1894.] MICROSCOPICAL JOURNAL 235 



grass-green colored glass (blue will not answer). This 

 slip must be placed on top of the condenser, or the slide 

 containing the living diatoms must rest directly upon 

 the green glass slip. The utility of, and necessity for, 

 the use of the green glass, arises from several causes. 

 The green glass gives a quasi- monochromatic field, and 

 limits all colors to black or white, and absorbs the chro- 

 matic rays, and more particularly the red rays so that 

 one will find it impossible to recognize the true color of 

 objects stained with any of the aniline stains, such as the 

 red of fuschin, or violet, methyl blue, etc. The green 

 glass intercepts the light from the mirror, but the green 

 glass does not interfere in the slightest degree with the 

 resolution of all lines or striations that the lens is cap- 

 able of showing. The other valuable analytical feature 

 is that the ciliary appendages of all inf usorians from the 

 minutest rotifer up are beautifully differentiated around 

 their peripheries. This is indicated by a shimmering 

 phosphorescent aureole surrounding the infusorians when 

 their ciliary processes are active. This phosphorescent 

 aureole is a prominent feature in determining the 

 activity of the exoplasmic epiderm of the Navicula 

 species. The slightest variation, or change of contour 

 in any living particle that has a motile power proper to 

 itself is thus readily made manifest, and only requires 

 resolving power, combined with magnification, carried 

 to the requisite degree with appropriate lenses. 



With the modern Abbe condensers, various accesory 

 modes of illumination are available in the study of the 

 motile phenomena of the diatom, such as the use of 

 oblique light, and central stop effects, in using the light. 

 I have only been enabled to use central light in my 

 studies. As a contrast to the evidence of ciliary action, 

 as indicated by the phosphoresent aureole, if one should 

 note and observe small particles of India ink under the 

 same condition, no aureole of pale light would be seen 



