96 THE FOOD-PREPARING SYSTEM 



the lipase of the pancreatic juice. Further along in the 

 wall of the intestine are tiny glands which secrete what 

 is called intestinal juice. This juice contains several 

 enzyms. Among them, one supplements the action of 

 trypsin, so that if any proteins escape digestion in the 

 upper part of the small intestine they are sure to be acted 

 upon as the food reaches the region where the intestinal 

 juice is secreted. The other enzyms of the intestinal 

 juice are those which convert cane sugar (ordinary table 

 sugar), milk sugar (one of the constituents of milk), and 

 the malt sugar which is produced from starch by the 

 action of ptyalin, into the simple sugar, glucose, which 

 is the actual carbohydrate that is made use of by the cells. 



Movements of the Alimentary Tract. — For the 

 digestive process to go on properly the food must be 

 mixed thoroughly with the digestive juices, and it must 

 be propelled slowly along the alimentary tract from re- 

 gion to region as well. The process begins in the mouth, 

 where, by the act of chewing, every particle of food is, 

 or should be, brought into contact with the saliva. Then 

 comes the process of swallowing, whereby the well- 

 moistened food is passed from the mouth into the 

 stomach. In the stomach the food mass is subjected to 

 a churning by the muscular action of the stomach walls, 

 which serves to mix it well with gastric juice, and is then 

 expelled little by little into the small intestine. This 

 process is a gradual one and is usually not completed for 

 two hours or more after the meal is eaten. The food that 

 enters the small intestine from the stomach is again 

 churned by muscular movements of the intestine to insure 

 that the pancreatic juice has access to every particle and 

 is propelled slowly along by other muscular movements. 

 Then, after the digested material has been absorbed ac- 

 cording to the description in the next paragraph, the 

 residue, which is of no further value, is passed into the 

 large intestine, whence it is discharged from the body. 



Absorption. — The digested food within the alimen- 



