Medical uses.-Leeches appear to have been first used by Themison.3 They are applied in cases where there is local congestion, and in febrile affections, accompanied with local inflammation, and in which local blood-letting is consequently necessary, as in ophthalmia; and particularly to places where cupping-glasses cannot be applied. In some habits, where there is a disposition to erysipelatous inflammation, their bites, which are triangular, occasion a considerable degree of irritation, and oedematous swellings follow, which are exceedingly troublesome; but in general they easily heal, and occasion no inconvenience. It is sometimes exceedingly difficult to make them bite, which they never will do when they are sick. The best mode of applying them, is to take them out of the water for some minutes before they are to be used, and to dry them well with a very soft cloth directly before they are applied. The part should also be well cleaned with soap and water, then washed with a little pure water, and made very dry. If there be any hairs on the spot, these must be close shaved.

I have found this method preferable to that of wetting the part with milk and sugar, blood, or any other matter.1 When they, nevertheless, will not readily fix, or when it is wished to apply them very exactly on a particular spot, as, for instance, close to the angle of the eye in ophthalmia, Dr. Johnson recommends to puncture the part with a lancet; but I find that putting them into a large quill cut at both ends, and applying the end at which the head of the animal lies to the part, with the finger over the other end, is an excellent mode of making them bite. The quill is withdrawn after they are firmly fixed. They drop off spontaneously whenever they have gorged themselves with blood; and they may be separated at any time by sprinkling a little salt on the head. Very few leeches can draw more than half a fluid ounce of blood; and, therefore, it is necessary, in order to increase the quantity, to keep the orifices bleeding by bathing them with hot water, or by the application of a hot dry towel or a poultice. It has been recommended to cut off the tail of the leech, so as to allow the blood to be discharged as fast as it is sucked, the leech continuing to suck notwithstanding this mutilation. The cause of the leech dropping off when it is full, has never been philosophically examined.

It appears to me to depend on the compression of the breathing vesicles2 of the animal, by the distension of the stomach and intestinal canal, opposed by the skin having only a limited extensibility, so that the animal being no longer able to breathe falls into

Horn's Archiv. fiir medizinische, etc. Jan. 1826.

2 Dr. Johnson says they live by adhering to and sucking the fluids of fish, frogs, etc.; but they take no kind of solid food.- Treatise on the Medicinal Leech, p. 61.

3 The annual consumption of leeches in Paris alone is three millions, Richard's Hist. Nat. Med. torn. i. p. 357.

1 Dr. Johnson recommends that they be put into a cup of porter, "which will induce them to bite with great avidity."-l. c.

2 These vesicles are arranged along each side of the animal, appearing by an external pore which is guarded with rays that act as gills when the animal is in the water.

a state of asphyxia; consequently it loses all muscular energy; and thus, being unable to retain itself longer on the-part, it drops off. After leeches drop off, the application of a very little salt makes them disgorge all the blood they have sucked : and if they be immediately thrown into clean water, and this repeatedly changed for three or four times, they soon recover their health and vigour. Dr. Johnson advises the use of vinegar instead of salt, which is not apt to blister the lips of the leech as salt does, preventing it from sucking for some considerable time; but, perhaps, it is still better merely to strip them through the fingers, and then throw them into clean water. Sometimes it is extremely difficult to stop the haemorrhage from leech-bites in children : every kind of styptic has been used without effect, and the result has proved fatal. In obstinate cases, a small sewing needle may be passed across the wound, and a thread twisted round it thusHirudo The medicinal Leech Continued 193 as in the operation for hare-lip.