INDUCTION

in logic, method of reasoning from a part to a whole, from particulars to generals, or from the individual to the universal. As it applies to logic in systems of the 20th century, the term is obsolete. Traditionally, logicians distinguished between deductive logic (inference in which the conclusion follows necessarily from the premise, or drawing new propositions out of premises in which they lie latent) and inductive logic, but the problems earlier subsumed under induction are considered to be concerns of the methodology of the natural sciences, and logic is generally taken to mean deductive logic. in enzymology, a metabolic control mechanism with the effect of increasing the rate of synthesis of an enzyme. In induction, synthesis of a specific enzyme, called an inducible enzyme (e.g., b-galactosidase in Escherichia coli), occurs when cells are exposed to the substance (substrate) upon which the enzyme acts to form a product. Formation of b-galactosidase has been shown to be controlled by a so-called regulator gene presumed to specify a protein, called a repressor protein, that binds to the region of deoxyribonucleic acid (DNA) responsible for directing the synthesis of the enzyme. If substrate is present, it acts as an inducer by combining with the repressor so as to prevent its binding to DNA. As a result, the enzyme is synthesized; i.e., its formation by the microorganism is induced. Such mechanisms are important in the cell because they prevent the synthesis of enzymes that a cell cannot use; e.g., b-galactosidase is needed only when its substrate (lactose or galactose) is present. in embryology, process by which the presence of one tissue influences the development of others. Certain tissues, especially in very young embryos, apparently have the potential to direct the differentiation of adjacent cells. Absence of the inducing tissue results in lack of or improper development of the induced tissue. The converse is often true as well; i.e., the addition of extra inducing tissue in an abnormal position in an embryo often results in aberrantly located induced tissue. An example of induction is the development of the eye lens from epidermis under influence of the eye cup, which grows toward the skin from the brain. As the eye cup comes into contact with any neighbouring epidermis, it transforms that particular region into a lens. The exact nature of the stimulus for lens induction is not known, although ribonucleic acid (RNA) has been implicated as a messenger. The range of the inductive effect is not unlimited, for only certain tissues are capable of being induced by a given structure and then only at certain times.