Under this name a number of substances resembling in their properties acacia gum, tragacanth, or cherry gum have been grouped together. They are all insoluble in alcohol, ether, etc, but dissolve or at least swell in water, yielding either viscous adhesive solutions or gelatinous mixtures.

When submitted to carefully regulated hydrolysis with dilute mineral acids various sugars are produced, but the gum is not entirely converted into sugars, about 20 per cent, resisting such treatment. This residue has proved in each gum investigated to be an organic acid with which the various sugars separated during the hydrolysis have been combined. Hence the gums must be regarded as consisting of glucosidal acids of high molecular weight. In some gums these acids exist almost wholly in the free state, but in the majority of gums they are partly combined with potassium, magnesium, or calcium in the form of salts.

Amongst the sugars that have been obtained from gums are the pentoses, arabinose, xylose, and tragacanthose, and the hexose, galactose. In addition to the glucosidal organic acid gums contain mineral matter (up to 5 per cent.) together with small quantities of sugars and of nitrogenous substances.

Gums are yielded by trees and shrubs belonging to a number of natural orders, but especially Leguminosoe, Bosaceoe, Rutaceoe, Ana-cardiacece, Combretaceoe, and Sterculiaceoe. They are produced by the conversion of the cell-walls of the tissues into gum (gummosis), doubtless by means of a diastasic enzyme of the origin of which nothing definite is known. Typical gums (acacia gum, cherry gum) are formed as a protective coating after the infliction of injury on the tree, and are to be regarded as pathological products. Mucilages, on the other hand, are normal products of the plant and are secreted in certain cells. Tragacanth occupies an intermediate position as it is not a pathological product.

The so-called artificial gum (dextrin) produced from starch differs essentially from the gums in being entirely converted into dextrose by dilute mineral acids; it is strongly dextrorotatory, most gums being slightly laevorotatory.