OCCURRENCE OF INDIGO-BLUE IN URINE. 243 



topper and an excess of caustic soda, it becomes greenish, and 

 if after being filtered it be heated for some time it gradually 

 deposits a tolerably large quantity of suboxide of copper, 

 which is a proof of the presence of sugar. That the latter 

 has been formed during the process and did not pre-exist, may 

 be ascertained by previously heating a portion of the urine 

 with a salt of copper and caustic soda, before treating the 

 remainder of it with acid. Samples of urine, which, when 

 tried in this way, afforded very doubtful or no indications of 

 their containing sugar, were found after being boiled with 

 acid, then filtered and made alkaline, to reduce oxide of copper 

 in a very marked manner. This reaction, which is so simple 

 that it is only surprising it should never before have been 

 observed, seems to me to prove that there is contained in urine 

 some body, which by decomposition with acids yields sugar, 

 the brown flocks precipitated at the same time being probably 

 the substance with which the sugar was originally associated 

 in the form of a copulated compound. From various con- 

 siderations, which I need not detail, I was led to infer that this 

 body could be no other than the very imperfectly known, so- 

 called extractive matter of urine, and I accordingly commenced 

 an investigation of this substance, which has led to conclusions 

 of considerable interest. On discovering that the composition 

 of the brown flocks formed by the action of strong acids on 

 urine is expressed by the formula C u H 7 N0 4 , which is also 

 that of anthranilic acid, a product of the decomposition of 

 indigo-blue, no further considerations were necessary to induce 

 me to proceed with the investigation, notwithstanding the 

 difficulties which I found attending it. Into the details of this 

 investigation I shall at present only enter so far as they relate 

 to the occurrence of indigo-blue in urine. 



When acetate of lead is added to urine it produces a cream- 

 coloured precipitate, which consists of chloride, sulphate, 

 phosphate, and urate of lead, and contains also a little of the 

 •extractive matter of urine, which is, as it were, merely attached 



