Imbecility.

Imbecility is a condition in which the mind is, from birth, unfitted for the active and thoughtful duties of life, and in which the person affected is said to be "half-witted," or wanting in general intellectual capacity. The condition may be attended. with moderately good health of body in early life, but as a rule there is some physical derangement connected with it, some inherent physical as well as mental feebleness due to a bad constitutional condition, such as scrofula. The family of imbeciles is, generally, very short-lived, the members of it dying of consumption, or of tubercle of the brain, or of diabetes, or of diseases dependent upon changes in the great nervous centres. Imbecility is, in many cases, of hereditary type, but, as with those who suffer from cretinism, the reproductive faculties of the imbecile are low, so that, happily, survival is not largely promoted.

Idiotcy.

Idiotcy is a born condition in which, with some constitutional physical taint, the mental faculties are below the natural intellectual development necessary for the maintenance of reasonable life. In the true idiot the head is of reduced size, and the capacity of the brain is considered to be insufficient for the manifestation of the full mental powers. The instinctive faculties and desires are either not controlled by the reason, or are imperfectly controlled. Many idiots are deaf and dumb, but most of them retain the power of sight. They are unimpressionable to a large extent. Their reproductive faculties are commonly either absent or in abeyance, and their lives are comparatively short.

CHAPTER VI.

DISEASES OF THE ORGANS OF THE SENSES.

THE diseases of the organs of the senses to be described in the present chapter are divisible into three groups according to the organs concerned. Diseases of the organs of sight, of hearing, of smell of the eye, the ear, the nose.

DISEASES OF THE EYE.

Seventy-five diseases are officially tabulated as affecting the eyes and their appendages. Of these diseases, fourteen are referred to the mucous membrane which covers the eyeball from the point where the skin terminates on the upper lid to the same point on the lower lid, the conjunctiva. Nine are referred to the cornea, the convexo-concave lens, which forms the first transparency of the eyeball. Two are referred to the sclerotic coat, or outer firm white covering or case of the eyeball. Seven belong to the iris or curtain, in the centre of which is the opening called the pupil. Seven are connected with the choroid or dark coat, and the nervous expanse known as the retina. Two are assigned to the vitreous humor, the large, cellular, and partly fluid lens which fills up the body of the eyeball posteriorly. Four relate to the crystalline lens, the great refracting medium which lies between the curtain or iris and the vitreous humor. Three are classified as general diseases of the eyeball, and six as "defects of sight." Four are named as diseases of the lachrymal apparatus; eleven, as diseases of the eyelids; six, as diseases within the orbits.

Diseases of the Conjunctiva-The Ophthalmias.

Under the general term ophthalmia the diseases affecting the external covering of the eyeball,-the mucous membrane called

the conjunctiva,--are arranged in the series of fourteen varieties. These are all commonly known as inflammations of the eyeball, although it is not usual for them to extend actually into the internal structure of the eye, nor even beyond that part of the external structure which is directly visible and is bounded by the enveloping eyelids. The varieties of the ophthalmias are as follow :

Pustular.-A form in which inflammation of the conjunctiva ends in the development of purulent matter in pustules. The disease occurs, usually, in the course of other diseases attended with pustular eruption, such as small-pox.

Purulent ophthalmia.-Ophthalmia of a contagious character, attended with a purulent discharge which is capable, by contact, of communicating the disease from one person to another. The contagious particles may be carried by the atmospheric air, and thus become the means of communication.

Purulent ophthalmia of infants.-Another form of purulent contagious ophthalmia occurring in infant life, especially in children who inhabit badly ventilated rooms and live under conditions leading to feebleness of body. Improper or insufficient nourishment is one of the most potent of these conditions.

Strumous or scrofulous ophthalmia.-An ophthalmia peculiar to those who are of scrofulous taint. It is often persistent in its course, and leads, in bad cases, to impairment or even actual loss of vision.

Exanthematous ophthalmia.-An ophthalmia of an exanthematous or eruptive character, occurring sometimes during the presence of the ordinary exanthematous or eruptive diseases, such as measles and small-pox.

