Variation in the amount and quality of influenza virus injected into the amniotic sac of the chick embryo led to differences not only in the yield of virus but also in the immunofluorescent cytology of the infection.

The production of infectious virus was associated with a predominance of cells in which the virus antigens were first detected along the cell surface in contact with the amniotic fluid, later deeper in the cytoplasm, and finally, though to a lesser extent, in the nucleus.

When the virus yield was primarily non-infectious hemagglutinin the virus antigens appeared in reverse sequence; i.e., nucleus first, then adjacent cytoplasm, and ultimately throughout the entire cell.

Under conditions of "autointerference," the immunofluorescence seen in some of the cells failed to progress beyond the nuclear or early cytoplasmic stage, while many other cells remained unreactive throughout the experimental period.

With the largest dose used a pale intranuclear reaction was localized 1 hour after injection but the embryo died shortly thereafter.

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