Claude Bernard was born on July 12, 1813, in the village of Saint-Julien, in France’s Beaujolais region. Bernard is known for his discoveries concerning the role of the pancreas in digestion, the glycogenic function of the liver, and the regulation of the blood supply by the vasomotor nerves.
On a broader stage, Bernard played a role in establishing the principles of experimentation in the life sciences, advancing beyond the vitalism and indeterminism of earlier physiologists to become one of the founders of Experimental Medicine.
Most importantly, Bernard introduced the concept of the milieu intérieur to describe the principle of dynamic internal physiological equilibrium to sustain the organism in an external environment typified by variability. This is the underlying principle of what would later be called homeostasis.
Bernard’s parents, Pierre François Bernard and Jeanne Saulnier, were vineyard workers who lived in very modest circumstances. All his life, he remained attached to the place of his birth, the hamlet of Chatenay on the outskirts of the village of Saint-Julien. Every fall he returned home to relax and to help with the grape harvest.
In fact, his entire life revolved around two locales: the laboratories of Paris and the vineyards of Beaujolais.
“For a man of science, there is no separate science of medicine or physiology, there is only a science of life.”
– Claude Bernard
Although he received his M.D. in Paris in 1843, Bernard never practiced medicine and always harbored ambivalent feelings about physicians.
Bernard’s doctoral thesis, Du suc gastrique et de son rôle dans la nutrition (1843), was a work both useful to medicine and dedicated to pure science, as it furnished new facts on gastric digestion and the transformation of carbohydrates in animals. In his thesis, Bernard published the first results of his experiments on the ingestion of food by other than natural means. His thesis offered two important discoveries:
(1) if so-called “type 1” sugar (sucrose) is injected directly into the blood, it is eliminated by the kidneys, while the so-called “type 2” sugar (glucose) is retained in the organism;
(2) gastric juice transforms sucrose into assimilable sugar, that is, sucrose exposed to the action of gastric juice and then injected into the blood no longer appears in the urine. “Type 2” sugars (in modern terminology, sugars of the monosaccharide group) represent the only “physiological” form of carbohydrates in the animal organism. Gastric juice changes all other forms of carbohydrates into assimilable physiological sugar.
In 1849, Bernard believed he had found a way to produce “artificial diabetes.” There soon followed the discoveries of the presence of sugar in amniotic fluid (1850) and in cerebro-spinal fluid (1855); the proposition to utilize the quantitative determination of sugar in the liver of a fresh corpse in order to establish whether death had been sudden (1855); and the observation that the liver manufactures sugar even after the death of an animal (1855).
By forcing a stream of water through hepatic vessels into the still-warm liver immediately following the death of an animal, the hepatic tissue is completely freed of its sugar content. But if the liver is kept at a moderate temperature, several hours afterward, or even the next day, the tissue will once again contain a quantity of sugar, produced post-irrigation. It was from this experiment that Bernard derived proof of the existence of a special “glycogenetic substance” or glycogen.
(Almost contemporaneously, V. Hensen, a young German physiologist, isolated glycogen by a process different from Bernard’s.)
The medical field was intrigued by Bernard’s discovery of the liver’s glycogenic function. In 1853, he received a Doctorate in Zoology from the Sorbonne after a brilliant presentation of his thesis, Recherches sur une nouvelle fonction du foie.
In 1854, a chair of general physiology was created for him at the Sorbonne, and he was elected to the Academy of Sciences. His discovery of glycogen was presented to the Académie des Sciences in 1855.
In 1856, Bernard discovered glycogen, a white starchy substance found in the liver. He found that this unique substance was built up by the body from sugar and served as a storage reserve of carbohydrates that could be broken down to sugars as needed, thereby keeping the sugar content of the blood at a constant level.
Bernard’s discovery showed that the digestive system not only breaks down complex molecules into simple ones, but also does the opposite, building up complex molecules from simpler ones.
