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The Spread of Microorganisms

銆€銆€There is scarcely a place on earth which is naturally free of microorganisms (寰敓鐗�). 46 . But on external body surfaces, on lining membranes(鍏�(n猫i)鑶�) and inside tubes and organs that are connected with the outside銇ｂ€曘仯such as the mouth, throat, nose, and large intestine(鑵�)銇ｂ€曘仯both harmless and pathogenic(鐥呭師鐨�)microbes(寰敓鐗�)live in large numbers. 47 . If these natural defenses are sound, a person may conceal many microbes without ill effect. However, if his resistance becomes lowered, an infection can result.

銆€銆€Microbes are spread about through an almost infinite variety of means. 48 . The more crowded the conditions, the greater the chances of epidemics(娴佽鐥�) breaking out. 49 .

銆€銆€Although microbes cannot fly, the dust of the air is alive with them. In close quarters the atmosphere is further polluted by bacteria-loaded tiny drops discharged by coughing and even normal conversation. Pathogenic microbes are also spread by rats, mice, flies and mosquitoes. 50 . In slum areas there is often a combination of crowded conditions and poor sanitation(鐠�(hu谩n)澧冭(w猫i)鐢�). In addition, many of the inhabitants have lowered resistance because of shortage of food and other undesirable unhealthy practices. As a result, epidemics are likely to begin in these districts.

銆€銆€All civilized societies establish and enforce measures designed to protect the health of their populations. Most of these practices are concerned with preventing the spread of the pathogenic organisms

銆€銆€A The atmosphere is a carrier of microorganisms

銆€銆€B One exception is the interior of normal body tissue

銆€銆€C Microbial growth is further helped by the widespread presence of dirt and the lack of sunlight

銆€銆€D The body has natural defenses against these organisms

銆€銆€E The body has no defenses against these organisms

銆€銆€F The simplest way is by person-to-person contact

銆€銆€鍙冭€冪瓟妗堬細46 B 47 D 48 F 49 A 50 C

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