QP3V 7^ Columbia SBnttiem'tp COLLEGE OF PHYSICLiNS AND SURGEONS LIBRARY Digitized by the Internet Archive in 2010 with funding from Open Knowledge Commons http://www.archive.org/details/humanphysiologysOOdrap HUMAN PHYSIOLOGY, STATICAL AND DYNAMICAL; OK, THE CONDITIONS AND COURSE LIFE OF MAN. JOHN WILLIAM DRAPER, M.D., LL.D. PROFESSOR OK CHEMISTRY AND PHYSIOLOGY IN THE UNIVERSITY OF NEW YORK. ILLUSTIlATEl) WITH NEARLY 300 WOOD ENGRAVINGS. NEW YORK: HARPER & BROTHERS, PUBLISHERS, FRANKLIN SQUARE. 1856. Entered, according to Act of Congress, in the year one thousand eight hundred and fifty-six, by HARPER & BROTHERS, in the Clerk's Office of the District Court of the Southern District of New York, PREFACE. The publication of the text of the Lectures on Physiology which the author has given for many years in the University was originally con- templated at the repeated solicitation of his pupils, who have felt the ne^ cessity of having an outline of the science in its present state sufficiently brief for their use. There are some advantages attending such a publication of matter which has been employed in Lectures. Among these, condensation or compactness may be particularly mentioned. It is not possible to in- struct, for any length of time, classes of many hundred persons without detecting the more obvious imperfections of the course. An intelligence quickly springs up between the professor and his audience, which un- mistakably indicates to him where he is too diffuse and where obscure. But there are also disadvantages, more especially where Lectm'es are not read, but delivered orally from a text. Such a text, if published, will show many obscurities in its descriptions which were perhaps re- moved in the discourse. To write a complete treatise on Physiology demands an extent of knowledge possessed by very few men. What science is there which is not involved in explaining our structure and functions ? Anatomy, Chem- istry, Zoology, Botany, Geology, the various branches of Natural PhUos- ophy, which themselves require as their foundation ]\Iathematics. Well, therefore, may the author of this book, in view of his own imperfections as tried by such a standard, express his opinions with hesitation, and, at the conclusion of his labor, feel regret that he has ever undertaken a work, the execution of which, with even a moderate success, is so hard, and in which the detection of multitudes of imperfections is so easy. The science of Physiology is the result of the labors of thousands of the ablest men continued for centuries. Though of course, in its ad- vance, physicians have taken the prominent part, it is also under mani- fest obligations to men who did not belong to the medical profession. To recall the names of its many cultivators would have converted the following pages into a scientific history. The author desires to draw liis readers' attention particularly to this point, since he has found him- self constrained, by the plan and size of liis book, to avoid such a course- iv PEEFACE. and may therefore have exposed himself to the imputation of disregard- ing that just tribute of respect which is due to those who have done so much for this science. He trusts, however, that in this he will not be misunderstood, and that his pupils and readers will constantly bear in mind that, beyond the suggestion of a trifling fact or idea here and there, the matter presented is not original with him, but derived from other sources — the author's reading, during many years, of the chief works on Physiology and its kindred subjects. It is, however, proper to remark, that of contemporary works, Dr. Carpenter's different treatises, Todd and Bowman's Physiological Anat- omy, and Kirkes' and Paget's Hand-book, are employed as books of reference in the University. vStudents who are familiar with these ex- cellent works will doubtless recognize, in many places on the follo-^ang ■pages, the effect of their daily use in imparting coincidences of expres- sion. The later volumes of Dr. Carpenter have become encyclopedic in their scope. They are repositories in which may be found all the known facts of Physiology lucidly arranged. As respects recent monographs, the language of the authors themselves is employed wherever it was possible. A list of wood-cuts is annexed, in which reference is given to the sources from which those not original have been derived. In the ex- planations of these engravings, the description used is that of the authors themselves wherever it was possible, and it is incorporated in the text ; as, for instance, in Book I., Chapter XVII., in which, the engravings be- ing derived from the Neui'ology of LeveiUe, the accompanying descrip- tions are merely translations firom the French ; or, again, in Book II., Chapter VII., in Dr. Prichard's statements of the methods of examining the skull. With respect to the original engravings, it will be seen that many have been obtained by the aid of microscopic photography, the process having been so far improved by the author as to be rendered very available for these uses. Among his friends who have taken an interest in his ex- periments on this subject, the author desires particularly to express his obhgations to Mr. Abbott, whose extensive collection of objects has been liberally open to him, and to whose love of science many of the best il- lustrations in this volume are due. Photography is destined to render important services to science as well as to art. Even in the minor application of enabling us to obtain, of any desu-ed size, correct copies of originals, it is of great use. IS^early all the copied engravings of this work have been thus obtamed tlirough the in- tervention of photographs. Having now mentioned the sources from which the material of this book, both textual and illustrative, has been derived, the author will take PEEFACE. V leave to moke a few remarks respecting the manner in which he has iisctl this material, and the general aspect he has given to his work. He has suggested the division of the whole suLject into two branches, Statical and Dynamical Physiology. The expediency of this has been impressed upon his attention by the necessity of conforming his course of Lectures to the wants of a medical class. The physician is chiefly concerned with the conditions of life — the organic functions, as diges- tion, respiration, secretion, etc. The doctrines of development, and the career of an organic form, are of less pressing interest. But it was very soon found that other advantages were derived from this subdivision, as might indeed have been expected, from its conformity to the usages of writers on other branches of Physical Science. Doubtless, if such a sep- aration be accepted by physiological authorities, it will tend to the more rapid progress of both portions of the subject, by imparting to each a more definite office. Throughout the work Physiology is treated after the manner known in Natural Philosophy. It was chiefly, indeed, for the sake of aiding in the removal of the mysticism which has pervaded the science that the au- thor was induced to print this book. Alone, of all the great departments of knowledge, Physiology still retains the metaphysical conceptions of the Middle Ages, from which Astronomy and Chemistry have made themselves free. To exorcise it from such nonentities as irritability, plastic power, vital force, is the duty of the rising generation of physi- cians. It is also their interest. Empiricism will never be banished from the practice of medicine until Physiology is made an exact science. The reader will also find that the opportunity is taken, wherever it oc- curs, of directing liis attention to those arguments which the subject of- fers for elucidating the moral nature of man. Believing that the right progress of society depends on its religious opinions, and observing with concern the growing carelessness which is manifested in these respects in our times, the author has not hesitated to show how advantage may be taken of the facts presented by Physiology. We live in a period of difficulty. Metaphysical Philosophy has lost its hold upon the human mind. The uncertainties, contradictions, and emptiness of the English, Scotch, French, and German schools are manifest. Already the belief is wide spread that their barrenness of result and consequent worthless- ness are the necessary incident of their method of investigation, and that we must look to some wholly new system as a guide to truth on the topics they have had under consideration. That guide is Positive Sci- ence. It would be in vain to discourage the cultivators of Positive Science from attempting the solution of questions which have foiled Speculative Philosophy. The attempt will certainly be made, and will inevitably VI PEEFACE. conduct us to the truth. Our concern should Ibe to direct it from the outset in the right course. The existence of God, his goodness, power, and other attributes ; the existence of the soul of man, its immortality and accountability ; the future life ; our relations to and position in the world ; its government : these are topics with which Physical Science is concerning itself, and from which Physiology can not hereafter be disconnected. In what is said upon these points, the author has ever kept in view the great influence, for good or for evil, which arguments based upon ma- terial and tangible facts exert ; and, without in any instance sacrificing what he believes to be philosophical truth, he has tried to present it in such a way as to be conducive to our highest and most enduring in- terests. If the actions of man are influenced by his organization, his career must be an exposition of his structural condition, and his history a branch of Physiology. In a very imperfect way, the author has attempted an innovation based on these considerations. It is only an outline of the manner in which that interesting and extensive subject might be dealt with. Viewed according to the methods of Positive Philosophy, there are but two classes of facts which can be admitted into our discussions respecting man. They are those which are furnished by his structure and functions, and those which may be gathered from his historical ca- reer. The proper presentation of the latter alone would requu-e a volume. To the medical profession, as matters now stand, nothing is of more importance than the dissemination of physiological knowledge. Empiri- cism could not flourish as it does if the structure and functions of the body of man were better understood. How many advantages would arise if the elements of this science were made a part of general educa- tion in America ! What branch of knowledge has intrinsically a better title thereto ? Is it at all to be wondered at that every kind of medical imposture prospers in communities where almost every one believes that a man has one rib less than a woman, and, even among persons pretend- ing to education, scarcely one can be found who has a distinct idea of the size, shape, and position of his own stomach ? Such a diffusion of physiological knowledge would not only tend to a repression of empiricism, but would also exert an effect in raising the standard of acquirement among medical men themselves. That a great revolution is impending in the practice of medicine, no one who is at all observant of the progress of science can doubt. The great physicians of the future will be the great physiologists. He who can best correct the imperfections of a macliine is he who best knows its structure and action. Why is it that from Astronomy, Chemistry, Mechanical Engineering, PKEFACE. Vll and such other subjects, empiricism has disappeared,? Is it not because exact knowledge has taken the place of speculation and mysticism ? The delusions of Astrology, Alchemy, and Magic have been unable to main- tain themselves against simple truth. And so of the numerous medical impostures of our times, they will die out as an exact knowledge of the structure and functions of man prevails. That this volume may aid in removing the great and noble science on which it treats from Speculative, and in attaching it to Natural Philoso- phy — that it may assist in establishing the great doctrine of the par- amount influence of physical laws over organization, is the earnest de- sire of the author. Conscious of the shortcomings of his work, he sub- mits it to the scientific world with hesitation, yet not without the hope that its errors and imperfections will be excused for the sake of the ol> ject it proposes to attain. C N T E N T S. B O O K I. STATICAL PHYSIOLOGY. CONDITIONS OF LIFE. CHAPTEE I. Conditions of Life. — Natwe and Sources of Substances supplied to the Body. — Annual Quantities required. — Table of Physiological Sta7idards. — Animals do not create, but transform Substan- ces. — Properties and Quantities of Matters received by the System. — Properties and Quantities of those it restores. — Heat of the Body arises from Combustion. — Cooling Agencies in an An- imal. — Necessity of Repairs in the System. — Physical Aspect of Man. — The Soid. — The Vital Principle, — Importance of Physical Science to Physiology Page 9 CHAPTER IL OF FOOD. Tlie natural Subdivisions of Physiology. — Of Food: its Sources and Classification — its Value not altogether dependent on its Composition. — Of Milk: its Composition, and Use of its Water, Casein, Sugar, Butter, and Salts. — Variations in the Composition of Milk. — Of Bread. — Of mixed Diets. — Of the embryonic Food of Birds. — Nutrition of carnivorous and herbivorous Animak. — Food formed by Plants and destroyed by Animals. — Uses of mixed Food and Cook- ing. — Absolute Amount of Food , , 26 CHAPTEE III. OF DIGESTION. TISSUE-MAKING OR HISTOGENBTIC DIGESTION, Nature of Digestion. — 77/6 Mouth, Teeth, Stomach. — The Salivary Glands. — Different Kinds of Saliva. — Properties of mixed Saliva : its Quantity, Composition, and Functions. — Relation of the Salivary Glands and Kidneys. — Tlte digestive Tract. — The Stomach. — Gastric Juice. — Organs for its Preparation. — Manner of producing Chyme. — Influence of the Nerves. — Artifi- cial Digestion. — Pi-eparation and Properties of Pepsin. — Regional and functionai Divisions of the Stomach in Animah and in Man. — Object of Stomach Digestion. — Peptones. — Use of Salt. — Digestibility of various Articles of Food 40 CHAPTEE IV. OF CALORIFACIENT OR INTESTINAL DIGESTION. Nature of Intestinal Digestion. — Sti'itcture of the Intestine. — Digestive Fluids of the Intestine. — Tlie Pancreatic Juice. — Tlie Enteric Juice. — Juice of Lieberkuhn. — Secretion of Peyer^s Glands. — Bile. — Digestion of the Carbohydrates and Hydrocarbons. — Properties and Varie- ties of Lactic Add. — Doctrine of the Effects of Acidity and Alkalinity of the Digestive Juices. — Illustration of Intestinal Digestion from the making of Wine. — Making of Bread. — Influence of Heat over Ferments. — Comparison of Gastric and Intestinal Digestion. — Changes of the In- testinal Contents. — The Faecal Residues 67 X CONTENTS. CHAPTER V. OF ABSORPTION. Double Mechanisvi for Absorption. — The Lacteak and Veiiis. — Lacteal Absorption. — Descrip- tion of a Villus. — Analogies in Plants. — Introduction of Fat by the Villi. — Tlie Cliyle. — Causes of the Flow of Chyle. — Intermediate Changes on its Passage to the Blood. — Action of Peyer^s Bodies. — Lymphatic Absorption. — Nature of Lymph. — Structure of the Lymphatic System. — Compaiison of Cliyle, Lymph., and Serum. — Function of the Lymphatic System. — Production of Fibrin. — Cutaneous Absorption. — Causes of the Flow of Lymph. — Ajiparent se- lecting power of the Absorbents. — Connection of the Lacteals and Lymphatics with the Locomo- tive and Respiratory Mechanism Page 84 CHAPTER VI. ABSORPTION BY THE BLOOD-VESSELS. Proof of Absorption by the Blood CajAllaries. — Occurs as a physical Necessity . — Nature of Cap- illary Attraction.— Its Phenomena in the Rise and Depression of Liquids. — Conditions for producing a Flow in a Capillary Tube. — Passage of Liquids through minute Pores. — Genei'at Propositio7is respecting Capillary Attraction. — Endosmosis and Exosmosis. — They depend on Capillary Attraction. — Force against ivhich these Movements may take place. — Illustrations of selecting Power. — General Vieiv of the entire Function of Absorption, lactealand venous 102 CHAPTER VII. OF THE BLOOD. T7ie Offices and Relation of Blood in the System. — The Plasma and Cells. — General Properties and Composition of the Blood. — Quantity in the Body. — Coagulation. — Blood-cells. — Their suc- cessive Forms. — Tlie perfect Cell. — Hcematin: its Properties. — Number of Blood-cells. — Plas- ma: its Composition, and Variations of its Ingredients. — Albumen, Fibrin, Fat, Sugar. — Min- eral Ingredients of the Cells and Plasma compared. — Gases of the Blood. — Changes occurring during the Circulation. — General Functions of the different Ingredients of the Blood. — Introduc- tion of Oxygen by the Cells. — Their transient Duration Ill CHAPTER Vni. OF THE CIRCULATION OF THE BLOOD. The Heart as a Machine. — Inadequacy of Harvefs doctrine of the Circulation. — Physical Prin- ciple of the Circulation; applied in the case of a Nucleated Cell, Pervious Tissue, Motion of Sap and of Blood. — Dependence of the Circulation on Respnration. — Forms of Circulation : Systemic, Pulmonary, Portal. — Description of the Heart ; its Movements. — Their Force, Num- ber, and Value. — Sounds of the Heart. — Cause of its Contractions. — Description of the Arte- ries, Capillaries, Veins. — Explanation of the Circulation of the Blood. — Facts supporting it. — The First Breath 129 CHAPTER IX. OF RE SPIRATION. Resjnration introduces and removes aerial Substances. — Coalescence of B^spiratoi-y and Urinary Organs in Fishes. ^Physical and chemical Conditions of Respiration. — Interstitial Movements of Solids, Liquids, and Gases. — Condition of Equilibrium in the Diffusion of Gases. — Con- densing Action of Membranes. — Forms of Resjnratory Mechanism. — The Lungs of Man. — Tliree Stages in the Introduction of Air : Atmospheric Pressure, Diffusion of Gases, and Condensation by Membranes. — Exchange of Carbonic Acid for Oxygen. — Divisions of the Con- tents of the Lungs. — Variations in the exjnred Air. — Removal of Water. — Effect of ii-resjnra- ble Gases. — Experiments of Regnault and Reiset. — Nervous Influence concerned in Respiration. — Results of Respiration 140 CONTENTS. xi CHAPTER X. OF ANIMAL HEAT Participation of Organic Forms in external Variations of Temperature. — Mechanism for counter- balandmj these Variations. — Development of Heat in Plants at Germination and Inflorescence. — Its Cause is Oxidation. — Connection of Respiration and Heat. — Temperature of Man. — His Power of Resistance. — The diiirnal Variations of Heat. — Connection of these Variations with organic Penodicities. — Annual Variations of Heat. — Control over them by Food, Clothing, and Shelter. — Source of Animal Heat. — Effect of Variations in the Food and in the respired Me- dium, both as respects its Nature and Rarefaction. — Hybernation. — Starvation. — Artificial Rcr- duction of Temperature by Blood-letting. — Principles of Reduction of Temperature. — Radia- tion. — Contact. — Evaporation. — Their Balance with the Heating Processes. — Local J'aria- tions eliminated by the Circulation. — Control by the Nervous System. — Its physical Nature. — Allotropism of Organic Bodies Page 17") CHAPTEE XI. OF SECRETION. SEEOTTS, MUCOUS, A2s'D HEPATIC SECKETIONS. Object of Secretion. — Type of secreting Mechanism. — Filtration and Cell Action. — Of Serous Membranes and their Secretions. — Of Mucous Membranes and their Secretions. — Of Hepatic Se- cretions. — TJie Liver: its Development and Structure. — Source, Quantity, Composition, Uses, and Flow of the Bile. — Existence of biliary Ingredients in the Blood. — Production of Sugar and Fat in the Liver. — Changes q/^ the Blood-cells in it. — General Summary of the four-fold Action of the Liver : it produces Sugar and Fat, eliminates Bile, is the Seat of the final Destruction of old Blood-cells, and of the Completion of new Ones. — Of the ductless Glands. — The Spleen: its Functions 181) CHAPTEE XII. OF EXCRETION. THE UEINE, MILK, ASV> CUTANEOUS EXCRETIONS. Secretion and Excretion. Of the Kidney: its Structure and Functions. — The Malpighian Circulation. — The Urine: its In- gredients, their Variations and Som-ces. — Abnormal Substances in it. — The Water and Salts exude by Filtration. — The Cells remove unoxidized Bodies. — Manner of Removal of the Liquid from the Malpighian Sac. Of the Mammary Gland: its Structure. — Colostrum and Milk. — Ingredients of Milk and their Variations. — Influence of Diet. — Inquiry into the Origin of the Ingredients of the Milk jits Fat, Casein, Salts, Sugar. — Manner of Action of the Gland by Strainage. Of the Skin. — Structure of its Epidenna and Derma. — Sudoripai'ous and Sebaceous Glands. — Nails. — Hair. — Ingredients of Perspiration. — Exhalation: its Amount. — Causes of the Vari- able Action of the Skin. — Its Double Action. — Abso7j>tion by the Skin. — Gene7-al Summary of the Cutaneous Functions 213 CHAPTEE Xni. OF DECAY AND NUTRITION. Of Decay : Loss of Weight in Starvation. — Interstitial Death. — Effect of Allotropism. Of Nutrition : Nutrition for Repair and Nutrition for Remodeling, illustrated in the cases of Fat and Bone respectively. Of Fat : Its Peculiarities, modes of Occurrence, and Oi'igin. — Inquiry whether Animals ever form Fat. — Artificial Production of it. — Animals both collect it and make it. — Accumulation of it expends Nitrogenized Tissue. — Conditions of the Fattening of Animals. — Summary of the Sources, Deposit, and manner of Removal of Fat. — Its partial Oxidations, — Summary of its Uses. — Nitrogenized Nutrition. XU CONTENTS. Of Bone: The Skeleton. — Structure and Chemical Composition of Bone. — Sources of its Con- stituents. — The Process of Ossification. — Experiments on the Growth of Bone. — Influence of Physical Agents on Development and Nutrition Page 2415 CHAPTER XIV. OF THE NERVOUS SYSTEM. Divisions of the Nervous System.. — Cerebrospinal and Sympathetic. — Fibrous and Vesicular. Structure and Functions of Nerve Fibres. — Centripetal and' Centrifugal. — Rate of Conductibility. Anatomical Examination of the Structure and Functions of Nerve Vesicles. — Tliey diffuse Influ- ences, are Magazines of Force. — Element of Time introduced by Registering Ganglia. — Oxida- tion necessary to Nerve Activity. — Necessity of Repair and Rest. — Electiical Examination of the Functions of Vesicles. — Anatomical and Electrical Examinations agree. Automatic Nerve Arc. — Cellated Nerve Arc. — Multiple Arcs. — Commissures. — Registering Nerve Arcs. — Sensorium. — Influential Arc. Suggestions derived from cerebral Structure respecting the Soul. — Its independent Existence and Immortality. Ideas of Time and Space. — Objective, subjective, and impersonal Operations. — Vestiges of Im- pressions and their Interpretation, — Finite Natui-e of Knowledge. — Mental Emotions 258 CHAPTER XV. THE SPINAL AXIS. Primitive Development of Nervous System. — Its final Condition in different Vertebrates. The Spinal Cord: its Structure. — Its Membranes. — Its TJiirty-one Pairs of Nerves. — Proper- ties of their Roots. — Functions of the Cord. — Belt's Discovery. — Transmission of Longitudinal and Transverse Influences. — Reflex Action of the Cord. — Nature of Reflex Action. — Motor and Sensory Tracts of the Cord. — Summary of its Functions. The Medulla Oblongata : its Structure and Functions. The Pons Varolii: its Structure and Functions. Dr. Carpenter''s Views of the Analogy between the Spinal Cord of Vertebrates and the Ventral Cord of Articulates , 291 CHAPTER XVI. OF THE BRAIN. The Brain : its Structure. — Its Motor and Sensory Parts, Hemispheres, and Commissures. — The Sensorium. — Variations of the Hemispheres in Size and Weight. — Instrumental Nature of Cerebrum. — The Cerebellum: its Structure and Functions. — Co-ordinates muscular Motions. — Connection with Amativeness. — Phrenology. — Conditions of Action of Brain. Symmetrical Doubleness of the Brain. — Function of each Half, and of both conjointly. — Independ- ence and Instibordination of each Hemisphere. — Double Thought. — Alternate Thought. — Senti- ment of Pre-existence. — Loss '• '• 336 166. The inferior Maxillary '• " " 336 167. The Facial NerA-e " " " 337 168. The Glosso-pharyngeal Nerve " •' '• 339 169. Diagram of Anastomoses.. '■ " " 339 170. The left Pneumogastric •' " " 341 171. Pulmonary Ganglia '' " " 342 172. The inferior Laryngeals " " " 342 173. The Hypoglossal Nerve " " " 343 174. The Phrenic Nerve " " " 344 175. Eelation of the Sympathetic and Spinal Todd and Bowman 345 176. The Great Sympathetic Photograph from Leveille 348 177. Abdominal Plexuses '• " " 349 178. The Solar Plexus '' '• " 350 179. The Mesenteric Plexuses. " " " 350 180. Spiracle of Insect Photograph by Author 352 181. Profile of Larynx Leveille 354 182. Posterior View of Larynx " 354 183. External, middle, and internal Ear " 362 184. Tympanic Cavity " 362 1 85. Facial in the Aqueduct of Fallopius " 362 186. Interior of Cochlea " 369 187. Section of Cochlea " 369 188. Magnified Section of Cochlea "' 370 189. Cochlear Nerve " 370 190. Auditoiy Nerve " 370 191. Ossicles and their Muscles " 370 192. Tympanic Face of Labyrinth " 374 193. Cranial Face of Labyrinth " 374 194. Interior of Labyrinth " 375 195. Interior of Labyrinth " 375 196. Profile of Eye " 883 197. Front View of Eye " 383 198. Section of Eye " 383 199. Veins of the Choroid " 385 200. Arteries of the Choroid " 385 201. Yellow Spot of Soemmering Soemmering 385 202. Membrane of Jacob Jacob 390 203. Simple Papilhe. , Todd and Bowman 420 204. Compound PapiUee Kolliker 420 205. Olfactory Nerve Leveille 424 206. Olfactory Nerve " 424 207. The Tongue Photograph from Leveille 428 208. Ciliated Cells Author 431 209. Ciliated Animalcule Ehrenberg 432 210. Hydra walking Trembley 432 211. Striated muscular Fasciculi Photograph by Author 433 212. Human Sarcolemma Bowman 433 213. Sarcolemma of Fish "._ 433 214. Ultimate muscular Fibre Photograph by Author 433 215. Unstriped muscular Fibre Author 435 LIST OF ILLUSTEATIONS. 5 PIO. PAGS 216. Unstriped Fibres in Acetic Acid Author 435 217. Muscle Cells KoUiker 435 218. Muscular Fasciculi torn in Discs Bowman 436 219. Transverse Section of human Muscle '• 437 220. Transverse Section of Muscle of Teal " 437 22 1 . Non-fibrillated Insect Fasciculi Photograph by Author 437 222. Non-fibrillated Insect Fasciculi '• " 437 223. Contracting Muscle of Dytiscus Bowman 438 224. Sarcolemma raised in Bullie Todd and Bowman 438 225. Fasciculus contracting " " 439 226. Distribution of muscular Capillaries Berres 439 227. jMuscular Arteries and Veins Kolliker 440 228. Distribution of muscular Nen'es Burdach 440 229. Volume of contracting Muscle Author 450 230. Ila'matococcus Binalis Hassall 494 23 1 . Conferva glomerata Mohl 495 232. Simple Cellular Tissue Photograph by Author 497 233. Muriform Cellular Tissue " " 497 234. Fibro-cellular Tissue " " 497 235. Spiral Vessels of Cactus '• " 498 236. Spiral Vessels of Banana " " 498 237. Woody Fibre of Pine : " " 498 238. Yellow Fibrous Tissue Author 499 239. White Fibrous Tissue " 499 240. Areolar Tissue " 499 241. Development of Frog Rusconi 509 242. Frog 510 243. Development of Crab Couch 510 244. Development of Insects Straus Durckheim 510 245. Zygnema Quininum Kiitzing 515 246. Testis Arnold 517 247. Development of Spermatozoa Wagner 518 248. Section of Ovary Kolliker 521 249. Section of Graafian Vesicle Von Biir 521 250. Ovum , BaiTy 521 251. Diagi-am of Graafian Vesicle Kirkes and Paget 521 252. Corpora Lutea Patterson and Montgomery 522 253. Ovarian Ovum 523 254. Ovarian Ovum 523 255. Segmentation of Ovum Bischoff 524 256. Segmentation of Ovum Kolliker and Bagg 524 257. Uterine Tubes Weber 525 258. Layers of Germinal Membrane Bischoff 527 259. Primitive Groove " 527 260. Origin of Brain * " 528 261 . Production of Vessels Wagner 529 262. Production of Lymphatics Kolliker 529 263. Rudimentary Heart • Thomson 529 264. Foetal Heart Von Bar 530 265. Hydra budding Trembley 534 266. Newton Photograph from Principia 563 267. Australian D'Urville. — Photographed from Prichard 563 268. Australians D'Urville.— " " " 564 269. Brahmin Branwhite. — " " '■ 573 270. Chinese " '■ " ♦.... 574 271. Kamtschatdale "■ " " 575 LIST OP ILLUSTRATIONS. f 10. 272. Sac Indian Catlin. — Photographed from Prichard 575 273. Cherokee Indian Catlin.— " " " 576 274. California Indian Choris.— " " '• 676 275. California Indian.s Choris.— '• " " 576 276. Abyssinian D'Abbadie.— ■■ " " 577 277. Native of Madagascar " " " 577 278. Native of Mozambique " " " 578 279. Negro of Guinea Author 579 280. Philippine Negro Choris. — Photographed from Prichard 579 28 L Skeleton of Man, Chimpanzee, and Orang Photograph by Author 581 282. Skull of European Prichard 582 283. Skull of Negro " 582 284. Skull of Chimpanzee '■ 582 285. Skull of Orang " 582 286. Caucasian Skull " 583 287. Mongol Skull " 583 288. Negro Skull " 584 289. Titicacan Skull " 584 290. Base of human Skull " 584 291. Base of Orang Skull " 584 292. Esquimaux Skull " 585 293. Negro Skull Author 587 294. Erench Skull " 587 295. Cephalic Ganglia Newport 607 296. Thoracic Portion of Ventral Cord " 607 lUMAN PHYSIOLOGY, STATICAL AND DYNAMICAL. HUMAN PHYSIOLO&Y. BOOK FIRST. STATICAL PHYSIOLOGY. CONDITIONS OF LIFE. CHAPTER I. Conditions of Life. — Nature and Sources of Substances supplied to the Body. — Annual Quantities required. — Table of Physiological Standards. — Animals do not create, but transform Substan- ces. — frojyerties and Quantities of Matters received by the System. — Properties and Quantities of those it restores. — Heat of the Body arises from Combustion. — Cooling Agencies in an An- imal.— Necessity of Repair sin the System. — Physical Aspect of Man. — Tlie Soul. — The Vital Principle. — Importance of Physical Science to Physiology. Foe tlie maintenance of the life of man three chemical conditions must be complied with. He must he furnished with air, water, and combusti- ble matter. Under the same conditions, also, all animals exist. Even in those which seem to furnish us with instances of departure from this Three condi- general rule, the exceptions are rather apparent than real. To *^°^^^ ^^^^^®- breathe, to drink, to eat, are the indispensable requisites of life. If there be among insects some which seem never to take water, or among fishes some which never taste solid food, these peculiarities disappear as soon as we understand them properly. Where a high development has been attained, as in man, experience assures us that the same inevitable result awaits a cessation of respiration for a few moments, an abstinence from water for a few hours, or from food for a few days. The supply of a part of these necessaries of life is adjusted to the ur- gency of the want. The act of breathing is incapable of de- sources of sup- lay, but the air is accordingly every where present, and al- ply of material, ways fit for use. We can bear with thirst for a little time, and the earth here and there furnishes her springs and other stores of water. But far otherwise is it in the obtaining of food. It is the lot of all animals to secure nourishment by labor, and even of men the larger proportion, both 10 EQUILIBRIUM OF LIFE. in civilized and savage countries, submit to a hard destiny. To obtain their daily bread is the great object of life. What is the philosophical explanation of this necessity for a supply of air, of water, of food ? Why is it that the system will bear so little delay ? The answer which Physiology gives to these questions is an answer , „ J , of ominous import, but the whole science is a commentary on Life depends ^ .... -,. on destruction its truth. The Condition of life is death. No part of a liv- of material. -^^g mechanism can act without wearing away, and for the continuance of its functions there is therefore an absolute necessity for repair. It has been greatly to the detriment of physiology and the practice of medicine that this conception has not been thoroughly realized until late times. The aspect of identity which an animal presents is an illusion, hiding from us the true state of the case. It has been the fruitful source of errors which have retarded the progress of these sciences. What could their career possibly be when men had persuaded themselves that a liv- ing being possesses a capacity for resisting any change, and that organic structures never yield to external physical influences until after death ? But life, far from being a condition of immobility, is a condition of ceaseless change. An organism, no matter of what grade it may be, is only a temporary form, which myriads of particles, passing through a de- terminate career, give rise to. It is like the flame of a lamp, which pre- sents for a long time the same aspect, being ceaselessly fed as it ceaselessly wastes away. But we never permit ourselves to be deceived by the sim- ulated michangeableness which such a natural appearance ofiers. We recognize it as only a form arising from the course which the disappear- ing particles take. And so it is even with man. He is fed with more than a ton weight of material in a year, and in the same time wastes more than a ton away. There is, therefore, a general condition of equilibrium which every an- ^ ,. . ^ „ imal presents, depending upon its receipts and its wastes, a equilibrium in proper knowledge of the conditions of which is at the founda- ™^°" tion of Physiology. That we may approach this problem un- der its simplest form, free it from all unnecessary complications, and make it of most interest to the special object of this book, the remarks now to be made will be confined to our own species, and, except when oth- erwise stated, to a condition of health, and to the adult period of life. To have a uniform standard of reference, we may assume one hundred and forty pounds as the weight of an adult healthy man. Now the con- stant consumption of food, water, and atmospheric air tends steadily to increase that weight, and even in a very short time a disturbance arising from these sources would be perceptible, were there not some causes of ANNUAL RECEIPTS AND WASTE IN MAN. 11 compensation. But even after a year, if a state of health is maintained, the Aveight may remain precisely what it was, and this may continue year after year in succession. The consumption of large quantities of solid, liquid, and gaseous matter does not therefore necessarily add to the weight. There are two periods of life for which this observation will not hold good. They are infancy and old age. During the former the weight in- creases from day to day, and during the latter it slowly declmes. If there be thus causes for the increase of weight of the living system, there are also causes for its diminution. Settmg aside the minor ones, these may be chiefly enumerated as loss by u.rine, by ffeces, by transpired and expired matters. By transpired matters, are meant such as escape under the form of liquids and gases from the skin, and by expired mat- ters, vapors and gases escaping from the kings. There is, therefore, a tendency to an increase and a tendency to a diminution of the weight, and, in the condition of equilibrium we are considering, these must bal- ance one another. If a man of the standard weight abstains from the taking of water and food, a good balance will prove that in the course of less than an hour he has become lighter. If he still persists, it needs no instrument to detect what is going on; the eye perceives it, for emaciation ensues. How, then, is it possible for a living being to continue at its standard, except the causes of increase are precisely equal in eifect to the causes of diminution ? Overlooking minor ones, we may therefore assert tliat the sum total of food, water, and atmospheric air taken in a given period of time is precisely equal to the sum total of all the losses by urine, fge- ces, transpired, and expired matters ; for if the receipts were greater, the weight must increase — if the losses were greater, the weight must dimin- ish. Persistency in this respect proves equality, and the case is just as simple as in the common affairs of life ; he who pays less than he receives grows rich ; if his payments are more than his receipts, he becomes poor ; but his condition is unchanged if his payments and receipts are equal. Infancy, old age, and manhood answer to these circumstances respect- ively. From the army and navy diet scales of France and England, which of course are based upon the recognized necessities of large Quantity of numbers of men in active life, it is hiferred that about 2^ ;"a"er required ' • * b}' man in a pounds avoirdupois of dry food per day are required for each year. individual ; of this about three quarters are vegetable and the rest animal. At the close of an entire year the amount is upward of 800 pounds. Enumeratmg under the title of water all the various drinks — coffee, tea, alcohol, wine, &c. — its estimated quantity is about 1500 pounds per an- num. That for oxygen may be taken at 800 pounds. 12 ANNUAL EECEIPTS AND WASTE IN JIAN. With these figures before us, we are able to see how the case stands. The food, water, and air which a man receives amount in the aggregate to more than 3000 pounds a year ; that is, to about a ton and a half, or to more than twenty times his weight. This enormous mass may well at- tract owe attention to the expenditure of material which is required for supporting life. It reveals to us the fact that the old physiological doc- trine, that a living being is not influenced by external agents, is altogether a fallacy. A living being is the result and representative of change on a prodigious scale. The condition of equilibrium which has just been set forth, moreover, Quantity of leads to the conclusion that the aggregate weight of urine, by maii*^in a^ fajccs, transpired, and expired matter is the same for the year. same period of time. In round numbers, we may take it at a ton and a half. It can not be questioned that the materials which are rendered back to the external world, after having subserved the purpose of the animal and passed through its system, are compounds of those which were originally received as food, drink, and air, though they may have assumed in their course other, and perhaps, in our estimation, viler forms. Recognizing as indisputable the physical fact that not an atom can be created any more than it can be destroyed, we should expect to discover in the sub- stances thus dismissed from the system every particle that had been taken in. What, then, is man ? Is he not a form, as is the flame of a lamp, the temporary result and representative of myriads of atoms that are fast passing through states of change — a mechanism, the parts of which are unceasingly taken asunder and as unceasingly replaced ? The appear- ance of corporeal identity he presents year after year is only an illusion. He begins to die the moment he begins to breathe. One particle after another is removed away, interstitial death occurring even in the inmost recesses of the body. From these general considerations we infer that the essential condition Great extent of of life is Waste of the body ; and this not only of the body the sIStem of™ ^^ *^^ aggregate, but even of each of its particular parts, man. Whatever part it may be that is exercised is wearing away, and wherever there is activity there is death. And since parts that are dead are useless, or even injurious to the economy, the necessities simul- taneously arise for their removal and for repair. Much of the compli- cated mechanism of animal structures is for the accomplishment of this double duty. For an organic being to live, its parts must die. The amount of activ- ity it displays is measured by the amount of death, and in this regard every member of the animal series stands on the same level. Here, at FIXED STANDARDS OF PHYSIOLOaY. 13 the very outset of our science, we must dismiss the vulgar error that the physical conditions of existence vary in different tribes, and that man is not to be compared with lower forms. We must steadily keep in view the interconnection of all, a doctrine which is the guiding light of modern physiology, and which authorizes us to appeal to the struj^ture and fanc- tions of one animal for an explanation of the structure and functions of another. The more steadily we keep before us this philosophical con- ception of the interconnection of all organic forms, the clearer \vill be our physiological views. There has never been created such a thing as an isolated living being. From the manner in which these general considerations of the mechan- ical and chemical equilibrium of the system of man have been Necessity and introduced, it will doubtless be seen that it is the first busi- ph'^ygioioHcli ness of the physiologist to disentangle the variable results standards. which that system presents, as far as may be possible, and offer them un- der a standard estimate ; that at th^ basis of this science there should be a table settmg forth with the utmost exactness all the quantities con- cerned in such a standard type. Thus, assuming the weight of an adult man at 140 pounds, as we have done, it should show the diumal consump- tion of combustible matter or food, of water, of air — the dim-nal loss by evaporation, by secretion, by respiration. In contrast with this it should also give the nocturnal. It should also represent the quantity of bile, of saliva, of pancreatic juice ; the weight of each one of the various salts and organic bodies they contain, the diurnal and nocturnal production of heat, &c. For the purpose of the practice of medicme, a standard of 140 pounds will perhaps be found most convenient, but in a scientific point of view, and especially for comparative physiology, a standard of 1000 parts is best assumed. I now present an attempt at the construction of such ta- bles, it being perhaps scarcely necessary to apologize for their extreme imperfection. Though offering the results at present received as most trustworthy, a very superficial examination will show how full they are of errors and contradictions. Perhaps it would not be too much to say that it will require the labor of many physicians, continued for centuries, to bring such tables to the truth. Yet the approach to precision in these hypothetical constants will in all times be a measure of the exactness of physiology, and it may be added, also, of the practice of medicine. The time is at hand when such a typical standard must be the starting-point for pathology, and no rational practice can exist without it. The passage of physiology, from a speculative to a positive science, is the signal for a revolution in the practice of medicine. Moreover, physiology should furnish formulas for the computation of variations in these tabular numbers under variable conditions ; as, for in- 14 FIXED STANDARDS OF PHYSIOLOGY. stance, under low and high aerial temperatures, change of atmospheric pressures, absolute quiescence, or the near approach thereto, the effect of a determined amount of locomotion, or other muscular exertion, &c. As the science becomes more perfect, it should likewise attempt to embrace pathological states ; as, for instance, the diurnal or periodic production of heat in fevers, the effect of the hygienic system of the bedroom. Physiology having attained to this high condition, the practice of med- icine in its great department of diagnosis will consist, in reality, in the solution of inverse problems. Given the variations from the standard ex- isting in any case, to determine the cause of those variations. At this point diagnosis becomes a science, and ceases to be an art. As in painting and statuary, the artist has an ideal model in his mind, a typical standard which no living being has perfectly reach- the following ed, though somc of the most beautiful may have approached *^ ^' thereto, so in physiology the standard or typical man pre- sents the combined and mean values, of all the human race. A less comprehensive view presents us with distinct national standards, instead of this universal one, for every country has its own peculiarities. Results of the highest interest are to be perceived when these national standards are compared with one another. Even the same nation must offer, from age to age, modifications in its type expressive of the secular perturbations it is undergoing, as it advances or descends in a knowledge of the arts of life and civilization. Moreover, there are typical standards of a still lower order, having ref- erence to the conditions of sex and the period of life. Of these six may be designated — ^the infant, the adult, the aged, of the male and female sex respectively. As illustrations of these remarks, and examples of the determination of the fundamental element of such a general physiological table, the stand- ard weight of the body, we may take the following estimates. An ex- amination of 20,000 infants, at the Matemite in Paris, gives for the weight of the new-bom 6|lbs. ; the same mean value obtains for the city of Brus- sels. For about a week after birth this weight undergoes an actual dim- inution, owing to the tissue destruction which ensues through the estab- lishment of aerial respiration, and which for the time exceeds the gain from nutrition. For the same age the male infant is heavier than the fe- male, but this difference gradually diminishes, and at twelve years their weight is sensibly the same. Three years later, at the period of puberty, the weight is one half of what it is finally to be, when full development is reached. The maximum weight eventually attained is a little more than twenty times that at birth, this holding good for both sexes ; but since the new-bom female weighs less than the standard, and the new- bom male more, the weight of the adult male is 136-j^^ lbs., and of the PHYSIOLOGICAL TABLES. 15 adiilt female I'il^^^-g- lbs. The mean weight of a man, irrespective of his period of life, is 103^^l^j lbs., and of a woman SS-j^^^g- lbs. The mean weight of a human being, without reference either to age or sex, is QQ_7 5 9 11-)=, For the preceding numbers we are indebted to the researches of M. Quetelet, who likewise has in an interesting manner extended the meth- ods of statistics to the illustration of the physical and moral career of man, and impressed us with the facts that in the discussion of the phe- nomena which masses present, individual peculiarity disappears and gen- eral laws emerge. The actions which seem to be the result of free -will in the individual, assume the guise of necessity in the community. Just as we are sure that man is bom, develops, and dies under the operation of laws that are absolutely invariable, so communities seem to be under the inlluence of unchangeable laws. " Li communities man commits the same number of murders each year, and does it with the same weapons. We might enumerate beforehand how many individuals will imbrue their hands in the blood of their kind, how many will forge, how many poison, very nearly as we enumerate beforehand how many births and deaths will take place." PHYSIOLOGICAL STANDARD TABLES. Diurnal Ingesta, SecretioDS, and Excretions of a Man whose Diurnal Ingesta, Secretions, and Excretions of a Man whose \ weight is 140 lbs. avoirdupois. weight is 1000 parts. | \Veis;ht ofbodj' 140.000 Weight of body 1000. OOU , ""Water 4.109 1- ^Vater 29.850 Oxygen 15.657 Oxygen 2 192 Dry vegetable food. . . 1.6S7 Dry vegetable food . . 12.050 Dry animal food 4.021 | pH ^Diy animal food 563 ^Saliva 3.300 ^Saliva 23..576 i Gastric juice 100.571 Gastric juice 14.0S0 Pancreatic juice 440 Pancreatic juice 3.143 i Bile 3.500 rri Bile 25.000 i c Carbon from lungs . . . .500 C Carbon from lungs. . . 3.571 i tS Intestinal j uice 440 Intestin al j uice 3. 143 ' Lossof water by lungs 1.440 Loss of water by lungs 10.286 j « skin. 2.234 X skin. 15.957 i W Fseces 0T8 y Fieces 557 -a J "^ J d Water 2.034 Urea 065 OS Water 14.529 Urea 464 Uric acid 002 Uric acid 014 1 g Sulphuric acid OOT Sulphuric acid 050 CQ Phosphoric acid OOS -JJi Phosphoric acid 057 Chloride of sodium . .009 Chloride of sodium . .064 ' Alkalies and earths. .010 Alkalies and earths. .114 L other bodies 002 other bodies 014 fBlood IT. 000, consisting of rBlood 121.429, consisting of Water 13.32S Water 95.200 Albumen 1.190 Albumen 8.500 o Fibrin 037 o Fibrin 264 S Discs 2.22T ^ Discs 15.907 Fats 022 ^ Fats 157 P. Chloride of sodium. ..061 o Chloride of sodium. .436 r. Chloride of potass.. .006 •-^^ Chloride of potass . . .043 Phosphate of soda . . .003 Phosphate of soda . . .021 5 Carbonate of soda . . .012 Carbonate of soda . . .086 a Sulphate of soda 004 ^ Sulphate of soda 029 ^ Phos. lime and mag. .004 Phos. lime and mag. .029 Oxide and phos. iron .008 Oxide and phos. iron .057 Other bodies 098 Other bodies 700 In this table the estimate is in the avoirdupois In this table the estimate is upon one thousand pound and decimals thereof. parts. It is to be received as a doctrine admittmg no controversy, that or- 16 NATURE OP MATTERS RECEIVED. ganic systems, whether vegetable or animal, whether humble or elaborate- An animal ere- ly developed, possess no power of creating material. Their but only trans- function is of necessity limited to the mere transformation of forms the sub- substanccs furnished to them. From this it follows, even in ceives. the casc of man, that the substances dismissed from the sys- tem are metamorphosed forms of those which have been received, and that, whatever their appearance may be, they must have arisen from the reaction of the food, water, and air upon one another. This reaction we may proceed to view as a purely chemical result : for, casting aside all the vain hypotheses of the older physiology, and per- mitting ourselves to be guided by the harmonies of nature, we should ex- pect to recognize in the changes taking place in organic systems, and in the phenomena which attend those changes, the same results which arise in the artificial or experimental reaction of food, water, and air on each other. A very superficial examination of the facts shows at once the The chemical Correctness of this expectation. On such an examination we properties of enter, premising; it with some general remarks needful for matters re- ' J^ o . ^ , -, ■, . ceived. our purpose on the nature and properties of tood, water, and air. 1st. Op Food. — No article is suitable for food except it be of a com- bustible nature. Its chemical constitution must be such that if its tem- perature be raised to a proper degree with a due access of atmospheric air it will take fire and burn, and the products of its combustion must be car- bonic acid gas and water, or those substances with nitrogen or its com- pounds. 2d. Of Water. — This may be taken as the type and representative of all the various liquids used as drinks. It evaporates at any tempera- ture, even at those which are lower than its freezing point, and in this evaporation produces cold. Water vaporizing from the skin absorbs 1114 degrees of heat, and hence exerts a most powerfal refrigerating action. Over saline substances there are few bodies which exercise so general a solvent eifect. In virtue of this property, it is enabled to introduce in the dissolved state such compounds as are wanted for the nutrition of the system, and in the same manner to carry away the wasted products of decay. 3d. Of Atmospheric Air. — The active principle of the air is oxygen gas, the effects of which are moderated by the presence of a large quanti- ty of nitrogen — four fifths of the air consisting of this latter substance. Physiologically, we often use the terms atmospheric air and oxygen syn- onymously. The chief materials which a living being receives from the external world are, therefore, combustible matter, water, o?:ygen gas ; and out of the action of these upon one another all the physical phenomena of its life arise. NATUEE OF MATTERS RESTORED. 17 Such being the nature and properties of the things received, we may now examine in the same general manner those which are Properties of dismissed from the system. Here, at the very outset, we en- substances PIT •Til 1 d'sm'sscd by counter the important fact that they are oxidized or burned the system. bodies. 1st. As respects the urine and its constituents. Its liquid part, wa- ter, is an oxide of hydrogen, of which, though the greater portion may not have been produced in the economy, yet a certain quantity unques- tionably has. In it, too, are to be found sulphuric acid, which is an ox- ide of sulphur ; phosphoric acid, wdiich is an oxide of phosphorus ; and its leading solid constituent, urea, is the representative of bodies which arise when processes of oxidation have been going on. 2d. The expired and transpired matters present similar burned com- pounds. At the head of these products stand carbonic acid gas, which is an oxide of carbon, and water, which, as we have already said, is an ox- ide of hydrogen. We here omit any consideration of the nature or con- stitution of the fa3cal matter, because much of it has never been properly in the interior of the system, though it has passed through the intestine. The general result at which we arrive is, then, that the food consists of combustible matter, and that the substances dismissed from the economy are oxidized bodies. A burning must, therefore, have been go- noi^bustion ing on, and this could only have been accomplished by the air occurs in the introduced by breathing acting upon the substance of the body °'^ ^' itself and its contents, and, to repair tlie waste which must have ensued, a due weight of food has been required. Since this, in its turn, as a part of the living mechanism, is destined to undergo the like destructive action, we may present the entire series of facts under consideration cor- rectly by regarding them as arising remotely from the action of the air upon the food. With this statement before us, we next inquire what ensues when sub- stances appropriate for food are exposed in artificial experiments at a cer- tain temperature to the action of atmospheric air. A piece of flesh, or even of any vegetable body, consisting of carbon, hydrogen, oxygen, and nitrogen, submitted to those condi- Results of arti- tions, undero;oes combustion. Its carbon, by unitiiip" with ox- ^^^^^ combus- -, ,. .-,. r ^ ^^°^ ^^^ same ygen, produces carbonic acid, its hydrogen for the most part as that in the water, but a residue thereof, combining with the nitrogen, may ^°^y- give rise to the production of ammonia. If there be any sulphur and phosphorus present, they also burn, and salts of sulphuric and phosphoric acids are the result. * Such is what occurs outside of the body in a common case of artificial combustion where atmospheric air has access. The constituents of which the food is composed thus satisfy their chemical afiinities, and the com- B 18 PEODUCTION OP HEAT. pounds we have mentioned arise. iSTow it is a fact of tlie utmost signifi- cance that the compounds thus originating from the direct artificial burn- ing of matters proper for food are the very same that are dismissed from the animal system in which food has heen submitted to the air introduced by resphation. They are such substances as carbonic acid, water, am- monia, sulphates and phosphates. It may impress these truths more deeply upon us to learn that the facts at which we have thus arrived may also be recognized in the changes of destruction presented by the vegetable kingdom. The leaves of trees, after they have fallen in autumn, quickly decay, and even the heart-wood itself has a limit beyond which it does not last. Sooner or later every part of a plant is destroyed by the atmospheric air. Such limits of diu'ation in animal stroctures are short. A veiy brief time, per- haps only a few hours, is all that is wanted for putrefaction to set m, and the entire mass, undergoing dissolution, is lost in the surrounding air. This final disappearance of all organized structures is brought about by the action of that energetic element, oxygen. If by any contrivance its influence is prevented and its presence avoided, these changes do not take place. Putrefaction and decay are slow combustions, true bui-nings takmg time. There equally arise from the fallen leaf and from the de- cayuig body carbonic acid, water, and ammonia, the self-same substances dismissed from the economy during the continuance of life. Processes of combustion and processes of decay are therefore both due to the action of atmospheric oxygen on the changmg substance. They differ chiefly from one another in the relative rapidity with which they are accomplished. The facts thus set forth wan-ant the following statements. The mat- ters which a man receives as food are combustible bodies ; those dismissed Production of from liis System have been biumed. To that, as to any other animal heat, g^^ch burning, oxygcn gas is absolutely requisite. There is, therefore, a plain conclusion before us, which, in its far-reaeliing conse- quences, covers the whole science of physiology, and betrays to us the function which every animal discharges, viz., that oxidation is mcessant- ly going on in the interior of the system through the agency of atmos- pheric air introduced by the process of breathing. An animal, in this point of view, is an oxidizmg machme, into the ul- terior of which atmospheric au- is constantly introduced. The active con- stituent, oxygen, satisfies its chemical affinities at the expense of those parts of the system which are wasthig away. And as the act of breath- ing, that i^, the introduction of this gas, takes place day and night, wak- ing and sleeping, so too must the production of burned bodies ; a part escaping by the Imigs, a part by the skm, a part in the luine. To com- pensate the loss which ensues, nearly 1000 pounds weight of combustible PRODUCTION OP HEAT. 19 matter must be used in the course of a year, and, for reasons to be exam- ined in detail presently, three quarters of a ton of water. But this is a very diiierent conclusion to the notion of the ancient physicians, that an animal during its life is exempt from participating in external changes, and is an enduring monument of the power possessed by the vital poece of resisting all physical influences. But carbon by uniting with oxygen can not turn into carbonic acid, nor can hydi'ogen turn into water, nor nitrogen into ammonia, without heat being produced. The very meaning we attach to the term indicates that every process of burning is attended with the liberation of heat. In domestic economy, we protect ourselves from the cold weather of winter, or attain any high temperature we want by the oxidation of some of the forms of carbon, such as wood or coal, in fire-places or stoves. We know that for the production of a given quantity of heat a given weight of combustible matter and of air is required, and that by employ- ing various mechanical contrivances for increasing the draught we can ac- celerate the bm-nmg. jMoreover, if in our laboratories we require the very highest tempera- ture that can be artificially obtained, we resort to the burning of hydro- gen. There are instmments, such as the compound blow-pipe, construct- ed on this principle. In the flame which arises in this combustion the most refractory substances melt or are deflagrated. But it may be said that though when a substance is rapidly oxid- izing it must be evolvmg heat, there is perhaps a slower Production of kind of combination, in which the particles unite without any f^^^^^^ anT^" disturbance of temperature. What proof could be ofiered, for decay, example, that a mouldering leaf is disengaging heat ? In answer to this it is not necessary to bring forward refined or direct experiments. Every leaf when it moulders is literally burning away. The extrication of warmth begins even when it is ready to fall. What does the farmer expect in making his hay, if he puts the grass up in too moist a state, or in too large a mass ? The temperature does not stop at the stage of bituminous fermentation, but the stack most probably takes fire. Of course what is going on in the whole mass is going on in each separate leaf, undisting-uishable, it is trae, in the latter case, because the heat of a single decaying leaf, taken alone, may be carried oiF by the cold surrounding air, or by the contact of good conductmg bodies, and so be lost to examination. From agricultural operations we may also learn that what holds good for vegetable bodies is true for animal substances. Heaps of manure or of ofial of any kind, if due access of air be given, exhibit the extrication of carbonic acid, steam, and ammonia, and the temperature promptly rises. The gardener avails himself of tliis fact. He uses the heat, as it is slowly 20 EEGULATION OF HEAT. set free by the putrefaction of manure in liis forcing frames, to bring forth plants in the early spring. There is no kind of decay, or putrefaction, or oxidation of organic matters, however slow it may be, that is not marked by the production of warmth. Man, in a state of health, maintains a nearly uniform temperature. Heat of man: Neglecting slight variations, to be hereafter critically exam- its cause, ined, it is 98 degrees. For the most part, it is immaterial in what climate of the earth he may reside, whether in the cold polar re- gions or the hot tropic ; he is so constituted that, either through the pro- visions of his own organization, or by resorting to the adventitious aid of clothing, or to special articles of food, he can maintain himself at about the same degree ; and as all this heat arises from interstitial oxidation continually taking place, it is obvious that within certain limits he has control over it. Thus, in the winter he sometimes resorts to violent mus- cular action in order to increase the rapidity of respiration and the de- struction of muscular tissue ; for the greater the quantity of air intro- duced in a given period of time, the higher the temperature rises, just as when we close the door of a stove, or place a blower on an anthracite fire, an increased draught is occasioned and the quantity of heat is in- creased. To breathe with rapidity and depth is certain to raise the tem- perature. . On the contrary, in summer, when the heat is oppressive, we instinct- ively abstain from muscular exertion, tranquil and slow respiration goes on, and the temperature is kept down. Again, there are means of occa- sioning an increased liberation of heat by changing the nature of the food and using highly combustible material, such as the various kinds of alco- holic preparations. The chemical constitution of alcohol is such that in the act of burning carbonic acid and water are produced with the libera- tion of so much heat that chemists find it one of the most suitable means of attaining a high temperature. On taking preparations of this substance, such as distilled liquors or wines, the first efiect is the production of a genial warmth all over the body, intoxication eventually coming on as a secondary result. These remarks are not limited in their application to our own species, the whole animal world furnishes us with commentaries on their truth. Man maintaining a temperature, as has been said, of about 98 degrees, other animals are at other degrees, some being cold-blooded and some hot. The particular point they reach depends, as direct observation shows, on the quantity of oxygen they consume, or, in other words, on their respira- tion. Birds, whose breathing mechanism is by far the most elaborate and extensively developed, have by far the highest temperature. The snake or the tortoise, whose rate of respiration is very slow, and which consume but little oxygen, have a correspondingly low degree of heat. USES OF WATER. 21 And in those creatures which at one period of the year are in full activity, but at another lie dormant or hibernate, as tliey begin to respire more slowly their temperature begins to decline, and when they have sunk into their winter's sleep their breathing is scarcely perceptible, and their warmth scarcely above that of the sm-rounding air. In what has been thus far said we have been considering those oper- ations of the system which tend to the production of heat, causes of cool- and the maintenance of the whole mass of the body at a tem- mg of the body. perature above that of the surrounding air. But it is obvious that pro- vision must be made to prevent any undue rise, so that between those causes of elevation and these of depression a due equilibrium may be main- tained. If a very large quantity of combustible matter, under the form of food, and about an equal weight of oxygen, are necessary for obtaining a proper heat, we should also recollect that nearly tlu-ee quarters of a ton of water are consumed each year. The duty which this water ^^ •' '' Uses of water, cuscharges we may next consider. That duty is twofold. 1st. The removal of solid material in a state of solution ; and, 2d. The production of cold by evaporation. It is the cooling agency which is of most interest to us in our present inquiry, but a few remarks as regards the removal of solid matter may not here be misplaced. 1st. Water, then, exerts its solvent power for the removal of all those substances which, arising incessantly in the animal system, can ns solvent not assume either the vaporous or gaseous state. In this con- po'^'^r. dition are the different saline bodies, such as the sulphates which are com- ing from the destruction of the muscular tissues, as volmitary and invol- untary motions are performed ; or the phosphates which are produced by the destruction of cerebral and nervous matter. In the same condition stand nearly all the nitrogenized results of the destruction of the soft parts, and which are to a great extent to be removed as urea. Water dis- soKang with more or less facility these various bodies permits their escape from the system by the secreting action of the kidneys, which, strain- mg or filtering them from the blood, dismiss them to the bladder, from which they are periodically removed. The skin is no inefficient auxiliary to the kidneys in effecting this re- moval of water charged with soluble matters. All over its surface are scattered in profusion the ducts of the perspiratory glands, which consist of a convoluted tubing abundantly supplied with blood-vessels. The final mode of action of these glands depends on extraneous circumstances. Most commonly the fluid is carried away under the form of a vapor or in- sensible perspiration, but when the secretion goes on more rapidly, or the dew-point of the suiTOunding air is high, it then accumulates as drops of sweat. The amount of water thus removed, even by insensible perspira- 22 COOLING BY EVAPOEATIOX. tion, is greater tlian might be supposed, yet it corresponds "svith the ex- tent of the pro-vision. The length of the water-secretmg tubing in the skin of a man is about twenty-eight miles. Thus by the action of the kidneys and the skin large quantities of wa- ter are dismissed, either under the liquid or vaporous form. A third or- gan is concerned in this important duty. It is the lungs. These, how- ever, are limited in their operation to its exlialation as vapor or steam. That water abundantly escapes from them is plainly shown when the days are cold, the moisture as it comes from the respiratory passages condens- ing into a visible cloud when it encounters the air. It is estimated that the loss of water by the skin and lungs conjointly is about IS gi-ains in a minute, of which 11 pass off from the skin and 7 from the lungs, flak- ing due allowance for the variable action of the skin as dependent on the dew-point and other such causes, we can scarcely set down the entire quantity at less than 1000 pounds a year. In the same period the quan- tity of water lost as urine may be taken at 900 pounds. It may perhaps be remarked, that here we are assuming a loss of 1900 pounds, when the quantity of water annually taken is only 1500 pounds. But it is to be recollected that not only does water form a very prominent constituent of the solid food, whether vegetable or animal, but also that much arises from the oxidation of hydrogen in the interior of the system. 2d. Water also exerts a cooling influence, arising from its evapora- Cooling influ- tion from the surface of the skin and the cells of the lungs, ence of water, rpj^^ difference between water in the state of an in^asible va- por and in the liquid condition consists in this, that the vapor contains 1114 degrees of heat which the liquid does not. When, therefore, it evaporates from a surface of any kind, as from the skin, it obtains there- from that large amount of latent heat, and so tends to cause the tempera- ture to decline. Not that this is the only cooling agency at work. Ra- diation might also be mentioned ; for, just as a warm inorganic body cools by the escape of radiant heat from it, so too does a li-ving being. These considerations explain how an equilibrium of temperature is es- Equnibriuin of tablished. By the process of respiration there is a constant heat m man. tendency to increase the heat ; but by evaporation of water, radiation, and other cooling causes, there is a constant tendency to dimin- ish it. A balance is struck between the two processes, and in man a temperature of 98 degrees is kept up. This average temperatiu'e is, however, easily departed from. Through some trivial cause the cooling agencies may be interfered with, and then, the heating processes getting the superiority, a high temperature or fe- ver comes on. Or the reverse may ensue. In x4.siatic cholera, the con- stitution of the blood is so changed that its cells can no longer carry ox- ygen into the system, the heat-making processes are put a stop to, and, PHYSICAL MECHANISM OF MAN. 23 the temperature declining, the body loecomes of a marble coldness charac- teristic of that terrible disease. The animal mechanism is thus the focus of intense chemical changes, and great quantities of material are required in very brief Necessity of re- spaces of time for its support. We have seen what is the ^f^^ "^ j^^® ^^®" use of the combustible matter employed as food, what of the wastes, water, what of the air, how, these reacting on one another, a high but reg- ulated temperature is kept up. Much of what has been thus far said has had reference only to the de- struction of tissues. This waste of matter arises for a double reason, partly to give origin to the heat which animals require, and partly as a consequence of intellectual acti^dty and muscular motion ; for no move- ment can be made without a destruction of muscular fibre, and all mental and nerv^ous actions imply the waste of a certain quantity of vesicular substance. For this reason, after an animal has undergone violent mus- cular exercise, the quantity of urea and sulphuric acid in the urine is in- creased, this bemg the chamiel through which those results of the de- struction of muscular fibre are removed ; or, after severe mental or intel- lectual duty, there is more phosphoric acid than usual in the urine, be- cause of the greater oxidation of phosphorus which has taken place in the bram. But of course this destruction of tissue must be compensated by a re- pair if a normal condition and health are preserved. The action of the air is not directly upon the food, for intermediately and temporarily the food is converted into the living mechanism. The dead material is awakened into life, and for a time, though only for a time, becomes a portion of the living and feeling mass. The functions and actions we have been considering imply the pro"\'i- sion of many complicated mechanisms. There must be means yarious mech- for effecting the introduction of the air ; these, in man, depend anisms wanted „.., ,.., . ^ n . 1 • for removal of on calling mto operation its pressure. A system ot tubes is ^^ste and for necessary for its distribution to the points at which it is re- repair. quired, and in like manner a system is required for carrying away the wasted products of decay. The new material which is destined to re- place the parts which are thus disappearing, and to keep the economy in repair, must be submitted to such processes of mechanical and chemical preparation that it may be dissolved in the blood, and carried wherever it is wanted. It must therefore be cut and crushed by teeth driven by pow- erful muscles, dissolved by acid and alkaline juices in digestive cavities set apart for that purpose. From these it must be taken by arrange- ments which can absorb it and cany it into the torrent of the circulation. Physical means must be resorted to, not only for the impulsion of these newly-absorbed nutritive juices, but likewise to drive the blood in its 24 THE SOUL. proper career of circulation. It is needless here to dwell on the manner in which the most refined principles of hydraulics are brought into play, or to speak of the manner in which forces of compression and elasticity are introduced ; how that there are valves which open only in one way to let the current pass, or how some of these, as in the like human con- trivances, are tied down in their action by cords. Moreover, since it is required that the animal shall go in search of its food, muscles of loco- motion, which act upon purely mechanical principles on the bony skele- ton, must be resorted to, and so the animal structure becomes a most elaborate and complicated machine. In this regard the human body may be spoken of as a mere instrument Physical as- 01' engine, which acts in accordance with the principles of me- pectof man. chanical and chemical philosophy, the bones being levers, the blood-vessels hydraulic tubes, the soft parts generally the seats of oxida- tion. But if we limit our view to such a description, it presents to us man in a most incomplete and unworthy aspect. There animates this machine a self-conscious and immortal principle — the soul. Though in the most enlarged acceptation it would fall under the prov- The soul • its ^^^® ^^ physiology to treat of this immortal principle, and to nature and re- consider its powcrs and responsibilities, these constitute a sponsi 1 1 les. g^^]3Jg(.^ ^^ once SO boundless and so important, that the phys- iologist is constrained to surrender it to the psychologist and theologian, and the more so since the proper and profitable treatment of it becomes inseparably involved with things that lie outside of his domain. Yet under these circumstances, considering the ever-increasing control which scientific truth exerts over the masses of men, considering too how much the welfare of the human family depends on the precision and soundness of its religious views, it is the duty of the physiologist, if for the reasons that have been specified he yields this great subject to others, to leave no ambiguity in the expression of the conclusion to which his own science brings him. Especially is it for him, whenever the oppor- tunity offers, to assert and to uphold the doctrine of the oneness, the im- mortality, the accountability of the soul, and to enforce those paramount truths with whatever evidence the structure of the body can furnish. For this reason, he can not recall but with regret the existing u.se of many terms, such as mind, intellect, vital principle, sj)irit, which, though they were at first doubtless employed as expressions of the functions or qualities of the soul, have in the course of time gathered other meanings and confused the popular ideas. They have brought about a condition of things in science not unlike that which prevailed in theology during the reign of poly theism. Constrained, perhaps, himself by the necessities of language to use such phraseology, it is for him at the outset to leave no doubt of the views he entertains, and, as far as he can, prevent such THE VITAL PRINCIPLE. 25 expressions from frittering away the great truth that, as there is but one God in the universe, so there is hut one spirit in man. On one of these terms, the vital principle, I may make a few remarks, since, from being a mere expression of convenience, it has by de- The vital grees risen among physicians and physiologists to the rank of pi'moiplc. designating an existing agent, by some regarded as of the same kind as light, heat, electricity, or gravitation — nay, even superior to them, since it is its peculiar attribute to hold them all in check. Animated by this ex- traordinary power, organic substances are supposed to withstand every external influence, and to submit to physical agents only after this prin- ciple has left them. Such a preposterous doctrine will not bear the touch of exact science for a moment. It is only a relic of the old meta- physical system of philosophizing, which accepted a name in lieu of an explanation, which preferred the dogma of the horror of a vacuum to the more simple but material view of the pressure of the air. By the aid of this imaginary principle, complete physiological systems have been wov- en, in which every act and every condition of the animal economy is spon- taneously explained, and nothing remains for solution. But by the stu- dent of nature, whose mind has been trained in positive science, the im- posture is detected. He sees at a glance that this is not the style of the Great Artist. The problems of organization are not to be solved by em- pirical schemes ; they require the patient application of all Importance of the aids that can be furnished by all other branches of hu- eu^ hf physi- man knowledge, and even then the solution comes tardily, ology. . Yet there is no cause for us to adopt those quick but visionary specula- tions, or to despair of giving the true explanation of all physiological facts. Since it is given us to know our own existence, and be conscious of our own individuality, we may rest assured that we have what is in reality a far less wonderful power, the capacity of comprehending all the conditions of our life. God has framed our understanding to grasp all these things. For my own part, I have no sympathy with those who say of this or that physiological problem, it is above our reason. My faith in the power of the intellect of man is profound. Far from suppos- ing that there are many things in the stmcture and functions of the body which we can never comprehend, I believe there is nothing in it that we shall not at last explain. Then, and not till then, will man be a perfect monument of the wisdom and ppwer of his Maker, a created being know- ing his own existence, and capable of explaining it. In the application of exact science to physiology, I look for the rise of that great and noble practice of medicine which, in a future age, will rival in precision the me- chanical engineering of my times. In it, too, are my hopes of the final extinction of empiricism. Even now this method is attended with results which must commend it to every thoughtful mind, since it is connecting 26 SUBDIVISIONS OF PHYSIOLOGY. itself with those great truths which concern the human family most closely, and is bringing into the region of physical demonstration the ex- istence and immortality of the soul of man, and furnishing conspicuous illustrations of the attributes of God. CHAPTER II. or FOOD. 77(6 natural Subdivisions of Physiology. — Of Food: its Sources and Classification — its Value not altogether dependent on its Composition. — Of Milk: its Composition, and Use of its Water, Casein, Sugar, Butter, and Salts. — Variations in the Composition of Milk. — Of Bread. — Of mixed Diets. — Of the embryonic Food of Birds. — Nutrition of carnivorous and herbivorous Animals. — Food formed by Plants and destroyed by Animals. — Uses of mixed Food and Cook- ing. — Absolute Amount of Food. Physiology possesses a very great advantage over many other sciences Subdivisions of in offering its leading problems and doctrines in a certain physiology. well-marked order or sequence, a connected whole, with only here and there points of digression, but those points often of very striking interest. Thus pursuing the train of reflections entered on in the pre- ceding chapter, we should have to consider the nature of the food, the manner of its preparation by the process of digestion, the mechanism by which it is taken up from the cavities in which it has been so prepared, and that by which it is distributed to every part. We should have to show the way in which it becomes incorporated as a portion of the living mass, its duration in that condition, and the manner of its decay. We should have to show by what physical means and through what mecha- nism the air is introduced to effect the destruction of the dying parts, and how, as the consequence of this, a fixed temperature is maintained. The causes which lead to variations of this temperature, and the manner in which the wasted products are removed by the skin, the lungs, the kid- neys, might next obtain our attention. The complicated machinery nec- essary to accomplish all these pui-poses requires to be made to act in uni- son in all its different parts, a condition which introduces to us the nerv- ous system. A consideration of the structure and gradual development of this system leads to the stmcture of the various organs of sense, and to the operations of the intellectual principle itself. Thus in succession we should have to treat of digestion, absorption, circulation, respiration, secretion, nutrition, and innervation, and to close the whole with the con- sideration of reproduction. This is the order which I propose to follow, and shall devote this chapter to the nature and qualities of the food. HISTOGENETIC AND CALORIFACIENT FOOD. 27 The supply of food to animals requires a more complicated provision than it does to plants, in which the elaborating organs, the c^^^^.^^^ of f d leaves, presenting themselves superficially, are always in for animals ami contact with the air, from which much of their nutrition is ^ ^^^ ^' derived. And as one portion after another becomes exhausted, it is re- newed by simple mechanical agencies, such as the tremblmg of the leaf, the warmth of the sun, or the winds. Food, therefore, comes spontaneously to plants, which need no powers of locomotion. And though, as we shall hereafter find, muscular move- ment requires as its essential condition the waste of tissue, it is not nec- essaiy for their nutrition that plants should destroy organized substance. But an animal must seek its food, and for this pui'pose is endowed with locomotion, mvolving the destruction of tissue. In a chemical point of view, plants are organizing, and animals destroying machines. Nor is this general assertion controverted by the apparent exceptions which are here and there presented, as, for example, that the herbivora can form sugar and fat from food in which those substances did not pre-exist, and the salts of the biliary acids, which are never found in plants. To obtain for animals the necessary supply of nutriment, the resources of nature are displayed in the most wonderful contrivances. According as their modes of life may be, one takes its food with its teeth, another with its lips, another with its fore member, another winds around it its whole body. The geometrical spider weaves a net, and lies in wait for his prey ; the ant lion digs a pit in the sand. Some rely upon labor, some upon force, some upon fraud. Man depends upon all. Viewed as regards its physiological distinction, the food is generally considered as of two kinds : Histogenetic or tissue-making, and classification Calorifacient or heat-making. Histogenetic food furnishes the ^^ foo"^ ™^^ ,.,, Ill • 1 histogenetic chemical substances — carbon, hydrogen, oxygen, nitrogen, sui- and calorifa- phur, chlorine, phosphorus, iron, potash, soda, lime, &c. Ca- '^^'^°*- lorifacient food furnishes carbon and hydrogen mainly. In consequence of this chemical constitution, tissue-making food is sometimes called ni- trogenized, and heat-making non-nitrogenized food. The former is also sometimes designated nutritive, and the latter respiratory. It is, however, to be distinctly understood that these divisions are only adopted for the sake of convenience, and that they have no natural foun- dation. Thus it will be found, when we examine the functions which the fats discharge, that though they are non-nitrogenized bodies, and are, therefore, considered as belonging to the class of respiratory food, there is every reason to believe that they are essentially necessary to tissue development, and that the metamorphoses of nitrogenized bodies can only go on in their presence. They are, therefore, as truly essential to nutrition as are the latter substances. 28 CLASSIFICATION OP FOOD. So, too, as respects the alburaenoid "bodies, of which it would be incor- rect to speak as though they were limited to nutrition. In their decay or descending metamorphosis in the organism, they give rise to the evo- lution of heat, and are at last dismissed under the aspect of products of oxidation. They are, therefore, as far as this goes, as much respiratory food as are the fats themselves. Other ciassifi- Perhaps the most convenient subdivision of food articles cations of food, jg presented in the four following groups: 1st. Carbohydrates, or compounds in which carbon is united with hydrogen and oxygen, their proportion being that for forming water. Starch, sugar, gum, cellulose, are examples. 2d. Hydrocarbons. Ck)mpounds containing unoxidized hydrogen. The oils, fats, and alcohol, are examples, 3d. Albumenoid bodies. These contain nitrogen. Albumen, fibrin, casein, are examples. 4th. Salts. Any classification of food articles which does not con- tain this group is imperfect ; for salts are not only absolutely essential to organic processes, but also to the construction of many tissues. As an example of the former case, the chloride of sodium may be mentioned; and of the latter, the phosphate of lime. It has been supposed that the tissue-making power of any kind of Value of food food depends on the quantity of nitrogen it contains, and does not de- ^j^g^^ jj-g yaluc may therefore be determined by chemical anal- pend wholly on . , . . . its coniposi- ysis. Upon this principle tables have been constructed, '^°°" showing the agricultural worth of diiferent articles of forage for domestic animals. But, as will be found hereafter, when we consider the physiological effect of the allotropism of bodies, these tables are not of the use supposed. Without entering into details at present, the case of gelatin may be taken as an example ; this, though a substance abomiding in nitrogen, possesses no tissue-making value, but in reality belongs to the calorifacient class, and therefore its administration in the sick-room, under the various well-known forms of jellies, soups, etc., is altogether deceptive as regards any nutritive power, since it undergoes speedy oxidation in the system, and the products of its change escape by the kidneys and the lungs. The value of food is not only dependent on the occurrence of certain chemical elements ; they must also be present in certain allotropic states. The same remark applies to the tables which have been constructed, showing the amount of caloric furnished by different varieties of heat- making food. The quantity of heat set free during the combustion of a substance depends not only on the nature of the elements composing it, but also on the particular states in which they occur. Combustibles may have the same chemical composition, but very different heating power. COMPOSITION OF MILK. 29 Food which is typically perfect, is presented by nature to the young of various animals. In milk, or in the egg, we should ex- Miikasanarti- pect to find whatever is necessary for the growth of the tis- cie of food: its sues, and for the performance of the functions. An exam- ^^^"^^ ination of milk will therefore illustrate the essential characters of the different elements of food. Com])osifion of Milk. Water 873. Casein 48. Sugar of milk 44. Butter 30. Phosphate of lime 2.30 Other salts. 2.70 1000.00 In this we notice, first, the large proportion of water present, almost nine tenths of the whole amount. The double duty of this The water of water has already been mentioned, to remove from the sys- "^i^^^- tem effete substances which are not of a vaporous or gaseous form, and which can not escape through the lungs, and to regulate the temperature by evaporation. We might have added to these that it imparts a due fluidity to the blood. These are conditions as necessary to the infani as to the adult, and it should be remembered that two thirds of the weight of the body are water. Next follows the nitrogenized principle casein, which is closely re- lated in composition to muscular flesh. It is the tissue-mak- The casein of ing, histogenetic, or nutritive element of the milk, and has been ™^^'^- elaborated from the albumenoid substances of the mother's system. It is to be converted into the muscular, gelatinous, and other soft tissues of the infant. Casein is one of a group designated as the neutral nitrogenized bodies, of which some of the more prominent are albumen, fibrin, Nature of pro- and globulin. From an opinion that these all contain the ^^^"^ iiodies. same organic radical, they are often termed the protein bodies. They appear to exist in two different physical conditions, soluble and insolu- ble in water ; they all contain sulphur, and exhibit a proneness to pass into the putrefactive fermentation. As this takes place when they have reached a certain stage of decay, they act upon other bodies as ferments. Their constitution is represented in common by the formula ^48 Hgfi Oj^ Ng. Of the whole group, albumen may be taken as the type and most import- ant member. Indeed, as will be found hereafter, in the process of digestion the others are invariably converted into it. The white of the egg and the serum of the blood are usually referred to as examples of albumen, though they differ in several particulars from one 30 CASEIN AND FIBRIN. another. Allbiimen forms "basic, neutral, and acid compounds. It is a basic albuminate of soda which is found in the egg and in serum of blood. In certain diseased conditions the blood contains the neutral al- buminate. Casein presents nearly the same constitution as albumen, but differs from it in its physical properties ; for, while a solution of albumen is coagulable by heat, one of casein is not, but lactic and acetic acids coagulate it, though they have no such effect on albumen. While, so far as their protein nucleus is concerned, the two substances agi'ee in composition, they differ in this respect, that casein appears to contain a less proportion of sulphur, and no phosphorus. It is interesting to re- mark that, during incubation, casein arises from albumen in the eggs of birds. Closely allied to albumen and casein, and having the same protein nu- cleus, is fibrin, which likewise exists in two states, soluble and insoluble. Its solidification or coagulation can be produced by the action of sulphuric ether, which does not affect albumen. Moreover, in the coagulated state fibrin decomposes the deutoxide of hydrogen, but albumen does not. The most important difference between them is, that in the act of coagulation albumen shows no disposition to assume a definite structure, but fibrin does — fibrillating, as it is termed. The analogy of constitution and closeness of relation of the two substances is demonstrated by the fact that by nitrate of potash coagulated fibrin may be changed into albumen, and the same conversion is accomplished in the stomach by the digestive juices. It is generally supposed, however, that fibrin contains a larger pro- portion of oxygen than albumen, a conclusion which seems to be confirm- ed by physiological considerations respecting its origin. For this reason, Mulder describes it as a higher oxide of his hypothetical protein. It al- ways is associated with fat, or, perhaps more correctly, with soaps of ammonia and lime. Fibrin is found in the chyle, lymph, and blood. In the latter fluid its quantity varies in different parts of the circulation. The blood of the portal vein yields it in smaller proportion than that of the jugiilar. It is also affected very much by diet : thus Lehmann found that under an ani- mal diet there was much more fibrin in his blood than under a vegeta- ble one, a result which has been confimied by experiments on dogs. It has also been observed that its quantity is increased during starvation. Biit the blood of herbivorous animals contains more than that of carnivo- rous ones, and that of birds contains the most of all. These remarks on the composition and physical properties of casein, albumen, and fibrin, have been introduced for the pui-pose of illustrating the facility with which these bodies are mutually convertible, and more OF THE SALTS, BUTTER, AND CURD OF MILK. 31 particularly for showing that tliere is nothing whatever mysterious in the casein or curd of milk arising from the albuminous serum of the mother's blood, and being transmuted into the fibrin structure of the muscular tissues of the infant. Returning now to our examination of the composition of milk, as set forth in the preceding table, we find that two respiratory el- The sugar and ements are next upon the list : 1st. Sugar of milk, which is Gutter of milk. to be converted into lactic acid, partly by the agency of the saliva, and chiefly in intestinal digestion ; 2d. Butter, which is the oleaginous or tatty portion, and of which a part is to be deposited in the adipose tis- sues for a time of need, and a part, along with the lactic acid and excess of sugar, is to be burned at once for the production of heat. The inorganic body, phosphate of lime, is necessary for the earthy por- tion of the skeleton, and probably the reason of the introduction ^, of casein, to the exclusion ol other protein compounds, depends milk, particu- on the power it possesses of holding phosphate of lime in solu- ^^^^th^°"d tion, not less than 6 per cent, of its weight of this earthy body chloride of so- being often obtainable from it. Among the other salts of ^"™' the milk, chloride of sodium may be pointed out as of special importance. It undergoes decomposition in the system of the infant, its hydrochloric acid giving acidity to the gastric juice, its soda entering into the compo- sition of the bile and various salivary secretions. It also imparts solu- bility to albumen, and, in some degree, regmlates the facility with which that substance coagulates. It impedes the coagulation of fibrin. Milk is not a chemical compound, but a variable mixture of different ingredients, which, under proper circumstances, may be sepa- Making- of rated. When the fluid is allowed to rest for some hours at the butter. ordinary temperature, the fat-globules rise to the surface as cream, which, submitted to a strong agitation with air in the process of churning, forms butter. The casein of milk can be readily coagulated by rennet (which is the mucous membrane of the stomach of the calf) at a temperature Makin"-of of 120°. If parted from the residual whey, mixed with a little cheese. salt and yellow coloring matter, and subjected to the action of a suitable press, it is formed into cheese. No better examples of the tissue-mak- ing and heat-making elements of food can be offered than cheese and butter respectively. When milk is exposed to the air, its sugar, under the influence of the casein or curd, gradually disappears, turning into lactic acid, Lactic acid in and the milk becomes sour. The composition of sugar and ^°^^^ "^i^^^- lactic acid is such, that we might, without much error, say that an atom of sugar symmetrically bisected will yield two atoms of lactic acid. This effect is produced by the casein commencing to pass into a state of de- 32 VAEIOUS KINDS OF MILK. cay under the influence of the atmospheric air. It is likewise produced during digestion by the saliva, and also by the pancreatic juice. The turning sour of milk on the stomach is due to the transmutation of its sugar into lactic acid. An infant finds in its mother's milk whatever it wants for the growth Physiological of its own Ibody. In its system the curd resumes the form uses of milk, of albumen, or passes into the condition of fibrin or syntonin, and in this manner its muscular and gelatinous tissues are made. • The butter is deposited in the adipose cells, or burned at once for the pro- duction of animal heat, a part of it, however, being incidentally consumed, as will be hereafter explained, in the fabrication of fibrin and for other histogenetic purposes. The phosphate of lime is carried to the osseous system, now in a state of rapid increase, and bone is formed from it. But though milk is so well adapted to the wants of infantile life, it is unsuited to the adult. Its nitrogenized principle, casein, though in suf- ficient quantity for the repair of muscular waste and development at the former period, is inadequate to these purposes at the latter, when de- struction, arising from the incessant activity of the muscular system, is „ . , . , so ffreatly increased. It is interesting to remark how the various kinds . . . . . of milk for dif- composition of milk is modified when there is a necessity to erentanimas. j^gg^ these indications, its nitrogenized principle being in- creased in the case of animals such as the cow and horse, the young of which commence locomotion almost at birth, or at a far earlier period than the human infant. This excess of casein is necessary for the re- pair of the resulting waste. The Constitution of Milk. Source. Casein. Sugar. Butter. Goat's milk Cow's milk Human milk 80 63 32 40 28 36 40 40 29 This table presents an explanation of the unsuitableness which is sometimes remarked in the milk of the cow when used for the nourish- ment of children. Milk which is adapted to the wants of the calf is not adapted to the fanctional wants of the child. Experience has taught the nurse that these difficulties may in part be removed by diluting it with water and sweetening it with sugar, the effect of this being to reduce the percentage of the nitrogenized element, the casein, and to increase that of the respiratory, and so approximate the composition more closely to that of human milk. Moreover, milk is not suitable as the sole nourishment of adult life, since it does not contain in sufficient quantity those phosphorized com- pounds which are necessary for the repair of the waste of the cerebral and nervous tissues, which at this period are much more active than in infancy. OF BREAD. 33 Variations in the composition of milk from its normal standard are ob- served to depend upon age and bodily liealtli. Young fe- influence of males, from tifteen to twenty, yield a milk more rich in sol- ^s« and health ' .... *^" ^"^ compo- ids than that which is given at thirty-tive or forty. Gesta- sitionofmiik. tion at a late period increases the solid portions. The following table of Vernois and Becquerel illustrates the influence of disease : Influence of Disease on the Constitution of Milk. In Health. Acuto Disease. Chronic Disease. Water Casein nncl extractive... 889.08 39.24 43.64 26.66 1.38 884.91 50.40 33.10 29.86 1.73 885.50 37.06 43.37 32.57 1.50 Butter Salts 1000.00 1000.00 1000.00 Of bread. From this consideration of the nature and properties of the food of in- fancy, we may pass to the examination of that of the mature period. Experience has shown that, of all articles of food, bread made from. wheaten flour meets best the requirements of the adult life of man. It seems to contain all that is necessary for support. A very simple analysis will show how it presents both the respiratory and nutritive elements. If such flour be made into a paste with water, and be gTadually waslied with a larger quantity, an elastic coherent mass is left, and Examination the water assumes a milky turbidity. After a time it be- °y]^e°tand f comes clear, through the settling of a white precipitate, which other grains, is starch, the leading member of the respiratory group. The elastic sub- stance is gluten, which is a true vegetable fibrin, mixed with another nitrogenized body, gliadine, which may be removed, along with a certain quantity of oil, by washing with ether and alcohol. Thus, simply by washing in water, flour may be separated into two physiological elements, respiratory and nutritive, the former being the starch, and the latter the gluten. The relative quantity of these substan- ces difters in different samples of flour, and, other things being equal, the greater the amount of gluten the more valuable the sample, because the more nutritious. It is interesting to remark that the liquid from whicli the starch has settled, if brought to the boiling point, becomes turbid again, from the coagulation of the vegetable albumen it contains. Other grains, treated in the same manner, yield similar results. The flour of barley and of the oat, when washed with water, do not, however, yield gluten, but a pure fibrin, with a separation of starch. The fibrin occurring in these grains is replaced in other nutritious seeds, such as peas and beans, by legumin, which, like the casein of milk, does not coagulate by boiling, but merely forms tenacious skins as it is evaporated. These may be removed by skimming. This substance,. C 34 OF MIXED DIETS. which pi'esents many analogies to casein, is coagulable by acetic acid and alcohol, and, if mixed with sugar, turns curdy, and becomes sour from the presence of lactic acid. It differs from casein in not dissolving in concentrated acetic acid, and, when precipitated by an acid, being un- acted on by carbonate of lime. It is, however, coagulated by rennet. Thus, when we use brea;d made of any of the common varieties of flour, we find in it both kinds of food, the respiratory and nutritive — the former as starch, and the latter as fibrin. But civilized man has greatly improved on the simple diet which Na- Use of butter ture fiuTiishes, and, without knowing the immediate or philo- on bread. sopliical rcason, has added articles which increase the respira- tory element. The proverb says, "It is good to have bread, but it is better to have bread and butter." Let us examine why it is so. Wheaten flour, in its relations to the animal system, is defective in one point — its respiratory element, the starch. Now the constitution of starch is, that in its dry state it contains much more than half its weight of wa- ter, none of its hydrogen being free, but all oxidized. It is, therefore, only by the use of very considerable quantities of bread that the neces- sary amount of respiratory food can be had for keeping up the tempera- ture to the proper degree. But if butter be put upon the bread, the effect is different. In common with all oleaginous bodies, butter contains an excess of hydrogen, and therefore, under the same weight, possesses a very high heating power. The defect of the flour is thus compensated, and by the use of quite a moderate quantity a high temperature can be maintained. It would be very interesting to examine in this way the physiological relations of the diets adopted by communities of men, and the gTcat changes which, at quite a recent period, have taken place through the in- troduction of tea, coffee, and chocolate on an extensive scale among civ- ilized nations. Before the discovery of the passage to the East by the Cape of Good Hope, and the establishment of direct commercial relations between Western Europe and China, the general diet of the agricultiu'al classes consisted chiefly of the common products of the farm and sub- Of mixed di- stanccs readily obtained in domestic economy, such as bread, cheese^ and^^^' ^^^ chccse, and beer. In a theoretical point of view, we can beer. Scarcely conceive of a diet more conducive to the sustenance of the bodily frame. The constitution of wheat flour shows that it con- tains the elements necessary for life ; and cheese, which may be regarded as the preserved curd of milk, is an excellent flesh-producing body, the casein of which it consists being readily convertible into muscle-fibrin. The common salt used in its preparation promotes the function of diges- tion, by furnishing hydrochloric acid and soda. In addition, there are also in the beer, an alcoholic and intoxicating liquid, all the advantages EMBRYONIC FOOD OF BIRDS. 35 of a IiigHj combustible body for the purposes of respiration. Whatever, therefore, is requisite for the well-being of the animal economy is present in abundance in such a diet. From an examination of the diet-scales of the educational and invalid establishments of London, the prisons and the hospitals, Beneke obtains the result that the nitrogenized should be to the non-nitrogenized food in weight as one to five. From other data, Frerichs calculates Ratio of nitro- that the diurnal consumption should be 2.17 oz. avoirdupois ^on-nrtro"en- of nitrogenized, and 15.54 oz. avoirdupois of non-nitrogen- izedfood. ized food, that is, about as one to seven. Whatever is taken more than this is superfluous. The peculiar advantages arising from the use of casein, which in a solu- ble form possesses the quality of dissolving large quantities of phosphate of lime, unquestionably determine its employment as a constituent of milk. But there are circumstances under which a necessity arises for the use of other nitrogenized compounds, such as albumen, in early nu- trition ; and then it is remarkable by what indirect methods the difficulty of its want of solvent power over that earthy body is compensated for. The foetal period of the life of birds furnishes an example. In the egg there is, of course, whatever is wanted for the development Development of the young animal : for, merely by the process of incuba- °,^ '^ '?™ •^ o^ ^ ' ' J J r ^ the egg: origin tion, or submitting the egg to a due temperature for a suita- or its parts, ble length of time, with the access of atmospheric air, the young chicken forms, Avith all its parts complete — its bony, muscular, nervous systems, feathers, beak, claws. The phosphate of lime required for the skeleton is not present as such, but is formed as incubation goes on ; for in the yolk there is free phosphorus, to which the air finds access through the pervious shell, and, effecting its oxidation, phosphoric acid is the result. This reacts on the carbonate of lime, of which the shell consists, decom- poses it, and the phosphate of lime forms. For this reason we observe, as the incubation proceeds, that the shell becomes lighter and thinner. The albuminous fluid which constitutes the white of the egg has little power of holding bone-earth in solution ; but by manufacturing the salt in this manner, as it is wanted, the development of the young bird goes on without difficulty. To insure the due supply of oxygen, an air-bub- ble is placed at the broad end of the egg, so that, should any transient circumstance interfere with the passage of air through the pores of the shell, there is a little reservoir of that material on which to rely. The mammalia find in milk all that they need in their infantile life for their nutritive purposes. In the same manner birds, in their foetal life, have whatever they require in the egg. For the former, casein is the nutritive element ; for the latter, albumen. In both cases a ready transmutation of that element into muscle-fibrin occurs. 36 FOOD OF CARNIVORA AND HERBIVOEA. At a maturer period of life, animals may be divided into two groups, carnivorous and herbivorous, or those which feed exclusively on flesh, and those which feed on vegetable substances. Between these may, perhaps, be introduced a minor group, partaking of the manner of life of both. The carnivorous animal finds in its prey all that is required for nutri- X trition of '^^°'^' ^"^ ^^^ discharge of its functions. Digestion under these carnivorous circumstances is reduced to its simplest conditions, and is animals. scarcely more than a process of solution. In the stomach the fibrin is brought into a soluble form ; in the duodenum the fats are re- duced to an emulsion. The digestive apparatus has but little complexi- ty. The stomach maybe regarded as a mere enlargement or pouch upon the alimentary canal, having, along with the intestine, the office of bring- ing the food into such a condition that it can be taken up by the veins and lacteals, and so pass into the circulation. The various constituents now revert into the same state in which they were before digestion be- gan, the fibrin aiding in the repair of the wasted muscular tissues, and the fats being deposited in the adipose cells. The bones, feathers; and other such matters as have not been dissolved by digestion, are cast out. In the production of heat and motion the carnivorous animal consumes itself, and, through the oxidation incessantly going on by means of the air introduced by respiration, carbonic acid, ammonia, water, sulphuric and phosphoric acids are constantly forming. On a superficial view it might be supposed that in the other gi-oup, the herbivorous, the case is quite different. These seem to Nutrition of ■,. ■ t • ■ n i mi j.i t. herbivorous Spend all then* lives m obtainmg lood. ihe ox or the horse, animals. ^^^ ^^^^ ^^-^^^ ^^^ pastures, is all the day long cropping the grass. On a comparison of the quality and nature of the food which they take with the substances of which their bodies consist, there seems to be nothing in common. It was not, therefore, without reason that the earlier physiologists imputed to the digestive organs of this class the power of forming flesh and blood from vegetable matters. When, how- ever, we come to a critical examination of the facts, we find that there is no essential difference between them and the carnivora. When the expressed juice of vegetables is permitted to stand for a time, though it may have been clear at first, a turbidity sets in, and a flaky material is deposited. The substance thus possessing the power of spon- taneous coagulation is identical in that property, and in composition, with animal fibrin. After its deposit, if the clear liquid be warmed to near the boiling point, it again becomes turbid, and a second nitrogenized sub- stance subsides, which, from its quality of coagulating by rise of tempera- ture and its knalysis, is inferred to be identical with animal albumen. When this has been separated by filtration or otherwise, and the juice is NUTRIENT MATTERS PRE-EXIST IN PLANTS. 37 slowly evaporated, tliere come on its surface skins of a body liaving the same qualities as casein ; so fibrin, albumen, and casein pre-exist in plants. Fatty matters of every description may also be extracted from vege- table products. From leaves, seeds, bark, wood, etc., oleaginous bodies can be obtained by the action of sulphuric ether, which removes the fat, and leaves it on subsequent evaporation. It being thus understood that the food of the graminivorous animals contains nitrogenized bodies and fats ready formed, we have clearer views of the function of digestion in those tribes. It is not necessary to im- pute to their digestive organs the power of creating flesh and fat from vegetable matter. The office of the animal is merely to collect. The two groups being compared together, the carnivorous animal receives un- der less compass the required amount of nutrition, and its digestive ap- paratus is more compact. But the graminivorous animal must all the day long collect large quantities of food, out of which it may extract the little nutrient matter they contain. The carcass of an animal, seized by a lion, is almost all digestible, but it would require a very large amount of herbage or of grain to be supplied to an ox to make up the same quan- tity of albumen or fat. Hence the necessary complexity and size of the digestive organs of the herbivorous group, and hence many of their hab- its of life. Moreover, we see that even in this apparently extreme case the ani- mal system does not clearly exhibit any quality of exerting Food formed a formative action, nor of grouping atoms into a state of ^esu-oyed by higher organization. It possesses no special power of mak- animals. ing flesh. To the vegetable world we have to look as the great forma- tive agent. In the organism of plants the various compounds wanted by animals are fabricated. Animals destroy those compounds, and in so doing maintain a high temperature, irrespective of atmospheric con- ditions, and give rise to the phenomena of motion and intellectuality. Universal experience, as well as direct experiment, proves that in the case of man health can not be maintained on a uniform diet, however it may be with animals. A mixed food, which varies from time to time, seems to be essential ; and there can not be a doubt that the changes which physicians have recognized in the nature of the predominating dis- eases, from century to century, are connected with changes which have taken place in the nature of .the diet. The introduction of tea, coffee, the potatoe, and tobacco, must have made a marked impression in these respects. Undue excesses of albumen, oil, or starch, in the diet of an individual, produce a liability to arthritic, bilious, and rheumatic aftec- Necessity of a tions. An abstinence from fresh vegetables and fruits devel- ™'^^^ an°d°use "^ ops scorbutic, and a deficiency of oleaginous materials scrofu- of cooking. 38 ABSOLUTE QUANTITY OF FOOD. lous disease. It is evident tliat a control over these affections may be ob- tained, or even their cure, to a considerable extent, acconiplislied, by suit- able changes in the nature of the food. This is strikingly seen in the improvement of the health of sailors during long voyages, since the intro- duction of vegetable preparations or acid juices. In 1726, Admiral Ho- sier sailed from England to the West Indies with seven ships of the line, and lost his wliolc crew twice by scurvy. The circumnavigation of the globe is now often accomplished without the loss of a single man. I have already remarked the insufficiency of the tables setting forth the value of articles of food as dependent on their chemical constitution. Such tables are of little use, agriculturally, in the case of animals, and still less, physiologically, in the case of man. The art of cooking does not minister alone to the gratification of the palate, it lends a real assist- ance to the operation of digestion. New elements may not have been added, nor existing ones removed in submitting the food to the action of a high temperature, yet such a change is thereby impressed upon it that it becomes more capable of digestion, and more subservient to^the wants of the economy. In determining the absolute quantities of nutrient substances required The absolute ^^ *^^*^ System, Lelimann observes that there are three mag- quantity of nitudes which we are especially called upon to consider : the first is, the quantity of food requisite to prevent the animal sinking from starvation ; the second is, that which affords the right sup- ply of nourishment for the perfect accomplishment of the functions ; and the last is, that which indicates the amount of nutrient matter which may, under the most favorable circumstances, be subjected to metamor- phosis in the blood. The method of finding the minimum of food nec- essary to support life by stopping all supplies without, and determining the quantities of matters which the organism uses by the excretion of urine, fasces, expired and transpired products, though it has yielded re- sults of the utmost importance to science, is nevertheless not altogether reliable, for in such a state of inanition the system is brought into a morbid condition, or, at all events, is not acting in a normal way. More- over, much depends on the activity with which the various functions are carried forward, a necessity for nourishment increasing with increase of external activity. And as to the amount of food demanded for the maintenance of the system at its standard, it must be borne in mind that of the four classes, the carbohydrates, the fats, the albuminous mat- ters, and the salts, no one alone will answer the purpose, but all must be employed together, and this in variable proportion, according as the local, and therefore variable, wastes of the system may have been. These considerations indicate how complicated the problem we have in view really is. QUANTITY OF FOOD REQUIRED. 39 From the experiments of Boussingault with reference to fat, and of Bidder and Sclunidt Avith reference to tlie albuminates, and Maximum lim- of Von Becker with reference to the carbohydrates, we learn ot-*|iufcrcn't^ ck that only definite quantities of these substances can be ab- mentsoffood. sorbed by the intestine in definite periods of time. This maximum limit is, however, far more than the necessities of the system require ; hence in overfeeding, though much of the excess of food passes away with the ex- crement, a very large portion is, as it were, needlessly absorbed, and, un- dergoing metamorphosis in the blood, is removed by the kidneys. To tliis portion Lehmann applies the designation introduced by Schmidt, luxus consumption, or superfluous consumption. Of course, the simplest condition under which we can investigate the normal quantity of food required is that of an invariable weight, and the difficulties of the inquiry are increased when growth, corpulence, pregnancy, or other such states, are included. Though we are very far from being able to offer a complete solution of the problem of the amount of food required, in its most general sense, yet, through the labors of many chemists, we have accumulated several facts which have a bearing on this question. Thus it is known that albu- minous substances alone can not be absorbed in quantity enough to com- pensate for the loss of carbon by respiration. A duck, as is shown by Boussingault, expires in one hour 1.25 grammes of carbon, but can only absorb of carbon in albuminates 1.00 gramme. So , in like manner, fat alone is inadequate, for of this substance 0.84 gramme, containing about 0.70 gramme of carbon, can only be taken up in an hour, and this is not much more than half of what the respiratory operation demands. The carbo- hydrates, however, can be absorbed in sufficient proportion, and in this mixed manner are all the requirements satisfied. Boussingault makes the curious remark that, in the quantity of starch, 5.26 parts, and the quantity of sugar, 5.62 parts, which this bird can absorb in one hour, there are nearly the same quantities, 2.37, of carbon. Among the special investigations which have been made to determine the amount of food used and the amount of educts from the Amount of system, should be mentioned that of Valentin upon himself, food, and His weight was 117 lbs.; his diurnal consumption of food, 6.451 lbs.; solid excrement, .42 lb.; urine, 4.686 lbs.; and 2.751 lbs. perspiration. From the more recent and very exact experiments of Bar- ral, it is inferred that of 100 grammes of carbon which have been ab- sorbed into the organism, 91.59 escape as carbonic acid through the lungs and skin, 4.58 appear in the urine, and 3.83 are re-excreted and appear in the feeces. Upon similar principles, Lehmann computes, from the data furnished by Barral, that for every 100 parts of absorbed nitrogen, 49.6 parts are removed through the skin and lungs, 42.07 are found in 40 OF DIGESTION. the urine, and 8.33 are re-excreted into the feces. As a general result, it follows, from these experiments, that an adult man oxidizes, on an average, 289 grammes of carbon, and 18.6 grammes of hydrogen in twenty-four hours. CHAPTER III. OF DIGESTION. TISSUE-MAKING OR HISTOGENETIC DIGESTION. Nature of Digestion. — The Mouth, Teeth, Stomach. — TJie Salivary Glands. — Different Kinds of Saliva. — Properties of mixed Saliva : its Quantity, Composition, and Functions. — Relation of the Salivary Glands and Kidneys. — The digestive Tract. — The Stoviach. — Gastric Juice.-^— Organs for its Preparation. — Manner of producing Chyme. — Influence of the Nerves. — Artifi- cial Digestion. — Preparation and Properties of Pepsin. — Regional and functional Divisions of the Stomach in Animals and in Man. — Object of Stomach Digestion.— Peptones. — Use of Salt. — Digestibility of various Articles of Food. Before the food can he absorbed and carried to all parts of the sys- Xature of '^em it must be submitted to certain preparatory operations. digestion. '^{xiCQ, it is either to be dissolved in the blood or transported as chyle through the lacteal vessels, it is absolutely necessary to bring it into a condition of solution in water, or at least into a state of minute suspension in that liquid. Received in masses of a certain size, it is first cut and crushed into smaller portions by the teeth, and then brought from an insoluble into a soluble or suspended state by the chemical ac- tion of the digestive juices. In the mouth the food is submitted to a twofold preparation. It is Functions of divided by the mechanical action of the teeth, and also simul- the moutii. taneously mingled with liquids secreted from the salivary- glands. The animal series present us with numberless contrivances for accom- plishing this comminution. The teeth, though of a bony nature, are not to be regarded as appertaining to the skeleton, but rather to the digestive mechanism. Their structure, number, and position differ very much in different tribes. In certain fishes the mouth is almost lined with them. In crabs they extend to the stomach, but in other cases they are restrict- ed to the pharynx, or are wholly absent ; this being the case, for instance, among; the ant-eaters. Those insects whose food is of a fluid nature have Instruments of no need of teeth ; but those which use solid material are ac- commmution commodatcd with suitable instruments of abrasion, such as m various am- _ _ _ ' _ mais. borers, chisels, saws, nippers, the particular mechanism re- THE TEETH. 41 Fig.X. The human lower jaw. sorted to being adapted to the nature of the food. It is to be understood that these mechanical terms are not mere metaphors, they indicate the actual nature of the apparatus. The object aimed at is to obtain the food in such small portions, and in such a bruised or pulpy condition, that di- o-estion can be accomplished promptly. In man the number of ^ . . . The teeth. temporary teeth is twenty, ten in each jaw. They are arranged in three classes — four incisors, two canines, and four molars for the up- per and under jaw respectively. The permanent teeth, which are eventu- ally substituted for these temporary ones, are thirty-tAvo in number, class- itied for each jaw as four incisors, two ca- nines, four bicuspids, and six molars. Their arrangement is exemplified in Fig. 1, representing the lower jaw, in which i is the middle and lateral incisor, c the canine, h the two bicuspids, and m the three molars. The movements of the teeth, aided by those of the tongue, accomplish a due abrasion of the food, and simultaneously incorporate it with the saliva. Tliis is, therefore, a purely mechanical operation. It is analogous to Mechanical na- the methods to which chemists resort in their laboratories ture of mastiea- when they prepare solid materials for exposure to reagents. The mingling of food with saliva, or insalivation, effects a double ob- ject. Coated over with a glairy juice, the bruised substance passes along the oesophageal tube into the stomach ; but there are also certain chemical changes, which, commencing in the mouth, are of essential im- portance to the completion of digestion. The stomach is an expansion of the alimentary canal between the oesophagus and duodenum, of a conical figure, the base of Description of which is to the left. It communicates with the oesophagus the human by its cardiac orifice, and by its pyloric with the duodenum. It consists of three coats or tunics — the serous or peritoneal, which is exterior ; the muscular, which is intermediate ; and the mucous, which is interior. They are connected with each other by cellular tissue. The fibres of the muscular coat run in three different directions, constituting three layers ; the superficial one^ are longitudinal, radiating from the oesoph- agus over the surface of the organ ; those of the middle layer are circular, • or ring-like; they are well developed about the middle of the stomach, and by their contractions sometimes make it assume a divided appear- ance, as though composed of two compartments. Toward the pylorus they are also greatly re-enforced. The fibres of the third layer take, for the most part, an oblique direction. The interior or mucous coat is some- 42 THE STOMACH. times termed the villous, from its velvety appearance. Its color is very variable ; it is folded into ruga?, which admit of variations in the disten- tion of the stomach, vp'ithout interference with the structure or functions of the membranes of which they are a part. The cardiac orifice is pli- cated, and the opening into the duodenum is through a circular fold with a central aperture — the pyloric valve, which being sun'ounded with a band of muscidar fibres, acting as a sphincter, the passage from the stom- ach to the intestine may be entirely obstructed. The stomach is seen in section Fig. 2, a being the oesophagus ; 5, the greater extremity ; c, the smaller curvature ; d, the great curvature ; e, the pyloric or less end ; /, A, the du- odenum ; ^, place of entTy of the ductus communis choledochus and pancre- atic duct. The place of junction of the oesophagus is the cardiac region: the The place of junction of the duodenum is Section of the human stomach showing its mucous interior. membrane is there plicated, the pyloric region. The typical form of the digestive apparatus is a sac with one aperture, Types of the which scrvcs the double purpose of affording an entrance to stomach. nutritive material, and an outlet to undigested remains. In a higher condition it may be conceived of as a tube open at both ends, and having a sac-like swelling on its middle part. The portion of the tube anterior to the sac is the type of the oesophagus, its aperture answ^ering to the mouth, the sac-like swelling being the type of the stomach, and the tube leading from it representing the intestinal canal. In the more ele- mentary of such forms, vessels arise from the walls of the digestive cav- ity, and pass to all other parts of the system. These serve to convey the elaborated material. Certain appendages are soon to be discovered in connection with this sim^jle digestive mechanism. They are for the preparation of salivary, gastric, pancreatic, or biliary juices. In size or development they vary with the habits of life of the animal, or with the nature of its food. Indeed, the same remark may be made as respects the entire digestive tract of the highest tribes. Thus, in the bat the length of the intestine is to that of the body as three to one, but in the sheep as twenty-eight to one. The ruminants generally have an intes- tinal tube of great length. In man and in monkeys the proportion is about five or six to one. Agam, as regards construction, there are many DIFFERENT KINDS OF SALIVA. 43 diversities, the number of digestive dilatations and their size coiTespond- ine in some measure to the nature of the food. Three pairs of glands, the parotid, submaxillary, and sublingual, se- crete saliva. Of these organs the parotid is the largest ; its Different kinds secretion is delivered through the duct of Steno. The sub- °f saliva. maxillary duct is Wharton's, but the sublingual pours its fluid through many small apertures near the frenum linguae. Besides these proper sali- vas, the lining membrane of the mouth yields a fluid, the buccal mucus. The parotid saliva is thin and watery, limpid and colorless, inodorous and tasteless. Secreted during fasting or under the use of xhe parotid sa- stimulating food, it is denser. It contains so large a quanti- l^'^'^- ty of lime that, on exposure to the air, it becomes covered with an in- crustation of the carbonate of that substance. It also contains sulpho- cyanide of potassium. Its organic ingredient, if not albuminate of soda, closely resembles that body. From the chemical constitution of the saliva of the parotids, the phys- iological function of those glands, as aquiparous organs, is established. They yield a certain quantity of watery juice, which, by reason of its thinness or fluidity, is readily incorporated with the food by the teeth. Parotid saliva appears to have no power of transmuting starch into sugar. The submaxillary saliva is also colorless and limpid, tasteless and in- odorous. It contains no morphological elements. It is The submaxil- lighter than the parotid, less alkaline, and contains less lime. ^^^Y saliva. For this reason, when exposed to the air, it does not become incruslfed with carbonate of that earth. It contains sulphocyanide of potassium. It is so viscid and glutinous that it may be drawn into threads. From this physical property it probably facilitates deglutition by furnishing a kind of anti-friction coating. The sublingual saliva is thin and watery, containing, like the parotid, but a small percentage of solid matter, and probably dis- The sublingual charging a similar function. saliva. Besides the special salivary juices, the lining membrane of the mouth pours forth a liquid — the buccal mucus — a thick and ten a- The buccal mu- cious substance, having many epithelial cells. It is alkaline ^"s- in its reaction, does not coagulate on heating, its insoluble salts contain- ing no carbonate of lime. It has been obtained for examination by tying the ducts of Steno and Wharton, keeping the nostrils open and the head inclined, so that, the animal being unable to swallow, the mucus flows out of the mouth. The buccal mucus, if mixed with parotid saliva, does not appear to possess the power of turning starch into sugar, but, if mixed with the submaxillary secretion, it accomplishes that transmutation with facility. The saliva, as obtained from the mouth, is therefore a mixture of the 44 PROPERTIES OF MIXED SALIVA. secretions of the various salivary glands. It may he doubted whether Properties of the method of obtaining it sometimes recommended, by mak- mixed salivas. {^^ pressure undcr the chin and tickling the fauces with a feather, yields it of normal constitution. It is described as an alkaline juice, of a bluish color or colorless, in consistency glairy, readily froth- ing, and therefore well adapted for entrapping atmospheric air. It con- tains, of solid matter, from 0.348 to 0.841 per cent. Its alkali appears, for the most part, to be combined with an organic substance, ptyaline, from which it may be separated by the weakest acids, such as carbonic. In the ash of saliva the alkali occurs chiefly as phosphate : this arises from rearrangement of the constituents during incineration. The saliva con- tains but a trace of alkaline sulphates, the chlorides of sodium and potas- sium preponderating over all the other mineral ingredients. On standing, saliva separates into two layers : a transparent one, which is supernatant, and a grayish turbid one below, which consists of a de- posit of particles of pavement epithelium and mucus corpuscles, derived from the lining membrane of the mouth and the salivary ducts. Its chemical reaction varies to some extent with the state of the system ; thus, after long-continued fasting, from being alkaline, it may approach the neu- tral state. By some it is asserted that under these conditions it may even become acid. There is no proof that this is owing to the appear- ance of lactic acid : it may be due to butyric acid, or even the acid phos- phate of soda. In morbid conditions this reaction is by no means infre- qllent : it has been commonly observed in intestinal inflammation, acute rheumatism, intermittent fever. Donne and Frerichs assert that acidity of the saliva depends on an irritation of the buccal mucous membrane. The specific gravity of mixed saliva varies from 1.004 to 1.009. These variations depend on many different causes, there being a diminution after the taking of drink, and a greater increase after taking food, than even is observed in the fasting state. An animal diet especially increases it. Under ordinary circumstances, the saliva is secreted to an amount of Quantity of fi'om 15 to 20 ounccs daily. The exudation is more copious saliva. during mastication, speaking, reading, more being produced by the use of hard than soft food. Mental emotions exert a control over its flow, sometimes diminishing it, as in moments of anxiety, sometimes in- creasing it, as by the anticipation of food. After eating, the flow contin- ues to a considerable extent ; it is also provoked by the use of aromatics. On irritation of the interior of the stomach through a gastric fistula, the flow is simultaneous with that of the gastric juice. The movements of the jaw and the pressure of the food give rise to va- riations in the quantity of saliva. It is perhaps for these reasons that the parotid gland on that side of the mouth which is most used in mastication secretes more than the other. Of the proportion of the different kinds of CONSTITUTION OF SALIVA. 45 saliva in the mixed secretion, nothing is known with certainty in the case of man, but it is said tliat in horses the parotids furnish two tliirds, the submaxillaries one twentieth, and the sublinguals and mucous follicles the rest. The secretion of the saliva goes on during sleep. To the active organic substance of the saliva the designation of jitya- line has been given. It is regarded as a ferment, possessing in several respects the properties of diastase, and hence has been called by ]\Iiallie diastase salivaire. For the purpose of analysis, saliva should be obtained in a perfectly fresh state, a condition not easily fullilled, for it decomposes or changes with rapidity. During these changes, alkaline carbonates, for example, are formed in abundance, though they may have existed but to a small extent at iirst. We have already seen that in this way parotid saliva, ex- Constitution of posed to the air, yields crystals of carbonate of lime. The saliva. following table is presented as offering an example of the average consti- tution of mixed saliva. Constitution of the Saliva (Frericks). Water 994.10 Epithelium and mucus 2.13 Fat 07 Ptyaline and alcohol extract 1.41 Suljihocyanide of potassium .10 Fixed salts 2.19 1000.00 Of the fixed salts the chief are, the phosphates of soda, lime, and mag- nesia, and the chlorides of sodium and potassium. The sulphocyanide of potassium varies in amount considerably : it increases after meals, and especially after the use of condiments, salt, pepper, spices. Those arti- cles which contain sulphur, as mustard, garlic, radishes, increase its amount in a very marked manner. Not only does the saliva, as derived from the different glands, present differences of constitution ; it likewise differs in various ani- Modifications mals, and in the same animal according to its age. This is of saliva. observed even in the case of man. The saliva of an infant at the breast possesses very little power of saccharizing starch, a transmutation which that of the adult accomplishes with energy. The action of this secretion appears to be limited to starch, and certain kinds of sugar, which first yield lactic and then butyric acid. It does not exert any influence in transforming albuminous matter. The saliva discharges many functions. It is a necessary intermedium in the sense of taste, for substances to be sapid must be more Functions of or less soluble in this juice. If insoluble, they are tasteless, saliva. It also moistens the interior of the mouth, and prevents the sensation of 46 SALIVARY DIGESTION IN THE STOMACH. dryness. But its chief duty seems to be that of promoting the digestive operation ; for, though the food remains in the mouth but a short time, the action of the saliva is prolonged after the masticated mass has been deposited in the stomach. Though the direct admixture of saliva with gastric juice injui'es the power of the latter, this effect does not ensue in the stomach, since they act for the most part separately. The action of the gastric juice is superficial, and two distinct operations are therefore conducted at the same moment, the sui-face of the food chano-ing under Action of the the influence of the gastric juice, and the inner portion under tfnueVhiThe '^^'^^^ of the saliva. I believe that in this manner the salivary stomach. juice lends itself to stomach digestion, for it is well knoAvn that by its aid starch changes into grape sugar, and the transmutation does not stop at that point, but goes on to the production of lactic acid. ^■^Ji acid juice is essential to stomach digestion. After the administration of balls of starch to animals in which gastric Production of fistulaj have been established, sugar may be detected in the sugar from stomacli in the course of ten or fifteen minutes. It does starch in tlie . , . -, . , stomach by the ^ot appear that there is any relation between tlie quantity saliva. of galiva incorporated by mastication and the quantity of starch in the food. Animals which swallow their food without mastica- tion have either no parotids, or those organs exist in only a rudimentary state ; commonly, however, their submaxillary glands are large. Un- der the most favorable circumstances, the digestion of starchy food is scarcely ever complete, a considerable portion being found in the excre- ment. The true function of the saliva has been well illustrated by in- serting amylaceous food into the stomach of dogs with gastric fistulse, after tying the salivary ducts, in which case no sugar can be detected. It has been suggested that the eventual arrest of the action of saliva on reaching the stomach may be due to the digestion of its ptyaline by the gastric juice. In artificial experiments, however, such a digestion or destruction can not be accomplished. The double digestion, partly salivary and partly gastric, occuiring in the stomach, is doubtless one of the causes of those differences which have been noticed between the natural action of that organ and the arti- ficial imitations of it. The influence of the saliva, even under these, which may seem at first sight to be unfavorable circumstances, is far from being trivial, an effect which is well illustrated by the instantane- ous manner in which a solution of starch in water, mixed with an equal quantity of saliva and agitated, is transmuted into a solution of sugar. In a few moments its viscidity is lost, it fails to give the blue reaction with iodine, becomes sweet to the taste, and readily answers to Trom- mer's test. Besides the duties wliich have been mentioned, the saliva incidentally EELATION OF THE SALIVARY GLANDS AND KIDNEYS. 47 accomplishes a sccondaiy object hy its power of retaining gases in its troth or foam. Atmospheric oxvsren by this means is incor- ^ ,. i . o ./ b.iliva carries porated with the food during mastication, and is tlius enabled air into the to exert an important influence in promoting the action of the gasti'ic juice. For to the inception of the change which that juice impresses on the food, oxygen is necessary. It is brought into the cav- ity of the stomach entangled or dissolved in the saliva. It has just been mentioned that the action of saliva on starch is not re- stricted to the production of sugar, but that it may end in the Lactic acid formation of lactic acid. K, therefore, any thing intervenes to ciei|eieTofhy- check the supply of hydrochloric acid, which usually gives drochioric. acidity to the gastric juice, the system possesses -^ithin itself the means of compensating for the difficulty. In the interior of the digesting mass lactic acid is being set free. This acid, as has long been known, can re- place hydrochloric acid in its physiological duty. Though so large a quantity of saliva as 20 ounces may be secreted in a day, this being about one half of the urinary discharge, it is to be re- membered that the water is not lost to the system, as in the latter case. When the impure habit of profuse spitting is indulged in, it Digg-ustin^ ef- is interesting to remark the reflected effect which takes place feet of profuse in the reduced quantity of the urine, and an instinctive desire ^^^^ for water, a kind of perpetual thirst. It is probable that, under these dis- gusting circumstances, the percentage amount of saline substances in the saliva is increased, and that, so far as that class of bodies is concerned, the salivary glands act vicariously for the kidneys, and the mouth is thus partially converted into a urinary aqueduct. The relation between the salivary glands and the kidneys is very well shown after the administration of such substances as the Eeiation of the iodide of potassium. If five grains of this salt be taken in ^^^^j^; ^i^, pills, and the mouth be then thoroughly washed, in the course neys. of a quarter of an hour the saliva will readily strike a blue tint when tested with nitric acid and starch, but the mine will not show that reac- tion until after a considerable interval, perhaps even an hoiu* or more. It would therefore appear that such a salt must pass again and again through the salivary glands before it is finally disposed of by the kidneys, which offer the only outlet for its total removal. Among; the functions of the saliva we ou2;ht not to overlook the influ- ence wdiich its ra^pid secretion must exert on tH^ state of tension of the blood-vessels, an influence which probably favors the absorption going on in the stomach and intestines. Thus prepared by mastication and insalivation, the food descends into the stomach, passing along the pharynx, which dilates to receive it. The iima glottidis spontaneously closes, and additional security is given to the 48 THE DIGESTIVE TRACT. tract. respiratory passage by the valve-like shutting of the epiglottis. Through the oesophagus the morsel advances by the contraction of the muscular coat, with a wave-like or undulating motion onward. Tlie food is now de- livered at the cardiac orifice of the stomach, and, entering that organ, is sub- mitted to the gastric juice, which is exuding from the mucous membrane. The digestive tract may be considered as presenting five prominent re- ^ eions — the mouth, the pharynx, the oesophasfus, the stomach, Illustration of & . ' , "^ . . rm • i • the digestive the Small mtestme, the large mtestme. Their relative posi- tion and subdivisions are illustrated in Figure 3. — 1, the tongue ; 2, 2, the pharynx ; 3, 3, the oesophagus ; 4, the velum pendulum palati ; 5, section of the larynx ; 6, the palate ; 7, the epiglottis ; 8, the thy- roid cartilage; 9, the medulla spina- lis; 10, 10, bodies of vertebrge; 11, 12, spinous processes of ditto ; 13, cardiac orifice of stomach ; 14, splenic extremity ; 15, pyloric extremity ; .16, 16, greater curvature; 17, the less cmwature ; 18, pylorus ; 19, superior transverse portion of duodenum ; 20, middle or perpendicular portion ; 21, inferior transverse portion ; 22, gall- bladder ; 23, cystic duct ; 24, hepatic duct ; 25, ductus communis choledo- chus ; 26, its aperture in the duode- num ; 27, duct of the pancreas, empty- ing into the duodenum near to the place of entry of the ductus communis chole- dochus ; 28, commencement of jeju- num ; 29, 29, 29, jejunum ; 30, 30, 30, ileum; 31, ileum opening into great intestine ; 32, ileo-colic valve ; 33, il- eo-coecal valve; 34, coecum; 35, ap- pendix vermiformis ; 36, 36, the as- cending colon ; 37, transverse arch of colon ; 38, descending colon ; 39, sig- moid flexure ; 40, rectum ; 41, anus. From the interior or mucous coat of the stomach the gastric juice exudes. Tliis fluid may be best obtained for ex- amination by gastric fistula3 artificially established in animals. As respects the The human digestive tract. '■ THE GASTRIC JUICE. 49 aspect of the interior of the stomach, Dr. Beaumont, who had an opportuni- ty of examining it in the case of Alexis St. ]\Iartin, describes Aspect of inte- it as of a light pink color, its velvety surface being coated riorofstomacii. over with mucus. On the introduction of food or any iiTitant, lucid points protrude from the mucous coat ; these are the mouths of the folli- cles from which the juice exudes. When in activity, the temperature of the interior of the organ is about 100° Fahr. The gastric juice is a viscid fluid, with an acid reaction and faint odor. After flltration through paper it is clear and transparent, and xhe gastrin possesses all its physiological qualities. The impurities thus J'^^'^^- separated from it are merely old undigested residues, on which, in no re- spect, its qualities depend. It does not become turbid at 212°, remains long undecomposed, and retains its digestive power even after it has be- come mouldy. It does not accumulate in the stomach while fasting, but requires a stimulus for its ejection, and even then is produced in a limit- ed quantity only. It is secreted by the follicles of the mucous membrane of the stomach, which follicles may be described as cup-shaped cavities, about the two hundredth of an inch in diameter, from the bottom of which project two or more parallel tubes, the mouth of the cup open- it is secreted bv ing into the stomach, and the tubes ending in a closed term- follicles. ination in the tissue beneath. Toward the pylorus the cups become deep- er, so as to assume the form of a cylinder, and the projecting tubes arc shorter. Between these follicles blood-vessels pass. They are ramifica- tions from the coeliac axis, and discharge a double function. As the ar- terial branches invest the roots of the tubes, they furnish nutrition for the cells which are produced in crowds at that part of the arrangement ; but when they have gained the interior of the mucous membrane, and are in the ridges between the follicles, having assumed the character of veins, they act as absorbents, conducting the material which is sufficiently di- gested into the portal circulation. Agreeably to this, these vessels have a larger diameter than capillaries generally. It seems, therefore, that the function of the tube is the production of cells, which, originating from germs at the bottom and sides of each tube, become perfected as they pass forward, and soon after their extension burst or deliquesce, and as the material they discharge does not possess the acid reaction, it is probably the pepsin element of the gastric juice. Constitution of the Gastric Juice of the Dog. Water Pepsin Hydrochloric acid Chlorides of pot., sod., calc, amm. Phosphates of lime, magn., iron.... D Gastric j uice, Gastric juice, without saliva. witli saliva. 973.062 971.171 17.127 17.336 3.050 2.337 4.724 6.418 2.037 2.738 1000.000 1000.000 50 STOMACH FOLLICLES. Fig. 4. The preceding table, from Hubbenet, shows that nearly two thirds of p . „ the solid material of the gastric juice is pepsin. Exposure the gastric to a very low temperature does not deteriorate the properties juice. ^£ ^j^^g substance, for it will resume its activity even after be- ing frozen. But, on the contrary, a temperature approaching ebullition destroys its solvent power, and the same effect ensues when it is neutral- ized by an alkali. The gastric juice acts on iron or zinc with evolution of hydrogen, an effect which the acid phosphate of lime can not produce. This seems to be decisive against the views of those physiologists who have imputed its reaction to the latter substance. The digestive power of this juice is impeded by the presence of almost any alkaline salt. To this remark common salt offers iio exception. It is owing to its alkalinity that saliva injures the digesting power of gas- tric juice. On the contrary, that power is very much increased by the presence of fat, which promotes the conversion of protein bodies into peptones. The mucous membrane of the stomach pre- sents a reticulated appearance, as shown in Fig. Stomach folii- 4. At the bottom of each compart- thek^'stmct^ure "^^nt are the mouths of the gastric and functions, folliclcs, the size and depth of which increase toward the pylorus. Their exterior is partly covered with columnar epithelium, which extends over the inter- Fig. 5. vening ridges ; the residue is glandular, and continu- ally gives origin to granules. The upper part of each follicle, as well as the entire surface of the mu- cous membrane, is usually covered with mucus. In Fig. 5 is a representation, given by Todd and Bowman, of stomach follicles and their tubes in a vertical section. The specimen is from the dog after twelve hours fasting. A represents these structures in the middle region of the stomach ; B in the pylor- ic region ; a a, orifices of the follicles on the inner surface of the stomach ; b b, different depths at which the columnar epithelium is exchanged for glandular : d, pyloric tubes terminating variously, and lined to their extremities with columnar epithelium. Fig. 6, K, horizontal section of a stomach folli- cle a little way within its orifice ; a, basement mem- brane ; b, columnar epithelium. AU but the centre of the cavity of the cell is occupied by a transparent mucus, which seems to have oozed from the open extremities of the epithelial particles ; c. Mucous membrane of the stomach magnified TO diameters. Vertical section of stomach follicles and tubes magni- fied 150 diameters. HYDEOID STRUCTUEE OF THE STOMACH. 51 Fig. 6. Varieties of stomach fol- licles. Horizontal section of stomach fol licles and tubes magnified 200 di- ameters. fibrous matrix surrounding and supporting tlie basement membrane ; d small blood-vessels. B, horizontal section of a set of stomach tuber^ proceeding from a single cell. The letters refer to corresponding parts. The epithelium is glan- dular, the nuclei very delicate, and the cavity oi the tubes very small, and in some cases not visi- ble. (From the dog, by Todd and Bowman, after twelve hours' fasting.) It thus appears that there are at least two dis- tinct classes of stomach follicles, diiFer- ing from each other in anatomical con- struction, and, as there is now reason to believe, also in physiological function, those which are near the pylorus yielding a secretion which, taken by itself, exerts only a tardy action in pro- ducing the solution of protein bodies, but those from the middle and other portions of the organ accomplishing that solution promptly. It is sus- pected that the acid of the gastric juice is yielded by one class of these structures, and the pepsin by the other. A general idea of the structure of these secreting follicles may perhaps be obtained by likening each of them to a little glove, the hand of which opens into the stomach, and the fingers project upon the submucous tissue beneath. From the sides and tip of each finger, cells may be supposed to arise continually, and, as they are crowded for- ward, they undergo development, leaving the hand in a perfect condition, and deli- quescing as they pass into the stomach. Though we have spoken of these folli- cles as excavations or cup-like depressions in the mucous tissue, according to the de- scription usually given of them Hy^roid con- by anatomists, it is to be under- struction of -,.-,, .1 . . c ,1 • the stomach. stood that this view ot their con- struction is philosophically incorrect, for each, instead of being a mere excavation, i;i truly a distinct crganism, analogous in struc- The hydra. turc and many of its functions to a polype. 52 > * QUANTITY OF GASTRIC JUICE. The liydra, a fresh-water polype, may he taken as the type of this organ- ism. This animal, Fig. 7, consists of a hag or digestive sac, a a, end- ing in a cylinder, h, the opening to which is furnished with numerous tentacles, c c c ; the tentacles enfold in their grasp objects on which the hydra feeds, and by their contractions carry them to the sac. Into the interior of the sac a juice exudes possessing digestive powers, and soon dissolving food. We may therefore regard the follicular structure of the stomach as a colony of polypes, the tentacles of which are converged into a muscular tube, constituting the oesophagus. In a stomach of ordinary size there are probably a million of these organisms. Digestion is undoubtedly conducted on the same physical principles in both cases, though in the polype the food matter enters the follicular cavity of which the body of the animal consists, but in man is contained in the stomach, into which the follicles open, and pour forth their digestive fluid. With respect to the acid constituent of the gastric juice, it appears to be hydrochloric or lactic. The latter has probably originated in the man- ner just described by the action of the saliva on amylaceous bodies ; the former undoubtedly comes from the common salt ingested. Perhaps, un- der a deficiency of common salt, lactic acid discharges the entire duty. Schmidt regards the digestive principle as a conjugated acid, the nega- tive constituent being hydrochloric acid, and pepsin being the adjunct, the compound being analogous to ligno-sulphuric acid. About twenty Quantity of parts of gastric juice are required to digest one part of dry al- gastric juice. ]bvimen, and about 70 ounces are secreted in a day. If the hourly destruction of fibrin in average muscular action is 62 grains, about 60 ounces of gastric juice would be required each day for muscular repair. A very large demand is therefore made upon the water in the system for this use. But here the same remark is to be made as in the case of the saliva ; the water, after accomplishing its object, is not lost to the econ- omy, but is immediately reabsorbed. It was remarked, in speaking of the salivary glands, that their secre- tion passes repeatedly through them, the saliva, as it exudes, sage of extra- being swallowcd, reabsorbed, and so secreted over and over throuoi°*the ^gain. In these repeated passages, many salt substances, stomach folli- such as the iodide and bromide of potassium, will accompany '^^^^' it, the kidneys, however, eventually removing such extraneous bodies. In like manner, heterogeneous matters will make a repeated cir- culation through the gastric folKcles before a final removal by the kid- neys. When the latter organs have been extirpated, the constituents of their secretion, such as urea, may appear in the stomach. On the deposit of the food in the stomach, a movement of translation is given to it by the alternate contraction and relaxation of the fibres of SUMMARY OP STOMACH DIGESTION. ' 53 tlie muscular coat, aided to a consideralDle extent by the respiratory movements of the abdominal walls. The course of this ro- jjojjQjjg f .j^g tation commonly is, that after passing the cardiac orifice the food in the food moves from right to left round the great extremity, and then alono- the laro-e curvature from left to rio-ht, returnins: alono- the small curvature, and occupying from one to three minutes to perform this revo- lution, the motion continuing for a few minutes at a time. While this is going forward digestion is rapidly taking place, and the portions which have suffered coiuplete action are oozing through the py- loric valve into the intestine as a semi-fluid and apparently Formation of homogeneous material called chyme. This process has fairly chj-me. set in in the course of an hour, and is usually finished in about four. In consistenc}^, color, and chemical reaction, the chyme varies with the nature of the food, its chemical constitution, and its quantity ; but under common circumstances it presents the acid reaction, for it is to be remem- bered that the diurnal supply of hydrochloric acid to the stomach is about the fifth of an ounce. Arrived in the intestine, the chyme is pushed for- ward by the peristaltic movements, and soon after its appearance in the duodenum is mixed with several important fluids — the bile, which is fur- nished by the liver, the secretion of the pancreas, and the enteric juice which is exuding from Brunner's glands. The digestion of the albuminous part of the food commences in the stomach, and in that cavity advances far toward completion. Summary oH The action is not merely for the purpose of bringing those dio-estionln substances into a state of solution in water, but also of modi- the stomach. fying them chemically. This change is so well marked that it has been found expedient to indicate it by a designation, and hence we speak of albumen peptone, fibrin peptone, casein peptone. These peptones are, for the most part, absorbed by the blood capillaries, though a portion of them enters the circulation as a constituent of chyle. In the system, whatever their origin may have been, they seem to revert to the state of blood albumen. But, though the production of these peptones is accom- plished to the extent that has been mentioned in the stomach by the gas- tric juice, the action is continued and brought to its completion in the small intestine by the aid of the intestinal juice. It does not appear ihaf the large intestine participates in this duty, since portions of coagulated albumen, or of flesh introduced into it through fistulous openings, are . voided through the rectum. Such is the general description of the act of digestion. We have next to enter on a physical examination of what it is that really influence of takes place in the stomach. It was formerly supposed that the nerves on digestion is entirely due to nervous agency, since, if the pneu- ° mogastric nerves be divided, the process is very much interfered with. 54 AETIFICIAL DIGESTION. But this interference takes place only in an indirect way, for tlie section of those nerves is attended with such a paralysis of the stomach that those movements which so well serve to mix up the food with the gas- tric juice, and expel it through the pyloric valve, are put an end to. Bidder and Schmidt, from an examination of four dogs with gastric Effect of section fistulse, demonstrated that the section of the pneumogastric of the pneumo- ncrves does not exert that influence on the secretion of the gas no nerves, g^g^^.-^ j^{qq which had been formerly supposed, for both in quantity and composition it remained the same. Even in those cases in which both they and others have observed a diminution in its amount, the result ought, probably, to be referred to the shock given to the entire system by the severity of the operation. The acidulating material of the gastric juice is hydrochloric acid. Is it possible by artificial mixtures containing that substance to reduce food articles to a digested condition ? This inquiry introduces a descrip- tion of the experimental investigations which have been made in artificial digestion. When water acidulated with hydrochloric acid is kept in contact with Artificial di- albumen, no action is perceptible at ordinary temperatures in a gestion. moderate period of time. If the temperature is raised to about 150° a slow dissolution ensues, which becomes better marked as the heat rises toward 212°. But if to the weak hydrochloric acid thus made to act on albumen, pepsin is added, the solution takes place with rapidity at moderate tem- peratures. An ounce of water, mixed with twelve drops of hydrochloric acid to which one grain of pepsin has been added, will completely dis- solve the white of an egg in two hours at a temperature of 100°. It acts in the same manner on cheese or flesh, these nitrogenized articles being converted into soluble non-coagulable bodies. The acid does not enter into chemical combination with the dissolving organic matter. It may be recovered from the solution by resorting to proper processes. When striated muscular tissue is submitted to artificial digestion, it is Artificial cii- ^^^^ divided into its constituent fasciculi, and the transverse gestion of mus- gtrige then disappear, the sarcolemma being destroyed. The course of the action seems to be the same in natural diges- tion. In the foecal matter, shreds of muscular fasciculi still bearing their striation may be discerned. These, having by chance escaped solution during their sojourn in the stomach, have passed through the whole length of the digestive tube unchanged. Pepsin — the substance resorted to in these experiments — may be ob- tained by macerating the mucous membrane of the stomach aration and* for a short time in lukewarm water. This water, along with properties of. ^ ^^^^^ of the pepsin, removes various impurities ; it may there- FUNCTIONS OF PEPSIN. 55 fore he cast away ; the maceration being then continued with a fresh por- tion of cold water, and this being submitted to filtration, and subsequent- ly evaporated at a low temperature to dryness, yields the pepsin as a gummy mass. From its solutions pepsin may be precipitated by corro- sive sublimate or acetate of lead, and it may be separated from those combinations by sulphureted hydrogen. Wasmann availed himself of this fact to obtain it in a pure state. Composition of Pepsin. (^From Schmidt.') Carbon 530.00 Hydrogen 67.00 Nitrogen 178.00 . Oxygen 225.00 1000.00 From this it would appear that it contains less carbon and more nitro- gen than the members of the protein group. A weak acid therefore possesses at a high temperature the power of brino-ino" into a state of solution the various nitroo-enized food ^ 11 1 r -1 f ^ -, ■ Pepsin re- matters, and at lower degrees tails ot that property ; but m places a high the presence of pepsin the solvent powers are assumed un- temperature. der the latter circumstances, and therefore it is said of this substance that it replaces a high temperature. By its aid, hydrochloric or lactic acids present in the stomach reduce the food to a uniform pulpy mass — the chyme. Of all acids, these, however, alone are capable of forming digestive fluids. Formerly it was supposed that the act of digestion was simply me- chanical, the food beins; ground down to chyme by the mo- ^ ° " . Keaumur s ex- tions of the stomach. Reaumur's experiments showed the perimentswith error of this supposition. He took small hollow silver balls, s^^^'"' ^laiis. perforated with holes, and, having filled them with meat, caused them to be swallowed by a dog. When they had remained in the animal's stom- ach a suitable length of time, they were withdrawn by a thread which had been previously attached to them. Now if the stomach acted by a triturating or grinding power, the material within the ball would be en- tirely protected, but if by a solvent power exerted by the gastric juice, the digestion should at most be only delayed. . Accordingly, it was found that this was what actually took place, digestion being fully, though more slowly accomplished, the action commencing on the outside of the mate- rial, and gradually reaching its centre. If the balls were kept in the stomach long enough, they came out quite empty at last. The idea that there is something more than a simple solution of the food eifected in the stomach, that some mysterious change is Chief object of impressed upon it by the vitality of that organ, may there- tio^s*the^solu' fore be abandoned. It does not appear that there is any es- tionofthefood. 56 NUTRITIVE MATTER IS DISSOLVED. sential diflference iDetween natural digestion and the artificial imitation of it, either as respects the order of action or the final result. j\Ioreover, the anatomical consideration that the food is yet outside the body, though it is inside the stomach, should be sufficient to remove all errors of that kind. A living surface, such as the skin, never exerts any chemical ac- tion at a distance ; and the lining membrane of the stomach, both as re- gards its physiological origin and its anatomical relation, is nothing more than a reflected continuation of the skin. The act of digestion is com- pleted long before the nutrient material is taken up by the lacteals and \-eins, and thrown into the torrent of the circulation. But then, and not till then, is the food fairly in the interior of the body. The lacteals and veins can not exert their absorbent action on a sub- stance presented to them unless it is dissolved in water. If not abso- lutely dissolved, at least it must be in that condition of minute subdivis- ion which we see in emulsions. Though it has been stated that insolu- ble substances, such as charcoal, can find their way into the circulation in the solid state, there does not appear to be a sufficient weight of evi- dence to support such an improbability. In the economy of plants, it is In plants, all ^ general rule that nothing can have access to the interior of nutrient mate- their system except it be dissolved in water. All the vari- rial must be in it -i , , i ■ i . • j • solution in wa- ous gases and salme substances they reqmre are obtamed m '^er. a state of solution ; the former are introduced, for the most part, through the leaves, the latter through the roots. The object aimed at in the construction of the digestive apparatus of the animal mechanism is absolutely the same. Plants use as their food inorganic matter only ; the chief materials on which they depend, such as the salts of ammonia and carbonic acid, are abundantly soluble in water. The ascending sap obtains the former from decaying organic residues in the ground ; the at- mosphere presents the latter unceasingly to the leaves ; and since the economy of many plants requires earthy salts, as silicates and phos- phates, which are of sparing solubility in water, the difficulty arising from that want of solubility is avoided by the introduction of an immense quan- tity of water, which, after bringing into the plant the needful amount of mineral material, is evaporated off at the leaves. But the food of animals is essentially organic, and this, before it can be received into their blood, must be brought into the dissolved state. It must be submitted to a pre- paratory operation or series of operations. However complicated these The operations or the mechanism which accomplishes them may be, the end on the food are aimed at is clear. The action begins by the cutting, tearing, lirind mech^n- and Crushing movements of the teeth, which break down all '^al. the larger portions, and carry on the process as far as it is possible by mechanical means. The stomach then continues the subdi- vision by chemical agency, to the end that a condition of solution may be OBJECTS OF DIGESTION. 57 attained. Digestion is not, therefore, to vitalize the food, as the ancients supposed, nor to communicate to it any new or obscure properties ; it is for the purpose of comminuting, subdividing, dissolving, or bringing it into that minutely suspended state that it can without difficulty submit to the absorbing action of the lacteals and veins. There is a complete analogy between this operation and the artificial processes to which the chemist resorts in his laboratory for the solution of various bodies. He, too, uses mechanical implements — the mortar and pestle to grind, the ham- mer to crush, the rasp to abrade. When these have carried the subdi- vision sufficiently far, he resorts to acids or other solvents, and thus breaks down the compactness of the hardest minerals, and brings them into the dissolved state. The animal world presents ns with a thousand Illustrations of the principles here set forth, mechanical contrivances curi- ously arranged. For instance, birds, whose plan of organization is such as to meet the case of locomotion through the air, could not have the an- terior part of their bodies loaded with teeth, accompanied as they must have been with a powerful muscular apparatus. Such a mechanism would have rendered the animal top-heavy, and would have been totally inconsistent with flying. But, to avoid this difficulty, that which might truly be regarded as the mouth is lodged in the interior of the body, nearer the centre of gravity. It is the gizzard. Instinct teaches the bird to swallow small angular stones, and the food, rasped between powerful mus- cular surfaces, is soon brought into a fit condition for the action of the stomach. The chemist, too, puts fragments of glass or of quartz into the mortar in which he is conducting the reduction of a tongh or resisting substance. The first object of digestion is, therefore, the subdivision of the food. The operation begins in the mouth by a resort to mechanical implements, and when these have carried the process as far as they can, the stomach continues the duty. In its cavity, when in full activity, the temperature is 100° ; a periodically increasing and relaxing motion of revolution is kept up, gastric juice exudes in definite quantity, the hydrochloric and lactic acids exert their action, and in the course of three or four hours a complete reduction is accomplished. Allusion has been made to the probability that different portions of the mucous membrane of the stomach discharge functions Regional divis- ■^t?^ which are wholly distinct, one portion being devoted to the ^diVr diffe™' elaboration of pepsin, another to the secretion of hydrochlo- ent functions. ric acid, another to the preparation of a special mucus. This view de- rives considerable support from many facts in comparative physiology. In those cases in which the food approaches, in its mechanical and chem- ical condition, to the form which it is destined to assume as a part of the body of the animal receiving it, the stomach is simple in construction, 58 DIGESTION IN INSECTS AND BIEDS. and is little more than a mere dilatation of the alimentary canal. But Analogous ar- when, as among the herbivora and granivora, Fig. 8. SfffSIirani^ *^^^® ^^ ^ g^^^^ difference between the fonn mais. of the food received and the form of the tis- sues to he made, the digestive sac no longer presents such a simple structure, but is parted off into distinct regions, or is actually converted into distinct organs. Thus, in the insect digestive tract shown in J^ig. 8, a is the phaiynx, b the oesophasrus, lead- Digestive com- . ,. i iiartments of ing into a crop or msauvatory pouch, c, and insects. ^j^-g ^^Q ^]^g gizzard, d, the function of which is to rasp up and abrade the more resisting portions of the food, which, when this is accomplished, passes into the true stomach, e, and from thence into the intestine, g. / ^ The delicate vessels about f are supposed to be bihar}- \j^ tubes, and h sclandular secreting organs. "^ ^ c . • i- 1 Digestive tract of a car- Even m these cases ot namute organization, tlie mu- nivorous beetle. cous structure remains the same as in larger animals of the same m.ode of life. The j)hoto,gTaphic representa- tion in Fig. 9 displays the same retic- idated appearance in the stomach of the carnivorous beetle as has been de- scribed in the case of that of man ; and undoubtedly, with similarity of structure there is similarity in the man- ner of action. A regional di'vision of the digestive apparatus is also presented in the case of many birds, as 0. is shown in the photo- graphic representation. Fig. 10, in which we have the digestive tract of the com- ^. ,. mon fowl, a being the oesophagus leading Digestive com- ... i 7 partmentsof into the insalivating pouch or crojo, 6, ^■'"■'^s- which empries into the stomach, c. and this into the gizzard, d. In the stomach, which is relatively small, the digesting material 5^ is mingled with the gastric juice before being submitted to the action of the gizzard. From the gizzard it is passed into the small intestine /,/. In the figure, e is the liver, g, g, the coeca, and ft tne cloaca. Digestive tract of the common fowl. Fig. 10. Mucous membrane of the stomach of a carnivo- rous beetle magnified 50 diameters. REGIONAL SUBDIVISIONS OF THE STOMACH. 59 In the ostrich, as shown in Fig. 11, the local distribution of the glan- ^'3- 11- dula3 very obviously marks out a regional dis- tribution of function. C is the cardiac cav- ity, the mucous membrane of which is stud- ded here and there with glands ; G G are the surfaces of the gizzard. Among the higher quadrupeds, the evidences of a similar divis- Fig. 12. Fig. 13. Interior of stomacli of Africau ostrich. Stomacli of dormouse. Stomach of Cape hyrax. ion of function are presented. Thus, in the dormouse, Fig. 12, there are two compartments : a cardiac, C, and a pyloric, P ; the same Dio-estive com- being exhibited more perfectly in the Cape hyrax, Fig. 13. partments of In these cases the cardiac compartment is often lined with °^™* ^" cuticle, but the pyloric not. An increase m the number of these cavities occurs as the food becomes more heterogeneous. In the porcupine. Fig. 14, there are four, and in the porpoise, Fig. 15, five. The stomach of Fig. 14. Fig. 15. / Stomach of porcupine. Stomach of porpoise. Stomach of kangaroo. the kangaroo, as shown in^"^. 16, possesses a multitude of these cham- bers or compartments, and therefore offers a good illustration of the sub- divisions of stomach digestion. Digestive cavities of a ruminant. The case of ruminants possesses a special inter- est. In these there are what might be termed four different digestive chambers, as is shown, in Fig. 17, in which a is the oesophagus ; h, the inglu- 60 DIGESTION IN EUMINANTS. vies or paunch; c, the reticulum or honey-comb stomach; 6?, the omasum, Digestive com- nianyplies, or third stomach; e, abomasum, reed, or fourth partments of stomach ; and y, the pylorus. The food, roughly triturated in the mouth, enters the ingluvies, in which it is moistened ; it then passes into the honey-comb or second stomach, which likewise receives directly the water that has been taken, and, after it has been thoroughly moistened therewith, it is returned to the mouth in small portions, to undergo a more complete mastication and insalivation. Be- ing swallowed again, it is now directed into the third stomach, from which it passes into the fourth. In this it is submitted to a true acid digestion, a gastric juice being secreted from the walls of this cavity. It is the mucous lining of this cavity which yields rennet. That these com- plicated motions and these successive actions of the different cavities are for the purpose of preparation for the true digestion of the fourth stom- ach, is clearly proved by the fact that in the calf the milk passes directly into the abomasum. Since fishes and water animals generally have no salivary glands, or Digestion ^nly rudimentary ones, some physiologists have inferred that the in fishes, ^^gg ^f ^j^g saliva is for the commingling of the food with a due portion of water. This would reduce the importance of insalivation very greatly, and, indeed, is scarcely consistent with the elaborate mechanism which has been just described in the case of ruminant animals. It is worthy of remark that, even among fishes, there are some which exhibit a true rumination, as, for example, the carp. This is not alone for the purpose of resubmitting the food to the abrading action of the pharyngeal teeth, but likewise for commingling it with the secretion of the pharyn- geal cavity. In view of the preceding facts, it may be concluded that, so far from there being any thing in contradiction to the doctrine that different por- tions of the digestive surface of the mucous membrane of the stomach are devoted to different duties, there is strong evidence in support of its truth, derived partly from the instances furnished by comparative anatomy, and partly from the anatomical structure of the gastric mucous membrane. The four separate digesting chambers of the ruminating herbivora are merely an elaboration of the structure which is presented by an appar- ently homogeneous mucous surface in man. But that this mucous sur- face is in reality heterogeneous, and in different regions possesses differ- ent powers, is shown by the fact that at one part it presents mucous fol- Reo-ional func- 1^^^®^' ^^ another pepsin follicles, at another follicles for the tions of human sccrction of hydrochloric acid. As we approach toward the pylorus, the existence of a new function is betrayed by the appearance of a new mechanism — the villi, which have been so well stud- ied by Dr. Neill, and this is even indicated externally in the posterior REUIUNAL DIVISIONS OF THE HUMAN STOMACH. 61 Posterior view ot liunian stomach. vieAV of tlie human stomach, Fig. 18, showing, according to Profess- or Retzius, that the antrum py- lori of the older anatomists is re- ally a special compartment of the general cavity. The figure is derived from numerous examin- ations of the stomach in bodies of middle-aged women, and, as represented at c c, d d, indicates the antrum pylori, a being the oesophagus, h the cardiac orifice. The antrum pylori is distinguish- ed by greater thickness of its mus- cular coat, more copious glandu- lar development, and the presence of the well-known plicas fimbriataj. The commencement of the duode- num also forms a special rounded cavity, which Professor Retzius pro- poses to name antrum duodeni, characterized internally by the absence of valvula3 conniventes, and by the dense array of Brmmer's glands be- neath its mucous membrane. This part constitutes what has been called the fourth stomach in the porpoise and some other cetaceans. The so- called ligaments of the pylorus are connected with the formation of the antrum pylori. It has been remarked that the first aim of digestion is the procuring of the food either in a dissolved state, or, at all events, in a con- Dio-estion ac- dition approaching thereto. But, in addition to this, pro- complishes so- . - •! r-iT 1 -1 lution and round changes m the very nature ot the digested material metamorphosis must, in an incidental way, be constantly occurring. Thus ^^ *^^ ^*'°'^- the action of saliva is to produce lactic acid from starch, and thus, in the stomach itself, starch is transmuted into sugar. In some cases the first stage of digestion seems to be actually the reverse of what has been here set forth. Milk, when received into the stomach, undergoes coagu- lation, and, in like manner, so also does soluble albumen. But these are only incidental changes, the temporary solids thus produced soon lique- fying as proper digestion sets in. There is reason to believe that all the protein bodies are passed into the condition of albuminose, and this though they may have been introduced in the liquid state. Even soups and broths require to be digested. A solution of gelatine, after q^^^^.-^^ ^^^^_ it has been in the stomach, refuses to gelatinize, a solution ges of the food of albumen to coagulate. The circumstance that gases may divisioL'and ' be evolved from digesting material, both in the stomach and assimilation of intestine, is a sufficient proof that that material is undergoing 62 USE OP cosmoN salt. a more or less extensive change. But these changes are altogether insig- nificant when compared with those great metamorphoses which the nu- trient material passes through after it has been absorbed from the digest- ive ca\dties ; and doubtless, at the most, they are only mere subdivisions, of which the sphtting of the sugar or starch atom into lactic acid may be taken as the type, or mere unions with water, of which the passage of cane sugar into milk sugar is an example. The gastric juice, therefore, not only dissolves, but also, in an incipient Production of ^^^1 indu'cct manner, modifies the food. Protein bodies and peptones. gelatinous matters yield' substances after its action of the same composition as their own, but with different physical and chemical properties, being readily soluble in water, and even in diluted alcohol, and not forming insoluble compounds with metalline salts. By Lehmann. who has examined these substances, they have been designated as pep- tones ; and since they may arise without the evolution or absorption of any gas, and the quantity of sulphur they contain is the same as that in the bodies from which they were derived, he infers that the action is real- ly an assimilation of water, the other ingredients remaining unchanged. Turning oiu" attention now to the origin of the gastric juice, it is inter- ^ , esting; to observe the economical manner in which its hydro- Use and man- " , _ i j • agement of chloric Ecid element is managed. To the proper understanding common salt. ^£ ^j^^^ -^ -^ j^g^essary to anticipate what will have to be more fully considered in describing the bile, a miiform mgi-edient of which is the oxide of sodium, or soda. The hydrochloric acid of the gastric juice and the soda of the bile are derived from the same soiu'ce — common salt, which is either present in the food, or pm-posely added as a condiment. It undergoes decomposition easily, yielding the two products specified, that is, hydrochloric acid and soda, and is readily formed by the reunion of these substances. There exists in the action of the kidneys a special provision for prevent- ing the quantity of chloride of sodium present in the blood fi-om rising over 41 parts in 10,000. This, of course, confrols the amoimt diffused through the tissues. The necessity of such a regulation becomes appar- ent when we consider that the rate of the solubility of albumen and ca- sern in water is governed by the presence of that substance, as is also the quickness with which the coagulation of fibrin takes place, and the re- pair of the waste of the muscles. Common salt introduced into the system undergoes decomposition, furnishing hydrochloric acid to the gastric juice, and soda to the bile. Considering the large quantity of these secretions produced in a short space of time, it is clear that the drain of common salt must be great — not less than a third of an ounce a day ; yet the quantities consumed, at most, are only small. • SUMMARY OF DIGESTION. 63 How, then, is this to he expLained? Assuredly there is no other soiu-ce from which these bodies can come than the one indicated — the common salt, and yet it seems to be totally inadequate. I think that this difficulty is rather imaginary than real. Things arc so arranged that a limited quantity of salt can produce unlimited quanti- ties of gastric juice and 1bile ; for the former, associated with the food it has digested, scarcely escapes fi'om the pyloric valve before it encounters the bile and pancreatic juices discharging into the duodenum, and through the length of the upper portion of the small intestines these secretions, together with the food they have acted upon, are brought into complete contact. The reproduction of chloride of sodium is therefore constantly taking place in intestinal digestion, and it returns back to the system through the absorbents. Again it undergoes decomposition, its acid re- appearing in the gastric juice, and its alkali in the pancreatic juice and bile. By thus using a small amount over and over again, g-reat effects can be produced, and it is then only necessary to restore those small por- tions that are wasted in carrying out the general scheme. In the low-pressure marine steam-engine we have an example of the same kind. A certain quantity of water is vaporized in the boiler and condensed in the engine ; pumped back into the boiler to be vaporized, and then recondensed in the engine. Comparatively little is required to supply the wants of the machine, and long voyages can be made with only as much water as will compensate for the necessary waste arising in the working. For the sake of presenting the consideration of the function of diges- tion with clearness, it is customary to leave out of consider- „ , ation the subordinate actions taking place both in the stom- gestion is his- ach and mtestine. This, however, involves a certain amount teftinaf dio-e°- of error, since respiratory or non-nitrogenized digestion oc- tion is caiorifa- curs in the former cavity, and nutritive or nitrogenized in the latter. Nevertheless, there can be no doubt that if our view is restricted to the more imposing characters, we are justified in accepting the dogma that "stomach digestion is histogenetic or nitrogenized, and intestinal digestion is calorifacient." Under the most comprehensive point of view, examining the action of the entire digestive tract from the mouth to the rectum, we r, , o ' (jeneral sum- discover a recurrent periodicity. In the mouth, the transi- mary of diges- tory digestion taking place is wholly expended upon the ca- lorifacient food ; in the stomach it is the nutritive portion which is chiefly attacked ; in the duodenum there is a return to the calorifacient, and in the coecum of animals a resumption of the nutritive. This last is lesE* apparent in man, for in him the coecum exists only in a rudimentary state, represented by the appendix vermiformis. 