(quasiAaiir«do,from haurio, to drawout). The Leech; sanguisuga, exos; first noticed by Themi-son. Those whose backs are striped, and bellies spotted, which are taken from clear running waters over a sandy bed, are preferable.

The hirudois a genus of aquatic vermes, characterised by an oblong body, very contractile; having each extremity capable of being expanded into a fleshy disc, by which they adhere to the body, with a kind of suction similar to that of a cupping glass; a triangular mouth situated under the anterior extremity.

The body of a leech is composed of numerous rings, or rather circular muscles, by which the particular motions of the animal are performed. Their skin is unequal and tuberculous in different degrees, in the different species, but always feels smooth to the touch, because it is covered by a slimy fluid, designed to facilitate its motions. Their head, in a state of contraction, is more pointed than the opposite end: but each extremity is equally enlarged when they fix. The mouth of the leech is a triangular aperture, placed at the bottom of what may be styled the anterior cupping glass, armed with three very sharp, strong teeth, which can pierce even the skins of horses and oxen. It is an instrument with three cutting edges, each of which is furnished with sixty little teeth. At the bottom of the mouth is a nipple of a firm fleshy consistence, which sucks the blood that exudes from the triangular wound by exhausting the air. In this operation the nipple fixes on the skin, and when drawn back a vacuum ensues. After the wound is made, the action is apparently repeated, and the power is so considerable as to fill the vessels around; a circumstance from which both advantages and inconveniences arise.

We next find the larynx, whose strong fibres contract the diameter of the canal, and carry the blood, which has been drawn, into the stomach. This viscus consists of a series of membranous sacs, furnished with valves, which can retain the blood for many months without coagulating. In a leech of a moderate size there are about twenty-four of these sacs. As the blood which they draw contains no heterogeneous particles, they require no aperture to carry off the excre-mentitious parts, and have consequently, it is said, no anus. M. Morand, from whose Memoir on Leeches much of this description is drawn, thinks that the slimy moisture on the surface, which is thrown off in blackish filaments, found in the water they inhabit, may form the whole of the excrementitious fluids of the constitution.

On each side, under the belly of the leech, are two longitudinal vessels which divide into branches; contract and dilate; carrying a grey fluid. In the middle is a nervous cord, composed of twenty-three ganglia; and on each side glands filled with a clear liquor. These glands have several vessels, which are lost in the body of the animal. So distant from the truth are those physiologists who deny that the Galvanic power acts on the nerves, because leeches are affected by it, supposed to have no nerves.

Leeches seem to breathe by the mouth, but have no organs which correspond to lungs. Insects which breathe by lateral spiracula are killed when covered with oil. When the leech is put into oil, it lives many days, and a slough separates from it, so tenacious, when taken out, as to retain the form of the body. The greater number of leeches have eyes, and some species have so many as eight; but in others no such organ has been observed. These animals swim, like eels, by a vermicular motion; but this is more generally in a longitudinal than in a lateral direction. When they walk they fix the fore part of the body by the mouth, and then draw the back part. They then fix the latter, and extend the former.

When the greater number of the species of hirudo are cut transversely, the two parts do not immediately die, for the head lives considerably longer than the tail. If the section is not complete, the animal raises the wounded part above the water, and keeps it in the air, till each end is cicatrised, for the parts never unite; and the fluids, usually carried downwards, are discharged in abundance from the wounded part. The operation greatly weakens them, and they soon become a prey to those with whom they are placed, after the cure has been completed.

Leeches are hermaphrodites, and generally viviparous. The organs of generation, according to Redi, resemble those of a snail. The penis lies under the oesophagus, and the aperture of the vagina immediately below it. Their young are born in the earliest part of the spring. As the animals are semitrans parent, the young are seen in the body of the mother, in the form of round seeds, and seventy have been counted in a single leech. In their progressive state they seem to grow not only by evolution but by augmentation, as the number of the rings seems to increase.they are found in fresh and salt water. The former prefer lakes or ponds where a great quantity of vegetables grow. They are common in every part of Europe; but less so in the southern regions. They appear to live for many years; but, independent of the danger of the lakes being dried, or the waters putrifying, they are devoured by fish, water fowl, by the larvae of insects, and by the insects themselves. They also devour each other; and Vauquelin found that the hungry leeches bled without mercy those which were full. When in want of blood, they suck the larvae of insects, worms, and other animals, which live or are found by accident in the water. They can live with little nourishment for many months, and pass the winter, often a great part of the summer, involved in the mud, when the lakes are dry, without eating.

Sea salt, tobacco, and every salt or acrid substance, kill these animals, and this is the method of disengaging them from the body; for if torn off, the head is left in the wound, and a troublesome suppuration ensues. If cut in two, the head continues the suction, while the blood is discharged from the wound, and all the consequences of an haemorrhage follow.

