Multiple Mechanisms of Drug Resistance 143 



growth which antagonizes the inhibitory action of proflavine. 

 The experiments showed that such a factor was the acidity 



Time (mins 



Fig. 1. Effect of bacterial filtrate from a sensitive culture on the 

 inhibitory action of proflavine on BacL lactis aerogenes. 



1. Filtrate 40 ml. + fresh medium 10 ml., to which proflavine 

 was added gradually then inoculated with washed ceils m 

 logarithmic phase 



2. Proflavine added gradually from 210 min. after inoculation 



3. Proflavine added at once at 210 min. after inoculation 



4. No proflavine added 



gradual proflavine addition 



66 [ig.lml. proflavine present 



no proflavine added 



Time from addition of cells in (1) and 210 min. after inoculation 

 in others. 



produced during the growth of the culture. Thus, if the pH 

 of a growing culture was kept neutral, growth ceased when the 



