WASHINGTON — Color-coded denim cloths cover the row upon row of black body bags atop cold metal tables. Blue means the body will eventually go into a common grave. Tan, the family wants those remains back for burial, eventually.

These are bodies donated to science, awaiting one of the most sensitive rites in becoming a doctor. Before first-year medical students lay their hands on the living, they learn anatomy from the dead.

Week after week, for six months, teams of students will file into in a laboratory at Georgetown University to slowly take apart "their" body.

First goes the skin on the back, peeled away from the yellow globs of fat that made up what in life someone may have called love handles.

They lay bare the spinal cord and marvel at how its lower roots resemble the tail of a horse.

Carefully probing a lump inside one chest, a team unearths what at first looks like a metal button — a port through which this man once received chemotherapy.

The room quiets as students unwrap the protective covering over each hand. One torso, they quickly learn, looks pretty much like another. But a hand is unique, somehow more intimate, as they hold it with their own blue-gloved hands. Many of the women's nails still bear polish. One year, shockingly, students found a wedding ring.

"You will be working with somebody's grandmother, father or wife," Dr. Carlos Suarez-Quian tells his 200 students before they unzip those body bags for the first time.

They're beginning a balancing act: How to steel their emotions so they can help people, without losing their compassion.

Dissecting cadavers is an evolving tradition. Sophisticated simulators and the plastic-infused organs of museum exhibits can't replace seeing and touching and lifting real bodies. In fact, demand is growing for whole-body donations.

What's changing is how they're used. Nearly one-third of medical schools have begun integrating nuts-and-bolts anatomy with clinical training spaced throughout their first year. That means Georgetown students dissect the heart, for example, the same week they begin learning how to tell the "lub-DUB" of a healthy heartbeat from the "lub-SHOOP" of a blocked valve.

"There's a very big difference between talking about chromosomes and having your knife in fat," says student Sarah Buchman of Bethesda, Md., as she eases through fat that, yes, looks like the squishy goo encountered on raw chicken.

The first day opens with an interdenominational prayer: "Make us grateful for these gifts these donors have given us," says the Rev. Paul McCarren as students wait silently amid the bodies.

Then Suarez-Quian has some class rules. Wear goggles when sawing bone, he warns. All the medical devices people have implanted today can mean flying bits of metal. And absolutely no photos of the bodies.

"We've been anticipating this moment a long time," says Christopher Chen of Irvine, Calif., anxious to get started. "It hits you — wow, you're a medical student."

But unzipping the lab's 44 body bags brings a surprise, and hesitation. The cadavers aren't lying on their stomachs, ready for students to make their initial cuts on the back. They have to be flipped over. The first lesson: How stiff and heavy a dead body is, especially one filled with at least eight gallons of embalming fluid.

"I was really worried the body would fall off the table," Chen admits.

Finally his team's cadaver is in position, and Chen asks to make the first cut, tracing the faintly visible spine with his scalpel.

"This skin's pretty thick. Can I have the forceps?" he asks, getting adjusted to how much force it can take to penetrate a body.

Suarez-Quian moves from table to table, showing students how to patiently peel back skin and then gently lift the triangular trapezius muscle without accidentally destroying the first nerve they'll encounter, the greater occipital nerve.

"This is not dissection by grenades. You have to go just deep enough," he calls to the room.

He stops to calm a nervous student. "If you make mistakes, that's fine. Your patient's not going to complain."

"All consciousness is past. Use this body well to enhance your knowledge and lessen the pain of another," says a letter one donor wrote to the medical school.

Who donates their bodies? In some programs, women more than men. They come from every demographic. But there are no national statistics or even federal monitoring of whole-body donations, although one estimate suggests there may be 20,000 a year.

This year, Suarez-Quian got a startling phone call a few weeks before class began: The morgue was almost full. Georgetown usually receives about 60 whole-body donations annually yet this year received between 80 and 90.

Schools don't pay for a body donation, but Suarez-Quian still worries that the economy may have played a role — with some families perhaps deciding on donation to avoid funeral costs — instead of a straightforward desire to contribute to science.

There's no evidence of a nationwide donor increase, says Dr. Richard Drake of the Cleveland Clinic, who took an informal survey for the American Association of Anatomists. About half of anatomy programs require that donors themselves, not their surviving relatives, make the decision.

The demand is growing with an increase in medical school enrollment.

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