EFFECTS OF BRIGHT LIGHT UPON THE EYES 53 



them. With the help of Mr. E. C. C. Baly, F.R.S., I have 

 recently investigated the absorption of ultra-violet rays by the 

 various parts of a freshly excised rabbit's eye. The cornea 

 or other structure is placed before the slit of a spectroscope, 

 all the constituent lenses and prisms of which are made of 

 quartz. We found that the cornea, lens and vitreous humour 

 all caused quite definite absorption. Considering the pre- 

 dominant fluorescence of the lens it was surprising to find how 

 much absorption was occasioned by the cornea and vitreous 

 humour. It is possible that the fluorescence of the lens has 

 been overestimated owing to its high refractive index which 

 would tend to exaggerate the effect of any possible escape 

 of luminous waves. Similar results have since been published 

 by Schanz and Stockhausen. 



The evidence, however, goes beyond this point. There is 

 definite experimental evidence of the actual changes which are 

 produced. Thus Widmark caused slight opacity in the lens 

 of the rabbit by prolonged action of concentrated light from 

 an arc lamp. Exposure for two to four hours in a 1,200 candle- 

 power lamp was necessary and he then only succeeded in four 

 out of eleven cases. On the other hand it must be stated that 

 OgnefT failed to obtain any change by the brief application of 

 a 5,000 — 6,000 candle-power lamp. More recently Hess found 

 microscopic changes in the anterior cells of the lens after 

 exposure for some hours to the light from Uviol mercury vapour 

 lamps. There was no actual o] acity of the lens but this was 

 probably because of the comparatively brief exposure. Birch- 

 Hirschfeld has shown that changes also occur in the retina 

 when exposed to ultra-violet rays. The nerve cells of the 

 retina show early stages of those changes which are known 

 to be followed by degeneration and atrophy if the stimulus 

 is sufficiently prolonged. The experiments were performed on 

 rabbits and it is striking that the effect was much greater if the 

 lens of the eye had been previously removed. The crystalline 

 lens, therefore, by its absorption of these rays acts as a protect- 

 ive mechanism to the perceptive structures. Hence, there is 

 ample evidence to show that ultra-violet rays are deleterious 

 to the eyes, not only in so far as the superficial structures are 

 concerned but also the deep ; further that prolonged action of 

 weak doses is also be avoided. 



All the more recent forms of electric lamp emit light rich 



