VITAL RESERVES 313 



as the stabilizing action of a gyroscope. Facilitation 

 through habit may result from a permanent change in 

 the structure of the nervous circuits. Or it may be an 

 expression of an enduring change in the dynamic pat- 

 tern of constantly recurring nervous discharges such 

 as to draw off into particular efferent pathways some 

 reserve nervous energy formerly unavailable. The re- 

 serves here drawn upon are generalized non-specific 

 energies whose actual expression is determined in each 

 case by the nature of the going concern into whose 

 activity they are incorporated. 



Even the simplest reflexes that are actually per- 

 formed by the living body involve the expenditure of 

 some accumulated reserves whose sources are knit in 

 with the reflex circuits. This gives to these "naturaF' 

 reactions their impulsive drive. The appropriate re- 

 action goes off "of itself" when the adequate stimulus 

 is applied because the body is made that way. This 

 free discharge of energy is satisfying if the appropriate 

 end is attained, if in biological terms the reaction 

 is adaptive. Otherwise the reaction continues un- 

 checked, and fresh reserves are drawn upon. 



In an unusual situation for which no appropriate 

 reflex circuit is already structurally in readiness the 

 internal reserves are repeatedly tapped in successive 

 trial-and-error reactions until an adaptive response is 

 achieved or fatigue puts an end to the process. These 

 trials may eventuate in overt action or they may take 

 the form of "implicit" reactions, trials whose pro- 



