Claude Bernard, a French researcher credited with founding the field of experimental medicine, was born on 12 July 1813. While conducting experiments on an animal fed a sugar-free diet, Bernard discovered that the liver stores sugar as glycogen. In other animal studies, he observed that pancreatic juices break down fats and starches and that certain nerves control blood flow by triggering veins to constrict or dilate. Bernard also discovered that red blood cells carry oxygen in the body. Bernard's most important theoretical contribution was his observation that life requires a stable internal environment, or "milieu interior."