新东方背诵文选续

加非

32 Botany

Botany, the study of plants, occupies a peculiar position in the history
of human knowledge. For many thousands of years it was the one field of
awareness about which humans had anything more than the vaguest of
insights. It is impossible to know today just what our Stone Age
ancestors knew about plants, but form what we can observe of pre-
industrial societies that still exist a detailed learning of plants and
their properties must be extremely ancient. This is logical. Plants are
the basis of the food pyramid for all living things even for other
plants. They have always been enormously important to the welfare of
people not only for food, but also for clothing, weapons, tools, dyes,
medicines, shelter, and a great many other purposes. Tribes living today
in the jungles of the Amazon recognize literally hundreds of plants and
know many properties of each. To them, botany, as such, has no name and
is probably not even recognized as a special branch of “ knowledge” at
all.

Unfortunately, the more industrialized we become the farther away we
move from direct contact with plants, and the less distinct our
knowledge of botany grows. Yet everyone comes unconsciously on an
amazing amount of botanical knowledge, and few people will fail to
recognize a rose, an apple, or an orchid. When our Neolithic ancestors,
living in the Middle East about 10,000 years ago, discovered that
certain grasses could be harvested and their seeds planted for richer
yields the next season the first great step in a new association of
plants and humans was taken. Grains were discovered and from them flowed
the marvel of agriculture: cultivated crops. From then on, humans would
increasingly take their living from the controlled production of a few
plants, rather than getting a little here and a little there from many
varieties that grew wild- and the accumulated knowledge of tens of
thousands of years of experience and intimacy with plants in the wild
would begin to fade away.


33 Plankton浮游生物. / ’plжηktэn; `plжηktэn/

Scattered through the seas of the world are billions of tons of small
plants and animals called plankton. Most of these plants and animals are
too small for the human eye to see. They drift about lazily with the
currents, providing a basic food for many larger animals.

Plankton has been described as the equivalent of the grasses that grow
on the dry land continents, and the comparison is an appropriate one. In
potential food value, however, plankton far outweighs that of the land
grasses. One scientist has estimated that while grasses of the world
produce about 49 billion tons of valuable carbohydrates each year, the
sea’s plankton generates more than twice as much.

Despite its enormous food potential, little effect was made until
recently to farm plankton as we farm grasses on land. Now marine
scientists have at last begun to study this possibility, especially as
the sea’s resources loom even more important as a means of feeding an
expanding world population.

No one yet has seriously suggested that “ plankton-burgers” may soon
become popular around the world. As a possible farmed supplementary food
source, however, plankton is gaining considerable interest among marine
scientists.

One type of plankton that seems to have great harvest possibilities is a
tiny shrimp-like creature called krill. Growing to two or three inches
long, krill provides the major food for the great blue whale, the
largest animal to ever inhabit the Earth. Realizing that this whale may
grow to 100 feet and weigh 150 tons at maturity, it is not surprising
that each one devours more than one ton of krill daily.


34 Raising Oysters

In the oysters were raised in much the same way as dirt farmers raised
tomatoes- by transplanting them. First, farmers selected the oyster bed,
cleared the bottom of old shells and other debris, then scattered clean
shells about. Next, they ”planted” fertilized oyster eggs, which
within two or three weeks hatched into larvae. The larvae drifted until
they attached themselves to the clean shells on the bottom. There they
remained and in time grew into baby oysters called seed or spat. The
spat grew larger by drawing in seawater from which they derived
microscopic particles of food. Before long, farmers gathered the baby
oysters, transplanted them once more into another body of water to
fatten them up.

Until recently the supply of wild oysters and those crudely farmed were
more than enough to satisfy people’s needs. But today the delectable
seafood is no longer available in abundance. The problem has become so
serious that some oyster beds have vanished entirely.

Fortunately, as far back as the early 1900’s marine biologists realized
that if new measures were not taken, oysters would become extinct or at
best a luxury food. So they set up well-equipped hatcheries and went to
work. But they did not have the proper equipment or the skill to handle
the eggs. They did not know when, what, and how to feed the larvae. And
they knew little about the predators that attack and eat baby oysters by
the millions. They failed, but they doggedly kept at it. Finally, in the
1940’s a significant breakthrough was made.

