pneuma

In ancient medicine, pneuma referred to a subtle vapor or invisible liquid believed to be essential for life and associated with respiration. The Alexandrian medical school, particularly the physician Erasistratus around 300 BC, theorized that pneuma was a vital spirit formed in the heart from air. This "vital spirit" was thought to travel through arteries, while a second type, the "animal spirit" formed in the brain, moved through nerves and caused movement. Erasistratus believed that disruptions to pneuma's function or an excess of blood caused disease, though he favored diet over bloodletting to manage these conditions. The concept of pneuma also extended to theology, referring to the soul or spirit, and to Stoic philosophy, where it was seen as a divine organizing principle of the universe.12