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:
It depends on how young is the child. For riding I would advise to wait at least up to 10 years old. When younger, however, a kid may begin to attend a riding school to get close to the animals and eventually ride a pony (Pony of the Americas and ... This page may be out of date. Save your draft before refreshing this page.