A microscope is the most
important instrument use to view the things that cannot be seen with the naked
The microscope was available
during the mid 1600s. In 1665 an English scientist named ROBERT HOOK develop optical microscope and made key observation .He
observed the cells using the optical microscope.
ANTON VAN LEEUWEN-HOEK ( 1632-1723) discover simple glass lens of
convex surface and made successful observation of microscopic organisms which
he named animalcules. He is consider as one of the first who give the correct
description of protozoa , fungi and bacteria.
In 1870 ERNT ABBE develop a compound microscope
lens that help to create magnified and fine images. He also develop oil
immersion lens for improve resolution as well as clarity of image.
Ø TYPES OF
There are two types of
1. Light microscope
2. Electron microscope
The light microscope which
is used in laboratory is called compound microscope in which visible light or
uv lights are used to illuminate the objects.
Light microscope consist
of four system.
a. The support system
b. The magnification system
c. The illumination system
d. The adjustment system
THE SUPPORTIN SYSTEM :
It include main body
Foot: The bottom of
the microscope used for support.
Resolving nosepiece: It holds two or more objective lenses and can
allow rotation to easily change the power.
Stage: The flat platform used to place the slide.
Stage clip: It holds the slide in proper place.
Arm: It is the tube connected to base of the microscope.
MAGNIFICATION SYSTEM :
It is fixed at the bottom
of the body tube just above the preparation under examination. This system
consist of two lenses:
1. Objective lens : It has different power
Low power 10x (5 – 6 mm)
High power 40x (0.5 – 1.5 mm)
Oil immersion 100x (0.15 – 0.20 mm)
Eye piece :
It is present on the top of the body tube where you place your eye it is also
Numerical aperture: It is the measurement of the angle maximum
cone of light that can enter the objective.
Resolving power: the ability of the lens to distinguish with
two objects at a particular distance apart.
Working distance: working distance of an objective is the
distance between the front lens of the objective and the object slide when the
slide is flows.
Total magnification = magnification
of objective lens x magnification of
THE ILLUMINATION SYSTEM :
Source of light: A steady light source used in place of a
Mirror: two type of mirror concave sight and plane sight , if
microscope has a mirror , it is used to reflect light.
Condenser: The purpose of the condenser lens is to focus
the light onto the specimen between the mirror and stage.
Diaphragm: It regulates the amount of light on the
ADJUSTMENT SYSTEM :
1. course adjustment system: It is used first to achieved an appropriate
2. Fine adjustment screw: It is used to bring objects into perfect
3. Condenser adjustment screw: It is used to raise or lower the condenser in
order to adjust the illumination.
4. Iris diaphragm lever: It can be moved to closed or open the
diaphragm this reducing or increasing the intensity of life.
5. The mechanical
stage: These are usually two screw which are use to
move the glass slide on mechanical stage. One of them is used to move a slide
backward and forward while the other moves the slide right and leftv BRIGHT
The area covered by the
specimen is known as field. The magnification power is 400x. It is the most
widely use microscopy.
PURPOSE: Bright field microscopy form its image when light is
transmitted through the specimen.
PRINCIPLE: Specimen being denser and more opaque then its
surrounding absorbe some of this light, the rest of the light is transmitted
directly up through the ocular into the field.
USES: Bright field microscopy is a multipurpose instrument that
can be used for both live , unstained material and preserved stain material
The magnification power of
dark field microscope is 400x
PURPOSE: Bright field microscopy can be adapted as dark fiel microscopy by
adding a special disk called “stop” to the condenser.
PRINCIPLE: The “stop” block all the light from entering light into the
object lens accept peripheral light that is reffered as the light is reflected
off the site of the specimen itself. The resulting image is particularly
stricking one that is brightly illuminated specimen surrounding by a dark
USES: The most effective use of DFM is to visualize living cells that could
be distorted by drying or heat or cannot be stain with the usuall method. It
can outline the organism shape and permit rapid identification of swimming cell
that might appear in dental and other infection.
CONTRAST MICROSCOPY :
The magnification power of
phase contrast microscopy is 400x
PURPOSE: Internal component of a live , unstain cell also lack contrast and can
be defficult to distinguish but cell structure do differ slightly in density
that they can alter the light that passes through them in specific way.
PRINCIPLE: This microscope contain device that transform the specific
changes in light waves passing through the specimen into difference in light
USES: It is the most useful microscopy for for observing intracellular
structure such as bacterial spores, granuells and organelles as well as the
locomotory structure of eukaryotic cell.
PURPOSE: It is the special modified compound microscope with an UV radiation
source and a filter that protect observer/viewer eyes from injury by these
dangerous rays. The name of microscope originates from the use of certain dyes.
PRINCIPLE: The dyes emits visible light when bombared by shorter UV rays. For an image to
be formed, the specimen must first be coated or placed in contect with a source
USES: It is the most useful application in diagnosing , infection cause by
specific bacteria , protozoa and viruses. This staning technique indecate
wheather the cell are alive or dead.
It is an instrument in
which a electron beam is use rather than a light to visualize a internal
aspects of objects. It was developed in 1933 by German physicist “ERNST RUSKA”.
Electron microscopy form an image with a beam of electron that can be made to
travel in wave like pattern when accelerated to high speed. These waves are
100,000 time shorter than the wave length of visible light because resolving
power is a function of wave length and electron have tremendous power to
resolve minute structure.
Electron microscope magnify by means of two system of lenses.
Condenser lens or objective lens, specimen holder and focusing
It produce beam of electron or waves through a vacuum to ring shape
electromagnet that focus this beam on specimen.
The specimen is pretreated with chemical or dyes to increase contrast
and cannot be observe in a light state.
The enlarge image is display on a viewing screen or photographed rather
eyepiece because image is produce by electron that lack colors electron
micrograph is a photographer of a microscopic object which are always black,
gray and white in color.
TYPES OF ELECTRON MICROSCOPY:
There are two type of electron microscope.
TRANSMISSION ELECTRON MICROSCOPE:
TEM produce it image by transmitting electron through the specimen which
is coated with metals because electron cannot readily penetrate thick
preparation for this purpose the specimen must be sectioned into extremely thin
slice (20-100nm thick)
It is useful for viewing the detailed structure of cell and viruses.SCANNING ELECTRON MICROSCOPY:
SEM produce it image without transmitting electron. It reacts with the surface
of metal coated specimen with electron while scanning back and forth over it.
USES:It produce an extremely detail 3 dimensional view of all kind of image
from plague on teeth to tape worm head.