THE RELATION BETWEEN THE OXYGEN CONCENTRA- 

 TION AND RATE OF REDUCTION OF METHYLENE 

 BLUE BY MILK. 



By E. NEWTON HARVEY. 



{From the Physiological Laboratory, Princeton University, Princeton.) 



(Received for publication, December 27, 1918.) 



After the discovery of the reducing power of milk^ and the proof 

 that its reducing action on methylene blue (decolorization) is not due 

 to bacteria but to a reducing enzyme,^ Bach,^ in a series of researches, 

 undertook the study of reducing enzymes in various tissues. Schar- 

 dinger^ had originally found that fresh cow's milk will reduce methylene 

 blue in the presence of an aldehyde but not in its absence and not if 

 the milk had previously been boiled. In one paper Bach^ showed 

 that nitrates could also be reduced to nitrites by Schardinger's enzyme 

 of milk and he studied the effect (on reduction) of nitrate, aldehyde, 

 and enzyme concentration, as well as the influence of temperature. 

 As the nitrate is still further reduced, the quantitative results ob- 

 tained by determining the amount of nitrate formed at successive in- 

 tervals of time after mixing varying quantities of nitrate, or aldehyde, 

 or milk, are not of much value. They do show, however, that rate of 

 nitrite formation increases with, but is not proportional to nitrate 

 concentration or aldehyde concentration. Bach found also that ni- 

 trite formation is proportional to enzyme concentration, at least in the 

 early stages of the reduction. He did not study the effect of oxygen 

 concentration in milk on the reduction of nitrate. 



^ Schardinger, F., Z. Untersuch. Nahrungs-u. Genus smittel, 1902, v, 1113; Chetn. 

 Zing., 1904, xxviii, 704. 



^ Trommsdorff, R., Centralhl. Bacterial., Ite Abt., Orig., 1909, xlix, 291. 



3 Bach, A., Biochem. Z., 1911, xxxi, 443; 1911, xxxiii, 282; 1912, xxxviii, 154; 

 1913, lii, 412. 



^ Bach, A., Biochem. Z., 1911, xxxiii, 282. 



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