768 WALKER. 



by vascularization. The ulcer formation as is usually the case, often 

 lead to, or was accompanied by, iritis. Corneal disturbance in snow 

 blinding has been occasionally reported. Hildige^^^ in 1861 and 

 Reich ^^* in 1880 saw small ulcers. 



Widmark *^^ in 1889 studied the progress of the earliest changes on 

 the cornea due to ultra violet rays. With the aid of the microscope 

 he found first in the corneal epithelium a swelling and necrosis of the 

 nuclei leading to necrosis of epithelial cells, and small areas of desqua- 

 mation followed sometimes by ulcerative conditions and usually by 

 opacities. These findings were at once verified by Ogneff^^^ and 

 Bresse ^^ and later by many others. Hertel ^P in 1903, repeating this 

 experiment and with rays of 309 m/x to 280 ^/x from the magnesium 

 spark, was able to produce the same corneal injuries, as well as to kill, 

 or at least demoralize bacilli enclosed in quartz containers and placed 

 in the anterior chamber. This could not be done when common glass 

 was interposed in the control experiment. That this fact may be 

 taken as evidence that rays of 280 mju were able to penetrate the cornea 

 does not follow, was pointed out two or three years later by Birch- 

 Hirschfeld, Schanz and Stockhausen, who considered that rays of 

 greater length than 280 mm in sufficient amount to kill organisms 

 could not be excluded (cf. page). 



Widmark made no attempt to determine the absorptive power of 

 the cornea by spectrophotographic methods. Schanz and Stock- 

 hausen ^^^ were among the first to attempt accurate measurements 

 in this way on the human as well as on the animal cornea. They 

 found that all rays below 300 mm are absorbed by the cornea. Hess, 

 Birch-Hirschfeld and Herzog verified this measurement and again 

 later Birch-Hirschfeld^^ attempting still greater accuracy, with the 

 same method, placed the absorptive limit at 306 mm- Parsons ^^® in 

 England in the same way found rays above 295 mm able to penetrate 

 the cornea. 



Still later, in 1909 Schanz and Stockhausen reconsidered the limit 

 of 300 ij.li for the absorptive power of the cornea placing it at 320 ijl/m 

 for all practical purposes, since the spectrum was so weakened be- 

 tween 320 fjLfjL and 300 hijl as to be without action on the lens. 300 nn 

 was however still considered the point of complete absorption. 



Martin ^^^ in 1912 agreed with Parsons that the cornea offered no 

 resistance to waves above 295 nix length but all beyond t^is limit were 

 completely cut off. 



