. . 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 direction
of the blood that entered and left the organ, but he did not appreciate
that it was a pump for distributing the blood, regarding it rather as
a fireplace from which the innate heat of the body was derived. He knew
that the pulsatile force was resident in the walls of the heart and in
the arteries, and he knew that the expansion, or diastole, drew blood
into its cavities, and that the systole forced blood out. Apparently his
view was that there was a sort of ebb and flow in both systems--and yet,
he uses language just such as we would, speaking of the venous system
as ". . . a conduit full of blood with a multitude of canals large and
small running out from it and distributing blood to all parts of the
body." He compares the mode of nutrition to irrigating canals and
gardens, with a wonderful dispensation by nature that they should
"neither lack a sufficient quantity of blood for absorption nor
be overloaded at any time with excessive supply.
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