THE BILE. 161 



color) because the innumerable tiny oil-drops floating in it 

 reflect all the light which falls on its surface. 



The Bile, Human bile when quite fresh is a golden 

 brown liquid. It is alkaline, and besides coloring matters, 

 mineral salts and water, contains the sodium salts of two 

 nitrogenized acids, taurocliolic and gtycocholic, the former 

 predominating in human bile. 



The Uses of Bile. Bile has no digestive action upon 

 starch or proteids. It does not break up fats, but to a 

 limited extent emulsifies them when shaken up with them 

 outside the body, though far less perfectly than the pancre- 

 atic secretion. It is even doubtful if this action is exerted 

 in the intestines at all. In many animals, as in man, the bile 

 and pancreatic ducts open together into the duodenum, so 

 that on killing the creature during digestion and finding 

 emulsified fats in the chyle it is impossible to say whether 

 or not the bile had a share in the process. In the rabbit, 

 however, the pancreatic duct opens into the intestine about 

 a foot farther from the stomach than the bile-duct, and it 

 is found that if a rabbit be killed after being fed with oil, 

 no milky chyle is found down to the point where the pan- 

 creatic duct opens. In this animal therefore the bile alone 

 does not emulsify fats, and since the bile is pretty much 

 the same in rabbits and other mammals it probably does not 

 emulsify fats in them either. From the inertness of bile 

 with riespect to most foodstuffs it has been doubted if it is 

 of any digestive use at all, and whether it should not be 

 regarded merely as an excretion, poured into the aliment- 

 Describe fresh human bile. What is its reaction? Name its 

 chief constituents. 



Name foods on which bile has no influence. How does it 

 act upon fats when shaken with them? Give a reason for doubl- 

 ing it' it emulsifies i'ats in the intestine. 



