“…Agglutination of several Staphylococcus aureus strains by normal sera (man, rabbit, mouse) has been observed by many investigators (3,4,9,16). Protein A, a cell wall component of S. aureus (6,13,15,23,34) which reacts with the Fc fragment of immunoglobulin G (IgG) from different species (8,9,18,20), has been suggested to be identical with the agglutinogen (16,17,34). Other investigators have shown that protein A and the agglutinogen are not identical substances (3,4,11).…”