Frank I. Katch


Santorio experiments breakthrough
in energy metabolism

Claude Bernard (1813-1878) 

Bernard, generally acclaimed as the greatest physiologist of all time, succeeded François Magendie as Professor of Medicine at the Collège de France. Bernard interned in medicine and surgery before serving as laboratory assistant (préparateur) to Magendie in 1839. Three years later, he followed Magendie to the Hôtel-Dieu hospital in Paris. For the next 35 years, Bernard discovered fundamental properties about physiology. He participated in the explosion of scientific knowledge in the mid century. Following Darwin's The Origin of Species (1859), Louis Pasteur (1822-1895) refuted spontaneous generation between 1860 and 1865 and stimulated the growth of microbiology. In 1865, Gregor Mendel (1822-1884) promulgated the laws of heredity. Artists too experimented with technique (Corbet, Courbet, Degas, Daumier, Manet, Millet, Monet, Renoir, and Rodin). Philosophers (de Tocqueville, Comte, Bergson, Proudhon) and writers (Balzac, Baudelaire, Dumas, Hugo, Flaubert, Maupassant, Stendhal) boldly explored new frontiers. Radical individualism that fostered science and art also encouraged social turmoil: coups, two revolutions (1848, 1870), and two wars against Austria and Prussia. Reflecting on this unrest, Marx and Engels drafted the Communist Manifesto in Paris 1848.

Bernard remained oblivious to all except his "physico-chemical science." Mayer (1951) writes about Bernard's approach to science:

Bernard combined with a capacity for hard and prolonged work in the laboratory his appreciation of the importance of leisure spent in quiet meditation. His adherence to exact truth was absolute, and he was always ready to recognize the limitations or the error of what had seemed like a promising idea until tested in the laboratory. His technical skill was superb, both as an experimental surgeon and as a biochemist. Yet essential as these characteristics were, they are not sufficient to explain his unequaled series of fertile discoveries.

Bernard, first of all, believed strongly in the necessity of always having a working hypothesis, derived from perusal of the literature and observation of natural phenomena, before starting on the experiment proper. He used to say: "He who does not know what he is looking for will not lay hold of what he has found when he gets it."

But imagination is not equivalent to genius unless it is joined to what was perhaps Bernard's outstanding characteristic, the ability to devise the single, definitive crucial experiment which will test a far-reaching hypothesis. Bernard, like a great general who maps and executes a campaign by striking at the vital points of the enemy hosts, and takes only those positions which have to be taken to bring decisive victory, never wasted any time on experiments which were not essential to his progress. And, of course, his skill allowed him to perform these experiments in a minimum of time and with a maximum of precision.

Bernard had an extraordinary capacity for extracting from his results the most general and far-reaching conclusions that could be solidly supported by them; hence, his role as a progenitor in so many branches of the biological sciences.

Claude Bernard surrounded by his pupils during one of his many experiments. The original is in the Department of Physiology, School of Medicine, Paris. Drawing by L'Hermitte.

Surgical instruments used by Bernard in his studies of electrical stimulation of tissues and the effects of the drug curare, a topic of extreme interest to him since his early school days.

Scientific apparatus used by Bernard in his classic experiments of blood flow in the brain

Bernard indicated his single-minded devotion to research by producing an M.D. thesis (1843) on gastric juice and its role in nutrition (Du sac gastrique et de son rôle dans la nutrition). Ten years later, he received the Doctorate in Natural Sciences for his study entitled Recherches sur une nouvelle fonction du foie, consideré comme organe producteur de matière sucrée chez l'homme et les animaux (Research on a new function of the liver as a producer of sugar in man and animals). Prior to his seminal research, scientists assumed that only plants could synthesize sugar, and sugar within animals must be derived from ingested plant matter. Bernard disproved this notion by documenting the presence of sugar in the hepatic vein of a dog whose diet lacked carbohydrate.

Bernard's experiments changed medicine (Fruton, 1979):

  • The discovery of the role of the pancreatic secretion in the digestion of fats (1848).
  • The discovery of a new function of the liver--the "internal secretion" of glucose into the blood (1848).
  • The induction of diabetes by puncture of the floor of the fourth ventricle (1849).
  • The discovery of the elevation of local skin temperature upon section of the cervical sympathetic nerve (1851).
  • The production of sugar by washed excised liver (1855) and the isolation of glycogen (1857).
  • The demonstration that curare specifically blocks motor nerve endings (1856).
  • The demonstration that carbon monoxide blocks the respiration of erythrocytes (1857).

Claude Bernard after winning a prestigIous award for his many scientific accomplishments.

Bernard's work also influenced other sciences. His discoveries in chemical physiology spawned physiological chemistry and biochemistry, which in turn created molecular biology. His contributions to regulatory physiology helped the next generation understand how metabolism and nutrition affected exercise.

Despite the importance of Bernard's discoveries, the French government barely supported scientific research. Germany, Russia, and England provided laboratories in universities and hospitals. Bernard's predecessors, Magendie and Bert, worked in small rooms, poorly lit and inadequately ventilated (Guerlac, 1977). Bernard spoke out against his government's neglect of science. Still, he continued to experiment.

Bernard's influential Introduction à l'étude de la médecine expérimentale (The Introduction to the Study of Experimental Medicine, 1865)4 illustrates the self control that enabled him to succeed despite external perturbations. It requires researchers to vigorously observe, hypothesize, and test their hypothesis. In the last third of the book, Bernard shares his strategies for verifying results. His disciplined approach remains valid, and should be required reading for all scientists, regardless of the field.

Bernard's life inspired appreciative works by the Cambridge physiologist Sir Michael Foster (1899) and historian Grmek (1971). A few days after his death, Bernard's friend and colleague Paul Bert wrote the following poignant eulogy (see preface of Bernard, 1927):

Nothing in his pure and harmonious life was turned aside from its chief aim. Enamored of literature, art and philosophy, Claude Bernard as a physiologist lost nothing by these noble passions; on the contrary, they all helped in developing the science with which he identified himself, and of which he is the highest and most complete embodiment. He as a physiologist such as no man had been before him. "Claude Bernard," said a foreign scientist, "is not merely a physiologist, he is physiology."

His very death seems to mark a new era in science. For the first time in our country, a man of science will receive those public honors hitherto reserved for political and military celebrities.... And one phrase... sums up all that we have said: "The light, which has just been extinguished, cannot be replaced."


Bernard, C. (1927).The introduction to the study of experimental medicine (translated by H. C. Greene). Henry Schuman, New York.

Foster, M. (1899). Claude Bernard. Longmans Green, New York.

Fruton, J. S. (1979). Claude Bernard the scientist. In E. D. Robin (Ed.) Claude Bernard and the internal environment. A memorial symposium. Marcel Dekker, New York.

Grmek, M. D. (1971). Claude Bernard. In Dictionary of scientific biography. Charles Scribner's Sons, New York.

Guerlac, H. G. (1977). Essays and papers in the history of modern science. Johns Hopkins University Press, Baltimore.

Mayer, J. (1951). Claude Bernard. Journal of Nutrition, 45, 3.

© Frank I. Katch, William D. McArdle, Victor L. Katch. 1997.

Copyright ©1997