Hippocrates (460-370 BC) was a Greek physician who is generally considered to be the father of medicine, although little is actually known about him. His influence survives in the Hippocratic oath, a code of medical ethics some medical students take on completion of their training. He founded a medical school on the Aegean island of Cos, where his ideas on medical conduct and practice were implemented. He advocated a rational approach to medicine, believing that disease was caused by physical phenomenon and not by the interference of the gods. Plant extracts, including willow bark and spiraea, of which salicylic acid was the active ingredient, had been known to help alleviate headaches, pains, and fevers since antiquity. Hippocrates left historical records describing the use of powder made from the bark and leaves of the willow tree to help these symptoms.