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French physiologist (1813–1878)

Bernard, the son of a poor wine grower from St. Julien, began writing plays to earn money but turned to medicine on the advice of a literary critic. His first experiences of medicine were discouraging but, following his appointment as assistant to François Magendie at the Collège de France, he began a period of extremely productive research. He drew attention to the importance of the pancreas in producing secretions for breaking down fat molecules into fatty acid and glycerine and showed that the main processes of digestion occur in the small intestine and not, as was previously thought, in the stomach. In 1856 he discovered glycogen, the starchlike substance in the liver, whose role is to build up a reserve of carbohydrate, which can be broken down to sugars as required; normally the sugar content of the blood remains steady as a result of this interaction. The digestive system, he found, is not just catabolic (breaking down complex molecules into simple ones), but anabolic, producing complex molecules (such as glycogen) from simple ones (such as sugars).

Bernard also did valuable work on the vasomotor system, demonstrating that certain nerves control the dilation and constriction of blood vessels; in hot weather blood vessels of the skin expand, releasing surplus heat, contracting during cold to conserve heat. The body is thus able to maintain a constant environment separate from outside influences. Apart from elucidating the role of the red blood corpuscles in transporting oxygen, Bernard's investigation of the action of carbon monoxide on the blood proved that the gas combines with hemoglobin, the effect being to cause oxygen starvation. He also carried out important work on the actions of drugs, such as the opium alkaloids and curare (curarine), on the sympathetic nerves.

Bernard's health deteriorated from 1860 and he spent less time in the laboratory. He thus turned to the philosophy of science and in 1865 published the famous Introduction à la médecine expérimentale (An Introduction to the Study of Experimental Medicine, 1927). The book discusses the importance of the constancy of the internal environment, refutes the notion of the ‘vital force’ to explain life, and emphasizes the need in planning experiments for a clear hypothesis to be stated, which may then be either proved or disproved. On the strength of this work he was elected to the French Academy in 1869.

Claude Bernard (1813-78) was a key figure in French nineteenth-century science, and one of the world's great physiologists. With good reason he has been called the ‘father of experimental medicine’.

Bernard was born in St Julien-en-Beaujolais, the son of a winegrower and schoolmaster. The greater part of his education was at the local Jesuit College at Villefranche; at the age of 19 he went to work for M. Millet, a pharmacist in the suburb of Lyons. At this time, Bernard's greatest enthusiasm was for the theatre — he wrote a Vaudeville, La Rose du Rhône, and a 5-act drama, Artur de Bretagne. M. Millet did not seem to be impressed, and he dispensed with Bernard's services. Bernard found himself, at age 21, in Paris, set on a career as a playwright; but Giraudin, the Professor of Literature who read his work, tactfully suggested a more reliable career.

So in 1834 Bernard became a medical student. He did not seem destined for medical fame, for he came twenty-third out of twenty six in the final examinations for his year. But he greatly admired François Magendie, who was Professor of Medicine at the Collège de France, and the most famous French physiologist of the time. Magendie would break off his ward rounds to test a point with an animal experiment, and Bernard was greatly impressed. In 1841 he became Magendie's assistant (‘préparateur’) and his career as a physiologist began.

His early findings were not striking: thus his MD thesis claimed that the acid in gastric juice was lactic (rather than hydrochloric) acid — a finding from experiments on rabbits, whose gastric juice often contains this acid produced by secondary fermentation. Towards the end of the 1840s, though, he began a series of remarkable discoveries. He began by showing that the pancreas, secreting its juice into the duodenum, was capable of digesting foodstuffs. Up to this time the stomach had been thought to be paramount in the process of digestion and the pancreas was believed to be an abdominal salivary gland. Then he demonstrated that both pancreatic juice and bile were necessary for the absorption of fat from the gut. In 1850 the Académie des Sciences awarded him its prize in Experimental Physiology for his work on the pancreas.

