The History of Medicine     

    2000 B.C. - Here, eat this root.     
    1000 A.D. - That root is heathen. Here, say this prayer.
    1850 A.D. - That prayer is superstition. Here, drink this potion.     
    1940 A.D. - That potion is snake oil. Here, swallow this pill.     
    1985 A.D. - That pill is ineffective. Here, take this antibiotic.     
    2000 A.D. - That antibiotic doesn't work anymore. Here, eat this root.