| 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) |
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| 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) |
| direct lytic factor of cobra venom | A polypeptide of 62 residues; action on cells is similar to that of melittin in that it promotes disruption of membranes; used as an investigational antirheumatic agent. Synonym: cobra toxin, direct lytic factor of cobra venom. (05 Mar 2000) |
| direct lytic factors | most abundant proteins in cobra (naja of the elapids) venom; basic polypeptides of 57 to 62 amino acids with four disulfide bonds and a molecular weight of less than 7000; causes skeletal and cardiac muscle contracture, interferes with neuromuscular and ganglionic transmission, depolarises nerve, muscle and blood cell membranes, thus causing haemolysis. Synonym: cobramine a; cobramine b; cobra cytotoxin; gamma toxin; membrane-active polypeptide. (12 Dec 1998) |
| direct maternal death | Death resulting from obstetric complications of the gestation, labour, or puerperium, and from interventions, omissions, incorrect treatment, or a chain of events caused by any of the above, indirect maternal death, an obstetric death resulting from previously existing disease or from disease developing during pregnancy, labour, or the puerperium; it is not directly due to obstetric causes, but to conditions aggravated by the physiological effects of pregnancy. (05 Mar 2000) |
| direct method for making inlays | In dentistry, an inlay technique in which the wax pattern is made directly in the prepared cavity in the tooth. Synonym: direct technique. (05 Mar 2000) |
| direct nuclear division | <cell biology> An unusual form of nuclear division, in which the nucleus simply constricts, rather like a cell without chromosome condensation or spindle formation. Partitioning of daughter chromosomes is haphazard. Observed in some Protozoa. (18 Nov 1997) |
| direct ophthalmoscope | <instrument> An instrument designed to visualise the interior of the eye, with the instrument relatively close to the subject's eye and the observer viewing an upright magnified image. (05 Mar 2000) |
| direct ophthalmoscopy | Ophthalmoscopy performed with a direct ophthalmoscope. (05 Mar 2000) |
| direct percussion | The striking of the part under examination directly with the finger or a plessor, without the intervention of another finger or plessimeter. Synonym: direct percussion. (05 Mar 2000) |
| direct pulp capping | A procedure for covering and protecting an exposed vital pulp. (05 Mar 2000) |
| direct pyramidal tract | Uncrossed fibres forming a small bundle in the pyramidal tract. See: pyramidal tract. Synonym: tractus corticospinalis anterior, tractus pyramidalis anterior, anterior corticospinal tract, anterior pyramidal fasciculus, direct pyramidal tract, fasciculus corticospinalis anterior, fasciculus pyramidalis anterior, Turck's bundle, Turck's column, Turck's tract. (05 Mar 2000) |
| direct rays | Cosmic ray's in the form in which they first strike the atmosphere, X-ray's generated at the focal spot of the tube. Synonym: direct rays. (05 Mar 2000) |