Claude Bernard

Father of Experimental Medicine · Physiologist · 1813–1878

The physiologist who showed that a body holds its own internal environment steady, and who set out how a controlled experiment in medicine must be done.

Who was Bernard?

Claude Bernard was born in 1813 at Saint-Julien in the Beaujolais, the son of a winegrower, and went to Paris intending to be a playwright. A critic read his tragedy, advised him to study medicine instead, and he took the advice. He became assistant to François Magendie at the Collège de France and never really left the laboratory. He showed that pancreatic juice digests fat; that the liver does not merely destroy sugar but manufactures and stores it, as a substance he named glycogen, releasing it into the blood — the first clear case of an organ secreting inwards rather than outwards; that a set of nerves controls the width of the blood vessels, and so the flow of blood and the warmth of a part; that curare paralyses precisely at the junction of nerve and muscle; and that carbon monoxide kills by taking oxygen's place in the blood. From this came the idea that outlasted all of it: that the fluid surrounding the tissues — the milieu intérieur — is held nearly constant, and that this constancy is what allows a complex animal to live independently of the weather outside it. His Introduction to the Study of Experimental Medicine of 1865 argued that medicine becomes a science only in the laboratory, and it is still read. The work rested on experiments upon living animals, which he defended in print and which his wife and daughters came to campaign against; she separated from him in 1870. He was given a public funeral in 1878, the first French scientist to be so honoured.

Major achievements

• Discovered the glycogenic function of the liver, and named glycogen
• Showed that pancreatic juice digests fats
• Identified the vasomotor nerves that widen and narrow blood vessels
• Established that curare acts at the junction of nerve and muscle
• Showed that carbon monoxide poisons by displacing oxygen in the blood

Life in brief

• 1813 — Born at Saint-Julien: In the Beaujolais, the son of a winegrower.
• 1834 — Turns from the theatre to medicine: A critic reads his tragedy and advises him to study something else.
• 1841 — Assistant to Magendie: At the Collège de France, where he learns the experimental method.
• 1848 — The liver makes sugar: Overturning the belief that animals only break substances down.
• 1852 — The vasomotor nerves: Showing that the flow of blood to a part is under nervous control.
• 1856 — Isolates glycogen: The store from which the liver releases glucose into the blood.
• 1865 — Introduction to the Study of Experimental Medicine: His account of how medicine becomes a science.
• 1878 — Dies in Paris: Given a public funeral — the first French scientist to receive one.

Explore the life of Bernard — five chapters

1. The Rejected Playwright — A winegrower's son told to find another profession
2. The Liver Makes Sugar — An organ that builds instead of destroying
3. Poisons as Instruments — Curare, carbon monoxide, and finding the exact point of action
4. The Internal Environment — The idea nobody wanted for fifty years
5. His Wife and Daughters Campaigned Against Him — Vivisection, a marriage ended, and a state funeral

Read the five-chapter life of Claude Bernard →

Where Bernard appears in your course

Claude Bernard has a genuine claim on 6 lessons of the Pearson Edexcel International GCSE science course built into Incandio:

• ADH and the Water Balance of the Blood — Biology: This lesson is one worked example of Bernard's central claim: that the fluid surrounding our cells is held nearly constant, and that an animal is free of its surroundings only because it carries its own conditions inside it. The water concentration of the blood is exactly the sort of thing he meant. He would also recognise the argument of the last question on this page — he spent his career showing that a function is proved by removing it and watching what fails.
• Homeostasis and the Control of Body Temperature — Biology: Bernard is the origin of this entire lesson. In the 1850s he argued that the fluid bathing our tissues — the milieu intérieur — is held nearly constant, and that this constancy is precisely what allows a complex animal to live independently of the weather outside it. He also found the mechanism this page describes: the vasomotor nerves that widen and narrow blood vessels, which is vasodilation and vasoconstriction by their older names. He never used the word homeostasis; Walter Cannon coined it in 1926, almost fifty years after Bernard died with the idea largely ignored.
• Synapses and the Reflex Arc — Biology: Bernard took an arrow poison and used it as an instrument. He showed that curare leaves the nerve able to carry its impulse and leaves the muscle able to contract when stimulated directly — yet the animal cannot move. The only place left for the poison to be acting is the junction between the two, which is exactly the interference this lesson's last question describes. It is one of the cleanest demonstrations in physiology that a thing can be located by finding out precisely what it is not.
• The Hormones — Sources, Roles and Effects — Biology: Insulin and adrenaline in this lesson do opposite things to one store of glycogen in the liver — and that store is Bernard's discovery. It had been assumed animals could only break down substances that plants had made; Bernard washed a liver until no sugar was left, waited, and found sugar in it again. The liver was manufacturing it. He named the stored form glycogen. Half a century before the word hormone existed, he had also described the liver secreting glucose inwards, into the blood, which is the idea the whole of this page depends on.
• The Menstrual Cycle — Biology: Progesterone inhibiting FSH so that no second egg matures is negative feedback, and Bernard is the origin of the idea that the body is a system holding itself in balance by exactly this kind of self-correction. He argued that an animal is free of its surroundings only because it maintains a constant internal environment, and he spent his career showing that a function can be identified by removing it and watching what fails — which is precisely how each hormone in this cycle was worked out.
• Burning Fuels — Chemistry: Statement 4.13 asks why carbon monoxide is poisonous, and the answer given on this page is Bernard's discovery. In the 1850s he showed that the poisoning is not damage to the lungs or to the tissues but a substitution in the blood itself: carbon monoxide takes the place oxygen would occupy and holds it, so the blood stays a bright red while the animal suffocates. That result is the reason the modern explanation is about haemoglobin rather than about the lungs, and Bernard is the right person to ask how you demonstrate a mechanism that is invisible from the outside.

Begin

• Start a conversation with Bernard — a dramatised, historically grounded AI portrayal
• Read the Historical Brief
• Explore the life of Bernard — five chapters
• Find your exam topics · Meet all 208 figures