692 YERHOEFF AND BELL. 



tophthalmia following exposure to the mercury vapor lamp that he 

 claims demonstrate the pathological action of ultra violet light upon 

 the retina. In these cases he found, for colors only, para- or peri- 

 central scotoma, central relative scotoma, and constriction of the peri- 

 pheral field. Later ^* he reports that after an exposure of less than 

 I hour to the Schott uviol lamp he himself was affected with mild 

 photophthalmia followed by color field changes. He found a relative 

 color scotoma in each eye beginning 15° from the fixation point that 

 persisted 6 days. After this had completely disappeared he exposed 

 his left eye to the same light through a colorless glass obstructing 

 all waves less than 330 fxn in length and obtained no changes of any 

 kind. He regarded this as proof of his contention that the field 

 changes previously obtained were due chiefly to waves between 300 n/j, 

 and 330 /XM- -"^s a matter of fact, however, Hallauer ^^^ has shown 

 that the adult human lens absorbs all waves less than 376 mx and most 

 of those less than 400 fxij. so that this experiment of Birch-Hirschfeld 

 proves, if it proves anything, that the field changes obtained in his 

 clinical cases and in his own case were chiefly subjective or at least did 

 not represent pathological conditions. Moreover, as pointed out 

 elsewhere (page 721) Birch-Hirschfeld*^ himself has recently taken 

 exception to the similar field changes reported by Jess ^^^ in cases 

 of eclipse blindness on the ground that they might well have been 

 obtained in normal eyes. 



Thermic Effects of Radiant Energy on the Eye. 



The Cornea. In passing through the cornea, light of any wave length 

 is absorbed to some extent. Waves less than 295 fxij. are completely 

 absorbed while those over 315 m/x in length (judging by the results 

 of our experiments) are very slightly absorbed. The absorption of the 

 latter is no doubt due in part at least to the lamellae of the cornea and 

 the corneal corpuscles, which cause internal reflections and refrac- 

 tions, especially of the relatively short waves. With ordinary light 

 intensities the amount of energy absorbed is so slight that no heat 

 effects are produced, but with extreme intensities it is obvious that 

 the latter could be produced even in the case of visible rays. In five 

 of our experiments definite heat eftects were observed in the cornea. 

 That the effects were due solely to accumulated heat and not in any 

 degree to abiotic action, is proved by the character of the changes 



