1950] 



PHOTOKEACTIVATIOX OF IXACTIVATED BACTERIOPHAGES 



343 



law one should obtain a straight line with slope 4 (see Oster, 1948, 323, formula 

 6). As shown in figure 8A, the curve, obtained from the same data used for figure 

 7A, is a straight line in the range of wave lengths 320 to 450 m^t; the slope of 

 the curve is 3.7, instead of 4, owing to the size of the phage particles, which is 

 larger than required for the strict application of Rayleigh's law (La Mer, 1948). 

 The pigment might be formed in the phage after UV irradiation. To check 

 this point a suspension of purified phage T2 containing 2.3 X 10'^ particles per ml 

 was irradiated in an open shallow container with the germicidal lamp at a dis- 

 tance of 12 inches for variable lengths of time up to 4 hours, and the absorption 



1800 





/400 



loo X 



Figure 8. The logarithm of the optical density, D, of purified phage T2 versus the lo- 

 garithm of the wave length for the range 320 to 450 mju. A. Active phage (the same data as 

 in figure 7 A). B. Phage after long UV irradiation (same data as in figure IB). Dashed line 

 shows the curve expected for pure scattering. 



spectrum was determined at regular intervals. The absorption spectrum was 

 found to undergo complex changes as the irradiation proceeded; we shall limit 

 our attention to the modifications occurring in the range of wave lengths longer 

 than 320 m^u. A general decrease in absorption in this region was observed, and 

 after about one hour of irradiation a faint band was noticed, which became more 

 evident during the next hour (figure 7B). This band has maximum absorption 

 around 330 m/i and extends to about 380 m/x on the side of longer wave lengths 

 (figure 85) ; its limit on the side of shorter wave lengths cannot be determined 

 because of overlapping with the general phage absorption. 



242 



