reaction

1. The response of a muscle or other living tissue or organism to a stimulus. 2. The color change effected in litmus and certain other organic pigments by contact with substances such as acids or alkalies; also the property that such substances possess of producing this change. 3. In chemistry, the intermolecular action of two or more substances upon each other, whereby these substances are caused to disappear, new ones being formed in their place (chemical r.). 4. In immunology, in vivo or in vitro action of an antibody on a specific antigen, with or without the involvement of a complement or other components of the immunologic system. [L. re-, again, backward, + actio, action]

- accelerated r. a response occurring in a shorter time than expected; the cutaneous manifestations occurring during the period between the second and tenth day following smallpox vaccination; because it is intermediate between a primary r. and an immediate r., it is regarded as evidence of some degree of resistance. SYN: vaccinoid r..

- acid r. 1. any test by which an acid r. is recognized, such as the change of blue litmus paper to red; 2. an excess of hydrogen ions over hydroxide ions in aqueous solution indicated by a pH value less than 7 (at 22°C). Cf.:dissociation constant of water.

- acute phase r. refers to the changes in synthesis of certain proteins within the serum during an inflammatory response; this response provides rapid protection for the host against microorganisms via nonspecific defense mechanisms. SYN: acute phase response.

- acute situational r. SYN: stress r..

- acute stress r. SYN: anxiety r..

- adverse r. any undesirable or unwanted consequence of a preventive, diagnostic, or therapeutic procedure or regimen.

- alarm r. the various phenomena, e.g., stimulated endocrine activity, which the body exhibits as an adaptive response to injury or stress; first phase of the general adaptation syndrome.

- aldehyde r. the r. of the indole derivatives with aromatic aldehydes; e.g., tryptophan and p-dimethylaminobenzaldehyde in H₂SO₄ give a red-violet color useful in assaying proteins for tryptophan content. SYN: Ehrlich r..

- alkaline r. 1. any test by which an alkaline r. is recognized, such as the change of red litmus paper to blue; 2. an excess of hydroxide ions over hydrogen ions in aqueous solution as indicated by a pH value >7 (at 22°C). Cf.:dissociation constant of water. SYN: basic r..

- allergic r. a local or general r. of an organism following contact with a specific allergen to which it has been previously exposed and sensitized; immunologic interaction of endogenous or exogenous antigen with antibody or sensitized lymphocytes gives rise to inflammation or tissue damage. Allergic reactions are classified into four major types: type I, anaphylactic and IgE dependent; type II, cytotoxic; type III, immune-complex mediated; type IV, cell mediated (delayed). SYN: hypersensitivity r..

- amphoteric r. a double r. possessed by certain fluids that have a combination of acid and alkaline properties.

- anamnestic r. augmented production of an antibody due to previous exposure of the subject to the same antigen.

- anaphylactic r. (an′a-fi-lak′tik) SYN: anaphylaxis.

- anaplerotic r. anaplerotic.

- antigen-antibody r. (AAR) the reversible phenomenon, occurring in vitro or in vivo, of an antibody combining with an 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 ALSO: skin test.

- anxiety r. a psychologic r. or experience involving the apprehension of danger accompanied by a feeling of dread and such physical symptoms as an increase in the rate of breathing, sweating, and tachycardia, in the absence of a clearly identifiable fear stimulus; when chronic, it is called generalized anxiety disorder. SEE ALSO: panic attack. SYN: acute stress r..

- Arias-Stella r. SYN: Arias-Stella phenomenon.

- arousal r. change in pattern of the brain waves when the subject is suddenly awakened and becomes alert.

- Arthus r. 1. SYN: Arthus phenomenon. 2. Arthus-type r.; r. in humans and other species that results from the same basic immunologic (allergic) mechanism that evokes, in the rabbit, the typical Arthus phenomenon. SEE ALSO: immune complex disease.

- Ascoli r. a method for confirming the diagnosis of anthrax by means of a precipitin r., which indicates the presence of heat-stable Bacillus anthracis antigen in the extracted tissue.

- associative r. a secondary or side r..

- basic r. SYN: alkaline r..

- Bence Jones r. the classic means of identifying Bence Jones protein, which precipitates when urine (from patients with this type of proteinuria) is gradually warmed to 45–70°C and redissolves as the urine is heated to near boiling; as the specimen cools, the Bence Jones protein precipitates in the indicated range of temperature and redissolves as the temperature of the specimen becomes less than 30–35°C.

