OF LIFE 207 



tion, there soon arrives a time when irritability and the exciting cause 

 are no longer sufficient by themselves for the acceleration needed in the 

 movements of the fluids ; nature then makes use of the nervous system 

 which increases the effects of the irritability of the parts by adding 

 the activity of certain muscles ; and when this system permits of 

 muscular movement, the heart becomes a powerful motor for accele- 

 rating the movement of the fluids ; finally, after the establishment 

 of pulmonary respiration muscular movement is once again necessary 

 to the performance of vital movements on account of the alternate 

 dilatations and contractions occurring in the cavity which contains 

 the respiratory organ and without which there could be no inspirations 

 or expirations. 



" Doubtless we are not called upon," says M. Cabanis, " to prove 

 again that physical sensibility is the origin of all the ideas and habits 

 constituting the moral existence of man ; Locke, Bonnet, Condillac 

 and Helvetius have pushed this truth to the last stage of demonstra- 

 tion. Among educated persons who use their reason there is now no 

 one who can throw the smallest doubt upon the matter. From 

 another standpoint, physiologists have proved that all vital movements 

 are the result of imjpressions received by sensitive parts, etc." {Rapports 

 du Physique et du Moral de l'Homme, vol. i., pp. 85, 86). 



I too recognise that physical sensibility is the source of all ideas, but 

 I am very far from admitting that all vital movements are the result 

 of impressions received by sensitive parts : that at most can only be 

 true with regard to such living bodies as possess a nervous system ; 

 for the vital movements of those which have no such system cannot 

 be the result of impressions received by sensitive parts : this is quite 

 obvious. 



If we wish to make a true analysis of life, we must necessarily 

 examine the facts which it presents in all bodies possessing it. Now 

 as soon as we deal with the subject in this way we see that what is 

 really essential to the presence of life in one plan of organisation is 

 by no means essential in another. 



No doubt nervous influence is necessary to the maintenance of life 

 in man, and in all animals which have a nervous system ; but this 

 does not prove that vital movements, even in man and in animals 

 provided with nerves, are due to impressions made on sensitive parts : 

 it only proves that their vital movements cannot occur without the 

 help of nervous influence. 



It is clear from the above exposition that life in general may exist in 

 a body, although the vital movements are not produced by impressions 

 received by the sensitive parts and although there is no muscular 

 activity ; it may even exist when the body possessing it has no 



