藏在土壤里的免疫故事
In a Finnish experiment, volunteers rubbed soil and moss against their hands for twenty seconds. Even after washing with tap water, the number and variety of microbes (微生物) on their hands rose sharply. “Their hands still looked clean, but the change was huge,” says ecologist Mira Grönroos.
Why does variety matter? Because a rich mix of species keeps itself in balance.When many harmless species live together, they displace the dangerous ones. To test this, her team replaced the stones of a kindergarten yard with forest floor and planting boxes. After 28 days of play, children there carried more kinds of bacteria on their skin — and fewer disease-causing kinds — than children in a yard without soil.
The effects go deeper than the skin. In a follow-up study, children played in sand areas filled with either microbe-rich soil or ordinary sand. Blood tests showed that the microbe-rich group’s immune systems fought illness without overreacting. The findings support the biodiversity theory: as natural habitats lose species, people meet fewer varied microbes, and problems such as asthma and skin allergies become more common. One soil bacterium was linked to more white blood cells that stop the body from attacking itself. Scientists cannot yet promise prevention, but Grönroos believes contact with nature“might reduce the possibility” of such diseases.
Adults gain from dirty hands, too. Volunteers growing vegetables in microbe-rich soil for a winter month developed more varied skin bacteria and calmer immune responses. Offices fitted with “green walls” of living plants saw workers’ skin microbes become more diverse within two weeks. “Such easy contact changed immune function, which was quite surprising,” Grönroos notes.
For Grönroos, the lesson is practical. She lets her children bring cones and sticks home to play, and wants cities designed so that people meet nature “on their way to work or school”. The advice costs nothing and carries little risk. Next time you pass a mossy tree or a patch of grass, sit down, reach out — and don’t be afraid of a bit of mud.
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1.1.What did the 20-second experiment find?
A Their hands looked dirty.
B More skin bacteria appeared.
C Washing killed the microbes.
D Soil harmed the volunteers.
解析：选B。B 细节理解题。根据第一段的“the number and variety of microbes on their hands rose sharply”以及“Their hands still looked clean”可知，20秒接触土壤和苔藓后，志愿者手上的微生物数量和种类明显增加，也就是更多皮肤细菌出现，选B。A项说手看起来脏，与原文“still looked clean”矛盾；C项说清洗杀死了微生物，与“Even after washing... rose sharply”相反；D项说土壤伤害了志愿者，文中没有依据，且整体强调接触自然可能有益。故选B。
2.2.What does the underlined phrase “displace” in Paragraph 2 most probably mean?
A Drive away.
B Mix with.
C Feed on.
D Depend on.
解析：选A。A 词义猜测题。根据第二段的“When many harmless species live together, they displace the dangerous ones.”以及后文幼儿园实验发现接触富含微生物土壤的孩子携带更多种细菌、更少致病菌，可知无害微生物增多会排挤、赶走危险微生物，因此“displace”最接近“Drive away”。B“Mix with”表示混合共存，不符合“减少致病菌”的结果；C“Feed on”表示以……为食，文中无此意；D“Depend on”表示依赖，逻辑不通。故选A。
3.3. What did the follow-up study find?
A Stronger immune attacks are needed.
B Dirt exposure calms immune responses.
C All soil bacteria prevent allergies.
D Dirty homes lead to asthma.
解析：选B。B 细节理解题。根据第三段后续研究可知，富含微生物土壤组孩子的免疫系统“fought illness without overreacting”，后文也提到成人出现“calmer immune responses”。这说明接触泥土等微生物环境会使免疫反应更平静，而不是更强攻击，选B。A项“需要更强免疫攻击”与“without overreacting”相反；C项“所有土壤细菌预防过敏”中“All”过于绝对，且原文说科学家尚不能承诺预防；D项“脏家导致哮喘”无中生有，原文是把哮喘等与自然栖息地物种减少、微生物多样性下降联系起来。故选B。
4.4.What is Grönroos’s attitude to keeping hands absolutely clean at all times?
A Doubtful.
B Favourable.
C Indifferent.
D Unclear.
解析：选A。A 观点态度题。根据最后一段Grönroos让孩子把球果和树枝带回家玩，希望城市设计让人们“on their way to work or school”接触自然，并建议“don’t be afraid of a bit of mud”，可知她不赞成一直把双手保持绝对干净，而认为适度接触泥土和自然有益。因此她对“绝对干净”持怀疑或不赞同态度，选Doubtful。B项Favourable是支持保持绝对干净，与文意相反；C项Indifferent是冷漠，不符合她积极倡导接触自然；D项Unclear是不明确，但文中态度明确。故选A。