Microscopes are powerful instruments that allow humans to magnify objects so that things that are too small to be seen with the naked eye are made large enough to observe. While there are many uses for microscopes, these tools are put to especially good use in hospitals.
History
In the 1600s, Robert Hooke (now known as the father of microscopy) discovered that living things were composed of cells while looking at a piece of cork under his primitive microscope. Since that time, microscopes have become increasingly sophisticated and capable of seeing even smaller things. They are now indispensable instruments in many areas of health care.
Significance
Many disease-causing organisms are microscopic. Hospitals routinely take samples from patients in an attempt to identify these microscopic organisms, which allows them to prescribe the appropriate medication. Bacterial cells are identified by shape, size and configuration. They are also identified using different staining techniques (such as Gram’s staining). Each of these methods of identification requires the use of a microscope.
Identification
Cells within body tissues all have characteristic shapes, sizes and configurations. Within hospitals, doctors can take samples of cells to determine whether the cells are functioning properly. Biopsies are small pieces of tissue from any part of the body that are taken for the purpose of examining them microscopically. These tissues are fixed, sliced and mounted on slides before being viewed by a pathologist to determine whether diseases such as cancer are present. Blood counts can also be performed microscopically. The number of red blood cells can indicate anemia or an individual’s level of fitness. If white blood cells are elevated, it can indicate infection. Furthermore, there are several classes of white blood cells, and elevation of any one type can indicate a specific type of affliction. For instance, a high number of basophils can indicate an allergic reaction. Sperm counts can be performed microscopically in the manner similar to blood cell counting.
Types
There are several types of microscopes that can be used by a hospital. Compound light microscopes are the most common type. The images are two dimensional, and are magnifed through a series of lenses and illuminated from a light source.
The ‘Light’ Part of a Microscope
A light microscope uses a beam of visible light to illuminate and contrast the object being viewed through the scope. The light source is typically an incandescent bulb which is turned on by a toggle switch at the side of the base. The beam of light shines up from a lamp in the microscope’s base, through a hole or ‘window’ in the stage (area of the scope where the specimen sits), ultimately up through the specimen.
Contrast results when the area surrounding the object is bright, from the light, and the object being viewed is darker in comparison. It is important to be able to control the level of contrast when using a light microscope, since too much light can make it difficult to see a somewhat transparent or light-colored object (this is called ‘burn out’ in scope speak). Illumination can usually be controlled two different ways:
By adjusting the iris diaphragm, just under the stage: This lever controls the amount of light that enters the condenser which will allow for appropriate contrast. In general, close the diaphragm on low power, (allowing for reduced amounts of light to reach the stage) and open the diaphragm to let more light through at the higher power objectives.
By adjusting a dial on the side of the base: This dial turns the light source up and down, making it brighter or dimmer.
The ‘Compound’ Part of a Microscope
The magnification of a compound microscope is the result of two lenses:
1. the ocular lens or lenses
2. the objective lenses
The ocular lens is the one closest to the eye, and usually magnifies objects ten times (10X) their actual size. The objectives are a collection of lenses located on the rotary nosepiece. There are usually three or four objective lenses, each allowing for different degrees of magnification:
• Scanning power objective: The shortest objective. This lens usually has a red stripe around it, and magnifies objects four times actual size (4X).
• Low power objective: The next shortest objective. This lens usually has a yellow stripe around it, and magnifies objects ten times their actual size (10X).
• High-dry objective: This is usually either the longest, or second longest objective. This lens typically has a blue stripe around it, and magnifies objects forty times their actual size (40 X).
• Oil immersion objective: If a compound scope has this lens, it is the longest, and typically has a black or both a black and white stripe around it. The oil immersion lens magnifies objects one hundred times (100X), and must be used with a drop of oil placed directly on the specimen and fills the space between the lens and specimen.
The total magnification is determined by multiplying the power of the objective by the power of the ocular. (For example, the total magnification at scanning power is 4X times 10X = 40X). Using these two sources of magnification is what makes a microscope compound.
Another type of microscopes that can be used by a hospital is an electron microscope. Electron microscopes are also available, but are very costly to own and operate. An electron microscope is a type of microscope that produces an electronically-magnified image of a specimen for detailed observation. The electron microscope (EM) uses a particle beam of electrons to illuminate the specimen and create a magnified image of it. The microscope has a greater resolving power (magnification) than a light-powered optical microscope, because it uses electrons that have wavelengths about 100,000 times shorter than visible light (photons), and can achieve magnifications of up to 1,000,000x, whereas light microscopes are limited to 1000x magnification.
The electron microscope uses electrostatic and electromagnetic “lenses” to control the electron beam and focus it to form an image. These lens are analogous to, but different from the glass lenses of an optical microscope that form a magnified image by focusing light on or through the specimen.
Electron microscopes are used to observe a wide range of biological and inorganic specimens including microorganisms, cells, large molecules, biopsy samples, metals, and crystals. Industrially, the electron microscope is primarily used for quality control and failure analysis in semiconductor device fabrication.