EFFECTS OF RADIANT ENERGY ON THE EYE. 751 



favorable influences to contend with. In any case they would not 

 justify the use of ultraviolet light in treatment of such conditions in 

 the absence of any germicidal effect of the light. 



In a later communication, HerteP reported in detail a series of 

 clinical cases of corneal ulcer treated by means of ultraviolet light 

 from a cadmium-zinc electrode. The latter he recommended as being 

 equal in efficiency to the magnesium electrode and at the same time 

 more practical to use. Twenty-six cases were treated with light 

 therapy alone, 8 cases with light therapy followed by Saemisch section, 

 and 13 cases with light therapy followed by cauterization or the latter 

 and Saemisch section. Thus in 21 out of his 47 cases of corneal ulcer, 

 the result of the light therapy was so unsuccessful that cauterization 

 or Saemisch section had to be undertaken. These results do not 

 seem impressive for an agent that is supposed to kill the bacteria 

 within the ulcers. Hertel exposed his patients from three to five 

 minutes two or three times daily. At the most this was equivalent to 

 a daily total exposure of only fifteen minutes. Now he had found 

 that it required from twenty-five to thirty minutes to kill (or inhibit)? 

 bacteria exposed through a perfectly clear cornea. How then could 

 it be expected that an exposure of fifteen minutes would suffice to kill 

 them in a purulent infiltrate which acts as a far more effective barrier 

 to ultraviolet light? 



In a communication to appear later, Louis Bell and I show that 

 interrupted exposures to ultraviolet light wdth intervals of less than 

 twenty-four hours have practically the same effect on the cornea as a 

 continuous exposure of the same total length. For this reason by 

 frequently repeating his exposvu'es, Hertel undoubtedly increased 

 the injury to the corneal tissue without at the same time, in all proba- 

 bility, obtaining a corresponding increase in germicidal action. 



In his experiments and in the treatment of his cases Hertel employed 

 no screens. Thus the cornea had not only to contend with the rays 

 that could penetrate it, but also with those stopped within the stroma 

 and at the surface. As the rays stopped near the surface are evi-, 

 dently useless so far as killing bacteria within the stroma is concerned 

 it occurred to me that by screening them out and so decreasing the 

 damage to the cornea, longer exposures might safely be used, thereby 

 increasing the possibility of a germicidal effect within the cornea. 

 The screen selected for this purpose was a crown glass, which permitted 



3 Hertel, E.: Experimentelles und klinisches iiber die Anwendung lokaler 

 Lichttherapie bei Erkrankungen des Bulbus, Arch. f. Ophth., 1907, Ixvi, No. 2, 

 p. 275. 



