# Leech (Hirudo medicinalis)

**Hirudo**

**Known today as.** The medicinal leech, *Hirudo medicinalis*.

Kind: Animal

## What was it used for?

Bloodletting where the lancet could not go: for inflammations, fevers, and congestion.

## What does modern science say?

Its saliva contains hirudin, an anticoagulant; leeches are used again after reconstructive surgery, and the FDA cleared them as a medical device in 2004. John Haycraft found in 1884 that the leech’s saliva stops blood from clotting; the substance, hirudin, is now made by recombinant techniques for anticoagulant drugs. Plastic surgeons returned to the living leech in the 1970s to drain congested blood from reattached fingers and grafted flaps, and the United States cleared it as a medical device in 2004. The wild leech is protected across Europe.

## Pharmacognosy and toxicology

- **hirudin**: a thrombin inhibitor
- **calin**: 
- **hyaluronidase**: 

**Mechanism.** Hirudin binds thrombin directly; the wound goes on bleeding steadily after the leech has detached, which is the surgical use.

**Dose.** Infection with *Aeromonas* from the leech’s gut is the hazard; antibiotics are given.

**Standing.** A medical device in the United States since 2004; recombinant hirudins are licensed anticoagulants.

## What lore surrounds it?

Wordsworth’s leech-gatherer, in “Resolution and Independence” (1807), old and poor, roamed “from Pond to Pond” and “from moor to moor,” stirring the waters about his feet, and complained that the leeches “have dwindled long by slow decay.” George Merryweather’s “tempest prognosticator,” explained to the Whitby Philosophical Society in 1851, rang a bell when leeches in bottles climbed before a storm.

## What did the older authorities say?

**François Broussais.** The French army physician reported in 1816 that the fever patients in his wards at the Val-de-Gr ce were all cured within days by bleeding and by leeches on the abdomen or the anus, repeated as often as the symptoms grew worse.

**The leech-mania.** Broussais’s theories made France, which had once exported its surplus leeches, the largest consumer in the world, using fifty to a hundred million a year and importing over fifty-seven million in 1832 alone; the Manchester Royal Infirmary used fifty thousand in 1831, and the harvest across Europe brought local populations almost to extinction.

## Sources

- Broussais, F. J. V. (1816). *Examen de la doctrine médicale*.
- Wordsworth, W. (1807). “Resolution and Independence.”
- Whitaker, I. S., et al. (2004). “Hirudo medicinalis: ancient origins of, and trends in the use of medicinal leeches throughout history.” *British Journal of Oral and Maxillofacial Surgery* 42.
- Wikipedia, “*Hirudo medicinalis*.”
- Wikipedia, “Hirudin.”
- Wikipedia, “Tempest prognosticator.”
- Copena, D., & G mez-Mart n, M. (2024). Spanish–French leech trade and its consequences: from the increase in medical demand to resource depletion and technical innovation. *Medical History* 68.
- Singh, S. K., & Rajoria, K. (2020). Medical leech therapy in Ayurveda and biomedicine: a review. *Journal of Ayurveda and Integrative Medicine* 11.
- Whitaker, I. S., et al. (2004). *British Journal of Oral and Maxillofacial Surgery* 42.

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*Leech.* In *Materia Medica*, edited by B. C. P. Statema. Version 1, revised 2026-10-03. The Thinking Press. https://thethinkingpress.org/materia-medica/leech

Historical description, not medical advice.