Manna is the dried saccharine juice exuded from the stems of Fraxinus Ornus, Linn., and F. rotundifolia (N.O. Oleaceae), small trees cultivated for the purpose in Sicily. It is official in the U.S.P. When the trees are about ten years old, a vertical series of oblique incisions is made; the juice which slowly exudes either dries on the stem (flake manna) or, in wet seasons, it drops from the stem and is caught upon tiles or cactus leaves, yielding inferior qualities in the latter case. Flake manna, which is the best variety, occurs in yellowish-white, brittle, stalactitic masses about 10 to 15 centimetres long, and 2 to 2.5 centimetres wide. They are more or less evidently triangular in section, the side by which they adhered to the tree being smoother than the others, and slightly concave. They are indistinctly crystalline in structure, have a slight, agreeable odour, and sweet taste. Inferior qualities (small or broken manna) consist of fragments agglutinated together, and are often darker in colour, and more glutinous, than flake manna. The term manna is extremely old, and is applied to the saccharine exudation of a number of plants, e.g., Quercus Vallonea, Kotschy, and Q. persica, Jaub. et Spach. (oak manna), Alhagi maurorum, Medic. (alhagi manna), Tamarix gallica, var. mannifera, Ehrenb. (tamarisk manna), and Larix Europaea, DC. (Briançon manna). None of these, however, has any commercial importance.
Constituents.—The chief constituent of manna is the hexahydric alcohol mannite (mannitol), C6H8(OH)6, of which it may contain from 40 to 60 per cent. Other constituents are manneotetrose (12 to 16 per cent.), manninotriose (6 to 16 per cent.), dextrose, mucilage, water (about 10 per cent.), and traces of a fluorescent substance (fraxin). Mannite can be isolated from manna by extracting with hot alcohol, cooling, and recrystallising the crystals that separate. Melting-point, 165° to 166°; specific gravity, 1.489; soluble in 6.5 of water at 16°; easily soluble in hot alcohol, sparingly in cold. Optically inactive. Manneotetrose is dextrorotatory, and each molecule yields on hydrolysis two molecules of galactose and one each of dextrose and levulose; each molecule of manninotriose yields two molecules of galactose and one of dextrose.
Action and Uses.—Manna is employed as a gentle laxative for infants and children. For the former, a piece about the size of a hazel-nut is dissolved in a little warm water and added to the food. To children, 2 or 4 grammes (30 to 60 grains) may be given dissolved in warm milk, or a mixture may be prepared with syrup or syrup of senna, and dill water. Syrups of manna are prepared, with, and without, other purgatives. Manna is sometimes used as a pill excipient, especially for calomel.
Dose.—4 to 16 grammes 60 to 240 grains).
- Syrupus Mannae, B.P.C. and Ph.G.—SYRUP OF MANNA. 1 in 10.
- A mild laxative for children. Dose.—4 to 15 mils (1 to 4 fluid drachms).
- Syrupus Mannae Compositus, B.P.C.—COMPOUND SYRUP OF MANNA. 1 in 10.
- Contains manna, senna, and fennel. A stronger laxative than Syrupus Mannae. Dose.—4 to 15 mils (1 to 4 fluid drachms).