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theory (the´or-e)

A reasoned explanation of known facts or phenomena that serves as a basis of investigation by which to reach the truth. See also hypothesis, postulate. [G. theoria, a beholding, speculation, theory, fr. theoros, a beholder]
adsorption t. of narcosis that a drug becomes concentrated at the surface of the cell as a result of adsorption, and thus alters permeability and metabolism.
Altmann's t. a t. that protoplasm consists of granular particles (called bioblasts) that are clustered and enclosed in indifferent matter.
Arrhenius-Madsen t. that the reaction of an antigen with its antibody is a reversible reaction, the equilibrium being determined according to the law of mass action by the concentrations of the reacting substances.
atomic t. that chemical compounds are formed by the union of atoms in certain definite proportions; in its modern form, first advanced in 1803 by John Dalton.
Baeyer's t. that carbon bonds are set at fixed angles (109° 28´) and that those carbon rings are most stable that least distort those angles; for this reason, planar rings composed of 5 or 6 carbon atoms (e.g., cyclopentane, benzene) are more common than rings containing less than 5 or more than 6 carbon atoms.
balance t. in social psychology, a t. which assumes that steady and unsteady states can be specified for cognitive units, such as an individual and his or her attitudes or acts, and that such units tend to seek steady states (balance); e.g., balance exists when both parts of a unit are evaluated the same, but disequilibrium arises when both parts are not evaluated the same, which causes either cognitive reevaluation of the parts or their segregation. See also cognitive dissonance t., consistency principle.
beta-oxidation-condensation t. that the two carbon fragments split from the fatty acid molecule by beta-oxidation are converted to acetic acid and then condensed to acetoacetic acid.
Bohr's t. that spectrum lines are produced 1) by the quantized emission of radiant energy when electrons drop from an orbit of a higher to one of a lower energy level, or 2) by absorption of radiation when an electron rises from a lower to a higher energy level.
Bordeau t. , Bordeu t. See de Bordeau t.
Bowman's t. that the urine is formed by passive filtration through the glomeruli and secretion by the epithelium of the tubules, the water and salts being separated from the plasma in the former situation, the urea and other urinary constituents in the latter. Parts of this t. are now known to be wrong.
Broonsted t. that an acid is a substance, charged or uncharged, liberating hydrogen ions in solution, and that a base is a substance that removes them from solution (e.g., NH4+, CH3COOH, and HSO4- are acids; NH3, CH3COO-, and SO4- are bases); useful in the concept of weak electrolytes and buffers. Cf. Broonsted acid, Broonsted base.
Burn and Rand t. that stimulation of sympathetic fibers results first in the production of acetylcholine in the postganglionic nerve endings, which then release norepinephrine to act on the active site of the effector cell.
Cannon-Bard t. the view that the feeling aspect of emotion and the pattern of emotional behavior are controlled by the hypothalamus.
Cannon's t. emergency t
catastrophe t. a branch of mathematics dealing with large changes in the total system that may result from a small change in a critical variable in the system; an example is the change in the physical properties of H2O as the temperature reaches zero or 100° C; many applications of catastrophe t. occur in clinical medicine and in epidemiology.
cellular immune t. a concept, put forth by Elie Metchnikoff, that cells, not antibodies, were responsible for the immune response of an organism.
celomic metaplasia t. of endometriosis that endometrial tissue arises directly from the peritoneal mesothelium.
chaos t. a branch of mathematics dealing with events and processes that cannot be predicted precisely on the basis of conventional mathematical t.'s or laws; some biological processes, e.g., spread of malignant disease, appear to conform to chaos t., at least sometimes.
chemiosmotic t. A hypothesis proposing that cellular energy requiring processes such as ATP synthesis and ion pumping may be driven by a pH and membrane potential gradient; proposed by Peter Mitchell in 1961.
cloacal t. the belief sometimes held by neurotic adults or children that a child is born, as a stool is passed, from a common opening.
clonal deletion t. the elimination of certain T cell populations in the thymus that have receptors for self-antigens. See immunologic tolerance.
clonal selection t. a t. which states that each lymphocyte has membrane bound immunoglobulin receptors specific for a particular antigen and once the receptor is engaged, proliferation of the cell occurs such that a clone of antibody producing cells (plasma cell) is produced.
cognitive dissonance t. a t. of attitude formation and behavior describing a motivational state that exists when an individual's cognitive elements (attitudes, perceived behaviors, etc.) are inconsistent with each other, such as the espousal of the Ten Commandments concurrent with the belief that it is all right to cheat on one's taxes; a t. which indicates that persons try to achieve consistency (consonance) and avoid dissonance which, when it arises, may be coped with by changing one's attitudes, rationalizing, selective perception, and other means. See also balance t., consistency principle.
