Fatigue, in physiology, inability to perform reasonable and necessary physical or mental activity. Muscle fatigue, for example, results when the contractile properties of muscle are reduced, a...

Ludwig, Carl Friedrich Wilhelm, 1816–95, German physiologist. He became world famous as professor (from 1865) and head of the physiological institute at the Univ. of Leipzig. Ludwig pioneered ...

Barany, Robert, 1876–1936, Austrian physician. For his work on the physiology and pathology of the vestibular apparatus of the ear he received the 1914 Nobel Prize in Physiology or Medicine. F...

Hess, Walter Rudolf, 1881–1973, Swiss physiologist. For his work on the control of organs by certain areas of the brain he shared with Egas Moniz the 1949 Nobel Prize in Physiology or Medicine...

Hyperactivity, excessive physical activity of emotional or physiological origin, usually seen in young children; one of the components of attention deficit hyperactivity disorder.

Optics, scientific study of light. Physical optics is concerned with the genesis, nature, and properties of light; physiological optics with the part light plays in vision; and geometrical opt...

, 1853–1927, German physiologist. He was professor at Heidelberg from 1901. He specialized in the physiological chemistry of the cell and its nucleus and of proteins, including nucleins. He di...

Leuckart, Karl Georg Friedrich Rudolf, 1823–98, German zoologist, a founder of the science of parasitology. He made important discoveries in animal physiology and in comparative morphology and...

Magendie, François, 1783–1855, French physician. He taught at the Collège de France and is considered a founder of experimental physiology. He distinguished the motor and sensory portions of p...

Hales, Stephen, 1677–1761, English physiologist and clergyman. From 1709 he was perpetual curate of Teddington. His experimental studies in animal and plant physiology contributed greatly to t...