DEHYDROASCORBIC ACID AND BACTERIA 605 factor is not replaceable by methylene blue, pyocyanine, glutathione, coenzyme ii, yeast extract, or boiled or unboiled whole yeast. 3. The effect of hydrogen-donator concentration on the rate of DHA reduction, as compared with the rate of methylene-blue reduction, indicates that the rate of hydrogen transfer may be greatly reduced in the DHA-reducing system. 4. Growth on lactate or formate in place of glucose increases the hydrogenase activity, but decreases the DHA-reducing activity. 5. When more than one hydrogen donator is present, the rates ofDHA reduction are not additive. The rate of reduction when formate, lactate and hydrogen are present together is not as great as when glucose is present alone.

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