and disposing of human waste helped to prevent the transmission of many diseases. Second, changes in public

behavior have advanced health. Early in the twentieth century, for example, people learned the importance of

boiling bottles before using them for food storage and baby’s milk, washing their hands, and protecting food

from flies. More recent behavioral changes include reducing the number of people who smoke tobacco and

precautions to limit sexually transmitted diseases. Third, medicine has played a large role. Scientists

developed immunizations for diphtheria, cholera, pertussis, tuberculosis, tetanus, and yellow fever between

1890 and 1930. Penicillin, discovered in 1941, led to a series of other antibiotic drugs for bringing infectious

diseases under control. In recent decades, drugs that reduce the risks of high blood pressure have had a

dramatic effect in extending lives.
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