156 PerspecfJves in Microbiology 



obtained with pneumonia virus of mice (11, 12). It may be 

 recalled that the only means to demonstrate an infective 

 particle is an intact susceptible cell, and that the virus 

 must be free to collide with and remain at the surface of 

 the cell before its presence can be detected. A decisive 

 demonstration that an animal virus particle does or does 

 not enter the cell intact would provide valuable evidence 

 on this problem and give a better indication of the ap- 

 plicability of phage theory to this field. 



This issue is of more than theoretical interest and may 

 affect the usefulness of efforts to control virus diseases 

 through chemical inhibition of virus reproduction. Some 

 important information bearing on this point has been ob- 

 tained with bacteriophages. An acridine compound, pro- 

 flavine, is strikingly effective in inhibiting the reproduc- 

 tion of phage T2 (17, 18). The substance affects late stages 

 in the intracellular reproductive process and prevents the 

 development of new infective particles. Thus it might be 

 thought of as an active antiviral compound with chemo- 

 therapeutic potentialities for infected bacteria. Unfortu- 

 nately, hoAvever, use of this substance provides no advan- 

 tage for the infected host cell, and although the full 

 maturation of new virus particles is inhibited, the bacterial 

 cell dies at the same time as do control infected cells (18). 

 It may be significant that proflavine does not inhibit all of 

 the processes associated with phage reproduction. Both 

 new phage protein and nucleic acid are produced, but 

 they are assembled only into tailless phage heads that are 

 unable to infect other bacteria (13). The action of pro- 

 flavine is not restricted, however, to an effect on the very 

 last stages of the maturation process. There is evidence that 

 neither the new phage protein nor the new phage nucleic 

 acid produced in its presence corresponds precisely with 

 that found in mature phage particles (13). Thus, it appears 

 that although a widespread effect on a number of bio- 

 synthetic processes is induced by the substance, this is not 



