540 THE SECRETIONS. 



that the so-called urohaematine contains a mixture of several 

 pigmentary substances. 



J. Passing from uroluematine, the student's attention is to 

 be drawn to the constant presence in urine of a very well- 

 defined bodyviz., indican, or white indigo (C 16 H 12 N 2 ? ) 

 which may readily be converted into indigo-blue and indigo- 

 red. To the indican present in urine, Heller, who first dis- 

 covered its presence, without, however, being aware of its 

 nature, gave the name of Uroxanthine, and to the indigo-blue 

 and indigo-red obtained from it, the names of-Uroglaucine and 

 T'rrhodin respectively. 



I-'or the method of obtaining indican, the reader is referred 

 to Hoppe-Seyler (op. cit. p. 163); it will be sufficient if the 

 student performs the following experiments: 



Precipitate 100 cubic cent imetres of perfectly fresh urine 

 with acetate of lead. The fluid is filtered. The filtrate con- 

 tains the whole of t lie indican. A strong solution of ammonia 

 is added, which precipitates hydrated lead oxide, together 

 with indican. The precipitate is collected on a filter, washed 

 with water and dilute dydrochloric acid. Very often the 

 filter is seen to contain blue particles, in consequence of the 

 production of indigo-blue, which contrasts with the chloride of 

 lead with which it is mixed. 



Tin* filtrate, when left to itself for twenty -four hours, gener- 

 ally becomes covered with a bluish-purple film, consisting of 

 indigo. 



^everal hundred cubic centimetres of pure urine are pre- 

 cipitated by acetate of lead and then filtered; the filtrate is 

 treated with excess of sulphuretted hydrogen, boiled and 

 filtered; the filtrate is now poured into an equal volume of 

 pure and strong hydrochloric acid. The fluid becomes either 

 violet or indigo-blue ; it is allowed to stand for twelve hours, 

 and diluted with an equal volume of water. After about 

 twenty-four hours, a deposit wfll generally have formed, which 

 is collected on a filter, washed, and dried. When treated with 

 ether, the deposit will generally yield to it a red coloring 

 matter, whilst indigo is left behind, and is to be purified by 

 solution in boiling alcohol. 



The student will remember that indigo-blue only differs from 

 indicau in the possession of two additional atoms of hydro- 

 gen, 



Indican, or white indigo C 16 H 12 N.,0 2 . 



Indigotin, or blue indigo QJ&J&fif 



In the production of indigo-blue from indican there are 

 other substances formed, such as a form of sugar, which is an 

 i.somer of glucose, but uufermentable, and the imperfectly' 



