| dark-adapted eye | An eye that has been in darkness or semidarkness and has undergone regeneration of rhodopsin (visual purple), which renders it more sensitive to reduced illumination. Synonym: scotopic eye. (05 Mar 2000) |
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| dark cell | Cell's in eccrine sweat glands having many ribosomes and mucoid secretory granules. (05 Mar 2000) |
| dark current | <physiology> Current caused by constant influx of sodium ions into the rod outer segment of retinal photoreceptors and that is blocked by light (leading to hyperpolarization). The plasma membrane sodium channel is controlled through a cascade of amplification reactions initiated by photon capture by rhodopsin in the disc membrane. (18 Nov 1997) |
| dark-ground illumination | dark-field illumination |
| dark reaction | <biochemistry, plant biology> The reactions in photosynthesis that occur after NADPH and ATP production and that take place in the stroma of the chloroplast. By means of the reaction, carbon dioxide is incorporated into carbohydrate. (18 Nov 1997) |
| dark t2 lesion | <radiology> (short T2), acute haemorrhage (deoxyHb), haemosiderin, physiologic iron (basal ganglia, etc.), mucinous lesions (?) most abnormalities have long T1 and T2 (dark/bright). Compare: bright T1 lesion. (07 Mar 2000) |
| binocular microscope | <instrument, microscopy> A microscope fitted with double eyepieces for vision with both eyes. The purpose in dividing the same image from a single objective of the usual compound micro-scope is to reduce eyestrain and muscular fatigue which may result from monocular, high-power microscopy. The purpose in obtaining a different image for each of two oculars is to provide stereoscopy by means of two different angles of view. There are two kinds of stereoscopic microscopes: binobjective (Greenough) older type and monobjective (common main objective) newer type. (See stereo microscope, Greenough microscope, etc.) (05 Aug 1998) |
| Rheinberg microscope | <instrument> A modified form of dark-field microscope in which the central opaque stop in the condenser is replaced by a coloured filter, producing a background of contrasting colour against which the specimen is illuminated. (05 Mar 2000) |
| Greenough microscope | <instrument, microscopy> One of two kinds of stereomicroscopes with two separate compound microscopes, one for each eye, focused on the same object. The other kind has a common main objective. See: binocular microscope. (05 Aug 1998) |
| phase-contrast microscope | <instrument> A specially constructed microscope that has a special condenser and objective containing a phase-shifting ring whereby small differences in index of refraction are made visible as intensity or contrast differences in the image; particularly useful for examining structural details in transparent specimens such as living or unstained cells and tissues. (05 Mar 2000) |
| microscope | <instrument> A piece of laboratory equipment that is used to magnify small things that are too small to be seen by the naked eye, or too small for the details to be seen by the naked eye, so that their finer details can be seen and studied. Examples are the light (or optical) microscope, electron microscope, X-ray microscope, and acoustic microscope. (09 Oct 1997) |
| microscope, compound | A microscope that consists of two microscopes in series, the first serving as the ocular lens (close to the eye) and the second serving as the objective lens (close to the object to be viewed). Credit for creating the compound microscope goes usually to the dutch spectaclemakers hans and zacharias janssen who in 1590 invented an instrument that could be used as either a microscope or telescope. The compound microscope evolved into the dominant type of optical microscope today. (12 Dec 1998) |
| microscope, electron | <microscopy> An electron-optical device which produces a magnified image of an object. Detail may be revealed by virtue of selective transmission, reflection, or emission of electrons by the object. (05 Aug 1998) |
| microscope, fluorescent | A microscope equipped to examine material that fluoresces under ultraviolet (uv) light. (12 Dec 1998) |
| microscope, Greenough | <microscopy> A stereoscopic microscope with paired objectives, prisms, and eyepieces invented by H. Greenough. The name is sometimes incorrectly used for any stereoscopic microscope with paired objectives showing erect images. (05 Aug 1998) |