The Selective Bactericidal Action of Methylene-blue

Since the publication of observations on the selective bactericidal action of gentian violet, 1 studies have been carried on in this laboratory with a large number of other dyes. The technique of divided plates, previously described, has been employed. The results with dyes similar in chemical structure to gentian violet have already been reported. 2 These dyes, like gentian violet, were found to prevent the growth of gentian-positive, and to be without effect on gentian-negative organisms. 8 In this communication the selective bactericidal action of a dye unrelated to gentian violet in chemicaI structure, namely, methylene-blue, will be reported. That this dye has bactericidal properties has, of course, long been known. It is to the selective feature that I wish to call attention. Briefly Stated, it has been found that methylene-blue, like gentian violet, is without effect on the growth of Bacillus typhosus and Bacillus coli; but that, unlike gentian violet, it exhibits a selective action when Bacillus subtilis and Micrococcus aureus are planted on divided plates containing it. The contrast between the action of the two dyes is shown in figures I and 2. Figure I is a divided plate containing gentian violet and has been stroked with