18 BACTERIOPHAGES 



for the influenza group of animal viruses (Hirst, 1948), for 

 phages T2 and T4 (Barrington and KozlofT, 1956; Koch and 

 Weidel, 1956b), and for a Klebsiella phage (Adams and Park, 

 1956). This topic is discussed in Chapter XI. 



4. Multiplication 



Of the basic mechanisms of intracellular phage multiplication 

 very little is known. As usual where knowledge is meagre, 

 hypothesis is rampant. We will not consider hypotheses but 

 merely describe briefly those events that are known to occur dur- 

 ing multiplication of phages related to T2. 



One type of information is obtained from the survival curves of 

 infected bacteria as a function of dosage of ultraviolet or X-ray 

 irradiation (Luria and Latarjet, 1947). The plaque-forming 

 ability of infected bacteria is as susceptible to ultraviolet inac- 

 tivation immediately after adsorption as is that of unadsorbed 

 phage. However, within a few minutes after adsorption the 

 infected bacteria become far more resistant to inactivation than 

 they were earlier. It is probable that this marked increase in re- 

 sistance is correlated with the first replication of the phage nucleic 

 acid in the interior of the host cell. The inactivation curves re- 

 main exponential until nearly half way through the latent period 

 and then rapidly become multiple hit curves. Apparently there 

 are few potential virus particles in the cell for the first half of the 

 latent period, but then the mean number of potential virus 

 particles per infected host cell rapidly increases. During the 

 initial quiescent period the cytological appearance of the infected 

 bacterium changes markedly, the "nuclear bodies" disintegrate, 

 and the chromatin appears to migrate to the cell periphery. 

 About the middle of the latent period the cell begins to fill with 

 granular chromatin (Luria and Human, 1950). 



Chemical studies of infected bacteria during the latent period 

 have also been of interest. Following phage adsorption cell 

 division stops. The synthesis of certain adaptive enzymes is in- 

 hibited but energy metabolism as judged by respiration con- 



