He drew blood from his arms. He saved his urine. He played computer games to test his memory fid reaction speed. He measured the shape of his eyes. Two hundred and forty miles below, Mr. Now, a comparison of these two men has provided a unique opportunity to learn what happens to the human body in space — down to the molecular level. On Thursday, just over three years after Mr. Kelly, 55, returned to Earth, NASA researchers reported that his body experienced a vast number of changes while in orbit. DNA amke in some of his cells.