DIGESTION 



247 



ceive food material for their growth and activities the 

 food must be prepared for being assimilated. Such prep- 

 aration is the work of the organs of digestion. These 

 organs act upon the food so as to convert it into a soluble 

 form capable of passing by osmosis into the tissues where 



Molars. 



Pre-molars. Canine. Incisors. 



PIG. 187. Human teeth. 



it is assimilated. The conversion of food into soluble 

 form commonly involves both mechanical and chemical 

 processes. In man and many other animals food is 

 chewed so that it is divided up into smaller particles 

 which can be acted on more readily by the digestive juices. 

 Another mechanical process 

 consists in moving the food 

 through the alimentary canal 

 where it is acted upon by 

 ferments and absorbed. 

 These functions involve 

 various organs which will 

 now be described. 



The Teeth. In man there 

 are thirty-two teeth. The 



N 



FIG. 1 8 8. Teeth of child of six 

 and one half years. /, incisors; O, 

 canine; M, molars; E, permanent 

 -, . incisors; C, canine; R, bicuspids; 



two front pairs in each jaw N mo i ar . (After Marshall.) 

 are the cutting or incisor 



teeth. Just outside of these are the canine or eye teeth; 

 then come two bicuspids on each side, and finally the three 

 molars or grinding teeth. The last of the molars appear 

 quite late in life and are commonly called the wisdom teeth. 

 The first set of teeth, or milk teeth, which the child begins 



