La ee eA Pe 
4 Sas 
MISSOURI BOTANICAL GARDEN BULLETIN 89 
wearing a linen mask for the face and a leather apron for the 
body when at work. After work the exposed parts are rubbed 
with a concoction of chestnuts, pine bark, saltpeter, and 
amaranth. 
Much scientific investigation has been devoted to attempt- 
ing to isolate and determine the character of the poison from 
poison ivy and related plants. While numerous ideas have 
been advanced from time to time, it is now pretty well estab- 
lished that the poisonous substance is a non-volatile oil, or 
yellowish brown viscous material, which must come in actual 
contact with the skin before the burning effect is produced. 
This does not necessarily mean that one must actually touch 
the plant, since the smoke from burning plants may carry the 
poison, and contact with articles of clothing, shoes, wagon and 
automobile tires, or anything that has passed through plants 
of poison ivy may sometime later be the cause of a case of 
poisoning in a person who is quite sure that he has been no 
place near the plant. Cases are on record where Christmas 
greens have carried the poisonous oil, although the poison ivy 
itself was not included in the shipment. Although it may 
not agree with what many who are subject to ivy poisoning 
regard as their experience, all the evidence points to the fact 
that the sap of the plant is the only part containing the poison 
and that those parts of the plant devoid of resin canals are 
harmless, thus eliminating as sources of the disease the 
anthers and pollen, the epidermis, and plant hairs. 
It should also be remembered that many other plants are 
capable of producing a dermatitis that can scarcely be distin- 
guished from that produced by a member of the genus Rhus. 
At least a hundred different plants are known to be respon- 
sible for producing eruptions on the skin and, while some of 
these effects are due to personal idiosyneracies, the fact re- 
mains that poison ivy and its near relatives should not have 
all the blame. At least three other types of disease of the 
skin caused by plant products are known in addition to that 
produced by species of Rhus. Perhaps the commonest is 
that produced by various stinging nettles. These plants are 
provided with hairs with small bulbous tips. A very slight 
touch is sufficient to break off the tip, leaving a finely pointed 
