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.
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.
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.
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 on Claude Bernard
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).