Microscope

An instrument for producing a magnified image of a small object. Microscopes are used to examine the structure and chemical composition of cells and tissues, and to investigate microorganisms and diseased tissues. In the operating theatre, microscopes are used in microsurgery. Compound microscopes are the most widely used type. They have 2 lens systems (the objective and the eyepiece), mounted at opposite ends of a tube called the body tube. There is a stage to hold the specimen, a light source, and an optical condenser which concentrates the light. The maximum magnification is about 1,500 times. Phase-contrast and interference microscopes are modified light microscopes that allow unstained transparent specimens to be seen. They are used for examining living cells and tissues. Fluorescence microscopes use ultraviolet light to study specimens stained with fluorescent dyes. Electron microscopes give much higher magnifications than light microscopes by using a beam of electrons instead of light. There are 2 types: transmission electron microscopes (TEMs) and scanning electron microscopes (SEMs). TEMs can magnify up to about 5,000,000 times, enabling tiny viruses and molecules to be seen. SEMs have a lower maximum magnification (100,000 times), but produce 3-dimensional images. This makes them useful for studying surface structures of cells and tissues.