Cohnheim's t. that neoplasms originate from various cell rests, i.e., embryonal cells thought to persist in various sites after the development of the fetal organs and tissues.emigration t;
colloid t. of narcosis that coagulation or flocculation of protein causes dehydration and reduction of metabolism.
darwinian t. the t. of the origin of species and of the development of higher organisms from lower forms through natural selection (survival of the fittest in the struggle for existence), and of the evolution of humans from an ancestor common to himself and the apes.
de Bordeau t. that each organ of the body manufactured a specific humor which it secreted into the bloodstream.
decay t. a t. of forgetting based on the premise that an engram or memory trace dissipates progressively with time during the interval when it is not activated.
Dieulafoy's t. an obsolete t. that appendicitis is always the result of the transformation of the appendicular canal into a closed cavity.
dipole t. a t. in which the activation current of the heart is conceived as a single net moving dipole, the positive pole leading.
duplicity t. of vision that the cones of the retina function in bright light and the rods function in dim light.
Ehrlich's side-chain t.
Ehrlich's t. See side-chain t.
t. of electrolytic dissociation See Arrhenius doctrine.
emergency t. a t. of the emotions, advanced by W.B. Cannon, that animal and human organisms respond to emergency situations by increased sympathetic nervous system activity including an increased catecholamine production with associated increases in blood pressure, heart and respiratory rates, and skeletal muscle blood flow. See also relaxation response.Cannon's t;
emigration t. Cohnheim's t
enzyme inhibition t. of narcosis that narcotics inhibit respiratory enzymes by suppression of the formation of high energy phosphate bonds within the cell.
Flourens' t. that thought is a process depending upon the action of the entire cerebrum.
Frerichs' t. that uremia represents a toxic condition caused by ammonium carbonate, which is formed as the result of the action of a plasma enzyme on the increased amounts of urea.
Freud's t. a comprehensive t. of how personality is formed and develops in normal and emotionally disturbed individuals; e.g., that an attack of conversion hysteria is due to a psychic trauma which was not adequately reacted to at the time it was received, and persists as an affect memory. See also psychoanalysis.
game t. the branch of mathematical logic concerned with the range of possible reactions to a particular strategy; each reaction can be assigned a probability and each reaction can lead to a counter-reaction by the "adversary" in the game. Used mainly in systems analysis, game t. has some applications in disease surveillance and control; it is one of the underlying t.'s in clinical decision analysis.
gastrea t. Haeckel's gastrea t
gate-control t. a theory to explain the mechanism of pain; small fiber afferent stimuli, particularly pain, entering the substantia gelatinosa can be modulated by large fiber afferent stimuli and descending spinal pathways so that their transmission to ascending spinal pathways is blocked (gated).gate-control hypothesis;
germ t. the t., now a doctrine, that infectious diseases are due to the presence and functional activity of microorganisms within the body.
germ layer t. the concept that young embryos differentiate three primary germ layers (ectoderm, mesoderm, and endoderm), each of which has the potentiality of forming different characteristic structures and organs in the developing body.
gestalt t. See gestaltism.
Haeckel's gastrea t. that the two-layered gastrula is the ancestral form of all multicellular animals.gastrea t;
Helmholtz t. of accommodation that the ciliary muscle relaxes for near vision and allows the anterior aspect of the lens to become more convex.
Helmholtz t. of color vision Young-Helmholtz t. of color vision
Helmholtz-Gibbs t. See Gibbs-Helmholtz equation.
Helmholtz t. of hearing resonance t. of hearing
hematogenous t. of endometriosis that endometrial tissue is carried, like metastases of a malignant tumor, through the blood stream.
Hering's t. of color vision that there are three opponent visual processes: blue-yellow, red-green, and white-black.
humoral t. See humoral doctrine.
hydrate microcrystal t. of anesthesia a t. of narcosis pertaining to nonhydrogen-bonding agents; postulates the interaction of the molecules of the anesthetic drug with water molecules in the brain.Pauling's t;
implantation t. of the production of endometriosis that, at the time of menstruation, cells of the uterine mucosa pass through the fallopian tubes and escape into the pelvic cavity where they implant themselves on the peritoneum.
incasement t. preformation t
information t. in the behavioral sciences, a system for studying the communication process through the detailed analysis, often mathematical, of all aspects of the process including the encoding, transmission, and decoding of signals; not concerned in any direct sense with the meaning of a message.
instructive t. a t. that states that an antibody learns or acquires its specificity after contact with a particular antigen.
