STAGES IN PHAGE MULTIPLICATION 163 



extracellular fluid were dclcrniined by ccntrifunation. The 

 results of this signihcant experiment are as follows. 



7, The plaque-forining potentiality of infected bacteria 

 is not afifected by agitation in the Waring Blendor. 



2. Seventy-five to 80 per cent of the phage sulfur can be 

 stripped from the infected cells in the Blendor. This liberated 

 sulfur is precipitabie by antiphage serum. 



3. Only 20 to 35 per cent of the phage phosphorus is 

 liberated into the medium, half of it without any agitation. 



These results demonstrate that, following adsorption of phage 

 T2, the phage membrane remains on the bacterial surface, 

 from which it can be stripped in the blendor without affecting 

 the course of infection. In contrast, most of the phage DNA 

 enters the host cell soon after phage adsorption. A similar 

 situation holds for the T5 serological group of phages. T5 

 injects its DNA into the host cell, while the complement-fixing 

 antigen remains on the host cell surface and can be liberated 

 in the Waring Blendor (Y. T. Lanni, 1954). 



Considered as "injection" of DNA, the penetration mech- 

 anism presents at least three problems : the opening of a hole in 

 the tail of the phage particle, the opening of a hole in the cell 

 wall, and the passage of DNA through these holes. Ore and 

 Pollard (1956) suggested that the passage of DNA into the cell 

 can be explained by purely physical mechanisms. The other 

 two problems have been partly clarified by several types of ex- 

 periments summarized below. 



h. Release of DNA from the Phage Particle 



Hershey and Chase (1952) noted that partial release of DNA 

 into solution, and complete exposure of viral DNA to deoxyri- 

 bonuclease, followed the attachment of T2 to the bacterial debris 

 left after lysis of infected cells. They also confirmed important 

 experiments by Graham (1953), showing that adsorption of T2 

 to heat-killed (but not living) bacteria resulted in exposure of the 

 viral DNA to enzyme action. These findings were extended to 

 the interaction between phage and isolated receptor substances. 



