The results of the partial saturation of precipitins with antigens related in derivation to the homologous one give no conclusive evidence of the regular existence in a single immune serum of multiple antibodies which act specifically on various chemical groups of the antigenic proteins. It seems possible to explain at least a part of the facts by the assumption that a single antibody will react to different degrees with several similar substances.

By the partial absorption of hemagglutinins with heterologous blood, specific fractions were obtained. By such means one may readily differentiate the blood of related species, even when precipitins show but little difference.

The peculiarities in specificity manifested by precipitinogens and agglutinogens suggest an essential difference in the chemical structures which determine the specificity of the two kinds of antigens.

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