the fibres of the human lens are undoubtedly very similar in structure to those of the lower animals, and further researches will probably clear up apparent differences. Some preparation and much care in manipulation are necessary, in order to obtain satisfactory specimens. The body of the animal when killed must be treated after Dr. Beale's method, and the lens and capsule, when removed, must be allowed to soak in glycerine for a month. The capsule having been opened and the lens rolled on to a glass slide, a few of its fibres must be detached with as much care and as little disturbance as possible-this is a point of the utmost importance; they should be allowed to fall into a drop of glycerine, and be gently covered by thin glass, without pressure. They should then be examined under a one-fiftieth or one-seventieth of an inch object lens.

Two classes of leus fibres may be thus distinguished; the one consisting of flattened bands of apparently homogeneous tissue with serrated edges, and the other of fibres having a clearly defined and regular outline, within which there is an appearance of longitudinal bands, running from end to end of the fibre, connected by transverse bands with spaces between them, and similar to those I have described as composing the primitive fibre of voluntary muscle; they are, however, far more difficult to define.

The relation between these two sets of fibres is as follows. The flattened serrated band is a detached and altered lens fibre, its normal condition having been that of a fibre with definite outline and internal structure, contained in a homogeneous case; but the latter having been broken through, by displacement or manipulation, the fibre spreads out into a flattened and serrated band. Each fibre is condensed and harder towards its extremities; in the middle of its course it is flattened and softer, and therefore more easily destroyed, so that we frequently meet with fibres in which the central portion presents a flattened and serrated appearance from injury, while at either extremity it may be a perfect fibre with a dark outline, and having indications of transverse and longitudinal band swithin. If now the striated extremity of such a fibre be kept in the field of the microscope, and the object-glass be gently screwed down on the covering plate, as we increase the pressure the outline of the fibre bursts open, its internal structure disappears, and all that remains is a flattened serrated band. It would seem as if the contents were elastic and confined by the homogeneous casing, their peculiar arrangement also depending on this confinement, for the moment it is removed the fibre expands into a serrated band.

The lens is made up of layers of these fibres, disposed, as Mr. Bowman observes, like the scales of an onion, one over the other; and in order to carry out the analogy between the lens and voluntary muscle, we have only to suppose the primitive fibres of the latter arranged in layers instead of bundles. I have traced nerves over the capsule of the lens, and there is no reason to suppose they do not enter its substance, if their presence there is necessary, of which we have no evidence. The germinal matter lining the capsule of the lens is probably sufficient to produce its formed material, and in the growing lens I have found germinal

matter scattered throughout its substance, so that there are really no elements in striped muscle not to be found in the lens, except bloodvessels and connective tissue, and these, from the nature and functions of the lens, could not be admitted into its substance; moreover, they form no part of the essential elements of muscle. If this be the case, and if it has been proved that the lens dilates and contracts, in obedience to a voluntary effort, in exactly the same way that striped muscle does, surely it is far more reasonable to suppose that these changes are effected through an inherent power residing in the lens, analogous to that which exists in voluntary muscle, than to fall back upon the ciliary body, as being the active agent in the accommodation of the eye.

CHAPTER II.

Methods employed in examining the Eye, and testing the patient's Vision - The Ophthalmoscope: its Principle and Use-Ophthalmoscopic Appearances of the Healthy Eye.

EXAMINATION OF THE EYE

THE first and most essential point to attend to in examining the eye, is, that it should be illuminated by a clear, bright light. The patient may conveniently be seated before a window, the surgeon standing in such a position that no part of his person intercepts the rays of light from falling directly on the patient's eye, and yet enabling him to examine the part thoroughly.

The next thing to be done is to open the eyelids, the upper one with the thumb of one hand, and the lower with the other. This manipulation, though simple enough, requires care; even slight pressure on the diseased eyeball frequently causing pain and irritation, followed by a gush of tears from the eye, which for the moment prevents us from proceeding with our examination. The lids having been separated as far as possible, the condition of the cilia, puncta, conjunctiva, sclerotic, cornea, and iris should be carefully noticed.

