M. DELBRUCK 



659 



curve and the experimental values is the amount of phage lost by adsorption. 

 The data show that about one hundred phage are lost per bacterium. It is 

 clear that this loss depends entirely on the rate of adsorption, which is 

 determined by the product kBo. If we wish to increase the yield per bac- 

 terium we have to decrease either Bo or k. Reduction of Bo brings us to 

 the condition employed in the one step growth curves. Here the maxi- 

 mum yield of phage growth per bacterium is obtained, but the actual con- 

 centrations of phage are of course very small. 



A promising way of increasing the end titre of phage would be to reduce 

 k, the adsorption rate constant. The very interesting experiments of 

 Krueger and his coworkers (8, 9) on the influence of the addition of salts 

 (NaCl and Na2S04) to a growth mixture of phage and bacteria would seem 

 to be completely in accord with the assumption that the adsorption rate 

 constant is diminished in the presence of salt. 



In fact, a diminished adsorption rate constant should manifest itself in 

 several ways in a phage growth curve, in which one starts with low concen- 

 trations of both phage and bacteria. Namely 



1. Delayed clearing, due to delayed adsorption, and therefore delayed 

 phage growth. 



2. Higher maximum concentration of bacteria, due to delayed lysis. 



3. Higher end titre of phage, due to 



(a) higher number of bacteria producing phage 



(b) reduced loss of phage by multiple adsorption. 



4. Higher ratio of free to bound phage during the stationary growth 

 phase, due to the fact, that every phage particle spends a longer time in the 

 free state between liberation and adsorption. 



5. A period of constant bacterial concentration preceding lysis, when all 

 bacteria are infected and cease to divide but when the phage concentration 

 is not yet sufficient for lysis. 



Precisely these five differences from the normal course and no others were 

 noted by Krueger and Strietmann (9) in their study of the influence of the 

 addition of Na2S04. 



SUMMARY 



1. A new strain of B. coli and of phage active against it is described, and 

 the relation between phage growth and lysis has been studied. It has been 

 found that the phage can lyse these bacteria in two distinct ways, which 

 have been designated lysis from within and lysis from without. 



2. Lysis from within is caused by infection of a bacterium by a single 

 phage particle and multiplication of this particle up to a threshold value. 



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