The mounting of Foraminifera in Canada Balsam without
Pressure.
Foraminifera tests are more usually mounted
dry to enable more natural views of these small shell like creatures to be
observed.
Although More frequently Mounted dry, the mounting
in Canada Balsam has surprising results. At the Turn of the centuary in 1900
Joseph Wright the clear leader of the Belfast “School” of Forams, discovered
that Canada Balsam mounting improved the clarity of vision and was particulary
lucid for arenaceous tests. He makes a clear statement in his account of the
Foraminifera of Rathlin Island.
QUOTE from THE IRISH NATUALIST VOL 11 in
1902 page211 from old copy
I
have since examined with transmitted light specimens mounted in
Canada balsam, and by this means. I have been enabled to see
most distinctly the arrangement of the chambers throughout the entire test. I
have examined In this way about 150 from dredgings taken off the Irish coast,
including These Rathlin specimens, with a large number of fossil specimens from
the Chalk of Co, Antrim; also the only perfect specimen, which I had of the variety
fistulosa, Brady, from Raine Island Torres Straits 166 fathoms. In all Cases
both the recent and fossil specimens when perfect had the early chambers
arranged in a spiral manner. Further
research since 1888 hasTherefore confirmed me in my belief that this
species is truly a Spiroplectaand not a
Textularia.
End of Quote
However those species
constructed of crystalline calcite do become quite transparent when mounted in
Canada balsam. The full beauty of the three dimensional spiral then becomes
both evident and optically enhanced. The tests must be much cleaner than
normally used for dry mounting and up to three days immersion in an open vessel
of hydrogen peroxide may be required followed by washing in a fine sieve of pure
water. The initial problem however, is ridding the mount of air bubbles before
mounting commences. The tests may be laid as a small central strew or equally
well they may be laid in a geometric or taxonomic array, depending upon the
quality of material available. The tests can be secured to the glass with the
Gum tragacanth more traditionally used for dry mounting and when dry, the
slides can be immersed in toluene overnight in a Coplin Jar half filled with
the solvent. Quite often vacuoles of air are trapped and unable to escape from
the natural apertures within the test, so before mounting, the need to be examined under the microscope.
Species of the Lagena genus only have one small aperture so the slide may need
to be inverted several times over two to three days. When the expulsion of air
is complete, the slide can be laid on a hot plate and two drops of Canada
balsam applied with a pipette and a coverslip laid. Since the tests are quite
thick and brittle compared to other micro-organisms the slip must be applied
without pressure and the simplest and best support is the use of three
peripheral disks of around 0.5mm thickness 1.5mm diameter. The disks should be
bonded to the coverslip before mounting using glass bond in sunlight followed
by washing in toluene and drying with paper tissue before use. The cutting tool
for these is flat nosed pliers drilled out for a piston on one side and a complimentary
hole on the other These tools are actually available for the amateur Jewellery
trade. Any burrs may be rubbed down on fine emery paper. Suitable brass or
aluminium sheet from model shops can be purchased in various thicknesses but
having been produced in the USA the measurements then tend to be imperial
rather than metric. A vernier gauge is also a useful tool for this work of
course. The space afforded by the three small discs also enables spontaneous bubbles
to escape quite freely during the drying process. After several days of
hardening the surplus balsam can be scraped away with a scalpel and the work
can be ringed and protected with black shellac in alcohol and dried. Suitable
labelling may then be applied. BD DEC 2012
