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).

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