260 



DIGESTION. 



FIG. 91. 



Crystalline scales of c-holcsterin. 



the ordinary saponifiable fats, there is a small quantity of 

 cholesterin (p. 20), which, with the other free fats, is probably 

 held in solution by the tauro-cholate of soda. 



A peculiar substance, which Dr. Flint has discovered in the 

 faeces, and named stercorin (p. 274), is closely allied to choles- 

 terin ; and Dr. Flint believes 

 that while one great function of 

 the liver is to excrete cholesterin 

 from the blood, as the kidney 

 excretes urea, the stercorin of 

 fseces is the modified form in 

 which cholesterin finally leaves 

 the body. Ten grains and a 

 half of stercorin, he reckons, are 

 excreted daily. 



The coloring matter of the bile 

 has not yet been obtained pure, 

 owing to the facility with which 

 it is decomposed. It occasionally 

 deposits itself in the gall-bladder 

 as a yellow substance mixed with 



mucus, and in this state has been frequently examined. It 

 is composed of two coloring matters, called biliverdin and 

 bilifalvin. By oxidizing agencies, as exposure to the air, or 

 the addition of nitric acid, it assumes a dark green color. In 

 cases of biliary obstruction, it is often reabsorbed, circulates 

 with the blood, and gives to the tissues the yellow tint charac- 

 teristic of jaundice. 



There seems to be some relationship between the coloring 

 matters of the blood and bile, and, it may be added, between 

 these and that of the urine also, so that it is possible they may 

 be, all of them, varieties of the same pigment, or derived from 

 the same source. Nothing, however, is at present certainly 

 known regarding the relation in which one of them stands to 

 the other. 



The mucus in bile is derived chiefly from the mucous mem- 

 brane of the gall-bladder, but in part also from the hepatic 

 ducts and their branches. It constitutes the residue after bile 

 is treated with alcohol. The epithelium with which it is 

 mixed may be detected in the bile with the microscope in the 

 form of cylindrical cells, either scattered or still held together 

 in layers. To the presence of this mucus is probably to be 

 ascribed the rapid decomposition undergone by the bilin ; for, 

 according to Berzelius, if the mucus be separated, bile will 

 remain unchanged for many days. 



The saline or inorganic constituents of the bile are similar to 



