STAGES IN PHAGE MULTIPLICATION 173 



devised. Several methods for inducing "premature lysis" are 

 described below. 



One method utilizes intense sonic vibration to disrupt the host 

 cell and liberate its contents (Anderson and Doermann, 1952a). 

 This method is limited to phages that are more resistant to sonic 

 vibrations than are their host cells. Phage T3 is suitable for this 

 purpose. The results of a typical experiment are presented in 

 Figure 4. The curve marked "control lysis" is an ordinary one- 

 step growth curve for phage T3 ; the latent period is 20 minutes 

 at 30° C. and the period of lysis covers the next 10 minutes. 

 The curve marked "sonic disruption of cells" gives the number of 

 infective centers found after sonic treatment of the samples. The 

 count of infective centers remains constant at about 10 per cent 

 of the number of infected bacteria until the 12th minute. This 

 count probably represents infected bacteria which were not dis- 

 rupted. The samples taken near the end of the latent period 

 (at 16 and 18 minutes) show a marked rise in phage count due to 

 the premature release of mature phage particles. Sonic treat- 

 ment at 24 minutes or later liberates the normal yield of phage 

 particles. 



A second method of premature lysis developed by Doermann 

 (1952) is based on the phenomenon of "lysis from without" 

 described by Delbruck (1940b). If bacteria are attacked by a 

 very large number of phage particles of the T2 species, they may 

 respond by lysing without liberating phage progeny. The 

 phenomenon is due to damage to the host cell membrane by the 

 phage particles rather than to infection in the usual sense. In 

 some cases, as with phage T2 itself, single infection may confer 

 resistance to lysis from without by a secondary challenge with 

 many T2 particles (Visconti, 1953). 



In the experiments of Anderson and Doermann (1952a), cells 

 infected with T3 were "lysed from without" by exposure to 

 large concentrations of phage T6 (plus cyanide added to "freeze" 

 the metabolism). By using B/6 as the plating bacterium, it is 

 possible to assay T3 without interference from the T6 present. 

 In Figure 4 the curve marked "lysis by KCN plus T6" gives the 



