parts of the eye, the optic nerve, the retina, and the crystalline lens, are, according to a general law, the earliest marked out. The cornea, the iris, the choroid, the vascular supply, the sclerotic, etc., ere all sec- ondary in importance and in f onnation to these, and are derived from the mesoblast, while the essential structures are traceable, like the nervous system itself, to the epiblastic layer. wwi i wi W i' fMaii iw w wy i w iwJJirwt i rj M wiw-aw - 'd day in the ihed inward, rior portion, iroper, while lent layer of perficial epi> s, the future sells peculiar 'entiation in le organ. It the eye, the :e, according nea, the iris, , are all seo- 1 are derived re traceable. VISION. 663 Any act of perfect vision in a mammal may be shown to consist of the following : (1) The focusing of rays of light from Fio. 407.— More adTanoed ataM o( derdopaieiit ot eye (after Oardlat). a, epithelial oeUa forminK lens, now mwdi anered : b, lena capmie ; e. cotaneoaa tianie about to form oon- JunctiTs ; d, e, two layers of optic vMicle, now folded back and (ormiiw retina ; /, mucoua iiMue forming vitreous humors ; g, interodlular substanoe ; k, developiBK optte nerve ; i, nerre-flbers entering rrthia. an object on the retina, so as to form a well-defined image ; (2) the conduction of the sensory impulses thus generated in the retina by the optic nerve inward to certain centers ; and (3) the elaboration of these data in consciousness. We thus have the formation of an image— a physical pro- cess; sensation, perception, and judgment— physiological and psychical processes. In the natural order of things we must discuss first those arrangements which are concerned with the focusing of light i e., the formation of the image on the retinal screen. DioPTBics OF Vision. One of the most satisfactory methods of ascertaining that the eye does form images of the objects in the field of vision is to remove the eye of a recently killed albino rabbit. On rti:'«X'"-W.''*Wft W M ii jruin wiiifi i itr y a- 564 ANIMAL PHYSIOLOGY. holding up before such an eye any small . Uject, as a pair of forceps, it may be readily observed that an inverted image of the object is formed on the back of the eye {fundus). If, how- ever, the lens be removed from such an eye, no image is formed. If the lens be itself held behind the object, an inverted image will be thrown upon a piece of paper held at a suitable (its focal) distance. By substituting an ordinary biconvex lens, the same effect follows. It thus appears, then, that the lens is the essential part of the refracting media, though the aqueous and vitreous humors and the cornea are also focusing mechanisms. The fiurfaces of the refracting media may all be considered to be centered on one of the axes, which meets the retina above and to the inner side of the fovea centralis. We may for practical purposes reason from a diagrammatic eye, the re- fracting surfaces of which are (1) the anterior surface of the cornea, (2) the anterior surface of the lens, and (3) the posterior surface of the lens. The media may be reduced to (1) the lens substance and {%) the aqueous, or, as it has about the same refracting power, the vitreous humor. By the posderior principal focus is meant the point at which all rays that fall on the cornea parallel to the optic axis are focused. It is 14-647 mm. behind the posterior surface of the lens, or 22*647 mm. behind the anterior surface of the cornea in Vm 408.— BBftmeUaB br mmm teoMs (after rUnt and WeMMM). The !«> mar be i tSwiJStotmmStSlmmS^tii ligun),tat Um aalwoC ■impUcity, though of oouna this to aot ■Metijr aoounte. the diagrammatic eye. In the actual eye the fovea of the retina must occupy this position when at rest, if a distinct image is to be formed. It will appear that we may represent the eye as reduced to " i »i ff<>i w "B m i wj w w-M iwwwiWI VISION. 666 as a pair of ted image of 8). If, how- a^ is formed, rerted image suitable (its ^ex lens, the e lens is the aqueous and aechanisms. le considered retina above Ne may for eye, the re- Lrface of the the posterior a (1) the lens ut the same nnt at which >ptic axis are urface of the the cornea in ^ ■U ^ ^.tlMNIghoC OOUM k of the retina tinct image is as reduced to the lens and the retina, and in many of the illustrations to fol- low this will be done. The experiments referred to above will convince the student that such is the case ; and we may here state that, while the various principles involved in the physiol- ' ogy of vision may be illustrated in great perfection by elab- orate experiments, we shall endeavor to supply the student with accounts of very simple methods of convincing himself by personal observation, such as may be readily repeaied at a future time, which is more than can be said for those that in- volve expensive apparatus. Accommodation of the Etb. Using the material already referred to, the student may observe that, with the natural eye of the albino rabbit, its lens (or better that of a bullock's eye, being larger), or a biconvex lens of glass, there is only one position of the instruments and objects which will produce a perfectly distinct image. If either the eye (retina), the lens, or the object be shifted, instead of a distinct image, a blurred one, or simply diffuaion-cirdes, appear. A photographer must alter either the position of the object or the position of his lend when the focus is not perfect. The eye may be compared to a camera, and since the retina and lens can not change position, either the shape of the lens must change or the object assume a different position in space. As a matter of fact, any one may observe that he can not see objects diatincUy within a certain limit of nearness to the eye, known as the near point (punctum proximum) ; while he be- comes conscious of no effect referable to the eye until objects approach within about sixty-five to seventy yards. Beyond the latter distance objects are seen dearly without any effort. We thus learn that the range of accommodation lies between about five inches and sixty to seventy yards, though it is cus- tomary to speak of the. far point as infinity («), which simply means that the rays from objects beyond the distance given above are practically parallel, and are, therefore, focused on the retina without any alteration in the shape of the lens {neg- aiive aecommodation) ; while nearer onds require this. When objects are nearer to the eye than about five inches, for most persons, the eye can not accommodate sufficiently to bring the rays of light emanating from them to a focus on tlie retina. There are many ways in which we may be led to realize these truths : 1. When one is reading a printed page it is only .3 566 ANIMAL PHTSIOLOOT. the very few words to which the eyes are then specially di- rected that are seen clearly, the rest of the page appearing blurred ; and the same holds for the objects in any small room. We speak of picking out an acquaintance in an audience or crowd, which implies that each of the individuals composing the throng is not distinctly seen at the same time. 2. If an ob- server hold up a finger before his eyes, and direct his gaze into the distance (relax his accommodation), presently he will be- hold a second shadowy finger beside the real one — i. e., he sees double : his eyes, being accommodated for the distant objects, can not adapt themselves at the same time for near ones. 3. The principle involved may be most precisely illustrated by Schein- ! -A Ito. 4n.— Dtasnunto oate tha oimmmiUuMea SdMiner'a , wlilobthera It (after LMidois). The dotted linep indi- double Tlaion. ». 410.— Tte wwleto 8dtBliiet»e wrperimeiit (elter P eraete to ). tlieoMMttaet a: thehiMia wpwe n tedV 6; and the retfaia mair Im at m, m, n.H, or 1,1. Am card with ita holM. c/todirMSttartaifrMitortbeleiia. It la plain Oat, if tiiennriiatrike the retina in anjr way •j" _. __ ."v ... .. . ...-...- .—jrrrr.^ w. (omllJS, ona or other of theae wiU > oardiaatopped; whioh of tbem will eaioept aa repreaanted at e, double imama muat be diaMMear aooordinc aa the right or left kola of the dependw olroanaBmea-i. e., aa to whaOMT tha cai caaa ia that flgured at «», m orl, i. ii»iiliii»MiiiiiWiiWHi'iiiim"i'wiii'mni»Mi VISION. 667 ipecially di- I appearing jmall room, iudience or composing 2. If an ob- is gaze into he will be- L e., he sees Etnt objects, aes. 3. The L by Schein- dottedUnepiiidl- » / lata: the lent to rd wtai it* holM, retina in MijrwMr theroftlMMwdl rhtohoftbemwUI m, t» or {, i. er's experiments (Figs. 409 and 410). Let two small holes be pricked in a card, at a distance from each other not greater than the diameter of the pupil ; fix the card upright on a piece of board, about two feet long, and, closing one eye, observe the effect of looking at two pins stuck into the board in line with each other, at different distances apart. It may be observed that as soon as the nearest pin is approximated to the card within a certain distance it fails to be distinctly seen, and appears double — ^i. e., the near point is exceeded ; that when the distant pin is in focus, the near one appears double, and vice versa. When the image is double, blocking one of the two holes causes one image to disappear, and this is the right or the left hand image, according as the one or the other hole is stopped, and as it is the distant or near pin that is seen as two. The reason of this will be plain from the above figures, but it must be remembered that an image on the right of the retina is ad- judged to be on the left of the visual field, as will be explained later. In what does accommodation consist ? If light from a can- dle or lamp be allowed to fall obliquely on the eye of a second person, through a card on which two triangular holes have been cut one above the other, three pairs of images of the flame (necessarily triangular) may be seen reflected from the eye of the observed subject, two of which are erect and one inverted; the brightest and most distinct being from the cornea, the sec- ond pair dimmer and larger from the anterior surface of the lens, and the smallest (c) from the posterior surface of the lens, inverted, since it is produced by a concave mirror. When the subject of the observation looks at a near object, only one of these pairs of images alters appreciably, viz., that from the anterior surface of the lens, the middle pair (b). The conclusion then follows that accommodation consists essentially in an alteration of the convexity of the anterior surface of the lens. The images appear nearer to each other the more convex the lens becomes. Without the help of a special instrument (phakoscope) the ob- server may fail to see the change, though that the other pairs da not alter position or size he may certainly readily observe. This change in the shape of the lens is accomplished as 411.— PurUnJe'i inwRcs. a h e during "ra, o, N e, dorinf porittra aocoamo- 668 ANIMAL PHYSIOLOGY. follows : The lens is naturally very elastic and is kept in a par- tially compressed condition by its capsule, to which is attached the suspensory ligament which has a posterior attachment to the choroid and ciliary processes. When the ciliary muscle. Ite. 41S.— niuatntM meohuim of Meominodation (after Viclo. The left tU» relation of parte duriiur the paMtre oonditioii of the ere (negative «« t for long dirtanoea) ; the rli^t aide, that fornear objeota. the ktion, or which operates from a fixed point the comeo-sclerotic junction, pulls upon the choroid, etc., it relaxes the suspensory ligament ; hence the lens, not being pressed upon in front as it is from behind by the vitreous humor (invested by its hyaloid mem- brane), is free to bulge and so increase its refractive power. The nearer an object approaches the eye, the greater the diver- gence of the ray^ of light proceeding from it, and hence the necessity for greater focusing power in the lens. If a person be observed closely when looking from a remote to a near object, it may be noticed that the eyes turn inward — i e., the visual axes converge and the pupils contract. These are not, however, essential in the sense in which the changes in the lens are ; for, as before stated, in the absence of the lens distinct vinon is quite impossible. Were additional evidence necessary to show that accommodation is effected as described, it might be st&ted that by stimulation of the lenticular gan- glion the ciliary muscle may in an animal thus experimented upon be shown to contract, the choroid to be drawn forward, and the anterior convexity of the lens to be increased. Vaso- motor changes or alterations in the size of the iris, if they have any effect upon the lens at all, must play a very unimportant pari The movements of the iris do, however, serve an impor- tant purpose, and to that subject we now turn. »a»w»Wpg«|Mj!| W i Migl !it i'JWWW»-tW i W|il WP» .iaaitl-fllB.W.M^ ^ ■v-v.-.v- ■' •• '-^TVfrii pt in a par- is attached ochment to Etry muscle. M0 depioto the oommomtion, or ic junction, y ligament; B it is from aloid mem- tive power. ir the diver- d hence the >m a remote m inward — ■act. These the changes of the lens lal evidence bs described, ticular gan- cperimented mi forward, hsed. Vaso- if they have inimportant '^e an impor- VISION. see Altkrations in the Size of the Pupil. The pupil varies in size according as the iris is in a greater or less degree active. All observers are agreed that the circu- lar fibers around the pupillary margin are muscular, forming the so-called sphincter of the iris ; but great differences of opin- ion still exist in regard to the radiating fibers. It is thought by many that all the changes in the iris may be explained by the elasticity of its structure without assuming the existence of muscular fibers other than those of the sphincter; thus a contraction of the latter would result in diminution of the pu- pillary aperture, its relaxation to an enlargement, provided the rest of the iris were highly elastic. The conclusions in regard to the innervation of the iris rest largely upon the results of certain experiments which we shall OpUceentn- Oetiio-motor.^ i. eentre \ •»^ DOator '^^r-ib'sr-^'K^vmsMX.-i ArnipatMIe tunw to mMoMna/ibnt fiiplnal Motor Mtitfv Vn. 4U.-1>iMnun to Uhutnte tenemtloB of Uw irto. Dotted Udm indloirte geami (Bno- «lo5>looiiBeetton(oorreleaon>. Coune a( imiNilMi indicaied Iqr wrows. 570 ANIMAL PHYSIOLOGY. now briefly detail : 1. When the third nerve is divided, stimu- lation of the optic nerve (or retina) does not cause contraction of the pupil as usual. 2. When the optic nerve isdivided, light no longer causes a contraction of the pupil, though stimulation of the third nerve or its center in the anterior portion of tho floor of the aqueduct of Sylvius does bring about this result. 3. Section of the cervical sympath^ttic is followed by contrac- tion and stimulation of its peripheral end by dilation of the pupil. From such experiments it has been concluded that — 1. The optic is the afferent nerve and the third nerve the efferent nerve concerned in the contraction of the pupil ; and that the center in the brain is situated as indicated above, so that the act is or- dinarily a reflex. 2. That the cervical sympathetic is the path of the efferent impulses regulating the action of the radiating fibers of the iris. Its center has been located near that for the contraction of the piipil, and it may be assumed to exert a tonic action over the iris comparable to that of the vaso-motor center over the blood-vessels. The impulses may be traced through the cervical sympa- thetic and its ganglia back to the first thoracic ganglion, and thence to the spinal cord and brain. There may be subsidiary centers in the cervical spinal cord. There are facts which it is difficult to explain in the above manner. Thus, whdn atropin is dropped into the eye, the dila- tation is greater than that which follows section of the optic nerve or the third nerve. In such a case, paralysis of the con- tracting mechanism, by which the dilating mechanism is left free to act, should produce, we might suppose, the greatest pos- sible dilation of the pupil, especially if we assume, as some do, that there are no radiating muscular fibers, but that all the , effects are produced through the sphincter of the iris ; but such is not the. case. The result has been set down to the action of the drug upon a local nervous mechanism, or the muscular fibers themselves, or to the v^so-motor changes said to be co- incident. This view is strengthened by the fact thai stimu- lation of the retina 'in a recently removed eye will cause some reflex contraction of the pupil. In explaining the action of drugs on the pupil we are not limited to either a purely local or a purely central influence ; some seem to act in one stage more upon the centers, in another more locally. Vaso-motor influences undoubtedly do affect the size of the pupil, full vessels Bi«i»mi»iiw i ii ii i i»i ii . i ji i .i i j i m». i j. i ) i .u.. wnwuBWHu i .u j>i>wj»w#)»itwMWtu i ui i> w a « i »>a ' ij »!groagaiBaia^ 1/ VISION. 671 ided, stimu- contractioit vided, light stimulation rtion of tho this result, by contrac- ition of the lat— 1, The erent nerve t the center le act is or- is the path le radiating itraction of action over ter over the Leal sympa- oiglion, and ) subsidiary n the above ye, the dila- * )f the optic I of the con- aism is left reatest pos- as some do, ihat all the B ; but such lie action of e muscular d to be co- thai stimu- cause some e action of lurely local ' i one stage Vaso-motor full vessels tending to contraction and the reverse to dilation. Upon the whole, it seems best to regard the two mechanisms as supple- mentary to one another, so that usually with increased action of the one there is diminished action of *he other. We find that the twO eyes move in harmony, and v .t the two pupils in health are always of the same size. Light thrown upon one eye contracts the pupil of the other. We are thus led to be- lieve in associated or consensual movement of the iris, owing to nervous connections between the various centers involved. These are physiological, but whether anatomical or not, in the sense that annectant fibers exist, is tmcertain ; and, however, in the evolution of function, they may have been at first pro- duced, have been so strengthened, according to the law of habit, that now it is with the greatest difficulty that one may learn to move one eye independently of the other, or modify the form of the pupils without also shifting the visual axes. It is to be remembered that, although the dilating center is automatic in action, it may also act reflexly, oi: be modified by unusual afferent impulses — ^as, e. g., the strong stimulation of any sensory nerve which causes enlargement of the pupil through inhibition of the center. To render the paths of impulses affecting the iris somewhat clearer, it is well to bear in mind the nervous supply of the part : 1. The third nerve, through the ciliary (ophthalmic, lenticular) ganglion, supplies short ciliary nerves to the iris, ciliary muscle, and choroid. 2. The cervical sympathetic reaches the iris chiefly through the long ciliary nerves and the ophthalmic division of the fifth. 3. There are sensory fibers from the fifth nerve ; and, according to some observers, also dilating fibers from this nerve inde- pendent of the sympathetic, as well as those that may reach the eye by the long ciliary nerves without entering the ciliary ganglion. 4. The centers from which both the contracting and dilating impulses proceed are situated near to each other in the floor of the aqueduct of Sylvius. It is of practical im- portance to remember the various circumstances under which the pupil contracts and dilates. Contradion (Myosis). — 1. Access of strong light to the retina. 2. Associated contraction on accommodation for near objecta 3. Similar associated contraction when the visual axes converge, as in accommodation for near objects. 4. Reflex stimulation of afferent nerves, as the nasal or ophthalmic divis- ion of the fifth nerve. 6. During sleep. 6. Upon stimulation of the optic or the third nerve, and the corpora quadrigemina J mmm 672 ANIMAL PHTSIOLOOT. or adjacent parts of the brain. 7. Under the effects of certain drugs, as physostigmin, morphia, etc. DiUUion {Mydriasis). — 1. In darkness, i. On stimulation of the cervical sympathetic. 8. During asphyxia or dyspnoea. 4. fiy painful sensations from irritation of peripheral parts. 5. From the action of certain drugs, as atropin, etc. The student may impress most of these facts upon his mind by making the necessary observations, which can be readily done. PitholofisaL— As showing the importance of such connec- tions, we may instance the fact that, in certain forms of nervous disease (e. g., locomotor ataxia), the pupil contracts when the eye is accommodated to near objects, but not to light (the Argyll-Robertson pupil). In other cases, owing to brain-dis- ease, the pupils may be constantly dilated or the reverse ; or one may be dilated and the other contracted. Optical Impkbfbctionb or the Eye. The defects to be noticed now ire common to all human eyes, and probably to the eyes of eXi. mammals, though in some persons certain of them, as astigmatism, are of so serious a character that they require special remedies. J^^hniMl AbmmUoB.— The nature of this defect may be best learned from an examination of Fig. 414, below. It will be seen that rays of light passing through the lens are brought to b li Mt pWflMStlr riMVPtr l»tatm»Atta,8, a focus, varjring with the point of the lens through which they pass, the focusing power of any ordinary convex lens being greater toward the circumference. This defect is believed to be corrected in the human eye, at least to some extent, by the following: 1. The iris cute off the more strongly refracted outer rays. 2. The corneal curvature is rather ellipsoidal, so that those rays farthest from the optical axis are least deviated by it. 8. The anterior and posterior curvatures of the lens are cor- rective of each other. 4. The power of refraction of the lens n*Mi RMn mmm i VISION. 578 ts of certain stimtilation or dyspnoea, theral parts. 1, etc. The lis mind by readily done, inch connec- ts of nervous ts when the light (the to brain-dis- 1 reverse: or o all human I, though in of so serious may behest . It will be ne brought to (•bfonnwIitSiS, h which they IX lens being B believed to ixtent, by the )d outer rays, lo that those mated by it. lens are cor- >n of the lens does not increase regularly from the c^i uter to th cirownf '' ence. ArtiffBMtifB. — In this defect the vertical meridian Ih ,>- posed to be more convex than the horizontal, as is partJ iy the case with the cornea of the eye, and it is to this body t^it astigmatism is usually referable, rather than to the lens, though the latter may also be clefective. In astigmatism, when a vertical line is in focus a horizontal can not be distinctly seen, and the reverse. This any one may readily demonstrate to himself by drawing one straight line at right angles to the center of another and looking at the figure ; when the one is seen distinctly, the other is blurred. It is to be borne in mind that, in order to see a horizontal line distinctly, it is of most importance that the rays that diverge from this line, in a series of vertical planes, be well focused, rather than those which diverge in the plane of the line itself ; so that, when the cornea is most curved in the vertical meridian, a horizontal line will be represented by an image of a horizontal line at the nearer focus—i. e., when the vertical is the most con- vex meridian, horizontal lines are soonest focused, and this holds, in fact, of most eyes. When the astigmatism affects several meridians, " irregular astigmatism " results. The defect in question is to be corrected by glasses made of sections of a cylinder, thickest in the region corresponding to that of greatest corneal, etc., dbfect. duromatie Abenratton. — In the figure below, in which 7i A rep- resents the lens, it will be seen that the violet and red rays have different foci, so that, when the eye is accommodated for the one set of rays, the others are seen indistinctly. Assuming Ito. 4l&-I)lNltam to OhMlntochraaMUe aiiamtion (aflMT 1^^ that the retina is at/, the rays will be blended ; but if between Fand/, or/ and U, the blue center will have a red circumfer- ence, and the reverse respectively. As the focal distances for near objects differs so little usual- ly, this defect is not observed by us ; but it may be made ob- 674 ANIMAL PHYSIOLOGY. \ muB by looking at a flame through cobalt-blue glass, which allows only the red and blue rays to pass : the flame may appear red surrounded by blue or blue surrounded by red, according to the character of the accommodation of the eye at the time. Since the eye has to be accommodated for violet (see Fig. 415) more than blue, bodies of equal size, red in color, always appear nearer than violet ones. Hence, also, it is difficult to see the red and violet gf the speqtrum with equal distinctness at the same time. Intoptie ThmooMiia. — Opaque bodies in any of the media of the eye may cast shadows on the retina. When movable, as they often are in the vitreous humor, they are known as mumxB voliiantea, from their fancied resem- blance to gnats. One looking through a microscope is apt at first to see what does not exist, apart from his own eye, owing to various forms of the nature now referred to, but which may be distinguished from real objects by the inability to fix them in the field of vision, for as soon as the attempt is made they vanish. Tears on the cornea and other inequalities from foreign bodies, pressure, etc., likewise give rise to such phenomena. . An interesting little experiment, which illustrates both the alterations in size of one's own pupils with the amount of light, and at the same time irregularities in their margins, if they exist, may be thus carried out : Let a pin-hole be pricked in a card, and, holding this close to the eye, look at a light or a bright surface. On opening and closing the other eye the changes in the size of the pupil of the first eye may be seen to alter with the amount of light admitted to the second — i. e., the field of view is alternately diminished and increased. AnomaliM of Befiractioa. — 1. We may speak of an eye in which the refractive power is such that, under the limitations referred to before (page 564), images are focused on the retina, as the emmetropic eye. The latter is illustrated by Fig. 416. In the upper figure, in which the eye is represented as passive (nega- tively accommodated), parallel rays— i. e., rays froija objects distant more than about seventy yards (according to some writers much less)— are focused on the retina ; but those from objects near at hand, the rays from which are divergent, are focused behind the retina. In the lower figure the lens is rep- resented as more bulging, from accommodation, as such diver- gent rays are properly focused. 2. In the myopic (near-sighted) eye the parallel rays cross •mmm glass, which ) may appear )d, according I at the time, see Fig. 415) [ways appear It to see the itness at the the media of eous humor, ^ncied resem- t to see what arious forms listinguished I the field of lish. 'rom foreign enomeua. . ites both the ount of light, gins, if they pricked in a a light or a (ther eye the may be seen second — i. e., reased. eye in which tions referred retina, as the , 416. In the lassive (nega- from objects ling to some it those from livergent, are le lens is rep- M such diver- lel rays cross VISION. 676 within the vitreous humor, and diffusion-circles being formed on the retina, the image of the object is necessarily blurred, Pio 416.— Diain«in« to illustrate conditions of refraction In normal eye when unaooommo- dated (passive, or negatively accommodated), and when accommodated for "near objects (after Landois). SO that an object must, in the case of such an eye, be brought unusually near, in order to be seen distinctly — i. e. the near Fio. 417. -Anomaliea of reftmotian in a myopic eye (after Landois). point vi abnormally near and the far point also, for parallel rays can not be focused ; so that objects must be near enough for the rays from them that enter the eye to be divergent. The myopic eye is usually a long eye, and, though the mechanism of accommodation may be normal, it is not so usually, the ciliary muscle being frequently defective in some of its fibers, which may be either hypertrophied or atrophied, or with some affected one way and others in the opposite. More- over, there is also generally, in bad cases, " spasm of accommo- dation" (i. e., of the ciliary muscle), with increased ocular tension, etc. The remedies are, rest of the accommodation mechanism and the use of concave glasses. 3. The opposite defect is hypermetropia. The hypermetropic 676 ANIMAL PHYSIOLOGY. eye (Fig. 418), being too short, parallel rays are focused be- hind the retina; hence no distinct image of distant objects can Fia. 4ia-AiMaiallM of nftMttoa In the hypennMropio qw (aftar Uuidato^ be formed, and they can only be seen clearly by the use of con- vex glasses, except by the strongest efforts at accommodation. When the eye is passive, no objects are seen distinctly beyond a certain distance — ^i. e., the near point is abnormally distant (eight to eighty inches). The defect is to be remedied by the use of convex glasses. 4. Presbyopia, resulting from the presbyopic eye of the old, is owing to defective focusing power, partly from diminished elasticity (and hence flattening) of the lens, but chiefly, proba- bly, to weakness of the ciliary muscle, so that the changes required in the shape of the lens, that near objects may be dis- tinctly seen, can not be made. The obvious remedy is to aid the weakened refractive power by convex glasses. It is prac- tically important to bear in mind that, as soon as any of these defects in refractive power (though the same remark applies to all ocular abnormalities) are recognized, the remedy should be at once applied, otherwise complications that may be to a large extent irremediable may ensue. YisnAL Sbnsations. We have thus far considered merely what takes place in the eye itself or the physical causes of vision, without reference to those nervous changes which are essential to the perception of an object It is true that an image of the object is formed on the retina, but it would be a very crude conception of nervous processes, indeed, to assume that anything resembling that image were formed on the cells of the brain, not to speak of the superposition of images inconsistent with that clear mem- ory of objects we retain. Before an object is " seen/' not only focused be- i objects cau Uadols). e use of con- ommodation. ttcfcly beyond nally distant odied by the 'e of the old, a diminished diefly, proba- the changes B may be dis- edy is to aid , It is prac- any of these mark applies >medy should may be to a s place in the ; reference to perception of is formed on »n of nervous ambling that t to speak of it clear mem- en/* not only VISION. 677 must there be a clear image formed on the retina, but impulses generated in that nerve expansion must be conducted to the brain, and rouse in certain cells there peculiar molecular condi- tions, upon which the perception finally depends. For the sake of clearness, we may speak of the changes effected in the retina as sensory impressions or impulses, which, when completed by corresponding changes in the brain, develop into sensations, which are represented psychically by percep- iions; hence, though all these have a natural connection, they may for the moment be considered separately. It is as yet beyond our power to explain how they are related to each other except in the most general way, and the manner in which a mental perception grows out of a physical alteration in the molecules of the brain is at present entirely beyond human comprehension. •■•J ■,^ FW. «•. . Fio. ' Fm: ■ 419.— Verttoal ■Mtfcm of ntiii* (after H. Kflller). 1. lnjrer of rods and oobm ; I, roda ; a, eonw ; 4, 6, e, extoriMl Knnnto Ikrar ; 7, intwiMl grwiule lajrer ; », 10, fliiely mmular grajr kw«r ; 11, lajrar of ncrveHMlls ; It, 14, flMn of f the retina ove requires Is, which, in Actorily: (1) 1 before the nove rapidly idle the sub- moved from id down, the at especially latever plan 9re, in order ixcessive ex- relaxation. 1 LapoliM.— 'pte (rhodop- chemioal ex- 1 animals, as was renewed t ; indeed an be made and leached part limbs of the Lnas of some )urple is also I of man and It is manifest >wn as an ex- ; besides, the I are entirely ion of chem- impulses has such is false, s as yet very 1. and examine VISION. 