4,000 years from Egypt's 'shepherd of the anus' to swallowable cameras, a gut surface the size of a small flat, and a drink of salt, sugar and water that has saved millions of children.
For most of history people knew food went in one end and waste came out the other, but not what happened in between. Ancient doctors thought food was cooked in the stomach and turned into blood by the liver. Slowly, by cutting, looking through lenses, swallowing things and taking X-rays, people found a long, folded tube that squeezes food along, breaks it down with juices, soaks it up through millions of tiny fingers and shares the job with trillions of bacteria. Knowing how the gut soaks up salt and sugar led to one of the simplest life-savers in medicine.
Egyptian doctors treat the bowels as blocked channels, and Galen teaches that food is cooked in the stomach and turned into blood by the liver. His ideas rule for well over a thousand years.
1550 BCE
c. 2200 BCE to c. 1550 BCE
Shepherds of the anus
Ancient Egyptian physiciansEgypt
Egypt had doctors who looked after the bowels, with a title that meant 'shepherd of the anus', recorded from around 2200 BCE. The Ebers Papyrus, from about 1550 BCE, lists remedies for constipation and other gut troubles. Egyptian doctors thought illness came from blocked channels inside the body, a bit like a blocked river, so they used laxatives and enemas to clear them.
Why it mattered. It is some of the oldest written evidence of people trying to understand and treat the gut.
Galen, a Greek doctor in the Roman Empire, taught that food is 'concocted', a kind of cooking, in the stomach into a juice called chyle. He said veins in the gut wall soak up the chyle and the portal vein carries it to the liver, which turns it into blood. His books were followed for well over a thousand years.
Why it mattered. He was right that the gut's blood goes straight to the liver, and his model shaped every later question about digestion.
Anatomists cut, look and draw for themselves. They find milky vessels for fat, folds, glands, patches and tiny pits in the gut wall, many still named after them.
1543
An anatomy book that looked for itself
Andreas VesaliusPadua, Italy (printed in Basel, Switzerland)
Vesalius, a young Flemish professor, dissected human bodies himself and published a huge illustrated book, De humani corporis fabrica. It showed the stomach, intestines and the rest of the body drawn from real dissections. Where Galen had described animals, Vesalius pointed out the differences in humans.
Why it mattered. It taught doctors to trust what they could see over what old books said.
Aselli opened a dog that had just eaten and saw white threads on its intestines that oozed a milky liquid. He named them lacteals, milky veins. His book about them came out in 1627, two years after he died, with some of the first anatomy pictures ever printed in colour.
Why it mattered. Lacteals are how the gut absorbs fat, and they were the first part of the lymph system to be found.
Kerckring, a Dutch doctor, described the ring-shaped folds that line the inside of the small intestine in his atlas, Spicilegium anatomicum. They are still sometimes called the valves of Kerckring. Today they are known as circular folds.
Why it mattered. The folds are the first of three layers of folding that give the gut a huge surface for soaking up food.
Peyer, a Swiss doctor, described clusters of little lumps in the wall of the small intestine. He thought they were glands. We now call them Peyer's patches and know they are part of the immune system.
Why it mattered. They are guard posts where the body checks what is passing through the gut.
Brunner, a Swiss anatomist, described glands in the wall of the duodenum, the first part of the small intestine, now called Brunner's glands. They make a slippery, alkaline mucus. A few years earlier, in 1683, he had removed a dog's pancreas and seen it become very thirsty, an early clue to diabetes.
Why it mattered. The mucus helps protect the gut from the acid that arrives from the stomach.
Lieberkühn, a German anatomist, filled blood vessels with coloured wax and studied the gut under the microscope. His book described the villi, tiny finger-like bumps, in great detail, and the small pits between them, now called the crypts of Lieberkühn. The crypts are where new gut lining cells are made.
Why it mattered. Villi and crypts are the heart of how the small intestine absorbs food and renews itself.
Scientists swallow bags of food, study a man with a hole in his stomach, and show that digestion is chemistry done by juices, with the pancreas as the great fat-breaker.
1780
1752 to 1783
Swallowing bags of food
René-Antoine Ferchault de Réaumur and Lazzaro SpallanzaniFrance and Pavia, Italy
In 1752 Réaumur got a pet kite, a bird, to swallow little tubes of food and cough them up half-digested. Spallanzani, an Italian priest and scientist, went further and swallowed linen bags and tubes of food himself, then looked at what was left. By 1783 he concluded digestion is chemical, done by juices, not just grinding.
