Walter Cannon Coined Both "Fight or Flight" and "Homeostasis" — From Watching Cats Eat

Walter Bradford Cannon was a first-year medical student at Harvard in 1898 when Wilhelm Röntgen's X-ray was three years old and not yet a clinical instrument. Cannon got hold of an apparatus, fed cats and dogs a paste of bismuth subnitrate, and produced the first real-time radiographs of mammalian digestion — the rhythmic constriction of the esophagus pushing food down, the way the stomach tilts during peristalsis. He published the work as a Harvard medical student. The technique he developed (later refined to use barium) is essentially the modern barium swallow.

What he kept noticing in those films was that the digestion stopped when the animal was scared. A cat that heard a strange noise across the room would freeze, stop the gastric churning, and not resume for several minutes after the threat was gone. By the early 1910s, Cannon had built a coherent theory around the observation. His 1915 book Bodily Changes in Pain, Hunger, Fear and Rage introduced the term "fight or flight" and traced the physiology — adrenal activation, redirection of blood from the gut to the muscles, glycogen conversion. The point was that the body's response to threat is integrated and biochemical, not metaphysical.

The sequel argument arrived in 1932 with The Wisdom of the Body, in which Cannon coined the word homeostasis to describe the way the body keeps blood pH, temperature, glucose, and electrolytes within tight ranges through dozens of feedback loops running simultaneously. The framing — the body as a self-regulating system rather than a passive plumbing arrangement — has been load-bearing in physiology, medicine, and engineering ever since. During WWI, Cannon also pioneered sodium-bicarbonate infusion as a treatment for surgical shock; the protocol saved lives at field hospitals through 1918.