- Berthelot r. the r. of ammonia with phenol-hypochlorite to give indophenol; the principle is used to analyze ammonia concentration in body fluids.

- bi bi r. a r. catalyzed by a single enzyme in which two substrates and two products are involved; the ping-pong mechanism may be involved in such a r.. Cf.:mechanism.

- Bittorf r. in cases of renal colic, pain radiating to the kidney upon squeezing the testicle or pressing the ovary.

- biuret r. the formation of biuret that gives a violet color as a result of the r. of a polypeptide of more than three aminoacyl residues with CuSO₄ in strongly alkaline solution; dipeptides and amino acid s (except histidine, serine, and threonine) do not so react; used for the detection and quantification of polypeptides, or proteins, in biologic fluids.

- Bloch r. SYN: dopa r..

- Bordet and Gengou r. See complement fixation.

- Brunn r. the increased absorption of water through the skin of the frog when the animal is injected with pituitrin and immersed in water; one of the physiologic reactions used to study and classify posterior pituitary polypeptides and their analogues.

- Burchard-Liebermann r. a blue-green color produced by acetic anhydride with cholesterol (and other sterols) dissolved in chloroform, when a few drops of concentrated sulfuric acid are added. See Liebermann-Burchard test.

- Cannizzaro r. formation of an acid and an alcohol by the simultaneous oxidation of one aldehyde molecule and reduction of another; a dismutation : 2RCHO → RCOOH + RCH₂OH; when the aldehydes are not identical, this is referred to as a crossed Cannizzaro r..

- capsular precipitation r. SYN: quellung r. (2).

- Carr-Price r. the r. of antimony trichloride with vitamin A to yield a brilliant blue color; this r. forms the basis of several quantitative techniques for the determination of vitamin A.

- catalatic r. decomposition of H₂O₂ to O₂ and H₂O, as in the action of catalase; analogous to peroxidase r..

- catastrophic r. the disorganized behavior that is the response to a severe shock or threatening situation with which the person cannot cope.

- cell-mediated r. immunologic r. of the delayed type, involving chiefly T lymphocytes, important in host defense against infection, in autoimmune diseases, and in transplant rejection. SEE ALSO: skin test.

- chain r. a self-perpetuating r. in which a product of one step in the r. itself serves to bring about the next step in the r.. Cf.:autocatalysis.

- Chantemesse r. a conjunctival r., especially as applied to typhoid.

- cholera-red r. 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 color from rose-pink to claret.

- chromaffin r. production of a yellow-brown to brown coloration 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 tumors which produce catecholamines.

- circular r. in sensorimotor theory, the tendency of an organism to repeat novel experiences.

- cocarde r., cockade r. Römer test.

- colloidal gold r. a test (now obsolete) based on precipitation of cerebrospinal fluid protein when mixed with colloidal gold. Abnormalities in this r. were observed in patients with syphilis, multiple sclerosis, poliomyelitis, and encephalitis.

- complement-fixation r. complement fixation.

- consensual r. contraction of the pupil of the fellow eye in consensus with the pupil of the illuminated eye. SYN: consensual light reflex, indirect pupillary r..

- constitutional r. a generalized r. in contrast to a focal or local r.; in allergy the immediate or delayed response, following the introduction of an allergen, occurring at sites remote from that of injection.

- conversion r. SYN: conversion hysteria.

- cross-r. a specific r. between an antiserum and an antigen complex other than the antigen complex that evoked the various specific antibodies of the antiserum. It is due to at least one antigenic determinant that is included among the determinants of the other complex.

- cutaneous graft versus host r. an acute erythematous maculopapular r. with bulla formation in the most severe cases; chronic changes may resemble lichen planus or scleroderma.

- cytotoxic r. an immunologic (allergic) r. in which noncytotropic IgG or IgM antibody combines with specific antigen on cell surfaces; the resulting complex initiates the activation of complement which causes cell lysis or other damage, or which, in the absence of complement, may lead to phagocytosis or enhance T lymphocyte involvement leading to cellular cytotoxicity.

- Dale r. Schultz-Dale r..

- dark r. in photosynthesis, the fixation of CO₂ into carbohydrate, which is independent in place and time of the absorption of light.

- decidual r. the cellular and vascular changes occurring in the endometrium at the time of implantation.

- delayed r. a local or generalized response that begins 24–48 hours after exposure to an antigen involving T cells. See cell-mediated r.. SYN: contact hypersensitivity (2), delayed hypersensitivity (2), late r., tuberculin-type hypersensitivity.

