*Production of the Intercellular Material.*—Though most of the cells of the body deposit to a slight extent this material, the greater part of it is produced by a single class of cells found in bone, cartilage, and connective tissue. Cartilage, bone, and connective tissue differ greatly from the other tissues in the amount of intercellular material which they contain, the difference being due to these cells. In the connective tissue they deposit the fibrous material so important in holding the different parts of the body together. In the cartilage they produce the gristly substance which forms by far its larger portion (Fig. 7). In the bones they deposit a material similar to that in the cartilage, except that with it is mixed a mineral substance which gives the bones their hardness and stiffness.(4) The intercellular material, in addition to connecting the cells, supplies to certain tissues important properties, such as the elasticity of cartilage and the stiffness of the bones. *Nature of the Body Organization.*—The division of labor carried on by the different organs, as shown in the preceding chapter, is in reality carried on by the cells that form the organs. To see that this is true we have only to observe the relation of cells to tissues and of tissues to organs. The cells form the tissues and the tissues form the organs. This arrangement enables the special work of different kinds of cells to be combined in the work of the organ as a whole. This is seen in the hand which, in grasping, uses motion supplied by the muscle cells, a controlling influence supplied by the nerve cells, a framework supplied by the bone cells, and so on. The cells supply the basis for the body organization and, properly speaking, the body is _an organization of cells_(5) (Recall the definition of an organization, page 10.) In this organization there are to be observed: 1. A definite arrangement of the cells to form the tissues. A tissue is a group of like cells. 2. A definite arrangement of the tissues in the organ. Each organ contains the tissues needed for its work. 3. In several instances there is a definite arrangement of organs to form systems. 4. The body as a whole is made up of organs and systems, together with the structures necessary for their support and protection. There now remains a further question for consideration. What is the one supreme end, or purpose, toward which all the activities of the body organization are directed? This purpose will naturally have some relation to the maintenance, or preservation, of the cell group which we call the body.