18 Perspecfives in Microbiology 



the phage nor that of the bacterium is responsible for the 

 defectivity. The most likely hypothesis is that defectivity 

 is correlated with an abnormal anchorage of the genetic 

 material of the phage on the bacterial chromosome. De- 

 fectivity is frequently observed in Pseudomonas pyocyanea. 

 Let us infect an apparently homogenous population of 

 bacteria with an apparently homogenous population of 

 bacteriophage and isolate lysogenic clones. The fraction 

 of bacteria able to produce phage varies with the clones 

 from 1 to 10-*. Here also, the defective as well as the 

 normal lysogenics produce the same type of phage. And 

 again, the simplest hypothesis is that normality or defec- 

 tivity is the consequence of the mode of attachment of the 

 genetic material of the phage to the bacterial chromosome. 

 It would, nevertheless, be dangerous to generalize from 

 this hypothetical conclusion. The lysogenic B. megaterium 

 10 [3] is defective. The strains M and Mox, when lyso- 

 genized with phage 3, give rise exclusively to defective 

 strains. Here defectivity is controlled by the genetic con- 

 stitution of the phage. The most general expression of 

 these hypotheses would be that normality and defectivity 

 are controlled by the genetic constitution of the phage as 

 modified in its expression by bacterial genes. Here again, 

 the character normality-defectivity is, in the last analysis, 

 controlled by the genetic constitution of the system as a 

 whole. 



Immunify and Dysgonia 



We have considered so far such properties of the lyso- 

 genic systems as are connected with the development and 

 maturation of bacteriophage from prophage. It is well 

 known, however, that prophage not only confers on the 

 bacterium the power to produce bacteriophage, but also 

 endows it with a specific immunity. The "homologous" 

 phage, the phage corresponding to the prophage, as well 



