LYSOGENY 



329 



Physical agents, such, as UV light or X-rays, are particularly suitable for 

 determining the dose-effect curves of induction. As shown in Fig. 5, the 

 fraction of induced bacteria first increases with the dose of radiation. It 

 reaches a maximum which varies according to the system under investiga- 

 tion and may be greater than 95 %. Then it decreases at a rate generally 

 controlled by the bacterial "capacity" to reproduce phage, that is, by the 



UV in seconds 



200 300 400 



Fig. 5. Induction curve of lysogenic Pseudommms aeruginosa 13 (8). The fractions of 

 bacteria as colony formers and plaque formers, and of free phages P8 as plaque formers 

 are plotted on a logarithmic scale versus the dose of UV light in seconds. (From Jacob 

 and Wollman, 1953.) 



survival, as a function of dose, of the bacterial ability to support midtiplica- 

 tion of the phage under study (Jacob, 1954; Marcovich, 1956a). Because of 

 their extreme sensitivity to the action of inducing agents, such as ionizing 

 radiations, lysogenic bacteria may be used as a convenient material for the 

 study of the biological effects of smaU doses of these agents (Marcovich, 

 1956b). 



3. Environmental Factors 



In order that exposure of inducible lysogenic bacteria to iuducing agents 



lead to phage production, bacteria must be grown under suitable conditions. 



Before exposure to radiations, the physiological state of the bacterial 



