1 1 1 r 



ACTIVE FROM INACTIVATED BACTERIOPHAGE 



T 1 r 



95 



' » I I I I L 



10 20 30 40 10 20 30 40 50 60 70 10 20 30 SECONDS 



Figure 1. — Inactivation of various phages by ultraviolet light. P/Po = proportion of active 

 phage particles after irradiation. r = In PoZ-f = average number of lethal hits per phage particle. 

 The doses are expressed in seconds of exposure. The deviations for high doses in the curves for 

 T2, T4, and T6 are due to reactivation occurring on the assay plates (see text). The broken lines 

 represent extrapolations from the logarithmic portions of the curves. 



bacteria should receive no particle and survive. By this means, we could 

 establish that for irradiated phages T2, T4, T5, and T6, even for high doses, 

 the rate of adsorption is the same as for unirradiated phage. An experiment of 

 this type is shown in table 1. Only for very high doses a slight reduction occurs 

 in the ability of phage to kill bacteria. This reduction is never such as to require 

 important corrections in the analysis presented in later sections. 



With phages T2, T4, T5, and T6 (the "large particle" phages) the plaque 

 counts on irradiated samples are not independent of the mode of assay. They 

 depend on the concentration of the samples when first mixed with bacteria, 

 in a way illustrated in table 2. In these experiments, bacteria were mixed with 

 various concentrations of irradiated phage. Before lysis and phage liberation 



Table 1 



Killing of bacteria by irradiated phage 



0.9 ml of a bacterial culture was mixed with 0.1 ml of each of five suspensions of phage T2r 

 that had received various doses of radiation. After 10 minutes, samples were diluted and plated 

 for viable bacterial count. 



249 



