PHYSIOLOGY. 



heart. This, however, is not so essen- 

 tially connected to the faculties of sen- 

 sation and motion as the business of di- 

 gestion ; for whole classes of animals (as 

 insects) possess no circulation, and are 

 nourished, like vegetables, by the mere 

 imbibing of fluids prepared in the intesti- 

 li a canal. 



The blood seems to be merely a ve- 

 hicle, receiving constantly from the intes- 

 tines, skin, and lungs, different substan- 

 ces, which it incorporates intimately, and 

 by which its losses, arising from the pre- 

 servation and growth of parts, are sup- 

 plied. The nutrition of the body is per- 

 formed during the course of the blood in 

 the minute extremities of the arteries ; 

 here the fluid changes its nature and co- 

 lour ; and it is only by the addition of the 

 various substances just pointed out, that 

 the venous blood again becomes proper 

 for the purposes of nutrition, or, in one 

 Word, again becomes arterial. 



The venous blood receives the snpplies 

 furnished to it by the skin and alimentary 

 canal, by a particular set of vessels, call- 

 ed lymphatics ; in the same way it re- 

 ceives also the particles detached from 

 various organs, in order to be sent out of 

 the body by the different secretions. 



The air entering the lungs, seems to 

 produce a sort of combustion in the ve- 

 nous blood, which is necessary for the 

 support of life in all organized bodies. 

 Vegetables, and such animals as have no 

 circulation, respire (for that is the name 

 given to this action of the atmosphere on 

 the nutritive fluid) by their whole surface, 

 or by means of particular vessels which 

 convey air into the interior of the body. 

 Those only, which enjoy true circulation, 

 breathe by means of a particular organ ; 

 because, in them, the blood constantly 

 flowing to and from the common source, 

 its vessels have been so arranged, that it 

 is not distributed to the other parts of the 

 body until after passingthrough the lungs ; 

 a circumstance which could not take place 

 where the nutritive fluid is distributed 

 uniformly through the body without be- 

 ing contained in vessels. Thus respira- 

 tion is a function of a third order, de- 

 pending entirely on circulation, and aris- 

 ing as a remote consequence from the fa- 

 culties which characterise animals. 



Generation is the only process in ani- 

 mals, the mode of which does not depend 

 on their peculiar faculties, at least as far 

 as the fecundation of the germs is con- 

 cerned. Their power of moving and ap- 

 proaching to each other, of desiring and 

 feeling, has allowed them to receive all 



the enjoyments of love, while the spermav 

 tic fluid is conveyed uncovered immedi- 

 ately upon the germs ; in vegetables, on 

 the contrary, which have no power of pro- 

 pelling this fluid, it is inclosed in small 

 capsules, capable of being transported by 

 the wind, and forming what is called the 

 dust of the stamina. Thus, while the or- 

 gans of the other functions are more com- 

 plicated in animals, on account of their pe- 

 culiar functions, generation is exercised 

 in them, for the very same reason, in a 

 more simple way than in vegetables. 



Such are the principal functions that 

 compose the animal economy ; they have 

 usually been arranged in three orders. 

 Some of them constitute animals what 

 they are, render them proper to fill the 

 space which nature has marked out for 

 them, in the general arrangement of the 

 universe, and would be sufficient for their 

 existence, if that were momentary. These 

 are the faculties of sensation and motion ; 

 of which the former determines them in 

 the choice of such actions as they are ca- 

 pable of, and the latter enables them to 

 execute these actions. Each animal may 

 then be considered as a partial machine, 

 co-ordinate to all the other machines, 

 which, by their assemblage, form this 

 world : the organs of motion are the wheels 

 and levers : in a word, all the passive 

 parts ; but the active principle, the spring 

 which sets all in motion, resides only in 

 the sensitive faculty, without which he 

 animal would be lost in a constant sleep, 

 and be really reduced to a merely vege- 

 tative life. These two functions, then, 

 form the first order, or the animal func- 

 tions. 



But the animal machine, in addition to 

 the powers which those of human con- 7 

 struction possess, is endowed with a prin- 

 ciple of preservation and repair, consist- 

 ing in the assemblage of functions which 

 contribute to nutrition, viz., digestion, ab- 

 sorption, circulation, respiration, and se- 

 cretion ; these form the second order, or 

 the vital functions. Lastly, as the duration 

 of each animal is limited according to its 

 species, the generative form a third order 

 of functions, by means of which the indi- 

 viduals that perish are replaced, and the 

 existence of the species preserved. 



This threefold division of the objects of 

 physiology is open to many objections, 

 which we* have not room to consider in 

 this place ; and we therefore add another 

 more complete and natural classification, 

 which will be sufficiently explained in the 

 subjoined tabular view. 



