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.

April 21, 2000 -- Vol. 4 Number 16

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We may or may not be majestic as a species,
but if one considers an astronomer sitting alone
on a cold night at a telescope on a mountain top,
one must conclude we are certainly obsessed with
knowing what and where we are.
-- Anonymous

-----------------------------------------------

The Editors of ScienceWeek express their condolences
to the families and friends of 5 members of an ecology
research team who died when their boat capsized in a
storm off the west coast of Mexico (in the Gulf of
California) on 27 March 2000.

The deceased researchers are as follows:

Takuya Abe (1945-2000) Kyoto University, JP
Masahiko Higashi (1955-2000) Kyoto University, JP
Shigeru Nakano (1963-2000) Kyoto University, JP
Gary Polis (1947-2000) University of California Davis, US
Michael Rose (1972-2000) University of California Davis, US

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Contents of This Issue:

1. Astrophysics:
The Formation and Evolution of the Milky Way Galaxy
---------------------------------------------------
Recent observations indicate that our Galaxy may have formed by
aggregation of gas and stars from a reservoir of preexisting
small galaxies in the local Universe, the process probably
beginning more than 12 billion years ago. (Includes related
background material.)

2. Materials Science:
Quantum Dots
------------
Quantum dots are essentially "designer" atoms, since their
electronic properties can be controlled via the synthetic method
used to prepare the dots. (Includes related background material.)

3. Molecular Biology:
Plant Genomics
--------------
The term "genomics" refers to the systematic study of whole
genomes, and current methods in plant genomics include a variety
of techniques to both achieve wholesale mutations in plants and
to determine the function of newly identified genes. (Includes
related background material.)

4. Cell Biology:
Apoptosis and Caspases
----------------------
Programmed cell death (apoptosis) involves the action of specific
proteolytic enzymes called "caspases". Until now, caspases were
thought to be localized in the plasma membrane and in
mitochondria, but new evidence indicates a new caspase (caspase-
12) is localized in the endoplasmic reticulum of cells and plays
a role in certain types of apoptosis. (Includes related
background material.)

5. Cognitive Science:
Numbers and Counting in a Chimpanzee
------------------------------------
A chimpanzee that has learned to use Arabic numerals to represent
numbers of items, and that can count from 0 to 9 items, is now
shown to remember the correct sequence of any 5 numbers selected
from the range 0 to 9.

6. Medical Biology:
On the Ingestion of Toxic Substances by Children
------------------------------------------------
According to current data, 1.08 million instances of ingestion of
a toxic substance by a child less than 6 years of age were
reported to US poison centers in 1998. (Includes related
background material.)

