G. S. STENT AND C. R. FUERST 457 



about three times as much total phosphorus per phage particle as those of the 

 second, it appears that the fraction of all P^- disintegrations which are lethal 

 is very nearly the same in all the strains. This fraction a depends on the tem- 

 perature at which decay is allowed to proceed, being 0.05 at — 196°C., 0.1 at 

 +4°C., and 0.3 at 65°C. 



Decay of P^^ taking place only after the penetration of the DNA of a radio- 

 active phage particle into the interior of the bacterial cell can still prevent the 

 reproduction of the parental phage, albeit inactivation now proceeds at a 

 slightly reduced rate. T2 phages inactivated by decay of P'^ can be cross- 

 reactivated; i.e., donate some of their genetic characters to the progeny of a 

 mixed infection with a non-radioactive phage. They do not, however, exhibit 

 any multiplicity reactivation or photoreactivation. 



The fact that at low temperatures less than one-tenth of the P^^ disintegra- 

 tions are lethal to the phage particle and the dependence of the fraction of 

 lethal disintegrations on temperature can be accounted for by the double 

 stranded structure of the DNA macromolecule. 



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296 



