 As the title of "Doubts on Galen" by al-Rāzi implies, as well as the writings of physicians such as Ibn Zuhr and Ibn al-Nafis, the works of Galen were not accepted unquestioningly, but as a challengeable basis for further inquiry.A strong emphasis on experimentation and empiricism led to new results and new observations, which were contrasted and combined with those of Galen by writers such as al-Rāzi, Ali ibn Abbas al-Majusi, Abu al-Qasim al-Zahrawi, Ibn Sina (Avicenna), Ibn Zuhr and Ibn al-Nafis.For example, Ibn al-Nafis' discovery of the pulmonary circulation contradicted the Galenic theory on the heart.