Induction of Chromosomal Aberrations 249 



able that chemical (non-enzymatic) and biochemical (enzy- 

 matic) events of comparable importance can be substituted. 

 It would appear, for example, that the initial action of DEPE 

 is chemical in nature since it is highly reactive, its effective- 

 ness is governed by the law of mass action (Revell, 1953), and 

 its action is not modified by pretreatment with DNP (Love- 

 less, 1953). EOC and MH, on the other hand, are modified in 

 their effectiveness by agents which inhibit oxidative phos- 

 phorylation, and it is likely that their initial action is through 

 enzymatically controlled steps in cellular metabolism. 



Wolff's data indicate that the restitution and recombination 

 of ends of chromosomes broken by events taking place in 

 stages I-III require energy supplied through oxidative meta- 

 bolism, and that the rejoining system is comparatively sensi- 

 tive to small amounts of radiant energy. Considerable pro- 

 tection is afforded it by anoxic conditions. It is suggested, as 

 a consequence, that the principal damage to the rejoining 

 system is inflicted by active radicals and their derivatives 

 which have been induced by radiation. It is further tempting 

 to see a connection between the results described above which 

 indicate a possible role of oxidative phosphorylation in the 

 production of chromosomal aberrations and the recent 

 findings of Allfrey, Mirsky and Osawa (1955) which point to 

 the oxidative generation of energy-rich phosphate within the 

 nucleus, a process heretofore considered to be confined to the 

 mitochondria. It would appear, therefore, that the nucleus 

 does not necessarily exist and function in an anaerobic environ- 

 ment as suggested by Stern (1955), but much remains to be 

 done before the links in the chain are connected. 



It has not been possible to separate breakage and rejoining 

 following exposure to chemical mutagens as Wolff seems to 

 have done in his radiation experiments. One cannot, therefore, 

 fully assess their effects on either system other than to point 

 out that with some chemicals oxidative phosphorylation 

 obviously determines their mutagenic effectiveness or in- 

 effectiveness. With other chemicals such a point of view 

 cannot be expressed with the same degree of surety. It is our 



