Claude Bernard
1813-1878
French Physiologist and Physician
Claude Bernard's research transformed many areas of physiology and demonstrated that many vital functions could be understood in term of chemistry rather than as aspects of animated anatomy. His most significant discoveriesincluded the glycogenic function of the liver, the role of the pancreatic juices in digestion, the functions of the vasomoter nerves, and the nature of the action of curare, carbon monoxide, and other poisons. Bernard believed that his demonstration of the glycogenic function of the liver was his most important piece of work, but the implications of his researches eventually revolutionized ideas about metabolism. Perhaps his most important contribution was his theoretical framework. He based this research career on his concept of determinism, that is, faith in the experimental method and its applicability to physiology, the science of life. Bernard insisted that instead of continuing ancient disputes about "vitalism" and "mechanism," scientists should analyze and compare relationships among phenomena in living beings and the inanimate world.
Born into a poor peasant family, Bernard was fortunate to have received instruction in classical subjects from the parish priest. After more advanced studies, Bernard taught language and mathematics at a Jesuit school while tutoring private pupils. Financial difficulties forced him to take a position as assistant to an apothecary at Lyons, but he found the work boring and dreamed of writing great plays for the Parisian theater. Soon after he arrived in Paris, he was advised to find another profession if he wanted to make a living. Bernard chose medicine and attended the Parisian School of Medicine. Finding himself unsuited to the private practice of medicine, he became assistant to the distinguished physiologist François Magendie (1783-1855). Eventually, Bernard replaced Magendie as professor.
Bernard's studies of sugar in the blood of carnivores proved that, contrary to prevailing theory, animal blood contains sugar even when it was not supplied by foodstuffs. In tests of the theory that sugar absorbed from food was destroyed when it passed through the liver, or lungs, or some other tissue, Bernard put dogs on a carbohydrate diet for several days and then killed the animals immediately after feeding. Large amounts of sugar appeared in the hepatic veins. To his surprise, animals in the control group, which had been fed only meat, had large amounts of sugar in their hepatic veins, but not in the intestines. Bernard had discovered gluconeogenesis, that is, the conversion of other substances into glucose in the liver. Further work led to the discovery of glycogen (the carbohydrate storage polymer of animals), as well as the synthesis and breakdown of glycogen. Theinvestigation of glucose metabolism led to the concept of the "internal secretions" which were products transmitted directly into the blood instead of being poured out to the exterior of the gland or organ secreting them.
Claude Bernard. (The Library of Congress. Reproduced by permission.)Bernard realized that the metabolic theory of the cell put forth by Theodor Schwann (1810-1882) was applicable to the fundamental problem of physiology, the relationship between the cells and their immediate environment. Bernard believed that he was the first scientist to insist that complex animals had two environments: an external environment in which the organism lived and an internal environment in which the cells functioned. Ultimately, vital phenomena occurred within the fluid internal environment bathing all the anatomical elements of the tissues. This was the basis of Bernard's well-known dictum: "The constancy of the internal milieu is the condition for free and independent life."
When Bernard was 47 years of age, exhaustion and illness forced him into a period of rest and reflection during which he wrote about the broader implications of his work. His Introduction to the Study of Experimental Medicine is a remarkably lucid and widely read text. A close examination of his research notebooks, however, indicates that the path to each of his discoveries was much more confused and tortuous than thepublished accounts admit. His work was extended by other scientists, most notably by Lawrence J. Henderson (1878-1942) and Walter Bradford Cannon (1871-1945) who emphasized the concept of the constancy of the internal environment and coined the word "homeostasis" to describe the conditions that maintained the constancy of the interior environment.
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