Using St. albus, the standard strain stocked in our laboratory, as the test bacteria, by studying the metabolic reactions of the bacteria, cultured both in the medium reduced of its Fe⁺⁺ content by addition of αα'-dipyridyl and in the medium with sufficient Fe⁺⁺, the author obtained the following results: 1. Irrespective of what the C-source may be, in the case of St. albus cultured in the medium with reduced Fe⁺⁺ by addition of αα'-dipyridyl the enzymatic activity involved in the complete oxidation of those below pyruvate in the process of glucose oxidation is lowered. 2. In the medium with glucose as its C-source with reduced Fe⁺⁺ there is developed a pathway different from that in the case of the medium containing sufficient Fe⁺⁺ in the course of the oxidation pathway from glucose to pyruvate. 3. In the medium with gluconate as its C-source there can be recognized no difference in the gluconate oxidation whether cultured in the medium with reduced Fe⁺⁺ or in the medium containing sufficient Fe⁺⁺.