ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 719 



in which to fit the lenses, which are just the li-inch and ^-inch 

 objectives, which give far better definition than common pocket lenses. 

 (3) A steady hand. (4) Patience and perseverance. 



Dry Mounts. — All diatoms and scales should be mounted on the 

 cover, not the slide. Lay a clean cover on a slide and keep it in 

 place by a drop of water between. As scales are larger than diatoms, 

 it is well to begin with them. Put several on a slide in the ordinary 

 way, pick out the ones wanted with a bristle under the simple Micro- 

 scope, 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. 



Balsam 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 thick 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 openings in opposite sides of the ring, 

 gum the top of the cell and insert the prepared cover on the 

 gummed surface. When dry apply benzine to one of the small 

 1 sluice gates,' and then balsam as before. Put the slide in a warm 

 place for several days, and finish off with white, black, or coloured 

 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 wrong time. The cement 

 cells should be quite dry and hard before mounting, or a dewiness 

 will appear and ruin the object. Soften the cement over the lamp, 

 press the cover down till it sticks all round, let stand a day or two, 

 and finish off. No doubt the diatoms would be more secure if burnt 



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