ScienceWeek

SCIENCE-WEEK

A Weekly Email Digest of the News of Science

A journal devoted to the improvement of communication
between the scientific disciplines, and between scientists,
science educators, and science policy makers.

June 18, 1999 -- Vol. 3 Number 25

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Theories come and theories go. The frog remains.
-- Jean Rostand

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Contents of This Issue:

1. On Two Cultures Forty Years Later
2. On the Existence of Black Holes
3. Mitochondrial Evolution
4. On New Nerve Cells in the Adult Human Brain
5. Inhibition of Angiogenesis by Green Tea
6. On Vaccines for Malaria

In Focus: On the Foundation of Modern Chemistry

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1. ON TWO CULTURES FORTY YEARS LATER
The novelist C.P. Snow (1905-1980) was a scientist before
becoming a novelist, having studied science at Leicester
University and Cambridge University. He held a position as a
tutor at Cambridge from 1935 to 1945, and during World War II, he
was chief of scientific personnel for the Ministry of Labor.
After the war, Snow became widely known for his novels about
power and prestige in the university and scientific communities,
and in 1959 he delivered what was to become a famous lecture
entitled "Two Cultures". In that lecture, Snow discussed the
dichotomy between science and literature and his belief in closer
contact between them. During the subsequent decades, the concept
was generally elaborated by the educated public to denote the
apparent deep cultural divide between the humanities and the
sciences, including that between professionals educated in these
two general areas. The phrase "Two Cultures" has often been used
to denote the divide between the scientific community and the
non-professional public in general, but that divide was not the
central focus of Snow's 1959 lecture. No matter these
distinctions, during the past 40 years the conceptual and
cultural divide between scientists and non-scientists has been a
subject of analysis, discussion, and concern. In a recent
unsigned editorial, however, the journal _Nature_ proposes that
for the most part Snow's concerns have become "gratifyingly
irrelevant". The editorial in _Nature_ makes the following
points:
     1) No one can complain, as C.P. Snow did 40 years ago, of a
lack of assimilation of science by novels, poetry, and paintings
that have been infused with science, and have wide appeal, for
that basic concern to be sustained.
     2) Few Western administrations and governments now suffer
fundamentally from a lack of scientific and technological
perspective.
     3) Although the public continues to have a low level of
scientific knowledge, the divide between the public and the
scientific community has narrowed, suggesting that scientists
willing to communicate, and science writers and publishers,
"should take their bow".
     4) Snow's prediction that the poor nations of the world will
take up technology in the 20th century has proved wrong and this
sounds a warning against optimistic technocratic naivety.
     5) However, Snow's concerns about scientific incomprehension
are as relevant as ever, as displayed in debates about the use of
genetically modified organisms, especially in Europe and parts of
the developing world.
     6) In summary: Although time has eroded many of the cultural
fissures that Snow addressed in 1959, current debates about
biotechnology highlight continuing problems of mutual
incomprehension.
-----------
[The Editors of ScienceWeek do not agree with most of the above
points made in the _Nature_ editorial. In particular, we do not
believe that the existence of more plays, novels, poetry, and
paintings apparently "infused" with science indicates any
narrowing of the divide between the Two Cultures. The enormous
increase in media density during the past four decades has
naturally produced more of everything in the media, but we
believe the divide noted by Snow is still wide in both the
university and other communities, and still a matter of concern.
We believe that in some aspects the divide is a wide and deep 
chasm, and a potential serious problem for the 21st century.]
-----------
(Nature 11 Mar 99 398:91)
QY: Editor [nature@nature.com]
-------------------
Summary by SCIENCE-WEEK [http://scienceweek.com] 18Jun99


