In this deliberately maintained ambiguity regarding the notion of irritation, the medicine of the late eighteenth century can demonstrate a continuity between a disposition (irritability) and a pathological event (irritation), but it can also maintain at the same time the idea of a condition particular to an organ, which experiences, in its own individual way, a generalised attack (the sensibility of each organ assuring this communication, which remains discontinuous), and the idea of a propagation inside the organism of a single condition that might attack any of its parts (the mobility of the fibres ensures that continuity, despite the different forms that it takes in different organs).