EFFECTS OF RADIANT ENERGY ON THE EYE. 677 



shown in one of his ilhistrations. Apparently he attributed the repair 

 of the injury chiefly to mitosis and not to recovery of the injured 

 individual cells. He states, however, that he has no evidence that 

 ultra violet light is a direct stimulant to mitosis. Widmark,^^* 

 strangely enough, found mitotic figures only in the exposed area and 

 regarded ultra violet light as a direct stimulant to cell proliferation. 

 Birch-Hirschfeld ^^ states that by means of a 20 diopter glass lens 

 he focussed the light of a 5 ampere arc light through a euphos glass 

 screen upon the eye of a rabbit for five minutes for three successive 

 days and on the day after the last exposure obtained the changes 

 described by Hess. The euphos screen obstructed all rays less than 

 400 ij-ix in length. II is not stated that a water cell was used, and the 

 diameter of the lens was not mentioned. In spite of such a remarkaljle 

 result it is not stated that the experiment w^as repeated. We have 

 been unable to obtain such a result through a light flint screen trans- 

 parent for waves down to 315 ^i/x with the magnetite arc and still 

 greater concentration of energy. ^Moreover in an experiment in which 

 we focussed sunlight upon the lens by means of a large mirror no 

 changes in the lens capsule resulted within the pupillary area, although 

 there was complete necrosis of the iris due to heat. The lens capsule 

 was affected only beneath the pupillary margin where it had been in 

 contact with the heated iris and even here the changes were not such 

 as are produced by abiotic action. We are therefore compelled to 

 believe that Birch-Hirschfeld was in error. Possibly he mistook a 

 heat effect similar to that just noted for the changes descrilied by 

 Hess. He had never previously obtained the latter changes in any 

 of his experiments and hence from personal observation was no doubt 

 unfamiliar with their appearance. 



POSSIBLE ABIOTIC EFFECTS OF RADIANT ENERGY ON 



THE RETINA. 



It might be supposed that if a source of light is not sufficiently rich 

 in abiotic rays to damage the cornea, the retina could not be injured 

 by these rays. This, however, is not necessarily true because if the 

 source of light is so small in size that the area of its retinal image is 

 less than that of the pupil, the intensity per unit area as concerns 

 transmissible rays will be greater on the retina than on the cornea. 



