Section III.
OP ANIUAJL OBOANIZATION.
I it 'I
We learn from the preceding observations that animid bodies are composed of fluid and solid materials, which, bwng iu intimate combination, must necessarily exert a mutual influence upon each other. This combination, which is distinguished by the name of orgmizalion, is esaential to the manifestation of the phenomena of life, and is consequently possessed by all living beings.*
• ^ felmttUng th»t an grguniwd nUucluiu b lequiMd for Ui« excrci»e of
ATlWtL OZ.OAX:ZAnOX.
■wram. jn ivc^^ii betv«cs tbe ^bres asd inns of tbe ■fi-nmaiMs jccc^ Tbsr pwytioa to ife btkr k so g=>>c. :aae ca* uebbI bocr b il'«3n sab. m ib l ^t T:*LiAtA is JB £]nau Ths pccpaobevKS' is
CLu^B : vestas, in die skcn padec: qmei. sad par> iscc^arT is c^ i-^^-^Jf. :bs qaaslkr ct sa6i ^^toal is ecasdsv»- iccreacicd- Tbe hiaxj^s cczi: to be re- pr^id 3s :rf£ r:r:«£ vrp^r7*~: eae5a.s cf' ceririaaskxi,
pcscrka irri dsoirspttaim cf 2» •'-^~«' rc>iv. ae rf- feescd. Iz. ±-£ icREiEs- ^tucesa tbd :;£.ricn« zuner is ii!.:;cidBC£ii ini: rt-e sysrici ir li-e ^rfs: re f:^ -. is the hrra-^ ^:3. :ii:se por^cks waka aii« 5rr » eaoin pe- r>:»i pefrriDiti £h<ir :tSs ia tb; ercorcr, kkI witidi thacKvc recuiTC co Sf nixw^. i» tfisBarrni &cci the both- in tbi biquiii cr ri^erta 5:r=-
In the lov^c hTtS^ :f j -~.r<. ib* h!:=icczs ifipnr to be afair»c if ec-c efidrsiT, h.':c5:T:=»i'-:<ii- *>: cai they carrel !» tiiscizzuisc!<»i itsa <a«:i ::ii.Lr rv ibar colcor
trsrx; ire fc«r diie«E: cSftsses cc f-_;-ij- I. Tboee whirii art ls:roduc»i iacu s^ >:ct cvc w^:ic«E, by ibe aiwccbinz poier ci a; =:-^vts cwciJmru; ud cf tike jiiB. i. "Hw ?ux>i. vhacfi i^ :z<e cvccnl mass of the eiratladcf Sui>^ 3. 7^ ntics which m sepa- nced W jecx«coa »<a tsu bbx>i. 4. TV im^ m^A
■ 4H A^ftitf <n^HiiBCciL Fx^tB -U ■*'■»- ^' fTitiniif"*t jf ite ■Mtftts
paamaaB viuch a« aliit»l«d n iaioc >>vcv takwo: vim ib* aAMK* of saKvoauBUui ]CB.isitt>. woh--^ m A ^HKc Ai.>ciJv iuoiKt loa ^M-
PLVI08 AND SOUBS.
arc ubsorlicd id the substance of the body, and are sub- sequently returned to the blood.
The RolitU derivc'ti from the fluids, contftin the Iiittcf and impress upon them those mowmentji which are ne- cessary for secretion and nutrition ; there is thus a mu- tuol chain of connexion between the organs and the bumourH, one being essential to the operations of the other.
This union of fluid and solid parts produces a peculiar structure, which is the most cfficic-nt'elemcDt of animal orp^iKation. It consists of a soft, areolated, and elaxtic texture, which, more or less mudified, constitutes the I' entire substance of some of the inferior animals, and in all it enters so largely into their composition that it produces, as it were, the mould of the entire body and of its individual jmrf*, so that if it were possible to remove those peciilior matters, which arc met with in the more perfect creatures, there would still remain a substance, retaining in an extraordinan,- manner, the form and tigurc of the original animal. This sub- stance, which is the common cellular membrane, is condensed upon the external surface, so as to form Uie covering cidlcd skin ; whilst in the interior, being modilied and somewliat more complicated, it gives rise to the mucous memiinme. Thus the substance of the body is contained betn'cen the skin and the raucous membrane.
