302 BACTERIOPHAGES 



TABLE XVII 



Role of L-Tryptophan and Indole in Adsorption of Different Phages 



"Delbruck(1948). 



'' Hershey and Davidson (1951). 



^Anderson (1948b). 



subculture at high bacterial concentrations, recovering the 

 phage after each passage by centrifuging out unlysed bacteria. 

 The procedure is interesting because it suggests a manner in 

 which slowly adsorbing phages might be maintained under 

 ordinary conditions of artificial culture, even though mutations 

 to rapid adsorption were occurring. The variant obtained by 

 Burnet and Freeman differed froin the parental stock as follows : 

 slower adsorption, decreased sensitivity to inactivation by bac- 

 terial extracts, greatly increased sensitivity to heat, slightly 

 increased rate of inactivation by antiserum, and larger size of 

 plaques. All of these changes, as in h mutants, could reflect a 

 single alteration of the tail protein of the phage particle. 



Some results of Schlesinger (1932b) suggested a similar type of 

 variation in coliphage WLL, and a slowly adsorbing mutant of a 

 pyocyanea phage was described by Jacob and Wollman (1953). 



d. Mulatioiu Affecting Lysis-Inhibilion 



Phages related to T2 exist in two forms, subject to lysis- 

 inhibition or not (Hershey, 1946a, b). Lysis-inhibition is pro- 

 duced in infected cultures when the concentration of infected 

 bacteria is high enough to cause continuous reinfection during the 

 latent period (not by multiple infection, as is sometimes stated) 

 (Doermann, 1948a). The effect is a greatly extended latent 

 period in most of the cells, and a greatly increased yield of 



