Monkey Business : People for the Ethical Treatment of Animals investigates, informs, inflames, terrorizes. And gets things done.

The sun’s shining today, but not here, deep inside the institution. The only sound is a big hum from old air shafts. The walls are cinder-block, the ceiling water-stained. The door to the lab is locked. They have to keep it locked now.

Someone, unseen, buzzes it open. No one is around, just steel sinks, banks of refrigerators, black countertops. The only thing moving is something called an orbit shaker, gently mixing a foil packet of runny brain tissue. It was once the gray matter of a cat. It is now grisly ordnance in the war on disease.

Way in the back, a young woman in blue jeans is saying hello, waving. The scientist will be with you shortly, she says. Have a seat.

The calls started last summer, she says. The caller sounds like a huffy man in his 50s. She hopes that all he knows about her is that she’s the administrative assistant at a medical research laboratory. She’s glad she wasn’t mentioned in the ad in the paper.

That ad. It was placed by People for the Ethical Treatment of Animals. It named the scientist. Named the lab. Named the university with which the lab is affiliated. It showed a cat in a frame used for brain surgery. The copy says, “Great Moments in Science: See the device on the right? We use it to hold cats’ heads still. Most animals don’t like it when we push things into their brains. Strap them in the old stereotaxic restraint, though, and our needles and electrodes just slide right in!”

There are the little cat ears, soft triangles. There are the places the eyes should be, pierced with one long rod. Or so it seems. The picture is grainy, the perspective misleading. The needles, electrodes and restraining device are real, and unsettling enough. But, in fact, the animal’s eyes are not gouged.

*

Twenty years ago, there was no animal rights movement. Today, from an unquiet warehouse in Rockville, Md., for better or for worse, PETA conducts an international campaign to eradicate animal cruelty. It investigates, it informs, it inflames, it unabashedly terrorizes those it sees as enemies.

It is an organization with an acute historical consciousness. Its members believe they are our underground railroad, blessed with vision, ahead of their time, indomitably fighting an evil the rest of the nation will eventually recognize. They were vigilantes long before the modern militias were born. They are mostly white, mostly women, young, good-looking, smart, MTV-bred, enamored of ideas. They are vegans; compared with them, conventional vegetarians seem like cannibals. They are presumably lefty, but there are Republicans and antiabortion activists among them. They are dismissed as misanthropes, but wrongly.

There’s a PETA line on almost everything.

Refer to pets as animal companions. Refer to animals as she and he , never it . Boycott cosmetic companies that do animal testing. Buy vegedog and vegecat food; if cats won’t take to it, try adding avocado.

Buy humane rat traps. Once rat is captured, drive to rural area, release to a long happy life. Never use Roach Motels (they tear off roach legs). Don’t buy musk oil, it comes from otter genitals.

Refrain from using animals in pejorative expressions, as in you jackass, weasel, swine, silly as a goose, stubborn as a mule, harebrained, dumb bunny.

No furs. No wool blankets. No soccer balls. No tortoise-shell jewelry or combs. No circus. No hunting. No fishing. Canvas running shoes are big for PETA men. Espadrilles for the women.

PETA people will go naked to make a point. But they are also skilled investigators; accomplished, nervy spies. They will go undercover for months at a time. They assume new identities, get jobs in labs or chicken farms, and do the acting job of their lives. Their activist demonstrations are close to performance art.

You could dismiss PETA and its people as loons, except for three things.

The first is that they are hardly benign. On behalf of animals, they hound people. They hurt people. They cannot be ignored.

The second is that PETA is inarguably effective. Its videos--some stolen from industry, some taken at personal risk by its amateur undercover investigators--have been formidable instruments for reform. One enormous room at PETA is devoted to videos. Many a public official--from Cabinet secretaries to university presidents--have seen PETA videos, experienced that sickened, stumbling feeling. Labs have closed. Rules and laws have changed. Medical protocols have been scrapped. Revlon, Avon and Benetton have given up animal testing.

The final reason PETA people cannot be dismissed is: They are committed.

*

Mary Beth Sweetland, 41, is the Joe Friday of PETA. She got her first rifle at 12. Dad was a big hunter. Many PETA people are the offspring of hunters, butchers, fishermen. Her family portrait shows a Montana girl in a red-checkered shirt, proudly holding a dead pheasant. Her growing up was an oblivion of beef stew and chops. She got married, worked on a career at Merrill Lynch. Then, in 1985, the world turned. Her son saw a PETA ad. He sent for information. A classic PETA slaughterhouse documentary called “Downed Cow” arrived.

“It really changed our lives,” Sweetland says. “It changed them overnight. And it changed us forever. My husband was a real meat-and-potato guy. He helped me empty my freezer that night. We threw out all the meat.”

She joined PETA as a volunteer, but it wasn’t enough. “I started to feel guilty about working at Merrill Lynch and making lots of money and not doing more for animals.”

