of the sun and a convex lens; for this purpose, place the microscope
about three feet from a southern window; take a deep convex lens, that
is mounted in a semicircle and fixed on a stand, so that its position
may be easily varied; place this lens between the object and the window,
so that it may collect a considerable number of the solar rays, and
refract them on the object, or the mirror of the microscope. If the
light thus collected from the sun be too powerful, it may be tempered by
placing a piece of oil paper, or a glass lightly greyed, between the
object and the lens: by these means, a convenient degree of light may be
obtained, and diffused in an equal manner over the whole surface of an
object, a circumstance that should be particularly attended to; for if
the light be thrown in an irregular manner, that is, larger portions of
it on some parts than on others, it will not be distinctly exhibited.
Where the solar light is preferred, it will be found very convenient to
darken the room, and to reflect the rays of the sun on the above
mentioned lens, by means of the mirror of a solar microscope fitted to
the window-shutter; for, by this apparatus, the observer will be enabled
to preserve the light on his object, notwithstanding the motion of the
sun.
Cutting off the adventitious light as much as possible, by darkening the
room where you are using the microscope, and admitting the light only
through a hole in the window-shutter, or at most, keeping one window
only open, will also be found very conducive towards producing a
distinct view of the object.
As the motion of the sun, and the variable state of our atmosphere,
render solar observations both tedious and inconvenient, it will be
proper for the observer to be furnished with a large tin lanthorn, made
something like the common magic lanthorn, fit to contain one of
Argand’s lamps.[41] The lanthorn should have an aperture in front, that
may be moved up and down, and capable of holding a lens; by this a
pleasing uniform dense light may be easily procured. The lamp should
move on a rod, that it may be readily elevated or depressed. The
lanthorn may be used for many other purposes, as for viewing of
pictures, exhibiting microscopic objects on a screen, &c.
[41] The lamp should not be of the fountain kind, because the
rarefaction of the air in the lanthorn will often force the oil over.
Many transparent objects are seen best in a weak light; among these we
may place the prepared eyes of flies and animalculæ in fluids; the
quantity of light from a lamp or candle may be lessened by removing the
microscope to a greater distance from them, or it may be more
effectually lessened by cutting off a part of the cone of rays that fall
on the object, either by placing the cone, as already described with the
apparatus to different microscopes, under the stage, or by forming
circular apertures of black paper of different sizes, and placing either
a large or small one on the reflecting mirror, as occasion may require.
There is an oblique position of the mirrors, and consequently of the
light, which is easily acquired by practice, but for which no general
rule can be given, that will exhibit an object more beautifully and more
distinctly than any other situation, shewing the surface, as well as
those parts through which the light is transmitted.
A better view of most objects is obtained by a candle or lamp than by
day-light; it is more easy to modify the former than the latter, and to
throw it on the object with different degrees of density. From what has
been said, the reader will have observed the importance of being able to
examine the object in the greatest variety of positions and appearances,
which cannot be effected with equal convenience by any microscope, but
the improved lucernal.
OF THE PREPARATION OF OBJECTS FOR THE MICROSCOPE.
In the preparation of objects, no man was more successful or more
indefatigable than Swammerdam. In minutely anatomizing, in patiently
investigating, and in curiously exhibiting the minute wonders of the
creation, he stands unrivalled, far exceeding all those that preceded,
as well as those which have succeeded him. Deeply impressed and warmly
animated by the amazing scenes that he continually discovered, his zeal
in pursuit of truth was not to be abated by disappointment, or alarmed
by difficulty; and he was never satisfied till he had attained a
rational and clear idea of the organization of the object, whose
structure he wished to explore; his “Book of Nature,” of which a
translation was published by Dr. Hill, is a work of such vast extent of
knowledge, and so excellent in execution, as to raise the highest
admiration in even a superficial observer.
It is much to be regretted, that we are ignorant of the methods he
employed in his investigations. To discover these, the great Boerhaave
examined with a scrupulous attention all the letters and manuscripts of
Swammerdam, and has communicated the result of his researches, which,
though but small, may enable us to form some idea of his immense labours
in the field of science.
