THERMAL INACTIVATION OF VIRUSES 



115 



Under some circumstances, different units may inactivate first 

 and so be the rate setting unit. It would appear as though 

 varying the ionic concentration causes a shift from one sensitive 

 unit to another. The consideration which determines the par- 

 ticular part is not an entrojiy but the actual rate at the chosen 

 temperature. The curves of Fig. 4.5, if plotted for rate con- 



-4 -3 -2-1 1 



Log Ionic Concentration 



Fig. 4.5. Effect of ionic strength on the rate constant for inactivation of T-5 

 phage. Data due to Adams (1949). 



stants at 30° C, show appreciable variation from what is shown, 

 notably in a more rapid dependence on ion concentration. 



It must therefore be remembered that, although thermal- 

 inactivation studies undoubtedly contain valuable information 

 about viruses, the unraveling of the various factors involved 

 will take time. 



It is of interest that thermal resistance can appear as a 

 mutation. Adams and Lark (1950) have shown that a mutant 



