The irritant exciting inflammation of the conjunctiva may be a very simple one, such as dust or cold, and in such cases the inflammation is usually slight and evanescent, being characterized by little more than Hyperaemia, with more or less serous exudation. In most cases of more severe conjunctivitis, the irritant is a morbid poison, and the disease is contracted by contagion.

(a) In ordinary Catarrhal conjunctivitis, the exact nature of the irritant is not determined, but most if not all cases are contagious. The disease is characterized by hyperemia eventuating in a mucous or mucopurulent exudation.

(b) Pujulent conjunctivitis (Purulent ophthalmia) is due to a pyogenic microbe. This is, in a large proportion of cases, the gonococcus, so that the term Gonorrheal ophthalmia is nearly equivalent to purulent conjunctivitis in the adult. A purulent conjunctivitis occurring in new-born children, and hence called Ophthalmia neonatorum, is generally due to infection from the maternal parts during parturition. In this form microbes have been observed, in most cases the gonococcus, but there is still some doubt whether this be so in all cases.

The pyogenic virus in purulent conjunctivitis induces a violent inflammation rapidly passing on to suppuration, and, if neglected, sometimes leading to necrosis and ulceration of the cornea.

(c) Granular conjunctivitis or Trachoma is a more chronic inflammation of the conjunctiva which is also due to a specific virus, which Sattler asserts to»be a micrococcus, but this is not absolutely determined. The disease is contagious, occurring sometimes in schools and in armies. Egyptian ophthalmia was a form observed in the French army in Egypt, and introduced by it into France and thence into this country. While due to a special virus, the disease occurs chiefly in unhealthy persons, and is hence most prevalent amongst the poor.

The lesion is in some respects like that in the specific new-formations, such as tubercle or frambeesia. There is a localized formation of round-celled tissue in a delicate reticulated meshwork, so that it resemble! lymphatic-gland tissue. These new-formations are usually defined ami appear as if surrounded by a distinct capsule, in this respect also resembling lymphoid follicles. There seems little tendency towards further development of this tissue, but the follicles frequently burst and discharge on the surface. These lesions are accompanied by catarrh, and by their mere presence, especially when on the conjunctiva of the upper lids, they often produce considerable irritation of the cornea which also becomes infected by the disease. In the more chronic. forms the conjunctiva may be indurated by cicatricial new formation, and this is accompanied by atrophy of the lymphoid masses. A sonic what frequent result of granular conjunctivitis is the vascularization of the cornea, to which the name Pannus is applied. Localized amyloid degeneration sometimes occurs in the new-formed follicles in trachoma, this fact also tending to associate the affection with the specific D formations. The amyloid condition is found in the cells and fibres, but not in the vessels (Leber).

(d) Diphtheritic conjunctivitis is a rare condition occurring along with diphtheria in the throat. There is necrosis, ulceration, and violent inflammation.

2. Tuberculosis

Tuberculosis is of rare occurrence in the conjunctiva, but tuberculous persons seem liable to. a subacute conjunctivitis which is often called scrofulous.