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Scientific Proceedings (131) 



we had previous prepared. We next fed phenyluramino cystine 

 which we had synthesized, to rabbits, to see whether this com- 

 pound would be excreted or some of it changed into the cystine 

 derivative. We found that much of it had been oxidized to the 

 cystine compound. 



This shows that the reaction 



Cystin«=*Cystein 



may be a common metabolic reaction and easily as well as pre- 

 cisely controlled by the living cell. It is interesting in as much 

 as it is closely allied with the finding of Hopkins 5 on his gluta- 

 thione work and is strongly corroborative. 



175 (2135) 



A micro colorimetric method of estimating the hydrogen ion 

 concentration of the blood. 



By V. C. MYERS, H. \V. SCHMITZ* and LELA E. BOOHER. 



[From the Department of Biochemistry, New York Post-Graduate 

 Medical School and Hospital, New York City.] 



A discussion of the bicolorimetric principle was first pre- 

 sented to this Society in November, 1921, 1 at which time we had 

 the present work in mind. The method described below is es- 

 sentially an adaptation of the colorimetric method of Cullen 2 

 for the determination of the P H of the blood plasma (or serum) 

 to the bicolorimeter described by one of us. 3 As modified the 

 final determination is carried out on 0.1 c.c. of plasma, and does 

 not require more than 10 minutes after the blood has been ob- 

 tained. The color comparison can be made with an accuracy 

 of ± P„ 0.02. 



B Hopkins, F. G., Biochcm. Jour., 1921, xv, 286. 



* Medical Fellow of the National Research Council. 



1 Myers, V. C, Proc. Soc. Exp. Biol, and Med., 1921, xix, 78. 



2 Cullen, G. E., J. Biol. Chem., 1922, lii, 501. 

 B Myers, V. C, J. Biol. Chem., 1922, liv, 675. 



