454 



SCIENCE 



[N. S. Vol. XL. No. 1030 



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. 



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. Ap- 

 proximately, the exposures are additive for in- 

 termissions of somewhat less than 24 hours. 

 Exposures of one third the liminal given daily 

 begin to show perceptible effect only after 

 about six exposures. Daily exposures of one 

 sixth 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. 



Abiotic action for living tissues is confined 

 to wave-lengths shorter than 305 ^u/*, at which 

 length abiotic effects are evanescent, while for 

 shorter wave-lengths they increase with con- 

 siderable rapidity. 



For the quartz arc and the magnetite are 

 the abiotic activity of the rays absorbed by 

 the cornea is eighteen times greater than those 

 which are transmitted by it. To effect the 

 media back of the cornea requires, therefore, at 

 least eighteen times the liminal exposure here- 

 tofore mentioned. 



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 ft,, and this superficial effect under- 

 goes in the rabbit complete repair. Such 

 enormously intensive exposures, which we ob- 

 tain with the magnetite arc and double quartz 

 lens system may completely destroy the corneal 

 epithelium, corpuscles and endothelium. The 

 corneal stroma may be strongly affected by 

 waves shorter than 295 yn^u, which it completely 

 absorbs, but is very slightly affected by the 

 remaining abiotic radiation. 



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 characteristic change is the breaking 

 up of the cytoplasm into eosinophilic and bas- 

 ophilic granules. 



Changes in the lens epithelium like those 

 following abiotic action, including the forma- 

 tion 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, char- 

 acteristic not of abiotic action alone, but of 

 chemical action in general. 



Abiotic radiations certainly do not directly 

 stimulate, but, on the contrary apparently 

 depress mitosis. Their action in this respect 

 also is materially different from that of heat. 



The lens protects completely the retina of 

 the normal eye even from the small proportion 

 of feebly abiotic rays which can penetrate the 

 cornea and vitreous. 



Experiments on rabbits, monkeys and the 

 human subject prove that the retina may be 

 flooded for an hour or m.ore with light of 

 extreme intensity (not less than 50,000 lux), 

 without any sign of permanent injury. The 

 resulting scotoma disappears within a few 

 hours. Only when the concentration of light 

 involves enough heat energy to produce defi- 

 nite thermic lesions is the retina likely to be 

 injured. 



The retina of the aphakic eye, owing to the 

 specific and general absorption of abiotic 

 radiations by the cornea and the vitreous body, 

 is adequately protected from injury from any 

 exposures possible under the ordinary condi- 

 tions of life, even without the added protec- 

 tion of the glasses necessary for aphakic pa- 

 tients. 



To injure the cornea, iris, or lens, by the 

 thermic effects of radiation, requires a con- 

 centration of energy obtainable only under 

 extreme experimental conditions. 



Infra-red rays have no specific action on the 

 tissues analogous to that of abiotic rays. Any 

 effect due to them is simply a matter of thermic 

 action, and such rays are in the main absorbed 

 by the media of the eye before reaching the 

 retina. 



Actual experiments made on the human eye 



