Rāzī’s Kitāb fī 'l-Jadarī wa-'l-ḥaṣba, or Liber de variolis et morbillis, is considered the oldest and most important original work on smallpox and measles, and a distinct original contribution to medicine by the Arabians. A pioneering work, it was the first to distinguish differences between the two diseases and noted for the modernity of its approach to clinical detail. It is followed here by translations of sections on the same subject from his Kitāb al-Manṣūrī (Liber ad Almansorem), Taqsīm al-`ilal (Divisio morborum) and Kitāb al-Ḥāwī (Liber continens). This version includes a detailed bibliography of previous editions and translations, from 1498 to 1787; the text of the Greek translator's preface; an extract from Richard Mead's preface to his Latin version, translated into English by Thomas Stack (1748); the Latin preface of John Channing's 1766 edition of the Arabic text; and the Latin preface of Albert von Haller's Latin version (1772). There are extensive 'Notes and Illustrations' and Arabic and English indexes. The Sydenham Society was a London-based publisher of classic medical works. William Greenhill (1814–94) was a physician and sanitary reformer who in the 1840s turned his attention to the study of Arabic and Greek medical writers.