442 EXCRETION. 



munis, in part by contractions of its walls, and in part, probably, by compression exerted 

 by the distended and congested digestive organs adjacent to it. It seems that this fluid, 

 which is necessarily produced by the liver without intermission, separating from the blood 

 certain excrementitious matters, is retained in the gall-bladder for use during digestion. 



Functions of the Bile. 



Although the function of the bile in intestinal digestion is essential to life, we know 

 very little of its mode of action ; and we have thought proper to defer until now a full 

 consideration of the properties and composition of this secretion. For an account of what 

 is known of its digestive function, the reader is referred to the chapters treating of diges- 

 tion. We shall show, in this connection, that the liver excretes one of the most important 

 of the effete principles ; but, before taking up the relations of the bile as an excretion, it 

 will be necessary to study its general properties and composition. 



General Properties 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 from 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 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 rule, the bile is dark-green in the carnivora and greenish- 

 yellow in the herbivora. 



The specific gravity of the human bile is from 1020 to 1026. When the bile is per- 

 fectly fresh, it is almost inodorous, but it readily undergoes putrefactive changes. It 

 has an excessively 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 invariably alkaline. This is true of the fluid dis- 

 charged 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 obser- 

 vations 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 illus- 

 trated in icterus, when even a small quantity of this coloring matter finds its way into the 

 circulation. 



Perfectly normal and fresh bile, examined with the microscope, presents a certain 

 amount of mucus, the characters of which we have already described. There are no 

 formed anatomical elements characteristic of this fluid. The fatty and coloring matters 

 are in solution and not in the form of globules or granules. 



Composition of the Bile. 



It is a remarkable fact, that, although the bile, in a perfectly fresh and normal con- 

 dition, may be obtained from the inferior animals with the greatest facility, no satisfac- 

 tory analyses of its characteristic principles were made before the examinations of ox- 

 gall by Strecker, in 1848. The bile is, however, one of the most important, but least 

 understood, of the animal fluids ; and our scanty information with regard to its func- 

 tions has been in a measure due to the want of an exact knowledge of its physiological 



