For a number of years, cases of dermatitis of unknown etiology have developed at the University of Michigan Biological Station on Douglas Lake, Mich., in persons who have waded in certain places for the collection of biologic specimens. A similar condition has also been noted at certain summer resorts in the same general region. While there has been a considerable amount of speculation and some experimentation on the cause of this dermatitis, the first definite evidence was obtained during the past summer, when lesions similar to those contracted from wading were produced experimentally by placing on the surface of the skin schistosome cercariae belonging to a species described by Miller1in 1923 asCercaria elvae. While it has not been established that this cercaria is the only factor in the production of the dermatitis of the region, the evidence available indicates that it is an important causative agent. The