Gum Resins , inspissated juices of certain plants, obtained by spontaneous exudation or from incisions purposely made. They consist of resin and gum, the proportions varying in the different varieties, and with these are commonly associated essential oil, and other vegetable substances, as starch, bassorine, extractive, etc. They are most of them hard and dry substances, brittle and opaque, rarely translucent like the resins. Some that are semi-liquid and viscid, as the sagapenum and galba-num, become hard in very cold weather, and may then be pulverized. At a moderate heat these are sufficiently fluid to be strained through a cloth; and all the gum resins may be thus strained and purified by first boiling them in water. They are partially soluble in water or in alcohol, and wholly so in a mixture of these. In water alone the gum dissolved holds for a time the finely divided resinous portion suspended, and thus emulsions are prepared for administering the substances in medicine, which is their principal use. Balsams are distinguished from gum resins by containing benzoic acid.
The most important gum resins are described in separate articles, as aloes, ammoniac, asa-foetida, bdellium, euphorbium, galbanum, gamboge, myrrh, sagapenum, scammony, etc.