304 
DR. HASSALL ON THE FREQUENT PRESENCE 
appeared black ; but the colouring matter contained in which, was, under the 
microscope, seen to be of a deep blue. 
In order that a doubt might not remain as to the blue colouring matter described 
in the present communication being really indigo, it had been suggested to me that 
it was highly desirable to collect it in sufficient quantity to allow of its conversion 
into aniline. 
With the above view, I set aside upwards of twenty urines obtained from a variety 
of different cases of disease, watching them from time to time. In four of these the 
blue substance was formed in considerable amount ; it was carefully collected, and 
subjected, both by Dr. Letheby and myself, to the following process of analysis. 
First. It was purified by steeping it for several days in dilute hydrochloric acid, 
by which means the phosphates, chlorides and urea were dissolved out, and the 
residue, when dried, had a brighter blue colour. 
Secondly. It was tested as follows : — 
a. When heated it sublimed in purple vapours ; and on further application of heat 
it evolved empyreumatic vapours, which possessed the properties of aniline and the 
odour of burnt indigo. 
(3. When treated with sulphuric acid, it furnished a blue solution, which was not 
destroyed by dilution with water, but was bleached by chloride of lime. 
y. When boiled with dilute nitric acid and evaporated to dryness, it yielded a dirty 
orange-yellow material (isatine), which, when subjected to heat and the action of 
potash, gave an alkaline volatile fluid, and this, when tested with a solution of chlo- 
ride of lime and with a piece of deal moistened with hydrochloric acid, furnished 
the characteristic reactions of aniline. 
Aniline was likewise procured by the simple distillation of the pigment with a 
concentrated solution of caustic potash, as shown by the development of the well- 
known violet-blue colour on the addition of a solution of chloride of lime. 
We have, in the next place, to consider the important question of the source and 
origin of indigo in urine. 
We have seen that blue indigo is not usually present in urine when first passed, 
and in which it afterwards makes its appearance, but that it is gradually formed some 
time subsequently, on exposure to the atmosphere, by a process of oxidation. One or 
two cases scarcely admitting of a doubt, are, however, recorded, in which coloured 
indigo has been voided with the urine. 
We must not conclude, from the absence of coloured indigo in fresh urine, that that 
substance was not present in the urine in a modified form when first voided, since 
there is a colourless or white indigo, which, in contact with oxygen, undergoes 
precisely the same transformations as those through which the blue indigo of the 
urine was observed to pass; changing, like it, from slaty -blue to light, and ultimately 
to deep blue. 
Whether the blue indigo of the urine is derived directly from white indigo, or 
