268 THE CONSTITUENTS OF BILE. [CH. XI. 



solution of barium chloride, drop by drop, boiling between each 

 addition. Continue to add the barium chloride until no further 

 precipitate is obtained. Allow the tube to stand for a minute. 

 Pour off the supernatant fluid as cleanly as possible or use a centrifuge . 

 To the precipitate add 3 to 5 cc. of 97 per cent, alcohol, two drops of 

 strong sulphuric acid, and two drops of a 5 per cent, aqueous solu- 

 tion of potassium chlorate. Oil for half a minute and allow the 

 barium sulphate to settle. The presence of bile pigments is indi- 

 cated by the alcoholic solution being coloured a greenish blue. 



NOTES. i. To render the test more delicate, pour off the alcoholic 

 solution from the barium sulphate into a dry tube. Add about one-third its 

 volume of chloroform and mix. To the solution add about an equal volume 

 of water, place the thumb on the tube, invert once or twice and allow the 

 chloroform to separate. It contains the bluish pigment in solution. 



2. The bile pigment is adsorbed on to the barium sulphate precipitate, 

 but passes into solution again in acid alcohol. The chlorate acts as a very 

 weak oxidising reagent, converting bilirubin and biliverdin to the characteristic 

 blue compound. 



3. The author claims that it is a very much more delicate test than the 

 one that follows. 



319. Gmelin's test for bile pigments. Take a few cc. of 

 fuming yellow nitric acid in a test-tube, and by means of a pipette 

 carefully place on the surface of this an equal amount of bile. Shake 

 the tube very gently from side to side, and note the play of colours 

 in the bile as it becomes oxidised by the acid. Proceeding from 

 acid to bile the colours are yellow, red, violet, blue, and green. 



NOTES. This test can be modified in many ways. 



1. Add a drop of yellow nitric acid to a thin film of bile on a white 

 porcelain plate. The drop of acid becomes surrounded by rings of the various 

 colours. 



2. Filter some diluted bile repeatedly through an ordinary filter paper, 

 and then place a drop of fuming nitric acid on the paper. The play of colours 

 is usually well seen. 



Cholesterol has been described on p. 161, and Lecithin 

 on p. 163. 



The Protein of Bile. 



When bile is treated with acetic acid a precipitate is 

 formed insoluble in excess. This was formerly thought 

 to be mucin. But it has been shown that it is nucleo- 

 protein, the bile salts present preventing the re-solution 



