Systematic Inspection of the Eye. 325 



able light. They may be still more clearly shown under focal 

 illumination (see below). 



nth. Changes in the iris and pupil may also be noticed in 

 a good light. The surface should be dark in the horse, and of 

 the various lighter shades in the smaller animals, but in all alike 

 clear, smooth and polished, without variation of shade in spots or 

 patches and without bulging or irregularity at intervals. Apart 

 from the congenital absence of pigment in whole or in part, 

 which may be found in certain sound eyes, a total or partial 

 change of the dark iris of the horse to a lighter red, brown or 

 yellow shade implies congestion, inflammation, or exudation. 

 The corpora nigra in the larger quadrupeds should be unbroken, 

 smooth, rounded, projecting masses outside the free border of the 

 upper portion of the iris. They should show a clear, polished sur- 

 face like the rest of the iris. The pupil should be evenly oval with 

 its long diameter transversely (horse, ruminant), circular (pig, 

 dog, bird), or round with an elliptical outline on contracting and 

 the long diameter vertical (cat). It should contract promptly in 

 light and dilate as quickly in darkness. Place the patient before 

 a window, cover one eye so as to exclude light, then cover the 

 other eye with the hand and quickly withdraw : The pupil 

 should be widely dilated when the hand is withdrawn and should 

 promptly contract, and it should actively widen and narrow al- 

 ternately until the proper accommodation has been secured. 

 Any failure to show these movements implies a lesion in the 

 brain, optic nerve, or eye which impairs or paralyzes vision, 

 interferes with accommodation or imprisons the iris. In loco- 

 motor ataxia the pupil contracts in accommodation to distance, but 

 not in response to light. 



12th. Other causes of pupillary immobility include : (a) 

 Permanence of a pupillary membrane, which has remained from 

 the foetal condition and may be recognized by obHque focal illu- 

 mination and invariability of the pupil : (b) Adhesion of the iris 

 to the capsule of the lens — complete or partial — in the latter 

 case the adherent portion only remains fixed, while the remainder 

 expands and contracts, giving rise to distortions and variations 

 from the smoothly curved outline : (c) Adhesion of the iris to 

 the back of the cornea — complete or partial — and leading to 

 similar distortions : (d) Glaucoma in which intraocular pressure 



