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.

(FIGURE 3.--The course of the blood from the right to the left side of
the heart (Realdus Columbus, 1559).)

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 l