For dissecting of small insects he had a brass table, which was made by
that excellent artist, S. Musschenbroeck; to this table were affixed
two brass arms, moveable at pleasure to any part of it. The upper
portion of these arms was constructed so as to have a slow vertical
motion, by which means the operator could readily alter their height, as
he saw most convenient to his purpose; the office of one of these arms
was to hold the minute bodies, and that of the other to apply the lens
or microscope.
His microscopes or lenses were of various foci, diameters, and sizes,
from the least to the greatest, and the best that could be procured in
regard to the exactness of the workmanship, and transparency of the
substance. His mode was, to begin his observations with the smallest
magnifiers, and from thence proceed by degrees to the greatest. Formed
by nature, and habituated by experience, he was so incomparably
dexterous in the management of these instruments, that he made every
observation subservient to the next, and all tend to confirm each other,
and complete the description.
His chief art seems to have been in constructing very fine scissars, and
giving them an extreme sharpness: these he made use of to cut very
minute objects, because they dissected them equally; whereas knives and
lancets, let them be ever so fine and sharp, are apt to disorder
delicate substances, as in going through them, they generally draw after
and displace some of the filaments. His knives, lancets and styles, were
so very fine, that he could not see to sharpen them without the
assistance of a magnifying glass; but with them he could dissect the
intestines of bees with the same accuracy and distinctness that the most
celebrated anatomist does those of large animals. He was particularly
expert in the management of small glass tubes, which were no thicker
than a bristle, and drawn to a very fine point at one end, but thicker
at the other. These he made use of to shew and blow up the smallest
vessels discovered by the microscope, to trace, distinguish, and
separate their courses and communications, or to inject them with very
subtil coloured liquors.
He used to suffocate the insects in spirit of wine, in water, or spirit
of turpentine, and likewise preserved them for some time in these
liquids; by which means he kept the parts from putrefaction, and
consequently from collapsing and mixing together; and added to them
besides such strength and firmness, as rendered the dissections more
easy and agreeable. When he had divided transversely with his fine
scissars the little creature he intended to examine, and had carefully
noted every thing that appeared without further dissection, he then
proceeded to extract the viscera in a very cautious and deliberate
manner, with other instruments of great fineness; first taking care to
wash away and separate with very fine pencils, the fat with which
insects are very plentifully supplied, and which always prejudices the
internal parts before it can be extracted. This operation is best
performed upon insects while in the nympha state.
Sometimes he put into water the delicate viscera of the insects he had
suffocated; and then shaking them gently he procured himself an
opportunity of examining them, especially the air vessels, which by
these means he could separate from all the other parts whole and intire,
to the great admiration of all those who beheld them; as these vessels
are not to be distinctly seen in any other manner, or indeed seen at all
without damaging them, he often made use of water, injected by a
syringe, to cleanse thoroughly the internal parts, then blew them up
with air and dried them, and thus rendered them durable, and fit for
examination at a proper opportunity. Sometimes he has examined with the
greatest success, and made the most important discoveries in insects
that he had preserved in balsam, and kept for years together in that
condition. Again, he has frequently made punctures in other insects with
a very fine needle, and after squeezing out all their moisture through
the holes made in this manner, he filled them with air, by means of very
slender glass tubes, then dried them in the shade, and last of all
anointed them with oil of spike, in which a little rosin had been
dissolved; by which process they retained their proper forms a long
time. He had a singular secret, whereby he could so preserve the nerves
of insects, that they used to continue as limber and perspicuous as ever
they had been.
