SYLLABUS lOl 



30 With mutants carrying two genetic markers. Recombina- 

 tion. Linkage. 



31 With unrelated strains. Interference and mutual exclusion. 



32 With related strains. (T2, T4, T6) 



VII. Reactivation Phenomena 



33 Photoreactivation. 



34 Multiplicity reactivation. 



35 VIII. UV Method for Following Early Stages of Intracellular 



Development 

 36 ... . IX. Cytology 

 37. . . .X. Lysogenesis 

 38 ... . XI. Lysis Inhibition 

 39 ... . XII. Lysis from Without 



1. Introduction.— Ax. first sight, the life cycle of a phage particle 

 seems simple. It attaches itself to a bacterium and multiplies inside 

 the bacterium. After a short time, something like 20 minutes, the bac- 

 teriiun bursts and several hundred phage particles are released. In the 

 past, this life cycle has been viewed from the perspective of two dis- 

 tinct analogues: 



( 1 ) The enzyme precursor analogue. The phage particle is looked 

 upon as a complex nucleo-protein molecule. The bacterium is assumed 

 to contain an ample supply of precursor molecules, so similar to the 

 infecting particle that the precursor can be transformed into phage by 

 a relatively simple reaction, analogous to the conversion of trypsinogen 

 into trypsin. 



(2) The intracellular parasite analogue. The phage is looked 

 upon as a micro-organism with exceedingly exacting growth require- 

 ments which can be satisfied only inside living cells. Specifically, one 

 imagines that the phage has lost its entire assimilatory equipment. It 

 therefore utilizes not only nutrients to be found inside the bacterium, 

 but the whole organized enzyme equipment. 



Phage research of the last decade has shown that both of these 

 points of view must be far off the mark. The precursor view is in- 

 compatible with the variety of types that can multiply on one and the 

 same bacterium and it is also incompatible with the fact that most of 

 the substance of the new phage is derived from material assimilated 

 after infection. The intracellular parasite view is contradicted by the 

 genetic recombination data and by the various lines of evidence which 

 point to a far-reaching disintegration of the infecting particle. The 

 infecting particle loses its identity after entering its host. It merges 

 with the bacterial organization and with other phage particles which 



