PART IV. HOW THE BODY IS CON- 

 TROLLED 



CHAPTER XVI 



THE NERVOUS SYSTEM 



511. Function of Nervous System. The ameba and 

 other one-celled animals need no nervous system, but the 

 larger animals, consisting of a colony of cells, as it were, 

 need a means of communication between the cells, in order 

 that their life may be harmonious. Robinson Crusoe could 

 not have used a telephone or a post office system, but a 

 number of individuals living together and practicing a 

 division of the labor of the community for their mutual 

 advantage, are compelled to communicate with each other 

 in order to make their necessities known. The lowest of 

 the many-celled animals, such as the sponges, have no cells 

 specially set apart for carrying messages between the 

 cells, but each cell passes the impulses it receives to its 

 neighbor cell. This will do for a small and simple com- 

 munity of cells, but a larger community, like one of the 

 higher animals, possesses certain cells, called nerve cells, 

 whose chief function is to keep up the communication 

 between the cells. In the chapter on the master tissues 

 you learned that the nerve cells did this by means of long 

 branches, which in some cases are several feet long. 



512. Communication is not All that is necessary. Did 

 you ever see a crowd of people at a fire when a neighbor's 

 house was burning ? Everybody ran about, yet very little 

 was done. Everybody shouted orders which nobody obeyed. 

 But on the arrival of the chief of the fire department or 

 the head of a fire company, who had had experience in 



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