DIGESTION AND ABSORPTION l8l 



solution and is, therefore, in a favorable medium in the small 

 intestine. 



As a result then of the digestion of fat by the gastric and 

 pancreatic lipases (mostly the latter) the fat of the food is 

 hydrolyzed into glycerol and fatty acids. The glycerol is 

 soluble in water and is diffusible through the cell membranes. 

 The free fatty acids are, however, practically insoluble in 

 water and are nondiffusible through the cell walls. They 

 become soluble and diffusible by reacting with the alkalies of 

 the pancreatic juice with the formation of alkali salts of the 

 fatty acids. These alkali salts of the fatty acids are, it will be 

 recalled, soaps. Soaps have the property of forming emulsions 

 with fats, and in the form of such an emulsion fats are diffusible 

 through the cell membranes. Fats are thus rendered diffusible 

 in two ways, (i) By a true process of digestion consisting of 

 hydrolysis into glycerol and fatty acids and the subsequent 

 formation of soluble salts of the acids by means of alkalies 

 present in the digestive juices. (2) By the formation of an 

 emulsion of unchanged fat with the soaps formed as a result 

 of the first process. In both of these resulting forms, i.e. 

 alkali salts of fatty acids or soaps and emulsions of free fats, 

 the fat food is absorbed through the cell walls of the digestive 

 tract and enters the circulation. 



The Bile 



There still remains one more digestive liquid to consider, 

 which, while it contains no digestive enzymes, assists in the 

 digestion of food constituents, especially the fats. The bile is a 

 secretion of the liver, from which it passes to the gall bladder, 

 which acts as a reservoir, and thence through the bile duct 

 to the small intestine joining with the duct of Wirzung, which 

 brings the pancreatic juice. The bile, therefore, mixes with 

 the pancreatic juice and it is here that it assists in the digestion 

 of the fats. 



Its first action is probably one in which it acts as a stimulator 

 of the steapsin of the pancreatic juice. This stimulation re- 



