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:
At 7:15 p.m., a cannon was fired and the rider bolted off to a waiting ferry boat. The Pony Express was set up to provide a fresh horse every 10-15 miles and a fresh rider every 75-100 miles. 75 horses were needed total to make a one-way trip. Average speed was 10 miles per hour. On April 9 at 6:45 p.m., the first rider from the east reached Salt Lake City, Utah.