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The raphides in the mature fruit of the fishtail palm Curyota mitis Lour. were isolated by mechanical separation. These were shown by X-ray crystal analysis to be calcium oxalate monohydrate (Whewellite). The application of an aqueous suspension of the raphides to intact human skin results in an immediate, severe itch sensation. An investigation of this phenomenon appears to indicate that this is due solely to a mechanical action of the calcium oxalate needle and not to the previously postulated action of organic toxins or enzymes introduced through the skin by the penetrating action of the raphides. Calcium salts are encountered frequently in discrete crystalline form throughout the plant kingdom. Indeed, needles (raphides) of calcium oxalate were among the first objects to be observed with a microscope; Leeuwenhoek described the raphides which occur in Arum in a letter written to H. Oldenberg on August 14, 1695 (Arnott and Pautard, 1970). Most toxicological interest concerning these calcium oxalate crystals has centered on the family Araceae (containing Diefinbachia, Philodendron, Monstera, Caladium, Arum, etc.) which, when uncooked may cause an intense painful burning sensation in the mouth. These plants are also respon