APPLICATIONS AND SOURCES OF ULTRAVIOLET 



45 



thus protect the organism itself. Perhaps the decreasing germicidal 

 action at wave lengths less than 2500 A found by some workers may 

 represent the absorption curves of the culture media rather than the 

 absolute susceptibility of naked bacteria to ultraviolet killing. 



8 



' o'i^^gth 



'^ J^ 9 !^Q 



A 

 o 



~ £\j O 





Fig. 2-3. Composite of Figs. 2-1 and 2. 



ACTION CURVE APPROXIMATE AT LONGER WAVE LENGTHS 



The germicidal action of radiant energy extends even into the visible 

 spectrum, the action decreasing rapidly with increasing wave length 

 (decreasing frecjuency and energy content of quanta). The action is of 

 the order of magnitude in the near ultraviolet and visible estimated by 

 Luckiesh and Taylor (1946; see also Hollaender and Claus, 1935-36) in 

 Fig. 2-4 where a logarithmic ordinate is used to extend the killing action 

 to lower effectiveness levels. The reactivating effects of wave lengths 

 3600-4400 A reported by Kelner (1949) suggest that, for all practical pur- 

 poses, the curve of Fig. 2-4 might well end at 3600 A. In any case, since 



