plex, higher structures. It may act as an enzyme to speed up a particular chemical reaction, or it may act as an antibody to neutralize the effects of some other specific protein molecule. Proteins can be created in a literally inexhaustible variety of forms, each with its own qualities.
             Macromolelcules may be combined to form small "organelles", such as mitochondria or muscle fibrils. When they are combined, the result is a cell - the unit of life, the miracle of creation - capable of reproduction and of independent existence.
             The more complex the system, the more complex its qualities. Organs may be built from cells; from organs may come an individual organism, such as a human being. Individuals in turn may be combined to form societies or populations, which again have their own rules. At each level of complexity are new qualities not present in the simpler levels. The study of each level yields new information for the biologist.
             The history of biology has been marked by a penetration into ever smaller dimensions. In the sixteenth century, Vesalius was dependent on his unaided eyesight for his study of the human body. In the following century, the optical microscope led to the discovery of many new details of structure. Marcello Malpighi observed the capillary vessels that complete the cycle of blood circulation and showed that even such tiny insects as the silkworm have an intricate internal structure. Anton van Leeuwenhoek described blood cells and the compound eyes of insects. Robert Hooke described the cellular structure of plants.
             As microscopes were improved, more and more details of structure were described. By the nineteenth century, it was becoming clear that all complex organisms are composed of semi-independent units called cells. The major structural features of cells were established. Bacteria were discovered and studied.
             In this century, the electron microscope has taken the scientist down to molecular dimensio...