mind one of the experience of Shelley's
Frankenstein. Franke's patient was successfully operated on for
congenital double cataract, at twenty-six years of age. The author
describes the difficulties the patient had of recognizing by means of
vision the objects he had hitherto known through his other senses, and
his slowness in learning to estimate distances and the comparative size
of objects.

Sight is popularly supposed to be occasionally restored without the aid
of art, after long years of blindness. Benjamin Rush saw a man of
forty-five who, twelve years before, became blind without ascertainable
cause, and recovered his sight equally without reason. St. Clair
mentions Marshal Vivian, who at the age of one hundred regained sight
that for nearly forty years had gradually been failing almost to
blindness, and preserved this new sight to the time of his death.

There are many superstitions prevalent among uneducated people as to
"second sight," recovery of vision, etc., which render their reports of
such things untrustworthy. The real explanations of such cases are too
varied for discussion here.

Nyctalopia etymologically means night blindness, but the general usage,
making the term mean night-vision, is so strongly intrenched that it is
useless and confusing to attempt any reinstatement of the old
significance. The condition in which one sees better by night,
relatively speaking, than by day is due to some lesion of the macular
region, rendering it blind. At night the pupil dilates more than in the
day-time, and hence vision with the extramacular or peripheral portions
of the retina is correspondingly better. It is, therefore, a symptom of
serious retinal disease. All night-prowling animals have widely
dilatable pupils, and in addition to this they have in the retina a
special organ called the tapetum lucidum, the function of which is to
reflect to a focus in front of them the relatively few rays of light
that enter the widely-dilated pupil and thus enable them the better to
see their way. Hence the luminous appearance of the eyes of such
animals in the dark.

Hemeralopia (etymologically day-blindness, but by common usage meaning
day-vision or night-blindness) is a symptom of a peculiar degenerative
disease of the retina, called retinitis pigmentosa. It also occurs in
some cases of extreme denutrition, numerous cases having been reported
among those who make the prolonged fasts customary in the Russian
church. I