Disease Results from Imbalance of Four Bodily Humours

The four-humours doctrine, inherited from Galen and Hippocrates, persisted in Britannica's medical entries far longer than in the most advanced clinical work, by the 1790s, leading physicians were already sceptical of strict humoralism, yet the encyclopedia continued to present it as established medicine. The theory had powerful appeal: it provided a mechanistic explanation for diverse phenomena (why anger reddens the face, why melancholy lingers), and bloodletting and purgatives, the prescribed treatments, sometimes provided temporary symptomatic relief (or seemed to, through the placebo effect and natural recovery). By the 1850s–1870s, the germ theory of disease and microscopic pathology rendered humoralism incoherent. Britannica gradually de-emphasised humoral explanations, replacing them with entries on bacterial infection, cellular inflammation, and specific disease etiologies.