494 DIGESTION. 



SECTION III. FUNCTIONS or THE LIVER. 

 BILE. 



133. General Characters of the Bile. Bile as it flows 

 from the liver is a thin liquid, but when it stays some time in 

 the gall bladder it becomes mixed with mucin, the presence of 

 which renders it tenacious. In man, it is, when fresh, of a 

 golden-yellow color, like yolk of egg, as may be seen when it 

 is vomited ; but after death the bile in the gall bladder is 

 generally brownish. In the dog it is also yellow, in the herbi- 

 vora it is green, but very frequently it has a decided brown 

 tinge in both. Its specific gravity and composition are not 

 always the same even in the same animal. 



Specific Gravity- and Solids. The specific gravity and 

 amount of solids, organic and inorganic, in bile are determined 

 in the same way as in saliva. The ash has a reddish tinge, 

 due to the presence of iron. For the method of determining 

 the amount of iron, see page 202. 



* Reaction. Bile discolors litmus so much as to hide the 

 reaction, it must therefore be first diluted and the reaction 

 tested afterwards. In fresh bile it is always alkaline. 



134. Composition of Bile. When obtained from the gall 

 bladder, the bile contains, 1, mucin ; 2, bile pigments ; 3, sodium 

 salts of biliary acids; 4, cholesterin; 5, lecithin ; 6, phosphates 

 of sodium, calcium, and iron, sodium chloride, and generally 

 traces of copper. 



* Mucin. Add common alcohol to bile, obtained from the 

 gall bladder of an ox; wash the abundant precipitate so ob- 

 tained with dilute alcohol ; add water, and the precipitate will 

 dissolve; add acetic acid, and a precipitate of mucin will fall 

 with traces of bile pigment adhering to it. For the reactions 

 of mucin, .see 45. 



Hili'. r/ </ments. The yellow color of fresh bile in man and 

 eaniivora is due to a coloring matter termed Bilirubin; the 

 green color possessed by the bile in herbivora, or acquired by 

 the bile of carnivora after standing, is due to Biliverdin, a pro- 

 duct of the oxidation of Bilirubin. When the bile is long in 

 the gall bladder,a small quantity of a third pigment, Biliprasin, 

 may als<5 be present. 



' 135. Test for Bile Pigments (Gmellin's Test.) 

 Vl hen strong nitric acid, which has been exposed to light, and 

 therefore contains nitrous acid, is added to a solution of bili- 

 rubin, it becomes oxidized, and the products of oxidation 

 which are successively produced, present the colors of the 

 Firt, biliverdin is produced, and the yellow color 

 of the bilirubin solution changes to green and then becomes 

 successively blue, violet, red, and lastly dirty yellow. If a so- 



