A soluble material has been isolated from schistosome eggs which in minute quantities without the addition of adjuvant induces sensitization to a delayed hypersensitivity type of granuloma forming around intact schistosome eggs. This material is secreted by intact eggs and is found in high concentration in the fluid released during the hatching process. When adsorbed to bentonite particles this substance elicits hypersensitivity type granuloma formation in specifically sensitized animals. The granuloma sensitizing factor also both induces and elicits delayed footpad swelling in mice. Quantities which sensitize with respect to these delayed type reactions do not induce antibody formation detectable by a sensitive hemagglutination. technique within the duration of the above experiments.

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