EMORY L. ELLIS AND MAX DELBRUCK 383 



SUMMARY 



1. An Sinti-Escherichia coli phage has been isolated and its behavior 

 studied. 



2. A plaque counting method for this phage is described, and shown 

 to give a number of plaques which is proportional to the phage concen- 

 tration. The number of plaques is shown to be independent of agar 

 concentration, temperature of plate incubation, and concentration of 

 the suspension of plating bacteria. 



3. The efliciency of plating, i.e. the probability of plaque formation 

 by a phage particle, depends somewhat on the culture of bacteria 

 used for plating, and averages around 0.4. 



4. Methods are described to avoid the inactivation of phage by 

 substances in the fresh lysates. 



5. The growth of phage can be divided into three periods: adsorp- 

 tion of the phage on the bacterium, growth upon or within the bac- 

 terium (latent period), and the release of the phage (burst). 



6. The rate of adsorption of phage was found to be proportional 

 to the concentration of phage and to the concentration of bacteria. 

 The rate constant ka is 1.2 X IQ-^ cm.Vmin. at 15°C. and 1.9 X IQ-' 

 cm.Vniin. at 25°. 



7. The average latent period varies with the temperature in the 

 same way as the division period of the bacteria. 



8. The latent period before a burst of individual infected bacteria 

 varies under constant conditions between a minimal value and about 

 twice this value. 



9. The average latent period and the average burst size are neither 

 increased nor decreased by a fourfold infection of the bacteria with 

 phage. 



10. The average burst size is independent of the temperature, and 

 is about 60 phage particles per bacterium. 



11. The individual bursts vary in size from a few particles to about 

 200. The same variability is found when the early bursts are mea- 

 sured separately, and when all the bursts are measured at a late time. 



One of us (E. L. E.) wishes to acknowledge a grant in aid from Mrs. 

 Seeley W. Mudd. Acknowledgment is also made of the assistance 

 of Mr. Dean Nichols during the preliminary phases of the work. 



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