问题 单项选择题

麻风的传染源最有意义的是

A.麻风病人

B.麻风杆菌携带者

C.带菌犰狳

D.带菌小鼠

E.带菌黑猩猩

答案

参考答案:A

解析:常见错误为选D,是把麻风杆菌的传染源与麻风杆菌的培养特性相混淆了。在自然界中只有人感染麻风,因此,传染源只是麻风患者。麻风杆菌可通过直接接触或由飞沫传播,如细菌随病人鼻分泌物、痰、汗液、乳汁、精液或 * * 分泌物排出,感染他人。

问答题

(46) It is known that the brain shrinks as the body ages, but the effects on mental ability are different from person to person. Interestingly, in a study of elderly men and women, those who had more education actually had more brain shrinkage.
"That may seem like bad news," said study author Dr. Edward Coffey, a professor of psychiatry and of neurology at Henry Ford Health System in Detroit. (47) However, he explained, the finding suggests that education allows people to withstand more brain tissue loss before their mental functioning begins to break down.
The study, published in the July issue of Neurology, is the first to provide biological evidence to support a concept called the "reserve" hypothesis, according to the researchers. In recent years, investigators have developed the idea that people who are more educated have greater cognitive reserves to draw upon as the brain ages; in essence, they have more brain tissue to spare.
(48) Examining brain scans of 320 healthy men and women aged 66 to 90, researchers found that for each year of education the subjects had, there was greater shrink age of the outer layer of the brain known as the cortex. Yet on tests of cognition and memory, all participants scored in the range indicating normal.
"Everyone has some degree of brain shrinkage," Coffey said. "People lose (on average) 2.5 percent per decade starting in adulthood."
There is, however, a "remarkable range "of shrinkage among people who show no signs of mental decline, Coffey noted. Overall health, he said, accounts for some differences in brain size. Alcohol or drug use, as well as medical conditions such as diabetes and high blood pressure, contribute to brain tissue loss throughout adulthood.
In the absence of such medical conditions, Coffey said, education level helps explain the range of brain shrinkage exhibited among the mentally-fit elderly. The more-educated can withstand greater loss.
(49) Coffey and colleagues gauged shrinkage of the cortex by measuring the cerebrospinal fluid surrounding the brain. The greater the amount of fluid, the greater the cortical shrinkage.
Controlling for the health factors that contribute to brain injury, the researchers found that education was related to the severity of brain shrinkage. For each year of education from first grade on, subjects had an average of 1.77 milliliters 11 more cerebrospinal fluid around the brain.
Just how education might affect brain cells is unknown. (50) In their report, the researchers speculated that in people with more education, certain brain structures deeper than the cortex may stay intact to compensate for cortical shrinkage.

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