28 S. G. ANDERSON 



He attributed this to an alteration of a polysaccharide, probably the breaking 

 of a bond between adjacent carbon atoms carrying two hydroxyl groups, or 

 one hydroxyl and one amino group. 



Later, Fazekas de St. Groth (1949) pointed out that even lower concen- 

 trations of periodate, in the range of 2 to 0.2 mg. potassium periodate per 

 gram of red cells, would modify red cell receptors so that virus would adsorb 

 but not elute. The reaction of periodate with red cell receptors and mucoids 

 has thrown considerable light on the chemistry of these substances and has 

 provided valuable biological tools in virus research. 



e. Formaldehyde. Red cells treated with formaldehyde in concentrations up 

 to 18 % still absorbed influenza hemagglutinin (Flick, 1948). NDV agglutin- 

 ated red cells made up as a 2 % suspension in 0.2 % formaldehyde (Burnet 

 et al, 1945). 



6. Increase in Titer of Hemagglutinin at 37°(7. in the Presence of Cells 



This phenomenon has been observed with the Victorian strain of New- 

 castle disease virus on fowl or human cells (Anderson, 1947a) and with 

 Enders's strain of mumps on human cells (Lind, 1948). It is demonstrated as 

 follows: If doubling dilutions of virus are made in normal saline in glass 

 tubes, and fowl or human red cells are added, an end point can be determined 

 by the pattern produced at 37°C. within 30 minutes. If the titration tubes are 

 shaken and again allowed to settle, the end point is 2- to 4-fold the previous 

 reading; a further increase appears after a second shaking and settling and 

 the whole increase may finally reach a total of 8-fold. NDV remaining in the 

 supernatant after absorption with red cells at 4°C. may show an increase in 

 hemagglutinin end point of up to 40-fold on incubation at 37°C. with fresh 

 cells. 



It was first suggested that disaggregation of clumps of hemagglutinating 

 units might explain this behavior (Anderson, 1947a), but photographs of 

 virus prepared for the electron microscope do not support this view (Bang, 

 1948; Cunha et al, 1947; Elford et al, 1948). Burnet (1950) suggested instead 

 that the increase in titer might be associated with the development of 

 agglutinin on stable cells and the increased adsorptive power of particles 

 already firmly attached to one red cell. 



C. Elution 



1. Production of Stabilized Cells 



Viruses of the myxovirus group which have adsorbed to red cells will elute 

 at 37°C. over a period of minutes or hours. Elution is due to a reaction 

 between an enzyme on the virus particle and mucoid substrate groupings on 

 the red cell surface. The chemical nature of the substrate is discussed in 



