Around the central cells, the next layers, comprising the chief thickness of the hair, by a process of lengthening and splitting, common in the economy of cells, are converted into fibres, and quite at the outer circumference a thin circle of cells is flattened into the form of scales, like those of the scarf skin. The arrangement of these scales is seen in the Merino, Southdown, end Leicester varieties, to be like that of the scales of a fish, though with less perfect regularity, and such differences as result from their being arranged around a cylindrical or oval form. They are the largest and most perfectly developed in the Lincoln, Leicester, and Southdown vasieties. In the Merino, the same perfection of arrangement is preserved, whilst they increase in nurnber and diminish in aize. Less regularity obtains in the Saxony, though the number further increases. With the larger diameter of the human hair, the scales are still less in magnitude, though greater in number. These observations lead to the conclusion that the order of growth is probably as follows :—(1) The secretion of the fluid obtained from the blood ; (2) its discharge from the gland ; (3) its conversion into granules, and then into cells distended with fluid ; (4) its protrusion to and through the exterior skin, where, on contact with the atmosphere, the outer layers of cells lose their liquid con tents by evapomtion, the cell-walls collapsing and flattening, so as to form the scales shown in such great numbers. This shrinkage of the cells causes the upper edges of each layer to overlap the base of those of the preceding one, thus composing the beautiful arrangement revealed by the microscope. The shrinkage being simultaneous all round the cylinder which forms the hair, the outer circles of cells form, as it were, a series of cups, tbe base of the upper one being inserted in the top of the lower one, by which in succession the hair is built up. Each cup is composed of the number of scales or collapsed cells required to form the circumference of the cylinder, and these having been globular, their arrangement in circlets gives the serrated upper edge to each cup. It is this peculiar mechanical structure of the wool fibre that adapts it so admirably for the purposes to which it is chiefly applied, as therein lies its felting capacity.
This. though Perhaps its chief characteristic, is not its only one ; another of hardly less importance is the spirally curling form of the fibre. Superficially, this constitutes the main dis tinguiahing quality between hair and wool. If a lock of wool be closely examined, each fibre will be seen to be twisted in a spiral direction from the base to the tip. The number of convolutions is greater in the fine or clothing wools than in the long or combing sorta. The processes through which wool is put in manufacturing woollen goods would to a great extent eliminate the curl of the long fibre ; but the greater number and the shorter apace occupied by the curl of the short wools allows them to be retained, by which means it is admirably adapted for the production of a woollen thread, which has to be fulled or partially felted in a subsequent atage. The more perfect parallelism of the fibres that would result in a yarn made from long wool would prove a great, if not an insuperable, obstacle to the satisfactory performance of the felting process. Figs. 1438, 1439 show this characteristic in both the clothing and combing varieties of wool.
The felting quality of wool, though known for centuries, or even thousands of years, was not thoroughly understood until the structure of the fibre was microscopically examined. It may
even be questioned now whether the fact is yet fully explained or not. The allegation that it is owing to the short curled lengths of the fibre (when spun into yarn or retained in the maaa) offering facilities for an interlocking of the fibres by means of the scales and convolutions, ia not quite satisfactory. The theory may fully account for the interlocking or entanglement of the fibres, but it leaves unexplained the principal characteristic of felting, viz. shrinkage. A woollen fabric, when subjected to moisture and warmth, ahrinks in every direction in a manner which the there interlocking of the fibres does not aufficiently explain. The first subjection to thia operation does not exhaust the property ; it may be repeated frequently, and the article will on every occasion be -further reduced in dimension. The introduction of acid into the bath in which the fabric may be dipped greatly accelerates the process, and increases its extent, aa is familiarly seen in the manu facture of felt cloths or hats. Thia is not in any way indebted to the milling process, though working the wool by the hands may be regarded as an equivalent. But this felting or shrinkage takes place without any such action, as, for instance, when cloth is dipped into water and hung up to drain in order to " shrink " it, as the proceas is technically called, before it is cut up for garment purposes. A similar result ensues, though to a less extent, in the cases of fabrics made from " non-felting " wools, as they are sometimes erroneously termed, when auch articles are inadvertently left in water, especially if the water is hot. The same effect is seen iu the case of dress fabrics of worsted materials, when the wearer gets caught in a shower of rain. Too often have such materials " run up " to such an extent as to render the dress unwearable afterwards ; and partially to this fact may be attributed the present unpopularity of Bradford goods.
It is proverbially easier to offer objections to an accepted theory than to propound a better, but it may be pertinent to observe that experience shows moisture to be essential to felting, and that the process is expedited and carried to a greater extent at a high temperature, or when the water employed is hot. It appears probable, therefore, that the wool fibre is partially dissolved, especially that part which contains the original cells still retaining their contenta. The walls of these cella, bursting by the heat or mechanical action, or a combination of both, and their contents being diacharged, shrinkage naturally takes place. The scales of the separate fibres, being in contact with one another, or already entangled, the fibres are drawn to each other, as it were, by a firm embrace. Probably also tho circlets of scales forming the seriea of oups of which the fibre appears to be composed may at the same time, and by the same canoe, be rendered capable of sliding more deeply one into the other. The pressure being exerted in each direction by the entangled acalea of the individual fibres, each of the latter is shortened in a corresponding degree, and shrinkage in every direction results thereby. This conjecture may be held to be supported by the fact that fine wools, which contain the greatest number of imbrications, are the best felting wools.