2. ON THE EXISTENCE OF BLACK HOLES
During their existence, stars are battlegrounds between
gravitational condensation and outward pressures from various
internal sources related to the star's structure and the burning
of its fuel. When the fuel of a star is exhausted, the outward
pressures may undergo a marked decrease relative to the
gravitational forces, with a resultant gravitational collapse.
If the terminal stages of star death, which may involve a "blow-
off" of a large amount of matter, leave a remnant star mass
greater than 3 solar masses, the ultimate gravitational collapse
is expected to produce a black hole, a relativistic singularity.
A black hole is a localized region of space from which neither
matter nor radiation can escape. The "trapping" occurs because
the requisite escape velocity, which can be calculated from the
relevant equations, exceeds the velocity of light and is
therefore unattainable. Another view of a black hole is that it
is a mass that has collapsed to such a small volume that its
gravity prevents the escape of all radiation. Space and time
essentially have no meaning in a black hole. The boundary of the
black hole is called the "event horizon", because any event
within the boundary is invisible outside, the invisibility
resulting from the fact that no radiation can escape to be
detected. The radius of the black hole depends upon how much
matter has fallen into the region; it is called the
"*Schwarzchild radius", and it is usually a few kilometers.
However, massive black holes are possible and are thought to be
the source of quasars (quasi-stellar objects), which are
extremely luminous sources radiating energy over the entire
spectrum from x-rays to radio waves, and which are apparently the
oldest and most distant objects in the universe. If quasars
indeed involve black holes, the radiation is from material just
outside the black hole, and not from anything within it. Nothing
inside a black hole can get out of it. A neutron star, on the
other hand, is something quite different. If, following its
terminal stages, the remnant mass of a star is between 1.4 and 2
to 3 solar masses, the star will collapse into a neutron star, a
body with a radius of 10 to 15 kilometers, with a core so dense
that its component protons and electrons have merged into
neutrons. The average density of a neutron star is 10^(15) grams
per cubic centimeter, and the weight of an object on the surface
of a neutron star would be 10^(11) its weight on the surface of
the Earth. Neutron stars apparently have an outer shell of iron,
but it is iron like no Earth iron, an iron of 4 orders of
magnitude greater density. Theory predicts that a neutron star
should rotate very rapidly, be extremely hot, and have an intense
magnetic field. Pulsars, sources of pulsed radio energy, are
evidently spinning neutron stars which emit beams of radiation
from their magnetic poles. A few pulsars have been found in
binary systems (a gravitational system involving two objects),
and the empirical estimated masses of the pulsars are consistent
with the masses predicted by neutron star models. Finally, there
is the case of exhausted stars with terminal masses less than 1.4
solar-mass (the "*Chandrasekhar limit"). These stars collapse to
become so-called "white dwarfs", stars about the size of Earth
but with a mass about that of the Sun. An "x-ray binary" is an x-
ray emitting binary system apparently consisting of a neutron
star (or evidently in a some cases a black hole or a white dwarf
star) and a normal star. The x-ray emission is a an expected
result of accretion of material by gravity from the normal
companion to the compact massive gravitationally collapsed
object. ... ... Jean-Pierre Lasota (Institute of Astrophysics
Paris, FR) presents a review of current studies of apparent black
holes and the evidence for the existence of black holes, the
author making the following points:
     1) To deduce the existence of black holes, astrophysicists
have had to rely on two indirect lines of argument. a) Near
galactic centers, stars are moving so rapidly that they would fly
off unless the gravity of a huge mass -- as large as the
equivalent of a billion Suns -- held them in. Whatever has this
mass must be extremely dense, and there is no known theoretical
alternative to a black hole. b) Many galactic centers and binary
star systems spew radiation and matter at enormous rates, which
suggests they contain an extraordinarily efficient mechanism for
generating energy. Again, in theory, the most efficient engine
possible is a black hole.
     2) The above lines of argument, however, are indirect, a
deduction by default: Such evidence indicates only the existence
of some kind of compact body, but it does not positively identify
black holes based on any of the unique characteristics of black
holes.
     3) A central problem in the study of black holes has been to
discover how to distinguish them from neutron stars. In recent
years, a method has been developed, a method based on x-ray
emissions from the vicinity of each type of body. This method has
allowed the demonstration that black holes are indeed a reality.
The x-ray emissions of x-ray binary systems have been
particularly revealing.
     4) The inferred temperature of the collapsed entity in
certain x-ray binary systems is of the order of 10^(7) degrees
kelvin, which is consistent with that expected for a black hole.
To generate the observed emission, a black hole would need to
swallow 10^(-9) to 10^(-8) solar mass per year -- which agrees
with estimates of how quickly the ordinary star in the binary
system is losing mass to its companion. Thus, certain x-ray
binaries could be the best proof that stellar-mass black holes
exist.
     5) It is known, however, that in many cases the compact
object in the binary systems is not a black hole. Radio pulsars
found in binaries are thought to be rapidly rotating magnetized
neutron stars. Astronomical black holes cannot have magnetic
fields. They are nearly featureless objects and cannot generate
the regular pulses observed in pulsars. Similarly, x-ray pulsars
cannot be black holes. Any regular stable pulsation rules out the
presence of a black hole. Even irregular x-ray bursts entail a
neutron star, which provides a surface on which matter can
accumulate and explode.
     6) Recently, evidence for the existence of black holes has
come from comparison of the brightness of objects exceeding 3
solar-mass with that of objects of less than 3 solar-mass. The
more massive objects are fainter than the less massive objects,
even under conditions where radiation should be emitted at the
same rate. The discrepancy can be explained if matter and energy
are disappearing, which only a black hole could accomplish.
     7) The theoretical modeling of flows into black holes is an
active field of research. Bodies too massive to be neutron stars
can now be moved from the category of black hole candidate to
confirmed black hole. Only an object with an event horizon can
cause energy to disappear in the manner that is inferred for
certain x-ray binary systems.
-----------
Jean-Pierre Lasota: Unmasking black holes.
(Scientific American May 1999)
QY: Jean-Pierre Lasota, Institute of Astrophysics, Paris FR.
-----------
Text Notes:
... ... *Schwarzchild radius: Named after the astronomer Karl
