THE ORGANIC CONSTITUENTS OF THE URINE. 223 



appears in the urine as urea. This transformation of mono-amido- 

 acids into urea may be represented by the following equations : 



(1) CH 2 (NH 2 ).COOH + 2O = NH 4 .COOH + CO 2 



Glycocoll. Ammonium 



formate. 



(2) 2NH 4 .COOH + 20 = (NH 4 ) 2 .CO 3 + H 2 O -f CO 2 



(3) (NH 4 ) 2 .C0 3 = C0<^ + 2H 2 



J^l 11 



Urea. 



Drechsel has further shown that the amido-acids yield carbamic 

 acid on oxidation, and that through alternate oxidation and reduction 

 urea can result from the ammonium salt, as shown in the equations : 



H 2 O 



(2) CO/ ^ + 2H = OX' -fH 2 O 



^O.NH 2 ^NH 2 



Carbamic acid. Urea. 



That carbamic acid is present in the normal acid urine of man 

 and the dog has been proved. Nencki and Hahn, moreover, 

 observed that in dogs in which the liver was temporarily excluded 

 from the general circulation larger amounts of carbamic acid 

 appeared in the urine than under normal conditions, and that the 

 animals showed symptoms of intoxication identical with those 

 observed when carbamates are directly introduced into the blood- 

 current. These symptoms were also present when carbamates were 

 introduced into the stomach, in which case normal dogs show no 

 .signs of poisoning. 



While it has been assumed above, that urea is largely referable to 

 a transformation of mono-amido-acids into ammonium carbonate or 

 carbamate, as the case may be, and while it has been shown that 

 such a transformation actually does occur, we must yet remember 

 that only traces of amido-acids are normally found in the tissues. 

 There is reason to believe that the greater portion of the albuminous 

 nitrogen is normally set free from the various organs of the body in 

 the form of the ammonium salt of paralactic acid, and there is a 

 tendency among physiologists at the present time to regard this 

 salt as the common antecedent of urea. It has been demonstrated, 

 as a matter of fact, that urea results when ammonium lactate is 

 passed through the isolated liver of a dog ; and clinically, also, we 

 observe that both ammonia and lactic acid appear in the urine in 

 increased amounts when the liver is extensively diseased. Similar 

 results are obtained in birds, in which uric acid represents the 

 principal end-product of nitrogenous metabolism. In geese it is 

 thus noted that after extirpation of the liver the greater portion of 

 the urinary nitrogen appears in the form of ammonium lactate. 



