"It is of frequent occurrence to find the capsule of the lens stained with black spots; these are stains left by the uveal pigment, and occur usually after an attack of iritis, when the iris has been in contact with the lens. When the iris has been adherent, a complete ring of pigment may often be seen on the surface of the lens. A day's experience at any ophthalmic clinique can mostly show examples of this condition; but it is only when these deposits are numerous, and in the central line of vision, that they become troublesome. They are then met with as the sequences of severe choroido-iritis, and usually coincide with further mischief in the vitreous and choroid. "The vitreous, under the influence most commonly of choroiditis, and usually syphilitic choroiditis, presents alterations of the most striking character for ophthalmoscopic observation. The patients who offer these changes complain usually of considerable dimness of sight, which on examination is found to include both diminution in the acuteness of visual perception, and restriction in _the field of vision_, or extent of any object seen at once. The great source of trouble to them is, that when they lift the eye or move the head, black corpuscles, or streaks, or webs float before their eyes, and obscure the object at which they are looking; and when the eyes are kept still, these fall again and disappear. Examine now the eyes of such an one, and you will see that the phenomena described are due to the existence of actual shreds, corpuscles, or webs of fibrous and albuminous exudation, which float in the vitreous, and at each motion of the eye rise in clouds and obscure the fundus, so that you can barely see it, or perhaps not at all. These conditions, I say, are mostly specific, but not invariably. They are sometimes the result of scrofula, and probably of other forms of choroiditis." Here, then, are a large number of cases in which the ophthalmoscope transports us at once from the regions of the known to the unknown. There are other classes of cases equally striking. Let me take illustrative examples. Two persons apply for advice, complaining that the sight has been gradually growing more and more dim, perhaps in one eye,--it may be in both. The progress of the disease has been insidious and nearly painless. The eyes are to all external appearance healthy, except probably that in both patients the pupils are partially dilated and sluggish. The ophthalmoscope helps us to solve the problem.