| slow ray | <microscopy> The slower of the two rays created by a crystal or fibre and the one that travels the path of higher refractive index. (05 Aug 1998) |
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| slow-reacting factor of anaphylaxis | Slow-reacting substance of anaphylaxis (SRS-A), a leukotriene of low molecular weight which is released in anaphylactic shock and produces slower and more prolonged contraction of muscle than does histamine; it is active in the presence of antihistamines (but not epinephrine) and seems not to occur preformed in mast cells, but as a result of an antigen-antibody reaction on the granules. Compare: peptidyl leukotrienes. Synonym: slow-reacting factor of anaphylaxis. (05 Mar 2000) |
| slow-reacting substance | Slow-reacting substance of anaphylaxis (SRS-A), a leukotriene of low molecular weight which is released in anaphylactic shock and produces slower and more prolonged contraction of muscle than does histamine; it is active in the presence of antihistamines (but not epinephrine) and seems not to occur preformed in mast cells, but as a result of an antigen-antibody reaction on the granules. Compare: peptidyl leukotrienes. Synonym: slow-reacting factor of anaphylaxis. (05 Mar 2000) |
| slow reacting substance of anaphylaxis | <immunology> Potent bronchoconstrictor and inflammatory agent released by mast cells, an important mediator of allergic bronchial asthma. A mixture of three leukotrienes (LTC4 mainly, LTD4 and LTE4) (18 Nov 1997) |
| slow scan | <microscopy> A system of video scanning in which the time used to read each line has been increased in comparison to standard video. The bandwidth needed to faithfully transmit or record the signal is reduced in inverse ratio to the scanning time. Slow scan allows the video signal to be transmitted over a telephone line, or line scans to be registered on a chart recorder. (19 Jan 1998) |
| slow virus | 1. <virology> Specifically one of the Lentivirinae 2. Any virus causing a disease that has a very slow onset. Diseases such as sub acute spongiform encephalopathy, Aleutian disease of mink, scrapie, kuru and Creutzfeldt Jacob disease may be caused by slow viruses. See: prion. (18 Nov 1997) |
| slow virus disease | A disease that follows a slow, progressive course spanning months to years, frequently involving the central nervous system, and ultimately leading to death, such as visna and maedi of sheep, caused by viruses of the subfamily Lentivirinae (family Retroviridae), and subacute sclerosing panencephalitis, seemingly caused by the measles virus; spongiform encephalopathies including kuru of man, scrapie of sheep, and transmissible encephalopathy of mink may also be classified under slow virus disease but their respective aetiologic agents have not been adequately characterised. (05 Mar 2000) |
| slow virus diseases | Diseases of viral origin, characterised by incubation periods of months to years, insidious onset of clinical manifestations, and protracted clinical course. Though the disease process is protracted, viral multiplication may not be unusually slow. Conventional viruses produce slow virus diseases such as subacute sclerosing panencephalitis, progressive multifocal leukoencephalopathy (leukoencephalopathy, progressive multifocal), and aids. Diseases produced by unconventional agents were originally considered part of this group. They are now called prion diseases. (12 Dec 1998) |