681 msmiMsiUi into the facts of comparative anatomy and physiology, there are many of a significance that we can not ignore ; the impor- tance of light to most protoplasmic processes, such as the ac- cumulation of pigment in certain regions marking the very beginnings of eyes ; the large amoimt of pigment found in the eyes of most groups of animals and of nearly all mammals sug- gesting that this is a provision for the retention of light, which we can scarcely conceive as acting in other than a chemical manner. At the same time, in keeping with the spirit of this work throughout, we suggest caution in believing that explana- tions based on our limited experience are the only ones possible. ^ It is worth while to bear in mind, however, that currents of rest and currents of action similar to those demonstrated to exist in muscle, glands, nerves, etc., may be shown to exist in the retina. In all the other cases these are in intensity parallel to the degree of functional (and chemical) activity of the part, and it makes the probability of there being a chemistry of the retina as a foundation for the impulses therein generated great- er. The subject is as yet, however, in the region rather of speculation than of ascertained fact. TIm iMVi of Batiaal ttimidation.— It may be noticed that, when a circular saw in a mill is rotated with extreme rapidity, it seems to be at rest. If a stick on fire at one end be rapidly moved about, there seems to be a continuous fiery circle. If a top painted in sections with various colors be spun, the different colors can not be distinguished, but there ia a color resulting from, the bloiding of the sensations from tiiem all, which will be white if the spectral colors be employed. When, on a dark night, a moving animal is illuminated by a flash of lightning, it seemB to be at rest, though the attitude is one we know to be appropriate for it during locomotion. It becomes necessary to explain these and similar phe- nomena. Another observation or two will furnish the data for the solution. If on awakening in the morning, when the eyes have been well rested and the retina is therefore not so readily fatigued, one looks at the window for a few seconds and then closes the eyes, he may xierceive that the picture still remains visible as a ppaitive after-^mcige ; while, if a light be gazed upon at night and the eyes suddenly closed, an after-image of the light may be observed. It thus appears, then, that the impression or sensation out- ^^ipaplUlilBa^Bi. ANIMAIi PHYSIOLOOT. iMts the stimulus in tl^ese cases, and this is the explanation into which all the above-mentioned facts fit. When the fiery point passing before the eyes in the case of the fire-brand stimu- lates the same parts of the retina more frequently than is con- sistent with the time required for the previous impression to fade, there is, of necessity, a continuous sensation, which is in- terpreted by the Qiind as referable to one object. In like man- ner, in the case of a moving object seen by an electric flash, the duration of the latter is so brief that the object illuminated can not make any appreciable change of position while it lasts ; a second flash would show an alteration, another part of the retina being stimulated, or the original impression having faded, etdi In the case of a top or (better seen) color-disk, painted into black and white sectors, it may be observed that with a faint light the different colors cease to appear distinct with a slower rotation than when a bright light is used. The variation is between about ^ and ^ of a second, according to the intensity of the light used. Fusion is also readier with some colors than others. It is a remarkable fact that one can distinguish as readily between the quantity of light emanating from 10 and 11 can- dles as between 100 and 110. Weber's law is a highly general- ized toriu of this statement pnplicable to all the senses. But with vision, as with a11 the senses, a lower and espe- cially an upper limit is soon reached, within which alone we can discriminate. It in not possible to distinguish between the difference in brightness of the central and the circumferential parts of the sun, though it is known that the actual difference is very great, while it is easy enough to recognize a marldd difference in the light of a room when two candles are used in- stead of one. Within certain limits we can appreciate a differ- ence in illuminating power of about j^ of a given total Th« Yiraul Aafl*.— If two points be marked out with ink on a sheet of white paper, so close together that they can be just distinguished as two at the distance of 12 to 20 inches, then on removing them a little farther away they seem to merge into one. The principle involved may be stated thus : When the dis- timce between two points is such that they subtend a less visual angle than 60 seconds, they cease to be distinguished as two. Fig. 426 illustrates the visual angle. It will be noticed that a largierol^t at a greater diistance subtends the same visual angle •■ a mudler one much nearer. The size of the retinal iffia mmm li^&SdCB^SKiM explanation en the fiery )rand stimu- bhan is con- apression to which is in- [n like man- ric flash, the iminated can e it lasts; a of the retina g faded, et(^ painted into with a faint ith a slower variation is the intensity e colors than sh as readily ) and 11 can- i^hly general- tnses. 'BT and espe- ich alone we between the rcumferential iial difference ize a marl.ed s are used in- ciate a diff er- 1 totaL t with ink on )y caxk. be just iches, then on to merg^ into iVhen the dis- i a less visual ished as two. .oticed that a ) same visual at the retinal VISION. 588 image corresponding to 60 seconds is '004 mm. (4 /i), and this is about the diameter of a single rod or cone. It is not, how- ris. 4».-TheTteMlMia:le. TlMobjMit«t^"«iiiWM«iM>lM«ertlMntlwone»til(Le.Ooiite). ever, true that when two cones are stimulated two objects are inferred to exist in every case by the mind ; for the retina varies in different parts very greatly in general sensibility and in sensibility to color. It is noticeable that visual discriminative power can be greatly improved by culture, a remark which applies especially to colors. It seems altogether probable that the change is cen- tral in the nerve-cells of the part or parts of the brain con- cerned, especially of the cortical region, where the cell processes involved in vision are finally completed. 0glor4«aiilifliuk— As this subject is still in a very unsettled condition, it will be well in discussing it to keep the facts of physiology and of physics distinct from each other and from the theories proposed to account for them. It is rare to see in nature the pure colors of the spectrum ; more frequently the reds, blues, etc., we behold are the corre- sponding colors of the spectrum, with the addition of a variable quantity of white light. In the spectrum itself there is an unlimited number of shades, not usually specially noticed, in- termediate between the main colors. Hence we may regard a color as dependent on (1) the wave- length of its constituent rays; (8) on the quantity of the par- ticular light falling on the retina; and (3) on the quantity of white light mixed with this. When no white light at all enters, the color is said to be saturated, such being heavy and eestheti- cally unattractive; when much of such light, bright, etc. A gray results from a certain mixture of white with black ; the browns by fusion of red, yellow, white, and black. But in this and all other instances in which we speak of " fusion," " blend- ing," "mixture," etc., we refer to physiological blending owing to contemporaneous stimulation by light of different wave- lengths. Thus, orange results from the action of the red and fellow rays at the same time, and can not be produced by any 53g3B»!S>83S«SSi! ■■'^f^^^^* 1 — > » , ■»■ ^**^''^-^'^j|ij^^^|^^_J|tj^^ ANIMAL PHYSIOLOGY. mixture of the wave-lengths of red and yellow. Again, certain colors known as complementary by psychic fusion gave rise to white, though no physical mixture of such colored pig- ments will produce white. These are red and blue-green; orange and blue; yellow and indigo-blue; green-yellow and violet. Now, when a child beholds orange, he has not the faintest idea that it is related to red, or that white can be in any way produced from any combination of colors, any more than, when he hears a perfect musical chord, has he any idea of its being produced by the simultaneous production of its component notes. To him both the colors and the chord are independent facts. But by simple experiments their origin may be illus- trated. As regards comple- mentary colors, Lambert's ex- periment may easily be per- formed: Place a red wafer (or a slip of paper) on a sheet of white paper, and about three inches behind it a blue one. Hold a plate of glass be- tween the two and vertically, so that while gazing at the red wafer through it a re- jected image of the blue one will be thrown into the eye in the same direction as that of the red image, the result being a sensation of purple. As before referred to, a rotating disk on which all the colors of the spectrum are represented in equal subdivisions, when the speed is sufficiently great, appears white from the fusion of the sensations. Of course, inste ad o f all the colors, complementary ones suffice. As a matter oflBBt, we may recognize six funda- mental oolowK-white, black, red, yellow, green, and blue— and these may be ^outcome of the physiological mixture of three " standard " sensations. "We now proceed to matters of speculation. At the present day two theories to account for color-vision monopolize atten- tion : 1. The Young-Eelmholtz theory assumes that there are only three primary sensations, or, in other words, that the reti- na is affected only by rays of light corresponding to red, green, and violet (or blue) ; and the manner in which any color is pro- duced (iA the mind) "will app^r from an examination of Fig. 487. Thus, when red is the color seen, though the retinal ;! K / \ \ T" ■ ( f TlMmtea ' - ptateataQiftarBMnMMii). mmimmmmmsmKimm ain, certain 1 gave rise solored pig- blue-green ; yellow and the faintest in any way than, when of its being component ndependent ay be illus- >ds comple- uubert's ex- sily be per- ad wafer (or 1 a sheet of about three % blue one. : glass be- 4 vertically, zing at the ^h it a re- tie blue one i that of the ,11 the colors 08, when the 'usion of the iplementary e six f unda- i blue— and lUte of three ; the present polize atten> at there are hat the reti- red, green, color is pro- ition of Fig. the retinal VISION. 686 stimulation is not confined solely to the rays of the red end of the spectrum,.it is chiefly by these that what we may call psy- chic red is produced — i. e., the mental perception of red is de- pendent on a specific stimulation of the retina by rays of a cer- tain wave-length, though at the same time there is a feebler sensation of green and violet. Orange would in like manner ii^^W^ Fio. 487.— niiMtntM the YouiiK-HelinhoIta- theory of c(rfor-vliioB. The lelton in the lower line indickte oolon of qpeSum in natural order, l.denotca the "red"; 8, "green"; S, "violet" primary-color wneation. The diagram ahowa hy the height of the curve in each instance to what extent the ptlmarr-oolor aenaatlona are reqwcthreljr excited bf vttirationa of diSWent waTe-lengUia (after Benwtein). result from a large admixture of red, considerable of green, and very little of violet. 2. Bering's theory is a chemical one. He assumes the existence of three kinds of visual substances: white-black, yellow-blue, red-green. Either in the retina or elsewhere in the eye it is believed that two processes are in con- stant operation, the opposite of each other, and which corre- spond to the changes assumed to take place in protoplasm generally, and to which we have referred already as ana- bolism and katabolism, or construction (assimilation) and de- struction (dissimilation). When dissimilation is in excess, the lighter colors result — ^white, yellow, red ; and the others when assimilation prevails Orange would be seen whep red and ■ yellow are simultaneously produced — ^i. e., when the red-green and yellow-blue substances both undergo dissimilation to a degree in excess of its opposite phase. One test of these theories would be their application to ex- plain the defect next to be mentioned. Oolor'BUndiMM.— There are all degrees of this defect, from' such as exists in every eye — i. e., inability to perceive color equally well by all parts of the retina, to complete loss of the faculty of discriminating color at all. 1. Complete coior-Jbilindnesa (achromatopsy) is marked by inability to distinguish any colors, the spectrum being brightest 5$6 ANIMAL PHYSIOLOGY. in the middle, but any picture appears as a photograph. It may be unilateral. 2. Yellow-Bit^ Blindneaif.— The spectrum presents only red and green, and hence is usually much shortened. It is occa- sionally unilateral. 3. Red-Qreen Mindnesa (Daltonism).— Yellow and blue may be discriminated, violet and blue seem alike, and red and green practically do not exist. It is to be borne in mind that it is very difficult to ascer- tain the exact condition of color-blind persons, from their in- ability to communicate their state of mind. They often make discriminations apparently based on color distinctions, but, in reality, on the form, texture, position, etc., of objects. It is also all but impossible to be precisely certain as to the extent to which the lower animals can distinguish between colors. To apply the above theories of color-vision to the explana- tion of color-blindness : In the case of red-green blindness, ac- cording to the Young-Helmholtz explanation, there is the ab- sence of one of the primary sensations (red), so that the colors seen are the result of mixtures of the other two primary sensa- tions. What we call yellow must be to the subject of this defect a bright green. According to Hering's theory such persons lack the red-green substance ; hence their color- vision must be limited to mixtures of yellow and blue alone. But, if blindness to red and green can exist separately, as has been as- serted, this theory fails to explain it, though the former would ; while total color-blindness is explicable by Hering's theory, but not by the rival one. It is probable that neither is broad enough to meet the facts, even if correct in principle. They serve the end of being provisional hypotheses till better are found. . Psychological Aspects of Vision. It is impossible to ignore entirely, in treating of the physi- ology of the senses, the mind, or perceiving ego. By virtue of our mental constitution, we refer what we " see " to the external world, though it is plain that all that we ' perceive is made up of certain sensations. We recognize the "visual field" as that part of the outer world within which alone our vision can act at any one time ; and this is, of course, smaller for one than for both eyes. If one takes a large sheet of paper and marks on its center a spot on which one or both eyes are fixed, by moving a point . atss. xiKssaSes^es^^ VISION. 687 >graph. It ts only red It is occa- d blue may i and green t to ascer- n their in- of ten make ons, but, in ects. It is the extent colors, le explana- indness, ac- I is theab- ) the colors nary sensa- ect of this lieory such ;olor-vision ae. But, if Las been as- tner would ; g's theory, ler is broad iple. They better are the physi- r what we all that we { the outer J one time ; eyes. a its center ing a point up or down, to the right or the left, he may ascertain the limits of the visual field for a plane surface. The visual field for both eyes measures about 180° in the horizontal meridian; for one eye about 145° ; and in the vertical meridian 100°. Lapcrfcotioiis of Vinul PuDoepUanii — We may now consider some defects which we know to exist by the use of our reason- ing powers in the mental perception we form of objects in the visual field : 1. Irradiation. — It is easy to notice that a white spot on a dark ground appears larger than a dark spot of equal size on a white ground. This has been spoken of as the result of Fio. «M.— nhMtntw imkUatiim. The iriiito patch in the (bwfc (tround i dark one tai the light grauiid (after Bematetn). I langer than the irradiation— a sort of overflow of sensation, though whether to be referred to the retina or to the brain-areas concerned is uncertain. 2. Contrast. — When a white strip of paper is laid between two black ones, the center of the white strip is not so bright as its edges, from contrast ; and experiments illustrating the same principle may be made with colored paper. This law of con- trast is very wide in its application, and will be referred to later. - , 3. The Mimd-Spot. — It might be supposed at first that one should perceive gaps in the field of vision on account of the blind-spot; biit, when it is remembered that to see black we must have a definito sensation, and that the nrind places objects Ijring on opposite sides of the spot close together, the reason that this defect in structure, if such it really be, is practically inoperative, becomes clearer. It is to be remembered that the image of an object (see Fig. 432) never falls on the blind-spot in both eyes; and, moreover, this area lies outside of that of greatest acuteness {macula Itiiea), on which images are focused. The macula lutea, and especially the fovea centralis, are the ^-■"^iumtmms/tsiiii^iM'^i^ «i»«B3eiiaMw Biit i taiiwafeSSl^P>'*'^7>^^'<*™*>>» point of SntioB (ortte ere : MmiHl mMe (after SMttahTp endLMidolt). T, temponl iide ; M , nMia ride ; w. ImniM while ; ■, for bhw ; B, lorred ; a, for giwn. rmrlkoe ■eniiHliagrain- ~, tMMindMT for VISION. 589 id color; or, \}y an object, NS most read- Bt, when the , as will be ts for vision f light that a this region and having noting when field, within Byond which Miper, by the ield for some fact, as such bange: thus, more or less this is espe- >ectrum> etc., rhite. I the inner Mirteo* re: lemi-diagraiB- ; w. boundaiT for Influence of the Pigment of the Macvla Lutea.— If we inter- pose a solution of chrome alum between the eye and a white cloud while the general field is purplish, a rosy patch appears in a position corresponding to the yellow spot. This is owing to the fact that the solution allows only the red and greenish- blue rays to pass, and, the latter being absorbed by the yellow spot, we see only the former in the part of the field of vision corresponding to this area. The experiment is also an excellent one to mark out the site of the spot. Since the macula lutea is the part of the retina concerned in the usual so-called " di- rect" vision, it will be evident that what would be yellow »but for the influence of the pigment of this spot appears to us white. Afl«r>ImafH *te> — Positive after-images have already been referred to; but an entirely different result, owing to exhaus- tion of the retina, may follow when the eye is turned from the object. If, after gazing some seconds at the sun, one turns away or merely closes the eyes, he may see black sunq: In like man- ner, when one turns to a gray surface after keeping the eyes fixed on a black spot on a white ground, he will see a light spot. Such are termed negative after-images, and these may them- selves be colored, as when one turns from a red to a white sur- face and sees the latter green. They may be explained upon either theory of color-vision. According to the theory of Toung and Helmholtz, in the latter case the green appears be- cause the primary color-sensation for red is exhausted, while the others become more prominent accordingly ; but it is more difficult to explain the black suns, etc., by this theory, though it is, of course, open to suppose that all the primary color-sen- sations have been exhausted. According to Hering's theory, the dark after-images as well as the colored ones are the result of the preponderance of one or the other of the two processes of assimilation and dissimila- tion. But, in truth, the subject is very difficult of complete solution at all by the kind of explanations we are at present employing. It is of some importance to remember that the retina is not equally sensitive to all colors. We see the blues of evening more readily than the reds or yellows, hence the employment of the former extensively by artists in depicting evening scenes. Since there is a maximum point of stimulation for each main color, it is possible to understand how, by increase of the inten- 4\ «i4ra,?!.";iSrSS>W»iSSWSrr«SWI»KE«IS?K3J^^ J 590 ANIMAL PHYSIOLOGY. sity of its light, one color passes into another: e. g., let violet light be gradually increased in intensity, and the retina soon fails to perceive this cqlor so strongly ; but the red and green sensations being as yet submaximal, we perceive a color the result of the blending of these two with violet, and so on till we may get such a mixture of the sensations of violet, red, and green as produces white. Fto. 4S0.— When looked •(with OM eye, the ltaMar«nB««r*OdMiiict at one time; this is in Dwt owinff to aatteiiMtiMii, bat in part sIm to insMlitjr to Mooumottete pert ecUy MMrt from any deteotoTthie kind tormon than* very UmiMd •!«•. When Tiewed with botti eyea, a number of ourioiia phenomena mar be obaerved, the explanation ot whkih we leave the atudent to worit ooft tor himaelf(iiner BefMtrin). lOiooMfftlau M to tlM Oompanti?* Um, et&, of Ol^feeti.— A glance at Figs. 430 and 431 will illustrate some surprising peculiarities. On a clear day distant mountains appear nearer, no. at.— niurtntee tlluaiona aa to iiae. In A the height aeeme at flnt greater than the breadth, though thejr are Mual : the nitr — " ~ Oan eitiier a?«he odban (after BmMtetai). tareadthj^^u{ii;h thejT^ra eouil ; the retene hi B ; whfle appears to cover a leas area VISION. 591 g., let violet retina soon d and green a color the knd so on till )let, red, and from being seen better. The full moon looks larger when near the horizon than when overhead, from the absence of objects in the latter case with which to compare it ; and in like manner distances on the water or on a vast plain seem less than they really are ; and so in innumerable instances the influence of a standard of comparison or its absence is evident. BaljeetiTe Phwuw i en a. — When the eyelids are shut in a dark room, the eye does not seem absolutely devoid of light. Such sensation of luminosity as may be feebly present is sometimes spoken of as the "proper, light of the retina." When the ball of the eye is pressed upon, colored circles of light appear when the eyes are closed, such being plainly due to mechanical stimu- lation of the retina. These are " phosphenes," and are akin to the stare seen when the eye receives a sudden blow, or to the sen- sations excited by electrical stimulation. But, apart from any stimulation of the retina, objects may apparently be seen in ex- cited conditions of the brain, as in insanity, delirium tremens, etc. Sometimes one object, instead of being recognized, seems to arouse the perception of another. The cause is traceable in many cases solely to the brain itself, especially the part of the cerebral cortex concerned in vision, and illustrates the impor- tance of this part of the 6entral visual mechanism, and much more into which we can not enter now. iMtfane; this is in ito peif ««Uy MMUt ■Uon nt which we if 01|)eeti.— A e surprising ppear nearer, t graater than the o cover » Vem are* CO-ORDINATIOM OF THB TwO EY*8 IN VISION. As a matter of fact, we are aware that an object va»Y be seen as one either with a single eye or with both. For bmoctilcvr vis- ion it may be shown that the images formed on the two retinas must fall in- variably on corresponding points. The position of the lat- ter may be gathered from Fig. 432. It will be noticed that the mcUar side of one eye corresponds to the na- sal side of the other, though upper always an- Wn.4m.- . Ml— Dtamm to ffluetrste cerwpo a Mm pointa (after fMfaHr). L, B, left and risht tmt'a^^, are poliita ia 0M«7e oomqioMiiiK to a,, 6^ c., intheothM'. The lower flmnaareiwoJectlonB of a» rattaa of the rliidit (Stand tlie laft(£)ey». It ni«r be ofaaenred Oat ttie malar ride of one retina ootreaponde to the naMi ride of the other. - -'■^^^"""•■n ytam MM 592 ANIMAL PHYSIOLOGY. 'X - swers to upper and lower to lower. This may also be made evident if two saucers (representing the fundus of each eye) be laid over each other and marked off, as in the figure. That such corresponding points do actually exist may be shown by turning one eye so that the image shall not fall, as indicated in the figure. Only now and then, however, is a per- son to be found who can voluntarily accomplish this, but it occurs in all kinds of natural or induced squint, as ia alcohol- ism, owing to partial paralysis of some of the ocular muscles. We are thus naturally led to consider the action of these muscles. Oeolar ]lo?«iiMiiitt. — Upon observing the movements of an individual's eyes, the head being kept stationary, it may be noticed that (1) both eyes may converge ; (9) one diverge and the other turn inwuxl ; (3) both move upward or downward ; fla. AS.— View of Uw two ejet and reUtod parti (after Hdmtaolta). (4) these movements may be accompanied by a certain degree of rotation of the eyeball. The eye can not be rotated around a horizontal axis without combining this movement with others. To accomplish the above movements it is obvious that certain muscles of the six with which the eye is provided must work in harmony, both as to the direction and degree of the movement — ^i. e., the move- ments of the eyes ure affected by very nice muscular co-ordina- tions. VISION. 698 Iso be made each eye) be •e. xist may be 1 not fall, as ver, is a per- this, but it » in alcohol- liar muscles, lese muscles, nents of an ', it may be diverge and downward ; torn. rtain degree axis without omplish the les of the six lony, both as J., the move- %r co-ordina- We may speak of that position of the eye when, with the head vertical in the standing position, the distant horizon is viewed as the primary position and all others as secondary positions. Fig. 434 is meant to illustrate diagrammatical- ly the movements of the eyeball. While the several recti muscles elevate or depress the eye, and turn it inward or outward, and the oblique muscles rotate it, the move- ments ^produced by the su- perior and inferior recti are always corrected by the assistance of the oblique muscles, since the former lend of themselves to turn the eye somewhat inward. In like manner the oblique muscles are corrected by ihe recti. ThefoUowingtab- ular statement will express the conditions of muscular contraction for the various movements of the eye : Tia. 4B4.— Dtagram intended to Ulnatrate actioii of ejctrimlo ocular mueotea (after Fick). The heavy Uoea repreaent the mn«ilea of Uie eyeball, and tha line linea the azato b/ movement Straight move- ments. Oblique move- monts. Eleyfttion Rectus superior and obliquus inferior. Depression Rectus inferior and obliquns superior. Adduction to nasal side. . .Rectus intemus. Adduction to malar side.. .Rectus extemus. ' Elevation witli adduction.. Rectus superior and intemus, with obli- quus inferior. Depression with adduction.Reotus inferior and internus with obliquus superior. Elevation with abduction. . Rectus superior and extemus with obliquus inferior. Depression with abduction.Rectus inferior and extemus, with obliquus superior. What is the nervous mechanism by which these "associ- ated " movements of the eyes are accomplished ? It has been found, experimentally, that when different parts of the corpora quadrigemina are stimulated, certain movements of the eyes 88 ^.^tgy.-- • >i liwjJtiiiaiii.irtiWhiftftiiWW 5M ANIMAL PHYSIOLOGY. s: follow. Thus, stimulation of the right side of the nates leads to movements of both eyes to the left, and the reverse when the opposite side is stimulated ; also, stimulation in the middle line causes convergence and downward move- ment, etc., with the corresponding movements of the iris. Since section of the nates in the middle line leads to movements confined to the eye of the same side, the center would ap- pear to be double. However, it may be that the cells actually concerned do not lie in the corpora quadrigemina, but below, or outside of them. The localization is as yet in- complete, f The Horoptar. — If we hold up one finger before another, in front of both eyes, when the accommodation is made for the one the other will appear double, owing to the images not fall- ing on corresponding parts of the retina ; for, if one eye be closed, one of the images disappears. Another way of putting the matter is, to say that the objects in the field under consideration do not lie in the horopter. The n*. 4B.— Diagi«m to IBaitrate de- on«attoD of flben in tiie op- tie QominlMun of naa (•fttr FUnL) rw. 4M.—TIM honvtor (aflar Le Canto). Wbaa tiw «;«■ an dlnetod to the potot it in the oindo, imagw (Tom any otiier part of It (■• D) CtU on oomaponding polnia of Hw retina. latter is that arrangement of points in space from which rays fall on corresponding (identical) parts of the retina. It must le nates leads reverse when lulated; also, le line causes iward move- orresponding Since section die line leads to the eye of er would ap- yer, it may be Boncemed do uadrigemina, 1 is as yet in- 'e another, in made for the iges not fall- f one eye be at the objects >ropter. The ) sthe point il in tbo iaitm of HW retina. n which rays dna. It must VISION. 696 vary with the position of the eyes, head, etc., and often consti- tutes a very complex geometrical figure when the various points are united. The simpler case is when standing upright we look toward the distant horizon, in which instance the horopter forms a plane drawn beneath us — i. e., is the ground on which we stand. This will appear from Fig. 436. Iitimatimi of the Sin and IMitaiMe of Ol^eoti.— The processes by which we form a judgment of the size and distance of objects are closely related. As we have already shown (page 683), the visual angle varies both with the size and the distance of an object. Knowing that two objects are at the same distance from the eye, we esti- mate that the one is larger than the other when the image one forms on the retina is larger, or when the visual angle it sub- tends is greater than in the other case, and conversely. Thus, knowing that two persons are at the distance of hedf a mile away, if one is judged by us to be smaller than the other, it will be because the retinal image corresponding to the object is smaller, other things being equal. But thd subject is n.ore complex than might be inferred from these statements. We have already pointed out that objects of a certain color seem nearer than others ; also those that are brighter, as in the case of mountains on a clear day. And not only do all the qualities of the image itself enter as data into the construction of the judgment, but numerous muscular sensations. The eyes accommodating and converging for near objects, from the law of association, give rise to the idea of nearness, for habitually such takes place when near objects are viewed, so that the subject becomes very complex. That we judge imperfectly of the position of an object with but one eye is realized on attempt- ing to stick a pin into a certain small spot, thread a needle, cork a small bottle, etc., when one eye is closed. SoUditj. — By the use of one eye alone we can form an idea of the shape of a solid bod;- ; though, in the case of such as are very complex, this process is felt to be both laborious and imperfect. From the limited nature of the visual field for distinct vision, it follows that we can not with one eye see equally dis- tinctly all the parts of a solid that is turned toward us. After a little practice one may learn to define for himself what he actually does see. Such a figure as that following results from the combina- tion, meTUaUy, of two others, which answer to the images fall- ing on the right and on the left eyes respectively. »'aiMlitlllMila 696 ANIMAL PHYSIOLOGY. , In order that such fusion shall take place, the respective images must fall on identical (corresponding) parts of the retina. V V i K — "PY 1 1 A A / m r n hS hSdoeiTOiiSCTSrty over the llguw, the image fomwd to tte right eyewhen^ Btto ctosat fl^wd ra tte righCwd lh«t SeiTwheii U» right eye tojsW to rep- SLnted tSthS fflSrtatlSrmflffi. No MpenxMitioa of theee figures wffl give P, yrt 'Tl wSd*! pwoSJSey «S^combtoed toto PrSeflgure m it wpem to both eye* (•fter As is well known, the pictures used for stereoscopes give different views of the one object, as represented on a flat sur- face. These are thrown upon corresponding points of the retina by the use either of prisms or mirrors, when the idea of solidity- is produced. As to whether movements of the eyes (converg- ence) are necessary for stereoscopic vision is disputed. It has been inferred, from the fact that objects appear solid during an electric flash, the duration of which is far too short to per- mit of movements of the ocular muscles, that such movements are not essential. The truth seems to lie midway ; for while simple figures may not require them, the more complex do, or, at all events, the judgment is very greatly assisted thereby. It is of the utmost importance to bear in mind that all visual judgments are the result of many processes, in which, not the sense of vision alone, but others, are concerned ; and the mutual dependence of one sense on another is great, probably beyond our powers to estimate. Reference has been made to this sub- ject previously. pROTKCTivB Mechanisms of the Eye. The eyelids have been appropriately compared to the shut- ters of a window. They are, however, not impervious to light, as any one may convince himself by noticing that he can locate the position of a bright light with the eyes shut ; also that a sensitive person (child) will turn j y (reflexly) from a light when sleeping if it be suddenly bro ight near the head. The Meibomian glands, a modification of the sebaceous, secrete an oily substance that seems to protect the lids against the lachry- ■■IHP 'r^-Trrr VISION. 