It had been more than a year since a train had stopped here, but one morning last month that same train returned: three rail cars from Buenos Aires full of doctors and dentists volunteering their assistance in Argentina's rural interior, where basic health services can be hard to find.

The last dentist left this town years ago, and the health clinic is staffed only a few times a week by a visiting doctor. The doctors who arrived on the train found that among the most widespread maladies is malnutrition, despite the fact that the country is one of the world's top producers of beef and soybeans.

The sleepy, rustic vibe here suggests a town from an earlier era, but outposts like this one might offer a glimpse of the world's rural future. While modern life has made much of the world seem smaller, rural expanses in countries such as Argentina seem ever larger and more isolated.

The global population is expected to change from mostly rural to mostly urban in the next year, thanks almost exclusively to rapid migration to the cities in developing countries. Latin America has already become the most urbanized region in the world, and by 2030 about 84 percent of its residents are expected to live in cities.

While urbanization brings certain benefits, experts say, governments are already struggling to provide health care for those left behind in the countryside.

"In most cases, the only time a child in those areas sees a medical professional is when our train comes," said Oscar Algranti, director of Foundation Alma, which organizes the trip to Chorotis.

The isolation of small towns has attracted attention in Argentina not merely as a demographic trend but as a human rights issue. Thousands of demonstrators from the provinces gathered in Buenos Aires this year holding signs proclaiming "Hunger Is a Crime." Here in the northern province of Chaco, during a five-week period that ended last month, 11 people died of what local activists labeled starvation. Last month, a nonprofit organization called Responde launched a nationwide program to improve the delivery of food to rural regions where populations are shrinking.

According to that organization, about 800 small towns in Argentina are at risk of simply disappearing.

"The children who live in the remote areas are undernourished, and so are the parents, and what is happening now is a humanitarian tragedy," said Rolando Nuñez, director of the Nelson Mandela Center, a nongovernmental human rights organization based in Chaco's provincial capital, Resistencia. "And it is getting worse."

Few Reasons to Stay

The train retrofitted to serve as a mobile clinic churned into this town about 6 a.m. on a recent weekday. Three pediatricians, two dentists, a nurse, a social worker and laboratory technicians sat in the train cars and waited for residents to notice them. The streets were quiet throughout the morning, save for the occasional sounds of a dog barking and a metal ring on a rope banging against a flagpole.

Chorotis is one of many small towns that lost its economic reason for being in 1993, when Argentina sold off its national railroad and passenger trains stopped servicing most of the country. The trains provided jobs for the townspeople and vital links to other parts of the country.

Those who remain are people such as Daniel Hofstatter, 38, one of several town administrators. He heard about the train's arrival and was among the first people to walk over the rocky railroad tracks and inquire inside the train's rear car, about six hours after it arrived.

His wife, Lilian, carried their 1-year-old son, Diego, who had been suffering diarrhea for days. Hofstatter told the doctors on board that he would like them to take a look at the boy and perhaps do a blood analysis in search of parasites.

"There aren't any other pediatricians here," he explained while he waited beside the tracks for the results of the blood test, which detected the presence of a parasite in the child. "This is the only way. Otherwise, we would have to go to Charata," more than 50 miles away.

The lack of those kinds of services means that those without family ties often find few reasons to stay, he said.

"A lot of people have left, especially the young ones," Hofstatter said. "They watch television and see what life is like in the cities, and then they all want to go."

Between the last two censuses, in 1990 and 2001, 90 towns fell off the map in rural Argentina, according to Responde, which is dedicated to helping disappearing villages. Marcela Benitez, a former geographical researcher who founded the organization in 1999 after becoming alarmed at what she was witnessing on fact-finding trips, has identified 602 towns with declining population trends that put them at risk of extinction, and she estimates that an additional 200 are in similar peril.

The fact that small towns rise and fall according to temporary economic opportunity is nothing new -- think of the ghost towns of the American West, for example. But a lot of small towns founded on railroads in the United States found other livelihoods after trains ceased to be major economic engines, she said. That hasn't happened here, yet.

