One of the most enduring metaphors of Western medicine has been its conception of illness as an invasive enemy against which the patient and doctor must join forces to do battle. Indeed, the more invisible and mysterious the processes of disease, the more vividly do people seem to invoke the metaphor. So it is not surprising to find that in antiquity, when the etiology and control of disease was considerably more elusive than it is today, the notion of the body as a battlefield pervaded the medical treatises both implicitly and explicitly.1