84 cotyledons
cotyledons Leaflike structures (seed leaves) pro- cedure introduced by Werner Forssmann and called
duced by the embryo of flowering plants, the dicots Forssmann’s procedure, now called cardiac catheteriza-
(Magnoliopsida), and the monocots (Liliopsida). They tion (a tube is passed into the heart from a vein at the
serve to absorb nutrients in the seed until the seedling elbow). This made it possible to study the functioning
is able to produce true leaves and begin photosynthesis. of the diseased human heart and to make more accu-
In monocots, the embryo has a single cotyledon, while rate diagnoses of the underlying anatomic defects. They
in dicots, the embryo has two cotyledons. also used the catheter to examine the pulmonary artery,
improving the diagnosis of lung diseases as well. He
See also DICOT; MONOCOT. shared the Nobel Prize in physiology or medicine with
Dickinson W. Richards and Werner FORSSMANN for
countercurrent exchange The effect caused when their discoveries concerning heart catheterization and
two fluids move past each other in opposite directions circulatory changes in 1956.
and facilitate the efficient exchange of heat, gas, or sub-
stance. For example: the passage of heat from one Cournand served on the editorial boards of many
blood vessel to another; rete mirabile, the countercur- medical and physiological publications, including Cir-
rent exchange structure of capillaries that allows gas culation, Physiological Reviews, The American Journal
uptake in a fish swim bladder; the kidney nephron of Physiology, and also Journal de Physiologie and
loop, a tubular section of nephron between the proxi- Revue Française d’Etúdes Cliniques et Biologiques. He
mal and distal convoluted tubules where water is con- was a member of numerous scientific organizations and
served and urine concentrates by a countercurrent received awards for his work. He died on February 19,
exchange system; and the upper airway where, upon 1988, at Great Barrington, Massachusetts.
expiration, heat and moisture are retained and given up
to relatively cool and dry inspired gases. court (lek) The area defended by individual males
within an area where birds gather for display and
Cournand, André-Frédéric (1895–1988) French courtship.
Physiologist André-Frédéric Cournand was born in
Paris on September 24, 1895, to Jules Cournand, a covalent bond A region of relatively high electron
stomatologist, and his wife Marguérite Weber. He density between nuclei that arises at least partly from
received his early education at the Lycée Condorcet, sharing of electrons and gives rise to an attractive force
received a bachelor’s degree at the Faculté des Lettres and characteristic internuclear distance.
of the Sorbonne in 1913, and received a diploma of
physics, chemistry, and biology of the Faculté des Sci- crista The inner membrane of mitochondrion, where
ences the following year. respiration takes place; location of the electron transport
chain and enzymes that catalyze ATP synthesis. Also the
He began medical studies in 1914, but served in term applied to sensory cells within an ear’s semicircular
the French Army from 1915 to 1918, returning to med- canal that detect fluid movement. Also means crest, such
ical studies at the Interne des Hôpitaux de Paris in as the crista galli, the comb on a rooster.
1925. He received an M.D. from the Faculté de
Médecine de Paris in May 1930 and secured a residen- Croll, James (1821–1890) British Carpenter, Physi-
cy in the Tuberculosis (later Chest) Service of the cist James Croll was born in Cargill, Perthshire, Scot-
Columbia University Division at Bellevue Hospital, land, on January 2, 1821. He was the son of David
New York. He became chief resident of this service and Croll, a stonemason from Little Whitefield, Perthshire,
conducted research on the physiology and phys- and Janet Ellis of Elgrin. He received an elementary
iopathology of respiration under the guidance of Dick- school education until he was 13 years old. His knowl-
inson W. RICHARDS. He became an American citizen in edge of science was the result of vigilance, since he was
1941 and retired from Columbia in 1964.
Together, Cournand and Richards collaborated in
clinical lung and heart research. They perfected a pro-
Croll, James 85
self-taught. On September 11, 1848, he married Isabel- axis), in this case the degree of Earth’s elliptic orbit, he
la MacDonald, daughter of John MacDonald. proposed, varied on a time scale of about 100,000
years. Since variations in eccentricity only produced
Croll started his career as a carpenter apprenticed small changes in the annual radiation budget of Earth,
to a wheelwright when he was young; then he became a and not enough to force an ice age, Croll developed the
joiner at Banchory and opened a shop in Elgin. In 1852, idea of climatic feedbacks, such as changes in surface
he opened a temperance hotel in Blairgowrie, and later, albedo (reflection). He predicted that the last ice age
in 1853, became an insurance agent for the Safety Light was over about 80,000 years ago.
Assurance Company ending up in Leicester.
During the 1860s, he published his theories in a
His first book, The Philosophy of Theism, was number of papers: “On the Physical Cause of Changes
published in 1857 and based on the influence of the of Climate during Geological Epochs” (1864); “The
metaphysics of Jonathan Edward. However due to an Eccentricity of the Earth’s Orbit” (1866, 1867); “Geo-
injury, he ended up obtaining a job as a janitor at logical Time and Date of Glacial and Miocene Periods”
Anderson’s College and Museum in Glasgow in 1859. (1868); “The Physical Cause of the Motion of
Being a janitor gave him enough free time after his Glaciers” (1869, 1870); “The Supposed Greater Loss
daily chores to utilize the museum’s extensive library. of Heat by the Southern Hemisphere” (1869); “Evolu-
There, he would spend the night reading books on tion by Force Impossible: A New Argument against
physics, including the works of Joseph A. Adhémar, Materialism” (1877). During this time he was the keep-
the French mathematician, who noted in 1842 that the er of maps and correspondence at the Scottish Geologi-
Earth’s orbit is elliptical rather than spherical. Adhé- cal Survey starting in 1867, where he mingled with
mar proposed in his book Revolutions de la Mer, Del- some of the best geologists of the time until he retired
uges Periodics (Revolutions of the sea, periodic floods) in 1880.
that the precession of the equinoxes produced varia-
tions in the amount of solar radiation striking the In 1875 he published Climate & Time in Their
planet’s two hemispheres during the winter time (inso- Geological Relations, where he summed up his
lation), and this, along with gravity effects from the research on the ancient condition of the Earth. On Jan-
sun and moon on the ice caps, is what produced ice uary 6, 1876, he was elected a fellow of the Royal Soci-
ages alternately in each hemisphere during a 26,000- ety of London. Charles Darwin was among the many
year cycle. Precession is the slow gyration of Earth’s supporters of his nomination. He received an LL.D.
axis around the pole of the ecliptic, caused mainly by (law degree) that year from St. Andrews College. While
the gravitational pull of the sun, moon, and other his main interests were in the field of paleoclimate
planets on Earth’s equatorial bulge. Croll also read change, he also put forth theories about ocean currents
about the new calculations of the Earth’s orbit by and their effects on climate during modern times.
French astronomer Urbain Jean Joseph Leverrier (a
discoverer of the planet Neptune). However, some of his thoughts and ideas were
wrong. For example, Croll believed that ice ages varied
Croll decided to work on the origins of the ice in the hemispheres, and his estimated age for the last
ages, since he did not agree with the prevailing attitude ice advance ending 80,000 to 100,000 years ago was
that they were leftover relics from the biblical Great wrong. It ended between 14,000 and 10,000 years ago,
Flood, and additionally he found errors in Adhémar’s as research currently shows. Because of these errors,
work. Croll came to the conclusion that the overriding Croll fell out of vogue until 1912, when Yugoslav geol-
force changing climate and creating the ice ages on ogist Milutin Milankovitch revised Croll’s theories in
Earth was due to variations in insolation, which is the his book, Canon of Insolation.
rate of delivery of solar radiation per unit of horizontal
surface, i.e., the sunlight hitting the Earth. Croll published close to 90 papers on a variety of
subjects, such as “Ocean Currents” (1870, 1871, 1874);
Croll first realized that Adhémar did not take into “Change of Obliquity of Ecliptic: Its Effect on Climate”
account the shape of the Earth’s orbit that varied over (1867); “Physical Cause of Submergence during Glacial
time and its effect on precession, so he calculated the Epoch” (1866, 1874); “Boulder Clay of Caithness &
eccentricity over several million years. This eccentricity Glaciation of North Sea” (1870); “Method of Deter-
(the distance between the center of an eccentric and its mining Mean Thickness of Sedimentary Rocks” (1871);
86 Cro-Magnon
and “What Determines Molecular Motion? The Funda- Many of them are important economic species for
mental Problem of Nature” (1872). human consumption.
A famous debate on the nature of deep-sea circula- cryptic Describes the ability to conceal or camouflage.
tion between Croll and Irish scientist William Carpen-
ter during the 1860s to 1880s was well discussed in the cryptic coloration A camouflage technique whereby
literature and around scientific circles via correspon- an organism matches its background, concealing itself
dence. In 1885, he published Climate and Cosmology from predators or prey, e.g., the peppered moth.
to answer critics of his earlier work Climate & Time in
Their Geological Relation. Five years later, plagued by See also MIMICRY.
ill health his whole life, he died in Perth on December
15, at age 69, shortly after publishing a small book
called The Philosophical Basis of Evolution.
Cro-Magnon An early group of Homo sapiens crystal field Crystal field theory is the theory that
(humans) that lived in Europe around 40,000 years ago. interprets the properties of COORDINATION entities on
the basis that the interaction of the LIGANDs and the
crossing over A process during meiosis when alleles CENTRAL ATOM is a strictly ionic or ion-dipole interac-
on homologous chromosomes (chromosomes that pair tion resulting from electrostatic attractions between the
with each other at meiosis) switch places, increasing the central atom and the ligands. The ligands are regarded
possible combinations of alleles and thus increasing the as point negative (or partially negative) charges sur-
variability of the whole genome. Also called recombi- rounding a central atom; covalent bonding is complete-
nation. ly neglected. The splitting or separation of energy levels
of the five degenerate d-orbitals in a transition metal,
See also RECOMBINANT. when the metal is surrounded by ligands arranged in a
particular geometry with respect to the metal center, is
called the crystal field splitting.
cross-pollination When pollen from the anther of a C-terminal amino acid residue See AMINO ACID
flower of one plant is transferred to the flowers (stig- RESIDUE.
ma) of a different plant.
See also POLLINATION.
cross-reactivity The ability of an immunoglobulin, Curie relation See MAGNETIC SUSCEPTIBILITY.
specific for one antigen, to react with a second antigen.
A measure of relatedness between two different anti- cuticle A protective impermeable waxy substance
genic substances. formed from the polymer cutan that covers the outside
of leaves, stems, and fruits and forms the protective
Crustacea All crustaceans have two pairs of anten- layer of arthropods.
nae, a pair of mandibles, a pair of compound eyes
(usually on stalks), two pair of maxillae on their cyanobacteria Bacteria, formerly known as blue-
heads, and a pair of appendages on each body segment green algae; aquatic and photosynthetic organisms that
(head, thorax, and abdomen). There are about 30,000 live in water and manufacture their own food. Their
species of this subphylum within five classes (Remi- fossils go back more than 3.5 billion years, making
pedia, Cephalocarida, Branchiopoda, Maxillopoda, them the oldest known species, and they are the con-
and Malacostraca). Includes lobsters, crabs, crayfish, tributors to the origin of plants.
shrimp, copepods, isopods, barnacles, and others.
See also ALGAE.
cytokinesis 87
cybernetics The science that studies the methods to occupied by strong field LIGANDs, regardless of the
control behavior and communication in animals (and oxidation state of iron. Cytochromes can be distin-
machines). guished by the wavelength of the α band, such as
cytochrome c-550. Certain specific cytochromes with
cyclic AMP (cAMP; 3’,5’-AMP) Cyclic adenosine particular functions are designated with suffixes, such
monophosphate. A compound synthesized from ATP as cytochrome a1, b2, etc.
(by the enzyme adenylyl cyclase) in living cells that acts
as an intercellular and extracellular second messenger cytochrome-c oxidase An ENZYME, ferrocyto-
mediating peptide and amine hormones. chrome-c: dioxygen OXIDOREDUCTASE, CYTOCHROME
aa3. The major respiratory protein of animal and plant
cyclic electron flow Two photosystems are present MITOCHONDRIA, it catalyzes the oxidation of Fe(II)-
in the thylakoid membrane of chloroplasts: photosys- cytochrome c, and the reduction of dioxygen to water.
tem I and photosystem II. The two photosystems work Contains two HEMEs and three copper atoms, arranged
together during the light reactions of photosynthesis. in three centers. Heme a3 and copper-B form a center
The light-induced flow of electrons beginning with and that reacts with dioxygen; the second heme is
returning to photosystem I to produce ATP without cytochrome a; the third site, copper-A, is a dinuclear
production of NADPH (nicotine adenine dinucleotide center.
phosphate with hydrogen ) is cyclic electron flow. The
generation of ATP by this process is called noncyclic See also NUCLEARITY.
photophosphorylation.
cytochrome P-450 General term for a group of
cyclin A protein found in dividing cells that activates HEME-containing MONOOXYGENASEs. Named from
protein kinases (cyclin-dependent protein kinases), a the prominent absorption band of the Fe(II)-carbonyl
type of enzyme that adds or removes a phosphate complex. The heme comprises PROTOPORPHYRIN IX,
group from a target protein and controls the progres- and the proximal LIGAND to iron is a cysteine sulfur.
sion of one phase of the cell cycle to the next. The con- Cytochromes P-450 of microsomes in tissues such as
centration of the cyclin increases and decreases during liver are responsible for METABOLISM of many XENO-
the cell cycle. BIOTICs, including drugs. Others, such as the mito-
chondrial ENZYMEs from adrenal glands, are
cyclin-dependent kinase A protein kinase, an involved in biosynthetic pathways such as those of
enzyme involved in regulating cell growth and division, steroids. The reaction with dioxygen appears to
that must be attached to cyclin to become activated. involve higher oxidation states of iron, such as
Fe(IV)=O.
See also MITOCHONDRIA.
cytochrome A HEME protein that transfers electrons cytokines Cytokines are soluble glycoproteins
and exhibits intense absorption bands (the α and β released by cells of the immune system (secreted pri-
bands, the α band having the longer wavelength) marily from leukocytes) that act nonenzymatically
through specific receptors to regulate immune respons-
between 510 and 615 nm in the reduced form. es. Cytokines resemble hormones in that they act at
low concentrations bound with high affinity to a spe-
Cytochromes are designated types a, b, c, or d, cific receptor.
depending on the position of the α band, which
cytokinesis The final stage of mitosis, when the
depends on the type of heme. The iron undergoes oxi- parent cell divides equally by cell-wall formation into
dation–reduction between oxidation states Fe(II) and
Fe(III). Most cytochromes are hemochromes, in which
the fifth and sixth COORDINATION sites in the iron are
88 cytoplasm
two daughter cells by way of a constriction and rials within cells, e.g., chloroplasts moving up to the
drawing in of an actin/myosin ring around the center surface of the leaf and then down, which appear to
of the cell. help in photosynthesis.
See also CELL.
cytoplasm The part of protoplasm in a cell outside cytoskeleton The internal support system and
of and surrounding the nucleus. The contents of a cell framework of a cell, comprising numerous microfila-
other than the nucleus. Cytoplasm consists of a fluid ments and tubules that branch throughout the cell. The
containing numerous structures, known as organelles, cytoskeleton serves not only as mechanical support but
that carry out essential cell functions. also in transport functions.
See also CELL. See also SKELETON.
cytoplasmic determinants Substances distributed in cytosol The semifluid portion of the cytoplasm, not
an embryo, but present in an unfertilized egg, that including organelles.
appear in different blastomeres at the initial cleavage
stage and influence their development fate.
cytoplasmic streaming The movement and flow of cytoxic T cells (T killer cells) Cells that kill target
cytoplasm, the living part of a cell outside the nuclear cells bearing appropriate antigen within the groove of
membrane. The primary method of movement of mate- an MHC (major histocompatibility complex) class I
molecule that is identical to that of the T cell.
D
Dale, Henry Hallett (1875–1968) British Physiolo- acetylcholine’s role as a chemical transmitter of nerve
gist Sir Henry Hallett Dale was born in London on impulses.
June 9, 1875, to Charles James Dale, a businessman,
and Frances Ann Hallett. He attended Tollington Park In 1936 he shared the Nobel Prize in physiology or
College in London, Leys School, Cambridge, and in medicine with his friend German pharmacologist Otto
1894 he entered Trinity College with a scholarship. He LOEWI for their discoveries in the chemical transmission
graduated through the Natural Sciences Tripos in 1898, of nerve impulses.
specializing in physiology and zoology.
He was knighted in 1932 and appointed to the
In 1900 he gained a scholarship and entered St. Order of Merit in 1944. In addition to numerous arti-
Bartholomew’s Hospital, London, for the clinical part cles in medical and scientific journals that record his
of the medical course. He received a B.Ch. at Cam- work, he was the author of Adventures in Physiology
bridge in 1903 and became an M.D. in 1909. (1953), and An Autumn Gleaning (1954).
He took an appointment as pharmacologist at the Sir Henry was president of the Royal Society
Wellcome Physiological Research Laboratories in 1904 (1940–45) and others, and he received many awards.
and became director of these laboratories in 1906, He married his first cousin Ellen Harriet Hallett in
working for some six years. In 1914, he was appointed 1904. He died on July 23, 1968, in Cambridge.
director of the department of biochemistry and phar-
macology at the National Institute for Medical dalton A unit of measurement of molecular weight
Research in London, and in 1928 he became the direc- based on the mass of one-twelfth the mass of 12C, i.e.,
tor of this institute, serving until his retirement in 1.656 × 10–24. A dalton is also called an atomic mass
1942, when he became professor of chemistry and a unit, or amu, and is used to measure atomic mass. Pro-
director of the Davy-Faraday Laboratory at the Royal tein molecules are express in kilodaltons (kDa). The
Institution, London. dalton was named in honor of John Dalton
(1766–1844), an English chemist and physicist.
