Mefapoietic InfegrafJons 19 



as some of its mutants, can be adsorbed on the lysogenic 

 bacterium. The genetic material of the infecting phage 

 passes into the bacterium, but it neither enters the vegeta- 

 tive phase nor is converted into prophage. It is not repro- 

 duced. So far as we know, it is not pathogenic. It is diluted 

 at each bacterial division and behaves as an inert proto- 

 plasmic particle. This is immunity. 



If the prophage develops in an immune superinfected 

 lysogenic bacterium, then the genetic material of the super- 

 infecting phage will also enter the vegetative phase. Im- 

 munity, which corresponds to a block in the development 

 of the superinfecting phage, disappears when the prophage, 

 entering the vegetative phase of the cycle, ceases to be a 

 prophage. Immunity is apparently bound to the prophage 

 as such. 



The two fundamental properties of the lysogenic system, 

 the hereditary power to produce bacteriophage and im- 

 munity, are specifically controlled by the specific prophage 

 and may be considered — somewhat arbitrarily perhaps — 

 as representative of its essence. With the study of dysgonia 

 we enter the field of nonspecific effects of the prophage. 



Many cases are known in which the presence of the pro- 

 phage modifies the response of the lysogenic bacterium 

 to "heterologous" phage, that is to say, phages nonsero- 

 logically related to the prophage. The modified response 

 of the lysogenic system may be related to phage develop- 

 ment or to lysogenization. Let us consider P. pyocyanea 

 and phages 4 and 8, which are not related serologically. 

 The nonlysogenic Pseudomonas infected with phage 8 

 gives rise to phage with a probability of one. If a lyso- 

 genic bacterium-perpetuating prophage 4 is infected in- 

 stead, the following results are obtained: 2 to 5 per cent 

 of the infected lysogenic bacteria produce phage 8, 50 to 

 60 per cent die without producing any phage, 40 per cent 

 survive. Thus the response of Pseudomonas to phage 8 

 is modified by the presence of prophage 4. 



