58 K. S. LASHLEY 



ideas of movement stored in the motor area and ideas of sen- 

 sation in the sensory areas, or with Loeb ('00) resonant vibra- 

 / tions involving the whole of the brain. The trained organism 

 differs from the untrained in its reflex reactions and it is the 

 task of physiology to trace through the reflex paths which 

 determine these reactions and to describe the mechanism by 

 which the direction of conduction is altered. 



The problem here seems clear enough but methods of solving 

 it are far to seek. We can not trace nerve impulses directly; 

 we can not make chemical analysis of individual nerve cells 

 and even if this were possible we could not interpret the results 

 until we had some notion of what cells are functional in learning. 

 1 An attempt at correlation of the learning function with struc- 

 / tural differentiations of the nervous system seems to offer almost 

 (^ the only present means of attacking the problem. Is the capac- 

 ity for formation of new functional connections inherent in all 

 nervous tissue, or is it characteristic only of a certain type of 

 organization? Does reintegration occur in the simple nerve 

 net or only after the appearance of synaptic connections? In 

 what portions of the reflex arc and in what gross divisions of 

 the nervous system does reintegration occur? Through what 

 portions of the nervous system are the propagated impulses of 

 learned reactions transmitted? Is there any type of nervous 

 organization which is particularly favorable to learning? An- 

 swers to these and similar questions may help us to formulate 

 experimental problems bearing more directly upon the mechanism 

 of fixation of habits. 



The questions which yield most easily to experimental attack 

 are those dealing with the function of gross anatomical divi- 

 sions of the nervous system. A good bit of evidence bearing 

 upon them has already been accumulated but its inconclusive 

 character may be judged from the conflicting opinions of recent 

 investigators. One finds statements to the effect that learning 

 occurs only as a function of the cerebrum (Loeb, '00; Lloyd 

 Morgan, '12), that it may occur also in lower centers (Luciani, 

 '15; Bechterew, '09), that it is the result of the combined action 

 of all parts of the cerebrum (Loeb, '00), that it is a function of 



