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 
