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:
The Pony Express ran day or night, summer or winter. It ran through 2 states California and Missouri. At that time the other states were territories. It ran through a portion of the Oregon Trail. There are 183 men known to have ridden for the Pony Express during the 19 months.