OXIDATION-REDUCTION EQUILIBRIA IN BIOLOGICAL SYSTEMS : II. POTENTIALS OF AEROBIC CULTURES OF B. TYPHOSUS.

1. The reduction potentials of B. typhosus in culture in bouillon which is given access to atmospheric oxygen show a negative drift that attains the values found in sterile bouillon when deaerated with nitrogen: Eh -0.085 to -0.095 volt at pH 7.6. The potential reaches this level after 6 to 8 hours incubation, and is maintained at this point for several hours. A slow decline to more negative values is then observed and continues for at least 48 hours, when a potential of -0.145 volt may be attained. 2. The bacteria influence the potentials in the first period of their growth by exhaustion of oxygen from the culture, thus permitting the characteristic potential of the culture medium to become manifest, and do not contribute the substances responsible for the observed potentials. The decline in potential to values more negative than those of the culture medium occurs during the time that the rate of dying of the bacteria approaches and exceeds the rate of multiplication; it is suggested that dissolution of bacteria liberates reductive substances. 3. Cultures in 0.5 per cent dextrose medium show a somewhat more , negative potential after 18 hours growth than cultures in medium without dextrose. This may be due to the more rapid "turn-over" of the bacteria and the liberation of larger amounts of reductive material from dissolution of larger numbers of bacteria. 4. The potential of cultures through which oxygen is passed continuously does not show a negative drift at any time. This indicates that reductive substances of bacterial origin in the case at least of the typhoid bacillus do not influence the electrode potentials in the presence of oxygen and confirms the importance of bacterial respiration as the means for the removal of oxygen and the consequent establishment of characteristic reduction potentials in cultures.