During the past half-century numerous attempts have been made to isolate and identify the toxic principle of the various species of the three leaflet, white-fruited forms of the Rhus family, scientifically known as Rhus radicans (Rhus toxicodendron), Rhus quercifolia, Rhus microcarpa, Rhus rydbergii and Rhus diversiloba, etc., and commonly known as poison ivy or poison oak. Some botanists still contend that slight differences exist between these many forms, basing their contentions on whether the habit of growth of the plant is chiefly erect or climbing and on variances in the texture, pubescence and degree of lobing of the leaflets. Since all these variations can be observed in the same species under different climatic, soil and other field conditions, conservative toxonomists now agree that the numerous species of poison ivy are identical. I have patch tested ivy-sensitive persons with acetone-diluted oleoresins extracted from the many so-called species of ivy collected in
SHELMIRE B. NATURE OF THE EXCITANT OF POISON IVY DERMATITIS. Arch Derm Syphilol. 1940;42(3):405–409. doi:10.1001/archderm.1940.01490150009002
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