Microscope INTRODUCTION Most advances in science are dependent upon the development

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Microscope INTRODUCTION Most advances in science are dependent upon the development Powered By Docstoc

             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

you deeper into the "InDepth Info on Microscopes" pages. For those readers

and researchers who want to drill down, simply click on a link in the text.

All of the pages on this site are also listed in the nav bar at the top of each

page. To read through all the pages on microscopes in the manner in the
order in which they were intended to be read, simply use the "next page"

links at the bottom of each article.

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