PROPERTIES AND COMPOSITION OF THE BILE. 401 



part, probably, by compression exerted by the distended and congested diges- 

 tive organs adjacent to it. It seems that this fluid, which is necessarily pro- 

 duced by the liver without intermission, separating from the blood certain 

 excrementitious matters, is retained in the gall-bladder for use during diges- 

 tion. 



Quantity of Bile. The estimates of the daily quantity of bile in the 

 human subject must be merely approximate ; and the ideas of physiologists 

 on this point are derived chiefly from experiments upon the inferior animals. 

 The most complete and reliable observations upon this subject are those of 

 Bidder and Schmidt, which were made upon animals with a fistula into the 

 gall-bladder, the ductus communis having been tied. These observers found 

 great variations in the daily quantity in different classes of animals, the quan- 

 tity in the carnivora being the smallest. Applying their results to the human 

 subject, assuming that the amount is about equal to the quantity secreted by 

 the carnivora, the daily secretion in a man weighing one hundred and forty 

 pounds (63-5 kilos.) would be about two and a half pounds (1,134 grammes). 



USES OF THE BILE. 



The uses of the bile in digestion have already been fully described ; but 

 before considering its characters as an excretion, it will be necessary to study 

 its general properties and composition. 



Properties and Composition of the Bile. The secretion as it comes 

 directly from the liver is somewhat viscid ; but after it has passed into the 

 gall-bladder, its viscidity is much increased by a farther admixture of mucus. 



The color of the bile is very variable within the limits of health. It may 

 be of any shade between a dark, yellowish-green and a reddish-brown. It is 

 semi-transparent, except -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 rule 

 the bile is dark-green in the carnivora and greenish-yellow in the herbivora. 



The specific gravity of human bile from the gall-bladder is 1026 to 1032 

 (Landois). When perfectly fresh it is almost inodorous, but it readily un- 

 dergoes putrefactive changes. It has a disagreeable 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 saponaceous constituents. 



It is generally stated that the bile is alkaline. This is true of the fluid 

 discharged from the hepatic duct, 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. 



The epithelium of the biliary passages is strongly tinged with yellow, even 

 in living animals. . This is due to the facility with which the coloring mat- 



