38-3 
several years old, and that they seem, in this respect, to be considerably influenced | 
by the contiguity of supporting objects.” 
My tinctures of both forms are exactly alike in physical properties; portions 
of each yielded the same amount of solid extract per ounce, after evaporation ; 
and as far as I can determine, they are identical. 
The bulk of our guiding symptoms are compiled from cases of poisoning, 
where the form causing the effect is not identified. I then, in the light of all this, 
would suggest that our tincture be made as follows : 
Take equal parts by weight of fresh leaves of each form, gathered on a cloudy, 
sultry day, just before the flowers are developed, chop and pound them to a pulp, 
and weigh, treating the resulting mass as in the preceding species. The resulting 
tincture should have a dark brown color by transmitted light, and will give off no 
characteristic odor; it will have a biting and astringent taste, and a strong acid 
reaction. 
CHEMICAL CONSTITUENTS.—Rihottannic Acid, C,,H,,O,, This specific 
tannin of Rhus is a yellowish-green, gummy mass, having a slightly bitter and 
astringent taste and an acid reaction (Wittstein). 
Toxicodendric Acid.—This peculiar, poisonous, volatile principle, was isolated 
from this plant by Prof. Maisch.* He describes it as resembling both formic 
and acetic acids in some of its reactions, but distinguishable in its failure to pro- 
duce a red color with neutral ferric salts. 
PHYSIOLOGICAL ACTION.—The toxic action of this species is one difficult 
to explain. The first noticeable peculiarity is its choice of victims, many persons 
being entirely devoid of response to its influences, many others peculiarly suscep- 
tible. Out of ten men employed to “clear out a twelve-acre lot that was completely 
filled with poison vine, cat briers, and brambles, the poison vine greatly predomi- 
nating,” four only escaped poisoning. “At first there was a lively fight between 
the poison vine and the men, and it looked as if the former would get the better 
of it: for most of the men soon began to show signs of being tired, and at the 
end of the fourth day six of the men were flat on their backs, too sick for any- 
thing.” ++ I remember one illustration. When a lad, while in bathing with five 
others, we all ran a race, stark naked, through the underbrush near by, passing in 
and out through a clump of what was afterward found to be poison ivy; two of 
the party were taken ill the next day and soon developed quite serious symptoms 
of poisoning; all the others, including myself, escaped. 
Another peculiarity is that in many cases it is not necessary to even touch the 
plant to be severely poisoned. While playing croquet one sultry day in June, with 
a young lady cousin, she struck her ball with sufficient force to cause it to roll 
underneath a clump of poison ivy that grew at a short distance from the edge of 
the lawn. She, knowing her susceptibility to the poison, carefully reached under 
the vine and extracted the ball without touching even a leaf. During the evening 
* Proc. Am. Phar. Assoc., 1865, 166. ¢ Rural New Yorker, quoted in daily press, original not accessible. 
