Rabbits were sensitized by a single intravenous injection of horse serum 6 days prior to the experiments. In these rabbits there appeared hemorrhagic and necrotic reactions in sites of intradermal tests with horse serum when the tests were preceded by 1 hour, or followed 18 to 24 hours later by an intravenous injection of potent bacterial filtrates. The skin-preparatory and reacting potencies of the filtrates were titrated by means of the phenomenon of local skin reactivity to bacterial filtrate. The experiments demonstrated that the ability of bacterial filtrates to elicit reactions in the antigen injected sites in sensitized animals is strictly conditioned by their skin-preparatory potency and seems to be quite independent of their provocative potency. Combinations of animal protein antigens with homologous antisera, which are endowed with provocative potency but are totally devoid of skin-preparatory potency, fail to elicit reactions in antigen-injected sites.

The various methods of elicitation of the phenomenon of local tissue reactivity are summarized and discussed in the text.

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