The first attempt to find the poisonous constituent of this plant was made by Khittel in 1857. His work was published in _Wittstein's Vierteljahrresschrift fuer praktische Pharmacie_, VII, 348-359.[14] Khittel obtained 37-1/2 ounces of fresh leaves of poison ivy from the botanical garden in Munich, dried them, and got a residue of 9-1/2 ounces which he analyzed. Not detecting anything to which the poisonous qualities of the plant could be attributed, he made another series of experiments which, as he thought, showed that a volatile alkaloid is the poisonous constituent. It was obtained by the following process: "3 ounces of the powdered leaves were infused with hot distilled water, after three days strained, expressed, the liquid evaporated to 3 ounces, and with the addition of potassa, carefully distilled to one-half. The clear, colorless distillate had an alkaline reaction, and an odor resembling henbane or hemlock. It was saturated with sulphuric acid, evaporated, and treated with a mixture of equal quantities of alcohol and ether which left sulphate of ammonia behind, the solution was evaporated spontaneously, distilled with potassa, the alkaline distillate neutralized with hydrochloric acid, and a precipitate could now be obtained with chloride of platinum. Want of material prevented further experiments." The editor of the _American Journal of Pharmacy_ inserts the following note: "It would have been more satisfactory if the author had given some physiological evidence of the poisonous nature of the alkaloid substance obtained. It is quite interesting to hear that the hitherto intangible venom of this plant has at last been detected." FOOTNOTES: [14] A free translation of this paper is given in Amer. Jour. Pharm. for 1858, p. 542. WORK OF MAISCH.[15] The next investigation of this plant was made by Maisch in 1864. He criticizes Khittel's experiments as follows: "It is well known that the _exhalations_ of _Rhus toxicodendron_ exert a poisonous influence on the human body; the poisonous principle must, therefore, be volatile and, at the same time, be naturally in such a loose state of combination as to be continually eliminated and separated with the usual products of vegetable exhalations. It is natural to suppose that during the process of drying, the greatest portion of the poisonous principle should be lost. The loss must be still greater if the dried leaves are powdered, a hot infusion prepared from them, and this infusion evaporated down to the original weight of the dried leaves. It is obvious that Dr. Khittel could not have selected a better method for obtaining the least possible quantity of the poisonous principle, if, indeed, it could be obtained by this process at all."