In 1988, six months away from being vested in her pension plan, Sweetland quit and took a job at PETA full time. “It was really love from the moment I stepped in here,” she said.

PETA’s budget is about $12 million a year, almost all from donations. Its paid staff is small, and the pay is modest: The highest-salaried person earns less than $60,000, according to the PETA annual report, and most full-timers get $25,000 or less.

Down the hall from Sweetland is Alex Pacheco. With his curling hair and Pepsodent smile, he looks like a lifeguard or a surfer. He is the son of a physician. He helped found PETA instead of finishing college. He is now, at 36, a very tired activist. He moves slowly. His nails are bitten down.

His radicalism was born from two epiphanies. The first dates from his childhood in rural Mexico. “There was a flock of parrots,” he recalls. “I pointed my rifle in the air and down came a huge beautiful parrot. He was still alive. He had a huge hole in his chest. His mouth was open. He looked like an old man.”

The second illumination was also unlikely, but more powerful. By chance, he toured a slaughterhouse where a college buddy had a summer job. He was one person before that tour, another afterward.

*

Jim Sicard dressed up as a bunny during a PETA demonstration earlier this year at Gillette headquarters in Boston. He’s super-skinny. With his wire-rim glasses and gentle intensity, his face recalls John Lennon.

Today, a bristling Saturday, he’s at a protest outside a McDonald’s in northwest Washington. At 28, Sicard’s almost avuncular to Paul Shapiro, who’s 15 and the leader of this particular “action.” Shapiro’s backpack is crusted with political buttons. Pro-choice. Anti-gun. Free Mumia Abu Jamal. He raises a poster that says: “The Meat Industry Equals Systematic Murder.”

The owner of the McDonald’s materializes. “You cannot block my entrances,” he says, shaking. “You cannot put things on my property. I’m calling the police.” The police never show. A woman in a cow costume lopes along.

This is standard PETA. Sicard puts down his poster and talks about his bunny exploits. He laughs, mimes, draws pictures. The conversation wends eventually toward more serious matters--medical research. Compared with fur, with cosmetics testing, with factory farming of animals, with eating that burger, using animals in medical research is “unquestionably the toughest” of the PETA issues. At first, he says, he supported it. Now, after years of studying it, he does not. He has not taken an aspirin in three years, even though aspirin wasn’t developed using animals.

Sicard’s thinking is still evolving, and has taken him so far that he is now beginning to wonder about his position on abortion. He has decided, for now, that as long as there is no suffering for the fetus, he supports it. But he is wavering.

He feels funny about something else. His older brother has a rare affliction called von Hippel-Lindau disease. It causes tumors in his eyes, spine and brain. His brother credits his survival, and quality of life, to medical research--and animal research.

They talk about it, but Sicard doesn’t proselytize. He loves his brother and worries that his views could somehow jeopardize his brother’s care at the National Institutes of Health.

*

Back at the lab, the scientist has been summoned. He is wearing a putty-colored shirt. No tie, no lab coat. His hair is gray and thinning, his face is wan, a face out of Botticelli, a mien distilled with weariness. He is speaking for publication with the proviso that his name, the name of his institution or even its location not be revealed. He wants no more trouble.

His voice is a gentle monotone. He is the voice of reason, tinged with sadness. His father was a clinical psychologist, his specialty criminal populations and dictatorship.

“I always had this dream of being a physician-scientist, ever since I was a little kid,” he explains. “The idea of somebody who was interested in curing disease, trying to come up with new cures, to do scientific research to get at that. That was my long-held dream.”

So he went to Amherst, then to Harvard for medical training. He chose neuroscience. He is 46.

He says he likes animals, is sorry he must kill them. He says he hopes his research may someday help in the fight against Alzheimer’s disease. His mother has Alzheimer’s. She can no longer speak.

The harassment began suddenly last year. He suspects a disgruntled graduate student who became a PETA informant.

First came the ad in the paper. Then there was a protest, about 20 people chanting and swaying, at the institution gates. Then there were calls--to the lab, to other doctors, to his home phone, to his neighbors. They said he tortured cats. “They were even asking some of my neighbors what I looked like. And that really got scary.”

Then there were letters to him--about a hundred or so. They wrote about how they’d like to operate on the scientist’s brain. His neighbors got letters too.

Says Ingrid Newkirk, PETA’s co-founder: “It’s psychological warfare. And it’s not pleasant. If someone hides what they do, they should be able to defend it to their neighbors. It’s like Nazi war criminals. It’s ugly, but as long as it’s not violent--because we’re totally opposed to violence--we do it.”

The scientist reported the harassment to his institution’s security department, to the police, to the FBI. “We were advised by the FBI to take different routes home. One has to take all these sorts of precautions,” the scientist says. “They have suggested that it has to be a way of life.”