| ARI | acute respiratory illness; airway reactivity index; anxiety reaction, intense |
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| ARM | adrenergic receptor material; aerosol rebreathing method; ambulatory renal monitor; anorectal manome... |
| ARMS | adverse reaction monitoring system; amplification refractory mutation system |
| ASR | aldosterone secretion rate; antistreptolysin reaction |
| ASSR | adult situation stress reaction |
| reaction centre | <plant biology> The site in the chloroplast that receives the energy trapped by chlorophyll and accessory pigments and initiates the electron transfer process. A photosynthetic complex containing chlorophyll (or bacteriochlorophyll) and other components, within which occurs the initial electron transfer reactions of photophosphorylation. (09 Oct 1997) |
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| reaction formation | In psychoanalysis, a postulated defense mechanism in which attitudes and behaviours that are adopted are the opposites of that which the individual would ordinarily be expected to express and actually feel at an unconscious level. (05 Mar 2000) |
| reaction intermediate | <biochemistry> Any biomolecule which iscreated and destroyed during the course of of a particular reaction pathway. (09 Oct 1997) |
| reaction of degeneration | The electrical reaction in a degenerated nerve and the muscles supplied by it; characterised by absence of response to both galvanic and faradic stimulus in the nerve and to faradic stimulus in the muscles; the muscles may still respond to galvanic stimulation, but the cathodal closing contraction is greater than the anodal closing contraction, the reverse of normal. (05 Mar 2000) |
| reaction of identity | See: gel diffusion precipitin tests in two dimensions. (05 Mar 2000) |
| reaction of nonidentity | See: gel diffusion precipitin tests in two dimensions. (05 Mar 2000) |
| reaction of partial identity | See: gel diffusion precipitin tests in two dimensions. (05 Mar 2000) |
| 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) |
| 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) |