Why it mattered. It turned digestion from guesswork into something you could test.
Wound 6 June 1822; experiments from 1825; book 1833
A window into a living stomach
William Beaumont and Alexis St. MartinMackinac Island, Michigan, USA
Alexis St. Martin, a French-Canadian fur trader, was shot in the stomach by accident, and the army surgeon William Beaumont saved him. The wound healed with a permanent hole into the stomach. Beaumont dangled food on strings through the hole and drew out digestive juice, and in 1833 published what he learned.
Why it mattered. It proved in a living person that digestion is done by chemical juices, and showed how food leaves the stomach for the intestine.
Bernard, a French physiologist, found in 1848 that pancreatic juice turns fat into a milky mix and splits it into smaller pieces. He showed that without this juice, fat is not digested. His famous memoir on the pancreas came out in 1856.
Why it mattered. It showed that the real work of digestion happens in the small intestine, helped by juice from the pancreas.
Gee, a London children's doctor, described children with pale, bulky stools, swollen bellies and poor growth in a paper called On the coeliac affection. He guessed that diet was the key to treating it. He did not yet know which food was to blame.
Why it mattered. It gave the disease a clear modern description, the starting point for finding its cause.
X-rays reveal the gut's waves of squeezing, the first hormone is found in the intestine, and doctors learn that gluten and too little fibre can make the gut sick.
1898
1896 to 1911
Watching the gut move by X-ray
Walter B. CannonHarvard Medical School, Boston, USA
Only months after X-rays were discovered, Cannon, a first-year medical student, fed animals food mixed with bismuth, which shows up on X-rays. He could watch waves of squeezing push food along the gut, and see that fear or distress could stop them. He summed up his work in The Mechanical Factors of Digestion in 1911.
Why it mattered. It was the first time people could watch peristalsis happening inside a living body.
William Bayliss and Ernest StarlingUniversity College London, England
Bayliss and Starling found that when something stretches the intestine, the muscle just behind it squeezes and the muscle just ahead of it relaxes. This pushes the contents forward. They called it the law of the intestine, and it works even when the gut's links to the brain are cut.
Why it mattered. It explained the reflex behind peristalsis and showed the gut has its own nervous system.
William Bayliss and Ernest StarlingUniversity College London, England
Bayliss and Starling showed that when acid from the stomach reaches the intestine, the gut lining releases a substance into the blood that makes the pancreas pour out its juice. They called it secretin. In 1905 Starling coined the word hormone for chemical messengers like this.
Why it mattered. Secretin is often called the first hormone, and it showed organs can talk to each other through the blood.
Willem-Karel DickeThe Hague and Utrecht, Netherlands
Dicke, a Dutch children's doctor, suspected wheat was harming children with coeliac disease. During the hunger winter of 1944 to 1945, when bread was scarce, some of his patients got better, and when bread returned they got worse, according to accounts of his work. In 1950 his thesis showed that removing wheat and some other grains cured the children.
Why it mattered. It gave the world the gluten-free diet.
Charlotte Anderson, Alastair Frazer and colleaguesBirmingham, England
Charlotte Anderson, an Australian doctor, worked with a Birmingham team measuring how well children with coeliac disease absorbed fat. They showed that gluten, a protein in wheat flour, was the part that did the harm. She later became the first woman professor of paediatrics in the UK.
Why it mattered. Pinning the blame on gluten explained why the damaged gut lining could not soak up food.
Joseph Szurszewski; Gaston Vantrappen and colleaguesMayo Clinic, USA, and Leuven, Belgium
Szurszewski found that between meals, a strong band of squeezing sweeps slowly down a fasting dog's small intestine, again and again. Eating stops it. In 1977 Vantrappen's team found the same pattern in people, and that it was missing in some patients with too many bacteria in the small intestine.
Why it mattered. This migrating motor complex acts as the gut's housekeeper, and may be part of why your tummy rumbles when you are hungry.
Denis BurkittLondon, England (after years in Uganda)
Burkitt, a surgeon who had worked for years in Uganda, noticed that bowel cancer and other bowel diseases were rare in rural Africa. He gathered reports from well over a thousand rural hospitals in Africa and India. In 1971 he suggested that fibre-rich food, which makes bigger, faster-moving stools, might protect the bowel.
