A microscope is the mostimportant instrument use to view the things that cannot be seen with the nakedeyes. Ø HISTORY:The microscope was availableduring the mid 1600s. In 1665 an English scientist named ROBERT HOOK develop optical microscope and made key observation .

Heobserved the cells using the optical microscope.ANTON VAN LEEUWEN-HOEK ( 1632-1723) discover simple glass lens ofconvex surface and made successful observation of microscopic organisms whichhe named animalcules. He is consider as one of the first who give the correctdescription of protozoa , fungi and bacteria.In 1870 ERNT ABBE develop a compound microscopelens that help to create magnified and fine images. He also develop oilimmersion lens for improve resolution as well as clarity of image.Ø TYPES OFMICROSCOPE:There are two types ofmicroscope.1.

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   Light microscope2.   Electron microscope  ü LIGHTMICROSCOPEThe light microscope whichis used in laboratory is called compound microscope in which visible light oruv lights are used to illuminate the objects.Light microscope consistof four system.a.   The support systemb.   The magnification systemc.

   The illumination systemd.   The adjustment systema.  THE SUPPORTIN SYSTEM :It include main bodycomponents.Foot: The bottom ofthe microscope used for support.Resolving nosepiece: It holds two or more objective lenses and canallow 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.b.  THEMAGNIFICATION SYSTEM :It is fixed at the bottomof the body tube just above the preparation under examination. This systemconsist of two lenses:1.   Objective lens : It has different powerLow power   10x   (5 – 6 mm)High power   40x   (0.5 – 1.

5 mm)Oil immersion   100x   (0.15 – 0.20 mm) 2.

  Eye piece :It is present on the top of the body  tube where you place your eye it is alsocalled ocular.Numerical aperture: It is the measurement of the angle maximumcone of light that can enter the objective. Resolving power: the ability of the lens to distinguish withtwo objects at a particular distance apart.Working distance: working distance of an objective is thedistance between the front lens of the objective and the object slide when theslide is flows.Total magnification: Total magnification = magnificationof objective lens x magnification of                                                                                       Eyepiecec.  THE ILLUMINATION SYSTEM :Source of light: A steady light source used in place of amirror.Mirror: two type of mirror concave sight and plane sight , ifmicroscope has a mirror , it is used to reflect light.

Condenser: The purpose of the condenser lens is to focusthe light onto the specimen between the mirror and stage.Diaphragm: It regulates the amount of light on thespecimen.d.  THEADJUSTMENT SYSTEM : 1.

course adjustment system: It is used first to achieved an appropriatefocus.2. Fine adjustment screw: It is used to bring objects into perfectfocus.3. Condenser adjustment screw: It is used to raise or lower the condenser inorder to adjust the illumination.4. Iris diaphragm lever: It can be moved to closed or open thediaphragm this reducing or increasing the intensity of life.

5. The mechanicalstage: These are usually two screw which are use tomove the glass slide on mechanical stage. One of them is used to move a slidebackward and forward while the other moves the slide right and leftv BRIGHTFIELD MICROSCOPE:The area covered by thespecimen is known as field. The magnification power is 400x. It is the mostwidely use microscopy.PURPOSE: Bright field microscopy form its image when light istransmitted through the specimen.PRINCIPLE: Specimen being denser and more opaque then itssurrounding absorbe some of this light, the rest of the light is transmitteddirectly up through the ocular into the field.USES: Bright field microscopy is a multipurpose instrument thatcan be used for both live , unstained material and preserved stain materialv DARKFIELD MICROSCOPE:.

The magnification power ofdark field microscope is 400xPURPOSE: Bright field microscopy can be adapted as dark fiel microscopy byadding a special disk called “stop” to the condenser.PRINCIPLE: The “stop” block all the light from entering light into theobject lens accept peripheral light that is reffered as the light is reflectedoff the site of the specimen itself. The resulting image is particularlystricking one that is brightly illuminated specimen surrounding by a darkfield.USES: The most effective use of DFM is to visualize living cells that couldbe distorted by drying or heat or cannot be stain with the usuall method. Itcan outline the organism shape and permit rapid identification of swimming cellthat might appear in dental and other infection.

  v PHASECONTRAST MICROSCOPY :The magnification power ofphase contrast microscopy is 400xPURPOSE: Internal component of a live , unstain cell also lack contrast and canbe defficult to distinguish but cell structure do differ slightly in densitythat they can alter the light that passes through them in specific way.PRINCIPLE: This microscope contain device that transform the specificchanges in light waves passing through the specimen into difference in lightintensities.USES: It is the most useful microscopy for for observing intracellularstructure such as bacterial spores, granuells and organelles as well as thelocomotory structure of eukaryotic cell.v FLOURESCENCEMICROSCOPY:PURPOSE: It is the special modified compound microscope with an UV radiationsource and a filter that protect observer/viewer eyes from injury by thesedangerous 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 tobe formed, the specimen must first be coated or placed in contect with a sourceof flourescene.

USES: It is the most useful application in diagnosing , infection cause byspecific bacteria , protozoa and viruses. This staning technique indecatewheather the cell are alive or dead.   ü ELECTRONMICROSCOPE:It is an instrument inwhich a electron beam is use rather than a light to visualize a internalaspects of objects. It was developed in 1933 by German physicist “ERNST RUSKA”.PROPERTIES:Electron microscopy form an image with a beam of electron that can be made totravel in wave like pattern when accelerated to high speed. These waves are100,000 time shorter than the wave length of visible light because resolvingpower is a function of wave length and electron have tremendous power toresolve minute structure.COMPONENT:       Electron microscope magnify by means of two system of lenses.

Condenser lens or objective lens, specimen holder and focusingapparatus.ELECTRON GUN:It produce beam of electron or waves through a vacuum to ring shapeelectromagnet that focus this beam on specimen.SPECIMEN:The specimen is pretreated with chemical or dyes to increase contrastand cannot be observe in a light state.VIEWING SCREEN:The enlarge image is display on a viewing screen or photographed rathereyepiece because image is produce by electron that lack colors electronmicrograph 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.

1.  Transmissionelectron microscopy2.  Scanningelectron microscopyTRANSMISSION ELECTRON MICROSCOPE:PRINCIPLE:TEM produce it image by transmitting electron through the specimen whichis coated with metals because electron cannot readily penetrate thickpreparation for this purpose the specimen must be sectioned into extremely thinslice (20-100nm thick)USES:It is useful for viewing the detailed structure of cell and viruses.SCANNING ELECTRON MICROSCOPY:PRINCIPLE:SEM produce it image without transmitting electron. It reacts with the surfaceof 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 imagefrom plague on teeth to tape worm head.