40 ON MOUNTING DIATOMS, ETC. 



J-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 Microscope, one at a time ; keep the cover flooded 

 with moisture from the breathy 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 geiitly breathed on is securely sealed, and cannot be dis- 

 lodged 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 



