For this purpose the veins of the forearm are generally selected, first because the arm is easy to get at, second because the veins are easily made prominent, and third because there are several to select from. In performing the operation it is advisable to place a bandage firmly about the arm two inches above the elbow tightly enough to impede the return circulation, but not tightly enough to stop the arterial flow. The right tension for this is easily found by observing the effect upon the veins which in a minute or two will stand out with great prominence.
Having thoroughly cleansed the skin and decided which vein shall be opened (the median basilic or median cephalic is the one generally chosen), grasp the forearm so as to steady the swollen vein between the thumb and finger of the left hand, and while so doing make an incision through the skin down to the vein. It is better to do this rather than attempt cutting skin and vein at one incision ; first; because as small a skin incision as possible is advisable, and second, because a vein has a tendency to roll from beneath the knife blade, apparently become lost, and necessitate a second trial. The incision in the vein may be either longitudinal or transverse.
The amount of blood to be withdrawn will, of course, depend entirely upon the individual and the condition, the time to stop being determined by the blood pressure as indicated by the pulse of the other arm.
If, for any reason, the blood ceases to flow freely before a sufficient quantity has been removed, it is usually duo to clotting about the incision in the vein. With a piece of sterile gauze wipe out the wound rather harshly, and the flow will usually proceed at once.
When a sufficient quantity has been withdrawn remove the constriction from the arm, put a compress over the incision, and bandage. If one chooses after the initial incision is made, a stitch may be put in, the ends left loose and tied at the completion of the operation. Of course, the entire procedure should be governed by the rules of asepsis.