KFFIOCT.S OF UAOIATIOX ON HACTKKIA 399 



range. Such frozen cells inactivatetl by 3000-4000 A radiation showed no 

 l)ii()toreacti\'ation in the liciuid phase. Thus, Heinmets and Taylor eon- 

 firm that radiation in this range can cause loss of viability of Ji. roll B cells 

 and that the mechanism of this inactivation is probably (luite different 

 from that of ultraviolet radiation of wave length shorter than 3000 A. 



No studies of mutation induction in l)acteria by irradiation at wave 

 lengths greater than 3800 A have been published. HoUaender and 

 Emmons (1946) observed morphological mutations following irradiation 

 of A. terreus conidia at wave lengths 2967 and 3130 A. The energy 

 required was much higher and the maximum proportion of mutants was 

 lower than for 2650 A ultraviolet. The expected mutagenicity of sun- 

 light, which contains appreciable amounts of energy in the 2900-3150 A 

 range, was realized experimentally (HoUaender and Emmons, 1946; 

 HoUaender et al, 1946). McAulay and his associates (INIcAulay and 

 Ford, 1947; McAulay et al. 1949; Ford and Kirwan, 1949) report muta- 

 tions in the fungus, Chaetomium glohosum, following irradiation with wave 

 lengths of 3354, 3654, and 4047 A. This work is discussed in more detail 

 later. 



In conclusion, it appears that, although irradiation with wave lengths 

 greater than 3000 A may produce mutations, the mutagenic efficiency is 

 markedly lower than for wave lengths near 2600 A. 



An interesting effect of visible light is photodynamic action, a complex 

 function of visible light and photodynamic dye which recjuires the pres- 

 ence of oxygen in order to be functional. Duggar (1936) briefly re\dewed 

 the earlier work in this field. That permanent hereditary changes in 

 microorganisms can be produced by photodynamic action has been 

 demonstrated by Kaplan. Thus microcolonies of a permanent nature 

 were observed in S. marcesccns following exposure to visible light in the 

 presence of erythrosin (Kaplan, 1950b). Similarly, reverse mutations in 

 a histidineless strain of E. coli (Kaplan, 1950c) and mutations to resist- 

 ance to coliphage T7 (Kaplan, 1950a) were produced by photodynamic 

 action. Perhaps the most striking effects were obtained with P. notatum 

 (Kaplan, 1950d) in which significant increases in colony morphology 

 mutations w^ere observed. Further studies of photodynamic action seem 

 indicated since, as yet, the mechanism and significance of this phe- 

 nomenon are not very well understood. 



PHYSIOLOGICAL PROPERTIES OF BACTERIA 

 FOLLOWING IRRADIATION 



Surprisingly few investigations have been concerned with the physi- 

 ology of irradiated bacteria, and much more work is needed in this field. 



The observation of filamentous cells following irradiation has been dis- 

 cussed. Chambers and Russ (1912) and Bruynoghe and Mund (1925) 



