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



But in order to do so, its daughter cells must have gone 

 through a stage in the division cycle when their resistance 

 was low. Nevertheless, they continue to grow and divide. 



Fig. 5B. Resistance to various concentrations of 



proflavine of cells in cultures of Esch. coli 36. Syn- 



ehxonized culture. Synchronization by cooling after 



90 min. from inoculation at 12° for 15 min. 



O total viable count expressed as number 



of generations 

 # number of cells in 0-1 ml. resistant to 



proflavine 5 {j.g./mg., expressed as log^^ 



Time from returning to 37° C at the end of cooling. 



This must mean that the apparently higher resistance is 

 really a higher adaptability, which is retained in the presence 

 of the drug throughout the whole of the subsequent division 

 cycles. Thus, the variation we find in the cycles is not a 