- depot r. reddening of the skin at the point where the needle entered, in the subcutaneous tuberculin test.

- depressive r. SYN: depression (4).

- dermotuberculin r. SYN: Pirquet test.

- diazo r. the r. of diazotized sulfanilic acid with bilirubin to form azobilirubin, which forms the basis of quantitating the amount of bilirubin in biologic fluids. See van den Bergh test. SYN: Ehrlich diazo r..

- digitonin r. the r. of naturally occurring steroids with 3β-hydroxyl groups with digitonin, a steroid glycoside, resulting in the formation of an insoluble precipitate; useful in determining the presence of cholesterol and ergosterol.

- Dische r. the assay of DNA by means of the blue color formed with diphenylamine in acid (Dische reagent).

- dissociative r. r. characterized by such dissociative behavior as amnesia, fugues, sleepwalking, and dream states.

- dopa r. a dark staining observed in fresh tissue sections to which a solution of dopa has been applied, presumably due to the presence of dopa oxidase in the protoplasm of certain cells. SYN: Bloch r..

- dystonic r. a state of abnormal tension or muscle tone, similar to dystonia, produced as a side effect of certain antipsychotic medication; a severe form, in which the eyes appear to roll up into the head, is called oculogyric crisis.

- early r. SYN: immediate r..

- echo r. SYN: echolalia.

- Ehrlich r. SYN: aldehyde r..

- Ehrlich benzaldehyde r. a test for urobilinogen in the urine, by dissolving 2 g of dimethyl-p-aminobenzaldehyde in 100 mL of 5% hydrochloric acid and adding this reagent to urine; a red color in the cold indicates the presence of an excessive amount of urobilinogen.

- Ehrlich diazo r. SYN: diazo r..

- eosinopenic r. reduction in the numbers of circulating eosinophils by ACTH or by adrenal corticoids.

- error-prone polymerase chain r. use of PCR under conditions in which misincorporation of bases is favored, e.g., where random mutants are sought for a portion of amplified DNA.

- eye-closure pupil r. a constriction of both pupils when an effort is made to close eyelids forcibly held apart; a variant of the pupil response to near vision. SYN: Galassi pupillary phenomenon, Gifford reflex, lid-closure r., orbicularis phenomenon, orbicularis pupillary reflex, Piltz sign, Westphal pupillary reflex, Westphal-Piltz phenomenon.

- false-negative r. an erroneous or mistakenly negative response.

- false-positive r. an erroneous or mistakenly positive response.

- Fenton r. 1. the use of H₂O₂ and ferrous salts (Fenton reagent) to oxidize α-hydroxy acids to α-keto acids or to convert 1,2-glycols to α-hydroxy aldehydes; 2. the formation of OH , OH⁻, and Fe³⁺ from the nonenzymatic r. of Fe²⁺ with H₂O₂; a r. of importance in the oxidative stress in blood cells and various tissues.

- Fernandez r. a delayed hypersensitivity lepromin r., similar to a tuberculin r., at the site of intradermal injection of Dharmendra antigen in a lepromin test.

- ferric chloride r. of epinephrine an intense emerald green color in a neutral or slightly acid solution of epinephrine when ferric chloride is added to it; a r. typical of catechols.

- Feulgen r. Feulgen stain.

- fight or flight r. the theory advanced by Walter Cannon, that in the autonomic nervous system and the effectors connected with it, the organism in situations of danger requiring either fight or flight is provided with a check-and-drive mechanism that puts it in readiness to meet emergencies with undivided energy output. Also known as the emergency theory.

- first-order r. a r. the rate of which is proportional to the concentration of the single substance undergoing change; radioactive decay is a first-order process, defined by the equation dN/dt = kN, where N is the number of atoms subject to decay (r.), t is time, and k is the first-order decay (r.) constant, i.e., the fraction of all atoms decaying per unit of time. SEE ALSO: decay constant, order.

- fixation r. complement fixation.

- flocculation r. a form of precipitin r. in which precipitation occurs over a narrow range of antigen-antibody ratio, owing chiefly to peculiarities of the antibody (precipitin).

- focal r. a r. that occurs at the point of entrance of an infecting organism or of an injection, as in the Arthus phenomenon. SYN: local r..

- Folin r. the r. of amino acid s in alkaline solution with 1,2-naphthoquinone-4-sulfonate (Folin reagent) to yield a red color; useful for quantitative assay. SYN: Folin reagent.

