324 DIGESTION. 



yellow substance mixed with mucus, and in this state has 

 been frequently examined. It is composed of two colour- 

 ing matters, called biliverdm and bilifulvin. By oxidising 

 agencies, as exposure to the air, or the addition of nitric 

 acid, it assumes a dark green colour. In cases of biliary 

 obstruction, it is often re-absorbed, circulates with the blood, 

 and gives to the tissues the yellow tint characteristic of 

 jaundice. 



There seems to be some relationship between the colour- 

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

 tween 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 

 membrane 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 those found in most other secreted fluids. It is possible 

 that the carbonate and neutral phosphate of sodium and 

 potassium, found in the ashes of bile, are formed in the 

 incineration, and do not exist as such in the fluid. Oxide 

 of iron is said to be a common constituent of the ashes of 

 bile, and copper is generally found in healthy bile, and 

 constantly in biliary calculi. 



Such are the principal chemical constituents of bile ; but 