597 ihe respective 3 of the retina. « looked at wltli tbo' e right ey« when the eye is cioaed la rep- gures will give P, yet n to both eyes (sner reoscopes give on a flat sar- ts of the retina idea of solidity eyes (converg- iputed. It has ^r solid during •o short to per- ich movement's inray; for while complex do, or, ed thereby. It that all visual which, not the md the mutual robably beyond ode to this sub- red to the shut- rvious to light, Eit he can locate mt ; also that a y) from a light the head. The eous, secrete an inst the lachry- mal fluid, and prevents the latter running over their edges as oil would on the margins of a vessel. The lachrymal gland is not in structure unlike the parotid, the secretion of which its own somewhat resembles. The saltness of the tears, owing to abundance of sodium chloride, is well known to all. The nervous mechanism of se* cretion of tears is usually reflex, the stimulus coming from the action of the air against the eyeball or from partial desiccation owing to evaporation. When the eyeball itself, or the nose, is irritated, the afferent nerves are the branches of the fifth, to which also belong the efferent nerves. The latter include also the cervical sympathetic. But it will, of course, be understood that the afferent impulses r • 'be derived through a large num- ber of nerves, and that i. > acreting cen- ter may be acted upon directly by the cerebrum (emotions). The excess of lach- rymal secretion is carried away by the nasal duct into which the lachrymal canals empty. While it is well known that closure of the lids by the orbicularis muscle favors the removal of the fluid, the method by which the latter is ac- complished is not agreed upon. Some believe that the closure of the lids forces the fluid on through the tubes, when they suck in a fresh quantity ; others that the orbicularis drives the fluid directly through the tubes, kept open by muscu- lar arrangements; and there are several other divergent opinions. The prevention of winking leads to irritation of the eye, which may assume a serious character, so that the obvious use of the secretion of tears is to keep the eye both moist and clean. Special Considerations. - OompantiTS.— It seems to be established that certain animals devoid of. eyes, as certain myriopods, are able to perceive the presence of light, even when the heat-rays are cut off. The most rudimentary beginning of a visual apparatus appears to be a mass of pigment with a nerve attached, as in certain worms ; though it is questionable whether mere collections of pigment without nerves may not in some instances represent still earlier UushirnuU ma, uid i CMIM, opened from ths fRiBt (after Bappeyj, 698 ANIMAL PHTSI0L06T. mdimentB of our eyes. Among invertebrates, eyes may in gen- eral be divided into two classes : 1. The compound or faceted eyes, the structure of which may be gathered from the accom- panying figures. It will be noted that in such the retina is con- vex, and is made up of large compound nerve-rods {retinulce), separated from one another by pigment-sheaths. The picture r Fio. MQ. Fie. 440. no. 48B.— DiMmamMtio mmwntetion of ooinpouiid ejre In an Arthropod (ultet Clwis}. C, oarat»;K,cmUaSaf» S^iP, pigBMnt; R, nerve-rod* of raUna; Fb, layer of flber*; Os, layer of gai^^ion oelli ; ly, retinal libera : Fie, croaring of libera. Sto. 4W.— Three ftMseta with retfatute fironi componnd ejre oC oodtdiafer (after Orenaoher). Pigment haa been dlaMlved away from two of the (koeta. F, corneal facet ; JT.onntalllne •one; i>, pigmeot-aheaUi ; P', chief pigment-oell ; P", pigmeat^sella of aeooad order; R, retlnuUB. formed by snjh eyes must represent a sort of m(»aic, and be I'atucr aedcient in definition and brightness. It will be noticed that in such eyes, both the cornea and crystalline lens of verte- brates are represented in multiple form. This form of eye is found in crustaceans and some insects. 2. The simple eye pre- vails among annelids, insects, arachnids, moUusks, and verte- brates. A more advanced form of such a visual organ is found in the cuttle-fish. It may be seen (Fig. 443) that such an eye corresponds fairly well with the eye of a vertebrate. The eye of the fish is characterized by flatness of the cornea ; ■ M i^ »n « l i iM iii>i "a m i^m t i^ wM n . ii tA m i aitm ' tmit « iosaic, and be ill be noticed lens of verte- trm of eye is nple eye pre- », and yerte- rgan is found t saob an eye fce. }ftlie cornea; 000 ANIMAL PHYSIOLOGY. organ known, is of peculiar shape as a whole, presenting a large posterior surface for retinal expansion ; a very convex cornea, a highly develojied lens, an extremely movable iris; eyelids and a nictitating membrane (third eyelid), which may be made to cover the whole of the exposed part of the eye, and thus shield screen-like from excess of light ; ossifications of the scle- rotic ; a structure which is a peculiar modification of the choroid, of which it is a sort of offshoot and like it very vascular, answering to the falciform process of the eye of the fish and the reptile. Prom its appearance it is termed the pecten. Birds, on account of a highly developed ciliary muscle, possess wonderful powers of accommo- dation, rendered important on account of their rapid mode of progression. They also seem to be able to alter the size of the pupil at will. Brolntimi. — From the above brief ac- count of the eye in different grades of animals, it will appear that its modifi- cations answer to differences in the environment. Adaptation is evident. Darwin believes this to have been effected partly by natural selection — ^i. e., the survival of the animal in which the form of eye appeared best adapted to its needs, and partly by the use or disuse of certain parts. The latter is illustrated— 1. By the blind fishes, insects, etc., of certain caves, as those of Kentucky ; and it is of extreme in- terest to note that various grades of transition toward complete blindness are observable, according to the degree of darkness in which the animal is found living, whether wholly within the cave or where there is still some light. A crab has been found with the eye-stalk still present, but the eye itself atrophied. Again, animals that burrow seem to be in process of losing their eyes, through inflammation from obvious causes ; and some of them, as the moles, have the eye still existing, though well- nigh or wholly covered with skin. Internal parasites are often without eyes. It is not difficult to understand how one bird of prey, with eyes superior to those of its fellows, would gain supremacy, and, in periods of scarcity, survive and leave off- spring when others would perish. ( ¥ia. 448.— Biye of noetunuU bird or prey (after Wiederriwim). Co, come* : L, lens : JM, ret- ina : P. pecten ; No, opUc nerre ; 8e, oMiflcatkm of acle- rptlo coat ; CM, etttary mus- cle. Birda have unuanally keen Tiaion, Rrrat power of accommodation, and eztreme mobiUty of the iris. Eite^«3S^s;SeTSa^»*&^t^*s*J»*«l»«««w^'«*^--- VISION. 601 enting a large onvex cornea, iris; eyelids may be made eye, and thus ns of the scle- is a peculiar d, of which it i like it very the falciform ) fish and the )arance it is 8, on account liary muscle, of accommo- it on account progression, e to alter the bove brief ac- ent grades of it its modifi- snces in the to have been vival of the adapted to its arts. , insects, etc., f extreme in- ard complete f darkness in ly within the 8 been found If atrophied. )ss of losing es ; and some though well- ites are often V one bird of would gain id leave off- It is, of course, impossible to trace each step by which the vertebrate eye has been developed from more rudimentary forms, though the data for such an attempt have greatly accumulated within the last few years ; and it is not to be for- gotten that even t1ie vertebrate eye has many imperfections, so that no doctrine of complete adaptation, according to the argument from design as usually understood, can apply. Certain acquired imperfections of the eye seem to be multi- plying at the present day, such as myopia, weakness of the accommodative mechanism, etc. The excessive use of the eyes, necessitating undue exercise of this apparatus or strain of the accommodation, is the fruitful source of evil. A good light — that is, one both sufficient in quantity and falling in the right direction upon the eyes and the objects to be viewed, together with adequate ventilation of the rooms occupied — is of great importance, though, as in the case of other organs, it is impos- sible to avoid wholly the penalties of over-use of the visual apparatus. It is of great importance to recognize that what we really see depends more upon the brain and the mind than the eye. If any one will observe how frequent are his incipient errors BrattnOime flMdiiOa Cmtre in rtgton tf^~ carp, quaOrigemina -Cortical eentn i-Centre (n optic OuOamm Fia. 444.— Diagram intended to Htaatrate the elaboration of Tinial impulaea, beoinninK In reUna and culmlnaWng in the cerebral cortex. Ooune of impidaea is Indicated brarruwa. Knowledge of auditory centers ia not yet exact enou^ to permit of the conatmction d* a diagram, thouirh doubtleaa eventnaUx the central proceMee will be looaliaed as with vtainn. The latter remark appUea to the other aenaea to nearly the aaiDo extent, poariUy quite aa much. MiiBWWKU^'i+i'J^-WrVtC'J.iJM^n-'-'S >..ip^»'«» I 608 ANIMAL PHYSIOLOGY. of vision speedily corrected, he will realize the truth of the above remark. Precisely the same data furnished by the eye are in one mind worked up in virtue of past experience (educa- tion) into an elaborate conception, while to another they an- swer only to certain vague forms and colors. And herein lies the great superiority of man's vision over that of all other animals. Within the limits of their mental vision do all creatures see. Man has not the keen ocular diisoriminating power of the ha >rk ; he can neither see so far nor so clearly ; nor has he the wide field of vision of the gazelle ; but he has the mental resource which enables him to make more out of the materials with which his eyes furnish him. It is by virtue of his higher cere- bral development that he has added to his natural eyes others in the microscope and telescope, which none of Nature's forms can approach. PathflloflwJ. — ^There may be ulceration of the cornea, inflam- mation of this part, or various other disorders which lead to opacity. The low vitality of this region, probably owing to absence of blood-vessels, is evidenced by the slowness with which small ulcers heal. Opacity of the lens (cataract) when complete causes blindness, which can be only partially reme- died by removal of the former. Inflammations of any part of the eye are serious, from possible adhesions, opacities, etc., fol- lowing. Should such be accompanied by great excess of intra- ocular tension, serious damage to the retina may result. Of course, atrpphy of the optic nerve (due to lesions in the brain, etc.) is irremediable, and involves blindness. Inspection of the internal parts of the eye (fundus oculi) often reveals the first evidence of disease in remote parts, as the kidneys. From what has been said of the movements of the two eyes in harmony, etc., the student might be led to inf^r that disease of one organ, in consequence of an evident close connection of the nervous mechanism of the eyes, would be likely to set up a corresponding condition in the other unless speedily checked. Such is the case, and is at once instructive and of great prac- tical moment. Paralysis of the various ocular muscles leads to squinting, as already noticed. Brief Sjnopiit «f the Phyiiokgy of Yinon.— All the other parts of the eye may be said to exist for the retina, since all are re- lated to the formation of a distinct image on this nervoi s ex- pansion. The principal refractive body is the crystalline lens. VISION. 608 truth of the d by the eye ience (educa- /her they an- d herein lies of all other creatures see. of thoha>rk; i he the wide ntal resource aterials with i higher cere- al eyes others ature's forms ornea, inflam- rhich lead to bly owing to lowness with itaract) when u^ially reme- if any part of ities, etc., fol- ccess of intra- ky result. Of I in the brain, pection of the iveals the first B. f the two eyes tr that disease connection of kely to set up Bdily checked. >f great prac- I to squinting, he other parts nee all are re- is nervoi s ex- ystalline lens. The iris serves to regulate the quantity of light admitted to the eye, and to cut oflf too divergent rays. In order that objects at different distances may be seen distinctly, the lens alters in shape in response to the actions of the ciliary muscle on the suspensory ligament, the anterior surface becoming more con- Accommodation is associated with convergence of the vex. visual axes and contraction of the pupil. The latter has circu- lar and radiating plain muscular fibers (striped in birds, that seem to be able to alter the size of the pupil at will), governed by the third, fifth, and sympathetic nerves. Contraction of the pupil is a reflex act, the nervous center lying in the front part of the floor of the aqueduct of Sylvius, while the action of the other center (near this one) through the sympathetic nerve is tonic. Accommodation through the ciliary musclo is governed by a center situated in the hind ■■- art of the floor r.t the third ven- tricle near the anterior bundl'.s of the third nerve, which latter is the medium of the change. There are certain imperfections common to all human eyes, such uti sph jrical and cbjomatic aberration, a limited degree oi astign?- ism, etr Whtii rays of light are focused anterior to the retina, the < ; e is myopic ; when posterior to it, hyperimetropic. The presbyopic eye is one in which +he mecaanism of ocom- modation is at fault, chiefly the cilie y -ouscle. The i >ait of entrance of the optic nerve (blind-sp t) is insensible to light ; and visual impulses can be shown to originate in the layers of rods and cones, probably through stimulation from chemical changes effected by light acting on the retina. The sensation outlasts the stimulus ; hence positive after-images occur. Nega- tive after-images occur in consequenc <^f excessive stimulation and exhaustion of the retina, or disorder of the chemical pro- cesses that excite visual impulses. When stimuli succeed one another with a certain degree of rapidity, sensation is continu- ous. The eye can distinguish degrees of light within certain limits, varying by about j^ of the total. Objects become fusee ;" are seen as one when the rays from them falling on the retiL- * pproximate too closely on that sur- face. The brain, as well as the eye itself, is concwmed in such discriminations, the former probably more than the latter. The various color sensatlous we have are the result either of definite single sensationp Oi the fusion physiologically of two or more of these, and have no reference to the fusion of pigments ex- ternal to the eye. All human eyes are to some extent color- .-rtisx Ill wiw f^nnni'itmt'ttm 604 ANIMAL PHYSIOLOGY. blind in the sense that it is probable that other animals (ant!9, etc.) can perceive colors not included in our spectrum, and also in the sense that all parts of the retina are not equally sensitive to rays of a certain wave-length ; but some persons are imable to perceive certain colors at all. The mactda lutea, and especially the fovea centralis, are the points of greatest retinal sensitiveness. When the images of objects are thrown on these parts, they are seen with complete distinctness ; and it is to effect this result that the movements of the two eyes in concert take place. An object is seen as one when the position of the eyes (visual axes) is such that the im- ages formed fall on corresponding parts of the retina. Binocu- lar vision is important to supply the sensory data for the idea of solidity. It is important to remember that, before an object is " seen " at all, the sensory impressions furnished by the^ retina and conveyed inward by the optic nerve are elaborated in the brain and brought under the cognizance of the perceiving ego. We recognize many visual illusions and imperfections of vari- ous kinds, the course of which it is difficult to locate in any one j^rt of the visual tract, such as are referred to "^irradia- tion," " contrast," etc. There may also be visual phenomena that are purely subjective, and others that result from sugges- tion rather than any definite sensory basis of retinal images. Hence what one sees depends on his state of mind at the time. This applies to appreciation of size and distance also, though in such cases we have the visual angle, certain muscular move- ments (muscular sense), the strain of accommodation, etc., as guides. l"^ HEABINO. As the end-organ of vision is protected both without and within, so is the still more complicated end-organ of the sense of hearing more perfectly guarded against injury, being in- closed within a membranous as well as bony covering and sur- rounded by fluid, which must shield it from stimulation, except through this medium. Hearing proper, as distinguished from the mere recognition of jars to the tissues, can, in fact, only be attained through the impulses conveyed to the auditory brain-centers, as originated in the end-organ by the vibrations of the fluid with which it is bathed. IPfWt MrinMMNMIMIMMMlf 311 HEARING. 605 nimals (ant*;, um, and also ally sensitive 18 are unable ralis, are the be images of 'ith complete e movements s seen as one that the im- na. Binocu- or the idea of ) an object is by the^ retina >rated in the rceiving ego. tions of vari- ocate in any . to " irradia- L phenomena from sugges- binal images, at the time. ) also, though .scular move- ation, etc., as without and of the sense ry, being in- ring and sur- lation, except e recognition through the as originated bh which it is It will be assumed that the student has made himself famil- iar with the general anatomy of the ear. The essential points in regard to sound are considered in the chapter on "The Voice." It will be remembered that what we term a musical tone, as distinguished from a noise, is characterized by the regularity of vibrations of the air that reach the ear ; and that just as ethereal vibrations of a certain wave-length give rise to the sensation of a particular color, so do aSrial vibrations of a definite wave-length originate a certain tone. In each case must we take into account a physical cause for the physiological effect, and these bear a very exact relationship to one another. As will be seen later, while in all animals that have a well- defined sense of hearing the process is essentially such as we have indicated above, the means leading up to the final stimu- lation of the end-organ are very various. At present we shall consider the acoustic mechanism in mammals, with special ref- erence to man. There are in fact three sets of apparatus : (1) Ito. MB.— SectlOB UvoiighwidNarracsaB (•»•¥- •xtemal Mid mmUUxt BMatUB wtth 0|Miriiig of ; t, 4, S, trnfttj of oondM, . . - _.^ i; D,in«mbraiuttyinpMii; r.antertorpwtariMMi; S, nwileua ;•, ton* hMidte o( mfikw, •tlwdted to internal nir- ^toe of tympMile mambnuie— it 1» MW» i wB»Mw »l ed m itnaffiy iiKlr»wii ; 10, tenaor tym- panl muacle ; 11, tpnpuSoeKfHj: It, lomclilMi tube; IS, mperlor Mmidrcular cmwI : 14, jMMterior aemiolrcular omwI ; IS, «xtwnal MMnieiroulMr cwuu ; IS, cochte* ; 17, Internal auditory meatua; 18, facial nerre; IB, large pfetroaal nerve; W, Tcatnmlar branch of auditory nerve ; «1, codilear branch of Mune. one for collecting the aSrial vibrations ; (3) one for transmit- ting them ; and (3) one for receiving the impression through a fluid medium ; in other words, an external, ndddle, and internal ear. :i 606 ANIMAL PHYSIOLOGY. The external ear in man being practically immovable, owing to the feeble development of its muscles, has, as compared with such animals as the horse or cow, but little use as a collecting organ for the vibrations of the air. The meatus or auditory canal may be regarded both as a conductor of vibrations and as protective to the middle ear, especially the delicate drum- head, since it is provided with hairs externally in particular, and with glands that secrete a bitter substance of an unctuous nature. The KMibnuia Tymptai is concavo^onvex in form, and, hav- ing attached to it the chain of bones shortly to be noticed, is well adapted to take up the vibrations communicated to it from the air ; though it also enters into sympathetic vibration when (•Iter rUnt Mid ~~" ----- meiit of tendon „ _ _ ins with nwDeuB; IS, Mterior pookat ; 18,oliordntynipMUiMr*er^^^^^^^ Md iimM-.o^citiirfflwn of trmpulo mwibrMMri. Mrma riii tram within withattMdi- mallmia ; 7, the bones of the head are the medium, as when a tuning-fork is held between the teeth. Ordinary stretched membranes ^»iL i iW]aw i i^'i JB .Li ii LW]tj>ijTl iii inrr;yW W jW pm w fM i t ii -tn i r ii - I ' W WP — w i wi ' w.wm HEARING. 60T have a fundamental (self-tone, proper tone) tone of their own, to which they respond more re»dily than to others. If such held for the membrana tympani, it is evident that >»in tones would be heard better than others, and that when ihe fundamental one was produced the result might be a sen- sation unpleasant from its intensity. This is partially obviated by the damping effect of the auditory ossicles, which also pre- vent after-vibrations. Soi&e suppose that what we denominate shrill or harsh sounds are, in part at least, owing to the auditory meatus hav- ing a corresponding fundamental note of its own. The Auditory OmIoIin.— Though these small bones are con- nected by perfect joints, permitting a certain amount of play upon one another, experiment has shown that they vibrate in response to the movements of the drum-head en masse j though 447.— SecUon of MidttoiT organ of hone (•ftorOhauraMi). A,mMtiorri t, ▼Mti6itoT7.k,£, outllM of Mmldrcttlv ommW; JT, oocUm; If, i ■eala tjnnpMii. 608 ANIMAL PHYSIOLOGY. the stapes has by no means the range of movement of the han- dle of the malleus ; in other words, there is loss in amplitude, but gain in intensity. A glance at Fig. 448 will show that the end attained by this arrangement of membrane and bony levers, which may be virtually reduced to one (as it is in the frog, etc.), is the transmission of the vibrations to thd membrane of the fenestra ovalis, through the stcpes finally, and so to the fluids within the internal ear. But it might be supposed that, for the rm. 44B.— Diagnmmatic repreMntatton fflualntiiur Auditory proceMM (after BeMinla). A, external ear; iB, mkldle ear ; C, internal ear; ^auricle; >, external andltory meatua ; 8, ^rmpanum; 4, membrana tratiiant; B, Biwtartitan tube; 6, nuMtoid ceUe; 10, foramen rotundum; U, forameo onde ; U, Tcatibule; IS. cochlea; 14, aoala tiympani; 15, aoala veatibuli ; i9, fleniciroQlar iTti**fl*t X. B.— The ear ia w> oompUoalMl an onan that it ia ahnoat imposrible to glTe a diaRram- matlc renreaiitaMon of it at once miple and complete in a angle llgure. A compariaoii of the whole aeriea of ottia ia tbertfore deriiabie. It le ewental to undertand how tlie end-oivaa within the aoala media ia ■rtmwlatert. avoidance of i^ocks and the better adaptation of the apparatrs to its work, some regulative apparatus, in the form of a nerv- ous and muscular mechanism, would have been evolved in the higher groups of animals. Such is found in the teosor tym- pani, lazator tympani, and stapedius muscles, as well as the Eustachian tube. MimdM of the Middle ler. — ^The tensor tympani regulates the degree of tension of the drum-head, and hence its amplitude of vibration, having a damping effect, and thus preventing the ill results of very loud soimds. Ordinarily this is, doubtless, a reflex act, in which the fifth HEARING. 609 t of the lian- 1 amplitude, low that the bony levers, le frog, etc.), >rane of the to the fluids that, for the ifter BeMinki). A, iicUtor]r meatus ; 8, odls ; 10, fanunmi TinpMii ; 15, MMla o glTe • diaRrain- irc. A comMriKMi nderaUnd EowUm he apparatrs m of a nerv- rolved in the tevsor tym- I well as the regulates the amplitude of anting the ill ich the fifth is usually the afferent nerve concerned. It is well-known that, when we are aware that an explosion is about to take place, we are not as much affected by it, which would seem to argue a voluntary power of accommodation ; but of this we must speak with caution. According to some authorities the laxcUor tympani is not a muscle, but a supporting ligament for the malleus. The stape- ditirS, however, has the important function of regulating the movements of the stapes, so that it shall not be too violently driven against the membrane covering the fenestra ovalis. The two muscles, stapedius and tensor, suggest the accom- modative mechanism of the iris. The motor nerve of the sta- pedius is derived from the facial ; of the tensor, from the tri- geminus through the otic ganglion. The luUdliiui Tube.— Manifestly, if the middle ear were closed permanently, its air would gra4ually be absorbed. The drum-head would be thrust in by outward pressure, and become useless for its vibrating function. The Eustachian tube, bj communicating with the throat, keeps the external and internal pressure of the middle ear balanced. Whether this canal is permanently open, or only during swallowing, is as yet unde- termined. One may satisfy himself that the middle ear and pharynx communicate, by closing the nostrils and then distending the upper air-passages by a forced expiratory effort, when a sense of distention within the ears is experienced, owing to the rise of atmospheric pressure in the tjrmpanum. FaUudflfiMd. — Inflammation of the tympanum may i-esult in adhesions of the small bones to other parts or to each other, or to occlusion of the Eustachian tube from excess of secretion, cicatrices, etc., in consequence of which the relations of atmos- pheric pressure become altered, the membrani tympani being indrawn, and the whole series of conditions on which the nor- mal transmission of vibrations de|»8nds disturbed, with the natural result, partial deafness. The hardness of hearing ex- perienced during a severe cold in the head (catarrh, etc.) is owing in great part to the occlusion btth^ Eustachian tube, which may be either partial or complete. By filling one or both of the ears external to the mem- brana tympani with cotton-wool, one may satisfy himself how essential for hearing is the vibratory mechanism, which is, of course, under such circumstances inactive or nearly so; hence the deafness. M),^nn i ipwmni « mmmii'im'm 610 ANIMAL PHYSIOLOGY. When the middle ear is not functionally active, it is still possible, so long as the auditory nerve is normal, to hear vibrations of a body (as a tuning-fork) held against the head ; though, as would be expected, discrimination as to pitch is very imperfect. Auditory impulaea originate ^ ithin the inner ear — that is to say, in the vestibule and possibly the semicircular canals. Fra. MB.— Diainm Intended to OhMtnte Uie pwcww * of beariac (•««■ LandolaV AO, •ztemal aiMUtorjr mwitut ; T, ^napanio membnuie : K, taaUium : a, inciia ; P. mlddte car: o, (eneatra oralis; r, (eneatra rotund*; fi, acala tymnani: vt, aeala TcatlbuU; v, veaUbule : 8, aateale : V, utricle ; H, aemidrottlar caaab ; TB, BuatadUaa tube. Lonff arroir iamnltm line of tnction of tenaor ^mpani ; abort curved one tbat o< Stapedius. but especially in the cochlea. It is to be remembered that the whole of the end-organ concerned in hearing is bathed by endo- lymph; and that the vibrations of the latter are originated by F». 460.— Beetkm tbrouith one o( ttaeooila U ootiUfM^imttarOtumrma). BT, icala Qrmpaai ; SF, soala veaUbuli ; OC, oodilear oanal (aeala metUa): Oo, organ of Oorti ; R, mMnbrane of itiJ>^J„limW«W..^ cal an expla- minute the f CXxtl (kfter Lmi- aerre-flbrlki tennK v rod of OorU: y, ■Beinbrwift renen- re can recog- f the fusion. ■tor. mudi maeni- rre-flber kwlns its : k,iH)dltory Mbr; re in membraimH HEARING. 618 etc., of three different fundamental sensations, or the result of chemical processes few in kind, why should not hearing be explained in an equally simple way ? Such views as those re- a.h. .,- B Fka. 4BB.— Loagltiidtaal mcMcmi of Miipiills, loiiiewliat JlaymwwHe (jMat Rwley). e. end of Mnpidl* JolliitriCHiiiieiraiilMroMMl; «,qmiiliic into utricle ; er, eriito MointioA with hair-oelliL to whieSmajr tw Men paMoft «, Hben of Miditofjr nervs ; et, ooBBecttTe-tiHue support fur Midltaty hiin. ferred to above seem to us utterly at variance with the f imda- mentAl conceptions of biology ; are so purely conceptions that have their birth in physics, that we deem it wiser to rest with* out any attempt at an explanation of the origin of auditory sensations in detail, than to accept such curtificial and inadequate solutions as have been proposed. Sv^dive sensations of hear- ing' are common enough in the insane, and answer to the visions of tne same clam of persons; so that we must recognize the possibility of such sensatiqns arising without the usual external stimulus. mmmir ^ 614 ANIMAL PHYSIOLOGY. Fra. 4B6.-IHMrMn lotMided to flluMnrte nIattTe portHoB o( Tarfaiaa parti of^ tor). ^JTeKtanMlMiilttarjiMttiM; !>. Jf, QmiMiilo iMmbraiw ; IV. tTnpMnm ; Mall, -DUkUewi; Inc. tow ; atp, atopy ; #.?, Uufttf owflto ; r. r./wwrtra rofama* ;.»», «u«tod»»- an tube; Jtf.I^niMnbniioMili^rnatlLaolsroaaof theaamieininlaroaiiaka^ liigwpwaaii t a d ;ato.r.flDtt.aCftarfc.ai«lwolcochla>. i« p f aaaa >« ilaaatra%lit(Macoaa» Ro. «vr.-I1iatognpWo diacram of lalTriitli (after fttnt and BOdlnmr). Vm» ,fl{!*nw : 1. utricle ; llaaooaS?; &!MMndicawH» ooeUea ; 4, oualia reonleiia ; 6. amtafreular mm^ 8, iaeonte: S,4,S,_amp«dtej fc^»J».iiMnlcirwilar canato ; 10. auditoiT^Te (pMtlj^ diu^ammatio)T Ji.li. IsTl*. U^ JUrftuilon at tmnebea of nerre to Teatlbule and r ' ' *3iw:> -■ ' si tstmiiim m | > >illli iM ii i i |M i n> I I I rui ii n r T ii r ii K iii HBARINO. 616 of ••r(«flerHin- tympMnim ; Mall, ■da; Ai,liiiaUMdit- uid ita MBDullab*- ITpfwr tgun : 1, MBlofreular ommIi stavolar canala; 10, IxmiiebM of nerre The structure of the ampull» of the semicircular canals, and other parts of the labyrinth besides those specially con- sidered, with their peculiar hair-cells, suggests an auditory function ; but what that may be is as yet quite undetermined. ' Via. M.— DiitrlfautioBofooddMHriiHTeliiqilnl Umiiiaaf Mitcra^iiteter pwi of ooefalM of right ew (after Smcy). 