In Focus: On Thermodynamics vs. Statistical Mechanics

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1. ASTROPHYSICS:
THE FORMATION AND EVOLUTION OF THE MILKY WAY GALAXY
The current consensus is that our Galaxy (the Milky Way) has four
major components:
     a) The Central Bulge, which consists of a dense spherical
agglomeration of stars surrounding an apparent central massive
*black hole of some millions of solar-masses (see related
background material below).
     b) A thin disk rotating around the Central Bulge, the disk
with a mass of approximately 6 x 10^(10) solar-masses and
consisting of relatively young stars, loose clusters of stars
(open clusters), and gas and dust (interstellar material), with
loose concentrations of the young stars and interstellar material
into spiral arms. The thin Galactic disk is approximately 1000
light-years thick, compared with a diameter of over 100,000
light-years.
     c) A faint roughly spherical halo with an estimated mass of
15 to 30 percent of the mass of the disk, the halo composed of
old stars, some of which are in globular clusters, plus small
amounts of hot gas, and all of it merging into the more
conspicuous bulge of stars at the center of the Galaxy. The
diameter of the halo is approximately the diameter of the disk.
     d) An unseen halo of non-radiative matter (dark matter) with
a total mass of at least 4 x 10^(11) solar-masses.
     It is estimated there are in total approximately 2 x 10^(11)
stars in our Galaxy, most of these with a mass less than the mass
of the Sun. The thin disk is estimated to be 10 billion years
old, and the globular clusters and most of the halo stars are
estimated to be 12 to 14 billion years old. The Sun lies
approximately 26,000 light-years from the center of the Galaxy,
in one of the spiral arms.
... ... Roland Buser (University of Basel, CH) presents a review
of current research on the formation and early evolution of our
Galaxy, the author reporting the following:
     1) In recent years it has become evident that in addition to
the flattened thin disk there are one or more diffuse thicker
disks superimposing the thin disk in the same plane, and a
similar disk structure has been observed in several other 
galaxies seen edge-on.
     2) Recent observations indicate that our Galaxy may have
formed by aggregation of gas and stars from a reservoir of
preexisting small galaxies in the local Universe. The process
probably began more than 12 billion years ago with material of
different original *angular momenta following two separate
evolutionary lines, one into the slowly rotating halo and central
bulge, and the other into the rapidly rotating disk.
     3) The author suggests that the existence of distinct thick
and thin disks in the Galaxy indicates that continuing mergers of
satellite galaxies probably also determined the early evolution
of the main structural component of the luminous Galaxy.
-----------
Roland Buser: The formation and early evolution of the Milky Way
galaxy.
(Science 7 Jan 00 287:69)
QY: Roland Buser [Roland.Buser@unibas.ch]
-----------
Text Notes:
... ... *black hole: If the terminal stages of star death leave
a remnant star mass greater than 3 solar-masses, the ultimate
gravitational collapse will 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. (Concerning the apparent
black hole at the center of our Galaxy, see related background
material below.)
... ... *angular momenta: The term "angular momentum" refers to
the momentum possessed by a body by virtue of rotation --
rotation about another body and/or rotation about its own axis.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 21Apr00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ASTRONOMY: ON DUST AND GAS IN THE MILKY WAY
We reside in a star system (the Milky Way Galaxy) over 100,000
light years in diameter and containing over 100 billion stars.
Almost every celestial object visible to the naked eye is part of
this Galaxy. Exceptions include the Magellanic clouds, which are
small irregular galaxies located in the southern sky, and which
are apparently satellites of our Galaxy but not part of it.
Another exception is the Andromeda galaxy, just visible to the
naked eye as a faint patch of light in the constellation
Andromeda. The Sun lies approximately 26,000 light years from the
center of the Galaxy. The Galaxy is apparently a spiral galaxy,
but attempts to measure the dimensions of individual spiral arms
and other aspects of the Galaxy are hampered by obscuring dust in
the Galactic disk and by the difficulty of estimating distances
within the Galaxy. The Galaxy is believed to be a "*barred
spiral", since there is some evidence for a bar-like structure in
the central regions. The age of the Galaxy is still uncertain,
but the disk is at least 10 billion years old, while the globular
clusters of stars and isolated stars (halo stars) in the
periphery are apparently 12 to 14 billion years old. The disk is
thin, approximately 1000 light years, compared with a diameter of
over 100,000 light years. In general, astronomers know more about
distant galaxies than they do about our own Milky Way Galaxy, and
the major reason for this is that other stars, the gas, and
especially all the dust in the disk obscure the full extent of
the structure of the Galaxy as observed from within it.
... ... Henry Freudenreich (NASA Goddard Space Flight Center, US)
presents a review of current research on the Milky Way Galaxy,
the author making the following points concerning gas and dust in
the Galaxy:
     1) The tenuous matter between the stars in our Galaxy is
approximately 90 percent hydrogen and 9 percent helium. The
remaining 1 percent consists of heavier elements collected into
fine particles called "dust". Most of these particles are less
than 1 micron in diameter and are rich in carbon and silicates.
     2) Although there is a diffuse distribution of dust
throughout the Galaxy, most of the dust is collected into ragged
clouds of various sizes and densities. The interiors of the more
massive clouds, which are shielded from starlight, are relatively
cool and dense. In these interiors, hydrogen atoms are able to
combine to form hydrogen molecules [H(sub2)], and for this reason
these dust agglomerations are called "molecular clouds". Such
dense molecular clouds are the birthplaces of stars.
     3) Dust particles have complex dynamic interactions. They
collide with each other and also with both neutral and ionized
atoms of gas, so that dust particles are subjected to
hydrodynamic and magnetic forces in addition to gravity. Dust is
also pushed around by *stellar winds, which are mostly protons
and electrons. As a result of these various forces, Galactic dust
exhibits a variety of large-scale features -- huge bubbles,
tendrils, and wavy sheets -- that are unique among the components
of the Galaxy. Some of the wispy dust formations are reminiscent
of cirrus clouds on Earth, and these formations are called
"Galactic cirrus".
     4) Radio-astronomers have used the radio emissions of atomic
hydrogen atoms and carbon monoxide molecules to map the
distribution of gas over most of the Galaxy. But such maps do not
necessarily correspond to the distribution of stars in the
Galaxy, and radio surveys provide only a partial picture of the
global structure of the Galaxy.
     5) The distribution of gas is also not useful for mapping
the inner part of the Galaxy (within approximately 15,000 light
years of the center). We do know that the density of gas and dust
increases as we move inward, peaking at a distance of
approximately 12,000 light years from the center, where it forms
a collection of clouds known as the "molecular ring". The density
is again lower inside the ring, where the apparent motions of the
gas are peculiar and poorly understood.
-----------
Henry Freudenreich: Deconstructing the Milky Way Galaxy.
(Amer. Scientist Sep/Oct 1999 87:418)
QY: Henry Freudenreich [henry.t.freudenreich.1@gsfc.nasa.gov]
-----------
Text Notes:
... ... *barred spiral: In general, a "barred spiral galaxy" is a
type of galaxy with spiral arms extending from an almost
rectangular or cigar-shaped bar of stars across its central
region.
... ... *stellar winds: In general, the term "stellar wind"
refers to the outflow of gas from the surface of a star. The Sun,
for example, loses approximately 10(-14) of its mass each year
via such a wind ("solar wind").
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 31Dec99
[For more information: http://scienceweek.com/swfr.htm]
-------------------
Related Background:
ON THE BLACK HOLE AT THE CENTER OF OUR GALAXY
Recent observations have led to the conclusion that at the center
of many galaxies there is an object producing effects
characteristic of a supermassive *black hole. Alexei V.
Filippenko (University of California Berkeley, US) reviews
current research on black holes, the author making the following
points concerning the apparent massive black hole at the center
of our own Galaxy:
     1) Some galaxies are known to have very "active" central
regions from which enormous amounts of energy are emitted each
second. These "active galactic nuclei" are probably powered by
accretion of matter into a supermassive black hole of 10^(6) to
10^(9) solar-masses. The center of our own Galaxy exhibits mild
activity, especially at radio wavelengths: so-called "nonthermal
radiation" characteristic of high-energy electrons spiraling in
magnetic fields is emitted by a compact object at the Galactic
center known as *Sagittarius A*. Does the center harbor a
supermassive black hole? One approach is to determine whether
stars in the central region are moving very rapidly, as would be
expected if a large mass were present. During the past 5 years,
two teams have obtained high-resolution images of our Galactic
center, each team on several occasions, so that temporal changes
in the positions of stars could be detected. The observations
were conducted at infrared wavelengths, which penetrate the gas
and dust between Earth and the Galactic center (a distance of
approximately 25,000 light years) much more readily than optical
light. In summary, the data are in excellent agreement with the
conclusion that the gravitational potential of the central region
of our Galaxy is dominated by a single object. The derived mass
of this object is (2.6 +- 0.2) x 10^(6) solar-masses, and the
mass density within a radius of 0.05 light-years is at least 6 x
10^(9) solar-masses per cubic light-year, effectively eliminating
all possibilities other than a black hole.
     2) Although our Galaxy provides the most convincing case for
the existence of supermassive black holes, observations of the
centers of a few other galaxies bolster the conclusion. For
example, very precise measurements of the galaxy NGC 4258 reveal
a central compact object with a derived mass 3.6 x 10^(7) solar-
masses. On somewhat larger scales, spectra obtained with the
Hubble Space Telescope show gas and stars rapidly moving in a
manner consistent with the presence of a supermassive black hole.
The most massive existing case, that of the giant elliptical
galaxy M87, is approximately 3 x 10^(9) solar-masses. Moreover,
x-ray observations of some active galactic nuclei reveal emission
from a hot disk of gas apparently very close to a black hole,
since extreme relativistic effects are detected. In general, it
now seems that a supermassive black hole is found in nearly every
large galaxy amenable to such observations.
     3) The author concludes: "In the last decade of the 20th
century, black holes have moved firmly from the arena of science
fiction to that of science fact. Their existence in some *binary
star systems, and at the centers of massive galaxies, is nearly
irrefutable. They provide marvelous laboratories in which the
strong-field predictions of Einstein's general theory of
relativity can be tested."
-----------
Alexei V. Filippenko: Black holes in the Milky Way galaxy.
(Proc. Natl. Acad. Sci. US 31 Aug 99 96:9993)
QY: Alexei V. Filippenko [alex@astro.berkeley.edu]
-----------
Text Notes:
... ... *black hole: See main report.
... ... *Sagittarius A*: Sagittarius A is a prominent radio
source in the constellation Sagittarius, coincident with or close
to the center of our Galaxy. It is a highly complex region
consisting of a central core approximately 50 light-years in
diameter. Sagittarius A* is a compact component at the heart of
the central core of Sagittarius A. Sagittarius A* is an intense
source of radio waves, and is apparently unique in our Galaxy:
while everything else in our Galaxy is on the move as they follow
their orbits, Sagittarius A* is absolutely stationary and must
therefore lie exactly at the Galaxy's center. Many astronomers,
in fact, use Sagittarius A* as the "Greenwich Meridian" of the
Galaxy.
... ... *binary star systems: Binary stars are a pair of stars
revolving around a common center of mass under the influence of
their mutual gravitational attraction, and apparently the
majority of stars in the Universe are binaries and not singlets.
In some cases the binary system is resolvable into two
components, and in other cases the presence of a second star is
inferred by perturbations in the motion or emitted radiation of
the first star. If the binaries are close enough, they may share
stellar material, and this results in a particular kind of
stellar evolution. In the black hole-binary systems mentioned in
this report, matter transfers from a relatively normal star
(known as the "secondary star") to a dark compact object (the
"primary"). Recent comparisons of x-ray and optical brightness
suggest that in many cases the dark primary in such a binary
system is a black hole.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 15Oct99
For more information: http://scienceweek.com/swfr.htm