64 DIGESTION OF GELATINE. As the alteration takes place from calorifacient to nutritive digestion, the active fluid changes its chemical relations. In the mouth and duo- denum, alkaline juices are resorted to ; in the stomach and coecum, acid ones. Whenever there is an accidental inversion of these conditions, the result correspondingly changes ; so when bile, which is alkaline, regur- gitates into the stomach, the digestion of nutritive food is instantly ai-- rested. In each of these cases the object is the same: it is to obtain the nutri- ent material under such forms that the absorbent vessels can readily take it up ; this, as we have seen, often involves a metamorphosis of the ele- ments of the food where mechanical subdivision would be insufficient. Fibrin has to be brought into a soluble state, and, indeed, albumen itself must be modified. If it has been taken uncoagulated or glairy, it be- comes opalescent, and passes into the allied form known as albuminose. In this condition it is neither precipitated by heat nor by nitric acid, though it is by corrosive sublimate. The cause of this transformation probably has reference to the relative facility with which albuminose can transude into the venous capillaries compared with albumen. There is thus reason to suppose that the result of stomach digestion is the reduction of the various nitrogenized constituents of the food to the condition of albuminose. It is plain that fibrin must come into this or some analogous condition, for it can not be absorbed as fibrin, and, ac- cordingly, it is found that the blood of the gastric and mesenteric veins abounds in albuminose. Intermediate between the classes of calorifacient and histogenetic food, Case of gela- belonging, by its composition and conditions of digestion, to ^^^^- the latter, but by the function it discharges to the former, is gelatine, a nitrogenized substance. It appears to be always derived from albumen, and any portion which may have been received in the food is never directly assimilated or used for the fabrication of tissue, but solely ministers to the production of heat. Though thus a calorifacient body, its place of digestion is the stomach. After it has suffered the action of that organ it has lost its power of gelatinizing, can no longer be precip- itated by chlorine, nor give the leather precipitate with tannin. The use of it under the form of jellies, soups, etc., is always attended with the ap- pearance of an unusual quantity of urea in the urine, and hence the ad- ministration of those domestic preparations, under an idea of their great nutritive value, is to be looked upon as only a popular error. In an in- direct way, however, under the conditions of restricted diet, usually met with in the sick-room, gelatine doubtless maintains an interesting relation to the albumenoid bodies in this, that it protects them from destruction by undergoing oxidation itself, and so satisfying the requirements of the respiratory mechanism ; for, were there not such a substance present to RELATIVE DIGESTIBILITY OF FOOD. 65 receive the attack, the respired oxygen would rapidly bring on the waste of the proper nitrogenized tissues. In relation to the gelatigenous tissues, it may be remarked that gela- tine is not an actual constituent of them, but arises from them Gelatine not by boiling with water. By a like process, sufficiently pro- sue^constitu-" longed, a similar substance may be obtained from cartilage, ent. designated cartilage-gelatine, or chondrine. In these cases the material unites with w^ater in the same manner that starch does in producing glu- cose. The food must therefore pass through various stages before it can be fitted for introduction into the circulation, and carried to all parts of the system. It is procured in portions of a suitable size either by the fin- gers, or, in civilized life, by resorting to artificial implements, the knife and fork. The incisor teeth next cut it up, and the molars crush or grind it, bemg worked for this purpose by a powerful system of muscles ; mean- time it is incorporated with saliva and atmospheric air. Passing into the stomach under the condition of a coarse pulpy mass, the gastric juice carries the process still farther, a more intimate disintegration of its structure ensues, and it is eventually brought into a soluble and changed form. The time required to produce this effect varies with Dio-estibiiitv the nature of the food. Thus it has been noticed that beef of different ar- is much more quickly acted on than mutton, and mutton ^'^ ^^ ° °° ' sooner than pork. ^^ --;?-'*?s.i Statements respecting the digestibility of different articles of food must, however, be received with many restrictions. If, as circumstances the earlier physiologists believed, the stomach was the sole interfering digestive cavity, and the intestine only for the purpose of ab- of dio-estibiii- sorption, they would doubtless be much nearer to the truth. *J'- But when we recall that the digestion of fats does not even begin until the intestine is reached, and that the digestion of the nitrogenized sub- stances is only in part accomplished by the gastric Juice, but goes on under the influence of the intestinal juice throughout the whole length of the small intestine, we see at once how imperfect and even incorrect are the indications afforded by such experiments as those of Spallanzani, who introduced food articles into the stomach through the oesophagus in perforated silver vessels, or those of Beaumont, who availed himself of a gastric fistula. Neither can we take, in all instances, the time which an article of food will remain in the stomach as a measure of its digestibil- ity, for this is known to vary with many conditions, as, for instance, the quantity mtroduced at a time, and the condition of the organ itself. As general illustrations of the digestibility of some of the ordinary elements of food, the examples, however, being more or less open to the preceding criticisms, the followmg facts may be offered. The white of an egg, rep- E 66 RELATIVE DIGESTIBILITY OF FOOD. resenting soluble albumen, if introduced into the stomach of a fasting dog through a gastric fistula, will disappear in less than an hour ; but if the whites of eight eggs be introduced, portions thereof can be recognized after four hours. Lehmann, who made these observations, adds that blood fibrin varies in its time for gastric solution according as it is in a finely comminuted or a massive state ; in the former instance disappear- ing from the stomach of a dog in an hour and a half, but the same weight in the latter condition requiring almost twice the time. Coagulated al- bumen indicates the commencement of digestion, and even its local com- pletion, in from five minutes to a quarter of an hour ; but here again much depends on the condition of the stomach and the general state of the sys- tem, whether the animal has been fasting, and whether the gastric juice is exuding in a dilute or concentrated state. So far as such examinations go, they do not exhibit any marked dif- Eespiratory cii- fcrencc between albumen, fibrin, and casein. Gelatine, how- i^estion, as of evcr, is actcd on with remarkable rapidity. Beaumont ob- fat does not be- t i • i -< irrv c • n i i t ^ . frT A'- extremity, b the middle por- tion, the jejunum, d the gall- Jiwvijpm.'^^^. H^fc''''-^"li ^^^^^^^' ^ *^® c^jBim duct,^ '^'~~ / rM ^r^'^^^^s^^^^^'.J^'^ir hepatic duct, c the ductus cor.i- (1/ '^v''^,.li|| munis, m pancreatic duct. Soon after the chyme has escaped through the pyloric valve into the duodenum, it Posterior view of the duodenum. comcs undcr the influence of the bile and pancreatic juices, which are sometimes discharged upon it at a common point, and sometimes at a little distance apart. Digestive flu- , ^ ,.. i • -i i i-i ids of the in- Almost Simultaneously it is submitted to the mecliamcal ac- testme. ^^^^ of the valvulse conniventes, which make their appearance in the vertical portion of the duodenum, and continue in large numbers until within the last two or three feet of the end of the tube. As the intestine is distended, these project with a certain degree of turgidity, and accomplish their mechanical object. But, besides the pancreatic and biliary fluids, there are other juices thrown upon the passing chyme — the enteric juice, which comes from Brunner's glands, and a liquid oozing from the follicles of Lieberkuhn. Moreover, the organisms known as Peyer's glands are affecting the con- tents of the tube. Of each of these it is necessary therefore to speak. 1st. The pancreatic juice, secreted by the pancreas, an organ bearing a Pancreatic resemblance in its anatomical construction to the salivary juice, constitu- p-j^nds, and hcnce usually regarded as one of that group. tion and prop- o ' t i • • • i i • • erties of. The juicc itself is analogous to saliva, being viscid, and m its reaction alkaline: its specific gravity is about 1.008. Alcohol coagulates it. It is said to contain no sulphocyanide nor any suspended particles. It acts upon starch even more energetically than saliva, transmuting it into sugar and lactic acid, and upon fats by forming them into an emul- sion, so that they are readily absorbed. This has been found to take place in artificial experiments by submitting fat substances to the juice at a temperature of 100°. Constitution of Pancreatic Juice of Dog. {From Schmidt.) Water 900.76 Organic matter 90.38 Inorganic " 8.86 1000.00 ENTEEIC JUICE AND SECRETION OF LIEBERKUHN. 69 Fig. 20. As would be inferred from the difference of emulsifying power between the saliva and this juice, its organic matter differs from ptyaline. It is estimated that the standard secretion of it is from five to seven ounces per diem. The action of the pancreatic juice appears to be limited to the upper half of the intestine, for it is in that region only that butyric acid is de- veloped from butter. 2d. The enteric juice is secreted by the organs known as Brunner's o-lands, the structure of which has a certain analogy to the _ -,. 1 Ti • 1 111 11 11- Enteric juice, preceding, and, like it, these doubtless belong to the salivary group. Brunner's glands occur chiefly in the upper part of the small in- testine, presenting themselves in the submucous tissue thereof as little bodies, commonly compared by anatomists to hemp-seeds. They consist of lobules with ducts communicating with a common outlet. Their se- cretion possesses a more energetic power when mixed with bile and pan- creatic juice, than the pancreatic juice alone, in producing fatty emulsions. In the opinion of Bidder and Schmidt, the intestinal juice, which they describe as being invariably alkaline, not only metamorphoses starch as rapidly as the saliva or pancreatic juice, but also exerts as powerful an action on flesh, albumen, and other protein bodies as that which occurs in the stomach itself. In Fig. 20, which is a half diagram of one of these glands, a a represents the mu- cous surface of the intestine, and h the lobulated gland, discharging its secretion Diagram of Brunner-s glands. thrOUgh a COmniOU duCt. 3d. The secretion of the follicles of Lieberkuhn, which, as shown in Fig. 21, are straight, narrow coecal de- ggcretionof pressions of the mucous membrane, found follicles of all over the small intestine, and in a gen- ^^ ^^ " °" eral manner analogous to the tubular follicles of the stomach. Their interior is lined with columnar epithelium, and in depth they are equal to the thick- ness of the mucous membrane, their closed ends be- ing therefore in contact with the submucous tissue, and their mouths opening into the intestine. In a state of health they contain a clear mucus-like secre- tion. In inflammations of the part they are filled with a more opaque, whitish liquid. From their re- semblance to the follicles of the stomach which secrete pepsin, it may be presumed that they possess a somewhat similar function ; but in the stomach, the resulting secretion is brought in relation with acids ; in the Fig. 21. Diagram of follicles of Lieber. kuhn. 70 peyee's bodies and the bile. intestine, with alkaline bodies ; and hence the physiological action may differ in the two positions, though the structure and primary function may he the same. 4th. The secretion of Peyer's glands. These may be described as cir- Secretion from cular spots, of a whitisli color, and about the tenth of an inch Peyer's glands, i^ diameter, constituting glandular patches full of cell germs, but without any excretory duct opening into the intestine. It is sup- posed that they discharge their contents by rupturing at a certain stage of their development. The solitary and agminate glands appear to be- Fig. 22. long to the same physiological group. The two conditions of the Peyerian glands ^ are shown in Fig. 22, the right one being J ' empty, its contents having been discharged, '!iy^K^£\iM^l| ■mPs! * *^® ^^^'^ ^^-'^ ^^^^^ ^^^' ""^^ some it is denied ^'^^^^^^^an/O/'^^^Wk'l) ^^^^ these bodies are connected with intes- '^^^^^W¥?5' " \l *^"^^^ digestion. The facts that vascular ^^^^^^'';^"- ^^^g ^____ ^^ loops pass into their granular contents, and Peyerian glands. that the lactcals bear a definite relation to them, seem to indicate that they are rather portions of the absorbent mechanism. 5th. The bile. Of this it is not now necessary to give a detailed description, since that will occur more appropriately in treat- ing of the functions of the liver. For the present purpose, it is sufficient to state that bile is a greenish-yellow liquid, of bitter taste and alkaline reaction. It is soluble in water, changes with rapidity under the influence of the air, or even spontaneously. Its specific grav- ity is about 1.028. An ultiiuate analysis of its organic material shows C^g, Hgg, O22, N2, with sulphur. Its aspect is therefore that of a hydro- carbon, and it stands in strong contrast with the nitrogenized bodies. It is a significant fact that, even in the lower tribes of fife, it is uniformly discharged into the upper part of the intestine. Bidder and Schmidt estimate the diurnal quantity of bile at 54 ounces, containing 5 per cent, of sohd matter ; they also give the following table of the diurnal amounts of the various digestive fluids secreted by a man of the stand- ard weight, 140 pounds : Diurnal Amount of Digestive Secretions. Saliva 3.30 lbs., containing solid matter 1. per cent. Bile 3.30 " " " " 5. Gastric Juice 14.08 " " " " 3. Pancreatic Juice .. . .44 " " " " .1 " Intestinal Juices ... .44 " " " " 1.5 " The bile does not appear to exert any agency in effecting the digestion of either nitrogenized or amylaceous bodies. The period of its max- POWER OF PANCREATIC JUICE. 71 imum production, which is 13 or 14 hours after a meal, does not coincide with the period of most energetic digestion. With these statements of the nature of the various juices Avliich pass into the small intestine, we may proceed to investigate the phenomena of the digestion carried on in that tube. In 1832, Dr. Bright, to whom medicine is so much indebted for his discoveries in relation to the pathology of the kidne j, pub- j, , .^ ^. lished three cases of disease of the pancreas, attended by the power of pan- appearance of a large quantity of fat in the fseces, and drew '^''^^ ^^J'"'^'^- the inference tliat in such morbid states the fats are imperfectly digested. More recently, j\I. Bernard has pubKshed experimental evidence to prove that the digestion of the fats consists in bringing tliem into the condition of an emulsion, and that the pancreatic juice accomplishes this object. Whatever influence tlie pancreatic and enteric juices can exert on starch and oil outside of the body, in artificial experiments, they un- doubtedly exert it in the small intestine as long as the temperature is the same. On starch, the action, as has already been stated, is to effect its conversion into sugar, and then into lactic acid. The oils are turned into emulsions. The constitutional relation between starch and lactic acid is such, that if, in presence of water, one atom of the s^i^division of former be equally and systematically split or divided into starch into lac- two portions, those portions are atoms of lactic acid. And since this substance contains no nitrogen, its oxidation either artificially or in the interior of the system gives origin to carbonic acid and water — bodies which can at once be removed by the action of the skin, or the lungs, or the kidneys. Respecting the digestion of the carbohydrates — cellulose, gum, starch, and the different kinds of sugars, it may be remarked, that eel- pj^estion of lulose, of which the pith of elder is an example, and which the carbohy- occurs in a pure form in Swedish filtering-paper, not only re- sists, in artificial experiments, the action of the digestive juices, but also it would appear to do so naturally in the higher tribes, and hence it is abundantly found in the excrement of the herbivora. To this statement, perhaps, however, the case of the beaver affords an exception, Dio-estionof there being reason to suppose that this animal possesses the cellulose, power of digesting cellulose. There can be no doubt, moreover, that many insects have the same power, for chitin, which may be obtained from their wing-cases, and which retains the appearance of the structure of the part, may be considered as cellulose united with a nitrogenized body, having the constitution of in- sect muscular fibre. This substance not only constitutes the skeleton of insects, their scales, hairs, and enters into the construction of their trachea?, but even forms one of the coats of their intestinal canal. Since 72 DIGESTION OF CAEBOHYDEATES. it does not appear that tliey can metamoi"phose other carhohydrates into this body, we may infer, as would indeed seem probable, considering the nature of the food of many of them, that they can digest woody fibre. The digestive apparatus of man, however, can not exert such a power. Neither does it appear that gum undergoes either digestion or absorp- Di^estion of tion. In artificial experiments it also resists the action of di- gura. gestive fluids, and is not changed when present during the fermentation of other bodies, even though its exposure thereto be contin- ued for several days. Administered to animals, it is almost entirely voided with the excrement. Thus Boussingault, having given to a duck fifty gi-ammes of gum-arabic, obtained forty-six grammes from the ex- crements in nine hours. In an experiment upon an old rabbit, to which, with a diet of cabbage-leaves, ten grammes of gum-arabic were daily given bv Lehmann, the gum being administered in solution in water by injec- tion into the stomach, no trace whatever of gum could be detected in the urine, none in the chyle of the thoracic duct, and none in the blood, but it was easily enough recognized in the excrement. From this he infers that the preparations of gum, which are such favorite medicines with some physicians, yield to the animal organism only an extremely small quantity of material of a nature to support the respiratory process, and that their uses, if they are of any use, can be merely negative in acute diseases. Of the carbohydrates, starch is perhaps the most important, occun-ing Dio-estionof as it does in abundance in vegetable food. It can not be made starch. -^gg gf in the system without first being transmuted into dex- trine, sugar, and eventually lactic acid, these changes being greatly ex- pedited if it has been previously prepared by boiling in water, or other equivalent operations of cooking. The saliva commences the action, which in man is even prolonged in the stomach, and in the herbivora still more decisively in the paunch, in birds in the crop. On gaining the stom- ach, the farther transmutation of the starch is arrested by the gasti-ie juice, but after reaching the duodenum it is resumed with greater energy than ever, under the influence of the pancreatic juice. Eeaching the ile- um, the intestinal juice continues the action, though with less vigor. In this passage to the large intestine, the starch is gradually assuming the condition of dextrine and sugar, the former substance passing into the latter with such facility that it can only be recognized transiently. Doubtless the sugar thus arising is in great part directly absorbed, though some, before the coecum is reached, is transmuted into lactic acid, and oth- er portions, after passing through the ileo-coecal valve, into butyric acid. From what has been obseri^ed respecting starch, it may be inferred hew Digestion of important sugar is, since through the condition of sugai- alone sugar. ig starch available for the uses of the system. It is to be rec- DIGESTION OF SUGAE. 73 ollected, liowever, that sugar itself is only an intermediate or transitory- stage, through which the carbohydrate is passing, a consideration which explains the circumstance that it does not occur even in the portal blood to such an extent as might be expected, nor yet in the chyle. Some have been led to infer from these facts that this substance, like gum, is in reality only very tardily absorbed, an opinion which they suppose to be strengthened by the circumstance that glucose or any other kind of sugar, introduced into the jugular vein, runs through the course of the circulation, and is secreted unchanged by the kidneys. But it is to be remembered that portal blood is very different from the proper systemic blood, and that there are many changes, beyond all question, which can take place with rapidity in the former, but which do not take place in the latter. Sugar, whether it has been received as an ingredient of the food, or arisen from the metamorphosis of starch, is, as we have said, only a tem- porary form, which passes quickly onward to the state of lactic acid. To this we must impute the acid reaction which is observed throughout the length of the small intestine, and which can not be attributed to the gas- tric juice, a reaction occurring in spite of the alkalinity of the bile and pancreatic secretion. This pushing of the carbohydrate forward to the state of lactic acid is very generally imputed to the intestinal juice, which greatly re-enforces the power of the saliva and pancreatic fluid ; some have even supposed that the bile aids in producing this effect. Of this, how- ever, there is no satisfactory proof. I'rom the experiments of Von Becker, who injected saccharine solu- tions at mtei-vals of a quarter of an hour into the stomach of rabbits, it was found that 4.5 parts of sugar were absorbed each hour for every 1000 parts weight of the animal. Whatever may have been the form of sugar administered, as, for instance, cane-sugar, it quickly passes into the con- dition of glucose in the intestine, and from that to lactic acid. Thus sug- ar of milk may be traced in an hour as far as the coecum, communica- ting to the contents of the small intestine an intense acid reaction. Since lactic acid discharges very important offices in the animal econ- omy, it may be worth while to observe its properties, and -r, ■, ^. , •i ^ ^ -J _ r r ' Production and the circumstances under which it is produced. Very many properties of liquids containing organic matter yield it abundantly: thus it ^^^^*^^'^^ • is found in sauer kraut, a preparation of cabbage. It is, however, more conveniently obtained from milk, and hence the term lactic acid. The diluted solution obtained from this source, being concentrated by evap- oration, furnishes a sirupy liquid, heavier than water, having an intense- ly sour taste, a great affinity for water, and therefore attracting it from the air, and dissolving freely in it. With metallic oxides it forms solu- ble salts, and in the concentrated sirupy state has the remarkable con- 74 LACTIC ACID. stitution that it contains six atoms of each of its elements, carbon, hy- drogen, and oxygen. The production of this acid in organic substances is veiy common. It depends on the same principle as presented in duodenal digestion, which it therefore very strikingly illustrates. As an example deserving of attentive consideration, its development in milk may be offered. When milk is exposed to the air it eventually turns sour, the sour- ness being due to the appearance of lactic acid. In its sweet state, the milk may be regarded as consisting of casein, or the curdy principle, a substance belonging to the protein group, insoluble in pui-e water, but abundantly soluble if a little free or carbonated alkali be present ; of milk sugar, dissolved, and of butter held in suspension in water. The ac- Productionof ^^^^ taking place during the souring is as _ follows : Under lactic acid the influence of atmospheric oxygen, which for tliis purpose rom mi . m^gt have access, the nitrogenized principle, the casein, be- gins to change, and, for reasons presently to be more particularly exam- ined, impresses a change on the sugar, splitting its atom so as to give rise to the production of lactic acid. As this forms, it renders the casein insoluble, and the milk begins to coagulate, to prevent which a little car- bonate of soda may from time to time be added. All the sugar origin- ally present in the milk is soon acidified, but a much stronger solution can be made by adding more milk sugar as the process of exhaustion goes on, and the change can be thus kept up until the casein itself is quite consumed. On examining this process critically, we observe that every thing de- pends on the change occui'ring in the nitrogenized principle, the casein. This, under the circumstances, takes on an incipient oxidation, and com- pels the sugar atom so to divide as to give rise to the production of lac- tic acid. This ceases the moment the casein ceases to change, and re- commences the moment the casein is peniiitted to reoxidize. The de- struction taking place in the casein is propagated to the sugar, the physical peculiarity being that the atom of sugar is merely divided, fis- sured, or split, and gives rise to the production of lactic acid, and no other substance. The whole process is therefore essentially one of sub- division, a conckision which should be carefully borne in mind in apply- ing these experimental principles to the physiological function of diges- tion. So far as the result is concerned, the two cases are the same. Many other organic liquids furnish similar illustrations. Thus, in p . „ the operation of making starch for commercial purposes, con- lactic acid siderable quantities of that substance are turned into lactic from starch, q^q^^^ constituting what the manufacturers term sour liquor. Nor is it even requisite that so much Avater should be present as to give the liquid condition ; for if wheat flour be made into a paste, and kept for LACTIC ACID IN THE SYSTEM. 75 some days in a warm place, its gluten induces sucli a change that the starch turns into lactic acid, and the paste becomes sour. Of lactic acid there are two kinds ; that derived, as hereafter stated, from muscle juice, is the alpha lactic acid, and that from the Alpha and beta fermentation of sugar the beta lactic acid. As it occurs in ^^'^^^^ ^^■"'• the gastric juice, associated with or replacing hydrochloric acid, it is of the beta variety. Whatever may have been the source of this portion of it, whether it has been derived by gastric secretion or through the transmutation of amylaceous food by the saliva, its abundant occurrence in the contents of both the small and large intestines, in which it is rec- ognized by the peculiarities of its zinc and magnesia salts, confirm the conclusion that in this case, at least, the beta form arises from the opera- tion of the digestive juices. Lactic acid undergoes rapid absorption through the intestine, and is as rapidly disposed of in the system. Thus Lehmann found, after tak- ing half an ounce of dry lactate of soda, that in thirteen minutes his m'ine had become alkaline. On injecting the same salt into the jugular vein, it appeared in from five to tAvelve minutes as carbonate of soda in the urine. Berzelius first discovered the existence of lactic acid in the juice of the muscles. Liebig showed that, in quantity, there is more production of present in this source than is sufficient to neutrahze the alkali lactic acid by of all the other liquids or juices of the body. Muscle lac- tic acid is removed away with rapidity by the lymphatics. Berzelius concluded that its quantity increases in proportion to the exercise the muscle has undergone ; and this would lead to the inference that it is one of the chief products of muscular waste ; for it is not to be supposed that its appearance in muscle juice is because those organs attract it from the blood, in wliicli it pre-exists, derived, perhaps, from the trans- formation of amylaceous substances in the intestine, for the muscles of the carnivora yield as much of it as those of the herbivora ; and though it can not be artificially made directly from albuminous material, yet it would seem that, with urea and ammonia, it might arise from the breaking up of creatine. From glycerine lactic acid may be also developed. When- ever an excess of it is produced in the system, either by muscular action, unusual diet, or imperfect oxidation in the blood, it may be detected in the urine. Under ordinary circumstances, doubtless, very large quanti- ties of it are destroyed in the circulation, giving rise to the production of carbonic acid and water with a disengagement of heat. We can not here fail to remark how the process of comminuting the food is carried forward to such an extent that the absorbent These digest- vessels are able to take it up. The action first begins, as has ^^^^ subdivi'°'^ been shown in detail, by cutting and crushing implements, ions. 76 DIGESTION OF FAT. the teetli, and when these have carried the subdivision as far as mechanical means can, it is continued by chemical agents. Upon these principles, the pancreatic juice divides starch into lactic acid in duodenal digestion — a product which, without difficulty, finds its way at once into the system. Besides starch and sugar, there is another group of bodies belonging Digestion of to the class of calorifacient food, which, in the case of carniv- ^^*- orous animals, seems to be exclusively employed. The fats and oils constitute this group. The action of the pancreatic and enteric juices upon these bodies, in bringing them into the condition of an emulsion, has already been stated. That this occurs in the intestine appears from the fact that if the pan- creatic duct be tied, no emulsion forms, and the chyle in the lacteals is limpid instead of being milky. In the rabbit this duct opens much lower in the intestme than the biliary, and it is observed that it is only after the food has passed that point that it becomes emulsioned. The place for pancreatic digestion seems to be very constant in tribes that are far apart in habits of life. Thus, in fishes, the pancreas consists of a cor- onet of coecal tubes, surrounding the pyloric extremity of the intestine, each opening into that organ by a separate mouth. The fats reach the duodenum without undergoing any change. There, under the influence of the pancreatic juice, they become subdivided into extremely minute portions, which, absorbed by the lacteals, give to the chyle its characteristic aspect. Beyond this condition of subdivision no other change is thus far impressed, the fat of the lacteals being abso- lutely the same as that of the chyme. To the introduction of fat into the lacteals, the presence of bile seems to be necessary, or, if not absolute- ly necessary, absorption is greatly facilitated by it. The gastric and pancreatic juices stand in a remarkable relation to one ■g ,, , another, the former being an acid liquid, having the power trine of the ef- of bringing into a state of solution nitrogenized bodies, such an^d alkalinity ^^ fibrin ; the latter alkaline, without action on nitrogenized in the digest- bodies, but opcratuig energetically on starch, sugar, and oils. From this it might be supposed that the intrinsic qualities of these juices are different, and that they act in this manner because of a special dissimilarity of constitution. Attempts have been made to prove that this difference of action de- pends wholly on the chemical relations of the juice itself. If pancreatic juice or saliva be piu-posely acidulated with hydrochloric acid, it is said that it loses at once the power of acting on calorifacient food, but can bring about the solution of the histogenetic. On the other hand, if gas- tric juice be rendered alkaline by admixture with soda, it no longer dis- solves fibrin or coagulated albumen, but gains the power of acting on starch and sugar. Since, then, it thus appears that the same organic body ORGANIC PRINCIPLE OF DIGESTIVE JUICES. 77 becomes endowed with one or other of these properties, according as it is acidulated or alkalinized, the function of digestion is j)resented to us un- der a simple aspect. It is upon these principles that we may explain the fact that the presence of bile in the stomach suspends or arrests the digestion going on in that organ. Though the views here expressed are such as are received among many- chemists, yet it is still open for consideration whether the The nature of nature of the result which is reached in these cases does not, ^^^ organic in- - - . gredient more to a great extent, depend upon the nature oi the organic important than changing body, the ferment, which first sets up the action. *^® reaction. Many circumstances would lead us to infer that this must be the case, and that, as with differences of temperature, so also with these differences, the final result may present distinct variations, though they may be with- in a certain range or limit. Thus, though the saliva and pancreatic juice are both alkaline, and both impress in a general way the same digestive change on starch and sugar, a minute examination of the results of their action would doubtless lead to the detection of shades of difference — ^va- riations which could only be attributed to the difference between the act- ive organic principle of the pancreatic juice, and ptyaline, the correspond- ing principle of the saliva. The imputed control which the alkalinity or acidity of the digesting juices exerts in determining the result, illustrates the import- j, i .• ant function discharged by common salt, which furnishes to common salt in the juices of the stomach and intestine the characteristic in- ' ^sestion. gredients they require by breaking up readily into hydrochloric acid and soda, and re-forming at once whenever these materials are brought in contact. There is, therefore, an important reason for the instinct which animals display in resorting to the use of this substance, as in the buffa- lo licks at the West, and the necessity which men experience to add it as a condiment to their food. But though, by furnishing an acid or al- kali, as the case may be, it determines the nature ofthe work which the secreting juices perform, it is not to be regarded as the prime mover of the change. It guides rather than works. The efficient principle bring- ing about digestion appears always to be a nitrogenized body, acidulated, perhaps, for the production of one duty, and rendered alkaline for the pro- duction of another. Directing our attention now .more particularly to the phenomena dis- played by such a changing nitrogenized principle, the following illustra- tions will serve to show that there is nothing mysterious in its operation. Out of many cases which might be selected, those now to be offered are more particularly interesting, since they refer to substances extensively used in the diet of man. First, of wine. A grape, if perfectly sound, will keep for a consider- 78 ILLUSTEATIONS FROM WINE AND BREAD. Illustration ^^^® length of time without undergoing any change ; but if from the mak- a puncture be made in it to give the air access, it rapidly de- ing wine. tcrioratcs. The precise change taking place is perhaps bet- ter understood by observations on the expressed juice of this fruit. If grapes be pressed beneath the surface of quicksilver, and the juice be col- lected in an inverted jar, without ever coming in contact with the atmos- pheric air, it may be kept for a long time without any apparent change : but if a small quantity of air, or only a single bubble of oxygen is per- mitted to enter the jar, and the temperature is that of a summer's day, an intestine commotion or fermentation at once ensues, carbonic acid escapes, alcohol arises in the liquid, and the sugar which was in the grape-juice disappears. But the quantity of sugar thus capable of being destroyed is limited, and a point is eventually reached at which no more sugar can be decomposed, and no more carbonic acid set free. The juice of the grape contains a nitrogenized principle resembling al- bumen. It is this which is in reality the active body. So long as ox- ygen is excluded, this nitrogenized substance remains unaltered, but the moment the air finds access, a, change begins. The sugar which is pres- ent in the juice becomes involved in the movement going on, which is propagated by degrees to all its atoms, dividing each into two well-known and well-marked bodies. The period at which no farther change takes place in portions of sugar which may have been purposely added is when tlie nitrogenized principle has disappeared. Carbonic acid and alcohol are the two substances arising in this de- composition. Their mode of origin is obvious when it is understood that one atom of sugar can be so divided as to yield four of carbonic acid and two of alcohol. In this artificial instance, the subdivision is even more complex than that which occurs in duodenal digestion, in which the sugar atom is subdivided into two equal and symmetrical parts, two atoms of lactic acid. In the following formulas, (1) represents the case of vinous production, (2) that of duodenal digestion : (1) C,H,,0,, = 4(CO) + 2(C,H,0,). (2) C,3H,, 0,3-2 (C,H,0,). Second, of bread. If, in the preceding case, a transmuting nitrogen- ized body breaks the sugar atom so that alcohol is one of the from making products, and upon this principle all wines and intoxicating of bread. hqnors are made, the instance now presented is of far more interest to the well-being of man. The use of wine undoubtedly adds not only to social enjoyment, but sometimes conduces to health — a ben- efit, alas ! often attended with a thousand ills. Not so with bread, em- phatically and truly described as the staff of life. The making; of wine and of leavened bread are two of the oldest chem- ILLUSTRATION FROM THE MAKING OF BREAD. 79 ical processes. Their origin is lost in a remote antiquity, and so uni- versally are their benetits acknowledged that their use is diftused all over the world. Experience proves that the best bread is made from fine wheaten flour, mixed into a paste with a due proportion of water. A certain quantity of a nitrogenized substance undergoing incipient oxidation, tenned yeast, is added, and the whole submitted to a gentle temperature. All flour contains a small quantity of sugar ; on this the yeast immediately acts, dividing it, as in the former case, into carbonic acid and alcohol. If enough sugar is not present, more under the circumstances is formed from starch. The acid gas, as it is set free, can not extricate itself from the surrounding dough, but expands into a thousand little vesicles or bub- bles, which give that peculiar porosity for Avliich this kind of bread is so highly prized. At this period, before baking, the other substance which has arisen from the destruction of the sugar — the alcohol — is contained in the dough, and is expelled therefrom along witli the excess of water by the high temperature of the oven, which also, by increasing the expan- sion of the included gas, adds to the porosity of the bread. In some baking establishments arrangements have occasionally been made to con- dense the alcohol as it rises from the bread. The good and evil of life are often closely intermixed. The advocate of total abstinence from al- cohol may with reason look upon half-baked bread distrustfully. The enemy is lying in ambush for him. On some occasions, instead of using yeast, a piece of leaven, that is, dough, in a state of incipient putrefaction, is employed. The mode of action is, however, the same. The use of this material well illustrates the progressive nature of these changes, and how the action gradually passes from point to point of the entire mass. It is written, "A little leaven leaveneth the whole lump." In the cases here presented the action is one of subdivision. A com- plex atom -has its constitution broken up, and is separated These actions, into distinct parts. When such a change is once commenced ' '^} °^^° ^' r o gestion, are in a mass, there is a liability for the whole to become in- subdivisions. volved, just as, when we ignite one point in a pile of combustibles, the fire spreads throughout ; or as, when on one part of a piece of fresh meat a small portion in a putrescent state is laid, the corruption, with measured rapidity, proceeds from part to part, until the wdiole is decayed. One after another, the particles submit in succession. Over all these subdividing actions heat exerts the most extraordinary influence, so that for a given effect to be produced it is abso- Influence of lutely necessary that a given temperature should be main- subdi°vidinff^^^ tained. Thus, if we take the saccharine juice of almost any actions, kind of finiit, and cause it to be-acted on by a changing nitrogenized body, 80 EFFECTS OF TEMPERATUEE ON FERMENTS. it will yield, as just stated, alcohol and carbonic acid so long as the tem- perature ranges about 75° ; but, every thing remaining the same, if the temperature be raised to 100° or 120°, neither alcohol nor carbonic acid is formed, but in their stead other products arise, such as lactic acid, gum, and manna. Though, therefore, decomposition will go on through- out all this range of temperature, the products will vary very much, al- cohol being formed at a low, and lactic acid at a high degree. Again, the decomposition of milk furnishes a very instructive instance. When the temperature ranges from 50° to 75°, the liquid turns sour, owing to the formation of lactic acid ; but if the temperature is over 90°, the products are different, for now a true vinous fermentation sets in, al- cohol and carbonic acid appearing. It is on this principle that the Tar- tars make an intoxicating liquid from mare's milk. The fermentation of milk, therefore, yields lactic acid at a low, and alcohol at a high degree. On comparing these illustrations, the results stand in direct contrast, but both show the great influence which a specific degree of heat exer- cises over such subdivisions ; and, as a consequence of this principle, which obtains equally in the physiological case, we recognize the neces- sity of maintaining the cavity of the stomach and intestine uniformly at a temperature which is fixed, otherwise there would cease to be any uniformity in the subdivision of the food, occasioned by the digestion there going on. These principles, moreover, lead to the explanation of the action of such stimulating substances as alcoholic liquids, pepper, etc., which at once determine a local elevation of temperature ; they also explain the injurious efiects which may ensue from intemperate draughts of ice-cold water. A nitrogenized substance, in a state of change, can thus bring about a 'definite action on fibrin, coagulated albumen, or casein in the stomach, or on starch in the intestine, so long as a temperature of 100° is main- Loss of power tained, but in every known instance this transmuting power ^\^'!^h"t"*^ ^^ ^® totally destroyed by exposure to a very low or very high ature. degree of heat. Large masses of animal matter — whole car- casses — may be preserved for many centuries unchanged if the tempera- ture is kept down to 32°. A striking example of this occurs in the case of the extinct elephants which are occasionally thrown on the shores of the Polar Sea from icebergs, in which they have been entombed for many thousand years, their flesh remaining in a perfectly fresh and un- decayed state. And as respects a high temperature, an exposure to 212° totally destroys the power. On this principle, all kinds of meat or veg- etable substances may be indefinitely preserved. If such are inclosed in metallic canisters, so as totally to exclude the atmospheric air, and ex- posed to a bath of boiling water, they may then be carried around the world without undergoing any change. ARTIFICIAL rRODUCTIOX OF FAT. 81 One of these illustrative cases still remains. It belongs to the class of changes now under consideration, and deserves a prominent examina- tion from its connection with duodenal digestion. It is the production of fatty bodies from starch and sugar. Physiological considerations assure us that there are circumstances under which oils and fats can be formed from starch and pj-oduction of sugar in the system. Animals can be fattened by feeding fats from ear- on potatoes, or other such food, in which the quantity of oil ° '"^ is quite insignificant. Bees can make wax, wdiicli strictly belongs to the group of fats, though they are fed on pure white sugar. Such results can be artificially imitated. If a strong solution of sugar be mixed ^^'ith a small quantity of casein and powdered chalk, and ex- posed to a temperature of more than 80°, carbonic acid and hydrogen are evolved, and butp-ic acid forms as the butyrate of lime. This acid sub- stance is a colorless oily liquid, lia^T.ng the odor of rancid butter, in which indeed it exists. From a review of all the preceding facts, we may conclude that a nitro- genized substance secreted by the follicles of the stomach. Contrast of and undergoing incipient oxidation, acidulated with hydro- feTt^inal d"io-es-' chloric acid obtained by the decomposition of common salt, tion. or with lactic acid produced by a continuation of salivary digestion, has the power of dissohdng coagulated albumen, and generally those articles of food which belong to the nitrogenized class ; that this goes on in the stomach, it bemg the function of that organ to effect the digestion of this kind of food, and thereby contribute to the general nutrition of the system. The muscular tissues are supplied from this source, and by the stomach their waste is repaired. Another and distinct digestion takes place in the intestine, commenc- ing immediately after the food gains the duodenum. It too is brought about by the action of a special liquid, a mixture of the pancreatic and intestinal juices. The chemical reaction of this juice is alkaline ; in this respect it is therefore antagonistic to the gastric juice. This quality is due to the soda it contains, a substance derived co-ordinately with hy- drochloric acid from the decomposition of common salt. The digestion of starchy and saccharine bodies is thus effected by dividing them so as to produce lactic acid. This done, common salt is reproduced by the commingling of the gas- tric, biliary, and pancreatic products together. The salt is carried by the absorbents into the interior of the system, to be again decomposed. Moreover, the pancreatic and enteric juices reduce the oleaginous and fatty bodies to the condition of an emulsion, or, if they be not present in the food, give origin to them in the way just described. The reaction of the intestinal contents not only differs in different por- F 82 SALTS AND GASES OF THE INTESTINE. Successive tions of the tube, Ibut in the same region, in different parts traTsftthrouo-h ^^ ^^^® mass, its exterior may be alkaline, its interior acid, or the intestine, the converse. The acidity which has been imparted by the gastric juice seems generally to have disappeared some time before the large intestine is reached. In this an alkaline reaction is observed. The causes of this prolonged acidity are very various. In part it depends on the nature of the food, in part upon the gastric juice, as has just been stated, and in part upon the production of lactic, butyric, and other acids. The resinous ingredients of the bile may be detected as far as the lower extremity of the ileum. Glucose, originating in the action of the pancre- atic and intestinal juices on starch, may be recognized throughout the whole length of the canal, but that which has been introduced in the food seems to be absorbed in the stomach itself; thus, in milk-fed ani- mals, sugar does not appear to descend beyond the jejunum. The trans- mutation and reabsorption of biliary matter commences in the small in- testine and proceeds continuously, so that by the time the middle of that portion of the tube is reached, half the bile is gone. Since the intestinal absorbents can only take up a definite proportion of fat, it might be expected, as is really the case, that after an unusually fatty diet, fat substances will be found in the excrement. Indeed, a cer- tain small proportion always so occurs. Of the salt substances usually occurring in the food, most disappear Salts of the in- during their passage through the intestine, and hence but lit- testine. tie is found in the feeces ; more particularly is this the case with those of a very soluble kind. Of the sulphates and chlorides of the food, not even a trace may occur in the excrement. If these substances should not be required for the uses of the system, they are promptly re- moved by the kidneys, and in the same manner are disposed of any ab- normal salt substances which may have been purposely administered, as, for instance, iodide of potassium. The gaseous contents of the intestine originate in part from the air Gases of the ^^^.t has been introduced during the mastication of the food, in intestine. p^rt from fermentative processes occurring after certain articles have been used which are only imperfectly digested, and in part from the endosmosis of gas from the blood through the walls of the intestinal cap- illaries. As compared with atmospheric air, though the composition must necessarily be very various, the intestinal gas shows a great excess ■of carbonic acid and nitrogen, a diminution and sometimes even a total absence of oxygen, the presence of pure hydrogen, and of its carburets and sulphurets. The quantity of this latter gas is less than might be expected from its odor, and, as would be anticipated from the circum- stances, the accumulation of gas is much more abundant in the large than in the small intestine. • FORMATION OF F.ECES. 83 Schmidt shows that the intermediate circulation of water toward the intestine is far more considerable than its final excretion, and Water fumish- amounts in one day to nearly one fourth of the whole quan- ^[J^^" ^''° '"'^*' tity of water in the body. As the digested mass passes onward, driven by the peristaltic motions through the convolutions of the intestine, it becomes of a Complex chan- more solid consistency, as the absorbents gradually remove fes\i"aicw"' its liquid portions. By the time it has reached the coecum, tents. the same etfect which arose in the stomach from salivary digestion is repeated, for the traces of unabsorbed lactic acid cause nutritive diges- tion to be again feebly resumed, at all events in herbivorous animals, if not in man, whose coecum is rudimentary, under the form of the appen- dix vermiformis. From Peyer's glands a secretion has exuded, which perhaps gives to the mass the characteristic odor it is now assuming, if, indeed, these organs are not connected with absorption. The effete re- mains are finally voided as faeces, which, due allowance being made for the water they contain, amounting to about 75 per cent., may be rep- resented as averaging about 1| ounce per day. These excrementitious remains, colored yellow by the coloring material of the bile, are partly de- rived from the residues of the food Avhich have been unacted upon, and partly from the decay of the system itself. The microscope shows the remains of cell membranes, and the walls of vegetable vas- Formation cular tissues, starch granules, and chlorophyll, the relics of car- ^^ feces. tilaginous and fibrous tissues, shreds of muscular fibre, fat-cells. From the digestive tract there have been derived mucus corpuscles, epitlielial cells, and the coloring matter of the bile. Perhaps, too, much of the wa- ter which gives consistency to the fgeces has been derived from the intes- tinal walls, for in quantity, under certain circumstances, it may exceed the amount that has been used as drink. In its passage through the intestine, that portion of the bile which has not been absorbed undergoes considerable changes, its conju- Disappearance gated acids degenerating into dyslysin, which may be recog- °^ ^^^ '^^^®- nized in the fa3ces, as is also the case with the modified pigmentary mat- ters ; the soluble mineral constituents are, for the most part, absorbed. The reducing agencies in the intestine, and the manner in which sub- stances can find their way into the urinary secretion, is well Incidenta] re- illustrated by the administration of indigo, which undergoes j^ tiiifintes-" deoxidation into the condition of suboxide of isatine, and will, tine, notwithstanding the agency of arterial blood, appear in that condition in the urine, to which, upon contact of the air, it imparts a blue tint, becom- ing more intense under a prolonged exposure, and eventually indigo-blue being deposited. Such a result not only shows how energetic are the re- ducing agencies in the intestine, but also with what facility very oxidiz- 84 ABSORPTION. able material may, under certain conditions, be exposed to arterial blood without oxidation. Yet that this want of action is wholly due to inci- dental circumstances is shown from the fact that salts of organic acids are much more quickly oxidized in the blood than they are in the open air. It is interesting thus to observe how the death of one part of the bod}^ ministers to the life of the rest ; for the nitrogrenized and act- Advantage . . ° . taken of the ivc principles of tho juices secreted for the accomplishment of ''ortion toor digestion are on the descending career, and are truly dying ganize an- matter. The incipient stage of decay tlirough which they are passing reacts on the food, and prepares it in a temporary manner to replace those parts of the body which are ceasing from activ- ity, and about to be removed. CHAPTEE V. OF ABSOKPTION. Dmhle Mechanism for Absorption. — The Lacteals and Veins. — Lacteal Absorption. — Desa'ip- tion of a Villus. — Analogies in Plants. — Introduction of Fat by the Villi. — 77ie Chyle. — Causes of the Flow of Chyle. — Intermediate Changes on its Passage to the Blood. — Action of Peyer's Bodies. — Lymphatic Absorption. — Nature of Lymph. — Structure of the Lymphatic System. — Comparison of Chyle, Lymph, and Serum. — Function of the Lymphatic System. — Production of Fibrin. — Cutaneaus AbsorjAion. — Causes of the Flow of Lymph. — Apparent se- lecting power of the Absorbents. — Connection of the Lacteals and Lymphatics with the Locomo- tive and Respiratory Mechanism. The food, after digestion, though in the alimentary tract, is exterior to , the animal system. ]\Ieans have therefore to be resorted to Double mecn- -^ . . , . ,.,..,. anism for ab- for its introduction mto the cn-culation, and its distribution sorption. ^^ evciy part. This is accomplished by a double mechanism, one portion of which is adapted to the digestion which has been going on in the stomach, the other to that which is completed in the intestine. The veins which are profusely spread on the walls of the digestive cav- ity constitute the former apparatus, the lacteal vessels the latter. The lacteal vessels may be described as delicate tubes, conveying ma- Description of terials absorbed fi'om the intestine into the blood. Their a villus. mode of origin may be rmderstood by considering them as projecting with a fine but blunt end upon the inner coat of the intestine. This projection is covered over with smooth muscle cells and a plexus of blood-vessels, a continuation, as it were, of those of the mucous coat of the intestine itself; they are held together by connective tissue, and over that is cast a covering of cylindiic epithehum. This construction con- DISTRIBUTION OF BLOOD-VESSELS TO THE VILLI. 85 stitutes what is called a villus, tlie slmpe of which is conical, or perhaps cylindrical. The villus may then be regarded as a process of mucous meniTbrane. Fig. 23 is a section of the wall of the ileum, a beins; the villi ; h. elands of Lie- „, , o ' ' o Structure of herkuhn ; een accepted by physiological writers, for in these results there is nothing more than what we should expect from the known principles of capillary attraction. The pores of a bladder, or of any other such organic texture, are nothing but short capillary tubes into which water readily finds its way, because it can wet the substance surrounding the pore. If the bladder be distended with air, and sunk under water, although the water wiU fill the pores, it ments are de- pendent on ca- pillary attrac- tion. FORCE OP ENDOSMOTIC MOVEMENT. 107 will not exude from them, and accumulate in the interior of the viscus, tor, as Ave have seen, a capillary tube can not establish a continued cur- rent or flow. But the case becomes totally different when the bladder is tilled with alcohol ; for then, as fast as the water presents itself on the in- ner end of the pore, it is dissolved away by the alcohol, and the necessary condition for a continuous flow is complied with. Meantime, through the pore itself a little alcohol passes in the opposite way by infiltrating through the incoming water, provided that the current be not too strong, and so endosmosis of the water and exosmosis of the alcohol take place, the current of the former greatly preponderating over that of the latter, and an accumulation of liquid in the interior of the bladder ensues. That in all this there is nothing specially dependent on the organic texture employed is obvious from the fact that the same results arise when any inorganic porous body is used. Vessels of unglazed earthen- Vv^are, pieces of baked slate or stucco, answer the purpose very well, as will also a glass vessel with a minute fissure or crack in it. An incorrect representation of the conditions under which endosmosis takes place is often made. It is said to depend on the relative specific gravity of the liquids. Thus it is stated that the lighter liquid always moves toward the denser, more abundantly than the denser to the lighter. The error of this is readily shown by many simple illustrations. Thus water endosmoses equally well to alcohol, which is lighter than it, and to gum water or salt water, which are heavier. The relation of specific gravity has nothing whatever to do with the action. The force with which a liquid will thus pass through a pore to mingle with anotlier liquid beyond is very great. I have observed po,.ce against these motions occurring against a pressure of many atmos- ^iiich these T110V611161ltS pheres. And, indeed, in practice we have no means of measur- may take ing its actual intensity ; for when a pressure of a certain de- V^^'^^- gree has accumulated, hydraulic leakage takes place backward through the pore, and conceals the true action. From the preceding statements respecting capillary attraction and en- dosmosis, we may therefore conclude that, whenever a liquid is in con- tact with a porous body the substance of which it can wet, it will freely pass into the pores thereof, and, if the necessary conditions for its re- moval are present, will percolate or transfuse with very great mechanical power ; that this will take place through pores that are not only invis- ible to the eye, but imperceptible by the aid of the microscope ; that some liquids pass thus with more readiness, some with less, some not at all — the result in these respects depending on the electro-chemical rela- tions subsisting between them and the solid they are in contact with, and their own force of cohesion ; that organic membranes present no peculiarities, their action arising, not because they are organic, but be- 108 SELECTING POWEK OF MEMBRANES. Selecting ponui- ol a memuriiue. arc porous ; that tlie so-called selecting power is purely physical, as are the separations and apparent decomposi- tions to which it gives rise. When a drop of colored water is put upon chalk, the water sinks in, but the color is left on the surface. When weak alcohol is tied up in a bladder, the water will escape through the 2)ores, and the spirit become anhydrous at last. If we take a glass tube, a, «, Fig. 41, over the lower end of which a piece of peritoneum, or other delicate membrane, J, 5, is tightly tied, and half fill it with litmus- water, and then place it in a glass of alcohol, c, c, the level of the liquids inside and outside being adjusted ac- cording to their specific gravity, so that there may be no hydrostatic pressure either one way or the other through the pores of the peritoneum — as soon as the arrangement is completed, if the observer be so placed as to view it by transmitted light, he will see the water descending from the pores of the peritoneum in striae and streams througli the alcohol in a perfectly colorless state. The membrane, therefore, has absorbed and transmitted the water, but has refused to the coloring matter a passage. It is to this particular experiment that allusion was made when speaking of the non-coloration of the chyle when certain coloring material had been mixed with the food. Such illustrations may therefore satisfy us that the selecting power of organic porous textures, like that of inorganic ones, is dependent on simple physical circumstances, and for these reasons I exclude from the mech- anism of animal absorption the influence of any vital or other mysterious principle, and adopt the sentiment of the Abbe Hauy, that "those specious causes and imaginary powers, to which, in the Middle Ages, all natural phenomena, even those of an astronomical kind, were referred, but which, througli the genius of Newton and Laplace, have been banished from the celestial spaces, have taken their last refuge in the recesses of organic beings, and from these retreats positive philosophy is preparing to expel them." In view of all the preceding facts, I therefore regard absorption by the o c blood-vessels as taking; place of necessity, because of the po- Summary of o -t^ •^ ' i: the nature of rous Structure of those tubes ; for, though the pores may be absorption. ^^^ small to be discerned even by microscopic aid, they arc abundantly large enough to permit such a percolation. Whatever ma- terial is existing in the chyme in a state of solution in water and also soluble in the blood, passes through the walls of the vessels, and is moved toward the liver, its percolation being greatly facilitated by the onward motion of the blood, in which liquid it is dissolved as fast as it presents COUESE OF ABSOliBED MATERIAL. 109 itself. Tlic double condition here speciiied must be complied with ; the material to be introduced must be dissolved in water, and must be sol- uble in the blood. If the latter condition be wanting, the vessels seem to manifest a selecting power, absorption not taking place, as in the case of litmus, presented above as an illustration — a coloring matter which, though soluble in water, is not soluble in alcohol, and so can not, under those circumstances, pass through a piece of bladder. While thus there is an introduction of digested material from the stom- ach and intestine into the blood, the physical principles which are guid- ing us in our explanation teach us that there must be a percolation of the more watery portions of the blood in the opposite direction — that is, into the digestive cavity. There is every reason to believe that this percolation is to a far greater amount than is generally supposed. Under certain circumstances, it is a matter of ordinary observation that the wa- ter discharged from the intestine is more in quantity than that which has been taken as drink. Turning our attention now to the course which is followed by the liq- uid which has been introduced from the dia-estive cavity „ „„ _ o J Course of the into the blood-vessels, Ave must bear in mind that the con- absorbed mate- tent of those vessels is composed of two distinct portions, ^Jf. n,"o(iiflca"' the matter thus recently introduced, and the original venous tions it under- blood. These together make their way through the portal ^'"^^" vein to the liver, a gland of double function, and, as we may say in this respect, of double structure ; for, though it has a duct for the disposal of the products which arise from its action on one portion of the material thus brought to it, the venous blood, it is ductless as regards the other portion, which has been received from the digestive cavity. This portion, under the influence of the cell structure of the liver, undergoes profound modification ; for instance, liver-sugar makes its appearance, though none existed before. It is not necessary for us to specify these changes par- ticularly here, since we shall have to examine them more in detail in a subsequent chapter; but it may be observed that the anatomical pe- culiarity of the liver in this branch of its duty is, that it simply impresses a change on the compounds thus brought to it, gives rise to no excretions, and therefore has no channel or duct of escape, unless indeed we say, as w^e are actually justified in doing, that the hepatic veins themselves are the ducts of the liver in this respect. Though it does not strictly appertain to the subject of which we are now speaking, absorption, we may, for the sake of completeness, describe, in a superficial manner, what occurs to the other constituent of the portal blood, its proper venous portion. This, brought into the liver, is acted upon by that organ and decomposed into two portions, one of which, con- stituting the bilc; is brought back eventually through the proper bile duct 110 SOIMAEY OF ABSORPTION. into the intestine. The other is can-led into the blood circuhition. I be- Ueve that this separation is of a purely physical kind, and is accomplish- ed by mere filtration, the elements of the bile all pre-existing in the blood. HoAvever that may be, the separation in a chemical sense is very distinct, for the nitrogenized ingredients are saved to the system, and carried into the general circulation through the hepatic veins ; but the bihary mate- p t fa ^'^^^ brought back into the intestine is a hydrocarbon tinctured part to the with a little coloring matter, which, being on a rapid career of retrograde metamorphosis, is prone to act as a ferment, and therefore unfit to remain in the system ; accordingly, it is removed with the excrement. The other portion, the hydrocarbon, which has been brought into the intestine, is not yet done with ; advantageous use can still be made of it. It can aid in the mtroduction of fats through the villi into the lacteals, and, from its combustible nature, is of an equal value to the system with the oils it thus helps to introduce. We may advan- tageously trace the course which it follows, for in so doing we shall com- plete our description of the function of absorption in its most general sense. The fat matters which have been subdivided into portions of micro- ti nner f scopical minutcuess, small globules, each of which is coated action of over witli a delicate film of albumen, and all brought therefore into the state of an emulsion, can make their way by reason of the peculiar properties of the investiture which thus covers them through the pores of the villi into the lacteal. For my own part, I do not believe that there is any passage through the epithelial cells, but that it is en- tirely interstitial, and that it is not unlikely that the biliary constituent aids in this progress. It signifies nothing that the spaces through which the fat globules have to go are less than their own diameter ; they can elongate into worm-like forms, just as, under the same circumstances, blood-cells can do, and, the moment they reach the cavity of the lacteal, reassume their sphericity by reason of their cohesion. The albumen that now accompanies them in the liquid form, as the other chief ingre- dient of the chyle, comes, for the most part, from the blood-vessels of the villi. The chyle moves onward to the mesenteric glands, and makes its passage through them either in naked tubes or through their pulpy structure, is submitted to cell action and to arterial blood, undergoes the morphological changes which have been described in the preceding chap- ter, and, gaining the thoracic duct, is brought into the general circula- tion. In the description here offered of the function of absorption, the agen- cy of physical forces alone has been considered, and these I conceive to be abundantly sufficient to enable us to account for all the phenomena. THE BLOOD. Ill CHAPTER VIL OF THE BLOOD. The Offices and Relation of Blood in the System. — The Plasma and Cells. — General Properties and Composition of the Blood. — Quantity in the Body. — Coagulation. — Blood-cells. — Their suc- cessive Forms. — The perfect Cell. — Hxmatin : its Properties. — Number of Blood-cells. — Plas- ma : its Composition, and Variations of its Ingredients. — A Ibitmen, Fibrin, Fat, Sugar. — ii/Jn- eral Ingredients of the Cells and Plasma compared. — Gases of the Blood. — Changes occurring during the Circidation. — General Functions of the different Ingredients oftheBhod. — Introduc- tion of Oxygen by the Cells. — Their ti'ansient Duration. It is necessary for the functional activity of every organized being that there shall circulate through all parts of it a nutritive liquid. In plants, it is the sap ; in animals, the blood. Since the life of plants manifests itself, for the most part, in a purely formative result, and involves little or no destruction of parts. The blood : its the circulating current is devoted almost entirely to nutrition, functions. But in animals, whose conditions of existence involve extensive and un- ceasing destruction, the current is burdened with another duty. It is also the means of removal of dying or wasted portions. In the first chapter it was shown that about a ton and a half of mate- rial is required by a man in the course of a year, and that in Introduction the same period a like amount is removed from the system. ^a^erial°b th When we reflect that the introduction and removal of this blood. immense mass is accomplished through the agency of the circulating blood, it is obvious that that fluid must be undergoing the most rapid changes. The rapidity with which dying matters are removed is strik- ingly illustrated by the minute extent to which they are permitted to ac- cumulate in a healthy state. These elements of decay are strained off or exhaled as quickly as they arise. That fancied power, the " vis med- icatrix natura;," is only an ideal expression of the perfection with which the various eliminating mechanisms work. Poisonous agents, whether they have been introduced from without or have originated from morbid actions within, like all other useless or noxious products, find their prop- er channel of escape, and the system will thus rid itself of intoxicating liquids and narcotic drugs if their quantity does not exceed the amount that it can destroy or excrete in a special period of time. Considered in its relation to nutrition, the circulating liquid presents many interesting aspects. Each of the thousand variously-constituted parts of the body is withdi-awing the supplies it needs: the muscular, the 112 PROPERTIES OF THE BLOOD. interconncc- nervous, the Ciirtilagiiious, the bony ; and hence there arises tioii ot all parts p-eneral balance in the system, eacli part makino- its demand through this >=> . circulation. at a Certain rate, and each observing a complementary ac- tion to all the rest. Many of those phenomena which, in the infancy of physiology, were regarded as instances of sympathy between different parts, are clearly dependent on these conditions ; for the development of one part, by abstracting special material from the circulating liquid, per- mits the co-ordinate development of another, or perhaps puts a stop to it. The minutest portion of the mechanism is thus indissolubly con- nected with all the rest through the medium of the blood. Seen as it circulates in the vessels, the blood consists of a colorless The plasma liquid containing corpuscles. In man, some of these corpuscles and cells. are white and others red. To the liquid in which they float, the designation of the plasma is given ; the colored corpuscles, from their Properties of shape, are called discs or cells. The specific gravity of the the blood. blood varics from 1.050 to 1.059, the variation being, to a con- siderable extent, due to variations in the quantity of the cells. The temperature is about 100° Fahr., the reaction always alkaline ; there is also a faint sickly odor, which differs in different animals. The capacity of blood for heat is in direct proportion to its density. The cells give to the blood its tint of color, and this, in the systemic arteries, is crimson, in the veins, deep blue. However, the color of arterial blood depends con- siderably on the condition of respiration. An imperfect introduction of oxygen, as in hot climates, causes the arterial blood to assume a dark color, and the same is observed when chloroform, ether, or diluted irrespirablc gases are breathed. The blood of the male sex is heavier than that of the female. Constitution of the Blood. Water..... 784.00 Albumen 70.00 Fibrin 2.20 _. (Globulin 123.50 ^^^^^ "(Hffimatin 7.50 f Fats ■ Cholesterine 0.08 I Cerebrine 0.40 J Seroline 0.02 \ Oleic and margaric acid ^ Volatile and odorous fatty acid > 0.80 V Fat containing phosphorus * -Chloride of sodium 3. GO Chloride of potassium 0.36 I Tribasic phosphate of soda ;... 0.20 Salts <^ Carbonate of soda 0.84 I Sulphate of soda 0.28 Phosphates of lime and magnesia 0.25 V Oxide and phosphate of iron 0.50 Extract, salivary matter, urea, biliary coloring \ .„ matter, accidental substances S ' ' 1000.00 C QUANTITY OF BLOOD. 113 Jikmentanj Composition of dried Ox Blood. Carbon 519.50 Hydrogen 71 .70 Nitrogen 150.70 Oxygen 213.90 Ashes 44.20 1000.00 This table leads to the hypothetical formula of the ultimate constitu- As to the quantity of blood in the circulation, it has been variously es- timated. It may perhaps be taken at one eighth of the weight q of the body, a number which is agreed upon by several authors, blood in the and in support of which Lehmann mentions the following ui- ° ' ' teresting observation: "JMy friend, E. Weber, determined, with my co- operation, the weights of two criminals before and after decapitation. The quantity of blood wliicli escaped from the body was determined in the following manner: Water was injected into the vessels of the trunk and head until the fluid escaping from the veins had only a pale red or yel- low color. The quantity of blood remaining in the body was then calcu- lated by instituting a comparison between the solid residue of this pale red aqueous fluid and that of the blood which first escaped. By way of illus- tration, I subjoin the results yielded by one of the experiments. The li^-ing body of one of the criminals weighed 60, 140 grammes ; and the same body, after the decapitation, 54,600 grammes; consequently, 5540 grammes of blood had escaped. 28.560 grammes of this blood yielded 5.36 gTammes of solid residue; 60.5 grammes of sanguineous water collected after the injection contained 3.724 grammes of solid substances. 6050 grammes of the sanguineous water that returned fr-om the veins were collected, and these contained 37.24 grammes of solid residue, which con-esponds to 1980 grammes of blood; consequently, the body contained 7520 gTammes of blood (5540 escaping m the act of decapitation, and 1980 remaining in the body) ; hence the weight of the whole blood was to that of the body nearly in the ratio of one to eight. The other experiment yielded a pre- cisely similar result." A short time after it has been dra-^ni, the blood midergoes coagnilation, and is then said to be composed of the serum and the clot. Spontaneous In this state it is sometimes spoken of as dead. The plasma fermn and*^ of living blood difiers from the serum of dead in containing clot, fibrin. The coagulation of the blood commences within about ten minutes after it has been drawn, and the clot undergoes a subsequent The coagula- condensation during one or two days. To understand the ^^^"^ °^ blood, phvsical nature of this sino-ular change, we may conveniently regard the H 114 COAGULATION OF THE BLOOD. living blood as containing three leading constituents — an albuminous liq- uid, tibrin dissolved therein, and the cells. The coagulation arises from the tendency of the fibrin particles to agglutinate together. As this takes place, the cells are caught in the meshes of the network that arises, and a voluminous red clot is the result. So the serum of dead blood con- tains no fibrin, and differs from the plasma of living blood in that impor- tant particular. It has been observed that exposure to cold retards coagulation, as does likewise the absence of air, or covering the blood over with a fihn of oil. The condition of rest promotes it, as also does the presence of rough or angular bodies. Blood will yield up its fibrin readily when stirred with The huffy ^ stick. When, for any reason, the cells sink more rapidly than <=°^*' usual from the surface of the blood, the fibrin of the supernatant portion coagulates alone, giving rise to a stratum free from the red color, and designated the bufiy coat, and on the subsequent contraction, since there are no cells to hiftder the fibrin, its parts upon this stratum are drawn more closely together, and the clot becomes cupped. By those who accept figurative expressions as an explanation of phys- Expianationof iological facts, the coagulation of the blood is said to be due coagulation. ^q j^g death ; some, however, have regarded it as an abortive attempt at organization, and therefore a manifestation of life. Such con- tradictory explanations lose much of their interest when we examine the facts of the case critically. I believe that nothing more takes place in blood which has been drawn into a cup than would have taken place had it remained in the body. In either case the fibrin would have equally coagulated. The entrapping of the cells is a mere accident. The hourly demand for fibrin amounts to 62 grains ; a simple arithmetical calculation will show that the entire mass of the blood would be exhausted of all the 'fibrin it contains in about four hours, so that the solidification of fibrin must be taking place at just as rapid a rate in the system as after it has been withdrawn. No clot forms in the blood-vessels, because the fibrin is picked out by the muscular tissues for their nourishment as fast as it is presented, nor would any clot form in a cup if we could by any means remove the fibrin granules as fast as they solidified. That blood-fibrin differs from muscle-fibrin in certain respects is to be admitted, but it does not follow that blood-fibrin is in a condition of ret- rograde metamorphosis. It may require modification before it can be received as the syntonin of muscles, but that such a conversion actually takes place I think there can be no doubt. In entering on a detailed examination of the constitution and func- tions of the blood, our attention will have to be directed, in the first place, to the cells. It is sufficient to arrest our thoughts at once when we learn that for every beat of the pulse nearly twenty millions of these SUCCESSIVE FORMS OF BL001>CELLS. 115 organisms die ! Physiology has its passing wonders as well as astron- omy. In the life of man there are three periods distinguished from each other by tlie nature or structure of the blood-cells. Those of the ^ J ... . . Successive first period originate simultaneously with, or even previously races of blood- to, the heart. These are sometimes designated as embryo cells, and in that view bear the same relation to those of the second pe- riod as do the lymph corpuscles to those of the third. They are color- less and spherical cells, containing granules of fatty material, and having a central nucleus. These are developed, by a process of internal deli- quescence, into cells of the second period, which have acquired a red col- or, and in oviparous vertebrates an elliptical form, though in man they are circular. They are flat or disc-like in shape, have a diameter of about Ybo^ of an inch, with a central nucleus of half that size. Some- times they appear to undergo multiplication by division of the nucleus. These cells of the second period are replaced by those of the third, the transition being clearly connected with the production of lymph and chyle coi-puscles. By the end of the second month of foetal existence the re- placement is complete, and the class of cells or discs that has now arisen is continued during life. The mode of their production, according to Mr, Paget, is this. The chyle or lymph corpuscle loses its granular aspect, and acquires a pale red color, which gradually deepens ; the corpuscle be- comes smooth, loses its spherical form, and, condensing, takes on a con- vex lenticular shape, and eventually a bi-concave. While this change of structure is going on, the specific gravity increases through the con- densation, and the development closes by the spherical white granular lymph corpuscle becoming a red, bi-concave, non-nucleated, circular, small, and heavy blood disc. The cell of the first period is therefore spherical, white, and nucleated ; that of the second, red, disc-shaped, and nucleated ; that of the third, red, disc-shaped, bi-concave, and non-nucleated. The primordial cell advances in development to different points in dif- ferent orders of living beings. The blood of invertebrated Development animals contains coarse granule cells, which pass forward to ^^ ^loo^-^eiis o ' jr m the animal the condition of the fine granule cells, and reach the utmost series. perfection they are there to attain in the colorless nucleated cell of the first period of man. In oviparous vertebrated animals the development is carried a step farther, the red nucleated cell arising, and in them it stops at this, the second period. In mammals the third stage is reached in the red, non-nucleated disc, which is therefore the most perfect form. This perfect form of blood cell, as it occurs in man, may be described as presenting a flattened shape ; the bright spot, which is sometimes seen in the centre, arising from a refraction of light due to the form of the 116 CIRCULAR AND ELLIPTIC CELLS. disc and not to a nucleus. The sac of each disc is elastic, so that it can D .■ , be swollen by water until it becomes convex or even srlobu- rroperties and •/ o size of the per- lar, or by immersion in thick sirup may be made to shrink,^ eflfects arising from the endosmotic infiltration or exudation through its wall. T\^ien passing through the fine capillaries in the course of the circulation, the cell, by reason of this elasticity, can make its way through very difficult passages, extending itself into a cylindroid form, or by bending, but it recovers its original shape as soon as relieved from pressure. The average diameter of the cell is estimated at -o-sW of Firj. 43. The average diameter of the cell is estimated at 3^2^ ^ an inch, the extremes being „„\ „ , and ^ y 28 00' The thickness of the cell is about an inch. 4000* ^— of 12400 The cell owes its color to hasma Human blood-cells magnified 500 diam- eters. at a a, chyle corpuscles. Fig. 43. tin, which exists in its interior in a state of solution, and associated with globulin. The facts mentioned in the preceding par- agraph are illustrated by the annexed en- graved photographs. J^ig- 42 represents hu- man blood-cells. Their form is circular : they have a central depression, but no nucleus. J^ig. 43 represents the elliptic nucleated blood-cells of the frog, with here and there, I^ig. 44 represents the endosmotic action of Fia. 44. Elliptic blood-cells of frog magnified 250 diame- ters. Action of water on elliptic cells. water on these cells. J^ig. 45, the action of acetic acid in darkening or concentrating the nucleus. In jFig. 46 we have an illustration of the size and appearance of the blood-cell in a reptile, the photograph from which this figure was taken having been made under the same magni- fying power as that employed in obtaining the photograph of human blood. FORMS OF BLOOD-CELLS. 117 Fig. 45. Fi{). 46. Action of acetic acid on elliptic cells. Eeptile blood-cells magnified 500 diameters. The mammals in wliich the Hood corpuscles are not round, but ellip- tic and bi-convex, are the camel, the dromedary, and the llama. In birds and amphibia they are oval. The diiFerence in the shape and size of these cells is of the more importance, since observations and measure- ments by the microscope may lead us to a correct reference of a sample of blood to its origin when chemical analysis would afford us no assist- ance. It is not to be forgotten, however, that both in size and form a blood-cell undergoes changes according to unequal pressures ya^^jg^^ions of exerted upon it, or to the physical circumstances mider which the form of it is placed, liquid readily finding its way into its interior or exuding therefrom according to the laws of endosmosis, the elastic sac perfectly accommodating itself to these changes. As a consequence of these modifications, there will, of course, follow variations of specific grav- ity in the cell, difierences in its tendency to sink in the plasma which surrounds it, and also difierences in its tint of color. By Mr. Wharton Jones, the colored blood-disc of the mammalian is regarded as being homologous with the nucleus of the color- jj^^j^^ t^jq^^ less corpuscle of the same blood, and it may therefore be disc is a ceiije- spoken of as a free cellajform nucleus, the cell itself having °^°^ "^"^ ^"®* deliquesced or become disintegrated, and the nucleus, filled with globulin and coloring matter, remaining. The cell wall of the blood-cells is generally admitted to be fibrin, or some substance allied thereto ; .but there has been much dif- ■^^^^J.Q ^f ^he ference of opinion respecting the constitution of the nucleus cell walls and of those cells which possess it. By some, this also has been regarded as fibrin ; by others, as fat ; and by others, as a species of horn, to which the designation of nucleine has been given. The cell wall of the white corpuscles does not appear to be elastic. It is viscid, and hence these bodies tend to agglutinate with one another t 118 COMPOSITION OF BLOOD-CELLS. in aspect it is granular. The contents appear to be an albuminous so- lution, in which fine granules are suspended. Though we have described the mesenteric glands as the original place of formation of the blood-cells, it is to be understood that these become perfected in the circulation of the blood ; and from what will be said respecting the function of the liver, it may be in- ferred that that gland is the seat of a most important change : there probably they receive their iron. That no special organ is exclusively charged with the duty of forming them appears from this, that the first form of blood-cells arises in the germinal area of the embryo when there is, as yet, no gland. Composition of Blood-cells. Water 688.00 Hsematin (including iron) 16.75 Globulin and cell membrane 282.22 Fat 2.31 Extractive 2.60 Mineral substances 8.12 1000.00 Leaving the water out of consideration, the predominating ingredients of blood-cells are therefore globulin and hasmatin. The' former is a sub- stance approaching, in properties, to casein, or perhaps intermediate be- tween casein and albumen. Its constituents, as determined by an ulti- mate analysis, are the same as in the case of those bodies. Hffimatin is distinguished by its red color. When isolated, it exhibits Changes of col- ^^^ changes of tint characteristic of arterialization in a doubt- er depending ful manner. There are, however, many facts which lead to theVornfof Uie the Supposition that the color of arterial and venous blood cells. ^Qgg not depend so much on a chemical change in the hajma- tin as on an alteration of the figure of the discs. The constitution of hasmatin is C^^, Hgg, N3, Og, Fe. It exists under Properties of ^wo forms, soluble and coagulated. It has hitherto been stud- hi»matin. jg^^ q^Aj in the latter state, and is soluble in weak alcohol acidulated with sulphuric or hydrochloric acid, but not in w^ater. Its solution is therefore precipitated by the addition of that liquid. In weak solutions of alkalies it readily dissolves. Formerly its characteristic red color was attributed to the iron it contains, but that metal may be en- tirely removed from it without changing its tint. The amount of iron it yields is about seven per cent. H^matin occurs in the blood-cells associated with globulin, and would seem to owe its origin to the action of the wall of the cell, if it be true that the red cells originate from' the white ones. In this formation of hsematin there are several reasons which lead us to infer that fat takes an essential share. COMPOSITION OF h.i>:matin. 119 Ultimate Analysis of Ilccmatin. Carbon 053.47 Hydrogen 54.45 Nitrogen lOS.OO ^ Oxygen 118.81 Iron G!).3 I 1000.00 The remarkable feature in the composition of this body is the large quantity of iron it contains. The percentage amount of this iron in the metal in the blood of the foetus is much greater than in that of ^^^^®- the mother. After birth the proportion declines, but it rises again at puberty. These variations in the amount of the iron are, however, de- pendent on corresponding variations in the amount of cells. The importance of the remark, when we arrive at the study of the bile, justifies us in repeating that the iron of the blood belongs to tlie liasraatin of the cells, its percentage proportion varying with their condi- tion, and also with the region of the circulation from w^hich they have been drawn. As derived from different animals, the cells present differ- ent quantities of this metal. Thus Schmidt found in 100 parts of dry blood-cells in man, 0.4348 ; in the ox, 0.509 ; in the pig, 0.448 ; and in the hen, 0.329. The crystalline substance of blood occurs under three different forms, in prisms, tetrahedra, and hexagonal tablets. In the pris- matic form it is derived from human blood, that of fishes, substance of and of some mammals ; in the tetrahedral form it is obtained ^^°°*^' F?'". 47. Fip. 48. 7 ^ Human blood-crystals. Blood-cry stei^^auiiiea-pig. from Guinea-pigs, rats, and mice ; in the hexagonal form, from squir- rels. Blood-crystals are of a red color, without smell or taste, losing their water of crystallization under exposure to the air, the different forms presenting different rates of solubility ; the tetrahedral being soluble 120 BLOOD-CEYSTALS. ^^- *^- in 600 parts of water, the prismatic in 90 parts only; tlie solution in the former case being pinkish, that of the latter, dark red. They are also dissolved by acetic acid, the red prussiate of potash producing a pre- cipitate therefrom, as in the case of other protein bodies. Chlorine de- colorizes their solutions and gives a white flaky precipitate. The crys- tals, when heated, swell, yield an odor like burnt horn, and, after com- bustion, leave a small quantity of Blood-crystals of squirrel. ash. From the difficulty of obtain- ing blood-crystals in a state of purity, their constitution is not known with absolute certainty. The ash which they yield consists of about 72 per cent, of oxide of iron, and 21 per cent, of phosphoric acid, the protein constituent being apparently identical with other protein bodies. The Mode of ob- ci'jstals may be obtained for examination by covering a mi- taining blood- nute drop of blood with a glass slide, and, after adding water, alcohol, or ether, to permit a gi-adual evaporation to ensue. The amount thus produced depends very much upon the presence of light; thus Lehmann found that while he could only obtain two per cent, of crystals from the blood of the Guinea-pig in the dark, he could obtain more than seven per cent, in the sunlight. Lehmann believes that the crystalline substance is not a mixture of a pigment and a protein body, but a pure chemical compound, having either a salt-like or conjugated constitution. The color of the blood, as dependent upon the tint of its cells, is, ac- Color of blood- cording io the views of Henle, connected to a considerable cells may de- ^gg;ree with the form of those organisms as they var^^ from a pend on tneir o o ./ j form. concave to a convex surface, and not with the state of the hsematin. Wlien they are more concave they are of a crimson, when of a more convex, of a darker hue. Moreover, during these variations their investing membrane must necessarily change in thickness, and this likewise must alter their mode of transmitting light. Among the causes which can impress a change on the figure of the blood-cells ought particularly to be specified exposure to oxygen and carbonic acid respectively, the latter causing them to become more opaque in their centre, broader upon their edge, the cell distending ; an opposite effect ensuing under exposure to the former. In the case of the blood- cells of frogs exposed to oxygen, the long and short diameters both di- minish, and the wall becomes granular ; after exposure to carbonic acid they increase, the wall becoming pellucid. NUMBER OF BLOOD-CELLS. 121 Constituted thus of an elastic sac filled with globulin and hasniatiu, the cells float in the plasma. They are nourished at its expense, and when they die, deliver up their contents by deliquescence to it. Accompany- ing them are the white corpuscles, from which new generations are to arise. It is usually stated that for every 50 red discs there The white is one white corpuscle. They may he readily discovered dur- corpuscles. ing the circulation by the microscope, many of them occupying the exte- rior of the cui-rent, as though they had a special relation to the soft tis- sues. It may perhaps be erroneous to regard these large white corpus- cles as the embryos of the red discs. Reasons could be assigned in sup- port of the doctrine that the same primitive germ going onward to devel- opment may, at a certain point, diverge in two directions ; if it passes through one, it will perfect itself as a white cell ; if through the other, as a red disc. The proportional number of blood corpuscles in different animals va- ries considerably. Generally cold-blooded mammals present Number of cells fewer than warm-blooded ones, birds having more than quad- ^^"fferentTni-" rupeds, and among these the carnivora more than the herbiv- mals. era. Of different domestic animals, the pig, the dog, the ox, the horse, the cat, the sheep, the goat, possess them in the order in which their names have been mentioned, the goat having only 86 to 145 in the pig. Then* proportional number also varies m different regions of the circula- tion ; thus it is said that arterial blood contains fewer than venous, the portal blood fewer than the jugular, the hepatic more than the portal. It is not, however, to be overlooked, that in all these determinations the quantity of water which chances to be present controls the estimates, and that therefore, as thus offered, they are really of less interest than might at first sight be supposed. We have next to speak of the plasma. It may be described as a clear and slightly yellowish colored fluid, consisting, as all animal Composition juices do, for the most part of water, holding in suspension or of plasma. solution albumen, fibrin, fats, and various mineral bodies, as the follow- ing analysis shows. Proximate Composition of the Plasma. Water 902.90 Albumen 78.84 Fibrin 4.05 Fat 1.72 Extractive 3.94 Mineral substances 8.55 1000.00 Of the water it may be remarked, that the usual percent- -^r^ter of the age estimate made of its quantity, as regards the entire blood, whole blood : is from 700 to 790 parts in 1000. Within these limits it is "' ^'^"^ti^^^- 122 TAEIATIONS IN WATEE, ALBUMEN, AND FIBKIN. liable to rapid variations, as dependent on the condition of thirst or the recent indulgence in drinks. It does not increase in proportion to the amount which has been imbibed, for the Malpighian bodies of the kidney, as will hereafter appear, strain it oif with great rapidity. When the blood-vessels are distended to a certain degree, they refuse an entrance to it. The necessity of these provisions arises from the fact that there is a certain state of viscidity which the blood must possess for its proper cir- culation. Respecting variations in the amount of water in the blood, it may be stated that that of women contains more water than that of men. Among different animals, the serum of the amphibia contains the largest quantity ; and among mammals, that of the herbivora more than that of the car- nivora. Obtained from different vessels, the arterial has more than venous blood, but the serum of the portal vein contains more than that of any other vein, the proportion depending on the amount and time of the ing;estion of water. The albumen varies in quantity from 60 to 70 in 1000. It is prob- er • .• • ably associated or combined with soda. It exists in the Variations m •/ .|uautity of ai- blood of the splenic and hepatic veins as the neutral albumi- jumen. riSite of soda. It does not appear to contain any phosphorus, as was at one time supposed. It is the plastic material from which all the soft tissues are nourished, and by it the cells themselves grow. Fibrin arises from it in the blood in the same manner as it does during the incubation of an egg ; every care is taken to economize it in the sys- tem, and it is never excreted except in disease. The quantity of albumen is greater in venous than in arterial blood, the proportion increasing during digestion. It also presents variations in different states of disease. Its condition varies in various parts of the circulation, a circumstance, to a considerable extent, due to the nature of the salts, or to the quantities of alkali with which it is associated. The fibrin is usually estimated at 2 or 3 parts in 1000 of blood. It „ . ,. . may fall as low as 1, or rise as his'h as 7i. There is a con- Variations m ./ _ ' . . the quantity of stant drain upon it for the nutrition of the muscular tissues ; and since it originates in the action of oxygen upon albu- men, we should expect, as is really the case, that arterial blood would be richer in it than venous. The portal blood contains it in minimum quan- tity. Its percentage rises if oxygen be inhaled, or the respiratory pro- cess be quickened ; for similar reasons, it uniformly increases in acute inflammations. The ultimate analyses of fibrin seem to show that it con- tains more oxygen than albumen, and this corresponds with its mode of origin. It is an important practical observation, that though it is easy to regulate the quantity of cells by variations of diet, the amount of fibrin can not so readily be changed in that manner, nor its development FIBEIN, FAT, AND SUGAR OF BLOOD. ' 123 checked by venesection. There is less fibrin in the blood of the carniv- ora than in that of the herbivora. It lias been asserted, as was mentioned before, that there is so wide a difference between the fibrin of blood and muscular fibre, pibrin is a his- that we can no longer regard the latter as arising from the togeneticbody. former, but must consider it merely as coagulated albumen ; and that, since the action of acetic acid upon it shows its relation to gelatine, it is probably more nearly related to the fibro-gelatinous than to the cellulo- albuminous tissues. But, although the fact that fibrin contains more oxygen than albumen seems to lend weight to such views, since oxida- tion appertains to the retrograde rather than to the ascending metamor- phosis, there are so many arguments in favor of the old doctrine, that I think it may be regarded as thus far unshaken. Moreover, it is now established beyond any doubt, that by nitrate of potash, and other salts, fibrin may be transmuted into a substance analogous to albumen. The fats vary very much in quantity at different times. The amount is usually stated at from 1.4 to 3.3 in 1000 of blood. After a meal the plasma may be actually milky, through the fat globules y^jj-ia^tjon " brought in by the chyle. We have already shown that the quantity of starch will give origin to fat, and oily substances can be ob- tained from lactic acid itself. The nitrogenized bodies, during their de- straction, likewise yield them, and it is a normal function of the liver to effect the production of fat. The serum contains only an insignificant quantity of free fat ; but there is a large proportion of saponified fat in it, as well as the lipoids cholesterine and serolin. The view heretofore taken, that this class of substances is not histo- genetic, but only respiratory, requires to be modified. There Uses of the fats is reason to believe that the blood-cells themselves can not of blood. be formed except in presence of oil, which is also necessary to enable ni- trogenized bodies to assume the ferment action. The nuclei of cells con- tain fats, as do also embryonic structures generally. Cholesterine, or liver-fat, is not saponifiable. It appears as a product of disintegration, increasing in quantity during acute diseases. The proportion of this sub- stance increases after 40 years ; it also forms a principal ingredient in biliary concretions. Among the special constituents of certain portions of the venous blood not mentioned in the preceding tables, we ought not to over- II 1 • 1 • • -,• ^1111 Liver-sugar. look sugar, wliicli exists as a constant ingredient of the blood contained in that part of the circulation intervening between the liver and the lungs. This, which is known as liver-sugar, may have originated in the transmutation of cane-sugar, or from the metamorphosis of the mus- cular tissues. It is to be remarked that the blood contains no gelatine. 124 THE MINERAL CONSTITUENTS OF BLOOD. Comparison of To the mineral substances in the cells and plasma of the constituents of hloocl respectively, attention should Ije particularly directed, the cells and gince they indicate the functions of these portions, plasma. "^ ^Mineral Constituents in 1000 Parts of the Blood. Chlorine Sulphuric acid Phosphoric acid ' Potassium Sodium Oxygen Phosphate of lime Phosphate of magnesia Iron excluded 1.686 0.066 1.134 3.328 1.052 0.667 0.114 0.073 8.120 I'lasiua. 3.01:4 0.115 0.191 0.323 3.341 0.408 0.311 0.222 8.550 The amount of inorganic matter in the cells and plasma, respectively, of 1000 parts of blood being nearly the same, the table shows that there is more than twice as much chlorine, and more than three times as much sodium in the plasma as in the cells. It may thence be inferred that the chloride of sodium is, for the most part, in the plasma. Moreover, there is six times as much phosphorus, and more than ten times as much po- tassium, m the cells as in the plasma ; and therefore it may be inferred, .since potash is required to so great an extent in the nutrition of the mus- cular system, and phosphorus as an element of the phosphorized oils in the nervous, that the cells have a direct functional relation to those im- portant mechanisms, and this m addition to their duty of introducing oxygen. The mineral constituents of the blood discharge very different duties, Functions of some, either directly or indirectly, acting functionally, others the mineral ^^ histogeiietic bodics. Thus the alkaline properties of the coiistitu6nts of ^ J. X the blood. blood are due to the presence of the carbonate and phosphate of soda, and this latter substance enables the seiaim to hold in solution carbonic acid, and thus it maintains a relation in the respiratory opera- tion. But the phosphate of lime discharges a true histogenetic function, since upon it the bony system depends for its nutrition. The mutual relations of these substances are, of course, very complex, though often of importance. Thus, of the two just mentioned, the phosphate of soda enables the serum to hold the phosphate of lime in solution. The tawny coloring matter of serum differs from cholepyrrhin in not Coloring mat- yielding the characteristic reaction of that body. The tint ter of serum, sometimes bccomes quite deep, o^wing to several different causes, such as the undue accumulation of the coloring matter of urine, through disturbance of renal action, or from bile pigment, as in icteras. The gases which can be disengaged from the blood occur in the cells, according to Magnus, a statement which, however, is very far from being FUNCTIONS OF THE CONSTITUENTS OF BLOOD. 125 substantiated : they are carbonic acid, oxygen, and nitrogen, ^ases of the He found that this liquid can absorb once and a half its vol- ^^^ood. ume of carbonic acid, and that in arterial blood the proportion of that acid to oxygen is as 16 to 6, in venous as 16 to 4. That the oxygen is very loosely retained is shown by the circumstance that it may for the most part be removed by exposure in a vacuum. The other gases may be withdrawn by a stream of hydrogen. At a temperature of 98°, water absorbs scarcely one per cent, of its' \'olume of oxygen gas, but the blood can take up from 10 to 13 times as much. This is accomplished by the coloring material. The amount is independent of variations in the pressure of the air, which would not be the case if the gas were received into the circulating fluid by mere solu- tion. This is the opinion of Liebig, by whom it is regarded as being to some extent substantiated by the fact that the respiration is accomplished with nearly the same result, so far as the absorption of oxygen is con- cerned, at considerable heights above and at the level of the sea, and that no more oxygen is received from an atmosphere very rich in that gas than from the ordinary air. However coiTcct this view may be, the facts cited in its support are very far from being undeniable. The preceding chemical examination of the special constituents of the blood leads us next to consider the general functions of this liquid in the aggregate. In this general sense, the blood discharges the following offices. Its albumen has the duty of giving origin to all the plastic tis- ^ , sues of the system. From it, for example, by cell action, as ment of the explained in treating of lacteal absorption, fibrin arises — theTiftbrent fibrin, which is used for the renovation and repair of the mus- constituents of cular tissues. The discs have a relation with the fonction of respiration ; they obtain oxygen in the pulmonary circulation, and carry it through the system. They contribute, moreover, to the development of muscular fibre, and also nervous material, and this not alone as regards the coloring matter of those tissues. The fats are necessary in the pro- duction of fibrin and for the nuclei of cells ; but, besides these histoge- netic relations, they eventually, with the exception of liver-fat, undergo oxidation, and so minister to the support of a high temperature. Of the saline substances, common salt promotes digestion by aiding in the prep- aration of gastric and pancreatic juices ; the phosphate of soda enables the plasma to hold carbonic acid in solution, and carry it to the lungs. It is interesting to observe the limits of variation which the blood may present in disturbed or diseased conditions. In inflammations, the fibrin may increase fourfold ; in typhoid fevers it may diminish to less than one half, and from these variations special results may arise. Thus diminution of its fibrin disposes the blood to preternatural oozing or fa- 126 CHANGES IN THE CIRCULATION. cilitj of escape. So also the cells have been known, in cases of chloro- sis, to sink to one fifth of the healthy amount. The albumen, too, ex- liibits like variations. In Bright's disease it greatly diminishes, much of it escaping in the urine by the straining action of the kidneys. Thus constituted, the blood, by a mechanism to be described in the next chapter, passes from the heart alternately to all parts Changes occur- i ^ x ./ a ^ ring during the of the System, and alternately to the cells of the lungs, giv- circuiation. ^^^ ^-g^ ^^ what have been termed the greater and less cir- culation, or the systemic and the pulmonary. In the systemic circula- tion, the blood, which leaves the heart in an arterialized condition, or as- sociated with atmospheric oxygen, gives up that element to the various tissues as it pervades them, and accomplishes a double result : the re- moval of all those particles which, having discharged their duty and un- dergone partial or perfect interstitial death, are ready to pass away, and also the liberation of a great amount of heat by the destructive oxidation ; so, at the same time, the wasted matter is removed and advantage taken of it to raise the temperature of the body. This done, the blood makes its way back to the heart, following the channel of the veins as they suc- cessively converge into trunks that are larger and larger. At the mo- ment of surrendering its oxygen and receiving the various products of combustion, a change of color occurs. The bright crimson turns to a deep blue, and the blood presents itself of that color at the heart. It now undergoes the less or pulmonary circulation. Leaving the heart, it passes over the air-cells of the lungs, and is there exposed to the aerating action of the atmosphere. From the interior of the cells the discs receive their supply of oxygen, the plasma sm-rendering up carbonic acid and the vapor of water. The color now changes back from the blue to the scarlet. In this condition it returns to the heart, to be dis- tributed in the systemic circulation once more. During this double round an incessant change is taking place in the T , . constitution of the blood : it is undergoing a continuous met- Less obvious . iiut important amorphosis. In some respects, as, for instance, in color, changes. ^j^.^ -^ obvious cnough. But the invisible changes infinite- ly exceed in importance and amount those that are obvious to the eye. All the soft tissues, since they are wasting away, require repair. This, inasmuch as it is accomplished either directly or indirectly by the albumen of the blood, gives rise to a constant drain of that substance, and demands a constant supply, which is provided by nutrition or stom- ach digestion. The cells, which constitute the other chief portions of the blood, are necessary to the production of a high temperature, by con- oxygen by the stautly transferring oxygen from the cells of the lungs to cells. every part of the body ; carriers of oxygen they have been GRADUAL DESTRUCTION OF BLOOD-CELLS. 127 truly called. That this is one of their duties has been proved experi- mentally, for a solution of albumen or the serum has but little power of absorbing oxygen, scarcely exceeding water itself in that respect, but the discs condense it at once. The change of color they exhibit as they alternately gain or lose that element, is in itself a proof of this fact, as is also the action of serum or blood-discs respectively on. a measured volume of air contained in a jar. If the discs be in the venous or pur- ple condition, they quickly absorb oxygen from the confined air, which therefore at once diminishes in amount, but the serum, or a solution of albumen, produces no such effect. The plasma serves, therefore, for the general nutrition of the system, and the discs, by transferring oxygen from point to point, discharge that part of their duty which is connect- ed with the production of heat. But the discs, though of a flattened form, are truly cells, and all that obtains in the case of cell life and cell action obtains for „ Iransitoiy du- them. They have not a duration at all comparable to the ration of the duration of the system, but are constantly coming into ex- '^^ ^' istence and disappearing. Each is an individual having its own partic- ular history, its time of birth, its time of maturity, its time of death. Each passes through a series of incidents proper to itself. Originating as has been described, they grow at the expense of the plasma, and in this regard it serves for their nutrition as well as for that of the body generally. On exposing blood-cells to oxygen and carbonic acid gases alternately, there is not only a change in their shape, which becomes corrugated, and star-like, but also in their chemical constitution, so that, after such an exposure of nine or ten times, they are entirely destroyed. Such alter- nations occurring in the system doubtless lead to the same result, though more slowly, since the oxygen is presented in a diluted condition. The corrugated and star-like blood-cells abound in the blood of the portal, though not in that of the hepatic vein. If their aspect arises from their tendency to disintegration, this is no more than might be expected in view of the func- tions of the liver. That the stellated aspect is an indication of a commencing disorganiza- tion, or other profound change, may be illus- trated, by an examination of the action of wa- ter on normal blood-cells, which, if they be exposed to that liquid, undergo a distention ; their thickness increasing more rapidly than their diameter, they lose their concavity, be- come convex, and at last appear as spheres of a less size than the original discs. When Dying cells. Stellated Wood-cells magnified 500 diameters. 128 ' ASSOCIATION OF H^MATIN AND OXYGEN. the quantity of water they have received has distended them to their ut- most capacity, they then are invisible ; but when it is withdrawn from them by establishing exosmosis through the addition of saline sub- stances, they may reappear in the corrugated or star shape, as seen in the photograph. Fig. 50. With respect to the action of the hamatin, it may be observed, that other nitroo-enized coloring materials present a similar rela- Action of najm- ° -, . ,. ^ . , atin illustrated tion to oxygen. As an example, mdigo maybe mentioned. by indigo. j consider that the properties of this substance illustrate in a signiticant manner the properties of hamiatin in the system. Indigo occurs in the leaves of the plant which yields it in a yellow and soluble state. It is easily extracted from them by maceration in water. Ex- posed to the air, it absorbs oxygen, becomes insoluble, and simultane- ously gains a deep blue tint. So lightly is the oxygen thus united to it, that by exposure to very feeble agents it surrenders it up, and repasses into the yellow and soluble condition. Once more exposed to the au% it turns blue, and once more may have that color removed from it by tak- ing its oxygen away. For many times in succession its tint may be thus changed, and made yellow or blue at pleasure. From this we perceive in what a loose manner oxygen is held by such a coloring material ; how readily it surrenders it, and how readily it re- covers it. Such a union can scarcely be called an oxidation or a com- bination ; it is rather an association. All this is precisely what occurs in the case of hasmatin. It takes up ^ , , . ^ oxYs;en with rapidity as it goes over the cells of the lungs, Feeble union of-^o r^ o o oxygen and and tums scarlet ; it surrenders that oxygen with equal ta- haematin. cility as it passcs the systemic capillaries, and tmiis blue. This change of color is incessantly taking place ; it is now red, and now blue, as the cells are passing m the gTcater and the less circulation. Formerly it was supposed that, m the act of respiration, oxygen from Reception and the au' United w^th carbon of the blood or of the cells, and transference carbonic acid formed, a combination or perfect oxidation 01 oxvgen by ' •*- the blood-ceils, taking place in the lung. But, if this were time, the tem- perature of those organs should be higher than that of the rest of the body, and this is by all admitted not to be the case. The cells are therefore carriers of oxygen. They receive that vivify- ing principle as they move over the respiratory cells, and, freighted with it, pass to all parts of the body, not united with it, nor disorganized, nor burnt up by it, but holding it loosely, and ready to give it up and go back again for a fresh supply. The sac containing the hasmatin offers no kind of resistance to these exchanges. It \\-ill be fully demonstrated in the chapter on respii-ation that this is the ease. Thick pieces of India-rubber, stout animal mem- CIRCULATION OF THE BLOOD. 129 branes, or even masses of stucco, present no obstacle to the passage of gases. The delicate "wall of these cells, a tissue of almost inconceivable tenuity, can offer no resistance. The gas passes in and out without im- pediment or restraint. But though in this manner these little organisms perform their duty, it is only for a time. They may take oxygen from the air- g ^ „ cells and give it up in the system, and do this perhaps many the function of thousand times, but it comes to an end at last. The inces- °° '^^ ^" sant motion stops, and the worn and exhausted disc is brought to its term. By degrees, as old age steals over it, it becomes corrugated and relaxed, is unable to withstand chemical reagents, as its younger comrades can do. Through the microscope it seems puckered and attenuated. The red color of its interior deteriorates into a tawny tint. As with a leaf in the autumn, the natural color of which disappears, and yellowness or other change precedes its fall, so with the dying disc. Unable any longer to discharge its duties, its existence is brought to a close, the de- cayed hffimatin is shed out to give a transient tawny tint to the plasma, but is presently strained off as one of the constituents of bile by the liver. jS^or is the illustration here used wholly metaphorical, for, in the case of herbivorous animals, Berzelius has shown that the colonng matter of their bile is identical with chlorophyll, the coloring matter of leaves. CHAPTER VIII. OF THE CIRCULATION OF THE BLOOD. TJie Heart as a MacJiine. — Inadequacy of Harvey^ s doctrine of the Ciradation. — Physical Prin- ciple of the Circulation ; applied in the case of a Nucleated Cell, Pervious Tissue, Motion of Sap and of Blood. — Dependence of the Circulation on Respiration. — Forms of Circulation : Systemic, Pulmonary, Portal. — Description of the Heart : its Movements. — Their Force, Num- ber, and Value. — Sounds of the Heart. — Cause of its Contractions. — Desci-iption of the Arte- ries, Cajyillaries, Veins. — Explanation of the Circulation of the Blood. — Facts supporting it. — The First Breath. No function of the animal mechanism illustrates more strikingly the doctrine that we must rely on physical agents for physiological explana- tions than that which we have now to consider, the circulation of the blood. We surrender some of the most beautiful recollections of classical mythology, and some of the most cherished popular illusions The heart as of our own times. The heart, which in the higher classes of ^^ engme. life is the central organ of impulse of the circulation, is to be degraded into a mere engine. We have to speak of its valves, its cords, its pipes. I 130 CIRCULATION OF THE BLOOD. We have to consider its exhausting and its forcing action — to deal with it just as we should deal with any hydraulic apparatus. In the old times this organ was looked upon as the seat of the thoughts and the passions ; it was the centre of all good and evil, purity and uncleanness, devotion and love. In the modern system the brain has succeeded to the functions which were once imputed to it. The heart, then, is no longer an altar on which flames are hurning, no longer the seat of the passions and the source of love. It is a machine, but what kind of a machine? How great is the admiration we may ex- press at its exquisite construction ! This little organ can execute three thousand millions of beats without a stop ! In the course of a life, such as we sometimes meet with, it has propelled half a million tons of blood, and, though momentarily wasting, has repaired its own waste all the time. The mathematical rhythm of its four moving cavities, the perfect closure of its mitral and semilunar valves, and the regurgitating play of its tri- cuspid, have never failed it. To the eye of the intellect there is nothing lost in transferring it from the regions of metaphor and speculation to the domain of physical science. The doctrine of the circulation of the blood was first propounded by Harvey's doc- Dr. Haevey about two hundred years ago. It originated trine of the cir- ^^ ^^iq discoverinp; of the valves of the veins by Fabricius ab (.■ulation of the o ... blood. Aquapendente. After many years of discussion, it was re- luctantly received by the medical profession. In this doctrine the circulation is referred to causes that are purely mechanical, in the strictest acceptation of that term. The contraction of the walls of the heart propels the blood through the arterial tubes, and even through the veins, the direction of its movement being insured by a proper arrangement of valves. But when comparative anatomy and physiological botany were more Its imperfec- extensively cultivated, it w^as seen that this doctrine is insuf- tions. ficient, for the unity of nature forbids us to believe that nu- tritious juices are circulated in different tribes of life by different forces. And though it may be that the contractions of that central impelling mechanism regulate the circulation in those organisms which have a heart, what is to be made of those countless numbers which have none ? In this group we find the whole vegetable creation, and a majority of the animal. There is a physical principle which has long appeared to me sufficient. Physical prin- Its use in an explanation of the motion of nutritive juices in cipie involved Qyg-anized systems of every class I have taught in the Uni- m the capillary o '> _^ i t n circulation. vcrsity for many years. It possesses the advantage of gen- erality, since it is applicable in every case, from the circulation taking place in a closed cell up to that of man. PHYSICAL TEINCirLE OF THE CIRCULATION. 131 111 Chapter YI. is a general statement of the phenomena and laws of capillaiy attraction ; the principle now to be employed is closely connect- ed therewith. It may be stated as follows : If two liquids communicate with one another in a capillary tube, for the substance of which they have affinities of different intensities, move- ment will ensue : the liquid having the highest affinity will occupy the tube, and may even drive the other before it. The same effect will en- sue in a porous structure. Fig. 51. Thus, let b, b, Fig. 51, be a capillary tube (^ ). .,.-,,1,.. ■■ . ,»3 »^.,^^p^--^-.-^-^ Qf ^j^^. kind, which is occupied conjointly by Motion ill ii capillary tube. -fwo Hquids, « and v, meeting each other in its middle, c/ « having a high and v but little affinity for the substance of which the tube consists, a will occupy the tube, pressing out v before it. Of course, it is to be understood that the liquids a and v respect- ively communicate with reservoirs that can furnish them a necessary , supply. The various phenomena described under the designation of endosmo- sis are experimental illustrations of the same kind. Thus, . i- j . .i^ when water is put on one side of a piece of bladder, and al- explanation of cohol on the other, the water, having the highest affinity for *^" osmosis. the substance of which the bladder consists, occupies the pores thereof, and expels the alcohol. Nor would any of the latter substance find its way in the opposite direction, back into the water, were it not so soluble or diffusible in that liquid. Exosmosis therefore takes place through the water, and constitutes a very subordinate or feeble current. Now it is precisely relations of this kind that are observed in the case of the circulating and nutritive juices of all organic beings. The simplest instance is presented by the fluid contents of certain nu- cleated cells, both amona; animals and plants, in which a cur- „. , ^. . ' o r ' ^ Circulation in rent moves toward, and then from, the nucleus, coming back nucleated in a returning path. The fluid which the cell contains yields ^^ *' to the nucleus, in which seems to be concentrated all the activity of the organism, the nutritive material it requires, and, this done, passes on to make way for other portions. The act of nutrition, therefore, is followed by motion, and this upon the above simple principle ; for the liquid, be- fore it approaches to the nucleus, is charged with material which the nu- cleus can attract ; but immediately after contact has taken place, and the material has been removed, the liquid maintains no longer any relation with* the nucleus, the affinity or attraction is satisfied, and, so to speak, it loses its hold thereupon, and is pressed off by new-coming portions. Before its approach, and after its departure, the liquid has opposite relations to the nucleus, and in this respect may be regarded as representing two liquids, the one having a high affinity, and the other none, for the nucleus. The 132 CIRCULATION IN CELLS. Circulation in vegetable cells. Circulation in Tradescantia. Fw- 52. circulation in vegetable cells is shown by the di- rection of the arrows in Fig. 52. The course taken by the current may be determined under the mi- croscope by the minute floating, or, rather, drifting Granules. It is to and then from the nucleus. O Fig. 53 represents one of Fig. os. the jointed hairs from the Tradescantia Yirginica. The engraving is fi-om the view given by J^Ir. Slack, correct- ed, however, by the aid of a photograph of a similar ob- ject. «, h, c, d are the suc- cessive cells of the hair. The dotted lines show the direction of the current to and from the nucleus. The juice which is about to nourish a part has , . for that part a certain affinitv, but, with the accomplishment ( irculation -t ^ . ". , '■ . through per- of that nutrition, the affinity is at once lost. Thus, for m- vious parts. g^^j^(.g^ ]^-^ i\^q systeiiiic circulation, the joarts to be nourished have a certain affinity for the arterial blood ; they take from it whatever their purposes require, and, that done, the relation at once ceases ; the blood, become venous, has lost its hold upon them, and is pressed off. We may conveniently describe this effect as a pressure of the unchanged upon the changed liquid. The motions of the sap in plants are clearly dependent on this prin- Explanation of ciple. Leaving out of consideration the minor movements ^'^^ "t of the^sa^' which take place for special purposes, or at specific epochs of plants. in the development, it may be truly said that the nutritive changes occurring in the leaf are the primary cause of the motion; for, as the ascending sap presents itself on the sky face of the leaf, it receives carbon, under the influence of the sunlight, from the air, and becomes con- verted into a gummy, glutinous liquid. And just as in the pores of a bladder, or in those of any pervious mineral, pure water will drive out gum-water, and occupy the pore, so will the ascending sap expel the gummy solution from the capillary tubes or intercellular spaces of the leaf. As fast as this takes place, the active liquid becomes inactive, by itself changing into a gummy solution, and the movement is perpetuated. And this ensues not only in the leaf, but in every part of the plant ; the liquid to be changed presses upon that which has changed, and forces it onward. In this manner, motions in various parts and of very great intricacy will ensue, but all of them, if duly considered, no matter whether their seat be in the root or in the bark, in the flowers or in the CAUSE OF THE CAPILLARY CIRCULATION. 13j-^ leaves, no matter whether they take place in the height of summer or just at the close ofwinter, when the sap first rises, or even in the germ- inating seed which is under the ground, and has never yet been exposed to the light, may, without difficulty, be referred to the nutritive change carried on in t]:e leaves of the plant under examination, or its parent, by the influence of the rays of the sun. All this holds good, not only in the nutrition of a cell, the more com- plicated nutrition of the various parts of a flowering plant, or Explanation «f even of an animal, but likewise in those destructive changes ciixuiation'^of restricted to the latter class, and arising in interstitial decay ; animals. for the blood has a double duty to perform : it not only serves for nutri- tion, but also for the removal of effete and dying parts. These it efiects the oxidation of, their carbon passing into carbonic acid, their hydrogen into water ; and this is accomplished by the oxygen which has been ob- tained in the process of respiration. The scarlet or arterial blood, charged with its oxygen, passes to all parts of the economy in search of organic particles ready to be removed ; it effects their disorganization, and, becom- ing thereby venous, is pressed onward. And now, if we recall that nu- trition in animals depends on the access of air — even fibrin can not arise from albumen except under that condition — we can not avoid tlie con- clusion that all operations of repair and all operations of waste are made to conspire together for the production of movement ; and though every part offers its own special cause, as depending on nutrition, or disente- gration, or secretion, they may be all grouped together as the necessary results of one more primitive operation, which is the supply of oxygen to the blood in the respiratory mechanism. In my view of this subject, it is therefore the arterialization of the blood in the lungs which is the cause of the circulation in ^^ , . o _ ^ ^ Dependence of man. I consider the circulation as the consequence of res- circulation in piration ; and though, in one sense, the minor causes are * ^ respiration. numerous, each portion of nervous material, each muscular fibre, every secreting cell working its own way, these subordinate actions are all referable to one primordial act, and that is the exposure of the blood to the air. Whatever, therefore, interferes with respiration, interferes with circula- tion. If an in-espirable gas is thrown into the cells of the lungs, the passage of the blood is instaiitly arrested, and asphyxia ensues. Or, if the access of the air is cut off, as in drowning, in vain the heart exerts its utmost convulsive throb — it is unable to drive forward the Case of res- blood ; and in those cases, by no means infi-equent, yet un- ShT/""™ doubtedly the most surprising occun-ing in the practice of drowning, medicine — restoration from death after drowning, the whole success turns on one condition, the re-establishment of the arterialization of the blood. 134 COUESE OF THE CIRCULATING BLOOD. If that he accomplished, the circulation is restored, and the heart pro- ceeds with its duty. And for these reasons, I believe that in many cases success would be had, where failures are now experienced, if, instead of resorting to atmospheric air, pure oxygen gas or protoxide of nitrogen were administered. In the more highly-developed organisms the objects of the circulation are threefold : 1st. To minister to the nutrition of the system ; 2d. To introdvxce oxygen; 3d. To remove the products of waste. In man, these various results are accomplished by several different arrangements : 1st. The ereater, or systemic circulation ; 2d. The less, or pulmo- DifFerent o -^ , . , . . , p^,, mr ^ • classes of nary circulation ; 3d. The portal cn-culation ; 4th. The Malpi- circulation. g|^.^^^ circulation, &c. The course taken by the blood is as follows. Leaving the left ventri- Course of the ^^^ ^^ *^^ heart, it passes into the aorta, and is distributed blood in its sys- by the ramifications thereof, constituting the systemic arte- moiiary^c^rcu-' ^i^-'^? '^0 all parts of the system. It moves onward through lations. fiiQ capillaries, which may at once be considered as the term- inal ramifications of the arteries and the commencing tubelets of the veins. These, converging into larger and larger venous trunks, the sys- temic veins, deliver it into the ascending and descending vena3 cavte, from which it flows into the right auricle, and from thence into the right ven- tricle of the heart. From thence it is driven into the pulmonary artery, to be distributed to the lungs, and, coming therefrom along the pulmo- nary veins, reaches the left auricle, and from thence it gains the left ven- tricle, which was its starting-point. In the pulmonary veins, the left cavities of the heart, and in the sys- ^. ., . ^ temic arteries, the blood is crimson. In the systemic veins. Distribution of ' "^ crimson and of the right cavities of the heart, and pulmonary artery and its blue blood. branches, it is blue. The change from crimson to blue takes place in the systemic capillaries, and from blue to crimson in the pulmo- nary. The systemic, or greater circulation, is considered as beginning at the left ventricle and ending at the right auricle ; the pulmonary, or less circulation, begins at the right ventricle and ends at the left auri- cle. This double course is sometimes, among authors, illustrated by likening it to the figure 8, the upper loop representing the pulmonary, the lower the systemic circulation, and the heart placed at the nodal point. As has just been remarked, there are other subordinate circulations, The portal but of these Only one need attract our attention at present — it circulation, jg ^he portal. This originates in a system of capillaries, the veins belonging to the digestive apparatus, which, converging rapidly to- gether, form a common trunk, the portal vein. This at once ramifies like an artery in the substance of the liver. From the resulting capilla- ries, the portal blood passes into the commencing capillaries of the hepat- ORIGIN OF THE HEART. 13^ ic veins, whicli empty into the inferior vena cava, and so it reaches the general circulation. The physical peculiarity of the portal cir- culation is, that it commences in a capillary system, and ends in one, without the intervention of any central organ of impulse, or heart. At a very early period, comparatiA'e anatomists were struck with Portal circui;:- the analoffv between the portal circulation in man and the ^ioniii"strato,i '^\ , ^ ... V tliat of a systemic circulation of fishes, both being carried on in the fish. same way, that is, without a heart. In iishes, the heart is a branchial, respiratory, or pulmonary one. Their systemic circulation, or circula- tion of crimson blood, commences in the capillaries of the respiratory ap- paratus, the gills ; a convergence takes place into an aorta, which ramifies into systemic capillaries. So the great circulation in these tubes is ac- complished without any heart. It is scarcely necessary to point out the bearing of such a fact on the theories of the movement of the blood. In J^ig. 54 is a diagram of the circulation of a fish ; a, is the auricle ; b, the ventricle ; c, the branchial or pulmo- nary artery ; e, e, the branchial or pulmonary veins, bring- ing blood from d, the branchise, and converging directly to f] the aorta, which distributes the systemic blood. This is collected into a vena cava, g, and so brought to the au- ricle, a. There is therefore no systemic heart. The further discussion of this subject will be continued as follows : We shall describe, 1st, the construction and action of the heart ; 2d, of the arteries ; 3d, of the capil- laries ; 4th, of the veins. We shall then present a view of the combined result of these various mechanisms. 1st, The Heart. The first appearance of the heart is as a cavity arising in a collection of cells, by deli- quescence or separation of the central ones. At this early period, and even before the cavity has fairly formed, pulsation may be observed. The organ soon assumes a tubular form ; and this, Fig. 55. becoming curved, as shown in J^ig, 55, differentiates into tlu'ee compart- ments, with arterial and venous con- nections ; 1, the venous trunks ; 2, the auricle ; 3, the ventricle ; 4, the bulbus arteriosus. The form to be eventually assumed is foreshadowed in the manner in which the curved tube develops, the arch of the curve, 2, bulging so as to form a conical ventricle. This tri-chambered heart remains permanent in fishes, as seen in tlie preceding figm-e (54), of which c is the third chamber. But in birds and mammals, the aortic bulb merges into the ventricle, through which, as well as through the auricle, a septum or partition is established, and Diagram of fish circulation. The heart. Rudimentary heart. 136 STRLTTUEE OF TPIE HEART. Fig. 56. thus a doulble heart, or one of four cham- bers, arises. The diagram, Fig. 56, represents a double-chambered heart, d being its auri- cle, e the ventricle, c, c, the veins converg- ing to the auricle, a the aorta or main arte- ry passing from the ventricle. The course of the blood is indicated by the aiTows. The heart with four cavities may be considered as arising from the conjunction of a pair of the preceding form, with their efferent and afferent tubes, or arteries and veins, so modified or arranged that IJiugram of single heart. , -ii • • -t -\ -\ n i the right heart receives its blood irom the system in an auricle, from which it passes into a ventricle, and thence to Fill. 57. the lungs. avx, of the dugong. From the lungs, after aeration, this blood is brought to the auricle of the left heart, thence into its ventricle, and thence to the aorta. Though all four cham- bers are generally coalesced into one conic- al form, the heart of the dugong. Fig. bl, presents the true typical structure ; E is the right or pulmonary ventricle, L the left or systemic ventricle, their apices being quite apart ; D is the right or systemic au- ricle, F the pulmonary artery, K the left or pulmonary auricle, and A the aorta. Fig. 58 is the anatomy of the human heart as viewed upon the right side, the figure and description being from Dr. E. Wilson. 1, the cavity of the right auricle ; 2, the appendix au- riculee ; 3, the superior vena cava, opening into the upper part of the right auricle ; 4, inferior vena cava ; 5, the fossa ovalis ; the prominent ridge suiTOunding it is the annulus ovalis ; 6, the Eustachian valve ; 7, the opening of the coronary vein ; 8, the coronary valve ; 9, the entrance of the auriculo- ventricular opening; a, the right ventricle ; b, c, the cavity of the right ventricle, on the walls of whicli the columna3 earner are seen ; c is placed in the channel leading upward Human heart on the nght bide STRUCTURE OF THE HEART. 137 to the pulmonary artery, d ; e,f, the tricuspid valve : e is placed on the anterior curtain, and/' on the right curtain ; g, the long columna carnea, to the apex of which the anterior and right curtains of the tricuspid valve are connected by the chorda; tendineas ; h, the long moderator band ; ^, the two columnai carnea^ of the right curtain ; k, the attach- ment by chordas tendineaj of the left limb of the anterior curtain ; I, I, chordiv tendinea^ of the fixed curtain of the valve ; Tii, the valve of the pulmonary artery : the letter of reference is placed on the inferior semi- lunar segment ; n, the apex of the right appendix auriculse ; o, the left ventricle ; j), the ascending aorta ; q, its arch, with the three arterial trunks which arise from the arch ; ?', the descending aorta. Fig. 59 exhibits the view of the organ on its left side. Like the pre- p^g 59 ceding, the figure and description are from Dr. Wilson. 1, cavity of the left auricle : the number is placed on that portion of the ^ septum auricularum correspond- ft Human heart on the left side. ing with the centre of the fossa ovalis ; 2, cavity of the appendix auriculee ; 3, opening of the two right pulmonary veins ; 4, the sinus into which the left pulmo- nary veins open ; 5, the left pul- monary veins ; 6, the auriculo- ventricular opening; 7, the coro- nary vein, lying in the auriculo-ventricular groove ; 8, the left ventricle ; 9, 9, the cavity of the left ventricle. The numbers rest on the septum ventriculorum. «, the mitral valve : its flaps are connected by chorda' tendineaj to b, b, b, the columnas carnege ; c, c, fixed columnse carnege, form- ing part of the internal surface of the ventricle ; d, the arch of the aorta, from the summit of which the three arterial trunks of the head and up- per extremities are seen arising ; e, the pulmonary artery ; f, the oblit- erated ductus arteriosus ; g, the left pulmonary artery ; h, the right ven- tricle ; ^, the point of the appendix of the right auricle. Externally, the heart is covered by a serous membrane, pericardium, and in its interior is sheathed by the endocardium, an extension of the inte- rior coat of the great blood-vessels. Though its movements are wholly in- voluntary, its muscular fibres are of the transversely striated kind. They are about one third less in diameter than M ISC iitrtibiL^ It thp heart tliosc of voluutary musclcs generally, f 138 COUESE OF THE BLOOD IX THE HEAET. and are especially characterized by their disposition to anastomose with one another, as represented in Fig. 60. In the ventricles, the arrange- ment is such that the fibres of the external and internal surfaces decus- sate. The motions of the heart consist in the relaxations and contractions of Relaxations the muscular "vvalls of its cavities. The two auricles contract and contrac- ^^ ^j^^ same moment, as do also the two ventricles, but the tions of the ... ... heart. contractions of the auricles coincide with the relaxations of the ventricles. The course of the blood through the heart is this. The venous blood, Course of the brought by the ascending and descending cavaj, flows into blood in the the right auricle as it is dilating, and for the moment pushes movements of forward to the ventricle, but the auricle, being of less capac- the valves. j^y than the ventricle, is filled to distention first ; at this in- stant it contracts, forcing its contents past the tricuspid valve into the ventricle, and fills it completely. The blood can not regurgitate into the veins to any extent while this is going on, because of the almost perfect closure of their valves. The right ventricle now commences to contract ; its fleshy columns shorten so as to pull upon the tendinous cords attach- ed to the flaps of the tricuspid valve : this enables the blood to get be- hind them, and they quietly close the aperture between the auricle and ventricle ; the closure is not, however, under all circumstances, perfect, the mechanism being such as to permit leakage or regurgitation to a lim- ited extent. The blood now rushes into the pulmonary artery, passing by its semilunar valves, which, the moment the ventricular pressure ceases, shut, so as to prevent any return to the heart. Having passed through the lungs and been submitted to the air, the blood now returns to the left auricle, which forces it into the left ventri- cle, the action on this side of the heart being the same as on the other; the mitral valve, which closes the opening from the auricle into the ven- tricle, is worked in the same manner as the tricuspid, and the blood is pressed into the aorta, the semilunar valves of which, at that instant, shut abruptly with an audible sound, and prevent any regurgitation. In this manner the distribution to the system is accomplished. On both sides of the heart, as soon as the auricles have finished theii- contraction, they begin to dilate, and continue to do so during the peri- od that the ventricles are contracting. Thus there is an accumulation in them when the ventricles are ready to dilate, and, as soon as that oc- curs, the blood flows freely forward into those cavities, the complete dis- tention of which is then accomplished by the contraction of the aiuicles, as before explained. Movements of The mode of action of the two sets of cavities is different. Ind Ventricles '^^^ auricles coutract suddenly, first at the place of junction MOVEMENTS OF THE HEART. 139 ot" their veins, the effect passing quickly forward ; the ventricles con- tract more slowly, but simultaneously in every part. During each beat of the heart two sounds may be heard, followed by a silence. The first sound is dull ; the second, which fol- Sounds of the lows it quickly, is sharp. They may be imitated by artic- ^'^'*'"''- ulating the syllables lubb, dup. The first is due to the contraction of the muscular fibres of the ventricles, and the striking of the apex of the heart against the wall of the chest ; to a certain extent, the opening of the semilunar valves, and the rush of the blood into the pulmonary- artery and aorta contribute to it. The second sound is due to the shut- ting of the semilunar valves of the aorta and pulmonary artery. At each contraction of the ventricles the heart strikes against the walls of the chest, usually between the fifth and sixth ribs, and an inch or two to the left of the sternum. This motion is partly due to the action of the spiral muscular fibres of the ventricles, which gives a tilt to the heart, and partly to the globular form which the whole organ suddenly assumes. The number of pulsations made by the heart differs very much at dif- ferent periods of life: at birth it is from 130 to 140 per Number of pul- rainute ; at the seventh year, from 80 to 85 ; during mature sations. life, from 70 to 75 ; and in old age, from 50 to 65. In females it is more frequent than in males. It observes a general relation with the number of respirations, five pulsations commonly occurring dm'ing one respiration. It varies with incidental circumstances. During sleep it declines in frequency ; after eating, or during exercise, it is quickened- Examined from morning to evening, it becomes slower by degrees. Ly- ing down, the pulse is slower ; in a sitting posture, more frequent ; and still more so when standing, the variations depending on muscular exer- tion. In conditions of disease, the ratio between the number of pulsa- tions and respirations is variable. The walls of the left ventricle are twice as thick as those of the right, and the force of its contractions is about double. The ca- „. . structure and pacity of the two ventricles is nearly the same, and is taken power of the at about three ounces. The active force with which the au- '''"^^^^' ricles dilate is feeble, and wholly incompetent to exert any thing like the suction power at one time supposed, yet that they are not distended by the mere influx of the blood is satisfactorily proved by their dilatation after the heart has been cut out. With respect to the absolute force which the left ventricle exerts for the propulsion of the blood into the systemic arteries, it is stated to be 13 lbs. This result is derived from the consideration that the pressure of the blood in the aorta is about 4 lbs. 3 oz. That the motions of the heart can not be referred to the presence of the 140 CAUSE OF THE MOTIONS OF THE HEAET. blood, or any reflex action arising from the cerebro-spinal motions of the system, but must be attributed to the organ itseli, is proved heart. -^^ their continuance after its excision from the body, or even after it has been cut in pieces. Some have supposed that the minute sympathetic gangUa with which it is fru'nished are the source of the mo- tive power ; others are disposed to impute it to a self-contractile power of its muscular fibres, irrespective of any nervous agency. Of course, it is admitted by all that the brain and spinal cord can influence these movements, but such effects are superadded and not uniform. Of these opinions, we shall find many reasons for preferring the first when we come to the description of the nervous mechanism. It will be then seen that one of the prominent functions of nervous ganglia of a cer- tain order, and particularly the ganglia of the sympathetic, is the storing up of impressions they have received, and thus becoming reservoirs or magazines of force. The power thus engendered or contained in them is by no means always delivered out in totality at once, but it may be in small portions, at intervals, for a long time ; and doubtless in this way the minute sympathetic ganglia of the substance of the heart retain a power of keeping up the motions of that organ for a certain period of time, even though great lesions or morbid changes may have supervened. Such a mechanism recalls the manner in which chronometers are kept going during the short time that the action of the main-spring is taken off when the watch is wound up. 2d. The arteries are tubes consisting of different tunics or layers va- Description of I'iously numbered by anatomists, but which may be suffi- the arteries. cicntly described as, 1st. The exterior tunic, containing fibres generally running lengthwise, connective and elastic tissue : it is of about the same thickness as the tunic below ; 2d. The middle tunic, character- ized by being composed of non-striated muscular fibres circularly ar- ranged ; 3d. The interior tunic, which is thin, and consists of a cellular or epithelial layer, smooth and polished, to permit of the ready passage of the blood. The elasticity of the arteries enables them to sustain the sudden action of the heart by distending to a certain degree as the blood is driven into them, and by then- gradual collapse when the ventricles cease their pres- sure, the jetting or intermitting flow is converted eventually into a con- , tinuous stream. The mechanical influence of the heart is thus decom- posed into two portions : one, which is of momentary duration, or, at all events, lasting only so long as the ventricle contracts ; and a second, which is occupied in distending the elastic arterial tube ; but this por- tion is not lost to the circulation, since the tube, as it contracts, yields it back again to the blood. The momentary impulse of the heart is thus spread over a considerable duration without loss. ACTION OF THE ARTERIES. 141 The muscularity of tlie arteries is shown by their contraction on ex- posure, their subsequent dilatation being due to their elasticity, this con- tractile property being- continued for some time after death. It is also ])roved by the great diminution of diameter which arteries exliibit when under the influence of an electric current. The quantity of muscular and elastic tissue in different arterial tubes is usually in an inverse pro- portion. In the great arteries the elastic tissue abounds, in the smaller ihe muscular increases. By their muscular coat the quantity of blood in these tubes can, within certain limits, be regulated. At each injection of blood into it an artery distends. It then con- tracts, and thus gives origin to a pulsation. Its increase is Action of the both in diameter and length, the tendency being to lift it at arteries. each pulsation. The distention does not occur at the same instant in all these tubes, but those nearest to the heart yield first, and the more distant a little later. There is therefore what may be termed a wave of distention passing throughout the length of each arterial tube, and an- other actual wave in the blood itself. These pass onward at different rates of speed. The interval of wave-motion from the heart to the wrist is about one seventh of a second. Of course this wave-motion is to be distinguished from the absolute movement of the blood, which is nmch slower. In the carotid artery the flow of the blood is about one foot in one second. A pressure or impact, communicated to a liquid in a long tube, is transmitted to the more distant end with vastly more rapidity than the liquid itself could flow through the same distance. Thus, if we were to suppose a very long metal tube to be filled completely with water, its two ends having been tightly closed by tying pieces of bladder over them, the tap of a finger on one of the pieces of bladder would be almost instantly felt by a finger laid on the other. Indeed, it has been pro- posed to establish telegraphic communication on this principle, though such attempts would prove abortive from the interference of collateral circumstances. This example may serve, however, to illustrate the es- sential difference between the flow of a liquid in a tube and the passage of a pulsation through such a liquid contained in such a tube. The capillaries may be regarded as tubular continuations of the arte- ries and the commencement of the veins. They ramify . rni p ■ i^ The capillanes. through the organic structures". They are of pretty uniform diameter, and may therefore be looked upon as cylinders. Their usual size is about -^-^-^ of an inch ; their mode of distribution varies with the structure and functions of the part they occur in : tlius, in muscles they run parallel ; in the papilla? they are looped. They consi^st essentially of a delicate structureless membrane, analo- gous to cell membrane, and the sarcolemma of voluntary muscles. It 142 THE CAPILtAftlES. possesses a certain degree of elasticity, and presents here and there cell nuclei. Fin. fil. Fiq. r,2. Capillary distiibiition to mucous membrane of stomach. Capillary distribution to villi of duodenum. The interspaces between adjacent capillaries vary much in size and Size of inter- shape, the latter variation being dependent on the mode of spaces. distribution, whether parallel, reticulated, looped, &c. ; as to size, in the liver the interspaces are of less diameter than the capillaries, in the choroid coat still smaller, but in the cellular coat of the arteries they are ten times larger than the vessels. These interstitial spaces are nourished by the matter which exudes through the thin walls of the cap- illaries. Ficj. 63. Fig. 63 represents the capillary circula- tion in the web of the frog's foot : «, venous trunk ; h, h, branches of venous trunk ; c, c, pigment cells. The elliptical blood- discs are seen in outline in the interior of the ves- sels. The blood flows tlirough the capilla- ries in an uninterrupt- ed stream, its jetting motion being entirely lost. The rate of cir- culation through the systemic capillaries is Capillary circulation ol frog's foot. STRUCTURE OF THE VEINS. 143 taken at three iiiclics per minute, that through the pulmo- ,, ,. ^ ^ , . Blotion of the nary being five times as quick, the length of the capillary tube blood in the to be passed -^ of an inch, so that the passage from the ar- '^"^^^ ^^^^^' tery to the vein may be accomplished in less than one second. It is to be remarked, however, that all parts of the cylindrical stream do not move with equal rapidity. Those parts which are nearest to the wall of the vessel are spoken of as the still layer, from their tardy movement. It is in this that the white coi"puscles may be seen. Fig- Gi- Fig. 64 shows a portion of a small vessel from a frog's foot: «, «, red blood elliptic cells, occupying the axis of the vessel, and exterior to them, moving- more slowly, or occupying the still lay- er, the white spherical cells ; ^, h, nucle- ated epithelium. 4th. The veins have a structure in some respects different from xhe veins : that of the arteries. Their their structure, elastic coat is by no means so much de- veloped, and their muscularity less dis- tinct. With the exception of those of the lungs, abdominal viscera, and brain, their interior is furnished with valves of single, double, or triple flaps, in aU instances opening toward the heart. The blood flows equably in them, the pulsating action of the ventricles having disappeared in the capillaries. Since they present an aggregate capacity two or three times that of the arteries, the motion of the circulation in them is proportion- ally slower. Fig. 65 is a diagram showing the manner in which the valves open when the blood flows in the course indicated by the arrows. Fig. 66. White corpuscles in the still layer. Valves of veins open. Valves of veins shut. Fig. 66 shows their application to each other, or to the sides of the vein, and the consequent bulging of that vessel when the current, as indicated by the arrows, is in the opposite direction. Having now described the structure and action of the heart, the arte- ries, capillaries, and veins respectively, as far as is necessary, it remains to group those actions together, and present the theory of the cu'culation at one view. But, before entering on this, it is proper to offer an ar- En-or of the doc- , -, . ^ , , . , . , .,-, trine that the gument against the doctrine oi those physiologists who still heart is the sole maintain that the circulation is whollv dependent on the heart, '^^'^}'^^ °^ ^^^ ^i""" . . ^ J- _ culation. and that that organ is entirely competent to carry it on. 144 ACTION OF THE HEART. The majority of the ch-culations we examine in organic forms are ac- complished Tvithout any heart. Plants have none ; lishes have no sys- temic heart ; even in man, at the first period of embryonic existence, there is no such central organ ; in his adult condition the portal circulation has none. The cun-ent of blood in the capillaries, seen under the microscope, exhibits no jetting movements, but, on the contrary, a steadiness of flow, sometimes for long in one channel, then a cessation, then perhaps a retrog-radation, and then a new path. It looks as though the blood was flowing spontaneously, and not by any force acting behind. The heart of an animal may be suddenly cut out, and yet the capillary motion may go on in the same direction as before. After death the arterial tubes are most commonly found empty : a result which is a mechanical impossibility on the supposition that the heart alone drives the blood, but which ensues as a necessary consequence if the capillaries draw it. In acardiac monsters the blood circulates without difiiculty, and, though it was at one time supposed that in these twins the hearted foetus drove the blood through the heartless one, this is now demonstrated not to be the case. The cu-culation, moreover, varies locally, and at special epochs, as in the development of the generative organs, the mammary glands, the flow to the erectile tissues. Ubi imtatio ibi fluxus is an old medical aphorism, and these local variations are incompatible vnih the action of one central imvamng force. In cases of spontaneous gangrene, it some- times occurs that the circulation through the part has declined, while the capillaries are all open, as subsequent examination proves. The appKca- tion of cold to a part checks the circulation through it, and this not through ary contraction of the vessels ; so, likewise, does a jet of carbon- ic acid gas du-ected upon them. :Moreover, any retardation in the supply of air to the lungs restrains the circulation, and this not alone in the pulmonary vessels, but also in the systemic capillaries, producing an in- creased pressure in the arterial tubes, a diminished one simultaneously occurring in the veins ; and if, in the various cases now mentioned, the propulsive action of the ventricles can not be relied on to explam the dif- ficulties, neither can any supposed suction or exhausting action of the auricles. When a ligature is tied round a vem, the action of the auricle is cut off, but the vein distends beyond the obstruction, showing that there is a force acting from the capillaiies. Flexible tubes, such as are those vessels, would at once collapse under the exertion of a very moder- ate suction power, far less in intensity than would be necessary to draw the blood m the veins. In spasmodic asthma, and in aU pulmonary congestions, the right side of the heart circulates the blood with difiiculty through the limgs, show- ing the existence of a great obstraction to its motion thi'ough the pulmo- nary capillaries. An exammation of the condition of the various per- CIRCULATION OF THE BLOOD. 145 tions of the circulatory apparatus after death presents facts utterly inex- plicable on the doctrine of the sufficiency of the heart. I have already mentioned the empty state of the systemic arteries ; to this may be add- ed what is often witnessed — the distended condition of the pulmonar}^ artery, into which the blood has been forced by the expiring beats of the right ventricle, but has been unable to get through the pulmonary capil- laries because of the cessation of respiration ; but in other cases, where respiration has come to an end more tranquilly or slowly, the left auricle is full of blood, which must have been driven into it by the pulmonary capillaries. In sudden death, as by hanging and drowning, the right heart is excessively distended, as is also the pulmonary artery. I might proceed to add to these other facts exhibiting local variations of the supply of blood in the periodicities of the system. There is a cer- tain amount sent to the brain during the day, and a less during the re- pose of the night ; in the muscular system, during the time of its action, the quantity demanded is greater; in its state of inactivity, less. A con- stant and invariable acting machine, such as is the heart, could by no possibility adjust these variable supplies. But the cases here offered arc more than enough, and it remains to be added that, though not one of them can be explained on the doctrine of the sufficiency of the heart, there is not one which does not follow as a necessary consequence of the doctrine now to be presented. On this view, the cu'culation is conducted in the follo"wing manner: The left ventricle of the heart impels the blood into all the ^^ lanationof aortic branches, any backward regui-gitation into the auricle the circulation being prevented by the shutting of the mitral valve ; the ° * "^ °° ' force employed is decomposed into two portions, one part exerting an in- stantaneous effect on the blood in pressing it forward, and ceasing in- stantaneously, and thus givmg origin to the pulse ; the second distend- ing the arterial tubes, but not being lost thereby, since their elasticity causes them to contract, and the semilunar valves at the origin of the aorta being at this period shut, a steady, onward pressure is exerted on the blood ; so the quickly-ending action of the ventricle gives origin to two distinct mechanical results — a sudden impact and a continuous press- ure. This suffices to bring the blood to the arterial origin of the capil- laries, and beyond that point the action of the heart may be considered not to extend. The relation between the interspaces of the capillaries and the blood thus introduced to them continues the current. The particular mode in which this relation is manifested differs in different parts. The oxidiz- ing arterial blood has a high affinity for those portions that have become wasted : it effects their disintegration, and then its affinity is lost. The various tissues require repair ; they have an affinity for one or other of K 146 CIRCULATION OF THE BLOOD. tlie constituents of tlie Tblood ; they tuke the material they need and their affinity is satisfied ; or secreting cells originate a drain upon the blood, and the moment they have removed from it the substance to be secreted, they have no longer any relation with it. So processes of oxidation, and processes of nutrition, and processes of secretion, all conspire to draw the current onward from the arteries, and to push it out toward the veins ; and though these processes may present themselves in many various as- pects, they are all modifications of the same simple physical principle. The blood has now reached the veins, and is forced onward in them by the power that has thus originated in the capillaries. The influence of the heart is here unfelt, the exhausting action of its right auricle is un- appreciable, and, thus pushed onward from the capillaries, it reaches the heart, completing its systemic or greater circulation. This circulation may therefore be said to be due to the high affinity which arterial blood has for the tissues, venous blood having none ; and the action of the heart is confined to the filling of the arterial tubes, and presenting fresh por- tions of blood to the capillaries. Arrived at the right auricle, the blood flows continuously into it and the right ventricle for a moment, but the ventricle holding more than the auricle, the latter cavity is fully distended first. At that instant it con- tracts, the valves in the veins shutting, and the blood, driven thus forcibly into the ventricle, distends it to the utmost. The ventricle, in its turn, now contracts, the tricuspid valve shutting, and the blood issues forth through the pulmonary artery, its valves then closing. At this moment an event occurs which, in these descriptions, is generally overlooked — an action analogous to that of the hydraulic ram. On the shutting of the tricuspid, the whole column of venous blood would be brought to a stop if the tubes containing it were unyielding, and a great force would be gen- erated from this stopping of its momentum ; but the auricle is ready to dilate, and into its cavity the blood, which would be otherwise checked, flows. I consider that this safety action of the auricle is one of its prime functions. The rapidity with which the dilatations and contractions are taking place furnish no argument against the occurrence of this action. I have a hydraulic ram, the pulsations of which may be so adjusted as to exceed greatly in frequency those of the heart, and, indeed, to give rise to a low murmuring sound, and yet, under these circumstances, the lat- eral force is so great as to throw a column of water more than forty feet high. If it were not for the dilatability of the auricles and their yield- ing texture, the veins would burst on the shutting of the tricuspid valve. The ramifications of the pulmonary artery bring the blood to the cap- illaries of the lungs, but beyond that the influence of the heart is not felt, for now the physical principle heretofore described comes again into ac- tion. The venous blood has a high affinity for the oxygen of the air, an THE heart's action. 147 affinity which is satisfied as soon as the blood presents itself in the cells of the lungs. Arterialization being accomplished, the portions to be changed exert a pressure on those that have changed, and the blood, mov- ing forward in the pulmonary veins, reaches the left auricle of the heart. For a moment it passes into the left auricle and ventricle continuously, but the auricle, being of less capacity, fills first. It contracts as soon as it is completely full, and drives its contents into the left ventricle, dis- tending it to the utmost. The ventricle now contracts, shutting the mi- tral valve, and the ram-lilce action is repeated on this side of the heart. But the blood expelled from the ventricle is urged into the aorta, its force being decomposed, as before described, one part acting instantaneously as an impact on the blood, the other on the arterial walls, and on the first moment of the recession of the walls of the ventricle the semilu- nar valves of the aorta shut, and this act completes one tour of the cir- culation of the blood. In this description I have said nothing of the circulation in the sub- stance of the heart itself, since it would have led to a needless complica- tion. It should be remembered, as an illustration of the working of the physical principle here explained, that the motion of the blood is contrary in the greater and less circulations, compared together. In the former, the current is from the crimson to the blue, in the latter, from the blue to the crimson side. The action of the heart is therefore limited to the filling of the arterial tubes, so as to present to the capillaries a constant supply of q^^j.^^^^ g^ . blood. There seems to be but little suction force exerted ment of the by the auricular cavities for the emptying of the veins. The valvular construction of these vessels economizes every pressiu'e that the muscles may exert on them in favor of the circulation, for every such pressure must, by reason of the valves, force the blood onward to the heart. This is, however, only an incidental result of the same character as the influence which the motions of respiration exert. They may be properly overlooked in a general statement of the causes of the circulation. By regarding the affinity between the blood and the tissues with which it is m contact as the great primary cause of the circulation, y . . we assign a reason for those various phenomena which can supporting this not be accounted for on Harvey's doctrine : the motions in '^^^ ^nation. the embryo ; the periodic and local variations ; the portal circulation ; the changes in the current, as seen under the microscope ; the movement in the capillaries after the heart is cut out ; the empty condition of the arteries after death ; the phenomena of acardiac foetuses ; local inflam- mations and congestions ; the gangrene of parts while their capillaries are pervious ; the retardation of the current on the application of cold or of carbonic acid gas ; the results of asphyxia and death by drowning or 148 THE FIEST BREATH. hanging ; the changes of pressure in the arteries and veins respectively during a check on the respiration ; the vis a tergo of the veins ; the eifects of a ligature on those vessels ; the action of irrespii'able gases when breathed, and the opposite conditions when oxygen gas or protoxide of nitrogen are used. Among the striking proofs of the truth of this doctrine, that the pri- mary cause of the circulation is the aeration of the blood, I would particularly direct attention to the effects which en- sue in the moment of birth at the first breath. That intercommunication between the two sides of the heart, established through the foramen ovale and through the ductus arteriosus, is suddenly put an end to. But this is not through any change in the mechanism of the heart itself, nor be- cause of any interruption in the action of the placenta. It is solely be- cause of the calling into operation of the principle we have been here en- forcing. Through the contact of the cold air, or other causes which might be assigned, the inspiratory muscles make their first contraction and dis- tend the lungs. At that instant, the commencing arterialization produces a pressure, in the manner I have explained, of the venous upon the now arterialized blood in the vessels of the pulmonary cells. There is no other possible issue to such an action than an instant drain upon the heart. The pulmonary or less circulation sets in with full vigor. The blood is not driven by the heart to the lungs, but drained by the lungs from the heart. If it were the heart's action that occasioned this sudden increase of force, because of the strain thrown upon it through the shut- ting 'tjfF of the influence of the placenta, it is inconceivable why the cur- rent should not continue to move through the great avenues already open to it from the right to the left auricle through the foramen ovale, and from' the right ventricle into the aorta through the ductus arteriosus. The arrest of its motion through these channels distinctly establishes that the seat of the new action is in the lungs, and the final closure of the foramen and shriveling of the duct confirm the correctness of this con- clusion. Though it does not strictly belong to the subject now under consid- eration, I can not avoid impressing on the reader the suddenness of tlie effect that thus ensues on the taking of the first breath. It is a crisis in the history of development. Of these changes by crisis much more will be said in the second book, and their important bearings on the theory of physiology pointed out. It is enough for the present pui-pose to com- mend to the attention of those naturalists who deny that physiological crises ever occur, the facts which have been considered in the preceding paragraph. A doctrine which accounts with simplicity for such a long list of mis- cellaneous facts commends itself to our attention at once. There are, OF respiiJation. 149 however, considerations of a still Aveightier character, which must compel us to adopt it. The affinity between the blood and the parts with which it is brought in contact is a chemical fact beyond contradiction. The pressures and motions I have been speaking of follow as the inevitable consequences of that affinity. We can not, therefore, gainsay their ex- istence in the living mechanism, and the only doubt we can entertain is as to whether they are of competent power to produce all the effects be- fore us. But after what has been already said respecting the energy of endosmotic movements displayed against pressures of many atmospheres, Ave may abandon those doubts ; and since we have here a force of uni- versality enough, and intensity enough, and in every instance acting in the right direction, it would be unphilosophical to look farther, since such a force onust^ under these conditions, exist in the physical necessity of the case. CHAPTER IX. OF RESPIRATION. Respii'ation introduces and removes aerial Substances. — Coalescence of Respiratory and Urinary Organs in Fishes. — Physical and chemical Conditions of Respiration. — Literstitial Movements of Solids, Liquids, and Gases. — Condition of Equilibrium in the Diffusion of Gases. — Con- densing Action of Membranes. — Forms of Respiratoi-y Mechanism. — The Lungs of Man. — Three Stages in the Tntroduction of Air : Atmospheric Pi-essure, Diffusion of Gases, and Condensation by Membranes. — Exchange of Carbonic Acid for Oxygen. — Divisions of the Con- tents of the Lungs. — Variations in the expiired Air. — Removal of Water. — Effect of irrespira- ble Gases. — Experiments ofRegnault and Reiset. — Nervous Influence concerned in Respiration. — Results of Respiration. Since it is essentially necessary to the life of all animals that the blood should pass to every part of the system, provision must objects of be made for securing aeration. The breathing apparatus is the respiration, skin, or some extension, reflection, or modification of it. Besides the great duty of originating the circulation, respiration is con- nected with others of equal importance. The functional activity of the nervous and muscular tissues is dependent on their oxidation, and this implies the introduction of air* In each tribe, moreover, it is necessary to keep the temperature up to a specific point. This also is accomplished by oxidation, either of the disintegrating material which is passing to waste, or of combustible substances, such as sugar or fat. All organic material, at its death, eventually gives origin, ^. , under the action of the air, to two products with which the of tissue meta- fanction of respiration is mainly concerned. These products ^^°''P^°^is- are carbonic acid and water. With the exception of gelatin, the other 150 NATUEE OF EESPIRATION. respiratory elements of food — fat, sugar, starch, &c., yield these two pro- ducts alone. The nutritive elements give rise to nitrogenized compounds in addition. The conditions of life are such that carbonic acid can not be permitted to accumulate in the system, and means have therefore to be resorted to for its removal. The introduction of oxygen and excre- tion of carbonic acid are accomplished by the same mechanism, the lungs, the action of which is dependent on a physical principle. Under its simplest condition, respiration consists in the passing of car- Respiration is Iconic acid with the vapor of water from the system, and the connected with reception of oxygcu in exchange. The construction of the porous matter apparatus which accomplishes this double duty in atmos- only. pheric animals is such that it can deal with substances in the aerial state alone. Nothing can be introduced through the lungs or escape therefrom except it be in the gaseous or vaporous form. All those products of disorganization which are not presented under this con- dition must therefore be removed by other organs, and this is more par- ticularly done by the kidneys. But in aquatic animals, as in fishes generally, there is not this restric- Coalescence of tion or concentration of function, for the gill, being in contact and^hiarvor- ^^^ Water, offers a channel for the passing away of many gans in fishes, products of Waste wliicli, from their non-aerial state, could never escape through a lung, and so I regard this organ, the gill, as in a measure sharing the duty of a kidney in eliminating nitrogenized and perhaps saline matters. Comparative anatomists have long recognized that the so-called kidney in fishes approaches in character the Wolffian bodies largely developed in the foetal condition of man. I am disposed to believe that the physical interpretation of this depends on the fact now before us, and that the gill in fishes, and the placenta, in part, in mam- mals, discharge at once the double office of a respiratory and urinary or- gan. It is consistent with the scheme of organic design that there should be this separation and concentration of function as development takes place. These considerations would therefore lead us to expect' that we should find in the respiration of air-breathing animals that function in its purest and least complicated form, and this is accordingly the case. If it be merely the skin that is relied on, as in the low orders of aerial life, or if the mechanism be constructed on the type of carrying the air to the blood, as in insects, or that of carrying the blood to the air, as in man, the operation consists essentially in the escape of carbonic acid and steam, and the reception of oxygen in return. Respiration, like circulation, furnishes us with a signal instance of the employment of purely physical principles for the accomplishment of physiological purposes. It is with the pressure of the atmosphere, the INTERSTITIAL MOVEMENTS OF SOLIDS, LIQUIDS, GASES. . 151 diffusion of e;ases, and the condensino^ action of membranes, ^, •1 -I rm • • T Physical prin- that we have now to deal. Ihese give us so precise and per- cipies alone k-- spicuous an explanation of the act of breathing that it is striic'd°t^'th°" needless to look beyond them ; yet on that act depend the respiratory en- highest operations of life. In this particular the Scriptiu-es ^^^^' have summed up the deductions of modern physiology in a single line — no metaphorical expression, but the simple assertion of a truth : He " breathed into his nostrils the breath of life, and man became a living- soul." Of the physical principles now to be dealt with, it is unnecessary to say any thing respecting the pressure of the atmosphere, since that is well understood; but not so with the phenomena of the diffusion of gas- es, and the condensing action of membranes. Though these are subjects which have been particularly examined by American physicians, the facts they have elicited are little known abroad. For example, the error of Valentin's statement respecting the diffusion exchanges of carbonic acid and oxygen, and the uselessness of the elaborate discussions which have originated therefrom, would at once have been recognized, had attention been directed to the facts developed here almost twenty years ago. Interstitial motions are exhibited by solids, liquids, and gases. I have had occasion to examine Roman silver coins, from the Interstitial interior of wliich the copper originally present had made its goiidTand liq- way out to the sui-face, forming the greenish incrustation iiids. known as patina by antiquarians, the silver being left almost pure. Li speaking of absorption by the blood-vessels in Chapter VI., we had oc- casion to dw^ell upon the same propensity as shown by liquids, the en- dosmosis of Dutrochet being an example of it. The ready mobility of this group of bodies, arising from their diminished cohesion, greatly pro- motes these effects. Mr. Boyle collected a number of cases of solid move- ments in his tract on the languid motions of bodies. Gases and vapors, by reason of their total want of cohesion, present the most striking examples of these effects. Their propensity to intermin- gle with each other is manifested, even though they be obliged to pass through crevices or winding passages. One of the first instances to which attention was directed occurred under the observation of Dr. Priestley's ob- Priestley, who found, on passing steam through an earthen ^^^ gnX m tube placed in a furnace, that air would be delivered at the of gases. farther end. For some time he supposed that this experiment demon- strated the conversion of water into air by a great heat, but eventually traced it to its proper cause — the escape of the steam outward through the pores of the earthen tube, and the intrusion in the opposite direc- tion of air from the furnace. This singular experiment may be well shown by attempting to pass steam through a red-hot tobacco-pipe, the 152 EXPEEIMENTS OF DALTON AND GRAHAM. iment on the diffusion of Fin. 6T. end of wliicli dips beneatli some water. A torrent of gas bubbles wiU escape. Mr. Dalton demonstrated that if a light gas be placed above a heavy Daiton's exper- gas in a suitable apparatus, the former, notwithstanding its levity, Avill descend, and the latter, notwithstanding its weight, will rise, and a complete and uniform intermixture will result. By such experiments he was led to believe that gases act as vacua to one another, and correctly explained the uniform composition of the atmosphere on this property of dif- fusion, or tendency of its constituents to intermix. Thus, if a vial filled with hydrogen be placed with its mouth downward over the mouth of a vial of the same size containing carbonic acid gas, as shown at h, c, Fig. 67, in the course of a few moments the diffusion will be complete, and if the mixture in either vial be examined, it will be found to contain equal quantities of the gases. Professor Graham extended Dr. Priestley's observations on „ , , the passage throuo-h porous barriers. The sub- Granam s ex- -t^ o _ or perimentswith stance he cMefly employed was a mass of dry stucco. plaster of Paris. This enabled him to prove that In the case of different gases diffusion takes place at different rates, which are dependent on the density of the gas. Per- haps the most satisfactory method of illustrating this class of ^ Q.^ ^. results is by taking a porous earthenware cup, Lhroughporous a «, Fig. 68, such as is used in Grove's voltaic enware. "j^attery, drying it perfectly, and cementing into its mouth an open glass tube, b, three quarters of an inch c in diameter, and a foot or more long. A wide-mouthed bot- tle, c c, being placed as a temporary cover over the porous cup, it may be filled with hydrogen gas by displacement ; and if the end of the glass tube be put into water contained in a reservoir, d, the water will rush up the moment the bottle is removed. Wlien this motion is completed, if a jai- of hydrogen be held over the porous cup, the water Avill be ^ driven down with great rapidity, and a number of air-bub- bles quickly escape. The extraordinary speed with which a gas will flow in and out of pores could not be better dis played. This rapidity of motion is an element with which Ditius^mi tiuJ^igh the physiologist has to deal, as we shall presently find. earthenware. Even when the texture of the substance is much closer, and the pores r^-r. . of extreme minuteness, similar results can be obtained, as was Dirrasion ' through In- shown in the experiments of Dr. Mitchell, of Philadelphia, who dia-rubber. gj^piQyg,^ i\-^\t^ sheets of India-rubber. If, over the mouth of Fill. PASSAGE OF GASES THROUGH POROUS FILMS. 153 Diffusion thiouirh India lubbc-r. a glass bottle, such a tliin tissue be tightly tied, and the bottle placed in an atmosphere of carbonic acid gas, movement at once takes place, a little air flowing out of the bottle into the carbonic acid, and so large a Fig, 60. quantity of the acid passing the opposite way that the India-rubber soon swells outward, and eventually caps the bottle like a dome, as in Fig. 69, at h. Or, if the conditions be re- versed, the bottle being filled with carbonic acid, and then exposed to the atmosphere, the India-rubber will be depressed, as at a, and stretch so as almost to sink to the bottom. Such experiments therefore prove that, even though barriers of a very close texture should intervene, gases will pass through them, and with so much force, as Dr. Mitchell showed, that many inches of mercury may be lifted, nor does the movement cease until the gases on both sides of the membrane have the same composition. Other substances having a close texture may be thus readily permea- ted. I found that a little bladder of shellac, blown on the Experiments end of a glass tube, permitted the passage of the vapor aris- ^^^^^ anTii^- ' F^g- 70. ing from water of ammonia. The uids. instantaneousness of these motions is, how- ever, most beautifully illustrated by employ- ing soap-bubbles, the liquid nature of which excludes the idea of pores in the strict accepta- tion of that term. If a bottle, a a, Fig. 70, be rinsed out with ammonia, and then, by means of a piece of glass tube, b b, a soap-bubble, c, be blown therein, the air from the bubble be- ing immediately drawn into the mouth with- out a moment's delay, the strong taste of the • ammonia is perceived. Or if a rod, dipped in hydrochloric acid, be presented to the projecting end of the glass tube, copious white fumes arise. This therefore shows that vapors will pass through barriers having no proper pores, the transit taking place instan- taneously. Soap films enable us to demonstrate the endosmosis of gases in a very advantageous manner, owing to their cohesiveness and thinness. If the finger be dipped in soap-water, and then rapidly passed over the mouth of an empty bottle, so as to leave a horizontal film attached across, on exposing the bottle to carbonic acid gas, the horizontality of the film is immediately disturbed, and it soon swells up into an almost spherical dome. Or if the bottle be filled with carbonic acid, and then exposed Instant m i ^e of gases thiou 'h tilms. 