80 THK NKHVOl S S1STKM AND ITS C( >.\\SKK VATK >.\ 



nit'iits of certain processes in the cerebral gray matter. 

 We must assume that the streams of energy flashing from 

 point to point in the cortex are very numerous, and we 

 cannot say why some are attended with corresponding 

 phenomena in our consciousness while others are not. 

 The problem of attention is suggested at once, and this 

 belongs to the psychologist. For the physiologist it is a 

 persistent mystery how the physical mechanism can be so 

 multifarious and the subjective experience so unified. 



The afferent fibers which have thus far been discussed 

 are those originating below the head. These exert direct- 

 ing influences upon the central mechanism which we are 

 not likely to overestimate, but their contribution to the 

 current of sensation is much less vivid and interesting than 

 that furnished by way of the cranial nerves. If there is a 

 partial exception to be conceded, it is in the case of the 

 fingers, with their wonderful sensory equipment. Other- 

 wise it needs no argument to prove the superior prominence 

 of the eye and the ear in guiding intelligent conduct. To 

 be without taste or smell would be a minor privation, but 

 deafness and blindness are grave calamities, and when the 

 two are conjoined we regard the victim with a pitying awe, 

 which may be displaced by reverent admiration when we 

 witness such triumphant emergences as those of Laura 

 Bridgman and Helen Keller. 



Something has been said previously of the afferent 

 service of the cranial nerves. It will be recalled that in 

 these nerves there is no clear assorting of sensory fibers to 

 form a scries of dorsal roots. In two or three cases t hen- 

 are ganglia in which are gathered the perikarya which 

 maintain the passing fibers. The largest of these ganglia 

 and the one most frequently referred to is the ( Jasserian 

 ganglion on the trunk of the great fifth (trigeminal) 

 nerve. 



Vision. The immense importance of the optic impulses 

 in determining the content of the human mind and the 

 conduct of human life is faithfully indicated in the large 

 size of the optic nerves. Nearly half a million fibers are 



