EFFECTS OF RADIATION ON BACTERIA 1123 



Thiele and Wolf (148) used cooled bouillon suspensions of several 

 species of bacteria for irradiation, and they also stirred the suspension 

 during irradiation. None of the organisms tested was resistant to 

 ultra-violet below 3000 A. Newcomer (108), using a fresh-water suspen- 

 sion of the typhoid bacillus and working under conditions essentially 

 quantitative, found practically zero efficiency of radiation at 2970 A, 

 while the maximum effect occurred at X2800 to 2100 A. Henri and 

 Moycho (74) found the most effective region for bactericidal action to 



o 



be around 2800 A, and they indicated the amount of energy required 

 to kill at 0.002 X 10^ erg/cm^. Irradiation for even 10 hr. at 3300 A 

 produced no effect. General confirmation of the restricted effective 

 region may be seen in the work of Eidinow (46, 47) and many others. 

 In order to obviate the possibility that the irradiation of the organic 

 medium might indirectly affect the results, Newcomer (108) used fresh- 

 water suspensions of typhoid bacilli in capillary quartz tubes held in the 

 spectrum of a quartz spectrograph. With sparks of several metals as 

 sources of radiation, no killing was obtained for wave-lengths longer than 

 3000 A. 



Improving somewhat upon an earlier (Ward, 155) method of deter- 

 mining lethal effects by throwing the spectrum of the source on an agar 

 plate sown to bacteria. Browning and Russ (19) exposed the agar plate 

 painted with bacteria (following Bang, 8) in a holder in a quartz spectro- 

 graph. No attempt was made to determine intensities. Clear lines, 

 coinciding with the emission lines, were found on the plate between 

 X2940 ^and 2380 A. Accordingly, they placed the effective region below 

 3000 A. Independent work along similar lines was done by Mashimo 

 (100), who used the spectrum of the iron spark and tested the response 

 of seven species of bacteria. He also made no intensity measurements, 

 and, accordingly, the data reflect both the intensity distribution of the 

 source and the sensitivity to wave-length. The data are, however, 

 consistent in showing the effective wave-lengths as beginning at about 

 2950 A and extending, in some cases, toward the beginning of atmospheric 

 absorption, i.e., somewhat below 1900 A. There was high efficiency in 

 the general region ca. 2300 to 2750 A. 



Mme. Henri (73), working with a filter system, reported that ultra- 

 violet efficiency increases down to 2144 A, and as a result of further work 

 it was concluded that the abiotic action is continually augmented as wave- 

 length diminishes. 



Careful work on wave-length limits for lethal action was done by 

 Bayne-Jones and Van der Lingen (10), who worked with Staphylococcus 

 aureus, S. albus, and B. coli. The bacteria were distributed on the 

 surface of agar spread upon glass plates fitting the plate holder of a 

 Hilger spectrograph, and thus exposed to the spectrum. Spark sources 

 of radiation with various metals as terminals were employed, and, accord- 



