Gey's 21-year-old assistant, Mary Kubicek, sat eating a tuna salad sandwich at a long stone culture bench that doubled as a break table. She and Margaret and the other women in the Gey lab spent many hours there, all in nearly identical cat's-eye glasses with fat dark frames and thick lenses, their hair pulled back in tight buns.

"I'm putting a new sample in your cubicle," Gey told Mary.

She pretended not to notice. "Not again," she thought, and kept eating her sandwich. Mary knew she shouldn't wait—every moment those cells sat in the dish made it more likely they'd die. But they always died anyway. "Why bother?" she thought.

At that point, there were many obstacles to growing cells successfully. For starters, no one knew exactly what nutrients they needed to survive or how best to supply them. But the biggest problem facing cell culture was contamination. Bacteria and a host of other microorganisms could find their way into cultures—from people's unwashed hands, their breath, and dust particles floating through the air—and destroy them. Margaret Gey had been trained as a surgical nurse, which meant sterility was her specialty—it was key to preventing deadly infections in patients in the operating room.

Margaret patrolled the lab, arms crossed, leaning over technicians' shoulders as they worked, inspecting glassware for spots or smudges. Mary followed Margaret's sterilizing rules meticulously to avoid her wrath. Only then did she pick up the pieces of Henrietta's cervix—forceps in one hand, scalpel in the other—and carefully slice them into one-millimeter squares. She sucked each square into a pipette, and dropped them one at a time onto chicken-blood clots she'd placed at the bottom of dozens of test tubes. She covered each clot with several drops of culture medium, plugged the tubes with rubber stoppers, and wrote "HeLa," for Henrietta and Lacks, in big black letters on the side of each tube. Then she put them in an incubator.

For the next few days, Mary started each morning with her usual sterilization drill. She'd peer into all the incubating tubes, laughing to herself and thinking, "Nothing's happening." "Big surprise." Then she saw what looked like little rings of fried egg white around the clots at the bottom of each tube. The cells were growing, but Mary didn't think much of it—other cells had survived for a while in the lab.

But Henrietta's cells weren't merely surviving—they were growing with mythological intensity. By the next morning, they'd doubled. Mary divided the contents of each tube in two, giving them room to grow, and soon she was dividing them into four tubes, then six. Henrietta's cells grew to fill as much space as Mary gave them.

Still, Gey wasn't ready to celebrate. "The cells could die any minute," he told Mary. But they didn't. The cells kept growing like nothing anyone had seen, doubling their numbers every 24 hours, accumulating by the millions. "Spreading like crabgrass!" Margaret said. As long as they had food and warmth, Henrietta's cancer cells seemed unstoppable.

Soon, George told a few of his closest colleagues that he thought his lab might have grown the first immortal human cells.

To which they replied, Can I have some? And George said yes.

George Gey sent Henrietta's cells to any scientist who wanted them for cancer research. HeLa cells rode into the mountains of Chile in the saddlebags of pack mules and flew around the country in the breast pockets of researchers until they were growing in laboratories in Texas, Amsterdam, India, and many places in between. The Tuskegee Institute set up facilities to mass-produce Henrietta's cells, and began shipping 20,000 tubes of HeLa—about six trillion cells—every week. And soon, a multibillion-dollar industry selling human biological materials was born.

HeLa cells allowed researchers to perform experiments that would have been impossible with a living human. Scientists exposed them to toxins, radiation, and infections. They bombarded them with drugs, hoping to find one that would kill malignant cells without destroying normal ones. They studied immune suppression and cancer growth by injecting HeLa into rats with weak immune systems, who developed malignant tumors much like Henrietta's. And if the cells died in the process, it didn't matter—scientists could just go back to their eternally growing HeLa stock and start over again.

But those cells grew as powerfully in Henrietta's body as they did in the lab: Within months of her diagnosis, tumors had taken over almost every organ in her body. Henrietta died on October 4, 1951, leaving five children behind, knowing nothing about her cells growing in laboratories around the world.

Henrietta's husband and children wouldn't find out about those cells until 25 years later, when researchers from Johns Hopkins decided to track down Henrietta's family to do research on them to learn more about HeLa.

When Henrietta's children learned of HeLa, they were consumed with questions: Had scientists killed their mother to harvest her cells? Were clones of their mother walking the streets of cities around the world? And if Henrietta was so vital to medicine, why couldn't they afford health insurance? Today, in Baltimore, her family still wrestles with feelings of betrayal and fear, but also pride. As her daughter Deborah once whispered to a vial of her mother's cells: "You're famous, just nobody knows it."

Adapted from The Immortal Life of Henrietta Lacks. Copyright © 2010 by Rebecca Skloot. Published by Crown Publishers, a division of Random House, Inc. On sale February 2.

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