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gum, colloidal plant substance

gum, term commonly applied to any of a wide variety of colloidal substances somewhat similar in appearance and general characteristics, exuded by or extracted from plants. In this classification, however, many substances that are not true gums are included, among them many resins, so-called gum resins, and such substances as frankincense, myrrh, labdanum, copal, amber, chicle, and rubber (gum elastic, India rubber). True gums are complex organic substances mostly obtained from plants, some of which are soluble in water and others of which, although insoluble in water, swell up by absorbing large quantities of it. With water they form thick, gluey fluids. Their chemical nature is complex. In general, they contain in various proportions carbon, hydrogen, oxygen, and such metals as calcium, magnesium, and potassium in the form of salts of various organic acids. Gum arabic, or gum acacia, is a typical, water-soluble gum obtained from various plants of the genus Acacia, chiefly those found in Africa. A complex polysaccharide containing metal salts, gum arabic varies in color from white to red and is used extensively in making inks, adhesives, and confections; in the textile industry for filling fabrics; and in medicine as an emollient. Gum senegal is very similar. Among the gum resins (mixtures of gums and resins) are ammoniac, asafetida, bdellium, gamboge, and myrrh. See also tragacanth.

Bibliography

See C. L. Mantell et al., The Technology of Natural Resins (1942); C. L. Mantell, The Water-Soluble Gums (1947, repr. 1965); R. L. Davidson, Handbook of Water-Soluble Gums and Resins (1980).

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gum, in anatomy

gum, in anatomy: see teeth.

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gum

In botany, an adhesive substance of vegetable origin, mostly obtained as exudate from the bark of trees or shrubs belonging to the pea family. Gum arabic (from a species of acacia) is used in lithography. Gum tragacanth (from several shrub species in the genus Astragalus) is used as a coating and binding agent in pill manufacture, as an emulsifier in processed foods, and as a thickener in sauces. Some plant gums are used in the manufacture of cosmetics.

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gum

 or gingiva

Mucous-membrane-covered connective tissue attached to and surrounding the necks of the teeth and the alveolar bone of the jaw. The edges of the gums around the teeth are free and extend into the spaces between the teeth. Fibres of the ligament that holds the teeth in their sockets enter the gum and hold it tightly against the teeth. Pink, speckled, and tough, healthy gums have limited sensitivity to pain, temperature, and pressure. Changes in colour, loss of speckling, or abnormal sensitivity are early signs of gingivitis, in which pockets form between the gum and teeth and become infected, with inflammation, bleeding, and, in severe cases, loss of teeth.

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GUM

 abbreviation of Gosudarstvenny Universalny Magazin (Russian: “State Department Store”)

Largest department store in Russia. Situated in Moscow's Red Square, it occupies a huge, ornate building (constructed 1889–93) that once housed more than 1,000 shops. GUM now includes about 150 shops selling food, clothing, home appliances, watches and cameras, and many other goods. It functions more like a Western-style shopping mall than a department store and is a popular tourist attraction.