Maisch then worked up 8-3/4 ounces of the leaves of the plant in a way to get the alkaloid, making some improvements on Khittel's method, but failed to find it. Believing that the poison was a volatile acid, he enclosed some fresh leaves of the plant in a tin box with several test papers. The blue litmus paper became red showing the presence of an acid. He concluded from this experiment that the exhalations of the leaves contained a volatile organic acid which he thought was the poisonous substance. To determine this point, he prepared the acid in larger quantity by macerating the leaves with water, expressing and distilling the expressed juice. He was poisoned in doing this work although he had not been affected by handling the living plant and had considered himself immune. He obtained an acid which investigation showed to be somewhat like formic acid, more like acetic acid, but having some reactions different from both. "Taking all the reactions together, it is unquestionably a new organic acid for which I propose the name of _Toxicodendric Acid_," writes Maisch. He further says: "That it is the principle to which poison oak owes its effects on the human system was proved to my entire satisfaction by the copious eruption and formation of numerous vesicles on the back of my hand, on the fingers, wrists, and bare arms while I was distilling and operating with it. Several persons coming into the room while I was engaged with it were more or less poisoned by the vapours diffused in the room; and I even transferred the poisonous effects to some persons, merely by shaking hands with them. "The diluted acid, as obtained by me, and stronger solutions of its salts, were applied to several persons, and eruptions were produced in several instances, probably by the former, though not always, which was most likely owing to the dilute state of the acid. Whenever this was boiled, I always felt the same itching sensation in the face, and on the bare arms, which I experience on continual exposure of my hands to the juice of the plant." Toxicodendric acid was thought to be the active principle from the time of Maisch's work until the investigation by Pfaff in 1895. FOOTNOTES: [15] Proc. Amer. Pharm. Assn. 1865, p. 166, and Amer. Jour. Pharm. 1866, p. 4. PFAFF'S WORK.