Tlie Germicidal Action of Ultra-Violet Radiation. 33 



REFERENCES. 



1. Chambers and Russ, ' Roy. Soc. Proc.,' B, vol. 86 (1913). 



2. Da Fano, ' Imp. Cancer Research Fund, 5th Report,' p. 57. 



3. Brancati, 'Tumori,' Anno II, fasc. 1, p. 74. 



4. Apolant, 'Zeits. f. Immunitats Forschung,' Originale 17, p. 219 (1913). 



5. Murphy and Morton, 'Journal Exp. Medicine,' vol. 22, p. 204 (1915). 



6. Murphy, ' Journal Exp. Medicine,' vol. 19, p. 181 (1914). 



7. Russell, ' Imp. Cancer Research Fund, 3rd Report,' p. 341. 



8. Aubertin and Beaujard, ' Arch, de Med. Experimentale et d' Anatomic Pathologique,' 



vol. 20, p. 273 (1908). 



The Germicidal Action of Ultra-Violet Radiation, and its 

 Correlation with Selective Absorption. 



By C. H. Bkowning, M.D., D.P.H., Director of the Bland-Sutton Institute 

 of Pathology, Middlesex Hospital, and Sidney Euss, D.Sc, Physicist 

 to the Middlesex Hospital. 



(Communicated by Prof. A. W. Porter, F.R.S. Received February 27, 1917.) 



[Plate 3.] 



A new method is here described which enables vis to say definitely what 

 portion of the ultra-violet spectrum is especially effective in germicidal 

 action and the wave-length of the radiation at which such action practically 

 ceases. Briefly the method consists of inoculating a gelatine* plate with 

 micro-organisms instead of sensitising it with a silver salt. We find that 

 when a spectrum is formed on this it produces what may be called an 

 image, where germicidal action occurs, and this image may be rendered 

 visible by a process of incubation, which encourages a copious growth of 

 those organisms which have not been affected by the radiation, whereas the 

 affected parts remain practically transparent. Such an exposed and 

 incubated plate can be used as an ordinary negative for producing positive 

 contact prints or, equally well, may be photographed by light reflected and 

 scattered from the bacterial surface. 



The study of the action of radiation, visible and otherwise, upon micro- 

 organisms is not a new one. The period 1894-6, associated with the work 



* For convenience, an agar plate was used in most of the experiments. 

 VOL. XG. — B. D 



