144 



PHYSIOLOGY 



CHAP. 



last is constantly present, and according to Lutschinoff forms the 

 fundamental acid of ox -bile. 



Chemists distinguish a numerous series of Hie pigments, which 

 represent various degrees of oxidation in the same molecular 

 aggregate. Under physiological conditions only two of these 

 pigments appear in the bile, the red or Mlirubin, and the green or 

 biliverdin. The first is less oxidised, and represents the mother 

 substance of all the other pigments, and it is readily transformed 

 into the second by simple exposure to air (Maly). Biliverdin 

 is, vice versa, converted into bilirubin by a process of reduction. 

 By action of hydrogen in the nascent state these pigments are 

 converted into hydrobUirubin, which, as we shall see, occurs 

 continually in the intestine ; a certain amount of hydrobilirubin 

 can, however, be found even in human bile. Bilirubin and 

 biliverdin usually co-exist in the bile, but the first largely 

 predominates in the bile of carnivora, the .second in that of 

 herbivora, while the one or the other predominates in that of man 

 (omnivora) according as the food is mainly animal or vegetable. 



Hammarsten's analysis of the chemical composition of human 

 bile, taken from the gall-bladder of persons operated on for 

 cholelithiasis, and from patients with a fistula of the gall-bladder, 

 give the following results : 



As shown by this table, besides the bile salts and pigments 

 (which are the specific substances of bile), fats, soaps, cholesterol, 

 and lecithin are never absent; these substances are compounds 

 present in other tissues and secretions. In the bile of certain 

 animals there is also a diastatic enzyme; this is probably not 

 hepatic in origin, but is absorbed from the pancreas, and eliminated 

 by the liver in the bile. Choline and glycero-phosphoric acid are 

 also found, which are probably decomposition products of lecithin. 



