Bernard, Claude

Bernard, Claude 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.