550 RADIATION BIOLOGY 



instance by the finding of Jensen et at. (1952) that a certain antoxidant 

 (nor-di-guairetic acid) prevents the mutagenic action of hydrogen per- 

 oxide but not that of direct ultraviolet irradiation on Neurospora. 



As Wagner et al. point out, it is too early to decide whether the lesser 

 output of the long-distance process is mainly because of the greater 

 chance that the active substances will be destroyed before they can act 

 upon the genetic material or because of their being less effective mutagens 

 than those produced by ultraviolet within the cell. It may be recalled 

 that the latter have been shown by the action spectrum of ultraviolet to 

 consist usually of nucleic acid compounds, at least for the most part. It 

 is therefore tempting to suppose that in their case the action on the 

 genetic material is more direct. Nevertheless, the evidence, given on 

 pp. 545-547, of a long time lag, even in that mutagenesis which is based on 

 the absorption of ultraviolet by chromatin (as shown by the interval 

 during which the final mutational step can still be prevented), calls for 

 caution in the adoption of this possibility. So too does the evidence, 

 given on pp. 541-542, showing the mutagenic action of visible light when 

 this is absorbed by fluorescent substances which had been introduced into 

 the cell. It is in fact quite possible that, even when nucleic acid is the 

 absorber of ultraviolet, much of the action is transferred to surrounding 

 substances (even water), which in turn react upon the genes. 



Despite the finding that hydrogen peroxide generated mutagenic 

 organic peroxides in the medium, it failed to do so within Staphylococcus 

 cells themselves, at least when they were not growing, since it was found 

 that the addition of hydrogen peroxide to an inorganic saline solution con- 

 taining the organisms resulted in no increase of their mutation rate (Wyss 

 et al., 1948). Evidently this is due to some biochemical peculiarity of 

 these organisms which effectively destroys or blocks the action of the 

 hydrogen peroxide itself within the cells or to the lack of suitable sub- 

 strates in their protoplasm; for in Neurospora, hydrogen peroxide applied 

 in the same way, as well as when applied to the nutrient medium, did 

 increase the mutation rate (Wagner et al., 1950). Additional experiments 

 on induced mutagenesis in Neurospora were carried on by Dickey et al. 

 (1949). These investigators, confining their attention to mutations of a 

 particular kind (from adenine dependent to adenine independent), 

 showed that the addition to the medium of organic peroxides of any one 

 of five types, without irradiation, resulted in a marked production of 

 mutations of the kind under observation. These findings then serve to 

 extend the conclusions of Stone and Wyss and their co-workers to specific 

 organic peroxides. 



The catalase and some of the other intracellular enzymes such as 

 cytochrome oxidases, by binding molecular oxygen and by reducing 

 hydrogen peroxide and some of the organic peroxides, must interfere with 

 the mutagenic potentialities of these substances. Thus the enhancement 



