334 BRAINS OF RATS AND MEN 



ergy within the central nervous system, as in the 

 "avalanche conduction" of the cerebellum (Herrick, 

 1924, pp. 263 fF.). These are knit in with the stereo- 

 typed action systems and supply the impulsive en- 

 ergy or "drive" of all reflex and instinctive behavior. 



The second kind of apparatus of neural reserves is 

 well developed only in the higher vertebrates and 

 pre-eminently in the association centers of the human 

 cerebral cortex. It is radically different from the 

 other. The first sorts of reserves support reaction pat- 

 terns which, in their broad outlines certainly, and ap- 

 parently often in detail, are laid down within the in- 

 nate organization and are with difficulty modified (in 

 lower animals) by personal experience. Here the as- 

 sociated reserves in general reinforce, prolong, or 

 otherwise facilitate the reflex and instinctive be- 

 havior. The second sorts of reserve mechanisms, on 

 the other hand, are superposed upon the innate ap- 

 paratus (not knit into it); they mature much later 

 (wholly postnatal in the human infant), and the pat- 

 terns of their development are largely shaped by indi- 

 vidual experience. They are functionally knit in with 

 individually modifiable behavior. 



Reflex and instinctive action function largely in 

 terms of racial experience. The association centers, 

 on the other hand, form in the aggregate the great 

 storehouse of personal memories, the residua of indi- 

 vidual experience. These centers contain countless 

 nerve cells with short axons (type II neurons) whose 



