DIGESTION 251 



the pancreatic juice, which contains three ferments; 

 one, amylopsin, which converts starch into dextrose, a 

 form of sugar; another, trypsin, which digests proteins; 

 and a third, lipase, which acts upon fats transforming 

 them in part into soap and converting them into an emul- 

 sion. The materials which escaped digestion in the stomach 

 are acted upon by the pancreatic juice in the small intestine. 



The liver is a very large, reddish organ lying near the 

 stomach in the right side of the abdomen. Its secretion, 

 the bile or gall, may accumulate in a small sac called the 

 gall bladder before it is discharged into the intestine. The 

 bile consists in part of waste products, and it plays little 

 part in digestion, but it facilitates the absorption of food 

 through the walls of the intestine. Besides the secretion 

 of bile the liver performs another important function in 

 storing up a sort of reserve food supply in the form of 

 glycogen. This substance is a carbohydrate, allied to 

 starch. The carbohydrates which are absorbed by the 

 blood in the form of sugar (dextrose) are in part converted 

 by the liver into glycogen which accumulates in the liver 

 cells. At other times, especially during hunger or severe 

 exercise, glycogen is converted into sugar which is given 

 off into the blood. The liver, therefore, serves as a sort 

 of temporary storehouse, converting the excess of carbo- 

 hydrate into the comparatively insoluble form of glycogen 

 which is given out again in times of greater need. 



The small intestine, which is the seat of important proc- 

 esses of digestion, is an organ especially adapted for the 

 absorption of digested food. A certain amount of absorp- 

 tion occurs in the stomach, and also in the large intestine, 

 but most of it occurs in the small intestine whose numerous 

 villi and folds with their rich supply of blood and lymph 

 vessels afford a large surface through which the soluble 

 products of digestion have ready access to the blood and 

 lymph. 



