The basic work on the subject was done by Claude Bernard, a pupil of the great Magendie, whose saying it is well to remember--"When entering a laboratory one should leave theories in the cloakroom." More than any other man of his generation, Claude Bernard appreciated the importance of experiment in practical medicine.

For him the experimental physician was the physician of the future--a view well borne out by the influence his epoch-making work has had on the treatment of disease.

His studies on the glycogenic functions of the liver opened the way for the modern fruitful researches on the internal secretions of the various glands.

About the same time that Bernard was developing the laboratory side of the problem, Addison, a physician to Guy's Hospital, in 1855, pointed out the relation of a remarkable group of symptoms to disease of the suprarenal glands, small bodies situated above the kidneys, the importance of which had not been previously recognized.

With the loss of the function of these glands by disease, the body was deprived of something formed by them which was essential to its proper working.
Then, in the last third of the century, came in rapid succession the demonstration of the relations of the pancreas to diabetes, of the vital importance of the thyroid gland and of the pituitary body.