1126 BIOLOGICAL EFFECTS OF RADIATION 



of yeast and the following bacteria: B. coli, B. prodigiosus, B. pyocyaneus, 

 Micrococcus candicans, Staphylococcus pyogenes aureus, and Vibrio 

 Finkler. The highest sensitivity for five of the organisms occurred at 



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approximately X2650 A, while for B. coli the maximum was at X2510 A, 



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and for B. prodigiosus, X2801 A. For the six bacteria the energy required 

 for 1 to 10 per cent kilhng at X2650 A ranged from 2900 to 5970 erg/cm. ^ 

 (or 29 to 60 erg/mm.^), whereas Gates obtained for Staphylococcus aureus 

 ca. 88 erg/mm. 2 for 50 per cent survival, which is to be contrasted with 

 Wyckoff's (166) values of 110 erg/mm. ^ for Staphylococcus aureus at 2d96 A. 

 The value obtained by Ehrismann and Noethling at 90 to 100 per cent 

 killing for B. coli is 174 erg/mm.^ It is further interesting to note that 

 at X3130 A, Ehrismann and Noethling find that 1 to 10 per cent killing 

 does not occur with an energy value of 3.7 X 10^ erg/cm. 2, while at 

 X3030 A the value for B. coli is 590,000 erg/cm. 2, or 5900 erg/mm. 2 

 This last value may be compared again with the result obtained by 

 Wyckoff at 3132 A where 5200 erg/mm.^ represents energy requirement 

 for 50 per cent killing. 



The experiments of Wyckoff (166) add some quantitative data for 

 B. coli and a few measurements for B. -aertrycke. The survival ratios 

 are presented for wave-lengths 3132, 2900, 2803, 2699, 2652, and 2536 A, 

 and these can be represented by straight lines plotted on semilogarithmic 

 paper. The effective energies are given as those required to kill approxi- 

 mately one-half the bacteria irradiated. The energies involved in 

 bactericidal action were determined for each wave-length. Using the 

 absorption data of Gates, he found the highest efficiency in the ultra- 

 violet at X2652 A. Comparing the results obtained in the ultra-violet 

 with his earlier series on X-rays, later cited, Wyckoff shows that the 

 energy required for killing in the ultra-violet is about 100 times greater 

 than that required for the same killing in the X-ray region. Wyckoff's 

 analysis of the data for X2699 A indicates that of the quanta absorbed, 

 only one in about four million is capable of causing the death of the cell, 

 and this might be supposed to occur within a sensitive volume about the 

 size of a protein molecule (see section of this paper on X-rays). Unfortu- 

 nately, it would seem, the author disregards the importance of effects 

 which do not result in killing. 



The use of ultra-violet radiation for the elimination of bacteria in 

 drinking water has received considerable attention on the part of those 

 concerned with the water supplies of cities, but apparently the adoption 

 of this as a practical procedure has been limited to a few French cities. 

 On the side of the more fundamental studies, as well as on that of the 

 applications, there is an extensive literature ( cf. Schwarz and Aumann, 

 138; Schroeter, 137, and others). More general use has been made of 

 ultra-violet in the partial sterilization of water of swimming pools. 



