NERVOUS INTEGRATIONS IN MAN 247 



in the central exchanges a reaction which often documents 

 itself to the mind as a perceptual experience. But that 

 sensual result accrues only when the central reaction 

 involves certain sets of the central exchanges. The central 

 reaction taken as a whole consists of much that does not 

 document itself to the mind. Therefore it is better in speaking 

 of the receiving station to replace the term "sense organ" 

 by the broader and simpler term "receptor." This latter 

 is suitable for the receiving station in respect of both of its 

 two central results, the non-mental "reflex" and the sensual 

 or other mental result; whereas "sense organ" is a misnomer 

 for the receiving station in respect of its purely reflex and 

 non-mental function. This distinction is the more important 

 because the pure reflex central reaction occurs sometimes 

 by itself, and can in experiment be cut off from the mental 

 by taking advantage of the partial separateness of the 

 central exchanges for the two, although the nerve from the 

 receptor leads to both. The conducting paths to the "mental" 

 nerve centers run for the most part through the "reflex" 

 nerve centers. 



The "exchanges" or "centers" consist of extensively 

 branched nerve cells "holding hands" with each other in 

 many, but precisely restricted, directions, these communica- 

 tions being for the most part capable of being opened or 

 closed as circumstances may require. The "lines" entering 

 and leaving the exchanges, and traversing them en route for 

 others, are built of long living threads (nerve fibers) each 

 one an extension from some nerve cell, and by it kept 

 alive. The cells and their fibers when followed in the direction 

 of their linkage can be traced as chains of which each link 

 is a living nerve cell with its nerve fibers. Along these living 

 chains travel, when a stimulus excites them at any point, 

 "nervous impulses," transient waves of physicochemical 

 change. A receptor acting on the nerve fibers which connect 

 it with its next nerve centers thus excites, when it is stimu- 

 lated, nervous impulses which run into, and in various direc- 

 tions along, the central nervous system. Everywhere and 

 whatever the receptor, whether the retina reacting to light, 

 the ear to sound, or the skin to touch, the nervous impulses 

 generated seem to be alike. Each is a brief disturbance 



