Columbia's astronauts performed the first embalming ever done in space Friday, replacing the blood of young rats with formaldehyde as part of a study of the brain.

The doctors on board, Jay Buckey Jr. and Dave Williams, injected an anesthetic overdose into eight 16-day-old rats and then pumped the formaldehyde into their hearts and through their blood vessels. Their blood was pushed out the other side of the heart, flowing along a wick.The astronauts dissected the animals and stored the brains and other vital body parts in the same preservative. The work was conducted in a sealed chamber with gloved openings for the men's hands.

Oswald Steward, a neuroscientist at the University of Virginia, said embalming is the only way to preserve delicate brain tissue for detailed analysis after the flight.

He and other researchers want to see how young brains develop in weightlessness; the findings could benefit the elderly, Alzheimer's victims and others suffering from memory loss.

"Really what this does is actually fix the tissue in exactly the state that it is at the time that the procedure is carried out," Steward said. "So it provides us with an opportunity to obtain almost a snapshot of the living brain."

There's a practical benefit, too: Now that it's been proven in space, the same technique could be used to embalm an astronaut who dies en route to Mars or some other far-off destination.

"It's an unfortunate thought, but yes," Steward said.

Friday's dissections were tricky given the rats' small size. Sixteen-day-old rats are as big as a man's thumb and weigh a mere half-ounce; their brains are the size of a fingernail.

Once Columbia returns to Earth at the beginning of May, Steward and his team will examine the brain cells under an electron microscope.