In 1911, he was the first to identify the compound
histamine in animal tissues, and he studied its physio- Dam, Henrik (1895–1976) Danish Biochemist Carl
logical effects, concluding that it was responsible for Peter Henrik Dam was born in Copenhagen on Febru-
some allergic and anaphylactic reactions. After success- ary 21, 1895, to druggist Emil Dam and his wife
fully isolating acetylcholine in 1914, he established that Emilie (née Peterson), a teacher. He attended the Poly-
it was found in animal tissue, and in the 1930s he technic Institute, Copenhagen, and graduated with a
showed that it is released at nerve endings in the
parasympathetic nervous system, thus establishing
89
90 darling effect
degree in chemistry in 1920. The same year he was the more it reproduces, the higher the fitness and the
appointed assistant instructor in chemistry at the higher the chance that a hereditary characteristic will
School of Agriculture and Veterinary Medicine, be reproduced.
advancing to full instructor in biochemistry at the
Physiological Laboratory of the University of Copen- Darwinism The evolutionary theory advanced by
hagen in 1923. Charles Darwin during the mid-19th century suggest-
ing that present-day species have evolved from simpler
In 1925 Dam became assistant professor at the ancestors. A newer version of the theory is incorporat-
Institute of Biochemistry, Copenhagen University, and ed as “neo-Darwinism” or “modern synthesis.”
three years later was promoted to associate professor
until 1941. On submitting a thesis Nogle Under- day-neutral plant A plant where the length of day is
søgelser over Sterinernes Biologiske Betydning (Some not an influence on development; the plant will flower
investigations on the biological significance of the ster- regardless of day length (photoperiodism). It is now
ines) to the University of Copenhagen in 1934, he known that it is not the length of the light period, but
received a Ph.D. in biochemistry. the length of uninterrupted darkness, that is critical to
floral development. Examples are tomato, corn, cucum-
He discovered vitamin K and its anticoagulant ber, and strawberries.
effects while studying the sterol metabolism of chicks in
Copenhagen and was awarded the Nobel Prize in phys- See also PHOTOPERIODISM.
iology or medicine in 1943 for this work.
decapods Crustaceans that have five pairs of walk-
He conducted research at Woods Hole Marine ing legs and a well-developed carapace, e.g., shrimps,
Biological Laboratories in Massachusetts during the lobsters, hermit crabs, and crabs.
summer and autumn of 1941 and was a senior
research associate at the University of Rochester, New deciduous A plant, tree, or shrub that sheds its
York, between 1942 and 1945, and he was an associ- leaves at the end of the growing season.
ate member at the Rockefeller Institute for Medical
Research in 1945. See also CONIFER.
Dam was appointed professor of biochemistry at decomposers A trophic level or group of organisms
the Polytechnic Institute, Copenhagen, in 1941, though such as fungi, bacteria, insects, and others that as a
the designation of his chair at the Polytechnic Institute group digest or break down organic matter (dead ani-
was changed to professor of biochemistry and nutrition mals, plants, or other organic waste) by ingesting,
in 1950. secreting enzymes or other chemicals, and turning them
into simpler inorganic molecules or compounds that
After his return to Denmark in 1946, he concen- are released back into the environment.
trated his research on vitamin K, vitamin E, fats,
cholesterol, and nutritional studies in relation to gall- decumbent A plant or part of the plant that is reclin-
stone formation. ing or lying on the ground but with the tip or apex
ascending or pointing up. Also called prostrate, as in a
He published over 300 articles in biochemistry and prostrate shrub.
was a member of numerous scientific organizations.
Dam died on April 17, 1976. dehiscent A fruit or seed capsule that splits open.
darling effect The stimulation of reproductive
activity by the activity of other members of the species
in addition to the mating pair. Also called the Fraser
darling effect.
Darwinian fitness The measure of an individual’s
relative genetic contribution to the gene pool of the
next generation; the longer an individual survives and
dendrite 91
dehydration reaction (condensation reaction) A Angelman syndrome, a combination of birth defects
chemical reaction in which two organic molecules caused by inheriting both copies of the No. 15 chromo-
become linked to each via COVALENT BONDs with the some from the father, and Prader-Willi syndrome, a
removal of a molecule of water; common in synthesis combination of birth defects caused by inheriting both
reactions of organic chemicals. copies of the No. 15 chromosome from the mother or
by inheriting a deletion of a region in the proximal
dehydrogenase An OXIDOREDUCTASE that catalyzes long arm of chromosome No. 15 from the father.
the removal of hydrogen atoms from a SUBSTRATE. Hypopigmentation, which is unusually lighter hair,
eyes, and skin color in relation to other family mem-
deletion A type of mutation where an alteration or bers, is common in Prader-Willi syndrome, especially in
loss of a segment of DNA occurs from a chromosome individuals with a partial deletion of the long arm of
as the consequence of transposition, i.e., when DNA is chromosome 15. Cri du Chat syndrome is a rare com-
being moved from one position from one genome to bination of birth defects caused by a deletion of chro-
another. Such mutations can lead to disease or genetic mosome 5p.
abnormality. A terminal deletion refers to breakage and
loss off the end of a chromosome, while an interstitial deme One or more local populations of a taxon that
deletion is the loss of material from within the chromo- can interbreed.
some, but between the ends. Examples of deletion are
demography The scientific inquiry into the vital
statistics of populations that includes sizes, age–sex
compositions, ratios, distributions, densities, growth,
natality, mortality, migration, and other characteristics
as well as the causes, characteristics, and consequences
of changes in these factors. Because the study seeks
those relationships that can be expressed precisely and
quantitatively, demographers use quantitative analyti-
cal methods, but they turn to other disciplines such as
anthropology, sociology, and others to explain them.
U.S. Census data are a major source of demography for
human studies.
denaturation In DNA denaturation, two strands of
DNA are separated as a result of the disruption of the
hydrogen bonds following exposure to extreme condi-
tions such as high temperature, chemical treatment, pH
changes, salt concentration, and others. Denaturation
in proteins by heat, acids, bases, or other means results
in a change in the three-dimensional structure of the
protein so that it cannot perform its function and
becomes biologically inactive.
A particular kind of mutation, i.e., the loss of a piece of DNA from dendrite The thin extension of a neuron that forms
a chromosome. Deletion of a gene or part of a gene can lead to a synapses by producing or responding to neurotrans-
disease or abnormality. (Courtesy of Darryl Leja, NHGRI, National mitters. A dendrite forms connections with the axons
Institutes of Health)
92 dendrochronology
of other neurons and transmits nerve impulses toward density-dependent factor An external process or
the cell body. A dendrite is also a branch or treelike biological factor, such as disease, competition, or pre-
figure produced on or in a rock or mineral or a lichen dation, that has a greater effect on a population as
form. the population density increases. A dense population
living closely together is more likely to have more of
See also NEURON. its individuals afflicted and affected by disease than a
population that is less dense, with individuals living
dendrochronology Tree-ring dating. The process of farther apart from one another. The term also refers
determining the age of a tree or wood by counting the to a population regulation factor in ecosystems where
number of annual growth rings. the communities have many species and where many
biological interactions are taking place. The term can
dendrogram A treelike or graphical diagram that also refer to limiting factors that have an increasing
summarizes the process of hierarchical clustering show- effect on a population as the population increases
ing evolutionary change. in size.
See also CLADISTICS. density-dependent inhibition A process where
most normal animal cells stop dividing when they come
dengue (dandy fever) An epidemic disease found in into contact with each other.
tropical and subtropical regions. Caused by the dengue
virus (genus Flavivirus [family Flaviviridae]), which is density-independent factor An external process or
carried by a mosquito of the genus Aedes (Aedes set of physical factors (weather, flooding, fire, pollu-
aegypti or Aedes albopictus). First described in 1827 in tion, etc.) that reduces a population, regardless of size.
Zanzibar; an outbreak occurred in Philadelphia in This can occur in areas with few species with few bio-
1780, then called breakbone fever. logical interactions. The term applies to limiting fac-
tors that affect all populations, regardless of their
denitrification The reduction of nitrates to nitrites, density.
nitrogen monoxide (nitric oxide), dinitrogen oxide
(nitrous oxide), and ultimately dinitrogen catalyzed by denticity The number of donor groups from a given
microorganisms, e.g., facultative AEROBIC soil bacteria LIGAND attached to the same CENTRAL ATOM.
under ANAEROBIC conditions.
De-nol Trade name for the potassium salt or mixed deoxyribonucleic acid (DNA) A high-molecular-
ammonium potassium salt of a bismuth citrate com- mass linear polymer, composed of NUCLEOTIDES con-
plex, used in the treatment of ulcers. taining 2-deoxyribose and linked between positions
3’ and 5’ by phosphodiester groups. DNA contains
de novo design The design of bioactive compounds the genetic information of organisms. The double-
by incremental construction of a ligand model within a stranded form consists of a DOUBLE HELIX of two
model of the RECEPTOR or ENZYME-active site, the complementary chains that run in opposite directions
structure of which is known from X-ray or nuclear and are held together by hydrogen bonds between
magnetic resonance (NMR) data. pairs of the complementary NUCLEOTIDES. The way
the helices are constructed may differ and is usually
density In biology, the number of individuals per designated as A, B, Z, etc. Occasionally, alternative
unit area or volume. structures are found, such as those with Hoogsteen
BASE PAIRING.
See also GENETICS.
dermal tissue system 93
deoxyribose A five-carbon sugar (C5H10O4) compo- deposit-feeder A land organism (e.g., earthworm) that
nent of DNA. Joins with a phosphate group and base eats sediment and processes it through a digestive tract or
to form a deoxyribose nucleotide, the subunit of nucle- an aquatic organism (e.g., marine annelid) that ingests
ic acids. bottom sediments such as the sand and mud of a water
body. Both digest the microorganisms and other organic
depolarization A process where a neuron’s electrical matter, with the rest of the material passing through the
charge becomes less negative as the membrane poten- gut. Examples of deposit feeders are most oligochaetes
tial moves from resting potential (70 mV) toward 0 (earthworms [family Lumbricidae] and small freshwater
mV; a decrease in voltage. The loss of membrane polar- forms like Tubifex), which includes about 3,500 species.
ity is caused by the inside of the cell membrane becom- Polychaetes (nonselective or selective deposit feeders),
ing less negative in comparison to the outside. such as Nereis (common clamworm) and other marine
Depolarization is caused by an influx of NA+ ions worms such as bloodworms, lugworms, fanworms, and
through voltage-gated Na+ channels in axons. scaleworms, number about 8,000 species. Forms include
the sedentary Arenicola (lugworm), which is a subsurface
Depolarization is a reduction in potential that (burrow dwelling) deposit feeder, and Amphrites (terre-
usually ends with more positive and less negative bellid), which is a tube-dwelling selective deposit feeder.
charge. Hyperpolarization is the opposite, an increase
in potential that ends with more negative and less dermal tissue system The outside protective cover-
positive charge. Repolarization is when the state ing (skin) of young plants consisting of a waxy type
returns to resting potential. Action potentials are (cuticle) epidermis, a tightly packed single outer layer
caused by depolarization in nerve cells. An action of cells that protects and reduces water loss. Stomata
potential is a one-way, self-renewing wave of mem- regulate gases passing in and out of the plant and are
brane depolarization that propagates at rapid speed usually located on the underside of leaves, and guard
(up to 120 m/sec) along the length of a nerve axon. cells regulate the opening by changing water pressure
Julius Bernstein first proposed the concept of depo- within the cell to swell or shrink. Also the outer tissue
larization in 1868.
sugar phosphate base pair nitrogeous base A Adenine G Guanine
backbone T Thymine C Cytosine
ATC A TG ATG AT G
AC AC G C
T
AG T C
A
DNA is the chemical inside the nucleus of a cell that carries the genetic instructions for making living organisms. (Courtesy of Darryl
Leja, NHGRI, National Institutes of Health)
94 desferal
hair sebaceous gland contact points between cells and “spot welds” between
follicle erector muscle cells and adjacent plasma membranes.
capillary loop pore determinate cleavage (mosaic cleavage) A type of
cleavage in protostomes, usually spiral, in which the
epidermis cornified layer fates of the cells (blastomeres) are fixed and cannot be
dermis changed very early in development. Determinate cleav-
granular layer age was first discovered in nematodes.
adipose tissue
Malpighian layer determinate growth A growth characteristic of spe-
sweat duct cific duration in which an organism stops growing after
nerve fiber it reaches a certain size or achieves a specific goal. As
sweat glands examples: a crop that stops growing and dries after
and capillaries producing grain; a human adult that stops growing
after achieving final height; a plant that ripens all of its
venule arteriole seeds at the same time; or an apical meristem that dif-
ferentiates into flowers, terminating the production of
The epidermis serves as a protective layer against invasion of for- additional leaves and stems.
eign substances, both chemical and animal (parasites).
determination In many organisms, the fates of the
of a secondary plant body, a periderm consisting of earliest embryonic cells are not determined and have
cork that serves as a protective packed-cell arrange- the potential to develop into many different cell types.
ment for woody stems. Determination is the process whereby cells are commit-
ted to a particular development fate as the embryo
desferal See DESFERRIOXAMINE. grows. Portions of the gene are selected for expression
in different embryonic cells, which gradually restricts
desferrioxamine (dfo) Chelating agent used world- cell fate. Cells can progress from being capable of
wide in the treatment of iron overload conditions, such forming any cell type (totipotent), such as the zygote;
as HEMOCHROMATOSIS and THALASSEMIA. to being capable of forming most tissues of an organ-
ism (pluripotent); to being fully determined.
See also CHELATION.
As an embryo develops, its cells become deter-
desmosome At certain points along adjacent surfaces mined and committed to developing into particular
of cells there are intercellular attachments: zonula occlu- parts of the embryo and later adult structures. Follow-
den (tight junction), zonula adherens (belt desmosome), ing determination, cells eventually differentiate into
and macula adherens (spot desmosome). Belt desmo- their final, and often specialized, forms.
somes are a specialized lateral cell-to-cell adhesion, or
anchoring junction, that anchors cells, usually epithelial Determination is a slow process in which a cell’s
cells, to each other or to extracellular matter. Consisting potency is progressively restricted as it develops, and
of dense protein plaques, they form tight attachments to the determined state is heritable (a type of cell memory)
other cells with intermediate filaments consisting of via somatic cell division. It is irreversible most of the
cytoskeleton material that serves as support and struc- time, but there have been examples of a cell reverting
ture between adjacent cells, between cells, and as an back to an undetermined state.
extracellular matrix. Found in tissues that have been
stretched or are subjected to friction, e.g., heart muscle. detritus Accumulated organic debris from dead
“Spot” desmosomes are found in all epithelial cells and organisms, often an important source of nutrients in a
other tissues such as smooth muscle and are buttonlike
diastole 95
food web. A detrivore is any organism that obtains diaphragm A dome-shaped sheet of thin skeletal
most of its nutrients from detritus. muscle that separates the lungs and heart from the
abdomen and assists in breathing. With inspiration,
deuterostomes One of the two groups of coelo- the diaphragm contracts and flattens downward, while
mates, animals that have a coelom or body cavity the volume of the thoracic cavity increases, allowing air
lined with mesoderm. The deuterostomes, which to enter the respiratory tract. After expiration, the
includes echinoderms and chordates, are animals diaphragm relaxes back to its dome shape until the
where the first opening in the embryo during next inspiration.
gastrulation becomes the anus, while the mouth
appears at the other end of the digestive system; A diaphragm is also a modern contraceptive
opposite of the protostomes (mollusks, annelids, devices that prevents sperm from reaching and entering
arthropods), where the mouth forms first during gas- the egg.
trulation and before the future anus. The blastopore,
which is the opening of the archenteron in the gastru- diastereoisomers STEREOISOMERs not related as
la, is the site of both mouth or anus development in mirror images.
both groups.
diastole One of two phases of the beating heart.
Devonian period A geological period that existed Diastole is the three-step phase when the heart muscle
during the middle of the Paleozoic era. The Devonian (ventricles) relaxes, causing blood to fill the heart
period existed between 406 and 360 million years ago chambers. SYSTOLE is when the ventricles contract.
and is separated into the Early Devonian period (406 Diastolic blood pressure is the blood pressure measured
to 387 million years ago), the Middle Devonian period during diastole, when the chambers fill with blood. It is
(387 to 374 million years ago), and the Late Devonian the force exerted by blood on arterial walls. The lowest
period (374 to 360 million years ago). It is also called blood pressure measured in the large arteries is about
the age of fishes. 80 mm Hg under normal conditions for a young adult
male.
See also GEOLOGICAL TIME.
The three phases—early, mid, and late diastole—
dfo See DESFERRIOXAMINE. deal with the conditions of the ventricle, semilunar
valve, and atrioventricula valve, while filling, and the
diabetes mellitus An ailment characterized by reactions of the SA (sinoatrial) node (the heart’s “pace-
hyperglycemia resulting from the body’s inability to use maker”) and AV (atrioventricular) node, which regulate
blood glucose for energy. There are two types. In type 1 contractions.
diabetes, the pancreas ceases to make insulin, and
blood glucose does not enter the cells to be used for See also BLOOD PRESSURE.
energy. In type 2 diabetes, the pancreas fails to make
sufficient insulin, or the body is unable to use insulin
correctly. It is estimated to affect some 17 million peo-
ple in the United States and is the sixth leading cause of
death.
diamagnetic Substances having a negative MAGNET- The Bacillariophyceae or diatoms are unicellar algae that are
IC SUSCEPTIBILITY are diamagnetic. They are repelled by found in single, colonial, or filamentous states. (Courtesy of
a magnetic field. Hideki Horikami)
96 diatoms
diatoms See ALGAE; CHROMISTA. of low concentration, stopping when the concentration
is equally dispersed.
dichotomous Either halving or branching by pairs. digestion The process by which living organisms
break down ingested food in the alimentary tract into
dicot (dicotyledon) A member of a subclass of the more easily absorbed and assimilated products using
angiosperms (division Anthophyta) characterized by enzymes and other chemicals. Digestion can occur in
the presence of two cotyledons in the seed, a reticulated aerobic conditions, where waste is decomposed by
netlike system of veins in the leaves, flower petals in microbial action in the presence of oxygen, or under
fours or fives, vascular system arranged in a ring in the anaerobic conditions when waste is decomposed under
cortex, root development from the radicle with a microbial action in the absence of oxygen. In anaerobic
fibrous root, and a three-pore pollen structure. conditions such as in a large animal facility (e.g., a
dairy farm), the by-product, a low-energy biogas that is
There are about 250,000 species of angiosperms made with the combination of methane and carbon
around the world. They make up the largest classifica- dioxide, can be used as an energy source.
tion of plants. It is the development of flowers for
reproduction that sets them apart from other plant dihybrid cross The inheritance of two characteristics
types. from two parents at the same time (e.g., leaf shape and
stem color). If one trait inherited does not affect the
Many of our food and economic staples are from other, the dihybrid cross is two monohybrid crosses
angiosperms, e.g., peanuts, flax, spinach, rice, corn, operating concurrently. Traits that do not influence the
cotton. inheritance of each other are said to assort indepen-
dently. Demonstrates that Mendel’s Principle of Inde-
The class Angiospermae (division Anthophyta) is pendent Assortment allows each trait to be considered
the largest classification of plants. Its distinctive charac- separately, since each trait is inherited independently of
teristic is the development of flowers, which are used the other.
for reproduction. The oldest angiosperm fossils came
from the Cretaceous period of the Mesozoic era. dihydrofolate An oxidation product of TETRAHY-
DROFOLATE that appears during DNA synthesis and
The other angiosperm class is the monocotyledons other reactions. It must be reduced to tetrahydrofolate
(monocots), which evolved from dicot ancestors early to be of further use.
in the development of flowering plants. There are many
more dicots than monocots, and the two groups differ See also FOLATE COENZYMES.
radically in many ways. Dicots are woody or herba-
ceous; monocots are only herbaceous. The monocots’s dikaryon The occurrence of two separate haploid
pollen (single pore), vascular arrangement in stems and nuclei in each cell in the mycelium of some forms
roots (scattered bundles), seed leaf (one), flower parts of fungi such as basidiomycetes. If the nuclei are
(multiples of three), and root structure (adventitious both the same genotype, it is said to be homokaryotic;
with taproot) are also different. if nuclei are of different genotypes, it is said to be
heterokaryotic.
