DIGESTION 



A tooth cut open. 



a enamel. 



b dentine or bone. 



c pulp cavity con- 

 taining blood 

 tubes and 

 nerves. 



d cement. 



child loses his first set of teeth and gets a whole new set 

 with eight additional ones. 



19. Structure of teeth. Through the center of each 

 tooth there runs a small tube which contains a nerve and a 

 blood tube. The outside of the part above 



the jaw is covered with a very hard sub- 

 stance called enamel, which protects the 

 inner part from decay and injury. Biting 

 hard things, like nuts or wood, often breaks 

 the enamel, and then the tooth decays. 

 When the decay reaches the nerve, the 

 tooth aches and becomes very tender. 



20. Care of the teeth. Bits of food 

 sometimes get between the teeth, and if left 

 there make the breath smell bad, and often 

 cause the teeth to decay. A wooden tooth- 

 pick used after each meal will best remove 

 these bits of food. 



A gray substance, called tartar, often collects upon the 

 teeth, making them rough and dirty. One should keep 

 this from forming by brushing the teeth with a tooth- 

 brush and water each morning and night. Tobacco-chew- \ 

 ing stains the teeth almost black and causes them to decay/ 

 quickly. * 



21. The jaws. The upper jaw is a part of the bone of 

 the face and cannot be moved. The lower jaw is a half 

 circle of bone with its two back ends turned up. It can 

 be moved up and down, forward and backward, and side- 

 wise. By its movements it causes the teeth to act upon 

 the food in every direction. 



22. The cheeks and tongue. The cheeks and tongue 

 are made up mostly of muscles which can roll the food 

 about in any direction. They have a fine sense of feeling, 



ov. PHYSIOL. (INTER.) 2 



