1. The immunological behavior of two cell constituents of nonhemolytic streptococci has been studied, (a) One, the so called nucleoprotein, is relatively non-specific and gives rise to an antibody which shows group reactions with nucleoproteins of related species. (b) The other is non-protein by qualitative chemical tests. Preliminary chemical examination has indicated that it may be a carbohydrate. Although this substance is highly reactive with the specific antibodies produced by the intact bacterial cell, yet in its chemically purified condition it is probably non-antigenic. Specific serological reactions with this substance are dosely related to specific agglutination of the microorganism.
2. The study of sera prepared by immunization with the chemically extracted protein has shown the presence of antibodies for nudeoproteins alone. No antibodies against the specific soluble substance have been found in these sera. The protein antibodies are little, if at all, concerned in causing agglutination. Precipitin tests, complement fixation reactions, and absorption experiments have been used to analyze the group relationships with the nucleoproteins of other species. The proteins of each species of Gram-positive cocci studied were immunologically similar within the species and showed definite relationships to the proteins from related species. Proteins from bacteria of unrelated species did not react with antisera against streptococcus protein.
3. Two distinct antibodies have been demonstrated in antisera prepared against living bacteria. By prolonged immunization it was found possible to produce sera with a high content of protein as well as specific antibodies. With ordinary methods, however, the immune sera had a low content of relatively non-specific protein antibodies but a high titer for specific antibodies. The specific antibodies were not reactive with proteins but were active with high dilutions of the soluble specific substance and were responsible for the parallel specific agglutination. Absorption experiments showed that the two antibodies in antibacterial sera were immunologically distinct.