lines body cavities, such as the gastrointestinal tract
and the lining of the lung. Epidermal growth factor
(EGF) is a hormone that causes epithelial tissues, such
as skin and the cells lining the gastrointestinal tract and
lungs, to grow and heal.
epitope(antigenic determinant) These are particular
chemical groups on a molecule that are antigenic, i.e.,
that elicit a specific immune response.
epizootic A rapid spread of a disease throughout an
area affecting an animal group, e.g., rabies (disease
affecting raccoons, fox) or epizootic catarrhal enteritis
(disease affecting mink). When it occurs in humans, it
is called an epidemic.
epoch A period or date of time, shorter than and
part of an era, that is used in geological time tables to
locate historical events. Usually refers to an event
(mountain building, appearance of a species, etc.). Also
called a series.
See alsoERA;GEOLOGICAL TIME.
EPR See ELECTRON PARAMAGNETIC RESONANCE
SPECTROSCOPY.
equator The area around the earth with a latitude of
0° that divides the Northern and Southern Hemi-
spheres. It lies equidistant from the poles.
equilibrium constant SeeACIDITY CONSTANT;STA-
BILITY CONSTANT.
era Aperiod or date of time used in geological time
tables to locate historical events. Usually refers to longer
periods of time and marks a new or distinctive period.
See alsoEPOCH;GEOLOGICAL TIME.
Erlanger, Joseph (1874–1965) AmericanNeurosci-
entist Joseph Erlanger was born on January 5, 1874,
inSan Francisco, California, to Herman and Sarah
Erlanger. He received a B.S. in chemistry at the Uni-
versity of California and later attended Johns Hopkins
University to study medicine, receiving an M.D.
degree in 1899. He was appointed assistant in the
department of physiology at the medical school, after
spending a year of hospital training at Johns Hopkins
Hospital, until 1906, moving up successively as
instructor, associate, and associate professor. He was
then appointed the first professor of physiology in the
newly established Medical School of the University of
Wisconsin. In 1910 he was appointed professor of
physiology in the reorganized Medical School of the
Washington University, St. Louis, retiring in 1946 as
chairman of the school.
In 1922, in collaboration with his student Herbert
Gasser, Erlanger adapted the cathode-ray oscillograph
for the study of nerve-action potentials. They ampli-
fied the electrical responses of single nerve fibers and
analyzed them by the use of the oscilloscope. The
characteristic wave pattern of an impulse generated in
a stimulated nerve fiber could be observed on the
screen and the components of the nerve’s response
studied.
Erlanger and Gasser were given the Nobel Prize in
medicine or physiology in 1944 for this work. Erlanger
later worked on the metabolism of dogs with shortened
intestines, on traumatic shock, and on the mechanism
of the production of sound in arteries.
With Gasser he wrote Electrical Signs of Nervous
Activity(1937). He died on December 5, 1965, in St.
Louis.erythrocyte Aconcave red blood cell that functions
totally within the cardiovascular system. It does not
have a nucleus or cytoplasmic organelles and produces
little enzyme activity. It contains the red pigment
hemoglobin, an oxygen-binding protein, and the cell
functions as an efficient vessel for the exchange of res-
piratory gas. Originates from bone marrow in adult
humans.
See alsoBLOOD.Escherichia coli A gram-negative, rodlike bacterium
that forms acid and gas in the presence of carbohy-
drates and is commonly found in human intestines and118 epitope