Instead of a jar-receiver, take a long-necked bottle open at both ends. If you place the hand on one of the open ends and exhaust the air, by attaching the long tube of the pump to the other you cannot remove the hand easily. Do not try to pump the air out entirely, as the suction may be too strong and draw blood. It is by the rarefaction of the air that the cupping-glass is applied to people who require bleeding. In the antiquated surgical operation of cupping, the doctor burned a few pieces of paper in small glass cups, which are then applied to the skin; the air, in getting cold, contracted and produced a partial vacuum, thus acting as the bottle did in the above experiment.