A Study of the Bactericidal Action of Ultra Violet Light I. the Reaction to Mon'ociiro3katic Radiations by Frederick L. Gates

During the past fifty years, many investigators have studied the bactericidal activity of ultra violet light, but a review of their reports shows that little has been learned about many essential factors in the reaction. There have been few contributions to a knowledge of the quantitative relations involved. Little precise information is available on differences in resistance of individual bacteria to monochromatic light and the consequent reaction curve of large numbers of organisms; on the effective range of ultra violet frequencies; on the relation between incident and absorbed energies at various wave lengths; on relations between time and intensity; on the temperature coefficient; on the action of polarized light; or indeed on any of the factors essential to the reaction on which an examination of its biophysical significance must be based. But the ultimate object of the present study has not been simply to determine a set of coefficients for the bactericidal action of ultra violet light. This particular reaction was chosen for study because less individual variation is to be expected among bacteria than among higher forms of life. They are easily handled in quantity, and the death or survival of microorganisms provides a clearcut endpoint which may be observed and statistically recorded with unusual accuracy for biological material. They seemed to afford the best available opportunity for a quantitative study of an effect of certain frequencies in the ultra violet on protoplasm: with the prospect that the reaction of the bacterial cells might open leads for further studies on higher organisms. I t is obvious that in such work a considerable number of factors 231