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2. MATERIALS SCIENCE:
QUANTUM DOTS
It is now possible to create extremely small crystals which
contain less than 1000 atoms, each crystal measuring a few
millionths of a millimeter across and thus in the nanoscale
domain. Certain of these nano-crystals, those of cadmium
selenide, for example, have peculiar attributes: crystals of
exactly the same composition but of different size exhibit quite
different properties, with the large nano-crystals of cadmium
selenide red in color, smaller crystals orange, and the smallest
(containing barely 100 atoms) yellow in color. The differences in
properties are due to quantum mechanical effects. These extremely
small atomic arrays are called "quantum dots", and there is a
current consensus that if quantum dots could be integrated onto a
chip, their unique electrical properties could be harnessed to
perform a function similar to a conventional transistor, while
requiring only a small fraction of the space. In consequence, the
creation of an appropriate regular array of quantum dots would
allow a computer processor many times more powerful than any
current supercomputer to be constructed on single chip.
... ... F. Remacle and R.D. Levine (2 installations, BE IL)
present a theoretical discussion of assemblies of metallic
quantum dots with each dot considered as an "atom". The dots are
taken as being packed close enough to be interacting. The authors
suggest that the key point is that such dots are essentially
"designer" atoms, since their electronic properties can be
controlled via the synthetic method used to prepare the dots. Of
direct significance are the size of the dot and the nature of the
ligands used to prevent coalescence of the dots. The energy
required to remove or add an electron to the dot is determined by
the size of the dot. The ligands control how closely the dots can
be packed and hence the strength of the coupling between adjacent
dots. An important parameter is the energy cost of adding an
electron to a dot: because of the large size of the dots, the
Coulomb repulsion of the added electron is low. Unlike most
ordinary atoms, quantum dots have a high capacity for
accommodating an additional electron.
-----------
F. Remacle and R.D. Levine: Architecture with designer atoms:
Simple theoretical considerations.
(Proc. Natl. Acad. Sci. US 18 Jan 00 97:553)
QY: R.D. Levine [rafi@fh.huji.ac.il]
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 21Apr00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
MATERIALS SCIENCE: LOCALIZATION-DELOCALIZATION IN QUANTUM DOTS
N.B. Zhitenev et al (US) report a study of the electron
localization-delocalization transition in quantum dots. The
problem of electron localization has remained a prime focus of
experiment and theoretical research over the past 40 years.
Single-electron capacitance spectroscopy precisely measures the
energies required to add individual electrons to a quantum dot.
The spatial extent of electronic wave functions was probed by
investigating the dependence of these energies on changes in the
dot confining potential. For low electron densities, electrons
occupy distinct spatial sites localized within the dot. At higher
densities, the electrons become delocalized, and all wave
functions are spread over the full dot area. Near the
delocalization transition, the last remaining localized states 
exist at the perimeter of the dot. Unexpectedly, these electrons
appear to bind with electrons in the dot center.
(Science 99/285:715) (SW Bulletin 6 Aug 99)
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
MICROWAVE SPECTROSCOPY OF A QUANTUM DOT MOLECULE
Quantum dots are small conductive regions in a semiconductor, the
regions containing a variable number of electrons (from 1 to
1000) that occupy well-defined, discrete quantum states -- for
which reason they are often referred to as "artificial atoms".
Connecting quantum dots to current and voltage contacts allows
the discrete energy spectra of the system to be probed by charge-
transport measurements. Two quantum dots can be connected to form
an "artificial molecule", and depending on the strength of the
inter-dot coupling (which supports *quantum-mechanical tunnelling
of electrons between the dots), the two dots can form "ionic" or
"covalent" bonds. In the ionic bond case, the electrons are
localized on individual dots, and in the covalent bond case, the
electrons are delocalized over both dots. ... ... T.H. Oosterkamp
et al now report a transition from ionic bonding to covalent
bonding in a quantum-dot "artificial molecule" probed by
microwave excitations. The authors suggest their results
demonstrate controllable *quantum coherence in single-electron
devices, an essential requirement for practical applications of
quantum-dot circuitry in the construction of quantum computers.
-----------
T.H. Oosterkamp et al (7 authors at 3 installations, NL JP)
Microwave spectroscopy of a quantum-dot molecule.
(Nature 29 Oct 98 395:873)
QY: T.H. Oosterkamp 
-----------
Text Notes:
... ... *quantum-mechanical tunnelling: "Tunnelling" is a quantum
mechanical phenomenon involving an effective penetration of an
energy barrier resulting from the width of the barrier being less
than the wavelength of the particle.
... ... *quantum coherence: In order for a system to be used to
process and transfer information, the system must be "coherent"
in its parts. In quantum physics, coherence is matter of locking
of phase differences between wave functions. The wave functions
of two or more particles are said to be coherent if the phase
difference between their wave functions remains constant. So if
new quantum electrodynamic information processing devices are to
be developed, methods must be found to keep the quantum states of
the parts of the system coherent long enough for information to
be processed and transferred from one place to another.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 27Nov98
-------------------
Related Background:
A TUNABLE KONDO EFFECT IN QUANTUM DOTS
Quantum dots are small electrically conducting regions, typically
less than 1 micron in diameter, that contain from one to a few
thousand electrons. Because of the small volume, the electron
energies within the dot are quantized, and the behavior of the
quantum dot is intermediate between that of an atom and that of a
classical macroscopic object. Such intermediate systems are
called "mesoscopic" systems, and in the past several years great
attention has been devoted to the physics of such systems, since
they apparently can provide insights into quantum systems in
general. The electronic states in quantum dots can be probed by
transport when a small *tunnel coupling is allowed between the
dot and nearby source and drain leads. ... ... Cronenwett et al
(3 authors at 2 installations, NL US) report the realization of a
tunable *Kondo effect in small quantum dots, with the capability
of switching a dot from a Kondo system to non-Kondo system as the
number of electrons on the dot is changed from odd to even. The
*Kondo temperature can be tuned by means of a gate voltage as a
single-particle energy state nears the *Fermi energy.
Measurements of the temperature and magnetic field dependence of
a *Coulomb-blockaded dot show good agreement with prediction of
both equilibrium and nonequilibrium Kondo effects.
QY: Sara M. Cronenwatt, Stanford University 415-723-0830.
(Science 24 Jul 98 281:540) (Science-Week 14 Aug 98)
-------------------
Related Background:
... ... *tunnel coupling: This refers to tunneling, a quantum
mechanical phenomenon involving an effective penetration of an
energy barrier resulting from the width of the barrier being less
than the wavelength of the particle.
... ... *Kondo effect: The Kondo effect is a large anomalous
increase in the resistance of certain dilute alloys of magnetic
materials in nonmagnetic hosts as the temperature is lowered. In
general, the Kondo effect occurs when an impurity atom with an
unpaired electron is placed in a metal, producing an interaction
of localized electrons with delocalized electrons.
... ... *Kondo temperature: The temperature at which the Kondo
effect predominates.
... ... *Fermi energy: The average energy of electrons in a
metal.
... ... *Coulomb-blockaded: This refers to an effective blockade
of quantum mechanical tunneling produced by specific energy
barrier constraints.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 14Aug98
For more information: http://scienceweek.com/swfr.htm

