THE AROMATIC CONSTITUENTS OF THE URINE. 265 



ers, the chromogen of this substance is identical with the so-called 

 urohaematin, and the pigment is probably the same as the red pig- 

 ment of Scherer, the urrhodin of Heller, the urorubin of Plosz, the 

 indirubin of Schunk, the indigo-purpurin of Bayer, the pigment 

 of Giacosa and others. 



The blue pigment which is found together with the red pigment 

 when urine is treated with a strong mineral acid and an oxidizing 

 agent is, as has been indicated, indigo-blue, and is identical with 

 urocyanin, cyanurin, Harnblau, uroglaucin, etc., of former observers. 

 As a general rule, its amount is far greater than that of the red pig- 

 ment, and is at times the only one that is obtained. In other cases, 

 however, the red seems to prevail, and in still others both are appar- 

 ently present in about equal proportion. The cause of these varia- 

 tions is not understood, but probably depends upon variations in 

 bacterial action in the intestinal tract. As a general rule, indeed, 

 notable quantities of the red pigment are observed only under patho- 

 logical conditions. 



Tests for Indican. All the tests employed for the purpose of 

 demonstrating the presence of indican in the urine are essentially 

 based upon the decomposition of the substance, with the liberation 

 of indoxyl and its oxidation to indigo-blue. 



JAFFE'S TEST, AS MODIFIED BY STOKVIS. A few cubic cen- 

 timeters of urine are treated with an equal volume of concentrated 

 hydrochloric acid, and two or three drops of a strong solution of 

 sodium hypochlorite. The indigo-blue which thus results is then 

 extracted by shaking with a little chloroform. If red pigment has 

 been formed at the same time, the color varies from a violet to a 

 purplish red. 



If it is desired to separate the two pigments, the chloroform extract 

 is evaporated to dryness and the residue washed with a mixture of 

 equal parts of 96 per cent, alcohol, ether, and water. This dissolves 

 the red pigment and leaves the indigo-blue behind. Care must be 

 had, however, not to add too much of the hypochlorite solution, as 

 otherwise the indigo-blue is oxidized to isatin, and no color at all is 

 obtained. Should this happen after the addition of only one or 

 two drops, the following test had better be employed, as a further 

 oxidation is here not effected : 



OBERMA YER'S TEST. A few cubic centimeters of urine are treated 

 with an equal volume of a 2 pro mille solution of ferric chloride in 

 concentrated hydrochloric acid. The indigo-blue is extracted, as 

 above, by shaking with a little chloroform. As in the above test, 

 indoxyl-red may thus also be obtained, and is separated from the 

 blue pigment as just described. 



Test for Urohsematin (so-called). A small amount of urine is thor- 

 oughly agitated with chloroform and allowed to stand for a few 

 days. The chromogen of indoxyl-red is thus extracted, for on adding 

 a drop of concentrated hydrochloric acid to the chloroform extract 

 a beautiful rose-color appears, which varies in intensity with the 



