374 



r. W. STAHL 



the survival curves would become progressively "multihit," gaining a shoulder 

 whose extent increased with the increase in the number of intracellular 

 particles. Such an ideal result is found for the phage T7 (Fig. 10). For the 

 T-even phages, however, the findings are not so easUj interpretable. 



Fig. 10. Survival curves for singly infected T7 complexes irradiated with ultraviolet 

 li^ht at different times during the latent period. Each curve is marked with the time in 

 minutes following infection. The latent period for T7 is 12 minutes long. This figure is 

 from Benzer (1952) and is reproduced by permission of the Williams and Wilkins 

 Company. 



b. Results with T-even Phage. Immediately following infection, the ability 

 of a cell infected singly with T2 or T4 to produce a plaque is lost at about 

 the same rate as is the plaque-forming abihty of free phage (Luria and 

 Latarjet, 1947; Benzer, 1952). The changes in sensitivity thereafter are best 

 seen in the precise survival curves obtained by Benzer (1952) with T2, which 

 are depicted in Fig. 11. It may be seen that between and 6 minutes the 

 sensitivity decreases by about a factor of two. Thereafter, there is a large 

 and rapid decrease in sensitivity to a value less than one-tenth the initial 

 value. In order to guide the discussion, we adopt the following hypothesis, 

 which is a direct consequence of our views on multiplicity reactivation: 



During the first 6 minutes, the phage performs those functions which are 

 required to initiate the synthesis of vegetative phage. On the simplest model, 



