A quantitative study of the action of ultra-violet light on bacteria

The experiments here recorded were made between 1929 and 1932. The work was then unfortunately interrupted, and since the death of the senior author the material has been prepared for publication by M. C.-R. Experiments on different species of infusoria carried out by Dreyer (1903), using the carbon arc as a source of light and different filters, showed that, although the greatest lethal effect was always obtained in that part of the spectrum which passes through glass, the relative sensitivity of different infusoria varied considerably in different parts of the spectrum. Sonne (1927) found that the line 2800 A of the mercury spectrum exhibited the greatest lethal effect on paramaecia, while in the case of haemolysis the most effective line was 2400 A. Hausser and Vahle (1921) found the erythema-producing maximum at 2970 A. Thus, the different spectral lines appeared to show some selectivity in their biological activity, and in view of this it was of interest to investigate the effect of these lines on different species of bacteria. Also, it would be of interest to investigate the changes in sensitivity to light induced by treating the organisms with erythrosin. As it was possible that the differences in some cases might be very slight, it was essential to use a technique which would reduce the experimental error as much as possible.