SECTION II. 



The Physiology of the Nervous System. 



The different functions of the animal body have been found to 

 require for their fulfillment divers structures different in location and in 

 mode of action. In any one of the single functions of the animal body, 

 such, for example, as the contraction of a muscle, a number of processes 

 are concerned ; thus, the inauguration of the muscular contraction 

 requires the conduction to a muscle of a stimulus. The muscle in con- 

 tracting uses up a large supply of oxygen and liberates more carbon 

 dioxide and other retrograde products. Increased muscular contraction, 

 therefore, necessitates a supply to the muscle of a larger amount of 

 arterial blood and the removal from the body through the lungs and kid- 

 neys of the products of the waste of muscular tissue. Muscular activity, 

 therefore, implies accelerated circulation, accelerated respiration, and 

 increased excretion. A similar complexity may be traced in all the other 

 different functions of the animal body. Each modification or even mani- 

 festation of function implies a reflection upon the activit}^ of other asso- 

 ciated processes. This co-ordination of operations, which may be widely 

 different in character and yet closely interdependent, is accomplished by 

 means of the nervous system. The primary object of the nervous system 

 is, therefore, to link together different and widely distant organs, and 

 thus act as the regulator of the actions of the animal body. 



In animals where specialization of function has not yet appeared no 

 such communication between different parts of the body is required, and, 

 as a consequence, in such no nervous system is present. As we found 

 that the organs of circulation were largely dependent for their degree of 

 development on the complexity of the alimentary apparatus, so it may 

 be found that in a general way the nervous system is developed in pro- 

 portion to the muscular system. This indicates one of the main func- 

 tions possessed by the nervous apparatus, for controlling and modifying 

 movement. This is, however, but one side of the importance of the 

 nervous system. 



In the nervous system is developed in the highest degree the func- 

 tion of automatism. By this term is meant the power possessed by the 

 lowest forms of protoplasm of receiving impulses from without and modi- 

 fying them into efferent impulses, which may take on the form of motion 

 as their most usual manifestation. It is thus seen that automatism 



(765) 



