EMORY L. ELLIS AND MAX DELBRUCK 373 



in which ^a was found to be 1.2 X lO-^cm.Vmin. at 15° and 1.9 X 10 "^ 

 cm.Vmin. at 25°C. These rate constants are about five times greater 

 than those reported by Krueger (10). With our ordinary 18 hour 

 bacteria cultures (containing 2 X 10^ B. coli/cc.) we thus obtain 70 

 per cent attachment of phage in 3 minutes and 98 per cent in 10 

 minutes. The adsorption follows the equation accurately until more 

 than 90 per cent attachment has been accomplished, and then slows 

 down somewhat, indicating either that not all the phage particles 

 have the same afiinity for the bacteria, or that equilibrium is being 

 approached. Other experiments not recorded here suggest that, if an 

 equilibrium exists, it lies too far in favor of adsorption to be readily 

 detected. This equation expresses the rate of adsorption even when a 

 tenfold excess of phage over bacteria is present, indicating that a 

 single bacterium can accommodate a large number of phage particles 

 on its surface, as found by several previous workers (5, 10). 



Krueger (10) found a true equilibrium between free and adsorbed 

 phage. The absence of a detectable desorption in our case may result 

 from the fixation of adsorbed phage by growth processes, since our 

 conditions permitted growth, whereas Krueger's experiments were 

 conducted at a temperature at which the phage could not grow. 



Growth of Phage 



Following adsorption of the phage particle on a susceptible bac- 

 terium, multiplication occurs, though this is not apparent as an in- 

 crease in the number of plaques until the bacterium releases the 

 resulting colony of phage particles into the solution. Because the 

 adsorption under proper conditions is so rapid and complete (as shown 

 above) experiments could be devised in which only the influence of the 

 processes following adsorption could be observed. 



The details of these experiments were as follows: 0.1 cc. of a phage 

 suspension of appropriate concentration was added to 0.9 cc. of an 18 

 hour broth bacterial culture, containing about 2 X 10^ B. coli / cc. 

 After standing for a few minutes, 70 to 90 per cent of the phage was 

 attached to the bacteria. At this time, the mixture was diluted 50- 

 fold in broth (previously adjusted to the required temperature) and 

 incubated. Samples were removed at regular intervals, and the 

 concentration of infective centers determined. 



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