446 



INACTIVATION OF B.^CTERIOPHAGES 



at these lower temperatures the rate of inactivation by P^^ decay of all five 

 strains was significantly reduced. Since the rate of radioactive decay is in- 

 dependent of temperature, it follows that a reduction in a by the altered 

 environmental conditions must be responsible for the reduced rate of bacteri- 

 ophage inactivation. Table II lists the observed values of the slope of the 

 inactivation curves at -f4, —20, and — 196°C. and the fractional reduction 

 of a compared to its magnitude at +4°C. It is seen that radioactive decay 

 proceeding at — 20°C. inactivates the phages with an efficiency of only 70 per 

 cent of decay proceeding at +4°C. Lowering the temperature to — 196°C. 



TABLE II 



The Relative Efficiency of P^ Inactivation at Low Temperatures 



* Refers to the value of -1.48 X lO'^ivxN. 



reduces the fraction of lethal disintegrations even further. At this temperature 

 the efficiency of killing in Tl, T3, T5, T7, and X is only 55 per cent and in T2 

 only 65 per cent of its value at +4°C. 



Since low temperatures appear to reduce the efficiency a, it seemed possible 

 that radioactive decay occurring at temperatures higher than +4°C. might 

 inactivate bacteriophages with greater efficiency. At elevated temperatures, 

 however, bacteriophages are subject to thermal inactivation, and it is only 

 possible to study the combined effects of heat inactivation and radioactive 

 decay. To examine, therefore, the efficiency a at reasonably high temperatures, 

 a heat-stable mutant, T53t, was first selected from our strain of T5 by the pro- 

 cedure of Adams (1953). When stored in glycerol-casamino acid medium at 



285 



