NEW YORK - Researchers are trying to find ways to regrow fingers - and someday, even limbs - with tricks that sound like magic spells from a Harry Potter novel.

There's the guy who sliced off a fingertip but grew it back after he treated the wound with an extract of pig bladder. And the scientists who grow extra arms on salamanders. And the laboratory mice with the eerie ability to heal themselves.

This summer, scientists are planning to see whether the powdered pig extract can help injured soldiers regrow parts of their fingers. And a large federally funded project is trying to unlock the secrets of how some animals regrow body parts so well, with hopes of applying the lessons to humans.

The lessons could aid the larger field of regenerative medicine, perhaps someday helping people replace damaged parts of their hearts and spinal cords, and heal wounds and burns with new skin instead of scar.

But that's in the future. For now, consider the situation of Lee Spievack, a hobby-store salesman in Cincinnati. One evening in August 2005, he was helping a customer with a risky engine on a model airplane. And accidentally, "I put my finger through the prop."

It sliced off his fingertip, leaving just a bit of the nail bed. The missing piece, three-eighths of an inch long, was never found.

An emergency room doctor sent him to a hand surgeon, who recommended a skin graft.

Instead, Spievack, now 68, consulted with his brother, Alan, a former Harvard surgeon who'd founded a company called ACell Inc., which makes an extract of pig bladder for promoting healing and tissue regeneration.

Lee Spievack took his brother's advice to forget about a skin graft and started applying the pig powder every two days. Within four weeks his finger had regained its original length, he says, and in four months "it looked like my normal finger."

None of this proves the powder was responsible. But those outcomes have helped inspire an effort to try the powder this summer at Fort Sam Houston in San Antonio on soldiers who have far more disabling finger loss because of burns.

Nobody is talking about regrowing an entire finger. The hope is to grow enough of a finger, maybe even less than an inch, to do pinching.

From a scientific standpoint, "this isn't ready for prime time," said Dr. Stephen Badylak, a regeneration expert at the University of Pittsburgh.

The broad outline is pretty straightforward. The powder is mostly collagen and a variety of substances, without any pig cells, said Badylak, who's a scientific adviser to ACell. It forms microscopic scaffolding for incoming human cells to occupy, and it emits chemical signals to encourage those cells to regenerate tissue, he said.

Badylak and other scientists also are studying the salamander, a star of the regeneration field. Chop off a salamander's arm, and it will grow back in a matter of weeks.

Why? The short answer is that rather than making a scar to heal quickly, as people do, the salamander forms a mound of cells called a blastema. This is a regeneration factory: If you cut off a salamander hand and transplant the resulting blastema to the creature's back, it will grow out a hand there.

Then there's the specially bred mouse strain that befuddled Ellen Heber-Katz a decade ago and has since become a focus of her research.

Heber-Katz, of the Wistar Institute in Philadelphia, was using the mouse strain known as MRL in a study of autoimmune diseases. Her team punched tiny holes in the animals' ears as markers. About three weeks later, the holes were gone.

Like salamanders, the mice were growing blastemas instead of scars. They also heal damage to their hearts.

But for regrowing digits, the mouse falls short. If a toe is cut off, the remnant produces a cell mass that looks like a blastema, but it doesn't grow the missing part back. (An ordinary mouse just develops a scar.)

At least, the MRL mouse "looks like it's trying," Heber-Katz said.