Simply because he imagined there must be
one. A lesson, this, for observers in the
physical sciences. Galen's theory was, that
the veins, like the arteries, carried the blood
to the members; but there were two bloods
—namely, the spirituous blood, the blood of
the arteries and of the left ventricle; and the
venous blood, the blood properly so called,
the blood of the veins and of the right heart.
And this, again, was an advance. It was the
first indication of two kinds of blood, now so
clearly distinguished, the arterial and the
venous blood, the red blood and the black
blood, the blood which has breathed, and
that which has not breathed. According to
Galen, each of his two bloods had a special
destination; the spirituous blood nourished
the light and delicate organs, such as the
lungs; the venous blood fed the coarse and
heavy organs, such as the liver. The spirit,
the purest portion of the blood, was only
formed in the left ventricle; and, as the
venous blood, to be serviceable for nutrition,
required a certain portion of spirit, therefore
the two ventricles must have a communication,
which took place by means of the
pretended holes in the partition which separates
them. For Galen, then, this partition was
traversable by the blood, because he had
adopted a theory which required it to be so.
For the early modern anatomists, this partition
was pierced, because Galen had said so.
Berenger de Carpi was the first to confess
that the holes were not very visible; and
Vésale, the father of modern anatomy, alone
dared to assert that they do not exist. But
he does not go so far as that all at once. He
begins by repeating, with all the others, that
the blood passed from one ventricle to the
other by the holes in the partition; but soon,
carried away by the force of the fact which
he beholds, and which he has within his
grasp, he declares that he only spoke in that
way to fall in with Galen's dogmas; for, in
reality, the tissue of which the partition is
composed is just as thick and compact as the
rest of the heart; and through this thick
tissue not a single drop of blood could pass.
Vésale had made a grand stride in advance.

The next step, the discovery of the pulmonary
circulation, was due to Servetus, as a
single admirable passage from his works
demonstrates. "The communication," he
says (that is, the passage of the blood from
the right ventricle into the left), "is not made
through the partition between them, as is
commonly imagined; but, by a long and
wonderful détour, the blood is conducted
through the lungs, where it is agitated and
prepared, where it becomes yellow, and passes
from the arterial vein into the venous artery."
The new idea is comprised in these words;
the completed idea, which gave us the pulmonary
circulation, consisted in comprehending
that the blood passes from the pulmonary
artery into the pulmonary vein; that the
blood, starting from, the right heart by the
pulmonary artery, returns to the left heart by
the pulmonary vein; that the blood,
proceeding from the heart, goes back to the
heart; that there is, consequently, a circulation,
a circuit. This idea, so grand, so novel,
of a circulation, a circuit, was first
entertained by Servetus. He was a man of
considerable genius: of his theological works this
is not the place to speak. But, whether his
doctrines were right or wrong, at least he
did not burn Calvin at the stake, but was
burnt by him. Singularly enough, the book
which brought him to a heretic's death, and
which contains his purely and profoundly
physiological discovery, is entitled,
"Christianismi Restitutio,"the Restitution of
Christianity. In theology, he persisted in
maintaining the literal sense of texts, and so
accepted the passage, "the blood is the life,"
—"anima est in sanguine; anima ipsa est
sanguis." Hence his researches into the for-
mation of the blood, and the inferences which
led him to the pulmonary circulation. He
called attention to the mingling of air with
the blood in the lungs, remarking that its
bright colour is given to the blood by the
lungs, and not by the heart. We now know
that it is not the whole of the air, but only
the oxygen contained in it, which produces
the change of colour. But with that exception,
with the exception of the analysis of the
air, which Servetus was unable to forestall,
and which is the marvel of modern chemistry,
how correct the idea is! Servetus not only
discovered the true course of the blood from
one side of the heart to the other, through
the lungs; but he discovered the true seat of
sanguification, of the transformation of the
blood, of the change of black blood into red.
Galen fixed the place of sanguification in the
liver; Servetus was the first who referred it
to the lungs. The truth was not remarked
at the time, and its scope was not understood
till much later; and, in fact, only received
its full development from the experiments
of more recent physiologists, as Goodwin and
Bichat.

Six years after Servetus, Realdo Colombo,
one of the best anatomists ever possessed by
Padua (where there have been many),
discovered independently the pulmonary
circulation. Finally, Césalpin, without quoting
Colombo (which he certainly would have
done had he known his publication),
discovered, in his turn, the pulmonary circulation;
and this time it is not merely the fact which
appears, but the word. Césalpin formally
styles the passage of the blood from one half
of the heart to the other, by the lungs,
"circulation." The pulmonary circulation was,
therefore, revealed; but, up to this point, up
to Césalpin—of the general circulation, of the
circulation of the whole body, of the circulation
which is called the grand, in distinction
to the pulmonary, which is called the little—
of the general circulation, not a single word.

Galen had contrived a very symmetrical