DIGESTION AND THE DIGESTIVE AGENTS. 343 



gall-bladder the secretion is allowed to accumulate in that, 

 from which in turn it is ejected in spurts at stated periods 

 into the duodenum. The average composition of bile in- 

 cludes the following substances in 1,000 parts: 



Water about 900 parts, 

 Mucin about 25 parts, 

 Bile salts about 30 parts, 

 Cholesterin about 2 parts, 

 Mineral salts about 10 parts, 



Also traces of soap, fats, and lecithin. In addition to these 

 there are traces of bile pigments, to which the color of the 

 bile is due. The large amount of water serves, of course, 

 as the fluid medium in which all the other substances are 

 dissolved and by which they are carried. 



The Bile Salts. The most important constituents of the 

 bile are the bile salts. These are the sodium salts of two 

 peculiar acids called glychocholic acid and taurocholic acid. 

 It would be out of place here to go into the chemistry of 

 these organic acids. It may, however, be of interest to call 

 attention to the point that the taurocholic acid contains 

 sulphur. These two acids are not found in the blood, but 

 are made by the cells of the liver and by these poured into 

 the bile-ducts. They are probably substances which have 

 resulted from the breaking down of some proteid or albu- 

 minoid substance in the process of metabolism, and are 

 primarily intended for removal from the body. It is inter- 

 esting, however, to note that these bile salts are re-digested 

 in the intestine, and are almost wholly re -absorbed into 

 the system. These bile salts have some important func- 

 tions; in fact, they are considered indispensable, and are 

 treated by some physiologists as by no means mere excre- 

 tions, but special secretions intended for specific purposes. 

 In the first place these bile salts hold in solution the cho- 

 lesterin of the bile. Cholesterin is insoluble in the bile as 

 soon as the bile salts are removed. It is a non-nitrogenous 

 substance very widely distributed in the body, being found 

 especially abundant in the white matter of nerve tissues. In 