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3. MOLECULAR BIOLOGY:
PLANT GENOMICS
In general, the term "genomics" refers to the systematic study of
whole genomes. In addition to the human and mouse genome
projects, a number of similar projects are underway in plant
science, and these projects are expected to have considerable
impact on agriculture in the 21st century. The most critical
objective in both animal and plant genomics, aside from
determination of the complete sequence of genes in a genome, is
the determination of the function of these genes. Although plant
genomes tend to be larger and more complicated than those of
mammals, plant scientists lack the funding and attention given to
human and animal genome projects, so progress is not as rapid.
Nevertheless, apparently during the next decade, there will be
important developments in plant genomics, most of which will be
announced by corporate research enterprises.
... ... Trisha Gura (Science, US) presents a review of plant
genomics, the author tabulating current methods in this field as
follows:
     1) Computer scanning of DNA databases (e.g., BLAST
searching): Assigns gene function based on similarity to known
genes. (BLAST is the name of a computer program used in this
method.)
     2) Comparison of chromosomal gene maps from different
species (synteny): Assigns gene function based on similarities in
sequence and location.
     3) Insertion of DNA/RNA hybrids into cells (chimeraplasty):
Generates specific gene mutations.
     4) Insertion of DNA that jumps into genes (e.g., TUSC: Trait
Utility System for Corn): Generates wholesale mutations in maize.
     5) Insertion of DNA enhancers via a plant-cell infecting
bacterium (activation tagging): Generates wholesale mutations in
plants.
     6) Infection of tobacco plants with genetically altered
tobacco mosaic virus (RNA silencing/Gene overexpression): Turns
tobacco genes either on or off.
     7) Use of DNA snippets on chips (microarray analysis):
Tracks gene activity.
     8) Use of systematic 2-dimensional gel electrophoresis of
proteins (proteomics): Tracks protein expression by cells.
     9) Use of gas chromatography and mass spectrometry profiles
(metanomics): Tracks metabolite expression by cells.
     Some of the above techniques are also used in animal and
human genomics. Microarrays, for example, are chips containing
hundreds or thousands of gene snippets laid out in precise arrays
that provide rapid snapshots of the expression of whole suites of
genes. The general method in microarray analysis is to a) isolate
messenger RNAs (mRNAs) produced by a genome; b) convert mRNA into
complimentary DNA (cDNA); c) add a fluorescent tag to the cDNA
for tracking purposes; d) wash a solution of tagged cDNAs over a
DNA microarray chip. Each DNA snippet on the chip will bind the
cDNA from the corresponding gene, and by measuring the
fluorescences arrayed on the chip, the profile of gene expression
is revealed.
     As might be expected for any research field heavily
dependent on available technology, the profile of methods used
will no doubt be different a decade from now. What will remain
intact is the intense effort of research in plant genomics.
-----------
Trisha Gura: Reaping the plant gene harvest.
(Science 21 Jan 00 287:412)
QY: Trisha Gura [science_editors@aaas.org]
-----------
Text Notes:
... ... messenger RNAs (mRNAs): A messenger RNA molecule is the
ribonucleic acid molecule transcribed from DNA that carries the
coded information specifying the sequence of amino acids in a
protein.
... ... complimentary DNA (cDNA): Complementary DNA is DNA that
is synthesized in vitro from an RNA template using the enzyme
reverse transcriptase, and it can be used in cloning to
investigate the presence of various genes, or as a probe for
homologous sequences in various tissues or species. Essentially,
the idea is that if the RNA template is active RNA in a
particular cell type, then the cDNA derived from that RNA can
demarcate the active (operational) genes in that cell type --
the original genes that produced the active RNA.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 21Apr00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
AGRICULTURAL GENOMICS PROPOSED AS 3RD TECHNOLOGICAL REVOLUTION
In an editorial in the journal Science, Philip H. Abelson
proposes that the next great revolution after the Industrial
Revolution and the computer-based revolution is already underway
and is the genomics revolution, and that the greatest ultimate
global impact of genomics will arise from the manipulation of the
DNA of plants. In the future, the world will obtain most of its
food, fuel, fiber, chemical feedstocks, and some of its
pharmaceuticals from genetically altered vegetation and trees.
Major companies such as Dow Chemical, DuPont, Monsanto, and
Novartis are spending billions of dollars annually on genetic
engineering and on acquiring stakes in genome-oriented companies.
Humans today employ the capabilities of relatively few plants.
Abelson suggests the major challenge is to explore the
opportunities inherent in the hundreds of thousands of plant
species.
QY: P.H. Abelson [science_editors@aaas.org]
(Science 27 Mar 98) (Science-Week 17 Apr 98)
-------------------
Related Background:
GENETIC ENGINEERING OF DISEASE-RESISTANT RICE CROPS
Genetic engineering is the general term used for recombinant DNA
technology, a set of methods for introducing foreign DNA into a
host organism. It usually but not always involves gene cloning,
and there have been some spectacular successes in this field, for
example, the production of human insulin by genetically
engineered bacteria, the insulin then available as a therapy for
human diabetes. One of the most exciting areas for the
application of genetic engineering is agriculture, in particular
food crops, where there is considerable and reasonable hope that
genetically engineered food crops will be of great importance in
increasing agricultural productivity in underdeveloped countries.
Pamela C. Ronald (University of California Davis, US) reviews the
recent genetic engineering of disease-resistant rice crops, and
suggests genetic engineering will be useful for changing
additional aspects of rice and other grains, including cold
tolerance and drought resistance, and that ultimately breeders
and farmers will be able to choose from a repertoire of
genetically engineered clones to increase food production in
places and under conditions where it is badly needed.
QY: P. C. Ronald, Univ. Calif. Davis, Plant Biol., (916) 752-7094
(Scientific American November 1997) (Science-Week 30 Oct 97)
For more information: http://scienceweek.com/swfr.htm

