﻿26 



BOTANICAL GAZETTE 



The examination of highly differentiated cells like those of 

 Spirogyra has shown that the visible changes produced by the light 

 are not the same in all protoplasmic structures. The change pro- 

 duced is often one which results in an alteration of the equilibrium 

 of the water content of the protoplasm, as shown by the shrink- 

 ing and swelling of various parts, by the bursting of spores, and by 

 the miscibility with the surrounding water of the protoplasm of 

 cytolyzed infusoria. 



As pointed out in a former paper (8), ultra-violet light causes 

 certain chemical changes in egg albumen, changes which lead to a 

 change in the time-temperature-coagulation curve. A study of the 

 nature of these chemical changes has shown that they result in a 

 decomposition of the albumen molecule. Preliminary experiments 

 upon the effects of ultra-violet light on other protein bodies show a 

 similar destructive action of the light. It would seem, therefore, 

 that the stimulus of light is to be classed with those exciting stimuli 

 which accelerate catabolic changes; and that using, as we have in 

 these experiments, light with high vibration frequencies, we have 

 been able within a short space of time and with no very great light 

 intensity to carry the chemical changes through fatigue and death, 

 and finally to a complete destruction and dissolution of tfye proto^ 

 plasm. 



The writer has found that spores dried in vacuo may be killed 

 by ultra-violet light. This becomes understandable from experi- 

 ments which the writer made, and which will be published later, 

 which show that albumen and other proteins, dried in vacuo, are 

 readily decomposed by ultra-violet light. The effect of these high- 

 frequency electromagnetic vibrations on proteins is comparable to 

 that of dry distillation at high temperature. 



These experiments suggest to us a mechanism of the killing 

 action of ultra-violet light, and furnish a clue which, it is hoped, will 

 explain the mechanism of all the effects of light on protoplasm, 

 including those which are not injurious; for it is evident that if the 

 decomposition of the protein molecule is not carried too far it may 

 stimulate the cell without producing injury. A good example of 

 this sort of stimulation is seen in artificial parthenogenesis, which 

 is produced by substances the action of which kills the egg if allowed 



