BIOLOGICAL ORDER 



100 infectious particles. This is most extraordinary. A bacterium 

 lives in harmony with its prophage. The prophage behaves as if it 

 were a normal bacterial gene. And suddenly, as a result of an irradi- 

 ation, the vegetative phase of the bacteriophage is initiated, and the 



i^r i V 



y- 





prophage (p) or corresponding autonomous D.N. A. 

 D.N. A. of homologous superinfecting phage 



Figure 29. Immunity. 



1-3. The lysogenic bacterium is superinfected with a mutant of the homolo- 

 gous phage. The genetic material of the superinfecting phage does not initiate 

 the vegetative phase, does not divide, and is diluted out at each division. One of 

 the daughter bacteria (3) contains only the prophage. 



4-5. The superinfected bacterium is induced, for example, by an irradiation 

 with ultraviolet light. The vegetative phase of both prophages and the super- 

 infecting phage are initiated, and infectious particles of both types will be 

 produced. 



lysogenic bacterium produces bacteriophage and dies. If, previous 

 to the irradiation, the lysogenic bacterium has been infected with 

 a mutant of the homologous phage toward which the bacterium is 

 immune, the mutant will develop together with the prophage. The 

 problem of the control of viral development is thus posed in the 

 most dramatic way. 



[72] 



