THE SKIN 



ence between the skins of those who use coffee and those 

 who do not ? Tobacco has an effect similar to that of coffee. 

 The injury that coffee and tobacco do to the stomach and 

 liver causes the blood to be impure, and the effect of im- 

 pure blood usually shows in the complexion. 



19. The Teeth may be regarded as a part of the skin, 

 since a tooth, like a hair or a nail, is developed from a 

 papilla of the true skin. A tooth extends down into a 

 depression in the jawbone, called a socket, and is held in 

 place largely by the tightness with which the root, or 

 lower part, fits into the socket. The visible part of the 

 tooth is called the crown. 



20. Number and Names of the Teeth. A complete set 

 of teeth in adults consists of sixteen in each jaw or thirty- 

 two in all. They 



are named accord- 

 ing to their form 

 and the uses to 

 which they are 

 adapted. There 

 are eight (Fig. 18) 

 in each quarter of 

 the mouth ; and if 

 the names of the 



FIG. 18. Teeth from One Side of the Lower Jaw 



of Man. 

 i, incisors; z, canine; 3, bicuspids; 4, molars. 



eight in one quarter are learned, you know the names 

 of the thirty-two, since they are designated by the same 

 names, in the same order in each quarter of the mouth. 

 Looking, then, at the teeth in one half of one jaw and 

 naming them in order from front to back, there are two 

 incisors, one canine, two bicuspids, and three molars. 

 How many of each kind are found in the whole mouth 

 (Fig. 18)? The eight in front are for cutting off the food, 

 and hence are called incisors, or cutters. They have chisel- 

 like edges. Do the edges of the upper and the lower 

 teeth usually meet in the mouth, or do they miss each 



