There are currently more than 750 such areas in the National Wilderness Preservation System comprising over 109 million acres -- roughly 5% of the United States by area. Need a refresher from the other 95%? The Active Times picked 10 wild places in the lower 48 states that are truly wild.
Polio, which struck children disproportionately, could attack the central nervous system and cause muscle deterioration, paralysis and even death. American virologist Jonas Salk, who was born 100 years today on October 28, 1914, developed the worldâs first safe and effective polio vaccine.
1894, first outbreak of polio in epidemic form in the U.S. occurs in Vermont, with 132 cases. 1908, Karl Landsteiner and Erwin Popper identify a virus as the cause of polio by transmitting the disease to a monkey.1916, large epidemic of polio within the United States.1921, Franklin Delano Roosevelt (FDR) contracts polio at age 39.908, Karl Landsteiner and Erwin Popper identify a virus as the cause of polio by transmitting the disease to a monkey. 1916, large epidemic of polio within the United States. 1921, Franklin Delano Roosevelt (FDR) contracts polio at age 39.