He used to make a small puncture or incision in the tail of worms, and
after having gently and with great patience squeezed out all their
humours, and great part of their viscera, he then injected them with
wax, so as to give and continue to them all the appearance of healthy
vigorous living creatures. He discovered that the fat of all insects was
perfectly dissoluble in oil of turpentine; thus he was enabled to shew
the viscera plainly; only after this dissolution he used to cleanse and
wash them well and often in clean water. He frequently spent whole days
in thus cleansing a single caterpillar of its fat, in order to discover
the true construction of this insect’s heart. His singular sagacity in
stripping off the skin of caterpillars that were upon the point of
spinning their cones, deserves particular notice. This he effected by
letting them drop by their threads into scalding water, and suddenly
withdrawing them; for, by these means the epidermis peeled off very
easily; and when this was done, he put them into distilled vinegar and
spirit of wine, mixed together in equal portions, which, by giving a
proper firmness to the parts, gave him an opportunity of separating them
with very little trouble from the exuviæ, or skins, without any danger
to the parts; so that by this contrivance, the nymph could be shewn to
be wrapped up in the caterpillar and the butterfly in the nymph. Those
who look into the works of Swammerdam, will be abundantly gratified,
whether they consider his astonishing labour and unremitted ardour in
these pursuits, or his wonderful devotion and piety. On one hand, his
genius urged him to examine the miracles of the great Creator in his
natural, productions; whilst, on the other, the love of that same
all-perfect Being rooted in his mind struggled hard to persuade him that
God alone, and not the creatures, were worthy of his researches, love,
and attention.
M. Lyonet always drowned first those insects he intended to anatomize,
as by these means he was enabled to preserve both the softness and
transparency of the parts. If the insect, &c. be very small, for
instance one-tenth of an inch, or a little more in length, it should be
dissected in water, on a glass which is a little concave; if, after a
few days, there be any fear that the insect will putrefy, it should be
placed in weak spirit of wine, instead of water. In order to fix the
little creature, it must be suffered to dry, and then be fastened by a
piece of soft wax; after which it may be again covered with water.
Larger objects require a different process; they should be placed in a
small trough of thin wood; the bottom of a common chip box will answer
very well, by surrounding the edge of it with soft wax, to keep in the
water or spirit of wine. The insect is then to be opened, and if the
parts be soft, like those of a caterpillar, they should be turned back
and fixed to the trough by small pins; the pins are to be set by a pair
of small nippers, the skin being stretched at the same instant by
another pair of finer forceps; the insect must then be placed in water,
and dissected therein, and after two or three days it should be covered
with spirit of wine, which should be renewed occasionally; by these
means the subject is preserved in perfection, and its parts may be
gradually unfolded, without any other change being perceived than that
the soft elastic parts become stiff and opake, and some others lose
their colour.
M. Lyonet used the following instruments in his curious dissection of
the caterpillar of the cossus. As small a pair of scissars as could be
made, the arms long and fine; a small and sharp knife, the end brought
to a point; a pair of forceps, the ends of which had been so adjusted,
that they would easily lay hold of a spider’s thread or a grain of sand.
But the most useful instruments were two fine steel needles, fixed in
small wooden handles, about 2³⁄₄ of an inch in length.
An observation of Dr. Hooke’s may be very useful if attended to, for
fixing objects intended to be delineated by the microscope. He found no
creature more troublesome to draw than the ant or pismire, not being
able to get the body quite in a natural posture. If, when alive, its
feet were fettered with wax or glue, it would so twist and twine its
body, that it was impossible any way to get a good view of it; if it was
killed, the body was so small, that the shape was often spoiled before
it could be examined. It is the nature of many minute bodies, when their
life is destroyed, for the parts to shrivel up immediately; this is very
observable in many small plants, as well as in insects; the surface of
these small bodies, if porous, being affected by almost every change of
the air, and this is particularly the case with the ant. But if the
little creature be dropped in well rectified spirit or wine, it is
immediately killed; and when taken out, the spirit of wine evaporates,
leaving the animal dry and in its natural posture, or at least so
constituted, that you may easily place it with a pin in what posture you
please.[42]
[42] Hooke’s Micrographia, p. 203.
