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Homeostasis turns up in almost every human physiology chapter: blood sugar, body temperature, water balance. The idea behind it came from one French physiologist, Claude Bernard, who also left a clear account of how he reasoned from experiments. This post covers what he found, the exact words of his most famous idea, and how it maps onto your NCERT chapters.
Who was Claude Bernard?
The Académie française records that Bernard was born at Saint-Julien, near Lyon, on 12 July 1813 and died on 10 February 1878. He became professor of experimental physiology at the Collège de France in 1855, a member of the Academy of Sciences in 1854, and was elected to the Académie française in 1868. Charles Gross, writing in The Neuroscientist (1998), calls him the founder of modern experimental physiology.
How did Bernard discover that the liver makes sugar?
In An Introduction to the Study of Experimental Medicine (1865, English translation by H. C. Greene), Bernard explains his starting point. The accepted theory said animals get sugar only from food and burn it in the body. He set out to find the organ that destroys sugar.
Instead he found sugar in the blood of animals on diets with no starch or sugar, and traced it to the liver. He wrote that he "abandoned my hypothesis on the spot" to follow the unexpected result, and stated the rule he lived by:
"When we meet a fact which contradicts a prevailing theory, we must accept the fact and abandon the theory, even when the theory is supported by great names and generally accepted."
He called this power of animals to produce sugar "animal glycogenesis". Today NCERT Class 11 Biology, Chapter 19 tells the same story in hormone language: glucagon acts on liver cells to break down glycogen and raise blood sugar, insulin promotes conversion of glucose to glycogen, and the two together maintain glucose homeostasis.
What did he learn from curare?
The same book describes his experiments with curare, an arrow poison. He injected it into a frog, opened the animal at once and tested each tissue. The heart still beat and the muscles still contracted when stimulated directly, but stimulating the motor nerves no longer made the muscles contract. He concluded that curare kills by knocking out motor nerves, without affecting sensory nerves.
How a nerve passes its signal to the organ it controls was worked out decades later. One key step was Otto Loewi's experiment showing that a chemical carries the signal, told in our post on the frog heart experiment.
What exactly did Bernard say about the internal environment?
The phrase comes from his *Leçons sur les phénomènes de la vie communs aux animaux et aux végétaux* (1878). On page 113 of volume 1 (scanned copy on the Internet Archive) he describes the plasma, the liquid part of the blood that bathes the tissues, as the "milieu liquide intérieur" in which the body's cells live. Then he writes:
"La fixité du milieu intérieur est la condition de la vie libre, indépendante."
In English: the fixity of the internal environment is the condition of free, independent life. He adds that this fixity requires an organism so refined that outside changes are "at every instant compensated and balanced".
Notice what he did not say. He did not claim the body ignores the outside world. He said the opposite: an advanced animal is in close relation with its surroundings, and its balance comes from continuous compensation.
How did the idea become "homeostasis"?
Gross notes that the idea had little impact in Bernard's lifetime. In 1929 the American physiologist Walter Cannon published Organization for physiological homeostasis, and as Modell and colleagues (2015) explain, Cannon introduced the word "homeostasis" and made Bernard's abstract notion concrete. They also point out that students are often confused by inconsistent vocabulary and argue for one simple model applied to every homeostatic mechanism.
How do you use the idea in an exam answer?
Take any regulated quantity and answer four questions:
What is held steady? Blood glucose.
What responds first? The islets of Langerhans in the pancreas.
What signal do they send? Insulin from β-cells when glucose rises; glucagon from α-cells when it falls.
What effect reverses the change? The liver stores glucose as glycogen, or releases it.
Common mistakes: saying homeostasis keeps values "constant" (they vary within a range), and mixing up glycogen (the stored polymer), glucagon (the hormone) and glycogenesis (making glycogen). Our posts on hormone feedback loops and chemical coordination give more worked cases.
What can a student take from Bernard's way of working?
Test each part. His curare autopsy checked heart, muscle and nerve one at a time.
Write down your hypothesis, then be ready to drop it.
Think in systems. The internal environment idea links blood, kidneys, liver and hormones into one question: what keeps this steady?
If you are unsure where to start revising human physiology, Fermi's AI tutor can work out what you already know and build a plan for the session, so you sit down to a clear next step.
Next step: pick body temperature and answer the four questions above in your own words, in under five lines.
