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Let us learn about Smear or Cells. After reading this article you will learn about: 1. Preparation of Specimens 2. Fixation of Cells (Smear) On the Slides.
Preparation of Specimens:
Prior to staining, fix the material to be observed over the slide. If preparation is not fixed or sticked over the slide, the cells are washed off during staining procedure.
Preparation of Smear:
Place a small drop of liquid culture with an inoculating loop on a clean slide. If the culture is taken from a solid medium. Place a small drop of water on the slide and thoroughly mix with it a small bit of culture. Spread the drop on slide uniformly to form a thin film of cells. This thin film of cells is called a smear which must be as uniform as possible.
Fixation of Cells (Smear) On the Slides:
After preparation of a uniform smear, it must be fixed or stuck over the slide. Fixation is the process by which internal and external structures of cells and micro-organisms are preserved and fixed in position. It inactivates enzymes that night disrupt cell morphology and toughness of cell structures so that they do not change during staining and observation.
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A cell is usually killed and ad her to slide during microscopic observation.
Fixation of Microbial Cell is Done in Two Ways:
Heat fixation or chemical fixation. Heat fixation is routinely used to observe prokaryotes. A film of cell is gently heated as a slide passes through a flame. Heat fixation preserves over all morphology but not structures within cell. Chemical fixation is used to protect fine cellular substructure and morphology of large and delicate microorganisms.
Chemical fixatives penetrate cell and react with cellular components, usually protein and lipids to render them inactive. Common fixative mixture contains ethanol, acetic acid, mercuric chloride, formaldehyde and glutaraldehyde.
