THE NERVOUS FLUID 319 



the production of acts depending on the hypocephalon, such as con- 

 tinuous thought, deep meditation, mental agitation produced by 

 passions, etc., make good their losses slowly and often incompletely ; 

 for muscular movement is then shght, the organic movements are 

 enfeebled, the organic faculties lose their energy, and the secretions, 

 which make up for the nervous fluid used, become less copious, and 

 mental repose very difficult. 



The nervous fluid in the brain does not merely convey sensations 

 from their nucleus, and move about in various ways, but it also stamps 

 impressions on the organs, and these impressions last longer or shorter 

 according to their depth. 



This statement is not one of those monstrous products begotten by 

 the imagination : in a brief review of the chief acts of intelligence, 

 I shall endeavour to show that it is well-founded, and that we are 

 obliged to recognise it as one of those truths, that can still only be 

 attained by irrefutable inductions. 



I shall conclude my remarks on this singular fluid by some observa- 

 tions which may throw much light over the various organic functions 

 fulfilled by means of this fluid. 



All parts of the nervous fluid are in communication, in the system 

 of organs which contains them ; so that, according to the causes which 

 excite it, either a part of the fluid may be set in motion, or nearly the 

 whole fluid, or at least such part of it as is free. 



The occasions when motion occurs only in parts of it, which may 

 even be quite small, are as follows : 



1. When it stimulates muscular activity, either dependent or 

 independent of the will of the individual ; 



2. When it performs some act of intelUgence. 



The same fluid, on the contrary, moves as a whole (so far as it is 

 free) : 



1. When it produces any sensation by some general movement of 

 reaction ; 



2. Whenever it causes emotions of the inner feehng by a general 

 agitation that does not constitute a reaction?) 



These details as to the movements of the nervous fluid cannot be 

 proved by individual experiments ; at least I do not see how ; but 

 the reader will probably think them justified, if he closely follows my 

 observations on the functions of the nervous system in this third part 

 of my Zoological Philosophy. In particular, the following facts should 

 be considered : 



1. That the nervous influence which moves the muscles only demands 

 a simple emission of a part of the nervous fluid towards the muscles 

 which have to act, and that the fluid here acts only as a stimulus ; 



