Action

It has the effect of lessening the systemic venous congestion and the plethora which exists in a stagnant circulation. In conditions of circulatory stagnation Bolton and Starling found that in all phases of respiration there is probably slight positive pressure in the big veins near the heart instead of the normal alternating positive and negative pressure, and that this was a definite obstruction to the emptying of the lymph into the venous system. They consider that venesection serves to relieve the distention at the venous end of the heart and so enables the heart to beat more effectively. Lazarus-Barlow noted a rise in the specific gravity of the tissues after bleeding, that is, tissue fluid had been removed. Burton-Opitz has shown that venesection regularly results in a lowered viscosity of the blood, and Starling has pointed out that by venesection not only is diffusible fluid removed from the plasma, but also proteins in large quantity, and that the blood volume is quickly restored by absorption of isotonic tissue fluid, so that it becomes more watery. Hill thought that this might result in the mobilization of the opsonins and bactericidal substances of the tissue lymph. Lawrence believes that repeated blood-letting when indicated does not have any ill effects on the composition of the blood, and Hamburger demonstrated that the freezing-point of the blood remains unaltered.

Miller and Mathews in experimental edema of the lungs found that before any effect could be seen on the pressure in the pulmonary artery it was necessary to withdraw a sufficient amount of blood to lower the general blood-pressure to a dangerous degree. The pressure in the pulmonary artery, however, is not the criterion of the value of any procedure in pulmonary edema, as this pressure is dependent on the relation of the right ventricular output to the caliber of the pulmonary arterioles. The pulmonary arterioles, though weak in muscle, are the gates which regulate capillary inflow and may be looked upon as protectors of the capillaries.

Rolla calls attention to the lessening of the alkalinity of the blood following venesection, and advises that when there is a tendency to acidosis it be accompanied by the administration of alkali.

Therapeutics

1. In conditions of high venous pressure, as in uremia or tricuspid regurgitation or tricuspid stenosis.

2. In conditions of venous accumulation due to a stagnant circulation.

3. In conditions with very high arterial pressure, as in uremia and eclampsia. In the author's clinical experience a marked and prolonged fall in pressure has usually followed venesection.

4. In acute pulmonary edema.

5. To remove poison - in uremia, in eclampsia, and in carbon monoxide (illuminating gas) poisoning. Its value in removing poisons is problematic, for in experiments with artificially introduced toxins Levin met with negative results by this method.

Blood-letting for the removal of marked local congestion is done by the wet-cup or the leech. It has no effect on general blood-pressure.

Wet-cupping is a process by which blood is drawn from the part by suction through one or more openings in the skin. These are made by a scalpel or by a special scarificator which makes 6 or 12 cuts in two parallel rows

Therapeutics 44

The suction is created in a cupping-glass or small tumbler by burning cotton in it or swabbing it inside with burning alcohol on a cotton swab. The mouth of the glass is quickly applied to the skin, and as the heated air cools, it creates suction, which results in the withdrawal of serum or blood. Cupping-glasses may also be had with rubber ball or syringe attachment for creating suction.

Wet-cupping is but little used today, though the scars are often seen in older patients. Its chief uses are - (a) to relieve edema of the lungs, the cups being placed on the chest wall; (b) to overcome suppression of urine, the cups being placed over the kidney region.

Dry-cupping - i. e., cupping without an incision in the skin - produces a local edema or congestion. It has been referred to with the counterirritants.

The leech (hirudo) is an annelid worm with a sucker at each end of its body. At its mouth end there are three teeth arranged in a triradiate manner, so that its bite consists of three short deep gashes radiating from a common center. To insure that the bite shall be at the desired spot, the leech is placed inside a glass tube or over a hole in a piece of paper, the mouth of the tube or the hole in the paper being placed over the spot to be bitten. If the leech does not take hold, the skin may be pricked or a drop of blood or milk placed upon it, or the leech may be put in very cold water for a minute or two to arouse it.

The effect of the leech is that of wet-cupping, more or less blood being extracted. As the mouth of the leech secretes a substance (hirudin) which prevents the coagulation of the blood, the bleeding may continue for a long time after the animal is removed. Indeed, it may be necessary to employ something to stop the bleeding, e. g., adrenaline. The leech may be removed easily by squeezing its head or by placing salt upon it. The Swedish leeches are considered the best, as they extract about half an ounce of blood, while the American leeches extract only 1 or 2 drams.

There are decided disadvantages in the use of leeches, viz.:

1. They may not be clean; in any case, they cannot be aseptic.

2. They may wander and get into one of the body orifices - e. g., the ear, nose, vagina, etc. 3. They remove an uncertain quantity of blood.

On these accounts the artificial leech is sometimes employed. It consists of a syringe with a cup-like nozzle and a graduated barrel with which slow suction is made over a cut in the skin. It is merely a process of wet-cupping with a graduated syringe.

Hirudin is employed in laboratory work to prevent coagulation of the blood, the small amount of 0.02 gm. (J grain) being sufficient to keep 1000 c.c. of blood fluid for a considerable time. It does not alter the viscosity of the blood, but if used in too large quantities, may cause agglutination and sedimentation of the corpuscles (Bence). Satterlee and Hooker have employed it as an anti-coagulant in blood transfusion, using 30 minims (2 c.c.) of a 1: 500 solution in saline to wet the inside of a 220 c.c. receptacle. This prevents coagulation for twenty minutes.