1, tntak of oodilMU- nerre : S. menibmiaiM aone of wftnA iMnin*; S, termtaMTeKpitaiion of ooohlear nerve ezpowd tliraagliout bj rHBOval of eap^ rior ptete of laaia* •ptraUe ; 4, orUloe of eommnnleation between eonla tympnal ud It has been thought that the parts, other than the cochlea, are concerned with the appreciation of noise, or perhaps the in- tensity of sounds ; but this is a matter of pure speculation. AuDiTOBT Sensations, Pbbceptions, and Judgments. We have thus far been concerned with the conduction of the a§rial vibrations that are the physical cause of hearing; but before we can claim to have " heard " a word in the highest sense, certain prooesaes, some of them physiological and some psychical, take place, as in the case of vision ; hence we may speak of the affection of the ond-organ or of auditory impulses, and of the processes by which these become, by the mediation of the brain, auditory sensations, and when brought under the cognizance of the mind as auditory perceptions and judg- ments. Auditory JnlgiMiita. — Such are much more frequently erro- neous than are our visual judgment.s, whether the direction or the distance of the sound be considered. As in the case of the eye, the muscular sense, from accommodation of the vibratory mechanism, may assist our judgments, being aided by our stored past experiences (memory) according to the law of 616 ANIMAL PHYSIOLOGY. asfiociation. Sounds are, how • j , ai r. i»yb ref erre^l to the world without U8. The animals with ;:> r^Mo -ar' greatly excel man in estimating the direction, it i^t vhe distance, of sounds. There are few physiological experiments rriure amusing than those performed on a person blindfolded, when attempting to determine either the distance or the direction of a sounding tuning-fork, so gross are the errors made. One who mfUces such observations on others may notice that most persons move the ears slightly when attempting to make the necessary discriminations, which of itself tends to show how valuable mobility of these organs must be to those animals that have it highly developed. Sang* of AwSHbuj DisBriifaaMw —If we compare the range of sense-perception of eye and ear, we And that the latter is in this respect far superior to the former. Assuming that the perception of red is owing to the influence of rays of light with four hundred and fifty-six billions of vibrations per second and violet at the opposite end of the spectrum with rays of six hun- dred and sixty-seven billions, it will be seen that the total range does not correspond with even one octave; while the ear can discriminate between tones answering on the one hand to about forty a§rial vibrations per second and on the other to thirty- eight thousand or more, though this latter is greater in the upward direction than most persons can appreciate. Such lim- its answer to at least ten times that for the eye. On the other hand, a sense-impression on the organ of hearing lasts a shorter time by far than in the case of the eye, so that fusion of audi- tory sense^impressions is less readily produced. \ Special Conbidbbations. Oompanttv*. — Among invertebrates steps of progressive de- velopment can be traced. Thus, in certain of the jelly-fishes we find an auditory vesicle (Fig. 459) inclosing fluid provided with one or more otoliths or calcareous nodules and auditory cells with attached cilia, the whole making up an end-organ connected with the auditory nerve. A not very dissimilar arrangement of parts exists in certain moUusks (Fig. 460). The vesicle may lie on a ganglion of the central nervous system. On the other hand, the vesicle may lie open to the exterior, as in decapod crustaceans; and the otoliths be replaced by grains of sand from without. It is difficult to decide what the function of otoliths may be in mammals ; but there seems to be little reason ■ 'juJi jwuWji»MiW i vJ-wiiiM-wiit.tiffi^«>f^ii>ii>si&lll^^:s^-^ 620 ANIMAL PHYSIOLOGY. have the qualifications of ear requisite to make a first-rate elo- cutionist. Following custom, we have spoken as though cer- tain defects and their opposites depended on the ear, but in reality we can not, in the case of man at all events, afi&rm that such is the case; indeed, it seems, on the whole, more likely that they are cerebral or mental. Auditory discriminations seem to be equally if not more susceptible of improvement by culture than visual ones, especially in the case of the young. A "good ear" seems to depend in no small degree on mem- ory of sounds, though the latter may again have its basis in the auditory end-organs or in the cerebral cortex, as concerned in hearing. The necessity for the close connection between the co-ordinations of the laryngeal apparatus in singing and speak- ing and the ear might be inferred from the fact that many ex- cellent musicians are themselves unable to vocalize the music they perfectly appreciate. Synopiii of the Phyiiology of Eouiag.— The ear can appreciate differences in pitch, loudness, and quality of sounds, though whether different parts of the inner ear are concerned in these discriminations is tmknown. Hearing is the result of a series of processes, having their physical counterpart in aerial vibra- tions, which begin in the end-organ in the labyrinth and ter- minate in the cerebral cortex. We recognize conducting ap- paratus which is membranous, bony, and fluid. The auditory nerve conveys the auditory impulses to the brain, though ex- actly what terminal cells are concerned and how in originating them must be regarded as undetermined. The essential part of the organ of hearing is bathed by endolymph, and the princi- pal part (in mammals) is within the cochlear canal. Man's power to locate sounds is very imperfect. The auditory brain center (or centers) has not been definitely located. Compara- tive anatomy and physiology point clearly to a progressive development of the sense of hearing. THE SENSE OF 8MELL. The nose internally may be divided into a respiratory and an olfactory region. The latter, which corresponds, of course, with the distribution of the olfactory nei ve, embraces the upper and part of the middle turbinated bone and the upper part of the septum, all of which differ in microscopic structure from the respiratory region. Among the ordinary cylindrical epi- i WMiw i ;iii f ,«ii,» ■H P) W rr).ii; i , i| j mj.j THE SBNSB- OF SMELL. ^21 first-rate elo- i though cer- e ear, but iu IS, afi&rm that , more likely scriminations jrovement by the young, gree ou mem- s basis in the concerned in between the Qg and speak- hat many ex- ize the music »n appreciate unds, though )med in these lilt of a series I aerial vibra- :inth and ter- mducting ap- The auditory n, though ex- in originating jential part of ad the princi- canal. Man's -uditory brain d. Compara- a progressive )spiratory and ids, of course, aces the upper upper part of tructure from ^lindrical epi- thelium of the olfactory region are found peculiar hair-cells highly suggestive of those of the labyrinth of the ear, and Fio. 468.-Parto concerned to (mwll (•fter HincMrid). 1. ^««Sonrj^U«i and nerree ; «, r IB. wo. i-mi* ™^ ^ ^^^^^^ ^^^^ dtatributed over Ute turbtoaled bones. which are to be regarded as the end-organs of smell. If aro- matic bodies be held before the nose, and respiration suspended, they will not be recognized as such, and it is well known that sniffing greatly assists the sense of smell. Again, if fluids, such as eau de Co- logne, be held in the nose, their aroma is not detected ; and immediately after water has been kept in the nostrils for a few seconds, it may be noticed that smell is greatly blunted. Such is the case also when the mucous membrane is much swollen from a cold. There can be no doubt that the presence of fluid in the above cases is injurious to the delicate hair-cells, and that smell is dependent upon the excitation of those cells by extremely minv/e particles emanating from aro- matic bodies. When ammonia- is held before the nose, a powerful sensation is experi- enced ; but this is not smell proper, but an affection of ordi- nary sensation, Owing to stimulation of the terminals of the 622 ANIMAL PHYSIOLOGY. fifth nerve. It is possible that the auditory nerve may also participate, though certainly not so as to produce a pure sen- sation of smell. Like the other sense-organs, that of smell is readily fa- tigued ; and perhaps the satisfaction from smelling a bouquet of mixed flowers is comparable to viewing the same, one scent after another being perceived, and no one remaining predomi- nant. Our judgment of the position of bodies possessing smell is less perfect even than for those emitting sounds ; but we always project our sensations into the outer world, never referring the object to the nose itself. Subjective sensations of smell are rare in the normal subject, though common enough among the diseased, as is complete or partial loss of smell. It has been found that injury to the fifth nerve interferes with smell, which is probably due to trophic changes in the olfactory region. Oompamtive. — The investigation of the senses in the lower forms of life is extremely difficult, an4 in the lowest presents almost insurmountable obstacles to the physiologist, because their psychic life is so far removed from our own in terms of which we must interpret, if at all. The earliest form of olfactory organ appears to be a depres- sion lined with speqial cells in connection with a nerve, which, indeed, suggests the embryonic beginnings of the olfactory organ in vertebrates, as an involution (pit) on the epithelium of the head region. It would appear that we must believe that in some of the lower forme of invertebrates the senses of smell and taste are blended, or possibly that a perception results which is totally different from anything known to us. The close relation of smell and taste, even in man, will be referred to presently. There are, perhaps, greater individual differences in sensitiveness of the nasal organ among mankind than of any other of the sense-organs. Women usually have a much keener perception of odors than men. The sense of smell in the dog is well known to b: . of extraordinary acuteness ; but there are not only great differences among the various breeds of dogs, but among individuals of the same breeds ; and this sense is being CQnstantly improved by a process of " artificial selection " on the part of m-in, owing to the institution of field trials for setters and pointers, the best dogs for hunting (largely deter- mined by the sense of smell) being us«d to breed from, to tho exclusion of the inferior in great part. ' ar own power to think in teims of smell is very feeble, and in this respecti the ^a6(WisaBS'!^.««w.«3*j«fs?v.. THE SENSE OF TASTE. 628 ye may also B a pure sen- I readily fa- ig a bouquet ae, one scent ng predomi- 3ing smell is at we always referring the of smell are ti among the It has been smell, which ■ region, in the lower rest presents ^st, because I in terms of be a depres- lerve, which, be olfactory pithelium of (lieve that in ises of smell 3tion results to us. The le referred to lifferences in than of any much keener 1 in the dog mt there are leda of dogs, this sense is al selection" Bid trials for argely deter- from, to tho vn power to B respect the dog and kindred animals probably have a world of their own to no small extent. Their memory of smells is also immeasur- ably better than our own. A dog has been known to detect an old hat, the property of his master, that had been given away two years before', as evidenced by his recoveiing it from a remote place. The importance of smell as a guide in the selection of food, in detecting the presence of prey or of enemies, etc., is very obvious. By culture some persons have learned to distinguish individuals by smell alone, like the dog, though to a less degree. THE SENSE OP TASTE. The tongue is provided with peculiar modifications of epi- thelial cells, etc., known as papillee and taste-buds which may be regarded as the end-organs of the glosso-pharyngeal and lingual nerves ; though that these all, especially the taste-buds, are concerned with taste alone, seems more than doubtful. In certain animals with rough tongues, the papilla, certain of them at least, answer to the hairs of a brush for the cleansing and general preservation of the coat of the animal in good con- dition. We may, perhaps, speak of certain fundamental taste- perceptions, such as sweet, bitter, acid, and saline. Certainly the natural power of gustatory discrimination is considerable ; ami, as in the case of tea-tasters, capable of extraordinary culti- vation. All parts of the tongue are not equally sensitive, nor is taste-sensation confined entirely to the tongue. It can be shown that the back edges and tip of the tongue, the soft palate, the anterior pillars of the fauces, and a limited portion of the back part of the hard palate, are concerned in tasting. Making allowances for individual differences, it may be said that the biick of the tf)ngue appreciates best bitter substances, the tip, sweet ones, and tho edgea acids. If any subst^ace with a decided taste be placed upon the tongue when wiped quite dry, it can not be tasted at all, show- ing that solutior. is essential. If a piece of apple, another of potato, and a third of onion, be placed upon the tongue of a person blindfolded, and with the nostrils closed, he will not be able to distinguish them, showing that the senses of smell and of taste are related ; or, perhaps, it may be said that much that we call tasting is in large part smelling. When the electrodes from a battery are ii^^Wf' : -^l^iJfHtHftPill ■Wiiiii'iiM 624 ANIMAL PHYSlOLOOr. . placed on the tongue, a sensation of taste is aroused, described differently by diflEerent persons ; also when the tongue is quick- Fia. «I6.— Pmllbe of tmigue (After Sappejr). 1, dnmmTallate p^rilte ; 8. fungifOm p*|iilla» ; 4, flUform papiUaB ; S, gunds at baae of tongue ; 7, tonalla. ly tapped, she ying that, though taste is usually the result of chemical stimulation, it may be excited by such as are electrical or mechanical. But it is not to be forgotten that we have usually no pure jt\;'.tatory sensations, but that these are necessarily blended with thofc ' of common sensation, temperature, etc., and that our judgments \yaBst, in the nature of the case, be based upon highly complex data, even leaving out of account other senses such as vision. ised, described mg^e is quick- 8, fungiform p*pill«» ; ly the result of as are electrical usually no pure ssarily blended ■jO., and that our 3ed upon highly r senses such as THE SENSE OP TASTE. ^25 The glosso-pharyngeal is the principal nerve for the back of the tongue, and for the tip, the lingual ; or according to some special fibers in this nerve, derived from thp chorda tympani. Vto. 4M. Fro. 407. Flo. 48S.— Ifodtum-riMd oircumTallate pHiUto ilUB (after Sa^pey). 1, fungiform ; S, 8, 4, S, 6, flUform ; 7, hemlqAerical paiiilte. It is worthy of note that temperature has much to do with gustatory sensations, a very low or a very high temperature being fatal to nice discrimihation, and, las would be expected, a 7^a. 468.— Tfl«te-buda, from tongue of rabbit (after Engelmanii). temperature not far removed from " body-hoat " (40' C.) is the most suitable. A certain amount of pressure is favorable to tasting, as any one may easily determine by simply allowing some solution of quinine to rest on the tongue, and comparing the sensation with that resulting when the same is rubbed into the organ ; hence the importance of the movements of the tongue in appreciating the sapid qiiM^ities of food. PttiioUflMil. — Among insane persons both olfactory and 40 ANIMAL PHYSIOLOGY. gustatory subjective sensations are common, and must be re- ferred to the central nervous system. After the injection of some drugs subcutaneously, certain tastes are expeidenced. Persons born deficient in the sense of smell to a marked degree are very frequently also wanting in tasting power. OaiiipanitiT«.-7-Among the lowest forms of life it is extremely diflBcult to determine to what extent taste and smell exist sepa- rately or at all, as we can conceive of them. The differentia- tion between ordinary tactile sensibility and these senses has no doubt been very gradually effected. Observations on our domestic animals show that their power of discrimination by taste as well as by smell is very pronounced, though their likes and dislikes are so different from our own in many instances. At the same time we find that they often coincide, and it is not unlikely that a dog's power of discriminating between a good beefsteak and a poor one is quite equal if not superior to man's, and certainly so if his sense of taste, as in the human subject, is developed in proportion to his smelling power. THE CBREBRO-SPINAL SYSTEM OP NERVES. I. Spinal Nerves. These (thirty-one pairs), which leave the spinal cord through the intervertebral foramina, are mixed nerves — ^i. e., their main trunks consist of motor and sensory fibers. But before they enter the spinal cord they separate into two groups, which are Flo. 4«.— DlMtnin of raoto of nliial nerre OhMtratliig effects of KcUon (utter Daltoa). The u gracttU Fio. 47ft,-Iiit«ided to show Mpedally the arigiB both deop and mperflol*! of cnaM Btrrej (•f ter T^andoia). Roman charactera are need to Indicate the nenrea aa they emerge, ana Arabic flgurea their nuclei or deep origin. The Motor-Oenli or Third- Herre.— With a deep origin in the gray matter of the floor and roof of the aqueduct of Sylvius, and indeed all ," if we are to special sense, ith the senses an worked out investigations, itomy of these hat is known his chapter, so at of the sub- oitf u nt U t mm Mtieum tMIHn \ ttduUaml Cnw lolal of cnuiial nervw • M tbey emerge, and ip origin in the luct of Sylvius, THE CEREBRO-SPINAL SYSTEM OP NERVES. 699 branches of distribution pass to the following muscles : 1. All of the muscles attached to the eyeball, with exception of the external rectus and the superior oblique. 2. The levator pal< pebree. 3. The circular muscle of the iris. 4. The ciliary muscle. Both the latter branches reach the muscles by the ciliary nerves, as they pass from the lenticular (ciliary, ophthal- mic) ganglion. The relation of the third nerve, as seen in the changes of the pupil with the movements of the eyeballs, has already been noticed. Paihological. — It follows that section or lesion of the third nerve must give rise to the following symptoms : 1. Drooping of the upper lid (ptosis). 2. Fixed position of the eye in the outer angle of the orbit (luscitas). 3. Immobility, with dilata- tion of the pupil (mydriasis). 4. Loss of accommodation. The TroehlMT or Fourth V«rv«.— This nerve, arising in the aqueduct of Sylvius, pas^f^s to the superior oblique muscle. Pathological. — Lesi this nerve leads to peculiar chang'es. As there is double visiv..., some alteration must have occurred in the usual position of the globe of the eye, though this is not easily seen on looking at a subject thus affected. The double image appears when the eyes are directed downward, and appears oblique and lower than that seen by the unaffected eye. Tho Abdvetor or fUzth Vorro. — Arising on the floor of the fourth ventricle, it passes to the external rectus of the eyeball, thus with the third and fourth nerve completing the innerva- tion of the external ocular muscles (extrinsic muscles). Pathological. — Lesion of this nerve causes paralysis of the above-mentioned muscle, and consiequently internal squint (strabismus). The Faeial, Portia Dora, or Borenfk Ser?*.— It arises in a gray nucleus in the floor of the fourth ventricle, and has an extensive distribution to the muscles of the face, and may be regarded, in fact, as the nerve of the facial muscles, since it supplies, (1) the muscles of expression, as those of the forehead, eyelids, nose, cheek, mouth, chin, outer ear, etc., and (2) certain muscles ofmasticalion, as the buccinator, posterior belly of the digastric, the stylohyoid, and also (3) to the stapedius, with branches to the soft palate and uvula. Paihdogical.— It follows that paralysis of this nerve must give rise to marked facial distortion, loss of expression, and flattening of the features, as well as possibly some deficiency in hearing, smelling, and swallowing. Mastioftticm is difBcult, •• 680 ANIMAI ?HTSIOLOOT. and the food not readily retained in the mouth. Speech is affected £rom paralysis of the lips, etc. Secretory fibers proceed (1) to the parotid gland by the super- ficial petrosal nerve, thence (2) to the otic ganglion, from which the fibers pass by the auriculo-temporal nerve to the gland. Ouataiory Fibers. — According to some, the chorda tym- pani really supplies the fibers to the lingual nerve that are con- cerned with taste. It will thus be seen that the facial nerve has a great variety of important functioiin, and that paralysis may be more or less serious, according to the number of fibers involved. The Trigtmimub TrifMial, or Fiflh Vervt.— This nerve has very extensive functions. It is the sensory nerve of the face ; but, as will be seen, it is peculiar, being a combination of the motor and sensory, or, in other words, has paths for both afferent and efferent impulses. The motor and less extensive division arises from a nucleus in the floor of the fourth ventricle. I'li" sen- sory, much the larger, seems to have a very wide origin. The nerve-fibers may be traced from the pons Varolii through the medulla oblongata to the lower boundary of the olivary body and to the posterior horn of the spinal cord. This origin sug- gests a resemblance to a spinal nerve, the motor root eorre- spcading to the anterior, and the sensory to a posterior root, the more so as there is a large ganglion connected with the sei fory part of the nerve within the brain-case. Ejf<"nt Fibers. — 1. Motor. — ^To certain muscles (1) of mas- tkisbioit :«n^poral, masseter, pterygoid, mylohyoid, and the fi : urior part of the digastric. 2. Secretory. — To the lachrymal fr'Ajid of the ciphthalmic division of this nerve. 3. Vaso-motor. — Probably to Ahe ocular vessels, those of the mucous mem- brane of the cheek and g^ms, etc. 4. Trophic. — From the re- sults ensuing on section of this nerve, it has been maintained that it contains special trophic fibera We have discussed this subject in an earlier chapter. Afferent Fibers.— 1. Sensory.— To the entire face. To par- ticularize regions : 1. The whole of the skin of the face and that of the anterior surface of the external ear. 2. The external auditory meatus. 3. The mucous lining of the cheeks, the floor of the mouth, and rfhe anterior region of the tongue. 4. The teeth and periosteum idf the jaws. 6. The lining membrane of the entire nasal cavity. <6. The conjunctiva, globe of the eye, and orbit. 7. The dura mater throughout. Many of these afl!eient .flbers.are, of course, intimately oon- i. Speech is by the super- i, from which ;he gland, chorda tym- that are con- great variety ) more or less d. erve has very he face; but, of the motor 1 afferent and iivision arises jle. Tli" Ben- ) origin. The through the olivary body is origin sug- )i' root corre- losterior root, cted with the 9B (1) of mas- toid, and the bhe lachrymal i. Vaso-motor. mucous mem- From the re- m maintained discussed this •ace. To par- the face and . The extermd leeks, the floor ngue. 4. The : membrane of be of the eye, itimately con- i^. ^ iS-l ' ^ ' 'ffi^i f t'-^ »jr? f v ^^?^- .' ^gp r ??'^gy! £i r #^, >. ^ ^v^ 4' K IMAGE EVALUATION TEST TARGET (MT-3) ^ ^ 1.0 I.I 11.25 ^ 122 12.2 ui lU ISi ■it 12,2 ■ 40 |20 ^' MMMi Photographic Sciences Corporation 23 WIST MAIN STRUT WnSTIR,N.V. 14S80 (716)S72-4S03 \ V ^ S> ^ . "^^W^ . ^ ^ v\ iMMHili ^,^j^>afc.aaasifi ms^^^^^Ms^^. ■ CIHM/ICMH Microfiche Series. CIHIVI/ICIVIH Collection de microfiches. jt Canadian Instituta for Historical Microreproductions / Institut Canadian da microraproductions historiquas i*sfiU-':ji*i'^w^iH<*' / THE GEREBRO-SPINAL SYSTEM OF NERVES. 681 cemed with reflexes, as sneezing, winking, etc. Certain secre- tory acts are often excited through this nerve, as lachrymation. Tta. 4n.— Limiti of eatHMOH dirtiflmtton of MMOfy dmtw to tow, hMd, and neck (after BCdard). 1, cutaneoaa dletribotion of (^thalmic divWon of fllltii nerre > S, of aaperior nwKillMrjr dmiim ; S, 8, of inferior mudllMT; 4, of witeriar bmodMa of oervlcal nerree ; 8, S, of poeterior iMHMlMi of oerrioal aerrea. when the nasal mucous membrane is stimulated ; indeed, the paths for afferent impulses giving rise to reflexes, including secretion, are very numerous. Oustatory impulses from the anterior end and lateral edges of the tongue are conveyed by the lingual (gustatory) branch of this nerve. Many are of opinion, however, that the fibers of the chorda tympani, which afterward leave the lingual to imite with the facial nerve, alone convey such impressions. The subject can not be regarded as quite settled. Tactile sensi- biUity in the tongue is very pronounced, as we have all experi- enced when a tooth, etc., has for some reason presented an un- usual surface quality, and beo- — -< — ■' 632 ANIMAL PHYSIOLOGY. oblique muscle (motor root). 2. From the nasal branch of the ophthalmic division of the fifth. .3. From the carotid plexus of the sympathetic. The efferent branches pass to the iris, are derived chiefly from the sympathetic, and cause dilatation of the pupil. There are also vaso-motor fibers to the choroid, iris, and retina. The afferent fibers are sen- sory, passing from the conjunctiva, cor- nea, etc. II. The Nasal or SpTieno - Palaiine Oanglion. — The motor root is derived from the facial through the great su- perficial petrosal nerve ; its sympathetic root from the carotid plexus. Both to- gether constitute the vidian nerve. It would seem that afferent impulses from the nasal chambers pass through this ganglion. The efferent paths are : 1. Motor to the levator palati and asygos uvulfiB. 2. Vaso-motor, derived from the sympathetic. 3. Secretory to the glands of the cheek, etc. III. The Otic Cfanglion. — Its roots are: 1. Motor, from the third division. 2. Sensory, from the inferior division of the fifth. 3. Sympathetic, from the plexus around the meningeal artery. It makes communication with the chorda tsrmpani and seventh, and supplies the parotid gland with some fine filaments. Motor fibers mixed with sensory ones pass to the tensor tympani and tensor palati. IV. The SuhnuixiUary Oanglion. — Its roots are : 1. Branches of the chorda tympani, from which pass (a) secretory fibers to the submaxillary and sublingual glands, (6) vaso-mo- tor (dilator) fibers to the vessels of the same glandd. 2. The sympathetic, derived from the superior cervical ganglion, pass- ing to the submaxillary gland. It is also thought to be the path of vaso-constrictor fibers to the gland. 3. The sensory, from the lingual nerve, supplying the gland substance, its ducts, etc. Pathological. — 1. The motor division of the nerve, when the medium of efferent impulses, owing to central disorder, may Fia. 478. — Unipolar cell from Qaawrton guifrtion (after Schwalbe). Wv, If, nudel of aheath ; T, fiber brandi- inK at a node of Banvier. / THE CEREBRO-SPINAL SYSTEM OF NERVES. 633 'auch of the otid plexus the iris, are lilatation of choroid, iris, )ers are sen- anctiva, cor- no - PcikUine is derived le great su- sympathetic s. Both to- n nerve. It ipulses from ihrough this aths are : 1. i and asygos ved from the ;o the glands 1. — Its roots ird division. )r division of 0, from the al artery. It li the chorda supplies the lue filaments, sensory ones li and tensor Ganglion. — )f the chorda (o) secretory , (6) vaso-mo- mdd. 2. The tnglion, pass- o be the path lensory, from its ducts, etc. ve, when the isorder, may cause trismus (locked-jaw) from tonic tetanic action of the mus- cles of mastication supplied by this nerve. 2. Paralysis of the same muscles may ensue from degeneration of the motor nuclei or pressure on the nerve in its course. 3. Neuralgia of any of the sensory branches may occur from a great variety of causes, and often maps out very exactly the course and distribution of the branches of the nerve. 4. Vaso-motor disturbances are not infrequently associated with neuralgia. Blushing is an evi- dence of the normal action of the vaso-motor fibers of the fifth nerve. 5. A variety of trophic (metabolic) disturbances may arise from disorder of this nerve, its nuclei of origin or its gan- glia, such as grayness and loss of hair (imperfect nutrition), eruptions of the skin along the course of the nerves, etc. Atro- phy of the face, on one or both sides, gradual and progressive, may occur. Such affections, as well as others, point in the most forcible manner to the influence of the nervous system over the metabolism of the body. The OloMOi^haryiigeal or Hinth Vtnre.— This nerve, together with the vagus and spinal accessory, constitutes the eighth pair, or rather trio. Functionally, however, they are quite dis- tinct. The glosso-pharyngeal arises in the floor of the fourth ven- tricle above the nucleus for the vagus. It is a mixed nerve with efferent and afferent fibers : 1. llfferent fibers, furnishing motor fibers to the middle constrictor of the pharynx, stylo- pharyngeus, levator palati, and asygos uvulae. 2. Afferent fibers, which are the paths of sensory impulses from the base of the tongue, the soft palate, the tonsils, the Eustachian tube, «ympanum, and anterior portion of the epiglottis. Stimulation of the regions just mentioned gives rise reflexly to the move- ments of swallowing and to reflex secretion of saliva. This nerve is also the special nerve of taste to the back of the tongue. The PnevnogMtri^ Vaipii, or Tenth Verve.— Most of the func- tions of this nerve have already been considered in previous chapters. In some of the lower vertebrates (sharks) the nerve arises by a series of distinct roots, some of which remain separate throughout. This fact explains its peculiarities, anatomical and functional, in the higher vertebrates. In these there have been concentration and blending, so that what seems to be one nerve is really made up of several distinct bundles of fibers, many of which leave the main trunk later. I iM Wim i i w iM i *wwf^ t» M ii ftf i ii lMi I ■-• ■ (**.'.■-. 6M ANIMAL PHYSIOLOGY. It may be regarded as the most complicated nerve-trunk in "the body, and the distribution of its fibers is of the most exten- sive character. Following our classification of efferent and afferent, we recognize : 1. Efferent fibers, which, are motor to an extensive tract in the respiratory and alimentary regions. Thus the constrictors of the pharynx, certain muscles of the palate, the oesophagus, the stomach, and the intestine, receive an abundant supply from this source. By the laryngeal nerves, probably derived originally from the spinal accessory, the mus- cles of the larynx are innervated. The muscles of the trachea, bronchi, etc., are also supplied by the pneumogastric. It is probable that vaso-motor fibers derived from the sympathetic run in branches of the vagus. The relations of this nerve to the heart and lungs have already been explained. 2. Afferent Fibers. — It may be said that afferent impulses from all the regions to which efferent fibers are supplied pass inward by the vagus. One of the widest tracts in the body for afferent impulses giving rise to reflexes is connected with the nerve-centers by the branches of this nerve, as evidenced by the many well-known phenomena of this character referable to the pharynx, larynx, lungs, stomach, etc., as vomiting, sneez- ing, coughing, etc. This nerve plays some important part in secretion, no doubt, but what that is has not been as yet well established. Pathologtcal. — Section of both vagi, as might be expected, leads to death, which may take place from a combination of pathological changes, the factors in which vary a good deal with the class of animals the subject of experiment. Thus, the heart in some animals (dog) beats with great rapidity and tends to exhaust itself. In birds especially is fatty degenera- tion of heart, stomach, intestines, etc., liable to follow. Paralysis of the muscles of the larsmx renders breathing laborious. From loss of sensibility food accumulates in the pharynx and finds its way into the larynx, favoring, if not actually exciting, inflammation of the air-passages. But it is not to be forgotten that upon the views' we advo- cate as to the constant influence of the nervous system over all parts of the bodily metabolism, it is plain that after section of the trunk of a nerve with fibers of such wide distribution and varied functions the most profound changes in so-called nutriucn must be expected, as well as the more obvious func- tional derangements ; or, to put it otherwise, the results that THE CEREBR0-8PINAL 8YSTEM OP NERVES. 686 erve-trunk in le most exten- efferent and nsive tract in Quscles of the Bstine, receive jrngeal nerves, sory, the mus- f the trachea, gastric. It is > sympathetic this nerve to irent impulses supplied pass I the body for cted with the evidenced by cter referable miting, sneez- >rtant part in m as yet well i be expected, >mbination of r a good deal at. Thus, the rapidity and btty degenera- Uow. ers breathing ulates in the iroring, if not )S. lews' we advo- i system over t after section e distribution « in so-called obvious func- e results that follow are in themselves evidence of the strongest kind for the doctrine of a constant neuro-metabolic influence which we ad- vocate. It will not be forgotten that the depressor nerve, which exerts reflexly so important an influence over blood-pressure, is itself derived from the vagus. The Spinal AooeMory or Sltrenth Htrw.— This nerve arises from the medulla oblongata somewhat far back, and from the spinal cord in the region of the fifth to the seventh vertebra. Leaving the lateral columns, its fibers run upward between the denticulate ligament and the posterior roots of the spinal nerve to enter the cranial cavity, which as they issue from the cra- nium subdivide into two bundles, one of which unites with the vagus, while the other pursues an independent course to reach the stemo-mastoid and trapezius muscles, to which they fur- nish the motor supply ; so that it may be considered function- ally equivalent to the anterior root of a spinal nerve. The portion joining the vagus seems to supply a large part of the motor fibers of that nerve. Pathological.— Tonic contraction of the flexors of the head causes wry-neck, and when they are paralyzed the head is drawn to the sound side. The EypogloMl or Twdfth Verro.— It arises from the lowest part of the calamus scriptorius and perhaps from the olivary body. The manner of its emergence between the anterior pyramid and the olivary body, on a line with the anterior spi- nal roots, suggests that it corresponds to the latter ; the more so as it is motor in function, though also containing some vaso- motor fibers, in all probability destined for the tongue. Such sensory fibers as it may contain are derived from other sources (vagus, trigeminus). It supplies motor fibers to the tongue and the muscles; attached to the hyoid bone. Pteffcotof/tcoi.