If there is one thing that we think we know about medicine in the Middle Ages it is that its practitioners made extensive use of herbs. In the wellresearched historical novels of Ellis Peters, the monk Brother Cadfael has his herb garden, and his credentials as healer and as detective depend crucially on his skill with herbs. He is an emblematic healer and herbalist. Whether we have in mind monks, university doctors, barber surgeons or wise women, we suppose that medieval healers of all kinds treated complaints with herbal simples, or with medicaments whose principal ingredients were herbs. Of course they made use in addition of animal parts or excreta, minerals, exotic spices and substances that evoke a satisfying frisson of disgust in the modern imagination, but medieval therapeutics depended first and foremost on herbs. It is not the purpose of this paper to dispute this picture of medieval medicine – in fact its argument will help to sustain the vision of herbal medicine that has proved so compelling – but to try to address the question of how the use of herbs might have been integrated into medical practice. If you were a medieval healer how did you make use of herbs in the course of treating patients, and how did this fit in with other kinds of treatment?

Medical literature of the Middle Ages is eloquent on the virtues of herbs. Herbals, recipe books and manuals on medical therapy can tell us what herbs, singly or in combination, were prescribed for a particular illness or complaint. Sometimes, but by no means always, they give instructions as to how the ingredients were to be collected, and the medicines prepared and administered to the patient. These documents are thus always prescriptive in character. Functionally this literature has much in common with the Merck Manual which, so we are told, “first appeared in 1899 as a slender 262-page text titled Merck’s Manual of the Materia Medica. It was expressly designed to meet the needs of general practitioners in selecting medications, noting that ‘memory is treacherous’ and even the most thoroughly informed physician needs a reminder ‘to make him at once master of the situation and enable him to prescribe exactly what his judgment tells him is needed for the occasion.’