sweet gum: see witch hazel.

sour gum: see black gum.

gum tree, name for the eucalyptus (see myrtle) in Australia and for several other trees, e.g., the sweet gum, of the family Hamamelidaceae (witch hazel family), and the black gum or tupelo in North America.

gum tragacanth: see tragacanth.

gum ammoniac: see ammoniac.

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.

chewing gum, confection consisting usually of chicle, flavorings, and corn syrup and sugar (or artificial sweeteners). Prehistoric people are believed to have chewed resins. Spruce resin was chewed as a thirst quencher by Native Americans, from whom pioneers adopted the custom. Refined paraffin was later used and then chicle, which was probably first imported into the United States through Mexico. A chicle gum was patented in 1869 by William and Semple. In the present-day manufacture of chewing gum blocks of chicle are ground, melted, and cleared in a whirling vat, and then the flavorings (e.g., fruits, licorice, mints) and other ingredients are added. The gum is rolled through sheeting machinery and chopped into sticks or into candy-coated pellets. Insoluble plastics may be mixed with or substituted for the chicle. The United States is the major producer, exporter, and consumer, of chewing gum.

black gum, ornamental deciduous tree (Nyssa sylvatica family Nyssaceae) native to E North America. The leaves turn bright scarlet in the fall. The very tough wood was used for wheel hubs and other purposes. It is sometimes called sour gum, tupelo, and pepperidge, names also given other species of the genus, some native to Asia. This is the source of the popular tupelo honey. The genus Nyssa is probably derived from an ancestral dogwood and is included by some botanists in the family Cornaceae (dogwood family) of the division Magnoliophyta, class Magnoliopsida, order Cornales.

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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