— Unilateral section of the nerve gives rise to a corresponding lingual paralysis, so that when the tongue is protruded it points to the injured side; when being drawn in, the reverse. Speech, singing, deglutition, and taste may also be abnormal, owing to the subject being unable to make the usual co-ordinated movements of the tongue essential for these acts. 686 ANIMAL PHYSIOLOGY. Relations of the Cerebro-spinal and Sympathetic Systems. No division of the nervous system has been so unsatisfactory, because so out of relation with other parts, as the sympathetic. It was also desirable to attempt to co-ordinate the cerebral and spinal nerves in a better fashion ; and various attempts in that direction have been made. Very recently a plan, by which the whole of the nerves issuing from the brain and cord may be brought into a unity of conception, has been proposed; and, though it would be premature to pronounce definitely as yet upon the scheme, yet it does seem to be worth while to lay it before the student, as at all events better than the isolation implied in the three divisions of the nerves which has been taught hitherto. Fw.474. Flo. 47& Fio. l7S.-aMigUonceU fn>m Rsrmpathetle iiaiiidton of f rogr : gNAtly tnAgnifled, and ihowtiig both •tntlgnt wid uoUed flben (after Quain). Fio. 474.— Multipolar miutllmi oella from a^mpathetic nritem of man, hlghlr magnlfled (after XaK Scbultae). a, oMl freed from capaule ; b, Inokwed within a mioleated caiMole. In both the prooe t a hare been broken away. Instead of the classification of nerves into efferent and afferent, connected with the anterior aud the posterior horns THE CEREBRO-SPINAL SYSTEM OP NERVB& 687 HPATHETIO insatisfactory, Q sympathetic, e cerebral and tempts in that , by which the d cord may be )ropo8ed; and, (finitely as yet while to lay it 1 the isolation hich has been lAgnifled, and ihowtiig liigUjr magnWed (after nuolcated caiwule. In l;o efferent and posterior horns of the gray matter of the spinal cord, another division has been proposed, viz., a division of nerve-fibers and their centers of origin in the gray matter for the supply of the internal and the external parts of the body — i. e., into splanchnic and somatic nerves. The centers of origin of the splanchnic nerves are referred to groups of cells in the gray matter of the cord around the central canal; while the somatic ner\'es spring from the gray cornua and supply the integument and the ordinary muscles of locomotion, etc. The splanchnic nerves supply certain muscles of respiration and deglutition, derived from the embryonic lateral plates of the mesoblast ; the somatic nerves, muscles formed from the muscle-plates of the same region. It is assumed that the segmentation of the vertebrate and invertebrate animal is related ; and that segmentation is pre- served in the cranial region of the vertebrate, as shown by the nerves themselves. The afferent fibers of both splanchnic and somatic nerves pass into the spinal ganglion, situated in the nerve-root, which may be regarded as stationary. It is different with the anterior roots. Some of the fibers are not connected with ganglia at all ; others with ganglia not fixed in position, but occurring at variiible distances from the central nervous system (these being the so-called sympathetic ganglia) : thus, the anterior root-fibers are divisible into two groups, both of which are efferent, viz., ganglionated and non- ganglionated. The ganglionated belong to the splanchnic sys- tem, and have relatively small fibers ; the non-ganglionated in- cludes both somatic and splanchnic nerves, composing the ordinary nerve-fibers of the voluntary striped muscles of respi- ration, deglutition, and locomotion. It would appear that these now isolated ganglia have been themselves derived from a primitive ganglion mass situated on the spinal nerves ; so that the dis+^Jiotion usually made of gan- glionated and non-ganglionated rt-f';. is not fundamental. A spinal nerve is, then, formed v.f — 1. A posterior root, the ganglion of which is stationary in position, and connected with splanchnic and somatic nerves, both of which are afferent. 2. An anterior root, the ganglion of which is vagrant, and con- nected with the efferent small-fibered splanchnic nerves. Among the lower vertebrates both anterior and posterior roots pass into the same stationary ganglion. Such is also the case in the first two cervical nerves of the dog» 688 ANIMAL PHTSIOLOOY. »y Does the above-mentioned plan of distribution, etc., hold for the cranial nerves ? Leaving out the nerves of special sense (olfactory, optic, and auditory), the other cranial nerves may be thus divided : 1. A foremost group of nerves, wholly efferent in man, viz., the third, fourth, motor division of the fifth, the sixth, and seventh. 2. A hindmost group of nerves of mixed character, viz., the ninth, tenth, eleventh, and twelfth. The nerves of the first group, since they have both large- fibered, non-ganglionated motor nerves, and also small-fibered splanchnic efferent nerves, with vagrant ganglia (ganglion oculomotorii, ganglion geniculatum, etc.), resemble a spinal nerve in respect to their anterior roots. They also resemble spinal nerves as to their posterior roots, for at their exit from the brain they pass a ganglion corresponding to the stationary posterior ganglion of the posterior root of a spinal nerve. These being, however, neither in roots nor ganglion functional, are to be regarded as the phylogenetically (ancestrally) degen- erated remnants of what were once functional ganglia and nerve-fibers ; in other words, the afferent roots of these nerves and their ganglia have degenerated. The hindmost group of cranial nerves also answers to the spinal nerves. They arise from nuclei of origin in the medulla and in the cervical region of the spinal cord, directly continu- ous with corresponding groups of nerve-cells in other parts of the spinal cord ; but in these nerves there is a scattering of the components of the corresponding spinal nerves. Certain pecul- iarities of these cranial nerves seem to become clearer if it be assumed that, in the development of the vertebrate, degenera- tion of some region once functional has occurred, in conse- quence of which certain portions of nerves, etc., have disap- peared or become functionless. It is also to be remembered that a double segmentation exists in the body, viz., a somatic, represented by vertebree and their related muscles, and a splanchnic represented by visceral and branchial clefts, and that these two have not followed the same lines of development ; so that in comparing spinal nerves arranged in regard to somatic segments with cranial nerves, the relations of the latter to the somatic muscles of the head miist be considered; in other words, like must be compared with like. L- THE VOICE AND SPEECH. tion, etc., hold [factory, optic, thus divided: t in man, viz., the sixth, and Lxed character, ve both large- small-fibered glia (ganglion imble a spinal f also resemble their exit from > the stationary \ spinal nerve, lion functional, astrally) degen- al ganglia and }f these nerves answers to the . in the medulla irectly continu- 1 other parts of cattering of the Certain pecul- clearer if it be brate, degenera- irred, in conse- )tc., have disap- le segmentation jy vertebrae and ated by visceral lot followed the ag spinal nerves cranial nerves, cles of the head ist be compared THE VOICE AND SPEECH. It is convenient to speak of the singing voice and the speak- ing voice, though there is no fundamental difference in their production. Since musical tones can be produced by instruments greatly resembling those of the human voice, it becomes evident that in explaining the human voice we must take large account of the principles of physics. It is to be remembered that sound is to us an affection of the nervous centers through the ear, as the result of a§rial vibra- tions. We are now to explain how such vibrations are caused by the vocal mechanisms of animals and especially of man. The tones of a piano or violin are demonstrably due to the vibrations of their strings ; of a clarionet to the vibration of its reed. But, however musical tones may be produced, we dis- tinguish in them differences in pitch, quantity, and quality. The pitch is dependent solely upon the number of vibrations within a given time as one second ; the quantity or loudness upon the amplitude of the vibrations, and the quality upon the form of the vibrations. The first two scarcely require any fur- ther notice ; but it is rather important for our purpose to under- stand clearly the nature of quality or timbre, which is a more complex matter. If a note be sounded near an open piano, it may be observed that not only the string capable of giving out the correspond- ing note passes into feeble vibration, but that several others also respond. These latter produce the over-tones or partials which enter into notes and determine the quality by which one instrument or one voice differs from another. In other words, every tone is in reality compound, being composed of a funda- mental tone and overtones. These vary in number and in rela- tive strength with each form of instrument a6d each voice ; and it is now customary to explain the differences in quality of voices solely in this way ; and this is, no doubt, correct in the main ; but when two individuals, using successively the same violin, play a scale nearly equal in loudness and as much alike in all respects as possible, are we to explain our ability to dis- criminate when the one or the other may be playing (out of our sight) solely by the overtones ? To answer this would lead us into very complex considerations, and we only raise the (}40 ANIMAL PHYSIOLOGY. \: question to keep the mind of the stuiient open to new or pos- sible additional factors in the explanation. What are the mechanisms by which voice is produced in man ? Observation proves that the following are essential: 1. A certain amount of tension of the vocal cords (bands). 2. A certain degree of approximation of their edges. 3. An expiratory blast of air. It will be noted that these are all conditions favorable to the vi- bration of the vocal bands. The greater the tension the higher the pitch; and the more occluded the glottic orifice the more effective the expiratory blast of air. The principle on which the vo- cal bands act may be illustrated in the simplest way by a well-known toy, consisting of an elastic bag tied upon a hollow stem of wood, across which rubber bands are stretched, and the vibration of which caused by the air within the distended bag gives rise to the note. The stu- dent who would really understand the mechanism of voice-production in man, should not only acquire a thorough knowledge of the anato- my of the larynx, especially of its muscles and their individual ac- tion, but by means of the laryngo- scope become familiar with the ap- pearances of the glottis and adja- cent parts during pronation. The latter is not difficult, and auto- laryngoscopy or self-examination may be made instructive beyond what can be indicated in any text-book. In order to acquire a knowledge of the human larynx, we recommend the dissection of the larynx of a pig, this being more like the organ of man than is that of the sheep or most other animals. It is especially important to reccgnize the na- ture, extent, and effect on the vocal bands of the movements of Pie. 475.— LonKttudliial aaeUoa of hu- Duui Uujax (after 8«ppej). 1, Ten- triole of Iwryax ; S, mperior vocal oord; S, Inferior vocal cord; 4, aryt- enoid oartilaga ; 5, wnUoD of aryt- enoid muMie ; 6, A, inferior portion of cavity of larvnx ; 7, aaetkm of poaterlor part of cricoid cartUaje ; B, wctioo of witerlor part of aame ; 0, superior border of cricoid car- tilage ; 10, Motion of thjrold car- tUaKe; 11, 11, nperior portion of cavity of larynx ; U, 18, arytenoid gland; 14, lA, epiglotda; 16, 17, adipoee tiame: 18, aection of hyoid bone; 19, 18, 80, trachea. THE VOICE AND SPEECH. 641 to new or pos- is produced in ire essential: 1. i (bands). 2. A )proximation of jxpiratory blast I that these are irable to the vi- 5al bands. The 1 the higher the re occluded the more effective it of air. >n which the vo- be illustrated in by a well-known a elastic bag tied a of wood, across ds are stretched, of which caused a the distended lenote. Thestu- eally understand voice-production )t only acquire a Ige of the anato- , especially of its ir individual ac- 8 of the laryngo- iliar with the ap- glottis and adja- pl^onation. The Bcult, and auto- self-examination J indicated in any iiuman larynx, we a pig, this being the sheep or most reccgnize the na- the movements of no. m. ^^- *"• tf&top^aSJneSTo'f ^riSvlK^^ muMle ; 4. facet of the artlcuUtlon of small - - - -- -'"- -rlcoW < cornu of thyroid cartilage with cri most marked around a ver- the arytenoid cartilages. These are tical axis, giving rise to an inward and outward movement of rota- tion, but there are also movements of less extent in all directions. It is in fact through the movements of these cartilages to which the vocal bands are attached posteri- orly, that most of the important changes in the tension, approxi- mation, etc., of the latter are pro- duced. The lungs are to be regarded as the bellows furnishing the neces- sary wind-power to set the vocal bauds vibrating, while the larynx has respiratory as well as vocal functions, as has been already learned. Assuming that the stu- dent has a good knowledge of the 41 lC-o^ ^»^ Fio. 478.— Larynx, Tiewed from above, o?Sir«aiaiiiiction (after Huxley^ Th, ithyroid cartilage : Cr, cricoid cartilARe ; V, edges of vocal llgar mentcibouDdlDg gloMa; Ary, a^te- noid cartilages ; Tfc.^. tt>y«-«3««: nold mimcfe: C.a.l. lateral crico- arytenoid muscle ; C.a.p, posterior crfco-arytenold muscle ; Ar.p, po( terior arytenoid muscles. poe- 642 ANIMAL PHYSIOLOGY. general anatomy of the larynx, we call attention briefly to the following : Widening of the glottis is effected by the crico - arytenoi- JcMS posticus pull- ing outward the pro- cessus vocalis or at- tachment posterior- ly of the vocal band, and a similar effect is produced by the ■s arytenoideus posti- S cus acting alone. Narrowing of the sfe« glottis is accom- B 11 plished by the crico- |«| arytenoideiks later- iM alis, and the follow- ing when acting either singly (except the arytenoideus posticus), or in con- ceri;, as the sphinc- gSg ter of the larynx, ||L viz., the thyro-aryt- «5|| enoidem extemus, ||l thyro • arytenoideus ' -' irUemv^, thyro-ary- epiglotticus, aryte- noideus posticus. Tension of the vo- ^e$ col bands is brought al-S about by the sphinc- ^ ^ ter group, and espe- cially by the exter- nal and internal thy- _ ro - arytenoid mus- f^ cles. ^|g^ Htrre Supplj.— a as The superior laryn- mVHapilHCM THE VOICE AND SPEECH. 643 al anatomy of irynx, we call bion briefly to >llowing : ^idening of the is eflfected by yrico - arytenoi- posticu3 pull- utward the pro- s vocalis or at- nent posterior- the vocal band, a similar effect •oduced by the inoideus posti- icting alone. harrowing of the is is accom- led by the crico- enoideus later- and the follow- when acting er singly (except aryteiioideus iicus), or in con- ;, as the sphinc- of the larynx, , the thyro-aryt- ideus extemus, ro • arytenoideus imua, thyro-ary- glotticua, aryte- deus posticus. Tension of the vo- bands is brought mt.by thesphinc- group, and espe- lly by the exter- and internal thy- • arytenoid mus- 3. Htnre Supply.— e superior laryn- geal contains the motor fibers for the crico-thyroid (possibly also the arytenoideus posticus) and also supplies the mucous membrane. The inferior laryngeal supplies all the other mus- cles. While both of these nerves are derived from the vagus, their fibers really belong to the spinal accessory. It is worthy of note that the entire group of muscles making up the sphinc- ter of the larynx is contracted when the inferior laryngeal is stimulated. Above the true vocal bands lie the so-called false vocal bands (cords) which take no essential part in voice-production. Between these two pairs of bands are the ventricles of Morgagni, which, as well as the adjacent parts, secrete mucus and allow of the movements of both sets of bands and in so far only as- sist in phonation. What is tho nature of the nervous connections by which the muscular movements necessary for voice-production is ac- complished. They are certainly more complex in nature, at least in all their highest manifestations, than might at first appear. Volition is unquestionably the starting-point, but the result is modified by a great variety of afferent impulses, including those from the larynx and 'supra-laryngeal cavities, the thorax, lungs, even the ear, and possibly the eye. Muscular co-ordina- tions of the most delicate kind must be effected, seeing the fine shades in pitch and quality which a first-rate singer can pro- duce. To watch, with the laryngoscope, these changes in the vocal bands alone, gives one an idea of the complexity and perfection of such adjustments which no verbal description can convey. It is impossible for a deaf man, or one defective in sensibility in the regions concerned in phonation, to produce good musical tones. No doubt one bom blind, and without those stored experiences derived from countless pictures, can but very im- perfectly make adaptations in singing dependent on such ex- perience ; and one has only . to hear deaf-mutes, who have learned to speak from imitation of the speech-movements of normal persons, to become convinced of how important a part the ear plays in vocalization. The efforts of such persons near- ly always seem to be out of harmony with the surroundings. There are many subjects connected with the production of the singing-voice especially which have been matters of ani- matied controversy, chiefly because investigators have restricted their observations to on unduly limited range of facts. 644 ANIMAL PHYSIOLOOT. The whole of the supra-laryngeal cavities, the trachea and bronchial tubes, may be regarded as resonant;e-chambers, the former of which are of the most importance, so far as the quality of the voice is concerned. There seems to be little doubt that they have much to do with determining the differ- ences by which one individual's voice at the same pitch differs from another ; nor is the view that they may have a slight in- fluence on the pitch of the voice, or even its intensity, to be ignored. The epiglottis, in so far as it has any effect, in all probability modifies the voice in the direction of quality. The range of any one voice in pitch is, of course, much less than what may be termed the human vocal limit — i. e., the range of the deepest, the intermediate, and the highest voices combined. The following graphic representation will serve a good pur- pose. It will be observed that the extreme limits are tones of about eighty and one thousand vibrations per second, respect- ively. I Soprano. 1024 m CkmtraTto. 684 I EFOAS cdefgab cK d' e' r g' a' b' ^ ^ rr o" d" e" I" g" a" b" o'" 80 BaaB. 842 VSd tenog. 51S Fla. 4S.— Thlg flgure lUuatimtea Um range of the different kinds of voices, and the number of ▼ibrationa aaswwinK to the oompaas of each. llieUiiiitahereUMUoatedare.otoouiae.iiot absolute. TIm Begiittn and fhe lUwtto-YoiM.— Among points most dis- puted even yet are the registers and the falsetto-voice. The subject of registers turns upon the answer to the question. What is the natural method of producing tones ? All admit that they may be sung with different vocal mechanisms, so to speak — i. e.. that different persons, as a matter of fact, do not co-ordinate the various parts of the larynx in quite the same way. In attempting to settle a question of this character a good deal of difference in individuality must be allowed for ; and, given equally effective results, viewed artistically, that THE VOICE AND SPEECH. 645 le trachea and •chambers, the so far as the as to be little ing the diflfer- le pitch differs ve a slight in- tttensity, to be all probability arse, much less limit — i. e., the highest voices rve a good pur- its are tones of second, respect- ao. 1024 684 n " e" £" g" a" b" c" loM, and the number of oMed M«, of coime, not points most dis- etto-voice. The bo the question, les ? All admit jchanisms, so to • of fact, do not I qxiite the same this character a ; be allowed for ; artistically, that may be considered as the natural method of singing a certain range of notes which leads to the least expenditure of energy ; and certain rules may be laid down for the average man, with, however, a good deal of latitude for special cases, as we have said. But certainly any method that disorders the larynx or mTuif^ of f e^ ditting production of head-tonem aa seen V tbe author, the general health can not be correct. Hence clinical and pathological observations become of great importance. One of the commonest faults consists in persons, whose laryngeal mechanism does not permit of the necessary changes within the power of those specially endowed, using a method of voice- production for higher tones, which is really, in their case at least, adapted only to lower ones, hence straining, congestions, fatigue, catarrh, and a host of attendant evils. It does not come within our province to treat of the artistic side of the question ; but we may point out that nearly all the compositions of the greatest masters of music are written with- in a comparatively small range of notes ; and when it is remem- bered that these are such as are most heard in the intercourse of daily life by the speaking-voice, or at least do not depart widely from them, we may understand how it is that such music has ever stirred, and does still appeal to, the heart (and ear) of man so generally, alike in the cultivated and unculti- vated. . Attempts have been made to explain the falsetto-votce by the action of the vocal bands alone ; but any one who will com- pare his sensations, his consciousness of altered muscular ar- rangement, and consequent changed relative position of parts in the supra-laryngeal cavities, even without the use of a laryngoscope at all, can not fail to perceive that the vocal 646 ANIMAL PHYSIOLOGY. I bands are not alone to be taken into account. But there can be no question of a very great difference in the behavior of the Fio.484. Flo. 485. Flo «4.-LaiTniH)«»plc view of the Riotti* durlnflr emtorion^ hlfdh-pitcbpd note* (I« Bon). 1 T bwe S touKue ; 8, 4. eplglotlfi : N 8, ph«ryiut ; 7, arytenoid car«U««» ; 8, opening cun^wm^rtili«e ; 1«, "uperior vooiU cordu; 18, inferior tociU corda (tenda). Fio. 4n!-OtotS^irSMn Cj lMyngo«»pe during production of cheat-Toloe (after MMidl and Gratmer). vocal bands in the production of the falsetto as compared with the chest voice. As has been suggested, in the higher tones of the falsetto, the vocal bands are shortened and come together posteriorly, at all events ; and this may be produced largely by the action of the thyro-arytenoideus intemus, and possibly several other mus- cles. There is little doubt that the whole breadth of the bands does not share in the vibrations. In many of its features, the high falsetto of the male voice is allied in production to the head- voice of females, in which only the central parts of the bands seem, in the highest notes, to be involved. In nearly all previous considerations of this topic, it seems to us that insufficient attention has been paid to the method of applying the blast of air by the lungs. The great importance of this in playing wind-instruments is practically recognized, yet in our own wind-instrument, the most perfect of all, it has received too little practical, and still less theoretical, attention. FttiholiogiflaL— The results of the paralysis of the several muscles of the larynx, of the soft palate, etc., throw a certain amount of light upon this subject; it is not to be forgotten, however, that in this instance, as in others, the usual (normal) mechanism may be obscured through adaptations by unusual methods, so that the best is made of a bad case : 1. When the widening of the glottis can not take place, and the glottic opening assumes the cadaveric position, owing to pa- ralysis of the crico-arytenoidei postici, there may be dyspnoea. 8. Paralysis of the arytenoideiM iransversua, in consequence of THB VOICB AND SPEECH. 647 But there can ahavior of the .48S. ttohrdnotMdieBoii). «rtiU«w ; 8, opening tage of Santorinl ; 11, d«n8 by unusual bake place, and n, owing to pa- iy be dyspnoea, consequence of which the glottic opening can not be sufficiently narrowed, allows of undue escape of air, and gives rise to feebleness and harshness of the voice. 3. There may be almost complete loss of voice from paralysis of both thyro-arytenoid muscles. 4. When the crico-thyroid muscles are paralyzed, owing to im- perfect tension of the vocal bands, the voice may become lower pitched and harsh. Any form of paralysis of the vocal bands should arrest attention and lead to a careful examination of the chest for aneurism, etc., and to general inqn iry, for even the brain may be involved. The importance of the muscles, by which the larynx is raised and steadied, must not be overlooked. In professional singers from constant practice they often become greatly enlarged. We may here remark upon the value of singing when not pushed to the verge of fatigue, when free from straining, and in a pure atmosphere, as a healthful exercise, the whole of '^hich does not consist in the good arising from the use of the chest, larynx, etc., or the additional amount of oxygen respired, but fJso from complicated and ill-understood nervous effects. At puberty, in both sexes, the larynx shares in those changes of relative and absolute size which the body then experiences so generally. The thickening from excess of blood and nerv- ous energy produces, especially in youths, a harsh voice, which is, in this instance, as in all others, an indication of the need of rest of the parts. To sing under such circumstances is, of course, liable to induce permanent injury in the form of weak- ness or harshness of voice ; but once this period is passed, regu- lar vocal gymnastics may be of great service in perfecting an organ unrivaled as a musical instrument, and by means of which man is raised through the endowment of speech vastly above all other animals. The subject of voice production and voice preservation is one of the utmost importance in education, though it receives comparatively little attention. The public taste for high- pitched vocalization does unquestionably tend to ruin voices, and is alike opposed to artistic and physiological principles. While a few may reach the prescribed standard of the public taste, the many fail in the attempt. OompantiTe. — Much more is ^own of the sounds emanating from the lower animals than of the mechanisms by which they are produced. This applies, of course, especially to such sounds as are not produced by external parts of the body, it being very difficult to investigate these experimentally or to observe 648 ANIMAL PHYSIOLOGY. the animal closely enough when producing the various vocal effects naturally. All of our domestic mammals have vocal bands and a larynx, not as widely different from that of man as might be supposed from the feeble range of their vocal powers. The actual behavior of the vocal bands has been studied experimentally in the dog when growling, barking, etc. And, so far as it goes, this mechanism of voice production is not essentially different from that of man. Growling is the result of the functional activity of the vocal mechanism, not unlike that of man when singing a bass note ; barking, of that analo- gous to coughing or laughing, when the vocal bands are rapidly approximated and separated. The grunting of hogs and the lowing and bawling of horned cattle is probably very similar in production, so far as the larynx is concerned, to the above. The cat has plainly very great command over the larynx, and can produce a wide range of tones. The quality of the voice of most animals appears harsh to our ears, owing probably to a great preponderance of over-tones, in consequence of an imperfect and unequal tension of the vocal bands ; but the influence of the su- pra-laryngeal cavities, often very large, must also be taken into ac- count. ' In certain of the primates, and especially in the howling monkeys, large cheek-pouches can be inflated with air from the larynx, and so add to the intensity of the note produced by the vocal bands that their voice may be heard for miles. Song-birds Fio. 488.-Lower tarynx (Syrinx) of produce their notes, as may be seen, S?m^dde'fT°Sfltm*1S by external movements low down at £r^yeUu"rtU?*SS?Sr! the bifurcation of the trachea (sy- K^SiuT?!^^" mSS; rinx). The notes are owing to the SSSrSdJ fSSS^JSTh ?^ vibration of two folds of the mucous ^eteatBie angle of biturcalion membrane, which project into each bronchus, and are regulated in their movements by muscles, the bronchial rings in this region being correspondingly modified. A large number of species of fishes produce sounds and in a variety of ways, in which the air-bladder, stomach, intestines. THE VOICE AND SPEECH. 649 various vocal 9 and a larynx, it be supposed I been studied ng, etc. And, luction is not g is the result }m,not unlike of that analo- ids are rapidly ling of horned so far as the s plainly very 9 a wide range )ears harsh to ) of over-tones, on of the vocal Qce of the su- i, often very laken into ac- priraates, and ling monkeys, an be inflated nx, and so add note produced lat their voice 8. Song-birds s may be seen, « low down at e trachea (sy- owing to the of the mucous ject into each ilated in their B region being sounds and in aoh, intestines. etc., take part. Most reptUes are voiceless, in the proper sense, though there are few that can not produce a sort of hissing sound, caused by the forcible emission of air through the upper respiratory passages. Frogs, as is well known, produce sounds of great variety in pitch, quality, and intensity, some species croaking so as to be heard at the distance of at least a mile. It is a matter of easy ob- servation that when frogs croak the capacity of the mouth cavity is greatly increased, owing to dis- tention of resonating sacs situated at each angle of the jaws. When tree-frogs croak, their throats are greatly distended, apparently in successive waves. But it is among insects that the greatest variety of methods of producing sounds is found. In bees and flies sounds are caused by the vibration of mus- cular reeds placed in the stigmata or openings of their tracheal tubes, also by the extremely rapid vibra- tion of their wings. The death- head moth is said to force air from its sucking stomach, and thus give rise to a sound in the same way as certain fishes. In the grasshopper a noise is produced by rubbing its rough legs against the wing-cases, and in allied forms (locusts) by moving the wing-cases against one another ; and in other groups different parts of the body are brought into mutual contact or rubbed or struck against foreign bodies. Speech. It may be noticed that the differences of voices, by which we are enabled to discriminate between individuals, are much more marked during speaking than singing. This is owing to greater prominence of over-tones in the speaking voice, as may be readUy shown. Fia. 48T.— Portton of trachea or air-tube of a caterpillar (after Oesenbaur), a. epitlieUal-llke cellular layer; 6, nuclei. The air-tubes in insects are kept up by colled chitinous tubes, as seen above ; ard, like the blood- vessels of mammals, penetrate every part of the body. ■:J-- 650 ANIMAL PHYSIOLOGY. If a series of tuning-forks be held before the open moiiih, it will be found that but one position of the buccal cavity and its contents answers to a certain note, but that when this is assumed it acts as a resonance-chamber; thus, for a tuning- fork sounding A, when the cavity takes the shape necessary to sound (speak) that note, the tone produced by the fork is greatly augmented when the latter is held before the mouth. It has thus been estimated that the fundamental tones of the vowel cavity are these : U = b, O = b', A = b'", I = b"". If the vowels of this series be whispered, their pitch rises. Whisper- ing may be termed speech without voice — L e., the vocal bands do not vibrate, but the total effect is produced by the blast (rf air acting through the supra-laryngeal parts as a resonance cavity. Now, if it be true that there is but one position of the supra- laryngeal cavities that will give a pure vowel-sound, and this sound corresponds in pitch to a certain note of the scale, it seems to us that the conclusion that the pitch of the voice, as well as its quality, is dependent to some extent upon these parts as well as the vocal bands. Such a view is, however, not that generally taught. Every singer knows that it is impossible to produce certain vowel-sounds pure with notes of a certain pitch. Usually, when the nasal cavity is shut off posteriorly by the soft palate, or stopped anteriorly by closing the nostrils, a change in quality of the vowel-sounds, characterized as nasal, is produced ; but, as illustrating well that the organism has more ways than one of accomplishing the larger part if not all its ends, by effort, and especially by practice, the vowels may be sounded nearly as well as usual under these unfavorable conditions. Con«nuuit& — The sounds produced by the vocal bands may be modified by interruption in their formation or otherwise, though it is plain, from what has been said, that the form of tha mouth, etc., can not be ignored in any form of vocalization. According to the parts of the supra-laryngeal cavities con- cerned in the modification referred to, may we have the basis of a physiological classification of the consonants, though it is obvious that they may be dealt with on wholly different prin- ciples. By the first method, which alone chiefly concerns us, we have a division into lahitda, denUUa, and guUtinUs, according as the lips, teeth, or soft palate and pharynx are chiefly con- cerned. Of course, several parts are involved in all sound-pro- duction, and we recommend the student to resort to the forma- THE VOICE AXD SPEECH. 