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The allergenic potencies of oleoresins extracted from portions of a single ivy plant vary according to the fat solvents employed for extraction of the oil. The dermatitis-producing fraction of the oleoresin is highly soluble in ether and only slightly less soluble in acetone. Dehydrated alcohol and carbon tetrachloride produce oleoresins approximately one fifth to one tenth as potent, according to biologic tests, as those extracted with ether or acetone. The solvent employed for extraction of ivy oleoresin is of paramount importance, since dilutions of ivy oleoresins employed for quantitative patch tests or for oral therapy may vary 1,000 per cent in potency, depending on the fat solvent employed for extraction of the oil.
Leaves from a single plant of Rhus toxicodendron radicans were collected and dried at room temperature for two weeks. After thorough drying, 120 Gm. of leaves was triturated and divided into four parts of 30 Gm.
HOWELL JB. SOLUBILITY OF THE DERMATITIS-PRODUCING FRACTION OF POISON IVY. Arch Derm Syphilol. 1941;44(4):665–666. doi:10.1001/archderm.1941.01500040120010