CHEMISTRY AND VIRAL GROWTH 



of maturation. The fact that nearly all the DNA in infected 

 cells, excepting that contained in resting phage particles, is 

 sensitive to deoxyribonuclease may be significant in this con- 

 nection. It is perhaps not quite established that the DNA-less 

 structures are intermediates at all. In view of these uncertain- 

 ties, little more can be said about them at present. 



The time course of maturation is linear, beginning about 10 

 minutes after infection and continuing until the cells burst. 

 During this time vegetative phage probably continues to multi- 

 ply, as indicated by progressive increase in proportion of re- 

 combinants (41), and continued synthesis of viral protein and 

 DNA (46,58). 



Since maturation is irreversible (22), there is no need to dis- 

 tinguish between mature intracellular virus and resting extra- 

 cellular virus. The individual particles probably play a passive 

 role, if any, in the release of virus from the cell. 



The Priming Substance 



We have seen that the interesting period in the life of a phage 

 particle begins when its charge of DNA enters a sensitive bacterial 

 cell to form vegetative phage. It is a question of considerable 

 ideological importance (64) whether this charge is exclusively 

 DNA or contains protein as well. Agreement about it has 

 not yet been reached at the level of experimental fact (62) and, 

 what is worse, it is doubtful whether direct analytical methods 

 can answer it satisfactorily (23). I wish to make the point that 

 the main biological implications of the injection phenomenon are 

 largely independent of this specific question. Let us assume al- 

 most the worst, namely, that the charge that enters the cell con- 

 sists of nucleoprotein fibers and that these, furthermore, are 

 functionless until they have made specific attachments to compli- 

 cated structures in the bacterium. What remains of our repro- 

 ductive cycle that is biologically unique? 



In my opinion three very important features. First, these 

 hypothetical fibers would have to carry all the intelligence that 