Ben?tez says such transformations are possible in Argentina with minimal investment, and she rejects the idea that migration to nearby medium and large cities might be a necessary part of a country's economic evolution. The fastest-growing parts of large cities in the region are its slums, she said, which she considers proof of the importance of restoring rural communities in developing countries.

"People have asked me: 'Why do you want people to stay in those places? If they migrate, they can find opportunities,' " Benitez said. "That might have been true years ago in the United States and Europe, but not now and not here."

Even so, staying in rural areas is becoming an increasingly difficult choice for many. Health concerns, particularly related to malnutrition, are so pressing in some areas that she said she has seen the energy and will of entire communities sapped, which only intensifies the problems for successive generations.

Agriculture is still a significant part of the economy, but its significance has changed. Large commercial fields of genetically modified soybeans have replaced smaller farms with cotton, tobacco and food crops. Those smaller farms employed about one person for every 20 acres, while the soybean farms employ one person for every 495 acres, according to a 2005 World Bank report on rural poverty in Argentina.

Algranti and others have suggested that rural residents should learn to use the soybeans and related products to supplement their diets, but it hasn't happened in most communities. Some nutritionists have warned that in places where it has, soy has proved a meager substitute for meat and dairy products and has compounded problems of malnutrition.

As the isolated communities try to respond to the changes, health professionals on the hospital train have noticed that fundamental health needs diminish the importance placed on other services.

"I'd say about 30 percent of the children go to school for education, and 70 percent go only for the food," Algranti said.

Accusations of Neglect

The issue of extreme rural isolation made headlines during Argentina's financial collapse in 2001, but it has persisted even after an economic rebound that has led the economy to grow about 7 percent annually in the past four years. Those conflicting factors -- general prosperity and particular privation -- prompted the march to Buenos Aires this year.

Meanwhile, the 11 deaths in Chaco -- along with newspaper and TV images of the victims' emaciated bodies -- have fueled the growing concerns over rural hunger and abandonment. Most of those who died belonged to the Toba indigenous tribe, who live in small communities in a northern part of the province.

Last month, newspapers and TV stations across the country displayed images of Rosa Molina, a 56-year-old woman who traveled to Resistencia to appeal for help at a local church after she said a local health clinic refused to admit her. She weighed just 52 pounds according to media reports, and her severely emaciated figure became a symbol of what the Buenos Aires newspaper La Nacion labeled a "critical situation" with malnutrition in several rural provinces.

Local health officials have defended themselves against accusations of neglect. They say they've made significant strides in medical outreach, investing in new ambulances, communication systems and health workers to serve their communities. Ricardo Mayol, Chaco province's minister of health, said none of the 11 deaths was caused by malnutrition alone, but rather by a combination of maladies, including tuberculosis and chagas, an insect-borne disease that is common to the region.

"Nobody can deny that these are cases of malnutrition, which can be seen just by looking at the photographic evidence, but these are not cases of malnutrition primarily," Mayol said. "These are not people who didn't have any help from the community, or the state, or from family. They suffered from chronic sicknesses that, in some cases, leave people malnourished in their final days."

Alejandro O'Donnell, director of the Center for Infantile Malnutrition Studies, acknowledged the presence of other factors in a column he recently wrote for La Nacion, but said the cases highlighted shortcomings of the services available in the country's rural interior.

"All of the cases could have been prevented if the primary health-care system would have detected them in time," O'Donnell wrote. "That is to say, the cases reveal inefficiencies of the primary health agents and the health centers."

Nuñez, of the Mandela Center, recently visited six women who he said were hospitalized in Chaco for malnutrition. Within weeks, three died.

"Nothing the government does to address life in the rural communities -- add ambulances, or doctors, or whatever -- will have any success whatsoever if they do not have a plan to seriously address malnutrition and hunger in these areas," he said. "The problems are seen everywhere. First the socioeconomic system collapsed, then the health system followed. And now we're starting to see the consequences of that."