1950] 



PHOTOREACTIVATION OF INACTIVATED BACTERIOPHAGES 



341 



PHTR in a given time was calculated from these data, and the reciprocal of this 

 dose (given in arbitrary units) was taken as a measure of the activity of that 

 wave length. In figure 6 the activity of the wave lengths tested is plotted against 

 the wave length. 



The activity of a given light may be underestimated, since it is known that 

 light of the wave lengths used in PHTR may damage the bacteria (Hollaender, 

 1943) or the phages (Wahl and Latarjet, 1947). The killing action of the seven 

 wave lengths on active phage adsorbed on bacteria was therefore determined, 

 and it was found that with the light intensity and the time of illumination used 

 in the PHTR experiments an appreciable killing activity was only evident for 

 wave length 313 m^. To correct for this killing activity, the amount of PHTR 



3 4000 5000 6000 



yVoi'e Lenq-i-h in A 



Figure 6. The action spectrum of PHTR. The activity of each wave length, given in 

 arbitrary units, is plotted against the wave length. Phage T2r was irradiated for 20 seconds 

 with the germicidal lamp, adsorbed on resting bacteria, and illuminated in liquid at 37 C. 



obtained after a given exposure to this light was increased bj^ a factor equal to 

 the decrease in titer of active phage adsorbed on B exposed to the same light 

 for the same length of time in equal experimental conditions. The curve of PHTR 

 as a function of the time of exposure to 313 m/z light, obtained in this way, was 

 almost linear and was used in calculating the activity of the light. 



The activity of the seven wave lengths tested gives only the general shape of 

 the action spectrum. It consists of a band covering the range from about 300 ran 

 on the side of the short wave lengths to about 500 m/x on the side of the long 

 ones, with a maximum around 365 m/x. The greatest photoreactivating activity 

 occurs therefore in the near ultraviolet. 



The action spectrum of PHTR is related to the absorption spectrum of the 



240 



