348 



F. JACOB AND E. L. WOLLMAN 



included under the name of latent viral infection may correspond to a variety 

 of types of relationships between host and virus, the analysis of which has 

 been made extremely difficult in most cases by the complex nature of the 

 host system and by the limitation of the procedures of titration of the virus. 



EE) 



Productive 

 infectio 





7c^ 







Induction 



Lysogenic b. [ — 1 



BQ 



CEJ 



Vegetative c^^s^=^ 

 phase I'^^^Ci-i^ 



.(E 



Fig. 6. Diagrammatic representation of lysogeny. (After Lwoff, 1953.) 



In view of the fact, however, that phage research itself has been so fruitful 

 a model for the study of animal and plant viruses, it is tempting to think 

 that situations which have been analyzed in the field of bacteriophage will 

 find their counterpart in other fields of virology. More especially, since we 

 know that the prophage may in certain instances modify in a specific way 

 some function of the host, it might be helpful to bring together lysogeny and 

 those cases of tumors where viruses appear to be the responsible agents. It is 

 likely that although many of the cases of latency wiU be finally ascribed to 

 complex interactions between viruses and the different cellular systems 

 present in metazoa, some of them wiU be shown to represent cases compar- 

 able to lysogeny, that is, cases whereby the genetic material of the virus 

 behaves as an integrated structure of the infected cell. Under this definition 

 a provirus, like a prophage, is a noninfectious form of a virus which exists 

 and is perpetuated in stable intracellular association with the structures of 

 the host ceU. Evidence for the existence of a provirus stage therefore will not 

 be obtainable until the relationship between viruses and their hosts at the 

 cellular level is better understood. 