The marine biologists discovered that by raising the temperature of the
water, they could induce oysters to spawn not only in the summer but
also in the fall, winter, and spring. Later they developed a technique
for feeding the larvae and rearing them to spat. Going still further,
they succeeded in breeding new strains that were resistant to diseases,
grew faster and larger, and flourished in water of different salinities
and temperatures. In addition, the cultivated oysters tasted better!


35.Oil Refining

An important new industry, oil refining, grew after the Civil war. Crude
oil, or petroleum - a dark, thick ooze from the earth - had been known
for hundreds of years, but little use had ever been made of it. In the
1850’s Samuel M. Kier, a manufacturer in western Pennsylvania, began
collecting the oil from local seepages and refining it into kerosene.
Refining, like smelting, is a process of removing impurities from a raw
material.

Kerosene was used to light lamps. It was a cheap substitute for whale
oil, which was becoming harder to get. Soon there was a large demand
for kerosene. People began to search for new supplies of petroleum.

The first oil well was drilled by E.L. Drake, a retired railroad
conductor. In 1859 he began drilling in Titusville, Pennsylvania. The
whole venture seemed so impractical and foolish that onlookers called it
“ Drake’s Folly”. But when he had drilled down about 70 feet(21
meters), Drake struck oil. His well began to yield 20 barrels of crude
oil a day.

News of Drake’s success brought oil prospectors to the scene. By the
early 1860’s these wildcatters were drilling for “ black gold” all
over western Pennsylvania. The boom rivaled the California gold rush of
1848 in its excitement and Wild West atmosphere. And it brought far more
wealth to the prospectors than any gold rush.

Crude oil could be refined into many products. For some years kerosene
continued to be the principal one. It was sold in grocery stores and
door-to-door. In the 1880’s refiners learned how to make other
petroleum products such as waxes and lubricating oils. Petroleum was not
then used to make gasoline or heating oil.


36.Plate Tectonics and Sea-floor Spreading

The theory of plate tectonics describes the motions of the lithosphere,
the comparatively rigid outer layer of the Earth that includes all the
crust and part of the underlying mantle. The lithosphere(n.[地]岩石圈)is
divided into a few dozen plates of various sizes and shapes, in general
the plates are in motion with respect to one another. A mid-ocean ridge
is a boundary between plates where new lithospheric material is injected
from below. As the plates diverge from a mid-ocean ridge they slide on a
more yielding layer at the base of the lithosphere.

Since the size of the Earth is essentially constant, new lithosphere can
be created at the mid-ocean ridges only if an equal amount of
lithospheric material is consumed elsewhere. The site of this
destruction is another kind of plate boundary: a subduction zone. There
one plate dives under the edge of another and is reincorporated into the
mantle. Both kinds of plate boundary are associated with fault systems,
earthquakes and volcanism, but the kinds of geologic activity observed
at the two boundaries are quite different.

The idea of sea-floor spreading actually preceded the theory of plate
tectonics. In its original version, in the early 1960’s, it described
the creation and destruction of the ocean floor, but it did not specify
rigid lithospheric plates. The hypothesis was substantiated soon
afterward by the discovery that periodic reversals of the Earth’s
magnetic field are recorded in the oceanic crust. As magma rises under
the mid-ocean ridge, ferromagnetic minerals in the magma become
magnetized in the direction of the magma become magnetized in the
direction of the geomagnetic field. When the magma cools and solidifies,
the direction and the polarity of the field are preserved in the
magnetized volcanic rock. Reversals of the field give rise to a series
of magnetic stripes running parallel to the axis of the rift. The
oceanic crust thus serves as a magnetic tape recording of the history of
the geomagnetic field that can be dated independently; the width of the
stripes indicates the rate of the sea-floor spreading.


37 Icebergs

Icebergs are among nature’s most spectacular creations, and yet most
people have never seen one. A vague air of mystery envelops them. They
come into being ----- somewhere ------in faraway, frigid waters, amid
thunderous noise and splashing turbulence, which in most cases no one
hears or sees. They exist only a short time and then slowly waste away
just as unnoticed.

