

UREA. 27 



Urine, if uncontaminated, may be kept for an indefinite 

 period without any change, excepting that its acidity and 

 colour increase slightly soon after it is passed (acid fermen- 

 tation). Under ordinary circumstances urine becomes 

 eventually alkaline when kept, in consequence of the pro- 

 duction of ammonic carbonate. This change takes place 

 rapidly in presence of a ferment which exists in the urine 

 in certain pathological conditions. The alkaline fermen- 

 tation is attended by the formation of triple phosphate. 



It is by the discharge of urea that the rate at which 

 nitrogen is discharged from the organism is estimated. 

 Thus we learn that the discharge of nitrogen is subject to 

 regular diurnal variations ; that it is largest when food is 

 albuminous and abundant ; that it is diminished rapidly 

 by inanition, gradually by a diet containing a large 

 proportion of carbonic hydrates ; that it is increased by 

 ingestion of water, sodic chloride, and ammonium salts, 

 and that it is very slightly augmented by muscular exer- 

 cises. 



Urea exists in all the animal liquids, and in most tissues, 

 excepting the muscular and nervous, in a proportion not 

 exceeding 0*03 per cent. This proportion is increased by 

 any interference with the renal excretion. Urea is a direct 

 product of the life of protoplasm. It is not as yet proved 

 that it is more actively produced in the liver than else- 

 where. 



CRYSTALLINE ORGANIC BODIES OF THE URINE. 



Urea or Carbamide (CO (NH 2 ) 2 ) exists as such in urine so abundantly in 

 that of the carnivora, that it crystallizes therefrom on evaporation. In human 

 urine it can be crystallized from the alcoholic extract of the dry residue. 

 Urea (U) is excessively soluble in water, soluble in alcohol, insoluble in ether; 

 it is isomeric "with ammonic cyanate (NH 4 CNO) ; takes up water in contact 

 with certain ferments, and is transformed into normal ammonic carbonate 

 (CO (NH 2 ) 2 +2H 2 O=CO 3 (NH 4 ) S ). A corresponding change occurs when U 

 is acted on by alkalies or by strong sulphuric acid, ammonia being given off in 

 the former case, carbonic anhydride in the latter. On the addition of nitric 

 acid to strong solution of U, a snow-white precipitate is formed of Urea-nitrate 

 (U, NO 3 H), consisting of rhombic plates having a characteristic imbricated 



