| natural language processing | Computer processing of a language with rules that reflect and describe current usage rather than prescribed usage. (12 Dec 1998) |
|---|---|
| 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) |
| abortion | 1. <obstetrics> The premature expulsion from the uterus of the products of conception of the embryo or of a nonviable foetus. The four classic symptoms, usually present in each type of abortion, are uterine contractions, uterine haemorrhage, softening and dilatation of the cervix and presentation or expulsion of all or part of the products of conception. The expulsion or removal of an embryo or foetus from the mother prematurely, this can be done as an artificial procedure, but it often happens naturally when the mother's body expels the foetus because it has died, has genetic or developmental defects, or because of infection or illness in the mother. Natural abortions are typically called miscarriages. Medically-induced abortions, which can be completed with surgery or with hormone drugs, are performed because the foetus is unwanted, deformed, not likely to live, or endangers the mother's life or health. 2. The premature stoppage of a natural or a pathological process. Origin: L. Abortio (18 Nov 1997) |
| abortion applicants | Individuals requesting induced abortions. (12 Dec 1998) |
| abortion, criminal | Illegal termination of pregnancy. (12 Dec 1998) |
| abortion, eugenic | Abortion performed because of possible foetal defects. (12 Dec 1998) |
| abortion, habitual | The miscarriage of 3 or more consecutive pregnancies. Recurrent abortion can be identically defined as 3 or more miscarriages (spontaneous abortions) with no intervening pregnancies. Habitual or recurrent abortion is a form of infertility. (12 Dec 1998) |
| abortion, incomplete | Abortion in which not all the products of conception have been expelled. (12 Dec 1998) |
| abortion, induced | Intentional removal of a foetus from the uterus by any of a number of techniques. (popline, 1978) (12 Dec 1998) |