Purified blood group A, B, and O substances from hog and human sources precipitate with Type XIV antipneumococcal horse serum and provide an explanation for the observation that Type XIV antibody agglutinates human erythrocytes of all four major blood groups.

Individual preparations of A substance or O substance from either species vary in their capacity to precipitate Type XIV antibody although the hog A substances did not differ in potency toward anti-A. Similarly, no correlation between A activity and reactivity with Type XIV antibody could be found among the human A substances.

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