In most uncivilized nations this conversion was accomplished by rubbing and working some oily or greasy substance into the hide, until it was thoroughly soft and flexible. Thus, in our Indian tribes, the old squaws would turn the deer skins and the pelts of various fur-bearing animals into beautifully soft and strong leather, by rubbing and working into them the brains of the animals. The Esquimaux and other Northern tribes from time immemorial, too, have worked out this method with great perfection. Indeed without it they would have been unable to survive at all. In other parts of the world it was discovered that rawhide could be made more durable by treatment with metallic salts, especially with alum, and then, by softening this product by rubbing in some oily material, a very fair leather could be produced. On the other hand, in warmer climates, as for instance among the Egyptians, the very earliest records show the use of vegetable extracts, containing the substances now known as tannins, for softening and preserving skins; and these races understood the art of dyeing, painting, gilding, and embossing the leather thus made, and used it for shoes, straps, aprons, and harness. The Romans and Babylonians were famous for their leather industry, and the ancient Romans not only imported but manufactured it themselves, and used it freely. In the Middle Ages the greatest developments in the art were made by the Moors in Spain, whose leather, commonly called Cordovan leather, from the city which was the centre of the industry, has probably never been equalled for beauty and importance. This Cordovan leather, of which fine specimens are still to be found in museums and private collections, was made of sheepskin, tanned with bark. It was ornamented with silver foil, laid on a backing of size, and covered with a yellow varnish or lacquer, sometimes tinted with bitumen. This protected both the leather and design very perfectly from injury by air or moderate moisture, and, being done on a large scale with splendid designs, was used largely for handsome wall coverings, competing favorably with tapestries manufactured in France and elsewhere for the same purposes. PREPARATION OF LEATHER. In general, we may say that at the present day there are the same three classes of leather as in the days of the ancients, according to whether the hide is treated with oil or fatty materials, with alum or other metallic salts, or with the bark of trees or other vegetable substances containing the compound known as tannin.