| Bowman's theory | 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 theory are now known to be wrong. (05 Mar 2000) |
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| Bronsted theory | 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. Compare: Bronsted acid, Bronsted base. (05 Mar 2000) |
| Burn and Rand theory | That stimulation of sympathetic fibres 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. (05 Mar 2000) |
| Cannon-Bard theory | The view that the feeling aspect of emotion and the pattern of emotional behaviour are controlled by the hypothalamus. (05 Mar 2000) |
| Cannon's theory | A theory 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: relaxation response. Synonym: Cannon's theory. (05 Mar 2000) |
| game theory | A mathematical theory that deals with action in a conflict situation as if it were a game in which each player seeks to maximise his opponent's losses. (12 Dec 1998) |
| van't Hoff's theory | That substances in dilute solution obey the gas laws. Compare: van't Hoff's law. (05 Mar 2000) |
| gastrea theory | That the two-layered gastrula is the ancestral form of all multicellular animals. Synonym: gastrea theory. (05 Mar 2000) |
| gate-control theory | A theory to explain the mechanism of pain; small fibre afferent stimuli, particularly pain, entering the substantia gelatinosa can be modulated by large fibre afferent stimuli and descending spinal pathways so that their transmission to ascending spinal pathways is blocked (gated). Synonym: gate-control hypothesis. (05 Mar 2000) |
| recapitulation theory | The theory 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 theory that ontogeny is an abbreviated recapitulation of phylogeny. Synonym: biogenetic law, law of biogenesis, Haeckel's law, law of recapitulation. (05 Mar 2000) |
| germ layer theory | The developmental biology theory that during early development, the animal embryo divides itself into two or three germ layers, each of which then proceed to further differentiate into organs and tissues specific to that particular layer. (09 Oct 1997) |
| germ theory | The theory, now a doctrine, that infectious diseases are due to the presence and functional activity of microorganisms within the body. (05 Mar 2000) |
| mass action theory | That large areas of brain tissue function as a whole in learned or intelligent action. (05 Mar 2000) |
| gestalt theory | A system which emphasizes that experience and behaviour contain basic patterns and relationships which cannot be reduced to simpler components; that is, the whole is greater than the sum of its parts. (12 Dec 1998) |
| Reed-Frost theory of epidemics | A mathematical theory to explain how epidemics originate and continue. (05 Mar 2000) |