776 WALKER. 



undiminished. Further he regarded fluorescence of the nature of a 

 catalytic chemical reaction if it was to be considered chemical at all, 

 emphasizing the fact that no chemical basis for this phenomenon 

 had ever been established. Against the proposition that fluorescence 

 decreased with the length of time of exposure, he cited an experiment 

 in which he exposed and fluoresced the rabbit's lens continuously 

 for five or six hours with no noticeable change in intensity of fluo- 

 rescence whatever. He objected to drawing any conclusions from 

 the lens of a gliomic eye since the presence of a pathological condition 

 might readily alter the properties of the lens although it was appar- 

 ently normal. 



Later in 1909 Schanz and Stockhausen^-^^ Ijy means of Wood's 

 light filter which absorbs the rays below 37.5 fxfj. were able to make 

 further investigations on the range of fluorescing rays in the same 

 manner previously employed. This filter inhibited the fluorescence 

 very little so that the range most effective in producing fluorescence 

 was placed at 375 fxn to 400 /x/i. The fresh clear lenses from eyes 

 removed by tumor or absolute glaucoma were vised. The absorption 

 power of the cornea and lens in these cases were studied by photo- 

 spectrographic methods with a quartz glass optical system in the 

 usual manner. From a study of these photographs they agreed with 

 Birch-Hirschfeld that the cornea had a greater absorption power than 

 glass and considered that the effectual absorption amounted to 320 ytiju 

 as mentioned under cornea. That absorption in the lens was increased 

 by age was further confirmed. 



Schanz and Stockliausen^-^^ further investigated the phenomena of 

 fluorescence with the result that they retracted their previous idea 

 that fluorescence represents a separate spectral color lavender-gray, 

 and returned to the theory of Helmholtz that it is made up of rays of 

 various length as is ordinary mixed or white light. They used the 

 crossed prism or crossed spectrum method of Newton to analyze the 

 fluorescent light in the following manner. With a quartz glass optical 

 system, the light from an arc light was concentrated on a prism, the 

 resulting spectrum was rendered linear by focussing it on a screen 

 with a cylindrical lens, axis parallel to the length of the spectrum. 

 Now when thin layers of fresh human lens were laid on the screen in 

 various regions of the spectrum fluorescence was noted to begin in the 

 blue region, become more intense in the violet region, and was strong- 

 est of all in the ultra violet region between 370 nfx and 400 juju. Below 

 370 nij. fluorescence diminished slowly. The maximum point of fluo- 

 rescence was at 385 nfx. This fluorescent light was further analyzed 



