May, 1921] 
MCNAIR TRANSMISSION OF RHUS POISON 
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the irritant, the quicker is its action on the skin. Formic acid acts very 
quickly; acetic acid, less volatile than formic, acts more slowly, but still 
much more quickly than poison ivy, the latent period of which is usually 
from two to five days. Pfaff thought that the volatile acid obtained by 
Maisch might have contained some of the poisonous principle as an im- 
purity, but that it could not produce the dermatitis if prepared in a pure 
state. He therefore prepared a quantity of the acid by distilling the 
finely divided fresh plant with steam. The yield was increased by acidu- 
lating the mixture with sulphuric acid before the distillation. The acid 
distillate so obtained was freed from a non-poisonous oily substance by 
shaking the solution, with ether. Barium and sodium salts were made by 
neutralizing the acid and were purified by crystallization. Analysis showed 
them to be salts of acetic acid, and they gave the characteristic tests for 
this acid. The toxicodendric acid" of Maisch was thus shown to be 
acetic acid, and not therefore the poisonous principle of the plant. 
Pfaff obtained the active principle by the process which he outlines. 
The lead compounds made in different preparations were analyzed and 
assigned the formula C2iH3o04Pb. The oil itself was not analyzed. Pfaff 
proposed the name toxicodendrol for the oil. He found that it is not 
volatile, is decomposed by heat, is soluble in alcohol, ether, chloroform, 
benzene, etc., but insoluble in water. Its effects upon the human skin 
were studied in many experiments upon himself and others. It was shown 
that an exceedingly minute quantity of the poison will produce the der- 
matitis, even i/iooo milligram appHed in olive oil being active. The oil 
was given internally to rabbits, its effects being most marked on the kidneys. 
Acree and Syme (i) found gallic acid, fisetin, rhamnose, and a ''poisonous 
tar, gum, or wax" in the extract prepared by maceration of the leaves and 
flowers of poison ivy with ether, and subsequent distillation of the solvent. 
The lead compound of this poisonous substance was found to be soluble in 
ether. The authors utilized this property to free the poisonous material 
from admixed non-poisonous substances. Lead compounds were first 
prepared by precipitating an alcoholic solution (of the ether extract of the 
drug) with lead acetate. The precipitate was washed with water, partially 
dried over sulphuric acid, placed in a Soxhlet apparatus, and extracted 
with ether until the solvent came over colorless. A green solution was 
obtained which was washed with water and decomposed with hydrogen 
sulphide. On evaporating the solvent, a black, poisonous "tar or gum" 
remained. Upon hydrolysis with 2 percent sulphuric acid, this poisonous 
substance gave fisetin, rhamnose, and gallic acid. The residue in the thimble 
was decomposed by hydrogen sulphide, shaken with ether, and evaporated. 
A hard, brittle, yellow, non-poisonous resin was obtained. The authors 
believe the poisonous principle of poison ivy to be a complex substance of 
glucosidal nature. 
Chyser in 1910 considered the poison of Rhus a toxalbumin formed by 
