slow is the progress of truth, that, within my time, the question of the active dilatation of the arteries has been discussed. Thus Harvey's contributions to physiology may be summed up as follows: In the first place, he was the first person who ever imagined, and still more who demonstrated, the true course of the circulation of the blood in the body; in the second place, he was the first person who ever understood the mechanism of the heart, and comprehended that its contraction was the cause of the motion of the blood; and thirdly, he was the first person who took a just view of the nature of the pulse. These are the three great contributions which he made to the science of physiology; and I shall not err in saying—I speak in the presence of distinguished physiologists, but I am perfectly certain that they will endorse what I say—that upon that foundation the whole of our knowledge of the human body, with the exception of the motor apparatus and the sense organs, has been gradually built up, and that upon that foundation the whole rests. And not only does scientific physiology rest upon it, but everything like scientific medicine also rests upon it. As you know—I hope it is now a matter of popular knowledge—it is the foundation of all rational speculation about morbid processes; it is the only key to the rational interpretation of that commonest of all indications of disease, the state of the pulse; so that, both theoretically and practically, this discovery, this demonstration of Harvey's, has had an effect which is absolutely incalculable, and the consequences of which will accumulate from age to age until they result in a complete body of physiological science. Fig.5.—The junction of the arteries and veins by capillary tubes, discovered by Malpighi (A.D. 1664).