Cleveland morning leader. [volume] (Cleveland [Ohio]) 1854-1865, 1864-01-21

| ject in view only ID. >. STEVENs.
The Eye.
The following is communicated by DR.. ].
F. Lawrence, the celebrated OcuIist and Au-
rist, from New York, who can be consulted
daily on all diseases of the Eye and Ear, at
the American Hotel, from 9A.M. to 5P.x.:
The Eye is nearly round in shape, with a
slight projection in front-henoe commonly
called the eyo-bsll or globe Of the eye. This
particular form is the very best that could be
contrived to enable it to move about with the
greatest facility and rapidity.
The Eye consists Of three orders or classes
/ of psrts-the first admit and modify the rays
Of light; the second receive and carry the i'm
pressions to the brain; and the third keep
those organs in q fitting state to fulfill their
functions.
The Eye is protected on all sides by the
bony socket, in Wkioh 1t is lodged, except in
front, and here We have the eye-lids, like
watchfaI Sentinels, ever on the alert, to guard
and protect it from approaching danger.
The Eye is composed Of four oosts-the
/ Sclerotic, the Choreid, the Retina, and the
| Cornea, and three humours-the Aqueous,
| the VitreOus and the Chrystsllins.
These humors or lenses are transparent
ed and supported by some strong substance.
For this purpose We have the outer coat or
case, termed the Sclerotic, or the " white of
the eye." Itis a strong and dense sub
stance, and exteI dS, surrounding the eye,
/ from the optic nerve behind to the Cornea in
/ front. Here it Is cut of and bsveled, so as
to allow the COrnea to ft into it, as a watch
| glass into its case. The SoIerotic is opaque,
| It being necessary not to admit any light ex-
oept through the pupil, just as the opician
| finds 1t essential to make the case for his
telescope impervious to light, and it Is out
of before to allow 3 space for the transpsr-
ent msmbrane-the Cornea. We shall here
after see that the muscles which give motion
to the bali, are attached to this case. The
Sclerotic in fishes is very dense and strong
and in many birds it consists of three lay
srs, the middle one being formed of bony
plates.
The COrnsa is the clear, polished and brill
liant substance that forms the front of the
eye. It is very tough and strong, so as to
protect the darts within and yet it is per-
fSetly transparent to admit tho rays Of light,
which are here first refracted.
Within the SclerOtic lies the Choroid,
which, like the former, is wanting In front.
It is very fine and delicate, and full Of blood
vessels. These secreto q dark ooloring mat
ter, the Pigmsntgm Nigrum, with which its
entire surface is coated or painted. This
dark substance absorbs all the supeIfuous
rays of light. 1t is wanting in the Albino
or animals of prey. These cannot see dis
tinstly into bright, strong light, but in dar-
ker situations their eyes concentrate snd re-
feet the light, and their power of vision is
then much more acute. The eyes of cats,
and such animals, appear in the dark to glow
with particular ferOeity this is not owing
to the animals being excited, but is occa-
stoned by the want Of this dark pigment.
The Choroid, externally, seems to terminate
In front, where the Sclerotio and COrnea are
Joined together, and where it is connected
with a white ring or ligamsnt, but it extends
inwsrds in the form of sixty or seventy beau
tiful folds, or processes, called the Cilisry.
These are arranged in a radiated manner
around the lens, on the front of the vitreous
humour; each Of these folds is covered With
the dark pigment, similar to the choroid
itself.
Interior Of the Choroid is the RslinG; this
is an expansion Of nervous matter connected
with the optic nerve. 1t is thin and deli
cato membrane, which commences at the
optic nerve, and extends around the sides Of
the Vitreous humOur, nearly as far forward
as the lens. 1t can be divided into three
layers. The external or serious was diseov
cred by DR.. Jacob, of Dublin, and called
after him the membrane jacob, or membrane
of Jacob. It is extremely delicste and fine
The second, or nervous, is soft a1d gray; and
the internal is vascular. The retins is, as
we have observed above, the nervous expan-
sion, and on it the inverted image Of the OBJ
ject we look at is depicted, just as We have
seen in the camera obscura.
We have said the humOurs of the Eye are
three in number-the Aqueous Yitreous and
Crystalline.
The Aqueous hVBour is a clear Watery fluid,
as its name implies; 1t is situated immedis-
tsly behind the cornsa, which it distsnds and
supports. This fluid passes from the front to
the back chamber of the eye through the
pupil. It aids slightly in reiraction. There
is q beautiful provision made (the membrane
Of the aqueous humour) whereby if it is lost
through wound Of the oornea, 1t is again
renewed within q few hours. The Aqueous
humOur is also of grest use in supporting and
enabling the iris to float about with perfect
freedom.
The Iris is the ooIored curtain which we
see on looking into the eye. It derives Its
name of iris or rainbow from the variety Of
cOlors it presents. It is a fat membrane,
circular in form, with round aperture in the
center this is the black spot, termed the
pupil, or sight Of the eye. The Iris divides
the eye into front and back chamber, and
these communicate through the central aper-
ture-the pupil. The Iris is very important
to vision it acts as curtain, regulating the
quantity of light that is admitted to the eye,
SO that the pupil contracts in bright light,
and enlarges in darkness or moderate light.
This can be observed by sitting opposite to
mirror and closing the eye for few seconds;
then suddenly opening them. We see that in
the interval, the pupil has become much en-
larged and now quickly diminishss.
It is to the Iris that the eye owes its
greatest attractions. Poets have sung of the
beauty Of the black and the gray. Lord
Byron says
"Blue eyes, OF Gray,
The last, if they have soul, are quite as good,
Or better as the best examples say;
Napoleon's, Mary's Queen OF Seotland) should
Lend to that color trancencent ray;
And Pallas also sanctions the same hue
Too wise to look through optics black or blue"
The Crystalline humor or lens is a trans
parent body of considerable frmness, having
the form Of double convex lens, and is
placed perpendie ulsrly behind the pupil it
is imbedded in the fore part Of the vitreous
humOr. The lens is the principal magnifsr
Of the eye
The third, or Vitreous hnmor, forms the
main bulk of the globe of the eye, filing its
two posterior thirds /; it is thin and watsry,
but is contained in numerous cells which
prevent its running out when cut or wounded.