- Forssman r. SYN: Forssman antigen-antibody r..

- Forssman antigen-antibody r. the combination of Forssman antibody with heterogenetic antigen of the Forssman type, as in the agglutination of sheep erythrocytes (which contain Forssman antigen) by serum from a person with infectious mononucleosis that contains Forssman antibody. SYN: Forssman r..

- fragment r. a r. used to assay the activity of peptidyl transferase.

- Frei-Hoffmann r. SYN: Frei test.

- fright r. after section and degeneration of the facial nerve of an animal, the denervated facial muscles contract if the animal is frightened or becomes angry; caused by the release of acetylcholine into the circulation.

- fuchsinophil r. the property possessed by certain elements, when stained with acid fuchsin, of retaining the stain when treated with picric acid alcohol.

- furfurol r. production of a red color on addition of furfurol to a solution of aniline.

- galvanic skin r. SYN: galvanic skin response.

- gel diffusion reactions SYN: gel diffusion precipitin tests, under test.

- Gell and Coombs reactions allergic r..

- gemistocytic r. a r. to injury resulting in the proliferation of reactive, protoplastic, or gemistocytic astrocytes.

- general adaptation r. general adaptation syndrome.

- Gerhardt r. SYN: Gerhardt test for acetoacetic acid.

- graft versus host r. (GVHR) clinical and histologic changes of graft versus host disease occurring in a specific organ.

- group r. a r. 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.

- Gruber r. SYN: Widal r..

- Gruber-Widal r. SYN: Widal r..

- Günning r. the formation of iodoform from acetone by iodine and ammonia in alcohol.

- Haber-Weiss r. the r. of superoxide (O₂ ⁻) with hydrogen peroxide to produce molecular oxygen (O₂), hydroxide radical (OH), and OH⁻; often, iron-catalyzed; a source of oxidative stress in blood cells and various tissues.

- harlequin r. sudden blanching of the lower half of the body of an infant lying on its side, leaving the remaining half of the body the normal color.

- heel-tap r. heel tap.

- hemoclastic r. hemolysis as observed in the laking of the blood.

- Henle r. dark brown staining of the medullary cells of the adrenal bodies when treated with the salts of chromium, the cortical cells remaining unstained.

- Herxheimer r. an inflammatory r. in syphilitic tissues (skin, mucous membrane, nervous system, or viscera) induced in certain cases by specific treatment with Salvarsan, mercury, or antibiotics; believed to be due to a rapid release of treponemal antigen with an associated allergic r. in the patient. SYN: Jarisch-Herxheimer r..

- Hill r. that portion of the photosynthesis r. that involves the photolysis of water and the liberation of oxygen and does not include carbon dioxide fixation. It involves the addition of oxidants (quinones or ferricyanide) to chloroplasts; upon illumination, O₂ is evolved and the added oxidant is reduced.

- homograft r. rejection of an allogenic graft by the host.

- hunting r. an unusual r. of digital blood vessel s exposed to cold; vasoconstriction is alternated with vasodilation in irregular repeated sequences, in an apparent hunting of equilibrium of skin temperature.

- hypersensitivity r. SYN: allergic r..

- id r. an allergic manifestation of candidiasis, the dermatophytoses, and other mycoses characterized by itching, vesicular lesions that appear in response to superficial infections that are distant from the id r. itself. SEE ALSO: dermatophytid, -id (1).

- r. of identity gel diffusion precipitin tests in two dimensions, under test.

- immediate r. local or generalized response that begins within a few minutes to about an hour after exposure to an antigen to which the individual has been sensitized. SEE ALSO: skin test, wheal-and-erythema r.. SYN: early r..

- immediate hypersensitivity r. an immune response mediated by antibody, usually IgE, which occurs within minutes after a second encounter with an antigen, resulting in the release of histamine and subsequent swelling and vasodilation.

- immune r. antigen-antibody r. indicating a certain degree of resistance, usually in reference to the 36- to 48-hour r. in vaccination against smallpox; because the degree of resistance indicated by the r. is not true immunity and may disappear relatively rapidly there is a tendency to refer to the immune r. as an allergic r..

- incompatible blood transfusion r. a syndrome due to intravascular hemolysis of transfused blood by serum antibodies of the recipient, which react with an antigen of the donor red cells; characterized by chills, fever, backache or muscle cramps, hemoglobinemia, hemoglobinuria, and oliguria, which may result in acute renal failure, DIC, and death.

