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AMERICAN JOURNAL OF BOTANY 
[Vol. 8 
this: I handle over and over dried specimens with impunity, but am very sensitive to the 
fresh plant. Then the poison is volatile, as shown by its affecting persons who do not 
touch it actually; that of the leaves, I should say, must escape and dry out in the dr^ang 
process, or in the course of time. In a stem it would not volatilize so soon; but I should 
not expect to be poisoned from any old herbarium specimen, either from twigs or leaves. 
Likewise, Mackie (28), writing on the value of oak leaves for forage, 
says : 
It would seem that the irritating and poisonous oil of poison oak is volatile at a com- 
paratively low temperature. In gathering the specimens the writer was badly poisoned 
even though gloves were worn; yet after drying at ordinary room temperature, and the 
leaves pressed into the mill with bare hands, no poisoning effects followed. 
Opposed to these opinions is the experience of Bogue (6) while investi- 
gating an herbarium specimen of R. venenata which had been deposited in 
the Ohio State University not less than three years. He was poisoned by 
the "sawdust" from the stems of the plant which was the result of borings 
rom a beetle. 
It has previously been conclusively shown that the poison is non-volatile, 
and the decrease in malignancy of the leaves in drying can be attributed 
only to a loss of fluidity of the sap and to the loss of toxicity of the poison 
from oxidation (McNair). 
In concluding the botanical investigation, it seems evident that the 
plant is capable of poisoning only when injured in such a manner that the 
poisonous resinous sap exudes. 
Poisoning without contact with the plant may occur by means of smoke 
from the burning plant or by contact with substances that have the poisonous 
sap on them, such as gloves (Hunt, 18; Ward, 47; Frost, 14; Kunze, 24); 
pocket-knife handles, croquet balls, and botanists' collecting cases (Hunt, 
18); hands of another (Hunt, 18; White, 49; Planchon, 38; Cantrell, 10; 
Maisch, 34); clothing (Balch, 2; White, 49; Bibb, 5; Lindley, 27; Cundell- 
Juler, 11); shoes one year after contact (Balch, 2; Ward, 47); instruments 
(Planchon, 38); leather hat bands (Leonard, 26); and firewood (Barnes, 3). 
Dermatitis caused by other plants is also sometimes attributed to Rhus; 
e.g., Cypripedium (Hurlbut, 19); eczema and other eruptions may also be 
confused with that caused by Rhus. 
Conclusions 
I. The principal dermatitant of Rhus diversiloha is not volatile, for: 
(a) It is not distillable normally by steam or under reduced pressure. 
It can not be carried by entrainment with a volatile substance. 
ib) The smoke of the burning plant is not poisonous when filtered 
through glass wool at a high temperature. 
{c) Possible emanations from leaves are non-toxic when (i) the leaves 
are fastened on the concave side of a watch-glass and then to the skin of a 
susceptible person; and (2) when a current of air is blown over the leaves 
and caused to bubble through alcohol, the alcohol is non-toxic. 
