gum

gum, in anatomy: see teeth.

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.

Any of the more than 500 species of mostly very large trees in the genus Eucalyptus, in the myrtle family, native to Australia, New Zealand, Tasmania, and nearby islands. Many species are grown widely throughout the temperate regions of the world as shade trees or in forestry plantations. Because they grow rapidly, many species attain great height. The leaf glands of many species, especially E. salicifolia and E. globulus, contain a volatile, aromatic oil known as eucalyptus oil, used mostly in medicines. Eucalyptus wood is used extensively in Australia as fuel, and the timber is commonly used in buildings and fencing. The bark of many species is used in papermaking and tanning.

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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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Sweetened product made from chicle and similar resilient substances that is chewed for its flavour. Tree resins have been chewed as teeth cleaners and breath fresheners since ancient times. The latex (called chicle) of the Central American sapodilla tree was first used to mass-produce chewing gum in the 19th century; its plasticity, insolubility in water, and ability to hold a flavour made it an ideal chewing-gum base. After World War II other gums and synthetic rubbers came to replace chicle.

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See Gum