| double refraction | <microscopy> The refraction of light in two slightly different directions to form two rays or vector components. Each ray is polarized, and their vibration directions are perpendicular to each other. Furthermore, each ray has a different velocity, and therefore a different refractive index. See: birefringence. (05 Aug 1998) |
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| double salt | A salt in which two different positive ions are bonded to the same negative ion, or vice versa; e.g., NaKSO4. (05 Mar 2000) |
| double-shock sound | Applied by J. B. Bouillaud to describe the cadence of a split-second heart sound, or of the second sound followed by an opening snap or early third heart sound. Synonym: double-shock sound. Origin: Fr. Drum-beat (05 Mar 2000) |
| double stain | <technique> A mixture of two dyes, each of which stains different portions of a tissue or cell. (05 Mar 2000) |
| double-strand break | A break in double-stranded DNA in which both strands have been cleaved; however, the two strands have not separated from each other. (05 Mar 2000) |
| double-stranded complimentary DNA | <molecular biology> A duplex DNA molecule copied from a copy DNA template. (09 Oct 1997) |
| double tachycardia | The simultaneous tachycardia of two ectopic pacemakers, e.g., atrial and junctional tachycardia. (05 Mar 2000) |
| double tertian | Denoting malarial infections with two different sets of organisms producing daily paroxysms. See: quotidian malaria. (05 Mar 2000) |
| double tertian malaria | See: quotidian malaria. (05 Mar 2000) |
| double thymidine block | <cell culture, procedure> A lab technique used to synchronise the cell cycles of all the cells in a culture. This is done by adding excessive amounts of thymidine (a deoxynucleoside) to the culture so that DNA replication is blocked. Eventually, all of the cells will reach the same point in the cell cycle and stop. (09 Oct 1997) |
| double track sign | In paediatric radiology, a less common sign of congenital pyloric stenosis, when barium is caught between mucosal folds in the hypertrophied pylorus. (05 Mar 2000) |
| double vision | <ophthalmology, symptom> The perception of two images of a single object. Synonym: ambiopia, double vision, binocular polyopia. (18 Nov 1997) |
| double-voided specimen | This refers to a urine specimen which is collected after first emptying the bladder and then waiting until another specimen can be collected. These double-voided urine specimens are more accurate for purposes of glucose testing (urinalysis). If you test a urine specimen that has been held in the bladder for an extended period of time, it will not accurately reflect the glucose content in the bloodstream. A freshly, double voided specimen is preferred. (27 Sep 1997) |
| Traube's double tone | A double sound heard on auscultation over the femoral vessels in cases of aortic and tricuspid insufficiency. (05 Mar 2000) |
| Abbe test plate | <equipment> A long, wedge-shaped coverslip about 0.20 mm thick at one end and 0.10 to 0.12 mm at the other end coated chemically with a silver film on which are ruled horizontal lines. at each variation in thickness of 0.01 mm there are vertical lines. By means of oblique illumination and by focusing on different portions of the plate, it is possible to determine the optimum coverslip thickness for any objective and also, for microscopes with drawtubes, the tube length for best objective performance. The approximate freedom from spherical and chromatic aberrations can also be estimated. Small isolated bits of silver near the edges of the lines form good objects for the star test (05 Aug 1998) |