152 HOW FOOD IS PREPARED FOR BODY USES 



medium stiff brush and work the bristles in a vertical direction 

 away from the gum so as to get between the teeth. Dental silk 

 should be used after meals. 



It has been recently found that fruit acids are very beneficial to 

 the teeth. Vinegar diluted to about half strength with water 

 makes an excellent dental wash. If one has an acid mouth, a good 

 tooth paste mixed with castile soap may be used. 



The teeth should be cleaned by a reliable dentist at least every 

 six months. In this way deposits which cover the teeth may be 

 removed and decay prevented. If we allow decay to start, it 

 means sooner or later the loss of the tooth. 



Decay usually begins where particles of food lodge. Here 

 bacteria feed and pour out substances which act upon the hard 

 enamel. Once this is eaten through, decay rapidly advances, and 

 before long the ache in the tooth announces that decay is approach- 

 ing the pulp cavity. It may then be too late to save the tooth. 

 For this reason alone, if for no other, a dentist should frequently 

 examine our teeth ; false teeth are a very poor substitute for lost 

 teeth. 



Chewing and Swallowing. — Food should simply be chewed and 

 relished, with no thought of swallowing. It will be found that if 

 you attend only to the agreeable task of extracting the flavors of 

 your food, nature will take care of the swallowing, and this will 

 become, like breathing, involuntary Thorough mastication takes 

 time, therefore one must not feel hurried at meals. 



After food has been chewed and mixed with saliva, it is rolled into 

 little balls and pushed by the tongue into such position that the 

 muscles of the throat cavity may seize it and force it downward. 

 Food, in order to reach the gullet from the mouth cavity, must pass 

 over the opening (glottis) into the trachea. When food is in the 

 course of being swallowed, the upper part of the gullet forms a 

 trapdoor over the opening. When this trapdoor, called the epi- 

 glottis, is not closed, and food '' goes down the wrong way," we 

 choke, and the food is expelled by coughing. 



The Gullet, or Esophagus. — Like the rest of the food tube, 

 the gullet is lined with soft and moist mucous membrane. The 

 wall is made up of two sets of muscles, — the inside ones running 

 around the tube; the outer layer taking a longitudinal course. 



