THE BILE. 147 



and the goat. In other animals the relation is variable, and in 

 some, it is stated, glycocholic acid only is found. 



Isolation. Collectively, the biliary acids, in the form of their 

 salts, can be obtained in the following manner : the bile is mixed 

 with animal charcoal, evaporated to dryness, and the residue ex- 

 tracted with absolute alcohol. This extract, which contains the 

 biliary acid salts, cholesterin, fats, soaps, and lecithin, is then 

 filtered, concentrated, and treated with a large excess of ether. In 

 this manner the salts of tho bile-acids are precipitated, while the 

 other substances remain in solution. On standing, the precipitate 

 gradually becomes crystalline, and is then spoken of as Platner's 

 crystallized bile. In this form the biliary acids are conveniently 

 estimated as a whole. If then it is desired to determine the rela- 

 tive amount of the two principal acids present, it is only necessary 

 to estimate the sulphur in Platner's bile, from which the corre- 

 sponding amount of taurocholic acid can be calculated. 



To separate the two acids from each other, Platner's bile is dis- 

 solved in water and completely precipitated with a solution of neutral 

 acetate of lead. The corresponding lead salts are thus formed, and 

 can now be readily separated from each other, as the glycocholate is 

 thrown down, while the taurocholate remains in solution. In the 

 filtrate the latter is then precipitated with ammonia. To obtain the 

 free acid from the glycocholate, the precipitated lead salt is sus- 

 pended in water and evaporated to dryness in the presence of sodium 

 carbonate. The sodium salt is thus obtained and extracted with 

 alcohol. The alcohol is evaporated off, the residue dissolved in 

 water and treated with hydrochloric acid, when the glycocholic acid 

 will separate out. The taurocholic acid can be similarly obtained 

 from its lead salt by decomposing the solution with hydrogen sul- 

 phide. The resulting plumbic sulphide is filtered off, the filtrate 

 evaporated to dryness, the residue dissolved with a small amount 

 of alcohol, and then precipitated with an excess of ether, when the 

 free acid is thrown down. 



Tests for the Bile-acids. Pettenkofer's Test. On treating the 

 biliary acids in aqueous or alcoholic solution with a few drops of an 

 0.1 per cent, solution of furfurol and 1 or 2 c.c. of concentrated, 

 chemically pure sulphuric acid, a beautiful purple color develops. 

 As furfurol results when concentrated sulphuric acid is added to 

 a carbohydrate, the test may also be conducted by treating the solu- 

 tion of the biliary acids (1 or 2 c.c.) with a few drops of a 10 per 

 cent, solution of cane-sugar and then with sulphuric acid. In either 

 case, however, care should be had that the temperature which results 

 during the reaction does not exceed 70 C., as otherwise the result- 

 ing pigment is destroyed. This may be obviated by substituting 

 strong phosphoric acid for the sulphuric acid, and placing the solu- 

 tion in boiling water. The resulting pigment shows two bands of 

 absorption on spectroscopic examination. One of these is situated 

 at F ; the other between D and E, near E. On diluting with 



