THE NERVOUS SYSTEM SI 



organs to a final effective outcome, cannot be 

 stated, and is perhaps, after all, a question of 

 no significance. For the nervous system, even 

 at its lowest physiological ebb, is never quies- 

 cent. It exhibits continuous activity. Even 

 in sleep our muscles show a slight contraction 

 due to a faint but incessant stimulation from 

 the nervous centers. The passage of a reflex 

 impulse through the nervous system, then, is 

 not so much like a brief period of activity in 

 an otherwise motionless machine as it is like 

 a momentary increase of motion in a slow con- 

 tinuous operation. From such a continuum 

 the voluntary impulses emerge. To seek their 

 origin is perhaps to look for that which does 

 not exist, at least in the definite and crystal- 

 lized form in which we often think of it. 



Just as memory affords a most taxing and 

 perplexing problem for science, so the volun- 

 tary act is a process about which there is very 

 little real understanding. The difficulty lies in 

 its freedom. Such acts give us every evidence 

 both outward and inward of self-control. They 

 seem to be self -determining and in this respect 

 to violate those principles of sequence that we 

 find to underlie so much of nature. 



Attempts have been made to show that the 