Schwarzchild (1873-1916). In 1916, he demonstrated that in the
general theory of relativity, a sphere of material approximating
to a star, collapsing under its own gravitational field to less
than a certain radius, would cease to radiate energy. The term
"black hole" was apparently first applied to such an object by
John Archibald Wheeler many years later (1968). The Schwarzchild
calculation yielded what is called a "Schwarzchild black hole",
which is a black hole without charge and without angular
momentum. The current consensus is that real black holes have
little or no charge but are almost certainly rotating, and these
black holes are called "Kerr black holes".
... ... *Chandrasekhar limit: Named after Subrahmanyan
Chandrasekhar (1910-1995), who presented the first theoretical
derivation of the limit in 1939. The limit actually ranges from
1.11 to 1.44 solar-mass, depending on the composition and
structure of the star.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 18Jun99
-------------------
Related Background:
ON BLACK HOLES
In an essay on black holes, Martin Rees (Cambridge University,
UK) makes the following points: 1) Black holes are expected in
many theories of gravity, not just in Einstein's general
relativity theory. Indeed, black holes were in essence
conjectured more than 200 years ago, when in 1783 John Michell
presented a paper to the Royal Society of London concerning the
effect of gravity on light. 2) But the term "black hole" was not
coined until 1968, when John Wheeler described how an infalling
object "becomes dimmer millisecond by millisecond... light and
particles incident from outside... go down the black hole only to
add to its mass and increase its gravitational attraction." 3)
Viewed from the outside, black holes are exactly standardized
objects -- no traces persist to distinguish how a particular hole
formed or what kind of objects it swallowed. The combined efforts
of several theorists had proved this result by the early 1970s.
4) The paradoxes within a black hole are as fundamental, and as
far-reaching in their implications, as the puzzles that
confronted Einstein's contemporaries at the beginning of the 20th
century and triggered the development of relativity and the
quantum theory. Black holes preclude space and time being a
seamless continuum, and they may be gateways to other space-times
sprouting from our own. The existence of black holes not only
allows, but may even require, a broadening cosmic perspective
that envisions our universe as just a member of an ensemble. 5)
Ad hoc explanations for observed cosmic phenomena that do not
involve black holes can be devised, but they are generally too
contrived to be convincing, and black holes remain the most
plausible endpoints for certain types of stellar evolution. 6)
The evidence for supermassive extra-Galactic black holes is now
even more compelling than for black holes within our own galaxy.
In the centers of some galaxies, gas and stars are evidently
swirling into a black hole weighing as much as millions or even
billions of Suns. They manifest themselves as quasars or as
intense sources of cosmic radio emission. These supermassive
black holes have diameters as large as our solar system. 7) Rees
concludes with a quotation from the astrophysicist Roger Penrose:
"It is ironic that the astrophysical object which is the
strangest and least familiar, the black hole, should be the one
for which our theoretical picture is most complete."
QY: Martin Rees, King's College, Cambridge University, UK.
(Astronomy July 1998) (Science-Week 3 Jul 98)
-------------------
Related Background:
ON BLACK HOLES AS REAL ASTRONOMICAL OBJECTS
... The Uhuru Satellite ("uhuru" is the Swahili word for
"freedom"), launched in 1970 and operating until 1973, was the
first artificial satellite for x-ray astronomy, producing a
catalogue containing 339 x-ray sources. ... ... G. Bisnovatyi-
Kogan (Space Research Institute Moscow, RU) reviews the papers
presented at a recent international conference on black holes
(11-17 January 1998, S.N. Bose National Centre for Basic Sciences
Calcutta, IN). This was perhaps the first conference devoted to
black holes as real astronomical objects. The first indications
for the actual existence of black holes came from x-ray observ-
ations of the UHURU satellite, but black holes were predicted
theoretically 60 years ago, and in fact Laplace in 1796 already
noted that light cannot leave a star when its free-fall velocity
as determined by the star's mass and radius is larger than the
speed of light as we have measured it. At the present time, if
the apparent mass of a discovered compact object exceeds the
limiting mass, and if we hold the theory of general relativity to
be valid, we say we have discovered a black hole. There are now
40 such objects that have been identified, 30 of them super-
massive objects each containing millions and billions of solar
masses and surrounded by dense stellar clusters in the strong
gravity of a black hole.
QY: G. Bisnovatyi-Kogan (gkogan@mx.iki.rssi.ru)
(Science 27 Feb 98) (Science-Week 20 Mar 98)
-------------------
Related Background:
GALACTIC BLACK HOLES: RADIATION AND PLASMA CONSUMPTION
... In physics, a "plasma" is a fully ionized gas consisting of
free electrons and positive ions, the plasma formed at high
temperatures such as the temperatures in stars or by
photoionization (e.g., in interstellar gas). R. Genzel (Max
Planck Inst. for Extraterrestrial Physics, DE), in a short review
of galactic center black holes, suggests there is probably a
massive black hole at the center of our own galaxy, and that the
apparently low radiation of such galactic center black holes may
be due to plasma effects involving the conversion of gravitat-
ional energy into thermal energy of ions rather than into
radiation produced by electrons.
QY: Reinhard Genzel 
(Nature 1 Jan 98) (cf. Narayan et al, Astrophys. J. 10 Jan 98)
(Science-Week 16 Jan 98)
-------------------
Related Background:
ANALYSIS OF A SUPERMASSIVE BLACK HOLE ACCRETION DISK
Matter with high angular momentum attracted to a black hole does
not fall directly into the black hole but forms a rapidly
spinning "accretion disk" around the black hole, and this can
produce considerable energy, particularly at x-ray wavelengths,
as the accretion disk loses angular momentum and spirals inward.
The dynamical evolution and fate of such accretion disks has been
the subject of much theoretical analysis and model simulations. 
Supermassive black holes are black holes with masses of the order
of 10^(6) to 10^(9) solar masses and are believed to occupy the
centers of some galaxies. The term "iron-line emission" refers to
emission at the frequency characteristic (the "line") of iron
atoms in transit from excited states to lower energy states.
Because of the nature of nucleosynthesis -- the fusion reactions
in stars -- the cores of many stars consist of iron. Bromley et
al (3 authors at 3 installations, US RU) present an analysis of
the iron-line emission of galaxy MCG-6-30-15 that is independent
of parametric details of the disk model used, and they deduce
that from this galaxy there are being observed emissions from
gravitationally bound material in the strong-field region of a
supermassive black hole.
QY: B.C. Bromley 
(Nature 1 Jan 98) (Science-Week 16 Jan 98)


