She works in a small industrial town for a factory that makes intravenous drip kits for hospitals. Once she lived with her family in a dirt-floored hovel at the end of a mud road in a forgotten hamlet called Two Dragons.

She left home at age 15 because her father decided she must. The family was poor, but there was an option: Every day, it seemed, more people from the villages were leaving for work in the city.

Bai Lin remembers clearly the day her father took her to the bus station. He cried. She held in her tears.

Her stoic nature defines her still. Bai Lin is a factory nun. She lives cloistered in the dreary compound of the medical instruments company, where she works 11 or 12 hours a day, seven days a week, for 11 months straight until the New Year's break. When she returns home for a month, her year's wages in her pocket, it amounts to about $500.

Bai Lin belongs to one family from one village that represents an infinitesimal piece of a very large story: one of the largest industrial migration trends in human history.

Over the past decade or so, legions of Chinese have left their farms for cities as China's communist government relaxed the travel and housing restrictions that once kept a strict divide between urban workers and country peasants.

Without the rise of a flexible migrant labor force, China's economy never would have developed into the formidable international competitor it has become. China's cities today teem with these domestic migrants, some comfortably settled in jobs, others arriving daily, risking everything--though often they have nothing to lose.

Many of the people working in China's newly established factories are from the countryside.

The men living and working round-the-clock at construction sites often are migrants.

The food hawker on a street corner in Nanjing, who rises at 3:30 each morning in his tiny apartment to make the noodles for his stand and doesn't close up and go home until 8:30 at night, is a migrant.

So, too, are three poorly dressed women, each hoisting over a shoulder a rotund, 80-pound sack stuffed with potential recyclables. They march single-file down a street, bent by the strain, cartoonishly tiny under their heavy, bobbing loads, hoping to earn a few pennies for a full afternoon of rummaging.

A shifting demographic

Counting or even defining migrants isn't easy. The Chinese talk about a "floating population," meaning anyone who has left the city in which they are officially registered. At some level, a destitute farmer collecting garbage on the streets can be considered part of the same mobile phenomenon as a lawyer from Beijing living in Shanghai.

Today there are more than 100 million peasants in the cities, but so many have come and gone through the years that the total number of participants likely is far higher. These migrant workers fit different categories. Some are seasonal workers who go home for the harvest. Others have been living in the city for years but are not recognized as official city dwellers because residency laws are murky and changing.

China's plunge into migrant-based employment represents capitalism that is basic and unfettered, which can mean exploitative.

Industrial workers typically put in punishing hours, often for little or no overtime pay, in factories that can rely on antiquated equipment and provide little training. China has one of the world's highest rates of industrial accidents; at least 5,000 workers die each year in the coal-mining industry alone. Stories are common of inadequately trained machine operators who lose limbs in accidents.

Migrants tend to fare the worst. They're unsophisticated, desperate and thus especially vulnerable to unscrupulous bosses who will work them to the bone and then refuse to pay them.

There are national labor laws governing workplace conditions, but oversight and enforcement often are lax or non-existent and there are no minimum-wage rules. There also are no independent unions and no labor activists to defend workers' rights because the Communist Party does not allow challenges to its authority.

Sometimes workers revolt, but mostly they endure, surviving lives in the city that are grueling and lonely. But at the end of the year there is money their pockets, where there would be little or none at home on the farm.

This is what the Bai family understood.

Wrenching sacrifice

Bai Lin's father, the second-oldest of the five Bai brothers of Two Dragons, is illiterate and realized he could not make it in the city. So he needed to make a wrenching decision: One of his older daughters would leave home.

The obvious girl to send first was the eldest, Bai Li Hua, but she was valuable on the farm and seemed a bit too quiet and insecure. The second daughter, however, responsible student Bai Lin, might handle herself better.

So it was decided that Bai Lin should go to Changshu, where an older cousin was employed with her husband. At least there would be someone to look out for her if things went badly.

Bai Lin wanted to stay home, but if she went to work in the city, perhaps her younger siblings would have a chance to at least finish middle school. Her dream to go to high school had been dashed years ago when it was clear that the family could not afford it. She had no real plan for her future.

"Who would want to marry a poor peasant girl with two younger sisters and a younger brother to support?" she asked.

Changshu is a city of 1 million people. On its outskirts is a small industrial suburb built on farming fields. There is no commercial center, no high-rise buildings. At night it's dark along the roads except for the bright fluorescent lights from small factory compounds. These are mainly garmentmakers, along with a few medical instrument companies. This is where Bai Lin found work.

