| aldehyde reaction | The reaction of the indole derivatives with aromatic aldehydes; e.g., tryptophan and p-dimethylaminobenzaldehyde in H2SO4 give a red-violet colour useful in assaying proteins for tryptophan content. Synonym: Ehrlich reaction. (05 Mar 2000) |
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| alkaline reaction | Any test by which an alkaline reaction is recognised, such as the change of red litmus paper to blue, an excess of hydroxide ions over hydrogen ions in aqueous solution as indicated by a pH value greater than 7 (at 22캜). Compare: dissociation constant of water. Synonym: basic reaction. (05 Mar 2000) |
| allergic reaction | <immunology> The bodys response to an allergic stimulus. This can be localised to one area or generalised and may include: rash, itching, hives, swelling, difficulty breathing, and/or low blood pressure. (27 Sep 1997) |
| amphoteric reaction | A double reaction possessed by certain fluids which have a combination of acid and alkaline properties. (05 Mar 2000) |
| anamnestic reaction | Augmented production of an antibody due to previous response of the subject to stimulus by the same antigen. (05 Mar 2000) |
| anaphylactic reaction | <immunology> A serious, often life-threatening allergic reaction that is characterised by low blood pressure, shock (poor tissue perfusion) and difficulty breathing. (27 Sep 1997) |
| anaplerotic reaction | <biochemistry> An enzyme-catalysed chemical reaction that recharges the supply of intermediate molecules in various metabolic reactions such asthe citric acid cycle. (09 Oct 1997) |
| antigen-antibody reaction | The phenomenon, occurring in vitro or in vivo, of antibody combining with antigen of the type that stimulated the formation of the antibody, thereby resulting in agglutination, precipitation, complement fixation, greater susceptibility to ingestion and destruction by phagocytes, or neutralization of exotoxin. See: skin test. (05 Mar 2000) |
| anxiety reaction | A sudden bout of anxiety that is often accompanied by the features of hyperventilation (tingling around mouth and in fingertips, rapid breathing, faintness or fainting). (27 Sep 1997) |
| Arias-Stella reaction | Focal, unusual, decidual changes in endometrial epithelium, consisting of intraluminal budding, and nuclear enlargement and hyperchromatism with cytoplasmic swelling and vacuolation; may be associated with ectopic or uterine pregnancy. Synonym: Arias-Stella effect, Arias-Stella reaction. (05 Mar 2000) |
| arousal reaction | Change in pattern of the brain waves when the subject is suddenly awakened and becomes alert. (05 Mar 2000) |
| Arthus reaction | <dermatology, immunology> A localised inflammation due to injection of antigen into an animal that has a high level of circulating antibody against that antigen. A haemorrhagic reaction with oedema occurs due to the destruction of small blood vessels by thrombi. It may occur, as in Farmer's Lung, as a reaction to natural exposure to antigen. (18 Nov 1997) |
| arthus-type reaction's | Reaction's in man and other species that result from the same basic immunologic (allergic) mechanism which evokes, in the rabbit, the typical Arthus phenomenon. See: immune complex disease. (05 Mar 2000) |
| Ascoli reaction | A method for confirming the diagnosis of anthrax by means of a precipitin reaction which indicates the presence of heat-stable Bacillus anthracis antigen in the extracted tissue. (05 Mar 2000) |
| associative reaction | A secondary or side reaction. (05 Mar 2000) |