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4. CELL BIOLOGY:
APOPTOSIS AND CASPASES
     From one perspective, the adult human organism is a highly
integrated colony of approximately 10^(12) individual biological
cells of various types, and for the sake of the viability of the
entire organism, many of these cells, particularly cells which
for one reason or another are defective, must be continually
eliminated and replaced. Programmed elimination of cells also
occurs during embryonic and childhood development, when
specialized tissues form and many normal cells must be discarded
as part of this formation.
     In general, the term "apoptosis" refers to programmed cell
death, whether as a part of normal tissue differentiation and
development, or as a program activated in a defective cell. In
the molecular biology of cancer, for example, apoptosis involves
programmed cell death provoked by proteins expressed by so-called
"tumor suppressor genes": malignant cells are essentially
defective cells with a deactivated apoptosis program, and this
deactivation of apoptosis allows malignant cells to survive and
replicate.
     Proteases are a class of enzymes that hydrolyze proteins,
splitting them into various groups of subunits, with the sites of
hydrolysis dependent on the particular enzyme and the protein
substrate, and a caspase is a type of protease implicated in
apoptosis.
     The term "endoplasmic reticulum" refers to a complex system
of flattened sacs in all biological cells that have a nucleus
(eukaryotes). The endoplasmic reticulum is the site of many
important syntheses, including the production of new surface
membrane and the intracellular transport of various biochemical
entities.
... ... Huseyin Mehmet (Imperial College, UK) presents a
commentary on current research concerning apoptosis and caspases,
the author making the following points:
     1) In the normal workings of the cell, apoptosis needs to be
tightly regulated by cellular mechanisms in order to avoid
unnecessary cell death and serious pathology (such as possibly
certain neurodegenerative diseases). One way in which the
prevention of unnecessary cell death is accomplished by the cell
is the physical separation of the various components of the
apoptotic machinery, so that only when the "death switch" is
actually tripped are the components involved in apoptosis brought
together and the suicide program activated. The two main cell
compartments now known to be involved in apoptosis are the plasma
membrane, where both death and survival receptors are located,
and the *mitochondria of cells, where several proteins that
regulate apoptosis reside.
     2) Among the most prominent apoptosis-specific enzymes are
the caspases, a family of cysteine-dependent aspartate-specific
proteases. These enzymes can be broadly divided into two groups:
a) initiator caspases (e.g., caspase-8 and caspase-9) whose main
function is activate other caspases; and b) executor caspases
(e.g., caspase-3, -6, and -7), which are responsible for
dismantling cellular proteins. The two main apoptotic pathways --
the death receptor pathway and the mitochondrial pathway -- are
activated by caspase-8 and caspase-9, respectively, both of which
are found in the cytoplasm. Caspase-8 is recruited by an
apoptosis-inducing signaling complex only when death receptors
are oligomerized after binding of specific ligands. In contrast,
caspase-9 is activated when *cytochrome-c is released into the
cytoplasm from the space between the inner and outer
mitochondrial membranes.
     3) T. Nakagawa et al (Nature 403:99 2000) have now
demonstrated that another caspase involved in apoptosis,
caspase-12, is localized in the endoplasmic reticulum. Caspase-12
is apparently specifically involved in apoptosis that results
from various biochemical stresses to the endoplasmic reticulum,
such as disruption of endoplasmic reticulum calcium ion
distributions. Apoptosis triggered through pathways that do not
involve the endoplasmic reticulum apparently does not result in
the activation of caspase-12.
     4) The author concludes that since caspases are central to
both normal programmed cell death and injury-dependent apoptosis,
any therapy that manipulates caspase activity must take into
account the possible effects on tissue viability. "If activation
of caspase-12 does turn out to be confined to only a narrow band
of cellular stress signals, it will be a promising potential
target for treating neurodegenerative diseases and cancer with
few side effects."
-----------
Husayin Mehmet: Caspases find a new place to hide.
(Nature 6 Jan 00 403:29)
QY: Husayin Mehmet [h.mehmet@ic.ac.uk]
-----------
Text Notes:
... ... *mitochondria: Organelles of the cell cytoplasm,
mitochondria are the principal energy source of the cell,
containing various enzymes involved in electron transport and
metabolic cycles.
... ... *cytochrome-c: The cytochromes are a system of electron-
transfer proteins with iron- or copper-porphyrin as a prosthetic
group. They are found in both animal and plant cells.
Cytochrome-c is found in mitochondria.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 21Apr00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
MOLECULAR BIOLOGY: APOPTOSIS, MITOCHONDRIA, AND CASPASES
Apoptosis (programmed cell death) is a rapid and specific process
involving the production of a number of enzymes in the cell
programmed to be destroyed. This programmed destruction is not
always harmful, or always the result of cellular damage of one
sort or another. In humans, for example, the lack of webbing
between fingers and toes is a result of apoptosis of cells of
webbing tissue occurring during embryological development, the
apoptosis in this case being a normal part of the larger
embryological program. In the mature organism, apoptosis is the
usual method of removing damaged cells after these cells are
recognized to be damaged by one mechanism or another. It is known
that normal cells carry an apoptosis receptor on their surfaces,
called CD95, and that when this surface receptor is cross-linked
by its specific ligand, this triggers the sequence of events
known as apoptosis. In the apoptosis sequence, certain
*proteolytic enzymes inside the cell are activated, and in
addition a variety of lipids that cause cell dysfunction are
synthesized. ... ... D.R. Green and J.C. Reed review the
involvement of *mitochondria with apoptosis in *metazoan cells,
and the authors make the following points: 1) The current
consensus among biologists is that approximately 2 billion years
ago the cells destined to become the ancestors of all *eukaryotes
entered into a partnership with an ancestor of today's *purple
bacteria, an ancestor that subsequently became the mitochondria
of today. 2) It has been hypothesized by several investigators
that the *endosymbiotic origins of mitochondria and the evolution
of aerobic metabolism in eukaryotes formed the basis for the
evolution of active cell death, which in metazoans is manifested
predominantly as apoptosis. Central roles for mitochondria as the
orchestrators  of apoptosis have been firmly established in many
systems. 3) In recent years it has become apparent that the
effectors of apoptosis are a family of intracellular proteases
known as caspases, although inhibiting these enzymes does not
always prevent apoptosis. 4) At least 3 general mechanisms have
been proposed for the involvement of mitochondria in the control
of cell life and death: a) disruption of *electron transport,
*oxidative phosphorylation, and adenosine triphosphate (ATP)
production; b) release of proteins that trigger activation of the
caspases family of proteases; c) alteration of cellular *redox
potentials. 5) In many apoptosis scenarios, the mitochondrial
inner electrical transmembrane potential collapses, indicating
the opening of large conductance channels through the inner
membrane. In contrast, certain stimuli can induce rupture of the
outer membrane of mitochondria and release of caspase-activation
proteins. The authors conclude: "Perhaps a few hundred million
years ago, either convergent or divergent evolutionary processes
allowed the ... fundamental framework for bacterial warfare to be
incorporated into the cell death mechanisms used by animal cells,
thereby establishing mitochondria as important participants not
only in animal cell life but also in active cell death." ... ...
In a companion and contiguous review of caspases and apoptosis,
N.A. Thornberry and Y. Lazebnik point out the following: 1)
Proteolysis is irreversible, which implies that regulation of
proteases is limited to control of their activity and
availability of substrate -- the only known way of "correcting" a
cleaved protein is to make it afresh. 2) Most proteases are
synthesized as precursors that have little if any catalytic
activity. The precursor is usually converted to the active enzyme
by proteolytic processing mediated either by another protease or
by autocatalysis. Thus large amounts of precursor can be
accumulated in advance and activated on demand. 3) Proteases can
regulate their own activation, resulting in an exponential rate
of activation. 4) Where there are proteases there are inhibitors,
and these inhibitors regulate the concentration of active
protease in the cell. 5) Proteolytic reactions can be specific,
determined by a combination of primary, secondary, or tertiary
structures of protein substrates. Proteolysis that governs
critical biological processes such as the cell cycle or cell
death is highly specific and involves a restricted set of
substrates. 6) The various caspases share similarities in amino
acid sequence, structure, and substrate specificity. 7) Caspases
are among the most specific of proteases with an unusual and
absolute requirement for cleavage after aspartic acid and
recognition of at least 4 amino acids terminal to the cleavage
site. 8) The strict specificity of caspases is consistent with
the observation that apoptosis is not accompanied by
indiscriminate protein digestion, but rather a select set of
proteins is cleaved in a coordinated manner, usually at a single
site, resulting in a loss or change in function. 9) Apoptotic
events include DNA fragmentation, *chromatin condensation,
*membrane blebbing, cell shrinkage, and disassembly into
membrane-enclosed vesicles (apoptotic bodies). In vivo, this
process culminates with the engulfment of apoptotic bodies by
other cells, preventing complications that would result from a
release of intracellular contents. In apoptosis, these changes
occur in a predictable reproducible sequence and can be completed
with 30 to 60 minutes. The authors conclude: "Substantial
progress has been made in understanding the structural and
catalytic properties of active caspases and their contribution to
apoptosis. The goal for future research is to understand the
regulation of these enzymes. This should facilitate efforts to
rationally manipulate the apoptotic machinery for therapeutic
gain."
-----------
D.R. Green and J.C. Reed (2 installations, US): Mitochondria and
apoptosis.
(Science 28 Aug 98 281:1309)
QY: Douglas R. Green, La Jolla Institute for Allergy and
Immunology, 10355 Science Center Drive, San Diego, CA 92121 US.
N.A. Thornberry and Y. Lazebnik (2 installations, US): Caspases:
enemies within.
(Science 28 Aug 98 281:1312)
QY: Nancy A. Thornberry, Merck Research Laboratories, Rahway, NJ
07065 US.
-----------
Text Notes:
... ... *proteolytic enzymes: These enzymes, also called
"proteases", split proteins and thereby degrade them. The enzymes
catalyze the hydrolysis of peptide bonds, fragmenting proteins
into polypeptide chains, and fragmenting polypeptide chains into
constituent amino acids. Sometimes proteolytic enzymes and
proteases are distinguished, with the term "proteases" reserved
for proteolytic enzymes with high specificity for peptide bonds
between particular amino acids.
... ... *mitochondria: Mitochondria are double-membrane enclosed
organelles of cells that are involved with several important
biochemical pathways, including electron transport and oxidative
metabolism, and across the membrane of the mitochondrion there
exists a potential difference apparently due primarily to a
concentration gradient of hydrogen ions. 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.
... ... *metazoan cells: Metazoans are multicellular animals.
... ... *eukaryotes: Cells (and organisms consisting of such
cells) that contain intracellular membrane-bound compartments
such as a nucleus (membrane-bound "organelles").
... ... *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.
... ... *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.
... ... *electron transport: 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.
... ... *oxidative phosphorylation: Production of ATP during
aerobic respiration. It takes place in the mitochondria of
eukaryotic cells and requires molecular oxygen as a terminal
electron acceptor.
... ... *redox potentials: Chemical potentials in a chemical
reaction involving the simultaneous reduction and oxidation of
two compounds by a transfer of electrons between them.
... ... *chromatin: The entire complex of a eukaryotic
chromosome, including DNA, chromosomal proteins, and chromosomal
RNA.
... ... *membrane blebbing: Refers to the macroscopic blistering
of the surfaces of cells when they die under certain conditions.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 2Oct98
For more information: http://scienceweek.com/swfr.htm

