| Weidel's reaction | A reaction showing the presence of xanthine; a solution of the suspected substance in chlorine water with a little nitric acid is evaporated in a water bath, and then exposed to the vapor of ammonia; the presence of xanthine is indicated when a red or purple colour develops. (05 Mar 2000) |
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| Pirquet's reaction | A cutaneous tuberculin test. (05 Mar 2000) |
| Weil-Felix reaction | <investigation> A serologic fluorescent antibody screen that indicates infection with the rickettsial bacteria which is responsible for Rocky Mountain spotted fever. This test may also be positive in brucellosis, salmonella infection and tularaemia. (27 Sep 1997) |
| Weinberg's reaction | A complement fixation test of the presence of hydatid disease. (05 Mar 2000) |
| Wernicke's reaction | In hemianopeia, a reaction due to damage of the optic tract, consisting in loss of pupillary constriction when the light is directed to the blind side of the retina; pupillary constriction is maintained when light stimulates the normal side. This sign cannot be seen with a bright light because of intraocular scatter onto the seeing half of the retina. Synonym: Wernicke's sign. (05 Mar 2000) |
| combustion reaction | <chemistry> The vigorous and exothermic reaction that takes place between certain substances, particularly organic compounds, and oxygen. (09 Jan 1998) |
| wheal-and-erythema reaction | The characteristic immediate reaction observed in the skin test; within 10 to 15 minutes after injection of antigen (allergen), an irregular, blanched, elevated wheal appears, surrounded by an area of erythema (flare). Synonym: wheal-and-flare reaction. (05 Mar 2000) |
| wheal-and-flare reaction | The characteristic immediate reaction observed in the skin test; within 10 to 15 minutes after injection of antigen (allergen), an irregular, blanched, elevated wheal appears, surrounded by an area of erythema (flare). Synonym: wheal-and-flare reaction. (05 Mar 2000) |
| whitegraft reaction | An immune reaction to a tissue graft that results in failure of graft vascularization and ensuing rejection. (05 Mar 2000) |
| white reaction | The response seen in many individuals after the skin is lightly stroked with a blunt instrument; it is attributed to capillary action. (05 Mar 2000) |
| Widal's reaction | Agglutination reaction as applied to the diagnosis of typhoid. Synonym: Gruber's reaction, Gruber-Widal reaction. (05 Mar 2000) |
| 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) |
| plasmal reaction | <chemistry> Long chain aliphatic aldehydes occurring in plasmalogens react with Schiff's reagent in the so called plasmal reaction, to form for example palmitaldehyde, stearaldehyde. (31 Dec 1997) |
| plasmocytic leukemoid reaction | The presence of unusual numbers of plasma cells, i.e., plasmocytosis, in the bone marrow; may be observed in association with sarcoidosis, rheumatoid arthritis, cirrhosis, Hodgkin's disease, and certain of the so-called collagen diseases. (05 Mar 2000) |
| pleural reaction | Thickening of the pleural stripe on chest radiographs, representing pleuritis, pleural effusion, or pleural fibrosis. (05 Mar 2000) |