696 VERHOEFF AND BELL. 



what beyond 315 /x/i. It is also evident that the energy absorbed 

 from waves of 305 /x/x or over in length, is converted almost exclusively 

 into heat, only the slightest traces of abiotic action being obtained 

 with weaves of 305 jUjU in length after the most intense and prolonged 

 exposures. 



It will be seen that the abiotic effects and heat effects of radiant 

 energy upon the tissues are essentially diiferent. In the case of heat, 

 a certain critical temperature is required before any effect is produced. 

 This is shown by the sharp transition from normal into injured corneal 

 corpuscles at the periphery of the exposed area, and also by the fact 

 that the epithelium, being kept cool by contact with the air, remains 

 unaffected. The heat effect therefore does not vary in direct ratio 

 with the intensity of exposure, obviously due to the fact that dissipa- 

 tion of heat enters into the equation. In the case of abiotic action 

 on the other hand the effect varies directly with the intensity of the 

 exposure. Heat of an intensity just below that sufficient to cause 

 cell destruction, causes cell proliferation. Abiotic action does not 

 directly cause cell proliferation no matter how intense or how slight 

 the exposure. Lastly, heat does not produce the eosinophilic and 

 basophilic granules in the cytoplasm that are produced by exposure 

 to abiotic radiation. 



On the other hand, while it is evident that heat does not produce 

 effects similar to those produced by moderate exposures to abiotic 

 waves, extreme exposures to the latter may produce effects not unlike 

 the severe effects of heat. Thus we have shown that se\'ere exposures 

 to waves shorter than 295 /x^t in length may lead to complete disap- 

 pearance of the corneal corpuscles and marked swelling of the corneal 

 stroma. In the case of heat, however, the posterior layers of the 

 cornea are more affected than the anterior la.^ers while in the case of 

 abiotic action the reverse is true. 



Thermic Effects of Radiant Energy upon the 

 Iris and Lens. 



In Experiment 97 in which the eye was exposed for one minute 

 through a uviol screen to sunlight concentrated by the large mirror, 

 the pigmented iris was severely burned in the exposed area, showing 

 complete hyaline necrosis. The lens epithelium examined, after 48 

 hours, was unaffected in the pupillary area, but beneath the pupillary 



