principle (prin´si-pl)

1. A general or fundamental doctrine or tenet. See also law, rule, theorem. 2. The essential ingredient in a substance, especially one that gives it its distinctive quality or effect. [L. principium, a beginning, fr. princeps, chief]
active p. a constituent of a drug, usually an alkaloid or glycoside, upon the presence of which the characteristic therapeutic action of the substance largely depends.
antianemic p. the material in liver (and certain other tissues) that stimulates hemopoiesis in pernicious anemia; for practical purposes, the antianemic effect of extracts from such tissues is approximately equivalent to the content of vitamin B12.
azygos vein p. a p. based on the observation that animals can survive prolonged vena caval occlusion without sequelae: if blood from the azygos vein alone is permitted to enter the heart, patients are perfused during cardiac and pulmonary bypass at flows much less than the normal resting cardiac output.low flow p;
Bernoulli's p. Bernoulli's law
bitter p.'s a class of plant substances with a bitter taste that produce a reflexive increase in saliva secretion as well as secretion of digestive juices.
closure p. in psychology, the p. that when one views fragmentary stimuli forming a nearly complete figure (e.g., an incomplete rectangle) one tends to ignore the missing parts and perceive the figure as whole. See gestalt.
consistency p. in psychology, the desire of the human being to be consistent, especially in his attitudes and beliefs; theories of attitude formation and change based on the consistency p. include balance theory, which suggests that the individual seeks to avoid incongruity in his various attitudes. See also cognitive dissonance theory.
Fick p. Fick method
follicle-stimulating p. follitropin
founder p. the conditional probabilities of the frequencies of a set of genes at any future date depend on the initial composition of the founders of the population and have in general no tendency to revert to the composition of the population from which the founders were themselves derived.
hematinic p. the p. previously thought to be produced by the action of Castle's intrinsic factor upon an extrinsic factor in food, now recognized as vitamin B12.
Huygens' p. used in ultrasound technology; the p. that any wave phenomenon can be analyzed as the sum of many simple sources properly chosen with regard to phase and amplitude.
p. of inertia repetition-compulsion p
Le Chatelier's p. Le Chatelier's law
low flow p. azygos vein p
luteinizing p. lutropin
melanophore-expanding p. melanotropin
Mitrofanoff p. appendicovesicostomy
nirvana p. in psychoanalysis, the p. that expresses the tendency toward the death instinct.
organic p. proximate p
pain-pleasure p. a psychoanalytic concept that, in a human's psychic functioning, he/she tends to seek pleasure and avoid pain; a term borrowed by experimental psychology to denote the same tendency of an animal in a learning situation.pleasure p;
Pauli's exclusion p. the theory limiting the number of electrons in the orbit or shell of an atom; that it is not possible for any two electrons to have all four quantum numbers identical.
pleasure p. pain-pleasure p
proximate p. in chemistry, an organic compound that may exist already formed as a part of some other more complex substance (e.g., various sugars, starches, and albumins).organic p;
reality p. the concept that the pleasure p. in personality development is modified by the demands of external reality; the p. or force that compels the growing child to adapt to the demands of external reality.
repetition-compulsion p. in psychoanalysis, the impulse to redramatize or reenact earlier emotional experiences or situations.p. of inertia;
Stewart-Hamilton p. used to determine blood flow from the concentration of dye or temperature dilution.
ultimate p. one of the chemical elements.


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