- indirect pupillary r. SYN: consensual r..

- intracutaneous r., intradermal r. a r. following the injection of antigen into the skin of a sensitive subject, such as in the case of the tuberculin test.

- iodate r. of epinephrine a r. dependent upon the oxidation of epinephrine by iodine liberated from iodate, which is decomposed by the hormone; a faint pink color results.

- iodine r. of epinephrine a r. resulting from the oxidation of the hormone, a faint pink color appearing upon the addition of iodine.

- irreversible r. a r. or response by the tissues to a pathogenic agent characterized by a permanent pathologic change.

- Jaffe r. a bright orange-red complex resulting from the treatment of creatinine with alkaline picrate solution; the basis of most routine creatinine tests.

- Jarisch-Herxheimer r. SYN: Herxheimer r..

- Jolly r. rapid loss of response to faradic stimulation of a muscle with the galvanic response and the power of voluntary contraction retained; an obsolete method for detecting myasthenia gravis. SYN: myasthenic r..

- Kiliani-Fischer r. Kiliani-Fischer synthesis.

- late r. SYN: delayed r..

- lengthening r. in the decerebrate animal, the rather sudden relaxation with lengthening of the extensor muscles when a limb is passively flexed; associated with clasp-knife spasticity.

- lepromin r. a delayed hypersensitivity r. at the site of an intradermal injection of a lepromin, such as the Dharmendra antigen or Mitsuda antigen, in a lepromin test; the reactions, such as the Fernandez or Mitsuda r., are variable, occurring in 48 hours or 3–5 weeks, but are uniformly negative in lepromatous leprosy, borderline leprosy, and mid-borderline leprosy.

- leukemoid r. leukemoid r..

- lid-closure r. SYN: eye-closure pupil r..

- Liebermann-Burchard r. Burchard-Liebermann r..

- ligase chain r. a technique for target amplification of DNA in which DNA ligase is used to join two complementary oligonucleotide probes that have bound to a target sequence in vitro. The ligation product is used as a template for ligation of complementary oligonucleotides that, through repeated enzymatic processing, allow for logarithmic accumulation of products that can be used to determine the presence of the target of interest.

- local r. SYN: focal r..

- local anesthetic r. a toxic r. due to absorption of local anesthetic drug during regional anesthesia, ranging from drowsiness to convulsions and cardiovascular collapse.

- Loewenthal r. the agglutinative r. in relapsing fever.

- Lohmann r. the r. catalyzed by creatine kinase.

- magnet r. a r. seen in an animal deprived of its cerebellum; when the animal is placed upon its back and the head strongly flexed, the four limbs become flexed in all their joints. Because of stimulation of receptors in the deep layers of the skin, light pressure made upon a toe-pad with the finger causes reflex contraction of the limb extensors; the limb is thus pressed gently against the finger, and when the finger is withdrawn slightly, the experimenter has the sensation that the finger is raising the limb or drawing it out as by a magnet.

- Marchi r. failure of the myelin sheath of a nerve to blacken when submitted to the action of osmic acid.

- Mazzotti r. SYN: Mazzotti test.

- Millon r. the r. of phenolic compounds ( e.g., tyrosine in protein) with Hg(NO₃)₂ in HNO₃ (and a trace of HNO₂) to give a red color.

- miostagmin r. a physiochemical immunity test, designed by Ascoli, consisting in determination of the surface tension of an immune serum to which its specific antigen has been added, before and after incubation at 37°C for 2 hours; in a positive r. the surface tension, as measured by the stalagmometer, is lowered.

- Mitsuda r. a delayed hypersensitivity lepromin r., in the form of erythematous papular nodules, at the site of intradermal injection of Mitsuda antigen in a lepromin test.

- mixed agglutination r. immune agglutination in which the aggregates contain cells of two different kinds but with common antigenic determinants; when used to identify isoantigens, the test cells are exposed to appropriate isoantibody, washed, and then mixed with indicator erythrocytes that combine with free sites on the test cell-attached isoantibody.

- mixed lymphocyte culture r. mixed lymphocyte culture test.

- monomolecular r. a r. involving a single molecule ( e.g., decomposition, intramolecular rearrangement, intramolecular oxidation or reduction), even if a catalytic agent, such as acid or alkali, is present in large excess, on a molecular basis, or is not rate-determining; such reactions are usually first-order reactions. Cf.:molecularity. SYN: unimolecular r..

