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 series stars a unicorn pony named Twilight Sparkle, who is a pupil of Equestriaâs ruler Princess Celestia. Seeing the young pony buried in books, the princess sends her to Ponyville and gives her the task of making friends.