CHAPTER XLVII 



NERVOUS SYSTEM 



Introduction. In the preceding chapters we have 

 learned that the body is composed of many organs, 

 each of which lias its special function. The human 

 body, however, is not simply a collection of working 

 organs, but it is a complete organism with its many 

 parts Avorking together harmoniously. 



Even in very simple operations, the coordinated 

 action of many parts of the body is involved. In 

 moving the arm, for example, the muscles contract and 

 relax and as a result, motion is produced. In this 

 process, however, they have consumed food and oxygen 

 and given off waste products. This increases the activ- 

 ity of the digestive, respiratory, circulatory, and 

 excretory systems. Obviously it would be utterly 

 impossible for all of these organs to work together 

 for the common good, unless there was some means of 

 communicating the needs of one organ to the others. 

 There must also exist some central system that con- 

 trols the action of each of the organs in our body, 

 and brings about cooperation among them. 



Xot only must the parts of our body be correlated 

 with each other, but also they must be adjusted to the 



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