Having thus given a general account of the methods used by Swammerdam
and Lyonet, in their examination and dissection of insects, we shall
proceed to shew how to prepare several of their parts for the
microscope, beginning with the WINGS. Many of these are so transparent
and clear, as to require no previous preparation; but the under wings of
those that are covered with elytra, or crustaceous cases, being
constantly folded up when at rest, they must be unfolded before they can
be examined by the microscope; for this purpose a considerable share of
dexterity and some patience is necessary, for the natural spring of the
wings is so strong, that they immediately fold themselves again, except
they are carefully prevented.
One of the most curious and beautiful wings of this kind, is that of the
FORFICULA AURICULARIA, or EARWIG, of which we have given a drawing,
Plate XIV. Fig. 1, represents it considerably magnified, and Fig. 2, the
same object of its natural size. When expanded, it is a tolerably large
wing, yet folds up under a case not one-eighth part of its size. It is
very difficult to unfold these wings, on account of their curious
texture. They are best opened immediately after the insect is killed.
Hold the earwig by the thorax, between the finger and thumb; then with a
blunt-pointed pin endeavour gently to open the wing by spreading it over
the fore-finger, gradually sliding at the same time the thumb over it.
When fully expanded, separate it from the insect by a sharp knife, or a
pair of scissars. The wing should be pressed for some time between the
thumb and finger before it be removed; it may then be placed between two
pieces of paper, and again pressed for at least an hour; after which it
may be put between the talcs without any danger of folding up again.
The wings of the NOTONECTA, or BOAT-FLY, and other water insects, as
well as most species of the grylli, require equal care and delicacy
with that of the earwig to display them properly.
The wings of BUTTERFLIES and MOTHS are covered with very minute scales
or feathers, that afford a beautiful object for the microscope; near the
shoulder, the thorax, the middle of the wing, and the fringes of the
wings, they are generally intermixed with hair. The scales of one part,
also, often differ in shape from those of another; they may be first
scraped off or loosened from the wing with a knife, and then brushed
into a piece of paper with a camel’s hair pencil; the scales may be
separated from the hairs with the assistance of a common magnifying
glass.
The proboscis of insects, as of the CULEX or GNAT, the TABANUS or
BREEZE-FLY, &c. requires much attention and considerable care to be
dissected properly for the microscope; and many must be prepared before
the observer desides upon the situation and shape of the parts; he will
often also be able to unfold in one specimen some parts that he can
scarce discover in another. It is well known that the COLLECTOR OF THE
BEE forms a most beautiful object; a figure of it is given in plate
XIII. Fig. 3, shews it greatly magnified, and Fig. 4, of the natural
size. In it is displayed a most wonderful mechanism, admirably adapted
to collect and extract the various sweets from flowers, &c. To prepare
this, it should first be carefully washed with spirit of turpentine, by
which means it will be freed from the unctuous and melliferous particles
which usually adhere to it; when dry, it must be again washed with a
camel’s hair pencil, to disengage and bring forward the small hairs
which form one part of its microscopic beauty.
The case which encloses THE STING OF THE BEE, the wasp, and the hornet,
are so hard, that it is very difficult to extract them without breaking
or otherwise injuring them. It will be found, perhaps, the best way to
soak the case, and the rest of the apparatus for some time in spirit of
wine or turpentine, then lay it on a piece of clean paper, and with a
blunt knife draw out the sting, holding the sheath by the nail of the
finger, or by any blunt instrument; great care is requisite to preserve
the feelers, which when cleaned add much to the beauty of the object.
The EYES OF THE LIBELLULA or DRAGON-FLY, and different flies, of the
LOBSTER, &c. are first to be cleaned from the blood and other extraneous
matter; they should then be soaked in water for some days, after which
you may separate one or two skins from the eye, which, if they remain,
render it too opake and confused; some care is, however requisite in
this separation, otherwise the skin may be made too thin, so as not to
enable you to form an accurate idea of its organization.
The EXUVIÆ or CAST-OFF OF SKINS of insects are in general very pleasing
objects, and require but little preparation. If they be curled or bent
up, keep them in a moist atmosphere for a few hours, and they will soon
become so relaxed that you may extend them with ease to their natural
positions. The steam of warm water answers the purpose very well.
