120 MAN AN ADAPTIVE MECHANISM 



The labile mechanisms in the brain transform some of 

 their energy into nerve impulses, which in turn excite 

 or inhibit the activity of certain muscles ; or, even if 

 muscular activity does not result, the glands whose 

 activity assists in the adaptive response of muscular 

 action in running or fighting are stimulated, while 

 other glands not useful in such action are inhibited. 

 For each adequate stimulus in the environment there 

 is postulated, as we have already stated in a preced- 

 ing chapter, a facilitated path or mechanism of action, 

 -"facilitated" through natural selection, a mecha- 

 nism consisting of receptor, conductor and effector 

 paths, and for convenience designated an action pattern. 



Thus, by infinitesimal changes in the length of light 

 waves are produced chemical and physical changes 

 in the rods and cones of the eye, as a result of which 

 variations in color are perceived. Thus slight varia- 

 tions in light waves result in the perception of one ani- 

 mal by another and become the adaptive stimuli which 

 excite the action pattern of fighting or of flight. In 

 like manner are excited the infinite number of action 

 patterns by which man responds adaptively to en- 

 vironment. As in the case of the muscular reflex, the 

 occurrence of the adequate stimulus acts like the 

 pressing of a button connected with a mechanism by 

 means of which a store of potential energy is con- 

 verted into kinetic energy in accordance with the 

 phylogenetic import of the exciting stimulus. 



There are many facts which support this postulate, 

 notable among which are the anatomy of the eye and 

 the chemical and histologic changes which take place 

 in that organ ; the specificity of response and the 



