EFFECTS OF RADIANT ENERGY ON THE EYE. 639 



The method of experimenting was as follows: The animal was 

 enclosed in a box without a cover through one end of which the head 

 protruded, being held in place by a sliding end piece. The eye was 

 held open b}' a Murdoch specuhmi made of proper size for the pur- 

 pose, and was then exposed at a known distance from the quartz 

 lamp working at standard intensity for a given period. A few hours 

 later, usually the next day, after the course of the experiments was 

 settled, careful examination was made of the external eye for any 

 signs of effect from the radiation, the unexposed eye being used as a 

 check. After a few preliminary trials we found that the occurrence 

 of slight conjunctivitis was less readily determinable than the damage 

 to the corneal epithelium showing in the reflection of light from the 

 cornea by a slight irregular crackled appearance giving way after 

 stronger exposures to faint stippling. A still greater severity of 

 exposure produces faint haziness. We also tried staining with fluo- 

 rescine as index of damage to the epithelium, but found in the first 

 stages disturbance of the corneal light reflection a more reliable guide. 

 This indicates a somewhat more severe exposure than produces the 

 first trace of conjunctivitis, but its presence or absence is quite definite 

 wdiereas the conjunctivitis may not be easy to determine if the rabbit's 

 eyes are naturally somewhat reddened. 



The minimum exposure at .5 meter required to produce the first 

 signs of pathological change on the surface of the cornea was deter- 

 mined to be six minutes. The following experiments show the results 

 leading to the establishment of this minimum, and it will be seen that 

 the liminal period was sometimes about a minute shorter or longer, 

 various animals differing somewhat in sensitiveness. It will be 

 observed that to produce loss of corneal epithelium required an expo- 

 sure about 2h times that necessary to produce slight photophthalmia. 



Experiments. 



Negative results. Exposures in minutes : 1; 2|; 3; 3; 3; 5; 5; 5; 7|. 



Slight but definite conjunctivitis with impairment of corneal light 

 reflection. Exposures in minutes : 7|; 5; 7^; 7|; 6; 6; 6; 7|; 6; 4 

 (albino). 



Marked conjunctivitis with slight haze of cornea but without loss 

 of corneal epithelium. Exposures in minutes: 10; 10. 



Marked conjunctivitis with haze of cornea and loss of corneal epithe- 

 lium. Exposure in minutes: 15. 



