EFFECTS OF RADIANT ENERGY ON THE EYE. 687 



aphakic eye in 6 days, while a total daily exposure of g the liminal, 

 in this case 4 minutes, would produce no effects even if inflefinitely 

 continued. These estimates do not allow for the pupillary contrac- 

 tion, which would result from the fixation of such a bright source and 

 which would in most cases increase the necessary exposures three or 

 four times, or for imperfect fixation. They also do not allow for the 

 thick cataract glasses which in most cases would be worn and which 

 w^ould increase the necessary exposures many times, since a 10 dioptre 

 lens would be almost impenetrable to abiotic radiations. For the 

 quartz mercury vapor lamp still longer exposures would be required 

 owing to the size and shape of the light source giving less concentration 

 in the image. It is, therefore, now apparent why there is no known 

 case of a human eye from which the lens has been removed in which 

 the retina has been injured by exposure to artificial light, and why 

 such injur}' is in the highest degree improbable. 



In endeavoring to demonstrate by direct experiment the possibility 

 of injuring the retina of the aphakic eye by abiotic radiation we have 

 found it difficult to obtain a satisfactory eye for the purpose. While 

 it was easily possible to remove the lens from the rabbit's eye, the 

 pupil became more or less completely obstructed in almost all cases. 

 In one animal, however, we finally obtained by means of repeated 

 discissions, a clear pupillary opening sufficient to admit the cone of 

 light from the quartz double lens system. According to our calcu- 

 lations an exposure of 35 minutes with the light focussed upon the 

 pupillary area should have been sufficient to produce abiotic effects 

 in the retina. No allowance, however, was made for absorption 

 by the vitreous humor. As a matter of fact no abiotic effects could 

 be demonstrated in the retina although marked heat effects were 

 obtained in the pigment epithelium (Exp. 89). This experiment 

 thus goes to show that the danger to the retina from exposing the 

 aphakic eye to abiotic radiations is even less than is indicated by the 

 above calculations. 



Birch-Hirschfeld's Observations. 



Since the results of our experiments especially in regard to the 

 retina are so greatly at variance with those of Birch-Hirschfeld ^^ 

 it may be well to review his experiments in some detail. This is all 

 the more necessary because his results and conclusions have not 

 hitherto either been confirmed or refuted. His experiments consist 

 of two series. In the first series he separated out the ultra violet 



