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To the Editor:
—The statement referred to by Dr. Mann, which is due to Dr. Franz Pfaff, formerly of the Harvard Medical School, is quoted correctly as printed. Several years ago I attempted (Pharm. J.83:562, 1909) to verify Dr. Pfaff's experiments, using the purified resin from the poison sumach instead of that from the poison ivy (the two poisons are believed to be identical). These attempts to obtain an exact quantitative limit to the amounts which would produce symptoms were discouraging, probably from want of a sufficiently sensitive subject on which to make the tests. The fact was verified, however, that the substance is poisonous in extremely minute quantities—far less than 0.001 gm. The minute dosage is obtained by suitable dilutions in alcohol.
Warren LE. "DESENSITIZATION OF PERSONS AGAINST IVY POISONING". JAMA. 1919;73(20):1543. doi:10.1001/jama.1919.02610460061028
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