64 BIOLOGY AND TECHNIQUE 



It has been shown by various authors that the influence of sunlight is 

 not to be attributed in any way to temperature, nor alw.ays to a direct 

 action of the light upon the bacteria, but depends largely upon photo- 

 chemical changes produced by the light rays in the media. Richardson ' 

 and Dieudonne ^ conclude that under ordinary aerobic conditions in fluid 

 environment peroxide of hydrogen is formed under the influence of light. 

 Novy and Freer ^ believe that the bactericidal effects in fluids noticed 

 as a result of exposure to light are too strong to be explained by the 

 formation of small quantities of peroxide of hydrogen, and attribute 

 this action to organic peroxides formed under the described conditions, 

 such as the peroxides of diacetyl, benzoylacetyl, and others. These 

 views are somewhat strengthened by the fact that exclusion of oxygen 

 from media markedly diminishes the bactericidal power of light.^ That 

 the photochemical changes alone, however, do not explain this action 

 follows from the fact that dried bacteria, not surrounded by media, are 

 subject to a similar action.' 



In analyzing sunlight in regard to its bactericidal power, it has been 

 found by various observers that the most powerful action is exerted by 

 the ultraviolet spectral rays, whereas the yellow, red, and ultra-red rays 

 are practically innocuous.* 



It is of importance to note that sunlight has been found also to have 

 a strong attenuating influence ' upon some bacterial poisons, as shown 

 by the experiments of Ferri and CeUi upon tetanus toxin. 



Electric hght exerts a distinct bactericidal action when applied in 

 strengths of 800 to 900 candle power for seven or eight hours. ^ 



Rontgen or a;-rays are said by Zeit,^ Blaise ^° and Sambac, and others 

 to be without appreciable germicidal power. Rieder," on the other 

 hand, has reported definite inhibition of bacterial growth after exposures 

 of half an hour to x-rays. 



1 Richardson, Jour. Chem. Soc, i, 1893, Ref. Deut. chem. Gesells., xxvi. 



2 Dieudonne, loc. cit. 



3 Novy and Freer, 3d Ann. Meeting Assn. Amer. Bacteriologists, Chicago, 1901. 

 » Roux, Ann. Inst. Past., ix, 1887. 



6 Dieudonne, loc. cit. 



8 Ward, Proc. Royal Soc, 52, 1893. 



' Fern and CeUi, Cent. f. Bakt., I, xii, 1892. 



8 Dievdonne, loc. cit. 



' Zeit, Jour. Amer. Med. Assn., xxxvii, 1901. 



>» Blaise and Sambac, Compt. rend, de la soc. de biol., 1896. 



" Rieder, Milnch. med. Woch., 1898. 



