OF AIEMBRANE.
BEFORE we proceed to give an account of any of the Before we proceed to give an account of any of the individual parts of the body, it will be proper to explain the term organization, as it is of frequent occurrence in physiology, and one, with the import of which it is pro per for us to be acquainted. In its most extensive accep tation, it may be regarded as nearly synonimous with the word arrangement, signifying that the parts of the or ganized body are placed according to some specific struc ture which is visible to the eye. Thus the serum of the blood, when coagulated and dried, in its chemical and mechanical properties, almost entirely agrees with mem branous matter, yet its texture is obviously different. The serum is not organized ; it has a perfectly homogeneous fabric, is cut or broken with equal facility in every direc tion, whereas, in a tendon which is organized, there is a regular distribution of the particles in a specific form, and according to a determinate arrangement.
The word organization is used by' physiologists in a more restricted, but, at the same time, in a more correct sense, when it is applied to a system composed of a num ber of individual parts, possessing each of them appro priate powers and functions, but all conducive to the ex istence and preservation of the whole. An animal body is thus said to be organized, or to consist of a number of organs or instruments. A vegetable, in like manner, is an organized being, composed of separate parts, as the root, the sap vessels, and the leaves; each of them con stituting a separate organ or instrument for performing some appropriate action, yet all composing one connected system. It is this species of organization which properly distinguishes living from dead matter ; and, where we are able to ascertain its existence, it may be regarded as a sufficient characteristic of the presence of life.
Under the term membrane, we propose to include, not merely those parts to which this name has been usually applied, but all those substances, whatever be their form, which possess a similar mechanical structure, and the same chemical properties. They nearly coincide with the white /tarts of the older anatomists, and with the cellular texture of Haller; but the former of these terms is ob viously too vague, and we conceive the latter to be objec tionable, as implicating a theoretical opinion respecting their nature, which is at least doubtful, if not incorrect.
According to this method of employing the term, we shall find the membranous matter to be the most simple in its properties of any of the organized parts of the body, while, at the same time, it is the most extensively diffused, and exists in the greatest proportion. The coverings, not
only of the whole body at large, but of each of its indi vidual parts, both internal and external, are principally composed of membrane, and it lines all the cavities in which the different organs are situated. It constitutes the main bulk of the bones, and determines their figure, the earthy matter upon which their strength and hardness de pend, being deposited in a tissue of membranous cells. Membrane also enters into the structure of the muscles, not only affording them an external sheath, in which they are each of them enclosed, but the same matter is also in terspersed between their fibres, separating them into bun dles, to which it, in like manner, affords a distinct cover ing, and these into still smaller bundles, until it appears at length to envelop each individual fibre. The mem branous matter composes very nearly the whole substance of the tendons, by which the muscles are attached to the bones; the ligaments, by which the bones and solid parts arc connected to each other, and the cartilages, which form the basis of many parts of the body, and supply the place of bone, and which also cover the ends of the bones, and assist in the formation of the joints. It enters very largely into the composition of horns, hair, feathers, nails, and other similar substances. It likewise composes what is called the cellular texture,a series of cells or interstices, which have been compared to those of a sponge, which extends over a great part of the body, fills up its intervals, and serves to unite the different parts to each other. The membranous matter chiefly forms the glands, and the viscera of all kinds; the brain is also enveloped in a covering of membrane, and it is probable that the matter of which the nerves are composed is deposited in a series of membranous cells. The pouches or bags, which are found in different parts of the body, such as the stomach and the bladder, are altrost entirely composed of mem brane; and what, perhaps, must be regarded as the most important of all the purposes which it serves, membrane composes the principal part of the tubes or essels of various kinds, with which the animal body is so plentifully furnished.