After studying the gain or loss of oxidizability of glucose or ribose by each of standard strain bacteria such as Sh. flexneri 1 a, 2 a and 3 a, the following results were obtained. 1. Oxidizability of gluconate gradually takes place if bacteria are kept in contact with gluconate for more than 2 hours, but when pepton is loaded in addition oxidizability is enhanced markedly. Since streptomycine has been found to inhibit the production of enzyme oxidizing gluconate, it appears that enzyme is being produced adaptibly. 2. Oxidizability of ribose can be gradually realized by keeping bacteria in contact with ribose for a long period of time, and with addition of glucose it is enhanced strikingly. Moreover, as it is not inhibited by streptomycine, it seems reasonable to assume that riboseoxidizing enzyme existed in bacteria themselves from the first. 3. Oxidizability of gluconate is attained in various degrees by shaking bacteria with glucose; and in the case of Sh. flexneri 1 a it is pronounced while in the cases of 2 a and 3 a it is attained but slightly. As for the oxidizability of ribose, when ribose is shaken either with glucose or gluconate, in the case of Sh. flexneri 1 a it is marked while in the cases of 2 a and 3 a it is attained only slightly. 4. Oxidizability of gluconate or ribose already obtained can last for a quite long time even when the bacteria are stripped of these substrates, however, when bacteria are successively cultured on the medium not containing such substrates the oxidizability is lost immediately.