448 



INACTIVATION OF BACTERIOPHAGES 



50, and 55°C., at which temperatures the non-radioactive control lysates 

 exhibited Httle or no heat inactivation. At 60 and 65°C., however, considerable 

 increases in the rate of inactivation of the radioactive TSst lysate are observed, 

 at which temperatures the non-radioactive control lysate now also exhibits an 

 increasing instability. Since the rate of loss of titer of the radioactive lysate 

 may be presumed to be the sum of the rate of death due to heat and to radio- 

 active decay, the rate of P^- inactivation can be estimated at any temperature 

 by subtraction of the slope of the survival curve of the non-radioactive con- 



-196° -20" +20° +40° +60° 



TEMPERATURE DURING DECAY 



Fig. 3. The efficiency of killing, a, in T5 at different temperatures. 



trol from that of the radioactive lysate. (This subtraction of slopes is justified 

 only in experiments of short duration, while (1 — e~^') is still approximated 

 by \t.) The efficiency of killing a at that temperature can then be computed 

 from this difference of rates by means of equation (2). The result of such 

 calculations based on the slopes of Fig. 2 is presented graphically in Fig. 3, 

 in which a has been plotted against the temperature of decay. It is evident 

 that a increases slowly between 4 and 55°C. and begins to rise sharply after 

 that point. At 65°C., a has reached the value 0.31, which means that now 

 almost one in every three P^^ disintegrations is lethal to T5sf Also included 

 in Fig. 3 are the results of the estimations of oc in T5 at low temperatures. 



287 



