Leeches are fascinating animals. They can be found everywhere, from ponds to streams, from polar seas to desert oases. Many of the about 300 species of leeches feed on small invertebrates, only some species are parasitic blood suckers. The leech’s spittle does not only contain enzymes which prevent blood clotting but also an anesthetic. So the host is not aware of the attack by the blade-like jaws or secreted enzymes that digest a hole through the skin. It is no accident that the most famous leech species is called Hirudo medicinalis. Leeches have a long tradition in medical treatment. Before using it for treatment, the leech needs to be washed and the gut content needs to be squeezed, because leeches just “attack” when their gut is empty. Interestingly, H.medicinalis does not produce any gut enzymes. Symbiotic bacteria, principally Aeromonas hydrophila, which are living in the leech’s gut, carry out the digestion. The medical treatment with leeches is a sort of improvement of the much older tradition of bloodletting, which origins are suspected to go back as far as the Stone Age. The advantage of leeches is that it is less painful and easier to use for body parts which are hard/dangerous to access with blades like eyes and rectum. This usage of leeches in medicine in mind, it seems logical that, in the past, the word “leech” had a second meaning as medical practitioner. However, as Robert N. Mory et al. (2000) pointed out, this is an example of folk etymology: a “type of linguistic development, in which an apparently logical connection is used to explain (or is understood as) the development of one meaning from another”. In reality, "leech" and "leech", the worm and the physician, have two different origins. Both are based on the Old English word “leace”. However, while the worm “leech” came from the Middle Dutch lieke, the physician “leech” has its origin in Germanic languages including Old Frisian letza, Old Saxon laki, and Old High German lakki. So, even if leeches and leeches worked together in the past, the origins of their names are not connected. Today the word “leech” for physician is outdated. Today, “leech” is used to describe people which download from file-sharing sites without uploading anything. There the logical connection to the worm “leech” is obvious. Both are parasites: taking without giving something back. "The leech and the physician: biology, etymology, and medical practice with Hirudinea medicinalis."
Robert N. Mory, David Mindell, and David A. Bloom World journal of surgery 24.7 (2000): 878-883.
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