What will cosmic rays do to a living organism? Will they destroy life, or produce immortality? The eminent Dr. Blair Gaddon thought he knew ... Fred Trent pulled his coupe into the curb and leaned his head out the open window beside him. "Hi, Joan, need any help?" He called to a trim-looking girl in a nurse's uniform. Joan Drake was holding on to a leash with both hands, and her slender body was tugging against the leash as she strained against the pull of a Great Dane on the other end. She look