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I. Staining: Routine Paraffin Embedded Sections
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Slide 1: Most mammalian tissues have no inherent color. Under a light microscope cells and tissues have color because they were stained with dyes during slide preparation. Slides #1-13 illustrate this point. You will note that after staining with different stains the same structures appear somewhat different. You are responsible for knowing the stains (and what they are used to demonstrate) which are listed in the course syllabus. Tissue or organ names in this Unit are given for the sake of completeness. You will learn the morphology of different tissues and organs as the course progresses.

Tissues and organs are routinely embeddded in paraffin or paraffin/plastic mixtures for routine light microscopic sectioning. Thinner sections can be made if the samples are prepared for electron microscopy and are embedded in plastic (such as methacrylates or Epon). These latter sections are usually better preserved. Several of the following slides illustrate the difference in appearance of this type of preparation.

This slide is of a small intestine stained with the most common light microscope stain called hematoxylin and eosin (H & E). Hematoxylin stains nucleic acids blue, (nuclei and cytoplasmic accumulations of ribosomes are mostly what pick up this stain). Eosin stains the cytoplasm of cells, and many extracellular components such as collagen, pink to orange depending on the type of eosin used. This is a typical section of paraffin embedded tissue. This type of section is typically 5-12 μm thick.