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5. COGNITIVE SCIENCE:
NUMBERS AND COUNTING IN A CHIMPANZEE
In this context, let us define "animals" as all living multi-
cellular creatures other than humans that are not plants. In
recent decades it has become apparent that the cognitive skills
of many animals, especially non-human primates, are greater than
previously suspected. Part of the problem in research on
cognition in animals has been the intrinsic difficulty in
communicating with or testing animals, a difficulty that makes
the outcome of a cognitive experiment heavily dependent on the
ingenuity of the experimental approach. Another problem is that
when investigating the non-human primates, the animals whose
cognitive skills are closest to that of humans, one cannot do
experiments on large populations because such populations either
do not exist or are prohibitively expensive to maintain. The
result is that in the area of primate cognitive research reported
experiments are often "anecdotal", i.e., experiments involving
only a few or even a single animal subject. But anecdotal
evidence can often be of great significance and have startling
implications: a report, even in a single animal, of important
abstract abilities, numeric or conceptual, is worthy of
attention, if only because it may destroy old myths and point to
new directions in methodology. In 1985, T. Matsuzawa reported
experiments with a female chimpanzee that had learned to use
Arabic numerals to represent numbers of items. This animal (which
is still alive and whose name is "Ai") can count from 0 to 9
items, which she demonstrates by touching the appropriate number
on a touch-sensitive monitor. Ai can also order the numbers from
0 to 9 in sequence.
... ... N. Kawai and T. Matsuzawa (Primate Research Institute
Kyoto, JP) now report an investigation of Ai's memory span by
testing her skill in numerical tasks, the authors making the
following points:
     1) The authors point out that humans can easily memorize
strings of codes such as phone numbers and postal codes if they
consist of up to 7 items, but above this number of items, humans
find memorization more difficult. This "magic number 7" effect,
as it is known in human information processing, represents an
apparent limit for the number of items that can be handled
simultaneously by the human brain.
     2) The authors report that the chimpanzee Ai can remember
the correct sequence of any 5 numbers selected from the range 0
to 9.
     3) The authors relate that in one testing session, after
choosing the first correct number in a sequence (all other
numbers still masked), "a fight broke out among a group of
chimpanzees outside the room, accompanied by loud screaming. Ai
abandoned her task and paid attention to the fight for about 20
seconds, after which she returned to the screen and completed the
trial without error."
     4) The authors conclude: "Ai's performance shows that
chimpanzees can remember the sequence of at least 5 numbers, the
same as (or even more than) preschool children. Our study and
others demonstrate the rudimentary form of numerical competence
in non-human primates."
-----------
N. Kawai and T. Matsuzawa: Numerical memory span in a chimpanzee.
(Nature 6 Jan 00 403:39)
QY: Tetsuro Matzuzawa [matsuzaw@pri.kyoto-u.ac.jp]
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 21Apr00

