(From to show). A rainbow. The forepart of the choroides of the eye, named from the variety of its colours. It lies floating and loose; is convex on the anterior, and concave on the posterior part; the perforation in its middle forms the pupil. The iris, by contracting or dilating, excludes or admits of light in such proportions as the variety of circumstances may require. Two orders of muscular fibres are found between the laminae of the iris; one circular, the other radiated, which produce these actions. See Uvea, Choroides, and Circulus arteriosus.

The operation of cutting the iris is required when a cataract adheres to it; and when, from the contraction of its muscular fibres, the pupil is closed up, a disease called synizesis, or caligo pupillae, is produced. Mr. Sharp, in his Operations, chap. xxix. directs the operator to proceed as follows: Place the patient as for couching; open and fix the eye with the speculum oculi; then introduce the knife in the same part of the conjunctiva that is wounded in couching; insinuate it with its blade held horizontally, and the back of it towards you, between the ligamentum ciliare and circumference of the iris, into the anterior chamber of the eye; and, after it is advanced to the further side, make your incision quite through the membrane; and, if the operation succeeds, it will, upon wounding, fly open, and appear a large orifice, though not so wide as it becomes afterwards. Mr. Sharp further observes, that when the pupil is contracted from a paralytic disorder, this operation cannot be encouraged.

Iris. A species of rash, included by Dr. Willan in his third order of exanthemata; but we have not yet received his description and explanation. We may find an opportunity of resuming this subject, if the number appears in time. See Cutanei morbi.

Iris, (from the resemblance of its flower to the rainbow). It is a perennial plant, with long, narrow, sword like leaves standing edgewise to the stalk, and naked flowers divided deeply into six segments, of which alternately one is erect, and another arched downward, with three smaller productions in the middle, inclosing the stamina and pistil: the roots are tuberous, irregular, and full of joints. (See Erysimum.) It is a name likewise of the hedge mustard, hermodac-tylus; a kind of ginger; a species of xyphium, and of a pastil, consisting of alum, saffron, myrrh.

Iris florentina. Florentine orris; iris I/lyrica, and white flower-de-luce, iris florcntina Lin. Sp. Pl. 55. It is supposed to be only a variety of the common iris; but its roots are brought from Italy, as superior to our own. They are in oblong, flattish pieces,frced from the fibres, and brownish externally, but with brownish specks internally, and easily reduced to a farinaceous powder.

The root, in its recent state, is nauseous, acrid, and purgative, but loses these qualities by drying. The dry root is unctuous, bitterish, and pungent; the taste not strong, but durable; with a light, agreeable smell, which resembles violets, or rather raspberries; and communicates a similar flavour to spirits and to wines.-as a medicine, the fresh root is a powerful cathartic; and its juice has been employed in the dose of 3 i. in dropsies: when dry it is a demulcent, and an expectorant, attenuating viscid phlegm, and promoting its discharge; but Dr. Cullen considers it as insignificant in this state. When cut in the form of peas it is used for promoting the discharge in issues.

In distillation it yields all its flavour to water; its bitter remaining in the extract. Rectified spirit brings over a part, and the extract is bitter and pungent in the mouth. See Lewis's Materia Medica; Neumann's Chemical Works.