Objects of sheerest beauty they have been called. Appearing in an
endless variety of shapes, they may be dazzlingly white, or they may be
glassy blue, green or purple, tinted faintly of in darker hues. They are
graceful, stately, inspiring ----- in calm, sunlight seas.

But they are also called frightening and dangerous, and that they are ---
- in the night, in the fog, and in storms. Even in clear weather one is
wise to stay a safe distance away from them. Most of their bulk is
hidden below the water, so their underwater parts may extend out far
beyond the visible top. Also, they may roll over unexpectedly, churning
the waters around them.

Icebergs are parts of glaciers that break off, drift into the water,
float about awhile, and finally melt. Icebergs afloat today are made of
snowflakes that have fallen over long ages of time. They embody snows
that drifted down hundreds, or many thousands, or in some cases maybe a
million years ago. The snows fell in polar regions and on cold
mountains, where they melted only a little or not at all, and so
collected to great depths over the years and centuries.

As each year’s snow accumulation lay on the surface, evaporation and
melting caused the snowflakes slowly to lose their feathery points and
become tiny grains of ice. When new snow fell on top of the old, it too
turned to icy grains. So blankets of snow and ice grains mounted layer
upon layer and were of such great thickness that the weight of the upper
layers compressed the lower ones. With time and pressure from above, the
many small ice grains joined and changed to larger crystals, and
eventually the deeper crystals merged into a solid mass of ice.


38 Topaz

Topaz is a hard, transparent mineral. It is a compound of aluminum,
silica, and fluorine. Gem topaz is valuable. Jewelers call this variety
of the stone “precious topaz”. The best-known precious topaz gems
range in color from rich yellow to light brown or pinkish red. Topaz is
one of the hardest gem minerals. In the mineral table of hardness, it
has a rating of 8, which means that a knife cannot cut it, and that
topaz will scratch quartz.

The golden variety of precious topaz is quite uncommon. Most of the
world’s topaz is white or blue. The white and blue crystals of topaz
are large, often weighing thousands of carats. For this reason, the
value of topaz does not depend so much on its size as it does with
diamonds and many other precious stones, where the value increases about
four times with each doubling of weight. The value of a topaz is largely
determined by its quality. But color is also important: blue topaz, for
instance, is often irradiated to deepen and improve its color.

Blue topaz is often sold as aquamarine and a variety of brown quartz is
widely sold as topaz. The quartz is much less brilliant and more
plentiful than true topaz. Most of it is variety of amethyst: that heat
has turned brown.

NOTE:
topaz / ’tэupжz; `topжz/ n (a) [U] transparent yellow mineral 黄玉（矿
物）.
(b) [C] semi-precious gem cut from this 黄玉; 黄宝石.


39 The Salinity of Ocean Waters

If the salinity of ocean waters is analyzed, it is found to vary only
slightly from place to place. Nevertheless, some of these small changes
are important. There are three basic processes that cause a change in
oceanic salinity. One of these is the subtraction of water from the
ocean by means of evaporation--- conversion of liquid water to water
vapor. In this manner the salinity is increased, since the salts stay
behind. If this is carried to the extreme, of course, white crystals of
salt would be left behind.

The opposite of evaporation is precipitation, such as rain, by which
water is added to the ocean. Here the ocean is being diluted so that the
salinity is decreased. This may occur in areas of high rainfall or in
coastal regions where rivers flow into the ocean. Thus salinity may be
increased by the subtraction of water by evaporation, or decreased by
the addition of fresh water by precipitation or runoff.

Normally, in tropical regions where the sun is very strong, the ocean
salinity is somewhat higher than it is in other parts of the world where
there is not as much evaporation. Similarly, in coastal regions where
rivers dilute the sea, salinity is somewhat lower than in other oceanic
areas.

A third process by which salinity may be altered is associated with the
formation and melting of sea ice. When sea water is frozen, the
dissolved materials are left behind. In this manner, sea water directly
materials are left behind. In this manner, sea water directly beneath
freshly formed sea ice has a higher salinity than it did before the ice
appeared. Of course, when this ice melts, it will tend to decrease the
salinity of the surrounding water.

In the Weddell Sea Antarctica, the densest water in the oceans is formed
as a result of this freezing process, which increases the salinity of
cold water. This heavy water sinks and is found in the deeper portions
of the oceans of the world.