3. MITOCHONDRIAL EVOLUTION
The classification schemes devised by biologists to bring some
conceptual order to the tremendous variety of living organisms
must depend upon what is known about the various living
organisms, both in general and in detail. Classification schemes,
therefore, can be expected to change as the science changes. At
the present time, all biological cells are classified into 2
broad categories, prokaryotes and eukaryotes. Prokaryotes are
defined as cells without internal membrane-bound organelles such
as a nucleus, and eukaryotes are defined as cells that do have
such internal membrane-bound organelles. (The prefix "eu-" means
"true", and "karyon" means nucleus; "eukaryote" literally means
possessing a true nucleus). One type of internal membrane-bound
organelle of great importance is the mitochondrion (plural:
mitochondria), often present in large numbers inside certain
eukaryotic cells. In general, mitochondria are found in all
eukaryotic cells in which aerobic respiration (the direct
utilization of oxygen) and energy production take place. Almost
all the adenosine triphosphate (ATP) in non-photosynthetic cells
is produced in mitochondria. Each mitochondrion is surrounded by
two phospholipid bilayer membranes similar to the plasma membrane
of the host cell. Apart from their role in cellular energy
production, what is most interesting about mitochondria is that
they are self-replicating entities, containing their own DNA-
based genome, and although their existence is dependent on the
viability of the host cell, the mitochondria have very much the
elements of integral living organisms. All the evidence, in fact,
suggests that mitochondria are indeed the substantial remnants of
independent living organisms that were somehow co-opted by
evolution into becoming part of the internal metabolic apparatus
of eukaryotic cells. The term "endosymbiosis" refers to an
arrangement in which one organism lives inside another organism,
but the term is usually restricted to arrangements of mutual
benefit, thus not including parasite-host relationships. A number
of eukaryotic cell organelles in addition to mitochondria are
believed to have originated from endosymbiotic relationships
between eukaryotic cells and simpler cells. Finally, we must note
the existence of the terms "eubacteria" and "proteobacteria". All
eubacteria are prokaryotes, i.e., they do not possess internal
membrane-bound organelles of any kind (again, the prefix "eu-"
means "true": the eubacteria are _not_ eukaryotes, but "true"
bacteria or prokaryotes). The term "proteobacteria" is a rather
loosely used rubric bringing together a large variety of
eubacteria subtypes into one group based on details of metabolic
energy sources. Most organisms in the world are classified as
"proteobacteria" (also called "purple bacteria"). Concerning
mitochondria, an important question is where do they come from?
If mitochondria were originally endosymbionts, from which
primitive life form do they derive? ... ... M.W. Gray et al (3
authors at 2 installations, CA) present an extensive review of
current research concerning the evolution of mitochondria, the
authors making the following points:
     1) The "serial endosymbiosis" theory is the favored model
for explaining the origin of mitochondria, a defining event in
the evolution of eukaryotic cells. As usually described, this
theory postulates that mitochondria are the direct descendants of
a bacterial endosymbiont that became established at an early
stage in a nucleus-containing host cell without mitochondria.
     2) Analysis of gene sequence data strongly supports a
single-species origin of the mitochondrion from a eubacterial
ancestor in the proteobacteria subgroup known as "alpha-
proteobacteria". Members of the rickettsial subdivision of the
alpha-proteobacteria are obligate intracellular parasites that
are considered to be among the closest known eubacterial
relatives of mitochondria.
     3) However, recent studies of unicellular eukaryotes
(*protists), some of these species little known, have provided
insights that challenge the traditional serial endosymbiosis view
of how the eukaryotic cell and its mitochondria came to exist.
These new data indicate that the mitochondrion arose in a common
ancestor of all extant eukaryotes, and the data raise the
possibility that mitochondria originated at essentially the same
time as the nucleus of the eukaryotic cell, rather than in a
separate subsequent event as is commonly believed.
-----------
M.W. Gray et al: Mitochondrial evolution.
(Science 5 Mar 99 283:1476)
QY: Michael W. Gray [m.w.gray@dal.ca]
-----------
Text Notes:
... ... *protists: (Proctista) One of the phylogenetic kingdoms,
this category is defined mostly by exclusion and contains all the
eukaryotic nucleated organisms that cannot be classified as
animal, plant, or fungus. Protists include protozoans, algae,
kelps, slime molds, and many obscure eukaryotes.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 18Jun99
-------------------
Related Background:
GENOME OF THE TYPHUS PARASITE AND THE ORIGIN OF MITOCHONDRIA
The Rickettsia are small bacteria (600 x 300 nanometers, or
spherical as "cocci"), classified as a type of proteobacteria
(i.e., "purple" bacteria, a huge phylum including many common
bacteria). The Rickettsia are obligate intracellular parasites
(i.e., they can replicate only inside living cells), and one of
the most notorious of these parasites is R. prowazekii, the agent
of epidemic louse-born typhus in humans. R. prowazekii is
estimated to have infected 20 to 30 million humans in the wake of
the First World War and killed another few million humans
following the Second World War. Because it is apparently the
descendent of free-living organisms, the genome of R. prowazekii
may provide insight into the adaptations producing an obligate
intracellular lifestyle. Also, phylogenetic analyses based on
sequences of *ribosomal RNA and *heat-shock proteins indicate
that *mitochondria may be derived from the proteobacteria, and
indeed the closest extant relatives of the ancestor to
mitochondria seem to be the Rickettsia. Finally, the genome of R.
prowazekii is a small one, making it amenable to genome analysis.
... ... S.G.E. Andersson et al now report the complete genome
sequence (1,111,523 *base pairs) of R. prowazekii. The authors
report this genome contains 834 protein-coding genes, the
functional profiles of which show similarities to those of
mitochondrial genes: no genes required for anaerobic glycolysis
are found in either R. prowazekii or mitochondrial genomes, but a
complete set of genes encoding components of the *tricarboxylic
acid cycle and the *respiratory-chain complex is found in R.
prowazekii (and in mitochondria). In effect, *ATP production in
Rickettsia is the same as that in mitochondria. Many genes
involved in the biosynthesis and regulation of biosynthesis of
amino acids and *nucleosides in free-living bacteria are absent
from R. prowazekii and mitochondria, and such genes have
apparently been replaced by homologues in the host genome. The R.
prowazekii genome contains the highest proportion of non-coding
DNA (24 percent) detected so far in a microbial genome, and the
authors suggest such non-coding sequences may be *degraded
remnants of "neutralized" genes that await elimination from the
genome. The authors finally suggest that phylogenetic analyses
indicate that R. prowazekii is more closely related to
mitochondria than is any other microbe studied thus far.
-----------
S.G.E. Andersson et al (10 authors at 2 installations, SE US)
The genome sequence of Rickettsia prowazekii and the origin of
mitochondria.
(Nature 12 Nov 98 396:133)
QY: Charles G. Kurland 
-----------
Text Notes:
... ... *ribosomal RNA: A class of RNA molecules that have an
important role in the structure of ribosomes, the large molecular
entities that carry out protein synthesis in all cells.
... ... *heat-shock proteins: A group of specific proteins
apparently synthesized by both prokaryotes (cells without
membrane-bound organelles) and eukaryotes (cells with membrane-
bound organelles) in response to a sudden elevation of ambient
temperature.
... ... *mitochondria: Mitochondria are double-membrane enclosed
organelles of cells that are involved with several important
biochemical pathways, including electron transport and oxidative
metabolism. Various types of eukaryotic cells may contain from a
few to several thousand mitochondria in each cell type. The
mitochondria are relatively large cylindrical structures up to 10
microns long and up to 2 microns in diameter, and most biologists
believe mitochondria are cell organelles that may have originated
as separate organisms that became resident in eukaryotic cells.
Mitochondrial DNA is independent of nuclear DNA. It consists of a
circular molecule, 16,569 base pairs long in humans, with a known
nucleotide sequence.
... ... *base pairs: The term "base pair" refers to the bases
(nucleotides) always found chemically bonded together in the DNA
double helix (adenine, for example, always bonds with thymine,
and guanine with cytosine).
... ... *tricarboxylic acid cycle: (Krebs cycle, citric acid
cycle) In aerobic respiration, the set of oxidative reactions
occurring after *glycolysis.
... ... *glycolysis: One of the 2 main energy-producing pathways
of the cell, this involves the anaerobic breakdown of glucose
with the generation of 2 molecules of adenosine triphosphate
(*ATP).
... ... *respiratory-chain complex: (electron transport chain)
Refers to a sequence of steps in the final stage of the aerobic
respiration biochemical pathway in which high energy electrons
are effectively passed through a series of membrane-bound carrier
molecules to support a proton gradient involved in energy
storage. The term "transport" here refers essentially to a
chemical flow diagram and not necessarily to an actual spatial
