EFFECTS OF RADIANT ENERGY ON THE EYE. 757 



period before any effects clinical or histological become perceptible. 

 This period of latency in a general way varies inversely with the 

 severity of the exposure, but a theoretical latency of 24 hours or more 

 corresponds to an exposure entirely subliminal. 



4. The combined effect of repeated exposures to abiotic radiations 

 is equivalent to that of a continuous exposure of the same total length, 

 provided the intermissions are not long enough to establish reparative 

 effects. Approximately the exposures are additive for intermissions 

 of somewhat less than 24 hours. Exposures of ^ the liminal given 

 daily begin to show perceptible effect after about 6 exposures. Daily 

 exposures of g the liminal repeated over long periods produce no effect 

 whatever, except to give the external eye a degree of immunity against 

 severer exposures. Actual abiotic damage to the external eye renders 

 it temporarily more sensitive to abiotic action. 



5. Abiotic action for living tissues is confined to wave lengths 

 shorter than 305 n^i, at which length abiotic effects are evanescent, 

 while for shorter wave lengths they increase with considerable rapidity. 



6. For the quartz arc and the magnetite arc the abiotic activity 

 of the rays absorbed by the cornea is eighteen times greater than those 

 which are transmitted by it. To affect any media back of the cornea 

 requires therefore at least eighteen times the liminal exposure hereto- 

 fore mentioned. 



7. Even with exposures as great as one hundred and fifty times the 

 liminal for photophthalmia the lens substance is affected to a depth 

 of less than 20 ^t, and this superficial effect undergoes in the rabbit 

 complete repair. Such enormously intensive exposures, which we 

 obtain with the magnetite arc and double quartz lens system may 

 completely destroy the corneal epithelium, corpuscles, and endothe- 

 lium. The corneal stroma may be strongly affected by waves shorter 

 than 295 h^jl, which it completely absorbs, but is very slightly affected 

 by the remaining abiotic radiation. 



8. The histological changes produced by abiotic radiation are 

 radically different from those produced by heat, and the cell changes 

 are best seen in flat preparations of the lens capsule. The most char- 

 acteristic change is the breaking up of the cytoplasm into eosinophilic 

 and basophilic granules. 



9. Changes in the lens epithelium like those following abiotic 

 action, including the formation of a "wall" beneath the pupillary 

 margin, are not exclusively characteristic of abiotic action, but may 

 be produced by ordinary chemical reagents. They are, therefore, 

 characteristic not of abiotic action alone, but of chemical action in 

 general. 



