| chemical reaction | <chemistry> A process in which one or more substances are changed chemically into one or more different substances. (09 Oct 1997) |
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| periodic acid Schiff reaction | <technique> A histochemical technique based on periodic acid oxidation of a substance containing the 1,2-glycol grouping. It is used for staining carbohydrates as the resulting dialdehyde reacts with Schiff reagent to form a coloured product. The adjacent hydroxyl groups are oxidized to form aldehydes by periodic acid (HIO4) and these aldehyde groups react with Schiff's reagent (basic fuchsin decolourised by sulphurous acid) to give a purple colour. Acronym: PAS (18 Nov 1997) |
| periosteal reaction | <radiology> In adults: hypertrophic osteoarthropathy (HOA), pachydermoperiostosis, vascular insufficiency, thyroid acropachy, fluorosis in kids: physiologic periostosis, Caffey disease, JRA, acute leukaemia, scurvy, rickets, congenital syphilis, hypervitaminosis A (12 Dec 1998) |
| periosteal reaction patterns | <radiology> Pattern most indicative of buttressing eosinophilic granuloma laminated Ewing sarcoma or hair-on-end Codman triangle osteo- or chondrosarcoma or sunburst (per Resnick) (12 Dec 1998) |
| peroxidase reaction | Formation of indophenol blue by the action of an oxidizing enzyme present in certain cells and tissues when they are treated with a solution of alpha-naphthol and dimethylparaphenylenediamine; by this method, cells of the myelocyte series, which give a positive reaction, may be distinguished from those of the lymphocyte series, which give a negative reaction; endothelial leukocytes give a variable reaction, probably positive when they have phagocytised the debris of myeloid cells. Synonym: Nadi reaction. (05 Mar 2000) |
| group reaction | A reaction with an agglutinin or other antibody that is common (though usually in varying concentrations) to an entire group of related bacteria, e.g., the coli group. (05 Mar 2000) |
| Gruber's reaction | Agglutination reaction as applied to the diagnosis of typhoid. Synonym: Gruber's reaction, Gruber-Widal reaction. (05 Mar 2000) |
| Gruber-Widal reaction | Agglutination reaction as applied to the diagnosis of typhoid. Synonym: Gruber's reaction, Gruber-Widal reaction. (05 Mar 2000) |
| cholera-red reaction | A test for cholera vibrio whereby the addition of 3 or 4 drops of sulfuric acid (concentrated, chemically pure) to an 18-hour-old bouillon or peptone culture of the organism produces a colour from rose-pink to claret. (05 Mar 2000) |
| Gunning's reaction | The formation of iodoform from acetone by iodine and ammonia in alcohol. (05 Mar 2000) |
| chromaffin reaction | Production of a yellow-brown to brown colouration in normal and abnormal cells containing epinephrine and norepinephrine, when fresh tissue slices are placed in a dichromate-chromate mixture overnight; useful for detection of pheochromocytoma (adrenal medulla) and other tumours which produce catecholamines. (05 Mar 2000) |
| circular reaction | In sensorimotor theory, the tendency of an organism to repeat novel experiences. (05 Mar 2000) |
| phosphoroclastic reaction | Cleavage of C-C bonds that involves phosphate transfer but not, as in phosphorolysis, directly to one of the products; e.g., the decomposition of pyruvate to acetate + CO2, in which Pi is added to ADP to form ATP. (05 Mar 2000) |
| Millon reaction | The reaction of phenolic compounds (e.g., tyrosine in protein) with Hg(NO3)2 in HNO3 (and a trace of HNO2) to give a red colour. (05 Mar 2000) |
| photosynthetic reaction centre, bacterial | A system consisting of proteins and cofactors which acts as a light-driven electron pump across the photosynthetic membrane of photosynthetic bacteria. (12 Dec 1998) |