Methods of preparation and certain properties of the "nucleoproteins" of the following organisms are described: gonococcus, meningococcus, Micrococcus catarrhalis, R pneumococcus, Streptococcus hemolyticus, Staphylococcus aureus. No essential differences between the nucleoproteins and the intact cells of gonococcus and meningococcus were observed in their ability to engender immune substances (precipitins), to induce bacterial allergy in rabbits, or to elicit cutaneous reactions (of the delayed type) in rabbits rendered hypersensitive to these organisms. Measured by their lethal action in mice, the toxicity of gonococcal and meningococcal nucleoproteins was found to be but slightly less than that of the intact cells. It seems probable, therefore, that the toxic action of these organisms is due, chiefly or entirely, to some constituent of the nucleoprotein fraction. Extraction with acetone and ether in the cold did not reduce appreciably the toxicity of these organisms and their nucleoproteins, nor alter their immunological behavior.

Cross-precipitin reactions suggested that gonococcal nucleoprotein contains an antigenic factor in common with the non-encapsulated pneumococcus cell, and meningococcal nucleoprotein one in common with the capsular material of Pneumococcus Type III. Tryptic digestion destroys these antigenic factors, but not those responsible for the cross-reactions within the genus Neisseria.

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