Why is pain so poorly understood? Why do we still distinguish between mental pain and physical pain, when pain is always an emotional experience? How can it be that science is about to clone a human being but still can't cure the pain of a bad back? If pain is the reason why most people visit the doctor, why are most doctors so bad at addressing the problem of suffering? Marni Jackson's "Pain: The Fifth Vital Sign" is a witty, personal and groundbreaking inquiry into the nature, treatment and definition of human pain, one of the most misunderstood and elusive subjects to challenge humankind. In the questing and narrative manner of Oliver Sacks, Jackson takes us back into the history of pain and forward into the possibilities of pain genetics, Jackson brings us stories both of people in pain and the pain pioneers: eccentrics and artists, wrestlers and writers, psychologists and philosophers, nurses and doctors. Above all, "Pain" makes an elusive subject vivid and readable. We all know what pain is. Now Marni Jackson has given it a voice.