The washed cells of Pneumococcus are able to reduce the various indicators of oxidation-reduction potentials in the presence of glucose. The relative velocity of reduction of these indicators is determined by the number of cells used in the test, the concentration of the dyes, and their position in the oxidation reduction scale.

Oxidized thiol compounds (glutathione, cystine, oxidized thioglycollic acid) are likewise rapidly reduced by glucose in the presence of washed cells of Pneumococcus.

This Pneumococcus-glucose system is able to form peroxide under aerobic conditions. Those substances which form peroxide in the presence of Pneumococcus cells are also the ones which Cole found to be active in changing hemoglobin into methemoglobin under the same conditions.

The power of washed cells of Pneumococcus to reduce methylene blue in the presence of glucose is dependent on at least 2 constituents: one which can be readily removed from the cell by washing. Sugar-free meat infusion will function instead of it. The other is inactivated more slowly by the process of washing and is destroyed by 10 minutes heating at 55°C.

The interreaction between the glucose and the cell seems to result in a fundamental reaction in which one molecule of glucose becomes able to reduce rapidly one molecule of methylene blue. The existence of side-reactions often obscures this ratio.

The significance of these observations is considered in relation to the nature and mechanism of the "activation" of metabolites, the preparation of synthetic media, the phenomena of growth, and the meaning of the expression "reducing power of a bacterial culture."