764 WALKER. 



exposure, while bacteria in the anterior chamber were killed in 25 to 

 30 min. but not in the control with common glass interposed (cf. 

 page 749) . In none of the eyes, 26 in all, was lens trouble noted. 



In 1904 definite pathological changes believed to be due to ultra 

 violet light were noted by Birch-Hirschfeld ^^ in the finer structures of 

 the retina. 



In 1906 and 1907 Vogt ^^^ and Hallauer ^^^ began the careful study 

 of transparent and colorless protection-glasses, and the latter produced 

 by a secret process the so called " Hallauer glass." 



In 1907 Schanz and Stockhausen ^°^ also invented and patented a 

 new glass, which they called " Euphos glas." 



In 1908 Birch-Hirschfeld ^^ studied in five cases visual field changes 

 produced by uviol lamps, showing sector and ring formed scotomata 

 for red and green to be the predominant varieties, but later (1912) 

 he objected ^^ to the ringscotoma found by Jess '^^^ in the same year. 



Voege^^^ in 1908 asserted that daylight might be taken as the ideal 

 light, especially "cloud light." He compared the spectra of various 

 high power lights protected with milk and opal glass coverings, with 

 the spectra of cloud light and found them to compare favorably, and 

 therefore concluded that these lights so protected are not to be con- 

 sidered dangerous when properly used. 



In 1909 Schanz and Stockhausen^^® vigorously opposed this attitude 

 and their view was supported in the same year, by the appearance of 

 the statistical study of Handmann ^^^ showing that the senile cataract 

 begins in the region of the lens most exposed to the short wave length 

 light of the sky, that is in the lower half. 



In this year Birch-Hirschfeld^^, Schanz and Stockhausen^^®, and 

 Hallauer ^^^ (on human lens only), by spectrophotographic method, 

 measured with the greatest care, the absorptive power of various kinds 

 of glass, the cornea, vitreous humor and lens of various animals and of 

 the human eye. They also made careful measurements of the spectral 

 range of a great variety of light sources with and without co^'ering 

 of common glass, milk glass and opal glass. 



In 1910 Schanz and Stockhausen ^^^ made a very careful study of the 

 fluorescence of the human lens by a hitherto unused method, and also 

 examined more carefully than before the spectrum of the glass blowers' 

 furnace and the conditions under which the glass blowers were forced 

 to work. They contended that the glass makers' cataract is due the 

 longer of the ultra violet rays with perhaps the assistance of the short- 

 est visible rays. 



Also in 1910 Hertel and Henker ^'^^ accepting Voege's idea that the 



