Tissue (biology)

“ All animal and vegetable structure arises from cellular tissue, and in fact is either cellular tissue or, as in the case of bones, scales, etc., the mineral deposit formed by the action of cells. The simplest living forms are composed of single cells, and the most complex and huge of them were each once nothing more than a single cell, possessed of the powers of development and growth. ”

“ Throughout life, millions of these cells retain their primary characters, and constitute the white corpuscles of blood, "phagocytes," and connective tissue corpuscles; others again, engage in the formation of material round themselves, and lie, in such cases, as gristle and bone, embedded in the substance they have formed; others again, undergo great changes in form and internal structure, and become permanently modified into, for instance, nerve fibres and muscle substance. ”

“ In biology the word is of general use for an aggregate of cells forming a texture or fabric; in animal anatomy it is thus applied to the primary layers of which the parts are composed, and named by some qualifying word denoting its substance or its use (see Connective Tissue and Epithelial, Endothelial and Glandular Tissue) . ”

“ Bridges of protoplasm have been seen between epithelium-cells, and it is maintained that cartilage-cells, connective tissue cells, the cells forming muscle-fibres, as well as nerve-cells, have protoplasmic unions. ”

“ Each part of the animal body is formed by aggregations of different kinds of cells. The skin and the cavities within the body as well as the glands are composed of epithelial cells, the bones and muscles are produced by special bone and muscle cells. Uniting the various special structures and cell layers in the body, we find the so-called connective tissue consisting of special cells (connective tissue cells) and their product, the connective tissue fibers. ”

“ In the adult, the individuality of these cells is usually lost, since they are united to form membranes, tissues, and fibres. In nearly all animals the tissues thus built up from cells fall into four groups—epithelium, connective tissue, muscular tissue, and nervous tissue. ”

“ All living structures, whether animal or vegetable, are built up of cells (which we shall consider in due course) , and these cells are grouped together for different purposes to form different tissues. The tissues are the different materials of which the body is made. There are eight principal tissues in the body: bone, gristle, muscle, nerve, skin, fat, fiber, and connecting tissue. ”

“ As a matter of fact, the idea that parts of the tissues of different animals may serve to replace one another has been employed repeatedly in science, especially in the science of medicine. But I believe that our ideas are not yet clear upon the matter. The erroneous impression to which I have alluded has arisen because we do not bear in mind that each tissue, each part of an organ, each cell, possesses, in addition to its obvious characters, very many characters that are invisible to us. ”

“ The constituent cells of the tissues of the plant retain their original form and individuality, while, in the animal, they undergo the greatest modifications, and their individuality is usually entirely lost. A vegetable tissue or organ may easily be shown to be made up of a mass of nearly similar cells, each of which is independent and sharply defined; while the tissues of animals present the greatest differences in structure and appearance, and sharply-defined individual cells are seldom to be seen. ”

“ In the third class come tissues the cells of which have fused by their walls, but whose cell-cavities are not in continuity, such as osseous tissue and cartilage. In the tissues of the fourth class, comprising the most highly specialised of all, not only are the cell-walls continuous but also the cell-cavities ”

“ It will be observed that the blood corpuscles, the epithelial tissues, the ganglionic corpuscles, the ova and the spermatozoa, are all demonstrably nucleated cells, more or less modified. The first form of connective tissue is so similar to epithelial tissue, that it may obviously be regarded as an aggregate of as many cells as it presents nuclei, the matrix representing the more or less modified and confluent bodies of the cells, or products of these. ”

“ I close the present one with one more protest against the entirely absurd terms 'par-enchyma,' for common cellular tissue, 'pros-enchyma,' for cellular tissue with longer cells;—'cambium' for an early state of both, and 'diachyma' for a peculiar position of one! [46] while the chemistry of all these substances is wholly neglected, and we have no idea given us of any difference in pith, wood, and bark, than that they are made of short or long—young or old—cells! ”

“ A tissue represents an aggregate of similar cells with the intercellular substances in relation with these as connective tissue, muscular tissue, etc. Where such cell aggregates are localized and where the cells are arranged in structures having definite form and size and performing a definite function, it is customary to designate such structures as organs, as the brain, liver, etc. ”

“ As the body is composed of individual organs, and each organ of separate tissues, so each tissue is made up of minute cells. Each cell is a little world by itself, too small to be seen by the naked eye, but open to the microscope. It has its own form and constitution as much as a special organ in the body. It absorbs from the blood such food as suits its purposes. Moreover, the number of cells in an organ is as constant as the number of organs. As the organs expand with the growth of the body, so the cells of each tissue enlarge, but shrink again with age and the decline of life. ”

“ We see, then, that variation among these related cells has led to differences in size, in form, in transparency, and in function; while the cell-products have been differentiated into those which are of lifelong value, such as bone, cartilage, connective tissue, horn, chitin, etc., together with a variety of colouring matters; those which are of temporary value, such as the digestive secretions, fat, etc.; and those which are valueless or noxious, such as carbonic acid gas and urea, which are excreted as soon as possible. ”

“ If we take a slice of the bone and examine it, we shall find that it is very like this diagram of a section of the bone of an ostrich, though differing, of course, in some details; and if we take any part whatsoever of the tissue, and examine it, we shall find it all has a minute structure, visible only under the microscope. All these parts constitute microscopic anatomy or 'Histology.' These parts are constantly being changed; every part is constantly growing, decaying, and being replaced during the life of the animal. The tissue is constantly replaced by new material ”