James-Lange t. that bodily changes, such as tachycardia or sweating, precede rather than follow the conscious perception of an emotion and by themselves evoke the emotional feeling.
kern-plasma relation t. a t. enunciated by Hertwig (1903) that a definite relation as to size normally exists in every cell between the mass of nuclear material and that of the protoplasm. [Ger. kern, kernel, nucleus]
Knoop's t. that the catabolism of fatty acids occurs in stages in each of which there is a loss of two carbon atoms as a result of oxidation at the beta-carbon atom, e.g.,
Ladd-Franklin t. molecular dissociation t
lamarckian t. that acquired characteristics may be transmitted to the descendants and that experience, and not biology alone, can change and thereby influence genetic transmission.
learning t. any of several prominent theories designed to explain learning, especially those promulgated by Pavlov, Thorndike, Guthrie, Hull, Kohler, Spence, Miller, Skinner, and their modern followers. See also conditioning.
libido t. Freud's t. that humans psychic life results mainly from instinctual or libidinal needs and the attempts to satisfy them.
Liebig's t. that the hydrocarbons that oxidize readily and burn are aliments that produce the greatest quantity of animal heat.
lipoid t. of narcosis that narcotic efficiency parallels the coefficient of partition between oil and water, and that lipoids in the cell and on the cell membrane absorb the drug because of this affinity.Meyer-Overton t. of narcosis;
lymphatic dissemination t. of endometriosis that endometrial tissue is transmitted by the lymphatic channels.
mass action t. that large areas of brain tissue function as a whole in learned or intelligent action.
t. of medicine the science, as distinguished from the art, or practice, of medicine.
membrane expansion t. that adsorption of anesthetics into membranes so alters membrane volume and/or configuration that membrane function is affected in such a way as to produce anesthesia.
Metchnikoff's t. the phagocytic t., that the body is protected against infection by the leukocytes and other cells that engulf and destroy the invading microorganisms.
Meyer-Overton t. of narcosis lipoid t. of narcosis
miasma t. (mI-az´ma) an explanation of the origin of epidemics, based on the false notion that they were caused by air of bad quality, e.g., emanating from rotting vegetation in marshes or swamps.
migration t. obsolete t. that sympathetic ophthalmia is caused by a migration of the pathogenic agent through the lymph channels of the optic nerve.
Miller's chemicoparasitic t. that dental caries is caused by microorganisms of the mouth fermenting dietary carbohydrates and producing acids that demineralize the teeth.
mnemic t. mnemic hypothesis
molecular dissociation t. a t., pertaining to color vision, that gray is the earliest of color sensations, from which are derived, by molecular change, two paired substances that, respectively, detect yellow and blue, and that the yellow gives rise to paired substances for detection of red and green.Ladd-Franklin t;
monophyletic t. monophyletism
myoelastic t. a t. stating that sound of the human voice is produced by vibrations of the vocal cords resulting from folding upward due to air pressure below, and subsequent movement downward due to elastic tension of cords.
myogenic t. that cardiac movements are due mainly to stimuli originating in the heart muscle itself and that the heart does not act solely in response to nerve stimulation.
Nernst's t. that the passage of an electric current through the tissues causes a dissociation of the ions, with consequent concentration of salts in the solution bathing the cell membranes, the electric stimulus being thereby effected.
neurochronaxic t. t. stating that variations in pitch of the human voice are produced by active muscular contractions synchronized with cycles per second of pitch, no longer believed to be true.
Ollier's t. a t. of compensatory growth; after resection of the articular extremity of a bone, the articular cartilage of the other bone entering into the structure of the joint takes on an increased growth.
omega-oxidation t. that the oxidation of fatty acids commences at the CH3 group, i.e., the terminal or omega-group; beta-oxidation then proceeds at both ends of the fatty acid chain.
overproduction t. Weigert's law
oxygen deprivation t. of narcosis that narcotics inhibit oxidation, which causes the cell to be narcotized.
