IONIZING RADIATION AND VIRUSES 95 



additional effect becomes apparent. Similar results have been 

 obtained independently by Bachofer (1953). 



These results show that a virus such as T-1 cannot be re- 

 garded as homogeneous, even within that part which is radiation 

 sensitive. The fact that there is an interplay between high- 

 energy (ionization) and low-energy (thermal) effects indicates 

 that either transfer of energy through the virus to a sensitive 

 part, or damage to a larger part of the virus, is facilitated by 

 irradiation at high temperature. 



A second experiment, carried out by Adams and the author 

 (1953), sheds some light on this question. The latent period 

 of T-1 was studied for those virus particles which had undergone 

 many deuteron hits but had survived. It was found that the 

 latent period for these survivors is increased significantly, 

 in agreement with a finding of Luria (1944) that ultraviolet 

 light produces such action. The increase in the latent period was 

 a function of the number of hits received, and this indicates 

 that there is apparently a part of the virus which does not 

 determine whether the virus will multiply but does determine 

 the rate. The results of deuteron bombardment of T-1, with 

 consequent action on the latent period, are shown in Fig. 3.9. 

 The ratio of the measured latent period to that found after 

 deuteron bombardment is plotted versus the number of deuteron 

 hits on an assumed maximum sensitive area of 2 X 10~^Vcm^. 

 A linear increase is observed, with a doubling of the latent period 

 for 15 hits. Some more recent work by Fluke indicates that the 

 burst size for radiation survivors is diminished. It is tempting to 

 suppose that a part of the virus consists of an enzyme system 

 which is related to the bacterial chemical content and which 

 produces virus precursors. By damaging individual enzyme 

 molecules, the rate of multiplication, and also the amount of 

 precursor material available for manufacture of virus, is reduced. 

 So we conclude that the virus contains a rather large number of 

 enzyme molecules which are only concerned with rate of multi- 

 plication. Probably not many types of viral enzymes are involved. 



The enhanced effect of temperature is thus to be thought of 

 as taking place on this enzyme-like system. The effect of tem- 



