SUMMARY: The multiplication of fowl-plague virus was studied in cultures prepared with suspensions of isolated cells of chick embryo tissues. Under favourable conditions, virus infectivity increased exponentially for 20 hr., after a latent period lasting 4–6 hr. Virus haemagglutinin production varied linearly with the number of cells added to the cultures, the regression line of this relationship showing a slope of approximately 1 when the cell concentration was kept constant and a slope higher than 1 when the number of cells was varied together with the cell concentration. Haemagglutinin production was decreased by increasing the size of the virus inoculum. A similar decrease was observed in cultures in which the depth of the fluid layer was increased. Cultures incubated at 32° for 2 days showed no haemagglutinin titres. The titres reached in cultures incubated at 35, 37 and 39° did not differ significantly. Cultures kept at 37° maintained their capacity to support virus multiplication at an approximately constant level for at least 3 days. At 22° and at 4° this capacity decreased progressively with time of storage, the decrease being more pronounced at the lower temperature. Virus multiplication was inhibited by horse serum.


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