154 PASSAGE OF GASES THROUGH POROUS FILMS. to the air, the fihii is promptlj depressed into a deep concavity, and bursts. By these methods the passage of all kinds of vapors and gases may be demonstrated, oxygen, hydrogen, carbonic acid, protoxide of ni- trogen, the vapors of peppermint, lavender, and various essential oils. By many experiments on such different substances, I found that the .,.^ law of equilibrium for gases and vapors is the same as for Lawof equilib- ^ ° , . , lium, and ex- liquids. No matter what the thickness or thinness of a po- ampies o± it. _^^^^ barrier may be, movement takes place through it, un- til the media on its opposite sides have the same chemical composition. The observed action, in particular cases, will therefore altogether depend on the circumstances under which the experiment is made. A soap-bub- ble full of carbonic acid, exposed to the air in a closed bottle, collapses only to a certain extent, when the percentage constitution of the air it contains is the same as that of the air in the bottle, contaminated with the carbonic acid which the bubble has yielded it. But if the bubble be exposed to the free atmosphere, it collapses almost completely, for now the carbonic acid escapes finally away. One of the most interesting facts connected with these results is the . . ^ , perfect manner in which a film of excessive tenuity will dis- Action through, -i .... lilms of ex- charge these mechanical functions. With a little care, a treme tenuitj. ^j^^^ ^^^ -j^^ obtained SO thin as to be invisible except in certain lights, when it presents a velvety black aspect. In this condi- tion, as Newton has proved, it is not thicker than three eighths of a millionth of an inch, yet endosmosis takes place perfectly through it : it expands and collapses, rises up into a dome, or is depressed into a con- cavity, as the circumstances of its exposure may be. And this should prepare us to admit that in organic tissues of the utmost degree of tenu- ity these physical phenomena may occur, and that even under these most unlikely circumstances such tissues may give origin to mechanical forces of the greatest intensity, as we shall now prove. Graham's law of the diffasion of gases has but a very limited physio- ,. , .,. logical application. The introduction of it in cases to which Inapplicability oxr of Graham's it docs not properly apply has led to several errors. Ihere ^^^'' is nothing common in the result of the movement of gases exposed freely to one another, and exposed with the intervention of a close-pored tissue. The tissue itself gives origin to mechanical force of such intensity as not only to modify the diffusion rate, but, in a great many of the most important cases, absolutely to invert the direction of the motion. Thus, through a stucco plug, in which the pores are of sensible size, atmospheric air passes more rapidly to carbonic acid than carbonic acid does to it, but through the thinnest film of water just the reverse takes place. A bubble full of that acid, exposed to the air, lets it escape with so much rapidity that in a few moments a complete col- FORCE OF PASSAGE THROUGH MEMBRANES. 155 lapse Iiaa occurred. If the law of dilftisioii here held good, the bubble should rapidly distend. Moist membranes and films of water, by reason of their chemical affin- ity for gaseous substances, and their consequent condensing „ . action, become the origin of great mechanical power. Under tion of mem- such conditions, I have seen carbonic acid pass into atmos- ''''^'^^*- pheric air, driven, as it were, by the action of the membrane against a pressure of ten atmospheres, and sulphureted hydrogen against a pres- sure of twenty-five atmospheres, and, even against these great resistances, the passage is accomplished with so much promptness as to lead to the inference that a membrane will cause one gas to diffuse into another, even though the apparent resistance be indefinitely great. Fi(f 71 In J^ig. 71 is given a representation of the arrangement by which these results were obtained. It consists of a strong fa glass tube, seven inches or more in length and half an inch in diameter, hermetically closed at one end, through which a pair of platina wires, b, c, pass into the interior of the tube parallel but not touching. The other end, a a, has a lip or rim turned on it. Between the platina wires, a gauge-tube, d, is dropped, to show the amount of condensation. On the top of the gauge- tube a small test-tube, J", is placed, to contain a reagent suited to the gas under trial, as lime-water for carbonic acid, acetate of lead for sulphureted hydrogen, litmus-water for sulphurous acid. Sometimes, instead of this test-tube, a piece of paper, soaked in the proper reagent, was employed. The Measure of the large tube was then filled with water to the height force of infii- e e. Its lip or rim, a a, being next smeared with burnt India-rubber, to insure absolute freedom from leakage, . a thin sheet of India-rubber was tied tightly over it, and over infiltration, this again, to give strength, a very stout piece of silk. Every thing being thus arranged, the projecting wires, b, c, were connected with a voltaic pile, decomposition of the water ensued, oxygen and hydrogen being disengaged, and a condensed mixture of atmospheric air and those gases accumulated in the space a a e e, the gauge-tube showing the ex- tent to which the condensation had gone. Now if the little tube, y, had been filled previously with lime-water, and the whole arrangement was introduced into a jar of carbonic acid gas, the upper part of the lime- water presently became milky, and after a time a copious precipitate of carbonate of lime subsided. This would readily take place when the gauge was indicating a pressure of ten atmospheres. In like manner, when a piece of paper imbued with carbonate of lead had been introduced into the tube, and a pressure of 24^ atmospheres accumulated, on intro- ducing the instrument into a vessel of sulphureted hydrogen, the paper 156 GENERAL PRINCIPLE OF DIFFUSION. quickly became brown. So sulphureted hydrogen can pass through a sheet of India-rubber and diffuse into an atmosphere of oxygen, hydro- gen, and atmospheric air beyond, though it is resisted by a pressure equal to that of 800 feet of water. The method of condensation here employed, because of its freedom from mechanical concussions, enabled me to continue these researches up to pressures of 50 atmospheres without leakage, in comparatively slender tubes, and even under these circumstances gaseous diffusion seemed to take place without any restraint. It would lead me too far from my present object to pursue the con- sideration of these facts, and I must therefore be content to General facts „, -, ^ ••i-iii t connected with refer the reader to the memoirs m which they have been spe- diftusion. cially discussed.* It is sufficient to understand, 1st. That o-ases simply exposed to each other inter-diffuse with great rapidity, and at a rate inversely proportioned to the square root of their densities ; 2d. That the same takes place through stucco plugs, or diaphragms with open pores ; 3d. That a gas dissolved in a liquid, or held in a condensed state by a solid mass, will exchange by inter-diffusion with any atmosphere to which it may be exposed, in these cases the liquid or the solid mass becoming a source of force ; 4th. That through a liquid, which, of course, has no pores, gases arranged on its opposite sides will diffuse, but their rate is no longer expressed by Graham's law ; 5th. That a liquid hold- ing a gas in solution permits it to diffuse with another gas held by an- other liquid in solution. On the first of these principles, the fresh air of the bronchial tubes ex- changes with the respired air of the pulmonary cells, the case being that of a gas exposed to a gas. On the third of these principles, arterializa- tion of the blood takes place, the case being that of a dissolved gas ex- changing with a free gas ; and on the fifth of these principles, aquatic or o-ill respiration depends, the case being that of a dissolved gas exchang- ing with another dissolved gas. Under its simplest aspect, the act of breathing consists in the elimina- tion of carbonic acid from the system, and the introduction Yarious forms ^ mi • i • i ,i • j. r of respiratory of oxygcn. The manner m which the respiratory surtace mechanism. ^^,^^^ itself fi'om the former, and secures new suppHes of the latter, differs very greatly. In the lower orders which lead an aquatic life, currents are estabhshed in the water by the aid of ciliary motion, and by these the necessary changes are made. In others, in which respira- tion is conducted by the skin, incessant locomotion is relied on ; and again, in others, the w^ater is drawn into the stomach and intestinal canal, and every part bathed with the aerating medium. In insects, the type of carrying air to the blood is developed to the ut- * American Journal of Medical Sciences, May, 1838. KESPIEATION OF INSECTS AND FISHES. 157 most degree, tliere being great numbers of tracheal tubes pervading all the soft parts. These oceasionallj present dilatations, acting as reser- voirs — the foreshadowing of the respiratory cavities of the higher tribes. Of such, Fig. 72, representing the air-sacs or tracheal dilatations of the Fiq 73 Air-sacs of insects. Spiiacle of insect scolia hortorum, is an illustration. The tracheal tubes Respiratioa of communicate with the external air through openings which insects. may be obstructed by a valvular arrangement, as represented in Fig. 73. The photograph from which this figure was taken shows such a spiracle magnified 75 diameters. These organs may be seen arranged jn rows on each side of the body ; thus, in the common caterpillar, there are ten pairs. The mode of guarding the orifice varies in different cases, some- times tufts of hair being resorted to, and sometimes, as in the figure, valves. The true lung is first recognized in the swimming bladder of fishes as a simple sac. In the carp, the tendency to a multi-chambered construc- tion already appears under the form of two such bladders, «, 5, communi- Fig 74 ia||||p tube. These are con- •'P^ neotedwith the oesoph- agus, 0, by means of the pipe c d, the fish being thus enabled to remove at pleasure a part of the air contained in the sacs by muscular compression. Though this mechanism is, as we have said, a mdiment- ary lung, it does not properly subserve the duty of such an organ, but is employed for producing variations in the specific gravity of the animal by compression or rarefaction of the included air. In these Respiration of tribes the gills are the mechanism for aeration, which is ac- ^^hes. eating with each oth- er through a narrow Air-sac of fish. 158 RESPIKATION OF FISHES AND REPTILES. Fiq. 75. complished in the following manner : The mouth is periodically filled with water, which is driven past the gills by muscular compression, and thereby the carbonic acid is removed from the blood which circulates in those organs, and oxygen is obtained in return. For this reason, a fish dies very quickly when its mouth is kept open. The angler knows that it is not owing to any loss of blood, nor to any injurious lesion that the hook may cause, but simply to suffocation, the water no longer lifting the gill covers, but merely passing out through the open mouth. The experiments of Humboldt and Proven9al clearly demonstrate the analogy between aquatic and aerial respirations ; for water is not de- composed by the breathing of fishes : it is the air dissolved in it that is used. In the sample examined by these chemists, there was 20.3 per cent, of its volume of air, consisting of oxygen 29.8, nitrogen 66.2, and carbonic acid 4.0, in the hundred parts. After the fishes had remained in it for a due time, it still contained 17.6 per cent, of its volume of air, but this in 100 parts now consisted of oxygen 2.3, nitrogen 63.9, and carbonic acid 33.8. There had therefore been a consumption of oxygen and evolution of carbonic acid, together with a slight removal of nitrogen, this being the general result witnessed in aerial respiration. In a sim- ilar course of experiments on the breathing of gold fishes, made by myself, the result corresponds to the preceding statement, only the water I used was richer in oxygen gas, and the transposition into carbonic acid did not seem by any means to be so complete. I also remarked the same diminution in the quantity of nitrogen, but am disposed to attribute it not so much to the consumption of that gas by the fishes as to its diffusion from the water into the atmo- sphere, the solvent power having changed by the substitu- tion of carbonic acid for oxygen. In reptiles the lung presents the sac-like form, as in Fig. Respiration of 75, a pulmonary artery passing on one side reptiles. ^-^^ ^ pulmonary vein returning on the other : a is the trachea ; b, its bifurcation ; c, pulmonary artery : d, d, pulmonary vein. It often occurs th3,t the two lungs are not equally developed, one of them, B, being rudiment- ary as compared with the other, A. Into such a sac in ser- pents the air is forced by muscular contraction, a kind of swallowing. It is expelled from them by the contraction of the abdominal muscles, and hence the hissing sound which it emits during its expulsion. From the simple sac to the cellular lung the advance is made by degrees, a de- velopment of parietal cells upon the inner surface taking place. At the intermediate stage, between the simple sac Lung ofTeptue. STRUCTUEE OF THE LUNGS. 159 and tlie liighly subdiA'idecl respiratoiy organ of the mammals, the condi- Fi{i. 76. tion of things is well illustrated by the kmgs of the frog. In J^ig. 76, a is the hyoid appa- ratus ; b, cartilaginous ring at the root of the lungs ; c, the pulmonar}' vessels ; and d, d, the pulmonary sacs. Of all tribes, the respiratory mechanism is most highly developed in birds, Respiration of birds. which, besides being provided with lungs, have air-sacs between the muscles, and respiratory membranes spread on the interior of the hollow bones. It is in consequence of this that a bird is killed so readily, even by a uingsofirog. very small shot, since it is scarcely possible to make a perforation into any part of the body without opening the respi- ratory cavity. In man, the bronchial tube, as it passes into each lung, branches forth like a tree, the walls of the tubelets thus arising having car- . , . ^ , . Lungs of man. tilagmous rnigs to preserve then- form under compression, circular organic muscular fibres to enable them to contract, and longitu- gitudinal fasces of elastic tissue to shorten them after extension. In their interior they are covered with mucous membrane provided witli cilia3. When the proper degTee of minuteness, about -^ of an inch, is reached, they consist alone of elastic membrane, interspersed with mus- cular fibres, and upon their sides the air-cells open ; sometimes single ones, or sometimes many cells communicating with one another, discharge through the same orifice, the tubelet itself ending in a cell. The air- cells have various dimensions, fi'om -J^ to y^g-o- of an inch. Their struc- ture is like that of the tubelet. The pulmonary capillaries are spread so closely upon them that the spaces between them are less than their own diameters, which, on an average, are g-oVo ^^ ^^^ inch. As the cells are close together, the blood-vessels passing between them are brought in communication with the air on both sides, and arterialization is thus rapidly and completely performed. Each tubelet, with the air-cells thus clustered upon it, is a miniature representation of the lung of a reptile. These cells themselves communicate by lateral apertures with one an- other. The membrane which lines their interior is sharply folded at the apertures, and there are reasons for supposing that it contains organic muscular fibres. It is stated that each terminal bronchus has nearly 20,000 air-cells clustered upon it, and that the total number is 600 millions. The mode of distribution of the air-tubes is represented in J^ig. 77. a is the larynx ; b b, the trachea, the upper letter corresponding to the 160 STEUCTUEE OF THE LUNGS. cricoid cartilage ; c, the left bronchus ; tZ, the right bronchus ; e, /, g, its ramifications in the right lung, j/^'/ h, i, ramifications of the left bron- chus in the left lung, k k. Fig. 11. Human air-tubes. The heart and lungs. Fig. 78, arrangement of the heart and lungs, the latter in part section. 1, left auricle of the heart ; 2, right auricle ; 3, left ventricle ; 4, right ventricle ; 5, pulmonary artery ; 6, aorta ; 7, superior vena cava ; 8, in- nominata; 9, left primitive carotid; 10, left subclavian, ; 11, 12, upper rings of trachea and cartilages of the larynx; 13, upper lobe of right lung; 14, upper lobe of left lung; 15, right pulmonary artery; 16, 16, lower lobes of lungs. Fig. T9. Jf'ig^ 79 illustrates the manner of distribution of blood-vessels on the air-cells of the lungs. As the blood to be arterialized passes through the pulmonary capil- laries, its discs can only move in sin- gle files, and even then probably un- dergo a compression which changes their form. As soon, however, as they escape into the larger vessels, their elasticity enables them to recov- Distribution of capillaries on air-cells of the lungs, ov +lipiv orio'ilial slianc By the aid of this elaborately constructed mechanism the air is brought Three stages in the introduc- tion of air. to the blood. There are three distinct stages through which The first is the filling of the trachea and it has to pass larger ramifications of the bronchial tubes : this is accom plished by atmospheric pressure, brought into play by muscular contrac- MOVEMENTS OF RESPIRATION. 161 tion. The second stage is the transhxtion of the fresh air from the larger bronchial tubes to the ultimate air-cells : this is accomplished on the principle of gaseous diffusion. The third stage is the passage from the air-cells into the blood : this is through the wall of the cell, the wall of the blood-vessel, and the sac of the blood disc ; it involves passage through membranes, and implies their condensing action. Each of these three stages we have now to consider. 1st. The introduction of fresh air into the trachea and larger ramifi- cations of the bronchial tubes is accomplished by muscular ^, ^ t f th • contraction, which calls into operation atmospheric pressure, pressure of the In tranquil respiration the diaphragm is nearly sufficient for this purpose. This muscle, forming the convex floor of the chest, as soon as it contracts, assumes more nearly a plane figure, thereby increasing the content of that cavity ; and, just as in a common bellows, when the lower board is depressed, the air flows in through the pipe, so, on the de- scent of the diaphragm, the air flows in through the trachea, forced by the external pressure. An experimental illustration of the manner in which the air is introduced into the cavity of the lungs by the descent of the floor of the chest, and then expelled by its elevation, is represented in Fig. 80, in which « « is a tube of glass half an inch or more in diameter, and six or eight inches long, to the lower end of which a blad- der, ^, is tightly attached. The tube is passed through the neck of a bell-jar, c c, air tight. A large glass reservoir of water, filled to the height d d, receives the bell-jar, as shown in the figure. When the jar is depressed in the water the air is expelled from the bladder, and when the jar is raised the air flows in. By alternately ele- vating and depressing the bell, the bladder exe- cutes movements like those of the lungs, of which, indeed, it is a representation; the glass tube be- ing the trachea, the bell-jar the walls of the chest, and the rising and falling water-level the rising In this illustration the bladder is, of course, per- fectly passive, as was at one time supposed to be the case with the lungs : an erroneous opinion, which will presently be corrected. In the mature period of life, and especially in deep respiration, the ac- tion of the diaphragm is insufficient for the introduction of air, jj^^j^g^ of in- and a still farther volume is obtained by raising the ribs, which troducing the increases the dimensions of the chest from right to left, and I. im of respiration. and falling diaphragm. 162 MOVEMENTS OF EESPIRATION. also from front to back. In men, this effect takes place more particular- ly through the movements of the lower ribs, and this form of respiration is therefore sometimes called the inferior-costal ; but in women the upper ribs are more movable, the dilatation of the chest is there greater, and the respiration therefore designated as the superior- costal. In these movements of the ribs, and especially in violent respiration, many mus- cles are involved. In the reverse act, that is, in expiration, or the expulsion of air through the trachea, the floor of the chest is raised. The diaphragm, when it contracted, made pressure upon the viscera of the abdomen, and forced the muscular walls of that cavity outward ; but, as soon as the diaphragm relaxes, the abdominal muscles contract, and thus an antagonizing force is originated which tends to expel the air. In this the elasticity of the lungs and of the walls of the thorax itself affords a great assistance. Owing to this elasticity, the muscular exertion required for the introduc- tion of the air greatly exceeds that required for its expulsion. In tranquil respiration, we may regard the changing of the air to be accomplished by the alternate depression and elevation of the diaphrag- matic floor of the chest. On an average, this takes place 17 times in a minute, and in an adult of the standard size we may assume that 17 cubic inches of air are introduced at each inspiration. Every fifth breath is usually deeper than the preceding four. The statement often made, that five pulsations correspond to one respiration, must be received with a certain restriction. In pneumonia, the respirations may be to the pul- sations as 1 to 2 ; in typhoid fevers, as 1 to 8 ; and even in a state of health there may be considerable variations. By muscular movements, which thus call into action atmospheric pres- sure, the air is drawn, but not forced, into the respiratory apparatus. Considering, however, the solid contents of the lungs, which can not be taken at less than 200 cubic inches, it is clear that the amount is not more than sufficient to fill the nasal passages, the trachea, and the larger ramifications of the bronchial tubes. Lying nearest to the outlet, it would be the first to be expelled by the act of expiration. There could be no exchange of the fresh for the foul air, unless some additional means were employed for accomplishing its transference from the larger ramifi- cations of the bronchial tubes to the remotest air-cells. 2d. The transference of fresh air to the cells is accomplished by re- sorting to two different principles, the diffusion of free gases into one an- other, and muscular contraction. An estimate of the relative share which each of these takes is arrived effect of gase- at by an examination of the absolute velocity with which ous diffusion._ p.^ges diffuse into one another. The statement that gases use of organic o o muscle fibres, act as vacua to each other has led to some very erroneous PASSAGE OF OXYGEN TO THE BLOOD. 163 conclusions. It has been taken for granted that the actual diffusion is very rapid, perhaps approacliing to the velocity with which gases rush into a void. But I have shown* that this is altogether a misconception, and that the transit of fresh air from the bronchi, exchanging with foul air from the cells, if conducted on that principle alone, would require a period greatly beyond the time occupied for one respiratory act, which is about three seconds and a half. To an additional agent we must therefore look for a complete explana- tion, and this, I think, is presented in the circular organic fibres of the bronchial tubes and cells. It has long been understood that these pos- sess the power of varying the capacity of the tubes. With this agency in view, this second stage of the process is accom- plished as follows : The carbonic acid, vapor of water, and excess of ni- trogen, if any, that have accumulated in the cells belonging to any given bronchial tree, are expelled therefrom by the muscular contraction of the circular organic fibres, and are delivered into the larger bronchial tubes, in which diffusion at once takes place with the air just introduced. As soon as the expiration is completed, relaxation of the muscular fibres oc- curs, and the passages and cells dilating, both through their own elastic- ity and the exhaustive effect arising from the simultaneous contraction of other bronchial trees, fresh air is drawn into them, the alternate expulsion and introduction being accomplished by muscular contraction and elas- ticity, the different bronchial trees coming into action at different periods of time, some being contracting while others are dilating. 3d. The third stage is the passage of oxygen fi-om the cells to the blood: it is through the wall of the cell, the wall of the blood-vessel, Passage of ox- and the sac of the blood disc. The carbonic acid issues from ^he^^em^branes the plasma, and passes through the wall of the blood-vessel to the blood. and the wall of the cell. ]\Iany physiologists have supposed that this exchange of oxygen for carbonic acid takes place on the principle of diffusion. On -^^^j^ n e of the authority of Valentin and Brunner, it has been asserted carbonic acid that the proportional exchange actually observed is 1174 of °^°^ys^°- oxygen for 1000 of carbonic acid, these being the theoretical quantities under the law of diffusion ; but there is no difficulty in proving that this is a physical impossibility, for the exchange is not merely that of oxy- gen and carbonic acid ; it is much more complicated. The lungs regu- late the quantity of free nitrogen in the system, and there is a constant escape of the vapor of water. These bodies, moreover, are not present- ed in the gaseous state, but in that of liquid solution ; and the wall of the cell, of the pulmonary capillary, and of the blood disc, by their con- densing action, totally disturb the conditions of diffusion. * American Journal of Med. Sciences, April, 1852. 164 ESCAPE OF CARBONIC ACID FROM THE BLOOD. If an aqueous film, not more than three eighths of a millionth of an inch in thickness, can completely disturb the law of diffusion by the condens- ing action it exerts on carbonic acid and oxygen, what may be expected from the moist walls of the air-cells and pulmonary artery, which con- jointly must be more than a thousand times as thick ? From these complications, it is not possible to assign any definite ratio as expressing the gaseous exchange between the interior of the cells and the blood, for, so far from this being a case, of exchange between two gas- es without any obstruction intervening, the condition under which alone the law of diffusion applies, the nitrogen is doubtless in a state of solu- tion in the blood, the steam in the liquid condition of water ; and re- specting the carbonic acid, nothing certain is known whether it be in so- lution or chemically combined. Perhaps it is united with soda in the blood as a bi-carbonate. From this latter substance hydrogen gas will expel one half of its carbonic acid, and in like manner a stream of hy- drogen gas passed through blood deprived of its fibrin removes carbonic acid. Upon such principles it has been supposed that atmospheric oxy- gen removes carbonic acid from the blood during respiration, just as w^ould a stream of hydrogen renjove half the acid from a solution of bi-carbon- ate of soda. The generation of carbonic acid in the system is commonly localized by referring it to the soft tissues. But, though doubtless riace of the ■/ ... . . generation of much originates in this way, as is illustrated by the case of carbonic aci . jj^gg^^g^ [-^ which the air is carried directly to the parenchyma of the organs without the intervention of any proper oxidizing blood, there can be no doubt that in man, as in all the higher tribes, a very large proportion is generated in the blood itself. If there were no other reason to bring us to this conclusion, it would be sufficient to recall that ultimate oxidation by no .means occurs at once, but that the various wasted products pass from stage to stage in their retrograde career. Thus, between the syntonin of muscular fibre and the urea of the urine, many steps or stages intervene, and that much of these changes is ac- complished in the blood itself is demonstrated by what occurs in the use of excesses of starch, albumen, or gelatine in the food. Such sub- stances, finding access through the absorbents in a modified form, but not wanted for the repair of any part, are dismissed without ever entering into the composition of any organ, by the lungs or the kidneys as prod- ucts of oxidation or derivatives thereof. The act of respiration in man is therefore accomplished in the follow- General state- ing way. The air, introduced by atmospheric pressure, n-ocesf of^res- brought into play by the action of the diaphragm and other piration. respiratory muscles, fills the nasal passages, the trachea, and larger ramifications of the bronchial tubes. Between it and the gas GENERAL STATEMENT OF THE RESPIRATORY ACT. 165 coming from the pulmonary vesicles, diffusion steadily takes place, tend- ing to remove the cell gas into the atmosphere ; but this gas is noi brought from the vesicles by diffusion alone, which could not act with sufficient speed, but by the contraction of the circular organic muscles of the bronchial tubelets and of the cells, the different bronchial trees not acting simultaneously, but successively. As soon as contraction is over, the tubes expand by their elasticity, and the air is drawn into the cells, each bronchial tree, by its contraction, aiding the expansion of the adja- cent ones. The lungs are therefore not altogether passive during respi- ration, as is sometimes said. The exchange between the gas in the cells and that in the blood does not take place through simple diffusion, or in quantities proportional to the diffusion volumes of oxygen and carbonic acid. It is a complex diffusion, in which the disturbances arise from the gases in the blood being either dissolved or combined, and through sev- eral intervening membranes, that of the air-cells, that of the pulmonary artery, and that of the blood disc, all of which exert a condensing action, of the result of which it is impossible to furnish any numerical estimate. The process ends by the expulsion of the foul air which hks accumulated in the larger bronchi and trachea, by the diminution which takes place in the capacity of the chest during expiration, occasioned by the contrac- tion of the expiratory muscles, the elasticity of the walls of the chest, and of the lungs themselves. Such is the arrangement by which fresh air is constantly presented to the blood, and the gases and vapors exhaling from it are removed. The degree of exhaustion occurring in the chest scarcely justifies the ex- pression sometimes used, "a tendency to a vacuum," since it is rarely more than competent to raise water a single inch. This may be readily proved by dipping a glass tube, open at both ends, and half an inch in diameter, into a cup of water, and placing the projecting extremity be- tween the lips, taking care to keep the muscles of the mouth at complete rest. It will then be seen that at each inspiration the water rises about an inch, and at each expiration is depressed to a similar extent. Its movements indicate the degree of rarefaction or compression occumng in the chest. It has been found convenient to consider the gaseous contents of the lungs under several different titles : 1st. The residual air is Divisions of that portion which can not be removed by the most power- contenrof^the ful expiration ; 2d. The supplemental air remains after tran- lungs. quil respiration, but can be removed at will ; 3d. The breathing or tidal air is that portion which changes by tranquil inspiration and expiration ; 4th. The complemental air is that which can be inhaled by the deepest inspiration, over and above that introduced by ordinary breathing. These are terms introduced by Mr. Jeffreys. 166 VOLUME AND CHANGES OF THE GAS. " The amount of air that can be expelled by the deepest expiration Connection be- after the fullest inspiration" bears a singular relation to the S^and ^''^^" height of the individual, as was discovered by Dr. Hutch- height, inson. " For every inch of stature from five to six feet, eight additional cubic inches of air at 60° Fahr. may be thus given out." The quantity of air which can be thus expelled for the stature of five feet one inch is 174 cubic inches, and for six feet, 262. It is independent of the absolute capacity of the chest. The diurnal amount of air introduced into the lungs has been variously ,. , , estimated from 226 to 399 cubic feet. A part, from 4 to 6 V olume and _ . . changes of the per Cent., of the oxygen thus introduced disappears in the respire gas. j^j^gg^ ^nd the expired air is charged with from 3 to 5 per cent, of carbonic acid. But that nothing analogous to combustion occurs in those organs is proved by their temperatiu'e, which is not higher than that of other parts of the system. Moreover, carbonic acid can be with- drawn from venous blood in a Torricellian vacuum, and still better by agitating the blood with such gases as hydrogen and nitrogen, proving that that gas pre-exists in the venous blood before its entry into the lungs, and is not formed in those organs, unless, indeed, it exists as a bi- carbonate, as already mentioned. The quantity of carbonic acid thus disengaged is less than the quantity of oxygen absorbed, because much of the latter is consumed in the production of sulphuric and phosphoric acids, which escape in the urinary secretion, as indeed does a large quan- tity of carbonic acid itself. The experiments of Vierordt show that the expiration, in a state of Vlerordt's Tcst, Contains 4.334 per cent, of carbonic acid; that, as the experiments, number of respirations per minute increases, the percentage amount of carbonic acid diminishes ; and that for every expiration, with- out reference to its duration, there is a constant amount of carbonic acid, namely, 2.5 per cent., to which we must add a second value, expressing the quantity of carbonic acid, and which is exactly proportional to the duration of the respiration, as is shown in the following table. Respirations per minute. Percentage of carbonic acid. Constants. Augmentation of tlie percentage of the carbonic acid for the duration of the respiration. 6 12 24 48 96 5.7 4.1 3.3 2.9 2.7 2.5 2.5 2.5 2.5 2.5 3.2 1.6 0.8 0.4 0.2 Vierordt also estimates that, for the entire removal of the carbonic acid from the blood, more than three hundred respiratory acts per minute would be required. To some extent, the depth of the respiration will compensate for want of frequency. Thus he shows that in an expiration of double the usual volume, the quantity of carbonic acid removed is EATIO OF INSPIRED AND EXPIRED OXYGEN. 167 nearly equal to that wliicli would be exhaled by respirations of three times the normal frequency, and on examining a single respiration, he demonstrates what, however, would obviously be foreseen from a consid- eration of the circumstances of the case, that the last portions of the ex- piration are the richest in carbonic acid. Thus the first half of a respi- ration contained only 3.72 per cent, of carbonic acid, the last half 5.44 per cent. With respect to the ratio between the quantity of oxygen inspired and that contained in the expired carbonic acid, a variation will ^ ^. ^ , . ^ _ , ' Ratio of the in- be observed, depending on many conditions, as, for example, spired and ex- on the nature of the food. Thus, with a carbohydrate, the P""^*^ o-^3'sen- quantity of oxygen in the carbonic acid will always be less than that in- spired, a portion being employed in the destruction of the systemic nitro- genized material w^hich is undergoing decay. This destruction of nitro- genized material is not sufficient for the support of animal heat, and hence either carbohydrates introduced by the food, or fat already exist- ing in the system, must be resorted to for the purpose of making up the deficiency. With such variations in the requirements of the system, and variations in the nature of the food, the ratio of the oxygen intro- duced to that in the carbonic acid removed must also vary. For the perfect oxidation of the different elements of food, very differ- ent quantities of oxygen are required ; thus, for the oxidation of 100 parts of fat, it would require 292. 14 of oxygen ; for that of starch, 1 1 8. 52 ; for that of muscle, 147.04. For reasons to be considered when we treat of the production of heat, the quantity of carbonic acid disengaged varies with external ^r ■ .- ^ •' ... Variations m circumstances. When the weather is cold it is greater than the respired when it is warm. Thus at 68° there is twice as much lib- ^^^" erated as at 106°. It increases during exercise and after eating, but diminishes during sleep. More is set free by men than by women ; it also varies with age, the proportion rising from eight years to thirty, re- maining stationary to forty, and then declining. It changes with the frequency of the respirations. The total quantity of carbon daily re- moved by respiration may be estimated at eight ounces. Besides the carbonic acid removed, a large quantity of water is ex- creted by the lungs, for the expired air may be regarded as water removed saturated, or containing the maximum quantity of water for ^^ respiration. 94°. For the vaporization of this water much heat is consumed, as is likewise the case for the warming of the introduced air, which, no mat- ter what the external temperature may have been, is brought to that of the lungs. With respect to the absolute amount of air expired, and also the quan- tity of water removed by the lungs, some experiments have recently been 168 QUANTITY OF AIE AND WATER. made by my son, Dr. J. C. Draper ; the principle upon.wliicli tlicy Avere n .-. r ■ conducted may be thus briefly stated. The air from the Quantity of air ^ -J _ •' expiredper lungs, which has a dew-point of 94°, was passed by a wide mmute. tube through a metaUic condenser kept at 32°, care being taken to have as little obstruction as possible to its egress. The weight of the water collected in the condenser furnished the means of calculating, by a simple formula, the quantity of air which had been expired, for the vapor, leaving the respiratory passages at 94°, and that lea^ang the con- denser at 32°, were at their maximum densities. Computations exe- cuted upon data obtained on this principle furnish the following, among other interesting results : 1. On making sixteen respirations in the minute, and continuing the experiment for twenty minutes, the average of five different series of ex- periments gives 622 cubic inches of air expired each minute. 2. On making six respirations in a minute, and continuing the trial for twenty minutes, the average of three series of experiments gives 511 cubic inches for the air expired each mmute. 3. On making thirty-three respirations in a minute, and continuing the experiment for twenty minutes, the average amount of air is 1077 cubic inches for the air expired in each minute. On comparing these three statements, it appears that, the first repre- senting normal, the second very slow, the third very quick respiration, the absolute amount of air removed from the lungs is directly proportion- al to the number of respiratory acts in a given period of time, and this notwithstanding such variations in the depth of the inspirations as un- der such circumstances are likely to occur. With respect to the quantity of water removed from the huigs, he also shows, 4. That, at an atmospheric temperatm-e of 55°, the dew- Qnantitvofwa- -r^ i n ,- • • • • j. ter exhaled per point bemg49°, the number ot expn-ations sixteen per mmute, minute. ^-^q quantity of water removed per minute is 4.416 gTains. 5. The other conditions remaining the same, but the respirations re- duced to six per minute, the amount of water removed per minute is 3.586 grains. 6. The other conditions remaining as before, but the number of res- pirations increased to thirty-three per minute, the amount of water re- moved per minute is 7.560 grains. From these statements it therefore appears that the quantity of water removed from the blood by respiration increases with the frequency of the respiratory acts, and this notwithstanding variations which, under such circumstances, must take place in their depth. Theoretically, it is also obvious that the absolute amount thus expired is dependent on the existing dew-point of the air. In the general table, given on page 15, EFFECT OF RESPIRATION ON THE BLOOD. 169 the amount of water is calculated from Seguiirs experiments, but it ap- pears from these results, which are obtained by a much more accurate process, that the number there given is undoubtedly too high. The thne of exposure of the blood to the air is only a second or two. The color changes, as has been described before, from blue to crimson, and the temperature rises a degree or two, as is shown by an examina- tion of the left cavities of the heart. The water thus removed is not pure, but contains animal matter in a state of decay. Though we have treated of the act of respiration as consisting of two separate and consecutive stages, inspiration and expiration, Respiration is T,., T ,• 1 Axj.1 'x continuous and m reality it proceeds contmuousiy. At the respn-atory sur- ^^^^ reciprocat- face, wdiich is the w^all of the air-cell, the passage of oxygen ing. inward, and of carbonic acid and steam outward, takes place in a steady and unvarying manner. The periodicity under which it has been conven- ient to speak of this function concerns only the introduction and removal of gases from the large air-ways. Considering, therefore, the continuous loss of water which the venous blood brought by the pulmonary arterial branches undergoes, Effect of respi- it must give rise necessarily to a greater density in the blood ^ensity°of the on the left side as compared with that of the right side of blood, the heart. The total quantity of blood passing through the lungs in one minute is 225 ounces, and the loss of water from this in the same time can not be more than 7 grains. This, therefore, shows that the actual loss of water by the blood during its passage over the air-cells is about ^ part, a quantity which is altogether inappreciable, so far as its in- fluence on the specific gravity is concerned, and showing us that the ob- servations which some experimenters have made on this point, with a view of demonstrating an increased spissitude, density, or cohesiveness of the blood on the left side of the heart, from the giving up of its water as it passed through the respiratory organ, are either exaggerated or ef- fected by some deceptive cause. The introduction of an irrespirable gas into the lungs, or the prevention of the access of the atmosphere, brings the circulation of the Effect of the in- blood to a stop ; for that movement depends, as I have shown, [rreJJ)fraMe°*' on the aeration taking place in the pulmonary capillaries. In gases. such cases there will be an engorgement of the right heart and vessels arising therefrom, but, if the stoppage has not lasted too long, the current may be re-established by re-establishing the respiration. Death com- monly ensues on an exclusion of the air for five minutes, and, in cases of drowning, it is rare for restoration to be effected if the immersion has lasted more than four. In the respiration of protoxide of nitrogen, a gas which is an energetic supporter of combustion, and acting more powerfully on the animal sys- 170 EXPEEIMENTS OF EEGNAULT AND EEISET. tem when respired than even oxygen itself, on account of its oxide of iiitro- ready condensibility by pressure, or by membranes, and sol- ^'^^' ubility in water, the circulation is greatly quickened at first, and a state of exhilaration ensues ; but this is soon followed by a con- dition of depression, or even of coma, for the quantity of carbonic acid produced in the system is now so great that the lungs are wholly inade- quate to effect its removal, and all the symptoms of poisoning by car- bonic acid come on. Zimmerman found that a rabbit exhaled 12^ grains of carbonic acid per hour when breathing atmospheric air, but that the quantity rose at once to 20 grains per hour when it was caused to breathe protoxide of nitrogen. But by far the most complete and important series of experi- Summary of Hients yet made in regard to the relations of the aerial me- Regnauit's and dium and the respiring animal is that of MM. Regnault and iments^on^res- Reisct, published in the Annales de Chimie, Juillet, 1849, of piration. which, since it may be taken as a model of physiological in- A'estigation, a brief abstract is here given. F»v^ si. The apparatus they employed is represented in J^iff. 81. It possesses the great advantage over all experimental arrange- ments heretofore employ- ed in permitting an ani- mal to be kept even for many days in a limited volume of air, but under such circumstances that iLxperiments on iv-spiration. that air WaS COnstautly kept at its normal composition by the automatic motions of the instru- ment itself: oxygen being thus furnished as it was required, and car- bonic acid removed. The arrangement consists of three parts : 1st, a chamber or bell, I, for inclosing the animal, surrounded by a jar filled with water, the tempera- ture of which could be ascertained by a thermometer, k. In the interior of the bell was a platform perforated with holes, by the aid of which the excretions could be collected. On one side, at^, was a pressure gauge, connected with the bell by a tube, and showing the condition of conden- sation or rarefaction of the included atmosphere. 2d. At the same side, the bell communicated, by means of India-rubber tubes, m, n, with two cylindric vessels, q, r, filled with a solution of caustic potassa, and which were driven by the aid of powerful clock-work in such a way that the one alternately rose and the other descended, the flexible tube s permit- EXPERIMENTS OF RECINAIILT AND EEISET. 171 ting this motion. The result of this was that a portion of the air of the bell was alternately drawn into each of the cylindric vessels, its carbon- ic acid removed by the potash, and then it was returned ; so, as fast as the animal produced that gas by breathing, the potash removed it, giving rise, therefore, to a tendency to a certain amount of rarefaction in the air of the bell ; but, 3d, on the opposite side of the bell were placed three receptacles, e, e\ e'\ filled Avith pure oxygen gas, which flowed into the bell through the tubes fh^ f^h, f'^h, to compensate for that rarefaction, coming in by a bubble at a time through the little potash flask i, the oxygen being pressed out of the reservoirs by a solution of chloride of calcium descending through a stop-cock, c, from a reservoir, b h\ kept at a constant level in the usual manner by the flasks a, a'^ a'\ As fast as one receptacle was exhausted, the pressure tube was successively con- nected with the others, and so the supply kept up. Attached to the stand supporting the animal was a eudiometer, o, which enabled a small quantity of air to be withdrawn from the bell at any moment for the purpose of analytical examination. For other details of this apparatus, and the particulars of its method of use, reference may be made to the original memoir itself. It is sufficient for the present purpose to under- stand that an animal could be kept in the interior of this bell for several days without showing any signs of discomfort, pure oxygen being sup- plied to it, and the carbonic acid produced by breathing removed by the play of the machine itself. The following is an abstract of the results obtained : 1st. Hot-blooded animals, mammifers and birds, under their ordinary- diet, always disengage a little nitrogen by respiration, the ^i ih\ d d amount varying from less than ^oo" *o -^-^ of the weight of animals on an .1 rv ordinary diet. tne oxygen they consume. ■' 2d. When these animals are fasting, they often absorb nitrogen in pro- portions similar to the preceding. In like manner, an absorp- The same tion of nitrogen was observed after starving the animal, and then fasting, submitting him to a diet very diflerent from his ordinary one, and also during sickness. 3d. The ratio between the quantity of oxygen contained in the car- bonic acid and the quantity consumed depends more on the ^ „ „ i- J t Influence of nature of the food than the -class to which the animal be- food and fast- longs, being, when the animals are starving, the same as it is ^"^" when they are fed upon meat, or perhaps a trifle less. From this the interesting conclusion may be drawn that a starving animal furnishes to the air of respiration his own substance, which is of course of the same nature as the flesh he eats when dieted on meat. All hot-blooded ani- mals present, when they are starving, the respiration of carnivora. The ratio for the same animal varies from 0.62 to 1.04, according to the na- ture of the diet. 172 EXPEEIMENTS OF REGNAULT AND EEISET. 4th. In fowls, submitted to their usual diet of grain, there is often Respiration niore oxygen in the carbonic acid disengaged than was furnished "^ birds. jj^ -j^j^Q j^^ ]jj respiration. The surplus of course comes from the food. 5th. The quantity of oxygen consumed in a given time varies with , a c "the state of dio-estion, motion, and other circumstances. Cora- influence of O ' ' ^ motion, age, pared together, the consumption is greater among the young than among adults, greater among those that are lean but in good health than among those that are fat. 6th. If we take an equal weight of the animals under examination, the Influence of quantity of oxvgen varies much with their absolute size ; the size of ani- thus it is ten timcs greater among little birds, such as spar- rows and green-finches, than among common fowls. This is owing to the fact that, since these different species have the same tem- perature, and the little ones present relatively a greater siu-face to the ambient air, they must consume relatively more oxygen to keep up their heat to the standard degree. 7th. Hibernating animals, such as marmots, when perfectly awake, ex- ■D ■ ,- e hibit no peculiarity, but when fast asleep often absorb nitro- Kespiration of . . . hibernating gen. The ratio of the oxygen contained in the carbonic acid anima s. ^^ ^|^^^ inspired is very low, scarcely amounting to 0.4, the missing oxygen escaping in the compounds of the urinary secretion : but since this removal takes place only periodically, the sleeping marmot exhibits the remarkable phenomenon of increasing in weight by respira- tion alone. 8th. The consumption of oxygen hy sleeping marmots is very small, scarcely -^^ of what they require when awake. At the moment they awaken from their lethargy, their respiration becomes extremely active, and during the period of their awakening they consume much more oxy- gen than when they are completely awake. Their temperature rises rap- idly, and their members gradually lose their stiffened state. While tor- pid they can remain without difficulty in an atmosphere which would suffocate them in a few moments if awake. 9th. Cold-blooded animals, for an equal weight, consume much less Res iration of oxygen than hot-blooded. Frogs with their lungs cut out cold-blooded continue to breathe with nearly the same acti^dty as before, animas. often living for several days, the proportions of the gases absorbed and disengaged differing little from what is observed in the case of uninjured frogs. This shows that their respiration can be con- ducted by the skin. The respiration of earthworms is the same as that of frogs, as regards the quantity of oxygen consumed, when they are com- pared under equal weight. 10th. The respiration of insects, such as May-bugs and silk- worms, NERVES OF RESPIRATION. 173 is much more active tlian that of reptiles. Under an equal Respiration of weight they consume nearly as much oxygen as mammalia : '"sects. the comparative lowness of their temperature is due to the relativelv great surface and moist exterior they present to the air. It is to be re- marked tliat we are here comparing the respiration of insects with that of mannnalia whose weights may he from 2000 to 10,000 times as great. 11th. The respiration of animals of different classes, in an air con- taining two or three times as much oxygen as the atmos- Effect of in- phere, does not diifer from existino; respiration : indeed, the *='"^^*"'& ^}}'^ . 1 -, -IT amount of ox- animals do not appear to perceive that they are in a medium ygen. different from the ordinary atmosphere. 12th. The respiration of animals in a medium in which, for the most part, hydrogen replaces the nitrogen of our atmosphere, scarcely differs from existing respiration ; only there is remarked a greater consumption of oxygen, due perhaps to the necessity of compensating for the increased cooling arising from the contact of hydrogen gas. The introduction of air into the system is, to a certain extent, auto- matic, and, to a certain extent, dependent on the will. In tranquil res- piration we are wholly unconscious of the motion ; the ex- ^^ ^ . . . . . , Nerves in- citing impression is made on the pneumogastrie nerves, and, voived in res- being conveyed to the respiratory ganglion, the medulla ob- P^'''^^'°'^- longata, is there so reflected that through the agency of the phrenic nerve motion takes place in the diaphragm. The automatic, and therefore un- conscious movement, to a certain extent, occurs in that way. But there is no doubt that the brain also participates in the function. No other evidence of this is required than that we can "hold the breath," and the relative share that the voluntary and automatic mechanisms take is illus- trated by the circumstance that this holding of the breath can only be persisted in for a certain time, when the necessity for respiring becomes altogether uncontrollable. It is not, however, to be supposed that so important a condition as that of the introduction of the air is only slenderly provided for. Many other nerves, besides those mentioned, take part in it directly or indi- rectly ; the iifth pair, the nerves of the general surface, and also the great sympathetic, the intercostals, the spinal accessory, which probably gives its motor property to the pneumogastrie. Opinion has differed respect- ing the cause which produces the necessary impression on the receiving- nerves, some referring it to the presence of venous blood in the capilla- ries of the lungs, and some to the carbonic acid in the cells. Moreover, there is reason to believe that the presence of an abnormal amount of venous blood in the respiratory ganglions will of itself give rise to res- piratory movements through the proper centrifugal nerves. 174 RESULTS OF RESPIRATION. The control possessed hj the will over the introduction of air stands Respiration in a close relation to the production of articulate or other tary and°part- sounds, and therefore to intercommunication between indi- ly automatic, viduals hj speech. This involves not merely a general con- trol alone, but also a particular one, which is reached by regulating the movements of the glottis by the agency of the superior and inferior laryn- geal nerves. But though the will for these important purposes exercises so marked a power of regiilation, it is to be looked upon as superadded or incidental, and during sleep, coma, and that larger portion of life which is spent in total inattention to the carrying on of this function, it is dis- charged in a purely automatic way. The mechanism which accomplishes the surprising results of respira- Resuits of res- tion may therefore Avell challenge our admiration. As a piration. self-acting or automatic contrivance, over which we have not a necessary control, it originates in a single year nearly nine millions of separate motions of breathing. It never fatigues us ; indeed, we are never conscious of its action. In the same time, a hundred thousand cubic feet of air have been introduced and expelled, and more than thir- ty-five hundred tons of blood have been aerated. In a future page wc shall have to present the wonderful mechanism by which aerial currents, as they pass in and out of the respiratory apparatus, are incidentally em- ployed as a means of producing musical notes or articulate sounds, and of thus establishing a relation and communication between different in- dividuals. By these the feelings and thoughts are diffused, and in a mechanical origin commence those bonds which hold society together. ANIMAL HEAT. 175 CHAPTER X. OF ANIMAL HEAT. Participation of Organic Forms in external Variations of Temperature. — Mechanisv^ for counter- balancing these Variations. — Development of Heat in Plants at Germination and Injiorescenct. — Its Caxise is Oxidation. — Connection of Respiration and Heat. — Temperature of Man. — His Power of Resistance. — The diwnal Variations of Heat. — Connection of these Variations with organic Periodicities. — Annual Variations of Heat. — Control over them by Food, Clothing, and Shelter. — Source of Animal Heat. — Effect of Variations in the Food and in the respired Me- dium, both as respects its Natwe and Rarefaction. — Hybernation. — Starvation. — Artificial Re- duction of Temperature by Blood-letting. — Principles of Reduction of Temperature. — Radich tion. — Contact. — Evaporation. — Their Balance with the Heating Processes. — Local Varia- tions eliminated by the Circulation. — Control by the Nervous System. — Its physical Nature. — AUotropism of Organic Bodies. Owing to the earth's diurnal rotation on its axis, and its annual move- ment of translation round the sun in an orbit inclined to the ^- . ,. V ariations of equator, variations of temperature arise, the vicissitudes of external tem- summer and winter, day and night. perature. In these variations all objects upon the surface of the planet partici- pate ; organic forms are no exception. As the heat of the medium in which they live ascends or descends, theirs follows it at a rate depend- ent on their conductibility. Like mineral substances, the more lowly forms of life submit to these changes. They have no provision for check or compensation. Organic forms In summer, the temperature of the stem of a tree rises with- ^^65^^13,-'^ out any restraint ; in winter it decKnes ; and, should the tions. point be reached at whicli those nutritive changes that give motion to the sap cease, nothing is done to arrest the descent, and the whole organism passes into a state of torpor, hybernation, or temporary death. Now, since this following of atmospheric temperatures must take place in every organism as well as in every mineral body, the con- Compensating struction of one having a uniform mode of existence in all onhe^hiffhw climates and all seasons implies a resort to some subsidiary tribes. mechanism, which, though it may not check, may yet compensate for these vicissitudes. Accordingly, so nearly is this equalization accom- plished in the highly-developed tribes, and a standard temperature so nearly attained for them, that many physiologists, misled by imperfect observations, have concluded that such living beings are emancipated by nature from the operation of physical laws : an erroneous conclusion, for in them that action is only concealed. 176 THE HEAT OF PLANTS. In different races, the nieclianism by which these variations of atmos- pheric temperature are balanced acts with different degrees of perfection. ^ „ , , On this a subdivision has been founded, and animals classi- Cold and hot blooded ani- tied as the cold and hot blooded. We are not, however, to ™^^^' attach much importance to such an arrangement : it is rather imaginary than founded on any real distinction. In man, the tempera- ture is near 100° ; in fishes, it is about that of the water in which they live. Insects, in their larva and puj)a condition, are cold-blooded; in their perfect condition, hot. We have now to explain what physical principles are resorted to in solving the problem of maintaining an organic form at a constant tem- perature in a medium the heat of which is variable ; and as we may reasonably anticipate that these principles are the same in every tribe of life, it will facilitate our investigations to commence with the simplest cases first. There are two periods in the life of a plant during which it simulates Two periods of the functions of an animal in maintaining a temperature heat in plants, higher than tliat of the surrounding air. These periods are, 1st, at the germination of the seed ; 2d, during the functional activity of the flower. K a mass of seeds be laid together, as in the making of malt, the op- Heat of germ- eration being conducted at a gentle temperature, and with the ination. acccss of atmospheric air, oxygen disappears, carbonic acid is set free, and the temperature rises forty or fifty degrees. A process of oxidation must therefore have been carried into effect, and to it we trace the heat disengaged, for carbon can not produce carbonic acid without a rise of temperature ensuing. The loss of weight which a seed exhibits is therefore due to its loss of carbon, and the whole effect is explained in the statement that atmospheric oxygen has united with a portion of car- bon contained in the seed, producing carbonic acid gas and an evolution of heat. Again, during flowering, the same action is repeated. The flower re- Heat of inflo- moves from the surrounding air a portion of the oxygen it rescence. contains, and replaces it with carbonic acid, the temperature rising, as accurate experiments have proved, in absolute correspondence with the quantity of oxygen consumed. Nor is this elevation insignifi- cant. A mass of flowers has been observed to raise the thermometer firom 66° to 121°. If thus the disengagement of warmth is the result of oxidation, it must Oxidation the depend on the presence of air, and be regulated by the rapidity ekvat?on?o? ^^^^^ which oxygcn can be supplied. As we pass fi-om the temperature, consideration of plants to that of animals, we discover that the production of heat must be connected with the power and precision with CONNECTION OF RESPIRATION AND HEAT. 177 which the respiratory apparatus works, for it is through its agency that air is introduced. Extensive observation accordingly cstabHshes a close cor- respondence in each animal tribe between the quantity of heat produced and the capability of respiratory apparatus. The lower tribes breathe slow- ly and are cold. Earthworms are only a degree or two warmer than the ground ; and even among vertebrates, fishes are only two or three degrees warmer than the water, a lowness of temperature in a great measure de- pending on the high cooling agencies which that liquid ex- Connection of erts, its specific heat, and the facility with which currents are respiration and established in it. However, even in these cases the produc- tion of heat depends on the power of the respiratory engine. The bonito can keep its heat 20° above that of the sea, and the narwhal maintains a steady temperature at 96°. The organic operations involved in nutrition, and also the retrograde changes of decay, can only go on at their accustomed rates so invariability long as standard limits of temperature are observed. The of organic ac- . „-,.„.,. ■,. tion implies a proper progress of the actions of lite implies a corresponding definite tem- adjustment of heat, and this irrespective of the mere size of perature. the animal. Even those that are microscopic must come under this rule. Wlien the temperature of a liquid containing infusorials is caused to de- scend to the freezing point gradually, the last portions which solidify are those which surround each of these little forms ; a drop is kept liquid by the heat they disengage. In the same individual, the absolute tempera- ture will depend on its respiratory condition ; thus insects, in passing- through each of their stages of metamorphosis, present a definite condi- tion as to their heat : the larva of the bee may be only two degrees above the air, while the perfect insect is 10°. Whatever accelerates the in- troduction and expulsion of the air, increases the warmth ; Variations of so a bee shaken in a bottle, and kept in a state of constant ^^50,^3 of condi- muscular exertion, will raise the temperature contained there- tion. in far higher than if he remains inactive. Among insects, those having the largest organs of respiration have always the highest temperature ; and, since muscular motion implies destruction of muscular tissue by ox- idation, and therefore development of heat, we should expect to find, as is actually the case, that animals possessing the highest powers of loco- motion will possess also the highest temperature. Of all, therefore, birds, the endurance and energy of whose powers of flight result from the per- fection of their respiratory mechanism, have the highest temperature. It is about 110°. Yet even here there are differences ; the sluggish barn- door fowl has not the heat of the energetic swallow. The standard temperature of man is usually stated to be 98°, but from this mean it ranges within certain limits upward and down. Temperature Much depends on the state of the health; of course, every thing of man. M 178 DIUENAL VAEIATIONS OF HEAT. on the respiration. In fevers it will rise to 105° ; in tetanus it may reach 110°; the contrary in asthma, when it may sink to 82°, owing to imper- fect access of air; in cyanosis to 77°, owing to imperfect aeration of the blood ; in Asiatic cholera to 75°, owing to the non-reception of oxygen by the cells in their diseased state. It also varies with the period of life : in the new-born infant it is 100° ; it presently sinks to 99°, and rises during childhood to 102°. Mental exercise in the adult increases it, bodily exertion still more. The special degree varies with tJie point on which the observation is made : the limbs are colder than the trunk, and this is the more marked as the point is more remote. On the leg the temperature may be 93° ; on the sole of the foot, 90° ; while that of the viscera is 101°. In his residence in different climates, man is exposed to variations of Resistance of temperature which extend over a scale of 200°. Toward the human or- -f^j-^g poles the cold of winter is often — 60° ; in the tropics ganism to ex- ii/. -,1 .,,. ^ tremes of tem- the heat of Summer + 130°. For a short period his power of perature. resistance is greatly beyond what these numbers would in- dicate; he can enter with impunity an oven heated to 600°, provided the air is dry. In these cases, though excessive evaporation from the skin moderates the effect and keeps it within bounds, there is always a mark- ed rise of temperature of the whole body. In a corresponding manner, exposure to cold produces depression, as shown in Dr. Davy's observa- tions. At 92° of the air, a thermometer under the tongue stood at 100^° : at 73° it stood at 99° ; at 60° it stood at 97|°. Among these variations there is one class which calls for critical at- T^. , . tention. It is the diurnal variation ; less marked in man, Uiurnal varia- ^ ' tion in the heat who instinctively makes provision against it, but well shown in the case of fasting animals. This illustrates, in an inter- esting manner, the controlling influence of external conditions ; for if ex- posure to a high temperature, as that of an oven, compels a rise of the heat of the whole body, in spite of the conservative arrangements, and exposure to extreme cold compels a descent, we ought to expect that ex- posure to more moderate degrees would, in like manner, produce an im- pression. The old astrologers were therefore not altogether wrong when they af- firmed the doctrine of planetary influences. The diurnal temperatures of a locality, as dependent on the position of the sun, are expressed in the system of man. The minimum of heat for the night, and the max- imum for the day, find a correspondence in the decline of animal temper- ature at the former, and its rise at the latter period. The experiments of Mr. Chossat on birds submitted to absolute starvation showed that, though in their normal state, at the commencement, the variation between midnight and noon was only 1^°, it gradually increased to 6°, until at CALORIFIC INFLUENCE OF FOOD. 179 last, the generation of heat wholly ceasing, the temperature gave way rapidly just previous to death. If, therefore, it was possible for life to eontinuc without the evolution of animal heat, it would be with the body as it is with the stem of a tree. It would follow the thermometric variations in the air, the maxima of heat and cold being somewhat later than the aerial ones, and within nar- rower limits, by reason of the low conducting power. The nearest ap- proach to this is in cases of absolute starvation, and though in man the effect is masked by the due taking of food, it none the less exists. In human communities there is some reason beyond mere cus- Influence of tom which has led to the mode of distributing the daily food in adjust- o J ing the temper- meals. A savage may dispatch his gluttonous repast, and ature. then starve for want of food ; but the more delicate constitution of the civilized man demands a perfect adjustment of the supply to the wants of the system, and that not only as respects the kind, but also the time. It seems to be against our instinct to commence the morning with a heavy meal. "We break fast, as it is significantly termed, but we do no more, postponing the taking of the chief supply until dinner, at the middle or after part of the day. If men were only guided by views of economy of time saved for the pursuits of business, or if, on this occasion, they put in practice the rule they observe on so many others, of never postponing the gratification of their desires, the first affair of the morn- ing would have been an abundant repast. But against this something within us revolts, and that in all classes, the laboring, the intellectual, the idle. I think there are many reasons for supposing, when we recall the time which must elapse between the taking of food and the comple- tion of respiratory digestion, that this distribution of meals is not so much a matter of custom as an instinctive preparation for the systemic rise and fall of temperature attending on the maxima and minima of daily heat. The light breakfast has a preparatory reference to noonday, the solid dinner to midnight. Once more I would remark, that we must not be deceived by the masked aspect which the system in this matter presents, connection of Its diurnal variations are concealed by agencies brought variations of .,, . '^1 Til •• heat with or- speciaily into operation tor that pui'pose, but tney exist m ganic periodi- the physical necessities of the- case ; and herein, I believe, ""^i^^- we have a first glimpse of the cause of those periodicities, which physi- cians from the earliest times have remarked ; for, though the nervous system, both in a state of health and disease, may seem to be their ori- gin, it is not impossible that its changes are connected with variations thus taking place in the external world. We have next to consider the effect of the annual varia- Annual varia- tions of temperature, which reach their maximum soon after *io"s <^ ^^^^^ 180 EFFECT OF ANNUAL VARIATIONS OF HEAT. mid-summer and their minimum soon after mid-winter, the manner in which the system comports itself under them, and the means which in- stinct and exj^erience teach us to employ in providing against them. The tables of mortality show that there is a loss of life at the annual p„. , „ maximum and minimum of temperature which greatly ex- Eftect of annu- i_ id J ai variations ceeds the average of any other period. In England and Bel- on man. gium, where the mean temperature of the summer months is moderate, this is not so strikingly marked for those months, and the chief loss falls upon the winter ; hut in New York, which has a summer cor- responding to that of the south of Europe and a winter like that of the north, the effect of these extremes Ibecomes so ohvious as even to he popularly connected with the position of the thermometer above or below 55°. Among infants and the aged, whose controlling powers over tem- perature are imperfect, these effects are most distinctly witnessed ; but among healthy adults, and even in Europe, we can detect them on crit- ical examination. Thus, in Brussels, the monthly mortality for January being taken as 105, that for July is 91, for August 96, and for October 93 ; and it is to be recollected that these are the residual traces of the operation of cold and heat after all the precautions have been used to ward them off. I might make here the same remark that was made when considering diurnal variations, that the true effect is so masked and concealed that we are liable to undervalue it, and do not properly appre- ciate this tax put upon the system. These annual variations of external temperature are chiefly combated Control over ^7 food, clothing, and shelter. The dietetic changes we make annual varia- between winter and summer are founded upon the principle clothing, shei- of using more combustible food for the former, and less com- **^''- bustible for the latter season ; and, since the calorific ef- fect of an article of food greatly depends on the quantity of oxidizable hydrogen it contains, the winter diet has more of that element than the summer. Partly thus by varying the nature, and partly by varying the quantity of the food, we can effect a compensation to a certain extent. Of the manner in which the diet-compensation is aided by variations in clothing little needs to be said. The experiments of Count Eumford established the fact that the conductibility of summer clothing is greater than that of winter, and therefore its resistance to the escape of heat is less. It is sufficient merely to allude to the control which is gained by difference of thickness in the garments, and by their amount or quan- tity. We instinctively make these adjustments to meet the existing ex- igencies, and, as far as may be, in this manner aim at a medium effect. The check upon external temperature by the use of clothing was doubt- less one of the first contrivances of the human race. Even of savage life it is a cardinal feature. The check by adjustment of diet belongs to a IMPERFECTIONS OF SHELTER. 18 1 civilized state, since it implies a certain control over tlie animal appetite and personal self-denial. Though great improvements in both of these will doubtless hereafter be made, when the principles of their operation are more generally and better understood, they must, even in their pres- ent condition, be regarded as having reached a higher perfection than the check by resorting to shelter. The art of constructing dwelling-houses may be said to be yet in its infancy in all parts of the world, j^^jg^jj^ -^^^ and yet in no particular is the physical condition of females perfections of and children, and especially of the sick, more nearly touched. ^ ^ ^^^' It is only within our own times that attention has been drawn to the proper methods for the admission of warmth, and air, and light ; the hy- gienic influences of furniture and decoration are unknown, beyond, per- haps, a popular impression that it is unhealthy to be in a recently-paint- ed apartment, inexpedient to sleep in a chamber where there are flowers, and unpleasant in summer to have a carpet on the floor, because it looks warm, and is thought to generate dust. The owner of a palace, on which w^ealth has been fruitlessly lavished, finds, on a cold day, that he can not obtain from his parlor fire the necessary warmth unless by alternate- ly turning round and round. The testy valetudinarian sits in his easy- chair, tormented by drafts coming in from every quarter. In his vain attempts to stop the offending crevices, it never occurs to him that his chimney is a great exhausting machine, which is drawing the air out of the room, and that his means of warming and ventilation are the most miserable that could be resorted to, since radiation can warm only one side of a thing at a time, and fresh air under those conditions can only be introduced by drafts. To warm rooms by contrivances such as the open fire-place or stove is obviously unphilosophical, since the effect of these is to ex- of artificial haust the air of the apartment. The modern method of warm- warmth, ing by furnaces, which act by throwing air duly moistened and of the right temperature into the rooms, and therefore by condensation, is clear- ly a better system, since it not only puts an end to all drafts, the tendency being to force air out through every crevice instead of drawing it in, but it possesses the inappreciable advantages of giving uniformity of warmth, a perfect control over the degree of heat, and likewise over the nature of the air, which need not be drawn from the cellar, or the con- taminated impurity of the street, but by suitable flues from the free and clear air above. Ventilating contrivances which can cheaply and effectu- ally force a supply of artificially cooled air in the summer, and warm air in the winter, into dwelling-houses, are still a great desideratum. By the aid of diet, clothing, and shelter, we are able to effect an almost complete compensation for the changes of diurnal and annual temper- atures, and even to occupy any climate of the globe. It is the manage- 182 ■ EFFECT OF COMBUSTIBLE ALIMENT. ment of caloric which makes man what he is, and constitutes his special prerogative ; his degree of skill therein is the measure of his civilization. The distribution of plants and animals, or, rather, their limitation within fixed boundaries, depends on the distribution of heat, but from these re- straints man is free, because he can control temperatures. From these considerations of the effect of external heat on the human mechanism, we return to a more critical examination of the modes by which heat is generated, and its degree regulated in the body. In every instance we assert that the production of animal heat is due Source of ani- to Oxidation taking place in the economy, and giving rise to mal heat. carbonic acid, water, and other collateral products. It is not necessary to attach any weight to the experiments of Dulong, which seem- ed to indicate that not more than four fifths of the heat actually pro- duced could be owmg to the oxidation of carbon, nor to those of a like kind of Despretz. The method they resorted to for the measurement of the disengaged heat was open to error ; the numbers they employed as representing the combustion heats were incorrect ; nor did they make any allowance for other substances, such as sulphur and phosphorus, which are simultaneously oxidizing, and the products of their combustion escap- ing by the kidneys. Reduced to its ultimate conditions, the evolution of animal heat de- Efrect of more pends on the reaction taking place between the air intro- aiimenf^as^ai- ^^^^"^^^ ^7 respiration and the food, and as either one or other coiioi. of these is touched, the result may be predicted. If, for ex- ample, into the digestive canal alcoholic preparations be introduced, they are absorbed, by reason of their liquid condition and diffusibility, with readiness. The combustibility of alcohol, and the amount of heat it yields, are so great, that the primary effect of the oxidation which ensues is a warmth or feverish sensation. By reason of the changes which are now taking place so actively in it, the blood circulates with unwonted rapidity, and the supply to the brain increasing, that organ exhibits an unusual functional activity. But this display of intellection is only tem- porary, and an opposite condition soon comes on, for, more carbonic acid accumulating in the blood than the lungs can get rid of, the depressing- effects of that body commence, and CA^entually the symptoms of poison- ing by it ensue. Not unlike this is the train of effects which arise when, instead of va- EfFectofamore rying the nature of the article ingested, we vary that of the portfr ofrespi- g^s respired. An energetic supporter of combustion, Hke the ration than air. protoxide of nitrogen, gives rise to a feverish glow, cerebral activity, to be followed eventually by a deep depression, the poisonous influence of the carbonic acid produced being exhibited. After a while the system casts it off, and recovers its condition of health completely. EFFECT OF EAREFIED AIR. 183 If there be an abstinence from food, since the introduction of air by respiration /noviul Fluid. (Fi-om Frerichs.) Water 948.00 Mucus and epithelium 5.00 Fat 0.70 Albumen and extractive 35.00 Salts 9.00 Loss 2.30 1000.00 I have introduced these tables not only for tlie purpose of exhibitin the nature of the fluid yielded by membranes of the serous Products of se aroup, but also for the sake of the important evidence they ?''f.^^°° pi'^-ex "3 ^ -T' _ r J istmg in the offer as regards the function of secretion itself. In the in- .blood. fancy of physiology it was universally believed that the special function of each gland arose from its peculiarity of construction ; that thus, by the liver, out of blood in which they did not pre-exist, cholesterine and its allied bile compounds were made ; that thus, by the kidney, urea was formed. Even in more recent times a modification of this doctrine has prevailed, and to the cells of which glands are so largely composed, the duty has been attributed of forming special products. In this way, wc still constantly speak of the bile-secreting cells of the liver; but the pre- ceding tables indisputably show that these very compounds, cholester- ine, biliphaein, urea, etc., may make their appearance in distant places, oozing Irom surfaces wholly devoid of the supposed special mechanism. In cases in which there occurs structural degeneration of the kidneys, for instance, urea at once makes its appearance in unaccustomed places, as though, when the readiest avenues through which it might have es- caped have failed, it bursts forth or oozes out at the weakest point. With such results, the idea of leakage or straining seems to be insepara- iD 196 OF ELECTIVE FILTRATION. blj connected ; and, moreover, an enlarged view of the operation of cell life seems to indicate that the general action of those organisms is to produce a formative result, the grouping of amorphous into organized material, and the elaboration of that material into more complicated and iiigher forms. But many of the most important constituents of the va- rious secretions are indisputably things which are on the downward ca- reer, fast passing to the inorganic state. Many of them, as presented in the bile or in the urine, run through a series of spontaneous changes, which end in the appearance of truly inorganic bodies. For the fabrica- tion of such substances, half inorganic themselves, it is scarcely to be thought that cell life should be necessary ; and these, with many other such considerations, recall the observation I made a few pages back, that the more profoundly we study the composition and constitution of se- creted fluids, and the more accurately we understand the function of se- cretion itself, the less are we disposed to invoke the agency of cell life, and to rely the more on the ordinary mechanical act of strainage. That the different secreting surfaces exercise an elective elimination on Elective fiitra- materials existing in the blood, some permitting the escape '^^'*'"' of one, and some of another ingredient more readily, may be demonstrated from their action on saline substances purposely introduced into the blood. Thus the iodide of potassium was detected by Bernard in the saliva, pancreatic juice, and the tears in less than one minute, but in the urine and bile not until after an hour. The ferrocyanide of potassium could be recognized in the urine in seven minutes, but not at all in the saliva. In like manner, cane-sugar and grape-sugar appear in the secretions of the kidneys and liver, but not in those of the pancreas and salivary glands. The lactate of iron, injected into the veins, fur- nishes no iron to the saliva, but both iodine and iron can be recognized in that secretion after the administration of the iodide of iron. Upon the whole, we may therefore conclude that very many substances are strained from the blood in which they naturally occur by membranes and glands, which, from the circumstance that they are of various con- struction and possess a different physical nature, are better adapted, some for the removal of one, and some for the removal of another compound. Among secreting surfaces the mucous membranes are usually enumer- Of mucous ated. Strictly speaking, however, they are scarcely so much andtheir severe- Secreting surfaccs as the seat of numberless secreting organ- tion. isms. They line the interior of the digestive, respiratory, urinary, and generative apparatuses, and are characterized by extreme vas- cularity. In structure they consist of several different layers or regions, the undermost being submucous cellular tissue, upon which is spread the proper mucous membrane, containing connective and elastic tissue, which affords a nidus for blood-vessels and nerves. Upon this is the basement PROPERTIES OF MUCUS. 197 membrane, covered with epithelial cells. In many regions this compound structure rises into elevations, as in the intestinal villi, or sinks into de- pressions, as in the follicles. The epithelial cells are of different kinds, sometimes flat, giving origin to tesselated or pavement epithelium, and sometimes cylin- droid, each cell, in this case, being set vertically upon the basement membrane. In many instances, the cylindroid nucleated cells are fiirnished upon their outer extremity with vibrating cilia, constituting ciliated cylindroid epithelium. Both forms of epithelium, the tesselated and the cylindroid, coexist in glandular ducts. The origin of the cells is in the basement membrane, from germs arising there ; and as the older and therefore superlicial cells exuviate or deliquesce, new ones arise to take their places. After what has been said, it is not necessary to give a detailed de- scription of mucous surfaces farther than to state that from propertiei^ them there is furnished a viscid, glairy fluid, of different shades °^ mucus. of color from white to yellow, denser than water, and insoluble therein. Examined by the microscope, it contains granular corpuscles and epithe- lial cells. Its reaction is alkaline, and its proximate constituent is a sub- stance to which the name of mucin has been given. Derived from dif- ferent sources, as the nasal, bronchial, and pulmonary surfaces, the in- testinal canal, and the urinary and gall bladders, it exhibits specific dif- ferences. Its quantity is often greatly increased by morbid causes, as, for example, in catarrh, its composition likewise varying at different stages of the same disease. Its use, for the most part, seems to be the protection of the delicate structure which secretes it. In some positions, as in the intestinal canal, it likewise probably acts in the way of reliev- ing friction of the substances passing over surfaces. OJ^ secretmg Glands. — The typical form of secreting cell-gland is a single cell, with its nucleus at the lower end, the other end simple sac-like having become open by deliquescence or dehiscence, and thus ceii-giand. constituting a sac. From the nucleus thus situated at the end of the cavity broods of young cells arise. These become more perfect as they advance toward the mouth of the sac. The outer wall, and especially the region of the nucleus, is furnished copiously with blood-vessels. Of such structures, variously -modifled, the different glands are com- posed. We shall now proceed to the description of the more important of these, as the liver, kidneys, mammary gland, &c., again impressing the remark that, though all these glands are the seats of myriads of cells, cell life is for increased organization, and secretion is in many instances nothing more than filtration or strainage. We shall endeavor, as the occasion arises, to show, in the case of each gland, what part of its action is due to cell influence, and what to such mechanical permeation. 198 DEVELOPMENT OF THE LIVEE. OF THE LIVER. The first appearance of a bile-secreting organ is the occiuTence of yel- Paidiment of lo^ cclls variously scattered upon the lining membrane of the the liver. digestive cavity, as in the hydra. A concentration or local- ization next ensues, such yellow cells being grouped upon the wall of the intestine at a definite spot. A coecal projection, in the higher tribes, seems next to force out the yellow cells, bearing them on its exterior, as in the nudibranchiate gasteropods ; and as these coeca are prolonged more and more, so, in a more definite manner, does the rudimentary liver appear. In molluscs this partition is sufficiently distinct. The special form which the hepatic apparatus presents in different tribes varies ver}^ greatly, though doubtless the principle of construction and of action is nq ^'' always the same. Thus, in insects, the liver con- sists of long tubes of delicate membrane, covered with secreting cells, small and germ-like near the distant end of the tube, but more perfect at the mouth. These tubes are in relation with an adi- pose mass, which is probably connected with the origin of the cells. The different condition of these cells, when compared at the bottom and at the mouth of the bile-sac, is well seen in tlie case of cnistaceans, as in Fig. 82, one of the he- patic coeca of the cray-fish. The letters at the side show the state of the cells in difterent posi- tions toward the mouth of the follicle. At a they contain yellow biliary matter only ; at h, oil glob- ules are appearing in them, whidi become more distinct at c ; and toward d and e they present the appearance of ordmary fat-cells. Thus, ex- amined at the bottom of the follicle, the cells are Hepatic ccecum ot cia) jibii biliary, and as we advance to the mouth they be- come fatty. The comparative anatomy of the liver is repeated in its order of devel- Development opment in the high vertebrated animals. In them it is first of the liver, detected in an evolution of cells upon the intestinal wall, at the point which is eventually to be the place of discharge of the common bile-duct. This agglomeration of bile-cells is next seen to project or bud off through the intrusion of a coecal pouch. In the amphioxus the con- dition thus reached remains permanent, and is the counterpart of the liver of a fowl about the fourth day of incubation. The coecal pouch next sends forth ramifications, which are likewise accommodated with cells, and these, branching again, give origin to a complicated structure. In STKUCTURE OF THE LIVER. 199 Fig. 83. this condition, the mouth of the cwcum hecomes drawn out and narrowed down, and so forms the rudiment of an hepatic duct. In man, the hver is the largest gland in the body : it is of a reddish- brown color, dense, and from three to five pounds in weight ; Description of convex on its upper, and concave on its inferior surface. It ^iic liver, lias five lobes : the right lobe, the left lobe, the lobus quadratus, the lo- bus spigelii, and lobus caudatus. It is held in its position by dupli- catures of peritoneum and by a fibrous cord termed its ligaments. Its peritoneal envelope is the cause of its glossy appearance ; its cellular en- velope extends into the interior as sheaths for the vessels. Five classes of vessels are found within it : the branches of the portal vein, those of the hepatic artery, those of the hepatic veins, the lymphatics, and the he- patic ducts ; the latter, converging eventually into a trunk, the hepatic duct, joins with the cystic duct to form the ductus communis choledo- chus, which discharges its contents into the duodenum, as seen in Fig. 83, in wdiich a is the gall-bladder, which constitutes a temporary recep- tacle for the bile, b the cystic duct, d the hepatic duct, c its branches, e the ductus choledochus, and h its opening into the duodenum. The gall-bladder is wanting in in- vertebrated animals, and first makes its appearance in a rudimentary condition as a dilatation of the bile-duct : it is absent in the horse, pres- ent in the ox ; in the camelopard it was absent in one individual, and the next that happened to be examined had two. The intimate structure of the liver in man is, in many particulars, still imperfectly known, though the attention of the most eminent j^^^j,^^ . anatomists has been devoted to it. It may, however, be un- ture of the iiv- derstood that each hepatic vein, commencing in the substance ^'' of the liver, bears upon its capillaries small portions called lobules, firom the Jjj to the -^ of an inch in diameter, in a manner which calls to mind the arrangement of leaves on a branch, or a bunch of grapes, as represented in Fig. .84, a being the vein, b, b, b, leaf-like lob- ules on its branches. Excluding the lym- phatics, it may be said that fom- diiferent systems of vessels are engaged in the liver, the portal vein and hepatic artery, the bile- ducts and hepatic veins. The first pair are afferent, the second pair efferent ves- TLe bile-ducts entering the duodenum. Pig. 84. a'6 Uupatic \ciiis in the lobules of the li\ti sels. The portal vein brings the blood from which bile is to be secrc- 200 STRUCTURE OF THE LIVER. Fig. 85. ted ; the hepatic artery brings aerated blood for the nourishment of the gland ; the bile-ducts cairj away the biliary secretion whicli has been separated from the portal blood, and the residue, taken charge of by the hepatic veins, is eventually carried back into the general circulation through the vena cava. A general idea of the mode of arrangement of the four vessels in the liver may be obtained by recalling the illustration just given, that the lobules are placed on the commence- j^^^^^i^^^^ Ix\^^^L. ment of the hepatic veins, Kke grapes /^^^^^^^^l^^^y/J^^'^ on their stalks. The vein originates in the centre of each lobule, as shown at a a, in J^iff. 85, and exhibits there a ray-like kind of divergence. On the periphery of each lobule, at b, b, b, as it were on the surface of the grape, the other three vessels ram- iiy. Of them the portal veinlets dip down into the substance of the lob- ule. The hepatic arteries likewise enter for the pui-pose of gi'vang nutri- In J^i^. 86, a, a are the commencing hepatic or intra- lobular veins of two lobules ; 5, ^, the biliary ducts ; c, interlobular tissue ; d d, parenchyma of the lob- ules. With respect to the bile- ducts, which are prominently rep- '^•^^i- resented in this figure, it is not pos- tively known whether they pro- ceed beyond the surface, and the manner in which they are related ^ to the secreting cells, and receive the liquid yielded by tliem, is a sub- ject of controversy. The inter- spaces between the capillaries that have entered the lobules are filled up with these cells. It is not known whether the hepatic artery discharges its blood into . the portal capillaries, or into those of the hepatic vein, and, for this reason, it is doubtful whether that blood takes part in the secretion of the bile. and are about the Origin of hepatic veins in the liver lobules. tion to the parts. Fig. 86. b Origin of bile-ducts on the liver lobules. The secreting cells have nucleolated nuclei, of an inch in diameter. In J^igf. 87, at a, a, a, their normal state is shown. They are fiUed with a yellowish, granular soft substance : a.t b b is the appearance of fat 2000 COURSE OF tup: bile. 20J globules, which increase in number and size at c, c, c, c. They thus con- tain both biliary material and oil globules, the quantity of the latter vary- Fvj. ST. ing with the nature of the food, and in certain diseased conditions occur- ring to so great an extent as to give rise to the aspect known as "fatty liver." This accumulation of fat is connected with the respiratory func- tion, not only in conditions of dis- ease, but even in a state of health ; Hepatic cells magnilied 400 diameters. f^j.^ ^^^ ^^^^^ eUCrgetic the rCSpiia- tion, the more free is the liver from fat. As the chyle passes through the mesenteric glands before it is dis- charged into the circulation, so do the matters which have been taken up by the vascular absorbents pass to the liver. In Chapter IV. the bile, which is secreted from the portal blood, is treated of as taking part in the function of digestion ; but there is another aspect under which we have now to regard it. We speak of the circulation of the blood, because, setting out from the heart, it comes back thereto, pursuing a course which returns ^ . , .^ j upon itself. In the same metaphorical manner, according to spiral course of the views of some, we might speak of the spiral motion of the bile ; for those of its constituents, which are first taken from the stom- ach and small intestine by their veins, appear to pass in the portal circu- lation to the liver. In that gland a preliminary partition of the constitu- ents of the portal blood ensues, one stream setting off to the general cir- culation through the hepatic veins, and another, the bile itself, returning to the intestine. In the intestine another partition ensues ; the coloring matter of the bile is dismissed with the fffices, and the residue, taken up by the lacteals, passes through the mesenteric glands, and, either by the thoracic duct or otherwise, gets into the blood circulation. It may there- fore be perhaps thought that the constituents of the bile have been twice, in close succession, in the digestive cavity, and have been twice absorb- ed, first by the veins, and then by the lacteals ; and that, as it were, a spiral course has been pursued. The question at once arises, wJiat is the object of such a course ? Why is there this return to the digestive cavity ? The answer commonly given is, the bile takes part in promoting the operation of digestion. But the return may perhaps be, not for the purpose of inducing digestion, but for the purpose of being acted on or digested itself. The separation of its coloring matter, just alluded to, is a significant fact. The portal blood, as it is preparing to enter the liver, may be regarded as systemic venous blood, the constitution of which has been altered 202 SOURCE or THE BILE. through the additions made to it by absorption of matters from the stom- „ ach and intestine. We may overlook for the present those Reparation of .... . the portal blood contributions it receives from the veins of the spleen and oth- m t e iver. ^^, sources. Regarding it, therefore, as systemic venous blood, charged with certain of the products of digestion, it enters the liver to be acted upon by that gland. The fitst effect upon it is, in a chemical point of view, well marked. The stream which sets off to the general circula- tion through the hepatic veins may be said to carry away the whole of the nitrogenized material ; for the bile, which is at this point parted out and sent back to the intestine through the biliary ducts, does not contain more than 4 per cent, of nitrogen, and this exclusive of the water which im- parts to it its liquid condition. Arrived in the intestine, a rep- separation of etition of the same process of partition takes place, the color- ^ ^ ^ ®" ing matter, which contains nearly the whole of this residual ni- trogen, being dismissed with the fgeces, and the remaining hydrocarbon taken up by the lacteals along with other fats. The first duty of the liver is therefore a separation of the nitrogenized principles of the portal blood, which are forthwith carried into the gen- eral circulation through the hepatic veins and the vena cava. The result is, that there is returned to the intestine a sulphureted hydrocarbon, still containing so much nitrogen as to form a very unstable product, prone even to spontaneous decomposition. In the intestine its nitrogen is whol- ly removed from it, and the combustible hydrocarbon is then absorbed. The portal blood, regarded under the aspect here presented, is obvi- ously composed of two constituents : 1st. Systemic venous From what J r ^ . . . ^ source is the blood ; 2d, Matters obtained from the digestive cavity. We bile derive ? j^g^^ inquire from which of these the bile is really derived. Besides the presumptive evidence arising from the consideration that if the bile originated from matters which had been just absorbed from the digestive cavity, it would be inconceivable why it should be returned forthwith thereto, its quality of extreme instability marks it out as a sub- stance fast approaching to final disorganization and decomposition. It bears no aspect of a histogenetic or formative body, but, on the contrary, it is on the downward course. We should scarcely expect to recognize it as a primary product of the digestive action, but should seek its prob- able origin in some source of decay. ; Whatever weight may attach to such considerations, we have, in addi- tion, direct evidence which places the source of the bile beyond doubt b}- referring it to the systemic venous blood, and not to the matters just ob- tained from the digestive cavity. During foetal life, the digestive organs are in an inactive state, but the liver, which is largely developed, discharges its secretion into the intes- tine. This secretion, which is known as the meconium, is a true bile, as the following analysis proves. BILE 18 DEKIVED FEOM VENOUS BLOOD. 203 Composition of Meconium . (^Fr cm Simon.) Cholesterine 160.00 Extractive and bilifellinic acid 140.00 Casein 340.00 Bilifellinic acid and bilin 60.00 Biliverdin and bilifellinic acid 40.00 • Cells, mucus, albnmen '. 260.00 1000.00 Dr. Davy found that the ash left after the incineration of a sample of meconium is of a reddish color, consisting chiefly of peroxide of iron and magnesia, with a trace of phosphate of lime and chloride of sodium. During foetal life the liver is therefore discharging the same function that it does after aerial respiration has commenced, that is it does not to. say, it secretes bile (meconium) into the intestine ; but at *^°'"f ^^?'" ?', '' _ _ ^ _ ' _ _ ' cently digested this period, since there is no true digestion, the bile can products. come from one source alone, and that source is the systemic venous blood. There therefore can remain no doubt that, in after life, the same effect takes place, and that the bile is never derived from materials which have just been brought from the digestive cavities. I therefore regard the bile as an excretion of materials which are de- composing and readv to be removed from the system. I in- ,. ^ '-' . . ^ . . . It comes from cline to the supposition that much of it is derived from the the venous cells of the blood, the life of which is only temporary, for the casern of the meconium is nothing but the globulin of the cells, the two substances being chemically allied, and the predominance of iron in the ash of meconium seems to establish a connection with haBiiiatin. More- over, this opinion is supported by the remarkable stability of many of the nitrogenized coloring matters, the analogies between haeraatin and chlorophyl, and particularly by the fact that in the herbivora the coloring matter of the bile is undistinguishable from clilorophyl, and in most oth- er tribes closely allied thereto. In any discussion of the action of the liver, it is thus to be constantly borne in mind that the portal blood consists of two distinct portions, sys- temic venous blood and matters absorbed from the digestive apparatus. Derived from the first of these portions, we trace the origin of the bile to the waste of the tissues, or to the blood-cells on their downward career ; and hence we arrive at the important conclusion that every proximate constituent of the bile pre-exists in the systemic venous blood. Lehmann, inclining to the view that the formation of the bile occurs in the liver itself, quotes the experiments of Miiller and Attempts to de- Kune, who, after tying the portal vein and applying liga- tect choiic acid tures to all the points of attachment of the liver in frogs, ex- ment in the tirpated that organ, and collected the blood of those which ^^°°'^- survived the operation for two or three days, by amputating their thighs. 204 CONSTITUTION OF BILE. [t was expected that in this hlood, Ibile pigment and cholic acid would be found if the original formation of those substances took place exter- nally to the liver. Such did not prove to he the case. It maj, however, be justly inferred that no reliable conclusion can be drawn after opera- tions of such magnitude and severity. The alleged inability to detect the constituents of the bile in the blood Cause of this of the portal vein is probably due to the defects of our ana- ^e^in'.^'biie hi' ^J^ical processcs, for it is very clear from the circumstance the blood. that the bile which is poured into the intestine must be reab- sorbed, with the exception of its coloring material, either by the lacteals or the veins, or by both, since it is not found in the excrement. Through whichever of these channels it passes, it must therefore regain the gen- eral circulation, for it can not be supposed that in the short period of its course it could have undergone complete metamorphosis. We may therefore assume that the proximate ingredients of bile pre- exist in the blood, and this conclusion is enforced by the fact that, after tying the vena porta, bile, though in a diminished quantity, is still se- creted. The same also occurs in those cases of malformation in which that vessel, instead of ramifying into the liver, empties directly into the vena cava. When there is any failure or delay in the removal of bile from the system, the effects are such as might even be predicted, nervous disturbance ensuing, and eventually all the symptoms of poisoning. The circumstance that this last effect often takes place suddenly, has been by some supposed to be dependent on the necessity for the bile to accumu- late, to a certain extent, but it is much more likely that it is determined by the metamorphosis of the decomposing bile having reached a certain point, when special poisonous products have spontaneously arisen from it. Bile, from whatever animal it may have been derived, contains a resin- Constitution of ous soda salt, a coloring material, cholesterine, and mucus. ^''^^- The acid of the soda salt is the taurocholic or glycocho- lic. The coloring matter in carnivorous and omnivorous animals is brown, the cholepyi'rhin of Berzelius ; but in birds, fishes, and amphibia, it is green, biliverdin. Strecker makes the curious remark respecting the bile of fishes, that in those which are of salt water, potash salts predom- inate ; and in those of fresh water, soda salts. Among the ultimate ele- ments occurring in the bile, and being of special interest, may be men- Constitution of tioned sulphur, which exists in taurine, of which the com- taurine. position is C^, H., N, 83, Og. It may be obtained from ox- gall ; it has likewise been made artificially by Strecker from the isethi- onate of ammonia. It is distinguished by evolving sulphurous acid when burnt in the open air. It does not exist in the bile in an insu- lated condition, but probably as an adjunct to cholic acid, and has been found in that secretion of both hot and cold-blooded animals. It has, QUANTITY OF BILK. 205 however, been asserted that sulphur, and therefore taurocholic acid, does not exist in the bile of the hog. The bile is secreted more slowly during a long period of fasting, and more rapidly during normal nutrition. To a certain extent, production of this variable rate depends on the general principle that a ^'^^'^• gland acts more energetically in proportion as the supply of blood sent to it is greater. If not wanted for the present purpose, the product is stored up, for a time, in the gall-bladder. When the bile has been long retained in the gall-bladder, it becomes concentrated through the removal of a portion of its water : change of bile it also undergoes a change of color. In animals whose he- after retention, patic bile is yellow or brown, the cystic bile has a tendency to gi-een, a change of color dependent on partial oxidation, occasioned by the arte- rial blood. The flow of bile takes place with different degrees of rapidity at dif- ferent diurnal periods : thus it reaches its maximum in from -n, ■ , ^ ^ ^ Period of max- thirteen to fifteen hours after the last full meal, and then imum flow of rapidly diminishes. Bidder and Schmidt estimate the diurnal secretion in an adult at 54 oz., containing 5 per cent, of solid matter, an estimate which is undoubt- edly too high, so far as an average diet and state of health are involved. It is asserted that a diet of flesh tends to produce more bile than one of a purely amylaceous kind. Even the use of a large quantity of water increases its amount, and this as regards its solid constituents. Reme- dial agents act in various ways. Calomel increases the fluid, but di- minishes the solid constituents. Carbonate of soda diminishes both. Again, there are great variations in the rate of its production: the circum- stance just mentioned, that its maximum flow is several hours after the maximum digestion, is important as regards the explanation of its forma- tion, showing significantly that it is not directly produced from matters recently absorbed from the intestine, but from the systemic venous blood. But the liver has other duties to discharge besides the separation of bile. It gives origin to sugar and fat, as is proved by the Other duties of circumstance that the blood of the hepatic veins is richer in *?!? ^^^^'^j'®' ^ sides produc- those ingredients than the blood of the portal. In this re- ing bile. spect its action seems more particularly to be that it converts other sug- ars into the particular form known as liver-sugar, which it can also pro- duce from the transforming albuminous bodies ; it forms fat from sugar, and makes from certain other fats the special one known as liver-fat. In this duty of forming sugar and fat, it exhibits an inverse power of action ; as the production of the one predominates, that of the other declines. From the point of view which we have now reached through this de- scription, we are able to see the double duty which this great gland dis- 206 BILE EEMOVED FROM BLOOD BY FILTRATION. The liver does charges, and must correct, to a certain extent, tlie popular Qot form bile, theory of its action. Does the liver really secrete bile ? Is it the business of the so-called bile-secreting cells to withdraw the constit- uents of that liquid from the blood, and combine them together into this viscid yellow liquid ? I think not ; for it is a matter of demonstration that not only every constituent of the bile, but the bile itself, pre-exists in the blood, and it is just as unphilosophical to burden those cells with the duty of formmg it as it would be to believe that a like agency is needful for the appearance of urea in the kidney. Moreover, we must constantly bear in mind the extreme instability of this substance, how readily the yellow bile of carnivorous animals becomes green by partial oxidation, and the green bile of the herbivora yellow by deoxidation. It spontane- ously changes in its downward career, and any differences in quality or character which we might impute to the action of the cells upon it may be equally well attributed to its own inherent principle of change. For these reasons, I believe that the bile simply transudes fr'om the Manner of blood, and that the cells of the lobules have no special relation removing it. ^q j^ beyoud this, that it oozes past their interstices, or, perhaps, by physical imbibition, finds access to then* interior. I see no reason that these cells should form it when it pre-exists in the blood, nor does the state of the affluent and effluent blood offer any contradiction to this conclusion. In all discussions of the functions of this organ founded upon a comparison of the portal and hepatic venous blood, the relative quantity of water which they contam, and its great and even rapid fluc- tuations, should always be borne in mind. As might be expected, portal blood contains far more water, and, even after abundant drinking, the amount in the hepatic venous blood has by no means increased to the extent that might have been expected. It is for these reasons that the bile varies so gTcatly at different periods in its specific gravity and fluidity. The blood of the portal vein is, moreover, periodically varying in its Variation in constitution, according to the state of activity of the organs the constitu- ^ which it is being derived. In the first stages of diges- tion of the por- O ^ 1 • • J tal blood. tion the stomach is supplying it in unusual quantities, and with the ingredients which its veins have been absorbing from the result of histogenetic digestion. A little later, the same thing occurs with the intestine. At another period the supply from the spleen varies. The explanation which ]\Ir. Handfield Jones has recently given of the Function of the function of the hepatic cells — that they manufacture Hver- hepatic cells, sugar — dcserves attentive consideration, more particularly if we likewise impute to them the production of liver-fat ; for this would at- tach them rather to the ramifications of the hepatic veins as a part of their instrumental mechanism, and assign them only a very indirect relation to PRODUCTION OF FAT AND SUGAR. 207 the bile-ducts. The contradictoiy statements which have been made by the most eminent anatomists respecting the connection of the bile-ducts and the bile-cells — some believing that the bile-ducts are covered inte- riorly with the cells ; others, that the ducts end on the outside of the lobules ; others, that the passages reported to have been seen among the cells are interstitial channels and not proper vessels — make it just as probable, anatomically, that the cells belong to the hepatic veins as that they belong to the biliary ducts. It is true that there may be a mixed action, and that presence of bil- iary matter may be necessary to the sugar and fat producing agency. This interworking and mutual dependency of functions is not without a parallel. Thus the lung, viewed as a secreting or excreting gland, has for its object the removal of carbonic acid from the system ; but it also discharges another duty, which is dependent for its accomplishment upon the physical or chemical qualities of the ha3matin of venous blood, the introduction of oxygen by aerating or arteriahzing. But the excre- tion of carbonic acid and the introduction of oxygen, though separate physiological events, and to be spoken of as distinct functions of the lung, are yet nevertheless interconnected ; the one is essential for the ac- complishment of the other, and the one eiFect is made the means by which the other is brought about. So it may be in the liver : the contact of bile with the secreting cells may be essential to their sugar or fat producing action. The deposit of fat and the production of bile seem to be inversely as each other. Bidder and Schmidt found that fat animals Relation of the yield less bile than lean ones, and that when they were fed <^eposit of fat *' . ■ ^ •> and production on fat the quantity was smaller than in the case of animals of bile. fed on a less fatty diet. From such facts, the inference has been drawn that the accumulation of fat is in consequence of a diminution of the se- cretion of bile, and not that the diminution is the consequence of the an- imal being fat. In such discussions' it should, however, be recollected, that the fats do not furnish all the substances required for the produc- tion of bile, but only a limited portion thereof. Thus there are reasons for the belief that sugar, lactic acid, or some other allied body is essen- tial to that process, and it is very clear that so too are the materials fru-nished fi-om the decay of the cells of the blood. With respect to the production of sugar in the liver, it may be re- marked, that the quantity of that substance in the solid res- p ^ .• idue of the sermn of hepatic blood is from ten to sixteen sugar and fat times greater than in the same residue from the portal blood ; "^ ^ ^® ^^®^- and in animals undergoing starvation, though no sugar could be found in portal blood, it occun-ed to such an extent in the corresponding hepatic venous blood, that Lehmann found that its quantity could be determined 208 INFLUENCE OF PNEUMOaASTEIC NERVE. by fermentation. From this there can be no doubt that, in the chano-cp which are occun-ing during the passage of the blood through the liver, there is a production of sugar, and this seems to be connected with a dim- inution in the quantity of fat ; for if an excess of fat and a deficiency of sugar enter that organ, and their quantities are inversely changed a1 their emergence from it, it would appear that fat may be decomposed act- ually, as Ave know is possible hypothetically, into cholic acid and sugar. But with respect to taurine, the adjunct of the cholic acid, since it is a Taurine comes nitrogenized body, we are obliged to seek for it in some oth- from blood- er sourcc, and this, it would appear from the facts set forth, must be the regressive metamorphosis of the blood-cells. Taurine has not as yet been detected in the portal blood. It can not be supposed that the sulphuric acid of the portal blood is used by deoxida- tion in the preparation of free sulphur for the taurine, since, if any thing, the quantity of that acid in the hepatic venous blood is increased. From whatever source it may have been derived, the sulphur of taurine entered the liver in an unoxidized state. When we reflect that the bile is the product of decay, that it pre-ex- ists in the blood, that on its amval in the intestine a part of it is cast out with the faecal matter, it seems very unlikely that an immense cell apparatus, constituting the largest gland in the whole system, should be Analogies in ncccssary for its removal. But when we moreover reflect dJdng sugar°" *^^* ™ *^^® mechanism of plants, from gum, or rather from and fat. carbonic acid and water, under the agency of cells in the leaves or other structures, both sugar and oils are formed, we recognize that there is a connection between those organisms and these products. M. Bernard's experiments seem to show that the sugar-forming func- influence of ^ion of the liver may be morbidly increased by wounding the the pneumo- medulla oblongata near the origin of the pneumoe;astric nerve, gastric nerve ,7 . p , . ° on the quanti- or by the application of galvanism to the same part, an arti- ty of sugar. ficial diabetes ensuing, and this within a few minutes after the operation, but it usually ceases after two or three days. It is accom- panied by a great derangement of respiration, a lowering of the tempera- ture, and a venous condition of the arterial blood. It by no means fol- lows, however, that the excess of sugar observed in Bernard's experi- ments arises from an increased action of the liver, or an increased energy of the sympathetic nerve : it may be, as Reynoso asserts, attributable to the injury inflicted on the pneumogastric, and diminished respiration. The administration of ether and chloroform, the conditions of old age and foetal life, the influence of many diseases, as chronic bronchitis, asthma, pleui-isy, all present a tendency to the accumulation of sugar in the urine, the sources in each of these cases being attributable to respiratory dis- turbance : for if any thing occurs to retard or delay the destruction by DESTRUCTION OF BLOOD-CELLS IN THE LIVEK. 209 oxidation of the sugar, constantly formed by the liver, the accumulation wOl make its appearance in the urine. The appearance of saccharine matter in that secretion may he equally well attributed to its non-de- struction in the system generally as to its over-production by the liver. This gland, besides producing sugar and fat, is the seat in which the worn-out blood-cells are finally disintegrated, and probably t) . t" the young ones pushed forward through a certain stage of biood-ceiis in their development ; advantage, moreover, being incidentally * ^® '^'^''' taken of the secreted bile, which possesses properties useful though not essential for promoting the digestion and absorption of fatty material, perhaps, also, of imparting a definite course to the transmutation of the semi-digested material in the intestme, and this both as regards nitro- genized, amylaceous, and fatty bodies. Of the influence of the bile in promoting the absorption of fat, the physical experiments which have been alluded to leave no doubt ; but that these uses are of a secondary or non-essential kind, and are only taken advantage of in an indirectly eco- nomical way, is established beyond all possibility of a doubt by the fact that animals can live for a long time, even for months, without the pas- sage of bile into the intestine, provision having been made for its escape externally through an artificial fistulous orifice. These conclusions respecting the fnnctions of the liver are in harmony with the appearances presented by the blood leaving and entering it : the predominance of colorless blood-cells, and of young cells well ad- vanced toward perfection in the former, and. of wasted, worn-out ones in the latter ; with the fact that the maximum secretion of bile does not take place until more than half a day after the ingestion of food ; and that during foetal life, in which there is no food, either in the stomach or intestine, to be digested, the liver is nevertheless in high activity, and bile is secreted. In view of all the preceding facts, we may therefore finally conclude that there are at least four distinct operations conducted in the liver ; 1. The production of sugar and fat ; 2. The separation of the bile ; 3. The destruction of old blood-cells ; 4. The completion or perfection of young blood-cells, perhaps by receiving their iron. With respect to these it may be remarked, First. The formation of sugar and fat, either from carbohydrates, or what, in this instance, is more pi'obable, from albumenoid bod- General sum- ies brought by the portal vein, can no longer be doubted, ^^n'^of the^liv' The prevalence of liver-sugar and liver-fat in all that region er. of the venous circulation included between the liver and the lungs must be attributed to this source. That the sugar undergoes rapid metamor- phosis in the pulmonary organs is plainly proved by the effects of irri- tation of the pneumogastrics, which, interfering with the function of res- O 210 SODL4EY OF THE ACTION OF THE LIYEE. piration, permit tliis substance to reach the aortic circulation, from which it is removed hj the kidneys, a dialetes arising. So far as the prepara- tion and course of this sugar is concerned, the liver is a ductless gland, and, -with ]\Ir. Handtield Jones, I believe that the cells of the liver are the agents which accomplish this duty. The production of fat appears to be inversely as that of sugar. In the crustacean bile-sac, J^iff. 82, we see the gradual stages of its appearance ; and the production of both bodies is well illustrated in the life of plants. Second. The bile is separated from the blood portion of the portal blood, and not from the products of digestion obtained from the chylo- poietic viscera. The elements of bile I believe to pre-exist in the blood, and to escape from the portal veinlets to the biliary ducts by mere filtra- tion or strainage. The precise source from which the bile is derived is probably the blood- cells, and in the changes which they are under- going the spleen is perhaps concerned. Tf this be so, the bile-duct is as much a duct for the spleen as it is for the hver itself. The bile may almost be looked upon as a hydrocarbon, containing a veiy changeable and therefore noxious coloring material, which, when the secretion reach- es the intestine, is parted from it and dismissed with the faces, the prop- er hydrocarbon being taken up by the absorbing an-angement for hydro- carbons, the lacteals, and so sent through the thoracic duct. Perhaps, also, by reason of its special adaptedness for that purpose, it aids in the absorption of other fats. At this point it may be remarked that the view here presented of the sugar-forming and bile-straining functions of the liver appears to be greatly strengthened by the anatomical construction of that organ. There is no ob^dous communication between the portal and hepatic vein- lets save through cells, but the portal veins and the bile-ducts nm in their ramifications side by side. Third. Whatever part of the disintegration of old blood-cells takes place in the spleen, their final destruction is doubtless accompHshed in the liver, this beino- the immediate source from which the bile itself is •derived. Though these metamorphoses are, to a greater or less extent, occmTing throughout the circulation, it is in these two gTeat glands that an opportunity is afforded for the destruction to reach its completion, and the resulting product of waste to be removed ; nor is there any thing in this view at all contradictory to the opinion I have enforced, that all the constituents of the bile may be found in the general circulation. Fourth. The liver also aids in the preparation or maturation of young blood-cells in an indirect way. There are certain of the mineral constit- uents of the disintegrated cells too valuable to be cast away, since they can subserve the duty of entering into the composition of young cells passing toward perfection. As such a substance may be mentioned iron. THE DUCTLESS GLANDS. 211 This view of the action of the liver appears also to he sustained hy the large numher of star-like and corrugated hlood-cells occurring in the portal blood of fasting animals, and which are replaced by such as appear to be young and perfect in the blood of the hepatic veins. It is not, however, to be supposed that all tlie iron is economized in this manner ; a considerable portion of it accompanies the pigment as an essential in- gredient, and is finally discharged through the intestine. OF THE DUCTLESS GLAISTDS. The salivary and sudoriparous glands discharge their secretion directly through ducts. The liver and kidneys have upon their ducts tj^^ ^uctiggg an additional mechanism, the gall bladder in the one case, and glands, the urinary in the other, which serve as receptacles for storing up the product of action in a temporary manner, and so converting the continu- ous effect of the gland into a periodical result. In each of these instances we may arrive at conclusions of a certain degree of exactness respecting the functions and use of the gland from a study of the secretion it yields ; but there are in the system other glandular organs which differ essen- tially from all the preceding in not being furnished with ducts. These are the spleen, the thymus and thyroid glands, and the supra-renal cap- sules. ]\Iuch diversity of opinion prevails respecting the true nature and ac- tion of these bodies. From their structure bearing a resem- Tj^gjj. supposed blance to that of the preceding, with the exception of the ab- fiuictions. sence of a duct, many have thought that, like them, they are really secret- ing organs. Others have supposed that they have a relation to the nu- trition of the system, in giving origin to the development of cells, or that they are connected with the organization of the blood itself; and that such is their duty is perhaps rendered probable by the circumstance that some of them, as the thymus and thyroid, exhibit their utmost develop- ment when the body is rapidly growing, and diminish when matm'ity is reached. That they enjoy a community of action, or that their function can be vicariously discharged by other organs, has been clearly estab- lished by the result of operations in which one or other of them has been extirpated. With respect to the spleen^ the views of Professor KoUiker are sup- ported by many facts. He supposes that one of the chief func- Function of tions of that gland is the dissolution of the disorganizing blood- ^^^ spleen, cells preparatory to the action of the liver, in which hasmatin is to be converted into the coloring matter of the bile. In the discussion entered into respecting the origin of the bile, we have come to the conclusion that it is derived from the systemic venous blood, and in the supposition here presented respecting the function of the spleen there is nothing con- 212 THE SPLEEN. tradictorj, for it is to be remembered that the blood of the spleen is a constituent of the portal circulation. It also appears to be a general opinion that the spleen likewise maintains a mechanical relation to the portal mechanism by serving as a receptacle for any excess of blood, and thus relieving the vessels of pressure, or by acting in like manner when there is any obstruction to the passage of blood through the liver. As our knowledge of the action of the ordinary glands becomes more Analogy of the accurate, the function of the ductless glands loses much of "^^'^tl^^duct ^*® peculiarity. As we have already stated, in a certain less. sense the liver itself may be said to be a ductless gland, for it appears to be one of the constant duties of that organ to prepare sugar from materials in which it did not pre-exist. And this sugar does not escape through the hepatic ducts in company with the bile, but is taken directly into the system through the hepatic veins. But this principle of action is identically what occurs in the case of every ductless gland, and hence it may be inferred that the changes which these impress on the blood are necessary for the development and nutrition of the system. If the doctrine of KoUiker be correct, the spleen is only an appendix to the liver, and the same duct answers as a common outlet for both. The views here alluded to are enforced by the examinations which Nature of have been made of the blood of the splenic vein. The fol- spienic blood, lowing table exhibits the contrast between it, that of the ex- ternal jugular, and that of the mammary artery. Constitution of Splenic Bhod. {From Scherer.) Mammary Artery. Ext. Jugular. Splenic Vein. 750.60 89.50 159.90 778.90 79.40 141.70 746.30 124.40 128.90 .40 Albumen Corpuscles and Fibrin.... Loss 1000.00 1000.00 1000.00 From which it appears that the blood, after circulating through the spleen, has lost a large portion of its cells, the relative quantity of its albumen is greatly increased, and, moreover, trom being the basic albu- minate of soda, the form under which it ordinarily occurs in the blood, it has become the neutral albuminate, as is proved by a turbid appear- ance on the addition of water, and this state it seems to retain during the portal circulation, for the blood of the hepatic veins exhibits the same peculiarity. OF EXCRETION. 2l3 CHAPTEE, XII. OF EXCKETION. THE tmiNE, MILK, AND CUTANEOUS EXCRETIONS. Sea'Cfion and Exa-eiion. Of the Kidneij: its Structure and Functions. — The Malpighian Circidation. — 77(6 Urine: its In- ffredients, their Variations and Sources. — Abnormal Substances in it. — T7ie Water and Salts exude by Filtration. — The Cells remove unoxidized Bodies. — Manner of Removal of the Liquid from the Malpighian Sac. Of the Mammary Gland: its Structure. — Colostrum and 3Iilk. — Ingredients of Milk and their Variations. — Influence of Diet. — Inquiry into the Origin of the Ingredients of the Milk, its Fat, Casein, Salts, Sugar. — Alanner of Action of the Gland by Strainage. Of the Shin. — Structure of its Epiderma and Derma. — Sudoriparous and Sebaceous Glands. — Nails. — Hair. — Ingredients of Perspiration. — Exhalation: its Amount. — Causes of the Vari- able Action of the Stin. — Its Double Action. — Absorption by the Ski7i. — Genei-al Summary of the Cutaneous Functions. The function of secretion is very commonly treated -of Iby physiolo- gists under two divisions, secretion and excretion. The pjgting^j ^ former refers to the separation from the blood of those fluids tween secretion which are required for the uses of the body, and wljich are therefore still retained ; the latter, to those which are effete, and to be cast out as excrementitious matter. Of secretions, the saliva or the pan- creatic juice may be taken as examples ; of excretions, the urine. But this subdivision is only one of convenience, and has no natural foundation. The so-called secretions are, m many instances, far from being more highly elaborated bodies ; in reality, they are often on their descending career. And among excretions, if milk be enumerated, as it ought to be, since it is a dismissed product of the system preparing it, we have, instead of an excrementitious, a pre-eminently nutritive body. Nevertheless, since this manner of considering the subject oifers con- siderable conveniences, I have resorted to it for the preceding and pres- ent chapters. In this I shall accordingly treat of the urine, the milk, and the products removed by the skin. OF THE KIDNEYS. The products of waste arising from oxidation in the functional activity of the system, and which are of a non-gaseous kind, the use- pj^ ^^j^^^ ^^^^ less materials, saline or otherwise, which have been absorb- tion of the kid- ed in the digestive tract, and carried into the circulation, ^^^' must be removed. Gaseous substances and vapors may pass away through the lungs, but solid material must be excreted in a state of so- 214 STEUCTURE OF THE KIDNEY. lution in water. To accomplish this object, a special mechanism, the kidney, is introduced. From this manner of considering the functional duty of the kidney, it is very clear that a special relation must exist between this excreting or- gan and the respiratory mechanism, for in the case of animals which breatlie by gills, or in those which, though subsequently atmospheric breathers, receive their suj)ply of aerated blood before birth by a placenta, the conditions under which aeration takes place are such as permit the removal of solid material by the respiratory mechanism. The urinary excreting apparatus of an animal breathing air is therefore necessarily burdened with an exclusive duty, which is shared by the gills and the; skin in a water-breather. In fishes, the renal apparatus is constructed under the condition here . indicated, and though in many it appears to be greatly de- birds, fishes, veloped, extending as a tubular arrangement from the skull insects, etc. through the abdominal cavity, it is to be regarded as analo- o-ous to the Wollfian bodies rather than to the true kidney. In reptiles the proper kidneys appear ; in birds they are well developed, but their secretion is, for the most part, a semi-solid substance, chiefly urate of ammonia. The tubular form is presented in both insects and arachni- dans, discharging its secretion into a cloaca. In man the kidneys may be described as a pair of dark-red ovoid bod- The kidneys in i^s, placed one on each side of the vertebral column, in the man. lumbar region, the right kidney being a little lower than the left. In the adult the kidney is four or five inches in length, and is en- veloped in a mass of fat. Blood is brought firom the aorta to supply the organ by the renal or emulgent artery, and is carried back by the emul- gent vein into the inferior vena cava. During its passage through the kidney there is removed from the blood a liquid secretion, the urine, which, flowing down a long channel, the ureter, is emptied into the blad- der, from which it may be periodically.removed. The supra-renal capsules are bodies Of a yellow-red color placed above Supra-renal tlie kidneys. They are much larger in the foetus than in the capsules. adult, and doubtless have a reference to the peculiar conditions of respiration obtaining at that time, for, as we have just observed, the renal and respiratory mechanisms are necessarily interconnected. The substance of the kidney is described as consisting of two por- tions, the cortical and the medullary or tubular, as, seen in jVIinutG stmc- ture of the kid- Fig. 88, in wliich 1 is the supra-renal capsule ; 2, the vascu- ^®^'- lar portion of the kidney; 3, 3, tubular portion grouped into cones ; 4, 4, papillee projecting into calices ; 5, 5, 5, the three infundi- bula ; 6, the pelvis ; 7, the ureter. (Wilson.) From which it appears that the cortical substance is the external portion, and the tubular is THE MALPIGHIAN CORPUSCLES. 215 Section of the kidnej ^'S- S3- grouped into cones, the base of each cone being- out ward, and the point toward the pelvis of the kidney. The cortical substance, however, envel- ops the cones nearly to their points. It is of a red color, and is the seat of the secretmg action. The urine, as it arises, passes along the line con- vergent vessels, the uriniferous tubes, and these, coalescing as they approach the points of the cones, o'ive orio-in to what are termed the ducts of Bellini. From these the secretion passes into the calices, thence into the pelvis, and so along the ureter into the bladder. In the cortical substance there are large numbers of dark points, the Malpighian bod- ies. Their diameter is about yi-g- of an inch. Mr. Bowman has demonstrated that the minute structure of the cortical portion is as follows : The uriniferous tubes, as they approach it, under- go bifurcation in such a way that the branches continually arising have, for the most part, a diameter of about -^-^ of an inch. As they enter it fhey are contorted, and at their ends present small capsules or ilask- shaped sacs. Each of the capsules is entered by a twig of gtructureofthe the renal artery, which at once divides into loop-like branch- Malpighian es constituting a tuft, and which delivers the blood to a '^°^^^'^^^ ^^^ vein orip'inatino- in the interior of each tuft. These structures are known as the ]\Ialpighian corpuscles. The vein and artery pass out of the cor- puscles usually at the same point ; the vein, however, instead of deliv- ering its blood at once to the renal vein, forms a plexus on the sides of a uriniferous tube, in this simulating the mechanism of the portal vein, which begins in a capillary system and ends in one. It is supposed that the exudation of the water of the urine takes place in the ]\Ialpighian body, an-d the secretion of the solid portions from the cells which cover the uriniferous tubes. The chief feature of this structure is, therefore, that in a sac formed upon a uriniferous tube, a tuft of capillaries, the walls of which are of ex- treme tenuity, permits water to escape from the blood supplied by the emulgent artery. The blood, thus concentrated by loss of its water, passes into the veinlets which, originate in the interior of the tuft ; these, converging into a little trunk, less in diameter than the twig r\rcn\ tion of of the emulgent artery, escape along with that vessel from thebioodinthd the capsule ; but, instead of discharging its contents into the ^ "^-^ " renal vein, it ramifies in a plexus on the walls of a uriniferous tube, thus afibrding a miniature representation of the portal vein, beginning in a capillary system and ending in one. From the plexus the commencing capillaries of the renal veins arise. 216 THE MALPIGHIAN CORPUSCLES. ■ert Half diagram of human Malpighian Fig. 00. Some anatomists suppose that the Malpighian capsule is not, in reality, rio so a flask-like expansion of the uriniferous tube, but that the tube, dilating, folds over the blood capillaries, and so receives them. However that may be, they form a loose ball in its in- terior, fastened to it only by the arterial twigs and its corresponding and juxtaposed vein. The foregoing description is illustrated by the annexed figures, Mg. 89 being half dia- grammatic, from Kolliker. 1, a Malpighian capsule, A, with the tubulus uriniferus, B, C, springing from it ; a, membrane of Malpighian body, continuous at b with the merabrana pro- pria of convoluted tubule; c, epithelium of Malpighian corpuscle ; d, that of tubule ; e, detached epithelium ; y, vas afferens ; g, vas efferens ; h, glomerulus Malpighianus : 2, three epithelial cells from convoluted tubule, mag-ni- corpuscle, magnified 300 diameters, g^^ 35Q diametCrS— OnC with oil drOpS. JP'ig. 90, Glomerulus, or tuft of blood-vessels from the innermost part of the cortex of the kidney of the horse : a, arteria interlobularis ; af, vas afferens ; tn on, glomerulus ; ef, vas efferens ; b, divisions of arteriola recta in the medullary substance. JPtg. 91 shows the ciliated epithelium of the uriniferous tube in the frog: a, cavity of the uriniferous tube ; b, its epithelium ; b^, ciliated portion thereof ; b'',de- Fig.di. tached ciliated epithelial cell ; c, basement mem- brane of the tube ; c^, that of the capsule ; m, capillaries of the tuft ; i, adjacent uriniferous tube. Mr. Bowman's expla- nation of the Malpighi- an circulation is repre- sented in I^ig. 92. a, branch of renal artery ; af, afferent vessels ; m, • j m, Malpighian tufts ; ef, Glomerulus fr^ojn_the^h^orse, magni- ^y- pffg^ent VCSSCls ; ^, CUia on~^inifc^us tube of frog THE MALPIGHIAN CORPUSCLES. 217 their plexus upon the uriniferous tube ; st, straight tube ; ct, convoluted tube. I am indebted to Dr. Isaacs for the followino- in- o structive figures and descriptions from his paper read before the Academy of Medicine. His method of Fig. 93. examination of the minute mechanism of the kidney, by rendering small por- tions of it transpa- rent, greatly facili- tates these research- es. Dr. Isaacs's in- vestigations are entirely confirmatory of Mr. Bowman's views, so far as structure is concerned. Fig. 93 is a view obtained by agitating scrapings of the kidney of a Maipiginan Fig 94 Diagram of Malpighian circu lation. tuft irith uriniferous tube, mag- nified 75 diameters. Paiptured Malpighian coil of the deer, magnified SO diameters. Nudeated cells on coil, magnified SO diameters. sheep (which had pre- viously been injected with chrome yellow and sulphuric ether) in a test-tube with water. The portion on the left shows the tuft alone, that on the right its reception in the urinif- erous capsule. Fig. 94 shows the artery, filled with in- jection, and the Mal- pighian coil or tuft rup- tured in the capsule. The injected material lies in broken portions. Fragments of the in- 218 THE URINE. jected vessels of the coil are seen passing clown the tube. From the kidney of the deer. A difference of opinion prevails among anatomists as to the existence of nucleated cells upon the Malpighian tuft or coil in the case of the higher animals. This question is finally settled by Dr. Isaacs in the following manner. An ethereal or watery-colored solution is injected into the ure- ter, so as to distend the tubes, burst, and throw off the capsule. The cells can then be seen upon the naked tuft or coil. Fig. 95 shows the ]\Ialpighian body and uriniferous tube of the kidney of the black bear. The artery had been first partially filled with injection, which had broken the coil in pieces. The injection from the ureter ruptured the capsule, which is seen in shreds. Nucleated cells are seen on the naked coil or tuft. In the upper part of the figure, to the left, is a broken tuft, on the right of which the ruptured capsule is perceived, and nucleated cells upon the uncovered tuft. In the upper part of the figure, to the right, are the fragments of a Malpighian tuft, with nucleated cells adhering to it. The capsule had been torn off with a fine needle. AU the above drawings were made under the microscope. The urine of man is a clear, amber-yellow liquid, the average specific •. gravity of which may be taken at 1.020, giving an acid re- The unne, its & •/ •'_ ' o o_ properties and action when first voided, but gradually becoming alkaline quantity. ^^^ turbid. Its composition varies greatly with preceding states of the system, and the nature and quantity of the food. It amounts, in the course of a day, to from 20 to 50 ounces ; this, however, depending on the quantity of water that has been taken, and on the ac- tivity of the skin. Its solid ingredients vary from 20 to 70 parts in 1000 of the urine, the leading substances being urea, uric acid, lactic acid, ves- ical mucus, epithelial debris, extractive, and salts. The urine of carnivorous differs from that of herbivorous animals, the latter being turbid, and having an alkaline reaction ; that of the former transparent, pale yellow, and acid. From Winter's experiments, it appears that for every thousand parts of his weight a man discharges 25.9 parts of urine per diem, the max- imum being 46.8, the minimum 14.0. A child, reduced to the same standard, discharges 47.4 parts ; but a cat, fed on a flesh diet, 91.036. The quantity of water thus removed depends, to a very gTcat extent, on the existing conditions of the system ; sometimes it is far less than would answer to the amount that has been taken ; sometimes, on the contrary, more. The solid material likewise exhibits very great fluctuations. Viewed as a group, the constituents of the urine are evidently the ox- ^ . . ^ ,, idized residues of the system, which, unable, from their not Ongm of the „ i i other urine possessing the vaporous or gaseous form, to escape througii constituents, ^j^^ lungs, are, from their solubility in water, readily removed COMPOSITION OF THE URINE. 219 hy the kidneys. The urea and uric acid are derived from muscular de- cay ; perhaps, of the two, the uric acid first arises, and is subsequently converted into urea ; this is not, however, its exclusive source, since the quantity of urea increases by the use of highly nitrogenized food. The mucus and epithelial debris are derived from the mucous membrane lin- ing the interior of the urinary apparatus. Of the salts, there are two of unusual interest, the sulphates and phosphates, each having, like the urea, a double origin, the food and tissue decay. Leaving out of consid- eration that part which has been supplied by the food, we recognize in the sulphates the final disposal of that sulphur which was once secreted by the liver, and subsequently reabsorbed. In the phosphates we recog- nize the oxidation of the free phosphorus of the nervous Constitution of vesicles during their period of activity. That portion of the ^"'i'^'^- solid constituents of the urine which is due to decay or retrograde met- amorphosis is shown when an animal is exclusively fed on sugar. Composition of Urine. {From Herzelius.^ Water 933.00 Urea 80.10 Uric acid 1.00 Lactic acid, lactate of ammonia, and extractive..... 17.14 Mucus 00.32 Sulphate of potash 3.71 Sulphate of soda 3.16 Phosphate of soda 2.94 Bi-phosphate of ammonia 1.65 Chloride of sodium 4.45 Muriate of ammonia 1.50 Phosphates of lime and magnesia 1.00 Silica 0.03 1000.00 The composition of urine is not only disturbed by variations in the amount of its normal ingredients, but likewise, in morbid states, by the appearance of unusual ones. Among these may be more particularly mentioned sugar, albumen, blood, bile, pus, fat. The presence of such abnormal ingTcdients is determined by chemical tests or microscopic ob- servations. Since the urinary apparatus is the sewer of the system, tables, like the preceding, which purport to set forth the composition of its Variability of excretion, can only be received as general illustrations. In its constitu- the urine must occur whatever materials have been gener- ated in the complicated disintegration of the economy, and whatever use- less substances have found their way in through the absorbents by rea- son of their solubility in water. Respecting the substances thus occurring, either normally or unusu- ally, in the urine, the following are observations of interest : The quantity of urea excreted depends more upon the nature of the 220 OEIGIN AND YARIATIOXS OF UEEA. Variations in ^^^^ ^^^^ upon any Other condition. It reaches its maxi- the quantity mum Under an absolute animal diet, and its minimum under ° ^^^^' a non-nitrogenized one. It still appears during fasting, and about to the same extent as during a non-nitrogenized diet. Its sources, therefore, are partly the waste of the tissues and partly the food. By several observers, urea has been detected in the blood under ordi- nary circumstances. After extirpation of the kidneys it has been re- peatedly recognized in that of the lower animals. It is removed "with such rapidity by the kidneys that its quantity is probably never per- mitted to exceed a fiftieth of one per cent, of the circulating blood. Its origin has generally been attributed to the waste of muscular tissue, though it has not yet been detected in muscle juice ; but then it should be remembered that creatine and inosic acid may produce it during theu* descending metamorphosis. Under this view, the seat of its production would be the blood itself, a conclusion which is enforced by the circum- stance that caffeine also increases its amount. In his inaugural dissertation, entitled, " Is muscular Motion the Cause Origin of the of the Production of Urea ?" Dr. John C. Draper, by experi- iirea. ments on the urine of persons in different conditions of motion and rest, and by an examination of the diurnal and nocturnal variations in the amount of urea voided, compared with an invariable standard, gives reasons for concluding that the differences in the amount of urea excreted are almost entirely attributable to the influence of the food, an individual in such a state of comparative rest as is observed during treat- ment for a fractured leg not excreting by any means so much less urea as might have been anticipated when compared with another individual who walked thirteen miles at the rate of four and a half miles an hour. But, on examining the influence of food, it appears to be well marked. The greatest amount of urea is excreted within a few hours after dinner. Another maximum also occurs just after breakfast ; but during the eight night hours far less is excreted than during the same period in the aft- ernoon. The ingestion of food thus exercising so rapid and marked an influ- ence on the quantity of urea, he refers to it as the cause of the increased excretion of that substance during the course of the day rather than to the increased motion of exercise then indulged in ; and in view of this conclusion, it becomes probable that the nitrogen of the wasting muscu- lar tissues escapes, not under the form of urea through the kidneys, but through the skin, or perhaps even as free nitrogen from the lungs. Of the variations of the sulphates, it may be observed that the aver- Variations of ^g® diumal cxcretion of sulphuric acid per thousand parts of the sulphates, man being 0.050 of a part, an increase is observed during di- gestion, a diminution occunring during the night, the minimum being EXTLACTIVE AND SALTS. 221 reached in the forenoon. Exercise to a moderate degree does not seem to influence it, though that of a more violent kind, and also mental ex- citement, do. Fasting for one day does not diminish it. Copious drafts of water increase it, but it subsequently declines. The admin- istration of sulphur, and of the sulphates of potash, soda, and magnesia, also increases it, the latter salts being removed from the system through the kidneys. The quantity of extractive matter excreted by children is much more than that excreted by adults, when estimated, as all such ^ •^ Quantity of ex- observations ought to be, by reduction to a common stand- tractive in ard. Thus Scherer found that for every thousand parts of ^^^^'^^' weight a child excreted 0.346 of a part of extractive per diem, but an adult, for each thousand parts of weight, excreted 0.156 of a part, which is less than half as much. The quantity of chlorine in the urine, as chlorides of sodium and po- tassium, undergoes many variations. Hea-ar shows that it -^^ . . . ° . ° Variations in is at a maximum m the afternoon, at a minimum in the the chloride of night, and rising toward morning. Its quantity is increased ^°*^^^"°^- after taking water, and then diminishes. Muscular exercise also in- creases it. It is interesting to remark that, in inflammatory conditions accompanied by copious exudations, the chlorides in the urine are so much diminished that that secretion in its fresh state will yield no pre- cipitate with nitrate of silver. Li 80 cases of pneumonia observed by Kedtenbacher, the acidified urine did not become turbid with nitrate of silver, but as the inflammatory action subsided the chlorides reappeared. Of medicaments and other unusual substances introduced into the or- ganism, those which are soluble in water, and have little t. ° . . n T ^ -liscape of unu- aninity for the constituent matters of the body, are removed suai salts in in the urine. In this list are found a great number of salts ^^^ ^^^^^' which escape in this manner without undergoing any change ; such, for example, as carbonate of potash, nitrate of potash, bromide of sodium. Other substances undergo change previously to their elimination, as, for instance, the alkaline sulphides, which become oxidized, and are then finally removed as alkaline sulphates. Dr. Bence Jones has satisfactori- ly shown, that, when ammonia is taken, it is removed as nitric acid in the urine. Under the administration of the neutral alkaline salts of vegeta- ble acids, alkaline carbonates in excess appear, owing to the oxidation of their acid in the blood. That this is the true seat of the oxidation, and that it takes place with great rapidity, is demonstrated by the in- jection of such salts into the jugular vein, which very soon are found as carbonates in the urine. When oxalate of lime is introduced into the stomach, it does not make its appearance in the urine, perhaps because of its insolubility present- 222 HIPPUEIC ACID, LACTATES, PROTEIN BODIES. ing a difficulty to its absorption. In the case of some animals it occurs Production of naturally in the excrement. When, in man, it is found in the ciis^urbeT ^^ urine, its occurrence may be often traced to a disturbance piration. of the respiratoiy function, or to abnorfnal metamorphosis occuiTing in the blood. Under such circumstances it presents itself in convalescence from typhus. That it can arise from such metamorphosis is proved by the circumstance that it is found in the urine after the in- jection of urates into the veins. When the kidneys act vicariously for the lungs, there tlius appears to be a tendency to the removal of carbon under the form of oxalic instead of carbonic acid. Hippuric acid may arise in the organism from the metamorphosis of Occurrence of bcnzoic and cinnamic acids, the administration of these sub- hippuric acid, gtanccs being followed by its excretion in the urine. If any thing was necessary to prove that the seat of its origin is the blood, its discovery therein, in the case of the ox, by Verdeil and Dollfass would be sufficient. Its general occurrence in the urine of gTaminivorous ani- mals, and its absence in that of the carnivora, indicate that its normal production is connected with the nature of the food. However, among some of the lower animals it is still excreted while they are in a state of starvation, and it has been recognized in the urine of diabetic patients under a strict animal diet. After the injection of alkaline lactates into the jugular, the urine be- Disappearance comes alkaline in the course of a quarter of an hour. If tates from the ^^^^7 ^^vc bccn taken into the stomach, in about double that blood. time. The passage of other salts is sometimes even more rapid ; thus the feri'ocyanide of potassium has been detected in the urine in less than two minutes. The excess of protein bodies absorbed from the digestive canal, and T. „ unnecessary for the repair of the system, is removed as urea Excess of pro- _ •'_ -^ _ •/ ' tein bodies re- and uric acid ; and, in like manner, the sulphur and phos- "^°^^ ■ phorus introduced by those bodies are, after oxidation, dis- charged as sulphates and phosphates. Under the use of a strictly ani- mal diet, the urine resembles that of carnivorous animals in color, acid reaction, and freedom from lactic and liippuric acids. Disa earance ^^^^ phosphatc of lime often almost totally disappears of phosphate of during pregnancy, and fractures unite at that period with ^'^^- difficulty. Many circumstances regulate the length of time that extraneous sub- Period that ex- stances will remain in the system ; thus it sometimes occurs traneous sub- that, after the administration of alkaline salts of organic acids, stances ma)' re- i n t • r- i • -m t • ^i r main in the the alkalinity 01 the urine will disappear in the course oi system. j^gjf g^ ^^j^ while on other occasions it will continue for sev- eral days. The period also varies very much with different individuals. IIEMOVAL OF URINE SALTS. 223 When the substance admmistered is of sucli a chemical nature that it can unite with any tissue, it may remain in the system for a very long time. The anatomical construction of the ]\Ialpighian bodies has led physi- ologists to infer that there are two distinct stag-es in the se- Manner of se- es O • f 1 cretion of urine. These have akeady been pointed out in urine "aUsbv the remark that the ]Malpighian bodies separate water from filtration. the blood, but that the solid ingredients are secreted from that delicate plexus of vessels which covers the walls of the urinary tubes. Before accepting this opinion, we may, however, observe, that the chief solid con- stituents of the urine, as urea, uric acid, sulphates, and phosphates, pre- exist in the blood, and are all soluble in water. It is not to be supposed that the water which oozes through the delicate walls of the JMalpio-hian tufts should leave such substances behind it. That the loss of water actually takes place in the tuft cii'culation appears to be proved by the fact that the vessel emerging from the tuft is less than the one entering it ; the volume of blood is less by the amount of abstracted water. We must, moreover, take care that we are not deceived by a name. The vessel emero-ino- from the tufts raav be conveniently „, . , o _ o _ •' , _ -^ The arterial enough called a vein, but is there any proof that such is its quality retain- physiological attitude ? There is no reason to believe that ^^ "^ *^® ^"^'^^ the blood has lost its arterial character while it has been in the tuft. At the most, it can only have lost the elements of ui'ine. It is not until it is distributed in the plexus on the walls of the uriniferous tubes that it really gains the venous character, and then through nourishing those ves- sels, and particularly the cells of their interior. These considerations therefore lead me to the suggestion that the inor- ganic bodies, as urea, mic acid, sulphates, and phosphates, which may all be regarded as products of final oxidation, pass out with the water in which they are dissolved while the blood is yet circulating in the Mal- pighian tuft. The loss of velocity in the current by the arterial twig breaking up into so many vessels must, as Mr. Bowman states, greatly favor this transudation, as does also the pressm-e that must arise from the blood having to pass through a narrow channel of exit, and still more through another capillary system just beyond. It was arterial blood that entered the tuft, and it is arterial blood that emerges, to be then directed upon the walls of the uriniferous tubes. And now the question may arise, What is the object of this second cap- illary circulation ? Though the statement is often made that The cells re- the constituents of the urine are the results of oxidation, it ^?°J^ ^uh^' is very far from being strictly tnie. The analysis of urine stances, shows that a very large proportion of them, classed as extractive, are real- ly combustible bodies, and not far advanced in their retrograde meta- 224 THE MAMMARY GLANDS. raorphosis. Tliej retain still, as it were, the traces of organization ; tliey belong rather to the hydrocarbon family than to the nitrogenized. It may be that, for the removal of these, cell action is necessary. Whatever importance may be attached to such a suggestion, it is very Modeofremov- clear that, notwithstanding the extreme thinness of the walls from \hV Mai- °^ ^^^® *^^-^^ vcsscls, the relaxation in the speed of the blood pighian sac. current through them, and the pressure brought to bear upon them, that water could not be separated by oozing through them unless there was an additional provision. The sac into which the exudation is to take place is already full, and it may be questioned whether ciliary mo- tion in the uriniferous tubes would exert a sufficient exhaustion to relieve the interior of the capsule from pressure ; but the introduction of a liquid of a different nature into the uriniferous tube may call at once into oper- ation the principle described at page 131 as acting in the capillary circu- lation of the blood, and thus the contents of the Malpighian sac are drawn forward into the uriniferous tube, just in the same manner that water is drawn from the inside of a bladder through the pores thereof by alcohol on the outside. THE MAMMAEY GLANDS. The mammary glands are situated on various portions of the abdom- „ . . „ inal and thoracic surfaces of animals of the class mammalia. Description of the mammary In the higher members of this class they present the appear- ^^^°'^' ance of racemose glands, rudimentary in the males, but well developed in the adult females, especially after, parturition. They separ- ate from the blood the white secretion, milk. In the ornithorynchus the mammary gland consists of an obtuse cone of coecal follicles, ending upon an areolar surface. There is no nipple. The milk is expelled, both in these and the marsupials, by direct mus- cular pressure. In cetaceans the nipple is included in a cleft of the in- Its compara- tegument, but in the higher mammalia it projects, so that, be- tive anatomy. ^^^ received into the mouth of the young, and suction being made, the pressure of the air takes effect upon the surface of the gland and expels the milk. In different cases the number of mammas differs. In the human spe- cies there are but two, placed upon the thoracic surface, and from their position favoring the care and nursing of the child. Among other ani- mals the number seems to have a relation to the number of young brought forth at a birth, there usually being a pair for each one. ,.Many excep- tions to this rule, however, occur. The mammary gland corresponds in anatomical structure to the paro- tid and pancreas. It consists of 15 or 20 lobes, each from | to 1 inch in width ; these are composed of lobules, and these, again, of coecal vesicles. The excretory ducts are lined with tesselated STEUCTUEE OF MAMMAEY GLAND. 225 Development ol the mammary gland. maiy gland Fig. 97. cpitlieliuni. The ducts converge toward the nipple, opening upon it by 10 or 15 apertures, and in their course dilating into ampullar, of small capacity in women, hut in the cow capable of holding a quart. Fig.^6. As regards its development, the mammary gland originates in the fourth or fifth its develop- montli as a papillary projection of the "^^'i'- mucous layer of the epidermis, as shown in Fig. 96, in which 1 is the rudimentary gland in the male embryo of five months, a being the horny, h, mucous layer of the epidermis ; c, process of the latter, the rudiment of the gland ; d, fibrous membrane round it. At 2 is the lacteal gland of a female embryo of seven months, seen from above : a, central substance of the gland ; b, c, budding outgrowths, the rudiments of the gland lobes. (Kolliker.) Fig. 97, vertical section* of the human mam- «, a, its pectoral surface ; b, b, skin on surface of the gland ; c, skin of nipple ; d, lobules and lobes of gland ; e, lac- tiferous tubes passing from the lobules to the nipple. As pregnancy advances, the cells of the gland begin to contain fat, in a manner not unlike that which is re- marked in the cells of the sebaceous follicles of the skin. When the gland becomes active after parturition, it is stated that the first-formed milk-cells break up in the lactiferous ducts into milk globules, their membrane and nucleus disappearing. The milk globules are minute particles, varying in their diameter from the ^L^ to the ^3^^^Q of an inch. They con- sist of oily material inclosed in an envelope, as is shown by the fact that, though they will resist for a short time the action of sulphuric ether, Fig. 98. they are finally dissolved by that substance. Be- sides these milk globules, there are other exceed- ingly minute fat particles present. The milk which is first secreted after delivery contains cor- puscles of considerable size, and of a granulated appearance, as seen in the photograph, Fig. 98. They are called colostrum corpuscles. They are soluble in ether, and therefore Milk with coiostrai corpuscles, contain fat. There is reason to suppose that all the fat globules of the milk are inclosed in cyst-like pellicles of casein. In the chapter on food (Chapter II.), a general description of the char- acter and constitution of milk has been given, together with its physio- Section of the human mammary gland. Milk globules. 226 COLOSTRUM AND MILK. Properties of logical relations in nutrition. It may now he added that fresh milk. milk presents an alkaline reaction, which continues longer in the milk of women than in that of cows. Left to itself, and the more quickly the warmer the air, milk turns sour through the production of lactic acid, the casein undergoing coagulation. That the oil globules just spoken of are coated with a film of a coagulated protein hody appears from the circumstance that it may be dissolved by acetic acid, and the in- cluded butter is then set free. One of the simplest methods for the analysis of milk consists in coag- Analysis of ulating it at a temperature of 212° with pulverized gypsum ; milk. i}^Q mass, being then evaporated to dryness, is pulverized, the butter being extracted by ether, and the sugar and soluble salts by hot alcohol. The amount of the soluble salts thus obtained may be determ- ined by incineration ; and since their amount is to that of the insoluble salts as 5 to 7, an approximate determination of the latter may be made, and thereby the weight of the sugar and casein corrected. This is the method of Haidlen. * It would appear, from examinations that have been made of the secre- tion of the mammary gland previous to parturition, that it lostrum and contains albumen in the place of casein, the casein gradually "" ■ appearing as the period of parturition approaches, but not reaching its maximum until a few days after that event. Colostra! milk differs essentially from the subsequent ordinary secretion, as the follow- ing table shows : Constitution of Colostrum and Milk. (From Simon.') Colostrum. Milk. Water Fat Casein Sugar of milk 828.00 50.00 40.00 70.00 3.10 8.90 1000.00 887.60 25.30 34.30 48.20 2.30 2.30 Ash Loss 1000.00 The specimens here presented were obtained from the same individual : and from the table it appears that the colostrum contains a much larger proportion of solid material than the milk. The quantity of fat is near- ly double ; the quantity of sugar is likewise much greater, but the rela- tive quantity of casein is less, this being in accordance with the state- ment that the production of that substance approaches gradually to a maximum which is not attained till a few days after parturition. The composition of milk varies with many circumstances. Thus, Variability in among COWS, it is Well known that there are certain breeds its composition, -vyhicli yield a milk in which butter predominates ; in others, a milk in which there is an excess of casein. It is in reference to this that such are, among agricultural people, often described as good butter VARIATIONS IN MILK. 227 cows, or good cheese cows, as the case may be. Such variations arc likewise often popularly referred to peculiarities in the color of these ani- mals ; and, indeed, there is a general impression of the same kind as re- spects the milk of women, that that of fair women is inferior to that of brunettes. L'Heritier, who has examined into this matter, selected two females of the same age, 22 years, and caused them to adopt the same diet and the same mode of life. The one was a blonde, the other a bru- nette. The following table exhibits the most marked of his results : Milk of Women of different Temperaments. (^From L'Hejitier.') . The Blonde. The Bruueite. Water Butter 892.00 35.50 10.00 58.50 4.00 853.30 54.80 16.20 71.20 4.50 Casein Sugar ot" milk Salts 1000.00 1000.00 The average of the various analyses he made shows the same general re- sult, though not so strikingly, the number being for the solid constitu- ents, in the case of the blonde, 120, and for that of the brunette, 134. As would be expected, the constitution of the milk varies greatly with the diet. Simon found that in the case of a very poor woman, influence of who had been almost deprived of the necessaries of life, the ^^^^ °° ™^^^- quantity of solid material was only 8. 6 per cent. On giving her a nutri- tious meat diet it rose to 11.9 per cent. Being again reduced, by cir- cumstances, to the utmost destitution, the solid residue sank to 9.8 per cent. ; and on once more being supplied with a nutritious meat diet, the percentage rose to 12.6. These results illustrate in a striking manner, as will be presently seen, the function of the mammary gland. Simon also found, in this particular case, that the relative quantities of casein and sugar do not greatly vary with these extreme dietary variations, but that the absolute quantitv of butter does. On the two occa- ^ . . „ , . ^ . '' ^ . Origin of the sions of starvation, it was as low as 8 parts m 1000 of milk, casein and of and on the two of full nutritious diet, it rose to 34 and 37 *^® ^'^"*''"" respectively. From this it seems to follow that while the amount of butter in milk is determined by the quantity and quality of the food, the amounts of casein and sugar are, to a considerable degree, independent thereof, and hence I believe their origin is to be attributed to changes taking place in the system, and that these substances are more immedi- ately furnished from metamorphoses of its structures. The casein and the sugar are reciprocally related to each other, the quantitv of casein steadily increasino- from the time of par- i, i .• ^ , , "^ , ... . Relative quan- turition until a fixed proportion is attained. At parturition tity of casein the quantity of sugar is at its maximum, a gradual decline '^" ^^Jgar. then occurring until its proportion likewise becomes nearly constant. 228 ACTION OF THE MAMMARY GLAND. Saline substances administered hj the stomacli or rectum do not al- Extraneous wajs appear in the milk ; thus the ferrocyanide of potassi- saits m milk. -^^^^ which may he quickly detected in the urine, can not be found in the milk. It is curious, that when iodide of potassium has been administered to the mother, in doses, for example, of tln-ee grains thrice a day, it can be readily detected in the urine of the infant by the usual test of starch and nitric acid. The diurnal quantity of milk yielded by the human female has been Diumal quan- estimated at from 32 to 64 ounces. This estimate is made tity of milk. ]-,^ determining the weight of the infant before and after suck- ling. Although a certain proportion is present in the gland, the secre- tion appears to take place for the most part with great rapidity. On the application of the infant the blood flows suddenly, and the milk pours into the ducts, constituting what is termed the draft. We now enter on a consideration of the function of the mammary M d f f gland, with a view of detennining whether it acts in virtue of the mamma- of its Special Construction, whether it fabricates in itself, by ry g an . ^-^^ agency of cells, the proximate constituents of milk, or whether it merely strains them from the blood in which they pre-exist. Due weight should here be given to the fact that, unlike the excretions of the lungs, the kidneys, or even the liver, the milk contains a very large percentage of histogenetic or formative bodies. Its casein can not be considered as in the career of retrograde transformation, since in the body of the infant it is presently changed into albumen. Such a fact might even lead us to suspect that we should detect some essential structural and functional differences between the mammas and other glands. The influence of special structure is, however, disposed of by the nu- Influence of i^^rous wcll-authenticated cases now on record, in which por- speciai struc- tions of the skin, or the stomach, the navel, intestines, the ax- illa, and glands in the groin have assumed a vicarious action, and secreted milk ; and though it has been said of the latter instance that it may be nothing more than an obscure manifestation of an attempt in the human species at a repetition of the mammary gland in a region near which it is normally present in the lower mammals, such a remark has no application m the other cases. We may therefore infer that the proxi- mate constituents of the milk are not manufactured by reason of any special structure of the gland which secretes them, since other structures can assume a vicarious action. This therefore narrows our inquiry down to the point, Does the mam- mary gland merely filter ofi" from the blood substances already existing in it, or, those substances not so pre-existing, are they made in this or- gan by cells ? Of the proximate elements of milk, many, such as the entire group SOURCE OF THE BUTTER OF MILK. 229 of its salts, are acknowledged on all hands to pre-exist in the rpj^^ ^^^^^ ^j. blood ; and these, constituting about ^V of its solid ingredi- milk exist in ents, must be admitted to pass into the secretion by strainage only. Of the other solid ingredients, the fat, which constitutes about one fourth, also exists in the blood, being derived by lacteal absorption from the food. Do milk-giving animals, then, find in their ordinary diet a sufficient quantity of oleaginous material to supply the drain establish- rpj^^ hvdrocar- ed through the mammary gland, and the calorifacient de- bons pre-exist mand, supposing none to be made in the system ? The re- searches of Dumas have definitely settled this question. Of these the following is an abridgment : Fat in Articles of Forage. Indian corn 8.75 per cent, Eice 1.00 " " Oats • 3.30 " " Rye 1.75 " " Wheat 2.10 " " Diy hay 2.00 " " Clover in flower 4.00 " " Wheat straw 8.20 " " Oat straw 5.10 " " Beetroot 0.05 " " Potatoes 0.08 " " A cow in good condition, eating 100 pounds of dry hay, will fiirnish 21 quarts of milk, from which there can be obtained 1^ pomids Quantity of fat of butter. If this butter was obtained exclusively from the i" forage. food, and none made in the system, we ought to find in the 100 pounds of dry hay 1^ pomids of fatty matter; but sulphuric ether can remove from such hay 2 pounds, and in several specimens of clover cut in flow- er, M. Boussingault found the proportion as high as 4 per cent. We may therefore affirm, relying on the universal experience of farmers, that the hay eaten by a milch cow contains more fat matter than the milk which she yields. Thus far, therefore, we are not authorized to regard the animal as capable of producing the butter found in its milk, but, on the contrary, we may be led to suppose that the whole of it is taken from the food. In a physiological point of view, a single experiment of this kind is insufficient. Errors may arise in comparing together hay taken by chance, and the produce of milk taken by chance. It would doubtless be far better to establish a direct experiment, giving the proportion of butter, determined by analysis, relatively to the proportion of fat matter consumed by a cow. This experiment has been made on such a scale and with so much care as to be very convincing. It lasted for a year, and was conducted on 7 milch cows, the milk, drawn twice a day, being 230 SOUECE OF THE BUTTER OF MILK. carefully measured. The 7 cows furnished 17,576 quarts of milk ; its weight was 36,382 pounds. Being analyzed from time to time, it was found to yield 3.7 per cent, of butter, completely deprived of water. From this it follows that these 7 cows furnished during the year 1346 pounds of butter. During this time they ate 30 pounds of hay, clover, and grass each day ; that is to say, the 7 cows consumed during the year 77,650 lbs. Now if in 100 pounds of hay there are 1.8 of fat, the 77,650 pounds represent 1378 ; recollecting, however, the use of clover, which is richer in fat, the amount should rise to more than 2000 pounds. But the but- ter obtained was only 1346 pounds. From this experiment, therefore, we gather, that a cow which is giving milk finds much more fat in the fodder she eats than is subsequently yielded in her butter. We may therefore conclude that such an animal extracts from her food most of the fat it contains, and that she either stores it up in her adipose cells, uses it for the production of heat, or con- verts it into butter. In the argTiment, as thus presented by M. Dumas, the question is con- sidered in its quantitative aspect, no allowance being made, however, for the amount of oily material accompanying the faeces, and no estimate of- fered of the proportion destroyed for the sake of producing heat. It might be that the entire amount of fat escapes in the former of these ways, and that, though a sufficiency occurs in the food, it is not absorbed therefrom into the system. There are many facts which show that the identical fat occurring in The identical the food is actually delivered by the mammary gland with is found in the ^^^y of its quantities unchanged. Thus, if by chance cows inilk. should eat the tender shoots of pine-trees, or wild onions, or other strong-smelling herbs, the milk is at once contaminated with the special flavor of their oils. The same, too, takes place when turnips are introduced in their diet. If half the allowance of hay for a cow is re- placed by an equivalent quantity of linseed-cake, rich in oil, the cow maintains herself in good condition, but the milk produces a butter more than usually soft, and tainted with a peculiar flavor derived from the lin- seed oil. To the preceding facts it is unnecessary to add any observations in re- lation to the carnivorous mammals, which obviously find in their prey large quantities of fat. In the chapter on calorifacient digestion, and in that on the functions of the liver, the evidence was presented both as regards the reception of oily material from the food, and likewise its fabri- Sufficient cation in the system. From these sources conjointly it may quantity of fat therefore be plainly seen that fats of various kinds must al- lu the blood. ^^^^ ^^-^^ ^ ^^^ blood. A simple arithmetical computation, CASEIN TKE-EXISTS IN BLOOD. 231 founded on the data furnished by the tables of the constitution of blood and of milk respectively, will show that there is at any moment a sufficient supply of fatty matters in the blood to furnish two thirds of the diurnal amount of milk. It does not seem, therefore, philosophical, under these circumstances, to impute to the mammary gland a power of forming but- ter. It doubtless obtains that substance directly from the blood ; and it may be that those bodies which are conceived of as cells, and which are supposed to arise in the lobules of the gland in successive broods, which run a rapid li\dng career, coming into existence, reaching maturity, dying and deliquescing with incredible rapidity, are, in reality, nothing more than oil globules which have coated themselves over with a cyst of coag- ulated casein, as in Ascherson's experiment, or just as they become coat- ed with a similar film immediately on passing from the intestine into the lacteal vessels ; and this, accordingly, is the opinion I entertain of their natui-e. Next of the casein. There has been much controversy among chem- ists respecting the existence of casein as a normal ingredi- Reasons for in- ent in the blood. Theoretically there does not appear any gei" exists\r' solid reason for denying that it may be one of those constit- blood. uents, considering the analogy of constitution which it shows with albu- men. The evidence is much more distinct and positive in the case of puerperal blood, and is greatly strengthened by the recognized tendenc}- to the occurrence of kiestine in the urine during gestation. This sub- stance, to which much attention has of late been devoted, makes its ap- pearance in such m'ine as a pellicle or membrane, which gradu- ally increases in thickness. It is not commonly seen before 30 liours after the urine is passed, nor later than the eighth day. Though sometimes appearing at an earlier period of gestation, it is more frequent in the seventh, eighth, or ninth months. The fact is not without signifi- cance for our present purpose, that it may reappear in the urine after par- turition if any thing occurs to check the secretion of milk. Moreover, Prout noticed it in the urine of a delicate child which was fed chiefly on milk. An examination of it shows that kiestine is composed of casein, a butyric fat, and the phosphate of magnesia. Such a constitution betrays at once its relation to the secretion of the mammary gland. Lehmann, who inclines to the belief that kiestine is nothing else but the formation of crystals of triple phosphate and fungoid and confervoid growths, which take place when the urine becomes alkaline, admits that, unless it has been the basic albuminate of soda which has been mistaken for it, casein does occasionally occur in the urine. From the acknowl- edged fact that the acid interstitial juice of muscle fibre contains casein, there can not be any doubt, I think, that that substance must pre-exist in the blood. 232 SOURCE OF THE CASEIN OF MILK. Tlie occurrence of casein under the form of kiestine in the urine, in quantity increasing as gestation advances, indicates therefore that the system is assuming a propensity for the generation of this suhstance from its albumenoid compomids ; and since, in cases of starvation, the percent- age of casein in the milk does not seem to "be materially affected, we arc to attribute its immediate source to the system rather than to the food. In this respect it differs from the oily constituent, butter, the percentage amount of which is instantly affected by variations in the nature and quantity of the food. It would seem, indeed, that, from the same plastic ingredient, albumen, the soft tissues of both mother and infant are fabri- cated, with this difference, that in the latter case the temporary condition of casein is intermediately assumed. We have already remarked on the identity of constitution of albumen, casein, and fibrin, so far as their car- bon, hydrogen, nitrogen, and oxygen are concerned ; and, indeed, these compounds differ far less in their physical characters from one another than albumen in its coagulated and uncoagulated state ; yet that differ- ence in physical quality may be readily brought about by so trifling an agency as rise of temperature through only a few degrees, and is proba- bly dependent upon the different allotropic forms which the carbon con- stituent is prone to assume. Giving due weight to these various consid- erations, we shall find reason to conclude that this constituent of the milk, the casein, is directly derived from the system, which can manufac- ture it at a rate of about 30 grains per hour, this being about one half the quantity of fibrin generated in the same period of time for the sup- port of the musclar tissues. Chemically, the transition from albumen to casein is not to be regarded either as an ascending or declining meta- morphosis, but only as the temporary assumption of a state of passage onward to the condition of fibrin. With respect to the constitution of casein there is considerable doubt. Complex na- The substance commonly passing under this title seems to ture of casein, consist of at Icast two different bodies ; at all events, it may be separated into two parts, one containing sulphur, and the other not ; moreover, if to milk, which has been perfectly freed from butter, there be added dilute hydrochloric acid, the ordinary precipitate is yielded, but there still remains in solution an analogous body, which does not precipi- tate until the mixture is boiled. In milk, though much of the casein is held in solution, much also exists in the coagulated state, forming the wall of the milk globules. Its existence under this membranous form may be demonstrated by the action of acetic acid on milk globules un- der the microscope, and also by shaking new milk with ether, which pro- duces very little change ; whereas, if the milk were only an emulsion, the ether should take up the fat and hold it in solution. Now, on the addi- tion of potash or its carbonate to milk before the action of ether, those THE ACTION OF THE MAMMARY GLAND. 