Pauling's t. hydrate microcrystal t. of anesthesia
permeability t. of narcosis that the permeability of the cell membrane is decreased by narcotic concentrations of aliphatic and other central nervous system depressants.
phlogiston t. See phlogiston.
pithecoid t. the t. of human's descent with the ape from a common ancestor. See also darwinian t.
place t. a t. of pitch perception which states that the perception of the pitch of a sound depends upon the level or region of the basilar membrane of the cochlea which is set into vibration by the sound waves. See also resonance t. of hearing.
Planck's t. quantum t
polyphyletic t. polyphyletism
preformation t. archaic t. that the embryo was fully formed in miniature within a gamete at the time of conception. See also homunculus.emboitement, incasement t;
quantum t. that energy can be emitted, transmitted, and absorbed only in discrete quantities (quanta), so that atoms and subatomic particles can exist only in certain energy states.Planck's t;
recapitulation t. the t. formulated by E.H. Haeckel that individuals in their embryonic development pass through stages similar in general structural plan to the stages their species passed through in its evolution; more technically phrased, the t. that ontogeny is an abbreviated recapitulation of phylogeny.biogenetic law, law of biogenesis, Haeckel's law, law of recapitulation;
Reed-Frost t. of epidemics a mathematical t. to explain how epidemics originate and continue.
reed instrument t. a no longer tenable t. stating that in human voice production the larynx functions in a manner similar to a reed musical instrument.
reentry t. that extrasystoles are due to reentry of an impulse initiated by the sinus impulse, to which the extrasystole is coupled, into the ectopic focus.
resonance t. of hearing that the basilar membrane of the cochlea acts as a resonating structure, recording low tones from its apical turns and high tones from its basal turns.Helmholtz t. of hearing;
Ribbert's t. that a neoplasm may result when a reduction in tension (exerted by adjacent tissues) leads to conditions favorable to uncontrolled growth of cell rests.
Semon-Hering t. mnemic hypothesis
sensorimotor t. in the developmental t. of Piaget, the postulation that during the first 18 months of life there occurs a transformation of action into thought; at first there is a gradual shift from inborn to acquired behavior, then from body-centered to object-centered activity, ultimately permitting intentional behavior and inventive thinking.
side-chain t. Ehrlich postulated that cells contained surface extensions or side chains (haptophores) that bind to the antigenic determinants of a toxin (toxophores); after a cell is stimulated, the haptophores are released into the circulation and become the antibodies. See also receptor.Ehrlich's postulate;
somatic mutation t. of cancer that cancer is caused by a mutation or mutations in the body cells (as opposed to germ cells), especially nonlethal mutations associated with increased proliferation of the mutant cells.
Spitzer's t. an interpretation of the partitioning of the heart of mammalian embryos primarily on the basis of recapitulations of the adult structural pattern of lower forms; most frequently cited in relation to the partitioning of the truncus arteriosus to form ascending aorta and pulmonary trunk, which is achieved by the phylogenetic development of the lungs.
stringed instrument t. a no longer tenable t. stating that in human voice production the vocal cords function in a manner similar to the strings in a stringed musical instrument.
surface tension t. of narcosis that substances which lower the surface tension of water pass more readily into the cell and cause narcosis by decreasing metabolism.
telephone t. a t. of pitch perception which states that the cochlea possesses no faculty of sound analysis, but that the frequency of the impulses transmitted over the auditory nerve fibers corresponds to the frequency of the sound vibrations, and is the sole basis for pitch discrimination; a t. no longer tenable.
thermodynamic t. of narcosis that the interposition of narcotic molecules in nonaqueous cellular phase causes changes that interfere with facilitation of ionic exchange.
two-sympathin t. a t., now obsolete, advanced by Cannon and Rosenblueth that two different types of substances (sympathin E and I) diffuse into circulation when adrenergic nerves are stimulated, although the mediator itself is the same.
van't Hoff's t. that substances in dilute solution obey the gas laws. Cf. van't Hoff's law.
Warburg's t. that the development of cancer is due to irreversible damage to the respiratory mechanism of cells, leading to the selective multiplication of cells with increased glycolytic metabolism, both aerobic and anaerobic.
Wollaston's t. a t. that the semidecussation of the optic nerves at the chiasm is proved by the homonymous hemianopia seen in brain lesions.
Young-Helmholtz t. of color vision a t. that there are three color-perceiving elements in the retina: red, green, and blue. Perception of other colors arises from the combined stimulation of these elements; deficiency or absence of any one of these elements results in inability to perceive that color and a misperception of any other color of which it forms a part.Helmholtz t. of color vision;


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