BIOLOGICAL ORDER 



bacteriophage particles. The so-called "lytic cycle" of the bacterio- 

 phage has been completed. Some bacteriophages, called viriile?it 

 phages, are multiplied only by the lytic cycle. Others, called 

 temperate phages, may evolve in two directions. 



/ 



c= bacterial chromosome r = receptor 

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



Figure 27. The Fate of an Infected Nonlysogenic Bacterium. 



1 and 2. The genetic material of the phage reaches the specific receptor 

 site (r) of the bacterial chromosome and becomes the prophage (p). The 

 bacterium is lysogenic. 



3 and 4. The vegetative phase is started, and infectious particles are produced. 



The temperate bacteriophage; lysogeny. After a bacterium has 

 been infected with a temperate phage, the vegetative phase may be 

 started, which culminates in the production of infectious particles 

 and bacterial death. Sometimes, however, the vegetative phase is not 

 started, and the bacterium survives. 



The survivors multiply normally (Figure 27). But they are now 

 endowed with a remarkable property. Each surviving bacterium 



[68] 



