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In Vitro StainingStains are used in biological and medical disciplines to highlight cell structures and organelles, cells, or tissues for viewing, usually with an instrument such as a microscope. In vitro staining is the process of dyeing living tissues (compare with in vivo staining of living cells or tissue). In vitro means, literally "in glass", indicating that the process is one carried out in laboratory glassware. By causing certain cells or structures to take on contrasting color(s), their form (morphology) or position within a cell or tissue can be readily established and studied. Common staining protocols In histology and medicine, certain stains are often combined to reveal more details and features than a single stain alone. Combined with specific protocols for fixation and sample preparation, scientists and physicians can use these standard techniques as consistent, repeatable diagnostic tools. Gram staining Gram staining is used to classify bacteria. Gram-positive bacteria stain purple or blue-black, and have a cell wall. Gram-negative bacteria lack a cell wall and appear red. Gram status is important in medicine; the presence or absence of a cell wall will change the bacterium's susceptibility to some antibiotics. Gram staining uses crystal violet to stain cell walls, iodine as a mordant, and a fuchsin or safranin counterstain to mark all bacteria. Haematoxylin and Eosin (H&E) staining This staining protocols is used frequently in histology to examine thin sections of tissue. Haematoxylin stains cell nuclei blue, while eosin stains cytoplasm and connective tissue pink or red. Eosin is strongly absorbed by red blood cells, colouring them bright red. Masson's trichrome Masson's trichrome is (as the name implies) a three-colour staining protocol. The recipe has evolved from Masson's original technique for different specific applications, but all are well-suited to distinguish cells from surrounding connective tissue. Most recipes will produce red keratin and muscle fibers, blue or green staining of collagen and bone, light red or pink staining of cytoplasm, and black cell nuclei. Romanowsky stains The Romanowsky stains are all based on a combination of eosinate (chemically reduced eosin) and methylene blue (sometimes with its oxidation products azure A and azure B). Common variants include Wright's stain, Jenner's stain, Leishman stain and Giemsa stain. All are used to examine blood or bone marrow samples. They are preferred over H&E for inspection of blood cells because different types of leukocytes (white blood cells) can be readily distinguished. All are also suited to examination of blood to detect blood-borne parasites like malaria. External link
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