110 



THE AMERICAN MONTHLY 



[June, 



first in a fluid of intermediate density. 

 Such a fluid is readily prepared by 

 mixing water and glycerin in various 

 proportions to suit different objects, 

 but the best plan of all is to transfer 

 the specimens from water to a few 

 drops of a mixture composed of water 

 2 parts, glycerin i part, alcohol 3 

 parts, and leave it exposed to the air 

 but shielded from dust in a watch- 

 glass until most of the alcohol and 

 water have evaporated. In this way 

 the density of the solution slowly in- 

 creases until it becomes approximate- 

 ly the same as the glycerin-jelly. The 

 objects may then be transferred to the 

 latter medium without fear of shrink- 

 ing or any change of form. 



When mounting in cells there is no 

 difficulty about placing the cell in the 

 centre of the slide, for the turn-table 

 aids in that. In mounting in glycerin- 

 jelly or in resinous compounds, it is 

 not usual to work with cells, and it is 

 therefore well to mark the centre of 

 the slide with a small dot of ink or 

 color from a brush. With a self-cen- 

 tering turn-table this is very quickly 

 done ; but perhaps it is just as well to 

 do it in this manner : rule a space 

 three inches by one on a white card 

 and draw diagonal lines from the four 

 corners. These lines cross at the cen- 

 tre, and by placing the slide over 

 the lines the centre can be instantly 

 marked. In mounting be sure the 

 dot is on the lower surface of the 

 slide, so it may be cleaned off' when 

 the work is done. 



Having centered the slide, the gly- 

 cerin-jelly is warmed slightly, either 

 over a lamp or by standing the bottle 

 in warm water, when it liquifies and 

 is ready for use. Place a portion on 

 the warmed slide, transfer the pre- 

 pared object to it, and be sure that no 

 bubbles of air are likely to be included 

 with the specimen. Then take a clean 

 cover-glass in the brass forceps, warm 

 it slightly and place it over the speci- 

 men, pressing it down gently. Should 

 there not be sufficient of the medium 

 to fill the space beneath the cover, 

 more may be applied at the margin 



of the cover, when it will run in and 

 fill every part. On cooling the jelly 

 will set, and may soon be cleaned off 

 the slide arovmd the cover, using first 

 a knife, afterward a cloth and cold 

 water. It is well to dry the jelly 

 somewhat at a temperature of about 

 125*^ F. before finishing the mount. 



The jelly does not become hard 

 enough to be trusted without some 

 protection. It is therefore necessary 

 to use a cement, which should be orna- 

 mental as well as useful. Simple shel- 

 lac or Bell's cement may be used, and 

 either of these may be colored by any 

 of the anilin colors. Over the shellac 

 asphalt is frequently applied, and this 

 makes a rich finish ; but perhaps the 

 neatest finish for mounts of this kind 

 is a border of some clear, colorless 

 medium, such as dammar. The ce- 

 ment should be applied in a narrow 

 ring which extends only far enough 

 over the edge of the cover to hold it 

 securely. 



Occasionally it is desirable to use 

 glycerin-jelly for mounting an object 

 which is so thick as to require a cell 

 or some device for supporting the 

 cover-glass above it. In the absence 

 of a cell an object not too thick may 

 be mounted with three pieces of cover- 

 glass cemented to the slide with balsam 

 so as to sustain the cover-glass. The 

 pieces of glass are scarcely visible in 

 the finished mount. Cells of glass may 

 be used, or what is more convenient, 

 shellac cells made with thick bleached 

 shellac or with benzole balsam, built 

 up in the manner to be described un- 

 der mounting in fluid media. The 

 cell properly prepared it should be 

 first filled with the jelly and no air- 

 bubbles should be left in it. The ob- 

 ject is then transferred, properly ar- 

 ranged, and the cover applied as be- 

 fore described. 



We have not deemed it necessary 

 to enter into detailed instructions to 

 meet every occasion that may arise in 

 mounting. These articles are in- 

 tended to open the way for the begin- 

 ner, and it is to be presumed that any 

 person who undertakes to mount ob- 



