ADSORPTION OF PHAGE TO HOST CELL 141 



and Wollman (1952). These results seem to show that a large 

 fraction of the collisions between phage and bacterium lead to 

 successful attachment. Tolmach (1957) and Hershey (1957) 

 question this interpretation, and we conclude here only that 

 adsorption-rate constants in the range 10"^ to 10~^ per minute 

 can be expected under optimal conditions. The optimal condi- 

 tions depend on size and condition of the bacterial cells (Del- 

 briick, 1940a; Hershey and Davidson, 1951), and numerous 

 environmental factors to be discussed below. 



2. The Ionic Environment 



Many reports in the early literature of the effect of salts on 

 phage lysis have been summarized by d'Herelle (1926) and by 

 Sertic (1937). For example, da Costa Cruz (1923) reported that 

 bacteria grown in salt-free Witte's peptone were not lysed by 

 phage, but that the addition of sodium chloride or calcium chlo- 

 ride resulted in lysis. Lisbonne and Carrere (1923) confirmed 

 this salt effect with three different phages. The addition of 

 sugars had no effect. These authors demonstrated that the effect 

 of the electrolytes was on the adsorption of phage to host cell ; if 

 phage and bacteria were mixed in salt-free peptone, they could 

 be readily separated by centrifugation. In the presence of salts, 

 the phage speedily became attached to the bacteria and could 

 not be separated by centrifugation. 



An interesting paper by Hershey, Kalmanson, and Bronfen- 

 brenner (1944) gave a preview of later developments in this field. 

 These authors found that the relative efficiency of plating (EOP) 

 of phage T2 varies markedly with the concentration of electro- 

 lyte added to the agar medium. The EOP is 0.001 or less in the 

 absence of added electrolyte, 0.1 in 0.03 M sodium ion, and 1.0 

 in 0.2 M sodium ion. Similar results were obtained with potas- 

 sium, lithium, and ammonium ions. Divalent cations were not 

 tested at comparable concentrations. The EOP was inde- 

 pendent of the nature of the anions present. 



In an attempt to determine whether the cation effect was on 

 adsorption, phage adsorption was studied with and without 



