14 LURIA 



How far results of phage research can throw light specifically on 

 the events of other virus infections, we do not know. Virus-host re- 

 lationship may include systems so different that the only similarities 

 to be postulated a priori are those implied in our definition of "virus." 

 Nevertheless, the picture of reproduction emerging from phage research 

 is likely to bear instructive similarities to other virus infections. Dis- 

 appearance of recoverable virus activity following infection of a host 

 cell is of general occurrence. Disruption of the genetic apparatus of 

 the host is certainly not general, since cells infected by any one of 

 several plant or animal viruses can still grow and divide. Changes in 

 the synthetic pattern of virus infected animal cells similar to those of 

 phage infected bacteria, however, have been recognized (19). 



Influenza virus in the chorioallantoic membrane of the chick em- 

 bryo behaves very much like bacteriophage in a culture of a susceptible 

 bacterium, with discrete cycles of intracellular growth and liberation, 

 mutual exclusion in cells infected by two virus strains, and other simi- 

 larities (13); a genetic analysis of this situation would be very desir- 

 able. As virus reproduction is apparently more on a level with the re- 

 production of the genetic material of other cells than with the reproduc- 

 tion of the whole cell itself, it does not seem rash to assume that in all 

 virus infections the material carrying virus activity will be found to 

 be differently organized in its intracellular, replicating, "dynamic" 

 state than in the extracellular, "static" condition. This makes it un- 

 likely that even the most careful and painstaking work on the physical 

 properties of extracellular virus particles (22, 32), although very inter- 

 esting from other points of view, can throw much light on the funda- 

 mental problem of virology: virus reproduction. The limitation appears 

 to be an operational one — the alteration, upon infection, of the very 

 properties that the physicochemist analyzes. 



In contrast, the limitation of chemical studies on virus-infected 

 cells is merely a technological one — the inadequacy of present day 

 organic chemistry to deal with the level of organization at which bio- 

 logical specificities are encountered. A sharp refinement of the chemical 

 tool is available, however — immunochemistry. Viruses are good anti- 

 gens and are in general completely distinct serologically from the un- 

 infected host cells. Can virus specificity be traced serologically during 

 virus reproduction, even in the absence of demonstrable virus activity, 

 to reveal to us the "intermediates" of virus synthesis? The beautiful 

 work of Hoyle (18) and Henle (14) on the complement-fixing antigens 

 in the various phases of influenza virus infection shows that these anti- 

 gens, which carry virus specificity without virus activity, increase in 

 amount before virus activity appears. Similar methods now being ap- 



