Bactericidal Effect of Ultraviolet Radiation

Abstract

The effects of ultraviolet radiation on microorganisms have been studied frequently. The lethal action of sunlight on certain bacteria was demonstrated by Downes and Blunt as early as 1877. Roux (1887) showed that spores as well as bacteria are destroyed by these radiations and in 1903 Barnard and Morgan reported that the bactericidal action of radiant energy is limited to wavelengths shorter than 3000k. The susceptibility of microorganisms to ultraviolet radiation under varying conditions has also received considerable attention. Wells and Wells (1936), Whiser (1940), and Koller (1939) claim that airborne bacteria are ten times as resistant to radiation at high relative humidity as when floating in air at low humidity. Koller's results indicate that floating bacteria are less resistant to ultraviolet than similar bacteria on the agar surface of a Petri plate and Wells (1940) states that airborne bacteria are about twenty times less resistant than those floating in a liquid suspension. Rentschler and Nagy (1940) report the same sensitivity for air borne and for identical bacteria on the surface of agar and no effect due to humidity. The Bunsen-Roscoe reciprocity law for the bactericidal action of ultraviolet has been tested by Coblentz and Fulton (1924), by Gates (1929) and by Koller (1939) with varying results. Conflicting theories have been advanced to explain the nature of the bactericidal action of ultraviolet radiation. In recent years a rapid and simple method for measuring ultraviolet radiation has been made available by one of us (Rent-745