112 



THE PHYSICS OF VIRUSES 



process of infectivity loss is due to the inactivation of nucleic 

 acid. It is regrettable that so little data on the thermal inactiva- 

 tion of nucleic acid measured in some biologically functional 

 way has been assembled. Some very preliminary work by 

 Fluke and Drew on the transforming factor for pneumococci 

 indicates a rather moderate entropy change. It may well be 



10x10 



90 C. 



Fig. 4.4. The rate constant for inactivation (dotted line) and denaturation 

 (sharply rising line) of TMV derived from Price's (1940) data. The slower in- 

 activation process is superseded by the faster denaturation process at higher 

 temperatures. 



that this depends on the lightness of the combination between 

 nucleic acid and protein. 



Smiilar results were found for tobacco ringspot virus but not 

 for alfalfa mosaic or tobacco necrosis virus. Cherry and Watson 

 (1949) observed a similar effect for a S. lactis phage, which 

 showed a very rapid rate of inactivation at 65° C. The values 

 deduced from their work are given in Table 4.1. 



A very careful study of the thermal inactivation of T-5 E. coli 

 bacteriophage has been made by Adams (1949). He observed 



