The methods of bleeding may be divided into the general and local. The former may be effected by opening a vein, or an artery; the operation being called venesection in the former case, and arteriotomy in the latter. Before it was known how rapidly the blood makes its round in the circulation, and how almost instantaneously the loss of it is everywhere felt from whatever portion of the circulation it may be drawn, the idea was entertained that, in certain cases, there was special advantage in dividing the temporal artery instead of a vein, and that, when venesection was used, it was advisable to take the blood, in certain cases, from one particular vessel, from the jugular vein, for example, in one case, or from a vein in the hand, the foot, or the thigh, in another. At present, general bleeding is effected almost exclusively by venesection; and one of the veins at the bend of the arm is usually preferred; or, if another is selected, it is so less from any supposed peculiarity of effect, than from mere convenience. I have myself no doubt, that every remedial effect which general bleeding is capable of producing, may be obtained by bleeding from the arm in the ordinary method.

1. General Bleeding or Venesection. As to the method of performing this operation, and the various cautions requisite, the reader is referred to works on surgery. The following observations have a bearing only on its effects. The quantity of blood to be taken at one time varies so much, according to the objects to be accomplished, the nature and seat of the disease, and the constitution, age, and sex of the patient, that no precise general rule can be given upon this point. It has before been stated that bleeding should never be carried to absolute syncope, unless in cases of spasm of a highly dangerous character, which could not otherwise be relaxed. in such instances, the patient should be bled sitting or standing, so that the object may be accomplished with the least possible loss of blood, and the opportunity, moreover, afforded of quick restoration by laying the patient down with his head low; an advantage which would be wanting if he were bled in the horizontal position. in the latter case, there might be some danger that the syncope would prove permanent. in strong local determinations of blood to the head or lungs, threatening cerebral or pulmonary apoplexy, and in violent sthenic inflammation of one of the vital organs involving life in danger, bleeding may be carried to the verge of fainting, but should stop short of it. in general, when this remedy is called for, it will be sufficient to proceed till some sensible impression is produced on the pulse; and it would be better to bleed a second or even a third time, than to incur unnecessary risk at the first operation. The occurrence of decided weakness or softness of the pulse, paleness of the lips, yawning, or nausea, should serve as a signal for closing the vein in all ordinary cases.

As a general rule, in an adult male, of good constitution and ordinary size, fifteen or sixteen fluidounces may be taken at the first bleeding; though, under varying circumstances, the quantity may fall as low as six fluidounces and rise as high as forty. When the loss required is less than six fluidounces, it is generally best to take the blood locally. in women one-quarter or one-third less should be taken than in men. in children of two years or upwards, the rule of Dr. Young, in relation to the modification of the dose of medicine, will apply also to bleeding. (See vol. i. page 34.) At three months it would seldom be proper to take more than a fluidounce, at six months one and a half fluidounces, at a year two, at two years three, at four years five, at eight years eight, and at twelve years ten fluidounces.

It has generally been thought better to bleed from a large than a small orifice; but this is true only when the object is to produce as great an immediate effect upon the system, with as little loss of blood, as possible. The rule is applicable in cases of spasm, in which the object is to induce relaxation, and to some extent in those of active sanguineous determination, when a prompt effect is desired in order to prevent hemorrhage in some vital organ, or an overwhelming influence upon its function. in inflammations, in which the indication is prominently to alter the character of the blood, and in which an immediately curative impression is seldom expected, I think that the loss by a small orifice is quite as effective, and perhaps more so; as more blood can thus be taken without endangering syncope.

Whenever it may be doubtful how much blood should be withdrawn, and a special necessity may exist for taking no more than may be absolutely necessary, the patient should be bled in the erect posture, either sitting or standing; the latter position being that which affords the greatest security against excess. The fingers of the operator, under such circumstances, should be placed on the wrist, and, at the first sign of a decided flagging in the pulse, the process should cease.

After bleeding, the blood should always be kept for a time, in order that its degree of coagulability may be observed, and whether or not it may present the buffy coat.

2. Local Bleeding. By this is meant the abstraction of blood from the capillaries or small vessels, in some particular part, with a view specially to a local impression. it is true that, in young infants, and very delicate subjects at a more advanced age, this method of bleeding is resorted to with the object of affecting the general circulation; and it is also true that, however small may be the quantity of blood abstracted, the system at large feels its loss in greater or less degree; but, nevertheless, the aim is chiefly to affect a special part or organ peculiarly, and more than could be done by the loss of an equal amount of blood from a large vessel, as in venesection. Abundant experience has proved that a certain amount of blood taken from an inflamed part, or its near vicinity, has much greater effect on the disease than an equal quantity taken elsewhere. I do not think that any one who has been much in the habit of using general and local bleeding, and of comparing their effects, can doubt this fact. it can be readily understood, moreover, how it should be so, when the blood is taken from the inflamed vessels themselves, or from those in the neighbourhood supplied by the same artery. But why local bleeding should be specially useful, when the vessels from which the blood is withdrawn have no immediate connection with those inflamed, is not so obvious. We can admit, for example, without hesitation, that cups to the side, in a case of costal pleurisy, in which the membrane inflamed and the surface scarified derive their blood from the same immediate source, shall be specially serviceable; but there would seem to be no reason why a few ounces of blood, taken from the epigastrium, should have more effect in relieving the stomach, which is supplied with blood from a wholly different source, than the same quantity taken from the back, or one of the extremities; yet, as I think, no fact in medicine is better demonstrated than the great efficacy of a few leeches to the pit of the stomach in gastritis, and that the few ounces thus abstracted have an incomparably greater effect than the same amount taken from the general circulation. I have in vain sought for any other explanation of this fact, than that of a supposed sympathy existing, through the organic nervous centres, between an interior organ and the surface of the body corresponding with it, by which an impression made on the vessels of the latter shall be peculiarly felt by those of the former. it may be reasonably supposed that such a sympathy has been established with conservative objects; for we naturally resort, in suffering of interior parts, to the corresponding outer surface in the application of means of relief. Of the fact, at any rate, I have not the least doubt, having seen it demonstrated beyond the possibility of disbelief.