In agreement with earlier observations the infectivity titer in the allantoic fluids of chick embryos injected with influenza A virus remains constant for 5 to 6 hours before an increase in this activity can be noted. In contrast, the titers of hemagglutinin and complement-fixing antigen (virus antigen) have already begun to rise after 3 hours. The origin of the hemagglutinating and complement-fixing but non-infectious material is still obscure.

In the allantoic membrane development of both the soluble and virus antigens can be demonstrated after the 2nd hour of incubation and 1 hour prior to an increase in hemagglutinins and 2 hours prior to a rise in infectivity. Thus there remain the first 2 hours during which no record of virus activity in the tissues can be obtained.

Similar relationships are noted on dilution of the seed both in the allantoic fluids and membranes as long as the various properties reach measurable levels during the experimental period of one infectious cycle.

Injection of high titered immune serum following infection with about 109 ID50 reduces the amount of demonstrable seed virus in the allantoic fluid and membrane without significantly affecting propagation of the agent in the tissues as measured by infectivity titrations. The production of hemagglutinins appears markedly reduced under these conditions whereas formation of complement-fixing antigen is only slightly delayed and decreased.

No definite explanations for the various discrepancies between the infectivity and hemagglutination can be given at present.

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