Abstract
THE sialidase of influenza virus has been investigated quantitatively using the method recently described by Warren1 for determining free sialic acid in the presence of the compound bound to muco-protein substrates. For this work, the substrate used was a mucoid derived from the nest-cementing substance of the swiftlet (Collocalia sp.). The crude material, available as Chinese ‘edible birds' nest’, was extracted with water at 60–65° to yield a product which contained 10 per cent acid-hydrolysable sialic acid and which in high titre inhibited the agglutination of chicken erythrocytes by ‘indicator’ virus. Active virus was sedimented from freshly gathered chorioallantoic fluid by centrifugation at 35,000g for 90 min. The virus pellet was re-suspended in water to a volume 1/50–1/100 that of the original fluid, effecting thereby a corresponding increment in haemagglutinin titre as well as separation of virus from interfering chromogens present in chorioallantoic fluid.
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