AMMONIACUM or GUM AMMONIAC, a exuded from the stem of a perennial herb (Dorema ammoniacum), family Umbelliferae. The plant grows to the height of 8 or 9ft., and its whole stem is pervaded with a milky juice, which oozes out on an incision being made at any part. This juice quickly hardens into round tear-like bodies, forming the "tear ammonia cum" of commerce. "Lump ammoniacum," the other form in which the substance is met with, consists of aggregations of "tears," frequently incorporating fragments of the plant itself, as well as other foreign bodies.