Like imhotep and Asclepius, though to a lesser degree, Hippocrates' life is so shrouded in myth that it is difficult to state many facts about the man. He certainly existed, hwoever, and was one of the first to apply true rules of logic and science to the practice of medicine. This was possible largely because of the changes made in philosophy both by the pre-Socratics, who determined that the gods were not responsible for the laws of nature, and the major Athenian philosophers such as Socrates, Plato, and Aristotle, who developed a system of rigorous logic that was attached to investigations of truth. Hippocrates focused on keeping the body healthy through preventative medicine, and that the body would often return to its natural state unaided -- thus the injunction to "do no harm."

Galen, a Greek physician...

His knowledge of the nervous and circulatory systems became extensive, however, especially when he was given gladiators with traumatic wounds that he could investigate. He didn't save as many as he possibly could have, instead taking time to increase his knowledge of anatomy. Galen's knowledge and reputation grew, affording him more opportunities both to practice medicine and to learn about human and animal anatomy, and also unfortunately giving him the prominence to start the widespread and long-lived practice of bloodletting -- not nearly as useful as the medicines compiled in his contemporary Dioscorides De material medica.