The battle against tuberculosis, the deadliest killer in history, is chronicled. Long thought to be hereditary, by the start of the 19th century the illness had killed one in seven of all the people who had lived up until that point. Fresh air and a pristine environment was believed to be the cure, which led to the development of such cities as Colorado Springs. After the 1882 discovery that it was contagious, however, a new approach took root: the segregation of the sick via sanatoriums.