176 THE DIGESTIVE FLUIDS. 



and D, near C ; another about D ; and a third very faint band 

 midway between' D and E. In acid solutions two bands are seen 

 between C and E. On treating the alcoholic solution of the pig- 

 ment with an ammoniacal solution of zinc chloride a distinct fluor- 

 escence is obtained. Its formula has not as yet been determined, 

 and, according to some observers, indeed, bilicyanin does not repre- 

 sent a separate substance. 



Bilipurpurin. This term has been applied to a red pigment 

 which is formed from bilirubin and biliverdin on treating with 

 nitric acid. A pigment of the same name has been isolated from 

 ox-gall by Lobisch and Fischler. Its formula is given as C^H^- 

 N 4 O 5 , which would suggest that the substance is an anhydride of 

 bilirubin. 



Choletelin, or bilixanthin, is generally regarded as the final 

 oxidation-product of the common bile-pigments. It is an amor- 

 phous brown substance, which is soluble in alcohol, ether, chloro- 

 form, and in solutions of the alkaline hydrates, from which latter it 

 can be precipitated by the addition of acids. Its formula is given, 

 as C 16 H 18 N 2 6 . 



Bilihumin is a pigment of unknown composition that has been 

 found in gall-stones. It is insoluble in all organic solvents. 



Cholesterin. 



Cholesterin is not exclusively a product of the activity of the 

 hepatic cells, but is found in other tissues as well. It is thus a con- 

 stituent of the red corpuscles of the blood, of the plasma, of the yolk 

 of eggs, of the semen, of the secretion of the sebaceous glands, 

 and is especially abundant in nerve-tissue. In the vegetable world 

 also cholesterin is widely distributed. The liver is probably the 

 organ through which the substance, wherever formed, is eliminated. 

 Ultimately it appears in the feces. In the urine it is found only 

 under exceptional conditions, and then only in very small amounts. 

 Of its mocle of formation nothing is known, but it is interesting to 

 note that wherever cholesterin is found lecithin is likewise observed. 

 In the brain a considerable amount of the substance occurs in com- 

 bination with a fatty acid, cholic acid, from which it can only be 

 separated by saponification. 



The amount of cholesterin which is found in the bile represents 

 about 2 per cent, of the total solids. Normally it is held in solution 

 owing to the presence of the biliary acids, but under pathologic con- 

 ditions it may separate out in crystalline form, either in the gall- 

 bladder itself or in the larger hepatic, ducts, and then gives rise to 

 the formation of stones. Of the origin of these concretions we know 

 little. Very often they contain a nucleus of epithelial cells or of 

 bacteria, around which the cholesterin, together with a variable 

 amount of bile-pigment and mineral salts, becomes deposited. The 

 stones which are usually found in man are for the most part very 



