Dr. Schunck on the Occurrence of Indigo-blue in Urine. 293 
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 be- 
comes 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, some- 
times 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 de- 
posit, 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 dissolyes 
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 undissolved, is a bright blue powder 
having the properties of indigo-blue. It dissolves in an alkaline 
solution of protoxide of tin, and the solution on exposure to the 
air becomes covered with a blue film. It is soluble in concen- 
trated sulphuric acid, forming a blue solution, which remains 
blue even after dilution with water. It imparts to boiling alcohol 
a bright blue colour, and the solution on cooling and standing 
deposits blue flocks. When heated in a tube, it gives a purple 
vapour which forms on the colder parts of the tube a blue sub- 
limate. 
Provided with this test, I proceeded to examine the urine of a 
number of individuals, and 1 succeeded in obtaining indigo-blue 
im so great a number of instances, that I have no hesitation in 
saying that the indigo-producing body, if not exactly one of the 
normal constituents of urine, occurs more frequently than any 
other of the abnormal ones. The urines containing it exhibit 
* It is 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. 
