STAGES IN PHAGE MULTIPLICATION 



179 



out by Luria and Latarjet (1947) and by Benzer (1952). The 

 results with this phage are strikingly different from those ob- 

 tained with T7. Immediately after infection, the infective cen- 

 ters have the same sensitivity to ultraviolet inactivation as free 

 phage, but there follows an increase in resistance to inactivation 

 until, at 5 or 6 minutes after infection, the resistance has doubled. 



100 200 300 



UV DOSE IN SECONDS 



Figure 6. Survival of phage-producing capacity of bacteria infected with 

 T7. The bacteria were irradiated at times after infection indicated on the 

 curves in minutes. Latent period (at 37° C.) 12 minutes. Reproduced 

 from S. Benzer, 1952, J. BacterioL, 63, 59, with permission. 



Thereafter the resistance increases with great rapidity until 

 maximum resistance, 20-fold greater than that of free phage, is 

 reached at about 10 minutes after infection. At this time the in- 

 activation curves become definitely multiple hit in character. 

 From 10 minutes to the end of the latent period the multiplicity 

 of the inactivation curves increases while the slope of the curve 



