20 Experiments m the Urine [Jan^ 



was afterwards induced, by farther experiments^ to adopt the 

 general belief of tlie complete absence of urea.* 



The test which has hitherto been employed to decide this 

 point, is the addition of nitric acid to the extract of urine dis- 

 solved in a small quantity of water. When lu'ea is present, a 

 copious precipitation is immediately produced of bright pearly 

 scales, resembling very nearly in their appearance the acid of 

 borax. And though this test appears to have been considered as 

 somewhat equivocal, from its affording a crystallized substance 

 by its action on sugar, as well as on urea,t yet a little attention 

 will obviate all uncertainty from this source. The change 

 effected by nitric acid on urea takes place at common tempera 

 tures ; and, when it does not happen immediately, is entirely 

 prevented by heating the mixture, in consequence of the decom- 

 position of a part of the acid by the urea, and the formation of 

 volatile alkali, which unites with the undecomposed acid, and 

 forms nitrate of ammonia. On the other hand, crystals of 

 oxalic acid are never produced, until after the application of a 

 high temperature. The shape of these crystals also is strikingly 

 different from that of the crystals of nitrate of urea ^ the latter 

 being readily discriminated, by their flat scaly form and pearly 

 lustre, from the crystals of oxalic acid, even when the figure of 

 the latter is modified, a& sometimes happens, by the presence of 

 other substances. In some cases, where doubts appear to have 

 existed as to the nature of the product resulting from the action 

 of nitric acid on the extract of urine, I suspect that it has been 

 a mixture of oxalic acid and nitrate of ammonia, both of which 

 have probably been generated, in consequence of the urine 

 having contained urea as well as sugar; a combination not 

 unusual in the less perfect forms of the disease. 



In decided cases of diabetes mellitus, it has invariably hap- 

 pened, within my own experience as well as that of other per- 

 sons, that the nitric acid, applied to the extract of the urine, 

 has failed to give any indications of the presence of urea. There 

 appeared to me, however, reason to suspect, that the action of 

 that acid on the urea might possibly be prevented, by its agencj 

 on the greater proportional mass of sugar. To determine this 

 point, nitric acid was added to artificial mixtures of the extract 

 from diabetic and natural urine, J with the following results. 



J? ^ t. r ^ \ J- u ^- fThe whole presently rendered 



iixtract from 1 measure diabetic j tj i ^ j . 



, r , 1 • < solid by the abundant pre- 



with 1 of natural urine. ) - J r . i- 



cipitation oi nitrate of urea, 



• Bardsley's Reports, p. 1T4. + Bostock in Med. Mem. vi. 251. 



:{: The diabetic urine was that of S. Brookes, whose case is described hf 

 J)r. Ferriar, in his Medical Histories and Refiections, 2d edit, vol. i. p. 135. 

 Jft had the specific gravity 1033. The natural urine was the portion first voidedt 

 in the morning by a ma^ in strong health, and bad the specific gravity 101 'J,, 



