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It is called staining to the dyeing process and result (grant a colour to one thing). The concept derives from the Latin word tinctĭo.

It is important to note that the act and the consequence of dyeing are also known as tincture . Thus, while in the colloquial language the idea of ​​dyeing is usually used, in the field of chemistry and of the medicine the term staining is preferred.

In this sense, a staining is called technique which is used in labs with the objective of optimize vision of what is observed through a microscope . Staining, in this way, consists in applying a dye to a substance or a tissue so that it is simpler to detect and analyze it.

With staining, it is possible to improve the definition of groups of cells or tissue fragments, to name a few options. Also, by special tinctures, the presence of certain substances or elements in a compound can be measured.

When you dye a living tissue, you talk about staining in vivo , supravital or vital . This allows to observe chemical reactions or morphological characteristics of living tissues while the cells fulfill their natural function. In general, the objective that scientists seek through this type of staining is to bring to light certain data about the cytostructure (the conformation of the cell) that could not be observed otherwise, although it also serves to indicate the location of a specific chemical, or of a reaction that occurs inside the tissues or cells.

One of the main characteristics of staining in vivo is that dyes are often used in highly diluted solutions, with values of concentration ranging from 1: 5,000 to 1: 50,000. However, this does not always prevent staining from being toxic to the body.

Talk about staining in vitro to define the coloration of structures or cells that are no longer in their context biological. Generally, various dyes are combined to obtain more detailed and accurate results. When this binds to certain sample preparation and fixation protocols, science is capable of producing consistent diagnoses.

The kind of analysis desired for each particular case affects the steps necessary to carry out the staining in vitro, and these are three: the fixation , which consists in modifying the physical and chemical properties of the proteins of a tissue or cell to preserve its shape to the maximum; the permeabilization , to dissolve the cell membrane so that the dye can penetrate it; he mounting , which seeks to increase the resistance of a sample so that it does not destroy or lose its structure Original throughout the process.

There is also the concept contratinction , which refer to the application of a second stain to a certain preparation to make visible those parts that could not be stained with the first. The staining, on the other hand, can be indirect or direct according to the interaction of the dye with the tissue .

One of the best known stains is the Gram stain , developed by Christian Gram , which allows to visualize bacteria in clinical samples. The bacteria that react by turning purple are called Gram positive bacteria , while those that turn pink are defined as Gram negative bacteria .

The wright staining , the hematoxylin-eosin staining and the argumentative staining They are other kinds of stains that can be used.

Picking up the term contratinction, we can see an example of this technique when applied Violet glass (a group of compounds that are often used as dyes and pH indicators and is also called gentian violet or methyl violet) to a sample of bacteria for a Gram stain, since only Gram positive are stained; for this reason the application from safranine, which affects all cells and, therefore, allows the identification of negative Gram.

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