Born Apr. 7, 1859, in Mayen, near Koblenz, Germany; died Feb. 11, 1924, in Hamilton, Bermuda. American biologist.

Loeb graduated from the University of Strasbourg in 1884 and worked in a number of German universities. From 1889 to 1891 he worked at the Naples Zoological Station. In 1891, Loeb went to the United States, where, in 1892, he became a professor at the University of Chicago; in 1902 he became a professor at the University of California. In 1910, Loeb began work at the Rockefeller Institute in New York City.

Loeb studied the physiology of the brain, animal behavior (he erroneously transferred the concept of tropisms from botany to zoology, attempting to explain animal behavior as a physico-chemical reaction to external stimuli), tissue regeneration (he advanced the chemical theory of regeneration), artificial parthenogenesis, and the antagonistic effect of salts on the living cell—particularly on the developing egg cell—which formed the basis for the ionic theory of excitation.