ANIMAL VIRUSES 483 



In both cases the infective particles are spherical, with an average dia- 

 meter of '^TO mn for fowl plague (Schafer et al., 1952), and '-^SO m/x for 

 influenza virus (Williams, 1953). The particle weight of the fowl plague 

 virus is 150 X 10*^ (Schafer et al., 1952) and for type A of influenza virus, the 

 type chemically analyzed in most detail, about 280 X 10^ (see Schramm, 

 1954a). 



The infective particles of both viruses contain at least two typcB of submiits 

 (Hoyle, 1952; Hoyle et al, 1953; Schafer and Zillig, 1954; Schafer, 1957b). 

 One of these is the hemagglutinin and the other the internal S antigen or 

 "gebundcnes" (G) antigen. In order to avoid confusion with free hemagglu- 

 tinins and the external S antigens the two subunits of the infective particles 

 wiU be designated as virus-hemagglutinin and G antigen in the following 

 discussion. Virus-hemagglutinin and G antigen may be obtained by treating 

 the virus particles with ether. They are not infectious, either separated or 

 in a mixture. 



The virus-hemagglutinin has a diameter of 30 m^, as determined for the 

 fowl plague virus. It is able to agglutinate red cells and corresponds serologi- 

 cally to the superficial virus antigen (V antigen) of the infective particles. 

 The G antigen is isolated from the fowl plague virus in chauilike arrays, with 

 individual spherical components, each having a diameter of approximately 

 15 m/x. It can be characterized as a virus-specific unit only by its serological 

 behavior. In the case of fowl plague, where the purest prejjarations of sub- 

 units were obtained, there is no cross reaction between G antigen and virus- 

 hemagglutinin. The above-mentioned serological relationship between the 

 infective particles of fowl plague and influenza seems to extend only to the 

 G antigens, which was demonstrated using the Rostock strain of fowl plague 

 and the FMl strain of influenza (Schafer, 1955b; Schafer, 1957b). 



For chemical investigations, highly purified infective particle preparations 

 of fowl plague and infiuenza viruses are usually obtained from the allantoic 

 fluids of infected chick embryos. The virus particles are first adsorbed on 

 erythrocytes, the cell/virus-complex is thoroughly washed in the cold, and 

 the virus then eluted from the cells at 25-37°C. This is followed by one or 

 several cycles of high- and low-speed centrifugation (Taylor, 1944; Ada and 

 Perry, 1954b; Zillig et al., 1955). In the case of fowl plague virus, 7 mg. of 

 proteui per liter of starting material is obtained by such a procedure. 



There are considerable difficulties associated with the tests for purity for 

 influenza and fowl plague infective particles. Preparations that are homo- 

 geneous with respect to their electrophoretic and ultracentrifugal behavior, 

 as well as by electron microscopy, still contain an antigenic moiety character- 

 istic of the host (Knight, 1946; Munk and Schafer, 1951; Schafer et al, 1952). 

 This antigen, designated as normal component, must somehow be tightly 

 bound to the virus, since it cannot be eliminated, even with the aid of specific 



