It has been shown that strains of influenza type A virus which originated in the same institutional outbreak from specimens collected on the same day, treated in the same manner, and isolated by identical procedures, exhibited certain biological differences. These consisted of dissimilarities in the capacity to agglutinate chicken and guinea pig red cells, agglutination patterns, speed of elution from red cells, and resistance to ultraviolet light. Furthermore, small but significant differences in the antigenic composition were demonstrated by agglutination-inhibition, complement fixation and neutralization tests. Antibody cross-absorption tests revealed specific antibodies for each strain thus studied.

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This work was performed under a contract with the Office of Naval Research.

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