AS TO SOUNDNESS. 15 



The iris we have already partially noticed. Care 

 should be taken to ascertain whether this important 

 muscle is in proper tone. Excluding the light from 

 the eye with both the hands, then suddenly uncover- 

 ing the eye under examination, will determine the 

 amount of tone the iris possesses. It should diminish 

 and enlarge the pupils slowly and steadily, but ob- 

 viously. Sometimes the "corpora nigra" hang more 

 loosely than usual, or they may be actually torn. I 

 have known several instances of hunters falling on 

 their heads and displacing these little black bodies. 

 When so displaced, the circumstance is not of import- 

 ance in itself, but the blow which caused it may have 

 displaced the lens, or even partially ruptured the cap- 

 sule of the lens, when — the aqueous humour being 

 admitted into that body — cataract results in the course 

 of a few hours. This is the explanation of cataract 

 suddenly forming after a severe fall or blow on the 

 head. 



The lens and its capsule next engage our attention. 

 After the cornea they are of most importance. 



Since the use of the ophthalmoscope has become 

 general, the catoptric test is now no longer used by 

 skilful surgeons in examining the lens, the oblique 

 illumination and the mirror of the ophthalmoscope 

 having quite displaced it. Although you may not 

 be able to use an ophthalmoscope in its entirety, still 

 you ought to carry one. The lens you use for oblique 

 illumination, and the mirror part, with a light, can be 



