A leech was a worm-like animal which fed on blood.

Leeches were sometimes used for medicinal purposes. Sir Isaac Newton once refused an offer of help for one of his seizures, as he knew it would involve leeches. (AUDIO: Summer) In 1794 Paris, a physician claimed he needed to go collect some leeches to treat Susan's illness. (TV: The Reign of Terror) When Barbara Wright offered Vicki some aspirin, Vicki compared taking the pills to sticking leeches on someone, as both treatments seemed medieval to her. (TV: The Web Planet) On Arcadia, leeches were used to try to treat Elaine Delahaye's madness. (PROSE: Deceit)

In 1699 on the Fancy, a leech bit De Florres, causing the Siren to take him to her ship. (TV: The Curse of the Black Spot)

In 1965, Alexander Lullington-Smythe was temporarily transformed into a leech by the Latter-Day Pantheon. (PROSE: Salvation)

Sarah Jane Smith was bitten by several leeches during a visit to Papua New Guinea. (PROSE: Conscription)

The Fourth Doctor called the Collector a blood-sucking leech. (TV: The Sun Makers)

Mula compared Zanak to an enormous leech after the Fourth Doctor explained how it consumed other planets. (TV: The Pirate Planet)

The Eighth Doctor called Miraculite a leech. (AUDIO: Faith Stealer)

The Process resembled a giant leech. (PROSE: Cat's Cradle: Time's Crucible)

Azoth created leech-like creatures and placed them in humans as part of his plan to destroy the Beast. (PROSE: The Taint)

Pelt was attacked by leeches on a planet in the Quadrille. (PROSE: The Dalek Factor)

The Eighth Doctor and Perfection encountered leeches on an island in the Divergent Universe. (AUDIO: The Next Life)

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