By means of compositional devices and a masterful use of Greek language that the author adapts to the contents, Galen achieves an accurate and didactic exposition, which presents the vivacity of oral speech. Dealing with a humoral unbalance that is on the basis of many local and general affections inflammation and fevers among them , this small treatise also includes key notions of Anatomy and Physiology. On those grounds it became a bestseller in the Middle Ages and the Renaissance (translations into Syrian, Arabic, Latin 8 versions and Hebrew; 14 commentaries from 1290 to 1567). This first critical edition presents a continuous text no chapters and points to the internal structure created by the author in order to make his text readily accessible and unforgettable. A thorough Introduction the textual transmission, the fundamental topics , is coupled by an ample Commentary that deals with alteration and pain, qualities and humours, no less than with scribal errors and grammatical explanations.