Oxidation-reduction potentials and ferricyanide reducing activities in glucose-peptone cultures and suspensions of Escherichia coli. Ibid. 561. o n

Oxidation-reduction potentials developed in cultures of Esch. coli have been reported by Cannan, Cohen, and Clark (1928), Hewitt (1931) and Boyd and Reed (1931). Boyd and Reed presented evidence that both gaseous (hydrogen) and non-gaseous electromotively active systems are responsible for the potentials observed at different periods of growth in anaerobic cultures of Esch. coli. The studies to be reported here were confined to the potentials developed in stationary and continuous flow cultures of Esch. coli in peptone, a somewhat less complex medium than those employed by other investigators. It has been reported (Clifton, 1933a) that broth cultures of Staphylococcus aureus in or near the maximum stationary growth phase reduce potassium ferricyanide at a rate in the neighborhood of 6.6 X 10-14 millimols per cell per minute. These studies have been extended to the rates of reduction of ferricyanide at different stages of growth in stationary and continuous flow cul-tures of Esch. coli. Studies on the influence of the concentra-tion of peptone, ferricyanide and organisms on the rate of reduc-tion of ferricyanide in suspensions of "resting " Esch. coli, as outlined in a preliminary paper by one of us (Clifton, 1933b), are also presented. METHODS Three-necked pyrex distilling flasks of 500 ml. capacity were employed as culture vessels. Two platinum electrodes, seale