OCCURRENCE OF INDIGO-BLUE IN URINE. 245 



in the cold. After the whole of the oxide of lead has combined 

 with the acid employed, the liquid is filtered. When there is 

 much of the indigo-producing body present the filter acquires 

 a blue tinge, small particles of blue pigment are seen dotting 

 the surface of the sulphate or chloride of lead, and the surface 

 of the liquid, which is of a brownish-purple colour, in a very 

 short time becomes covered with a thin pellicle, which is blue 

 by transmitted and copper-coloured by reflected light, particles 

 of the same blue substance being at the same time found 

 attached to the sides of the vessel. When there is less of the 

 indigo-producing body present, this pellicle only appears after 

 some time, sometimes not until the next day. After twenty- 

 four hours however the action of the acid is always completed, 

 so that if no indigo-blue then appears or can be detected on 

 examination of the deposit, the total absence of the indigo- 

 producing body may be inferred. On the succeeding day, 

 however large the quantity of blue deposit formed may be, the 

 liquid no longer appears purplish, but brown, and after being 

 filtered and boiled deposits a dark brown powder, having 

 exactly the same appearance as that produced by the action 

 of acids on the ordinary extractive matter of urine. The 

 matter left on the filter after being washed is treated with 

 caustic soda, which dissolves a portion acquiring thereby a 

 brown colour. The portion which remains undissolved after 

 being again collected on a filter and washed, is treated 

 with boiling alcohol. In most cases the alcohol acquires 

 thereby a bright blue colour. When however the quantity 

 of deposit formed is tolerably large, the boiling alcohol 

 first dissolves another substance, which imparts to it a 

 fine purple colour, and which I consider to be identical with 

 indirubine.* That which the boiling alcohol leaves undissolvd 

 is a bright blue powder having the properties of indigo-blue. 



* It it very probable that Heller's urrhodine, as well as Golding Bird's 

 purpurine are also identical with indirubine, which, as I have shown, has the 

 same composition as indigo-blue 



