EFFECTS OF RADIANT ENERGY ON THE EYE. 709 



Under window glass and violet or blue glass it was slight, even after 

 considerable exposures, while with yellow, red, green or black glass 

 it was absent, although in each case the primary erythema was 

 marked. No investigation was made of the absorption of the various 

 glasses, but from our experiments the clear, the blue and the violet 

 glasses are likely to let through the margin of the abiotic radiations 

 in the thickness, 2 mm., here employed. Yellow, red, green and black 

 glasses would certainly cut these off. The skin in open exposure to 

 sunshine is very much more exposed to the full energy of the solar 

 radiations than is the surface of the cornea and conjunctiva and for 

 abiotic effects on the skin practically the full strength of solar radia- 

 tion is available. One would therefore expect to get action from 

 the abiotic rays in, at most, half the time noted with respect to the 

 cornea and conjunctiva for a similar degree of effect. In other words, 

 one should get in a couple of hours well marked effects and undoubtedly 

 slight erythema in an hour or so, as experience well shows is the case, 

 assuming somewhat similar degree of sensitiveness in the epithelial 

 cells. In case of extreme exposure to heat radiation distinct heat 

 effects may be found in either case. Dr. deLaroquette's observations 

 on the human skin were fully checked by exposures on shaven areas 

 on the skin of a guinea pig showing the same general phenomena. 

 Dr. deLaroquette also suggests that low temperature and wind drying 

 the epidermis and provoking intense superficial vaso-constriction 

 tends to exaggerate solar erythema. In this way some rational 

 account can be given of its occurrence under conditions of cold and 

 severe wind alone w^hen the abiotic action of the solar radiation would 

 be small or even wanting, in which case the effect would be a primary 

 rather than a secondary one. Finally, in solar erythema, as in pho- 

 tophthalmia, repeated exposures of somewhat subnormal intensity 

 give acquired tolerance, while the skin is, as well known, somewhat 

 hypersensitive to severe exposures following each other without 

 time for the lesions to undergo repair. 



Our experiments with the bai'e magnetite arc as source indicate 

 that the liminal exposure for perceptible abiotic effects is practically 

 the same for the more sensitive parts of the skin as for the conjunctiva. 

 The inner portion of the forearm was the portion of the body exposed 

 in our w^ork on liminal exposures. Here with 6 minutes at .5 meter, 

 which corresponds very well with the production of mild photoph- 

 thalmia, a slight reddening of the skin appeared some few hours 

 after exposure, rose to its maximum inside of the first 24 hours and 

 vanished within a day or tw^o leaving no trace. Through the double 



