364 S. GARD AND O. MAAL0E 



solution of gelatin was shaken before adding the phage, it afforded no pro- 

 tection. As little as one gamma of gelatin per milliliter protected effectively 

 for 14 minutes; with bovine albumin, about 10 times as much; and with gum 

 arable and yeast nucleic acid, about 100 times as much had to be used. 

 Adams points out that, in the last two cases, protection may have been due 

 to contaminating protein. 



It may be recalled that neutral proteins also were found to protect virus 

 particles against inactivation by sonic treatment. It would seem likely that 

 sonics act, at least in part, by creating a large liquid/gas interface on which 

 inactivation can occur, as in the case of mechanical shaking or bubbling. 

 The protective role of protein is probably the same in both cases. 



3. Inactivation at High Pressure 



Being of purely theoretical interest and requiring unusual equipment, few 

 experiments of inactivation at high pressure have been made. Johnson et al. 

 (1948) studied the heat denaturation of TMV at different pressures. As pre- 

 dicted by the theories of absolute reaction rates, denaturation was retarded 

 by increasing the pressure, and consistent values for the volume increase of 

 activation, AV*, were obtained. 



Foster et al. (1949) extended this work by experiments with some of the 

 coliphages of the T-series. Phage T7 was unique in the sense that inactivation 

 was accelerated by increasing the pressure; there is no simple explanation for 

 this unexpected observation. For phage T5, at 66°C. inactivation rates were 

 obtamed which corresponded to a AV* of 113 ml./mole. 



Basset et al. (1956) observed slow inactivation of poliovi^us at 37°C. when 

 the pressure reached 6-8,000 kg./cm.^. 



B. Ionizing and Nonionizing Radiations 

 1. General Aspects 



It is characteristic of the different types of radiation grouped together in 

 this section that, under a variety of experimental conditions, inactivation 

 proceeds exponentially. Before discussing individual cases in detail, we shall 

 briefly consider what this implies: 



As mentioned in Section A2, surface inactivation is exponential. The sim- 

 plest way to account for this is to assume that a virus particle remains com- 

 pletely unaffected until it is caught at an inter-face, and that, once caught, it 

 is irreversibly inactivated. If the conditions are such that the chance of being 

 caught is the same throughout the experiment we shall find that, per minute, 

 a constant fraction of the still active particles are inactivated. This describes a 

 typical first-order reaction, which may be expressed by the equation 



NJNo = e exp(— kt), 



