DIGESTION AND ABSORPTION OF NUTBIJENTS 87 



Examine carefully each of the teeth in your mouth and 

 indicate in a table like the following the number of 

 cavities (unfilled) and the number of fillings that 

 you find. 



116. Arrangement of the teeth. — Within the mouth 

 cavity the solid food is cut into small pieces, mixed with 

 the juices of the mouth, and then 

 ground into a pulpy mass. A 

 large part of this work is done 

 by the teeth, which are arranged 

 in two semicircular arches (Fig. 

 29). In a normal set of teeth 

 each tooth in the lower jaw works 

 against a corresponding tooth in 

 the upper jaw, and this is very 

 necessary in order to chew the food properly and to keep teeth 

 and gums in a healthy condition. If, however, the teeth do 

 not develop as described above, a competent dentist should 

 be employed to correct the irregularities. 



117. Milk teeth. — During early childhood there appears a 

 first set of milk teeth, which later are gradually loosened and dis- 



FiG. 29. — Arrangement of the 

 teeth. 



