208 Release of Function in the Nervous System. 



been profoundly modified by the advent of the new centres, which utilise and 

 develop some of the functions originally possessed by the older mechanism. 



(5) This dominance of higher over lower forms of neural activity is the 

 consequence of integration within the central nervous system ; it is carried 

 out partly by qualitative selection, but to an even greater extent by the 

 struggle for expression between incompatible physiological reactions. This 

 involves permanent inhibition, under normal conditions, of one group of 

 processes, or temporary suppression of these primitive activities until the need 

 should arise for a more impulsive mode of response. 



(6) All newly acquired abilities depend on a fresh adjustment of co-ordi- 

 nated reflexes, and even certain responses from normal sense-organs may be 

 suppressed or held in check. This demands the exercise of permanent 

 physiological control, which may break down under certain conditions, and 

 permit the dominated function to express itself unchecked. A stimulus of 

 excessive vehemence or prolonged duration, any abnormal state which lowers 

 the vitality of the nervous system, and even some inherent want of resistance 

 may all lead to unexpectedly disagreeable and impulsive reactions. 



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