During the Middle Ages, the Arab world preserved the knowledge of the Greeks and Romans and continued to flourish intellectually while Europe lay dormant. One of the great Arab physicians of that era was Al-Razi, known in the West as Rhazes. Born in Persia, he studied in Baghdad, Palestine, Egypt, and Spain. Rhazes is well known for his description of smallpox and measles, the first authentic account of these diseases (Garrison 129). He was also the first to distinguish these two diseases from each other and to propose the theory of acquired immunity by recognizing that individuals surviving smallpox never get it again.
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