290 Raymond Lataiuet 



quantitative experiments on the actions of radiations or . 

 other aggressors upon the specific biological activity of DNA.' 



In collaboration with Miss N. Cherrier, we have recently 

 undertaken a first series of experiments. Our TP, extracted 

 from a streptomycin-resistant strain of Pneumococcus and then 

 purified, showed a titre of 10^ transforming units per [xg. of 

 DNA. A solution containing 6x10-^ [ig. of DNA per ml. of 

 distilled water was brought into contact with the peroxide 

 at various times at 37°. After contact, aliquots were diluted 

 a hundred-fold in the transforming medium in the presence of 

 sensitive bacteria. After the transformations were effected, 

 the bacteria were plated in triplicate on agar supplemented 

 with streptomycin. The transformed clones were enumerated 

 after 2 days of incubation. Controls were done in order to 

 ascertain that the hundred-fold diluted peroxide remaining 

 in the transforming medium did not curb the transformations. 



The following results have been obtained so far. I 



(1) Surprisingly, cumene peroxide at concentrations ranging 

 from 10"^ to saturation (about 10-^) produced no noticeable 

 inactivation after contacts of from 1 to 3 hours, either in the 

 dark, or in visible light. 



(2) However, succinic peroxide proved to be extremely 

 toxic : 



(a) control experiments showed that, at a concentration of 

 5 X 10-^ in the transforming medium, the peroxide 

 decreased the number of the transformations induced 

 by untreated TP to about 20 per cent of the normal 

 value. At a concentration of 1 X 10-^, there was no 

 further toxicity. On the contrary, the peroxide increased 

 the number of transformations by a factor of about 

 1 • 5 ; this recalls the previously mentioned increase in 

 the activity of pepsin (see p. 288) ; 



(b) contact with TP in distilled water was done at peroxide 

 concentrations of from 3 X 10-^ to 1 X 10-^. In all 

 experiments, there was a very sharp exponential 

 inactivation during the first few minutes of contact, 