translocation of electrons.
... ... *ATP: (adenosine triphosphate) ATP is the most important
chemical energy source in all living cells, intimately involved
in various cell functions and cell metabolism, and an entity in
numerous cyclic chemical pathways involved in the synthesis of
components.
... ... *nucleosides: The base-sugar moieties of nucleotides.
... ... *degraded remnants: In this context, the idea is that the
Rickettsia are descendents of bacteria with substantially larger
genomes, and that both Rickettsia and mitochondria are the
products of several types of reductive evolution.
-------------------
Summary & Notes by SCIENCE-WEEK  18Dec98
-------------------
Related Background:
ORIGIN OF A CHLOROPLAST PROTEIN IMPORTER
In general, photosynthesis is the utilization of light energy to
power biosynthesis, and chloroplasts are the plant cell
organelles in which photosynthesis occurs, the chloroplasts
containing several photosynthetic pigments (chlorophylls).
Chloroplasts are found in all photosynthetic plant cells, but not
in photosynthetic prokaryotes (i.e., not in cells without
membrane-bound organelles). The typical higher plant chloroplast
is lens-shaped, approximately 5 microns across the larger
dimension, and the number of chloroplasts per cell can vary from
1 to 100 depending on the type of cell. A mature chloroplast is
typically bounded by two membranes, an inner membrane and an
outer membrane, the membranes possessing significantly different
chemical constituents. In addition to a number of enzymes
involved in photosynthesis, chloroplasts also contain in their
interior a circular DNA molecule and protein synthetic machinery
typical of prokaryotes. The current consensus is that
chloroplasts may have originated from *cyanobacteria that became
*endosymbionts, an origin similar to that of mitochondria, which
are believed to have originated from so-called "*purple
bacteria". During evolution, chloroplasts (like mitochondria)
have apparently relinquished the majority of their genes to the
host nucleus, since chloroplast DNA codes only for some of the
proteins required by chloroplasts. The protein products of such
transferred genes are evidently imported into chloroplasts with
the help of biochemical import machinery distributed across the
inner and outer chloroplast membranes. The evolutionary origin of
this machinery is considered a puzzle, since the two bounding
membranes of the cyanobacteria have exhibited no functionally
similar protein import system. Recently, however, in the genome
of a species of cyanobacteria (Synechocystis), an apparent gene
(an "*open reading frame") has been identified that codes for an
amino acid sequence that shares an approximate 22 percent amino
acid identity with a protein-transporting channel in the outer
envelope of pea chloroplasts. ... ... B. Bolter et al (5 authors
at 2 installations, DE) now report that the protein coded by the
open reading frame of the Synechocystis cyanobacterium is located
in the outer membrane of that organism (the lipopolysaccharide
layer), and apparently transports polyamines and peptides. The
authors suggest their results indicate that a component of the
chloroplast protein import system may have been recruited from a
preexisting channel-forming protein of the cyanobacterial outer
membrane, and that in addition the presence of a protein in the
chloroplast outer envelope which is *homologous to a
cyanobacterial protein provides support for the general
prokaryotic nature of the outer membrane of chloroplasts.
-----------
B. Bolter et al: Origin of a chloroplast protein importer.
(Proc. Natl. Acad. Sci. US 22 Dec 98 95:15831)
QY: Jurgen Soll [jsoll@bot.uni-kiel.de]
-----------
Text Notes:
... ... *cyanobacteria: A phylum of bacteria characterized by
blue-green (cyan) photosynthetic pigments, abundant in a variety
of habitats, particularly in fresh water and soil. Cyanobacteria
are responsible for generating a large portion of the free oxygen
in the Earth's atmosphere. They apparently produced stromatolite
limestone deposits, as well as the bulk of modern petroleum
deposits. (Stromatolites are laminated calcareous microbial
fossil deposits formed principally by cyanobacteria and algae.)
... ... *endosymbionts: Endosymbiosis is an arrangement in which
one organism lives inside another organism, but the term is
usually restricted to arrangements of mutual benefit, thus not
including parasite-host relationships. A number of eukaryotic
cell organelles (including mitochondria) are believed to have
originated from endosymbiotic relationships between eukaryotic
cells and simpler cells.
... ... *purple bacteria: Specifically, any of the various
photosynthetic bacteria that contain bacteriochlorophyll, and are
thus distinguished by purplish or reddish-brown pigments. But the
term "purple bacteria" is sometimes used as a synonym for the
phylum Proteobacteria, a general category comprising a large
number of diverse forms.
... ... *open reading frame: The term "reading frame" refers to a
specific permutation of nucleotide triplets in DNA as "framed" by
a preceding start triplet (start codon), and an open reading
frame is any DNA sequence of triplets that potentially encodes a
protein.
... ... *homologous: In this context, the term refers to similar
sequences of amino acids in two proteins.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 26Mar99
-------------------
Related Background:
A HYDROGENOSOME WITH A GENOME
Certain *anaerobic *protozoa and *fungi possess membrane-bound
organelles known as "hydrogenosomes". These organelles are
approximately 1 micron in diameter and are so called because they
produce molecular hydrogen. The anaerobic *ciliate protozoan
Nyctotherus ovalis, found in the hindgut of several species of
cockroach, has numerous hydrogenosomes that are intimately
associated with *endosymbiotic methane-producing *Archaea, the
latter using the hydrogen produced by the hydrogenosomes. Like
*mitochondria, the hydrogenosomes are bound by distinct double
membranes and have an inner membrane with *cristae-like
projections. The matrix contains *ribosome-like particles of the
same size as a numerous type of ribosome (70s) of the
endosymbiotic methanogenic Archaea. It has been postulated that
hydrogenosomes evolved from mitochondria by the concomitant loss
of their respiration and organellar genomes, and indeed so far no
hydrogenosome has been found that has a genome.
... ... A. Akhmanova et al (8 authors at 2 installations, NL) now
report evidence of a hydrogenosomal genome of apparent
mitochondrial descent, and also evidence that the protozoan N.
ovalis possesses a new type of nucleus-encoded "iron-only"
*hydrogenase. The authors suggest their results indicate that N.
ovalis hydrogenosomes evolved from mitochondria, but that
contrary to what has been proposed by others, the hydrogenosomes
have not relinquished their genomes. The authors further suggest
that the evolutionary origin of the N. ovalis nuclear hydrogenase
gene remains puzzling.
-----------
A. Akhmanova et al: A hydrogenosome with a genome.
(Nature 10 Dec 98 396:527)
QY: Johannes H.P. Hackstein [hack@sci.kun.nl]
-----------
Text Notes:
... ... *anaerobic: Refers to a life form or process sustained in
the absence of free (gaseous or dissolved) oxygen.
... ... *protozoa: A phylum (or subkingdom) comprising
unicellular and colonial animals of varied form, cells ranging
from simple to extremely complex macro-structures.
... ... *fungi: A kingdom of primarily multicellular organisms
lacking chlorophyll and existing as parasites, symbionts, or
saprophytes. In general, "symbionts" are organisms that live in
close association (symbiosis) with other organisms; saprophytes
are organisms that feed on dead or decaying life forms.
... ... *ciliate: Cilia are short threadlike extensions, hundreds
usually present on an individual ciliated cell, the cilia
undergoing synchronized movements to produce locomotion of the
protozoan.
... ... *endosymbiotic: Endosymbiosis is an arrangement in which
one organism lives inside another organism, but the term is
usually restricted to arrangements of mutual benefit, thus not
including parasite-host relationships. A number of eukaryotic
cell organelles (including mitochondria) are believed to have
originated from endosymbiotic relationships between eukaryotic
cells and simpler cells.
... ... *Archaea: The archaebacteria (also called the Archaea)
are a subkingdom of bacteria considered to be ancient compared to
other bacterial kingdoms, and possibly the most ancient life
forms and the ancestors of all eukaryotes (cells and organisms
with intracellular membrane-bound organelles). They typically
exist in extreme environments, and include the methane-producing
bacteria (methanogens), the "salt-loving" bacteria (halophilic
bacteria), and the sulfur-acid tolerant thermoacidophilic
bacteria.
... ... *mitochondria: Mitochondria are double-membrane enclosed
organelles of cells that are involved with several important
biochemical pathways, including electron transport and oxidative
metabolism.
... ... *cristae: The folds of the inner mitochondrial membrane.
They contain the enzymes and other proteins involved in
mitochondrial metabolism.
... ... *ribosome: A ribosome (not to be confused with riboZYME)
is a small particle, a complex of various ribonucleic acid
component subunits and proteins that functions as the site of
protein synthesis.
... ... *hydrogenase: (hydrogenlyase) An enzyme that catalyzes
the interaction of reduced *ferredoxin with ionic hydrogen to
produce oxidized ferredoxin and molecular hydrogen. 
... ... *ferredoxin: In general, a simple non-enzymic iron-sulfur
protein. Such proteins act as electron carriers in a variety of
oxidation-reduction systems and are found in a wide range of
microorganisms, in chloroplasts, and in some types of
mitochondria.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 12Feb99


