Most advances in science are dependent upon the development
of appropriate techniques to demonstrate them. Over the last 150 years there
has been a painstaking development of new techniques for light and electron
microscopy, which facilitates the precise analysis of cell and tissue structure.
In addition, these techniques demonstrate more clearly the changes, which
pathological processes bring about.
Microscopes are one of the vital tools that have allowed science
to leap forward in many fields, biology, medicine, and anatomy, just to name
a few. The microscope gives humans the ability to study the very small. This
view of a realm that is beyond our vision with the naked eye enables
understanding of how new drugs work, the way genes are constructed, even
how atoms bind together to form larger molecules.
It has been said that the scientist of today stands on the shoulders of
giants. This is meant to signify that we have before us the body of thought
and the work of the greats of the past who compiled the information and
formulated the ideas we use to advance scientific fields. To reconstruct the
work of a man such as Robert Hooke would take the average person a life-
time. In a similar way, it is in microscope history that we see the
development of this device that revolutionized science, and remains the most
vital tool of many sciences.
The microscope as we know it was developed by a father and son team,
spectacle makers named Zaccaria and Hans Janssen, who thought of lining
up two lenses in a tube. This now over 400 year old arrangement has
remained fundamental to the compound microscope. It had long been known
that a glass crystal in the general shape of a lentil would magnify. But
arranging two in line would magnify the magnification of an object to the
point where a flea would appear to be as large as an elephant. A compound
microscope works by bending light rays as they strike first one lens and then
another. When the light rays pass from a specimen to the naked eye, the
object appears much larger.
This arrangement was sufficient for many years, but by the 1900s scientists
wanted to start viewing objects even smaller than the light compound
microscope could possibly reveal. Objects can be so small that they can be
missed between individual light waves. To solve this problem scientists
developed the electron microscope. Electron beams have a much smaller
wavelength than light. With an electron microscope, objects can be
magnified up to 10,000 times, small enough to actually see atoms.
Yet because of the ease of use, low cost, and the clarity of magnified images
(up to a certain limit), compound light microscopes are still prevalent,
especially in fields such as biology, and anatomy. In viewing objects through
a microscope, it is important to use proper procedure for mounting
specimens. This helps to ensure easily manipulated, quality images.
A well-cared for microscope can last many years even with constant use.
When transporting a microscope, grasp it by the handle and place another
hand beneath the base. Walk carefully from one location to another. Don't
touch lenses with your fingers. When it needs to be cleaned, use lens paper.
When finished with use, put the microscope on the lowest magnification.
Wipe away any spilled fluids. Cover the microscope between uses, so that
when it sets for long periods the parts of the microscope not gather dust.
This short introduction to microscopes is meant as a table of contents to take
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In delving into a history of the microscope, we must begin in the time of pre-
history, before written records were made. Humans are curious creatures,
and it is assumed that someone found a clear rock or crystal that was
relatively smooth, but wider in the middle than on the edges. This crystal
would have made objects behind it look larger. Not only this, when the sun's
rays came through it, the object upon which it was directed would be heated
to the point of catching fire. Later in Rome, where practical things were
appreciated, these magnifying rocks were noted in the writings of Seneca
and as cauterizing crystals by Pliny the Elder.
Although they were used for limited magnification in some crafts,
such crystals were relatively rare and thus not widely used. It was also
known by ancients that water in a clear receptacle could magnify, but the
distortion of the image and the expense often made common use impractical.
However, about the end of the 1200s, glass making techniques coupled with
advances in understanding in optics allowed for the invention of eye-glasses
or spectacles from the lens (called lens because of its similarity in
appearance to a lentil1).
A majority of the subjects examined or photographed through a
conventional microscope appear either dark or colored against a light
background. When they appear dark, it is due to light absorption within their
elements. When they appear colored, it is usually because they have been
treated with biological stains to produce color contrast.
This color contrast is a result of differential absorption of
various stains by the elements of the specimen. Whether the subject appears
dark or colored, the effect is called “bright-field illumination”.
In an unstained condition, many specimens exhibit little or no
contrast when viewed against a bright background in a compound
microscope. They are colorless and comparatively transparent.
Consequently, they are practically invisible. When staining a specimen is
either impossible or undesirable, a conventional bright-field microscope
cannot be used for photomicrography. Another microscopical technique
must be used to make the specimen visible. The particular method selected
depends on the specimen itself and the particular results desired. The
following discussions are intended to present brief descriptions of those
special techniques that will either, produce better optical contrast between
the elements of a specimen and its background or, allow images to be
viewed or photographed with finer resolution.
The microscope is the most commonly used piece of apparatus
in the laboratory, and yet it is probably the instrument about which least is
known by its users. It is generally thought that the microscope can be used
effectively without any knowledge of its limitations or construction, but this
is, of course, a complete misconception. An ill-adjusted, badly illuminated
microscope can, when one is using high-power objectives, give completely
misleading information as to the structure of an object. For this reason it is
advisable to gain a knowledge of how the magnified images are produced by
the microscope before attempting to assess the information obtained by its