233 substances dissolve the membrane, and then the ether takes up the fat and forms a dhuly-clear solution. We may therefore conclude that the substance we designate as casein consists of two ingredients, the protein compound, which exists in a state of solution in milk, and also that which forms the membrane of the fat corpuscles. Many of the remarks just made respecting the origin of casein are ap- plicable to the saccharine constituent of the milk, the origin Origin of the of which is not to be attributed so much to the food directly sugar of milk, as to the system ; for, in starvation, the sugar, like the casein, still con- tinues to form to nearly the normal amount. I think it is probable that its production is due to the liver, and is, in reality, nothing more than an indication of the continued action of that gland, one of the prime func- tions of which is the generation of saccharine compounds. From the data now before us respecting the origin of the diiferent con- stituents of the milk, the casein, the butter, the sua-ar, and t.. ' ' _ ' o ' ihe mammary the salts, we are able to come to a definite conclusion re- gland acts by garding the physiological action of the mammary gland. I have entered on this long disquisition from the important bearing which the decision we arrive at has upon the whole theory of secretion ; for if there be a gland in the body in which we should expect to find proofs of formative power, through the agency of cell life or otherwise, in giving rise to products that did not pre-exist in the blood, it is certainly the mammary. But now, as it appears that all the constituents which its secretion contains are found in the blood, we can scarcely suppose that the gland itself does more than merely strain them out ; of course, in com- mon with all such structures, it possesses what might aptly be termed an elective filtrating power ; thus it permits the exudation of the iodide of potassium from the blood, but refuses a passage to the ferrocyanide. And, finally, the conclusion to which we thus come recalls the remark heretofore made, that the more thoroughly we study the secretions deliv- ered by the various glands, and the more perfectly we identify the sources from which their constituent ingredients have been derived, the more we should be disposed to impute glandular action to the physical process of elective filtration, and the less to the agency of cell life. OF THE SKIN. The skin is composed of two layers, the epidermis or cuticle, and the derma or cutis. It contains two systems of glands, one for the removal of water, and another for that of oily substances. It also presents sub- sidiary parts or appendages, such as the nails and hair. The epidermis, which is the exterior portion of the skin, originates from the cutis. It has a different thickness in different parts; The epidermis: the contrast, in this respect, being very well shown upon the ^*^ structure. 234 THE EETE MUCOSUM AND THE TEUE SKIN. soles of the feet and the eyelids. In this respect its use is mechanical. It serves as a protective covering to the parts it envelops, being thick where pressure and hard usage have to be provided for, and thinner where there is a necessity for motion. It consists of an aggregation of nucle- ated particles adliering together, the deepest being granules, the inter- mediate more perfect cells, which gradually become flattened scales as they are examined nearer the surface. They undergo constant exuvia- tion, and are as constantly replaced from beneath, the superficial ones becoming dry and horny, thus furnishing a resisting tegument, the oper- ation of which is very well displayed by the action of vesicating agents : a watery discharge from the vessels of the cutis soaks through the lower substance of the cuticle, and raises the dry layers above. The chemical composition of these dry scales is the same as that of nail, hair, horn, and is C^g, Hgg, N^, O^g. At one tim'e it was supposed that the rete mucosum, or layer of Mal- pighi, which is the lowest portion of the cuticle, and there- llete mucosum ir & ' .... . and its color- fore resting on the cutis, is a distinct structure. It is, how- mg matter. ever, merely the most recently-formed portion of the cuticle. The netted appearance it presents originates in the eminences of the pap- illary structure below. Many of its constituent particles contain col- oring matter, especially in the dark races. The pigment seems to be produced by the agency of the sunlight and continued high temperature, though it disappears gradually as the cells containing it approach the surface. It yields a very large percentage of carbon. Beneath the epidermis is the derma or true skin. It is composed of ^„ ^ fibrous tissue, which also serves to connect it with the parts 1 he derma : . t • i its construe- beneath, blood-vessels, lymphatics, and nerves. In its areolar ^^^'^' tissue both the white and yellow fibrous elements are found, the proportion of each varying according to the mechanical function the part has to discharge, the yellow predominating where elasticity is re- quired, and the white where a resistance to pressure. The derma also contains organic muscular fibres, to which its property of corrugation, as in cutis anserina, is due. On different parts it is of different thickness, being thinnest where motion has to be provided for. A deposit of fatty material, lodged beneath, gives it a yielding support. Its outer surface presents a papillary structure, which is the instrument of touch. This is more perfectly developed on the inner surface of the palm of the hand and fingers. The furrowed aspect of the cutis arises from this. A farther consideration of the mechanism and functions of the papilla3 is deferred to the description of the sense of touch. The photographic engraving, .Fiff. 99, represents a thin section of the epidermis of the foot of the dog. The general method of arrangement of the constituent portions of the THE CUTICLE. 235 Fig. 9:1. i^l iiS Epidermis of dog, magnified 20 diameters. Pli I II 1 I I ti II ( skm of e II lu 1^11 ill 1 ll> di unitcrs skin may Ibe gathered from the perpendicular section of that of the ex- ternal auditory meatus in Fig. 100. «, the derma ; h, rete mucosum ; c, horny layer of epiderma ; d, coil of ceruminous glands ; e, their excre- tory ducts ; f, their apertures ; g, hair-sacs ; A, sebaceous glands ; ?", masses of fat. (Kolliker.) Fig. 101 shows the under surface of the cuticle detached by macera- tion from the palm, exhibiting double rows of depressions, in which the papilla have been lodged, with the hard epithelium lining the sudoripa- rous ducts in their course through the cutis. Some of them are con- torted at the end, where they have entered the sweat gland. (Todd and Firj. 101. Bowman.) Fig. 102, papillse of the palm, the cuticle being - de- tached. (Todd and Bow- man.) Fin. 102. Under surface of the cuticle. Papillae of palm, magnified 35 diameters. Fig. 103, surface of tlie skin of the palm, showing the ridges, ftiiTows, cross grooves, and orifices of the sweat - ducts. The scaly texture of the cuticle is indicated by the irregular lines on the surface. (Todd and Bowman.) 236 THE NAILS AND HAIR. Fi/;. 103. The nails. of the fingers and the toes The Nails constitute one of the appendages of the epiderraa. They are horny coverings protecting the extremities They originate in a fold of tlie cutis, and become free at their outer extremity. The nail grows from its roots, increasing in length, and simultaneously in thickness. Its rate of growth depends upon the general rate of nutrition. During periods of sickness or abstinence, its growth in both directions is retarded, as is indicated by a mark or impression on its surface, and so the nail becomes a register of the condition of nutrition during the period of its own existence. The thumb nail is said to occupy about 20 weeks Skin of palm, magnified 20 diameters. in its growth from the root to the extremity ; that of the great toe about two years — an estimate which is probably too long. The Haie. — Each hair originates in a flask-shaped follicle, formed by a depression of the cutis, and lined by a continuation of the cu- ticle, and, like it, presenting scales on its superficies and round cells beneath. The bottom of the follicle is the place of origin. The hair consists of two portions, the outer or cortical, and the inner or me- dullary, the proportions of which differ very much in different cases. The surface of the hair presents a layer of imbricated scales, within which, at the lower part, are minute cells, but farther from the root the cells be- come larger and begin to contain pigment, the coloring matter being dis- tributed unequally, sometimes producing a tubular appearance in the axis. The hair grows by constant prolongation from the follicle, its color being due to a peculiar col- ored oil ; and in the black varieties, iron predom- inates. The diameter of the hairs varies from The hair. Fig. 104. lio^o 1500 of an inch. Uuman hair in section. In Fig. 104, the structure of the root of a hair and part of its shaft is displayed. Bulb of a small black hair from the scrotum, seen in sec- tion : a, basement membrane of the follicle ; J, layer of epidermic cells resting upon it, and be- coming more scaly as they approach c, a layer of imbricated cells forming the outer lamina or cor- tex of the hair : they are more flattened and com- pressed the higher they are traced on the bulb. Within the cortex is the proper substance of the hair, consisting, at the base, where it rests on OF THE SUDORIPAROUS GLANDS. 237 Fig. 105. I J' f %J Transverse section of buiuan hair, magnified 200 diameters. the basement membrane, of small angular cells, scarcely larger than tlicir nuclei. At d these cells are more bulky, and the bulb consequently thicker : there is also pigment developed in them ; above d they assume a decidedly fibrous char- acter, and become condensed ; e, a mass of cells in the axis of the hair, much loaded with pigment. (Todd and Bowman.) Fig. 105 is an engraving of a photo- graph of a transverse section of human hair from the head. The outer line shows the cortex ; in some the pigment- ary axis is seen ; in most, however, it is absent. The Sudoriparous Glands originate in depressions of the cutis or tissues beneath, occurring in some parts, as in the axilla, ^j^^ sudoripa- more numerously than in others. They consist of a tube rousgiauds. wound on itself, and sometimes dividing in convoluted branches. The knot thus arising is contained in a cell, the wall of which is copiously supplied Avitli blood-vessels : the duct passes through the superjacent tis- sues. The tube is formed of a cylinder of basement mem- brane lined with epithelium. The basement membrane may be considered to be derived from the outer surface of the papilla3, and the epithelium is an external projection of the cuticle. The duct, on its passage outward, loses its basement membrane as it escapes between the papillaa ; and it has a spiral or helical aspect, an arrangement prob- ably intended to keep the calibre open. It is estimated that the number of sudoriparous glands is about seven mill- ions, and the total length of their tubing about 28 miles. Fig. 106 is a sudoriparous gland from the palm of the hand : a, a, knot of tubes with two excretory ducts, b, b, uniting into a helical canal, which perforates the epidermis at (7, and opens on its surface at d : the gland is imbedded in fat vesicles at e, e, e, e. (Wagner.) The Sebaceous Glands are distributed in diflferent Sudoriparous gland, abuudancc in various parts, their office beins; tiip =;phaopoii thing which can commence the primitive impression, for with- external agent out it the mechanism can display no kind of result. More- °^ action. 284 INVERSE PHYSIOLOGICAL TROBLEMS. over, there must be an adaptation between the nature of that agent and the structure thus brought in relation with it, as is strikingly illustrated by each of the organs of sense. Thus the peripheral extremities of the fibrils of the optic nerve are involved in a combination of a purely phys- ical kind, having relation to the properties of light : the convex surface of the cornea, the unequicurved lens, the diaphragmatic iris, the interior investiture of black pigment, these are all structures the object of which we clearly understand. We know that the rays of light must undergo refraction at the curved surfaces upon which they are incident, and de- pict the images of external forms on the retina or black pigment, the iris expanding or contracting, as the case may be, to regulate the entrance of Adaptation be- the light. So Completely do we admit this principle of an tweentheagent adaptation of Structure to the nature of the agent which is and the mech- ^ _ _ . . , . anism. to Set it in activity, that in this particular mstance, without any hesitation, we class the eye among optical instruments, and include its description in our optical treatises. But in the same manner that, starting from the well-known properties of light, we advance to the ex- planation of the uses of each of the various parts of the eye, there can be no doubt that the converse of this method of reasoning Avould be possi- ble to an intellect of sufficient power, who, from a full consideration of the structure of the eye, might determine the properties of light, guided in doing this by the principle that there must be an adaptation between such structures and such properties ; and, in the same manner, a man deaf and dumb, but of an intellect of great capacity, might doubtless, from the critical study of the construction of the ear, determine the na- ture of sounds. Nay, even more, it is not impossible that he should be able to compare together the physical peculiarity of the movements which constitute light or sound respectively, and to demonstrate that these originate in normal, and those in transverse vibrations. So, therefore, these problems present themselves under a double aspect, Nature of in- and are capable both of a direct and an inverse solution : io<^fcai'^^'rob- driven the nature of light, to determine what must necessarily lems. be the construction of the organ of vision ; or. Given the con- struction of the eye, to determine what is the nature of light ; and the same might be said of the organ of hearing. This inverse method of treating natural agents is still in its infancy, because of the extreme im- perfection of our knowledge ; but doubtless what has been said will re- call to the mind of the reader the parallel example which is furnished by astronomy, and which, within a few years past, has yielded such a splen- did result. The mass of a planet being known, the perturbations which it can cause in another are capable of direct computation, but it was re- served for Leverrier to discuss the inverse problem, and from the per- turbations to find the place of the planet. The discovery of Neptune was the result. OF THE EXISTENCE OF THE SOUL. 285 Now the proLlcni avc are dealing with is of tliis inverse kind. It may be stated, (Jiven the structure of the cerebrum, to determine the nature of tlie agent that sets it in action. And herein the fact which chief!}- guides us is the absohite analogy in construction between the elementary arrangement of the cerebrum and any other nervous arc. In it we plainly recognize the centripetal and centrifugal fibres, and their con- External influ- vergence to the sensory ganglia, the corpus striatum and ^"^^y^q""""'! optic thalamus ; we notice the vesicular material at their tiai arc. external periphery as presented in the convolutions of the human brain ; and if in other nervous arcs the structure is merely automatic, and can display no phenomena of itself, but requires the influence of an external agent — if the optical apparatus be inert and without value save under the influences of light — if the auditory apparatus yields no result save under the impressions of sound — since there is between these structures and the elementary structure of the cerebrum a perfect analogy, we are entitled to come to the same conclusion in this instance as in those, and, asserting the absolute inertness of the cerebral structure in itself, to impute the phenomena it displays to an agent as perfectly external to the body and as independent of it as are light and sound, and that agent is the soul. It w^ould not comport with the object of this work to pursue this ar- gument in its details, yet I can not forbear observing that, even so far as ^Ye have already advanced, the point which, after all, is of the utmost importance, is completely attained. Those who have accused physiology of tending toward materialism have never duly weighed the accusation they make, and certainly have never understood the nature of the argu- ments it can present ; for such as the one here imperfectly set forth, from their tangible nature, will commend themselves to many minds who do not appreciate the strength of purely metaphysical arguments, and herein they may become subservient to the highest and most enduring interests of our race. And thus it may be proved that those actions which we term intellectual do not spring from mere matter alone, nor are they functions r , ••^ o_ _ _ .... Independence of mere material combinations ; for though it is indisputably and immortal- true that the mind seems to grow with the bodily structure, ^^^'^ ^^^ ®°" ' and declines with it, exhibiting the full perfection of its powers at the period of bodily maturity, it may be demonstrated that all this arises from the increase, perfection, and diminution of the instrument through which it is working. An accomplished artisan can not display his power through an imperfect tool, nor, if the tool should be broken, or become useless through impairment, is it any proof that the artisan has ceased to exist ; and so, though we admit that there is a correspondence between the development of the mind and the growth of the body, we deny that 286 OPINIONS RESPECTING THE SOUL. it follows from that, either that the mind did not pre-exist, or that the death of the body implies its annihilation. If it fell within the compass of our plan, we might proceed to consider ^ . . how far, since the mind can act upon external nature throusrh Opinions re- ' _ ^ ^ o specting the the intervention of the bodily mechanism, the converse is aspect of the ^^gg^^^jg . Iiq^t since the face of things around us can be soul entertain- r ' ' o ed by difterent changed bj our Voluntary exertions, the intellectual faculties nations. ^^^ ^^ changed by the action of external nature through the bodily mechanism. And since we have established the existence of the intellectual principle as external to the body, we might proceed, for now we are entitled so to do, to reason respecting its nature from the phenom- ena it displays. I do not, however, propose to enter on those considera- tions now, and shall close these remarks with a reference to some doc- trines proposed by the most highly-advanced and intellectual portions of the human family. It is said that the spirit of man is created in the image of God, an ob- servation strikingly illustrated by the fact that, as regards both, two es- sentially different doctrines have been held — the pantheistic, by some of the most highly advanced of the Asiatics, and the anthropomorphic, by the Europeans. The pantheistic supposes the human soul to be a part of the Deity, and therefore devoid of form ; the anthropomorphic as hav- ing the likeness of the body. The Asiatics, then, regarding the Deity as a principle diffused in and throughout nature, consider the spirit of man as a part or portion thereof, and often use such illustrative allusions as those of a drop of water in the ocean, a spark of a universal and vital flame ; or, if they do not accept this view of a oneness in the nature of spirit and Deity, they regard the former as arising in some manner from the latter, just as waves may exist upon the sea, or sounds may arise in the air. They believe that at death there is, as it were, a reunion of the part with the whole, as every drop of water sooner or later finds its way back to the sea, or waves become quiet and disappear, or sounds die away in the air. But with European nations there has been, from their very infancy, a tendency to the anthropomorphic conception. The barbarians before the Roman empire, in their legendary fables, accepted the idea of disembod- ied spirits u.nder the shape of men, and through the intervening ages up to our own times, such notions, under various forms, have been held. The rural populations entertain an undoubted faith in fairies and ghosts, so that it might be asserted that this manner of viewing the thing is almost natural to us. We instinctively represent to ourselves in this way the immaterial principle, and in the case of each individual expect a correspondence between it and his bodily form. Whatever may be our authority for arriving at such a conclusion, there can be no doubt that it OKGANS OF SPACE AND TIME. 287 SO specializes and intensifies our ideas, and is so connected with many of our most highly cherished recollections, that, even were the evidence in its behalf far weaker than it actually is, we should look Avithout favor on any attempt to invalidate the doctrine, and, if forced to do so, should abandon it with regret. The pantheistic is a grand but cold philosoph- ical idea ; the anthropomorphic embodies our recollections, and restoj'cs to us our dead. The one is the dream of the intellect, the other is the hope of the heart. We have thus traced out the essential elements of the nervous ma- chine in its highest complexity, and shown its gradual rise imperfection from the purely automatic to the influential. We may there- °l ^etaphysic- r J ^ ^ ^ •' al investiga- fore comprehend the difficulties under which metaphysicians tions. labor, who confound all these parts and all these functions together, and pass over as of no account the guiding instructions which are furnished by the study of structure. It is not difficult for the physiologist, en- lightened by the knowledge he possesses, to recognize the various points at which these philosophers go astray — the point at which their theories cease to be representations of the truth. He acknowledges the existence of an external nature, and equally the existence of an immaterial spirit, and to their action on or relation to each other he traces the resulting phenomena. He admits that, among certain classes of life, every motion and every sensation is due to external nature alone, but to these purely automatic groups man does not belong. He repudiates the doctrines of the idealist, because, though they may maintain themselves in the uncer- tainties of metaphysical argument, they are dissipated at once in the more severe trial of anatomical discussion. There are two fundamental ideas essentially attached to all our per- ceptions of external things : they are space and time, and Provision in the for these an early provision is made in the nervous mechan- ^'^''y°"s system •/ _i _ _ for ideas of ism, while yet it is in an almost rudimentary state. The space and time, development of the eye and the ear, as we shall more particularly find when we come to the description of these organs, is for this purpose. In a philosophical respect the eye is the organ of space, and the ear of time ; the perceptions of which, by the elaborate mechanism of these structures, become infinitely more precise than would be possible if the sense of touch alone were resorted to. The indications thus gathered are trans- mitted by the optic and auditory nerves respectively to the brain. In its highest condition of development, the nervous mechanism has a threefold operation, objective, subjective, and impersonal. Objective, sub- Obiective ideas arise in external facts ; subjective in register- J^*^*^^^'^- ^"*^ •^ _ 'J o impersonal op- ed impressions ; the impersonal, as, for example, the abstract erations. truths of geometry, issue of pure reason, and are therefore to be attrib- uted to the essential nature of the soul. Of these three elementary con- stituents all human knowledge consists. 288 VESTIGES OF GANaLIONlC IMPRESSIONS. As respects subjective or registered impressions, a few remarks maj ^ be here made. There can not be a doubt that the registry Illustrations of ^ . , i i • -i the vestiges of of inipressions involves an actual structural change m the impressions. ganglion, wliich is of a permanent character. These changes may be rudely and imperfectly illustrated by experiments, such as I pub- lished years ago, of which the following may be taken as examples : If, on a cold, polished piece of metal, any object, as a wafer, is laid, and the metal then be breathed upon, and, when the moisture has had time to disappear, the wafer be thrown off, though now upon the polished surface the most critical inspection can discover no trace of any form, if we breathe upon it a spectral figure of the wafer comes into view, and this may be done again and again. Nay, even more ; if the polished metal be carefully put aside where nothing can deteriorate its surface, and be so kept for many months (I have witnessed it even after a year), on breath- ing again upon it, the shadowy form emerges ; or, if a sheet of paper on which a key or other object is laid be carried for a few moments into the sunshine, and then instantaneously viewed in the dark, the key being simultaneously removed, a fading spectre of the key on the paper will be seen ; and if the paper be put away where nothing can disturb it, and so kept for many months, at the end thereof, if it be carried into a dark place and laid on a piece of hot metal, the spectre of the key will come forth. In the case of bodies more highly phosphorescent than paper, the spectres of many different objects which may have been in succession laid originally thereupon will, on warming, emerge in their proper order. I introduce these illustrations for the purpose of showing how trivial are the impressions which may be thus registered and preserved. In- deed, I believe that a shadow never falls upon a wall without leaving thereupon its permanent trace — a trace which might be made visible by resorting to proper processes. All kinds of photographic drawing are in their degree examples of the kind. Of the moral consequences of such facts it is not my object liere to speak. The world would be none the worse if every secret action might thus be made plain. But if on such inorganic surfaces impressions may in this way be preserved, how much more likely is it that the same thing occurs in the purposely-constituted ganglion I Not that there is any necessary coincidence between an ex- ternal form and its ganglionic impression any more than there is be- tween the letters of a message delivered in a telegraphic office and the sig- r , , ,. nals which the telegraph gives to the distant station, yet these Interpretation _ o r & . . of such ves- signals are easily retranslated into the original words — no ^^^^' more than there is between the letters of a printed page and the acts or scenes they may chance to describe, but those letters call up with clearness in the mind of the reader the events and scenes. Indeed, the quickness with which the mind interprets such traces or impressions SPONTANEOUS FUNCTIONS OF GANGLIA. 289 in its registering ganglia is illustrated by tlic rapidity with which wc gather the sense of a printed page without individualizing each of the letters it contains, or as a skillful accountant runs his eye over a long colmnn of ligures, and seems to come by intuition at once to the correct sum. The capability which avc thus possess of determining a final per- ception or judgment of results, without dwelling on the intermediate traces or steps, is also illustrated by our appreciation of nuisic without concentrating our thoughts on the time and intensities of vibration or in- terferences of the notes, though these mathematical relations are at the very bottom of the harmony ; and conspicuously does the Supreme In- telligence, God, reach with unerring truth to every final result without any necessary concern in the intermediate steps. From tlie preceding considerations we may infer that there is a neces- sary limitation of the amount of impressions capable of beine; ^,. ., "f . _ . I'lnite naturi! registered in the organism, and therefore, in this regard, all of human human knoAvledge is finite. Yet its term is much farther off '^^°'^i®'^s®- than might at first sight appear. A library of a given size may only be able to contain a given number of books upon its shelves, but the amount of information it is capable of containing may be made to vary with the condensation and perspicuity of the books. In the hypothetical language of physiology, the nervous centres are spoken of as the origin of the nervous influence or force. A conclusion re- close examination of the phenomena they display leads us, specting the , . ■ -, ■ • -xi J. • X spontaneous however, to receive sucli an impression with a certain amount function of of limitation. Most of the ganglia produce no motor im- ganglia. pulses except under the action of external impression, and under the el- ementary view we have just presented regarding the function of the brain, the same remark applies even to it, since the immaterial principle, whose instrument it is, must be regarded as an agent distinct from it, and in that respect external. Indeed, the cases in which the nervous centres seem to display the quality of spontaneously originating force are so few, and in their nature so doubtful, that we are almost entitled to dis- regard them. For example, the ganglia of the heart are by some sup- posed to cause, by their own inherent power, the contractions of that or- gan, which in cold-blooded animals, long after it has been excised, will continue its rhythmic motions. But it is far more agreeable to the anal- ogies of the nervous system to regard these cardiac ganglia, not as orig- inators of power, but as merely depositories, reseiwoirs, or magazines of it. There is nothing more extraordinary in their ability to keejD up the motions of the organ with which they are connected than there is in the subsidiary spring of a chronometer, which maintains the movement of that instrument for the period during which the action of the mainspring is taken off while it is being wound up. Yet the mainspring, and the T 290 MENTAL EMOTIONS. sabsidiaiy spring too, derive their mechanical power originally from the force which has wound up the chronometer. In this particular of the storing up of power for its utilization in the time of need, the whole gan- glionic or sympathetic system of nerves may be taken as the great ex- ample. The conveyance of an impression through the great nervous centres is „ , „ , more complicated than it is through the nerve trunks. It Nature of the ^ _ ^ ... action of nerve may he conducted, if of sufficient intensity, through one gan- centres. glion after another in succession. The intermedium through which this is done is probably the nerve-tubes in a majority of instances, though perhaps, in those cases in which a longer period of time is occu- pied, it may be rather from vesicle to vesicle than through the tubes. Impressions may be thus transferred from one set of tubes to others, or Conveyance of they may be diffused from a nerve centre to many tubes impressions around, and so produce a wider circle of influence. That through cen- ' ir tres. transfer of impressions from centripetal to centrifugal fibres which has been previously described as reflex action, though commonly involuntary, may in many instances be governed by a direct exertion of the will. Thus the respiratory movements for the introduction of air may be controlled to a certain extent, as in holding the breath, but this is only during a short time, for the necessity of permitting the normal action to occur presently becomes insuperable. Of reflex actions, the majority are obviously for the accomplishment of some special object so long as the system is in health — they are means for an end ; but in dis- eased conditions they very often occur in an objectless or useless way. In its most perfect condition, the nervous system thus consists of two Nature of men- Separate mechanisms, the automatic and the influential, and fal emotions, these are so related that they can mutually act on one an- other. The will can exert a control over the so-called reflecting func- tion of the automatic part, and external impressions which have been received by that part can exert a reaction upon the will. It is in this way that mental emotions may be explained, the power of external influ- ences which antagonize or even overcome the will. THE SPINAL AXIS. 291 CHAPTER XV. THE SPINAL AXIS. Primitive Development of Nervous Syatem. — Its final Condition in different Vertebrates. The Spinal Cord : its Striicture. — Its Membranes. — Its Thirty-one Pairs of Nerves. — Proper- ties of their Roots. — Functions of the Cord. — Bell's Discovery. — Transmission of Longitudinal and Transverse Influences.— Reflex Action of the Cord. — Nature of Reflex Action. — Motor and Sensory Tracts of the Cord. — Summary of its Functions. The Medulla Oblongata : its Structure and Functions. The Pons Varolii : its Structure and Functions. Dr. Carpenter's Vieios of the Analogy between the Spinal Cord of Vertebrates and the Ventral Cord of Articulates. We now commence a more detailed examination of the nervous sys- tem, presenting a description of its structm-e as far as may Subdivisions be necessary for the understanding of its functions. We °^ *^^ subject. shall follow the usual division of this subject as adopted by authors. This will therefore lead us to speak in succession of the spinal cord and medulla oblongata, of the sensory ganglia, of the cerebellum and cere- brum, of the nerves generally, and, lastly, of the sympathetic system. The important position occupied by the nervous mechanism in the an- imal body will always draw to it the closest attention of the physiol- ogist, and yet it must be admitted that hitherto it is the least ad- vanced portion of the science. If metaphysicians are to be blamed for casting away the advantages which arise from a study of Advantages de- structure, the earlier physiologists were almost equally in pjrative'physi- error in confining themselves to human anatomy alone, oiogy. They did this under an impression that there is an essential and intrinsic difference between the functions of this system in man and in the lower animals. There is an analogy of construction in all the forms of nervous system presented by the different animal tribes, which, in the infancy of the sci- ences of organization, was attributed to a unity of design pervading the plan of Nature, but which, when seen from a higher and more philosoph- ical point of view, is plainly the necessary result of a universal and un- varying law of development. This conclusion, which, when better un- derstood, is doubtless destined to become one of the most important sug- gestions ever furnished by science respecting the management of the world, is strikingly enforced by the analogies between the ^^^^nta^-es de- successive transitory stages of development of this system rived from de- at different epochs in the life of man, and the permanent ^^ op™ent. form it assumes in members of the entire animal series. Since there can 292 DEVELOPMENT OF THE CEREBEO-SPINAL AXIS. be no doubt that every animal function, from the automatic motions of the obscurest living form up to processes of intellection of man, depend upon this structure as on an instrument, we may, by a due comparison of the habits, instincts, or other phenomena in such cases with the existing nervous development, arrive at true conclusions of the connection between its structure and its functions. We shall therefore indicate, in a general manner, the order of development of this system in man, and then its permanent stages in the animal series. The nervous system first makes its appearance in the serous lamina Course of de- of the germinal membrane and in the midst of the pellucid veiopmentof ^^.^^ ^g ^^iq primitive trace, a delicate and pale-white line ris- human nerv- i ^ ^ ous system, ing somewliat above the general surface of the germinal area. This line soon presents a conical aspect ; the thicker portion is destined to become the head of the embryo. After a short interval, the membrane is gathered into a fold on each side of the primitive trace, and these folds, advancing toward each other, constitute the dorsal laminas, which, when their edges have met and coalesced, form a tubular cavity — a rudimentary preparation for the vertebral column. Beneath the tube so arising may be discovered, at this stage, a line of nucleated cells — the chorda dorsalis. As the edges of the dorsal lamina approach each other, they assume a wavy form, and simultaneously a bending forward or curvature of the embryo occurs, so that the vertebral tube becomes arched. In the middle wavy portion are now to be seen rectangular plates, the elements of the future vertebras. The coalescence of the middle part of the dorsal lamina? takes place first, the ends as yet diverging in the portions which corre- spond respectively to the head and the sacrum. The spinal marrow and the brain thus arise at the primitive trace, the brain being a superposed or .additional structure to the spinal marrow ; for now the wavy edges of the anterior extremity are gradually seen to give origin to three cells by their juxtaposition : 1st. The epencephalon, a single cell, to produce the medulla oblongata : its cavity is to be the fourth ventricle ; 2d. The mes- encephalon, also a single cell, for the corpora quadrigemina : its cavity is to be the ventricle of Sylvius ; 3d. The deutencephalon, a single cell, for the optic thalami : its cavity is to be the third ventricle. Though at first transparent and fluid, the nervous matter becomes by degrees more (consistent and covered over with a thin layer of membrane, the indica- tion of its future investitures. The rudiment of an eye, under the form of a protrusion, now appears from the most anterior cell ; and in like manner the auditory apparatus emerges from the cell of the medulla ob- longata, from the anterior part of which, by the coalescence of a pair of fasciculi which have arisen, the cerebellum begins to form. At this peri- od, through the continued curvature of the embryo, the cell of the cor- pora quadrigemina has become most anterior. DEVELOPMENT OF THE CEREBRO-SPINAL AXIS. 293 Tlie origin of the spinal cord and brain is illustrated in the annexed figures from BischofF. Fiq. 136 shows upon a dark eround ^ . ,. , -11 ■ -i .-i Origin of the a portion ol the germinal membrane, m tlie midst of which is spinal cord and the area pellucida and primitive trace : «, the area pellucida; ^^^^ ^'^^'"" b^ the dorsal larainaj ; c, the primitive trace. Fvj. ] The primitive trace, magnified 8 diameters. Origin of tlie brain upon the spinal cord, magnilied 8 diameters. Fig. 137, the same at a later stage, preparation for the brain being made. The dorsal lamina are approaching each other, particularly to- ward the middle : «, the dilated upper extremity or cephalic end, the three cells appearing : the epencephalon, mesencephalon, and deutenceph- alon ; ^, chorda dorsalis along the bottom of the groove ; c, rudiments of vertebras ; d, lancet-shaped dilatation. In both figures the pale borders along the primitive trace are pellucid nerve substance. The dorsal cord, which is only a transitory structure, now disappears, the spinal marrow commencing to exhibit a division into four strands, right and left, upper and under. The medulla oblongata flattens next in its upper part, its fasciculi- parting from each other ; the interval so arising between them is to be the fourth ventricle. The hemispheres now appear as a double cell, the prosencephalon, and as development o-oes on, they soon exceed the corpora quadrigemina in size, and, as they ad- vance, force these bodies backward and under them. From this it appears that the type of construction of the nervous sys- tem is, that upon the rudimentary spinal marrow a series of vesicles is developed. They constitute eventually the medulla oblongata, the cer- ebellum, the corpora quadrigemina, the thalami optici, the corpora striata, the olfactive ganglia, and in front of all, but destined to cover the anterior portions over, the hemispheres. Turning now to the animal series, we find in the lowest members of 294 THE SPINAL COED. the vertebrata, as in the amphioxus, the spinal cord, medulla Comparative ' ^ . , nervous system oblongata, and the elementary representatives of the sensory m vertebrates, g^j^g^^^ alone, and as, in succession, we pass to the higher ones, we recognize a cerebellum appearing over the medulla oblongata, and cerebral hemispheres over the sensory ganglia. These organs in the upward career become more and more developed, the hemispheres, for example, soon equaling in size the quadrigemina, and then greatly sur- passing them, and with this increase of size a higher grade of intelligence is reached. In fishes there are four ganglia, corresponding respectively to the cerebellum, quadrigemina, cerebral hemispheres, and olfactive gan- glia. In reptiles the number of ganglia and their order of occurrence is the same, but the cerebral hemispheres have now greatly increased, an increase which is even better marked in birds, for in them the hem- ispheres have expanded in front so as to cover the olfactive ganglia, and posteriorly the optic, a condition of things analogous to that presented by the human brain at about the close of the third month of foetal life, and approaching that permanently exhibited by the lower mammals, as, for instance, the marsupials. It is to be understood that what is here spoken of as the hemispheres answers in reality only to the anterior lobe of the cerebrum of man ; and as in him, during the fourth and fifth months, the middle lobes are developed in the upward and backward direction from the anterior, and still later the posterior lobes from the posterior of these, the same course is followed in the animal series, the final type of development, the trilobed cerebrum, being only reached by the highest carnivora and quadrumanous animals. Commencing now more particularly with human nervous anatomy — STEUCTUKE OF THE SPINAL COKD. The spinal cord is placed in the midst of the vertebral canal. In form Description of it is cylindroid, its section being elliptical, the lateral diame- the spinal cord, ^gj, "bgi^g iI^q long One. Longitudinally it shows two en- largements, one about its upper third, the other toward its termination. Exteriorly it is white, but its section shows a gray substance, arranged in the form of two crescents connected by an isthmus. Above, it is con- tinuous with the brain, which, indeed, is a development upon it, and be- low it terminates at the cauda equina. Its relative length is much great- er in foetal life, at the third month of which it extends into the sacrum. In adult life it only occupies about the upper two thirds of the verte- bral canal ; it is generally stated that its termination is about the first or second lumbar vertebra. Moreover, it does not fill the vertebral ca- nal, being, by reason of the transverse dimensions of that cavity, rather suspended in than confined by it. The rest of the space, amount- ing to about one third, is occupied by the roots of the nerves, liga- THE SPINAL COED. 295 The spinal cord. Fig. 139. mg. 138. ments, the investitures of the cord, blood-vessels, and a liquid. J^ig. 138, A, A, shows the front view of the spina] cord, with the medulla oblongata ; B, B, the posterior view ; and C, C, the decussation of its strands, from which it appears that the organ is composed of two equi- lateral portions. They are united by an interior com- missure, but separated in front by the anterior, and be- hind by the posterior fissure. Of these the posterior fissure is the deeper, the anterior being wider. Besides these regional divisions, the cord also presents longi- tudinal furrows, two for each side, dividing it into the anterior, the middle or lateral, and posterior columns or tracts, as shown in the figures. With respect to the interior constitution of the cord, it has already been stated that it is composed exteriorly of white, and interiorly of gray material. The relative quantities of these, and the particular form and distribu- tion of. the gray substance, may, perhaps, be best understood from the sections given in Fig. 139, from one to nineteen, 1 show- ing a transverse section as high as the cerebral pedun- cles ; 2, through the medulla oblongata; and the remaining figures, to 19, at lower and lower points. In the first of these sec- tions, 1 is the interpeduncu- lar space ; 2, 2, inferior tract ; 3, 3, middle tract ; 4, 4, locus niger ; 5, 5, superior tract ; 6, section of the aqueduct of Sylvius ; 7, 7, section of the superior peduncles of the cer- ebellum ; 8, 8, section of the two tubercula quadrigemina. In the second section : 1,1, the pyramidal bodies ; 2, 2, olivary bodies ; 3, 3, resti- form ; 4, 4, section of middle strands ; 5, floor of fourth ventricle. In the fourth of these sections : 1, the right half of the cord ; 2, left half; 3, anterior median fissure; 4, posterior median fissure; 5, 5, pos- i4 IS 16 17 18 19 ® Sections of the spinal cord. 296 STEUCTURE OF THE SPINAL CORD. terior furrows : 6, white or anterior commissure ; 7, gray or posterior commissure ; 8, anterior liorn of right crescent ; 9, posterior horn of dit- to : it is prolonged to the posterior fuiTow ; 10, antero-lateral columns; 11, 11, posterior colimms: these are all of white tubular substance. The symmetrical reference numbers on one side are omitted for the sake of clearness. The spinal cord is surrounded by three membranes, continuous with Membranes of tliosc of the cranium : the dura mater, the arachnoid, and the the spinal cord, pij^ mater. The latter embraces the cord so closely as to ex- ert a compression upon it. This is shown on slightly wounding it, when the white substance protrudes through the orifice. ^"J 14o. Fig. 140 : 1, spinal dura mater laid open and drawn ■ aside ; 2, 2, sheaths formed by this membrane round the roots and spinal ganglia ; 3, spinal arachnoid ; 4, 4, sheaths formed by the arachnoid around the i-oots of the nerves and dentated ligament ; 5, 5, points of communication of the visceral layer of the arach- noid, with its parietal layer ; 6, pia mater ; 7, denta- ted ligament separating the anterior roots from the posterior roots of the spinal nerves, and serving as a communication between the dura mater and pia mater. From the spinal cord there arise thirty-one pairs The spinal ^^ nerves, each nerve having two roots, an nerves. anterior or motor, and a posterior or sensory. The anterior roots issue from the anterior furrow, Roots of the "the posterior from the posterior furrow, spinal nerves, y/here the gray substance emerges. Of the two the latter are the larger, and have more radicles. They also have, in the intervertebral foramen, a ganglion. Beyond the ganglion the two roots coalesce, and the resulting nerve trunk, passing through the intervertebral foramen, divides into an anterior and posterior branch, for the anterior and posterior portions of the body. To this general descrip- tion there are, however, some exceptions. Thus the posterior root of the first cervical nerve is smaller than the anterior, and very often it has no ganglion. The spinal nerves are enumerated as eight cervical, twelve dorsal, five lumbar, and six sacral pairs. The cervical pass off to their distribution transversely, the dorsal obliquely, and the lumbar and sacral vertically. The latter constitute the cauda equina. Fig. 141 illustrates the origin of the anterior roots of the spinal nerves. 1, pons varolii ; 2, large and small root of the fifth pair ; 3, sixth pair ; 4, facial nerve ; 5, auditory nerve ; 6, intermedian nerve ; 7, glosso-pharyngeal ; 8, pneumogastric ; 9, spinal accessory ; 10, hypo- glossal. Spinal dura mater laid open. STKUCTURE OF THE SPINAL CORD. 297 Origin of anteiioi roots of nerves. Fig. 142. PjV/. 141. From 11 to 11, the eight anterior roots of the eervical nerves; from 12 downward, the same roots of the dorsal nerves : those of the lumbar and sacral are not shown in the figure. As at 15, are shown the anterior branches of the spinal nerves ; as at 16, their posterior branches ; at 17, spinal ganglia formed on the posterior roots ; 18, ante- rior roots cut ; 19, anterior roots cut beyond the ganglion : 20, dentated ligament, separating anterior from posterior roots ; 21, insertion of this ligament on dura mater by its dentated edge ; 22, insertion of same ligament on the pia mater. I^ig. 142 illustrates the origin of the posterior roots of the spinal nerves. 1, tubercnla quadrigemina ; 2, trian- gular band ; 3, 3, superior peduncles of the cerebellum ; 4, 4, middle peduncles of cerebellum ; 5, 5, inferior pedun- cles of cerebellum ; 6, anterior wall of fourth ventricle ; 7, glosso-pharyngeal ; 8, pneumogastric ; 9, spinal accessory; from 10 to 10, posterior roots of eight cervical pairs: the dorsal, the lumbar, and the sacral below 11 are not shown in the figure. From 14 downward, a dotted line arising from the tearing away of the posterior roots ; 15, 15, an- terior roots of spinal nerves, the dentated ligament being visible through the removal of the posterior roots ; 16, spi- nal ganglia, of which there are thirty pairs, the first pair of nerves not being furnished with them ; 17, 17, anterior branches of spinal nerves ; 18, 18, posterior branches ; 19, 19, dentated ligament, placed between the posterior and anterior roots ; 20, same ligament brought into view. J^iff. 143 shows a portion of the spinal cord pig.us, surrounded by its envelopes, and seen in pro- file, so as to display at once the origin of the anterior and posterior roots. 1, 1, posterior roots of spinal nerves and their ganglia ; 2, 2, anterior roots of the same nerves anastomosing with the anterior portions of these ganglia ; 3, 4, anterior and posterior roots cut ; 5, dentated ligament ; 6, dura mater, preserved to show the sheaths which it forms around these ganglia and the branches of the spinal nerves ; 7, vertical section of the sheath of the anterior and posterior roots, to show the little lamella which separates the one root from the other ; 8, 8, interior face of the dura mater, which is drawn aside to show the smooth rior^and^poste- aspect which it possesses, owing to the parietal layer of the ^^"^ '"°°'^" arachnoid which covers it. Origin of posterior roots of nerves. 298 LONGITUDINAL TRANSMISSION IN THE CORD. Tlie white or fibrous portion of the spinal cord is composed in part of the spinal nerve fibres and in part of commissural ones. At one time it was supposed that every one of the preceding continued uninterruptedly to the brain. On this point, however, the weight of evidence will lead us to infer that the vertical distance through Avhich these fibres pass is not very great, and that they are soon brought in connection with the interior vesicular substance. If all the fibres passed uninterruptedly to the brain, we should expect that the cord would increase in thickness by a regular progression upward ; but this, as is shown in Fig. 138, is not the case. Its enlargements correspond to the number of nerve roots given ofi" from the localities in which they occur. Thus, where many nerve roots are required for the upper extremities, and again for the lower ones, we notice such corresponding enlargements. The experiments of Volk- mann show that these dilatations are as much owing to an increase of the vesicular material as to an increased number of fibres. In the view presented in the preceding chapter respecting nerve-arcs and the functions of nerve-cells, we should be led to infer that every centrifugal and cen- tripetal fibre of the cord is brought in connection with such a cell of the gray material, and that it does not extend very far from its point of exit or entrance. Functions of the Spinal Cord. — The determination of the func- Functions of tions of the roots of the spinal nerves by Bell has already the spinal cord, jbeen referred to as one of the great discoveries of physiol- ogy, and as furnishing a solid foundation for an exact knowledge of the functions of the nervous system. The evidence of the truth of the doc- trine that the anterior roots of these nerves are motor and the posterior Bell's dis- sensory, is complete. Thus, if the anterior root of one of these covery. nerves be divided, all those parts which are supplied by that nerve will exhibit loss of motion, though their sensation is unimpaired ; if the posterior root be divided, the sensibility of the parts is lost, though the power of motion is unaffected. Similar evidence may also be ob- tained by irritating the ends of the divided roots, muscular motion or pain, as the case may be, being correspondingly observed. The spinal cord transmits impressions from the periphery to the brain, T .^ V 1 and conversely enables the brain to brins' into action the Longitudinal .... . transmission of motor nerves. Division of it at once causes an interruption in uences. ^£ voluntary motion and sensation in those parts supplied by nerves below the place of the operation, the functions of the parts above remaining unimpaired. But, though the influenoe of the brain in exciting voluntary motion, and its capability of receiving sensations, is thus cut off, the severed portion of tiie cord still possesses an automatic power. This transmission of influences upward or downward is doubtless, to TRANSVERSE TRANSMISSION. 299 a considerable degree, accomplislied througli the vesicular substance, the quality of which, iu this respect, has been explained in the preceding chapter. But, besides this, the exterior fibrous structures possess a like function, correspondingly as they are connected with the motor or sen- sory roots of the nerves, the anterior columns being motor, and the pos- terior apparently sensory. The spinal cord not only permits the passage of influences in its longi- tudinal, but also in its transverse direction. This is what rr ' _ ^ _ Iransverse might be anticipated from the structure and functions of the transmis&ion of cells of its gray interior. If the cord be cut half through in "^ '^^'^'^^s- a given place, and again be cut half through on the opposite side, at a little distance above or below, impressions may be conducted through the intermediate portion, the vesicular material being then their only channel. In a memoir on the distribu.tion of the fibres of the sensitive roots, and on the transmission of impressions in the spinal cord, Dr. -d o ^ ■*• -i _ Brown-Sequard Brown-Sequard, referring to the two theories entertained at on the conduc- present — 1st. That sensitive impressions reaching the cord ^^^""'^ t ecor . pass in totality to the brain along the posterior columns ; 2d. That such impressions so arriving pass directly to the central gray substance, which transmits them upward — offers reasons for supposing that both these theories, and especially the first, are contradicted by facts. It is his opinion that sensitive impressions reaching the cord pass in different directions, some ascending, others descending, but both going in part by the posterior columns, and in part by the posterior gray horns, and perhaps by the lateral columns, to penetrate, after a short distance, the gray central substance by which, or in which, they are transmitted to the brain. He also shows that sensitive impressions of one lateral half of the body are transmitted principally in a crossed manner, that is to say, that they follow more particularly the opposite half of the cord to reach the brain ; that the decussation of the conducting elements for sensitive im- pressions is not made, as is commonly said, at the anterior extremity of the pons ; that the gray substance does not possess the property of transmitting sensitive impressions in every direction, as some have sup- posed ; that most, if not all the conducting elements for sensitive im- pressions decussate in the spinal cord, the decussation occurring in part almost immediately on their entry into the cord, but that a few make their decussation at a certain distance above the point of entry, the ma- jority, however, descending in the cord, and making their decussation below the point of entry ; that if there are conducting elements for sen- sitive impressions which ascend throughout the entire length of the cord to make their decussation in the brain, their number must be very small ; 300 REFLEX ACTION. and that alterations capable of producing a paralysis of sensibility, and situated upon any point of a lateral half of the cerebro-spinal axis, al- ways produce a paralysis of sensibility on the opposite half of the body, and that there is no difference between the brain and the spinal marrov' in this respect. Thus constructed, the spinal cord, as we shall presently show from . , Dr. Carpenter, evidently agrees with the gangiiated ventral ventral cord cord of the articulata, each portion of it from which a pair of of articulata. j-^gj-ygg jg given off representing each ganglion of that ventral cord, the diiference in the two structures being, that in the spinal col- umn the ganglia are commissured, so as to form, in appearance, one con- tinuous mass, and agreeably to this view of its construction are the circumstances under which its enlargements occur. In those animal forms in which the entire trunk is concerned in locomotion, as in snakes and eels, the cord is nearly cylindrical ; but as soon as special members for locomotion are developed, a corresponding increase of diameter is ob- served. Thus, in birds, the ganglionic enlargement corresponds with the region from which the nerves for the wings are given off; but in that tribe, as in the ostrich, the mode of locomotion of which is by the legs rather than by the wings, a corresponding posterior enlargement occurs. The same observations may even be more distinctly made during metamorph- oses ; thus, in frogs, while they are in the tadpole state the spinal cord is cylindrical, but bulging ensues in it anteriorly and posteriorly as soon as the anterior and posterior members are developed. The translation of impressions which have been brought along the Reflex action Centripetal fibres into motions, the exciting influence of which of the cord, jg conveycd along the centrifugal fibres, includes what is un- derstood as the reflex action of the spinal cord as developed by Dr. Hall. Its essential condition is its independence of the agency of the brain, and therefore unconscious nature. As general examples may be mentioned the movements which occur in swallowing ; for after the food has been carried by voluntary action into the fauces, its passage onward to the stomach is perfectly involuntary. In like manner, the introduction of air into the lungs in ordinary respiration is involuntary ; for though it may be, to a certain extent, under the control of the will, yet that extent is limited, a necessity for the motion presently arising, which soon becomes uncontrollable. The action of the valvular arrangements at the cardiac and pyloric orifices of the stomach, and the constant contraction of the sphincter ani, are farther illustrations. To these may be added those impulsive movements which we instinctively make on the approach of danger or in the act of falling, and perhaps, too, automatic walking, as we go from place to place in a state of mental abstraction, paying no at- tention to the course we take. REFLEX ACTION. 301 Tlie cord is to be regarded as a longitudinal series of simple automatic nerve arcs, or, as we have termed it, a multiple automatic Automatic ac- arc. Each segment of it has therefore an independent action tionofthecord. of its own, but can conspire with its neighbors or be influenced by the Fia. 144. brain, by means of its commissural fibres, an arrangement of which num- berless interesting instances might be furnished. The one represented in Fig. 144, which is from the cord of spirostreptus, may, however, suffice: A, under surface of a portion ; B, up- per surface ; a, inferior longitudinal fibres ; e, superior longitudinal fibres ; f, fibres of re-enforcement, seen also at h and c\ g, commissural fibres, seen also at d. The power which the cord displays in this simple action is most striking- ly seen when it is cut off" from its cranial connections. The decapitated frog props himself up stiffly on his legs, and, if his cutaneous surface be Portion of cord of spirostreptus. irritated, exhibits antagonizing mo- tions ; such motions are all of the reflex character, and are commonly much more strikingly seen in cold than in warm-blooded animals ; but even in man precisely the same results are witnessed during periods of the suspension of the activity of the brain, as, when the palm of the hand of a sleeping child is touched with the finger, the finger is at once grasped. As above stated, this reflex function of the cord is therefore independ- ent of the brain, though the brain can control it, and this j^g^g^ ^g^i^^ the more perfectly the higher the organization of the animal, independent of Breathing can go on, whether we pay attention to it or not, but we can arrest it if we choose for a time ; and since in man this in- troduction of air is incidentally used for very refined purposes, by volun- tary exertion we moderate or regulate it, as in the production of musical sounds in singing or of articulate soimds in speech. In a general way, there is not much difficulty in distinguishing be- tween simple actions of the cord and those in which the brain Distinction be- is participating. In the former, no weariness or fatigue is anrcerebrai ever experienced ; in the latter it is ; and perhaps, even in action. these last, involving voluntary muscular action, though the control is to be attributed to the brain, the source of the force is in the cord. These nonual phenomena which the cord displays become greatly ex- 302 EELATIONS OF THE SPINAL CORD AND BRAIN. Increase of aggerated in certain conditions of disease, as, for example, in spinal action, tetanus, in which the slightest peripheral irritation may be followed by violent convulsive movement, or the same occurs by the agency of powerful poisonous substances, as strychnine. In these cases the action may be either limited simply to the cord, as in the tetanus brought on by opium in frogs, or the brain may be involved in it, as in cases of hydrophobia, in which the sound or sight of water, operating thi'ough the cerebrum, will produce spasmodic convulsions. From the facts presented by the lower animals, it may be inferred that the spinal cord does not act as a single organ, but rather should be re- garded as a collection of ganglia, special duties being discharged by spe- cial parts of it. With respect to the commissural action of the spinal cord, reference has ^ already been made to the structural connection between the Connection of •' . ^ . , . ^ . the cord and cord and the nervous regions above it, and m referring to the brain. ^^^ anatomical doctrine that each of the spinal nerves is con- nected by continuous fibres with the brain, due weight has been given to the fact that the cord does not increase in thickness as it approaches the brain, but that its bulgings correspond to the regions from which it is necessary that an unusual supply of ner^^es should be given off. The force of this argument is, however, considerably diminished when we recollect that the nerve-tubes are by no means of uniform diameter, but are doubly conical in shape. Even, therefore, with a diminished diame- ter of the spinal cord, there might be an upward continuation of spinal fibres, the diameter of which is becoming less and less ; and this seems to be rendered more likely from the analogy of the structure of the ven- tral cord of the articulata, in which fibres are sent to the cephalic gan- glia for the purpose of establishing a communication between them and the roots of the nerves. But, however that may be, there can be no question of the influence of the brain over spinal action, and this, of course, implies structural connection of some kind — an intercommunication — which, if it does not take place solely through the white columns, must take place through the gray material. It is, however, important to ob- serve that the gray material has no direct communication with that of the cerebrum, but, passing through the optic thalamus, ends in the cor- pus striatum, extending therefore in one continued mass tlu'ough the cord, and terminating in that ganglionic organ. By one or both of these chan- nels, white or gi-ay, the impressions which are made upon the spinal sensitive nerves are presented to the brain, and in a similar manner the influences which produce voluntary motions are transmitted doAvn. A section of any part of the .spinal cord at once incapacitates the sionsofthe' will from acting upon the parts beyond, the motions of which '^'■^- become therefore purely automatic, though the parts above still FUNCTIONS OP THE SPINAL CORD. 303 display their customaiy phenomena. These effects are sometimes in- structively witnessed in man when lesions of the cord have occurred through disease. If the view that has heen presented respecting the continuation of fibres from the cord to the brain be correct, these fibres dis- ,, , Motor and seii- charge a commissural duty. This would lead us to sup- sory tracts oi pose that there is a correspondence between the functions of ^ ^°^ ' the columns of the cord and those of the roots of the spinal nerves, the anterior columns being motiferous, or in unison with the motor root of the nerves, the posterior being sensiferous, or in unison with the sensor}* root of the nerves. Agreeably to this, if the anterior columns be irri- tated, motions are excited in all those parts which are supplied with nerves beyond the irritated point ; and if the posterior columns be irri- tated, in like manner pain is experienced. In this instance, however, a certain amount of motion is occasionally observed, but this has common- ly been explained by referring it to reflexion within the cord. It has also been observed, as strengthening these views, that if the posterior columns be irritated after complete section of the cord, the result will de- pend on which of the cut portions be disturbed ; if it be the lower, there will be no effect. An examination, under the same circumstances, of the anterior columns, demonstrates that, if the upper section be irritated, there is no effect produced ; if the lower, there are convulsive movements of the parts supplied with nerves beyond. From these results we should infer that the physiological functions of the anterior and posterior roots of the spinal nerves are participated in by the anterior and posterior columns of the cord, and might therefore expect that those functions would be continued in the higher distribu- tion of the columns above the medulla oblono-ata. o From the point of view under which we have thus presented it, the action of the spinal cord is therefore simple^ or it is disturb- General func- ed by the agency of the brain ; in the first case it offers it- tions of the self purely as an automatic instrument ; in the latter, its com- missural connections with the brain make a compound apparatus. The former state is closely represented in the construction of the amphioxus, the nervous system of which has no rudiment of a cerebrum or cerebel- lum ; in this animal, therefore, since also the sensory ganglia are merely in a rudimentary state, the mode of life must be purely mechanical, just as it is with an artificial automaton, of which, when a given spring is touched, a given motion is made. Even among the highest vertebrated animals, man himself at the periodic times of quiescence of the cerebrum, as in sleep, when the cerebral influence over other portions is, to a certain extent, suspended, an approach to a similar condition occurs ; but in periods of activity of the cerebrum, it can hold the spinal cord in check, 304 TPIE MEDULLA OBLONGATA. controlling, and in some cases arresting its action, and this is done through influences propagated along the tubular structures of the posterior and an- terior columns, which therefore are to be regarded, in this respect, as commissures to the brain. OF THE MEDULLA OBLONGATA. The medulla oblongata is a conical body, lying between the spinal cord J. . » j^ and the brain. It is generally understood to be bounded at medulla obion- its Upper portion by tlie pons varolii, but this is not a true ^^ ^' limit, since its structure extends through the pons varolii to the crura of the brain. There is the same indefiniteness of limit as re- spects its lower boundary, which is generally said to be marked by some decussating fibres which appear on its front. Like the spinal cord, it Its subdivis- has an anterior and posterior fissure, which divide it into two ions. symmetrical lateral halves ; the former is a continuation of the anterior spinal fissure, the latter of the posterior, and ends in the ca- lamus scriptorius above. The lateral halves thus produced are marked by three grooves, producing four eminences, which pass under the follow- ing names : 1st. The anterior pyramids ; 2d. The olivary bodies ; 3d. The restiform bodies ; 4th. The posterior pyramids. The anterior fis- sure is crossed about an inch below the pons varolii by decussating fibres, and hence injuries on one side of the brain produce nervous effects on the opposite side of the body. First. The anterior pyramids consist of white fibres originating near The anterior the decussating fasciculi. They have a compound structure, pyramids. for each contains fibres arising from the inner side of the op- posite anterior column of the cord, and also fibres from its own side : they pass through the pons varolii into the crus cerebri. From these pyramids curved fibres pass round the olivary body, and are lost in the restiform. They are called arciform fibres. Second. The corpora olivaria receive their name from their olive shape. The olivary They are separated by a groove from the preceding in front, bodies. and by another groove from the restiform bodies behind. Ex- ternally, they are formed of white tubular tissue, which incloses a vesic- ular mass, the olivary ganglion, which connects with the vesicular struc- ture of the pons above, and that of the cord below. The fibres of these ganglia are called the olivary tracts. They are continuous with the cen- tral part of the medulla oblongata, passing behind the pyramids, extend- ing upward along the posterior part of the crura cerebri to the optic thai- ami and tubercula quadrigemina. The olivary bodies exist only in man and tlie monkey tribe. Third. The restiform bodies are separated from the olivary by a groove. They are continuous with the posterior and antero-lateral col- THE MEDULLA OBLONGATA. 305 umns of the cord. Ascending, they enter the ccrehellum, and xhe restiform are continuous with the inner part of its ciTis. They there- bodies. fore are a tract of communication from the spinal cord to the cerebellum. They each inclose a gray nucleus, which is the ganglion of the pneumo- gastric nerves, and of some of the roots of the glosso-pharyngeal. Fourth. The posterior pyramids are doubtfully marked off from the restiform bodies in front, and are separated from each other The posterior by the posterior fissure. Superiorly, their fibres are contin- pyramids. uous with the sensory tract of the crura cerebri : their gray nuclei are the ganglia of the auditory nerves. Fig. 145. The structure of the meduUa oblongata is exempli- fied in the annexed figures. J^igf. 145: 1, chiasm of the optic nerves; 2, crus cere- bri; 3, tuber cinereum; 4, corpora albicantia ; 5, locus perforatus ; 6, pons varolii ; 7, section of the middle peduncle of cerebellum ; 8, transverse fissure, separa- ting the ineduUa from the pons ; 9, first enlargement of the cord, or medulla oblongata ; 10, anterior pyra- mid; 11, olivary body; 12, anterior portion of resti- form body; 13, neck of the medulla oblongata; from 16 downward is the anterior median fissure ; from 17 downward, the anterior lateral furrow. I^igf. 146: 1, section of optic tract; 2, tubercula quadrigemina ; 3, triangular band ; 4, section of crus cerebelli ; 5, medulla oblongata ; 6, anterior floor of the fourth ven- tricle ; 7, median fissure of the fourth ventricle, aid- ing to form the calamus scriptorius ; 8, mammiUary swelling near the nib of the pen ; 9, posterior portion of the restiform body; from 12 down- ward, posterior median fissure ; from 13 downward, lateral furrow ; from 14 downward, posterior furrow. Mg. 147 cord, divided superiorly into two portions, of which the most internal one contributes to the formation of the cor- responding pyramid ; 7, middle or lateral column, di- vided superiorly into three or four portions, decussating with as many portions of the column of the opposite side, the decussation taking place both laterally and antero- posteriorly : it is the origin of the internal two thirds of the pyramid ; 8, 8, pyramids ; 9, white fibres of the pyramid, traversing the pons, and continuing to the crus ' ' U Fig. 146. Front of medulla ob- longata. ^ . , „ , Posterior view of medulla 6, anterior column or the oblongata. I nterior construction of the medulla and pons. 306 THE MEDULLA OBLONGATA. Fig. 148. Posterior view ot medulla oblongata. cerebri; 10, superficial section of the trans- verse fibres of the pons ; 11, deeper section of the transverse fibres of the pons ; 12, oli- vary bod J ; 13, right olivary body, brought into view by removal of the corresponding pyramid. Fig. 148 is a posterior view of the me- dulla oblongata : j^i !>■> posterior pyramids, separated by a posterior fissure ; 7\ r, resti- form bodies, composed of, c, c, posterior col- umns, and d, d, part of antero-lateral col- umns of the cord ; «, «, olivary columns, as seen on the floor of the fourth ventricle, sep- arated by s, the median fissure, and crossed by some fibres of origin of, n, n, the seventh pair of nerves. EUNCTIONS OF THE MEDULLA OBLONGATA. Viewed as a superposed continuation of the spinal cord, the medulla Functions of oblongata is the tract of communication between that organ the medulla : ^nd the brain : the anterior pyramids and olivary tracts con- it is a tract of communica- vcy motor influences, and the restiform tracts and posterior ''°'^- pyramids sensations. By experiments similar to those which have been performed upon the cord, these conclusions have been main- tained. But, besides this function of conduction, the medulla oblongata dis- charges a most important duty as a nervous centre ; on it depend respi- ration and deglutition. The brain may be wholly removed above, and the spinal cord below, as far as the origin of the phrenic nerve, without death necessarily ensuing, but on wounding the medulla oblongata, the muscular movements necessary for the introduction of air are necessarily stopped. Moreover, the medulla oblongata exhibits the property of reflex action. Its relations to So far as the function of respiration is concerned, its chief respiration. centripetal nerve is the pneumogastric, but the power which it possesses is participated in by many others, perhaps by reason of the venous condition into which the blood is brought from want of proper aeration. The violent respiratory movements by the sudden application of cold to the skin, the shower-bath, or dashing cold water on the face, are converted by it into respiratory muscular motions. From it also arise the movements required in the act of deglutition. Under this view of the functions of the medulla oblongata, it is to be regarded as an exclusively automatic instrument, which can continue its THE PONS VAROLII. 307 operation after the excision of tlie brain. As with the spinal cord, so with it : its simple action may continue though its commissural action has ceased, and this either through conditions of disease or by the ad- ministration of drugs. In lesions of the brain respiration may still con- tinue, as it may also when sensation and voluntary motion have been ar- rested by the breathing of chloroform. OF THE PONS VAEOLII. The pons varolii consists of a loop of fibres passing from one crus cerebelli to the other, around the tracts of communication structure of the- between the cord and the brain. As shown in Fig. 145, ^^^^ varolii, they do not form a continuous superficial commissure, but, at a certain distance below, interlace with the fibres of the pyramids ; moreover, among their deeper fibres gray vesicular matter occurs. That they con- stitute mainly a commissure for the cerebellum is apparent from the cir- cumstance that, in those animals which have the median cerebellar lobe only, there is no pons, and in other cases its relative magnitude is in proportion to the size of the cerebellar hemispheres. FUNCTIONS OF THE PONS VAPOLII. The functions of the pons varoHi are therefore twofold : it acts as a conductor, and also as a nerve centre. In the first respect, it Functions of is the channel from the spinal column to the cerebrum and *^^ P""^®- cerebellum, and also between the cerebellar halves, and experiments upon it, in giving rise to sensations and motions, are in conformity with what we should anticipate from the structure and fiinctions of the spinal cord. In the second respect, as a nervous centre, it has been stated that, when the cerebrum and cerebellum are removed, but the pons left untouched, an animal gives tokens of sensation when pinched or irritated, and like- wise executes motions which have an object ; these, however, were no longer observed after the removal of the pons. We have had repeated occasion already to mention that the surest guide which can be followed in interpretations of the func- .. /..I . • 1 • 1 r-\ Dr. Carpen- tions 01 tile nervous system is comparative physiology. (Jur ter's views of views of the action of the spinal cord, medulla oblongata, the analogy be- ■■^ •I'll tween the spi- and even portions above, hereafter to be described, will be nai cord of ver- rendered clear by a knowledge of the structure and func- t^g^^en^tr^* tions of the ventral cord of the articulata, the analogy of cord of articu- which to the parts we have had under consideration was first correctly pointed out by Dr. Carpenter. I therefore transcribe irom his General and Comparative Physiology the following paragraphs, which present his views with perspicuity. " The plan on which the nervous system is distributed in the sub- 808 FUNCTIONS OF THE COED. Fig. 149. kingdom articulata exhibits a remarkable uniformity throughout the whole series, while its character gradually becomes more elevated as we trace it from the lowest to the highest divisions of the group. It usu- ally consists of a double nervous cord studded with ganglia at intervals, and the more alike the different seg-ments, the more equal are these gan- glia. The two filaments of the nervous cord are sometimes at a considerable distance from one another, and the ganglia are distinct, but more frequently they are in close apposition, and their ganglia appear single and common to both. That which may seem as the typical conformation of the nervous system of this group is seen in the ganglionic cord of scolo- penclra, or in that of the larvae of most insects, such as that of the sjyhinx ligiistri. Fig. 149. Here we see the nervous cord nearly uniform throughout, its two halves being sepa- rated, however, in the anterior portion of the body. The ganglia are disposed at tolerably regular intervals, are simi- lar to each other in size (with the exception of the last, which is formed by the coalescence of two), and every one supplies its own segment, and has little connection with any other. The two filaments of the cord diverge behind the head to inclose the oesophagus, above which we find a pair of ganglia that receive the nerves of the eyes and antennae. We shall find that in the higher classes the inequality in the formation and office of the different segments, and the in- creased powers of special sensation, involve a considerable change in the nervous system, which is concentrated about the head and thorax. In the simplest vermiform tribes, on the other hand, we lose all trace of separate ganglia, the nervous cord passmg without evident enlargement fi'om one extremity to the other. Whatever may be the degree of multiplication of the ganglia of the trunk, they seem but repetitions of one another, the functions of each segment being the same with those of the rest. The cephalic ganglia, however, are always larger and more important. They are connected with the organs of special sense, and they evidently possess a power of directing and controlling the movements of the entire body, while the power of each ganglion of the trunk is confined to its own segment. " The longitudinal ganglionic cord of the articulata occupies a position which seems at first sight altoo-ether different from that of the nervous system of vertebrated animals, being found in the neighborhood of the ventral or inferior surface of their bodies, instead of lying just beneath their dorsal or upper surface. From the history of their development, however, and from some other considerations, it has been suggested that the loTiole body of these animals may be considered as in an inverted po- Nervons system of larva of sphinx ligiistri. FUNCTIONS OF THE COED. 309 sition, the part in which the segmentation is first distinguished in insects being the equivalent of the dorsal region in vertebrata, and that over which the germinal membrane is last to close in, being homologous with the ventral region. This view applies also to the position of the dorsal vessel, Avhich would then be on the ventral side of the axis, as in verte- brata. Regarded under this aspect, the longitudinal nervous tract of ar- ticulata corresponds with the spinal cord of vertebrated animals in posi- tion, as we shall find it does in function. "When the structure of the chain of ganglia is more particularly in- quired into, it is found to consist of two distinct tracts, one of which is composed of nerve fibres only, and passes backward from the cephalic ganglia over the surface of all the ganglia of the trunk, giving off branches to the nerves that proceed fi-om them, while the other includes the ganglia themselves. Hence, as in the moUusca, every part of the body has two sets of nervous connections, one with the cephalic ganglia, and the other with the ganglion of its own segment. Impressions made upon the afferent fibres which proceed from any part of the body to the cephalic ganglia become sensations when conveyed to the latter, while in respondence to these, the consensual impulses, operating through the ce- phalic ganglia, harmonize and direct the general movements of the body by means of the efferent nerves proceeding from them. For the purely reflex operations, on the other hand, the ganglia of the ventral cord are sufficient, each one ministering to the actions of its own segment, and to a certain extent, also, to those of other segments. It has been ascertained by the careful dissections of Mr. Newport, to whom we owe all our most accurate knowledge of the nervous system in articulated animals, that of the fibres constituting the roots by which the nerves are implanted in the ganglia, some pass into the vesicular matter of the ganglion, and, after coming into relation with its vesicular substance, pass out agaii> on the same side {Fig. 150, y, X'), while a second set, after traversing the vesic- ular matter, pass out by the trunks proceeding from the opposite side of the same ganglion, and a third set run along the portion of the cord which Fig. 160. connects the ganglia of different segments, and enter the nervous trunks that issue from them at a distance of one or more ganglia above or below. '■''Fig. 150, fi-om ganglionic tract of poly- desmus maculatus. J, interganglionic cord ; c, anterior nerves ; d, posterior ; f, k, fibres of reflex action ; g. A, commissural fibres ; i, longitudinal fibres, softened and enlarged as they pass through the ganglionic matter. " Thus it appears that an impression con- G-anglioD of polydesmus maculatus. 310 FUNCTIONS OF THE COED. vejed by an afferent fibre to any ganglion may excite motion in the mus- cles of the same side of its own segment, or in those of the opposite side, or in those of segments at a greater or less distance, according to the point at which the efferent fibres leave the cord ; and as the function of these ganglia is altogether related to the locomotive actions of the seg- ments, we may regard them as so many repetitions of the pedal ganglia of the mollusca, their multiplication being in precise accordance with that of the instruments which they supply. " The general conformation of articulated animals, and the arrangement of the parts of their nervous systems, render them peculiarly favorable subjects for the study of the reflex actions, some of the principal phe- nomena of which will now be described. The mantis religiosa custom- arily places itself in a curious position, especially when threatened or at- tacked, resting on its two posterior pairs of legs, and elevating its thorax with the anterior pair, which are armed with powerful claws ; now if the anterior segment of the thorax, with its attached members, be removed, the posterior part of the body will still remain balanced upon the four legs which belong to it, resisting any attempts to overthrow it, recover- ing its position when disturbed, and performing the same agitated move- ments of the wings and elytra as when the unmutilated insect is irritated : on the other hand, the detached portion of the thorax, which contains a ganglion, will, when separated from the head, set in motion its long arras, and impress their hooks on the fingers which hold it. If the head of a centipede be cut off while it is in motion, the body will continue to move onward by the action of the legs, and the same will take place in the separate parts if the body be divided into several distinct portions. After these actions have come to an end, they may be excited again by irritating any part of the nervous centres, or the cut extremity of the nervous cord. The body is moved forward by the regular and successive action of the legs, as in the natural state, but its movements are always forward, never backward, and are only directed to one side when the for- ward movement is checked by an interposed obstacle. Hence, though they might seem to indicate consciousness and a guiding will, they do not so in reality, for they are carried on, as it were, mechanically, and show no direction of object, no avoidance of danger. If the body be op- posed in its progress by an obstacle of not more than half of its own height, it mounts over it, and moves directly onward as in its natural state ; but if the obstacle be equal to its own height, its progress is arrest- ed, and the cut extremity of the body remains forced up against the op- posing substance, the legs still continuing to move. If, again, the nerv- ous cord of a centipede be divided in the middle of the trunk, so that the hinder legs are cut off from connection with the cephalic ganglia, they will continue to move, but not in harmony with those of the fore part of FUNCTIONS OF THE CORD, 311 the body, being completely paralyzed, so far as the animal's controlling power is concerned, though still capable of performing reflex movements by the influence of their own ganglia, which may thus continue to propel the body in opposition to the determinations of the animal itself. The case is still more remarkable when the nervous cord is not merely di- vided, but a portion of it is entirely removed from the middle of the trunk ; for the anterior legs still remain obedient to the animal's control, the legs of the segments from which the nervous cord has been removed are allo- getlier motionless, while those of the posterior segments continue to act through the reflex powers of their own ganglia, in a manner which shows that the animal has no power of checking or directing them. " The stimulus to the reflex movements of the legs in the foregoing cases appears to be given by the contact of the extremities with the solid surface on which they rest. In other instances the appropriate impression can only be made by the contact of liquid. Thus a dytiscus (a kind of water-beetle), having had its cephalic ganglia removed, remained motion- less as long as it rested upon a dry surface, but when cast into water it executed the usual swimming motions with great energy and rapidity, striking all its comrades to one side by its violence, and persisting in these for more than half an hour. Other movements again may be ex- cited through the respiratory surface. Thus, if the head of a centipede be cut off, and, while it remains at rest, some irritating vapor (such as that of ammonia or muriatic acid) be caused to enter the air-tubes on one side of the trunk, the body will be immediately bent in the opposite direc- tion, so as to withdraw itself as much as possible from the influence of the vapor ; if the same irritation be then applied to the other side, the re- verse movement will take place, and the body may be caused to bend in two or three different curves by bringing the irritating vapor into the neighborhood of different parts of either side. This movement is evi- dently a reflex one, and serves to withdraw the entrances of the air-tubes from the source of irritation, in the same manner as the acts of coughing and sneezing in the higher animals cause the expulsion from the air-pas- sages of solid, liquid, or gaseous irritating matters which may have found their way into them. "From these and similar facts, it appears that the ordinary movements of the legs and wings of articulated animals are of a reflex nature, and may be effected solely through the ganglia with which these organs are severally connected; while, in the perfect being, they are harmonized, controlled, and directed by impulses which act through the cephalic gan- glia, and the nerves proceeding from them. There is strong reason to believe that the operations to which these ganglia are subservient are al- most entirely of a consensual nature, being immediately prompted by sensations, chiefly those of sight, and seldom or never by any processes 312 FUNCTIONS OF THE CORD. of a truly rational character. When we attentively consider the habits of these animals, we find that their actions, though evidently directed to the attainment of certain ends, are very far from being of the same spon- taneous nature, or from possessing the same designed adaptation of means to ends as those performed by ourselves, or by the more intelligent ver- tebrata under like circumstances. We judge of this by their unvarying character, the different individuals of the same species executing pre- cisely the same movements when the circumstances are the same, and by the very elaborate nature of the mental emotions which would be re- quired in many instances to arrive at the same results by an effort of reason. Of such we can not have a more remarkable example than is to be found in the operations of bees, wasps, and other social insects, which construct habitations for themselves upon a plan which the most enlightened human intelligence, working according to the most refined geometrical principles, could not surpass, but which yet do so without education communicated by their parents or progressive attempts of their own, and with no trace of hesitation, confusion, or interruption, the dif- ferent individuals of the community all laboring effectively to one pur- pose, because their automatic impulses (producing what are usually term- ed instinctive actions) are all of the same nature. " Not only are the locomotive ganglia multiplied in accordance with the repetition of segments and members, but the respiratory ganglia are mul- tiplied in like manner in accordance with a repetition of respiratory or- gans. The respiratory division of the nervous system consists of a chain of minute ganglia lying upon the larger cord, and sending off its delicate nerves between those that proceed from the ganglia of the latter, as seen in Fig. 151. These respiratory ganglia and their nerves are best seen in the thoracic portion of the cord, where the cords of communication be- tween the pedal ganglia diverge or separate from one another ; and this is particularly the case in the pupa state, when the whole cord is being shortened and their divergence is increased. The thoracic portion of the cord is shown in Fig. 152, B, which represents the second, third, and fourth double ganglia of the ventral cord, the cords of connection between them here widely diverging laterally, and the small respiratory ganglia which are connected with each other by delicate filaments that pass over the ganglia of the ventral cord, and which send off lateral branches that are distributed to the air-tubes and other parts of the respiratory apparatus, and communicate with those of the other system." Illustrations of the nervous system of the articulata. Fig. 151, A, single ganglion of cejitipede, much enlarged, showing the distinctness of the purely fibrous tract, 5, from ^^ pede. *^^'^*'' the ganglionic column, a. Fig. 152, B, portion of the THE BRAIN. 313 fw ir>3. doulble cord from the thorax of the pupa of sphinx ligustri, showing the respiratory gan- glia and nerves between the gangha 2, 3, 4, and the sepa- rated cords of the locomotive system. Fig. 153, C, view of the two systems combined, showing their arrangement in the larva : «, ganglion of the ventral cord ; 5, fibrous tract passing over it ; c, 3. Thoracic portion of cord of spliinx ligustri. Combination of respiratory and locomotive ganglia. CHAPTEE XVI. OF THE BEAIN. The Brain: its Structwe. — Its Motor and Sensory Parts, Hemispheres, and Conunissures. — The Sensorium. — Variations of the Hemispheres in Size and Weight. — Instrumental Nature of Cerebrum. — The Cerebellum: its Structure and Functions. — Co-ordinates muscular Motions. — Connection with Amativeness. — Phrenology. — Conditions of Action of Brain. Symmetrical Doubleness of the Brain. — Function of each Half, and cf both conjointly. — Independ- ence and Insubordination of each Hemisphere. — Double Thought, — Alternate Thought. Senti- ment of Pre-existence. — Loss of Perception of Time. The cerebrum and cerebellum, being organs additional to the spinal cord, and developed, as has been shown in the last chapter, ^ ,,. ,, Ti • f Oreneral view upon it, the cord being able to discharge its own functions of structure of independently of them, we shall find it at once the most '^'^^'°' natural and most commodious method to consider their structures as arising out of its structure, and their functions as having relation to its functions. A general idea of the structure of the brain as an appendage to the ;}14 THE BEAIN. spinal cord may be gathered by considering that a biflu'cation of the fibres takes place in the medulla oblongata, and upon one of the result- ing bundles, the crus cerebri, the cerebrum is found, on the other the cer- ebellum. The crus cerebri is thus composed of three strands : an infe- rior, the fibres of which have come from the anterior pyramids, and in part from the olivary bodies. This strand ends in the corpus striatum, its fibres not, however, blending abruptly with the vesicular matter, but passing into it in bundles. It is essentially motor. A superior, which is derived from the posterior pyramids, and terminates in the thalamus. It is essentially sensory. Between these, constituting the third portion — strand it can scarcely with propriety be called — is a layer of dark vesic- ular material, the locus niger. It is to be understood that the motor strands of the opposite sides decussate in the medulla oblongata ; the sensory strands decussate in the mesocephalon. The other bundle, arising in the original bifurcation, assumes the des- Formation of ignation of crus cerebelli. On it the cerebellum is devel- the cerebellum, oped. It consists essentially of fibres from the restiform bodies, re-enforced by others which have come from the anterior pyramids under the name of arciform fibres. These together make their way to the interior ganglion of the cerebellum, the corpus dentatum, and there they end. But the crus cerebelli contains likewise two other great strands : an inferior, which constitutes the commissures of the two cere- bellar hemispheres, and which, running round the entire prolongations of the spinal cord, forms the pons varolii ; a superior, the processus cere- belli ad testes, which unites the cerebellum and cerebrum. Of the portions of the spinal cord on which the cerebrum is to be de- veloped, those which are sensory end in the optic thalamus, those which are motor in the corpus striatum. The thalamus and striatum of each side may be regarded as one compound ganglion, since, like the columns of the cord, they are entered by a gray and a white commissure. Of the portions on which the cerebellum is to be developed, the termination is in the central ganglion of the cerebellum, the corpus dentatum. At the place of bifurcation of the constituent strands of the crus cere- bri and crus cerebelli from each other in the medulla oblon- ^^^^^ ' gata, there is intercalated or included a ganglion, which, with its apparatus, constitutes the olivary body, the fibres of which make their way upward between the two preceding bundles, and, having bi- furcated, one branch goes to the quadrigemina and the other to the op- tic thalamus, the latter constituting, as has been said, a part of the crus cerebri. The seat of power of the medulla oblongata is in this ganglion. Such being the anatomical construction of the crus cerebri, it may be physiologically regarded as a compound strand, the anterior portion of THE BKAIN. 315 which is motor, the posterior sensory ; and "between these a Nerves of the dark vesicuhir deposit, the locus nigcr, which is continuous "oryTtraiuisre' between the vesicular matter in the spinal cord and that of spectiveiy. the thalamus and corpus striatum. From the lowest extremity of the cord to these great ganglia there is, therefore, an unbroken vesicular channel. In its progress onward to the corpus striatum, the anterior strand yields roots of the spinal accessory, hypoglossal, facial, abducens, the small root of the fifth, the trochlearis, and the oculo-motor nerves. If there were no other proof of the motor character of this strand, the motor property of all these nerves would be sufficient to determine it. In like manner, the posterior strand yields the pneumogastric, the glosso- pharyngeal, and the sensory root of the fifth, from the sensory functions of which its sensory character is established. The layer of vesicular matter which is found upon the cerebral convo- lutions, and which is doubtless the seat of the hig-her Intel- Relation of the lectual qualities, has therefore no communication with the ter of the ^m" vesicular matter of the spinal axis, by contact or continua- ispheres. tion, but only through the intervention of fibres which radiate upon it in all directions from the thalamus and striatum, or rather through some which radiate from the great sensory centre, the thalamus, to the periph- ery of the cerebrum, and others which converge from that periphery to the great motor centre, the striatum. If the diameter of these fibres be assumed to be -^^j^qq of an inch, there must be many millions of them in the aggregate. The vesicular matter of the hemisphere is arranged on the superficies instead of centrally, on account of the necessities of their structure and condition of activity, for thereby a great surface is obtained, which is further increased by the artifice of convolutions, a ve- sicular surface which, counting in that of the cerebellum, has been esti- mated at 670 square inches, and blood can be copiously supplied and freely removed. But the thalamus and striatum are only two of a chain of ganglia be- neath the cerebral hemispheres. Anteriorly we find the ol- (jano-na at the factive ganglia, or bulbs of the olfactory nerves, which are base of the seated upon peduncles, though their character is manifest from the gray matter they contain. Behind these are the tubercula quadri- gemina, to which the optic nerves run, and which are therefore their gan- glionic centres. What answers to the auditory ganglion is lodged at a distance back, at the fourth ventricle, and the gustatory ganglion is in the medulla oblongata. These are the ganglia of special sense, and to be regarded as subordinate to the thalamus, which is their common register. All these parts are commissured with one another, and with their fel- lows of the opposite half of the brain. Indeed, so likewise are all its 316 THE BEAIN. Commissures of parts, the diiferent cerebral lolbes, the opposite hemispheres, the bram. adjacent and distant convolutions, the cerebrum with the cerebellum. Hence arises a structure of extreme complexitj. Among the commissural apparatus may be more particularly mentioned the cor- pus callosum, the fornix, the anterior, the posterior, the soft, and the su- perior longitudinal commissures. For the sake of a clear conception of the structure of the brain, so far Aspects of the as is required for physiological purposes, the annexed repre- brain. sentations of its superficial aspects are given. These are a preparation for the diagrammatic sketches which follow, and which ena- ble us to understand the relation and dependence of the more prominent parts. It need scarcely be added that the uses and functions of nearly all the subordinate parts are at present wholly unknown. For the time being, they are therefore objects of interest to the anatomist rather than to the physiologist. Fig. 154, external lateral face of the right half of the brain: 1, me- dulla oblongata ; 2, pons varolii ; 3, cerebellum ; 4, pneumogastric lob- ule ; 5, frontal convolutions ; 6, parietal convolutions ; 7, occipital con- volutions ; 8, fissure of Sylvius ; 9, 9, its two branches. T/./ r.( Fig. 155. External lateral face of the brain. Fig. 155, superior aspect of the brain : 1,1, anterior lobes ; 2, 2, posterior lobes ; 3, 3, great median fissure ; 4, 4, fissures ^"^^^""^ '^^p^'^' "' "^^ ^^"^• of Rolando ; 5, 5, anterior parietal convolutions ; 6, 6, posterior parietal convolutions ; 7, 7, rudimentary parietal convolutions ; 8, 8, frontal con- volutions ; 9, 9, occipital convolutions. Fig. 156, internal lateral face of the right half of the brain: 1, half of medulla oblongata ; 2, half of pons varolii ; 3, half of crus cerebri ; 4. arbor vit^ of cerebellum ; 5, aqueduct of Sylvius ; 6, half of the valve of Vieussens ; 7, two of the tubercula quadrigemina; 8, half of the pin- eal gland ; 9, its inferior peduncle ; 10, its anterior peduncle ; 11, trans- verse portion of the fissure of Bichat ; 12, superior face of the optic tract ; THE BRAIN. 317 Internal lateral face of the brain. 13, its internal face ; 14, commis- sura mollis; 15, infundibulmu; 16, portion of pituitary gland ; 17, por- tion of tuber cinereum ; 18, pisiform tubercle; 19, locus perforatus; 20, oculo-motor nerve ; 21, portion of optic nerve ; 22, anterior cerebral commissure ; 23, foramen of Mon- roe ; 24, fornix ; 25, septum luci- dum ; 26, corpus callosum ; 27, splenium ; 28, genu ; 29, sinus of tlie corpus callosum ; 30, gyrus fornicatus ; 31, internal convolu- tion of the antei-ior lobe ; 32, deep anfractuosity ; 33, convolution of pos- terior lobe ; 34, anfractuosity. Fig- 157. _pig, 157, base of tlie brain, pboto- graplied from a wax cast : 1, 1, anteri- or lobes ; 2, 2, middle lobes ; 3, 3, pos- terior lobes; 4, anterior portion of great median fissure ; 5, its posterior portion ; 6, 6, fissures of Sylvius ; 7, 7, antero- posterior portions of the great fissure of Bichat ; 8, tuber cinereum ; 9, 9, corpora albicantia; 10, locus perforatus medius ; 11, 11, crura cerebri; 12, pons varolii ; 13, medulla oblongata ; 14, 14, anterior pyramids; 15, 15, olivary bodies; 16, 16, restiform bodies; 17, 17, lateral lobes of the cerebellum ; 18, Base of the brain. portioii of its middle lobc ; 19, 19, two small antero-posterior convolutions of the frontal lobe, separated by the groove of the olfactory nerve ; 20, oblique convolution, limiting the fissure of Sylvius ; 21, convolution of the great cerebral fissure ; 22, ol- factory nerve ; 23, its bulb ; 24, 24, optic nerves and their chiasm ; 25, 25, oculo-motor nerves ; 26, 26, pathetici ; 27, 27, great and small roots of the trifacial; 28, 28, external oculo-motor nerves; 29, 29, facial nerves ; 30, 30, auditory; 31, 31, giosso- pharyngeal; 32, 32, pneumogastric nerves ; 33, 33, spinal accessory ; 34, 34, great hypoglossal. In this engraving several of the symmetrical numbers are not repeated, for the sake of clearness. J^i(/. 158 is an analytical diagram of the brain in a vertical section (from Mayo). It serves to impress on the mind the foregoing structure of structural descriptions, s, Spinal cord preparing for bifurca- *^^ ^^^^°- 318 STRUCTUEE OF THE BEAIN. Fig. 158. Diagram of the structure of the brain. tion ; r, restiform bodies passing to c, the cerelbellimi ; d, corpus denta- tura of the cerehellura ; o, intercalation of the olivary body ; /*, columns continuous with the olivary bodies and central part of the medulla ob- longata, and ascending to the tubercula quadrigemina and optic thalami : p, anterior pyramids : v, pons varolii ; 7i, b, tubercula quadrigemina : g, geniculate body of the optic thalamus ; t, processus cerebelli ad testes : a, anterior lobe of the brain ; q, posterior lobe of the brain. J'ig. 159, the motor tract (from Sir C. Bell). A, A, fibres of the hem- ispheres converging to form the anterior portion of the crus cerebri ; B, the same tract when passing the crus cerebri ; C, the right pyramidal body, a little above the point of decussation ; D, the remaining part of the pons varolii, a portion having been dissected off to expose B. 1, olfactory nerve in outline ; 2, union of optic nerves ; 3, 3, motor oculi ; 4, 4, patheticus ; 5, 5, trigeminus ; 6, 6, its muscular division ; 7, 7, its sensory root ; 8, origin of sensoiy root from the posterior part of the me- dulla oblongata ; 9, abducens oculi ; 10, auditory nerve; 11, facial nerve: THE MOTOR TRACT. Fig. 159. 319 The motor tiatt 12, eighth pair; 13, hypoglossal; 14, spinal nerves; 15, spinal acces- sory of right side, separated from par vagum and glosso-pharyngeal. Fig. 160 (on the following page), the sensory tract (from Sir C. Bell). A, pons varolii ; B, B, sensory tract separated ; C, union of posterior columns ; D, D, posterior roots of spinal nerves ; E, sensory roots of the fifth pair. The ganglia at the base of the brain are regarded by Dr. Carpenter as constituting the true sensorium, a doctrine which he has es- _, -,.,-, . , • 11-1-11 The sensorium. tablished by many weighty arguments, and which is doubt- less one of the most important thus far introduced by any physiologist. The idea here intended to be conveyed is, that the thalami, striata, sensory ganglia, and nervous arrangements below, constitute an isolated apparatus ; distinct from which, and superadded, are the cerebral hem- ispheres. From observations on the animal series, the conclusion seems to be un- 320 THE SENSORY TEACT. Fig. 160. The sensory tract avoidable that the chain of ganglia now under consideration must con- stitute a sensorium, the centripetal iibres communicating their impression and motion ensuing, the impressions being attended with consciousness. This view is moreover substantiated by observations made after excision of the cerebrum, a certain degree of consciousness remaining, not unlike that exhibited by a man who is half asleep. This condition of things is natorallj presented in the amphioxus. But after the cerebral hemispheres are added, an impression received Effect of the ad- '•^P^^^ ^^'^^ thalamus, whether it has come in through the sen- ditionofthe sorj ganglia, or any other sensory part of the cranio-spinal cere rum. axis, is transmitted to the convolutions along the radiating fibres. From the convolutions, the influence which is to produce mo- tion descends along the converging fibres to the striatum, thence along the inferior layers of the eras, through the mesocephalon to the anterior pyramids, and by their decussation to the opposite side of the cord. Such is the view which Dr. Carpenter presents of the functions of the sensory ganglia and spinal axis ; or, emplopng the terms we have pre- \'iously defined, the cord alone is a longitudmal series of automatic arcs ; on the addition of the thalamus and striatum, it becomes a compound registering arc, the cerebral hemispheres finally annexed to it constitut- ing an influential arc. In a simple arc, an impression is at once converted mto motion, and leaves behind it no traces ; its expenditure is instantaneous and complete. Tn a registering arc, a part of the impression is stored up or remains — THE CEREBRUM. 321 nay, even the whole of it may be so received and retained. It is not to be overlooked that, as soon as this effect occurs, the evidences of sensation arise ; and, since sensation necessarily implies the existence of ideas ideas themselves are doubtless dependent on this partial retention or reo-- istry of impressions. We may therefore adopt the doctrine of Dr. Car- penter, as regards the sensorial functions of the cranio-spinal apparatus, not only from the arguments he has presented, but also from other con- siderations. There can be no doubt that the cerebral hemispheres constitute the in- strument through which the mind exerts its influences on the General result body. Any injury of sufficient severity inflicted upon them °f variations is at once attended with a total loss of intellectual power; weight of the any malformation or lesion by disease is attended by a dete- iiemispheres. rioration below the customary mental standard; any unusual develop- ment with eon-espondingly increased powers of intellection ; and this not only as regards animals of different tribes, or individuals at special peri- ods of their lives, but also of different men when compared with one an- other. The general impression is founded in fact that those who have distinguished themselves for mental attainments or intellectual power have been marked by the unusual development of their cerebral hemi- spheres. It is to be understood that, in thus asserting a correspondence between the development of the cerebrum and intellectual capabilitv, -r ^ 111- r J ' Instrumental we are not to overlook the mstrumental nature of that orran. nature of cere- Though imperfections in it may produce a manifest inferior- ^"'°' ity, that inferiority is by no means to be referred to the intellectual prin- ciple itself. The mode of action being by an instrument, if that instru- ment becomes imperfect the action becomes imperfect too. Under such circumstances, in any human contrivance, we should never think of im- puting inferiority to the prime mover. From this point of view we may therefore consider the intellectual prin- ciple as possessing powers, properties, and faculties of its own ; as being- acted on by impressions existing in the thalamus, and delivered tln-ough the intervening fibrous structures to the vesicular material of the convolu- tions of the cerebral hemispheres. In this region they act upon the in- tellectual principle and are acted upon by it, the returning influence, if any, coming down through tHe converging tubular structures to the cor- pus striatum, and by its commissural connections sent off to particular ganglia, passing along the inferior strand of the crus through the meso- cephalon to the anterior pyramids, and by their decussation to the oppo- site side of the cord. Having thus spoken of the sensory ganglia and the cerebral hemi- spheres, it remains to add some remarks respecting the cerebellum. It X 322 STRUCTURE OF THE CEREBELLUM. The cerebel- arises, as has been stated, from the triple strand of the cms lum. cerebelH, of which one layer of fibres is connected with the corpora quadrigemina, and through them with the optic thalami ; a sec- ond with the restiform bodies ; and the third is commissural, and passes forward as the pons varolii. Like the cerebrum, this organ is vesicular on its surface, which pre- sents a number of parallel lines, which are fissures descending to the in- terior. Their object is apparently the same as that of the convolutions of the brain, the augmentation of surface. Of these fissures, the deep are termed the primary : they divide the organ into lobes. Those which descend to a less depth are termed secondaiy : the divisions they give rise to are lobules. The gray vesicular material does not, however, de- scend to the bottom of the primary fissures, and in this respect they dif- fer from the cerebral convolutions. Moreover, from this cu'cumstance, that material is not continuous all over the cerebellum, but is in divided portions. Such are the appearances presented on an exterior examination of Structure of "the cerebellum. Viewed as a development upon the crura thecerebeUum. cerebelli, it may be described as consisting of a median lobe and two hemispheres ; the former is, however, found existing alone in fish- es and reptiles, the latter being subsequently added in the higher tribes. From the central column of each hemisphere white fibrous planes are given off, and from these, again, secondary, and again, teitiary planes proceed. The planes are covered with vesicular matter, and thus- give rise to the appearance spoken of in the preceding paragraph, in the exte- rior examination of the cerebellum, as primaiy and secondary fissures. They are lined with pia mater. The median lobe is formed on the same plan. Its fibrous stem comes from the processus cerebelli ad testes, or, more properly, from the optic thalamus. The weight of the cerebellum, compared w^ith that of the cerebrum, is usually stated as being about 1 to 8. Much diversity of opinion prevails respecting the time function of the cerebellum, some supposing that it is the centre of common sensation, others that it is for the purpose of co-ordinating muscular movement, and others that it is the seat of sexual instinct. That the cerebellum is one of the sensory ganglia may be inferred from Function of the 'the history of its development and its anatomical connec- cerebeiium. tions. Its median lobe is the first to appear, as in fishes, and the hemispheres arise subsequently as appendages thereto, as in birds. The size which these eventually attain gives them a deceptive prominence, and hides their subordinate character. Eegarding the lobe, therefore, as the essential and ftmdamental portion of the stnicture, the significance of its cerebral connection with the thalamus through tlie pro- cessus ad testes is too obvious to be overlooked. As by this its sense- FUNCTIONS OF THE CEREBELLUM. 323 rj character is displayed, so the same holds good for the hemispheres, their relations with the spinal cord through the restiform bodies beino* also of a sensory nature. It seems probable that the superficial vesicu- lar material is in anatomical connection with the thalamus, and the cor- pus dentatum or inner ganglia with the posterior or sensory columns of the cord. The arguments which have been brought forward by those who sup- pose the cerebellum to have for its office the co-ordination of The doctrine general muscular movement, may be briefly quoted as fol- ^^^^^ ^^ ^°-°^^^- o ' ./ ^ 1 nates musculai" lows : There appears to be a general correspondence between motion, its size and the degTce of energy and complication of the motor powers in various animals. Thus, in fishes, and likewise in birds, those tribes which excel in their powers of motion, or are distinguished by the com- plication of their movements, are characterized by the manner in which this organ is developed ; and the same may be said even of the mamma- lia, quadrupeds whose locomotive mechanism is simple possessing it in a lower state of development than those which either temporarily or constantly move on the posterior extremities. Among apes, those which more frequently assume the erect posture, which is normal to man, have their cerebellum of a size more closely approaching to his. On examining such facts, it appears that it is not so much muscular power as the quality of co-ordinating and governing minute muscular motions. To maintain the standing position motionless, there are, in re- ality, a great many muscular movements required, which serve to antag- onize all the little incidents producing a tendency to fall ; and if this be so in standing, how much more difficult must such antagonizing and compensating actions become in walking, running, and such movements. Theoretically, it might be expected that some special organ is necessary to combine such various actions, and that organ seems to be the cere- bellum. In confirmation of this are the experimental results which have been obtained. The cerebellum, on irritation, gives rise to no Results of ex- convulsive motions, nor to sensations. If removed by de- rfnmentsof ' _ _ _ -^ the cerebel- grees in successive slices, the motions of the animal become lum. irregular, and, finally, it loses all povfer of walking or of maintaining its equilibrium. Though the powers of the animal in bringing its muscles into contraction seem not to' have suffered, it can not co-ordinate or com- bine the necessary muscular exertions, and, as is graphically stated, stag- gers and falls over like a drunken man, still making efforts to maintain its balance. Such experiments have been repeatedly made in the case of different animals, and with the same results. Connected with these results of experimental lesions of the cerebellmn are the rotations, as they are termed, wliich occur, for example, when one I 324 DOCTEINE OF PHRENOLG|GY. Rotary motions of the crura cerebelH is cut, the animal rolling upon its lon- of animals. gitudinal axis for a long time and with great rapidity. From such facts, it has therefore been concluded that the function of the cerebellum is neither for sensation nor intellection, nor is it the source of voluntary movements, but that it is for the government or control of combined muscular action. This is the view of M. Flourens. M. Foville supposes that the cerebellum is for the perception of the Doctrine that scnsations derived from the muscles, and enabling the mind cerebellum is to cxcrt a guiding action. The facts which support the pre- tion of muscu- Ceding vicw support this also, there being, moreover, in this lar sensations, casc, an additional argument derived from the connection which the cerebellum has l^een shown to maintain with the sensory col- umns of the cord, and the pain experienced on irritating the restiform columns. It has likewise been pointed out that this hypothesis illus- trates the connection between the cerebellum and the optic ganglia, as if it were for the purpose of bringing the organs of sight to the aid of this co-ordination of muscular motion. A third hypothesis, to which allusion has been made, is, that the cere- bellum is the organ of sexual instinct, or of amativeness, as Doctrme that , , *^, , . —., . , r- i • i it is the organ it IS termed by phrenologists. Ihe evidence ot this, when ofamativeness. f^-j.]^ examined, is, however, very far from affording a full proof; indeed, in many instances the facts are in direct opposition to the doctrine. In castrated animals the cerebellum undergoes no dimi- nution. There is no coincidence between the intensity of that instinct in the different animal tribes and the degree of development of this or- gan : and where it has been in a diseased condition, there has not been a o - necessary correspondence between the lesion and the loss of the instinct. This view of the function of the cerebellum is connected with the doc- trine of special localization, or phrenology, which may therefore be here briefly considered ; the general expression of this doctrine being that par- ticular regions of the brain are devoted to special functions, reno ogj . ^^^ ^-^^^ -^^ ^^ inspection of the exterior of the cranium men- tal peculiarities may be detected. Drs. Gall and Spurzheim considered that this view is supported by the fact that the specialization of function in the brain is agreeable to the general mechanism of the system, in which particular organs are charged with particular duties ; that, in any individual, the mental powers are not equally or proportionally developed, but some at one and some at another period of life, and so likewise of their decline, some remaining at their original strength, while others may have Arguments in bccome sciiously impaired. It does not appear how such foc°aHzItlon o? ^^^^^ ^^^^ ^^ explained upon the hypothesis that the whole functions. brain acts as a imit. They may be readily understood if it be supposed to act by parts which are developed in succession. The WEIGHT OF THE BRAIN. 325 same conclusion is arrived at from well-known facts connected with in- sanity, in Avlaich it very frequently happens that some of the faculties •alone are deranged, while the others retain their power, and some may even become more perfect than before ; so, likewise, in dreaming, some of the faculties retain their activity, while others have become torpid ; and so, likewise, when different individuals are compared, some exhibit a superiority in one, and some in another mental particular ; and it is as- serted that where the same peculiarity has predominated in different in- dividuals, it has always been attended by an unusual development of a special locality of the brain. Nor is there, in these views, any thing that stands in contradiction to the general plan upon which the nervous sys- tem itself is constituted, as is manifested by the different sensory gan- glia for vision, hearing, or smell, or the arrangement for motion or sensa- tion presented by the spinal cord ; and, moreover, they are supported by the comparative anatomy of this system ; for, whatever grade of animal life we may consider, the appearance of a new function or of a new in- stinct is certain to be connected with a new and contemporaneous devel- opment of some part of the nervous system. The facts which have been observed in cases where one cerebral hem- isphere has either suffered lesions or lost its functions, do not present any contradiction to the preceding doctrines ; for, though the remaining hemisphere may seem to act equally well alone, as did both together, we are very apt to deceive ourselves as regards the' actual facts, a statement which may be illustrated by recollecting how easily we persuade our- selves that we see with one eye as well as with two. No doubt, in many of the ordinary cases, one hemisphere of the brain may, like one eye, seem to act well enough, but a more critical examination proves that in other cases this is far from being true. That the two hemispheres act sever- ally and separately is clear from what sometimes ensues in diseased con- ditions of one of them, or when, perhaps, there is a want of symmetry between them, those remarkable forms of mental derangement, some- times known under the designation of double life or duality of mind, then ensuing. In man, the weight of the brain averages about fifty ounces ; in fe- males, about forty-five ; the maximum being about sixty-four, weight of the and the minimum about twenty ; in the case of idiots, the ^^^^°- mean specific gTavity of the gray matter is stated by Dr. Sankey to be, in both sexes, 1.034, but somewhat less early and late in life. The specific gravity. of the white is 1.041, and this varies less with sex and time of life than the former. The functional activity of the brain depends on the copious supply of arterial blood. It is computed that one fifth of the whole quantity in the circulation is sent to this organ. It is delivered through the two 326 PRESSURE ON THE BRAIN. o 1 - internal carotid and two vertebral arteries. The impetus of Supply of -i blood "to the the current is checked by the sinuous course these vessels ^^^^' take, or by their breaking promptly into capillary branches. • A freedom of anastomosis among them, as is well displayed in the circle of Willis, affords abundant provision for accidental stoppages or re- straints. Although the brain is inclosed in an unyielding cavity, it is subject to . , . the pressure of the air, a fact which, though it has been de- Atmosphenc ^ i • i • r -n • pressure on the nied by some physiologists, follows from ordinary physical brain. principles. And since the quantity of blood present at any moment in the organ varies with the contemporaneous functional activ- ity, being greater as that activity is greater, the cerebro-spinal fluid also varies in amount. Through this fluid an equality of pi'essure is there- fore insured, no matter what may be the quantity of blood in the brain. The cerebro-spinal fluid, the quantity of which has been estimated at Gerebro-spinai two ounces, is readily absorbed and as readily reproduced, fluid. rpj^g ^^^ ^£ adjustment between it and the blood requiring a certain period for its completion, the brain can not instantaneously be brought to its maximum action. Thus, as all persons observe, when we undertake any unusual intellectual duty, there is a certain preparatory period to be passed through, as the common expression is, " for compos- ing the thoughts." Pressure upon the brain, either applied mechanically or through acci- Effect of me- dental effusions, produces at once functional inactivity, prob- chanicai pres- ably by interference with the due circulation of the blood ; changes in the and, in like manner, any marked change in the chemical re- blood, lations of that fluid exerts on the brain a corresponding ef- fect. Thus, when oxygen gas is breathed, or, still better, protoxide of nitrogen, which is more soluble in the blood, the processes of intellection go on in an exaggerated way, and ideas in rapid succession, and in unu- sual forms of combination, flit through the mind ; but, as the consequence of this, since the lungs can not remove with the necessary promptness the carbonic acid which is arising, the narcotic effects of that body are soon experienced ; and this is also the case in alcoholic intoxication, in the advanced stages of which the accumulation of carbonic acid in the blood gives rise to the same result. That different regions of the brain have independent though mutually Effect of size commissured faculties, is fully established by the phenomena tion of^he^" ^^ *^® nerves of sense, nor can there be any doubt that these brain. differences of physiological function are directly dependent on differences of anatomical structure. It is, indeed, to structural differences that we should impute the greater or less efficiency of the whole organ, as much as to differences of its weight. Because of a higher elaboration, DOUBLENESS OF THE NEIIVOUS SYSTEM. 327 the brain of one person may Ibe more energetic than that of another, even though its weight may be less. It is not to be denied, however, that there is a connection between mental power and the quantity of cerebral matter, when individuals of the same kind are compared, or that in the animal series the psychical powers decline as the cerebrum diminishes in size. Few topics are more worthy of the attention of the physiologist than that of the variable psychical powers of man, and yet few have r 1 1 1 -r. • 1 1 1 • 1 ^*'® variable been more overlooked. By variable psychical powers I mean psychical those periodicities of increase and diminution in our intellect- P'^^®''^- ual efficiency, which may be noticed not only in diseased, but also in healthy states. On the principles we have presented, these find their explanation in the temporary physical states of the organ, such as its condition of repair, its existing facility for oxidation, and the constitution of the blood as respects a proper arterialization. The most striking structural characteristic of the nervous system is its symmetrical doubleness, the cranial and spinal nerves com- Symmetrical ino; forth by pairs to their distribution on the riffht and left '^o'^^i'^n^ss of ^o ^ L o nervous sys- sides of the body. The manner of development from the tem. spinal axis laterally implies such a construction, and, indeed, gives ori- gin to two halves so equal and alike that it has often been said each person consists of two separate individuals. Examining those organs which, by reason of the elaborateness of their mechanism and principles of action, enable us to determine with satisfactory precision p .• ^ the function discharged by each one of the members of the each lateral pair, as in the case of the eye or the ear, we may come to the °^^^^- following conclusions : Each is a distinct organ in itself, capable of its meeting the requirements of the economy in a sufficiently satisfactory manner, and therefore forms a distinct whole ; but the pair can likewise act simultaneously, re-enforcinei:, to a certain decree, each oth- , 7 1 • 1 • 1 ^ 1 • T 1 Conjointly er s power, though m this double action there by no means double organs arises a double intensity of effect. The closure of one ear ^Z ^^^ '}°^^^^ • -,..., , , eftects, but in- to a sound does not diminish the loudness by one half, nor crease their does the shutting of one eye reduce to one half the bright- P'"^'^!^!""- ness of a light ; but, though there is not such a doubling of effect when both eyes or both ears are employed, there is a degree of precision in the resulting indication which is not to be gained by the use of one of these organs alone. In such a double organ, then, the result is not so much a heightening of the final impression as the giving to it of a greater de- gree of precision. Moreover, each organ seems to exert a compensating influence over its fellow in any deficiencies or imperfections it may possess. Compensatioa Thus it is rare that both eyes are of an equal optical good- °^ defects, ness, as most individuals wiU find on making a personal examination;. 328 INDEPENDENT ACTION OF EACH HEMISPHERE. but in vision with Iboth eyes the faults of the more imperfect one are merged in the indications of the better, and the same might be remark- ed of the ear ; from which it woukl appear that this doubleness of or- gans is rather for the purpose of introducing a principle of compensation than one of conspiring action, the object intended to be gained being a justness of perception rather than an increase of effect. These observations apply to double organs in their normal states, or, Effect of tem- if not their normal, their habitual ones ; but if to the eye, porary disturb- ^^^ example, a temporary disturbance is given, as by press- gan. ure which renders its optical axis oblique, the fellow organ being permitted to retain its usual position, double sight is the result. It is true that, in the habitual divergence of strabismus, such is not the effect, one of the images disappearing, or perhaps the mind, accommodat- ing itself to the habitual condition, combines the two into one. These circumstances indicate that each member of a double organ can, under conditions of distm-bance, exercise an independent and even opposing ac- tion to its fellow. It has by some been supposed that the mind pays attention to the im- Theindicatious prcssions of Only one of the pair of organs at a time ; thus, of one organ ^^^^ ^^ g^^ ^j^g imao;es fumished by only one eye, though we contemplated o _ _ -^ -^ . -^ i r at a time. can with very gi-eat quickness direct attention to those fur- nished by the other, and therefore, deceived by the rapidity with which this alternation of attention can be accomplished, our belief in the syn- chronous use of both organs is an error. If two differently colored ob- jects, such as differently tinted wafers, be so placed as to be separately and yet simultaneously viewed by both eyes, the mind vainly attempts to combine the two images together. We do not see the resulting form of a green tint, but we see, according as our attention is given to the right or left, a blue or a yellow, if these have been the colors of the wa- fers, and these colors can quickly merge into one another, like dissolving Illustrative views. There is a simple experiment which serves to support experiment, -fchis view, and wliich any one may readily make. If the open hand be placed along the nose, so as to divide the right eye from the left, and we look upon the surface of a uniformly-illuminated sheet of paper covered with writing, it will be found that we can only read with one eye at a time, but that the mind can with great rapidity determine which ey-e it will use. In this little experiment, we have, moreover, the means of estimating the relative sensitiveness of the two eyes, and other of their optical peculiarities ; thus it will be commonly remarked that, though the paper be, as we have said, uniformly illuminated, that part of it which is regarded by one eye is brighter than that seen by the other, this being due to a difference in their sensibility. It will also frequently occur that the two portions of the page will present different shades of tint, DOUBLE TRAINS OP THOUGHT. 329 the one, perhaps, "being a taint greenish gray, while the otlier is of a yel- lowish white, the jn'oper color given to it by the candle or lamp hy which it is seen. In this feature of double construction the brain itself participates, pre- senting a right and left half approaching one another in form, without being absolutely identical. Much, therefore, of wdiat has been said re- specting the mutual relations of the right and left eye, and the right and left ear, must apply to the right and left hemispheres of the brain ; and it is under this point of view that Dr. Wia;an has regarded it in ^ , ■^ "^ o Independent his work on the Duality of the Mind. Nor can there be any action of each doubt that each hemisphere is a distinct organ, having the ^'^""^P^*'^*^- power of carrying on its functions independently of its fellow; that, though each can thus act separately, both can act simultaneously ; and, judg- ing from the cases that have just been presented, it would seem that we are justified in inferring that the common action of the two hemispheres is not for the purpose of a heightening of effect, but only for greater pre- cision, and that in the same manner as it is a rare thing to find two eyes or two ears of equal goodness, so also it is unusual to have two hemi- spheres which are precisely alike. The defects of the one may insubordina- be compensated by the superiorities of the other, and thus tion of one 1,1 ,, • 1 1 hemisphere. a mean result be attained ; and as one eye or one ear can, under the proper circumstances, overpower its fellow, so likewise can one hemisphere of the brain, except in certain cases, which have been some- what imaginatively described as insubordination of one of the hemi- spheres, when insanity is the result, the healthy half being unable to control the diseased one ; and for this reason, we often observe of the insane that they have synchronously, or, at all events, in a very rapid al- ternation, two distinct trains of thought, and, consequently. Double train of two distinct utterances, each of which may, so to speak, be thought. perfectly continuous and even sane by itself, but the incongruities that arise from the mingling of the two betray the condition of such persons. In this case doubleness of action is seen in its most exaggerated aspect, but in a less degree, it may be remarked, in the thinking operations of those whose minds are perfectly sound. Thus there is no student but must have observed, when busily engaged in reading, that his mind will wander off to other things, though he may mechanically cast his eyes over page after page ; and the same may occur in listening to a lecture or sermon. But, though the insane man may indulge in two synchro- nous trains of thought, he never indulges in three, for the simple reason that he has not three hemispheres to do it with, the same remark apply- ing to the sane man in the accidental wanderings of his thoughts. The overcoming of this insubordination of one of the hemispheres may, to a very considerable degree, be accomplished by education, of which 330 CASTLE-BUILDIXG. Effect of edu- One of the chief results is that it exercises us in the habit of cation. thinking of one tiling at a time, of thinking therefore with- out confusion, and of arriving at conclusions with precision and decision. And these considerations should also, in Dr.Wigan's view, be our chief guide in the cure of insanity, doing all in our power to invigorate the ac- tion of the healthy hemisphere, and enable it to subdue the insubordina- tion of the diseased one. If both hemispheres are diseased, the case is almost hopeless. Of the independent and yet complete action of each of the cerebral hem- „ . ienheres w^e have abundant and interesting; proof. Mental Perfect action ^ .,. c -n -i- of a single operations can be earned on m a proioundly diseased state oi hemisphere. ^^^ of these Organs, as multitudes of well-authenticated cases attest — nay, even when the lesion has gone so far as to amount to an absolute and entire disorganization of one of the hemispheres. Similar evidence is also fiimished by those interesting cases in which, by accident, as by gunshot wound, destruction of one side has occurred. Even in a state of health we have numerous examples of this inde- . , pendent action of each hemisphere. While engaged in ordi- Intermixed ac- -t _ i • i i tion of the two nary pursuits which imply a continued mental occupation, hemispheres. ^^ ^^.^ occasionally troubled with suggestions of a different kmd. A strain of music, or even a few notes, may be perpetually ob- truding, and such an occurrence we could scarcely explain save upon the principle of the separate action of these organs, the one interfering with the other. That precision w^hich we have remarked as arising from the conjoint use of two eyes and two ears is doubtless also attained where the two hemispheres are acting in unison. We can, moreover, volunta- rily permit one to rest while the other continues its duty, as we can vol- untarily make use of one eye, disregarding the indications of the other ; but where it is necessary to execute a critical comparison or arrive at an accurate judgment of things, both hemispheres are brought into action, as are both eyes when we intently consider an object. Among other phenomena, Dr. Wigan calls attention to the operation Castle- of castle-building, as it is designated, as illustrating the volunta- building. J.J jjianner in which we permit one hemisphere to act, presenting fancifal delusions ; the other, as it were, watching with satisfaction the operation, and in this respect lending itself to it. Xot that for a moment we suppose there is any tmth in the ideas suggested, and in this the phenomenon differs essentially from that of dreaming, in which it never occurs to us that the scenes and actions are unsubstantial. Still more strikingly do those singular cases, which from time to time J, , , present themselves to the physician, of double or alternate temate con- consciousiiess, illustrate this isolated function of the hemi- sciousness. gpi^eres. In some of these, which have been carefully ob- SENTIMENT OF PEE-EXISTENCE. 331 served cand authentically recorded, each of these portions of the brain has continued its action for a period of days, or even weeks, and tlien, relaps- ing into a quiescent state, has been succeeded by the other, thus present- ing in some degree an analogy of what is observed in ordinary cases of insanity, so far as the reciprocating action of the two organs is concerned, but differing in tlie period of duration of their function ; and thus, if one of them should have undergone deterioration, or have suffered lesion, so that it has been reduced to what might be termed an infantile state, the impressions formerly stored up in it having been for the most part lost, or there being an incapacity in it to make use of them, the patient will alternately exhibit what has been aptly termed child life and mature life. For a few days, or perhaps weeks, he will conduct himself in the ordi- nary manner of an adult, reading, reasoning, and acting, and then, for a similar period, will pass into a condition in which he does not even know his letters, and reasons and acts like a child. These phenomena of al- ternate and double intellection are interesting in the highest degree, and seem to be explicable on no other principle than that which this author suggests. But I do not think that the explanation which he offers of the senti- ment of pre-existence is correct. By this term is under- Sentiment of stood that strange impression, which all persons have occa- pie-existence, sionally observed in the course of their lives, that some incident or scene at the moment occurring to them, it may be of quite a trivial nature, has been witnessed by them once before, and is in an instant recognized. Though this opinion that we have seen a present incident once before sometimes occurs in cases where the circumstances are of profound in- terest to us, the experience of most persons assures us that it is more fre- quently in trivial events. Dr. Wigan's view is, that it arises from the almost contemporaneous action of the two hemispheres, and that, under the circumstances, we have a confusion of memory, and are led to be- lieve that there has been an interval of indefinite duration, when, in point of fact, it was an impression in each hemisphere closely coincident in point of time. This explanation turns on the assumption that this sentiment of pre-existence occurs but once. He denies that we ever suppose that we have seen the thing twice before. But I believe that the experience of many individuals assures them that this is not the case, and that they are under a firm persuasion that they have witnessed the same incidents more than once before, nay, perhaps even many times. The instance which this author furnishes as occurring to himself, in which, on the occasion of attending the funeral of an exalted personage, and at the time of the coffin being deposited in the vault, with the strik- ing solemnities of the occasion there rushed upon his mind the idea that he had been present at this same scene once before, a thing which was, 332 LOSS OF PERCEPTION OF TIME. of course, an impossibility, is very instructive. But the difficulty in the way of his liypothesis lies in the fact that it offers us no explanation of those cases in which we are perfectly persuaded that we have witnessed the thing more than once before, though it may answer in the particular L - f true iiistance here cited. Perhaps we may appropriately recall the perception of well-known fact offered to us in dreaming, and to which at- *"^^' tention hereafter will be more particularly directed, that there are circumstances under which our mental operations are carried forward mth the most marvelous speed. Thus a sudden sound, which awakes us, or even a flash of lightning, which is over in a moment, may be in- corporated or expanded into a long dream, diversified with a various multitude of incidents, all appearing to follow one another in an appro- priate order, and occupying, as we judge, quite a long time, yet all nec- essarily arising in an instantaneous manner, for we awake at the moment of the disturbance. Of the same kind is that remarkable deception, which is authentically related by those who have recovered fi-om death by drowning, that in the last moment of their agony all the various events of their past life, even those of a trivial kind, have come rushing before them with miraculous clearness. ]\Iental operations, therefore, both as regards old recollections and new suggestions, may take effect with wonderful rapidity, and if the sentiment of pre-existence is to be explained on the principle of the double action of the brain, it must like- wise be dependent upon the fact here presented. THE CRANIAL NERVES. 333 CHAPTEE XVII. OF THE CRANIAL NERVES AND THE GREAT SYMPATHETIC. Enumeration of the Cranial Nerves. — The Third Pair, or Oculo-motor. — Tlie Fourth Pair, or Pa- thetici. — The Fifth Pair, or Trigemini. — Tlie Sixth Pair, or Abducentes. — Illustrations of the Third, Fourth, Fifth, and Sixth Pairs. — The Seventh Pair, or Facial. — Illustration of the Facial. — The Ninth Pair, or Glosso-pharyngeal. — Illustration of the Glosso-pharyngeal. — The Tenth Pair, or Pneumogastric. — Illustration of the Pneumogastric. — Illustration of the Laryn- geals. — The Eleventh Pair, or Spinal Accessory. — The Twelfth Pair, or Hypoglossal. — Il- lustration of the Hypoglossal. The Phrenic Nei-ve. Of the Great Sympathetic System. — Position, Structure, and Origin of the Sympathetic. — Its Re- lation icith the Pneumogastric. — Its Connection with the Spinal System. — Its Plexuses. — Its Ganglia. — They are Reservoirs of Force. — Summary of the Functions of the Sympathetic. — Illustration of the Sympathetic. — Tlie Abdominal Plexuses. — The Solar Plexus. — The Mesen- teric Plexuses. There are twelve pairs of cranial nerves ? 1st. The olfactory; 2cl. The optic ; 3cl. The oculo-motor ; 4th. The pathetic ; 5th. The tri- i^^ cranial facial ; 6th. The abducent ; 7th. The facial ; 8th. The audito- nerves. rj; 9th. The glosso-pharjngeal ; 10th. The pneumogastric; 11th. The spinal accessory ; 12th. The hypoglossal. Of these, the first, the second, and the eighth, being nerves of special sensation, may be more conveniently studied in connection with the or- gans of special sense — the nose, the eye, the ear. OF THE THIRD PAIE, OR OCULO-3IOTOR NERVES. The motor-oculi nerve arises from the inner side of the crus cerebri, near to the pons varolii, some of its fibres passing into the The third pair, gray substance of the crus. Advancing forward, it divides or oculo-motor. into two branches, one of which supplies the superior rectus and levator palpebra3, the other the internal rectus, inferior rectus, and inferior ob- lique. Considering the place of origin, it would be expected that this nerve is wholly motor, and this is confirmed by experiment. When the nerve is irritated the muscles which it supplies are convulsed, and when it is divided they are paralyzed. Through its connection with the len- ticular ganglion, it furnishes motor filaments to the iris. The optic nerve, the corpora quadrigemina, and this nerve togcllicr constitute a complete nervous arc, and impressions made on the retina occasion mo- tions in the iris. 334 THE FOURTH, FIFTH, AND SIXTH PAXES. OP THE FOURTH PAIK, PATHETIC!, OR TROCHLEAR NERVES. This nerve arises from the valve of Yieussens, near the testis, and, The fourth pair, passing arouncl the eras cerebri, enters the orbit, and is dis- orpathetici. tributed to the orbital surface of the superior oblique, or trochlear muscle, for which it is the motor nerve. When it is irritated that muscle is convulsed. OF THE FIFTH PALE, TRIFACIAL, OR TRIGEMEa. The fifth nerve has a construction so closely analogous to that of the The fifth pair Spinal nerves, that it has been designated the spinal nerve of or trigemini. ^]^q Jiead. It ariscs by two roots, the anterior of which is the smaller, the posterior having a large ganglion, the ganglion of Gas- ser ; with this ganglion the anterior root is in contact, but not in con- nection : it passes forward to the inferior maxillary nerve. From the gano-lion three branches diverge, the ophthalmic, the superior maxillary, and inferior maxillary, the first proceeding from the upper angle of the ganglion, the second from the middle, the third from the inferior angle. This last receives the motor portion of the nerve ; the first and second branches are sensory, the third is sensory and motor also. From the sensory portions the anterior and most of the antero-lateral portions of the head are furnished, as also the organs of special sense themselves, so far as their common sensation is concerned. The motor branch supplies the muscles of mastication. Fig. 161. OF THE SIXTH PATE, OR ABDUCENTES. This nerve arises by several filaments from the upper part of the cor- The sixth pair, pus pyramidale, near to the pons varolii, and is distributed or abducentes. ^q ^|-^q external rectus. From its origin, distribution, and from experiments made upon it, it is known to be a motor nerve. ILLrSTRATIONS OF THE THEBD, FOtTBTH, FIFTH, AJSTD SIXTH PAIRS OF ^TERTES. J^ig. 161: 1, chiasm of optic nerves; 2, third pair ; 3, nasal neiwe ; 4, external oculo- motor ; 5, ganglion of Gasser; 6, nasal nerve and its two branches, internal and external ; 7, nerve of obliquus inferior ; 8, ophthalmic ganglion ; 9, ciliaiy nerves ; a, portion of le- vator palpebrae superioris and rectus superi- or ; b, rectus internus ; c, rectus extern us ; d, fibrous ring of the recti muscles. NERVES IN THE ORBITAL CAVITT. I^ig. 162 : 1, 1, optic nerve and globe of the Xerves of the orbit THE FIFTH NERVE. 335 Fig. 162. Nerves in the orbital cavity. eye; 2, third nerve; 3, superior branch; 4, nerve of obliquus inferior; 5, external oculo-motor ; 6, ganghon of Gasser ; 7, ophthahnic branch ; 8, nasal nerve ; 9, ophthalmic ganglion; 10, short root of oplithalmic ganglion ; 11, ciliary nerves ; 12, frontal nerve; «, levator palpebras superioris and rectus superior ; b, rectus inferior ; c, obliquus inferior ; d, rectus externus ; e, ring of the recti muscles. DIAGRAM OF THE FIFTH NEKVE. ^^- ^^^- Fig. 163 : 1, ganglion of Gasser ; 2, ophthalmic ganglion ; 3, its long root furnished by the nasal branch ; 4, short root ; 5, sympathetic, from the plexus surrounding the inter- nal carotid ; 6, ciliary nerves trav- ersing the sclerotic ; 7, ciliary gan- glion ; 8, ganglion of Meckel ; 9, its sensory roots from the superior maxillary ; 10, petrous branch of vidian nerve, or motor roo.t of the ganglion of Meckel; 11, its sym- pathetic root ; 12, naso- palatine ganglion, receiving at its upper an- gle the naso-palatine nerve, and at its inferior the anterior palatine ; 13, otic ganglion ; 14, small superficial petrosal ; 15, submaxillary ganglion ; 16, subungual ganglion ; 17, geniculated ganglion; 18, cavernous ganglion. Diagram ot the fifth nerve. GANGLION OF GASSBK AND ADJACENT PARTS. Fig. 1C4. Fig. 164 : 1, ganglion of Gas- ser ; 2, ophthalmic nerve ; 3, front- al branch ; 4, lachrymal ; 5, nasal ; 6, opthalmic ganglion; 7, superior maxillary nerve ; 8, orbital branch ; 9, ganglion of Meckel ; 10, petrosal branch of vidian nerve ; 11, palatine nerves ; 12, anastomosis of the gan- glion of Meckel with the nervous plexus surrounding the internal max- illary artery; 13, posterior and su- pei-ior dental nerves ; 14, suborbital nerve, its anastomoses with facial Ganglion of Gasser. 336 THE FIFTH NERVE. and nasal; 15, inferior maxillary, receiving the motor portion of the fifth pair; 16, superficial auriculo-temporal nerve ; 17, buccal nerve ; 18, sec- tion of other collateral branches of inferior maxillary ; 19, inferior den- tal; 20, mental nerve; 21, lingual; 22, chorda tympani ; 23, facial nerve ; A, external carotid artery ; B, facial artery ; C, temporal artery ; D, internal maxillary ; E, its dental branch ; F, middle meningeal ; «, membrana tympani ; b, glenoid cavity ; c, orbicularis oris ; d, buccina- tor ; e, pterygoideus internus ; f, pterygoideus externus ; g, digastric ; h, sterno-cleido-mastoid muscle. THE FIFTH NERVE, THE GANGLION OF GASSER BEING REMOVED. Firj. 165. Fig. 165 : 1, ophthalmic, cut ; 2, superior maxillary, cut at both ex- tremities ; 3, ganglion of Meckel ; 4, petrosal and carotid branch of vidian nerve ; 5, abducent ; 6, nerve of Ja- cobson ; 7, superior and posterior dental nerves ; 8, anterior and supe- rior dental nerve ; 9, otic ganglion ; 10, gustatory nerve ; 11, chorda tym- pani ; 12, submaxillary ganglion ; 13, anastomosis of lingual with hy- 15, terminal branches of gustatory or lingual nerve ; 16, inferior dental ; 17, mylo-hyoid branch ; 18, mental ; 19, incisive nerve ; 20, ganglion of glosso-pharyngeal ; 21, facial, in the aqueduct of Fallopius ; 22, hypoglossal ; a, superior maxillary bone ; b, cartilages of the nose ; c, internal wall of tympanic cavity ; d, ptery- goideus internus muscle ; e, buccinator, cut ; f, mylo-hyoid muscle ; g, part of anterior belly of digastric ; h, sterno-cleido-mastoid, turned aside. The fifth nerve. poglossal ; 14, sublingual plexus Fig. 166 ILLUSTEATION OP THE TERMINAL BRANCHES OF THE INFERIOR MAXILLARY NERVE. Fig. 166 : 1, motor and sensory roots of ganglion of Gasser ; 2, junction of mo- tor root with inferior maxillary; 3, auricu- lo-temporal nerve ; 5, buccal nerve ; 6, pterygoid nerves ; 7, cut branches of tem- poral and masseteric nerves ; 8, gustatory nerve; 9, chorda tympani; 10, facial; 11, anastomosis of gustatory and inferior den- tal nerves ; 12, tonsillar branch ; 13, sub- The inferior maxillary. maxillary gaugliou ; 14, Sublingual plex- us; 15, anastomosis of gustatory and hypoglossal nerves; 16, branches THE FACIAL NERVE. 337 of gustatory; 17, inferior dental; 18, mylo-liyoid nerve; 19, incisive branch of dental nerve ; 20, branch of mental, cut ; «, pterygoideus in- ternus ; b, part of pterygoideus externus muscle ; c, mylo-hyoid muscle ; d, portion of anterior belly of the digastric ; 6, hypoglossal muscle ; f, portion of submaxillary gland. OF THE SEVENTH PAIR, THE FACIAL NERVE. This nerve arises from the upper part of the groove between the oli- vary and restiform bodies, and near the pons varolii. With tj^^ seventh the auditory nerve, or portio mollis, it constitutes the seventh P'^ii". or f'^ciai. nerve in the nomenclature of Willis, and derives the name portio dura, under which it sometimes passes, from the density and closeness of its texture. It supplies all the muscles of the face except those of mastica- tion, which are supplied by the fifth nerve, those of the palate, the sta- pedius, laxator tympani, and tensor tympani ; also the muscles of the ex- ternal ear, and some of those of the tongue. The facial is a centrifugal nerve. If irritated near its origin, there is no sensation of pain ; but sub- sequently it obtains fibres from other sources, as from the fifth and the pneumogastric. After it has been joined by these, irritation is acutely felt. It is therefore to be regarded as the general motor nerve of the face, influencing the function of respiration through reflex action, but not being connected with the function of mastication. Injury of it produces paralysis of the parts to which it is distributed, as, for example, the orbic- ularis palpebrarum, causing inflammation of the eye and opacity of the cornea, through inability of that organ to free itself from dust and spread the lachrymal secretion over its surface. In like manner, the sense of hearing may be injured througli loss of control over the muscular struc- tures of the ear, and the acuteness of the sense of smell diminished from Fig. 16T. inability to introduce the air in a strong current, or the sense of taste, if the point of injury be previous to the giving off of the chorda tympani. In paralysis of the facial nerve the muscles of the face become powerless, and the countenance, therefore, dis- torted. ILLUSTRATION OF THE FACIAL NEKVE. Fig. 167 : 1, trunk of the facial at its emergence from the aqueduct of Fallopius ; 2, occipito- auricular branch ; 3, auricular of the cervical plexus ; 4, twig of the occipital mus- Y ~m The facial neiTe. 338 THE GLOSSO-PHARYNGEAL NERVE. cle ; 5, twig of the posterior auricular muscle ; 6, twig of the superior auricular ; 7, anastomosis of the facial with the auricular of the cervical plexus ; 8, branch for the stylo-hyoid and posterior belly of the digastric ; 9, temporo-facial anastomosis with the superficial auriculo-temporal of the fifth pair ; 10, temporal ramifications of the facial ; 11, frontal twigs ; 12, superior palpebral twigs ; 13, middle palpebral twigs ; 14, inferior or motor palpebral twigs ; 15, suborbital twigs ; 16, suborbital plexus ; 17, superior buccal; 18, cervico-facial branch; 19, buccal branches, anas- tomosing with, 20, buccal nerve of fifth pair ; 21, mental twigs, forming with, 22, mental nerve of fifth pair, the mental plexus ; 23, cervical branches ; 24, transverse cervical branch of cervical plexus ; 25, parotid branches of the superficial auriculo-temporal ; 26, parotid branches of the facial ; a, frontal muscle ; 5, occipital muscle ; c, anterior auricular ; d, superior auricular ; e, posterior auricular; f^ orbicularis palpebrarum; g, zjgomaticus major ; A, buccinator ; i, orbicularis oris ; A;, masseter ; I, parotid gland ; r/i, platysma ; n, stylo-hjoid and posterior belly of di- gastric ; c, stemo-cleido-mastoid ; __p, trapezius. OF THE NINTH PATE, OE GLOSSO-PHAETKGEAL. This nerve arises by five or six filaments from the groove between .J. the olivary and restiform bodies. Its origin may be traced or giosso-pha- to the vesicular substance in the floor of the fourth ventricle : '^^^^ ■ passing forward, it is distributed to the mucous membrane of the base of the tongue and fauces. While in the jugular fossa it forms two ganglia, a small one produced by its posterior fibres, and call- ed the superior ganglion ; a second, much larger, termed the inferior, or o-anglion of Andersch. The branches given oft" by the glosso-pharyngeal are the muscular, the tympanic or Jacobson's nerve, which is distributed to the inner wall of the tympanum and interior portions of the ear ; the pharyngeal, which supphes the pharynx, and, with branches of the pneu- mogastric and s}Tnpathetic, foinns the pharyngeal plexus ; the lingual supplies the mucous membrane of the sides and base of the tongue : the tonsillitic, which supplies the mucous membrane of the fauces and soft palate, and forms a plexus round the base of the tonsil. Besides these, the glosso-pharjmgeal anastomoses with the facial, pneumogastric, accessory, and sympathetic. Examined in the usual way, the glosso-pharyngeal proves to be a cen- tripetal nerve, ha\dng the power of producing reflex motions through the nerves of deglutition, its motor influence being chiefly due to its con- nections with the pneumogastric and accessory. Though thus a sen- sory nerve, it is doubtful whether it be the only nerve of taste, or whether that function is not likewise participated in by the hngual branch of the fifth pair. It is certain that section of the lingual does not destroy the THE GLOSSO-PHARYNGEAL NERVE. 339 sense of taste, and also that those parts of the tongue to which the glosso-pharyngeal is distributed present that sense in the most marked manner. The inference which is usually drawn is that this nerve and the lingual are both tactile and gustative, and this renders appropriate its description in this place rather than among the nerves of special sense. ILLUSTRATION OF THE GLOSSO-PHARYNGEAL. The glosso-pharyngeal. Fig. 168 : 1, origin of the glosso-pharyngeal between, 2, the pneumogastric, and, 3, the facial ; 4, ganglion of Andersch ; 5, pharyngeal branches ; 6, anastomosis of the glosso-pharyngeal with the lingual branch of the facial ; 7, application of the spinal to the superior ganglion of the pneumo- gastric ; 8, branch of jugular fossa ; 9, plexiform ganglion of par vagum ; 10, carotid branch ; 11, superior laryngeal nerve ; 12, external laryngeal; 13, inferior or recurrent laryngeal; 14, cervical branch of the spinal ; 15, bulbar branch of same nerve ; the union of these forms a trunk which divides into two branches ; 16, external branch ; 17, internal branch ; 18, cervical portion of sym- pathetic ; 19, hypoglossal, cut. DIAGRA3I OF GLOSSO-PHAETNGEAL. Fig. 169. Fig.X^'d'. 1, facial; 2, glosso-pharyngeal; 3, pneumo- gastric ; 4, spinal ; 5, hypoglossal ; . 6, superior cervical ganglion ; 7, 7, anterior branches of the two first cervical pairs; 8, plexus enveloping the internal carotid artery; 9, Jacobson's nerve ; 10, its anastomotic branch with the carotid plexus ; 11, small deep petrosal, which passes into the great superficial petrosal; 13, otic ganglion ; 14, anas- tomosis of glosso-pharyngeal with lingual branch of the facial; 15, anastomosis of glosso-pharyngeal and pneumo- gastric ; 16, anastomosis of the pharyngeal of the glosso- pharyngeal with that of the pneumogastric and of the spinal ; 17, auricular twig of Arnold ; 18, application of the trunk of the spinal to the superior ganglion of the pneumogastric ; 19, anastomosis of internal branch of the spinal with the ganglion of the trunk of the par vagum ; 20, anastomosis of pneumogastric and hypoglossal ; 21, anastomosis of hypoglossal with the loop formed by first and second cervical ; 22, 22, anastomosis of the two first pairs with the cervical ganglion ; 23, pharyngeal plexus ; 24, laryngeal plexus ; 25, anastomosis of the external branch of the spmal with the anterior branch of the third cervical pair. Diagram of anasto- moses. 340 THE PNEUMOGASTRIC NERVE. OF THE TENTH PAIR, THE PAU VAGXJIH, OR PNEUMOGASTRIC NERVE. The pneumogastric nerve arises hj six or eight filaments from the groove "between the olivary and restiform bodies below the glosso-pha- ryngeal, and, like it, may be traced to the vesicular material of the floor , . of the fourth ventricle. It first presents a small ganglion, The tenth pair, , • i • i i n i i or pneumogas- and soon after a second, nearly an inch m length, called the ^"^- plexus gangliformis. The nerve then descends the neck in the sheath of the carotid vessels, and in its course differs on the right and left sides respectively. On the right side it passes between the sub- clavian artery and vein, descending toward the stomach and solar plexus on the posterior portion of the oesophagus ; on the left it enters the chest nearly parallel with the left subclavian, and passes to the stomach and solar plexus along the anterior portion of the oesophagus. The chief branches of the pneumogastric are the auricular, the pharyn- geal, the superior laryngeal, the cardiac, the inferior laryngeal or recur- rent, the anterior pulmonary, the posterior pulmonary, the oesophageal, and the gastric. The pneumogastric presents several plexuses in its course, and, even when distributed on the stomach, exhibits flat, membraniform ganglia. It supplies three great classes of organs: 1st. The digestive, as the pha- rynx, oesophagus, stomach, liver; 2d. Respiratory, as the larynx, trachea, lungs ; 3d. Circulatory, as the heart and great vessels. It associates it- self intimately with the sympathetic, and aids it in forming several great plexuses. At its root the pneumogastric is sensory, but in its trunk it possesses a double function, arising from its intermingling with other nerves, as the spinal accessory and sympathetic. Though the trunk, if irritated, gives rise to pain, we are not, under ordinary circumstances, conscious of indi- cations, as, for example, in the act of breathing, in which we do not per- ceive the necessity of respiration, except the access of the air be too long delayed. The pharyngeal branch is the chief motor nerve of the pharynx and palate. The superior laryngeal is the sensory nerve of the larynx, the inferior laryngeal being the motor. Considered along with the spi- nal accessory, the pneumogastric presents an analogy to a spinal nerve ; the accessory constituting the anterior or motor root, and the pneumo- gastric, with its ganglion, the sensory root. The pneumogastric nerve was formerly regarded as taking an influen- tial part in the action of the stomach during digestion. The precise na- ture of its agency in this respect has been already alluded to. In addi- tion, it may be remarked that probably through this nerve is the sensa- tion of hunger conveyed to the mind. THE PNEUMOGASTRIC NERVE. 341 Fitj. 170. «j*«iw ILLUSTRATION OF THE LEFT PNEUMOGASTRIC NERVE. Fig. 170 : 1, 1, 1, the pneumogastric nerve ; 2, anastomosis of it with the hypoglossal ; 3, anastomosis of plexiform ganglion with internal branch of the spinal ; 4, pharyngeal, passing in front of the internal car- otid artery ; 5, superior laryngeal, behind the internal carotid artery ; 6, external laryngeal ; 7, laryngeal plexus, formed by external laryngeal and great sympathetic ; 8, superior cardiac ; 9, middle cardiac ; 10, 10, inferior laryngeal, or recurrent, forming a curve round the arch of the aorta ; 11, pulmonary gan- glion ; 12, its anastomosis with the great sympathetic ; 13, pos- terior pulmonary plexus ; 14, oesophageal plexus; 15, curves formed around the oesophagus by the right and left pneumo- gastrics ; 16, oesophageal strand traversing the diaphragm ; 17, plexus formed by the strand upon the anterior face of the car- diac end ; 18, branches for the great end of the stomach ; 19, o branches for the small curva- ture ; 20, branches for the ante- rior face of the stomach ; 21, hepatic branches commingling with the hepatic plexus of the great sympathetic, and ramify- ing in the substance of the liver; 22, glosso- pharyngeal, 23, its lingual branch , 24, pharyngeal branch ; 25, branch for the sty- lo-pharyngeal muscle; 26, spi- nal ; 27, internal branch, aiding to form the pharyngeal nerve ; _^^ - 28, external branch; 29, twig The left pneumogastric nerve. of external branch anastomos- ing with the third cervical ; 30, anastomosis with trapezian branch of the fourth cervical ; 31, cervical portion of great sympathetic ; 32, 32, thoracic portion ; a, thyroid body ; b, trachea ; c, left lung, drawn to the right ; d, liver, raised ; e, oesophagus ; /, great end of the stomach, drawn to the left ; g, arch of the aorta ; . the carotid, and subclavian ar- teries, cut. 342 THE SPINAL ACCESSORY NERVE. F!rt. ITI. ILLUSTRATION OF PULMONARY GANGLIA. Fig. 171 : 1, 1, pulmonary ganglia ; 2, median anas- tomoses of these ganglia at the posterior face of the trachea, and origin of the bronchi ; 3, left laryngeal nerve, aiding to form the bronchial plexus ; 4, anas- tomoses of the two pneumogastrics on the posterior face of the oesophagus. ILLUSTRATION OF INFERIOR LARTNGEALS, ANTERIOR PULMONARY, AND CARDIAC PLEXUS. Fig. 172, 1, 1, pneumogastric ; 2, 2, superior laryngeal; 3, 3, exter- nal laryngeal ; 4, superior car- diac nerve; 5, 5, middle cardiac nerves ; 6, inferior cardiacs ; 7, cardiac ganglion and plexus ; 8, 8, nerves from this plexus surround- ing the coronary plexus ; 9, 9, an- terior pulmonary plexus ; 10, 10, inferior laryngeal: the left em- bracing the arch of the aorta, the right the subclavian artery, both go to the posterior face of the larynx ; 11, tracheal branches ; A, pulmonary artery ; B, its left branch ; C, its right branch ; D, arch of the aorta ; E, fibrous cord The inferior laryngeais. arising from obliteration of the ductus arteriosus ; F, left subclavian ; G, G, left primitive carotid ; H, brachio-cephalic trunk, cut to show cardiac nerves ; I, vena cava supe- rior ; K, left coronary artery and vein ; L, right coronary artery and vein ; a, os hyoides ; b, projecting portion of the larynx ; c, trachea ; d, thyro-hyoid muscle ; e, e, crico-thyroid ; /, /, scalenus anticus ; g, g, thyroid body ; A, h, diaphragm ; i, i, pericardium, cut away. OF THE ELEVENTH PAIR, OR SPINAL ACCESSORY NERVE. The spinal accessory arises by several filaments from the side of the The eleventh spinal cord, as low as the fifth or sixth cervical nerve. In pair, or spinal its upward coursc it communicates with the posterior roots accessory. ^^ ^j^^ ^^^^ cervical. It then divides into two branches, the smaller joining the pneumogastric, the main trunk passing onward, and being eventually distributed to the trapezius muscle, and also furnishing supplies to the sterno-mastoid. The spinal accessory is a motor nerve, as appears from the usual evi- THE HYPOGLOSSAL AND PHRENIC NERVES. 343 dence of irritation, and also from its origin and distribution. Its action is not essential in ordinary or involuntary respiration. In voluntary res- piration it is brought into play. OF THE TWELFTH PAIR, OR HYPOGLOSSAL NERVE. This nerve arises in the groove between the pyramidal and olivary bodies, by 8 or 10 filaments, which are collected into two -pj^^ twelfth bundles. It next passes forward and crosses inward, pur- pair, or hypo- sues a course which is concave upward, and supplies the ^ °^^^ ' genio-hyoglossus and muscles of the tong-ue generally, giving off the following branches in its course : the descendens noni, the tliyro-hyoid, and hlaments connecting the gustative nerve. It also anastomoses with the pneumogastric, spinal accessory, first and second cer\T.cal nerves, and sjTnpathetic. The hypoglossal is the motor nerve of the tongue, irritation of it giv- ing rise to movements throughout that organ, the lingual branch of the fifth being the sensory. The hypoglossal causes the muscles of the neck to aid in the movements necessary for articulate speech. ILLUSTRATION OF THE HYPOGLOSSAL NERVE. J^ig.nS: 1, medulla oblongata ; 2, glosso-pharyngeal ; 3, pneumo- gastric ; 4, superior laryngeal ; 5, spi- nal ; 6, first cervical pair ; 7, second pair ; 8, third pair ; 9, fourth pair ; 10, lingual ; 11, origin of hypoglos- sal ; 12, anastomosis of hypoglossal with first cervical; 13, anastomosis with nervous loop of two first cervi- cals ; 14, descending branch of hy- poglossal, anastomosing with, 15, de- scending branches of cervical plexus ; 16, twig of thyro-hyoid muscle ; 17, The hypoglossal nerve. branclics of hyoglossus ; 18, recur- rent branch of stylo-glossus ; 19, branches of genio-hyoid ; 20, plexiform branches of hypoglossal ; 21, anastomotic branch with the lingual ; 22, branch for submaxillary ganglion ; A, vertebral artery ; B, external car- otid ; C, lingual ; D, temporal ; E, internal maxillary ; a, portion of the condyle of the occipital bone ; b, median section of atlas ; c, styloid pro- cess ; d, stylo-glossus ; e, stylo-pharyngeus ; /, hyoglossus ; g, genio- glossus ; h, pterygoideus externus ; i, pterygoideus intemus. OF THE PHRENIC NERVE. Although the phrenic, or internal respirator)^ nerve is not strictly in- 344 THE GEEAT SYMPATHETIC. The phrenic cluded in the group now under consideration, yet, considering nerve. j^s important connection with the motions of respiration, it is proper to describe and illustrate it here. It arises from the third and fourth cervical nerves, aided by a branch from the fifth, or from the brachial plexus, and from the sympathetic. In its descent it communicates with the lower cervical ganglion, enters the thorax between the subclavian vein and artery, and, passing along the side of the pericardium, descends to the diaphragm, the right phrenic being perpendicular, and the left running obliquely round the apex of the heart. It is distributed, for the most part, to both faces of the diaphragm, superior and inferior. It is the motor nerve of the diaphragm. The phrenic nerve. ILLUSTKATIOK OF THE PHRENIC NERVE. Fig. 174: 1, 1, root of the phrenic nerve, furnished by the fourth cervi- cal ; 2, 2, roots from the brachial plexus ; anastomosis of this nerve with branch of the subclavian ; 4, anastomosis with the inferior cer- vical ganglion ; 5, 5, curve of the hypoglossal, cut, sending a twig to the phrenic nerve ; 6, 6, pericardiac branches of the phrenic nerve ; 7, 7, branches to the superior face of the diaphragm ; 8, 8, branches to the inferior face of the diaphragm ; 9, anastomoses of these branches with, 10, the solar plexus ; 11, transverse communication of the phrenic nerves. OF THE GREAT SYMPATHETIC NERVE. Under the designations of sympathetic, visceral, trisplanchnic, gangli- Position and *^^^^' intcrcostal, or nerve of organic life, passes a series of structure of the reddish or gray ganglia, interconnected by nervous strands, sympathetic, extending along each side of the vertebral column, from the head to the coccyx, communicating with all other nerves of the body, and distributing branches to the internal viscera, or organs of involunta- ry function. These ganglia are less numerous than the vertebra ; the chain on each side communicates with its colleague through plexuses, and the ganglion impar is the common uniting point on the coccyx be- low. By some it is supposed that the ganglion of Ribes, and by others that the pituitary body has the same function in the cranium above. CONNECTION OF SYMPATHETIC AND SPINAL. 345 What are here spoken of as nervous strandg arc perhaps more correctly prolongations of the ganglia themselves. The origin of the sympathetic has been long a subject of dispute, some supposing that it is a special system, of which the ganglia are orii insect an alternate pressure and relaxation upon the tracheal tubes. The air, thus passing in and out, throws into vibration the valves of the spiracle, which, as seen in J^ig. 180, are sus- pended upon a dozen or more flexible supports ; but their free edges, ap- proaching within a certain distance of each other, are thrown into quick vi- bration by the passing current, in the same manner as is the vibrating spring of the accordeon. These- vibrating plates of insects are the rudiments of what will become the perfect vocal ap- paratus in man. Again, in others, the swiftlj-recurring beating of the wings produces a sound, as, for example, in the musquito. Among ver- tebrated animals, those which breathe the air are vocal, nearly all fishes Sounds of rep- being mute. From iishes, as we pass upward, the sound tiles and birds. ^^^ ^]^g instrument which makes it increase together in com- plexity. Through a simple chink, the air expelled from the respiratory sacs of snakes, by the contraction of their abdominal muscles, issues forth as a mere hiss, the sound being increased in the frog by the devel- opment of resonant cavities. From these simple noises we are conduct- ed to the musical notes of birds, some of which are of exquisite purity and sweetness. In these, the vocal glottis is situated at the bifurcation of the trachea, another glottis being above for the tinal es- cape of the air. These vertebrated animals first introduce us to the mechanism for articulate speech, the raven and parrot being able to pronounce words with distinctness. The articulation is effected, as in man, by the motions o'f the tongue and other portions of the mouth. For the further consideration of this subject, it is necessary to under- ^. . . , stand that there is a distinction between song and speech. Distmction be- ^ . , , . ^^ , tween song and Song is produced by the glottis, speech by the moutli; or, speech. perhaps, a more correct statement would be, that the larynx is the organ of song, the mouth of that form of speech wliich we call whispering, and for which nothing is required but a stream of air issmng from the fauces, the tongue and other organs giving it articulation ; but for audible speech, a noise is created in the larynx, and modified by ar- ticulation in the mouth. The double larynx of birds is replaced by a single larynx in man, which serves at the same time for the entrance and exit of air, and like- wise for vocalization. Those birds in which the lower larynx is absent are voiceless. A general idea of the construction of the organ of voice Talking birds. ACTION OF THE VOCAL CORDS. 353 in man may be gathered by supposing it to be composed of three por- tions, the trachea, the larynx, and the mouth. The trachea Description of is the tube by which air is brought from the lungs and de- the larynx. livercd into the larynx, which is a superposed structure, arranged upon the cricoid cartilage, on which is articulated the thyroid cartilage by its lower horns, around which a certain degree of rotation can be accomplish- ed, so that the front of the thyroid may be elevated or depressed with a kind of bowing motion. Posteriorly, on the cricoid cartilage are placed the arytenoid cartilages, which can be approached or separated from each other, and from their summits pass to the front of the thyroid cartilage the inferior laryngeal ligaments or vocal cords. These constitute the essential' organ of sound. The thyroid cartilage, by its motions, can de- termine the strain put upon them, and the arytenoids can either bring them into parallelism, or place them at an acute angle. The chink or fis- sure between them is the rima glottidis : its figure and width vary with the recession or approximation of the vocal cords, which, as the air passes by them, are thrown into vibration in the same manner as the reed in mu- sical instruments. The epiglottis cartilage, which is above, guards the passage, and may also be supposed, by its descent, to deaden the sounds. The slowness or rapidity of the vibration is dependent on the stretch of the vocal cords. The manner in which various degrees Keguiation of of tension can be given to the cords is readily understood by thevocai cords, considering their attachments. In front, as We have said, they are fast- ened to the thyroid cartilage, posteriorly to the arytenoids. When the thyroid cartilage executes a bowing motion forward, the vocal cords are put upon the stretch, and similar variations of their tension and also of their position can be given by the movements of the arytenoid cartilages behind. When the air is moving in and out without giving rise to any sound, the chink of the glottis is angular, its point being forward, and from that the cords diverge posteriorly. For the production of sound, the cords must be brought parallel, or even inclining toward each other. If they incline away from each other, no sound will be produced. The pitch of the note will be determined by the stretch of the cords, and this, in its turn, will be determined by the contraction of the vocal muscles. The crico-thyroid and sterno-thyroid bow the front of the thyroid cartil- age down, the thyro-arytenoid and thyro-hyoid carry it back ; the for- mer therefore stretch the cords, and the latter relax them. The opening of the glottis is likewise determined by other muscles, the posterior cri- eo-arytenoid dilating it, and the lateral crico-arytenoid and the transverse arytenoid closing it. Fig. 181, p. 354, is the larynx, seen in profile : a, a, half of the hyoid bone; ^, thyroid cartilage, cut; c, thyro-hyoid membrane; 6?, cricoid cartilage ; 6, trachea ; y, oesophagus ; g^ epiglottis ; A, great horn of the Z 354 ACTION OF THE VOCAL ORGANS. Fi i of vision. scnted by comparative anatomy. It is just as difficult to take a complicated organ, such as the eye of man, and from the study of it to deduce the significance of its various parts, as it would be tq take a complicated human contrivance and determine from it the properties of its mechanical elements. It is scarcely from the watch or other delicate machine that we should expect to make plain the properties of the lever or the wheel, and experience shows that it is only by the attentive study of the cases presented by comparative physiology — those experiments made for us by nature, as CuviEE has called them — that we can hope to advance to the perfect solution of this problem. Treating the subject, therefore, in this way, we observe that, in the an- imal series, long; before any thing like a distinct organ of vis- Confused per- . -, T -, 1 . • rTi 1 ception of lou Can be detected, there is yet a perception ol hght and warmth. dai'kncss. The hydra, a fr-esh-water polype, offers an exam- ple, for this animal seeks the sunny side of the vessel in which it is placed, preferring it to the shade. In the absence of every vestige of a visual organ, there can not be a doubt that its movements depend on the perception of warmth, just as when a man who is totally blind passes from the sun into the shade, his feelings at once notify him of the change. In a physiological sense, it is of no interest to us to inquire into the phys- ical nature of this effect, whether light is identical with heat, or whether, when light falls upon a body, it turns into heat. We have only to ac- cept it as a fact capable of abundant experimental proof, that, whenever rays of light fall on a surface, that surface becomes warm. This, as we shall now find, is the key of aU the explanations we have to give. Dr. Franklin made an experiment to the following effect. He placed Dr. Franklin's on the snow, on a sunshiny winter day, pieces of cloth of dif- experiment. ferent colors — black, yellow, white, etc., etc. — in such a posi- tion that the sun's rays fell equally on them. After a certain length of time, on examining them, he found that the black cloth had melted its way deeply into the snow, the yellow to a less depth, and the white scarcely at all. He therefore drew the conclusion that, when they are receiving light, surfaces become warm in proportion to the depth of their tint, and that, of aU surfaces, one having a velvety blackness is most sen- sitive, because it can exert the most powerful absorbent agency. On this principle seem to be constructed the ocelli of the lower tribes. Ocelli of lower Thcsc consist of a collection of pigment granules, usually animals con- Qf ^ red, black, or dark color, seated on the expansion of a Franklin's nervous thread. The principle which is clearly contained in principle. ^]^-g jjiechanism is that of relieving the general surface from OPTICAL PRINCIPLES OF THE EYE. 381 the impression of light, or rather of rendering it more intense by central- izing it upon a special locality. Such a construction involves at once a change in the nervous mechanism, by devoting a particular system of nerve tubules to the new duty. But, notwithstanding this increasing- complexity of structure, the physical principle is still as simple as be- fore. It is indeed almost as though a blind man should paint upon his skin a black space, so that, as in Franklin's experiment, it might be more sensitive to the sun. With this devotion to a new duty the nerv- ous tubules doubtless assume an isolated function, and thus there arise •; a nerve of special sense. The ocelli of the lower animals are sometimes quite numerous. From this a new power is at once derived, the power of determining the position of the source of light, a property which doubt- less becomes more perfectly marked in proportion to the number and symmetry of arrangement of the ocelli. As we ascend the animal series in our examination, we soon find that complexity is being introduced. A membranous hood, arising from a little fold of the external tegument, shadows forth the rudiment of an eyelid, and seems to indicate to us that, even in these low grades, the condition which we shall eventually find so strikingly marked in the high ones already exists, that functional ac- tivity involves destruction, and that the sensory mechanism must have its period of repose. Approaching the more highly-developed conditions of the organ of vision, we may next consider the cases presented by the j^^^. , . eyes of insects and the eyes of higher mammalia. In these converging me- a new physical principle has been introduced, the optical ^^' property of the convex lens, a transparent solid, having one or both of its surfaces curved, and obtaining therefrom the power of forming repre- sentations, or images of objects which may be in front of it, at a certain focal distance behind. Such images are seen when we take a magnify- ing glass or a convex lens, and, holding a piece of paper be- tj, f - ti hind it at a particular point, there will be depicted upon the its variations paper the inverted forms of whatever objects may be in front. '^^ distance. That distance is the focal length of the lens. But we may farther no- tice, and to this observation our attention will be required hereafter, that the focal length is variable. If the object be near, the focal length is greater ; if distant, it is less. The instrument laiown as the camera obscura represents the optical construction of the eye. Upon a receiving surface or screen. The camera placed at the focal distance behind its lens, images are depicted obscura. of whatever objects may chance to be in front ; but — and this is a remark of interest to us now — the visual range, or field of view, is quite limited. In animals, the perfection of whose vision requires that, instead of being restricted in their view to a narrow space, they should be able, as it 382 STRUCTURE OF THE EYE. were, to take in almost a hemisphere at a glance, this extension of the visual function can only be accomplished in one of two different ways. Different co '^^ ^^® ^^^ illustration wc havc been employing, it may be trivances for reached by having innumerable cameree pointing in innumer- larger field of ^^^® directions, and conveying the resulting images to one view by the common surfacc, or by having one, or at most two, cameras set upon a movable stand, which can quickly point them in any direction, and so enable them to inspect successive fields of view with almost instantaneous rapidity. The former plan is resorted to in most insects, the latter in man. In insects, the immobility of the head upon the trunk would interfere with any rapid rotation of the visual or- gan ; in man, the facility with which rotation can take place upon the neck as on an axis, and the movement of the eye in its orbit, accom- plishes the object without any kind of difficulty. In continuing an investigation of the structure of the eye, it is con- venient to consider it under three heads : 1st. Its optical mechanism ; 2d. Its nervous mechanism ; 3d. Its accessory apparatus. 