Blood-Letting, in surgery, is performed with a view either to diminish the quantity of the circulating fluid, or to relieve a particu-lar part, in case of inflammation, and, consequently, it is either general or local.

General blood-letting, is that which is performed upon a vein or an artery : hence we have the terms phlebotomy and arteriotomy,

Local, or topical blood-letting, is performed by scarification and cupping-glasses, by leeches, or by punctures made with a lancet, according to the nature of the disorder. This latter, or topical bloodletting, is never dangerous hut in many cases has been found effectual in relieving the patient. With respect to venesection, however, as different opinions are entertained of its utility by different physicians, it may not be improper to offer a few remarks.

There was a period, during which blood-letting was in very general use, and obtained great credit, as-one of the most effectual means of prolonging life : while a plethoric habit was supposed to be a principal cause of early dissolution. Through the veins thus regularly opened, at certain seasons, the superfluous or vitiated blood was emitted, while that of a more salubrious quality was supposed to be left behind. It is now well known, however, that the corrupted part of the blood cannot be separated from the mass, so as to preserve the remaining particles sound and uncor-rupted. If the quality of the blood ever become vitiated and diseased ; if it be too thick and viscous, or too acrid and serous, the whole mass necessarily participates in the infection: neither is it in the power of art to contrive any method, by which the corrupted part may be separated from that which is in a sound state. It would be equally unreasonable to expect, that a spoiled cask of wine could be cured of its tartness, by attempting to draw the acid and impure portion from the top, in order to leave the sweet and wholesome part behind.

Considered as a remedy, phlebotomy must certainly be allowed to possess its uses; it is sometimes a necessary expedient, to produce an immediate diminution of the fulness of the blood, particularly when the time is too short, and the danger too pressing, to admit of any other method for effect-ing that purpose. As there can be no doubt, that blood-letting is an invaluable remedy in some disorders, it is the more peculiarly incumbent on the practitioner, to distinguish with care those cases in which imminent danger may be averted, and health restored by the use of it. There are two cases, and perhaps only two, in which venesection is likely to be attended with real advantage; 1. When it is required to prevent the fluids from gaining access to the parts more essential to life; and 2. Where means must be speedily used to counteract a threatened inflammation in the intestines. But even in those two cases, the intelligent physician is at no loss for other remedies, which may be frequently administered with greater safety and equal success.

The blood contains in itself, and affords to the. vessels, nerves, muscles, membranes, tendons, ligaments, bones, in short, to the whole organized body, all the sub-stance and properties which enter into the formation of each, and constitute them what they are. Each of these parts is evolved from the blood, and adapted to its proper place, in so wonderful a manner, that the human mind is totally at a loss to comprehend how this operation is performed ; neither have the researches of the most acute and attentive, observer been able to account for it. And as the blood serves to supply the waste, and to make up the losses which those parts occasionally sustain, it may be considered as the original source of our whole orga-nization. Now it requires little reflection to perceive, that by wasting this vital fluid, the sources of animal support and regenera-tion are in a great measure obstructed and diminished. Although it be true, that the blood lost by periodical bleedings is soon reproduced by the activity of the vital powers, yet this restoration is not effected without considerable efforts, and at the expence of the whole machine. As this exertion, therefore, is a great pressure upon the vital powers, it must of course be attended with a proportionate degree of their consumption. And experience has shewn in numberless instances, that persons accustomed to frequent blood-letting are not only rendered more delicate in their constitutions, and more subject to diseases, but also that they die in general at an earlier age than others.

The absurd notion, that bleeding is useful and necessary to the prolongation of human life, is still pretty generally received among the common people of all countries. Yet neither the good nor the had days, superstitiously marked in the almanacks for the amusement of the vulgar, can palliate or iustify the mischief with which this dangerous error is pregnant : for bleeding can only be of service in some urgent cases, and when performed at the proper time : but to the healthy it is always injurious.

Blood-letting, in farriery, an operation often undertaken when it is as useless and pernicious as in the human species. Such horses, however, as stand much in stable, and are full fed, occasionally require bleeding, especially when their eyes are heavy and inflamed, or when they feel unusually hot, and champ their hay.

Young horses should be bled when they are shedding their teeth, as it allays those feverish heats to which they are subject at that period ; but the cases that more particularly require bleeding, are colds, falls, injuries of the eyes, strains, and all inflammatory disorders.

These noble creatures should always be bled by measure ; two or three quarts are generally a suffi-cient quantity ; and when venesection is repeated, strict attention should be paid both to the disease and constitution of the animal.