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:
Frank E. Webner. Pony Express rider ca. 1861. Missouri and Sacramento, California. The distance was divided into a series of relays 75 to 100 miles in length over which a lone rider would race, changing his horse every 10 to 15 miles before handing his cargo off to the next rider.