Petite and dimpled, she is in her fourth year as a factory drone at Changshu Medical Instruments Ltd. Day after day she sits quietly alone in her factory's "clean room," covered head to toe in surgical garb, carefully snipping and stacking pieces of threadlike rubber hose that will become feed tubes and IV drips for hospitals in Switzerland, France and other countries. An unpleasant odor of glue permeates the room.

There is little escape from the drudgery. Bai Lin never ventures outside the walls of the factory and knows little of the real world, having visited no place beyond Two Dragons or Changshu. She has never used the Internet. She doesn't own a cellular phone. She has seen perhaps one or two Hollywood movies on television; she recalls seeing "Titanic." She has never eaten at a McDonald's. In fact, she never has gone to a restaurant in the factory town. She doesn't read newspapers. Or magazines. There is no dating at the factory--there are few males working there--so there is no chance to meet men.

She just works.

When work is over, Bai Lin walks the few yards to the factory dormitory, a squalid line of concrete rooms that look like connected sheds. They are dusty and foul-smelling. It is cold inside. The walls are peeling. An unframed mirror sits on a bureau. Boxes and discarded luggage are strewn about.

The only personal decor Bai Lin has added to her room is a photograph of a pretty woman from a package of socks; she attached it to her bunk bed. The woman on the package smiles out at a view that otherwise is utterly depressing. Outside Bai Lin's door, in the concrete courtyard, sits a jumble of discarded sinks and chairs.

When the factory owner wanders into Bai Lin's room, as if for the first time, he acts embarrassed by what he sees and scolds her for not doing more to tidy it.

"I'd like to build better housing, maybe with two stories," he offers, but it doesn't seem likely.

Yet when Bai Lin's mother and father see photographs of their daughter at work and in her dorm, nothing seems amiss. To them the factory looks clean, and her dorm room seems a step up from home. At least there is a concrete floor.

"The conditions seem pretty good," her mother says, satisfied.

Bai Lin makes life harder on herself by watching every penny. She rarely buys clothes; her most expensive item is a $7.50 winter coat. She will not eat in the company cafeteria because it charges 40 cents a meal. She prefers to make her own rice and eat it in her room with some vegetables. She doesn't buy meat; she considers it too expensive.

She gets about $12 a month for living expenses and $500 a year in annual salary, paid in January just before the New Year's break. If she tries to quit and go home before the end of the year, she risks not getting paid at all. This is the system of migrant laborers in China. They are trapped.

Missing home

When Bai Lin went home for the last Chinese New Year holiday, she turned over her entire year's earnings to her father. About half went to help pay for the wedding of her older sister, who subsequently left Two Dragons for the first time and moved to the city with her husband. The other half went to help pay for school fees for her two younger sisters and youngest brother.

Bai loved being at home at New Year's, helping her mother keep house by pumping well water to wash dishes, stoking the stove fire and chopping vegetables for dinner. Yet her facial expression rarely seemed to change. She looked worried, unable to hide her sadness at being home for so short a time, but also feeling guilty that she could not earn more for her family.

She returned in February to start another year at the factory.

If she could make one suggestion to the owner, it would be to put a hot water dispenser in the clean room so workers could have tea. But he frets so much about the cost of electricity that she doubts he would agree. He already has tried to ban television from the dorm because of the cost, but at least one of the girls has a small, illicit set.

The boss has problems of his own. Sales are booming--up 20 percent in the past year--but the medical supply business is highly competitive and he believes he needs to watch costs like a hawk.

He started work at the factory nearly 20 years ago as a painter when it was a government-owned manufacturer of clocks and radios. It switched product lines several times and eventually failed, allowing him to invest in the factory and take it over as a private enterprise.

He got the deal because he was ambitious and studied management in night school, but the fact that his father is a local Communist Party chief certainly helped, he admits.

Perhaps in an attempt to rectify the incongruity of a party boss' son going capitalist, local officials rewarded him with membership in the party. Chinese citizens are not all members of the Communist Party. Only about 6 percent have this exclusive distinction.

Today the government is even more actively recruiting entrepreneurs to join the party as a means of modernizing the image of China's leadership and keeping the party relevant by merging the identities of communism and capitalism.

The prevailing philosophy is the statement widely attributed to Deng Xiaoping when he was first trying to engineer China's shift from socialism to modernity: "To get rich is glorious."

As Bai Lin sits there, keeping up her little responsibility on an assembly line that employs several dozen women, there is little to think about except how miserable it all seems.

"I just want to go home--the sooner the better," Bai Lin often says to herself.