=Suppurative Keratitis.=—(1) Ulcer of the cornea; (2) Serpiginous ulcer; (3) Keratomalacia or Xerosis; (4) Keratitis neuroparalytica. =Non-suppurative Keratitis.=—(A) SUPERFICIAL: (1) Pannus, or keratitis with blood vessels; (2) Phlyctenular, or keratitis with vesicles. (B) DEEP: (1) Parenchymatous or interstitial. In keratitis there is first an infiltration or the increase of cells in the substantia propria or the parenchyma of the cornea. This is the exudate of the inflammation. It causes the cornea to look more or less dull or cloudy. The disease may clear up at this point or go on to suppuration. If it clears up it is known as =resorption=. If the lamellæ of the substantia propria are not destroyed by the process, resorption takes place with no loss of substance. The exudate disappears and there is perfect transparency of the cornea again. There may be slight damage of the stroma preventing perfect transparency. Resorption of the exudate may not be quite complete which may become partly organized and left permanently fixed in the cornea. Cases resorbing without destruction of the stroma are forms of the non-suppurative keratitis group. If the stroma breaks, suppuration occurs. This is the second stage and is associated with a localized destruction of the cornea. These cases are known as =suppurative keratitis= or =ulceration of the cornea=. The disintegration begins in the most anterior layers of the cornea. A slight depression in the cornea can be noticed. The infiltration is all about the ulcer, getting less as it is more remote from it. If the floor and walls of the ulcer are foul with the infiltrate it is known as a =progressive= ulcer. =Sloughing= may continue to spread the ulcer. If the cloudiness around it disappears and the ulcer acquires a smooth transparent base and edges it is known as a =retrogressive= or clean ulcer. The disintegrated areas of the cornea may be replaced by newly formed tissue. This is the third stage or that of =cicatrization=. This new tissue is connective tissue. It is opaque, leaving a permanent opacity. =Stages of keratitis=: =Suppurative.=—(1) Infiltration; (2) Suppuration and (3) Cicatrization or Reparation. The suppuration is progressive or retrogressive. =Non-suppurative.=—(1) Infiltration; (2) Resorption. In the diagnosis of a keratitis one should look at it very carefully. A loupe which has thick plus sphere lenses will magnify the field and may be of great assistance in observing closely the condition. If the cornea is clouded and dull the trouble is recent and if there is no loss of substance it is an infiltrate (first stage). If there is loss of substance it is a progressive ulcer (second stage.) If the surface is lustrous but cloudy the trouble is an old one and if there is loss of substance it is a retrogressive ulcer; if no loss of substance it is a cicatrix.