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SUMMARYCultures of RK 13 and BHK2I ceils infected with rubella virus were examined by electron microscopy when the cultures showed maximal cytopathic effects. Infected RK 13 cells contained crystalline inclusions (spacing t9o X) as well as typical virus particles of total diameter 60o X, with a dense 300 ~, core. Identical particles also occurred in infected BHK2I ceils, but in these no crystals were observed. Neither crystals nor particles were found in control cells. The particles did not resemble myxoviruses.

A test for the immunogenicity of influenza viruses is described, which is based upon the intranasal vaccinating dose required to induce inhibition of multiplication of unadapted influenza viruses in the lungs of mice. This test is more sensitive than an antigen extinction procedure, in which immunogenicity is measured according to the dose required to induce the formation of hemagglutination-inhibition antibody. The clearance test has been used to demonstrate that a) influenza A/Northern Territory/60/68 virus is a better immunogen than A/Victoria/3/75 and both are probably superior to A/U.S.S.R./92/77; b) for A/Northern Territory/60/68, vaccination by the intranasal route in 25 g mice is at least 43,600 times more efficient than by the intraperitoneal route and c) common immunogenic relationships exist between various H3N2 viruses and an H1N1 strain.