394 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



The principal function of the bile in digestion is the aid which 

 it renders to the digestion and absorption of fats. Bile has a solvent 

 action on fats in small quantities, and assists in the eraulsification of fats. 

 We shall iind that the pancreatic juice, in its action on fats, liberates 

 fatty acids. A similar action is also manifested, although to a very much 

 less extent, by the bile of the horse, ox, and sheep ; it is absent in that 

 of the hog and dog. These fatty acids, thus liberated, unite with the 

 alkalies of the bile and pancreatic juice and form soaps, and so greatly 

 assist in the formation of a permanent emulsion. By means of the 

 emulsion thus formed the absorption of fat is greatly assisted; while, in 

 addition, it has been found that when membranes are moistened with 

 bile, or with solutions of bile salts, the passage of fats through such 

 membranes is greatly facilitated. Thus, if two filters are moistened, the 

 one with a solution of bile salts and the other with water, oil will pass 

 with comparative readiness through the former, while it scarcely suc- 

 ceeds at all in passing through the filter moistened with water. Oil- 

 drops placed on the surface of bile spread into a thin layer, like solutions 

 of corrosive sublimate on mercury, and in tubes moistened with bile 

 the oil will rise above its level outside of the tube, facts which point 

 still further to the assistance which the bile renders in the absorption 

 of fats. The bile of most animals contains a lactic acid ferment. On 

 other food-stuffs bile is quite inert. 



It is evident from the above that the uses of bile must be manifested 

 in some other direction than as a digestive fluid ; for while it would be 

 presumed from the fact that we have here the largest gland in the body, 

 pouring an immense volume of fluid into the digestive tract at a point at 

 which digestion has barely commenced, that that fluid must have some 

 important role to fulfill in digestion, the facts above mentioned, attained 

 through chemical examination, show that this assumption is not entirely 

 warranted. Still another method of examination, that of the production 

 of permanent biliary fistulae, also shows that the functions of the bile are 

 not solely manifested in assisting in digestion. In other words, the bile 

 is not only a digestive secretion, even though of secondary importance, 

 but is also an excretion. The most valuable data as to the functions 

 which the bile fulfills in the economy are obtained from the maintenance 

 of biliary fistulae. 



Biliary fistulas may be either temporary or permanent. The former 

 are of special importance for the study of the secretion of bile as to the 

 influence of drugs and other agents on the amount of bile poured out. 

 Dogs are most suitable for such an operation, which may be performed 

 upon them without any difficulty. 



The dog should have been allowed to fast for several hours before the 

 operation, as then the gall-bladder will be apt to be filled with bile. After 



