220 BACTERIOPHAGES 



firmed with P'' '^-labeled phage T4 by Watson and Maal0e 

 (1953). This cause of reduced efficiency of transfer can be elimi- 

 nated by making the adsorption period less than one minute. 



2. Readsorption of progeny phage. If some of the labeled prog- 

 eny phage is lost either by readsorption to yet unlysed bacteria 

 or to bacterial debris, this fraction of the transferred label will be 

 lost from the progeny. This will cause an apparent decrease in 

 the efficiency of transfer of parental materials to progeny phage. 

 This loss of daughter phage was prevented in the experiments of 

 Watson and Maal0e (1953) by treating the infected bacteria 

 with antibacterial serum toward the end of the latent period. 

 Antibacterial serum effectively prevents adsorption of phage to 

 otherwise susceptible bacteria (Delbriick, 1945b). In earlier 

 studies Maal0e and Watson (1951) prevented loss of progeny T2 

 phage by saturating the bacterial receptors with ultraviolet- 

 killed, unlabeled T2 phage. These or similar devices have been 

 used in most subsequent experiments. 



3. Latent period and burst size. In infections with P"'--labeled 

 T4r phage, lysis occurs at the end of the usual latent period with a 

 burst size of about 140 and a transfer of P^^ ^q progeny of 40 to 50 

 per cent (Watson and Maal0e, 1 953). About half of the parental 

 P^2 is liberated into the medium in a nonsedimentable form. A 

 natural question is whether or not some of this wasted P^^ would 

 be converted into mature phage if the infectious process had not 

 been interrupted by lysis. To answer this question Watson 

 and Maal0e (1953) infected bacteria with labeled T4r+ and 

 then produced lysis inhibition by reinfection with unlabeled 

 phage. Although the burst size was increased to 350 the transfer 

 of parental P^^ was still only 50 per cent indicating that essentially 

 no parental P^^ was transferred to phage particles formed after 

 the end of the normal latent period. 



The converse experiment, shortening the latent period by pre- 

 mature lysis, has been done several times. Maal0e and Watson 

 (1951) using P'^--labeled T2/-+ for infection, lysed the infected 

 culture prematurely at 1 1 minutes, before there was one mature 

 phage per cell. With an excess of ultraviolet-inactivated T2 



