M. DELBRUCK 645 



(b) In the case of B. megatherium 36, sensitive, (Northrop (5)) the same 

 relations hold. 



(c) In the case of B. megatherimn 899, lysogenic, (Northrop (5)), lysis 

 from without does not occur, although the bacteria can adsorb a few phage 

 particles each. Both the phage production capacity and the phage ad- 

 sorption capacity are far smaller than the corresponding value for the same 

 phage acting on the sensitive strain. 



The equation 



Adsorption capacity = maximum yield of phage per bacterium 



was found to hold true both for bacteria in the phase of rapid growth, and 

 for saturated bacterial cultures that had been aerated for 24 hours and 

 consisted only of very small bacteria. 



This equality points to a material connection between the bacterial con- 

 stituents which can adsorb the phage and the new phage formed when it 

 grows. These bacterial constituents we shall call b. It might be assumed 

 that b, which the bacterium constantly produces without the help of phage 

 (and in some cases also secretes), is part of the precursor which under 

 favorable conditions is transformed into phage after combination of the 

 bacterium with a phage particle from without. The complex bP might be 

 the catalyst which in the cell transforms uncombined b into phage. The 

 difference between a sensitive strain and a lysogenic strain would consist 

 in this: in the sensitive strain the reaction 



catalyzed by bP 

 b > phage (in the cell) 



would be faster than the production of b (in the cell). In the lysogenic 

 strain b would be produced faster than it is converted into phage. This 

 permits the bacterium and the phage to grow. 



The extremely interesting but puzzling observations of Burnet and McKie 

 (6) on lysogenesis of different variants of one strain of B. enteriditis Gaertner, 

 and of Burnet and Lush (7) on induction of resistance and lysogenesis by 

 the phage in a strain of Staphylococcus albus may perhaps allow further 

 analysis in the light of these speculations. 



EXPERIMENTAL 



The strains of B. coli and of homologous phage used in this work were obtained from 

 the Pasadena Junior College, through the courtesy of Mr. F. Gardner. They have 

 not been studied before and will be designated as B2 and P2, in distinction to the strains 

 Bi and Pi used last year by Ellis and Delbriick (1). 



Growth curves of B2 in Difco nutrient broth at 37° (by colony counts) are shown in 

 Fig. 1. The maximum division rate is considerably smaller than that of Bi. 



59 



