De variolis et morbillis commentarius.

The first medical description of smallpox was written by Rhazes, about the year 910… The above work is the first edition of the Arabic text with a parallel Latin translation by the English pharmacist and scholar, John Channing, concerning whom see E. Savage-Smith, "John Channing: Eighteenth-century apothecary and arabist," Pharmacy in history, 30 (1988) 63-80. For an English translation see Medical Classics, 1939, 4, 22-84. A translation was also published by the Sydenham Society, 1848. See Nos. 2527 & 5441. In his Treatise on the smallpox and measles, Rhazes stated that survival from smallpox infection prevented an individual from ever acquiring the disease again. His explanation for why the disease does not strike the same individual twice is the first theory of acquired immunity.