Part II.

Materia Medica,

Diib.

149

HlRUDO MEDICINALIS.

The leech.

CI. Vermes. Ord. Helmintheca.

Only one species of leech is used in medicine. It has aflat and slimy body, composed of rings, tapering towards thehead, which is turbinated, commonly about two or three in-ches long, and of the thickness of a goose-quill, but capableof elongating or contracting itself very much. Its back is ofa dull olive-green colour, divided into three nearly equal partsby four yellow longitudinal lines, the two lateral entire, thetwo central broken with black. Besides these, between thelateral and central lines on each side, there are two others,resembling a chain of black and yellow. The belly is turkeyblue, irregularly marked with yellow spots. It attaches itselfto solid substances by either end, being furnished with a cir-cular sucker at the anal extremity, and a horse-shoe one atthe head, with a triangular mouth in the centre.

They should be collected in summer, in waters having aclear sandy bottom, as the bite of those found in stagnant wa-ters and marshes is said to cause pain and inflammation. Forthe same reason, the horse-leech, which is entirely brown, oronly marked with a marginal yellow line, is commonly reject-ed, although they are used frequently in the North of Europe,and during the late scarcity of leeches have occasionally beenemployed, without any bad consequences, in this country.The vulgar story of their drawing the whole blood out of thebody, by evacuating it at one end as fast as they sucked it inat the other, if true, would give them a superiority over theothers, as when a sufficient quantity of blood was drawn, therecould be no difficulty in making them quit, even without pass-ing a ligature round their necks.

Leeches are best preserved for use in a bottle half filled withpure spring or river water, and covered with gauze or muslin,although they are said not to.die even in an exhausted receiv-er, or in a vessel filled with oil. It is advisable frequently tochange the water in which they are kept, although there areinstances of their living many months, and even years, in thesame water ; and it is remarkable that water, in which theyare, keeps much longer sweet than by itself. It is scarcelynecessary to observe, that whenever the water becomes turbid,or foul, or gets an unpleasant smell, or any of the leeches diesin it, it should be changed. They should always be kept in amoderate temperature, about 50° Fahr. Some recommendthrowing a little bran into the water; but it is so well ascer-tained that they will live for years without any such addition,that it is better not to attempt to feed them, until we are bet-