TISSUE

n. Ti2sh'u2. Gr., i<rr6?. Lat., text us. textura. Ma. Fr., ti u. Ger., Gewebe. A collection of cells or structural elements so modified in form, size, and arrangement as to have a constant and recognizable structure, wherever it may occur (being modified in different situations only so far as local connections and uses render nece ary), and to be adapted to the performance of a special and definite function. All of one kind of t. in the body forms a system, such as the nervous or the muscular system, while the fs combined form organs. While the general idea of what constitutes a t. is quite definite, it has not been po ible up to the present time to give a universally satisfactory cla ification of them. Two systems are used, the oldest and most common being based upon the appearance in the adult, and the other upon the origin from the different germ layers of the ovum. According to the first method, one of the most satisfactory cla ifications is the division into four groups epithelium, connective t., muscular t., and nervous t.; according to the second, t's are ectodermic, entodermic, or mesodermic. [J, 12, 21, 30, 31.] Adenoid t. Of His, the reticular framework of the lymphatic glands, alimentary mucosa, etc., the meshes of the reticulum being filled with lymphoid cells. This framework is described by many authors as made up of anastomosing branched cells, which mostly retain their nuclei; by others as composed of connective-t. fibres united into a network, the appearance of nuclei being given by the presence of endothelial cells. Adenoid t. may occur with indefinite boundaries, as in the mucosa of the alimentary canal. It is then sometimes called diffuse adenoid t. In other situations, as in the spleen, pleura, and omenturn, it may form cords, cylinders, or patches. In the tonsils, the spleen, and the alimentary mucosa it often occurs in well-defined ma es, the lymph-follicles. [J, 21, 24, 30, 31, 32, 42.] Adipose t. 1. Areolar t. in which the areolee are more or le filled with fat-cells, a condition which may occur in any part of the body except the eyelids and parts of the male sexual apparatus. This accumulation of fat-cells is usually abundant in well-fed individuals, especially in the subcutaneous areolar t., which is then often called the panniculus adiposus (q. v.). Adipose t. is abundantly supplied with blood ve els and lymphatics, but has no nerves. 2. The fat-cells exclusive of the areolar t. in which they are found. [J, 21, 30, 31, 33, 35, 42.] Alveolar t. The t. forming the framework of the pulmonary alveoli. It consists of areolar t. in which the elastic fibres are numerous, and there are also a considerable number of muscular fibre-cells. [J, 35.] Amorphous connective t. [Henle]. See Areolar t. Animal t. The t. of an animal in contradistinction to that of a plant. [J.] Aqueous t. Water (or water-storing) t.; t., such as that of most succulent plants, containing parenchyma cells stored with sap and more or le mucilage. |a, 35.] Areolar t., Areolated connective t. That part of the connective t. of the body in which white and yellow connective-t. fibres and bundles cro at all angles and continually unite to form larger bundles or divide to form smaller ones, thus making a kind of network. Except in the immature condition, the ground-substance has partly disappeared, leaving irregular cleft-like spaces, the so called cells or areolae, which are often filled with fat-cells. Areolar too; U2, blue; U 3. lull: U, full; Us, urn; U, like u (German). [s. 627]