1952] 



ULTRAVIOLET LIGHT INDEX IN BACTERIOPHAGE 



67 



double target. However, the fit may be fortuitous, since slight inhomogeneities 

 in the stage of development are to be expected. At the time of maximum resis- 

 tance, those complexes which are either slightly ahead or behind in stage of de- 

 velopment have lower resistances, causing a distortion of the true curve at the 

 moment of maximum resistance. Thereafter, the curve retains a multiple-target 

 shape, but the resistance of the individual targets, as judged by the final slope, 

 decreases progressively as the end of the latent period is approached. 



I 9-^ 

 0.9- ~ 

 0.8- 

 07- 



O.Gr 

 0.6 



0.4 

 03 



0.2 



o 0.1 

 ,0.09 

 <0.08 

 >0.07 

 >0.06 



i>^0.05 

 0.04 



0.03 



theoreticol ^ 

 curve 



600 800 1000 

 IN SECONDS 



200 400 



UV DOSE 



Figure 6. Circles: Survival data obtained for T2r complexes irradiated at the phase of 

 highest resistance to ultraviolet (i = 10 minutes). 



Dashed curve: Theoretical survival curve for a double-target complex. 



The late curves have slight "tails" which may be due to a small fraction of 

 cells in which the development is retarded. 



In some experiments, peculiar composite survival curves were obtained as though the 

 development in about half the cells was arrested at a stage corresponding to around 8 

 minutes, while the remaining cells continued normally. It has not been found possible to 

 clarify the conditions leading to this result. 



According to Doermann's findings, there may be a few infective phage particles 

 per cell at the latest time here studied (15 minutes). These would presumably 

 have the resistance of free phages. If survival as an infective center depends 

 upon survival of either the complex or at least one completed phage, the effect 



306 



