*The Tissues.*—After examining the external features of the body, we naturally inquire about its internal structures. These are not so easily investigated, and much which is of interest to advanced students must be omitted from an elementary course. We may, however, as a first step in this study, determine what kinds of materials enter into the construction of the body. For this purpose the body of some small animal should be dissected and studied. (See observation at close of chapter.) 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. Most of these present different varieties, making all together some fifteen different kinds of tissues that enter into the construction of the body.(2) *General Purposes of the Tissues.*—The tissues, first of all, _form the body_. As a house is constructed of wood, stone, plaster, iron, and other building materials, so is the body made up of its various tissues. For this reason the tissues have been called the _building materials_ of the body. In addition to forming the body, the tissues supply the means through which its work is carried on. They are thus the _working materials_ of the body. In serving this purpose the tissues play an active rôle. All of them must perform the activities of growth and repair, and certain ones (the so-called active tissues) must do work which benefits the body as a whole. *Purposes of the Different Tissues.*—In the construction of the body and also in the work which it carries on, the different tissues are made to serve different purposes. The osseous tissue is the chief substance in the bony framework, or skeleton, while the muscular tissue produces the different movements of the body. The connective tissue, which is everywhere abundant, serves the general purpose of connecting the different parts together. Cartilaginous tissue forms smooth coverings over the ends of the bones and, in addition to this, supplies the necessary stiffness in organs like the larynx and the ear. The nervous tissue controls the body and brings it into proper relations with its surroundings, while the epithelial tissue (found upon the body surfaces and in the glands) supplies it with protective coverings and secretes liquids. The adipose tissue (fat) prevents the too rapid escape of heat from the body, supplies it with nourishment in time of need, and forms soft pads for delicate organs like the eyeball.