THE BILE 



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bilirubin, C 16 H 18 N 2 O 3 , is crystallizable and insoluble in water, and soluble in 

 chloroform or carbon disulphide. A green coloring matter, biliverdin, 

 C 16 H 18 N 2 O 4 , which always exists in large amount in the bile of herbivora, is 

 formed from bilirubin on exposure to the air or by subjecting the bile to any 

 other oxidizing agency, as by adding nitric acid. Biliverdin is soluble in 

 alcohol, glacial acetic acid, and strong sulphuric acid, but insoluble in water, 

 in chloroform, and ether. It is usually amorphous, but may sometimes 

 crystallize in green rhombic plates. 



There is a close relationship between the coloring matters of the blood 

 and of the bile and, it may be added, between these and that of the urine, 

 urobilin, and of the feces, stercobilin. It is probable they are, all of them, 

 varieties of the same pigment, or derived from 

 the same source. Cholesterol C 27 H 45 OH, 

 and lecithin, C 43 H 84 NPO 8 are constant con- 

 stituents of bile. Iron is found among the 

 salts of the ash. 



The Role of Bile in Intestinal Digestion. 

 Though it is not a true digestive fluid, in 

 that it has no ferment and digests nothing 

 itself, yet it must be regarded as an important 

 aid to digestion for the following reasons: (a) 

 Bile assists in emulsifying the fats of the food, 

 and dissolves the fatty acids thus rendering 

 them more capable of absorption. For it has 

 appeared in some experiments in which the common bile-duct was tied that, 

 although the process of digestion in the stomach was unaffected, chyle 

 was no longer well formed. The contents of the lacteals consisted of clear, 

 colorless fluid, instead of being opaque and white, as they ordinarily are 

 after feeding. It is, however, the combined action of the bile with the 

 pancreatic juice to which the emulsification is due rather than to that of the 

 bile alone. The bile itself has a very feeble emulsifying power. If the 

 theory be accepted that fats are absorbed as fatty acids and soaps, in 

 solution, the action of the bile becomes very important because solutions of 

 bile salts have the power of dissolving the fatty acids. The moistening of 

 the mucous membrane of the intestines with bile, for this very reason, 

 facilitates absorption of fatty matters through it. 



(6) The bile, like the gastric fluid, has a certain but not very considerable 

 antiseptic power, and may serve to prevent the decomposition of food during 

 the time of its sojourn in the intestines. Experiments show that the contents 

 of the intestines are much more fetid after the common bile-duct has been 

 tied than at other times. Moreover, it is found that the mixture of bile with 

 a fermenting fluid stops the process of fermentation. Contact with bile 

 also destroys the digestive action of pepsin on protein. 



FIG. 273. Crystalline Scales of 

 Cholesterol. 



