VIRUSES 



activity somewhat akin to that possessed by certain protein hormones 

 and enzymes. To them, virus activity appeared no less wonderful 

 and possibly no more complicated than the changes that can be induced 

 within cells by enzymes and hormones. The mental barrier of the 

 living state is being eliminated gradually and chemists are recognizing 

 and accepting Nature's gift of the viruses. The true issue is only 

 beclouded by the insistence in some quarters for a decision as to whether 

 a given structure is living or inanimate. The fundamental meaning- 

 lessness of such terms has been commented on before and is becoming 

 ever more apparent. In the meantime, the requirements for the 

 solution of the riddle of virus reproduction — perhaps the most impor- 

 tant problem in all of biochemistry — are becoming clearer. 



Many studies on the nature and mode of virus reproduction are in 

 progress, and it seems certain that such studies will increase in the 

 future, not only in volume, but also in scope and in diversity. It is 

 possible that the solution of this very important and fundamental 

 problem will not be realized until after new weapons of the hand and 

 mind have been brought into play. So far, the most spectacular ad- 

 vances have been made along three lines, each of which merits con- 

 siderable further attention: (a) studies on the very favorable bacterial 

 cell-bacteriophage system; (b) studies on the changing of the chemical 

 structure of a virus by means of known chemical reactions; and (c) 

 studies on the nature of the differences in chemical structure that are 

 responsible for the existence of virus strains. The bacterial cell- 

 bacteriophage system provides an extraordinary opportunity to follow 

 the interaction of a virus with its host cell. The host cells can be 

 grown in vitro on artificial media in large quantities and under constant 

 and reproducible conditions. The metabolism of the host can be con- 

 trolled to a certain extent and analyses can be made on the system 

 throughout the reaction. The bacterial and phage or virus materials 

 can be differentiated up to the entrance of the virus into the cells and 

 following the lysis of the cells. Studies on this system have permitted 

 the conclusion that multiple infection of a bacterial cell with several 

 virus particles of the same type has the same effect, both qualitatively 

 and quantitatively, as infection with a single virus particle. It was 

 also found that infection of a bacterial cell with two kinds of virus 

 particles resulted in the reproduction of only one kind and the sup- 

 pression of growth of the other kind. However, more than one virus 



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