54 ELEMENTARY PHYSIOLOGY. 



Where are the extremities of the nerve of taste located ? 



What gives the tongue its velvety appearance ? 



Why are dry or solid substances tasteless ? 



What provision is made to make food more perceptible to 



the taste ? 

 Why does food have no taste to us when we are sick ? 



THE CIRCULATORY SYSTEM. 



Besides the material which the body needs for its 

 growth, during twenty years or more, it is constantly 

 exposed to wear and tear, and, consequently, it must 

 be supplied continually with material for repair. It 

 is impossible altogether to avoid the wearing out of 

 parts of the body. Some of the muscles, like those 

 of the heart, for example, are on constant duty. 

 Every contraction of a muscle destroys a part of its 

 fiber. The nervous system is also constantly suffer- 

 ing wear. The slightest effort of body or mind pro- 

 duces damage which must be made good to maintain 

 our strength. The simplest thought which occupies 

 the mind lays a tax on the structure of the brain. 

 Either a wink or a whisper destroys muscular fibers. 

 If even these gentle movements are wearng, how 

 great must be the destruction throughout the body ? 

 by labor which exercises vigorously the brain and 

 many muscles. 



So a system of organs is provided in the body, 

 whose work it is to carry to all parts a supply of 



