274 EXCRETION. 



This principle is precipitated from the bile by boiling 

 with milk of lime. The filtered residue is then decomposed 

 with hydrochloric acid, which unites with the lime and 

 leaves a fatty residue of an intense green color. The fat is 

 then removed by repeated washings with ether (a very long 

 and difficult process). The precipitate is then redissolved 

 in alcohol with ether added, which gives to the liquid a 

 bluish-green color, and leaves, after evaporation, a dark- 

 green powder. This powder contains iron, but its pro- 

 portion has never been accurately estimated. The mat- 

 ter thus obtained is insoluble in water and in chloroform, 

 but is soluble in ether, alcohol, sulphuric and hydrochloric 

 acid. 1 



It is unnecessary to follow out in detail all of the chemi- 

 cal investigations which have been made into the ultimate 

 composition and the modifications of this and the other col- 

 oring matters. According to Robin, 8 the empirical formula 

 for biliverdine, deduced from the analyses of Scherer, is 

 C 24 H 16 NO 4 . No account is taken in these analyses of the 

 iron, the existence of which cannot be doubted. 



Upon the addition of nitric acid, or better, of nitric mixed 

 with nitrous acid, biliverdine is acted upon in a peculiar way, 

 producing a play of colors, which is recognized as one of the 

 tests for bile. 



Tests for Bile. 



It is frequently desired, particularly in pathological in- 

 vestigations, to ascertain, by some easy test, the fact of the 

 presence or absence of bile in various of the fluids and solids 

 of the body. It is, indeed, a most interesting physiological 

 question to determine the course and destination of the 

 biliary salts after the bile has passed into the intestinal 

 canal ; and this can be done only by the application of ap- 

 propriate tests to the contents of the alimentary tract and 



1 ROBIN ET VERDEIL, Traite de chimie anatomique, Paris, 1853, tomeiii., p. 389. 

 '.ROBIN, jtepong.sw les humeurs, Paris, 1867, p. 550. 



