“…The fact that irradiated virus remains elutable from red cells suggests that it is capable of destrojdng the red cell receptors. Since many similarities exist between these receptors on red cells and hemagglutinin-inhibitory (VHI) substances extractable from erythrocytes (Friedewald et al, 1947, deBurgh et al, 1948, normal serum (Francis 1947) and various fluids and tissues of susceptible species (Friedewald et al, 1947, Svedmyr i948a,b, Hardy and Horsfall 1948, Schlesinger 1949b, it may be assumed that these inhibitors are cellular receptors in solution. Active influenza virus is capable of destroying these substances in vitro and also in the infected host, and it is likely, in view of its elutability, that irradiated virus can do the same.…”