there were still two skeletons. He himself dissected chiefly
apes and pigs. His osteology was admirable, and his little tractate "De
Ossibus" could, with very few changes, be used today by a hygiene class
as a manual. His description of the muscles and of the organs is very
full, covering, of course, many sins of omission and of commission, but
it was the culmination of the study of the subject by Greek physicians.

His work as a physiologist was even more important, for, so far as we
know, he was the first to carry out experiments on a large scale. In the
first place, he was within an ace of discovering the circulation of
the blood. You may remember that through the errors of Praxagoras and
Erasistratus, the arteries were believed to contain air and got their
name on that account: Galen showed by experiment that the arteries
contain blood and not air. He studied particularly the movements of
the heart, the action of the valves, and the pulsatile forces in the
arteries. Of the two kinds of blood, the one, contained in the venous
system, was dark and thick and rich in grosser elements, and served for
the general nutrition of the body. This system took its origin, as
is clearly shown in the figure, in the liver, the central organ of
nutrition and of sanguification. From the portal system were absorbed,
through the stomach and intestines, the products of digestion. From the
liver extend the venae cavae, one to supply the head and arms, the other
the lower extremities: extending from the right heart was a branch,
corresponding to the pulmonary artery, the arterial vein which
distributed blood to the lungs. This was the closed venous system. The
arterial system, shown, as you see, quite separate in Figure 31, was
full of a thinner, brighter, warmer blood, characterized by the presence
of an abundance of the vital spirits. Warmed in the ventricle, it
distributed vital heat to all parts of the body. The two systems were
closed and communicated with each other only through certain pores or
perforations in the septum separating the ventricles. At the periphery,
however, Galen recognized (as had been done already by the Alexandrians)
that the arteries anastomose with the veins, ". . . and they mutually
receive from each other blood and spirits through certain invisible and
extremely small vessels."

It is difficult to understand how Galen missed the circulation of the
blood. He knew that the valves of the heart determined the di