| periodic acid Schiff reaction | <technique> A histochemical technique based on periodic acid oxidation of a substance containing the 1,2-glycol grouping. It is used for staining carbohydrates as the resulting dialdehyde reacts with Schiff reagent to form a coloured product. The adjacent hydroxyl groups are oxidized to form aldehydes by periodic acid (HIO4) and these aldehyde groups react with Schiff's reagent (basic fuchsin decolourised by sulphurous acid) to give a purple colour. Acronym: PAS (18 Nov 1997) |
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| periodic acid Schiff stain | <technique> A histochemical technique based on periodic acid oxidation of a substance containing the 1,2-glycol grouping. It is used for staining carbohydrates as the resulting dialdehyde reacts with Schiff reagent to form a coloured product. Substances that can be demonstrated include carbohydrates, mucins, cartilage matrix, collagen, reticulum, basement membranes, fibrin, thyroid colloid, amyloid, glomerular hyaline deposits, and a number of other secretions or tissue constituents. Also used in for staining gels on which glycoproteins have been run. See: periodic acid Schiff reaction Synonym: PAS stain. (22 Sep 2002) |
| Schiff base | The reaction of a primary amine with an aldehyde or ketone yields an imine sometimes called a Schiff base. When an arylamine is used the Schiff base may form an intermediate in a staining reaction, for example for polysaccharides. (18 Nov 1997) |
| schiff bases | Condensation products of aromatic amines and aldehydes forming azomethines substituted on the n atom, containing the general formula r-n:chr. (12 Dec 1998) |
| Schiff, Hugo | <person> German chemist in Florence, 1834-1915. See: Schiff base, Schiff's reagent, Kasten's fluorescent Schiff reagents, periodic acid-Schiff stain, ninhydrin-Schiff stain for proteins. (05 Mar 2000) |
| Schiff, Moritz | <person> German physiologist, 1823-1896. See: Schiff-Sherrington phenomenon. (05 Mar 2000) |
| Schiff-Sherrington phenomenon | When the spinal cord is transected in the midthoracic region or a little lower, the stretch and other postural reflexes of the upper extremity become exaggerated; if the transection is made in the sacral cord, a similar effect is observed in the lower limbs. The effect is regarded as a release phenomenon, i.e., release from an inhibitory influence normally exerted by the spinal segments below the transection. (05 Mar 2000) |
| Schiff's reagent | An aqueous solution of basic fuchsin or pararosaniline which is decolorised by sulfur dioxide, commonly prepared by addition of hydrochloric acid to a dye solution containing a metabisulphite or bisulphite salt; used for aldehydes and in histochemistry to detect polysaccharides, DNA, and proteins. See: Feulgen stain, periodic acid-Schiff stain, ninhydrin-Schiff stain for proteins. (05 Mar 2000) |
| ninhydrin-Schiff stain | <technique> For proteins, proteins are revealed by using ninhydrin or alloxan to produce aldehydes from primary aliphatic amines by oxidative deamination; the aldehydes are shown by reaction with Schiff's reagent. (05 Mar 2000) |
| Kasten's fluorescent Schiff reagents | Fluorescent analogues of Schiff's reagent which are fluorescent basic dyes lacking acidic side groups and containing one or more primary amine groups; used in cytochemical detection of DNA in Kasten's fluorescent Feulgen stain, polysaccharides in Kasten's fluorescent PAS stain, and proteins in the ninhydrin-Schiff stain; such analogues include acriflavine, auramine O, and flavophosphine N. (05 Mar 2000) |
| accelerated reaction | A response occurring in a shorter time than expected; the cutaneous manifestations occurring during the period between the second and tenth day following smallpox vaccination; because it is intermediate between a primary reaction and an immediate reaction, it is regarded as evidence of some degree of resistance. Synonym: vaccinoid reaction. (05 Mar 2000) |
| acid reaction | Any test by which an acid reaction is recognised such as the change of blue litmus paper to red, an excess of hydrogen ions over hydroxide ions in aqueous solution indicated by a pH value less than 7 (at 22캜). Compare: dissociation constant of water. (05 Mar 2000) |
| acute-phase reaction | <immunology, rheumatology> Refers to the changes in synthesis of certain proteins within the serum during an inflammatory response, which provides rapid protection for the host against microorganisms via non-specific defense mechanisms. It consists of fever, an increase in inflammatory humoral factors, and an increased synthesis by hepatocytes of a number of proteins or glycoproteins usually found in the plasma; the reaction is mediated by endogenous pyrogens, the hypothalamus, adrenal hormones, and other factors. (12 Jul 2000) |
| acute situational reaction | An acute emotional reaction related to extreme environmental stress. Synonym: acute situational reaction. (05 Mar 2000) |
| acute stress reaction | A sudden bout of anxiety that is often accompanied by the features of hyperventilation (tingling around mouth and in fingertips, rapid breathing, faintness or fainting). (27 Sep 1997) |