FOOD AND DIGESTION 



99 



jaw. At the age of twelve or thirteen years all the 

 permanent set have appeared except the four wisdom 

 teeth, which appear between the ages of seventeen and 



3rd molar 1st molar 1st pi-ftmolar v Latsral rncisor | 



2nd molar 2nd preraolar Ca^me Central incisor 



FIG. 92. THE PERMANENT TEETH in right half of lower jaw. 



twenty-five. The second set not only replaces the twenty 

 of the first set, but to fill the larger jaws twelve molars are 

 added, three at the back in each half jaw, making thirty- 

 two teeth in the second set(Exp. 

 7). The teeth in each quarter of 

 the mouth, named in order from 

 the front, are : two incisors, one 

 canine, two premolars, three molars. 

 Care of the Teeth. The best 

 way to care for the teeth is to 

 keep the digestion perfect. Perfect 

 digestion tends to preserve the 

 teeth, and sound teeth tend to 

 keep the digestion perfect. The teeth should be washed 

 regularly. Prepared chalk is the best dentifrice. Do not 

 rub across, but from gums to teeth, to prevent rubbing the 

 gums loose from the teeth. An unclean brush may har- 

 bor germs. TootJipicks and dental floss are useful. If 

 one eats only soft food, in which the mill and the 

 cooking stove have left no work for the teeth, the teeth 

 will decay ; for it seems to be a law of nature that 

 useless organs are removed. The pressure from chewing 



FIG. 93. UPPER JAW WITH 

 TEETH. 



