372 ULTRA-VIOLET LIGHT ON BACTERIA AND PRODUCTS 



colors of the spectrum. He also agreed with Downe;> and Blunt that oxygen was an 

 essential factor in the germicidal action and that ve.riations in the germicidal action 

 of light of different character or intensity was due to its effect on oxidizing reactions. 

 Duclaux appears to concur in this conclusion as docs also Roux/ who studied the in- 

 fluence of light and of air on anthrax cells and spo -es. 



Buchner,^ in 1892, using both suspensions of bacteria and agar plates, demonstrat- 

 ed the germicidal action of direct sunlight on a number of species of bacteria such as 

 the typhoid bacillus, Bad. coli, B. pyocyaneus, B. prodigiosus, and the cholera vibrio. 

 Buchner's papers are of historic interest since we find here the illustration, similar to 

 that in most modern bacteriologies, of an agar plate showing growth of bacteria in 

 those parts protected against sunlight and no growth on the exposed portions. 



In 1892 and 1893 Ward^ published a series of articles on the action of light on 

 anthrax bacilli and spores. He believed that the action of light was direct and not due 

 to a secondary action involving oxygen. Ward demonstrated by the use of colored 

 glasses and light filters composed of chemical solutions that the active germicidal rays 

 from the sun were in the blue-violet region of the spectrum. By substituting quartz 

 for the glass plates employed by previous investigators he also showed that the ultra- 

 violet region was active in destroying bacteria and their spores. Ward experimented 

 with the carbon arc as well as with solar rays. 



During the last thirty-five years an extensive literature has accumulated on the 

 action of ultra-violet light on bacteria. It is possible, here, to refer only to the more 

 important contributions and to present a summary of the present state of our 

 knowledge. 



THE ErrECTIVE SPECTRAL REGION 



The results of the earlier workers established this region only in a general way. 

 In 1903 Barnard and Morgan^ attempted to distinguish between light rays which 

 caused a reaction in living tissue and those which were bactericidal. Although not 

 successful in their first objective, they did obtain fairly accurate data on germicidal 

 action. Wave-lengths between 3,287 A and 2,265 ^ were found to be effective. The 

 longer rays appeared to be physiologically active. A number of investigators, notably 

 Thiele and Wolf,^ Bazzoni,'' Newcomer,^ Browning and Russ,^ Cernovodeanu and 

 Henri,'' Bayne- Jones and Van der Lingen," and Coblentz and Fulton," have made 

 similar studies. 



' Roux, E.: Ann. dc I'Insl. Pasteur., 1, 445. 1887. 

 ^ Buchner, H.: Ccnlralbl. f. Bakleriol., 11, 781. 1892; 12, 217. 1892. 



JWard, M. H.: Proc. Roy. Soc.,S2, 2>9i. 1892-93; 53, 23. iS93;54, 472. 1893; Frankland, P. F., 

 and Ward, M. H.: ibid., 53, 177. 1893. 



-i Barnard, J. E., and Morgan, H.: Brit. M.J., 2, 1269. 1903. 

 5 Thiele, H., and Wolf, K.: Arch. f. Ilyg., 57, 29. 1906. 



* Bazzoni, C. B.: Am. J. Pub. Health, 4, 975. 1914. 

 'Newcomer, H. S.: J. E.vpcr. Med., 26, 841. 1917. 



* Browning, C. H., and Russ, S.: Proc. Roy. Soc, 90, 33. 1917. 



' Cernovodeanu, B., and Henri, V.: Cotnpt. rend. Acad, dc Sci., 150, 52. 1910. 



■» Bayne- Jones, S., and Van der Lingen, J. E.: Bidl. Johns Hopkins Hosp., 34, 11. 1923. 



" Coblentz, W. W., and Fulton, H. R. : Scientific Papers of the Bureau of Standards, No. 495. 1924. 



