The cause of the parallelism between the gram reaction and the gentian violet reaction

Abstract

In previous studies, published at intervals since 1912, it has been shown that a striking parallelism exists between the Gram reaction and the gentian violet reaction. The Gram positive organisms are killed by the stain and will not grow in agar containing it; the Gram negative organisms survive staining and grow vigorously in the presence of the dye. To this rule there are about 10 per cent. of exceptions.

Does this parallelism indicate that the two reactions have fundamentally the same explanation and that the power of the Gram positive organisms to fix the dye, so that it is retained in the Gram process, enables them also to fix it so that it leads to their death, or prevents their growth in media containing it? An attempt was made to answer this question by training a Gram positive organism (B. subtilis) to grow on agar containing gentian violet, working up gradually from minimal dilutions (1-1,000,000) to greater strengths. If a Gram positive organism so trained ceased to retain the stain by Gram's method the problem would be solved. This attempt was, however, wholly unsuccessful; it was impossible to train B. subtilis to grow in the presence of the dye.

A study of a Cram negative organism (B. coli)-which is also gentian negative-gave a partial answer to the question. If thick suspensions of this organism be stroked across a divided gentian violet plate, growth is equally vigorous on the two sides; the organism is apparently in no way restrained by the dye. If, however, instead of a thick suspension increasingly weak dilutions of the suspension be used for the stroking, the colonies on the gentian violet side of the plate become rapidly fewer as the dilution increases, and soon disappear altogether.