Part 398

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.

Ir"ri*ta*ble (?), a. [L. irritabilis: cf. F. irritable. See Irritate.]

1. Capable of being irritated.

2. Very susceptible of anger or passion; easily inflamed or exasperated; as, an irritable temper.

Vicious, old, and irritable.

Tennyson.

3. (Physiol.) Endowed with irritability; susceptible of irritation; capable of being excited to action by the application of certain stimuli.

4. (Med.) Susceptible of irritation; unduly sensitive to irritants or stimuli. See Irritation, n., 3.

Syn. -- Excitable; irascible; touchy; fretful; peevish.

Ir"ri*ta*ble*ness, n. Irritability.

Ir"ri*ta*bly, adv. In an irritable manner.

Ir"ri*tan*cy (?), n. [From 1st Irritant.] (Scots Law) The state or quality of being null and void; invalidity; forfeiture. Burrill.

Ir"ri*tan*cy, n. [From 2d Irritant.] The state or quality of being irritant or irritating.

Ir"ri*tant (?), a. [LL. irritants, -antis, p. pr. of irritare to make null, fr. L. irritus void; pref. ir- not + ratus established.] (Scots Law) Rendering null and void; conditionally invalidating.

The states elected Harry, Duke of Anjou, for their king, with this clause irritant; that, if he did violate any part of his oath, the people should owe him no allegiance.

Hayward.

Ir"ri*tant, a. [L. irritans, -antis, p. pr. of irritare: cf. F. irritant. See Irritate to excite.] Irritating; producing irritation or inflammation.

Ir"ri*tant, n. [Cf. F. irritant.]

1. That which irritates or excites.

2. (Physiol. & Med.) Any agent by which irritation is produced; as, a chemical irritant; a mechanical or electrical irritant.

3. (Toxicology) A poison that produces inflammation.

Counter irritant. See under Counter. -- Pure irritant (Toxicology), a poison that produces inflammation without any corrosive action upon the tissues.

Ir"ri*tate (?), v. t. [See 1 st Irritant.] To render null and void. [R.] Abp. Bramhall.

Ir"ri*tate, v. t. [imp. & p. p. Irritated (?); p. pr. & vb. n. Irritating (?).] [L. irritatus, p. p. of irritare. Of doubtful origin.]

1. To increase the action or violence of; to heighten excitement in; to intensify; to stimulate.

Cold maketh the spirits vigorous and irritateth them.

Bacon.