The classification of poisonous plants according to their effects is a somewhat difficult process, since more than one prominent symptom may be produced by the same plant. Two classifications, however, may be given as examples, the first that of Blyth, and the second that of A. B. Smith. These must be regarded as essentially applicable to human beings, though serving more or less as a guide in case of poisoning of farm live-stock. Blyth’s Classification (after Pammel). =A.—Poisons causing death immediately or in a few minutes=: Prussic acid, cyanides, oxalic acid, and occasionally strychnine. =B.—Irritant Poisons=, with symptoms chiefly pain, vomiting, and purging: Ergot, digitalis, colchicum, yew, laburnum. =C.—Irritant and Narcotic Poisons=, with symptoms of an irritant nature, with more or less cerebral indications: Oxalic acid or oxalates. =D.—Poisons more especially affecting the Nervous System=: 1. NARCOTICS.—Symptoms: insensibility, which may be preceded by more or less cerebral excitement. Opium. 2. DELIRIANTS.—Delirium, for the most part, a prominent symptom: Belladonna, hyoscyamus, stramonium, and other _Solanaceæ_, Lolium temulentum, Oenanthe crocata, poisonous fungi. 3. CONVULSIVES.—Almost every poison has been known to produce convulsive effects, but the only true convulsive poisons are the alkaloids of the strychnine class. 4. COMPLEX NERVOUS PHENOMENA.—Aconite, digitalis. A. Bernhard Smith’s Classification. =A.—Poisons acting on the Brain.= 1. NARCOTICS.—_Symptoms_: Giddiness; dimness of sight; contracted pupils; headache; noises in the ears; confusion of ideas, and drowsiness, passing into insensibility. _British Plants included_: Papaver somniferum. 2. DELIRIANTS.—_Symptoms_: Spectral illusions; delirium; dilated pupils; thirst and dryness of the mouth; incoordination. Occasionally, though rarely, there are paralysis and tetanoid spasms. _British Plants included_: Datura Stramonium, Hyoscyamus niger, Solanum Dulcamara, Solanum nigrum, Atropa Belladonna, Lolium temulentum. 3. INEBRIANTS.—_Symptoms_: Excitement of cerebral functions and of the circulation; loss of power of coordination and of muscular movements, with double vision; leading to profound sleep and deep coma. _British Plants included_: Pinus pinaster, Pinus larix, Artemisia maritima, Artemisia Absinthium. =B.=—=Poisons acting on the Spinal Cord.= CONVULSIVES.—_Symptoms_: Clonic (intermittent) spasms, extending from above downwards. Opisthotonos very violent; but trismus (lockjaw) rare. Swallowing spasmodic. Death, usually, in less than three hours, or rapid recovery. _British Plants included_: none. =C.=—=Poisons acting on the Heart.= 1. DEPRESSANTS.—_Symptoms_: Vertigo; vomiting; abdominal pain; confused vision; convulsions; occasional delirium; paralysis; syncope; sometimes asphyxia. _British Plants included_: Conium maculatum, Cytisus Scoparius.