DNA AND Effects of Radiation and Peroxides 295 



(4) Influence of dissolved oxygen and hydrogen. We have 

 observed that the X-ray sensitivity of TP in hquid 1 per cent 

 yeast extract, a condition where the indirect effect is predomi- 

 nant, is influenced neither by oxygen nor by hydrogen. The 

 rate of inactivation is the same (a) under normal conditions 

 (saturation with oxygen); (b) after oxygen has been removed; 

 and (c) after new saturation with hydrogen. Apparent lack 

 of eff'ect of hydrogen may be due to the fact that the high 

 doses used can themselves produce a lot of hydrogen in the 

 solution. We are dealing here with the specific biological 

 activity of a DNA molecule. Its inactivation may result from 

 some kind of structural change of a nature resembling those 

 involved in gene radiomutations, which, as a matter of fact, 

 are also oxygen-independent. It follows that radiobiological 

 effects sensitive to the presence of these gases should not be 

 considered as the end-results of primary injury to DNA. In 

 particular, those radiation-induced mutations which display 

 high oxygen dependence (chromosome breaks), are likely to 

 result from primary attack upon other material than DNA. 



Summary and conclusions 



Cumene hydroperoxide and succinic peracid have been 

 used on bacteria-bacteriophage, and on a transforming agent 

 of Pneumococcus (TP). The effects observed have been com- 

 pared to those produced by radiation under similar conditions. 



1. Both peroxides inactivate bacteria. Sensitivities of dif- 

 ferent bacteria to peroxide are of the same order as their 

 sensitivities to radiation. 



2. Bacteriophages are inactivated by peroxides. After 

 contact, damage is observed both on the abihty of the phage 

 to kill its host, and on its abihty to multiply after attach- 

 ment to the host has taken place. 



3. A posteffect similar to that produced by X-radiation has 

 been observed in bacteria-bacteriophage complexes treated 

 with organic peroxide. 



4. Phage T4 treated with a sublethal dose of cumene 



