EFFECTS OF RADIANT ENERGY ON THE EYE. 731 



The possible effects on the lens of heat radiation persisting over a very 

 long period we have considered in discussing glass blowers cataract 

 (page 734). Thermic effects on the cornea we have shown to be 

 obtainable only under extreme experimental conditions (page 692). 

 The media of the eyes generally, as we have already shown, are of 

 substantially the same absorbing character as water so far as concerns 

 visible and infra red rays and therefore take up chiefly radiant energy 

 of long wave length such as is prominent in radiation received from 

 low temperature sources like hot metals or molten glass. The pig- 

 mented iris and the pigment epithelium of the fundus are exceptions 

 in that they absorb quite completely radiant energy irrespective of 

 wave length. There is, therefore, a tendency to produce localized 

 thermic effects in both these structures, as we have shown in various 

 of our experiments. The lesions occurring under these circumstances 

 have already been described. In case of the iris, the heat effects may 

 proceed all the way from moderate irritation to serious permanent 

 injury (see page 696). This phase of the matter was recently inves- 

 tigated by Reichen^^^. This observer studied the effects of con- 

 centration of infra red radiation on the eye by cutting off the visible 

 and ultra violet spectrum by a filter of iodine in bisulphide of carbon, 

 and absorbing the extreme infra red by a water filter. In this way 

 the rays with which he was concerned were substantially those be- 

 tween 800 and 1200 /jl/jl. Using as source the electric arc between 

 carbon electrodes, by means of a rock salt lens he concentrated the 

 filtered energy upon the eyes of rabbits for periods from 1 to 33 min- 

 utes. The only effect noted was contraction of the pupil lasting some 

 hours and generally slight, evidently depending on the direct heat 

 effect tl>rough the filters used, since the visible rays were practically 

 excluded from the retina. Such pupillary contraction is reasonably 

 to be expected after moderate irritation of the iris, such as would be 

 furnished by this heat stimulus and may occur as some of our experi- 

 ments show, in the absence of any recognizable histological changes. 

 Violent and persistent effects were hardly to be expected inasmuch as 

 the source used is not rich in rays transmissible through Reichen's 

 filters. Most of the energy from a carbon arc is intercepted by a water 

 filter and a good deal of the remaining energy by the iodine in carbon 

 bisulphides. This selective action is well shown in one of Reichen's 

 experiments in which the water screen, which was quite close to the 

 arc, was boiling violently after 7^ minutes exposure. Reichen's experi- 

 ments, therefore, merely show a mild irritation not in the least peculiar 

 to the region of the spectrum employed. It would seem quite im- 



