or Rhus toxicodendron). a, spray showing aerial rootlets and leaves; b, fruit—both one-fourth natural size. (Chesnut, Bulletin No. 20, Division of Botany, U. S. Department of Agriculture.)" title="" tag="{http://www.w3.org/1999/xhtml}img"/> Fig. 1.—Poison ivy (Rhus radicans or Rhus toxicodendron). a, spray showing aerial rootlets and leaves; b, fruit—both one-fourth natural size.
(Chesnut, Bulletin No. 20, Division of Botany, U. S. Department of Agriculture.)

In the general description of the order Anacardiaciæ, Gray[3] says: "Juice or exhalations often poisonous." Whether it is contact with some part of the plant, or with the exhalation from the plant, that causes the well-known skin eruption has been a topic for discussion ever since its source was known. On account of its intangible nature there has been more speculation than experimental evidence bearing on this question, although a few investigations have been made with the object of isolating the poison. It is most generally believed that the exhalations are poisonous. Dr. J. H. Hunt[4] states that the exhalations have been collected in a jar and found to be capable of inflaming and blistering the skin of an arm plunged into it.

Fig. 3—Poison sumach (Rhus vernix), showing leaves, fruit, and leaf-scars, one-fourth natural size.
(Chesnut, Bulletin No. 20, Division of Botany, U. S. Department of Agriculture.)

Prof. J. J. Rein,[5] in his treatise on Lacquer Work, describes the poison of the Japanese lac tree, Rhus vernicifera, as being volatile, as do also the Japanese chemist Yoshida[6] and the French chemist Bertrand.[7] Recent work by Prof. A. B. Stevens,[8] however, seems to show that this poison is not volatile, and is similar to, if not identical with that obtained by Pfaff[9] from Rhus toxicodendron and Rhus venenata.

Not many cases of internal poisoning by Rhus toxicodendron are on record in medical literature. Two cases of poisoning from eating the fruit of this plant have been described.[10] The subjects of these cases were two children who had eaten nearly a pint of the fruit. The symptoms are described in detail, being in general, similar to those of alkaloidal poisoning. Warm water was given to promote emesis; afterwards large quantities of carbonate of soda were given in solution under the belief that it was an antidote to the poison. Otherwise they were treated on general principles. Both children recovered.

Another case of internal poisoning is the following:[11] Three children drank an infusion of the root of poison ivy thinking it was sassafras tea. The first of these cases was diagnosed as measles, but on the appearance of similar symptoms in the sisters of the first patient, the cause of the trouble was found. All recovered.

Dr. Pfaff[12] explains the few fatal cases that have followed Rhus poisoning on the assumption that enough of the poison was absorbed through the skin to cause renal complications in persons having chronic kidney trouble. He showed that the poison, when given internally, produces a marked effect on the kidneys, causing nephritis and fatty degeneration of this organ.

The irritating action of poison ivy has been attributed at different times to the "exhalation," to a volatile alkaloid, to a volatile acid, and to a non-volatile oil. Pfaff,[13] who made the most recent investigation of this poison, obtained from the plant a non-volatile oil having the same action on the skin as the plant itself. He found this oil in all parts of the plant and concluded that it was the active principle, and that one could be poisoned only by actual contact with some part of the plant. He assumed minute quantities of pollen dust to be in the air to account for the cases of "action at a distance" so frequently quoted. Pfaff says: "In my opinion, it is more than doubtful if ever a case of ivy poisoning has occurred without direct contact with the plant or with some article that has been in contact with the plant. The long latent period of the eruption in some cases may obviously render mistakes extremely easy as to the occasion when contact with the plant really occurred." Granting, however, that the active principle is practically non-volatile when isolated from the plant, we cannot say positively that it is not volatile in the juices of the plant, or under the influence of vital forces. It is quite conceivable that the water transpired by the leaves of the plant may carry with it a quantity of the poison sufficient to produce the dermatitis on a person very susceptible to its action. It is also conceivable that a volatile poison manufactured by a living plant could become non-volatile by changes in it consequent upon the death of the plant.

Up to the present time, only three important chemical investigations of the active principle of Rhus toxicodendron have appeared in medical and chemical literature, these being the researches of Dr. J. Khittel, J. M. Maisch, a pharmacist, and Dr. Franz Pfaff, of the Harvard University Medical School, to whose work reference has been frequently made. The chemical work of these investigators and their conclusions are given here in some detail for the sake of completeness.