pneuma, what we can call air in a very loose translation, was thought to be the primordial matter upon which all life is based; thus, the cause of all diseases was a disturbance among the body's humors which created an imbalance of the pneuma in the body. This belief that an imbalance of some form of substance or substances within the body caused all diseases was to be a recurring theme in the history of medicine, and would haunt the development of medicine well into the 19th century.