Harvey's De Motu Cordis

Harvey's case began with a sum. He calculated how much blood passes through a ventricle of the heart in an hour and found it came to more than three times the weight of a man. Food could not supply that much blood, and the body could not use it up. The same blood, he concluded, must pass through the heart again and again.

Physicians had followed Galen on this since about AD 150. In Galen's scheme the liver turned digested food into venous blood, which ebbed and flowed in the veins and nourished the body, while the heart made a separate arterial blood charged with vital spirits. Nothing in it moved in a circle.

William Harvey was born in Folkestone in 1578, studied at Gonville and Caius College, Cambridge, and took his MD at Padua in 1602 under Fabricius, who described the valves of the veins in a book of 1603. He was elected physician to St Bartholomew's Hospital in 1609 and Lumleian lecturer at the College of Physicians in 1615. His lecture notes from 1616 already state that blood passes through the lungs into the aorta, crosses from the arteries to the veins, and moves perpetually in a circle driven by the heartbeat.

The book did not appear until 1628, badly printed on thin paper by William Fitzer, an obscure printer in Frankfurt. Harvey argued from observation that the heart is a muscle whose contraction is its active phase, and from experiment: a tourniquet on an artery swelled the vessels on the heart side, while one on a vein swelled them on the far side. Plates based on Fabricius's book on the venous valves showed a simple ligature experiment proving that veins and arteries must connect.

Only a few writers of the time challenged the doctrine. Jean Riolan, dean of the Paris medical faculty, was the only critic Harvey answered in writing, and a 1647 Leiden edition set Harvey's text paragraph by paragraph against the refutations of Parisanus. One link was still missing. Harvey supposed that small vessels joined arteries to veins but never saw them, and apparently never used a microscope; Marcello Malpighi found the capillaries of the lung in 1661, four years after Harvey died.