NOTE：
salinity / sэ’linэti; sэ`linэti/
n [U] the high salinity of sea water 海水的高含盐量.
-à>>saline / ’seilain; US -li:n; `selin/
1.adj [attrib 作定语] (fml 文) containing salt; salty 含盐的; 咸的:
* a saline lake 盐湖 * saline springs 盐泉
* saline solution, eg as used for gargling, storing contact lenses, etc
盐溶液（如用于漱喉、存放隐形眼镜等）.
2. n [U] (medical 医) solution of salt and water 盐水.


40 Cohesion-tension Theory

Atmospheric pressure can support a column of water up to 10 meters high.
But plants can move water much higher; the sequoia tree can pump water
to its very top more than 100 meters above the ground. Until the end of
the nineteenth century, the movement of water in trees and other tall
plants was a mystery. Some botanists hypothesized that the living cells
of plants acted as pumps. But many experiments demonstrated that the
stems of plants in which all the cells are killed can still move water
to appreciable heights. Other explanations for the movement of water in
plants have been based on root pressure, a push on the water from the
roots at the bottom of the plant. But root pressure is not nearly great
enough to push water to the tops of tall trees. Furthermore, the
conifers, which are among the tallest trees, have unusually low root
pressures.

If water is not pumped to the top of a tall tree, and if it is not
pushed to the top of a tall tree, then we may ask: how does it get
there? According to the currently accepted cohesion-tension theory,
water is pulled there. The pull on a rising column of water in a plant
results from the evaporation of water at the top of the plant. As water
is lost from the surface of the leaves, a negative pressure, or tension,
is created. The evaporated water is replaced by water moving from inside
the plant in unbroken columns that extend from the top of a plant to its
roots. The same forces that create surface tension in any sample of
water are responsible for the maintenance of these unbroken columns of
water. When water is confined in tubes of very small bore, the forces of
cohesion (the attraction between water molecules) are so great that the
strength of a column of water compares with the strength of a steel wire
of the same diameter. This cohesive strength permits columns of water to
be pulled to great heights without being broken.


41.American black bears

American black bears appear in a variety of colors despite their name.
In the eastern part of their range, most of these brown, red, or even
yellow coats. To the north, the black bear is actually gray or white in
color. Even in the same litter, both brown and black furred bears may be
born.

Black bears are the smallest of all American bears, ranging in length
from five to six feet, weighing from three hundred to five hundred
pounds Their eyes and ears are small and their eyesight and hearing are
not as good as their sense of smell.

Like all bears, the black bear is timid, clumsy, and rarely dangerous ,
but if attacked, most can climb trees and cover ground at great speeds.
When angry or frightened, it is a formidable enemy.

Black bears feed on leaves, herbs. Fruit, berries, insects, fish, and
even larger animals. One of the most interesting characteristics of
bears, including the black bear, is their winter sleep. Unlike
squirrels, woodchucks, and many other woodland animals, bears do not
actually hibernate. Although the bear does not during the winter moths,
sustaining itself from body fat, its temperature remains almost normal,
and it breathes regularly four or five times per minute.

Most black bears live alone, except during mating season. They prefer to
live in caves, hollow logs, or dense thickets. A little of one to four
cubs is born in January or February after a gestation period of six to
nine months, and they remain with their mother until they are fully
grown or about one and a half years old. Black bears can live as long as
thirty years in the wild , and even longer in game preserves set aside
for them.


42.Coal-fired power plants

The invention of the incandescent light bulb by Thomas A. Edison in 1879
created a demand for a cheap, readily available fuel with which to
generate large amounts of electric power. Coal seemed to fit the bill,
and it fueled the earliest power stations. (which were set up at the end
of the nineteenth century by Edison himself). As more power plants were
constructed throughout the country, the reliance on coal increased
throughout the country, the reliance on coal increased. Since the First
World War, coal-fired power plants had a combined in the United States
each year. In 1986 such plants had a combined generating capacity of
289,000 megawatts and consumed 83 percent of the nearly 900 million tons
of coal mined in the country that year. Given the uncertainty in the
future growth of the nearly 900 million tons of coal mined in the
country that year. Given the uncertainty in the future growth of nuclear
power and in the supply of oil and natural gas, coal-fired power plants
could well provide up to 70 percent of the electric power in the United
States by the end of the century.

