CHAPTER XXVI 

 NERVOUS SYSTEM 



General function of the nervous system. — The di- 

 gestive system takes care of the food we eat; it crushes it, 

 mixes it with digestive juices and gets it ready for the use 

 of the body tissues. The respiratory system furnishes the 

 blood with oxygen for the tissues. The circulatory system 

 carries the food and oxygen to the tissues. The excretory 

 system eliminates waste from the body. The muscles by 

 reason of their property of contractility, enable the body to 

 accomplish all of its movements, whether voluntary or in- 

 voluntary. 



The life of the cells of all the tissues, depends upon the 

 harmonious working together of all the systems. The activi- 

 ties of the body must therefore be co-ordinated. This is 

 brought about by the nervous system. Fibers from the cen- 

 tral nervous system pass to every organ and tissue of the 

 body. The distribution of nerves is so extensive that, as Dr. 

 Hardesty says, if all other tissues of the body could be "dis- 

 solved away there would still be left, in gossamer, its form and 

 proportions — a phantom of the body composed entirely of 

 nerves." 



The nervous system, therefore, controls and harmonizes 

 the functions of all the other organs of the body. 



Structure of the nervous system. — In the human body, 

 the brain and spinal cord lie essentially as they do in the 

 frog and other vertebrate animals studied. The brain (fig. 

 1 79, F T O) is enclosed by the bony plates of the skull. It is 

 continued downward, as the spinal cord, through the spinal 



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