As has been said, felt may be made of any kind of animal fur, wool, or hair, provided it be bent, crimped, or curled, for if straight as a bristle it would work out of the mass as readily as into it, and lose itself in the operator's hands. All materials intended for felting must be cut from the pelt or skin, and not pulled, for the obvious reason that a pulled hair invariably brings with it its root, in the form of a button or bulb, which would greatly impede its progressive motion in the act of working, as each and every hair under the operation of felting bores into and amongst the other filaments of the fur composing the mass, root end foremost, a sharp point therefore is obtained by cutting. This rule is universally and invariably adopted by all hat furriers. Wool of any great length of staple, after being carded, is pressed, and either clipped, cut, or chopped into shorter lengths, which facilitates the felting operation, and improves the solidity of the felt that is produced.[B] The various materials most used in hat-making are the furs of the beaver, the otter, the rabbit, the hare, a species of the muskrat, a species of the monkey, a species of the seal, and a few others, together with Saxony and Spanish wools and the hair of camels and goats. Numerous as are these various names, most of the animals produce five or six different qualities of stuff, from particular parts of the same skin, varying greatly in price or value. The finest furs all come from those animals that inhabit the coldest climates, and the season of the year in which any of them are killed greatly influences the quality of the fur; a summer skin of some of these animals being comparatively valueless, however excellent it might be in the winter season. And what is particularly worthy of the hatter's attention is, that fur that has been kept one or two years, after being cut from the skin, produces a better working, and a more solid article of felt, than fur from a newly-killed animal. The lamina of such fur seem to rise and erect themselves upon the stem of the hair by being kept, which may account for its better felting quality. This would appear to be confirmed by the well-known fact that the 5 lb. bags in which old fur stuffs have been kept are generally burst open. One or two properties peculiar to furs and wools may still be mentioned, as, for instance, all felting, by whatever means accomplished, necessitates either a damp or wet process with the aid of heat, and the facility of thickening or solidifying is accelerated by the application of soap to the material under the operation. Or the water may be acidulated for the same purpose with a little sulphuric acid, as either of these acts as a penetrating solvent upon the natural oil of the animal which still remains between the stem and lamina or scales of the hair, thus baring the barbed points of the crusty scales, the better to catch and hold their grip upon each other.