CEREBRAL FUNCTION IN LEARNING 57 



an organism which is not equipped with a differentiated conduc- 

 tion system. 



The theories of the mnemonic nature of growth and evolution 

 and of extra-neural learning in general need therefore not detain 

 us further here. There is certainly need for continued investi- 

 gations in these fields, but Whatever the condition in embryonic 

 tissues may be, it is evident that learning in the individual is 

 chronologically and functionally first and that in all metazoa, 

 at least, learning is coexistent with differentiated conductive 

 tissue. 



Whether or not learning is restricted solely to the activity 

 of this tissue is, however, not certainly established. It has 

 been suggested by the writer ('17) and by Dunlap ('17) that 

 endocrine activity may play a part in the fixation of habit, 

 but some recent experiments (to be reported in another paper) 

 make this seem improbable. There is no conclusive evidence 

 for the general activity of any extra-neural structure in learning 

 while there is clear evidence that nervous organization is of 

 fundamental importance for the process. Upon the mechanism 

 of nervous activity in learning we have no direct observations { 

 but studies of the mechanism of nervous conduction in general 

 define rather clearly the type of activity which we may expect 

 to find. 



The most important neurological concept bearing upon nervous 

 function in learning is that of the reflex character of all behavior. 

 Theories of the fixation of "traces" in particular cells or areas of 

 the brain and of the arousal of images by the excitation of these 

 cells or areas have now little more than historical interest. 

 The doctrine of the image seems pretty well exploded and the 

 vast amount of data upon the reflex nature of spinal and bulbar 

 reactions accumulated within recent years leaves little room for 

 doubt that every reaction of the organism is carried out by 

 transmission of impulses over reflex paths differing only in the 

 number of cells and the complexity of organization intervening 

 between receptor and effector. The problem of nervous func- 

 tion in memory is, then, no longer one of the locus in which 

 memories are stored; we can not hypothetize with Ferrier ('76) 



