The medicinal leech (Hirudo medicinalis, left) is thirsty for blood. It uses rows of teeth (pictured on the right through a high-powered microscope) to latch onto and cut human skin, while its saliva contains an anti-clotting agent called hirudin that keeps the flow of nourishing blood steady. Usually found in tropical forests, during medieval times leeches could also be found swimming in jars in a doctor’s surgery. In a time when many ailments were attributed to ‘excess blood’, a course of leeches may have been prescribed as an alternative to the more ‘hands-on’ forms of blood-letting – draining blood from veins with a small knife. Today leeches – which can guzzle a tablespoon of blood before they drop off the skin – are sometimes used to drain ‘bruise blood’ (haematoma) from a wound, or to reduce clotting and stimulate blood flow back into re-attached body parts like fingers or ears.
Written by John Ankers
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