See also MONOCOT.
differentiation A process in embryonic development
where unspecialized cells take on their individual
traits, reach mature form, and progressively become
specialized for specific functions such as tissues and
organs.
diffusion The random dispersion or spreading out of dikaryotic Mycelium or spores containing two
molecules from a region of high concentration to one sexually compatible nuclei per cell. Common in the
BASIDIOMYCETES.
dismutase 97
dimorphism The ability of a species to have more malaria, yellow fever), while others are important polli-
than one color or body form, such as differences nators, pest predators, and parasites. Dipterons under-
between sexes. go complete metamorphosis and usually have more
than one generation per year.
See also SEXUAL DIMORPHISM.
dinoflagellates See ALGAE. directional selection When natural selection favors
a phenotype at one extreme of the phenotypic range,
dinosaurs Animals that arose from a common reptil- giving it an advantage over other individuals in the
ian ancestor that had developed a hole in the bone of population, then that particular trait becomes more
its hip socket, was erect, was bipedal or quadrupedal, common in that population as other traits are reduced
lived on land, and only lived during the Mesozoic era or eliminated from the population. Over geologic
between 245–144 million years ago. Birds are the time, directional selection can lead to major changes
direct descendents of dinosaurs. in morphology and behavior of a population or
species.
dinuclear See NUCLEARITY.
The classic example is England’s peppered moth
dioecious A term describing individual organisms (Biston betularia) and industrial melanism, the gradual
that produce only one type of gamete. Asparagus is a darkening of the wings of many species of moths and
dioecious plant species, having a male (staminate) and butterflies living in woodlands darkened by industrial
female (pistillate) flowers on separate plants. The term pollution. The light form of the moth was camouflaged
applies to species where sexes are always separate, e.g., among light-colored lichens on London’s darker-col-
humans. It is the opposite of MONOECIOUS. ored trees before the Industrial Revolution. The dark
form of the moth was not observed until 1848, since it
dioxygenase An ENZYME that catalyzes the INSER- was eaten by predators that easily spotted it. After the
TION of two oxygen atoms into a SUBSTRATE, both oxy- lichens were killed off by the effects of soot pollution
gens being derived from O2. from the Industrial Revolution, the dark form increased
in number, and by 1948, 90 percent of the peppered
moths were dark colored. The light form of the moth
continues to dominate populations in unpolluted areas
outside London. Antibiotic resistance in bacteria and
pesticide resistance in insects are other examples of
directional selection.
diploid cell A cell with two sets of chromosomes, disaccharide A class of sugar, a carbohydrate, creat-
with one set inherited from one parent and the other ed by linking together a pair of monosaccharides,
set inherited from the other parent. which are simple sugars. An example of a disaccharide
is sucrose, which is glucose joined to fructose. Other
diplopods A subclass of Myriapoda, the common examples include lactose, which is glucose joined with
millipede. They are cylindrical and bear two pairs of galactose, and maltose, which is two glucoses joined
legs on each segment and were one of the first animals together. While disaccharides can be decomposed into
to venture onto dry land, in the Silurian period (438 monosaccharides, monosaccharides cannot be degrad-
million to 408 million years ago). ed by hydrolysis. However, disaccharides can be
degraded by hydrolysis into monosaccharides.
Diptera Insects in the order Diptera include dismutase An ENZYME that catalyzes a DISPROPOR-
mosquitoes, flies, gnats, and midges. Dipterons have TIONATION reaction.
two wings. Some dipterons are disease vectors (e.g.,
98 dismutation
dismutation See DISPROPORTIONATION. does not exclude the possibility of other effects or side
effects of the distomer.
dispersion The distribution pattern, or spacing apart,
of individuals from each other within geographic popu- See also EUTOMER.
lation boundaries. Dispersion can be an aggregated
clump, where individuals are concentrated in specific DNA See DEOXYRIBONUCLEIC ACID.
locations of their habitat, the most common example.
This is usually because of unequal distribution of avail- DNA ligase A linking enzyme involved in replicat-
able resources or due to social or reproduction associa- ing and repairing DNA molecules. It seals “nicks” in
tions. Uniform dispersion, where everyone is evenly the backbone of a single strand of a double-stranded
spaced, is based on individual interactions such as com- DNA molecule; connects Okazaki fragments—short,
petition. Random dispersion is when individuals are single-stranded DNA fragments on the lagging
spaced randomly in an unpredictable manner. strand—during DNA replication, producing a comple-
mentary strand of DNA; and links two DNA
disposition See DRUG DISPOSITION. molecules together by catalyzing the formation of a
(phosphodiester) bond between the 5’ and 3’ ends of
the nicked DNA backbone.
disproportionation (dismutation) Any chemical reac- DNA methylation A biochemical event that adds a
tion of the type A + A m’ + A” where A, A’, and A” methyl group (–CH3) to DNA, usually at the base
are different chemical species. The reverse of dispropor- cytosine or adenosine, and may be a signal for a gene
tionation is called COMPROPORTIONATION. or part of a chromosome to turn off gene expression
and become inactive.
disruptive selection (diversifying selection) Acts
against individuals in the middle of the range of pheno- DNA polymerase An enzyme that catalyzes the
types, instead favoring both ends of extreme or unusual synthesis of new complementary DNA molecules
traits and working against common traits in a popula- from single-stranded DNA templates and primers.
tion. Species may evolve into separate ecotypes, that is, Different DNA polymerases are responsible for
types of individuals within the same species that have replication and repair of DNA, and they extend the
adapted to the special conditions they occupy. BATESIAN chain by adding nucleotides to the 3’ end of the
MIMICRY is often used as an example of disruptive growing DNA. DNA polymerase catalyzes the
selection. Diversifying selection results in an overall formation of covalent bonds between the 3’ end of a
increase in genetic diversity. new DNA fragment and the 5’ end of the growing
strand.
dissimilatory Related to the conversion of food or
other nutrients into products plus energy-containing DNA probe A single strand of DNA that is labeled
compounds. or tagged with a fluorescent or radioactive substance
and binds specifically to a complementary DNA
dissociation constant See STABILITY CONSTANT. sequence. The probe is used to detect its incorporation
through hybridization with another DNA sample.
distomer The enantiomer of a chiral compound that DNA probes can provide rapid identification of certain
is the less potent for a particular action. This definition species like mycobacterium.
See also NUCLEIC ACID PROBE.
Doisy, Edward Adelbert 99
docking studies Molecular modeling studies aiming at Hume, Illinois, on November 3, 1893, to Edward Perez
finding a proper fit between a ligand and its binding site. and his wife Ada (née Alley). Doisy was educated at the
University of Illinois, receiving a B.A. degree in 1914
dodo A large and plump bird (Raphus cucullatus) and an M.S. degree in 1916. He received a Ph.D. in
that is now extinct. Dutch sailors began using the Indi- 1920 from Harvard University.
an Ocean island of Mauritius as a stopover in 1598;
the last dodo was killed in 1681. The bird’s extinction From 1915 until 1917 he was assistant in biochem-
was due to destruction of its habitat and the importa- istry at Harvard Medical School, and the following two
tion of animals such as pigs, rats, and monkeys that ate years he served in war in the sanitary corps of the U.S.
its eggs and cut off its food supply. Overhunting also Army. From 1919 until 1923 he was an instructor,
contributed to the bird’s demise. Recently scientists associate, and associate professor at Washington Uni-
have determined, through DNA analysis, that the long- versity School of Medicine. In 1923 he became profes-
extinct dodo belongs in the dove and pigeon family. sor of biochemistry at St. Louis University School of
Medicine, and the following year he was appointed
Doisy, Edward Adelbert (1893–1986) American director of the department of biochemistry retiring in
Biochemist Edward Adelbert Doisy was born in 1965 (emeritus 1965–86).
Doisy and his associates isolated the sex hormones
estrone (1929), estriol (1930), and estradiol (1935). He
also isolated two forms of vitamin K and synthesized it
Laboratory worker reviewing DNA band patterns. (Courtesy of Centers for Disease Control and Prevention)
100 Domagk, Gerhard Johannes Paul
in 1936–39. For his work on vitamin K, Doisy was the 1939 Nobel Prize in physiology or medicine for his
awarded the Nobel Prize in physiology or medicine for discovery. He died on April 24, 1964.
1943.
domain An independently folded unit within a pro-
Later, Doisy improved the methods used for the tein, often joined by a flexible segment of the polypep-
isolation and identification of insulin and contributed tide chain. Domain is also the highest taxonomic rank
to the knowledge of antibiotics, blood buffer systems, in the animal kingdom, which consists of three
and bile acid metabolism. domains: Eukarya, Bacteria, and Archaea. The Archaea
are commonly known as extremophiles, occurring in
In 1936 he published Sex Hormones and in 1939 the deep sea vents and hot sulfur springs, whereas the
published, in collaboration with Edgar Allen and C. H. Eukarya comprise the higher life forms, including
Danforth, a book entitled Sex and Internal Secretions. humans.
He died on October 23, 1986, in St. Louis.
dominance hierarchy A social order, or ranking,
Domagk, Gerhard Johannes Paul (1895–1964) developed by a group of individuals that live together
German Biochemist Gerhard Johannes Paul Domagk by which certain individuals gain status and exert
was born on October 30, 1895, in Lagow, a small town power over others. Every individual in the group is
in the Brandenburg Marches. He attended school in ranked relative to all other community members of the
Sommerfeld, where his father was assistant headmaster, same sex. Female rank is usually determined by the rel-
until age 14. His mother, Martha Reimer, came from ative rank of their mothers, and male ranking may also
farming stock in the Marches, where she lived in Som- be determined by the mother’s rank, or by competition
merfeld until 1945, when she was expelled from her with other males. Individuals who are higher in the
home and died from starvation in a refugee camp. dominance hierarchy usually have greater access to
food, sex, and other resources. Those males or females
Domagk became a medical student at Kiel and at the highest level of ranking are called alpha male
served in the army during World War I. After being and alpha female.
wounded in 1914, he worked in the cholera hospitals
in Russia. He noticed that medicine of the time had lit- dominant allele An allele that controls the pheno-
tle success, and he was moved by the helplessness of type produced and blocks the phenotype expression of
the medical men of that time in treating cholera, another allele of the same gene, whether or not that
typhus, diarrhea infections, and other infectious dis- gene is dominant or recessive. This is in contrast to a
eases. He recognized that surgery had little value in the recessive allele, which is expressed only when its coun-
treatment of these diseases, and also noticed that terpart allele on the matching chromosome is recessive.
amputations and other radical treatments were often
followed by severe bacterial infections. donor atom symbol A polydentate LIGAND possess-
es more than one donor site, some or all of which may
In 1918 he resumed his medical studies at Kiel and be involved in COORDINATION. To indicate the points
graduated in 1921. In 1923 he moved to Greifswald of ligation, a system is needed. The general and system-
and a year later became a university lecturer in patho- atic system for doing this is called the kappa conven-
logical anatomy. In 1925 he held the same post at the tion: single ligating atom attachments of a polyatomic
University of Münster and in 1958 became a professor. ligand to a coordination center are indicated by the
italic element symbol preceded by a Greek kappa, κ. In
During the years 1927–29 he was given a leave of earlier practice, the different donors of the ligand were
absence from the University of Münster to do research denoted by adding to the end of the name of the ligand
in the laboratories of the I. G. Farbenindustrie, at Wup-
pertal. In 1932 he tested a red dye, Prontosil rubrum.
While the dye itself had no antibacterial properties,
when he slightly changed its chemical makeup, it
showed a remarkable ability to stop infections caused
by streptococcal bacteria in mice. He had discovered
the sulfa drugs that have since revolutionized medicine
and saved many thousands of lives. He was awarded
Down’s syndrome 101
the italicized symbol(s) for the atom or atoms through Down’s syndrome The most common and readily
which attachment to the metal occurs. identifiable chromosomal abnormality associated with
mental retardation. There are 47 instead of the usual
double-blind study A clinical study of potential 46 chromosomes, and the extra chromosome, chro-
and marketed DRUGs, where neither the investigators mosome 21, changes the orderly development of the
nor the subjects know which subjects will be treated body and brain, showing several symptoms including
with the active principle and which ones will receive a a characteristic body type, mental retardation,
placebo. increased susceptibility to infections, and various
heart and other organ abnormalities. It is caused by
one of the parent’s gametes not dividing properly or
double circulation A transportation system for the
blood that has separate pulmonary and systemic sys-
tems. The heart pumps blood to the lungs and back,
then to the body and back via a network of blood ves-
sels. In humans (but not all animals) the blood travels
through the heart twice on each complete journey
around the body. There is no mixing of the two kinds
of blood (oxygen-rich blood is completely separated
from oxygen-poor blood). A double circulation system
maintains the high blood pressure needed for efficient
transport of materials around the body.
double fertilization Restricted to angiosperms, the
flowering plants, it is a process where one male sperm
cell pollinates an egg to form a zygote, a diploid
embryo, while another male sperm joins with two
other polar nuclei to form a triploid cell, becoming the
endosperm in the ovule. Corn is an example.
double helix Two strands of DNA coiled about a This photograph depicts a newborn with the genetic disorder
central axis, usually a right-handed HELIX. The two Down’s syndrome due to the presence of an extra 21st chromo-
sugar–phosphate backbones wind around the outside some. The estimated incidence of Down’s syndrome is between
of the bases (A = adenine, G = guanine, T = thymine, C 1:1,000 to 1:1,1000 live births. Each year approximately 3,000
= cytosine). The strands are antiparallel, thus the phos- to 5,000 children are born with this chromosomal disorder.
phodiester bonds run in opposite directions. As a (Courtesy of Centers for Disease Control and Prevention)
result, the structure has major and minor grooves at
the surface. Each adenine in one strand of DNA is
hydrogen bonded to a thymine in the second strand;
each guanine is hydrogen bonded to a cytosine.
See also DEOXYRIBONUCLEIC ACID.
double prodrug (pro-prodrug) A biologically inac-
tive molecule that is transformed in vivo in two steps
(enzymatically and/or chemically) to the active species.
102 drug
where one of the parents has chromosome 14 and 21 After food mixes with stomach acid, it moves into the
merge. duodenum and mixes with digestive juices from the
pancreas, liver, and gallbladder, which starts the pro-
Approximately 4,000 children with a Down’s syn- cess of breaking down food into its constituent parts.
drome are born in the United States each year, or about
one in every 800 to 1,000 live births. The incidence is duplication A specific kind of mutation: production
higher for women over age 35, but the condition can of one or more copies of any piece of DNA, including a
occur at any age for women. gene or even an entire chromosome. A chromosome
structural aberration from an error in meiosis. Duplica-
drug Any substance presented for treating, curing, or tion of a portion of a chromosome resulting from fusion
preventing disease in human beings or in animals. A with a fragment from a homologous chromosome.
drug can also be used for making a medical diagnosis
or for restoring, correcting, or modifying physiological dwarfism Animals that evolve on islands are affected
functions (e.g., the contraceptive pill). by gigantism or dwarfism, the evolution of body form
drug disposition Refers to all processes involved in Before duplication After duplication
the absorption, distribution, METABOLISM, and excre-
tion of DRUGs in a living organism.
drug latentiation The chemical modification of a
biologically active compound to form a new compound,
which in vivo will liberate the parent compound. Drug
latentiation is synonymous with PRODRUG design.
drug targeting A strategy aiming at the delivery of a duplicated area
compound to a particular tissue of the body.
drumlin An oval or elongated hill of glacial drift that
looks like an overturned canoe from the air.
drupe A fleshy or pulpy fruit with a single seed
enclosed in a pit.
dual-action drug A compound that combines two
desired different pharmacological actions at a similarly
efficacious dose.
duodenum The first part of the small intestine; A duplication is a particular kind of mutation resulting in the pro-
short, wide, U-shaped, about 12 inches long, and clos- duction of one or more copies of any piece of DNA, including a
est to the stomach. The bile duct (gallbladder) and pan- gene or even an entire chromosome. (Courtesy of Darryl Leja,
creatic duct (pancreas) both open into the duodenum. NHGRI, National Institutes of Health)
dysentery 103
as either large (e.g., Komodo dragon weighs up to 365
pounds) or small (e.g., Island fox in the Channel
Islands). Island animal populations tend to acquire dif-
ferent sizes than their mainland counterparts. Dwarfism
may be due to limited food supply, but the reasons for
both gigantism and dwarfism are not known fully.
See also GIGANTISM.
dynein A molecular motor, a complex believed to be The dynein motor, a cellular complex believed to be composed of
made of 12 distinct protein parts, that performs basic 12 distinct protein parts, performs fundamental transportation
transportation tasks critical to the cell. Converts chem- tasks critical to the cell. Defects in its structure can prove fatal.
ical energy stored in an ATP molecule into mechanical This machine converts chemical energy stored in an ATP
energy that moves material though the cell along slen- molecule into mechanical energy that moves material though the
der filaments called microtubules. One of the most cell along slender filaments called microtubules. One of the
important functions occurs during cell division, when dynein motor’s most important functions occurs during cell divi-
it helps move chromosomes into proper position. It sion, when it helps move chromosomes into proper position.
also plays a part in the movement of eukaryotic flagel- (Courtesy of U.S. Department of Energy Genomes to Life program:
la and cilia. www.DOEGenomesToLife.org)
Molecular motors play a critical role in a host of cell dysentery Sickness that usually involves the
functions, such as membrane trafficking and cell move- abdomen causing cramps, vomiting, and swelling.
ment during interphase, and for cell asymmetry develop- Caused by a bacterium, Shigella bacillus, or a proto-
ment. During cell division, they are responsible for zoon, Entamoeba histolytica.
establishing the mitotic or meiotic spindle, as well as seg-
regating chromosomes and dividing the cell at cytokine-
sis. It is the last part of the mitotic cycle during which
the two daughter cells separate. Motors either move
along actin tracks (members of the myosin superfamily)
or microtubules (the dynein and kinesin superfamilies).
Based on the Greek dunamis, meaning “power.”
See also ATP.
