September 25j 1914] 



SCIENCE 



453 



minants as dangerous by reason of injurious 

 effects of the ultra-violet radiation delivered 

 by them. The literature of the subject is 

 large, but unhappily most of the investigations 

 have entirely neglected any quantitative rela- 

 tion between the radiation and its supposed 

 pathological effects. One can not stigmatize 

 an illuminant which emits ultra-violet as 

 dangerous for this reason any more than one 

 can declare a stove unfit for use because it is 

 possible to burn the finger by deliberately 

 touching it. The vital question is not whether 

 a light source gives ultra-violet radiations, but 

 whether it gives them of such kind, and in 

 sufficient quantity, as to make any injury to 

 the eye possible under practical conditions. A 

 second point frequently neglected in the dis- 

 cussion of this subject has been the action of 

 the eye itself in focusing radiation falling upon 

 it, with the resulting effects upon the intensity 

 of the radiation in the media of the eye. 

 Pinally a great many errors have been made 

 and unwarrantable conclusions reached owing 

 to the fact that in the solar spectrum the 

 maximum intensity of radiation is in the 

 brilliantly luminous part of the spectrum, 

 where in addition the so-called actinic power 

 is considerable, so that phenomena possibly 

 having their origin in specific effects of radia- 

 tion of particular wave-length become difficult 

 to separate from those of purely thermic origin. 

 During more than two years past the writers 

 have spent a large amount of their time in an 

 investigation from a quantitative standpoint 

 of the effects of radiation on the various media 

 of the eye from the corneal epithelium back 

 to the retina, and have investigated with con- 

 siderable care the maladies reputed by one 

 writer or another to be due to the specific 

 effects of radiation. Broadly we have found 

 that no artificial source of light used for 

 illuminating purposes contains enough ultra- 

 violet radiation to involve the slightest danger 

 to the eye from its effects under any readily 

 conceivable conditions of use, and that such 

 pathological action as can be obtained experi- 

 mentally from the ultra-violet is confined to 

 a strictly limited region of the spectrum and 

 obeys perfectly definite quantitative laws in 



its action. Incidentally we have found most 

 extraordinary resisting power of the eye as 

 respects radiations outside this particular 

 range, which is in fact the whole body of radia- 

 tion present in any material quantity in the 

 energy normally received from the sun at the 

 surface of the earth. 



Our conclusions regarding these funda- 

 mental matters and respecting the various 

 alleged pathological effects which have been 

 charged up against radiation are appended as 

 preliminary to the more complete publica- 

 tion of the methods and results of our inves- 

 tigations. Most of the experiments were made 

 upon the eyes of rabbits and monkeys. An 

 especially noteworthy experiment, however, 

 relating to the possibility of abiotic action on 

 the retina, was made upon a human patient 

 affected with cancer of the eye-lids, twenty- 

 four hours before the eye was removed. A 

 number of crucial experiments were also made 

 upon our own eyes. It should be especially 

 noted that while the abiotic effects of the ex- 

 treme ultra-violet on the outer eye are well 

 defined, they are limited to a particular region 

 and their extent in case of exposure to any 

 given radiant can be definitely predicted and 

 effectively guarded against. 



Conclusions 



The liminal exposure capable of producing 

 photophthalmia to the extent of conjunctivitis 

 accompanied by stippling of the cornea, is in 

 terms of energy 2 X 10" ©rg seconds per square 

 cm. of abiotic radiation of the character 

 derived, for example, from the quartz lamp 

 or the magnetite arc. About two and a half 

 times this exposure, i. e., 5 X 10^ erg seconds 

 per square cm., is required to produce loss of 

 corneal epithelium. 



The abiotic action on the cornea and con- 

 junctiva produced by any radiating source 

 follows the law of inverse squares and is 

 directly proportional to the total abiotic energy 

 received. It can therefore be definitely pre- 

 dicted from the physical properties of the 

 source. 



After exposure of the eye to abiotic radiations 

 there is a latent period before any effects, 



