The well-known writer George Sarton says in his Introduction to the History of Science that "Rhazes was the greatest physician of Islam and the Medieval Ages." And the Encyclopedia of Islam remarks that "Rhazes remained up to the 17th century the indisputable authority of medicine." The Bulletin of the World Health Organization (WHO), May 1970, pays tribute to him by stating: "His writings on smallpox and measles show originality and accuracy, and his essay on infectious diseases was the first scientific treatise on the subject." Abu Bakr Muhammad Ibn Zakariya Al-Razi was born at the Persian city of Ray near modern Tehra