324 A YEAR IN SCIENCE 



quarts of gastric juice are formed in twenty-four 

 hours. 



Digestion in intestine. The food as it enters the small 

 intestine is composed of very fine particles mixed with 

 much fluid. These particles are partly digested. Aside 

 from the mechanical action on the food, part of the 

 starch has been changed to sugar in the mouth, and 

 protein has been partly digested in the stomach. The 

 remainder of the starch and protein and all of the 

 fats need now to be acted upon by the three digestive 

 juices in the small intestine. These juices are all 

 alkaline. 



The intestinal juice acts upon starch, changing it to 

 sugar. It also acts upon all the complex sugars, reduc- 

 ing them to sugars of very simple composition. 



Bile assists in the digestion of fats. The pancreatic 

 juice, the most important of the digestive juices, acts 

 upon all kinds of foods. It contains one enzyme which 

 acts on starches and sugars, another which acts on 

 proteins, and still another which converts some of the 

 fat into soap, fatty acids, and glycerine. 



By the action of the muscles in the walls of the 

 intestine the food is slowly moved along in the small 

 intestine. At the same time that the undigested food is 

 being acted upon, the digested food is being diffused into 

 the blood. It probably requires seven or eight hours for 

 food to pass the length of the small intestine. 



Large intestine. The food passes very slowly 

 through the large intestine. There are no new digestive 



