One of the greatest names in medieval medicine is that ofAbu Bakr Muhammad ibn Zakariya' al-Razi, who was born in the Iranian City of Rayy in 865 (251 H) and died in the same town about 925 (312 H). A physician learned in philosophy as well as music and alchemy, he served at the Samanid court in Central Asia and headed hospitals in Rayy and Baghdad. A story is related that he was instrumental in determining the location in Baghdad of the hospital founded by `Adud al-Dawlah, for he is said to have chosen its position by hanging pieces of meat in various quarters of the city and finding the quarter in which the putrefaction of the meat was the slowest. Since, however, the `Adudi hospital was founded in 980 (370 H), more than 50 years after al-Razi died, it must be an earlier hospital, probably the one founded during the reign of al-Mu`tadid (ruled 892-902/279-289 H), which he helped locate and of which he was later director.

The most sought after of all his compositions was The Comprehensive Book on Medicine (Kitab al-Hawi fi al-tibb) -- a large private notebook or commonplace book into which he placed extracts from earlier authors regarding diseases and therapy and also recorded clinical cases of his own experience. The material comprising the Hawi is arranged under headings of different diseases, with separate sections on pharmacological topics. The National Library of Medicine is fortunate in having the oldest recorded copy of this treatise, or rather part of the treatise, for the manuscript contains only the section on gastrointestinal complaints. The unnamed scribe completed the copy on the 19th of the month Dhu al-Qa`dah in the year 487 of the Muslim era, which is equivalent to 30 November 1094.

Following al-Razi's death, Ibn al-`Amid, a statesman and scholar appointed vizier to the Persian ruler Rukn al-Dawlah in 939 (327 H), happened to be in the town of Rayy and purchased from al-Razi's sister the notes comprising the Hawi, or Comprehensive Book. He then arranged for the pupils of al-Razi to put the notes in order and make them available. The Hawi is an extremely important source for our knowledge of Greek, Indian, and early Arabic writings now lost, for al-Razi was meticulous about crediting his sources. Moreover, the clinical cases, while not unique, are the most numerous and varied in the Islamic medieval medical literature.
Europe knew al-Razi by the Latinized form of his name, Rhazes. His Comprehensive Book on Medicine, the Hawi, was translated into Latin in 1279 under the title Continens by Faraj ben Salim, a physician of Sicilian-Jewish origin employed by Charles of Anjou to translate medical works. Even more influential in Europe was al-Razi's Book of Medicine Dedicated to Mansur, a short general textbook on medicine in ten chapters which he had dedicated in 903 (290 H) to the Samanid prince Abu Salih al-Mansur ibn Ishaq, governor of Rayy. The treatise was translated into Latin in Toledo by Gerard of Cremona (d. 1187) and was known as Liber ad Almansoris. It became one of the most widely read medieval medical manuals in Europe, and the ninth chapter, on therapeutics, frequently circulated by itself under the title Liber nonus ad Almansorem. In the Renaissance many editions of it were printed with commentaries by the prominent physicians of the day, such as Andreas Vesalius.
A third treatise by al-Razi that was also influential in Europe was his book on smallpox and measles (Kitab fi al-jadari wa-al-hasbah). His was not the earliest monograph on the subject -- that honor goes to Thabit ibn Qurrah, a 9th-century Sabian Syriac-speaking translator and scholar working in Baghdad who became one of the great names in the history of Islamic science, especially in mathematics and astronomy. Al-Razi's treatise on smallpox and measles was, however, the more influential and was twice translated into Latin in the 18th century at a time when there was much interest in inoculation or variolation around 1720 following the description of the procedure in Turkey by Lady Mary Wortley Montagu, wife of the Ambassador Extraordinary to the Turkish Court in Istanbul.
Among al-Razi's smaller medical tracts were treatises on colic, on stones in the kidney and bladder, on curing diseases in one hour (such as headache, toothache, haemorrhoids, and dysentery in small children), on diseases of children, on diabetes, on food for the sick, on maladies of the joints, on medicine for one who is unattended by a physician, on medical aphorisms, and on the fact that some mild diseases are more difficult to diagnose and treat than the serious ones. He also composed a book on the reason why the heads of people swell at the time of the roses and produce catarrh, in which he was apparently the first to relate hay fever to the scent of roses.
Throughout his writings, al-Razi displayed a primary interest in therapeutics, lacking the concern of later writers for refining the classification of symptoms. He was not in such awe of Galen that he refrained from correcting him, but his criticism was in the areas of logic and clinical applications. For example, he said that in his experience in hospitals in Baghdad and Rayy he had seen as many cases whose courses did not follow Galen's description of fevers as did. He also stated in regard to a certain urinary ailment that, while Galen had seen only three cases, he had seen hundreds and consequently knew more about it. While al-Razi was critical of specific points, one can only conclude that he considered the medical theory adequate for his purposes, for he displayed no interest in altering its theoretical foundations.