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



The variation in adaptability during the division cycles 

 can explain the rise in resistance in a growing culture to which 

 proflavine is added. It can also explain the continuous curve 

 of resistance in a culture, which will have cells at all stages of 

 the division cycle and so with the complete range of degrees 

 of adaptability. We cannot, however, exclude the possibility 

 that part of the explanation for the continuous curve of 

 resistance is a superimposed clonal variation. 



Lamarckian inheritance 



The work of Akiba (1954) and of Szybalski (1955) indicates 

 that Esch. coli may acquire resistance to streptomycin by 

 direct induction, and that the resistance so acquired is in- 

 herited. We may therefore speak of this type of induction as 

 Lamarckian inheritance. Our own experiments on Lamarc- 

 kian inheritance of proflavine resistance in Esch. coli were 

 made both with growing cultures and with non-dividing 

 organisms. 



Most of the work was carried out with rough strains derived 

 from our original smooth strain of Esch. coli. In some of these 

 strains, growing cultures in the presence of proflavine, cell 

 extracts and tap water gave a high increase in resistance in 

 up to 10 per cent of the cells. A much smaller increase occurs 

 if cell extracts are not present, recafling the experiments on 

 phenotypic adaptation. Since extracts from sensitive or from 

 resistant cells are equally effective, the increase in resistance 

 is not due to transformation. We believe that it is due to 

 Lamarckian induction, though we were not able to exclude 

 the possibility of selection of pre-existing mutants. 



In non-dividing cells of some rough strains, washed and 

 suspended in phosphate buffer, the presence of small con- 

 centrations of proflavine produced, in 10-14 days, levels of 

 resistance of about that of first-step mutants in up to 80 per 

 cent of the surviving cells (Table II). A somewhat lower 

 increase was achieved with the original smooth strain. A mini- 

 mal concentration of proflavine was needed; with increasing 

 concentrations, there was an increase in the rate of induction. 