- myasthenic r. SYN: Jolly r..

- Nadi r. SYN: peroxidase r..

- near r. the pupillary constriction associated with a near vision effort, i.e., with accommodation and convergence.

- nested polymerase chain r. use of the PCR in series such that a specified piece of DNA is amplified, then a portion contained within the first piece is amplified further; used where extremely low amounts of DNA are present, or where there are problems with background or contaminating DNA.

- Neufeld r. SYN: Neufeld capsular swelling.

- neurotonic r. muscular contraction continuing well after cessation of stimulation.

- neutral r. pH of 7.00; H⁺ and OH⁻ ion concentrations equal at 10⁻⁷ mol/L at 22°C. Cf.:dissociation constant of water.

- ninhydrin r. a test for proteins, peptones, peptides, and amino acid s possessing free carboxyl and α-amino groups that is based upon the r. with triketohydrinene hydrate; a blue color r. is used to quantitate free amino acid s ( e.g., after hydrolysis and separation of the amino acid s of a protein). SYN: triketohydrindene r..

- nitritoid r. a severe r. resembling that following the administration of nitrites, sometimes following intravenous administration of arsphenamine or other drugs; consists of flushing of the face, edema of the tongue and lips, vomiting, profuse sweating, a fall in blood pressure, and sometimes death.

- r. of nonidentity gel diffusion precipitin tests in two dimensions, under test.

- nuclear r. the interaction of two atomic nuclei or of one such with a subatomic particle, or of the subatomic particles within an atomic nucleus, resulting in a change in the nature of the nuclei concerned or in the energy content of the nuclei or both, usually manifested by transmutation (accompanied by emission of alpha-, beta-, and/or gamma-rays) or by fission or fusion of the nuclei.

- oxidase r. 1. the formation of indol blue when a blood smear containing myeloid leukocytes is treated with a mixture of α-naphthol and p-dimethylaniline sulfate; the myeloid leukocytes contain an oxidase that catalyzes this r., and the lymphoid leukocytes do not; 2. in bacteriology, a r. that depends on the presence of certain oxidases in some bacteria that catalyze the transport of electrons between electron donors in the bacteria and an oxidation reduction dye, such as tetramethyl-p-phenylenediamine; the dye is reduced to a blue or black color.

- oxidation-reduction r. oxidation-reduction.

- pain r. dilation of the pupil or any other involuntary act occurring in response to a stimulus causing sharp pain anywhere.

- Pandy r. a test to determine the presence of proteins (chiefly globulins) in the spinal fluid, by adding one drop of spinal fluid to 1 mL of solution ( e.g., carbolic acid crystals in distilled water, cresol, or pyrogallic acid); the r. varies from a faint turbidity to a dense “milky” precipitate according to the degree of protein content. SYN: Pandy test.

- r. of partial identity gel diffusion precipitin tests in two dimensions, under test.

- passive cutaneous anaphylactic r. passive cutaneous anaphylaxis.

- Paul r. 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 36–48 hours; the sputum of a smallpox patient is said to cause the same r.. SYN: Paul test.

- performic acid r. 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.

- periosteal r. radiographically detectable new subperiosteal bone formed as a r. to soft tissue or osseous disease.

- peroxidase r. 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 α-naphthol and dimethylparaphenylenediamine; by this method, cells of the myelocyte series, which give a positive r., may be distinguished from those of the lymphocyte series, which give a negative r.. SYN: Nadi r..

- phosphoroclastic r. 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 orthophosphate is added to ADP to form ATP.

- Pirquet r. SYN: Pirquet test.

- plasmal r. a histochemical technique that uses mercuric chloride to unmask the aldehyde group of acetalphosphatides and permit Schiff staining.

- pleural r. thickening of the pleural stripe on chest radiographs, representing pleuritis, pleural effusion, or pleural fibrosis.

