eful 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 more before
these men, finding themselves in the presence of a master--finding that
all their lives were occupied in attempting to ascertain for themselves
that which was familiar to him--I say it took the best part of a hundred
years before they could fairly see that their business was not to follow
him, but to follow his example--namely, to look into the facts of nature
for themselves, and to carry on, in his spirit, the work he had begun.
That was first done by Vesalius, one of the greatest anatomists who ever
lived; but his work does not specially bear upon the question we are
now concerned with. So far as regards the motions of the heart and the
course of the blood, the first man in the Middle Ages, and indeed the
only man who did anything which was of real importance, was one Realdus
Columbus, who was professor at Padua in the year 1559, and published a
great anatomical treatise. What Realdus Columbus did was this; once
more resorting to the method of Galen, turning to the living animal,
experimenting, he came upon new facts, and one of these new facts was
that there was not merely a subordinate communication between the blood
of the right side of the heart and that of the left side of the heart,
through the lungs, but that there was a constant steady current of
bl