E
ecdysone A juvenile steroid hormone that affects objects, seek food, and communicate. Bats, for exam-
arthropods and that belongs to the larger class of ecdy- ple, send out a series of short, high-pitched sounds,
steroids, sterol derivatives that as a whole affect a variety called echoes, that travel, hit an object, and bounce
of conditions relating to molting and metamorphosis, back, giving the bat the ability to judge distance, size,
including eliciting molting, regulating growth of motor shape, and motion.
neurons, controlling choriogenesis, stimulating growth
and development of imaginal discs, initiating break- eclosion The emergence of an adult insect from the
down of larval structures during metamorphosis, and pupa case or, less commonly, the hatching of an egg.
eliciting the deposition of cuticle by the epidermis. In
insects, ecdysone primarily elicits and stimulates molt- EC nomenclature for enzymes A classification of
ing. It acts on specific genes, stimulating the synthesis of ENZYMEs according to the Enzyme Commission of the
proteins involved in these bodily changes, and is pro- International Union of Biochemistry and Molecular
duced by prothoracic glands in insects and Y-organs (a Biology. Enzymes are allocated four numbers, the first
gland near the external adductor muscles) in crus- of which defines the type of reaction catalyzed; the next
taceans. Ecdysone—formerly called alpha ecdysone, and two define the SUBSTRATES; and the fourth is a catalog
beta ecdysone, or ecdysterone (now called 20-hydroxy- number. Categories of enzymes are EC 1, OXIDOREDUC-
ecdysone [20-HE])—is believed to be the active form. TASEs; EC 2, TRANSFERASEs; EC 3, HYDROLASEs; EC 4,
Ecdysone is not the active molting hormone. Various LYASEs; EC 5, ISOMERASEs; EC 6, LIGASEs (synthetases).
tissues, including the fat body, convert ecdysone to 20-
hydroxyecdysone, the active form of molting hormone.
echinoderm Diversified marine animals (phylum ecological efficiency Each transfer of energy from
Echinodermata) that include the classes Crinoidea (sea one trophic level to another has an ecological efficien-
lilies), Asteroidea (starfish), Ophiuroidea (brittle stars cy associated with it. Ecological efficiency refers to
or snake stars), Echinoidea (sea urchins and sand dol- the transfer of energy up trophic levels; it is the ratio
lars), and Holothuroidea (sea cucumbers). of secondary productivity to primary productivity
consumed.
echolocation A form of sensory perception used by
animals like bats to orient themselves in flight, detect Ecological efficiency goes down as you move up the
trophic levels. Ecological efficiencies generally range
from 5 to 20 percent, meaning that this percentage of
105
106 ecological niche
primary-producer biomass consumed is converted into from the external environment (sun); e.g., snakes, alli-
new consumer biomass. gators, lizards, fish, or amphibians.
Ecological efficiency depends on assimilation effi- EDRF See ENDOTHELIUM-DERIVED RELAXING FACTOR.
ciency (that portion of the consumed energy assimilat-
ed) and on net production efficacy (that portion of the effector cell A cell that performs a specific function
consumed energy converted into biomass). Assimilation in response to a stimulus. A gland or muscle cell that
efficiencies are greater for carnivores (50–90 percent) responds to stimuli from the body. Cells with full
than for herbivores (20–60 percent). immune functions capable of participating in the
immune response by destroying foreign cells or tissues;
ecological niche The totality of biotic and abiotic effector lymphocytes can mediate the removal of
resources an organism interacts with while living in its pathogens from the body.
environment.
ecological succession A transitional change in the efficacy Describes the relative intensity with which
biological community, where a group of plant and/or AGONISTs vary in the response they produce, even when
animal species gives way to another set of species over they occupy the same number of RECEPTORs and with
time, in response to a sequence of events such as fire, the same AFFINITY. Efficacy is not synonymous with
storms, human activities, or other natural or human- INTRINSIC ACTIVITY.
made occurrences. The term also refers to the normal
evolution of a community from pioneer stage to climax Efficacy is the property that enables DRUGs to pro-
community when equilibrium between species and its duce responses. It is convenient to differentiate the
environment occurs. properties of drugs into two groups: those that cause
them to associate with the receptors (affinity) and those
ecology The study of all life forms and their interac- that produce stimulus (efficacy). This term is often used
tions with their environment. to characterize the level of maximal responses induced
by agonists. In fact, not all agonists of a receptor are
ecosystem Any natural system—including biotic and capable of inducing identical levels of maximal
abiotic parts—that interacts as a unit to produce a sta- response. Maximal response depends on the efficiency
ble functioning system through cyclical exchange of of receptor coupling, i.e., from the cascade of events
materials. that, from the binding of the drug to the receptor, leads
to the observed biological effect.
ectoderm The outer layer of an embryo’s three pri- EF-hand A common structure to bind Ca2+ in
mary germ layers (endoderm, mesoderm, ectoderm) CALMODULIN and other Ca2+-binding proteins consist-
that gives rise to the nervous system and epidermis in ing of a HELIX (E), a loop, and another helix (F).
vertebrates.
egg The mature female reproductive cell.
ectoparasite A parasite that feeds from the exterior Ehrlich, Paul (1854–1915) German/Polish Immunol-
of its host. ogist Paul Ehrlich was born on March 14, 1854, near
Breslau, Germany (now Wroclaw, Poland), to Ismar
ectotherm A cold-blooded organism that relies on Ehrlich and his wife Rosa Weigert, whose nephew was
obtaining its heat from certain behavior techniques and the great bacteriologist Karl Weigert.
Eijkman, Christiaan 107
Ehrlich was educated at the Breslau Gymnasium Medal of the German Chemical Society in 1911, and in
and then at the Universities of Breslau, Strassburg, 1914 the Cameron Prize of Edinburgh. In 1908 he
Freiburg-im-Breisgau, and Leipzig. He received his doc- shared, with Ilya Ilyich Mechnikov, the Nobel Prize in
torate in medicine in 1878 for his dissertation on the recognition for his work on immunity.
theory and practice of staining animal tissues based on
the work of aniline dyes discovered by W. H. Perkin in The Prussian government elected him privy medical
1853. counsel in 1897, to a higher rank of the counsel in
1907, and in 1911 he reached the highest rank possi-
In 1878 Ehrlich was appointed assistant professor ble, real privy counsel with the title of excellency. He
at the Berlin Medical Clinic, where he continued his died on August 20, 1915, from a stroke.
work with dyes used for staining tissues, classifying
them as being basic, acid, or neutral. His work on Eijkman, Christiaan (1858–1930) Dutch Physician
staining granules in blood cells laid the foundation for Christiaan Eijkman was born on August 11, 1858, at
future work on hematology (the study of blood and Nijkerk in Gelderland (The Netherlands) to Christiaan
blood-forming tissues) and in the field of staining of Eijkman, the headmaster of a local school, and Johan-
tissues. na Alida Pool. He received his education at his father’s
school in Zaandam. In 1875 he entered the Military
In 1882 Ehrlich published his method of staining Medical School of the University of Amsterdam and
the tubercle bacillus that Robert Koch had discovered, received training as a medical officer for the Nether-
and it was this technique that later became the precur- lands Indies Army. From 1879 to 1881 he wrote his
sor for the currently used Gram method of staining thesis “On Polarization of the Nerves,” which gained
bacteria. Ehrlich himself had a bout of tuberculosis. him his doctor’s degree, with honors, on July 13, 1883.
Ehrlich also discovered the blood–brain barrier when On a trip to the Indies he caught malaria and returned
he noticed that the dyes injected into an animal brain to Europe in 1885.
would not stain.
Eijkman was director of the Geneeskundig Labora-
In 1899 he became director of the newly created torium (medical laboratory) in Batavia from 1888 to
Royal Institute of Experimental Therapy in Frankfurt 1896, and during that time he made a number of
and of the Georg-Speyer Haus, founded by Frau important researches in nutritional science. In 1893 he
Franziska Speyer for chemotherapy studies, which was discovered that the cause of beriberi was a deficiency of
built next door to Ehrlich’s institute. It is here that he vitamins and not, as thought by the scientific communi-
began work on serum antitoxins and chemotherapy ty, of bacterial origin. He discovered vitamin B, and
and came up with the concept of the “magic bullet,” a this discovery led to the whole concept of vitamins. For
compound that could be made to selectively target a this discovery he was awarded the Nobel Prize in phys-
disease-causing organism, killing only that organism. iology or medicine for 1929.
His research programs were guided by his theory that
the germicidal capability of a molecule depended on its He wrote two textbooks for his students at the
structure, especially its side chains, which could bind to Java Medical School, one on physiology and the other
the disease-causing organism. After many trials search- on organic chemistry.
ing hundreds of agents with the help of the nearby Cas-
sella chemical works, which donated samples of new In 1898 he became a professor of hygiene and
compounds produced in their laboratory, in 1909 he forensic medicine at Utrecht, but he also engaged in
found a cure for syphilis. The agent he identified was problems of water supply, housing, school hygiene,
arsphenamine, trade name Salvarsan (the 606th sub- and physical education. As a member of the Gezond-
stance tested) and later Neosalvaran (the 914th sub- heidsraad (health council) and the Gezondheids Com-
stance tested). Ehrlich became one of the founders of missie (health commission), he participated in the
chemotherapy. struggle against alcoholism and tuberculosis. He was
also the founder of the Vereeniging tot Bestrijding van
Ehrlich received the Tiedemann Prize of the Senck- de Tuberculose (Society for the struggle against tuber-
enberg Naturforschende Gesellschaft at Frankfurt/Main culosis). Eijkman died in Utrecht on November 5,
in 1887, the Prize of Honor at the XVth International 1930.
Congress of Medicine at Lisbon in 1906, the Liebig
108 Einthoven, Willem
Eijkman’s syndrome, a complex of nervous stance (ions or molecules) across the plasma membrane
against its energy gradient (active transport). The
symptoms in animals deprived of vitamin B1, is named pump, which can be ATP-dependent or Na+-dependent,
for him. moves net electrical charges across the membrane.
Einthoven, Willem (1860–1927) Dutch Physiologist electromagnetic spectrum The entire spectrum of
Willem Einthoven was born on May 21, 1860, in radiation arranged according to frequency and wave-
Semarang on the island of Java, Indonesia, to Jacob length that includes visible light, radio waves,
Einthoven, an army medical officer in the Indies, and microwaves, infrared, ultraviolet light, X rays, and
Louise M. M. C. de Vogel, daughter of the then- gamma rays. Wavelengths range from less than a
director of finance in the Indies. nanometer, i.e., X and gamma rays (1 nanometer is
about the length of 10 atoms in a row), to more than
Upon the death of his father, Einthoven and his a kilometer, i.e., radio waves. Wavelength is directly
family moved to Holland and settled in Utrecht, where related to the amount of energy the waves carry. The
he attended school. In 1878 he entered the University shorter the radiation’s wavelength, the higher its
of Utrecht as a medical student. In 1885, after receiving energy. Frequencies of the electromagnetic spectrum
his medical doctorate, he was appointed successor to range from high (gamma rays) to low (AM radio). All
A. Heynsius, professor of physiology at the University electromagnetic radiation travels through space at the
of Leiden, where he stayed until his death. speed of light, or 186,000 miles (300,000 km) per
second.
He conducted a great deal of research on the heart.
To measure the electric currents created by the heart, electron A negatively charged subatomic particle of
he invented a string galvanometer (called the Einthoven an atom or ion.
galvanometer) and was able to measure the changes of
electrical potential caused by contractions of the heart electron acceptor A substance that receives elec-
muscle and to record them by creating the electrocar- trons in an oxidation-reduction reaction.
diograph (EKG), a word he coined. The EKG provides
a graphic record of the action of the heart. This work
earned him the Nobel Prize in physiology or medicine
for 1924. He published many scientific papers in jour-
nals of the time. He died on September 29, 1927.
electrochemical gradient The relative concentration electronegativity Each kind of atom has a certain
of charged ions across a membrane. Ions move across attraction for the electrons involved in a chemical
the membrane due to the concentration difference on bond. This attraction can be listed numerically on a
the two sides of the membrane as well as the difference scale of electronegativity. Since the element fluorine
in electrical charge across the membrane. has the greatest attraction for electrons in bond-
forming, it has the highest value on the scale. Metals
electrode potential Electrode potential of an elec- usually have a low electronegativity, while nonmetals
trode is defined as the electromotive force (emf) of a usually have high electronegativity. When atoms react
cell in which the electrode on the left is a standard with one another, the atom with the higher elec-
hydrogen electrode and the electrode on the right is the tronegativity value will always pull the electrons
electrode in question. away from the atom that has the lower electronega-
tivity value.
See also REDOX POTENTIAL.
electrogenic pump Any large, integral membrane electron magnetic resonance (EMR) spectroscopy
protein (pump) that mediates the movement of a sub- See ELECTRON PARAMAGNETIC RESONANCE SPEC-
TROSCOPY.
electron-transfer protein 109
electron microscope (EM) A very large tubular by: h ν = gµBB, where h is the Planck constant, µB is the
microscope that focuses a highly energetic electron Bohr magneton, and the dimensionless scalar g is called
beam instead of light through a specimen, resulting in a the g-factor. When the paramagnetic species exhibits an
resolving power thousands of times greater than that of ANISOTROPY, the spatial dependency of the g-factor is
a regular light microscope. A transmission EM (TEM) is represented by a 3 × 3 matrix. The interaction energy
used to study the internal structure of thin sections of between the electron spin and a magnetic nucleus is
cells, while a scanning EM (SEM) is used to study the characterized by the hyperfine coupling constant A.
ultrastructure of surfaces. The transmission electron When the paramagnetic species has anisotropy, the
microscope, the first type of electron microscope, was hyperfine coupling is expressed by a 3 × 3 matrix called
developed in 1931 by Max Knoll and Ernst Ruska in a hyperfine-coupling matrix. Hyperfine interaction usu-
Germany and was patterned exactly on the light trans- ally results in splitting of lines in an EPR spectrum. The
mission microscope except that it used a focused beam nuclear species giving rise to the hyperfine interaction
of electrons instead of light to see through the specimen. should be explicitly stated, e.g., “the hyperfine splitting
The first scanning electron microscope was built in due to 65Cu.” When additional hyperfine splittings due
1942, but it was not available commercially until 1965. to other nuclear species are resolved (“superhyperfine”),
the nomenclature should include the designation of the
electron-nuclear double resonance (ENDOR) A nucleus and the isotope number.
magnetic resonance spectroscopic technique for the
determination of HYPERFINE interactions between elec- electron spin-echo (ESE) spectroscopy A pulsed
trons and nuclear spins. There are two principal tech- technique in ELECTRON PARAMAGNETIC RESONANCE, in
niques. In continuous-wave ENDOR, the intensity of some ways analogous to pulsed techniques in NMR
an ELECTRON PARAMAGNETIC RESONANCE signal, par- (NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY). ESE
tially saturated with microwave power, is measured as can be used for measurements of electron spin relax-
radio frequency is applied. In pulsed ENDOR the radio ation times, as they are influenced by neighboring para-
frequency is applied as pulses and the EPR signal is magnets or molecular motion. It can also be used to
detected as a spin-echo. In each case an enhancement of measure anisotropic nuclear hyperfine couplings. The
the EPR signal is observed when the radio frequency is effect is known as electron spin-echo envelope modula-
in resonance with the coupled nuclei. tion (ESEEM). The intensity of the electron spin-echo
resulting from the application of two or more
electron paramagnetic resonance (EPR) spec- microwave pulses is measured as a function of the tem-
troscopy The form of spectroscopy concerned with poral spacing between the pulses. The echo intensity is
microwave-induced transitions between magnetic ener- modulated as a result of interactions with the nuclear
gy levels of electrons having a net spin and orbital angu- spins. The frequency-domain spectrum corresponds to
lar momentum. The spectrum is normally obtained by hyperfine transition frequencies.
magnetic-field scanning. Also known as electron spin-
resonance (ESR) spectroscopy or electron magnetic res- electron spin-echo envelope modulation (ESEEM)
onance (EMR) spectroscopy. The frequency (ν) of the See ELECTRON SPIN-ECHO SPECTROSCOPY.
oscillating magnetic field to induce transitions between
the magnetic energy levels of electrons is measured in electron spin-resonance (ESR) spectroscopy See
gigahertz (GHz) or megahertz (MHz). The following ELECTRON PARAMAGNETIC RESONANCE SPECTROSCOPY.
band designations are used: L (1.1 GHz), S (3.0 GHz) ,
X (9.5 GHz), K (22.0 GHz), and Q (35.0 GHz). The electron-transfer protein A protein, often contain-
static magnetic field at which the EPR spectrometer ing a metal ion, that oxidizes and reduces other
operates is measured by the magnetic flux density (B), molecules by means of electron transfer.
and its recommended unit is the tesla (T). In the absence
of nuclear hyperfine interactions, B and ν are related
110 electron-transport chain
electron-transport chain A chain of electron accep- EMR (electron magnetic resonance) See ELECTRON
tors embedded in the inner membrane of the mitochon- PARAMAGNETIC RESONANCE SPECTROSCOPY.
drion. These acceptors separate hydrogen protons from
their electrons. When electrons enter the transport emulsion Droplets of a liquid substance dispersed in
chain, the electrons lose their energy, and some of it is another immiscible liquid. Milk in salad dressing is an
used to pump protons across the inner membrane of emulsion.
the mitochondria, creating an electrochemical gradient
across the inner membrane that provides the energy enantiomer One of a pair of molecular entities that
needed for ATP (adenosine triphosphate) synthesis. The are mirror images of each other and nonsuperimposable.
function of this chain is to permit the controlled release
of free energy to drive the synthesis of ATP.
See also ATP.
element A substance consisting of atoms that have endangered species The classification provided to
the same number of protons in their nuclei. Elements an animal or plant in danger of extinction within the
are defined by the number of protons they possess. foreseeable future throughout all or a significant por-
tion of its range.
elephantiasis (lymphedema filariasis) A visibly gro-
tesque enlargement and hardening of the skin and
subcutaneous tissues, usually in the leg or region of the
testis, caused by obstruction of the lymphatic system
when the lymph node is infested by the nematode
worm, Wuchereria bancrofti.
elimination The process achieving the reduction of
the concentration of a XENOBIOTIC compound, includ-
ing its reduction via METABOLISM.
embryo The resulting organism that grows from a fer-
tilized egg following rapid development and eventually
becomes an offspring (in humans, a baby). In plants, it is
the undeveloped plant contained within a seed.
embryo sac A large cell that develops in the ovule of Colored scanning electron micrograph (SEM) of a human embryo
flowering plants (angiosperms). It contains the egg cell, at the 16-cell stage, four days after fertilization. Known as a moru-
the female gametophyte, where pollination occurs, and la, this is a cluster of large rounded cells called blastomeres. The
when fertilized it becomes an embryo and eventually a surface of each cell is covered in microvilli. The smaller spheri-
seed. It is formed from the growth and division of the cal structures seen will degenerate. This embryo is at the early
megaspore into a multicellular structure with eight hap- stage of transformation into a human composed of millions of
loid nuclei. cells. Here it is in the process of dividing to form a hollow ball of
cells (the blastocyst). At this 16-cell stage, the morula has not yet
emigration The process of an individual or group implanted in the uterus (womb). Magnification: ×620 at 6 × 7 cm
leaving a population. size; ×2,300 at 8 × 10 in. size; × 960 at 4 × 5 in. size. (Courtesy ©
Dr. Yorgos Nikas/Photo Researchers, Inc.)
