The Non-Protein Nitrogen of Blood. 



ii5 



68 (1246) 



The non-protein nitrogen of blood : 1. The removal of the protein. 

 2. The estimation of creatine. 



By ISIDOR GREENWALD. 



[From the Harriman Research Laboratory, Roosevelt Hospital, New 



York.] 



In a previous publication, 1 the author described a modification 

 of the method of Folin and Denis 2 for the determination of non- 

 protein nitrogen in blood. Trichloracetic acid was used to precipi- 

 tate the protein and the trace that remained in the filtrate was 

 removed by shaking with kaolin. It was shown that the nitrogen 

 of an amino-acid mixture added to blood could be completely 

 recovered by this method and that no nitrogen was split off from 

 proteins by this treatment. Bock 3 recently described another 

 method for obtaining protein-free filtrates from blood. He co- 

 agulated the protein by running the blood into boiling 0.01 N 

 acetic acid, evaporated the filtrate to a small volume, precipitated 

 most of the remaining protein with trichloracetic acid and removed 

 the last traces with kaolin. It seemed that it should be possible 

 to remove the protein from the filtrate from the coagulum by 

 means of kaolin, directly, without the use of trichloracetic acid. 

 This was found to be the case. Kaolin is added to the filtrate 

 from the coagulum, shaking the mixture thoroughly, until the 

 foam, which is at first voluminous and persistent, becomes scanty 

 and comparatively evanescent. One drop of glacial acetic acid 

 for each 100 c.c. of fluid is then added in order to agglutinate the 

 kaolin and the mixture is then filtered. The filtrate is protein- 

 free, so nearly as may be determined by the usual tests. It may 

 be evaporated to small volume (less than one tenth that of the 

 original blood) either at atmospheric or reduced pressure without 

 foaming. Determinations of the nitrogen in such filtrates agree 

 with those obtained by the trichloracetic acid-kaolin method. 

 However, both methods are made inaccurate through the removal 



1 Greenwald, Journal of Biological Chemistry, 1915, 21, 61. 

 1 O. Folin and W. Denis, Ibid., 1913, II, 527. 

 •Bock, Ibid., 1917, 28, 357. 



