ent, totally
failed in his attempt to cut down upon the aorta, to the no small
amusement of his pupils, who, thereupon taking up the experiment
themselves, made an opening into the thorax in the way in which they had
been instructed by Galen, passed one ligature round the aorta at the
part where it attaches itself to the spine, and another at its origin,
and then, by opening the intervening portion of the artery, showed that
blood was contained in it.

The arteries, Galen thought, possessed a pulsative and attractive power
of their own, independently of the heart, the moment of their dilatation
being the moment of their activity. They, in fact, _drew_ their charge
from the heart, as the heart by its diastole _drew_ its charge from the
vena cava and the pulmonary vein. The pulse of the arteries, he also
thought, was propagated by their coats, not by the wave of blood thrown
into them by the heart. He taught that at every systole of the arteries
a certain portion of their contents was discharged at their extremities,
namely, by the exhalents and secretory vessels. Though he demonstrated
the anastomosis of arteries and veins, he nowhere hints his belief that
the contents of the former pass into the latter, to be conveyed back to
the heart, and from it to be again diffused over the body. He made a
near approach to the Harveian theory of the circulation, as Harvey
himself admits in his "De Motu Cordis;"[18] but the grand point of
difference between Galen and Harvey is the question whether or not, at
every systole of the left ventricle, more blood is thrown out than is
expended on exhalation, secretion, and nutrition. Upon this point Galen
held the negative, and Harvey, as we all know, the affirmative.

The famous Asclepiads held that respiration was for the generation of
the soul itself, breath and life being thus considered to be identical.
Hippocrates thought it was for the nutrition and refrigeration of the
innate heat, Aristotle for its ventilation, Erasistratus for the
filling of the arteries with spirits. All these opinions are discussed
and commented upon by Galen, who determines the purposes of respiration
to be (1) to preserve the animal heat; (2) to evacuate from the blood
the products of combustion.

He conjectured that there was in atmospheric air not only a quality
friendly to the vital spirit, but also a quality inimical to it, which
conjecture he drew from observation of the various phenomena
accompanying t