The hirudo medicinalis Lin. is the species chiefly employed; and the hirudo sanguisuga, or black leech, is accounted poisonous. It seems, however, only to make a larger wound, and to suck with more violence. They must be collected in the spring, kept in pure water, which must be frequently renewed, in a place not too warm. It is advised that some clots of blood should be occasionally thrown into the water, while a certain proportion should be kept hungry, for immediate use. Some years since, leeches were supposed to be useful barometers, and it was said that they lay at the bottom of the vessel when the following day would be clear and warm; but that when rain would come on before the noon, they mounted to the surface, and continued there till the fine weather returned. When a storm of wind approached, they were said to run round their prison with considerable celerity, and to stop only when the wind began to blow. When a tempest approached, the leech was said to rise out of the water, and continue above it many days, appearing restless and agitated; that it remained at the bottom of the bottle, contracted to a round ball, during a frost; and during snow and rain it fixed itself to the stopper of the bottle, remaining at rest. These phenomena may be correctly stated,and a single leech may appear to feel the variations of the atmosphere; but whoever has observed many of these animals in a glass vessel, will have perceived that, in any circumstances, they have appeared sometimes still, occasionally restless, some at the bottom, others at the top, of the vessel, some unquiet, others at rest. They are certainly very susceptible of the effects of lightning, and often killed by it. A small species was found in Egypt, not larger than a hair when not gorged with blood. They often fixed in the throat of the soldiers, and were only removed by forceps. In medicine we employ only the two following:

1. Hirudo medicinalis, long, blackish, with lines of different colours, spotted with yellow below, and without eyes. 2. Hirudo sanguisuga, the horse leech,long, black, of a greyish green colour belw . About four teen or fifteen species are known, one of which is de-scribed in the first volume of the Linnaean Transactions. p. 188, and said to breathe by gills; but should the latter be true, the animal must be referred to another genus. The author, however. Mr. Menzies, is not explicit on this part of his subject: the setae he describes may not be, or may not lead to, gills. Another leech is described in the same volume by Dr. Shaw, p. 93, hirudo viridis. It is oviparous, and, like some other species, is reproduced by cutting.

We have enlarged more fully on this subject because we have no accurate description of this useful animal in our own language. We must now return to whs more strictly our object, their medical use.

Leeches have lately become a fashionable remedy in every topical inflammation, in topical pains, and in the greater number of tumours, internal bruises, and obstructions. In scirrhi and incipient cancers they are highly commended; in the white swelling of the knee, in swellings of the periosteum, in the inflammatory state of buboes, they are supposed to be highly useful. In fact, they have been so much employed that our ponds and lakes have been, in a great measure, depopulated; and in many parts of the kingdom they are with difficulty procured. The mode of their operation must be afterwards considered, but the principles are sufficiently explained under the article of Blisters, q. v. The peculiar advantages which result from their use seem to be owing to their exhaustion. They fill the vessels around, and not only relieve from the quantity of blood which they draw, but from that which they accumulate in the subcutaneous vessels. By this effect they are often singularly useful; but from the same circumstance, the bleeding, if a bone be not subjacent, is with great difficulty stopped. Equal advantages may be often obtained by cupping with scarifications, without the same disadvantages; and this operation should, in many instances, be preferred.

The leech, when full of blood, drops off; but should it not do so in time, a little salt will always induce it to quit its hold. Salt has been thrown on the animal to make it disgorge the blood which it has sucked, but the leech is generally killed in the experiment. A more easy way to discharge the blood, and save the animal, is to hold it in the hand, and gently squeeze it in a napkin from the head downward. The blood flows copiously from what may appear the anus, or through the ruptured extremity of the intestinal canal, and the worm is not essentially injured.

Leeches must be kept hungry, and the part to which they are to be applied must be wetted with warm milk, blood, or syrup. If a sufficient quantity of blood is not drawn, cloths wrung out of warm water must be applied on the orifice, or the part may be put into warm water: in either way the bleeding may be prolonged.

Leeches are sometimes applied to the anus when the haemorrhoids are suppressed, and to the gums in inflammations from teething. In each case they may escape into the intestine or the throat; but an injection of salt, dissolved in the infusion of tobacco, will destroy them in the former instance, and gargles or draughts of salt water in the latter. In general a healthy leech will suck about an ounce of blood; but warm cloths

5D will continue the evacuation for some time after the animal is satiated.

The curious may consult the following writers on leeches, viz. Aldrovandrus, Gesner, Swammerdam, Redi, and Stahl. Among the moderns, the Memoirs of Morand, Bosc, and Vauquelin.