Leeches are oviparous. The ova remain in the uterus for some time, where they become invested first with a serous membrane, and then with a glutinous fluid, which remains attached to them after their expulsion, and serves as a protecting covering after they are deposited in the clay and holes bf the sides of the ponds. The leeches generally deposit the cocoons from May to the end of September. It would seem that these animals do not multiply in great abundance unless they have tasted blood, particularly that of cows. On this account the leech-dealers of Bretagne drive horses and cows into the ponds to such an extent that the cattle of the district are in general wretched-looking, and the leech-gatherers not much better.
About five years are required before the leech attains a state of maturity ; while very young they are quite unfit for medical purposes. They are caught in various ways, by the hand, or by a person wading in the shallow waters during the spring of the year, when they adhere to his naked legs ; but in summer, as they have retired to deeper waters, a raft is constructed of twigs and rushes, by which a few are entangled. Baits are deposited, generally pieces of decayed animal matter or liver, to which the leeches resort, and are then caught ; but this last method is thought to injure the health of the animal. Many sicken and die on the journey, especially during warm weather. They are conveyed tither in bags or small barrels with a canvas cover.
Leeches are subject to many diseases, several of which are epidemic, and spread in the troughs with great rapidity. On the first appearance of illness the sick should be immediately separated from the healthy. Care should be at all times taken that different species of leeches be not associated in the same trough, for they prey upon each other. The Themopsis vorax, and H. nigra (Pieudobdella, Blainv.), or common black leech, devour greedily the S. medicinalis or S. vulgaris, though they cannot penetrate the akin of vertebrated animals. The horse-leech, Htemopsis sanguisodea, Say. (the Ihrudo sanguisuga, Linn.; Hypobdella, Blaine.), is not certainly without the power of penetrating the human skin, though the black leech, often confounded with it, has no such power, from want of teeth.
A leech may be known to be in good health if it be active in the water and plump when taken out. In Prussia leeches are divided into three classes, according to their weight : the first not exceeding 30 grains ; the second weighing between 30 and 60 grains; the third from 60 to 90. Leeches above 90 grains are not to be used, unless specially ordered. In each prescription the physician is required to state what description of leech he intends should be used. In the case of children
such regulations are highly proper, as an excess of blood abstracted may easily produce serious and often fatal consequences. Leeches vary in the quantity they can abstract, from one drachm to half an ounce : from one to two drachms is the The quantity is often doubled by the expedients resorted to after leech has been removed, either dry or wet clothes being applied, or in many cases cupping-glasses, but cataplasma of linseed-meal are most beneficial where they can be applied.
One gray or German leech is deemed equivalent to two green or Hungarian leeches. The cases requiring or justifying the application of leeches are stated under the respective diseases, and need not be repeated here. It is of more importance to indicate the proper mode of applying them. The leech, though not so accurate an index of the weather as is commonly believed, is yet sensible of atmospheric changes, and in some (probably peculiarly electric) conditions of the atmosphere cannot be induced to bite. In such cases time ought not to be wasted, nor the patient exposed injuriously or kept in a fatiguing position, but some other mode of blood-letting should be had recourse to. More over, if the leech bo sickly, it can rarely be made to bite. Certain states of the patient also hinder or indispose them to bite. Where the skin is very thick they cannot puncture it; or if the person has been using sulphur, the exhalation of the sulphuretted hydrogen is disagree able to them ; even the fumes of tobacco, vinegar, &c., will prevent them biting; also if greens, ash, or vinegar be on the spot to which they are applied, they refuse to attach themselves to it. The existence of heirs on the spot seem te hinder them flora biting, and also from forming a vacuum to suck up the fluid, on which account they should be carefully shared off. The leeches should be taken out of the water, and &Bossed to creep for some time over a dry warm cloth; in the Ilioaavtil., the part where It is intended to apply them should be washed with plain (not perfumed) soap and water, then with water alone, afterwards with milk or porter. It is difficult to make them fix themselves on t b. particular spot wirffied; but a leeeleglaes will gene rally effect this. seal is preferable to holding the leech in the hand. When they sodl refuse to bite. slightly puncturing the part with any sharp instrument. so as to cause a little blood to ooze out, is a useful expedient ; or if we pluck a feather from the wing of any bird, and, cutting off the end, allow the liquid contained in it to be dropped on the spot, the leech will bite readily.