In the present report there is described the isolation of a particulate component from the chorio-allantoic fluid of chick-embryos infected with the virus of swine-influenza. With these particles in the purified concentrates were associated the hemagglutinative and infectious attributes of the virus-infected chorio-allantoic fluid from which the particles were derived, either by adsorption on and elution from chickens' red blood cells followed by ultracentrifugation or by ultracentrifugation alone. From electron-micrographs the particles appeared to be rounded or ovoid and of variable size. A parallel finding with respect to variation in size was the slightly diffuse boundaries observed in sedimentation-velocity studies. The average diameter of the particles estimated from electron-micrographs was 78.3 mμ. From the sedimentation-constant, S20° = 662 × 10−13, the density, 1.18, determined by pycnometric measurement, and the assumption of spherical shape, the average diameter of the particles was 81.5 mμ. Chemically, the particles were a complex of lipid (24.0 per cent), and non-lipid, carbohydrate and protein (77.76 per cent) containing, on the basis of non-lipid-phosphorus content, about 4.8 per cent nucleic acid, probably of the desoxypentose type. The total carbohydrate-content was 10 per cent, an amount greatly in excess of that which could have been present in the nucleic acid.

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This work was aided by the Dorothy Beard Research Fund and by a grant to Duke University from Lederle Laboratories, Inc., Pearl River, N. Y. The investigation was also supported through the Commission on Acute Respiratory Diseases, Board for the Investigation and Control of Influenza and Other Epidemic Diseases in the Army, Preventive Medicine Division, Office of The Surgeon General, United States Army, and by grants from the Commonwealth Fund, the W. K. Kellogg Foundation, the John and Mary R. Markle Foundation, and the International Health Division of the Rockefeller Foundation to the Board for the Investigation and Control of Influenza and Other Epidemic Diseases for the Commission on Acute Respiratory Diseases.

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