 She is one that comes easily to the lips of scientists. It serves to explain a multitude of phenomena which might otherwise remain inexplicable. But perhaps it is used too often as an explanation in instances where it explains nothing at all. Witness, for example, the curious case of William Duncan's family. Saturday afternoon was a busy time in the office of Dr. Martin Brady of Newton, Massachusetts. And ordinarily the doctor would never have dreamed of leaving his office to pay a visit to a patient's home. But there was nothing ordinary about the telephone call he received on a Saturday afternoon in question. The afternoon of May 21st, 1928. Yes, Dr. Brady speaking. Who is this? Five minutes later, Dr. Brady drove his coupé down Chestnut Street. He parked it in front of William Duncan's house. He walked and climbed the porch steps. Hmm, that's strange. He tried the door and found that it was unlocked. So he stepped into the living room. Hello! Hello in there! The doctor wandered through the first floor, but he found no one there. He mounted the stairs and as he approached the top, he caught a full view of the master bedroom at the head of the hall. And he staggered back, shocked by what he saw on the floor of the room. There the unconscious bodies of William Duncan, his wife, and his two sons. Everything about them suggested that they had been asphyxiated. But nowhere was there the slightest odor of gas. The doctor bent over them and went to work. Slowly they struggled back to consciousness. When he could speak again, William Duncan explained, My wife sent me up for her bedroom slippers. I walked into the room and that's all I know. I guess she got worried about me and came up to see what had happened. She saw me lying there and then I guess the same thing happened to her. The two sons of William Duncan told precisely the same story. They had stepped into the room and fallen unconscious. I saw what happened to mom and dad and Joe and I felt it sneaking up on me. I managed to reach you and then I passed out. I see. But how do you explain it, Doc? This is an example of what we medical men call mass psychology. A sort of an epidemic of hysteria, you might say. And that's all it was. And so the strange affair of William Duncan's family was set down in the medical records as a case of mass psychology. And no one thought to raise the question of why William Duncan himself had become unconscious in the first place or why three intelligent adults should have been overcome at the sight of him. Mass psychology apparently explained it all, at least to the satisfaction of the good doctor. But there are others who remain unconvinced who continue to look upon the affair as an unsolved mystery. A mystery incredible but true.