416 GENERAL STRUCTURE AND FUNCTIONS, ETC. 



Reflex Action of the Nervous System. The nervous system thus 

 stands as a medium of communication between different parts of the 

 living body, so that a stimulus applied to one organ may excite the 

 activity of another. This communication between adjacent or distant 

 parts is never direct, but always a circuitous one. It passes invariably 

 through an intermediate nervous centre, which receives the impression 

 conveyed to it by nerve fibres from one organ, and reacts by sending 

 out a stimulus which calls into activity the other. This is called 

 the "reflex action" of the nervous system, because the stimulus is first 

 sent inward to the nervous centre and then returned or reflected in the 

 opposite direction. In this process, the intermediate act between the 

 inward and outward passage of the nervous stimulus is accomplished in 

 the gray substance of the nervous centres. 



