Abstract
2,3-dichloro-1,4-naphthoquinone, an antifungal agent now in practical use, has been recognized as an analog of vitamin K. This substance has been found to be exceedingly toxic to yeasts and moderately harmful to the growth of bacteria. Its effect on yeast was reversed competitively by vitamins K over a limited range of concentration. While the effect on the growth of bacteria was not influenced by vitamin K in the form of 2-methyl-naphthoquinone, it was probable that this was due to the toxicity of the vitamin for these species.