Cnicus. Cirsium arvense (L.) Scop. (Cnicus arvensis, Hoffm.) Canada Thistle.—This European composite plant, to which have been attributed diaphoretic, emetic, and tonic properties, according to Herman J. Pierce (A. J. P., lxviii, 1896), contains a volatile alkaloid, and also Cnicin, C42H56O15, which is said to possess emetic and emmenagogue properties.