Herophilus' fellow researcher in Alexandria was Erasistratus, who lived between 310‑250 B.C.E., and who was renowned as the father of physiology, though not the physiology we study today. He rejected the concept of the 4 elements of Empedocles and the 4 humors. Instead, Erasistratus looked to the body's tissues and organs as the location of diseases, a relatively modern sounding concept.  He also believed that the blood provided nourishment throughout the body and that pneuma, which we can define as air, was the substance required for life.