158 Perspectives in Microbiology 



one of the major premises on which the current theory of 

 phage reproduction is erected. 



The chemical composition of animal viruses has not yet 

 been adequately established, partly because of difficulties 

 in purification. It is too early to conclude that such viruses 

 are composed wholly of protein and nucleic acid or that 

 their nucleic acids are of the desoxypentose type, as in the 

 case with phage (9). Recent studies with the electron micro- 

 scope on ultra-thin sections of infected cells raise the pos- 

 sibility that even relatively small viruses, such as influenza 

 and herpes simplex, may have surface membranes and a 

 central morphological structure analogous to a nucleus 

 (33). Moreover, animal viruses do not usually cause death 

 and lysis of the host cells they infect in nature. Their re- 

 production is followed by a trickle or leakage of new virus 

 particles (7, 14), not by the lysis and bursting that typically 

 result from the reproduction of phage in a bacterial cell. 

 In a number of instances, as with mumps virus in the chick 

 embryo, extensive multiplication does not result in any 

 demonstrable host cell abnormality. Thus, whatever the 

 mechanism of animal virus reproduction may be, it seems 

 apparent that the effects of the process on the host cell are 

 generally very different from those caused by phage multi- 

 plication. 



InhibJfion of Infracellular Reproducfion 



Can these dissimilarities be turned to account and lead 

 to effective means for the control of diseases induced by 

 animal viruses? Before this question can be answered, a 

 number of related problems probably will need more study. 

 It is clear now that it is possible to inhibit the intracellular 

 reproduction of certain animal viruses through application 

 of some chemical substances (27). Compounds of high 

 molecular weight and uncertain structure, like polysac- 

 charides derived from the capsules of Klebsiella pneu- 



