EFFECTS OF RADIATION ON BACTERIA 



371 



tides and Serratia marcescens. Lea et at. (1936) found the rate of iuacti- 

 vation of B. mesentericus spores by a and particles to be independent of 

 temperature between -20° and +50°C. No influence of temperature 

 was noted on the rate of inactivation of *S. aureus. These results differ 

 markedly from the high temperature coefficients experienced with chemi- 

 cal disinfectants. Lea e( al. (1937) showed that varying the temperature 

 from 0° 37°C had no influence on the survival of E. colt exposed to y rays. 

 Lea et al. (1936) observed that a sixfold variation in intensity of a-par- 

 ticle flux had no effect on the proportion of organisms surviving a given 

 dose. This was confirmed by experiments in which a given dose was 

 administered in a number of fractions, no effect on survival being observed. 



30- 



_i 

 o 

 o 



CO 



o 



ir 

 uj 20 



(ij 



5 



o 



I 



BETA RAYS 

 Oc-GAMMA RAYS 



SOFT X RAYS I 5 A 

 O' \ O-SOFT X RAYS 83 a 



O-NEUTRONS 



(- 



10- 



ALPHARAYS 



1^34 

 IONS PER cm(xlO^) IN BIOLOGICAL MATERIAL 



Fig. 10-2. Curve showing ratio of MLD mesentericus: MLD coli plotted against ion 

 density for a number of different radiations. {Adapted from Spear, 1944.) 



Lea et al. (1941) reported further data on the lack of an intensity effect 

 of a particles and 8.3 A X rays. A seventy-fivefold variation in intensity 

 was employed in the latter case. Extremely high intensities of /3 par- 

 ticles have been shown by Huber (1951) to be bactericidally effective. 



The observation of filamentous forms in bacterial cultures following 

 ultraviolet irradiation was reported by Gates (1933) who concluded that 

 the mechanism of cell division was more sensitive to radiation than the 

 processes of growth. Similar observations have been reported by several 

 investigators (Spencer, 1935; Luria, 1939; Witkin, 1947; Rolierts and 

 Aldous, 1949). Lea et al. (1937) observed such filamentous forms follow- 

 ing continuous y irradiation of growing E. coli cultures. Subsequent 

 experiments indicated that the filamentous cells reacted to y rays in the 

 same manner as the normal cells, i.e., they were equally sensitive to 

 radiation and were inactivated in an exponential manner. 



Careful studies of the effect of ionization density on the biological effec- 



