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 " U viol " 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 [J [J 



the ultraviolet rays FIG. 21. Reichert Fluorescence Microscope. 



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, 



