ULTRAVIOLET LIGHT MEIER 



359 



of two fungi was vigorously increased when they were grown on car- 

 rot medium that had been irradiated with ultraviolet light. 



Bailey (1931) reported that the ultraviolet rays increase the 

 formation of reproductive bodies in certain lower forms of plants. 

 A bulb-rotting organism that never had been known to produce 

 spores by which the proper classification of the organism might be 

 made was induced to form these bodies after irradiation with ultra- 

 violet light. Coblentz and Fulton (1924) found some indication of 

 stimulation in their irradiation work at very low intensities. In this 



2500 7-aOC 27O0 2ISC0 2S00 3000 3!0O 



Figure 3. — Radiotoxlc spectral sensitivity of the alga ChloreUa vulgaris to ultraviolet rays. 

 The abscissae are wave lengths in Augstroms. The ordinates are relative lethal effec- 

 tlvonesa In arbitrary units. Black line, smooth curve ; dash line, actual values ; dot line, 

 curve obtained by Meier (1932). 



work they studied the effect of ultraviolet light when the exposure 

 was applied continuously and intermittently witli long or short in- 

 tervals of rest. No differences in the density of the growth could be 

 observed, whatever the method of exposure. This evidence seems to 

 indicate that the intermittent exposure docs not have a latent effect 

 in stimulating growth or in continuing the lethal action during the 

 intervals of rest, and that the lethal effect is cuniulativo. When the 

 intensities were reduced the lethal action was greatly retarded; for 

 example, using an intensity reduced to 1/50 it was necessary to expose 

 the inoculated plate of bacteria for 75 to 80 seconds instead of 50 

 seconds in order to secure the same lethal effect. At still lower 

 intensities there were some indications of stimulation instead of 

 lethal action. 



