natural purification (자정 작용
| natural language processing | Computer processing of a language with rules that reflect and describe current usage rather than prescribed usage. (12 Dec 1998) |
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| natural mutation | A mutation which occurs by itself without first being affected by a mutagen, for example during the process of DNA replication. Spontaneous mutations arise at a remarkably constant rate. The rate that spontaneous mutations arise has been used as an evolutionary clock to estimate how closely related two (or more) separate species are to each other. (09 Oct 1997) |
| natural passive immunity | Immunity conferred by the mother on the foetus or newborn. (14 Nov 1997) |
| natural pigment | A naturally occurring coloured compound; absorbs light in the visible range of the electromagnetic spectrum. Compare: structural colour. Synonym: biochrome. (05 Mar 2000) |
| natural products | Naturally occurring compounds that are end products of secondary metabolism; often, they are unique compounds for particular organisms or classes of organisms. (05 Mar 2000) |
| natural selection | The hypothesis that genotype environment interactions occurring at the phenotypic level lead to differential reproductive success of individuals and hence to modification of the gene pool of a population. (18 Nov 1997) |
| immunity, natural | The capacity of a normal organism to remain unaffected by microorganisms and their toxins. It results from non-specific mechanisms such as genetic endowment, naturally occurring antiviral and bactericidal substances, phagocytosis, and constitutional factors such as body temperature, oxygen tension, and age. (12 Dec 1998) |
| killer cells, natural | Cells responsible for spontaneous cytotoxicity of a variety of tumour cells without prior immunization. These natural killer cells are found in non-immune humans and experimental animals and are thought by some to be the same as killer cells (killing by antibody-dependent cell cytotoxicity), but they can also kill in the absence of antibody. (12 Dec 1998) |
| paroxysmal cold haemoglobinuria | <haematology> A rare blood disorder caused by antibodies which destroy red blood cells upon exposure to the cold. The antibodies are formed against a specific blood group and are triggered by the cold. The cause is unknown but the disease has been associated with syphilis and some viral infections. Serum haemoglobin and urine haemoglobin are increased during the attacks. The disease is chronic and treatment is difficult. Some cases resolve spontaneously without treatment. Origin: Gr. Ouron = urine (27 Sep 1997) |
| rose cold | Allergic rhinitis occurring in the spring and early summer. (05 Mar 2000) |
| warm-cold haemolysin | Haemolysin which combines with red blood cells at temperatures below 20캜 and are eluted at warmer temperatures, e.g., 30 to 37캜. See: Donath-Landsteiner cold autoantibody, haemagglutinating cold autoantibody. (05 Mar 2000) |
| cold | <virology> A slang term that describes a viral upper respiratory infection which results from inflammation of the mucous membranes of the nasal cavity. (27 Sep 1997) |
| cold abscess | An abscess without heat or other usual signs of inflammation. Synonym: tuberculous abscess. (05 Mar 2000) |
| cold agglutination | The agglutination of red blood cells by their own serum (see autoagglutination), or by any other serum when the blood is cooled below body temperature, but most pronounced below 25캜; the phenomenon results from cold agglutinins; may be seen occasionally in the blood of apparently normal persons or as a pathologic finding in patients with primary atypical pneumonia, infectious mononucleosis, and other viral diseases, certain protozoan infections, or lymphoproliferative neoplasms. See: autoagglutination. (05 Mar 2000) |
| cold agglutination test | <investigation> A test for blood antibodies which are present in certain peculiar types of pneumonia (atypical pneumonia, Mycoplasma) (27 Sep 1997) |