Abstract
Sterile plain broth contains an active oxidation-reduction system, the characteristics of which have been analyzed. 1. Intensity factor: Under vaseline seal, the lot of broth used in these experiments reaches a reduction potential corresponding to reduced indigo disulfonate (rH = 10). All the indicators with a more positive E(0)' are reduced, the others are not affected. It seems probable that fresh broth, which has not undergone oxidation by molecular oxygen, would give a higher reduction potential. 2. Capacity factor: The maximum amounts of different indicators that can be reduced correspond to equimolecular concentrations. This seems to indicate either (a) that the broth does not contain several "independent" reducing systems (at least in appreciable amounts), or (b) that these hypothetical "independent" systems all have about the same reduction potential. 3. Time factor: The different indicators of oxidation-reduction potentials are reduced in the order of the electromotive series. 4. Nature of the system: The system seems to be reversible (this not excluding the possibility of irreversible autoxidations) and does not appear to be of the nature of a sugar. The relation of these phenomena to the cultivation of different species of bacteria will be reported later.