682 URINE. 



tion and very great variations seem to occur not only in the healthy 

 individual, but also and to a greater degree in diseased conditions. 1 



Formation of Urea in the Organism. The older statements of BE CHAMP 

 that urea is directly formed from proteins by oxidation has been denied 

 by several investigators but according to recent statements of FOSSE 2 

 this is correct. On the hydrolysis of proteins arginine is found among 

 other products, and as it is also produced in tryptic digestion, it is possible 

 that a small portion of the urea is produced in this manner, varying 

 according to the kind of protein. DRECHSEL claims that about 10 per 

 cent of the urea can be accounted for in this way. 



The possibility of a formation of urea from arginine has gained in 

 interest since KOSSEL and DAKIN have discovered the presence of an 

 enzyme, arginase, in the liver and other organs, which has the power 

 of splitting arginine with the formation of urea. THOMPSON 3 has given 

 a direct proof for the formation of urea from arginine. The introduc- 

 tion of arginine into the body of a dog either per os or subcutaneously 

 has in his experiments led to an elimination of urea. While outside of 

 the body only one-half of the nitrogen of arginine is split off as urea 

 and the other half as ornithine, in the above experiments the increase 

 in urea in several instances corresponded to the greater part if not the 

 whole of the nitrogen of the arginine introduced. This increased forma- 

 tion of urea makes it probable that also ornithine is deamidized and the 

 urea is formed from the ammonia split off. 



By the action of alkalies, as above mentioned (Chapter X), urea may 

 be formed from creatinine; still such an origin of urea in the animal body 

 has not thus far been proved. 



The amino-acids are considered as special mother-substances of urea. 

 By numerous, generally older experiments with these acids, it has been 

 proved that the amino-acids of the animal body are transformed in part 

 into urea. The investigations by 'SALASKIN with the three amino-acids, 

 glycocoll, leucine, and aspartic acid, have unmistakably shown that the 

 surviving dog-liver, supplied with arterial blood, has the property of 

 transforming the above amino-acids into urea or a closely allied sub- 

 stance. 4 Like the amino-acids the polypeptides are also transformed into 



1 See Satta, Hofmeister's Beitrage, 6, which also gives the literature, and Erben, 

 Zeitschr. f. Heilkunde, 25. 



2 Compt. Rend., 154. 



3 Kossel and Dakin, Zeitschr. f. physiol. Chem., 41; Thompson, Journ. of PhysioL, 

 32 and 33. 



4 Schultzen and Nencki, Zeitschr. f. Biologic, 8; v. Knieriem, ibid., 10; Salkowski, 

 Zeitschr. f. physiol. Chem., 4; Salaskin, ibid., 25; Stolte, Hofmeister's Beitrage, 5; 

 Levene and Meyer, Amer. Journ. of PhysioL, 25; see also Loewi, Zeitschr. f. physiol. 

 Chem., 25; Richet, Compt. Rend., 118, and Compt. rend. Soc. biol., 49; Ascoli, 

 Pfliiger's Arch., 72. 



