INTRODUCTION 



mutations on the part of bacterium and virus evidently can sometimes be 

 repeated over a great many cycles, and is of some economic importance in the 

 acetone fermentation industry. These mutations in bacteriophage have been 

 used as the basis for further genetic studies which have revealed the occurrence 

 of genetic recombination among viruses (as well as in bacteria) (19, 20). Two 

 lines of attack are exemplified in the papers here. One uses patent markers, 

 such as host range and plaque morphology. For the other, recombination among 

 lethal mutations induced by UV is used to explain multiplicity reactivation, 

 or the cooperation of several particles damaged by UV to initiate phage growth, 

 in contrast to the ineffectiveness of individual damaged particles. 



This work has naturally stimulated attempts to show similar phenomena in 

 animal viruses. At present these are represented by reports by Burnet and 

 Lind (37) of probable recombination in the influenza virus, and similar investi- 

 gations are under way in other laboratories. Plant and animal viruses are likely 

 to be more difficult to study from this point of view, chiefly because of technical 

 difficulties in initiating infections with single virus particles (35, 62, 79). 



Genetic study of bacteria and viruses is closely interwoven with the most 

 general problems of their biology; this is not surprising, for the same has hap- 

 pened in other areas of biology. But it is to be hoped that genetics will be re- 

 garded not as a unique or isolated part of bacteriological study, but as an ele- 

 ment of all teaching and research in microbiology. 



