Mercury - Dog's Mercury
The Mercuriallis perennis (Dog's Mercury) grows commonly in our hedges and ditches, occurring in large patches, with egg-shaped pointed leaves, square stems, and light green flowers, developed in spikes and it is decidedly poisonous, even when cooked.
The old herbalists called it Smerewort, and gave it for agues, as well as to cure melancholy humours. It has been eaten in mistake for Good King Henry, which is sometimes called Mercury Goosefoot. Some persons style it "Kentish Balsam."
The name Dog's Mercury or Dog's Cole was given either because of its supposed worthlessness, or to distinguish it from the Mercury Goosefoot aforesaid. A medicinal tincture is made from the whole plant freshly collected when in flower and fruit, with spirit of wine; and the dose of this in a diluted form is from five to ten drops, of the third decimal strength, two or three times a day, with a spoonful of water. The condition which indicates its medicinal use, is that of a severe catarrh, with chilliness, a heavy head, sneezing, a dry mouth, and general aching, lassitude, with stupor, and heat of face. Its chemical constituents have not been ascertained. In the Isle of Skye it is used for causing salivation, as a vegetable mercury; and per contra for curing a sore mouth.
Such virtues as the herb possesses were thought to have been taught by the god Mercury. The Greeks called it Mercury's Grass (Ermou poa). When boiled and eaten with fried bacon in error for the English spinach, Good King Henry, it has produced sickness, drowsiness, and convulsive twitchings. The root affords both a blue and a crimson colour for dyeing.