601 e openmoaih, ;cal cavity and t when this is for a ttming- lape necessary by the fork is >re the mouth. b1 tones of the = b"". If the ses. Whisper- le vocal bands by the blast ot as a resonance n of the snpra- ound, and this 3f the scale, it >f the voice, as pon these parte ^ever, not that s impossible to a certain pitch, iteriorly by the the nostrils, a irized as nasal, > organism has ■ part if not all he vowels may se unfavorable >cal bands may 1 or otherwise, at the form of of vocalization, al cavities con- have the basis its, though it is different prin- ly concerns us, inds, according are chiefly con- i all sound-pro- rt to the forma- tion of the vowels and consonants before a mirror, in order to acquire a practical knowledge of the relative share taken by the different parts of the supra-laryngeal vocal organs. Ordi- narily the tongue does, of course, function as the most impor- tant organ of speech ; but the extent to which this organ, the front teeth, the lips, etc., can by practice be dispensed with is surprising in the extreme. Persons with more than half of the tongue removed manage to speak quite intelligibly. Consonants may be further classified- according to the nature of the movements associated with their formation : thus, they may be either contimurus or explosive, the meaning of which will be clear from the classification given below, and the basis of the latter from an inspection of the parts by a mirror dur- ing their formation, supplemented by consultation of our sen- sations at the time. The following tabulation may be of service, as representing at least certain aspects of the subject : Explosives : Labials, P, B. Denials, T, D. OvMurals, K, G. Aspirates: Labials,F,Y. Dentals, L, S, Sh, Th, Z. Qutturdls, Ch (as in loch), Gh (as in laugh). Besonants: Lai)ials,M.. . Dentals, TS. OvUurals, N, G. Vibratory: Labial. Dental, B (common). Chittural, B (guttural). It is remarkable that certain consonantal (and vowel) sounds are wholly absent from some languages. All are familiar with the difficulty Europeans find in sounding the English th, as in thin. Their vocal organs fail to make the necessary co-ordina- tions, these not having been practised in youth. PathologiMa.— Paralysis of the soft palate, giving rise to a nasal quality of voice, illustrates the importance of this little muscular curtain. Stammering is believed to be caused by long-continued spasm of the diaphragm— ^iu other words, upon tonic contrac- tion of this muscle in the inspiratory position, usually depend- ent on some form of psychic excitement. Stuttering, on the other hand, is temporary inability to form the sounds desired ; lack of co-ordination of parts principally. The various paraly- ....„j-,- 652 ANIMAL PHYSIOLOGY. sea of the vocal bands affect speech as well as voice, though to a less extent ; and whispering is, of course, always possible. Special Considerations and Summary. Evolntion. — The very lowest forms, and in fact most inverte- brate groups, seem to be voiceless. Darwin has shown that voice is, in a large number of groups, confined either entirely to the male, or that it is so much more developed in him as to become what he terms a " sexual character." There is abundant evidence that males are chosen as mates by the females, among birds especially, not alone for superiority in beauty of plumage, but also for their song. Thus, by a process of natural selection (sexual selection), the voice would tend to improve with the lapse of time, if we admit heredity, which is an undeniable fact, even among men — whole families for generations, as the Bachs, having been musicians. One can also understand why on these principles voice should be especially developed in certain groups (birds), while among others (mammals) form and strength should determine sexual selection, the strongest winning in the contests for the possession of the females, and so propagating their species under the more favorable circumstances of chance of the most desira- ble females. Pathology teaches that, when certain parts of the brain (speech-centers) of man are injured by accident or disease, the power of speech may be lost. From this it is evident that the vocal apparatus may be perfect and yet there be no speech ; so that it becomes comprehensible that the vocal powers of, e. g., a dog, are so limited, notwithstanding his comparatively highly developed larynx. He lacks the energizing and directive ma- chinery situated in the brain. Some believe that there was a period when man did not pos- sess the power of speech at all ; and many are convinced that the human race has undergone a gradual development in this as in other respects. Certain it is that races differ still very widely in capacity to express ideas by spoken words. We may regard the development of a race of speaking ani- mals as dependent upon a corresponding advance in brain- structure, whether that was acquired by a sudden and pro- nounced variation, or by gradual additions of increase in cer- tain regions of the brain, or whether to the first there was then added the second. THE VOICE AND SPEECH. 66$ as voice, though always possible. UMARY. Fact most inverte- has shown that id either entirely oped in him as to 'here is abundant e females, among auty of plumage, natural selection nprove with the I undeniable fact, >ns, as the Bachs, principles voice ps (birds), while hould determine contests for the eir species under the most desira- •ts of the brain t or disease, the evident that the )e no speech ; so powers of, e. g., iratively highly id directive ma- lan did not pos- convinced that lopment in this differ still very ords. >f speaking ani- 'ance in braiii- idden and pro- ncrease in cer- there was then It is not unlikely that, whether sexual selection has played any considerable part, natural selection at all events has had not a little to do with the preservation of those individuals and races that soonest and most fully developed the speech-cen- ters ; for it is to be remembered that the principle of correlated growth must be taken into account. In nature generally, as in social life, success very frequently leads to success. As man's superiority over the highest of the mammals below him is largely due to his possession of a speaking (and writing) faculty, so must we concede that racial superiority is in part traceable to the same cause. It is well known that the leaders among savage tribes are frequently eflEective in speech as well as strong of heart and arm. This subject is a very large, suggestive, and complex one, and is worthy of some thought. Apart from speech proper, there is a language of the face and body generally, in which there is much that we share with lower forms, especially lower mammals. Darwin, noticing this resemblance, regarded it as evidence strengthening the belief that man is derived from lower forms. Why should the forms of facial expression associated with certain emotions so widely among different races of Inen be so similar to each other and to those which the lower animals employ, if there is not some community of origin ? This is Darwin's query, and he con- sidered, as has been stated, that the answer to be given was in harmony with his views of man's origin, as based on an alto- gether different sort of testimony. The high functional development of the hand and arm in man, and the ase of these parts in writing, are suggestive. Bnminaiy. — The musical tones of the voice are caused by the vibrations of the vocal bands, owing to the action on them of an expiratory blast of air from the lungs. In order that the bands may act effectively, they must be rendered tense and ap- proximated, which is accomplished by the action of the laryn- geal muscles, especially those attached to the arytenoid car- tilages. We may speak of the respiratoiy glottis and the vocalizing glottis, according as we consider the position and movements of the vocal bands in respiration or in phonation. The pitch of the voice is determined by the length and the tension of the vocal bands, and frequently both shortening and increased tension are combined ; perhaps we may say that al- tered (not necessarily increased) tension and length are always combined. fM ANIMAL PHirSIOIiOOY. . The quality of the voice depends chiefly upon the supra- laryngeal cavities. The vocal bands of the child and of woman, being both shorter and lighter, account largely for the differences in pitch, quality, and loudness of their voices as compared with that of man. Success in vocalization is dependent, not only on a suit- able laryngeal and other mechanism, but upon the rapidity and completeness with which a large number of muscular and nerv- ous co-ordinations can be made. Speech may be either reflex or voluntary, but for high-class results many afferent impulses uiust determine or modify the nature of the efferent impulses. There is no essential difference in the mechanism of the speaking and singing voice ; in the latter, however, the vocal bands take a relatively greater share than in the former, in which the supra-laryngeal parts are more concerned. This applies especially to the utterance of consonants, which may be classified according to the part of the above-mentioned ap- paratus that is more especially employed. It is important to remember that in all phonation, in the case of man at least, many parts combine to produce the result ; so that voice-production is complex and variable in mechan- ism, beyond what would be inferred from the apparent sim- plicity of the mechanism involved ; while the central nervous processes are, when comparison is made with phonation in lower animals, seen to be the most involved and important of the whole— a fact which the results of disease of the brain are well calculated to impress, inasmuch as interruptions anywhere among a class of cerebral connections, now known to be very ex- tensive, suffice to abolish voice, and especially speech-production. It is of great practical moment for each individual to recog- nize both the limit of his natural powers, especially of his range in singing, and at the same time to appreciate the large margin there is for improvement, more particularly when cul- tivation of the voice is commenced in childhood, and resumed soon after the age of puberty is attained. Among mammals below man the vocal bands and lar]mgeal and thoracic mechanism are very similar, but less perfectly and complexly co-ordinated ; so that their vocalization is more limited in range, and their tones characterized by a quality which to the human ear is less agreeable. Man's superiority as a speaking animal is to be traced chiefly to the special de- velopment of his cerebrum, both generally and in certain definite regions. LOCOMOTION'. 655 on the supra- n, being both Bnces in pitch, d with that of 3nly on a suit- 6 rapidity and alar and nerv- •e either reflex )rent impulses ent impulses, lanism of the ver, the vocal he former, in cerned. This )s, which may nentioned ap- nation, in the ice the result ; le in mechan- ipparent sim- )ntral nervous phonation in important of the brain are ions anywhere to be very ex- sh-production. dual to recog- Bcially of his late the large rly when cul- , and resumed »nd lar]mgeal less perfectly sation is more by a quality 's superiority tie special de- id in certain B 1 LOCOMOTION. The entire locomotor system of tissues is derived from the embryonic mew)bla8t. These include the muscles, bones, carti- lage, and ; onnective ttiid fibrous tissues; and the tissues that make up the vascular system or the motor apparatus for the circula f i on of the blood. Locomotion in the mammal is effected by the movement of certain bony levers, while the equilibrium of the body is maintained. The whole series of levers is bound together by muscles, tendons, ligaments, etc., and play over one another at certain points where they are invested with car- tilage, and kept moist by a se- cretion from the cells covering ^^^a^^^^i^m the synovial membranes that I A form the inner linings of joints. Cartilage, a very low form of tissue destitute of blood-ves- ,1^ ^g^ sels, and hence badly repaired when lost by injury or disease, forms a series of smooth sur- faces admirably adapted for joints, and especially fitted to act as a series of elastic buffers, and thus prevent shocks. Bone, though brittle in the dried state, possesses, when alive, a favora- ble degree of elasticity, while sufficiently rigid. Provision is made by its vascular periosteum and central marrow (in the case of the long bones), as well as by the blood-supply derived from no. 490. the nutrient artery and its rami- , fications throughout the osseous tissue, for abundant nourish- ment, growth, and repair after injury. We find in the body of mammals, including man, examples of all three kinds of levers. It sometimes happens that there is an apparent sacrifice of energy, the best leverage not being exemplified ; but on closer examination it will be seen that the weight must either be moved with nice precision or through large distances, and these objects can not be accomplished al- ways by the arrangements that would simply furnish the most Fio. 4Mk B -9 dsd ANIMAL PHYSIOLOGY. powerful lever. This is illustrated by the action of the biceps on l^ie forearm. It "s to be remembered that, while the flexors and extensors of a limb act in a certain degree the opposite of one another. Fia. 4S1.— Skeleton of deer. The bones in the extremities of th's the fle«(«wt of quadrupeds •re inclined very obliquely toward each other and toward the scapular and fliac boges. This arrangement increafies the leverage of the muscular system and confers great rapidity on the moving parts. It augments elasticity, diminishes shock, and indiractly, begets continuity of movement, a, angle formed by femur with ilium ; 6, angle fonaed by tibia and flbula with ttomur ; c, single formed by phalanges with cannon-bone ; «. an^ formed by humerus with scapula ; 7, ai " * (Pettigrew). angle farmed by radius and ulna with hmuMus there is also, in all cases perhaps, a united action; the one set, however, preponderating over the other, and usually sev- eral muscles, whether of the same or different classes, act together. Standing itself requires the exercise of a large number of similar and antagonistic muscles so coordinated that the line of gravity falls within the area of the feet. An unconscious person falls, which is itself an evidence of the truth of the above remarks. The following statements in regard to the direction of the line of gravity may prove useful : 1. That for the head falls in front of the occipital articulation, as exemplified by the nod- ding of the head in a drowsy person occupying the sitting atti- tude. 2. That for the head and trunk together passes behind a line joining the centers of the two hip-joints, hence the uncor- rected tendency of the erect body of man is to fall backward. 3. That for i]\e head, trunk, and thighs falls behind the knee> :(^«^l«!®ffiaffla8^E?; LOCOMOTION. 657 . of the biceps and extensors f one another. IP-"^ e«tasses behind a ace the uncor- fall backward, lind the knee- joints somewhat, which would also favor falling backward (bending of the knees). 4. The line of gravity of the whole body passes in front pf a line joining the two ankle-joints, so that the body would tend, but for the contraction of the mus- cles of the calves of the legs, to fall forward. Taking these different facts into consideration explains the various directions in which an individual, when erect, may fall according as one or the other line (center) of gravity is dis- placed for a long enough time. Walking (man) implies the alternate movement of each leg forward, pendulxuu-like, so that for a moment the entire body 4«c«^«r Twrtkiri rwwtloiM durlBK rwekm paw (Itowy). LOCOMOTION. 659 temApnemOUnj)- ad, the toe still % fulcrum that ^ ■ IMOMdUMr). the body-weight is moved forward, when a similar action is taken up by the opposite leg. It follows that to prevent a fall there must be a leaning of the body to one side, so that the line of gravity may pass through each stationary foot. It follows that a walking person describes a series of vertical curves with the head, and of hori- zontal ones with the body, the resulting total being complex. The peculiarities of the gait of different persons are natu- rally determined by their height, length of leg, and a variety of other factors, which are often inherited with great exactness. We instinctively adopt that gait which economizes energy, both physical and mental. Running differs from walking, in that both feet are for a period of the cycle off the ground at the same time, owing to a very energetic action of the foot acting as a fulcrum. Jumping implies the propulsion of the body by the impulse given by both feet at the same moment. Hopping is the same act accomplished by the use of one leg. Oonpurativ*. — ^The movements of quadrupeds are naturally very complicated, but have now been well worked out by .-^y Vloa. 488 mM «>7.-«liowliw the more OT leM perpenmoular diraetiaii of ttte itroke of the wi^ in the fflcht of the Mmngull}: bow the wing u Kradually extended aa it la devated (e,f,g)i how it deaoenda aa • long terer untit it- aanunea the poaition indicated by h ; how it is flemd toward dw tennination of tbedown-«trok«,a8aaowDath,i,i, to convert it into a abort leTer (a, b) and nrepare it for m^dng the up-atroke. Tbe dUTerenoe in the length of the wtec durtaig Hexlon and eztenaion ia indicated hy Ute iihort and long leTera a, b and e, d <*, O. the body to elevated (r). ?1«. 488 ihowa that the wtaun ara eleratod aa ihort leven (e) uutU toward the termination of the upstroke, when thCT are giwhially expwided (/. «) to nrepare them f or m^iM U»e dowiwit«*e. ^ i^ws thtt theirinn dMoend u bmtc leven (ft) unUl toward the termlnatton of the down- atroke, when they are Kradually folded or flexed (i, J) to rob them of thirir momratam and prepare them for makSng the up-ataroke. .OcnnjMUPe with Mga. 4Q6and 4W .. ^S«» "««*• &e lUr beneath the winga is Tigoroualy aeiied during the down-^ke, while th«t aboye it h avoided dnrinc the upstroke. The ooncavo-oonvex form of uie wings Mid the forward travel of tlie body contributea to this result The wings, it will be obsenred, act as a para- diute both during the up and down strokea. Fig. «W shows also the compound rotation of the whig, howlt rotates upon a, as a center, with a radius at, b, n, and upon a, e, b aa a center, witb a radhis fc, i (mtigrew). movements are to be accounted for by the multiplicity of their levers rather than the rapidity with which they are moved. FM. BOft-ChUHngham buU (Bos Sootteas). . Shows powwfut heavy body, ud the smaU eztreiStlMadapted for land tranrit Also the flgure-of-8 movenynta made by the feet and Unba in waU^ and running. u,t,ourveamadebyrMit«iid MtMrtolcreztoemi- ttas- r roureaHuBe by rii^rtMd ikt posterior ez^^ The right fore md^Uw Mt ^d%^mo^tMitiSer&^tk>rm the waved Uiie(t, tt) : the left tore and the rts^t Und toM move together wlorm the waved line (r.t). TheourveB(oraudbytheaiileite(t,w) and paalMJcir(r, s) eztramitieB form eUlpacs (PsttlgMw). LOCOMOTION. 661 The length and flexibility of their bodies must also be taken into account, rendering many legs necessary for support. We / 7 fkllii («) ; and that ;.4Wdiowatiiatthe the upstroke, when nm-Dtvoke. Fia.tfB tnation of the down- heir momentum and 407. By this means , while Oiat aboye it Dgs and the forward ervadi act as a para- )Oompound rotation , and upon a, c, b as >licity of their >y are moved. I iMdy, and the small Bts made hj the feet Mt anterior eztraml- « rlc^ fore and Uw we and the riidit hind ibytbeanMrtorlt,*) Fra. 801.— Bepnaentatlon of bone at walking paoedfafsgr). can only briefly refer to the method of locomotion well exem- plified by our domestic quadrupeds. However, the whole sub- ject will become plainer after a careful study of the cuts intro- duced in this chapter. FW. am-Horselnaotor trattfav. Inttila,aa toaU the.o tlisrp aws.thebodyof.aiahorse> levered forward by a diagonal twistina of trunk and extremities, the extremities describ- ing a flgure-of -8 traekUmrt). The llgun-ef -8 is produced by the attentate plaar of Uie ^remffies and feet, two of which are always on the ground (a, b). llius the right fore- foot describee the eurre maiiLsd (.the left hind-foot that marked r, left for»«Mt that marked «, and riiriit hind-foot,*. Tha (set on ground in the present Instance are left f era aad ria^thiad (Kttigrew). ir 662 ANIMAL PHYSIOLOGY. In walking, quadrupeds like the horse use the limbs alter- nately, and in a diagonal sequence, so that the right fore-leg Fio 508.— Red-throated dragon (Draco kcematopootm. Gray), shows • Iwfte inembranoaa eSSin^(M)^i»irtSrbeJi^im anterior (d,Wiu>A poSwIof extremlttM, Md ™pp«Mted to^ ribs. The dnunn by thto •rrancement cu take ext^rive hsm with fierfect safety. Fw.'*M^?lylng tem^nS&ttlec^ ^^^^^^^ §»),ttkmwtQimrerytUi^tim5re»M(awarfmBg. Thewnfaceerooaedhy the Satexoeefi £at dlsplued by muqrinsecta and birds. Tto winn of ^ bat aro deei^ S5m»»SiSd»«SelQethew£Siofhe^ The bo^ot the arm (r). forearm {S^and^hw? (». ». ») »' «» V^.5S*??**™^^2'»kI Sick margtai and the rzttemttr of the wing, and may not inaptly be compared to the nemires In correapondlng positions in wing (n beetle (Fetngrew). and the left hind-leg are associated. Trotting corresponds to running in man, and there is the same diagonal action. There Fio. 805.-The bat (Phtfiwrkina graeUi; Peters). Here the t«»'«Unf ••^•«* ,<»"*« J^*^,?) areenormouBly Inweaaed as compared with that of Uw land and water antmala generally (Pettlgrew), r, arm ; d, forearm ; e/, » n n, hand of bat. is also a gait natural to some horses, some dogs, the camel, etc., termed ambling, or pacing, characterized by both legs on the same side working simultaneously and alike. This is perhaps comparable to human walking. In galloping, all four feet are ofiE the ground together for a portion of the cycle, though they do not strike the ground again at the same moment. Evolution.— It is noteworthy that with almost all quadrupeds the gallop is the natural method for rapid propulsion. In all MAN CONSIDERED PHTSIOLOOICALLT. 668 limbs alter- ight fore-leg large membranooa tttea, and supported with perfect lafety. ir tiie membnuioiis ported by the neck, flying lemur takes he bifi, I^v^ofl^i^*!* Face ezpoaed by the : the batare deeply -winged birds. toB orttne antorior or le compMed to the orresponds to ction. There animals, either bred by man to attain great speed, as the race- horse and greyhound, or those that have become so by the pro- cess of natural selection, the entire conformation of the body has been modified in harmony with the changes that have taken place in the legs and feet. This is seen in the greyhound among domestic animals, and in the wild deer of the plain and forest. Such instances illustrate not only the principle of natural se- lection as a whole, but the subordinate one of correlated growth. Any one observing the modes of locomotion of quadrupeds, especially horses and dogs, will perceive the advantages of the four-legged arrangement. Not only is there a variety of modes of progression, as walking, trotting, galloping, cantering, the alternations of which permit of rest to certain groups of mus- cles, with their corresponding nervous connections, etc., but on occasion some of these animals can progress fairly well with three legs. Sometimes it may also be noticed that a horse that prefers one gait, as pacing, for his easy, slow movements, will break into a trot when pushed to a higher rate of speed. Trotting can not be considered the natural gait for high speed in the horse, yet, by a process of "artificial selection" (by man) from horses that have shown capacity for great speed by this mode of progression, strains of racers have been bred, showing that even an acquired mode of locomotion may be hereditary ; while that galloping is the more natural mode of locomotion of the horse is evident, among other things, by the tendency of even the best trotting racers to break into a gallop when unduly pushed — an instance also of an hereditary tend- ency of more ancient origin prevailing over one more recent. The bipedal modes of progression of birds are naturally very like those of man. « (rdef,annn) »r animals generally he camel, etc., h legs on the [lis is perhaps 1 four feet are ), though they int. ,11 quadrupeds alsion. In aU MAN 0ONSIDEBE3) PHTSIOLOOICALLT AT THB DIFFEBENT PERIODS OF HIS EXISTENCE. Growfh. — As a result of the intra-uterine development of two cells, neither of which is visible by the naked eye, the human being reaches about one third of its total length and one twentieth of its maximum weight. In the infant the rela- tively larger size of the head and face is obvious, while among internal organs the liver is especially large. The child's future inci«ase in weight is chiefly from growth of muscles. Increase .™--:i>->i-^^V™K35SW*a 664 ANIMAL PHTSIOLOOT. s in stature continues up to about the twenty-fifth year, though the increase is most rapid during infancy and puberty, when, in fact, the weight is also greatly augmented. IHgMtiT* lyitem.— While it is now established that all of the digestive secreting mechanisms are active at or shortly after birth, it must be borne in mind that these, like the other organs, adapt gradually to the new conditions. This is a matter of practical importance in infant feeding. Thus, while it is true that the young infant's saliva will act on starch, it is not to be supposed that its amylolytic powers are equal to those of the adult. CHreiiktory aad Saspinitary tyiUaM.— The babe's heart is larger than that of the adult relatively to its body-weight, and its action more rapid ; hence the circulation is accomplished in a 8hort«r space of time, an advantage when it is considered that the need for oxygen and tissue-food in the young organism is so great. The respirations are correspondingly rapid, and the actual amount of the respiratory interchanges is greater than in adult life. There appears, however, to be a storing up of oxygen — i. e., all of the oxygen used up does not shortly appear again as carbonic anhydride. The metabolism of the infant is very active, and is spent largely in construction ; growth is in excess of waste ; indeed, this feature is characteristic of the metabolism of all young animals. There is, in consequence of the excessive loss of heat, from a relatively larger surface than in the adult, the need for a more active metabolism ; the young animal must eat more, to meet this waste. It is, moreover, in consequence of this fact that infants, when not protected better than adults, perish from a fall in the temperature, which their sensitive organizations can not endure. Immediately after birth the adaptation to the new environ- ment is less perfect than at a later period ; respiration is feeble ; the blood is imperfectly aSrated ; the temperature is lower ; the entire metabolism goes on but feebly : hence it is that newly bom kittens, puppies, etc., can be immersed in water for a con- siderable period (twenty to thirty minutes) without drowning. The tissues do not demand much oxygen ; they live on what they already have stored up, after that in the blood is ex- hausted — in a word, they behave much as they did during intra- uterine life. The excretions, as would be supposed from the rapid metabolism, are more abundant than in the adult. There ^? V MAN CONSIDERED PHTSIOLOOICALLT. 666 year, though uberty, when, that all of the shortly after i other organs, s a matter of hile it is true it is not to be those of the ftbe's heart is ly- weight, and ;complished in onsidered that ig organism is md the actual r than in adult ip of oxygen— ppear again as >, and is spent waste; indeed, 1 of all young ve loss of heat. It, the need for nusteat more, ace of this fact its, perish from 9 organizations e new environ- ation is feeble ; •e is lower ; the b is that newly irater for a con- tout drowning. y live on what le blood is ex- id during intra- )osed from the ie adult. There is more urine passed and more urea excreted in proportion to the weight. The lymphaiic system, as a whole, is more pronounced in youth. Certain glands, the functions r* which are not well understood, for which reason we have t. ight it well to pass them over entirely, are at their highest development during infantile life, as the thymus and thyroid. These atrophy as puberty approaches, especially the thymus gland. The prominence of the lymphatic system harmonizes with what we know of the functions of the colorless corpuscles of the blood in the work of building up tissues. They may be re- garded as remnants of embryonic life, undifferentiated cells awaiting their opportunity to develop, though we do not, of course, mean to affirm that in the blood and elsewhere they have no other functions ; in fact, it has been shown that in the alimentary tract they are porters of digestive products (fat, etc.) ; and they also likely play an imi)ortant part as scavengers and as guardians of the nobler cells against micro-organisms, etc. DentitioiL — The change in the metabolic powers of the ani- mal is foreshadowed by the gradual appearance of teeth for the preparation of a more solid food to meet the altered wants of the economy. The first appearance of teeth is in the upper jaw, the two central incisors, soon to be followed by the corresponding ones of the lower jaw. This is at about the seventh or eighth month, to be succeeded by the lateral incisors a couple of months later ; the first molars about the end of the first year of life; the canines (eye-teeth) half a year later ; and the whole of the temporary set before the second year is completed. The permanent teeth replace the milk-teeth very gradually, and are thus adapted to the growing jaws. The new dentition begins to appear about the sixth year, and may continue for six or eight years. The last molar (wisdom tooth) appears very late, between the seventeenth and the twenty-fifth year. It is noteworthy that this tooth seems to be more and more delayed, and often never appears at all, which may be said of some others, especially the lateral incisors ; so that it looks as if, as civilization progressed, the jaw were becoming smaller and the teeth suffering atrophy. Both the teeth and the hair are epi- dermic structures, and their defective growth at the present time in so many individuals raises suggestive questions. The face of civilized man seems also to be getting smaller relatively 669 ANIMAL PHTSIOLOOT. to the head. Is this an example of correlated growth, to be explained by the predominance of the cerebrum ? Vtrrooi Syitom. — The nervous system, like all the others, is highly sensitive; it reacts powerfully to moderate stimuli; its equilibrium is more readily disturbed than that of any other ; and, since to it belongs the work of guiding the metabolic pro- cesses of the various tissues, this peculiarity explains the readi- ness with which the health of the infant can be deranged or restored. Hence it follows that a prognosis in the case of in- fants must be unusually guarded. As has been already indicated, the cortical cells of the cere- brum, and other parts of the brain, are but indifferently devel- oped at birth ; so that stimulation of the cerebral surface in young animals (though there is great difference in this respect) must not be expected to give precisely the same results as in adults. From the share that we now know the cortex of the cere- brum to take in the elaboration of probably all sensory im- pulses, it follows that in the infaiii<. all of the senses must be to a certain extent imperfect, even &EWuming that the peripheral mechanisms are as perfect fun 3tioually as in the adult, which is not likely. In some respects, however, the eye of the infant is more perfect. Its power of accommodation for near objects is won- derful, while at a very early age the pupil acts perfectly, and binocular vision is established. Touch is fairly developed, and probably also taste and smell ; though as tc the last two there is more doubt. On the other hand, hearing in the infant is very imperfect ; power to discriminate between the pitch and quality of sounds is rudi- mentary ; while ajypreciation of direction, which is largely the result of experience, is necessarily of the crudest. It is doubtful if the middle ear is properly pervious to air, on which its functioning depends g^roatly for some time after birth. But certainly, as regards the processes of the peripheral mechanisms of the senses, the child that has passed the years of infancy knows a perfection, to which he becomes more and more a stranger as years pass by. Later he will, in consequence of accumulating experience, xnake more out of his sensory data; his cerebral cortex will be more developed, both strnct- urally and functionally. Maturitf (Pabatj).