Continuing with his nutritional theme, he proceeded to show that sugar absorbed from the gut was stored in an insoluble form in the liver. Bernard demonstrated that in fasting conditions this insoluble form released its sugar into the blood. He called it ‘glycogenic’ (sugar-forming), and subsequently isolated the pure substance, glycogen, in 1857. Many consider its discovery to be Bernard's greatest achievement. He described the release of glucose from glycogen as ‘internal secretion’; unfortunately, when hormones were discovered half a century later, the phrase was also used to describe their entry into the blood — a very different biological process.

Bernard was always intrigued by the role of nerves in controlling the activities of the body, and in 1852 he showed how nerves controlled the diameter of blood vessels, and hence blood flow. His observation was simple enough, but required sound anatomical knowledge: cutting the cervical sympathetic nerve on one side in the neck raised the temperature of the skin on that side of the head. Electrical stimulation of the cut end of the nerve reversed the change, so that Bernard concluded that under normal circumstances the nerve was narrowing the diameter of skin blood vessels: it had a ‘vasoconstrictor’ function. This ‘vasomotor’ activity of nerves laid the foundation for the concept of the autonomic nervous system, whose inception had to wait for another forty years or so.

In 1855 Magendie died, and Bernard succeeded him as Professor of Medicine at the Collège de France. His wife felt let down by his lifestyle: she had expected to lead the life of a prosperous physician's wife. Instead Bernard treated no patients, and spent most of his time on animal experiments. Mme Bernard and the daughters disapproved so strongly of his life that they set up a home for stray animals, many of whom, it was said, were subjects of Bernard's experiments. Shortly afterwards he separated from his wife and two daughters. (He had married in 1845.)

His lectures at the Collège de France were published and one of these, in 1859, contained perhaps his most fertile idea. He saw the animal's external environment (‘le milieu extérieur’) as constantly changing: but the composition of the fluids within the body (‘le milieu intérieur’) was kept remarkably constant, so protecting the cells of the body from the vicissitudes of the external environment. This constancy (homeostasis) has provided many subsequent scientists with a first step in understanding the body's activities. Many of Bernard's ideas on the internal milieu came from his observations on blood sugar.

His health started to deteriorate — though no exact diagnosis of his chronic abdominal pain was made. In 1863 he published nothing and went to live in his house and vineyard in St Julien. During his enforced leisure he tried to provide some sort of rationale to his science, and collected his thoughts in a book, An introduction to experimental medicine. This was published in 1865. Bernard believed that there was no ‘life-force’ (vitalism was a common belief at the time). The only sure way forward in experimental medicine was to design experiments in which every variable was controlled. Furthermore, every experiment should be based on a hypothesis; if the hypothesis were disproved, it should be changed, and the experiment repeated.

The Introduction was a great success. The rather disreputable world of the animal experimenter was transformed into an intellectually attractive system of enquiry. It was written with style, and so was read by people who would otherwise have no interest in physiology. Among its admirers was a businessman's wife, Mme Raffalovich, who became Bernard's companion in his last years. The Introduction led to Bernard's election to the French Academy in 1868.

His health improved, and he returned to lecturing. But he did little new research, except — in the last year of his life, 1877 — to work on a new theory of alcoholic fermentation. Rather unfortunately, his experimental notes were published after his death, and they were found to contradict some of the findings of his friend Louis Pasteur. In his final days he was diagnosed as having pyelonephritis, a kidney infection, and was nursed by Mme Raffalovich and her daughter, who tactfully withdrew from the room whenever Bernard had a visitor. His death was marked by a ceremonial state funeral: no French scientist had ever been so honoured. His pupil Paul Bert, in a memorable funeral oration, declared ‘No one ever made discoveries more simply, more naïvely. He discovered as others breathed.’

— John Henderson

Bibliography

• Bernard, C. (1949). An introduction to the study of experimental medicine, (trans. H. C. Greene), introduction by L. J. Henderson. Henry Schuman, New York

(1813-1878) French physiologist; discovered glycogen and the role of the liver in synthesizing glucose.

