Abstract
In the preceding communication the chemical similarity of the specific soluble substance of this strain to that of the Type II pneumococcus was pointed out. These two micro-organisms, widely different in biological characters, were compared immunologically and found to correspond closely. The “E” strain and other serologically related strains of Friedländer bacillus are agglutinated by Type II anti-pneumococcus serum, and not by Type I and Type III antisera; while the Type II pneumococcus is agglutinated by “E” Friedländer antiserum, but not by the antiserum of a strain of Friedländer bacillus serologically distinct from the “E” strain. Absorption of “E” Friedländer antiserum and Type II anti-pneumococcus serum with the homologous organism removes the agglutinins for both, while absorption with the heterologous organism removes only the agglutinins for it, leaving the homologous agglutinins scarcely diminished in titer. The specific soluble substances of the two organisms under comparison react at practically as high dilutions in the opposite antisera as in the antisera to the organisms from which they were derived. Precipitin absorption parallels the agglutinin absorption. Crossprotection was equally striking, Type I1 anti-pneumococcus serum protecting against many thousand lethal doses of highly virulent “E” Friedlander bacillus, and the “E” antiserum protecting against Type I1 pneumococcus at least as well as the Type II antiserum itself. Typical protection protocols follow.
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