FIXING — the processing of biological objects (cells, fabrics, microorganisms) chemical or physical agents providing more or less full preservation of their intravital structure and chemical composition.
At the heart of F. the termination of functional activity of proteins and nucleinic to - t by binding of their functional groups, coagulation or dehydration lies. The substances having such property are called fixers, or the fixing agents; solutions of fixers — the fixing liquids. The mechanism of operation of the most widespread chemical fixers (formaldehyde, corrosive sublimate, salts of chrome) — see. Histologic methods of a research.
T., stopping functional activity of proteins, involves these or those disturbances microscopic, ultramikroskopichesko-go and chemical structures of objects. The majority of fixers causes compression and consolidation of fabrics, and even within one body of a cell can unequally change depending on their arrangement in relation to a surface of an object, from extent of their hydration, etc. After fixing fabric elements refract light differently, than native structures. Owing to this fact at F. the structural details which are not seen at microscopic examination of an unstable object can come to light. Sometimes at F. there can be distortions of structure which are not connected with a true structure of an object — so-called artifacts (see).
Methods F. subdivide on chemical and physical. Chemical F. consists in immersion of an object in the fixing liquid. As a rule, immerse in liquid thin (5 — 10 mm) plates of fabric; sometimes, especially at cytologic or electronic mikroskopi-cheskom a research, it is necessary to take pieces up to 1 — 2 mm thick. In nek-ry cases the fixer is entered into blood vessels of the studied object. T. small objects, cuts and smears it is possible to make also on glass in pairs of the fixer (osmium tetroxide, formalin). The volume of the fixing liquid, in to-ruyu the body, pieces of fabric and other objects immerse, shall exceed the bulk volume of subjects to fixing approximately by 20 times. It is not recommended before F. to wash the fixed material, especially nervous tissue, water. Walls of hollow bodies before F. usually stretch on a cardboard or a stopper; pieces of fabric protect from adhesion, interlaying them with a gauze or cotton wool. It is recommended to apply freshly cooked r-ry fixers, replacing them as required; re-using of solutions is inadmissible. More often F. make at the room temperature, but sometimes for acceleration of penetration of the fixer into fabric — in the thermostat at t ° 37 °, and for weakening of processes of an autolysis (see) — in the refrigerator at f 0 ° — 10 °. Duration F. depends both on properties of the fixing liquid, and on the sizes and features of an object. T. it is considered finished when the fixer impregnates all thickness of an object. In nek-ry fixers (formalin, alcohol) an object can remain for years, in others — mixes Carnoy (see the Card and liquid), Tsenkera, Horta, etc. — the perederzhivaniye of an object is undesirable.
The fixing liquids divide on simple, turning on only one fixer, and difficult, consisting of mix of different fixers. From simple solution of formalin is most spread by 10 — 20% (see). To the special purposes apply also 96 — 100% alcohol (see), saturated solution of corrosive sublimate (see Mercury), anhydrous acetone (see) and chloroform (see), and to the subsequent submicroscopy — buffering (pH 7,4) solutions of osmium tetroxide (1 — 2%), glutaric dialdehyde (4 — 5,6%), potassium permanganate (
1,2 — 1,5%, on cold), is more rare — acrolein (10%) and oxyadipinic aldehyde (12,5%). Fixing in 1,5 — 3% solution of glutaric dialdehyde yields good results at a research of intracellular localization of enzymes.
The complex fixing liquids represent a combination of different fixers in one solution. E.g., acetic to - that, alcohol and chloroform make the mix Carnoy applied for bystry F. cells. Good results are yielded by the mix «suz» on Geydengayna, a cut corrosive sublimate (4,5 g), sodium chloride (0,5 g), a distilled water (80 ml), trichloroacetic to - that (2 g), ice acetic to - that (4 ml), formalin (20 ml) are a part. This mix dissolves salts of calcium in this connection it can be applied also for F. bones of small animals (see Decalcification). From other fixing mixes containing corrosive sublimate often use Tsenker, Maximov's liquids, Dominichi (see Dominichi methods); dropping out at the same time in fabric of draft of carbonates and mercuric phosphates delete with iodination (see Iodine). Picric to - that (75 ml of saturated water solution), formalin (25 ml) and ice vinegar -
a share to - that (5 ml) make Buen's mix — one of the most widespread fixing liquids. For a number of histochemical reactions, especially for identification of a glycogen, it is recommended to apply Shabadash's mix consisting of 96% of alcohol (100 ml), cupric nitrate (1,8 g), calcium nitrate (0,9 g), formalin (10 ml).
In mix for F. also chromic compounds, salts of heavy metals, etc. enter.
To physical methods F. freezing drying belongs (see Drying, Lyophilizing). This way F. widely apply in a histochemistry of enzymes along with F. in buffering solutions of formalin or glutaric dialdehyde. In hematology and bacteriology use F. the smears dried on air over a flame of a torch (flaming) or on a copper plate at t ° 120 ° (see. Bacteriological techniques, Colouring of microorganisms).
Choice of a way F. is defined by properties of the fixed object and research objectives, i.e. compliance of the chosen method F. to the next ways of filling and coloring of drug. If long-term storage of material as museum drug is supposed, then resort to special ways F., allowing to keep close to natural outward and coloring of drug (see Kai-zerlinga a method, Drugs anatomic).
See also Histochemical methods of a research.
Bibliography: Lille R. Patogistologi
the chesky equipment and a practical histochemistry, the lane with English, page 34, M., 1969; Lloyd 3. and d river. A histochemistry of enzymes, the lane with English, page 42, M., 1982; L at p p and X. Bases of a histochemistry, the lane with it., page 31, M., 1980; Merkulov G. A. A course - the patologogistologichesky equipment, page 8, L. 1969; Pearce E. Histochemistry, lane of € English, page 54, M., 1962; Romeys B. Mikroskopicheskaya of the technician, the lane with it., page 48, M., 1954; The Guide to cytology under the editorship of A.S. Troshin, t. 1, page 73, M. — L., 1965. Ya. E. Hesinonim