Many patients in Europe and America today think it perfectly plausible that a cure for their insomnia or headaches, say, might be found in the Yellow Emperor's Classic of Medicine of Han dynasty China, that approaches to the body conceived in a distant culture, more than two thousand years ago, might solve their suffering here and now. Yet they wouldn't dream of seeking succor in the works of Galen. Why? How have the beliefs and practices that guided Western medicine up through the eighteenth century come to seem, paradoxically, more alien and distant than ancient Chinese notions of qi? To understand this strange forgetfulness about the Western past, we must linger on a defining feature of traditional humoralism, often slighted in modern synopses: the haunting fear of excrement.