DIGESTION AND ABSORPTION OF NUTRIENTS 87 



4. 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. 



FIG. 29. Arrangement of the 

 teeth. 



117. Milk teeth. During early childhood there appears a 

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



