Plants belonging to the natural order Anacardiaciae (Cashew family or
Sumach family) are found in all the temperate climates of the world and
quite frequently in semi-tropical climates. Many of these plants play
important parts in economic botany, yielding dye-stuffs, tanning
material, wax, varnish, and drugs. Several species are poisonous. At
least three poisonous species of the genus _Rhus_ are found in the
United States. These three are all common and well-known plants, but
confusion frequently arises concerning them on account of the different
names by which they are known in different localities. For example,
poison ivy (_Rhus toxicodendron_ or _Rhus radicans_) probably the best
known poisonous plant in America, being found in all the States except
those in the extreme West, is often confounded with and popularly called
"poison oak." The true poison oak is the _Rhus diversiloba_ of the
Western States.[1] The third and most poisonous species of this plant is
_Rhus venenata_ or _Rhus vernix_; it is the _Rhus vernicifera_ of Japan,
from which Japanese lac is obtained. It is popularly known in the United
States as "poison sumach," "poison dogwood" and "poison elder." It grows
in swamps from Canada to Florida.
As the poison ivy is by far the most common of these plants in the
Eastern States, a brief description of it is given here:[2] A shrub
climbing by rootlets over rocks, etc., or ascending trees, or sometimes
low and erect; leaflets 3, rhombic-ovate, mostly pointed, and rather
downy beneath, variously notched, sinuate, or cut-lobed; high climbing
plants (_R. radicans_) having usually more entire leaves. It is found in
thickets, low grounds, etc. Greenish flowers appear in June.
[Illustration: 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.)]
[Illustration: Fig. 2.--Poison oak (_Rhus diversiloba_) showing leaves,
flowers, and fruit, one-third natural size.
(Chesnut, Bulletin No. 20, Division of Botany, U. S. Department of
Agriculture.)]
In the general description of the order Anacardiaciae, 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.
[Illustration: 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.