[Precipitinogen activity of Newcastle disease virus and humoral immunity in birds].

Studies was the precipitinogenic activity of the strains La Sota, 'H', and 'II' of the Newcastle disease virus, using chick embryos. It was found that all three of the strains produce precipitinogens. An antigen was obtained for the precipitation reaction in agar gel and the demonstration of precipitins that were specific for the ND virus in the blood serum of birds. Contrary to the hemagglutinins and precipitinogens proved heatresistant. There was a correlation between the antihemagglutinins and the precipitinogens in the blood serum of the immune birds. The low percent of birds (up to 12%) having precipitins in their serum spoke of the development of solid immunity against Newcastle disease within the flock. On the other hand, the high percent of birds having precipitins (over 50%) indicated that the infection persisted, and because of the immunity present it fairly often assumed atypical course or was manifested with low mortality rate.