How did Claude Bernard’s concept of the internal environment influence later physiology and medicine?

Claude Bernard’s concept of the milieu intérieur, or "internal environment," is considered his most seminal contribution to science. By proposing that the body maintains a stable internal state despite external fluctuations, he provided the foundational framework for the modern understanding of homeostasis.21

This concept fundamentally shifted the trajectory of physiology and medicine by establishing that vital processes are mechanistically determined by physico-chemical forces rather than an abstract "vital force". Bernard argued that for medicine to progress, it must be grounded in experimental physiology, where researchers use guiding hypotheses to investigate these biological mechanisms. His work effectively moved the field away from earlier, less rigorous methods, helping to establish the principles of experimentation that define modern biology today.21