EFFECTS OF RADIANT ENERGY ON THE EYE. 651 



an exposure of 20 minutes at 20 cm., in case of the magnetite arc, 

 is required to produce photophthalmia, or an exposure of 85 hours 

 at 1 meter. The ratio of the abiotic activity of the whole spectrum 

 to that of the portion exceeding 295 /x/x is y. This holds approxi- 

 mately true also for the quartz mercury vapor lamp. 



In regard to the lens epithelium, it should be noted that only 

 abiotic changes were obtained, and these with wave lengths as long 

 as 305 iJLix as already stated. With light of this wave length, however, 

 as shown by the above computation it is evident that they could not 

 be obtained by means of the direct light from any artificial light 

 sources at any distance at which the eye could bear the heat. With 

 wave lengths of 295 fx/j. and over, the lens epithelium was affected by 

 an exposure of 5 minutes to the double lens system, the liminal expo- 

 sure probably being about 3 minutes. Since the cornea itself cuts off 

 the waves at this point, it follows that an exposure to the bare mag- 

 netite arc of 54 minutes at 20 cm. or of 22 hours at 1 meter would be 

 required to affect the lens epithelium. Hess, strangely enough, was 

 unable to obtain lens changes through a screen transparent to waves 

 of 2S0 iJLn, and drew the inconsistent conclusion, in view of the fact 

 that the cornea was known by him to obstruct still longer waves, 

 that lens changes are produced only by the very short waves of the 

 spectrum. The character of the lens changes produced in our experi- 

 ments is described on page 671. 



Judging by the effects on the cornea, the abiotic intensity at the 

 focus for the single lens system was about ^ that for the double lens 

 system. 



Comparing the results obtained with the quartz mercury vapor 

 lamp and those with the magnetite arc it is found that the abiotic 

 activity of the entire spectrum of each is in about the ratio of 6 for 

 the mercury lamp to 5 for the magnetite arc. This ratio holds with 

 and without the crown screen (295 ^t^u) . 



These ratios obtained from the pathological effects are in fairly 

 close accord with those derived from the experiments of one of us by 

 purely radiometric methods. Taking average conditions of the two 

 sources here referred to, the abiotic radiations from the quartz lamp 

 should aggregate about 4200 ergs per second per square cm. at the 

 standard distance of .5 meter. The magnetite arc as used gave abio- 

 tic radiations aggregating about 3300 ergs per second per square cm. 

 at the same distance. The ratio between these two quantities is 

 5 to 6.35 as compared with the 5 to 6 of the pathological results, an 

 agreement quite as close as could reasonably be expected considering 

 the nature of the case. 



