G. S. STENT AND C. R. FUERST 



445 



(1951) and by Hershey and Chase (1952). The agreement is poor, however, with the 

 estimations of the phosphorus contents of Tl, T2, T3, T5, and T7 by Labaw (1951) 

 whose values are about twice as great as those found here. No values are listed in 

 Table I for the phosphorus content of X, since it was not possible to prepare a puri- 

 fied suspension of P^^-labelled X in which the bulk of the radioactivity could be ad- 

 sorbed specifically to sensitive bacteria. Neither the reason for this behavior of X nor 

 the nature of the non-adsorbed material has yet been discovered. 



The last column of Table I lists the efficiency of killing, a, of P^^ decay in 

 each of the five strains of T phage. It is seen that in all the strains studied 

 here, a is near the value 0.09 originally observed by Hershey et al.; i.e., on the 



TABLE I 



Evaluation of the Parameters of the Equation 

 log,o5 = -1.48 X 10-MoaiV^(l - e'^') 

 at 4°C. 



* Determined radiochemically. 



J Determined by comparison with control T2 stock. 



average one of about every ten P^- disintegrations inactivates any phage 

 particle in which it occurs. 



Effect of Temperature on the Efficiency a. — 



The rate of inactivation by decay of P^^ was also measured at two lower 

 temperatures in the frozen state. For this purpose, aliquots of diluted radio- 

 active lysates of all six phage strains were stored either at +4°C., or in the 

 frozen state at — 20°C. or — 196°C. (the temperature of boiling liquid nitro- 

 gen). Samples were then thawed from day to day and assayed for the fraction 

 of surviving infective centers. Frozen controls with corresponding non-radio- 

 active lysates showed that, depending on the strain, from 45 to 90 per cent of 

 the infective centers survive freezing and thawing and that, except in the 

 case of storage of T2 at — 20°C., the fraction recovered is independent of the 

 length of time of storage (Sanderson, 1925; Rivers, 1927). It was found that 



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