| pithecoid theory | The theory of human's descent with the ape from a common ancestor. See: darwinian theory. (05 Mar 2000) |
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| place theory | A theory 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: resonance theory of hearing. (05 Mar 2000) |
| Planck's theory | The theory that the radiation and absorption of energy take place in definite quantities called quanta (e) which vary in size and are defined by the equation e=hv in which h is planck's constant and v is the frequency of the radiation. (12 Dec 1998) |
| Wollaston's theory | A theory that the semidecussation of the optic nerves at the chiasm is proved by the homonymous hemianopia seen in brain lesions. (05 Mar 2000) |
| polyphyletic theory | In haematology, the theory that blood cells are derived from several different stem cells, depending on the particular cell type. Synonym: polyphyletic theory. Origin: poly-+ G. Phyle, tribe (05 Mar 2000) |
| myoelastic theory | A theory 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. (05 Mar 2000) |
| myogenic theory | 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. (05 Mar 2000) |
| Haeckel's gastrea theory | That the two-layered gastrula is the ancestral form of all multicellular animals. Synonym: gastrea theory. (05 Mar 2000) |
| haematogenous theory of endometriosis | That endometrial tissue is carried, like metastases of a malignant tumour, through the blood stream. (05 Mar 2000) |
| preformation theory | Archaic theory that the embryo was fully formed in miniature within a gamete at the time of conception. See: homunculus. Synonym: emboitement, incasement theory. (05 Mar 2000) |
| probability theory | The branch of mathematics dealing with the purely logical properties of probability. Its theorems underlie most statistical methods. (12 Dec 1998) |
| Helmholtz-Gibbs theory | An equation expressing the relationship in a galvanic cell between the chemical energy transformed and the maximal electromotive force obtainable. (05 Mar 2000) |
| Helmholtz theory of accommodation | That the ciliary muscle relaxes for near vision and allows the anterior aspect of the lens to become more convex. (05 Mar 2000) |
| Helmholtz theory of colour vision | A theory that there are three colour-perceiving elements in the retina: red, green, and blue. Perception of other colours arises from the combined stimulation of these elements; deficiency or absence of any one of these elements results in inability to perceive that colour and a misperception of any other colour of which it forms a part. Synonym: Helmholtz theory of colour vision. (05 Mar 2000) |
| Helmholtz theory 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. Synonym: Helmholtz theory of hearing. (05 Mar 2000) |