208 Modern Microscopy 



up with a pair of forceps, and bring its balsamed surface in 

 contact with the centre of a warmed slide. The balsam 

 should then run to a neat bevelled edge all round the 

 cover ; should it not do so, warm the slide a little more 

 until it does. 



Unselected Polycystina. — Take the forms from the 

 bottle with a glass tube, and spread them on a slide ; dry 

 them over a spirit-lamp. Now clean a cover-glass, fasten 

 it to a slip with your breath, and place a drop or two of 

 balsam on it ; take up some of the polycystina on the 

 point of a knife and place them in the balsam ; stir them 

 well up with a needle and put away for twelve hours. 

 Bake over a spirit-lamp for ten minutes, and while warm 

 stir up again gently with a needle, and spread the forms 

 evenly over the cover. Warm a glass slide, and proceed as 

 directed for unselected diatoms. 



Unselected Polycystina as Opaque Objects. — Dry 

 some polycystina on a slide, then take a platinum capsule, 

 put the dried material into it, and heat over a spirit-lamp 

 to a dull red. Clean a cover-glass, fasten it to a slide with 

 your breath, and apply a few drops of balsam. Take up 

 some of the dried forms, put them into the balsam, and stir 

 up with a needle until they are evenly spread over the 

 cover ; put away out of reach of dust for twelve hours, so 

 that the air may escape from the forms. Now place on a 

 hot plate and apply gentle heat for ten to fifteen minutes to 

 bake the balsam. Clean another cover-glass, add a drop 

 or two of balsam to the hardened balsam, and apply the 

 second cover-glass ; warm again, and with a needle press 

 gently on the upper cover until it lies perfectly flat ; then 

 allow to cool, apply a coat of black shellac cement all over 

 one side of the upper cover, and put away to dry. In the 

 meantime take a slip, put it in a turn-table, and run on a 

 disc of black varnish of the same size as the cover ; let this 

 dry, then add a drop of strong gum or glue ; take up the 

 covers with a pair of forceps, and put the blackened side 

 into the glue ; press down with a needle until the glue 



