6.2 Theories are regarded as uncertain—William Harvey overturned theories developed by the ancient Greek philosopher Galen on movement of blood in the body.
This NOS highlights the advancement of knowledge in biology (and the Natural Sciences) – new discoveries, led by advancing technology or new insights, leads to previous theories being overturned as we develop new understandings.
Galen of Pergamon was a scientist and philosopher in the second century AD and provided the first systematic explanation of the circulatory system.
The key points of this theory included (key parts in bold):
- Blood is created in the liver from ingested food
- Some of this is sent to the lungs via the right side of the heart
- Some blood crosses invisible pores from the right to the left side of the heart
- Air from the lungs mixes with blood in the left side of the heart
- Blood is used by the tissues; any that is not is dissipated away
Galen was highly educated for the time and an accomplished physician and based his conclusions on some experimental work and deductive logic. He was on the right track in some places – structural and blood differences between veins and arteries, the heart is myogenic, arteries contain blood (not air) – but was clearly wayward on many other key points.
His central premise – that blood is continually produced and consumed by the body – was to undermine faulty medical practices for over a thousand years in Europe.
Harvey, a 17th-century physician, identified that if blood were to be consumed, the liver would have to produce many times a person’s body weight in blood each day, something that did not seem possible. He also identified that veins and arteries were connected in a circuit, circulating the same blood between them.
Schematic of the cardiovascular system over time. (Aird, W. C.)
Harvey’s work was based on a range of experiments and observations, including applying ligatures to arms to compare the flow of blood through arteries and veins and to establish the role of valves and some live experimentation on the hearts and vessels of fish and snakes.
Schematic of Harvey’s experiments with ligatures (Aird, W.C)
Harvey’s work is often regarded as the basis of modern medicine, yet it was ridiculed in his own lifetime. In fact, he became a recluse after publishing his work, not wanting to attract any more attention to himself. This is often seen when long-standing dogma is threatened by new ideas.
AIRD, W. C. ‘Discovery Of The Cardiovascular System: From Galen To William Harvey’. Journal of Thrombosis and Haemostasis 9 (2011): 118-129. Web. 18 Nov. 2015.
Bbc.co.uk,. ‘BBC – GCSE Bitesize Science – Circulatory Systems And The Cardiac Cycle : Revision, Page 5’. N. p., 2015. Web. 18 Nov. 2015.
Busch, Georg Paul. Portrait of Galen. Photograph of original from The Lancet. Wikimedia Commons. Accessed March 15 2018.
Membercentral.aaas.org,. ‘The Circulatory System, From Galen To Harvey | AAAS Member-central’. N. p., 2015. Web. 18 Nov. 2015.
Mijtens, Daniël. Portrait of William Harvey. National Portrait Gallery, London. Photograph original, 2012. Wikimedia Commons. Accessed Mar 15 2018.