12 



ANIMAL CHEMISTR1. 



in vegetables. In both, the same cause de- 

 termines the increase of mass. This con- 

 stitutes the true vegetative life, which is 

 carried on without consciousness. 



The activity of vegetative life manifests 

 itself, in vegetables, with the aid of external 

 influences ; in animals, by means of in- 

 fluences produced within their organism. 

 Digestion, circulation, secretion, are no 

 doubt under the influence of the nervous 

 system ; but the force which gives to the 

 germ, Ue leaf, and the radical fibres of the 

 vegetable the same wonderful properties, is 

 the same as that residing in the secreting 

 membranes and glands of animals, and 

 which enables every animal organ to per- 

 form its own proper function. It is only 

 the source of motion that differs in the two 

 great classes of organized beings. 



While the organs of. the vital motions are 

 never wanting in the lowest orders of ani- 

 mals, as in the impregnated germ of the 

 ovum, in which they are developed first of 

 all, we find, in the higher orders of animals, 

 peculiar organs of feeling and sensation, of 

 consciousness and of a higher intellectual 

 existence. 



Pathology informs us that the true vege- 

 tative life is in no way dependant on the 

 presence of this apparatus ; that the process 

 of nutrition proceeds in those parts of the 

 body where the nerves of sensation and 

 voluntary motion are paralysed, exactly in 

 the same way as in other parts where these 

 nerves are in the normal condition ; and, on 

 the other hand, that the most energetic voli- 

 tion is incapable of exerting any influence 

 on the contractions of the heart, on the mo- 

 tion of the intestines, or on the processes 

 of secretion. 



The higher phenomena of mental exist- 

 ence cannot, in the present state of science, 

 be referred to their proximate, and still less 

 to their ultimate causes. We only know of 

 them, that they exist ; we ascribe them to 

 an immaterial agency, and that, in so- far as 

 its manifestations are connected with matter, 

 an agency entirely distinct from the vital 

 force, with which it has nothing in common. 



It cannot be denied that this peculiar force 

 exercises a certain influence on the activity 

 of vegetative life, just as other immaterial 

 agents, such as Light, Heat, Electricity, and 

 Magnetism dp ; but this influence is not of 

 a determinative kind, and manifests itself 

 only as an acceleration, a retarding, or a dis- 

 turbance of the process of vegetative life. In 

 a manner exactly analogous, the vegetative 

 life re-acts on the conscious mental existence. 



There are thus two forces which are found 

 in activity together; but consciousness and 

 intellect may be absent in animals as they 

 are in living vegetables, without their vitality 

 being otherwise affected than by the want 

 of a peculiar source of increased energy or 

 of disturbance. Except in regard to this, 

 all the vital chemical processes go on pre- 

 cisely in the same way in man and in the 

 lower animals. 



The efforts of philosophers, constantly re 

 newed, to penetrate the relations of the soul 

 to animal life, have all along retarded the 

 progress of physiology. In this attempt 

 men left the province of philosophical re- 

 search for that of fancy ; physiologists, car- 

 ried away by imagination, were far from 

 being acquainted with the laws of purely 

 animal life. None of them had a clear con- 

 ception of the process of development and 

 nutrition, or of the true cause of death. 

 They professed to explain the most obscure 

 psychological phenomena, and yet they were 

 unable to say what fever is, and in what 

 way quinine acts in curing it. 



For the purpose of investigating the laws 

 of vital motion in the animal body, only one 

 condition, namely, the knowledge of the 

 apparatus which serves for its production, 

 was ascertained ; but the substance of the 

 organs, the changes which food undergoes 

 in the living body, its transformation into 

 portions of organs, and its reconversion into 

 lifeless compounds, the share which the at- 

 mosphere takes in the processes of vitality ; 

 all these foundations for future conclusions 

 were still wanting. 



What has the soul, what have conscious- 

 ness and intellect to do with the develop- 

 ment of the human foetus, or the foetus in a 

 fowl's egg? not more, surely, than with the 

 development of the seeds of a plant. Let 

 us first endeavour % to refer to their ultimate 

 causes those phenomena of life which are 

 not physiological ; and let us beware of 

 drawing conclusions before we have a 

 groundwork. We know exactly the me- 

 chanism of the eye; but neither anatomy 

 nor chemistry will ever explain how the 

 rays of light act on consciousness, so as to 

 produce vision. Natural science has fixed 

 limits which cannot be passed; and it must 

 always be borne in mind that, with all our 

 discoveries, we shall never know what light, 

 electricity, and magnetism are in their es- 

 sence, because, even of those things which 

 are material, the human intellect has only 

 conceptions. We can ascertain, however, 

 the laws which regulate their motion and 

 rest, because these are manifested in pheno- 

 mena. In like manner the laws of vitality, 

 and of all that disturbs, promotes, or alters 

 it, may certainly be discovered, although we 

 shall never learn what life is. Thus the 

 discovery of the laws of gravitation and of 

 the planetary motions led to an entirely new 

 conception of the cause of these phenomena. 

 This conception could not have been formed 

 in all its clearness without a knowledge of 

 phenomena out of which it was evolved ; 

 for, considered by itself, gravity, like light 

 to one born blind, is a mere word, devoid of 

 meaning. 



The modern science of physiology has 

 left the track of Aristotle. To the eternal 

 advantage of science, and to the benefit of 

 mankind, it no longer invents a horror vacvi, 

 a quinta essentia, in order to furnish credu- 

 lous hearers with solutions and explanations 