In most animals another solid is found, toljilly dif- ferent from the cvUulfur tissue, namely, the muscular 6brc. It forms the basis of the muKcIt-s which are fiir- nished for the production of the various motions of the body.
The nervous fibre is another solid, equally distinct
10 OBSAV8 or AKIMALS.
bom the ceflidar and the moscdbr; it nmstitides the basis (rf* the nerrous system, wfaicfa is the instiaiuatf o£ tauibiBtj.
These three tubrtances, the cdhilar, tibe nBseolar, aad the nerrous, form, hj their nrious comfaiBatioBs ■Bd modifications, the differoit organs (rf* the animal bod^. These majr be now vtry briedT oiiHnented. Every animal, with the exceptioD probably of some of the auimalcube, possesses an external sldn, an internal mucous membrane whidi forms the wgan of digctfion, and a spongy ceDular tissue contained bdireen than. In most animals there are vessds, by which the nutri- tive matter, absorbed &om tbeir digesttve appar^ns, is carried to every part of the body ; in many animals there are organs of secretion, in which this matter is pmified by losing a portion of its substance ; and also internal organs of respiration, which are dther diqiersed in the form of tracbese, or concentrated in that of gills or lungs ; in each case the nutritious fluid is subjected to the influence of the atmosphere, and in consequence undergoes several important changes. The preceding structures, with the exception of the skin, are subser- vient to the process of nutrition.
The greater number of am'TTjuk ue provided with muscles for voluntary motion ; senses, for the recqition of external impressions i nerves, for the transmission of sensation and volition ; and, lastly, in many species, there is a brain, the oi^an of perception and volition.
All animals are capable of reproduction ; but all do not possess distinct organs of generadon ; in most in- stances, however, there are male and female organs, which are either united in one animal, producing a com- plete hermaphrodism, or they are divided between two
FOKM OF ANIMALS.
iodindtulg, so OS to give rUc to the distinction of tJie sexes. I
The form of every animal body, iihhough it is more or less rouudcd, presents an ahnmt intinice variety in the diffcrmt species, each of which has a contigur&tion pro- per to itself. In several of the lower classes, the body presents a radiated disposition, so that its diftWont parts are placed around a coiiimoo centre. In nil the more perfect animals, the body is ver)' exactly divided by a median and perpendicular plahe, into t^vo equal and sym- metrical halves. This division is not restricted to the surface, but extends into many of the internal parts of the body.
There are certain modifications of the external form, which have an immedinte influence on tlie exercise of the animal functions ; for example, in the superior classes the body is divided into a head, a trunk, and extremities, j
The head, which is often subdi'ided into the cra- nium ond Jiice, contains the great centre of the nervous system, the organs of pt;culiar sensations, and also of mastication. The trunk is usually separated into two preat cavities, called the chest and the abdomen ; in the former, the central organs of (he circulation of the blood and of respiration are lodged ; in the latter are contained the principal parts of the apparatus of diges- tion, of the secretion of urine, and of generation. Ma- ny peculiarities are exhibited in these divisions ; for instance, in some animals, the body possesses but a «ngle cai-ity, which contains all the organs, particularly those of digestion ; in others, a distinct head is added, whilst others have a thorax either separate fi-om the hc-ad and abdomen, or confounded with these cavities, nie rerlebrateil animals, who enjoy the most perfect
14
rtJKCTIONS.
organinttion, hnvc alwars a distioct hend, although the chest and abdomen arc somedrnes confounded.
