390 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



of the bile, and forms the bulk of the so-called white gall-stones. Choles- 

 terin rotates the plane of polarized light to the left, and forms transparent, 

 rhombic plates, which usually have a small, oblong piece cut out of one 

 corner. Cholesterin is insoluble in alkalies, dilute acids and alcohol, 

 and cold water, and is soluble in hot alcohol, ether, glycerin, chloroform, 

 and soap solution and alcohol. In the bile it is kept in solution through 

 the, union of bile salts. Cholesterin is widely distributed through the 

 body, occurring usually in the cerebro-spinal axis and nerves, and, in 

 fact, seems to originate from the breaking down of nerve-tissues. It is 

 likewise found in the yelk of eggs, in the spleen, and in various patho- 

 logical deposits in the animal body. 



It may be prepared by powdering white gall-stones, boiling in water con- 

 taining caustic potash, filtering when cold, and washing the resulting mass with 

 boiling alcohol, and filtering while still hot. Cholesterin crystallizes out of the 

 alcohol when cold. It may be purified by redissolving in boiling ether, and 

 adding half its volume of alcohol, and allowing it to evaporate spontaneously. 

 Cholesterin crystals give a violet color with 80 per cent, sulphuric acid (Mole- 

 schott). 



When treated with nitric acid, dried, and touched with a drop of ammonia, 

 a deep-red color is produced, which is not altered by the addition of caustic soda. 

 (Schiff). 



"When dissolved in chloroform and agitated with an equal volume of strong 

 sulphuric acid, a blood-red solution is obtained, which becomes gradually violet, 

 blue, green, and then yellow, and then disappears if a trace of water is present. 

 The layer of sulphuric acid in this test shows green fluorescence. If crystals of 

 cholesterin are heated with tolerably strong sulphuric acid, and afterward with 

 a little iodine, a play of colors is produced, passing from violet through blue, 

 green, red, and yellow to brown. 



Among the other organic constituents of the bile, lecithin, which 

 belongs to the group of the complex nitrogenous fats, is to be men- 

 tioned. Its formula is C„H go NP0 6 . It occurs widely distributed through- 

 out the body, occurring especially in the brain, nerves, yelk of eggs, 

 semen, and pus. When pure, it is a colorless, partially crystalline body, 

 soluble in cold and .hot alcohol, less so in ether, and soluble in chloro- 

 form, carbon disulphide, and fats. 



It is not yet clearly established as to whether the lecithin found in 

 the bile and other secretions and tissues is derived from the breaking 

 down of food-stuffs in pancreatic digestion, or whether it is found syn- 

 thetically. The reabsorption of lecithin, however, is complete, since no 

 trace of lecithin or glycerin-phosphoric acid is to be found in the feces. 



(e) The Inorganic Constituents of the Bile. — Of the inorganic con- 

 stituents of the bile, iron is of special importance, as indicating the red 

 blood-corpuscles as the source of bilirubin, from which process of decom- 

 position the iron also undoubtedly originates. No close relation, how- 

 ever, between its quantity and that of the bile coloring-matters has been 

 ever distinctly made out. The following table, after Hoppe-Seyler, indi- 

 cates the quantitative composition of the solids found in bile of the do" 