“ Sometimes a number of cells are laid end to end, and, by the absorption of the transverse partitions, form a continuous tube, as in the sap vessels of plants, or in muscular and nervous fibre; and when the cells are thus woven together, they are called cellular tissue, which, in the human body, forms a fine net-like membrane, enveloping or connecting most of its structures. In pulpy fruits, the cells may be easily separated, one from the other; and within the cells are smaller cells, commonly known as pulp. Among the cells contents of some plants are beautiful crystals, called raphides. ”

“ Two fundamental forms of tissue were assumed from the first, the succulent cellular tissue composed of chambers or tubes, and, in contrast to this, the elongated usually fibrous or tubular elementary organs, the distinction of which into open canals or vessels and fibres with closed ends continued to be doubtful. ”

“ Eventually the component cells form the limiting epithelium of a series of follicles or vesicles embedded in a matrix of connective tissue and blood-vessels, and the characteristic adult structure is attained. ”

“ Of the Composition of the Tissues and of the Secretions in Health and Disease.—Having described thus individually the constituents of the tissues, we shall now present such results as have been hitherto obtained as to the quantitative composition of the organized tissues formed by their reunion, their secretory products and morbid alterations.
The skin of animals is a congeries of finely constructed organs, sensitive and secretory, imbedded in a peculiar tissue, which is one of those most yielding gelatine, whence the process of tanning skins. ”

“ This epithelium consists really of a modification of the upper layer of the skin, and we see this modification familiarly in the difference between the skin of the face and the layer which is infolded to form the covering of the lips and the lining membrane of the mouth. No tissue is more familiar to the student of physiology than epithelium, composed as it is of epithelial cells or microscopic elements, which in one form or another are found in almost every important tissue of the body. ”

“ The cells of bone differ from those of cartilage mainly in the different consistency of the substances secreted by the cells to lie between them; skin cells are soft-walled masses lying close together; even blood is a tissue, although it is fluid and its cells are the corpuscles which float freely in a liquid serum. Thus an organism proves to be a complex mechanism composed of cells as structural units, just as a building is ultimately a collection of bricks and girders and bolts, related to one another in definite ways. ”

“ An organ may be composed of several tissues. Thus the heart has contractile tissue in its muscular walls, epithelial tissue lining its cavities, and skeletal tissue forming its framework. Still, notwithstanding their aggregation [21] into tissues and organs, it remains true that the body of one of the higher animals is composed of cells, together with certain cell-products, horny, calcareous, or other. The simplest animals, called protozoa, are, however, unicellular, each organism being constituted by a single cell. ”

“ For instance, in a given tissue or organ, not all cells are capable of dividing into two daughter cells. In the epidermis, which is the thin outer layer of the skin, only cells in the deepest portion can divide. ”

“ The different materials found by such a dissection correspond closely to the substances, called tissues, which make up the human body. The main tissues of the body, as ordinarily named, are the muscular tissue, the osseous tissue, the connective tissue, the nervous tissue, the adipose tissue, the cartilaginous tissue, and the epithelial and glandular tissue. ”

“ From long years of practical experience I have found that the special cells of each tissue will take up only those constituents which they need for the construction of their respective tissue, as taught by the law of chemotaxis. ”

“ In cellular tissue is therefore the seat of life. But the vegetative mass simply lives that it may live, while the animal lives, in order to combine the universe337 with the life. The animal elements live only in order to feel and move, in order to act freely like the world; the vegetative only, that they may subsist as planet. The latter are an image of the planet, the former of the world; the one deal with matter, the other with spirit.
Integument.
1859. The cellular tissue does not continue a mere parenchyma in the animal as in the plant, but it obtains a definite anatomical form. ”

“ In the study of the minute structure of plants and animals the observer has frequently to deal with tissues and organs, most of which possess such softness and delicacy of substance and outline that, even when microscopes of the best construction are employed, the determination of the intimate nature of the tissue, and the precise relation which one element of an organ bears to the other constituent elements, is, in many instances, a matter of difficulty. ”

“ It seems probable, however, that these cells, separate as they seem, are in some cases united to each other by minute protoplasmic filaments. In the higher animals the cells in different parts of the body take on different forms and perform different functions. Like cells with like functions are also aggregated together into tissues. Thus the surfaces of the body, external and internal, are bounded by or lined with epithelial tissue; the bones and framework of the body are composed of skeletal tissue; nervous tissue goes to form the brain and nerves; contractile tissue is found in the muscles ”

“ Malpighi, Grew and Leeuwenhoek had chiefly set themselves the task of studying the different tissues in their mutual connection; the moderns were chiefly concerned to get a clearer understanding of the more delicate construction of the various tissues themselves, to know what was the true account of cell-structure in parenchymatous tissue, and the real nature of vessels and fibres. ”

“ To the fundamental system also belongs the chlorophyll cells of leaves, the thin-walled cells of the pith and medullary rays, the cells of the cortex of stems and roots, and most of the soft cellular tissues in all plants. 459
The lower plants consist almost entirely of fundamental tissue. In the herbaceous forms of the higher plants the ground tissues largely predominate, while in woody plants they are present in much smaller proportion, the vascular tissues being the most abundant. In aquatic plants generally, the fundamental tissues constitute the principal system. ”

“ It is a tissue found in large quantities under the skin, covering the muscles, the blood-vessels, and nerves, and in various parts forming a kind of protective covering for delicate and important organs. It is because of its general distribution, and because of its binding various structures together, that it is called connective.—In botany the term is sometimes applied to the non-vascular substance, composed entirely of untransformed cells, which forms the soft substance of plants. ”