150 ALICK ISAACS 



Beale and Finter (1956) studied the ability of preparations of incomplete 

 virus to produce soluble antigen in the chorioallantoic membrane after 

 inoculation into the allantoic cavity. They measured the appearance of 

 soluble antigen 6 hours after inoculation and compared the amount found with 

 that produced by corresponding amounts of standard virus when similarly 

 inoculated. It was found that preparations of incomplete virus produced much 

 more soluble antigen in this test than would have been expected on the basis 

 of their infectivity, although less was produced than by the same number of 

 standard virus particles (assessed by the hemagglutinin titer). In these 

 respects the findings are strictly analogous to those of Burnet et al. (1954) on 

 the production of viral hemagglutinin by incomplete virus. Furthermore, as a 

 parallel to the findings of Paucker and Henle (1955b) on the production of 

 hemagglutinin by virus inactivated at 37°C, Isaacs and Fulton (1953) found 

 that virus inactivated by heating at 56°C. for 8 minutes produced signifi- 

 cantly more soluble antigen when grown on the chick chorion than would have 

 been expected from the infectivity of the inoculum. Beale (1954) has also 

 found that the virus present in the chorioallantoic membrane 4| hours after 

 inoculating a large dose of influenza virus has a low I /HA ratio, and that 

 this, too, when examined by the 6-hour soluble antigen test, produces more 

 soluble antigen than would be expected on the basis of its infectivity. 

 Presumably, this is another manifestation of the behavior of incomplete 

 virus, in this case present in the chorioallantoic cells 4| hours after inoculation 

 and before being liberated. However, a precursor to fully infective virus 

 might be present in such membrane extracts and it would be interesting to 

 test the behavior of the "S" hemagglutinin in experiments of this kind. 



Incomplete influenza virus is not wholly noninfective, therefore, but is 

 capable of initiating a partial cycle of virus multiplication, though not a 

 complete cycle. In addition, virus which has been inactivated by heating at 

 37°C, or 56°C. for a short period, behaves in a way which is superficially 

 similar to incomplete virus in this respect. It appears that virus which lacks 

 its normal complement of nucleic acid, although unable to complete the 

 virus multiplication cycle, may nevertheless initiate the synthesis of some 

 viral constituents. 



D. Incomplete Viruses Other Than Influenza 



Although the formation of incomplete viruses is an important phenomenon 

 to understand in itself and also because of the light it throws on virus multi- 

 plication processes in general, almost all the work on the subject has had to 

 be carried out with influenza viruses. Even such closely related viruses as 

 NDV and fowl plague apparently do not give rise to incomplete virus when 

 passaged by similar techniques to those used by von Magnus for influenza, 



