ON BACTERIOLOGY IN ITS RELATIONS TO CHEMICAL SCIENCE. 459 



through the earlier researches of Pasteur, Lister, Burdon Sanderson, and 

 Tyndall, now about a quarter of a century ago, the important discovery 

 was made by Downes and Bhint that these minute organisms were 

 remarkably susceptible to direct sunshine.' Notwithstanding the 

 novelty of the subject and the peculiar difficulties which then attended 

 such researches, these two investigators worked out their discovery in 

 such a very complete manner that I am of opinion it should be regarded 

 as one of the most important additions made to the subject of bacteriology 

 prior to the introduction of the more modern methods of studying 

 bacteria. They clearly showed that this bactericidal action of sunlight is 

 independent of any rise in temperature ; that they are the rays at the blue 

 end of the spectrum which are the most effective, the red rays being 

 almost quite inert ; further, that the action is highly favoured if not 

 entirely dependent on the simultaneous presence ot oxygen. Again, 

 they showed that the action was quite independent of the presence of any 

 culture medium, for if bacteria which had been suspended in distilled 

 water were allowed to become air-dry on glass they were destroyed by 

 subsequent insolation. Again, they found that the culture media which 

 they employed (Pasteur solution) were not rendered anfit by insolation 

 for the subsequent cultivation of micro-organisms. Another highly 

 important point to which they drew attention was that the action of sun- 

 light is much less effective if the bacteria are suspended in water than if 

 they are present in culture solutions. They further showed that mould 

 and yeast forms were Jess susceptible to light than bacteria, and they 

 even extended their investigations to the soluble ferment invertase, the 

 activity of which they also found succumbed to insolation. These classical 

 investigations have been confirmed in practically every detail by the 

 subsequent researches made with pure c.'iltures of particular bacteria by 

 Duclaux,^ Arloing,'* Straus,'* Roux,'' Gaillard,^ Uffelraann,^ Panzini," 

 Laurent,^ Santorini,"* Janowski,'' Geisler,'^ Kotljar,'^ Buchner,'* 

 Moment,''' Marshall Ward, and myself."' 



Of special interest in connection with this subject are some recent 

 experiments by Richardson,'^ who shows that when urine is exposed to 

 direct sunshine peroxide of hydrogen is formed, the presence of which 

 prevents the development of growths. There are several very interesting 

 and important points arising out of this investigation : — 



1. There can be no doubt that peroxide of hydrogen was formed in. 



' Proceedings Eoyal Society, 1877 and 1878. 

 ^ Comptes liendvs, c. and ci. (1885). 



' Hid., c. p. 378 ; ci. p. 511 ; civ. p. 701 ; Arcldves de Physiol, norm, et Path., 

 vii. (1886), p. 209. 



* Societe de Biologic, 1886, p. 47.3. 



* Annates de I'lnst. Pasteur, i. (1887), p. 445. 



' De VInfluence de la LuvnvTc sur les Micro-organiswes, "Lyons, 1888. 



' Die hygienische Bcdeutung des Sonnenlichtes, 1889. 



' Rirista d'Igieiie, 1889. 



" Ann. de VInst. Pasteur, iv. (1890), p. 478. 

 '" Dull, delta Accad. Med. di Uoma, xvi. (1889-90). 

 " Centralhl.f. Bakteriolvgie, viii. (1890), pp. 167, 193, 230, 262. 

 '= lUd., xi. (1892), p. 161. 

 " Ihid., xii. (1892), p. 836. 

 '< lUd., xi. p. 781 ; xii. p. 217. 

 '^ Ann. de I'Inst. Pastevr, vi. (1892), p. 21. 

 '« Proc. Roy. Soc, 1893. 

 " Trans. Chem. Soc, 1893. 



8 



