CHAPTER XIX 

 HOW HABITS ARE FORMED 



Problems : To learn what instincts are. 



To learn what habits are and how they are formed. 



To learn some rules for hahit forming. 



To know some useful health habits. 



To find out the effect of alcohol on the nervous system. 



Laboeatory Suggestions 



Demonstration. Instinctive acts on the part of a newly hatched chick. 



Class Exercise. To list good and bad habits. 



Demonstration. To show some eye defects and how they are corrected. 



Class Exercise. To sum up the bad effects of alcohol on man. 



The Body a Self-directed Machine. — The body has been 

 likened to an engine in that, while burning fuel, or food, it has done 

 work. If the comparison is carried further, however, the simile 

 ceases ; for the engine is directed from the outside, while the body 

 machine is self -directed. 



Moreover, most of the acts we perform during a day's work are 

 the results of the automatic working of this body machine. The 

 heart pumps; the blood circulates its load of food, oxygen, and 

 wastes; the movements of breathing are performed; the thou- 

 sand and one complicated acts that go on every day within the 

 body are seemingly undirected. But the chemical messengers 

 called the hormones, and the autonomic nervous system, at all 

 times have these activities under control. 



Instincts. — In many animals certain important activities of 

 life are instinctive, that is, they are performed for the first time 

 without being learned. A wasp lays its eggs in the body of a 

 caterpillar, which it first paralyzes by stinging ; the oriole weaves 

 its nest, or the swallow builds its nest of mud.; the trapdoor spider 

 makes its tunnel in the ground and tonishes it with a door — 



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