Selective Bactericidal Effect. 



289 



the latter. The experiments on which this statement is based 

 were done with B. subtilis, B. megatherium, B. anthracis, B. 

 typhosus, B. coli communis, B. prodigiosus, B. pyocyaneus, B. 

 proteus vulgaris. In the case of gentian violet the reaction is 

 evident if the stain is applied to the organisms at room tempera- 

 ture; but in the case of acid fuchsin, while long exposure to the 

 dye at room temperature produces the reaction, a slight increase 

 in temperature (to 45 0 C.) makes it much sharper and speedier. 



In the case of gentian violet it was shown, by a study of the 

 whole bacterial field, that the gentian-violet reaction and the 

 gram reaction ran parallel in a striking way. Not only did the 

 cleavage hold between gram-negative organisms and the commoner 

 spore-bearing aerobes', it also held between gram-negative bacteria 

 and the great majority of non-spore-bearing gram-positive organisms. 

 That a reverse parallelism holds for acid fuchsin has not been 

 proven. Of the greater susceptibility to this dye of the gram- 

 negative organisms (as compared with the gram-positive spore 

 bearers) there is no doubt; it is not established that a similar 

 cleavage holds between gram-negatives and gram-positive non- 

 spore bearers. An interesting practical point is the susceptibility 

 of the gram-negative B. pyocyaneus to acid fuchsin; this organism 

 is often a great nuisance in open wounds and resists ordinary 

 antiseptics. 



What has been said of acid fuchsin is true also of another and 

 wholly unrelated acid dye — ponceau P.R. It is also true of sodium 

 chloride. When the commoner gram-negative organisms are 

 exposed to saturated solutions of any of these three substances 

 at 45 0 C, they are killed; while gram-positive spore bearers are 

 unaffected under similar conditions. This is the exact reverse 

 of the behavior of these two classes of bacteria toward basic 

 gentian violet. 



In the case of gentian violet, the selective effect of the dye may 

 be demonstrated either by staining the organisms and planting 

 them on plain agar or by planting them unstained on agar con- 

 taining the dye. The gram negatives grow well in the presence 

 of the dye, while the gram positives will not grow at all, even when 

 the stain is present in the media in very small amounts. For 

 this and other reasons the activity of the dye has been referred to 



