What they discovered was startling. It turned out that the rats in isolated cages used up to 25 milligrams of morphine a day, as in the earlier experiments. But the rats in the happy cages used hardly any morphine at all—less than 5 milligrams. “These guys [in Rat Park] have a complete total twenty-four-hour supply” of morphine, Bruce said, “and they don’t use it.” They don’t kill themselves. They choose to spend their lives doing other things.
