160 BIOPHYSICALLY ACTIVE LIGHT 



TABLE IV-3 



Effect of Ultraviolet Radiation on Bacteria 



Finsen and Dreyer (1903) were probably the first to show that light 

 of short wavelengths is virucidal. Except in the more recent investiga- 

 tions in this field, monochromatic radiation has not been used, nor has 

 the amount of energy which is associated with the lethal wavelengths 

 been determined. In a study of the ultraviolet effect upon vaccine virus 

 by Rivers and Gates [1928], a series of experiments showed that the 

 effect of monochromatic ultraviolet radiation in terms of the incident 

 energy required to inactivate all of a given specimen of vaccine virus is a 

 maximum at about 2650 A. More significant than the involved absolute 

 energies is the general shape of these lethal curves. They exhibit a 

 rapid drop in the required lethal energy between 3000 and 2800 A, a 

 minimum at 2650, and a rise towards 2250 A corresponding closely to 

 the curve representing the absorption of ultraviolet energy by protein 

 substances. In an attempt to narrow the energy band that is required 

 for a lethal exposure the results obtained by others as shown in Table 

 IV-3 must be examined. The maximum lethal effects for Escherichia coli 



o „ 



are obtained on the average near 2650 A, and it takes about 14 X 10~° 

 erg per bacterium to produce death. 



Inactivation data by Hollaender and Emmons [1939] on the skin 

 fungus Trichophyton mentagrophytes indicate that 2537 A is the most 

 effective region. It takes about 7 X 10 -4 erg to obtain 50 per cent 

 inactivation of these spores. 



