302 ZOOLOGICAL PHILOSOPHY 



fluid of the nerves should always travel from the point of the body that 

 is affected towards the nucleus or centre of communication of the 

 system and there start an agitation which affects all the nerves 

 serving for feehng ; their fluid then reacts and sensation is produced. 



Not only do these two sorts of functions of the nervous system differ, 

 in that there is no sensation produced by any muscular movement and 

 that there is not necessarily any muscular movement for the production 

 of a sensation ; but these functions differ also, as we have just seen, 

 by the fact that in one the nervous fluid is driven from its reservoir 

 to the parts, whereas in the other it is driven from the parts to the 

 nucleus or centre of communication of the system of sensations. These 

 facts are manifest, although we cannot witness the movements which 

 cause them. 



The function of the nervous system which consists in bringing 

 about emotions of the inner feeling, and which works by means of a 

 general disturbance of the free mass of nervous fluid — a disturbance 

 which is followed by no reaction and therefore produces no distinct 

 sensation- — is yet quite peculiar and very different from the two that 

 I have named ; in the account that I shall give of it (Chapter IV.) 

 we shall find that its study is very curious and interesting. 



Whereas the function, by which the nervous system sets the muscles 

 in action and assists the performance of organic functions, is different 

 from the function by which this system produces feeehng as also from 

 that which constitutes the emotions of the inner feeling, I have now to 

 remark that when the system is sufficiently developed to have obtained 

 that special accessory organ constituted by the wrinkled cerebral 

 hemispheres, it then has the faculty of performing a fourth kind of 

 function, very different from the three others. 



Indeed, by means of the accessory organ that I have mentioned, 

 the nervous system gives rise to the formation of ideas, judgments, 

 thoughts, will, etc. ; phenomena which assuredly could not be produced 

 by the first three kinds of functions. Now the accessory organ, in 

 which are carried out functions capable of giving rise to these pheno- 

 mena, is only a passive organ, on account of its extreme softness ; 

 and it receives no excitation because none of its parts would be capable 

 of reacting ; but it preserves the impressions received, and these 

 impressions modify the movements of the subtle fluids in its numerous 

 parts. 



An ingenious idea, though destitute of proof or any adequate basis, 

 has been expressed by Cabanis, who said that the brain acts on the 

 impressions which the nerves conveyed to it as the stomach acts on 

 the food poured in from the oesophagus ; that it digests them in its 

 own way, and that when agitated by movement transmitted to it, it 



