GUM exists in the juices of almost all plants, but is produced in its purest form by various species of Acacia, e.g., Acacia Verek (Guil. and Perrottet), A. horrida, A. arabica (Wildenow), A. Seyel (Delile), and A. stenocarpa (Hochst). The name is applied to those exudations from plants, stems, branches, or fruits which are entirely soluble or soften in water, and form with it a thick glutinous liquid or mucilage insoluble in alcohol of 60 per cent., and yield mucic and oxalic acids when treated with nitric acid. In structure gum is quite amorphous, being neither organized like starch nor crystallized like sugar. According to Trecul, the acacias and the Rosacea: yield their gums most abundantly when sickly and in an abnormal state, caused by a fulness of sap in the young tissues, whereby the new cells are softened and finally disorganized; the cavities thus formed fill with liquid, which exudes, dries, and con-stitutes the gum.

The chief varieties have hitherto been divided as follows :—(1) gum arabic, (2) gum tragacanth, (3) cherry tree gum, (4) gum of Bassora, (5) mucilage. The artificial gum dextrin has been already treated of, vol. vii. p. 146.

Gum Arabic may be taken as the type of the gums entirely soluble in water. The principal kinds are dis-tinguished as Turkey Picked Gum, Gedda, Amrad, Gheziri, Senegal, Talca, Australian, Barbary, Cape, and East India (from Bombay and Aden). Another variety, spoken of as likely, from its abundance, to be soon in the market, is obtained from the Prosopis didcis, a leguminous plant, and is called gum mesquite or mezquite; it comes from Western Texas and Mexico, and is yellowish in colour, very brittle, and quite soluble in water (Pharm. Journ. (3), vol. vi. p. 942).

Gum arabic occurs in pieces of varying size, and some kinds are fuil of minute cracks. The specific gravity of Turkey picked gum (the purest variety) is 1'487, or, when dried at 100° 0., 1'525. It is soiuble in water to an indefinite extent; boiled with dilute sulphuric acid it is converted first into dextrin, and then into a fermentable variety of sugar. Moderately strong nitric acid changes it into mucic, saccharic, tartaric, and oxalic acids. Under the influence of yeast it does not enter into the alcoholic fermentation, but Berthelot, by digesting with chalk and cheese, obtained from it 12 per cent, of its weight of alcohol, along with lactate of calcium, but no appreciable quantity of sugar. According to Fremy, gum arabic may be regarded as a potassium and calcium salt of gummic or arabic acid, of the formula CaK2C12H22On. 6C12H22On. Graham (Chemical and Physical He-searches) gives dialysis as the simplest and best mode of preparing gummic acid, and states that the power of gum to penetrate the colloid septum is 400 times less than that of chloride of sodium, and further that by mixing the gum with substances of the crystalloid class the diffusibility is lowered, and may be even reduced to nothing. The mucilage must be acidulated with hydrochloric acid before dialysing, to set free the gummic acid. Gummic acid reddens litmus, its reaction being about equal to carbonic acid. When solutions of gum arabic and gelatin are mixed, oily drops of a compound of the two are precipitated, which on standing form a nearly colourless jelly, melting at 25° C., or by the heat of the hand. This substance can he washed without decomposition. Gummic acid is soluble in water ; when well dried at 100° C, it becomes transformed into metagummic acid, which is insoluble, but swells up in water like gum tragacanth.

Gum arabic, when heated to 150° C. with two parts of acetic anhydride, swells up to a mass which, when washed with boiling water, and then wdth alcohol, gives a white amorphous insoluble powder called acetyl arabin C6H8(C2H30)206. It is saponified by alkalies, with reproduction of soluble gum. Gum arabic is not precipitated from solution by alum, stannous chloride, sulphate or nitrate of copper, or neutral lead acetate ; with basic lead acetate it forms a white jelly, with ferric chloride it yields a stiff clear gelatinoid mass, and its solutions are also precipitated by borax.

