ae ee a ee ae ee ee re i —_ ~~. ir Se ee ee te ee ra | 1 aa eee aes -—~ - - “a¥ i ' é hn: . : * . - 4 a SS 2 a ae el : ’ Zs ; IT TF tah a Sa neberwascicenas = ; sows ~~ Sper te ares Teen, , Mad bi ate ates iis — - nee ¥ ’ a TT rT ee “at ; ye — a lan ae i A ll “a ai ’ ’ " ~ ~- - = Ape te wert nig nee eg qe ce age pe oo Py os < <6 52 K & ete +<8><¥> ei a o. S2 ERIS * Ww Brag £0 OS RUEMERE wis, ib —_ vr . a - \ ‘ s — < , i = - C i. ra 3 E . L Ks Sd Sf THE PHILOSOPHY OF NATURAL HISTORY. By JOHN WARE, M.D. PREPARED ON THE PLAN, AND RETAINING PORTIONS, OF THE WORK OF WILLIAM SMELLIE, MEMBER OF THE ANTIQUARIAN AND ROYAL SOCIETIES OF EDINBURGH. BOSTON: PUBLISHED BY BROWN AND TAGGARD. 27 AND 29 CORNHILL. 1860. Entered according to Act of Congress, in the year 1860, by JOHN WARE, | in the Clerk’s Office of the District Court of the District of Massachusetts. RIVERSIDE, CAMBRIDGE: STEREOTYPED AND PRINTED BY H. 0. HOUGHTON. PREFACE. Tue origin and purpose of the work upon which the present one is founded are explained in the following extracts from the Preface of its author. “ About fifteen years ago, in a conversation with the late worthy, respectable, and ingenious Lord Kames, upon the too general neglect of natural knowledge, his Lordship suggested the idea of composing a book on the PaitosopHy or Natura History. In a work of this kind, he proposed that the productions of Nature, which to us are almost infinite, should, instead of being treated of individ- ually, be arranged under. general heads;, that, in each of these divisions, the known facts, as well as reasonings, should be collected and methodized in the form of regular discourses; that as few technical terms as possible should be employed; and that all useful and amusing views arising from the different subjects should be exhibited in such a manner as to convey both pleasure and _ infor- mation. “This task his Lordship was pleased to think me not altogether unqualified to attempt. The idea struck me. I thought that a work of this kind, if executed even with moderate abilities, might excite a taste for examining the various objects which everywhere solicit our attention. A habit of observation refines our feelings. It is a source of interesting amusement, prevents idle or vicious propensi- ties, and exalts the mind to a love of virtue and of rational enter- tainment. I likewise reflected, that men of learning often betray _ an ignorance on. the most common subjects of Natural History, which it is painful to remark.” iv PREFACE. “Upon the whole, the general design of this publication is to convey to the minds of youth, and of such as may have paid little attention to the study of Nature, a species of knowledge which it is not difficult to acquire. The knowledge will be a perpetual and inexhaustible source of many pleasures; it will afford innocent and virtuous amusement, and will occupy agreeably the leisure or vacant hours of life.” . | The book of Mr. Smellie, prepared in accordance with these views, was first published about seventy years since, and continued in use during the early part of the present century. In the year 1824, at the suggestion of my friend Mr. George B. Emerson, it underwent a variety of alterations, intended to adapt it for use in the - school of which he was then the teacher. An Introduc- tion was substituted for the first two chapters, “ contain- ing some very general views of animal and vegetable life, and a brief sketch of the structure and classification of the whole animal kingdom.” Of the remainder of the work some chapters were omitted, some portions were re-written, and many passages were added; but it re- mained essentially the same. Since its preparation, eapeelally during the last fit- teen years, the work has been extensively used in the schools of the United States, and has been re-published in Great Britain. At the request of the publishers a new revision was undertaken, in order to adapt it more perfectly to the present wants of education. | In the present edition the subjects of the Introduc- tion have been much more fully treated. In the body of the work, the original plan has been still adhered to, but extensive alterations have been made, and most of the chapters have been prepared anew. ‘These altera- PREFACE. Vv tions consist chiefly in a more full consideration of those parts of the animal economy which relate to the exter- nal life of animals, and which are consequently closely connected with the study of their characters, manners, habits, and mental characteristics. Complete state- ments of physiological details were not consistent with the plan or the limits of the work, and a full scientific view of Physiology was therefore not attempted. The object of the book is not to teach Natural History, technically speaking,—a task the author would not have ventured to undertake — but to present such views of it as would be intelligible to the young student and to the general reader, and prepare them for, and lead them to engage in, a more extended study of the sub- ject as it is presented in treatises more strictly scien- tific and in the works of Nature. J. W. Boston, August, 1860. CONTENTS. INTRODUCTION. CHAP. PAGE I. GENERAL CHARACTERISTICS OF Livinc BopIEs - 1-12 Tl. CHARACTERISTICS OF ANIMALS AS DISTINGUISHED TEER, Die] ST Dp SS ES erica co Bib iic 1 OG aie cag 6 12—20 Till. GENERAL STRUCTURE QF ANIMALS --::-=-- esee §=©620-381 IV. STRUCTURE OF ANIMALS AS COMPARED WITH ERACT. GFE VLAN (© «2 2 oo cee a's ete ois a ee Ste atemetaveners 82-42 V. GENERAL SUBDIVISIONS OF THE ANIMAL KING- no E Mictiatiattes lela wos alee se eas le is) ss) enelaiena ss 666 6 6 sy eie 43-46 VI. First BRANCH OF THE ANIMAL KINGDOM.— VER- TEBRATA, OR VERTEBRAL ANIMALS ---:>---::> 46-113 Section I. Class I. Mammalia -...--...-. 47-87 Section II. Class I]. Birds --.---....... 87-102 Section III. Class III. Reptiles .---.------ 102-107 Section IV. Class IV. Fishes ------------. 108-113 VII. Seconp BRANCH OF THE ANIMAL KINGDOM. — AR- TICULATA, OR ARTICULATED ANIMALS :-:>=-- 113-127 VIII. Torry BRANCH OF THE ANIMAL Kinapom.— MoL- LuSCA, OR MoxLuuscous ANIMALS ---+-++--->: 127-131 IX. Fourts BRANcH OF THE ANIMAL Kingpom. — Ra- DIATA, OR RADIATED ANIMALS -++--++eeeees 131-136 Vill CONTENTS. PHILOSOPHY OF NATURAL HISTORY. CHAP. W.* 1E Se eee l,l ii: Il. 43 ss co ei s VIL. W. XVIII. Or THE Foop, DIGESTION, AND BLooD OF ANIMALS <*2 sce oad S8i ws Ss oe Or CIRCULATION AND RESPIRATION -::-- Or THE CONNECTION oF ANIMALS WITH HEAT, LIGHT, AND ELECTRICITY -:--:-- : . Or THE MOTIONS OF ANIMALS ¢++:+eeees . OF THE VOICE OF ANIMALS, AND THEIR MoprEs oF COMMUNICATION «cesses . ie . OF SENSATION IN GENERAL. — FEELING AND Toucn. — TASTEs.—— SMELL ++ 2-5 -s25eee “On Fm ARInG -< «<2 6'<% 2c 0 0 ss) ss ee Eee Or SicgHT.— EDUCATION OF THE SENSES, AND THEIR COMBINATION AND RECIPRO- CAT, RELADIONS. 2:2.2%5.6 nicks » aceculeee . Or REPRODUCTION AND TRANSFORMATION . OF THE DISTRIBUTION OF ANIMALS. — COVERING, MIGRATION, AND HYBERNA- TTON:.. 6 seine oie 250s oe 2 Sel Ree Bes ee See . Or THE HABITATIONS OF ANIMALS ----::- . OF THE RELATION OF ANIMALS TO MAN. — THEIR EDUCATION AND DOMESTICA- TION ® s «0m es 8 eee 6 ais @eseneeneenue es 2 2. eS ee . OF THE ARTIFICES OF ANIMALS «-::---=:- . OF THE ASSOCIATION OF ANIMALS --::-:- . OF THE HOSTILITIES OF ANIMALS AND THE DESTRUCTION OF ANIMAL LIFE -:----- . OF THE DURATION OF LIFE «++--+-+++--++-- . Or INSTINCT AND INTELLLIGENCE, AND OF THE MENTAL CONSTITUTION OF ANIMALS CONCLUSION: 2.90%. oie se ee fee ere eees QUESTIONS «e+e e ee eee eee e ee eeees es hs 5 6 ee PAGE. 137-159 160-176 (177-185 185-199 199-205 206-213 214-225 225-254 255-264 265-282 283-315 315-335 330-347 3848-357 357-374 374-386 386-407 407-418 419-448 * The Chapters which are taken chiefly from the original work are marked S.; those prepared wholly or principally for the present edition are marked W. THE PHILOSOPHY = OF : - NATURAL HISTORY. INTRODUCTION. CHAPTER I. GENERAL CHARACTERISTICS OF LIVING BODIES. Natura History in its largest sense embraces a very wide field of investigation. It gives the history not only of animate but of all inanimate matter, and thus extends to the mineral as well as the vegetable and animal kingdoms. It includes an account of the form,.size, color, and other sensible qualities of minerals; of their position with respect to each other; their arrangement and relations as forming parts of the globe; and their relation also to the living things which now inhabit or have inhabited it. -It teaches the circumstances in which vegetable and animal differ from mineral substances. It describes their structure