THE MUTATED GENE 



61 



curve might also represent the increase in phage if it would be 

 proportional to the bacterial growth, as has been silently 

 assumed in the vestigial case for the production of the decisive 

 stuff. This assumption, which works in case of a growth sub- 

 stance, would not work in the case of production of a lytic sub- 

 stance, as we must account for the different time of onset of 



I 2 3 4 5 



Hours 

 Fig. 21. — Graphic representation of bacterial'growth, phage production and 

 lytic ratios with and without MnCl 2 . Originating in the bacterial growth curve o 



are the curves of bacterial lysis with MnCh ( — ) and without ( ). 



Above are two lines paralleling the logarithmic phase of the growth curve. Both 

 are crossed by a series of steep curves representing phage formation for various 

 initial phage concentrations. The intercepts of these latter lines with the two 

 parallel lines indicate attainment of the lytic phage bacteria ratios requisite for 

 lysis. At corresponding time intervals on the curve for bacterial growth the 

 curves of lytic destruction of bacteria begin. {From Kroeger and West, 1935, 

 J. Gen. Phys. 19.) 



action. In Krueger's diagram, the different times of onset of 

 lytic action and the consequent dropping of the curves for bac- 

 terial growth are visible, and their similarity to the curves for 

 wing growth is obvious. Here we find, in addition, the steep 

 curves for growth of the phage drawn for four different initial 

 concentrations. Their intercept with a line parallel to the growth 

 curve, representing the assumed ratio of quantity phage/ 

 bacterium necessary for lytic action, i- then the lytic threshold. 

 In the vestigial curve, this threshold has been indicated directly, 

 but it might as well be represented as in Krueger's graph. The 



