Many generations of mice have travelled around the sides of this rotating exercise wheel utilized to determine the effect of exercise on normal aging and on recovery from radiation injury. The two groups of mice at the top of the photo also used in the studies demonstrate the aging effect of radiation. The mice are all the same age, but the group at the right which turned gray and aged prematurely from exposure to radiation, present a marked contrast to the unexposed group at left. Long term studies of this type are yielding data on genetics vital to the human race.