Many have tried to account for the uses of the Yolk, but nothing like satisfactory conclusions have been come to: some considering it goes to form the filament, and is consolidated into a transparent mass while the pile is growing; while others argue, that it is a peculiar secretion which exudes through the skin, and by mixing with the pile renders it soft and pliable, affecting it in the way that oil does a piece of leather. In the latter opinion I coincide. For my part, I view it as a secretion, depending very much on good food and steadiness of temperature, and, therefore, indicative of a fine fleece only so far as the health of the animal is concerned. In the human being the state of the skin may often guide us, though blind-fold, to the quality of the hair, so that the latter may be pronounced either dry and coarse, or glossy, soft, and silky, as the skin may prove either harsh and ungrateful, or pleasant, and, if I may be allowed the expression, alkaline to the touch. Every thing having a tendency to affect the health may always be considered as calculated to diminish this secretion, and, consequently, to deteriorate the quality of the wool.

The relative positions of the layers of the skin, the mode in which the hairs rise from them, and the form and situation of the sebaceous follicles, will be better understood by referring to the following cross section Fig 5. Pl. V., in which the line marked

(28.) Periodical decidence of Wool.—It is affirmed that the only real difference between hair and wool is in the latter falling off periodically; but the same change takes place in animals totally covered with hair; in fact, almost every animal is subject to moulting, or a periodical decidence of its protecting covering. The fleece of the sheep has been proved in many instances not to be liable to annual changes of this description;—Lord Western having, among others, shown that the wool of the merino may be retained at least three years without the slightest disposition to separate.

The annual employment of shearing, to anticipate this falling off of the wool, is now common in most parts of the world; yet some, as the Icelanders and Kamtschadales, still retain the primeval custom of rowing, or pulling off the fleece in a mass, about the end of May, at which time it is nearly loosened. This loosening of the attachments of the fibre is supposed to be owing to a diminution, during winter, of the nutritive process at the root of the hair, so that the fibre is liable to give way at the tender part when the fleece becomes heavy during Spring. This attempt at an explanation meets, however, with the insurmountable objection, that long-woolled are less liable than short-woolled sheep to this occurrence, a circumstance which ought to be the reverse, if weight had any thing to do in the case.

(29.) Falling off of Wool prevented by Clipping.—Clipping has a curious influence over the duration of the covering of animals, as is well exemplified by the correct popular idea, that the only way to prevent the hair of children dropping off (as it sometimes has a tendency to do) is to cut it short: we may suppose the benefit in this case to result from the removal of a portion of each hair, which, if allowed to remain, would lead to a sacrifice of the whole, by robbing the root of a quantity of nutritious matter, which, owing to a diminution of reproductive power, it could ill afford. In this way only can we account for the power which shearing evinces, in putting a stop to the attempt sometimes made by nature to change the coverings of some sheep. In the valley which separates the most eastern chain of the Cordilleras from the central, the wool grows upon the lambs in the same manner as in temperate climates, provided they are sheared so soon as it has arrived at a certain thickness; in which case the wool grows again, preserving the same order. But, if the period for denuding the animal be allowed to pass, the wool detaches itself in flakes, leaving behind a short, glossy, and compact hair, exactly resembling that of the common goat in the same climate.

(30.) Form of woolly fibre.—The fibre of wool is circular, differing in diameter in the various breeds, and different parts of the same fleece. The following à propos observations are from the article on the Sheep, in the Library of Useful Knowledge: "The filaments of white wool, when cleansed from grease, are semitransparent; their surface in some places is beautifully polished, in others curiously encrusted, and they reflect the rays of light in a very pleasing manner. When viewed by the aid of a powerful achromatic microscope, the central part of the fibre has a singularly glittering appearance. Very irregularly placed minuter filaments are sometimes seen branching from the main trunk, like boughs from the principal stem. This exterior polish varies much in different wools, and in wools from the same breed of sheep at different times. When the animal is in good condition, and the fleece healthy, the appearance of the fibre is really brilliant; but, when the sheep has been half starved, the wool seems to have sympathized with the state of the constitution, and either a wan pale light, or sometimes scarcely any, is reflected."

The more transparent the filament the better is the fleece, and its value is impaired by the transparency being different in the same fleece, or, as often happens, in the same filament; while that which possesses fineness with a close ground, pureness, elasticity, colour, tenacity, and not much pitch-mark, is the most esteemed, and preferred by the manufacturer. Wethers have considerably more wool than ewes. In every fleece there are several qualities, even so many as nine different sorts, which are all separated from each other in England by men called woolstaplers, who are appointed for the purpose, and sworn to do justice between the grower, and the merchant or manufacturer. In this manner the latter obtains, without trouble or risk, the very kind which he knows will suit his purpose; for though the sorter, surrounded by a number of baskets, divides the wool according to its properties without the slightest hesitation, and with a rapidity truly surprising, yet such is the amount of the dexterity acquired by practice, that a mistake seldom occurs, and his judgment can as rarely be disputed.

(31.) Structure and properties of Hair and Wool.—Each hair is composed of a number of filaments, or smaller hairs, ranged side by side, and this we can perceive without the slightest trouble, from the tendency it sometimes has to unravel at the apex; and again, by drawing a hair through the fingers from point to root, when we feel a roughness occasioned by projecting filaments, which only proceed a certain distance up the trunk, the longest being most internal.

Pl. V. Fig. 5, e, exhibits those points in a hair considerably magnified.