114 THE PHYSICS OF VIRUSES 



inactivation according to the first-order kinetics already 

 described, and his measurements of the reaction constants for 

 virus in broth lead to the values 81,000 for AIP and 165 for 

 AS^. The important feature of Adam's studies, however, lies in 

 the effect of varying the concentration of monovalent and 

 divalent ions on the over-all process of thermal inactivation. 

 It was found that if the phage were maintained in ])hosphate 

 buffer (0.001 J/), 0.15.1/ NaCl, and a little salt-free gelatin, the 

 activity at 37° C was lost in a matter of an hour or two. Adding 

 small concentrations of divalent ions radically changed the rate 

 of inactivation. In following this observation further, Adams 

 measured the reaction constants in O.IA^ NaCl and 0.1 sodium 

 citrate at various concentrations in the absence of divalent ions 

 and then in the i)resence of various concentrations of divalent 

 ions. The kind of effect produced is illustrated in Fig. 4.5. The 

 velocity constant in fraction per second at 50° C is plotted 

 against the concentration of sodium or magnesium ions. The 

 remarkable change in value is clearly shown together with the 

 fact that the same range of rate change is covered at a much 

 higher concentration of sodium than magnesium. For mag- 

 nesium, the rate constant changes proportionally to the third 

 power of the ion concentration, and for sodium it changes 

 approximately as the sixth power. 



Adams suggests that the lower reaction rates are due to 

 the formation of a complex between phage and magnesium which 

 is much more stable. 



It is interesting that if AS^ values are calculated for various 

 concentrations of Mg++, the values do not vary monotonically 

 but rise from 35 entropy units (calories/mole/ °C) to 90 at lO^'^J/, 

 fall to 40 at 10-\ and rise to about 90 for lO'^J/ and broth. 

 This lack of a regular behavior ])robably shows the inherent 

 complexity of thermal inactivation. After all, every part of 

 the virus, whether protein or nucleo})rotein, is thermally 

 sensitive, and, moreover, the virus unquestionably comprises 

 many parts combined together by loose physical forces. The 

 inactivation of the virus as regards its infectivity probably in- 

 volves the change of specific structure of only one of these. 



