PROPERTIES OF THE BILE. 259 



of health. It may be of any shade between a dark, yellow- 

 ish green and a reddish brown. It is semitransparent, ex- 

 cept when the color is very dark. In different classes of 

 animals the variations in color are very great. In the pig 

 it is bright yellow ; in the dog it is dark brown ; -and in the 

 ox it is greenish yellow. As a rale, the bile is dark green 

 in the carnivora and greenish yellow in the herbivora. 



The specific gravity of the human bile, according to Prof. 

 Dalton, is 1018 ; 1 but this is somewhat lower than the aver- 

 age usually given, which is from 1020 to 1026. 3 "When the 

 bile is perfectly fresh, it is almost inodorous, but it readily 

 undergoes putrefactive changes. It has an excessively dis- 

 agreeable and bitter taste. It is not coagulated by heat. 

 When mixed with water and shaken, it becomes frothy, 

 probably on account of the tenacious mucus and its sapona- 

 ceous constituents. 



It is generally stated that the bile is invariably alkaline. 

 This is true of the fluid discharged from the hepatic duct, 3 

 although the alkalinity is not strongly marked; but the 

 reaction varies after it has passed into the gall-bladder. 

 Bernard found it sometimes acid and sometimes alkaline 

 in the gall-bladder, in animals dogs and rabbits killed 

 under various conditions ; * but many of these animals were 

 suffering from the effects of severe operations. In the 

 hepatic ducts the reaction is always alkaline ; and there are 

 no observations on human bile that show that the fluid is 

 not alkaline in all of the biliary passages. 



We have already noted the fact that the epithelium of 

 the biliary passages is strongly tinged with yellow, even in 

 living animals. This is due to the remarkable facility with 

 which the coloring principle of the bile stains the animal 

 tissues. This is very well illustrated in icterus, when even a 



1 DALTON, Treatise on Human Physiology, Philadelphia, 1867, p. 159. 



2 LONGET, Traite de physiologic, Paris, 1868, tome i., p. 278. 



3 ROBIN, Lemons sur les humeurs, Paris, 1867, p. 538. 



4 BERNARD, Liquides de forganisme, Paris. 1859, tome ii., p. 212. 



