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To heat-fix a sample, a thin layer of the specimen is spread on the slide (called a smear), and the slide is then briefly heated over a heat source ( Figure 2.31). In addition to attaching the specimen to the slide, fixation also kills microorganisms in the specimen, stopping their movement and metabolism while preserving the integrity of their cellular components for observation. Fixation is often achieved either by heating ( heat fixing) or chemically treating the specimen.
The “fixing” of a sample refers to the process of attaching cells to a slide. The second method of preparing specimens for light microscopy is fixation. Once the liquid has been added to the slide, a coverslip is placed on top and the specimen is ready for examination under the microscope. Sometimes the liquid used is simply water, but often stains are added to enhance contrast.
INDIA INK STAINING PROTOCOL LUNGS SKIN
Solid specimens, such as a skin scraping, can be placed on the slide before adding a drop of liquid to prepare the wet mount. Some specimens, such as a drop of urine, are already in a liquid form and can be deposited on the slide using a dropper. The simplest type of preparation is the wet mount, in which the specimen is placed on the slide in a drop of liquid. There are two basic types of preparation used to view specimens with a light microscope: wet mounts and fixed specimens. In clinical settings, light microscopes are the most commonly used microscopes. Here, we will focus on the most clinically relevant techniques. Indeed, numerous methods have been developed to identify specific microbes, cellular structures, DNA sequences, or indicators of infection in tissue samples, under the microscope. We have already alluded to certain techniques involving stains and fluorescent dyes, and in this section we will discuss specific techniques for sample preparation in greater detail. This makes it difficult, if not impossible, to detect important cellular structures and their distinguishing characteristics without artificially treating specimens. In their natural state, most of the cells and microorganisms that we observe under the microscope lack color and contrast. Explain the procedures and name clinical applications for Gram, endospore, acid-fast, negative capsule, and flagella staining.Describe the unique features of commonly used stains.Differentiate between simple and differential stains.By the end of this section, you will be able to:
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