REABSORPTION OF BILE SALTS. 391 



Cholesterin. The amount of cholesterin in bile is very variable, 

 ranging from 0'5 to 5 per cent. Cholesterin is insoluble in water or 

 dilute saline solution, and is dissolved in bile by the agency of the bile 

 salts, in solutions of which it is easily soluble. When the amount of bile 

 salts is insufficient to hold it in solution, it slowly passes out of solution 

 in a concretionary form around any particle of foreign matter present in 

 the bile, or around an existing concretion forming in this manner a 

 variety of gall stone. 



According to Hoppe-Seyler, cholesterin is a cleavage product, 

 constantly formed in the metabolic changes of the living cell ; and for 

 this reason it is that cholesterin is invariably found as a chemical 

 constituent of both animal and vegetable cells. Cholesterin does not 

 easily undergo decomposition in the animal organism when once formed, 

 and is principally excreted in the higher animals in the bile. It is 

 found in increased quantity in tissue which is undergoing pathological 

 change ; this may, perhaps, be due to increased inability on the part of 

 the cells in their vitiated condition to break up the stable cholesterin. 

 Cholesterin is found in largest quantity as a constituent of the myelin 

 of nerve fibres and in the blood corpuscles. It is probably formed most 

 in the metabolism of nerve tissue,, taken up by the liver cells from the 

 blood, and passed as an excretion into the bile ducts. 



Cholesterin is purely an excretion, and is not reabsorbed, but passes 

 out of the body with the faeces. This is also the fate of the bile 

 pigments, which are gradually reduced to hydrobilirubin (stercobilin) 

 in their passage along the intestine. This substance may easily be 

 extracted from the fseces by absolute alcohol, after making acid with 

 sulphuric acid. The bile pigments have a poisonous action when 

 injected 'into a vein, which indicates that if they are reabsorbed at all 

 they must be changed in the process. 1 



Lecithin. The amount of lecithin present in bile is much greater 

 than in any of the other secretions. All the lecithin, and any direct 

 products of its decomposition to be removed from the body, are carried 

 off' in the bile. As lecithin, as well as cholesterin, is one of the con- 

 stituents of nerve tissue, the liver, by means of the bile, may be looked 

 upon as the great channel for the removal of the products of nervous 

 metabolism. Lecithin is also held in solution by the bile salts. 



Reabsorption of bile salts Their functions in the organism. 

 The bile salts differ from the other biliary constituents in that they are 

 not purely an excretion. They are to a large extent reabsorbed, and 

 undergo a circulation in the body, with the probable function of acting 

 as carriers for the otherwise insoluble cholesterin in the bile. Such an 

 absorption of bile salts has been shown to take place in different ways, 

 which are, briefly, as follows : 



1. Bile salts taken by the mouth, cause an increased flow of bile ; 

 indeed, from recent observations by various experimenters, 2 it seems that 

 the bile salts are the only substances which truly act as cholalogues. 

 This action can only be due to their absorption followed by an increased 

 elimination of them by the liver. 



2. The bile of the dog contains only taurocholates. If impaired 



1 De Bruin, Centralbl. f. klin. Med., Bonn, 1890, Bd. xi. S. 491. 



' 2 Baldi, Arch. ital. de biol., Turin, 1883, tome iii. p. 395; Paschkis, Schmidt's Jahrb., 

 Leipzig, 1885, Bd. ccvi. S. 19 ; Nissen, Centralbl. f. d. med. Wissensch., Berlin, 1890, Bd. 

 xxviii. 1 S. 948. 



