Reduction Intensity of Sterile Bouillon

Abstract

The reduction potential which may be attained under anaerobic conditions in sterile bouillon has been reported 1 as reaching an apparent equilibrium at E_H—0.085 to 0.095 volt at pH 7.5.

Dubos 2 has found, however, that the reduction intensity of sterile broth is sufficient to bring about the reduction of dyes more positive in Eo value than indigo disulfonate, and at least the partial reduction of this dye. This corresponds to a potential considerably more negative than those reported for electrode measurement. Simultaneous measurement of dye reduction and electrode potential is necessary to explain the discrepancy and to throw light on the possible catalytic effect of the dyes. This is the subject of the present paper.

The procedure for measurement of the electrode potentials has been described elsewhere. 1 In the present work a quadrant electrometer was used instead of a galvanometer in order to minimize polarization of the electrodes. Sterility of the bouillon was maintained throughout. The bouillon represented various lots of the infusion medium used in this laboratory for growth of the streptococcus. It was adjusted to pH 7.6, buffered by phosphate in M/10 concentration and autoclaved immediately before use in each experiment. Determination of the final pH was made with the hydrogen electrode at the close of the experiment, in some cases.

The time-potential course of the bouillon without addition of dye was followed first for a period of one or more weeks. The potential was regarded as having attained its equilibrium value when no further negative drift was observed over a period of at least 48 hours. At this point a sufficient amount of the indicator dye in deaerated solution was added through an anaerobic burette to give a distinct color to the bouillon, and the subsequent course of the electrode potentials was followed until again a value was reached which remained constant for 48 hours or longer.