The French physiologist Claude Bernard (1813-1878) originated the experimental approach to medicine and established general physiology as a distinct discipline.

Claude Bernard was born on July 12, 1813, in the village of Saint-Julien in the Rhône Department. His father, Pierre Jean François Bernard, was a wine maker. At 17 Claude went to the College of Thoissey, where he remained for only a year because his family could not afford to continue his education. He was apprenticed to a pharmacist in Lyons but left after 18 months.

A Medical Career

Bernard enrolled in the Paris School of Medicine in 1834, and in 1839 he passed the examination for an internship. After obtaining his medical degree in 1843, he embarked on a lifetime of research. Recognition of his work followed and he was awarded the prize in experimental physiology of the Academy of Sciences (1847), was named a chevalier of the Legion of Honor (1849), was granted the degree of doctor of natural sciences (1853), and was elected a member of the Academy of Sciences (1854). In 1854 at the Sorbonne, a special chair of physiology was founded, to which Bernard was appointed. He also became professor of medicine at the Collège de France and held both chairs concurrently for the next 13 years.

At the Collège de France Bernard delivered most of the lectures that were published in the series of volumes known as the Leçons. The first volume appeared in 1855 and the last one in 1879.

A few months after Bernard's Introduction to the Study of Experimental Medicine (1865) appeared, Louis Pasteur wrote, "Never has anything clearer, more complete, more profound, been written about the difficult art of experiment." It has been reprinted and translated many times and remains a pertinent, widely read, and much-quoted classic. It established Bernard's literary reputation and led to his election to the Académie Française in 1869.

Bernard studied the gases in arterial and venous blood under the direction of J. L. Gay-Lussac, the chemist, in 1842; the work was not completed. Bernard's first paper, which appeared in 1843, gave an account of the chorda tympani nerve, accurately describing its anatomy but misinterpreting its functions. His next investigation, into the role of gastric juice in digestion, was presented as his doctoral thesis in 1843. His third published work studied the function of the spinal accessory nerve, which he wrongly believed controlled the movement of the vocal cords.

Pancreatic Function

One of Bernard's major discoveries was to define the functions of pancreatic secretion. His experiments followed a chance observation that starved rabbits had clear urine, while on their normal vegetable diet they had cloudy urine. He deduced that the nutrition of a starved rabbit was maintained by breakdown of its own tissues. When he fed rabbits on meat, killed them, and examined their intestines, he found fine, whitish vessels, filled with emulsified fat called chyle, radiating from the lower intestines in the region of the pancreatic duct. He deduced that pancreatic juice must play a part in the absorption of fat from the intestine. In a series of investigations he further demonstrated that pancreatic secretion could digest starch, and he went some way toward defining the protein breakdown produced by pancreatic juice. He found that the pancreas did not begin to secrete until ingested food had passed into the duodenum. This effect is now known to be due to the action of a hormone, secretin.

Glycogenic Function of the Liver

In 1843 Bernard found that cane sugar injected into the veins of an animal was excreted in the urine, whereas a similar intravenous injection of glucose disappeared. He also found sugar to be present in the liver of dogs that were fed exclusively on meat. Several years later he discovered that injury to the floor of the fourth ventricle of the brain caused sugar to appear in the blood and urine, thus producing a form of "artificial diabetes." Bernard demonstrated that blood leaving the liver contained larger quantities of sugar than did blood entering the liver, and he consequently introduced the concept that the liver has two functions: an external secretion of bile and an internal secretion of sugar which then enters the circulation.

After washing away the sugar in a freshly removed dog's liver Bernard noted that the liver was again rich in sugar a day later. He inferred that a sugar-forming (glycogenic) substance must be present in the liver, and in 1857 he isolated pure glycogen from the liver. Bernard evolved the theory that carbohydrate is stored as glycogen in the liver and released, when necessary, as glucose into the blood, and this hypothesis in its essentials has since been abundantly proved.