1st. Of the Optical Mechanism of the Eye. The human eye is of a globular fonn, and about one inch in diameter. The human I* is not perfectly spherical, its lateral diameter being shorter ^y^- than its antero-posterior by about one twentieth part. It may be described as consisting of three coats, which, forming a shell, contain transparent media and the optical apparatus. It might also be consid- ered as arising from an expansion of the optic nerve into an almost spherical cavity, and which, being fortified by certain tissues behind, has a dioptric mechanism in front. The coats of the eye are three in number : the sclerotic, the choroid, and the retina. The sclerotic, which is the exterior, is a white fibrous membrane, very tough, and possessing the necessary resistance to give mechanical protection to the parts within. Within this is the choroid, a vascular layer or tunic, presenting on its interior the black pigment which darkens the interior of the eye. The innermost coat is the retina, an ex- pansion of the optic nerve. The sclerotic coat is perforated in front, and into the circular aperture so arising the transparent cornea is let, like a watch-glass. Many anatomists, however, consider that the cornea is absolutely continuous with the sclerotic, and a part of it ; the sclerotic and the choroid are united round the edge of the cornea by the ciliary ligament. The iris is perforated in its centre, the aperture being desig- nated as its pupil. Posterior to the iris is the crystalline lens, the space between the lens and the cornea being filled with the aqueOus humor, in which the iris floats, dividing it into two regions, called, from their posi- tion, the anterior and posterior chambers. All the rest of the globe be- STRUCTURE OF THE EYE. P>83 tween the back of the lens and the retina is tilled with a substance ex- tremely transparent, and known as the vitreous humor. The aqueous humor, the crystalline lens, and the vitreous humor, by reason of their transparency, offer, therefore, no obstacle to the passage of light. ILLUSTKATIONS OF THE EYE. Fig. 196 : «, «, sclerotic, turned over ; h, choroid ; c, c, ciliary nerves traversing sclerotic, and going between it and choroid ; <;?, retina ; e, vit- reous body ; /, crystalline ; g, middle section of iris ; A, middle section of cornea ; ^, anterior chamber ; j, posterior chamber ; k, canal of Fonta- na, between the ciliary circle and iris on one side, and sclerotic and cornea on the other. Fig. 196. FiQ. lOT. Profile view of the eye. Front ^ lew ol the eye. JPtg. 197: <2, transparent cornea ; J, 5, sclerotic ; c, iris ; 6?, pupil; e, ciliary circle ; J", choroid, on which is seen the dichotomous termination of the ciliary nerves ; g, ciliary processes ; h, crystalline. SECTION OF THE EYE, J^ig. 198 : a, upper eyelid ; b, lower eyelid, showing the different lay- Fig. if>8. ers composing them ; c, c, conjunc- tiva, reflected from posterior face of eyelid upon the anterior face of the globe of the eye ; d, d, orbito-oc- ular aponeurosis, prolonged upon, e, the sheath of the optic nerve, and sending sheaths to the muscles ; J^, the superior rectus ; g, the inferior rectus ; A, h, sclerotic, re-enforced behind by sheath of optic nerve, Section of the eye. and in frout by aponeurotic expan- sion of recti muscles ; i, transparent cornea, cut to show its lamellar tex- ture ; j, j, choroid ; k, ciliary circle ; I, ciliary body and processes ; m, iris and pupil ; n, ?i, canal of Fontana ; o, o, retina, continuous with sub- 384 STEUCTURE OF THE EYE. stance of optic nerve ; ^, ciliary circle of Zinn ; §', §", hyaloid mem- brane ; r, capsular artery, lodged in hyaloid canal ; 5, s, vitreous humor and its cells ; t, crystalline and its capsule ; u, u, canal of Petit ; v, an- terior chamber ; x, posterior chamber. To this general description of the conformation of the eye may be add- ed a few remarks on each of its constituent parts. The sclerotic coat consists of white tibrous tissue, which, in addition The sclerotic ^o '^h® ^^e before mentioned, affords the means of insertion of coat. the muscular mechanism for moving the ball. It is thicker behind than in front, its relative thickness differing in difierent animals according to the mechanical circumstances to which they have to be ex- posed. In the whale, which has to resist the pressure of a deep sea, the sclerotic is an inch thick. In some instances cartilage is included in it, in others bone. Besides the aperture in front, into which the cornea is let, there is another behind for the passage of the optic nerve. This method of description, though very convenient, is, however, scarcely cor- rect, if we consider the coats of the eye as arising from expansions of the optic nerve, for then the sclerotic answers to the exterior investiture, and the tubules of the nerve gain access to the interior of the eye without passing through an aperture, properly speaking. The place at which the nerve enters is not in the optical axis, but at a distance of about its own diameter on the interior side. The aperture is smaller on the in- side of the sclerotic than on the outside; thus it presents a conical shape. It is not a single hole, but rather a collection of sieve-like openings, through which the optic tubules pass. The cornea, which is let into the sclerotic in front, is of greater cm-va- ture than the sclerotic. Its front and back faces are parallel. 6 cornea, rpi^^^gj^ j^ Seems to be pellucid as glass, it has a very intri- cate construction, being composed of at least five separate layers ; the innermost one, or cornea proper, consisting, it is said, of more than sixty lamellae. The choroid coat is arranged, like the sclerotic, for the passage of the The choroid: optic ncrvc. The iris is commonly described as a process its arrange- of it. The choroid is a sheet of blood capillaries arranged ment for intro- . , , • i i • i j. ducing and re- m two layers, an arterial and a venous, m sucn a way as to moving blood, gjyg ^hc utmost freedom of access for the arterial blood to the retina within. The veins which remove this blood are placed in curved forms, and are designated vasa vorticosa ; from the choroid also the dark pigment is secreted. Those animals in which it is absent are called albinos. Near to the iris the choroid merges in the ciliary hga- ment, and gives forth the ciliary processes, being covered in front by the ciliary muscle. Mff. 199 : a, a, section of sclerotic ; b, exterior surface of the choroid, THE IRIS, RETINA, AND HUMORS. 385 on which are seen, c, c, the vasa vorticosa ; d, d, ciliary nerves ; e, ciliary ligaments ; y, anterior face of iris ; ff, pupil. Fig. 100. Fill. 200. The veins of the choroid. Tlie ailLiKb of the choioid. J^ig. 200: a, a, exterior surface of the choroid and the iris, showing the arterial network of these two membranes, supplied by the ciliary arteries, which, after having traversed the sclerotic, divide into, b, b, posterior cili- aries for the choroid, and c, c, anterior ciliaries for the iris. The iris, though arising, as has been said, from the choroid, is con- structed in a different way, its tissue mainly consisting of un- striped muscular fibre, except in the case of birds, which present the striped variety. It is extremely vascular, its arteries being derived from the ciliary. The color of the eye depends on the color of the front of the iris ; the posterior portion is covered with black pigment. The ciliary muscle, for such it has been proved to be by Dr. Wallace, of New York, is of the unstriped kind ; its action is to move the lens. In birds it is of the striped variety. The retina intervenes between the vitreous humor and the choroid coat : it arises from the tubules of the optic nerve, which have ^, . . . 1 . Ill ^^® retina, cast off their covermg investitures on their passage through the sclerotic. It extends forward to the ciliary body ; is perfectly trans- parent during life, though it soon becomes semi-transparent. Its struc- ture, a knowledge of which is of the utmost importance in the theory of vision, will be presently described. In the optical axis of the eye there is upon the ret- ina a spot of about the twentieth of an inch in diam- eter, called the yellow spot of Soemmering. Its posi- tion is shown in jPtg. 201. The entrance of the optic nerve is at the blind spot which is marked at some dis- tance on one side. The vitreous humor is contained in YeiiowlprtTf soem- a dcHcate mesh of transparent tissue, which The vitreous °'''"°^' causes it, when removed, to present the aspect ^^^°^- of a jelly. In front it receives the crystalline lens, which is contained in a closed capsule. Round the lens there is a passage, known as the canal of Petit, which enables the ciliary muscle to move the lens. The Bb Fin. 201. 386 OPTICAL ACTION OF THE EYE. analysis of the vitreous humor shows that it consists of water contain- ing about one and a third per cent, of common salt, with a trace of al- bumen. , The crystalline lens is a double convex of unequal curvatures, the an- The crystalline terior surface being the flattest, the shape changing with the •ens. period of life, as also does the density of its parts, its cen- tral portions being always the most dense. In construction it is ex- tremely complex, being made up of fibres ranged side by side, and so forming successive laminas. The fibres are about the -^jjq part of an inch thick. The refracting power of the lens differs at the centre and circumference : in the former region it is greater. In chemical composi- tion, the lens consists of about fifty-eight per cent, of water, and thirty- six per cent, of a form of albumen known as globulin. The aqueous humor fills up the space between the lens and the cornea : A ueous humor ^* ^^ composed of water containing about one per cent, of common salt. , Of the Optical Action of the Eye. It is the province of the works on natural philosophy to explain how, ^ when rays of lio-ht fall upon a convex lens, or upon combi- Bormation 01*'^° ■■■_ , . ■■- images by nations of such Icnscs, an image of the object will form at the lenses. proper focal distance. For the purposes of physiology, it is sufiicient to receive this as a fact, which may be easily illustrated by ob- serving the images of external objects depicted upon a sheet of white paper when a convex lens or magnifying-glass is held at a particular distance between the object and the paper. In making such an experiment, some other facts which concern the Effect of dis- physiologist may be readily demonstrated: 1st. That the tanceoftheob- focal distance, that is, the distance between the lens and the ject and curv- . .,,.. .„,. , , ature of the paper, IS Variable : it is greater lor objects that are near, less ^^°^- for those that are remote ; 2d. That lenses of different curv- atures being compared together, the flatter ones have the longest focus for objects at the same distance; 3d. That lenses of the same focus, but of different diameters, give images unequally sharp, an indefiniteness be- ing perceived in the image given by the lens of large diameter. This in- distinctness is due to the spherical figure of the lens, and would not have Spherical and occurred had the surface been ground to another conic sec- chromatic aber- tion. It is Called spherical aberration ; 4th. Unless the lens be of very long focus, or its aperture or diameter be veiy small, the edges of the images it yields will be fringed with rainboAv colors, and thereby a second cause of indistinctness arises. It is called chromatic aberration. This aberration may be destroyed by properly combining together lenses made of different refracting media, and witli THE RECEIVING SCREEN. 387 surfaces of suitable curvatures; a combination in which this has been ef- tectecl is termed an achromatic lens ; and if, at the same time, by proper arrangements, the spherical aberration has been destroyed, the lens is termed aplanatic. Now the aqueous humor, as bounded by the cornea in front and the crystalline lens behind, acts as a convex, and therefore con- co,ivei.o-ent verging lens, and to this effect the crystalline itself adds pow- media of the erfully, the two conjointly causing the images of external ob- ^•^^' jects to form upon the black pigment. These images are, of course, in- verted. The adjustment of the eye for perfect vision of objects at different dis- tances is accomplished by the action of the ciliary muscle, Adiustment by the requisite movement being to draw the lens farther from the ciliary mus- the black pigment when the object is near. There has been ^ °^ "^ '* ^^^^' much controversy as to the manner by which this adjustment for dis- tance is effected, but it is generally now agreed that it is done in the manner just mentioned. There has also been a difference of opinion as respects the actual screen upon which the images form. Some of the early optical writers regarded the black pigment as being xhe receivino- that receiving surface, an opinion which has been universal- screen is the 111,. . , . , p , .-, -, black picfiTient, ly abandoned, the function havmg been of late attributed to and not the ret- the retina, but, as it appears to me, on totally insufficient "^^• grounds. The arguments against the retina, both optical and anatom- ical, are perfectly unanswerable. During life it is a transparent medium, as incapable of receiving an image as a sheet of clear glass, or the at- mospheric air itself; and, as will presently be found, when we come to describe its structure, its sensory surface is its exterior one, that is, the one nearest to the choroid coat. But the black pigment, from its perfect opacity, not only completely absorbs the rays of light, turning them, if such a phrase may be used, into heat, no matter how faint they may be, but also discharges the well-known duty of darkening the interior of the eye, and therefore preventing indistinctness through the straying of the rays of light. Perfection of vision requires that the images should form on a mathematical superficies, and not in the midst of a transparent me- dium. The black pigment satisfies that condition, the retina does not. Spherical aberration is compensated for partly by tlie increasing dens- ity of the lens toward its centre, and partly by the action correction for of the iris, which stops such rays of light as are at any con- spherical aber- siderable distance from the axis of the eye, acting in the same manner as a perforated plate or diaphragm in ordinary optical in- struments. It does not appear that there is any attempt at correcting the chromat- ic aberration of the eye, though it is popularly supposed that the cornea, 388 LONG AND SHORT SIGHT. ,. , the aqueous humor, the lens, and the vitreous humor act to- Chromatic ab- ^ . . , . eiration is un- gether in the same manner as the different pieces of glass in corrected. ^^ achromatic arrangement. Optical reasons, however, found- ed upon the constitution and refractive powers of those suljstances, lead us to abandon that view, and in a theoretical respect to regard the eye as imperfect in this particular. Adjustment for the variable intensity of light is effected by the dilata- tions and contractions of the iris, the pupillary opening of the intensity whicli varies from the ^-g- to the -^ of an inch in diameter, variations. -^^ ^^^ thus enabled to bring to the same degree of illumin- ating effect upon the retina lights whicli differ in brilliancy in the pro- portion of one to forty-five. The means by which this is accomplished will be more particularly described when we speak of the nervous mech- anism of the eye. It has been already observed that the actual field of view at a given moment is quite limited. We are liable to deceive ourselves on this point from the rapidity with which the eyeball can be directed, to differ- ent parts in succession. In what has been said, reference is made to a perfect eye ; but imper- Long and short fections are very common. Two may be more particularly cOTrection b"^^^ pointed out — long-sightedncss and short-sightedness. In spectacles. the former, objects, to be seen distinctly, must be placed farther off than the usual distance ; in the latter they must be brought nearer. Long-sightedness arises from the flatness of the lens or cornea, so that the focal images given do not fall truly on the black pigment, but would be, at a certain distance, exterior to it ; hence the indistinctness that results. Short-sightedness is due to an excess of curvature in the cornea or lens, the rays forming their focal images before the black pig- ment is reached. The former defect may be removed by the use of con- vex lenses as spectacles, the latter by concave. It is often said that short-sightedness is a defect of early life, long-sightedness of old age. However this may be in another respect, it is not so optically. Indeed, cases sometimes occur in which one eye is affected with the former and the other with the latter difiiculty. Very frequently the two eyes, com- ])ared together, will be found differently advanced in their degree of im- perfection, and hence the difficulty of obtaining a pair of spectacles, though the selection is attempted to be made out of a large assortment. In such cases, each eye should be accommodated with a lens to suit it- self. Compared with the organ of hearing, the eye is much more limited in its Limit of vision action ; for, while the ear can distinguish sounds which vary is one octave, through many octaves, the eye can only perceive vibrations which, to use the language of acoustics, differ by a single octave only. EFFECTS OF HEAT. 389 To one octave, therefore, its range is limited. The extreme red ray, which is emitted by a substance just becoming red hot at a temperature of 1026° Fahr., and which is the least refrangible that can affect the eye, is caused by vibrations that are exactly half as frequent as the extreme violet ray emitted by the sun. It is important, in the explanations wc are giving, to understand that, in a perfect solar spectrum, the distribution of the colored spaces is totally different from what it is in the case of the prismatic. In such a spectrum, as produced by the interference of rays passing through a surface of glass on which have been ruled with a point of a diamond parallel lines the y-Q-oyo °^ ^^ inch, apart, the yellow occu- pies the middle region, and from this the light grades off, terminating at equal distances with the extreme red on one side and the extreme violet on the other. The circumstances of such an experiment prove that, the wave length for the red light being compared with that for the yellow, and also for that of the violet, they bear to one another the extraordinary and simple relation of 1, 1-|, 2, establishing the assertion just made, that the extreme limit of perception of the eye is comprised in a single octave. I may refer to the experiments published by myself on this point, and also to those both antecedently and subsequently published by M. ]\Ielloni, in proof of the unreliability of the method of colored rays is examining the solar spectrum by the prism in the manner '" proportion introduced by Newton. More particularly to the discussion minating pow- now before us does this remark apply ; for the prism, as ^^' may be gathered from what has just been said, spreads out the colors of light unduly, and gives false indications respecting the distribution of heat. There can now remain no doubt, although the prism indicates, the contrary, that the yellow, or brightest ray of light, is the hottest, and that the warming power of the others, orange, green, &c., follows in the order of their luminous intensity. When we have finished a descrip- tion of the nervous mechanism of the eye, we shall find that the expla- nation of its function turns on the admission of this fact. The eye is limited in another respect ; it can not simultaneously com- pare lights which differ from one another in brilliancy if the Limit in the one should be upward of 64 times as bright as the other. Jhrbn^htnets The more luminous overpowers or extinguishes the feebler, of lights. We can not see the light of a candle if we hold it up against the sun. I may again refer to the experiments I have published, establishing that upon this fact is founded the most exact method of photometry yet known. 2d. Of the Nervous Mechanism of the Eye. In the preceding description it was stated that the retina, commonly 390 STRUCTURE OF THE RETINA. described as an expansion of the optic nerve, intervenes between the rit- reous humor and the choroid coat. Regarding it as composed of distinct layers, the innermost of which. Construction in contact with the hyaloid membrane, is called the fibrous '^^d^j'^^'"^ gray layer, arises from the tubules of the optic nerve, which membrane, have cast oft' the white substance of Schwann ; and in pass- ing, we may dwell emphatically upon the point that at that spot, Avhere it exists alone, that is to say, where the optic nerve is entering the eye, vision can not be performed. Beneath, or outside this fibrous layer, comes the gray vesicular layer: it is analogous to the vesicular matter of the brain. The two layers thus far described are served with capillary blood-vessels of extreme minuteness. Outside of the gray vesicular lay- er is the granular layer, which, as its name imports, consists of a conge- ries of granules, which are probably the origin of the vesicles, new ones arising from this layer continually. Yet again, outside of the granular layer, comes a delicate sheet, known as the membrane of Jacob, but which is formed, in reality, from the juxtaposition of a set of rod-shaped and conical bodies, the thicker ends of the rods being outward, the thinner inward. jPt^. 202 shows the partial detachment of the membrane of Jacob from the exterior of the retina. The membrane appears as delicate shreds, and may be advantageously demon- strated after the removal of the choroid, the specimen being placed under water. In the preceding description I have followed the course usually taken by former anatomists, who describe the retina as consisting of suc- cessive layers or strata, but much more philo- .Membrane of Jacob. sophical vicws are obtained by considering it in ,. , the manner introduced by H. Miiller, that is to say, in its Perpeiitlicular •; , i <> examination radial scction. From this it appears that the four strata of the retma. j^-j^^^g mentioned, viz., 1. Jacob's layer of rods and cones ; 2. The granular layer ; 3. The vesicular layer ; 4. The fibres of the optic nerve, are, in reality, all connected in such a way that, passing in a radial direction as respects the globe of the eye, all these different elements are successively combined, constituting what is termed the radiated fibre system. Thus from each of the proper fibres of the optic nerve a thread- Radial fibre like body passes radially through the thickness of the retina, system. including in its outward passage a vesicle, and again, beyond that, a granule, and, still farther, a cone, and terminating in a rod ; so that from the extremity of the rod there is a continuous communication through the thickness of the retina to the fibres of the optic nerve ; the THE OPTIC NERVES. 391 rods are therefore to be regarded as the termination of the optic fibres. In the opinion of Miiller and Kolliker, the rods and cones composing- Jacob's membrane are the tnie percipients of light, communicating their condition to the fibres of the optic nerve by means of the connection which they thus maintain with it ; or, perhaps, the rods and cones are conductors of the luminous impressions to the nerve-cells of the retina, which constitute a ganglion capable of perceiving light, and the fibres of the optic nerve merely communicate those impressions to the sensorium. Whichever of these descriptions we may follow, the physiological fact which I desire to present with emphasis still remains the same. It is, that the sentient or receiving part of the retina is the posterior, that which is in contact with the black pigment. The second pair of nerves, from which the retina is thus derived, are, from their function, designated the optic nerves. They do The optic not enter the sclerotic in its optical axis, but a,t a little dis- nerves: their ., TIT 1 •• 111 • chiasm and tance on one side, and obliquely — a provision doubtless m- passage to the tended, in a measure, to avoid the occurrence of the blind ^""^i"- spot on the centre of the field of vision, and to place it unsymmetrically in the two eyes, so that each eye shall compensate the defect of the oth- er. The nerves from each eye converge to their chiasm, which is a com- missure consisting of three distinct systems of tubules — an anterior set, which are commissures between the two retinaa, a posterior set, commis- sures between the two optic thalami, and an interior set, the proper tu- bules of the optic nerve, which cross, those from the right eye going to the left side of the brain, and those from the left eye going to the right side of the brain. The chiasm is therefore to be regarded as a complex structure, its posterior region being independent of the other parts, and existing in animals in which the optic nerve is not found, as, for exam- ple, in the mole. Besides the optic nerve, which is exclusively the nerve of vision, the collateral parts of the eye are supplied from various sources. mi 1 • 1 • ^ -1 -IM Gr\ GS lO 1x16 ihe third pair, or motores-oculorum, supply the superior, in- eye-ball and ferior, and internal recti muscles, the inferior oblique, and the ^""^^^^"^ P*"^*^- levator palpebrse. The fourth pair, or pathetici, supply the superior ob- lique or trochlear muscles. Of the fifth pair, supplies are derived from the frontal branch, lachrymal, the ciliary, and the infra-trochlear. The sixth pair, or abducent, pass to the external recti : supplies are also de- rived from the sympathetic. Of these nerves, the fiinctions are very va- rious ; some are for the movement of the ball, or for general sensibility of the surface, or for the movements of the eyelids, or for those ©f the iris, and some for the lachrymal apparatus. 392 NEEVOUS MECHANISM OF THE EYE. Of the Function of the Nervous Mechanism of the Eye. The reasons have already been given for considering that it is the The black pig- hlack pigment which acts as the receiving or optical screen, ment, and not and not the retina. If no other argument was adduced for the receivino- departing from the opinion usually expressed, which attrib- screen. -^^gg -jjiig function to the retina, the thickness of that struc- ture would be sufficient ; images can only form with precision or sharp- ness upon an abrupt surface. And since it is now indisputably ascer- tained that both the chemical effect and the heating effect of the rays of light depend upon their absorption, those effects being in direct propor- tion to the completeness with which absorption is taking place, we are justified in inferring that, since the eye is sensible to rays of so low a degree of intensity, and to each of the colored ones equally, its screen of reception must not only be a superficies, but likewise a black one. Such a surface the black pigment is. In the case of albinos, and animals in which the black pigment is imperfectly developed, the receiving surface or screen is still the interior of the choroid. Under such circumstances, vision must be indistinct. Eecalling what has been said respecting the diffuse sensibility of the Heating effect lowcr members of the animal series to light, and the struc- on the pigment, turc of occlli, it accords wcU therewith to consider that the primary effect of the rays of light upon the black pigment is to raise its temperature, and this to a degree which is in relation to their intensity and intrinsic color ; light which is of a yellow tint exerting, as has been said, the most energetic action, and rays which correspond to the extreme red and the extreme violet the feeblest. The varied images of external objects which are thus painted upon the black pigment raise its temperature in becoming extinguished, and that in the order of their brill- iancy and color ; the pigment thus discharging a double duty, as a sur- face of extreme sensibility for calorific impressions, and also as darken- ing the interior of the globe. In this local disturbance of temperature, in my opinion, the act of Manner of er- "^i^ion Commences, this doctrine being in perfect harmony ception by the with the anatomical structure of the retina, the posterior retina. surface of which is its sensory surface, and not the anterior, as it ought to be if the explanation usually given of the nature of vision is correct ; and therefore, as when we pass the tip of the finger over the surfaces of bodies, and recognize warm and cold spaces thereupon, the same occurs with infinitely more, delicacy in the eye. The club- shaped particles of Jacob's membrane are truly tactile organs, which communicate to the sensory surface of the retina the condition of tem- perature of the black pigment. niOTOGUArHIC RELATIONS OF THE EYE. 393 But tins communication of a variation of temperature implies a varia- tion in the waste and repair of the retina itself, for there can be no doubt that all such changes are accelerated bj an increase of heat, and dimin- ished by its decrease. And though in this manner the origin of the ac- tion which has been set up is calorific, and therefore physical, it imme- diately becomes converted into a physiological equivalent in the meta- morphosis and destruction of a nervous tissue. The eye can not perceive rays which come from a luminous source the temperature of which is lower than 1000° F., for such rays can not pass through a stratum of water or through the humors of the eye. Natural philosophers, in making a distinction between light and heat, have too often overlooked the fact that, though thermometers are sensi- tive to rays of every sort, the eye is not. Its indications are complicated by the necessary introduction of absorbent media, which stop all rays the refrangibility of which is low. Many years ago, Count Eumford, from a limited examination of cases, concluded that all photographic effects are the effects of Photographic a his;h temperature. From an examination, continued for l^^^^^ ^^'^ ^^' , or ' fects of a high many years, of numerous phenomena of the same class, which temperature. have since been described, I have come to the same conclusion. The impinging of a ray of light on a point raises the temperature of that point to the same degree as that possessed by the source from which the ray comes, but an immediate descent takes place through conduction to the neighboring particles. This conducted heat, by reason of its indef- initely lower intensity, ceases to have any chemical effect, and hence photographic images are perfectly sharp on their edges. It may be dem- onstrated that the same thing takes place in vision, and in this respect it might almost be said that vision is a photographic effect, the receiving surface being a mathematical superficies, acting under the preceding con- dition. All objects will therefore be definite, and sharply defined upon it, nor can there be any thing like a lateral spreading. If vision took place in the retina as a receiving medium, all objects would be nebulous on the edges. This sharpness and grading off are happily illustrated by the metal daguerreotype and paper photograph respectively. Perhaps it might be thought that the sharpness of impressions upon coUodion or albumen stands in opposition to what is here Absorption nec- said respecting the inefficiency of translucent media. Those f^^'^'^-*'/?'^ ^^"" substances, however, would be totally inert unless there had tion. been purposely mingled with them some compound of easy decomposi- bility, capable of absorbing the blue rays, which are in these cases the effective photographic ones. Such a compound must commonly be of a yellow color. In these substances the absorption takes place with en- ergy the moment the light has entered their surface. In the Philosoph- 394 FUNCTION OF THE EETINA AND CIIOEOID. ical Magazine, September, 1840, I have given proofs that the essential condition of the chemical activity of a ray of light is its being thus ab- sorbed. As an illustration may be given the well-known result, that if chlorine and hydrogen be exposed to the sun, they unite with a violent explosion, but, under the same circumstances, oxygen and hydrogen will utterly refuse to unite, no matter how long the period of exposure may be, nor what the brilliancy of the light ; and the difference in the two cases is merely this, that the chlorine, being of a yellowish color, can ab- sorb the violet light, and therefore be influenced by it ; but the oxygen, being uncolored, can not. For photographic effects, as well as calorific, the essential condition is absorption. A medium like the retina, which is without absorbing action, pennits rays to pass through it without any kind of effect, but a surface like the black pigment, whicli receives them all equally, whatever their color may be, and absorbs them all equally, is equally affected by them all. The • impression arising from the disturbed condition of the retinal Function of the vcsiclcs is Carried by the optic tubules to the chiasm of the two chief laj-- ly^Q nerves. Apart from the general facts elsewhere pre- ers of the reti- . . r>iTi i naandthecho- scnted by physiology, the existence of a blmd spot at the roid. entrance of the optic nerve, where there is a necessary ab- sence of vesicular structure, is a clear proof of the insensibility of the tubular structure to the influence of light. Considering, therefore, the retina as typically composed of three layers, one of tubules, one of vesi- cles, and one of granules, and these in health being perfectly transparent, the luminous beams pass through them just as they do through the at- mosphere, without exerting the slightest effect ; and as, when those rays strike the opaque surface of the earth, or are absorbed by the sea, heat is disengaged and effects ensue, so likewise, when they have reached the black pigment, the changes I have been designating arise. The vesicu- lar layer undergoes rapid metamorphosis, the effect of that change is transmitted by the tubular layer, and in the granular the germs are con- stantly arising from which the waste of the middle layer is repaired. So, therefore, the tubular layer is for conduction, the vesicular layer for waste, the granular layer for repair ; and now appears the significance of the construction and proximity of the choroid coat, for the waste of the ve- sicular layer can not occur save under the oxidizing influence of the ar- terial blood, nor can the nutrition of the granular layer be accomplished except under the same condition. Moreover, the resulting products of waste require to be quickly removed, and it is not possible to conceive the construction of an arrangement better adapted for this triple object than that which the choroid presents. On the old view of the nature of vision, the construction of the choroid seems to be without significance. The analogy between the mechanism of the retina and that of the SINGLE VISION. 395 skin, so far as waste and restoration are concerned, can not fail to be noticed. The effect which has thus been communicated to the vesicular layer of the retina, through the intervention of Jacob's rods and . ^ ' o • Interconnection cones, is now carried along the nervous tubules out of the of the right and globe of the eye. The nerves from each eye, converging, '^ ^ ^^^' encounter one another at the chiasm, the triple structure of which has already been described. Here it is, howevei-, to be understood that,, while the proper optic tubules of the right eye go to the left brain, and of the left eye to the right brain, the anterior band of commissural tu- bules brings the two eyes into a special relation with one another, the right side of one eye corresponding with the right of the other, and the left Avith the left ; or, to put the same statement under a more simple yet more instructive form, the outer side of one eye corresponds with the in- ner of the other, and in this manner the two retinas become as if they were virtually incased the one within the shell of the other, an arrange- ment which obviously, as has been already remarked, compensates in a degree for the blind spot of each eye, and, indeed, eliminates the effect of all accidental irregularities, for numberless such irregularities must exist, there being a necessity, for example, that blood-vessels should cross through the sensitive to the conducting structures, and such blood-ves- sels give rise to lines of inertness. From this commissural arrangement it comes to pass that each retina possesses regions of symmetry with the other, and on this single and singleness of vision depends; each point of the outer portion double vision, of the retina of the right eye has its point of symmetry in an inner portion of the left, and when from a distant object rays fall on these symmetrical points, that object will be seen single ; but if, by the pressure of the fin- p:er or otherwise, we compel the image to fall in one of the eyes upon another, and, therefore, non-symmetrical point, the object at once becomes double. It should be remarked that this exchange of symmetry concerns only the lateral divisions, for the upper portion of one eye corresponds with the upper portion of the other, and the lower with the lower. If the view which I have presented respecting the scalse of the laby- rinth of the ear be correct, that sinp-ular structure finds its . , , _ ' o Analogy be- equivalent in the black pigment of the eye; for though we tweenthescala? only know in an indistinct manner the physical condition of ^° pigmen . black opacity, we may be certain that it arises fi'om total interference of rays, and such, it is presumed, is the office of the scalas of the ear. Impressions made upon the retina do not disappear instantly, but grad- ually fade away, and in so doing occupy a certain period of p^j-ation of time, which varies with the brightness of the original light, the impressions existing condition of the eye, and the illumination to which it " ^ ^^^' 396 EEECT VISION. is exposed. This duration of impressions is coramonlj estimated at about one third of a second. It is a phenomenon analogous to that of the continuance of sound in the ear, and subserves an important purpose of keeping vision continuous and distinct during the winking of the eyelids. Commonly it is ilkistrated by referring to the familiar experiment of a stick lighted at one end and twirled rapidly round, wliich gives rise to the appearance of a continuous fiery circle. Many ingenious and interest- ing toys, such as the thauraatrope or wonder-turner, act on this principle. When the eye, particularly after a period of repose, as when we first Ocular spectra wake in the morning, is turned to the window or some bright mentTry^coi- ^^S^^i ^^^ ^^^®^ closcd, a Spectral impression is for a long ors. time presented to the mind. If, instead of closing the eyes after looking at a bright light, they are directed to some white surface, a dark spectral appearance of the luminous object is seen. The explana- tion of this is evidently that those parts of the retina which have just undergone change are less fit to be acted upon by the more moderate light to wliich they are now exposed than those which have hitherto been unaffected. Under similar circumstances arise what are termed comple- mentary colors. Thus, if we intently regard a red wafer on which the sun-rays are brightly shining, and then turn our eyes away to a feebly illuminated white wall, a green spectre of the wafer will be seen ; and so of other colors. The complementary tint is that color which, added to the original one, forms white light. The explanation of these colored spectra depends upon the principle just mentioned. There have been few optical problems more warmly contested than that of erect vision. The image at the bottom of the eye is Erect vision. . ° a ^ -i inverted, but we see the object upright, feome have supposed that we really see things upside down, but have learned to correct the error by the sense of touch. Doubtless the tme explanation is to be found in the anatomical construction of the eye. It should be borne in mind that there is a very wide difference between the image formed at the bottom of an eye as we look at it, and, if such an expression may be used, as the eye itself looks at it. We see it from behind, the retina sees it from the front. Or, to put the statement perhaps more clearly, it is one thing to look at the images on the ground glass of a camera ob- scura from behind the instrument, and another to see them, as it were, from the interior of the box. The two positions are upon the opposite sides of a vertical axis, round which we may consider that we have turn- ed, and hence the lateral inversion is corrected. That portion of the im- age which, seen from behind, was on the right of the spectator, is on his left if seen in front. A similar event must ensue in the case of the ret- ina. As we have seen, it is its posterior face, looking at the black pig- ment, which is its sensitive surface. It sees, as it were, looking back- IDEAS OF SOLIDITY. 397 ward, Lilt not forward, and hence there arises a correction for -. . , . ' ' Jjaterai inver- the lateral inversion. This, of course, implies the existence sion corrected of some structural arrangement which shall either correspond- ^ ^ ^^ "^*' ingly correct the vertical inversion, or bring back the lateral to its orig- inal erroneous state, and thereby establish a harmony of position in the two directions ; and if, in the retina itself, the means exist for the cor- rection of inversion, vertical as well as lateral, by changing the direction of the conducting tubules, it necessarily must be that that place of cor- rection is where the retina is intersected by the optical axis of the eye. I think it is to be greatly regretted that we are not bet- Suggestion re- ter acquainted with the construction of the yellow spot of yellow fpot*^ of Soemmering, which occurs at this very point. The ridge- Soemmering. like form it presents, the thin, uncolored spot in its centre, its more def- inite occurrence in those animals, as man, the quadiTimana, and some saurians, the axes of whose eyes are nearly parallel to one another, seem to indicate, in a very significant manner, that at this place the correction in question is made. There are many ways in which we may conceive this to be done by varying the direction of the nervous tubules. As an illustration, it may be remarked that if, through a small hole made in a sheet of paper, a number of threads, the end of each of which is fasten- ed to the back of the sheet, be caused to pass, under the condition that they do not cross one another in the hole, but leave its aperture open, their direction in space as they retire from the hole will be inverted as respects the direction in which they approached to it. The analogy be- tween such an aperture and the foramen of Soemmering is too striking to be overlooked. The stereoscope, invented by Professor Wheatstone, shows to what an extent our ideas of the solidity of obiects depend on the dif- ^, •^ ^ ^ . ,.^ The stereoscope, ferences of the images in each eye. By reason of then* dif- ference of position, each of the two eyes will have a different picture upon its black pigment of any solid object, and the mind, combining these dis- similar pictures into one, gathers therefrom the idea of solidity. If thus we offer to the eyes two pictures of a given object, presenting the same form as that object would have done when seen from each eye respect- ively, the mind combines these flat pictures together, and can not divest itself of the idea of a solid body. This is the principle of the stereo- scope. It is shown by this instrument that, when two such pictures of different sizes are used, the mind combines them into one of intermediate magnitude. Probably this effect is involved in the circumstance that, when we look at an object unequally distant from the two eyes, we stiU see it single. When two images of different colors are employed, the mind can not combine them, but sees first the one and then the other, the brightest one continuing the longest. 398 SUBJECTIVE IMAGES. The eye is adjusted to the varying intensities of light by the motions . ,. ^ . ^ of the iris, which admits more or fewer rays accordina; to its Adjustment to ... variations of state of contraction, an action which, on certain occasions, is rig tness. aided by the orbicularis palpebrarum, which, by bringing the eyelids together, limits the number of rays passing to the pupil. In man, the muscular fibres of the iris are of the unstriped form ; in birds they are striped. Our perceptions of the intensities of light, as gather- ed from the state of tlie iris, can never be so distinct as the indications for sound yielded by the tensor tympani and stapedius muscles. In birds, however, it is probably different. We gather, to a great extent, our notion of the brilliancy of light from the rapidity of structural change taking place in the retina itself. Although many images may be simultaneously existing upon the ret- ~ , ,. ina, the mind possesses the power of sinpiing any one of them Concentration ' \ ^ ^ . . of attention on out and fastening attention upon it, just as among a number one image. ^£ musical instruments simultaneously played, one, and that perhaps the feeblest, may be selected, and its notes exclusively followed. These phenomena, however, are not dependent upon any peculiarity of construction of any of the organs of sense ; and as the mind can perceive the images of external things, so can it give rise to spectral illusions which may simulate perfectly the aspect of external forms. The anec- dotes of such occurrences which are to be found among all people are not the fabrications commonly supposed. The mind can be readily deceived, even in spite of itself, as the phenomena of the stereoscope prove ; and spectres, having their origin in natural or diseased conditions of the brain, may accurately replace images that have been painted in the eye. It is „ , . , . said, however, that we may readily distinguish, by means of Subjective im- ' / "^ ,...^ ages, and test a simple Optical test, a true external apparition, if any ex- for them. ^^^^^ ^^.^^^ ^ phantom of diseased imagination ; for by press- ing duly with the finger on the ball of one of the eyes, external objects are at once doubled, but it is not so with a mental illusion ; and we may therefore suspect that, even in the best authenticated cases of the ap- pearances of these unnatural forms, had this test been applied, their true character would have been ascertained ; and that, since none of them would have undergone duplication, they would at once have been detect- ed as mere hallucinations of the mind. The explanation of the function of vision which I have given on the preceding pages might be termed the calorific hypothesis, since it rests essentially on the fact tliat the temperature of the receiving screen of the eye is raised by the impinging of light upon it. The result thus far is of a purely physical nature, but it becomes physiological when Ave farther admit that chano-es of constitution ensue in the vesicular structure of the retina. These changes are rendered more rapid as the temperature is ACCESSORY APPARATUS. ' 399 higher. It remains now to add tliat this is only one manner of looking at the thing. According as our hypothesis of the nature of Hght, of its relations to heat, and of its manner of establishing chemical changes may be, the special explanations we give of the functions of the eye will differ ; yet there is such a relationship among these hypotheses that Translation of we can, without any difficulty, convert an explanation derived t'^^ calorific from one into an explanation derived from another. It re- other forms of ally comes to little more than a translation of phraseology, expression. I have found the calorific hypothesis convenient, because we are led to it by the comparative anatomy of the eye in starting from the ocelli of the lower forms ; yet, with almost equal convenience, the function might have been treated otherwise, viewing light as arising from ethereal undulations, the additional advantage then being obtained of establishing a parallel- ism between the action of the organ of sight and that of hearing. Or, in like manner, the case might have been viewed in its purely chemical aspect, photographically, as it might be said, the destruction of the vesic- ular structure of the retina through the agency of arterial oxygen being taken as the primary physical act. But this, again, amounts only to a different mode of stating the same effect, since, as I have shown (London and Edinburgh Philosophical Magazine, May, 1851), all chemical changes accomplished in material substances are occasioned by the establishment of vibratory motions therein, and Ampere has already demonstrated that all the phenomena of heat may be explained upon the doctrine of the vi- brations of the constituent molecules of bodies. Divesting ourselves, therefore, of any farther concern in making a se- lection among the various hypotheses, we have adopted the view that the change of the retina originates in a calorific disturbance, because it ap- pears to be somewhat more convenient for our use. It is to be understood that the sensation of light is, however, purely mental, and whatever can disturb the nutrition or waste of r^, Ihe sensation the retina will give rise to luminous impressions. The press- of light purely ure of the finger on the ball of the eye, a blow, the passage "^^"^^^ • of an electric current, and divers other causes, will at once produce the appearance of light, and even of colors. Heat is only one out of a mul- titude of agents that can disturb the retina. 3d. Of the Accessory Apparatus of the Eye. The accessory apparatus of the eye consists chiefly of the eyebrows, the eyelids, the Meibomian glands, the lachrymal mechanism, and the muscles for the movement of the ball. The eyebrows are two arches of integument, covered with hair, on the upper edge of the orbit. They are usually classed with the xhe evebvows appendages of the eye upon the supposition that they protect ^"^^ eyelids. 400 THE LACHRYMAL APPARATUS. that organ from undue intensity of liglit, or preserve it from the ingress of drops of sweat. They aid greatly in the expression of mental emo- tions, but perhaps should rather Le looked upon as among the remaining vestiges of the hairy tegument which afibrds a protection to the entire skin of other mammals below man in the animal series. The eyelids may be described as a pair of valves, the upper one having a much great- er latitude of motion than the lower. Their use is to afford protection to the eye by closing entirely over it, more particularly during sleep ; to keep its optical surface moist and free from dust by their winking mo- tion. They are brought into action by the contact of air or of irritating particles, through the fibres of the fifth and facial nerves, or by the agency of light upon the retina. The edges of the lids are furnished with rows of curved hairs, the eyelashes, which add greatly to the protection of the delicate organ beneath, while permitting vision to take place to a certain extent. Opening upon the edges of the eyelids are the foramina of the Meibomian glands, in the upper lid there being about thirty, in the low- er somewhat fewer. The glands themselves are imbedded on the in- ternal surface of the cartilage of the lids, and afford an oily secretion, which discharges the double duty of preventing adhesion of the lids, and, by its relation of capillary attraction, hindering the overflow of the water which moistens the eye upon the cheek. Of the lachrymal apparatus, it may be said that in the same manner The lachrj-mal '^^^^ ^^^ breathe Upon a spectacle glass and wipe it that its apparatus. surface may be perfectly clean, so it is necessary for the op- tical action of the cornea that its surface should be constantly washed, and even more so, for its lamellated structure is such that, if it be not kept constantly damp, it loses much of its transparency. This therefore renders it necessary that there should be a mechanism for the supply of water, another for spreading that water uniformly over the surface of the cornea, and a waste-pipe for carrying any surplus away. The lachrymal gland discharges the first of these duties. It is situated in the upper and outer angle of the orbit ; its secretion, which is a bitter and some- what saline water, is brought to the surface of the conjunctiva by eight or ten little ducts aiTanged in a row for the purpose of equalizing their dis- charge. The spreading of this fluid over the eye, and the simultaneous wiping of the surface, is accomplished by the eyelids. Usually the wa- ter that has been employed is dissipated by evaporation into the air; but if, by reason of meteorological circumstances, such as the dampness of the atmosphere, or by the supply being too abundant, there should arise an excess, it is carried off through two minute orifices which are upon the edge of the eyelids, the puncta lachrymalia. These draw off any collection of water that may have accumulated in the lachrymal lake, and, carrying it into the lachrymal sac, discharge it through the nasal duct into the CEREBEAL SIGHT. 401 cavity of the nose. From this it is removed by evaporation, the current of air alternately introduced and expired affording the means of accom- plishing that object in a remarkable manner. But should the discharge of water from the lachrymal gland become excessive, as in weeping, this draining mechanism is insufficient, and the water is discharged as tears down the cheek. Of the muscles for the movement of the eye, the description has, in part, been given under that of the nerves. It may, how- Motions of the ever, be here remarked that the eyeball is moved by six eyeball, muscles, the four straight and the two oblique. The straight muscles arise at the optic foramen, and are inserted into the sclerotic in the four quadrantal positions above, below, right, and left. The action of each of these muscles is to turn the eyeball toward itself; when they contract all together, they fix it. The superior oblique muscle arises from the same place, passes through a pulley beneath the internal angular process of the frontal bone, its tendon being inserted into the sclerotic near to the entrance of the optic nerve. The inferior oblique rises from the in- ner margin of the superior maxillary bone, passes beneath the inferior straight muscle, and is inserted into the sclerotic on its outer and pos- terior part, near the entrance of the optic nerve. The superior oblique rolls the globe inward and forward, the inferior rolls it outward and back- ward ; acting together, they draw the globe forward and converge the axes of the eyes. The nervous supply for these various muscles has al- ready been specified in page 334. CHAPTER XXI. OF CEREBRAL SIGHT OR INVERSE VISION. Difference between ordinary Vision and cerebral Sight. — Inverse Vision depends on the Vestiges of Impressions existing in the Bi'ain. Condition of our perceiving these Impressions is that they must be equal in Intensity to present Sensations. — Two Methods of accomplishing this Equalization : \st, by re-enfordng the old Im- pressions ; 2d, by diminishing the present Sensations. Emergence of old Imjiressions in Sleep, Fever, Death. — Ai'tificial Emergence of such Vestiges by Protoxide of Nitrogen, Opium, etc. Cerebral Sight used teleologically to indicate the Immortality of the Soul. The perception of external objects depends on the rays of light enter- ing the eye, and converging so as to produce images which make an im- pression on the retina, and, through the optic nerve, are recognized by the brain. The direction of the influences, so far as the observer is con- cerned, is from without to within, fr'om the object to the brain. Cc 402 INVEESE VISION. But the inverse of this is possible. Impressions already existing in the brain may take, as it were, an outward direction, and be projected or localized among external forms ; or if the eyes be closed, or the ob- server is in darkness, they will fill up the empty space before him with scenery of their own. Inverse vision depends primarily on the condition that former impres- sions, which are inclosed in the optic thalami or registering ganglia at the base of the brain, assume such a degree of relative intensity that they can arrest the attention of the mind. The moment that an equal- ity is established between the intensity of these vestiges and sensations contemporaneously received from the outer world, or that the latter arc wholly extinguished, as in sleep, inverse vision occurs, presenting itself as the conditions may vary, under different forms, apparitions, visions^ dreams. From the moral effect to which these give rise, we are very liable to regard them as connected with the supernatural. In truth, however, they are the natural result of the action of the nervous mechanism, whicli of necessity produces them whenever it is placed, either by normal, or morbid, or artificial causes, in the proper condition. It can act either di- rectly, as in ordinary vision, or inversely, as in cerebral sight, and in this respect resembles those instruments which equally yield a musical note whether the air is blown through them or drawn in. The hours of sleep constantly present us, in a state of perfect health, Difference be- illusions which appear to address themselves to the eye rath- tween sleeping ^^ t}iQ,n to anv other sense, and these commonlv combine into and waking il- •/ _ \ _ ■^ lusions. moving and acting sceneries, a dream being truly a drama of the night. In certain states, appearances of a like nature intrude themselves before us even in the open day, but these, being con*ected by the realities with which they are surrounded, impress us very differently to the phantoms of our sleep. The want of unison between such im- ages and the things among which they have intruded themselves, the anachronism of their advent, or other obvious incongruities, restrain the mind from delivering itself up to that absolute belief in their reality which so completely possesses us in our dreams. Yet, nevertheless, such is the constitution of man, the bravest and the wisest encounter these fictions of their own organization with awe. If we measure the importance of events occurring to us by their fre- p „ quency, the depth of the impression they make, the influ- mentalhailuci- encc they exert on our own individual career, or have ex- na ions. erted on the progTcss of the whole human race, there are very few more deserving the discussions of physiology than visual hal- lucinations. With respect to frequency, it may be reasonably said that, if images arise in the mind by night as numerously as sensible forms EFFECT OF THESE ILLUSIONS. 403 present themselves by day, it is not likely that they should be better borne in memory ; but of the thousands of objects we encounter every day of our lives, how few there are that we can distinctly recollect at its close. We think we explain this wonderful forgetfulness by saying we have paid no attention to them ; and, in like manner, the dreams we re- member are perhaps only a very insignificant proportion of those which have been presented to the mind. It has been said that a belief in apparitions is natural to every man. However much we may dissent from the correctness of such a xheir moral general assertion, there can be no doubt that it has a founda- ^ff^^t. tion in truth. The faith of a child in this particular is only gradually sapped as he grows up to be a man. Nay, even in mature life there may always be found those who have an unwavering confidence in the reality of these illusions, and many of these are persons characterized by their moral courage and love of truth. I have just remarked that few things have exerted a greater influence on the career of the human race than a firm belief in these spiritual visitations. The visions of the Arabian prophet have ended in tincturing the daily life of half the people of Asia and Africa for a thousand years. A spectre that came into the camp at Sardis unnerved the heart of Brutus, and thereby put an end to the po- litical system that had made the great republic the arbiter of the world. Another, that appeared to Constantine, strengthened his hand to the ac- complishment of that most difficult of all th& tasks of a statesman,- the destruction of an ancient faith. But these were all impostures, it may be said. Not so ; they were no impostures of the persons to whom they are reported to have occurred, and who assuredly firmly believed in the real existence of what they thought they saw. To the two or three instances mentioned above, scores of a like kind might be added, which have issued in the commit- ting of men to the most earnest kind of work. So often do historians notice an element of this kind mingling in the career of those who have made the deepest mark on our race, that some are to be found who as- sert the necessity of such a condition to any widespread and permanent political event. Whatever we may think of such a conclusion, the prem- ises on which it is founded are well worthy of our consideration. The physiologist is not at liberty to. deny that lunatic and delirious men have faith in what they see. Their senses may deceive them, but they are not impostors. It is for him to consider how phantoms may arise in conditions of apparent health as well as in states of disease ; in the tran- quillity of the solitary man as well as in the feverish excitement of the enthusiast. Visual hallucinations are of two kinds, those which are seen when the eyes are open, and those perceived when they are closed. To the for- 404 RETINAL DISTUEBANCE. Apparitions KiG^? the designation of apparitions ; to the latter, that of vis- and visions. JQj^g j^ay ]jq given. Dreams therefore come under the latter class. The simplest form of apparition is that known among physicians as Muscee voli- muscge volitantes. These are dark specks, like flies, which tantes. seem to be floating in a devious course in the air. Thej are owing to disturbances or changes in the retina. They often appear to occupy the dying. Of visions the most common, because they can be voluntarily pro- Remains of op- duced, are those which depend on the remains of impressions tic impressions. {^^ i]^q retina and optic centres. If, when we awake in the morning, our eyes are turned for a moment to a window or other bright object, and then closed, there still appears to the mind a spectral repre- sentation of the object, which gradually fades away. These illusions can be caused to have, as it were, a movement in the dark space before us, answering to the voluntary rotation of the eyeball. Sometimes, when the light is not sufficiently intense, or the nervous organs not sensitive enough, the vision does not make its appearance on the closing of the eyelids, but, after fastening the attention on the position in which it is ex- '„ ^ „ . pected to come, it slowly emerges at last. That it consists Seat of appan- -t _ ' _ •/ o tions and vis- in a real impression which has been made on those organs, ^°^^' and is not a mere product of the unaided imagination, is very clear from the fact that we may discern, by attentively considering it, many little peculiarities which we have not had time to notice in the original object ; thus, if there has been a lace curtain, or other such well- marked body before us, we can not only see in the vision the places where its folds intersect the windows, but likewise, if the impression be a good one, all the peculiarities of its figured pattern ; and that our conclusions in these respects are correct is proved as soon as we re-open our eyes. Between apparitions and visions is an intermediate class, of which it . is not my object now to say much ; they may, however, be styled deceptions. These take their origin in some outward existing reality, and are exaggerations of the fancy. They are commonly encountered in the evening twilight, or in places feebly illuminated. Sir W. Scott says of children that lying is natural to them, and that to tell the truth is an acquired habit. If they are thus by nature prone to de- ceive those around them, they are none the less prone to deceive them- selves. To them, a white object, faintly descried in the obscurity, is easily expanded into a moving and supernatural thing. In a physiological sense I consider that simple apparitions arise from disturbances or disease of the retina; visions from the traces of im- pressions inclosed at a former time in the corpora quadrigemina and op- RETINAL DISTURBANCE. 405 tic thalami. In their most higlily-marked state the former may be treated of as results of insanity of the retina, the latter as of cerebral vision. Disturbance of the retina, brought on by any cause whatever, may give rise to simple spectral apparitions, which, as the circumstances , r i^ . . . Apparitions change, will have an indefinite contour or a definite form ; nor from retinal are they merely shades and shadows : they may be presented 'ii^*^'^'"^^°'=s- in colors, which, however, are usually dim or subdued. Thus, if, the eye- lids being closed, we press gently with the tip of the finger on the inner or outer angle of one of the eyes, a gray spot surrounded by colors makes its appearance on the opposite side of the same eye, and dances about as the pressure of the finger varies. With a more extensive and heavier pressure clouds of various rainbow tints fill up all the imaginary space before us. In like manner, the passage of an electric current from a vol- taic pair induces a flash of light of considerable brilliancy. Internal pressures and spontaneous variations in the rate of metamorphosis and nutrition of the retina act in a manner analogous to external disturbances. From the muscas volitantes, which may be regarded as the first rudi- ments of apparitions, it is but a step to the intercalation of simple or even grotesque images among the real objects at which we are looking; and, indeed, this is the manner in which they always offer themselves, as rest- ing or moving among the actually existing things. I do not undertake to say how far we are liable to practice deception upon ourselves, after the manner we have spoken of in children, when we have once detected the fact that we are liable to this infirmity. An inanimate object — for in- stance, a stick — is seen upon the floor; we go to take it up; we find there is nothing there ; we return to our first position, but we can observe no shadow or other reality that can be offered as an explanation of what we have seen. An event of this kind predisposes us, perhaps, to return to that disposition of exaggeration so natural to our early life, and the next time the retina deceives us we involuntarily give to the hallucination mo- tion and a more definite form. Insects flying in the air, or, rather, floating in vacancy before us, pre- sent the incipient form of retinal malady. It may be provoked by un- due use of the eyes, as reading by lamp-light. I remark it constantly, in my own case, after prolonged use of the microscope. In a more ag- gravated form, it less frequently occurs as producing stars or sparks of light. From the earliest times, physicians have observed that it is a "bad sign" when the patient localizes these images. " If the sick man says there be little holes in the curtains, or black spots on his bed- clothes, then is it plain that his end is at hand." Under the title of pseudoblepsis, or false vision, medical authors enu- merate several varieties of the foregoing phenomena ; but when, as is 406 HALLUCINATIONS OCCASIONED BY DEUGS. Co-existence most commonly the case, the derangement which gives origin of retinal in- ^^ ^j^^g^ appearances is not limited to the retina, but, arising sanity and cer- cr o ebral sight. in some Constitutional affection, involves more or less com- pletely the entire nervous apparatus of the eye, retinal insanity and cerebral vision occur together. In those cases which have been investigated in a philosophical manner by the patients themselves, this complication is often distinctly recognized. Thus Nicolai, the Prussian bookseller, who published in the Memoirs of the Eoyal Academy of Berlin an interesting account of his own sufferings, states that, of the apparitions of men and women with which he was troubled, there were some which disappeared on shutting the eyes, but some did not. In such a case there can be no doubt that the disease affected the corpora quadrigemina and the optic thalami as well as the retina. This condition, in which the receiving centres and registering ganglia at the base of the brain are engaged, is the one which yields the most striking instances of hallucinations in which apparitions and visions co- Brought on ar- exist. It Can, like the less complicated forms, be brought tificiaiiy by ai- ^^ artificiallv, as in the delirium tremens which follows a cohol, opium, •/ ' ^ 1 1 1 • 1 &c. cessation from the customary use of alcohol, or m the exalt- ation by the purposed administration of opium or other drugs. In this, as in those forms, it is the localization of the phantom among the bodies and things around us that begins to give power to the illusion. The form of a cloud no bigger than the hand is perhaps first seen floating over the carpet, but this, as the eye foUows it, takes on a sharp contour and definite shape, and the sufferer sees with dismay a moping raven on some of the more distant articles of furniture. Or, out of an indistinct cloud, faces, sometimes of surprising loveliness, emerge, one face succeed- ing as another dies away. The mind, ever ready to practice imposture upon itself, will at last accompany the illusion with grotesque or even dreadful inventions. A sarcophagus, painted after the manner of the Egyptians, distresses the visionary with the rolling of its eyes. Martin Luther thus more than once saw the devil under the well-known form popularly assigned to him in the Middle Ages. As the nervous centres have been more profoundly involved, these ^. . ^ . , visions become more impressive. Instead of a solitary Visions of false -T . , ,. . , or exaggerated phantom intruding itself among recognized realities, as the scenery. gbade of a deceased friend opens the door and noiselessly steps in, the complicated scenes of a true drama are displayed. The brain becomes, as it were, a theatre. According as the travel or the reading of the sick man may have been, the illusion takes a style : black vistas of Oriental architecture, that stretch away into infinite night; tem- ples, and fanes, and the battlemented walls of cities ; colossal Pharaohs, sitting in everlasting silence, with their hands upon their knees. " ] rOEMS OF SPECTEES. 407 saw," says De Quincey, in his Confessions of an Opium-eater, " as I lay awake in bed, vast processions, that passed along in mournful pomp ; .friezes of never-ending stories, that to my feelings were as sad and sol- emn as if they were stories drawn from times before OEdipus or Priam, before Tyre, before Memphis ; and, at the same time, a corresponding change took place in my dreams ; a theatre seemed suddenly opened and lighted up within my brain, which presented nightly spectacles of more than earthly splendor." Apparitions are the result of a false interpretation of impressions con- temporaneously made on the retina ; visions are a presentment of the relics of old ones which yet remain in the registering ganglia of the brain. We convince ourselves of the truth of this general assertion not so well from an examination of one or more well-related or authenticated cases as from what may be termed the natural history of ghosts. The Greeks and Romans of antiquity were just as much liable to Secular varia- disorders of the nervous system as we are, but to them su- pe"t^and cos-^" pernatural appearances came under mythologic forms, Venus, tume of spirits. and Mars, and Minerva. The places of these were taken in the dreams of the ascetics of the Middle Ages by phantoms of the Virgin and of the saints. At a still later time, in Northern Europe, and even in England, where the old pagan superstitions are scarcely yet rooted out of the vul- gar mind, even though the Reformation has broken the system of ecclesi- astical thought, fairies, and brownies, and Robin Goodfellow survive. The form of phantoms has changed with change of the creeds of commur nities, and we may therefore, with good Reginald Scot, inquire, " If the apparitions which have been seen by true men and brave men in all ages of the world were real existences, what has become of the swarms of them in these latter times ?"' One class of apparitions — perhaps it was the first to exist, as it is the last to remain — has survived all these changes — survived them because it is connected with a thing that never varies — the affection of the hu- man heart. To the people of every age the images of their dead have appeared. They are not infrequent even in our own times. It would be an ungracious task to enter on an examination of the best authenti- cated of such anecdotes. Inquiries of this kind can scarcely be freed from the liability to an imputation on personal veracity, perceptive pow- er, or moral courage ; and, after all, it is not necessary to entangle our- selves with these causes of offense. It is enough for us to perceive that even here incongruities may be pointed out. The Roman saw the shade of his friend clothed in the well-known toga ; the European sees his in our own grotesque garb. The spirit of Maupertuis, which stood by the bay window of the library at Berlin, had on knee-breeches, silk stock- ings, and shoes with large silver buckles. To the philosopher it may 408 SPECTEES OEIGINATE IN PAST EVENTS. perhaps occur that it is very doubtful if, among the awful solemnities of the other world, the fashions ever vary. Let us pause before we carry the vanities of life beyond the grave. From such reflections as the preceding, I think it may therefore be concluded that there are two sources from which spectral appearances are derived : 1st. Disturbance of the retina, which presents masses of light and shade or colors to the mind, and these are worked by the fancy into definite forms on the same principle that we figure to ourselves pictures of faces among glowing embers. This constitutes retinal insanity. 2d. Gradual emergence from the registering ganglia of the brain of old im- pressions, which are rendered as intense and distinct as contemporaneous sensations. The two forms may, however, coexist. Of the latter, I may observe that the views of Dr. Hibbert, in his work on Apparitions, appear to me to approach nearer to the truth than those of any other author. It will be perceived, however, after perusing his interesting book, that I have not laid the stress he has done on the mechanical influence of the circu- lation of the blood, but view the efiect as of a more purely nervous kind. As the emergence of old images which have been registered in the op- tic thalami is not only connected with the physiological explanations we have given of the functions of the brain, but also occurs under circum- stances of such singularity as to border upon the supernatural, we may pursue the consideration of it a little farther. It may, I think, be broad- .„ , , Iv asserted that all spectral appearances refer to things that All spectral ap- •' r ri o pearances refer are past, persons who are dead, events which have taken to pas even s. pjg^gg^ sccnes that we have visited ; or, if we have not seen the actual reality, then pictures, statues, or other such representations thereof. It has never yet occurred that any one has seen a phantom the indications of the bodily presence or representation of which, until that moment, he had never known. Thus, in the Middle Ages, the spectres of African negroes were common enough, but no man ever witnessed one of an American Indian, yet these, in their turn, prevailed after the voy- age of Columbus. They were no strangers to the early colonial settlers. The same may be said of all kinds of inanimate objects. As illustrating the manner in which impressions of the past may emersre from the registering ffanelia, I shall here farnish an Illustration of. & ....f" ^ ° ^ , the emergence instance which borders closely upon the supernatural, and ofoldimpres- f^jj-iy represents the most marvelous of these psychological sions in a rep- j r _ ^ j. ./ o ^ etition of phenomena. It occurred to a physician, who related it m dreams. ^^ hearing to a circle whose conversation had turned on the subject of personal fear. " What you are saying," he remarked, " may be very true, but I can assure you that the sentiment of fear, in its ut- most degree, is much less common than you suppose ; and, though you may be surprised to hear me say it, I know from personal experience that EMERGENCE OF OLD IMPRESSIONS. 409 this is certainly so. When I was live or six years old, I dreamed that I was passing Iby a large pond of water in a very solitary place. On the opposite side of it there stood a great tree, that looked as if it had been struck by lightning ; and in the pond, at another part, an old fallen trunk, on one of the prone limbs of which there was a turtle sunning himself. On a sudden a wind arose, which forced me into the pond, and in my dy- ing struggles to extricate myself from its green and slimy waters, I awoke, trembling witli terror. "About eight years subsequently, while recovering from a nearly fatal attack of scarlet fever, this dream presented itself to me, identical in all respects, again. Even up to this time I do not think I had ever seen a living tortoise or turtle, but I indistinctly remembered there was the picture of one in tlie first spelling-book that had been given me. Per- haps, on account of my critical condition, this second dream impressed me more dreadfully than the hrst. " A dozen years more elapsed. I had become a physician, and was now actively pm'suing my professional duties in one of the Southern states. It so fell out that one July afternoon I had to take a long and wearisome ride on horseback. It was Sunday, and extremely hot ; the path was solitary, and not a house for miles. The forest had that in- tense silence which is so characteristic of this part of the day ; all the wild animals and birds seemed to have gone to their retreats, to be rid of the heat of the sun. Suddenly, at one point of the road I came upon a great stagnant water-pool, and, casting my eyes across it, there stood a pine-tree blasted by lightning, and on a log that was nearly even with the surface, a turtle was basking in the sun. The dream of my infancy was upon me ; the bridle fell from my hands ; an unutterable fear over- shadowed me as I slunk away from the accursed place. " Though business occasionally afterward would have drawn me that way, I could not summon the resolution to go, and actually have taken roundabout paths. It seemed to me profoundly amazing that the dream that I had had should, after twenty years, be realized without respect to difference of scenery, or climate, or age. A good clergyman of my ac- quaintance took the opportunity of improving the circumstance to my spiritual advantage ; and in his kind enthusiasm, for he knew that I had more than once been brought to the point of death by such fevers, inter- preted my dream that I should die of marsh miasm. "Most persons have doubtless observed that they suddenly encounter circumstances or events of a trivial nature in their course of life of which they have an indistinct recollection that they have dreamed before. It seemed for a long time to me that this was a case of that kind, and that it might be set down among the mysterious and unaccountable. How wonderful it is that we so often fail to see the simple explanation of 410 IMPRESSIONS AND SENSATIONS EQUALIZED. things, when that explanation is actually intruding itself before us. And so in this case ; it was long before the truth gleamed in upon me, before my reasoning powers shook oiF the delusive impressions of my senses. But it occurred at last ; for I said to myself, Is it more probable that such a mystery is true, or that I have dreamed for the third time that which I had already dreamed of twice before ? Have I really seen the blasted tree and the sunning turtle ? Are a weary ride of fifty miles, the noontide heat, the silence that could almost be felt, no provocatives to a dream ? I have ridden under such circumstances many a nlile, fast asleep, and have awoke and known it ; and so I resolved that if ever circumstances carried me to those parts again, I would satisfy myself as to the matter. "Accordingly, when, after a few years, an incident led me to travel there, I revisited the well-remembered scene. There still was the stag- nant pool, but the blasted pine-tree was gone ; and after I had pushed my horse through the marshy thicket as far as I could force him, and then dismounted, and pursued a close investigation on foot in every di- rection round the spot, I was clearly convinced that no pine-tree had ever grown there ; not a stump, nor any token of its remains, could be seen ; and so now I have concluded that, at the gliinpse of the water, with the readiness of those who are falling asleep, I had adopted an external fact into a dream ; that it had aroused the trains of thought which, in former years, had occupied me ; and that, in fine, the mystery was all a delusion, and that I had been frightened with less than a shadow." The instructive story of this physician teaches us how readily, and yet how impressively, the remains of old ideas may be recalled ; how they may, as it were, be projected into the space beyond us, and take a posi- tion among existing realities. That such images arise from a physical impression, which has formerly been made in the registering ganglia, it is impossible to doubt, and that for their emergence from their dormant state it is necessary that there should be a dulling or blunting of con- Equalization of temporaneous sensations, so that these latent relics may old impressions present themselves with a relatively equal force. This and new sensa- ,.. n t • • c ii- • -i tions necessary equalization ot the intensity oi an old impression with a for visions. present sensation may be brought about in two different ways : 1st. By diminishing the force of present sensations, as when we Modes of ac- are in a reverie, or have fallen asleep, or by breathing vapors that^e'^ua"^ unsuited for the support of respiration ; 2d. By increasing the zation. activity of those parts of the brain in which the old impres- sions are stored up. On each of these a few remarks may be made. Cerebral vision depends on an equalization in intensity between pres- ent sensations and old impressions. So long as the former predominate in power, the latter excite no attention or are wholly overlooked. This EMERGENCE OF OLD IMPRESSIONS. 411 condition is illustrated by such facts as that the flame of illustrations of a candle, held against the sun, is utterly overpowered and ""P""essions o . . . overpowering imperceptible, but is seen of its proper brightness when it each other, is in presence only of another flame like itself; or as the stars, which are concealed by day, are plain enough when the sun sets. Ancient im- pressions, harbored in the optic thalami, can not make themselves felt against sensations just establishing themselves ; for as, when we have looked at a bright window and then closed our eyes, the retinal phantom we see becomes paler and paler, and after a while dies out, so do cerebral images undergo a diminution of intensity with lapse of time, though it may be questioned whether they ever entirely wear out. The law which obtains in our economy for other organs of sense applies in these cases too. Even in contemporaneously-occurring sensations, unless there is something like an equality between them, the weaker makes no im- pression upon us. In the presence of a bright light, a less brilliant one can not be seen ; a feeble sound is made inaudible by an intensely loud one ; minute variations of temperature become imperceptible when we are submitted to a great heat or cold. Ideas are no more than the ves- tiges of what were once sensations, and are subjected to the same phys- ical law. For them to become embodied, and to cheat the mind into a belief of their re-existence, equivalent in all regards to outward and actu- ally-existing things, the impressions of these latter must be diminished in their power, or the vigor of the former must be re-enforced. So, when we are passing away in sleep, the organs of sense no longer convey their special impressions with the clearness and force -^ „ •' y ^ _ liimergence of that they did in our waking hours, and this gives to the de- old impressions caying traces which are stored in the registering ganglia the ^" ^ ^^^' power of drawing upon themselves the attention of the mind. So, likewise, in the delirium of fevers, the spectral phantoms which trouble the sick are first seen when the apartment is dark- „ „ i^ _ Emergence of ened and kept silent, and especially when the patient closes old impressions his eyes. Until the senses are more completely overwhelm- of fevers^ anTin ed, these shadows will disappear on brightly illuminating the article of the room or on opening the eyes. And so, too, in the hour of death, when outer things are losing their force upon the dim eye, and dull ear, and worn-out body, images that have reference to the manner of our past life emerge ; the innocent and good being attended in their solemn journey by visions in unison with their prior actions and thoughts, the evil with scenes of terror and despair ; and it is right that it should be so. The enfeebling of sensations which we are in the act of receiving from external sources, so as to bring them on an equality with those which have been long ago impressed, not only occurs in the condition 412 ACTION OF PROTOXIDE OF NITEOGEN. Emergence of of sleep, and in the article of death, but may, in a temporary byartffidal°'^^ manner, be established by resorting to certain physical means. agents and drugs. Pressure upon the brain, either accident- ally or purposely applied, is well known to produce such a result, and, in like manner, the inhalation of various agents, such as pure hydrogen gas, the vapor of ether or cliloroform, or other non-supporters of respira- tion. On breathing these substances, anassthesia is soon induced; the external world disappears ; and, on carrying forward the operation to its due extent, the mind and the brain are literally left to themselves. Opium acts in like manner, more particularly in the case of those who have ac- customed themselves to its undue use. It, however, not only blunts the force of new impressions, but exerts a positive agency in intensifying the decaying remains of old ones. Under its full influence, the true re- lations of space and of time disappear: a century of events is lived through in a single night ; the vision can comprehend distances ap- proaching to the infinite ; and yet, under these circumstances, the mind does not perceive a riot of incongruous combinations, but every thing is presented in a methodical and orderly way — pictures, all the parts of which are in just proportions and severe keeping to each other, and long sequences of events which maintain a mutual harmony. But, as I have just remarked, the equalization of new sensations with Artificial!}- in- ^^^ impressions, which is necessary for phantom appearances, creased func- ^j^d the incarnation and outward localization of ideas — that tional activity . ,,.. iiti-i- of the brain in- IS, Cerebral vision — may take place by heightening or re-en- creases them, foi-cing the old impressions, as well as by diminishing the intensity of the new sensations ; and as in the former case, so in this, the result can be reached in many different ways. Whatever will cause in- creased functional activity of the cerebral structure may recall these old images in force. It is almost unnecessary to allude to the delirium which attends inflammatory states of the brain. Artificial experiments are more instructive. For the purpose of increasing the functional activity of the cerebral Case of protox- Structure, protoxide of nitrogen, by reason of its greater solu- ide of nitrogen, bility in the blood, exceeds in power even oxygen gas itself. This substance, when respired, at once awakens long trains of vivid ideas, the recollection of all kinds of former scenes. Its action is divisible into two periods, the first corresponding to the heightened sensibility arising from the increased oxidation it is establishing in the economy, the sec- ond to the depression which soon comes on through the consequent ac- cumulation of carbonic acid, and which the lungs and skin are miable with sufficient quickness to remove. Su* H. Davy, who first recognized its physiological power, has given us a graphic description of these ef- fects. He says, "A thrilling, extending from the chest to the extremi- EEGISTEEED IMPRESSIONS. 413 ties, was almost immediately produced. I felt a sense of tangible exten- sion, highly pleasurable, in every limb. My visible impressions were dazzling and apparently magnified. I heard distinctly every sound in the room, and was perfectly aware of my situation. By degrees, as the pleasurable sensation increased, I lost all connection with external things ; trains of vivid visible images rapidly passed through my mind, and were connected with words in such a manner as to produce sensa- tions perfectly novel. I existed in a world of newly-connected and newly-modified ideas. When I was awakened from this semi-delirious trance by Dr. Kinglake, who took the bag from my mouth, indignation and pride were the first feelings produced by the sight of the persons about me. My emotions were enthusiastic and sublime, and for a mo- ment I walked round the room perfectly regardless of what was said to me. As I recovered my former state of mind, I felt an inclination to communicate the discoveries I had made during the experiment. I en- deavored to recall the ideas ; they were feeble and indistinct. One rec- ollection of terms, however, presented itself, and Avith the most intense belief and prophetic manner I exclaimed to Dr. Kinglake, ' Nothing ex- ists but thoughts ; the universe is composed of impressions, ideas, pleas- ures, and pains.'" In like manner, the intoxication that arises from alcohol has two dis- tinct stages, depending on entirely different phases of its chemical action. At first there is an exaltation of effects, because of the increased function- al activity established ; but this, after a time, is succeeded by a dullness, or even stupefaction, attributable to the impression which the carbonic acid arising from the oxidation of the alcohol is making upon the nerv- ous centres. By two different methods, therefore, ancient impressions Two methods of may be equalized, as respects intensity, with new sensations, equalization of The vigor of the former may be increased, or the effect of and existing the latter diminished. sensations. Equalized in any way in their force, the mind is ready to confound its own ideas and external forms together. A cause which, perhaps, might seem to be trivial, fastens the attention, and at once a solitary form, or even the machinery of a long drama, emerges. It is no more possible for us to say why the thought runs in one course rather than another, and lays hold of image after image in succession, than we can foretell the way of a spark that moves darkling on the ashes of a piece of burned pa- per. Yet it too runs in connected lines. No better evidence can be given that the images we are speaking of are impressions of past events registered in the brain, and which gain the power of drawing upon themselves the attention of the mind, either by their assuming an unwonted intensity, or by the diminution of the in- 414 EEGISTERED IMPEESSIONS. _ . „ , fluence of newly-arrivina: sensations, than the philosophical Proof of the ex- , . , , i i i r xi, i, istence of im- observations which have been made by some ot those wno pressions in the j^^^^ ^^^^^ liable to thcse infirmities on their own cases. registering gan- i • i glia and their Thus, in such a casc recorded in Nicholson's Philosophical emergence. j^^^^^al, and alluded to bj Dr. Hibbert: "I had a visit," said the patient, "from Dr. C , to whom, among other remarks, I ob- served that I then enjoyed the satisfaction of having cultivated my mor- al habits, and particularly in having always endeavored to avoid being the slave of fear. ' I tliink,' said I, 'that this is the breaking up of the system, and that it is now in progress to speedy destruction. In this state, when the senses have become confused, and no longer tell me the truth, they stiU present me with pleasing fictions, and my sufferings arc mitigated by that calmness which allows me to find amusement in what are probably the concluding scenes of life.' I give these self-congratula- tions without scruple, more particularly because they led to an observa- tion of fact which deserves notice. When the doctor left me, my relax- ed attention turned to the phantasms, and some time afterward, instead of a pleasing face, a visage of extreme rage appeared, which presented a gun at me, and made me start ; but it remained the usual time, and then gradually faded away. This immediately showed me the probability of some connection between my thoughts and these images, for I ascribed the angry phantasm to the general reflection I had fornied in conversa- tion with Dr. C . I recollected some disquisitions of Locke, in his treatise on the Conduct of the Mind, where he endeavors to account for the appearance of faces to persons of nervous habits. It seemed to me as if faces in all their modifications, being so associated with our recol- lections of the affections of passions, would be most likely to offer them- selves in delirium ; but I now thought it probable that other objects could be seen, if previously meditated upon. With this motive it was that I reflected upon landscapes and scenes of architectural grandeur while the faces were flashing before me, and after a considerable interval of time, of which I can form no precise judgment, a rural scene of hills, valleys, and fields appeared before me, which was succeeded by another and another in ceaseless succession, the manner and times of their respect- ive appearance, duration, and vanishing being not sensibly different from that of the faces. All the scenes were calm and still, without any strong light or glare, and delightfully calculated to inspire notions of retirement, of tranquillity, and happy meditation." The same writer adds in anoth- er place, " The figures returned, but now they consisted either of books, or parchments, or papers containing printed matter. I do not know whether I read any of them, but am at present inclined to think that they were not either distinctly legible, or did not remain a sufficient time be- fore they vanished. I was now so well aware of the connection of thought USE OF INVERSE VISION. 415 with their appearances, that, by fixing my mind on the consideration of manuscript instead of printed type, the paper appeared, after a time, only with manuscript writing ; and afterward, by the same process, instead of being erect, they were all inverted, or appeared upside down." We can not fail to remark the close resemblance between these illu- sions, arising from a fixed meditation on recollected scenery, ^jj^temai loc l and the phantoms which are witnessed after our gaze has ization of phan- been steadily directed to some brightly-illuminated object, ^^™^' as a window, when we first awake. In both there is the same subdued and uncertain brilliancy of etfect ; in both the same gradual fading away ; in both the mind does not refer the image it contemplates to an inward point or place, but sets it forth outwardly, projecting it into the empty or occupied region beyond. In inverse as in ordinary vision, the law of the line of visible direction is enforced, and this reference of cerebral im- ages to a definite point in outer space is a phenomenon of the same kind as the appearance of the invisible coin on pouring water into a basin, the lifting of ships into the air by atmospheric refraction, the appearance of the sun and moon every day above the horizon before they have actu- ally risen and after they have set, and many other optical illusions that mio-ht be mentioned. o Physiology, though full of teleological illustrations — that is, examples of the use of means for the accomplishment of an end — has „, ^ _ _ _ Ihe nervous none more worthy of our consideration than this of inverse mechanism con- vision. ]\Ien in every part of the world, even among na- d\catrthe°im- tions the most abject and barbarous, have an abiding faith mortality of the not only in the existence of a spirit that animates us, but also in its immortality. Of these there are multitudes who have been shut out fifom all communion with civilized countries, who have never been enlightened by revelation, and who are mentally incapable of rea- soning out for themselves arguments in support of those great truths. Under such cu'cumstances, it is not very likely that the uncertainties of tradition derived from remote ages could be any guide to them, for tra- ditions soon disappear except they be connected with the wants of daily life. Can there be, in a philosophical view, any thing more interesting than the manner in which these defects have been provided for, by im- planting in the very organization of every man the means of constantly admonishing him of these facts, of recalling them with an unexpected vividness before Kim, even after they have become so faint as almost to die out? Let him be as debased and benighted a savage as he may, shut out from all communion with races whom Providence has placed in happier circumstances, he has still the same organization, and is liable to the same physiological incidents as ourselves. Like us, he sees in his visions the fading forms of landscapes, which are, perhaps, connected with 416 USE OF INVEESE VISION. some of his most grateful recollections ; and what other conclusion can he possibly derive from these unreal pictures tlian that they are the fore- shadowings of another land beyond that in which his lot is cast ? Like us, he is visited at intervals by the resemblances of those whom he has loved or hated while they were alive ; nor can he ever be so brutalized as not to discern in such manifestations suggestions which to him are in- controvertible proofs of the existence and immortality of the soul. Even in the most refined social conditions we are never able to shake off the impression of these occurrences, and are perpetually drawing from them the same conclusions as did our uncivilized ancestors. Our more ele- vated condition of life in no respect relieves us from the inevitable con- sequences of our own organization any more than it relieves us from in- firmities and disease. In these respects, all over the globe, we are on an equality. Savage or civilized, we carry about within us a mechanism in- tended to present us with mementoes of the most solemn facts with which we can be concerned, and the voice of history tells us that it has ever been true to its design. It wants only moments of repose or of sickness, when the influence of external things is diminished, to come into full play, and these are precisely the moments when we are best prepared for the truths it is going to suggest. Such a mechanism is in keeping with the man- ner in which the course of nature is fulfilled, and bears in its very style the impress of invariability of action. It is no respecter of persons. It neither permits the haughtiest to be free from the monitions, nor leaves the humblest without the consolation of a knowledge of another life. Liable to no mischances, open to no opportunities of being tampered with by the designing or interested, requiring no extraneous human agency for its effect, but always present with each man, wherever he may go, it marvelously extracts from vestiges of the impressions of the past over- whelming proofs of the reality of the future, and, gathering its power from what would seem to be a most unlikely source, it insensibly leads us, no matter who or where we may be, to a profound belief in the immortal and imperishable, from phantoms which have scarcely made their appear- ance before they are ready to vanish away. It is scarcely necessary for me to do more than barely refer to the as- sertions of those who would have it believed that they look upon all these appearances as fictions and deliberate impostures. What is to be- come of all history if such a doctrine could be maintained ? Human ev- idence must be regarded as utterly worthless. Moreover, no one denies the existence of dreams, and the phenomena we have been here treating of are philosophically of the same order. OF TOUCH. 417 CHAPTER XXII. OF TOUCH, AXD THE DETERMINATION OF PRESSUEES ANT) TEMPERA- TURES. Functions of the tactile Meclianism : its Structure. — Regions of different Sensitiveness. — Compar- ative Physiology of Touch. — Estimate of physical Qualities. Perception of Temperature. — Subjective Sensations of Temperature. The tactile organ is the skin, or some part, modification, or append- age of it. The general functions of the skm have been al- Functions of ready described. It remains to speak of it in connection with mechanism the sense of touch. An impression has long prevailed among physiologists that this sense should be considered as offering several subdivisions. Thus, for in- stance, we have a consciousness of the general condition of the muscular system — muscular sense, as it might be termed — and this, in some cases, is exquisitely perfect, as may be gathered from what has been said re- garding the tensor tympani and stapedius muscles in the chapter on hearing. Distinct from this is our appreciation of pain or pleasure, and so also om- estimation of temperatures. Adelon has indeed maintained that the cognizance of temperatures is the primary or chief function of this sense. It will be sufficient, however, for our purpose, leaving out these minor subdivisions, to du-ect our attention to the more important, and to consider the tactile organ as devoted to two uses : 1st, the appre- ciation of pressures ; 2d, of temperatui-es. Pressures doubtless act upon the skin in a purely mechanical way ; temperatures operate by inducing a variation in the rate of waste and nutrition. At a certain point, even this distmction ceases, for pressures, when they reach a sufficient intensi- ty, interfere with the supply of arterial blood or the removal of venous-, and thereby change the rate of nutrition and waste, acting, as far as this goes, m a manner not unlike that of the variations of temperature. In man, the skin possesses tactility to a different degree in different regions. On the tips of the fingers and on the lips the sen- j^go-ionai dif. sory perception is most acute, while it is at a minimum on ference in tac- the trunk and thigh. In other mammals, which are covered ^ ^ ' with hair or wool, the sense of touch is much more restricted. Its proper organ is to be regarded as arising from a concentration of general sensibility of the skin upon a special construction, the papillary body, as it is termed. The organs of vision and hearing consist essentially o£ Dd 418 THE ORGAN OF TOUCH. two portions, a receiving and a nervous, the former being constructed on the principles of optics in the one case, and of acoustics in tiic other. A simihir doublcness of structure may be recognized in the instance now before us, though with a difference of effect, for in those cases the outer or receiving organ is for the purpose of more powerfully concentrating the influence received, but in touch it is the reverse. The office of the cuticle, which covers over the true skin, is to render it less sensitive to external impressions, and for this reason, therefore, it varies in thick- ness in different regions, being less developed on those portions that ai-e more particularly devoted to tactile sensibility. Considering the hand, Structure of or- o^"' perhaps, more correctly, the tips of the fingers, as being gari of touch, chiefly devoted to the purposes of touch, no construction could be conceived of better adapted to that end. Placed at the extrem- ity of the arm, a lever which is jointed at its middle, the elbow, and the fore part of which has a motion of partial rotation, pronation, and supina- tion upon its own axis, the hand being carried so that its palm presents upward or downward, or in any of the intermediate positions included in the half-circular motion — jointed again by the bones of the wrist, so as to obtain a hinge-like movement, the hand may be flexed or extended almost 180 degrees upon the forearm. Its bony structure, subdivided into suitable pieces, is clothed with a multitude of muscles or their ten- dons. In the fingers and thumb the structure breaks up into five sep- arate pieces, possessed of an incredible firmness when we consider the numberless motions which can be accomplished. The position and ar- ticulation of the thumb, which enables it to set itself in opposition to the other four digits, a feature which constitutes a hand, properly speak- ing, gives the power of gi-asping things perfectly, and makes the Avhole organ a perfect mechanism of prehension. The papillary structure, de- veloped in its utmost refinement on the tips of the fingers, and fortified behind by the nails, which present moderate resistance to pressures, com- pletes this contrivance, which, from its perfect adaptation to the uses to which it is devoted, its power, its delicacy, and the infinite movements which it can accomplish, is not surpassed as an example of the adapta- tion of means for the accomplishment of an end by any other structure of the body. There have been authors who have asserted that the su- periority of man over other animals may be entirely accounted for by his possession of a hand — a statement which, though it can not be main- tained in its generality, is yet a very good proof of the appreciation in which this wonderful instrument is held by those who have studied its construction and functions most closely. Between the indications that have to be dealt with by the hand as an organ of touch, and those dealt with by the eye and ear, there is an essential difference. The eye, for example, receives the pictures of ex- EXAMINATION OF SOLIDITY. 419 ternal objects upon a surface, but the hand cxarnines the so- p,,jj„^i„j^^j lidity of bodies, "^riie fovnicr is occupied with knigth and of solidity by breadth ; the latter witli all three dimensions, length, breadth, ^'"^ ''""^• and thickness conjointly. Our notions of solidity are to no little extent obtained in this way, as was proved in the case of Ghesclden's patient, who had been blind from birth, and to whom vision was given hy a suc- cessful operation for cataract, and still more recently by a similar case of Franz. In this instance, "a solid cube and a sphere, each of four inches diameter, were placed before the patient, at the distance of three feet, and on a level with the eye. After attentively examining these bodies, he said he saw a quadrangular and a circular figure, and, after some consideration, he pronounced the one a square and the other a disk. His eye being then closed, the cube was taken away, and a disk of equal size substituted, and placed next to the sphere. On again opening his eye, he observed no difference in these objects, but regarded them both as disks. The solid cube was now placed in a somewhat oblique posi- tion before the eye, and, close beside it, a figure cut out of pasteboard, representing a plain outline prospect of the cube when in this position : both objects he took to be somewhat like a flat quadi;ate. A pyramid placed before him, with one of its sides turned toward his eye, he saw as a plain triangle. This object was now turned a little, so as to present two of its sides to view, but rather more of one side than of the other : after considering and examining it for a long time, he said that this was a very extraordinary figure ; it was neither a triangle, nor a quadrangle, nor a circle — he had no idea of it, and could not describe it : 'in fact,' said he, ' I must give it up.' An example of the close association which exists between the sense of touch and that of sight, in enabling the mind to form a correct idea of an object, is afforded in the statement of this patient, that, although by the sense of sight he could detect a difference in the cube and sphere, and perceive that they were not drawings, yet he could not form from them the idea of a square and a disk until he perceived a sensation of what he saw in the points of his fingers as if he really touched the objects. When he took the sphere, cube, and pyra- mid into his hand, he was astonished that he had not recognized them as such by sight, being well acquainted with them by touch." The mechanism for touch, as distinguished from the general dermoid sensibility, is the papillaj, which may be described as conical §^^^^^^^3 ^j eminences on the cutis, at once solid and flexible, sometimes papiiias of clavate in form, and sometimes having numerous points. They are about the -j^ of an inch in height, and the -gfo of an inch in diam- eter at their base, these dimensions varying, however, very greatly with the situation. They contain a loop of blood-vessels and a twig of a sensory nerve, for all the centripetal nerves, with the exception of those 420 THE PACINIAN BODIES. devoted to the special senses, may Ibe regarded as concerned in this func- tion. The papilla3 contain an elastic substance — axile body, as it is term- ed — which serves to heighten the sense, and the yielding structure of the skin aids in the same effect. The papilla are covered over with the cuti- cle, through which, therefore, all -P'i'- 204. action on them must take place, i — m,' m/A Fin ens Simple papiUc?, magnified ^5 diameters. Couii i i uiieteis. Fig. 203 (Todd and Bowman) represents simple papilla? of the palm, the cuticle having been detached. Fig. 204 (KoUiker), compound papil- lae, with two, three, or four points : a, base of a papilla ; h, b, h, separate processes; c, c, c, processes of papilla? whose bases are not visible. The mode in which the nerve fibre terminates in the papilla is as yet The Pacinian doubtful, some asserting that it is arranged as a returning bodies. loop, and some that it is by a pointed extremity. This lat- ter mode is thought to be illustrated by the structure of the bodies term- ed Pacinian, which are ovoid in form, ^^ fo -^Ig- of an inch in length, -^ to JL in breadth, and attached by a pedicle to many of the cerebro-spinal and sympathetic nerve branches. Each consists of many concentric membranous layers, arranged like the coats of an onion, the interior ones closer than the exterior. They have a central cavity, distended by a fluid, which also intervenes between the coats. Across this cavity, and occupying exactly its axis, a nerve fibre, which has cast off its white sheath, passes, terminating at the other end either in branches or a knob. The use of these bodies is wholly unknown, and even their structure is doubtful, the existence of the central liquid referred to being denied by some anatomists. . The sensitiveness of a part is in proportion to the number of papilla m, V if contains. Tables have been constructed setting forth the The sensitive- _ ... ness of dififer- relations of different regions, as determined by placing a pair ent regions. ^^ compasses, the points of which were covered with cork, on the parts to be tried, the eyes being shut, and closing the compasses un- til the pieces of cork could no longer be distinguished as separate. It appears that this will take place on the tip of the tongue when the points are the -^ of an inch apart ; on the tip of the third phalanx, at the ^ of an inch ; on the lips, the one sixth of an inch ; tip of the great toe, half an inch ; the lower part of the occiput, 1 inch ; and on the middle of the thigh, 2^ inches. No part of the skin is entirely devoid of sensitiveness, as Kolliker has NERVES OF THE PAPILLAE. 421 shown by exmninations with a fine needle. At first he ^ .1 1 1 1 1 ,■ 1 1 T • 1 •. • . Every part of thought he Jiad loiincl some places whien were quite insensi- the skin is sen- bk^ while in others the sKghtest touch produced sensation ; ®''^^"^°' but on carrying the investigation farther, it appeared that the very same phxce was sometimes sensible and sometimes not, so that finally he came to the conclusion that the very smallest portions of the skin are sensi- tive. But since, even in the palm of the hand, the papillas containing nerves are widely dispersed, and. in other places occur but rarely, or even not at all, he infers that it is necessary to assume the existence of non-medullated fibres in all the papilla, or to have recourse to the nerv- ous plexus at their base, since he believes it is not possible to demon- strate nerves in every one of those bodies. The nerves supplying the papillae may perhaps be said, to ascend through the cutis, continually branching, and forming eventu- papiUary ally terminal plexuses. The primitive tubules themselves di- nerves. viding at an acute angle into two, and. entering the papillse, they are united at their extremities in a loop. Of course, this construction in- volves the fact that they have freed themselves from the white substance of Schwann. The impression made on these exposed nervous fibrils is by many regarded as of a purely mechanical kind. They may be affect- ed not merely by vertical pressures, but likewise by those exerted in the direction of the plane of the skin, and this accounts for tactile sensation on portions of that surface which are either sparsely or not at all sup- plied with nerve fibrils. To this effect the miyielding and horny texture of the cuticle doubtless contributes. No papillffi are found in invertebrate animals. Among vertebrates they are variously disposed. In lizards they occur under xouch in other the toes ; in the chameleon, and some of the ant-eaters, which vertebrates. use their tails for tactile purposes, they are found upon that organ. In the spring season of the year they are temporarily developed on the thumb of the frog. Among birds they are found upon the toes, or, if web-foot- ed, upon the web ; in the mole on the tip of the snout. In the tapir and elephant they occur upon the trunk ; among the quadrumana, on the hands and feet, and in some also upon the tail. The whiskers of the cat, the rat, the rabbit, may be regarded as appendages to the tactile organs, enabling them to find their way through narrow passages in the dark. Among articulata the antennas have doubtless, with their other functions, a similar use. Men who have become blind often guide their steps by means of a stick, judging from the sensations which its contact with sur- rounding bodies imparts to the hand : it is in all respects a temporary antenna. Our estimates of the hardness and softness, roughness and smoothness of bodies, is primarily dependent on indications derived from the sense 422 FEELING AND TOUCHING. Estimate of of touch. We should make a distinction, however, with physical quaii- Magcndie, between feeling and touching, the former being essentially passive, the latter active ; and though we usu- twee'n fedhio-^' ^^^Y suppose that, of all our senses, touch is the most reli- and touciiing. able, it often conveys to the mind illusory impressions, as, for instance, in the well-known experiment of Aristotle, when the tips of the fingers are crossed over each other, and a pea rolled beneath them, it seems as if there were two peas, one under each finger. The indications of touch are generally more correct than those of feeling. Thus, if we close our eyes, and another person moves the tip of our finger over an unknown surface, he can completely deceive us by duly varying the press- ure, and make us believe that it is concave or convex, whereas it may be flat ; but if we pass our fingers over the surface ourselves, we very quick- ly come to a true conclusion, because now we are conscious of the exer- tion of muscular power ; and from what has been said respecting hearing, we may infer how delicate our estimate of muscular exertion is. The former is therefore an example of feeling, the latter of touch. Connected with this distinction are the singular phenomena of tick- lino- ; the reo-ions most readily aifected by this are those of low °' tactile sensibility. A person can not tickle himself, though it is said that cases are upon record in which one has been tickled to death by another. As in the other cases, the mind can direct attention exclu- sively, for the time being, to some one indication of touch, which, though it may be apparently insignificant in itself, becomes, after a while, per- fectly intolerable, as the pressure of a hair, a gentle draught, or the fall- Remains of im- iiig of water, drop by drop, on the top of the head ; and, as pressions. with them, an impression which is made does not instanta- neously disappear, but will sometimes continue for quite a considerable time. A ring or other article that has been long worn will leave a sen- sation, though it may have been removed. Besides afibrding an estimate of external pressures, the sensory organ enables us to discover variations of temperature. It may therefore be thus effected by bodies upon contact or by bodies at a distance ; and Perception of though wc usually confound the two indications together, temperature there is, in reality, a distinction between them ; thus, in cer- that of press- tain conditions of paralysis, the indications of the contact of ^^^- bodies may remain, but those of heat and cold may have to- tally disappeared. On examining a surface from which the skin has been removed, it does not appear capable of distinguishing hot from cold bodies, but only communicates to the mind an indefinite sensation of Ideas of heat pain ; nor can we create sensations of heat or cold by any ir- and cold can j.^^atiQ^ of the ncrvcs. The measure of temperature by the not arise arti- , ^ i i ficiaiiy. agency of the skin is very far from being exact, as has been OF SMELLING. 423 proved by the simple experiment of dipping the finger into veiy warm water, and then the whole hand into water many degrees cooler. The increased extent of surface seems to overcompensate for the ^^ , , 11- Deceptions of lower temperature, and we come to the erroneous conclusion the sense of that the cooler specimen is the warmer of the two samples, touch. As sounds may be heard which have no reality, but merely originate in the brain, or spectral illusions may be seen, so the sense Subjective sen- of touch is subject to similar hallucinations, as a sensation nations of touch ■^ _ _ ' and tempera- of pressure or weight, or the crawling of insects on the skin ; ture. and though we can not, by artificial irritation of the nerves, give rise to impressions of heat and cold, those effects very frequently occur in this interior or subjective way. CHAPTER XXIII. OF SMELLING, AKD THE MEANS OF DISTINGUISHmG GASEOUS AKD VA- POROUS SUBSTANCES. Structure of the Organ of Smell. — Its proper Instrument the First Pair of Nerves. — Limited Rbt- gion of Smell. — Conditions of its perfect Action. — Duration of Odors. — Tlieir Localization. — Subjective Odors. By the sense of smell we are able to distinguish many gaseous and vaporous substances from one another. They enter the nos- „ ^ ■,-, . . . '' Sense of smell trils with the respiratory current, and are brought in con- for gases and tact with the olfactory or Schneiderian membrane. Though "^'^P°^^- received at first in the elastic state, they become dissolved in the mucus which moistens that membrane. It does not follow, however, that all vaporous substances give rise to the perception of an odor ; for example, water itself communicates no sensation whatever. Again, there are other bodies, as, for instance, musk, which yield an odor far more Delicacy of this powerful than corresponds to their loss of weight. Thus it perception. is said that that substance may be exposed for years in an apartment, dif- fusing all the time its penetrating emanations, and yet not becoming lighter. Such statements are, however, on their face, exaggerations. There can be no doubt that the olfactory organs detect extremely minute portions of matter. In most cases, elevation of the temperature of a body increases its odorous effect. The primary uses of the function of smell are for a discrimination of the qualities of food, or its condition, and also for enabling an animal with greater facility to provide itself with supplies. Hence the development of this structure takes place in the utmost per- fection among the carnivora, which often depend almost exclusively upon 424 THE OLFACTORY ORGAN. this faculty for the pursuit of their prey. But even in the herbivora it is well marked, and furnishes them, though less exactly, similar indica- tions. In man, though this sense is less acutely developed, it applies itself to a greater variety of objects, and doubtless enables him to appre- ciate differences among odors in a more correct manner than in the case of the lower animals. The general principle involved in the construction of the organ of smell is to expose an extensive and constantly moistened surface Mechanism of ^ . ■ '' the olfactory to the air brought ni by the respiratory current. Ot course, '""S^"' other things being equal, the larger the surface, the more per- fect the sense. The object of gaining a great extent of superficial ex- posure under a relatively small volume is accomplished by spreading the sensitive mucous membrane on projections or shelves, which also serve the purpose of intercepting the incoming current of air. It is in reptiles and birds that turbinated processes first make their appearance. In air-breathing animals, the organ of smell is essentially an appendix to the respiratory mechanism, its action depending entirely upon the' play thereof. But, though the material submitted to the olfactory mem- brane in this manner is presented in the vaporous or gaseous state, it is intermediately dissolved, as has been stated, in the liquid mucus which covers that membrane, before it can affect the ramifications of the olfac- tory nerve. The nose, thus constituting the commencement of the respiratory tract, forms a characteristic feature of the countenance. It is composed in part of bones and in part of cartilages, covered over with muscles and integument. Its five cartilages give to it shape in its inferior portion, and, by their elasticity, enable it to resist external injury. The whole surface of the nasal cavities is covered over with mucous membrane, to which the names of pituitary or Schneiderian membrane have been given. This mucous membrane likewise extends into the maxillary antrum, ethnoid, and sphenoid cells, or sinuses which are adjacent, and open into the same nasal cavity. The Schneiderian membrane is highly vascular, and receives its nervous supply from the nasal branches of the fifth pair, which give it common sensibility, but its olfactory function de- Fin. 205. Fie;. 206. pcuds On the distribution which a certain portion of it receives from the first, or olfactory nerve. Fig. 205 illustrates the distribu- tion of the olfactory nerve on the septum of the nose. Fig. 206 is its distribution on the outer wall of the nasal fossa. That the function of the first pair of nerves is olfactory is proved by THE OLFACTORY NERVES. 425 many facts. Animals in wliicli these nerves liave been di- ^ ,. •11 rt- 1 1 i> 1-1 Function of the vided are no longer aiiected by odors oi any kind, and, gen- first pair of erally speaking, the greater the development of these nerves, ^'^^''^^^^■ the acuter is the sense of smell. In persons in whom this sense has been defective or totally absent, or in those who have been troubled with unpleasant odors of a subjective kind, post-mortem examinations have shown a corresponding absence or lesion of these nerves. In man, the proper olfactory organ is formed by the distribution of the olfactory, or first pair of nerves, on the mucous membrane which covers the upper part of the nose, the internal set of filaments being disposed on that of the septum, the external on that of the superior and middle spongy bones. The membrane is very vascular, and covered with a thick, pulpy epitlielium. The filaments distributed to it have lost the white substance of Schwann. It is those parts alone to w^hich these filaments are distributed which possess the sense of smell, the adjacent cavities, as, for example, the frontal sinuses, not participating in the function, as has been proved by the injecting of the vapor of camphor or other odo- riferotis bodies into them. It seems to be necessary for the vaporous or o-aseous substances to be dissolved in the moisture which covers the ol- o factory membrane in order to their exerting a proper effect. If, by chance, the membrane is too dry, the sense of smell is temporarily lost, and the same likewise occurs if it be unusually moist. From the mode of distribution of the olfactory nerve, it follows that the sense of smellino- is restricted to the upper portion of t- • ^ o _ . Limited region the nasal cavity ; and, for this reason, when we desire to de- for the sense of tect odors with unusual precision, the air is drawn violently ^™^ " into that region by sniffing. On the contrary, we avoid the perception of odors by breathing through the mouth, or, as the common pond'ti f phrase is, by holding the nose. Since the perfection of the its perfect ac- sense requires that the olfactory surface shall neither be too dry nor too cold, an advantage is gained by placing it high in the cav- ity, w^here it is free from the disturbing effects of the dry air introduced by inspiration, which becomes moistened and warm before it reaches the place of action. Just as we make a distinction between a musical sound and a noise, so should we distinguish between an odor and such impres- Distmction be- sions as arise from tickling, pressures, the use of snuff, mus- tween odors ,1 1 xT.j-i'xi X •• and irritation. tard, pepper, and pungent bodies, for tliese act as mere irri- tants, and many of them can produce analogous effects on other portions of the surface of the skin. Odors do not give rise to the impressions of pain, and, indeed, the nervous mechanism having charge of the action is totally different in the two cases. Odors operate, as we have said, upon the olfactory nerve, but these other impressions are made upon the nasal 426 DURATION AND LOCALIZATION OP ODOES. supplies from the fifth pair. The upper part of the nasal cavity is there- fore devoted to the proper sense of smell, the lower portion to general sensation. In one respect there is a striking difference betAveen this sense and Duration of vision and hearing. We can perceive many luminous im- odors. pressions at the same time, or hear many sounds in rapid suc- cession ; but not so with odors. We can smell only one thing at a time, or, at all events, the impression remains long upon the olfactory appara- tus, perliaps because the odoriferous substance remains dissolved in the attached moisture. The identification of substances by their odor nec- essarily implies a resort to recollection or memory, and sometimes we have to apply the fragrant object again and again to the nose, before we can recall with satisfactory precision its name. In the lower animals the sense of smell is probably localized in some parts of the skin ; many of them display instincts which seem Comparative ^ . ■"■ anatomy of to imply the posscssion of such a sense. Insects also, by ^^^^^' smell, are often led to their food or to one another. The variable current of air introduced by respiration compensates in some degree for the want of mobility of the nose, which may be regard- ed, in air-breathing vertebrated animals, as consisting of a diverticulum from the respiratory passages. In fishes, however, the olfactory cavity is not connected with the respiratory passages : there are no posterior nares. The circumstance of their living under water disables them from appreci- ating the odorous peculiarities of gases and vapors. In the whale the or- gan is altogether absent, being replaced by the mechanism for receiving air and blowing out water. In other tribes the acuteness of the spnse is in proportion to the development of the olfactory ganglia : in reptiles it is feeble ; in birds, more developed ; in carnivorous animals, still more. But here again it exhibits a special restriction, since there is reason for supposing that carnivorous animals are insensible to the perfume of flow- ers, while herbivorous ones distinguish them perfectly. In man, as we have said, the sense is less developed, but it has a wider range. The localization of odors is effected in a much less perfect manner than Localization '^^i© localization of sounds. The principle by which it is ac- of odors. complished is obviously that of detennining the direction of maximum intensity, and this involves necessarily the constant exercise of memory and comparison. The surprising manner in which this can be accomplished by animals whose sense of smell is acute, as, for exam- ple, by the dog, is extremely interesting. From the different manner in which various odors affect different individuals, there is no general stand- ard of comparison to which they may be referred, as there is in the case of colors and of sound. Scents which may be highly disagreeable to one are acceptable to another person. By constant exposure, the faculty may OF TASTE. 427 become so benumbed as to be unable to distinguish some altogether. Thus Turner found "that the flower of the iris persica was ,^ . '■ Various efFects pronouneed of pleasant odor by forty-one out of fifty-four of odorous im- persons, by four to have little scent, and by one to be ill- P'''^^*'^"®- scented. Of thirty persons, twenty-three held the anemone nemorosa agreeable in its perfume, and seven did not think that it snielled at all." Diseases of the central organs will sometimes give rise to the percep- tion of subjective odors, just as they do to spectral illusions or Subjective sounds in the ears. odors. CHAPTER XXIV. OE TASTE. Conditions Jo?' Taste. — Sti'ucture and Functions of the Tongue. — Tactile and Gustative Regions of the Tongue. — Complementary/ Tastes. — Subjective Tastes. Though the function is participated in by other portions of the oral cavity, the tongue is to be regarded as the organ of taste. Conditions for The physical conditions under which savors are perceived is *^®'^^- that the substance shall be presented in solution in water, or, at all events, in the saliva. From vision, hearing, and smell, the sense of taste differs in the circumstance that it requires the contact of the acting body; and, to a certain extent, the same distinction which has been made re- garding such substances as can act on the olfactory mechanism might also be made here ; that is to say, that there are two classes of agents which affect the organ — those which produce a mere pungent sensation, and those which excite savors, properly speaking, for tlie irritations and former will frequently give rise to specific action when ap- savors. plied to other portions of the surface of the skin. Sensations of taste are very frequently conjoined with olfactory per- ceptions, so that we mistake the one for the other. There Connection of are many substances, reputed to have a powerful flavor, ce^TionTami" which become tasteless when the nose is held ; and this re- tastes. mark applies more particularly to such as are at the same time volatile and soluble in water. However, irrespectively of this, some of those bodies which produce the most intense and permanent impression on the organs of taste do so merely in virtue of their solubility, as, for exam- ple, quinine, which is a non-volatile body. The intensity of such action depends on the duration of contact and the degree of exposure of the substance to the tongue, so that the papillas may, as it were, become thoroughly permeated. 428 PAPILLA OF THE TONGUE. The idea of taste may arise irrespectively of the presence of any actual substance. A shari) blow will produce it, as also the passage ent on acci- of a feeble voltaic current. It was, indeed, m this way that dental agents, ^j^^ ^^,^^ observation in galvanic electricity was made. A narrow jet of air directed upon the tongue causes a taste resembling that of saltpetre. If the tongue be dry and parched, its power of discrim- inating tastes is greatly enfeebled, and the same thing takes place if its temperature is very much changed, either by elevation or depression, as by keeping it for a short time in contact with hot or very cold water. The action of the tongue, as the organ of taste, depends upon the pa- „ pillse which are on its surface. These structures give to the Structure of -f^ . rm the papiiiiE of upper portion of the tongue its rough appearance, ihey are taste. of three kinds: 1st. The conical papillae, which are the most numerous ; 2d. The circiimvallate papillas, which are situate near the base of the organ, and which are from ^ to ^ of an inch in diameter, with a crater-like depression, roimd the edge of which is a groove, and again a circular elevation ; 3d. The fungiform papilla, which are chiefly on the sides and tip, their shape being conical, the narrow end of the cone being downward. The epithelium of the tongue is less dense over the fungiform papilla, and hence their projecting appearance : it is more dense over the conical papillae, and projects from them in processes which pre- sent an aspect like that of haii's. Some of them contain hair-tubes. Besides these, the surface of the tongue presents a papillary structure resembling that of the skin — secondary papillge, as they are termed. It is supposed that the conical papillfe are cliiefly organs of prehension ; the others are organs of taste, but that function is participated in by other portions of the surface of the mouth, as, for example, the soft palate, its arches, and the tonsils. F'ig. 207 represents the surface of the tongue and the adjacent parts : a, a, lingual papillas ; b, b, circumvallate papil- lge, disposed along two converging lines form- ing the lingual V ; c, foramen coecum ; d, d, fungiform papilla ; e, e, filiform papillas ; /, fra?num epiglottidis ; g, epiglottis ; h, anterior pillar of velum ; i, stylo-glossus ; I, isthmus of the fauces ; m, uvula ; n, velum pendulum palati ; o, hard palate ; J9, raphe ; q, q, orifices of the excretory ducts of the palatine glands ; ?', palatine glands, the mucous membrane be- ing removed ; s, palatine glandules ; t, mu- cous membrane covering the same glands ; u, palatine tubercle ; v, v, section of the lower The tongue. J^^' NERVES Of the tongue. 429 The organ of taste is placed at the comnienccnient of the digestive ca- nal ; hence the characters of substances may be examined uses of the with deliberation while they are yet under the control of the s^"s<2 of taste. will, for when once a body has entered the oesophagus it is swallowed in- voluntarily. The tongue, therefore, gives warning of the presence of del- eterious substances, and in no small degree excites the appetite by receiv- ing the impression of pleasant flavors. The essential condition under which it acts is a moist state of its surface, for the dry tongue, though it enjoys common sensibility, after the manner of any portion of the exter- nal teg-ument, does not enjoy taste. One of the duties of the salivary glands is incidentally to maintain this moistened condition. To a cer- tain degree, taste may be regarded as a refinement on touch. It differs from vision and hearing in the peculiarity that there is no sin- Serves of the gle nerve of special sense individually devoted to it, for the tongue. front of the tongue is supplied by the lingual branch of the fifth pair, and the back by the glosso-pharyngeal. Its entire nervous supply is derived from four different sources : the lingual, the hypoglossal, the glosso-pharyngeal, and the sympathetic, representing therefore special sensibility, muscular motion, common sensibility, and sympathetic rela- tion. That the hypoglossal is the nerve of motion, or muscular nerve, is proved beyond doubt by its section, after which the motions of the tongue are destroyed, but taste and touch remain. The individual duty dis- charged by the glosso-pharyngeal, and the lingual branch of the fifth pair respectively, is not so clearly determined. Section of the former is at- tended with loss of taste, though it is not yet proved that there is a loss of all kinds of taste. If the lingual branch of the fifth be divided, com- mon sensation at the tip of the tongue is destroyed, and there is evidence that with this the appreciation of certain tastes disappears. The glosso- pharjmgeal is distributed to the circumvallate papilla, and it is said that in some birds the lingual is suppressed. Upon the whole, therefore, it may be concluded that these nerves are conjointly engaged in the sense of taste, the glosso-pharyngeal being engaged with those flavors which affect the back part of the tongue, the lingual with those which affect the tip. Illustrations of the distribution of the hypoglossal nerve have already been given in its description, under the title of the twelfth pair. The surface of the tongue presents the tactile and gustative powers in an inverse manner. Examined by the method described in Tactile and the chapter on touch, the compasses must be opened to a great l^onf of^the' extent, as we pass from the tip toward the back of the tongue, tongue. in order that a double impression may be perceived. This condition ap- pears to be in accordance with the requirements of the organ, common tactile sensibility being most necessary at its outer extremity, and this 430 COMPLEMENTARY AND SUBJECTIVE TASTES. gradually passing off into the refinement of taste. The action of any- given substance may be increased by motion and pressure, as when it is rolled over the tongue, or held thereby. Its sense of discrimination may be rendered more acute by education. As with the organs of the other senses, so with this, an impression Duration of niade upon it does not instantaneously cease, but remains for tastes. a certain period of time, indeed, in this instance longer than in those. Hence many substances acting in rapid succession give rise to a confused effect, though it is said that, out of such interminglings, an accomplished epicure can fasten his attention on one, and continue to recognize it just as we recognize and follow the sound of one instrument in an orchestra. No explanation has as yet been given of the manner of action of different tastes, though it is asserted that some act upon one, and some upon another set of the papillas. After-tastes are also observed. Complement- which are occasionally of a complementary kind, as, for in- ary tastes. stance, the intensely bitter taste of tannin is followed by a sweetness. These after eflfecis modify the taste of substances which may be taken while they last. They therefore form an ample subject for the profound contemplation of the epicure, and should occupy the serious at- tention of the cook. They may be illustrated in a general manner by the injurious effect of sweet substances upon the flavor of delicate wines. It has been mentioned that the passage of a voltaic current through ^n^ ,. ■ ^ i tlic touffuc causcs an alkaline or acid taste. Some experi- Electncal and o _ -i subjective menters deny the correctness of this statement, and assert tastes. ^j^^^ ^i^g impression is merely metallic. The effect, however, depends upon the intensity of the current employed, or on the nature of the pieces of metal used. If the current has power enough to decom- pose the salts of the saliva, acid or alkaline tastes will be detected, ac- cording as the direction of the current is made to vary, and the acid or alkaline body is disengaged on the upper or under side of the tongue. Subjective tastes arise in diseases of the nervous centres, but these are often rendered obscure by the exudations and furred condition of the tongue. Dogs, into the blood-vessels of Avhich milk has been injected, have been observed to lick their lips ; and from this it has been inferred that the presence of substances artificially introduced into the circulato- ry current may be detected by the organ of taste. ANIMAL MOTION. 431 CHAPTER XXV. OF ANBIAL MOTION. Ciliary and Muscular Motion. — Description of Cilia and the Manner of Action. Muscular Fibre : its Forms, Non-striated and Striated. — Muscle Juice. — Manner of Contraction, of a Muscle: its supply of Blood-vessels and Nerves. — Its Chemical Change during Activity. — Its Rise of Temperature. — Effect of Electrical Currents. — Uuration of Contractility. Doctrine that Muscle Contraction is the residt of Muscle Disintegration. — Manner in which ordi- nary Cohesion is brought into play. — Manner of Restoration. — Removal of the Heat and Oxi- dized Bodies. Rigor Mortis. — Connection of Muscle for Locomotion. — Of Standing. — Walking. — Running. It was formerly" held that animals are distmguished from plants by the possession of the power of locomotion, a doctrine which . . , ^ '- TIT Animal motion. can now no longer be regarded as true. It was also be- lieved that the muscular movements of animals are due to the influence of the nerves, and that a muscular fibre contracts only when stimulated to do so by a nerve. This makes the possession of a nervous system essential to the motions of animals. These doctrines also are erroneous. Animal motion is of two different kinds : 1st. It is accomplished by vibrating cilia ; 2d. By the contraction of cells arranged in the form of a fibre. OP CILIARY MOTION. The epithelial cells of the cylindrical and of the tesselated kind are occasionally arranged with delicate projecting strias on their Description of firee extremities. The length of these varies from the -q-^-q cilia and their to the -^Q^QQ of an inch. Tliese stria are termed cilia, and the cells are said to be ciliated. Examples are presented by the mucous p. 2og membrane of the respiratory surface and of the nasal cavities ; an illustration is given in Fig. 208. The cilia may be regarded as prolongations of the cell wall itself. They exhibit a vibrating motion back and forth, which recalls the movements of stalks of grain ■ " '' n ■■ ' in a field as the wind is passing over it, the ears bend- Caiated cells. . -, -. . . ..,, ■, ■, mg down and rising again m the breeze, and throwing the whole surface into waves. The cilia also exhibit a movement like that known as the feathering of an oar, or sometimes as turning round upon the point of attachment, as upon a centre, giving rise to a sort of conical motion, the free end describing a circle. These motions seem to 432 CILIARY MOTION. be perfectly involuntary, for they not only take place long after death, but even in detached portions, the ciliary cell being uninjured and entire. The seats of ciliary action are always moistened surfaces. The condi- tion for the continuance of the motion after death is accordingly that the surface shall be kept moist, but it is also necessary that a certain tem- perature should be observed, which in warm-blooded animals must not fall below 42° F. Even after the motion has completely ceased, a solu- tion of carbonate of potash re-excites it, but this does not take place with ammonia, because it injures the ciliated cells. Ciliary motion is independent of nervous agency. The control of tem- perature and of chemical reagents over it shows that it is of a physical nature. In the lower orders of life ciliary movement is relied on both for the tises of ciliary purposes of locomotion and prehension. Fii eoo motiou. jrig^ 209 illustrates this in the case of a vorticella, the upper edge of which shows such a ^ mechanism. It is often stated that in the higher an- imals the object is to determine a movement of the liquid which moistens the ciliated cells in the direc- tion of the outlet of the tube, or other siirface which they line. In this way the action of the cilia may tend to the expulsion of material from the air-cells of the lungs into the bronchial tubes. In reptiles, whose urinary tubelets are furnished with this mech- anism, the secretion may be urged thereby in the proper direction. The contractile tissue which enables such animals as the hydra {Fig. „ , . 210") to execute movements of prehension and locomotion Embryonic / ^ contractile tis- may perhaps be regarded as the rudimentary state of the ^^^' structures next to be described. The annexed sketch, from Fig. 210. Trembley, illustrates the manner of progression of this animal. No trace of a proper muscular fibre, and none of a nervous Hydra walking. systcm, liavc hithcrto been detected in it. Ciliated animalcule. Of Muscular Motion. The muscular system consists of muscular fibres, tendons, bones, to- gether with various accessory parts, such as ligaments, sheaths, bursas mucosEe, synovial capsules, fascia. Its action depends on the primary fact that, under appropriate influences, muscular fibre shortens. Each voluntary muscle consists of a collection of fasciculi, which ex- MUSCULAR FASCICT^LI AND FIBRILS. 43a Fig. 211, Libit the cliaracteristic appearanc(: of transverse striation, as in tlie F>(l. 212. lluuuin surunluiiiiiia. Firy. 213. feiSsiH:^': Striated muscular fasciculi, maguified 1-5 diameters. Sarcolemma of fish. photograph of muscular structure of the frog {JPtg. 211). voluntary mus- The primary fascicuH are collected into larger bundles, cuiar fasciculi, secondary muscular fasciculi, held together by connective tissue, and these, again, into still larger, the tertiary. The primitive fasciculus is enveloped in a delicate sheath, the sarco- lemma, as shown in Fig. 212, in* which the fasciculus, though torn across, is held together by the sarcolemma. The specimen is from the human muscle. Fig. 213 is a good representation of the same fact. It is given by Todd and Bowman from the skate. The sarcolemma is a delicate membrane, which, though of great tenuity in man, may be made visible by the action of acetic acid or alkalies. Within the sarcolemma the primitive fasciculus is seen to be composed of many parallel fibrils, which may, by maceration or chemical agents, be separated from one an- other. These fibrils present a beaded aspect, and, since their constituent elements are arranged side by side in parallel planes, they ultimate mus- give to the fasciculus the appearance of striation it presents, ^"^^i" fibril. The longitudinal striation of the fas- ciculus arises from the fibrils them- selves. Here and there, in the inte- rior of the sarcolemma, nuclei occur ir- regularly, and with them fat granules. The fibrils, with the fat and a liquid, fill the sarcolemma, without leaving any central canal or hollow axis. Fig. 214 is a photograph of ulti- mate muscular fibre of the pig, from one of Mr.Lealand's preparations. The rectangular form of the constituent cells is well seen at a, «, a. At h,. E F. Fin. 214. Ultimate muscular fibre, maguified 200 diameters 434 MUSCLE JUICE. probably by reason of a twist, tension, or undue strain, a spiral appear- ance is presented ; c, c are the primitive fasciculi. A fluid surrounds the fibres of striped muscles, and the fibre cells of smooth ones, which is wholly different from the plasma of juice, ^j^^ blood. The experiments of Schultz show that this fluid contains a large amount of casein, a conclusion of considerable import- ance, since, if there were any doubt of the occurrence of that substance in the blood, this fact, at all events, renders it certain that the mammary gland is not necessary to its formation. That the substance thus occur- ring is casein is proved by the action of rennet. Muscle juice undoubtedly arises within the sarcolemma through which it exudes. Each fibre therefore presents four objects : the syntonin, the nucleus, the sarcolemma, and the muscle juice. That the muscle juice arises in part from the functional activity of the fibre, and is immediate- ly derived from the waste of its syntonin, and that, in its tm^n, the syn- tonin is closely allied to the substance of the nucleus, is shown by their exhibiting almost the same chemical reactions with alkalies, acids, etc. The sarcolemma is not, however, filled with syntonin; it contains be- sides, as stated above, a certain quantity of fat, as may be demonstrated by removing from the sarcolemma its syntonin by acids, when a granu- lar material will be left. That this is fat is proved by its solubility in sulphuric ether. The sarcolemma does not belong to the protein class of bodies, but is Sarcolem- rather analogous to elastic tissue. The color of muscle appears '^^- to be not so much due to the blood as to a special pigment, which, perhaps, adheres in a free state to the fibrils. The muscle juice contains relatively far more potash salts and phosphates than the blood, as is shown by the following table from Liebig. For one hundred parts of soda there occur, In the hen, 40.8 of potash in the blood, and 381 in the muscle juice. " ox, 5.9 '^ " " 27a " " horse, 9.5 " " " 285 " " fox, — " '• " 214 " " " pike, — " " " 497 " '' It is commonly stated that muscular motion is accomplished by fibres Two forms of ^f two different kinds: 1st. The simple, non-striated, un- muscular striped, or organic fibre ; 2d. The striated, striped, or volun- striated and ta^J fibre just described. Though this subdivision may be striated. convenient, it can scarcely be regarded as accurate, since the former variety passes by insensible degi'ees during development into the latter, and cases, indeed, are not wanting in which the same fasciculus presents in different parts both conditions at once. The non-striated muscular fibre, J^/^. 215, consists of translucent bands FORMS OF MUSCLE. 435 of a soft granular material, varying from the 2u\) o ^^ 5 o^o ^^ ^" ^"^^^ ^^ Fig. 215. Fig. 21 G. Fig. 21T. Muscle cells, 350 dia- meters. Unstriped fibres. Unstriped fibres in acetic acid. breadth, and exhibiting here and there the traces of Non-stria- nuclei, particularly after the fibre has been acted on by ^^^ ^^'■^• acetic acid, as is shown in Fig. 216. Each fibre may be re- garded as an arrangement of nucleated cells, the nucleus be- ing of a cylindroid or spindle form. The contractile content within is syntonin. Non-striated fibre is not usually attach- ed to fixed points, as to bone, but by being collected into par- allel bundles, different bundles interlacing with one another, contractile planes or surfaces are formed, such as the cylindri- cal coat of muscular structure of the digestive tube, or the contractile layer of the urinary bladder. Similar fibres, im- bedded in the skin and connective tissues, communicate to '''' them the quality of corrugation or contractility. The fascic- uli are bathed externally with an acid juice, characterized by con- taining salts of potash, phosphoric acid, creatine, and inosite. The general appearance of fibre cells of this class is given \nFig. 217: a is from the small intestine of man ; h, from the fibrous invest- ment of the spleen of the dog. (Kolliker.) Contractile fibre cells present the following reactions : Acetic acid causes the fibre to swell, and makes the nucleus more Contractile visible; it occasions a complete dissolution when in a fii^re-ceUs. concentrated state. Diliite hydrochloric acts in a similar manner, the effect in this instance being the same with the fibres of both smooth and striped muscle. The examinations thus far made have shown no difference in ultimate composition between these forms. The striated muscular fibre consists therefore of fasciculi, with an elastic investment of sarcolemma, collected into bundles, striated and invested with perimysium. The contractile constituent ^^^^- 436 STRUCTURE OF MUSCLE. is syntonin ; and tlioiigli the general rule is that the primitive bundles shall run isolatedly and parallel to each other, in certain cases they anas- tomose, Fig. 60. In its ultimate construction, the form of fibre may be regarded as consisting of a series of cells, as shown in Fig. 214, the di- ameter of which varies according to the actual condition of the muscle, whether it is in the contracted or relaxed state, but which may be taken, on an average, at the -^- q ^ q ^ of an inch. The cells are placed end to end, the boundary walls upon the end presenting the appearance of a delicate transverse line. Each cell consists of two portions, a central spot and a pellucid border. The pellucid border is considered by Dr. Carpenter, whose views of muscular structure we are here presenting, to be the cell wall, the central space being the cavity of the cell filled with some highly refracting substance. Dr. Carpenter speaks of the central spot as dark ; an inspection of the photograph. Fig. 214, proves that it may be light if exactly in focus. When the fibril is in a relaxed state the longest axis of each cell coincides with the length of the fibril, but when contraction occurs this axis shortens, and a shortening of the entire fibril is the re- sult. A number of these fibrils, placed side by side, constitute a fascicu- lus ; indeed, there may be many hundreds of them thus bound together. When such a fasciculus is forcibly ruptured it presents diflferent appear- ances, according as the ends or sides of its constituent cells have cohered most strongly together. If the lateral cohesion is weakest, the fascicu- lus tears into its constituent fibrils, as was shown in Fig. 214, but if the end cohesion is the weakest, it will tear into discs or plates, as in Fig. Fig. 218. 218. The fasciculus is thus a bundle of fibrils, its diameter varying very greatly, and being, in man, from the y^ 5 to the g-^ of an inch ; in females it is, on an average, smaller. Each fibril is a linear series of coalesced cells. The cells, as they form the fibril, lose their rounded and assume a rectan- gular appearance, as shown at a, a, Fig. 214. It therefore appears that each fibril must have its own investing sheath, the representative of the walls of the little cells which have coalesced, and this, though not usually admitted by anatomists, ap- pears plainly in the photograph from which that figure is taken. In length, muscular fasciculi vary from the sixth of an inch to two feet. The larger animals furnish some that are even much longer. The nor- mal form is doubtless cylindrical, but this is constantly departed from, each accommodating itself to the pressure of the adjacent ones. The sarcolemma serves as a partition between its included fibrils and the cap- illary blood-vessels and nerves, which imbed themselves in the rounded angular spaces between adjacent bundles. The cross section of a por- tion of muscle shows the manner in which the sarcolemma and the fibres Muscular fasciculi torn in discs. STRUCTURE OF MUSCLE. 437 are arranged. Fig. 219 is from the human biceps, and Fig. 220 from Fici. 210. r / -yv. Tians\cise section of muscle of teal a Transverse section of human muscle. .4i;' ;>'u" Muscular fos- the pectoral ^^^[ cicuii. muscle of the "^j^ teaL Since it is in the ffv^:^ interspaces between the \fS4-i rounded fasciculi that ""-hy^ the blood-vessels lie, the tissue is more vascular as its fasciculi are of less diameter. It has already been stated, in connection with Fig. 211, that the stri- ated form of muscular fibre derived its name from the circumstance that, when examined by a sufficiently high power, it appears to be crossed by delicate transverse lines, the longitudinal separations between the fibrils being also visible. This is seen in the specimen of insect muscle repre- sented in the photograph, Fig. 221, and under a still higher magnifying Fiq. 221. Fig. 22?. Non-fibrillated insect fasciculi, magnified 200 diameters. Non-fibrillated insect fasciculi, magnified 50 diameters. power in that of Fig. 222. The dis- tance between the transverse strias va- ries with the condition of the muscle, but on an average it is represented as being about the -g-oVo °^ ^^ inch. Many more stri« are crowded together when contraction takes place, and they retire from each other as soon as relaxation occurs. It is said that the voluntary muscles contain in their muscle juice more acid than is enough to neutralize all the alkali of the blood. The electro-chemical relations of this interfascicular 438 MANNER OF MUSCULAR CONTRACTION. acid juice and the alkaline plasma of the blood are doubtless the cause of the production of those electric currents which have been demonstrated in the muscles. It does not follow, therefore,, that these currents occur in the natural state : they may be the result of the experimental arrange- ment for their own detection, since it has long been known that an acid and an alkaline juice, separated from each other by a conducting organic body, will form an effective voltaic circle. Of the contractile element of muscular fibre, syntonin, it may be re- marked that it can be dissolved by the aid of dilute hydrochlo- jn omn. ^.^ ^cid, and that it differs from fibrin of blood not only in that respect, but also both in its ultimate composition and physical and chem- ical qualities. In certain cases it seems to degenerate into fatty sub- stance. In the growth of a muscle, the constituent fibrils increase in number and in length, their diameter remaining, however, nearly the same as in the early periods of life. The thickening of a muscle is, therefore, not so much due to the thickening of its constituent fibrils as to their increase of number. The contraction of a muscular fibre does not take place throughout its whole leno;th at once ; it generally begins at the end, a change Manner of con- o 'o jo o traction of a of aspcct arising from the approach of the opaque centres of muscle. ^YiQ cells to One another, and this occurring simultaneously across the whole fibre. This approach may, however, ensue in different parts of the length at the same time, the sarcolemma being raised up in bulla? as the contraction takes place. This effect is shown in Fig. 223, Fig. 223. Contracting muscle of Uytiscus. in which the thickened portion of the contracted middle space of the mus- cle is surrounded with the sarcolera- Fiq. 224. mic bullae. The same is demon- strated in J^ig. 224, which repre- sents the border of a muscular fas- ciculus in a young crab, with a spot of contraction, and the sarcolemma elevated along the edge. In these cases the contraction is brought on by the action of water, which, in some measure, may exaggerate or disturb the phenomena. -Fiff. 225 exhibits, under the same circumstances, a fasciculus from the eel, a being the uncontracted, b the contracted part, on the edge of which the sarco- Sarcolemma raised in bull*. ATTACHMENT OF MUSCLE TO BONE. 439 Fig. 225. Fasciculus coutractiut: lemma is again raised up. The two latter illustrations are from Todd and Bowman. Different portions of the length of the iibre assume this condition at dif- ferent moments, and hence the Avhole structure is thrown into a form which The zigzag appearance pointed out by circumstance that when relaxa- into the not brought at once recalls the motion of a worm. Prevost and Dumas arises from the tion of the Iibre occurs all its parts same state, but while some are contracted others are in the opposite con- dition. A muscle, during its contraction, appears to have nearly the same solid dimensioiis which it had during its relaxation. This has led to the deceptive conclusion that whatever it has lost in length it has gained in thickness. There must, however, be a diminution correspond- ing to the recognized amount of waste, for it is well known that destruc- tion of a portion of its tissue is the essential condition of the activity of a muscle. The various degrees of energy with which the contraction takes place at different times is to be explained not so much by the more or less energetic shortening of the cells as by the varying number of fibres which are simultaneously contracting, or by the different frac- tional portion of each which is going into action at once. As the mus- cular effect is more energetic, so will the sense of fatigue be more speedy, for while one fibre is acting another is resting, and the same remark ap- plies to different parts of even the same fibre. It is to this reciproca- tion of motion that the solind usually emitted while the muscle is in ac- tion, a low ringing sound, is to be attributed. Striated muscle is often attached to bone, or other substance on which it has to exert its mechanical power, by intervening fibrous -^i^^^^^ attach tissue constituting tendon. These fibres are collected in ed to bone by groups, so as to present primary, secondary, and tertiary fas- ciculi. The tendinous fibres are brought in relation with the sarcolem- ma, and thus form a sheath connected with adjacent ones by other de- tached fibres. These may be considered as converging from all parts of the muscle to its extremities, and thus giving rise to its tendon. In some instances the muscular fibres attach them- selves to the side of the tendon, which does not then undergo subdivision. From the peculiar structure of muscular tis- sue, the capillary vessels which are distributed to it must run in a direction for the most part parallel to its fibres, as in I^ig. 226. Their Distribution of muscular capillaries, mode of branching, transvcrsc and longitudinal, Fig. 226. 440 DISTEIBUTION OF VESSELS AXD NERVES. is shown in Fig. 227, a Ijeing the arteiy, h the T.. , ., ,. f vein, (?, capillary plexus. Each ar- Distnbulion of ' ' r J I blood-vessels to tei'ial branch has usually two vena3 •1 "^"^'^ ^' comitcs, and the supply of these capillaries has a general correspondence to the number of fibrils. The lymphatics are not nu- merous. Vascular distribution to the tendons is much more sparing. By the muscular blood- vessels a triple function has to be discharged: they furnish oxidized blood, on which the action of the muscle depends ; they remove the waste which arises as the consequence of that activity ; they also repair that waste by presenting the elements of nutrition. The younger Liebig has demonstrated that a muscle can not contract ex- cept it be furnished with oxygen, and that, as long as the capacity for contraction continues, it absorbs oxygen and yields carbonic acid. In the same general manner that the blood- vessels are distributed, so likewise are the • An example of this is seenin J^i^. 228. the sarcolemma, / nerves. IMusciilar arteries and veins. They never penetrate Distribution of ^ , ;,, nerves to mus- but run in close jl;"-^^ ^ *^' contiguity with ^ ^ it, their distribution to dif- ferent parts of the fasciculi being very unequal, some parts being quite scantily fur- nished, the nerve filaments coming in contact, as it were, at occasional points. The opinion is generally maintain- ed among physiologists that the nerves present toward their extremities a looped arrangement, as shown in Fig. 228, but by some it is asserted that the termination is in an extremely delicate point, or bifid, or trifid, without exhibiting any return. Of the two forms of muscular tissue, the striated is, for the most part, supplied from the cere- bro-spmal system, the non-striated from the sympathetic. The manner of development of muscular fasciculus seems to be, that Development the sarcolcmma is first produced as a thin and delicate tube of muscle. i^y j-j^^g coalesccnce of cells arranged linearly, the walls of which, where they come in contact at the ends, are obliterated, giving origin to Distribution ui mubculdr nerves COMPOSITION OF IVIUSCLE. 441 an elongated band. A granular material then oecnpies the interior of the tube. Mewing the sarcolemma as the sum of the coalesced cell walls, the fibrils are to be regarded as a development from the granular cell con- tents. They form, by a sort of endogenous process, from without to within. The nuclei, as has already been remarked, are on the inner sur- face of the sarcolemma, and not within the cells. The structure is not evident until after the end of the second month of foetal life, but by the fourth month it has so much advanced that the muscle assumes a pale red aspect; the tendons, which have already begun to be distinctly dif- ferentiated, are gray. At birth the structure has become so far com- pleted that the fibres can be isolated. The condition which the non- striated fibre presents is, therefore, that beyond which the striated fibre has passed, and in this respect the former may be regarded as an embry- onic state of the latter. In some insect muscles an instructive interme- diate condition is seen; fibres may be found striated toward the middle, and non-striated at the ends, as though imperfectly developed. The thoracic muscles of insects, which offer a beautiful example of muscular structure, are not, hoAvever, to be regarded as presenting primitive fibrils, but rather non-fibrillated primitive bundles. This I consider to be the case with the specimens from which the photographs, Figs. 221, 222, were taken. Though not so apparent, nuclei exist in the striated fibre even of adult life, and discharge an active function. At this period, the increase of thickness of the muscles is to be attributed to an increase in the number of the contained fibrils, which individually have about the same dimensions as before birth. Composition of Ox Muscle. Herzelius. Braconnot. Marchand. Water 771.70 ' 770.30 766.00 Fibrin, cells, vessels, and nerves... 177.00 181.80 180.00 Albumen and htemato-Eclobulin ... 22.00 27.00 25.00 Alcohol extract and salts 18.00 19.40 17.00 Water extract and salts 10.50 ; 11.50 11.00 Phosphates of lime and albumen.. 00.80 1.00 1000.00 1010.00 1000.00 Composition of IJuman Muscle. Marc li and. L'Heritier. 771.00 158.00 : 34.00 1 12.00 1 25.00 ; 780.00 170.00 23.00 16.00 10.00 1.00 JMatter insoluble in cold water Soluble albumen and coloring matter.... Alcohol extract with salts .• Water extract with salts Phosphate of lime with albumen...,, 1000.00 1 1000.00 1 The result of the chemical change which muscular fibre undergoes dur- ing the periods of its activity is eventually manifested by the Chemical appearance of carbonic acid and urea, and also salts of sulphuric ^^^"fcti^l"^" acid, the two latter escaping from the system through the uri- of muscle. ' 442 FUNCTION OP MUSCULAR FIBEE. nary apparatus ; the former, in part, through the kings. That these prod- ucts are to be attributed to muscular waste is inferred from their in- crease or diminution with increases or diminutions of muscular exertion. In the voluntary fibres there is commonly a necessity for repose, during which repair of the waste is taking place ; but in those organs which are in ceaseless action, as the heart and diaphragm, the repair or nutri- tion goes forward at an equal rate with the waste, and no period of rest is required. It necessarily happens, during the destruction of this tis- _. „^ sue by the arterial blood, that a rise of temperature must Rise of temper- «/ _ ' ^ ature in mus- ensue, and such a rise has been actually observed to the cuiar action. ^^Q^^t of a degree or more, notwithstanding the constant tendency to the removal of the heat by the constant current of venous blood flowing from the muscle. There is no necessity to attribute the elevation of temperature to friction among muscular fibres, and, indeed, the amount that could arise in that way must be very insignificant, and not to be for a moment compared with that due to the oxidation. Even in muscles which have been removed from the body, and made to con- tract by the aid of magneto-electric currents, changes of composition may be detected. OF THE FUNCTION OF MUSCULAR FIBRE. The mechanical action of muscular fibre depends, as we have seen, on Nature of the shortening of the long axis of the cells of which the fibres contractility, ^re composed. To this result the designation of contractility is given, and the property by which the fibre is enabled to exhibit this shortening is designated, agreeably to the metaphysical system of the old physiologists, who were content to accept a word as an explanation of a fact, by the term irritability ; this, as being useless, may be discarded ; the former we may continue to employ. At one time it was supposed that the contraction of a muscular fibre Contractility depends so completely upon the agency of the nervous system not depend- ^t^^^ ^^ miffht be considered as the direct function thereof; but ent on the o _ nerves. a more critical examination of the circumstances of the short- ening of the fibre cells shows that it possesses many features in common with the same contraction of the cells of plants, which have no nervous system. The influence passing along the nerve fibrils is only one out of many which can cause muscular contraction. There is abundant evi- dence in support of the position that contractility is the result of the structure of the muscular fibre, and that it belongs to it, and is not a spe- cial function of nerves. When muscular fibres are touched by a pointed instrument, they ex- hibit contraction even after they have been detached from the body, pro- vided- that too long a period of time has not elapsed. If it be of the stria- CONTRACTION OF MUSCULAll FIBRE. 443 ted variety, the bundle that has been disturbed alone contracts, ^. , 1 ,. 1 1 . , - 1 1 1 DifTerence in and presently alter relaxes ; but there is no lateral spread or the contiac- dift'usion of the effect to adjacent bundles, except in the case tio"*"f^*"a- '' ' _ ted and non- of the heart, in which it would appear that the contraction of striated mus- one part is diffused laterally, and a single disturbance is fol- ^ ^^' lowed by many alternating contractions and relaxations, simulating, as it were, the normal function of the whole organ. But where the non-stria- ted form is in like manner examined, the contraction takes place more slowly, spreads laterally to a wider extent, and is followed by a relaxa- tion. The effect of an intermitting magneto-electric current is different in the two forms of tissue, the striated contracting and keeping j-^.^^j, ^^ contracted as long as the action is kept up, but the effect ceasing electrical when the current stops. In the non-striated the action is tardy, ^""^"*^- and relaxations may ensue even while the current is passing, and con- tractions contiime to occur after it has stopped. The effect becomes of more interest when a weak, continuous electrical current is passed through the centrifugal nerves supplying any muscle, for then the whole muscle contracts, and remains in that state as long as the current flows. If the current be passed through the ganglionic centre of those nerves contrac- tion again ensues, and is maintained for a time even after the current has ceased. If the current be sent through the centripetal fibre, alternate contractions and relaxations of the muscle are the result. The interpret- ation of these different cases has already been given (p. 276). The capability of contracting continues in muscle fibre for a certain time after death, a period which is shorter as the rate of res- Experiments piration is higher, and hence these effects were first observed °^ Gaivani. by Gaivani and others in the case of the frog and cold-blooded animals. Even after it has disappeared, it may be re-established by t, . , rr ^ ^ J J Experiments continuing the supply of arterial blood, as Dr. Brown-Sequard of Brown-Se- has shown : a fact which illustrates in a striking manner the ^"^^ ' independence of the muscular contraction of the nervous system. Of course, as would have been expected, whatever interferes with due arte- rialization interferes with muscular power. This is the reason of the inability for exertion which is experienced in the thin air of mountain tops, the relaxation of the muscular system in asphyxia, the same con- dition in the respiration of the vapors of ether or of chloroform ; it is also to a great extent the cause of the wayward and staggering gait of the drunkard. The converse of this likewise holds good : the higher the rate of respiration, the more energetic the muscular power ; and therefore, in birds, which respire most perfectly, muscular contractility is exhibited with the greatest energy. The contractility of the muscular tissues, as being independent of the activity of the nervous system, is well illustrated by the remarkable ob- 444 DOCTEINE OF MUSCULAE CONTRACTION. Experiments servations of Dr. Dowler, of New Orleans, on the automatic of Dr. Dowler. niovements that sometimes take place after death Iby yellow fever. After respiration had ceased, each hand in succession was car- ried to the throat, and then to the crown of the head, and so back again to the breast. In another instance, on being stimulated by a blow, the arm was extended upward, and the hand could even be made to slap the mouth ; or when the leg hung down, if the flexors of the hamstring were struck, the heel was drawn upward. These manifestations continued for between three and four hours, and even occurred in amputated limbs. Contractility lasts for a different period, not only in different animals. Duration of ^^^^ even in different parts of the same animal. Thus, in man, contractility, [i declines in the following order : in the left ventricle first, then in the intestines and stomach, the urinary bladder, right ventricle, oesophagus, iris, in the voluntary muscles of the trunk, lower and upper extremities, and, finally, in the left and right auricle of the heart. Assuming that the diameter of each muscular fibre is, on an average. Distance at ^^^^ -^ q ^ q q of an inch, and that each fasciculus is the ^-^ of which a muscle ^^ inch, it may be inferred that each fasciculus contains about may be influ- ^--^ ^^ -nt • i i j i i enced by a ooO fibres. JNow, smce tlie nerves do not penetrate the sar- nerve. colcmnia, the influence which they exhibit must be efficacious at a distance ; and if we take the maximum measurements which have been made of muscular fasciculus, we may safely conclude that that in- fluence extends at least through a distance of -^^ part of an inch. It is not necessary for us, in this place, to enter on a discussion of the ^, , . functions of nerve fibres, whether they exert a magnetic The doctrme . „ ^ , that muscular agency, or act by rise of temperature, or, from an abrupt po- contraction re- j^^, termination deprived of its white substance of Schwann suits irom mus- -t cuiar disinte- permit the cscape of their current into the muscle fibril, and gra ion. tliencc into the corresponding denuded pole of a centripetal nerve beyond, the current being determined through the muscle by rea- son of the better conducting power of that strvicture. The immediate cause of muscular contraction is to be sought for in the muscles them- selves, and this, I think, is much more obvious than is generally sup- posed. So far from there being any thing mysterious or incomprehen- sible about it, as some writers insist, we probably shall not be very far from the truth if we assert that muscular contraction is the necessary physical result of muscular disintegration, and without here consider- ing the various ways by which that muscular disintegration may be brought about, such is the doctrine that I now present. Reviewing the various conditions under which contraction occurs, I re- ^, . sard destructive metamorphosis as the primary and leading Change in mus- & -"^ ^ . ^ cie after con- One. Evcry thing seems to indicate that the contraction of traction. ^ ^^^ ^^^ ^^^ ^^^ ^^^^^ Without the loss of a part of its CHANGE IN MUSCLE BY CONTRACTION. 445 substance, and tliis ensues even in the artilicial motions that are estab- lished by electric currents in amputated muscles, as is satisfactorily shown by the experiments of Ilelmholtz. Of these the following synopsis is given by Dr. Day : "Powerful muscular contractions Avere induced bypassing an electric' current through the amputated leg of a frog as long as convulsions con- tinued to be manifested. The Hesh of both legs was then analyzed. The albumen was apparently scarcely afiected, the mean of six experi- ments giving 210 per 10,000 of albumen in the electrized, and 213 in the non-electrized flesh. With regard to the extractive matters, it ap- peared that in all the experiments, without a single exception, the water extract in the electrized flesh was diminished, while on the other the spirit and alcohol extracts were increased. The results are expressed in the following tables : Change in Miiscle after Electric Contraction. Alcohol extract from 100 parts recent frog's flesh. Exp. a. In electrized portion. | b. In non-electrized portion. 0.752 0.569 0.664 0.652 0.575 0.606 0.427 0.481 0.493 0.433 a: b L24T"r 1.33: 1 1.38:1 1.32:1 1.33:1 - XLiXir d,cieu witu aic jiioi 01 yi, per cent. 6 1.020 1 0.748 1 Spirit extract 1.36:1 Water ext •act. 1 a. 0. a: u ' a. b. 1 a:b 7 1.21 1.63 0.79 : 1 1.69 1.50 • 1.13:1 8 0.93 1.23 0.76 : 1 1.65 1.35 ' 1.22:1 9 0.72 0.90 0.80 : 1 1.76 1.53 i 1.15:1 Mean 0.95 1.25 0.78 : 1 1.70 1.46 1 1.16:1 "■"The amount of fat was unaffected. No urea could be found in the alcohol extract. " There is great difficulty in performing experiments of this nature on warm-blooded animals, in consequence of the rapidity with which iso- lated portions of the muscle lose their contractility. "The best results were obtained with decapitated pigeons : a. In electrized muscle. I Albumen I Water extract j Spirit extract. 2.04 0.64 1.68 b. In nou-electrized muscle. a: b 2.13 0.73 1.58 1.06 " The above facts sufficiently show that muscular action is always ac- companied by a chemical change in the composition of the acting mus- cle." It appears that after electrization the alcohol extract increases be- tween 24 and 38 per cent. ; the water extract diminishes between 24 and 20 per cent. ; the spirit extract increases between 13 and 22 per cent. I therefore regard disintegration of the muscular structure as the prim- itive act, so far as the fibril itself is concerned, and contraction as the 446 IMANNER OF CONTRACTION. Balanced state necessaiy consequeiice, that disintegration being brought of a muscle about bv the oxidizing ao;ency of arterial blood. It must, through waste '' ..?ii- • iii,-j. and repair. hovvever, be bome m mind that this waste is masked by its incessant repair, and that its condition at any moment of its action repre- sents the actual balancing at that instant of the waste and repair re- spectively ; and since the repair does not proceed with the same rapidity as the destruction, it needs must follow that, sooner or later, a point will be arrived at when there is an absolute necessity for repose to give to the renovating processes the opportunity or time for effecting a complete restoration. Accepting, therefore, the fact that a fibre can not contract without loss of its substance, and regarding that loss as the cause and the wS contrac- contraction as the effect, it is plain that whatever influence tion occurs. ^^^ accomplish an oxidation will produce a shortening of the fibre. Perhaps it may be that the nerve tubule does it by occasioning a rise of temperature ; perhaps it may be, if nerves do not end in loops, but in denuded points, by the current escaping into the muscle from those points, and occasioning such an allotropic change in the contents of the muscle cells as enables the blood to destroy them, in the manner set forth in Chapter X. With such theories we need not now embar- rass ourselves, but confine our attention to the result with which we are concerned, that is to say, the destruction of the material contained in the muscle cells, which destruction is practically brought about by the ac- cess of arterial blood. When this takes place, the cell affected under- goes an actual diminution of size, through loss of part of its contained material, its longer axis shortening from no other cause than the cohe- sion of its included granules thus suddenly brought into play. The cell which we have under consideration, like an entire muscular fasciculus, ^ possesses no power of active dilatation, and so remains with- Eestoration of J^ ., . . i t i • m ^ . • j. i the contracted- out change Until it IS Stretched by similar contractions tat- °'^^^' ing place in the components of other and perhaps distant antagonist muscles. Coincident, however, with this destruction of its interior substance, and loss of its prolate form, is the act of repair, the nucleus of the cell reproducing other granules from materials furnished by the blood ; for the arterial capillaries not only bring the means of oxidation, but they bring the plastic elements of nutrition, and so per- mit the cell to recover its dimensions, and to be stretched "to its orig- inal shape by the contraction of antagonist fibres. The destruction was almost instantaneous ; the repair is an affair of a little longer time, and thus, while one part is resting, other portions of the muscular mass take up the action in succession, one after another contracting. Such is the first series of changes ; let us now examine the second. For, as the result of that first stage, there has been a liberation of prod- PRODUCTS OF MUSCULAR WASTE. 447 nets of oxidation, which are eventually to find their way into the urinary secretion, or to escape by the respiratory surfaces. It is immaterial what the first aspect of these substances may be, creatine, urea, extractive, etc. ; this much is absolutely certain, that they are on the downward career, and will end as urea, sulphuric, carbonic acids, etc. The experiments both of Reymond and Liebia; prove that the muscles, when at ^ , . . . IT- 1 • Products of rest, contain no acid juice, and during their activity it is known muscular that the degree of acidity is proportional to the energy with "'^'^^'^^• which they have been contracting. It can not for a moment be sup- posed that this acidity is the cause of the contraction ; on the contrary, it is its result. Among the products arising during muscular action may be more par- ticularly mentioned inosite, or muscle sugar, which is isomeric inosite and with glucose, and creatine, which, though it contains so large creatine. a proportion of nitrogen, must be regarded as a product of the waste go- ing on. By the loss of two atoms of the element of water, it gives origin to creatinine, which is accordingly found in the muscle juice, the blood, and the urine. Indeed, these two substances seem to be inversely pro- portional to each other. The partial oxidation which has given rise to these various products can not occur without an elevation of temperature. A second stage of the process of muscular action consists in the removal of the heat and of the partially oxidized bodies. We have only to look at the minute anatomy of the parts under con- sideration to recognize the manner in which this double re- Removal of the moval is accomplished. The arterial capillaries, when thev ^'f^^*^"*^ "^i- .,.