Active locomotion of cells or organisms depends on intrinsic cellular mechanisms which are influenced by factors from the environment. Responses to environmental stimuli which take the form of directed orientation reactions are called taxes; those which take the form of undirected locomotion are called kineses (for review, see 1). The words chemotaxis (2) and chemokinesis (3) may be used to describe such reactions when the stimulus from the environment is chemical. Chemotaxis and chemokinesis play a considerable role in cell locomotion particularly in leukocytes (4–6). Analysis of leukocyte locomotion in the presence of a source of a chemical attractant shows that these cells a) become morphologically oriented in the concentration gradient and b) migrate directionally toward the source of the gradient (7). Cells exposed to certain chemical stimuli in the absence of a gradient show enhanced locomotion whose speed is determined by the stimulus but which is not directional (8–11).

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