“Poison Oak’’ is often applied when the plant is shrubby. It 
scrambles over fences and walls; or in thickets and woods it 
climbs stumps and trees to considerable heights, clinging by 
means of tiny rootlets. 
It is a well-known fact that individuals vary as to suscep- 
tibility to poisoning by this plant. There are those who claim 
immunity and who seem to be able to touch the leaves or stems 
with impunity. It is doubtful, however, that anyone can hope to 
allow this plant to touch him indiscriminately and always escape, 
for even those most “immune” are liable to be affected under 
certain circumstances; for example, if the plant touches more 
tender portions of the skin, or places where the skin is scratched 
or injured, especially if the parts touched are not washed with 
soap, or otherwise treated, soon after contact with the plant. 
Most people are especially susceptible when their skin is moist 
and perspiring. There are, on the other hand, those who suffer 
greatly from the slightest contact with poison ivy; those who feel 
its effects not only in a localized irritation and blistering of the 
skin where the plant touched it, but who suffer irritation or rash 
over a considerable area, or even, in extreme cases, over the 
whole body ! And there are those who claim that they are affected 
even by proximity to a plant, or through passing by a fire where 
it is burning, without even having touched it. 
The symptoms of poisoning, as stated above, are irritation 
and redness, followed by “water blisters.” There is a great 
temptation to scratch the inflamed areas, resulting in breaking 
the blisters and spreading the poison. 
It is an interesting fact that cattle and other herbivorous 
animals can eat this plant with impunity. Dogs, however, are 
liable to be poisoned, especially about the mouth, through con- 
tact with the poison ivy plant. 
For obvious reasons, poison ivy is not a tempting plant with 
which to experiment. Consequently the poisonous principle is 
as yet a matter of some discussion. It has been considered by 
different investigators to be a volatile acid, volatile alkaloid, 
or volatile oil that caused the disease. The volatile nature of the 
substance was thought to explain poisoning through merely pass- 
ing near the plant. However, there is considerable evidence that 
the poisonous principle is in reality a non-volatile oil. Very 
minute quantities of this irritating oil may cause the poisoning. 
Regarding the length of time it takes for the disease to appear 
after contact with the plant, it has been found that it may vary 
from eighteen hours to nine days. Thus it may readily be under- 
stood that one may have been in a position to touch a plant, and 
after a week, when the poisoning finally results, have forgotten the 
occasion. This may explain many of the cases where poisoning 
