DIGESTION IN THE INTESTINE 167 



itself, when it enters the intestine is said to increase the bile 

 secretion. The point is thus still uncertain. 



Composition. Function. Human bile is a clear, watery, yel- 

 low, brown or greenish liquid as it is poured into the gall blad- 

 der. Here, however, it becomes somewhat more viscous, due in 

 part at least to the addition to it of mucinous material from the 

 mucous membrane of the gall bladder and biliary passages. Bile 

 has a bitter taste, is usually somewhat alkaline in reaction and 

 contains a variety of substances, among them bile pigments, bile 

 salts, cholesterol, a mucinous material, inorganic substances and 

 many other things. Although the bile itself does not contain 

 digestive enzymes, at least in any important amount, it is of the 

 greatest importance in the processes of intestinal digestion. This 

 is especially true in the case of fat digestion. The addition of 

 bile to a mixture of olive oil and pancreatic juice increases the 

 amount of oil digested several fold. (5-10 times). There has 

 been much discussion as to the constituent of bile responsible 

 for this effect. Latest opinions ascribe it to the action of the 

 bile salts, sodium glycocholate and taurocholate. There also 

 are conflicting reports as to the effect of bile on the action of 

 trypsin and amylase, but probably the former is not affected, and 

 the latter slightly if at all. The function of the bile in connec- 

 tion with absorption will be discussed later. 



Bile tends to reduce putrefaction in the intestine. It is not 

 itself bacteriocidal, and probably this effect is due to its power 

 of increasing digestion and stimulating the muscular movements 

 of the alimentary canal, thus hurrying the food in its passage 

 through this region. 



Bile serves as an excretory medium for certain substances, 

 among them cholesterol, the bile pigments and other materials. 



Bile Pigments. The bile contains a variety of colored com- 

 pounds, the bile pigments. Bilirubin, a reddish brown pigment 

 is probably the mother substance of most of the others. On 

 oxidation it yields biliverdin (green), bilicyanin, and other 

 compounds. On reduction it yields urobilin, one of the urinary 

 pigments. The bile pigments are formed by the breaking down 



