Cupping is one of the simplest and most popular methods of producing local depletion, by the application of partially exhausted cupping-glasses to the surface of the skin. By this means the blood is diverted from deeper structures to the surface of an affected part, whence it may be removed by scarifying the skin (wet cupping), or where it may be allowed to remain exuded in the subcutaneous tissues like a Bruise (q.v.), until it be removed by absorption (dry cupping).
Cupping has been a part of surgical practice from the earliest times, and instruments for performing it have been found in use among the least civilised nations. Of old, the cups were either small horns, open at both ends, from which the air was withdrawn by suction at the narrow extremity, or glasses of various shapes, with a small hole in the bottom of each. This hole was plugged with wax, the air exhausted by heat, and when the operator wished to remove them, he withdrew the plug, and allowed the air to enter. The modern cupping-glass is a beaker containing 3 to 6 fluid ounces, with a finely-ground rim, which adheres closely to the surface of the skin.
The principal improvements have been in the methods of incising the skin. This used to be effected with a common lancet or narrow knife, with a short blade and convex edge, set in a long elastic handle, which the operator struck rapidly with his finger, so as to drive the blade 20 or 30 times into the skin. This was so tedious an operation, that a number of similar blades came to be used at once. These are contained in a box, which has slits pierced in it corresponding to the number of blades; the latter can be caused to emerge by setting free a spring, which causes them to revolve suddenly, and in doing so they protrude at the slits more or less, according to the regulation of the instrument by the operator. This apparatus is known as a 'scarificator.' A scarificator, glasses, a torch, some spirits of wine, and a lighted candle are placed ready at hand; the part is sponged with hot water, so as to cause an increased flow of blood into it; then dried with a warm towel; the torch, previously saturated with the spirits of wine and lighted, is held for an instant in one of the glasses. By this means the air in the glass is quickly expanded, and when the glass is then rapidly applied to the smooth damp surface of the skin, the rapid rarefaction of its contained air causes it to adhere tightly, and gives rise to determination of blood to the part to which it is applied. When the skin under the glass has become red and swollen, the cupper removes it, applies the scarificator, and as rapidly as possible again exhausts the air from the glass, which he re-applies. The blood will now flow into it; and when enough has been taken, the glass is removed, and some lint applied to the wounds. The number of glasses applied depends on the quantity of blood it is thought desirable to abstract; each one will probably withdraw from 3 to 5 ounces. This apparently simple proceeding requires considerable skill. The difficulties consist in regulating the depth of the cuts; for should they be either too deep or too shallow, the blood will not flow; in the one case, because the deeper vessels of the true skin are not opened; in the other, because the skin being completely cut through, the fat which lies beneath it is drawn up into the wounds, which it plugs, and stops the flow of blood. If, on the other hand, the glasses be completely exhausted of air, their rims press so firmly on the surface as to prevent the flow of blood to the part from surrounding areas of the skin, and as a result, very little blood flows from the wounds.
There are many modifications of the ordinary cupping apparatus, but all act on the same principle; and it need scarcely be added that extempore cups may be found in tumblers, finger-glasses, or any air-tight vessel with a smooth rim.
Dry Cupping is simply applying the cups as described, but not wounding the skin. A hard mass of extravasated blood is found occupying the skin at the site of this operation. The mass, at first cherry-red, becomes in a few days a dead black colour, then greenish, and finally yellow, following the usual course observed in the healing of a bruise.