488 W. SCHAFER 



precipitation with anmionium sulfate (40 %), and high- and low-speed 

 centrifugation. Such preparations were free from impurities, as demonstrated 

 by ultracentrifugation, electrophoresis, electron microscopy, and also by 

 serological investigation with antiserum to normal component. 



Chemical studies on the S antigen strengthened the concept that it is very 

 closely related to the G antigen. S antigen also proved to be a ribonucleo- 

 protein (Schafer et al., 1956; Schafer, 1957b). But the RNA content of 

 individual S antigen preparations varied to a greater degree. This is not 

 unexpected, since the S antigen is not protected from degradation during the 

 purification procedure as is the G antigen, which is within the virus particle. 

 The RNA content of the fowl plague S antigen was found to be between 6 

 and 14 %. Studies of the composition of the RNA and the protein, which 

 would be useful in a further clarification of the relationship between the two 

 antigens of fowl plague, have not yet been made. 



Attempts to purify influenza S antigen from chick embryo lung extracts 

 were carried out by methanol precipitation and treatment with chloroform, 

 or by ultracentrifugation in a sucrose density gradient (Ada et al., 1952), It 

 is difficult to judge the purity of the preparations obtained since extensive 

 tests of purity have not been made. 



As far as one can judge from studies on such preparations and on precipi- 

 tates of these by specific antiserum to S antigen (Ada and Perry, 1954a), the 

 influenza S antigen also seems to be a ribonucleoprotein. It contains about 

 6 % RNA. This corresponds approximately to the RNA content of the 

 G antigen of the influenza virus. 



In an S antigen preparation from infected chorioallantoic membranes, only 

 0.7 % RNA was found (Ada, 1957). This antigen had been isolated by ultra- 

 centrifugation and extraction with ether. The reason for this discrepancy is 

 not clear. 



The mcomplete forms of influenza and fowl plague virus may be purified 

 by cycles of adsorption on and elution from red blood cells, since they possess 

 hemagglutinating and enzymatic activities like the infective particles 

 (Schafer et al., 1954; Ada and Perry, 1956; Paucker et al., 1956). This can be 

 followed by several cycles of high- and low-speed centrifugation, which are 

 chiefly useful in the removal of the infective particles stiU present, resulting in 

 preparations quite pure physically (ultracentrifuge, electrophoresis, and 

 electron microscope) (Schafer e^ ai, 1954; Pye et al., 1956). However in the 

 case of fowl plague, a normal component could still be demonstrated 

 serologically (Schafer, 1955c). 



Chemical studies have been made on influenza incomplete forms obtained 

 from allantoic fluid after serial undiluted passage or infection with heat- 

 inactivated (37°C.) standard virus. Reduction in the infectivity /hemag- 

 glutination ratio was accompanied by decrease in the nucleic acid content 



