3 68 



FOOD AND DIGESTION 



FIG. 273. Crystalline Scales of 

 Cholesterol. 



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 thus renders them capable of passing into 

 the lacteals by absorption. For it has ap- 

 peared 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. 



(b) 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. 



Bile is also an excretive fluid carrying waste products thrown off by the 

 liver. The liver during fetal life is proportionately larger than it is after 

 birth, and the secretion of bile is active, although there is no food in the in- 

 testinal canal upon which it can exercise any digestive property. At birth, 

 the intestinal canal contains concentrated bile, mixed with intestinal secretion 



