ctions and theories as to the
functions of organs, the cause of diseases, and his methods of treating
them, would be recognized as absurd by a modern school-boy of average
intelligence. His greatness must be judged in comparison with
ancient, not with modern, scientists. He maintained, for example, that
respiration and the pulse-beat were for one and the same purpose--that
of the reception of air into the arteries of the body. To him the act of
breathing was for the purpose of admitting air into the lungs, whence it
found its way into the heart, and from there was distributed throughout
the body by means of the arteries. The skin also played an important
part in supplying the body with air, the pores absorbing the air and
distributing it through the arteries. But, as we know that he was
aware of the fact that the arteries also contained blood, he must have
believed that these vessels contained a mixture of the two.

Modern anatomists know that the heart is divided into two approximately
equal parts by an impermeable septum of tough fibres. Yet, Galen, who
dissected the hearts of a vast number of the lower animals according to
his own account, maintained that this septum was permeable, and that the
air, entering one side of the heart from the lungs, passed through it
into the opposite side and was then transferred to the arteries.

He was equally at fault, although perhaps more excusably so, in his
explanation of the action of the nerves. He had rightly pointed out that
nerves were merely connections between the brain and spinal-cord and
distant muscles and organs, and had recognized that there were two kinds
of nerves, but his explanation of the action of these nerves was
that "nervous spirits" were carried to the cavities of the brain by
blood-vessels, and from there transmitted through the body along the
nerve-trunks.

In the human skull, overlying the nasal cavity, there are two thin
plates of bone perforated with numerous small apertures. These apertures
allow the passage of numerous nerve-filaments which extend from a group
of cells in the brain to the delicate membranes in the nasal cavity.
These perforations in the bone, therefore, are simply to allow the
passage of the nerves. But Galen gave a very different explanation. He
believed that impure "animal spirits" were carried to the cavities of
the brain by the arteries in the neck and from there were sifted out
through these perforated bones, and so expelled fr