1 Syst. Nat. Gmelin. i. 3095. Div.3. Cl.1. Articulata, Annelidae, Cuv. G. 280. Body oblong, truncated at both extremities, cartilaginous, moving by dilating the head and tail. Sp. 2. H. medicinalis. The medicinal Leech. Amoenit. Academ.

vii. 40. Treatise on the Med. Leech, by J. R. Johnson, Lond.

1816. Hist. Nat. des Sangsnes, par J. L. Derheims, Paris,

1825. Officinal. Hirudo, Lond. Hirudo medicinalis, Dub. The Leech.

Syn. Sangsue (F.), Blutegel, Aegle, Lyche-lake (G.), Blodigle (Ban.), Pijavoka (Polish), Sanguisuca, Mignatta (I.), Sanguijuela (S.), Kheruheen (Arab.), Jonc (H.), Jelauca (Sans.), Utter (Tarn.), Patchet (Malay), Zeloo (Pers.), Lek, Leikeis (Maeso-Gothic), La?c, Lece (Saxon), Laekare, Lzeknare ( Gothic and Swed.), Likaer (Sclav.).

This species of leech is common throughout Europe, America, and India, inhabiting lakes and stagnant pools. Many of the leeches used in England are brought from France, which again is supplied from Spain, Bohemia, and the frontiers of Turkey. The body is about three inches long, tapering towards the head, composed of semi-cartilaginous, dilatable rings, usually about one hundred, increasing in size, but not in number, with age. They are capable of only a certain degree of extension. The body is capable of being very much lengthened and contracted. The colour of the back is dark olive, divided by four yellow, or buff-coloured, longitudinal lines, two of which are lateral, with a black line running through their centres : and the other two, which are on the upper part of the back, dividing it into three nearly equal parts, are broken with black macula. Within these lateral and upper lines are two others, which appear like chains of black and yellow. The belly is pale olive, thickly maculated with black, or very dark blue, irregular spots. The skin is mucose, spongy, and covered with a black pigment, formed of molecules of various sizes. The surface is extremely susceptible of touch.

The head, when the animal is at rest, is a disk of a horse-shoe shape, composed of three capillary straight muscles, radiating from the gorge to the circumference of the disk. There are ten points arranged in a crescent at the back of the head, deep black, and when moistened having a fine lustre, which are supposed to be eyes. The mouth consists of two lips, placed in the centre of a horse-shoe sucker which is under the head; within it are three small white bodies which act as teeth: these are somewhat pyramidal, plaited, lanceolate, and hollow; they can be dilated with air by the animal, so as to assume this form, in which state they are sufficiently tense to pierce the skin of man and other animals. When all the three teeth are forced into the skin they form a triangular puncture.1 Straus-Durkheim says that the teeth are small, horny, numerous, and form a kind of saw2: and at the anal extremity there is a broad circular sucker, fibrous, with the fibres, which are fleshy, divaricating from a central point3, by which the animal attaches itself to different bodies.

Graecorum. Named by the Romans haurio, expressive of its well-known peculiar action,-Johnson's Treatise, p. 40.

Leeches are oviparous. They are androgynous, and the generative process is performed by reciprocal and spontaneous impregnation. The ova are cocoons, each of which contains nine leeches. The young escape from the cocoon in 26 to 28 days.4 All the cocoons are discharged in one involucre, near the surface and the margins of pools, and are hatched by the heat of the sun. They do not cast the skin, as has been generally supposed, but at certain times throw off a tough slimy substance from their bodies, apparently the production of disease; and from which they get disencumbered by drawing themselves through between the moss and the matted roots of rushes.5 During winter they remain almost torpid, hid amongst the thick network of aquatic roots which surround the pools. They are very tenacious of life; for they live for many days in the exhausted receiver of an air-pump, and in gases and other media which in general are destructive of animal life. This is to be explained by the slow oxygenation of the blood which takes place in the breathing vesicles.

Norfolk supplies a great part of the leeches which are brought -to the London market; some are taken also in Suffolk, Hampshire, Kent, Essex, and Wales, but many are imported from Bourdeaux and Lisbon.6 La Brenne in France furnishes a large number. They are caught in spring and autumn by people who wade into the pools and allow them to fasten on their limbs; or, more generally, the catchers beat, as they wade in, the surface of the water with poles, which sets the leeches in motion, and brings them to the surface; when they are taken with the hand and put into bags. As they come to the surface just before a thunderstorm, this is regarded as a good time for collecting them. They are put into bags and pressed very closely together. They are best preserved in wooden vessels half filled with soft water, kept in an equal and moderate temperature (50° Fahr.), and covered over with a coarse cloth so as to admit the air. When the number is great, the water should be drawn off by a cock, placed about 2 1/2 inches above the bottom of the vessel, which should be covered with a layer of moss-turf and wood charcoal, with some small stones heavy enough to keep the turf in its place; and several small roots of the Acorus calamus should be placed in the vessel to vegetate, as this plant is supposed to yield nutriment to the leeches.1 The water should be changed once a week; and all the dead or sickly leeches,-such, for instance, as feel flabby, or exhibit protuberances or white ulcerated spots on the body,-should be removed from the general stock, for they are subject to many diseases and great mortality.

When the water is not changed, the leech suffers from inflammation of the intestinal canal, in which case it will not suck. Leeches which have been used should not be returned to the stock till they appear to have completely regained their health and vigour, which is known by their feeling hard and firm when handled. As we are ignorant of their proper and natural food, it is useless to attempt to feed them2; but in winter it would, perhaps, be advantageous to put some moss into the vessel in which they are preserved. Owing to the scarcity of the medicinal leech, a species, named troctina by Dr. Johnson, has been much used. It differs from the medicinal leech in being marked with golden-coloured rings surrounding a black spot, on a brown ground: the sides are yellowish, and the belly greenish yellow, spotted with black.

1 Derheims, Hist. Nat. des Sangsues.

Consid. generates sur l'anatomie cornp. des animaux articules, p. 220.

3 The organs of touch are supposed to reside in the lips and disc of the caudal extremity; those of taste, in some nervous fibrillar in the upper part of the oesophagus; those of hearing, unknown; and of smell, probably, in the punctata respiratoria. The leech, however, breathes by oscula with gills, under which are small bags situated beneath the intestinal canal.

4 Journ. de Phys. experien. tome vii. 1827.

5 I give this on the authority of Mr. Dickson of Covent Garden, who has made many curious observations on the economy of the leech.

6 These differ from English leeches chiefly in having the belly of one uniform colour.