ILLUMINATION OF OBJECTS; ULTRA VIOLET LIGHT 
49 
not to the light rays resulting from the fluorescing of the sub¬ 
stance; the ultraviolet rays, however, readily penetrate quartz. 
We have, therefore, only to substitute quartz for glass in the 
condenser in order to concentrate the ultra rays on the object 
upon the stage. It follows from this that although the illu¬ 
minating devices must be of quartz, as also the object slide upon 
which the object lies, the objective and ocular may be those 
ordinarily employed. 
Either a carbon arc with special carbons or a mercury vapor 
lamp may be employed as radiant. 
Fig. 21 shows diagrammatically the construction of a fluores¬ 
cence microscope. The rays from the radiant R are concen¬ 
trated by the quartz condensing lens Q. then pass 
through the Wood-Lehmann filter F consisting of 
a quartz or of a blue “ Uviol ” glass cell, thence 
the rays pass to the reflecting quartz prism P which 
in turn reflects 
them into the ^ 
quartz lens dark- 
ground condenser. 
This device brings 
the ultraviolet rays 
to a focus upon the 
object supported upon the stage by means of an object slide of 
quartz or of Uviol glass. Ordinary glass, besides being practic¬ 
ally opaque to rays of very short wave-length, as stated above, 
fluoresces with a violet or bluish tint under the action of the 
ultraviolet rays and cannot therefore be employed as a support. 
If it is necessary to cover the preparation ordinary glass cover- 
glasses may be employed, but glass should never be used if 
thin quartz cover-glasses are available. 
As in all dark-ground illuminators, an immersion fluid between 
condenser and object slide is essential. In this case glycerine is 
employed {n = 1.47). 
The light filter whose function is the removal of waves of 
long wave-length, affecting the eye as light, consists of two com¬ 
partments, one filled with a 20 per cent copper sulphate solution. 
Fig. 21. Reichert Fluorescence Microscope. 
