PART II 



CONSCIOUS NERVOUS OPERATIONS: MOTION 

 AND SENSATION 



Of many of the processes which have to do with man's 

 life he is wholly or partly unconscious. The wonderful 

 operations of growth and development go on chiefly with- 

 out his knowledge. The nerve cells which order and 

 direct all the vital activities carry on their work so silently, 

 so regularly, so skillfully without jar or confusion 

 that neighboring cells may not even know that they are 

 busy. 



Of other nervous activities a man is fully conscious, and 

 without his consciousness the object of those operations 

 is not accomplished. A large part of the nervous system 

 and a large part of the other tissues and organs of the 

 body have for their chief business the production of con- 

 scious motion. Other sets of nerves, nerve cells, and 

 special organs are employed in bringing about those 

 experiences called sensations. These two objects are 

 effected through what may be called conscious nervous 

 operations : motion being the result of the action of cer- 

 tain nervous impulses upon bones and muscles ; sensation, 

 the result of the action of other nervous impulses upon 

 the special organs for sensation. 



In order to understand these conscious nervous opera- 

 tions it is necessary to study the skeleton and joints, the 

 muscular system, the skin as a sense organ, the senses 

 of taste, smell, sight, and hearing, and the apparatus for 

 speech. 



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