Medicinal leeches. Bottles containing leeches used for medicinal purposes. Leeches are parasitic worms that feed on blood. They attach themselves to the skin using suckers and create a wound with three sharp jaw plates, which contain over 600 teeth. Their saliva contains hirudin, a chemical which prevents blood from clotting. Leeches are used in modern medicine to drain blood from haematomas (accumulations of blood) and to draw blood into transplanted tissues until circulation is established. Photographed in Istanbul, Turkey.