12 OXALATE OF UREA URIC ACID. 



Oxalate of urea (C 2 H 4 N 2 2 HO, C 2 3 ) may be 

 obtained by adding oxalic acid to a concentrated solution of 

 urea or nitrate of urea ; it crystallizes in rhombic plates and 

 rhombic prisms. (Fig. 157.) 



Urea forms several insoluble com- 

 pounds with nitrate of protoxide of 

 mercury. 



Urea is the principal and by far 

 the most important of the solid con- 

 stituents of the urine; in man its 

 ratio to the other solid constituents is 



Fig. 157. Crystals of Oxalate T 



of Urea, obtained by adding ox- about 9 to 11. In the Urilie of the 



xlif* toconcentrated nrine - horse, it bears a proportion of about 

 1 to 8 or 1 to 9 of all the others. 



Having examined some of the properties of urea, the 

 question arises, whether urea exists in the blood or is formed 

 in the kidneys? Undoubtedly, urea exists in the blood, 

 and is only separated by the renal organs; for it can be 

 detected in the blood of healthy animals, and accumulates 

 in the blood, whenever, from any cause, the kidneys cease 

 to discharge their proper functions. Whether urea be formed 

 in the blood or muscles, has not been positively determined, 

 though most facts support the former hypothesis ; that it is 

 the product of the waste of nitrogenous tissues is, however, 

 undoubted, as also that the quantity excreted daily bears a 

 definite relation to the amount of nitrogenized food taken into 

 the body. 



Uric acid has the composition C 5 HN 2 2 HO; it occurs 

 in the urine of man, and almost all the carnivora. The urine 

 of herbivorous animals, if any, only contains traces of this 

 acid; it is in them replaced by another acid, the hippuric. 

 According to Boussingault and Von Bibra, the urine of the 

 pig does not contain uric acid. 