and powers; the conditions of their existence ; the laws according to which their structure and organization are made to _ vary, and the relation to external circumstances which renders variation of structure necessary. It arranges the individuals of these kingdoms into groups, according to certain principles of classification. It gives each individual a place in this arrange- ment. It enters into the history of each one; investigates its structure, its mode of life, its relation to external nature; in short, it determines and describes in detail every particular which can illustrate the character of its existence. Tt is manifest that no human industry can master this whole subject. It has accordingly been subdivided into many depart- 1 : Petey ped hes seer Eyre ys a Pama PMN EI ee Tot a ae a I Si ses Cnc es dain SW ae Es See Bee SET aE Bt ae 2 a —— 2 CHARACTERISTICS OF LIVING BODIES. menis, and each department affords ample material for the inves- tigation of a lifetime. But the minute details which occupy the attention of the professed naturalist, are not caleulated to engage the interest of the general student, or to constitute a part of the preliminary education of the young. For these they have not the taste, nor the time. Their purpose is better answered by the study of what has been denominated the PHiLosopHy or NATURAL History, a more general method of presenting the same sub- jects. Its purpose, beside a similar consideration of the objects of inanimate nature, is to illustrate principles according to which plants and animals are constructed ; the laws by which their ex- istence is governed ; the conditions under which they come into existence, continue their existence, and terminate their existence ; and thus to exhibit the plan of creation and the designs of the great Author of Nature, as they are displayed in this portion of his works. ‘The Philosophy of Natural History is-indeed little less than a system of Natural Theology drawn from the history of nature, and in no way can the power and wisdom of the Creator be more clearly illustrated. The purpose of the present work is to illustrate this subject chiefly in connection with the animal kingdom, and chiefly also with those portions of this kingdom in which animal life is ex- hibited in its highest and most perfect state. To attempt more than this, would open a wider theme than could be clearly or profitably treated. It is not its object to teach the details of nat- ural history except so far as they are necessary to the illustration of principles; and the phenomena exhibited by the mineral and vegetable kingdoms will only be so far adverted to as they have some relation to the conditions under which animals exist, the functions by which their existence is maintained, the rela- tions they bear to each other, and the character —= severally manifest. If a common foe were asked in what respect an animal differs from a stone, he would answer without hesitation that it differs in being alive. If the same question were put with regard to a plant, the answer would probably be the same. Supposing it to be then inquired how the plant is distinguished from the animal; the solution might seem more difficult. Very CHARACTERISTICS OF LIVING BODIES. 3 likely, however, it would be thought sufficient to say that the animal could feel and move, and that the plant could not. In point of fact these answers are sufficiently accurate, as far as they go, and yet how few of those who would make them, actually comprehend in their full extent the meaning of the very terms in which they are expressed. Our familiarity with animal and vegetable life, and our constant habit of making the distinction between the bodies possessed of them, actually pre- vent our perception of the wonderful and mysterious character with which they are invested. Till the conditions under which a living thing exists are deliberately considered, it is impossible fully to appreciate how strange and interesting is the simple pos- session of life. It impresses us most forcibly when viewed in its connection with the ordinary laws of matter, and in those species in which its attributes are most variously displayed. Strictly speaking, life is as completely possessed by the lowest plant as by the highest animal; but we can best appreciate its wonderful character when we consider it in connection with ourselves. , | When a man dies, his body is speedily decomposed. If the results of its. decomposition are examined, it is found to have been made up chiefly of water, nitrogen, a little phosphorus, a little sulphur, some charcoal and lime, with a few other earthy and some saline ingredients. But there is nothing peculiar in the materials of which it is composed. ‘They are elements which are constantly present in the universe about us, and which enter into the composition of a thousand other bodies. ‘They have in themselves, separately considered, none of those properties which are found in the animal into whose composition they enter. In- deed, their original physical and chemical tendencies are actually at variance with the relation they maintain to each other as com- ponent parts of a living system; so much so, that if the myste- rious bond of connection which holds them together be dissolved by death, they separate sooner or later from each other, in con- formity with their original and inherent tendencies. This mysterious bond is the Principle of Life. By its influ- ence we are enabled to maintain our existence in the midst of agents which are constantly seeking our destruction. Our bodies 4 CHARACTERISTICS OF LIVING BODIES. are composed of elements which exist everywhere in the matter around us, but gathered into new combinations and moulded into peculiar forms. The tendency of the common laws of matter is to dissolve these combinations and destroy these forms. Fire, air, and water, the cold of winter and the heat of summer, are alike our enemies. We have a chemical composition of our own, —a temperature of our own,—a power of spontaneous motion of our own. We maintain them in spite of the chemical affin- ities, the temperature, and the mechanical influences of the bodies that surround us. Deprive us of life, and our resistance to all these tendencies is at an end. Our power of motion is lost, and we yield at once to the force of gravity which brings us to the earth;— our temperature falls or rises to that of the medium by which we are surrounded ;— and the chemical laws of matter, sooner or later, resolve our bodies into their original elements. ; We are so familiar with the spectacle of life in nature around us, as well as with the consciousness of our own existence, that we are apt to lose sight of what is most wonderful in animals and in ourselves. We wonder at the strange and curious chemistry of digestion ; at the nice mechanism of the heart; at the beauti- ful adjustment of the eye and ear, and their adaptation to light and sound. The greater wonder is that we can exist at all in the midst of a material world constituted as it is, and governed as it is by fixed laws. ; Consider these laws: of Gravitation, universal, unerring, in- evitable. Governing an atom as it governs a planet. Ruling all bodies, at rest or in motion, by one immutable principle. Of Heat, no less absolute and irresistible, — always tending to dis- tribute itself-in certain regulated proportions to all substances, and in the accomplishment of its laws producing the most vio- lent effects, cleaving rocks and tearing open hills. Of Chemical Affinity, extending its sway over the same substances as the pre- ceding, but for purposes entirely distinct. By its agency solid bodies dissolving and disappearing in apparently inert and impo- tent liquids ; airs changing into liquids and liquids into solids ; fire springing up in the midst of water, and water increasing the intensity of fire. CHARACTERISTICS OF LIVING BODIES. 