144 M. J. Thornley, J. Sinai and J. Yudkin 



proflavine additions were made (Fig. 2). On the other hand, if 

 a growing culture was acidified, growth continued even if all 



.o 3 



P 2 



•o I 



60 I20 I80 24.0 



Time (mins) 



Fig. 2. Effect of maintaining neutral pH in culture during pro- 

 flavine additions, and of acidifying the culture when large single 

 addition of proflavine made, on growth of Bad. lactis aerogenes. 



1. pH maintained neutral throughout incubation, proflavine 

 added gradually 



2. Culture acidified to pH 4-9, then all proflavine added at once 



3. Proflavine added graduaUy 



4. No proflavine added 



gradual proflavine addition 



65 ^g./ml. proflavine present 



no proflavine added 



Time from beginning of proflavine additions. 



the proflavine was added at once. Finally, acidified fresh 

 medium with the whole amount of proflavine added supported 



