A. H. DOERMANN 655 



Still retain a single hit character. During the last 4 minutes of this period the 

 curves take on a multiple hit character. In the tinal segment, from time 13 

 minutes to the end of the latent period, the curves retain the multiple hit charac- 

 ter, but gradually regain the original x-ray sensitivity characteristic of free 

 phage. These .\-ray experiments suggest again that a rather drastic alteration 

 occurs to the infecting particle, and that particles with the original character- 

 istics are not found in the cell until the second half of the latent period. This is 

 precisely what is observed in the results presented here. Our experiments were 

 done with T4, but comparison seems legitimate since the two viruses are quite 

 closely related (17). 



Results of a similar nature to those discussed here were published by Foster 

 (18). In studying the effect of proflavine on the growth of phage T2, Foster 

 found that the time at which this poison was added influenced the amount of 

 phage liberated by the bacteria. No phage is liberated from T2-infected cells 

 (latent period 21 minutes) if proflavine is added during the first 12 minutes 

 after infection even though lysis of the cells does occur at the normal time. 

 When proflavine is added at later points in the latent period, lysis yields phage 

 particles, the number depending on the time of proflavine addition. When the 

 results of these single infection experiments are compared to the cyanide single 

 infection experiments (Fig. 1) the results are seen to be quite similar. From 

 other experiments Foster concluded that proflavine inhibits one of the final 

 stages in the formation of fully infective phage. These facts, taken together, 

 suggests that proflavine experiments were, in fact, measuring intracellular 

 phage. 



SUMMARY 



A method is described for liberating and estimating intracellular bacterio- 

 phage at any stage during the latent period by arresting phage growth and induc- 

 ing premature lysis of the infected cells. This is brought about by placing the 

 infected bacteria into the growth medium supplemented with 0.01 m cyanide 

 and with a high titer T6 lysate. It was found in some of the later experiments 

 that the T6 lysate is essential only during the first half of the latent period. 

 Cyanide alone will induce lysis during the latter part of the latent period. 



Using this method on T4-infected bacteria it is found that during the first 

 half of the latent period no phage particles, not even those originally infecting 

 the bacteria, are recovered. This result is in agreement with the gradually 

 emerging concept that a profound alteration of the infecting phage particle 

 takes place before reproduction ensues. During the second half of the latent 

 period mature phage is found to accumulate within the bacteria at a rate which 

 is parallel to the approximately linear increase of intracellular DNA in this 

 system. However, the phage production lags several minutes behind DNA 

 production. 



85 



