328 ZOOLOGICAL PHILOSOPHY 



the nerves excite muscular action, yet he obviously had a general idea 

 of what actually occurs in the production of sensations ; he expresses 

 himself as follows : 



" The operations of sensibility may be regarded as being made up 

 of two phases. In the first place the extremities of the nerves receive 

 and transmit the original impression either to the entire sensitive 

 organ, or, as we shall see later, to one of its isolated systems ; the sen- 

 sitive organ then reacts on the nerve endings, so that the sensibility, 

 which in the first phase seems to have travelled from the periphery 

 to the centre, returns in the second phase from the centre to the 

 periphery ; and the nerves, to put it briefly, exert a real reaction on 

 themselves for producing feeling, just as they do on the muscular parts 

 for producing movement." {Rapports du Physique et du Moral, vol. i., 

 p. 143.) 



The only deficiency in the above statement is the omission to state 

 that the nerve at whose extremity the original impression was received 

 is the only one which does not subsequently react ; and that for this 

 reason the general reaction from the other nerves of the system, on 

 reaching the common nucleus, is necessarily transmitted into the only 

 nerve that is at the moment in a passive state, and thus conveys to 

 the point first affected the general effect of the system, that is to say, 

 sensation. 



As to the statement of Cabanis that the nerves exert a similar reaction 

 on the muscular parts for setting them in motion, I believe that this 

 comparison between two very different acts of the nervous system has no 

 true foundation ; but that a simple emission of the fluid of the nerves 

 from its reservoir to the muscles is a sufficient explanation : there is no 

 necessity to assume any nervous reaction. 



I shall conclude my observations on the physical causes of feeling 

 by the following reflections, for the purpose of showing that it is a 

 mistake to confuse the perception of an object with the idea that may 

 be called up by the sensation of that object, and also to imagine that 

 every sensation necessarily yields an idea. 



To experience a sensation and to distinguish it are two very different 

 things : the former without the latter constitutes only a simple per- 

 ception ; whereas the latter, which is never found apart from the former, 

 alone gives rise to the idea. 



When we feel a sensation from some external object and distinguish 

 that sensation, although we only feel what is within ourselves and 

 although we have to make one or more comparisons in order to differ- 

 entiate the object from our own existence and form an idea of it, we 

 carry out almost simultaneously by means of our organs two acts of 

 essentially different kinds, one of which makes us feel while the other 



