A. D. HERSHEY AND MARTHA CHASE 



47 



blendor (semimicro size) at 10,000 r.p.m. The suspension was cooled briefly 

 in ice water at the end of each 60 second running period. Samples were removed 

 at intervals, titrated (through antiphage serum) to measure the number of 

 bacteria capable of yielding phage, and centrifuged to measure the proportion 

 of isotope released from the cells. 



The results of one experiment with each isotope are shown in Fig. 1. The 

 data for S^^ and survival of infected bacteria come from the same experiment, 

 in which the ratio of added phage to bacteria was 0.28, and the concentrations 



© 



Infected bactema 



© 



35 

 ® ExtpacellalQP 5 



Extracellulap P 



32 



Min. 



8 



2 3 4 



l^unninq time in blendop 



Fig. 1. Removal of S'^ and P^^ from bacteria infected with radioactive phage, and 

 survival of the infected bacteria, during agitation in a Waring blendor. 



of bacteria were 2.5 X 10* per ml. infected, and 9.7 X 10^ per ml. total, by 

 direct titration. The experiment with P^Mabeled phage was very similar. 

 In connection with these results, it should be recalled that Anderson (1949) 

 found that adsorption of phage to bacteria could be prevented by rapid stir- 

 ring of the suspension. 



At higher ratios of infection, considerable amounts of phage sulfur elute 

 from the cells spontaneously under the conditions of these experiments, though 

 the elution of P^'" and the survival of infected cells are not affected by multi- 

 plicity of infection (Table V). This shows that there is a cooperative action 

 among phage particles in producing alterations of the bacterial membrane 

 which weaken the attachment of the phage. The cellular changes detected in 



95 



