﻿BOTANICAL GAZETTE 



always marked out exactly the outline of the window of the dis- 

 charge tube may be taken as evidence that no toxic substances were 

 formed in the solution. The observations made on other species 

 of organisms lead to the same conclusion, that the action of the 

 light is on the organism itself. 



Notwithstanding the fact that the light was from an exceed- 

 ingly feeble source, the changes in the organisms were imme- 

 diate. In the small swarm spores with thin transparent cell walls 

 the changes appeared the instant the discharge tube was excited. 

 It is evident that the Schumann rays are very destructive to proto- 

 plasm. The examples just given of the visible effects of these rays 

 upon organisms are sufficient to make it apparent that we are deal- 

 ing here with a powerful cytolytic agent, and one which warrants 

 further study. 



The relation between the wave length and the destructive action 

 of light in the Schumann region of the spectrum has not been pre- 

 viously studied. For the longer light waves this relation has been 

 investigated to some extent, as will appear from the brief summary 

 which follows. 



Downes and Blunt, using colored screens, showed that blue 

 light is more destructive to bacteria than red light. Ward, using 

 a quartz prism, confirmed the results of Downes and Blunt, and 

 showed that the killing power extends into the ultra-violet. 



Two papers appeared in 1905 on the bactericidal action of light, 

 describing experiments in which not only the wave length but also 

 the intensity of the light was measured. Bang spread the light of 

 a carbon arc into a spectrum by means of quartz lenses and a quartz 

 prism, and measured the relative destructive action of the various 

 parts of the spectrum by determining the length of time it took in 

 a given region of the spectrum to kill an organism {Bacillus pro- 

 digiosus) growing on the surface of an agar plate. His results 

 showed that, in general, as the wave length of the light decreases 

 the destructive action increases, but that the curve is not uniform, 

 showing a break in the region of wave length 3000 Angstrom units. 

 In this region the light is several hundred times less destructive than 

 in the regions on either side, so that the curve shows two maxima. 

 The secondary maximum is in the region of wave length 3500 



