For one and one half millennia Galen of Pergamum influenced the practice of medicine in the Western world, and for rather longer in some parts outside it. That in the hands of his successors this influence became stultifying and inhibitory of progress was no fault of his, although critics, from Paracelsus in the sixteenth century to others in the present day, have tried to diminish his importance. Yet even fifty years ago, when antibiotic therapy was in its infancy and synthetic pharmaceuticals were far less common than now, any pharmacy in the Western world would have stocked a range of basic medicaments known as ‘galenicals’ – tinctures, syrups, extracts and the like – which were the building blocks for many of the prescribed medicines of the time. Nor was the term merely a memorial, for many of these galenicals stood in a direct line of succession from Galen's own medicaments. Indeed some were virtually identical, and used for much the same purposes that he had recommended. And to this day his views on foods from vegetable sources are referred to with obvious sincerity in some modern herbals.

I commence this introduction by discussing the man and his work in general terms. After this I deal with several matters that arise so frequently throughout the book that it seems better to discuss them now than to make repeated comment as the work proceeds.