-... ■"■ •' clized bodies by break up for their final distribution, run parallel with the the blood. muscular fibres, as also do the attendant veins. From one to the other, at short intervals, as seen in J^ig. 227, intercommunicating vessels trans- versely pass, the whole being arranged on such a system as to afford the readiest means of removal of the blood as fast as it becomes venous — a facility of removal of the last importance for carrying off the wasted products of oxidation ; and in this manner, those products, whatever they may in the first instance be, find a ready means of escape, and so the muscular fibre by degrees is relieved from these results of fiinctional ac- tivity. As for the heat which has arisen in a secondary way from the meta- morphosis which has been going on in the fibre, that is in like manner extracted. It is difficult to conceive of a more effective method by which the heat could be taken away from the wasted fibre, or indeed we might say" from the interior of the whole mass of the muscle. The current of venous blood bears away with it not only the products that have arisen in the oxidation, but likewise the heat. 448 RHYTHMIC CONTRACTION. It is probable tliat one cause of cessation of muscular contraction in Effect of accu- anj one point of a fibre is the momentary accumulation of '-^teTmate Wasted material, as might be illustrated in a coarse manner rial. bj the difficulty of causing a fire to continue burning when the ashes are permitted to accumulate, and the necessity of their removal before the combustion can go on. Two separate events have to occur before a fibril that has been in contraction is ready to contract again: these are the removal of the oxidized products, and the renovation of the interior of the cells. The two probably go on coincidently, the veins taking one part of the duty, and the arterial capillaries the other. In non-striated muscular fibre, in which the supply of blood-vessels is Peculiarity in niuch less copious, there is a possibility for a lateral propa- of ''non-striated g^tion of effect, because of the possibility of the lateral prop- fibre, agation of the heat, either supplied directly from tlie nerve tubule or arising from the oxidation going on. The sluggishness of its first contraction, the longer continuance, the propagation from fibre to fibre laterally until the effect wears out or is re-enforced by some new stimulus, might almost seem to be the necessary result of the imperfect supply of arterial blood, the sluggish removal of the products of waste, and the more perfect opportunity for the diffusion of heat. This doc- trine therefore meets with a very happy illustration in the phenomenon displayed by the contraction of the two kinds of fibre. It may still farther illustrate these views to examine that other variety Rhythmic con- of contraction, rhythmic in its nature, which is exhibited, for tractions. example, by the heart, of which it may be said that the fibres show a simultaneous contraction alternating with periods of repose, con- traction and relaxation succeeding each other at definite intervals. If, as we have just said, the cessation of contractility arises from the mo- mentary accumulation of products of waste, and the capacity for its re- newal is due to restoration of the original state by nutrition, rhythmic ac- tion may follow as the consequence of an arrangement of muscular fibrils with an adjusted supply of arterial and venous capillaries. An original excitation producing a contraction can not act in a permanent way, for ' the result of that contraction is an accumulation of wasted material which must be removed. It may require but a moment for the removal to take place to a sufficient extent to enable the original disturbance to act once more, and be checked in its action again. Whatever value there may be in such explanations as these, they undoubtedly gather a deep inter- est from thus enabling us to comprehend that it is possible to resolve such mysterious phenomena as rhythmic periodicities into the results of ordinary mechanical laws. But the question returns upon us. Admitting the descriptions that have now been given to be a true representation of the facts, and also of CONTRACTION OF ]\tUSCLE. 449 tlieir natural sequence, what is the actual physical cause of _ 1 1 . . , 1 ,-i -1 o A n 1 1 Possibility of the shortening ot the muscular tibrii i Ali that we have extensivemus- tlius far said can be received at the Ibest as only a statement cuiar contrac- m 11 y^ slight of a succession or order of facts. To say that that shorten- muscular ing is the direct consequence of loss of material involves us "^^^'®- at once in the inquiry whether it be possible, through the destruction of so small an amount of material as we know to occur, that any thing like the required extent of motion could be produced. Could a muscle be made to shorten several inches, and, upon these principles, lose only an insignificant amount of weight, the shortening being nevertheless the, consequence of that loss of weight or destruction of substance ? To an- swer this inquiry, we have, in the first place, to recall the fact that a whole muscle is never in contraction at once, but only an insignificant portion thereof, one bundle of fibrils after another taking up the action in succession, and each particular fibril undergoing change, not throughout its whole length, but only in isolated portions here and there. We have, moreover, to recall the insignificant weight of these fibrils, for a simple computation will show that thirty thousand of them a foot long weigh only a single grain. To these recollections we should add the intense energy of the molecular force of attraction, as displayed at such distances as those which we have here under consideration — distances which we may regard as being virtually inappreciable, and these recollections place the problem in its true light, and set it in its proper attitude before us. For it is capable of demonstration that muscular contraction ensues as the direct consequence of destruction of muscular substance, and that a great linear extent of movement may be accomplished by the removal of an insignificant amount of substance. If 100,000 fibrils lost one third of their entire substance — a thing which, of course, could scarcely take place — the diminution of weight would only amount to a single grain. Our conception of this action may perhaps be rendered clearer by an il- lustration. If we had an iron thread of excessive tenuity, illustration of composed, for instance, of a single row of iron atoms set end of ^'^^"4^16^'°" to end, and could, by suitable processes, effect the removal, fibre, here and there, of atoms in the line, an instantaneous, contraction would be the result, the thread shortening in proportion to the number of atoms removed, but shortening with an energy commensurate with the cohesive force of the iron itself, and yet ready to return to its original length the moment that fresh iron atoms present themselves to be introduced in the place of the abstracted ones ; and so with muscular fibre, the molecular force of cohesion developed here and there by the removal of tissue is to be measured only by the cohesion of the fibre, though the loss of mate- rial which may have been the cause of that force coming into play may be very small indeed : nor does the quickness of relaxation present any Ft 450 VOLUME OF CONTRACTING MUSCLE. difficulty wlien we consider the rapidity with which interstitial nutrition takes place, and the small quantity of matter to be supplied. We have now analyzed the phenomenon of muscular contraction, and , , , set forth the conditions on which it depends. These we may deneral state- \ _ ... mentoftiiis here reproduce together for the more distinct continuation of (.octrine. ^-^^ argument. The primary act is the destruction of the muscular material by the agency of arterial blood; an incipient oxidation setting in, the wasting particles can no longer retain the places they have occupied. They have lost their hold on the particles with which they , were associated. At that instant molecular attraction comes into play, and shortening of the fibre is the result. The wasted material is already being absorbed by the venous capillaries, and already repair is taking place by the introduction of new fibrinous material from the arterial blood; but the renewal or repair proceeds much more slowly than the removal of the waste; the latter effect, as might be inferred from what has been said under th^ head of absorption, occurs almost instantly, the former gradually; and thus muscular contraction presents itself as a composite result, depending, under normal circumstances, partly on oxi- dation, partly on removal of: waste, partly on repair by nutrition, yet so that if any one of these conditions be interfered with it can not take place at all. I can not at this point avoid offering a criticism on the experiments Volume of a ^7 which it has been attempted to prove that a muscle, when muscle after it contracts, loscs nonc of its bulk ; the loss that does in real- ity occur is, it is true, very minute, perhaps so minute that, in the coarse apparatus which has been resorted to in these experiments, it Fig. 229. would be altogether inappreciable. Such a contrivance is represented in J^iff. 229, in which a, a is a wide tube for containing the muscle, g,' it is also to be filled with water, i^ and from its side a narrow tube, d, projects, the water reaching to some such point as e. The tube, a, a, being closed at both its extremities water-tight by means of corks, b, c, whenever the muscle is made to contract by an elec- tric current, applied by means of the spring wires, f, f, or otherwise, if enlargement occurred the water would rise at e, and if diminution it would descend ; but as, upon trial, it is found that no movement whatever takes place, it has been inferred that the volume of the muscle remains un- changed. But no compensation whatever for temperature is provided ! Yet it is positively known that when a mus- cle contracts it becomes warm, and, doubtless, these in- struments, if delicate enough, would have led to the pre- posterous conclusion that a muscle after contraction is larger than it was Volume of contract- ing muscle. CONTRACTION BY WATER. 451 before. But, even setting disturbances of temperature aside, such ex- periments are of no kind of value, since they contain no provision for the removal of the wasted material of the muscle, which still continues a part thereof, though it has become, to all intents and purposes, extraneous, and would, if in the lining system, have been instantly removed by the veins. And now, by the aid of these doctrines, we may comprehend the full significance of those conditions, which have been long; known ^ , . , . 1 • T 1 1 Correctness to physiologists, which have cast such a mystery over muscu- of partial hy- lar contraction, and led to such a diversity of views as re- p°*^®^^- spects its true explanation. We see that they were right who asserted that muscular contraction is a function of nutrition, though they were wrong in saying that it is therefore of a vital, and consequently of an inexplicable nature. They, too, were right who asserted that muscular contraction depends on respiration, and that the higher the rate of that iiinction the more energetic the muscular power will be. They, too, were right who asserted that muscular contraction is manifested by a waste of tissue, and that that waste may be measured, if certain corrections are applied, by the quantity of urea and sulphuric acid in the urine. They, too, were right who asserted that there is a connection between the co- agulability of the blood and the energy of muscular contraction in the various tribes of life, for the speed of repair depends on the percentage of fibrin in the blood, and so, too, does the speed of coagulation. They, too, were right who asserted the connection between muscular contrac- tion and the speed or slowness of the circulation of the blood. All these, and many other partial hypotheses, are the necessary consequences of the more general doctrine, that muscular contraction is the result of loss of muscular substance. There remains a phenomenon to which our attention has to be direct- ed in the conclusion of this subject. It is the contractions ^ T T 1 . {> • Contraction which may be observed under the microscope when a fascicu- produced by lus is submitted to water. These contractions commence in ^^'^*®^" isolated places, from which they spread in all directions, and so move about from end to end, often interfering with one another, the fasciculus thickening where the contraction is greatest, and eventually the whole length becoming involved. The ultimate degree of contraction that can be reached reduces the fasciculus to one third of its original length. With this contraction, through the agency of water or other such liquids, we may connect those contractions which ensue under the pressure or dis- turbance of some hard body, as by the touch of a pin. From these cases it might be supposed that muscular contractility can take place independently of chemical destruction, but a more critical ex- amination of them will satisfy us that they ensue as the natural conse- 452 EIGOR MORTIS. quences of the preceding views. They are not to be regarded as pure or uncomplicated manifestations of the qualities of muscular fibre itself, but as the consequences of the impression that has been made upon it by the treatment through which it has passed. The preparation of a fasciculus can not be made without cutting or rending the parts, mutilating the nerves of supply, and totally destroying the functions of the arteries and veins. In the act of exsecting such a fasciculus, the disturbance im- pressed upon it, however great it may be, is never fully answered to by the due amount of contraction ; for with the destruction of the vascular mechanism there is no means of removing the products of waste, and con- traction can not go on to its full completion, but in this condition the fasciculus, placed in water, gradually gives up here and there the prod- ucts of waste, and with their removal the opportunity arises for the re- maining muscular elements to approach one another, and, finally, com- plete contraction ensues ; a contraction not due to the immediate action of the water, but to the change impressed upon the fasciculus by the op- eration for its exsection. So as regards disturbance by the touch of foreign bodies, we might Contraction recall tliose numerous instances known in chemistry, in which by touch. decompositions or other mechanical results are brought about in a similar way. The difierent compounds which undergo explosive de- composition by the lightest friction might furnish us with illustrations ; but, in this instance, the eifect is more piu-ely mechanical, and arises from the forced equilibrium into which the fasciculus has fallen by the act of exsecting it being more or less perfectly overcome. The elements of a part of a fasciculus are brought by that touch within a nearer range of one another, the products of waste which had failed to escape because of the destruction of the absorbent function of the veins are pressed aside, one motion gives rise to another, a worm-like action spreads here and there irregularly through the length, and ends in a final contraction. Connected with the phenomena described in the preceding paragrapli is that general rigidity of the muscles which occurs a certain time after death, and hence known as rigor mortis. This usually commences in the lower jaw and neck, invading next the upper extremities, and reaching eventually the lower ones. After continuing for a period longer in proportion to the lateness of its beginning, relaxa- tion ensues, the parts being aifected in the same order as they were made rigid. The rigor mortis sometimes begins as soon as ten minutes after death, sometimes it is postponed as long as seven hours. In those who have died of chronic diseases it occurs and ceases very quickly. Both classes of muscles, striped and unstriped, are affected by it, and when it is over they present an unresisting and lax condition, and putrefactive change presently sets in. Even after cadaveric rigidity has been as- OF STANDING AND WALKING. 453 sumed, the contractile power of muscles may Ibe restored by furnishinp; them, through a suitable arrangement, arterial blood ; for this fact we are indebted to Dr. Brown- Sequard, his experiments having been made both upon man and animals. The arterial blood employed assumed during its passage through the limb which was the subject of the trial, the venous character, and issued of a dark color. This restoration of contractility was by no means imperfect or transient ; in one instance it continued for two hours. By means of tendon the muscles are attached to the skeleton, which constitutes the solid framework of the system. Operatinfr r. •^ -T o Connection of thus through the skeleton, the muscles are enabled to keep muscle for lo- the entire body in the erect or standing position, and also to *^°'"*^'^'°"- give it locomotion. The conditions of standing and locomotion have been well studied by the brothers Weber, the following being a brief synopsis of their statements. In man, the power of standing implies the conservation of the line of direction of the whole body within the narrow basis covered by the feet and between them. The head is balanced on the at- las so nearly under its centre of gravity that no ligamentura nuchas is required, as in the case of other animals, to prevent it from falling for- ward. Nevertheless, a forward motion can be executed, amounting to about 75 degrees from the perpendicular, and a lateral motion right and left of from 45 to 50 degrees. In standing, the weight of the entire body is transmitted perpendicularly to the feet. These rest on the heel and the fore ends of the metatarsal bones, especially of the great and little toes, and on the points of the toes. The general centre of gravity of the entire body is a little above the transverse axis connecting the heads of the thigh bones, and for equilibrium to be maintained, a perpendicular line drawn from this centre must always fall within the basis inclosed by the contour of the feet. Even in the most perfect condition of rest that we can assume while maintaining the standing position, a great many separate muscular acts are necessarily required. x4.part from those little voluntary changes which are incessantly occurring, the rhythmic action of the muscles in- volved in respiration, especially those of the abdominal walls, is perpet- ually changing the position of the centre of gravity, and therefore those muscles which are employed in keeping the spine erect are obliged to assume an antagonizing rhythmic action. This is at once the reason of the fatigue we experience in long standing, and of the difficulty which infants encounter in their attempts to maintain the erect position. In walking, the legs act like a pair of pendulums. The head of the thigh bone, which is their centre of motion, is held in its sock- et, not by muscular exertion, nor by its ligamentous arrange- ^^ ^°^' 454 OF RUNNING. ments, but by the pressure of the air, a fact that may be proved by very simple experiments. If the pressure of the air be removed, as in an ex- hausted receiver, spontaneous dislocation ensues. The trunk of the body is like a rod balanced on an axis passing through the hip joints, and ad- vancing with the movement of the legs like a rod balanced on the tip of the finger. It is inclined forward or backward in correspondence with the motion or with the resistance of the wind ; if the wind blows in front, we lean forward ; if behind, we lean backward ; the angle of inclination be- ing in proportion to its force. In walking there are two distinct periods : the body is first poised on one of the limbs, and then rests for a moment on both. The advancing limb swings like a pendulum, bending at the knee so as to be shortened one ninth ; the other straightening at the knee and hip joint, and so pushing the pelvis and trunk forward to be received on the limb that has just advanced. It is only in slow walking that the whole arc of motion is swung through, the time occupied being two thirds of a second. In quick walking and running only half a vibration is ac- complished, and this in half a second of time. In slow walking each foot rests upon the ground one third of a second. The longest step made is half the entire span of the two extremities. To prevent swaying from side to side, the arms swing with the legs. In running there is a moment when both feet are off the ground at once, and the body actually projected into the air. In walk- ing there is a moment when both feet are on the ground to- gether, the one not being raised till the other is planted. In running the steps are, on an average, twice as long as in walking ; and the number of steps made in a given time in running and walking respectively is as 3 to 2. HUMAI PHYSIOLOGY. BOOK SECOND. DYNAMICAL PHYSIOLOGY. COUESE OF LIFE. CHAPTER I. OF THE PRINCIPLE OF ORGANIZATION, OR PLASTIC POWER. Remarks on the Subdivision of Physiology. Career of an Organic Fo7-m. — Three Modes of Development. Inquiry respecting the special Principle of Organization. — Illustration from the Growth of a Plant in Darkness aJid Light. — Inference respecting Plastic Power : its Nature and Properties. — Of the ordinary Groivth of a Plant, and the Sources f-om which its Materials are derived. Relation of all Organisms to each other. Correction of the Doctrine of a Plastic Poiver, f-om Considerations regarding the Individuality of a Plant. — Plants ai-e Operations, not Individuals. — Physical Illustration of this View. Conclusion respecting the Nature of the Plastic Power : that it is a continued Manifestation of an antecedent physical Impression. Eegarding phjsiologj as a branch of natural philosophy, I have been led in this work to introduce the methods of considering it Divisions of which are familiar to writers on mechanics ; for, as there are piiysiology. two distinct divisions of that subject, according as we treat of the equi- librium or the motion of inorganic bodies, so likewise there must be in physiology a statical and dynamical branch, the one including the con- ditions of equilibrium of an organized form, the other those of its devel- opment — development being no more than its motion. If we establish this subdivision in physiology, similar advantages will doubtless be obtained for this science as those which so Advantao-es of quickly accrued to mechanics after Galileo had formally in- ^^^^ division, troduced the same partition therein. Moreover, in this case there are collateral reasons not applying to that. Whatever may be the views which the advance of science causes us to take of the various functions maintaining a living animal in its normal state — whatever may be the 456 CAREER OF AN ORGANIC FORM. general conception we entertain of the nature of its equilibrium, it is scarcely possible to present the subject in a manner that will coincide with the diversified views of the profession. It is almost exclusively with statical physiology that the physician has to deal. The healthy and diseased states of the apparatus for digestion, absorption, respira- tion, circulation, innervation, etc., are the things with which he is con- cerned. It is respecting these that his mind is filled with the early prej- udices of his education, and that his social necessities compel him to ex- press with decision opinions unsuited to a close philosophical examina- tion. He is to be pardoned for the mystification which circumstances oblige him to cast upon the subjects of his study ; for resorting to the vital principle as an explanation of his difficulties ; and for throwing upon the nervous system the burden of every thing for which the imperfect state of physiology does not enable him to account. He is not to be blamed that the circumstances under which he is placed compel him to appear to know more socially than he actually does know philosophically ; and Avhere, under such a false position of things, men have been spend- ing their lives, it is not at all extraordinary that they should resist any attempt at a reformation which strikes at the very existence of the doc- trines they have adopted, and to which they stand committed. The old physician must have his vital princij^le and his nervous agent, or he must begin the alphabet of his studies again. If, therefore, statical phys- iology stood alone, it must depend for its progress in the gradual removal of error and introduction of truth upon one generation of physicians suc- ceeding another ; but, fortunately, there is a circumstance which aids it in this march, for the great branch on which we are now entering pre- sents connections and considerations of a more purely philosophical kind, free, at all events, from the entanglements of professional interests. Ca- pable of being treated in the rigid manner of the positive sciences, and re- moved, by reason of the nature of the topics with which it is concerned, from the strifes of medical sectarianism, this noble subject can develop itself in silence, without disturbance and without restraint ; and yet such an advance can not take place without comjDclling a reflected effect to ensue in statical physiology, and hastening the time when, by the united consent of all physicians, it, too, will be cleared from every mystification, and brought within the pale of exact and positive science. In the preceding book we have investigated the conditions of the Career of an or- equilibrium of the animal mechanism : in this, therefore, we game form. havc to treat of its motion or career. Indeed, we might gen- eralize our expression, and include the vegetable along with the animal, for the two are so inseparably connected that we can not speak of the one without, at the same time, dealing with the other. Viewed as re- spects its motion or career, an organism presents us with the striking GEOMETRICAL MODES OF DEVELOPMENT. 457 fact tliat it passes through a definite series of changes. Commencing at first as a simple cell, to which what might be termed a momentum of de- velopment has been imparted, it assumes one form after another in suc- cession, but is ever ready, like the moving bodies of mechanics, to obey the impulses which extraneous forces may impress upon it. Properly speaking, we can never say of an organized being that it is in a condi- tion of rest. In truth, it is always in motion. It has a past and a fu- ture — coming from one state and going to another ; and though, to use the language of mechanics, the inertia that it has at any moment must tend to continue it in the state at which it is then found, since it varies by degrees from one condition to another, we are obliged to look upon it in these variations just as we should upon an inorganic mass under sim- ilar circumstances, and, guided by the incontrovertible law of physics, that every change of motion is to be attributed to the influence of a force, we must impute its passage from state to state to the intervention of a like agency. In this respect, the career of an organic combination, in its two conditions of maintaining for a time a similarity or passing through metamorphoses, presents a general analogy to the uniform rectilinear, and to the varied motion of mechanics. As we have just remarked, the most elementary organic combination appears to be a simple cell. This, under circumstances „, •Ti ^ ' _ Ihree geomet- which we shall presently consider, may pass into develop- ricai modes of ment by multiplication in three diiferent ways, geometrical- '^^ ^ opmen . ly distinct. Its development may be in one, two, or three dimensions — linear, superficial, or solid. As illustrations may be offered the proto- coccus, which is a simple cell ; the linear confervas, consisting of a row of cells which perpetually undergo terminal extension, the line becoming longer and longer as development of new cells at the end goes on ; the ulvas, in which increase takes place simultaneously in length and breadth ; and any of the higher fomis, which grow simultaneously in length, breadth, and thickness. Whatever the manner of development may be, or whatever the condition presented as the combination passes from phase to phase, no doubt can be entertained that it takes place in conse- quence of the agency of forces which are acting under definite laws ; and though, even in the case of organisms low in the series, a geometrical definition of their form is impossible, this is because of the imperfection of our knowledge, and is no kind of indication that there has been any irregularity or wantonness of play in the forces at work. Asserting thus in the broadest manner the influence of physical forces over development, and seeing that dynamical physiology must jnquiiy into be committed to those conditions, and those alone, which are the existence universally recognized in positive science, I shall proceed, in principie^f this chapter, to set forth the views we entertain respecting the organization. 458 GERMINATION OP A SEED. existence and nature of a special principle of organization. The conclu- sions at which we shall arrive, though apparently very different from what we might have expected, are the necessary consequences of the physical doctrine. It may, perhaps, aid the reader if I give, at the outset, a synopsis of Outline of the ^^^^ argument. Selecting as a general illustration the famil- argument. iar casc of the germination of a seed and the growth of a plant, we shall investigate the results of growth, in light and darkness, witli their attendant phenomena. From this we shall draw apparent ev- idence of the existence of a special principle of organization, or plastic power, and ascertain, in a general way, its functions ; but, from an ex- amination of the attitude in which the resulting organism stands, as re- spects its individuality, we shall learn to correct that view, and reach the final conclusion that that plastic power is not an agent, but a condition of things, the result or the manifestation of antecedent physical influ- ences. Every living being springs from a germ. The animal and vegetable Primordial kingdoms present us with numberless forms, differing from one cell- another in aspect, in construction, and in function ; but the or- igin of all is the same — a cell or vesicle, which, under the influence of external cii'cumstances, develops into a determinate shape. A seed may be kept in a dry place for many years without undergo- ing any visible change, or losing its power of germination. It may be exposed to all the annual variations of temperature occurring in the dif- ferent seasons ; it may have the free access of atmospheric air. Its vi- tality is dormant ; there is no attempt at evolving its parts. But if some water be supplied, and a certain degree of dampness be Germination thereby communicatcd, the seed does not fail, as soon as the of a seed. temperature reaches that of a summer's day, to germinate. Under the influence of air, heat, and moisture, the embryo consumes the nourishment stored up for it in the seed, a gradual unfolding of its parts ensues, a root is put forth, a stem rises from the ground, and leaves make their appearance : so heat, air, and water have enabled the seed to become a plant. These physical agents are not, however, sufficient to carry the growth Effects of sun- forward to its full extent. Another is essential : it is light ; light. for if growth be conducted in darkness, heat, air, and water can not cause the young plant to add any thing to its substance. It is feeding on the seed. Indeed, when the experiment is carefully made, it is found that there is an actual loss of substance, the resulting plant, if dried, weighing less then than the dry seed from which it came. CONSUMPTION OF LIGHT BY PLANTS. 459 In a dark place, then, it is possible for a seed to grow, but it grows in a certain way, and only to a certain extent. Its stem and its leaves are of a sickly yellowish hue : exposure to the sunshine soon produces a green color in these parts, and the weight of the plant increases. Growth in darkness leads to one result, and growth in the sunshine to another. From these facts it therefore might appear, from a superficial considi. eration of the thing, that the development of a plant depends partial infer- on two distinct conditions — an innate power which resides ence respecting • . tli6 GxistcncG m the germ, by the action of which the matters previously of a plastic stored up in the seed by the parent plant are regrouped, and po'^^'er- so arranged as to constitute a new organization ; but this power does not extend to the obtaining of new material ; it is only a power of arrange- ment — a PLASTIC POWEE. Whatever new material is required must be furnished by a totally distinct agency, the sunlight ; and just as the plastic power can not collect, the sunlight can not arrange. Each has its own sphere of duty. The one gives the substance, the other moulds it. Every flowering plant, no matter how humble it may be, is, then, a rep- resentative of the action of these double influences, and, when Consumption properly considered, may well extend the views we ought to "ecreubie" entertain of the system of nature. The supplying or furnish- development. ing agent, the light, comes from a star which is at a distance of almost a hundred millions of miles, and is the pivot of all the planetary motions. Without this extraneous, this foreign force, the whole surface of the earth would be a desolate waste, presenting no semblance of life. The leaf, the flower, the bud, the stem, the root, are all made of substance that has been given by the sun, derived, it is true, from one of the constituents of the air, but forced to take on the special state which suits the needs of the plastic power by that distant agent ; and, in order for this to oc- cur, it is plain, from mechanical considerations, that there must have been an expenditure of power, or of the acting principle itself, for light can not produce these effects without losing its own peculiar form. For the decomposition of a given weight of carbonic acid, and the formation of a given weight of gum, a fixed and invariable quantity of light is required ; just as it is necessary, in moving a mass of a certain weight, to expend an equivalent and definite force, so the substance of which plant-organs con- sist has been brought into an available state by the consumption of a definite quantity of light — perhaps its incorporation, under some other form, in the resulting mass. It may be pent up and imprisoned in the organic structure for any imaginable time, even for centuries, but is ever ready to resume its primitive state when favorable circumstances exist. The coal-fields which furnish us with fuel are the remains of primeval forests which grew in the ultra-tropical climate of the secondary times, 460 NATUEE OF THE PLASTIC POWER. and the light and heat we derive from them are the same that came from the sun in those ancient days. If, then, our earth does not possess in herself the power of sustaining Is the plastic the Varied forms of vegetable life, but borrows it from an ex- power a uni- traneous source ; if light, in producing these effects, never fused agent Undergoes destruction, but only modifies its state — for nei- like the ether? |]^g]. force nor matter can be annihilated, though they may be changed — what shall we say of the plastic power which we have thus assumed to reside in the germ, the co-worker with the luminous agent ? Does their partnership in action indicate a resemblance in position or na- ture ? If the one consists of motion arising in an ethereal, intangible, and weightless medium, diffused throughout the universe, may we suppose that the other is the manifestation of a similarly diffused principle? There is no necessity, as many have thought, to impute to the first-crea- ted germ a formative power for all its successors, as though whatever force or qualities they possess were originally concentrated and included in it. It is possible that countless millions of organic beings may have originated from one primordial germ, just as we see an extensive confla- gration originating from a single spark. That such a plastic principle exists has long been admitted by philos- ophers, both speculative and experimental. It is a doctrine which seems to have arisen in the infancy of human knowledge, and is to be met with in almost all the old Asiatic and European systems. The archeus and soul of the world of the alchemists were only the reproduction of a very ancient idea. The term " vital spark" was once something more than a mere metaphorical expression ; and, indeed, there is a classic* noble- ness in the thought which recognizes a universal spirit diffused every where. In different countries and by different authors, the nature and function of this principle are variously represented ; imperfect concep- tions of what is so significantly but briefly set forth in the opening words of the Sacred Scriptures, which plainly recognize the true conditions un- der which all vegetable organisms arose — formless matter, the simlight, and a brooding spirit. I shall continue to speak of this principle under the designation of the plastic power, because that expression points out aptly the function dis- charged, and to assume that all those organisms which possess the qual- ity of converting inorganic bodies into organic structures do so under the double influence of light and of this interior principle. This, of course, * Principio coelum, ac terras, camposque ; liquentes Lucentemque globi;m Lunae, Titaniaque astra Spiritus intus alit, totamque infusa per artus Mens agitat molem et magno se corpore miscet. Inde hominum pecudumque ; genus, vitaque ; volantum, Et qu£e marmoreo fert monstra sub a?quore pontus. — ViEG. JEi'S., 1. vi., 724. ACTION OP DIFFERENT RAYS. 461 includes nearly all vegetable forms, for we may leave out of considera- tion the fungi, a group which stands intermediately between plants and animals. The distinctive character of a plant is to form, from carbonic acid of the air, solid organic structures. The distinctive character of an animal is, by the oxidizing processes going on in it, to restore the or- ganic bodies which have served it as food to their original formless state. The group referred to differs from true plants in feeding on matter al- ready organized, and breathing like animals. It therefore does not re- quire the influence of light to collect material for it, and bring it to the, proper state. In the development of this group the plastic principle is alone concerned. Since the sunlight is composed of many differently colored rays and different principles, it becomes an interesting inquiry which of these is the immecliate agent in ministering to the nutri- ferent colored tion of plants. In 1843, by causing plants to effect the de- ""^^^ °^"s^*- composition of carbonic acid in the prismatic spectrum, I found that the yellow is by far the most effective, the relative power of the various col- ors being as follows : Yellow, Blue, Green, Indigo, Orange, Violet. Eed, My experiments on the production of hydrochloric acid by the direct union of chlorine and hydrogen under the influence of light, phenomena of both artificial and solar, and also on the decomposition of *^he action of peroxalate of iron, from which carbonic acid is readily disen- growth of gaged, conclusively establish the fact that the primary con- v^^^^^- dition essential for the chemical action of light is the absorption of some particular ray. If the physical condition of substances otherwise easily decomposable is such that they transmit light without absorbing any, no chemical change ever ensues in them, and the same condition obtains in cases of combination. Thus oxygen and hydrogen can not be made to unite, even by the most intense radiation, because neither of them ex- ert any absorptive action ; but chlorine and hydrogen unite with energy, because the chlorine absorbs the indigo ray. The same experiments prove that the amount of decomposition or oth- er work done by light is always proportional to its quantity ; hence, by the aid of converging mirrors and lenses, chemical changes can be ac- complished with great rapidity. These instruments, however, when even of the largest size, are unable to produce any other effect than would be brought about by a feebler ray if applied sufficiently long. The great- ly increased intensity of light which they can present does not enable us either to bring about combinations or decompositions of substances which 462 PLANTS LIBERATE OXYGEN. are unacted upon by rays of a more moderate brilliancy, for the general rule under which the chemical action of light occurs is, the amount of chemical change is as the quantity of light absorbed. These facts are of importance in all discussions respecting the prim- itive formation of organic matter by plants. Guided by them, we infer that, though vegetation may greatly differ in its luxuriance in different climates of the globe, the manner of action of the light is always the same. Nothing is gained under the brilliancy of the tropical skies be- yond a shortening of the time required for the accomplishment of a given amount of work. No substances are there decomposed, even in the or- ganisms of plants, which could not equally well be decomposed by the feebler light of more temperate climates, only in these it would demand more time. The oils and other substances, almost or quite free from oxygen, which abound in the plants of the torrid zone, are not excep- tions to, but illustrations of, the doctrine here set forth. It is proper here to correct the statement which is usually made by It is not the Vegetable physiologists, that the decomposition of carbonic green parts of q^q{^ })j plants is accomplished by their green parts. A decompose car- plant which has been etiolated, or, indeed, one which has bonic acid. been raised from a seed in total darkness, when brought into the sunshine, decomposes carbonic acid, liberates oxygen, and its pale and sickly leaves presently turn green. This, therefore, demonstrates that the green portions are not the seat nor the origin of the decomposi- tion, but are, properly speaking, its effect. Thus, under the influence of sunshine, the leave's of plants decompose Plants liberate carbonic acid, liberate its oxygen, which, for the most part, oxygen. escapcs into the atmosphere, the amount of gas decomposed depending primarily on the quantity of light supplied, and therefore, among other conditions, on the surface of exposure of the leaves, and not upon their thickness or mass. But I found, on an examination of the gas thus evolved, that it is never pure oxygen, but always contains a certain though variable proportion of nitrogen. From this it follows that a part of the oxygen appertaining to the carbonic acid is appropri- ated for the uses of the plant. Such, in a general way, is what takes place in the daytime, but at night the process is to a certain degree inverted, a plant absorbing oxy- gen from the air, and yielding carbonic acid. The explanation which Liebig offers of this state of things is doubtless correct, that the evolu- tion of carbonic acid is a purely physical process, and the absoi-ption of oxygen due to the chemical action of the various deoxidized bodies which have been accumulating during the day. As respects the sources from which the various constituents of the plant organism are derived, they are suflficiently obvious. The carbon SOURCES OF THE CONSTITUENTS OP PLANTS. 463 may doubtless be entirely attributed to carbonic acid, ob- sources from tained either directly from the atmosphere or furnished by which the con- the gradual decay of humus in the soil. For the hydrogen li^H^ are de- a double source may be assigned — water and ammonia, li^^'^d. Ofcar- The abundant occurrence of resins, oils, fats, in which this element preponderates, conclusively establishes the fact that ^ logen. the supply of ammonia, as indicated by the nitrogenized compounds which have been formed, is insufficient to account for the quantity of hy- drogen, and for which there would appear no other source than water ; and though the most brilliant light, even though concentrated by a pow- erful burning-glass, can not alone effect the decomposition of this liquid, there will be no difficulty in admitting that such a decomposition does take place, when we recall that carbon is being presented in what might be termed its nascent state. Of the nitrogen necessary for the formation of the protein bodies of plants, it is o-enerally concluded that ammonia is the only ^„ . Til • T T 1 1 • 1 Ofnitrogen. source, and that these organisms do not dn'ectly obtam that element from the atmospheric air ; moreover, it occurs apparently to a sufficient extent in their sap, having been introduced by absorption through the roots. As essential to the production of the same group of bodies, the protein substances, both sulphur and phosphorus are in- troduced through the same channel, from the soil, as sul- of sulphur and phates and phosphates, which undergo decomposition and phosphorus. deoxidation within the organism, so as to yield the sulphur and phos- phorus in an unoxidized state. We can not overlook the saline substances, or mineral bodies, which occur in different parts of plants, and which obviously are of saline sub- absolutely essential to their constitution. The circumstance stances. that, in any given plant, they are found fixed in their nature, definite in their quantity, and deposited in determinate regions, is sufficient to es- tablish that conclusion. As is very well known, we can not judge of their nature or condition during the life of the plant from the aspect they present when its ash is examined. Thus those which have been exist- ing as neutral or acid salts of organic acids must appear in the ash as carbonates ; and though it has been established that basic and mineral substances generally will to some degree replace one another — nay, that even the plant itself, by generating vegetable alkaloids, may dispense with bases of the mineral kind, the extent to which this can be carried is as yet undetermined. The occurrence of sulphates and phosphates in the leaves and seeds, and wherever organic activity has to be dis- played, and protein bodies are found, is sufficient to establish a con- nection between those substances and the neutral nitrogenized bodies, though of the manner in which, from carbonic acid, water, ammonia, 464 ACTION OP PLANTS ON THE AIE. sulphates, and phosphates, those bodies are formed, we are as yet alto- gether ignorant. By some chemists it has been supposed that the decomposition of car- The decompo- bonic acid by plants in the sunshine is not instantaneously sition of car- complete, but that a gradual process of reduction takes place, not parUai, but the carbon losing by little and little its oxygen, but never, total. perhaps, losing it all. My own experiments, previously al- luded to, which show that the quantity of oxygen set free is never quite equal to that of the carbonic acid consumed, have been used in support of this view. But this, I think, is an interpretation which they will scarcely bear. There are many facts connected with the chemical action of light which might be cited as offering abundant proof that the decom- position in question is, on the contrary, instantaneous and complete, and in that I am led to believe really consists the primary function of the light, the carbon thus obtained being subsequently employed in accom- plishing the decomposition of water, and other processes of reduction known to go on in the vegetable organism, but with which, under the circumstances of the case, it is impossible that the sunlight should be di- rectly concerned. I separate as distinct factors in the life of a plant the obtaining of carbon from the air, which is accomplished by the influ- ence of an external agent, and the moulding or modifying it with other ingredients into organized material, which we have thus far imputed to a plastic power in the plant itself, and respecting which more will be pres- ently said. Free carbon once obtained, we can easily conceive that all other operations of reduction may follow, and that this division of the action of plants into two distinct stages or factors, as we have just term- ed them, is not a mere speculation, but represents what in reaHty occurs, will perhaps be admittecl on recalling what has been remarked on growth in the sunshine and in darkness respectively. As a summary of the action of vegetation on the air, it is on all hands Summary of admitted that plants tend, by the removal of carbonic acid ^ kiTtf on"the therefrom and the return of oxygen thereto, to compensate for atmosphere, the disturbance occasioned by animals, which is to the oppo- site effect. In this way, through very many centuries, the same percent- age constitution of the atmosphere is maintained, the sum total of veg- etable being automatically adjusted to the sum total of animal life ; auto- matically, and not by any interference of Providence ; for if we admit, what has been conclusively established by direct experiment, that plants would grow more luxuriantly in an atmosphere somewhat richer in car- bonic acid than the existing one, we may see how upon this condition de- pends a principle of conservation, which must forever retain the air at its present constitution, no matter how animal life may vary. The proofs that are sometimes offered that there has been no change in this respect CONDITIONS OF GROWTH. 465 for at least 2000 years, and which are drawn from an examination of the aerial contents of vessels said to have been obtained from Pompeii or Herculanciim, are of very little account. We have only to recollect how easily diflasion takes place through crevices, and even almost invisible pores. But there are proofs of a far higher order, and of a much more general kind, which might be brought forward, if this were the proper place, establishing beyond all possibility of contradiction the fact that in a slow manner, through countless ages, the constitution of the atmosphere has changed, and that now, through the operation of conditions which have spontaneously arisen, it has come into a condition of apparent equilibrium. When, therefore, a seed is placed in the ground in the warm season of the year, the germ it contains develops, and, after a few days, makes its appearance as a young plant at the surface. If the growing structure is examined during its passage through the soil, it presents a pale yellow- ish aspect, which is exchanged for a bright green tint as soon as it escapes from its confinement, and unfolds itself to the sunlight and the air. From the first moment, until the green color is assumed, the young plant is nourished, as we have seen, at the expense of the , - ., , seed. In anticipation of this, the parent had laid up a stock adult life of of nutritive material. On this the embryo draws, consuming ^' '^"'^^' a part in the support of its life, and incorporating the residue in its structure ;. but as soon as the surface of the soil is gained, this life of de- pendence ends ; the plant weans itself, and, abandoning its temporary support, commences to collect from the air and the earth the materials of which it is to consist. Its infantile seed-life has closed ; its independ- ent aerial life has begun. In this aerial life, which is the mode of existence destined to continue until absolute death occurs, the two essential conditions to q „.. ,„<. oLiiniiiHiy or which we have drawn attention are recognized. There must the conditions be a steady supply of material for the building up of the ^ ^^°^^ growing structures, and this has to be derived from external sources. There must also be a capability of so grouping or moulding the material thus acquired that the various parts that are wanted — leaves or fruits, flowers or thorns, may be made. The manner in Avhich these conditions are satisfied presents to a re- flecting mind one of the most wonderful examples of the system of na- ture. We have already shown that the power of moulding and group- ing is inherent in the plant. In virtue of this, while it was yet in the ground, and therefore in the dark, the germ could put up its stem and fashion its imperfect leaves, but it did not possess any power to gather nourishment beyond that which was stored up in the seed, and had that stock been exhausted before it reached the surface, it must have died. 466 RELATION OF ORGANIC FORMS. We have also shown that the supply of new material is always fur- nished hy the sun. In the absence of his rays the plant may organize, but can not increase, and, indeed, it was to the influence of light that the green color of the first leaflets was due. All the day long, and with the more activity as the day is brighter, the leaves, which are the collecting organs, are absorbing material from the air ; they cease to do it at night. The sunbeam enables them to take from the air carbon, hydrogen, and nitrogen. They feed by day and fast at night. Astronomers say that the sun is the most sublime object the eye of man can contemplate. They speak of his prodigious mass, and describe how he compels the planets to move in obedient circles around him. To the physiologist he is not less sublime. The most insignificant moss that grows on the wall was called into existence by his heat, and is daily fed by his light. The sunbeam is the finger of God. The nutrition of plants is therefore dependent on physical causes. The carbonic acid required being brought to them by aerial currents, oc- casioned partly by the warming influence of the sun on their leaves and partly by the winds, the tendency of gases to difiuse into one another aids in producing the same result. In this manner, as they exhaust the surrounding air, fresh quantities are supplied, the separation of carbon from it being brought about by the agency of the yellow rays. The leaves, also, sometimes follow the motion of the sun, or present themselves in the most favorable position under the influence of the indigo rays. The water requisite is obtained from the soil by the spongioles of the roots. With it there are carried into the interior of the plant the saline and inorganic substances necessary for its structure. These, since they are often of sparing solubility in water, will require large quantities of that liquid to effect their introduction to a proper amount. During the course of a summer there may pass through the system of the plant perhaps many hundred times its weight of water — a prodigious amount when the phenomenon is considered on the great scale. Cuvier speaks of the inferior organisms as furnishing us with a series „ , ,. ^ of experiments made by the hand of Nature, r.n idea often Relation of or- -^ -^ ganisms to quotcd and often admired, but which is, perhaps, scarcely con- each ot er. sistent with enlarged conceptions of the system of the world. An organism, no matter how high or low, is not in an attitude of isola- tion. It is connected by intimate bonds with those above and those be- neath. It is no product of an experimental attempt, which, either on the part of Nature or otherwise, has ended in failure or only partial success. The. organic series — an expression which is full of signiflcance and full of truth, for it implies the interconnection of all organic forms — the or- ganic series is not the result of numberless creative blunders, abortive at- tempts, or freaks of Nature. It presents a far nobler aspect. Every RELATION OF ORGANIC FOKMS. 467 member of it, even the humblest plant, is perfect in itself. From a com- mon origin, a simple cell, all have arisen : there is no perceptible micro- scopic difference between the primordial vesicle which is to produce the lowest plant, and that which is to produce the highest ; but the one, un- der the favoring circumstances to which it has been exposed, has contin- ued in the march of development, the career of the other has been stop- ped at an earlier point. The organic aspect at last assumed xhe forms of is the strict representation of the physical agencies which have organization depend on been at work. Had these for any reason varied, that varia- physical tion would at once have been expressed in the resulting form, ^S^"'^^- which is, therefore, actually a geometrical embodiment of the antecedent physical conditions. For what reason is an offspring like its parent, except that it has been exposed, during development, to the same condi- tions as was its parent ? Comparative physiology is not a fortuitous col- lection of experiments. Our noblest conception of it is the conception we have of analytical geometry, and, speaking in mathematical language, each member of the organic series is an embodied result of a discussion of the equation of life for one special case. Nay, I would present the whole system of Nature as included in the same idea. The inorganic and lifeless combinations which are all around us are, to my mind, in truth, in that equation of life, the analogues of the imaginary solutions of the calculus. It was a felicitous thought of Descartes that we may represent a geo- metrical form in an algebraical equation, and, by the proper ,,, consideration and discussion of such an expression, determ- the relation of ine and delineate all the peculiarities of such a form ; that here ^gff "e\| f""^^ it should become concave and there convex, here it should analytical ge- run out to infinity, there have a cusp. The equation determ- °"^*^ '■^' ines all the peculiarities of the form, and enables us to construct it. But if the original conditions are inconsistent with one another, the construc- tion can not be fulfilled, it having become impossible. In the same man- ner are all living and lifeless forms related : an increase in the value of one condition carries development forward in one direction, and increase in the value of another condition determines development in another way, and these variations give rise in their succession to the whole organic series. But in these, as in the other case, if inconsistent conditions have existed, their presence is indicated in the resulting solution, which can not be constructed as an organic form, but is represented as a lifeless mass. " God ever geometrizes," and, it might be added, ever materializes. Every organism is the result of the development of a vesicle under given conditions, carried out into material execution. It is the incarnation, the embodiment, the lasting register of physical influences ; for, if such Ian- 468 NATURE OF INDIVIDUALITY. guage raaj be with propriety used, the consequences of the action of nat- ural agents do not remain as a barren idea in the creative mind, but are presented as a material and tangible result. Such a mathematical conception of the relations of the various forms around us obliterates at once the line of demarcation which natural his- tory has thus far vainly attempted to define with correctness between the organic and inorganic worlds. In the system of creation no such boundaiy exists ; neither does one exist between the vegetable and ani- mal groups. On every form, all existing influences have exerted their sway: gravitation, heat, electricity; the result is the issue of their action. The shape of any great mountain is thus the record of every thing that has affected its mass since it was first uplifted. Its ancient peaks are the register of every summer's sun, every frost, every falling rain, every lightning stroke. It is what it is because of them ; and so also of the lichen which unfolds itself on some favorable spot on the rock. Would it be there at all, or would it have the special aspect it presents, if there was not a due proportion of sunshine, *a proper supply of moisture, a suitable temperature "? It is such conditions which have called it forth. It is what it is because of them. In this respect, betv^een the inorganic and organic, there is no difference. The preceding elementary examination of the circumstances under Correction of wliich plants grow has led us to the inference that in their this doctrine of gg^.^jj there resides a plastic power whose fanction it is to a plastic pow- o . er. model the organic matter, as it is furnished by the sunlight, into definite shapes or organs. We now proceed to correct the concep- tion we have thus formed, and to show that it is more philosophical to decline the idea of an agent and to accept that of a condition. Perhaps the most simple method of illustrating this idea is from con- siderations connected with the individuality of the organisms which have thus arisen. Directing their attention to plants, botanists have occupied themselves in endeavoring to determine what is the attitude in which Considerations they Stand. They have tried to find out wherein the indi- inlvidufiitv^ viduality of a plant consists, for this question of individual- of a plant. " ity lies truly at the basis of the position Avhich those struc- tures occupy. There are oaks that have lasted a thousand years, but are they to be regarded as individuals that are a thousand years old '? Is not such a tree rather like a nation, a collection or colony of indi\Tiduals, the individuality belonging to each bud, to each leaf it has borne ; for there is a close analogy, if not an absolute identity, between the process of development of a seed in the ground and of a bud upon a branch ; both have their infantile, both their aerial life. The leaves of the oak, which expand in the spring, fall in the autumn. Their origin and du- ties are connected with astronomical events. Each annual generation, NATURE OP INDIVIDUALITY. 469 while it lasted, carried forward all the functions of the tree, as, in a na- tion that may have endured for a thousand years, each generation of men has borne its part in the general scheme, and made provision for its suc- cessors. The individuality therefore lies not in the tree, but, perhaps, as thus far considered, should be referred to the bud. But, moreover, when we consider the modes by which a tree may be propagated, as, for instance, in the horticultural processes of budding or grafting, our views of this question of individuality must again be modi- fied. By these artificial operations an original stock may be multiplied again and again, and each of the plants so arising is undistinguishable from any other that may have come in the same way. Setting aside the inci- dental difference that, through the intervention of artificial means, the buds fi'ora which two such plants have originated have been brought under the condition of physical independence of one another, the one, perhaps, grow- ing in America, the other in Europe, is there any absolute and essential difference between them more than there would have been had they been permitted to remain upon the parent stock, and to develop themselves into two branches thereof? Such facts suggest to us that individuality does not belong to plants, as they thus present themselves to us, and that perhaps we ought to assume an individuality of a higher order — a" race individuality, as it were. In this manner, all weeping willows in Europe and in America are one individual, because they have all been derived from one original imported Babylonian stock ; and the same might be said of every one of our cultivated fruits. But of these, if a seed be plant- ed, the general aspect of the resulting growth may possibly be the same as that derived from a graft, and how shall we then make a distinction between the one and the other? for, though by seed development the plant may chance to run back to a wilder form or to produce a new va- riety, this result is by no means absolutely necessary. From similar considerations, some physiologists have been led to deny individuality to the bud and the seed, and to refer it to the primary cell ; but here, again, precisely the same difficulties are encountered. A cell may multiply itself by fissure through its nucleus, as well as in an en- dogenous way ; moreover, cells arise from granular material. Individu- ality, therefore, except it be that of a lower order, can not be attributed to them, and the question of the determination of it rests precisely where we found it. In truth, are not all such discussions, in their very nature, illusory, so long as we have no more definite idea of the term individu- The idea of in- ality ? If a natural philosopher were to occupy himself with inapnU^caWe'to similar discussions respecting the flame of a lamp, he too, plants. doubtless, would be led to precisely the same empty conclusion. He might show how, in such a flame, there are separate, well-marked re- 470 ANALOGY BETWEEN A PLANT AND A FLAME. gions, some of which were present at the first moment of its existence, and remain to its end, as, for example, the blue portion which is at its under part. He might show how every one of these flames tends to as- sume a definite or determinate form — conical, for instance — and proceed to argue that this is the result of the interaction of external causes, as the passage of currents in the air, and some interior principle or power pos- sessed by the flame itself. He might consider how that from one flame another can be kindled, in all respects like its parent in qualities or shape ; and how, in succession, from one original, myriads upon myriads might so arise. He might engage himself in disquisitions as to the man- ner in which such an extraordinary result is to be explained, and as to the source to which he should impute with exactness the origin of each of these independent flames, and their mutual interrelation. He might inquire if the force which each possesses was originally contained in the original flame, and how it came to give it forth without loss of any of its own power. He might also amuse himself with questions of individu- ality, and, in doing all this, it would be no more than physiologists have done before. Between the case of the trees and flames, of which we have been speaking, it is not difficult to see that there is an analogy. Ai'e plants, in truth, then, nothing more than temporary states through „, ^ which material substance is passing, because of some original Plants are op- _ . . erations, not physical imprcssion made upon it, and the present operation individuals. ^£ g-jcternal circumstances ? Can individuality be applied to them any more than to a flame ? Instead of being individuals, are they not rather the transitory results of an operation ? The lamp, which we have been using as an illustration, may serve to enlighten our path a little farther. In the infancy of chemis- tween a plant try, it might have been said of it that it possessed a burning and a flame, p^^gj.^ which enabled it to dispose of the matter with which it was fed, just as we say of a plant, in the infancy of physiology, that it possesses a plastic power, which groups into definite forms the substance with which it is furnished. The so-called burning power was derived from another flame, in all respects analogous to that which manifests it, and is nothing more than an extension of a physical operation, the tend- ency of which, so far from being to check, is to continue as long as the proper material is furnished. The lighting of a second flame is essen- tially the same condition as the continued combustion in the first. The fact of separateness changes the phenomenon in no respect whatever ; the relation of two separate flames is the same as that of two different parts of the same flame ; and so the derivation of a plastic power by a plant from its ancestor is essentially the same thing as the manifestation of a similar power in different parts of its own system. Though it may therefore be convenient to speak hypothetically of this NATURE OF THE PLASTIC POWER. 471 principle Avhicli accomplishes in a plant the grouping of its parts as if it were an agent, the foregoing illustrations show us that all the facts of the case arc equally well satisiied on the supposition that it is the continua- tion of an oj)t'ration. A multitude of parallel instances present them- selves. In the making of leavened bread, all the phenomena would seem to be accounted for either upon the hypothesis that there resides in the leaven or ferment an agent, whose quality it is to determine a specific change in the flour, or that there is a7i oj^eration which, because of the chemical conditions existing, is gradually spreading, and which will not cease until all the material submitted to it has been affected, and this no matter whether it be in the same mass or in successive portions. Of such hypotheses, the first is merely an elementary idea, the latter in- volves a philosophical conception. In this way, therefore, the so-called plastic power of a cell or the germ of a seed may be regarded as the continued manifestation Nature of the of an antecedent impression long ago made, and which, un- plastic power. der the existing conditions, has no liability to wear out or die away ; and that impression may have been purely physical in its nature. Viewed in this attitude, the life of plants is a physical phenomenon. The parts of Avhich they are composed are furnished to them The life of by influences of a mechanical kind : their carbon is taken by ^jf " j^^i ^ a true chemical decomposition from the carbonic acid of the phenomenon. air ; their nitrogen comes from ammonia or from the atmosphere. Wa- ter is drawn by capillary attraction firom the ground. In virtue of its chemical qualities, it carries into the growing system the various saline bodies present in the soil, and which are needful for the economy. The sunlight, heat, rain, winds, are the supplying and nurturing powers, and the grouping agencies residing in the plant are of the same mechanical derivation or order. The germination of a seed and the growth of a plant, as thus consid- ered, show us to what an extent physical forces are concerned in vege- table organization. The conclusion thus indicated is enforced in no common manner when we direct our attention to the series instead of to a single plant. This is what I propose to do in the following chapter. 472 GEOGRAPHY OF PLANTS. CHAPTER II. ON THE INFLUENCE OF PHYSICAL AGENTS ON THE ORGANIC SERIES. Of the Geography of Plants : their horizontal and vertical Localization. — Influence of Heat on or- ganic Distribution : isotheral and isochimenal Conditions. — Effects of Variations in the Dens- ity of the Air, Moisture, Soil, Sunlight, Length of Day. — Definite Quantity of Heat required hy Plants. Secular Perturbations in the Species of Plants. — Long Periods of Time required. — Secular geo- logical Clianges. Inverse Problem of the Investigation of the Parth's History from her fossil Flora. — Two great terrestrial Epochs : Cliange in the Constitution of the Air, and Localization of Organisms through Decline of the EartKs Interior Heat. Difference betiveen abrupt and gradual Impressions.rt— Invariable Causes may produce abrupt Crises. Extension of the above Principles to the Case of Animals.— Case of the Inca Indians. General Argument supported by the Extinction of Forms. — Development is under the Influence of Law. — Rudimentary Organs and Excesses of Development. — The Idea of Development by Law consistent with natural Facts. The publication of Humboldt's Essay on the Geography of Plants r. ^. , first formally drew the attention of botanists to the connec- Geographical •' distribution of tion between the distribution of vegetables and the distribu- plants. ^-^^ ^|. j^g^^ ^^ ^j^g surface of the globe. Starting from the equator and advancing to the pole, in either hemisphere, the mean annual temperature declines as the latitude becomes greater, and in succession a series of vegetable zones, merging gradually into each other, though each, where best marked, perfectly distinguished from the succeeding, is encoun- tered. In the tropics we have the palms, which give so striking a charac- teristic to the forests, the broad-leaved bananas, and the great climbing plants, which throw themselves from stem to stem like the rigging of a ship. Next follows a zone described as that of evergreen woods, in which the orange and the citron come to perfection. Beyond this, another of deciduous trees — the oak, the chestnut, and the fruit-trees with which, in this climate, we are so well acquainted, and here the great climbers of the tropics are replaced by the hop and the ivy. Still farther advanc- ing, we pass through a belt of conifers — firs, larches, pines, and other needle-leaved trees, and these, leading through a range of birches, which become more and more stunted, introduce us to a region of mosses and saxifrages, but which at length has no tree nor shrub ; and finally, as the perpetual polar ices are reached, the red snow-alga is the last trace of vegetable organization. A similar series of facts had been observed by Tournefort in an ascent GEOGRAPHY OF PLANTS. 473 of Mount Ararat. He found that the distribution of the vea;- ,^ . , ,. ^ V Grticul uiS" etation from the base to the top of the mountain bore a gen- tribution of eral resembhance to the distribution from the base toward the P'^"*^^- Arctic regions. These facts by subsequent observers were generalized, it having been established that there exists an analogy between horizon- tal distribution on the surface of the globe and vertical distribution at different altitudes above the level of the sea. Even in the tropics, if a mountain be sufficiently high, a very short ascent suffices to carry us from the characteristic endogenous growths at its foot, in succession, through a zone of evergreens into one of deciduous trees, and this, again, into one of conifers, the vegetation declining through mosses and lichens as we reach the region of perpetual snow. In these two cases of horizontal and vertical distribution respectively, which thus present such a striking botanical resemblance. Distribution there is likewise so clear a meteorological analogy that it is ofheatdeterm- ., 1 , . 1 . , ji 1 • 1 IT in^s the distri- impossible to avoid coming to the conclusion that the dis- butionof tribution of plants depends on the distribution of heat. The pl^^^ts. same climate variation encountered on a surface journey directed from the equator toward the poles is again encountered as we leave the foot of a tropical mountain and go toward its summit ; for it is a well-ascer- tained fact that the temperature of the atmosphere declines as we rise to greater altitudes, and that, no matter how high the summer heat may be, we may, by a vertical ascent at any locality, come to a region where the temperature is never above 32° Fahr., and where ice and snow, there- fore, never melt. If, in any locality, the mountain ranges are of sufficient height to g^in that region, their tops will be covered with perpetual snow. The vertical ascent thus to be made is less as the latitude is greater. At the equator it is 15,200 feet, and at the eightieth degree it is within 450 feet of the ground. Beyond this, the surface itself is per- petually frozen. The mean temperature of a place determines its vegetable growth, and hence there will ever be a resemblance between the vegetation of places of the same mean temperature, though they may be geographically very wide apart. But this, though a resemblance, is very far from being an identity. We can not always designate by name the particular plants of a high latitude which should be found at a corresponding elevation in the momitains of the tropics. There may be the general resemblance of which we have been speaking, and yet the genera and species of plants in the two places may be quite distinct. But this fact, far from affecting the truth to which we have arrived of the control of a physical agent such as heat over the distribution of plants, leads us to ex- ^ n ^ Influence of tend it, and teaches us that, though we might expect, in other physical places far apart, identically the same vegetable growths if *^°"'^''^°'^^- 474 INFLUENCE OF PHYSICAL CONDITIONS. all the physical conditions were identical, yet, since heat is only one of these conditions, it alone is insufficient, and that differences in the press- ure of the air, the amount of moisture, the quantity of carbonic acid, as also variations in the constitution of the soil, must have their effect. In- stead, then, of limiting our views to the control of temperature over the occurrence of plants, we must enlarge them in such a way as to include divers other influences, some of which are those just mentioned, and all are equally of a physical kind. This therefore brings before us, in an impressive manner, the subject to which this chapter is devoted, the influence of physical agents generally over organization. That the conditions of temperature alone are insufficient to account for the occurrence and distribution of plants may be clearly established by the aid of another series of facts. Throughout the old continent, with the exception of its torrid zone, from the south of Africa to the north of Europe, heaths abound, their species being very numerous in the south- ern latitudes, less so in the northern, but the individuals increasing in number as the species diminish. At the extreme north the common heather remains as the sole representative of the whole group, and so universally covers the surface as to give a characteristic feature to tlie landscape. But in America, which reaches through all corresponding degrees of latitude, and has in its proper localities the same mean tem- peratures, not a single heath ever occurs. Again, in the New World, through forty degrees on each side of the equator, the cactus tribe of all kinds of grotesque forms abounds, but in Africa, though there are local- ities of corresponding temperature, not a single cactus is to be seen. The spurges there make their appearance. So, again, in Australia, the forests present a melancholy and shadeless character from their leafless casuari^ nas, acacias, and eucalypti, whereas, if temperature alone were concern- ed, they should offer the same aspect as the forests of North America and- Europe. Kestricting our examination for the present to the influence of heat, it Influence of may be observed that this is by no means so simple as might h^atrand win- ^* ^^'^^ appear. Its distribution does not correspond with ter colds. the latitude, the lines of equal mean temperature, isothermal lines, not coinciding with the parallels of latitude. If we examine the zones of plant distribution just described, we find that they follow the isothermal lines much more closely than the latitudes ; but even here, again, there are very great deviations — deviations which, however, are to some extent understood when we recall that it is not so much with the mean annual temperature that plants are concerned as with the special temperature of particular moments of the year. For the most part they are affected by the heat of the summer season, which is their period of INFLUENCE OF THE AIR AND MOISTURE. 475 growth, and though two locaUtics may have the same mean annual tem- perature, it does not follow that their maximum of cold for the winter, and their maximum of heat for the summer, should coincide. It was such considerations that led to the construction of isotheral lines, or those of equal summer heat, and isochimenal lines, or those of equal winter cold. Into the causes which bring about this difference of heat distribution it is not necessary for us here to inquire minutely. They Causes of the are very various. The prevalent winds at different seasons ti.[^utio,j J^' of the year, ocean currents, tlie geological structure of a coun- heat. try, even what might be termed its optical qualities, that is, its power of absorbing the rays of the sun (for instance, the great Desert of Sahara disturbs the temperature of all Europe), and upon like principles must act the removal of extensive forests, and their substitution by equivalent surfaces of cultivated, differently colored, and differently absorbing lands, elevation above the sea level, for the higher the country the lower its temperature : these, and a multitude of other such conditions, impress an effect upon the distribution of heat. The mean annual temperature represents these and all other such influences, and includes all the varia- tions, diurnal and nocturnal, monthly and seasonal, for the year. The organic functions of a plant demand particular temperatures at particular times. There is, doubtless, a special degree best suited to the period of germination, another to the period of aerial growth, another to the period of fertilization, and another to that of ripening the seeds ; and these degrees differ in the case of different plants. Where the require- ments become so complicated, it would be eiToneous to expect that the mean annual temperature should satisfy them all. Connected in part with temperature, and in part w^ith elevation above the sea, are the variations in the density of the air. These influence of va- control, to a certain extent, the aerial supply to plants, the liations in the -, , . 1 -,...,. ,1- density of the quantity presented to their leaves diminishing as the density air— moisture, becomes less. ®''^- The same observation may be made respecting moisture, which, as is very well known, constitutes one of the most influential conditions in de- termining the growth of plants, and this in a double way, either as va- por contained in the air or as rain. The effect of rain in this respect is twofold : it diminishes the -quantity of atmospheric carbonic acid by exerting over it a solvent power, carrying it into the ground, and thereby reducing, by sometimes as much as one half, the supply on which the leaves are depending ; it also brings in larger quantities to the interior of the plant the saline constituents of the soil which are requisite for tis- sue development. To variations in the temperature, the density of the air, and its moist- 476 INFLUENCE OF THE SOIL AND LIGHT. Influence of uvG, as affecting the well-Leing of plants, may be added the the soil. chemical constitution of the soil upon which they grow. Lime- plants can never be developed except on soils in which that earth abund- antly occurs, and the same may be said of potash or soda plants, or, in short, of any w'hich demand some special mineral ingi-edient. Thus, for instance, the salsolas and salicornias, which grow abundantly on the At- lantic shores of France, and which require for their development the saline ingredients of the sea, are nowhere to be seen throughout Central Europe, though they reappear on the salt steppes of Russia, and abound around the Caspian. AVe should scarcely expect that sea-weeds, into the composition of which bromine and iodine abundantly enter, should ever grow in waters from which these chemical elements are totally ab- sent. Upcin these principles, the vegetation of extensive tracts of coun- try has undergone a change in an artificial way. Thus, for instance, in Virginia and other Southern States, we may pass for miles in succession through tracts in Avhich the ancient forest-growths have been replaced by the Pinus tffida, or old field pine. These are tracts from which the potash salts have been removed, to a great extent, by the culture of to- bacco. And of the indigenous trees, this pine requires the smallest pro- portion of those salts. It therefore can flourish where the others can not exist. From what has been said in the last chapter, it may be inferred that Influence of among the various conditions thus influencing the growth of the sun's light. ^ plant, none are of greater importance than the amount of light furnished to it. Through this agent the decomposition of carbonic acid is effected, and the plant obtains from the air the carbon it requires, out of which its solid structures are for the most part built. The rapid- ity with which the reduction of the carbonic acid takes place depends upon the brilliancy of the light, and the amount of carbon thus obtained upon that condition and the time of exposure conjointly. The amount of light received from the sun in any locality depends in a general way, as does the heat, upon the latitude ; but in both cases a multitude of disturb- ing agencies intervene. Variations of moisture control the supply of light by peraiitting a translucency, or establishing its opposite, a cloudiness or murkiness of the air. Other meteorological causes, as, for example, winds, by condensing or removing moisture, act in like manner ; so also do as- Influence of tronomical conditions, especially by influencing the relative the position of length of the day and night ; for, as Ave advance toward the the sun and , , . , i i • i i i length of the pole, the Summer sun is above the horizon longer and longer. '^^y- In Northern Europe, during the month of June, he never sets, but remains all night, if night it can be called, above the horizon ; and, as Berzelius well remarks, "Under the influence of this midnight sun of the Xorth, the life of plants runs tlirough the same cycle of change in DEFINITE QUANTITY OF HEAT REQUIRED. 477 six weeks avIucIi it takes four or five montlis to accomplish in beautiful Italy." Attempts have been made to establish the doctrine that every plant requires, from the time of its germination to the close of its Definite quan- organic activity, a definite amount of heat. The following l^'^-y,"^ ^^^^^ ^^' example, in the case of barley, is furnished by Schleiden. plants. " In Egypt, on the banks of the Nile, barley is sown at the end of No- vember, and harvested at the end of February ; the period of vegetation, therefore, amounts to about 90 days, and the mean temperature of this season is 69° 48^ In Tuqueres, near to Cumbal, under the equator, the time of sowing in the mountains for barley is about the 1st of June, the time of harvest the middle of November ; the mean temperature of this vegetating season of 168 days is 50° 12''. At Santa Fe de Bogota they number 122 days between seed-time and harvest, Avith a mean tempera- ture of 57° 24^. If, now, the number of days is multiplied by the figures of the mean temperature, we obtain 6282 for Egypt, 8433-||^ for Tuque- res, for Santa Fe 6489-|-| ; therefore as nearly the same number as the uncertainty in the estimate of the days, the accurate mean temperature, and the want of knowledge whether or not the same kind of barley is cultivated in all the places, will allow us to expect. Similar results are obtained for wheat, maize, the potato, and other cultivated plants. We may express these results thus : Every cultivated plant requires a cer- tain quantity of heat for its development, but it is the same thing wheth- er this heat is distributed over a shorter or longer space of time, so that certain limits are not exceeded; for where the mean temperature sinks be- low 36° 24^, or where it rises above 71° 36'', barley wiU no longer ripen. Consequently, to define accurately the conditions of temperature which a plant requires to maintain it in a flourishing condition, we must state within what limits its period of vegetation may vary, and what quantity of heat it requires. This most remarkable circumstance was first ob- served -by Boussingault, but, unfortunately, we as yet possess not nearly sufficiently accurate accounts of the conditions of culture in the various regions of the earth to enable us to follow out this ingenious view in all its details." Respecting the calculations ofiered in the preceding paragraph, the re- mark may be made that they contain an element which vi- xhe effect of tiates their correctness, and that, if the proper data were re- the intensity 1 1 1 • ■ -I • Till T ^'^'i quantity sorted to, the general prmciple intended to be demonstrated of heat consid- would be far more clearly established. The degrees of the ®'^^*^- thermometer are not the data required, for that instrument indicates the intensity, but not the quantity of heat. If some form of calorimeter were substituted for it, the result would turn out very differently. As an illus- tration, if a mass of ice of constant surface was exposed to the warmth in 478 GENERATION OF HEAT. each of these various cases, the quantity of water arising from its melt- ing should be the same at the close of the specified number of days. In this case the true element is introduced — the element of quantity, as de- termined by one of the ordinary calorimetric methods. It is not, however, to be inferred from this criticism that the peculiar quality of heat Avhich we recognize indifferently by the terms intensity, temperature, or degree, is without significance in the case of plants : the limiting maxima and minima between which a given plant can exist prove that both conditions exert an influence, though they exert it in a different way. Doubtless a plant, from the time of its germination to that of the completion of its organic life, must have a definite quantity of heat measured out to it, but its organic functions might be fatally in- terfered with if the temperature should rise above a limiting maximum, or sink beneath a minimum. The definite quantity of heat in this manner demanded by each plant is probably connected with a purely mechanical effect — the necessity for the evaporation of a definite quantity of water by the leaves. The inor- ganic salt substances required by every plant are introduced through its roots in a state of solution in water, and, since these salts are mostly of sparing solubility, a great quantity of water is required to accomplish the object. Nevertheless, they are dissolved at a given heat-degree in an invariable proportion in the liquid, and are required by the plant in a determinate proportion as compared with its mass ; so that, were there no other reason, this doubtless would be sufficient to account for the cir- cumstance under consideration. It should also be remembered that §very plant generates a certain Disturbance amount of heat, which varies with its organic condition at the arising from time. The experiments of Professor Paine present this in an tiou ot"hIat interesting point of view. The following extract is from the in plants. Medical and Pliysiological Commentaries, vol. ii., p. 75 : "On the 9th of April, 1839, we repaired to a forest in New Jersey, Prof. Paine's provided with very dehcate thermometers, of Fahrenheit's experiments, scale. Constructed for our object. The bulbs were no larger than the stem, the range of the mercuiy extensive, and the degrees marked upon the glass. The stems filled exactly the bore of a small spiral auger, and when the glass was introduced the air was excluded by applying a silk handkerchief around the hole. The perforations were all made on the northern side of the trees. Fifteen minutes, at least, were allowed for the subsidence of the heat that arose from the friction of the pei-forator, and the thermometer was generally reapplied at different in- tervals afterward. The perforations were made about four feet above the ground, and the diameters of the trees were ascertained at this point. When the diameter was five inches or more, the perforations were made VARIATIONS IN THE SPECIES. 479 to the depth of two and a half inches. When tlic diameter was less than five inches, the thermometer was introduced as far as the centre of the tree." Of the tables given by Professor Paine I select the following : " Range of thermometer in the shade during the observations, which lasted six hours, from 38° to 52° : near freezing at sunrise. "A dead upright dry tree was selected as a standard of comparison. Its diameter was twelve inches. The temperature of this tree, at the close of our observations, was 45° at the centre and in all other parts. " Juglans squamosa, d lametc .1- 10 in ches, 48'^ Buds slightly e do. do. a 6 " 49° do. Fagus svlvatica, a 10 40° Buds swelling. Quercus tinctoria, a 7 49° No budding. Castanea Americaua, 11 12 " 50° do. Betula nigra, <( 4 " 51° Flowering. Salix Babylonica, u 18 53° Buds unfolded do. do. a 18 58° do. Pinus Canadensis, u IS 54° Platanus Occidentalis, (( 18 50° No budding. do. do. i( 6 54° do. do. do. i( i " 55° do. Juniperus Viginiana, (( i " 55° Eobinia pseudacacia, (( 3 " 62° do. Populus Isevigata, (( 4 " 62° In bloom. do. do. (C 4 64° do. do. do. 11 3 " 63° do. do. do. (( 3 65° do. do. do. (( 2 67° do. do. do. (( If 68° do." The heat which is thus liberated by plants stands in the stead of a certain amount of atmospheric heat, and therefore complicates the preced- ing considerations. By such facts as those which have now been presented, We may be satisfied that the well-being of plants is afiected, and even Accompiish- their existence determined by the influence of external agents, "j'onsinth^sp^c^ and that, in this manner, they are capable of having changes cies of plants, impressed upon them even in an artificial way. If we furnish to them those materials or conditions which their circumstances require, they will grow with luxuriance, or under an opposite state of things will dwarf away ; and where, for a long period of time, such conditions are imposed upon successive generations of them, a permanent change may be effect- ed, those which have appeared as varieties assuming the more definite tbrm and persistency of sub-species. The general impression alluded to in the last chapter, that such peculiarities are only to be extended by budding or other equivalent operations, and that those which we regard as different individuals are truly fragments or parts of the same individ- ual, does not here j)roperly apply. A like propagation of peculiarity is. 480 SECULAR CHANGES IN PLANTS. in a multitude of instances, accomplislied by the use of seeds, and this precisely in the instance in which we should be led to expect it. Of our kitchen-garden plants, the carrot, the beet, tlie turnip, the cabbage, the pea, etc., we propagate the expected kind without any uncertainty by the use of seeds, never supposing that they will run back to the wild stock, or give origin to plants different to those from Avhich they were derived. The care of man, exerted for many years upon these vegetables, has, then, impressed upon them a change veiy far from ephemeral in its nature, and enabled tliem to pass from the condition of mere varieties into that of actual sub-species. Acknowledging, therefore, the influence which physical agents exert on Necessity of the growth and development of plants, and admitting that long periods of f^vorino; circumstances will briner on a modification of forai, time for chang- o _ ~ ing plants. especially if applied long enough, and that man himself, by his arts of culture, can, without difficulty, establish similar variations, we might be led to expect that more profound changes in external circum- stances, if steadily applied through extended periods of time, would give origin to more striking results. A variation in the constitution of the air, in the brilliancy of light, in the mean temperature, moisture, or chemical constitution of the soil, if kept up for thousands of years, or permanent- ly established, could not fail to exert a prodigious effect upon the whole vegetable world. If, for example, the brilliancy of the sun in the slow lapse of centuries should gradually decline, or the mean temperature of the surface of the earth should descend, or enormous quantities of car- bonic acid be permanently removed from the air and replaced by equiva- lent volumes of oxygen gas ; if carbonate of lime, to an extent sufficient for the formation of geological sti'ata, were removed from the waters, in which it could no longer be held in solution because of the withdrawal of carbonic acid from the atmosphere, it must follow, as a matter of inev- itable necessity, that the whole vegetable world would feel the change. Plants that at one time existed could exist no more ; others, by gradu- ally accommodating themselves to the slow revolution, would exhibit here the development of one part, there the development of another, and some, which perhaps maintain themselves with difficulty under the old state of things, would now begin to develop themselves in a more luxu- riant way. The changes here spoken of hypothetically have, however, actually oc- Secular changes curred in the history of the earth. We can not shut our occurring to the eycs to the corresponding march which vegetation has made, sfonin^°v-aria-^" Commencing in the earliest geological times with the stem- tions in plants, less ciyptogamia, followed by those provided with stems and leaves, the gymnospores, such as the conifers and cycadeaa, next making their appearance, after these, monocotyledons, and at last the EPOCHS OF THE GLOBE. 481 dicotyledons — a steady progression from those which we may term of a lower to those of a more elevated organization, and all this was produced by the inliuencc of physical agents. On so lirm a footing may we regard this doctrine as now placed, that we can use it for the purpose of determining from the ascer- ^ j.^^^. tained botanical condition of our planet at any period the these principles physical conditions under which she then existed, and this ^'^'^'^^^^ ■>'• with a precision constantly becoming greater. Among the more impor- tant facts which have been distinctly made out, a few may be cited as illustrations of the subject now treated of. For example, 1st. The ex- istence of a tropical climate in regions of very high latitude, as is proved by the occuiTence of fossil tropical plants therein ; 2d. That all over the globe the temperature was once nearly uniform, nothing answering to what we now terra climates existing, as is proved by the uniformity of the vegetable growths preserved as coal from the equator to near the polar circles — great arborescent cryptogamia, exceeding in size the arborescent ferns now growing in the Pacific islands under the equinoctial line. From such a botanical fact, we reason without error to the Succession of conclusion that in those times the influence of the sun, so climates on the far as the supply of heat was concerned, must have been ined from its wholly overpowered, the intrinsic temperature of the planet ^°^®'^ ^°^^- obliterating all climate subdivisions. 3d. That these climate subdivis- ions, which are now presented as existing side by side in zones upon the planet, were introduced for each latitude in an order of succession as to time ; that even the frigid zone, by reason of the cooling of the earth, ]ias passed through an ultra-tropical, a tropical, and a temperate degree of heat to reach its present state ; 4th. That the extinction of the old vegetable forms was accomplished by an inability of those organisms to maintain themselves in the physical revolution that was gradually taking- place. Among such may be mentioned the dying out of gigantic equi- setums or horsetails twenty feet high, club mosses rivaling forest trees, calamites and stigmarias, these, as they disappeared, being replaced by cycadacea3, and coniferse, and tree-like liliaceas. Even long after the de- posit of the coal there flourished in England innumerable palms, whicli maintained themselves, with their tropical associates, into the tertiary times. Among the physical events which geological researches disclose, there are two of surpassing importance in the history of the globe, ,j,^^ epochs in and both of them immediately connected with the doctrine the history of we have under discussion ; these are the change impressed ® s o e. on the atmosphere by the withdrawal from it of those enormous masses of carbon deposited under the different forms of coal, and the localiza- tion of plants and animals in climate distribution as the sun's rays be- Hh 482 LOCALIZATION OF PLANTS. gan to assert their influence through the lowering of the surface temper- Change in the ature of the globe. The first of these events was not alone thratmos-'^ ° limited in its effect to a disturbance of the organic functions phere. of plants by diminishing the amount of gaseous material from which they gathered their support in the air : its influence was also felt in animal life by rendering that possible which was not possible before — the existence of the quickly-respiring and hot-blooded tribes ; for it fol- lows as a chemical necessity that, under the circumstances of the case, the removal of the carbonic acid was attended with the evolution of an equal volume of oxygen gas. As respects the influence of the sun, which gradually led to the establishment of climates, first in an order of time, and then in an order of place, this was the signal for the localization of Definite locaii- P^^^^^ ^^^ animals in definite regions. From many coun- zation of plants tries which they had thus far inhabited they were now ex- pelled, and barriers of temperature placed around them which they could never again overpass. And as these great changes occurred, they were attended by the extinction of countless forms in both king- doms, which were utterly unable to maintain themselves in the new cir- cumstances around them, their places being occupied by the extension of contemporaneous forms, or by the appearance of others that were whol- ly new. As an illustration of the manner in which a vegetable organism may Example of the ^® tised in this inverse way for the determination of physic- inverse method al conditions, I may introduce the following quotation from rom c ei en. gQ}jjgj(jQ22 : " The gradual conversion of the universal trop- ical climate into the present climatal zones may be shown in another very interesting manner in quite a special instance. All ligneous trunks of coniferous trees continually increase in thickness at all parts of their circumference. In the equatorial regions, where the climate retains the same character uninterruptedly throughout the year, this thickening of the trunk proceeds without interruption and homogeneously ; no mark betrays, in a smooth, transverse section of the stem, the time which was required for its formation. As we proceed toward the north, however, as the climatal conditions produce continually-increasing diversity in the particular seasons, the corresponding growth in thickness shows itself to have been furthered by the favorable season, and restrained or altogether interrupted by the unpropitious times. In a cross section of a stem are seen, the higher the latitude in which it has grown, the greater difier- ences in the structure of the successive portions of the wood, until final- ly, in the latitudes where there is a severe alternation of winter and sum- mer, so striking becomes the difference between the wood last formed in summer and that first produced in the next spring, that we may count, in the number of annular marks thus produced in a cross section, with ABRUPT AND GRADUAL IMPRESSIONS. 483 great certainty and accuracy, the number of years which have been oc- cupied in the formation of the trunk. The circular lines upon the cross section, well known to every forester, are thence called annual rings. When, fortiiied Avith the knowledge of this fact, we compare with each other the trunks of the conifers which we obtain from the various epochs of formation, we find that the oldest remains exhibit no trace whatever of annual rings, but, in the course of time, they become continually more defined, so that lastly, in the most recent formations — for instance, in the upper brown coal — they appear marked just as distinctly as in the trees now living in the same localities." In speaking of artificial changes impressed by culture upon domestic plants which have been converted from varieties into sub- Difference be- species, the importance of the element of time was insisted t^^^en abrupt -P , • 1 1 1 • 1 1 ^'^^^ gradual upon, in the same manner, m the changes wmcn have oc- impressions on curred during geological periods, the successive replacement pi^^^s. of one class of vegetable forms by another, that element again obtrudes itself upon our notice. If a few years serve to establish such minor changes as the perpetuation of varieties into sub-species, what should be expected from the enduring influence of innumerable centuries ? More- over, in these artificial results there is a necessary abruptness, the appli- cation of the disturbance, which can not but exert an unfavorable influ- ence. No time is afforded to the organism to suit itself gradually to the force exerted upon it, none for acclimating itself to the external variation. It must either yield at once or perish. But how difierent as respects the method of application in the case of the organic series ! If it be de- cline of temperature that we consider, how shall we enumerate the suc- cessive centuries that must have elapsed as the descent was made from degree to degree ? In these later times, as is admitted on all hands, the mean temperature of the surface could not decline the tenth part of a Fahrenheit degree in the lapse of 10,000 years. Yet the interval has transpired during which there has been a gradual descent firom those high thermometric points at which the existence of organic life was bare- ly possible, and, in truth, through a far greater range than that. It sig- nifies nothing that this descent might have been more rapid the higher the degree ; in any case, it implies a prodigious interval of time. Or, if we consider variations in the light of the sun, either because of his being a variable star, or because of the gradual clearing up and improving transparency of the atmosphere, we are brought again to the same re- sult — long periods of time ; for, though there may be among the fixed stars some whose periods of variation, as respects brilliancy, are short, included perhaps within a few days, or even hours, if we had no better evidence, history assures that our sun is not one of that quickly-varying group. Or, again, if we consider the changes which have indisputably 484 SECULAR PHYSICAL CHANGES. occurred in the chemical constitution of the air, the diminution of its an- cient amount of carbonic acid, the reduction of the mean percentage of its vapor of water, the increase of its oxygen, these again are changes of a secular kind, the time required for the accomplishment of which is wholly beyond our finite comprehension. In such a gradual advance, organisms for many generations might show but little change, yet, in the end, the effect must come to be profound. Indeed, all the great nat- ural effects we witness are accomplished in this quiet and gradual way : the traces of tempests and other catastrophes are very soon effaced, no matter how violent the original commotion may have been ; but warmth, and light, and moisture — causes which act so gently that we might over- look them — are the agents which control the universal aspect of things. In this, as in other respects, the strong are always the silent ; and in the Secular phys- slow lapse of many centuries, by the gradual operation of icai changes at- -universal forccs thus gently applied, organic forms had an ductions^nd Opportunity of accommodating or acclimating themselves to extinctions. ^j^g ^^^ state, or, if they failed to do so through some want of correspondence in their structure, they gradually passed away and be- came extinct. It is no argument against the transmutation of species, or even of genera, that we have never witnessed such an event. We can never witness the necessary combination of circumstances which should bring it about, above all, as regards the needful lapse of time, the slow yielding and accommodation which such a change implies. In this, as in those great modifications that have occurred in the stratification of the globe, the like of which has never been seen in the periods of human record, our want of familiarity with them is a matter of very little mo- ment. The remark of an eminent geologist applies with equal force in both cases : " Changes that are rare in time become frequent in eter- nity." But it may be said that if by external influences the successive spe- Graduai change cies and genera in this manner arose, we ought to find, produTe^efffect^ ®^®^^ between those which are most closely allied, many in- by abrupt crises, termcdiate forms ; for, since the active causes were gi-adual in their operation, one organism should pass into another by slow de- grees — so insensibly, indeed, that it would perhaps be impossible to indi- cate the point at which the proper transition was made. Such an ex- pectation is, however, founded upon a total misconception of the charac- ter of these progresses, for a force applied for thousands of years ma}' show no effect, but at last may manifest itself by an instant crisis. Mul- titudes of illustrations might be furnished of this principle ; for instance, the motion of a comet may be toward the sun in a path which is almost a straight line for scores of centuries, but on a sudden it assumes a curvi- linear course, and accomplishes its perihelion passage in perhaps a few MECHANICAL ILLUSTEATION OF CRISES. 485 houi's, and then, receding from that luminary, takes a course not sensi- bly differing from a straight line, and occupying perhaps centuries in its accomplishment. The variations of direction and of velocity are, how- ever, the necessary results of the conditions under which its movement is taking place, and may he truly said to have heen originally included therein. This instantaneous or critical assumption of a new phase may also he illustrated by the functions of organic beings. Thus the j,, foetal mammal, though provided with lungs, a mechanism in from the life all respects ready for aerial respiration, does not pass by ° ™^°" graduated steps from placental, which is truly aquatic breathing, but the change takes place on a sudden at the moment of birth. These and other such instances may therefore satisfy us that what an imperfect in- duction would lead us to look upon as a departure from the existing rule, or as a breach of the law, may, in reality, be nothing more than the im- mediate or legitimate consequence of it. They may teach us that, in the natural progress of things, variations do not necessarily always take place in so gradual a manner as to be undistinguishable from stage to stage, but sometimes instantaneously, and, as it were, by a crisis. Again, this variation by crises may be illustrated by many familiar mechanical contrivances. The case of the common seconds Mechanical ii- striking clock may furnish an example. Let us trace the lustrations, successive conclusions to which an ingenious man might have come at the first introduction of this instrument, his investigation of it being sup- posed to exclude an inspection of its parts. After listening for a length of time to the beats of its pendulum, he would observe that these suc- ceeded at precisely regular intervals, and after extending his examination through two or three thousand of such occurrences, he would doubtless teel justified in coming to the conclusion that the construction was of such a nature that the passage of successive small intervals of time was indicated by the occurrence of a brief, dull sound. His first conclusion, therefore, would be, that the instrument would go on doing this continu- ously. At the close of 3600 such observations, when the truth of his in- duction appeared to have become irresistible, his attention would be ar- rested, and his faith in the correctness and completeness of the extensive inductive conclusion he had just drawn would be shaken by hearing one loud stroke upon a bell. Now, probably, he would suspect that the struc- ture of the instrument was such that it indicated the lapse of each 3600 minor beats by oiie louder stroke. This would be his second and more improved induction. Setting himself to verify the truth of this hypothesis, he would watch the instrument through 3600 beats more, confidently expecting that, at 486 MECHANICAL ILLUSTEATION OF CRISES. the conclusion thereof, the hypothesis to which he had thus hastened would be confirmed. True to the time, the hell would again strike, but, instead of striking only once, it would strike twice. Admonished of the hastiness of his hypothesis, our philosopher might now be induced to pause before he generalized again, and, after watching through 3600 more beats, the clock would strike thrice. Now, surely, he would feel absolutely certain of having reached the true interpretation of the action of the machine at last. His third and corrected conclusion would be that each group of 3600 beats was register- ed by the bell, the number of strokes upon which indicated the number of such groups, and that this it would do continuously. Patiently listening through many thousand beats, he would find that every thing confirmed his new and improved induction. He would hear, in their regular succession, ten, eleven, and twelve strokes made by the clock. Of course, his expectation would now be confirmed that at the next time the clock struck it would be thirteen. How great would be his surprise to find it was only one ! Perseveringly continuing his examination, he would reach, at last, the true law regulating the indications of the machine, and would find that the partial conclusions to which he had successively arrived, and which he had thought, at the time, to be substantiated by a superfluity of facts, were in themselves incomplete, and in that respect erroneous ; but he would also observe that whatever truth there was in them was embraced in the final induction that the machine was not as simple as he had at first supposed, and that the critical variations which in succession had surprised him were all embraced in the original plan of its construction. Our imaginary philosopher has passed through a mental exercise precise- ly like that which is befalling modern comparative physiologists. From his labors, disappointments, and eventual success, they may gather en- couragement. The clock of the universe does not forever go on vibrat- ing monotonously. A thousand years upon it are only as the beat of a pendulum ; but it, too, has its periods of critical variation — variations that were included in its original device. The point which I wish to impress by these illustrations is, that there , ,. ,. „ is a definite career which an organism must follow, accord- Application 01 • 1 • 1 J • • J 1 the preceding ing to its cxposurc to cxistmg physical conditions, and that, lUustration. though this career may seem to be continuous, it by no means follows that it shall not exhibit an instantaneous and critical change, and that, on a sudden, the organism may assume a specifically new aspect ; and though, in what has thus far been said, reference has been had chief- influence of ly to plants, these observations all apply, in like manner, to physical agents animals. I do not propose, however, to enter on that branch on the form of ^^ • c i • n man. of the inquiry now, but, as an illustration of the miluence oi THE INCA INDIANS. 487 physical agents, even on the highest — man himsell' — shall offer the fol- lowing example : ]\L D'Orbigny, in his description of the Inca Indians of South Amer- ica, remarks, " It has always been observed that the trunk is case of the longer in proportion than among other Americans, and that, l"ca Indians, for the same reason, the extremities are, on the contrary, shorter. Wc endeavored, at the same time, to explain this fact by the greater devel- opment of the chest. It would appear that any part of the body may take a greater extension from any adequate cause, while other parts fol- low the ordinary course. An evident proof of this fact may be found in the phenomena of imperfect conformation, in which a certain part of the body, in consequence of deformity, does not assume, in external appear- ance, its complete natural development, as we see in the trunk of a dwarf, while this defect does not prevent the extremities from acquiring those proportions that they would have had if the trunk had received its full growth. This accounts for the w^ant of symmetry in the persons of dwarfs, and for that length of the upper and lower limbs so much out of proportion to the body. If we admit this fact, difficult to contest, w^hy, in the case in question, may we not as well admit that the chest, from a cause which we shall explain, having acquired a more than ordinary ex- tension, might naturally lengthen the trunk without causing the extrem- ities to lose their normal proportion, which would make it appear, as in- deed it would be, longer than among other men where no accident can have altered the form common to the race ? " Let us return to the causes which occasion in the Incas the great volume of chest which has been observed in them. Many considera- tions have led us to attribute it to the influence of the elevated regions in which they live, and to the modifications occasioned by the extreme expansion of the air. The plateaux which they inhabit are always com- prised between the limits of 7500 to 15,000 feet above the level of the sea. There the air is so rarefied that a much gi'eater quantity must be inhaled at each inspiration than at the level of the ocean. The lungs require, in consequence of their great necessary volume, and of their greater dilatation in breathing, a cavity larger than in the lower regions. This cavity receives from infancy and during the time of its growth a great development entirely independent of that of the other parts. We were desirous of determining -ivhether, as we might suppose a pno?^, the lungs, in consequence of their great size, were not subject to extraordi- nary modifications. Inhabiting the city of La Paz, upward of 11,000 feet above the level of the ocean, and being informed that in the hospital there were constantly Indians from the populous plateaux still more ele- vated, we had recourse to the kindness of our countryman, M. Burnier, physician to the hospital, and he permitted us to make a post mortem 488 EXTINCTION OF FORMS. examination of some of these Indians from the highest regions. In these we have, as we expected, found the lungs of an extraordinary dimension, which the external form of the chest clearly indicated. We remarked that the cells were much larger and more in number than in those of the lungs we had dissected in France ; a condition very necessary to increase the surface in contact with the ambient fluid. To conclude, we have discovered, 1st. That the cells were more dilated ; 2d. That their dilata- tion increases considerably the volume of the lungs ; 3d. That, conse- quently, they must have to contain them a larger cavity; 4th. That, therefore, the chest has a much larger capacity than in the nomial state ; oth. That this great development of the chest elongates the trunk beyond its natural proportions, and places it almost out of harmony with the length of the extremities, this remaining the same as if the chest had preserved its natural dimensions." With respect to the doctrine of the influence of physical agents on or- ,. sranization o-eneraUy, we admit without hesitation that the Argument from o o J ' the extinction extinction of forms has been accomplished through outward of forms. causes, decline of heat, etc. These extinctions are intimate- ly connected with the appearance of new organisms, and, indeed, are to be regarded as being, with them, essential parts of a common plan. It would not appear agreeable to the mode in which the scheme of Nature is carried out to invoke one class of influences for the removal of the vanishing forms, and a totally different one for the introduction of the new-comers. There seems to be a better harmony in the supposition that all these things are managed upon similar principles, and that, since it is the failure of congenial conditions which closes the term of life of a race, it was the suitability of those conditions, or their conspiring together, which gave it origin. The influence of decline of temperature appears when we examine par- j „ „ ticular individuals or particular species either of plants or of decline of tem- animals. Thus the Virginia cherry attains the height of 100 perature. £^^^ -^ ^^^ Southern States, and is dwarfed to a shrub of not more than five feet at the great Slave Lake ; the nasturtium, which is a woody shrub in warm climates, becomes a succulent annual in cold. Or, if we examine some special tribe of life, as Milne Edwards has done in the case of crustaceans, the higher the temperature, the greater the lia- bility to variations of species, the more numerous also the diflerences of Ibrm, and the attainment of a greater individual size. That these varia- tions are the actual consequences of the physical conditions, and not merely collateral results, is shown by supplying the condition that is wanting. We can imitate the natural result, in an artificial way, in hot- houses ; the plants of the warmest climate may be grown, and the effects of summer imitated at any season of the year. What better proof could METAIMOKPIIOSIS OF ORGANISMS. 489 we have of the control of the agent licat over development, than the well- ascertained fact that the time of emersion of larvae depends upon the temperature ? The silk-grower, by placing the eggs of the insect in an ice-house, retards them as long as he pleases. The amputated limbs of the water-newt can only be reproduced at a temperature from 58° to 75°. The tadpole, kept in the dark, does not pass on to development as a frog. In decaying organic solutions, animalcules do not appear if light be ex- cluded. Upon the whole, therefore, we conclude that organisms of every kind, so tar from presenting any resistance to change, are im- Changes of or- pressed without any difficulty by every exterior condition : s^^^^^^^on de- ■^ ^ _ _ '' ./././ ■> pend on inva- and since existing natural circumstances have been main- riable laws, tained for a long time without any apparent change, their sameness pro- duces a sameness in the order and manner of development. But it should be borne in mind that this idea of sameness can be entertained only on an imperfect view of the state of Nature, for there is scarce one of those conditions, to the sameness of which we have been referring, which has not, in reality, undergone slow secular variations ; and with those changes there have been changes in the manner of development. In truth, as I have on a former page observed, the only things which are absolutely unchangeable are the laws of Nature, such, for instance, as that of gravitation ; every thing else is to be looked upon as an effect, or as a changeable phenomenon arising from the operation of those laws. So, therefore, though, in this chapter, the terms physical in- Successive met- fluences and natural conditions have been repeatedly used, consequence^of yet a higher and more philosophical view of the case brings invariable law. us inevitably at last to the idea of law ; and therefore I accept the in- terpretation of all these facts, which has of late years been impressing itself more and more strongly and clearly on the minds of physiologists, that the development of every organism, from a primordial cell to its iinal condition, however elevated that condition may be, is the inevitable consequence of the operation of a universal, invariable, and eternal law. All animals, no matter what position they occupy in the scale of na- ture, unquestionably arise in the first instance from a cell, which, possess- ing the power of giving birth to other cells, a congeries at last arises, the size and form of which is determined wholly by external circumstances. In all cases, the material from which these cells are formed is obtained from without, and, whatever the eventual shape of the structure may be, the first cell is in all instances alike. There is no perceptible ditFerence between the primordial cell which is to produce the lowest plant and that which is to evolve itself into the most elaborate animal. The mode of growth, and the arrangement of the new cells as they com'e into exist- ence, determining not only the form, but also the functions of the new 490 METAMORPHOSIS OF ORGANISMS. Leing, depend on the particular physical conditions under which the growth is taking place. The germ which is to produce a lichen obtains from materials around it the substances it wants as best it may ; but the germ which is to end in the development of man is brought in suc- cession under the influence of many distinct states. As a consequence of this, it gives rise in succession to a series of animated forms, which, as- suming by degrees a higher complexity, end at last in the perfect human being. At one time it was believed that these metamorphoses, as they are termed^ are limited to insects and frogs : the insect, which at first appears under the form of a caterpillar as it comes from the egg, and, passing through the pupa state, at last takes its true position as a wing- ed being ; the frog, which, appearing at first from the ovum as a true fish, whose respiration is carried forward by gills, and whose life is lim- ited to the water, at last assumes a new constitution and a new organi- zation, breathes by lungs, and becomes an amphibious reptile. But it is now known that these, so far from being exceptions, are only instances of a general rule, which is, that all organized beings shall begin existence at the bottom of the scale, and, taking on one type of life after another, in more or less rapid succession, end, finally, in assuming a size and form analogous to those of the parent which gave them birth. There is a general resemblance between the life of an individual and the life of a species. Each has its time of birth, its time of maturity, its time of decline ; each also has its embryonic states. The fossH forms of the early geological ages are in many cases the embryos of existing animals. Upon each all natural agents have exerted their effects, push- ing forward or retarding development ; and this applies not only to an- imals, but also to plants : it is in accordance with the principles we are setting forth that over the whole domain of life natural forces exert their sway. Change the conditions under which growth is taking place, and you at once change resulting form and function. It is in this man- ner that, on a small scale, the horticulturist works in furnishing us what are called improved varieties of flowers and fruits. It is in this manner that animals, known to have been indisputably of the same original kind, assume such different forms and characters in various climates. It is true, we can not expect in an abrupt manner to bring about such strik- ing modifications in a solitary individual, for the life of an individual is readily destroyed, but not so the life of a race ; and Nature, carrying on her operations in the slow lapse of centuries, and deahng with races rather than individuals, forces them up to any point of development she may desire, but still the impress of the laws under which they have been brought to that condition is upon them, and each betrays, in the embry- onic and foetal forms, a manifestation of the metamorphoses through which his race has run. RUDIMENTARY ORGANS. 491 Our attention might here be directed to that interesting class of phe- nomena known to comparative anatomists under the title of Rudimentary rudimentary organs — that is to say, organs which exist in an thdThuer- apparently undeveloped and useless condition, such, for in- pretation. stance, as the mammae of the male mammalian, or the subcutaneous feet of certain snakes — for these are facts intimately connected with the sub- ject before us. It looks as if Nature stopped short in her attempt at reaching perfection, but it proves to us the constancy of the plans on which she works. In the case of the whale, which, though apparently belonging to the fishes, is a warm-blooded mammal and suckles its young, the general type of its class is observed even down to minute particulars ; it is the attribute of those belonging to it that they shall have seven cer- vical vertebra^ and this is equally the case with the camelopard, witli its long, graceful neck, and the mole, which seems to have no neck at all. In the whale, which conforms to that general rule, the teeth are, moreover, found in the jaw, in the earlier period of life, uncut, precisely as we find them at birth in the human infant. In this last instance we think we see a wise provision and foresight of nature, which does not give to man these masticating organs before the time they are wanted ; but what are we to make of the former case ? Man is not always a true interpreter of the works of God. Shut up, as they are, in the interior of the bony mass of the jaw, never to be developed and never to be used, does not that look to a careless observer something like a work of super- erogation ? Or, in the case of such snakes as the anguis, typhlops, and amphisbasna, why is it that Nature has placed under the skin the bony representatives of the extremities : the mode of progression of those an- imals is by the use of the ribs, and organs such as feet are never wanted. We may also turn to the other department of physiology, the vegeta- ble world, and what do we there see? Rudimentary organs and excess of development are every where presented. An attentive examination of any flower proves that we may with truth regard it as a transformed branch, the law of development being such that that which might have passed forward to the condition of a branch has turned to the condition of a flower ; or, in still minuter particulars, we witness the same prin- ciple : that which might have evolved into a leaf turns indifferently, as circumstances may direct, into a sepal, a petal, or a stamen. But is it possible that there" is all this confusion and want of precision in the works of Nature ? Not so. If we consider rightly, Appearance of we shall come to the conclusion that Nature never works rudimentary , t T . organs the con- contmgently, nor resorts to a sudden contrivance to meet an sequence of exigency. All her operations are carried forward under far- ^^^^'• reaching and universal laws. These rudimentary and perhaps useless organs come into existence through a general plan, of which they are 492 OF THE ORGANIC CELL. witnesses to us, if they subserve no other duty. They tell the same great fact which is so loudly proclaimed by all the phenomena of the res- toration of parts and renovation of tissues, that the grouping of orga- nized matter into definite and special forms is not a wanton or chance ef- fect, but is the direct and inevitable consequence of invariable physical laws. Expedients are for the vacillating and weak, law is for the strong. It takes from the merit of any human contrivance if the engineer has to be constantly tampering with it to keep it going ; we admire the machine that continues its movements without variation after it has left its maker's hand. I think we can have no nobler conception of the great Author of the wonderful forms around us than to regard them all, the vegetable and animal, the living and lifeless, the earth, and the stars, and the numberless worlds that are beyond our vision, as the offspring of one primitive idea, and the consequences of one primordial law. CHAPTER III. OF THE ORGANIC CELL : ITS DEVELOPMENT, REPRODUCTION, AND DIF- FERENTIATION OF STRUCTURE AND FUNCTION. Simple and Nucleated Cells. — The Simple Cell: its Parts and Functions. — The Nucleated Cell: its Parts and Functions. — Activity of the Nucleus. — Other Forms of Cells. — Cells arise hy Self-origination and Reproduction. — Reproduction by Subdivision and Endogenously . The Animal Cell. — Forms of Cellular Tissue. — Forms of Vascular Tissue. — Spiral Vessels, Ducts, etc. Differentiation of Cells. — Acquisition of new Functions. — Differentiation of the Animal Cell — Depends on Physical Causes. — Influence of Heat and Air. — Epoch of Differentiation. The organic cell, which is the starting-point of every organism, veg- Simpieandnu- etablc or animal, consists of a vesicle or shell, with included cieated cells, contents. If the vesicle be of uniform thickness all over, the cell is a simple one ; but if there be upon some portion of it a thick- ened granular spot, the cell is said to be nucleated. The vesicle of the simple vegetable cell, more closely examined. The simple is found to be composed of different lamina or strata. The vegetable cell : innermost, designated the primordial utricle, consists of an cie,^and' endo- azotizcd substancc, a member of the protein group. On the chrome. extcrior of tliis pellicle, and, as it were, arising from its sur- face, lies the cell wall, which serves to give protection to the parts with- in. The cell wall is not a mere extension by thickening of the primor- dial utricle, as is proved by its chemical constitution ; for, though it may vary in physical condition from a mere glairy mucus to a firm woody THE NUCLEATED CELL. 493 texture, it unifoniily consists' of a non-nitrogenized body, gummy, amy- laceous, or ligneous. Indeed, though the vegetable cell is usually said to have two concentric investitures, the nitrogenized primordial utricle and the non-nitrogenized wall, it is more exact to describe the latter as consisting of several pellicles, which have been generated in succession from the outside surface of the utricle, and these differ from one another in their physical qualities, according as they are nearer to the surface of the utricle or nearer to the general exterior, recalling, in this respect, the analogous condition of the cuticle under circumstances that are some- what parallel. Within the primordial utricle, the cell contents present themselves of a different nature and different form, according as the species of the cell may be. In different cases they are colored of various tints, and are of various consistency, more solid or more liquid. To the cell-contents the convenient designation of endochrome is given. This interior content is not to be understood as having a homogenous constitution, since sometimes even its colored portions are separated out and arranged in dots or spiral lines, which are very distinct from the remaining uncolored material. The active portion of such a cell consists of the utricle and endochrome conjointly, the cell wall only discharging a mechanical office. In the simple cell, all parts of the utricle appear to be endowed with equal pow- er for carrying on the functions of the organism. But in those cells which possess a nucleus, the energy is no longer dif- fused with uniformity, the nucleus concentrating much of „ , , ,, the power in itself, and serving as a centre of activity. Its activity of its nitrogenized constitution indicates that it is in relation with ^^^ ®"^' the primordial utricle, and not with the cell wall ; a conclusion which is corroborated by its physiological activity, as also by the fact that in those nucleated cells which exhibit currents, the nucleus appears to be the starting-point from which they diverge in various directions. There are subordinate species of cells, as the spiral and the dotted. These exhibit points of re-enforcement or thickening, such Subordinate as the appearance of a thread wound spirally, or in dots here ^°^™^ °^ ^^^^'*- and there on the interior of the wall. There would seem to be a tend- ency during the development of a cell for these parts to assume a spiral arrangement. Even the endochrome shows this peculiarity, the green material being often arranged in a spiral course on the interior of the cell. Thus constituted, each cell runs through a definite cycle or career, hav- ing its moment of birth, its period of maturity, its time of death. Dur- ing its mature life it discharges with activity the special function to whicli it is devoted, but in so doing becomes eventually worn out and old. The period of activity of cells of different species is very different, some passing away quickly, and others having a longer duration. 494 llEPEODUCTION BY SUBDIVISION. The commencement of cells is either, 1st, by self-origination, or, 2d, ■ i f 11 ^y reproduction. 1st. Cells arise in an obscure manner from ijyseif-origina- homogeneous particles floating in a protoplasraa, which, tak- ^^'^' ing on development, have a vesicle thrown over them, and, being of a spherical shape, present the aspect of a cell wall and cavity. The granular content by degrees increases as the young cell grows in all its dimensions. From that granular content new cells may arise. Though this process is spoken of as one of self-origination, it is quite probable that the spherical and homogeneous particles floating in the protoplasma, and which were the points of origin of the cells that have arisen, were themselves nothing more than germs which had been pre- pared by an antecedent generation of cells. This is the opinion com- monly entertained of their nature, though its truth has never yet been demonstrated by actual observation. It is adopted because of its proba- bility, for we usually observe that every new organism is the descendant of an older one ; yet it should not be forgotten that there must have been a time when the first organic cell arose from inorganic material, and it is not unphilosophical to suppose that what must have occurred once may occur again. Origin of cells 2d. Cclls are reproduced from antecedent ones of the by reproduction, game kind by subdivision, by budding, by endogenous gen- eration. The reproduction of cells hy subdivision is strikingly illustrated by Reproduction theHasmatococcus binalis. The manner of the process seems by subdivision. \q Ijq as follows. The endoclirome of the original spherical cell, «, Fig. 230, begins to undergo bi-par- tition as at ^, and as the dividing portions recede from one another the primordial utri- cle bends round them. Next a layer of per- manent cell wall, of a mucous character on its exterior, is produced, which accompanies the inflection of the primordial utricle as at /^m) /^m =^^' "■' ^' ^'^^' ^^^^^ ^ while, the bi-partition is com- '9^ \^^ W^/^ v^p/ plete, and the separated portions constitute /^ /^^^^ distinct individual cells. The subdivision ^ '^/ may be repeated as at d. The seat of the ^Keproduction of H^matococcus binalis primaij action is Said to be in the endo- chrome ; but of this there may be reasonable doubt, since generally the primordial utricle is the place of energy of the cell ; and where nucleated cells undergo multiplication by this process of fissure, the nucleus di- vides along with the endochrome, so that both the resulting portions pos- sess a part of it. But if the utricle, with its nucleus, was inert during this operation, it would seem that the vesicle should tear any where REPRODUCTION BY BUDDING. 495 rather than through that thickened and stronger place. The phenomena are equally well accounted for by imputing the first action to the utricle itself, which, exerting a constrictive pressure upon the endochrome in the direction of one of the great circles of the cell, divides it in the manner that Ave see. This process of multiplication is exhibited in Fig. 231, in Conferv." A B Fig. 231. Wm Cell reproduction in ConfeiTa glomerata. glomerata, which consists of a system of cells arranged in a filament. At A two states are shown, complete partition at 5, and incomplete at a ; at B, C, D, the successive steps of partition, a being the primordial utricle, b the endochrome, c cell membrane, d mucous investment. At E the primordial utricles are separated, and the cell membrane intervenes. At r the membrane is completed so as to exhibit laminse. The cells which have thus arisen by subdivision soon grow to the size of the one from which they were derived, and are ready for subdi- vision in their turn. Indeed, it often happens that traces of incipient subdivision may be detected long before the cell has reached its mature dimensions. The reproduction of cells hy hudding may be illustrated by the vesi- cles of the yeast-plant ; and though, in those cases in which the budding- cell possesses a nucleus, the nucleus is not necessarily involved, yet the conclusion indicated in the preceding paragraph is greatly strengthened, for we must clearly attribute the result wliich now takes place to an in- creased nutrition of the primordial utricle upon a restricted portion of its surface, and not to a distention arising from a pressiu*e of the endo- chrome within. So closely does this resemble the preceding mode of re- production, that they are commonly said to be really of the same kind, or, rather, to offer no other distinction than this, that in the former the 496 THE ANIMAL CELL. cell divides into portions wliicli are sensibly equal, in this into unequal parts. Cells are said to arise from endogenous generation when they make E doo-en us ^^^^^^' ^^'^t appearance in the cavity of a former cell, of which generation of the endochrome exhibits a disposition to divide into man}' small portions, at first doubtfully, then more distinctly, and each one of these portions obtaining a covering investiture or primordial utricle for itself. The process continues until the young brood of cells has reached a certain degree of perfection, when they escape from their confinement, either by the fissuring or deliquescence of the old cell wall. The young cells may now lead an independent life and grow rapidly. In this manner zoospores arise, which are young cells having for a time a power of locomotion, from cilia which have been developed from their walls, or for other reasons. The reproduction of cells hy endogenous generation is commonly at- tributed to an action arising in the endochrome which brings on its sub- division into portions. From the fact that these portions are eventually found clothed with a primordial utricle, we might be led to suspect that the original seat of the action is in this, as in the preceding cases, that portion of the original cell which, undergoing projection internally, di- vides the endochrome and incloses the portions in its meshes. Such membranous projections may be difficult of detection in the first instance, because of their extreme tenuity ; nor is the fact that the zoospores move freely in the cavity of the mother cell just before their escape at all in contradiction to this. The animal cell presents a structural arrangement dififering from Peculiarity of the Vegetable in this, that it does not possess a proper cell the animal cell. -^^11, but consists of a primordial utricle and interior con- tent alone. Its manner of reproduction is of three kinds: 1st. From germs ; 2d. By fissure ; 3d. .Endogenously. Where animal cells orig- inate from germs, these seem to be granules of af substance analogous to fibrin, which are floating in the formative liquid. In duplication by sub- division, the import of the nucleus is shown by the fact that the action begins at it. It may be said of animal cells that the nucleus maintains a more conspicuous relation than it does in the case of vegetable ones. Reproduction in the endogenous manner is carried forward in the case of these cells in the manner described in a preceding paragraph. OF THE CONSTRUCTION OF CELLTJLAK AND VASCULAE TISSUES. By their development and juxtaposition with one another, cells give ^ „ , ,. rise to continuous fabrics of various kinds, or cellular tissue. Cellular tissue, its various . If the development of new cells occurs in a space where there forms. -g freedom from pressure, the cells maintain their original CELLULAR TISSUE. 497 Fn > spherical form, as seen in the photogi-aph, I^'i//. 232. But slioukl tlie development occm* in a confined space, or under circumstances of pressure, the intercellular spaces Avhich necessarily ex- ist in the former case by reason of the spherical shape, are nowencroachedupon, and the cells assume various angular forms, such as parallelopipedons, rhom- bic dodecahedrons, &c. Of the former Ave have an example in the photograph, J^i(jf. 233, which represents a section of muriform cellular tissue. In other cases, with a view of giving resistance to press- Mmple cellular tissue, magnified 50 diameters, ^-^^.g^ ^^^^ interior of Cach of the CClls is fortified by a fibre, and thus arises the tissue of which we have an exam- Firj. 1?D4. Fig. 23r>. ilurlform cellular tissue, magnified 60 diameters. Fibro-cellular tissue, magnified 50 diameters. pie in the photograph, J^ig. 234. Two or more fibres may, in this man- ner, be employed, and \then such is the case, it is observed that they do not cross one another, the one winding from right to left, the other from left to right, but they are laid parallel to each other, and form a com- pound strand. In other cases the constituent cells of the tissue assume much more complicated forms, as, for instance, in the stellate variety. These more complicated forms prove that it is not altogether through the influence of a force of comptession that cells assume modified shapes, but that on many occasions the disposition of their primordial utricle to branch in various directions, of which mention has been made in a pre- ceding paragraph, is the true cause of the variations in question. This disposition to grow spontaneously in one direction rather than in another is the cause of the production of the different kinds of vascular tissue. A cell undergoing extreme elongation in one direction, either by II 498 VASCULAR TISSUE. Vascular tissue 1*6^^011 of this quality of its primordial utricle, or through un- and its modifi- equal nutrition, or other cause, gives origin to a tube. And if, of several cells thus elongated, and placed end to end on each other, the terminal portions should be obliterated either by rup- ture or absorption, a vessel permeable throughout is the result. In this manner vascular tissue arises. These vessels still exhibit the structural peculiarity of the cells from which they have originated in this, that they may be fortified in their interior with fibres wound in a spiral, and so constituting a spiral vessel ; or wound in rmgs, and forming annular ducts. In Hke manner, through similar modifications, the varieties known as reticulated and dotted ducts arise. In these fibro-vascular tissues it frequently happens that the fortifying thread is double or even quadru- ple. Of spiral vessels derived from a cactus we have an example in the photogTaph, Fig. 235, and in those from the banana in that of Fig. 236. Fig. 236. Fi(]. 235. '^ l^piral vessels of cactus, magnified 50 diameters. Spiral vessels of banana, magnified 50 diameters. The spiral vessels of plants contain air. Other tubes are for the Spiral vessels, conveyance of liquid; the laticiferous vessels, for example, Ve"3st/eo- ^-tich are branching tubes nifers. for transmitting the latex of plants. Again, in other cases, the interior of the vessel is more or less completely filled up by a gradual de- posit of solid material, it being in this manner that proper woody fibre is formed from long, spindle-shaped cells. Vascular tissue in coniferous plants presents a peculiar dotted as- pect from disc-like forms, exhibiting a pair of concentric circles, which are set at regular intervals upon it, as shown in the photograph, Fig. 'i?ri. Woody fibre of piiie, magaifieJ 50 diamettirs. YELLOW AND WHITE FIBROUS TISSUE. 499 which is dotted woody fibre from pine. The circular discs or glands run in single rows except in one place, where a double row is seen. Among true living pines more than two rows are not met with. In the Arauca- ria the rows are sometimes triple or even quadruple. Animal vascular tissue arises in the same manner as vegetable, by the conjunction of elongated cells and the obliteration of their Ygn a terminations. The physiological purposes these vessels sub- white fibrous serve are, as in the other instance, the conveyance of gases or *^^®"*^- liquids. But fibres may form in animal fabrics without the previous in- termedium of cells, either directly from fibrin, the parts of which possess the quality of agglutinating into threads, or from the coalescence under like circumstances of substances allied to gelatine, which yield the varie- ties of fibrous tissue known respectively as the yellow and the white, the former being composed of branching filaments, as seen in J^ig. 238. It is unacted upon by warm acetic acid, and, fr'om its extraordinary elas- Fig. 23S. Fig. 239. Yellow fibrous tissue, magnified 300 diameters. White fibrous tissue, magnified 300 diameters. ticity, is used wherever that quality is required. The latter, which is represented inFig. 239, shows strands of a wavy appearance: it is inelas- tic, softens under the action of acetic acid, being thereby distinguished from the pre- ceding, and is employed on account of its tenacity wherever resistance to exten- sion is required, as, for example, in the ligaments of the joints. The solid ani- ;!^ mal fibres are therefore employed where physical qualities are necessary, the hol- low tubes for organic processes. By some physiologists it is believed that both yellow and white fibrous tissue arise from cells. Areolar tissue, magnified ib diameters. Areolar or Connective tissue. Fig. 240, 500 DIFFEREXTIATIOX OF CELLS. is composed of the two preceding elements, the yellow and white fibrous- interwoven with each other so as to constitute a porous structure, with a multitude of intercommunicating spaces. It is to be understood that these interstices are wholly distinct from cells ; hence the inapplicability of the term cellular, sometimes employed for this tissue. Areolar tissue is employed for uniting the various animal parts. Its interspaces are filled with a fluid, which, when in excess, is spoken of as dropsical effu- sion. Air, artificially or accidentally mtroduced at any point into it, may pass to every part, as is illustrated in cases of emphysema. The speci- men from which the figure is taken was in this manner inflated. By the differentiation of cells is meant the assumption of a variation Differentiation in their Structure from which follows, as a consequence, the of cells. capacity of discharging new functions. When the red snow- alga multiplies, as previously described, each of the young cells resem- bles that from which it was derived in structure, and discharges a simi- lar office. In such a case there is development, but not differentiation. When, on the contrary, a lichen grows on a rock, though the original tendency in development may have been for the production of cells firom the first germ absolutely similar in all directions, yet the circumstances of growth are such that very soon the physical conditions under which the cells of different parts of the growing mass are generated become dif- ferent. Those which are next to the rock are screened by the superin- cumbent ones from the sunlight and the air ; they are therefore develop- ed in a comparative obscurity, and in the presence of moisture holding in Acquisition of solution inorganic salts. Under such circumstances, it is to new functions, ^jq expected that a modification will ensue in their construc- tion, and that they will be different from those which are developing on the exterior in contact with the dry air ; and, since a change of structure invariably implies a change of ftmction, we might expect, as in reality is the case, that the outer cells are for the obtaining of carbon from the air, being acted upon by the simlight, and the under cells for procuring moist- ure and such saline substances as may be wanted from the rock surface below. In such a case as this there is a differentiation both of structure and of function. Structural differentiation is to be received as the cause of functional Differentiation differentiation, which is its consequence. The former, in in a regular se- every instance, arises from the changed circumstances under to be determ- which cclls are being generated, and if this change of circum- ined by law. gtanccs follows a regular order or sequence, the differentia- tion will assume the appearance of being guided by a fixed law. Many physiologists, who have not been disposed to accord to physical agents a due influence in this respect, have therefore imputed to the developing cell a power or property of spontaneously pursuing a determinate career. DIFFERENTIATION OF ANIMALS. 501 It is clear that the facts are capable of interpretation either upon tlie doc- trine that external conditions guide or compel the cell in its development- al career, or that it, by reason of an innate power, spontaneously pursues a determinate course in spite of them ; determinate, because that power is acting under a law. The mixed doctrine, which imputes the career of development in part to the innate power of the cell, and in part to the in- fluence of external conditions, it is needless for us here to consider. No doubt can be entertained of the fact that a cell or congeries of cells will differentiate Avhen submitted to new physical conditions while in the act of development. Thus certain lichens pass into forms analogous to algffi if the normal conditions of their production be reversed — if, instead of developing in places that are dry and brightly illuminated, they are supplied with moisture, and made to grow in obscurity; and, in like man- ner, some of the fungi will simulate algas if they are compelled to vege- tate in water. The separation of the organ for the reception of water and that for the reception of carbon, which is first shadowed forth in the under and outer surface of the lichens, is manifested in perfection by highly-developed plants, in which the root discharges the former, and the leaves the latter duty, and these are separated widely apart from each other by the as- cending axis or stem. The remarks here made respecting plants might be repeated as re- gards animals, which, during their development, exhibit the -^.^ principle of differentiation even in a more striking way. of the animal Thus, in the protozoa, as in the protophyta, cells undergo '^^ ' duplication, and, by development in new positions, or under changed cir- cumstances, exhibit differentiation. The trivial circumstances under which new functions are assumed are well shown in Trembley's experi- ments with the hydra. This polype, which is nothing more Experiments than a gastric sac furnished with prehensile tentacles, re- ^ith tiie hydra, spires on its outer surface and digests on its inner ; but so closely are these functions blended together that, if the animal be turned inside out, the surface that did respire will now digest, and that which did digest will now respire. Indeed, we may in an ideal manner con- jg^^^^ differen- ceive of the production of the more elementary animal forms tiation of ani- as arising from a simple sac or bag, which, furnishing a start- ing-point, exhibits its first acquirement of localization of function by the doubling of one half into the other, thereby giving rise to a cup or pocket shaped form, so that respiration and digestion, which were confusedly and conjointly carried forward upon the same surface, are now parted from each other, the outside of the cup being devoted to the one, and the in- side to the other. Increased endowments are obtained by crimping or dividing the edge of the cup, prehensile organs of less or greater lengtii 502 CAUSE OF DIFFEEENTIATION. and power thereby arising ; and this, in reality, is the structure of the hydra just alluded to. Another advance is made by the preparation of new and complicated structures, fashioned out in the substance between the inner and the outer wall, and in this manner arise the various mech- anisms for respiration and reproduction. Such a state of things is pre- sented by the Actinia. It will be found, when we describe the development of the higher ani- Individuai and mals, that a parallelism is observed between the career of race develop- g^^h individual and that of the series to which it belongs, mais by differ- The evidence furnished by natural history and palgeontology entiation. proves that, in the development of animal species, there has been an orderly progress, not so much from those of a lower to those of a higher form, as from the general to the special ; a gradual parting out of structures and functions that were once commingled and coalesced, an elaboration which may be attributed either to a melioration of the cir- cumstances under which species were successively forming, or to the innate power possessed by the organic structure itself. Even at the pres- ent time our knowledge of the order of geological change is sufficiently exact to enable us to institute an inquiry into the probability of the cor- Differentiation rectness of each of these hypotheses, upon the principle that, depends on since there is that parallelism between the career of individ- pnysical cir- -t cumstances. ual development and race development, there should also be an analogy in the physical circumstances under which they have taken place. Among conditions in animal development, two prominent ones may be mentioned ; they are the degree of temperature at which the pro- cess is carried forward, and the quality or nature of the medium supplied for respiration. No doubt can now exist that, as regards the former, there has been a gradual diminution from the early times, and that, as respects the latter, the quantity of oxygen furnished in the medium of respiration has been increased. It has long been observed, in a general way, that there is a correspondence between the activity of respiration and the degree of animal endowment, both as regards the individual and I fl n f *^® race. The provision made for the more perfect conduc- the aerial tion of the process from the moment that the embryo exhibits ^^ ^^' any arterialization of its blood, is always attended with, if it is not the cause of, increasing animal power. The supply of oxygen at the first period is very imperfect, but instrumental means are introduced in succession to increase the amount. When a mere membrane has be- come insufficient to meet the requirements, branchi^ are resorted to, and these, in their turn, are replaced by lungs. In a double way, therefore, an increased supply is secured, by alterations in the mechanism obtain- ing it, which gradually becomes more and more adapted to the end in view, or by variations in the chemical constitution of the medium which INFLUENCE OF EXTERNAL AGENTS. 503 I'urnishcs it. Thus, in the development of a mammal, the first and lim- ited supply of oxygen is from the portion contained in the liquids of the ovum ; a far more copious one, at a later period, is derived from the pla- cental mechanism ; Ibut these subordinate states eventually give place to the direct respiration of the open atmospheric air. As this gradual march in the evolution of the respiratory function is going forward, it is attend- ed by a corresponding development of all the animal capabilities. So, too, on the great scale with genera and species. In the impure at- mosphere of the earliest geological times, it was not possible that energet- ic respiration could be carried on either by aquatic or by aerial animals. Both may be included in the remark, for it is demonstrable that, on ordi- nary physical principles, there must ever be a correspondence between the chemical constitution of the atmospheric air and the gas of respiration dissolved in the sea, or other natural waters. Abundant geological evi- dence is before us to the effect that the entire respiratory medium, both atmospheric and aquatic, has passed through a gradual amelioration, the percentage amount of its irrespirable elements declining, and that of its oxygen correspondingly increasing. The removal of those prodigious masses of carbon deposited as coal satisfactorily establishes this point ; and, therefore, as far as that medium is concerned, there is a general re- semblance between the conditions under which the entire animal series and the single individual have been placed. We might include in these remarks the vegetable as well as the ani- mal series ; for, as respects flowering plants, it is the special function of their floral or reproductive apparatus to discharge at a particular epoch the functions of an animal in taking oxygen from the air, and replacing it by carbonic acid. There would, therefore, be no cause for surprise if, in that ancient carbonated atmosphere, cryptogamic plants alone could maintain themselves, and that the flowering tribes could only appear after a due change in the aerial constitution, which also gave to hot-blooded animals the opportunity of coming forth. That change, as we have said, consisted essentially in the appearance of a great excess of oxygen gas. Such a superficial examination of the question shows that there is a par- allelism between the physical conditions under which the animal series, in the lapse of countless centuries, has been placed, and those to which, in the shorter period of its history, the developing individual is submit- ted, at least as respects the respiratory function. But it is to be re- membered that respiration is the prime function in the animal economy. As regards the influence of heat, it has been remarked in the preceding- chapter that, at the period of the first appearance of organic influence of forms, there was not only a high, but likewise a uniform tem- ^^^at. perature all over the globe. The evidence establishing this is already given ; but if thus, in what might be termed the infancy of the organic 504 EPOCHS OF DIFFEEENTIATION. series, such a perfect uniformity in the condition of temperature obtain- ed, the same is often observed in the first periods of individual develop- ment. The circumstances under which the ovum commences its career, even in the highest tribes, insure for it a perfect relief from every varia- tion of heat. Included in the body of the female, it is cut off from all external causes of disturbance, and kept at the temperature of her body, whatever that temperature may be. In those cases, as in birds, in which the embryo is developed under circumstances of necessaiy exposure, a strong instinct is called into operation, and, by the incubation of the pa- rent, the necessary uniformity is secured. Again, in other instances, as in the ova of insects, which, by reason of their minuteness and their fre- quently exposed position, although they may run through their earlier changes with relatively great rapidity, some accomplishing them in the almost uniform warmth of a summer's day, development never does nor can occur until the required condition, even if it be temporary, as to uni- formity of tempera-^ure, is reached. These considerations, though not affording an absolute proof that the career of development is guided by the influence of external physical conditions, are sufficiently significant to cast an air of probability over that doctrine ; and even if we adopt the view that the developing germ possesses a plastic power, which spontaneously compels it to run forward from stage to stage in a predestined career — if we recall what has already been said respecting that plastic power, that perhaps it is itself nothing more than a manifestation of the remains of antecedent physical impres- sions, we are really brought back to the same starting-point ; and, under any hypothesis, we encounter, sooner or later, as a necessary postulate, the grand doctrine that, directly or indirectly, development is a function of external physical condition. It is not to be supposed that differentiation takes place with equal Epochs of dif- ease at all periods of the history of organic forms, whether ferentiation. -^q consider them in the great scale, as constituting the ani- mal series, or on the small, in the individual. There are undoubtedly epochs in each of their histories at which the exertion of an external in- fluence will produce an effect infinitely greater than that which would occur at any other moment. If we may be permitted to use such a me- chanical illustration, the career of an organism recalls the flight of a heavy projectile, as a shell, thrown upward, which, at the first moments of its ascent and the last of its descent, pursues its way irresistibly, but when it is at the top of its flight, and the momentum which had been im- parted to it is just ceasing, the slightest breath of air, or the exertion of any other insignificant force, will divert it into a path different ft'om that in which it would have gone ; and so, in the career of an organism, there are moments when forces, which, at another time, would have been unfelt. KEPEODUCTION AND DEVELOPMENT. 505 can bring on differentiation, and, throngli it, call into existence new func- tions, and thereby forever determine a new course, through which it must pass. It is because a due weight has not been given to this considera- tion that many physiologists have depreciated the influence of external circumstances, or even denied it altogether, for they have assumed that, since we can not produce a more marked change than we do in the way of accomplishing a variation in species by artificially altering the condi- tions under which they exist, such conditions can have had but little power in bringing them to their present state. * Upon the whole, there can be no doubt that differentiation will occur in a more marked manner according as the exciting impres- Organic chan- sion is made at an earlier period of the organic career. Con- p^in'^'Xe^ first versely, the more advanced the organism, the less the prob- periods of life, ability of differentiation. For this reason it is that striking changes of this kind are rarely witnessed in individual life : they occur chiefly in the first embryonic states, and therefore, for the most part, require for their full manifestation generation after generation. Great organic varia- tions are not, then, to be expected in the individual, though they may be distinctly manifested in the course of time by the race to which it be- longs. CHAPTER IV. OF EEPRODUCTION AOT) DEVELOPMENT. Relation of Organic Beings : they come from a similar Cell and develop to different Points. — Their Division by Classification is fictitious. — Development and Differentiation. — Homogenesis find Heter agenesis. — They depend on physical Conditions. — The reprodiictive State closes De- velopment. Development is from the General to the Special. — Law of Von Bar. — Invariable Sequence in Differ en tia tion. Op Reproduction: 1st. By Generation. — Conjugation and Filaments. — The Sperm-cell: itx Production. — Spermatozoa. — The Germ-cell: its Production. Ovum in the Ovary. — Its Structure. — Corpus Luteum. Ovum in the Oviduct. — Mulberry Mass. — Germinal Membrane. — The Cliorion. Ovum in the Uterus. — Membrana Deddua. — Placenta. — Development of the Embryo. — Types of Nutrition. — Of Conception. — Of Gestation. — Of Parturition. — Influence of both Parents. '2d. By Gemmation. — Budding of Plants and Animals. — Of Grafting. — Limit of Gemmation. — Influence of Temperature on Gemmation. Alternations of Generation. — Its Explanation. In the popular view of the organic world, each individual being is re- garded as maintaining an existence independent and irre- Popular view spective of all others, or, at most, only connected with those pendenceofor- of its own race or kind. Without any apparent disturb- ganic beings. 506 THE PRIMOEDIAL GERM. ance of the general system, this or that species or genus might never have existed, since it stands in no relation as being the product of others, nor as having been concerned in giving origin to others. But these superficial conceptions are now to be replaced by others of a far more general and philosophical order, which present to us organic creation under an aspect of sublime grandeur, each class of beings standing in an intercommunication or conneccion with others — a part of a plan, the manifestations of which are not limited to the forms now existing, but also include those presented by the ancient geological times. These views cast a flood of light not only upon the relations of the vailous races of life to one another, but also of the human family to them, illustrating the course through which man has hitherto passed, and indicating that through which, in future ages, he is to go. Starting from a solitary cell, development takes place, and, according All organic be- as cxtraneous forces may be brought into action, variable in ings start from ^j^gjj. nature, and differing in their intensity, the resulting or- tne same germ ... . or cell. ganisms will differ. If such language may be used, the aim of Nature is to reach a certain ideal model or archetype. As the pas- sage toward this ideal model is more or less perfectly accomplished, form after form, in varied succession, arises. The original substratum or ma- terial is in every instance alike ; for it matters not what may be the class of animals or of plants, the primordial germ, as far as investigation has gone, is in every instance the same. The microscope shows no differ- ence, but, on the contrary, demonstrates the identity of the first cell, which, if it passes but a little way on its forward course, ends in pre- senting the obscure cryptogamic plant, or, if it runs forward . toward reaching the archetype, ends in the production of man. The diversity of form that is eventually presented depends then, not upon the consti- tution or aspect of the primitive cell, but upon the influence of the many surrounding agencies to which it is exposed. In one instance, through The primitive the interworking of these agencies — perhaps by cessation of ward'trdlfifer- *^^^' ^^ perhaps by its increased intensity — development ent points. comes up rapidly to a certain point, and there stops. In another case, through change in the conditions, it runs to a farther de- gree, and there stops. Organic beings are, therefore, the materialized embodiment of what must take place through the action of given forces, of a given intensity, and under given conditions, on an evolving cell ; The ciassifica- and, though it may suit the purposes of description to classify hTstor°^ arrfic- ^^'^^^ ^^^^ Orders, genera, species, or other such subdivisions, titious. it must never be forgotten that these are artificial fictions, and have no real foundation in nature. Not only is the primordial cell in all instances, the same, but the first stages of its career are in all instances identical, and this whether we VALUE OF EMRRYONIC FORMS. 507 consider it in tlic lowest or the liiglicst cases, Ibeloiiging either to the veg- etable or the animal kingdom. It is a process of repetition or reproduc- tion, cell arising from cell. And here at once we may correct the lan- guage so often used — indeed, which we have ourselves just used in this respect, for such terms as high and low are only to be employed in a very restricted sense. The evolving cell gives rise to other cells, but for a pe- riod of time no indication is presented as to which of the two kingdoms it is to belong, animal or plant. By degrees, as the develop- Development ment goes on, that point is determined, and so, one after an- i^ attended br- other, the unfolding mass gradually reveals the class, order, evolving of pc- family, genus, species, and, finally, its sex and individual pe- cuhanties. culiarities. In all this there is an evolving of the special out of the gen- eral ; one after another, peculiarities, which are more and more minute, arise ; and thus we are not to regard the progress of development as tak- ing place from the lower to the higher, forms that are more and more com- plex arising in succession, but we are to regard it as the gradual unfold- ing of the special from the general. This career of development applies equally to the case of any individ- ual animal, or any race of animals. Thus man himself, in Analogy of de- succession, passes through a great' variety of forms, from the J'he°hKihidual condition of a simple cell; these forms merging by degrees and in the race, into one another, the form of the serpent, of the fish, of the bird, and this not only as regards the entire system in the aggregate, but also as re- gards each one of its constituent mechanisms — the nervous system, the circulatory, the digestive. Now, on the passage onward, these forms are to be regarded, as has been well expressed, each one as the scaffolding by which the next is built ; and just as man, in his embryonic transit, presents these successive aspects on the small scale, so does the entire animal series present them in the world on the great scale. Races of animals are not to be compared as though they were more perfect or low- er than one another, but as having advanced more or less in the direction from the general to the special ; and therefore, in this philosophical view, we are justified in regarding those animated forms which heretofore have been spoken of as lower in the animal scale as being, in reality, the em- bryos of those that are higher ; and this should lead us to a juster esti- mate of their relation of value toward one another, since we are very apt to contrast them in that respect. In the case of an individ- vaiueofem- ual, as in man, we put at once a true interpretation on the ^ryonic forms. ^alue of the various transitory conditions through which he has passed, estimating these as of but little intrinsic importance ; as being, as it were, no more than links in a chain ; and this may teach us a more just appre- ciation of the relations of animal races to one another and to the human species. It may teach us the folly of comparing, as some have endeav- 508 DEVELOPMENT OF THE SPECIAL FROM THE GENERAL. ored to do, the animal tribes with ourselves ; of measuring their instincts with our mental operations ; things which are different terms of two dif- ferent series, and things which are incommensurable. There are three cases in which we might consider this career. These are, first, in the development of particular organs, as the digestive, res- piratory, or circulatory ; second, in the development of individual beings, which pass in their onward progress, as we have said, through various forms in succession; third, in the development of species, presenting what have been formerly designated as successive stages of increasing perfection. For all these various cases a single illustration may suffice. Hlustration of Thus, in the primitive period of life, a single membrane dis- the unfolding charges promiscuously and contemporaneously all the va- of the special . • r .• •. i- . -x • -j. j. from the o-en- rious Organic functions — it digests, it respires, it secretes ; erai. ]but, a little advance onward, special portions of it are allot- ted for one and another of these uses, and a localization, a centralization of function ensues, and things that were mixed in confusion become sep- arate and distinct. As the passage onward is made, still farther special- izations are introduced, and so on in succession. Thus at the two ex- tremes we may contemplate the single germinal membrane of the ovum, which is discharging contemporaneously every function — digesting, ab- sorbing, respiring, etc. — and the complete organic apparatus of man, the stomach, the lungs, the skin, the kidneys, and the liver — mechanisms set apart each for the discharge of a special duty, yet each having arisen, as we know positively from watching their order of development, from that simple germinal membrane. We must not, therefore, permit our- selves to be deceived by the appearance of complexity they exhibit, since, intricate as may be their construction, they have all arisen through gradual centralization, one duty being separated from another, and hav- ing an appropriate mechanism for itself; and so, at last, it comes to pass that even the minutest conditions are discharged by a special part. Thu.s, in the kidney' the salts are removed by one portion of the struc- ture and the organic constituents by another ; yet, even in these ut- most conditions of refinement, the primitive condition is at all times ready to be reproduced, and, when driven to it, each of these structures can act vicariously for the others, and discharge for the others their duty. It is unnecessary for our purpose to multiply instances, since every page of natural history, comparative anatomy, and embryology presents them in abundance ; but it may be to the purpose to remark that this doctrine leads to more worthy conceptions of the system of nature : for if we suppose that there has been, in the case of the animal series. a passage from things that are less perfect to things that are more so, though this may be agreeable to our own experience, which is essen- ILLUSTEATIONS OF DEVELOPMENT. 509 tially tentative, it gives us very base notions of the manner Base nature of in which natural operations are conducted, since we can not ^'.'^ popular f ^ ' _ view ol the or- divest ourselves of the idea that such a passage from imper- ganic world. fection to perfection implies trial, verification, and improvement : a pro- cess which, though it is suited to the limited knowledge of man, is not in accordance with the precision, perfection, and energy of Nature, and is to be rejected the moment we consider that we deal with the acts of Omniscience and Omnipotence. Moreover, that erroneous view leads to fallacious estimates, both in the animal series and in the individual, or the character of transitory forms, conferring on them too much inde- pendence, and therefore too much dignity ; for the transitory forms of embryonic life and the forms of animal species are the equivalents of each other. Every living being, therefore, springs from a germ, which will develop itself into the likeness of its parent, provided it is submit- career and stop- ted to the same conditions throuo'h which its parent pass- P^se of a devei- •f 1 T- 1 1 1 • -n -1 1 oping germ de- ed ; but II the conditions be changed, it will either take pends on exter- on a new aspect, or if they have become incompatible, it ^^^ conditions. will cease to exist. Similarity of development depends on similarity of condition, as is abundantly proved by such instances as the almost per- fect resemblance of the two sides of the body, which, in reality, may be regarded as distinct individual forms. To the proof thus derived from bilateral symmetry as occurring in man might be added such suggestions as arise from the well-known resemblance of twins ; and as identity of condition will thus give origin to analogy of development, so we may fairly infer that difference of condition, no matter in what respect the dif- ference may be, will give rise to difference of structure ; thus experienced gardeners have shown that the sex of flowers is, to a very great extent, determined by the brilliancy of the light in which they grow. Differ- ence in the supply of nutritive material removes the spines from one plant, or doubles the flowers of another, by changing its stamens into petals, or alters the cycle of career, and makes annuals into biennials. As illustrations of the complete changes of form during development, jT,-^ 241. tl^e three following cases may be presented : in J^ig. 241 are shown the ova of the frog, which are trans- parent spherical bodies, containing a dark globule. From this, by de- velopment, the tadpole, which is a true fish, breathing by gills, arises. Development of the frog. rphc figurcs represent a side and Tipper view. After growth has taken place to a certain degree, a change of structure becomes apparent, limbs gradually emerging, and the aui- 510 ILLUSTRATIONS OF DEVELOPMENT. Fig. 242. mal, after passing through an inter- mediate state, eventually loses its gills and tail, ceases its aquatic, and commences aerial respiration, and shows the aspect. Fig. 242, of the ^;i*. perfect frog. Fig. 243 represents the success- ive metamorphoses of the Carcinus msenas, or edible crab, as given by Mr. Couch. A represents the animal Fig. 243. Development of the crab. on its emergence from the egg. It has a hemispherical shield on the head and thorax, with a projecting spine, a tail formed of six segments, the two last being joined laterally. The second form, at B, exhibits a great change : the spine has disappeared, the shield is depressed, the eyes on footstalks ; there are claws, and the tail is often carried bent under the body. When this shell, like its predecessor, has been cast, the third form, C, is assumed, the transition adapting the animal for walking rather than swimming. The final form, D, is taken on at the next moult, and now development ceases, and growth only takes place. Fig. 244 illustrates the metamorphoses of a lepidopterous insect, the Fig. 244. Bombyx mori, or moth of the silk- worm. From the eggs there arises a caterpillar, which not on- ly possesses the means of locomotion by feet, etc., but also contains within it the rudiments of the organs to be eventually assumed. In this state the insect passes under the name of a larva, because it is covered with. a series of teguments, Development of insects. GROWTH, DIFFERENTIATION, DEVELOPMENT. 511 which, lilve masks, conceal the interior structure. These, in succession, are cast off. After many such successive castings of the skin, the insect enters into the pupa or chrjsaKs state. It has no organs of locomotion, and, as it lias been, with some degree of imagination, said, becomes an egg again. After resting in this state for a certain time, it bursts its confinement, and assumes the form of an aerial, swift-moving winged insect. This is its imago state. It will now be convenient to give a more precise definition to terms which have been hitherto used with a certain latitude. By the term growth is to be understood the increase in size of a struc- ture, without its assuming any variation as respects the na- Definition of ture of its fibric or of the functions it discharges. enUatio'n 'ami By differentiation is meant an increase involving modifica- development. tion of fabric and the assumption of new function. By development is meant a differentiation of a higher order, or com- pound differentiation. Usually it implies growth and differentiation con- jointly. As illustrations of the preceding definitions, it may be said that a crys- tal grows, its enlargement presenting no structural variation and no new quality. Cells differentiate from their normal spherical form, and, assum- ing a cylindi'oid figure, give origin to vascular tissue, the vessels so aris- ing serving for new purposes, as for the conveyance of gases or liquids. A seed develops, for the organism to which it gives rise not only offers continually increasing dimensions, but at all points the origination of novel structures, arising by differentiation from adjacent and pre-esisting ones, these new structures having also new functions. By homogenesis is meant the production of an organism in all respects like its parent ; by heteroffenesis, the production of an or- „ ■T _ J •/ o ' -t Homogenesis ganism unlike its parent. and he^terogen- For the sake of brevity and simplicity, we may suppose ^*^®' that there resides in every germ, and, therefore, in every organism, a prin- ciple or quality which governs the collocation or grouping of new parts, the same to which allusion has heretofore been made under the designa- tion of plastic power. It is unnecessary for us here to burden our con-» ceptions of such a power with any hypotheses respecting its nature, it being understood that we use the title of this supposed agent only as an expression of convenience. The production of every organism appears, as far as existing observa- tions and experiments go, to be referable to a previously ex- ^^ organic isting organism. This being admitted, generation and repro- molecule the duction imply, as their starting-point, an organic molecule. ^^^^ ° ongm. Such a combination, furnished with nutrition, grows, its plastic power 512 HOMOGENESIS AND HETEROGENESIS. grouping the new material. But such a growth can not take place to any extent without a variation being encountered in the surrounding condi- tions, and the instant that this occurs, differentiation ensues as its neces- sary consequence. Growth under changed circumstances is then differ- entiation. If the order of variation, as regards condition, is exactly the ^ ,. . ^ same in the case of two growing and differentiating combi- simiiarity of nations, their career of development will be exactly alike, and eve opraent. ^^^ forms they will present at the same epoch of their course will be the same. According as the career is short, the probabilities of identity are greater, since the chances of variation, which might be en- countered in the two cases, are less. But where the career is more pro- tracted, and many conditions in succession must be encountered, it can not happen that there will be an exact resemblance in the course of two organic combmations, and therefore there never can be an absolute iden- tity in the aspect of any two resulting forms. The general result of every development is heterogenesis. No parent Development Organism ever reproduces another absolutely like itself, un- tendTto'hete ^^^^ ^* ^® ^" *^^ lowcst developed types, in which the oppor- rogeiiesis. tunity for change is at a minimum. Homogenesis is only ap- proached as the conditions bringing on differentiation approach similari- ty; it therefore sinks into a special case coming under a more general law, and, indeed, speaking with exactness, we might say that in the nat- ural world it never occurs, the prevalent notion which regards it as the rule and heteiK)genesis as the exception being altogether illusory. Ev- ery grade of organism, vegetable and animal, furnishes us with examples of this truth. Let us look for a moment at the highest tribes ; and in them reproduction never takes place except by pairs of individuals of dif- ferent sexes. Eigorously, therefore, the births should also be by pairs of different sexes. Moreover, if it be necessary in these general and super- ficial considerations, let us direct our attention to the special case of man. The infant necessarily differs from one of its parents in sex, and from both in size, weight, endowments, and physical attributes. It is like neither of them. The popular notion may suggest that a closer resem- blance will be reached, perhaps, after the lapse of thirty or forty years, . when a nearer approach to the form of one of the parents may be offered with elements incorporated from the lineaments of the other ; but even in this case a rigorous examination compels us to admit that like has not produced like. Reflecting on this popular illustration more profoundly, we discern Cycles of pro- wherein the error consists. Instead of comparing cycles of cess to be com- proccss, wc have been blundering with isolated forms, which individual arise at different epochs therein. Without going into tedi- forms. Q^g details, man presents, as regards the most important of EEPRODUCTIVE STATE ENDS DEVELOPMENT. 