STAGES IN PHAGE MULTIPLICATION 175 



phage serves both as a lysing agent and as an inhibitor of adsorp- 

 tion but the specificities are difl'erent: T2, T4, and T6 cause 

 lysis fi'om without but only T2 can compete with the adsorption 

 of T2 (Hershey and Chase, 1952). 



The lysing agents mentioned above doubtless act in many dif- 

 ferent ways. Two extremes may be noted. Cyanide promptly 

 stops biosynthesis generally by blocking certain steps in respira- 

 tory metabolism, and lysis ensues shortly. Proflavine does not 

 stop synthesis of phage-specific materials, but blocks some final 

 step in maturation of phage particles (DeMars, 1 955) . Lysis fol- 

 lows only at the end of the normal latent period. 



Cyanide and chloroform are perhaps the most generally useful 

 lysing agents. 



To summarize, premature lysis of infected cells may be induced 

 by various means. During an eclipse period lasting half way 

 through the latent period no intact phage particles can be de- 

 tected within the cell. The noninfective form of the phage be- 

 lieved to multiply in the cells during this time is called" vegeta- 

 tive phage" (Doermann, 1953). Its nature was a mystery until 

 the discoveries of Hershey and Chase (1952) and subsequent 

 work pointing to the identity of vegetative phage and phage-pre- 

 cursor DNA (Chapter XIV). 



5. Phage Multiplication Studied by Irradiation of Infected Bacteria 



The theoretical basis for this method of studying phage multi- 

 plication is quite simple, but as often happens in biological sys- 

 tems the interpretation of the experiments is unexpectedly com- 

 plicated. The inactivation of a suspension of phage particles by 

 ultraviolet light or X-rays is a close approximation to a "one-hit" 

 phenomenon, that is, the surviving fraction is an exponential 

 function of the dose of radiation (Chapter VI). The survival 

 fraction jy equals e~''^ where D is the dose of radiation and the 

 coeflficient k depends on the dosage unit and on the sensitivity 

 of the phage. If a bacterium contains n phage particles and the 

 survival of any one of these is sufficient for survival of the plaque- 



