1 8 Scientific Proceedings (109). 



reaction and the gentian violet reaction. The Gram positive 

 organisms are killed by the stain and will not grow in agar con- 

 taining 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 Gram 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 in- 

 creases, and soon disappear altogether. The same result was 

 obtained by similar experiments with other Gram negatives 

 (B. typhosus and B. prodigiosus). That is to say: In a thick 

 suspension of a Gram negative organism only a small proportion of 

 the individuals are Gentian negative; it is possible to isolate the 

 Gentian positive individuals in pure culture, and when so isolated 

 they are found to be as definitely Gram negative as the Gentian negative 

 individuals. The factor which determines the reaction of an or- 

 ganism to the Gram process of staining is therefore not the same as 

 the factor which determines its reaction on divided gentian violet 

 plates, or after staining with the dye. 



