1886.] 



Action of Sunlight on Micro-organisms , SfC. 



1 5 



similar conditions of temperature and the like, but screened from 

 light, swarmed in a very few days with countless saprophytes. 



By means of suitable absorptive media, we learned that the most 

 active rays were those of the more refrangible end of the spectrum » 



Seeking an explanation of the facts thus observed, we proceeded 

 in the first instance by analogy. 



We found that light had an oxidising action on many organic sub- 

 stances of comparatively simple composition, and we demonstrated 

 that, in the presence of free oxygen, the molecule of oxalic acid might 

 be speedily and entirely resolved into water and carbonic acid by the 

 action of light, more especially by those rays to which I have 

 already referred. 



Proceeding to more complex substances, we applied the same method 

 to one of those singular bodies, the so-called soluble or indirect 

 ferments. 



In less than a month the properties, and, inferentially, the sub- 

 stance, of the invertive diastase of yeast were destroyed by light. 



Once more we found that we had to deal with an oxidation. 

 Finally, our inference that the action of sunlight on the organisms of 

 our cultures would likewise prove to be an oxidation was confirmed 

 by direct experiments, in which the effect varied in proportion to the 

 amount of free oxygen present. 



As yet no one has repeated these investigations in their entirety, 

 but sufficient confirmatory evidence has accumulated to justify me, 

 I think, in briefly placing the case before the Society as it now stands, 

 with one or two additional observations of my own, and to afford me 

 an opportunity of replying to one or two points of criticism. 



The earliest corroboration of our work came out on the readme of 



o 



our first memoir on this subject. 



Mr. Warington had that same evening, in a paper to the Chemical 

 Society, notified, but was unable to explain, the inhibitory action of 

 light on the process of nitrification. Our experiments at once sug- 

 gested to Dr. Gilbert the interpretation, since confirmed by several 

 observers,* that light was inimical to the nitrifying ferment. 



Gladstone and Tribe ("Journ. Chem. Soc," August, 1883) found 

 that light was detrimental to the development of fungoid growths in 

 solutions of cane-sugar exposed to atmospheric air.f Tyndall re- 



* Soyka, in " Zeit. f. Biol.," 1878 ; Schloesing and Muntz, " Journ. of Chem. 

 Soc." (AbstT.), April, 1880. 



+ It is right to state that van Tieghem in his investigations on the organisms 

 appearing in olive oil ("Bull. Soc. Bot.," xxviii, p. 186), found that Penicillium 

 glaucum developed in oil at the most illuminated spots. I have not been able to 

 see the original paper, and am therefore not acquainted with the conditions of the 

 experiment, especially as regards the nature of the illumination, aud the access of 

 free oxygen. 



M 



