Use of the medicinal leech Hirudo medicinalis in the treatment of haemotoma, an accmulation of blood within the tissues that clots to form a solid swelling. Haemotoma is usually caused by an injury (as here), by a clotting disorder of the blood or disease of the blood vessels. The leech attaches its sucker (disclike) near the injury, makes an incision & deposits an anticoagulant called hirudin mixed with saliva into the wound. Hirudin prevents the blood from clotting & in the case where a clot is already in existence, dissolves it away. Introduced into European medicine in 50 BC, the leech is still used today.