INSIDE THE EYE. 
467 
of acuteness in tlie perception of small objects^ the warning 
is very urgent. A diminution in the field of vision is another 
important indication of internal changes in the eye, of which 
only the ophthalmoscope can detect the true nature. It would 
be difficult, perhaps, to say whether more mischief is done 
and more suffering is caused by the total neglect of such 
symptoms or by their ignorant palliation by the aid of common 
spectacles, chosen empirically, because they facilitate vision for 
the time. The great use of the ophthalmoscope, then, is this : 
that it arms us with an instrument of precision, by which 
we can determine the precise local condition of the parts of 
the eye in which the function of sight is resident and through 
which it is regulated. If it cannot do all that we might ask, 
it is because the sense of sight is in truth a cerebral function, 
of which the eye is only an instrument ; and in dealing with 
cerebral affections of the sight, it can indeed give us informa- 
tion which without it we should lack, but it leaves still to be 
desired more intimate acquaintance with first causes, which at 
present we can only discuss infer entially. To the amateur in 
science, and to the lover of nature, it discloses an exquisite 
spectacle, unknown till now, that carries observation into 
the inner chambers of the living eye, and displays its wonders 
and its beauties- The observation is perfectly painless, and 
may easily be effected : rabbits, for example, submit to it 
with great calmness and composure, and at the College of 
Physicians^ soiree last year, a little pet white rabbit of mine 
sat up calmly in a box which I had made for the purpose, and 
was examined, by the aid of a modification which I devised of 
Liebreicffis demonstrating ophthalmoscope, by many score of 
observers. Another modification of Liebreicffis ophthalmo- 
scope by Messrs. Smith and Beck is figured on page 458. Mine 
has the advantage of being adapted for use even amid a blaze 
of light, and it cannot easily be disarranged ; two qualities 
valuable in an instrument for demonstration. 
2 I 
VOL. IV. NO. XVI. 
