TISSUE, a very fine transparent silk stuff used for veils; white or colored. It was formerly interwoven with gold or silver threads and embossed with figures. Also a very thin kind of paper and cloth interwoven with gold. In entomol ogy, a European geometer moth, Scotosia dubitata. The fore wings have numer ous transverse wavy lines; the larva feeds on buckthorn.
In histology, a set of cells modified for the performance of a special function; the fabric of which the organs of plants and animals are composed. The struc ture of tissues, with very few excep tions, is imperceptible to the unassisted eye, and requires the aid of the micro scope for its resolution. Tissues which are absent from plants occur in animals; these are called animal tissues, and have a relation to movement or to sensation, as the muscles and nerves. But plants preserve, protect, and sustain themselves, and the corresponding tissues in animals are spoken of as the vegetable tissues; of this kind are epithelium and bone. Tis sues always present the same general ar rangement in the same organism, but are combined in different ways in different organisms. In the lower forms of life, whether animal or vegetable, the distinc tions between tissues become less and less obvious, and there are organisms so ex tremely simple that the tissue of their bodies is of a uniform cellular charac ter.
Animal Tissues.—The term tissue is used in dealing with (a) the structure of organs, which are composed of various tissues; and (b) specially of the com ponent parts of organs. In the first and wider sense, the anatomical individual is made up of osseous tissue, or bone; mus cular tissue, or flesh; adipose tissue, or fat; cartilaginous tissue, or gristle; con nective tissue, serving to bind the whole together; and pigmentary tissue, or color ing matter. In dealing with animal tis
sues in the strict sense, histological analy sis shows them to be much more dif ferentiated and elaborate in structure than those of plants. They may be divided into (a) Epithelium, consisting of nucleated protoplasmic cells, forming continuous masses, either arranged in a single layer, or stratified and forming several superimposed layers. The lining of the tubes and alveoli of secreting and excreting glands and the sensory or ter minal parts of the organs of sense consist of epithelium. (b) Connective tissue, a name applied to a variety of tissues de veloped from the same embryonal ele ment, serving more or less as framework or connecting substance for nervous, mus cular, glandular, and vascular tissues. In the embryo and in the growing condition one may be changed into the other, and in the adult they gradually shade off one into the other. These tissues are divided into three groups: The epidermal, which covers the exterior of the plant, and usu ally consists of a single layer of cells; (2) the fibro-vascular, which traverses the body of the plant in the form of bundles, and is characterized by the pres ence of tubes and vessels, and of long, pointed, prosenchymatous cells the wood fibers; (3) the fundamental tissue, which fills up the rest of the space, and con sists principally of parenchyma.