Shortly after his discovery of glycogen, Bernard discovered that the vasomotor nerves control the dilation and constriction of blood vessels in response to temperature changes in the environment. Hence, when exposed to cold, the skin’s blood vessels constrict to conserve heat, while heat causes the vessels to dilate and dissipate excess heat. Through the work of Brown-Séquard, Schiff, and Bernard, the knowledge of the vasoconstrictor nerves was incorporated into science.
But to Bernard alone we are indebted for the second stage in the explanation of vasomotor function: the discovery of the vasodilator nerves and the establishment of the concept of the physiological equilibrium of the two antagonistic innervations.
This control mechanism, like the glycogenic functions of the liver, illustrates how the body maintains a stable internal environment during changing external conditions. This fundamental phenomenon came to be known as homeostasis, a term coined by Walter Cannon in 1926.
Introduction à la
(1865; An Introduction
to the Study of
Bernard’s aim in the Introduction was to demonstrate that for medicine to progress, it must be founded on experimental physiology.
Other key points:
(1) the physical and chemical sciences provide the foundation for physiology, although it is not reducible to them;
(2) the notion of “vital force” does not explain life;
(3) vivisection is indispensable for physiological research; and
(4) biology depends on recognizing that the processes of life are mechanistically determined by physico-chemical forces.
Maintaining that scientific truth is objective and demonstrable, not revealed or imposed, and that phenomena must always be approached with the question of “how” rather than “why,” Bernard based his “method” on three cardinal principles: observation, experimentation, and deductive reasoning.
In his Introduction à la médecine expérimentale, he further described the concept and importance of the milieu intérieur or internal milieu, the body’s regulatory ability to maintain a constant internal environment being essential for life and independent of the external environment. The concept was later extended to include any biological system from the cell to the entire biosphere (all areas of Earth inhabited by living things).
Bernard was aware that anatomy remained the basis of physiology, but he made it clear that physiological processes cannot be explained based solely on anatomy. He stated that humoral or physicochemical components, which cannot be dissected and constitute our internal environment, had been neglected for too long. This concept exerted a profound and long-lasting influence on biologists and physicians. The book brought new honors to Bernard, notably election to the French Academy in 1868.
“The milieu intérieur has to be liquid because water is essential for chemical reactions and for displaying the properties of living matter.”
– Claude Bernard
With little money and few educational opportunities, young Bernard enrolled in the parochial school of Saint-Julien, where he studied Latin with his local priest. (Natural sciences were not offered.) He was not a very promising student.
At his secondary school, the Royal College in Thoissey, he became interested in philosophy – in particular, René Descartes’ emphasis on the quest for truth stimulated by doubt.
Bernard dropped out of school when he was 18, and became apprenticed to an apothecary in a Lyon suburb. His main interests at this time were Romantic writers (Victor Hugo) and painters (Eugene Delacroix). Bernard himself wrote two works, a vaudeville comedy (“La Rose du Rhône”) and a five-act historical tragedy (“Arthur de Bretagne”).
In 1834, the literary critic Saint-Marc Girardin read Bernard’s play – and advised him to pursue medicine. That same year, with great difficulty, Bernard passed the baccalaureate and entered the Faculty of Medicine in Paris.
Bernard passed the examinations for internship in the Paris municipal hospitals in 1839. A protégé of Pierre Rayer, he worked at the Charité and shared lodging with Charles Lassègue (who would go on to become a prominent neurologist).
After attending a series of lectures by François Magendie, Professor of Experimental Medicine at the Collège de France, Bernard decided to devote his career to experimental physiology. Magendie noticed Bernard’s skillful dissections and took him on as a research assistant (préparateur).
A former surgeon, Magendie had published multiple papers on experimental physiology, including the celebrated Elementary compendium of physiology, which had long been a standard work in the field. Bernard became involved in Magendie’s research on spinal nerves. His first publication dealt with the chorda tympani (a branch of the facial nerve), while his medical dissertation was devoted to the function of gastric juice in nutrition.
