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1. Serving to fix, bind, or make firm or stable. 2. A substance used for the preservation of gross and histologic specimens of tissue, or individual cells, usually by denaturing and precipitating or cross-linking the protein constituents. SEE ALSO: fluid, solution.
- acetone f. acetone used at low temperatures to fix enzymes, particularly phosphatases; it removes fat and glycogen.
- AFA f. a combination of alcohol, formalin, and acetic acid used for the fixation of nematodes, trematodes, and cestodes.
- Bouin f. a solution of glacial acetic acid, formalin, and picric acid, useful for soft and delicate tissues (as those of embryos) and small pieces of tissues; it preserves glycogen and nuclei and permits brilliant staining, but penetrates slowly, distorts kidney tissue and mitochondria, and does not permit Feulgen stain for DNA.
- Carnoy f. ethanol, chloroform, and acetic acid (6:3:1) or ethanol and acetic acid (3:1), an extremely rapid f. used for glycogen preservation and as a nuclear f..
- Champy f. a mixture of potassium bichromate, chromic acid, and osmic acid, considered an excellent cytologic f. with advantages and disadvantages similar to those of Flemming's f.; it differs from Flemming f. in substituting bichromate for acetic acid.
- Flemming f. a mixture of chromic acid, osmic acid, and acetic acid that makes an excellent cytoplasmic and chromosomal f., especially when acetic acid is omitted; disadvantages are that it penetrates poorly, requires lengthy washing, and deterioriates rapidly.
- formaldehyde f. a widely used fixing agent for pathologic histology; the commercial solution is 37–40% formaldehyde and is known as 100% formalin or formol; a common impurity is formic acid, which must be neutralized or the f. made in buffer solution; tissues fixed may have a pigment artifact precipitated.
- formol-calcium f. a f. for preservation of lipids.
- formol-Müller f. Müller f. containing 2% commercial formalin.
- formol-saline f. a general f. for histologic and histochemical preparations.
- glutaraldehyde f. a f. used in phosphate or cacodylate buffer for electron microscopy, and as a chromatin and enzyme f.; may be used preceding osmic acid as a second f. to add membrane preservation for electron microscopy.
- Golgi osmiobichromate f. an osmic-bichromate mixture used to demonstrate nerve cells and their processes.
- Helly f. a combination of potassium dichromate, mercuric chloride, formaldehyde, and distilled water, used as a microanatomic f. for cytoplasmic granules and nuclear staining; has the same disadvantages as Zenker f..
- Kaiserling f. a method of preserving histologic and pathologic specimens without altering the color, by immersing them in an aqueous solution of potassium nitrate, potassium acetate, and formalin.
- Luft potassium permanganate f. a f. useful in electron microscopy for cytologic preservation of lipoprotein complexes in membranes and myelin, because of its oxidative properties.
- Marchi f. a mixture of Müller f. with osmium tetroxide, with potassium chlorate substituted for the potassium dichromate of Müller f. for better results; used to demonstrate degenerating myelin. SEE ALSO: Marchi stain.
- Müller f. a hardening f. composed of potassium dichromate, sodium sulfate, and distilled water, similar to Regaud f..
- neutral buffered formalin f. a general histologic f. less likely to leave formalin deposits in tissue than formol-saline f..
- Newcomer f. a f. containing isopropanol, propionic acid, and dioxane, recommended as a substitute for Carnoy f. in preservation of chromatin; also useful for fixing polysaccharides; small pieces of tissue must be used, although excessive shrinkage may still occur.
- Orth f. formalin added to Müller f., used for bringing out chromaffin, studying early degenerative processes and necrosis, and for demonstrating rickettsiae and bacteria.
- osmic acid f. a f. used alone in buffer or as a postfixative after a glutaraldehyde f. in electron microscopy; an excellent membrane f. but a poor preservative of chromatin.
- Park-Williams f. a f. for spirochetes, comprised of a 2% solution of osmic acid to the fumes of which the bacteria are exposed for a few seconds.
- PVA f. schaudinn f. using either a mercuric chloride, zinc sulfate, or copper sulfate base; contains polyvinyl alcohol plastic powder that is used as an adhesive for fecal specimens in the preparation of permanent smears for subsequent staining.
- Regaud f. a f. containing formaldehyde and sodium dichromate, used to preserve mitochondria but not fat; requires afterchroming and extensive washing.
- SAF f. sodium acetate-acetic acid-formalin mixture used to fix fecal specimens for subsequent concentration and staining of smears.
- Schaudinn f. a solution of mercuric chloride, sodium chloride, alcohol, and glacial acetic acid, used on wet smears for cytologic fixation.
- single vial fixatives proprietary and commercially available solutions used for stool fixation; from the single vial, a concentration, permanent stain, and some immunoassay procedures can be performed.
- Thoma f. nitric acid in 95% alcohol, used for decalcifying bone in the preparation of histologic specimens.
- Zenker f. a rapid f. consisting of mercuric chloride, potassium dichromate, sodium sulfate, glacial acetic acid, and water, useful for trichrome stains; must be washed to remove potassium dichromate and treated with iodine solution to remove mercuric chloride; tissues tend to become brittle if left in the f. for more than 24 hours.
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fix·a·tive 'fik-sət-iv n a substance used to fix living tissue
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n.
a chemical agent, e.g. alcohol or osmium tetroxide, used for the preservation and hardening of tissues for microscopical study. See fixation.
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fix·a·tive (fikґsə-tiv) a fluid, often a mixture of several reactive chemicals, into which histological or cytological specimens are placed so that, by processes such as denaturation and cross-linking of proteins, autolysis is prevented, the specimen is hardened to withstand further processing, and the specimen is preserved in a close facsimile of the living state in regard to both cellular morphology and the location of subcellular constituents.Medical dictionary. 2011.