Yet, in spite of the fact that coal has long been a source of
electricity and may remain on for many years(coal represents about 80
percent of United States fossil-fuel reserves), it has actually never
been the most desirable fossil fuel for power plants. Coal contains less
energy per unit of weight than weight than natural gas or oil; it is
difficult to transport, and it is associated with a host of
environmental issues, among them acid rain. Since the late 1960’s
problems of emission control and waste disposal have sharply reduced the
appeal of coal-fired power plants. The cost of ameliorating these
environment problems along with the rising cost of building a facility
as large and complex as a coal-fired power plant, have also made such
plants less attractive from a purely economic perspective.

Changes in the technological base of coal-fired power plants could
restore their attractiveness, however. Whereas some of these changes are
intended mainly to increase the productivity of existing plants,
completely new technologies for burning coal cleanly are also being
developed.


43.Statistics

There were two widely divergent influences on the early development of
statistical methods. Statistics had a mother who was dedicated to
keeping orderly records of government units (states and statistics come
from the same Latin root status) and a gentlemanly gambling father who
relied on mathematics to increase his skill at playing the odds in games
of chance. The influence of the mother on the offspring, statistics, is
represented by counting, measuring, describing, tabulating, ordering,
and the taking of censuses-all of which led to modern descriptive
statistics. From the influence of the father came modern inferential
statistics, which is based squarely on theories of probability.

Describing collections involves tabulating, depicting and describing
collections of data. These data may be quantitative such as measures of
height, intelligence or grade level------variables that are
characterized by an underlying continuum---or the data may represent
qualitative variables, such as sex, college major or personality type.
Large masses of data must generally undergo a process of summarization
or reduction before they are comprehensible. Descriptive statistics is a
tool for describing or summarizing or reducing to comprehensible form
the properties of an otherwise unwieldy mass of data.

Inferential statistics is a formalized body of methods for solving
another class of problems that present great of problems
characteristically involves attempts to make predictions using a sample
of observations. For example, a school superintendent wishes to
determine the proportion of children in a large school system who come
to school without breakfast, have been vaccinated for flu, or whatever.
Having a little knowledge of statistics, the superintendent would know
that it is unnecessary and inefficient to question each child: the
proportion for the sample of as few as 100 children. Thus , the purpose
of inferential statistics is to predict or estimate characteristics of a
population from a knowledge of the characteristics of only a sample of
the population.


44.Obtaining Fresh water from icebergs 你好，我是胖胖：--）

The concept of obtaining fresh water from icebergs that are towed to
populated areas and arid regions of the world was once treated as a joke
more appropriate to cartoons than real life. But now it is being
considered quite seriously by many nations, especially since scientists
have warned that the human race will outgrow its fresh water supply
faster than it runs out of food.

Glaciers are a possible source of fresh water that has been overlooked
until recently. Three-quarters of the Earth’s fresh water supply is
still tied up in glacial ice, a reservoir of untapped fresh water so
immense that it could sustain all the rivers of the world for 1,000
years. Floating on the oceans every year are 7,659 trillion metric tons
of ice encased in 10000 icebergs that break away from the polar ice
caps, more than ninety percent of them from Antarctica.

Huge glaciers that stretch over the shallow continental shelf give birth
to icebergs throughout the year. Icebergs are not like sea ice, which is
formed when the sea itself freezes, rather, they are formed entirely on
land, breaking off when glaciers spread over the sea. As they drift away
from the polar region, icebergs sometimes move mysteriously in a
direction opposite to the wind, pulled by subsurface currents. Because
they melt more slowly than smaller pieces of ice, icebergs have been
known to drift as far north as 35 degrees south of the equator in the
Atlantic Ocean. To corral them and steer them to parts of the world
where they are needed would not be too difficult.

The difficulty arises in other technical matters, such as the prevention
of rapid melting in warmer climates and the funneling of fresh water to
shore in great volume. But even if the icebergs lost half of their
volume in towing, the water they could provide would be far cheaper than
that produced by desalinization, or removing salt from water.


