162 THE DIGESTIVE FLUIDS. 



precipitated by the addition of acids. Its formula is given as 

 C, 6 H 1? NA. 



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 has thus been 

 encountered in the red corpuscles of the blood, in the plasma, in the 

 yolk of eggs, in the semen, and in the secretion of the sebaceous 

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

 world also cholesterin is 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 mode 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. It is 

 possible that they result owing to a temporary absence of the biliary 

 acids, but this is only a supposition. The stones which are usually 

 found in man are for the most part very rich in cholesterin, while 

 the pigment-stones which are so common in cattle are less frequently 

 seen in the human being. 



The common cholesterin which is found in the animal body has 

 the composition C 27 H 45 .OH (Obermiiller), and is usually regarded as 

 a monatomic alcohol. Of its structure, however, nothing is known. 

 It combines with fatty acids to form compound ethers which are 

 analogous to the fats, and in this form also, as has been shown 

 (page 67) cholesterin occurs widely distributed in the animal 

 world. The common lanolin of wool-fat thus contains large 

 amounts of such compound ethers, both of cholesterin and its 

 isomeric compound isocholesterin. On treating cholesterin with 

 concentrated sulphuric acid the substance gives rise to the formation 

 of certain hydrocarbons, which are termed cholcxterilinx, and which 

 are supposed to stand in a close relation to the terpene group. With 

 iodine these bodies give a blue color. 