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6. MEDICAL BIOLOGY:
ON THE INGESTION OF TOXIC SUBSTANCES BY CHILDREN
Despite the many educational programs aimed at prevention,
exposure to a poison is still the most common nonfatal
childhood accident in the home. Poisoning can occur by many
routes, including oral ingestion, absorption through the skin,
and infiltration of the eyes (ocular installation).
... ... Michael Shannon (Harvard University, US) presents a
review of current efforts at prevention and treatment of
ingestion of toxic substances by children, the author making the
following points:
     1) According to current data, 1.08 million instances of
ingestion of a toxic substance by a child less than 6 years of
age were reported to US poison centers in 1998. However, the
proportion of incidents reported to poison centers is estimated
to be as low as 26 percent, suggesting a true incidence of more
than 4 million poisonings annually.
     2) The toxic substances most commonly ingested by children
are, in order of frequency, cosmetics and personal care products,
cleaning products, pain medications (analgesics), plants, cough
and cold preparations, foreign bodies, topical agents,
pesticides, vitamins, hydrocarbons. Substances that are most
accessible to children, such as cosmetics and personal care
products, cleaning products, analgesics, and cough and cold
preparations, account for 58 percent of the cases reported.
Medications, both prescription drugs and over-the-counter drugs,
were responsible for 52 percent of the deaths from poisoning. The
pharmacological substances associated with the greatest risk of
death to children include cocaine, anticonvulsant drugs,
antidepressant drugs, and iron supplements.
     3) The author concludes: "The reduction in the incidence of
childhood poisonings [in the US] in the past half-century has
been dramatic. This reduction is largely the result of the
combination of highly effective active and passive methods of
intervention. Important passive interventions have included the
federal regulation of products and product safety and the
introduction of child-resistant containers for drugs and other
dangerous household products. Child-resistant containers have
been particularly effective in reducing the incidence of death
from the ingestion of prescription drugs by children. Active
interventions, which require a change in behavior by parents and
caretakers, have included the safe storage of household products.
Finally, poison centers, which were established [in the US]
nearly 50 years ago, will continue to have a vital role in the
management of poisoning in children by effectively reducing
unneeded visits to the emergency department and providing
education about poisoning to the public."
-----------
Michael Shannon: Ingestion of toxic substances by children.
(New England J. Med. 20 Jan 00 342:186)
QY: Michael Shannon [shannon@al.tch.harvard.edu]
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 21Apr00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
EVOLVING TRENDS IN PEDIATRIC POISONING
... In the US, more than 1 million children younger than 6 years
experience toxic exposure annually, making poisoning a major and
persistent cause of injury-related *morbidity. Significant
advances have been made in the prevention and treatment of
pediatric poisoning in the past 5 decades: in the 1940s,
childhood poisonings were responsible for an estimated 500 deaths
per year and were attributed primarily to household products; in
1972, the number of pediatric poisoning deaths in the US was 216;
in 1997, the number of pediatric poisoning deaths in the US was
25.
... ... E.L. Liebelt and C.D. DeAngelis (Johns Hopkins
University, US) present a review of evolving trends in pediatric
poisoning, with a focus on epidemiology, prevention, and
treatment. The authors make the following points:
     1) Concerning human toxic exposures and fatalities, children
younger than 6 years have persistently accounted for 50 to 60
percent of these exposures. Cosmetics and personal care products,
plants, and cough and cold preparations have consistently been
the top 5 categories for pediatric poison exposures in the last
10 years.
     2) More than half of the poison fatalities in children
younger than 6 years are caused by non-pharmaceutical and
household products. The authors tabulate the following non-
pharmaceutical and household products toxic in children:
... ... Alcohols: beverage ethanol, methanol (windshield wiper
fluid), ethylene glycol (antifreeze).
... ... Caustic agents: alkalis (drain and oven cleaners, perm
relaxers, Clinitest tablets); acids (toilet bowl cleaners, anti-
rust compounds).
... ... Food-flavoring additives: methylsalicylate (Oil of
Wintergreen) [*Note #1].
... ... Hydrocarbons: kerosene, lamp oil, mineral seal oil
(furniture polish), mineral spirits (paint thinner), naphtha
(lighter fluid).
... ... Industrial chemicals: methylene chloride (paint
stripper), selenious acid (gun bluing), zinc chloride (soldering
flux).
... ... Nail products: acetonitrile (sculptured nail remover),
methacrylic acid (artificial nail primer), nitromethane
(artificial nail remover).
... ... Pesticides and/or insecticides: organophosphates,
lindane, paraquat.
     3) Pharmaceutical products responsible for significant
morbidity and mortality in young children have included the
following: iron supplements, tricyclic antidepressants,
cardiovascular medications (calcium channel blockers, beta-
blockers), oral hypoglycemic agents, narcotic analgesics, and
antimalarials (chloroquine). Iron supplements continue to be one
of the leading causes of poisoning deaths due to pharmaceutical
products in children younger than 6 years.
     4) The US Consumer Product Safety Commission estimates that
child-resistant packaging for aspirin and oral prescription
medications has saved the lives of approximately 800 children
since requirements went into effect in the mid 1970s.
     5) The authors conclude: "In the past 40 years,
extraordinary advances have been made in the prevention and
treatment of poisonings in young children. Future challenges
include further development and funding of poison information
centers, clinical and basic science research, development of
regional poison treatment centers, and the continued training of
health professionals dedicated to clinical toxicology."
-----------
Editor's note: This review by Liebelt and DeAngelis does not
consider pediatric lead poisoning, although lead poisoning is
usually designated a significant source of pediatric toxic
exposure. In the related background material below, we have
included two reports on lead poisoning from previous issues of
SW.]
-----------
E.L. Liebelt and C.D. DeAngelis: Evolving trends and treatment
advances in pediatric poisoning.
(J. Amer. Med. Assoc. 22/29 Sep 99 282:1113)
QY: Erica L. Liebelt [eliebelt@welch.jhu.edu]
-----------
Text Notes:
... ... *morbidity: In general, this refers to a diseased state;
in particular, the term refers to the ratio of the diseased to
the well in a community.
... ... *Note #1: Death has been reported from ingestion of less
than 1 teaspoon of methyl salicylate (Oil of Wintergreen) in a
young child. Any internal exposure in quantity to methyl
salicylate (found in liniments and in solutions used in hot
vaporizers) is potentially lethal.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 8Oct99
-------------------
Related Background:
A DANGEROUS NEW SOURCE OF ENVIRONMENTAL LEAD
There is ample evidence that the developing nervous system of a
child is highly sensitive to a number of toxic substances, the
effects of which are various encephalopathies (brain disorders)
[*Note #1]. One environmental toxic substance of considerable
importance in this context is lead, an urban environmental
contaminant that in the past few decades has become a focus of
public awareness. The classical sources of urban environmental
lead contamination are the gasoline exhaust fumes of motor
vehicles and lead-based paints, but recently another important
source of such contamination has become apparent.
... ... Howard W. Mielke (Xavier University New Orleans, US)
presents a review of the problem of lead in inner cities with
emphasis on the newly recognized danger of lead contamination of
inner city soil and dust. The author makes the following points:
1) Since the 1920s, millions of US children have been quietly
poisoned by lead, and thousands of deaths are attributed to this
over the long term. 2) Although childhood lead exposure in the
US has diminished during the past 2 decades, the problem has not
been solved. Instead, the demographics has shifted. 3) Over 50
percent (and perhaps even 70 percent) of children living in the
inner city of New Orleans and Philadelphia have blood lead
levels above the current guideline of 10 micrograms per
deciliter [*Note #2]. In contrast, in the concrete "jungle" of
Manhattan, where very little of the soil is exposed and almost
all apartments and housing contain lead-based paints, only
between 5 and 7 percent of children under the age of 6 have been
reported to have blood-lead levels of 10 micrograms per
deciliter or higher. It is of significance that in Brooklyn,
across the river from Manhattan, where yards containing soil are
common, the percentage of affected children is several times
higher than in Manhattan. 4) The serious of the problem has been
recognized by the US Centers for Disease Control and Prevention
since the early 1990s, which has called pediatric lead poisoning
"entirely preventable". 5) The author suggests that effective
prevention assumes an accurate identification of the
environmental reservoirs of lead, and that current policies to
reduce lead exposure are based on the assumption that the
greatest lead hazard comes from lead-based paints [*Note #3].
Most lead-based have now been removed from the market, and
parents have been instructed to guard their children from eating
paint flakes. However, for children, paint is now neither the
most abundant nor the most accessible source of lead. The common
problem is lead dust in the environment, with the soil a giant
reservoir of tiny particles of lead. The greatest risk for
exposure of inner city children is in the yards around houses
and to a lesser extent in public playgrounds. 6) The author
suggests that an accurate and complete appreciation of the
distribution of lead in the environment can help shape policies
that more effectively protect the health of children. The author
concludes: "It took nearly 10 decades for lead to accumulate to
its current levels in urban areas. With judicious planning, the
problem can be resolved in much less time."
-----------
Howard W. Mielke: Lead in inner cities.
(American Scientist Jan/Feb 1999 87:62)
QY: Howard W. Mielke 
-----------
Text Notes:
... ... *Note #1: There is much data concerning certain
syndromes, e.g., fetal alcohol syndrome, lead poisoning, etc. One
research problem is that effects of low levels of environmental
toxins on the developing nervous system can be subtle and not
detected unless specific rather than general behavioral measures
are applied.
... ... *Note #2: There is hardly a consensus concerning
acceptable levels of lead in the whole blood of children. Some
clinicians consider the danger point to be in the region of 50
micrograms per deciliter whole blood; other clinicians consider
anything above 10 micrograms per deciliter as a cause for alarm.
In terms of low-level effects on the developing central nervous
system, general concentration cut-off points are perhaps
arbitrary, since there is considerable individual variation in
toxic susceptibility.
... ... *Note #3: In the US, lead was used in residential paint
between 1884 and 1978, and leaded paint remains on the walls of
many old buildings.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 15Jan99
-------------------
Related Background:
PRENATAL LEAD EXPOSURE AND POSTNATAL LEAD TOXICITY
Lead is a highly toxic metal, especially in children, but
unfortunately the incidence of lead poisoning in metropolitan
slums remains high due to past widespread use of lead based
paints and lead water pipes. There are also other sources that
contribute to dangerous concentrations in the environment. In
children, concentrations of lead in the range 40 micrograms per
deciliter, and probably as low as 10 micrograms per deciliter,
will produce definite serious cognitive deficits. Higher blood
concentrations produce encephalopathies that are both malignant
and difficult to treat. In the past, the focus has been on the
exposure of young children to environmental lead, since children
are the most vulnerable and environmental lead the apparent
primary source. Now William H. Bowen et al (University of Roch-
ester, US) present evidence that in rats toxic concentrations of
lead can pass from mother to offspring when mother rats are
drinking water that produces blood lead levels of only 40 micro-
grams per deciliter, with transmission evidently occurring via
blood to the fetus and via milk to the postnatal rat pup.
Evidently one consequence in these lead-exposed rat pups is a
high incidence of dental caries. Bowen's group is a dental
research group, and they apparently became interested in the
problem after considering that although dental caries in children
has shown a marked drop in prevalence in the U.S., about 80 per
cent of the cases that still occur are occurring in only about
20% of the children -- those that live in inner cities, where
lead exposures can still be relatively high. Metropolitan
children are thus faced with another source of lead poisoning --
lead of maternal origin.
QY: W. Bowen, University of Rochester (716) 275-3221
(Nature Medicine September 1997) (Science-Week 12 Sep 97)

