URINE. 193 



evaporation ; the residue will contain bilin and bilifellinic acid, 

 in addition to urea, alcoholic-extract, and the lactates ; their 

 presence may be recognized by the taste. 



[The best method of ascertaining the presence of f bilin (or 

 choleic acid) is one recently published by Pettinkofer. 1 A 

 small quantity of the urine or other fluid, supposed to contain 

 bile, must be poured into a test-tube and treated with about 

 two thirds of its volume of sulphuric acid, added by drops. 

 Considerable heat is evolved, and the mixture must be kept below 

 144, otherwise the bilin will be decomposed. A few drops of 

 a solution of cane-sugar (five parts of water to one of sugar) are 

 added, and the mixture shaken. If bilin be present, a violet- 

 red colour will appear, the distinctness of which will vary with 

 the amount of bilin. The following precautions must be at- 

 tended to : 1st, the temperature must not exceed 144, other- 

 wise the colour, although formed, will be again destroyed : 

 2dly, the quantity of sugar must not be too large, lest sul- 

 phurous acid should be formed, and the solution become of a 

 dark brown colour : 3dly, the sulphuric acid must be free from 

 sulphurous acid : 4thly, if albumen be present, it is advisable 

 to coagulate and remove it before applying the test, since it 

 gives origin (when present in a large quantity) to a tint some- 

 what resembling that produced by bilin : 5thly, a great excess 

 of chlorides produces a brownish-red colour. 



In liquids where the bile is in very small quantity, as in the 

 urine and other secretions, it is often necessary to make a 

 spirituous extract, to evaporate this nearly to dryness on the 

 water-bath, and to transfer the moist residue into a watch- 

 glass. When quite cold, sulphuric acid and a very small quan- 

 tity of syrup are added, so that the temperature of the solution 

 remains low. In the course of a few minutes, if the most 

 minute trace of bile is present, the colour is produced. In em- 

 ploying this test grape-sugar, or any substance convertible into 

 grape-sugar, may be substituted for cane-sugar. 



The nature of this reaction is unknown ; it was at first con- 

 sidered that the peculiar violet tint might be dependent on the 

 decomposition of the bile-pigment, but it was found to occur, 



1 Liebig's und Wohler's Annalen, vol. 52, part 1. 

 ii. 13 



