EFFECTS OF RADIANT ENEEGY ON THE EYE. 779 



the central damaged area but under cover of the iris was a ring or 

 "wall" of deeply stained cells crowded together perhaps by the swollen 

 central cells, first damaged. These changes appeared in the pupillary 

 region and would show regeneration as indicated by numerous mitotic 

 figures in the course of 2 to 4 days, if no further or stronger exposure 

 was made. He found that interposition of glass plates cutting out 

 rays below 313 fxiJ, or even 280 ^t/x prevented lens trouble. He agreed 

 with Widmark in thinking the glass blower's cataract due to ultra 

 violet light. 



Birch-Hirschfeld '^^, however, took up this point in 1909. He ex- 

 posed a rabbit's eye for 5 minutes at a time on three successive days 

 to the light from a 5 amp. arc light which traversed first a " Euphos- 

 glas" and was then concentrated with a 20 diopter common glass lens. 

 No heat filter was used. On the 4th day he found on microscopical 

 examination the same lens changes recorded by Widmark and Hess. 

 Therefore he concluded that rays in the neighborhood of 400 ^t/x must 

 be responsible, and that probably some of the shorter blue and violet 

 rays were effective as well as the longer ultra violet rays. Further he 

 argued that this same group of rays was in all probability responsible 

 for the production of the glass blowers cataract and possibly also for 

 the production of the senile cataract, though this latter he regarded 

 as far from proven (cf. page 677). 



Without experimental evidence Wenzel *^^ in 1806, von Beer in 1817 

 and Plenk in 1877 ^* pointed out the disposition to cataract among 

 glass blowers, and Meyhofer ^^^ in 1886, found the percentage to be 

 11.6 in glass blowers under 40 years old. These cataracts commonly 

 began on the left side which was most severely exposed to the heat. 

 Robinson ^^^ and Stein ^*^ later confirmed these findings. 



Schanz and Stockhausen ^^° in 1910, measured the quantity and 

 quality of the radiations from the glass blowers furnace, and the 

 temperatures to which his head was subjected at different stages of 

 his work. By accurate spectro-photographic measurements of the 

 light at the distance at which the glass blower worked, they found the 

 spectrum to be especially strong in the region from 400 MM to 350 /x/i, 

 shading down to 320 h/jl below which there were no rays. At once 

 they considered they had the explanation why these people had lens 

 trouble without anterior eye trouble. The worker's head was exposed 

 to a temperature of 110 degrees C. in taking the glass from the oven 

 and to 45 degrees C. during the process of blowing. This temperature, 

 while it might be a factor, is not so great as that to which many iron 

 and blast furnace workers are exposed without receiving any eye 



