1. A skin reaction elicited by the injection of the Pneumococcus "nucleoprotein," or of a solution of the cells from which the acid and heat-coagulable proteins have been removed is described in rabbits which have previously received repeated intracutaneous injections of heat-killed pneumococci.

2. In terms of bacterial specificity, the skin reaction is considered to be not type-specific, but species-specific.

3. A similar skin reaction to the proteins of Pneumococcus occurs in rabbits following the repeated administration by the intravenous or intracutaneous route of the heat-killed organisms or their protein derivatives.

4. The skin reaction may occur independently of resistance to infection.

5. The skin reaction appears to be related to the presence of circulating species-specific antibodies.

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