THE CEREBRUM 139 



dently unlike each other and unlike the neighboring areas 

 from which electric stimulation elicits no visible reaction. 

 They are believed to contain the perikarya, from which 

 motor projection fibers extend downward to make synaptic 

 connections with neurons which directly innervate the 

 muscles. 



But in our discussion of fatigue we have insisted that 

 the perikarya at the origin of any set of projection fibers 

 cannot be regarded as the ultimate source of the impulses 

 which traverse these fibers. By losing sight of this fact 

 many writers have probably made too much of the cere- 

 bral motor areas. They have been spoken of as though 

 they were creative in function or as though they were 

 certainly the precise spots where the metaphysical force 

 impinged upon the material mechanism. Loeb protested 

 against such nai've views and presented the alternative 

 with great clearness in his "Comparative Physiology of 

 the Brain." 



Activity in the motor areas doubtless precedes most of 

 our muscular activity. But what takes place in the 

 motor areas is the result of currents arriving within their 

 boundaries from other parts of the brain. So the re- 

 responsibility is shifted to these other regions, and from 

 these again to others. The true fountain-head is not 

 found in the cerebrum at all, but in the receptors of the 

 afferent system or in the energies of the external world. 

 When this is said we merely reiterate the statement that 

 the type of nervous action is the reflex, and that we cannot 

 make an exception of those processes which are directed 

 through the cerebrum. "Through" rather than "by" 

 is the preposition, and the distinction is of the greatest 

 importance. 



The central exchange of the telephone system is an 

 impressive example of intricate mechanism, but it is, after 

 all, an intermediate point, and its function is to give di- 

 rection rather than to originate communications. More 

 damage can be done to the whole system by destroying 

 the exchange than by attacking any other single feature, 



