. Materia medica : pharmacology, therapeutics and prescription writing for students and practitioners. into an excised mammal eye, the pupil dilates, and if ananimal is atropinized, stimulation of the third nerve, eithercentral or peripheral to the ciliary ganglia, is without effect onthe pupil. The action is, therefore, a purely peripheral it is not a direct effect upon the muscle, for in the atropinized 378 PHARMACOLOGY AND THERAPEUTICS animal direct stimulation of the circular muscle results in con-traction; therefore the site of the paralyzing action of the drugmust be confined to
. Materia medica : pharmacology, therapeutics and prescription writing for students and practitioners. into an excised mammal eye, the pupil dilates, and if ananimal is atropinized, stimulation of the third nerve, eithercentral or peripheral to the ciliary ganglia, is without effect onthe pupil. The action is, therefore, a purely peripheral it is not a direct effect upon the muscle, for in the atropinized 378 PHARMACOLOGY AND THERAPEUTICS animal direct stimulation of the circular muscle results in con-traction; therefore the site of the paralyzing action of the drugmust be confined to the third-nerve endings or the neuromuscularjunction. The dilatation from atropine is, therefore, the result of theunopposed action of the radial muscles. It is, however, fre-quently strong enough to break weak adhesions between corneaand iris, or to make an iris which is strongly attached at twopoints bow out between the points of attachment. The pupilgradually regains its power, but is not fully restored to normalfor one or two weeks. That there is no stimulation of the radial mechanism is evi-. Fig. 46.—Increased convexity of the lens during accommodation. The solidwhite outline of the lens, /, shows its form when relaxed. The dotted line showsthe increased curvature of the anterior surface during accommodation, and itsadvancement forward into the anterior chamber, a. z is the suspensory ligament;m, the ciliary muscle; and i, the iris (Landolt). dent, for, after atropine, stimulation of the cervical sympa-thetic results in a still greater dilatation; and, in addition, afterremoval of the superior cervical ganglion and the subsequentdegeneration of the sympathetic nerve-fibers, atropine fails todilate the pupil. A drug which causes dilatation of the pupil is called a mydri-atic. Belladonna gets its name from this mydriatic action (bella,beautiful; donna, lady), which makes the eye seem bright andsparkling. (b) Accommodation depends essentially on the curvatureof the crystal
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