- polymerase chain r. (PCR) (po-lim′er-as) an enzymatic method for the repeated copying of the two strands of DNA of a particular gene sequence. It is widely used to amplify minute quantities of biological material so as to provide adequate specimens for laboratory study.The replication of DNA in the living cell is facilitated by polymerases. The two DNA chains of the double helix first unzip from one another, and DNA polymerase then generates a copy of each strand by adding free nucleotides to form a sequence of base pairs complementary with the sequence in the strand. The laboratory technique known as polymerase chain r., for which the American biochemist Kary Mullis won a Nobel Prize in Chemistry in 1993, exploits the capacity of DNA polymerase to assemble new DNA. Taq polymerase, named for its source, Thermus aquaticus, a thermophilic bacterium, is added to a mixture of free nucleotides and primers. (Primers are specially prepared units containing both RNA and DNA with a free terminus where the polymerase will react.) The short sequence of DNA to be amplified is flanked by two primers. Once the r. begins, the polymerase generates numerous copies of the target sequence. The sequential phases of the r. are initiated simply by making a series of strategic changes in the temperature of the system. Millions of copies of the target sequence can be generated by cyclically repeating these temperature changes as many as 30 times, each DNA strand produced by one cycle giving rise to many more in the next. The technique is used to amplify specimens for diagnosis of both infectious and genetic diseases, to carry out DNA fingerprinting, and in genomic research.

- Porter-Silber r. the basis of the 17-hydroxycorticosteroid test; C-21 adrenocorticosteroids, which contain a dihydroxyacetone group at carbons 19, 20, and 21, react with phenylhydrazine.

- Prausnitz-Küstner r. a test for the presence of immediate hypersensitivity in humans; test serum from an atopic individual is injected intradermally into a normal subject; the normal subject is challenged 24–48 hours later with the antigen suspected of causing the immediate hypersensitivity r. in the atopic individual, usually in the form of a wheal flare. SYN: P-K test.

- precipitin r. See precipitin, precipitin test.

- primary r. SYN: vaccinia.

- prozone r. prozone.

- psychogalvanic r., psychogalvanic skin r. SYN: galvanic skin response.

- quellung r. 1. SYN: Neufeld capsular swelling. 2. if pneumococcal organisms, India ink, and specific antisera are mixed, the antibodies present in the sera will bind to the polysaccharide antigens of the pneumococcal capsule and the capsule will appear more opaque and swollen. This test will identify the organism as being pneumococci as well as the specific capsular types. SYN: capsular precipitation r.. [Ger. Quellung, swelling]

- reversed Prausnitz-Küstner r. the appearance of an urticarial r. 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.

- reverse transcriptase polymerase chain r. (RT-PCR) a process for specific mRNA amplification wherein reverse transcriptase added to the in vitro r. uses mRNA as a template to produce one cDNA, which is then amplified by the usual PCR.

- reversible r. a chemical r. that takes place in either direction, i.e., from the forward or reverse direction; ionization is such a r., as are reactions involving racemases, isomerases, mutases, transferases, etc.

- Sakaguchi r. guanidines in alkaline solution develop an intense red color when treated with α-naphthol and sodium hypochlorite; a qualitative test for arginine, free or in a protein.

- Schardinger r. the reduction of methylene blue to methylene white by formaldehyde is rapidly catalyzed by fresh milk but not by boiled milk, the catalyzing agent being xanthine oxidase (Schardinger enzyme); an example of oxidation in the absence of O₂ with an organic hydrogen acceptor (the dye).

- Schultz r. Schultz stain.

- Schultz-Charlton r. the specific blanching of a scarlatinal rash at the site of intracutaneous injection of scarlatina antiserum. SYN: Schultz-Charlton phenomenon.

- Schultz-Dale r. the contraction of an excised intestinal loop (Schultz) or of an excised strip of virginal uterus (Dale) from a sensitized animal (guinea pig) that occurs when the tissue is exposed to the specific antigen.

- serum r. SYN: serum sickness.

- shortening r. the adaptive shortening of the extensor muscles of the limb of a decerebrate animal when the limb is extended after it has been flexed. Cf.:lengthening r..

- Shwartzman r. SYN: Shwartzman phenomenon.

- skin r. SYN: skin test.

- specific r. the phenomena produced by an agent that is identical with or immunologically related to the one that has already caused an alteration in capacity of the tissue to react.

- startle r. SYN: startle reflex.

- Straus r. a diagnostic test for glanders. Male guinea pig s are inoculated intraperitoneally with suspected material; if the glanders organism is present, it will usually set up a necrotizing inflammation in the scrotal sac within a few days and the specific organism can be confirmed bacteriologically.

- stress r. an acute emotional r. related to extreme environmental threat or challenge. SYN: acute situational r..

- supporting reactions described by Magnus, who distinguished two types: positive supporting reactions, consisting of those reflex muscular contractions whereby the body is supported against gravity; seen in an exaggerated form in the decerebrate animal; negative supporting reactions, consisting of inhibition of the extensor muscles and unfixing of the joints that thus enable the limb to be flexed and moved into a new position. SYN: supporting reflexes.

