Abstract
Summary
The difference between purified and unpurified swine influenza virus with respect to development of inhibitor sensitivity on heating is ascribed to a factor, identified as calcium, occurring in, normal and virus-infected allantoic fluids. The factor, which is lost, or considerably diminished, during purification, may be removed also by dialysis or neutralized by citrate and oxalate. Calcium, in low concentration, depresses the development of inhibitor sensitivity by swine influenza virus on heating; magnesium is ineffective. In contrast with the swine virus, influenza virus A (PR8 strain) is relatively insensitive to calcium. This difference between two viruses suggests a possible explanation for the generally observed variation among influenza viruses with respect to development of inhibitor sensitivity on heating.
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