4. ON NEW NERVE CELLS IN THE ADULT HUMAN BRAIN
During most of this century, one of the dogmas in neurobiology
was that in the adult human brain new connections between neurons
may arise, but never new neurons. The dogma, in other words, was
that in the adult human brain new nerve cells are not produced,
and the neurons present at birth are the neurons present in the
adult, albeit a maximum number of nerve cells at birth, since a)
the number of neurons in the healthy adult human brain apparently
decreases with age beginning at about age 35; and b) various
neurodegenerative diseases can markedly reduce the population of
neurons in either specific regions of the brain or globally
nearly everywhere in the brain. In recent years, this dogma, the
idea that new nerve cells are not produced in the adult human
brain, has effectively crumbled for at least one specific and
important brain locus called the "hippocampus", which is a region
of the cerebral cortex in the *medial part of the temporal lobe.
In humans, among other functions, the hippocampus is apparently
involved in short-term memory, and analysis of the neurological
correlates of learning behavior in animals indicates that the
hippocampus is also involved in memory in other species.
... ... G. Kempermann and F.H. Gage (2 installations, DE US)
present a review of past and current research in adult
neurogenesis in humans, the authors making the following points:
     1) In 1965, Altman and Das reported neurogenesis in the
hippocampus of rats, in a subregion of the hippocampus called the
"dentate gyrus". But this data was not viewed as evidence of
significant neurogenesis in adult mammals, primarily because the
methods available then could not accurately estimate the number
of new neurons nor demonstrate definitively that the new cells
were indeed nerve cells. In addition, the concept of *stem cells
in the brain had not yet been introduced, and the belief was that
for new neurons to appear, the only source would be replication
(i.e., mitosis) of adult neurons. There was also no evidence that
neurogenesis occurred in non-human primates, and so the relevance
of the rat data for the human brain seemed remote.
     2) In the mid 1980s, Nottebohm discovered that neurogenesis
occurred in adult canaries in brain centers responsible for song
learning, and that the process accelerated during the seasons in
which the adult birds acquired their songs. Nottebohm and his co-
workers then demonstrated that neurogenesis also occurred in the
hippocampus of adult chickadees, particularly during seasons when
the birds had to keep track of dispersed food storage sites.
     3) In 1997, Gould and McEwan reported that some neurogenesis
occurs in the hippocampus of the primate-like tree shrew, and in
1998, these authors found the same phenomenon in marmoset
monkeys, which are classified as actual primates.
     4) Because of research difficulties, demonstration of
neurogenesis in the adult human brain had to await special
techniques. In 1998, Peter S. Eriksson reported the use of
bromodeoxyruridine as a marker for neurogenesis and the first
evidence for neurogenesis in the hippocampus of adult humans. The
use of this marker depended on its already established use as a
tumor marker in cancer patients. Bromodeoxyuridine is a marker
that becomes integrated only into the DNA of cells preparing to
divide, and the marker was in use with terminally ill patients
with cancer of the tongue or larynx. Eriksson obtained consent
from a number of patients to investigate their brains after
death, and when 5 patients died, all 5 brains displayed new
neurons in the dentate gyrus subregion of the hippocampus. At the
same time as this study was reported, other research groups
reported nerve cell production in the hippocampus of adult rhesus
monkeys, which are primates closer to humans than marmoset
monkeys.
     5) In their review, the authors refer to their own work,
noting that beginning in 1997, they have demonstrated that adult
mice given enriched living conditions generate substantial
increases in dentate gyrus hippocampal neurons over that found in
genetically identical control animals.
     6) The authors suggest that studies of neurogenesis in the
adult human brain, while difficult, may lead to better treatments
for a variety of neurological diseases. The authors conclude:
"The expected benefits of unlocking the brain's regenerative
potential justify all the effort that will be required."
-----------
G. Kempermann and F.H. Gage: New nerve cells in the adult brain.
(Scientific American May 1999)
QY: Gerd Kempermann, University of Regensburg, DE.
-----------
Text Notes: 
... ... *medial part of the temporal lobe: The temporal lobes are
roughly the lower sides of the brain, above the ears and behind
the temporal bones of the skull, but when the human brain is
viewed from the side, as it usually is in common gross
depictions, the large and functionally important ventral and
infolded parts of the temporal lobes are not visible. In general,
the larger anatomical regions of the human brain are best
visualized as highly corrugated lobular structures extensively
folded and densely packed to fit inside the volume-limiting
protective skull. Isolated verbal descriptions of the
architecture are of limited use: anatomical graphics are the best
sources for visualization of gross brain structures.
... ... *stem cells: In general, the term "stem" cells
refers to undifferentiated cells that upon differentiation can
give rise to various specialized cell lines such as blood cells,
skin cells, nerve cells, etc. Adult bone marrow, for example,
contains stem cells that are the precursors of the various
specialized types of blood cells.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 18Jun99