The finer varieties are used as an emollient and demulcent in medicine, and in the manufacture of confectionery; the commoner qualities are used as an adhesive paste, for giving lustre to crape, silk, &c, in cloth finishing to stiffen the fibres, and in calico-printing. For labels, &c, it is usual to mix sugar or glycerin with it to prevent it from cracking.
Physiologically nothing is yet definitely known of gum as a food material. Animals fed thereon soon die of inanition. Lehmann says it is not absorbed by the system, but according to Pavy, it is to a slight extent, as shown by the formation of amyloid substance in the liver of subjects fed on gum.

Gum Senegal, a varietyof gum arabic produced by A. Verek, occurs in pieces generally rounded, of the size of a pigeon's egg, and of a reddish or yellow colour, and specific gravity 1 '436. It gives with water a somewhat stronger mucilage than gum arabic, from which it is distinguished by its clear interior, fewer cracks, and greater toughness. It is imported from the river Gambia, and from Senegal and Bathurst, and is collected in December and March yearly.

Chagual gum, a new variety brought from St Iago de Chili, resembles gum Senegal. About 75 per cent, is soluble in water. Its solution is not thickened by borax, and is precipitated by neutral lead acetate ; and dilute sul-phuric acid converts it into dextro-glucose.
The imports of gum arabic into England during 1878 (including all the varieties) may be estimated as follows :—_

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Of this about one-half is exported. These figures are only approximate, as, since the repeal of the duties in 1845, the returns do not discriminate between the various descriptions which are all classed together under the head of gum.

Gum Tragacanth, familiarly called gum dragon, exudes from the stem, the lower part especially, of the various species of Astragalus, and is collected in Asia Minor, the chief port of shipment being Smyrna. Formerly only what exuded spontaneously was gathered; this was often of a brownish colour; but now the flow of the gum is aided by incisions cut near the root, and the product is the fine, white, flaky variety so much valued in com-merce. The chief flow of gum takes place during the night, and hot and dry weather is the most favourable for its production.

In colour gum tragacanth is of a dull white ; it occurs in horny, flexible, and tough, thin, twisted flakes, translucent, and with peculiar wavy lines on the surface. When dried at temperatures under 100° C. it loses about 14 per cent, of water, and is then easily powdered. Its specific gravity is 1'384. With water it swells by absorption, and with even fifty times its weight of that liquid forms a thick mucilage. Part of it only is soluble in water, and that resembles gummic acid in being precipitated by alcohol and ammonium oxalate, but differs from it in giving a precipitate with neutral lead acetate and none with borax. The insoluble part of the gum is a calcium salt of bassorin (C12H20O10), which is devoid of taste and smell, forms a gelatinoid mass with water, but by con-tinued boiling is rendered soluble, owing, according to M. Giraud, to its being changed into pectin. A small quantity of starch is always naturally present in gum tragacanth. The composition of gum tragacanth is generally given as arabin 53 per cent., bassorin and starch 33, water 11 (but M. Giraud considers its composition to be water 20 per cent.), mineral matter 3, a pectinous principle (apparently identical with the pectose of Fremy) 60, soluble gum 10, cellulose 3, starch 3, mineral matter 3, with traces of nitro-genous matter. Graham (Chemical and Physical Researches, p. 589) speaks of its being likely that native gums insoluble in water are the pectous form of soluble gum, and Giraud's experiments point to the correctness of that surmise.

Gum tragacanth is used in calico-printing as a thickener of colours and mordants; in medicine as a demulcent and vehicle for insoluble powders, and as an excipient in pills; and for setting and mending beetles and other insects. The imports during 1878 were—

== TABLE ==

Gum kuteera resembles in appearance gum tragacanth, for which the attempt has occasionally been made to substitute it. It is said to be the product of Sterculia urens, a plant of the natural order Stercuiiacece, and is un-known to British commerce.
Cherry Tree Gum is an exudation from trees of the genera Prurvus and Cerasus. It occurs in shiny reddish lumps, resembling the commoner kinds of gum arabic. With water, in which it is only partially soluble, it forms a thick mucilage. The soluble portion is arabin, the insoluble cerasin, which according to Fremy is a calcium salt of meta-gummic acid (C12H22On). It is not used commercially.





