Role of Microscope
The basic flow of procedures involved in the laboratory diagnosis of infectious disease is as follows :
Direct examination of patient for the presence of agents.
-Growth & cultivation of the agents from these same specimens.
-Analysis of the cultivated organisms to established their identification & other characteristics.
Microscope is defined as the use of it to magnify (visually enlarge) objects too small to be visualized with naked eye so that their characteristics are readily observable because most infectious agents cannot be detected with naked eye.
Types of Microscope
A- Bright — Field (Light or Compound ) Microscope
The compound microscope uses lenses and light to enlarge the image and is also called an optical or light microscope. The simplest optical microscope is the magnification and. is good to about ten time (lOX) magnification. The compound microscope has two systems of lenses for greater magnification, 1) the ocular, or eyepiece lens that one looks into and
2) the objective lens, or the lens closest to the object.
Before purchasing or using a microscope, it is important to know the functions of each part.
Eyepiece Lens: the lens at the top that you look through. They are usually 10X or 15X power.
Tube: Connects the eyepiece to the objective lenses
Arm: Supports the tube and connects it to the bases
Base: The bottom of the microscope, used for support
Illuminator: A steady light source (110 volts) used in place of a mirror. If your microscope has a mirror, it is used to reflect light from an external light source up through the bottom of the stage.
Stage: The flat platform where you place your slides. Stage clips hold the slides in place. If your microscope has a mechanical stage, you will be able to move the slide around by turning two knobs. One moves it left and right, the other moves it up and down.
Revolving Nosepiece or Turret: This is the part that holds two or more objective lenses and can be rotated to easily change power.
Objective Lenses: Usually you will find 3 or 4 objective lenses on a microscope. They almost always consist of 4X, l0X, 40X and 100X powers.
Rack Stop: This is an adjustment that determines how close the objective lens can get to the slide.
Condenser Lens: The purpose of the condenser lens is to focus the light onto the specimen. Condenser lenses are most useful at the highest powers (400X and above).
Diaphragm or iris: Many microscopes have a rotating disk under the stage. This diaphragm has different sized holes and is used to vary the intensity and size of the cone of light that is projected upward into the slide
How to Focus Your Microscope: The proper way to focus a microscope is to start with the lowest power objective lens first and while looking from the side, crank the lens down as close to the specimen as possible without touching it .Dyes (stains ) can be used to stain cells or their organelles to be easy to see with eye.
B- Phase Contrast Microscope
It was developed to improve contrast deferens between cells and the surrounding medium . making it possible to see living cells without staining them.
C- Dark — Field Microscope
It is a light microscope in which the lighting system has been modified to reach the specimen from the sides only by use a special condenser that blocks direct rays & deflects light off mirror on the side of the condenser at an oblique angle.
D- Fluorescent Microscope
Certain dyes called fluors or fluorochromes can be raised to higher energy level after absorbing ultraviolet light , when the dye molecules return to their normal, lower energy state , they release excess energy in the form of visible light this, process is called florescence
E-Differential -Interference Contrast (DIC) Microscope
Its employ a polarizer to produce polarized light which used for observing unstained cells because of its ability to generate images of internal cell structures that are less apparent by bright — field techniques.
F-Electron Microscope
It is used electrons instead of light to visualize small objects instead of lenses the electrons are focused by electromagnetic fields & form an image on a fluorescent screen, like a T.V screen . Magnification in excess of I 00000xcompared with 1000 x magnification provided by light microscope.They are two general types of it:
1- Transmission electron microscope (TEM) which pass the electron beam through objects & allows visualization of internal structures.
2- Scanning electron microscope ( SEM) which use electron beam to scan the surface of objects & provides three dimensional views of surface structures
G- Confocal Scanning Laser Microscope
IT couples a laser light source to a light microscope . the laser beam bounced off a minor that directs the through a scanning device Its equipped with computer software to assemble digital images for subsequent image processing ,then digi±ally produce three dimensional image of the inter specimen.