FORMATION OF UREA. 649 



formation of urea occurs; but there is no doubt that a formation of 

 ammonia is here of great importance. 



The possibility of a formation of urea from ammonia has been pos- 

 itively shown. Thus the researches of v. KNIERIEM, SALKOWSKI, FEDER, 



I. MUNK, CORANDA, SCHMIEDERBERG and FR. WALTER, HALLERVORDEN, 



and POHL and MUNZER/ on the behavior of ammonium salts in the animal 

 body and the elimination of the ammonia under various conditions, 

 have shown that not only ammonium carbonate, but also those ammonium 

 salts which are burnt into carbonate in the organism, are transformed 

 into urea by carnivora as well as herbivora. v. ScHROEDER, 2 by irrigat- 

 ing the surviving dog's liver with blood treated with ammonium car- 

 bonate or ammonium formate, has shown that the formation of urea 

 takes place, at least in part, in this organ. NENCKI, PAWLOW, ZALESKI 

 and SALASKIN 3 have also found that, in dogs, the quantity of ammonia 

 in the blood from the portal vein is considerably greater than that from 

 the hepatic vein, and they claim that the liver retains in great part the 

 ammonia thus supplied. The formation of urea from ammonia in the 

 liver is a positively proven fact, and the urea formation from ammonium 

 carbonate is to be considered as a synthesis with the elimination of 

 water. 



The assumption of a splitting off of ammonia from amino-acids is 

 not difficult of conception, as now, especially from the investigations 

 mentioned in Chapter VIII, we know with positiveness that deamidation 

 of amino-acids does take place in the animal body. The ammonia 

 split off finds in the blood and tissues the carbon dioxide necessary for 

 the formation of carbonate, and the investigations of NOLF, as well 

 as those of MACLEOD and HASKiNS, 4 on the equilibrium of car- 

 bonate and carbamate solutions and the conditions for the formation 

 of both salts, must also be abundant evidence of a carbamate formation. 



Important observations have been made which give support to the 

 views of SCHULTZEN and NENCKi, 5 namely, that the amino-acids are 

 transformed into urea with carbamic acid as an intermediate step. 

 DRECHSEL has shown that the amino-acids yield carbamic acid by oxida- 

 tion in alkaline fluid outside of the organism, and he obtained urea from 

 ammonium carbamate by passing an alternating electric current through 

 its solution, i.e., by alternate oxidation and reduction. DRECHSEL has 



1 v. Knieriem, Zeitschr. f. Biologie, 10; Feder, ibid., 13; Salkowski, Zeitschr. f. 

 Biologie, 1; Munk, ibid., 2; Coranda, Arch. f. exp. Path. u. Pharm., 12; Schmiede- 

 berg and Walter, ibid., 7; Hallervorden, ibid., 10; Pohl and Mtinzer, Arch., f. exp. 

 Path. u. Pharm., 43. 



2 Arch. f. exp. Path. u. Pharm., 15. See also Solomon, Virchow's Arch., 97. 



3 Arch, des sciencs biol. de St. Pe*tersbourg, 4; see also Chapter VI, p. 317. 



4 Nolf, Zeitschr. f. physiol. Chem., 23; Macleod and Haskins, Journ. of biol. Chem., 1. 



5 Zeitschr. f. Biologie, 8. 



