OF THE UNDERSTANDING 375 



To try to determine how the agitations of the nervous fluid trace or 

 engrave an idea on the organ of understanding, would be to court the 

 risk of committing one of those numerous errors to which the imagina- 

 tion is liable ; all that we can be sure of is that the fluid in question is 

 the actual agent which traces and impresses the idea ; that each kind 

 of sensation gives a special agitation to this fluid and consequently 

 causes it to impress equally special outhnes on the organ ; and, 

 lastly, that the fluid acts upon an organ so soft and delicate and 

 finds its way into such narrow interstices and tiny cavities, that it 

 can impress on their delicate walls traces more or less deep of every 

 kind of movement by which it may be agitated. 



Do we not know that in old age, when the organ of intelhgence has 

 lost some of its dehcacy and softness, ideas are graven less deeply and 

 with greater difficulty ; that memory, which is gradually being lost, 

 only recalls ideas graven long ago upon the organ, since they were 

 then more easily and deeply impressed ? 



Moreover, with regard to the organic phenomenon of ideas, we are 

 deahng exclusively with relations between moving fluids and the 

 special organ which contains them. Now for operations so swift as 

 ideas and all intellectual acts, what other fluid could produce them but 

 the subtle and invisible fluid of the nerves, a fluid so analogous to 

 electricity ; and what organ could be more appropriate for these delicate 

 operations than the brain ? 



Thus a simple or direct idea is formed, whenever the fluid of the 

 nerves is agitated by some external impression or even by some internal 

 pain, and conveys the agitation to the nucleus of sensations, and when 

 attention has prepared the way for the further conveyance of that 

 agitation to the organ of intelhgence. 



As soon as these conditions are fulfilled, the impression is immediately 

 traced upon the organ, the idea comes into existence and is at once 

 perceived because the individual's inner feeling is affected by it ; 

 lastly, the idea may be called up afresh by memory, although obscurely, 

 whenever the individual directs the nervous fluid over the subsisting 

 traces of that idea. 



Every idea recalled by memory is therefore much vaguer than when 

 it was formed ; because the fact which renders it perceptible does 

 not then result from a present sensation. 



Complex Ideas. 



By a complex or indirect idea, I mean one that does not arise immedi- 

 ately from the sensation of some object, but is the result of an act of 

 intelhgence working on ideas already acquired. 



The act of understanding which gives rise to the formation of a 



