Heartburn, burning sensation beneath the breastbone, also called pyrosis. Heartburn does not indicate heart malfunction but results from nervous tension or overindulgence in food or drink. The...

Condillac, Étienne Bonnot de, 1715–80, French philosopher who developed the theory of sensationalism (i.e., that all knowledge comes from the senses and that there are no innate ideas). He too...

Hartley, David, 1705–57, English physician and philosopher, founder of associational psychology. In his Observations on Man (2 vol., 1749) he stated that all mental phenomena are due to sensat...

Thirst, sensation indicating the body's need for water. Dry or salty food and dry, dusty air may induce such a sensation by depleting moisture in the mucous membranes of the mouth and throat. ...

Sense, faculty by which external or internal stimuli are conveyed to the brain centers, where they are registered as sensations. Sensory reception occurs in higher animals through a process kn...

Touch, tactile sensation received by the skin, enabling the organism to detect objects or substances in contact with the body. End organs (nerve endings) in the skin convey the impression to t...

Palpitation, abnormal heartbeat that is often associated with a sensation of fluttering or thumping. The normal heartbeat is not noticeable to the individual. Palpitation may be a symptom of o...

Müller, Johannes Peter, 1801–58, German physiologist and anatomist. From 1833 until the end of his career he was professor at Berlin. He was famed as a teacher; for his extensive research in m...

Nausea, sensation of discomfort, or queasiness, in the stomach. It may be caused by irritation of the stomach by food or drugs, unpleasant odors, overeating, fright, or psychological stress. I...

Vertigo, sensations of moving in space or of objects moving about a person and the resultant difficulty in maintaining equilibrium. True vertigo, as distinguished from faintness, lightheadedne...