In 1844, Bernard failed the examinations which would have allowed him to teach at the Faculty of Medicine; he tried in vain to organize a free course in experimental physiology (along with his friend Charles Lasègue), and found himself destitute.
Bernard married his way out of his economic troubles: in 1845, he wed Fanny Martin, daughter of a Paris physician. It was an unhappy marriage, but his wife’s dowry enabled him to continue his physiological research.
In 1847, Bernard was made suppléant to Magendie at the Collège de France. This period was marked by a series of important experiments and discoveries. In 1848, the Société de Biologie was founded, and Bernard became its first vice-president. That same year, Bernard noted the presence of sugar in the blood of an animal from which all solid food had been withheld for several days. Greatly surprised, he turned his research in a new direction.
He soon discovered that (1) glycemia is a normal and constant phenomenon, independent of food intake and (2) the liver produces sugar and empties it into the blood.
Published in “De L’origine du Sucre dans I’économic animale,” the discovery of the glycogenetic function of the liver compelled physiologists to revise certain fundamental ideas and shed new light on the understanding of diabetes.
Bernard also conducted several studies on the effects of various poisons, such as carbon monoxide and curare on the body. He showed that carbon monoxide could substitute for oxygen and combine with hemoglobin, thereby causing oxygen starvation. His experiments with curare showed how this unique botanical poison causes paralysis and death by attacking the motor nerves, while having no effect on the sensory nerves. He demonstrated that, because of this selectivity, curare could be used as an experimental tool in
differentiating neuromuscular from primary muscular mechanisms. No one before him had understood so well the role of drug metabolization.
Bernard regarded poisoning as a local phenomenon and advocated the use of certain poisons in physiological research. These discoveries made Bernard famous.
Bernard’s “Experimental Medicine” laid the foundation for 20th-century physiology and provided the framework for inductive biological thought. Contemporary with the life of Charles Darwin, Bernard’s accomplishments were truly remarkable and foundational to the future of experimental physiology.
In 1863, Bernard and his family moved to a larger apartment at 14, rue St. Honoré. He, however, was rarely there; returning only to eat and sleep. He had little contact with his wife and discovered that she had recruited their daughters to help with her anti-vivisection and general animal-protection activities. It was probably around this time that Bernard first suggested a legal separation – a proposal that Fanny firmly rejected at first, claiming it dishonored her and went against her religious principles.
Bernard’s health began to fail (chronic enteritis, with symptoms affecting the pancreas and liver), which eventually led him to spend more time at Saint-Julien (where he had bought the manor house of the landlord on whose farm he had been born), and less time in the laboratory.
His illness, however, left Bernard with more time to write and reflect, out of which came his masterpiece, Introduction à la médecine expérimentale (1865; An Introduction to the Study of Experimental Medicine). This work was conceived of as the preface of a great treatise, Principes de médecine expérimentale, for which Bernard wrote the rough drafts of several chapters.
“all the vital mechanisms, varied as they are, have only one object: that of preserving constant the conditions of life.”
– Claude Bernard
In 1869, after a three-year hiatus, Bernard resumed his courses in experimental medicine at the Collège de France. Considered only a mediocre lecturer, he was still able to hold the attention of his audience by the novelty and vividness of his arguments and by the experiments he improvised in the amphitheater to support his statements. At the beginning of his career, Bernard’s audiences had been composed mostly of physicians and physiologists, especially foreigners. Over time, however, they became larger, more varied.
Bernard was bestowed with many honors in the final years of his life: he was made commander of the Légion d’Honneur (1867), president of the Société de Biologie(1867), senator of the Empire (6 May 1869), member of the Académie Françise (27 May 1869) and its president (1869).
In 1869, he and his wife legally separated. Fanny and their two daughters moved to a house on the far side of the Luxembourg gardens. His legal separation and the Franco-Prussian War further affected his health.
