DNA AND Effects of Radiation and Peroxides 289 



determined by Anson's method (with a precision of 3 per cent) 

 before and after treatment. Table IV groups the main 

 results obtained so far: 



Inactivation is only slightly increased at pH 3-6. Two 

 main facts may be pointed out : 



(a) the very great resistance to peroxide of the enzymatic 

 activity, when compared with that of DNA ; 



(b) the slight enhancement of enzymatic activity by short 

 exposures. 



Inactivation of a transforming agent by peroxide 



Transforming agents (or transforming principles, TP) are 

 pure DNA of bacterial origin, endowed with specific biological 

 properties, which can be extracted and transferred without 

 losing their activity. When accepted by a suitable cell, a 

 transforming agent endows this cell with a character possessed 

 by the strain from which it has been extracted. The "trans- 

 formed " cell perpetuates this character. One unit of the agent 

 can be detected by the formation of one transformed bacterial 

 clone. Therefore, such agents provide a unique material for 



RAD. 



11 



