IONIZING EADIATION AND VIRUSES 



99 



actually a rather larger fraction than is found for T-1 phage, and 

 shows that some characterization of viruses in this way is 

 possible. 



Bacterial Killing Ability. The results of studying the reduction 

 of bacterial colony counts by T-2 phage after irradiation are 

 shown in Fig. 3.10. It can be seen that a semilogarithmic in- 

 activatioii of the killing fraction takes place. The inactivation 



3xlO'r 



Dose 



Fig. 3.10. Inactivation of bacterial killing power (solid line) and ability to 

 form plaques (dotted line) as a result of X-ray bombardment. Data due to 

 Watson (1950). The killing power inactivation volume is clearly less. 



volume for this is one-third of that for virus activity, and so is 

 about one-eighteenth of the whole virus. 



Lysis from Without. If enough virus particles attach to a 

 bacterium, it is lysed without being entered by the virus. This 

 ability is not destroyed by X-irradiation even when the ability 

 to kill has been destroyed. Presumably this property also has a 

 small inactivation volume. 



