, suggested, demonstrated, and confirmed the fact that certain quinones are bactericidal. Interference with this property by serum and peptones precluded their use as germicides in man (Morgan and Cooper, 1924). Interest in quinones as antibacterial agents, however, has been stimulated somewhat in recent years by the discovery by Oxford and Raistrick (1942) and by Waksman and Woodruff (1942) of the quinone structure in certain antibiotics derived from molds. Fosdick, Fancher, and Calandra (1942) found that 2-methyl-1 ,4-naphthoquinone inhibited acid formation from glucose in saliva without effect on bacterial growth in the concentration employed (1 mg per 100 ml). Armstrong and his co-workers (1943) claimed that this effect was due to the quinone structure and noted in vitro inhibition of certain strains of streptococcus, staphylococcus, and pneumococcus by several quinones, including 2-methyl-1,4-naphthoquinone. They stated that none of the quinones tested in a concentration as high as 29 X 104 mols per 100 ml inhibited the growth of Escherichia coli. Observations of fungus-inhibitory properties of 2-methyl-1 ,4-naphthoquinone by Hyman and Sheehy of this company (unpublished) have received confirmation in a recent report by Gonzalez (1945). Synthetic 2-methyl-1 ,4-naphthoquinone as tested in this laboratory has also been found bacteriostatic and bactericidal for both gram-negative and grampositive bacteria. In the course of studies made with Escherichia coli it was noted that minimal effective antibacterial concentrations were lower in a chemically defined medium than in the usual peptone broth or agar (0.00125 per cent to 0.0025 per cent instead of 0.005 per cent to 0.02 per cent); also that in freshly prepared Brewer's medium antibacterial effects were nullified, although in the same medium prepared some three months previous to use and thoroughly shaken to insure oxygenation, bacteriostatic and bactericidal end points were similar to those obtained in other peptone media. The effect of the Brewer medium did not appear to be due to its anaerobic properties, since tests incubated in an anaerobic jar had the same end points as those incubated in air. The following work was undertaken to explain this behavior (Colwell and McCall, 1945). METHODS Quinones employed included 2-methyl-1 ,4-naphthoquinone, the water-soluble sodium bisulfite addition product of 2-methyl-1,4-naphthoquinone, 2-methyl-3-chloro-1 ,4-naphthoquinone, 2,6-dimethyl-1 ,4-naphthoquinone, and 2-methyl-3-methoxy-1 ,4-naphthoquinone, all pure synthetic compounds prepared in the 659