302 MAN --AN ADAPTIVE MECHANISM 



taneously compete for entrance, the brain patterns of 

 man have been modified and the complex reactions of 

 social adaptations have succeeded the simple processes 

 of food-getting and injury-avoidance which were suffi- 

 cient for the primitive organism. 



Theoretical Structure of Action Patterns Effector 

 Ceptors 



The manner in which this vast multiplicity of 

 adaptive responses is achieved and their specificity 

 established may be inferred from the facts that the 

 nerve paths over which impulses pass from the periph- 

 ery to the brain are insulated ; that the nerve paths 

 over which pass the motor impulses from the brain 

 to the periphery are insulated ; and that the innumer- 

 able conducting paths in the brain are not insulated. 

 From this arrangement we infer that it is necessaiy 

 that impulses from the sense organs to the brain, and 

 impulses from the brain to the muscles, be carried in- 

 tact and undisturbed ; whereas within the brain it is 

 necessary or immaterial that impulses be dis- 

 seminated freely. 



Reflection upon these two opposite types of struc- 

 ture within the brain and without the brain suggests 

 the following .hypothesis regarding the manner in 

 which action patterns are constructed. 



Let us suppose that the brain is composed of 

 mechanisms of three general types, one for supplying 

 motor power the brain-cells ; another for conduct- 

 ing this motor power as action currents; and the 

 third, specific receptor mechanisms within the brain 



