228 Royal Society. 



evaporation, it gave a further supply of indigo, which was formed 

 most freely at the edge of the liquid. The residue was made black 

 by concentrated sulphuric acid and deep brown by potash. 



The blue colouring matter. — Of two samples of this in a dry state, 

 mixed with a large quantity of earthy phosphates, vjJ>riones, mucus, 

 and epithelium, one gave a dark brown solution with concentrated 

 sulphuric acid, and the other a dirty blue. Both of these solutions 

 were decomposed by water, furnishing in the former case a dark 

 brown deposit, and in the latter a dirty green. In most of their 

 other reactions, however, they presented the characters of indigo ; 

 and it is especially deserving of notice, that they were reduced by 

 lime and sugar, giving a liquid from which hydrochloric acid threw 

 down a greenish- blue precipitate. 



The cause of concentrated sulphuric acid giving with one of these 

 samples a brown solution, and with the other only a dirty blue, was, 

 the author considers, mainly owing to the large quantity of animal 

 matter with which the specimens were contaminated ; the acid, from 

 its charring effect on this, would produce a brown or blackish solu- 

 tion, thus obscuring the colour of the solution of indigo. 



The brown extractive. — The brown extractive yielded nearly the 

 same results as on its first analysis, and the aqueous solution fur- 

 nished a few blue flocculi. A portion of the alcoholic extract was 

 heated with Liq. Potassse for the purpose of ascertaining whether it 

 contained leucine, and the product, on being treated with hydro- 

 chloric acid, gave off a powerful odour, which was somewhat like 

 valerianic acid; but the result was too doubtful to be of much value. 

 The author had already referred to the peculiar smell of Valerian 

 emitted by the extractive of more than one of the samples. He con- 

 siders that the clearest and most positive evidence was thus obtained 

 that the blue colouring matter in this case was indigo. 



It was not very long after the occurrence of the first case of blue 

 urine that numerous other instances fell under the author's observa- 

 tion. The urines of all these cases underwent very nearly the same 

 changes as in the first ; in some, the quantity of blue colouring mat- 

 ter found was very considerable, in others less; and in the third 

 class of cases the microscope was necessary for its discovery. In 

 nearly all these cases the blue colouring matter was submitted to 

 analysis, and ascertained, on the clearest evidence, to be indigo. 



The author in the next place considers the question of the source 

 and origin of indigo in the urine. 



It appeared that in the cases related by the author, coloured 

 indigo was not present in urine when first voided, but that it was 

 gradually formed some time afterwards by a process of oxidation on 

 exposure to the air, being in most of the cases probably derived from 

 the brown extractive, which in its chemical manifestations so closely 

 resembles hsematin. 



The author contrasts cyanourine with the indigo detected in urine. 

 He observes that the most distinctive tests laid down for cyanourine 

 are its solubility in boiling alcohol, and the action of sulphuric acid 

 upon it, which give a reddish-brown solution ; and states he had 