The Karner Blue— endangered species 111
New York’s Endangered Butterfly
apart. The butterfly was historically known from sites in
by Robert Dirig Maine, New Hampshire, Massachusetts, New York, New
Jersey, Pennsylvania, Ohio, Indiana, Illinois, Wisconsin,
The Karner blue (Lycaeides melissa samuelis) is a small, Iowa, Minnesota, Michigan, and Ontario. Many locality
beautifully colored blue butterfly that died out in southern records are very old, and the butterfly has since been extir-
Canada in the early 1990s and was listed as an endangered pated in areas such as Brooklyn, in New York City, and the
species by the U.S. government in 1992. suburbs of Chicago. More recently, Karner blues have died
out in New England and from New York City to Illinois along
The wings of male Karner blues are deep purplish-blue the southern edge of their range, except for northern Indi-
with a narrow black rim above, but females have wider dark ana. The butterfly is presently known to persist naturally
gray borders around blue central areas on all four wings, only in Indiana, Michigan, Minnesota, Wisconsin, and the
and a row of bright orange spots on the upper hindwing upper Hudson River Valley in New York, with reintroductions
edges. In both sexes, the wings have elegant white fringes, attempted in Ohio and planned for several other areas
and are pale gray beneath with arcs of black, white-rimmed where it formerly lived.
dots and orange and satiny blue spots along the hindwing
margin. The wings expand about an inch, so the butterfly is The Karner blue’s annual life cycle proceeds like
quite small. clockwork: the first hatch of Karner blue adults flies in late
May and early June, when the lupines bloom. After mating,
The Karner blue was first discovered in Canada near females lay tiny greenish-white, turban-shaped eggs on
London, Ontario, by lepidopterist William Saunders in 1861, lupine plants at the same season. Within a week, minuscule
and in the United States at Center (now Karner), New York, caterpillars hatch from the eggs and begin to feed on lupine
by Joseph Albert Lintner in 1869. It was originally con- leaflets, leaving translucent holes as their unique feeding
fused with Scudder’s blue (Lycaeides idas scudderi), a sign. They are often attended by ants, which feed on a
very similar and closely related but more northern butter- sweet fluid the caterpillars produce in glands on their
fly. Vladimir Nabokov, the world-famous author best abdomens, incidentally reducing predation and parasitism.
known for his controversial novel Lolita, also studied but- When fully grown three weeks later, the caterpillars are half
terflies and described the Karner blue as new to science an inch long, with black heads, velvety green bodies, a dark
in 1943. stripe along their backs, and light stripes along their sides.
They crawl off the plant to find a sheltered place in the litter
The Karner blue is restricted to a special kind of dry, for their chrysalis, which is smooth, bright green, and held
sandy habitat where wild blue lupine (Lupinus perennis), its to the substrate by a white silken thread around the middle
one caterpillar food plant, grows. Such areas of extensive and by microscopic hooks embedded in a silk pad at the tail
sand, commonly called “sand plains,” are of postglacial ori- end. Over the next week the developing butterfly’s wings
gin and occur along major rivers or around large lakes in slowly change from green to white to orange and finally to
northeastern and north-central North America. purplish-blue inside the transparent chrysalis skin. The sec-
ond brood of adults hatches from mid-July to early August,
The type locality, or the place from which the Karner and after mating, females again lay eggs on or near the
blue was first scientifically described, is the Karner Pine lupine plants, which by now have largely withered. These
Bush, a large inland pine barrens between Albany and Sch- summer eggs do not hatch until the following April, when
enectady, New York. This habitat is unusual in being formed new lupine leaves are pushing through the sand. The tiny
on undulating sand dunes that are stabilized by a low plant spring caterpillars grow, pupate, and produce a new brood
cover and widely scattered pitch pines (Pinus rigida). of butterflies in late May, finishing the cycle of two full
Resplendent clumps of wild blue lupine bloom in open areas broods per year. These dates are for New York State. The
between shrubby oaks (Quercus ilicifolia and Q. prinoides), timing of this annual calendar may shift a week or two later
blueberries (Vaccinium angustifolium and V. pallidum), at the northern and western edges of the butterfly’s range,
prairie grasses (Schizachyrium scoparium), and other low but the sequence remains the same.
herbaceous plants that carpet the dunes. Such landscapes
are a type of savannah, maintained by a natural fire cycle Because this butterfly naturally occurred along or near
that keeps them open. Their parklike vegetation is often waterways where major human settlements have grown,
very beautiful and quite different from the dense forests that the Karner blue has been frequently subjected to urbaniza-
surround the sand plains.
(continues)
The Karner blue occurs very locally throughout its
range, with small clusters of populations living many miles
112 Endangered Species Act of 1973 preservation strategies. Habitat conservation efforts have
continued at Karner (Albany Pine Bush), where approxi-
The Karner Blue— mately 2,750 acres of the type locality have been preserved
New York’s Endangered Butterfly to date. Managing this large preserve is challenging, as its
location between urban centers discourages the fires that
(continued) are needed to maintain the open vegetation Karner blues
require. Additional preserves have been set aside for the
tion stresses ever since Europeans colonized North Ameri- butterfly and its habitat in many places throughout its range.
ca. Human disturbance and degradation of its habitat are
primarily responsible for this butterfly’s endangered status The Xerces Society was founded in 1971 to focus on
throughout its range. A more subtle effect has been disrup- insect conservation, and initially emphasized imperiled
tion of the natural fire cycles that keep its habitats open and North American butterflies. This group’s scope has broad-
sunny. Without fire, the barrens grow up into forests, shad- ened over the past three decades to include all terrestrial
ing out open areas the butterflies need for mating, feeding, and marine invertebrates, and has had an important, if sub-
and egg laying, and reducing the lupine plants that are nec- tle, impact on North American conservation efforts. It is
essary for its caterpillars to survive. Global warming may named for the Xerces blue (Glaucopsyche xerces), a Califor-
also be taking its toll: relatively mild winters in the North- nia butterfly similar to the Karner blue that became extinct in
east since the early 1970s have reduced or eliminated the the 1940s. This vanished insect lived on coastal sand dunes,
annual snowpack that shelters the overwintering eggs from where its caterpillars fed on a small legume in San Francis-
December to March, forcing them to hatch too early, dessi- co, before its habitat was ruined. Other butterflies that the
cate on sunbaked spring sand, or lie exposed to predators Xerces Society has championed include the Atala hairstreak
and parasitoids during this defenseless life stage. (Eumaeus atala) and Schaus’ swallowtail (Papilio aristode-
mus ponceanus) in southern Florida; and Smith’s blue
Intensive scientific studies of the Karner blue have (Euphilotes enoptes smithi), El Segundo blue (Euphilotes
been conducted since 1973, when people first realized that battoides allyni), mission blue (Icaricia icarioides missionen-
it was declining in New York. Private conservation efforts sis), and the San Bruno elfin (Callophrys mossii bayensis) in
began soon after, starting with the Pine Bush Historic California. This organization has also expended much effort
Preservation Project (headed by Don Rittner), the Karner in trying to help protect the migratory monarch’s (Danaus
Blue Project (conducted by Robert Dirig and John F. Cryan), plexippus) spectacular overwintering sites in Mexico.
and the Xerces Society (led by Robert Michael Pyle and Jo
Brewer). Spider Barbour of the rock group Chrysalis com- Among these, the Karner blue is an enduring example
posed the song “Shepherd’s Purse” in the 1970s to highlight of ongoing human commitment to preserve an endangered
the butterfly’s plight. After the Karner blue was classified as insect in an increasingly crowded world.
threatened or endangered in various states, governmental
funding became available, and many ecological studies —Robert Dirig is assistant curator/curator of
were conducted by professional scientists. Today the Karn- lichens at Bailey Hortorium Herbarium,
er blue is extremely well known biologically (for example, Cornell University, in Ithaca, New York.
we know the elemental composition of its eggshell), and the
butterfly has also been the subject of several studies of
Endangered Species Act of 1973 (amended) Fed- endergonic reaction A chemical reaction that con-
eral legislation in the United States intended to provide sumes energy rather than releases energy. Endergonic
a means whereby the ecosystems upon which endan- reactions are not spontaneous because they do not
gered and threatened species depend may be conserved, release energy.
and to provide programs for the conservation of those
species in the hope of preventing extinction of native Enders, John Franklin (1897–1985) American Virol-
plants and animals. ogist John Franklin Enders was born on February 10,
1897, at West Hartford, Connecticut, to John Ostrom
endemic species A species native and confined to a Enders, a banker in Hartford, and Harriet Goulden
certain region; a species having comparatively restricted Enders (née Whitmore). He was educated at the Noah
distribution. Webster School at Hartford and St. Paul’s School in
endomembrane system 113
Concord, New Hampshire. In 1915 he went to Yale endocrine system A collection of glands that work
University, left to become an air force pilot in 1918, interdependently and produce hormones that regulate
and returned to get his B.A. in 1920. He received a the body’s growth, metabolism, and sexual develop-
Ph.D. at Harvard in 1930 for a thesis that presented ment and function. The endocrine system consists of:
evidence that bacterial anaphylaxis and hypersensitivity two adrenal glands, located on the top of each kidney;
of the tuberculin type are distinct phenomena, and he the pancreas, found in the abdominal cavity behind the
stayed at Harvard until 1946 as a teacher. stomach; the parathyroid and thyroid, located at the
base of the neck; the pituitary, located at the base of
In 1938 Enders began the study of some of the the brain; and the ovaries and testes, the female and
mammalian viruses and undertook, in 1941, in collabo- male sex glands.
ration with others, a study of the virus of mumps. This
work provided serological tests for the diagnosis of this Each of the endocrine glands produces hormones
disease and a skin test for susceptibility to it. It also that are targeted to a particular area of the body and are
demonstrated the immunizing effect of inactivated released into the bloodstream and serve to regulate the
mumps virus and the possibility of attenuating the viru- activity of various organs, tissues, and body functions.
lence of this virus by passing it through chick embryos.
It showed that mumps often occurs in a form that is not endocytosis A process by which liquids or solid par-
apparent but that nevertheless confers a resistance that ticles are taken up by a cell through invagination of the
is as effective as that conferred by the visible disease. plasma membrane. The plasma membrane creates a
“well” in which the substances settle, become sur-
In 1946 Enders established a laboratory for rounded, and are then pinched off into a vesicle that
research in infectious diseases at the Children’s Medical can be transported through the cell.
Center at Boston. The understanding of viruses at the
time was scant, and development of an antipolio vac- See also PHAGOCYTOSIS; PINOCYTOSIS.
cine depended on gaining the ability to grow sufficient
quantities of the polio virus under laboratory control. endoderm One of three primary germ layers in
The stumbling block was that poliovirus cultures could embryonic development (along with mesoderm and
be kept alive for a useful length of time only in nerve ectoderm). The endoderm is the inner layer of cells and
tissue, and that was hard to obtain and maintain. gives rise to organs and tissues associated with diges-
tion and respiration.
Enders, along with T. H. WELLER and F. C. ROB-
BINS, found that viruses could be grown on tissues endodermis A parenchyma tissue that regulates the
treated with penicillin to retard bacterial growth, and transport of materials into the vascular bundles of most
they were also successful in growing mumps and polio roots, stems, and leaves. It surrounds the vascular
viruses as well. The ability to grow and study polio led cylinder; is especially prominent in roots; and has
to the development of a vaccine later by Salk and suberized Casparian strips, a band of suberin (waxy
Sabin. The research opened the way to other vaccines substance) within the anticlinal walls. It is the inner-
against highly contagious childhood diseases such as most layer of the cortex in plant roots.
measles, German measles (rubella), and mumps.
Enders, Robbins, and Weller shared the 1954 Nobel endogenous Originating internally. In the description
Prize in medicine for this pioneering work. of metal ion COORDINATION in metalloproteins, endoge-
nous refers to internal, or protein-derived, LIGANDs.
Enders was a member of many organizations. Con-
sidered one of the most important contributors of the
20th century, Enders also provided insight to links
between viruses and cancer, and the pattern and pro-
cess of tumor growth. He died on September 8, 1985.
endocrine gland A ductless organ that produces and endomembrane system The collection or network
secretes hormones into the bloodstream. of membranous organelles, such as the endoplasmic
See also GLANDS.
114 endometrium
reticulum and the Golgi apparatus, that are inside a produced in the brain and anterior pituitary that are
eukaryotic cell; divides the cytoplasm into compart- chemically similar to opiate drugs (such as morphine)
ments with various functions, with the compartments and are released to cope with acute stress and to deal
related via direct physical contact or by the use of with pain.
membranous vesicles.
endometrium The lining (mucous membrane) of the endoskeleton An internal skeleton.
uterus and cervix. The endometrium becomes thicker See also SKELETON.
as the menstrual cycle advances in preparation for a
fertilized egg. If fertilization does not occur, the endosperm A nutrient, food-storage tissue, formed
endometrium is shed with the menstrual flow. It con- from double fertilization (sperm cell fuses to two polar
sists of the stratum functionale, a thick part of nuclei) in the seeds of angiosperms, which nourishes
endometrium that is lost during menstruation, and the the developing embryo.
stratum basal, a layer retained during menstruation
that serves as a stem source for regeneration of the endospore A thick-coated, environmentally resis-
upper stratum functionale. tant protective seedlike cell produced within a bacte-
rial cell that is exposed to harsh conditions. In
A cancerous growth in the endometrium is called mycology, it is the term for spores formed on the
endometrial cancer, and an overgrowth in the inside of a sporangium; a spore produced within a
endometrium, called endometrial hyperplasia, can spherule.
cause abnormal menstrual bleeding and become pre-
cancerous.
endoparasite Any parasitic organism that lives and endosymbiotic theory A theory on the evolution of
feeds from inside its host. eukaryotic cells. Originally mitochondria and chloro-
plasts were free-living self-replicating cells that devel-
See also ECTOPARASITE. oped a symbiotic relationship with prokaryote cells and
eventually lost their independence.
endoplasmic reticulum (ER) An extensive convo-
luted membranous network in the cytoplasm of endothelium The simple thin layer of endothelial
eukaryotic cells containing two types. The first is a cells that lines blood and lymph vessels. It plays a num-
rough endoplasmic reticulum, so called because it ber of roles, including acting as a selective barrier for
appears to be rough due to its surface being covered molecules and cells between the blood and surrounding
with ribosomes, that functions to help cells process tissues, and secreting and modifying several veinous
proteins in sacs called cisternae. The second type of signaling molecules. The endothelium also helps to
ER is smooth ER and helps cells to process fats. ER make up the blood-brain barrier between the central
generally contains enzymes to break down both pro- nervous system and the rest of the body; summons and
teins and fats. captures white blood cells (leukocytes) to the site of
infections; regulates coagulation of the blood at trauma
See also CELL. sites; controls contraction and relaxation of veins; and
regulates the growth of the veinous muscular cells,
ENDOR See ELECTRON-NUCLEAR DOUBLE RESO- among others.
NANCE.
It is also the term used for the innermost layer of
endorphin (endogenous morphine or opiod) A the eye’s cornea, one cell layer thick (5–10 microns or
class of endogenous (made in the body) hormones 0.005–0.01 millimeters), that provides hydration bal-
ance to maintain the cornea’s transparency.
enzyme 115
endothelium-derived relaxing factor (EDRF) The enterobactin A SIDEROPHORE found in enteric bacte-
factor originally described as EDRF is NO., produced ria such as Escherichia coli; sometimes called ente-
by a specific P-450-type of ENZYME from arginine upon rochelin.
response of a cell to a biological signal (molecule). Dif-
ferent types of cells respond differently to the presence enterochelin See ENTEROBACTIN.
of NO..
See also CYTOCHROME P-450.
endotherm A warm-blooded animal, one is which entomology The scientific study of the world of
the internal temperature does not fluctuate with tem- insects; a branch of zoology.
perature of environment, but is maintained by a con-
stant internal temperature regulated by metabolic entomophilous Refers to a flower pollinated by
processes. Examples include birds and mammals. insects.
endothermic The state of being warm-blooded or entropy The amount of energy in a closed system
producing heat internally. In chemistry, it is a reaction that is not available for doing work; disorder and ran-
where heat enters into a system, with the energy domness in a system. The higher the entropy, the less
absorbed by a reactant. energy available for work. The Second Law of Thermo-
dynamics states that the entropy of the universe will
endotoxin A large toxic molecule consisting of always increase.
polysaccharide, lipid A, and other components found
in the outer cell wall of specific gram-negative bacteria. environment The total living and nonliving condi-
Also called pyrogen or lipopolysaccharide. tions of an organism’s internal and external surround-
ings that affect an organism’s complete life span.
energy Classically defined as the capacity for doing environmental grain Describes an organism’s own
work, energy can occur in many forms such as heat perception of its environment and how it will react to
(thermal), light, movement (mechanical), electrical, it; a scale based on the use of space in relation to the
chemical, sound, or radiation. The first law of thermo- size of an organism. Grains can be coarse (large patch-
dynamics is often called the Law of Conservation of es) or fine (small patches).
Energy and states that energy cannot be created or
destroyed but only transformed from one form into enzootic Affecting animals living in a specific area or
another. limited region. Slime-blotch disease caused by Brook-
lynella hostilis and its associates caused a Caribbean-
enhancer A regulatory element of a gene. A site on wide mass fish mortality in 1980 and similar ones in
DNA that increases transcription of a region even if it south Florida and Bermuda. In 1990, enzootic pneu-
is distant from the transcribed region. One gene can monia, caused by Mycoplasma hyopneumoniae was
have many enhancers. evident in 80 percent of Iowa farms, and on these
farms, 32 percent of the pigs were actively infected.
entatic state A state of an atom or group that, due
to its binding in a protein, has its geometric or elec- enzyme A macromolecule that functions as a BIO-
tronic condition adapted for function. Derived from CATALYST by increasing the reaction rate, frequently
the Greek entasis, meaning tension.
116 enzyme induction
containing or requiring one or more metal ions. In gen- with parasitic larvae infections (helminths). Eosinophil
eral, an enzyme catalyzes only one reaction type (reac- secretory products inactivate many of the chemical
tion specificity) and operates on only a narrow range of mediators of inflammation and destroy cancer cells.
SUBSTRATES (substrate specificity). Substrate molecules This phenomenon is most obvious with mast-cell-
are attacked at the same site (regiospecificity), and only derived mediators. Mast cells produce a chemotactic
one, or preferentially one of the ENANTIOMERs of chiral factor for eosinophils.
substrate or of RACEMIC mixtures, is attacked (enan-
tiospecificity). Eosinophils are produced in the bone marrow, then
migrate to tissues throughout the body. When a foreign
See also CHIRALITY; COENZYME. substance enters the body, lymphocytes and neutrophils
release certain substances to attract eosinophils, which
enzyme induction The process whereby an (inducible) release toxic substances to kill the invader.
