AFFERENT IMPULSES SENSATIONS. 283 



of the afferent nerves ; all life long nervous impulses, now 

 more, now fewer, are continually 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 fur- 

 nished 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 continu- 

 ally 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 ordinary 

 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 general anaesthesia. Whenever 

 the sound eye was closed he went to sleep." Text Book of 

 Physiology, FOSTER. 



Let us turn from the consideration of outgoing, or efferent, 

 nerve impulses and their resulting action, to the incoming, or 

 afferent, nerve impulses and the activity which they rouse in 

 the gray matter of the cerebrum Sensation. 



READIN^J. Wear and Tear, Mitchell. 



