1952] 



ULTRAVIOLET LIGHT INDEX IN BACTERIOPHAGE 



69 



To illustrate the effect of such a wide distribution upon our survival curves, a 

 composite curve is plotted in figure 8, assuming a population consisting of equal 

 numbers of cells having the various multiplicities in figure 1. By extrapolation 

 to zero dose of the asymptotic slope of such a curve, it is possible, in principle, 

 to determine the average multiplicity. However, this requires precise data at 

 low survival values and cannot be done accurately with the points in figure 7. 



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 DOSE 



Figure 8. Theoretical survival curves for complexes containing various numbers 



of targets (as in figure 1). 



Theoretical survival curve for a mixed population of complexes. The mixture is 



assumed to contain equal proportions of complexes having multiplicities 1, 2, 5, 10, 20, 50, 

 and 100. 



Note: It is possible, by assumption of a suitable population containing a very wide dis- 

 tribution of multiplicities, to obtain a composite theoretical survival curve which is expo- 

 nential, simulating a "one-hit" curve (Dulbecco, personal communication). 



DISCUSSION 



The original intent of Luria and Latarjet's experiment, namely to observe 

 the increase in the number of intracellular phage particles during the latent 

 period, has been achieved with T7. The pattern of growth, so far as radiation 

 resistance is concerned, does not exhibit the anomalies of (T2 and) T2r. There 

 appears to be simply an increase with time of the average number of targets 

 per cell, each target being similar radiologically to a T7 particle. 



This result shows that irradiation of intracellular phage, in the case of T7, 



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