An Absolute M E T H O D for Assay of Virus Hemagglutinins

The ability of certain viruses to agglutinate red cells (1) is widely employed as a basis of titration, because of the speed and simplicity of the reaction. Usefulness of the method has been limited, however, by lack of a reliable means of translating hemagglutinating activity into an absolute number of active particles per cubic centimeter, so tha t values obtained for a single virus can only be expressed in relation to that of some standard suspension, and different viruses cannot be compared at all. Moreover the relationship between hemaggintination and infectiousness is often complex, wide variations in the ratios of these activities being produced by various t reatment of virus suspensions (2). An absolute method for determination of the number of hemagglutinating particles would materially increase the usefulness of the virus assay when the two activities are closely associated, and make possible precise analysis of the relationship between infectivity and agglutination in cases in which they are separable. Such a method is described in this communication.