5) The empire of these laws over matter in its ordinary state is constant. There are no exceptions to it. But existing in the midst of them, the animal sets them all at defiance. He moves in opposition to and independently of the law of gravitation. He resists the influence of that external heat which subdues everything else. He maintains a chemical composition incon- sistent not only with the chemical attractions of the substances by which he is everywhere surrounded, but inconsistent even with those of the elements of which he is himself composed. ‘This is the position which we maintain in the midst of creation, and there is no wonder in the creation greater than this. This is the universal condition of animal life. It is most strikingly exhibited and most clearly illustrated in man and the higher animals, but essentially the principle is of the same character in all, and is displayed by similar phenomena. Still, though thus alike in this fundamental principle, animals differ indefinitely in secondary particulars. They exist in different states, under different circumstances. ‘They live on a variety of food. They inhabit the air, the water, the earth. Some are exposed to continued cold; some to continued heat; whilst others are undergoing a series of vicissitudes from heat to cold and from cold to heat. This renders necessary an immense variety in structure. The animal that flies cannot be built like the animal that runs; nor the animal that runs like the animal that swims. The animal that breathes in air and the one that breathes in water must each have an arrangement suited to the medium in which it lives. The necessities of all as to food, climate, habita- tions, require modifications in bodily.structure to fit them for the place they are designed to fill. This is the origin and final cause of the varieties in animal form. The study of this subject lays open to us a prospect of the wonderful economy with which Nature manages her resources. Notwithstanding the wonderful variety of animal forms, the fundamental operations by which life is maintained are essen- tially the same in all. It is in secondary particulars that the variation chiefly takes place. “Nature,” as was happily ob- served by a celebrated physiologist, “is prodigal of ends, but economical of means.” She uses but few materials and few 5 ' t = . L j J 6 CHARACTERISTICS OF LIVING BODIES. tools; but the works she accomplishes are almost infinitely di- versified in form, in character, and in purpose. The first and fundamental distinction among the objects of the material world is, then, between those possessed of life and those not possessed of life; the former including plants and animals, the latter all other bodies. But in order fully to comprehend the nature of this distinction, it is necessary to study more in de- tail the conditions under which these two classes of bodies are found to exist. The first distinction is in the character of their structure and the mode of their origin. Living bodies are made up of a va- riety of parts peculiar in their texture, each of which exercises an office subordinate to the purposes of the whole individual. Other bodies are on the contrary either of a. uniform structure throughout, or, if not so, the several parts of which they are com- posed have no peculiar relation to each other more than to other matter, and contribute nothing to the relations of the whole mass into whose composition they enter except to its size and weight. Their existence is a continued one. Their structure and forms remain very much as they were in their original formation. It is true that convulsions of nature have brought about some reyo- lutions in them, and accidental causes of less importance fre- quently produce some minor changes. But through all, the powers and properties remain the same. Matter always gravi- tates, and its elements, however divided and disturbed, always maintain the same relations, combine in the same forms, in the same proportions, and according to the same af_inities. But while the universe of common matter is thus permanent, that of living matter is in a state of constant revolution. Bodies are constantly going out of existence and new ones as constantly coming into existence. Change is the characteristic law of the latter, as permanency is of the former. Both in the animal and vegetable world each individual has but a limited term of exist- ence. It is produced, grows, flourishes for a while, and then dies and decays. Hence the necessity of that provision by which they may be regarded as successively created, namely, that each individual is the offspring of another individual like itself. : a —_— CHARACTERISTICS OF LIVING BODIES. 7 This is a very complete distinction. No substance not possess- ed of life is ever brought into existence in this way. It is true that new bodies in the mineral world are formed by the acci- dental aggregation of particles, or by the spontaneous combina- tions which are the result of chemical laws; but this is clearly something very different from the mode of production which takes place in living bodies. One stone does not produce another like itself; a crystal does not produce a crystal, nor one grain of sand another. There is nothing like the relation of parent and ‘offspring. Connected with this circumstance, namely, the relation of parent and offspring, is another, not less important, — the relation of sex. This, more or less perfectly exhibited, is found in all the subjects of both the vegetable and animal kingdoms. ‘To the continuance of every species this distinction is necessary, either existing in separate individuals, as in most animals, or combined in the same, as in most plants. It is true that in some species, as in bees and ants, there is a race of neuters, which possesses the properties of neither sex; but it is probable that these are rather to be regarded as individuals imperfectly developed, than as orig- inally deficient in the appropriate characteristics. In the second place, living bodies differ as to the mode of their existence, insomuch as they are dependent upon other things beside themselves for the continuance of that existence. The matter of which their active parts are composed undergoes, with more or less frequency, an entire change. It is, in fact, only common matter endowed for a certain period with the powers of life, in consequence of being united to living systems. By the various internal operations constantly going on, part of this matter is expended, is sent out of the system. This loss must be repaired by the addition of new matter. Hence the necessity of nourishment to the support of life; hence the necessity of a regular supply, to everything living, of a certain quantity of food adapted in kind to the nature of the individual. This food is operated upon by the organs of the animal or vegetable, is assim- ilated to it, and its properties are modified until it becomes fit to enter into its composition. This is Nutrition, an essential process of living bodies, by which they are enabled to increase in size : | : | | | | 8 CHARACTERISTICS OF LIVING BODIES. and strength, to modify the structure of their different parts, and to maintain them in a fit state for performing the offices for which they are designed. Minerals, on the contrary, have no such de- pendence ; the matter of which they consist is always the same; they contain within themselves everything which is essential to their existence, and have, of course, no necessity for nutrition or growth. It is true that these substances sometimes increase in size, as happens with regard to stalactites, the deposition of erys- tals, and the formation of alluvia. But there is this marked dif- ference between all such instances of growth and that of animals or vegetables: that, in the former case, it amounts to the mere juxtaposition of similar particles, unchanged in their nature ; whilst in the latter, the particles are changed in their nature, and subjected to the operation of entirely new laws. In the former case, the growth depends upon a principle operating from with- out ; in the latter, upon a principle operating from within. In the third place, although in this way dependent on other substances for the necessary materials by which their existence is supported, living bodies, in another point of view, exhibit a species of independence of other matter. As has been already stated, they are removed, to a certain degree, out of the influence of physical and chemical laws; they are enabled to resist their ordinary operation by an inherent principle, and without this would speedily cease to exist. They depend upon the things around them for the materials for their support; but the power of altering the nature of these materials, and appropriating them to their own use, is peculiar to themselves. The functions of living systems are not only performed without the assistance of the physical powers of matter, but often in direct opposition to them ; and the substances which are introduced into them lose to a certain extent their chemical relations, and are combined according to new laws, and for new purposes. _ This power of insulation, possessed by living systems, is in no instance more strikingly evinced, than in the possession by many animals of a certain degree of vital heat, which they preserve under all circumstances, short of those which impair or destroy the texture of their parts. This degree of heat,— which in man is about 98° of Fahrenheit’s thermometer, — continues al- CHARACTERISTIUS OF LIVING BODIES. 