45.The source of Energy

A summary of the physical and chemical nature of life must begin, not on
the Earth, but in the Sun; in fact, at the Sun’s very center. It is
here that is to be found the source of the energy that the Sun
constantly pours out into space as light and heat. This energy is
librated at the center of the Sun as billions upon billions of nuclei of
hydrogen atoms collide with each other and fuse together to form nuclei
of helium, and in doing so, release some of the energy that is stored in
the nuclei of atoms. The output of light and heat of the Sun requires
that some 600 million tons of hydrogen be converted into helium in the
Sun every second. This the Sun has been doing for several thousands of
millions of year.

The nuclear energy is released at the Sun’s center as high-energy gamma
radiation, a form of electromagnetic radiation like light and radio
waves, only of very much shorter wavelength. This gamma radiation is
absorbed by atoms inside the Sun to be reemitted at slightly longer
wavelengths. This radiation , in its turn is absorbed and reemitted. As
the energy filters through the layers of the solar interior, it passes
through the X-ray part of the spectrum eventually becoming light. At
this stage, it has reached what we call the solar surface, and can
escape into space without being absorbed further by solar atoms. A very
small fraction of the Sun’s light and heat is emitted in such
directions that after passing unhindered through interplanetary space,
it hits the Earth.


46.Vision by 胖胖

Human vision like that of other primates has evolved in an arboreal
environment. In the dense complex world of a tropical forest, it is more
important to see well that to develop an acute sense of smell. In the
course of evolution members of the primate line have acquired large eyes
while the snout has shrunk to give the eye an unimpeded view. Of mammals
only humans and some primates enjoy color vision. The red flag is black
to the bull. Horses live in a monochrome world .light visible to human
eyes however occupies only a very narrow band in the whole
electromagnetic spectrum. Ultraviolet rays are invisible to humans
though ants and honeybees are sensitive to them. Humans though ants and
honeybees are sensitive to them. Humans have no direct perception of
infrared rays unlike the rattlesnake which has receptors tuned into
wavelengths longer than 0.7 micron. The world would look eerily
different if human eyes were sensitive to infrared radiation. Then
instead of the darkness of night, we would be able to move easily in a
strange shadowless world where objects glowed with varying degrees of
intensity. But human eyes excel in other ways. They are in fact
remarkably discerning in color gradation. The color sensitivity of
normal human vision is rarely surpassed even by sophisticated technical
devices.


47 Folk Cultures 胖胖提供：）

A folk culture is a small isolated, cohesive, conservative, nearly self-
sufficient group that is homogeneous in custom and race with a strong
family or clan structure and highly developed rituals. Order is
maintained through sanctions based in the religion or family and
interpersonal. Relationships are strong. Tradition is paramount, and
change comes infrequently and slowly. There is relatively little
division of labor into specialized duties. Rather, each person is
expected to perform a great variety of tasks, though duties may differ
between the sexes. Most goods are handmade and subsistence economy
prevails. Individualism is weakly developed in folk cultures as are
social classes. Unaltered folk cultures no longer exist in
industrialized countries such as the United States and Canada. Perhaps
the nearest modern equivalent in Anglo America is the Amish, a German
American farming sect that largely renounces the products and labor
saving devices of
the industrial age. In Amish areas, horse drawn buggies still serve as a
local transportation device and the faithful are not permitted to own
automobiles. The Amish’s central religious concept of Demut
“humility”, clearly reflects the weakness of individualism and social
class so typical of folk cultures and there is a corresponding strength
of Amish group identity. Rarely do the Amish marry outside their sect.
The religion, a variety of the Mennonite faith, provides the principal
mechanism for maintaining order.

By contrast a popular culture is a large heterogeneous group often
highly individualistic and a pronounced many specialized professions.
Secular institutions of control such as the police and army take the
place of religion and family in maintaining order, and a money-based
economy prevails. Because of these contrasts, “popular” may be viewed
as clearly different from “folk”. The popular is replacing the folk in
industrialized countries and in many developing nations. Folk-made
objects give way to their popular equivalent, usually because the
popular item is more quickly or cheaply produced, is easier or time
saving to use or leads more prestige to the owner.