— Though most of the organs of the body continue to improve, and certainly the organism, as a whol^ 1 MAN CONSIDERED PHTBIOT •OICA.LLT. wt growth, to be the others, is » stimuli; its of any other; netabolic pro- ains the readi- e deranged or he case of in- Us of the cere- Ferently devel- ral surface in n this respect) le results as in of the cere- 11 sensory im- ses must be to the peripheral e adult, which infant is more objects is won- perfectly, and dso taste and loubt. On the feet; power to lounds is rudi- i is largely the t. lervions to air, >me time after the peripheral «8ed the years omes more and in consequence of his sensory d, both strnct- 018 of the body m, as a wholes up to about the fortieth year of life < iater, pub ty is tltal period of life which is most remarkable iur sudden, ^. riknfi: velopment. While this is in some respects most pronouni > the sexual organs and related parts, as the pelvis and mamir y glands of the female, yet a whole host of other changes ^e place simultaneously, in such a way as to leave no doubt . at they are related to those of the sexual organs. Not only the characteristic form of the body, but the psychic peculiarities of the sexes, appear and become fully established with an extraor- dinary rapidity. There is, therefore, no period of life fraught with so much of developmental good or ill as puberty. A host of diseases may now show themselves, according to the laws of heredity, as a result of deficient resistance, etc. The 8«iM. — ^While the differentiation of sex becomes greatly more pronounced at puberty, there are decided differences be- tween the male and female infant. The male from birth is the taller and the heavier. This inequality is maintained in adult life. The average woman is shorter and lighter than the man ; her muscular and bony systems are less developed, both abso- lutely and relatively; her brain is some ounces lighter; her blood is poorer in hsemoglobin, of lighter specific gravity, and, as a whole, less in quantity. Woman's metabolism, if we may judge by the income and expenditure, is both absolutely and relatively less. Man's physical strength is nearly double that of woman. These facts have an important bearing on some of the burn- ing questions of the day. There are, it will be seen, deep-lying differences between the sexes, \vhich can not be ignored in our education and civilization generally, without running counter to that sexual differentiation which Nature, through long ages, has been bringing toward higher and higher development. (Hd Agt. — From middle life onward, in most persons, there is a gradual process of deterioration going on in every tissue. Elasticity diminishes and rigidity of tissues becomes more and more marked. The arteries undergo changes which, whether fatty or calcareous, greatly impair their usefulness ; the carti- lages of the ribs and other parts tend to become calcareous, so that the chest-walls possess less of elasticity ; this, combined with a general impairment of muscular power, lessens the cai>ability of thoracic movement. Protoplasm everywhere has less vital potential, so to speak ; hence with the approach of old age we often find adipose tissue in excess. It becomes a bur- 668 ANIMAL PHYSIOLOOT. den to an already weakened organism. Nervous discharges tend more and more to be slow, weak, and to take the lines fixed by long usage ; hence, perhaps, that undue conservation of mind common to the old ; that lack of enterprise, which is strengthened by the consciousness of inability, physical and mental, for the strain of new undertakings. Hence also the natural failure of acquiring power and the memory. The judgment, dependent as it is on accumulating experience, im- proves. With extreme old age there is a reversion to the infantile condition, marked by irritability of tissues, weak- ness, etc. The laws of habit and rhythm are illustrated abundantly in the subjects we have been considering. Rhythm seems to be a sort of key-note to the interpretation of the universe ; but since we have frequently referred to this subject throughout the volume, it will not be further dwelt upon now. OompantiTa. — All mammals have their periods of rapid growth, slower decay, and death. Their growth is usually more rapid than man's, and as their whole lives are shorter, with few exceptions, their rate of decay is faster. There are great differences between various mammals in their degree of development at birth. Among some (the marsupials) they separate from the mother internally, to become attached to the nipples externally when very imperfectly developed. Though puppies, kittens, and other members of the groups to which they belong (comivora) are bom with the eyes unopened, no mammal is so helpless as the human infant when ushered into the world. Most animals learn the use of their muscles, and to provide for themselves in a very short period. Slowness of development is, however, even among the lower animals, fre- quently associated with the attainment of an ultimately higher functional status, and the precocious child should be the object of some anxiety. It may develop into a prodigy of talent, rise little above mediocrity, or become the subject of some serious or fatal form of disease. It is important to recognize that sexual maturity, in the sense of ability to produce ripe ova and spermatozoa, does not correspond with the full development of the animal ; so that it may be as unscientific to breed together animals that are very young as those that are deca3ring from age. Especially is it undesirable to mate two very young or very old animals. Such a principle applies, of course, also to man. DMth. — If the continuance of life is dependent on the cease- MAN CONSIDERED PHYSIOLOGICALLY. 669 as discharges ake the lines conservation irise, which is physical and ence also the lemory. The xperience, im- ersion to the issues, weak- ed abundantly rthm geems to universe; but ct throughout w. iods of rapid irth is usually as are shorter, er. There are Iheir degree of Lrsupials) they Attached to the oped. Though >oups to which 8 unopened, no m ushered into muscles, and to .. Slowness of )r animals, f re- bimately higher id be the object f of talent, rise »f some serious less adaptation of internal to external conditions, it becomes clear that death may be said to be ever imminent ; and in the highest mammals the vital organism is so complex and so delicately balanced, that it is marvelous that life lasts so long as it does. Few animals perish from simple decay leading to a gradual slowing of the vital machinery, down to zero, so to speak ; but when death is not due to violence, as it frequently is, it rather arises from some Essential part getting out of gear, either directly or indirectly. So great is the need of a constant supply of free oxygen in the mammal, that an arrest of the respiration always implies a stoppage of the circulation. These results may be brought about by the direct action of poisoned blood on the heart, or on the nervous centers presiding over lungs, heart, and other organs. Death may then be due to central influences, though finally the arrest of the circulation is the real proximate cause. When the circulation is so ar- rested that it can not be started again, somatic or body death must follow, which is to be distinguished from the death of the individual tissues. Somatic death marks the first stage of the return of a vital organism toward the inorganic world, whence it was, in a sense, derived. That molecular arrangement or movement peculiar to living things once being permanently deranged, its resolution into the less complex forms of the inorganic compounds speedily follows, though the rate will depend much upon circumstances in any individual case. Life is much more of a mystery than death. Physiology attempts to de- fine the conditions under which life exists, but can not explain life itself. Will it ever lift the veil ? laturity, in the btozoa, does not imal; so that it B that are very Especially is it animals. Such i at on the cease- Va«. APPENDIX. ANIMAL CHEMISTKT. An attempt will be made in this chafiter to give a brief a4KX>unt of the principal substances entering into or derivable from the mammalian body, or resulting from its metabolism. We may repeat that, inasmuch as chemical treatment kills living organisms, we can only know the chemical constitution of the dead body. The cells and tissues of the body of a mammal are made up of proto- plasm, which belongs to that large class of bodies known as proteids. However, it is seldom, if ever, that pure protoplasm is found, for even in the youngest cells and in imicellular animals and plants this sub- sti^Qce usually contains some representatives of the class of bodies known as carbohydrates and fats. Protoplasm Is, moreover, the producer or builder of both fats and carbohydi-ates, as has been already learned. In one sense all the chemistry of the body is the chemistry of protoplasm, in that it is either by one or other phase of the metabolism of cells that the various secretions, excretions, and reserve products of cells arise. We have already considered this aspect of the subject in connection with the treatment of the metabolism of the animal body, and shall now direct attention in more detail to certain chemical facta, groupings, and principles, largely with the purpose of illustrating the resemblances between the products of our laboratories and of our bodies. At the same time it is to be borne in mind, as we have often remarked in the main body of the work, that we are generally unable to say whether the syntheses and analyses of the body resemble those made by the chemist in the laboratory or not Indeed, the whole subject, from this point of view, is as yet in a very crude condition. PROTEIDa These include a large class of bodies as yet very imperfectly under- stood chemically. According to Hoppe-Seyler, the following percentage composition may be assigned to them : O N HO 8 90D-M-5. W-S-17-0, •♦-T-S, 51-»^'6, 0»-«U Usually on ignition a very small quantity of ash remains. 672 ANIMAL PHTSIOLOOT. Proteids are amorphous ; insoluble in alcohol and ether ; some of them soluble in water ; soluble with change of constitution in strong acids and alkalies, and laevo-rotatory. T«ftS for Froteids.— 1. With Millon's reagent (mercury dissolved in its own weig]'t of nitric acid, and the solution diluted with twice its volume of water) a precipitate, rendered red by boiling. 2. Heated with strong nitric acid, they become yellow. On adding ammonia or caustic soda, or potash, the yellow is replaced by an orange {xantho- proteic reaction). 3. On adding caustic alkali and a drop or two of copper sulphate, a violet color is produced, which can be deepened by boiling. 4. To the suspected fluid add enough acetic acid to render it decidedly acid, and then a few drops of potassium ferrocyanide. A white precipitate indicates that proteids are present. 6. To the fluid rendered decidedly acid, add a strong solution of sodium sulphate and boil. If a precipitate falls, some proteid was present The first three tests are the most reliable, and apply to all classes of proteids. PBOPBBTIES and CliABSmOATION OF THK PBOTEIDB. I. Native AUmnUns. These occur naturally in the tissues and fluids of the body. They are soluble in water, are not thrown down by the alkaline carbonates, by sodium chloride, or by very dilute acids. Their ccagulation-point lies below 70° C. They may be dried with change of color to a pale yellow, but remain soluble. 1. Sgg*Albllllli]L— This may be obtained for purposes of experiment by cutting up raw white of egg with scissors, diluting with water, strain- ing through cotton, a? d afterward through filter-paper. The resulting fluid is almost colorless at flrst, but on standing darkenJs gradually. It may be precipitated by strong alcohol, which does not seem to alt«r its chemical constitution, or by strong acids, when a great chemical change takes place. Various, mineral salts, as silver nitrate, mercuric chloride, etc., form with albumin insoluble compounds. Whether albu- min ever e^dsts entirely free from combination with salts in the animal body is a question ; probably not By the addition of strong acetic acid or caustic alkali, a clear, jelly- like mass results, being, in the flnt case, acid-albumin, and in tLe second alkali-albumm. It is laevo-rotatory to the extent of SS-S" (— 86-5"). 2. BemmnAnramin.— This compound greatly resembles th.e foregoing, but may be distinguished by the following characteristics: (a) Serum- albumin is not like egg-albumin, coagulated by ether, (b) Serum-albu- min is less readily coagulated by strong hydrocUorio add, and any pre- cipitate formed is easily diMwlved by excess of add, in which respects it is the reverse of ^^g^lbumin. (o) Coagulated serum-albumin is readily soluble in strong nitric acid, the reverse holding for egg^lbumin. (d) The specific rotation of egg^lbumin is —85-5° ; of serum-albumin, —56°. (e) Serum-albumin occun in blood, lymph, chyle, milk, and pathological her ; some of ion in strong y dissolved in vrith twice its I. 2. Heated f ammonia or uige {xantho- rop or two of e deepened by id to render it rocyanide. A . To the fluid I sulphate and o all classes of XIDS. e body. They ine carbonates, Bgulation-point color to a pale I of experiment b. water, strun- The resulting i gradually. It t seem to alter great chemical itrate, mercuric Whether albu- ts in the animal li, a dear, jelly- id in tLe second >s thp foregoing, tics: (o) Serum- (6) Serum-albu- i5id,andanypre- trhich respects it bumin is readily (g-albumin. (d) t-albumin, —66°. uid pathological APPENDIX. 678 transudations ; and, when injected into the blood, doea not reappear in Ihe urine, while the injection of egg-|||bumin is followed by its appear- ance in the urine apparently unaltered. In fact, this form of proteid constitutes a great part of the "albumin" of the urine of such signifi- cance in pathological conditions. However, increasing knowledge seems to point to the "albumin " of the urine, like many other forms of pro- teid, being more complex than was once supposed. II. Derived Albumins (Albuminates). 1. Aeid-AIbninill.— This may be formed by the addition of a strong acid to egg-albumin, or, more gradually, by heating a weaker solution of egg-albumin with an extremely dilute acid. Acid-albumin is characterized by non-precipitation on boiling, com- plete precipitation on the addition of a dilute alkali to the point of neu- tralization—that is, acid-albumin is insoluble in water or such like neu- tral liquids. It is soluble in an excess of acid or of alkali. By treating finely minced muscle with a weak acid, a substance is obtained not readily distinguishable from acid-albumin, but known as syntonin. This is probably not identical Mrith acid-albumin as formed by the method indicated above, though a distinguishing test of a wholly satisfactory character is not known. Neither this substance nor acid- albumin coagulates on boiling, in which it bears a resemblance to pep- tone. The parapeptone of digestion seems to be very similar to acid- , albumin. A solution of acid-albumin in acid may be precipitated by the addition of an excess of common salt. 2. AlkaUfAUnuilin.— This corresponds to the fon^ing, and may be formed in a similar way by the addition of an alkali instead of an acid. It is not ooagulable on boiling, and is precipitated by dilute acid, in excess of which and of alkali it is soluble, but, like acid-albumin, is in- soluble in water and solution of neutral salts. The specific rotation varies with the mode of preparation, from which, as well as on other gvounds, it is more than likely that there are different kinds of alkali- albumin. It is highly probable that acid-albumin and alkali-albumin are combinations of an acid or an alkali, as the case may be, with albu- min, and that the neutralization precipitate is not in itself either one or the other. 3. CMein.— This substance is the proteid most characteristic of milk, from which it may be obtained by dilution ten to fifteen times with water, adding acetic acid till a precipitate begins to form, and then sending a current of CX>t through the fluid. After standing, the precipitate may be collected in a filter. It is freed from salts, sugar, fat, etc., by first washing with water and then with alcohol and ether. It is so like alkali-albttmin that there is no agreement yet as to the differences between them. However, the presence in milk of potassium phosphate modifies the reactions of casein in this fiuid. It may be precipi- tated also by adding magnesium sulphate to saturation to milk. This pre- cipitate is, however, easily soluble in water. The specific rotation of casein, when in solution in water is —80°, but in other solutions is different. 48 674 ANIMAL PHYSIOLOGY. m. Globulins. This class of bodies is characterized by being insoluble in water, solu- ble in dilute saline solutions (especially sodium chloride) ; soluble in dilute acids and alkalies, when they are transformed into acid-albumin and alkali-albimiin respectively. Most of the globulins are preoipitxted by saturation with solid sodium chloride. 1. Globulin (Crystallin).— When the crystalline lens of the eye is rubbed up with fine sand and extracted with water, upon filtration and passing a stream of carbon dioxide through the filtrate, a precipitation of globulin is obtained. Though strongly resembling paraglobulin and fibrinogen, it is not known to favor fibrin-formation. 2. FangloboUll (Fibrinopla«tin).— This body may be obtained from blood-serum by passing through it a current of carbonic anhydride, when a flocculent precipitate falls, which later becomes very finely gran- ular, and may be separated by filtration. Addition of solid sodium chloride precipitates this substance only in part. It is very readily changed into alkali-albumin, and still more so to acid-albumin, by addi- tion of dilute alkalies or acids. This body is not easUy precipitated by alcohol. Its coagulation-point is about 70° C. Paraglobulin has been found in blood-serum, lymph, chyle, serous fiuids, the aqueous humor, the cornea, connective tissue, and in the pale and colored corpuscles. It occasionally appears in urine as a patho- 'logical product. , . ,. • * 3 MwillOgeil.— Wliile greatly resembling paraglobulm m most characteristics, the coagulation-pomt is different, being 62" to 55° when in solution in dilute sodium chloride. It is not so readily precipitated from diluted solutions as the body previously described, and is viscous rather than granular. x- xu „». It may be obtained from blood-plasma by special preaiutions^ though more readily from hydrocele-fluid. Fibrinogen occurs m blood, chyle, serous fiuid^ and numerous transudations. It has been considered by many observers to be essential m the formation of flbnn. 4 MyoHiil, as its name implies, is derivable from musde-plasma, and may be regarded as the latter substance in an altered f onn. It may be pre'pared from washed muscle, by treatment with a ten-peiM^ent solution of common salt, and dropping the viscid product slowly mto distilled water, when it falls as a flocculent, whitish precipitate. It is readay con- verted into syntonin (a form of acid-albumin, as has been pomt^l out) by acids, and into alkaU-albumin by alkalies. In very w^k acids and alkalies it is soluble without conversion into a different substance. The coagulation-point of myosin is low, 66° to 60° C. . 6 Vitellln.-Thb body, probably united witii lecithm, is the chief prot^id constituent of the yelk of egg, from which it is usually prepared. It differs from most of the globulms in not being precipitated f rom ite solutions by sodium chloride. The coagukition-point Ues between 70 and 80° 0. , . _j j ♦».„ 6. Olobln is a doubtful member of this ckss. It is regarded as the .!!MLlE,it'yiJ.l' ' -^■i4JJ',gJ'. " L APPENDIX. 676 in water, boIu- le) ; soluble in acid-albumin ire preoipitxted ; of the eye is 1 filtration and a precipitation ,ra£ri6bulin and obtained from nic anhydride, sry finely gran- [ solid sodium is very readily lumin, by addi- precipitated by h, chyle, serous and in the pale ine as a patho- tbulin in most 62" to 55° when lily precipitated , and is viscous autioos, though m blood, chyle, I considered by I. scle-plasma, and rm. It may be [ler-cent solution ly into distilled It is readily con- en pointed out) weak acids and substance. The hui, is the chief isually prepared, ipitated from its lies between 70° regarded as the proteid residue of heemoglobin. It is not easily soluble in dilute acids or sodium chloride, hence it is with hesitation ranked with the other globulins. IV. Fibrin. This body has peculiarities which warrant, in the present state of our knowledge, its separation from the foregoing and placing it in a sepa- rate division. It is insoluble in water and dilute solutions of sodium chloride ; dissolved only with difficulty in concentrated neutral saline solutions, and in dilute acids and alkalies. Fibrin is highly elastic. It always swells under the action of weak (1 to 6 per cent) hydrochloric acid. But continued action of the acid changes the fibrin to syntonin. Heat hastens the process. By the ac- tion of alkalies, especially when aided by warming, fibrin is converted into alkali-albumin. By the prolonged action of solutions of sodium chloride (10 per cent), sodium sulphate, etc., conversion into a substance very like myosin or globulin is effected. Myosin may be regarded as an intermediate product, lying between globulin and fibrin. ^This be- comes clear when comparing their respective solubilities in a ten-per- cent solution of sodium chloride. Fibrin and myosin, it will be re- membered, are both the products of coagulation processes. The highly filamentous character of fibrin distinguishes it physically from all other proteids. V. Coagulated Proteida. This class of bodies may be obtained from a variety of others by the use of heat, alcohol, acids, etc. By heating to about 70° C, solutions of egg-albumin, serum-albumin, and globulins are coagulated. Precipi- tated acid-albunun and alkali-albumin, and fibrin in solution in salines, are converted into coagulated proteids by boiling. The digestive juices act readily on them, converting them finally into peptones. VI. P^tonea. Peptones are proteids which, though possessing little absolute difFa- sibility, as compared with solutions of ordinary salts, yet pass through animal membranes with much greater readiness than any other proteids. Also, unlike most other proteids, they are not coagulated by boiling. They are not precipitated by cupric sulphate, ferric chloride, nor usually by potassium ferrocyanide and acetic acid. Though precipitated by alcohol from solution in water, they do not undergo a true coagulation, even after standing long under this liquid. Peptones are coagulated by chlorine, iodine, tannin, the nitrates of mercury and silver, mercuric chloride, and the lead acetates. A mere trace of cuprio sulphate to which a strong solution of caustic alkali has been added, introduced into a solution of peptones, gives rise to a red (pink) color. If more than a trace of the copper salt be added, the u«ual proteid reaction results. Peptones may be formed through the action of dilute or stronger acids at medium temperatures, or by the action of distilled water heated 676 ANIMAL PHYSIOLOGY. above the boiling-point under pressure in a special apparatus. The usual SXd ^ howeveV. by the action of gastric or pancreatic juice on white ^'Tsi^t^^SrVrS::^ that the bodies fonned by ^e different methods indicated above ar^ not identical, though harmg many proper- tii in common. Between the original proteid and the peptone other bodies seem to be formed either as by-p^tsor ^ u^r^^os^; ies, and the rektion of these has been expressed m tabuhir form (Foster) ihuB : Decompomlion of Pnteida by Digeatton. Albumin. A Antialbumose. Hemialbumoee .| I Antipeptone. r Leucin. Tyrosin, etc. Leucin. Tyrosin, etc. e> Antipeptone. Heraipeptone. Hemineptone. i| DeeomporiHon by Adda. 1. By -25 per cent HCl at 40' C. Albumin. Antialbumate. AntialDumid. Hemialbumose. Hemiiteptone, Hemipeptoue. 2. By 3 to 5 per cent H«S04 at 100' C. Albumin. Antialoumid. Hemialbumose. Hemipeptone. 1 Hemipeptone. Leucin, Tyrosin, etc. Leucin, TytosJn, etc. It will be observed that antialbumose and »»«™i»>^«'"'«« *~ "^f^ mediate p«>ducte of digestion, and they occur in both peptic and tryptic ^**^Sbumate takes the place of antialbumose when albmninte di- aested with dilute hydrochloric acid at 40° C, or when pepUc digestK,n K'or^ally active. It can be changed into peptone by tryp«r^ but not by pepsinfand seems to correspond with the parapeptone of some ;lo«Tri8;ner). The table is also meant to indicate that antmlbu- APPENDIX. 677 tus. The tisual : juice on white by the different g many proper- 9 peptone other itennediate bod- uf form (Foster) .4 ' ». emipeptone. ^ "§ icin. Tyrosin, etc. imose. HemipiBptoue. w. Hemipeptone. cin, Tyft)8Jn, etc. ibumose are inter- peptic and tryptic len albumin is di- m. peptic digestion ne by trypsin, but •aj)eptone of some »te that antialbtt- mose and hemialbumose both result from peptic digestion, and it is assumed that these both split up into two molecules of antipeptone or hemipeptone, according as the digestion is either peptic or tiyptic. Evi- dently, trypsin carries the processes much further than pepsin. Vn. Lardaeein (Amyloid Substance). This body is not found in the tissues in health, but results from a pathological process, and is most frequently found in the spleen, liver, kidneys, lungs, blood-vessels, etc. It consists of CHNO and a little sul- phur in some oxidized form. It is insoluble in water, dilute acids and alkalies, and neutral saline solutions. like other proteids, it can be con- verted into acid-albumin and alkali-albumin; but, unlike all other pro- teids, it is not affected by the digestive juices. It may be recognized by giving a red color with iodine, and a violet or blue when heated with iodine and sulphuric acid. We are still in ignorance of the real molecular constitution of pro- teids. and our whole knowledge of this class of bodies is in the empirical rather than the scientific stage. NrntooBNOus No»-obtbtaixiot! Bodies aixied to Proteids. These bodies resemble each other much less than the proteids proper : 1. Mndn (CHNO). It is the characteristic body of mucus, which abounds in the bile of the gall-bladder and in snails, from either of which it may be prepared. It may be precipitated from its solutions by alcohol, alum, mineral acids, and acetic acid. The precipitate is dissolved by excess of mineral acids, but not by acetic acid, so that the latter forms one of the best tests for mucin. 2. dumdrin (CHNOS). This substance may be extracted from hyaline cartilage, and less easily from elastic cartilage. It readily gelatinizes from its solutions on standing; is soluble in hot water, alkalies, and ammonia; insoluble in cold water. It is very doubtful whether chondrin of itself exists in car- tilage; it is more likely an allied product. 3. CMAtin, or QHtia (CHNOS). This substance may be obtained by heating connective tissue for days with dilute acetic acid at about 16°, or by prolonged treatment with water under high pressures. It forms, when not ^ure, the well-known "glue." Though swelling in cold water, it does not dissolve, but is readily soluble in warm water. It forms insoluble precipitates with tan- nic acid and mercuric chloride. 4. mMtin (CHNO). This is one of the most insoluble substances derivable from animal tissues. It, however, yields to concentrated nitric and sulphuric acids in the cold and to boiling alkalies, and may be precipitated from its solu- tions by tannic *cid. The substance is best obtained from the liga- mentum nuchse of the ox. ■tnritirtjtwvwnfan 678 ANIMAL .PHYSIOLOGY. 6. Ktntin (CHNOS). It makes up a large part of horn, hair, nails, feathers, and is also a highly insoluble body. In all probability it is not a simple substance. 6. Hndein (CHNOP). This body is derivable from the nuclei of cells, from yeast, semen, and from the yellow corpuscles of the yelk of eggs. It is slightly solu- ble in water, easily so in alkalies, though the solubility changes on keep- ing. It is best prepared from pus-corpuscles, and contains a notably large quantity of phosphorus— nine to ten per cent 7. Ohitin (CHNO). Though not occurring in appreciable quantity, at all events in the body of the mammal, it makes up a good part of the hard covering of insects, crustaceans, etc. It has been regarded as analogous to the cellu- lose at plants. It is a highly insoluble substance, resisting all reagents except strong mineral acids. It may be obtained pure, as a white amor- phous body. The insolubility of the above products as a class is remark- able. Most of them yield either leucin or tyrosin, or both, under hydro- lytic treatment. Their relations are very ill understood, and it is doubt- ful if any of them are simple substances, or exist as such in the tissues from which they are extracted with so much difficulty in most instances. No attempt has been made to give the percentage composition of the above bodies. CABBOHTDRATBa. Of this class glycogen, dextrose (grape-sugar, glucose), maltose, milk- sugar, and inosit occur normally in the mammalian body. The exact chemical constitution and relations of the sugars are still under discussion ; we shall, therefore, pass this subject over in this brief outline. 1. DoctroM (grape-sugar). CiHitOt. The occurrence of this body in the various fluids and tissues h^ been already considered. This sugar ctystallixes from aqueous solutions in prisms, which may be agglutinated into lumps, and is, when chemically pure, colorless, readily soluble in warm water, more slowly soluble in cold water, spar- ingly soluble in alcohol, and insoluble in ether. Specific rotation, + 104«»— i. e., dextro-rotatory 104' for yellow Ught In the presence of yeastH»lls, and at a temperatnre of from 5° to 45° O. (best at about 25° C), dextrose undergoes the alcoholic fermentation. The reactions may be thus expressed: 0.H..0. = SC.H..OH 4- 2C0t. In the presence of decomposing nitrogenous matter, as the casein of milk, the lactic fermentation resolta. Reactions: (a) CtHitOt = SCiHtOt. LMtlCMid. (b) SC*H.O« =! C«HiOi + SCOt 4- 2Hi. Butyric ftdd. T^ APPENDIX. 679 I, and is also a tie substance. I yeast, semen, 8 slightly solu- anges on keep- Eiins a notably events in the ird covering of lus to the eellu- ag all reagents I a white amor- ;lass is remark- 1, under hydro- and it is doubt- L in the tissues most instances, position of the . maltose, milk- r. sugars are still rer in this brief tissues hffii been ons, which may pure, colorless, old water, spar- leciflo rotation, the presence of at about 25° C), aactioiu may be as the casein of A temperature of about 35» C. is the most favorable for this fermen- tation. Dextrose readily reduces copper salts in the presence of caustic alkali. This sugar may be artificially produced by the action of dtastaae, a ferment obtained from malted barley, on starch. 3C.H..0i + H.0 = C.tH«0.. + C.H..O.. BtMxeh. Maltose. De«rin. It may also be formed by the action of dilute sulphuric acid on starch It reduces coppersalts; is dextro-rotatory ; ferments with yeast, and crystallises in fine needles. It seems to be the principal sugar formed in the natural digestive processes. ]Ii]k<8ligar aactose). C.tHt«On. This form of sugar is found in the mUk of aU animals normally, and occasionally in the urine of animals during lactation. It crystallizes in rhombic prisms ; its taste is slightly "weetish ; is dextro-rotatory ; much less soluble in water than <«ne-sugar. When the hictoae of milk ferments; it breaks up into alcohol and lactic acid, hence the souring of milk. It reduces solutions of copper salts, but less perfectly than dextrose, and is dextro-rotatory. iBOrit. CHifO.. ^^ , „ , This substance has been obtained sparingly from the muscle^lls of the heart and from some bther organs. It crystallizes m rhombic prisms; readUy soluble in water but insoluble in alcohol and ether. 'Hus sugar has no specific action on Ught, and is susceptible ot the laattc fer- mentation. Dextrin. C«Hi*0*. This substance may be formed by the action of dilute acids on starch, or by the action of diastase on the same body. It is strongly dextro- rotatory, does not reduce solutions of copper salts, gives a red color with iodine, is soluble in water, and precipitated by alcohpL It is a product of both artificial and natural digestion. By the action of acids and ferments on starch, certain modifications of dextrin are formed. Of these, erythrodextrin becomes sugar by the continued action of ferments. Achroodextrin remains unaltered and is characterized by giving no red color with iodme. It may be converted into dextrose by boiling with dilute hydrochloric_^acid. Olyeogen. C«H>«Of. This substance is pretty widely distributed in the oi^ns of the body especially in the mammalian foetus, and is found in abundance in the liver of the adult in both vertebrates and invertebrates. Olycogen when pure is white, amorphous, tasteless, easily soluble in water, insoluble in alcohol and ether, highly dextro-rotatory, and does not reduce metallic oxides. It is changed by the digestive ferments into a form of «ugar and of dextrin, and gives a red (port-wine) color with iodine, which ^s- appears on warming but returns on cooling, by which latter it is distin- MVMpUMWK'nXAM 6S0 ANIMAL PHrSIOLOOr. guished from dextrin. It is best extracted from the liwr, removed as Hoon as possible after killing an animal and minoed, by boiling water, then inuifled and precipitated. Twkidii. CtHuO*. This body is closely allied to the cellulose of plants, and forms the greater part of the integument of ascidians or tunioites. like ohitin, it is extremely insoluble. '" Fats, Fatty Acids, bto. General formula of series : C.Hk(X or C.H„^,.