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  3. A 19th Century Killer Disease: Tuberculosis In 1882, Robert Koch, a German country doctor, succeeded in isolating the bacill

A 19th Century Killer Disease: Tuberculosis In 1882, Robert Koch, a German country doctor, succeeded in isolating the bacill

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问题            A 19th Century Killer Disease: Tuberculosis
    In 1882, Robert Koch, a German country doctor, succeeded in isolating the bacillus of tuberculosis. This discovery came at a time when this disease was the greatest single killer of the human race.
    All during the 19th century it had spread remorselessly with the growth of cities, until it had reached epidemic proportions throughout the industrialized world.
    Its record in the United States was one of frightful devastation. Immigrants from Europe, many of them debilitated from famines at home, flooded into the poorest and dirtiest sections of cities, there to die of the disease by the thousand. Working children were infected in staggering numbers. Hundreds of thousands of children worked twelve hours a day, six days a week. Chronically exhausted and undernourished, they made particularly susceptible victims. Since tuberculosis was not considered contagious, its victims spread the disease amongst those about them as they coughed, spat and drank from communal cups.
    It is now known that tuberculosis is chiefly spread by droplet infection. It can also occur as a result of drinking unpasteurized milk from tubercular cows, where the pathogen penetrates the body through the alimentary canal. However, entry of the bacillus into the body is not necessarily followed by a clinical illness, the development of which depends on several other factors. Many people, for instance, seem to have a high natural resistance and although acquired immunity is not fully understood, it has been proved that if a person contracts and recovers from a primary tuberculosis infection, he is less likely to develop active tuberculosis on subsequent exposure to the tubercle bacillus than a patient who has not previously been infected.
    Tuberculosis has notoriously been associated with poverty, with its accompanying malnutrition, overcrowding and stress, and while the exact role of nutrition is uncertain, it seems that a diet based on cheap carbohydrate and a lack of protein and vitamins is another contributing factor.
    In addition, a condition such as diabetes mellitus also leads to increased risk of developing the disease, and statistics from certain mining areas in Africa show that sufferers of respiratory disorders, such as silicosis, are especially vulnerable to attacks of pulmonary tuberculosis.
    The introduction of mass immunization against TB by the use of BCG vaccine, and of mass radiography, where it is possible to screen large numbers of people for early signs of tuberculosis, has dramatically reduced the incidence of the disease in the last few decades.
    Summary :
    Despite the fact that tuberculosis was the number one killer in the 19th century, it was not proved that the disease was【61】until 1882 when Robert Koch succeeded in isolating the tubercle bacillus. While it is now well known that tuberculosis is spread by【62】infection, it is also evident that entry of the tubercle bacillus does not necessarily lead to development of the disease. Although we do not yet fully understand【63】, there is evidence to show that a person who has contracted and recovered from the disease is【64】likely to develop active tuberculosis on subsequent exposure to the bacillus than a patient who has not been previously infected. As with all diseases spread by droplet infection, living in overcrowded insanitary conditions greatly increases the risk of【65】.
选项
答案droplet
解析 (第四段开头，It is now known that tuberculosis is chiefly spread by droplet infection.，即现在人们都知道了肺结核主要是通过飞沫传染的。)
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