William Harvey & the Great Plague 1665
William Harvey and Blood Circulation
William Harvey (1578–1657) was an English physician who made one of the most important discoveries in the history of medicine: that blood circulates around the body in a one-way system, pumped by the heart. Before Harvey, physicians followed Galen’s teaching that the liver constantly produced new blood, which the body then “used up.” Galen believed blood passed from one side of the heart to the other through invisible holes in the septum — holes that did not exist.
Harvey proved that blood travels in a one-way circulation system, pumped by the heart through arteries and returning through veins. This disproved Galen’s 1,400-year-old theory that the liver constantly made new blood.
How Did Harvey Prove His Theory?
Harvey used the scientific method — observation, experiment, and measurement. He dissected human and animal hearts, observing that the valves in veins only allowed blood to flow in one direction. He calculated the volume of blood pumped by the heart in an hour and showed it was far too much for the liver to produce constantly — proving that the same blood must circulate repeatedly.
Harvey also performed a famous experiment by tying a ligature around a patient’s arm. When the ligature was tightened, veins below it swelled (showing blood could not return to the heart), while veins above it emptied (showing blood had already passed through). This proved blood flowed in one direction through the veins.
Harvey published his findings in 1628 in a book called De Motu Cordis (“On the Motion of the Heart”). However, many physicians rejected his ideas. Some lost patients because people thought a doctor who disagreed with Galen must be unreliable. Others pointed out that Harvey could not explain how blood passed from arteries to veins — he could not see capillaries because microscopes were not yet powerful enough. Capillaries were finally observed by Marcello Malpighi in 1661, confirming Harvey’s theory.
The Significance of Harvey’s Discovery
Harvey’s work was significant in several ways. He disproved Galen, further undermining the authority of ancient texts. He demonstrated the power of the scientific method — observation and experiment could reveal truths that reading books could not. His discovery eventually led to major advances in surgery, blood transfusions, and understanding how medicines travel through the body.
However, Harvey’s discovery did not immediately improve treatments. Knowing that blood circulated did not explain what caused disease. Physicians continued to use bloodletting for another 200 years — ironically, Harvey’s work was sometimes used to justify the practice by arguing it helped remove “bad” blood from the system faster.
Harvey’s discovery was a landmark in medical knowledge but did not immediately improve treatments. Bloodletting continued for another 200 years. His real significance was proving the value of the scientific method over ancient authority.
The Great Plague of London, 1665
In 1665, the Great Plague struck London, killing approximately 100,000 people — roughly one-quarter of London’s population. It was the worst outbreak of plague in England since the Black Death over 300 years earlier, and it exposed how little medical progress had been made in preventing and treating epidemic disease.
Treatment During the Great Plague
Treatments in 1665 were remarkably similar to those used during the Black Death in 1348. Physicians still recommended bloodletting, purging, and herbal remedies. Posies of flowers were carried to ward off miasma. Plague doctors wore beak-shaped masks stuffed with sweet-smelling herbs, believing this would filter the bad air. Some quack remedies included swallowing mercury, placing a live chicken against buboes, or drinking “plague water” made from herbs and spices. Prayer remained a common response.
The government took stronger action than during the Black Death, showing some progress in public health thinking. Quarantine was enforced: infected houses were sealed shut for 40 days, with a red cross painted on the door and the words “Lord have mercy upon us.” Watchmen were posted to prevent anyone leaving. Plague orders required the killing of dogs and cats (ironically, this may have worsened the outbreak by removing the animals that killed plague-carrying rats). Bodies were collected by “dead carts” at night and buried in plague pits. Large gatherings were banned, and some people fled London for the countryside.
Comparing the Great Plague with the Black Death
Comparing the two outbreaks reveals both continuity and change in English medicine over 300 years:
Same Wrong Ideas
Both outbreaks were blamed on miasma, God’s punishment, and the humours. The actual cause (bacteria carried by fleas on rats) remained unknown until 1894.
Same Treatments
Bloodletting, purging, posies, and prayer were used in both 1348 and 1665. No effective cure existed for either outbreak.
Stronger Government Action
In 1665, the government enforced quarantine with watchmen, issued plague orders, and organised burial in plague pits — more systematic than medieval responses.
Declining Supernatural Beliefs
By 1665, educated people relied less on purely religious explanations. Flagellants did not appear. However, prayer was still common and many people still saw plague as God’s punishment.
Comparing the Great Plague (1665) with the Black Death (1348) shows strong continuity in wrong disease explanations and ineffective treatments, but some change in stronger government intervention and a slight decline in supernatural beliefs.