ANIMAL VIRUSES 499 



these units have a lower RNA content than the mfcctive particles. At the 

 moment, this has only been proved for the incomplete forms of influenza 

 obtauied from allantoic fluid. Further investigations are also needed on the 

 glucose-6-phosphatase observed to be associated with the incomplete forms 

 from fowl plague. 



V. Origin and Function of the Chemical Constituents of Animal 



Viruses 



Considerations concerning the origm and function of the various com- 

 ponents unfortmiately must remain speculative, because of insufficient 

 information. Nevertheless, such a discussion will conclude this chapter in 

 order to suggest and stimulate further experiments. 



The lipids apparently maintain the integrity of the uifective particles and 

 protect them. When they are removed from some myxoviruses with ether, the 

 particles disintegrate and the viral subunits are released. Studies using P^- 

 for labelmg fowl plague virus have brought some insight as to the origin of 

 the lipids (Wecker, 1957). When the tissue cultures are incubated with P^^ 

 prior to infection, the specific activity of the lipid fraction of the new virus 

 particles is significantly higher. It increases with the time of preincubation 

 with constant amounts of the isotope. This increased activity suggests that 

 the cellular phospholipid, as such, is transferred to the virus particle. It is 

 quite likely that this hpid comes from the cell membrane, since ultrahisto- 

 logical studies show that the infective particle of fowl plague virus appears as 

 an unified organized unit only at the cell membrane (Hotz and Schafer, 1955). 



It is possible that the lipid fraction of some incomplete forms has an origin 

 other than that of the infective particles. The hypothesis was advanced that 

 the 'mcomplete forms' of fowl plague are microsomes of the host cells loaded 

 with virus-specific material (Schafer, 1957a). This hypothesis is strengthened 

 by the observation that these incomplete forms and the microsomes of normal 

 cells are morphologically very similar. Further, there is some evidence that 

 these incomplete forms are situated in the cytoplasm (Breitenfeld and 

 Schafer, 1957) and that they contain glucose-6-phosphatase, an enzyme 

 known to be located iu the microsomes. 



The carbohydrates present in the infective particles of myxoviruses seem 

 to be a part of a mucoprotein. The composition of the virus mucoprotein 

 resembles a normal mucoprotein of the host (Ada and Gottschalk, 1956). 

 This fact and the observation that influenza and fowl plague virus always 

 contain a non -removable, normal component have led to the suggestion that 

 the presence of mucoproteins in these virus particles is a necessary conco- 

 mitant of the process by which the myxoviruses mentioned are formed (Ada 

 and Gottschallc, 1956). 



