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Base Excess

Arterial Blood Gases

It is defined as the amount of acid required to restore a litre of blood to its normal pH at a PaCO2 of 40 mmHg. The base excess increases in metabolic alkalosis and decreases (or becomes more negative) in metabolic acidosis, but its utility in interpreting blood gas results is controversial.

Endospore Stain

Endospores are dormant forms of living bacteria and should not be confused with reproductive spores produced by fungi. These structures are produced by a few genera of Gram-positive bacteria, almost all bacilli, in response to adverse environmental conditions. Two common bacteria that produce endospores are Bacillus or Clostridum. Both live primarily in soil and as symbionts of plants and animals, and produce endospores to survive in an environment that change rapidly and often. Endospore stain procedural steps. Step […]

Acid Fast Stain

Some bacteria produce the waxy substance mycolic acid when they construct their cell walls. Mycolic acid acts as a barrier, protecting the cells from dehydrating, as well as from phagocytosis by immune system cells in a host. This waxy barrier also prevents stains from penetrating the cell, which is why the Gram stain does not work with mycobacteria such as Mycobacterium, which are pathogens of humans and animals. For these bacteria, the acid–fast staining technique […]

Immunohistochemistry Stain

Binding of specific cell or tissue structures (usually proteins) by an antibody directed against that protein. This antibody is often raised in a species other than the one from which the specimen is taken. For example, antibodies may be developed in rabbits to a protein present in human tissue. There are several methods for visualizing where these antibodies have bound to the tissue. In the example above, other antibodies directed against rabbit proteins that are […]

Metachromasia Stain

The property of certain biological compounds to change the color of such dyes as toluidine blue or thionine. For example, glycosaminoglycans/proteoglycans found in cartilage matrix and mast cell granules will stain red or violet instead of blue with toluidine blue. The phenomenon is apparently caused by a change in the electronic structure of the dye molecule as it interacts with the electrons of the binding polymer and other dye molecules.

Feulgen Reaction Stain

This is a specific and quantitative reaction for the demonstration of DNA. Hydrolysis with HCl forms aldehyde groups on the DNA sugar (deoxyribose) but not on RNA sugar (ribose). The aldehydes then react with reduced basic fuchsin (Schiff’s reagent) to form a characteristic red-blue (magenta) color. The specificity of this stain for DNA can be confirmed by pretreatment of the tissue with DNAase, which depolymerizes DNA and abolishes staining.

Giemsa Stain

A combined blood stain, consisting of methylene blue, azure and eosin composition and results are similar to those of Wright’s stain. Also useful for staining chromosome spreads (G-banding).

Wright’s Blood Stain

Uses alcoholic mixture of eosin and methylene blue to differentiate blood cell types in smears of peripheral blood or bone marrow. Red cells are pink/red, nuclei are dark blue and granules in the cytoplasm of some white blood cells stain differently depending on the cell type (red in eosinophils and blue in basophils, for example)

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