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:
Only one rider and one shipment of mail were lost during the running of the Pony Express. Riders would travel 75 to 100 miles a day, switching horses every 10 to 12 miles. The fastest delivery in the history of the Pony Express was seven days and seventeen hours.