(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."