9 ways nearly the same. In some countries, in which the degree of cold is for many months in the year very much below the freezing point of mercury, men not only exist, but enjoy all the comforts of life. In some high latitudes, Europeans have been exposed to temperatures as low as — 50° or even — 60° of Fah- renheit’s thermometer, that is, about 150° below the natural standard of animal heat, and have escaped every ill consequence. Many years since, the whole of two ships’ crews wintered in 7d° of north latitude in perfect safety, where the temperature of the air was, for many weeks together, almost constantly be- low — 30°, and where they became so accustomed to severe cold, that the atmosphere, when at zero, felt mild and comfort- able. In one of the more recent arctic expeditions a still lower temperature was endured, not only with impunity, but with com- parative comfort. On the other hand, in many countries men exist without difficulty under a high degree of heat. In Sicily, during certain winds, the thermometer has been observed at 112°, in South America by Humboldt at 115°, in Africa at 125°. But, for a limited period, much higher degrees of arti- ficial heat have been borne without injury. Individuals have exposed themselves voluntarily to the air of ovens at tempera- tures from 260° to 315° of Fahrenheit’s thermometer, without any great inconvenience, while water was boiling and meat bak- ing in the same atmosphere. Life has even been maintained by some of the lower classes under circumstances still more extraor- dinary. In some hot springs in the island of Ceylon fishes have been found swimming about in water from 87° to 115°; in Bar- bary at 172°; in Manilla at 187°, and, according to Humboldt, they have been thrown up alive from a volcano with water at 210°. These facts show a power of resisting the operation of external causes, which is possessed by no substances except such _ as are endowed with life, and is, probably, possessed in some de- gree by all that are. For, although vegetables and the lower kinds of animals are not capable of resisting to the same extent the influence of heat and cold, yet they all show, in some meas- ure, the existence of the same power. And in the most imper- fect species, where there is no other evidence, this power is evinced by the fact that the individual freezes with greater nes Se ed IP ROE ORE ET PT ER nT me se sey eCommerce RE om SENT Eee oe oe RE - equal.* 10 CHARACTERISTICS OF LIVING BODIES. difficulty before than after death, other circumstances being The same principle is exhibited in the resistance which living bodies offer to the causes of chemical decomposition by which they are surrounded. This resistance ceases as soon as. life. ceases, and is consequently due to its influence. We are exposed while alive to the same heat and moisture which work so speedy a change upon us after death; the composi- tion and texture of our bodies are the same. We resist their influence by virtue of the possession of the principle of Life. This suggests to us, in the fourth place, another distinction of living substances, namely: that they all terminate their existence in death. By this event, the materials which entered into their composition are deprived of the bond that held them together and gave to them their peculiar form. They therefore separate, and retain only those properties that they possessed before be- coming parts of a living system. Dust returns to dust, earth to earth. It is true that some of the parts of living bodies, both animal and vegetable, do not very readily undergo the process of decay. The bones, teeth, shells, and horns of animals; the trunks, branches, and roots of trees, retain, for an almost in- definite length of time, under certain circumstances, their shape * In quadrupeds and birds the animal heat is generally greater than, whilst in animals of the inferior classes it is seldom very different from, that of the me- dium in which they live. The former are called warm-blooded, and the latter cold-blooded. In the former, the temperature is capable of but slight variation from external causes; in the latter, its range is pretty extensive, and it varies a great number of degrees. The temperature of a man plunged into cold salt- water at 44°, has been known to sink to 83°, and when exposed to a heated atmosphere, to rise to 100°; in other warm-blooded animals similar varieties have been observed. But the temperature of the viper, a cold-blooded animal, when exposed to a heat of 108°, rises to 92°, and when exposed to a cold of 10°, sinks to about the freezing point of water, showing at once an extensive range of temperature within which the functions can go on, and at the same time a decided power of resistance against any further alteration. Eggs possess an analogous power. A new-laid egg, and one which has been frozen and thawed, being exposed in a freezing mixture together, the former will be some minutes longer in freezing than the latter. This has been ascer- tained by experiment. The same is true of the lower orders of animals and vegetables. CHARACTERISTICS OF LIVING BODIES. 11 and substance. This, however, is owing, not to their continuing to possess life itself, but partly to the particular character of the texture of which they are composed, and partly to their pro- tection, by accident or intention, from the influence of air, warmth, and moisture. Nothing like this takes place in other substances : they can be destroyed only by the action of some mechanical agent, which separates their parts, or by that of some chemical one, which alters their combinations. There is still a fifth circumstance in which Sientukeed differ essentially from unorganized bodies. The properties which the latter possess, and the laws by which they are governed, are definite in their character. Uniform causes produce uniform re- sults; and these results are capable of being calculated and measured. It is widely different in living bodies, so far at least as we are able to analyze the conditions under which they exist. This peculiarity is most distinctly exhibited among the higher classes of animals, but is to be everywhere recognized. Indiyid- uals of the same species differ indefinitely as to the mode and degree in which they are influenced by external causes. We can predict of any inorganic body, that it will be always affected in the same way by the same agents. We cannot predict this of any organic body; on the contrary it is hardly ever influenced in precisely the same way at different periods by the same cause. A remarkable result of this peculiarity is the formation of habits. All living things are believed to be capable of this. No others are capable of it in the slightest degree. It is one of the most striking differences between the two great divisions of natural objects. It is exhibited in a variety of ways. The life of many, both plants and animals, is a history of the forma- tion of habits, some of which are confined to, and terminate with, the individual, others are transmitted to the offspring. Thus the physical character and even structure of plants are altered by climate, by modes of cultivation, by kinds of food; and not only is the same true of animals, but it goes even further, and we see changes formed and transmitted, so to speak, in their instincts, their intellect, and even in their passions and _ propensities. Hence it is in the subjects of organic life alone that we discover the existence of a proper individuality. Derm tte ae re te i a ae eB amo, Se 12 CHARACTERISTICS OF ANIMALS There are other phenomena which further illustrate the dis- tinction between the organic and inorganic modes of existence. Animals and vegetables are capable of passing into a condition in which there is a suspension, for a time, of many and some- times of all their functions, which after a time they resume. Of ; this we have examples in the daily sleep of animals, and the torpid state into which many animals and almost all plants fall during certain portions of the year. There is, in these cases, an intermission in the exhibition of those properties by which the individual is particularly characterized. Nothing truly analogous to this takes place among mineral substances. CHAPTER IL. CHARACTERISTICS OF ANIMALS AS DISTINGUISHED FROM PLANTS. . PRACTICALLY there is not often any difficulty in distinguishing an animal from a vegetable. But when it is attempted to point out the philosophical or essential principle in which their differ- ence consists, the task is not so easy. In fact, there does not appear to be any such principle lying at the foundation of the distinction between animals and plants, that there is between organized and unorganized bodies, namely the principle of life. There are certain close points of resemblance between the com- position, the structure, the functions, and the conditions of exist- ence of animals and vegetables, which do not exist between either of them and minerals. So much is this the case, that some writers, among whom was the celebrated Buffon, have believed that there is no exact boundary, but that so close a resemblance of characteristics exists between those living at the two extremes, that individuals possessing the peculiarities of animal life in the lowest degree, are not essentially different from the plants which possess them in the highest. AS DISTINGUISHED FROM PLANTS. 