natural purification (자정 작용
| conservation of natural resources | The protection, preservation, restoration, and rational use of all resources in the total environment. (12 Dec 1998) |
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| natural | 1. Fixed or determined by nature; pertaining to the constitution of a thing; belonging to native character; according to nature; essential; characteristic; not artifical, foreign, assumed, put on, or acquired; as, the natural growth of animals or plants; the natural motion of a gravitating body; natural strength or disposition; the natural heat of the body; natural colour. "With strong natural sense, and rare force of will." (Macaulay) 2. Conformed to the order, laws, or actual facts, of nature; consonant to the methods of nature; according to the stated course of things, or in accordance with the laws which govern events, feelings, etc.; not exceptional or violent; legitimate; normal; regular; as, the natural consequence of crime; a natural death. "What can be more natural than the circumstances in the behavior of those women who had lost their husbands on this fatal day?" (Addison) 3. Having to do with existing system to things; dealing with, or derived from, the creation, or the world of matter and mind, as known by man; within the scope of human reason or experience; not supernatural; as, a natural law; natural science; history, theology. "I call that natural religion which men might know . By the mere principles of reason, improved by consideration and experience, without the help of revelation." (Bp. Wilkins) 4. Conformed to truth or reality; as: Springing from true sentiment; not artifical or exaggerated; said of action, delivery, etc.; as, a natural gesture, tone, etc. Resembling the object imitated; true to nature; according to the life; said of anything copied or imitated; as, a portrait is natural. 5. Having the character or sentiments properly belonging to one's position; not unnatural in feelings. "To leave his wife, to leave his babes, . He wants the natural touch." (Shak) 6. Connected by the ties of consanguinity. "Natural friends." 7. Begotten without the sanction of law; born out of wedlock; illegitimate; bastard; as, a natural child. 8. Of or pertaining to the lower or animal nature, as contrasted with the higher or moral powers, or that which is spiritual; being in a state of nature; unregenerate. "The natural man receiveth not the things of the Spirit of God." (1 Cor. Ii. 14) 9. <mathematics> Belonging to, to be taken in, or referred to, some system, in which the base is 1; said or certain functions or numbers; as, natural numbers, those commencing at 1; natural sines, cosines, etc, those taken in arcs whose radii are 1. 10. Produced by natural organs, as those of the human throat, in distinction from instrumental music. Of or pertaining to a key which has neither a flat nor a sharp for its signature, as the key of C major. Applied to an air or modulation of harmony which moves by easy and smooth transitions, digressing but little from the original key. Natural day, the space of twenty-four hours. Natural fats, Natural gas, etc. See Fat, Gas. Etc. Natural Harmony, a classification based upon real affinities, as shown in the structure of all parts of the organisms, and by their embryology. "It should be borne in mind that the natural system of botany is natural only in the constitution of its genera, tribes, orders, etc, and in its grand divisions." (Gray) Natural theology, or Natural religion, that part of theological science which treats of those evidences of the existence and attributes of the Supreme Being which are exhibited in nature; distinguished from revealed religion. See Quotation under Natural. Natural vowel, the vowel sound heard in urn, furl, sir, her, etc.; so called as being uttered in the easiest open position of the mouth organs. See Neutral vowel. Synonym: See Native. Origin: OE. Naturel, F. Naturel, fr. L. Naturalis, fr. Natura. See Nature. Source: Websters Dictionary (01 Mar 1998) |
| natural antibody | Antibody demonstrable in the serum or plasma of various persons or animals not known to have been stimulated by specific antigen, either artificially or as the result of naturally occurring contact. Synonym: natural antibody. (05 Mar 2000) |
| natural childbirth | Psychophysical relaxation techniques that are used to facilitate childbirth. (12 Dec 1998) |
| natural classification | <zoology> Classification based on inferences concerning the phylogenetic relationships of animals. (09 Jan 1998) |
| natural dentition | See: dentition. (05 Mar 2000) |
| natural disasters | Sudden calamitous events producing great material damage, loss, and distress. They are the result of natural phenomena such as earthquakes, floods, etc. (12 Dec 1998) |
| natural dyes | Dye's obtained from animals or plants; examples include carmine, obtained from cochineal in the dried female insect Dactylopius cacti of Central America, and haematoxylin, extracted from the bark of the logwood tree Haematoxylon campechianum in the Caribbean area. (05 Mar 2000) |
| natural focus of infection | An ecosystem in which an infectious agent normally persists in nature; e.g., yellow fever virus in a jungle monkey-Haemagogus mosquito ecosystem. (05 Mar 2000) |
| natural haemolysin | Haemolysin occurring in the plasma of an animal of one species, e.g., a dog, which fixes complement with the red blood cells of some other species, e.g., a rabbit, thereby causing haemolysis of the cells of the rabbit, although the dog was not previously exposed to antigenic stimulation with such cells. (05 Mar 2000) |
| natural history | A former branch of knowledge embracing the study, description, and classification of natural objects (as animals, plants, and minerals) and thus including the modern sciences of zoology, botany, and mineralogy insofar as they existed at that time. In the 17th, 18th, and 19th centuries it was much used for the generalised pursuit of certain areas of science. (webster, 3d ed; from dr. James h. Cassedy, nlm history of medicine division) (12 Dec 1998) |
| natural immunity | This includes local barriers to infection such as skin, stomach acid, mucous, the cough reflex, enzymes in tears and saliva and skin oils. (27 Sep 1997) |
| natural killer cell | <haematology, immunology> A certain type of white blood cell that attacks tumour cells and infected body cells by binding to a tumour cell and releasing lethal chemicals. Natural killer cells are thought to play a key role in cancer prevention by killing abnormal cells before they multiply and grow. (16 Dec 1997) |
| natural killer cells | Large granular lymphocytes which do not express markers of either T or B-cell lineage. These cells do possess Fc receptors for IgG and can kill target cells using antibody-dependent cell-mediated cytotoxicity. NK cells can also use perforin to kill cells in the absence of antibody. Killing may occur without previous sensitization. Synonym: NK cells. (05 Mar 2000) |
| natural killer cell stimulating factor | <cytokine> A 75 kD heterodimeric cytokine composed of disulfide-bonded 40 kD and 35 kD subunits that was originally identified by its ability to induce cytotoxic effector cells in synergy with less than optimal concentrations of interleukin-2. It is released by macrophages in response to infection and promotes the activation of cell-mediated immunity. Specifically, IL-12 triggers the maturation of Thl CD4 cells, specific cytotoxic T-lymphocyte responses and an increase in the activity of NK cells and consequently, it is the initiator of cell-mediated immunity. It enhances the lytic activity of NK cells, induces interferon production, stimulates the proliferation of activated T-cells and NK cells. Is secreted by human B lymphoblastoid cells (NC 37). May play a role in controlling immunoglobulin isotype selection as it also inhibits IgE synthesis (even in the presence of anti-IFN monoclonal antibody) and as a growth factor for activated CD4+ and CD8+ T-cells independently of interleukin-2, and for CD56+ NK cells but not resting peripheral blood mononuclear cells or resting or activated tonsillar B-cells. It is likely that interleukin 12 has a major role in protective immunity against viruses and is under study as an immunotherapy in HIV infection. Formerly referred to as cytotoxic lymphocyte maturation factor. Acronym: IL-12 (12 Dec 1998) |