MefapoJefic I nf eg rations 17 



systems were obtained. In so far as inducibility is con- 

 cerned, therefore, the phages produced by the lysogenic 

 noninducible strains 91 B give rise to inducible systems 

 in the appropriate bacterial strains M and Mox. 



Among the phages of B. megaterium is phage 3, which 

 is inducible in the original strain B. megaterium 10[3], 

 as well as in the lysogenized strains M and Mox. Moreover, 

 strain 91B[3] is also inducible. Thus, the development of 

 phages 1 and 3 is inducible in the lysogenic systems M 

 and Mox, whereas in the lysogenic 9 IB, only the develop- 

 ment of phage 3 is inducible. 



Inducibility is apparently a genetic property of neither 

 the phage nor the bacterium but a property of the lyso- 

 genic system as a whole. We have no right to speak of 

 inducible or noninducible prophage. It is the lysogenic 

 system which is or is not inducible, and inducibility is 

 obviously the result of the interaction of the genetic ma- 

 terial of the phage and of the bacterium. 



Defecfive Strains 



In a "normal" inducible lysogenic strain, virtually all 

 the bacteria will produce phage after irradiation with an 

 adequate dose of ultraviolet light. In a "defective" strain, 

 only a small fraction of the bacteria — of the order of lO""^ 

 — will produce phage after irradiation, despite the fact 

 that phage development has been initiated by the inducing 

 agent. All bacteria, nevertheless, die as a consequence of 

 an abortive development of phage. 



The defective lysogenic B. megaterium 91 [1+] may 

 loose its prophage. The nonlysogenic strains thus obtained, 

 when lysogenized, prove to be normal. Moreover, the phage 

 produced by the original defective 91 [1+], when infecting 

 a nonlysogenic bacterium, gives rise to normal lysogenic 

 systems. 



It seems as though neither the genetic constitution of 



