CHAPTER III - THE BODY ORGANIZATION
What is the nature of the body organization? What are the individual parts, or units, that make it up? What general work do these carry on and upon what basis do they practice the division of labor? The answers to these questions will suggest the main problems in the study of the body.
Fig. 3—Diagram showing the relation of the cells and the intercellular material. C. Cells. I. Intercellular material.
Complex Nature of the Tissues.—To the unaided eye the tissues have the appearance of simple structures. The microscope, however, shows just the reverse to be true. When any one of the tissues is suitably prepared and carefully examined with this instrument, at least two classes of materials can be made out. One of these consists of minute particles, called cells; the other is a substance lying between the cells, known as the intercellular material (Fig. 3). The cells and the intercellular material, though varying in their relative proportions, are present in all the tissues.
The Body a Cell Group.—The biologist has found that the bodies of all living things, plants as well as animals, consist either of single cells or of groups of cells. The single cells live independently of one another, but the cells that form groups are attached to, and are more or less dependent upon, one another. In the first condition are [pg 014] found the very lowest forms of life. In the second, life reaches its greatest development. The body of man, which represents the highest type of life, is recognized as a group of cells. In this group each cell is usually separate and distinct from the others, but is attached to them, and is held in place by the intercellular material.
Protoplasm, the Cell Substance.—The cell is properly regarded as an organized bit of a peculiar material, called protoplasm. This is a semi-liquid and somewhat granular substance which resembles in appearance the white of a raw egg. Its true nature and composition are unknown, because any attempt to analyze it kills it, and dead protoplasm is essentially different from living protoplasm. It is known, however, to be a highly complex substance and to undergo chemical change readily. It appears to be the only kind of matter with which life is ever associated, and for this reason protoplasm is called the physical basis of life. Its organization into separate bits, or cells, is necessary to the life activities that take place within it.
Structure of the Cell.—Though all portions of the cell are formed from the protoplasm, this essential substance differs both in structure and in function at different places in the cell. For this reason the cell is looked upon as a complex body having several distinct parts. At or near the center is a clear, rounded body, called the nucleus. This plays some part in the nourishment of the cell and also in the formation of new cells. If it be absent, as is sometimes the case, the cell is short-lived and unable to reproduce itself. The variety of protoplasm contained in the nucleus is called the nucleoplasm.
Fig. 4—Diagram of a typical cell (after Wilson). 1. Main body. 2. Nucleus. 3. Attraction sphere. 4. Food particles and waste. 5. Cell-wall. 6. Masses of active material found in certain cells, called plastids.