513 his constituent structures, his nervous system, the successive character- istics of an avcrtebrated animal, a iish, a turtle, a hircl, a quadruped, a quadrunuxnous animal, before he assumes the special human character- istics. This is his cycle of life, and it is the same cycle in one case as in another. But the moment that our view is thus enlarged, we see that it is not the individual with which we should deal, for an individual we can scarce- ly define, since he is continually differing from himself. It is with a cy- cle of proceeding, or a course of operations that we are engaged, a series of forms being the outward manifestation of the succeeding periods of that cycle or course. An infant, though unlike both its parents in form, has run through a career like that passed through by them both. Sexual differentiation, which indeed is one of the last differentiations occurring, offers no excep- tion to the truth of this remark. The similitude lies in the career, not in the form taken at different epochs. The essential principle, then, is, not that an organism produces a like organism, but it produces a germ which, being placed under r^j^^ reproduct- similar circumstances, passes through a like career of devel- ive state closes. , 1 , • -iji? 11 • n development. opment, and at successive periods otters an orderly series of forms. The career is commonly observed to close as soon as the capac- ity for reproduction is assumed. Hence, in every organism, the assump- tion of the reproductive state is the signal that the end of development is at hand. It does not plainly appear what are the circumstances which give rise to the assumption of this capacity ; nevertheless, it may take place at any moment of the career. In the Volvox globator it occurs almost at the close of the first stage, for the germ only reaches the condition de- scribed hereafter as the mulberry mass when it becomes capable of re- production ; but in man the developing organism has a long journey to perform beyond this first step. Except in the condition here dwelt upon, he differs in no respect from his humbler comrade at this point. The- tendency to a gliding off into the reproductive phase is in him repressed; and therefore differentiation and development continue to go on. During the development of any new organism, the new parts uniformly arise from the old ones ; they are not built from foreign mate- All the parts of rials depositing themselves upon new centres, but are educed ^" organism by the unfolding, enlarging, and modeling of parts already common cen- existing. An organism is not developed as we enlarge a ti'alongm. house, by building part to part, but it all expands from one common or single centre. As the sphere of its expansion becomes greater, the op- portunity arises for devoting different regions to different uses, and thus offices which were confusedly intermingled become separated out, and,. Kk 514 LAW OP VON BAR. as, in social undertakings, llie division of labor gives greater perfection to the work, so in this, functions which, because they were blended, were imperfectly discharged, now assume precision and power, because they are disentangled from what were perhaps countervailing conditions. By these considerations, we are gradually led to the general law of de- velopment, first recognized by Von Bar, and passing under his name. This is somewhat obscurely enunciated in the following terms : " The heterogeneous arises from the homogeneous by a gradual process of change." By this it is meant that, in the process of development, the stages are not from forms that are of a degraded to those of a higher type, but that from the general the special, which was therein included, is gradually involved. In conclusion of these preliminary remarks on reproduction, it may be Invariable se- C)^served that, even in the highest and most elaborate types, quence and dif- the causes which bring on differentiation follow each other in such a predetermined sequence, that the whole phenomenon might be said to be under the dominion of mathematical conditions. As a striking instance of this may be mentioned, in the case of man, the nu- merical equality of the sexes ; and that this singular result is determined by the alternate preponderance of conditions which are otlierwise nicely balanced, is shown by the interesting instances occumng among insects of dimidiate and quadrate hermaphroditism, in the former of which the resulting insect is of different sexes on the two sides of its body, and in the latter the male and female portions are quadrantally arranged. If the left side of the head and thorax are those of a male insect, the right half of the abdomen is of the same kind, the intervening portions being of the other sex. The neuter state might even be imagined to arise from the more precise blending, balancing, and confusing of such •conditions as here give evidence of an incipient tendency to separate from one another. In the farther discussion of reproduction we shall find it conveniently Divisions of Considered under two distinct divisions ; first, generation ; reproduction, second, gemmation. Our attention may, then, be profitably directed to the singular facts known under the designation of alternation of generations. As illustrations of the terms here employed, it may be stated that the production of a seed and the development of a plant there- from are to be considered in connection witli generation, and that the ob- taining of new plants and trees by budding and gi'afting, and the pro- duction of many new hydras by their sprouting forth from an old one, are to be considered under gemmation. By the alternation of genera- tions is meant that an organism. A, will give rise to a second one, B, wholly unlike itself, and that this second organism, B, will give rise to a third, C, unlike itself, but C shall resemble A. This singular condition GENERATION. 51i of things will Lc shown to originate in the periodical alternation of gen- eration and genniiation respectively. 1st. of generation. Reproduction by generation is accomplished on two different types : 1st. By the conjugation of two similar cells ; 2d. By filaments. In the first, that is, hy the conjugation of two similar cells, a third body, called a sporangium, results. Of this process there „ . appear to be three different modifications : 1st. The two sim- cations of con- ilar conjugating cells discharge their endochronie, or coloring •'"^^ '°"' material, each voiding itself completely, and the sporangium arises from the mixture ; 2d. A dilatation forms on the point of union of the two conjugating cells, and into this dilatation the endochromes of both cells are passed ; 3d. The endochrome of one cell is wholly retained, and that of the other is added to it, the one becoming void, and in the other the sporangium being produced. This, occurring in the lowest vegetables, among which it was for a long time supposed that the type of reproduc- tion is totally different from that of flowering plants and animals, pre- sents us with the first traces of Avhat is eventually displayed as differ- ence of sex. This shadowing forth of the difference of sexes is illustrated in a very instructive manner by the Zygnema quininum, a fresh-water conferva. Its manner of growth is what has been already described in the case of the Conferva glomerata, Fig. 231. In the annexed Fig. 245 is repre- Fig. 245. Development and reproduction of Zygnema quininum. sented at A the process of growth by the subdivision of cells, ah c repre- senting three such cells, the middle one, 5, being in the act of subdivision. At B two threads are in the act of conjugation. The endochromes of both are spirally arranged, and dilatations reaching from one to the other are here and there seen. At C the endochromes of one thread, a, have wholly passed over to the other thread, 5, and the round bodies, or spo- 516 SPERM-CELLS. rangia, are the result. It is this passage from one thread to the other which betrays the first indications of sex. In the second, that is, by filaments, two cells are again necessary, which, difFerino; in construction and also in function, are des- Two modihca- '-' n i n • i tions by liia- ignated the sperm-cell and germ-cell respectively. Of this ments. ^^^^^ there are two modifications : 1st. Reproduction by mov- ing filaments, as presented in the higher alga; and ferns ; 2d. By elon- gating filaments, as in flowering plants. The moving filaments, which were discovered in the case of animals soon after the introduction of the microscope, were regarded as animalcules, and passed under the designa- tion of spermatozoa. The germ which arises in the first of these modi- fications is, in the lower tribes, unprovided with any nutritive supply ; in the higher, a stock of food is prepared for it by the parent. In the second, the sperm-cell, or, as it is frequently termed, pollen grain, does not produce a moving filament, but elongates itself into a delicate tube until it reaches the germ-cell. A stock of nutritious matter is placed around the resulting embryo, and this is the ordinary construction of seeds. Restricting our description to the case which more immediately inter- ests us, we shall first consider the mode of origin and nature of the sperm-cell and its filaments in animals, and then of the germ-cell and its process of development when fertilized. 1st. Of the Sperm-cell. — The testes are the organs in which the sperm-cells and filaments arise in man. They are of an ovoid form: each is covered with a white envelope, the tunica alhuginea. A serous membrane, folded as a shut sac, overlies this tunic. From the inner surface a number of delicate projections arise, which divide the organ into several compartments. In these compartments are lodged lobules aris- ing from the tubuli seminiferi and their supplying blood-vessels. There ^ J ,. J, are about 450 lobules in each testis ; their shape is conical, Production of , ^ sperm-cells by the diameter of the tubes of which they are composed about the testes. ^j^^ _2_ ^£ ^^ -^^^^y-^. The total length of this tubular struc- ture is about three quarters of a mile. Before the tubuli of each lobule reach the rete testis, they cease to be convoluted, and bundles of them, uniting into larger vessels, are designated tubuli recti. In the rete tes- tis there are from half a dozen to a dozen of these tubes, which various- ly anastomose with one another and divide. They empty into the vasa efferentia, which, from being straight, become convoluted, a series oi' cones arising, which together form the globus major of the epididymis. This is a convoluted canal, of about twenty feet in length, which, de- scending, receives beyond its globus minor the vasculum aberrans. It then empties into the vas deferens. Fig. 246, human testis : a, testis ; b, lobes ; c, tubuh recti ; d, rete THE TESTIS. 517 Fig. 246. The testis. vasculosum ; e, vasa efferentia ; y, coni vasculosi ; (/, epididymis ; h, vas deferens ; i, vas abcrrans ; m, branches of the spermatica inter- na of the testis and epididymis ; n, ramification on the testis ; o, ar- teria deferentialis ; p, anastomosis with a branch of the spermatic. (x4.rnold.) The secretion of the testis must be taken for examination from the vas deferens or epididymis, before it has been mixed with the fluid of the prostate and Cowper's glands, or with mucus. It may be min- gled with a little albumen or se- rum for the purpose of dilution, and, when examined with a power of 500 diameters, exhibits multitudes of moving bodies. These are the seminal animalcules, or spermato- zoa. Among them are to be seen, here and there, round granular bod- ies, the seminal granules. These, with the spermatozoa, are sustained in a clear and transparent liquid. The examination of these different constituents is conducted with difficulty, since they can not be separated from one another by means of filtration. The spermatozoa arise fi'om the seminal granules. The spermatozoa are found in the spermatic fluid of all animals after puberty, their form being different in different classes and Spermatozoa species. Generally they may be described as consisting of description of. a little OA'al-shaped head, from which a delicate filament or tail projects. The motion of the spermatozoa is accomplished by means of their fil- ament. It takes place in different ways, sometimes the filament vibrat- ing like a whip, sometimes rotating like a screw, and sometimes a spin- ning round, as it were, upon a pivot, occurs, the filament having been ooiled like a watch-spring. The rate of motion seems under the micro- scope to be rapid ; it is, however, estimated at an inch in thirteen min- utes. In man, their entire length may be estimated at about the -g^ of an inch, the length of the head being about the -g^-g-, and its Human sper- breadth the yo'oTJ^* They continue to exhibit motion in matozoa. birds for fifteen or twenty minutes after death ; in cold-blooded animals even after days. They withstand, for a time, the action of solutions of sugar and salt, but are destroyed at once by alcohol and dilute acids, 518 SPERMATOZOA. which appear to affect then- organization. Strychnia, opium, and hy- drocyanic acid likewise stop their motions, but without causing any change in their form. The production of spermatozoa is best studied in the case of birds. Spermatozoa ^0^ ^^^^^ purpose Wagner recommends that one of the order in birds. of Passcrcs be taken in the pairing time. The condition of the testes indicates the state of evolution of the spermatozoa. In win- ter those organs are of the size of a pin's head, but in spring they have increased twenty or thirty fold. Exteriorly they exhibit convolutions like those of the brain, and contain granules and seminal globules. After pairing time is over, they relapse to their original diminutive state. The seminal globules appear to be derived from the epithelial cells lining the tubuli seminiferi. They are developed into what are termed primary cells, each of which contains a number of secondary cells or vesicles of evolution. In the interior of tliese vesicles the spermatozoa originate, as a derivation or development from the nucleus, each vesicle giving rise Evolution of ■to one spermatozoon. When this has reached perfection, the spermatozoa, vesicle dcliqucsces and sets it free. There are from one to twenty vesicles of evolution in each primary cell. In birds the filaments may be retained for a length of time in the primary cell after deliquescence of the vesicle, but in mammals, as soon as the filament is mature it es- capes. In the former case the filaments aggregate into bundles, but they break up into individuals when the primary cell deliquesces. ^. 2^^ Fig. 24:7, spermatozoic filaments, develop- "~~^" ing in Certhea vulgaris : a, seminal granule; b, cyst, with two vesicles of evolution, many granules, and a bundle of spermatozoa ; c, oval cyst, with spermatozoa coiled up. (Wagner. ) Of the formation of spermatic filaments Dr. Burnett gives an account somewhat dif ferent from the preceding. According to him, "the morphological changes in the sperm- Deveiopment of spermatozoa. ^^jj preceding the formation of the spermatic filaments are identical in their character with the changes in the ovum which are antecedent to the formation of the new being. When the gen- erative function begins to be developed, the character of the epithelial cells lining the tubules is modified. The cells pass to a higher degree in function, but do not undergo any change in structure, except a slight increase in size. In this condition they divide and subdivide, by a pro- cess similar to the segmentation of the yolk, until they are entirely con- verted into a mulberry mass. A liquefaction of the segmented contents into a minute granular blastema then ensues, and from this the spermatic filaments are developed. In the Plagiostomes, Dr. Burnett was able to THE GERM-CELL. 519 observe the disappearance of the mulbeny mass, and its replacement by a fasciculus of spermatic filaments, although the exact metamorphosis by which tlie granular 'cellular mass formed the bodies of the spermatozoids could not be detected. The spermatic filaments, Dr. Burnett thinks, are not formed, as stated by Kolliker, by a deposit from the contents of the sperm-cell or nucleus, but by an elongation of the nucleus itself. The body of the spermatozoid is developed from the cell, while the tail is probably subsequently formed by an accumulation of minute particles." (Kolliker, Am. ed., p. 625.) In man, the production of spermatozoa commences between the four- teenth and sixteenth year, the time of puberty, and continues until the sixty-fifth or seventieth, or even much longer. This period of commence- ment is marked by a great change in the physical and moral constitution. The spermatic fluid of mule animals contains no spermatozoa. This fact has been established in an interesting manner by Wagner in the case of birds, of which many of those which are domesticated readily cross. There can be no doubt that these bodies are the essential portion of the fluid, and that it is their action upon the ovum which establishes its fer- tilization. There has been much controversy whether the spermatozoa present traces of organization, properly speaking. Though it is convenient to designate their dilated portion as the head, and the filament as the tail, it has never yet been established that any thing answering to a true structural arrangement exists, and, upon the whole, it may be concluded that the appearances which have been by some supposed to indicate or- ganization are, in reality, only an optical illusion. Id. Of the GerTYiTcell. — In mammals the female reproductive appara- tus consists essentially of the ovaries, oviduct, and uterus. „ •^ _ , . . . 1' emale repro- Tlie ovaries are two ovoid bodies situated on either side ductive appa- of the uterus. They consist of a stroma in which vesicles ^*'^"^' are imbedded : these vesicles give origin to the ova. In the manner to be presently described, the ova, being received at the fimbriated extrem- ities of the Fallopian tubes, those tubes being therefore appropriately termed oviducts, are carried into the cavity of the uterus. At the time of puberty in the human female, which occurs between the 14th and 16th year, a physical and moral change takes . The cataraenia. place, answering to that which" has been already alluded to as occumng in the male. From this period a sanguinolent discharge makes its appearance monthly : it is the catamenia. The interval from time to time is commonly estimated at four weeks ; it varies, however, with individuals, and it is said also with climates, the discharge occurring in the hotter more frequently, and in greater quantity. It is essentially blood, which has been deprived of its quality of coagulating by inter- 520 OVUM IN THE OVARY. mixture with acid mucus of the vagina. So long as these periods con- tinue, the individual possesses the reproductive power, the first appear- ance of the catamenia indicating the capacity for conception, and the dis- appearance, at about the 45th year, its end. During gestation the cata- menia are suspended, and, indeed, it is this event which is usually taken as the indication that conception has occurred. The periodical occurrence of this discharge in the human female, though more frequent, is essentially the same as the periodically occurring heat of other animals, which is also attended with a sero-sanguinolent dis- charge. In other respects, likewise, the analogy is maintained, for in those animals, the appearance of this discharge and its attendant phe- nomena constituting an indication of a simultaneous capacity for con- ception, in women the same thing holds good, conception occurring in them at the time of the close of the menstrual discharge. I. Ovum in the Ovary. The ovaiy is the organism in which the ova are prepared, these bodies arising in the following way : In the stroma of the ovary there occur at a time ten, twenty, or many Production more cells, Avhich have received the designation of Graafian ves- ofova. icles or ovisacs. These originate in the interior of the ovary, and, as they become perfected, pass to its surface, presenting themselves thereupon as prominences which are covered over exteriorly with peri- toneum. Each of these vesicles has a membranous envelope connecting it with the substance of the ovary exteriorly, and covered interiorly with a layer of nucleated cells, designated membrana granulosa. It is filled with a fluid in which multitudes of granules float, aixl in its centre is the ovule. This, as it becomes mature, is pushed up toward the surface of the ovisac by an accumulation of liquid in the lower part thereof, and is so brought into close relation with the membrana granulosa at the place where it is upon the surface of the ovary. At this point there col- lects on the ovum a zone of 2;ranules, to which the desimation of discus j)roligerus is given. Fig. 248, transverse section through the ovary of a woman dead in the fifth month of pregnancy : «, Graafian follicle of inferior, and, 5, of superior surface ; c, peritoneal lamella of ligamentum latum, continued upon the ovary, and coalescing with, cZ, the tunica albuginea : in the in- lerior two corpora albicantia (old corpora lutea) are visible; e, stroma of the ovary. (Kolliker.) Fig. 249, section of the Graafian vesicle : 1, stroma of ovary, with l)lood- vessels ; 2, peritoneum ; 3 and 5, layers of the external coat of the Graafian vesicle; 4, membrana granulosa; 6, fluid of the vesicle ; 7, gran- ular zone, or discus proligerus ; 8, the ovum. (Von Bar.) THE OVUM. 521 Fuj. 24S. A. Fig. 249. Fig. 250. Section of Urdj,tidii vesicle. Section of ovary. Fig. 250, ovum of tlie sow : 1, germinal spot ; 2, germinal vesicle : 3, yolk ; 4, zona pellucida ; 5, discus proligerus ; 6, adherent granules or cells. (Barry.) Tlie diameter of the human ovum varies from the ^1^ to the -^^ of an inch. It consists of an exterior transparent membrane, Description of the -g^-Q of an inch in thickness, which, when compressed ^"^^ 0Y\xm. for the purpose of examination, appears like a diaphanous circle, and hence called zona pellucida. Within this zone, and inclosed by it, is the yolk, a granular material suspended in or intermingled with fluid, the granules being of different sizes ; those near the pellucid zone are the largest. For the most part, the yolk consists of albumen and oil globules. Its condi- tion, as regards liquidity, varies in different animals ; in some it is al- most a soft solid, so that, when water percolates through the zona pellu- cida, it isolates the yolk by surrounding it on all sides, and parting it off from the zone. Within the substance of the yolk is a distinct cell, the germinal vesicle, which gradually makes its way from the interior to the place of peritoneal contact. As it advances to perfection, it consists of a delicate spherical membrane containing a liquid, in which granules are suspended. Upon that portion of it nearest to the place of peritoneal contact is its nucleus, the germinal spot, about the -g-^^ of an inch in diameter, and consisting of yel- low granules. Fig. 251, diagram of a Graa- fian vesicle and ovum : 1, stroma of ovary ; 2, 3, external and in- ternal tunics of the Graafian ves- icle ; 4, cavity of vesicle ; 5, thick tunic of the ovum or yolk-sac ; 6, the yolk ; 7, the germinal vesicle : 8, the germinal spot. The most mature ova are near- est the surface of the ovary, but are separated from its peritoneum Fig. 251. Diagram of Graafian vesicle. 522 COKPUS LUTEUM. by a thin, fibrous layer of stroma. The Graafian vesicle is, there- fore, the parent of the ovum. Periodically, as development is going on, the Graafian vesicle bursts, and tlie ovum is set free. This effect arises, in part, from the circumstance that, the space between the vesicle and ovum being filled with cells, those near the surface of the ovary disap- pear, and an albuminous liquid, which accumulates below, pushes the ovum up. This extrusion of ova occurs even in childhood. The ovisac, or Graafian vesicle, thus changed into a follicle, is gradually filled up, its walls wrinkling, and red-colored material, arising from the membrana granulosa, being deposited in it until it is almost filled. This deposit gradually turns yellow, and is eventually com- posed of cells interiorly, and fibres arising therefrom exteriorly. When the deposit is completed, a stellated cicatrix is observed in its midst. The yellow body thus arising passes under the designation of corpus lu- teum. If impregnation does not occur, the yellow substance forms to but a small extent, and after a time disappears. It is relatively more abundant in animals than in women. Attempts have been made to use the indications of the corpus luteum for determining the question of preg- nancy. The following points are presented by Dr. Dalton as offering characteristics by which the corpora lutea of pregnancy and menstruation may be distinguished : " The corpus luteum of pregnancy arrives more slowly at its maximum development, and afterward remains for a long- time as a noticeable tumor instead of undergoing rapid atrophy. It re- tains a globular or only slightly flattened form, and gives to the touch a sense of resistance and solidity. It has a more advanced organization than the other kind, and its convoluted wall is much thicker. Its color is not of so decided a yellow, but of a more dusky hue, and if the period of pregnancy is at all advanced, it is not found, like the other, in com- pany with unruptured vesicles in active process of development." Fig. 252, corpora lutea of different periods : a, corpus luteum two Fiq. 252. Corpora lutea. days after delivery ; h, corpus luteum of about sixth week after impreg- nation, showing its plicated form at that period ; 1, substance of ovary ; 2, substance of corpus luteum ; 3, grayish coagulum in its cavity ; d, in OVUM IN THE OVIDUCT. 523 tlie twelfth week after deliveiy. {a and h, Dr. Patterson ; d, Dr. Mont- gomery.) II. Fertilized Ovum in the Oviduct. Such being a description of the ordinary or unfertilized ovum, we have next to follow tlie changes which ensue if fertilization has taken place. The spermatozoa having become enveloped in the pellucid zone or passing through it, the ovum is received by the fimbriated extremities of the Fallopian tube, along which it is carried by peristaltic contraction or ciliary motion. The first change which takes place in it is the disap- pearance of its germinal vesicle and germinal spot. This disappearance is, however, stated by some to be preceded by a development of cells originating in the nucleus or germinal spot ; nor is it the result of fertil- ization, since it occurs in the unimpreo-nated ovum. The ^, y o Changes of the cells of the membrana granulosa, which surround the ovum, fertilized ovum become first of a conical shape, but their rounded form is re- "^ ^^^ oviduct. sumed on passing into the tube. Fig. 253. Fig. 253, ovarian ovum of dog, exhibiting the elongated form and stellate arrangement of the cells of the discus proligerus round the zona pel- lucida. Fig. 254, same ovum after the removal of most of the club- shaped cells. The yolk is next observed to contract so as to leave a clear space between it and the zona pellucida. As the pas- sage along the tube is taking place, the zona assumes a coating of albuminous material, which is what is call- ed in birds the white of the egg. It eventually becomes the chorion. Meantime, after the disappearance of the germinal vesicle, a new cell, the embryo cell, arises, and this undergoes subdivision or segmentation, an effect in which the yolk itself presently becomes involved, each new or daughter embryo cell so arising assuming a part of the yolk. A constant process of bisection is thus established, the yolk dividing first into two portions, then into four, eight, sixteen, etc., each division containing a nucleated cell. At this period may be seen the spermatozoa involved in the zona pellucida, and, as the process of bisection goes on, xhe mulberry the mass assumes a mulberry aspect, and finally becomes °^^ss. granular. This is, for the most part, finished by the time the ovum en- ters the uterus. Fig. 255, ova of the dog in various stages : a, from the oviduct, half an inch from the uterus, spermatozoids being in the pellucid zone, the yolk Ovarian ovum. Ovarian ovum. 524 SEGMENTATION OF OVUM. bisecterl ; 5, cells of tunica granulosa have disappeared, and the yolk is in four segments ; c, continued advance in segmentation ; d, the zona has become thicker, and the segmentation more complete ; e, ovum burst by compression : some of the segments have escaped ; each shows a bright spot or vesicle. Fig. 255. Segmentation of ovum. Fig. 256, cleavage of the yolk after fecundation : a, an ovum of As- caris nigrovenosa, the yolk of which is divided into two equal portions : the upper portion contains a cell with a large nucleus, the lower a sim- ilar cell with two small nuclei ; b, ovum subdivided into four portions ; c, the subdivision has reached sixteen, each possessing a mono-nucleated cell ; d, ovum of Ascaris acuminata, showing the stages of subdivision, the portions becoming very small ; e, the portions preparing to be mould- ed into the young worm, {a, h, c, Kolliker ; d, e, Bagge.) Segmentation of ovum. As the ovum is about to enter the uterus, each portion which has arisen from the segmentation of the yolk has become a perfect cell. This cell formation having been accomplished at the surface of the yolk first, the cells there begin to coalesce into a membrane, with an aspect like that of hexagonal pavement epithelium, and, as the change passes toward the centre, the cells, as they form, come toward the membrane and thicken it, leaving a clear liquid within. In this manner a secondary vesicle forms within the zona pellucida : it is the blastodermic vesicle : it is the UTERINE NUTRITION. 525 The chorion. temporary stomach of the embryo. Its wall constitutes the germinal membrane, upon which the embryo arises. New cells being constanth' added, the membrane increases in thickness ; and here it may xhe germinal be remarked that, in most types, the yolk is to be considered membrane, as presenting two portions — the germ-yolk and the food-yolk ; the for- mer being immediately employed in the development of the embryo, and the latter being a stock for more advanced supply. In mammals, for whom other means of nutrition are quickly provided, the food-yolk is im- perceptible, and, moreover, in them the albuminous coating of the zona pellucida is small ; but in birds, the embryo of which has to be nourish- ed independently of the parent, the quantity is necessarily large. As we have said, this albuminous covering and the zona together constitute the chorion, the exterior of which presents a rugged aspect, from the appear- ance of absorbing radicles, which, becoming imbedded or dove- tailed in the deciduous membrane, presently to be described, establishes the necessary connection for tuft nutrition, and thereby ob- taining albumen from the parent. III. Fertilized Ovum in the Uterus. While the ovum is passing through the Fallopian tube or oviduct, it obtains a coating of albuminous material outside of its zona pellucida, as has been said. This coating becomes the means of attachment to the uterus, and thereby of the absorption of nutriment in the following way. The outside surface of the incipient chorion presents a layer of cells, and soon after assumes a iibrous structure. In this condi- uterine nutri- TPiq 25T tion the ovum makes its appearance in *^°"- the uterus, on the interior of the surface of which the mouths of a great number of follicles open. These follicles are not unlike those which the stomach presents. Their general appearance is illustrated by Fig. 257 ; d, csecal terminations of glands ; i. 261. ^^^Pw^ Production m vessels. V Fin. ?G'?. inal membmne of a fowl at thirty-sixth hour of in- cubation. (Wagner.) The formation of vessels from the coalescence of nucleated cells, the touching ends becoming pervious or elongating, is continued to a mucli later period of development, as is demonstrated by Fig. 262. Capillary lymphatic from the tail of the tadpole : a, membrane ; h, processes formed by it ; c, re- mains of the contents of the cells forming these vessels, in which nuclei are concealed ; e, coecal terminations of the ves- sels ; y, one of these termina- tions still recognizable as a form- ative cell ; g, isolated formative cells about to join with actual vessels, magnified 350 diame- ters. (Kolliker.) It is at this time that nutri- tion by cells ceases, and vascu- lar nutrition commences, as pre- viously described. The embryo has now become too large for promiscuous cell nutrition to an- swer ; moreover, development is required to take place at differ- ent rates at isolated and special points. The formation of the amnion coincides with these events. The heart appears first as a canal or tube, arising in the vascular layer from a columnar mass of cells, of which the inner ones Development have deliquesced to form a tube. This then becomes tri- of the heart. chambered, containing an auricle, a ventricle, and the bulbus arteriosus, 2^ 263. ^^9' ^^^' of which a description is given on p. 135. Subsequently the auricle and ventricle are each divi- ded by septa, that in the ventricle being commenced about the fourth, and finished about the eighth week. The auricular septum is not completed until after birth. Fig. 264, page 530, shows the human heart at about the fifth week : A, the lieart opened on the abdominal aspect; 1, the bulbus arteriosus; Ll Production of vessels : capillary lymphatic, magnified 350 diameters. Rudimentary heart. 530 THE AMNION. Fcetal heart. ^!}- 2^- 2, 2, two aortic arches, uniting posteriorly to form the aorta ; 3, the auricle ; 4, the opening from tlie auricle into the ventricle, 6, which is laid open ; 5, the septum rising from the lowest part of the cavity of the ven- tricle ; . 7, the vena cava inferior : B, view from behind ; 1, the trachea ; 2, the lungs ; 3, tlie ventricle ; 4, 5, the large atrium cor- dis, or auricle ; 6, the diaphragm ; 7, the aorta descendens; 8, the pneuraogastric ; 9, its branches ; 10, its continu- ation. (Von Bar.) As soon as the capillary system is fairly established, the change in the character of the function of nutrition alluded to is accomplished, and in those animals which depend for then- development on a food yolk, it is eventually entirely covered with ramifications of these vessels. The blood-cells of the first order or series are evolved from the nuclei of the cells which coalesced for the formation of blood-vessels. The development of the embryo still continuing, it assumes a form Elevation of whicli has been aptly described as resembling that of a boat Che embryo, placed upside down, the bottom of the boat rising higher and higher above the surface of the germinal membrane, and lifting with it that portion of the membrane to which it is attached. The two ends of the boat-shaped body bend under toward one another ; the larger of the two is destined to become the head of the embryo. As this elevation takes place, the embryo becomes separated by a constricted space from the surrounding germinal membrane, its abdominal parietes being still open and in contact wdth the yolk. From the layer which thus lines the interior of the cavity of the embryo, the intestinal canal arises as a tube from the coalescence of a pair of lateral ridges, and the surrounding and exterior portions of the germinal membrane, elevating themselves above the constricted space, coalesce over the back of the embryo, and thus inclose it in a sac. This sac constitutes the amnion, and in this manner, by folding, the interior of the germinal membrane is used as a digestive surface, the outer as one for secretion. The umbilical cord obtains a sheath from the amnion, which at one end is continuous with the skin of the fcetus, and the other is reflected over the surface of the placenta. The amnion therefore constitutes a closed sac, which contains a fluid, the liquor amnii. The place at which the germinal membrane is constricted, so as to be able to act as a digestive surface to the embryo, though linear at first, is gradually narrowed down, and constitutes the umbilicus. Tliis con- stricted part is now the omphalo-mesenteric duct, which of course com- municates with the cavity of the yolk-sac, which, at this stage of devel- The amnion. THE CIRCULATORY SYSTEM. 531 opment in mammalia, is the umbilical vesicle. In birds, the yolk-sac is carried completely into the abdomen through the umbilical opening ; in mammals it remains exterior. It does not appear that the contents of the yolk are directly absorbed from the cavity of the sac, but they are carried by the ramifying vessels to the liver. These vessels are there- fore counterparts of the mesenteric. Everrtually folds arise on the lin- ing membrane of the yolk-sac over which these vessels pass, and which facilitate absorption. In fish, at this stage, the yolk-bag hangs down, and respiration takes place upon its surface. From the caudal extremity of the embryo the allantois emerges as a mass of cells, of which the interior liquefy, and the exterior T-1-1 T ■ -I • 1 The allantois. then constitute a sac. in birds and m reptiles it readies considerable development ; in the former extending entirely over the yolk-sac, but in mammals it is soon replaced and shrivels up. It dis- charges the function of a urinary bladder, and, indeed, a portion of it continues to do so in man. Its disappearance is the signal that the em- bryo is now depending on the placenta. To return now to the development of the circulatory system. At about the end of the eighth week, as we have seen, the ven- peveiopment tricle is divided by a septum, the division of the auricle not of the circula- occurring till a little after, and even then not being perfect, °''^®^^ ®™' an aperture, the foramen ovale, existing. This is the state of things at about the twelfth week : of the five branchial arches two disappear, the aortic bulb then divides into two tubes, which are to be the aorta and pulmonary artery respectively. Next, one of the branchial arches forms the subclavian and carotid arteries. Of the middle pair, the right is obliterated, but the left remains to constitute the arch of the aorta. Of the lowest pair, the right forms the right and left pulmonary arteries, and the left constitutes the ductus arteriosus. The blood-system having reached its full development, the foetal circu- lation may be described as follows : From the placenta ox- The foetal cir- idized blood is brought through the umbilical vein, a part culation. passing into the ascending cava through the ductus venosus, and the rest into the liver through the vena portal, from which, by the hepatic vein, it also reaches the ascending cava. In its passage to the heart it be- comes adulterated with blood derived from the trunk and lower extrem- ities. It next gains into the right auricle, and, to some extent, is kept from contamination with the venous blood coming through the descend- ing cava by means of the Eustachian valve, which directs the arteri- alized blood through the foramen ovale into the left auricle, from which it gains the left ventricle, and also directs the venous blood of the de- scending cava into the right ventricle. The blood which is in the left ventricle is driven therefrom into the ascending aorta, and supplies the 532 TYPES OF NUTEITION. head ; but the venous blood which is in the right ventricle is driven therefrom through the pulmonary artery and ductus arteriosus into the descending aorta, and, mingling with the arterial blood therein, passes to the trunk and legs. Of this blood a portion is then carried to the placenta to be arterialized. At the moment of birth a change takes place in the manner of the cir- culation, which is now arranged upon the type described at page 134. This is accomplished as described at page 148. From the description which has thus been given, it may be gathered Three u-pes of i^sit, up to the period of birth, three distinct types of nutri- nutrition. fion have been followed. They may, with sufficient accura- cy, be designated, 1st. Yolk nutrition ; 2d. Tuft nutrition ; 3d. Placental nutrition. To these may be added the two followed at a later period : 4th. Lactation, and, after the dental mechanism is supplied, 5th. The diet of mature life. Respecting the development of special organs, it may be remarked that The vertebral ^f those wliicli are permanent, the vertebral column is one of column. {[-^Q £rst to appear ; it shows itself under the form of isolated quadrangular elements. The gelatinous cellular structure, chorda dorsa- Hs, acquires a sheath, which assumes a fibrous structure, and from this, in the lower vertebrates, the vertebrae are evolved. In man, the ele- mentary quadrangular plates are considered to have an independent ori- gin. As they increase in number and size they surround the chorda, and projections springing from their superior surface form arches to en- velop the spinal cord. Each vertebra, therefore, is constructed by the union of two pieces, one on either side. These first assume the condi- tion of cartilage, and, later, the body and arches ossify from separate points. The chorda dorsalis, which has, during this development, been gradually evolved in the bodies of the vertebrae, disappears. The bones of the skull are metamorphosed vertebrae, of which, accord- ing to Professor Owen, four appear to have undergone change. To these the auditory, gustative, optic, and olfactory nerves are respectively re- lated, in the same manner that the spinal nerves are to their vertebrae. In the descriptions given in the preceding part of this work, incident- Development al allusion to a sufficient extent has been made to the devel- of the appara- Qpj^gn^ of most of the apparatus of organic and also animal tus of organic r rr o life. life. It may therefore here be briefly stated that the ali- mentary canal originates in the pinching oif of a part of the blastodermic vesicle below the spinal column. At first it is a straight tube, which communicates about its middle with that vesicle, but after a time shows its eventual division into oesophagus, stomach, large and small intestines, assuming an oblique position on the part to be occupied by the stomach, and then curving in the region of the intestine. From a part of this tube , INDICATIONS OF CONCErTION. 533 the liver emerges as a thickened deposit of cells, into which the wall of the intestine hulges so as to form a kind of sac, and from this rudiment a ramified structure arises, which at last recedes from its place of origin, and is connected with the intestine by the hepatic duct. The commence- ment of this structure is about the third week, but it proceeds with so much rapidity that in the third month it nearly fills the abdominal cav- ity. The functions of the liver at this period have already been pointed out, the meconium it secretes being modified bile (page 202). In like manner, from the digestive tract, the pancreas and salivary glands orig- inate from masses of cells, ducts being formed by deliquescence of por- tions within. From the alimentary canal, also by budding and deliques- cence, the lungs arise, their cavity communicating at first by several aper- tures with the pharynx. This occurs about the sixth week. These organs are gTadually removed from the place of origin, as in the case of the liver. The Wolffian bodies are temporary urinary organs, which precede the kidneys and eventually disappear. They are of an ovoid The Wolffian shape, and consist of a duct from which transverse canals bodies, branch forth, the duct discharging into the sinus urogenitalis. They originate about the end of the first month, and commence to degenerate in the third. In fishes they remain as the permanent urinary apparatus. The testes or ovaries arise from the inner margin of the Wolffian body, the former being guided into the scrotum by the gubernaculum. This descent commences between the fourth and fifth month, and is completed at birth or shortly after. Among the indications that conception has occurred are usually enu- merated, stoppage of the menses, the placental murmur, the indications of development of the mammary gland, its sense of pain or ten- conception, derness, the color of the areola, the turgescence of the areola and nipple, irritability of the stomach. Quickening, as it is termed, usually occurs about the eighteenth week, and parturition in the fortieth, or at the close of 280 days. With respect to this, it is admitted that the term may be possibly prolonged, in very rare cases, by 40 days. The French laws le- gitimatize a child born within 300 days ; and that such variations of the proper term may occur is proved by observations made upon domestic animals, in which the duration of pregnancy can be ascertain- period of ges- ed with precision. In the cow, which has the same period of tation. gestation as the human female, the shortest period hitherto observed is 213 days, the longest 336. The shortest period at which human par- turition can occur, consistent with the viability of the child, appears to be about 23 weeks. The act of parturition in its first stage is to be referred to a contrac- tion of the muscular fibres of the fundus and body of the Mechanism of Uterus with a synchronous relaxation of those of the cervix, parturition. 534 GEJiEVIATION. At a later period the contraction of the expiratory muscles assists. After Lirtli is accomplished, the mouths of the uterine vessels are closed through the contraction of the organ, the lochial discharge carrying with it any disintegrated residues of the deciduous membrane, and also large quanti- ties of fat, derived probably from the degeneration of the uterine stnic- ture itself. That both parents are concerned in imparting characteristics to the Influence of child there can be no doubt : it is fully established where they both parents, ^re of different races, as white and black, or white and red ; and equally in the case of animals, as in mules, produced by the mix- ture of different kinds. It is scarcely necessary to remark that this ex- tends to the communication of more refined peculiarities, the resemblance of countenance, figure, gesture, and even mental qualities, family like- nesses which we daily observe. These impressions are of a much more profound character than might at first be supposed, as is proved by the fact that the third generation will exhibit peculiarities belonging to its progenitors, though those peculiarities have not occurred in the second. Even after parturition is over there still remains impressed upon the fe- male a definite change : this is illustrated by the well-known case of a mare which had borne a colt by a quagga, her subsequent colts by horses being distinctly marked like the first ; and in the human female cases are of common occurrence in which the offspring of a widow, who has been married a second time, resemble her first husband. ]\Iarriage pro- duces in this respect a permanent change in the female, a constitutional impression not disappearing in any length of time, the influence of the first husband reappearing in the children of a subsequent contract. 2d. gemmation. The ascending axis of a plant is terminated by a differentiating part. Gem f f surrounded by protecting structures. From this, as growth plants and ani- takes placc, Icavcs or their modifications are produced. This ^^ ^' differentiating part is a bud. In like manner may be found in the axils of leaves similar buds, which pass by development into branches, but sooner or later the terminal buds are checked in their lon- gitudinal increase, and the parts to which they would have given origin Fig. 265. Spirally being compressed into circles, a flower arises, and further development ceases, the reproductive phase being now assumed. Among the lower animals propagation by buds is also observed. Thus the hydra exhibits this manner of increase, as seen in I^ig. 265 ; and even upon the buds thus produced, other buds, of a second order or Hydra budding. generation, are found. METHODS OF GKAFTING. 535 Propagation tlivough the agency of buds is termed gemmation. It may be accomplished cither by the natural or artiticial separation of the buds from the parent stock. Thus, in the hydra, the buds may spon- taneously be separated from the parent, and thereby give rise to free in- dividuals, or they may be purposely cut otf with the same result. In the case of plants, artificial separation is constantly resorted to, as in the various methods of budding and grafting employed by horticulturists for obtaining the finer varieties of flowers or fruits. It consists Methods of essentially in placing a bud of the plant which it is desired to grafting, propagate upon a stock of a different kind, in such a way that, as devel- opment of the bud or scion takes place, union or incorporation with the stock shall occur. There are many different ways in which grafting may be performed ; they all depend for their success, however, upon causing the alburnum of the scion to coincide with that of the stock, so that the vessels of the former may receive the sap arising from those of the latter. When the parts are thus adjusted, they are to be retained in their posi- tion by bandages or other suitable means, and protected from the air and rain by means of clay or wax. The most suitable time for this opera- tion is in the spring, just previous to the rising of the sap. There are certain limits witliin which the operation of grafting must be performed. The stock and the scion must be nearly re- Limits of gem- lated to each other. If species of different natural orders be ™ation. grafted they will not take, but the species of the same genus may. If in this manner we take a bud, and graft it on a stock of an allied kind, it will continue to grow and develop in the same man- „ , ner that it might have done without detachment from the propagation parent plant, and in the same manner from the new plant that ^ g^mma ion. has thus arisen, by a repetition of the process, plant after plant, for many generations, can be secured. Experience has taught us that, whatever might have been the peculiarities of the original from which the first bud was taken, those peculiarities, whether of odor, taste, color, or shape, will reappear in the product ; but experience has also taught us that there is a limit beyond which these repetitions can not be conducted. The val- ued fruits and flowers of the old times have thus disappeared. Propaga- tion by gemmation is therefore considered as tending to exhaust the orig^ inal plastic power. But it is to be remarked that, if from these artificial growths seeds be taken and caused to germinate, the plants so arising no- longer present the special, and, perhaps, valued peculiarity, but in many- instances run back at once to the original and wild stock. We are apt to attach to propagation by gemmation more importance- than it really deserves in a philosophical point of view when it thus ap- pears to have given rise to new and successive generations of individuals. But, after all, wherein does it differ essentially Irom what goes on natur- 536 SPONTANEOUS GEMMATION. ally ? The manner of extension of any given plant is by bud after bud in succession, either terminal or axillary ; but this extension does not go on indefinitely ; it reaches a limit both as respects size and duration. We never notice in the development of a bud which remains attached to its parent stock the spontaneous appearance of novel qualities. The flowers and fruits are like all the others upon the same plant. If such a bud, then, removed from its parent seat, be permitted, under favorable conditions, to grow elsewhere, it might be expected, as is actually the case, that it would go on in its development without exhibiting any alterations. Essentially of an exhausting nature, reproduction by gemmation is limited. It can only be repeated a definite number of times. At the most, all that we do in this artificial process is to obtain a part of an old individual under a new and isolated form. We thereby relieve such new growth from the chance of those accidents which may befall the original stock ; but both for the one and for the other there is a definite term of life. When that term is approached, though we may take sci- ons or buds, and treat them with every care in the usual operation of grafting or budding, the operation will fail. There is a certain analogy between this incorporation of the parts of difierent plants and the so-called grafting or Taliacotian operations which are sometimes performed on the parts of animals, as the transplantation of the spur of one bird on the top of the comb of another, or many of the plastic operations of surgery ; but these parts do not necessarily perish in the manner which has been indicated by Butler in his Hudibras. Propagation by gemmation and reproduction by generation are, in many instances in the animal series, resorted to alternately for the con- tinuation of the race. Thus, during the summer season, propagation by gemmation may serve to increase the number of a given kind, but if these should be unable to maintain themselves during the cold of winter, the race would inevitably become extinct, unless reproduction by ova were resorted to ; for though the developed animal may not be able to with- influence of Stand the decline of temperature, the ova may. Thus, in sporiuneous ""^ ^ hydra, propagation by gemmation continues until the ex- gemmation, ternal temperature lowers to a certain degree, and that at once brings on a reversion to the other process. The same thing has been observed in the case of the aphis, which multiplies by gemmation until there is a reduction of temperature, and then it multiplies by gener- ation. We have already dwelt at length on the control which external circumstances have over development; it is, therefore, no more than might be expected that they should, in like manner, determme the processes of propagation and reproduction. Gemmation occurs only in a very doubtful way and under special cir- cumstances among the more advanced members of the animal series. In ALTERNATION OF GENERATIONS. 537 man, there is reason to suppose that gemmation can only take place in the earliest periods of existence, perhaps at the epoch of the formation of the mulberry mass. Upon this principle an explanation of the occur- rence of double monsters has been given. 3d. alternation op GBNEEATIONS. It has been abeady explained that by this phrase is meant that a pa- rent plant or animal will give origin to a form wholly unlike Alternate "-em- itself, and this form, perhaps after the lapse of years, will mation and give origin to another unlike itself, but similar to the original S^"*^'^ ^""• progenitor. Thus the Salpa?. present themselves under two different as- pects, the solitary and the aggregated, the latter being produced from the former by being budded off in an internal stolon, the individuals being united to one another in an aggregation or chain after they have been separated from the parent. These aggregated salpffi alone have sexual organs and produce ova. From each ovum a solitary salpa arises, which repeats the process described again. The solitary salpa, therefore, mul- tiplies by gemmation, the aggregate by generation. Nor is this process confined to animals ; it is also observed in the case of plants. Thus, in ferns, the spore produces the prothallium, which becomes a distinct or- ganism, separated from its parent, and carrying on its nutritive processes independently for itself. From it arises by generation a fern like the original, which, like it, by gemmation, produces prothallia, but never directly produces a fern. Therefore between each fern and its descend- ant a prothallium intervenes, the prothallium arising by gemmation from the fern, and a fern arising by generation from the prothallium. After a careful examination of Steenstrap's doctrine of alternations of generation. Dr. Carpenter concludes that it can not be re- -^ , & _ _ ' -C^ _ Explanation ceived in the form originally presented, since we should re- of alternations gard a generation as embracing the entire product from gen- ° s^"<^i^ ^°^- erative act to act. Indeed, the intermediate forms are often nothing more than sexual organs, furnished or not with an apparatus of locomo- tion, or, in the more complicated cases, having a mechanism of nutrition attached sufficient for their purpose. The correctness of this interpreta- tion may be illustrated by such cases as the development of medusa buds, which, being first attached to the parent, gradually exhibit the formation of an independent digestive apparatus, and when this has reached a cer- tain degTee of perfection, they are separated and swim off, generative or- gans then arising in these buds by which true ova are formed. In the Sentularidse buds are developed in ovarian capsules, and these reproduce in their turn ova by generation. The rate at which gemmation goes on in many of these instances is obviously connected with physical condi- tions, more particularly the degree of temperature and the supply of food. 538 GROWTH OF MAN. The fact of tlie apparent dissimilarity "between tlie product of gemma- tion and the product of generation ceases to have any force as soon as we consider the former in the attitude which it really ought to occupy, as not constituting a distinct individual, but merely a part, a derivative, or an appendix of the product of generation ; and this view of Dr. Car- penter's seems, therefore, to be the proper interpretation of the whole case. CHAPTER V. THE GROWTH OF MAN. Infancy. — Weight and Size of the Infant.— Weight and Size at subsequent Periods. — Develop- ment of the Intellect. — Maturity of Man. — Tendency to Crime. — Maxima of Physical and Men- tal Strength. Mental and Physical Decline. — Mortality at different Periods of Life. — Comparative Structure. Functions., and Mortality of the two Sexes. Artificial Epochs of Lfe. — Gradual Change in the Mental Qualities. — Independent Existence of the Soul. In the last chapter the successive stages of embryonic development were described. It was shown that at one period nutrition is solely at the expense of the yolk of the ovum, which is appropriated by a simple surface-imbibition ; and that this, in due time, is succeeded by what has been designated tuft nutrition. At a later period, this mode, in its turn, is replaced by another, depending on a vascular arrangement, the pla- Infancy of ccnta. For a considerable period after birth a fourth system is man. relied on, nourishment by milk ; and it is only by degrees, when the necessary changes have been made in the digestive mechanism, the teeth being cut, that the tinal mode of nutrition is assumed. Even after this the human infant leads a dependent life, because of its own weak- ness and imbecility, irrespectively of any peculiarities of our social state. So far, therefore, from man not exhibiting those metamorphoses which are undergone by the lower members of the animal series, he of all dis- plays them in the most marked way, for they do not cease at the period of birth, but reach through many subsequent years — a gradual develop- ment of the body, attended by a gradual change in the manifestations of the mind. At birth, the human infant is the very representative of weakness and imbecility. Though, unlike many other mammals, it opens its eyes at once, it exhibits no token of visual perceptions ; though it may be sub- jected to sounds or noises of various kinds, it takes no notice whatever of them. This condition of inertness is followed by a condition of con- fused sensation, which by degrees is succeeded by a capability of ap- THE TEETH, 539 preciating special ideas. Bulibn has very trul}- said that the earliest period of conscious existence is a scene of pain, the life of the infant be- ing divided between sleep and ciying ; from its slumbers it is awakened only by the pains of hunger ; nor is it until after the lapse of many days, or even weeks, that the first smile is seen. It is too feeble to turn from side to side, but remains in the position in which it was placed. Its skin, which at birth was covered over with a whitish incrastation, tlie vernix caseosa, becomes reddish, the depth of this tint, however, shortly passing away. At this period, moreover, life is purely vegetative, the in- fant feeding and sleeping. The biliary matter, meconium, which had ac- cumulated in its intestine during foetal life, is discharged in the course of a day or so after birth, and the digestive apparatus enters on its functions with activity. It is said that the infant smiles soon after it is forty days old ; though it can cry it can not shed tears. Before long it gives indications of its satisfactions and dislikes. The power of moving in an erect posture is gained by it in the course of a year, and by the close of that time it can masticate. Of its teeth, the central incisors appear about the seventh month, those of the lower jaw lirst ; the lateral incisors about the eight or tenth, the anterior molars about the twelfth, and the ca- nines about the eighteenth, the posterior molars being cut between that time and three years. The average date of the appearance of the peraia- nent teeth is, the front molars about the seventh year ; middle incisors, eighth ; lateral incisors, ninth ; anterior bicuspids, tenth ; second bicuspids, eleventh ; canines, twelfth to thirteenth ; second molars, twelfth to four- teenth; and the last molars from the seventeenth to the twenty-lirst year. The power of articulate speech is displayed within twelve or fifteen months, some letters being more easily gained than others ; among them are A, B, P, M. ^^^'^ From henceforth the mind emerges with rapidity from the confusion of a multitude of impressions, and learns to concentrate itself ^ mi • 1 •!• ' 11 Concentration at pleasure upon one. i his capability ot mental abstraction of the atten- is a process of specialization, and is a manifestation of the ^^°°' law of Von Bar. The intellectual ditFerence which we eventually observ'^e between one man and another is, to no inconsiderable degree, dependent upon such an ability of concentrating thought. He who conceives of a thing distinctly is very likely to express himself of it clearly. Throughout infancy and childhood, the features, and even the gestures, indicate the profound constitutional changes which are going on. The countenance, instead of expressing pleasure and pain in the aggregate by smiling or crying, as was tlie case at first, gains the faculty of represent- ing every grade of feeling. Long before maturity is reached we read without difficulty the thoughts which are passing in the mind from the 540 MAXIMUM AND MINIMUM OF HEIGHT. movements of the lip or the eye, and the painter can express every shade of feeling, and every emotion, by the mere configuration of the outward form. The monthly growth of the foetus for six months before birth is es- Mean length tablished at tw^o inches. At birth, the mean length of boys of the infant. |g ]^gi. inches, and of girls 18^ inches, the former being there- fore a little the longer. At sixteen or seventeen years the growth of girls is relatively as much Growth of boys advanced as that of youths of eighteen or nineteen. For and girls. t|^e most part, the inhabitants of towns are taller than those of the country. The full height is not reached, in some instances, until twenty-five years ; in very warm and very cold climates it is more quick- ly attained. The recumbent position is regarded as being favorable to growth, and, influenced by his own weight, an individual is shorter in the evening than when he first rises from bed in the morning. With regard to the rate of growth, it may be observed that it is most rapid immediately after birth, and continually diminishes until about five years, the epoch of maximum of probable life. It then remains equable to about sixteen years, the annual growth being 21 inches. After pu- berty it declines, being, from sixteen to seventeen years, 1^ inches, and during the next two 1 inch only. The annual increment relatively to the height then attained continually diminishes from birth. The foetus grows as much in length in a month as the child from 6 to 16 years does in a year. The limits of growth of the two sexes are unequal, be- cause women are smaller than men, terminate their gi-owth sooner, and annually grow less. Individuals in affluent circumstances may often surpass the standard height, but misery and fatigue are liable to produce the opposite effect. Longevity is generally less for persons of great, height. As to the maximum and minimum of height, it may be remarked that „ . , Frederick the Great had a Swedish body-guard whose height minimum was eight fcct three inches ; and, on the other hand, Birch height of man. ^^^^^^ ^j^^^ ^Yiem was an individual, 37 years old, whose height was sixteen inches. In view of these and other such facts, Quetelet fixes on 8 feet 3 inches as the maximum, and 1 foot 5 inches as the minimum of height ; he gives as the mean 5 feet 4 inches. Half the men of France, at the age of conscription, are between 5 feet 2 inches and 5 feet 6 inches, but the wars incident on the great Kevolution made a permanent impression on the French in this respect by lowering the standard through the consumption of the taller men. M. Quetelet more- over remarks, that in ten milHons of men there is but one more than 6 feet 8 inches, and one less than 4 feet. There is reason, however, to be- lieve that this statement will not hold good of America. WEIGHT AND HEIGHT. 541 As -regards weight, new-born boys are heavier than girls. An average taken from 20,000 gives 6^ lbs. as the weight at birth; the weight of maxima and minima have been 10^ lbs. and 2-} lbs. For about infants. a week after birth the weight diminishes, owing to the eifect of aerial respiration. The difference in weight between the two sexes gradually diminishes until about the twelfth year, when an equality is reached. The maximum weight is attained about 40, and as 60 is ap- ^r^j j^^ ^^ ^jjf, proached a diminution is perceived, which reaches 12 lbs. ferent periods at about 80 years, the stature likewise correspondingly di- minishing by about 2| inches ; the female reaches her maximum weight somewhat later, at about 50 years. The extreme limits of weight in men are 108 lbs. and 216 lbs. ; in women, 87^ lbs. and 206^ lbs. The mean weight at nineteen is nearly that of old age in both sexes. At full development the male and female weigh almost exactly 20 times as much as at birth. In the first year the infant of both sexes triples its weight. It requires six years more to double that, and thirteen to quadruple it. Immediately after puberty both sexes have half their ultimate weight. Between the ages of 25 and 40 the mean weight of the male is 136^ lbs., and of the female 120| lbs. With respect to the relation between weight and height, if man increased equally in all his dimensions, the weight would be as the cube p^g]ation of of the height ; but since this is not so, development taking place height and unequally, the proportion is not observed, and it is found that ° from the end of the first year to puberty the weights are as the squares of the heights. M. Quetelet gives as an approximate rule that during development the squares of the weights at different ages are as the fifth power of the heights, the transverse growth being less than the growth in height. The mean weight of a male, without reference to age, is 103 lbs. ; of a female, 93|. A similar calculation for the population of the United States as that which has been given by this philosopher for Brus- sels would give for the total weight of all Americans two thousand six hundred and thirteen millions of pounds. The weight of an individual, considered without reference to age or sex, is lOO^^Q- lbs. From birtii until puberty the mode of life is essentially vegetative, all the instincts having relation to the individual and corporeal development. Except through the intervention' of education, the desires of the child are chiefly directed to the pleasures of mere vegetative existence, eating and drinking ; and this, in savage races, is witnessed in a much more mark- ed manner than in those that are qivilized, in whom the manner of life is affected through the intervention of parental care. In this particular it may be remarked that maternal love is divisible into an in- Maternal love stinctive and a moral affection, the former of a lower and of ^^^ kinds. 542 MATURITY OF MAN. more animal kind, the latter of a higher and intellectual ; the former lim- ited to the period of infantile helplessness and dependence, and succeed- ed by the latter as maturer years are attained. In savage races, howev- er, instinctive affection seems alone to exist, and the intensity of moral affection is, to a certain extent, a measure of civilization. Throughout the first fifteen years of life, with the gradual development vviifirflCLGr or -i • ii i the life of chil- of the body there is also a steady intellectual progress, the ^^^' gains of which seem to be greatest at the earlier periods, and less and less marked as maturity is approached. When we recall the wonderful advance accomplished in the first years, embracing the acqui- sition of speech, and a knowledge of the nature and qualities of a thou- sand surrounding objects, we might be led to suppose that our mental acquisitions decline with the progress of life ; but this is altogether de- ceptive ; for, though the acquirements of later years be less obvious, they are none the less important and none the less profound. Through the successive changes to which allusion has now been made, The maturity ©ach of which is a strict metamorphosis, and each of which, of man. ^yj^h its special structures, has its special functions, man at last reaches maturity. In some cases, as we have seen, the stature contin- ues increasing until after the twenty-fifth year, and throughout the whole mature period, even after what has been termed the meridian of life is gained, the weight also becomes greater. This increase of weight, how- ever, has not so much a relation to the muscular as to the respiratory sys- tem, for the former reaches its perfection at a much earlier date, the in- creasing development of the middle period of life being due to a continued tendency to the accumulation of fat. At this period, moreover, the object of life has undergone an entire change ; the vegetative propensity, or that for the exclusive development of the individual, has declined in prom- inence, and the reproductive has been assumed. With this there have been awakened new sentiments and new emotions, affording still another corroborative proof of the connection of mental habitudes and structural condition. The psychical powers are now advancing toward maturity, an advance which they continue to make until about the fiftieth year. Throughout this whole period, and even at this extreme date, we still notice how much intellectual capacity is connected with the perfection of corporeal development. It needs but a little experience for us to de- termine at a glance the intelhgent from the obtuse, and to read even the minor shades of character in the aspect of the face. Without being aware of it, we are constantly putting into requisition the principles of phrenology and physiognomy, and drawing conclusions respecting char- acter to a certain degree correct, from the expression of the eyes, tlielin- eaments of the countenance, or the configuration of the head. The actions of man are closely connected with the physical and moral TENDENCY TO CRIME. 543 circumstances under wliich lie is placed. The greatest num- „, , , '■ . ^ _ The tendency ber of crimes against persons and property is among the inhab- to crime in " itants of river- banks. The period of the maximum of crimes ^^^'^' against persons coincides with that which is the minimum against prop- erty, and is the summer season. As respects each individual, his tend- ency to crime is at first against property, and this reaches its maximum at about ,25 years of age, whereas the tendency to crime against persons commences later than that against property, and increases with the in- crease of strength. In crime, man, as he grows older, substitutes strata- gem for force. If brought up in a liberal profession, his tendency in crime is against persons, but that of the workman is against property. Elementary instruction, so far as reading and writing go, does not lead to the diminution, but rather to the increase of crime : a very p^g-y^ij^^jj^i gf. important conclusion, more particularly in the United States, feet of low ed- in many portions of which this kind of education is chiefly patronized by government, to the exclusion, to a certain extent, of that which is of a higher grade, and which serves to correct this important defect. Moreover, superficial education makes the mind a ready recep- tacle for every kind of imposture, and has been the cause of the rapid spread of many modern delusions, such as spiritualism and homceopathy. As regards women, their tendency to crime, when compared with that of men, is as 23 to 100 : at least this is the case in France. „, , , ' ... The tendency Their tendency for the perpetration of crimes against persons to crime in ' is less than that for crimes against property in the propor- '^'°™®°- tion of 16 to 26. It is interesting to observe that the physical force of woman, as compared Avith that of man, is also as 16 to 26. From such considerations, it may therefore, perhaps, be concluded that the morality of women is about the same as that of men, their physical feebleness and modesty being taken into account. In women, the maximum tendency for crime occurs at about 30 years, but then she relinquishes that dispo- sition sooner than man. Her tendency to theft, however, begins early, and lasts through life. When she desires to commit murder, she em- ploys, by preference, poison. In this may be discerned the influence of her constitutional element, physical feebleness. Timid at explosions and at the sight of blood, if driven to the extremity of self-destruction, she instinctively resorts to drowning. Women, like men, who are the res- idents of towns, are much less moral than those who live in the country. This may be inferred from such facts as that the annual percentage of still-births occurring in the former is very near double of that occurring in the latter case ; and though this may be, to a certain extent, connect- ed with the fashionable restraints of clothing and social dissipations, it is far more due to female depravity. • The illegitimate births of tOAvns compared with those of the country are as 23 to 7. Among the still- 544 MAXIMA OF STRENGTH. born, the illegitimates are to the legitimates as 5 to 3. In the city of Berlin, the illegitimate still-births are to the legitimate in as high a pro- portion as 3 to 1. The passions of man are gratified in a manner that seems to be inde- pendent of religious profession. The open dissoluteness of one country is counterpoised by the secret crime of another. Protestant England and Catholic France exhibit a striking illustration. In the former, in 1845, the number of illegitimates was 70 per thousand of the whole num- ber of children born. In France it was about 71. During the process of the development of the intellect of man, various Succession of Psychical persuasions in succession arise, which are frequent- ps)»chical per- ly imputed to education or tradition, but of which the origin is undoubtedly to be traced to the organization. Those gen- eral ideas that are found all over the world, among all races of mankind, whatever may be the climate in which they live, their social condition, or religious opinions — ideas of what is good and evil, of virtue, of the efficacy of penance and of prayer, of rewards and punishments, and of another world: these, from the uniformity of their existence in all ages and in all places, must be imputed to the stamp that has been put upon our cerebral organization. In the same light we must view, as Dr. Prich- ard has said, the delusions and fictions which are universal, such as ghosts and genii, giants and pigmies. Universal opinions are not the result of accident, nor always of tradition. They are often creations of the mind, arising from peculiarities of its constitution. Arrived at maturity, the system of man commences at once to decline, Successive max- the cpochs of the maximum of physical and mental strength a™d mental ^^^^ ^^^^ howevcr, coinciding ; that for the former occurring at strength. about the 25th year, as previously remarked, but that for the latter not until between the 45th and 50th year. At this period, when the powers of imagination and reason have reached their highest degree, the liability to mental alienation and insanity is also at its max- Order of men- i™^"^' Somewhat later, the physical system plainly be- tai and physi- trays that it is pursuing its downward course, retracing the steps through which it passed forward to development. Soon there is an evident decrease of weight, the nutritive operations being no longer able to repair the waste of the body. There is also a diminution of the height. This corporeal decay is the signal for a depression of the mental powers, the first which begins to yield being probably that of con- centrating or abstracting the thought. As years pass on, external im- pressions exert a diminished influence, and he who at an earlier period reached the meaning of things, as it were, almost by intuition, now casts his eyes over page after page without an idea being communicated to his miiid. The old man querulously complains that he reads his book, but LONGEVITY. 545 does not understand what it means. With this failure of per- Extreme old ception the powers of memory decline, recent events fading ^e<^- away iirst, Ibut those of early life being recollected last. The present no longer possesses an interest, for the brain is less capable of receiving any new impressions. One after another, the organs of sense fail to discharge their functions ; the sight becomes misty, the hearing dull ; there is an indisposition for exertion, a desire for repose. The white-bearded pa- triarch of a hundred years sits quietly by the fireside, resting his hands on the top of his staff. Instances of Longevity. Years. Attila 124 Margaret Patten 137 The Countess of Desmond 145 Thomas Parr 152 Thomas Damme 154 John Rovin ) 172 His wife.... S 164 Peter Torton 185 The mortality of towns is greater than that of the country. As we advance from the midst of the temperate region toward the Local mor- equator or toward the poles, it also increases : thus, in the taiity. northern portions of Europe, the annual mortality is as 1 to 41 ; that of Central Europe, 1 to 40^^^ ; that of Southern Europe, 1 to 33^. Con- sidered as respects different periods of life, the rate of mor- -^q^^^i^ ^^ taiity varies very much. Of both sexes, 22 per cent, die different peri- before they are one year old, and 37 per cent, before they are five years old. Male infants are, however, more liable to die imme- diately after birth than female, but at the close of about two years their mortality is the same. Nine twentieths of the whole number born die before they are fifteen years of age, that is, before they have become use- ful to the community. The mortality among girls increases between 14 and 18, and among men between 21 and 26. In France and Belarium, from 26 „ , ^. o ' Relative mor- to 30 is the epoch of marriage, and at this period the mortal- taiity of the ity is the same in both sexes. It then increases for the ^®^^^" women during the years of childbearing, and afterward again becomes equal for both. At 25 years half the births are dead. The mean life may be estimated at 33 years. The maximum expectancy of life is at 5 years, at which age the risk of mortality is suddenly reduced, and be- comes small till puberty, when, especially among girls, it becomes great. From 60 to 65 the chances of life are again at a minimum. To the foregoing statements, in which contrasts have been drawn be- tween the male and female, the following may be added : Not only is there a difference in the entire stature, but the different portions of the Mm 546 PECULIAEITIES OF THE FEMALE. Comparison of body have not the same relative size. The capacity of the of the maielnd ^^^^^ ^^ ^^^ female is less ; the body is longer ; the lower ex- female, tremities shorter ; the pelvis of greater size, especially in its transverse diameter ; the heads of the thigh bones, therefore, farther apart, and the bones themselves including a larger angle than in the case of the male; the chest and the abdomen are respectively more convex; the trans- verse diameter at the shoulders smaller, and the upper extremities, like the lower, shorter; the hands and feet, fingers and toes, of less size. The surface presents a more elegantly rounded form, without angularities ; the skin thinner and more translucent ; the hair of the head is longer and finer, but other portions of the skin less covered with hair ; the nails smaller and thinner. The strength of the female is to that of the male as 16 to 26. Her ^ ^. , muscles contract with less eners-y, and are more easily wea- Functional pe- , ... . cuiiarities of ried. The peculiarities of the construction of the bones of the fema e. ^^^ pelvis and chest respectively give rise to peculiarities in the movements of the lower and upper extremities ; hence the character- istic manner of walking and movement of the arm in attempting to throw a stone. In the chapter on the voice we have already pointed out the female peculiarities in speaking and singing, and its piore acute quality. With respect to her moral and intellectual peculiarities, these are man- , ^ ifested from the earliest infancy in the sports and games Her moral and in r^ • • intellectual pe- which slic instinctively follows. Commg to maturity more cuiianties. rapidly than the male, she abandons these, though they may .still be enjoyed by boys of her own age, whom, for the course of a year or two, she regards with neglect or even disrespect, a feeling soon after to be followed by timidity. Education and the position in which she may have been placed may, to a certain extent, control or disguise her habits, but they can never wholly obliterate the striking predominance of her moral over her intellectual qualities, as compared with man. Es- sentially religious, her faith is applied to almost all the ordinary affairs of life, though when she finds that she has been deceived she is ever dis- trustful. From the earliest times it has been remarked that her revenge, more particularly when it concerns wounded pride, is implacable. Much more than the male she is delighted with the adornments of dress. . Her reasoning powers are less vigorous, though her sensations are more acute, yet she bears pain with more resignation than man. Her judgment is not so evenly balanced, and is often perverted by the preponderance of her feelings. It has been asserted that these moral and intellectual pe- culiarities which she presents when compared with man are distinctly traceable to the phrenological predominance of the moral over the intel- lectual regions of the brain. The physiologist who is thus obliged to speak of the constitutional EPOCHS OF LIFE. 547 and mental imperfections of the female, may be permitted to turn with delight from the dry details of statistics and anatomy to the family and social relations, for it is therein that her beautiful qualities shine forth. At the close of a long life, checkered with pleasures and misfortunes, how often does the aged man with emotion confess that, though all the ephemeral acquaintances and attachments of his career have ended in dis- appointment and alienation, the wife of his youth is still his friend. In a world from which every thing else seems to be passing away, her affec- tion alone is unchanged ; true to him in sickness as in health, in misfor- tune as in prosperity, true in the hour of death. When the schemes that occupied his active years have vanished, or, if realized, are now no more to him than vanities which hardly fasten his thoughts ; when, in the feeble extremity of age, every thing is a burden to him, and the pass- ing excitements of others can not even arouse his attention, the echo of those prayers is still heard which his unskillful tongue first learned at his mother's knee. The stern, the avaricious, the hard-hearted, the intellect- ual, all are equally brought to confess who was their first and who is their last true friend. The necessities of society have led to the establishment of artificial epochs in the life of man. In most countries, the first recog- Artificial uized movements of the foetus are taken as the period from epochs of life, which independent life begins, and the twenty-first year is fixed as the time of maturity. These arbitrary dates answer the purpose very well, but they have not that physiological significance which is commonly sup- posed, for neither of them coincides with any great change in the mode of life. Of the metamorphoses through which we pass, the final one, oc- curring at puberty, which separates the merely vegetative from the re- productive period of life, is, under the circumstances of the case, with the exception of the assumption of aerial respiration at birth, the only obvious one. The change which then ensues is in no respect less marked than the passage to the perfect or imago state by insects. Development sud- denly takes on a new phase, and with the physical change correspond- ingly occur changes in the psychical endowments — modesty and woman- ly sentiments in the one sex, courage, the perception of honor, and manly qualities in the other, the capability of mutual love in both. Even among animals under the same conditions, analogous results are presented, though in a less refined way. The human species is no exception to the observation long ago made, that the undue extension of the vegetative period of life into Encroachment the reproductive is at the expense of the latter. In the same tfye"^ 6^0^01' manner that a tree overladen with foliage presents its flow- life, ers scantily, so a love for the pleasures of the table and a predominating epicurean turn is often the indication of incapability. 548 CHANGE OF MENTAL QUALITIES. Up to the fourteenth year, the human being lives solely for itself; its Gradual instincts are for the gratification of its present wants, and mental '"iiaii- ^^^^se wants are, for the most part, connected with its vegeta- ties. tive development. After that period its life is for the future, and is in relation to the race. With this more elevated condition, new emotions and passions have been awakened ; there is a gradual unfolding of the mental powers, and a balancing arising from increased knowledge and increased experience ; yet, even now, the mental qualities that are most marked are only the extension of those the germ of which may be discovered at the first dawn of reason, and the same may be said even of our intellectual impressions. The ideas we have gathered as members of a family are reproduced and expanded in our religious views, and the government of God is presented to the human heart less acceptably when he is set forth as the Almighty Maker of the world than as the Universal Father and Giver of all good. In a preceding chapter I have already shown how the existence of the Parallel of cor- immaterial spirit of man may be investigated physiologically. ^"'n^aiXvel- ^^ ™^7 ^^^ ^^ ^^^ ^^ place here to dispose of an argument opment. that some have insisted on, that, since the development of the mind proceeds in an equal step with the development of the body, each expanding or declining with the other, the dissolution of the animal fabric is the token of the death of the soul. Against this doctrine the whole human family, in all ages, has borne its testimony, and, if univer- sal impressions arise from physical constitution far more than they do from tradition, it may be truly said that that doctrine is incompatible with the organization of man. Probably there is no question which has received a greater amount of individual and general attention — none which has more deeply exercised the thought of the profoundest intellect ; and what is the actual result ? Whatever may be the social state, bar- barous or polished, whatever the manner of life, whatever the climate, whatever the form of religion, the assertion of the existence of the spirit after death is so universal, that it may be termed one of the organic dog- mas of our race. Indeed, we may affirm that the mind has to be edu- cated, trained, or strained before it becomes capable of an opposite view, which, even then, will be doubtingly entertained. If there is a point in natural philosophy which may be regarded as , . finally settled, it is the imperishability of the chemical ele- 111 (16D 611 dent ^ X •z existence of ments and the everlasting duration of force. With the sys- the soul. ^g^ ^£ j^g^^^g existing as it is, we can not admit that an atom of any kind can ever be destroyed ; and a like assertion may be made of force. Heat may give rise to motion, motion to electricity, electricity to heat : one kind of force may be converted into another, there being a perfect correlation or quality of substitution among them. The quan- THE SOUL. 549 tity of power is now the same as it ever was. Its variations are analo- gous to the apparent transmutations of ponderable material. They arc mere metamorphoses. ]\Iatter and force are equally incapable of destniction. Each constitu- ent atom of the animal mechanism, though it may be dismissed for the time as useless, is not lost, but sooner or later is economized in some organic form again. The heat w'hich seems to arise from the most in- significant muscular contraction has been, so to speak, many a time in existence before, and after it has escaped from the system is not lost to the world, but discharges one function after another forever ; and if thus neither matter nor force can die, it would be a great anomaly if the prin- ciple of conscious identity were capable of annihilation. Like them, it may be capable of modification or change, and, like them, it is not capa- ble of loss of existence. The creeds of various nations recognize this great truth ; they differ only in their ideas of what that future state of modification may be. Perhaps in some age hereafter physiology will find herself sufficiently advanced to offer her opinion on tliis profound topic, for I can not think that God has left us without a witness in this matter, even in the struc- ture and development of the body itself. From the moment that we see the first traces of the nervous mechanism lying m the primitive groove, we recognize the subordination of every other part to that mechanism. For it, and because of it, are introduced the digestive, the circulatory, the secretory, the respiratory apparatus. They are merely its ministers. And, fastening our attention on the course which it pursues, we see that it is at once a course of concentration and development. The special is at each instant coming out of the more general, and, from the beginning to the end, the whole aim is at psychical development. The germinal membrane is cast away as soon as a stomach can be prepared, aquatic respiration ceases as soon as aerial can be maintained. The scaffolding that was of use at one moment is thrown aside as soon as a new eleva- tion is reached. The germ, the embryo, the infant, are only successive points in a progi'ess which at every instant displays this casting away of the means that have been used as soon as they are done with. That is the style in which the work is carried on. The principle which ob- scurely animated the germ is the same which in a higher way animates the embryo, and this again is the same which, in a more exalted condi- tion, animates the infant and the man. The cloudy speck which ushers in the phantasmagoria of life expands as the great Artist directs until every lineament has become visible. That active agent which was first laid in a fold of the germinal mem- brane was not annihilated when its type of life was changed to placental and therefore aquatic respiration. It withstood the shock when again, 550 THE SOUL. after a due season, it was suddenly made to breathe the air. Arrived at the mature condition, there is not in its companion-body a single particle that was present at birth. All has changed. And, what is still more important, not only has there been this interstitial removal, but, in suc- cession, the very nature of every one of its organs has changed. It is needless now to repeat how many different systems of nutrition it has depended on — how many sorts of stomachs in succession it has had — how it has breathed by a membrane, by gills, and by lungs — how it has carried on its circulation without a heart, with a heart of one cavity, and finally with one of four. Through all these losses and changes the im- material principle has passed unscathed, and even gathering strength. In the broadest manner that a fact can be set forth, we see herein the complete subordination of structure and the enduring character of spirit. Whatever may be the mechanism that is wanted, it is in readiness for its time ; and when it has finished its duty, is neglected and disappears. There is, therefore, a sound reason in the conclusion to which mankind, perhaps from a mere instinctive impression, have come, that the soul will exist after death, for, after surviving so many mutations, the removal of so many of what seemed to be its firm and essential supports, we are jus- tified in expecting that it will bear without ruin the entire withdrawal of the whole scaffolding. As I have pointed out, we have precisely the same reason for believ- ing the existence of the immortal spirit that we have for knowing that there is an external world. The two facts are of the same order. Of the futuro continuance of that external world, irrespective of ourselves, we entertain no doubt ; indeed, in certain cases, as in those presented by astronomy, we are able to tell its state a thousand years hence. So long as our attention was confined to statical physiology, every thing connect- ed with the subject now under consideration was enveloped in darkness, but it will be very different when dynamical physiology begins to be cultivated — dynamical physiology, which speaks of the course of life, of organs, individuals, and races. The law of development will guide us to an interpretation of many things which are now shrouded in ob- scurity, and teach us, from a consideration of what we have learned of our past, and what we know of our present, what we may expect of oui- future state ; and then it will appear that the universal opinion of the ages and nations is not a vulgar illusion, but a solemn philosophical fact. So, therefore, the decline of the mental faculties with advancing years is no indication of the hebetude of the spirit, or premonitory to its final dissolution. It is only the gradual wearing out of the instrument, the intervention of which has established relations with the outer world. When a tool becomes blunted and old, the workman can no longer man- ifest his former skill ; but the skill may nevertheless remain. Though OF SLEEP. 551 the apparatus for the reception of external impressions, as well as that for voluntary action, may be failing, it implies nothing as regards the prime mover. The eye may be dim, the ear dull, and touch imperfect, the voice may be feeble, and the limbs trembling, but all this indicates nothing more than that what has been passed through so often before is about to be passed through again. The organs that have done their duty are to be cast away, but the result of their action is to remain. It may not, perhaps, fall within the proper compass of a treatise on physiology to speak of that future condition, and yet so deeply The future interesting are these subjects to all men that a single observa- state. tion may in this place be excused. The whole course of life, from its very beginning, has been one of development and concentration. We comprehend this the more perfectly as we extend our views beyond our present state, and examine what we have in succession been, and in what manner our existing condition was reached. It is not credible that that system is to be all at once abandoned, or replaced by a contradictory one. Such is not the style in which the affairs of the organic world are at any time carried on. The slowly emerging consequences of the primitive law came forth one after the other in their proper and unvarying sequence, and the law holds on inexorably forever. And since we may say that, throughout those prior states, the idea aimed at is the isolation of a con- scious intelligence, every organ being shaped and every function bent to that end, we are reasonably led to the expectation that in a future state that archetype will be completely reached. It would be strange indeed if a blank oblivion should crown such a work. CHAPTER yi. OF SLEEP AKD DEATH. Causes of the Necessity for Sleep. — Its Duration and Manner of Approach. — Manner of Awak- ing. — Cause of Niyht-sleep. — Increased Warmth required. — Connection of Sleep and Food. Of Dreams : their Origin and Phenomena. — Somnambulism. — Nightmare. Of Death. — Old Age. — Internal Causes of Decline. — Death by Accident and by Old Age. — Tlie Hippocratic Face. — Final Insensibility. 1st. of sleep. One thu'd of the life of man is spent in sleep, a condition of modified sensibility, in which the mind performs its functions in an im- perfect w^ay, and voluntary motion is nearly suspended. This ^^^^" state, occupying so large a portion of the short period of time allotted to us, is therefore well deserving of the consideration of the physiologist, 552 APPROACH OF SLEEP. and the more so since it presents, in the various phenomena of dreams, significant illustrations of the manner of action of the nervous system. All animals sleep. Many, perhaps most, dream. The necessity for a season of repose arises from the preponderance of the waste of the sys- tem over its repair during our waking hours. By bringing the animal functions into a condition of rest, an opportunity is afforded for renovar tion, and the equilibrium can be maintained. In early infancy, when it is necessary for the nutritive operations to be carried forward with the utmost vigor, and attended -with as 0&US6S 01 1X16 "TIT 11- • necessity for little waste as possible, the whole time is spent in sleeping *^^^P' and eating. The waking period is gradually increased as the child advances, but not so as to make it continuous, for the day is broken into intervals of sleep. Even at three or four years of age we sleep more Duration and than oncc a day. In mature life eight hours are on an aver- flepth of sleep, ^ge required, but the precise time varies with different indi- viduals, and even with the same individual in different constitutional states. The time is not, however, always a true measure of the amount of rest, for sleep varies very much in the degree of its completeness or intensity ; there is a slumber so disturbed that we are unrefreshed by it, and a sleep so profound that we awake weary. Old age, as it advances, admonishes us to spare the system as much as we may, for repair is con- ducted with difficulty ; and this period, characterized by its resemblance in so many respects to childhood, like it, is often marked by frequently- recurring and prolonged slumber. Moreover, various accidental and other circumstances are liable at all times to disturb its proper periodic- ity — a warm afternoon, a hearty dinner, an ill-ventilated apartment, mo- notonous sounds, the attention devoted to one object, bodily quiescence, ceasing to think, the use of narcotics, extreme cold, a horizontal posi- tion, &c. Sleep is commonly preceded by a sense of drowsiness of more or less Approach of intensity, which is gradually followed by a loss of sensibility, sleep. Objects cease to make an impression on the eyes, the lids be- come heavy and close. If we are not in the horizontal position, but re- quire muscular support, as in sitting, the head droops, and the hands seek a support. Successively the senses of smelling, hearing, and touch pass away, as the sight has done ; but, before this progress is completed, we start at any sound or disturbance, voluntary muscular action being in- stantly assumed, though in the midst of a surprise. We are nodding. If we are in the horizontal position, as in bed, the body is thrown into a form requiring the least muscular exertion — the limbs are semiflexed. As sight, smell, hearing, touch, again in succession fail, all voluntary mo- tions cease, those which are now executed being of a purely automatic kind. The eyes are turned upward and inward, the iris is contracted. IMANNER OF AWAKENING. 553 the heart and the hings act more slowly hut more powerfully ; a gentle delirium, which exists while the centres of the special senses are coming into repose, introduces us to profound and unconscious sleep. This condition of profound sleep, though it may he quickly, is yet gradually reached by passing through certain well-marked pro^'ress of stages. Once gained, we sleep with heaviness in the early night-sleep. part of the night, and more and more lightly as morning approaches. It wovild, however, be erroneous to suppose that this falling into insensi- bility and awakening are perfectly continuous events ; there are, undoubt- edly, subordinate periods of more and less complete repose, but under no circumstances are we ever aware that we are asleep. At any time of the night sleep may be abruptly broken, the mind re- suming its power after passing through a momentary interval Manner of of confusion. Toward the close of the customary time, the awakening. senses resume their power in an order inverse to that in which they lost it — the touch, the hearing, the smell, the sight. For a short period after awakening, the organs seem to be in a state of unusual acuteness, more particularly that of sight — an effect arising from the obliteration of the vestiges of old impressions. From profound sleep we pass to the wak- ing state through an intermediate condition of slumber. In the former, the movements which we may execute, under the influence of external impressions, are wholly of an automatic kind, such as turning in bed in various positions. The length of time spent in sleep and slumber re- spectively is by no means constant, many causes increasing the one at the expense of the other. On awakening, we are apt to indulge in cer- tain muscular movements — we rub our eyes, stretch, and yawn. If we are suddenly aroused, our motions are feeble and uncertain on attempt- ing to walk at once ; but if we spontaneously awake at an unusual period, and more particularly if it be toward the morning, we commonly remark a clearness of intellect or mental power. Many of our most judicious and correct conclusions occur to us under these circumstances. Though it is said that the sleep of man lasts about eight hours, there are many variations. Authentic cases are on record in which ,. ■ , .' Maximum and individuals have, for a considerable time and apparently with- minimum out injury, slept only for one hour, and others in which that *^"^ °^ ^^^' state has been prolonged for an entire week. Man shows much greater differences than other animals ; birds, for instance, sleep lightly, and cold- blooded animals generally profoundly. Since the object of sleep is to afford an opportunity for repairing the waste of the system, the length of the needful time depends on conditions that are themselves variable : the extent of the antecedent waste, and the rapidity of the repair. In winter we sleep longer and usually deeper than in summer, for the hour- ly waste in winter is greater. Habit, however, controls us very much. 554 NIGHT-SLEEP. It' has been supposed by some that it is to habit that our tendency to Cause of night- slcep at night is to be imputed. It is, however, more properly sleep. ^Q -jjg attributed to the ordinary circumstances of our life — the day being spent in muscular or mental exercise, since we can then sec to perform our duties, and this tax upon the system being necessarily followed by a feeling of weariness. Those animals which seek their food in the dark sleep by day. It is not, therefore, to any external physical condition that we should impute our nocturnal sleep, but to the interior condition of our system, though it is quite true that physical agents, such as cold, and others that have been mentioned, will provoke a sensa- tion of drowsiness. In sleep we require additional warmth, and this we obtain by instinct- Increased ively using more clothing for the purpose of economizing the warmth re- animal heat. The amount of caloric generated in the system quire in s eep. ^^ diminished through the cessation of muscular exercise, and therefore reduction of decay. The same may be said, to a certain extent, of the waste of the brain through its intellectual acts, and of the nervous system generally. This diminished amount of interstitial death corresponds with a diminished respiration, the hourly amount of oxygen consumed exhibiting a decline. The negro, who is much more sensitive than the white man to this decline of temperature, instinctively envelops his head with clothing, so that the air may be warmed by its contact therewith before it enters the respiratory organs. For the same reason, he sleeps with his head toward the fire, while the white man sleeps with his away. On similar principles we may account for the control which food has over sleep, the one seeming, to a certain degree, to replace the other. The French proverb says, "He who sleeps, dines," and this is Uniformity of true ; for during sleep the waste of the system is reduced to ed wit^h un'i-'' ^ minimum, and the necessity for food correspondingly di- formityoffood. minished. The quality of the food likewise exerts an influ- ence on the length of sleep, for that which is of a nutritious kind, and easily assimilated, can more speedily execute whatever repairs the sys- tem may demand. It is probably owing to his variable diet that, even in a state of perfect health, man is so variable a slee2:)er, and that ani- mals, the nature of whose food is so constant, sleep with so much uni- formity. By some it has been supposed that the amount of sleep required by different animals is dependent upon the size of their brain ; but if we keep in view that the object of sleep is the repair of waste, and that this is accomplished by the agency of the different mechanisms involved in organic life, we can easily see that such a statement can not be true. Its fallacy appears from common observation, apart from any physiological considerations. The brain of a turtle or of a serpent is relatively small, OF DREAMS. 555 and yet those animals sleep long and profoundly ; but if we reflect on how many ditferent conditions, external and internal, the repair of waste. depends, we shall see that the time of sleep can not have any such arbi- trary measure as that of the size of the brain. Among external causes which influence the rate of repair may be mentioned the digestibility of the food, some varieties of whicli, by reason of their chemical or physi- cal qualities, yield more slowly than others. The internal causes are very numerous: the size of the ditrestive organs in relation to the ^ ,..• r o _ o _ _ Conditions of body, and the energy with which their function is accom- the duration of plished ; the condition of development of the absorbent sys- ^ ^^^' tem, and the rapidity of its action ; the rate of the circulation of tlie blood, which hurries the nutritive supply in its course ; the amount of oxygen introduced into the system by the respiratory apparatus, which discharges, as we have elsewhere explained, the double function of re- moving the wasted products of decay, and of grouping into appropriate forms, so as to be available for their uses, the elements of nutrition that are being introduced. All these, and other conditions that might be named, determine the rate at which repair can be executed, and therefore the necessary duration of sleep. If, out of these various elements, we were to select one which would represent it, the activity of the respira- tory organs would aiford a more accurate measure than the size of the brain. As the necessary repairs are accomplished, we pass through a condi- tion of slumber, and our organs gradually awake in the manner that has been described. It is during this intermediate passage, that is, toward the morning chiefly, as the brain is resuming its functions, of dreams: that dreams occur. They may, however, happen at any other their origin. period of the night, though then they are liable to present greater in- congruities and more obvious violations of the proper order of events. It is quite correct that morning dreams are more likely to be prophetic, for they are more likely to be in themselves true. Dreams never strike us with surprise, no matter what may be the ex- traordinary scenery they present — no matter how great the violations ol' truth and reality. The dead may appear with the most astonishing clear- ness ; their voices, perhaps long forgotten, may be heard ; we may be transported to places where we have spent past years of our lives ; com- binations of the most grotesque and impossible kinds may be spread be- fore us : we accept all as reality, perhaps not even suspecting that we dream. The germs from which have originated all these strange com- binations are impressions stored up in the registering ganglia of the brain, more particularly in its optic thalami. These, as outward impressions have for the time ceased, are enabled to attract tlie attention of the mind, and emerge from their latent state. That all dreams originate in such 556 OF DEEAMS. impressions is illustrated by the history of the blind, who still dream of things that they formerly saw. Thus it is stated that Huber, after he had been blind for fifty years, still dreamed of things he had seen when a boy. But little explanation can be given of the manner in which these vestiges may be grouped — a grouping which is so frequently in vi- olation of all correctness that a dream which presents us with a logical sequence of events, and which we recognize on awakening to be natu- rally true, is sure to be an impressive one ; and yet we can not doubt that the causes which suggest dreams are often purely physical, as when, in dropsy of the chest, the dreamer fancies he is drowning, or even suf- fers under the same delusion when his hand is dipped in water ; or when a candle is carried into the room, and he awakens stricken with terror that the house is on fire ; or, on the occurrence of noise, he believes that he is in a thunder-storm, or, perhaps, on a field of battle. Hence arises an automatism which becomes most striking when the dreamer answers questions put in a whisper to him, an incident of which cases are record- ed in which individuals have revealed important events of their lives, which, when waking, they would never have divulged. Automatic actions are usually considered as occurring without sensa- tion, but this, in some instances, as in those now before us, can not be regarded as altogether true. Suggested thus by external circumstances, or arising spontaneously Deceptive ap- without any obvious cause, dreams pass before us with an pearance of air of truthfulness so imposing that we never suspect their fallacies. It may be truly said that they have a logic ot their own. Indeed, so complete is the illusion, that instances are not wanting, and many have been recorded, in which, at the moment of awakening, the sleeper has been struck with the correctness of the con- clusions to which he had arrived, and it was not until he had recovered from the delirious confusion of the moment, and reason had resumed her sway, that he perceived how incorrect they were. Thus great mathe- maticians have thought they had solved difiicult problems, poets that they had composed stanzas of force and beauty ; but these, on a mo- ment's reflection, they have discovered to be an inconsequent flow of ideas, and mere nonsense. A few exceptions undoubtedly have occur- red, as in the case of Mr. Coleridge, who affirms that, under these cir- cumstances, he composed Kublai Khan, and remembered it in part on awaking. The French mathematician, Condorcet, makes the same state- ment with respect to several of his writings. One of the most extraordinary phenomena presented in the dreaming Instantaneous State is the instantaneous manner in which a long series ot aTon"\Tahf of ^vcnts may be offered to the mind, the exciting cause being events. truly of Only a momentary duration. Some sudden noise FORGETFULNESS OF DKEAMS. 557 arouses us, and, in the act of waking, a long drama connected with that noise appears Ibefore us ; or, in like manner, we are disturbed perhaps by a flash of lightning, and with that flash occurs a dream which seems to us to occupy a space of hours or even days, so many are the incidents with which it is tilled. It has long been known that a like peculiarity has offered itself to those who have suffered by drowning, and have been subsequently restored. They have related that in their moment of su- preme agony, the whole series of events of their past life has, as it were, flowed in an instant upon them with the most appalling vividness, their good and evil works, and even the most trifling incidents presenting themselves with distinctness — a tide of memory. And doubtless it is owing to like causes that, under the influence of opium or other narcotic drugs, the relations of space and time are so totally destroyed that we seem to live through a century in a single night, or to take in our view scenery, the distances and magnitudes of which are utterly beyond the reach of mortal vision. It has been truly said that the province of dreams is one of intense exaggeration. It is so in a double sense, for with equal facility we spread out a single and perhaps in- ^, significant circumstance, so that it occupies the entire night, of one idea over or we crowd a thousand strange, though perhaps connected, ^ °"^ *"^®' representations into the twinkling of an eye. Nor is it by any means the least extraordinary part of these wonderful facts that the mind occu- pies itself in an undiverted and unbroken manner for so long a time, with an insignificant idea in the one case, and perceives, with miraculous perspicuity, the rapidly disappearing occurrences in the other ; that of a majority of dreams it retains no precise recollection, though they may have been presented with an intense energy, as we are assured from the impression of dread or melancholy, or even the physical results they have left, as when we awake and feel the heart throbbing rorgetfuiness violently and the whole frame trembling with terror, yet can °^ dreams. not, with the utmost exertion of memory, recollect what it was that we saw. The remembrance of dreams by no means, therefore, depends on the intensity of the impression that they made for the time ; doubtless the majority of them are forgotten and can never be recalled. In some instances, which almost every one can recall, we dream a second time the same dream which we failed to remember when awake, and, it is said, even occasionally dream that we are dreaming. Our mental capability for recalling the scenes that have occupied us in our sleep is therefore dependent upon something more than the depth of the impression they have made. Whether it be, as some suppose, through an inertness of the mind, an incapability or indisposition of pay- ing attention to the things thus presented to it, or whether it be thai, through accidental causes, the vestiges of impressions remaining in the 558 SOMNAMBULISM. optic thalami are brought out sometimes with more and sometimes with less force, there is every grade of intensity presented, from those floating indistinct aerial scenes, which seem scarcely to leave the slightest trace behind them, to those which, in spite of their outraging all reality, and even all probability, leave us in a horror-stricken state ; such as, for ex- ample, the celebrated dream of the Emperor Caligula, in which he thought that the sea spoke to him. Yet there can be no doubt that in all these cases, no matter how indistinct or energetic, how false or how true, how harmonious as a whole, or how contradictory and grotesque, der which the elements of which all dreams are composed are impres- .ireams arise, gj^j^g ^f things that wc havc Seen or heard, or which have been otherwise submitted to the senses, the traces of which still remain imprinted in the registering ganglia of the brain. During the day, while we are exposed to light, and sounds, and other sources of disturbance, the impressions arising therefrom totally overpower, by reason of their new- ness and intensity, these ancient residues, so that the attention of the mind, in a state of health, is never directed to them ; but when we close our eyes in the silence of night, all such external impressions are at an end, the organs of sense, sight, hearing, smell, and touch, are successive- ly benumbed, and there is nothing to prevent the mind thus separated from outer things from occupying itself with these old impressions, any one or more of which, through accidental circumstances, presents itself in vigor, and a dream is the result. The phenomena of dreams therefore illustrate, in a significant manner, the remarks that we have made respecting the functions of the cephalic ganglia of insects as magazines for the registry of impressions received by the organs of sense. No explanation of dreaming can be possibly given without admitting for a part of the human brain a like duty. The important advantages which accrue to our physiological explanations of the action of the human mind from the admission of this doctrine have already been dwelt upon. Connected with dreams, and being, indeed, a dream carried into action, Somnambu- is somnambulism, or sleep-walking, of which there are several lism. grades, from mere sleep-conversation and sleep-crying to the actual performance of difficult and even hazardous feats. The young in- fant evinces its discomforts by crying in its slumber, yet it can be com- forted without awaking by the well-known voice of its mother. Chil- dren often show a propensity to talking in their sleep, and can sometimes be brought to give a few rational replies to inquiries put to them. At their time of life, the disposition is more frequently manifested to get out of bed and move about the house, or even out into the open air under the influence of a dream. When sleep-walking occurs in the adult, it is lia- ble to be accompanied by actions of an apparently connected kind, though NIGHTMARE. 559 their object may be quite trivial, and in its attainment considerable risks may be run. In these cases it seems as if the mind was absolutely wrap- ped up in one idea, and wholly unable to comprehend any thing else. If the eyes of the somnambulist are wide open, he sees nothing, and even tliough a bright light be presented before him, the iris will not contract, yet he moves about in a manner as if he were, in one respect, guided by understanding, the air of his movements being as if he knew what he was about, yet in another respect as though he was impelled by the most unaccountable folly, walking along the roof of the house, seating himself on the chimney, and finding his way in safety over precipitous places, past which it would be impossible he should go if awake, no mat- ter how steady his head might be. Besides this complete condition of somnambulism there are intermediate forms, during which the various senses of seeing, hearing, etc., are in partial activity. There are also differences in the intensity or depth of the state, as is shown by the ease or difficulty with which the individual is aroused ; sometimes to speak to him is enough, sometimes he must be violently shaken or otherwise roughly treated. It has been observed in some cases that where the pa- tient spontaneously wakens under circumstances that affright him, he is at once broken of the habit. With dreams and somnambulism is also to be classed that sensation which often surprises and disturbs us when we are just passing Sensation into sleep, a sensation as though we were suddenly falling down °^ falling. stairs. This, with some persons, is of almost nightly occurrence. Its opposite, an inability to move, as though we were oppressed by some great weight, or spell-bound in some incomprehensible way, is nightmare. In this distressing affection there is a sense of oppression at Nightmare: the epigastrium, and a difficulty, or rather impossibility, of ^*^ causes. moving or speaking. A frightful dream, in which some alarming object is depicted with intolerable distinctness, accompanies these symptoms, the attack terminating by a struggle to shake off the object of dread, or to escape by flight, or to speak. On awaking, the sufferer finds himself trembling with terror, the respiration hurried, and the heart throbbing violently. The intellectual faculties are on different occasions in vari- ous states of activity, and sometimes the dream, and our actions conse- quent upon it, offer no violation of reason. Indeed, some individuals are affected by this trouble during -the daytime, when they are wide awake and perfectly aware of what is going on ; but, whether it occurs by night or by day, the sentiment with which it oppresses is that of unspeakable dread. Even at night we sometimes are conscious of its approach, when we are in the intermediate state between sleeping and waking. The cause of nightmare, in all its variety of forms, is disturbance of the respiratory function, which, by interfering with the arterialization of 560 OF DEATH. the blood, affects the brain. This disturbance may be brought on in many ways, as by the pressure of the stomach after a hearty supper, or in diseased conditions, such as hydrothorax ; but it is popularly supposed, where these morbid conditions are not obviously concerned, to be attrib- uted to sleeping on the back. Though this is undoubtedly true in a great many instances, it is very far from being an essential condition, for nightmare may occur in any position that the sleeper may possibly as- sume. The restraint upon the arterialization of the blood, which appears to be its essential condition, interferes with the circulation through the lungs on the principles that have been described in a preceding chapter, nor can the heart force a passage, however violently it may throb. The effect depends not so much upon the apparent rate and power with which the respiration is going on, for any embarrassment or difficulty in the in- troduction of air merely leads to snoring, which is in no manner connected with nightmare. The cause of this latter affection is to be sought for in the air-cells, which are unable to rid themselves, with their accustomed facility, of the carbonic acid and other effete products of respiration which they contain. 2d. of death. At all periods of life, the functional activity of the system occasions a ^ ,. . ^ waste of its tissues by the interstitial death of their parts, and Condition of • /• • c< i i healthy equi- therefore involves a necessity of repair. So long as the repa- hbnum. ration balances the waste, a healthy equilibrium is maintained ; but when the nutritive powers decline, as old age approaches, a gradual deterioration of the system ensues. The period of greatest activity is also that of greatest waste, and of the most active and perfect repair, interstitial death and the removal of decayed material then occurring in the most rapid manner. The energy of life is thus dependent on the amount and completeness of death. At a later period, with advancing years, although the loss of substance through functional activity may be lessened, the renewal and restoration of the portions which are necessarily consumed are far more than corre- spondingly diminished. We thus become incapacitated corporeally and mentally, and, if no accident intervenes, we die through mere old age. On several occasions we have already noticed the analogy between the Death of a ^^^^ of individuals and that of species. An analogy also may molecule, of an ^^^q traced in the circumstances and causes of their death, for gan^m"of a ' the discovcrics of geology abundantly show that thousands species. Qf gpecies in the organic series have become extinct. The death of a constituent molecule in an animal body, the death of the in- dividual animal itself, the death of the species to which it belongs, are all philosophical facts of the same kind, though presenting, perhaps, in GRADUAL DEATH. 561 their aspect a difference of interest and importance. The death of indi- viduals, as has been said, may occur in two ways, hj acci- Deathfromac- dent or by old age. But death from old age is very unusual, cident and by for even in the case of those who are very far advanced in ° ^^^" life, its close, is ordinarily brought about by some lesion or derangement of the vital organs, thus, in reality, constituting accidental death. ]\Iost men desire that their final scene may be attended with as little derangement as possible of their ordinary mental powers, and that it may be very brief. If this constitute the euthanasia, or happy death, it certainly can not be thought that extreme old age is desirable, constituting, as it does, a long-continued and dreary disease. The senses fail us in the same manner and in the same order that they do when we are falling asleep, their gradual deterioration bringing us back to the helplessness and imbecility of infancy. In the long interval dur- ing which this is going on, the aged man is not only a burden to himself, but a sad spectacle to every one around him ; his perceptions are being gradually blunted ; and though he is, as it were, by degrees passing into a final slumber, it is in that disturbed way which all have witnessed when they fall asleep after severe fatigue. The different portions of the body die in succession : the system of animal life before that of organic, and of the former the sens- „ , , , ^ ■ n -1 r- 1 • 1-11 Gradual death. ory functions fail first, voluntary motion next, while the pow- er of muscular contraction under external stimulus still feebly continues. The blood, in gradual death, first ceases to reach the extremities, its pulsa- tions becoming less and less energetic, so that, failing to gain the periph- ery, it passes but a little way fi-om the heart ; the feet and hands become cold as the circulating fluid leaves them, the decline of temperature gradu- ally invading the interior. No one has ever yet offered a more accurate picture of the appearance of the dying than that presented by Hippocrates: " If the patient Kes on his back, his arms stretched out, and his legs hanging down, it is a sign of great weakness ; when he slides down in the bed it denotes death. If, in a burning fever, he is continually feel- ing about with his hands and fingers, and moves them up before his face and eyes as if he were going to take away something before them, or on his bed-covermg as if he was picking or searching for little straws, or taking away some speck, or drawing out little flocks of wool, all this is a sign that he is delirious, and' that he will die. When his lips hang relaxed and cold, when he can not bear the light, when he sheds tears involuntarily, when, dozing, some part of the white of the eye is seen, un- less he usually sleeps in that manner, these signs prognosticate danger. When his eyes are sparkling, fierce, and fixed, he is delirious, The Hippo- or soon will be so ; when they are deadened, as it were, with '^^^^^'^ ^^'^'^• a mist spread over them, or their brightness lost, it presages death or Nn 562 THE AGONY. great weakness. When the patient has his nose sharp, his eyes sunk, his temples hollow, his ears cold and contracted, the skin of his forehead tense and dry, and the color of his face tending to a pale gi-een or leaden tint, one may give out for certain that death is veiy near, unless the strength of the patient has been exhausted all at once by long watchings, or by a looseness, or being a long time without eating." Even after death some of the organic functions continue for a time, Post-mortem more particularly secretion and the development of heat. In tio^TaD^d°*as- ^ former chapter, page 444, the capability of extraordinary sions. muscular motions has been referred to. From other inter- esting observations on those who have been instantaneously decapitated by the guillotine, it has been asserted that the body can display what has been termed post-mortem passion and resentment. It may, however, be doubted whether this is really true. Perhaps these effects are only analogous to those convulsive manifestations which may be easily pro- duced, in an intensely interesting way, by the application of voltaic bat- teries to those who have been dead for some time. Physiologists often quote the sentiment of Montaigne, "With how r ., ..,•. little anxiety do we lose the consciousness of light and of Insensibility •' , _ ° before the final ourselvcs." By this they would convey the idea that the agony. ^^^ q£ dying is as painless as the act of falling asleep, and also as little perceived. They recall the fact which seems to support this view, that those who have been recovered after apparent death from drownmg, and after sensation has been totally lost, report that they have experienced no pain ; and, indeed, when we reflect that the sensory pow- ers are the first to decline, the eye and the ear, at an early period in the article of death, failing to discharge their duty, and the general sense of touch becoming rapidly more and more obtuse, we can scarcely put any other interpretation upon the final struggles which constitute what is so significantly called the agony, than that they are purely automatic and therefore unfelt. Doubtless the mind, in this solemn moment, is some- times occupied with an instantaneous review of impressions long before made upon the brain, and which offer themselves with clearness and energy now that present circumstances are failing to excite its attention, through loss of sensorial power of the peripheral organs, this state of things having also been testified to by those who have been recovered from drowning. Life closes at last in various ways. Some pass away as though they were really falling asleep ; others with a deep sigh or groan ; others with a gasp ; and some with a convulsive struggle. DIFFERENCES IN MEN. 563 CHAPTER VII. ON THE LNTLUENCE OF PHYSICAL AGENTS ON THE ASPECT AND FORM OF IVIAN AND ON HIS INTELLECTUAL QUALITIES. Differences in Form, Habits, and Color of Men. — Ideal Type of Man. — Its Ascent and Descent, — Causes of these Variations. Doctrine of the Unity of the Human Race. — Doctrine of its Origin from many Centres. Influence of Heat on Complexion. — Cause of Climate Variations. — Influence of Heat illustrated by the cases of the Indo-Europeans, the Mongols, the American Indians, and the Africans. — Distribution of Complexion in the Tropical Races. Variations in the Skeleton. — Four Modes of examining the Skull. — Connection of the Shape of the Skidl and Manner of Life. — Physical Causes of Variation of the Skull. Influence of the Action of the Liver on Complexion. — Influence of the Action of the Liver on the Form of the Skull. — Base Foi-m of Skull arising from Low as well as High Temperatures. — Disappearance of the Red-haired and Blue-eyed Men in Europe. The Intellectual Qualities of Nations. — Synthetical Mind of the Asiatic. — Analytical Mind of the European. — Their respective Contributions to Human Civilization. — Spread of Mohammedan- ism in Africa. — Spread of Christianity in America. — Manner of the Progress of all Nations in Civilization. There are great differences in the aspect of men. The portrait of Newton is from the frontispiece of his immortal Prin- F'^'^ 266 Cipia. " Does he eat, Differences in and drink, and sleep, S™',!!".?:/ like other people?" ask- men. Sir Isaac Newton. Australian. ed the Marquis de I'Hopital, himself a great contemporary French math- 564 DIFFERENCES IN MEN. Fig. 268. ematician: " I represent him to myself as a celestial genius entirely dis- engaged from matter." And, truly, transcendent intellect shines out in every lineament of that noble countenance. What a contrast between the astronomer, of whom the human race may be justly proud, and the Australian savage whose portrait Dr. Prich- ard has furnished I This man lives in a hollow tree, which he has in part excavated by fire, and obtains a precarious support from shell-fish, or bruised ants and grass. He can make a hook of a piece of oyster, and can fasten a line to it. He is lost in filth and vermin. His life is like that of a beast ; it is concerned only with to-day. The early navi- gators accused him of cannibalism. We can not say that his features acquit him of the charge. History teaches us that a nation may pass through an ascending or descending career. It may, by long-continued mental culture, exhibit a general mental advance, and under such circumstances may produce, here and there, an intellect of the first order ; or it may go through a course of degradation until it reaches conditions inconsistent with its continued existence, and then it dies out. Man is accordingly distributed over the face of the earth in various con- ditions. Here he presents the civilization of the Euro- pean, there the abject mise- ry of the Australian. What more humiliating spectacle could be offered to us than the annexed engraving, jFig- ure 268, from M. d'Urville? Even a negro of Guinea might look down on such a specimen of human imbecil- ity and physical weakness with contempt, and refuse to recognize such a being as a man at all. What is it that has brought this man and his companion to such a pass ? Australians. Au aluiost tropical suu, a Causes of these pestilential climate, starvation, nakedness, the want of shel- differences. ter, personal fear : these have done their work on the suc- cessive generations of his miserable ancestors, who have been forced from step to step in a descending career, and here is the result. Among the causes which influence the aspect of man, there are two IDEAL TYPE OF JIAN. 565 "which are pre-eminent : heat determines his complexion ; social condi- tion the form of his Tbrain, and, therefore, that of his skull. The aspect of man in form and color oscillates between two extremes. Submitted for a due time to a high temperature, any race, . irrespectively of its original color, will become dark; or if to scent of human a low temperature, it will become fair. Under such condi- ^^S^^^^^^^on. tions as will be set forth in this chapter, it will pass to the elliptical ; un - der others, to the prognathous form of skull. No race is in a state of absolute equilibrium, or able successfully to maintain its present physi- ognomy, if the circumstances under which it lives undergo a change. It holds itself ready, with equal facility, to descend to a baser, or rise to a more elevated state, in correspondence with those circumstances. I think that this principle has not been recognized with sufficient dis- tinctness by those who have studied the natural history of man. They have occupied themselves too completely with the idea of fixity in the aspect of human families, and have treated of them as though they were perfectly and definitely distinct, or in a condition of equilibrium. They have described them as they are found in the various countries of the globe, and since these descriptions remain correct during a long time, the general inference of an invariability has gathered strength, until some writers are to be found who suppose that there have been as many sep- arate creations of man as there are races which can be distinguished from each other. We are perpetually mistaking the slow movements of Na- ture for absolute rest. We compound temporary equilibration with final equilibrium. Man can not occupy a new climate without an organic change occur- ring; in his economy, which by degrees comes to a corre- „ , c3 _ ./ ' .."... Correspondence spondence with the conditions by which it is surrounded, of climate and In this career, each individual, as a member of one genera- ^^S^^^^^ ^°^- tion, may only make a partial advance, for differentiation most commonly occurs in the early periods of embryonic life, as described at page 505 ; but, since all individual peculiarities are liable to hereditary transmission, the cumulative effect becomes strongly marked at last. So dominating is the control which physical influences exert over us, that invariability of our aspect for several generations maybe received as a proof that those influences have been stationary in kind and degree. In such a perfect manner is that aspect dependent on them that it is truly their represent- ative. If they change, it must change too. I do not, therefore, contemplate the human race as consisting of vari- eties, much less of distinct species, but rather as ofiering numberless rep- resentations of the different forms which an ideal type can be made to as- sume under exposure to different conditions. I beKeve that that i^eai type ideal type may still be recognized, even in cases that ofier, when °^ ^^^- 566 HABITS OF NATIONS. compared together, complete discordances ; and that, if such an illustra- tion be permissible, it is like a general expression in algebra, which gives rise to different results according as we assign different values to its quantities, yet in every one of those results the original expression exists. From this it therefore follows that there is a capability of metamor- phosis or transmutation from form to form ; that the human system pos- sesses no inherent resistance to change, no physiological inertia, but will pass indifferently upward and downward, toward perfection or toward degradation, as circumstances overrule, yet is it the same human system throughout. Nor is it of any consequence that the progress of these . , changes may be, as we term them, tardy, and that for their Time required & J ' _ . I for physioiog- completion a long time may be required. Jiiven a mass of ical change, inorganic matter — a rock — transferred from the equator toward the pole, or from the pole to the equator, would not change its temperature to that of the new locality at once; it would come to its destined equilibrium in a gradual way, in a time depending on its mass and conducting power. We should not impute its slow manner of yielding to any inherent principle of resistance which it possessed. The physiological metamorphosis of man is an affair of centuries. The universal recognition of the principle that such changes are possible lies at the bottom of all our attempts to elevate commmiities by ameliorating their social condition and by education. In the remarks which follow, it will therefore be understood that I re- ceive the classifications of Blumenbach and other authors as offering a convenience in description, but do not attach to them any essential sig- nificance. Though plants and animals are limited to certain localities of the earth's Habits of dif- surfacc, some species being formed in one and some in an- ferent nations, other region, the human family lives indifferently all over the surface of the globe. It occupies countries where the thermometer falls to 50° below zero, or where the temperature of the midday sun is 160°. In these different climates, the most marked differences in color, stature, conformation, and habits are exhibited, there being every shade, from a jet black to a fair white ; every stature, from the pigmy Esquimaux and Laplanders to the tall Patagonian ; every variety of facial angle, from that acute one which characterizes the ape to the classical aspect of the Greek, which is more than 90° ; every pursuit of life, hunting, fishing, the keeping of flocks, agriculture, commerce, and the arts of civilized so- ciety. To these might be added the use of every variety of food, from a wretched subsistence on worms and roots scratched out of the ground to the luxurious habits of the epicure ; every grade of locomotion, from those who never leave the hill or valley where they were born to those who are perpetually wandering all over a continent, nay, even all over EEALMS OF PLANTS AND ANIMALS. 567 tlie globe. There might, too, be added every variety of character and every degree of intellectuality. Among these differences, the variations of language are by no means the least important. It is estimated that more than three thousand dialects are spoken. Among these races- certain common traditions prevail, historical rem- iniscences handed down from one generation to another. Traditions of which convey the deeds of former great men who have either nations. distinguished themselves by their achievements in war or by their in- ventions in the peaceful arts ; traditions which have also communicated the religion or the superstition of the ancient times, and which, among people inhabiting countries remote from one another, present such an as- pect of sameness, that we must either refer them to one common and more ancient source, or regard them as arising from analogous peculiarities in the mental structure of the whole race. There can not be a doubt that in the lapse of many ages the influ- ence of external physical agents must have made a marked ^ „ „ impression upon the original characters of men. Few ques- temai agents tions have been more critically discussed than the extent to which this change of aspect by physical agents can go, many naturalists believing that the sole cause of national difference is the influence of cli- mate or temperature — an influence which is sufficient to account for all other organic peculiarities we have just specified ; for if we admit that the same original germ may develop itself into countless forms, accord- ing as it has been exposed to different physical agents, much more is it probable that the various races composing the human family, exposed as they have been to different physical circumstances, may by degrees have assumed the discordant features they present, although they have de- scended from one original stock. Here we shall have to consider the weight which should be attached to a very remarkable observation which has of late been Geographical made as respects the distribution of man. With regard to ^^^^l^ ^^^^^_ ° plants, it has long been known that they are grouped round mais,andman. certain centres, which may be regarded as their foci of origin, and one of such groups compared with another presents striking contrasts ; the veg- etation of Central Africa is wholly distinct from that of Europe, the veg- etation of Europe distinct from that of North America, and this, again, from New Holland. There are no laurinee in Central Africa, no heaths in the New World. The forests of New Holland gain their most strik- ing features from their leafless acacias and eucalypti. So, in like man- ner, there are foci of origin and circles of distribution as regards animal life. The fauna of Asia is wholly dissimilar from that of Europe, the fauna of Europe is dissimilar from that of North America, and this, again, from that of Africa and New Holland. Without specifying details, we 568 ORIGIN OF NATIONS. may recall that the hippopotamus and camelopard are natives of Africa, and are restricted to it ; the tiger is a native of India ; the armadillos and ant-eaters, of South America ; the kangaroo and ornithorhynchus, of New Holland. The earth's surface might thus be divided into regions or realms, each possessing its own special flora and fauna. And more than this, the oceans, too, might in like manner be parted off, and this not only as regards their surface, but also in strata at different depths. Now these botanical centres and circles are coincident with the zoological centres and circles, and hence there has arisen the idea that such centres have been truly points of original development, both for one and the oth- er of these natural kingdoms, and that the globe has not been filled by a process of dispersion or diffusion from one point, but co-ordinately, and, perhaps, contemporaneously from many such foci, and that we can still recognize the position of these foci by a critical study of animals and plants. As to the discussions which have of late years arisen on this question, The two hy- the reader may refer to the work of Drs. Nott and Gliddon potheses of the ^j^^ tvnes of mankind for arguments in support of a mul- origin of na- •'J^ _"='_ i j' -r\ -rt • tions. titude of centres of human origin, and to that of Dr. Prich- ard on the natural history of man for those in behalf of the unity of the race. In these works, respectively, will be found most of the facts hith- erto brought forward. In the former of these works. Professor Agassiz draws attention to the ^ , . „ circumstance that all around the Arctic circle, and therefore in Doctrine of Professor every longitude, is to be found one race offering characters that Agassiz. ^^^ strikingly homogeneous in aspect, intellect, and habits of life, represented in America by the Esquimaux, in Europe by the Laplanders, and in Asia by the Samoiedes. These live in a region of which the ^, , , , fauna and flora are likewise homogeneous. It has every where Floral, faunal, " -it pi • t and human the Same dreary expanses, covered with dwarf birches, moss- groups, gg^ ^^^ lichens ; in its waters there are the same fishes, as the salmon, and the same molluscs and echinoderms. In the air it has the same birds. Among its mammals found thus with uniformity, the white bear, the reindeer, the walrus, and the whale may be mentioned. With a special fauna thus coinciding with a special flora, there is also a special variety of man. What has here been said respecting Arctic life may be generalized. Each of the coincident floral and faunal circles has its own species of man. Thus, in the temperate zone, may be distinguished three such primary realms, each of which is distinct as regards its botany and zoology; and, in correspondence, we find that in the first, in the country of the Mongo- lians, to the east beyond the Caspian Sea, there are nations whose com- HABITS OF NATIONS. 669 plexion is yellow ; in the second, upon the shore of the Mediterranean and throughout Europe, there are others whose complexion is white ; in the third, in America, others whose complexion is red; and though these three widely-extended races touch, upon their north boundary, the homogenous Arctic inhabitants, in every respect they may be distin- guished from them. The temperature of the zone in which they live ranges from 32° to 74° ; it permits the growth of pines, nut and fniit trees, and among its animals might be mentioned the bear, the wolf, the otter, the deer, the squirrel, and the rat ; these animals, however, respect- ively exhibiting striking differences characteristic of their three focal cen- tres : the black bear belongs to North America, the brown bear to Europe, and the bear of Thibet to Asia. The European stag finds its American analogue in the wapiti, and in Asia in the musk deer. The wild ox of Lithuania differs from the North American buffalo, and this, again, from the Mongolian yak. Even among plants the same differences may be traced ; the pines of Europe are not the same as the pines of America, and thus it would appear that each of the three great organic circles be- longing to the temperate zone has a flora, a fauna, and a human species of its own. The same general result might be established for the tropical regions, and special centres assigned for Africa, Malaya, and Polynesia. In view of this distribution as connected with habits, Dr.Prichard thus expresses himself in his Natural History of Man : " Let us Habits of na- imagine, for a moment, a stranger from another planet to visit ^ions. our globe, and to contemplate and compare the manners of its inhabit- ants, and let him first witness some brilliant spectacle in one of the high- ly-civilized countries of Europe : the coronation of a monarch, the in- stallation of St. Louis on the throne of his ancestors, surrounded by an august assembly of peers, and barons, and mitred abbots, anointed from the craise of sacred oil brought by an angel to ratify the divine privilege of kings ; let the same person be carried into a hamlet in Negroland, in the hour when the sable race recreate themselves with dancing and bar- barous music ; let him then be transported to the saline plains over which bald and tawny Mongols roam, differing but little in hue from the yellow soil of their steppes, brightened by the saffron flowers of the iris and tulip ; let him be placed near the solitary den of the Bushman, where the lean and hungry savage crouches in silence like a beast of prey, watch- ing with fixed eyes the creatures which enter his pitfall, or the insects and reptiles which chance brings within his grasp ; let the traveler be carried into the midst of an Australian fo.rest, where the squalid com- panions of kangaroos may be seen crawling in procession in imitation of quadrupeds ; can it be supposed that such a person would conclude the various groups of beings whom he had surveyed to be of one nature, one 570 EESEMBLANCES OF NATIONS. tribe, or the oifspring of the same original stock ? It is much more proL- able that he would arrive at an opposite conclusion." On this it may be remarked that much would depend on the previous training of the illustrious stranger. If his mind had been imbued with a better philosophy than that which prevails in this our lower world, he might look with an equal eye on the transitory fashions before him, and penetrate to the first principles of things through the false glare of pomp or through debasement and degradation, and so arrive at a conclusion precisely the opposite of the foregoing, in the same manner as has Dr. Prichard himself. For, from such an elevated point of \dew, the plumed pageant of civ- ilized life might only appear to be a modified phase of the ceremonials of equinoctial Africa, where the inliabitants, on their festival occasions, adorn their naked bodies with leaves, and present oblations of palm oil with many genuflexions to their chiefs and enchanters. Beneath the feathers in the one case, and the leaves in the other, he might discern the same ruling idea, and detect the same human nature ; or, if his vision could reach into the past, and recall the credulous Greek worshiping be- fore the escjuisitely perfect statues of the deities of his country, beseeching them for sunshine or for rain, and then turn to the savage Amaiman, who commences his fasts by taking a vomit, and, for want of a better goddess, adores a dried cow's tail, imploring it for all earthly goods, and particu- larly to pay his debts — again the same principle would emerge, only il- lustrated by the circumstance that the savage is more thorough, more earnest in his work. In fact, wherever we look, man is the same. Stripped of exterior cov- Resemblances crings, there is in every chmate a common body and a com- among nations, ^-^q^^ mind. Are not all of us liable to th'e same diseases ? Have not all a tendency to exist the same length of time ? Is it the temperature of our body, the beat of the pulse, the respiration that we observe — are they not every where alike ? Or, turning to the manifesta- tions of the mind, is there not, among all the tribes of our race, a behef in the existence and goodness of God ? in unseen agents, intermediate between him and ourselves ? and in a future life ? Do we not all put a reliance m the efficacy of prayers ? and all, in our youth, have a dread of ghosts ? How many of us, in all parts of the world, attach a value to pilgrimages, sacrificial ofierings, fastings, and unlucky days, and in our worldly proceedings are guided by codes of law and ideas of the nature of property I Have we not all the same fears, the same delights, the same aversions, and do we not resort to the use of fire, domestic animals, and weapons ? Do we not all expect that the dififerences which surromid us here will be balanced hereafter, and that there are rewards and punish- ments ? Is there not a common interpretation of all the varied forms of LOCAL TEMPERATURES. 571 funeral ceremonies? a common sentiment of the sacredness of the tomb? Have we not always, and do we not every where set apart a sacerdotal order, who may mediate for us ? In our less advanced civilization, do we not all believe in sorceries, witches, and charms ? It signifies nothing in what particular form our mental conceptions are embodied ; it is the conception that concerns us, and not the aspect it has assumed. Thus equally do the views of the various nations demonstrate their innate be- lief of a future world — the undisturbed hunting-ground of the American Indian, the voluptuous Paradise and society of the houris of the Ara- bian, or the snow hut of the Esquimaux, in which the righteous feed on the blubber of whales. Turning our attention to the influence of temperature, it may be ob- served that the development of coloring matter in the skin de- influence of pends on the heat to which we are exposed. Generally, it on^Xe'^com- might therefore appear tbat there should be a correspondence piexion. between the complexion and the latitude of the place of our abode, the skin being darker as we approach the equator, and fairer toward the poles, because, since all the heat that we receive comes fi-om the sun, the amount which is furnished to us depends upon the obliquity of his rays, and therefore upon the latitude. But this is true only in a very general way, and many exceptions at once spontaneously suggest them- selves. I may point out some of these variations. The temperature of a place depends on tln-ee leading circumstances, its latitude, its elevation above the sea, and on meteorolog- Causes of local ical conditions. Respecting the latitude, nothing need be temperatures. added to the remarks already offered ; and as regards the influence of elevation above the sea, it is to be remembered that there is a decline of temperature as we" ascend in the atmosphere from any point of the globe, and for this reason, as has been already explained at page 473, even un- der the equator there will be an arrangement answering to climates on every high mountain, its top, if sufficiently elevated, being covered with perpetual snow. Of meteorological conditions, it may be said that they are so numerous as to render it almost impossible to give a fuR and yet brief statement of them, but as illustrations may be mentioned the prox- imity of the sea, or of great desert tracts, ocean currents, the prevailing winds ; thus, in our hemisphere, a north wind predominating lowers the mean temperature of the place, a "south wind tends to raise it ; and thus, also, the great desert of Sahara and the American Gulf Stream increase by many degrees the temperature of Europe. For such reasons, therefore, the lines of equal heat do not correspond to the parallels of latitude, but, as an inspection of a chart of them will show, deviate greatly therefrom. In treating of the influence of heat on plants, it was shown that, when 572 EELATIONS OF HEAT. we make our examination in a critical manner, the problem is not so sim- ple as appears at first sight, and that there are several different relations of the heat which must be considered. Thus the geography of plants is not wholly determined by the mean temperature of the whole year, nor by the greatest heat of the summer, nor the greatest cold of winter ; that is to say, it neither follows the isothermal, isotheral, or isochimenal lines. Moreover, the luxuriance of vegetation is not so much dependent upon the temperature or intensity of heat as it is upon the quantity. These Intensit - and ^^^^^^s apply with much forcc to the case now before us, quantity of for the change of complexion is not so much dependent upon eat compare . ^-^^ intensity of heat determined by the thermometer as it is upon the absolute annual quantity ; for, though these conditions of in- tensity and quantity of heat are essentially distinct, yet it will generally happen that they may increase or diminish together, without there being an absolute correspondence between them. There can be no doubt that the quantity of heat annually furnished in Guinea vastly exceeds the quantity annually furnished to any part of tropical America. It is upon this condition, and not upon the height of the thermometer, that the dark- ening of the human complexion depends. To the reader who is not familiar with the technicalities of Natural Philosophy, an explanatory illustration of the statement here made may be of value. If he ^Yill suppose that he examines a wine-glass of water, boiling hot, and a gallon of tepid water by a thermometer, he will find that that instrument will stand much higher in the wine-glass than in the gallon. But if he proceeds to determine how much ice the two por- tions of water will respectively melt, he will find that the greatest effect is produced by the lukewarm water. We say, therefore, that though the thermometer has indicated the intensity of the heat in the two portions of water respectively, that is to say, their temperatures, it has not indi- cated the quantity present in each, but the melting of the ice has revealed the fact that the tepid water, by reason of its larger proportion, contains a larger quantity of heat. It may be repeated, therefore, that the absolute quantity of heat an- nually furnished to any locality is by no means indicated by the maxi- mum height to which the thermometer will rise in the summer season, yet it is upon that condition, quantity, that the tint of the complexion depends. That climate does thus influence color is clearly demonstrated by the Onantit of ^^^^ ^^^^ ^ family of men, indisputably derived from a com- heat influences mon stock, have different complexions in different countries. complexion. rj^j^^ Jews of the uorth of Europe are fair men, often having red beards and blue eyes. As we trace them in their southeasterly dis- tribution, their color deepens by degrees. In their original country they INDO-EUROPEANS. 573 are tawny, still farther on they are deep brown, and in Malabar almost black. A more interesting and more general instance is offered by the race to which we belong, the Indo-European, which reaches, in one un- broken column, across Western Asia, through Europe, from Hindostan to the British Islands. That this is one homogeneous family, derived from a common stock, is proved beyond all possibility of a doubt by the affin- ities of its languages, all showing an affinity with the ancient Sanscrit, and even betraying, by their varied designations of certain objects, in an approximate manner, the time at which the progress of this column was made — that it was anterior to the introduction of the metals, in the age of stone, as some authors have designated it, when weapons and imple- ments of that material alone were employed, for the names of the metals are different in many of the different languages of this race. But how is it as regards the complexion of the Indo-European s ? To the northwest it is lia;ht, but it darkens toward the extreme Variations im- southeast in India, the distribution in this respect having indo-European been doubtless much better marked in former times, before race. it was disturbed by the influences of civilization. Thus the Homan au- thors speak of the northern Germans, of the Britons, and the Gauls, as being red-haired, blue-eyed, and very light in their complexion. It is not to be understood, however, that the tint deepens through various shades of olive and brown by a steady progress as we pass toward India, for the physical principles on which we have been dwelling would pre- pare us to expect that, whenever we reach regions more elevated above the level of the sea, the com- plexion of the natives wiU be lighter. For this reason, the inhabitants of the range of the Caucasus, and again those of the great elevations of the Him- malaya Mountains and sour- ces of the Ganges, are as light as the southern Europeans, ;ind there very frequently is seen the auburn-bearded, and blue or gray eyed man. While the complexion thus depends on the heat, the form of the skull is determined by the condition of development of the brain, and this is the more perfect where life is main- tained in circumstances of Fig. 269. Brahmin. 574 MONGOLS. plenty, indolence, luxury, ease. In Hindostan, among the natives of high caste, have from time to time arisen men v^^hose mental endowments have been in no respect inferior to those of Europeans — statesmen, poets, soldiers, astronomers, mathematicians. Complexion apart, the portrait of Kam Ruttum, a Brahmin, Fig. 269, taken by Mr. Bran white, presents an intelligent and agreeable countenance, though, perhaps, with an air of effeminacy. Let us examine a second of our subdivisions, the Mongol, character- ized as descending from a common stock by the affinities of Variations im- ° . ,.,,...,.„ pressed on the its languages, though havmg a geographical distribution from Mongol race. ^^^ Indian Ocean to the shores of the Polar Sea. As with the Indo-European race, so with this, the color becomes darker as ^he tropic is approached — so dark, indeed, that, in the lowest latitudes to which its nations reach, they may be said to be black. From this they pass through various shades of brown and oHve as a progress to the higher latitudes is made, the pale countenance reappearing in North Tar- tary, and attaining to whiteness in the fish-feeding tribes, Samoiedes, on the shores of the Icy Sea. But here, again, the complexion and the lati- tude are not in correspondence : on the low shores of China the natives are tawny, but in the mountainous regions of the northwest of that country there are tribes spoken of by those who have seen them as of surprising whiteness, and a similar circumstance occurs among the Tartar tribes of the very elevated plateaux of Central Asia. Although the Chinese countenance, both of the indigenous race and the dominant Tartars, is very characteris- tic, as seen in the annexed portrait. Fig. 270, from Dr. Prichard, the form of the skull expresses a high intellec- tual culture, of which also their civil- ization and their polity are a surpris- _ ing proof. The difficulties of govern- Fig 2T0 ing masses of men concentrated in a narrow space seem, by the statesmen of that nation, to have been in a great measure overcome. On the Chinese rivers there are many great cities, vast- ly outnumbering in their population the largest European capitals. Under the government of the emperor, it is said that there live, in security and repose, one third of the human race! Such a spectacle may impress even the philosopher with sentiments of respect and admiration. The hardships of life have left their impression on the form of the skull of the North Asiatic, whose energies have to be directed to the support of AMERICAN INDIANS. 575 Firi. -27 1. Kamtschatdale. animal existence. The portrait of a Kamtschatdale, J^ig. 271, selected by Dr. Prichard as an example, shows the projecting muzzle, that invariable index of want, and true animal feature. The complexion is nevertheless in coiTespondence with the low temperature of the country. A like examination of a third of the subdivisions Variations im- ofmen,theAmeri-P'-t°„°lL'' can, equally well il- dian race. lustrates the influence of heat. These, though popularly spoken of as red, and often regarded as presenting the same color from the North Polar Sea to Terra del Fuego, are very far from offering such a uniform- ity. The Esquimaux on the north, and the Fuegians on the south, are light, the tint of the native races deepening, to a certain degree, as the equator is approached — a gradual deepening, much better marked in South than in North America, and on the Pacific than on the Atlantic Fig.2r2. slope. As examples of the North American Indians, we may take the portraits, by Mr. Catlin, of Black Hawk, Fig. 272, and Tuch- ee,Fig. 273, page 576; the former a Sac, the latter a Cherokee. It is sufficient to compare the counte- nances of these Indians with those of California, as figured in the Voyage Pit- toresque of Choris, Fig. 21 A, page 576, to realize how erroneous is the preva- lent statement that all the American tribes, both of the north and south conti- tinent, are alike. The ol- ive-black Indians of the Pacific slope, though their lips are thick and their noses flat, have lank and not woolly hair. Fig. 275, page 576. On the Atlantic shore, as is well known, the temperature, in passing to lower 576 AMERICAN INDIANS. latitudes, does not so rapidly vary ; and on the Pacific the mean heat is much higher than on the Atlantic American Indian. for the same parallel of latitude. California Indian. Fig. 275. California Indians In South America, the so-called red race, as we have just ohserved, is deeper in complexion as we pass from Terra del Fuego and Patagonia northward toward the line. The Chilians are darker than the Fuegians, and the Peruvians darker than the Chilians. As the topographical con- struction of that continent would lead us to infer, there is an analogous distribution from west to east, crossing the preceding at right angles ; the Inca race, who inhabit the plateaux of the Andes, are lighter than AFEICANS. 577 corresponds to the latitude ; Ibut from tliis point, passing to the east, the Brazilio-Giiarani are darker as we approach the Atlantic Ocean. It may with tmth be said that the intervention of the Gulf of Mexico and Ca- ribbean Sea has lightened the complexion of the aboriginal tribes of North and South America. In the last place, we may consider, in like manner, the African races. These are, as we should expect from the high temperature y • .• of that continent, all dark, yet not equally so, for the Berbers pressed on the toward the Mediterranean shore, and the Hottentots and Kaf- ^^^^^ ^^'^^^^ firs adjacent to the Cape of Good Hope, are of a lighter hue. In this class we ought also to enumerate, as an example of no common interest, the native Egyptians, who are, perhaps, the lightest of all. It does not appear that there has been any marked change in the complexion of the aboriginal Egyptian for the last three thousand years, so far as can be judged from a comparison of the descriptions and paintings which have descended to our times, with the existing Copts. Leaving the Mediter- ranean shore, and advancing to the south, we pass through bands of pop- ulation sensibly becoming darker, save where a disturbance arises by rea- son of the elevation of the mountain ranges. On the north of the equa- tor the negro land is not reached until we are within 10° lati- The negro tude. The true negro occupies a zone crossing through the con- ^°'^®- tment west and east. If our examination be made meridionally, in the manner just supposed, but along the Red Sea coast, the complexion of the inhabitants is observed to darken through Upper Egypt and in Abys- synia. Of this country it is interesting to remark that it still retains the Christian faith as delivered to it in the remotest times of the Church. The portrait of an Abyssinian, ^^o- 2tt. Fig. 276, from M. d'Abbadie, shows Fig. 2T6. Abyssinian. Native of Madagascar an admixture of the Arab lineaments, though there is no reason to suppose Oo 578 AFEICANS. that this is due to the admixture of Arab blood. Of the two classes of Abyssinians, those who inhabit the more southerly parts have a coun- tenance much more approaching to the negro. They are, indeed, an in- trusive race, who conquered in more recent times the regions in which they are settled. It is said that the Amharic, the language of the true Abyssinians, is singularly analogous to the Hebrew. As resembling the Abyssinians in many respects, though on the op- posite side of the equator, may be mentioned the natives of Madagascar, Fig. 277, p. 577. Presenting, in some particulars, the traces of Arab in- fluence, it has nevertheless been inferred, partly from their language and partly from their features, that the most numerous class is of Malay ori- gin. Though among the inferior tribes there are some which are black, the complexion of this is olive, and the hair is not woolly, though it curls. It should be constantly borne in mind that the resemblance of features Evidences from is no proof of a Community of origin. The influence of cli- simiianty of m^te and of manner of life is so srreat that in a due period countenance _ _ _ o ... and language, of time the most diverse tribes will show similar lineaments. Analogy in the structure of languages and identity in vocabulary is much better evidence, though even this must be received with caution. In reference to this, it has been very significantly remarked that birds of the same kind sing the same notes in all countries, even though under such circumstances as to exclude the possibility of their having been taught by their parents. The annexed figure, 278, is given by Dr. Prichard as a specimen of the natives of Mo- zambique. The expression is undoubtedly much superior to that prevailing on the West African coast. Of some of these tribes it is said that the Native of Mozambique. hair is Hot wooUy, but merely frizzled. It grows long, and hangs in slender curls. Examining the zone designated as negro land, we find that the negro Amelioration character of its inhabitants is not in all parts developed with f tto^t£° equal intensity. The maximum is shown in the Guinea east. countries, and fi-om thence across the continent to the east the physiognomy improves. The negro characteristics may be specified as intense blackness of the skin, woolly hair, thick lips, gaping nostrils, Fig. 2T8. THE NEGRO. 579 Fij. 270. Negro of C Fnu '2S0, and a prognathous skull. But the negro aspect is not limited to the African con- tinent ; it is prolonged or projected through the Indian into the Pacific Ocean, north and south of the equator, in a zone of many degrees. Sumatra, Borneo, Celebes, New Guinea, and part of Australia, lie in this zone. In these various countries, one or another of the characteristics we have men- tioned predominate, in part through the in- 1 lence of climate, and in part througli ad- ixture of blood. In some of these people ■< I e hair is not woolly ; in some, the lips e thin, and the nose projecting ; in some, .he form of the skull indicates a great su- periority over the West African tribes. But, whatever these modifica- tions may be, the black races of the Pacific present in their general ap- pearance so predominating a negro as- pect that they have by all travelers been classed with that tribe. Of one of these nations, Dampier, the early navigator, speaks as " shock, curl-pa- ted, New Guinea negroes." The por- trait, i^%. 280, from Choris's Voyage Pittoresque, of a girl of the island of Luzon, one of the Philippines, may il- lustrate this remark ; for, though the form of the head shows a very great advance upon that of the Guinea ne- gro, the facial angle, respecting which ^ more will shortly be said, being much K- larger, and the relative size of the brain therefore increased, the counte- nance is essentially that of tropical Africa. The projection of the African type into the Pacific is crossed at a cer- tain point by a like projection of the dark Asiatic type, and y^riations im- in the region of this intersection or commingling we find the pressed on the , , , T . ^1 . , Pacific race. most degraded specimens ot humanity. From these regions, as we pass eastwardly toward the American con- tinent, the improvement becomes very striking; thus the ^jneiioration of natives of the Society Islands, though living within the the Pelagian tropic, are of a clear olive or brunette. In the opinion of ^^^ ° Philippine negro. 580 COMPAEISON OF THE SKELETON. some, if it were not for a slight thickness of the lips and spreading of the nostrils, the countenance would be European. The men are de- scribed as "tall, strong, well-limbed, and finely shaped." Many of the children have flaxen hair ; and sailors, who are generally competent judges of such matters, universally yield a tribute of admiration to the prettiness of the women. Captain Bligh attributed the mutiny in his ship to that interesting cause. We may next consider variations in the form of the skeleton. Here, more particularly in the classification of the forms of skulls, I Comparison adopt the division introduced by Dr. Prichard, from whose of skeletons, "work, above alluded to, the following passages are extracted : " In all other races, compared with Em'opeans, the limbs are more crooked and badly formed. In the negro the bones of the leg are bent outward. Soemmering and Lawrence have observed that the tibia and fibula in the negro are more convex in front than in Eu- ropeans ; the calves of the legs are very high, so as to encroach upon the hams ; the feet and hands, but particularly the former, are flat ; the os calcis, instead of being arched, is continued nearly in a straight line with the other bones of the foot, which is remarkably broad." "It was observed by White, and has been generally believed, that the lensfth of the forearm is so much greater in the negro than The arm. • . ^ . . ® in the European as to constitute a real approximation to the character of the ape. Facts, however, prove but a very slight difference, and by no means greater than the varieties which are every day to be observed on comparing many individuals of any race or nation. On the other hand, the difference between adult apes and men in the length of the extremities is so great as to render all such comparisons very remote, and of very doubtful importance with respect to any ulterior conclusion. According to Mr. Owen, the arms of the orang reach to the heel, or at least to the ankle-joint, while in the chimpanzee, or troglodyte, they ex- tend below the knee-joint. This is a most decided and widely-marked dif- ference between the most anthropoid apes and the uncultivated races of men. Yet even the slightest approach to the former shape would be a curious circumstance ; if it could be fully established, it would tend, with other facts, to imply that the savage races of mankind have somewhat more of the animal, even in their physical conformation, than the more cultivated races, or those whose improvement by civilization may be dated from a very remote era in the history of the world." "It has been a general opinion, since the time of Soemmering, that the head of the negro is placed so much farther backward on magnum of the the vertebral column as to occasion a material difference in ^^''^' the figure of the whole body. It was observed by Dauben- ton that the foramen magnum is placed in quadrupeds behind the centre FOUR METHODS OF EXAMINING THE SKULL. 581 of gravity, Avlience an important difference arises in the relative position of the head and trunk in man and in inferior animals. The extent of this difference, when the human skeleton is compared with that of the simian has been most fully made known by Mr. Owen, who has shown that it is much greater in respect to the adult ape than it has hitherto been supposed. But there is, in reality, no difference in human races. The foramen magnum is only posterior in the negro skull to its place in the European, in consequence of the projection of the upper jaw, par- ticularly of the alveolar process." In illustration of the statement of Mr. Owen respecting the relative Fi(j. 2S1. length of the arm in man and in the more anthropoid apes, I give the annexed photograph, J^ig. 281, of the human skeleton and those of the chimpanzee and orang. Of the chim- panzee it should be ob- served that the specimen Avas young. They are all brought nearly to the same size by adjusting the dis- tances at which they were taken. The human skele- Skeleton of man, chimpanzee, and Srang. tOU WaS that of a man more than six feet in height. There are four different views from which an examination ^ l^oiir modes ot of the skull of man and animals may be made : 1st. The lat- examining the eral ; 2d. The vertical ; 3d. The basilar ; 4th. The front. '^"^^• 1st. The lateral view, or Camper's method, is thus described by the anatomist who introduced it, and whose name it bears. " The basis on which a distinction of nations is founded may be dis- played by two straight lines, one of which is to be drawn m, j , , through the meatus auditorius to the base of the nose, and view, or Cam- the other touching the prominent centre of the forehead, and ^^^ ^ ^^^ ° * falling thence on the most advancing part of the upper jaw-bone, the head being viewed in profile. In the angle produced by these two lines may be said to consist not only the distinctions between the skulls of the several species of animals, but also those which are found to exist between different nations ; and it might be concluded that Nature has availed herself, at the same time, of this angle to mark out the diversi- ties of the animal kingdom, and to establish a sort of scale from the in- ferior tribes up to the most beautiful forms which are found in the human 582 THE LATERAL VIEW, OR CAJMPER's IMETIlOD. species. Thus it will be found that the heads of birds display the small- est angle, and that it always becomes of greater extent in proportion as the animal approaches more nearly the human figure. Thus there is one species of the ape tribe in which the head has a facial angle of forty- two degrees ; in another, of the same family, which is one of those simia? most approximating in figure to mankind, the facial angle contains ex- actly fifty degrees. Next to this is the head of the African negro, which, as well as that of the Kalmuck, forms an angle of seventy degrees, while the angle discovered in the heads of Europeans contains eighty degrees. On this difference of ten degrees in the facial angle the superior beauty of the European depends ; while that character of sublime beauty, which is so striking in some works of ancient statuary, as in the head of Apollo and in the Medusa of Sisocles, is given by an angle which amounts to one hundred degrees." As illustrations of this view, the subjoined profiles of the skull of the European, Fig. 282, the negro, Fig. 283, the chimpanzee. Fig. 284, and Fig. 2S2. Fig. 283. European. Negro. the orang, Fig. 285, are given. Of the latter, which, of apes, are among Fig. 284. Fig. 285. Chimpanzee. those most closely approaching to man, the chimpanzee is a native of tropical Africa, and the orang of the Indian Archipelago. 2d. The vertical view, or Blumenbach's method Orang. THE VERTICAL VIEW, OR BLUMENBACH S METHOD. 583 " Blumenbach gives the following account of the way of describing heads, which, he says, is the result of his own observations The vertical in a long and constant study of his collections of the skulls menbach'^^"" of different nations : He remarks that the comparison of the method, breadth of the head, particularly of the vertex, points out the principal and most strongly-marked differences in the general configuration of the cranium. He adds that the whole cranium is susceptible of so many va- rieties in its form, the parts which contribute more or less to determine the national character displaying such different proportions and direc- tions, that it is impossible to subject all these diversities to the measure- ment of any lines or angles. In comparing and arranging skulls accord- ing to the varieties in their shape, it is preferable to survey them in that method which presents at one view the greatest number of characteristic peculiarities. ' The best way of obtaining this end is to place a series of skulls with the cheek-bones on the same horizontal line, resting on the lower jaws, and then, viewing them from behind, and fixing the eye on the vertex of each, to mark all the varieties in the shape of parts that contribute most to the national character, whether they consist in the di- rection of the maxillary and malar bones, in the breadth or narrowness of the oval figure presented by the vertex, or in the flattened or vaulted form of the frontal bone.' " By this means of comparison Blumenbach obtains a division of skulls into three classes, the Caucasian, Mongol, and Negro. They are repre- sented in Fig. 286, Fig. 287, Fig. 288, and Dr. Prichard has added to these figures Fig. 289, the artificially elongated skull of an ancient Pe- ruvian, from the burial-places of Titicaca. Fig- 286. Fig. 28T. „ . Mongol. Caucasian. ° 3. The basilar view, or Owen's method. " No single view of the skull determines so much in regard to its gen- eral configuration as that of the basis. The importance of ,j,, , ., this manner of examining the bony structure of the head view, or Owen's has been demonstrated in the fullest manner by Mr. Owen, "^^* ° " 584 THE BASIL AK, OR OWEN kS METHOD. Fiiy. '2«S. Pig. 280. Negro. in his excellent memoir on the struc- iiucacan. ture of the orang and chimpanzee. The relative proportions and extent, and the peculiarities of formation of the different parts of the cranium, are more fully discovered hj this mode of comparison, which has hitherto been much neglected, than by any other method." Fig. 290. Skull of orang. Human skull. " It may be observed, in this view of the cranium, that the antero- posterior diameter of the basis of the skull is in the orang very much larger than in man. The most striking circumstance which displays this difference is the situation occupied by the zygomatic arch in the plane of 'the basis of the skull. In all races of men, and even in human idiots, the entire zygoma is included in the anterior half of the basis cra- nii ; in the head of the adult troglodyte, or chimpanzee, as well as in that of the satyr, or orang, the zygoma is situated in the middle region of the skull, and in the basis occupies just one third part of the entire length of its diameter. Posterior to the zygomata, the petrous portions have, in the simise, a larger development in the antero-posterior direction. THE FRONT VIEW, OR PRICHARD S METHOD. 585 Another most remarkable character, in respect to which those anatomists have been greatly deceived who compared only young troglodytes with man, is the great occipital foramen, a feature most important as to the general character of structure and to the habits of the whole being. This foramen, in the human head, is very near the middle of the basis of the sladl, or, rather, it is situated immediately behind the middle transverse diameter, while in the adult chimpanzee it is placed in the middle of the posterior third of the basis cranii. A third characteristic in the ape is the greater size and development of the bony palate, in con- sequence of which the teeth are much larger and more spread, and want that continuity which is, generally speaking, a characteristic of man; and intervals between the laniary, cutting, and bicuspid teeth admit, as in the lower tribes of animals, the apices of teeth belonging to the opposite jaws. Fourthly, the basis of the skull is flat, owing to the want of that downward development of the brain, and of the bony case connected with the greater dimension which the cerebral organ acquires in the human being compared with the lower tribes." 