Page:The Harveian oration 1905.djvu/73

 predecessors. I take it for granted that this learned assembly is familiar with the details of the work and teaching of Harvey, in establishing among other points the muscular structure and contractility of the heart, whether known previously or not, and in demonstrating its mode of action and mechanism, and the effects thereby produced; at the same time proving that the blood moves in a constant stream and in a definite direction, and that there is a complete double circulation, pulmonary and general. He sums the matter up in the words: "By the impulse of the heart there is a perpetual movement of the blood in a circle." Though he had absolute proof that the blood did somehow find its way from the terminal arteries into the commencing veins, he did not know how, and conjectured that it was the result of percolation through the organs and tissues. With his simple magnifying lens or perspicillum he could not see the delicate network of capillaries, which were only observed when the microscope was sufficiently developed, by means of which apparatus the capillary circulation in the frog's lung and mesentery was first observed by Malpighi, and the continuity of the circulation thus definitely established. Nor did Harvey understand the meaning of the pulmonary circulation, knowing nothing about the mechanism or chemistry of respiration, which were only brought to light at a much later period; and this constituted a most important advance.