(Dobrovolskaya, 1971;Daugharty et al., 1972;Brown and O'Leary, 1973;Urquhart, 1974;Buchner et al., 1976). The present study aimed to show the frequency with which sucrose density gradient ultracentrifugation followed by haemagglutination inhibition (HI) could detect specific serum IgM antibodies in patients recently infected with influenza A. The results obtained by this technique were compared with the standard complement fixation test. Material and methods VIRUSThe virus used in all haemagglutination-inhibition tests was A/Port Chalmers/1/73 (A/PC/73) which was propagated in fertile hens' eggs.

Sucrose density gradient ultracentrifugation can be used to detect specific 19S antibodies of the IgM class in the sera of patients recently infected with influenza A virus, provided steps are taken to remove non-specific inhibitors of haemagglutination. The usefulness of the procedure for the diagnosis of influenza requires further evaluation.

Summary By means of infectivity titrations and immunofluorescent staining, the pathogenesis of Theiler's GD VII virus infection in mice was studied. After intracerebral inoculation of virus, infection appeared to start at the site of inoculation and then spread along the ventral part of the brain and the hippocampus. Following intranasal inoculation, virus gained entrance to the central nervous system (CNS) through the olfactory bulbs and olfactory tracts to initiate infection in the brain. By feeding mice with GD VII virus, small amounts of the virus could be demonstrated in visceral organs by infectivity titrations while much larger amounts of virus were found in the CNS when encephalitis became apparent. Use of the immunofluorescence technique did not enable us to localize the primary sites of viral multiplication prior to invasion of the central nervous system in mice infected by gavage.

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