The U.S. agency that regulates drugs and medical devices last week approved the application of French company Ricarimpex SAS to sell leeches for medical use in the United States, joining other companies in the American leech market. Leeches are some of the oldest and newest tools used in health care.

Leeches have been used for medical purposes since antiquity, although their usefulness has been questioned since the acceptance of the germ theory of disease in the late 19th century. But before that, the creatures were indispensable to what was then state-of-the-art medicine.

"Leeches would pull the blood out of the body and, this medical thinking went, that would make you get better," said Conevery Bolten Valencius, a senior fellow at the Dibner Institute for the History of Science and Technology in Cambridge, Massachusetts. "Because leeches are painless they [healers] would put them on various body parts to draw out blood. And this is because of a medical philosophy that held that having too much fluid in your body - and in particular having too much blood - made you sick."

To a person used to the treatments of modern medical science, a description of how leeches were used in the 1800s seems rather, well, disgusting.

"You could put on one or two, or up to 30 or 40 leeches on a body part," Conevery Bolten Valencius said. "[Up to 30 or 40 leeches?] Yes. They could be put on an arm or a leg if the inflammation was thought to be in a limb of the body, or they could be put on the feet if the idea was to draw inflammation away from the head. Sometimes people's heads would be shaved, and they'd be put on their scalp, or on their more delicate body parts."

Leeches continue to be used for bloodletting by traditional healers in some parts of the world. And they are also used in some of the world's most advanced health care settings for their unique properties. Dr. Randy Vecchione, a plastic surgeon in San Diego, California, has used leeches in his practice.

"I do a lot of emergency room injuries, and I've used leeches for replantation of digits, as well as, for example, a severed ear," he said.

After surgeons re-attach a finger that has been cut off in a workshop accident, say, blood flows into the restored finger but can't flow back into the body until veins are re-established. So for a week or 10 days, leeches will be used to remove the blood that would otherwise pool up in the re-attached finger.

"We have not as yet been able to find anything that would take the place of a leech in this particular situation," Dr. Vecchione said.

Leeches excrete a natural anesthetic, so you don't feel anything, and San Diego surgeon Dr. Randy Vecchione and others who work with the animals say patients are surprisingly accepting of having leeches attached to their bodies.