Gonorrheal ophthalmia.—An ophthalmia connected with the disease called gonorrhoea, and produced by the contact of the specific discharge from that disease with the conjunctiva. An acute and very troublesome affection, leading occasionally to deep inflammation and loss of sight.

Chronic ophthalmia.-A slowly progressing ophthalmia, or a continuance, in a modified form, of one of the other of the varieties of ophthalmia in the slow or chronic condition.

In addition to these diseases the conjunctival membrane is subject to œdema, or dropsy, chemosis; to fatty and other tumors attached to its surface; to parasitic disease; to granular change;

to a triangular or wing-like red and fleshy formation called pterygium; and to metallic stains derived from nitrate of silver, or from lead.

Diseases of the Cornea.

The cornea, the horny, transparent, cancavo-convex lens, which lies immediately beneath the mucous conjunctival membrane, is subject to the following local affections:

Keratitis, or acute inflammation of its structure.

Chronic interstitial keratitis.-Inflammation of long standing, with interposition of fluid between the layers of which the cornea is composed.

Keratitis, with suppuration.-A long, continued inflammation of the cornea, with formation of matter or pus in the layers of the structure. The appearance produced by the presence of the purulent fluid has caused the term onyx to be applied to the affection.

Ulcer.-A condition, following usually upon inflammation, in which there is active destruction or loss of substance of the cornea.

Leucoma.-An opacity of the cornea, due to a cicatrix.

Arcus senilis.-A white line running round the cornea at its circumference, in whole or in part, and commonly seen in the old or prematurely aged. The white structure is composed, chiefly, of fatty substance. At one time the arcus senilis was viewed by practitioners of medicine as an outward and visible sign of fatty degeneration of the heart and other internal organs, and great importance was therefore attached to it; but later experience has not so fully confirmed this inference as to render it absolute as a sign of internal disease.

In addition to the above, the cornea is subject to three other varieties of disease, namely, conical cornea, in which the structure is pushed forward in the form of a conical projection: staphyloma, or a white prominence of a dead and disorganized cornea: and, parasitic disease, hydatids of the anterior chamber immediately behind the cornea.

Diseases of the Sclerotic Coat.

The sclerotic or investing coat of the eyeball is subject to inflammation, sclerotitis,-and to inflammation connected with

acute rheumatism,-rheumatic sclerotitis. These affections are extremely painful, and are attended with fever and much general disturbance of the body. The sclerotic is also subject to staphyloma, or protrusion from its surface, and to tumors attached to it.

Diseases of the Iris.

Six out of the seven diseases of the iris or curtain of the eye, named on the College list, are inflammatory in character, and the term iritis is used to denote them. In the simplest form of inflammation, the word iritis alone is employed. When a wound is the cause of the disease, traumatic iritis is the mode of expres sion. Sometimes the iritis is an accompaniment of other diseases, such as rheumatic fever, arthritis, or inflammation of joints, syphilis, gonorrhoea, or scrofula. Then the iritis is said to be rheumatic, arthritic, syphilitic, gonorrhaal, or scrofulous. The sequelæ of iritis are included under this same head of inflammation, and consist of adhesion of the iris to surrounding parts; exudation of lymph and protrusion; permanent contraction; permanent dilatation; closure; and, irregularity of the pupil.

Diseases of the Choroid and Retina.

The dark or choroid coat of the eye is subject to inflammation, called, technically, choroiditis, and to congestion of its vessels, choroidal apoplexy; but these are rarely, if ever, distinct forms of disease affecting the choroid coat alone.

Retinitis.-Inflammation of the retina, the nervous screen or coat lying in front of the choroid coat.

Amaurosis.-A disease of the retina, dependent upon various changes of the retinal surface, and ending in an inability of the nervous expanse to receive and transmit impressions from the outer world to the brain. Amaurosis may be produced by the exposure of the eye for a long time to a white, dazzling object, like snow, and "snow blindness" is the most familiar example of this disease. It occurs also from other accidents, as from lightning-stroke, and from blows on the head. It has sometimes its origin in degenerative changes of the retina, in inflammatory changes following exhausting diseases, and in sympathetic irritation. It is occasionally induced by smoking tobacco.

Musca volitantes.-Small specks or spots crossing the field of vision, generally floating, and often taking a slight upward direc