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Abstract Interferon could be titrated by the amount of interference induced in fragments of chorio-allantoic membranes challenged with influenza A virus. Over a ten-fold range, inverse proportion between interferon concentration and haemagglutinin titre reached by the challenge virus was observed. Interferon proved stable at 2°C for 2 weeks. Marked inactivation took place after 1 h at 60°C. Interferon was not measurably sedimented by 100 000 g for ½ h. It was held back by gradocol filters of a. p. d. 0.6 μ. It was not dialyzable. Interferon was active against influenza A, Sendai, Newcastle disease and vaccinia viruses. It was not neutralized by anti-MEL rabbit serum and only slightly inhibited by pooled human serum rich in complement-fixing antibody to influenza A soluble antigen.
Isaacs et al. (Thu,) studied this question.