Gum of Bassora, from Bassora or Bussorah in Asia, is sometimes imported into the London market under the name of the hog tragacanth. It is insipid, crackles between the teeth, occurs in variable-sized pieces, is tough, of a yellowish-white colour, and opaque, and has properties similar to gum tragacanth. Its specific gravity is 1 '3591. It contains only 1 per cent, of soluble gum or arabin. Under the name of Caramania gum it is mixed with inferior kinds of gum tragacanth before exportation.

Mucilage.—Very many seeds, roots, &c, when infused in boiling water, yield mucilages which, for the most part, consist of bassorin. Linseed, quince seed, and marsh-mallow root yield it in large quantity (see also GUMBO). In their reactions the different kinds of mucilage present differences; e.g., quince seed yields only oxalic acid when treated with nitric acid, and with a solution of iodine in zinc iodide it gives, after some time, a beautiful red tint. Linseed does not give the latter reaction ; by treat-ment with boiling nitric acid it yields mucic and oxalic acids.

Gum Resins.—This term is applied to the inspissated milky juices of certain plants, which consist of gum soluble in water, resin and essential oil soluble in alcohol, other vegetable matter, and a small amount of mineral matter. They are generally opaque and solid, and often brittle. Their chief uses are in medicine. They include the follow-ing :—ammoniacum, asafcetida, bdellium, euphorbium, frankincense or olibanum, galbanum, gamboge, myrrh, opoponax, sagapanum, and scammony. Several of the resins are often improperly called gums; e.g., benzoin or ben-jamin, copal, dammar, elemi or animi, kawrie or cowdie or Australian copal, mastic, sandrac, and shellac. (J. ST.)

GUMBLNNEN, the chief town of a government district of the same name in the Prussian province of East Prussia, is situated on the Pissa, an affluent of the Pregel, and on the Eastern Railway, 22 miles south-west of Eydtkuhnen on the Russian boundaries. The surrounding country is pleasant and fruitful, and the town is well built, with spacious and regular streets shaded by linden trees. It has three Evangelical churches, a synagogue, a gymnasium, a higher burgher school, a public library, a hospital, and an infirmary. In the market square there is a statue by Rauch of Frederick William I., who in 1724 raised Gum-binnen to the rank of a town, and in 1732 brought to it a number of persons who had been driven from Salzburg by religious persecution. On the bridge over the Pissa a monument has been erected to those of the inhabitants who fell in the Franco-German war of 1870-71. Iron founding and the manufacture of machinery, wool, cotton, and linen weaving, stocking-making, tanning, brewing, and brandy-making are the principal industries. There are horse and cattle markets, and some trade in corn and linseed. The population in 1875 was, including the garri-son, 9114.

