PROPERTIES AND COMPOSITION OF THE BILE 365 



human subject must be merely approximate; and the ideas of physiolo- 

 gists on this point are derived chiefly from experiments on the inferior 

 animals. There are great variations in the daily quantity in different 

 classes of animals, the quantity in the carnivora being the smallest. 

 Applying the results of experiments on the lower animals to the human 

 subject, and 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 kilograms) would be about two and a 

 half pounds (1134 grams). 



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 further 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 semitransparent except when the color is very dark. In 

 different classes of animals the variations in color are considerable. 

 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 car- 

 nivora and greenish yellow in the herbivora. 



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

 1032. When perfectly fresh it is almost inodorous but it readily under- 

 goes 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 usually is stated that the bile is alkaline. This is true of the 

 liquid discharged from the hepatic duct, although the alkalinity is not 

 strongly marked ; but the reaction varies after it has passed into the 

 gall-bladder. In the hepatic ducts the reaction always is alkaline ; and 

 there are no observations on human bile that show that it is not alkaline 

 in all 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 color- 

 ing matter of the bile stains the animal tissues. 



Perfectly normal and fresh bile, examined with the microscope, pre- 

 sents a certain quantity of mucus, the characters of which have already 



