Surfactant prevents this collapse by reducing the surface tension of the fluids that line the lungs and helping to equalize the pressures between large and small air spaces. Surface tension is a measure of the attraction molecules of a fluid have for each other.
Buffalo Bill Cody, who later became famous for his Wild West Show, was a rider for the Pony Express and wrote of his experiences. We join Bill's story as he is hired - at the age of 15 - to ride a section of the trail that lies in modern-day Wyoming:
Pony Express Postmark, 1860, westbound. The Pony Express was a mail service delivering messages, newspapers, mail, and small packages from St. Joseph, Missouri, across the Great Plains, over the Rocky Mountains and the Sierra Nevada to Sacramento, California, by horseback, using a series of relay stations.