This section is from the book "A Text-Book Of Pharmacology, Therapeutics And Materia Medica", by T. Lauder Brunton. Also available from Amazon: A text-book of pharmacology, therapeutics and materia medica.
(1) Sanguisuga medicinalis, the speckled leech; (2) S. officinalis, the green leech. Collected in Spain, France, Italy, and Hungary.
Characters. - Body elongated, two or three inches long, tapering at each -end, plano-convex, wrinkled transversely; back olive-green with six rusty-red longitudinal stripes. (1) Belly greenish-yellow, spotted with black; (2) belly olive-green, not spotted.
Action. - At the anterior extremity the leech has a sucking disc, in the middle of which is a triradiate mouth furnished with sharp teeth. Fixing itself to the surface by its disc, it saws through the skin and sucks the blood. This process is facilitated by the power of destroying the coagulability of the blood which the secretion from the pharynx of the leech possesses (Haycraft). This secretion is probably the cause of the ecchymoses which frequently occur at the bites as well as of the persistent haemorrhage they sometimes occasion.
Uses. - Leeches may be employed as a substitute for general blood-letting in women and children. They are more generally employed for the purpose of local depletion in inflammation. The irritation occasioned by the bites has probably a certain counter-irritant action (p. 341), but the relief they afford is chiefly due to the depletion. They are useful in bruises, fractures, inflamed joints, meningitis, otitis, ophthalmia, persistent headache, laryngitis, pleurisy, pneumonia, pericarditis, hepatitis, orchitis, and haemorrhoids.
Application. - Each leech draws on an average about one and a half fluid drachm of blood. By applying fomentations afterwards, as much again, or even more, may be withdrawn. Care should be taken that leeches which have been applied to anyone suffering from an infective disease should not be used again, lest they convey the virus. When they are to be applied to a mucous membrane, such as the tonsil, they should be put in a leech-glass. This is a small syringe large enough to hold a leech. The head of the animal is introduced first, and the body gently pushed down with a piston. The nozzle of the leech-glass is large enough to allow the head of the animal to protrude, but not to allow the body to follow.
Leeches may be applied to the skin by simply confining them to the spot with a pill-box; or a piece of blotting-paper, with holes in it at the points where we wish the leeches to fix, may be laid on the skin, and the leeches kept over this by a wine-glass or tumbler. It is sometimes difficult to make leeches bite. The skin should be carefully washed, and thoroughly dried and warmed, and, if necessary, shaved. The room should be well ventilated and free from tobacco-smoke, and from the fumes of vinegar or disinfectants. Leeches should be dried in a soft warm cloth and then applied. If a single one is to be used, the body may simply be held in the cloth, and the head allowed to reach the skin. A slight movement of withdrawal being now made, the leech will probably fix. Care should be taken not to withdraw it so strongly as to tear it from its hold. When difficulty is still experienced in making the leeches bite, a little warm milk, sweetened with sugar, may be rubbed over the skin, or a drop of blood extracted from the finger by a needle may be used for the same purpose. Usually leeches fall off when they are full, but if they do not they can be detached by sprinkling salt over them. If it is desirable to encourage the bleeding, warm fomentations, poultices, or cupping-glasses may be employed. The bleeding may be stopped by applying a small piece of absorbent cotton-wool, or of lint rolled into a hard cone and fixed over the bite with a compress and bandage. Cobwebs used in the same manner are very efficacious. If these are insufficient, a piece of absorbent cotton-wool dipped in strong solution of perchloride of iron and dried, or the styptic collodion of the U.S.P., may be applied. When other means fail a pointed stick of nitrate of silver may be pushed into the bite, or the bite may be transfixed with a needle and a silk thread passed in a figure-of-8 around it. If possible, leeches should not be applied at night, especially to feeble individuals or children, unless the-patients are carefully watched, as, if haemorrhage from the bite should occur, it might not be noticed until much blood had been lost. Leeches should not be applied over loose cellular tissues where pressure cannot be applied. In inflammation of the eyes they should be applied to the temples, and not to the eyelids; and in inflammation of the testicles to the perineum, and not to the scrotum. As the marks of the bites are permanent, care should be taken to apply leeches, if possible, where the marks will not appear. Thus, in applying them to the temples the hair may be shaved off a spot and the leeches applied. When the hair grows the marks will be hidden. In applying them to the chest in girls they should, if possible, be placed so low down that the marks will not be seen when evening dress is worn.
If leeches should get into any mucous cavity - nose, stomach, or rectum - they may be dislodged by the injection of strong; brine.