The history
From Galen's one-way blood to blood banks, cuffs and clot science: 1,800 years of finding the loop.
For well over a thousand years, doctors believed blood was made in the liver and used up by the body. It took a Cairo physician, an English doctor with a stopwatch mind and an Italian with a microscope to show it goes round in a loop. Then people learned to measure its pressure, explain what leaks out at the capillaries, and share blood safely between strangers.
c. 1242
Correct description of the lung loop
Ibn al-Nafis, Egypt
1628
Circulation of the blood proved
William Harvey, England
1661
Capillaries seen
Marcello Malpighi, Italy
c. 1710, published 1733
Blood pressure measured
Stephen Hales, England
1818
Human-to-human transfusion
James Blundell, England
1901
ABO blood groups
Karl Landsteiner, Austria
1942
Blood bank in India
Kolkata
150 – 1300
Galen's liver-made blood rules for centuries, until Ibn al-Nafis sends it through the lungs.
170
2nd century CE
Galen, a Greek doctor in the Roman Empire, taught that the liver makes blood from food and the veins carry it out to be used up. He thought blood seeped from the right side of the heart to the left through tiny invisible pores. His books were followed for well over a thousand years.
Why it mattered. It was a one-way model, not a loop, and it took centuries to overturn.
1242
c. 1242 (usual dating)
In a commentary on Avicenna's Canon, the Damascus-born doctor Ibn al-Nafis said there are no pores in the heart's middle wall. Blood from the right side must travel through the lungs, mix with air, and return to the left side. Europe only learned of his work in the 20th century.
Why it mattered. It is the first known correct description of the pulmonary loop.
1500 – 1700
The lung loop, Harvey's circulation, the lymphatics, capillaries and red cells.
1553
Servetus, a Spanish doctor and theologian, described blood passing through the lungs inside a book about religion. His ideas were judged heresy, and he and nearly every copy of the book were burned in Geneva in 1553. Only a few copies survived.
Why it mattered. The lung loop was found again in Europe, and almost lost again.
1628
Harvey published De Motu Cordis, On the Motion of the Heart and Blood. With experiments and simple sums he showed the heart pumps far more blood in an hour than the body could make from food. So the same blood must go out in the arteries and come back in the veins, in a circle.
Why it mattered. It is the moment circulation was born.
1653
1651–1653
Pecquet found the thoracic duct emptying into the veins in 1651. The young Swede Rudbeck showed lymph vessels all over the body in 1652, and the Dane Bartholin published first, in 1653, and named them lymphatics. A famous quarrel over who came first followed.
Why it mattered. It showed that fluid leaking from the blood has its own way back.
1661
Harvey could not see how blood got from arteries to veins. Malpighi looked at a frog's thin lung through an early microscope and saw tiny vessels joining the two. He described them in De pulmonibus in 1661.
Why it mattered. It closed the last gap in Harvey's circle.
1674
Using his own tiny, powerful lenses, the Delft cloth merchant van Leeuwenhoek described his blood as small round globules floating in a clear liquid, and later measured them. Jan Swammerdam had probably seen red cells in frog blood earlier, but his notes were only printed decades after his death.
Why it mattered. Blood turned out to be a liquid full of cells, not a simple fluid.
1700 – 1910
Pressure in a horse, the fourth-power law, platelets, Starling forces and the cuff.
1733
Experiment c. 1710; published 1733
Hales, a vicar and scientist, tied a glass tube about 9 feet long into an artery of a mare. The blood rose about 8 feet 3 inches up the tube and bobbed with every heartbeat. He described it in his book Haemastaticks in 1733.
Why it mattered. It was the first measurement of blood pressure.
1770
Hewson, a surgeon and anatomist, showed the Royal Society that blood clots because of a substance in its liquid part, not because the cells stick together. He also studied the lymph vessels and the shape of red cells.
Why it mattered. He found the idea behind fibrin, and is often called the father of haematology.
1840
1840–1846
Poiseuille, a doctor who had already measured blood pressure with a mercury gauge, timed water flowing through fine glass tubes. He found the flow depends on the radius to the fourth power: halve the width and only a sixteenth gets through. Gotthilf Hagen found the same rule in Germany in 1839.
Why it mattered. It explains why tiny arterioles control where your blood goes.
1882
Bizzozero showed that tiny discs in blood, which others thought were broken cells or even germs, are a separate part of blood. In living animals they were the first to stick to a damaged vessel wall and they started clots.
Why it mattered. Platelets are the first responders to every cut.
1896
Starling showed that blood pressure pushes fluid out of capillaries while the proteins in plasma pull it back by osmosis. The balance of these Starling forces decides whether tissues stay just moist or swell.
Why it mattered. It explains swelling (oedema) and why the lymph is needed.
1896
Riva-Rocci wrapped an inflatable cuff around the upper arm and read the pressure on a column of mercury. When the pulse at the wrist vanished, the cuff pressure matched the top blood pressure.
