Dirt has a bad image. Muck, we think: yuck.
But getting your hands dirty can also be irresistible, as every child knows.
A major new museum exhibition in London asks visitors to think again about the filthy and the fetid, exploring the role of dirt as humanity's enemy and ally in history, art, science and medicine.
"Dirt is something we make and encounter every day," said James Peto, senior curator at the Wellcome Collection, where the exhibition opens Thursday.
Peto said the exhibition _ "Dirt: The Filthy Reality of Everyday Life" _ explores both the good and bad sides of dirt.
"Some of it, in the right quantities and the right place, is good for us," he said. "Soil in the sense of 'soiled sheets' is bad, but soil where vegetables grow feeds us.
"And it's where we all end up in the end."
Filth's intimacy and omnipresence may explain some of the terror and fascination that dirt _ defined by the exhibition as "dust, excrement, rubbish, bacteria and soil" _ holds for us.
We abhor it, but it's also a mark of progress _ the more cities, industry and civilization there are, the more dirt, and finding ways to dispose of it has taxed societies for centuries.
Dirt has also created commercial opportunities.
The exhibition, which ranges from 17th-century Holland to 21st century New York, looks at those who have made money from dirt, from river-combing mudlarks and the "toshers" who hunted for treasures in 19th-century sewers, to the manual scavengers of India, who clean latrines by hand _ a practice that persists despite official attempts to ban it.
"The relationship between dirt and commerce is a long-standing one," said another curator, Kate Forde. "In medieval times, London's waste was sold to farmers outside the city to fertilize crops." Today, electricity is generated from incinerating some of the city's waste.
Dirt is also strongly linked to disease, and the exhibition charts several historic triumphs for hygiene. They include Joseph Bazalgette's network of sewers, which cured Victorian London of its "great stink" and are still in use today, and physician John Snow's discovery that cholera was spread through contaminated water, not foul air. He closed a public water pump and an outbreak that had killed hundreds in the Soho area of the city was stopped in its tracks.
One room is devoted to a 19th-century Glasgow infirmary so filthy that patients arriving with a broken limb had a 90 percent chance of amputation. It was transformed when Joseph Lister discovered that washing with carbolic acid before surgery sharply reduced the infection rate.
Despite such advances, the exhibition notes that "we live in unmistakably filthy times," and dealing with dust is still a huge undertaking.
The exhibition looks at plans to deal with the Fresh Kills dump on New York's Staten Island _ once the world's largest municipal landfill, towering higher than the Statue of Liberty. It shut after becoming the main site for debris from the Sept. 11, 2001 attacks and is now scheduled to become part of a vast new green space , almost three times the size of Central Park.
The park project, due to last until 2030, is beset by challenges. Recently the site was discovered to be sinking.
Lest we think cleanliness is all good, the show includes a section devoted to the German Hygiene Museum, which in the 1930s embraced the Nazi ideology of "racial hygiene" and advocated the sterilization of Jews and others seen as posing a threat to "racial health."
The exhibition contains several pleasingly icky exhibits, including "intestinal excreta" from a 19th-century cholera victim.
Scattered throughout are artworks, including sculptures made from human feces _ thankfully, they're odorless _ and a pile of bricks containing dust donated by London households. One contains a pinch of carpet dust from Benjamin Franklin's house, another a dash of dust from writer J.G. Ballard's bookshelves.
London's King's Cross, now famous for its railway station, was previously home to the "Great Dustheap," an ugly mountain of cinder dust, bones and garbage, surrounded by slums. It is long gone, but Londoners still live with it, and in it _ dust from the mound was used in bricks that built the city's Victorian houses.
The exhibition, which runs to Aug. 31, is curated by the Wellcome Collection, which seeks to bring together science, medicine and art.
"Dirt," Forde said, "is a very important and profound element in the way we shape our cities."