APPENDIX 485 



Study effects of the antimetabolite, 5-niethyltryptophan (5- 

 MT), on phage-infected E. coli. The suspension of infected 

 bacteria can be diluted into 5-MT at any time during the 

 latent period, and the action of the inhibitor can be stopped 

 at any subsequent time by further dilution into tryptophan 

 which overcomes the inhibition. As long as 5-MT is present in 

 the growth medium, phage is not liberated from infected 

 bacteria. In fact there is progressive loss of plaque-forming 

 ability of infected bacteria on incubation with the inhibitor. 

 It is a rather general observation that interference with phage 

 synthesis in infected bacteria during the early portion of the 

 latent period results in gradual irreversible inactivation of 

 infected bacteria. This has been found when the interfering 

 agent is 5-MT, KCN (Doermann, 1948a), proflavine (Foster, 

 1948), and citrate in the case of T5 (Adams, 1949b). 



Cohen also found that the latent period measured from the 

 time of dilution of 5-MT-inhibited, infected bacteria into trypto- 

 phan was the same as it would haxe been had no inhibitor been 

 used. The time of contact with 5-MT is a hiatus in the latent 

 period. 



Similar results were noted by Fowler and Cohen (1948) when 

 methionine sulfoxide was the antimetabolite and inhibition was 

 reversed by dilution into glutamic acid. This method has been 

 extensively used by Foster (1948) in investigation of the inhibi- 

 tory effect of proflavine on phage multiplication. 



The potentialities of the one-step growth method in studying 

 the effects of inhibitors, nutrients, salts and other chemical agents 

 on the multiplication of bacterial viruses have scarcely been real- 

 ized. 



Single-Cell Method of Studying Virus Multiplication 



This method consists essentially in diluting a suspension of in- 

 fected bacteria to the point that small samples of the dilution 

 contain no more than 1 infected bacterium. These samples are 

 incubated until all bacteria have burst, then the samples are 

 plated to determine the phage yield of the single infected bac- 