Bernard went on to develop an endearing friendship with Marie Raffalovich, a newspaper journalist in St. Petersburg. Fluent in both German and her native Russian, she translated many articles for Bernard and wrote letters to colleagues in Germany and Russia on his behalf. These contacts greatly enriched his professional life.
A warm correspondence soon developed between them; he wrote some 500 letters to Marie Raffalovich over the following ten years. Most have been published, and show little evidence of any romance – only a desire to communicate about his work and the world in a way that he had never been able to express before.
In 1869, Bernard’s appointment to the Senate of the Second Empire of Louis Napoleon further confirmed his standing in the community. This also provided him with a substantial annual salary of 60,000 francs. His new responsibility provided more interest than actual work, since senators mainly “rubber-stamped” the autocratic intentions of the Emperor. Bernard continued to develop his concept of the milieu intérieur.
In 1870, shortly after Bernard’s inaugural lecture at the Museum, Louis Napoleon declared war on Germany. Along with so many others, Bernard escaped from Paris just as the Kaiser’s troops marched into the city. At his country refuge in Saint-Julien, Bernard continued to prepare his lectures for the Museum and the Collège, and to further develop his ideas on body heat – in particular, how the temperature of blood affects various biological processes.
In 1871, Bernard returned to a vanquished capital, badly damaged by war and divisive politics. His laboratories were intact, but Lemaistre, his préparateur at the Museum, had been killed in the war, and it took time to rebuild his research program.
Bernard was chosen to be the first president of the French Association for the Advancement of Science – according to the press, a sign of his being France’s foremost scientist. From 1873 onwards, he devoted himself to this responsibility, and to extensive lecturing at the Museum and Collège. With his remaining (and last) préparateur, Arsène d’Arsonval, he continued to experiment with poisons like strychnine and arsenic and the effect of anesthetic plant agents.
During the latter half of 1877, it was clear that Bernard’s health was rapidly failing. His maid often had to assist him across the rue des Écoles to the Collège, and he spent longer periods in his apartment, visited by Madame Raffalovich and several colleagues who furnished him with reading matter and academic gossip. One evening towards the end, as his bedridden legs were being covered with a travelling rug, he commented: “This time it will serve me for the voyage from which there is no return: the voyage of eternity.”
Claude Bernard died in his apartment on February 10, 1878, in the company of his maid Mariette Rey, d’Arsonval, Madame Raffalovich and her daughter Sophie (but neither of his own daughters). He was given a national funeral, an honor reserved until then for France’s military and political leaders, and was buried in the Père Lachaise cemetery in Paris.
Bernard’s scientific method, discoveries, and vocabulary left a lasting mark on medicine. He worked on a range of topics in parallel between 1844 and 1865: hepatic glycogenesis, nutrition and pancreatic secretion, the effects of curare, gas exchange in red blood cells, and sensory and motor innervation. This monumental undertaking had but a single aim: to define the concept of the milieu intérieur (“environment within”) that nurtures and balances all animal and plant life.
The concept of the milieu intérieur (which he developed between 1851 and 1878) was his major contribution. As he stated in 1857: “Physiologic phenomena in higher organisms take place in organic and highly perfected milieux intérieurs possessing balanced physicochemical properties.”
The milieu intérieur regulates blood acidity and body temperature, allowing the body to adjust to changes external to the body. In studying the vectors of cell interaction (although without developing the concept of remotely-acting hormones), he expounded the concept of “internal secretion,” namely an organ’s ability to secrete a substance and release it directly into the bloodstream.
“The constancy of the milieu intérieur is the condition for a free and independent life”. According to Bernard, the ability of our ancestor organisms to leave the oceans required that they develop the ability to “carry the ocean with them” in the form of an internal ocean, bathing their cells constantly in fluids that resembled the very seas from which they evolved.
Thus Bernard opened the door to one of the most intriguing and fascinating fields in biological science, one of regulation, adaption and compensation – the concept of homeostasis, a foundational pillar of current bioregulatory medicine.