The sensitizing substances present in plants of the family Anacardiaceae are sometimes referred to as urushiols, a name of Japanese origin. It does not refer to a single substance but rather to a group of closely related substances. To quote from the 1883 paper of Yoshida,1 “urushi is the milky secretion of Rhus vernicifera [currently known as Toxicodendron vernicifluum], and is the material for the well-known Japanese lacquer-varnish. The pure and unaltered urushi is a thick greyish fluid of dextrinous consistency, which under the microscope is found to consist of minute globules… the whole being held mixed in the form of an intimate emulsion. If the juice be exposed to moist air in a thin layer at about 20 °, it rapidly darkens in color and dries up to a lustrous translucent varnish. It contains a small quantity of volatile poison, which acts terribly on some persons, producing very disagreeable itching. Urushi juice (lacquer) consists essentially of four substances, viz, urushic acid, gum, water, and a peculiar diastatic matter; and the phenomenon of drying is due to the oxidation of urushic acid into oxy-urushic acid which takes place by the aid of diastase in the presence of oxygen and moisture.”