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 of the Americas is an ideal riding horse for children due to its small stature, athleticism, and gentle personality. For young equestrian riders, who are too big for the smaller ponies yet not quite ready for a full sized horse, the Pony of the Americas is a perfect match. The growing popularity of the Pony of the Americas lends itself to being a breed for children to ride and show. It is a pony breed with a good appearance, speed, and stamina.