The_Invention_of_Surgery

toward your hand. The blood simply can’t go “backward” in the limb
because of the valves inside the vein. Releasing the tourniquet allows the
blood to continue its path to the heart.)
Harvey was on the verge of his great synthesis. Contemplating the vast
quantity of blood pulsating across the heart, considering the “vivification”
of the blood in the lungs and the transmission of the scarlet blood to the
body’s tissues via the arteries, combined with this new insight of the one-
way passage of blood from the limbs back to heart, Harvey had his eureka
moment. He later wrote, “... and when I had a long time considered with
my self ... I perceived ... the blood did pass through the arteries to the
veins, and so return into the right ventricle of the heart.”
Harvey finally had it. The blood was forcefully expelled out of the
powerful left side of the heart, pulsated through the aorta and arteries into
the entire body, and through some mysterious exchange, the same blood
itself was conveyed into the venous system to return to the heart, where it
would be pushed into the lungs for aeration. It was, therefore, a closed
system. His investigations were performed before the development of the
compound microscope, and his naked eye could not see the microscopic
branching of the ever-smaller arteries that exist in every organ of the body
in what is called the “capillary bed.”
Harvey, at the summit, recalled, “And so, I began to bethink my self if
the blood might not have a circular motion [emphasis mine]...”
Hippocrates, Aristotle, Galen, and all our ancestors were blinded to the
truth of the function of our heart. Harvey, the man who knew Galileo in
Padua, had declared that our blood orbited in our bodies through a double-
circuit, one to the body and the other to the lungs. Instead of blood simply
pouring into end-organs, it stayed within vessels as it passed through the
organs and muscles, and the new instruments of microscopy would unveil
this secret shortly after Harvey’s death. In a word, circulation embodies
Harvey’s great revelation.
Marcello Malpighi (1628–1694) was an Italian scientist who first
described the microscopic vessels that serve as the connection between
tiny arteries and minuscule veins. His first breakthrough came when he
was examining still pulsating blood in the lung of a frog, and with the aid
of a simple magnifying glass, saw the tangle of tissue that he perceived
was the intermediary tissue between arteries and veins. The circulatory
pathway had finally been visualized, and Malpighi called them capillaries.