1950] 



PHOTOREACTIVATION OF INACTIVATED BACTERIOPHAGES 



337 



merits showed that resting bacteria that have adsorbed active phage do not 

 Uberate any phage in this time interval. The active fraction always increased 

 with the time of illumination, the increase becoming less and less with increasing 

 time, so that a maximum was reached as is shown in figure 3. The time at which 

 the maximum was reached depended on the light intensity, a longer time being 

 required when the intensity was lower; when the light intensity was varied in 

 such a way that the maximum was reached in a period between 20 and 140 

 minutes, approximately the same maximum was reached in all cases, as is shown 

 in figure 3. 



6 y 10 



5 xlO' 



.-2 



n r 



"I I I r 



ZO 30 40 50 60 70 80 90 



Exposure to fhe Reaciivafin^ Ligh-h (minufes) 



Figure 3. The fraction of active particles as a function of the time of illumination and of 

 the light intensity. The active fraction is plotted against the time of illumination (in 

 minutes). Phage T2r was irradiated for 20 seconds with the germicidal lamp, adsorbed 

 on resting bacteria, and illuminated in liquid at 37 C. Curve 1 was obtained with a light 

 of intensity 10 (in arbitrary units), curve 2 with a light of intensity 2.9, and curve 3 with 

 a light of intensity 0.6. 



The amount of PHTR (defined in previous section) observed in a sample of 

 UVP after a given time of illumination (pit)), divided by the amount of PHTR 

 obtained in the same sample when PHTR has reached the maximum value (p 

 (qo)), will be indicated at the "relative amount of PHTR"; it can vary between 

 zero and one. 



By subtracting the relative amount of PHTR from unity, one obtains the 

 fraction of photoreactivable particles that are still inactive after a time, t, of 



illumination ( = 1 — — - — : 1 . The logarithm of this quantity plotted against 



the time of illumination always gave a straight line for different intensities of 



236 