The extremities or appendages are even more direr- sifted in their dispodtioo than the truok of the body. The radiated animals have certain appendages around the mouth, calli-d tentacula, which are destined to mo- tion and to feeling. The antennx of the Crustacea and in&ects appear to be organs of sensation. !n most ani- mals the appendages are placed in pairs upon tlie sides of the body, and are more* especially de^'oted to motion ; their number is 'arious, but in the %'ertebr8ta, there arc never more than four members.
In concluding this review of the organization of ani- mals, 1 shall offer a few remarks on the functions which they exercise. AH organized beings exhibit certain phenomena, to which, taken collectively, is given the term of Life. This forms a marked distinction betweea organized and inorganized bodies. Tlic former are, like the latter, subjected to the influence of the general pro* perties of matter ; but this influence is modified and controlled by the principle uf life.
The animal functions have been variously arranged fay writers on physiology, but as I shall have occasion here- after to notice some of the most celebrateil of these clas* aificationst I shall in this place merely point out the arrangement which appears to be the most judicious, lliexe phenomena may be divided into two great classes:
- Those which are connected with the individual. 2. Thoac which belong to tiiu species. 'ITie first include llm functions of nutrition and of external relation, and the veoond those of generation.
Nutrition, which is common to all organized bodies.*
•S«p.4.
p
NurniTiON.
is a simple process in the lovrest animals ; but it be- comes complicated in the more perfect species. This complexity results from the endowment of voluntary motion, which, by preventing llie direct ubsorptioii from the earth of particles ready prepared for Douri^hment, a process which occurs in plants, renders it necessai-y that the alimentary matter of an animal should be introduced into tl^ body, in order to undet^ those changes by which it may be fitted for nutrition. The principal function by which these chant's are cfFccted, is diges- tion. The food in every animal, with some unimport- ant exceptions, ts received into thetr intestinal structure, in which it is influenced by certain juices ; so tliat one part, the chyle, is separated from the mass and then ab- sorbed ; it is subsequently exposed to the influence of the atmosphere, and is thus converted into a proper nutritious fluid, which is usually observed under the form of blood. In order to purify the nutritive fluid, it is necessary that its effete parts should be separated; this elimination is accomplished by the various secrc- tion».
The real nature of nutrition and the mechanism by which it is effected, arc but very imperfectly imderstoocl. The little success that has attended the best directed at- tempts to penetrate the mystery of this wonderful pro- cess, ought not to excite our surprise, when we reflect upon the extreme minuteness of the instruments em- ployed in it, and upon the diversilied character of the various substance which are elaborated from the com- mon mass of the circulating fluids. Our knowledge of nutrition is in fact limited to the obser-ation of its effecta ; we only know that in tlie higher classes of animals, the blood is the common source from which
14
EXTERNAL RELATION.
»
tbe particles required for the mippcHt of the different organs, bowc*er dissimilar they may be, are derived ; tnd a decomposition takes place in the t;llimate res- ads, by which means a portion of the blood becomett Bolid and is deposited in the suliiitance of each organ of the body, whilst a part of the organ, whaterer it may be, becomes fluid and is carried into the torrent of the circulation, 'lliis reciprocal action of composilion and decomposition, is est^culud to the preNer%'Htion of the vital actions, so that a ^try short suspension of it proves destructive to life. The activity of the process varies in the different epochs of existence ; in the commence- ment, the deposition of nutritive matter exceeds in quantity the absoqition of old partides ; it is u[>on this excess that the phenomenon of growth depends. In the adult period, when the body is perfectly formed, tJiere is an etjuiUbrium of action. In the advance of age, the power of absorption surpasses that of deposi- tion, so that the bulk of the body is considerably dimi- nished. This formati*e process may be justly n^rded as the most imporlitut operation of the i-conomy, for it is not only essential to the denJojiement and preserva- tion of the animnl body, but it is equally re({uired in the repiuration of the effects of accident and disease.
The second class of fiuielions connected with tbe support of tlie individual, are those by whidi the exter- nal relations are established with surrounding objects. They are entirely confined to tlie animal creation, upon whicli they bestow a new kind of existence tobdly dis- tinct from mere vegetative life.
