This paper describes the antituberculous activity of B. 663, a recently synthesized member of the series of phenazine dyes which these workers have been investigating for some years [this Bulletin, 1957, v. 32, 245]. B. 663 has the formula:[img 1T323198. tif] The dye is taken up by living mycobacteria and, in Proskauer and Beck medium containing 5% human serum, B. 663 inhibits the growth of H37Rv for 14 days at a concentration of 0.8 µm. per ml.

Under anaerobic conditions the bacilli decolorize the dye. Experiments, with Myco. smegmatis showed that 20% of the respiratory hydrogen can be transferred from a respiratory enzyme, probably a flavo-protein, to B. 663, but the authors do not consider that this degree of interference would result in complete inhibition of cell growth. However, when B. 663 is reoxidized hydrogen peroxide is formed and this, they suggest, may play a part in the antituberculous action, especially as catalase-negative isonia-zid-resistant strains are exceptionally sensitive to the dye.