4. The front view, or Prichard's method. "Neither the facial angle of Camper, nor the method of viewing the skull proposed by Blumenbach, affords a satisfactory display xhe front view of the characteristics of the pyramidal or lozenge-faced skull." or Prichard's ^^\nFig. 292, which is the drawing of the skull of an method. Pig_ 292. Esquimaux, the lines drawn from the zygomatic arch, touching the temples, meeting over the forehead, form with the basis a triangular figure. These two lines in well -formed European heads are parallel, the forehead being very much broader than in the heads of Esquimaux, and other races whose skulls belong to the same great division of human crania, among whom are the Mono-olians, and other nomadic nations of Northern Asia. The most striking characteristic of these skulls is the great Esquimaux. lateral or outward projection of the zyg- omatic arch. The cheek-bones, rising from under the middle of the or- bit, do not project forward and downward under the eyes, as in the prog- nathous skull of the negro, but take a direction laterally or outward, and turn backward to meet a corresponding projection of the process of the temporal bone, and form with it a large, rounded sweep or segment of a circle. The orbits are large and deep. The upper part of the face being remarkably plane or flat, the nose flat, and the nasal bones, as well as the 586 CLASSIFICATION OF SKULLS. space between the eyebrows, nearlj on the same plane with the cheek- bones, the triangular space described by the lines (drawn on the wood- cut) may be compared to one of the faces of a pyramid. The whole face, instead of an oval form, as in most Europeans and many Africans, is of a lozenge shape." " Another characteristic in most of the pyramidal skulls, or, rather, in the form of the face to which this configuration of the skull gives rise, is the apparently angular position of the aperture of the eyelids. There is no want of parallelism in the orbits, or, rather, of coincidence in the transverse sections of the orbital cavities. The obliquity consists in the structure of the lids themselves ; the skin, being tightly drawn over the large protuberance of the malar bone, under the outer angle of the eye, and at the inner extremity smoothly extended over the lower nasal bones, while the bridge of the nose is scarcely elevated above the plane of the suborbital spaces, gives to the eye the appearance of being placed with the inner angle downward." " The oval or elliptical form is that of Europeans, and the southern Asiatics who resemble them ; the zygomatic bones and the jaws being- less protuberant, the entire outline of the head, viewed from above, has no projecting angular parts, and is defined by an oval circumference. But in that oval figure, or rather ellipse, the two diameters vary considera- bly in proportion ; in other words, some nations have rounder, others more elongated heads. The shape of the brain, and of the skull at its basis, is in the rounder heads more like that of the pyramidal skull, or the cranium of the northern Asiatics ; in the narrower heads it approaches the figure of the elongated, or negro head." We may therefore conveniently classify skulls in three divisions : 1st. The prognathous, which is represented in Fig. 293, being the Classification skuU of a negro of very forbidding aspect. This form is of skulls. marked by a forward projection of the jaws, the brain being therefore, as it were, thrown backward as respects the face, the forehead being more horizontal and low. 2d. The pyramidal. Fig. 292, which gives rise, as has been stated above, to the lozenge-shaped face. 3d. The elliptical or oval, which, viewed from above, has an oval con- tour without projecting parts, and in the profile shows a large facial an- gle, as in the French skull, Fig. 294. These forms of skull seem to be connected very closely with habits Connection of of life : the prognatlious with the savage state, or that of the skuiTand ^"^'^^i^g ? "t^e pyramidal with a wandering pastoral life ; and manner of life, the elliptical with that of civilization. With respect to the form of the pelvis in different nations, the varia- tions are by no means so significant as in the case of the cranium, inas- EFFECTS OF WANT AND DEGllADATION. Fig. 293. Fi(j. 294 587 French. The pelvis. much as tliey are of indiscriminate oc- currence. It may perhaps be maintained in a general way, that in the less advanced tribes, as in the female Hottentot, there is an approximation to the form exhibited by the simia3, the iliac bones being more vertical, and the whole structure characterized by its length and narrowness. Professor Weber, who has examined this sub- ject with care, concludes that no particular figure of the pelvis is a char- acteristic of any one race. The remarks which have been made respecting variations of complex- ion, as exhibited in different climates, might almost be re- The physical peated as respects variations of the form of the skull, origi- aticfn In thT" nating in difference of physical circumstances ; for as the skull. complexion varies in different temperatures, so does the figure of the skull in different social conditions. The elliptical skull, which beyond all doubt is that which belongs to man in his most civilized state, may be deteriorated and degraded even to the lowest prognathous form. Want and squalid misery will produce this result. Igno- its degradation ranee, mere animal life, social degradation, lead to its ap- ^y ^^^^t. proach in varied degTces. Even in the large European cities we recog- nize the incipient stages of it in those classes who follow a precarious life — the projecting jaw, the retreating forehead, the mouth habitually open, or the lips parted so as to show the teeth. Mr. Thackrah, in his work on the Effects of Arts, Trades, etc., on Health and Longevity, says, " I stood in Oxford Road, Manchester, and observed the stream of oper- atives as they left the mills at twelve o'clock. The children were almost universally ill-looking, small, sickly, barefoot, and ill-clad. Many ap- jjeared to be no older than seven. The men, generally from sixteen to twenty-four, and none aged, were almost as pallid and thin as the chil- dren. The women were the most respectable in appearance, but I saw no fresh, fine-looking individuals among them. Here I saw, or thought I saw, a degenerate race — human beings stunted, enfeebled, depraved." Under the opposite circumstances, where life is maintained in indolence 588 PEOGNATHOUS AND ELLIPTICAL SKULLS. and plenty, the converse effects may take place. Of this, perhaps the Its rectification Kiost Striking illustration is that pointed out by Dr. Prichard by luxury. q{ ^hc loss of the pyramidal form of skull by the European Turks, a form which appertained to their Asiatic ancestors, and the as- sumption of the elliptical, the skull not of a wandering, but of a station- ary and civilized race. JSTor has this transmutation taken place in them, in the short period since they made their European conquest, because of the influence exercised by the Circassian and Georgian women intro- duced into their harems, for this has been upon too small a scale to pro- duce such a general result, and is a luxury which can only be indulged in by the wealthier classes. As a descent is made to the skull of the prognathous form, the coun- Contrast be- tenancc loscs those features which we regard as being beau- nathous Imdel- ^^f^l, and assumes a baser cast. When it has reached the liptical skulls, limit in that direction, it is actually hideous, recalling at once the detestable aspect of the ape. In this state, in the tropical cli- mates, the lips are thick, the hair woolly, the nostrils gaping. The in- tellectual powers are correspondingly depressed ; the dullness of the eye, its porcelain-like sclerotic contrasting with the blackness of the skin, is in correspondence with the low and degraded mental power. On the contrary, when the passage is made toward the elliptical form, the coun- tenance becomes more beautiful and interesting, capable of expressing the most refined mental emotions. The eyes, in an indescribable but sig- nificant manner, manifest the exalted powers of the mind, and the lips are composed or compressed. If I am not mistaken, darkness of the skin and a prognathous form of Mode in which skull may be dependent in the dark tribes on the same cir- dark^compiex- ciimstance. Functionally the liver is in connection with the ion. calorifacient apparatus, its secretion, the bile, as shown in Chapter XI., coinciding in habitudes with a hydrocarbon. Much of it is therefore reabsorbed, and eventually devoted for the support of a high temperature. But, besides this combustible material, the bile likewise contains a coloring matter, which is in all respects an effete body, and useless to the system. This pigment is derived firom the blood-discs, or, rather, from their heematin, as is proved by the fact that it occurs in the meconium of the new-born infant, and likewise, like htematin, it is rich in iron. Its source is, therefore, not immediately from the food. To remove this useless material is thus one of the primary functions of the liver. Now there is no organ which is more quickly disturbed in its duty by Influence of the a high temperature than the liver. Whether such a high Uveron^th^^ temperature produces its effect through a disturbance of the complexion. action of the lungs, or through an impression on the skin, is ORIGIN OF COLOR. 589 quite immaterial. If the organ be in any manner enfeebled in its duty, and no other avenue is open through which the degenerating ha^matin may escape, it must accumulate in the circulation, and be deposited here and there in suitable places. Under such circumstances, there arises a tendency for its accumulation in a temporary manner in the lower and more spherical cells of the cuticle, from which it is removed by their gradual exuviation and destruction as they become superficial. The temporary deposit of the coloring matter in this situation imparts to the skin a shade more or less deep. It may amount to a perfect blackness ; for the origin of the black pigment of the negro is the same as The color of the that of the black pigment of the eye in all races, and the pre- ^^in derived -.. ^ . . 1 • 1 -I from the hse.- dommatmg percentage oi iron it presents plainly betrays matin of the that it arises from a degenerating hsematin, in which the ^^°°'^- same metal abounds. I believe, therefore, that the coloration of the skin, whatever the par- ticular tint may be, tawny-yellow, olive-red, or black, is connected with the manner in which the liver is discharging its function. That de- posits of black pigment can normally arise in the way of a true secretion by cell action is satisfactorily proved by their occurrence in angular and ramified patches in the skin of such animals as the frog ; and that has- matin, in its degeneration, may give rise to many different tints, is sub- stantiated by the colors exhibited by ecchymoses. It is not to be forgotten that coloration of the skin, though apparently persistent, is tending continually to a removal, because of Constantre- the oxidation which is taking place as the pigment cells ap- ™°Jifof°th proach the surface of the cuticle in their process of desquama- skin. tion ; but as this goes on, new cells and new pigment are perpetually forming beneath, to undergo destruction in their turn. Under this point of view, the complexion of the skin is an index of the energy with which that tissue is addressing itself for the removal of metamorphosing hse- matin. In accomplishing this removal, the liver, in the fair races of man- kind, exerts a sufficient activity ; but in hot climates, the habitation of the black races, either through a diminished power of that gland, or be- cause of an increased production of effete pigment, the skin has to lend its aid, and the degree to which it does this is betrayed by the depth of its hue. Having thus traced the coloration of the skin to existing peculiarities of hepatic action, I may repeat the remark already made, Influence of the that it is not improbable that, in the most degraded negro er orthe form'^f type, the prognathous form of the skull may be attributed the skull. to the same cause. Not that this alone is always the cause, for a prognathous skull can by degrees arise, as we have seen, in any race, even the white, from a 590 EFFECT OP TEMPERATURE ON THE SKULL. variety of causes, such as misery, want, or an oppressed social state. It is, however, on all hands admitted that nothing so quickly disturbs the brain in its action as functional disturbance of the liver. If, through a partial failure in the operation of that great gland, the products which it should normally secrete begin to accumulate in the blood, or have to seek new channels for their escape, the vigor of the intellect is at once impaired. It is with the brain as it is with any other organ, a decline in its activity is soon followed by a deterioration or diminution of its structure, and we must not forget that it is not the brain which accom- modates itself to the capacity of the skull, but the skull which accommo- dates itself to the shape and size of the brain. Whatever the causes may be, and of course they are very numerous, which tend tot lessen the en- tire cerebral mass, or by inequality in their effect produce the develop- ment of one part with the contemporaneous diminution of another, they will inevitably give rise to a modification in the figure of the skull ; and observation, as well as phrenological considerations, would cause us to anticipate that, if the effect takes place in such a way as to involve the higher powers of intellection, the skull, answering in its change thereto, will assume the prognathous cast. From what I have said respecting the relationship of different nations TT ^-j of men, it will be gathered that the peculiarities on which we transmission have been dwelling, the complexion and form of the skull, as varia ions, (^^gpgj^fjg jj|; upon hepatic action, are capable of hereditary trans- mission ; for such a modified glandular action, in whatever manner it may have been occasioned, can be propagated in that way. In these remarks it will be perceived that I have mainly had in view Base form of that degradation from the more perfect standard of man which skull arising • encountered in hot climates, and which finds its expression from low tem- _ ' ^ perature. in a blackness of the skin and a base form of the skull. But there is likewise a white degraded form. It is that which we meet in the highest latitudes, and it is therefore dependent upon climate, that is to say, temperature. Here no such tax is thrown upon the skin as is the case in the torrid zone, but here the intellectual powers are greatly enfeebled, if for no other reason, at least because of the hardships under which life must be maintained. It is not, therefore, in very high or very low latitudes that we should expect to find man in his ^est estate, and this is corroborated by the history of all races. It is true that, by the artificial control which we have obtained over temperature by the aid of clothing and improved modes of shelter, we have, in some degree, with- drawn ourselves from the absolute dominion of climate ; but, putting these disturbances of civilization aside, and looking only to our natural state, we shall be constrained to admit that the man of maximum intel- lectual capacity is of a faint brown hue. Nor was it through any acci- DISAPPEAEANCE OF THE FAIR RACES. 591 dental circumstance, but because of physiological conditions, ]\raximum of that civilization arose in Egypt and in the Mesopotamian "/,i!'J^'?ntbro'\va countries. It was for a like physiological reason that it races. spread next through the nations on the north shore of the Mediterranean, and never spontaneously originated in Arctic Europe or Tropical Africa. Moreover, it must be observed how forcibly the doctrine here urged of the passage of man from one complexion to another, and Disappearance through successively different forms of skull in the course of of thered-hair- 7 .,, 1 T 1 • 1 • 1 • 1 ^'^^ f^"'^ blue- ages, is illustrated by the singular circumstance to which at- eyed people in tention has of late years been directed, of the gradual disap- Europe. pearance of the red-haired and blue-eyed men from Europe. Less than two thousand years ago, the Roman authors bear their concurrent testi- mony to the fact that the inhabitants of Britain, Gaul, and a large portion of Germany were of that kind. But no one would accept such a descrip- tion as correct in our times. By some writers, who have not taken en- larged physiological views, this curious circumstance has been attempted to be explained on the hypothesis of a more prolific power of the brown or black haired and darker man. That this is correct not a shadow of evidence can be offered. The supplanting of the red by the black haired man is neither on account of any insidious or involuntary extermination, nor because of the numerical pressure alluded to. The true ^^^^^^^ ^^ ^^^^ reason is that the red-haired man has himself been slowly apparent dis- changing to get into correspondence with the conditions that ^pp®^^^"*^^- have been introduced through the gradual spread of civilization — condi- tions of a purely physical kind, and with which the darker man was more nearly in unison; for though it might be shown that the climate of Europe, by reason of the removal of forests, and other causes, chiefly agri- cultural in their nature, has undergone a change, this is nothing compared with the changes that have been accomplished in domestic economy by better clothing, and more comfortable lodging and food, and these are par- allel to actual changes in climate. What a contrast between the starved, naked, and almost houseless peasant-savages of the times of Caesar, and the well-fed, well-clothed, and well-housed agricultural laborers or manu- facturing operatives of ours, who, though they may be living in the same geographical region, are literally in a warmer and more genial climate — a climate with which man is only in correspondence when his skin is of a darker shade, and his hair of a brown or black color ! From these investigations of the anatomical peculiarities of the nations of men, we ; may turn to those of a mental kind, which, in- of th ' 1 11 deed, are derivatives thereof. Doubtless the intellectual uai qualities of qualities are manifested in the expression of the countenance °^*^°"^- and in the capacity of the form of the skull. Considering, for the sake of convenience, groups of nations as they 592 MENTAL QUALITIES OF THE EUEOPEAN AND ASIATIC. are distributed geographically, though, as we have seen, this is a divis- ion which has no philosophical foundation, we may proceed to an exam- ination of the psychical state of the European and Asiatic, whose history furnishes us abundant materials for this purpose. The black nations of Africa and the red tribes of America, from the imperfect advances they have made toward civilization, can supply but few facts for such an in- vestigation. We can not read the histories of Europe and Asia — we can not exam- g thetical ^^^ ^^^^ present condition of those continents, without coming miuciof the to the conclusion that the people inhabiting them possess a lyticai mind of distinct mental constitution. After what has been said re- the European, gpecting the influence of physical circumstances on the or- ganization of man, it is unnecessary for us to inquire here in what that distinction has originated. It is, perhaps, most significantly expressed if we say that the mind of the Asiatic is essentially synthetic, that of the European analytic. The former is the creator of systems of theology, law, science, some of which have endured for thousands of years, and have been adopted by a large portion of the human race. The latter pursues his course in a way less grand, but which, since it has a better ascertained foundation, leads to more certain, and, in the course of cen- turies, will show more powerful, widespread, and equally lasting results. The intellectual peculiarity of the Asiatic has been attended with the ad- vantage of producing an almost definite social state. In Asia the cus- toms remain invariable ; every thing is in a state, as we might term it, of stagnation, or, as they consider it, of repose. On the other hand, the analytical tendency of the European has led to the intellectual and polit- ical anarchy of our times, when fundamental doctrines of every kind are called in question, and scarce two men can be found whose views on re- ligious, political, and social questions coincide. In Asia there are no questions, but only affirmations. Europe, except when the Church for a thousand years enforced the Asiatic system, has ever been prone to ask questions. Since the fourteenth century, when she returned to this pro- pensity, she has been passing through a chaos of doubt in the innumer- able answers she receives. With an intellect of this analytical kind, it may be doubtful whether Necessity of the European could ever have spontaneously entered on the the Asiatic to career of civilization. The contact of the Asiatic was essen- European civ- i • i i iiization. tial to him, as giving hmi the material on which to work. Nor was it of importance whether the basis from which he thus started, and the additions which, from time to time, he has received, were trae or false ; they furnished him with the essential condition that was wanting. The dissector must have his subject. The history of Europe, whether as regards philosophical, religious, or political affairs, bears the impress INFLUENCE OF EUROPE AND ASIA ON AFRICA. 593 of the analytical mind of the white man. In Asia, on all these points they tend to tlie homogeneous. In Europe, every day makes us more and more heterogeneous. Thus compared with that of the Asiatic, it can not be denied that the mind of the European is of the higher order. Moreover, though Comparison our moral qualities are not equal to our intellectual, the man- and^Em-o ^e'^i ner in which we act in the conditions in which we are placed intellect, asserts our superiority even in that regard. The instances are many in Avhich we do not dare to carry our convictions into execution, and each of these illustrates the inequality here set forth. To be content with the chances of things, to suffer the events of life uncomplainingly, is surely not so worthy a character as to demand a reason, and to accept the con- sequences of resistance. The intellectual superiority of the European over the Asiatic is strik- ingly illustrated by their relative power over the African, who rru • o J J ^ r ' Their respect is confessedly, in this respect, beneath them both. To go no ive influence farther back than the last ten centuries, both have, in their special way, exerted their influence. Here and there, on the outskirts of that great continent, the European has made a faint, but, at the best, only a transitory impression : the Asiatic has pervaded it through and through. Of the promising churches, which, in the early days of Chris- tianity, fringed the northern coast, scarce any vestige now remains ; the faith of Arabia has not only supplanted them, but is spreading even to- ward the Cape of Good Hope, and this, as it would appear, spontaneous- ly. On the other hand, the European, with that universal charity which is his noblest attribute, has spared no exertions and no expense to dif- fuse the blessings which have been conferred by Providence upon him ; and yet it would seem to be in vain, though enforced by the great exam- ple of his civilization and power. In this we see the affinity of the mind of Africa with that of Asia, of which it is an exaggeration, and its incon- gruity with that of Europe. It can not, in its present state^ appreciate our manner of thinking ; it can not embrace our conceptions of truth, but delivers itself unresistingly to the dogmas of the East, with all their er- rors of faith and all their imperfections of polity. Since I have been drawn into a psychical comparison of the Asiatic and European in the foregoing particulars, it may not be p^gj^j^jj ^f amiss to consider the two races in another important respect, women in Asia the condition of their females. In the barbarous state, the ^" ^" ^-urope. woman is the slave of the man ; the Mohammedan makes her his toy, the European his companion. The avarice of the former for beauty is re- placed in the latter by an avarice for wealth. The treasures of the one are placed in a harem ; those of the other are perhaps invested in the public stocks. Pp 594 POLYGAMY AND MONOGAMY. The natural position of the female sex in this respect is indicated at once hy the relation of numbers. In Europe, for every 106 male births there are 100 female, and as the sex of offspring is influenced bj the relative ages of the parents, the older parent giving a tendency to its own sex, we may reasonably suppose that in the infants born of polygamy the males will preponderate, reversing the result which is observed in the great cities of Western Europe, in which the ratio of female births rises above its true mean by nearly four per cent, when those births are ille- gitimate. In that term of the market, four per cent., what a volume of information is here conveyed ! It tells us that the European female does not fall at once ; that there intervene years of resistance to temptation, a struggle of virtue against penury and distress, but it also reveals the precocious wickedness of man I Considering, therefore, the near equality of male and female births, we may truly assert that monogamy is the proper condition of our species, and that, apart from its social evils and criminality, polygamy is an un- natural state. I shall pass, as unworthy of notice, the assertion of those who, in this Christian country, practice so shameful a vice, that we might as well divide the number of square acres on the face of the globe by the number of its inhabitants, and declare it to be immoral in any one to possess a larger estate than corresponds to the quotient thereof. Ac- knowledging the natui-al depravity of the human heart, I accept with humiliation the rebuke that the most enlightened communities exhibit in these respects a deplorable spectacle, and that the vices of the Mo- hammedan harems find their full countei'poise in the general, the awful, and, in many places, the legalized prostitution of Christian cities. Europe has adopted as the fundamental basis of its religious system -p,- „ the grand Asiatic truth of the unity of God, but in its family lygamy and systcm it has rejected the immemorial and widespread Asi- monogamy. ^^^^ practice of polygamy. That circumstance has made it what it is. The monogamous habit has tended to draw the family tie more firmly, and has led to the accumulation and transmission of wealth from generation to generation in the same house. With this has arisen a liability to concentration of power in castes, and the use of surnames which have perpetuated family interests and family pride. In Europe the career of improvement is in the society ; in Asia it is in the individ- ual ; the unknown, starving, illiterate, but strong-willed soldier of to-day is the Pasha, the Caliph, the Emperor to-morrow. The castes of India The respective form but a trifling exception to the fact that, in the midst of progress of ^ universal despotism, the primest democratic element is Asia and Lu- . rope. concealed, for the career is open to talent. Through this, Asia has asserted her superiority again and again. Europe has never produced a great lawgiver ; Asia has produced many. Generations of ASIATIC CONTRIBUTIONS TO CIVILIZATION. 595 three hundred millions of men have followed the maxims of Confucius for two thousand years, three hundred millions are the followers of Moham- med. The faiths which govern the daily life of two thirds of the human race may well be an awful spectacle to us — the more awful because we know that they are a delusion. The only approach to these great results in the Western Continent is in the supremacy of the Italian Church ; but Rome owed the origin of her system to Asiatic missionaries ; nor was it the completed work of the hand of one man, it was the offspring of cen- turies, the joint issue of a long line of illustrious sacerdotal kings. In military life the highest qualities shine forth. If the talent for command and the capacity of a statesman are to be measured by the grandeur of un- dertakings and their success, it still remains for Europe to produce a sol- dier the equal of Genghis Khan, and a king like Tamerlane. These great captains held almost all Asia in their iron grasp. The opinions we com- -monly hold respecting these illustrious men have come to us through perverted channels. Such prodigious successes as theirs imply the high- est intellectual powers. Their true character appears when we compare them with their European contemporaries. At the same time that Charles VII. of France was mystifying his people with the imposture of Joan of Arc, and Henry VI. of England was engaged in the burning of necromancers who had attempted his life by melting an enchanted wax image before the fire, Ulug Beg, the grandson of Tamerlane, was de- termining with precision the latitude of Samarcand, his capital, with a mural quadrant of 180 feet radius, and making a catalogue of the stars from his own observations, which more than 200 years subsequently was printed at the University of Oxford. If the European wishes to know how much he owes to the Asiatic, he has only to cast a glance at an hour of his daily life. The Contributions clock which summons him from his bed in the mornins; was f ^^ Asiatic t5 to P^uropean ■the invention of the East, as were also clepsydras and sun- civilization, dials. The prayer for his daily bread which he has said from his in- fancy first rose from the side of a Syrian mountain. The linens and cottons with which he clothes himself, though they may be very fine, are inferior to those which have been made time immemorial in the looms of India. The silk was stolen by some missionaries, for his benefit, from China. He could buy better steel than that with which he shaves him- self in the old city of Damascus, where it was first invented. The cof- fee he expects at breakfast was first grown by the Arabians, and the na- tives of Upper India prepared the sugar with which he sweetens it. A schoolboy can tell the meaning of the Sanscrit words sacchara canda. If his tastes are light, and he prefers tea, the virtues of that excellent leaf were first pointed out by the industrious Chinese. They also taught him how to make and use the cup and saucer in which to serve 596 ASIATIC COXTRIBUTIONS TO ART AND SCIENCE. it. His breakfast-tray was lacquered in Japan. There is a tradition that leavened bread was first made of the waters of the Ganges. The egg he is breaking was laid by a fowl whose ancestors were domesticated by the IMalaccans, unless she may have been, though that will not alter the case, a modern Shanghai. If there are preserves and fruits on his board, let him remember with thankfulness that Persia first gave him the cherry, the peach, the plum. If in any of those delicate preparations he detects the flavor of alcohol, let it remind him that that substance was first distilled by the Arabians, who have set him the praiseworthy exam- ple, which it will be for his benefit to follow, of abstaining from its use. When he talks about coffee and alcohol, he is using Arabic words. A thousand years before it had occurred to him to enact laws of restriction on the use of intoxicating drinks, the Prophet of ]\Iecca had accomplish- ed the same object, and, what is more to the purpose, has compelled, to this day, all Asia and Africa to obey it. We gratify our taste for per- sonal ornament in the way the Orientals have taught us, with pearls, ru- bies, sapphires, diamonds. Of public amusements it is the same: the most magnificent fireworks are still to be seen in India and China ; and as regards the pastimes of private life, Europe has produced no invention Asiatic contri- '"'hich can rival the game of chess. We have no hydraulic butions in art. constructions as great as the Chinese canal — no fortifications as extensive as the Chinese wall ; we have no artesian wells that can at all approach in depth some of theirs ; we have not yet resorted to the practice of obtaining coal-gas from the interior of the earth : they have borings for that purpose more than 3000 feet deep. Similar observations may be made if we examine the Asiatic contribu- ... . tions to science. While the learned of Europe were forbid- Asiatic contri- . inir- butions in sci- ding, as a heresy, the doctnne of the globular figure of the *^°^^' earth, the Caliph Al Maimon was measuring the length of a degree along the shore of the Pied Sea. He and his successors repeat- edly determined the obliquity of the ecliptic. A Saracen constructed the first table of sines, another explained the nature of twilight, and showed the importance of allowing for atmospheric refraction in astronomical ob- servations. Algebra itself was invented and brought into Europe by the Mohammedans, who gave it the name it bears. The same may be said of chemistry. It is needless to pursue these statements, for whoever will take the trouble to look into the history of any branch of science existing in the seventeenth century will find how deep are its obligations to Asia. I shall therefore add but one fact more, the invention of the figures of arithmetic, which in reality gave birth to that science, and laid knowl- edge and commerce equally under obligations. From its simplicity, beauty, and universality, this invention alone is enough to command the gratitude of the human race. The manner of using the cif»her and SPEEAD OF MOHAMMEDANISM IN AFRICA. 597 placing the figures is one of the happiest suggestions of the genius of man. I shall not set in contrast with these statements a catalogue of the contributions of the European. We know our own doings well enough ; but such facts as the preceding may serve to remind us that the Euro- pean is no more justified in ignoring the obligations he is under to the Asiatic than the Asiatic is justified in regarding him as a barbarian. In the advance of our common humanity, both have taken and still are taking their share. The European has brought to the new continent he discovered his religion, his laws, his literature, his science, and it may be a profitable subject of reflection to him that under them the Indian is dy- ing away. The Asiatic has likewise carried the Koran into „^ ^ ^ ", . , . The spread of Afi'ica. Our prejudices and education ought not to conceal Mohammedan- from us that there must surely be some adaptedness, even ^^^iii^^ca. if it be in a sensual respect, between its doctrines and the ideas of many climates, many nations, many colors. The light of the Arabian crescent shines on all countries from the Gulf of Guinea to the Chinese wall. In those pestilential and sun-burnt forests under the equinoctial line, cit- ies are springing up with their ten, their twenty, their fifty thousand in- habitants. That implies subordination, law, civilization. It may be that this is not a course of events which would have been chosen by the French on the north, with their military colonies ; the English on the south, with their commercial establishments ; the Americans on the west, with their political institutions ; but it is the course of Providence. Let us be thankful if the African is rescued from the abyss of barbarism, and brought to a knowledge of our higher morality and holier religion, as brought he will be at last, even though it be by the hand of the Prophet. In the following chapter I shall have some remarks to make respect- ing" the manner in which the civilization of Europe was ac- r, o _ -"^ _ Prospective complished, and shall offer reasons for supposing that its es- civilization of sential condition was a physiological change in the inhabit- "^** ants. Without troubling the reader with details, I may here incident- ally observe that the spread of Mohammedanism in Africa is altogether owing to its having been introduced in the right direction. It appears to me hopeless to attempt the amelioration of that continent from its west- em shore. Whatever is done must be done from the East. In power of intellect, and in a disposition to appreciate our civilization, the inhab- itants of the countries hordering on the Red Sea are not to be compared with those on the Atlantic. It does not seem well to begin with those who are the least prepared. We do not commonly expect success from operations conducted at an eccentric point. The Koran has spread be- cause it has availed itself of the great lines of trade, which reach from the Red Sea to the interior of the continent ; it has spread, not because 698 SPREAD OF CHRISTIANITY IN AMERICA. of its doctrinal theology or theoretical politics, but because it is concern- ed in the amendment of the social condition of the people. That is pre- cisely the principle which accomplished the civilization of Europe ; and, with regard to the capacity of those nations to receive Christianity, we may, even to our shame, recall the circumstance that the Abyssinians arc yet a Christian people, still retaining the ancient faith delivered to them in the apostolic ages, when our forefathers were pagan barbarians. Sur- rounded by the most depressing and antagonizing influences, they have held fast to their faith for nearly eighteen centuries. The hoary Abys- sinian Church carries us back beyond the Council of Chalcedon and the disputes of the Eutychians ; its literature is full of the questions which exercised the faithful in the primitive times of the brethren at Jerusalem — circumcision, things strangled, meats prohibited by the law of Moses ; and yet, to the discredit of the European and American, it must be said that this Church, full of incidents of the most singular and touching in- terest, has scarcely had (with one exception) any sympathy extended to it by other Christian people. From these considerations of the effects of Asiatic civilization upon Spread of Africa, we may profitably turn to a brief statement of that of SeTwo^Amer" Europe upon the red races of America. This result in the icas. two continents, north and south, is, that in the latter, out of almost 1,700,000 aborigines, nearly 1,600,000 have embraced Christian- ity, less than 100,000 remaining in the savage state. No such favorable impression has been made upon the aborigines of the northern continent, who, as is well known, are steadily diminishing in numbers, and many tribes that were once numerous have disappeared. This has taken place notwithstanding the care which has been manifested by the government of the United States for all those who are within its territories. It does not appear that the conclusion which has been drawn by some eminent authors in view of these facts can be maintained, that " this considera- tion, if we can separate it from the events of the Spanish conquest, for which it is to be hoped that the soldiers, and not the ministers of relig- ion, are responsible, must be allowed to reflect honor on the Roman Cath- olic Church, and cast a deep shade on the history of Protestantism." That this conclusion is incorrect is shown at once by the very tables that are relied on for its support. Out of the 100,000 aborigines of South America who remain heathen, more than 66,000, that is to say, two thirds, belong to the Araucanian and Patagonian branches, who are the counterparts for that continent of the Indians of the United States and British American territories in this. Upon these it may be truly said that no impression whatever has been made. Of the Patagonian branch, estimated at more than 32,000, only 100 individuals are stated to have embraced Christianity, and of the Araucanian branch, consisting EFFECT OF CLIMATE ON CIVILIZATION. 599 ot' 34,000, not one. It is by bringing into these discussions the singu- lar and widespread error that all the aboriginal American tribes are alike, and by not making due allowance for their habits of life, their physical and mental endowments, that this mistake has arisen ; but whoever will consider the facts as they actually stand must come to the conclusion that there are just as well-marked differences among these people as there are in the climates and circumstances in which they live. Intellectually, there is even a greater difference between the Indian of the United States and the Indian of Peru than there is in their physical aspect. The one is an intractable savage, the other docile and easily led ; the one has never yet been enslaved, the other prospers and in- creases in number, though he has sustained all the consequences of the atrocities of the Spanish Conquest. By chance, or perhaps, as we should more truly say, through Providence, the field of Catholic labor has been among the more docile races, that of Protestant among the more untam- able, and the result is exactly such as, under those circumstances, the philosopher would be led to expect. I can not here avoid recalling to the attention of the reader what I have said respecting the comparative progress of Christianity and Mohammed- anism in Africa, for we find upon our own continent a repetition of the facts which were presented to us there. The chances, if such a term can, on this occasion, with propriety be used, of the diffusion of Christian civ- ilization, are directly proportional to the existing intellectual development of the community among whom the attempt is made. Mohammedanism has diffused itself in Africa for precisely the same reason that Catholi- cism has succeeded in America — because its operation was commenced upon those tribes best prepared to receive it. We can not have a more striking instance of the effect of climate on civilization than that which is offered by the American In- illustration of dians. As is well known, though throughout all those lati- cHmalronciv- tudes in which life is maintained with difficulty, by reason iiization. of their inclemency, all the tribes, both of the north and south continent, were in a barbarous state, yet in those more pleasant countries toward the equator, in which, by reason of the natural fertility of the soil and a higher mean temperature, the inhabitants had little occasion to work, and passed their lives in comparative plenty and ease, a special civilization had arisen. It is of no little interest to observe how the main features of Asiatic and European civilization were presented in this case, doubt- less without any communication with those continents, for it shows how the human mind is ever prone to unfold itself in the same way, to give birth to the same ideas and to the same inventions. The ^. .,. ,. Civilization of civilized Americans of Mexico and Peru were organized in the tropical in- coramunities not unlike those with which the white man is ^^^^' 600 EXTINCTION OF THE INDIANS. elsewhere familiar, living in cities whicli were regulated by municipal laws familiar enough to us, maintaining among their social institutions, fixed ideas respecting property and family rights, having a national relig- ion, an established priesthood, and the means of recording events, which, though imperfect, were not unlike those which obtained in the earlier pe- riods of our own civilization. If they had not a knowledge of iron and the plow, they had already fallen upon the early Asiatic plan of subju- gating and domesticating such animals as were suitable for their pur- poses. Civilization arose among these people in similar localities and under similar circumstances of life as it had arisen among our ancestors in the Old World, and, such is the sameness of constitution of the human mind, was advancing in exactly the same way. Although, for a time, among the degenerate descendants of the Span- Gradual ex- iards, the South American Indian may maintain himself, but tinction of the little doubt can be entertained that the same destiny awaits temperate him which has befallen his North American brother. He zone. jjgjj j^Qt withstand that enterprise and activity which are leading to the extension of the white invaders of his native soil. Even though the age of cruelty to these unfortunates has passed away, never more to return, and enlightened governments, animated by sentiments into which no mercenary consideration enters, interest themselves in their welfare, it is not to be supposed that nations depending on such an arti- ficial support can long continue to exist. In this inevitable decline, the tropical races may far more worthily excite our commiseration than those of the higher latitudes ; nor is their departure unavenged : they leave behind them two curses, tobacco and syphilis. In conclusion of this partial examination of the progress of the human Manner of family under varied circumstances, we may remark a repeti- progress of all ^^ £ jj|^ scrics of changes to those which have been nations m civ- o iiization. traced in the psychical career of the individual, and this, whether we consider the progress in theology, policy, philosophy, or any other respect. It is a continued passage from the general to the special — from the homogeneous to the heterogeneous. The history of any of the ancient nations might be brought forward as an example. Emerging from the barbarous state, they shake off their Fetichism, that union of the supernatural with the natural, which gives to every wood, every tree, every river, its presiding genius ; to families, their Penates ; to the city, and even to the road, their Lares ; to stars, and to stones, and to med- icines, their spirits ; to the night, its apparitions and fairies. It is in vain that we say these are the subjects of African credulity. They are found in the origin of all people. Our forefathers once cherished the il- lusions which still occupy the negro mind. The time came when intel- lectual development outgrew such base superstitions, and for a crowd of PROGRESS OF CIVILIZATION. 601 imagiiiaiy inanities were substituted the chosen forms of Polytheism. It is true that, among Egyptians, Hindoos, or Greeks, there were deities enough, but the process of specialization may be nevertheless plainly dis- cerned. The Fetich stage, the Polytheistic stage, are necessarily in- cluded in the onward progress to a pure metaphysical Monotheistic con- ception. In this it is to be remarked that the Asiatic races Their religious of men have led the way, both in the priority and strictness persuasions. of their views. The great statesmen of China, of India, of Arabia, and of Judea, centuries ago, seized upon this as the pivot of their intellectu- al and even political systems. To the last country, Europe itself, as history proves, is indebted for this noble idea. European Monotheism is not indigenous, but imported from the He- brews, an Asiatic race. The intellectual condition of the nations among whom it was introduced was but little advanced, and hence among some it came to be degraded — mixed up with the remains of popular and an- thropomorphic conceptions, which otherwise were gradually dying out. For a length of time the pagan creeds maintained a conflict with it, and with difficulty it disentangled itself from the base features which they endeavored to impress upon it, as with the Hebrews themselves of old, the people seemed to be reluctant to surrender altogether their Polythe- istic ideas. These remarks are to be understood as not applying to individuals, for in every age and nation great men have arisen, whose views on these and other subjects of like vital importance were far in advance of their times. In their best days, both in Greece and Rome, there were men who had attained to the standard here alluded to, but then* teachino- was without eftect on the popular mass. There was a want of equivalency between the individual attainment and the race attainment. Though individuals may be progressive, races are essentially conservative ; and hence there will constantly arise against individual attempts at an ad- vance discountenance and resistance, an opposition which in too many instances becomes a tyranny. Masses of men are not like inorganic mass- es, which resist a change by their inertia alone. The biography of ev- ery great reformer shows that the popular mind resents any disturbance of its repose. Resistance has to be overcome in the moving of things, resentment is added in the moving of men. To the philanthropist it is a most delightful spectacle that the various nations, in spite of the diiference of their interests, their Existence of a creeds, and their politics, can yet present certain great prin- raiTt™°v^ith dis ciples which they recognize in common, and this is becom- cordant creeds, ing more and more marked with the onward advance of the world. In the course of events, the special is ever coming out of the general, and the great principles of a common morality are gradually disentangling and 602 SOCIAL MECHANICS. unfolding themselves from contradictory forms of faith. The Chinese, the Hindoo, or the Turk, though they may not coincide with the Amer- ican or European as to what is to be looked upon as true, will yet agree as to what is just. The sentiment of honor, the ideas of personal integ- rity, are fast becoming universal. Yet even in these later ages, there is in this respect nothing new. The tendency of the human mind, whether individual or collective, to the same direction is continually manifest — a premarked and predestined course in which it must go. Our most refined notions of rectitude contain noth- ing more than is to be found in the little epitome of the ancient lawgiv- er ; for if we strike from the ten commandments whatever is explanatory or threatening, retaining the mandatory parts alone, there remains what commends itself to the understanding of the intelligent men even of the most diverse nations — the acknowledgment of the unity of God, the ven- eration due to him, the expediency of a day of rest for the laborer, the duty of filial affection, the enormity of murder, the sin of adultery, the crime of stealing, the shame of lying, and a strict regard for the property of another : these are things which exact for themselves a spontaneous and universal assent. CHAPTER Vin. SOCIAL MECHANICS. Comparative Sociology. — Connection of Structure and Habit. — Connection of History and Phys- iology. — Insect Society. — Descartes' s Doctrine that Insects are Automata. — Necessity of a Mechanism of Registry for Instinct, Reason, and Civilization. Nature of Man. — Influence of surrounding Circumstances on him. — Definiteness of his Career. Geneeal Facts of Eijropean History. — Introduction of Egyptian Civilization into Europe. — ■ The Registry of Facts by Writing. — Egyptian Philosophy in the Greek Schools. — The Persian Empire : its Influence. — Analytical Quality of the European Mind. — Influence of the Greek Schools on modern Philosophy. • Origin of European Commerce. — Discovery of the Straits of Gibraltar. — Macedonian Campaign. — Reconstruction of Monarchy in Egypt. The Roman Empire : its centralizing and civilizing Power. — Fall of European Paganism. — In- fluence of the Christian Church. — The Sabbath Day. — 77*6 Reformation. Influence of Mohammedanism on Eiirope. — The Arab physical Science. — Hie Crusades. — Dis- covery of America by the Spaniards. — Fall of the Spanish Power. Later Mental Changes in Europe. — Disappearance of Credulity. — Physiological Change of Eu- ropeans. — Effect of Mohammedanism in changing the Centre of Intellect of Europe. — Analyt- ical Tendency of the European Mind. — Advantages resulting therefrom. Having described man as an individual, we have next to consider him Dene d f ^'^ ^^^ social relations ; for so closely are his actions connect- soeiai career on ed with his organization, that it may be said that universal rue ure. history is only a chapter of physiology. It is acknowledged, COMPARATIVE SOCIOLOGY. 603 even by those who have given but a superficial attention to the subject, that there is a connection between corporeal development and historical career ; that those races who have led the way in the course of civiliza- tion, and those who still remain in the savage state, are characterized by striking anatomical peculiarities, particularly in the size and development of their cerebral hemispheres. Such general conclusions are strengthened by our observations on the animal series, the lower members of which offer together a sameness of structure and an identity in their course of life. In those the metamorphoses of which have been stud- ^^ , a •T Structure and ied, it is always noticed that every change of structure is at habit in the once followed by a change of habit, yet, during the continuance ^^^'^ ° '"^^^ '"'■ of a given condition, their manner of life is without any variation. The actions of one insect are for the most part the actions of another of the same kind and in the same state, whether larva, pupa, or imago. But in the midst of all this automatism there are, however, the glimmerings of a free will. The animal world presents forcible illustrations on every hand on the connection of structure and habit. Philosophical views of human sociology are only to be attained by treating that great problem in the same manner that we have Comparative learned to treat so many others in physiology. We must in- sociology. elude in our discussion all other animal races, and not close our eyes to the fact that there is such a thing as compar^ttive sociology. We ob- serve the republican propensities of the ant, the monarchical life of bees, the solitary habit of other tribes. Is it not, at least in part, because of cerebral peculiarities that one kind of bird is polygamous, and another observes an annual or perpetual monogamy ; that the buffalo delights in the society of his kind, but the lion will tolerate no neighbor ; that the horse runs in herds, and adopts an organized system, submitting to a cap- tain whose motions he follows ? We can not suppose that these habits are the sole result of a present and immediately active external influence which calls them forth ; an internal influence is also at work, an internal influence dependent on organization. A discussion of the problem of human sociology could, therefore, only be completed after a study of the same problem in the entire animal se- ries — a task requiring varied and profound knowledge of natural his- tory and comparative anatomy. Indeed, the present state of these sci- ences does not enable us to accomplish it. The remarks I am about to make are, therefore, of a very imperfect kind. The social problems pre- sented to us by animals are a fitting introduction to the social problems of man. For the clearer understanding of what follows, it may Distinction be- therefore be observed that w^e may receive the term instinct tween instinct as indicating a faculty incapable of improvement, and possess- ^° "ason. 604 COMPARATIVE SOCIOLOGY. ed by eacli individual exhibiting it spontaneously, without experience or imitation. The suggestions of instinct are often instantaneous and always unvarying ; those of reason involve deliberation, and into them the element of time enters. They also involve error. Animals which, for a thousand years, nay, indeed, through all time, have never invented, never improved, never varied, all of the same kind being equally skill- ful, are to be considered as actuated by instinct, not by reason. Those of which it may be said that they perceive, remember, think, compare, and then form a judgment, are to be considered as possessing reason, and this the more as they the more perfectly accomplish that end. In this respect, man is approached by the quadrumana, the elephant, the dog, but the immense interval which separates him from them is at once in- dicated by the fact that they appreciate only good and evil, so far as in- volved in pleasure and pain ; but he contemplates equally the good, the beautiful, and the true. The historian may perhaps view with resentment an attempt on the „ part of phvsioloeists to accomplish the annexation of the ter- Connection of -l J- " o ^'^ history and ritory in which he labors. With difficulty will he be brought physioiogj-. ^^ admit the dogma that the history of men and of nations is only a chapter of physiology. He doubtless will smile at the absurd- ities of a doctrine which places under a common point of view the doings of caterpillars, ants, and wasps, with the high resolves of senates and emperors — which undertakes to consider how, out of the most obscure, the most augnist may proceed. But it is none the less trae that there exists a comparative sociology, as well as a comparative anatomy and a comparative physiology. Struc- ture, function, and career are all inseparably connected. When we were considering, in a former chapter, the nervous mechan- ism of insects, we saw how that, from the purely automatic, the volun- tary is gradually produced by the development on the ventral cord of an apparatus for the registry of impressions, the cephalic ganglia. These registered impressions are the cause of the most surprising psychical re- sults. The action of barbarian communities is as purely automatic as the ac- Barbarismand ^ion of an inscct, which never had, or from which there have civilization. "been removed, the registering ganglia. Irritate the decap- itated wasp, it will sting. The uninjured wasp has a choice of action ; it may possibly fly away. The action of civilized communities is of a far higher kind : they are guided in what they do by experience. In the progress of civilization there have arisen the means of permanently re- cording past events. Such records influence us in deciding how we shall act. They constitute knowledge. If we may compare small things with great, is there not an analogy INSECT SOCIETY. 605 between tlie manner in which the registering mechanism of Analog}- be- an insect or other animal is evolved, and the manner in t^^^^" individ- which the means of perpetuating and disseminating a knowl- mentandsociai edge of events has arisen in human society ? The one, it is <=areer. true, appertains to individual life ; but is there an j fact more clearly made manifest by physiology than that of the parallelism of race life and individual life, no matter how lowly that individual life may be ? An insect presents us with surprising actions, because it possesses within itself the means of registering the events which occur in its little circle. Nations act wisely and well, according as they are guided by their store of experience. If our pride can be so far overcome as to admit that in the history of the life, even of an insect, the progress of mankind is shadowed forth, that is to say, universal history is seen in a microscopic manner, it will not be too much to hope that we shall then entertain physical or mechan- ical ideas of the social career, that society advances in a definite way, has its laws of equilibrium and movement, its centre of intelligence, its centre of power, in short its statics and dynamics. Though it is only one out of many instances that might be presented, let us briefly consider social life in the inferior tribe to which reference has been made ; let us also look at some of the individual peculiarities of insects. Our sentiments of exclusiveness and pride may be corrected thereby. Insects form societies for mutual assistance, defense, invasion, emigra- tion, mere pleasure — societies which undoubtedly arise in - . p, . 1 1 1 f /-^i^ 1 Insect society. the experience oi passions, such as love and tear. (Jr these the duration is variable ; some last through the larva state only, some are confined to the imago, some are maintained through life. The organiza- tion by which their object is accomplished is various, m'onarchical, re- publican. The caterpillars of the processionary moths are guided in their march by a leader ; the termites obey at once a king and a queen. The lust of power is not alone felt among human monarchs ; the queen bee never rests till she has assassinated her rival. All insects of the same kind are not bom equal, nor do all pursue the same occupation ; some follow a life of leisure, some devote themselves to the profession of arms, some are laborers. When the metropolis of the termites is attack- ed, the laborers, as non-combatants, retire, but the soldiers come out. The ants, with which we are more familiar, engage in military and filli- bustering expeditions ; they make reconnoissances, set sentinels, march in a definite order, the van alternately falling to the rear ; their lines of com- munication are maintained, and, if necessary, swift couriers are dispatch- ed for re-enforcements. If successful, they not only carry off the ene- mies' stores, but reduce the vanquished to actual servitude, compelling 606 HABITS OF INSECTS. them to work as slaves. They have notions of property, and, though some of them practice cannibalism, they will amuse themselves in more pleasant occupations, tumbling and playing together like kittens or pup- Habits of pi^s- With a sentiment of strict justice, the wasp who has re- insects, turned from a successful foray divides his booty among the males, females, and the laborers who have been working in the vespiary ; nor is the sentinel, who is doing duty at the door, forgotten. If, through the chances of war or by accident, any one has sustained a grave injury, in some tribes the most devoted sympathy is shown : the ant will carry his wounded friend out of the hot of the fight ; in other tribes a more than Roman firmness is displayed : the sufferer is put out of pain by his companion. Expecting an attack, some insects will shut their doors at night, and barricade them within, or, if the danger is continual, will build masked gateways in succession, with interior walls that command them. They are no contemptible engineers. They can construct and maintain roads of great length, with paths branching from them, which, if neces- sary, they keep mown. They cross streams by throwing themselves into floating bridges, and the damage done to their premises by an in- vader they show the most singular skill and alacrity in repairing. How many are the contrivances to which insects resort to carry out their pur- poses ! The caterpillar of the cabbage butterfly makes a ladder and goes up it ; the geometrical caterpillar lets down a rope, and, for fear of hurt- ing himself, drops a foot at a time. The gossamer spider sends forth a thread fine enough to act like a balloon, and, floating in the air, he de- scends or rises by winding it up or letting it out. There are other in- sects which make diving-bells, and go under the water. No bird makes a net, no beast a pitfall : men and insects do both. A gang of sailors will carry a spar by supporting it on alternate sides on their shoulders ; a gang of ant* will, in like manner, carry a straw or a long worm. There are spiders which show as much dexterity as an Indian in sneaking for- ward to get in reach of their prey. In their domestic economy, how wonderful ! Some build their houses of artificial stone, some of pasteboard which they make. Some cover their rooms with tapestry, some lay carpets of silk on the floor, some liang their doors on silk hinges, so that they shut by their own weight. They make arches, domes, colonnades, stair-cases. They practice con- cealment of food. Ray, an accurate observer and a very pious man, says of a sand-wasp that it carried a caterpillar fifteen feet, removed a pellet that closed the mouth of a hole, deposited its booty therein, came out, and rolled the pellet back on the hole, scratched dust thereon like a dog, went for rosin to agglutinate it, leveled the ground, and put two pine leaves to mark the place. However much we may smile at this anec- dote, it may satisfy us of the high opinion entertained of the accom- THE CEPHALIC GANGLIA. 607 plishments of insects by those who have been close observers of their habits. Dr. Lavcock remarks, when speaking of the cephalic ganglia of insects (Med. Chir. Rev., July, 1853) : " On what structures de- instincts of in- pend, if not on these cephalic ganglia, all those wonderful their te^h"r"" instincts which mimic in their operation the arts of man? ganglia. There is hardly a mechanical pursuit in which insects do not excel. They are excellent weavers, house-builders, architects. They make diving- bells, bore galleries, raise vaults, construct bridges. They line their houses with tapestry, clean them, ventilate them, and close them with admirably-fitted swing-doors. They build and store warehouses, con- struct traps in the greatest variety, hunt skillfully, rob, and plunder. They poison, sabre, and stab their enemies. They have social laws, a common language, divisions of labor, and gradations of rank. They maintain armies, go to war, send out scouts, appoint sentinels, carry oflf prisoners, keep slaves, and tend domestic animals. In short, they are mentally a miniature copy of man." The surprising character of some of these facts might disappear were we acquainted with what may be termed the spring of the action. It has been said by Dr. Whateley that the building of a comb is like the provisioning of a city, in which, through the desire of the dealers to get wealth, is solved what is probably the most intricate of social problems. It is done by no design of theirs, and yet they advance to it as if im- pelled by gravitation or some other insuperable force. A printer may put types together to get money without ever troubling himself about the diffusion of knowledge. A bee may find gratification in what he is doing without any concern about the final use of the comb. Of the cephalic ganglia spoken of in the preceding paragraphs, Fig. Fig.iQ5. 295 is an illustration from Mr. Newport,. in the case of the imago of the Sphinx ligustri : a, cephalic ganglia ; b, h, eyes ; c, anterior median ganglia ; d, d, posterior lat- eral ganglia of the stomato-gastric system ; Nervous system e,f, large ganglionic masses in the thorax, of insects, giving nerves to the legs and wings. It is Fig. 296. to be understood that upon these ganglia the voluntary action of insects depends. They are the places of reception of the im- pressions on the organs of special sense and Cephalic ganglia, the scat of mcmory. ' The automatic or in- voluntary apparatus is in part seen at Fig. 296, which is the thoracic portion of the nervous system of the pupa of the same insect : a, h, c, three ganglia of the ventral cord ; d, d. their ° ° . 7 11 Thoracic portion connecting trunks ; e, e, respiratory ganglia. The entire °^ ventral cord. 608 MEMORY OF INSECTS. nervous mechanism for the larva state has been shown in Fig. 126 ; for the pupa, 127 ; for the imago, 128 ; from which it will be recognized that the nervous system of insects, as they pass through their metamor- Changes in the phoses, Undergoes change. In the larva state, the nerves, as nervous system ^j^gj branch forth from the ventral cord, indicate by their uni- metamorpho- formity the equality of the segments of the body. In many sis- cases the cord is separated throughout its whole length into its two constituent strands, and the cephalic ganglia are minute because of the imperfect condition of the organs of sense. In the pupa state there is a general approach of the ventral ganglia, an increase of the cephalic, and a thickening of the strands which connect that organ with the suboesophageal. In the imago state the cephalic ganglia have still farther increased to a size which corresponds to the great development of the organs of sense ; the ventral ganglia appear to have coalesced in the thorax. The general result of these changes during metamorphosis is therefore to effect a concentration of the nervous centres in the head and in the thorax, the ganglia of special sensation coalescing in the for- mer, and those of motion in the latter region. We may remark that these modifications strikingly illustrate the observation that change in habits of life is always attended by change of the nervous system. Besides being the repository of the impressions of the special senses. Seat of mem- ^^^ cephalic ganglia discharge a function of a more general ory in insects, and most important kind, since doubtless they are the seat of memory. That insects of the more elevated kind have the power of recollection there can not be any doubt. If there were no other fact, their recognition of their homes would be sufficient to establish this. A thousand trivial incidents offer indirect, but instructive and interesting proofs of the same thing. When a spider who has been disturbed feigns death in order to avoid the cause of his alarm, he proves his capacity of recollection, as also when he has been brought out from his concealment by touching his web, and, discovering the nature of the imposition that has been practiced upon him, refuses to come forth upon a repetition of the trial. The power which the cephalic ganglia thus possess of bear- ing upon themselves the enduring traces of impressions received througli the sensory organs scarcely requires here to be more particularly exam- ined. In the preceding book, in the chapter on inverse vision, various facts have been mentioned which illustrate the faculty possessed by the optic centres in man of retaining visual impressions for a considerable period of time ; as, for instance, if, when we awake in the morning, our eyes are directed to the bright window and then closed, a representation thereof will still continue to be seen in its natural colors and relations, a representation which gradually fades away; and, in like manner, the cephalic ganglia register the impressions they receive from the optic, DESCARTES'S DOCTRINE. 609 tiie auditory, olfactive, and other nerves that pass to them, ^^^ ^^ j^^j... and preserve the vestiges thereof; for, if this be not the case, ganglia are it is wholly impossible to explain how insects should have the ^^^^^ ^^^' power of remembering, even though it be indistinctly or imperfectly, things that are past : those things or effects must have left upon them an enduring mark. The ganglia of the ventral cord, with their related nerve trunks, con- stitute a series of automatic nerve arcs, their immediate ob- A.ction of the ject being locomotion. As has been said, the impression of ventral cord the surface upon which the insect rests gives rise, under or- dinary circumstances, to muscular contraction, and thereby motion, and the same thing occurs under circumstances of unusual experimental dis- turbance, as when irritation of any kind — for instance, the pungent va- por of ammonia — is applied to one side of a centipede, the body is flex- ed in such a way as to get rid, as far as possible, of the noxious fume. These movements are purely reflex, and in their production the cephalic ganglia are in no manner concerned. Guiding and controlling these purely reflex operations, the cephalic ganglia, by means of the fibres which they send in company Controlling with the trunks of tlie ventral cord, can exert their influence action of the cephalic gaii- in the remotest part of the body. That influence we distin- giia. guish as being of a twofold nature: in part it is due to impressions which are being at that moment received through the various organs of sense — the eye, the ear, or whatever other such organ the insect under consideration may possess, and in part arising from the residues of old impressions which the ganglion has formerly received. It does not therefore seem possible, at least as regards the more perfect of these tribes, to accept the views of Descartes, who regarded all insects as mere automata. They are automata only so far as the action of Descartes's their ventral cord and that portion of their cephalic ganglia ^o*^'""!"^ ^^^^ ^ _ . . insects are aii- which deals with contemporaneous impressions is concerned, tomata. but they are not automata, since they are under the influence of those ganglia as the registers of past impressions. What has been said respecting insects applies to all higher tribes of life. Man himself is no exception. In the preceding book we have shown that, so far as his spinal nervous system is concerned, he is simply an automaton, and that it is the development of a brain thereupon whicli makes him capable of voluntary action. We have seen that in his indi- vidual progress part is evolved from part, an ever-increasing complexity and an ever-continuing improvement. ^ , , r • 1 1 1-1111 Cerebral mech- it IS the same, also, with the group to which he belongs — anism in anl- the vertebrates. Just in proportion to the advance of their '^disconnected ^. ^ , . with psychical cerebral mechanism are their psychical powers. The amphi- powers." Qq 610 WRITING AS A RECORD. oxus, which has no cerebral hemispheres, represents the condition of man when the action of his brain is suspended in sleep ; the fish, the reptile, the bird, follow in an ascending order — an order which man himself passes through in his individual progress of development. And man in the aggregate — in society — in the race — does the same, his historical career being a transcript of his individual career. Generation after generation leads a purely automatic life, the life of barbarism; but, by degrees, there is evolved in such conditions the means of registry or Writin is the I'^^ord. The acts and thoughts of one age can then be trans- means of record mitted to another, and can influence its acts and thoughts, or socie y. Civilization can not exist without writing, or the means of record in some shape. Writing once invented, the advance in society is again precisely as it is in the individual. In part it is regulated by the physical circum- ;3tances around, in part by the interior — the acquired principle. In the superficial sketch which I intend now to give of the progress of European civilization, there are certain facts which, from their promi- nence, can not fail to arrest our attention. They are, 1. Europe remained in the barbarous state until it obtained the means ,, ,f of perpetuating ideas, that is to say, until it learned the art of of European writing. liistory. 2^ xjig progress of civilization in Europe was attended by ;in absolute physiological change in its inhabitants. They were brought nearer to the condition of the inhabitants of a more temperate climate. On this point, however, we have dwelt to a sufficient extent in the pre- ceding chapter. 3. The European mind is analytic, that of Asia is synthetic. In Eu- rope, the action in philosophy, in religion, in politics, tends to the inces- sant decomposition of a thing into its parts, and their separate discus- sion. The results of this tendency are seen in many of the practical social difficulties of modern times. Before entering on this, the conclusion of his work, the author may recall by a few passing remarks the general views which have been in- cidentally scattered through preceding pages respecting the nature of man, the influence of surrounding circumstances over him, his social posi- tion, the definiteness of his career, a definiteness which authorizes us to treat his history, not as though it were composed of chance events, but as a fitting subject for the contemplation of physiology. Man is every where constructed upon the same essential type, and hence, in one sense, he acts in an invariable manner, but that type passes forward in development to many different aspects, and hence, in another sense, he exhibits differences in his determinations and movements. With the form and size of the brain, the intellectual capacity of man NATUEE OP MAN. 611 varies. In a state of nature, his mental powers are in close relation with the climate in which he lives, attaining their greatest perfection in the warmer portion of the temperate zone ; but under the artificial condition of civilization, in which the vicissitudes of the seasons are compensated for by food, fire, shelter, and clothing, properly adjusted, he gains his maximum development in a somewhat higher latitude. After what has been said in the last chapter respecting the influence of physical circumstances on the structure of man, producing modified development in our typical form, and thereby giving rise to many dis- tinct families, it will be anticipated that those circumstances must con- sequently modify our mental operations, our manner of thinking and act- ing, that is to say, must leave their marks on our history as nations. For a long time this has been recognized in a general manner: the mount- aineer thinks differently and acts differently to the native of the low- lands ; he whose life is spent on the borders of the sea to him who lives in the great plains in the interior of continents. But it is not to these influences as operating by association on the individual that I now refer ; it is rather to the profound effect they have had in producing a special cerebral, and, therefore, mental organization in the course of many gen- erations on races and nations. Let us always remember that there is a common principle which un- derlies the varied movements and determinations of men every where — a principle from which no one can disentangle himself. At the bottom of even the most diverse actions it may be discerned, just as we can detect the fundamental type of our organization under the most varied forms. As from the physical point of view there is a standard man who, in vfeiffht, heiffht, strength, and other such like particulars, rep- ^^ , . , n n • • n i • N^ature of man. resents the entire human family, so, m an intellectual point of view, there is a standard man who, in mental progress, manner of thinking and of acting, represents the whole race. There are also sub- ordinate standards, the representatives of particular groups or nations. It is to these standards that we are continually appealing in arriving at a judgment of the acts of individuals. The special history of these phases constitutes, in a philosophical sense, national history. The rec- ord of the development of the fundamental type constitutes universal liistory. I have abeady remarked that universal history is only a chapter in physiology. Since, by reason of the similarity of construction of the cerebral apparatus, the actions of men will present a uniformity when under the influence of similar motives or impulses, there is not only a resemblance between such actions among different persons. Influence of but also it may be discerned when nation is compared with ci'rcum^tances nation, and race with race ; for the movements of communi- on him. 612 CAREER OF MAN. ties depend on the same motives as the movements of individuals, being indeed the sum of individual determinations. But when multitudes and masses are thus brought under our consideration, the element of free-will seems for the most part to disappear, and events assume an air of pre- destination. To this principle it is that history owes its chief value, and truly becomes, as is often said, philosophy teaching by example. The intelligent man who lived twenty centuries ago would doubtless have come to the same decision which is reached by the intelligent man of our times ; the same propositions being submitted to both, both guiding themselves by similar principles to a like result. The logic of truth is eternal, for it is the expression of the manner of action of our cerebral ap- paratus, the type of which never changes ; and since there is thus no essential change in the typical construction of man, and therefore none in the manner of operation of his mental processes, since physical nature Definiteness of ^^ unvarying, and the events of life spring one out of another his career. j^ ^ regular order or sequence, there must arise those same analogies in the history of race compared with race, and nation compared with nation, that are so obvious when individual is compared with indi- vidual. Of every great future event there is therefore a past history, for every such event has had its precedent in other histories, and therefore its prognostic. Things will follow in a definite order so long as the in- fluences of external nature are the same, and so long as the construction of the human brain is the same. The political foresight of the most eminent sta,tesmen depends on a gift of appreciating national mental types, like that possessed by great sculptors or painters of appreciating a standard of beauty. It is this which enables them to foresee the probable consequences of events, and to realize the expected action of individuals, and even of masses of men. In such actions there is far more uniformity than is commonly supposed. The same general conditions which yield to the post-office a definite percentage of misdirected letters every year — which, with mar- velous fidelity, give to the hospitals, the jails, the bills of mortality, their expected numbers, operate from age to age, and in one nation as in an- other, and hence arises that appearance of fate in the action of masses to which we have alluded ; hence also it is that the same cycle of events re-occurs again and again, diversified, perhaps, but never essen- tially changed by the influence of individual free-will. As the compar- ative anatomist exhibits, in the different members of the living series, their common points of resemblance — that this organ in one animal is the homologue of that in another, and this function the analogue of that, so the philosophical statesman, acknowledging the essential principle of compavntive history, reasons from nation to nation and from age to age. PRIMITIVE STATE OP EUROPE. 613 CHIEF EVENTS IN THE CIVILIZATION OF EUROPE. The Odyssey presents us a vivid picture of the state of Europe a thousand years before the birth of Christ. A twilia-ht was ,, •^ . _ ... Europe eiiierg- breaking on the most eastern verge in the countries adjoin- ing from bar- ing the Hellespont, but the West and the North were im- ^''"'"'• mersed in a night of barbarism. The unfolding mind is ever prone to fill darkness with imaginary creations, and it was with the white race at that period as it is with a child. Every shore of the Mediterranean and Black Seas was full of prodigies. To the Greek no fiction was too marvelous for belief if it was separated from his view by a hundred years or a hundred miles, the exaggeration of tradition confirming it in the one case, and the difficulties of travel in the other. His horizon was crowded with enchantresses like Circe, sorcerers like Tiresias, monsters like the Cyclops. Gods and goddesses were perpetually flying through the air ; every hill had its supernatural legend, every forest its phantom. Even the mouth of hell was on the farther side of the Euxine. A religion of superstition is very liable to be connected with a life of evil works. The maritime enterprise of those days seems to have re- ceived no little incitement from the temptations of piracy — a temptation to which, even at a later period, the Greek appears instinctively to turn ; nor were the felonious expeditions restricted to the taking of goods ; they drew an additional profit from the stealing of men. The evidences of even a still darker crime may also be discerned, since there were people accused by common fame of eating the captives who fell into their hands. The white man, therefore, emerges from his state of barbarism a pirate, a slaver, a cannibal, cruel in his moment of power, and debased by an incredible superstition in his moment of fear. Unable to originate his civilization for himself, he drew the elements of it from another country. By the concurrina; testimony of ^. .,. ,. •; •' _ o _ _ •' Civilization all authors, as well as the internal evidences of ancient history, originated that great blessing is the gift of Egypt. For thirty-four cen- ^" "g^P*- turies before our era that country was governed by dynasties of kings, succeeding each other without interruption. Its soil, proverbially fer- tile, sustained a population, estimated, in the most prosperous times, at about seven millions ; and repeated military expeditions into Asia and Ethiopia had, in the course of ages, concentrated in it immense wealth, the spoils of conquered nations, and crowded with captives and slaves the Valley of the Nile. For this long continuance of the Egyptian polity satisfactory reasons may be assigned. In early ages, when maritime expeditions Ancient condi- were necessarily feeble, the country was open to invasion tion of Egypt. only across a narrow neck of land on the east, and was protected from any attack on the west by impassable and interminable deserts. Under 614 THE EGYPTIANS. the military system of remote antiquity Egypt was almost inaccessible : but through the changes of later times, and ever since naval expeditions have been carried to any extent, her position has been that of extreme weakness. The uniform experience of twenty -five centuries, from the Persian wars to those of the French Revolution, has shown that the pos- session of the mouths of the river is equivalent to the conquest of th* • country. In the security of this inaccessible retreat, and under political institu- tions of a favorable character, the civilization which was to be conferred on the white man originated. For a succession of centuries, industrial art, and its parent, natural knowledge, appear to have undergone a stead}' development ; perhaps, as in other countries at a later time, advancing in the more prosperous political seasons, and becoming stationary in the decay of the empire. The statements furnished to us by Greek authors are of very little value, for as long a period of time intervened between the first Egyptian kings and them as from them until now. It is rather from the monuments of the Egyptians that we must judge. Each year since their country has been open to investigation, and their hieroglyphic system understood, the impressions we have received of their intellectual advancement have been more and more favorable. The vocal statue of Memnon at Thebes, it is said, emitted a musical sound when touched by the rays of the sun. In the light of modem criticism, every obelisk and monument in those desolated palaces is finding a voice. The public works attest to this day the greatness and permanence of Manners of the the Egyptian monarchy, and the peculiarities of the Egyp- Egyptians. -f-jg^j^ mind. From the statues and ruins of the temples of the Greeks we see what a vivid perception that people had of the beauti- ful. The statues, and tombs, and temples of the Egyptians offer a strik- ing contrast; the useful every where predominates. The vases of the one were adorned with emblematical and graceful forms; the tombs of the oth- er were covered with sculptures and paintings, commemorating the ordi- nary pursuits of life, and various processes in the arts and manufactures. These sculptures and paintings show to what an extent the physical sciences and arts depending on them had been cultivated. They set be- fore us the domestic life and daily business and trades of the people : cookery, confectionery, glass-blowing, weaving, potterj^-making, manu- facture of cotton, painting on wood and stone, staining of glass, and a hundred other occupations. Among the pictured representations, a chem- ist sees with pleasure the apparatus of his art, siphons, bellows, blo-\\- pipes, etc. Shut up by its political system from the Mediterranean nations in the same manner that the Chinese and Japanese empires have been in later times from other states, Egypt was to the Greek a land of mystery and INTRODUCTION OF WRITING. 615 marvels. The exaggerated legends which had been brought from it at distant intervals by those who had escaped by stealth, or in troublous times had, like Cecrops and Danaus, led forth colonies of emigrants, lost none of their wonders in the traditions of successive generations, but were rather verified by the roving pirates who had seen the pyramids, obelisks, and sphinxes, and the great temples on the banks of the Nile. The first step in civilization is the invention of some system of per- manent record — some method of writing. Without this, it intj-oduction may be truly said that law can not exist. Law can not main- of writing from tain itself in the uncertainties of tradition — law, without ^-^'^ " which we can not conceive of society. The legendary history of Europe is doubtless correct in referring to some of these Egyptian fugitives or emigrants the contemporaneous introduction of writing, and a system of jurisprudence. Even if the former was derived from Phoenicia, accord- ing to the story of Cadmus, the Phoenicians had originally borrowed it from Egypt. It is an interesting illustration of the tendency of the Eu- ropean mind to analysis, that of the forms of writing known in those times, the ideographic or picture-writing, the syllabic or the representa- tion of syllable sounds by signs, and the alphabetic, the latter alone maintained its foothold in Europe. This form, as described at page 356, essentially consists in decomposing articulate expressions into their con- stituent vowel and consonant sounds, and assigning for each of those sounds a letter. About seven hundred years before Christ, events took place which led to the extension of Egyptian civilization to Europe. The an- introduction cient power of the kings had declined, through disputes and of Egyptian compromises occurring between them and the priesthood. Be- tween the priests and the military caste there was an open quarrel, many of the former having been deprived of their lands. These rivalries broke out in revolts and insurrections, and for two years the country was in a state of anarchy, from which a partial respite was obtained by an entire change in its institutions. Twelve of the most influential persons divided it among them, each having a province which he ruled as an independent king. The old monarchy had degenerated into an oligarchy, and it was this revolution which introduced African science into Europe. Psammetichus, one of the twelve, had for his province the country which borders on the Mediterranean Sea. Availing himself of his position, he established an intercourse with the neighboring nations, particularly the Greeks and Phoenicians, and amassed from it so much wealth that his colleagues, jealous of his increasing power, resolved to dispossess him. Until this time, all foreigners had been held in the utmost contempt, and rigidly excluded. Psammetichus called in the aid of Ionian pirates, and other Mediterranean adventurers, and, having collected a sufficient body 616 THE PEESIAN EMPIRE. of such mercenaries, defeated his colleagues at the battle of Momemphis. and became sole ruler of the whole country. By the aid of a foreign force the revolution had been ended, but the Opening of the position of Psammetichus was essentially different from that ports of Egypt. q{ ^U preceding princes. A foreign force had given liim the throne, and a foreign force alone could maintain him on it. Under such circumstances, he took his most politic course, and, breaking through the traditions of twenty-five centuries, opened the ports of Egypt. This event necessarily led to a closer intercourse among the ]\Iediter- ranean nations, and insured communication between Europe and Africa. The foreign element quickly made its influence manifest; In the very next reign the Cape of Good Hope was doubled, and Africa circumnavi- gated, and in the course of a very few years we find Pythagoras, Solon, and Thales visiting Egypt, and bringing from thence to Europe the ele- ments of law and natural science. The Persian empire in the mean time had attained an attitude of su- Th P • premacy in Western Asia. Following the inspirations of its empire : its in- Babylonian predecessors, it was engaged in continual wars uence. with its African neighbor. From the battle of Pelusium, and the conquest of Egypt by Cambyses, the political interests of that country and Greece became essentially the same. The Persian con- r[uerors, operating alternately on the north and south shores of the Medi- terranean, betrayed a determination to extend their rule around that sea, and make it a Persian lake. On the one hand they were resisted by the Greeks, on the other by the Egyptians, between whom active communi- cations were kept up. For several centuries these operations were con- ducted with various success. The kings of Persia, several of whom seem to have been men of great capacity, comprehended the political ad- vantages which would arise from the possession of the sea, and would have doubtless carried out their plans as respects the south shore, if the Phoenicians had not opposed obstacles for the sake of their colony at Carthage. And though the Greek historians, with a pardonable motive, speak of the various movements on the north as failures, there are many circumstances which lead us to receive their accounts with allowances. If Memphis was sacked, Athens also was burned ; and even at the open- ing of the Macedonian expedition, Greek history is full of Persian inci- dents and intrigues. In speaking of the Egyptian cultivators of philosophy as priests, the ^ . « signification which is now attached to that word gives us an Introduction of o '-' i:gyptian phi- erroncous idea of what they really were. I he colleges at losophy. Memphis, Thebes, Heliopolis, and Sais, wei-e, in reality, each the head-quarters of a fraternity of artists and professional men, and bore no sort of resemblance to our modern ecclesiastical institutions. Among THE GREEK SCHOOLS. 617 them were architects, lawyers, pliysicians, pahiters, chemists, astrono- mers. These men were, moreover, the great landowners ; not only were the temples richly endowed as corporations, but the individual members were persons of wealth. They enjoyed monopolies of all kinds; for in- stance, among other things they had extensive factories for cottons, and laboratories for the preparation of chemical products. From these institutions the Greek philosophers brouglit natural sci- ence. Pythagoras had resided at Thebes, Thales and Democ- xhe Greek ritus at Memphis, Plato at Heliopolis, Solon at Sais. They schools. (lid at first little more than expound the doctrines they had learned. Their mode of instruction seems to have been, in many instances, found- ed on the Egyptian model. The Pythagorean establishment at Crotona may be regarded as a partial imitation of the African colleges. It is not my intention to enter on an examination, or even enumera- tion, of ancient philosophical opinions, nor to show that many of the doc- trines which have been brought forward witliin the last three centuries existed in embryo in those times. It may, however, be observed that, in the midst of much error, there were those who held just views of the . ^■arious problems of theology, law, politics, philosophy, and particularly of the fundamental doctrines of natural science, the constitution of the so- lar system, the geological history of the earth, the nature of chemical forces, the physiological relations of animals and plants. It is supposed by many, whose attention has been casually drawn to the philosophical opinions of antiquity, that the doctrines which we still letain as true came to the knowledge of the old philosophers not so much by processes of legitimate investigation as by mere guessing or crude speculation, for which there was an equal chance whether they were right or wrong ; but a closer examination will show that many of them must have depended on results previously determined or observed by the Af- ricans or Asiatics, and thus they seem to indicate that the human mind has undergone in twenty centuries but little change in its manner of ac- tion, and that, commencing with the same data, it always comes to the same conclusions. Nor is this at all dependent on any inherent logic of truth. A^ery many of the errors of antiquity have reappeared in our times. If the Greek schools were infected with materialism, pantheism, and atheism, the later progress of philosophy has shown the same char- acters. To a certain extent, such doctrines will receive an impression from the prevailing creeds, but the arguments which have been appealed to in their favor have always been the same. The distinction between these heresies in ancient and modern times lies chiefly in the grosser characters which they formerly assumed, arising partly from the reflected influence of the existing mythology, and partly from the imperfections of exact knowledge. Even the errors of early antiquity are venerable. 618 ANALYTICAL MIND OF THE EUROPEAN. We must judge our predecessors by the same rules tliat we hope pos- terity will judge us, making a generous allowance for the imperfections of reason, the infirmities of character, and especially for the prejudices of the times. To have devoutly believed in the existence of a human soul, to have looked forward to its continuing after the death of the body, to have expected a future state of rewards and punishments, and to have drawn therefrom, as a philosophical conclusion, the necessity of leading a virtuous life — these, though they may be enveloped in a cloud of errors, are noble results of the intellect of man. The analytical quality of the European mind already manifested itself Analytical in this decomposition of knowledge derived from foreign coun- Euro'^ea^n*^'^ tries, in this establishment of a host of schools, this exaraina- mind. tion and discussion of the fundamental elements of the im- ported philosophy. As there are differences in the physiognomy of races, so there are differences in their intellectual endowments, which, arising in peculiarities of cerebral construction, communicate peculiarities to the processes of thinking. The physical science of Egypt, transported to Greece, rapidly degenerated into speculative philosophy, and in so doing produced an instability of opinion which entailed as its conse- quence a laxity of morals. Such a social condition led naturally to the results which history indicates. It is not surprising that the most em- inent men were open to bribery, and that the glory of those ages was so often the brilliancy of corruption. These are the necessary results at- tending such political conditions. Too often it fell out that the great men of Greece accused, and too often convicted each other of being in- fluenced by Persian intrigues and Persian gold. In the general demor- alization, they seem to have taken for their guide a perverted interpreta- tion of the admirable precept of Solon, " In every thing thou doest, con- sider the end." Added to this, the public faith in things once implicitly believed was shaken. Xerxes in a very unceremonious way violated the temples and carried oif their treasures, showing the same contempt for the gods of Europe that Cambyses had shown for those of Africa. If there lingered in the minds of the philosophers any latent belief in the national faith, a relic of the impressions of childhood or of popular opinion, such a prac- Greek irre- tical demonstration could scarcely be lost. During the fifty ligion. years of that war, the philosophical opinions of the Persians had full opportunity to find their way among a class of men quite open to receive them, and from this time we perceive a striking similarity be- tween many of the doctrines of the schools and the well-known dogmas of the Orientals. The Greeks, like the Hindoos, in the possession of the mere rudiments of science, passed at once to the discussion of the most important and elevated problems with which the human mind can be en- ORIGIN OF EUROPEAN COMMERCE. 619 gaged, and, as an inevitable consequence, were led away from true phi- losophy into sophistry and irreligion. It has been remarked a few pages back, that in the progress of nations events follow in repeating cycles, and that for any one we may generally find its precursor, and therefore its prognostic. Greece dealt with the philosophy she had received from the southern people, African or Asi- atic, exactly in the same manner that Europe dealt with Italian theology the moment that liberty of action was permitted by the Reformation, In each case the issue was not the prompt and final substitution of a sys- tem correcting apparent and acknowledged defects, a system in unison with the existing tone of thought. There was no such stoppage of ac- tion ; but from the bosom of each principle and sect many other princi- ples and sects arose, until there seemed to be no end to the subdivision. If thus we consider the political position of Greece, the condition of Asia Minor, occupied by Persian troops, the destruction that influence of the had overtaken Egypt, the excitements and calamities of a war on mockrn pM- of half a century, we can readily understand that this was losophy. not a season when the tedious and slow processes of true philosophy were Hkely to flourish, and that it was far more conducive to imposture than to science. The seeds of knowledge which had been brought from Egypt shot up into a rank growth, and Europe did not free herself of these weeds for sixteen centuries. The character of a long train of' events is often determined at its inception ; for this reason, I have dwelt in detail on those times, and it is well worthy of remark that the posi- tive science of the European was not fairly established until after three distinct impulses from Egypt : once, as we have seen, under her Pha- raohs ; again, under her Ptolemies ; and still again, under her caliphs and sultans. While these events were taking place in the southeast of Europe, do- mestic and foreign commerce were preparing the way for a ^_.^. „y gradual diffusion of civilization. A trade with the countries ropean com- bordering on the Baltic Sea for the amber which is found on ™®'''^®- those shores had gradually arisen, and, in like manner, another with Spain, France, and England for tin. The tin of Cornwall was carried through France and shipped by the Phoenicians at Marseilles, a certain quantity of the same metal being also obtained fi'om the Spanish mines. Early in their history the Phoenicians had established colonies on several points of the Black Sea, and from these depots they brought the various products of those countries, among which may be mentioned gold, which had apparently been originally derived from the washing of the Uralian deposits. This Black Sea commerce seems, however, to have been event- ually abandoned for the more profitable Spanish trade, and on the with- drawal of the Phoenicians from the Euxine, the Greeks occupied their 620 THE MACEDONIAN CAMPAIGN. i)i over of P^^^®* Meantime the enterprise of the Tyrian sailors had the Straits of carried them through the Straits of Gibraltar, and enabled them to have direct access with the tin and amber countries v.'ithout the intervention of any overland traffic. It was doubtless the discovery of this outlet to the Atlantic which led to the destruction of the Gaulish trade in tin and the German trade in amber. So greatly was this latter substance prized, that the overland commerce in it had many ramifications : thus amber was carried into Italy by the Etruscans, who had a sacred road under the protection of the adjacent tribes to the Baltic Sea. With their commerce the Phoenicians disseminated a knowledge of many inventions peculiar to themselves, among which may be mentioned the use of stamped metallic coinage. Their great African colony, Car- thage, exerted in these movements eventually a more powerful influence than even the parent country. Emulating the enterprise of the Phoenicians, the Greek mariners un- dertook expeditions both to the east and to the west, succeeding, as we have seen, in establishing themselves on the shores of the Euxine, and eventually passing, under Coloeus of Samos, through the Straits of Gib- raltar into the Atlantic Ocean ; but even up to the time of the Mace- 'ihe Macedoni- donian expedition, their geographical ideas were very crude ail campaign, ^nd full of crrors. Of the expedition of Alexander, Hum- boldt remarks that it partook as much of the character of a scientific as of a military undertaking, and its consequences, both immediate and re- mote, upon Europe can scarcely be exaggerated. That great commander surrounded himself with whatever talent was to be found in Greece, and made his military successes for a time subservient to the science of his native country. It was through this that Aristotle obtained that com- manding influence which not only gave him an authority over the active mind, of his own times, but which was felt even until the introduction of the Baconian system of philosophy. The campaigns of Alexander doub- led the geography of the Greeks in longitude, opened to their investi- gation new countries even to the tropics, brought them acquainted with races of men who had been the depositaries of science, as it then existed, for thousands of years, and, in short, added Asiatic to Grecian knowl- edge. It is a significant fact that, after the taking of Babylon, Alexander sent to Aristotle a series of astronomical observations reaching back through 1903 years. The Macedonian expedition not only made a profound impression on r, . ,. . the European mind by its immediate results — its influence is Kcstoration of ^ / tut. monarchy in equally palpable in its remoter consequences. It would be Hyv^- impossible, in such a sketch as this, to do justice to that great event in all its details ; for nations can not be thus brought in contact THE PTOLEMIES. 621 without prodigious mental results, the extinction of old, and the appear- ance of new ideas. But of the influences which thus arose, there is, how- ever, one which deserves to fasten our attention, and the more so since we have had already, and shall have again, the occasion for alluding to it. It was the establishment of a regal government in Egypt. Under tlie Ptolemies, who may he truly characterized as the most .,1 ... J, ... . , The Ptolemies. illustrious kings ot antiquity, that ancient country recovered licr pristine glory. Among the works accomplished by these great men may be mentioned, as examples of their high-toned policy, the sending out of an exploring expedition to equinoctial Africa ; the establishment of menageries and zoological gardens at Bruchium ; their attempts at determ- ining the cause of the overflow of the Nile; the library at Alexandria; the museum at Bhakotis ; the measurement of a degree on the earth's surface between Alexandria and Syene; the ascertaining of the prodigious distance of the region of the fixed stars ; the recognition of the motion of rotation of the earth upon her axis, and of her translation around the sun ; the precession of the equinoxes ; the attempt at constructing a map of the world by the aid of degrees, based on lunar observations and on shadows ; the improvement of the methods of astronomical observation by the invention of water-clocks, and instruments for the more accurate measurement of angles. Along with these. Baron Humboldt, in his Cos- mos, has enumerated many other philosophical works of the Ptolemies, which exerted a profomid influence both upon the knowledge and intel- lect of Europe. Greece now repaid what she had formerly borrowed ; lier schools of philosophy were translated to Alexandria, and the great names of Euclid, Apollonius, and Archimedes testify to the return of these ages to exact science. The decline of Greece and her final absorption into the Eoman em- pire was the necessary consequence of her mode of life. In Decline of policy as in philosophy, her essential tendency was to sub- jJe'^of'the Uo- i. ^ , ^ '' , , P . . Eesult of the by writing, which at once aided, in the most marked manner, introduction of the dissemination of this improving condition, especially by ^'"'^^"S- leading to the consolidation of society through the introduction of durable systems of law. By this, the influence of men and of generations was indefinitely extended. The opinions and thoughts of those times have actually, in many instances, descended to us. Elsewhere we have dwelt on the £xt that these effects in the progress of humanity are foreshadow- ed and illustrated in the course of individual development. A higli psy- chical condition demands as its essential, both in the individual and in the race, a mechanism of registry. From the preceding imperfect narration we may moreover gather that the progress of civilization in Europe has not been in the way Centre ofintel- of a diffusion from a central point, but that there has been a ^^^^ °^ Europe, shifting of the centre of intellect. For a length of time it was in Greece ; then it passed to Italy ; in our times it is still more to the west. In a philosophical respect, the result of Mohammedanism on Europe has been, through the introduction of physical science by the Arabians, to coalesce the centre of intellect and the centre of force. Henceforth upon that continent physical power must be subordinate to mtellectual. In this we see what is the true interpretation of the influence which Mohammedanism has exerted on Europe — an influence which, Effect of Mo- though popularly, is very miworthily represented as an oc- tammedanism . on th.e centre cupation of Spain for a few centuries and the capture of Con- of intellect of stantinople. In truth, it was of a far higher and very dif- Europe, ferent order. The Koran of the Arabians failed to make its way through Europe, but it was very different with the physical science of the Arabi- ans. Its spread was the true foundation of modern national power, for it at once occupied itself with the development of material resources and the introduction of useful inventions. The manner of thought it engen- dered lies reaUy at the basis of the great intellectual controversy of our times. The translation of the centre of intellect from Italy to the West is the legitimate issue of the Moorish invasion of Spain. As regards that propensity to the decomposition of every thing into its constituent elements which is the tendency of the Euro- Result of the pean, though doubtless it has its disadvantages, we are not g^g^'^'^f f^e^E^' to suppose that it leads of necessity to an intellectual chaos, ropean mind. Those authors who view with dismay our present state, who represent us as though, both in polity and religion, we were crumbling to pieces, and that the multiplicity of opinions and sects, which are ever on the increase, is the precursor of a universal anarchy, have never duly con- sidered that out of such a state it is possible in an instant for fixed 636 CONDITION OF EUEOPEAN BIPROYEilENT. principles of order to emerge, and this not by any process of compression or suppression, but spontaneously in the natural course of events. In the outset of this brief historical description I have alluded to the adop- tion of alphabetic writing in Europe as a signal illustration of the mental peculiarity of the inhabitants ; this may also serve to make clear the paradoxical assertion that systems founded on indefinite subdivision may suddenly free themselves from complexity and become simple and perspicuous. On a superficial consideration of the thing, one might im- agine that to decompose articulate sounds into their constituent syllables, with a view of representing those syllables by symbols, would be at- tended with a prodigious complication, and that such is the case the Chi- nese have found, who have pursued this plan in its details until it is said that their alphabet contains 80,000 letters ; but still more would it be supposed that if those syllables were in their turn decomposed into their constituent parts, the required elements would be utterly unman- ageable by reason of their number, and the art of writing utterly imprac- ticable ; yet do we not find, on the contrary — and it may be an instruct- ive lesson to us — that when the decomposition is thus pushed to its ex- treme, instead of myriads of characters being required, as we might have plausibly expected, an alphabet of 20 or 30 letters is all we want ? The state of opinion in Europe is illustrated by the state of writing in China. In view of the facts presented in this and the foregoing chapter, we may come to the general conclusion that the extremes of humanity, which are represented by a prognathous aspect and by a complexion either very dark or very fair, are equally unfavorable to intellect, which reaches its greatest perfection in the intermediate phase ; that, even in the condition which was presented by the inhabitants of Europe three thousand years ago, no advance in civilization was possible, save by first accomplishing an absolute physical change in their constitution through European im- modifications in their habits of life equivalent to a true cli- provement. j^^^g change — a preparation for a higher mental development by an amelioration of their condition of life. The civilization of the European could never have been accomplished save by preparing the way through such a physical change. It followed that change in the manner that effect follows its cause. Its incident was 'he transformation of the fair race which then occupied all Europe to an- other of a darker hue ; the extinction of the disappearing people not be- ing accomplished by such means as an extermination, after the manner in which the North American Indian is dying out, but by a slow and true metamorphosis into another form. Advance in civihzation takes place during such a metamorphosis. Asia, Stationary con- which, at an early period, must have exhibited a mental de- dition of Asia, yelopment of great rapidity, has long ago become stationary. ADVANTAGES OF THE ANALYTICAL MIND. 637 In her physical life there is no change, and hence none in her intellect- ual. Her wandering central tribes encamp on the steppes in the same felt huts that their ancestors did two thousand years ago ; her southern people never vary their customs. That which, in a philosophical respect, is the most important condition, domestic economy, has undergone no kind of modification. But with us, how different ! The hardships of life have to a very great extent heen removed, and Ave are familiar with a degree of comfort to which our predecessors were wholly strangers. Not that we have been freed from all trials ; it has only been an exchange of bodily sufferings for mental anxieties. Our higher condition has created new wants and new sources of pain. With the transformations through which, as a race, we have passed, and with the assumption of that analytical mental character Advantao-es to which I have referred, there has been gained a capability arising from an of indefinitely modifying our state, and, therefore, of improv- mental constl- ing it. It is this which pre-eminently distinguishes the Eu- t^^^^o"- ropean ; that whatever scientific discovery he makes, or whatever inven- tion occurs to him, he forthwith applies it to economic advantage, and is thereby perpetually impressing a change on his own state. In this re- spect, even a single generation often suffices to show the advances which are made. We have only to recall the greatly improved means of loco- motion ; the instantaneous transmission of intelligence through many thousand miles ; the development of industrial art, and the rendering- available mechanical powers for many new purposes, which have been achieved in less than a single century. Nor does there seem to be any possible limit to human advance in this path. Since thus the mind of the European is essentially analytic, his ad- vance in civilization, as it were in a geometrical progression, is the neces- sary consequence thereof. If we examine his career in subordinate par- ticulars, it illustrates equally his mental physiognomy ; it is the same whether we look to his passage in philosophy, science, politics, or religion. If I may be permitted without offense so to say, his divergence from a single form of faith, the springing up of those numberless denominations and sects which constitute the most observable feature of his present re- ligious state, is a result which he can not help, for it is the consequence of his organization. Things which were possible in the eighth century had become impossible in the new state of the sixteenth. And so, too, it is in his political relations. Herein consists the superiority of the analytical over the synthetical mind. To the work of him who pulls to pieces there is no end, but he who puts things together comes to an end of his task. INDEX. A. ^\:bducentes, 33i. Aberration, chromatic and spherical, 386. Abrupt and gradual impressions, 483. Absorbed material, course of, 109. Absorption, forces of, 110 ; by blood-vessels, 49, 84, 1 02 ; nutritive, 84 ; double mecha- nism for, 84 ; in plants, 86 ; summary of, 108 ; by lacteals, 84, 86 ; by lungs, 163 ; by gene'ral surface, 98 ; by skin, 98, 241 ; two kinds of, 86 ; interstitial, 98 ; selecting power in, 99. Abyssinian, 577. Acid, hydi-ochloric, use of, 52. Activity of the brain depends on arterializa- tion,'326. Affinitv for tissues the cause of circulation, 133,' 147. Africa, influence of Europe and Asia on, 593 ; prospective civilization of, 597 ; inhabit- ants of, 577. Agassiz on origin of nations, 568. Age, influence of, 61, 172 ; old, 545. Agents, external, influence of, on man, 567. Agony, final, 562. An-, introduction of, 1 60 ; expired per min- ute, 168 : passages, evaporation from, 186. Air-cells of lungs, 159, 160. Albitmen, 29 ; transformation of, into fibrin, 100 ; quantity of, 121. Albiuninose, 61, 64. Alcohol, use of, in supporting heat, 20 ; effect of, 182, 406. Alexander, expedition of, 620. Alexandria, library of, 624. Aliment, necessity for, 10. Allantois, 531. Allotropism of bodies, 188; decay depends on, 244. Alpha and Beta lactic acid, 75. Alphabetic -mriting, 358. Alternate consciousness, 330. Alternation of generations, 514, 537. Amber, trade in, 619. Amelioration of negro, 578. America, discovery of, 632 ; spread of Chris- tianity in, 598 ; Indians, 575. Amnion, 530. Amphibia, blood of, 121. Analog}^ of spinal and ventral cord, 308. Analytical mind of Eiu'opean, 592 ; advan- tages of, 618, 635, 637. Animal, capillary circulation of, 133 ; heat illustrated by locomotive, 187 ; makes fat, 247 ; motion, 431. Animal kingdom, subdi^-isions of, 176. Anterior roots of spinal cord, 296. Anthropomorphism, 286. , Antrum duodeni, 61 ; pylori, 61. Ants, habits of, 605. Aplysia, 280. Apparitions, 402. Appendix vermifoiinis, 63. Approach of sleep, 532. Aqueous humor, 386. Ai"abs, discoveries of, 629 ; influence of, 620. Araucanians, 598. Arc, automatic, 277 ; cellated, 278 ; influen- tial, 282; commissm-ed, 279; multiple, 278 : registering, 281. Ai-istotle, 620. Arm, 580. Art, contributions of Asia to, 595. Aiteries, coats of, 140 ; contractility of, 141 : stnictm'e of, 140. Article of death, 411. Ai'tificial larynx, 355. Ascaris acuminata, 524 ; nigrovenosa, 524. Ascent of sap, causes of, 87. Ascherson on use of fat, 101. Asia, stationary condition of, 636. Asiatic contributions, 595. Asterias, nervous system of, 279. Astrology, 178. Atmosphere, action of, on plants, 464, 482. Attraction, capillary, 104. Auditory Mec ha nism, general view of. 376. Auditory muscles, estimate of contraction of, 367; nerve, 361. Auricles of heart, 138, 146. Australian, 563 ; forests, 474. Automata, insects are, 609. Automatic arc, 277, 283; registering, 281. Awakening, 553. Axmann on neiTes, 263. B. Bacon, Roger, 625. Balance between heating and cooling, 186. Barbarism, 604. Ban-al on food distribution, 39. Basilar view of skull, 584. Beaumont on food, 66. Becquei-el, table from, 33. Bee, formation of fat by, 248, Beef, digestibility of, 65. Bell, dis'coveries of, 259, 298, 318. Beueke on hospital diet, 35. Bernard on digestion, 76 ; on fat, 71 ; on sali- va, 196 ; on liver-sugar, 208. BemouiUi, principle of, 90. 640 INDEX. Berzelius on lactic acid, 75; on perspiration, 240. Bibra, Von, on bi-ain fat, 274. Bidder on albuminates, 39 ; on section of pneumogastric, 54. Bidder and Schmidt on intestinal juice, 69 ; on bile, 70 ; table by, 70. Bile, secretion of, 70, 110, 202 ; composition of, 204; formed from venous blood, 110, 303 ; sources of, 202 ; aids in introducing fat, 91 ; spiral course of, 201 ; change by retention of, 205 ; period of maximum flow of, 205 ; not formed in the liver, 206 ; man- ner of removal of, 206. Bipolar nerve-cell, 264, 268. Bird, digestive tract of, 58 ; respiration and heat of, 159 ; talking, 352. Bishop of Chiapa, his accusation, 632. Black pigment, 387. Black Sea trade, 619.. Blastodermic vesicle, 524. Bligh on Pelagians, 580. Blood, 111; properties of, 112 ; composition of, 1 12 ; total amount in body, 113 ; coag- ulation of, 1 13 ; buffy coat of, 1 1 4 ; changes produced in by respiration, 120, 126, 134 ; excretion of carbonic acid from, 126, 167 ; changes of color of, 169 ; density of, 169 ; salts of, 124; gases of, 125; functions of constituents, 125 ; course of, 134 ; distribu- tion of, 144; glandular change of, 190. Bloodof spleen, 212. Blood-cells, form of, 115; constitution of, 118; origin of, 94, 115 ; destruction of, 209 ; increase of, 125 ; diminution of, 126 ; short life of, 127; changes in form, 117; cell wall of, is fibrin, 117. Blood, colorless, corpuscles of, 115, 120. Blood crystals, 119. Bloodletting, reduction of temperature by, 184. Blood-vessels, origin of, 528. Blumenbach's method of examining the skull, 582. Bone, 253 ; sources of, 257 ; composition, 254 ; growth of, 256. Bonito, 177. Boussingault on expiration, 39 ; on gum, 72 ; on fat, 39, 229. Bovista giganteum, 88. Bowman on kidney, 223. Brahmin, 573. Brain, 313. See Cerebrum and Cerebellum. Brazen men, 634. Bread, 33 ; use of butter on, 34 ; making of, illustrates digestion, 78 ; sets free alcohol, 79. Breath, the first, 148. Breathing, act of, 156. Bright on pancreas, 71. Bronchial tubes, 159. Brown-Sequard on muscle, 443 ; ou rigor mortis, 453 ; on spinal cord, 299. Bruchium, gardens of, 621. Bud, its nature, 469. Budding, 469, 535 ; reproduction by, 495, 535. Buffon on infancy, 539. Buffy coat, 114. Burning lenses, 401. Butter, making of, 31. Califoknians, 576. Calorific hypothesis of vision, 599. Calorifacient digestion, 63. Camelopard, 491. Camera obscura, 381. Camper's method of examining skulls, 58). Canaliculi, 253. Canals, semicircular, 375. Cape of Good Hope, discovery of, 34, 631. Cape Hyrax, stomach of, 59. Capillary Vessels, 39, 141, 160; move- ment of blood in, 145 ; of muscle, 459. Capillary absorption, 103 ; attraction, 104 ; propositions respecting, 105; motion, 131. Capillary circulation, 142 ; phenomena of, 145 ; in acardiac foetus, 144 ; in asphyxia, 145; local excitement, 144. Carbohydrates, 71 ; turn into fat, 81 ; make up deficit of albumen, 39. Carbonic acid excretion, 164; sources of, 164, 252 ; introduces oxygen, 165 ; decomposed by light, 461. Carcinus msenas, 510. Career of man, 612 ; of organic form, 456. Carnivora consume themselves, 36 ; fibrin of their blood, 123 ; find fat in their food, 248. Carp, lung of, 157. Carpenter on nervous system, 259 ; on sen- sorium, 319; on analogy between spinal and ventral cords, 307 ; on generation, 537. Casein, 30, 31, 231 ; pre-exists in plants, 36 ; changes into fibrin, 35 ; dissolves phos- phate of lime, 35. Castle building, 330. Catamenia, 519. Caudate vesicles, 264. Causes of sleep, 552. Cells, primordial, 458 ; simple and nucle- ated, 492; animal, 496 ; circulation in, 132. Cells of blood, 116; uses of, 129; numbers of, in different animals, 121. Cells of kidney remove nnoxidized bodies, 223. Cells in lungs, 159. Cells, nerve, 264. Cellulose, 71. Centre of intellect, 635. Centres of nerves, 290. Centripetal and centrifugal fibres, 265. Cephalic ganglia, 271, 607. Cerebellum, 322 ; development of, 314; ex- periments on, 323 ; structure and function of, 322. Cerebral sight, 401. Cerebro-spinal fluid, 326. Cerebrum, structure of, 317; development of, 314; aspects of, 316 ; tracts of, 318; ganglia at base, 319; weight of, 325; at- mospheric pressure on, 326. Cheese, making of, 31. INDEX. G4] Cheselden's case of cataract, 419 ; on the ear, 365. Chest, type of, 161, Chilians, 576. Chimpanzee, 581. Chinese, 57-1: ; writing, 636. Chitin in wings of insects, 71. Chlorine and hydi'ogen, 471. Cholepvrrhin, 124. Cholera, eftect of, 22. Cholesterine, 275. Chorda dorsalis, 528. Chorion, 523 ; changes in, 525. Choroid coat, 384 ; function of, 394. Chossat on inanition, 178, 243. Christian Church, 626 ; spread of, in Amer- ica, 598. Chromatic aberration, 386. Chronometer, illustration of heart by, 140. Chyle, 53 ; absorption of, 87 ; causes of the flow of, 89 ; composition of, 92 ; corpuscles, first appearance of, 94 ; action of water and acetic acid on, 94. Chyme, 53. Cilia, 431. Ciliated animacule, 432. CiECULATioN, 145 ; objects of. 111, 134 ; changes during, 126 ; course of, 134 ; in plants, 132 ; in lawer animals, 135 ; action of heart in, 138 ; sounds of heart in, 139 ; nervous influence on, 140; foetal, 531 ; pla- cental, 527 ; portal, 134 ; connection of parts by, 112 ; dependence of, on respira- tion, 133. Civil law, 628. Civilization, effect of climate on, 599 ; com- pared with barbarism, 604. Classification of natural history, 506 ; of skulls, 586. Climates, botanical, 481. Clock, illustration from, 485. Coagulation of blood, 1 13. Cochlea, 364, 368 ; comparative anatomy of, 373. Cceliac axis, ramifications of, 49. Coinage, introduction of, 620. Cold-blooded animals, 172, 176. Coleridge on dreams, 556. Colladon on diving-bell, 366. Color, origin of, 589. Colored rays, effect of, 461. Colostrum, 225. Combustion, artificial, 17 ; organic, 17, 18. Commerce, origin of European. 619. Comminution instruments, 40. Commissures, function of nervous, 280. Comparative history, 612. Compartments of ruminant's stomach, 60. Complemental air, 165. Complexion of man, 571, 572. Conception, 530. Condensing action of membranes, 155. Condition of dreams, 558. Condorcet on di'eams, 556. Conductibility in nerves, 265. Conferva, 495. Congelation, perpetual, 473. S Conjugation, modification of, 515. Consonants, 356 ; explosive and continuous, 357. Constant temperature, problem of, 176. Constituents of plants, sources of, 463 ; of the blood, functions of, 125. Contarini, Cardinal, on circumnavigation, 625. Contractile fibre-cells, 435. Contractility of muscle, 442, 449 ; nature of, 442. Contraction, hypothesis of, 451 ; by water, 451 ; by touch, 452 ; after death, 444. Control of heat by nerves, 186. Converging media, 381. Cooling agencies, 184. Cord, spinal, 294 ; conduction by, 299. Cornea, 384. Corpuscles, of milk, 225 ; of fat, 246 ; of blood, 116; origin of, 101, 115; colorless, 93, 115; of chyle, 93, 143; proportion of, 125. Cotyledons, 526. Couch on metamorphosis, 510. Course of the bile, 202. Crab, edible, 510. Cranial nerves, 333. Creatine, 447. Crevice, passage of water through, 105. Crime, tendency to, 543. Crises, change by, 148, 484. Crus cerebri, 314 ; cerebelli, 314, Crusades, 630. Crystalline lens, 386. Crystals of blood, 119. Cutaneous absorption, 98. Cuvier on organisms, 466. Cycles of progress, 512. D. Dalton on corpus luteum, 622 ; on diffusion, 152. Daubenton on skull, 580. Davy on animal heat, 178; on meconium, 203; on protoxide of nitrogen, 412. Deafness in diving-bell, 366 ; partial, of infe- rior animals, 377. Death, 560 ; from accident and old age, 561. Decay, 243. Deception, 404 ; of touch, 421. Deleau on the voice, 356. Descartes on insects, 609. Descent of sap, causes of, 87, 132. Despretz on animal heat, 182. Deutencephalon, 292. Development, 505 ; of the ear, 378 ; of the eye, 380 ; of muscle, 440 ; geometrical modes, 447; ofbii'd, 35; of heart, 135. Diaphragm movements, 161. Diastose salivaire, 45. Diet, 34. Differences in men, 563. Differentiation, 500 ; causes of, 502 ; in- fluence of heat on, 503 ; epochs of, 504 ; defined, 511. Diffusion of gases, 152 ; force of, 153, 156 ; general facts of, 156 ; effect of, 162. S 642 IXDEX. Diffusion of influence in granular nerve ma- I terial, 268. DiGESTio>-, nature of, 16, 40, 52, 63 ; object of, I 61,66; histogenetic, 63 ; calorifacient, 63 ; is mechanical and chemical, 57 ; double, ; 46 ; processes of, as insalivation, 40, 46 ; deglutition, 46 ; passage into duodenum, 52, 67 ; passage along intestine, 67. Digestion, artificial, 52, 54. Digestion of gum, 71 ; of cellulose, 71 ; of starch, 72 ; of sugar, 72 ; of fat, 76 ; intes- tinal and stomach, contrasted, 81. Digestive tract, divisions of, 48 ; of insect, 58 ; of vai-ious animals, 59 ; juices, their or- ganic ingredient, 77 ; power injured by sal- i iva, 50. I Discs of muscular fasciculi, 436 ; of blood, see Cells. Discus proligerus, 520. Distribution, vertical, of plants, 473 ; of heat, 473. Diurnal amount of air used, 166. Diurnal variations of heat, 178. Donne on saliva, 44. D'Orbigny on Inca Indians, 487. Dormouse, stomach of, 59. Dorsal cord, 293 ; lamina, 527. Double trains of thought, 329. Doubleness of brain, 327. Dowler's experiments, 444. Draper, J. C, on respiration, 168, 239 ; on urea, 220. Dreaming, 555. Dro\\Tiing, restoration from, 133. Drum of ear, 364. Duality of mind, 329. Duct, thoracic, 90. Ductless glands, 211. Ducts, dotted, 498. Dufay, law of, 104. Dugong, heart of, 136. Dulong on animal heat, 182. Dumas on fat, 248. Duti-ochet on endosmosis, 106. Dyslysin, 83. Dytiscus, 438. E. Eae, structure of, 376 ; external, 360; action of, 359 ; auditoiy nen-e of, 368 ; labyrinth of, 375 ; tvmpanum of, 365. Education, effect of, 330, 543. Edwards, Milne, on cnastaceans, 488 ; on fat, 248. Egg, development of bird from, 35. Egypt, 613, 614. Elasticitj-, heat of, 185. Elective filtration, 196. Electrical tastes, 430 ; currents in muscles, 443 ; conductors, neiTes resemble, 266. Electricity, 275. Eleventh pair, 342. Elixir of life, 633. Elliptical skull, 586. Emkeyo, 538 ; germinal membrane of, 525 ; -vertebral column of, 532 ; vascular area of, 527; allantois, 538 ; circulation, 531 ; in- fluence of mother, 534 ; size and weight ol. at birth, 540, 541 ; viability of, 545. Embrj-onic development of brain, 313; oi circulating apparatus, 531 ; forms, 507. Emergence of impressions from brain, 408. Emotions, mental, 290. Empiricism, extinction of, 25. Endocardium, 137. Endochrome, 493. Endogenous generation, 496. Endosmosis, 105, 107, 131 ; through films, 154; through stucco, 107; force of, 107. 153. Enteric juice, 369. Epencephalon, 292, 528. Epidei-mis, 233 ; functions, 234. Epithelium, 197, 234 ; cylindiic, tesselated. ciliated, 197. Epochs of globe, 481 ; of life, 547. Equilibrium, conditions of, 10, 22, 560. Erect vision, 396. Esquimaux, 568. Europe, primitive state of, 613. European historj", 610. Eustachian tube, 367. Euthanasia, 561. Evapioration, 185. Excretion, 213. Exhalation by lungs, 21, 22. Exosmosis, 106, 131. Expectoration, 47. Explosive consonants, 357. Extinction of Indians, 600. Extinctions, 484, 488. Eye, structure of, 382 ; nervous mechanism of, 389, 394 ; accessary apparatus of, 399. Eyeball, motions of, 401. Eyebrows, 399. Eyelids, 399. F. Fabricius ae Aquape>-dente on veins, 13fi. Eseces, 83. Fair races, disappearance of, 591, 636. Falling, sensation of, 559. Fasciculi of muscle, 433, 436 ; digestion oi. 54. Fat, 246 ; oxidizes gi-adually, 252 ; relation of, to bile, 207 ; to nitrogenized tissue, 250 :. in articles of forage, 229 ; emulsifying of. 71 ; produced from carbohydrates, 81 ; in- troduction into villi, 91 ; saponification of. 93. Faunal groups, 568. Feeling and touching, distinction between. 422. Female and male compared, 546. Fenestra ovalis and rotunda, 361. Femients, 45, 80. Feudal system, 631. FiBEES-, 30, 93, 97, 114; loss of, .52; ve..:et.:- ble, 33 ; not an effete body, 98 ; organiz;;- tion, 113; difference of, in blood and nni>- cle, 114; variations in quantity, 122. Fifth pair of neri-es, 334. INDEX. 643 Filtering action of glands, 191. Filtration, elective, 19G. Final agony, 562. Finite nature of knowledge, 289. Fire-place, exhausting nature of, 181. First breath, 485. First pair of nen-^es, 425. Fishes, digestion of, GO ; circulation in, 135 ; respiration of, 150, 157. Flame and plant, analogy between, 470. Floral groups, 568. Flour, 33. Foetus, circulation in, 531. See Embryo. Follicles, gastric, 49, 50 ; varieties of, 51. Food, 16, 26; sources of, 27; classification of, 27 ; value of, 28 ; different kinds of, 27, 28 ; of carnivora, 36 ; of herbivora, 36, 37 ; nitrogen, 27, 35 ; movements of, 53 ; ad- justs temperature, 179; demand for, 179; allowance of, 1*1 ; digestibility of, 36, 66 ; formed by plants and destroyed by animals, 37 ; minimum quantity of, 38. Foramen magnum, 580. Force of endosmosis, 107. Forgetfulness of dreams, 557. Formic acid, 240. Fourcroy on perspiration, 240. Fourth pair of nerves, 334. Fowl, digestive tract of, 58. Franklin on heat, 380. Frerichs on food, 35 ; on saliva, 44. Frog, lungs of, 159 ; development of, 509, Front view of skull, 585. Future state, 551. G. Galileo, 455. Gall on brain, 259. Gall-bladder, 199. V Galvani, experiments of, 443. Ganglia, structure of, 263 ; spontaneous func- tion, 289 ; of sympathetic, 140, 264 ; of special sense, 315 ; cephalic, 607. Gases of intestine, 82. Gastric changes are subdivisions and assim- ilation of water, 62. Gastric juice, 49, 50 ; quantity of, 52 ; acid of, 52, 54 ; relation of nervous influence to, 54. Gelatine, 64, 65. Gemmation, 534. Generation, 515, 516 ; spermatozoa in, 517, 618. Geogi-aphical distribution, 567. Geography of plants, 472. Geological changes, 480. Geometrical modes of development, 457. Germ-cell, 519. Germinal membrane, 525 ; its layers, 527 ; vesicle and spot, 521. Germination, 458 ^ heat of, 176. Gestation, 533. Gibraltar, Straits of, 620. Gills, 135, 150, 157. Gland, 189 ; type of, 189, 197 ; vicarious ac- tion of, 190 ; filtering action of, 190 ; par- otid, 43 ; salivary, 43 ; submaxillar}', 43 ; sublingual, 43 ; mesenteric, 89 ; ductless, 211 ; mammary, 225. Glandular blood, change in, 190. Globulin, 118. Glosso-pharyngeal nerve, 338. Glucose, 73. Gluten, 33. Glycerine, 245. Goodsir on lymphatics, 97. Graafian follicle, 521. Gradual death, 561. Grafting, 469, 535. Graham on diffusion, 152, 154. Greeks, 613 ; schools of, 617. Growth, 511, 538, 540; conditions of, 465. Guinea, negro of, 579. Gum, digestion of, 71. Gundelach on fat, 248. H. Habits of nations, 566, 569 ; of insects, 605. Hsematin, 118; analysis of, 119. HiEmatococcus binalis, 494. Hair, 236. Hall, discoveries of, 259. Hallucination, 402. Harvey on circulation, 130. Hearing, sense of, 359 ; structure of organ of, 360 ; use of tympanum in, 364 ; audi- tory neiTe of, 368. Heart, 135; fibres of, 137; valves of, 138; development of, 135; of dugong, 136; ac- tion of nerves on, 140; statement of action of, 147 ; number of beats of, 130. Heat, 17, 18, 19, 20; che«k upon, 21, 22, 184; equilibrium of, 22 ; animal, 175, 177 ; car- bonic acid, relation to, 19, 20, 176 ; varia- tions, 178 ; diurnal, 178 ; extreme, endura- ble, 178; annual, 179; source of, 182; of light rays, 389 ; removed from muscle, 447 ; quantity for plants, 477 ; intensity and quantity of, 477 ; decline of, 488 ; relations of, 572 ; effect of, on skull, 590. Heaths, absence of, from America, 474. Height of man, 541. Helmholtz on nef\'e, 266 ; on muscle, 445. Hepatic artery, 200 ; cells, duct, vein, 200, 206. Herbivora, 36. Herculaneum, 465. Hereditary transmission, 590. Hermaphroditism, 574. Hibbert on apparitions, 408. Hippocratic face, 561. Histogenetic digestion, 40, 63. History a branch of Physiology, 604 ; Euro- pean, 610 ; universal, 611 ; prognostics in, 612; comparative, 612. Homogenesis and heterogenesis, 511. Hot-blooded animals, 176. Hottentots, 577. Hubbenet, table by, 49. Huber, 556. Human groujjs, 568. 644 INDEX. Humboldt on respiration, 158 ; on plants, 471. Humors of the eye, 386. Hunter on reflexa, 596. Hutchison on respiration, 166. Hybemating animals, 172, 183. Hydra, 51, 52, 432, 501, 534. Hydraulic action of auricle, 146. Hydrochloric acid, 52, 62. Hydrogen, use of, 17, 19. Hj'poglossal nerve, 343. I. Ideal type of man, 565. Idiot, composition of brain of, 273. Illusions, 402. Imago, 511. Immortality of the soul, 415. Impersonal operations, 287. Impressions, vestiges of, 288. Improvability of man, 15. Inanition, experiments on, 178, 243. Inca Indians, 487. Incombustible men, 634. Independence and immortality of the soul, 285. Independent action of each half of the brain, 328. Index of prohibited books, 624. Indians, 575 ; extinction of, 600. India-rubber, diflfusion through, 152, Individuality, nature of, 468. Indo-Europeans, 573. Infancy of man, 538. Inflorescence, heat of, 176. Influence of agents on man, 563, 567, 671 ; of parent on child, 534. Influential arc, 282. Infusorials, heat of, 177. Inosite, 447. Inquisition, establishment of, 624, Insalivation, 40. Insanity of retina, 406. Insect, digestive tract of, 58 ; cephalic gan- glia, 271 ; nei-vous system, 271 ; respira- tion of, 157; development of, 510; struc- ture and habit of, 603, 605 ; memory and metamorphoses of, 608. Instantaneousness of dreams, 556. Instinct distinguished from reason, 603. Insubordination of one hemisphere, 329. Intellect, maximum of, 591 ; centre of, 635. Intensity, adjustment for variations of, in eye, 388. Intensity of heat, 477, 572. Interference, mechanism of, in ear, 372 ; of nen'ous impressions, 269. Interstitial death, 244; movements, 151. Intestine, length of, 42 ; salts and gases of, 82 ; digestion in, 63, 68, 81 ; contents, changes of, 83 ; section of wall of, 85 ; per- istaltic movements of, 68 ; passage of food through, 67, 81 ; glands and secretion of, 69, 70. Inverse problems, 284, 482. .Inverse Vision, 401 ; use of, 416. Ii-is, 385. Iron acted on by gastric juice, 50 ; somxe uf. in blood-cells, 118. Irrespirable gas, action of, 133, 169. Isaacs on kidney, 217. J. Jackson on the ear, 373. Jacob's membrane, 390. Jeffreys on respiration, 165. Jesuits, 624. Jones, Bence, on urine, 221. Jones, Handfield, on hepatic cells, 206, Jones, W., on blood-cells, 117. K. Kaffirs, 577. Kamtschatdale, 575. Kangaroo, 59. Kidney, 213; structure of, 214; tubuli uri- niferi of, 215; circulation in, 215; devel- opment of, 214; vicarious action, 186. Kiestine, 231. Kolliker on skin, 420 ; on retina, 391 ; spleen. 211. Koumiss, 80. Krause on sebaceous secretion, 240. Kreatine, 447. Kune on bile, 203. L. Labteinth, 361. Lachrymal gland, 400. Lacteals, 84, 86, 87, 91, 111 ; function of, 85 ; and lymphatics, connection of, with respi- ration, 100. Lactic acid, 47, 52, 73, 74, 75. Lacunae of^one, 253. Lamina spiralis, 359. Landerer on perspiration, 240. Languages, 357. Laplandei', 568. Larva, 510. Larynx, 353 ; double, of birds, 352 ; artificial, 355. Lateral inversion, 397. Lateral view of skull, 581. Law, civil, 628. Lawrence on the leg, 580. Laycock on cephalic ganglia, 607. Leg, 580. Legumin, 33. Lehmann on absorbed nitrogen, 39 ; peji- tones, 62 ; gastric solution, 66 ; gum, 72 ; urine, 75; quantity of blood, 113; blood crystals, 120; bile, 203; kiestine, 231. Leidy on liver, 198. Length of infant, 540 ; of sleep, 553. L'Heritier on chyle, 96. Lieberkuhn, follicles of, 69. Liebig on lactic acid, 75 ; on fibrin, 98 ; on blood gases, 125. Life, conditions of, 9, 12. Light, nature of, 399 ; influence of, 459, Lime, phosphate of, 35. INDEX. 645 Liquor, san2;uinis, 121 ; aninii, 530. LiVEK, 209'; structure of, lUl), 200, 201 ; de- velopment of, 191, 198 ; secretion, 203, 205 ; sugar, 123 ; production of sugar and fat in, 207 ; destruction of blood-cells in, 209 ; absorbed material goes to, 107 ; effect of, on complexion, 588. See Bile. Localization of functions in brain, 324 ; of plants and animals, 482. Longevity, 545. Loss of perception of time, 332. Lungs, structure of, 157, 159, 160; capillaries of, 160 ; capacity of, 162 ; organic fibres of, 1 63 ; chemical changes in, 1 63. See Res- piration. Luther, Martin, vision of, 406. Luxury, effect of, on skull, 588. Lymph, 95 ; salts of, 96 ; flow of, 99. Lymphatic glands, 94. Lymphatics, distribution of, 97 ; function of, 96, 98 ; origin of, 529. M. Macedonian campaign, 620. Machines, speaking, 356. Madagascar, native of, 577. Madder in bone, 256. Magellan, voyage of, 624. Male and female, comparison of, 546. Malpighian bodies, 215 ; sac, removal of li- quid from, 224. Mammary gland, 224 ; development of, 225 ; action, 233. Man, physical aspect of, 24 ; soul of, 25 ; ma- turity of, 542. Margarine, 246. Mariolatry, 631. Marmots, 172. Mastication, 40. Matters received, 16 ; dismissed, 17. Maturity of man, 542. Meconium, 202. Medulla oblongata, 304 ; functions of, 306. Melloni on light, 389. Membrana granulosa, 520 ; decidua, 525, 526. Membranes, selecting power of, 107. Memory of insects, 608. Menstruation, 519. Mental emotions, nature of, 290. Mental hallucination, 402. Mental qualities of different nations, 592. Mental strength, maximum of, 544. Mesencephalon, 292, 528. Mesenteric glands, structure of, 89 ; plexuses, 350. Metacetonic acid, 246. Metamorphosis, 490. Metamorphosis of batrachians, 509. Metaphysics, 259. Midnight sun, 476. Milk, 29, 31, 32 ; casein of, 29, 227, 231 ; sugar of, 81, 227, 233 ; butter of, 31 ; salts of, 31, 228 ; lactic acid of, 31 ; effect of disease of, 33 ; composition of, 225, 226 ; analysis of, 226 • vicarious secretion of, 228. Mind, 24. Miracles, true, 624. Mitchell on diff'usion, 152. Mohammedanism, influence of, 629 ; spread of, in Africa, 597. Moisture, influence of, 475. Mongols, 574. Monogamy, 594. Monotheism, 601. Mortality, 545. Motion, ciliary, 431 ; muscular, 432. Motor oculi nerve, 391. Motor tract of brain, 319 ; of cord, 308. Mouth, functions of, 40. Mozambique, native of, 578. Mucous membrane, 196 ; layer, 527. Mucus, 43, 197; buccal, 43. Mulberry mass, 523. Miiller on bile, 203; on vision, 891 ; on voice, 354. Multipolar nerve-cell, 264, 268. Municipal system, 628. Muscae volitantes, 404. Muscle juice, 484, 487. Muscular fibre, structure of, 438 ; non-stri- ated, 435 ; motion of, 432 ; movements, co- ordination of, 328 ; contraction of, 486 ; reparation of, 446; blood-vessels of, 440; contraction of, after death, 444 ; develop- ment of, 440; analysis of, 441 ; capillaries of, 439 ; effects of electricity on, 443. Muza, his threat, 623. N. Nails, 286. Narwhal, 177. Nations, origin of, 568 ; habits of, 569 ; prog- ress of, 600. Natural history, classification of, 506. Negro, 579. Neill on villi, 60. Nerves, division of, 259 ; rate of conduction in, 265 ; sheath of, 261 ; fibres of, 262 ; function of fibres, 265 ; function of vesicles, 267 ; necessity of rest for, 272. Nervous agency, magazines of, 268 ; trans- mission of, 265 ; retention of, 269 ; inter- ference of, 269. Nervous arcs, 277 ; condition for action, 283 ; centres, 290. NeiTOUs system, 258 ; controls heat, 186 ; de- velopment of, 292 ; metamorphosis of, 608 ; structure and functions of, 298. Nervous vesicular matter, 260 ; ganglia, 263 ; activity, 267 ; tissue, composition of, 273 ; regeneration, 274. Ne^vjDort on insects, 309. Newton, colored rings of, 105. Nicolai on apparitions, 406. Nightmare, 559. Night sleep, 554. Ninth pair of nerves, 888. Nitrogen, use of, 16 ; in respiration, 171 ; prot- oxide of, 412. Nodal lines, 871. Non-striated fibre, 485. Nose, 424. 646 INDEX. Nucleated cells, circulation in, 131. Nucleine, 1 1 7. Nucleus, 493. Nutrition, 245, 252 ; connection with nerv- ous agency, 186, 244 ; selecting power in, 245 ; three types of, 532 ; of camivora and herbivora, 36. O. Objective opekations, 287. Ocelli, 380. Octopus, nervous system of, 279. Ocular spectra, 396. Oculo-motor nerve, 333. Odoks, sensibility to, 424 ; localization of, 426. Odyssey, 613. Oil, emulsifying of, 71 ; globules on villus, 88. Old age, 545. Oleaginous principles of food, 30, 81. Oleine, 246. Olfactory organ, mechanism of, 424. Olivary bodies, 304, 314. Omphalo-mesenteric duct, 530 ; vessels, 531. Operations, plants are, 470. Opium, effects of, 406. Optic nene, 391. Orang, 581. Organic FORai, career of, 456. Organic life, nerve of, 344. Organic periodicities connected with heat, 179. Organisms, metamorphosis of, 489. Organization, principle of, 457. Organized bodies, allotropism of, 188. Organs of sense, 359. Origin of nations, 568. Ornithorynchus, 224. Ossicles, 367. Ossification, 255. Osterlein on villi, 86. Ostrich, stomach of, 59. Oval skull, 586. Ovarium, origin of ova in, 520 ; coi-pus lute- um of, 522. Ovisac, 520. Ovum, 521 ; discharge of from ovary, 523 ; changes of, 524 ; segmentation of, 524. Owen on the ann, 380 ; on skull, 532, 584. Oxalic acid in urine, 222. Oxygen, uses of, 47, 101, 134 ; in respiration, 134, 163, 182 ; influence of, on blood, 126 ; changes albumen into fibrin, 101, 176 ; lib- erated by plants, 461. Pacinian bodies, 420. Paganism, fall of, 622. Paine, Professor, on plants, 478. Pale people, disappearance of, in Europe, 634. Palingenesis, 634. Pancreas, 68 ; juice of, 68. Pantheism, 288. Papal government, 623. Papillae of skin, 419 ; of tongue, 428. Parotid gland, 43. Parturition, 533. Par vagum, 340 ; influence of, on liver, 208. Patagonians, 578. Patella, nervous system of, 279. Pathetici, 334. Patina, 151. Pelagian tvpe, 579. Pepsin, 49', 54, 55. Peptones, 50, 63, 62. Perception of time, loss of, 332. Pericardium, 137. Peristaltic movements, 53. Peroxalate of iron decomposed by light, 461. Persecution, result of, 624. Persian empire, 616. Perspiration, 238. Persuasions, 544. Peruvian, 576. Peyer's bodies, 70, 94. Phantasms, localization of, 415. Philippine negro, 578. Philosopher's stone, 633. Philosophy, suppression of, 624. Phcenicians, 619. Phosphorus, 17, 23, 27, 32, 275. Photographic effects of temperature, 393. Phrenic nerve, 344. Phrenology, 324. Physiology, subdivisions of, 26 ; statical, 9 ; dynamical, 455. Piles of Ritter, 277. Pine, woody fibre of, 498. Placenta, 526. Plants, individuality of, 468 ; quantity of heat for, 467 ; secular changes of, 480 ; lo- calization, 482. Plasma, 121. Plastic power, 459, 471. Pneumogastric nerve, 340. . Polygamy, 594. Polype, 51. Polytheism, 601. Pompeii, 465. Pons varolii, 307. Porcupine, 59. Porpoise, stomach of, 59. Portal circulation, 119, 134, 201, 202. Ports of Egypt, opening of, 616. Posterior roots of spinal nerves, 296. Potassium, iodide of, experiments with, 47. 52. Powder of projection, 633. Pre-existence, sentiment of, 331. Prevost and Dumas on muscle, 439. Prichard on habits of men, 569 ; on skull, 580, 585. Priestley on gaseous endosmosis, 151. Primitive trace, 293, 527. Primordial cell, 458. Principle of organization, 457. Printing, 358. Prognathous skull, 586. Protein bodies removed by urine, 220, 222. Provencal on respiration, 155. Psammetichus, 615. Psychical powers, 327. INDEX. 647 Ptolemies, 621. Ptyaline, 45. Pulsation of heart, 138; of arteries, 141. Pulse, 139. Pupa, 511. Pyramidal skull, 586. Pyramids, anterior and posterior, 304. Q. QUAIN ON ADIFOCIRE, 247. Quality of sounds, estimation of, 375. Quantity of heat, 477. Quetelet, researches of, 1 5, 540. Quick respiration, effect of, 168. Quincey, De, on opium, 407. E. Radial fibre system, 390. Radiation of heat, 185. Ramlike action of heart, 147. Rarefied air, effect of, 1 83. Ray on insect habits, 606. Reaumur on digestion, 55. Reduction of temperature, 184. Reflex action, 280 ; of insects, 609. Reformation, 619, 625. Registered impressions, 414. Registering ganglia, 259 ; nerve arc, 281, 282. Registry of sounds, 358. Regnault and Reiset on respiration, 170. Repair, necessity of, 244. Repai'ation, 23. Reproduction of cells, 494 ; and develop- ment, 505 ; closes development, 513. Reptile respiration, 158. Residual air, 165. Respiration, 151, 156, 157, 170, 171, 174; water removed by, 168 ; gases of, 163, 167, 171,176; movements in, 162 ; movements of air in, 163 ; number of movements, 162 ; influence of nervous agents on, 173; gen- eral statement of, 174. Respiratory digestion, 63. Restiform bodies, 304. Resurrection of roses, 634. Retina, 390, 392, 394 ; structure of, 385, 390 ; disturbance of, 405. Retzius on stomach, 61. Reynoso on sugar, 208. Rhakotis, 621. Rhythmic contractions, 448. Rigor mortis, 452. Roman coins, 151. Roman empire, 622. Rotation of animals, 324. Rudimentary oi'gans, 491. Rudimentary sounds, 325. Rumford on clothing, 180. Ruminant, stomach of, 59. Running, 454. S. Sabbath dat, 627. Sahara, Desert of, 475. Saladin, 631. Saliva, 43 ; action of, 46 ; quantity of, 44, 47 ; specific gravity of, 44 ; composition of 45 ; action of, in stomach, 46, 50 ; aeration by, 47. Salivarv glands, 43. Salpa;, 537. Salt, use of, 62. Samoiedes, 568. Sankey on brain, 325. Sap, ascending, 87, 132. Sarcolemma, 433, 438. Scala; of ear, 368. Scherer on urine, 221. Schlossberger on brain, 274. Schmidt on albuminates, 39 ; on blood-cells, 119 ; on pneumogasti'ic, 54 ; on pepsin, 55 ; on pancreatic juice, 68 ; on intestinal wa- ter, 83 ; on transudation, 95. Schneiderian membrane, 424. Schultz on muscle juice, 434. Schwann on nerves, 261. Science, contributions of Asia to, 596. Sclerotic, 384. Scot, Reginald, on spirits, 407. Scott, Walter, on lying, 404. j Sebaceous glands, 227. I Secreted matters pre-exist in blood, 192, 195. I Secretion, 189 ; structures for, 1^3 ; by serous membranes, 193 ; by mucous, 196. ] Seeing. See Vision. I Seguin on exhalation, 238. I Selecting power, 99. i Semicircular canals, 361, 364, 374. Sensation of falling, 559. I Senses, 359. Sensorium, 281,319. I Sensory tract of cord, 303, 320 ; of brain, 320; I ganglia, 282. Sentiment of pre-existence, 331. Serous fluids, 193. Serous layer, 527. Serous membrane, 193. Serpents, legs of, 491. Serum, salts of, 96. Seventh pair, 337. Sexes, mortality of, 545. Shelter, imperfections of, 181, Sight, cerebral, 401. Silk-worm, 489. Silver balls in digestion, 55. Singing, 355. Single vision, 395. Sisocles, 582. Sixth pair, 334. Skeleton, 253, 580. Skin, 233 ; absorption by, 241 ; transpiration from, 185, 237; glands of, 235: exudation of, 185, 239. Skulls, examination of, 581 ; forms of, 582; classification of, 586 ; effect of heat on, 590. Slack on circulation in cells, 132. Sleep, 551. Slow respiration, 168. Smell, 423 ; condition of, 425. Soap-bubble, diffusion through, 153. 648 INDEX. Social mechanics, 602. Society of insects, 604. Sociology, comjjarative, G02. Sodium, chloride of, 62 ; use of, 77. Soemmering on leg, HSO ; spot of, 385, 397. Soil, influence of, 476. Solar plexus, 350. Somnambulism, 557. Song and speech, distinctions of, 352. Soul, existence of, 283 ; independence of, 285, 548. Sound, peculiarities of, 361 ; analogy of, to light, 379 ; articulate, 539. Spain, colonial empire of, 632. Spallanzani on food, 65. Speaking machines, 356. Species of plants, 479; changes in, 480, 484. Speech, 539. Spermatic fluid, 517. Spermatozoa, 517 ; development of, 518. Sperai-cell, 516. Spherical aberration, 386. Sphinx ligustri, 279, 308, 313, 607. Spinal axis, 291. Spinal coed, 294, 296 ; reflex action of, 300; comparative anatomy of, 300 ; divisions of, 296 ; connection of, with brain, 302 ; func- tions of, 303. Spinal nen^es, roots of, 303. Spiracle of insect, 157, 352. Spiral vessels, 498. Spirit, 24. Spirostreptus, 301. Spissitude of blood, 169, 190. Spitting, habit of, 47. Spleen, 211. Spongioles, 87, 466. Spontaneous gemmation, 536. Stages in introduction of air, 160. Standards, fixed physiological, 13 ; tables of, 15. Standing, 453. Stapedius, 365. Starch, 71. Star\'ation, 182. Stearine, 246. Steenstrup on generation, 537. Steno, duct of, 43. Stereoscope, 397. Still layer, 143. Stomach, 41, 42; types of, 42 ; temperature of, 49 ; regions of, 60 ; histogenetic diges- tion of, 63 ; blood-vessels of, 102 ; mucous surface of, 50, 58 ; follicles of, 50 ; hydroid nature of, 51 ; trituration by, 55 ; secife- tions of, 48 ; various forms of, 59 ; move- ments of, 52. Stove, warming by, 181. Strecker on bile, 204. Striated muscular fibre, 433, 436. Stucco, endosmosis through, 107, 152. Subdivisions influenced by heat, 79. Subjective operations, 287 ; images, 398. Submaxillary saliva, 43. Suction, act of, 228. Sudoriparous glands, 237, 238. Sulphocyanide of potassium, 43. Sulphur, 17, 23, 27. Sunlight, 458 ; consumption of, 459 ; uses of, 466 ; variation of, 483. Supplemental air, 165. Supra-renal capsules, 214. Swimming bladder, 157. Sympathetic system, 344 ; peculiar fibres of, 262 ; origin of, 345 ; connected with spinal, 345 ; ganglia of, 346. Sympathy depends on circulation, 112. Synthetical mind of Asiatic, 592. Syntonin, 438. Systemic circulation, 134. Tadpole, experiments with, 489. Talking birds, 352. Taste, 427 ; nerves of, 429. Taurine, 204, 208. Teeth, 40 ; development of, 539. Teleology, 415. Temperature, effect of, on body, 177 on skull, 590 ; extremes, 178. Tendons, 439. Tensor tympani, 365. Tenth pair of nerves, 340. Testis, 516; secretion of, 517. Thackrah on effect of want, 587. Thenard on perspiration, 240. Third pair of nerves, 333. Thoracic duct, 90. Tickling, 422. ^ Tidal air, 165. j Time, introduction of, into nen'ous mecha- ! nism, 269, 287. i Tin, trade in, 619. j Tissue, cellular, 497; mtirifomi, 497 ; fibro- ! cellular, 497; vascular, 498 ; yellow fibrous, : 499 ; white fibrous, 499 ; areolar, 499. ' Tongue, 428. Touch, structure of organ of, 417, 418 ; acute- ness of, 420 ; in animals, 421 ; connected with vision, 419. Tournefort on plants, 472. Toynbee on ear, 365. Tracts of spinal cord, 303; of brain, 318. Tradescantia Virginica, circulation in, 132. Traditions, 567. Trains of thought, 329. Transverse transmission in spinal cord, 298. Tremblev on hydra, 501. Trigemini, 334. Trisplanchnic nerve, 344. Turner on smell, 427. Twelfth pair, 343. Twins, similaritv of, 509. Tympanum, 360, 365. Type, ideal, of man, 565, 611. U. Unipolae neeve-cells, 263, 268. Universal history, 611. Urea, 447. Urine, 218 ; composition of, 219; urea con- tained in it, 220 ; hippuric acid in, 222 ; INDEX. 649 variability of, 219 ; sulphates in, 220 ; in- fluence of diet on, 220 ; saline matter of, 220. Uterine nutrition, 525 ; tubes, 525. Utricle, 416. V. VAcrrM, tendency to a, in respiration, 165. Valentin on diifusion, 163 ; on perspiration, 229 ; on food, 39. Valves of the heart, 138 ; sounds of, 139. Valvula; conniventes, 67. Variable results from invariable causes, 270, 281. Variations of heat, 179; effect of, on man, 180; of species of plants, 479. Vasculak area, 528 ; lamina, 528 ; system, origin of, 528. Vep;etable cells, circulation in, 132, 466. Veins, absorption bv, 84, 143. Ventral cord, 300, 307, 609. Ventricles, 138; force of, 139. Venturi, principle of, 90. Vermiform appendix, 63. Vernois, table from, 53. Vertebra, 528. Vertebral canal, 294. Vertebrata, 294. Vertical view of skull, 582. Vesicular matter, composition of, 274 ; re- lations of, 315. Vestibule, 374. Vestiges of nervous impressions, 269, 288. Vibration of sound, time measured by, 372. Vicarious action, 47, 190. Vierordt, 164. Villi, 84, 86, 87, 110 ; cells of, 88 ; action of, 110. Vircliow on adipocire, 247. Vision, 379 ; comparative anatomy of, 880 ; single and double, 395 ; inverse, 401. Visions, 404 ; conditions of, 410. Visual hallucinations, 403. Vital principle, 24, 25, 55, 108, 456. Vital spark, 460. Vitreous humor, 385. Vocal sounds, 352, 354. Voice, 351 ; artificial larvnx, 355; pitch of, 356. Volkmann on muscular contraction, 276. Volume of contracting muscle, 450. Volvox globator, 511. Von Bar, law of, 514. Von Becker on carbohydrates, 39 ; on sugar. 73. Vowels, 356. W. Walking, 453. Wallace on eye, 385. Want, effect of, 587. Wannth, artificial, 181 ; increased quantity required in sleep, 554. Wasmann on pepsin, 55. Wasp, habits of, 606. Waste of tissue, 12, 23, 52. Water, use of, 16, 21, 22 ; solvent power of, 21 ; use in milk, 29 ; absorption of, 52 ; quantity exhaled, 168 ; cooling effect of, 185; of blood, 121. Wave in blood, 141. Weaning of plants, 465. Weber on pelvis, 587 ; on quantity of blood, 113 ; on standing, 453. Weight of man, 13, 14, 541 ; of infants, 14. Whale, 491. Wheatstone, 397. Whispering, 356. White on arm, 580. Wigan on duality of mind, 329, 331. Willow, 469. Wilson on heart, 136. Wine-making, 78. Wolffian bodies, 150, 533. Women in Asia and Europe, 593. Words, origin of, 356. Worship, public, influence of, 628. Writing, 358, 610, 615, 635. Zigzag appearance of muscle, 439. Zimmerman on respiration, 1 70. Zinc acted on by gastric juice, 50. Zona pellucida, 523, 525. Zoospores, 496. Zygnema quininum, 515. THE END. Lossing's Pictorial Field-Book of the Revolution ; or, Illustrations, by Pen and Pencil, of the History, Biography, Scenery, Relics, and Traditions, of the War for Independence. 2 vols. Royal 8vo, Muslin, $8 00; Sheep er.tra, $9 00; Half Calf, $10 00; Morocco, gilt edges, $15 00. A new and carefully revised edition of this magnificent work is just completed In two impe- rial octavo volumes of equal size, containing 1500 pages and 1100 engravings. As the plan, scope, and beauty of the work were originally developed, eminent literary men, and the lead- ing presses of the United States and Great Britain, pronounced it one of the most valuable his- torical productions ever issued in America. The preparation of this work occupied the Author more than four years, during which he traveled nearly ten thousand miles in order to visit the prominent scenes of Revolutionary his- tory, gather up local traditions, and explore records and histories. In the use of his pencil, he was governed by the determination to withhold nothing of importance or interest. Being him- self both artist and writer, he has been able to combine the materials he had collected in both departments into a work possessing perfect unity of purpose and execution. The prime object of the Author in arranging his plan was to reproduce the history of the American Revolution in such an attractive manner, as to entice the youth of his country to read the wonderful story, stxidy its philosophy and teachings, and to become familiar with the found- ers of our Republic and the value of their labors. In this he has been eminently successful ; for the young read the pages of the Field-Book yf'iih. the same avidity as those of a romance; while the abundant stores of information, and the careful manner in which it has been arranged and set forth, render it no less attractive to the general reader and the ripe scholar of more mature years. Explanatory notes are profusely given upon every page in the volumes, and also a brief bi©- graphical sketch of every man distinguished in the evants of the Revolution, the history of whose life is known. A Suppplement of forty pages contains a History of the Naval Operations of the Revolution ; of the Diplomacy ; of the Confederation and Federal Constitution ; the Prisons and Prison-Ships of New York ; Lives of the Signers of the J)eclaratio7i of Independence, and other matters of cu- rious interest to the student of our history. A new and very elaborate Analytical Index has been prepared, to which we call special atten- tion. It embraces eighty-five closely printed pages, and possesses rare value for every student of our Revolutionary history. It is in itself, a complete synopsis of the History and Biography of that period, and will be found exceedingly useful for reference by every reader. As a whole, the work contains all the essential facts of the early history of our Republic, which are scattered through scores of volumes, often inaccessible to the great mass of readers. The illustrations make the whole subject of the American Revolution so clear to the reader that, on rising from its perusal, he feels thoroughly acquainted, not only with the history, but with every important locality made memorable by the events of the "War for Independence; and it forms a complete Ghiide-Book to the tourist seeking for fields consecrated by patriotism, which lie scattered over our broad land. Nothing has been spared to make it complete, reliable, and eminently useful to all classes of citizens.- Upward of THIRTY-FIVE THOUSAND DOLLARS were expended in the publication of the first edition. The exquisite wood-cuts, engraved under the immediate supervision of the author from his own drawings, in the highest style of the art, required the greatest care in printing. To this end the efforts of the publishers have been di- , rected ; and we take great pleasure in presenting these volumes as the best specimen of typo- graphy ever issued from the American press. The publication of the work having been commenced in numbers before its preparation was completed, the Volumes of the first edition were made quite unequal in size. That defect has been remedied, and the work is now presented in two volumes of equal size, containing about 780 pages each. PUBLISHED BY HARPER & BROTHERS, FRANKLIN SQUARE, NEW YORK. 2 LOSSING'S PICTORIAL FIELD-BOOK OF THE REVOLUTIOK From numerous Complimentary Letters received by the Author and Publishers, the following are se- lected as specimens of the opinions of men familiar with the subject, and well known to the Public. iFrom the Hon. Edward Everett.] Boston, 15th October, 1655. My Dear Sir, I have much pleasure in expressing my very favorable opinion of your " Field Book of the Revolution." I have found it one of the most useful books of reference in my possession, for the period which is covered by it. I have never consulted it. without finding in it every thing which could reasonably be expected from such a work, and gen- erally much that is not to be found elsewhere. Besides collecting all that is contained in the best authorities, your laborious personal examination of th? interesting localities, and the tasteful and spirited pictorial illustrations intro- duced by you, have enabled you to give great distinctness to our knowledge of Revolutionary events and scenes. I remain, Dear Sir, very respectfully yours, CL-^^^'^^o^-c^'^y^-'^^ oZu^q-'-c^f'J' {Trom the President of the United States.'j Washington, January. 7, 1853. Dear Sir, A splendid copy of your Field-Book of the Revolution came to hand on the 15th inst. for which I beg leave to re- ttu-n vou iny sincere thanks. I have only found time to glance at its contents, and its rich and beautifuriUustrations, but I'can not doubt that when 1 shall have more leisure, 1 shall read the whole work with pleasure and profit. I consider that you have rendered a great service to the country by publishing so interesting and useful a work upot; that great event in our national history, and again I beg leave to repeat to you my thanks for the honor you hav« done me in presenting me this beautiful copy. Respectfully yours, t^^uZ^Ou^Z^ ,/i(U->^^ '^0 {From. Robert Chambers, Editor of Charnbers^s Edinbwgh Jowmal, Chamiers's Miscellany, etc., etc ] London, August, 27, 1653. 1 had the pleasure three evenings ago of receiving your letter of the 26th ult. accompanied by the copy of your Pictorial Field-Book of the Revolution, which you have done me the honor of sending by our common friend Mr. Wil- son. When I tell you that I have hardly done any thing since but read and pore over your book — read it for hours in mv bed and for hours sitting up — you will see some reason to believe that I arn not ungrateful for it. It is indeed a book entirely after my own heart : and large as it is. and occupied as I arn. I shall not be content till I have perused it all. The whole storj- of the American War for Independence engages my warmest sympathies for the patr otic par- ty, and to see so many personal and local traits of the conflict here gathered together, and illustrated so vividly, is a treat of the highest kind. It is but speakine the soberest truth to say, that you have performed, in the most success- ful manner, a task which your country will never cease to thank you for undertaking, while any sense of the serv- ices of the patriots of 1775^1783 remains. Respectfully and sincerely yours, ^Le/d'^'^iyi^ ^ iFrom Messrs. Jacob Abbott, Author of " Young Christian Series," " Abbott's Histories," etc., John S. C. Abbott, Author of " Memoirs of Xapoleon," and Goeham D. Abbott, Principal of the Spingler Institute.'^ We consider Lossing's Pictorial Field-Book of the Revolution, an eminently desirable work for school Libraries throughout the Country, for the Ibllowing reasons : 1. The subject of it is the foundation of this Republic, a subject on which it is of the highest importance that the youth of this <'ountry- should be well informed 2. The work is written with great care, and is thoroughly reliable in aU its statements. 3. The plan and the design of the work are such that it contains a very large amount of instructive and entertain- ing details, which renders it verj' attractive in the hands of the young. 4 The maps, plans, and pictorial illustrations, which invests the work with so powerful a charm for youthful read- ers, are not mere embellishments intended to allure and amuse, but are made the means of conveying accurate antJ important geographical and historical knowledge. These illustrations, which have been obtained for the work at great expense of time and labor, adapt it, in an admirable manner, to instruct all readers, and young readers especi- ally, and to lead them to form clear, discriminating, and exact ideas of the facts connected with our early history. 5. The moral influence of the work is, in every respect, of the best and most unexceptional chEiracter. LOSSING'S PICTORIAL FIELD-BOOK OF THE REVOLUTION. 3 IFrom the Rev. Francis L. Hawks, D. D., LL. D.] New York, January 4, 1853. My Dear Sir, C heartily congratulate you on the completion of your valuable and deeply interesting " Pictorial Field-Book of the Revolution," and wish that a copy of it might go into the hands of every American child. An acquaintance with the incidents o'four Hevolutionary struggle can not but nurture in the minds of our young people an appreciation of that freedom and union which cost our fathers so much. An enlightened patriotism will necessarily result. As to the artistic illustrations, they need not any man's commendation — they speak for themselves. I, for one, thank you for the book, and hope you may live to make many others about our own dear country quite as good. Very truly yours, T^iCt^H^C^ Q^ ufh^u^ \J?rom the Hon. John P. Kennedy, Secretary of the Navy.'i I have had frequent occasion to admire this work as I saw it in detached parts, and now, having it complete, I find great gratification in the perusal of its beautiful sketches, so rich in the legends of the Revolution, and so artistically illustrated by your pencil. From the rambling, desultory character of your researches, you have the advantage of ex- citing a constant expectation in your readers of pleasant surprises and most agreeable alternations into the nooks and eddies of history, which receive additional interest from the graceful spirit of the narrative. I have never met a book which more happily supplies a fund of instructive reading for tlio.se broken hours (horee subseciva) which I am able to gather out of the intervals of business, and none that ever illustrated an historical epoch more fully, in its way, than this. I am sure the Country will appreciate it as it deserves, and will do justice to the abdity which you have manifested in constructing it, the extreme accuracy of your patient labor, and the perfect art of the engraved pictures whicb are so thickly studded over its pages. With the heartiest good wuhOE for your success, I am, my Dear Sir, ' Very truly yours. J^r^ ^ Jc^yv^^z^^ iProm Jaeed Sparks, LL.D the Eistorian.l Cambridge, March, 19, 1853. 1 have perused Mr. Lossing's " Field-Book of the Revolution," duiing the progress of its publication, and have found m)-self much interested and instructed by the large collection of facts which the author's extensive researches have enabled him to brinz together, and the manner in which he has presented them. As illustrative of local inci- dents and scenery, with which some of the most important events of the Revolution are connected, and as containing numerous biographical notices of individuals who were actors in these events, the whole work possesses a high val- ue. The details in which the narrative abounds, convey a lively impression of the spirit of the times, and the work, as a whole, may be justly regarded as contributing essential aids to a full understanding of the operations of the war described by more formal and elaborate histories. Sfh^cL^-mixA/iiA iFrom Dr. Beck, Secretary of the Board of Regents of the State of New York.l Having carefully read Mr. Lossing's work, I cordially unite with others in commending it as one of great value and interest, and worthy of a place in every public and private library in our country. iFrom Washington Irvino.] I have the work constantly by me for perusal and reference. While I have been delighted by the^ freshness freedom, and spirit of vour narrative, and the graphic effect of your descriptions, I have been gratified at finding how scrupu- louslv attentive vou have been to accuracy as to facts, which is so essential in writmgs of an historical nature. There is a genial spirit throughout vour whole wwk that wins for you the good-will of the reader. ^ .,. . I am surprised to find in how short a time vou have accomplished your undertaking, considering you have had to tray el "from Dan to Beersheba" to collect facts and anecdotes, sketch, engrave, WTite, print, and correct the press-and, with all this, to have accomplished it in so satisfactor>- a manner. I think it a work calctilated to make its way into every American famUy, high and low, and to be kept at hand for constant thumbing by old and young. Believe me, my dear sir, with cordial regard, Yours very truly. 4 LOSSING'S PICTORIAL FIELD-BOOK OF THE REVOLUTIOlf. iFromtheHon. George Bancroft.] New York, 1st January, 1853. My Dear Sir, The good opinion which I expressed to you some time ago of your " Field-Book of the Revolution" has been confirmi ■! by every succeeding number. Your pictured pages are not only charming and instructive from the illustrations, bi.i you have used copious materials ; have given your narrative in an unafl'ecied and attractive style, and have brouglil to your work uniform candor of judgment. 1 shall be very glad to hear of any success that may contribute toward yew remuneration ; and I often take occasion to express my high estimate of the merit of your work. i remain your friend, [From the Hon. David L. Sw in. President of the North Carolina University. 1 I have read with care and increasing Interest a considerable portion of Lossing's " Pictorial Field-Book of the Revo - lution." In the chapters which relate to those sections of the Union, and the series of events with which 1 am mo n, I retKn you my thanks, and I trust you will find a generous public to reward you for your toils and expenses. I am very sincerely your friend, /^%3U~- ^r^^T^^--^^^ iFrom the Neiv York State Librarian.'! Albany, January 12, 1853. Mv Dear Sir, . . It affords me great pleasure to say that I have examined your " Pictorial Field-Book of the Revolution," and ap- prove it most heartily. Independently of its masterly execution, the design of the work is original and excellent. The Piihject is treated in a familiar, yet dignified manner, the reader rainbling with you from point to point celebrated in our Sevolutionary annals, and listening to the stories and traditions connected with each spot. An.I not only is the subject addressed through tlie medium of words, but you have brought the exquisite delineafnii of your pencil in aid of your task. Thus the battlefield, old fort, and homestead, made memorable by some RevcJu- t-ona--y event, are brought to the knowledge of the eye, and rendered, in connection with your picturesque descriptions. doubly interesting and valuable. To the youth, particulary of our country, the " Pictorial Field-Book," must prove exceedingly valuable, clothni';. as it does, our Revolutionary history in the most attractive garb by its scenic delineations and legendary facts. With my best wishes, believe me, very truly yours. ALFRED B. STREET, State Librarian. iFrom the Regents of the University of the State of New York.-\ Albany, January 14, 1853. Sir, At a meeting of the Regents of the University of the State of New York, held January 13, 1853, on motion of the Secretary of State, it was unanimously ^ , j > . u Resolved, That Lossing's Field-book or the REVOLrTiON be placed in the list of books reccommended to bf purchased by Academies for their libraries. _ „, „„„., „ T. ROMEYN BECK, Seoretaby L O O M I S' Series of School and College TEXT- BOOKS. Tho Course of Mathematics by Prof. Loomis has now been for several years before the public, and lias received tlie general approbation of teachers throughout the coun- I. y. The following are some of the institutions in which I lis Course has been introduced, either wholly or in part : Dartmouth College, N. H. , Williams College, Mass. ; Am- Inrst College, Mass. ; Yale College, Conn. ; Trinity Col- lege, Conn. ; Wesleyan University, Conn. ; Hamilton Col- l3ge, N. Y. ; Hobart Free College, N. Y. : New York University, N. Y. ; Rochester University, N. Y. ; Dickin- son College, Penn. ; Jefferson College, Penn. ; Alleghany College, Penn. ; Lafayette College, Penn. : St.Jamcs's CoUogc, Md. ; Emory and Henry C^ollegc, Va. ; Bethany College, Va. ; South Carolina College, S. C. ; La Grange College, Ala. ; Transylvania University, Ky. : Cumber- land College, Ky. ; Western Reserve College, Ohio ; Ober- lin College, Ohio ; Antioch College, Ohio ; Asburj' Uni- versity, Ind. ; Wabash College, Ind. ; Illinois College, 111. ; Shurtleff College, 111.; McKendree College, 111.; Knox College, 111. ; Missouri University, Mo. ; University of Michigan, Mich. , Beloit College, Wisconsin. A Treatise on Arithmetic, Thereotical and Practical. 12mo. This volume explains, in a simple and philosophical manner, the theory of all the ordinary operations of Ariib- inetic, and illustrates them by examples sufficient'- nierous to impress them indelibly upon the mind liie pupil. It is designed for the use of advanced s .dents in our public schools, and furnishes a complete preparation for the study of algebra, as well as for tlie practical dutie.") of the counting house. This volume is in press, and will be published in a few weeks. Elements of Algebra. Designed for the use of Beginners. Seventh Edition. This volume is intended for the use of students who have just completed the study of arithmetic. It is believed that it will be found sufficiently clear and simple to be ;>.,iapted to the wants of a large class of students in our <• jnimon schools. It explains the method of solving equa- t Ions of the first degree, with one, two, or more unknown quantities , the principles of involution and of evolution ; the solution of equations of the second degree ; the prin- ciples of ratio and proportion, with arithmetical and geo- metrical progression. Every principle is illustrated by a 12mo, pp. 268, Sheep extra, 621- cents. copious collection of examples ; and a variety of miscel- laneous problems will be found at the close of the boo!;. I have used Loomis' Elements of Algebra in my sehu- 1 for several years, and have found it fitted in a high ri - gree to give the pupil a clear and comprehensive kiiuvvl- cflge of the elements of the science. I believe teachers of Academies and High Schools wiil find it all that they can desire as a text-book on this branch of Mathematics. — Prof Alonzo Gray, Brookiyn Heights Seminary. A Treatise on Algebra. Thirteenth Edition. 8vo, pp. 834, Sheep extra, $1 00. This treatise is designed to contain as much of algebra as can be profitably read in the time allotted to this study in most of our colleges, and those subjects have been se- lected which are most important in a course of mathe- matical study. Particular pains have been taken to cul- tivate in the mind of the student a habit of generaliza- tion, and to lead him to reduce every principle to its most general form. It is believed that, in respect of difficulty, lliis treatise need not discourage any youth of fifteen years (if age who possesses average abilities, while it is designed to form close habits of reasoning, and cultivate a truly philosophical spirit in more mature minds. Prof Loo.mis has here aimed at exhibiting the "first principles of Algebra in a form which, while level with the capacity of ordinary students and the present state of the science, is fitted to elicit that degree of effort which educational purposes require. Throughout the work, whenever it can be done with advantage, the practice is followed of generalizing particular examples, or of ex- tending a question proposed relative to a particular quan- tity, to the class of quantities to which it belongs, a prac- tice of obvious utility, as accustoming the student to pass from the particular to the general, and as fitted to impress a iTiain distinction between the literal and numeral cal- culus. The general doctrine of Equations is expounded with clearness and independence. The author has de- veloped this subject in an order of his own. We venture to say that there will be but one opinion respecting tho general character of the exposition. — American Journal of Science and Arts. Elements of Geometry and Conic Sections. Tenth Edition. The arrangement of the propositions in this treatise is I'enerally the same as in Legendre's Geometry, but the tbrm of the demonstrations is reduced more nearly to the model of Euclid. The propositions are all enunciated in general terms, with the utmost brevity which is consist- ent with clearness. The short treatise on Conic Sections, appended to this volume, is designed particularly for those who have not time or inclination for the study nf analyt- ical geometry. Prof Loomis' Geometry is characterized by the same 8vo, pp. 226, Sheep extra, 75 cents, neatness and elegance which were exhibited in his .A.lge- bra. While the logical form of argumentation peculiar ta Playfair's Euclid is preserved, more completeness and symmetry is secured by additions in solid and spherical geometry, and by a difl'erent arrangement of th ■ proposi- tions. It will be a favorite with those who admire the chaste forms of argumentation of the old school ; and it is a question whether these are not the best for the purposes of mental discipline.— iVorJ/iem Christian Advocate. LOOMIS' SCHOOL AND COLLEGE TEXT-BOOKS. Trigonometry and Tables. Kiiith Edition. 8vo, pp. 344, Shf-ep extra, .$1 50. Tlie Trigonomelry and Tables, bound sej arately. The Trigonometry, $1 00 ; Tables, 50 cents. This work contains an exposition of the nature and properties of logarithms ; the principles of plane trigonom- etry ; the mensuration of surfaces and solids ; the princi- ples of land surveying, with a full description of the in- struments employed ; the elements of navigation, and of spherical trigonometry. The tables furnish the logarithms of numbers to 10,000, with the proportional parts for a fifth figure in the natural number , logarithmic sines and tangents for every ten seconds of the quadrant, with the proportional parts to single seconds ; natural sines and tangents for every minute of the quadrant ; a traverse ta- ble ; a table of meridional parts, &c. In this work the principles of Trigonometry and its ap- plications are discussed with the same clearness that diaracteri7.es the previous volumes. The portion appro- jirialed to Mensuration, Surveying, &c , will especially commend itself to teachers, by the judgment exhibited in the extent to which they are carried, and the practically useful character of the matter introduced. What I have particularly admired in this, as well as the previous vol- umes, is the constant recognition of the difficulties, pres- ent and prospective, which are likely to embarrass the learner, and the skill and tact with which they are re- moved. The Logarithmic Tables will be found unsur- passed in practical convenience by any others of the same extent. — Augustus W. Smith, LL.D., President of the Wesleyan University. , Elements of Analytical Geometry aad of the Differential and Integral Calculus. Seventh Edition. 8vo, pp. 2*78, Sheep extra, $1 50- by an extensive collection of examples. The work was prepared to meet the wants of the mass of college students of average abilities. The first part of this volume treats of the application of algebra to geometry, the construction of equations, the properties of a straight line, a circle, parabola, ellipse, and hyperbola , the classification of algebraic curves, and the more important transcendental curves. The second part treats of the differentiation of algebraic functions, of Ma- rlaurin's and Taylor's theorems, of maxima and minima, transcendental functions, theory of curves, and evolutes. The third part exhibits the method of obtaining the in- tegrals of a great variety of differentials, and their appli- cation to the rectification and quadrature of curves, and the cubature of solids. All the principles are illustrated Analytical Geometry is treated, amply enough for ele- mentary instruction, in the short compass of 112 pages, so that nothing need l)e omitted, and the studen can mas- ter his text-book as, a whole. The Calculus is treated in like manner in 167 pages, and the opening chapter makes the nature of the art as clear as it can possibly be made. We recommend this work, without reserve or limitation, as the best text-book on the subject we have yet seen. — Methodist Quarterly Review. Introduction to Practical Astronomy, with a Collection of Astronomical Tables. Sto, pp. 497, Sheep extra, $1 50. This work furnishes a description of the instruments required in the outfit of an observatory, as also the meth- ods of employing them, and the computations growing out of their use. It treats particularly of the Transit In- strument and of Graduated Circles ; of the method of de- termining time, latitude, and longitude : with the compu- tation of eclipses and occultations. The work is designed for the use of amateur obser\'ers, practical surveyors, and engineers, as well as students who are engaged in a course of training in our colleges. The tables which ac- company this volume are such as have been found most useful in astronomical computations, and to them has been added a catalogue of 1500 stars, with the constants required for reducing the mean to the apparent places. Letters commendatory of this work have been received from G. B. Airy, Astronomer Royal of England ; from William Whewell, D.D., Master of Trinity College, Cam- bridge, Eng. ; from Prof. J. Challis, Plumian Professor of Astronomy in the University of Cambridge, Eng. : from .1. C. Adams, late President of the Royal Astronomical Society ; from Augustus De Morgan. Professor of Mathe- matics in University College, London ; from M. J. John- eon, Director of the Radcliffe Observatory, Oxford, Eng. ; from William Lassell, Astronomer of Liverpool, Eng. ; from C. Piazzi Smyth, Astronomer Royal for Scotland ; from Edward J. Cooper, of Markree C:astle Observatory, Ireland , and from numerous astronomers from every part of the United States. It appears to me that Prof. Loomis' work on Practical Astronomy is likely to be extensively useful, as contain- ing the most recent information on the subject, and giving the information in such a manner as to make it accessi- ble to a large class of readers. I am of opinion that Prac- tical Astronomy is a good educational subject even for those who may never take observations, and that a work like this of Prof Loomis should be a text-book in every University. The want of such a work has long been felt here, and if my astronomical duties had permitted, 1 should have made an attempt to supply it. It is remark- able, that in England, where Practical Astronomy is so much attended to. no book has been written which is at all adapted to making a learner acquainted with the recent improvements and actual state of the science. — James Challis, Plumian Professor of Astronomy in the Uni- versity of Cambridge, Eng. The science of the age was most assuredly in want of a work on Practical Astronomy, and I am delighted to find that want now supplied from America, and from the pen of Prof Loomis. I propose to make this volume a text- book for my class of Practical Astronomy in the Univcr sity of Edinburgh. — C. Piazzi Smyth, Astronomer Roy- al for Scotland. No work since that of Professor Woodhouse places the reader so directly in communication with the interior of the Observatory as the work on Practical Astronomy by Prof Loomis ; and he has supplied a want which young astronomers, actually wishing to observe, must have felt for a long time. It is more than possible that this work may establish itself as a text-book in England. — Augus- tus De Morgan, Professor of Mathematics m Universi- ty College, London. Recent Progress of Astronomy, especially in the United States. A thoroughly revised Edition of this "Work is now in conr.^c of Preparation. This volume is designed to exhibit, in a popular form, the most important astronomical discoveries of the past ten years. U treats particularly of the discovery of the planet Neptune, of the new asteroids, of the new satellite, and the new ring of Saturn, of the great comet of 1843, Biela's comet. Miss Mitchell's comet, &c. ; of the paral- lax of fixed stars, motion of the stars, resolution of the nebulae, &c. ; the history of American observatories. d«- termination of longitude by the electric telegraph, manu- facture of telescopes in the United States,