€X)bH. The fatty acid series answers to ttie series of monatomic alcohols: thus, formic acid corresponds to methyl alcohol, and acetic acid to ethyl or ordinary alcohol. C5.H«0 + O. = C.H«0. + H.0, or O.H..OH + O. = CH..OO.OH + H.O. From which it appears that O has taken the place of Ht in the alco- hol to form the acid— i. e., the acid is an oxidised alcohol. The lowest, members of the line are vob^le liquids with strongly acid reactions. As the series is ascended, fluidity diminishes, and finally the acids are solids, greatly resembling the neutral fata in appearance. The derivatives of the fatty acids are very important in the animal economy, but the free acids occur sparingly. PonnioMdd. H.COtH. A strongly corrosive liquid, boiling at lOO" C, solidifying at 0°, and mixing readily with water and alcohol. It has been extracted from various organs. Aoetie add. CH«.CO«H. An acid liquid of characteristio odor, boiling at 117' C, solidifying at 5** C. BeadUy miscible with alcohol and water. It often occurs in the stomach, from fermentative changes. Fropimiie Mid. CtH>.C99H. Resembles acetic acid, soluble in water and boiling at 141° 0. It is found in perspiration, the stomach, diabetic urine when ferment- ing, etc. ' Botyrifl add. C>Ht.COtH. An oily, colorless liquid, with the smell of rancid butter, soluble in water, alcohol, ether ; and boiling at 162' C. It is found in sweat, faeces, urine, and the contents of the' large in- testine. ▼ali^iuiie aeid. C.H..CO.H. An oily liquid of strong smell and taste, soluble in water, and more so in alcohol and ether. It is found in solid excrement In fatty de- generation of the liver it may occur in the urine, as a result of the decomposition of leucin, which appears in abundance in the urine in the above disease. DUIi i ll-llM I IW ' J I WllfW — !-»;WTO«ww» P WlHI'U li l-le in water and . water. Tauro- .0. le human body. ) extracted from which it forms a tod and especial- . solution in hot n and heated, or hich changes on of the camiTora >m which it may lition, by extract- tted with nitrous acid it undergoes a series of oxidations, giving rise to distinct products of which one is the green biliverdin. These oxidations are the basis of QmdM» test for bile-pigment, which consists in adding a drop of strong nitric acid containing nitrous acid to bile, when a series of rather rapid changes in color in a certain order takes place. BiliTtrdin. C»Hi.N.04. It is this pigment which gives the characteristic color to ox-gall, from which it is best prepared. It is not soluble in ether or chloroform, but dissolves readily in alcohoL In all probability both the bile-pigmente and their derivatives are the result of the final transformations of haemoglobin. Chdtteliii. CuH..N.O*. This is the final product of the oxidation of bilirubin. Hydrobilirnbin. CnHulftO,. When an alkaline solution of bilirubin is acted upon by sodium amal- gam, the above results. It is thought by many to be identical with ster- cobilin, a product of the decomposition, etc. , of bile in the intestine. Since hydrogen in the nascent condition probably occurs in the intestines as the result of fermentations, the conditions for the formation of this sub- stance seem to be met. Pigmentg of Urine, It seems to bo more than probable that the urine contains a great number of pigments. But few of these, however, have been isolated. The best known are the following: XTrobilin. C.iH«.N«0.. The formulae of all these bodies are but indifferently known. Urobilin is thought to be identical with hydrobilirnbin. It is pres- ent, but in small quantities, in normal urine, though often largely in the urine of febrile conditions. It is supposed to be an oxidized form of chromogen. ITroerythrin. Supposed to abound in the urine of rheumatic patients. It becomes greenish on addition of caustic alkali, and reddish or reddish-yellow when concentrated hydrochloric acid is added. The Indigo Series. Indioui. CmHiiNOii. Some regard indican as indoxyl sulphuric acid, which does not occur in the free state, but as a salt of potassium. It represents in the urine the indol of the alimentary canal. Indigo. C>«HitN«Ot. It occasionally occurs in sweat and urine as an oxidation product of indican. It may be obtained from human urine, and still more readily from that of Uie herbivora, by the cautious addition of a weak solution of ■^'»i/.i-7,*i>i:Jf'^\ii:r.: f. iitf»^^^^'^~y'. 686 ANIMAL PHYSIOLOGY. chlorinated lime to some urine to vrhich an equal bulk of strong hydro- chloric acid has been added. Unless gfreat care is employed in mixing up the fluids, in the drop-by-drop addition of the solution of chlorinated lime, the indigo-blue will be oxidized (bleached) to indigo-white. "riie substance is soluble in chloroform which, being heavy, falls to the bottom of the glass and carries with it the indigo. IndoL CHtN. A substance to which the odor of fasces is in part due. It occurs in artificial and natural pancreatic digestion as a product of the action of bacteria. It is crystalline, soluble in boiling water, alcohol, and ether. Its alcoholic solution when nitrous acid is added gives a red color and j its aqueous solution a red precipitate. SkatdL C.H.N(?). A substance occurring under the same circumstances as indol. It does not give the same reactions with nitrous acid as indol, but gives a violet-red color, when in urine, on the aidd'tion of concentrated hydro- chloric acid. It may, like the preceding, be obtained in crystalline form. NrntoaBNOus Metaboutis. As may be gathered by a perusal of the chaptbr oh the metabolism of the body, the nitrogenous metabolism, while most interesting and important, presents problems which as yet are in great. part unsolved. However, something more of the nature of certain nitrogenous chemical compounds, either occurring in the body or related to such as are pw serj, may now be considered with advantage. Vreft. CO ,/NH, nNH» Urea may be regarded as the' most important and by far the most abxmdant solid of the urine of man and many other mammals, includ- ing practically, so far as known, all the camivora and several other groups. It also occurs to a slight extent in the urine of birds. It is found in small quantity in blood and many of the fluids of the mam- malian body, though not at all or to but the smallest extent in muscles. It may be prepared from urine and obtained in colorless needles, soluble in water and alcohol, but not in anhydrous ether. When urine decom- poses, urea, possibly \mder the action of a ferment, becomes ammonium carbonate: CO(g|; -I- H.0 = (NH.).CO.. Urea may be made in the laboratory in several ways, some of which are indicated in the following equations: 1. By heating ammonium carbonate: ^"\ONH* - CON.H. + H,0. S. By heating ethyl carbonate with ammonia: CO(gg;|; + 2Nfl. = CON.H« + 2C.H.0. APPENDIX. 687 f strong hydro- oyed in mixing of chlorinated >-white. ' heavy, falls to e. It occurs in of the action of Dhol, and ether, a red color and «8 as indol. It idol, but gives a entrated hydro- 1 in crystalline the metabolism interesting and part unsolved, ^nous chemical h as are prrseiii by far the most ammals, includ- id several other ) of birds. It is ids of the mam- tent in muscles. I needles, soluble len urine deoom- >mes ammonium me of which are ). 3. By addition of water to cyan-amide: CN.NH. -H H.0 = CON.H4. 4. By evaporation of ammonium cyanate in aqueous solution : CN(ONH.) = CON,H«. The last reaction possesses a historical interest, for it was by tiiis method that an organic compound occurring in the animal body was first formed from inorganic substances in the laboratory by Wohler in 1828. Urea forms compounds with acids, the most interesting of which to the student of animal chemistry is the following: ^Vrea nitrate. CH4N.0.HN0t. When urine is concentrated, and strong nitric acid added cautiously, the above crystallizes out in glistening six-sided or rhombic tablets, solu- ble in water, but insoluble in ether. This makes a reliable and fairly delicate test for the presence of urea. ITricaeid. C»H«N40.. This metabolite occurs in the spleen and several other organs and tissues; sparingly in the urine of noan and most mammals; abundantly in that of birds and serpents, in which it takes the place of urea. In its purest form it presents itself as a colorless crystalline powder, tasteless and odorless. Its crystalline forms, arising spontaneously from urine, are very variable and always colored. Very insoluble in cold water, ether, and alcohol ; readily soluble in sulphuric acid, caustic alkalies, and some of their salts. The most important salts of uric acid are the urates of sodium, potassium, and ammonium, all of which occur in urin- ary sediments. The mureaeid teat for uric acid is as follows: Add strong nitric acid in very small quantity, and evaporate to dryness, when a red color should appear, which on addition of ammonia gr.ves rise to a purple. The following equations will show the relations oi uric acid to urea, etc., so far as laboratory reactions are concerned. We have in the body of the work shown that uric acid is not in all probability itself an anteced- ent of urea in the body: C.H4N4O. + H,0 -f O = C«H,N.O« -t- CN.H«0. Urioaoid. AUozmi. Urea. C4N,H.0« + 2H.O = CHtOt + 0N,H40. Alloxan. HeBozaUc ticid. Urea. CtH4N40. -I- H.0 -I- O = C«H.N40i -I- CO.. Uric acid. Allantoin. C4H.N«0. + H,0 = CH4N.O -I- C.H4N,0. Allantoin. Urea. AUanturic acid. Uric acid has been made artificially by fusing together urea and glyoo- cin (glycin, glycocoll, or amido4oetic acid) : OiMtin. C4H*NiOi. This body may be abstracted from dead muscle, and obtained either in a white amorphous condition or in rhombic prisms, soluble in cold 688 ANIMAL PHYSIOLOGY. water and in ether; less so in alcohol. Creatin maybe changed into urea and sarcosin or methyl-glycin : C.H.N,Oi + H.0 = C.H,NO. + CON.H4. Creatin. Barcorin. Unsa. It may also be formed synthetically under the action of acids. Creatin may by dehydration be transformed into creatinin. Cieatiiiin. CiHiNiO. This body may be regarded as dehydrated creatin. It occurs nor- mally in fleah and urine, and may be obtained in prisms; soluble in water and alcohol, but not appreciably in ether. It acts as a strong base, the most important salt being the zinc chloride (C«HtNtO)iZnCli. • AUutoin. C4H.N.O.. ,.. ^ 1.. V A body characteristic of the allantoic fluid of foetal life, and which may occur in tiie urine. Its relations to uric acid and urea have been indicated above. Eyposaatllill (sarkin). CiHiNtO. Occurs in flesh, in the spleen, liver, medulla of the bones, etc. It may be obtained in One needles, soluble in hot water. Xuthin. C.H.N«0.. May be derived from muscles, the liver, spleen, thymus, and some other organs and tissues. It is probably a normal constituent of the urine in minute quantity. It may be obtained as a colorless powder, only slightly soluble in water, but soluble in dilute acids and alkalies. Xanthin may be regarded as the oxidized form of hypoxanthin. Oumiii. CtH.N40t. , . , ui Occurs in extinct of flesh, and may be obtained in crystals, insoluble in alcohol and ether, but slightly soluble in cold water, and more so in hut water. GKuiiin. CiH«N»0. ^ * v j \ •* So called because first obtained from guano (excrement of buds); it is. however, also to be extracted from several organs and tissues; as a white amorphous powder, insoluble in water, alcohol, ether, etc. By treatment with nitrous acid it may be converted mto xanthin. Kymreiiit add. CmHkNiOi. This body has been found in the urine of dogs. Qlydli. (Glycocoll, glycocin, amido-acetic acid.) CiH.NOt, or «TT /NHt *^»nOO.H- This is one of that important class of compounds, the iunido-acid% and may be formed m tiie laboratory from mono^hlowicetio acid and ammonia: C.H,C10, + 2(NH.) - C.H.(NH.)0(0H) + NH.a. It is peculiar in having both acid and basic properties-i. e., it unites with both acids and bases to form crystallimble compounds. Olyc™ itself may be obtained in crystalline form soluble in water. Though APPENDIX. 689 le changed into I acids. Creatin It occurs nor- isms; soluble in acts as a strong ,H,N.O).Znai. I life, and which I urea have been le bones, etc. It lymus, and soine Dnstituent of the rolorless powder, ids and alkalies, izanthin. irystals, insoluble r, and more so in nentof birds); it and tissues; as a 1, ether, etc. By an thin. ) CiHiNOi, or I, the amido-acids, lor^cetio acid and des— i. e., it unites mpounds. Glyoin n water. Though C«HJf,0., or C.H.(NH.);^J^*-i. e., not found in the free state as yet in the body, it may be split off from bile acids and hippuric acid. Taflrin. CHtNOiS, or C.H<|^^. This is an amido-isethionic acid, and may be made artificially by a laboratory synthesis, as well as derived from the taurocholic acid of the bile. It assumes the form of large prisms, soluble in water, and is a remarkably stable compound. Taurin has been extracted from several organs of the mammalian body. Lendn. O.H..NOi or OH., CH..CH,CH..C5H(NH«).C0.H— i. e.. an amido-caproic acid. This compound, which may be obtained from the pancreas, spleen, thymus, and thyroid bodies, the liver, etc., and occurs as a product of natural and artificial pancreatic digestion, and in the urine in acute atrophy of the liver, in thin whitish, glistening, flat crjrstals, soluble in water. Leudn is one of the chief products of the decomposition of nitrogenous (proteid) matter. A^angin, AmidiMmodiuunie add. Found in many plants— as asparagus, licorice, haets, peas, beau , etc. —but not in the animal body, so far as is yet known. AMgutio add (or Amido-succinic acid). C«H,NO« orC.H.(NH.)(gg|g. Found, like the preceding, most abundantiy in seeds, but said also to occur, in minute quantity, among the products of pancreatic digestion. Olvtaminio add. aH.N04. Seems to occur, under similar natural conditions, to those giving rise to the preceding compound. It has not, however, as yet been shown to arise in tiie digestive processes of animals. Ojitin. CHrNSOi. By some chemists this compound is believed to be an amido-add. It appears occasionally in the urine, but is chiefly of importance as making up the greater part of certain urinary calculi in men, dogs, etc. The body is crystalline : insoluble in water, alcohol, and ether, but soluble in ammonia, other alkali^ and the mineml acids. Acids of the Benzine or Aromatic Seriea. Buuoieadd. C.H».CO.H. The add itself is not known to exist in the body, but may arise in urine, especially that of the herbivora, from fermentative decomposi- tion : O.H.NO. + H,0 = C,H.NO. + C,H.O.. HIppurioMrid. Oljcin. BenioioMid. Benzoic acid is very sparingly scluble in water, but readily dissolved by alcohol and ether. 44 690 ANIMAL PHYSIOLOGY. Hippuio add (Bemoyl-Glycin, or Bensoyl-amido- acetic Acid). This acid abounds in the urine of the herbivora, being derived, proba- bly, from some benzoic r«ddue in the food (hay). It occurs m only smaU quantity in tiie urine of man. It may be obtamed m pinsms, solu- ble in boiling water and in alcohol. Fhend (Carbolic acid). C.H..OH. This compound occurs under the same circumstances as mdol in the alimentary tract, and may be extascted from the fseces and the urme. SUghtiy soluble in water, it readily dissolves in alcohol and etiier. This substance, the molecular constitution of which is still m doubt, is certainly an aromatic body, which may be obtained in needles ; solu- ble in hot water, acids, and alkaUes, but insoluble in alcohol and etiier. Tyrosin occurs with leucin in ttie decomposition of protaids, and abundantiy in tiie natiind and artificial digestion of tiie proteids, by teypsin. A substance greatly resembling it has been made arbficudly, in the laboratory, by a syntheos. I ^ io-aoetio Acid). ig derived, proba- t occurs in only d in piHsms, solu- } !e8 as indol in ihe is and the urine. 1 and ether. 1 is still in doubt, in needles ; solu- loohol and ether, of protsids, and f the proteids, by tade artificially, in INDEX. Aberration, chromstie, 578. spherical of the lens, 572. Absorption of digested food, HI by lymphatics, 841. l^ skin, 418. Accelerator nerves of heart, 370. Accommodation of eye, 5irth, 181. liration, 400. intoiy systemtt, man, mal kingdom, 88. istinguishing chatme ,188. >gioal, blood, 168. Clinical and Pathological, taste, 035. spinal nerves, 687. cranial nerves, 689. voice, 646. speech, 651. Coagulation of the blood, 157. Coitus, 181. Collateral fibers, 510. Color-sensations, 588. Color-blindness, 586. Columns of TQrck, 488. Burdach, 489. Gall, 489. Commissural fibers in brain, 518. Comparative re blood, 143. heart's pulsations, 243. pulse, 861. circulation, 868. capillaries, 881. digestion, 896, 819, 867. teeth, 804. saliva, 80a bile, 814. stomach, 880. swallowing, 885. vomiting. 889. movements of lymi^, 848. respiration, 875. hemoglobin, 889. protective f nnction of skin, 818. respiration by skin, 415. kidney, 419. urine, 486. fM,445. heat, 468. spinal cord, 405. vision, 687. hearing, 616. smell, 688. .tMte,686. voice and speech, 647. locomotion, 660. Conjugation, 17. Oonstitution of animal body, 187. Constitution, chemical, of the animai body, 186. Constituents of dead muscle, 198. Contraction, tetanic, 188. a single simple muscular, 178. law of, 19a of pupil (myosisV 671. Contrast, 687. Go-ordination, 490. of the two eyes in vision, 691. Corpuscles, composition of, 155. Corpus luteiini, 118. striatum, functions of, 686. Corpora quadrigeiAhia, functions of, 589. striata, 518. Coughing, 406. Cranial nerves, 68a Cramp, 806. Creatin, 197. 087. Creatinin, 446. Crura cerebri, functions of, 541. Crusta,588. Crying, 406. Curve, the muscle, 180. Cystin,689. Death, 66a Decussation, 480. Defecation, 887. Deglutition, 880. Dentition, 666. Deyelopment, physioloj^cal aspects of, 118. post-embryonic, of blood-cells, 158. Dextrin, 679. Dextrose, 678. Diapedesis, 881. Diastole, 840. Diabetes, artificial, 486. Dicrotic, 849. Dioidua vera, scrotina, reflexa, 81. Diet, 468. tata and carbohydrates in, 467. salts, etc., in. 45a pathological, 450. Diffusion-circles 665. Differentiation of unicelluhir animals, 80. Digestion of food, 890. comparative, 806, 819, 867. pathological,'B67. summary, 864. Digestive juices, 806. action of bile, 818. organs, self-digestion of, 887. movements, 881. evolution, 308. system, man, 664. Dilation (mydriasis), 672. Dioptrics of visioUi 66a ANIMAL PHYSIOLOGY. Direct obiervation, method of, 141. oerebellw tnots, 488. Discus proligeriu, 58. Divisions o£ food-stuffs, aW. Dreaming, 627. Ductus venosus, 104. Dyspnoea, 887. Ectoplasm, 7. Efferent nerves, 482. Elasticity of muscle, 187. Blastin,677. Electrical phenomena of moMle, loo. organs, 199. Electrodes non-polariaable, 189. Blectrotonus, 197. Embryo, 54. development of, 90. Bmbryologioal, alimentory traot, 295. nerrooa system, 542. virion, 502. Endoplasm, 7. End-plates, nerve, 170. End-bulbs of Krause, 540. Energy of the animal body, 459. Entoptic phenomena, 574. Epiblart,98. Estimation of the slw and distance objects. 605. Eustachian tnbe, 600. Evolution of vascular system, 285. digestive organs, 868. respiratory organs, 400. uric acid, 448. digestion, 468. spinal cord, 496. nervous system, 048. evidences of, 48. placenta, 89. organic, reconsidoced, 127. vision, 600. ▼oioe and speech, 662. locomotion, 662. hearing, 616. Excretion of perspiration, 416. by kidney, 419. pathological, 864 Experimental, reflex action, 212. Expulsion of urine, 429. Extractives of muade, 194. Bye, optical imperfections of, 572* protective mechanisms, 696. PiBce8,858. Fallopian tube, 114. Fatigue, 200. Fats, the, 189. peculiar, 140. In milk, 292. Pat, the construction of, 440. formation of, 441. pathological, 446. comparative, 445. Feeding experiments, 454. Ferments, unorganised, 160. ^ Fibrin, 676. Fibrin-ferment, 160. Fibrinogen, 159, 674 , Fission, 11. FoBtal circulation, 108-118. Food, digestion of, 290. , special considerations, 868. Food-stuffs, divisions of, 290. Forced movements, 604 Formic acid, 680. Prog, the rheoscopio, 191. Fungi, 16. Ganglia, cardiac, 278. Ganglion, ciliary, otic, etc., «l. of Gas-pump, mercurial (Ludwig^s), »J4. Gases, foreign in respiration, 892. Gastric juice, 806. characters of, 809. Oastmla, the, 66. Gelatine, 677. Gelatine in diet, 467. Gemmation, 11. Germinal vesicle, 54. spot, 64 ridge, 57. Globin, 674 i Globulins, 674 I Glomerolas, 42. Glyoin, 688. Glycocholio aoid, 812. Glyooooll (glycln), 812-. Glycogen, 482, 679. uses of, 484 pathological, 485. Olutaminic acid, 689. Goll, columns of, ^9. GolU, experiments of, 628. Graafian follicles, 57. Gray matter of cerebrum, 512. INDEX. 696 of.4ML 1.464. sed,160. 08-118. 890. ions, 858. M of, 390. 504. 0,191. itic, etc., 681. ial (Ludwig'8), 884. ispintion, 889. B5. its of, 538. ^67. etebmm, 512. Unphic method, applications of, 171. Growth St different periods, 6tt8. j Guanin, 688. Habit, the law of, 4a Hnmatoblasts. 149. Hsmatin, 889. Hninin, 889. Hnmoglobin, 885 comparatire, 889. Hearing. 604. ^ Heart, the mammalian, 317, 383. the action of, 338. impolco, 388. sounds, eausea of, 386b work, 341. nenrons system in relation to, 361. beat, causation of, 370. aooelerator, nerves of, 885. Heat, animal. 461. comparative, 463. production of, 465. pathological, 467. Heat-producing power of foods, 460. Hermaphroditism, 35. Hibernation, 465, 470, 537. Hiooough, 407. Hipporio add, 4^. Holoblaatio, 70. Homotothermer, 465. Horopter, the, 694. HypluB, 15. Hypemoea, 897. Hydra, 33. Hydrobilimbin, 686. Hypnotism, 538. Hypoblast, 69, 98. Hypozanthin, 688. Imperftetions of visual perceptions, 587. Impulse of the heart., 388. Impulses, path of, in spinal cord, 481. Indioan, 686. Indigo seriee, 685. Indol, 818, 686. Induotorinm, Du Bois-Reymond's, 176. Influence of pigment of macula Intea, 689. Infusoria, 83. Inhibition, venous, 316. of reflexes, 485. Inosit, 679. Interoerebral fibers, 518. Internal capsule, 586. Intestinal movements, 887. Inspiration, act of, 870. Irradiation, 587. Irritability of muscle and nerve, 168. Juice, gastric, 806. pancreatic, 815. Juices, the digestive, 806. characteristics of, 807. KaryokinesiB, 6, 66. KataoroUo pulse, 349. .' Kathode, 197. Keratin, 67a Kidney, excretion by, 419. comparative, 419. Kymograph, 381. Kynurenic acid, 688. Latent period, 181. Lardacein, 677. Laughing, 406. Law of contraction, 196, rhythm, 300. Lecithin, 688. Lenticular nucleus, 686, Leuoin, 816. Leuoooytes, 160» Liquor amnii, 74 sanguinis, 150. Liver, metabolism of, 490. Localisation, in cerebral cortex, 638. 680. Locomotion, 665. Looomotor ataxia. 490. Lymph, 843. movements of. comparative. 848. Lymphatics, absorption of food by. 841. Macula lutea. influence of pigment* of, 588. Malpigfaian tubules. 431. Maltose, 679. Man at different periods of his existence. MB Man's place in the animal kingdom, 86. Maturity (puberty), 666. Mastication, 883. Maximal stimulus. 185. Medulla oblongata. 543. M«ia)fflNMJknDpapi, 606. 696 ANIMAL PHYSIOLOGY. Membnuien, embryonio, of birds. 72. foDtal of mammal, 76. Menstniation, lltt. Heroblaatic, 70. Meaoblast, 98. Mesonephrofl, 100. Metanephroa, 100. MeUbolism, the. of the body, 481. of the liver, 482. of the apieen, 480. in formation of urea, urio aoid, hippu- rio acid, etc., 440. proteid, 455. influence of nervooa syttem on, 471. summary ot 470. Meta»>a,5. Methsmoglobin, 880. Micturition. 480. pathological, 480. Middle ear, muscles of, 008. Millc, pioteids of, 291. fats, 292. sugar of. 292, 679. salts, 292. Minimal stimulus, 185. Misconceptions as to comparative size, etc., of objects, 690. Moist chamber, 170. Morphology, definition of, 1. Motor area, 525. . Moyements, cardiac, 282. ciliary, 108. stomach, 885. intestinal, 887. digestive organs, 881. ocular, 592. Mucin, 827, 077. Mucor mucedo, 15. Muoigen, 827. MDllerian duct, 108. Multicellular organism, 22. Munk, experiments of, 524. Muscle, 167. irritability of, 109. onrre, 180. changes in, during contraction, 180. elasticity of, 187. electrical phenomena of, 188. electrical uurrents in, 190. chemical changes in, 192: dead, constituents of, 194. thermal changes in contracting, 195. Muscle, unstriped, 204. comparative, 205. Muscles of respiration, 872. of middle ear, OOH. Muscular note, 184 worlc. 199. sense, 557. energy, sources of, 401. Mydriasis, 572. Myosis, 571. Myograph, pendulum, 179. Myosin, 198, 074 Nerve-supply, 048. Nerves, the physiology of, 197. clinical and pathological, 198. irritability '>f, 109. afferent and efferent, 482. oerebro-spinal, 620. third, fourth, etc., 628, 629. Nervous system, 210. in relation to the heart, 261. relation to respiration, 898. man, 666. Nervous supply, muscles of mastication, 882. Nervous mechanism in the sexual act, 124 Neurin, 688. Neuralgia, 517. Neutral fats, 681. Nitrogenous metabolites, 140, 686. equilibrium, 450. fats, complex, 088. Non-crystalline bodies, 677. Non-crystalline bodies, certain, 188. Non-nitrogenous metabolites, 141. Note, the muscular, 184 Nucleus, 6. Nucleolus, 5. Nuclein, 678. Objects, estimation of sice and distance, 590. Observation, direct method of, 141. graphic method of, 148. summary of methods of, 147. Ocular movements, 592. Old age, 667. Oligemia. 104 Oncograph, 488. Ofisperm, the, 62. fl, certain, 188, Mbolites, 141. 184 Dethod of, 141 ,148. ids ojt, 147. INDEX. 697 Optio thkUmi, S18. Optio th«laniii!i. functions of, S80. Optical imperfectiuns of tlie eye, 572. Oifanio eTolution, 41. Organs, electrical, 100. . Origin, the, of the germs of life, 41. Orary, origin of, 110. Orulation, 116. Ovum, the, 54. origin and development of, 57. changes in, 50. fertilization of, 62. nutrition of, 115. Oxyhemoglobin, 880. Pacinian corpuscles, 552. Pancreatic juice, 815. I'hysiology of secretion, 828. Paraglobulin, 150, 674. Parthenogenesis, 58. Parturition, 120. Patellar reflex, 494. Path of impulses in spinal cord, 401. Peduncles of the brain, 537. Pepnn, 811. Peptone, 810, 815. Peptones, 675. Perspiration, excretion of, 416. Pettenltofer's test, 684. Phenol, 600. Physiology of secretion, 810. sweating, 417. Pigments of urine, 685. Placenta, 80. the discoidal and meta-discoidal, 81. the zonary, diffuse, polycotyledonary, 86. evolution of, 80. Poikilcthermer, 465. Pokur cells of globules, 59. Polyps, 22. Pons Varolii, 518. functions ot 541. Prediorotio, 240. Pressure sensations, 554 Pressures, endocardial, 288. Primitive strealc, 71. groove, 71. Pro-amnion, 78. Production of heat, 465. Pronephros, 06. Pronucleus, female, 00. Protagon, 688. Protective mechanism of the eye, 596. Proteid metabolism, 455, Proteid^ 671. properties and clitssiflcation of the, 673. general characteristics of, 188. classification and distinguishing char- acters of, 188. of milk, 201. metabolism, 455. tests for, 672. coagulated, 675. Protococcus, morphology and physiology of, 11, 12. Protoplasm, 2, 27. Protovertebm, 05. Psychological aspects of vision, 686. Pulse, the, 244 venous, 251. Pupil, alteratior?; in the size of the, 660. Quantity of air respired, 878.' lioctioi time, 586. ' , Redur-^ reaction time, 68^. Refle.- action, 21) functions of sp' ^ cord, 484 time, 486. Reflexes, inhilition of, 485. Ref ■_>, . 11, anomalies of, F .1. Rr rulati '< of temperature, 464 Reijurgitation, 840. Reproduction, 60. Research and reasoning, phyaiologicai, W. Respiratory system, 865. sounds, 870. Respiration, muscles of, 872. types of, 878. comparative, 875. pathological, 870. in the blood, 388. in the tissues, 802. relation of nervous system to, 198. influence of oonditica of blood in, 897. Cheyne-Stokes, 806. effects of variaMoas in atmo^teric pressure, 390. influence on circulation, 400. clinical and pathological, 408. evolution, 400. Resting stage of ovum, 65. f 698 ANIMAL PHYSIOLOGY. Rhythm, law of, 206. .' - in nature, 86. appetite, 863. respiratory, 879. Retina, affections of, S78. Retinid stimulation, laws of, 580. Rigor mortis, 192. Rheoscopic frog, 191. Rouleaux of blood-cells, 158. Saliva, 806. amylolytic action of, 806. of parotid gland, 807. comparative, 806. pathological, 806. Salivary glands, physiology of secretion of, 819. Salte of milk, 292. Sarcolemma, 170. Secretion, physiology of, 819. nature of the act of, 826. of urine, 426. Segmentation of ovum, 66. Segregation, 180. Self^digestion of digestive organs, 829. Semicircular canals, co-ordinating', func- tions of, 502. Sensation^ visual, 576. Senses, general remarks, 646. Sensory area, 525. Serum, composition of, 156. Sexes at different periods, 667. Sexu«l selection, 42. Sighing, 407. Skatol, 686. Skin, functions of, 412. protective functions of, oomparativc, 418. laapiration by, comparative, 416. absorptlim by, 418. as an organ of sense, 451. Sleep, 526. Smell, sense of, 620. Sneenng, 407. Sobbing, 406. SoUdity in vision, 595. Somatopleure, 74. Somnambulism, 529. Sound, cardiac, MArey's, 284. Sounds, cardiac, 285. respiratory, 981. Special considentioiu as to food, 868. Special considerations as to digestion, 468. vision, 597. hearing, 616. voice and speech, 652. Spectrum of hsm^globin, 886. SpermatojioOn, 62. origin of, 61. Speech, 6tt. consonants, 650. Spherical aberration, 672. Sphygmograph, the, 247. Spinal nerves, 626. cord, 480. i reflex functions of, 484. as a conductor of impulses, 487. automatic functions of, 498. comparative, 496. evolution, 496. Splanchnopleure, 74 Sporangia, 16. Spleen, metabolism of, 486. nervous system's influence on, 489. pulp, comparative, 487. Stasis, 281. Starvation, influence on metabolism, 460. Steapsin, 810. Stimulation, laws of retinal, 681. Stimulus, 170. maximal, 186. minimal, 186. 8ub-maximal, 186. Stomach of ruminants, 800. : physiology of secretion by, 828. comparative, 880. movements of, 886. Subjective phenomena, 691. Suoous enterieus, 817. Summary of physiology of blood, 166. muscle and nerve, 208. oinulation, 286. digestion, 856-864. respiration, 410. fniwtions of the skin, 413. ' urine, 480. reproduction, 60. voice and speech, 668. spinal cord, 497. functions of the brain, 648. of evidences of evolution, 47. Swallowing, comparative, 884, 886. Sweating, 416. physiologj of, 417. •*- INDEX. 699 as to digestion, 468. (2. bin, 386. 573. 47. 1,484. impulses, 487. >iis of, 498. ,486. flaence on, 480. 487. }n metabolism, 4G0. etinal, 681. 8,800. ;ion hj, 888. t, AOl. 17 of blood, 165. 108. ii,4ia tin, 548. ution, 47. Ave, 884, 885. Synopsis, brief, of physiology of vision, 602. physiology of hearing, 620. Systole, 240. Tactile sensibility, 556. Tambour of Marey, 177. Taste, sense of, dSXS. Taurin, 812. Ttturocholio acid, 812. Teeth, comparatire, 804. Tegmentum, 688L Temperature, influence of, oh muscle, 202. regulation of, 464. Testes, 61. Tests for proteids, 672. Tetanic contraction, 188. Thermal changes in contracting muscle, 195. sensations, 554. Thoracic breathing, 878. Time, cerebral, 586. Tissues, the contraotile, IW. respiration in, 892. oomparatiye, 167. Traube-Hering curree, 408. Trypsin, 816. Tunicin, 680. TQrbk, columns of, 488. Types of respiration, 878. Tyrosin, 816. Unicellular animals, 20. Umbilical vesicle, 72. Urea, 4M, 686. and uric acid, metabolism, in forma- tion of, 446. nitrate, 687. Urie acid, 448. evolution, 448. ^ Urine, chemically and physiologically considered. ^2. quantity, 428. constituents of, salts of, 424. abnormal, 425. oompuative, 43)6. secretion of, 426. expulsion of, 439. pigments of, 685. UrobiUn, 686. Uroerythrin, 685. Urogenital system, development of, 106. Uses of glycogen, 484. Vagus, influence on the heart, 266. Valves of the heart, 219. Valvulaa conniventes, 857. 'Variations, functional, in muscle, 207. of cardiac pulsation, 242. Vascular system, evolution of the, 285. development of the, 108. Vaso-motor influences, 277. Vas deferens, origin of, 110. Veins, 221. valves of, 222. Velocity, the, of the blood, 224 of nervous impulse, measurement of, 181. Venous pulse, 261. Ventricles, of the heart, 218. \ ision, 569. embryological, 502. dioptrics of, 568. psychological agptat oi, 588. synopsis of physiology of, 602. astigmatic, 678. spherical aberration of, 572. chromatic aberration of, 578. entoptic phenomena of, 574. anomalies of refraction of, 674. sensations of, 676. affections of the retina in, 578. psychological aspects of, 686. oo-ordin&tion of the two eyes in. 691. estimation of solidity by, 695. Visual sensations, 576. impulses, nature of, 580. angle, SS2j -perceptions, imperfections of, 587. VitelUn, 674 Vitelline membrane, 65. Voice and speech, 689. registers and falsetto, 644 pathological, 646. comparative, 647. •volution, 652. summary, 652. Vomiting, comparative, 888, 889. pathological, 889. Wolfllan duct, 08, 100. bodies, 100. Work, muscular, 199. of the heart. 241. 700 ANIMAL PHYSIOLOGY. 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