Abū Bakr Muhammad Zakariyyā Rāzī (Persian: ابوبكر محمّد زکرياى رازى‎ Abūbakr Mohammad-e Zakariyā-ye Rāzī, also known by his Latinized name Rhazes (/ˈrɑːziːz/) or Rasis; 854–925 CE), was a Persian polymath, physician, alchemist, philosopher, and important figure in the history of medicine. He also wrote on logic, astronomy and grammar. According to the Encyclopædia Britannica (1911), he was among the first to use humoral theory to distinguish one contagious disease from another, and wrote a pioneering book about smallpox and measles providing clinical characterization of the diseases.