Why it mattered. It started decades of research into how fibre and gut health are linked.
From yogurt bacteria to genome sequencing, people discover that the gut is home to trillions of microbes, and new tools measure and film the gut as never before.
1907
1905 to 1907
Good bacteria in yogurt
Élie Metchnikoff and Stamen GrigorovParis, France and Geneva, Switzerland
In 1905 Stamen Grigorov, a young Bulgarian doctor in Geneva, found the rod-shaped bacterium that turns milk into yogurt. Metchnikoff, a Russian-born scientist at the Pasteur Institute, argued in his 1907 book The Prolongation of Life that such bacteria could crowd out harmful gut microbes. He won a Nobel Prize in 1908, for his separate work on immunity.
Why it mattered. It was the start of the idea that some gut bacteria are good for us.
Gavriel Iddan, Paul Swain and Given ImagingYokneam, Israel, and London, England
Engineers at the Israeli company Given Imaging, working with doctors including Paul Swain in London, built a camera the size of a large pill. It takes photos as the gut squeezes it along and sends them by radio to a recorder. Their paper appeared in Nature in 2000, and the US cleared it for use in 2001.
Why it mattered. For the first time doctors could see the whole small intestine without surgery.
Human Microbiome Project Consortium, NIHAbout 80 institutions, mainly in the USA
The US National Institutes of Health launched the Human Microbiome Project in 2007. Scientists sampled 242 healthy adults at many body sites and read the genes of the microbes they found. In 2012 they published a map of the normal microbes of healthy people, with the gut among the richest places.
Why it mattered. It turned the gut's bacteria from a curiosity into a major field of science.
Herbert Helander and Lars FändriksUniversity of Gothenburg, Sweden
Textbooks often said the inside of the gut had the area of a tennis court, about 260 to 300 square metres. Helander and Fändriks measured it carefully under the microscope and got about 30 to 40 square metres, about 32 on average. Almost all of it is in the small intestine.
Why it mattered. It fixed a famous wrong number, though the gut's folds, villi and microvilli still make its surface huge.
Ron Sender, Shai Fuchs and Ron MiloWeizmann Institute of Science, Rehovot, Israel
For decades people said bacteria outnumber our own cells ten to one, a rough guess that goes back to a 1972 estimate. Sender, Fuchs and Milo worked it out again and found about 38 trillion bacteria and 30 trillion human cells in a typical adult. Most of the bacteria live in the large intestine.
Why it mattered. It showed we are roughly half microbe by cell count, not ninety percent.
Knowing how the gut pulls in sodium and glucose together leads to oral rehydration salts, first proved in Bangladesh and India, and then used to save millions of children worldwide.
1960
August 1960
Sodium and sugar travel together
Robert K. CranePrague, Czechoslovakia (worked in St. Louis, USA)
At a meeting in Prague, the American biochemist Robert Crane proposed that gut lining cells pull in glucose and sodium together, through the same doorway. The sodium carries the sugar in with it. Many experts doubted him at first, but he was right.
Why it mattered. It is the reason a drink of salt and sugar can rehydrate a person even when diarrhoea is pouring water out.
David Nalin, Richard Cash, Norbert Hirschhorn, Nathaniel Pierce, Rafiqul Islam, A. Majid Molla and othersDhaka, then East Pakistan, and Calcutta (Kolkata), India
Cholera can drain a person of litres of water a day, and the treatment was a drip into a vein. Teams at the Cholera Research Laboratory in Dhaka and the Johns Hopkins centre in Calcutta tested drinks of glucose and salt. In 1968 Nalin and Cash showed that such a drink cut the need for drip fluid by about 80 percent.
Why it mattered. It proved the gut can keep absorbing water during cholera if you give it sugar and salt together.
During the Bangladesh Liberation War, millions fled to India and cholera broke out in the camps. With drips running out, the Kolkata doctor Dilip Mahalanabis and his team gave packets of salt, sugar and baking soda to mix with water, handed out even by people with no medical training. Among about 3,700 patients treated, 3.6 percent died, compared with around 30 percent before.
Why it mattered. It proved oral rehydration works in a real disaster, not just in a hospital.
The most important medical advance of the century?
The Lancet; World Health OrganizationLondon, England, and Geneva, Switzerland
In 1978 the medical journal The Lancet wrote that the discovery that glucose helps the gut absorb sodium and water was potentially the most important medical advance of the century. The same year, WHO started its programme to control diarrhoeal diseases. It spread oral rehydration salts around the world with UNICEF.
