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At the turn of the 20th century, Dutch physician Christiaan Eijkman showed that disease can be caused not only by microorganisms but by a dietary efficiency of certain substances now called vitamins. In 1909 German bacteriologist Paul Ehrlich introduced the world's first bactericide, a chemical designed to kill specific lands of bacteria with killing the patient's cells as well.(1)____(2)____
Following the discovery of penicillin in 1928 by British bacteriologist Sir Alexander Fleming, antibiotics joined medicine's Chemical armory making the fight against bacterial infection almost a routine matter. Antibiotics cannot act as viruses, but vaccines have been used to greatly effect to prevent some of the deadliest viral diseases. Smallpox, once a worldwide killer, was completely eradicated by the late 1970s,and in the United States a number of polio cases dropped from 38,000 in the 1950s to less than 10 a ye3r‘by the 21st century.(3)____(4)____(5)____
By the middle of the 20th century scientists believed they were well on the way to treating,preventing, or eradicating many of the most deadly infectious diseases that plagued humankind for centuries.(6)____ And by the 1980s the medical community’s confidence in its ability to control the infectious disease had been shaken by the emergency of new types of disease-causing microorganisms.(7)____(8)____(9)____New cases of tuberculosis developed, caused by bacteria;trains that were resistant to antibiotics. New, deadly infections on which there was no known cure also appeared, including the viruses that cause hemorrhagic fever and the human immunodeficiency virus (HIV), the cause of acquired immunodeficiency syndrome.(10)____
