664 VERHOEFF AND BELL. 



maximum in about 48 hours, when, as will he pointed out, there is 

 some leueocytic infiltration. 



After 3 days the purulent conjunctival discharge becomes less, 

 but it may not entirely subside for about 9 days. The corneal epi- 

 thelium is usually reformed on about the 4th day. Haziness of the 

 cornea noticeably begins to subside in 3 to 10 days. After five weeks 

 only a slight central haze remains. Following sufficiently intense 

 exposures, new vessels are seen extending into the cornea from the 

 hmbus in about six days. 



The conjunctival reaction that occurs after moderate exposure 

 to abiotic radiations, is only in very small part reflexly due to irrita- 

 tion of the cornea. This is proved by several experiments in which 

 the cornea was exposed through a diaphragm which protected the 

 conjunctiva. Here, although the cornea was markedly affected, and 

 the epithelium destroyed, the conjunctiva showed no reaction until 

 after about 48 hours, and then only slight hyperemia. 



The foregoing description applies to the effect produced on the 

 cornea by moderate exposures to the bare mercury vapor quartz 

 lamp, or bare magnetite arc, and by relatively long exposures (5 to 

 20 minutes) to the magnetite arc through a water cell, quartz lens 

 system, and crown screen. The latter absorbs all rays less than 

 295 ju/z in length and thus protects the corneal stroma from injury. 

 With the magnetite arc, and quartz lens system, but without 

 any screen, a very much greater as well as different effect may be 

 produced. With this arrangement and an exposure of 20 minutes a 

 dosage is obtained that is more than one hundred and fifty times as 

 great as that of a liminal exposure necessary to produce slight keratitis. 

 Following such an exposure the following changes occur. Immediately 

 after the exposure the cornea is perfectly clear. At the end of thirty 

 minutes there is slight hyperemia of the conjunctiva and central 

 haziness of the cornea. At the end of four hours the conjunctivitis 

 is marked and the corneal haze much greater. The exposed area is 

 completely anaesthetic. The epithelium is intact, but stains slightly 

 in flourescine. The iris is highly congested. At the end of twenty- 

 four hours there is a marked general inflammatory reaction of the 

 conjunctiva with oedema and purulent discharge. The epithelium 

 is lost from the exposed area in twenty-four hours, and reformed 

 about thirty-six hours later. On the fourth or fifth day the cornea, 

 without becoming more hazy, begins to swell in the exposed region. 

 This swelling increases and the aft'ected area becomes softened until 

 an appearance is produced on about the eighth day of a large flaccid 