ENZYME is synthesized in response to a specific inducer
molecule. The inducer molecule (often a substrate that See also EOSINOPHILIA.
needs the catalytic activity of the inducible enzyme for
its METABOLISM) combines with a repressor and thereby eosinophil chemotactic factor of anaphylaxis
prevents the blocking of an operator by the repressor (ECF-A) A substrate released from mast cells and
leading to the translation of the gene for the enzyme. An basophils during anaphylaxis, which attracts eosinophils.
inducible enzyme is one whose synthesis does not occur A tetrapeptide mediator of immediate hypersensitivity.
unless a specific chemical (inducer) is present, which is
often the substrate of that enzyme. eosinophilia (blood eosinophilia) An abnormally
high number of eosinophils in the blood. Not a disease
enzyme repression The mode by which the synthe- in itself but usually a response to a disease. An elevated
sis of an ENZYME is prevented by repressor molecules. number of eosinophils usually indicates a response to
abnormal cells, parasites, or allergens.
In many cases, the end product of a synthesis chain
(e.g., an amino acid) acts as a feedback corepressor by See also EOSINOPHIL.
combining with an intracellular aporepressor protein,
so that this complex is able to block the function of an ephemeral Transitory, lasting for a brief time.
operator. As a result, the whole operation is prevented
from being transcribed into mRNA, and the expression epidermis Both plants and animals have epidermis,
of all enzymes necessary for the synthesis of the end- the “skin.” Epidermis serves as a protective layer
product enzyme is abolished. against invasion of foreign substances both chemical
and animal (parasites).
Eocene Part of the Tertiary period during the Ceno-
zoic era, lasting from about 54.8 to 33.7 million years In plants, it protects against desiccation; partici-
ago. Most of the orders of truly warm-blooded mam- pates in gas exchange and secretion of metabolic com-
mals were present by the early Eocene. pounds; absorbs water; and is the site of receptors for
light and mechanical stimuli.
See also GEOLOGICAL TIME.
In mammals, the epidermis is a superficial layer of
eosinophil One of the five different types of white the skin and is subdivided into five layers or strata—
blood cell (WBC) belonging to the subgroup of WBCs the stratum corneum, the stratum basale, the stratum
called polymorphonuclear leukocytes. Characterized by spinosum, the stratum granulosum, and the stratum
large red (i.e., eosinophilic) cytoplasmic granules. lucidum—each with their own functions.
Eosinophil function is incompletely understood. epigenesis The complete and progressive develop-
They are prominent at sites of allergic reactions and ment and differentiation that starts from the beginning
epithelial tissues 117
of a fertilized egg or spore through each stage of epinephrine Another name for adrenaline. A hor-
change, guided by genetics and environment until the mone and neurotransmitter secreted by the adrenal
final adult stage is completed. A process where a geno- gland (adrenal medulla) to react to stress, exercise, low
type becomes expressed and transformed into a final blood glucose. It is also a major component of the
phenotype. fight-or-flight reaction, the reaction that happens in the
body when, faced with a sudden unexpected threat or
epiglottis A leaflike cartilaginous flap that closes and stress situation, both epinephrine and norepinephrine
covers the glottis (middle part of the larynx) to prevent are released.
food and other objects from entering the trachea and
lungs while ingesting. The drug of choice for the treatment of anaphylax-
is. Individuals who are allergic to insect stings and cer-
epilepsy A neurological or brain condition in tain foods should always carry a self-injecting syringe
which a person has a tendency to have repeated of epinephrine.
seizures. Clusters of nerve cells, or neurons, in the
brain sometimes signal abnormally. It affects more Epinephrine increases the speed and force of heart-
than 2 million Americans, with over 180,000 new beats and, therefore, the work that can be done by the
cases each year. heart. It dilates the airways to improve breathing and
narrows blood vessels in the skin and intestine so that
an increased flow of blood reaches the muscles and
allows them to cope with the demands of exercise. Usu-
ally treatment with this hormone stops an anaphylactic
reaction. Epinephrine has been produced synthetically
as a drug since 1900.
epiparasite Any organism that extracts nutrients
from its host plant by means of intermediates.
epiphyte Any nonparasitic plant, fungus, or microor-
ganism that grows on the surface of another plant for
support but provides its own nourishment. Epiphytes
can form “mats” that contain a surface of canopy
plants with suspended soil and other material. A facul-
tative epiphyte is one that commonly grows epiphytical-
ly and terrestrially, but will usually exhibit a preference
for one or the other habit in a particular habitat.
episome A plasmid (circular piece of DNA ) that can
attach to and integrate its DNA in a cell and at other
times exist freely and still replicate itself alone, e.g., cer-
tain bacterial viruses.
Endoscope view of a healthy larynx (voice box) showing resting epitasis Interaction between nonallelic genes, with
vocal cords (v-shaped, center left and right). The vocal cords are one gene altering the expression of the other gene.
responsible for the production of sound. Normally the epiglottis, a
leaflike cartilaginous flap, closes and covers the glottis (middle epithelial tissues Closely packed layers of epithelial
part of the larynx) to prevent food and other objects from entering cells, a membranelike tissue that covers the body and
the trachea and lungs while ingesting. (Courtesy © CNRI/Photo
Researchers, Inc.)
118 epitope
lines body cavities, such as the gastrointestinal tract in San Francisco, California, to Herman and Sarah
and the lining of the lung. Epidermal growth factor Erlanger. He received a B.S. in chemistry at the Uni-
(EGF) is a hormone that causes epithelial tissues, such versity of California and later attended Johns Hopkins
as skin and the cells lining the gastrointestinal tract and University to study medicine, receiving an M.D.
lungs, to grow and heal. degree in 1899. He was appointed assistant in the
department of physiology at the medical school, after
epitope (antigenic determinant) These are particular spending a year of hospital training at Johns Hopkins
chemical groups on a molecule that are antigenic, i.e., Hospital, until 1906, moving up successively as
that elicit a specific immune response. instructor, associate, and associate professor. He was
then appointed the first professor of physiology in the
epizootic A rapid spread of a disease throughout an newly established Medical School of the University of
area affecting an animal group, e.g., rabies (disease Wisconsin. In 1910 he was appointed professor of
affecting raccoons, fox) or epizootic catarrhal enteritis physiology in the reorganized Medical School of the
(disease affecting mink). When it occurs in humans, it Washington University, St. Louis, retiring in 1946 as
is called an epidemic. chairman of the school.
epoch A period or date of time, shorter than and In 1922, in collaboration with his student Herbert
part of an era, that is used in geological time tables to Gasser, Erlanger adapted the cathode-ray oscillograph
locate historical events. Usually refers to an event for the study of nerve-action potentials. They ampli-
(mountain building, appearance of a species, etc.). Also fied the electrical responses of single nerve fibers and
called a series. analyzed them by the use of the oscilloscope. The
characteristic wave pattern of an impulse generated in
See also ERA; GEOLOGICAL TIME. a stimulated nerve fiber could be observed on the
screen and the components of the nerve’s response
EPR See ELECTRON PARAMAGNETIC RESONANCE studied.
SPECTROSCOPY.
Erlanger and Gasser were given the Nobel Prize in
equator The area around the earth with a latitude of medicine or physiology in 1944 for this work. Erlanger
0° that divides the Northern and Southern Hemi- later worked on the metabolism of dogs with shortened
spheres. It lies equidistant from the poles. intestines, on traumatic shock, and on the mechanism
of the production of sound in arteries.
equilibrium constant See ACIDITY CONSTANT; STA-
BILITY CONSTANT. With Gasser he wrote Electrical Signs of Nervous
Activity (1937). He died on December 5, 1965, in St.
era A period or date of time used in geological time Louis.
tables to locate historical events. Usually refers to longer
periods of time and marks a new or distinctive period. erythrocyte A concave red blood cell that functions
totally within the cardiovascular system. It does not
See also EPOCH; GEOLOGICAL TIME. 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 also BLOOD.
Erlanger, Joseph (1874–1965) American Neurosci- Escherichia coli A gram-negative, rodlike bacterium
entist Joseph Erlanger was born on January 5, 1874, that forms acid and gas in the presence of carbohy-
drates and is commonly found in human intestines and
eumetazoa 119
in many other animals. It can be pathogenic and is estrous cycle (heat cycle) The period from one ovula-
implicated in a number of food-borne illnesses, with an tion to the next in female mammals; a period of sexual
estimated 10,000 to 20,000 cases of infection occurring receptiveness preceding ovulation; in humans it occurs
in the United States each year. There are hundreds of every 21 to 23 days. It is characterized by rising and
strains of this one species. falling levels of estrogens and progesterone in the
bloodstream.
ESE See ELECTRON SPIN-ECHO SPECTROSCOPY. estrus The “heat” cycle in reproduction, the time
when the female is sexually receptive.
ESEEM (Electron spin-echo envelope modulation)
See ELECTRON SPIN-ECHO SPECTROSCOPY. ethology The study of natural animal behavior.
esophagus The muscular tube of the digestive tract ethylene (C2H4) A reactive chemical made from nat-
between the throat (pharynx) and stomach. ural gas or crude-oil components (occurs naturally in
both petroleum and natural gas) that acts as a plant
ESR (electron spin resonance) See ELECTRON PARA- hormone, the only gaseous hormone. It is used for
MAGNETIC RESONANCE SPECTROSCOPY. accelerating fruit ripening (bananas); maturing citrus
fruit color; increasing the growth rate of seedlings, veg-
essential amino acids Amino acids that cannot be etables, and fruit trees; leaf abscission; and aging.
synthesized in the human body and must be provided
from another source (food). These amino acids are his- etiology (aetiology) The scientific study or theory of
tidine, isoleucine, leucine, lysine, methionine, pheny- the causes of a certain disease.
lalanine, threonine, tryptophan, and valine.
euchromatin Within a nucleus of eukaryotes there
See also AMINO ACID. are two types of a mixture of nucleic acid and protein
called chromatin that make up a chromosome: euchro-
estivation (aestivation) A state of stagnation or dor- matin and heterochromatin. During interphase, the
mancy with slow metabolism (no eating, moving, or genetically active euchromatin is uncoiled and is avail-
growing) during periods of hot temperature and little able for transcription, while heterochromatin is denser
water supply; a physiological condition for survival. and usually not transcribed.
estrogens Primary female sex hormones. Estrogens eudismic ratio The POTENCY of the EUTOMER rela-
cause growth and development of female sex organs tive to that of the DISTOMER.
and support the maintenance of sexual characteristics,
including growth of underarm and pubic hair and eukaryotes Organisms whose cells have their GENET-
shaping of body contours and skeleton; increase secre- IC material packed in a membrane-surrounded, struc-
tions from the cervix and growth of the endometrium turally discrete nucleus and who have well-developed
(inner lining) of the uterus; and reduce concentrations cell organelles.
of bad cholesterol (LDL cholesterol) while increasing
good cholesterol (HDL). Estrogen is produced in the eumetazoa A subkingdom of the animalia king-
ovary by the developing follicle and by the corpus dom that includes all animals with the exception of
luteum.
See also HORMONE.
120 Eurasia
sponges; animals with cells that form tissues and rooted plants, and contain limited oxygen in the bot-
organs, a mouth, and digestive tract. Two branches tom layer of water.
exist, the radiata and the bilateria. The radiata have
radial symmetry, i.e., all longitudinal planes are equal See also MESOTROPHIC LAKE; OLIGOTROPHIC LAKE.
around a central body axis, while the bilateria
are animals that have bilateral symmetry, i.e., they evaporative cooling Temperature reduction when
have a definite front and rear, and left and right body water absorbs latent heat from the surrounding air as it
surfaces. evaporates. Similarly, “cooling” of the skin from the
evaporation of sweat is evaporative cooling and is a
Eurasia Europe plus Asia considered as one conti- process for the body to lose excess heat.
nent. Used in political, economic, and geographical
terms. evolution The long process of change that occurs in
populations of organisms. It began with the first life
eusocial A social system of insects, belonging to the forms on Earth and created the diversity of life forms
order Isoptera (termites) and the order Hymenoptera that exist today and that will exist in the future.
(ants, bees, and wasps), in which the individuals coop-
erate in caring for the young after one female produces evolutionary species concept A species comprises
offspring. There is a reproductive division of labor, and the totality of individuals that share a common evolu-
previous generations aid in rearing. This trait also tionary history. A species is a lineage evolving separate-
occurs in two species of mammals (mole rats). ly from others.
eutherian mammals (placental mammals) The female evolve Change slowly.
has a placenta that is connected to an embryo within Ewens–Bassett number See OXIDATION NUMBER.
the uterus that supplies it with nutrients and oxygen
and acts as an excretory system. Humans are eutherian
mammals.
eutomer The enantiomer of a chiral compound that EXAFS See EXTENDED X-RAY ABSORPTION FINE
is the more potent for a particular action. STRUCTURE.
See also DISTOMER. exaptation The adoption of an attribute that had
one function in an ancestral form but now has a new
eutrophication The accelerated loading or dumping and different form, e.g., swim bladders becoming
of nutrients in a lake by natural or human-induced lungs, or three jaw bones of mammal ancestors becom-
causes. Natural eutrophication changes the character of ing the middle bones of the ear. Formerly called
a lake very gradually, sometimes taking centuries, but preadaptation.
humanmade or cultural eutrophication speeds up the
aging of a lake, changing its qualities quickly, often in a excitatory postsynaptic potential (EPSP) Electri-
matter of years. cal change in the membrane of a postsynaptic neuron
caused by binding of an excitatory neurotransmitter
eutrophic lake Any lake that has an excessive supply from a presynaptic cell to a postsynaptic receptor. Pro-
of nutrients, usually nitrates and phosphates. Eutrophic motes firing of an action potential in the postsynaptic
lakes are usually not deep, contain abundant algae or cell.
extinct species 121
excretion The process of separating and removing exponential population growth Rapid population
waste products of metabolism from the body through growth; populations increase at a constant proportion
the discharge of urine, feces, or expired air. from one generation to the next. For example, the
human population is doubling every 40 years. The rate
exegetic reaction A spontaneous reaction in which of increase is not limited by environmental factors,
energy flows out of the system; a decrease in free ener- only biotic or intrinsic factors. If birth rates exceed
gy. A reaction that liberates heat. death rates, population size will increase exponentially;
likewise if death rates exceed birth, population size will
exobiology The study of the origin of life other than decrease exponentially. Also known as J-shaped popu-
on planet Earth. lation growth.
exocytosis The process in which a cell discharges expression The cellular production of the protein
large substances to the outside using secretory vesicles, encoded by a particular GENE. The process includes
storage organelles, that are then fused with the plasma TRANSCRIPTION of DNA, processing of the resulting
membrane where they open for export. mRNA product, and its TRANSLATION into an active
protein. A recombinant gene inserted into a host cell by
exogenous Originating externally. In the context means of a vector is said to be expressed if the synthe-
of metalloprotein LIGANDs, exogenous describes sis of the encoded polypeptide can be demonstrated.
ligands added from an external source, such as CO For the expression of metalloproteins, usually other
or O2. gene products will be required.
exon A section of DNA that carries the coding extended X-ray absorption fine structure (EXAFS)
SEQUENCE for a protein or part of it. Exons are separat- EXAFS effects arise because of electron scattering by
ed by intervening, noncoding sequences (called atoms surrounding a particular atom of interest as that
INTRONs). In EUKARYOTES, most GENEs consist of a special atom absorbs X rays and emits electrons. The
number of exons. atom of interest absorbs photons at a characteristic
wavelength, and the emitted electrons, undergoing con-
exoskeleton The hard external skeleton made from structive or destructive interference as they are scat-
chitin and connective tissue that attaches it to the tered by the surrounding atoms, modulate the
underlying parts of a body of animals such as arthro- absorption spectrum. The modulation frequency corre-
pods (insects, spiders, crabs, lobsters). Serves as protec- sponds directly to the distance of the surrounding
tion, antidessicant, and sensory interface with the atoms, while the amplitude is related to the type and
environment. number of atoms. EXAFS studies are a probe of the
local structure. EXAFS can be applied to systems that
See also SKELETON. have local structure, but not necessarily long-range
structure, such as noncrystalline materials. In particu-
exothermic A reaction that produces heat and lar, bond lengths and local symmetry (COORDINATION
absorbs heat from the surroundings. numbers) can be derived. The X-ray absorption spec-
trum can also show detailed structure below the
absorption edge. This X-ray absorption near-edge
structure (XANES) arises from excitation of core elec-
trons to high-level vacant orbitals.
exotoxin A toxic substance produced by bacteria extinct species A species no longer in existence.
and then released outside its cell into its environment. See also ENDANGERED SPECIES.
122 extirpated species
extirpated species A species no longer surviving in composed of proteoglycans, polysaccharides, and pro-
regions that were once part of its range. teins. Plays a role in cell shape, growth, migration, and
differentiation.
extracellular matrix (ECM) Material produced by extraembryonic membranes The YOLK SAC,
animal cells and secreted into the surrounding area, AMNION, CHORION, AND ALLANTOIS, four membranes
serving as a glue to hold cells together in tissues. It is that support and nourish the developing embryo in rep-
tiles, birds, and mammals. The allantois performs gas
free ribosomes microvilli exchange and is a repository for the embryo’s nitroge-
nous waste. It is involved in the development of the uri-
mitochondrion plasma membrane nary bladder. The chorion is the outermost layer and
smooth contributes to the formation of the placenta. The
cytoplasm endoplasmic reticulum amnion, the innermost layer, forms a fluid-filled sac
lysosome around the embryo to protect it from jarring. The yolk
microtubules vacuole sac surrounds the yolk and is the site of blood-cell for-
ribosomes pinocytotic vesicle mation and germ-cell formation, which are the prede-
nuclear envelope cessors of male and female gametes.
rough chromatin
endoplasmic reticulum inside nucleus extrinsic asthma Asthma triggered by external
nuclear pore agents such as pollen or chemicals. Most cases of
2 centrioles nucleolus extrinsic asthma have an allergic origin and are caused
at right angles by an IgE-mediated response to an inhaled allergen.
microfibrils This is the type of asthma commonly diagnosed in
Golgi vesicle early life. Many patients with extrinsic asthma respond
Golgi apparatus to immunotherapy.
Material produced by animal cells and secreted into the sur-
rounding area serves as a glue to hold cells together in tissues.
F
F-430 A tetrapyrrole structure containing nickel, a facultative symbiont Any organism that chooses a
component of the ENZYME methyl-coenzyme M reduc- symbiotic relationship with a host only if the relation-
tase, which is involved in the formation of methane in ship presents itself but is not physiologically required
methanogenic bacteria. The highly reduced macrocyclic to do so for survival.
structure, related to PORPHYRINs and CORRINs, is
termed a CORPHIN. Fahrenheit, Daniel Gabriel (1686–1736) German
Instrument Maker, Physicist Daniel Gabriel Fahren-
See also METHANOGENS; OXIDOREDUCTASE. heit, a German instrument maker and physicist, was
facilitated diffusion A process by which carrier pro-
teins, also called permeases or transporters or ion chan-
nels, in the cell membrane transport substances such as
glucose, sodium, and chloride ions into or out of cells
down a concentration (electrochemical) gradient; does
not require the use of metabolic energy.