- symptomatic r. an allergic response similar to the original one, but occurring after the use of a test or therapeutic dose of an allergen or atopen.

- thermoprecipitin r. the throwing down of a precipitate on the application of heat, as in the case of proteinaceous urine.

- transcription-based chain r. a technique for target amplification of DNA or RNA in which reverse transcriptase is used to produce a single-stranded DNA molecule for each DNA or RNA target; this molecule is used as a template for further amplification.

- Treponema pallidum immobilization r. SYN: Treponema pallidum immobilization test.

- triketohydrindene r. SYN: ninhydrin r..

- type III hypersensitivity r. SYN: immune complex disease.

- unimolecular r. SYN: monomolecular r..

- vaccinoid r. SYN: accelerated r..

- Voges-Proskauer r. a chemical r. 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 r. consists of the development of an eosin-like pink color, due to the production of acetylmethylcarbinol, which in the presence of alkali and oxygen is oxidized to diacetyl.

- Wassermann r. (W.r.) SYN: Wassermann test.

- Weidel r. a r. showing the presence of xanthine; a solution of the suspected substance in chlorine water with a little nitric acid is evaporated in a water bath, and then exposed to the vapor of ammonia; the presence of xanthine is indicated when a red or purple color develops.

- Weil-Felix r. SYN: Weil-Felix test.

- Weinberg r. a complement fixation test of the presence of hydatid disease.

- Wernicke r. in hemianopia, a r. due to damage of the optic tract, consisting in loss of pupillary constriction when the light is directed to the blind side of the retina; pupillary constriction is maintained when light stimulates the normal side. This sign cannot be seen with a bright light because of intraocular scatter onto the seeing half of the retina. SYN: Wernicke sign.

- wheal-and-erythema r. the characteristic immediate r. observed in the skin test; within 10–15 minutes after injection of antigen (allergen), an irregular, blanched, elevated wheal appears, surrounded by an area of erythema (flare). SYN: wheal-and-flare r..

- wheal-and-flare r. SYN: wheal-and-erythema r..

- white r. the response seen in many individuals after the skin is lightly stroked with a blunt instrument; it is attributed to capillary action.

- whitegraft r. an immune r. to a incompatible tissue graft that results in failure of graft vascularization and ensuing rejection.

- Widal r. agglutination r. as applied to the diagnosis of typhoid. SYN: Gruber r., Gruber-Widal r..

- xanthoprotein r. a qualitative test for proteins; a yellow product is formed by reacting proteins with hot, concentrated nitric acid.

- Yorke autolytic r. a test for paroxysmal hemoglobinuria; serum is placed in an ice chest and kept at 0°C for 5–7 minutes, then in an incubator at 37°C with erythrocytes for 1 hour, at which time, if the r. is positive, hemolysis occurs; if the serum is kept at 1°C for an hour and then placed in the incubator with erythrocytes there is little hemolysis.

- zero-order r. a r. that proceeds at a particular rate independently of the concentration of the reactant or reactants.

- Zimmermann r. a chemical r. between an alkaline solution of meta-dinitrobenzene and an active methylene group (carbon-16) of 17-ketosteroids; it is the basis of the 17-ketogenic steroid assay test; more generally, a r. between methylene ketones and aromatic polynitro compounds in alkaline solutions. SYN: Zimmermann test.

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re·ac·tion rē-'ak-shən n

1) the act or process or an instance of reacting

2) bodily response to or activity aroused by a stimulus:

a) an action induced by vital resistance to another action esp the response of tissues to a foreign substance (as an antigen or infective agent)

b) depression or exhaustion due to excessive exertion or stimulation

c) abnormally heightened activity succeeding depression or shock

d) a mental or emotional disorder forming an individual's response to his or her life situation

3) the force that a body subjected to the action of a force from another body exerts in the opposite direction

4 a ) (1) chemical transformation or change: the interaction of chemical entities (2) the state resulting from such a reaction

b) a process involving change in atomic nuclei

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re·ac·tion (re-akґshən) [re- + L. agere to act] 1. opposite action, or counteraction. 2. response. 3. the phenomena caused by the action of chemical agents; a chemical process in which one substance is transformed into another substance or substances. For named reactions not defined here, see under test. 4. in psychology, the mental and/or emotional state elicited in response to any particular situation.