902 The American Naturalist. [October, 
action according as they are more or less volatile. In the case of Rhus 
poisoning the latent period between exposure and the first symptoms 
of dermatitis, is a comparatively long one, amounting often to several 
days. This would suggest that the poison is not a volatile substance 
but something of a more fixed nature. However, as the prevailing 
opinion strongly favored the idea that Rhus poison pervaded the air in 
the neighborhood of the plant, Dr. Pfaff first proceeded to extract by 
steam distillation Maisch’s “ toxicodendric acid,” which after combina- 
tion with barium and sodium was found to be nothing more nor less 
than acetic acid. Hethen tried quite a different plan and by distilling 
alcoholic extracts of Rhus toxicodendron and R. venenata he obtained 
a black oily residue, which when purified gave an oil of agreeable odor. 
This oil was readily soluble in alcohol, ether, benzol, etc., but insoluble 
in water. On prolonged exposure to air it turned toa resin. The 
effects of the oil, for which the appropriate name Towicodendrol is sug- 
gested, were repeatedly tried upon the persons of several assistants and 
others offering themselves as subjects. In all cases it proved a most 
active skin irritant, producing, even when applied in very small quan- 
tities, highly characteristic cases of Rhus poisoning. There can, there- 
fore, be scarcely a doubt that the true principle has now been discov- 
ere 
Notwithstanding the popular impression that a volatile poison emi- 
nates from the Rhus, which thus acts upon sensitive persons even at a 
distance, no signs of such action have been detected by Dr. Pfaff and 
his assistants. Although they have experimented upon many pounds 
of fresh R. toxicodendron and R. venenata, no case of poisoning has 
occured except after actual contact with the plants or with objects 
which the plants have touched. Dr. Pfaff suggests that the pollen may 
at the time of anthesis act as a transporting agent, but that the popu- 
lar opinion has probably arisen through frequent cases of poisoning by 
. unconscious contact with the plants or with clothing or other objects to 
which the viscid oil has adhered. The extended latent period, of 
course, adds greatly to the difficulty of eliminating such possibilities in 
particular cases. The practical outcome of Dr. Pfaff’s discoveries 18 
that we may now have an intelligent treatment in cases of Rhus poison- 
ing, and he points out that the best remedy at all stages is the very 
simple one of removing the irritant by thoroughly brushing the affected 
parts with soap and water, while on the other hand, the application of 
oils, vaseline, or even alcohol, if not at once removed, only serves to 
spread the poisonous principle, since it is readily soluble in these 
media. 
