INTRODUCTION 1 1 



The intracellular phage in lysogenic bacteria is noninfectious; 

 it is prophage. 



4. Infection of a susceptible bacterial culture by a temperate 

 phage may result in the conversion of a considerable proportion 

 of the bacterial cells to the lysogenic condition, potentially ca- 

 pable of liberating the same kind of phage that was used to infect 

 them. 



5. Lysogenic bacteria can multiply without liberating mature 

 phage and can undergo many cell divisions in the absence of ex- 

 ternal phage without losing the lysogenic propensity. 



6. Lysis of single lysogenic bacterial cells spontaneously or 

 after a characteristic latent period following induction is ac- 

 companied by the release of many mature phage particles. 

 Lysogeny is potentially lethal to the bacterial cell. 



One may define lysogenic bacteria as bacteria in which the 

 capacity to produce bacteriophage is a hereditary property 

 perpetuated without intervention of mature phage particles. 



Lysogenic bacteria are very common in nature and probably 

 constitute the principal reservoir of bacteriophages. Lysogeny 

 resembles in some respects the phenomenon of latency in ani- 

 mal and plant viruses, but work in the latter fields has not pro- 

 gressed to the point that permits one to judge the validity of the 

 analogy. The phenomenon of lysogenesis is intimately related 

 to the problems of bacterial genetics and has already served as a 

 powerful tool in the study of genetic structure and function in 

 certain genera of bacteria. These and other aspects of lysogeny 

 will be discussed in detail in later chapters. 



6. Classification of Phages 



Phages are conveniently described as typhoid phages, staphy- 

 lococcal phages, or coliphages, meaning phages attacking the in- 

 dicated types of bacteria. In addition, phages are known by 

 individual designations, such as lambda, Tl, or P8, which serve 

 to identify the particular phage. These specific symbols usually 

 have no meaning in themselves, except to indicate that the phage 

 eame from a particular collection. The coliphages Tl, T2, 