48 Bacteria by胖胖：）

Bacteria are extremely small living things. While we measure our own
sizes in inches or centimeters, bacterial size is measured in microns.
One micron is a thousandth of a millimeter: a pinhead is about a
millimeter across. Rod-shaped bacteria are usually from two to four
microns long, while rounded ones are generally one micron in diameter.
Thus if you enlarged a rounded bacterium a thousand times, it would be
just about the size of a pinhead. An adult human magnified by the same
amount would be over a mile(1.6 kilometer) tall.

Even with an ordinary microscope, you must look closely to see bacteria.
Using a magnification of 100 times, one finds that bacteria are barely
visible as tiny rods or dots. One cannot make out anything of their
structure. Using special stains, one can see that some bacteria have
attached to them wavy-looking “hairs” called flagella. Others have
only one flagellum. The flagella rotate, pushing the bacteria through
the water. Many bacteria lack flagella and cannot move about by their
own power, while others can glide along over surfaces by some little-
understood mechanism.

From the bacteria point of view, the world is a very different place
from what it is to humans. To a bacterium water is as thick as molasses
is to us. Bacteria are so small that they are influenced by the
movements of the chemical molecules around them. Bacteria under the
microscope, even those with no flagella, often bounce about in the
water. This is because they collide with the watery molecules and are
pushed this way and that. Molecules move so rapidly that within a tenth
of a second the molecules around a bacteria have all been replaced by
new ones; even bacteria without flagella are thus constantly exposed to
a changing environment.


49 Sleep 呵呵，还是胖胖：）

Sleet is part of a person’s daily activity cycle. There are several
different stages of sleep, and they too occur in cycles. If you are an
average sleeper, your sleep cycle is as follows. When you fist drift off
into slumber, your eyes will roll about a bit, you temperature will drop
slightly, your muscles will relax, and your breathing well slow and
become quite regular. Your brain waves slow and become quite regular.
Your brain waves slow down a bit too, with the alpha rhythm of rather
fast waves 1 sleep. For the next half hour or so, as you relax more and
more, you will drift down through stage 2 and stage 3 sleep. The lower
your stage of sleep. slower your brain waves will be. Then about 40to 69
minutes after you lose consciousness you will have reached the deepest
sleep of all. Your brain will show the large slow waves that are known
as the delta rhythm. This is stage 4 sleep.

You do not remain at this deep fourth stage all night long, but instead
about 80 minutes after you fall into slumber, your brain activity level
will increase again slightly. The delta rhythm will disappear, to be
replaced by the activity pattern of brain waves. Your eyes will begin to
dart around under your closed eyelids as if you were looking at
something occurring in front of you. This period of rapid eye movement
lasts for some 8 to 15 minutes and is called REM sleep. It is during REM
sleep period, your body will soon relax again, your breathing will slip
gently back from stage 1 to stage 4 sleep----only to rise once again to
the surface of near consciousness some 80 minutes later.


50. Cells and Temperature 　胖胖提供JJJ

Cells cannot remain alive outside certain limits of temperature and much
narrower limits mark the boundaries of effective functioning. Enzyme
systems of mammals and birds are most efficient only within a narrow
range around 37C;a departure of a few degrees from this value seriously
impairs their functioning. Even though cells can survive wider
fluctuations the integrated actions of bodily systems are impaired.
Other animals have a wider tolerance for changes of bodily temperature.

For centuries it has been recognized that mammals and birds differ from
other animals in the way they regulate body temperature. Ways of
characterizing the difference have become more accurate and meaningful
over time, but popular terminology still reflects the old division into
“warm-blooded” and “cold-blooded” species; warm-blooded included
mammals and birds whereas all other creatures were considered cold-
blooded. As more species were studied, it became evident that this
classification was inadequate. A fence lizard or a desert iguana-each
cold-blooded----usually has a body temperature only a degree or two
below that of humans and so is not cold. Therefore the next distinction
was made between animals that maintain a constant body temperature,
called home0therms, and those whose body temperature varies with their
environments, called poikilotherms. But this classification also proved
inadequate, because among mammals there are many that vary their body
temperatures during hibernation. Furthermore, many invertebrates that
live in the depths of the ocean never experience change in the depths of
the ocean never experience change in the chill of the deep water, and
their body temperatures remain constant.