He explores and renews all the physiology of that time, and is particularly interested  in the digestive secretions. He evidences the role of the pancreas in the digestion of fats (1848, 1856), analyzes that of sugars, which direct himself to the discovery of the glycogenic function of the liver and the isolation of glycogen.

The glycogenic function of the liver is the first example of the internal secretions.Glucose then appears to be the fuel of organisms. Claude Bernard also discovers the role of the nervous system grand sympatheticin the regulation of the glucose level in the blood and proposes the central notion in physiology of the internal fluids constancy.

He was Professeur in Paris at Collège de France, at La Sorbonne (the old name of the Paris' university), then at  the  Museum National d'Histoire Naturelle. His scientific accomplishments were broadly diffused due to the publication of his courses in a series of volumes. These extraordinary achievements were obtained in very precarious material circumstances :

"I knew,wrote Claude Bernard, the scientist's pain who, by absence of supports, cannot carry out the experiments that he conceives, and who is forced to abandon certain researches, or to leave his discovery in a state of an outset."