484 BACTERIOPHAGES 



proceed from the time of the resuspension. Benzer (1952) 

 has modified this procedure by starving the washed bacteria 

 by incubating them with aeration for one hour before adding the 

 phage. This procedure while ensuring greater precision in the 

 initiation of phage development may also give rise to many 

 abortive infections. (2) The second procedure which was 

 developed by Benzer and Jacob (1953) is even simpler and more 

 useful. Broth-grown bacteria are reversibly poisoned by the 

 addition of KCN (final concentration 0.01 M). After 2 min. 

 have elapsed, the phage is added and adsorption proceeds. The 

 infected bacteria can be safely kept in this manner for periods 

 up to an hour. To initiate phage development the infected 

 bacteria are either diluted a factor of 100 into growth medium 

 or centrifuged and resuspended in growth medium. This 

 technique combined with the chloroform technique for meas- 

 uring free phage (unadsorbed) makes for a simple method for 

 measuring the rate of phage adsorption.] 



Investigations of Chemical Action on Virus Growth 



In the one-step growth experiment the adsorption of virus 

 to bacterium is usually carried out under conditions such that 

 the concentration of infected bacteria is between 10^ and 10^ 

 cells/ml. This suspension is then diluted during the latent 

 period so that the concentration of infected bacteria in S.G.T. 

 is about 10 cells/ml. This dilution factor of lO^^-lO"'' per- 

 mits the addition and removal by dilution of several reagents 

 in succession at definite time intervals during the latent period, 

 permitting great flexibility in the design of experiments. 



An obvious example of this is the use of antiphage serum in 

 the one-step growth curve. The adsorption mixture is di- 

 luted in antiserum to stop adsorption and neutralize free phage. 

 After sufficient contact with antiserum the suspension of in- 

 fected bacteria is further diluted to such an extent that the 

 antiserum will have no effect on the phage liberated from lysing 

 bacteria in F.G.T. and S.G.T. 



This technique was used by Cohen and Fowler (1947) to 



