Heritage Centre : William Harvey

Harvey’s Discovery

a. anatomical table – arteries the space in the brain and the testes show Harvey’s theory of the circulation of the blood. Because he could not see capillaries, he saw these spaces as areas of ‘free exchange’ where the blood could move from the arteries to the veins..

b. Illustration of circulation from Vesalius The circulation of the blood as shown in Vesalius’ De Humani Corporis Fabrica, 1543.

‘Coepi egomet mecum cogitane…’

‘I began to think there might be movement, in a circle…’

In 1628 William Harvey published his description of the circulation of the blood. For some years he had experimented on live animals and dissected the bodies of executed criminals. Through observation and careful reasoning Harvey was able to prove that the heart acted as a pump forcing blood around the body through arteries. Veins returned the blood to the heart where it was recycled. Harvey realised that the valves in the veins prevented blood from travelling back the wrong way to the heart.

‘The animal’s heart is the bases of its life, its chief member, the sun of its microcosm: on the heart all activity depends. From the heart all its liveliness and strength arise’.

Harvey did not believe that the body was a machine, but he was able to use machinery to help him explain it. He answered two simple questions:

• What happens when our heart beats?
• How does blood move around our body?

In Harvey’s day the body was believed to function in the way described by the Roman philosopher Galen:

There were two types of blood, venous and arterial, each with distinct pathways and functions relating to the three chief body centres of the liver (nutrition and growth), heart (vitality) and the brain (sensation and reason). Nourishment and growth came from venous blood originating in the liver, while vitality was carried to all parts of the body by the arterial blood originating in the heart. Arterial blood contained pneuma (spirituous air) and blood, and was spread around only as needed. Therefore it did not return to the heart as it was all used up. It moved in a tide-like ebb and flow movement. The heart was active when blood entered it (diastole) and the arteries pulsed driving the blood around the body. The venous blood travelled though hidden holes in the septum (fleshy wall separating the heart ventricles). The pulmonary vein carried air from the lungs to the left of the heart. Sooty vapours were a by-product travelling back the same way and then being exhaled.

Through observation Harvey was able to show that the main action of the heart is that of pumping out blood (systole), rather that drawing it in (diastole). The left side pumps blood around the body and the right side pumps blood into the lungs. He also measured the volume of blood leaving the heart in a given time. Far too much blood was pumped out for the body to use it up and replace it. He examined the septum of the heart (fleshy wall separating the heart ventricles (chambers)) and showed that it contained no holes.

Harvey was questioning the fundamentals of Galenic belief, that the liver was not a blood-making organ. Partly because of the strong belief in Galen’s writings, Harvey’s discovery had very little effect on the practice of medicine at the time. People then did not realise that this new discovery was progress.

However, there were still several questions that Harvey was unable to answer. What makes the heart beat? How does the blood flow from the arteries to the veins? What life-giving force does the blood carry? These are all questions that we can answer today.

Marcello Malphigi (1628-1684) completed Harvey’s circle. By using stronger microscopes he saw the capillaries (tiny blood vessels), which connect the veins with the arteries.

Harvey’s discovery is now seen as the foundation of all modern research on the heart. We can appreciate this when the doctor checks our blood flow by taking our pulse. Also his calculation of cardiac output signposted the way to present-day measurements of blood and fluid loss during operations.

Harvey’s use of scientific experiment has been said to lead the way to all future scientific discovery. His method of careful experiment and measurement had solved one important problem. Perhaps it could be used to solve others?

In 1962 Max Perutz was awarded the Nobel Prize for his work in discovering a protein called ‘haemoglobin’ – the oxygen carrier in the blood. Of course oxygen was not discovered for another 130 years after Harvey made his discovery.

 

 

 

This page last updated on May 16, 2005