The living material of most organisms is organized into discrete units called cells, and the study of their features is known as cytology. The cellular contents, when viewed through a microscope at low magnification, usually appear to consist of granules or fibrils of dense material, droplets of fatty substances, and fluid-filled vacuoles suspended in a clear, continuous, semifluid substance called cytoplasm. The remarkable structural complexity of the cell is more fully revealed at the higher magnifications attainable with the electron microscope. Structural details of various cellular components, or organelles, as revealed by the technique known as X-ray diffraction analysis, have ...(100 of 5614 words)