After Galen's time came the collapse of the Roman Empire, the extinction of physical knowledge, and the repression of every kind of scientific inquiry, by its powerful and consistent enemy, the Church; and that state of things lasted until the latter part of the Middle Ages saw the revival of learning. That revival of learning, so far as anatomy and physiology are concerned, is due to the renewed influence of the philosophers of ancient Greece, and indeed, of Galen. Arabic commentators had translated Galen, and portions of his works had got into the language of the learned in the Middle Ages, in that way; but, by the study of the classical languages, the original text became accessible to the men who were then endeavouring to learn for themselves something about the facts of nature. It was a century or more before these men, finding themselves in the presence of a master—finding that all their lives were occupied in attempting to ascertain for themselves that which was familiar to him—I say it took the best part of a hundred years before they could fairly see that their business was not to follow him, but to follow his example—namely, to look into the facts of nature for themselves, and to carry on, in his spirit, the work he had begun. That was first done by Vesalius, one of the greatest anatomists who ever lived; but his work does not specially bear upon the question we are now concerned with. So far as regards the motions of the heart and the course of the blood, the first man in the Middle Ages, and indeed the only man who did anything which was of real importance, was one Realdus Columbus, who was professor at Padua in the year 1559, and published a great anatomical treatise. What Realdus Columbus did was this; once more resorting to the method of Galen, turning to the living animal, experimenting, he came upon new facts, and one of these new facts was that there was not merely a subordinate communication between the blood of the right side of the heart and that of the left side of the heart, through the lungs, but that there was a constant steady current of blood, setting through the pulmonary artery on the right side, through the lungs, and back by the pulmonary veins to the left side of the heart (Fig.3). Such was the capital discovery and demonstration of Realdus Columbus. He is the man who discovered what is loosely called the 'pulmonary circulation'; and it really is quite absurd, in the face of the fact, that twenty years afterwards we find Ambrose Pare, the great French surgeon, ascribing this discovery to him as a matter of common notoriety, to find that attempts are made to give the credit of it to other people. So far as I know, this discovery of the course of the blood through the