110 THE PHYSICS OF VIRUSES 



form, which transmits hereditarily, is much more stable at low 

 salt concentrations. This mutant adsorbs in the same way and 

 has the same serological affinity and the same latent period as 

 the wild type. At high broth concentrations, the wild type and 

 the mutant are the same. 



The latent period and the burst size of T-5 are both modified 

 by citrate, which shows that a part of the virus which is not 

 concerned with duplication itself, but rather with rate, exists. 

 This follows the same line as has been mentioned for latent- 

 period increase due to X-ray and deuteron bombardment. 



The thermal inactivation of four bacteriophages has been 

 studied by Marjorie Reaume and the author (Pollard and 

 Reaume, 1951). The inactivation, both wet and dry, was studied 

 with results which can be seen from Table 4.1. The striking fact is 

 that in the dry state the entropy is very greatly reduced and is 

 actually very nearly zero. The entropy does not seem to be 

 related to the size of the virus either in the dry or wet state. 

 This means that the virus inactivation is taking place in rela- 

 tively small regions and is again indicative of structure and func- 

 tion in the virus. The contrasting character of inactivation and 

 denaturation calls attention to a minimum of two different parts 

 of the structure. If it were true that thermal inactivation showed 

 characteristic behavior for different substances, then the figures 

 of Table 4.1 could be used to determine which proteins, nucleo- 

 proteins, etc., were involved in the activity measured. Unfortu- 

 nately this is only partly true. Possibly in the dry state, where 

 very little work has been done, it is possible to characterize 

 an enzyme or protein by its inactivation constants. In the wet 

 state, many factors must first be considered. 



Inactivation as a Function of pH 



If the percent infectivity of T-1 phage, or of TMV, remaining 

 after a fixed time of exposure to thermal action, is plotted against 

 the pH, the type of result shown in Fig. 4,6 is obtained. There is a 

 region of relative stability with rather sharp edges. Steinhardt 

 (1937) has shown that for pepsin the rate of denaturation varies 

 as the cube of the hydrogen-ion concentration, and concludes 