13 It is probable, however, that the difference between these two classes of bodies is essential and fundamental; and it is worth while to enter somewhat into the examination of it, not simply on account of its intrinsic importance, but because such an ex- amination will serve to illustrate not only the differences between animals and vegetables, but the nature of their life, the tenure and conditions of their existence, and the general character of the structure and functions by which their existence is originated and maintained. It has been remarked that a vegetable may be compared to an animal asleep, since it exercises, throughout its whole existence, just those functions, and no others, which an animal continues to exercise during sleep. “Sleep,” says Buffon, “ which appears to be a state purely passive, a species of death, is, on the con- trary, the original condition of animated beings, and the very foundation of life itself. It is not a privation of certain qualities and exertions, but a real and more general mode of existence than any other.” This remark is more ingenious than just. It is founded on an imperfect view of the nature of sleep. The essential quality of this state is that it implies the suspension of certain functions during its continuance, which may be exercised at other times. A living body cannot justly be regarded in a state of sleep, which is in the actual performance of all the functions of which it is capable. Strictly considered, the remark means only this: that, during sleep, animals continue to perform only those functions which are absolutely necessary to the existence of a living thing; that these functions are those which vegetables always perform; and that there is consequently an analogy be- tween an animal, when its peculiar functions are suspended, and a vegetable in its ordinary state of existence. This analogy, though fanciful in the terms in which it is expressed, is founded upon the real differences between the two forms of life; and vegetable life, though not a more real, may justly be regarded as “a more general mode. of existence” than animal. The animal life seems to be, in fact, superinduced upon the vegetable. The fundamental operations of living systems — those by which they are brought into, and continued in existence — are the same in both. They have been called, by way of distinction, | RL LT TL LO a I LT pn pte me ene aici tere tre err me ee SN I RN cer ee oe 14 CHARACTERISTICS OF ANIMALS the vegetable or organic functions. Animals perform, in ad- dition to these, certain others peculiar to themselves; chiefly reducible to the two, sensation and motion; and these are de- nominated the animal functions. It is in the structure by which, and the mode in which, these several functions are performed, that the real distinction between the two kingdoms is to be sought; and although there may be certain individuals in each, with regard to which it is difficult to detect the details of the distinction, there is reason to infer, from the well-established uniformity of the laws upon which the creation proceeds, that they exist.* | 7 We find a marked difference between animals and vegetables, as to the manner in which the functions common to both are per- formed, as well as in the possession by the former of certain others, which are not possessed by the latter. To both, as already remarked, a male and female parent is necessary. In the vegetable, the new individual is produced by means of a seed; in the animal, of an egg; for though many animals are viviparous or produce their young alive, the process is in them essentially the same as in the oviparous, differing only in the cir- cumstance that incubation takes place within the body of the mother. = The seed, then, corresponds to the egg, but there is a difference in the mode of their development. The organs of the animal are formed within the egg, and it is not extruded till it is capable of performing all those functions which are essential to its life. During this process it is nourished by the contents of the egg, or by materials derived from a subsequent continued connection * A doubt has sometimes arisen in regard to certain species, — whether they should be considered as belonging to the vegetable or animal kingdom. But the existence of this doubt does not involve any question as to the essential distinc- tion between these kingdoms. In fact, the very controversy involves the recognition of their fundamental difference. It may be further observed that this doubt has always existed with regard to individuals at the very lowest boundary of the two kingdoms. Now it is in the highest forms at which the two ever arrive that we are to seek for the distinction between them, and here we readily detect sufficient evidence that this distinction is an essential one. If we cannot detect this among the lower and more obscure forms, we have reason to infer, not that it does not exist, but that from a deficiency in our means of observation it eludes the scrutiny. AS DISTINGUISHED FROM PLANTS. 15 with its parent. In the seed, on the contrary, although it con- tains the germ of the future plant, and the process of development begins within it, yet it mainly takes place without, and it is not till after it has sent its roots into the earth, and its stem into the air, that the organs necessary to its future existence are con- structed. Plants and animals are equally dependent upon food, for the continuance of existence and the performance of their functions ; but they differ from each other in the manner in which it is done. In the plant it is effected by means of roots. ‘These are usually distributed under the earth, but sometimes they float loosely in the water, are attached to other plants, or in some rare eases are only exposed to the air. In animals, on the contrary, food is received into an internal cavity, and undergoes the pro- cess of digestion, before it is-admitted into the circulation, and applied to the nourishment of the system. ‘The difference then is, that plants absorb their food by an external surface, whilst animals absorb it by an internal surface. They differ also in the nature of their food. Animals derive their nourishment chiefly, if not exclusively, from matter which has been already organized, either in some vegetable or animal system. Plants, on the contrary, derive it chiefly, if not exclu- sively, from elementary matter, or matter which is not in an organized state. It is true that they flourish best in a soil which contains the rémains of vegetables and animals; but it is only after these remains have lost their peculiar structure, and are in a state of decomposition, that they answer this purpose. A plant cannot subsist upon animal or vegetable substances as such, nor an animal upon simple unorganized matter. They differ again in their chemical composition. To vegetable - substances three elements are principally necessary, — hydrogen, oxygen, and carbon. Animals in addition to these require a fourth, azote or nitrogen. It is true that there are some important vegetable substances into whose composition nitrogen enters, and some animal ones into whose composition it does not; and that in ,addition to these principal ingredients there are certain sec- ondary ones which are more or less constantly present in both, such ¢ as, aa lime, sulphur, phosphorus, iron, and some others. a YS. LOE Sng OO ge, PPI “ in ngenirenrtas ae ee 16 CHARACTERISTICS OF ANIMALS Still the predominance of nitrogen in animal substances