THE URINE. 339 



ammonium carbonate or ammonium formate through a dog's liver, 

 he found that a considerable formation of urea took place. The 

 very careful observations of SALOMON confirm this, and also the 

 above-mentioned decrease of urea and increase of ammonia in the 

 urine in certain diseases of the liver. 



It cannot be denied that the formation of urea in the liver is of 

 great physiological importance ; but still it does not follow that all 

 the urea has its origin in this organ. The possibility of a formation 

 of urea from creatin or xanthin bodies is not to be rejected without 

 further inquiry, and other possibilities as to its formation are con- 

 ceivable. 



The question in which organ urea is formed has been the 

 subject of much discussion. From the researches of numerous 

 investigators, PREVOST and DUMAS, MEISSNER, VOIT, GREHANT, 

 GSCHEIDLEN, SALKOWSKI, and v. SCHRODER, it has been found that 

 the extirpation of the kidneys causes a considerable increase in 

 the quantity of urea in the blood. The kidneys, therefore, although 

 they may produce urea generally, are not the only organs which 

 produce it. By experiments performed on the removed kidneys, 

 which were analogous to the above-mentioned experiments on the 

 removed liver, v. SCHRODER has shown that neither the kidneys 

 nor the muscles nor the remaining tissues of the lower extremities 

 of the dog have the property of forming urea from ammonium car- 

 bonate. The only organ in which a formation of urea has been 

 proved with certainty, thus far, is the liver, but this does not ex- 

 clude the possibility that urea may also be formed in other organs, 

 perhaps from other material than ammonium carbonate and in 

 other ways. 



Properties and Reactions of Urea. Urea crystallizes in needles 

 or in long, colorless, four-sided, often hollow, anhydrous rhombic 

 prisms. It has a neutral reaction and produces a cooling sensation 

 on the tongue like saltpetre. It melts at 130-132 C., but decom- 

 poses already at about 100 C. At ordinary temperatures it dis- 

 solves in equal weight of water and in five parts alcohol; it requires 

 one part boiling alcohol for solution; it is sparingly soluble in 

 ether. If urea in substance is heated in a test-tube it melts, de- 

 composes, gives off ammonia, and leaves finally a non-transparent 

 white residue which, among other substances, contains biuret and 



