238 THE URINE. 



current. These symptoms were also present when carbamates were 



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



r, 

 signs ot poisoning. 



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

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

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

 such a transformation can actually occur, we must yet remember 

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

 The question hence arises : In what form does the waste nitrogen 

 leave the tissues ? The prevailing idea has been that the greater 

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

 the form of the ammonium salt of paralactic acid, and the tendency 

 has been to regard this salt as the 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 dogs, 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. 



Under normal conditions it is then assumed that the lactate is 

 transformed into ammonium carbonate, which in turn yields the car- 

 bamate, and that the urea finally results through a synthetic process, 

 which is supposedly effected through the agency of a certain fer- 

 ment. We may further imagine that the paralactic acid in the last 

 instance may result from a decomposition of the mono-amino-radicles 

 of the albuminous molecules, and in this form the theory would em- 

 brace the two outlined above. The various changes may be repre- 

 sented by the equations : 



(1) 2NH 4 .C 3 H 5 3 + 120 = (NH 4 ) 2 C0 3 + 5CO 2 + 5H 2 O 

 Ammonium lactate. 



/NH 2 



(2) (NH 4 ) 2 C0 3 - C0< + H 2 



X).NH 4 

 Ammonium 

 carbamate. 



/ 



NH 2 



(3) CO = CO + H 2 



\O.NH 4 \NH, 



Urea. 



The ultimate formation of urea takes place in the liver. Of 

 this we have abundant proof. It has thus been shown that in 

 diseases of this organ which are associated with extensive destruc- 

 tion of the glandular elements a diminished amount of urea is found 

 in the urine, while ammonia and lactic acid are present in increased 

 quantity, and mono-amino-acids may indeed appear as such. In cases 

 of this kind as much as 37 per cent, of the total amount of urinary 

 nitrogen has been found in the form of ammonia. In the mammal, 



