The founding father of modern physiology, Claude Bernard, was born on 12 July 1813 in Saint-Julien en Beaujolais in France. This year, we mark his 200th birthday.
When Claude Bernard started exploring metabolism and diabetes, strange hypotheses were circulating in the medical community. One of them, formulated by Mialhe, was that glucose was transported by the lymphatic system into the blood and burned there. Some assumed that the lung was the place where this “burning” occurred. In 1845, Claude Bernard wrote in his red notebook, “The digestion of carbohydrates takes place in two steps; first: transformation into glucose, second: glucose is burned in the lung. If this doesn’t happen, diabetes occurs.” Claude Bernard asked, “Is this true?” Quoting Claude Bernard’s own words, let us explore the steps leading to his major discovery:
To clarify this question, I had to find the sugar in the blood, and to look for the sugar from the vessel of the intestine where it is absorbed to find finally the place where it is burned. To study this question I gave sweet milk soup to a dog and sacrificed the dog during digestion. I detected sugar in the vena hepatica. It was logic to conclude that all the glucose that I found in this vein resulted from the sugar the dog had eaten. More than one researcher would have stopped here and would have thought that any control experiment was useless. But I performed a control experiment because I am convinced that in physiology you should always doubt even if the doubt doesn’t seem to be permitted. As a control experiment I chose a dog that was exclusively fed with meat. This animal was sacrificed during digestion and the glucose content of the vena hepatica was examined. I was very astonished noticing that the vena hepatica contained sugar even if the dog hadn’t eaten any sugar (1).
Following this observation, Claude Bernard wrote in his little notebook, “I don’t understand anything anymore.”
He summarized these findings in the article “About the Origin of Sugar” published in 1848 (2). In this publication, he states, “Normally there is always sugar in the blood of the heart and the liver. The sugar is formed by the liver; this is independent of the nutrition with sugar or carbohydrates.” Now another question had to be answered, In what form is the sugar stored in the liver? After many experiments, in February 1855, Bernard isolated glycogen. One of the photos shows Bernard’s handwriting and reads, “I baptize this substance glycogen” (3,4).
Two other publications by Claude Bernard deserve special mention. The first one is his Lessons of Phenomena of Life in Animals and Plants (5). In this publication, he is the first to describe the “milieu intérieur.” He writes, “I think I was the first to express the idea that for animals there are in fact two environments, one milieu which is outside the body and an inner milieu, in which the components of living tissues are embedded. The real existence of the animal doesn’t take place in the external world but inside the liquid medium of circulating organic fluid. This fluid is the expression of all local nutrition and the source and mouth of elementary exchange” (5).
In 1865, Claude Bernard published his masterpiece Introduction Into Experimental Medicine (1). In it he writes, “There are physicians who are fanatical about the effects of the drugs they prescribe. They do not accept critical comments which are based upon experiments. They say you can only prescribe drugs which you believe in, and they think that prescribing a drug to a patient you doubt about shows a lack of medical ethics. I don’t accept this way of thinking, it means deceiving oneself and deceiving others.”
Nearly all relevant founders of U.S. physiology went to Paris. In particular, the French American researcher Charles-Édouard Brown-Séquard, who taught for several years in the U.S., should be mentioned as one who brought Claude Bernard’s ideas to the U.S. He ultimately succeeded Bernard as professor of medicine at the Collège de France in 1879.
Obituaries were published in all respectable medical journals worldwide when Claude Bernard died in Paris on 10 February 1878 (6). Immediately after his death, his friends and students collected money for a bronze monument in front of the Collège de France. Sadly, the monument was melted during the Nazi occupation but was replaced after the war with a stone monument.
The European Association for the Study of Diabetes honored Claude Bernard by inaugurating a lecture in his name. The first two winners of this lecture were subsequently awarded with the Nobel Prize in physiology and medicine.