468 



HOWARD B. NEWCOMBE 



The purpose of these calculations was to determine whether mutation rate 

 when estimated from the older mutant clones only is higher than when esti- 

 mated from the average numbers of resistant bacteria per culture. If the delay 

 is sufficiently variable and of sufficient magnitude, it would be expected that 



Table 9 



Mutation rates of strains B and B/r to resistance to phage Tljrom series of similar liquid cultures 

 started with small inocula, using methods 1, 2, and 5 and calculating from data of Luria and Del- 

 bruck (1943, table 3, experiment 23), Demerec and Fano (1945, table 4), and the present paper 

 (tables 1 and <?). All the experiments which are suitable for the application of the three methods have 

 been used. 



in these older clones a higher proportion of the mutants would have become 

 phenotypically resistant. 



Not all experiments show a difference between estimates of rate from the 

 average resistant bacteria (method 2) and estimates from the highest number 

 of resistant bacteria, of which the majority are presumably descended from 

 an early mutation (method 5). Examining data from all sources, the estimates 

 from method 5 and from method 2 do not differ significantly. 



70 



