THE MICROSCOPE. 27 



simple microscope, one at a time ; keep the cover flooded with 

 moisture from the breath, and deposit the scales picked up wherever 

 wanted in lines or patterns. They will readily leave the bristle for 

 the wet glass, and can be pushed about quite easily. When the 

 moisture dries off, no stain is left, and the objects will adhere 

 with sufficient firmness to resist anything short of a sharp jar. 

 When the line or pattern is finished, mount in a shallow cement 

 cell. 



Ba/sam Mounts. — The cover must have a film of a gelatinous 

 nature which is insoluble in balsam and its solvents. A thin aqueous 

 solution of isinglass carefully filtered serves well. A single drop is 

 placed on a clean cover, and spread out as thin as possible with a 

 clean needle. It dries almost instantly in warm weather, and in a 

 few seconds in winter. A diatom placed on this film and gently 

 breathed on is securely sealed, and cannot be dislodged without 

 moisture. Care must be taken to place the diatom in position while 

 the film is quite dry ; then breathe on it ; allow the film to dry 

 again ; then place another diatom, and so on, till the line or pattern 

 is finished. If any of the diatoms are thich or likely to be crushed, 

 stick three bits of cover-glass under the edge of the cover with gum, 

 and place a dot of gum on each before placing the cover in position 

 on the slide. This, when dry, will keep the cover in its place while 

 introducing the balsam, before doing which, allow a little benzine 

 to run under by capillary attraction, which soon displaces the air 

 from the diatoms. Then apply a little balsam to the edge of the 

 cover and a bit of blotting-paper to the opposite edge. This draws 

 away the benzine, and the balsam follows and takes its place. 

 Another plan is to gum a piece of good cream-laid paper on the 

 slide, centre on the turn-table, and make two cuts through the 

 paper, removing the middle and outer portions and leaving a ring of 

 paper to form a cell as large as the cover ; then cut two small open- 

 ings in opposite sides of the ring, gum the top of the cell and place 

 the prepared cover on the gummed surface. When dry apply ben- 

 zine to one of the small "sluice gates," and then balsam as before. 

 Put the slide in a warm place for several days, and finish off with 

 white, black, or colored varnish to fancy. Winter is the best time 

 for dry mounts, as the breath dries off too soon in hot weather ; and 

 summer is the best time for the balsam mounts, as it is difficult in 

 the winter to keep the breath from moistening the isinglass at the 