is a dis- tinct and important peculiarity, and not only influences their textures during life, = the results of their decomposition after death. aes. They differ, also, in their relation to the external atmosphere. The influence of the air is necessary to the existence of each, but in a different way. The lungs or other breathing organs of animals give out carbonic acid as the result of the function of respiration. Tbe leaves, which are the breathing organs of plants, fake in carbon as the result of their function of respira- tion. : They differ again as to the manner in which their- circulation is performed. Both are supported by means of a fluid which is distributed to every part, —the sap and the blood. But the mode of distribution differs. ‘The vessels of plants are cylindrical ; they proceed parallel to each other from their origin in the root to the extremity of the branches, of the same size, without division, and, as some assert, without intercommunication. In animals, on the contrary, the vessels begin in large trunks, often from some central organ, or heart; are constantly subdivided, and diminish in calibre as we approach their extremities; are not parallel to each other; and are frequently intercommuni- cating through their whole course. This at least is true of all those in which the arrangements of the circulation are capable of a careful examination. Another important difference is in the degree of permanence of the organs by which their principal functions are performed. In plants, no matter what their age may be, these endure but for a single season. Not only the leaves, but the circulating vessels, which exist in the inner layer of the bark and in the alburnum, or external layer of wood, are annually renewed. In animals, on the contrary, all the important organs are permanent, and en- dure as long as the individual. _ This depends upon a difference in the laws according to which nutrition and growth take place in the two kingdoms. In each, the several organs require renovation and repair. In vegetables this is effected by the virtual death of the organ. It ceases to have any connection with the functions of the plant, even where AS DISTINGUISHED FROM PLANTS. 17 it does not, as in the bark and wood of trees, undergo an actual separation. In animals the organ is not removed as a whole. It does not lose its shape, its texture, or its vital connection with the individual. Its separate particles are removed one by one and new ones substituted in their place, so that it is probably re- newed many times in the course of a year; but the principle upon which this is done differs essentially from the corresponding one in plants. | The final cause for this difference, as observed in plants which have a long continued existence, is at once wonderful and beau- tiful. Were the organs of plants renewed, like those of animals, by an interstitial growth, never increasing in size and strength after arriving at maturity, they would not be able to support the growth of many years. The parts by which nutrition is car- ried on form a thin cylindrical cavity, a mere shell, quite inad- equate to support the weight of the branches and leaves. But year by year a new growth is formed around it; the old wood ceases to live, but continues its mechanical connection in order to give support and strength to the trunk, of which it afterward forms a part. By this deposit of new matter, as the wood is thrown inward the bark is thrown outward, and thus an annual increase of wood is insured, to.support the corresponding increase - in the amount of branches, leaves, and fruit ; meanwhile the bark dries, cracks open, and forms a hard, rough, and irregular crust on the outside. Hence it is that animals arrive at a limited size in a limited time, and for the greater part of their existence do not grow at all. The bones, when they have arrived at the hardness of mature life, cease to increase in bulk, and the other organs not being renewed every season, as in plants, gradually lose the perfectness of their texture and become unable to perform their functions. Some vegetables, as trees, on the contrary, have no such definite term of existence. They may live almost indefi- nitely, and grow as long as they live, because their organs are wholly new every year, and because those parts which correspond to bones increase in size and strength, in proportion to the amount of leaves and branches which they have to support. Even, then, in those functions which are common to both, Ee 18 CHARACTERISTICS OF ANIMALS vegetables and animals differ from each other. But beside this there are certain others possessed by animals which vege- tables do not possess at all. These are sensation and voluntary motion. ea By means of sensation, the individual is informed of the ex- istence of other things beside himself; of their qualities, and of their relations to himself; he is rendered capable of pleasure and pain; in short, sensation is the indication of a conscious existence. By the power of voluntary motion, he is enabled to move the different parts of his body upon each other, and to move the whole body from place to place. To the exclusive possession of these powers by animals, there are apparent exceptions. Some vegetables do move from place to place with as much apparent volition as certain animals; whilst there are some animals as immovably fixed to one spot as vegetables by their roots. There are also plants which ex- hibit motions seemingly as voluntary as those of some of the lowest animals, and for as definite a purpose. The sensi- tive plant is a striking example of this kind. ‘The slightest touch makes its leaves suddenly shrink, and together with the branch bend down towards the earth. But the moving plant, or Hledysarum gyrans, furnishes a more astonishing example of vegetable motion. Its movements are not excited by the con- tact of external bodies, but solely by the influence of the sun’s rays.* Its motions are confined to the leaves, which are sup- ported by long flexible footstalks. When the sun shines, the leaves move briskly in every direction. ‘Their general motion, however, is upward and downward. But they not unfrequently turn almost round; and then their footstalks are evidently twisted. These motions go on incessantly, as long as the heat of the sun continues. But they cease during the night, and when the weather is cold and cloudy. The Dionea muscipula, or Venus’s flytrap, a plant of Carolina, affords another instance of rapid vegetable motion. Its leaves are jointed, and furnished with two rows of strong spines. ‘Their surfaces are covered with a number of minute glands, which secrete a sweet liquor, and * Sir J. E. Smith states that light is not necessary, but that only a warm, still atmosphere is required to produce this phenomenon in perfection. AS DISTINGUISHED FROM PLANTS. i allure the approach of flies. When these parts are touched by the legs of the fly, the two lobes of the leaf instantly rise up, the rows of spines lock themselves fast together, and squeeze the unwary animal to death. If a straw or pin be introduced be- tween the lobes, the same motions are excited.’ The common barberry is another instance to the same effect. When its flower is fully expanded, if the inside of one of the filaments of its stamens be just touched by a pin or a straw, it contracts instantly, and throws its anther forward with some force against the stigma. ‘When a seed is sown in a reversed position, the young root turns downward to enter the earth, and the stem berids upward into the air. Confine a young stem to an inclined position, and its extremity will soon assume its former perpendicular direction.’ The roots of a tree growing on dry or barren ground, in the neighborhood of that which is moist or fertile, become larger, longer, and more full in that direction than in any other, as if extending themselves to obtain the nourishment which can there be afforded them. If we twist the branch of a tree, so that the under surface of the leaves shall come uppermost, they gradually turn upon their footstalks till the proper side is exposed to the rays of the sun. This they will do repeatedly, until they have become injured by the exertion; and if the leaf be confined, so that it cannot resume its natural position, its stalk will become twisted by the éffort to accomplish it. The sunflower, the leaves of the mallow, and some other plants, generally turn their faces towards the sun. The tendrils of plants, on the other hand, move towards the shade, in whatever direction it may be. In a green- house, if exposed to the morning light, they direct themselves towards the west, at noon to the north, and at night to the east. They are also attracted by opaque bodies. Instances of a similar nature are afforded by what has been denominated the sleep of plants. The leaves of many are folded together during the night, and droop as if dying. In some in- stances they are so arranged, when in this state, as to serve as a cover to the flowers or young fruit. The flowers of other plants follow the same law, and close at the approach of night, for the apparent object of shelter and protection. 