pits, which really exist there, as holes, and he supposed that the greater part of the blood passed through these holes from the right to the left ventricle (Fig 2). It is of great importance you should clearly understand these teachings of Galen, because, as I said just now, they sum up all that anybody knew until the revival of learning; and they come to this—that the blood having passed from the stomach and intestines through the liver, and having entered the great veins, was by them distributed to every part of the body; that part of the blood, thus distributed, entered the arterial system by the 'anastomoses', as Galen called them, in the lungs; that a very small portion of it entered the arteries by the 'anastomoses' in the body generally; but that the greater part of it passed through the septum of the heart, and so entered the left side and mingled with the pneumatised blood, which had been subjected to the air in the lungs, and was then distributed by the arteries, and eventually mixed with the currents of blood, coming the other way, through the veins. Yet one other point about the views of Galen. He thought that both the contractions and dilatations of the heart—what we call the 'systole' or contraction of the heart, and the 'diastole' or dilatation—Galen thought that these were both active movements; that the heart actively dilated, so that it had a sort of sucking power upon the fluids which had access to it. And again, with respect to the movements of the pulse, which anybody can feel at the wrist and elsewhere, Galen was of opinion that the walls of the arteries partook of that which he supposed to be the nature of the walls of the heart, and that they had the power of alternately actively contracting and actively dilating, so that he is careful to say that the nature of the pulse is comparable, not to the movement of a bag, which we fill by blowing into it, and which we empty by drawing the air out of it, but to the action of a bellows, which is actively dilated and actively compressed. Fig 3.—The course of the blood from the right to the left side of the heart (Realdus Columbus, 1559).