326 Veterinary Medicine. 



determines a permanent dilatation of the pupil and depression of 

 the optic disc : (e) The pupil is narrowed in iritis, and is less 

 responsive to atropia or other mydriatic : (f ) I,esions of the oculo- 

 motor nerve may paralyze the iris and fix the pupil. The first 

 three and the fifth of these conditions may be recognized by the 

 naked eye, alone, or with the aid of focal illumination, the fourth 

 may require the aid of the ophthalmoscope and the sixth which 

 cannot be reached by such methods, might in exceptional cases 

 be betrayed by other disorders of the oculo-motor nerve (dropping 

 of the upper eyelid, protrusion of the eyeball, squinting outward). 



13th. Coloboma {fenestrated iris), and lacerated iris are 

 recognizable by the naked eye in a good light, or by the aid of 

 focal illumination. 



14th. Tension of the eyeball {Tonometry'). Elaborate in- 

 struments constructed for ascertaining ocular tension are of very 

 little use in the lower animals. The simplest and most practicable 

 method is with the two index fingers placed on the upper lid to 

 press the eyeball downward upon the wall of the orbit using the 

 one finger alternately with the other as if in search of fluctuation. 

 The other fingers rest on the margin of the orbit. All normal 

 eyes have about the same measure of tension and one can use his 

 own eye as a means of comparison. The educated touch is 

 essential. In increased tension, the sense of hardness and resist- 

 ance, and the indisposition to become indented on pressure is 

 present in the early stages of internal ophthalmias (iritis, 

 choroiditis, retinitis), phlegmon of the eyeball, glaucoma, 

 hydrophthalmos, and tumors of the bulb. 



Oblique Focal Illumination. 



This is so essential to clear and definite conclusions and is so 

 easily practiced on the domestic animals that every veterinarian 

 should make himself familiar with the method. The method is 

 based on the fact that when two perfectly transparent media 

 touch each other a reflection of luminous rays takes place only 

 at the surface. But in case any opacity exists in any part of the 

 thickness of one of these media, it reflects the rays from its surface 

 no matter what may be its position in the medium. Thus corneal 

 opacities appear as gray blotches and under careful focal illumi- 