20 GENERAL STRUCTURE OF ANIMALS. In many of these instances the motions so nearly resemble those of some of the lower animals, that it is not easy to say wherein they differ in principle, although in such cases there is no danger of supposing the plant to be an animal. Probably the principle of distinction is this. In the plant, the phenomena are-purely local, and do not imply any connection with, and consciousness of, the individual considered as a whole. In the animal, on the contrary, we have reason to believe that the whole individual experiences a degree of consciousness. ‘Touch a stamen of the barberry and a leaf of the sensitive plant, and that stamen and that leaf contract. But touch the petals of the barberry, and the stamen will not contract ; touch the stem of the sensitive plant, and the leaf will not. On the contrary, touch any part of an oyster whose shell is open, and the muscle which closes the shell, though at a distance, contracts and closes it. So when the arms or feelers of a snail are extended, touch any one, or touch any part of the body, and they will all be contracted. The inference is, that in an animal there is some central power or principle giving to it a unity of being and purpose, which is wanting in a vegetable. This is called the sensorial power. It is that directing and controlling principle which receives all im- pressions from without, and from which proceed all the voluntary motions. Its residence is in the brain and nervous system. Its powers become less complete and extensive as we descend from man to the lower animals, in proportion as the brain and nervous system become less perfect; but, go as low as we will, traces of it are still to be found. CHAPTER III. GENERAL STRUCTURE OF ANIMALS. Tiavine thus endeavored to illustrate the relation which ani- mals bear to other bodies, and the peculiarities by which their GENERAL STRUCTURE OF ANIMALS. 21 mode of existence is characterized, it is our next object to inquire how their existence is maintained. This will be done most clearly by an examination of the sub- - ject in connection with man, the animal in whom all the purposes of life are carried out on the largest scale and in the most com- plete manner. We call him the most perfect of animals. Not that the structure of the lowest is less perfect in itself than that of the highest. Each species is adapted equally well to its own end. But the end of his being is higher in man; its purposes are more numerous, varied, and elevated ; we place him, therefore, at the head of the creation, and yet in the lowest animals the purposes of their existence, such as they are, are carried out with as much skill and by as perfect an apparatus as in him. The life of animals is maintained, as has been already stated, by two sets of functions; one set common to all living things, by which the life of the individual is maintained; and another set by which the individual maintains a connection with the external world. ‘The former are called the organic functions, or functions of organic life; the latter, the animal functions, or functions of animal life. The former are in man wholly subsidiary to the latter. It is the animal functions which make him what he is. He digests no better, he breathes no better, he circulates no better than the lowest of his class. It is in the combined per- fection of sensation, motion, intelligence, and speech that he excels them all. As the distinctive character of man depends upon the mode in which these functions are performed, so his external form is the expression of that character. The organs of intellect, of sense, of motion, of voice, constitute this form. As the basis or sup- port of it, there is a bony structure or skeleton, which will be first described. The bones of the human body are divided into those of the head, trunk, and extremities. The head includes the erantum, or skull, and the face. The skull is a large bony cavity, composed of several wide, thin, and arched bones, united together by what are called sutures. It contains the brain, and gives passage to the spinal nerve through a hole situated in its lower part, where it proceeds from the ot Ue He eS ine se 7 i a3 f 22 GENERAL STRUCTURE OF ANIMALS. brain, and goes to the backbone. The face is formed of the upper and lower jaws, and of the organs of seeing, smeiling, and tasting. ‘The bones which form the basis of these organs, are very numerous and difficult to describe. When taken together they give the general shape and configuration of the counte- nance. ; The head is placed on the top of the backbone, and is capable of a variety of motions upon it. The backbone is the main support of the trunk of the body, and is composed of twenty-four distinct bones called vertebra, placed one above another, so as to form a kind of pillar or column. The body of each vertebra consists of a solid cylindrical piece of bone, and this is united firmly to those contiguous to it, above and below, by strong and elastic cartilages. The body of the vertebra is solid; but behind | it, and on each side, are projections of bone, called pro- cesses, which are arched over and connected together in such a manner as to form a canal from one end of the spine to the other. This canal contains the spinal nerve | or marrow, and between the vertebre are holes through Vertebra. which branches are sent out to the different parts of the body. (Fig. 1 and Fig. 2.) Seven of the vertebra belong to the neck, twelve to the back, and five to the loins. ‘They are called respectively the cervical, dorsal, and lumbar vertebra. They increase in size from above downwards, so that the lumbar vertebre are much larger, thicker, and stronger than those of the back and neck. ‘To the dorsal vertebre are affixed twelve ribs on each side, which arch over forwards, and are joined to the sternum or breastbone by means of cartilage or gristle. In this way they form the cavity of the thorax or chest, which contains the heart and lungs. This cavity is terminated below by a muscular membrane, called the dia- phragm or midriff, which extends from the edges of the lower ribs, and stretches across to the backbone, so as to form a com- plete curtain or division between the chest, and the abdomen > which les below it. This is another important cavity, usually called the belly, containing the stomach, liver, spleen, intes- tines, and other important organs. It is formed below by four bones attached to the lower end of the back, which spread out GENERAL STRUCTURE OF ANIMALS. Fig. 2. SKELETON oF MAN. Frontal bone. Under jaw. Mecieler ati neck: 32st Palle Scapula or shoul- der-blade. Humerus or Lumbar vertebrae. -.._-...--—--- rants We q il ~~-—----------->+f Hip-bones or Ulna. Radius e----- = ---- Wrist or carpal bones. Z AT Metacarpal bones.~~--- Zia’ fy Api Fingers Coal 2) Co eee MY] fy Ph |) langes. ff / f 5 Thigh. wn nnn == --- ++ ee Tibia. os MER ANS Ds TIE | Fibula. 7 Tarsal or ankle -bones. 