66 



THE AMEKICAK MOKTHLY 



[April, 



twenty-foiu" hours, until after cooling 

 it is found to be very brittle ; it will 

 dry a great deal faster in mounts af- 

 terwards. 



In general moiniting, transfer with 

 a pipette the quantity needed from 

 the previously well-cleaned material 

 to a bottle, and fill up with distilled 

 water. After the diatoms have set- 

 tled, drain oft' the water and renew, 

 and continue this process till the last 

 trace of alcohol in which the cleaned 

 diatoms had been kept is removed. 

 Now place the well-cleaned covers 

 on a smooth, preferably black, plate 

 of glass or hard rubber ; by breath- 

 ing on the glass before placing each 

 coyer and lightlv pressing them down, 

 they will adhere sufticicntly. After 

 agitating the material, take up and 

 drop on each cover sufticient to fill 

 the whole surface, and protect them 

 from floating dust under a bell-glass, 

 and let them remain till they are dry. 

 To prevent jarring the settling dia- 

 toms and secure an even distribution, 

 it is safest to let the covers remain 

 where they have been filled. Treated 

 thus the diatoms will settle very uni- 

 formlv, and all annoyance from the 

 tendency diatoms not freed from al- 

 cohol have to form clusters and run 

 together on applying heat will be 

 avoided. Attention has to be paid to 

 the proper density of the material. 

 If the covers, as has been recom- 

 mended, have been placed on a dark 

 surface, on«e soon gains experience 

 enough to be able to tell Avhether 

 things appear about right. As soon 

 as the covers are dry, transfer them 

 on a slide to the mounting micro- 

 scope and examine for particles of 

 dust that may have settled on them. 

 Remove them to the glass plate as 

 before and put a drop of the mount- 

 ing medium on each ; letthem dry un- 

 der the bell-glass to the consistency 

 of syrup. Now put them on the 

 well-cleaned and centered slides, ap- 

 ply gentle heat and the covers will 

 settle level, and the medium will 

 distribute itself evenly to the edge if 

 the right quantity has been used. In 



using a chloroform solution the cov- 

 ers may be transferred to the slides at 

 once. Remove the mounted slides to 

 a tin case with removable shelves of 

 stift' cardboard that have strips pasted 

 on them, and place them covers 

 downward. This will tend to keep 

 the diatoms in contact with cover 

 and insure free circulation. To fa- 

 cilitate drying, the tin case may be 

 placed on a stove or in an oven, but 

 care must be taken not to let the 

 temperature rise above 50° Celsius. 



If the material has been well 

 cleaned, the often recommended burn- 

 ing of diatoms on the covers becomes 

 not only unnecessary, but often proves 

 injurious, as many of the finer forms, 

 also polycystina and sponge spicules 

 often present in fossil material, are 

 apt to warp and crack or turn black. 

 In mounting diatoms as test objects 

 burning is advantageous, as it brings 

 the diatoms in closer contact with the 

 cover, and the cracks are not of as 

 much consequence if the structure is 

 well preserved. 



For dry mounts, it is well to al- 

 ways have a nunil)er of slides ringed 

 with shellac cement, or Canada bal- 

 sam in chloroform on hand, to insure 

 the thorough hardening of the cells. 

 Place the covers on the cell and run 

 a hot glass rod around the cover to 

 soften the surface of cell ; this will 

 attach the mount firmly. 



In mounting selected diatoms, 

 transfer the material freed from alco- 

 hol to large covers, protect them from 

 dust, and let the water evaporate ; 

 place the cover containing the ma- 

 terial and another to hold the selected 

 forms on a slide, and put it under the 

 mounting microscope, using powers 

 of from thirty to sixty diameters. The 

 bristles from the e}"elash of the hog, 

 fastened to wooden handles, make 

 a good instrument for transferring. 

 They are very stift', elastic, and taper 

 to fine points. A number of these 

 mounters ought to be prepared, as it 

 is an easy matter to select them from 

 finest to coarse, and have them ready 

 as occasions require. The selected 



