[Fr., from Gk. kommi.] The sticky or adhesive juice of certain trees or plants. Vegetable resins are insoluble in water, but soluble in spirits. Gum resins are soluble in either water or spirits. Gum copal is a fossil dug out of the ground in various parts of the earth. It is brought in large quantities from the east coast of Africa. It is found in the sandy plains about a foot from the surface, and is derived from trees of recent times, while amber is from forests of a past geological period. Gum arabic is the juice of several acacia trees that grow in Arabia, India, and Africa, and dissolves in water. Dextrin is made from starch by mixing it with nitric acid, and is now used instead of natural gums. It is used in calico-printing and for postage-stamps. The Gum tree of Australia is the eucalyptus (q.v.), with rigid leaves turned to the zenith, and secreting resinous gums. Two American trees are known as the sour gum and the sweet gum.