,! jii
acquainted with their general appearance, it remains for me to
point out the method to he observed in their collection, and to
furnish the student with a few directions as to their subsequent
preservation.
Let him provide himself in the first place with the necessary
apparatus. For the field, this includes a good stock of small
wide-mouthed bottles, that each gathering may be kept perfectly
distinct ; a long rod or stick, to which can be attached a small
muslin net ; a cutting hook, of about three inches in length ;
and a broad fiat spoon : the first, to collect such specimens as
float upon the surface, or are held in suspension by the water ;
the second, to remove the^ larger Algæ which may be covered
with parasitic Diatoms ; and the third, to skim the sm-face of the
mud for those which lie at the bottom of tbe pool.
He will probably find, notwithstanding every care, that his
specimens are mixed Avith much foreign matter, in the form of
minute particles of mud or sand, which impair their value, and
interfere with observation, especially with the higher powers of his
instrument. These substances the student may remove in various
ways ; by repeated washings in pure wafer, and at the same
time, profiting by the various specific gravities of the Diatoms
and the intermixed substances, to secure their separation ; but
more particularly, by availing himself of the tendency which the
Diatomaceæ, in common with all growing plants, possess, of
making their way towards the light. The free forms may be
thus prociu’ed in a tolerably clean state ; all that is necessary
being, to place the gathering which contains them in a shallow
vessel, and leave them undisturbed for a sufficient length of
time in the sunlight, and then carefully to remove them from
the surface of the mud or water.
Having performed these operations, which a little practice will
render comparatively easy and generally successful, the next proceeding
is to preserve the specimens in such a manner as to
render them suitable for examination by the microscope at any
futm-e time. This may be done in various ways, according to
the nature of the species and the precise object desired.
The simplest method, and the one most generally useful to
the scientific observer, is simply to dry the specimens upon small
portions of talc, which can at any time be placed under the
microscope, and examined without further preparation ; and this
mode possesses one great advantage, that the specimens can be
submitted without further preparation to a heat sufficient to
remove all the cell-contents and softer parts, leaving the siliceous
epiderm in a transparent state. But this method will not preserve
the natural appearance of the filamentous, stipitate, or frondose
forms ; nor will it satisfy the amateur who desires a specimen
for his cabinet, and demands a mounting of a permanent kind
and neat appearance.
To meet these requirements, it is necessary that the specimen
should be preserved in fluid or balsam. The inodes of mounting
objects in both these ways are best learnt by the examination of
specimens thus prepared; and the manipulation required can
only be successfully acquired by practice.
I have never found written or verbal directions of much real
value, and shall confine myself to a feiv hints, which may supplement
the discernment and patience of the operator, but cannot
supersede their presence nor supply their absence.
The walls of the artificial cell for the filamentous and stipitate
forms, I invariably form of litharge (protoxide of lead) and japan-
ners gold-size ; and I attach the thin glass covers with a cement
of gold-size, mixing ivith it a little lamp-black, to give a dai'ker
colour to the last coating applied.
The fluid I employ is distilled water, without any mixture
whatever, having found all compound fluids not merely unnecessary,
but injmious.
If the filamentous and stipitate, forms are not, however,
mounted in a fresh state, the frustules separate from each other'
part from their stipes, and lose their characteristic appearance!
To remedy these inconveniences, I immerse such specimens as
cannot be placed in cells when freshly gathered, in spirits of wine
and water—one part of the former to six of the latter, and their
attachment to their stipes remains afterwards undisturbed, unless
violence be employed to separate them.
In preserving the Diatomaceæ in balsam, the siliceous valves
are the portions alone required. Indeed, it would be impracticable
satisfactorily to mount specimens in their natural state -