Who proposed the theory that the body's internal milieu changes constantly to meet daily demands?

The theory regarding the body's internal environment and its constant adjustments to meet daily demands is attributed to Claude Bernard. He introduced the concept of "milieu intérieur," which refers to the stable internal conditions that organisms maintain despite varying external environments. Bernard emphasized the importance of this internal balance for physiological functions, highlighting how the body adapts to changes through various mechanisms such as homeostasis. This foundational concept is critical in understanding how the body responds to stressors and maintains overall health, making Bernard's work essential to fields like physiology and medicine.