540 SPECIAL PHYSIOLOGY. 



excess of some base; for, though often neutral, it may be feebly alka- 

 line. The substance of the liver has, or rapidly acquires after death, 

 an acid reaction. The proportions of glycocholic and taurocholic acids 

 vary in the bile of different animals, but are tolerably constant in each 

 species. In the dog, the glycocholic acid is scanty, and sometimes ab- 

 sent. In the pig, another allied acid is found, named hyocholic, and a 

 small quantity of an acid analogous to the taurocholic. In the goose, 

 a different allied acid exists, named tauro-chenolic. Although varied 

 in different animals, and present in variable proportions, the character- 

 istic constituent of the bile is, in all cases, a soda salt of some fatty 

 acid, resembling the acids of fatty and resinous bodies. The sulphu- 

 retted and nitrogenous body, taurin, is always present. 



The next most characteristic constituent of the bile is its coloring 

 matter, named by different chemists cholepyrrhin, bilipyrrhin^ and bili- 

 phcein. This forms about 5 per cent, of the secretion. According 

 to Berzelius two modifications of coloring matter exist in bile. The 

 one, a yellowish coloring substance, was named by him bilifulvin ; it 

 seems to coincide with the cholepyrrhin and biliphsein of other writers. 

 It is uncrystallizable. insoluble in water, only slightly soluble or in- 

 soluble (Brucke) in alcohol, but especially so in caustic alkalies, and 

 in chloroform. It affords a peculiar reaction with nitric acid or ni- 

 trates, which, when added in small quantities to the yellow alkaline 

 solution, first produce a green color, then blue, violet, and red, and 

 finally yellow again, owing, it is supposed, to the occurrence of differ- 

 ent degrees of oxidation. The other coloring matter of the bile, 

 smaller in quantity, is green, and hence was named by Berzelius bili- 

 verdin; it was supposed by him, though not proved so, to be identical 

 with chlorophyll. It is insoluble in chloroform, slightly so in alcohol, 

 and insoluble in water; it appears to be a more highly oxidized form 

 of bilifulvin. These coloring matters are closely allied to the haema- 

 tin, or cruorm of the blood ; but neither these, nor the fatty acids of 

 the bile, pre-exist in the blood ; they are formed in the liver by the 

 hepatic cells. 



In addition to these, its essential constituents, bile contains about 

 1 per cent, of ordinary fats, margarin and olein, or alkaline marga- 

 rates and oleates. It also presents traces of cholesterin, the fatty, or 

 resinoid body, which likewise exists in nervous substance, in the blood, 

 and in certain diseased exudations. [Cholesterin is probably derived 

 from the metamorphosis of nervous tissues, whence it is absorbed by the 

 capillaries and conducted to the liver, where it is eliminated. F. G. S.] 

 Cholesterin crystallizes in brilliant colorless plates, insoluble in water, 

 soluble in boiling alcohol and in ether, and absolutely resisting sa- 

 ponification. In the living body it is probably held in solution by 

 fluid fats. The bile contains about 1 per cent, of salts, its ashes yield- 

 ing, besides soda, in large proportion, traces of potash, magnesia, and 

 lime, in combination with phosphoric acid and chlorine. The mucus 

 found in bile, indicated by the presence of mucous and epithelial cells, 

 is an adventitious substance, derived from the walls and follicles of the 

 fbile ducts, or gall-bladder. 



