| reaction quotient | <chemistry> A constant represented by the symbol Q which is defined as the product of the concentrations of the products, each raised to the power that corresponds to its coefficient in the balanced equation, divided by the product of the concentrations of reactants, each raised to the power that corresponds to its coefficient in the balanced equation (see the equation in the equations page). at equilibrium conditions Q=K, the equilibrium constant. (09 Jan 1998) |
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| reaction time | The time from the onset of a stimulus until the organism responds. (12 Dec 1998) |
| Marchi's reaction | Failure of the myelin sheath of a nerve to blacken when submitted to the action of osmic acid. (05 Mar 2000) |
| Gerhardt's reaction | In fresh urine a red colour develops upon addition of FeCl3; no colour develops if the urine has first been boiled; this test has low specificity and sensitivity. Synonym: Gerhardt's reaction. (05 Mar 2000) |
| Carr-Price reaction | The reaction of antimony trichloride with vitamin A to yield a brilliant blue colour; this reaction forms the basis of several quantitative techniques for the determination of vitamin A. (05 Mar 2000) |
| redox reaction | <chemistry> A reaction in which one or more electrons are transferred. (09 Jan 1998) |
| catalatic reaction | Decomposition of H2O2 to O2 and H2O, as in the action of catalase; analogous to peroxidase reaction. (05 Mar 2000) |
| 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) |