758 VERHOEFF AND BELL. 



10. 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. 



11. The lens protects completely the retina of the normal eye even 

 from the small proportion of feebly abiotic raj's which can penetrate 

 the cornea and vitreous humor. 



12. Experiments on rabbits, monkeys and the human subject 

 prove that the retina may be flooded for an hour or more 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 definite thermic lesions is the retina likely to be 

 injured. 



13. The retina of the aphakic eye, owing to the specific and general 

 absorption of abiotic radiations by the cornea and the vitreous body, 

 ij adequately protected from injury from any exposures possible under 

 the ordinary conditions of life, even without the added protection of 

 the glasses necessary for aphakic patients. 



14. To injure the cornea, iris, or lens, by the thermic effects of 

 radiation, requires a concentration of energy obtainable only under 

 extreme experimental conditions. 



15. 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. 



16. Actual experiments made on the human eye show conclu- 

 sively that no concentration of radiation on the retina from any 

 artificial illuminant is sufficient to produce injury thereto under any 

 practical conditions. 



17. Eclipse blindness, the only thermic effect on the retina of 

 common occurrence clinically, is due to the action of the concentrated 

 heat on the pigment epithelium and choroid, this heat being almost 

 wholly due to radiations of the visible spectrum within which the 

 maximum solar energy lies. 



18. The abiotic energy in the solar spectrum is a meagre remnant 

 between wave lengths 295 (jlijl and 305 /xju, aggregating hardly a quarter 

 of 1% of the total. At high altitudes and in clear air it is sufficient 

 to produce slight abiotic effects such as are noted in snow blindness 

 and solar erythema, the former only occurring with long exposures 

 under very favorable circumstances and the latter being in ordinary 

 cases complicated by an erythema due to heat alone. The amount 



