Ammoniacum, or gum ammoniac , is a gum-resin exuded from the stem of a perennial herb (Dorema ammoniacum), natural order Umbelliferae. The plant grows to the height of 8 or 9 ft., 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 tears, forming the "tear ammoniacum" 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. Ammoniacum has a faintly fetid, unpleasant odor, which becomes more distinct on heating; externally it possesses a reddish-yellow appearance, and when the tears or lumps are freshly fractured they exhibit a waxy luster. It is chiefly collected in central Persia, and comes to the European market by way of Bombay. Ammoniacum is closely related to asafoetida and galbanum (from which, however, it differs in yielding no umbelliferone) both in regard to the plant which yields it and its therapeutical effects. Internally it is used in conjunction with squills in bronchial affections; and in asthma and chronic colds it is found useful, but it has no advantages over a number of other substances of more constant and active properties (Sir Thomas Fraser). Only the "tear ammoniacum" is officinal. African ammoniacum is the product of a plant said to be Ferula tingitana, which grows in North Africa; it is a dark colored gum-resin, possessed of a very weak odor and a persistent acrid taste.