There are cases, however, which baffle all our efforts to obtain a satisfactory view of these parts, the patient suffering from such intense intolerance of light that he not only involuntarily closes the lids, but if they are forcibly separated, the cornea is instantly turned upwards and inwards, to such an extent that little beyond its lower border can be seen. This difficulty is greatly increased with young children, and there seems to be only one rational method of overcoming it, which is to render the patient insensible with chloroform. This is

it

especially necessary when we are uncertain as to the Use of exact nature of the changes going on in the eye; and chloroform. appears to me a far more reasonable plan than that of fixing the patient's head between one's knees, and forcibly dragging open the eyelids, as has been sometimes recommended. There is always danger of rupturing the cornea by this rude manipulation should it happen to be ulcerated, a condition not unfrequently met with among young children suffering from great intolerance of light. If, therefore, we cannot obtain a perfectly satisfactory view of the patient's eyes, we are bound, I think, at once to render him so far insensible as may enable us thoroughly to examine them; and I repeat, it is not advisable to attempt to separate the lids by force when they are involuntarily closed by the patient, especially on a first visit.

compared.

If one eye only is diseased, it is advisable to compare The two its condition with the sound eye; slight alterations in eyes to be the colour and brightness of the iris, which may nevertheless be very significant, are often thus distinguishable, and any abnormal prominence or flattening of one cornea will be made more apparent by contrast with the other. It is, moreover, by comparative examination of this kind, that we ascertain the nature of the various derangements that are met with in connexion with the muscular apparatus and movements of the eyeball.

ment of

An instrument called a strabismometer has been de- Measurevised for measuring the degree of diplopia, or squint, strabismus. existing in any particular case. It consists of a graduated plate made to fit against the lower eyelid; under ordinary circumstances the vertical line through the pupil, when the patient looks straight in front of him, will correspond to the centre of the plate, but if the eye deviates outwards or inwards, the centre of the pupil will be one or more lines to the right or left of this spot, and the extent of the deviation is measured by referring to the marks on the scale.

The same information may be obtained by directing the patient to look at a distant object in front of him, and then making a mark on the lid opposite to the centre of the pupil of the squinting eye; if now the sound eye be closed, and the patient still directed to look at the distant object, the squinting eye will move into its normal position, and another mark must then

Activity of the pupil.

be made on the lid below the pupil; the distance between the first and second dots will measure the angle of squinting.

Examination of the Iris.-It will frequently be necessary, in examining the diseased eye, to ascertain if the iris responds to the stimulus of light, or in other words, if the pupil dilates and contracts freely. To determine this, the patient should be placed before a moderately strong light, which falls obliquely, from one side only, on the eye. The unaffected eye should be closed over with a folded cloth, so that no light can reach it. The surgeon then places himself in such a position, that while he throws a very dark shadow on the uncovered eye with his hand, he keeps the pupil well in sight. Fixing his eye on the edge of the pupil he quickly removes his hand so as to allow a bright light to fall on the eye, and then the eye is again shaded, and so If the iris be healthy the pupils will have dilated while the light was shaded from the eye, but will contract again the instant that luminous rays reach Value of its the retina. Any deviations from this rule should be

indications.

Use of atropine.

Pupil measurement.

on.

carefully noticed, for, in the absence of synechia or other mechanical impediment to the motions of the iris, the character of its response to luminous impressions affords us valuable information in many disorders affecting the deep-seated structures of the eye. The retina may, however, be extensively diseased and yet the pupils dilate and contract on the stimulus of light, and, on the other hand, an inactive and dilated pupil does not invariably indicate a diseased condition of the retina.

In all doubtful cases atropine must be applied to the eye; it often demonstrates the presence of synechia, the existence of which was unsuspected, by the pupil dilating irregularly under its influence. Should this not be the case, the atropine will still be useful in enabling us the better to examine the deeper structures with the ophthalmoscope.

An instrument called a pupillometer* has been invented to measure the size of the pupil under different circumstances. It consists of a graduated horizontal

"A Handy-Book of Ophthalmic Surgery," J. Z. Laurence, p. 4.