TORONTO - Leeches have been used in medicine for thousands of years but now the critters are marketed in the U.S. as medical devices.

• FROM DEC. 13, 2001: Mechanical leech beats blood sucker

Doctors use leeches on reattached digits.

In medieval times, doctors believed leeches could rid patients of poisons in the blood.

"Three or four might be applied for some things," said Dr. Jock Murray, a medical historian in Halifax. "I saw one reference to 90 leeches being applied to a patient."

Bloodletting fell out of favour in the late 1800s. In the last decade, leeches have made a comeback, especially in surgery to reattach amputated fingers and toes.

If there is congestion after a digit is reattached then doctors become concerned the blood will stop moving.

When doctors see congestion or a drop in temperature they may apply a leech to a reattached digit.

Leeches suck out excess blood and inject a naturally-occurring anti-coagulant from their saliva, which helps keep the blood from clotting.

The critters usually feed for 20 minutes and fall off once full.

"The design and efficiency is amazing," said Dr. Herb von Shroeder, a hand surgeon in Toronto. "Right from the saliva to the way they digest, to how much they eat, to the way they sense the blood is truly amazing."

When Comfort Antipim cut off half her finger at work with a meat slicer, surgeons at Toronto Western Hospital reattached it.

Then the leeches or blood suckers did their job. At first, she was skeptical but now that the therapy is over, she's changed her opinion about leeches.

"It has helped me," said Antipim. "So I think the leeches are good."

Doctors noted leeches are also a barometer of whether a reattachment is taking. If they don't start feeding, it's a sign the surgery wasn't successful.