650 VERHOEFF AND BELL. 



vapor lamp through a crown screen (295 fxfx) necessary to produce 

 photophthalmia. The thermic effects produced in these experiments 

 as well as the character of the abiotic effects are discussed elsewhere 

 (pages 662 and 692). 



For determining the critical wave length of abiotic action it will be 

 seen that the crucial experiments were Experiments 81 to 85. These 

 showed that for light of extreme intensity no effects either abiotic 

 or thermic, were produced on the cornea or lens epithelium by an 

 exposure of 1| hours to waves over 315 mx in length, and that no 

 abiotic effects but slight thermic effects were produced by light con- 

 taining wave lengths of 310 /x/x and longer. Light containing wave 

 lengths of 305 fx^ and longer, produced marked thermic effects but 

 no abiotic effects after one hour exposure, but after 1| hours exposure 

 produce marked thermic eft'ects and the slightest possible trace of 

 abiotic effects. That is to say, the limit of abiotic action with refer- 

 ence to wave length for corneal cells is almost exactly 305 (jl/jl. In 

 Experiment 82, in which the light was focussed on the cornea, the only 

 evidence of abiotic action was the loss of corneal epithelium, while 

 in the Experiment 83, in which the light was focussed on the anterior 

 siu-face of the lens, the only evidences of such action were the slight 

 but characteristic changes in the lens epithelium. In any other 

 available tissues than the cornea and lens such slight abiotic effects 

 would undoubtedly have been completely masked by extreme heat 

 effects, but in none of these experiments did the lens show the slight- 

 est thermic effects. 



The insignificance of the abiotic action at wave length 305 ^t^t 

 becomes more apparent when the equivalent critical time is computed 

 for exposure to the direct radiations from the magnetite arc. Our 

 experiments show that the intensity of light at the focus of the double 

 lens system is at least eighteen times the intensity of the bare arc at a 

 distance of 20 cm. This means that to obtain slight loss of corneal 

 epithelium with direct waves of 305 ^t/i in length from the magnetite 

 arc, an exposure of 27 hours at a distance of 20 cm. or an exposure 

 of 28 days at a distance of 1 meter would be required. To produce 

 mild photophthalmia the time required would be about one-third 

 these figures. As a matter of fact however, our experiments on 

 frequently repeated subliminal exposures, already given, prove that 

 at 1 meter no eft'ects whatever would be produced by such slight 

 abiotic action per unit of time owing to the vital activities of the cells. 



Similar calculations for the portion of the spectrum including 

 only waves longer than 295 fxfx, as well as direct experiments, show that 



