Microbiology Lab Practices

Care and Use of the Microscope

The Microscope

Parts Ocular lens (eyepiece): Tube (body) Arm Nosepiece and objective lenses(4X, 10X, 40X, and 100X.) Stage, stage clips, and stage adjustment knob. Condenser and iris diaphragm Fine and course adjustment knobs Base and in-base illuminator. Light intensity control

Objective lenses 4X: scanning lens 10X: low power 40X: high power 100X: oil immersion lens.

Course adjustment knob: for focusing with 4X and 10X. Fine adjustment Knob: for focusing 40X and 100X

Characteristics of light microscope Total magnification of a specimen: is obtained by multiplying the objective lens times the ocular. Resolution (resolving power): Ability to show details. (0.2 micrometer for light, vary for electron microscope). Field of vision: is the area seen through a microscope.

Types Light microscope Electron Microscope

Light microscope: - Bright field microscope - Dark field microscope - Phase contrast microscope - Differential interference microscope - Fluorescence microscope

Light microscope Bright field---most widely used, specimen is darker than surrounding field. Dark field---brightly illuminated specimen surrounded by dark field. Phase-contrast---transforms subtle changes in light waves passing through the specimen into differences in light intensity, best for observing intracelluar structures.

Fluorescence microscope---modified compound microscope with an ultraviolet radiation source and a filter that protects the viewer’s eye. Uses dyes that emit visible light when bombed with shorter UV rays. Useful in diagnosing infections (syphilis, tuberculosis).

Electron microscope: 1- Transmission electron microscope TEM 2- Scanning electron microscope SEM. Forms an image with a beam of electrons that can be made to travel in wavelike patterns when accelerated to high speeds.

Transmission : To observe internal cellular structures Highest magnification 1,000,000 X Resolution power: 0.2 nm Allows the observation of viruses. Allows 2 D images.

Scanning : To observe surface structures. Magnification power: 100,000 X Resolution power: 2,5 nm Allows the observation of viruses Allows colored, 3D images.

Care and Use of the Microscope How to take care of the microscope.

The Use of oil immersion The most important lens in microbiology is the oil immersion lens, It has the highest magnification and must be used with oil. The purpose is to decrease the refraction of light while increasing the amount of light directed into the objective lens, also enhances the resolution of the image.