A total of 75 untreated and unfiltered nasopharyngeal washings from normal individuals, from patients ill with sporadic febrile upper respiratory disease, and from patients ill during epidemics of influenza were inoculated into the allantois of chick embryos. Repeated passage by the allantoic route demonstrated that chick embryos were little affected by gross bacterial contamination with organisms from the nasopharynges of these patients. Influenza A virus in throat-washings was found to grow readily in the bacterially contaminated embryos. The red blood cell agglutination-phenomenon was used as an indicator of the presence of virus.

In a current epidemic, influenza A virus was isolated and identified in nine out of 20 throat-washings taken at random and examined by the technic described above. Four of the 20 washings produced agglutination on primary egg inoculation. One of these four strains was identified as influenza A virus within 48 hours after the first cases in the epidemic were observed. Human sera of known titer for standard strains of influenza A and B virus were used for the identification of all the strains isolated.

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The studies and observations on which this paper is based were conducted with the support and under the auspices of the International Health Division of The Rockefeller Foundation.

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