Ir`ri*ta*bil"i*ty (?), n. [L.
irritabilitas: cf. F. irritabilité.]
1. The state or quality of being irritable;
quick excitability; petulance; fretfulness; as, irritability
of temper.
2. (Physiol.) A natural
susceptibility, characteristic of all living organisms, tissues, and
cells, to the influence of certain stimuli, response being manifested
in a variety of ways, -- as that quality in plants by which they
exhibit motion under suitable stimulation; esp., the property which
living muscle possesses, of responding either to a direct stimulus of
its substance, or to the stimulating influence of its nerve fibers,
the response being indicated by a change of form, or contraction;
contractility.
3. (Med.) A condition of morbid
excitability of an organ or part of the body; undue susceptibility to
the influence of stimuli. See Irritation,
n., 3.