Editing Staining (section)

== ''In vivo'' vs ''In vitro'' ==
''[[In vivo]] staining'' (also called [[vital staining]] or intravital staining) is the process of dyeing living tissues. By causing certain cells or structures to take on contrasting colours, their form ([[Morphology (biology)|morphology]]) or position within a cell or tissue can be readily seen and studied. The usual purpose is to reveal cytological details that might otherwise not be apparent; however, staining can also reveal where certain chemicals or specific chemical reactions are taking place within cells or tissues.

''[[In vitro]]'' staining involves colouring cells or structures that have been removed from their biological context. Certain stains are often combined to reveal more details and features than a single stain alone.  Combined with specific protocols for [[fixation (histology)|fixation]] and sample preparation, scientists and physicians can use these standard techniques as consistent, repeatable diagnostic tools. A [[counterstain]] is stain that makes cells or structures more visible, when not completely visible with the principal stain.
* Crystal violet stains both Gram positive and Gram negative organisms. Treatment with alcohol removes the crystal violet colour from gram negative organisms only. [[Safranin]] as counterstain is used to colour the gram negative organisms that got decolorised by alcohol.

While ex vivo, many cells continue to live and metabolize until they are "fixed". Some staining methods are based on this property. Those stains excluded by the living cells but taken up by the  already dead cells are called [[vital stain]]s (e.g. [[trypan blue]] or [[propidium iodide]] for eukaryotic cells). Those that enter and stain living cells are called [[supravital stain]]s (e.g. [[New Methylene Blue]] and [[brilliant cresyl blue]] for [[reticulocyte]] staining). However, these stains are eventually toxic to the organism, some more so than others.  Partly due to their toxic interaction inside a living cell, when supravital stains enter a living cell, they might produce a characteristic pattern of staining different from the staining of an already fixed cell (e.g. "reticulocyte" look versus diffuse "polychromasia"). To achieve desired effects, the stains are used in very dilute solutions ranging from {{gaps|1|:|5|000}} to {{gaps|1|:|500|000}} (Howey, 2000). Note that many stains may be used in both living and fixed cells.