1. The transforming substance of Pneumococcus Type III is inactivated by treatment with ascorbic acid. This effect of ascorbic acid is catalyzed by traces of cupric ion and is prevented by the presence of sulfhydryl compounds.

2. Under certain conditions, the activity of transforming substance treated with ascorbic acid can be restored by the use of glutathione and other sulfhydryl compounds.

3. Other compounds, such as catechol, hydroquinone, and p-phenylenediamine, which undergo autoxidation similar to that of ascorbic acid, have an analogous effect on the transforming substance.

4. The effect of these compounds on the transforming substance is nullified by exclusion of oxygen or by the use of catalase.

5. It is concluded that inactivation of the transforming substance is probably oxidative in character and depends on the formation of peroxides in the course of autoxidation of ascorbic acid or related compounds.

6. The relation of this phenomenon to that of the inactivation of other biologically active substances by ascorbic acid is discussed.

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