ACTION OF LIGHT ON MICRO-ORGANISMS 345 



are far less injured by the action of light in the absence 

 of air, and in order to further elucidate this pheno- 

 menon, he conducted experiments to ascertain what 

 was the effect of insolation on the culture material 

 itself. 



For this purpose flasks (A) containing sterile bouillon, 

 .and others (B) into which anthrax spores had been 

 introduced, were exposed side by side to the sun's rays. 

 At the end of .each hour a flask of each series was with- 

 drawn, and into the sterile one spores were introduced, 

 and both flasks were then placed in the incubator. 

 Usually after two hours' exposure the (B) or infected 

 flasks were found incapable of yielding growths, whilst 

 in the case of the (A) or sterile flasks, into which the 

 spores were introduced just before being placed in the 

 incubator, growths usually made their appearance. If, 

 however, the insolation of the sterile flasks had been pro- 

 longed for three or four hours, the bouillon contained in 

 them proved to be no longer a suitable culture medium, 

 for in spite of the introduction of the anthrax spores 

 no signs of growth were visible. Under the action of 

 the sun's rays in the presence of air, the bouillon 

 had, therefore, undergone some chemical change which 

 rendered it unsuitable for the germination of the 

 spores. 



The spores themselves, however, had not been de- 

 stroyed either by two or even by seven hours' insolation, 

 for when they were removed from the bouillon in which 

 they had been insolated but in which they had not ger- 

 minated, and were introduced into bouillon which had 

 not been exposed to light, germination followed. The 

 germination was, however, retarded according to the 

 length of time during which they had been insolated or 

 had been in contact with the insolated bouillon. If, 

 however, instead of sowing the sterile insolated bouillon 



