I have been asked to speak about the history of the experimental method in medicine, with particular reference to the nineteenth century. This indication, though I do not propose to regard it as setting a limit, seems to have a special fitness, since it is to the nineteenth century, and especially to its latter half, that we must look for the effective beginning and astonishingly rapid development, the veritable outburst, indeed, of activity in the application of the experimental method to medicine, which opened the new era of medical progress in which we are living today. It is curious, perhaps, that this should have come so late in the history of science. For medicine had figured early in man's attempts to understand nature and his relation to it, and many departments of science which have long ago achieved recognition as independent bodies of knowledge originated as aspects of the physician's equipment—botany, for example, zoology and chemistry, as well as human anatomy and physiology, which still retain their attachment to the medical group of the scientific disciplines. From this point of view, then, it is not surprising to find two physicians, William Gilbert and William Harvey, as the leaders in this country of the scientific revolution which had begun in Europe in 1543 with the publication, within a few weeks of one another, of two books—one by Copernicus of Cracow, De Revolutionibus Orbium Coelestium, and the other by Vesalius of Padua, De Humani Corporis Fabrica. Both Gilbert and Harvey, we may be proud to remember, studied and first graduated in Medicine here, in Cambridge.