EFFECTS OF RADIANT ENERGY ON THE EYE. 681 



apparent changes be found in the exposed retinae that could not be 

 found in unexposed retinae prepared by the same method. Certainly 

 if there were any differences in regard to the Nissl bodies of the gang- 

 lion cells they were too slight to be of any pathological significance. 



These experiments thus show that, so far as can be determined by 

 histological examination, the retina of the normal eye, exclusive of 

 heat effects, is fully protected from abiotic action by the lens. Since 

 however, the objection may be brought forward that the retina may be 

 injured so far as its function is concerned without showing any histo- 

 logical evidence of the fact, we have endeavored to exclude this possi- 

 bility also. For this purpose we employed the monkey instead of the 

 rabbit because this animal possesses a macula similar to that of man. 

 With the lens system described it is easily possible to illuminate 

 intensely a sufficient area of the retina to insure that the macula is 

 always included. If under these circumstances the light has an 

 injurious action on the retina it will be rendered evident, since the 

 macula is injured, by marked impairment in sight and particularly 

 by a loss or impairment of the pupillary reaction. To avoid injury 

 to the cornea by abiotic rays and injury to the retina by heat we made 

 use of a H% solution of copper chloride in a quartz cell 5 cm. thick. 

 The spectrum of this solution (PI. 5, Fig. 4) shows that it absorbs all 

 waves shorter than 320 /x/x as well as all the so-called heat waves. It 

 thus does not obstruct any short waves that could otherwise reach tlie 

 retina through the lens. 



In these experiments two monkeys were employed in each of which 

 the left eye was blind. One was an old female monkey, whose left 

 eye had been rendered blind by an experimental Kronlein operation 

 involving injury to the optic nerve, one year previous to the first of 

 the present experiments. The otlier was a young full grown male 

 monkey, whose left eye had been rendered blind by injection of 

 alcohol into the orbit nine months previous to the first of the experi- 

 ments. Ophthalmoscopic examination showed complete optic atrophy 

 in the left eye of each. Neither monkey could find the way about 

 when the right eye was excluded from vision. Direct pupillary re- 

 action to light was absent, but the consensual reaction was well 

 marked. This made it possible to determine the presence of a pupil- 

 lary reaction while the right eye was under the influence of the mydri- 

 atic, while the fact that the left eye was blind made it easy to detect 

 any impairment of vision of the right eye. In each animal the visual 

 acuity of the right eye was high, as shown by the ease with which it 

 was able to catch flies and lice. The absence of binocular vision did 



