98 
Journal of the 
one rather stout for large diatoms, the other not thicker than a 
human hair, and preferably somewhat curved, for lifting small 
valves, and also for removing particles of dust which frequently 
settle on or among the diatoms during the process of mounting; 
but for moving the diatoms into the exact position which they are 
to occupy on the slide a fine needle is almost indispensable, bristles 
being too elastic. If, however, it should be necessary to draw a 
diatom towards the operator’s hand a bristle or hair must be used. 
When the objects are to be mounted in balsam, the slide should 
be allowed to dry, and a small drop of carbolic acid placed on the 
diatoms, which are then to be examined with the microscope, as it 
frequently happens that the gum, if not thin enough, seals up the 
minute cells in the valve, or even the whole cavity beneath it, 
preventing the entrance of the acid. In this case a drop of spirits 
of wine placed on the diatoms will usually find speedy entrance 
and dispel all bubbles, and while the diatoms are still wet with 
the spirit the carbolic acid may be placed upon them. Gentle 
warmth will then evaporate the spirit, leaving the acid, and it 
only remains to apply a small drop of balsam and a cover, taking 
care, if any of the valves are very convex, to provide rests to 
prevent the cover from crushing them. It is better to let the 
balsam fall on the diatoms than to apply the cover first and let it 
run in, as it very often carries in with it particles of dust, cotton 
fibres, tkc., which may be on the slide or the edge of the cover, 
and which are apt to come in contact with the diatoms and remain 
there. The running-in process is only necessary when the valves 
are not cemented to the slide, and when, consequently, balsam let 
fall on them would be almost certain to disperse thorn. 
In most cases it is advantageous to mount the diatoms on the 
cover, which is easily done by first fastening it to a slide with a 
drop of glycerine, which will not evaporate during the process of 
mounting, and is easily removed afterwards. I have found that 
lar^e diatoms, such as 4 rachnoiducus, when mounted on the slide 
and examined by reflected light, are apt to show a slight haze 
surrounding the group, instead of the intense black ground which 
should be presented when all light is shut off from below the stage. 
This is caused by reflection from the under surface of the slide, 
and can be avoided by mounting on the cover and placing some 
dead-black material at the bottom of the cell. It is also advisable 
