13 



, 



so that they are not easily started rnmr Ilium places. They 

 are composed of soft bone within, but are covered on the 

 outside with an enamel of very hard texture, which admits 

 of an exquisitely fine polish. This enamel comes in contact 

 with the food, the drinks, and the air. It will bear great variety 

 of exposure, and resist the wear of great friction. Yet, when 

 the mouth is neglected, the enamel is apt to decay. If any 

 of the food, which has been masticated and mixed with the 

 saliva, be suffered to remain about the teeth, this mixture 

 undergoes a corrupting fermentation, and acts upon the hard 

 enamel. After a while, a hole is eaten through this cover- 

 ing; and then, when this decay reaches the softer sub- 

 stance of the body of the teeth, it acts much more rapidly. 



13. This decay is assisted also by the gathering of the 

 secretions of the mouth. The salts and acids of the saliva 

 combine with the food, and form tartar, which covers parts 

 of the teeth with a hard crust. This can be easily prevented 

 by washing the teeth frequently, and completely removing 

 all the food arid other gatherings of the mouth, after each 

 meal, and also in the morning, after an interval of sleep. 



14. The teeth have blood-vessels and nerves; they are 

 endowed with life ; and, as most people have occasion to 

 know, they also have an exquisite sensibility. When they 

 are sound, they seem to have little or no sensation ; but when 

 they are decayed, and exposed to extremes of temperature, to 

 very hot or very cold matters, or even to the air, they suffer 

 acute pain. 



CHAPTER II. 



Salivary Glands. Flow of Saliva. Mastication necessary. Ef- 

 fect of imperfect Mastication. Pharynx. (Esophagus. Epi- 

 glottis. Swallowing. 



15. THE teeth can only grind the food to powder. In 

 this condition, it can neither be swallowed, nor is it fit for the 



