EFFECTS OF RADIANT ENERGY ON THE EYE. 697 



margin it showed an incomplete ring which under the low power of 

 the microscope resembled the wall produced in other experiments hy 

 abiotic radiations. Examination under a higher power however, 

 showed that the appearance was due chiefly to the fact that the cells 

 were here in a state of active proliferation, almost every cell being in 

 some stage of mitosis. It was evident that the heat from the pigment 

 layer of the iris, where the latter was in contact with the lens capsule, 

 had stimulated the cells of the latter to proliferation. It is note- 

 worthy that in Experiment 99 in which the exposure was 1| minutes 

 but in which the iris was unpigmented, neither the iris or lens 

 capsule was affected. 



In none of our experiments was the lens injured by the heat gener- 

 ated by the stoppage of rays within its own substance. That clouding 

 of the lens can be so produced, however, even by visible rays alone, 

 with sufficient intensity and prolonged exposure, has already been 

 demonstrated by Czerny ^^ and Deutschman ^^ in the case of sunlight, 

 and by Herzog ^^^ who used the carbon arc and suitable filters. 



The iris in no other experiment showed heat effects comparable to 

 those just described. In most of the experiments with the magnetite 

 arc and double lens system the iris was not greatly exposed to the light 

 owing to the artificial mydriasis, but in Experiment 88 in which the 

 most intense heat effect was obtained in the cornea, the iris showed 

 hemorrhages near the pupil. In Experiments 83 and 90 the iris 

 became greatly contracted towards the end of the exposures, and 

 remained so for several hours, but again diluted within 24 hours. 



Thermic Effects of Radiant Energy upon the Retina. 



In a number of our experiments, some of which were made with 

 other purposes in view, we obtained heat effects in the retina in spite 

 of an interposed water cell 5 cm. thick. They were obtained mainly 

 in two ways, one by the use of sunlight reflected from a silvered 

 glass concave mirror 26 cm. in diameter and 1.5 meters in focal length, 

 and the other by the use of the magnetite arc light concentrated l)y the 

 single quartz lens system. A full description of the mirror and the 

 calculated energy derived from it is given on page 721. The calcu- 

 lated energy on the retina given by the c^uartz single lens system is 

 given on page 724. The burns were obtained through screens that 

 obstructed all waves less than 335 fxfx in length as well as througli 



