Today, we meet the man who showed us how blood
flows. The University of Houston's College of
Engineering presents this series about the machines
that make our civilization run, and the people
whose ingenuity created them.
The old Roman physician
Galen told us that blood is generated in our liver,
that it passes only once through the heart, and
that it's consumed in the outlying body tissues.
Food is converted to blood, Galen said. Then it
carries nutrients to the far corners of the body.
Doctors still believed those old Galenic doctrines
in 1600, but one thing puzzled them. The left side
of the heart supplies fresh red blood to the
extremities. The right side pumps dark blood into
the lungs. But where does that blood come from?
According to Galen, blood leaked through
microscopic pores in the septum to get into the
right side. The right side was no more than a
secondary supply system for the lungs.
The fresh winds of modern science were just
gathering in northern Italy. The University of
Padua was on the cutting edge of the science of
anatomy. And it was there that a young Englishman
named William Harvey went to study. He completed
his doctorate on blood flow in 1602.
He published a little 72-page book 26 years later.
It was compact and beautifully illustrated. With
wonderful economy Harvey quite literally went to
the heart of the matter. He gave us all a fine
lesson on using our head.
First he demolished the Galenic idea that each gram
of blood passes through the heart only once. Harvey
counted the pulse and estimated the outflow of each
stroke of the heart. He found that it puts out
three times our body weight each hour. Imagine
eating food fast enough to replenish that much
And the right side of the heart? It receives the
used blood from the extremities and sends it to the
lungs to be refreshed. Harvey didn't know about
oxygen, but he saw that the blood flowed from one
side of the heart to the other, not through the
septum, but through the lungs, where it was
Harvey had to add an unproven doctrine of his own
to complete a new blood-flow theory. How did blood
get from the tiny outlying arteries back into the
veins? He guessed that a structure of capillaries
made the connection. He couldn't see any
capillaries, but his guess fared better than
Galen's. The new microscope lenses found his
capillaries four years after he died.
Harvey was a great genius in an age rich with
genius. Galen's doctrines, grooved into the
collective conscious of medicine, were a tough
hurdle. To get around them, Harvey had to show us
more than a clear head and keen insight. He had to
give us all a lesson in dancing to our own drum.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds