Bernard's first major work was on the functions of the
pancreas. His discovery that the
juices of the pancreas play a significant role in the
digestive process won him the prize for experimental physiology from the
French Academy of Sciences. His findings specifically showed that the pancreas secreted a fluid containing a lipolytic enzyme that split neutral fats into glycerol and fatty acids. Prior to his research, the function of the pancreas was poorly understood, with many physiologists considering it to be a gland of little significance. Bernard also discovered that introducing
ether into the stomach or
duodenum induced pancreatic secretions. The physiologist
William Bayliss credited Bernard's work as influential in the latter's discovery of
secretin, the first
hormone to be isolated. In perhaps his most famous experiment, Bernard discovered the
glycogenic function of the
liver. The liver, in addition to secreting
bile, also produces the sugars that can cause
hyperglycemia, which helped advance study of
diabetes mellitus and its causes. In 1851, while examining the effects produced in the temperature of various parts of the body by each section of the nerve or nerves belonging to them, Bernard noticed that division of the
cervical sympathetic nerve resulted in more active circulation and more forcible pulsation of the
arteries in certain parts of the head. A few months later, he observed that electrical excitation of the upper portion of the divided nerve had the contrary effect. This discovery of the
vasomotor system also established the existence of both
vasodilator and
vasoconstrictor nerves. His use of vivisection disgusted his wife and daughters, who returned at home once to discover that he had vivisected the family dog. The couple was officially separated in 1869 and his wife went on to actively campaign against the practice of vivisection. Some in the scientific community were also uncomfortable with the practice. The physician-scientist George Hoggan spent four months observing and working in Bernard's laboratory, later writing that his experiences there had "prepared [him] to see not only science, but even mankind, perish rather than have recourse to such means of saving it." Hoggan was a founding member of the
National Anti-Vivisection Society in the mid-1870s.
Milieu intérieur, the "internal environment", is the key concept with which Bernard is associated. He explained that the body is "relatively independent" of the outside world, and that a healthy "internal environment" adapts to deficiencies in the surrounding environment, thus keeping the physiology balanced. This is the underlying principle of what would later be called
homeostasis, a term coined by
Walter Cannon. Bernard was also interested in the physiological action of poisons, particularly
curare and
carbon monoxide gas. He is credited with first describing carbon monoxide's affinity for
hemoglobin in 1857, although
James Watt had drawn similar conclusions about
hydrocarbonate's affinity for blood acting as "an antidote to the oxygen" in 1794 prior to the discoveries of carbon monoxide and hemoglobin. Throughout his career, Bernard sought to establish the use in medicine of what would later become the
scientific method. In
An Introduction to the Study of Experimental Medicine (1865), he emphasized the importance of trusting evidence over clout, even if it "contradicts a prevailing theory," as "[t]heories are only hypotheses" proven or disproven by facts. He criticized scientists who
cherry-picked their data only to prove their own hypotheses. Unlike many scientific writers of his time, Bernard wrote using the first person when discussing his own experiments and thoughts. == Honors and awards ==