POSTCGENAL UREA EXCRETION 105 



fully explained by the difference of food. According to 

 Eppinger it is not difficult to poison with acid dogs kept on 

 protein-free diet; conversely the inherently low acid-re- 

 sistance of rabbits and sheep is at once raised by food rich 

 in protein. 14 That a similar defensive influence is manifest 

 also from injected urea and aminoacids is denied by Pohl. 15 



Arginase. A small cleavage fraction of the nitrogen in 

 the protein molecule arises, not by the roundabout way of 

 total dissociation and combustion, but by direct separation 

 from the arginin-group by the action of a special ferment, 

 arginase of Kossel. In an earlier lecture (Yol. I of this 

 series, p. 94, Chemistry of the Tissues) some attention was 

 given to the mode of action of the latter. Experiments on 

 protamines have indicated that arginase is able to seize upon 

 not only the free arginin but to attack even that which is 

 present in the interior of the protein molecular structure. 

 Eacemic arginin undergoes asymmetrical cleavage ; creatin 

 and guanidin are not affected. 16 It is probable that some of 

 the older statements in literature with reference to fermen- 

 tative production of urea 17 in tissue extracts, are explicable 

 as due to the influence of arginase. 



Postccenal Urea Excretion. The catabolism of ingested 

 protein in the normal organism occurs so promptly that the 

 process is complete within the course of a few hours. Ob- 

 servations upon the excretion of urea from hour to hour 

 after meals, conducted in the laboratory of Ernest Freund, 

 have shown that in normal individuals it reaches its maxi- 

 mal grade as early as four to five hours after the ingestion 



"H. Eppinger, Wiener klin. Wochenschr., 1906, No. 5; Zeitschr. f. exper. 

 Pathol., 8, 530, 1906; H. Eppinger and F. Tedesko, Biochem. Zeitschr., 16, 207, 

 1909. 



"J. Pohl and E. Mtinzer, Centralbl. f. Physiol., 20, 232, 1906; J. Pohl, 

 Biochem. Zeitschr., 18, 24, 1909. 



"A. Kossel and H. D. Dakin, Zeitschr. f. physiol. Chem., 41, 321, 1904; 

 42, 181, 1904; H. D. Dakin, Journ. of Biol. Chem., 8, 435, 1907; Rieszer (Kos- 

 sel's Lab., Heidelberg), Zeitschr. f. physiol. Chem., 49, 210, 1906. 



17 Ch. Richet, Chassevant, Spitzer, D. Lowi; cf. O. Lowi (Hofmeister's Lab., 

 Strassburg), Zeitschr. f. physiol. Chem., 25, 512, 1898. 