See also ACTIVE TRANSPORT; VOLTAGE-GATED
CHANNELS.
facultative anaerobe A facultative anaerobe is a
microorganism that makes ATP by aerobic respiration if
oxygen is present but, if absent, switches to fermenta-
tion under anaerobic conditions.
facultative organism Any organism that changes a Bacillus cereus showing hemolysis on sheep-blood agar. B.
metabolic pathway to another when needed. cereus is a gram-positive beta hemolytic bacteria that can live in
an environment with or without the presence of oxygen (i.e., a
facultative saprophyte Any organism that is usually facultative anaerobe). (Centers for Disease Control/Courtesy of
parasitic but can also live as a SAPROPHYTE. Larry Stauffer, Oregon State Public Health Laboratory)
123
124 Fahrenheit, Daniel Gabriel
born in Danzig, Germany (now Gdansk, Poland), in 1709 and the first mercury or “quicksilver” ther-
1686, the oldest of five children. Fahrenheit’s major mometer in 1714.
contributions lay in the creation of the first accurate
thermometers in 1709 and a temperature scale in 1724 Fahrenheit’s first thermometers, from about 1709 to
that bears his name today. 1715, contained a column of alcohol that directly
expanded and contracted, based on a design made by
When he was 15 years of age, his parents died of Danish astronomer Olaus Romer in 1708, which Fahren-
mushroom poisoning. The city council placed the four heit personally reviewed. Romer used alcohol (actually
younger Fahrenheit orphans in foster homes and wine) as the liquid, but his thermometer had two fixed
apprenticed Daniel to a merchant who taught him reference points. He selected 60 degrees for the tempera-
bookkeeping. He was sent to Amsterdam around 1714, ture of boiling water and 7.5 degrees for melting ice.
where he learned of the Florentine thermometer, invent-
ed in Italy 60 years prior in 1654 by the grand duke of Fahrenheit eventually devised a temperature scale
Tuscany, Ferdinand II (1610–70), a member of the for his alcohol thermometers with three points calibrated
powerful Medici family. For some unknown reason, it at 32 degrees for freezing water, 96 degrees for body
sparked his curiosity and he decided to make ther- temperature (based on the thermometer being in a
mometers for a living. He abandoned his bookkeeping healthy man’s mouth or under the armpit), and zero
apprenticeship, whereby Dutch authorities issued war- degrees fixed at the freezing point of ice and salt,
rants for his arrest. While on the run, he spent several believed at the time to be the coldest possible tempera-
years traveling around Europe and meeting scientists, ture. The scale was etched in 12 major points (with zero,
such as Danish astronomer Olaus Roemer. Eventually four, and 12 as three points) and eight gradations
he returned to Amsterdam in 1717 and remained in the between the major points, giving him a total of 96 points
Netherlands for the rest of his life. for his scale for body temperature on his thermometer.
What seems so simple today—having a fixed scale Because his thermometers showed such consistency
and fixed points on a thermometer—was not obvious in their measurements, mathematician Christian Wolf
in Fahrenheit’s time, when several makers used differ- at Halle, Prussia, devoted a whole paper in an edition
ent types of scales and liquids for measuring. In 1694 of Acta Eruditorum, one of the most important inter-
Carlo Renaldini, a member of the Academia del Cimen- national journals of the time, on two of Fahrenheit’s
to and professor of philosophy at the University of thermometers that were given to him in 1714. From
Pisa, was the first to suggest taking the boiling and 1682 until it ceased publication in 1731, the Latin Acta
freezing points of water as the fixed points. The acade- Eruditorum, published monthly in Leipzig and sup-
my was founded by Prince Leopoldo de Medici and the ported by the duke of Saxony, was one of the most
Grand Duke Ferdinand II in 1657 with the purpose of important international journals. The periodical was
examining the natural philosophy of Aristotle. The founded by Otto Mencke, professor of morals and
academy was active sporadically over 10 years and practical philosophy, and mathematician Gottfried Wil-
concluded its work in 1667 with the publication of the helm Leibnitz. Written in Latin, the journal covered sci-
Saggi di Naturali Esperienze. ence and social science and was primarily a vehicle for
reviewing books. In 1724 Fahrenheit published a paper,
Unfortunately, Florentine thermometers, or any “Experimenta circa gradum caloris liquorum nonnullo-
thermometers of the time, were not very accurate; no rum ebullientium instituta (Experiments done on the
two thermometers gave the same temperature, since degree of heat of a few boiling liquids), in the Royal
there was no universal acceptance of liquid type or Society’s publication Philosophical Transactions and
agreement on what to use for a scale. Makers of Flo- was admitted to the Royal Society the same year.
rentine thermometers marked the low end of the scale
as the coldest day in Florence that year and the high Fahrenheit decided to substitute mercury for the
end of the scale as the hottest day. Because tempera- alcohol because its rate of expansion was more con-
ture fluctuations naturally occur over the years, no stant than that of alcohol and could be used over a
two thermometers gave the same temperature. For sev- wider range of temperatures. Fahrenheit, like ISAAC
eral years Fahrenheit experimented with this problem, NEWTON before him, realized that it was more accurate
finally devising an accurate alcohol thermometer in to base the thermometer on a substance that changed
consistently based on temperature instead of simply on
fauna 125
the hottest or coldest day of the year, like the Floren- of the eye. The eye is too short or the cornea is too flat,
tine models. Mercury also had a much wider tempera- so that the images focus beyond the retina and cause
ture range than alcohol. The choice of mercury as a close objects to appear blurry. Also called hyperopia or
benchmark was contrary to the common thought at the presbyopia, when the lens of the eye begins to lose elas-
time, promoted by Halley as late as 1693, who believed ticity (normal aging process).
that mercury could not be used for thermometers
because of its low coefficient of expansion. fat (general) Any substance made up of lipids or fatty
acids that supply calories to the body and can be found
Fahrenheit later adjusted his temperature scale to in solid or liquid form (e.g., margarine, vegetable oil);
ignore body temperature as a fixed point, bringing the three fatty acids linked to a glycerol molecule form fat.
scale to just the freezing and boiling of water. After his
death, scientists recalibrated his thermometer so that fat (triacylglycerol) Triacylglycerols are storage lipids,
the boiling point of water was the highest point, chang- comprising three fatty acids attached to a glycerol
ing it to 212 degrees, as Fahrenheit had earlier indicat- molecule, found mostly stored in adipose (fat) cells and
ed in a publication on the boiling points of various tissues. They are highly concentrated regions of
liquids. The freezing point became 32 degrees, and metabolic energy. Because there are abundant reduced
body temperature became 98.6 degrees. This is the CH groups available in fats for oxidation-required
scale that is presently used in thermometers in the Unit- energy production, they are excellent storage contain-
ed States and some English-speaking countries, ers of energy. Fats can be found in plants, animals, and
although most scientists use the Celsius scale. animal plasma lipoproteins for lipid transport. Former-
ly known as triglyceride.
By 1779 there were some 19 different scales being
used for thermometers, but it was Fahrenheit, along fatty acid Fatty acids are the components of two
with astronomer ANDERS CELSIUS and Jean Christin— lipid types mostly found in cells in the form of large
whose scales were presented in 1742 and 1743—who lipids or small amounts in free form: storage fats and
helped finally set the standards for an accurate ther- structural phospholipids. They consist of long hydro-
mometer that are still used today. Besides making ther- carbon chains of varying length (from four to 24
mometers, Fahrenheit also was the first to show that carbon atoms), containing a terminal carbonyl group
the boiling point of liquids varies at different atmo- at one end and may be saturated (has only a single
spheric pressures, and he suggested this as a principle carbon-to-carbon bond) or unsaturated (one or more
for the construction of barometers. Among his other double or triple carbon-to-carbon bonds). The number
contributions were a pumping device for draining the and location of double bonds also vary for the different
Dutch polders and a hygrometer for measuring atmo- fatty acids. More than 70 different kinds have been
spheric humidity. found in cells. Saturated fatty acids have higher levels
of blood cholesterol, since they have a regulating effect
Fahrenheit died on September 16, 1736, in The on its synthesis, but unsaturated ones do not have that
Hague at the age of 50 years. There is virtually no one effect and thus they are more often promoted nutrition-
in the English-speaking countries today who does not ally. Some fatty acids are palmitic acid, palmitoleic
have a thermometer with his initial (F) on it. acid, alpha-linolenic acid, eleostearic acid, linoleic acid,
oleic acid, and elaidic acid. Three fatty acids linked to a
See also CELSIUS SCALE. glycerol molecule form fat.
family The taxonomic category between order and
tribe, but if no tribe exists, then it is the category
between order and genus. Also a social unit related by
marriage, descent, or kinship.
farsightedness A condition in eyesight where distant fauna All wild birds and all wild animals (both
objects can be seen better than objects that are closer. It aquatic and terrestrial); includes wild mammals, reptiles,
is the inability of images to focus properly on the retina
126 feedback inhibition
amphibians, and aquatic and nonaquatic invertebrate bacteria, molds, or yeast, called ferments, on a fermen-
animals, and all such wild animals’ eggs, larvae, pupae, tation substrate that produce simpler substances or
or other immature stage and young. some other desired effect, such as the yielding of
ethanol and carbon dioxide from yeast for commercial
feedback inhibition (end-product inhibition) A way purposes, the production of ATP and energy produc-
for the end product of a cell’s biosynthetic pathway to tion, and the development of antibiotics and enzymes.
stop the activity of the first enzymes in that pathway, Fermentation is used by microflora of the large intes-
thereby controlling the enzymatic activity; it stops the tine to break down indigestible carbohydrates.
synthesis of the product.
Large fermentors are used to culture microorgan-
isms for the production of some commercially valuable
products such as bread, beer, wine, and other beverages.
female Sex classification by gender. The individual in ferredoxin A protein containing more than one iron
a sexually reproducing species that produces eggs. and ACID-LABILE SULFIDE that displays electron-transfer
Female mammals, for example, nourish their young with activity but not classical ENZYME function.
milk. In humans, females have two X chromosomes.
See also HIPIP.
FeMo-cofactor An inorganic CLUSTER that is found ferriheme An iron(III) PORPHYRIN COORDINATION
in the FeMo protein of the molybdenum-NITROGENASE complex.
and is essential for the catalytic reduction of N2 to
ammonia. This cluster contains Fe, Mo, and S in a ferritin An iron storage protein consisting of a shell
7:1:9 ratio. The structure of the COFACTOR within the of 24 protein SUBUNITs encapsulating up to 4,500 iron
FeMo protein can be described in terms of two atoms in the form of a hydrated iron(III) oxide.
cuboidal SUBUNITs, Fe4S3 and MoFe3S3 bridged by
three S2– ions and “anchored” to the protein by a histi- ferrochelatase An ENZYME that catalyzes the inser-
dine bound via an imidazole group to the Mo atom tion of iron into PROTOPORPHYRIN IX to form HEME.
and by a cysteine bound via a deprotonated SH group The mammalian enzyme contains an IRON-SULFUR
to an Fe atom of the Fe4S3 subunit. The Mo atom at CLUSTER.
the periphery of the molecule is six-coordinate and, in
addition to the three sulfido LIGANDs and the histidine ferroheme An iron(II) PORPHYRIN COORDINATION
imidazole, is also bound to two oxygen atoms from an complex.
(R)-homocitrate molecule.
ferromagnetic If there is coupling between the indi-
See also COORDINATION. vidual magnetic dipole moments of a PARAMAGNETIC
sample, spontaneous ordering of the moments will
Fenton reaction Fe2+ + H2O2 Fe3+ + OH. + OH–. occur at low temperatures. If this ordering results in an
This is the iron-salt-dependent decomposition of dihy- electronic ground state in which the moments are
drogen peroxide, generating the highly reactive hydrox- aligned in the same direction (parallel), the substance is
yl radical, possibly via an oxoiron(IV) intermediate. said to be “ferromagnetic.” If the ordering results in an
Addition of a reducing agent such as ascorbate leads to electronic ground state in which the moments are
formation of an acyclic compound, which increases the aligned in opposite directions, the substance is said to
damage to biological molecules. be “antiferromagnetic.”
See also HABER-WEISS REACTION.
fermentation The anaerobic decomposition of com-
plex organic substances by microorganisms such as
fiber 127
fertilization The combining of two gametes from individuals; or double fertilized, in which two sepa-
different sexes to form a zygote, e.g., the penetration rate sperm cells unite with two cells in the embryo
of sperm into the egg and the resulting combining of sac to form the zygote and endosperm, such as in
genetic material from both that develops into an angiosperms.
embryo. The process involves karyogamy, the fusion
of nuclei of both gametes, and plasmogamy, the In agriculture, fertilization means the application
fusion of cytoplasm. Each gamete contains a haploid of nutrients, a fertilizer, to soil in order to promote
set of chromosomes, with the resulting nucleus con- growth and development of domestic or crop plants.
taining a diploid set of chromosomes. Fertilization
can also be self-induced by the fusion of male and [2Fe-2S] Designation of a two-iron, two-labile-sulfur
female gametes from the same euploid (nucleus of a CLUSTER in a protein, comprising two sulfido-bridged
cell contains exact multiples of the haploid number of iron atoms. The oxidation levels of the clusters are
chromosomes) organism; cross fertilized by the fusion indicated by adding the charges on the iron and sulfide
of male and female gametes from different euploid atoms, i.e., [2Fe-2S]2+; [2Fe-2S]+. The alternative desig-
nation, which conforms to inorganic chemical conven-
tion, is to include the charges on the LIGANDs; this is
more appropriate where the ligands are other than the
usual cysteine sulfurs, such as in the RIESKE IRON–SUL-
FUR PROTEINs.
See also FERREDOXIN.
[4Fe-4S] Designation of a four-iron, four-labile-sul-
fur CLUSTER in a protein. (See [2FE-2S].) Possible oxida-
tion levels of the clusters are [4Fe-4S]3+; [4Fe-4S]2+;
[4Fe-4S]+.
See also FERREDOXIN; HIPIP.
fetus An unborn offspring in the postembryonic
stage where the major features of the organism can be
seen.
Colored scanning electron micrograph (SEM) of sperm clustered F factor A bacterial plasmid, which is a piece of
around a human egg (ovum) during fertilization. The rounded egg DNA that is able to replicate independently of the
(at center) is seen on human tissue. Sperm attached to its surface chromosome, that allows a prokaryote (cell with no
appear as fine hairlike structures; each sperm has a rounded nucleus) to join together with and pass DNA. An epi-
head and a long tail. They are penetrating the thick spongy sur- some that can replicate by itself or in integrated form
face of the zona pellucida of the egg, a surface layer that attracts and move from one bacterium to another while conju-
sperm to the egg and enables the sperm to attach. The human gating. A circular piece of DNA that can replicate inde-
female usually produces a single large egg, and only one of the pendently of the bacterial chromosome or integrate and
millions of male sperm may penetrate the egg’s wall to fuse with replicate as part of the chromosome.
the egg nucleus. Once fertilized, the egg begins its process of
growth by cell division. (Courtesy © K.H. Kjeldsen/Photo fiber A long-walled plant cell that is often dead at
Researchers, Inc.) maturity, is lignified, and reinforces the xylem of
angiosperms, giving elasticity, flexibility, tensile
128 Fibiger, Johannes Andreas Grib
strength, and mechanical support to plant structure. carcinogens and led to the development of modern
Also part of sclerenchyma tissue, which is thickened cancer research.
cell walls of lignin, composed of both sclereids, short
cells, and the longer fibers, and lacking a living proto- Fibiger was a founding member and joint editor of
plast when mature. the Acta Pathologica et Microbiologica Scandinavica,
and coeditor of Ziegler’s Beiträge zur pathologischen
In human nutrition, fiber is a carbohydrate that Anatomie und zur allgemeinen Pathologie. He received
resists the action of digestive enzymes and passes the 1927 Nobel Prize in physiology or medicine for his
through the human digestive system virtually work on cancer, specifically for his “discovery of the
unchanged, without being broken down into nutrients. Spiroptera carcinoma.” Fibiger died on January 30,
There are insoluble fibers, found in wholegrain prod- 1928, in Copenhagen.
ucts and vegetables, that help the digestive system by
moving stools through the digestive tract by keeping fibril A small or microscopic thread of cellulose that
them soft. Soluble fiber slows the digestive process and is part of the cellulose matrix of plant cell walls. The
is water-soluble. Found in beans, fruits, and oat prod- contractile unit of a muscle cell or a bundle of filaments
ucts, it is thought to help lower blood fats and blood in a striated muscle cell; the thin fibrous structure of a
glucose (sugar). nerve; a long fine hair or fiber; many fibrils bundle
together to form a fiber. Makes up the smallest unit of
Fiber is also a slender, elongated natural or syn- paper fibers. Also a linear feature in the H alpha chro-
thetic filament capable of being spun into yarn, e.g., mosphere of the Sun, found near strong sunspots and
cotton. plages or in filament channels. Fibrils parallel strong
magnetic fields.
Fibiger, Johannes Andreas Grib (1867–1928) Dan-
ish Pathologist Johannes Andreas Grib Fibiger was fibrin An insoluble stringy protein derived from fib-
born in Silkeborg, Denmark, on April 23, 1867, to C. rinogen that facilitates blood clotting by forming
E. A. Fibiger, a local medical practitioner, and Elfride threads and creating the mesh around the clot. A blood
Muller, a writer. clot is also called a fibrin clot. Coagulation begins usu-
ally with an injury to some part of the body. The body
Fibiger studied under bacteriologists Robert KOCH forms a clot from a mixture of the blood protein fibrin
and Emil von Behring, and from 1891 to 1894 he was and platelets. After the bleeding stops, a blood protein
assistant to Professor C. J. Salomonsen at the depart- dissolves the clot by breaking down the fibrin into tiny
ment of bacteriology at the University of Copenhagen. fragments.
