| Tracer | n. One who, or that which, traces. [ 1913 Webster ] 2. A person engaged (esp. in the express or railway service) in tracing, or searching out, missing articles, as packages or freight cars. [ Webster 1913 Suppl. ] 3. An inquiry sent out (esp. in transportation service) for a missing article, as a letter or an express package. [ Webster 1913 Suppl. ] 4. (Mil.) a type of ammunition that emits light or smoke as it moves toward its target, providing a visible path of the projectile in flight so that the point of impact may be observed; -- called also tracer ammunition. [ PJC ] 5. (Mil.) the chemical substance used in tracer ammunition to cause it to be visible in flight. [ PJC ] 6. a chemical substance with properties, such as radioactivity or fluorescence, which make it easily measurable, used to observe the movements of chemically related substances through a biological, physical, or chemical system; -- in biochemistry, also called labeled compounds. Radioactive tracers are used, for example, to measure the retention or distribution of residues of drugs after administration to an animal, to determine the type and rate of metabolism; also, to measure the rate of motion of molecules in electrophoresis or the leakage of small quantities of material from a container. Small fluorescent tracers may be attached in many cases to macromolecules such as proteins or nucleic acids, allowing the motions of such macromolecules to be easily observed by their acquired fluorescence, without appreciably changing their properties. In biological and biochemial systems the common radioactive isotopes used in tracers are carbon-14, tritium (hydrogen-3), sulfur-35, phosphorus-32, and iodine-131; other isotopes are also used, including non-radioactive isotopes such as carbon-13. [ PJC ] |
| Tracer/y | n.; pl. Traceries /plu> (Arch.) 1. Ornamental work with rambled lines. Especially: -- (a) The decorative head of a Gothic window. [ 1913 Webster ] ☞ Window tracery is of two sorts, plate tracery and bar tracery. Plate tracery, common in Italy, consists of a series of ornamental patterns cut through a flat plate of stone. Bar tracery is a decorative pattern formed by the curves and intersections of the molded bars of the mullions. Window tracery is imitated in many decorative objects, as panels of wood or metal either pierced or in relief. See also Stump tracery under Stump, and Fan tracery under Fan. [ 1913 Webster ] (b) A similar decoration in some styles of vaulting, the ribs of the vault giving off the minor bars of which the tracery is composed. [ 1913 Webster ] 2. A tracing of lines; a system of lines produced by, or as if by, tracing, esp. when interweaving or branching out in ornamental or graceful figures. “Knit with curious tracery.” Burns. [ Webster 1913 Suppl. ] |
