Claude Bernard, the father of modern physiology, did not merely study life; he redefined it as a controlled environment. In the 1850s, this French physiologist introduced the concept of the milieu interieur, or internal environment, arguing that the body must maintain a stable state despite external chaos. This idea, later named homeostasis by Walter B. Cannon in 1929, became the cornerstone of understanding how organisms survive. Bernard, depicted in oil paintings with his pupils, believed that the body functioned like a factory where organs were workers producing the phenomena of life. His work shifted the focus from simple observation to experimental manipulation, proving that physiological state was not a passive condition but an active, regulated process. Before Bernard, the body was seen as a vessel of humors, but he showed it was a machine of precise chemical and physical mechanisms.
Humors and Experiments
The study of life began in classical Greece with Hippocrates, who proposed that four basic substances, earth, water, air, and fire, corresponded to four humors: black bile, phlegm, blood, and yellow bile. This theory of humorism dominated medicine for centuries, suggesting that disease resulted from an imbalance of these fluids. Galen, who lived until 200 AD, expanded on this by linking emotions to specific humors, creating temperaments like sanguine, phlegmatic, choleric, and melancholic. However, Galen was also the first to use experiments to probe the functions of the body, arguing that imbalances could be located in specific organs. For the next 1,400 years, Galenic physiology remained a powerful tool, yet it was not until the 17th century that the term physiology was officially introduced by Jean Fernel. The transition from philosophical speculation to experimental science began with William Harvey, who described the circulation of blood, and Santorio Santorio, who in the 1610s used a pulsilogium to measure pulse rates and a thermoscope to measure temperature.Electricity and Division
In 1791, Luigi Galvani described the role of electricity in the nerves of dissected frogs, revealing that biological processes could be driven by electrical currents. This discovery paved the way for understanding how the nervous system communicates with muscles and organs. By 1811, César Julien Jean Legallois studied respiration in animal dissection and found the center of respiration in the medulla oblongata, while Charles Bell completed work on the Bell, Magendie law, which compared functional differences between dorsal and ventral roots of the spinal cord. In the 1820s, Henri Milne-Edwards introduced the notion of physiological division of labor, comparing the body to a factory where organs worked incessantly to produce life. This concept allowed scientists to study living things as if they were machines created by human industry. Milne-Edwards wrote that the body of all living beings resembled a factory, where organs, comparable to workers, produced the phenomena that constituted life. This mechanistic view of physiology became a foundation for modern research, enabling the study of how different systems interact to maintain homeostasis.