Galen’s most significant contribution was to synthesize existing knowledge, including the Ancient Greek heritage of humoral medicine. However, he also made original observations. He was the first to convincingly demonstrate that arteries contain blood. His argument that blood must normally pass from veins to arteries via anastomoses in the lung and periphery was novel as was his misguided reference to imaginary holes in the interventricular septum. The question of how blood got from the right ventricle of the heart to the left ventricle would challenge investigators for the next 1500 years. Its answer would provide an important clue about the circulation of blood.

Source: Wiley Online Library