FATE OF INFECTING PHAGE PARTICLES 213 



adsorption, and that the amount liberated depended on the 

 multiplicity and timing of the infection (Lesley, French, and 

 Graham, 1950). This phenomenon, which is called "superin- 

 fection breakdown," has been studied further with results sum- 

 marized by Graham (1953). The essential features of the 

 phenomenon may be summarized as follows. 



7. At a multiplicity of 0.2 T2r+ phage particles per bacterium, 

 about 5 per cent of the phage P^^ is liberated within 10 minutes of 

 adsorption. No more P^^ is liberated until bacterial lysis when 

 readsorption of the first phage liberated occuis. During the 

 ensuing period of lysis inhibition about 20 per cent more of the 

 phage P^2 is liberated. 



2. At multiplicities of 3 to 10, about 15 per cent of the P^^ is 

 liberated in the first 10 minutes, followed by a slow liberation of 

 P'^2 starting at 30 minutes. 



3. If bacteria are infected with unlabeled phage, followed 5 

 minutes later by labeled phage, about 50 per cent of the P^^ of the 

 superinfecting phage is liberated within the next 10 minutes. 

 This phenomenon of superinfection breakdown is in part responsible 

 for the small amount of P^^ released after primary infection at low 

 multiplicity. 



4. If the time interval between primary infection and super- 

 infection is varied, it is found that the amount of P'^^ liberated is 

 30 per cent after a 1 minute interval and nearly maximal after a 

 2 minute interval. The physiological condition responsible for 

 superinfection breakdown is established within 2 minutes after 

 primary infection. 



5. Primary infection with one phage particle per cell is enough 

 to establish the conditions for superinfection breakdown and in- 

 creasing the multiplicity to 10 has no further effect. 



6. The multiplicity of the superinfecting phage is also without 

 effect. 



7. The phenomenon can be demonstrated repeatedly with the 

 same batch of infected bacteria under conditions of lysis inhibi- 

 tion. Superinfection with a multiplicity of 3 labeled phage at 

 5 minutes, 23 minutes, and 43 minutes after primary infection re- 