'llie animal functions, or those of relation, result from two i;reat properties, sent^ibility and contractility: upon these powers L-qualiy depend tlw simple pheno-
MN8ATIOB AND VOLITION.
meoa exhibited in the poh-pus, and the complicated operations in maa. lo some naimals sensibility is coo- fined to tile perception of impri'-ssions which are marte upon the surface of the Itotly ; and motion, to the general contmcdon which Ls the result of those imprcitsionit. But in most classes there are organs for the* exercise of special scn^^tioDs. by means of whicli, ideas of the pro- perties of surrounding bodies are acqiiireii. These bodies make impressioufi cither upon the skin or upon the peculiar r)rgans of sensi:, which arc transmitted by the nerves to the central mass of the ner-ous system, where perception takes place. This last organ is also the seat of those mental properties, such as memoty, nssocia- Uon, imitation, &c., which are enjoyed by animals.
In the inferior tribes of animated beings Uic pheno- mena resulting from contractility, are few in number and simple in character. But the superior animals, which are endowed with a more perfect organization, have the power of exercising the most complicated mo- tions with astonishing ease and rapidity : thus tliey can produce, by an effort of volition, the most trilling move- ment of each individual part of the body, or a change in the position of the whole machine. Tlic muscles are the material and obedient agents by which these com- mands of tlie will are accomplished. They are also connected with various other actions, and in Uiose creatures who breathe by the concentrated organs called lungs, they are especially the agents of the voice.
We hare in the last place to consider tlie functions which are destined for the preser'ation of the species, namely, tliose of generation. As death is the natunj and invariable termination of life, the organized world must soon have ceased to exist, if the Almighty Being,
16
GRNKRATION.
in his infinitu wisdom, had not provided for the reno- vation of the different tribes of animals nnd plants.
Ever)' li%Hng being is endowed with the faculty of reproduction. This faculty, which is inseparably con- nected with orgonimition, is cxcrclsvd in so diversified n miuiner that it has no character which is proper to, nor any thing which is common to, all animals.
In many respects, especially among the lower animals, the process of generation is similar to that of vegetables. Several classes have no particular organs, but the body ia divided into parts, each of whicli acquires the pro- perties of the whole ; tlius the millepede has been ob- sen'cd to divide (ipontaneously into two portions, upon the smaller of which a head and a biil were subsequently formed.*
' In the animals rather higher in the scale, generation is accomplished by means ofgenoos, which arc atliichedfora certain period to the parent, and are then separated, and ocqiiire on independent existence ; Uiere are, howei'er, no distinct organs. In the vertebrala, and in many classes of the moUusctt and articulnta. there arc spceial struc- tures provided for the process of reproduction, which arc called tlie sexual organs. By the o])eration of the female organs certain bodies called ova are formed ; Uiesc eggs, being influenced by the organs of the male, are capal)le of commencing an action within themselves, by which the embryo of a new animal is produced. Tlic oMim is either retained in the body of the parent untU the new beittg is sufficiently perfected to sustain an independent existence, or it is discharged at an early
- Tiemblry, Mfmolm poui I'lfiUoini ifuii 0<ci«<)e Colypc*. Ucduil, AoUomie Wmunle, p. 29.
op THE HUMAN BODY.
period, and in this case the embryo is developed by the operation of external circumstances.
Iq concluding this sketch of animal oi^nization, I am anxious to impres.^ upon the mind of the reader, that every attempt which \b made to dinde and arrange tlie organs and functions of animated beings, must, from the inseparuble connexion which exists between all parts of the living body, be imperfect. Thus, the pro- cess of nutrition has un influence on that of generation, whilst both are modiBed and assisled by the operations of the nervous and muscular systems. On the contrar)-, the animal functions are affected by the organic, and depend on these for their support. We may agree, then, with a distinguished writer,* when he says, that in animids whouc orgajiization is very greatly developed, life appears essentially to consist of the reciprocal action of the central organ of the vegetative functions, the heart, and of the principal organ of the