"The poisonous weed, being in shape but little different from our English ivie; but being touched causeth reddness, itchings, and lastly blysters, the which howsoever, after a while they pass away of themselves without further harme; yet because for the time they are somewhat painefull, and in aspect dangerous, it hath gotten itselfe an ill name, although questionless of noe very ill nature." The recorded history of poison ivy dermatitis begins with these words of Captain John Smith in 1609.* McNair's wonderful little book ``Rhus Dermatitis" is the most complete treatment of the subject; in it knowledge is summarized up to 1923.1The modern master is Bedford Shelmire; his original studies are impressive examples of biological research at the clinical level.2-7Exclusive of biochemical accomplishments, the remaining literature is excessively preoccupied with prophylaxis and therapy; the yield therefrom is not in proportion to the