Cleaning and Mounting Diatoms, etc. 209 



spreads evenly under the cover, and put away to dry. When 

 dry, finish off with a coat of black cement. 



Selected Diatoms and Polycystina. — Take an ounce of 

 distilled water, add 6 or 8 drops of ordinary gum water, and 

 filter. Clean a cover-glass, and place a drop of the diluted 

 gum upon it ; put away to dry. 



Spread the diatoms or polycystina on a slip, and dry 

 them over a spirit-lamp. Select the desired forms with a 

 fine brush or bristle, and breathe upon the gummed surface 

 of the cover, and place the forms upon it. When dry, 

 apply a drop of balsam, and put away out of reach of 

 dust for twelve hours. Bake and finish as directed for un- 

 selected slides. 



In mounting selected polycystina, they must be between 

 two covers ; if on a single cover, the forms would be upside 

 down when the cover was reversed. If a transparent 

 mount is desired, the two covers can be fastened to the- 

 slide with a drop of balsam. If opaque, the forms must h& 

 burnt, and one side must be blackened ; in other respects, 

 proceed exactly as you would for unselected opaque mounts. 



Polycystina may also be mounted in a dry opaque cell. 

 Take a slide, run on a disc of black varnish, and when this, 

 has dried, fasten a disc of black gummed paper over it- 

 Then take a shallow cell, apply a coat of cement to on& 

 side of it, and let it nearly dry ; then fasten to the paper 

 disc, and put away to dry. Apply a little dilute gum 

 water to the bottom of the cell, select the specimens, and 

 put them into the gum ; if they do not adhere, breathe on 

 the surface of the gum. When all are arranged, put the 

 slide away until everything is quite dry ; then add a coat 

 of cement to the upper side of the cell, let it nearly dry, 

 and then apply the cover-glass. 



Foraminifera — Unselected Transparent Mounts. — 

 Dry the forms on a slide with the aid of gentle heat, and 

 scrape them off into a bottle of turpentine, in which they 

 must soak until all trace of air has disappeared. Then 

 clean a cover-glass, fasten it to a slide with condensed 



14 



