It is, however, to be remarked, that, by far the greatest part of the gum which is sold in the shops under this name is not such, but is the production of another species of tree (Mimosa Senegal), and is properly called gum Senegal, The latter is imported from Senegal, Guinea, and other parts of Africa. It is generally seen in large rough pieces, of roundish figure, and brownish hue, more or less pure; possesses similar properties to the other, and is much cheaper.
On account of their mucilaginous qualities, these two kinds of gum, under the name of gum arabic, were formerly used for several purposes in medicine; and, in coughs and hoarsenesses, were considered of great service. They are now principally in request by the manufacturers of water-colours; by dyers, and artificers of different kinds. In Africa the latter constitutes a principal ingredient in the food of the inhabitants. They sometimes dissolve it in milk: and this solution of it is esteemed a favourite repast by some of the tribes.
The dried juice of the unripe fruit of Egyptian mimosa is called acacia, and is to this day much used in medicine by the Egyptians. It is sometimes imported into this country in roundish masses, wrapped in thin bladders; and is externally of deep brown colour, and of a yellowish or reddish brown within.
274. MYRRH is a gummy, resinous substance, obtained from a tree which grows in Abyssinia, Arabia, and other countries of the East, but respecting which we are hitherto possessed of no certain account. Mr. Bruce, however, imagined it to be a species of mimosa.
This drug is generally imported in a kind of grains, of irregular form; of brownish or reddish yellow colour, and somewhat transparent. Its smell is aromatic; and its taste is pungent and bitter. In its medicinal effects, myrrh, when taken into the stomach, is supposed to warm and strengthen it, and also to strengthen the other viscera. It is believed to resist putrefaction in all parts of the body; and, hence, has been recommended as a medicine in malignant, putrid, and pestilential fevers; and in small-pox.
At the East India Company's sales this drug is sold at the rate of about twenty pounds per hundred weight. It is, however, liable to great abuses. The larger masses, in particular, are frequently an artificial composition, skilfully incrusted with a coat of myrrh.
DIŒCIA.
275. MANNA is a concrete or dried juice, procured from several species of ash-tree, but particularly from the Flowering Ash (Fraxinus ornus, Fig. 76), which is much cultivated in Calabria and Sicily.
This tree somewhat resembles the common ash. It has winged leaves, with an odd one at the end, the leaflets oblong, pointed, serrated, and veined, standing on footstalks, and of bright green colour. The flowers are whitish, and appear in close bunches, about the month of May or June.
The trees that are cultivated for the production of manna are chiefly planted on the eastern sides of hills. This substance exudes spontaneously from them; but as the supply thus obtained would be insufficient for the demand, incisions are made in the bark to obtain it more copiously. These incisions are formed, in the summer time, lengthwise in the tree, and each about a span long. They are begun at the lower part of the trunk, and repeated upward, at a little distance from each other, as high as the branches. One side of the tree is first cut; the other side being reserved until the ensuing year, when it undergoes a similar treatment. From the wounds thus made a thick whitish juice immediately begins to flow, which gradually hardens on the bark, and in the course of a few days acquires a sufficient consistence to be taken off. It is collected in baskets, and afterwards packed in chests or boxes. Sometimes the manna flows in such abundance that it runs upon the ground, and thus becomes mixed with various impurities, unless it be prevented, as is sometimes the case, by placing for its reception large leaves, stones, chips of wood, or straw. The collecting of manna generally terminates about the end of September.