178 BACTERIOPHAGES 



growth in the population of infected bacteria synchronized as 

 much as possible, and to be able to arrest phage development 

 during the irradiation. Benzcr (1952) devised techniques which 

 solved these problems for T2 and 17. The bacteria were grown 

 in broth, then aerated in buffer at 37 ° C. for one hour to starve 

 them. Adsorption of phage added to such bacteria is rapid but 

 the infective process is arrested at a very early stage. If broth 

 at 37 ° C. is subsequently added, phage growth starts and pro- 

 gresses normally. This technique permits the separation of 

 adsorption from growth, and presumably phage growth starts in 

 all bacteria simultaneously when broth is added. A defect of 

 this method is that a considerable proportion of the adsorbed 

 phage particles may be inactivated during the adsorption period, 

 a phenomenon known as "abortive infection." Another tech- 

 nique for arresting development without interfering with adsorp- 

 tion is the use of cyanide. When the cyanide is removed by dilu- 

 tion, development starts promptly (Benzer and Jacob, 1953). 



Phage growth can be stopped at chosen times during the latent 

 period by dilution in chilled buffer. Chilling halts phage de- 

 velopm^ent and the samples can then be irradiated at conven- 

 ience; dilution serves to reduce the ultraviolet absorptivity of the 

 medium, which is prohibitive with broth. The results for phage 

 T7 (Benzer, 1952) come close to the theoretical expectations as 

 may be seen in Figure 6. For the first 3 minutes of the latent 

 period the survival curves are similar to that for free phage T7. 

 At later times, the curves become multiple hit in character, in- 

 dicating that phage multiplication has started. By the sixth 

 minute, the curve indicates a relatively high multiplicity but the 

 ultimate slope is only slightly less steep than for free phage. 

 For the remainder of the latent period the multiplicity increases 

 further and the ultimate slope decreases som.ewhat. These sur- 

 vival curves do not have the flat initial plateau seen in the 

 theoretical curves of Figure 6, but have a steeper initial gradient. 

 Benzer (1952) suggested that this may reflect lack of synchroni- 

 zation of phage growth in different bacterial cells. 



Similar experiments with T2-infected bacteria were carried 



