What are the procedures of preparation of the biological specimens to be analyzed under a microscope?

There are several steps that are necessary in order to analyze biological specimens under a microscope. For a sample to be seen under a microscope, the sample must be fixed; it must be transparent, so light can pass through it; it must be thin and flat, so only a single layer of cells are present.

The first step is fixation of the cell. Typically, formalin is used to fixate the specimen. Fixation is important because it stabilizes the cell, prevents decaying, and preserves cells in a life-like state.

The next step is dehydrating or freezing the specimen. The samples start in an aqueous solution and must be passed through dehydrating and clearing solvents such as acetone or ethanol. This dehydration process gradually replaces the water content in the specimen with organic solvents. 

The next step after processing is embedding. In this step, the cells are hardened using a paraffin embedding medium. This makes the sample hard enough to withstand the pressures of sectioning and cutting.

The next step is sectioning. Sections are sliced using a microtome using fine steel blades. Paraffin sections are typically cut at a thickness of 3-5 micrometers, which ensures only a single layer of cells are present. Sections are then floated onto the surface of warm water to be flattened and dried on microscope slides.

During staining, hematoxylin and eosin stains are the most commonly used dyes for providing crucial structural information. If these dyes alone are not enough, additional unique stains are used to define specific structures. IHC methods can also be used to localize antibodies. Wet mount is another type of preparation, and is the simplest type.  A specimen is placed on a slide in a drop of liquid. Solid samples like skin scraping can be placed on the slide before adding drops of liquid to prepare the wet mount. Stains are often added to enhance contrast, and once the liquid is added to the slide, a coverslip is simply placed on top. The sample is then ready for visualization under the microscope.