THE BIOCHEMICAL PROCESSES OF DIGESTION 493 



Interesting observations have been collected on the amount of the secre- 

 tion from a fistula both in man and in the lower animals. In man it is 

 commonly stated that about 500 c.c. of bile are secreted daily, the 

 amount varying considerably during the different hours of the day. The 

 secretion of bile is greatly reduced by hemorrhage. It is greater on a 

 meat diet than on one of carbohydrates. It is reduced during starva- 

 tion, but continues to be secreted up to the moment of death. 



FUNCTIONS OF BILE 



One of the main functions of the bile salts is that they greatly assist, 

 not only in the digestion, but also in the absorption of fats. When bile 

 is excluded from the intestine, the feces are loaded with fatty acids 

 which have been split off partly by the now less effective lipase and 

 partly by the action of bacteria. The fatty acid thus liberated in the 

 absence of bile salts is not absorbed, because the bile salts serve as the 

 carriers of fatty acids into the epithelial cells and lacteals. They com- 

 bine with the fatty acids, probably by forming some chemical compounds, 

 in which they carry them into the endothelial cells where the compounds 

 become disrupted, the fatty acid combining with glycerine to again form 

 neutral fat and the bile salts being carried to the liver and reexcreted. 

 The influence of bile salts in assisting the action of lipase is probably 

 due to a lowering of the surface tension, thus bringing water and fat 

 into closer union. This accelerating influence has also been demonstrated 

 when synthetic bile salts have been used, showing clearly that it is really 

 these and not any other constituent of the bile that are responsible for 

 its accelerating influence. 



Bile also functionates as a regulator of intestinal putrefaction. This 

 it does apparently because of its slight laxative properties, by which 

 the intestinal contents are expelled before the bacteria have grown to 

 any great extent in them. Bile itself is a favorable culture medium for 

 certain bacteria, so that it can have no antiseptic action. Its assistance 

 in the action of trypsin and amylopsin depends very largely upon the 

 alkali which it contains. 



As an excretory vehicle bile is important, because it possesses the 

 power of dissolving cholesterol. Toxins and metallic poisons of various 

 kinds are also excreted in it. 



Although not directly concerned with the digestive function, it will be 

 convenient to say something here concerning the chemical nature and 

 derivation of the various biliary constituents. 



