A case is recorded in New South Wales in which cattle and horses ate Shepherd’s Purse (_Capsella Bursa-pastoris_). The cattle were unaffected, but the horses scoured, though most of them soon recovered when removed from the cultivated paddock containing the weed. Two young horses, however, showed signs of colic, became bloated, and died. It was then found that they contained balls of fibrous material (one weighed 1 lb. 9½ oz.) which consisted to the extent of nearly 50 per cent. of fibres from Shepherd’s Purse, and death was due to simple mechanical obstruction of the bowel (155).
Chickweed (_Stellaria media_) has been found to cause digestive disorder in lambs and sheep when eaten in large quantities (48), and has caused the death of many a lamb. It would appear to be due entirely to the formation of large lumps of the weed in the stomach, and subsequent fermentation (_Farmer and Stockbreeder_, Mar. 16, 1908).
According to Cornevin, Black Bindweed (_P. Convolvulus_ L.) may prove injurious, owing to the occurrence of the hard, trigonous, and pointed “seeds” in cereal grains. Galtier published facts which show that oats which contain too many of the “seeds” may, by prolonged use, occasion a more or less serious enteritis, which is sometimes fatal, particularly when the grain is fed to greedy horses which scarcely grind their food (73). The fruits or “seeds” of Knot-weed (_Polygonum Aviculare_ L.) may similarly prove injurious, and probably the seeds of other plants.
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.
=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.