RADIATION STUDIES ON FUNGI 



441 



ameliorating effect of visible light applied following irradiation with 

 ultraviolet, a phenomenon which is fully discussed by Dulbecco (Chap. 12 

 of this volume). This has been shown for several kinds of ultraviolet 

 effects on numerous organisms including the killing of Strcptomyces 

 griseus, P. rtotatum, and S. cerevisiae (Kelner, 1949a, b), killing and muta- 

 tion of .V. crassa (Goodgal, 1949), reverse mutation of inositolless Neuro- 

 spora (Brown, 1951), killing and mutation of haploid and diploid Saccha- 

 romyces (Pomper, unpublished), and suppression of enzymatic adaptation 

 in Saccharomyces (Swenson, 1950). Photoreactivation provides a striking 

 demonstration of the existence of intermediate states between the absorp- 



tion of ultraviolet cjuanta and their final biological effects, and it is 

 economical to suppose that killing, mutation, and impaired enzymatic 

 adaptation are mediated through similar mechanisms at the stage where 

 photoreactivation occurs. It should be emphasized that all work 

 reported with ultraviolet radiation must be scrutinized carefully to see 

 whether or not the results have been influenced in an unrecognized 

 manner by the effects of visible light. This is especially true of material 

 published before 1949, when the photoreactivation phenomenon was so 

 clearly demonstrated (Kelner, 1949a). 



Other factors or agents have been considered which might influence the 

 sensitivity of microorganisms to ultraviolet radiation. Nitrogen mustard, 