5. INHIBITION OF ANGIOGENESIS BY GREEN TEA
Angiogenesis, the origin and development of blood vessels, is an
important consideration in the growth of cancerous tumors, since
the tumor provokes directed angiogenesis into itself with the end
result that the tumor is supplied with oxygen and nutrients.
Without angiogenesis, tumors can attain only a small size before
becoming self-inhibiting. (The essential point is that effective
distribution of oxygen and nutrients by simple diffusion is
limited by the size (i.e., volume) of the population of cells.)
Consumption of tea has been shown to inhibit the growth of
several tumor types in animals, including cancers of the lung and
esophagus. Drinking tea, especially green tea, is also associated
with a lower incidence of human cancer. The mechanisms of cancer
inhibition are not known, although several hypotheses have been
proposed, including the possibility of inhibition of
angiogenesis. ... ... Y. Cao and R. Cao (Karolinska Institute,
SE) now report the results of an investigation of the effects of
drinking green tea on angiogenesis. The authors investigated both
the effects of green tea and of one of its components,
epigallocatechin-3-gallate (EGCG). The authors report that EGCG
suppresses *endothelial cell growth in vitro (bovine capillary
endothelial cells), and the formation of new blood vessels in
chick *chorioallantoic membrane. The authors report that drinking
green tea significantly prevents corneal neovascularization
induced by the potent angiogenic factor VEGF (*vascular
endothelial growth factor). The green tea experiments were done
with mice, the animals having green tea as the sole drinking
fluid. The amount of green tea in the drinking water was 4.69
milligrams per milliliter, containing 708 micrograms per
milliliter EGCG, which produces an EGCG plasma concentration in
the range 0.1 to 0.3 micromolar, which is similar to levels in
humans after drinking 2 or 3 cups of tea. The authors suggest
that because the growth of all solid tumors is dependent on
angiogenesis, their findings may explain why drinking green tea
prevents the growth of a variety of different types of tumor.
-----------
Editor's note: For related material, see the SW Focus Report
"Biology of Cancer: Angiogenesis Inhibition" available at URL
[http://www.scienceweek.com/swfr028.htm].
-----------
Y. Cao and R. Cao: Angiogenesis inhibited by drinking tea.
(Nature 1 Apr 99 398:381)
QY: Yihai Cao [yihai.cao@mtc.ki.se]
-----------
Text Notes:
... ... *endothelial cell: Flat cells forming a layer lining
blood vessels, lymphatic vessels, the heart, etc.
... ... *chorioallantoic membrane: An extra-embryonic membrane.
In avian embryos such as that of the chicken, it is fused with
the egg shell and is crucial for chick embryonic development.
... ... *vascular endothelial growth factor: (vascular
permeability growth factor; vasculotropin) A protein produced by
epithelial and other types of cells, active in angiogenesis and
endothelial cell growth.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 18Jun99