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IN FOCUS: ON THERMODYNAMICS VS. STATISTICAL MECHANICS
"In some of his more exalted moments, the physicist ascribes to
the first and second laws of thermodynamics the most far-reaching
generality he has ever achieved in formulating laws of nature,
while on other grayer mornings he depreciates the insight
attainable by thermodynamic analysis, extols the superior virtues
of statistical mechanics and kinetic theory, and may even go so
far as to maintain that the existence of phenomena like the
Brownian fluctuations is positively inconsistent with the truth
of thermodynamics. The latter mood seems to me by far the more
common. There can be no doubt, I think, that the average
physicist is made a little uncomfortable by thermodynamics. He is
suspicious of its ostensible generality, and he doesn't quite see
how anybody has a right to expect to achieve that kind of
generality. He finds much more congenial the approach of
statistical mechanics, with its analysis reaching into the
details of those microscopic processes which in their larger
aggregates constitute the subject matter of thermodynamics. He
feels, rightly or wrongly, that by the methods of statistical
mechanics and kinetic theory he has achieved a deeper insight. It
must be admitted, I think, that the laws of thermodynamics have a
different feel from most of the others laws of the physicist.
There is something more palpably verbal about them -- they smell
more of their human origin. The guiding motif is strange to most
of physics: namely, a capitalizing of the universal failure of
human beings to construct perpetual motion machines of either the
first or the second kind. Why should we expect nature to be
interested either positively or negatively in the purposes of
human beings, particularly purposes of such an unblushing
economic tinge? Or why should we expect that a formulation of
regularities which we observe when we try to achieve these
purposes should have a significance wider than the reach of the
purposes themselves? The whole thing strikes one rather as a
verbal tour de force, as an attempt to take the citadel by
surprise... An understanding of the attitude of physicists toward
thermodynamics and kinetic theory is, I think, to be sought only
in the realm of psychology... It just seems to be a fact about
our thinking machinery that we must have our atoms; we cannot
think of the velocity of a uniform fluid without imagining the
'particles' of which the fluid is composed, nor can the most
advanced speculations of quantum mechanics do without their
ultimate particles. Perhaps the human necessity for its particles
is connected with the necessity for 'identification' in thinking;
the very words we use are little islands of identification in the
amorphous sea of our cerebration, and the particle of a fluid is
a little materialized piece of identifiability."
-----------
P.W. Bridgman: _The Nature of Thermodynamics_
(Harper Bros., New York 1941)
[Editor's note: Percy W. Bridgman (1882-1961) received the Nobel
Prize in Physics in 1946 for his research into machinery
producing high pressure.]
-------------------
SCIENCE-WEEK http://scienceweek.com 21Apr00
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