natural (redirected from natural killer (NK) cell)

natural /nat·u·ral/ (nach´ah-r'l) neither artificial nor pathologic.

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natural

occurs in nature, without the intervention of humans.

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natural experiments

occur by chance when all variables for a population are constant except one, which is different for one large part of the population compared with the other, e.g. when half of a flock comes from one climate and the other half is a local resident in another climate.

natural focus

the ecology that is best suited to a biological system, e.g. an individual insect-borne disease; the area in which the disease naturally flourishes best; an ecological niche.

natural history

history of a process or organism as it occurs in nature, e.g. course of a disease from infection to resolution.

natural killer (NK) cell

see natural killer cell.

natural selection

selection occurring in nature, without any human intervention, direct or indirect.

natural ventilation

ventilation without the use of artificially induced energy and the machines which it drives; the forces used are wind and the exchange of heat from within the barn and the external air, controlled by ventilation devices in the walls and the ceiling.