| complement-fixation reaction | <immunology> Binding of complement as a result of its interaction with immune complexes (the classical pathway) or particular surfaces (alternative pathway). (18 Nov 1997) |
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| complement-fixation test | An immunological test for determining the presence of a particular antigen or antibody when one of the two is known to be present, based on the fact that complement is "fixed" in the presence of antigen and its specific antibody. See: Bordet-Gengou phenomenon. (05 Mar 2000) |
| complement fixation tests | Serologic tests based on inactivation of complement by the antigen-antibody complex (stage 1). Binding of free complement can be visualised by addition of a second antigen-antibody system such as red cells and appropriate red cell antibody (haemolysin) requiring complement for its completion (stage 2). Failure of the red cells to lyse indicates that a specific antigen-antibody reaction has taken place in stage 1. If red cells lyse, free complement is present indicating no antigen-antibody reaction occurred in stage 1. (12 Dec 1998) |
| point of fixation | The point on the retina at which the rays coming from an object regarded directly are focused. Synonym: point of regard. (05 Mar 2000) |
| craniofacial fixation | Stabilization of facial fractures to the cranial base by direct wiring or by external skeletal pin fixation. (05 Mar 2000) |
| crossed fixation | In convergent strabismus, the use of the right inturned eye to look at objects to the left and the left inturned eye to look at objects to the right, in order to avoid ocular rotation. (05 Mar 2000) |
| crossover fixation | <molecular biology> The addition of extra copies of segments of DNA on the same strand by unequal crossing over during meiosis. An explanation for the existence of satellite DNA, which are highly-repeated, non-transcribed sequences of DNA with no clear function. An alternative explanation to saltatory replication. (03 Jul 1999) |
| nasomandibular fixation | Mandibular immobilization, especially for edentulous jaws, with maxillomandibular splints, attached by connecting a circum-mandibular wire with an intraoral interosseous wire passed through a hole drilled into the anterior nasal spine of the maxillae. (05 Mar 2000) |
| nitrogen fixation | <biochemistry> The incorporation of atmospheric nitrogen into ammonia by various bacteria, catalysed by nitrogenase. This is an essential stage in the nitrogen cycle and is the ultimate source of all nitrogen in living organisms. In the sea, the main nitrogen fixers are Cyanobacteria. There are several free living bacteria in soil that fix nitrogen including species of Azotobacter, Clostridium and Klebsiella. Rhizobium only fixes nitrogen when in symbiotic association, in root nodules, with leguminous plants. The oxygen sensitive nitrogenase is protected by plant produced leghaemoglobin and the plant obtains fixed nitrogen from the bacteria. See: Frankia. (18 Nov 1997) |
| intermaxillary fixation | Fixation of fractures of the mandible or maxilla by applying elastic bands or stainless steel wire between the maxillary and mandibular arch bars or other types of splint. Synonym: mandibulomaxillary fixation, maxillomandibular fixation. (05 Mar 2000) |
| internal fixation | The use of internal metal plates, screws or rods to stabilise bone fragments. A procedure used to correct serious orthopaedic bone fractures that cannot be stabilised by casting or splinting. See: external fixation. (27 Sep 1997) |
| intraosseous fixation | The use of internal metal plates, screws or rods to stabilise bone fragments. A procedure used to correct serious orthopaedic bone fractures that cannot be stabilised by casting or splinting. See: external fixation. (27 Sep 1997) |
| orthopedic fixation devices | Devices which are used in the treatment of orthopedic injuries and diseases. (12 Dec 1998) |
| eccentric fixation | A monocular condition in which the line of sight connects the object and an extrafoveal retinal area. (05 Mar 2000) |
| thyrotoxic complement-fixation factor | A form of thyrotoxin; an antigen found most readily in thyroid tissue from thyrotoxic individuals; known to be chemically and immunologically distinct from thyroglobulin, and fixes complement when combined with antibody related to the gamma-globulin fraction of serum. With the exception of extremely small concentrations, the antigen is rarely found in normal glands or in diseased glands that are not associated with thyrotoxicosis; it is probably an intracellular substance (possibly a constituent of the "microsomal fraction"), and does not contain iodine in significant quantity. Not related to the complement-fixation reaction occurring with serum in Hashimoto's disease, in which the antigen is thyroglobulin. (05 Mar 2000) |