328 Veterinary Medicine. 



existence only, but the exact seat of such opacit}^ is easily demon- 

 strated. Opacities on the cornea cause blurring of the bright, 

 erect image of the flame as it passes over that part : opacities on 

 the anterior capsule of the lens blur the dim, erect image when 

 passed over them : finally, opacities in the body of the lens or 

 on its posterior capsule, blur the small inverted image as it passes 

 over them. 



Add to this method the oblique focal illumination and the 

 images of the flame reflected from the three mirror surfaces 

 (cornea, anterior and posterior lens surfaces) are made much 

 clearer and more distinct than in any other way. To do this 

 effectively the convex lens should be held so as to focus the flame 

 in the air nearly in front of the cornea. The Purkinje-San.son 

 images are made very definite and clear. If the lens is ap- 

 proached nearer to the eye so as to throw the image of the flame 

 within or behind the lens, a gray phosphorescent streak of light 

 is seen in the depth of the pupil. This is due to the laminated 

 structure of the lens as well as to the fact that the lens itself is 

 not perfectly transparent even in its normal condition. The ab- 

 sence of the lens or its dislocation and displacement downward, 

 below the line of vision may be inferred from the absence of this 

 gray luminous reflection under this test. 



OPHTHALMOSCOPE. 



Principle of ophthalmoscope : Angle of incidence and angle of reflection 

 in same line, light close to one side of the eye, reflected into it by a mirror, 

 having a hole in the centre for eye of observer. Opacities show a dense 

 white in transparent media : if in front of lens move with rolling of eye : if 

 behind in opposite direction. To see fundus must use biconvex lens. 

 Emmetropic eye : myopic : hypermetropic. Static refraction. Mydriatics : 

 Atropine, homatropine, daturine, duboisine, hyoscyamine. 



In the healthy eye, the pupil and iris, and in cataract, even the 

 opaque anterior capsule of the lens, can be clearly seen. The re- 

 flection of the pupil, however, is dark and no object back of the 

 iris can be observed. The reason of the difference is that the 

 rays of light, entering through the whole cornea, are reflected at 

 the same angle at which they strike the surface of the iris. The 



