VIRUS GENETICS, MULTIPLICATION, AND PHYSICS 189 



The characteristic behavior of P{n) is that if small values of n 

 are to be expected on the whole, then values several times larger 

 have a very low probability. Thus, in Luria's work, the average 

 number of mutations per plate (several bursts to a plate) 

 was 0.25. We then have P(l) = 0.195; P(2) = 0.024; and 

 P(3) = 0.0022. Thus there is roughly a factor of 10 less for each 



(c) Not synchronized 



Fig. 8.1. Three different methods of observing spontaneous mutants accord- 

 ing to three processes of multiplication, (a) is the template which mu- 

 tates, (b) shows a synchronized exponential multiplication, and (c) a non- 

 synchronous process. Illustrates Luria's experiments on mutation of bacterial 

 viruses. 



increase of one in the number of mutants per plate. This very 

 definite characteristic should be easy to confirm. « 



A second possibility is essentially the same but it supposes that 

 mutations take place in the template itself which thus, after 

 stamping out a certain number of replicas, changes its character 

 and stamps out a whole new succession of mutant phages. The 

 character change can occur at any time, with no preference, and 

 so this process should cause a distribution of mutants per burst 

 which extends evenly from one to the burst size. This process is 



