Blood cultures of embryos killed by the synergistic action of swine influenza virus and Hemophilus influenzae suis are consistently negative, and embryos infected with swine influenza virus may be killed both by filtered extracts of frozen and dried Hemophilus and by suspensions of heat-killed bacteria. The addition of Hemophilus to the chorioallantoic membrane of embryos infected with swine influenza virus causes the virus to spread from the membrane to the allantoic fluid and embryo. This spreading effect also obtains when a purified preparation of hyaluronidase is used instead of Hemophilus, but it is unaccompanied by a comparable increase in mortality. It is probable that the spread of the virus produced by the bacteria is only partly responsible for the development of the complex infection and that products of these organisms other than the spreading factor play a large part in the mortality of embryos receiving the combination of virus and bacterium.

This content is only available as a PDF.