Another 16th-century anatomist, Andrea Cesalpino, is considered by the Italians to have been a discoverer of the circulation of the blood before Harvey; he certainly had a more or less clear idea of the circulation, but, as in the case of the "organic evolutionists before Darwin," he failed to prove his point by conclusive demonstration. [Sidenote: William Harvey (1578-1657).] William Harvey, the great Englishman who founded modern experimental physiology and was the first to establish not only the fact of the circulation but also the physical laws governing it, is commonly reckoned the Father of Modern Medicine. He owed his interest in the movements of the blood to Fabricio of Acquapendente, his tutor at Padua, who drew his attention to the valves in the veins, thus suggesting the idea of a circular as opposed to a to-and-fro motion. Harvey's great generalisation, based upon a long series of experiments _in vivo_, was considered to have given the _coup de grâce_ to the Galenic physiology, and hence threw temporary discredit upon the whole system of medicine associated therewith. Modern medicine, based upon a painstaking research into the details of physiological function, had begun. [Sidenote: Back to Galen!] While we cannot sufficiently commend the results of the long modern period of research-work to which the labours of the Renascence anatomists from Vesalius to Harvey form a fitting prelude, we yet by no means allow that Galen's general medical outlook was so entirely invalidated as many imagine by the conclusive demonstration of his anatomical errors. It is time for us now to turn to Galen again after three hundred years of virtual neglect: it may be that he will help us to see something fundamentally important for medical practice which is beyond the power even of our microscopes and _X_-rays to reveal. While the value of his work undoubtedly lies mainly in its enabling us to envisage one of the greatest of the early steps attained by man in medical knowledge, it also has a very definite intrinsic value of its own. [Sidenote: Galen's Debt to his Precursors.] No attempt can be made here to determine how much of Galen's work is, in the true sense of the word, original, and how much is drawn from the labours of his predecessors. In any case, there is no doubt that he was much more than a mere compiler and systematizer of other men's work: he was great enough to be able not merely to collect, to digest, and to assimilate all the best of the work done before his time, but, adding to this the outcome of his own observations, experiments, and reflections, to present the whole in an articulated "system" showing that perfect balance of parts which is the essential criterion of a work of art. Constantly, however, in his writings we shall come across traces of the influence of, among others, Plato, Aristotle, and writers of the Stoic school. [Sidenote: Influence of Hippocrates on Galen.]