He received his doctorate from the University of
Copenhagen in 1895 based on research into the bacte- fibroblast (fibrocyte) A flat, elongated, branched,
riology of diphtheria. irregular and motile cell type found in vertebrate con-
nective tissue that produces extracellular collagen and
He was appointed prosector at the university’s elastin fibers; spindlelike with long cytoplasmic exten-
Institute of Pathological Anatomy (1897–1900), princi- sions at each end and with oval, vesicular nuclei; most
pal of the Laboratory of Clinical Bacteriology of the abundant cell type found in the skin. Fibroblasts differ-
Army (1890–1905), and in 1905 became the director entiate into chondroblasts that secrete cartilage matrix,
of the central laboratory of the army and consultant collagenoblasts that proliferate at chronic inflammation
physician to the Army Medical Service. sites, and osteoblasts that secrete bone matrix. They
form the fibrous tissues in the body, tendons, and
Fibiger’s early research dealt with diphtheria aponeuroses, the shiny, broad sheets of connective tis-
and tuberculosis, and he developed laboratory sue that bind muscle fibers together to form muscles, as
methods for growing the causing bacteria as well as well as supporting and binding tissues.
a serum to protect against the disease. Fibiger
achieved the first controlled induction of cancer in
laboratory animals, after research in studying tumors
in the stomachs of animals, by feeding mice and
rats with cockroaches infected with a worm. His
work led others to pursue the research on chemical
Finsen, Niels Ryberg 129
fight-or-flight reaction The reaction in the body 1860, in the capital city Thorshavn in the Faroe Islands
when faced with a sudden and unexpected threat or (Denmark) to Johanne Fröman and Hannes Steingrim
stress. The reaction is immediate to either run or stay Finsen, an Icelandic family that could trace its ancestry
and fight. In humans, a sudden release of the hormones back to the 10th century and occupied many of the
epinephrine and norepinephrine increases blood flow highest positions in the administration of the Faroe
to the muscles and increases blood pressure. The result- Islands. He received his early education in schools at
ing increase in muscle strength and mental ability pre- Thorshavn and then at Herlufsholm in Denmark.
pares the body for either reaction that is chosen. In
other animals such as the wood thrush (Hylocichla In 1882 Finsen went to Copenhagen to study
mustelina), flight is preferred over fight. medicine. After taking his final examination in 1890, he
became prosector of anatomy at the University of Copen-
filial generation (offspring generation) The succes- hagen until 1893. He continued with private tutoring of
sive generations of progeny in a controlled series of medical students to make a moderate income.
crosses, beginning with two specific parents (the P gen-
eration), and intercrossing the progeny of each new By 1883 he was diagnosed with Pick’s disease,
generation. F1 is the first offspring or filial generation characterized by progressive thickening of the connec-
between any two parents, the first generation of tive tissue of certain membranes in the liver, the heart,
descent; F2 is the second (grandchildren); and so on. and the spleen, with long-term impairment of the func-
tions of these organs. He also developed symptoms of
filter feeding The filtering of suspended food parti- heart trouble and ascites, and became more and more
cles from a water current by using gill rakers or similar of an invalid until finally during his last years he was
organs. confined to a wheelchair. It did not prevent him from
making contributions to medicine.
fingerprinting In genetics, the identification of multi-
ple specific alleles on a person’s DNA to produce a He was instrumental in discovering the effects of
unique identifier for that person; used in forensics. There light—and in particular ultraviolet light (then called
are six steps to DNA fingerprinting. First the DNA must red light)—as phototherapy against diseases such as
be isolated and removed from the cells of the animal or lupus vulgaris in 1893. In 1895 he made a great break-
plant. Then special enzymes, called restriction enzymes, through that established his international reputation by
are used to cut the DNA at specific places, and the DNA introducing the revolutionary carbon-arc treatment
are sorted by size. The DNA pieces are then transferred (Finsen’s therapy) of lupus. In 1896 he founded the Fin-
to a nylon sheet, which is then probed. The fingerprint is sen Medical Light Institute (now the Finsen Institute) in
generated by adding tagged probes to the nylon sheet, Copenhagen.
and each probe sticks in only one or two specific places,
wherever the sequences match. The final DNA finger- He received the Nobel Prize in physiology or
print is created by using several different probes, with medicine on December 10, 1903, for his work in treat-
the resulting end product looking like a grocery store bar ing diseases with light.
code. DNA fingerprinting is increasingly being used in
criminal cases, and people have been freed from prison Among the many publications by Finsen, two are
based on DNA fingerprinting. especially noteworthy: Om Lysets Indvirkninger paa
Huden (On the effects of light on the skin) appeared in
See also GALTON, SIR FRANCIS. 1893, and the classical treatise Om Anvendelse i
Medicinen af koncentrerede kemiske Lysstraaler (The
Finsen, Niels Ryberg (1860–1904) Danish Physi- use of concentrated chemical light rays in medicine)
cian Niels Ryberg Finsen was born on December 15, was published in 1896. The results of much of his
research are contained in the communications pub-
lished by his institute. Finsen tried to combat his illness
in various ways, including keeping a diet poor in salt
during his last years. This led to his last publication, a
thorough study of En Ophobning af Salt i Organismen
(An accumulation of salt in the organism) in 1904.
In 1899 he became Knight of the Order of Dan-
nebrog, and a few years later the Silver Cross was
130 firefly
added. He was a member or honorary member of fixed action pattern (FAP) A series of innate behav-
numerous societies in Scandinavia, Iceland, Russia, and ior patterns (a fixed action) in response to a specific
Germany. He received a Danish gold medal for merit, stimulus (called a sign stimulus or innate releaser) that
and in 1904 the Cameron Prize was given to him from continues until the response is completed. FAPs are
the University of Edinburgh. genetic and not individually learned. For example, a
group of spined larvae of the buck moth (Hemileuca
In 1892 Finsen married Ingeborg Balslev, the maia) will all instantly raise their bodies and thrash
daughter of Bishop Balslev at Ribe. They had four chil- back and forth when a predator (bird) approaches.
dren. Finsen died on September 24, 1904.
firefly Commonly called a lightning bug, they are flaccid Limp, soft condition, e.g., walled cells are
neither flies nor bugs. They belong to the order flaccid in isotonic surroundings; low turgid pressure;
Coleoptera, family Lampyridae, which are beetles. opposite of turgid.
These small flying beetles produce their own light, from
a chemical called luciferase, from structures in their flagellum A long whiplike structure that is used to
abdomen. Females of some species, which are wingless, propel certain kinds of prokaryote and eukaryote cells.
and many larvae also produce light and are called The cells can have an individual flagellum or a few
glowworms. Fireflies can be seen in early summer (late flagella per cell. In prokaryote organisms the flagellum
May), appearing at dusk. Males and females attract is composed of a protein called flagellin. In the eukary-
each other with a flashing green light in their ote organism, it is longer than a CILIUM but has the
abdomens. The wingless females flash from the ground same construction of nine outer double microtubules
and the males look for them. There are more than and two inner single microtubules.
2,000 species of firefly in temperate and tropical envi-
ronments worldwide.
first law of thermodynamics Simply put, energy flanking region The DNA sequences extending on
can neither be created nor destroyed, only trans- either side of a specific gene or locus; a region preced-
formed or transferred from one molecule to another; ing or following the transcribed region. The 3’ flanking
in effect, the total amount of energy in the universe is region (downstream flanking region) is found immedi-
constant. Also known as the Law of Conservation of ately distal (distant) to the part of a gene that specifies
Energy. Thermodynamics is the study of the conver- the mRNA and where a variety of regulatory sequences
sion of energy between heat and other forms, e.g., are located. The 3’ flanking region often contains
mechanical. sequences that affect the formation of the 3’ end of the
message and may contain enhancers or other sites to
See also SECOND LAW OF THERMODYNAMICS. which proteins may bind. The 5’ flanking region flanks
the position that corresponds to the 5’ end of the
fission (binary fission) Asexual reproduction or divi- mRNA and is that part of DNA that precedes the tran-
sion of a single-celled individual, such as a prokaryote, scription-start site for a particular gene. The 5’ flanking
into two new single-celled individuals of equal size and region contains the promoter (transcription control
genetic composition, without mitosis occurring. From region) and other enhancers or protein binding sites.
the Latin fissilis, meaning “easily split.”
flatworms Organisms that comprise the phylum
fixation The complete prevalence of one gene form Platyhelminthes. These are normally hermaphroditic
(allele), resulting in the total exclusion of the other. organisms that have flat bodies and are bilaterally sym-
Genes that confer a reproductive advantage generally metrical, with defined head and tail, centralized ner-
go to fixation. vous system, and eyespots (light-sensitive cells). They
include flukes (trematodes), tapeworms (Cestoda), and
Florey, Sir Howard Walter 131
free-living flatworms (Turbellaria), and it is estimated when diluted 800 times. He named the active substance
that more than 20,000 species exist. Millions of penicillin.
humans are host to these parasites.
Sir Alexander wrote numerous papers on bacteriol-
flavin A PROSTHETIC GROUP found in flavoproteins ogy, immunology, and chemotherapy, including original
and involved in biological oxidation and reduction. descriptions of lysozyme and penicillin. He was the
Forms the basis of natural yellow pigments like recipient of numerous awards and honors in scientific
riboflavin. societies worldwide. Fleming shared the Nobel Prize in
physiology or medicine in 1945 with Ernst Boris CHAIN
flea A major group of bloodsucking insects that feed and Howard Walter FLOREY, who both (from 1939)
on animals, belonging to the order Siphonaptera. There carried Fleming’s basic discovery forward in the isola-
are about 2,000 known species existing on all conti- tion, purification, testing, and quantity production of
nents. Some species are vectors for diseases. They are penicillin. Fleming died on March 11, 1955, and is
wingless, flattened-body types with legs with long buried in St. Paul’s Cathedral.
claws. They can jump from 14 to 16 inches.
flicker fusion rate (critical flicker frequency) The
While they tend to be associated with pets such as rate beyond which the human eye can no longer recog-
cats and dogs (Ctenocephalides canis [dog flea] and nize discontinuous changes in brightness as a flicker,
Ctenocephalides felis [cat flea]), they do include i.e., the rate is the frequency at which the “flicker” of
humans as hosts. an image cannot be distinguished as an individual event.
The flicker fusion rate (FFR) is 31.25 Hz, or 60 frames
Fleming, Sir Alexander (1881–1955) British Bacte- per second (bright light) and 24 frames per second (dim
riologist Sir Alexander Fleming was born on a farm light) in humans. When a frame rate is above this num-
at Lochfield near Darvel in Ayrshire, Scotland, on ber, the eye sees the signal as a consistent image (as on
August 6, 1881. He attended Louden Moor School, television). A fly has an FFR of 300 frames per second.
Darvel School, and Kilmarnock Academy before mov-
ing to London, where he attended the Polytechnic Insti- flora The term for all plants in a given location or,
tute. He spent four years in a shipping office before collectively, on the planet.
entering St. Mary’s Medical School, London University,
where he received an M.B., B.S., with gold medal in Florey, Sir Howard Walter (1898–1968) Australian
1908, and became a lecturer at St. Mary’s until 1914, Pathologist Sir Howard Walter Florey was born on
when he served during World War I, returning to St. September 24, 1898, in Adelaide, South Australia, to
Mary’s in 1918. He was elected professor of the school Joseph and Bertha Mary Florey. His early education
in 1928 and emeritus professor of bacteriology, Univer- was at St. Peter’s Collegiate School, Adelaide, and then
sity of London, in 1948. Adelaide University, where he graduated M.B., B.S., in
1921. He was awarded a Rhodes Scholarship to Mag-
Fleming was interested in the natural bacterial dalen College, Oxford, leading to the degrees of B.Sc.
action of the blood and in antiseptics, and he worked and M.A. in 1924. He then attended Cambridge as a
on antibacterial substances that would not be toxic to John Lucas Walker student.
animal tissues. In 1921 he discovered an important
bacteriolytic substance that he named lysozyme. In In 1925, he visited the United States on a Rocke-
1928 he made his most important discovery while feller traveling fellowship for a year, returning in 1926
working on an influenza virus. He noticed that mold to a fellowship at Gonville and Caius College, Cam-
had developed accidentally on a staphylococcus culture bridge, receiving a Ph.D. in 1927. At this time he also
plate and that the mold had created a bacteria-free cir- held the Freedom Research Fellowship at the London
cle around itself. Further experiments found that a Hospital. In 1927, he was appointed Huddersfield
mold culture prevented growth of staphylococci, even Lecturer in Special Pathology at Cambridge. In 1931 he
132 flower
succeeded to the Joseph Hunter Chair of Pathology at flower The reproductive part of a plant. Can be both
the University of Sheffield. male and female, producing both pollen and ovule.
Flowers are the most commonly used part in identify-
In 1935 he became professor of pathology and a ing a plant and are often showy and colorful.
fellow of Lincoln College, Oxford. He was made an
honorary fellow of Gonville and Caius College, Cam- fluid feeder An animal that lives by sucking nutrient-
bridge, in 1946, and an honorary fellow of Magdalen rich fluids from another living organism. The two main
College, Oxford, in 1952. From 1945 to 1957 he was ways to fluid-feed are piercing and sucking, and cutting
involved in the planning of the John Curtin School of and licking. Examples of insects that pierce and suck are
Medical Research in the new Australian National Uni- platyhelminths, nematodes, annelids, and arthropods,
versity. In 1962 he was made provost of Queen’s Col- which all have distinct mouth parts that bore into their
lege, Oxford. prey and then suck out the prey’s body fluids with a
pharynx. Secreted enzymes help aid in the digestion of
During World War II he was appointed honorary the fluids. Piercing by insects typically involves the use
consultant in pathology to the army, and in 1944 he of a proboscis formed by the maxillae and composed of
became Nuffield visiting professor to Australia and two canals. The first canal carries in the prey’s blood,
New Zealand. and the other delivers saliva and anticoagulants.
His collaboration with Ernst Boris CHAIN, which The cutting-and-licking technique is used by black
began in 1938, led to the systematic investigation of flies and vampire bats, who cut the prey’s body with
the properties of naturally occurring antibacterial sub- teeth or sharp mouthparts and then lick the fluids
stances. Lysozyme, an antibacterial substance found in while injecting anticoagulants to prevent clotting.
saliva and human tears, discovered by Sir Alexander
FLEMING, was their original interest, but they moved to fluid mosaic model The model proposes that a plas-
substances now known as antibiotics. The work on ma membrane surrounds all cells and is composed of
penicillin was a result. about half lipids, mostly phospholipids and cholesterol,
and half proteins, with the proteins and phospholipids
In 1939 Florey and Chain headed a team of floating around the membrane in constant motion
British scientists, financed by a grant from the Rocke- unless they bind to something. By being fluid, the lipid
feller Foundation, whose efforts led to the successful molecules can move to open up as a channel whereby
small-scale manufacture of penicillin. They showed substances can enter or leave. The protein molecules in
that penicillin could protect against infection but that the membrane act as carrier, channel, or active trans-
the concentration of penicillin in the human body— port mechanisms for larger molecules that must enter
and the length of time of treatment—were important or leave the cell.
factors for successful treatment. In 1940 a report was
issued describing how penicillin had been found to be fluke An organism belonging to the phylum Platy-
a chemotherapeutic agent capable of killing sensitive helminthes, a flatworm of the class Trematoda. Flukes
germs in the living body. An effort was made to create are flat, unsegmented, and parasitic. Two orders exist,
sufficient quantities for use in World War II to treat the Mongenea (monogenetic flukes) and Digenea (dige-
war wounds, and it is estimated to have saved thou- netic flukes). Humans become hosts for Schistosoma
sands of lives. In 1945 Florey was awarded a Nobel mansoni (human blood fluke) and Fasciola hepatica
Prize in medicine with Alexander Fleming and Ernst (sheep liver fluke).
Chain.
Also a single lobe of a whale’s tail.
Florey was a contributor to and editor of Antibi-
otics (1949). He was also coauthor of a book of lec- folate coenzymes A group of heterocyclic com-
tures on general pathology and has had many papers pounds that are based on the 4-(2-amino-3,4-dihydro-
published on physiology and pathology.
In 1944 he was created a knight bachelor. When a
life peerage was conferred on him in 1965, he chose to
be styled Lord Florey of Adelaide and Marston. He
was provost of Queen’s College, Oxford, from 1962
until he died on February 21, 1968.
Forssmann, Werner Theodor Otto 133
4-oxopteridin-6-ylmethylamino) benzoic acid (pteroic medical devices, food and color additives, infant for-
acid) and conjugated with one or more L-glutamate mulas, and animal drugs. Also, the FDA monitors the
units. Folate derivatives are important in DNA synthe- manufacture, import, transport, storage, and sale of
sis and erythrocyte formation. Folate deficiency leads about $1 trillion worth of products annually at a cost
to ANEMIA. to taxpayers of about $3 per person. Investigators and
inspectors visit more than 16,000 facilities a year and
folivore An animal whose primary source of food is arrange with state governments to help increase the
foliage. For example, the larvae of the buck moth number of facilities checked.
(Hemileuca maia [Drury]) eats only the leaves of oak,
favoring scrub, live, blackjack, and post oaks; the food chain The energy path in a community by way
Karner blue butterfly (Lycaeides melissa samuelis) lar- of food from those who produce it to those that feed
vae feed only on the leaves of wild blue lupine (Lupi- on them. For example, plants are eaten by herbivores
nus perennis). that are eaten by carnivores. Food chains that are inter-
connected are called food webs.
See also HERBIVORE.
follicle Any enclosing cluster or jacket of cells, or a forensics The use of social and physical sciences to
small sac or pore, that protects and nourishes within it combat crime, e.g., the science of using DNA for iden-
a cell or structure. A fluid-filled follicle in the ovary tification. It has been used to identify victims; estab-
harbors the developing egg cell. When the follicle rup- lish paternity in child-support cases; and prove the
tures (ovulation), an egg is released. A hair follicle presence of a suspect at a crime scene. Forensic sci-
envelops the root of hair. ence can be used for issues from burglary to environ-
mental protection.
Food and Drug Administration (FDA) A U.S. fed- formation constant See STABILITY CONSTANT.
eral agency responsible for regulating the development,
use, and safety of drugs, medical devices, food, cosmet- formula An exact representation of the structure of a
ics, and related products. molecule, ion, or compound showing the proportion of
atoms that compose the material, e.g., H2O.
The U.S. Food and Drug Administration is a scien-
tific, regulatory, and public health agency that oversees Forssmann, Werner Theodor Otto (1904–1979)
items accounting for 25 cents of every dollar spent by German Surgeon Werner Theodor Otto Forssmann
consumers. Its jurisdiction encompasses most food was born in Berlin on August 29, 1904, to Julius Forss-
products (other than meat and poultry); human and mann and Emmy Hindenberg. He was educated at the
animal drugs; therapeutic agents of biological origin; Askanische Gymnasium (secondary grammar school) in
medical devices; radiation-emitting products for con- Berlin. In 1922 he went to the University of Berlin to
sumer, medical, and occupational use; cosmetics; and study medicine, passing his state examination in 1929.
animal feed. The agency grew from a single chemist in For his clinical training he attended the University
the U.S. Department of Agriculture in 1862 to a staff of Medical Clinic and in 1929 went to the August Victo-
approximately 9,100 employees and a budget of ria Home at Eberswalde near Berlin.
$1.294 billion in 2001, comprising chemists, pharma-
cologists, physicians, microbiologists, veterinarians, He developed the first technique for the catheteri-
pharmacists, lawyers, and many others. About one- zation of the heart by inserting a cannula into his own
third of the agency’s employees are stationed outside of antecubital vein, through which he passed a catheter
the Washington, D.C., area, staffing over 150 field for 65 cm. He then walked into the X-ray department
offices and laboratories, including five regional offices
and 20 district offices. Agency scientists evaluate appli-
cations for new human drugs and biologics, complex