The BEARD OF THE LEPAS ANATIFERA or BARNACLE is to be soaked in clean
soft water, and frequently brushed, while wet, with a camel’s hair
pencil; it may then be left to dry; after which it must be again brushed
with a dry pencil, to disengage and separate the hairs, which are apt to
adhere together. A picture of this object is represented in plate XIII.
Fig. 1, magnified; Fig. 2, natural size.
To view the MUSCULAR FIBRES, take a very thin piece of dried flesh, lay
it upon a slip of glass, and moisten it with warm water; when this is
evaporated, the vessels will appear plain and more visible, and by
repeated macerations the parts may be further disengaged.
To examine FAT, BRAINS, and other similar substances, we are advised by
Dr. Hooke to render the surface smooth, by pressing it between two thin
plates of flat glass, by which the substance will be made much thinner
and more transparent; otherwise, the parts lying thick one upon the
other, it appears confused and indistinct.
Some substances are, however, so organized, that if their peculiar form
be altered, the parts we wish to discover are destroyed; such as nerves,
tendons, muscular fibres, pith of wood, &c. Many of these are best to be
examined while floating in some convenient transparent fluid. For
instance, very few of the fibres of any of the muscles can be discovered
when they are viewed in the open air; but if placed in water or oil,
great part of their wonderful fabric may be discovered. If the thread of
a ligament be viewed in this manner, it will be seen to consist of an
indefinite number of smooth round threads lying close together.
Objects of an elastic nature should be pulled or stretched out while
they are under the microscope, that the texture and nature of those
parts, whose figure is altered by being thus pulled out, may be more
fully discovered.
To examine BONES with the microscope. These should first be viewed as
opake objects; afterwards, by procuring thin sections, they should be
looked at as if transparent. The sections should be cut in all
directions, and be well washed and cleaned; a degree of maceration will
be useful in some cases. Or the bones may be put in a clear fire till
they are red hot, and then taken out; by these means the bony cells will
appear more conspicuous and visible, being freed from extraneous matter.
To examine the PORES OF THE SKIN. First, cut or pare off with a razor as
thin a slice as possible of the upper skin; then cut a second from the
same place; apply the last to the microscope.
The SCALES OF FISH should be soaked in water for a few days, and then be
carefully rubbed, to clean them from the skin and dirt which may adhere
to them.
To procure the scales of the eel, which are a great curiosity, and the
more so, as the eel was not known to have any, till they were discovered
by the microscope, take a piece of the skin of the eel that grows on the
side, and while it is moist spread it on a piece of glass, that it may
dry very smooth; when thus dried, the surface will appear all over
dimpled or pitted by the scales, which lie under a sort of cuticle or
thin skin; this skin may be raised with the sharp point of a penknife,
together with the scales which will then easily slip out, and thus you
may procure as many as you please.[43]
[43] Martin’s Micrographia Nova, p. 29.
On the lizard, the guana, &c. are two skins; one of these is very
transparent, the other is thicker and more opake; by separating these we
procure two beautiful objects.
The LEAVES of many trees, and some plants, when dissected, form a very
pleasing object. To dissect them, take a few of the most perfect leaves
you can find, and place them in a pan with clean water; let them remain
three weeks or a month without changing the water, then take them up,
and try if they feel very soft, and appear almost rotten; if so, they
are sufficiently soaked. You are then to lay them on a flat board, and
holding them by the stalk, draw the edge of the knife over the upper
side of the leaf, which will take off most of the skin; turn the leaf,
and do the same with the under side. When the skin is taken off on both
sides, wash out the pulpy matter, and the fibres will be exhibited in a
beautiful manner. By slitting the stalk you may separate the anatomized
leaf into two parts. The skins that are peeled from the fibres will also
make a very good object. The autumn is the best season for the foregoing
operation, as the fibres of the leaves are much stronger at that season,
and less liable to break.
ORES and MINERALS should all be carefully washed and cleansed with a
small brush, to remove any extraneous matter that may adhere to them.
SHELLS may be ground down on a hone, by which their internal structure
will be displayed.