Influence of ultraviolet irradiation on the growth of bacteria and Arndt-Schultz law.

Regarding the influence of ultraviolet irradiation on the growth of bacteria, numerous studies have been accomplished and it has been known that there exists a relation of exponential function between the bactericidal effect and the amount of ultraviolet ray irradiated. The methods employed in those studies,1),2),3),4) a,b, however, are mostly so called plate method in which the irradiation is made on ordinary agar plates inoculated with a known quantity of bacteria. We prepared a bacterial suspension of E. coli using physiological saline as its dispersion medium. Placing the suspension in quartz tubes, ultraviolet irradiation was applied to determine 50 % survival time. The survival time thus determined was found to differ considerably from the one determined by plate method in which the same bacterial suspension was used5). Thus, our attention was directed to the broth which was the chief component of the agar plate. A bacterial suspension was prepared using the broth as its dispersion medium. Upon investigation the survival curve and the biological characters of the survival bacteria after irradiation made on this suspension, extremely interesting facts were observed.