Why it mattered. Blood pressure could now be measured safely on anyone, without cutting an artery.
1905
8 November 1905
Korotkoff, a young army surgeon, put a stethoscope below a pressure cuff and let the air out slowly. Tapping sounds started and then stopped, marking the top and bottom blood pressure. His report was less than a page long.
Why it mattered. The 120 over 80 you get at a clinic still comes from his method.
1925 – 1965
Angiograms, catheters, baroreceptors and the clotting cascade.
1927
28 June 1927
After several failed attempts, Moniz injected a dye that shows up on X-rays into the carotid artery of a patient and took pictures of the brain's vessels. Leg arteries had been imaged a few years earlier, but this was the first cerebral angiogram.
Why it mattered. Angiography let doctors see blocked or burst vessels without surgery.
1929
Forssmann, a junior doctor, slid a thin tube into a vein in his own arm and pushed it up into his heart, then walked to the X-ray room to photograph it. His bosses thought it a stunt. In 1956 he shared a Nobel Prize for it.
Why it mattered. It began cardiac catheterisation, now used to find and open blocked arteries.
1938
1938 (prize presented in 1939)
Heymans, building on Heinrich Hering's work, showed with dogs that sensors in the carotid artery and aorta detect blood pressure and blood chemistry and adjust breathing and circulation through reflexes. His Nobel Prize citation names breathing.
Why it mattered. These baroreceptors are why you do not faint every time you stand up.
1953
Seldinger put a needle into an artery, slid a thin wire through it, took the needle out and slipped a flexible tube over the wire. His short paper made reaching any big vessel safe and simple.
Why it mattered. Almost every angiogram, stent and heart catheter still starts this way.
1964
Within weeks of each other, two teams proposed that clotting proteins work in a chain: each switched-on factor switches on many copies of the next, like a waterfall that grows as it falls. The chain ends with thrombin turning fibrinogen into fibrin.
Why it mattered. It explained how a tiny wound makes a big clot fast, and what goes wrong in haemophilia.
1975 – 2025
Voluntary donation, a court ruling, online blood banks and counting hypertension.
1975
1 October 1975
India first marked National Voluntary Blood Donation Day on 1 October 1975, the birthday of the society's founder, Dr J. G. Jolly. It is still held every year to encourage unpaid donors.
Why it mattered. Voluntary, unpaid donors give the safest blood.
1996
4 January 1996
In the case Common Cause v. Union of India, the Supreme Court ordered an end to professional (paid) blood donation, licensing of blood banks, and a National Blood Transfusion Council. The ban on paid donors took effect on 1 January 1998, and a National Blood Policy followed in 2002.
Why it mattered. It pushed India towards safer, voluntary donation.
2016
7 April 2016
India launched e-RaktKosh on World Health Day, an online system that links blood centres so people can see where blood of each group is available. By 2024 India was collecting about 1.46 crore (14.6 million) units a year.
Why it mattered. It helps blood reach patients faster and wastes less.
2023
19 September 2023
The WHO's first report on high blood pressure found it affects about 1 in 3 adults, double the number of 1990, and that nearly half do not know. In India, the NFHS-5 survey (2019–21) had found raised blood pressure in about 1 in 4 adults.
Why it mattered. Measuring blood pressure is cheap, and treating it prevents many heart attacks and strokes.
By the numbers
NCD-RisC (Lancet, 2021): the number doubled in 30 years, mostly because there are more and older people; the share of adults stayed at about a third.
Did you know?
At rest, a drop of blood takes about a minute to go all the way round your body, and spends most of that time in the veins.
Your capillaries together are about 1,000 times wider than your aorta, so blood slows from about 33 cm a second to about 0.3 mm a second.
The famous claim of 100,000 km of blood vessels comes from a rough 1922 estimate; newer estimates for the capillaries are about 9,000 to 19,000 km.
Your bone marrow makes about 2 to 3 million red blood cells every second.
Stephen Hales's horse pushed its blood about 2.5 metres up a glass tube.
The people
1213 – 1288 · Physician · Damascus, worked in Cairo
Described blood passing through the lungs about 400 years before Europe accepted it.
1578 – 1657 · Physician · England
Proved with experiments and arithmetic that blood circulates.
1628 – 1694 · Anatomist · Italy
Saw the capillaries that join arteries to veins.
1866 – 1927 · Physiologist · England
Explained the push and pull of fluid at the capillaries.
1868 – 1943 · Pathologist · Austria
Discovered blood groups, making transfusion safe.
1899 – 1993 · Haematologist · England
Set up blood depots for London before the Second World War.
1904 – 1950 · Surgeon · USA
Turned plasma storage into mass production and led the first Red Cross blood bank.
Where it happened
Sources
Dates marked “c.” are approximate, and historians sometimes disagree about who was first. If you spot a mistake, tell us.
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