The origin of their introduction in the practice of medicine is uncertain. They were well known to the ancients under the name of hirudo. Thus Horace:

Non missura cutem nisi plena cruoris hirudo.

The Greeks called them ?Ôe??a, and Pliny states that elephants were often cruelly tormented by them when they swallowed any of these worms in their water: “Cruciatum in potu maximum sentiunt haust hirudine, quam sanguisugam vulgo coepisse appellari adverto.”

Leeches are oviparous, and their ova are discharged in one involucre near the surface and margin of pools, and are hatched by the heat of the sun. They do not cast their skin, as is generally supposed, but merely throw off a tough slimy membrane, which appears to be produced by disease, and from which they get disencumbered by straining themselves through grass and rushes. During winter they remain in a torpid state. They are most tenacious of life; some say they can live for several days in the exhausted receiver of the air-pump, and in other media destructive of other animals. This phenomenon is attributed to the slow oxygenation of the blood in the respiratory vesicles.

In regard to their food we are ignorant, although Dr. Johnson says that they live by sucking the blood of fish and reptiles.

The collection of leeches constitutes a lucrative trade on the Continent, but more particularly in France, where it is called a leech-fishery, and where, in Paris alone, three millions are annually consumed. The following is an interesting description of the miserable people engaged in this occupation from the Gazette des HÔpitaux.

“If ever you pass through La Brenne, you will see a man, pale and straight-haired, with a woollen cap on his head, and his legs and arms naked; he walks along the borders of a marsh, among the spots left dry by the surrounding waters. This man is a leech-fisher. To see him from a distance,—his wobegone aspect, his hollow eyes, his livid lips, his singular gestures, you would take him for a maniac. If you observe him every now and then raising his legs and examining them one after another, you might suppose him a fool; but he is an intelligent leech-fisher. The leeches attach themselves to his legs and feet as he moves among their haunts; he feels their bite, and gathers them as they cluster about the roots of the bulrushes and aquatic weeds, or beneath the stones covered with a green and slimy moss. He may thus collect ten or twelve dozen in three or four hours. In summer, when the leeches retire into deep water, the fishers move about upon rafts made of twigs and rushes. One of these traders was known to collect, with the aid of his children, seventeen thousand five hundred leeches in the course of a few months; these he had deposited in a reservoir, where, in night, they were all frozen en masse.” But congelation does not kill them, and they can easily be thawed into life, by melting the ice that surrounds them. Leeches, it appears, can bear much rougher usage than one might imagine: they are packed up closely in wet bags, carried on pack-saddles, and it is well known that they will attach themselves with more avidity when rubbed in a dry napkin previous to their application. Leech-gatherers are in general short-lived, and become early victims to agues, and other diseases brought on by the damp and noxious air that constantly surrounds them; the effects of which they seek to counteract by the use of strong liquors.

Leeches kept in a glass bottle may serve as a barometer, as they invariably ascend or descend in the water as the weather changes from dry to wet, and they generally rise to the surface prior to a thunder-storm. They are most voracious, and are frequently observed to destroy one another by suction; the strong ones attaching themselves to the weaker.

The quantity of blood drawn by leeches has been a subject of much controversy; but it is pretty nearly ascertained that a healthy leech, when fully gorged, has extracted about half an ounce. When they will not readily fix, Dr. Johnson recommends that they be put into a cup of porter. The cause of a leech falling off when full is not clearly ascertained, but it is supposed to arise from a state of asphyxia brought on by the compression of the breathing vesicles, and the distension of the alimentary tube.

Many serious accidents have arisen from leeches being swallowed in the water of swamps and marshes, too frequently drunk with avidity by the thirsty and exhausted soldier. Larrey mentions several cases of the kind during the French campaign in Egypt, and two fatal instances fell under my observation during the Peninsular war; draughts of salt water, vinegar, and various stimulating injections could not loosen their hold, and they were too deeply attached in the throat to be seized with a forceps. Zacutus Lusitanus had witnessed the same unfortunate results. The leech thus swallowed is generally the hirudo Alpina.

Norfolk supplies the greater part of the leeches brought to London, but they are also found in Kent, Suffolk, Essex, and Wales. The leeches imported from France differ from ours, in having the belly of one uniform colour. The best are the green, with yellow stripes along the body. The horse-leech, which is used in the north of Europe, but also common in England, is entirely brown, or only marked with a marginal yellow line. A popular belief prevails, that the application of this variety is most dangerous, as they are said to suck out all the blood in the body.