After reading Gabriel’s last post regarding modern preconceptions of premodern physicians and caregivers, I was reminded of an old New Yorker article on leeches that I had only recently read. (I used to subscribe to the New Yorker and have a backlog of old issues.) The article is about an American-born zoologist, Roy T. Sawyer, who was reintroducing the ancient practice of using leeches for medicinal purposes. Sawyer is the founder of Biopharm (an international company and leech farm based in Hendy, South Wales in the United Kingdom) and the author of Leech Biology and Behaviour. In 1983, he created Biopharm with the goal of identifying all the curative chemicals in the leech.

The earliest references to the medicinal uses of leeches appear in ancient Sanskrit writings. Indian physicians applied leeches to snakebites and boils and around diseased eyes. Asian healers mixed dried leeches in water for a variety of symptoms. However, just like bloodletting and trepanning, the use of leeches in medicine came to be viewed as barbaric and devoid of any legitimate purpose. Sawyer has helped to change the misconceptions many hold about the medicinal uses of leeches.

There are more than 650 species of leech. Hirudo medicinales is the primary species that is used for medical purposes. In the course of writing his book, Sawyer became convinced that the medicinal uses of leeches in the past were “based on a high degree of evolutionary adaptation.” In 1884, a British physiologist identified the anticoagulant hirudin in the saliva of H medicinales. Subsequently, it was purified in the 1950s and cloned in 1986.

Like most species of leech, H medicinales has 3 jaws designed for sucking blood, and each jaw has about 100 teeth.* These “medicinal leeches” secrete saliva containing several chemical compounds that are injected into a wound while it is feeding. As already mentioned, hirudin is a powerful anticoagulant; calin is another chemical (ie, a platelet adhesion inhibitor) that is responsible for prolonged bleeding, and it is this continual flow of blood that can provide the time needed for a body part or appendage to reestablish its own circulation after microsurgery. The leech decongests blood as it feeds and promotes continual decongestion long after it has finished feeding and has dropped off.

Roy T. Sawyer’s findings seems to be in line with the finding of the 2 researchers at the University of Nottingham mentioned in Gabriel’s post, the ones who made that surprising medical discovery in an enigmatic 1000-year-old text called Bald’s Leechbook. Also, I like the slogan of Sawyer’s company, Biopharm Leeches: “The Biting Edge of Science.”—Paul Ruich

*Editor’s note: I think they’re kind of cute!