CHAPTER VIII 



THE NERVOUS SYSTEM 



Review Questions introducing this Subject. What is a cell ? What 

 are the five supporting tissues? What are the two master tissues? 

 Why are they so called? What kind of cells have many branches? 

 Does the food ever come in contact with the salivary glands? When 

 you look at a basket of apples, the sight ' makes your mouth water." 

 Is there a connection between the eye and the mouth? What two tis- 

 sues enable the skin to blanch and to blush ? Do the different organs 

 share the blood in the same proportions at all times ? How can this 

 proportion be changed? How is the brain protected from injury? 

 How is the spinal cord protected? Is the hole for the spinal cord 

 through the main body of the vertebra, or behind the main body? 



Harmonious Activity. Strike suddenly at the eye of 

 another, and the lids fall to protect it, and the hands rise 

 'to ward off the blow. If a grain of dust gets into the eye, 

 the tear glands form tears to wash it out. If you touch 

 the hand unexpectedly to a hot iron, the muscles of the 

 arm jerk the hand away. If the foot of a sleeping person 

 is tickled, the muscles of the leg pull it away. Many 

 muscles cooperate in the act of running. If the human 

 being were merely an assemblage of working organs, the 

 organs might act independently, and there would be such 

 confusion that the body would be powerless, and life could 

 not be maintained. The nervous system enables the or- 

 gans to work together for the common good. Why does 

 an ameba not need a nervous system ? 



The Need of Nerve Centers as well as Nerves. If there 

 were no central office in a telephone system of one thou- 

 sand subscribers, then every subscriber, in order to com- 



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