GUMBO, or OKRA, termed also Okro, Ochro, Ketmia, Gubbo, and Syrian Mallow (Sanskrit, Tindisa ; Bengali, JDheras ; Persian, Bamiyah _— the Bammia of Prosper Alpinus ; French, Gombaut, or better Gombo, and Ketmie comestible), Hibiscus esculentus, L. (H. longifolius, Roxb. ; Abelmoschus escule/itus, Guill. and Perr.), an herbaceous hairy annual plant of the natural order Malvacece, a native of the Old World, and now naturalized or cultivated in all tropical countries. The leaves are cordate, and 3 to 5-lobed, and the flowers yellow, with a crimson centre ; the ovary is 5-celled, and the fruit or pod, the Bendi-Kai of the Europeans of southern India, is a tapering, 10-angled, loculicidal capsule, 4 to 10 inches in length, except in the dwarf varieties of the plant, and contains numerous oval dark-coloured seeds, hairy at the base. Three distinct varieties of the gumbo (Quiabo and Quimgombo) in Brazil have been described by Pacheco. The unripe fruit is eaten either pickled, or prepared like asparagus. It is also an ingredient in various dishes, e.g., the gumbo of the Southern United States, and the calalou of Jamaica ; and on account of the large amount of mucilage it contains, it is extensively consumed, both fresh and in the form of the prepared powder, for the thickening of broths and soups. For winter use it is salted, or sliced and dried. The fruit is grown on a very large scale in the vicinity of Constanti-nople. It was one of the esculents of Egypt in the time of Abul-Abbas el-Nebâti, who journeyed to Alexandria in 1216 (Wiistenfeld, Gesch. d. Arab. Aerzte, p. 118, Gott., 1840), and, according to Popp, is still cultivated by the Egyptians, who called it Bammgé.
The seeds of the gumbo are used as a substitute for coffee. From their demulcent and emollient properties, the leaves and immature fruit have long been in repute in the East for the preparation of poultices and fomentations. Alpinus (1592) mentions the employment of their decoction in Egypt in ophthalmia, and in uterine and other complaints. In the Pharmacopoeia of India the decoction of the fruit is recommended in catarrh, and in diseases of the genitourinary tract, and its hot vapour in affections of the throat and fauces.
The Musk Okra (Sanskrit, Latdkasturikd, cf. the Greek ___-___ ; Bengali, Latdkastnri ; German, Bisamkornerstrauch ; French, Ket-mie musquée), Hibiscus Abelmoschus, L. (Abelmoschus moschatus, Mch. ), indigenous to India, and, it is said, to Guiana and Central America, and cultivated in most warm regions of the globe, is a suffruticose plant, bearing a conical 5-ridged pod about 3 inches in length, within which are numerous brown renif orm seeds, smaller than those of H. esculentus. The seeds possess a musky odour, due to an oleo-resin present in the integument, and are known to per-fumers under the name of ambrette as a substitute for musk, instead of which drug it has been proposed to employ them medicinally. They are stated to be used by the Arabs for scenting coffee. In India they are employed for perfuming medicinal oils, and being regarded as tonic and carminative form part of sundry pharmaceu-tical preparations. The seeds (in the Fantee language, Incroma-horn), as we learn from Mr E. M. Holmes, are used in Africa as beads ; and powdered and steeped in rum they are valued in the West Indies as a remedy for snake-bites. The plant yields an excellent fibre, and, being rich in mucilage, is employed in Upper India for the clarifying of sugar. The best-perfumed seeds are reported to come from Martinique.
See P. Alpinus, De Plantis AEgypti, cap. xxvii. p. 38, Ven., 1592; Macfadyen, Tile Flora of Jamaica, p. 67, 1837; J. Sontheimer's Abd Allah ibn Ahmad, &c, i. p. 118, Stuttg., 1840-42; P. P. Pacheco, "La Ketmie Potagère ou Comestible," La Belgique Horticole, iv. p. 63,1853; Della Sudda, " De l'Emploi à Constantinople de la Racine de l'Hibiscus esculentus," Répert. de Pharm., Jan. I860, p, 229; Bentham and Hooker, ___. Plant., i. pp. 207, 208, 1S62 ; Griscbach, Flora of the Brit. West Ind.Is^ p. 84, 1864; E. J. Waring, Pharm. of India, p. 35, 1868; _. Popp, "Ueber die Aschenbestandtheile der Samen von Acacia nilotica und Hibiscus esculentus in Aegypten," Arch, der Pharm., cxcv. p. 140, 1871; Hooker, Flora of Brit. India, i. pp. 342, 343, 1872 ; Drill')', The Useful Plants of India, pp. 1, 2, 2d edit., 1S73; U. C. Dutt, The Mat. Med. of the Hindus, pp. 123, 321, 1877; and Lanessan, Hist, des Brogues, i. pp. 181-184, 1878.




Footnotes

For varieties of gum arabic, see Pharmacographia, pp. 209, 210 ; Catalogue Museum Pharm. Soc., pp. 37, 38 ; also Pereira, Mat. Med., vol. ii., pt. ii., p. 334 ; for physiological properties, Pavy, Foods and Dietetics, 2ded., pp. 112, 438 ; and for chemistry, Watts's Dictionary, vol. ii. p. 953.