This section is from the book "Materia Medica Pharmacy, Pharmacology And Therapeutics", by W. Hale White. Also available from Amazon: Materia Medica Pharmacy, Pharmacology And Therapeutics..
B. P., not official. - Two species are employed: (1) Sanguisuga medicinalis, the speckled leech (belly greenish-yellow, spotted with black); (2) Sanguisuga officinalis, the green leech (belly olive-green, not spotted), (nat. ord., Annelida).
Characters of both species. - Body soft, smooth, 5 or more cm. long, tapering to each end plano-convex, wrinkled transversely, back olive-green, with six rusty-red longitudinal stripes. Each leech has a muscular disc at each end. In the centre of the anterior one is a tri-radiate mouth, provided with three saws and two rows of teeth.
The leech, although not a drug, is considered with this group for convenience.
Leeches are used to remove blood. They are usually applied over deep seated organs when they are congested, and great relief is often afforded. For example, three or four leeches near the liver, when that organ is enlarged in heart disease, or one or two behind the ear, when the tympanic cavity is inflamed frequently do good. The leech being applied to the skin, the animal fixes itself by its sucker-like disc, makes a tri-radiate cut with its mouth, and draws into its body, which consequently becomes swollen, about a drachm and a half 6. c.c. of blood. If this is not sufficient, a hot fomentation put on, after the animal is removed, may increase the quantity to half a fluid ounce; 15. c.c.. The skin should be well washed with a little milk before the leech is applied. Occasionally the haemorrhage requires pressure, or some local styptic, as ferric chloride or better styptic collodion, to stop it. If leeches have to be applied to the mouth, rectum, or uterus, leech glasses, which only allow the head to protrude, should be used.