360 THE URINE. 



formed more rapidly if the urine have been previously concen- 

 trated by evaporation. 



Urea is colorless when pure ; when impure, yellow or brown ; 

 without smell, and of a cooling, nitre-like taste ; has neither an 

 acid nor an alkaline reaction, and deliquesces in a moist and 

 warm atmosphere. At 59 F. it requires for its solution less 

 than its weight of water ; it is dissolved in all proportions by 

 boiling water ; but it requires five times its weight of cold 

 alcohol for its solution. At 248 F. it melts without under- 

 going decomposition ; at a still higher temperature ebullition 

 takes place, and carbonate of ammonia sublimes ; the melting 

 mass gradually acquires a pulpy consistence ; and, if the heat 

 is carefully regulated, leaves a gray-white powder, cyanic acid. 



Urea is identical in composition with cyanate of ammonia, 

 and was first artificially produced by Wohler from this sub- 

 stance. Thus : 



Cyanate of Ammonia. Urea. 



CHNO. H 3 N = CH 4 N 2 0. 



The action of heat upon urea in evolving carbonate of am- 

 monia, and leaving cyanic acid, is thus explained. A similar 

 decomposition of the urea with development of carbonate of 

 ammonia ensues spontaneously when urine is kept for some 

 days after being voided, and explains the ammoniacal odor 

 then evolved. It is probable that this spontaneous decom- 

 position is accelerated by the mucus and other animal matters 

 in the urine, which, by becoming putrid, act the part of a 

 ferment and excite a change of composition in the surrounding 

 compounds. It is chiefly thus that the urea is sometimes de- 

 composed before it leaves the bladder, when the mucous mem- 

 brane is diseased, and the mucus secreted by it is both more 

 abundant and, probably, more prone than usual to become 

 putrid. The same occurs also in some affections of the nervous 

 system, particularly in paraplegia. 



The quantity of urea excreted is, like that of the urine itself, 

 subject to considerable variation. It is materially influenced 

 by diet, being greater when animal food is exclusively used, 

 less when the diet is mixed, and least of all with a vegetable 

 diet. As a rule, men excrete a larger quantity than women, 

 and persons in the middle periods of life a larger quantity than 

 infants or old people (Lecanu). The quantity of urea does not 

 necessarily increase and decrease with that of the urine, though 

 on the whole it would seem that whenever the amount of urine 

 is much augmented, the quantity of urea also is usually in- 

 creased (Becquerel) ; and it appears from observations of Genth, 

 that the quantity of urea, as of urine, may be especially in- 