Why it mattered. It turned a lab discovery into a worldwide life-saving campaign.
World Health Organization and UNICEFGeneva, Switzerland, and New York, USA
In 2002 WHO released a new oral rehydration formula with less salt and sugar, which the gut absorbs even better. In 2004 WHO and UNICEF advised giving it together with zinc tablets for 10 to 14 days. Zinc shortens bouts of diarrhoea and makes them milder.
Why it mattered. These small changes mean fewer children need a drip or a hospital bed.
Rita Colwell and colleagues at icddr,bMatlab, Bangladesh
Rita Colwell, an American microbiologist, knew cholera bacteria cling to tiny water animals. Her team showed village women how to pour pond and river water through an old sari folded several times. In the villages that filtered their water, cholera cases fell by about half.
Why it mattered. Stopping germs before they reach the gut is as important as treating them after.
Children under 5 dying from diarrhoea each year, worldwide, as estimated at the time
Estimates published by WHO and its researchers: deaths fell sharply as oral rehydration spread. Early figures were rough, and the 1980 number rests mostly on surveys from the 1960s and 1970s.
1980 Snyder & Merson, WHO Bulletin (1982), as cited by Victora et al. (2000): 4.6 million
1999 Victora et al., WHO Bulletin (2000): about 1.5 million
2019 WHO fact sheet on diarrhoeal disease: about 444,000 a year (recent estimate)
By the numbers
The same deaths, re-estimated later with modern methods
Black et al. (Journal of Global Health, 2019) rebuilt the trend with newer data. They put 1980 lower than the old 4.6 million, but still show a fall of about 80 percent by 2015.
1980 Black et al. (2019): 2.7 million (range 2.2 to 3.1 million)
1990 Black et al. (2019): 2.0 million
2015 Black et al. (2019): 0.5 million (range 0.4 to 0.7 million)
Did you know?
The inside of your gut covers about 32 square metres, roughly the floor of a small studio flat, not the tennis court that old textbooks claimed.
A typical adult carries about 38 trillion bacteria and about 30 trillion human cells, so the famous 'ten bacteria for every human cell' was wrong.
Lazzaro Spallanzani swallowed linen bags full of food and then searched for them afterwards to see what his gut had done.
Alexis St. Martin lived for decades with a hole in his stomach and outlived William Beaumont, the doctor who studied him.
In the 1971 refugee camps, packets of salt, sugar and baking soda cut cholera deaths from about 30 in every 100 patients to under 4.
The people
Who figured it out
GP
Galen of Pergamon
129 – c. 216 · Physician · Pergamon (now Turkey), worked in Rome
Taught that food is cooked in the stomach and turned into blood by the liver, an idea trusted for over a thousand years.
GA
Gaspare Aselli
1581 – 1625 · Anatomist · Cremona, Italy
Discovered the milky lacteals that carry absorbed fat away from the gut.
CB
Claude Bernard
1813 – 1878 · Physiologist · France
Showed that pancreatic juice breaks down fat in the small intestine.
ES
Ernest Starling
1866 – 1927 · Physiologist · England
With William Bayliss found the law of the intestine and secretin, and coined the word hormone.
M
Élie Metchnikoff
1845 – 1916 · Zoologist and immunologist · Russian Empire (now Ukraine), worked in Paris
Nobel Prize winner who popularised the idea that some gut bacteria, like those in yogurt, are good for us.
SG
Stamen Grigorov
1878 – 1945 · Physician and microbiologist · Bulgaria
Found the bacterium that makes yogurt, later named Lactobacillus bulgaricus.
CA
Charlotte Anderson
1915 – 2002 · Paediatrician and gut scientist · Melbourne, Australia
Helped show gluten is the harmful part of wheat in coeliac disease, and became the UK's first woman professor of paediatrics.
RK
Robert K. Crane
1919 – 2010 · Biochemist · United States
Discovered that the gut pulls in sodium and glucose together, the science behind oral rehydration.
DM
Dilip Mahalanabis
1934 – 2022 · Paediatrician · West Bengal, India
Proved oral rehydration salts could save lives on a huge scale in the 1971 refugee camps.
RC
Rita Colwell
born 1934 · Microbiologist · United States
Showed that filtering water through folded sari cloth cut cholera in Bangladeshi villages by about half.