684 VERHOEFF AND BELL. 



extreme intensity and length, but insufficient to produce heat effects, 

 it is impossible to injure the retina by light containing any or all rays 

 capable of reaching it through the lens. They exclude both the pos- 

 sibility of injuring the retina by over stimulating its perceptive 

 mechanism, and also of injuring it l)y the abiotic action of light. 

 Most surprising was the rapidity with which the retina regained its 

 function. Thus in all four experiments within six minutes the con- 

 sensual pupillary reaction was fully reestablished. There was in both 

 sets of experiments, however, a marked difference between the young 

 and the old monkey in regard to the time required for the restoration 

 of usefid vision. In the case of the young monkey sufficient vision to 

 enable him to see his way about, avoid hand movements, etc., was 

 present in ten minutes after the exposure ended. The old monkey 

 on the other hand was practically blind for an hour or more. In fact 

 her visual acuity did not seem to l)e fully restored until the morning 

 following the exposure. Both animals were able to catch fiies with 

 their usual expertness after the mydriasis had disappeared.* 



The results obtained in these experiments would also seem to be of 

 some significance in regard to the question of light adaptation. They 

 suggest that after a certain state of retinal fatigue is reached no 

 further effect is produced, however long the exposure. In fact it would 

 seem, in young individuals at least, that after this stage is reached the 

 recuperati^'e processes begin while the retina is still exposed. This 

 aspect of the question, however, does not concern us here and further 

 experiments would be necessary to elucidate it fully. 



In addition to the experiments on the eyes of monkeys we have 

 availed ourselves of an exceptional opportunity to make a similar 

 experiment upon a human eye. The subject was a female patient 

 aged 50 years affected with carcinoma of the eyelid and orbit, the 

 growth being so extensive as to necessitate removal of the eye. The 

 left eye itself was apparently normal, the media being clear and the 

 fundus normal. The visual acuity was reduced to fg— (unimproved 

 by lenses) for some reason not definitely determined, but probably 

 due to some irregularity in refraction resulting from the pressure of 

 the upper lid. The lower lid was almost completely destroyed, while 

 the upper lid was somewhat drawn down by cicatricial tissue at the 

 outer canthus. It was therefore necessary for the observer to hold 

 up the eyelid by finger pressure during the experiment. The right 



* Both of these monkeys were later killed, one after seven months, the other 

 after fourteen months, and on microscopic examination the eyes that had 

 been exposed wer3 found normal. 