Vasomotor Functions

In 1851 Bernard cut the cervical sympathetic nerve in a rabbit and noted that part of the head, on the side of the served nerve, became warmer. In 1852 he showed that paralysis of the cervical sympathetic nerve in the dog causes drooping of the eyelid and constriction of the pupil on the side of the paralysis. Bernard went on to stimulate electrically the cut sympathetic nerve and found that the skin on the same side became pale and blood flow therein was reduced. Thus he defined both constrictor and dilator elements of the vasomotor system, by which blood vessel caliber, and hence blood flow, is determined.

Miscellaneous Researches

Bernard started to study the effect of curare, a South American poison, in 1844. During the next 12 years he demonstrated that the paralysis it produced arose from impairment of the functions of nerves as they entered the muscles. Studies on carbon monoxide poisoning, which started in 1846, led Bernard to conclude that red blood cells carried oxygen, bound to a chemical. The nature of this chemical substance, hemoglobin, was discovered by E. F. Hoppe-Seyler in 1857.

In a series of experiments on severed nerves, Bernard noted the degeneration of tissues robbed of their nerve supply. He thus discovered the trophic effects of nerves. He also cut the dorsal columns of the frog's spinal cord and thereafter noted the impairment of function in the legs. In experiments on muscle he demonstrated that actively contracting muscles utilize oxygen faster than resting muscles.

Bernard's contributions to physiological science were immense. He also explored the fields of clinical pharmacology and experimental pathology. He believed that the chief aim of physiological experimentation was to throw light upon morbid conditions. He regarded the physician of his time as an empiricist, awaiting the advances in medicine that would enable him to become a scientist, and he deplored the contemporary view of a physician as an artist.

Bernard died in Paris on Feb. 10, 1878. He was given a state funeral, the first occasion of which a French scientist was so honored.

Further Reading

The most comprehensive and readable biography of Bernard is J.M. D. Olmsted, Claude Bernard, Physiologist (1938). See also Michael Foster, Claude Bernard (1899). Short accounts of Bernard's life and work are in F. H. Garrison, An Introduction to the History of Medicine (1913; 4th ed. 1929), and in Henry E. Sigerist, Great Doctors: A Biographical History of Medicine (1932; trans. 1933). To understand the philosophy of Bernard's work it is essential to read his An Introduction to the Study of Experimental Medicine (1865; trans. 1927).

For more information on Claude Bernard, visit Britannica.com.

Bernard, Claude (1813-78). French physiologist and professor at the Collège de France, a leading figure in the development of experimental science as a system of hypothesis, proof, and refutation. In his Introduction à la médecine expérimentale (1865), he defined systematic medical experiment, distinguishing it from the randomness of empirical observation, and asserted the principle of scientific determinism, which, he held, was not to be confused with philosophical fatalism. Naturalist novelists, and particularly Zola in Le Roman expérimental, published two years after Bernard's La Science expérimentale (1878), claimed mistakenly that Bernard's scientific method, which they did not understand clearly, could be applied in the novel.

[Bernard Swift]

(klōd bĕrnär') , 1813–78, French physiologist. He turned from literature to medicine, working in Paris under Magendie and teaching at the Collège de France and at the Sorbonne. One of the great scientific investigators, he is known as the founder of experimental medicine because of his work on digestive processes, especially the discovery of the glycogenic function of the liver and of the action of pancreatic juice, and on the vasomotor mechanism. He wrote An Introduction to the Study of Experimental Medicine (1865, tr. 1927).

Bibliography

See J. M. D. Olmsted and E. H. Olmsted, Claude Bernard and the Experimental Method in Medicine (1952); R. Virtanen, Claude Bernard and His Place in the History of Ideas (1960).

Quotes:

"A fact in itself is nothing. It is valuable only for the idea attached to it, or for the proof which it furnishes."

"It is what we think we know already that often prevents us from learning."

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