| direct contamination | <dentistry> Direct contact with impurities or germs. (for example by a patient sneezing on the assistant.) (08 Jan 1998) |
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| direct Coombs' test | A test for detecting sensitised erythrocytes in erythroblastosis foetalis and in cases of acquired immune haemolytic anaemia: the patient's erythrocytes are washed with saline to remove serum and unattached antibody protein, then incubated with Coombs' anti-human globulin (usually serum from a rabbit or goat previously immunised with human globulin); after incubation, the system is centrifuged and examined for agglutination, which indicates the presence of so-called incomplete or univalent antibodies on the surface of the erythrocytes. (05 Mar 2000) |
| direct current | (DC) Electric current which travels continuously in the same direction over a sustained period of time, contrast with AC (Alternating Current) which oscillates as a function of time. (09 Oct 1997) |
| direct diuretic | A diuretic whose primary effect is on renal tubular function. (05 Mar 2000) |
| direct embolism | Embolism occurring in the direction of the blood current. (05 Mar 2000) |
| direct filling resin | An autopolymerizing resin especially designed as a dental restorative material. (05 Mar 2000) |
| direct flap | A flap raised completely and transferred at the same stage. Synonym: immediate flap. (05 Mar 2000) |
| direct fluorescent antibody | The straightforward detection of antigens using fluorescent labelled antigen-specific antibody. Because detection of the antigen in a substrate of patient sample (cellular smear, fluid or patient-inoculated culture medium) is the goal, direct fluorescent antibody is seldom quantitative. (05 Mar 2000) |
| direct fluorescent antibody test | Test for tissue antigen using either a direct method, by conjugation of antibody with fluorescent dye (fluorescent antibody technique, direct) or an indirect method, by formation of antigen-antibody complex which is then labelled with fluorescein-conjugated anti-immunoglobulin antibody (fluorescent antibody technique, indirect). The tissue is then examined by fluorescence microscopy. (12 Dec 1998) |
| direct fracture | A fracture, especially of the skull, occurring at the point of injury. (05 Mar 2000) |
| direct illumination | An illumination in which the rays of light are directed downward, almost perpendicularly onto the upper surface of the object, which reflects the rays upward into the optical system. Synonym: erect illumination, vertical illumination. (05 Mar 2000) |
| direct image | <microscopy> Such as seen in a mirror or through a magnifier. A virtual image has no real existence in space as does a real image from a lens. It does have a definite location, however, caused by the angles of divergence of the rays received by the eye. This can be shown by the common school experiment of placing a pin coincident with its mirror image behind a sheet of glass acting as a partial mirror. Its location can also be placed in design by extrapolating backwards to a focus. If a magnifier is used as it should be, with the object at its focus, the virtual image is at infinity. The same is true for a microscope focused for the relaxed eye. See: distance of virtual image. (05 Aug 1998) |
| direct inguinal hernia | See: inguinal hernia. (05 Mar 2000) |
| direct lead | In electrocardiography, a unipolar lead recorded with the exploring electrode placed directly on the surface of the exposed heart. (05 Mar 2000) |
| direct life cycle | <epidemiology> A life cycle in which a parasite is transmitted directly from one host to the next without an intermediate host or vector of another species. (05 Dec 1998) |