| catalatic reaction | Decomposition of H2O2 to O2 and H2O, as in the action of catalase; analogous to peroxidase reaction. (05 Mar 2000) |
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| catastrophic reaction | The disorganised behaviour that is the response to a severe shock or threatening situation with which the person cannot cope. (05 Mar 2000) |
| Mazzotti reaction | A test for onchocerciasis using an oral test dose of diethylcarbamazine (50 or 100 mg), resulting in the appearance of an acute rash in 2 to 24 hours from death of microfilariae in the skin. Synonym: Mazzotti reaction. (05 Mar 2000) |
| Paul's reaction | Pus is rubbed into a scarification on a rabbit's eye; if the pus is from a variolous or vaccinal pustule a condition of epitheliosis develops in from 36 to 48 hours; the sputum of a smallpox patient is said to cause the same reaction. Synonym: Paul's test. (05 Mar 2000) |
| cell-mediated reaction | Immunological reaction of the delayed type, involving chiefly T lymphocytes, important in host defense against infection, in autoimmune diseases, and in transplant rejection. See: skin test. (05 Mar 2000) |
| Voges-Proskauer reaction | A chemical reaction used in testing for the production of acetyl methyl carbinol by various bacteria; potassium hydroxide is added to a 24-hour culture in a suitable medium and thoroughly mixed; the treated culture is exposed to air and is observed at intervals of 2, 12, and 24 hours; a positive reaction consists of the development of an eosin-like pink colour, due to the production of acetylmethylcarbinol, which in the presence of alkali and oxygen is oxidised to diacetyl. (05 Mar 2000) |
| chain reaction | A reaction in which a product reacts and thus continues the reaction. (09 Oct 1997) |
| Chantemesse reaction | A conjunctival reaction, especially as applied to typhoid. (05 Mar 2000) |
| reversed Prausnitz-Kustner reaction | The appearance of an urticarial reaction at the site of injection when serum containing reaginic antibody is injected into the skin of a person in whom the allergen is already present. (05 Mar 2000) |
| performic acid reaction | Oxidative destruction of the ethylene double bond (-HC==CH-) which is converted to a Schiff-reactive double aldehyde; used to indicate the presence of unsaturated lipids, such as phospholipids and cerebrosides, as well as cystine-rich substances, such as keratin, in tissue sections. (05 Mar 2000) |
| reversible reaction | A chemical reaction that takes place in either direction i.e., from the forward or reverse direction; ionization is such a reaction, as are reaction's involving racemases, isomerases, mutases, transferases, etc. (05 Mar 2000) |
| graft-versus-host reaction | <haematology> A common and serious, complication of bone marrow transplantation where there is a reaction of donated bone marrow against a patient's own tissue. When donor lymphocytes or a graft containing lymphocytes that are immunologically competent are given to a patient that has low immunological competence, an incompatibility reaction can result. This is due to antibodies from the donor against antigens in the host. This is due to mismatch of MHC Class I antigens and can produce lymphocyte clones that will react by a variety of processes against the host and cause damage. The clinical condition can be fatal and is due to the donor's immune cells recognising the host cells as foreign. The clinical entity characterised by anorexia, diarrhoea, loss of hair, leukopenia, thrombocytopenia, growth retardation, and eventual death brought about by the graft-versus-host reaction. It can occur in either chronic or acute forms and is treatable by immunosuppressive drugs. Seen most commonly following bone marrow transplantation, acute disease is seen after 5-40 days and chronic disease weeks to months after transplantation, affecting, principally, the gastrointestinal tract, liver, and skin. Radiological appearances of the gastrointestinal tract include; thickened wall, mucosal folds thickened or effaced, increased secretions most likely to be rapid transit of GI tract, mass most likely to be focal oedema, fibrosis, hallmark: diffuse, uniform thickening of small bowel. Synonym: GVH disease. Acronym: GVHD (20 Sep 2002) |
| chemical reaction | <chemistry> A process in which one or more substances are changed chemically into one or more different substances. (09 Oct 1997) |
| 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) |