NERVOUS SYSTEM IN GENERAL. 269 



their activity. The only other efferent currents, so far 

 as known, are those which possibly go to the cells of 

 the tissues to regulate their nutrition or their heat pro- 

 duction. 



Having given so much attention to the outgo of nerve 

 impulses, let us ask the question, " What about the in- 

 coming nerve currents ? " 



Afferent Currents. " All life long the never-ceasing 

 changes of the external world continually break as waves 

 on the peripheral endings of the afferent nerves ; all life 

 long nervous impulses, now more, now fewer, are continu- 

 ally sweeping inward toward the center; and the nervous 

 metabolism, which is the basis of nervous action, must be 

 at least as largely dependent on these influences from 

 without as on the mere chemical supply furnished by the 

 blood. We must regard the supereminent activity of the 

 cortex and the characters of the processes taking place in 

 it as due not so much to the intrinsic chemical nature of 

 the nervous substance, which is built up into the cortical 

 gray matter, as to the fact that impulses are continually 

 streaming into it from all parts of the body ; that almost 

 all influences brought to bear on the body make themselves 

 felt by it. To put the matter in a bald way we may ask 

 the question, What would happen in the cortex if, its or- 

 dinary nutritive supply remaining as before, it were cut 

 adrift from afferent impulses of all kinds ? We can hardly 

 doubt but that volitional and other psychical processes 

 would soon come to a standstill, and consciousness vanish. 

 This is, indeed, roughly indicated by the remarkable case 

 of a patient whose almost only communication with the 

 external world was by means of one eye, he being blind in 

 the other eye, deaf of both ears, and suffering from gen- 



