NATURE OF THE GENETIC EFFECTS 417 



nor has the course of chemical action been worked out in the case of even 

 one mutagen, although there have of course been varied speculations. 

 It is moreover likely that, in one sense, there can never be a unified 

 interpretation, since it seems probable, a priori, that some chemicals 

 would produce their biological effects through far more devious chemical 

 pathways than others, yet happen to arrive at equivalent end results, 

 perhaps through the same final pathway. An illustration of condition- 

 ality in mutagenesis is furnished by formaldehyde, since it has been 

 found to cause a marked increase of the mutation rate when it is applied 

 to the food of the Drosophila male, as shown by Rapoport (1946a) and 

 confirmed by Kaplan (1948), yet it is ineffective when applied to the 

 male at certain stages or under certain conditions, as shown by Auerbach 

 (1949a) and by Herskowitz (1949), and quite nonmutagenic when applied 

 to the female in any manner, as shown by Herskowitz (1950) and by 

 Auerbach (1951). 



Several whole groups of mutagens besides the mustards and carbamates 

 do require specific mention here, however. Perhaps the first in impor- 

 tance is the group of organic and other peroxides, recently found to be 

 mutagenic in both bacteria and molds, by Wyss, Clark, Haas, and Stone 

 (1948), Dickey, Cleland, and Lotz (1949), and Wagner, Haddox, Fuerst, 

 and Stone (1950). This group is of special interest for the present review 

 because of the relation of radiation mutagenesis to oxidation. In fact, 

 even oxygen itself has been found, by Conger and Fairchild (1952), to 

 cause chromosome changes in Tradescantia. Possibly related in mode of 

 action to the peroxides are certain other compounds, reported to be 

 mutagenic in Drosophila. These include potassium permanganate, evi- 

 dence for the mutagenicity of which was obtained as early as 1936 by 

 Naumenko, and perhaps the epoxides, aldehydes, ketones, and even 

 glycols, reported mutagenic by Rapoport (1946a, 1948a, b). However, 

 the above-mentioned indirectness or special conditions of action found 

 for one member of the aldehyde group — formaldehyde — when more 

 detailed tests were made, shows that much caution is necessary in 

 interpreting these results. 



Recent tests of chemicals by Demerec, Bertani, and Flint (1951) have 

 indicated that many different agents, when used in such concentration as 

 to be very detrimental to bacteria {E. coli), occasion at the same time a 

 moderate increase in their rftutation frequency, by a factor, for instance, 

 of 2 or 3. We are reminded here of the effects of both abnormal heat 

 and abnormal cold, and of some reports of other detrimental conditions 

 (see pp. 413-414), on Drosophila and on Antirrhinum. That is, the 

 results indicate a biochemical disorganization in which the processes 

 normally tending to hold the mutation frequency in check are to some 

 extent interfered with. These agents, then, are not to be considered as 

 being, like the mustards, directly mutagenic. The fact that this non- 



