Ultraviolet Radiation;Stimulation and Inhibition in Lower Organisms.

Abstract

The statement is sometimes made that radiation depends for its effectiveness as a stimulating or an inhibiting agent upon wavelength rather than upon dosage. Quality rather than quantity is the factor which decides whether an effect is to be stimulative or inhibitory. However, a number of workers, among them Bovie, L. Loeb, and Packard, using ultraviolet, x-ray, and radium, respectively, found that it is possible to produce both types of effect with the same region of the spectrum. A survey of about 5 years'work with the lower animals shows this to be the case in at least 2 regions of the spectrum, ultraviolet, and the visible region (following the action of sensitizing dyes). While the experiments were originally not conducted to test this point, it soon became apparent that with the same spectral region, short exposures produced primarily stimulation, and longer exposures, depression. Later work included experiments in which the rate of a physiological process was modified in either of 2 directions following exposure for short and long periods to the unscreened radiation from a quartz mercury-vapor arc.

Such studies were made with yeast. Ordinary baking yeast was suspended in distilled water and exposed, in open dishes, to radiation from the quartz mercury-vapor arc at various distances from the center of the arc. In these experiments, distilled water was used because it had previously been found that the action of ultra-violet radiation upon the constituents of the ordinary nutrient solution produces substances which are toxic to yeast. Earlier studies made by Woodrow, Bailey, and Fulmer reported only depression of sugar-fermenting- power as a consequence of the action of ultra-violet radiation upon the nutrient solution itself.