Blood theory

Blood theory is a historical medical concept suggesting that certain qualities—such as warmth, enthusiasm, and sociability—were believed to be linked to the presence of blood in the body. This theory, part of the ancient humoral system, posited that an abundance of blood made a person upbeat and lively, while too little could cause traits like melancholy. Although outdated today, it influenced early ideas about health and personality. Modern medicine has replaced this with a scientific understanding of physiology and genetics, but the blood’s vital role in oxygen transport and immune function remains central.