托福阅读辅导：怎样节省托福阅读时间？

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托福阅读辅导：怎样节省托福阅读时间？
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Up to the beginning of the twentieth century, the nervous system was thought to control
all communication within the body and the resulting integration of behavior. Scientists had
determined that nerves ran, essentially, on electrical impulses. These impulses were thought
to be the engine for thought, emotion, movement, and internal processes such as digestion. However,
experiments by William Bayliss and Ernest Starling on the chemical secretin, which is produced
in the small intestine when food enters the stomach, eventually challenged that view. From the
small intestine, secretin travels through the bloodstream to the pancreas. There, it stimulates
the release of digestive chemicals. In this fashion, the intestinal cells that produce secretin
ultimately regulate the production of different chemicals in a different organ, the pancreas.
Such a coordination of processes had been thought to require control by the nervous system;
Bayliss and Starling showed that it could occur through chemicals alone. This discovery spurred
Starling to coin the term hormone to refer to secretin, taking it from the Greek word hormon,
meaning “to excite” or “to set in motion.” A hormone is a chemical produced by one tissue
to make things happen elsewhere.
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glands that produce substances that are used outside the bloodstream, primarily for digestion.
The pancreas is one such organ, although it secretes some chemicals into the blood and thus
is also part of the endocrine system.
Much has been learned about hormones since their discovery. Some play such key roles in
regulating bodily processes or behavior that their absence would cause immediate death. The
most abundant hormones have effects that are less obviously urgent but can be more far-reaching
and difficult to track: They modify moods and affect human behavior, even some behavior we normally
think of as voluntary. Hormonal systems are very intricate. Even minute amounts of the right
chemicals can suppress appetite, calm aggression, and change the attitude of a parent toward
a child. Certain hormones accelerate the development of the body, regulating growth and form;
others may e ven define an individual’s personality characteristics. The quantities and
proportions of hormones produced change with age, so scientists have given a great deal of study
to shifts in the endocrine system over time in the hopes of alleviating ailments associated
with aging.