6. ON VACCINES FOR MALARIA
The disease malaria is caused by a protozoan parasite of the
genus Plasmodium, and it is one of the most dangerous diseases
infecting human populations. Approximately 300 million to 500
million people are infected annually, and 1.5 million to 2.7
million lives are lost to malaria each year, with most deaths
occurring among children in sub-Saharan Africa. Of the 4 species
that cause malaria in humans, P. falciparum is the greatest cause
of *morbidity and mortality. The resistance of the malaria
parasite to drugs and the resistance of mosquitoes to
insecticides have resulted in a resurgence of malaria in many
parts of the world and a pressing need for vaccines and new
drugs. The identification of new targets for vaccine and drug
development is dependent on the expansion of our understanding of
parasite biology, an understanding that is hampered by the
*complexity of the parasite life cycle (see Notes below).
... ... Anthony A. Holder (National Institute for Medical
Research, UK) presents a review of current efforts to develop
malaria vaccines, the review emphasizing the "multivalent"
approach (defined below), with the author making the following
points:
     1) The concept that vaccination may be a useful tool to
control malaria is based on a number of observations: a)
Individuals exposed to infection by the responsible parasitic
protozoan do eventually develop immunity to the disease. b)
*Passive immunization with antibody from immune donors can have a
dramatic effect on *blood stage parasitemia. c) Inoculation of
live attenuated parasites can protect naive volunteers against
infection. d) Immunization with whole killed organisms can
protect in animal models.
     2) By its very nature, malaria vaccine research is a mix of
empirical and rational approaches. The research is hampered by
the complexity of the parasite life cycle, imperfect tools to
assess the efficacy of immune responses, and limited knowledge
and understanding of the factors that determine the outcome of an
infection.
     3) One approach, the "multivalent-multistage" approach, is
to identify the individual elements of the parasite on which to
focus the immune response, and then combine these elements into
an *immunogen that will prime the immune system to attack several
different stages and targets in the life cycle of the parasite.
An example of this is to string together, as a synthetic gene,
sequences coding for peptides that form important *epitopes. The
*recombinant protein expressed from this gene contains the
epitopes from several different proteins expressed at each stage
of the parasite life cycle. Thus, this approach is used to target
multiple *antigens expressed at different stages of the life
cycle.
     4) The life cycle of the malaria parasite is complex, the
several stages in humans are morphologically and antigenically
distinct, and immunity is stage specific. The genome of P.
falciparum contains approximately 5000 genes, with only a subset
of these genes expressed at any one stage in the life cycle. It
is only now becoming possible to define these patterns of
expression and identify the full spectrum of proteins present at
each stage.
     5) In the near future, the entire genome of P. falciparum
will be sequenced. This work will undoubtedly reveal many genes
that code for proteins as yet unknown, and some of these proteins
may be good candidates for vaccine development. In a multivalent-
multistage vaccine strategy there will be almost limitless
combinations of antigens or epitopes to analyze and assess.
     6) The author concludes: "If we are to develop an optimal
vaccine against malaria it will have to be based in large part on
an understanding of the important immune mechanisms involved in
protection against the parasite and the disease (pathogenesis,
immune evasion), the role of individual proteins in the parasite-
host interaction, and the development of sensitive and meaningful
in vitro methods to study these aspects."
-----------
Editor's note: In addition to the related background material
below, see the SW Focus Report "Biology of Malaria" available at
URL [http://www.scienceweek.com/swfr064.htm].
-----------
Anthony A. Holder: Malaria vaccines.
(Proc. Natl. Acad. Sci. US 16 Feb 99 96:1167)
QY: Anthony A. Holder [aholder@nimr.mrc.ac.uk]
-----------
Text Notes:
... ... *morbidity: In general, this refers to a diseased state;
in particular, the term refers to the ratio of the diseased
population to the well population in a community.
... ... *complexity of the parasite life cycle: The protozoan
organism (Plasmodium) that causes malaria is characterized by a
sequence of life cycles involving different organismic forms. The
asexual cycle occurs in the liver and red blood cells of
vertebrates (including humans), and the sexual cycle occurs in
mosquitoes. Essentially, the asexual form is ingested by
blood-sucking mosquitoes, and in the mosquito the asexual form is
induced to produce the sexual form necessary to complete the
total life cycle. The details of the process are as follows:
Plasmodium cells called "gametocytes" (precursors of gametes) in
human blood are ingested by the mosquito, and in the mosquito,
apparently within seconds, gametocytes are induced into
"gametogenesis", producing gametes. These gametes produce a
cell-type called "sporozoites", which accumulate in the salivary
gland of the mosquito, from where they are injected into the
vertebrate blood stream when the mosquito feeds on vertebrate
blood. The sporozoites accumulate in the vertebrate liver, where
they multiply and produce a form (merozoites) that invades red
blood cells, replicates, destroys red blood cells, and so on,
with an eventual decline in this asexual replication. However,
after invasion of red blood cells, some merozoites produce
gametocytes, which have the genomic potential for restarting the
total life cycle. These gametocytes cannot self-replicate, and
they die unless ingested by a mosquito, but once in the mosquito,
the total life cycle begins again. There are apparently 2
inducers of gametogenesis in vivo (i.e., in the mosquito): one
inducer is a pH of 7.5 to 7.6, and the other inducer has been
thought to be an unknown mosquito-derived gametocyte-activating
factor.
... ... *Passive immunization: In general, resistance acquired
from the transfer of antibodies from another person or from an
animal. For example, immunity acquired by the fetus from the
mother.
... ... *blood stage parasitemia: In general, the term
"parasitemia" refers to the presence of parasites in the
circulating blood. In this context, "blood stage" refers to the
life cycle stages of the malarial parasite when it is present in
human blood.
... ... *immunogen: In general, any "antigen", i.e., any chemical
entity that activates an immune response, especially an entity
originating outside the body. An "antibody" is a protein molecule
produced by the immune system of vertebrate organisms, the
molecule designed to specifically interact with a particular
antigen.
... ... *epitopes: In general, the term "epitope" refers to the
region of an antigen molecule responsible for its specificity in
an antigen-antibody interaction: the epitope is recognized by the
antigen-binding site of a specific antibody molecule.
... ... *recombinant protein: In general, any protein synthesized
by a living system as a result of genetic engineering, i.e., as a
result of controlled alteration of the DNA of that organism,
usually by insertion of a new gene encoding for the protein.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 18Jun99
-------------------
Related Background:
MAJOR DRUG COMPANIES REFUSE ANTI-MALARIA COLLABORATION
An anti-malaria joint effort originally designed by the Wellcome
Trust, the World Health Organization, the World Bank, the
Association of the British Pharmaceutical Industry, and the drug
companies Roche and Glaxo-Wellcome has apparently disintegrated
as a result of a decision of the pharmaceutical interests not to
support it. The idea was to gather US$180 million for a joint
project to develop new treatments for the world's most
threatening tropical diseases, particularly for malaria. Now the
pharmaceutical industry leaders say, "There are drugs and
vaccines for malaria already in development within the
pharmaceutical industry." Malaria researchers have expressed
their disappointment. Brian Greenwood (London School of Hygiene
and Tropical Medicine) says, "We really thought industry was
wanting to help."
(Science 5 Dec 97) (Science-Week 26 Dec 97)
-------------------
Related Background:
INERTIA IN INTERNATIONAL EFFORTS TO CURB MALARIA
Malaria, an infectious disease caused by a parasitic protozoan
transmitted by a mosquito bite, blood transfusion, or the use of
a common syringe by drug addicts, kills one or two million people
each year. There are actually 4 types of protozoan parasites that
cause the disease, with Plasmodium falciparum the most dangerous.
The drug chloroquine is quite effective, except with P.
falciparum, which is usually resistant to it. Treatment of
falciparum malaria requires the administration of a number of
drugs simultaneously and close technological monitoring of the
patient. Falciparum malaria is hyperendemic in East Africa,
Central and South America, and the Far East, and if untreated it
has a high fatality rate. Attempts by the international community
to control malaria have been underway for many decades. In
January there was another meeting of the scientific community
involved with the disease. Last week in The Hague (NL), there was
another meeting of high-level government officials, foundation
managers, and pharmaceutical company representatives. The
apparent consensus was that we cannot collaborate because we
don't know how, and even if we did collaborate, we cannot
manufacture the old drugs or new drugs or possible vaccines
because the people who need them cannot afford them and there is
thus no market of commercial interest. Everyone agreed to meet
again, perhaps in six months.
(Science 18 Jul 97) (Science-Week 25 Jul 97)


=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= 

IN FOCUS: ON THE FOUNDATION OF MODERN CHEMISTRY
"It is interesting that it was not until the early years of the
17th century that the word 'gas' was used. This word was invented
by a Belgian physician, J.B. van Helmont (1577-1644), to fill the
need caused by the new idea that different kinds of 'airs'
existed. Van Helmont discovered that a gas (the gas that we now
call carbon dioxide) is formed when limestone is treated with
acid, and that this gas differs from air in that when respired it
does not support life and that it is heavier than air. He also
found that the same gas is produced by fermentation, and that it
is present in the Grotto del Cane, a cave in Italy in which dogs
were observed to become unconscious (carbon dioxide escaping from
fissures in the floor displaces the air in the lower part of the
cave). During the 17th and 18th centuries, other gases were
discovered, including hydrogen, oxygen, and nitrogen, and many of
their properties were investigated. It was not until nearly the
end of the 18th century, however, that these three gases were
recognized as elements. When Lavoisier recognized that oxygen is
an element, and that combustion is the process of combining with
oxygen, the foundation of modern chemistry was laid."

-- Linus Pauling: _General Chemistry_
   (W.H. Freeman, San Francisco 1970, p.306)


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