On August 9, 1945, when the atomic bomb “Little Boy” exploded over Nagasaki, Dr. Takashi Nagai was working at a university hospital near the epicenter. Barely escaping from the half-destroyed building, and despite serious injuries, together with other doctors he began helping the survivors. The report on those first terrifying days after the atomic bombing became the basis for the book “The Bells of Nagasaki.” Dr. Nagai died of leukemia two years after publication. His essay became both a unique testimony of an eyewitness to the catastrophe and a scientist’s reflection on the nature of the atomic bomb—along with a humanist call: such a thing must never happen again.