144 



ANTISEPTICS 



antiseptics — act most efficiently in acid media, while basic 

 dyes {e.g., gentian violet, basic fucbsin, all flavine dyes) 

 are more bacteriostatic in alkaline media (see Table 29). 

 Hoffmann (1943) found that with gentian violet, only the 

 bacteriostatic effect changes with pH while the bacteri- 

 cidal effect is not altered appreciably. As the reduc- 

 tion potential of dyes and of most culture media is great- 

 ly affected by pH, it is not surprising that their bacterio- 

 static action changes correspondingly. Hoffmann further- 

 more showed that the effect of acidity upon bacteriostasis 

 had nothing to do with the electrolytic dissociation of the 

 dye. 



While the investigation of the detailed antiseptic 

 mechanism of the dyes has been worked out almost en- 

 tirel}^ with crystal violet, the principles apply to many 

 other dyes. As already mentioned, Dubos (1929), com- 

 paring the effect of 15 dyes, found that the oxidized indo- 



Fig. 29. Effect of acidity on the length of the lag phase of Strep- 

 tococcus lactis treated with various concentrations of crystal violet. 

 (From data of Hoffmann, 1943.) 



