EFFECTS OF RADIANT ENERGY ON THE EYE. 701 



is the temperature required to injure tissues. In all cases the pigment 

 epithelium was the most severely affected of any portion of the retina, 

 and in the slightest burns it alone was affected. This was true also in 

 albinotic rabbits in which the epithelium was free from pigment. The 

 other structures were affected in the following order according to the 

 intensity of the action, the rods and cones, the chorio-capillaris, the 

 outer nuclear layer. The inner nuclear layer, the ganglion cells, and 

 nerve fibre layer, were affected only after extremely intense exposures 

 and in our experiments were not affected after exposures to the magne- 

 tite arc but only when concentrated sunlight was used. 



The slightest change that can be definitely made out in the pig- 

 ment epithelium 48 hours after exposure consists in the cytoplasm 

 of a greater or less number of cells staining intensely in eosin. When 

 the effect is somewhat greater, vacuoles appear and may be so large 

 and numerous that the cells appear almost completely transparent, 

 the cytoplasm showing a delicate reticulum with the minute nodes at 

 the junction points. In case the epithelium is pigmented the pigment 

 appears to be separated from the membrane of Bruch by large vacuoles, 

 and the nucleus may show marked pycknosis. When the effect is still 

 greater the cell reticulum completely disappears leaving only the 

 nucleus in the clear space thus formed. The nucleus may show 

 fragmentation or simply chromatolysis. The basophilic and eosino- 

 philic granules characteristic of abiotic action are not seen. In the 

 somewhat more severe burns the pigment cells entirely disappear 

 leaving only the pigment. In one eye examined six days after ex- 

 posure the injured epithelium is found replaced by epithelium which 

 has evidently grown in from the periphery, but between the new layer 

 and the rods and cones numerous swollen vaculated and otherwise 

 altered pigment cells remain. The changes in the pigment epithelium 

 are best seen in plane section, and to determine the character of the 

 slightest changes it is important to compare the appearances seen in 

 the exposed eye with those of a normal eye. 



Forty-eight hours after exposures sufficient to affect the rods and 

 cones, the outer limbs of the latter are found to be broken up into 

 coarse granules, while the inner limbs are swollen to large bladder-like 

 structures each containing a few fine granules. There may also be a 

 greater or less number of red blood corpuscles among the rods and 

 cones due to diapedesis from the chorio-capillaris, and also a certain 

 amount of serum. When the outer nuclear layer is aft'ected, the nuclei 

 lose their peculiar cross striations, becoming intensely pycknotic 

 and some of them undergoing fragmentation. With this degree of 