23 Parietal bone. Temporal bone. Clavicle or collar- bone. Arm. Pelvis. Forearm. Thich. Kneepan. Leg. Tarsus. Metatarsus. Phalanges. ies Laptueeteties ee et ey seas ene Seager eens tener wT nag | 24 GENERAL STRUCTURE OF ANIMALS. and constitute a sort of basin, called the pelvis. This serves as a solid basis to support all the heavy organs contained in the abdomen, which is protected before and at its sides only by skin, fat, and muscles, and has no bones, except below and behind. The limbs of man and other animals are called eee extrem- ities. ‘The arm, or upper extremity, is composed of the shoulder, which has two bones, the collar-bone and shoulder-blade, by which it is connected with the trunk; the arm, which has only one bone, long and firm, extending to the elbow; the fore- arm, which has two long bones, parallel to each other, extending from the elbow to the wrist; the wrist, having eight small and irregular bones; and the hand, on which there are four fingers, each with four bones, and the thumb with three. ‘These bones are united together, so as to form movable joints of various degrees of flexibility and power, by means of firm substances called liga- ments. ‘The surfaces which move upon one another are covered by a smooth, polished substance, cartilage, always lubricated by a fluid like the white of eggs, that renders all their motions easy and free from impediment. The lower extremities are constructed in a similar manner. The thigh-bone, the largest and strongest bone in the body, is connected above with one of the bones of the pelvis, by means of a large, round head, which is received into a socket of corre- sponding size, and thus forms the hip-joint. Its lower end, to- gether with the kneepan and one of the two bones of the leg, contributes to form the knee-joint. These last are parallel to each other, and extend from the knee to the ankle. The ankle is composed, like the wrist, of a number of small bones, of which there are seven, one of them projecting behind to form the heel. The toes have the same number of bones as the fingers and thumbs, but are shorter and less capable of free and extensive motions. These different bones are covered by muscles, fat, ed skin, which constitute the principal soft parts of the body. The mus- cles are fibrous organs, which, attached to the bones generally by tendons, by their contractions put the bones in motion, and thus originate all the movements of which we are capable. They act, GENERAL STRUCTURE OF ANIMALS. 25 in fact, like cords attached to levers, and operate according to strict mechanical principles. | The organs, by whose operation the digestion of food, the cir- culation of the blood, and the other important functions are per-— formed, are contained in the three cavities of the cranium, the thorax, and the abdomen, which have been already cursorily described. We proceed to a consideration of these several func- tions, beginning with those of the brain and senses. The brain, in man, is the grand centre of sensation and per- ception. It is the instrument through which the mind maintains its connection with the body; and this connection is extended from the brain to the other parts by means of nerves. The brain is a large organ, of a peculiar texture, occupying the whole of the cavity of the cranium, and consisting of several distinct parts. Several pairs of nerves proceed from it through different apertures in the skull, and are distributed to the parts about the head, to convey to them the powers of sensation and motion. But besides these, there is another large single nerve passing down into the canal formed by the vertebre, already described, and supplying the greater part of the body and limbs. (Fig. 3.) Through the nerves, impressions are transmitted from all parts of the body to the brain; and on the other hand, all the acts of the will produce an effect upon the different organs by their means. ‘The nerves are necessary to the exercise of the senses (which in man. are five: seeing, hearing, smelling, tasting, and feeling) ; for if the nerve going to the organ of either of these senses be injured, the mind no longer receives any impression from that sense, as happens in the disease. of the eye called gutta serena, or amaurosis. And if the nerve going to any of the limbs be destroyed or obstructed, both sensation and power of motion in that limb are either destroyed or suspended. This happens when a limb, from long-continued pressure upon it, is said to be asleep ; as, in sitting for some time in one particular position, the nerve going to one of the legs is pressed upon, and the connection with the brain being thus interrupted, the consequence is a loss of feeling and motion, which is sometimes so great as to cause the person affected to fall down, on attempting to walk. The senses, taken altogether, are more perfect in man than ‘ 2 | th Hi We Si ce RS OY PM lan a al Tl seate fa ie Sy hia oe Mig plates a mR i tet lh NRE at TO er ee a 26 Nervous System IN MAN. — In this figure is represented the general distribution of the brain and nerves throughout the body. : a, the principal portions of the brain or cerebrum, called the hemispheres; 6, a smaller distinct portion, — the cerebellum; c, the spinal nerve which passes down the back through a canal formed by the vertebrze; d, nerves of the face; e, a network or col- lection of nerves to supply the arm; f, g, A, i, nerves of the arm; j, of the ribs; %, of — the loins; /, of the hip and thigh or the sciatic; mm, 1, 0, of the leg. GENERAL STRUCTURE OF ANIMALS. oF in any other animal. Yet in each of them, individually, he is probably excelled by some particular species. ‘Thus, in sight, he is exceeded by the vulture and eagle; in hearing, by the greater number of rapacious quadrupeds; in smell, by the dog; in taste, by a great many animals; and in nicety and delicacy of touch and feeling, by most insects. In performing the function of digestion, the food is in the first place taken into the mouth, mixed with the saliva, and ground into a kind of paste, by the action of the Jaws and teeth. It is then swallowed through a long muscular canal, the cesophagus or gullet, which passes through the thorax behind the heart and lungs, near the backbone, and is conveyed into the stomach, through its upper or cardiac orifice. This is an irregularly- shaped muscular bag or sack, situated in the upper part of the abdomen, at the spot usually called the pit of the stomach. It is capable of great distention or contraction, according to the quantity which is put into it. In the stomach, the food is acted on by a peculiar fluid, called the gastric juice. It has no re- markable sensible qualities, and is nearly tasteless and destitute of odor; but its operation upon the substances exposed to its influence is very decided and powerful. They are gradually reduced, of whatever kind they may be, to one homogeneous mass, called chyme, of a grayish color, and of a consistence like that of thick cream. This operation being completed, the chyme passes out of the stomach, by its lower or pyloric orifice, situated towards the right side, into the intestines, which form a long canal, and, taken together, are many times longer than the body. In the intestines, the chyme is subjected to the action of the bile and pancreatic juice. ‘The bile, or gall, is a brown-colored, viscid, and very bitter fluid, prepared by the liver, a large organ on the right side, just beneath the ribs, and collected into the gall-bladder, where’ a part of it is reserved for use. The pan- creatic juice resembles very nearly the saliva in color and ap- pearance, and is prepared by the pancreas, an organ situated just below the stomach. These two fluids, the whole of whose office is only imperfectly understood, are mixed with the chyme, which is then separated into two parts. One of these is a thin, milky fluid, called chyle ; the remainder consists of those portions ge SS eee se ee i ee ae a i el Oe ly A eds Jee a RTI NF EE a As a Sa acriynse te re pen ae. eee i it i a i tos Abe Sie SF, 28 GENERAL STRUCTURE OF ANIMALS. of the food which are not fit for the nourishment of the system, but are rejected and thrown out of it, as useless. The chyle is gradually absorbed by capillary vessels, called the lacteals, open- ing into the intestines through nearly their whole course, and conveyed into a vessel called the thoracic duct. ‘This duct as- cends from the abdomen along the back into the thorax, and there empties its contents into the vein coming from the left arm, or left subclavian, where the chyle is immediately mingled with the mass of blood, and enters with it into the circulation. The - chyle is essentially of the same composition from whatever sub- stance it is prepared, when the digestion is perfect. Some kinds of food, however, are capable of furnishing a larger proportion of it than others: this is the case with animal food, of which it takes a smaller quantity to supply the system with nourishment, than of vegetable. Animal substances are not required to undergo so great a change in their conversion into chyle, as vegetable; and hence it is observed, that in animals subsist- ing on vegetables, the digestive organs are more various, exten- sive, and complicated, than in those which are carnivorous. The chyle, being mixed with the blood, becomes a part of it, although it is not known where or how its change from the white Fig. 4. Windpipe and bloodvessels. Lungs. —— => = 2 a = es, === = 2 Sa ‘ ——— , : =® : 7 = ; 5 WA YN > X FA ; yee = BN GS i SNe A —— WS ES a “ [ZZ —= 9 “iy z KN S SE ) eK a+ 0-0 A LBZEZEZRGR Yi NO) W222 = J BZign Y— SS Y): ee ee i y ~ Nps y y) ——_ (ZA W= S ZZ VN = = y Y = SSN