STAGES IN PHAGE MULTIPLICATION 177 



In these curves the length of the initial plateau is related to the 

 number of particles per cell, and the ultimate slope of the linear 

 portion is determined by k, characterizing the sensitivity of the 

 individual particles to the radiation. Therefore the survival 

 curves obtained at various times during the latent period should 

 give a clue to the kinetics of phage reproduction. This approach 

 to the study of phage multiplication was made by a number of 

 investigators including T. F. Anderson (1944), Luria and Latar- 

 jet (1947), Latarjet (1948), Benzer (1952), and Benzer and 

 Jacob (1953). The subject has been reviewed by Latarjet 

 (1953). 



An assumption underlying this method is that the loss of the 

 plaque-forming ability of infected bacteria is due to the effect of 

 the radiation on the intracellular phage particles, rather than on 

 the host cell mechanisms required for phage multiplication. 

 Anderson (1944, 1948d) and Benzer (1952) demonstrated that 

 E. coli B treated with many lethal doses of ultraviolet light re- 

 tained the capacity to support multiplication of bacteriophage 

 T2. The same result for bacteria killed by X-rays was observed 

 by Rouyer and Latarjet (1946) and Labaw, Mosley, and Wyck- 

 ofF (1953). Very heavy doses could render bacteria incapable 

 of serving as hosts for phage growth, but such doses were much 

 larger than those used in the inactivation of intracellular phage. 

 In the case of some phage-bacterium systems, however, the 

 "capacity" may be very sensitive (Benzer and Jacob, 1953). 

 The essential steps in a so-called "Luria-Latarjet experiment" 

 are the following: (7) phage is mixed with bacteria and ad- 

 sorption permitted to occur for a short period of time; (2) un- 

 adsorbed phage is eliminated, and the number of infected bac- 

 teria is determined; {3) phage multiplication is permitted to 

 take place, and samples are removed at intervals during the 

 latent period; (4) each sample is exposed to several doses of 

 radiation; and (5) the surviving fraction of infective centers is 

 determined for each dose of radiation, and a survival curve is 

 constructed for each time of sampling. 



In experiments of this type it is important to have phage 



