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The Germicidal Action of Ultra-violet Radiation and its 

 Correlation with Selective Absorption. — Addendum. 

 By C. H. Browning, M.D., and Sidney Russ, D.Sc. 

 (Communicated by W. B. Hardy, Sec. R.S. Received November 6, 1917.) 



Our attention has been drawn to the work of Barnard and Morgan,* 

 mention of which was unfortunately omitted from our paper on " The 

 Germicidal Action of Ultra-violet Radiation and its Correlation with 

 Selective Absorption."f 



Our work was suggested by the necessity for a strictly scientific analysis 

 of recent statements regarding (1) the differentiation and isolation of allied 

 organisms on the basis of varying susceptibility to the lethal action of this 

 radiation ; and (2) the possibility of exercising a therapeutic effect in deep- 

 seated infective lesions by exposing the adjacent body surface to a source of 

 the radiation. 



We regret that the above-cited communication was unknown to us at the 

 time, since the authors have investigated the problem of bactericidal action 

 by ultra-violet radiation by a method in general similar to that which we 

 adopted, although their results differ from ours in several respects. Thus, 

 these authors state that, for a number of organisms, the germicidal radiation 

 ranges between wave-lengths 3287 and 2265, but they do not refer to 

 differences in vulnerability among the various organisms. Our own observa- 

 tions showed that the most germicidal region of the ultra-violet spectrum of 

 the tungsten arc lies between wave-lengths 2940 and 2380, and that, with 

 prolonged exposure, the extent to which bactericidal action occurs on either 

 side of these wave-lengths depends upon the particular organism investigated. 

 With regard to selective absorption of the rays, the authors state : " We 

 have been unable to find that any of the radiations contained in the spectrum 

 are penetrative to organic substances such as agar, or dead animal or vegetable 

 tissue. Neither can they penetrate living tissues, but we are continuing 

 experiments in this direction to more exactly determine their action." 

 Although it appears that they had given consideration to this point, the 

 correlation of the germicidal action with the remarkably sharp selective 

 absorption of the lethal radiations exhibited by suspensions of bacteria, 

 solutions of protein, etc., which we have demonstrated, does not seem to have 

 been put to experimental test. 



* ' Roy. Soc. Proc.,' vol. 72, p. 126 (1903). 

 t ' Eoy. Soc. Proc.,' B, vol. 90, p. 33. 



VOL. XC. — B. 



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