(From fiber, extreme). A fibre. Haller observes, that the least discoverable fibres are of two kinds. The first are lineal; the second are conjoined with a breadth frequently larger than their length; and the latter, he informs us, are those of which the cellular membrane is made up.

On the different proportions of the terrestrial matter.

and the gelatine which forms the simple fibre, depend probably their different degrees of cohesion, and from hence Boerhaave deduces the general source of diseases. Sec Boerhaave's Aphorisms, and Haller's Physiology, under the title of Animal fibre.

Each of these opinions, however, is fallacious; and indeed, when we speak of the cellular substance as a fibre or a membrane, we convey ideas which mislead. The human body seems to be originally fibrous. At the earliest period when the embryo can be subjected to our senses, it seems to resemble the tadpole, with a tail only extended from a rounded head. There appears to be little doubt of this being exclusively the brain and spinal marrow, for the lower extremities are developed at a much later period. If this be true, the fibrous structure of the human body is only the nervous system; on its fibres are deposited the nutriment formed in successive eras by the powers of the constitution, and these direct the form and the shape of the different parts of the body. In reality, this is the moule interieure of which Buffon so often speaks. This system, which we hope to render more probable in other parts of the work, requires that the productions of this aboriginal nervous germ, viz. the nerves, should be convoluted within a small space, capable of a certain degree of extension, different according to the organs which they are to form or supply. Beyond this power of extension, or, in other words, their length, the organ cannot expand; and the different extent of the nerves, in each part, depends on the individual constitution. This theory involves no contradiction, scarcely any difficulty, except the extreme minuteness of these fibres; but minuteness is only relative, and will disappear, if we reflect that even the mite probably nourishes some parasite animal, and that this last must possess vessels, arteries, and muscular fibres, peculiarly its own.

According to these views the fibrous ports of the human body are the nerves, the muscles, the blood, and absorbent vessels; consequently the great bodies of the glands, as composed of vessels and membranes. The other parts are the cellular substance, which is only a connecting medium, and which, in every instance of adhesive inflammation, is formed before our eyes.

The diseases of the fibres are only those from too great rigidity or laxity; but, if we consider these as nervous, or prolongations of the brain and spinal marrow, we shall reduce them to excessive tone and relaxation. The connection between the state of the simple fibres and the nervous system we have already noticed at sufficient length. See Astringentia.

The strength or weakness of a fibre is wholly relative. Soon after conception the cohesion may be destroyed by the slightest touch; but the cohesion increases till the degree is attained which gives perfection to the being. The perfection of cohesion is when a fibre will bear a greater force than what its state and office regularly require. Many, though equally unsatisfactory, are the rules laid down to distinguish betwixt the rigid and lax fibre, in particular constitutions; but with a view to practice, a rigid fibre is a concomitant of strength, and the lax fibre of its deficiency.