44 S. G. ANDERSON 



lung. These can be removed by heating at 70 to 80°C. for 5 to 30 minutes 

 (Mills and Dochez, 1944), or by treatment with alkali (Crimen and Horsfall, 

 1947). The hemagglutinin so liberated is about 40 m/x in diameter (Curnen 

 et al. 1947). There is no associated enzyme. 



The hemagglutinin, which is probably identical with the virus particle, 

 agglutinates red cells of mouse and hamster but not of human, cat, dog, 

 sheep, ferret, rat, guinea pig, or fowl (Mills and Dochez, 1945). 



III. Hemagglutinin Separate from the Virus Particle 

 A. Psittacosis Group 



Mouse meningopneumonitis virus grown in the chick allantoic cavity 

 agglutinated mouse erythrocytes, but not red blood cells from 11 other species 

 tested (Hilleman et al., 1951). 



Agglutination occurred at pH 7.0, at 24 or 37°C, but not at 4°C; it was 

 inhibited by specific antibody. The hemagglutinin was also inhibited by 

 calcium ions in concentrations as low as 0.00078 M and by 0.005 M mag- 

 nesium, and therefore was not active in undiluted allantoic fluid. 



The hemagglutinin was smaller than the infectious particles, which could 

 be removed by centr irrigation at 13,000 r.p.m. About half the hemagglutinin 

 was sedimented at 18,000 r.p.m. 



A similar hemagglutinin is formed in the chick allantoic cavity by the 

 feline pneumonitis virus of Baker (Gogolak, 1954) and by psittacosis. 



The psittacosis hemagglutinin is a complex of lecithin and nucleoprotein, 

 both of which are also present in the infective virus particle (Gogolak and 

 Ross, 1955). These authors believed that the hemagglutinin was either in- 

 complete virus material not incorporated in the elementary body, or a de- 

 gradation product of the virus; they showed that nonhemagglutinating dead 

 virus particles would stimulate the formation by roosters of antibody specific 

 for the hemagglutinin. They demonstrated similar antigenic factors in the 

 hemagglutinin and the virus elementary body. 



The biological behavior of the hemagglutinin closely resembled that de- 

 scribed for mouse meningopneumonitis virus and the two hemagglutinations 

 were serologically identical. 



B. Poxviruses 



Vaccinia hemagglutinin was first described by Nagler (1942). After several 

 hints that the virus produced two hemagglutinins (Chu, 1948a,b; Burnet and 

 Stone, 1946), Gillen and associates (1950) separated the two by centrifuga- 

 tion of chorioallantoic membrane extract at 17,000 r.p.m. in a Sorval head. 

 In native membrane extracts the two are apparently linked and behave as a 



