Jacques Loeb

Jacques Loeb (/lb/;[1] German: [løːp]; April 7, 1859 – February 11, 1924) was a German-born American physiologist and biologist.

Jacques Loeb
BornApril 7, 1859
DiedFebruary 11, 1924(1924-02-11) (aged 64)
ChildrenLeonard Benedict Loeb
Scientific career
FieldsPhysiology, Biology


Loeb, firstborn son of a Jewish family from the German Eifel region, was educated at the universities of Berlin, Munich, and Strasburg (M.D. 1884). He took postgraduate courses at the universities of Strasburg and Berlin, and in 1886 became assistant at the physiological institute of the University of Würzburg, remaining there till 1888. In a similar capacity, he then went to Strasburg University. During his vacations he pursued biological researches, at Kiel in 1888, and at Naples in 1889 and 1890.

In 1892 he was called to the University of Chicago as assistant professor of physiology and experimental biology, becoming associate professor in 1895, and professor of physiology in 1899. John B. Watson (the "father of Behaviorism") was a student of Loebs neurology classes at University of Chicago.[2] In 1902 he was called to fill a similar chair at the University of California.

In 1910 Loeb moved to the Rockefeller Institute for Medical Research in New York, where he headed a department created for him. He remained at Rockefeller (now Rockefeller University) until his death. Throughout most of these years Loeb spent his summers at the Marine Biological Laboratory in Woods Hole, Massachusetts, performing experiments on various marine invertebrates. It was there that Jacques Loeb performed his most famous experiment, on artificial parthenogenesis. Loeb was able to cause the eggs of sea urchins to begin embryonic development without sperm. This was achieved by slight chemical modifications of the water in which the eggs were kept, which served as the stimulus for the development to begin.[3][4] In 1918 Loeb established and became the first Editor of the Journal of General Physiology.

Loeb became one of the most famous scientists in America, widely covered in newspapers and magazines. He was the model for the character of Max Gottlieb in Sinclair Lewis's Pulitzer-winning novel Arrowsmith, the first great work of fiction to idealize and idolize pure science.[5] Mark Twain also wrote an essay titled "Dr. Loeb's Incredible Discovery", which urges the reader not to support a rigid general consensus, but instead be open to new scientific advances.[6]

Loeb was nominated many times for the Nobel Prize but never won.

Loeb was an atheist.[7][8]

Research area

The main subjects of Loeb's work were:

  • Animal tropisms and their relation to the instincts of animals
  • Heteromorphosis, the replacement of an injured or removed organ by a different organ
  • Toxic and antitoxic effects of ions
  • Artificial parthenogenesis
  • Hybridization of the eggs of sea-urchins by the sperm of starfish


Among Loeb's works the following may be mentioned:

  • Der Heliotropismus der Thiere und seine Uebereinstimmung mit dem Heliotropismus der Pflanzen, Würzburg: Verlag von Georg Hertz, 1890.
  • Untersuchungen zur physiologischen Morphologie der Thiere, Würzburg: Verlag von Georg Hertz, 18911892. 2 vols., vol. 1: Ueber Heteromorphose, vol. 2: Organbildung und Wachsthum.
  • Einleitung in die vergleichende Gehirnphysiologie und vergleichende Psychologie, Leipzig: J. A. Barth, 1899. English ed., Comparative physiology of the brain and comparative psychology, New York: Putnam, 1900.
  • Studies in general physiology, Chicago: The University of Chicago Press, 1905.
  • The dynamics of living matter, New York: Columbia University Press, 1906.
  • The mechanistic conception of life: biological essays, Chicago: The University of Chicago Press, 1912; reprint, Cambridge, Mass.: Harvard University Press, 1964.
  • Artificial parthenogenesis and fertilization, tr. from German by W. O. Redman King, rev. and ed. by Loeb. Chicago: The University of Chicago Press, 1913.
  • The organism as a whole, from a physicochemical viewpoint, New York: Putnam, 1916.
  • Forced movements, tropisms, and animal conduct, Philadelphia: Lippincott, 1918.
  • Proteins and the theory of colloidal behavior, New York: McGraw-Hill, 1922.

The Mechanistic Conception of Life is Loeb's most famous and influential work. It contains English translations of some of his previous publications in German.


His younger brother Leo also emigrated to the United States where he became a noted pathologist.


  1. "Loeb". Random House Webster's Unabridged Dictionary.
  2. Introduction to: "Psychology as the Behaviorist Views it."
  3. Loeb, J (1914), "ACTIVATION OF THE UNFERTILIZED EGG BY ULTRA-VIOLET RAYS." (PDF), Science (published Nov 6, 1914), 40 (1036), pp. 680–681, doi:10.1126/science.40.1036.680, PMID 17742992
  4. Ball, Philip (2016). "Man Made: A History of Synthetic Life". Distillations. 2 (1): 15–23. Retrieved 22 March 2018.
  5. The novel Arrowsmith, Paul de Kruif (1890-1971) and Jacques Loeb (1859–1924): a literary portrait of "medical science", H. M. Fangerau, Medical Humanities 32 (2006), pp. 8287.
  6. Mark Twain on the Damned Human Race, edited by Janet Smith, Hill and Wang, New York, 1994, pp. 4549.
  7. Rasmussen, Charles, and Rick Tilman. Jacques Loeb: His Science and Social Activism and Their Philosophical Foundations, Volume 229. N.p.: American Philosophical Society, 1998. Print. "An avowed atheist and materialist, he espoused secular humanism..."
  8. Stout, Harry S., and D. G. Hart. New Directions in American Religious History. New York: Oxford UP, 1997. Print. Loeb was a forthright atheist..."


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