CHAPTER FOUR 



THERMAL INACTI\ ATION OF VIRUSES 



One of the outstanding features of living things is their insta- 

 bility when acted on by heat. This is not an all or nothing affair — 

 some organisms, like bacterial spores, are stable over a wide 

 temperature range, others are highly sensitive. Now heat is a 

 physical agent, and the careful characterization of the action of 

 heat on viruses should at least offer a guide in classifying them 

 and possibly can give information about their structure. 



As in the case of radiation action, we propose first to give a 

 description of the nature of thermal action. In doing this we are 

 aided by many studies on the thermal denaturation of proteins 

 and the thermal inactivation of enzymes which have been made 

 and analyzed in terms of theory. The basic theory is set out by 

 Glasstone, Laidler, and Eyring (1941), and, more specifically 

 for proteins, by Stearn (1949). A brief account of this theory, 

 modified to suit the present purpose, is here presented. 



Outline of the Theory of Thermal Inactivation 



A virus, or an enzyme, is a large and complex molecular 

 structure. It owes its ability to function to the fact of having 

 inherited a certain rather precise structure from the living cell 

 in which it originated. Heat, the thermal agitation of the atoms 

 that form the molecular structure, is steadily and ceaselessly 

 vibrating the atoms back and forth, and twisting and stretching 

 chemical bonds, and so exerts a steady tendency to alter the 

 structure. It seems likely that biologically formed molecules are 

 not ultimately stable, by which we mean that probably some 

 similar configurations have a lower total potential energy; but 

 they certainly possess a local stability, by which we mean that 



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