280 COORDINATION AND SENSATION 



of work, in the variations of the circulation of the blood in 

 the skin, and in the movements for protecting the body. 1 

 Work of the Nervous System. How are the different 

 activities of the body controlled and coordinated? How 

 is the body adjusted to its surroundings? The answer is 

 found in the study of the nervous system. Briefly speak- 

 ing, the nervous system controls, coordinates, and adjusts 

 the different parts of the body by fulfilling two conditions : 



1. It provides a complete system of connections 

 throughout the body, thereby bringing all parts into com- 

 munication. 



2. It supplies a means of controlling action (the so-called 

 impulse) which it passes along the nervous connections 

 from one part of the body to another. 



The present chapter deals with the first of these condi- 

 tions; the chapter following, with the second. 



The Nerve Skeleton. If all the other tissues are re- 

 moved, leaving only the nervous tissue, a complete skele- 

 ton outline of the body still remains. This nerve skeleton, 

 as it has been called, has the general form of the framework 

 of bones, but differs from it greatly in the fineness of its 

 structures and the extent to which it represents every 

 portion of the body. An examination of a nerve skeleton, 

 or a diagram of one (Fig. 125), shows the main structures 

 of the nervous system and their connection with the dif- 

 ferent parts of the body. 



Corresponding to the skull and the spinal column is 

 a central nervous axis, made up of two parts, the brain and 

 the spinal cord. From this central axis white, cord-like 

 bodies emerge and pass to different parts of the body. 



1 In a larger sense adjustment includes all those activities by means of which 

 the body is brought into proper relations with its environment, including the 

 changes which the body makes in its surroundings to adapt them to its purposes. 



