OF A SUBSTANCE EESEMBLING QUININE. 
o o 
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A guinea-pig was given quinine, and, for comparison, another guinea-pig was killed 
at the same time, having had no quinine. 
In the pig that had taken quinine, each organ was heated in a water-bath with very- 
dilute sulphuric acid. This extraction was repeated over and over again. The acid 
extracts were mixed and filtered after cooling, neutralized with caustic soda, and re¬ 
peatedly shaken up with their own bulk of ether. The residue left after evaporation of 
the ether, was taken up by dilute sulphuric acid, filtered and tested for fluorescence. 
The pig that had taken no quinine, had each organ treated in a precisely similar way. 
To our great disappointment, at first, we found that not only had the pig that had 
taken quinine a fluorescent substance in the textures, but that an almost exactly similar 
substance was extracted from the organs of the pig that had taken no quinine. Every* 
texture was examined, and in every one this fluorescent substance occurred. 
We then endeavoured, in every possible way, to find a means of separating the 
natural from the induced fluorescence. And as every method failed, and we were com¬ 
pelled to recognize the close similarity of the substance that exists in the textures to 
quinine itself, we for a time dropped the original inquiry, and proceeded to a more com¬ 
plete investigation of the natural fluorescent substance in animals. 
Without any preparation this substance can be shown to exist in the living and in the 
dead textures. There is one transparent substance which is above all most suited for 
this inquiry. 
Here are some lenses removed from the eyes of bullocks, guinea-pigs, and man. You 
see how clear, white, and transparent these substances are; and if I take a bullock’s eye, 
which by gentle pressure has been flattened so that the structure can be distinctly made 
out, there is plainly no colouring matter. As in quinine, nothing is seen until the blue 
rays of the electric light fall on the lenses; then look at the splendour of the reaction. 
Here, with the guinea-pig’s lenses, the same is seen; and here, with the flattened 
bullock’s-eye. You might be tempted to think that this is a -post-mortem change, a 
result of decay; but here is a fresh bullock’s eye, look at this blaze of bluish-green light; 
but still more full of suggestion is an experiment with a dilated pupil in a living animal 
or in man. Let me show you my own eye, for in it you can see the lens shining w'ith 
this unnatural, because unaccustomed, light, looking like an opaque substance, a blue- 
green cataract. 
Life and death then have nothing to do with the existence of this substance; here, it 
is present in the living lens; it does not disappear from lenses that have been kept for 
months in glycerine. 
I have already said that this substance not only exists in the lens, but that it can be 
found everywhere b^’- treating any animal substance, first with dilute acid, then neutra¬ 
lizing with alkali, and then extracting with ether: thus we obtain solutions having 
exactly the same properties as you see in the lens. Here, for example, is such an extract 
from the liver; here, from the kidney; here, from the heart. When an acid solution 
of this substance is treated with ether, no fluorescent substance is obtained. First, as 
with quinine, the acid must be neutralized before this substance or the quinine can be 
taken up by the ether. 
Having then obtained these solutions, we were able to compare them with solutions 
of quinine in their actions on the spectrum. And first, the solution of the natural sub¬ 
stance begins to fluoresce a little before the solution of quinine; but on carrying it on 
through the spectrum it ends where quinine ends. 
The fluorescent light of the natural substance is a little more greenish than the fluo¬ 
rescent light of quinine. 
If a quartz-cell containing this fluid is interposed between the source of light and a so¬ 
lution of quinine, no fluorescence takes place in the quinine; and if quinine is interposed 
between the light and this natural solution, scarcely any fluorescence is observed in it. 
When a solution of salt is added to the naturally fluorescing substance, it is almost 
entirely destroyed, as happens with quinine. 
If the natural solution is boiled with permanganate of potash, it does not lose its fluo¬ 
rescence, nor does quinine; but when permanganate with excess of alkali acts upon this 
substance or upon quinine, the fluorescent substance is entirely oxidized. 
Hence this substance, by the mode of its extraction and by its remarkable action on 
light, is very closely related to quinine; and this led us to apply the chemical tests for 
quinine to this natural fluorescent substance, after extraction from the body. 
VOL. VITT. 
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