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1. A study in which the investigator intentionally alters one or more factors under controlled conditions in order to study the effects of doing so. 2. In nuclear magnetic resonance, the term applied to a pulse sequence. [L. experimentum, fr. experior, to test, try]
Carr-Purcell e. in magnetic resonance, the multiple spin echo technique.
control e. an e. used to check another, to verify the result, or to demonstrate what would have occurred had the factor under study been omitted. See also control, control animal.
delayed reaction e. a method of measuring memory: a stimulus is presented and removed before the organism is permitted to respond to it; the interval during which the stimulus is absent, providing the organism responds correctly, is an indication of the length of memory.
double blind e. an e. conducted with neither experimenter nor subjects knowing which e. is the control; prevents bias in recording results. See also double-masked e.
double-masked e. a double-blind study conducted so neither the subject nor the observer know the identity of the control or variable.
factorial e.'s an experimental design in which two or more series of treatments are tried in all combinations.
hertzian e.'s e.'s demonstrating that electromagnetic induction is propagated in waves, analogous to waves of light but not affecting the retina.
Mariotte's e. an e. in which one looks fixedly with one eye (the other being closed), at a black dot on a card, on which is also marked a black cross; as the card is moved to or from the eye, at a certain distance the cross becomes invisible but appears again as the card is moved further; this proves the absence of photoreceptors where the optic nerve enters the eye.
Nussbaum's e. exclusion of the glomeruli of the kidney from the circulation by ligation of the renal artery in animals, such as the frog, that have a renal portal system to maintain circulation to the tubules.
pulse-chase e. an e. in which an enzyme, a metabolic pathway, a culture of cells, etc., interacts with a brief addition (pulse) of a labeled compound followed by its removal and replacement (chase) by an excess of unlabeled compound.
Scheiner's e. a demonstration of accommodation; through two minute holes in a card, separated from each other by less than the diameter of the pupil, one looks at a pin; at a short distance from the eye the pin appears double; as it is moved from the eye a point is found where it appears single, and beyond which it remains single for the emmetropic eye, but for the myopic eye it soon again becomes double.
Stensen's e. compression of the abdominal aorta of an animal promptly causes paralysis of the posterior portions of the body since the blood supply to the lumbar cord is almost entirely shut off.
Weber's e. if the peripheral end of the divided vagus nerve is stimulated the heart is arrested in diastole.
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