THE CEREBRUM 137 



we consider the cerebrum we are too apt to assume that 

 conditions there differ radically from those at lower 

 stations. We cannot ignore the relation of the cerebral 

 structures to our consciousness, but we shall escape much 

 confusion if we hold fast so far as we may to the reflex 

 arc as the fundamental fact in the organization. 



Impulses enter the cerebral cortex from the afferent 

 division of the nervous system as they enter other parts 

 of the gray matter. Only here the direction which may 

 be given to these impulses is far less certain than in the 

 lower central complexes. The net of pathways has that 

 individual character which has been emphasized, and be- 

 cause of this no two cerebral cortices can react in just the 

 same manner. The great number of simultaneous proc- 

 esses going on in the cerebrum results in apparent col- 

 lisions and interferences which make it still harder to 

 predict the effect produced by a stimulus be it sight, 

 sound, or other external influence. Finally, a most im- 

 portant fact about cerebral reaction is the indefinitely 

 long time that may elapse between the stimulus and the 

 expressed result. A condition which operated on the 

 cortex at a certain time may seem to have been wholly 

 ineffective, but it may modify the reaction to another 

 stimulus much later. A bit of information which was 

 read with indifference and apparently forgotten may 

 shape one's course of conduct in a future emergency. 



It is held by some, among others by Morton Prince, that 

 nothing is ever forgotten. Difficulties and limitations in 

 the way of recollecting must be admitted, but it remains 

 probable that every impression made upon the cortical 

 organization is a permanent one. Every stimulus modi- 

 fies the cortical structure in some degree, and it is forever 

 unlike what it would have been if that stimulus had never 

 been applied to the receptors. The psychologic corollary 

 is that we are likely to recall under particular conditions 

 anything that we have ever heard, read, or witnessed. 

 The difficulty is to control the "conditions" referred to. 

 The images from the distant past, often of very trivial 



