Before any attempts are made to view blood smears, urinary sediments, bacteria, parasites, etc., it is absolutely essential that beginners know the instrument with which they will be spending considerable time-the microscope. The microscope is a precision instrument used extensively in clinical laboratories to make visible objects too small to be seen by the unaided eye. Most laboratories are equipped with binocular (two-eyepiece) microscopes, but monocular microscopes are also commonly used. The type of microscope most often used in the laboratory is referred to as the compound microscope. See figure 7-5. A compound microscope contains a system of lenses of sufficient magnification and resolving power (ability to show, separate, and distinguish) so that small elements lying close together in a specimen appear larger and distinctly separated. In the following sections, the compound microscope's framework, illumination system, magnification system, and focusing system will be discussed.

FRAMEWORK
The framework of the compound microscope consists of four parts: the arm, the stage, the mechanical stage, and the base (fig. 7-5).

Arm
The arm is the structure that supports the magnification and focusing system. It is the handle by which the microscope is carried.

Stage
The stage is the platform on which a specimen is placed for examination. In the center of the stage is an aperture or hole that allows the passage of light from the condenser.

Figure 7-5.-Compound microscope.

Mechanical Stage
The mechanical (movable) stage holds the specimen in place and is the means by which the specimen may be moved about on the stage.

Base
The base is the structure on which the microscope rests.