TEXT C
The would-be sleeper who refights his daily battles in bed——or rehearses tomorrow’s problems——finds it hard to fall asleep. Then he starts worrying about his inability to sleep, which increases his insomnia, which increases his worries,which... In a new development that may help the insomnia to break this vicious cycle, Dr. Werner P. Koella of the Worcester Foundation for the Experimental Biology has discovered a chemical in the brain that may control normal sleep.
The substance, known as serotonin, is one of a number of so-called neurohormones in the brain that researchers suspect play an important part in controlling the mind and the emotions. Such chemicals, researchers have learned, assist in transmitting nerve impulses from one nerve cell to another. Serotonin, Koella notes, is produced in particularly high concentrations in the hypothalamus, the “primitive” lower part of the brain and the brain stem, which joins the brain to the top of the spinal cord and is known to contain the centers controlling the level of transmitter substance in the brain stem and hypothalamus that regulate sleep.In preliminary experiments, Koella found that giving serotonon to cats produced signs of sleep. Electrode leads were implanted in the cats’ brains and attached to an EEG (electroencephalogram) machine to record the brain waves; next, the serotonin was injected directly into the brain or an artery in the neck. The pupils of the animals’ eyes narrowed and the electroencephalograms showed slow waves characteristic of deep sleep within five to ten minutes.
More recently, Koella deprived cats of serotonin. The animals, again equipped with implanted electrodes, were given PCPA, a drug that blocks the formation of serotonin. They were then placed in small compartments fitted with one-way mirrors and watched round the clock.
Normally cats sleep about 15 hours a day; but Koella’s cats, after receiving PCPA, spent about 30 minutes of each day sleeping. Most of the time, their EEGs showed the brainwave patterns of arousal. Occasionally the cats would curl up as if to go to sleep, but would soon get back on their feet to wander about. The animals showed signs of irritability and often meowed complainingly after a few days of sleep deprivation, but had normal reflexes. The effects of the PCPA wore off eight days to two weeks after administration of the drug; the cats returned to their normal sleeping patterns as serotonin levels in their brains rose again.
Koella believes that at least some types of chronic insomnia may be caused by a drop in brain-serotonin levels. The Worcester physiologist is now working on chemical ways to raise the brain’s serotonin levels and produce, in his words, “a truly physiological sleeping pill.” Synthetic sleeping pills, such as barbiturates, bring sleep, but at a price: they depress the central nervous system, reduce heart action and respiration——and they can become habit-forming or even addictive.
In one promising experiment toward the goal of letting the body “make its own pill,” Koella has found that administration of 5-hydroxytryptophan, the chemical substance from which the body derives serotonin, will quickly restore a normal sleeping pattern to cats lacking in serotonin.
73. The brain stem is located (Paragraph 2)____.
A. in the hypothalamus
B. between the brain and the spinal cord
C. in the transmitter nerve cells
D. between the hypothalamus and the brain
74. The information in paragraph 5 indicates that PCPA was responsible for____.
A. a lack of sleepB. the cats’ meowing
C. normal sleeping patternsD. sleeping about 15 hours a day
75. The language used in this article indicates that Dr. Koella____.
A. is positive that serotonin controls sleep
B. is quite uncertain whether serotonin controls sleep
C. thinks that serotonin can’t be extracted
D. thinks that serotonin might control sleep
76. A good title for this article would be____.
A. The Cats Want to Sleep
B. I Can’t Sleep Tonight
C. How to Get Asleep
D. Some New Sleep Research
TEXT D
As the costof gas and oil for home heating has gone up, many Americans have switched from these fuels to wood for heating their homes. In 1973, approximately 200,000 wood-burning stoves, intended for home use, were sold in the United States; by 1979, this figure had reached one million; and by the end of 1981, there were as many as seven million home-owned wood-burning units in operation in the U.S.
In addition to low fuel bills, many people choose these stoves because their initial cost is very low (the prices range from $50 kits to $5,000 top-of-the-line models), and because new technology has made wood fires more efficient, cleaner, and, therefore, safer than ever before.
One new technological feature of this type is the catalytic(催化) combustor which adds about $100 to $200 to the cost of the stove, but which causes much more complete combustion(燃燒) of the wood and therefore burns up more of the pollutants left by incomplete combustion and produces more heat.
A second cost-saving innovation is a device which agitates the wood, increasing the amount of oxygen that reaches the center of the wood pile, and leading to more efficient combustion. The real advantage of this device is that it allows the owner to make use of cheap sources of wood such as dirty wood chips (an industrial by-product) that have almost no commercial value, cost as little as $20 a ton, and burn very inefficiently in furnaces without an agitator.
77.According to the passage, the number of wood-burning stove sold for home use____.
A. went up fivefold over a six-year period.
B. rose to seven million during the seventies.
C. multiplied thirty-five times between 1973 and the beginning of 1981.
D. increased by 6,000,000 over an eight-year period.
78. Which one of the following is NOT true for the reason why people prefer to buy wood-burning stoves?
A. The initial cost is very low.
B. The fuel costs are cheaper.
C. Wood fires are more efficient, cleaner, and safer than ever before.
D. The wood-burning stoves are more efficient than gas or oil ones.
79. Which of the following statements is NOT true?
A. Wood-burning stoves are safer and more efficient than they used to be.
B. No factories exist for the purpose of producing dirty wood chips.
C. Both catalytic combustors and wood agitators save money in the long run.
D. Wood-burning stoves with catalytic combustors cost between $100 and $200.
80. The passage states that____.
A. many Americans have switched from hydrocarbon-based fuels to wood because the price of the latter has risen.
B. some wood-burning stoves cost up to one hundred times more than others.
C. catalytic combustors increase the amount of pollution caused by wood burning stoves.
D. agitators are cheaper addition to wood-burning stoves than catalytic combustors.