750 VERHOEFF AND BELL. 



placed within the anterior chamber of a rabbit's eye, by exposing them 

 to the action of ultraviolet light passing through the cornea. The 

 source of the light was a magnesium electrode giving off rays with 

 wave-lengths from 0.28 to 0.309 microns, and the exposures were from 

 twenty-five to thirty minutes. The current was from 3 to 4 amperes. 

 Later he obtained the same result with his cadmium-zinc electrode. 

 Hertel assumed that the bacteria were actually killed, but he did not 

 state that this was demonstrated by means of cultures. He also did 

 not exclude the possibility that the effect on the bacilli was due to heat. 



Hertel, in addition, tested the therapeutic action of ultraviolet 

 light on a series of rabbits' eyes in which he had produced staphy- 

 lococcic corneal ulcers and obtained " pleasing results." The resulting 

 scars were slight and no changes could be found in the depths of the 

 eyes. These results, however, it seems to me, lose any possible 

 significance when it is considered that staphylococcic corneal ulcers 

 artificially produced in rabbits as a rule promptly heal without any 

 treatment, as I have frequently observed. 



Hertel maintains that light of short wave-lengths has a greater 

 deleterious effect on bacteria than on tissue-cells. This may be true 

 for very short waves, but it is certainly not true for waves which are 

 able to pass through the cornea. Thus, I found that severe keratitis 

 could be produced by exposing the cornea through a crown screen to a 

 quartz mercury -vapor lamp at a distance of 20 cm. for one and one- 

 half hours, whereas staphylococci suspended in distilled water and 

 exposed under the same conditions were not killed in six hours ^. 

 This experiment also would seem almost alone sufficient to prove the 

 impossibility of destroying bacteria within the clear cornea without 

 producing too much injury to the corneal cells. This being the case, 

 it is almost inconceivable that bacteria could be destroyed in a cornea 

 infiltrated with pus-cells and so made practically impassable to germi- 

 cidal waves. 



Hertel also attached importance from a therapeutic point of view 

 to the conjunctival hyperemia and cell irritation produced by ultra- 

 violet light. The practical value of these factors is questionable, and 

 the latter factor would seem more likely to do harm than good in the 

 case of corneal ulcers in which the cells already have sufficient un- 



2 It is important to note that for these long exposures it is necessary to keep 

 the bacterial container surrounded by cool water, as otherwise the bacteria 

 may be killed in an hour or so by the accumulated heat. The lamp and 

 screen used in this experiment are described later. 



